Research ArticleUse of Geochemical Fossils as Indicators of Thermal MaturationAn Example from the Anambra Basin Southeastern Nigeria

Olumuyiwa Adedotun Odundun

Department of Earth Sciences Adekunle Ajasin University Akungba Akoko Ondo State Nigeria

Correspondence should be addressed to Olumuyiwa Adedotun Odundun smeksyahoofr

Received 28 April 2014 Revised 31 August 2014 Accepted 1 September 2014

Academic Editor Franco Tassi

Copyright copy 2015 Olumuyiwa Adedotun Odundun This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Organic geochemical studies and fossil molecules distribution results have been employed in characterizing subsurface sedimentsfrom some sections of Anambra Basin southeasternNigeriaThe total organic carbon (TOC) and soluble organicmatter (SOM) arein the range of 161 to 6951 wt and 2501 to 40952 ppm respectively implying that the source rocks are moderately to fairly rich inorganic matter Based on data of the paper the organic matter is interpreted as Type III (gas prone) with little oil The geochemicalfossils and chemical compositions suggest immature to marginally mature status for the sediments with methyl phenanthreneindex (MPI-1) and methyl dibenzothiopene ratio (MDR) showing ranges of 014ndash076 and 099ndash421 respectively The abundanceof 125-TMN (Trimethyl naphthalene) in the sediments suggests a significant land plant contribution to the organic matter Thepristanephytane ratio values of 72ndash89 also point to terrestrial organic input under oxic conditions However the presence of C

27

to C29steranes and diasteranes indicates mixed sourcesmdashmarine and terrigenousmdashwith prospects to generate both oil and gas

1 Introduction

The Anambra Basin is a late CretaceousndashPaleocene deltacomplex located in the southern Benue Trough (Figure 1)It is characterized by enormous lithologic heterogeneity inboth lateral and vertical extension derived from a rangeof paleoenvironmental settings ranging from Campanian toRecent [1]

The search for commercial crude oil in the AnambraBasin has remained a real source of concern especiallyto oil companies and research groups Initial efforts wereunrewarding and this led to the neglect of this basin in favourof the Niger Delta where hydrocarbon reserves have beenreportedly put at 40 billion barrels of oil and about 170 trillionstandard cubic feet of gas [2ndash4]

The Nigerian sedimentary basin was formed after thebreakup of the South American and African continents inthe Early Cretaceous [5 6] Various lines of geomorpho-logic structural stratigraphic and paleontological evidenceshave been presented to support a rift model [7ndash10] Thestratigraphic history of the region is characterised by three

sedimentary phases [11] during which the axis of the sedi-mentary basin shiftedMore than 3000mof rocks comprisingthose belonging to Asu River Group and the Eze-Aku andAwgu Formationswere deposited during the first phase in theAbakaliki-Benue Basin and the Calabar Flank The resultingsuccession from the second sedimentary phase comprises theNkporo Group Mamu Formation Ajali Sandstone NsukkaFormation Imo Formation and Ameki Group The thirdphase credited for the formation of the petroliferous NigerDelta commenced in the Late Eocene as a result of a majorearth movement that structurally inverted the Abakalikiregion displacing the depositional axis further to the southof the Anambra basin [12]

Reports of various authors are valuable in the explorationactivities in the Anambra Basin Avbovbo and Ayoola [13]reviewed exploratory drilling result for the Anambra Basinand proposed that most parts of the basin probably con-tain gas-condensates due to abnormal geothermal gradientAgagu and Ekweozor [14] concluded that the senonian shalesin the Anambra syncline have good organic matter richnesswith maturity increasing significantly with depth Unomah

Hindawi Publishing CorporationJournal of GeochemistryVolume 2015 Article ID 809780 11 pageshttpdxdoiorg1011552015809780

2 Journal of Geochemistry

[15] evaluated the quality of organic matter in the UpperCretaceous shales of the Lower Benue Trough as the basisfor the reconstruction of the factors influencing organicsedimentation He deduced that the organic matter andshales were deposited under a low rate of deposition Specificreferences to the organic richness quality and thermalmaturity in the Mamu Formation and Nkporo shales havebeen reported by Unomah and Ekweozor [16] Akaegbobi[1] and Ekweozor [17] They reported that the sedimentsare organic rich but of immature status Iheanacho [18]investigated aspects of hydrocarbon source potential of theorganic rich shales belonging to some parts of the Anambrabasin He indicated the source rocks as shales and coalswhich present good prospects in terms of economic viabilityas typified by the quantity and quality of organic matter theycontain

This study thereby aims at producing an extensive molec-ular fossil record of some parts of Enugu Shale and coalmeasures of the Mamu Formation

2 Location of Study Area and Geology

The study area is located between latitude 6∘151015840Nndash6∘451015840Nand longitude 7∘151015840Endash7∘301015840E and falls within the Anam-bra Basin (Figure 1) The stratigraphic succession of theAnambra Basin at the second sedimentary phase comprisesthe Campanian-Maastrichtian EnuguNkporoOwelli For-mations (which are lateral equivalents) This is succeeded bytheMaastrichtianMamu Formation andAjali SandstoneThesequence is capped by the Tertiary Nsukka Formation andImo Shale These are discussed below

21 Nkporo-Enugu Shale Group These units consist of darkgrey fissile soft shales and mudstone with occasional thinbeds of sandy shale sandstone and shelly limestone Ashallow marine shelf environment has been predicted dueto the presence of foraminifera Milliamina plant remainspoorly preservedmolluscs and algal spores [2 19 20] Nyong[21] inferred the Nkporo Shale to have been deposited in avariety of environments including shallow open marine toparalic and continental settings

North of Awgu theNkporo Shale shows a well-developedmedium to coarse-grained sandstone facies referred to asOwelli SandstoneTheOwelli Sandstonemember is about 600metres thick [19]

22 Mamu Formation This formation is also known asldquoLower Coal Measuresrdquo It contains a distinctive assem-blage of sandstone sandy shale shale mudstone and coalseams [19] Surface sections reveal that the Mamu Forma-tion comprises mainly white fine-grained and well-sortedsands There are frequent interbeds of carbonaceous shaleswith sparse arenaceous microfauna and coal beds [20] Theexposed thickness of this Formation ranges from 5 to 15mAccording to Reyment [19] the coals occurring in Enuguarea are in five seams ranging from 30 cm to nearly 2mThe middle seammdashthe thickestmdashoutcrops along the Enugu

Geologic boundary approximateGeologic boundary inferredAnticlinal axis

Synclinal axis

Imsh

Nsh

LCM Lower coal measures

Ansh Shale and limestone (Awgu Fm)

Ess Sandstone (Eze-Aku group)

Esh Black shale siltstone and sandstone (Eze-Aku group)

Enugu 1325 wellEnugu 1331 wellRiversRailway

N7∘00

998400E 7∘30

998400E 8∘00

998400E7∘00

998400N

6∘30

998400N

6∘00

998400N

Shale and mudstone (Nkporo formation)

Clay and shale with limestone intercalationsmdashImo group

Figure 1 Geologic map of the Anambra Basin showing the studyarea

Escarpment for 11 km The coals of Enugu area form only apart of the total coal resources of Nigeria [19]

23 Ajali Sandstone This is a Maastrichtian sandy unit over-lying theMamu Formation It consists of white thick friablepoorly sorted cross-bedded sands with thin beds of whitemudstone near the base [22] Studies have suggested thatthe Ajali Sandstone is a continentalfluviodeltaic sequencecharacterised by a regressive phase of a short-lived Maas-trichtian transgression with sediments derived fromWesterlyareas of Abakaliki anticlinorium and the granitic basementunits of Adamawa-ObanMassifs [23] The Formation whereexposed is often overlain by red earth formed by weatheringand ferruginization of the Formation [24] According toNwajide and Reijers [25] the coal-bearingMamu Formationand Ajali Sandstone accumulated during the regressive phaseof the Nkporo Group with associated progradation Theauthors characterised the Ajali Sandstones as tidal sands

24 Nsukka Formation The Nsukka Formation is a LateMaastrichtian unit lying conformably on theAjali Sandstone

Journal of Geochemistry 3

The unit consists of alternating succession of sandstone darkshales and sandy shales with thin coal seams at varioushorizons hence termed the ldquoUpper Coal Measuresrdquo [22]TheFormation begins with coarse tomedium-grained sandstonespassing upward into well-bedded blue clays fine-grainedsandstones and carbonaceous shales with thin bands of lime-stone [12 19] Agagu et al [20] reported that the Formationhas a thickness range of 200ndash300mand consists of alternatingsuccession of fine-grained sandstonesiltstones and grey-dark shale with coal seams at various horizons A strandplainmarsh environment with occasional fluvial incursionssimilar to that of the Mamu Formation was inferred for thisFormation

25 Imo Shale The Imo Shale overlies the Nsukka Formationin the Anambra Basin and consists of blue-grey clays andblack shales with bands of calcareous sandstone marl andlimestone [19] Ostracod and foraminifera recovered fromthe basal limestone unit indicate a Paleocene age for theFormation [26] Lithology and trace fossils of the basalsandstone unit reflect foreshore and shoreface or delta frontsedimentation [27] The Imo Formation is the lateral equiv-alent of the Akata Formation in the subsurface Niger Delta[11] The Formation becomes sandier towards the top whereit consists of alternations of sandstone and shale [26]Nwajideand Reijers [25] interpreted the Imo Shale to reflect productof shallow-marine shelf in which foreshore and shoreface areoccasionally preserved

3 Weathering and Contaminationof Rock Samples

Borehole samples are preferred because they provide a con-tinuity of vertical sections over tens or hundreds of metresEven some of the best natural outcrops or exposures do notprovide this coverage because beds are weathered away [28]The weathering of outcrop samples and contamination couldgive rise to false and pessimistic indications of hydrocarbonpotential Although well samples can be contaminated bydrilling fluid additives (diesel contamination eg can berecognised from gas chromatography by the high concentra-tions of 119899-alkanes up to C

20) steranes and triterpenes should

be unaffected Borehole samples were therefore used for thisstudy

4 Analytical Methods

Borehole samples from Enugu 1325 and 1331 wells wereobtained from Nigerian Geological Survey Agency (NGSA)Kaduna and used in this study The borehole samples Enugu1325 range in depths from 165 to 177m while Well 1331 rangein depths from 219 to 233m Enugu well 1325 has a sequencebeginning from shale overlain by siltstone coal shale andsiltstone successively (Figure 2) The shales are dark grey andfissile the siltstone is brown to light grey while the coal isblackish Enugu well 1331 has a bottom to top sequence whichbegins from coal shale and siltstone successively In themiddle section is a siltstone-shale sequence which is overlain

Siltstone light grey to brown

Shale dark grey fissile

Shale dark grey fissile

Shale dark grey fissile Shale dark grey fissile

Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

P1

P2

P3

P4P5

Coal Shale Siltstone

Lithologic description

minus165

minus167

minus169

minus171

minus173

minus175

minus177

Scale 16 cm to 1m

Figure 2 Lithostratigraphic log of Enugu 1325 well

by another coal shale and siltstone succession (Figure 3)Thirteen (13) representative core samples made up of four (4)coal samples and nine (9) shale samples were subjected toorganic geochemical analysis

41 Total Organic Carbon (TOC) Determination Approx-imately 010 g of each pulverized sample was accuratelyweighed and then treated with concentrated hydrochloricacid (HCl) to remove carbonates The samples were left inhydrochloric acid for a minimum of two (2) hours The acidwas separated from the sample with a filtration apparatusfitted with a glass microfiber filter The filter was placed ina LECO crucible and dried at 110∘C for a minimum of onehour After drying the sample was analysed with a LECO600 Carbon Analyzer The analysis was carried out at theWeatherford Geochemical Laboratory Texas USA

42 Rock Eval Pyrolysis The thirteen samples were furthercharacterised by rock eval pyrolysis to identify the typeand maturity of organic matter and petroleum potentialin the studied area Rock-Eval II Pyroanalyzer was usedfor this analysis Pulverised samples were heated in aninert environment to measure the yield of three groups ofcompounds (S

1 S2 and S

3) measured as three peaks on a

program Sample heating at 300∘C for 3 minutes producedthe S1peak by vapourising the free hydrocarbons High

S1values indicate either large amounts of kerogen derived

bitumen or the presence of migrated hydrocarbonsThe oventemperature was increased by 25∘C per minute to 600∘C

4 Journal of Geochemistry

Lithologic description

Shale dark grey fissile

Coal blackish Coal blackish

Siltstone brown to light grey

Shale dark grey fissile

Shale dark grey fissile

Siltstone brown to light grey

Shale dark grey fissile Shale dark grey fissile Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

V4

V3V2V1

V5

V6

V8V7

minus219

minus221

minus223

minus225

minus227

minus229

minus231

minus233 Scale 14 cm to 5m

Coal Shale Siltstone

Figure 3 Lithostratigraphic log of Enugu 1331 well

The S2and S

3peaks were measured from the pyrolytic

degradation of the kerogen in the sample The S2peak is

proportional to the amount of hydrogen-rich kerogen inthe rock and the S

3peak measures the carbon dioxide

released providing an assessment of the oxygen content of therock The temperature at which S

2peak reaches maximummdash

119879maxmdashis a measure of the source rock maturity

43 Determination of Soluble Organic Matter (SOM) Thesoluble organic matter content of both shale and coal sampleswas carried out to estimate the free hydrogen content ofthe samples This was done using the Soxhlet System HT2Extraction Unit and Methylene ChlorideMethanol mixture(9 1) as the solvent Each pulverised sample after beenweighed was placed into labelled cellulose thimbles andplugged with glass wool and adapter For shale sample 20 gwas taken while 2ndash4 g was taken for coal The thimbleextraction cups and 100mls of methylene chloride methylsolution were placed inside a tecator system The solvent wasallowed to boil and then the thimbles were lowered into thesolvent and left for an hourThe stop corkwas closed for fasterevaporation After evaporation soluble matter were turnedinto preweighed labeled 20mL glass vials and dried withnitrogen at 40∘C The dried extract was weighed at roomtemperature

The soluble organic matter was then calculated thus

SOM (ppm) =Weight of extract (g)Weight of sample

times 106 (1)

The extraction was carried out at Exxon Mobil GeochemicalLaboratory Que Iboe Terminal (QIT) Eket

44 Gas Chromatography of Whole Oil The analyses werecarried out in a Hewlett Packard 6890A gas chromatographequipped with dual flame ionization detectors The chro-matograph was fitted with HP-1 capillary column (30m times032mm ID times 052 microns) using helium as the carriergas The column temperature was programmed at 35∘C to300∘Cmin with a flow rate of 11mlsmin The bitumenextract (SOM) was diluted with drops of carbon disulphidewhile agitating until sample is dissolved A little volume wasplaced in a labeled auto-sampler vial which was transferredto the autosampler tray for the analysis to run 10120583L of thediluted extract was rapidly injected to the gas chromatographin split mode using a graduated Hp 10120583L injection syringeThis analysis was carried out at the ExxonMobilGeochemicalLaboratory (QIT) Eket Nigeria

45 Gas Chromatography Mass Spectrometry For GCMSto be carried out on an extract (soluble organic matter)it must be separated into its fractions that is saturatearomatic asphaltene and resin The gravimetric columnchromatography method was applied in the separation ofextract into saturate aromatic resin and asphaltene fractions(SARA) It is modified from the ldquoSARArdquo procedure (ExxonMobil operation manual)

The saturate and aromatic fractions recovered from theliquid chromatography were analysed for their biomarkerby gas chromatographymass spectrometry (GCMS) usingthe selected ion monitoring mode (SIM) Hexane was addedto each sample vial containing the saturates and aromaticfractions to obtain concentrations of 25120583g120583L and 125 120583g120583Lrespectively The samples were mixed with a vortex mixerto agitate and then transferred to an auto-sampler vial andcapped Vials were then placed on the auto-sampler to be runin an HP 6890 gas chromatograph silica capillary column(30m times 025mm ID 025 120583m film thickness) coupled withHP 5973 Mass Selective Detector (MSD) The extract wasrapidly injected into the gas chromatograph using a 10120583Lsyringe Helium was used as the carrier gas with oventemperature programmed from 80∘C to 290∘C The massspectrometer was operated at electron energy of 70 Ev an ionsource temperature of 250∘C and separation temperature of250∘C The chromatographic data were acquired using MsChemstation software version G1701BA for Microsoft NTThis analysis was carried out at Exxon Mobil GeochemicalLaboratory Eket

46 Aromatic Biomarker Parameters According to Radkeet al [29] MPI-1 (methyl phenanthrene index) DNR-1(dimethyl naphthalene ratio) and MDR (methyl dibenzoth-iopene ratio) can be used as source and maturity parametersThe necessary calculations were made using the resultsobtained from peak identification and height of aromaticbiomarkers of the studied wells (see Table 2)

Journal of Geochemistry 5

Table 1 Data of TOC and rock-eval pyrolysis

Sample IDnumber

Depth(meter)

SOM(ppm)

TOC(wt)

S1(mgg)

S2(mgg)

S3(mgg)

119879max(∘C) HI OI S2S3 PI

(S1S1 + S2)GP

(S1 + S2)V1 minus2245 ND 33 055 457 111 428 138 34 412 011 512V2 minus223 3381 6624 428 1537 1207 431 232 18 1273 003 15851V3 minus222 3160 6351 387 1558 1579 434 245 25 987 002 15967V4 minus2205 ND 191 012 354 111 432 185 58 319 003 366V5 minus2275 4678 749 054 1771 167 433 237 22 106 003 1825V6 minus2315 19048 852 071 1425 233 426 167 27 612 005 1495V7 minus2325 ND 32 028 266 131 428 83 41 203 01 294V8 minus232 40952 6951 775 16961 1433 429 244 20 1184 004 17736P1 minus1685 5467 798 077 1255 253 435 157 32 496 006 1332P2 minus169 ND 6777 622 15335 1268 427 226 19 1209 004 15957P3 minus1725 2501 224 037 37 13 431 165 58 285 009 407P4 minus1745 ND 161 031 225 143 431 142 90 157 012 256P5 minus1755 ND 196 025 209 049 427 107 25 427 011 234Notes TOC=weight percentage organic carbon in rock S1 S2 =mg hydrocarbons per gram of rock S3 =mg carbon dioxide per gram of rock GP = petroleumgeneric potential = S1 + S2 ND = not done HI = Hydrogen Index = S2 times 100TOC OI = oxygen index = S3 times 100TOC 119879max =

∘C PI = production index =S1(S1 + S2)

5 Organic Richness

According to Conford [30] adequate amount of organicmatter measured as percentage total organic carbon is aprerequisite for sediment to generate oil or gas Shown inTable 1 are the results of total organic matter content (TOC)The coal samples from both wells show a higher organicrichness than shale Nevertheless both wells have valuesabove the threshold of 05 wt considered as minimum forclastic source rocks to generate petroleum [31] The solubleorganic matter (SOM) of the samples generally exceeds500 ppm except for samples P3 (EN 1325) and V5 (EN 1331)with SOM values of 2501 and 4678 ppm respectively Theseshow that the samples can be classified as fair to excellentsource rocks Based on the quality definition of Baker [32] theorganic matter is adequate and indicates good hydrocarbonpotential for the studied wells

6 Organic Matter Type

The organic matter type in a sedimentary rock among otherconditions influences to a large extent the type and quality ofhydrocarbon generated due to different organic matter typeconvertibilities [31] The Hydrogen Index (HI) for the shaleand coal samples ranges from 83 to 245mgHCgTOC withan average value of 178mgHCgTOCThis can be interpretedas type III (gas prone) The plot of hydrocarbon potentialversus TOC (Figure 4) indicates type IIIII organic matterwhich means a potential to generate oil and gasThemajorityfall within the type III organic matter indicating that gas willdominantly be generated with little oil Peters [33] suggestedthat at thermal maturity equivalent to vitrinite reflectanceof 06 (119879max 435∘C) rocks with HI gt 300mgHCgTOCproduce oil those with HI between 150mgHCgTOC and300mgHCgTOCproduce oil and gas thosewithHI between

Type IV inert

10 20 30 40 50 60 70 80

300

250

200

150

100

50

0

Well 1325Well 1331

Rem

aini

ng h

ydro

carb

on p

oten

tial S2

(mgH

Cg)

Type IIoil-proneusually marine

Mixed type II-IIIoil-gas-prone

Type IIIgas-prone

Type Ioil-proneusually lacustrine

Total organic carbonmdashTOC (wt)

Figure 4 A plot of hydrocarbon potential against TOC

50mgHCgTOC and 150mgHCgTOC produce gas andthose with HI lt 50mgHCgTOC are inert From this studythe range of HI is from 83 to 245 for the shales and coal Thisindicates oil and gas prone

Petroleum generating potential (GP) is the sum of S1

and S2values obtained from rock eval pyrolysis (Table 1)

The values obtained range from 234 to 17736 According toDyman et al [34] values greater than 2 kgHCton of rockindicate good source rockThis suggests oil and gas potential

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EarthquakesJournal of

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Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

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Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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MineralogyInternational Journal of

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MeteorologyAdvances in

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Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

2 Journal of Geochemistry

[15] evaluated the quality of organic matter in the UpperCretaceous shales of the Lower Benue Trough as the basisfor the reconstruction of the factors influencing organicsedimentation He deduced that the organic matter andshales were deposited under a low rate of deposition Specificreferences to the organic richness quality and thermalmaturity in the Mamu Formation and Nkporo shales havebeen reported by Unomah and Ekweozor [16] Akaegbobi[1] and Ekweozor [17] They reported that the sedimentsare organic rich but of immature status Iheanacho [18]investigated aspects of hydrocarbon source potential of theorganic rich shales belonging to some parts of the Anambrabasin He indicated the source rocks as shales and coalswhich present good prospects in terms of economic viabilityas typified by the quantity and quality of organic matter theycontain

This study thereby aims at producing an extensive molec-ular fossil record of some parts of Enugu Shale and coalmeasures of the Mamu Formation

2 Location of Study Area and Geology

The study area is located between latitude 6∘151015840Nndash6∘451015840Nand longitude 7∘151015840Endash7∘301015840E and falls within the Anam-bra Basin (Figure 1) The stratigraphic succession of theAnambra Basin at the second sedimentary phase comprisesthe Campanian-Maastrichtian EnuguNkporoOwelli For-mations (which are lateral equivalents) This is succeeded bytheMaastrichtianMamu Formation andAjali SandstoneThesequence is capped by the Tertiary Nsukka Formation andImo Shale These are discussed below

21 Nkporo-Enugu Shale Group These units consist of darkgrey fissile soft shales and mudstone with occasional thinbeds of sandy shale sandstone and shelly limestone Ashallow marine shelf environment has been predicted dueto the presence of foraminifera Milliamina plant remainspoorly preservedmolluscs and algal spores [2 19 20] Nyong[21] inferred the Nkporo Shale to have been deposited in avariety of environments including shallow open marine toparalic and continental settings

North of Awgu theNkporo Shale shows a well-developedmedium to coarse-grained sandstone facies referred to asOwelli SandstoneTheOwelli Sandstonemember is about 600metres thick [19]

22 Mamu Formation This formation is also known asldquoLower Coal Measuresrdquo It contains a distinctive assem-blage of sandstone sandy shale shale mudstone and coalseams [19] Surface sections reveal that the Mamu Forma-tion comprises mainly white fine-grained and well-sortedsands There are frequent interbeds of carbonaceous shaleswith sparse arenaceous microfauna and coal beds [20] Theexposed thickness of this Formation ranges from 5 to 15mAccording to Reyment [19] the coals occurring in Enuguarea are in five seams ranging from 30 cm to nearly 2mThe middle seammdashthe thickestmdashoutcrops along the Enugu

Geologic boundary approximateGeologic boundary inferredAnticlinal axis

Synclinal axis

Imsh

Nsh

LCM Lower coal measures

Ansh Shale and limestone (Awgu Fm)

Ess Sandstone (Eze-Aku group)

Esh Black shale siltstone and sandstone (Eze-Aku group)

Enugu 1325 wellEnugu 1331 wellRiversRailway

N7∘00

998400E 7∘30

998400E 8∘00

998400E7∘00

998400N

6∘30

998400N

6∘00

998400N

Shale and mudstone (Nkporo formation)

Clay and shale with limestone intercalationsmdashImo group

Figure 1 Geologic map of the Anambra Basin showing the studyarea

Escarpment for 11 km The coals of Enugu area form only apart of the total coal resources of Nigeria [19]

23 Ajali Sandstone This is a Maastrichtian sandy unit over-lying theMamu Formation It consists of white thick friablepoorly sorted cross-bedded sands with thin beds of whitemudstone near the base [22] Studies have suggested thatthe Ajali Sandstone is a continentalfluviodeltaic sequencecharacterised by a regressive phase of a short-lived Maas-trichtian transgression with sediments derived fromWesterlyareas of Abakaliki anticlinorium and the granitic basementunits of Adamawa-ObanMassifs [23] The Formation whereexposed is often overlain by red earth formed by weatheringand ferruginization of the Formation [24] According toNwajide and Reijers [25] the coal-bearingMamu Formationand Ajali Sandstone accumulated during the regressive phaseof the Nkporo Group with associated progradation Theauthors characterised the Ajali Sandstones as tidal sands

24 Nsukka Formation The Nsukka Formation is a LateMaastrichtian unit lying conformably on theAjali Sandstone

Journal of Geochemistry 3

The unit consists of alternating succession of sandstone darkshales and sandy shales with thin coal seams at varioushorizons hence termed the ldquoUpper Coal Measuresrdquo [22]TheFormation begins with coarse tomedium-grained sandstonespassing upward into well-bedded blue clays fine-grainedsandstones and carbonaceous shales with thin bands of lime-stone [12 19] Agagu et al [20] reported that the Formationhas a thickness range of 200ndash300mand consists of alternatingsuccession of fine-grained sandstonesiltstones and grey-dark shale with coal seams at various horizons A strandplainmarsh environment with occasional fluvial incursionssimilar to that of the Mamu Formation was inferred for thisFormation

25 Imo Shale The Imo Shale overlies the Nsukka Formationin the Anambra Basin and consists of blue-grey clays andblack shales with bands of calcareous sandstone marl andlimestone [19] Ostracod and foraminifera recovered fromthe basal limestone unit indicate a Paleocene age for theFormation [26] Lithology and trace fossils of the basalsandstone unit reflect foreshore and shoreface or delta frontsedimentation [27] The Imo Formation is the lateral equiv-alent of the Akata Formation in the subsurface Niger Delta[11] The Formation becomes sandier towards the top whereit consists of alternations of sandstone and shale [26]Nwajideand Reijers [25] interpreted the Imo Shale to reflect productof shallow-marine shelf in which foreshore and shoreface areoccasionally preserved

3 Weathering and Contaminationof Rock Samples

Borehole samples are preferred because they provide a con-tinuity of vertical sections over tens or hundreds of metresEven some of the best natural outcrops or exposures do notprovide this coverage because beds are weathered away [28]The weathering of outcrop samples and contamination couldgive rise to false and pessimistic indications of hydrocarbonpotential Although well samples can be contaminated bydrilling fluid additives (diesel contamination eg can berecognised from gas chromatography by the high concentra-tions of 119899-alkanes up to C

20) steranes and triterpenes should

be unaffected Borehole samples were therefore used for thisstudy

4 Analytical Methods

Borehole samples from Enugu 1325 and 1331 wells wereobtained from Nigerian Geological Survey Agency (NGSA)Kaduna and used in this study The borehole samples Enugu1325 range in depths from 165 to 177m while Well 1331 rangein depths from 219 to 233m Enugu well 1325 has a sequencebeginning from shale overlain by siltstone coal shale andsiltstone successively (Figure 2) The shales are dark grey andfissile the siltstone is brown to light grey while the coal isblackish Enugu well 1331 has a bottom to top sequence whichbegins from coal shale and siltstone successively In themiddle section is a siltstone-shale sequence which is overlain

Siltstone light grey to brown

Shale dark grey fissile

Shale dark grey fissile

Shale dark grey fissile Shale dark grey fissile

Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

P1

P2

P3

P4P5

Coal Shale Siltstone

Lithologic description

minus165

minus167

minus169

minus171

minus173

minus175

minus177

Scale 16 cm to 1m

Figure 2 Lithostratigraphic log of Enugu 1325 well

by another coal shale and siltstone succession (Figure 3)Thirteen (13) representative core samples made up of four (4)coal samples and nine (9) shale samples were subjected toorganic geochemical analysis

41 Total Organic Carbon (TOC) Determination Approx-imately 010 g of each pulverized sample was accuratelyweighed and then treated with concentrated hydrochloricacid (HCl) to remove carbonates The samples were left inhydrochloric acid for a minimum of two (2) hours The acidwas separated from the sample with a filtration apparatusfitted with a glass microfiber filter The filter was placed ina LECO crucible and dried at 110∘C for a minimum of onehour After drying the sample was analysed with a LECO600 Carbon Analyzer The analysis was carried out at theWeatherford Geochemical Laboratory Texas USA

42 Rock Eval Pyrolysis The thirteen samples were furthercharacterised by rock eval pyrolysis to identify the typeand maturity of organic matter and petroleum potentialin the studied area Rock-Eval II Pyroanalyzer was usedfor this analysis Pulverised samples were heated in aninert environment to measure the yield of three groups ofcompounds (S

1 S2 and S

3) measured as three peaks on a

program Sample heating at 300∘C for 3 minutes producedthe S1peak by vapourising the free hydrocarbons High

S1values indicate either large amounts of kerogen derived

bitumen or the presence of migrated hydrocarbonsThe oventemperature was increased by 25∘C per minute to 600∘C

4 Journal of Geochemistry

Lithologic description

Shale dark grey fissile

Coal blackish Coal blackish

Siltstone brown to light grey

Shale dark grey fissile

Shale dark grey fissile

Siltstone brown to light grey

Shale dark grey fissile Shale dark grey fissile Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

V4

V3V2V1

V5

V6

V8V7

minus219

minus221

minus223

minus225

minus227

minus229

minus231

minus233 Scale 14 cm to 5m

Coal Shale Siltstone

Figure 3 Lithostratigraphic log of Enugu 1331 well

The S2and S

3peaks were measured from the pyrolytic

degradation of the kerogen in the sample The S2peak is

proportional to the amount of hydrogen-rich kerogen inthe rock and the S

3peak measures the carbon dioxide

released providing an assessment of the oxygen content of therock The temperature at which S

2peak reaches maximummdash

119879maxmdashis a measure of the source rock maturity

43 Determination of Soluble Organic Matter (SOM) Thesoluble organic matter content of both shale and coal sampleswas carried out to estimate the free hydrogen content ofthe samples This was done using the Soxhlet System HT2Extraction Unit and Methylene ChlorideMethanol mixture(9 1) as the solvent Each pulverised sample after beenweighed was placed into labelled cellulose thimbles andplugged with glass wool and adapter For shale sample 20 gwas taken while 2ndash4 g was taken for coal The thimbleextraction cups and 100mls of methylene chloride methylsolution were placed inside a tecator system The solvent wasallowed to boil and then the thimbles were lowered into thesolvent and left for an hourThe stop corkwas closed for fasterevaporation After evaporation soluble matter were turnedinto preweighed labeled 20mL glass vials and dried withnitrogen at 40∘C The dried extract was weighed at roomtemperature

The soluble organic matter was then calculated thus

SOM (ppm) =Weight of extract (g)Weight of sample

times 106 (1)

The extraction was carried out at Exxon Mobil GeochemicalLaboratory Que Iboe Terminal (QIT) Eket

44 Gas Chromatography of Whole Oil The analyses werecarried out in a Hewlett Packard 6890A gas chromatographequipped with dual flame ionization detectors The chro-matograph was fitted with HP-1 capillary column (30m times032mm ID times 052 microns) using helium as the carriergas The column temperature was programmed at 35∘C to300∘Cmin with a flow rate of 11mlsmin The bitumenextract (SOM) was diluted with drops of carbon disulphidewhile agitating until sample is dissolved A little volume wasplaced in a labeled auto-sampler vial which was transferredto the autosampler tray for the analysis to run 10120583L of thediluted extract was rapidly injected to the gas chromatographin split mode using a graduated Hp 10120583L injection syringeThis analysis was carried out at the ExxonMobilGeochemicalLaboratory (QIT) Eket Nigeria

45 Gas Chromatography Mass Spectrometry For GCMSto be carried out on an extract (soluble organic matter)it must be separated into its fractions that is saturatearomatic asphaltene and resin The gravimetric columnchromatography method was applied in the separation ofextract into saturate aromatic resin and asphaltene fractions(SARA) It is modified from the ldquoSARArdquo procedure (ExxonMobil operation manual)

The saturate and aromatic fractions recovered from theliquid chromatography were analysed for their biomarkerby gas chromatographymass spectrometry (GCMS) usingthe selected ion monitoring mode (SIM) Hexane was addedto each sample vial containing the saturates and aromaticfractions to obtain concentrations of 25120583g120583L and 125 120583g120583Lrespectively The samples were mixed with a vortex mixerto agitate and then transferred to an auto-sampler vial andcapped Vials were then placed on the auto-sampler to be runin an HP 6890 gas chromatograph silica capillary column(30m times 025mm ID 025 120583m film thickness) coupled withHP 5973 Mass Selective Detector (MSD) The extract wasrapidly injected into the gas chromatograph using a 10120583Lsyringe Helium was used as the carrier gas with oventemperature programmed from 80∘C to 290∘C The massspectrometer was operated at electron energy of 70 Ev an ionsource temperature of 250∘C and separation temperature of250∘C The chromatographic data were acquired using MsChemstation software version G1701BA for Microsoft NTThis analysis was carried out at Exxon Mobil GeochemicalLaboratory Eket

46 Aromatic Biomarker Parameters According to Radkeet al [29] MPI-1 (methyl phenanthrene index) DNR-1(dimethyl naphthalene ratio) and MDR (methyl dibenzoth-iopene ratio) can be used as source and maturity parametersThe necessary calculations were made using the resultsobtained from peak identification and height of aromaticbiomarkers of the studied wells (see Table 2)

Journal of Geochemistry 5

Table 1 Data of TOC and rock-eval pyrolysis

Sample IDnumber

Depth(meter)

SOM(ppm)

TOC(wt)

S1(mgg)

S2(mgg)

S3(mgg)

119879max(∘C) HI OI S2S3 PI

(S1S1 + S2)GP

(S1 + S2)V1 minus2245 ND 33 055 457 111 428 138 34 412 011 512V2 minus223 3381 6624 428 1537 1207 431 232 18 1273 003 15851V3 minus222 3160 6351 387 1558 1579 434 245 25 987 002 15967V4 minus2205 ND 191 012 354 111 432 185 58 319 003 366V5 minus2275 4678 749 054 1771 167 433 237 22 106 003 1825V6 minus2315 19048 852 071 1425 233 426 167 27 612 005 1495V7 minus2325 ND 32 028 266 131 428 83 41 203 01 294V8 minus232 40952 6951 775 16961 1433 429 244 20 1184 004 17736P1 minus1685 5467 798 077 1255 253 435 157 32 496 006 1332P2 minus169 ND 6777 622 15335 1268 427 226 19 1209 004 15957P3 minus1725 2501 224 037 37 13 431 165 58 285 009 407P4 minus1745 ND 161 031 225 143 431 142 90 157 012 256P5 minus1755 ND 196 025 209 049 427 107 25 427 011 234Notes TOC=weight percentage organic carbon in rock S1 S2 =mg hydrocarbons per gram of rock S3 =mg carbon dioxide per gram of rock GP = petroleumgeneric potential = S1 + S2 ND = not done HI = Hydrogen Index = S2 times 100TOC OI = oxygen index = S3 times 100TOC 119879max =

∘C PI = production index =S1(S1 + S2)

5 Organic Richness

According to Conford [30] adequate amount of organicmatter measured as percentage total organic carbon is aprerequisite for sediment to generate oil or gas Shown inTable 1 are the results of total organic matter content (TOC)The coal samples from both wells show a higher organicrichness than shale Nevertheless both wells have valuesabove the threshold of 05 wt considered as minimum forclastic source rocks to generate petroleum [31] The solubleorganic matter (SOM) of the samples generally exceeds500 ppm except for samples P3 (EN 1325) and V5 (EN 1331)with SOM values of 2501 and 4678 ppm respectively Theseshow that the samples can be classified as fair to excellentsource rocks Based on the quality definition of Baker [32] theorganic matter is adequate and indicates good hydrocarbonpotential for the studied wells

6 Organic Matter Type

The organic matter type in a sedimentary rock among otherconditions influences to a large extent the type and quality ofhydrocarbon generated due to different organic matter typeconvertibilities [31] The Hydrogen Index (HI) for the shaleand coal samples ranges from 83 to 245mgHCgTOC withan average value of 178mgHCgTOCThis can be interpretedas type III (gas prone) The plot of hydrocarbon potentialversus TOC (Figure 4) indicates type IIIII organic matterwhich means a potential to generate oil and gasThemajorityfall within the type III organic matter indicating that gas willdominantly be generated with little oil Peters [33] suggestedthat at thermal maturity equivalent to vitrinite reflectanceof 06 (119879max 435∘C) rocks with HI gt 300mgHCgTOCproduce oil those with HI between 150mgHCgTOC and300mgHCgTOCproduce oil and gas thosewithHI between

Type IV inert

10 20 30 40 50 60 70 80

300

250

200

150

100

50

0

Well 1325Well 1331

Rem

aini

ng h

ydro

carb

on p

oten

tial S2

(mgH

Cg)

Type IIoil-proneusually marine

Mixed type II-IIIoil-gas-prone

Type IIIgas-prone

Type Ioil-proneusually lacustrine

Total organic carbonmdashTOC (wt)

Figure 4 A plot of hydrocarbon potential against TOC

50mgHCgTOC and 150mgHCgTOC produce gas andthose with HI lt 50mgHCgTOC are inert From this studythe range of HI is from 83 to 245 for the shales and coal Thisindicates oil and gas prone

Petroleum generating potential (GP) is the sum of S1

and S2values obtained from rock eval pyrolysis (Table 1)

The values obtained range from 234 to 17736 According toDyman et al [34] values greater than 2 kgHCton of rockindicate good source rockThis suggests oil and gas potential

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geology Advances in

Journal of Geochemistry 3

The unit consists of alternating succession of sandstone darkshales and sandy shales with thin coal seams at varioushorizons hence termed the ldquoUpper Coal Measuresrdquo [22]TheFormation begins with coarse tomedium-grained sandstonespassing upward into well-bedded blue clays fine-grainedsandstones and carbonaceous shales with thin bands of lime-stone [12 19] Agagu et al [20] reported that the Formationhas a thickness range of 200ndash300mand consists of alternatingsuccession of fine-grained sandstonesiltstones and grey-dark shale with coal seams at various horizons A strandplainmarsh environment with occasional fluvial incursionssimilar to that of the Mamu Formation was inferred for thisFormation

25 Imo Shale The Imo Shale overlies the Nsukka Formationin the Anambra Basin and consists of blue-grey clays andblack shales with bands of calcareous sandstone marl andlimestone [19] Ostracod and foraminifera recovered fromthe basal limestone unit indicate a Paleocene age for theFormation [26] Lithology and trace fossils of the basalsandstone unit reflect foreshore and shoreface or delta frontsedimentation [27] The Imo Formation is the lateral equiv-alent of the Akata Formation in the subsurface Niger Delta[11] The Formation becomes sandier towards the top whereit consists of alternations of sandstone and shale [26]Nwajideand Reijers [25] interpreted the Imo Shale to reflect productof shallow-marine shelf in which foreshore and shoreface areoccasionally preserved

3 Weathering and Contaminationof Rock Samples

Borehole samples are preferred because they provide a con-tinuity of vertical sections over tens or hundreds of metresEven some of the best natural outcrops or exposures do notprovide this coverage because beds are weathered away [28]The weathering of outcrop samples and contamination couldgive rise to false and pessimistic indications of hydrocarbonpotential Although well samples can be contaminated bydrilling fluid additives (diesel contamination eg can berecognised from gas chromatography by the high concentra-tions of 119899-alkanes up to C

20) steranes and triterpenes should

be unaffected Borehole samples were therefore used for thisstudy

4 Analytical Methods

Borehole samples from Enugu 1325 and 1331 wells wereobtained from Nigerian Geological Survey Agency (NGSA)Kaduna and used in this study The borehole samples Enugu1325 range in depths from 165 to 177m while Well 1331 rangein depths from 219 to 233m Enugu well 1325 has a sequencebeginning from shale overlain by siltstone coal shale andsiltstone successively (Figure 2) The shales are dark grey andfissile the siltstone is brown to light grey while the coal isblackish Enugu well 1331 has a bottom to top sequence whichbegins from coal shale and siltstone successively In themiddle section is a siltstone-shale sequence which is overlain

Siltstone light grey to brown

Shale dark grey fissile

Shale dark grey fissile

Shale dark grey fissile Shale dark grey fissile

Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

P1

P2

P3

P4P5

Coal Shale Siltstone

Lithologic description

minus165

minus167

minus169

minus171

minus173

minus175

minus177

Scale 16 cm to 1m

Figure 2 Lithostratigraphic log of Enugu 1325 well

by another coal shale and siltstone succession (Figure 3)Thirteen (13) representative core samples made up of four (4)coal samples and nine (9) shale samples were subjected toorganic geochemical analysis

41 Total Organic Carbon (TOC) Determination Approx-imately 010 g of each pulverized sample was accuratelyweighed and then treated with concentrated hydrochloricacid (HCl) to remove carbonates The samples were left inhydrochloric acid for a minimum of two (2) hours The acidwas separated from the sample with a filtration apparatusfitted with a glass microfiber filter The filter was placed ina LECO crucible and dried at 110∘C for a minimum of onehour After drying the sample was analysed with a LECO600 Carbon Analyzer The analysis was carried out at theWeatherford Geochemical Laboratory Texas USA

42 Rock Eval Pyrolysis The thirteen samples were furthercharacterised by rock eval pyrolysis to identify the typeand maturity of organic matter and petroleum potentialin the studied area Rock-Eval II Pyroanalyzer was usedfor this analysis Pulverised samples were heated in aninert environment to measure the yield of three groups ofcompounds (S

1 S2 and S

3) measured as three peaks on a

program Sample heating at 300∘C for 3 minutes producedthe S1peak by vapourising the free hydrocarbons High

S1values indicate either large amounts of kerogen derived

bitumen or the presence of migrated hydrocarbonsThe oventemperature was increased by 25∘C per minute to 600∘C

4 Journal of Geochemistry

Lithologic description

Shale dark grey fissile

Coal blackish Coal blackish

Siltstone brown to light grey

Shale dark grey fissile

Shale dark grey fissile

Siltstone brown to light grey

Shale dark grey fissile Shale dark grey fissile Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

V4

V3V2V1

V5

V6

V8V7

minus219

minus221

minus223

minus225

minus227

minus229

minus231

minus233 Scale 14 cm to 5m

Coal Shale Siltstone

Figure 3 Lithostratigraphic log of Enugu 1331 well

The S2and S

3peaks were measured from the pyrolytic

degradation of the kerogen in the sample The S2peak is

proportional to the amount of hydrogen-rich kerogen inthe rock and the S

3peak measures the carbon dioxide

released providing an assessment of the oxygen content of therock The temperature at which S

2peak reaches maximummdash

119879maxmdashis a measure of the source rock maturity

43 Determination of Soluble Organic Matter (SOM) Thesoluble organic matter content of both shale and coal sampleswas carried out to estimate the free hydrogen content ofthe samples This was done using the Soxhlet System HT2Extraction Unit and Methylene ChlorideMethanol mixture(9 1) as the solvent Each pulverised sample after beenweighed was placed into labelled cellulose thimbles andplugged with glass wool and adapter For shale sample 20 gwas taken while 2ndash4 g was taken for coal The thimbleextraction cups and 100mls of methylene chloride methylsolution were placed inside a tecator system The solvent wasallowed to boil and then the thimbles were lowered into thesolvent and left for an hourThe stop corkwas closed for fasterevaporation After evaporation soluble matter were turnedinto preweighed labeled 20mL glass vials and dried withnitrogen at 40∘C The dried extract was weighed at roomtemperature

The soluble organic matter was then calculated thus

SOM (ppm) =Weight of extract (g)Weight of sample

times 106 (1)

The extraction was carried out at Exxon Mobil GeochemicalLaboratory Que Iboe Terminal (QIT) Eket

44 Gas Chromatography of Whole Oil The analyses werecarried out in a Hewlett Packard 6890A gas chromatographequipped with dual flame ionization detectors The chro-matograph was fitted with HP-1 capillary column (30m times032mm ID times 052 microns) using helium as the carriergas The column temperature was programmed at 35∘C to300∘Cmin with a flow rate of 11mlsmin The bitumenextract (SOM) was diluted with drops of carbon disulphidewhile agitating until sample is dissolved A little volume wasplaced in a labeled auto-sampler vial which was transferredto the autosampler tray for the analysis to run 10120583L of thediluted extract was rapidly injected to the gas chromatographin split mode using a graduated Hp 10120583L injection syringeThis analysis was carried out at the ExxonMobilGeochemicalLaboratory (QIT) Eket Nigeria

45 Gas Chromatography Mass Spectrometry For GCMSto be carried out on an extract (soluble organic matter)it must be separated into its fractions that is saturatearomatic asphaltene and resin The gravimetric columnchromatography method was applied in the separation ofextract into saturate aromatic resin and asphaltene fractions(SARA) It is modified from the ldquoSARArdquo procedure (ExxonMobil operation manual)

The saturate and aromatic fractions recovered from theliquid chromatography were analysed for their biomarkerby gas chromatographymass spectrometry (GCMS) usingthe selected ion monitoring mode (SIM) Hexane was addedto each sample vial containing the saturates and aromaticfractions to obtain concentrations of 25120583g120583L and 125 120583g120583Lrespectively The samples were mixed with a vortex mixerto agitate and then transferred to an auto-sampler vial andcapped Vials were then placed on the auto-sampler to be runin an HP 6890 gas chromatograph silica capillary column(30m times 025mm ID 025 120583m film thickness) coupled withHP 5973 Mass Selective Detector (MSD) The extract wasrapidly injected into the gas chromatograph using a 10120583Lsyringe Helium was used as the carrier gas with oventemperature programmed from 80∘C to 290∘C The massspectrometer was operated at electron energy of 70 Ev an ionsource temperature of 250∘C and separation temperature of250∘C The chromatographic data were acquired using MsChemstation software version G1701BA for Microsoft NTThis analysis was carried out at Exxon Mobil GeochemicalLaboratory Eket

46 Aromatic Biomarker Parameters According to Radkeet al [29] MPI-1 (methyl phenanthrene index) DNR-1(dimethyl naphthalene ratio) and MDR (methyl dibenzoth-iopene ratio) can be used as source and maturity parametersThe necessary calculations were made using the resultsobtained from peak identification and height of aromaticbiomarkers of the studied wells (see Table 2)

Journal of Geochemistry 5

Table 1 Data of TOC and rock-eval pyrolysis

Sample IDnumber

Depth(meter)

SOM(ppm)

TOC(wt)

S1(mgg)

S2(mgg)

S3(mgg)

119879max(∘C) HI OI S2S3 PI

(S1S1 + S2)GP

(S1 + S2)V1 minus2245 ND 33 055 457 111 428 138 34 412 011 512V2 minus223 3381 6624 428 1537 1207 431 232 18 1273 003 15851V3 minus222 3160 6351 387 1558 1579 434 245 25 987 002 15967V4 minus2205 ND 191 012 354 111 432 185 58 319 003 366V5 minus2275 4678 749 054 1771 167 433 237 22 106 003 1825V6 minus2315 19048 852 071 1425 233 426 167 27 612 005 1495V7 minus2325 ND 32 028 266 131 428 83 41 203 01 294V8 minus232 40952 6951 775 16961 1433 429 244 20 1184 004 17736P1 minus1685 5467 798 077 1255 253 435 157 32 496 006 1332P2 minus169 ND 6777 622 15335 1268 427 226 19 1209 004 15957P3 minus1725 2501 224 037 37 13 431 165 58 285 009 407P4 minus1745 ND 161 031 225 143 431 142 90 157 012 256P5 minus1755 ND 196 025 209 049 427 107 25 427 011 234Notes TOC=weight percentage organic carbon in rock S1 S2 =mg hydrocarbons per gram of rock S3 =mg carbon dioxide per gram of rock GP = petroleumgeneric potential = S1 + S2 ND = not done HI = Hydrogen Index = S2 times 100TOC OI = oxygen index = S3 times 100TOC 119879max =

∘C PI = production index =S1(S1 + S2)

5 Organic Richness

According to Conford [30] adequate amount of organicmatter measured as percentage total organic carbon is aprerequisite for sediment to generate oil or gas Shown inTable 1 are the results of total organic matter content (TOC)The coal samples from both wells show a higher organicrichness than shale Nevertheless both wells have valuesabove the threshold of 05 wt considered as minimum forclastic source rocks to generate petroleum [31] The solubleorganic matter (SOM) of the samples generally exceeds500 ppm except for samples P3 (EN 1325) and V5 (EN 1331)with SOM values of 2501 and 4678 ppm respectively Theseshow that the samples can be classified as fair to excellentsource rocks Based on the quality definition of Baker [32] theorganic matter is adequate and indicates good hydrocarbonpotential for the studied wells

6 Organic Matter Type

The organic matter type in a sedimentary rock among otherconditions influences to a large extent the type and quality ofhydrocarbon generated due to different organic matter typeconvertibilities [31] The Hydrogen Index (HI) for the shaleand coal samples ranges from 83 to 245mgHCgTOC withan average value of 178mgHCgTOCThis can be interpretedas type III (gas prone) The plot of hydrocarbon potentialversus TOC (Figure 4) indicates type IIIII organic matterwhich means a potential to generate oil and gasThemajorityfall within the type III organic matter indicating that gas willdominantly be generated with little oil Peters [33] suggestedthat at thermal maturity equivalent to vitrinite reflectanceof 06 (119879max 435∘C) rocks with HI gt 300mgHCgTOCproduce oil those with HI between 150mgHCgTOC and300mgHCgTOCproduce oil and gas thosewithHI between

Type IV inert

10 20 30 40 50 60 70 80

300

250

200

150

100

50

0

Well 1325Well 1331

Rem

aini

ng h

ydro

carb

on p

oten

tial S2

(mgH

Cg)

Type IIoil-proneusually marine

Mixed type II-IIIoil-gas-prone

Type IIIgas-prone

Type Ioil-proneusually lacustrine

Total organic carbonmdashTOC (wt)

Figure 4 A plot of hydrocarbon potential against TOC

50mgHCgTOC and 150mgHCgTOC produce gas andthose with HI lt 50mgHCgTOC are inert From this studythe range of HI is from 83 to 245 for the shales and coal Thisindicates oil and gas prone

Petroleum generating potential (GP) is the sum of S1

and S2values obtained from rock eval pyrolysis (Table 1)

The values obtained range from 234 to 17736 According toDyman et al [34] values greater than 2 kgHCton of rockindicate good source rockThis suggests oil and gas potential

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EarthquakesJournal of

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Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

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OceanographyInternational Journal of

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Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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MineralogyInternational Journal of

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MeteorologyAdvances in

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Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

4 Journal of Geochemistry

Lithologic description

Shale dark grey fissile

Coal blackish Coal blackish

Siltstone brown to light grey

Shale dark grey fissile

Shale dark grey fissile

Siltstone brown to light grey

Shale dark grey fissile Shale dark grey fissile Coal blackish

Sam

ple I

D

num

ber

Lith

olog

y

Thic

knes

s (m

)

V4

V3V2V1

V5

V6

V8V7

minus219

minus221

minus223

minus225

minus227

minus229

minus231

minus233 Scale 14 cm to 5m

Coal Shale Siltstone

Figure 3 Lithostratigraphic log of Enugu 1331 well

The S2and S

3peaks were measured from the pyrolytic

degradation of the kerogen in the sample The S2peak is

proportional to the amount of hydrogen-rich kerogen inthe rock and the S

3peak measures the carbon dioxide

released providing an assessment of the oxygen content of therock The temperature at which S

2peak reaches maximummdash

119879maxmdashis a measure of the source rock maturity

43 Determination of Soluble Organic Matter (SOM) Thesoluble organic matter content of both shale and coal sampleswas carried out to estimate the free hydrogen content ofthe samples This was done using the Soxhlet System HT2Extraction Unit and Methylene ChlorideMethanol mixture(9 1) as the solvent Each pulverised sample after beenweighed was placed into labelled cellulose thimbles andplugged with glass wool and adapter For shale sample 20 gwas taken while 2ndash4 g was taken for coal The thimbleextraction cups and 100mls of methylene chloride methylsolution were placed inside a tecator system The solvent wasallowed to boil and then the thimbles were lowered into thesolvent and left for an hourThe stop corkwas closed for fasterevaporation After evaporation soluble matter were turnedinto preweighed labeled 20mL glass vials and dried withnitrogen at 40∘C The dried extract was weighed at roomtemperature

The soluble organic matter was then calculated thus

SOM (ppm) =Weight of extract (g)Weight of sample

times 106 (1)

The extraction was carried out at Exxon Mobil GeochemicalLaboratory Que Iboe Terminal (QIT) Eket

44 Gas Chromatography of Whole Oil The analyses werecarried out in a Hewlett Packard 6890A gas chromatographequipped with dual flame ionization detectors The chro-matograph was fitted with HP-1 capillary column (30m times032mm ID times 052 microns) using helium as the carriergas The column temperature was programmed at 35∘C to300∘Cmin with a flow rate of 11mlsmin The bitumenextract (SOM) was diluted with drops of carbon disulphidewhile agitating until sample is dissolved A little volume wasplaced in a labeled auto-sampler vial which was transferredto the autosampler tray for the analysis to run 10120583L of thediluted extract was rapidly injected to the gas chromatographin split mode using a graduated Hp 10120583L injection syringeThis analysis was carried out at the ExxonMobilGeochemicalLaboratory (QIT) Eket Nigeria

45 Gas Chromatography Mass Spectrometry For GCMSto be carried out on an extract (soluble organic matter)it must be separated into its fractions that is saturatearomatic asphaltene and resin The gravimetric columnchromatography method was applied in the separation ofextract into saturate aromatic resin and asphaltene fractions(SARA) It is modified from the ldquoSARArdquo procedure (ExxonMobil operation manual)

The saturate and aromatic fractions recovered from theliquid chromatography were analysed for their biomarkerby gas chromatographymass spectrometry (GCMS) usingthe selected ion monitoring mode (SIM) Hexane was addedto each sample vial containing the saturates and aromaticfractions to obtain concentrations of 25120583g120583L and 125 120583g120583Lrespectively The samples were mixed with a vortex mixerto agitate and then transferred to an auto-sampler vial andcapped Vials were then placed on the auto-sampler to be runin an HP 6890 gas chromatograph silica capillary column(30m times 025mm ID 025 120583m film thickness) coupled withHP 5973 Mass Selective Detector (MSD) The extract wasrapidly injected into the gas chromatograph using a 10120583Lsyringe Helium was used as the carrier gas with oventemperature programmed from 80∘C to 290∘C The massspectrometer was operated at electron energy of 70 Ev an ionsource temperature of 250∘C and separation temperature of250∘C The chromatographic data were acquired using MsChemstation software version G1701BA for Microsoft NTThis analysis was carried out at Exxon Mobil GeochemicalLaboratory Eket

46 Aromatic Biomarker Parameters According to Radkeet al [29] MPI-1 (methyl phenanthrene index) DNR-1(dimethyl naphthalene ratio) and MDR (methyl dibenzoth-iopene ratio) can be used as source and maturity parametersThe necessary calculations were made using the resultsobtained from peak identification and height of aromaticbiomarkers of the studied wells (see Table 2)

Journal of Geochemistry 5

Table 1 Data of TOC and rock-eval pyrolysis

Sample IDnumber

Depth(meter)

SOM(ppm)

TOC(wt)

S1(mgg)

S2(mgg)

S3(mgg)

119879max(∘C) HI OI S2S3 PI

(S1S1 + S2)GP

(S1 + S2)V1 minus2245 ND 33 055 457 111 428 138 34 412 011 512V2 minus223 3381 6624 428 1537 1207 431 232 18 1273 003 15851V3 minus222 3160 6351 387 1558 1579 434 245 25 987 002 15967V4 minus2205 ND 191 012 354 111 432 185 58 319 003 366V5 minus2275 4678 749 054 1771 167 433 237 22 106 003 1825V6 minus2315 19048 852 071 1425 233 426 167 27 612 005 1495V7 minus2325 ND 32 028 266 131 428 83 41 203 01 294V8 minus232 40952 6951 775 16961 1433 429 244 20 1184 004 17736P1 minus1685 5467 798 077 1255 253 435 157 32 496 006 1332P2 minus169 ND 6777 622 15335 1268 427 226 19 1209 004 15957P3 minus1725 2501 224 037 37 13 431 165 58 285 009 407P4 minus1745 ND 161 031 225 143 431 142 90 157 012 256P5 minus1755 ND 196 025 209 049 427 107 25 427 011 234Notes TOC=weight percentage organic carbon in rock S1 S2 =mg hydrocarbons per gram of rock S3 =mg carbon dioxide per gram of rock GP = petroleumgeneric potential = S1 + S2 ND = not done HI = Hydrogen Index = S2 times 100TOC OI = oxygen index = S3 times 100TOC 119879max =

∘C PI = production index =S1(S1 + S2)

5 Organic Richness

According to Conford [30] adequate amount of organicmatter measured as percentage total organic carbon is aprerequisite for sediment to generate oil or gas Shown inTable 1 are the results of total organic matter content (TOC)The coal samples from both wells show a higher organicrichness than shale Nevertheless both wells have valuesabove the threshold of 05 wt considered as minimum forclastic source rocks to generate petroleum [31] The solubleorganic matter (SOM) of the samples generally exceeds500 ppm except for samples P3 (EN 1325) and V5 (EN 1331)with SOM values of 2501 and 4678 ppm respectively Theseshow that the samples can be classified as fair to excellentsource rocks Based on the quality definition of Baker [32] theorganic matter is adequate and indicates good hydrocarbonpotential for the studied wells

6 Organic Matter Type

The organic matter type in a sedimentary rock among otherconditions influences to a large extent the type and quality ofhydrocarbon generated due to different organic matter typeconvertibilities [31] The Hydrogen Index (HI) for the shaleand coal samples ranges from 83 to 245mgHCgTOC withan average value of 178mgHCgTOCThis can be interpretedas type III (gas prone) The plot of hydrocarbon potentialversus TOC (Figure 4) indicates type IIIII organic matterwhich means a potential to generate oil and gasThemajorityfall within the type III organic matter indicating that gas willdominantly be generated with little oil Peters [33] suggestedthat at thermal maturity equivalent to vitrinite reflectanceof 06 (119879max 435∘C) rocks with HI gt 300mgHCgTOCproduce oil those with HI between 150mgHCgTOC and300mgHCgTOCproduce oil and gas thosewithHI between

Type IV inert

10 20 30 40 50 60 70 80

300

250

200

150

100

50

0

Well 1325Well 1331

Rem

aini

ng h

ydro

carb

on p

oten

tial S2

(mgH

Cg)

Type IIoil-proneusually marine

Mixed type II-IIIoil-gas-prone

Type IIIgas-prone

Type Ioil-proneusually lacustrine

Total organic carbonmdashTOC (wt)

Figure 4 A plot of hydrocarbon potential against TOC

50mgHCgTOC and 150mgHCgTOC produce gas andthose with HI lt 50mgHCgTOC are inert From this studythe range of HI is from 83 to 245 for the shales and coal Thisindicates oil and gas prone

Petroleum generating potential (GP) is the sum of S1

and S2values obtained from rock eval pyrolysis (Table 1)

The values obtained range from 234 to 17736 According toDyman et al [34] values greater than 2 kgHCton of rockindicate good source rockThis suggests oil and gas potential

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Journal of Geochemistry 5

Table 1 Data of TOC and rock-eval pyrolysis

Sample IDnumber

Depth(meter)

SOM(ppm)

TOC(wt)

S1(mgg)

S2(mgg)

S3(mgg)

119879max(∘C) HI OI S2S3 PI

(S1S1 + S2)GP

(S1 + S2)V1 minus2245 ND 33 055 457 111 428 138 34 412 011 512V2 minus223 3381 6624 428 1537 1207 431 232 18 1273 003 15851V3 minus222 3160 6351 387 1558 1579 434 245 25 987 002 15967V4 minus2205 ND 191 012 354 111 432 185 58 319 003 366V5 minus2275 4678 749 054 1771 167 433 237 22 106 003 1825V6 minus2315 19048 852 071 1425 233 426 167 27 612 005 1495V7 minus2325 ND 32 028 266 131 428 83 41 203 01 294V8 minus232 40952 6951 775 16961 1433 429 244 20 1184 004 17736P1 minus1685 5467 798 077 1255 253 435 157 32 496 006 1332P2 minus169 ND 6777 622 15335 1268 427 226 19 1209 004 15957P3 minus1725 2501 224 037 37 13 431 165 58 285 009 407P4 minus1745 ND 161 031 225 143 431 142 90 157 012 256P5 minus1755 ND 196 025 209 049 427 107 25 427 011 234Notes TOC=weight percentage organic carbon in rock S1 S2 =mg hydrocarbons per gram of rock S3 =mg carbon dioxide per gram of rock GP = petroleumgeneric potential = S1 + S2 ND = not done HI = Hydrogen Index = S2 times 100TOC OI = oxygen index = S3 times 100TOC 119879max =

∘C PI = production index =S1(S1 + S2)

5 Organic Richness

According to Conford [30] adequate amount of organicmatter measured as percentage total organic carbon is aprerequisite for sediment to generate oil or gas Shown inTable 1 are the results of total organic matter content (TOC)The coal samples from both wells show a higher organicrichness than shale Nevertheless both wells have valuesabove the threshold of 05 wt considered as minimum forclastic source rocks to generate petroleum [31] The solubleorganic matter (SOM) of the samples generally exceeds500 ppm except for samples P3 (EN 1325) and V5 (EN 1331)with SOM values of 2501 and 4678 ppm respectively Theseshow that the samples can be classified as fair to excellentsource rocks Based on the quality definition of Baker [32] theorganic matter is adequate and indicates good hydrocarbonpotential for the studied wells

6 Organic Matter Type

The organic matter type in a sedimentary rock among otherconditions influences to a large extent the type and quality ofhydrocarbon generated due to different organic matter typeconvertibilities [31] The Hydrogen Index (HI) for the shaleand coal samples ranges from 83 to 245mgHCgTOC withan average value of 178mgHCgTOCThis can be interpretedas type III (gas prone) The plot of hydrocarbon potentialversus TOC (Figure 4) indicates type IIIII organic matterwhich means a potential to generate oil and gasThemajorityfall within the type III organic matter indicating that gas willdominantly be generated with little oil Peters [33] suggestedthat at thermal maturity equivalent to vitrinite reflectanceof 06 (119879max 435∘C) rocks with HI gt 300mgHCgTOCproduce oil those with HI between 150mgHCgTOC and300mgHCgTOCproduce oil and gas thosewithHI between

Type IV inert

10 20 30 40 50 60 70 80

300

250

200

150

100

50

0

Well 1325Well 1331

Rem

aini

ng h

ydro

carb

on p

oten

tial S2

(mgH

Cg)

Type IIoil-proneusually marine

Mixed type II-IIIoil-gas-prone

Type IIIgas-prone

Type Ioil-proneusually lacustrine

Total organic carbonmdashTOC (wt)

Figure 4 A plot of hydrocarbon potential against TOC

50mgHCgTOC and 150mgHCgTOC produce gas andthose with HI lt 50mgHCgTOC are inert From this studythe range of HI is from 83 to 245 for the shales and coal Thisindicates oil and gas prone

Petroleum generating potential (GP) is the sum of S1

and S2values obtained from rock eval pyrolysis (Table 1)

The values obtained range from 234 to 17736 According toDyman et al [34] values greater than 2 kgHCton of rockindicate good source rockThis suggests oil and gas potential

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

6 Journal of Geochemistry

Table2Datao

fmolecular

parametersfor

thes

tudied

wells

Sample

ID119879119904(119879119904+119879119898)

Oleananeho

pane

Hop

ane

C 30C 29

Hop

ane

C 32

Hop

ane

C 29

Hop

ane

C 30

Sterane

C 29

Tetracyclictr

icyclic

C 24

DiaReg

C 27

Tri

C 19C 20

ratio

DNR

TMNR

MPI-1

MDR

P1002

062

198

049

049

052

015

15093

129

215

019

047

099

P3019

018

017

05

032

02

026

225

055

141

212

017

076

421

V8

001

002

101

053

055

057

013

184

038

137

164

048

034

268

V6

005

012

132

049

037

042

024

174

128

075

225

05

026

104

V5

002

003

112

049

051

056

014

222

027

109

075

021

024

2V2

005

008

072

056

05

051

027

186

044

11251

044

017

202

V3

001

001

109

054

057

059

016

216

055

134

154

048

014

12NotesD

NR-1=

(26DMN+27DMN)15

DMNT

MNR=(137TM

N)(137TM

N+12

5TM

N)MPI-1=15

(2MP+3M

P)(P+1M

P+9M

P)M

DR=4M

DBT

1MDBT

4MDBT

=4methyld

ibenzothiopene

2627DMN=2627dimethyln

aphthalene15DMN=15

dimethyln

aphthalene137=13

7trim

ethyln

aphthalene1239

MP=12

39

methylphenanthrene

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Journal of Geochemistry 7

0

100

200

300

400

500

600

700

800

900

1000

400 425 450 475 500

Hyd

roge

n In

dex

( HI

mgH

CgT

OC)

Immature PostmatureMature

+

++ ++

+

lowastlowast lowastlowastlowast

lowastlowast

lowast

Type Ioil-prone

usually lacustrine

Type IIoil-prone

usually marine

Type II-III

Type IIIgas-prone

Type IVinert

Con

dens

ate-

wet

gas

zone

Dry gas window

Oil window

Well 1325Well 1331

Tmax (∘C)

Figure 5 A plot of Hydrogen Index against 119879max for the studiedwells

7 Thermal Maturity

The degree of thermal evolution of the sedimentary organicmatter was derived from Rock Eval 119879max and biomarkerparameter According to Peters et al [35] biomarkers (geo-chemical fossils) can provide information on the organicsource materials environmental conditions during its depo-sition the thermal maturity experienced by a rock or oil andthe degree of biodegradation

The 119879max values (Table 1) range from 425 to 435∘C Theseindicate that the shales and coal range from immature to earlypeak mature (oil window) but on the average are immatureThe interpretation is in line with those given by Peters [33]Dow [36] and Miles [37] This is further highlighted by theplot of HI versus 119879max (Figure 5)119879119898(C27 17120572(H)-222930-Trisnorhopane) represents bio-

logically produced structures and 119879119904(C27 18120572(H)-222930-

Trisnorneohopane) generated in sediments and rocks bydiagenetic or thermal process or both 119879

119904(119879119904+ 119879119898) is a

ratio used as both source and maturity parameters The119898119911 191 (hopanes) (Figure 6) and 217 steranes (Figure 7)chromatograms of all the samples are similar H

30(hopanes)

are the most abundant in the 119898119911 191 chromatogramThe maturity and source parameters derived from thehopane distributions in the shales and coals are shown inTables 2 and 4 Also shown are calculated parameters ofaromatic biomarkers Parameters such as MPI-1 (methylphenanthrene index) DNR-1 (dimethyl naphthalene ratio)TMNR (trimethyl naphthalene ratio) and MDR (methyldibenzothiopene ratio) with respective range of values 014ndash076 075ndash251 017ndash050 and 099ndash421 all indicate that thesamples are immature to marginally mature [29] Accordingto Sonibare et al [38] the abundance of 125 TMN (trimethylnaphthalene) suggests a significant land plant contribution tothe organic matter (Figure 8)

Some 119899-alkane ratios can be used to estimate the thermalmaturity of sediments [39] Pristane119899C

17and phytane119899C

18

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000

Time

Time

Abun

danc

eAb

unda

nce

Ion 19100 (19070 to 19170) V6SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50000100000150000200000250000300000350000400000450000500000550000600000650000

Ion 19100 (19070 to 19170) V8SD

T19

T20

T21

T22

T23

T24 T2

5

Tet2

4T2

6ST2

8R

T30S

H28

H29

H30

NM

Mor

H31

SH

31R

H32

SH

32R

H33

SH

33R

H34

S

T19 Tet2

4

XH

29N

MH

30M

or H31

SH

31R

H32

SH

32R

H33

SH

33R

H43

R

T20

T21

T22 T2

4 T28R

T30S

Ts

Tm

Ts

Tm

Figure 6 119898119911 191 chromatograms showing the distribution oftricyclic triterpenes and hopanes in the samples

Table 3 Gas chromatographic data showing values of n-alkanesratio and their CPI

Sample ID PrPh PrnC17 PhnC18 CPI OEP-1 OEP-2EN 1331 (V2) 588 08 057 157 04 057EN 1331 (V5) 726 198 033 183 043 056EN 1331 (V6) 897 391 046 153 04 057EN 1325 (P1) 55 162 04 169 056 057EN 1325 (P3) 508 11 02 175 043 061Notes CPI = carbon preference index = 2(C23 + C25 + C27 + C29)(C22 +2(C24 + C26 + C28) + C30) OEP-1 = (C21 + C23 + C25)(4C22 + 4C24) OEP-2= (C25 + C27 + C29)(4C26 + 4C28) OEP = odd-even predominance

can be used to calculate thermal maturity For the stud-ied wells the Pr119899C

17values ranged between 08 and 391

(Table 3) this falls in the immature zone Ph119899C18

valuesranged from 02 to 057 which is below the threshold valueindicating immature organic matter

Carbon preference index (CPI) is the relative abundanceof odd versus even carbon-numbered 119899-alkanes and can alsobe used to estimate thermal maturity of organic matter [40]In this study the CPI values obtained range from 153 to 183(Table 3) Hunt [41] has pointed out that CPI considerably

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

8 Journal of Geochemistry

2500 3000 3500 4000 4500 5000 5500 6000 65000

500010000150002000025000300003500040000450005000055000

Time

Ion 21700 (21670 to 21770) P1SD

2500 3000 3500 4000 4500 5000 5500 6000 65000

50001000015000200002500030000350004000045000500005500060000

Time

Ion 21700 (21670 to 21770) P3SD

Abun

danc

eAb

unda

nce

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

d27b

R

i i28

bR

d27a

Sd2

7bS

i27

bR+

d29

bS

S29

aR+

S30

aSS29

aR+

S30

aS

Figure 7 119898119911 217 chromatograms showing the distribution ofsteranes in samples P3 and V5

600 800 1000 1200 1400 1600 1800 2000 2200 24000

100020003000400050006000700080009000

100001100012000130001400015000160001700018000190002000021000

Time

Abun

danc

e

Ion 17000 (16970 to 17070) V5AD (+)

13

6TM

N1

27+1

67

TMN

12

6TM

N 12

5TM

N

12

4TM

N

Figure 8119898119911 170 mass chromatogram showing the distribution ofnaphthalene in representative sample V5 (ENUGU 1331)

greater than 10 shows contribution from terrestrial continen-tal plants and immaturity Maxwell et al [42] have shownthat strong oddeven bias of heavy 119899-alkanes is indicativeof sediment immaturity For this study the odd numbered119899-alkanes are more abundant than the even numbered 119899-alkanes indicating that the sediments are immature Theodd-even predominance (OEP) values are less than 10 thisis indicative of low maturity [43]

04

035

03

025

02

015

01

005

00 01 02 03 04 05 06 07

Anoxic carbonate

Anoxic shale

Thermal maturation

Eh effect

PH effect

Suboxic strata

Dia(dia + reg) C27 steranes

Ts(Ts+Tm

)

Figure 9 A plot of 119879119904(119879119904+ 119879119898) versus dia(dia + reg)C

27steranes

showing the environment inwhich the organicmatter was deposited(After [44])

8 Palaeodepositional Environment

Moldowan et al [44] have indicated that the presence ofbisnorhopane and diasterane is indicative of suboxic con-ditions A plot of 119879

119904(119879119904+ 119879119898) versus dia(dia + reg)C

27

steranes as shown in Figure 9 is indicative of a suboxiccondition Pristanephytane (PrPh) ratio of sediments can beused to infer depositional environment [35] PrPh ratios lt1 indicate anoxic depositional environment while PrPh gt1 indicate oxic conditions PrPh 1 lt 2 indicate a marine-sourced organic matter and PrPh gt 3 indicates terrige-nous organic matter input with oxic conditions The valuesobtained from the studied wells ranged from 508 to 897 thusindicating that the samples have terrigenous-sourced organicmatter deposited in an oxidizing environment CrossplotsPr119899C

17versus Ph119899C

18(Figure 10) reveal that the sediments

were deposited in an oxidizing environment and are fromterrestrial and peat environments This is consistent with thesamples as some of them are of coal environment

Dahl et al [45] reported that a low ratio of homophaneindex is characteristic of a suboxic environment (Table 4)On the other hand PrPh ratio tend to be high (gt3) inmore oxidizing environment such as in swamps High PrPhvalues from the work indicate a terrigenous input under oxicconditions A large proportion of the results point to the factthat a suboxic condition prevailed in the deposited sedimentsThese indicate that a significant portion of the facies wereprobably deposited in an offshore shallow to intermediatemarine environment under suboxic water conditions whichprobably had no connection with the widespread Cretaceousanoxic events but are related to theCampanian-Maastrichtiantransgression

9 Summary and Conclusion

Detailed geochemical analysis of the coal and shale intervalsgotten from the Anambra Basin Nigeria has been used

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Journal of Geochemistry 9

10

1

0101 101

Samples

Maturat

ion

Terrest

rial o

rganic m

atter

Peat co

al envir

onment

Mixed orga

nic source

Marine o

rganic m

atter

Biodegrad

ation

Oxidizing

Reducing

PhnC18

Prn

C17

Figure 10 Plot of pristane119899C17versus phytane119899C

18(After [44])

Table 4 Results and interpretations of geochemical fossils

Parameters Values RemarksC29steranes

20S20S + 20R 013ndash027 Immature [46]

C27diasteranes

steranes 027ndash128 Immature [47]

C29hopanes120573120572120572120573 032ndash057 Immature [44]

C30120573120572120572120573

(hopanes) 020ndash059 Immature [39]

119879119904(119879119904+ 119879119898) 001ndash019 Immature [39]

C30C29119879119904

017ndash198 Suboxic conditions [46]C35homophane

Index C34and C

35low Suboxic conditions high

Eh terrigenous input [45]Diasteraneregsterane 033ndash12 Suboxic to oxic conditions

[47]

to investigate the aspects of their molecular fossil Thelithostratigraphic sequence penetrated by both wells (Enugu1325 and 1331) consists of shales coal and siltstones Theshales are dark grey and fissile The siltstones are brown tolight grey in colour while the coal is blackish

Organic richness of the samples was deduced from SOMand TOC as fair to excellent The organic matter type ispredominantly terrestrial This is based on the HI values HI-119879max plot the presence of oleanane the abundance and pre-dominance of C

29 C35homophane index and the abundance

of 125 Trimethyl NaphthaleneBiomarker parameters were used to determine the degree

of thermal evolution of the sediment organic matter Thepresence of bisnorhopane diasterane plot of 119879

119904(119879119904+ 119879119898)

against dia(dia + reg)C27sterane and the homophane index

all indicate suboxic and high Eh conditionsDiscrepancies were observed in the results used in the

interpretation of physicochemical conditions prevailing inthe deposited sediments These varied between oxic andsuboxic conditions It is thereby concluded that the lithologiesfrom the core samples are those of the Mamu Formation andEnugu-Shale Group which were deposited in a partial or nor-mal marine (suboxic to oxic water conditions) environmentThere is no strong evidence to show that the shales and coalshave expelled petroleum although they possess what it takesto be economic largely in terms of gas thus presenting a goodprospect

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The author is grateful to the Nigerian Geological SurveyAgency (NGSA) Kaduna for provision of borehole sam-ples The author remains grateful to the members of staffof Weatherford Geochemical Laboratory Texas USA andExxonMobil Geochemical Laboratory Eket Nigeria for thetechnical services rendered The authorrsquos sincere gratitudegoes to DrM E Nton of theDepartment of Geology Univer-sity of Ibadan for his suggestionsThe author also thanks theanonymous reviewers for their constructive comments whichled to improving this paper

References

[1] I M Akaegbobi ldquoThe crabrsquos eye-view of the organic sedimento-logical evolution of the Anambra Basin Nigeria Hydrocarbonsource potential and economic implicationsrdquo in Faculty Lecturepp 1ndash32 Ibadan University Press Ibadan Nigeria 2005

[2] A Whiteman Nigeria Its Petroleum Geology Resources andPotential Vol 1 Grantman and Trontman London UK 1982

[3] T J A Reijers Selected Chapters on Geology SPDC Nigeria1996

[4] I Nexant ldquoNational oil and gas policy a draft report preparedfor the Bureau of Public Enterprises (Nigeria)rdquo Tech RepNexant Griffin House London UK 2003

[5] R C Murat ldquoStratigraphy and paleogeography of the Cre-taceous and Lower Tertiary in southern Nigeriardquo in AfricanGeology T F J Dessauvagie and A Whiteman Eds pp 257ndash266 Ibadan University Press Ibadan Nigeria 1972

[6] K C Burke ldquoThe African platerdquo South African Journal ofGeology vol 99 no 4 pp 341ndash409 1996

[7] K C Burke T F J Dessauvagie and A J Whiteman ldquoGeologichistory of the Benue valley and adjacent areasrdquo in AfricanGeology T F J Dessauvagie and A J Whiteman Eds pp 187ndash218 University of Ibadan Press Ibadan Nigeria 1972

[8] J D Fairhead and C M Green ldquoControls on rifting in Africaand the regional tectonic model for the Nigeria and East Nigerrift basinsrdquo Journal of African Earth Sciences vol 8 no 2ndash4 pp231ndash249 1989

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

10 Journal of Geochemistry

[9] J Benkhelil ldquoThe origin and evolution of the Cretaceous BenueTrough (Nigeria)rdquo Journal of African Earth Sciences vol 8 no2ndash4 pp 251ndash282 1989

[10] W Khunt J P Herbin J Thurow and J Wiedmann ldquoWesternmediterranean and along the adjacent Atlantic marginrdquo inDeposition of Organic Facies A Y Hue Ed AAPG Studies inGeology no 30 pp 138ndash159 1990

[11] K C Short andA J Stauble ldquoOutline of geology ofNigerDeltardquoAAPG Bulletin vol 51 no 5 pp 761ndash779 1967

[12] G C Obi and C O Okogbue Sedimentary Response to Tec-tonism in the Campanian-Maastrichtian Succession AnambraBasin Southeastern Nigeria University of Nigeria NsukkaNigeria 2001

[13] A Avbovbo and EO Ayoola ldquoPetroleumprospects of southernNigeriarsquos Anambra BasinrdquoOil and Gas Journal vol 79 pp 334ndash348 1981

[14] O Agagu and C M Ekweozor ldquoSource rocks characterisationsof Senonian shales in the Anambra Basinrdquo Journal of MiningGeology vol 19 pp 52ndash61 1982

[15] G I Unomah Petroleum geochemical evaluation of the uppercretaceous shales in the lower benue trough [PhD thesis]Department of Geology University of Ibadan Ibadan Nigeria1989

[16] G I Unomah and C M Ekweozor ldquoPetroleum source rockassessment of the campanian Nkporo shale Lower BenueTrough NigeriardquoNAPE Bulletin vol 8 no 2 pp 172ndash186 1993

[17] CM Ekweozor ldquoInvestigation of geohistory ofAnambra Basinpart 5 case history 3rdquo in Basic Geochemistry Lecture Presentedat the Oil and Gas Academy Port Harcourt Nigeria May 2006

[18] P U Iheanacho Subsurface evaluation of source rock andhydrocarbon potential of the Anambra Basin SoutheasternNigeria [MS Dissertation] Department of Geology Universityof Ibadan Ibadan Nigeria 2010

[19] R A Reyment Aspect of the Geology of Nigeria University ofIbadan Press 1965

[20] O K Agagu E A Fayose and S W Petters ldquoStratigraphyand sedimentation in the senonian Anambra Basin of EasternNigeriardquo Nigeria Journal of Mining Geology vol 22 no 1-2 pp26ndash26 1985

[21] E E Nyong ldquoCretaceous sediments in the Calabar Flankrdquoin Geological Excursion Guide to Oban Massif Calabar Flankand Mamfe Embayment Southeastern Nigeria 31st AnnualConference B N Ekwueme E E Nyong and SW Petters Edspp 14ndash25 Nigerian Mining and Geoscience Society 1995

[22] M N Tijani M E Nton and R Kitagawa ldquoTextural andgeochemical characteristics of the Ajali Sandstone AnambraBasin SE Nigeria implication for its provenancerdquo ComptesRendus Geoscience vol 342 no 2 pp 136ndash150 2010

[23] O S Adegoke ldquoEocene stratigraphy of southernNigeriardquo in 3rdColloque sur lEocene vol 69 pp 22ndash48 Bureau de RecherchesGeologiques et Minieres 1969

[24] C A Kogbe ldquoPaleogeographic history of Nigeria from Albiantimesrdquo inTheGeology of Nigeria C A Kogbe Ed pp 237ndash252University of Ife 1975

[25] C S Nwajide and T J A Reijers ldquoSequence architecture ofthe Campanian Nkporo and Eocene Nanka formation of theAnambra BasinNigeriardquoNAPEBulletin vol 12 no 1 pp 75ndash871996

[26] I Arua ldquoPaleocene macrofossils from the Imo Shale in Anam-bra Basin Nigeriardquo Journal of Mining and Geology vol 17 pp81ndash84 1980

[27] T J A Reijers S W Petters and C S Nwajide ldquoThe niger deltabasinrdquo in African Basins R C Selley Ed pp 151ndash172 ElsevierAmsterdam The Netherlands 1997

[28] G Nichols Sedimentology and Stratigraphy Wiley-BlackwellWest Sussex UK 2009

[29] M Radke D H Welte and H Willsch ldquoMaturity parametersbased on aromatic hydrocarbons influence of the organicmatter typerdquo Organic Geochemistry vol 10 no 1ndash3 pp 51ndash631986

[30] C Conford ldquoSource rock and hydrocarbons of the North Seardquoin Introduction to The Petroleum Geology of The North Sea KW Glenuie Ed pp 197ndash236 1986

[31] B G Tissot and D H Welte Petroleum Formation and Occur-rence A New Approach Oil and Gas Exploration SpringerBerlin Germany 1984

[32] D R Baker ldquoOrganic geochemistry and geological interpreta-tionsrdquo Journal of Geological Education vol 20 no 5 pp 221ndash234 1974

[33] K E Peters ldquoGuidelines for evaluating petroleum sourcerocks using programmed pyrolysisrdquo American Association ofPetroleum Geologists Bulletin vol 70 no 3 pp 318ndash329 1986

[34] T S Dyman J G Palacas R G Tysdal W J Perry Jr and MJ Pawlewicz ldquoSource rock potential of middle cretaceous rocksin Southwestern Montanardquo AAPG Bulletin vol 80 no 8 pp1177ndash1184 1996

[35] K E Peters C C Walters and J M Moldowan BiomarkerGuide Biomarker and Isotopes in Petroleum Exploration andEarth History Cambridge University Press Cambridge UK2005

[36] W G Dow ldquoKerogen studies and geological interpretationsrdquoJournal of Geochemical Exploration vol 7 pp 79ndash99 1977

[37] J A Miles Illustrated Glossary of Petroleum GeochemistryOxford Science Publication Oxford University Press 1989

[38] O O Sonibare T Adedosu A O Ekundayo and D JarvieldquoHydrocarbon potential and organic geochemistry of coalsfrom Benue Trough Nigeriardquo Journal of Applied SciencesResearch vol 4 no 11 pp 1511ndash1520 2008

[39] H L ten Haven J W de Leeuw J Rullkotter and J S SDamste ldquoRestricted utility of the pristanephytane ratio as apalaeoenvironmental indicatorrdquo Nature vol 330 no 6149 pp641ndash643 1987

[40] K E Peters and J W Moldowan The Biomarker Guide Inter-preting Molecular Fossils in Petroleum and Ancient SedimentsPrentice Hall Englewood Cliffs NJ USA 1998

[41] J M Hunt Petroleum Geochemistry and Geology W H Free-man and Company San Francisco Calif USA 1979

[42] J R Maxwell C T Pillinger and G Eglinton ldquoOrganicgeochemistryrdquo Quarterly Reviews Chemical Society vol 25 no4 pp 571ndash628 1971

[43] E S Scalan and J E Smith ldquoAn improved measure of the odd-even predominance in the normal alkanes of sediment extractsand petroleumrdquo Geochimica et Cosmochimica Acta vol 34 no5 pp 611ndash620 1970

[44] J M Moldowan J Dahl B J Huizinga et al ldquoThe molecularfossil record of oleanane and its relation to angiospermsrdquoScience vol 265 no 5173 pp 768ndash771 1994

[45] J E Dahl J M Moldowan S C Teerman M A McCaffreyM Pena and C E Stelting ldquoSource rock quality determinationfromoil biomarkersmdashan example from theAspen shale ScullyrsquosGap Wyomingrdquo American Association of Petroleum GeologistBulletin vol 78 no 10 pp 1507ndash1526 1994

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Journal of Geochemistry 11

[46] W-Y Huang and W G Meinschein ldquoSterols as ecologicalindicatorsrdquoGeochimica et Cosmochimica Acta vol 43 no 5 pp739ndash745 1979

[47] I Rubinstein O Sieskind and P Albrecht ldquoRearranged sterenesin a shale occurrence and simulated formationrdquo Journal of theChemical Society Perkin Transactions vol 1 no 19 pp 1833ndash1836 1975

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in