sedimentology and reservoir characterization of the aptian

Sedimentology and Reservoir Characterization of

the Aptian Lower Qamchuqa Formation from

Selected Wells in Bai- Hassan Oilfield/Northern Iraq

By

Sabir Subhi Shahab

Supervisor

Prof. DR. Lafta S. Kadhim Prof. Dr. Dler H. Baban

1

Chapter One

2

The Study Area

• The studied area located at Bai-Hassan Oilfield

includes three wells BH-86, BH-102 and BH-96.

• The field situated in NE-Iraq between both Kirkuk

and Qara Chuq structures that are tectonically located

at the Low Folded Zone within the unstable shelf.

3

4

A

B

6

Aims of the Study

1. Determining the sedimentology and petrographical properties

of Lower Qamchuqa Formation in the studied wells.

2. Detecting the paleo-depositional environment of the formation

in the study area.

3. Determining the reservoir potentiality of the formation and the

saturations of the contained fluids.

4. Subdividing the formation to reservoir units and calculating

the Net to Gross reservoir, pay, and productive ratios for the

studying formation in the studied wells.

The Data and Methodology

• Data and Sampling

The available data of each:

1. Rock samples for the Lower Qamchuqa Formation in three

studied wells at Bai-Hassan Oilfield.

2. The conventional log data of Caliper, Gamma ray, Sonic,

Density, Neutron, and Resistivity logs.

3. Porosity and permeability values from core test analysis.

4. The available thin sections were exist in NOC.7

8

Studied

Wells

Coordinate

UTM

System

Samples Lower Qamchuqa FormationThin

Sections

Cutting

and

Core

Top

m

Bottom

m

Thickness

m

NOC +

Author

BH-86Y= 139 48 227.97

X= 399 651.3821 2174 2321 147 70+21

BH-102Y= 13940 412.75

X= 4133806 2113 2154 41 24+5

BH-96Y= 139 43 321.64

X= 411 466.68 1991 2040 49 40+8

Research Methodology

• Preparing 34, with 134 thin sections by author and from NOC.

• Analysing 35 samples by Calcimetry test to determine the

calcite, dolomite, and residual materials ratios.

• Digitizing the available logs using Neural software.

• Calculating the reservoir parameters and re-plotting the

digitized curves using Excel and Grapher softwares.

• Drawing the stratigraphic columns, correlations, maps, and the

crossplots using Log Plot, GIS and Grapher softwares.

• Making lateral variation (correlation) in the studied wells for

the formation by using Petrel software.9

Lower Qamchuqa Formation

• The Qamchuqa sequence studied in its type section was represented by

massive, rather argillaceous, fossiliferous limestones, usually dolomitized,

interbedded with crystalline dolomites.

• The Lower Qamchuqa Formation thickness in High Folded Zone was about

250 to 300 m.

• The Lower Qamchuqa Formation was deposited in a purely marine neritic

environment which affected slightly by terrigenous supply.

• The formation at Bai-Hassan Oilfield is overlained unconformably by the

shale beds of Nahr Umr Formation and underlained conformably by Garagu

Formation.

• The Lower Qamchuqa Formation age considered being Early-Aptian

depending on some index fossils such as O. lenticularis, Choffatella

decipiens and Orbitolina cf with Acicularia cf.10

Chapter Two

Petrography and Diagenesis

processes

11

• This chapter focused on the thin sections

analysis which include the skeletal and non-

skeletal components, with different types of

diagenetic processes in three studied wells

BH-86, BH-96, BH-102 for Lower Qamchuqa

Formation.

12

Skeletal components

• The skeletal grains commonly consists of benthonic

foraminifer’s represented by Orbitolina, Textularia,

Meliolids, Radiolaria spines, Cyclammina lenticularis

and Chofatella, with others Echinoderm, Bioclast and

Algae (Acicularia), whereas the non-skeletal grains

included pellets and lithoclasts (extraclasts) with

Quartz grains in parts.

13

Common Diagenesis processes of Lower Qamchuqa

Carbonate Rocks

• Many types of diagenetic processes were observed in

the present study which represented by; cementation,

micritization, dissolution, mechanical and chemical

compactions (including pressure dissolution),

Stylolite, neomorphism (recrystallization and

inversion), anhydritization, and dolomitization.

14

15

This figure shows different types of diagenesis, porosities and

skeletal grains with depth for the L. Qamchuqa Fn. in the studied

well BH-86.

16

This figure shows

different types of

diagenesis, porosities

and skeletal grains

with depth for the L.

Qamchuqa Fn. in the

studied well BH-102.

17

This figure shows

different types of

diagenesis, porosities

and skeletal grains

with depth for the L.

Qamchuqa Fn. in the

studied well BH-96.

18

Orbitolina

Chofatella Radiolaria spines Cyclammina

MeliolideTextularia

19

Aciculina Pellet

BioclastsLenticulariaEchinoderm

Extraclast & Quartz grains

20

Micritization

DissolutionAnhydritization

Inversion

Common Diagenesis

Processes

Chapter Three

Microfacies and Depositional

Environments

21

• This chapter focused on the stratigraphy study.

• Detecting microfacies for the L. Qamchuqa

Formation depending on the classification of Dunham

(1962).

• Detecting the paleo-depositional environment of the

formation.

22

23

Four types of microfacies with five sub-microfacies kinds

detected in the Lower Qamchuqa Formation.

Lithological Description of Lower Qamchuqa

Formation

The lithology of the Lower Qamchuqa Formation

determined depending on:

• Optically from the microscopic study of thin sections

• From the gamma ray log.

• Calcimetry analysis for a number of selected rock

samples.

• The results checked with the descriptions done for the

formation in the final reports (NOC). 24

25

calcimetry test Showing

CaCo3

& Mg (CaCo3)2

Ratios

26

Str

atig

raph

icco

lum

nan

dm

icro

faci

eso

fth

e

Low

erQ

amch

uq

aF

orm

atio

nin

the

wel

lB

H-

86

.

27

Str

atig

raph

icco

lum

nan

dm

icro

faci

eso

fth

e

Low

erQ

amch

uq

aF

orm

atio

nin

the

wel

lB

H-

10

2.

28Str

atig

raphic

colu

mn

and

mic

rofa

cies

of

the

Low

erQ

amch

uq

aF

orm

atio

nin

the

wel

lB

H-

96

.

29

This figure representing the

microfacies correlation that

showing the vertical and

lateral facies changes in the

studied wells for the Lower

Qamchuqa Formation.

Depositional environment Model

30

Chapter Four

Shale Volume Calculation and

Porosity Log

31

32

Gamma ray log for the L.

Qamchuqa Formation

including uppermost part of

Nahr-Umr Formation in the

studied wells, BH-86, BH-

102 and BH-96.

The middle part of the

formation of being lower

gamma ray radiation than the

lower and upper parts of the

formation.

The highest recorded values

of gamma ray was around

70API.

So no pure shale beds are

expected to be exist in the

studied Lower Qamchuqa

Formation

33

*After applying the Larionov

equation the shale volume

being estimated.Vsh =0.33[2(2*IGr)-1.0] for the

rocks older than Tertiary

The upper 20-25m of the Lower

Qamchuqa Formation looks to be

generally a shaly interval followed

by around 35m clean zone with less

than 10% shale content.

Depending on standard proposed

by Ghorab, 2008 the shale content

zonation detected.

<10%...... Clean Zone

10-35%... Shaley Zone

>35%....... Shale Zone

Wells FormationDepth

Interval mZonation

Thickness

m

Avg.

V-Sh %

BH-86

Nahr Umr 2172-2174 Shaly-shale zone 2 31.67

Lower Qamchuqa

2174-2202 Shaly zone 28 24.05

2202-2237 Clean zone 35 3.63

2237-2240 Shaly zone 3 18.92

2240-2248 Clean zone 8 6.07

2248-2269 Shaly zone 21 15.91

2269-2288 Clean zone 19 8.09

2288-2295 Shaly zone 7 19.65

2295-2299 Clean zone 4 4.03

2299-2302 Shaly zone 3 14.75

2302-2309 Clean zone 7 6.57

2309-2316 Shaly zone 7 14.75

2316-2320(TD) Clean zone 4 5.30

BH-102

Nahr Umr2110-2112 Shaly zone 2 31.64

2112-2113 Shale zone 1 37.34

Lower Qamchuqa2113-2131 Shaly zone 18 16.68

2131- 2140(TD) Clean zone 9 2.45

BH-96

Nahr Umr 1989-1991 Shale zone 2 36.59

1991-2010 Shaly zone 19 18.80

34

35

• This figure shows the bulk

density recording in the

three studied wells for the

Lower Qamchuqa

Formation.

36

*For converting the recorded

bulk density to density

porosity (ΦD), the below

equation has been applied.

ΦD= (ρma-ρb) / (ρma-ρfl)

*The upper part of the

formation generally has a

porosity ranging between (6-

12) %.

*Middle part is not of

observable difference from

the upper part in well BH-86.

*Lower part (2-10%)

*Highest porosity values

observed between depths

2202 and 2212m in the well

BH-86 at which porosity

between 15 - 20%.

37

*This figure shows the

neutron porosity logs

reading for the Lower

Qamchuqa Formation in

the three studied wells,

BH-86, BH-102 and BH-

96.

*The recorded Neutron

porosity values (ΦN) are

almost the same as the

calculated porosity from

the density log.

38

*This figure displayed Δt

reading for the Lower


the three studied wells,

BH-86, BH-102 and BH-

96.

*In most parts of the

formation Δt values

ranging between 50 and

60 μsec/ft.

*Relatively higher Δt

values have been recorded

between depths 2202 and

2012m in the well BH-86.

39

*For converting the

recorded Δt to sonic

porosity (ΦS), the

below equation has

been applied

ΦS = (∆tlog-∆tma) /

(∆tfl-∆tlog)

*As no significant

difference observed

between the calculated

porosities from

density, neutron, and

sonic logs for Lower

Qamchuqa Formation

in the studied wells.

Correction of Porosity from Shale Impact

The shale impact applying by equations proposed by Dewan

(1983):

• Correction of Φ-Density: ΦDcor= ϕD- (Vsh*ρsh)

• Correction of Φ-Neutron: ΦNcor = ΦN – (Vsh* ΦNsh).

• Correction of Φ-Sonic: ΦScor = ϕS - Vsh*(Δtsh-Δtma /

Δtfl-Δtma).

• The highest reduction in the porosity values due to

correction can be seen in the upper part of the formation in

the three studied wells.

• The both ΦN and ΦS were more influenced by shale

impact than ΦD because density logging tool is less

affected by the existence of shale.40

45

*To further evaluating and

characterizing Lower


this study, the calculated

ΦN-Dcor values will be

mainly depended on

because this type of

measured porosity is best

representing the existed

primary and secondary

porosities.

*The North standard,1985

for evaluating porosity

ranges will be used for

describing the porosity

qualitatively in this study.

Permeability

• In the present study, the permeability data from core test

analysis was available for selected intervals for the Lower

Qamchuqa Formation in the three studied wells.

• To obtain permeability in mD for the whole studied

sections of Lower Qamchuqa Formation, the Multiple

Linear Regressions (MLR) method was used.

47

48

Measured permeability

from core test analysis

(green line) and the

calculated permeability

from log data using

equation (red line) for the

Lower Qamchuqa

Formation in the three

studied wells.

49

*Measured permeability

from log data using

equation for the Lower


the studied wells.

*Permeability in the L.

Qamchuqa Formation

ranged between

0.001mD to 2mD.

50

• Reservoir Units

L. Qamchuqa Formation in

the well BH-86 subdivided

into 6 RU & 2 sub-RU

depending on the shale

content, porosity, and

permeability values,

regardless which type of

fluid are stored in the

reservoir.

55

This Figure is showing a correlation

between the identified reservoir units of

Lower Qamchuqa Formation in the

three studied wells.

Chapter Five

Saturations and Reservoir

Characterization

56

57

*The used resistivity logging tools,

(MSFL),, (LLS), and (LLD)

represented by Rxo, Ri, and Rt

were recorded respectively for the

Lower Qamchuqa Formation in the


*The non-separated between Rxo and Rt

curves will be an indication to

hydrocarbon bearing zones and vice

versa.

Water Saturation and Hydrocarbon

*The Archie equation

using to calculating water

saturation from log data.

* For better representing

the hydrocarbon

saturation, both movable

and residual hydrocarbon

percentages have been

calculated.

• Water Saturation:

• SW = 𝑛 𝐹∗𝑅𝑤

𝑅𝑡= (𝐹 ∗

𝑅𝑤

𝑅𝑡)1/n

• Movable hydrocarbon:

saturation

Shm = Sxo – Sw.

• Residual hydrocarbon

saturation

Shr = 1.0 – Sxo

59

60

*RU-6: Lowest Sh exists in the

well BH-96, whereas in the

two other wells this unit is

almost of similar Sh but the

percentages of the Shr is higher

in the well BH-86.

RU-5: is of high Sh

percentages which most of

them is movable except a

noticeable percentage of Shr in

the well BH-86.

RU-4: is almost like RU-5 in

the well BH-86 but with a

lower percentage of Sw.

RU-3 to RU-1: are of high

Shm in the well BH-86 except

some horizons in which

noticeable Shr can be seen.

61

*The Movable HydrocarbonIndex (MHI) is used to estimatethe movability of thehydrocarbons.

𝐌𝐇𝐈 =𝑺𝒘

𝑺𝒙𝒐

=

𝑹𝒙𝒐

𝑹𝒕𝑹𝒎𝒇

𝑹𝒘

*The upper part of theformation in the wells of BH-86, BH-102, and BH-96representing by RU-5 and RU-6 are totally containingmovable hydrocarbons.

*Most parts of the formation inthe well BH-86 are containingmovable hydrocarbons withnarrow horizons of non-movable hydrocarbons.

62

• The effective contribution

of fractures in flowing can

obviously be seen in most

of the reservoir units in the


• The less contribution of the

fractures with matrix

porosity can be noticed in

the RU-5 in the well BH-

86.

Fluid Flow within Lower Qamchuqa Formation

Fo

ur

gro

ups

of

FZ

Iv

alu

es

reco

gn

ized

dep

end

ing

on

the

chan

ge

inth

esl

op

eo

fth

etr

end

lin

eso

fd

istr

ibu

ted

FZ

Isa

mp

le

po

ints

.

64

• Lower Qamchuqa Formation in the studied wells looks to own four unique

Hydraulic Flow Units (HFU) with the FZI ranges and average values

shown in the figure below.

• The less potential flow unit looked to be HFU-1 in the well BH-86 and the

best appeared to be HFU-4 in the well BH-96.

Wells FZI Range Average FZIHydraulic

Flow Units

BH-86

0-0.5 0.28 HU-1

0.5-2 1.03 HU-2

2-5 3.06 HU-3

>5 205.77 HU-4

BH-102

0 -1 0.64 HU-1

1-2 1.42 HU-2

2-5 3.23 HU-3

>5 158.34 HU-4

BH-96

0-2 0.61 HU-1

2-3 1.45 HU-2

3-5 2.96 HU-3

>5 254.63 HU-465

Net to Gross Reservoir and Pay Ratios

• Net reservoir thickness is the total thickness of the reservoir,

which Vsh, Φ, and K cutoffs are applied.

• Net pay thickness comprises those hydrocarbon bearing

reservoir intervals, additionally by log derived water saturation

cutoff.

• The thickness of the net production considered to be the

fraction of the net pay (reservoir) thickness that subjected to

the MHI cutoff.

66

67

Well

Øcutoff using

Kcutoff 0.1

%

Øcutoff using

Kcutoff 1.0

%

BH-86 4.8% for gas 16% for oil

BH-102 8.4% for gas 20% for oil

BH-96 9.9% for gas 24.9% for oil

68

Well

Swcutoff using

Øcutoff 16

%

Swcutoff using

Øcutoff 4.8

%

BH-86 17% for oil 42% for gas

BH-102 19% for oil 42% for gas

BH-96 10% for gas 26% for gas

69

Fo

rma

tio

n

Res

erv

oir

Un

its Gross

Thick.

(m)

Net

Reservoi

r

Thick.

(m)

Net

Pay

Thick.

(m)

Net

Productio

n

Thick.

(m)

N/G

Reservoi

r

(%)

N/G

Pay

(%)

N/G

Product.

(%)

Lo

wer

Qa

mch

uq

a

6 28 0.0 0.0 0.0 0.0 0.0 0.0

5 15 4 1.9 1.4 2.73 1.3 0.95

4 19 0.0 0.0 0.0 0.0 0.0 0.0

3 32 7.1 2.4 2.4 4.86 1.64 1.64

2B 20 0.6 0.4 0.4 0.41 0.27 0.27

2A 14 0.0 0.0 0.0 0.0 0.0 0.0

1 18 0.0 0.0 0.0 0.0 0.0 0.0

Total 146 11.7 4.7 4.2 8.0 3.21 2.86

Calculated N/G reservoir, pay, and productive ratios for the

Lower Qamchuqa Formation in the studied well BH-86 (case of

oil production).

71

Fo

rma

tio

n

Res

erv

oir

Un

its Gross

Thick.

(m)

Net

Reservo

ir

Thick.

(m)

Net

Pay

Thick.

(m)

Net

Productio

n

Thick.

(m)

N/G

Reservo

ir

(%)

N/G

Pay

(%)

N/G

Product.

(%)

Lo

wer

Qa

mch

uq

a

6 28 17.8 9.45 5.8 12.19 3.97 3.97

5 15 15 15 12 10.27 10.27 8.21

4 19 18 17.3 17.3 12.32 11.84 11.84

3 32 22.8 20.28 20.08 15.61 13.89 13.75

2A 20 13.4 10.9 10.2 9.17 7.46 6.98

2B 14 8.55 5.75 5.75 5.85 3.93 3.93

1 18 4.55 2.6 2.05 3.11 1.78 1.4

Total 146 100.1 81.28 73.18 68.52 53.14 50.08



gas production).

73

Fo

rma

tio

n

Res

erv

oir

Un

its Gross

Thick.

(m)

Net

Reservoir

Thick.

(m)

Net

Pay

Thick.

(m)

Net

Production

Thick.

(m)

N/G

Reservoir

(%)

N/G

Pay

(%)

N/G

Productiv

e

(%)

Lo

wer

Qa

mch

uq

a

6 18 0.0 0.0 0.0 0.0 0.0 0.0

5 19 1.2 0.0 0.0 6.3 0.0 0.0

Total 37 1.2 0.0 0.0 6.3 0.0 0.0


Lower Qamchuqa Formation in the studied well BH-102 (case

of gas production).

74

1

This figure Showing

net reservoir, net

pay, and net

productive zones

with the used cutoffs

for the Lower

Qamchuqa

Formation in the

studied well BH-102.

75

Fo

rma

tio

n

Res

erv

oir

Un

its Gross

Thick.

(m)

Net

Reserv

oir

Thick.

(m)

Net

Pay

Thick.

(m)

Net

Producti

on

Thick.

(m)

N/G

Reserv

oir

(%)

N/G

Pay

(%)

N/G

Product

ion

(%)

Lo

wer

Qa

mch

uq

a 6 19 0.0 0.0 0.0 0.0 0.0 0.0

5 26 1.5 1.2 1.2 3.33 2.66 2.66

Total 45 1.5 1.2 1.2 3.33 2.66 2.66



gas production).

76

1

This figure Showing

net reservoir, net pay,

and net productive

zones with the used

cutoffs for the Lower

Qamchuqa

Formation in the

studied well BH-96.

• RU-3 looked to be the most potential reservoir unit to

produce gas followed by RU-4 in the well BH-86.

• Whereas RU-1 at the lower part of the formation showed

the least potentiality for gas production among the

identified reservoir units.

• The whole penetrated part of the formation in the two wells

BH-102 & BH-96 appeared to be of no any ability to

produce oil or even to be considered as a reservoir or pay.

• The formation's greatest problem in the mentioned two

wells is the lack in the require porosity. 77

Chapter Six

Conclusions and

Recommendations

78

Conclusions

1. Depending on petrographic study, gamma ray log, and calcimetry test; the upper

part of Lower Qamchuqa Formation in the study area looks to be composed of

shaly limestone, limestone, dolomitic limestone, interbedded occasionally with

thin beds of marl. Whereas, the middle and lower part of the formation as

appeared in the well BH-86 composed of dolomite, shaly limestone, dolomitic

limestone, and limestone.

2. The skeletal components in the formation as appeared from petrography study

are mainly consist of benthonic foraminifera (Orbitolina, Textularia, Choffatella,

and Meliolids) in addition to echinoderms, bioclasts, and algae; whereas the non-

skeletal grains considered as extraclasts (Quartz grains) and pellets.

3. Diagenetic processes which affected the formation are; micritization, dissolution,

mechanical and chemical compactions (stylolite), cementation, and

dolomitization.

4. Different types of secondary porosity co-exist in the formation such as;

interparticle, intrafossils, intercrystalline, fracture, channel, vuggy, cavern, and

moldic porosities as a result of the diagenesis processes.

79

4-Lime mudstone microfacies, Dolostone microfacies, Lime

wackestone microfacies (subdivided into benthonic foraminiferals lime

wackestone sub-microfacies, benthonic foraminiferals lime mudstone /

wackestone sub-microfacies, pelloidal lime mudstone/wackestone sub-

microfacies, bioclast lime wackestone sub-microfacies, and Orbitolina

lime wackestone sub-microfacies), and Orbitolina Lime packstone

microfacies.

5. The paleo-depositional environment of the Lower Qamchuqa

Formation in the studied area is restricted and shallow open marine

environment (interior platform).

6. The formation (depending on petrophysics and log analysis study) is

of relatively low shale content (<35%), except some horizons at the

upper part of the formation in which the shale content reached to

about 70%.

80

7. The upper part of the formation in the three studied wells can be subdivided into

two reservoir units (RU-5 and RU-6). The middle and lower parts of the formation

in well BH-86 can be subdivided to four additional reservoir units (RU-1 to RU-4).

8. RU-5 is of the best reservoir property among the distinguished reservoir units of

the formation especially in the well BH-86 (average 3.135% shale content, 6.2%

porosity, and 1.75mD permeability). On the other hand, RU-1 in the well BH-86 is

of the least reservoir property with average 9.48% shale content, 3.64% porosity,

and 0.5mD permeability.

9. Almost the whole parts of the formation in the well BH-86 is containing

hydrocarbon with different saturations with being RU-6 in the well BH-96 of the

lowest hydrocarbon saturation.

10. Fractures contributed effectively in the flow of the fluids within the formation in

the three studied wells.

81

14. The fluids within the Lower Qamchuqa Formation in the studied wells are

flowing as four hydraulic flow units with different average FZI values.

15. Only about 8% of the gross 146m of the formation (in the well BH-86) is

expected to be of the required reservoir properties for oil production. The

actual productive thickness is only about 2.8%.

16. In the well BH-86 and for the case of gas production; 68% from the gross

thickness of the formation is of acceptable reservoir properties. More than 50%

as actual productive thickness from the gross 146m of the formation.

17. The whole penetrated parts of the formation in the two wells BH-102 and BH-

96 are of no any ability to produce oil or even to be considered as an

acceptable reservoir. The same is true for gas production also except about

1.2m within RU-5 in the well BH-102.

82

83

Thanks for

your attention

sedimentology and reservoir characterization of the aptian

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