Annex 3

“Numerous seismic prospects dot concessions off Cote d’Ivoire”, Oil & Gas Journal (4 Apr. 1994)

EXPLORATION

Numerous seismic prospects dot concessions on Cote d'lvoire

A recently announced significant oil discovery off Cote d'Ivoire in

West Africa has piqued in­dustry interest in the area.

The Lion-1 well, operat­ed by United Meridian Inter­national Corp. (UMIC), en­coun tered approximately 205 ft of log indicated net hydrocarbon pay. The three intervals tested at this writ­ing flowed a combined 14,263 b/d of oil through 3Y2 in. tubing from intervals deeper than those previous­ly tested in the area.

The well, drilled in the CI-11 block in 70 m of water about 12 km offshore, comes several weeks after UMIC announced a sizable gas/ condensate discovery in the sam e block. UMIC and part­ners plan further drilling.

Petroci, the Cote d 'Ivoire state oil company and work­ing interest partner in the two new discoveries, is of­fering three large evaluation concessions to the interna­tional oil industry (Fig. 1). The 5,000 sq km concessions are situated east of the above mentioned UMIC discovery; commercial production has been established on two of the concessions, and numer­ous seismically defined pros­pects are present on all three. The area is referred to

N'Dri Koffi Petroci Abidjan Eric W. Barton Gustavson Associates Inc. Boulder, Colo.

PROSPECTS IN CONCESSION AREAS

9aCI-Q2 ·.

~ Maastrichtian

D Cenomanian-Senonian

0 Aibian

- Intra-Albian

C:J Gas field

.Oilfield

o'f====~20 Miles 0 32 Km

as the Abidjan margin. This current concession

round represents the first time in recent years that the region has been opened for petroleum exploration activi­ty. In a major change, Cote d'Ivoire just reduced its in­come tax rate for the oil in­dustry to 35% from 50%.

Moussa Fanny, president

and director general of Pe­troci, stated that "we are de­termined to reestablish oil production in our country to the extent that many terms and conditions are now ne­gotiable."

Cote d' Ivoire offers an ex­tensive geological database, production history from off­setting fields, and oil shows

Fig. 1

\ )

OGJ

in numerous wells. In addi­tion to the advantageous tax regime for developers and favorable concession condi­tions, other recent and at­tractive governmental policy changes are now in effect.

A market outlet for oil is provided through a local 50,000 b/d refinery, and ex­isting infrastructu re is con-

Reprinted from the April 4, 1994 edition of OIL & GAS JOURNAL Copyright 1994 by PennWell Publishing Company

I \

EXPLORATION

COTE D'IVOIRE CROSS SECTION

® Paleocene-Pliocene \

® . . Three postrift Maastnchl!an J prograding sequences

® Cenomanian-Lower Senonian G) Albian-rift sequence

South

Oceanic ; crust', '

I

/ ' ; ----- \

Tectonic stages

C Gravity faults-postrift stage B Block faulting- terminal rift stage A Book shelf mechanism-rift stage

sidered to be excellen t.

ESPOIR OIL FIELD

+

Lagunes fault zone

+ +

+

+ Paleozoic?

+ + Continental

crust

No scale

Fig . 2

North

OGJ

Fig. 3

A gas market is indicated by a gas fired electrical co­generation plant currently proposed. The plant is even­tually expected to be built on the coast adjacent to the new field and nearby Foxtrot field. Foxtrot has about 500 be£ of recoverable reserves and could supply fuel to the proposed plant for as long as 20 years.

,---- - -------i Espoir field If---------,

Iden tical informa tion about Cote d' Ivoire is avail­able in data rooms in Abi­djan and Boulder th rough June 31, 1994.

Structure The Abidjan margin is

considered to be a typical transform margin emplaced during the earliest Creta­ceous by the progressive opening of the South Atlan­tic Ocean.

The origin and further de­velopm e nt of th e Co te d ' lvoire sedimentary basin took place as three distinc­tive stages referred to as prerift, rift, and postrift. The presence of these stages has strongly influenced the type of deformational history of the basin (Fig. 2). The struc­tural evolu tion can be sum­marized by:

* Oil and gas wells

--400 -- Water depth It

0'========'3 Km o 1.8 Miles

', .,.""' , _______ ____ __ __ _

,----------j West Espoir field 11--- ---- --, Southwest

E .r::. a. Q)

0

A 1,800 *

0 1 Km

o .6 Mile

2,200

I c::::=J Sandstone

• A lengthy prerift stage that underwent a complex history involving primarily

/

* Northeast

A'

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Paleozoic rocks . These earli­er events have only an indi­rect influence on petroleum

occurrence. • A rift stage that was the

site of nonmarine deposition and controlled tectonically by n ort h east-sou th wes t shear and northwest-south­east extensional graben for­mation. Paleozoic, Triassic, and Lower Cretaceous rift infill sequences were affect­ed. This stage is character­ized by extensive fracturing and downwarp of the entire margin along the Lagunes fault. As much as 10,000 m of displacement may have occurred here.

Albian rocks are the pri­mary target associated with the rift stage. The complete Albian sequences have nei­ther been en tirely seen on seismic sections nor pene­trated by d rilling. Traps can be differentia ted into intra­Albian and uppermost Al­bian located immediately be­low the regional unconfor­mity.

• A postrift, or drift, stage that m arks the initiation of the Cenomanian transgres­sion following the oceanic opening. This stage lasts well into the Tertiary as the sedimen tary prism contin­ues to prograde basinward. In general, gravity deforma­tion along listric normal faults and associated roll­overs are typical. Other fea­tures include slumps, glides, and growth faults that sole out in the undercompacted shales of the Paleocene.

Cenomanian to Maastrich­tian objectives characterize th is stage. Structural clo­sures are less common up­wards, but m ore subtle trap­ping opportunities are pro­vided by the complex ar­rangement of sand bodies in local deltaic systems.

Stratigraphy The Albian has been only

partly penetrated south of the Lagunes fault, which forms the northern edge of the Cote d ' lvoire sedimenta­ry basin.

The sequence comprises mainly clastic rocks with fre­quen t sandstone intercala­tions and basement elem ent conglomerates. Provenance area for these terrigenous materials is the topographic

scarp created by the La­gunes fault zone. Two main lateral subdivisions appear along the shelf with in the Abidjan margin:

• The western part charac­terized by frequen t sand­stone intervals;

• The eastern portion con­sisting of a series of shaly and silty sections with limit­ed evidence of sandstone oc­currence in the rela tively shallow depths drilled to date.

Th e Upper Cretaceou s section in general includes three sedimentary cycles identified from the three di­mensional arrangement of strata. These are the:

1. Infill series 2. Prograda tion series,

and 3. Gravi ty deposits that

control the sand distribu­tion.

The three depositional units are separated by two regional unconformities in th e upper Senonian and Miocene. These features are clearly distinguished on seis­mic and well control.

The Cenoman ian se ­quence is deposited over the eroded surface of the Albian rift series. It consists of shale with fine-grained sandstone

fOXTROT GAS FIELD

EXPLORATION

Fig. 4

BELlER OIL FIELD

interbeds on the shelf area and con tains very fine­grained debris flows on the slope. Channel system s in­c! u ding coarser-grained sandstone are likely to be present in deeper offshore areas. Platform carbonates are present mainly in the lower section of the Ceno­manian . The sequence gen­erally thickens and deepens from west to east.

Top Lower Senonian structure

1 Km

I• Oil well 0 .6 Mile

The distribution of the Lower Senonian sediments is related to the presence of depocenters that correspond to clastic material accumulat­ed at the top of the slope. A north-sou th axis of maxi­mum thickness converging on the depocenters corre­sponds to the transport fair­ways of fluvial material com­ing from rela tively small lo­cal rivers. Thickening to the east also characterizes the Lower Senonian.

Belier field A A'

A-8 A-4 A-18 A-17 A-7 A-23 A-22

Within the Maastrichtian of the Abidjan margin, de­position was initially con­trolled by paleotopography. The sequence is composed of primarily of grey, micro­micaceous, calcareous, glau­conitic shales. Along the eastern extent of the margin there is a clastic series with coarse-grained sandstones,

conglomerates, and occa­sional bioclastic limestones. Elsewhere one finds evi-

Fig . 5

~~~------~F~o~xt~r~o~tf~ie~l~~----------~ I Southwest Northeast

A A'

0~~~====~*===~*=====~

4 From seismic

I I

Albian

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dence of find- to medium, locally coarse-grained sand­stones.

The Maastrichtian repre­sents the youngest in terval with hydrocarbon potential. The depocenter for Maas­trichtian sed iments is per­haps 20 km south of that of the Albian, reflecting the re­gressive nature of the pas­sive continental margin.

The Paleocen e-Pliocene section is composed of sev­eral prograda tional se­quences, and its thicker de­velopment is usually located slightly north of the presen t sh elf sed imen tary prism. Thinning of the section sea­ward is due to both the limit­ed influx of terrigenous de­trital material, and also to the trunca tion of the Eocene margin before Miocene de­position.

Espoir oil field Espoir field is on the conti­

nental shelf edge about 19 km offsh ore and 60 km southwest of Abidjan in 105-900 ft of water. The hydro-

EXPLORATION

THE AUTHORS

Koffi Bartm1

N'Dri Koffi has been working for Petroci, the Cote d'lvoire stale oil company, since 1977. He began his career as a wei/site geologist in Cote d'Jvoire drilling operations and continued in that position through 1981 . Early in 1982 he left Petroci and joined Phillips Petroleum Co., where he became involved in onshore and offshore opera/ions in Louisiana and Texas . He returned to Petroci early in 1984 and has been exploration manager since late 1984.

He has studied many oil and gas fields in Canada, the U.S ., Brazil, Argentina, and Angola, and has contributed to geological modeling, mapping, and drilling within tire Cote d'Ivoire sedimentary basin. He has a degree in geological engineering from University Laval, Quebec City.

Eric W. Barton has been with Gustavson Associates Inc. since 1988. He begarr his career in 1977 in Libya, where he performed reservoir studies on stratigraphically complex Samah field, which later became the basis for his MS in geology from the University of New Orleans. He was subsequently employed by Getty Oil Co. and Sohio Petroleum Co. He has petroleum exploration experience in the U.S. Gulf Coast and several Rocky Mountain basins.

Since joining Gustavson Associates he has prepared basin model-ing studies and hydrocarbon favorabil ity reports for various Middle East locations, Mexico, Argentina, Southeast Asia, West Africa, and the former Soviet Union. He has managed fair market value appraisals of U.S. and international oil and gas properties.

carbons occur in Albian sandstones at 1,800-2,136 m below sea level (Fig. 3).

The size and shape of the field is largely controlled by faults and by the post-Al­bian unconformity. The field is elongated northwest­southeast for abou t 13 km and is 3 km wide at its broadest part. The overall field area is about 25 sq km. Seven reservoir zones origi­nally contained about 420 million bbl of oil in place.

The field was brought on s tream in August 1982 with four wells in East Espoir and one well in West Espoir at an initial18,000-20,000 b/d. Sev­en more development wells were drilled. The field was shut-in in October 1988 after having produced 31 million sHk bbl, only 7% of the OOIP.

Belier oil field Belier field is in the east­

ern part of the Abidjan mar-

gin 15 km offshore and 30 km southeast of Abidjan in an average 60 m of water. The hydrocarbon accum ula­tion lies in Lower Senonian sandstones at 1,885-2,005 m subsea (Fig . 4).

Belier is an an ticline, elon­gated north-south for abou t 4 km, and 3 km wide . Its overall extent is about 8 sq km. The vertical closure is abou t 140 m at top Alb ian and 120 m at the level of the Lower Senonian reservoir. A major east-west trending normal fault down thrown to the south crosses the middle of the structure. Some other minor faults are present.

The reservoirs generally consist of coarse- to very coarse-grained friable sand­stone with thin layers of dark grey shale and silt­stone. Porosity averages 18-20%, and permeability varies from 200-500 md.

These sandstones are in­terpreted to be submarine fan deposits. The field axis comprises p redominantly channel deposits, while the sandstone lobes are more ex­tensive laterally . The reser­voir is absent on the western flank of the structure, where levee mudstones are found.

Twenty-four developmen t wells were d rilled (22 pro­duction wells and two water injection wells) . Production started under natural deple­tion in 1980. Pressure main­tenance by water injection was later initiated in four wells that had been oil pro­ducers. Production at the end of 1988 was about 18 million sHk bbl or 28% of OOIP.

Foxtrot gas field Foxtrot field is immediate­

ly north of the continen tal

shelf edge 15 km offshore and 80 km west-southwest of Abidjan. Water is 90-100 m deep over the field's cen­ter. Hydrocarbons occur in Upper Albian sandstones ly­ing a t depths below sea level of between 2,100-2,503 m (Fig. 5) .

The field's size and shape are controlled by the post­Albian unconformity. The field extends north-south for 9 km, its widest part being over 8 km. The overall area is about 50 sq km. The field comprises a large paleo-high cut by four major northwest­southeast trending normal faults, downthrown to the south. The Late Albian sedi­ments dip 10-1 2° to the north-northwest and are truncated by the post-Albian unconformity . Cenomanian and Lower Senonian shales lying immediately above the unconformity p rovide a seal to the hydrocarbons.

The reservoir consists of a m ono tonou s sequence of sandstone, finely interbed­ded with dark grey shale, siltstone, and some stringers of microcr ystalline lime­stone. The sandstone is gen­erally fine- to very fine­grained, rarely medium- to coarse-grained, angular to subrou nded, moderately sorted, with argillaceous and calcareous cemen t.

Porosity averages 21 %. The permeability is generally low bu t increases in the up­permost section, where it averages 15-20 md wi th some values up to 100 md or more .

Total gas in p lace in the Foxtrot structu re as a whole is estimated to be around 940 bscf. The field has not been developed.

COVER PHOTO: UNITED MERIDIAN CORP. flares gas and condensate at high rates from a wel l off Cote d'lvoire, West Africa. This well confirmed a commercial accumulation discovered by a previous operator, while a more recent well flowed oil at significant rates from untested zones. This article describes acreage the country is offering near these wells. Photo courtesy UMC.

To schedule a block of time for access to

the CONCESSION DATA ROOM or for more

information on the current bidding round,

please contact Eric Barton or N' Dri Koffi at:

GUSTAVSON ASSOCIATES 5757 Central Ave. Suite D Boulder, Colorado 80301 U.S.A. (303)443 - 2209 Fax (303)443-3156 Telex 5101008402

PETROCI

PETROCI

IMMEUBLE LES HEVEAS

BPV 194 ABIDJAN (COTE D'IVOIRE)

Tel (225) 20.25.82

Fax (225) 21.68.24