INTERNATIONAL FEATURE

INTERNATIONAL EXPLORATION OPPORTUNITIES IN KENYA

Kivuti Nyagah, Assistant Exploration Manager John J. Cloeter, Exploration Advisor (member HGS) National Oil Corporation of Kenya

General Information on the Sedimentary Geology The sedimentary region of Kenya, covering an area of

approximately 317,814 sq. km., comprises four major sedimentary basins, the Mandera, Anza, Lamu and Western Kenya Rift Basins (Figure 1).

The Mandera Basin, which is a cratonic rift basin extending into Ethiopia and Somalia, contains up to 8,000 -10,000m. of Karroo (Carboniferous - Triassic) and Jurassic through Cretaceous fluvial-continental, lacustrine and marine sediments. The Anza Basin is separated from the Mandera basin by the Lagh Bogal fault and is thought to be continuous with the Abu Gabra Rift Basin of southern Sudan. I t contains Jurassic to Tertiary continental fluvio- deltaic, lacustrine and marine sediments varying in thick- ness from 2,000 - 8,000m. along its length. The Lamu Basin incudes depocenters located in both onshore and offshore locations of southeast Kenya and consists of Karroo through Tertiary strata that vary from continental rift basin sandstones and shales to fluvio-deltaic sandstones, marine shales and carbonates. The onshore depocenter has a sediment thickness ranging from 3000m. in the northern boundary, to 10,000m. in the coastal areas. The offshore sedimentary column is 12,000m. - 13,000m. thick. The offshore depocenter constitutes a southern section of the western Somalia Basin, the growth of which is linked to the east-west separation of Madagascar from the east Africa coast and evolution of the southwestern Indian Ocean. Progradational sedimentary sequences, growth faulting and salt diapiric structures are recognized from seismic profiles and indicate that the basin developed as part of a passive margin following the opening of the Indian Ocean. The Turkana, Lokichar, Suguta-Magadi, South Kerio and Nyanza troughs constitute the western Kenya Basin. The strata in these sub-basins mainly comprise lacustrine and fluvio-lacustrine deposits interbedded with abundant vol- canic extrusives. The sediments in the Nyanza and South Kerio troughs are Late Miocene to Quaternary in age, while in the Turkana Basin they are Cretaceous through Quater- nary in age.

These sedimentary basins have been subdivided into different exploration blocks (Figure 2) with each block corresponding to part of a basin or sub-basin.

Recent Prospect Evaluation Studies. A study currently in progress by the National Oil

Corporat~on of Kenya of the coastal Lamu Basin and the offshore area, integrating for the first time all of the well control, seismic, gravity and magnetic into a regional

Fig. 1. Location of sedimentary basins in the Kenya region.

synthesis, will be completed by the end of 1992. Preliminary results have indicated a possible new trend play not pre- viously recognized, a Paleogene deltaic series confined in areally restricted depocenters, as yet untested by the drill.

Early exploratory drilling in the Lamu Basin focused primarily on Mesozoic objectives, marine Jurassic and Cre- taceous rocks, which are seen at a few poorly exposed outcrops, and large block-faulted structures on intrabasinal highs and platform areas. Only in the latter stages did the drilling activity move into the Tertiary depocenters, where the most encouraging wet gas shows in the basin were encountered. At that point drilling and exploratory activities ceased in the coastal area.

The breakup of Gondwanaland, which began in the Permo-Triassic, initiated an extensive marine transgression in the Jurassic and a still-stand in the Cretaceous. Moderate epeirogenic block faulting in the Late Cretaceous modified

Buller,n Houston Gro log~r ; i l S o c ~ ~ t y . September 1992 16

the coastal basin geometry, forming intrabasinal highs and imposing narrow graben lows that became the natural depocenters for the regressive cycle that followed. The regression continued into the Paleogene with thick clastic sequences concentrated in the Tana syncline, the Pate embayment, and southwestern Somalia. Composite Cre- taceous and Paleogene thicknesses in excess of 3000 meters each are present, varying according to the basin position. In the Late Paleogene, clastic deposition changed to a mixed clastic and predominantly carbonate shelf facies, which continued through the Miocene. Both listric down-to- the-basin growth faults and antithetic faults are seen onshore and in the near offshore.

Prospects will be structures in the delta front sands of the prograding series, sourced from prodelta and delta front shales. The major part of the prospective area lies onshore and the remainder in the shallow water near shore.

Historical Review of Petroleum Exploration in Kenya The first Oil Exploration License (OEL 1) in Kenya was

granted to British d'Arcy Exploration Company and Shell Overseas Exploration Company in 1954. Three dry holes, .Walu-1, Pandangua-1 a d Meri-1, weredrilled todepthsnot ,oxceeding%Mm. ThePandangua-1 well t e s t 4 minor amounts of gas in the BQlrrep Beds (Middle ~ocenea igocene ) .

In 1961 the oti$inal licenses yere.eonverkd to Special 'oil ~ r o s ~ e c t ~ ' I d c e n s e s (96PL 1 and 2), which allowed greater drilling and -1,mger berat ing periods. The company pderrned mbre sdphisticated seismic work and

Fig. 2. Exploration blocks subdividing sedimentary basins in Kenya.

drilled seven wells, Mararani-1, Walu-2, Dodori-1, Wal- merer-l, Garissa-l, Pate-l and Kipini-l in the Lamu Basin between 1961 and 1971. Oil staining and gas shows were observed in Tertiary strata in the Dodori-1, Mararani-1, Kipini-1 and Pate-1 wells. The Dodori-1 well tested small amounts of wet gas in sands of Paleocene age. The Pate well encountered a 9.5m. thick Paloeogene porous sand at 4177 m. The well kickedand the open hole had to be cemented off

"Prospects will be structures in the delta front sands of the prograding series, sourced from prodelfa and delta front shales."

to control the well. During the kill operation the well flowed back mud, water and wet gas. The well was plugged and abandoned at 4188 m.

Chevron conducted an extensive seismic program and drilled two wells in what is now South Anza Basin. The wells were dry and the company withdrew from the area in 1977.

Whitestone and LL&E were granted licenses in 1973 that covered the eastern and north-eastern sectors of the Lamu Basin. In 1975 they farmed out to Texas Pacific, and Texas Pacific drilled the Hagarso-1 well. Oil and gas shows were encountered in the well within strata of Cretaceous age.

In 1972, Total Exploration Company and Elf Aquitaine signed a Deep Water Offshore Exploration Agreement and conducted non-exclusive operations over an area of 39,500 sq. km. After conducting a seismic survey, the companies converted the agreement to a Special Oil Prospecting License and drilled the first offshore well, Simba-1, in 1978 on a large, well-defined and closed structure in 921m. of water. Exploration in the offshore area has been dormant since 1985 when the Cities Service group, which included Marathon and Union Oil, completed two dry holes, Maridad-1 in 1981 and Kofia-1. Although the activities in the offshore area were disappointing, they revealed the pre- sence of a possible Jurassic salt basin that might have undergone sizeable halokinetic movement.

Between 1985 and 1989 various companies signed Production Sharing Contracts on acreage mainly located in the Anza Basin. In 1985 Amoco drilled two wells, Elgal-1 and Elgal-2 to test strata of the Karroo sequence in the South Anza Basin, followed by three wells, Sirus-1, Bellatrix-1 and Chalbi-3 which produced hydrocarbon shows of non- economic significance.

A group of companies comprising Marathon, Mobil and Total acquired acreage in the Anza Basin under a Product- ion Sharing Agreement signed in 1985, and three wells, all dry, (Ndovu-1, Duma-1 and Kaisut-1) were drilled. Fluid inclusion studies performed on samples of an oolitic lime- stone outcropping at the Matasade High revealed the presence of mature hydrocarbons within the pore spaces. Other results from an oil seep study jointly conducted by Total arid Amoco at Tarbaj indicated a mature Jurassic basinal source rock and attracted interest in the southern part of the Mandera Basin. In late 1989 the area was awarded to a group of companies comprising Total, Amoco, Marathon and Texaco.

Elsewhere in the Lamu Basin, a joint Government/ Petro-Canada International Assistance Co-operation

Bulletin Houston G.ologlcrl Saclow. Smarnbor 1992

Agency project drilled the KenCan- l well, which tested Jurassic strata in the northern part o f the Lamu Basin in 1985.

Only ten wells have been drilled in the Lamu Basin, many of them poorly located in the basin and some of them testing questionable structures. Three wells were drilled in the offshore area.

Quantity of Exploration Data. Explorationdata from surveysconductedin thevarious

basins are held in the National Oil Corporation of Kenya. A computer-supported data storage system was installed in 1989 to improve maintenance and retrieval. The technical database is comprised of geological reports and maps. well information including well logs, geochemical and petro- physical samples and accompanying reports, geophysical data and reports covering a wide spectrum of scientific studies. All well cuttings samples and cores are kept at a recently completed core storage facility. Magnetic tapes belonging to various geophysical surveys are stored at a facility under suitable temperatureand humidity conditions.

A total o f 15,997 line.km. of seismic reflection and refraction data were recorded onshore in the Lamu Basin. In the offshore area there is 11.671 line-km. of data. In the AnzaBasin 13,251 line-km. of goodquality seismic reflection data have been acquired. A 707 line-km. seismic survey for the Total-Amoco-Marathon-Texaco group was recently completed in the Block 1 area of Mandera Basin. The National Oil Corporation o f Kenya through funding f rom the Wor ld Bank acquired 100 line-km of seismic reflection data in 1989 in the South Kerio and Nyanza troughs of the western Kenya Rift Basins.

Between 1959 and 1983 approximately 49.744 km. o f aeromagnetic data were acquired in the Lamu Basin, another 64,061 km. in the Anza Basin, 4.895 km. in the Mandera Basin, and 29,399 km. in the Rift Valley.

The gravity measurements in the Lamu Basin cover 5,997 km.. those in the Mandera Basin3,968 km., and 14,212 km. in the Anza Basin. In 1987 BElClP produced a complete Bouger Anomaly map of Kenya at a scale of 1:250.000 utilizing all available gravity data. Geological and geo- structural maps produced at a similar scale are also available.

Exploration Legislation ThepetroleumExploration and Production Legislation

in Kenya was revised in 1986 to provide suitable incentives and flexibility to attract international exploration interest in the country. The legislation incorporates the model pro- duction sharing agreement which outlines the terms of the exploration and production contract which are negotiable between a company and the Government. These include:

Recovery of all exploration c o s ~ s at a negotiated and agreed percentage of the total production, and a profit oil split on aslidingscale based o n production rates, the percentages of which, are negotiated and determined during negotiations of the exploration contract. Recovery of capital expenditure at an agreed percentage amorlixation commencing from the fiscal year in which expenditures are incurred. Tax.deductible benefits that allow companies todeduct

exploration and drilling costs of non-productive wells capital expenditures on plants and machinery alr

buildings

administration and management costs and profes. sional fees interest o n loans for operations conducted in the country losses arising from petroleum production.

In addition, there are exemptions from customs duties andVAT on allexports and importsrelated to equipment and materials for petroleum operations. as well as exemptions from foreign exchange control requirements, hence allowingretention of profits and payment ofexpatriateemployees in foreign accounts. There is a guarantee r ~ f investment through the Fore~gn Investment Protection Act, whichallows the company to transfer

profits after tax original equity investment principal o f foreign loans and interests.

Exploration companies may apply for non.exclusive erploration permits that allow holders to acquire geological and geophysical data from a selected area for a limited period of one year.

Contact: Mr. Joseph Kwamba: Managing Director National Oil Corporztion of Kenya P.O. Box 58567 Nairohi. KENYA