WEST AFRICA: West African offshore activity promises huge petroleum potential

This report was compiled by editors for Global E&P Reporting Services for IHS Energy.

E&P activity offshore West Africa during 2002 has underlined the region's potential to become one of the world's most signifi-cant petroleum production centers. The region holds huge petroleum potential, and the US regards the area as strategically important in its search for diversity of supply.

Deepwater prospecting still poses problems for two reasons. First, there is poor understanding of local differences in maturity of source rocks and the hydrocarbon migration paths. Second, there is difficulty in identifying the presence, continuity, and geometry of reservoirs in the submarine palaeo-channel setting. The risks are augmented by local biodegradation of oil and lack of a gas drive in some areas. The predominance of gas in many structures may or may not be commercially viable. There is potential for LNG exports, but that requires costly infrastructure. Even for oil, economics of production could be problematic in areas like Angola, where high signature bonuses were paid.

During 2002, Woodside Petroleum appraised the deepwater Chinguetti discovery made off Mauritania in 2001 in block 4. Three exploration wells aimed at Upper Cretaceous/Tertiary series of a salt-induced structure. A fourth was a new discovery (Banda) in a separate, canyon-head play. Chinguetti's recoverable reserves are estimated at 110 MMbbl.

Petrosen is offering three blocks on the Senegal shelf and three in deeper water. The petroleum potential of the area is considered promising. The Dome Flore concession, with its heavy oil accumulation (500-900 MMbbl), is also open in the Senegal/Guinea Bissau (Joint Exploration Zone).

Off Guinea Bissau, Premier Oil abandoned a wildcat as a dry hole on the Sinapa Uma structure in block 2.

The government of Guinea decreed in September 2002 that all petroleum-related powers were vested in the president's office, with control assigned to a special cabinet. A data inventory is now underway, with a view to launching a new promotion of the national hydrocarbon sector. Plans include a fresh look at Guinea's sedimentary basins, which are unlicensed and open for exploration.

The current bidding round off Sierra Leone offers seven offshore blocks with a closing date in March 2003. TGS-Nopec acquired a grid of 2D seismic data and undertook a geological evaluation to support the bid round.

Liberia could open a licensing round in 2003, but the political climate is a deterrent. Twelve offshore blocks, of 4,000 sq km, will eventually be offered.

Activity off mid West Africa

Canadian Natural Resources drilled discovery well Baobab 1X in 2001 in block CI-40 off Côte d'Ivoire in 2002. Appraisal Baobab 2X flowed over 10,000 b/d. CNR is going ahead to recover 200 MMbbl in an FPSO operation. It also drilled nearby Kossipo 1, which was sub-commercial.

CNR-operated Espoir delivered first oil in a field redevelopment project in early 2002. Output reached over 12,000 b/d by year-end and will significantly increase in 2003.

Off Ghana, Dana Petroleum's shallow-water appraisal well WT2X, in the Western Tano block, proved the lateral extent of the year-2000 WT-1X discovery. The operator is now concentrating on the deepwater potential.
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Devon Energy identified multiple deepwater fans from the ancient Volta Delta in the Keta block. The first deepwater well is planned for 1Q 2003.

Hunt Oil/Petronas will drill Barracuda 1, the first deepwater well off Togo in 1Q 2003.

In December 2002, Kerr McGee/Petronas spudded Benin's first-ever deepwater well, Fifa 1 in block 4 (testing the Kaba and Atacora Com-plex turbidite prospects). A second well is planned back-to-back.

The big producers

Activities offshore Nigeria remain high, and exploration drilling showed spectacular success ratios – seven discoveries were made in 2001, eight in 2002.

Amni International, indigenous E&P operator, drilled the Setu prospect in OML 112 in 2002 and discovered oil. Recoverable reserves are estimated at 5-20 MMbbl.

ChevronTexaco's deepwater Aparo oil discovery in OPL 213 in December 2001 was successfully appraised with well Aparo 2. Aparo (OPL 213) and large Bonga SW (OML 118) discoveries share a common structure. Unitization is possible.

Shell drilled another major deepwater discovery, Bolia 1, in OPL 219 as well as successful appraisal well Bolia 2. Shell Bonga SW 1 discovery, with recoverable reserves of 600 MMbbl (2001), was appraised with two wells, Bonga SW2 and Bonga SW3. And Shell PDC made discovery JN 2 in OML 74, an HP/HT well that discovered oil and gas.

ConocoPhillips drilled deepwater appraisal well Chota 2 in OPL 220 on the east side of the structure, but of three hydrocarbon-bearing intervals, the two deeper levels were gas-bearing.

ExxonMobil announced oil discovery made with the Oyobio 1ST well (OML 67) and oil/gas with the Ebiya 1 well (OML 70).

South Atlantic Petroleum/TotalFinaElf/Bras-petro suspended wildcat Doa 1 in deepwater OPL 246. Although the well was tight, IHS considers it a significant oil discovery.

Statoil confirmed the Nnwa discovery in OPL 218 with the expensive Nnwa 2 appraisal well. Gas reserves of the Doro-Nnwa complex (OPL 218/219) are > 5 tcf.

TotalFinaElf was successful with the Ofon South 1 (OML 102; 900 b/d) and deepwater Usan 1 (OML 222) wells. Appraisals Usan 2 and Usan 3 were drilled at year-end to be followed by Ukot 2 in the same block. Ukot-Usan recoverable reserves could be 250 MMbbl.

Three offshore fields began production in 2002: Okono (OML 119; Agip/NPDC); EA (OML 79; Shell/TFE/NNPC); and Yoho (OML 104; ExxonMobil/NNPC). A full licensing round should start after the presidential elections in April 2003. Remaining potential is huge.

Off Equatorial Guinea, Amerada Hess made six significant oil discoveries last year – Abang, Akom, Ebano, Elon, G-9 (Elon Extension), G-13 – in blocks F and G in the Rio Muni basin. Except G-13, the discoveries were incorporated into the Okume-Oveng complex of fields that holds reserves estimated at 500 MMbbl. Disc-overy G-11 (sub-commercial) flowed liquid hydrocarbons from a Tertiary succession, possibly opening a new chapter in prospecting.

Off Angola, ChevronTexaco made its seventh, eighth, and ninth significant oil discoveries in block 14 (Tombua 1 tested an aggregate of 10,022 b/d of 39° API oil; Gabela 1 tested 1,000 b/d of 17° API oil; Negage 1 tested 8,630 b/d of 33° API oil). ExxonMobil announced the 12th and 13th oil discovery made in block 15 (Mavacola 1 tested 3,280 b/d; Reco-Reco 1 tested 2,640 b/d). TotalFinaElf made the 11th, 12th and 13th oil discoveries in block 17 (Violeta 1; Anturio 1; Zinia 1, 3,650 b/d). In November 2002, TFE was also operating wildcat Gindungo 1 in ultra-deepwater block 32, possibly another oil discovery.

BP made an oil discovery with Plutão 1, its second well in ultra-deepwater block 31. The well tested up to 5,357 b/d. This discovery could change the negative perception of the prospectivity of the ultra-deepwater in the Congo Fan.

In the southern part of the Kwanza Basin (Benguela sub-basin), ExxonMobil abandoned wildcat Semba 1 in block 24 as a sub-commercial oil discovery. Two zones, one in the Cretaceous and one in the Tertiary, yielded a combined flow of 3,039 b/d. A second well was abandoned with oil shows. The results document a working petroleum system.

Emerging areas

In the Nigeria/São Tomé and Príncipe Joint Development Zone, the long-awaited bidding round has been postponed due to complex contractual disagreements. Interest remains very high. In the São Tomé Exclusive Economic Zone, a licensing round could open in 2003, but not concurrently with a JDZ licensing round.

ConocoPhillips' Coco Marine 1 well off Cameroon tested up to 3,000 b/d of 34° API oil and 1.8 MMcf/d of gas, the first Tertiary oil discovery in the Douala Basin.

Pioneer made one oil discovery, Olowi Marine 1 in the South Gabon sub-basin, in 2001 and appraised it during 2002, confirming continuity of the Aptian-age Lower Gamba reservoir. Estimated reserves range from 100 to 500 MMbbl and 1.5-2.5 tcf.

Perenco discovered the Ompoyi field in the Gombe Marin Sud permit, testing up to 6,300 b/d in the Eocene Ozouri formation. Oil-in-place is estimated at 85 MMbbl. The Vaalco-operated Etame Marine field was brought on-stream in 2002, the first offshore field in Gabon to produce from the pre-salt Gamba.

Off Congo, Agip made one oil discovery in the Marine X permit (Awa Marine 1), which tested > 2,000 b/d of 32° API oil from the Albian Sendji carbonates. Anadarko abandoned well Rita Marine 1 (non-commercial gas discovery) in the Marine IX permit.

Shell's wildcat 2814/7-2 ST1 in block 2814A (Orange Basin) off Namibia has proven a disappointment, yielding only traces of gas. A second appraisal well was also negative. Shell elected to withdraw, but partners ChevronTexaco and Energy Africa are continuing.

Off the west coast of South Africa, Forest Oil undertook a major drilling program in 2001/2002 around the Ibhubezi gas/condensate field in block 2. Reservoirs were found in a series of complex discrete sand channels within the Upper Cretaceous (drift) succession. Forest is working on securing gas markets in the Western Cape area.