Activity is growing offshore Cameroon and Equatorial Guinea as independents work substantial gas discoveries. (Map courtesy of IHS Inc.)

Since 2002, 14 new-field wildcats have been drilled in the Douala Basin, with 40% success in finding hydrocarbons, mainly gas and condensate in Miocene sandstone reservoirs. In 2007 alone, four out of six were positive.

The Douala Basin covers some 10,232 sq miles (26,500 sq km). About 70% is located offshore, half of which in deep water. The basin lays mainly onshore and offshore Cameroon. But to the west and southwest, the basin extends into the territorial waters of Equatorial Guinea.

A number of geological features demarcate the basin — the Cameroon Volcanic Line to the northwest, the Pan African Fold Belt to the east, and the Kribi Fracture Zone to the south. The western boundary has been set arbitrarily at the 6,562-ft (2,000-m) isobath; similar geology is expected westward into the Douala-Gabon Deep Sea Basin.
Proven reservoirs are the Mundeck Formation (mainly of Lower Cretaceous age) comprising non-marine sandstones and fluvial arkoses, Upper Cretaceous Logbaba and Tertiary N’Kapa and Souellaba formations of mainly fan and channel sands enclosed in offshore slope and basin mudstones. Trapping styles are dominated by unconformity and stratigraphic types.

The hydrocarbon source rock has not yet been definitely recognized. The main contenders are a Lower Cretaceous lacustrine source, an early Upper Cretaceous marine source, and a Tertiary marine source (N’Kapa).

Exploration history

There have been 61 new-field wildcats drilled in the basin. Most of the 22 discoveries were made in the Cretaceous. These finds are mainly located on the eastern side of the basin. Recent exploration has focused on the Tertiary.

Most of the wells were drilled in Cameroon where exploration started in the 1950s. There have been 54 new-field wildcats and 24 outposts.
The first discovery was made in 1954, with Bomono 101. Gas and condensate were found in the Paleocene N’Kapa Formation. The well tested 275 Mcf/d of gas below 6,152 ft (1,875 m). Oil and gas in the Miocene Souellaba Formation were found for the first time in 1956 in new-field wildcat, Souellaba 2.

Elf drilled Nyong Marine 1 offshore in 1965. In total, eight wildcats were drilled, but none resulted in a discovery.

A new exploration phase started at the end of the 1970s, with offshore well Sanaga Sud A 1 drilled by Damson Oil. Gas and condensate were found in the Mundeck Formation. Drilling turned up 11 discoveries, all in the Cretaceous, two with secondary reservoirs in the Tertiary.

In the 1990s, most of the drilling operations focused on the appraisal and development of the shallowwater Kribi B and F structures. Perenco acquired the production rights for the Kribi area in 1996. The only production in the basin was established in January 1997 from these two fields currently located in the C-31 (Ebome Marine) block. So far, about 16 million bbl of oil have been recovered.

Since 2000, apart from the Bome 1 oil and gas well drilled by CMS, all of the drilling efforts have been offshore. In 2002, ConocoPhillips drilled the shallow-marine Coco Marine 1 in PH-77 (Nyong II). The 8,629-ft (2,630-m) well tested up to 3,000 b/d of 34° API gravity oil and 1.8 MMcf/d gas from Lower Tertiary, the best result so far. The average reservoir porosity was found to be 20%, with permeabilities around 1 Darcy. The trap consists in an updip pinchout of channel sands.

A second wildcat, Londji Marine 1, was abandoned as dry in 2005. The next well, Coco Marine 2, encountered a thin oil column. Noble Energy took over the acreage in 2006. In 2007, the D-1R well, drilled by BowLeven PLC subsidiary Euroil Cameroon Inc. in adjoining block MLHP-5, PH-74 (Etinde) tested 25 MMcf/d gas and 1,400 barrels of condensate a day (bc/d) from Miocene sands. The same year, Noble Energy’s Yoyo 1 tested 31 MMcf/d gas and 330 bc/d in block PH-77.
There have only been seven wildcats and three outposts drilled in Equatorial Guinea.

The first discovery was made in 2005. The O-1 wildcat, drilled by Noble Energy on the Belinda prospect, tested up to 24 MMcf/d gas and 1,225 bc/d from high quality Miocene channel sands.

As technical operator in blocks O and I, Noble Energy began a six-well program in March 2007. The first well, O-2, failed to encounter hydrocarbons in the Adriana prospect. The subsequent well, wildcat I-1, targeted the Benita prospect in 2,907 ft (886 m) of water and tested 34.3 MMcf/d gas and 1,038 bc/d. The reservoir section was found to be thicker than at Belinda.

Benita was the second discovery in Equatorial Guinea. O-3, a Belinda appraisal, tested up to 30.4 MMcf/d gas and 1,540 bc/d. I-2, a Benita appraisal, ended at 10,581 ft (3,225 m). It encountered an estimated 30 ft (10 m) of net gas underlain by 115 ft (35 m) of net oil. Preliminary analysis indicates an oil gravity of 32° API.
A third discovery was made with I-3 on Yolanda. Drilled in 2,940 ft (896 m) of water, the well tested 36 MMcf/d gas and 371 bc/d from a Miocene reservoir. It is believed that I-3 is on trend with Yoyo 1 in Cameroon.

Finally, the recent success of appraisal well I-4 indicates that the resource potential of Belinda ranges from 200 to 320 million boe, with a liquid content of 40%.

Future plans

Four operators are present offshore Cameroon, and there are no blocks currently available.

BowLeven has plans to drill four exploratory wells in the southern part of the PH-74 (Etinde) license in the third quarter of 2008 and is seeking partners.
Noble Energy has not released specific plans yet, but analysis suggests further activity will likely be focused on developing its discoveries in both Cameroon and Equatorial Guinea together.

Perenco, which holds the largest exploration acreage (Kombe and Nsepe onshore, and Ebodje Marine offshore), has plans to develop the offshore Sanaga Sud gas field in the MLHP-4 lease. Up to 40 MMcf/d gas will be delivered to a planned 150 MW power plant at Kribi.

Sterling Energy, owner of the PH-78 (Ntem) block, is waiting for the resolution of the border issue before drilling a well.

Three operators are present on the Equatorial Guinea side. Glencore and Starc bid for block EG-07 in the latest bidding round. ONGC bid on block EG-12. Unleased acreage is very limited.

Noble Energy, the most active company, has plans to drill two exploration wells in Block I in first half 2008, a Benita appraisal well and a wildcat on the Diega prospect. The most likely export route for gas would be the liquefied natural gas (LNG) plant on Bioko Island.

PetroSA and Roc Oil will drill exploration wells in blocks Q and H.

The offshore is not the only area receiving renewed interest. Several companies are presently gearing up onshore Cameroon. BowLeven is one of the players, having been granted the Bomono exploration permit last year. Perenco has plans to drill two exploration wells in 2008. And Rodeo, Turnberry and Globex are looking into developing the gas reserves near Douala for the local market.

Conclusions

Exploration in Cameroon was spurred by the creation of a dedicated gas unit at SNH in June 2007 and the enactment of the new gas code containing many incentives for gas development and production.

Recent discoveries in the offshore Tertiary play of the Douala Basin have commercial potential, and gas development options are being considered. The oil potential needs to be further assessed.

In Equatorial Guinea, the newly established LNG plant on Bioko Island provides an outlet for gas resources in the region. The installation of a second train is under evaluation. The Douala Basin discoveries are helping to speed the decision.

Cameroon and Equatorial Guinea have signed Heads of Agreement relating to exportation of natural gas to Equatorial Guinea. Studies have confirmed that Cameroon has sufficient natural gas reserves to export 200 MMcf/d over 20 years by 2010-2011.

If the existence of accumulations straddling the border between the two countries is confirmed, development will certainly be conditioned on defining a common limit. A commission is working on the demarcation of the maritime boundary.