Hydrocarbon Prediction in Offshore Deepwater Niger Delta: Case study of Fold Play

Chidi Chukwueke and Emmanuel I. Enu
Shell Internmational Exploration and Production, Houston, TX

In the first round of deep-water awards in Nigeria in 1993, two oil-prospecting licenses (OPL) on the continental slope were granted to Shell (SNEPCO). The blocks are located to the west and to the east of the Niger Delta: OPL 212 and 219 respectively in 200 to 1500 m of water. No well had previously been drilled in this deep-water province.

SNERGO have drilled six exploration wells (Ngolo-1X & ST, Ngolo-2X, Doro-1X, Bolia-1X and Bolia-2X) in OPL-219 situated, in the fold belt, testing three major anticlinal structures, Ngolo, NnwaDoro and Bolia-Chota. This resulted in the discovery of oil and gas accumulations in lower Miocene to lower Pliocene turbidites, which were deposited on the lower slope. Seismic imaging suggests that the most likely depositional environments are channelised fan-lobes, amalgamated, sinuous channels, and channel-levee complexes, possibly isolated from one another by shale-filled channels. The reservoirs therefore include a strong stratigraphic component along with structural closure to form hydrocarbon traps.

The first well ( well-1) in the block, was drilled to test the potential for oil fill in Tertiary turbiditic sandstones of amalgamated channel levee, slope fan facies, expressed by AVO supported seismic amplitude anomalies. The well encountered gas in its primary objectives and oil in deeper reservoirs.

The second well was drilled to further test the prospect and the northern structural trend. It encountered amplitude supported gas and deeper oil reservoirs. The well is located some 6.5 km West and downdip of the first well. It was designed to provide optimal penetrations of reservoirs that were found oil bearing in well-1, albeit in separate channels, and to fully evaluate their potential by coring and, if justified, production testing. Furthermore, well-2 targeted deeper, not previously penetrated reservoirs and encountered reservoirs as predicted but gas at same oil levels in well-1.