Depositional Control on Hydrocarbon Accumulations in Deepwater Nigeria

Xijin Liu
ConocoPhillips, Houston, TX

Seafloor geomorphology controls deepwater sand deposition which, combined with structural configurations, controls hydrocarbon accumulation. Structural control of hydrocarbon accumulations is nothing new, but depositional control seems to be very important in some deepwater exploration area. This is demonstrated by a case study of the deepwater Nigeria.

Major hydrocarbon discoveries in the deepwater Nigeria have been made in anticlinal structures from the shale-diapir province through the inner thrust belt and translational province to the outer toe-thrust belt. One of the most interesting observations is that most of the discoveries were made in the lee-side (basinward) of the anticlines. Two possible explanations, among others, become obvious. One is sand deposition preferentially occurs on the lee-side of the structures, at the time of deposition synchronous with structural growth related shale diapirism or thrusting, due to relatively greater accommodation space. The second one is that hydrocarbon migration and charge preferentially occur, along a regional depositional slope, in an updip (landward) direction.

The finding of the hydrocarbon accumulation pattern in the Deepwater Nigeria can potentially be applied to other deepwater exploration regions such as the Gulf of Mexico and offshore Angola. However, it does not apply to those accumulations where structural growth postdate sand deposition.