--> Structural Timing and Hydrocarbon Charge Modeling in the Southeastern Deepwater Niger Delta, by Sankar Muhuri, Michael Roberts, and Michael Hertle; #90037 (2005)
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Structural Timing and Hydrocarbon Charge Modeling in the Southeastern Deepwater Niger Delta

Sankar Muhuri, Previous HitMichaelNext Hit Roberts, and Previous HitMichaelTop Hertle
Chevron Texaco, Bellaire, TX

The southeastern deepwater Niger Delta has yielded numerous large discoveries, including Agbami, Nnwa-Doro, Bolia-Chota, Akpo and Usan. This province is bounded by the Charcot seamount trend on the west and the Cameroon volcanic chain on the east. These imposed rigid boundaries constrain numerous transpressional episodes which advance basinward through time. The cumulative strain manifests as an inner contractional trend of thrusted shale diapirs and an outer trend of imbricate thrust stacks. Interestingly, nestled between two distinct structural provinces is a less intensely structured "quiet zone" with isolated large detachment folds.

A series of 2D restorations and isopach maps between major third-order sequences in the "quiet zone" indicate multiple periods of structuring. Ductile shale flowage serves as the primary means of structural readjustment in this area. The Akpo Field and the synclinally separated structures around it illustrate these multiple growth stages. Structural closures adjacent to the Akpo field formed earlier near the end of Middle Miocene time. Hydrocarbon charge modeling suggests that migration into these surrounding structures commenced in the late Miocene. Independent closure on the Akpo structure did not form until the Pliocene when the surrounding deep kitchens were in a more gas-prone maturity state. The Akpo structure continues to enlarge through time by synclinal migration away from its core. The late timing history and gas prone character of the Akpo discovery suggests that the surrounding early forming Middle Miocene structures may be more oil prone.