Migration effects on the composition of hydrocarbon accumulations in the OML 67-70 areas of the Niger Delta

Systematic changes in gas-oil ratios in the OML 67-70 area (joint venture acreage) of the Niger Delta (Nigeria) illustrate the effects of hydrocarbon migration on the compositional changes observed in the accumulations over large depth intervals. One interpretation is that the reservoirs are currently both filling and leaking hydrocarbons, indicating that trap styles affect the migration pathways in this region of the Niger Delta. The accumulations are more liquid prone with depth, based on the bubble point of the fluids in the reservoir. Applying these results to regional exploration opportunities indicates that fluid contacts in the normally pressured section are controlled by leaking seals (class III traps). The potential exists for pressure-controlled filled-to-spill traps (class II traps) in the overpressured section, where a high-quality seal impedes the vertical flux of hydrocarbon fluids. Although these conclusions apply to a specific portion of the Niger Delta, combining the concept of trap style with compositional changes resulting from migration processes is useful in identifying new play concepts and opportunities in other regions of the world.