Fault seal analysis with pressure driven approach to assess vertical sealing potential in ATM field Niger Delta Nigeria

Abstract

The Niger Delta Basin, though rich in hydrocarbons, continues to face challenges with dry hole drilling, often caused by seal failures, even with the application of advanced shale-based evaluation techniques. The shale based (SGR) technique usually depends on shale content as indirect indicator of lateral sealing potential of fault, however, this static method often leads to false seal predictions, and consequently resulted in dry holes drilling, as it ignores variations in pressure and stress. This research applied a pressure-based approach that integrated pore pressure and stress state information to dynamically evaluate the vertical sealing potential of fault-bound reservoir in ATM field Niger Delta, Nigeria. The implication of this approach provided a more realistic and data-driven assessment of fault sealing integrity; thereby reducing uncertainty and the likelihood of dry holes drilling in the basin. The results of the vertical shale smear coefficient (Q) revealed differences in the sealing efficiency of faults across the two mapped reservoirs in the study field. The Q values of 0.55, 0.54, and 0.63, of faults F2, F4, and F5 in reservoir 1, suggested they are vertically sealed with ability to prevent vertical hydrocarbon migration. Conversely, Reservoir 2 exhibited inconsistent sealing capabilities. Faults F2 and F5 are vertically sealed with Q values of 0.47 and 0.45, while F4 demonstrated poor vertical sealing behaviour of Q value 0.34, potentially serving as a vertical conduit for hydrocarbons leakage. These findings helped discriminate between well-sealed and leaking reservoirs, thereby reducing uncertainty and the likelihood of dry holes drilling in the Niger Delta Basin.