EVALUATION OF ABNORMAL PORE PRESSURE ZONES IN OML-58, NIGER DELTA OIL AND GAS FIELD

Accurate knowledge of formation pore pressure is crucial in oil and gas sedimentary basins, both from technical and socioeconomic perspectives. It ensures safe and cost-effective drilling, enables assessment of fluid migration pathways and trap integrity, assists in basin modeling, and determines seal reliability. This study identified abnormal pore pressure zones using sonic porosity logs from two wells (Well A and Well B) in OML-58, Niger Delta. Assuming the basin is extensional and that compaction disequilibrium is the primary cause of high pore pressure, sonic log slowness was digitized at 25 m depth intervals. Sonic compressional velocities were calculated as the inverse of slowness, and porosities were computed using Wyllie’s equation. The deviation-from-normal-compaction-trend method was applied to detect abnormal pore pressures. Results show that in Well A, porosity and slowness decrease with depth while sonic compressional velocity increases, consistent with normal compaction trends, indicating no abnormal pore pressure zones. In contrast, Well B exhibited significant deviations from normal trends in depth-porosity, depth-slowness, and depth-velocity profiles, revealing an abnormal high pore pressure zone between 2700 m and 2775 m. This depth range aligns with previously reported abnormal pressure zones in the Niger Delta. The study demonstrates the effectiveness of sonic log analysis for identifying abnormal pore pressures, which is critical for safe drilling and reservoir management in the Niger Delta.