PORE-PRESSURE PREDICTION FROM SEIMIC DATA IN PARTS OF THE ONSHORE NIGER DELTA SEDIMENTARY BASIN

Abstract

Pore pressure prediction in parts of the Onshore Niger Delta Sedimentary Basin using seismic reflection data has been carried out. The Bower’s technique of velocity-to-pore pressure transform was adopted. The seismic velocities were derived from the seismic data using layer cake velocity model and were later compared with the available sonic logs velocities obtained from the area. Parameters in the velocity-to-pore pressure transform were estimated using the seismic interval velocities. The top of overpressure zone is about 3500 m which is in agreement with available data. The overpressure occurs within the shale rich region of the Agbada and top of Akata Formations in the basin. Comparison of the overpressure zone with available geophysical logs shows that the interval has lower bulk density, lower interval velocity and high porosity. With regard to the young age of the basin, the factors that might be responsible for the overpressure are mechanical compaction, chemical compaction and hydrocarbon generation. The results of the analysis revealed that the overpressure in the area is associated with simple rollover structures bounded by growth faults, especially the hanging walls. This method of pore pressure prediction is very useful because it helps to predict pore pressure ahead of the bit.