Abstract

Pore pressure prediction is a key factor to reduce risk and ensure safe well engineering by planning wells with proper mud program and casing design in anticipated high overpressure zones and prevent a variety of drilling problems. Proper integration and careful calibration of traditional wireline logs, petrophysical logs, seismic velocity data, vertical seismic profile data and field test data is required in formation pressure analysis. The scope of our work is to derive a 3D pore pressure model in Lakwa area of North Assam shelf where various downhole complications were encountered in drilling thick Kopili formations. During the well data analysis, it was found that a high pressured shale within Kopili formation indicating a pronounced lowering in sonic velocities is consistent in all the wells of the area. The main objective of our study is to identify the causative mechanism of overpressure and to generate a pore pressure model to delineate high pressure locales in the area. This is accomplished by performing a fine grid seismic velocity analysis on inverse NMO corrected PSTM gathers and utilizing velocity to effective stress transforms for deriving 3D pore pressure and fracture gradient volumes. The predictive reliability of the model is determined by a blind test procedure using drilled well and the pore pressure output extracted from 3D volume fairly matches with the drilled results.