Formation Pressure Prediction With Seismic Data From the Gulf of Mexico

Abstract

Summary In this study, we derive seismic formation-pressure logs using seismic data from offshore Louisiana to delineate the distribution of overpressured zones in the subsurface. The seismic-data processing consists of velocity modeling, wavelet processing, and seismic inversion. From the acoustic impedances produced by seismic inversion, we derive seismic velocity and density logs at every seismic trace location using a relationship between sonic velocities and acoustic impedances. We use these logs to compute the seismic formation-pressure logs vs. depth. Formation-pressure logs are calculated with the assumption that compressional velocity, mean density, and depth are proportional to formation pressure. These logs are constrained at every depth by estimated matrix and fluid compressional velocities (vmax and vmin). vmax and vmin are derived from porosity and sonic well-log information. Results include profiles of seismic-velocity, seismic-density, and formation-pressure logs for two intersecting seismic lines from offshore Louisiana. Logs from one well are used to constrain the data processing. The seismic formation-pressure sections delineate a large region of overpressured shales in the subsurface.