Pre-drill pore pressure prediction using seismic velocities for prospect areas at Beni Suef Oil Field, Western Desert, Egypt

Abstract

Pre-drill prediction of formation pore pressure from surface seismic survey is very important for drilling, production, and reservoir engineering because it affects drilling operations and well-planning processes. If it is not properly evaluated, it can lead to numerous drilling problems such as dangerous well kicks, lost circulation, blowouts, stuck pipe, excessive costs, and borehole instability. Pre-drill pore pressure estimation has been obtained from transform models using seismic interval velocities. However, the accuracy of this estimate of pore pressure is directly related to the reliability of these interval velocities. Bulk density was estimated from seismic interval velocity and transit time. Normal pore pressure gradient is estimated from the slope of a trendline that is generated from logarithm transit times versus depth. Overburden pressure at any depth was calculated from the integration of the average interval bulk densities and thicknesses above that depth. Pore pressure has been obtained from overburden pressure and observed interval velocities using modified Eaton’s equation. 154 CDPs were used along 28 seismic lines at Beni Suef basin, Western Desert, Egypt, to accomplish the purpose of this study. Two velocity reversal zones showing abnormally high pore pressure were detected and correlated to Abu Roash and Bahariya Formations. Moreover, pore pressure gradient maps were established for these two zones to predict the possible horizontal fluid flow (migration paths) for the proposal of prospects with lower pressures and less drilling risks. Finally, it is possible to calculate and recommend the required heavier mud weight to drill.