Pore Pressure Prediction from 3D Seismic Data: A Feasibility Study for Unconventional Gas in Saudi Arabia

摘要

The purpose of this study is to provide a pore pressure prediction from seismic data targeting unconventional gas plays (i.e., the Qusaiba Member hot shale and the underlying Sarah Formation). The area of interest (AOI) located in NW Saudi Arabia, and is covered by 1,600 km~2 of 3D pre-stack time migrated (PSTM) data. The pore pressure prediction workflow consists of three main steps: pre-stack seismic data conditioning, seismic velocity calibration with sonic and density logs from offset wells, calibrated effective stress vs. velocity relationship and stratigraphic model-based pore pressure prediction. Three wells in the AOI are used to calibrate the interval velocities and densities prior to pore pressure prediction. In addition, formation pressures from the Repeat Formation Tester (RFT) tool, mud weights and drilling history are incorporated to constrain the predicted pore pressures. As a result, the pore pressure gradient variations in the Qusaiba Member hot shale and the Sarah Formation are mapped in the AOI. 2D seismic lines are used in this study to extrapolate pore pressure prediction results to satellite well locations outside the 3D seismic area. The resulting pore pressure maps for the Qusaiba Member hot shale and Sarah Formation highlight potential drilling hazards. Importantly, areas of higher pore pressure may ultimately represent potential areas of higher gas production (i.e., sweet spots). This work is the first application of pore pressure prediction in unconventional resources in Saudi Aramco, opening the door for more comprehensive efforts to predict pore pressures in other areas targeting shale gas and other unconventional plays in Saudi Arabia.