Predrill pore pressure prediction using reflection tomography

Abstract

Summary An accurate knowledge of formation pore pressure is required for the safe and economic drilling of deepwater wells. A predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform. However, seismic velocities obtained by conventional methods average the velocity over the seismic aperture and are therefore not suitable for pore pressure prediction in the presence of lateral variations, as may arise from the presence of dipping structures, lithology variations, salt layers of various thickness, fault blocks or variations in compaction and pore pressure. Reflection tomography gives improved spatial resolution of the velocity field and allows a more reliable predrill pore pressure cube to be obtained given a suitable velocity to pore pressure transform. The velocity to pore pressure transform can be calibrated using an inversion of offset well data, and the approach is illustrated for a deepwater Gulf of Mexico case study.