Pore pressure prediction using well-conditioned seismic velocities

Abstract

Abnormal pore pressures are encountered worldwide, often resulting in drilling problems such as borehole instability, stuck pipe, lost circulation, kicks, and blow-outs (Dutta, 1997). To optimize the choice of casing and mud weight while drilling abnormally pressured formations, a pre-drill prediction of pore pressure is required. A pre-drill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated from offset well data. However, velocities obtained from processing seismic reflection data often lack the spatial resolution needed for accurate pore pressure prediction, due to assumptions such as layered media and hyperbolic moveout. In addition, the uncertainty in velocity is often not quantified. In this example from the Gulf of Mexico, seismic velocities obtained using reflection tomography are combined with well data to produce a refined velocity field that honours the available well information. The refined velocity field is then used to predict pore pressure.