Pore pressure estimation in reservoir rocks from seismic reflection data

A method is used to obtain pore pressure in shaly sandstones based upon an acoustic model for seismic velocity versus clay content and effective pressure. Calibration of the model requires log data-porosity, clay content, and sonic velocities-to obtain the dry-rock moduli and the effective stress coefficients as a function of depth and pore pressure. The seismic P-wave velocity, derived from reflection tomography, is fitted to the theoretical velocity by using pore pressure as the fitting parameter. This approach, based on a rock-physics model, is an improvement over existing pore-pressure prediction methods, which mainly rely on empirical relations between velocity and pressure. The method is applied to the Tune field in the Viking Graben sedimentary basin of the North Sea. We have obtained a high-resolution velocity map that reveals the sensitivity to pore pressure and fluid saturation in the Tarbert reservoir. The velocity map of the Tarbert reservoir and the inverted pressure distribution agree with the structural features of the Tarbert Formation and its known pressure compartments.