Overpressure detection from compressional‐ and shear‐wave data

By analyzing experimental data we show that in many room‐dry rocks, the Poisson's ratio (PR) decreases with decreasing differential pressure (confining minus pore pressure). This means that in gas‐saturated rocks, PR decreases with increasing pore pressure. We confirm the generality of the observed effect by theoretically reproducing it via effective medium modeling. This effect can be used as a new tool for overpressure detection from surface seismic, cross‐well, sonic logs and measurements ahead of the drill bit.