Abstract
Changes in seismic two-way travel time in the overburden can be attributed to pore pressure changes in the underlying reservoir. Since cap rock permeability is very small, these stress changes occur without drainage on short term, which means that, depending on stress path, pore pressure may also change in the overburden. The direct impact of this on 4D seismic has not been thoroughly addressed in the literature. Here, laboratory data with an overburden shale core are presented, showing stress path dependent changes in P-wave velocity and pore pressure. The expected impact on 4D seismic can be significant.