Effect of differential pressure on the pore structure and wave response of tight sandstones

Understanding seismic wave propagation can improve seismic interpretation and reservoir characterization, especially in media containing pores and cracks as a function of differential pressure, i.e., confining minus pore pressure. Production from tight-sandstone gas reservoirs develops cracks where high effective stresses show up. We have performed ultrasonic P- and S-wave velocity measurements on gas- and water-saturated tight-sandstone samples as a function of differential pressure. Based on these measurements, we estimated properties as crack porosity and crack density by a parametric inversion of different gas-saturated samples. We adopted a double-porosity model to compute the velocity dispersion and attenuation of water-saturated samples as a function of differential pressure, and the predicted results agree well with the measured results of P-wave velocity. We analyzed the crack parameters of tight sandstones for different differential pressure and porosities. The three-parameter fitting results validate the presented method for predicting reservoir crack properties for seismic exploration and reservoir monitoring.