Analysis of the Velocity Anisotropy and Its Causative Factors in Shales and Mudstones

Abstract

Abstract We investigate the velocity anisotropy in laminated shale and mudstone at laboratory ultrasonic frequency. Our purpose is to find variation rules of wave velocity in different diretions as a function of confining pressure in dry and oil‐saturated situation. Using the X‐ray diffraction techniques and scanning electron microscope, we analyze the causative factors for anisotropy and conclude that the clay minerals and microcracks are the intrinsic factors that result in such strong anisotropy in rock samples. With the increasing confining pressure, microcracks are gradually closed, which lower the anisotropy. Pore fluids increase the pore rigidity and decrease the tendency of anisotropy change with confining pressure.