The Effect of Stress on Velocity Anisotropy of Synthetic Shale with Different Types of Clay Minerals

Clay minerals are important components in shale, controlling elastic properties and anisotropy of shale. Knowing the elastic properties of shale with different types of clay minerals is therefore imperative to fully understand seismic properties of the reservoir. In this study, three sets of samples with different type of clay minerals were made. Ultrasonic experiments have been conducted to study ultrasonic anisotropy in dry synthetic shale sample as a function of applied axial stress. It has been confirmed by experimental results that synthetic shale has stable construction process and shares high similarity with natural shale. The experimental results show that the types of clay minerals have great influence on the velocity and velocity anisotropy. Structure difference and compositional variations of clay minerals may explain some of the behavior. The velocities of samples increase with applied pressure, but the rate of velocity increase for samples was higher at low pressures (< 20 MPa). We also observed that the degree of velocity anisotropy can be as large as 0.51, these anisotropy parameters decrease with the increase of stress and are sensitive to stress and lithology.