A Numerical Study of Acoustic Wave Propagation in Partially Saturated Poroelastic Rock

Abstract

AbstractBased on the Biot theory we use a high‐order staggered finite‐difference algorithm to carry out numerical experiments on wave propagation in a rock sample partially saturated by multi‐phase fluids with random fluid distributions. The ultrasonic source frequencies are 25, 50, 75kHz and 100kHz, respectively. The first modeling sample is homogeneous isotropic sandstone partially filled with two phase pore fluids (water and gas), which are defined by their different elastic characteristic parameters of saturation, viscosity, compressibility, and density, respectively. We assume that the two different pore‐fills occupy different macroscopic regions and the wavelength of acoustic wave is much larger than the scale of these regions. The result shown that the P‐wave velocity and attenuation change with fluid saturations (water and gas) and central frequencies of the acoustic source. These numerical results are qualitatively in agreement with the White and Gassmann's models. The second modeling sample is partially filled with 3 phase pore fluids (water, oil, and gas). We keep the saturation of water with a constant and change the saturations of oil and gas. Under these conditions, the velocity of P‐wave shows an increasing trend with the increasing saturation of oil. The snapshot of the acoustic wave field shows that the energy of P‐wave is converted into several kinds of slow P‐waves and S‐waves which occur at the interfaces between water, oil and gas. These modeling results have great significance in seismic exploration and acoustic well logging interpretations.