Three-Dimensional Numerical Study of Frequency-Dependent Anisotropy of Cracked Rocks Due to Squirt Flow

Abstract

Summary Activities involving CO2 geological sequestration, exploitation of geothermal energy, and hydrocarbon exploration require a deep understanding of cracked rocks’ behavior under different conditions, so that non-invasive monitoring methods, based on seismic methods, for example, can be developed. Many studies highlight that seismic waves propagation is highly affected by the presence of micro-cracks, grain-scale discontinuities and moving fluids at the pore scale. Strong velocity dispersion and wave attenuation due to fluid flow at the pore scale, known as squirt flow, have been observed in many experimental studies. We perform a three-dimensional numerical study of the fluid-solid deformation at the pore scale based on solving quasistatic equations for solid and fluid phases. We show that seismic anisotropy exhibits frequency-dependent behavior due to squirt flow between interconnected cracks. We demonstrate that the overall anisotropy of the model mainly increases due to squirt flow. We analyze the Thomsen anisotropic parameters and use another scalar parameter to measure the overall anisotropy of the numerical model. Our analysis suggests that seismic anisotropy variations with frequency are nonlinear with frequency, very sensitive to the material properties and the pore space geometry, thus, a general prediction of the seismic anisotropy behavior in different scenarios is not possible.