Effects of CO2on Elastic Characteristics of Fluid-Saturated Sandstone

Currently, investigating the mechanism by which CO affects the elastic response of porous media is of significant scientific value for ensuring the safety and efficiency of CCUS injection operations. However, existing studies have inadequately considered the mixing effects of CO and other fluids, and there is a paucity of quantitative research on the elastic parameters of sandstone under varying CO properties. To address this, we employ a rock physics modeling approach. Firstly, we estimate the equivalent elastic parameters of the rock matrix using the VRH averaging method. Subsequently, we utilize the Krief model to quantify the influence of pores on the elastic characteristics of the rock skeleton, and simulate the elastic properties of the CO-water mixed fluid via the Brie model. Finally, we couple the influence of the mixed fluid with Biot-Gassmann theory to construct a rock physics model for saturated sandstones, and further calculate their elastic moduli as well as P-wave and S-wave velocities. We investigate the laws governing how porosity, CO saturation, and density affect the elastic parameters of sandstone. The results indicate that with increasing porosity, the rock's bulk modulus, shear modulus, and P-wave and S-wave velocities decrease; following CO injection, both CO saturation and density exert an influence on the rock's elastic parameters: the higher the CO saturation, the smaller the rock's bulk modulus, while the P-wave velocity first decreases and then increases, the S-wave velocity increases, and the shear modulus is independent of CO properties; the greater the CO density, the smaller the bulk modulus and P-wave and S-wave velocities, with the shear modulus remaining essentially unchanged.