Preliminary Experimental Study of Effect of CO2-H2O Biphasic Fluid on Mechanical Behavior of Sandstone under True Triaxial Compression

Understanding the mechanical behavior of a reservoir is essential for securing the safety of CO2 storage projects. In this study, the effect of CO2-H2O biphasic fluid on the mechanical behavior and failure characteristics of sandstone was revealed. The preliminary results indicate that CO2-H2O biphasic fluid could significantly affect the mechanical behavior of sandstone, including reducing the strength, elastic modulus, Poisson's ratio, and bulk modulus of sandstone; enhancing the bulk compaction; and postponing the onset dilatancy of sandstone. However, the strength of water-bearing sandstone is weakly increased when CO2 is injected into the sample due to the capillary forces that develop under the unsaturated conditions. In addition, CO2-H2O biphasic fluid notably affects the failure characteristics of sandstone at macro- and microscales. A complex network of cracks is generated at macrostructure scale. The bonds between particles are damaged by CO2-H2O biphasic fluid at the microstructure scale.