Mechanical properties and failure characteristics of supercritical carbon dioxide soak in water-bearing coal rocks

Water has an important influence on the mechanical properties of coal rock during CO2 sequestration. In this paper, uniaxial and true triaxial mechanical tests were conducted on bituminous coal under different moisture contents before and after SCCO2 treatment. The experimental results demonstrate that SCCO2 and water deteriorate the coal sample strength and elastic modulus under uniaxial conditions, and the reduction rate exhibits a trend of first increasing and then decreasing. When the water saturation is 80 %, the maximum strength reduction rate of coal samples before and after SCCO2 treatment reached 39.30 %. However, under deep in-situ stress, the strength and elastic modulus of bituminous coal do not exhibit a marked weakening effect under the action of SCCO2 and water, the average strength reduction rate is only 4.03 %. The CT results demonstrate that under the action of water and SCCO2, the failure mode of bituminous coal changes from brittle failure to ductile failure. The cohesion and internal friction angle of coal sample have a near-linear relationship with moisture content. When the water saturation was 65%–80 %, the SCCO2–water–coal reaction was violent, and the damage degree peaked.