Investigation on the influences of CO2 adsorption on the mechanical properties of anthracite by Brazilian splitting test

To understand CO2 sequestration in coal seam, the Brazilian splitting test is adopted to examine the effect of CO2 saturation pressure on anthracite mechanical properties, and the variations in the internal structure of coal are analyzed using X-ray diffraction and low-pressure N-2 adsorption methods. The results show that as the CO2 adsorption pressure increases, the Brazilian splitting strength, Brazilian splitting modulus, absorbed energy, and Brittleness index of anthracite decrease by 11.5%-49.2%, 11.0%-44.2%, 17%-42.3%, and 6.7%-49.3%, respectively, while the BET-SSA, DFT and BJH pore volumes increase by 60.3%-225.1%, 11.6%-61.3% and 10.1%-42.7%, respectively. Moreover, the influence of supercritical CO2 on coal pore structure and mechanical property is more prominent than that of subcritical CO2. The mineral dissolution, organic matter extraction and molecular structure rearrangement caused by CO2 intrusion develop the pore structure of anthracite, which resultes in the degradation of coal mechanical properties. In addition, the swelling, plasticity, and 'Rehbinder effect' caused by CO2 adsorption contribute to the mechanical damage of anthracite. Due to the remarkable impact of high-pressure CO2 on the pore structure and mechanical properties of coal, the critical point pressure of CO2 should be used in the storage process to ensure enhanced CO2 storage capacity while reducing storage risks.