Mechanical response and pore structure evolution of anthracite induced by CO2 adsorption: Effect of adsorption pressure

Abstract

To find the optimal CO2 storage pressure in anthracite seams, the modification of CO2 invasion at different pressures on the anthracite pore and mechanical properties are studied through mercury intrusion method, low-pressure nitrogen gas adsorption and uniaxial compression tests, and their evolution mechanisms are determined by X-ray diffraction and Fourier transform infrared spectroscopy. It is found that after 12 MPa CO2 treatment, the pore volume and specific surface area of the anthracite increased from 11.34 × 10−3 cc/g and 0.610 m2/g to 14.50 × 10−3cc/g and 1.983 m2/g, respectively. After CO2 reaction at 4, 8 and 12 MPa, uniaxial compressive strength of the anthracite decreased by 6.29 %, 33.45 % and 34.93 %, respectively, and elastic modulus reduced by 2.53 %, 11.84 % and 14.30 %, respectively. After supercritical CO2 saturation, the pore structure is more advanced and the mechanical degradation is more remarkable of the anthracite, which is mainly due to more significant minerals dissolution, functional groups extraction, the destruction of microcrystalline structure, order decrease and plastic effect. The conclusions suggest that the CO2 pressure near the critical point should be selected for CO2 sequestration in anthracite coal seams, so as to not only increase the sequestration amount of CO2, but also ensure the safety of sequestration.