Anisotropic strain of anthracite induced by different phase CO2 injection and its effect on permeability

Abstract

To study the swelling/shrinkage strain effects of different phases of CO2 when injected into anthracite and the influence that has on the dynamic evolution of coal permeability, an experimental study of coal anisotropic adsorption of CO2 was carried out by using a triaxial compression test device, and the relationship between the swelling/shrinkage strain and permeability of the coal was discussed. The results show that the adsorption strain and time of gas exposure throughout different phase states of the CO2 injected show three stages of evolutionary behavior. The adsorption swelling of the coal sample increases with rising gas pressure. The adsorption strain of coals under the action of supercritical CO2 increased by 16.28% and 17.36% against the action of subcritical CO2, respectively. The coal portrayed anisotropic characteristics during the process of adsorption-caused swelling deformation and desorption-caused contraction, and the deformation in the vertical layer direction was greater than that in the parallel layer direction, and the anisotropy gradually weakened with increasing pressure. The permeability of the coal and the temperature is a quadratic function relationship under different effective stress conditions, and there is a zone where the changes occur. The study provides a theoretical basis CO2- Enhanced coalbed methane recovery.