The displacement behaviors of CH4-containing anthracite under various injection pressures: The critical role of mineral dissolution and precipitation

Abstract

Accurate prediction of CH₄-containing anthracite replacement and storage efficiency under supercritical CO₂ (Sc-CO₂) injection is crucial for enhancing both coalbed methane production and CO₂ geological storage. This study investigates pore structure evolution, mineral dissolution/precipitation characteristics, and their effects on adsorption behavior and storage efficiency at various injection pressures using GC, LT-N₂, SEM-EDS, and XRD analyses. Results show increased CH₄ adsorption in CH₄-containing anthracite due to CO₂ injection, influenced by injection pressure. The highest storage efficiencies of 24.95% and 24.36% were observed at 7.59 MPa and 10.81 MPa, respectively. Adsorption selectivity shifts from CH₄ to CO₂ with increasing pressure (>10.81 MPa). Injection pressure affects specific surface area (SSA) and pore volume (PV), reducing them by 7.16% and 25.68%, respectively. Fractal dimension D_L2 exceeds D_L1 and decreases gradually. Silicate mineral surfaces become rough, which causes irregular cracks. Meanwhile, secondary precipitation consists mainly of carbonate minerals. Micropores exhibit lower non-homogeneity than mesopores, and overall pore structure complexity diminishes. Mineral dissolution/precipitation mechanisms expand storage space and enhance Sc-CO₂ interaction with CH₄-containing anthracite. These findings provide new insights into displacement behaviors of CH₄-containing anthracite seams after CO₂ injection, which can be valuable for guiding efficient injection of CO₂-ECBM.