Mineralization Adsorption of CO2 in Composite Feldspar Reservoirs with Enhanced Shale Gas Recovery by Molecular Simulations

Geological sequestration of CO2 (CS) in shale reservoirs by chemical adsorption is a promising strategy for enhancing shale gas recovery (EGR) and offsetting CO2 emission. However, insights into the chemical adsorption of CO2 with enhanced shale gas recovery in shale reservoirs are relatively scarce. In this work, the adsorption mechanisms of CO2 and CH4 in composite feldspar reservoirs composed of K+-riched orthoclase, Ca2+-riched anorthite, and Na+-riched albite were investigated by molecular simulations. Density functional theory calculations corroborate the formation of a distinct carbonate structure on each type of feldspar surface when CO2 is adsorbed, showing the mineralization adsorption potential of feldspar to CO2. Grand canonical Monte Carlo and molecular dynamics simulations elucidate the adsorption priority of CO2 on the feldspar surface: orthoclase > albite > anorthite. The K+-riched orthoclase is the most beneficial to the in situ adsorption sequestration of CO2. The absolute adsorption capacity of CO2 in feldspar micropores accounts for 80% of the total loading. Shallow geological depth values (600–1000 m) are economically favorable for the storage of CO2 in the adsorbed state. The enrichment region of adsorbed CH4 is at over 2000 m. The recovery efficiency of CH4 is positively correlated with the mole fraction of CO2 injected (yCO2). More than 90% of the adsorbed CH4 is displaced at the yCO2 of 0.8. These findings provide dependable theoretical bases for the application of shale-based CS-EGR technology.