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

Abstract

Geological sequestration of CO 2 (CS) in shale reservoirs by chemical adsorption is a promising strategy for enhancing shale gas recovery (EGR) and offsetting CO 2 emission. However, insights into the chemical adsorption of CO 2 with enhanced shale gas recovery in shale reservoirs are relatively scarce. In this work, the adsorption mechanisms of CO 2 and CH 4 in composite feldspar reservoirs composed of K + -riched orthoclase, Ca 2+ -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 CO 2 is adsorbed, showing the mineralization adsorption potential of feldspar to CO 2 . Grand canonical Monte Carlo and molecular dynamics simulations elucidate the adsorption priority of CO 2 on the feldspar surface: orthoclase > albite > anorthite. The K + -riched orthoclase is the most beneficial to the in situ adsorption sequestration of CO 2 . The absolute adsorption capacity of CO 2 in feldspar micropores accounts for 80% of the total loading. Shallow geological depth values (600−1000 m) are economically favorable for the storage of CO 2 in the adsorbed state. The enrichment region of adsorbed CH 4 is at over 2000 m. The recovery efficiency of CH 4 is positively correlated with the mole fraction of CO 2 injected (y COd 2 ). More than 90% of the adsorbed CH 4 is displaced at the y COd 2 of 0.8. These findings provide dependable theoretical bases for the application of shale-based CS-EGR technology.