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Geological sequestration of CO2(CS) in shale reservoirs by chemical adsorption is a promising strategy for enhancing shale gas recovery (EGR) and offsetting CO2emission. However, insights into the chemical adsorption of CO2with enhanced shale gas recovery in shale reservoirs are relatively scarce. In this work, the adsorption mechanisms of CO2and CH4in 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 CO2is adsorbed, showing the mineralization adsorption potential of feldspar to CO2. Grand canonical Monte Carlo and molecular dynamics simulations elucidate the adsorption priority of CO2on 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 CO2in feldspar micropores accounts for 80% of the total loading. Shallow geological depth values (600–1000 m) are economically favorable for the storage of CO2in the adsorbed state. The enrichment region of adsorbed CH4is at over 2000 m. The recovery efficiency of CH4is positively correlated with the mole fraction of CO2injected (yCO2). More than 90% of the adsorbed CH4is displaced at the yCO2of 0.8. These findings provide dependable theoretical bases for the application of shale-based CS-EGR technology.

Mango proposed a significant invariance of four isoheptanes, in which a ratio of sums (K1) remains at approximately 1, regardless of the absolute concentrations. Gas chromatographic analyses of 70 oils from the Tarim Basin demonstrated that most of these oils share invariant K1values close to 1.0, even if they are derived from different sources and have varying degrees of maturity and biodegradation. However, a few unexpectedly high K1values occurred in certain oils from the Tazhong-4 Oilfield in the Tazhong Uplift, and these oils are characterized by abnormally high contents of dibenzothiophenes (DBTs). An excellent positive correlation between the elevated K1values and the abnormally high DBT contents indicated that the thermochemical sulfate reduction (TSR) alteration, which contributed to the increased DBT contents, likely resulted in the elevated K1values. Methylhexanes (MHs) are assumed to be more susceptible to TSR than dimethylpentanes (DMPs), and the terminal methyl groups of C7compounds are more resistant than their mid-chain isomers in the TSR-altered oils. Therefore, in the oils affected by TSR alteration, a decrease in the 2,3-DMP/2,4-DMP ratios will not be sufficient to offset the increased 2-MH/3-MH ratios, which results in elevated K1values. A positive correlation between the increased 2-MH/3-MH ratios and the elevated K1values has validated this hypothesis.