CO2 mineralization and CH4 effective recovery in orthoclase slit by molecular simulation

Knowledge of the competitive adsorption behaviors of shale gas and CO2 in shale is crucial for understanding the fluid storage, exploration and segmentation. In this work, Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations as well as DFT calculation were carried out to study the adsorption mechanisms of CH4 and its mixtures with CO2 in orthoclase slit. The dependence of gas adsorption behavior on geological depth, water content and CO2 mole fraction, y(CO2), were explicitly examined. Quantum chemistry calculation characterizes the chemical adsorption of CO2 on orthoclase surface by forming a carbonate-like structure, showing the feasibility of CO2 enhanced shale gas recovery and geological sequestration of CO2 in orthoclase. The enrichment region of pure CH4 in orthoclase slit is inferred to be at the geological depth of approximately 2600 m, which accords with the high methane yield in 2000-3200 m by CO2 injection. The adsorbed methane molecules are favorably loaded at slits with low water content (0-2 wt%). The adsorption capacity of CH4 in the binary mixture decreases with the increasing y(CO2) . The favorable mining conditions are predicted to at 2000-3200 m with an economical y(CO2) of 0.3. Shallow geological depth (200-400 m) is helpful for the sequestration of CO2. This study has gained deep insights into the adsorption and recovery mechanisms of shale gas in orthoclase slit and has shed light on the efficiencies of CO2 enhanced recovery of shale gas and the mineralization of CO2 in shale.