Molecular Insights on competitive adsorption and enhanced displacement effects of CO2/CH4 in coal for low-carbon energy technologies

Injection of carbon dioxide (CO2) into coals is one of the key strategies in low-carbon energy technology to enhance energy production and mitigate environmental impacts of fossil fuels from industrial processes in clean energy transitions. Geological factors dominate the displacement performance of methane (CH4) by CO2 injection due to the complexity of physicochemical processes in micro-nanopore networks. The concept of molecular dynamics (MD) is a promising way to reveal the gas transport mechanisms therein at the fundamental level. This work systematically investigates the kinetics of competitive adsorption process and quantitatively evaluate CO2- enhanced CH4 recovery performance by considering the effects of different decisive influencing factors at real subsurface environments using MD simulations. We elucidate that the increasing water and ethane contents reduce CH4 uptake and discourage adsorption process. Additionally, moisture, ethane and the increasing tem-perature promote the pressure drawdown-induced recovery efficiency of CH4. Further, low moisture contents inhibit CH4 displacement efficiency by CO2, whereas high moisture contents above 3 wt% favor the displacement process, particularly at high pressures. This work provides an in-depth understanding of CO2 utilization in gas development and carbon storage feasibility in unconventional reservoirs, which would shed light on CO2- enhanced gas recovery projects in practical field production.