How gas recovery and carbon storage capacity response to dynamic deformation of kerogen upon CO2/CH4 competitive adsorption for CCUS? Evidence from molecular dynamics

Unconventional natural gas in organic-rich shale and coal seams, which primarily consists of methane (CH4), is a dominant alternative to conventional energy because of its large deposit and environmental friendliness. In recent decades, carbon dioxide (CO2) injection into unconventional sedimentary reservoirs has become a worldwide promising strategy for promoting gas recovery and carbon storage. Most gas resides in nanopores owing to the large surface and abundant adsorption sites of kerogen, which leads to considerable synergistic effects of adsorption-induced kerogen swelling and pressure-induced compression. It therefore re-distributes the pore space and contributes to nontrivial consequences on industrial gas production and storage processes. However, the deformation mechanism response to gas adsorption characteristics still remains unclear. Herein, we implement the concept of molecular dynamics to quantitatively assess how dynamic deformation of kerogen upon CH4/CO2 competitive adsorption affects the gas recovery efficiency and carbon storage capacity. It is evident from our investigations that the flexible nature of kerogen has 10% more capacity for CH4 adsorption and 40% more for CO2 storage when compared to the rigid matrix. Simultaneously, preferential selectivity increases at least 5 times, which reveals that the CH4/CO2 competitive adsorption has been dramatically underestimated in previous studies. The implication of such underestimated results thereby indicates that the enhancement of CO2 storage capacity and gas displacement efficiency in unconventional reservoirs hold great potential. Generally, our findings improve the fundamental understanding of gas recovery mechanism and offer a practical exami-nation of feasibility on gas production and long-term CO2 sequestration under realistic underground environments.

Automated summary

This study investigates the dynamic deformation of kerogen upon CH4/CO2 competitive adsorption in unconventional shale and coal seams, showing that the flexible nature of kerogen leads to increased capacity for CH4 adsorption and CO2 storage, as well as enhanced selectivity in competitive adsorption.