NMR-monitored CH4 adsorption/desorption dynamics in shale: Implications for CO2-ESGR and in-situ sequestration

Addressing the inherent challenges of low recovery rates and difficulties in shale gas extraction, this study investigates the application potential of CO 2 -enhanced shale gas recovery (CO 2 -ESGR) coupled with carbon sequestration (CS). Utilizing low-field nuclear magnetic resonance (NMR) technology, we conducted real-time monitoring of methane adsorption and desorption processes within collected shale samples. Through the analysis of T 2 spectra and corresponding peak areas, we achieved quantitative differentiation among adsorbed CH 4 , free CH 4 within pore spaces, and free CH 4 within fractures. The results demonstrate that within a pressure range of 0.01–10 MPa, the total methane volume increased progressively from 79.4 to 177.83 cm 3 /g. Following CO 2 injection, a significant weakening of the short- T 2 signal (representing adsorbed CH 4 ) was observed, accompanied by a concomitant enhancement of the long- T 2 signal (representing free-phase CH 4 ). Furthermore, depressurization desorption experiments revealed that CO 2 injection increased the methane desorption rate by approximately 10%, while simultaneously facilitating the long-term, stable sequestration of CO 2 within the shale matrix. These findings not only validate the mechanism of competitive adsorption, whereby CO 2 enhances shale gas recovery, but also highlight the significant carbon sequestration potential of shale reservoirs. Consequently, this research provides a crucial theoretical basis and technical support for advancing both shale gas development and carbon emission reduction strategies.