CO₂/CH₄ Competitive Adsorption in Shale: Implications for Enhancement in Gas Production and Reduction in Carbon Emissions

CO 2 /CH 4 interaction determines the prospects for complementary enhanced gas recovery (EGR) associated with CO 2 sequestration in shale. We characterize the competitive adsorption of CO 2 and CH 4 in shale using low-field NMR. Competitive sorption of CO 2 relative to CH 4 is defined as the CO 2 /CH 4 competitive adsorption ratio (CO 2 /CH 4 CAR for short) when CO 2 and CH 4 have the same original partial pressure in shale. Results indicate the CO 2 /CH 4 CAR decreases with the logarithm of increasing pressure. Observed CO 2 /CH 4 CARs are on the order of 4.28–5.81 (YDN-1) to 3.43–5.57 (YDN-2), describing the remarkable competitive advantage of CO 2 sorption relative to CH 4 for shale. Results also indicate that increasing the CO 2 /CH 4 pressure ratio (1) increases the adsorption capacity of shales to CO 2 and decreases that to CH 4 logarithmically with pressure, and (2) boosts CO 2 –CH 4 displacement and generates greater EGR efficiency in shale, where the EGR efficiency can be inferred by the CO 2 /CH 4 pressure ratio using a Langmuir-like function. Furthermore, the maximum sequestration capacity of adsorbed CO 2 during CO 2 –CH 4 competition is on the order of ∼3.87 cm 3 /g (YDN-1) to ∼5.13 cm 3 /g (YDN-2). These promising results for EGR and CO 2 storage reveal the considerable potential for carbon capture and geological sequestration in shale.