CO/CH Competitive Adsorption in Shale: Implications for Enhancement in Gas Production and Reduction in Carbon Emissions.

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