Influences of the composition and pore structure of a shale on its selective adsorption of CO2 over CH4

The adsorption capacities of CO2 and CH4 and selectivity of CO2 over CH4 (αCO2/CH4) are important parameters to evaluate the feasibility for applying CO2-ESGR technique (enhance shale gas recovery by CO2 injection) to a shale. Composition and pore structure of shales from different districts of Sichuan basin and their effects on the adsorption capacities of CO2 and CH4 and αCO2/CH4 at different temperatures were studied. Results indicate that shales from Sichuan basin have high TOC (total organic carbon) contents, lots of brittle minerals, large interparticle porosity and wide pore size distributions. The adsorption of CO2 turns from multilayer to monolayer with the increase of temperature, while that of CH4 is mainly in monolayer. The larger adsorption capacity of CO2 than CH4 in shales is not due to the interaction of CO2-shale. High TOC and clay minerals content together improve adsorption capacities of CH4 and CO2. The pore structure parameters have no simple relationship with the adsorption capacity and αCO2/CH4. A shale with a lower TOC content, a smaller amount of micropores and a larger amount of clay minerals has a larger αCO2/CH4, and is more suitable for the its application in CO2-ESGR technique. αCO2/CH4 decreases with the increasing temperature.