Competitive adsorption between CO2 and CH4 in tight sandstone and its influence on CO2-injection enhanced gas recovery (EGR)

Abstract

CO2 flooding is a new promising way of achieving enhanced natural gas recovery (EGR) and CO2 sequestration in tight gas reservoirs. CO2 adsorption is a reality that cannot be ignored during CO2 flooding process. However, the adsorption behavior of CO2 in tight cores remains unclear. Here, the CO2CH4 competitive adsorption characteristics in tight sandstone were experimentally investigated. The results indicate that the CO2 show significantly higher adsorption capacity in the tight cores compared to CH4 and that competitive adsorption occurs after CO2 is injected into tight core preadsorbed with CH4, with over 30% of the CH4 being replaced by the injected CO2 under an ambient pressure of 24 MPa. Further, the results of sensitivity experiments demonstrated that CO2CH4 competitive adsorption is more significant in tight cores with lower permeability, higher rock fragment content, and lower water saturation, while experiments on CO2-EGR and CO2 storage showed that for tight cores with lower permeability or higher rock fragment content, the higher degree of competitive adsorption resulted in greater EGR efficiency and CO2 storage capacity. For water saturated cores, however, the dissolution of CO2 in water has a greater impact on EGR and CO2 storage compared to competitive adsorption, resulting in better EGR and CO2 sequestration efficiency at higher water saturation.