CO2 geological sequestration: Displacement behavior of shale gas methane by carbon dioxide injection

Carbon dioxide (CO2) sequestration in deep shale reservoirs with enhanced shale gas methane (CH4) recovery contributes to both CH4 recovery and CO2 emission mitigation. In this work, the adsorption behaviors of pure CH4 and CO2 on shales, and the displacement behaviors of CH4 adsorbed on shales by CO2 injection were investigated. The single component adsorption indicates that the simplified Ono-Kondo lattice model can well describe both CH4 and CO2 adsorption on shales. The maximum adsorption capacity of CH4 obtained from the simplified Ono-Kondo lattice model shows significant linear correlation with the micropore parameters of shales, while this linear correlation is weak for CO2. The investigation on the displacement behaviors based on the improved experimental procedure and data processing method raised in this work confirms that CH4 adsorbed on shales can be displaced by CO2, which provides the experimental evidence for the feasibility of CO2 sequestration in shale reservoirs with enhanced CH4 recovery. The amounts of recovered CH4 and stored CO2 increase with CO2 injection pressure. The recovery yield of CH4 due to CO2 injection is higher for shales with smaller micropore parameters or lower adsorption performance. The microscopic mechanism of the displacement process is strongly related to the injection pressure of CO2. Based on the conceptual model established for the process of CH4 adsorbed on shales displaced by CO2 injection, it is recommended to inject CO2 after partial desorption of CH4, which can improve CH4 recovery and CO2 sequestration of the target shale reservoirs.