Summary Methane (CH4) dissolved in an aquifer within a gas reservoir can be replaced by carbon dioxide (CO2) injection, which presents a promising route for carbon utilization and sequestration. However, the processes and mechanisms of CO2-CH4 codissolution and mass transfer remain unclear in multicomponent systems containing brine, CO2, CH4, and nitrogen (N2). In this work, water samples and simulated gases are prepared with respect to Zone IIIU of the S gas field with potential water-soluble gas. First, dissolving equilibrium experiments are performed to investigate the solubility of different injected gases in brine. The dynamic process of CO2-CH4 mass transfer in water after CO2 injection is further analyzed by competitive replacement experiments. The alterations of dissolved and undissolved gases and brine are observed using ion chromatography. Results indicate the following gas solubility ranking: CO2 impure CO2 CH4 hydrocarbon gas N2. The dynamic variations between hydrocarbon gas entry into the aquifer during water-soluble gas accumulation and CH4 release from the aqueous system during primary depletion production are elucidated. Since the original vapor/liquid phase equilibrium of water-soluble gas is broken by CO2 injection, a new aqueous system is rebuilt after CO2-CH4-brine interaction. The dissolution and modification of impure CO2 demonstrate potential for enhanced gas recovery (EGR) and geological carbon storage (GCS) in gas reservoirs with aquifers. The results of this study are important not only for EGR in water-soluble gas production from an aquifer but also for all GCS reservoir types, especially depleted gas reservoirs. Furthermore, the findings provide essential solubility parameters for thermodynamic calculation and numerical simulation of multicomponent phase equilibrium.
Tang et al. (Sun,) studied this question.