Water Solubility at Saturation for CO2–CH4 Mixtures at 323.2 K and 9.000 MPa

The concentration of H2O dissolved in CO2–CH4 supercritical fluids is an important parameter that can control shale permeability, affect CH4 transmissivity, and ultimately impact the efficiency of CO2 enhanced gas recovery (EGR) operations. Here, we use in situ high-pressure infrared (IR) spectroscopic titrations to quantify the solubility of H2O in six CO2–CH4 mixtures, ranging from pure CO2 to pure CH4, at shallow shale reservoir conditions of 323.2 K and 9.000 MPa. Measured concentrations of H2O at saturation increase with increasing mole percent CO2, and our results are in agreement with limited data available in the literature. We use these experimental results to benchmark three current thermodynamic multiphase routines: the mixed-solvent electrolyte (MSE), STOMP-COMP, and the Statistical Associating Fluid Theory for variable range Mie potentials (SAFT γ-Mie) equations of state. Of these models, MSE and STOMP-COMP accurately predict maximum H2O solubilities of the binary CO2–H2O and CH4–H2O systems, and they also reproduce the shape of the water solubility curve as a function of mole percent CO2. Hence, these routines should work well to predict H2O content in reservoir simulations and help to make informed decisions concerning injection strategies for CO2 EGR in shale plays at shallow depths.