Theoretical Adsorption Models for the Methane-Shale System

Gas sorption behavior needs to be understood very well to quantify the reservoir potential of unconventional reservoirs. To quantify adsorption capacity of rock samples, experiments are performed for a wide range of pressure and temperature with relevant fluid. By utilizing experimental adsorption data, adsorption isotherms are deployed to quantify the amount of gas adsorbed into a rock and its equilibrium state. Currently, this study is considering the adsorption data of methane (CH₄)-shale system from literature databases under various pressures and specific temperatures, including moisture, compressional and non-compression conditions. This study aims to assess the maximum CH₄ adsorption capacity and the effect of deformation on the selectivity of isotherms equilibrium constants. More specifically, a modeling approach was used to evaluate the suitability of Langmuir, Toth, and Henry isotherms for a methane/shale system using experimental adsorption data. The key conceptual novelty of this research lies in evaluating the predictive power of traditionally accepted gas adsorption isotherms on or against methane/shale adsorption data, specifically up to 15 MPa but at 30°C and moisture conditions. Results obtained by ranking of isotherms produced as Langmuir = Toth > Henry based on RMSE and R² for both samples, including no effect of rock deformation on selectivity of isotherms.