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.