Determination of the absolute CH4 adsorption using simplified local density theory and comparison with the modified Langmuir adsorption model

Abstract

Accurately determining the adsorbed amount of CH₄ on shale is significant for understanding the mechanisms of shale gas storage and shale methane recovery from shale gas reservoirs. Excess CH₄ adsorption is measured using the thermogravimetric method. Simplified local density (SLD) theory is applied to calculate the adsorbed CH₄ density to obtain the absolute adsorption. Moreover, the modified Langmuir adsorption model is employed to fit the excess adsorption to describe the absolute adsorption. The adsorbed CH₄ density from the SLD model is affected by the system pressure and temperature, while such density obtained from the modified Langmuir model is only a function of temperature. Compared to the modified Langmuir model, the SLD model can better capture the adsorbed CH₄ density, which allows accurate determination of the absolute CH₄ adsorption.