Modelling Methane Adsorption Isotherms on Shale at Different Temperatures

Prediction of adsorption isotherms under different temperatures is significant to reserve estimation of shale gas reservoirs. Based on the Polanyi adsorption potential theory and Langmuir adsorption theory, a method was presented to predict adsorption isotherms at different temperatures. In this method, the relationship between Langmuir pressure and temperature was quantified. By utilizing this method, we predicted adsorption isotherms of Longmaxi shale from 45 °C to 120 °C according to experimental data at 30 °C. Meanwhile, by considering the pressure and temperature gradients, we also predicted the adsorption capacity of Longmaxi shale with geologic depth. Results show that the adsorption data predicted by our method are in accord with experimental data and the error coefficient is less than 5%. In addition, the isosteric heat of adsorption for Longmaxi shale can be calculated by predicted adsorption data based on the Clausius–Clapeyron equation of capillary systems. Therefore, our study illustrates theoretical foundations for the efficient evaluation of adsorbed gas content in shale gas reservoirs at geologic conditions.