Measurement and modeling of the adsorption isotherms of CH4 and C2H6 on shale samples

摘要

CH4 and C2H6 are two common components in shale gas. Adsorption isotherms of CH4, C2H6, and their binary mixtures on shale samples are significant for understanding the fundamental mechanisms of shale gas storage and the recovery of shale resources from shale reservoirs. In this study, the thermogravimetric method is applied to obtain the adsorption isotherms of CH4, C2H6 and their binary mixtures on two typical shale core samples. A simplified local density theory/Peng-Robinson equation of state (SLD-PR EOS) model is then applied to calculate the adsorption of CH4 and C2H6 on shale, and the efficiency of the SLD-PR EOS model is thus evaluated. The results show that C2H6 exhibits a higher adsorption capacity than CH4 on shale samples, indicating the greater affinity of C2H6 to organic shale. As the molar fraction of C2H6 increases in the CH4/C2H6 mixtures, the adsorption capacity of the gas mixtures increases, indicating the preferential adsorption of C2H6 on shale. Based on the predicted results from the SLD-PR EOS model, a reasonable agreement has been achieved with the measured adsorption isotherms of CH4 and C2H6, validating the reliability of the SLD-PR EOS model for predicting adsorption isotherms of CH4 and C2H6 on shale samples. In addition, the SLD-PR EOS model is more accurate in predicting the adsorption of CH4 on shale than that of C2H6. This study is expected to inspire a new strategy for predicting the adsorption of hydrocarbons on shale and to provide a basic understanding of competitive adsorption of gas mixtures in shale reservoirs.