Measurement and modeling of the adsorption isotherms of CH(4) and C(2)H(6) on shale samples

CH(4) and C(2)H(6) are two common components in shale gas. Adsorption isotherms of CH(4), C(2)H(6), 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 CH(4), C(2)H(6) 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 CH(4) and C(2)H(6) on shale, and the efficiency of the SLD-PR EOS model is thus evaluated. The results show that C(2)H(6) exhibits a higher adsorption capacity than CH(4) on shale samples, indicating the greater affinity of C(2)H(6) to organic shale. As the molar fraction of C(2)H(6) increases in the CH(4)/C(2)H(6) mixtures, the adsorption capacity of the gas mixtures increases, indicating the preferential adsorption of C(2)H(6) 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 CH(4) and C(2)H(6), validating the reliability of the SLD-PR EOS model for predicting adsorption isotherms of CH(4) and C(2)H(6) on shale samples. In addition, the SLD-PR EOS model is more accurate in predicting the adsorption of CH(4) on shale than that of C(2)H(6). 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.