Effect of adsorbed phase density on the correction of methane excess adsorption to absolute adsorption in shale

In order to evaluate the accuracy of different methods for the methane excess adsorption correction, the Polanyi adsorption potential theory was introduced to analyze the absolute methane adsorption amount obtained by correction. One shale sample from the Lower Silurian Longmaxi Formation in the southern Sichuan Basin, China was selected to conduct high-pressure methane adsorption experiments at 40.6 degrees C, 60.6 degrees C, 75.6 degrees C, and 95.6 degrees C at pressures up to 52 MPa. Based on the experimental results at different temperatures, four densities (the liquid density of methane at boiling temperature and ambient pressure, the van der Waals density, the adsorbed phase density based on the falling segment fitting of excess adsorption isotherm, and the adsorbed phase density obtained by fitting excess adsorption isotherm using modified Langmuir equation) were used for the correction of excess adsorption to absolute adsorption. At the same time, in order to enhance the reliability and accuracy of the conclusions in this study, the results of methane adsorption experiments on shale in the reference were used for a comparative study to further support our conclusions. The results indicate that the greater the constant adsorbed phase density used for the excess adsorption correction, the lower the degree of overlap of the adsorption characteristic curves at different temperatures. The adsorbed phase density used for methane excess adsorption correction may be in the vicinity of 0.30 g/cm(3) to 0.40 g/cm(3). Particularly, it should not be greater than the liquid density of methane at boiling temperature and ambient pressure, which is 0.421 g/cm(3). Although the adsorbed phase density differs across different temperatures and pressures, the current results show that 0.373 g/cm(3) can be used as the adsorbed phase density for the excess adsorption correction, which may be a convenient method and can yield results close to the actual adsorption.