Correction calculation of shale gas absolute adsorption capacity and its influencing factors analysis

In this study, the total organic carbon (TOC) content analysis, X-ray diffraction (XRD) tests, low-temperature N2 adsorption tests and CH4 isothermal adsorption tests were carried out on the shale samples from Longmaxi, Wufeng and Yanchang formations, to obtain the relationship between the mineral composition, pore structure and its fractal dimension on adsorption characteristics of shale. Based on the two calculation methods, including the hypothesis of constant adsorbed phase volume Va and constant adsorbed phase density ρa, the absolute adsorption amount of shale gas was corrected and was fitted by Langmuir model, then the relationships between shale mineral composition, pore structure and Langmuir model parameters were obtained. The results show that the Langmuir model can fit well with the adsorption data of CH4 on different shales under the experimental conditions, and the Langmuir model has higher accuracy in fitting the absolute adsorption amount of shale gas obtained based on the hypothesis ofadsorbed phase volume Va Langmuir volume VL is positively correlated with TOC and quartz content, specific surface area and pore volume, and is negatively correlated with the average pore diameter, and poorly correlated with clay minerals. The fractal dimension D of pore structure in shale is positively correlated with TOC content, quartz content, specific surface area and pore volume, and is negatively correlated with average pore diameter, and poorly correlated with clay minerals. The fractal dimension D is positively correlated with VL, and negatively correlated with Langmuir pressure PL, indicating that a larger fractal dimension D correspond stronger adsorption capacity of shale.