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• 106 Wufeng-Longmaxi shale samples are utilized to evaluate 12 inversion models. • Correlation Analysis of PSDs from LTCA, LTNA isotherms and LAM-SEM images. • Disclosing PSD difference and underlying mechanism with different models. • CO 2 -GCMC and N 2 -Sl/Cy-QSDFT-Equ are selected as the most suitable inversion models. • Both LTCA and LTNA methods are needed to obtain SSA that affects methane adsorption. The pore space in gas shale spans multiple scales, ranging from nanometers to micrometers with an extremely complex structure and strong microscopic heterogeneity. Existing low-temperature gas adsorption (LTGA) pore size distribution (PSD) analysis models are based on the assumption of a one-dimensional tubular model and there is a lack of sufficient basis for selecting the most appropriate inversion model among the various types available. In this study, a comprehensive characterization of numerous samples from the Wufeng and Longmaxi Formation in the southern Sichuan Basin was conducted using different methods and inversion models. Based on multiple dimensions, such as fitting errors, the correlation between different methods including low-temperature CO2 adsorption (LTCA), nitrogen adsorption (LTNA), and large-scale mosaic Scanning Electron Microscopy (LAM-SEM), the most suitable one-dimensional models for LTCA and LTNA PSD analysis for the studied shale samples are determined. The simulation of gas condensation processes on LAM-SEM images yielded pore volume (PV) in the range of 32–48 nm comparable to the PV characterized by LTNA. Furthermore, the differences observed in PSDs between the gas condensation simulation procedure and the equivalent circular area diameter method indicate that irregular corner regions within larger pores are attributed to the volume of smaller-sized pores during gas adsorption characterization. It is revealed that the correlation between stitched surface area (SA) and maximum methane adsorption is stronger than individual characterizations, indicating that both micropores and mesopores contribute significantly to adsorption, and both characterization methods need to be employed to obtain SSA that influences methane adsorption. The research findings are helpful to the improvement of the multi-scale pore characterization level and evaluation of shale reservoirs. [ABSTRACT FROM AUTHOR]

• High-pressure methane adsorption isotherms of 106 Wufeng-Longmaxi shales are measured. • Organic matter and clay are main compositions controlling factors of methane adsorption. • The isotherm of a shale is a linear superposition of those of its organic matter and clay. • V L , P L and ρ ads are found to be definite but different for unit organic matter and clay. • A quantitative composition-based model for adsorbed methane amount are proposed. The Wufeng-Longmaxi Formation shale in Sichuan Basin is the main strata of shale gas exploration and development in China. Adsorbed methane is an important part of the total shale gas content. The influence of shale composition on adsorption characteristics is complex, and it is difficult to obtain a comprehensive understanding without a sufficient amount of data. In this work, the total organic carbon (TOC), X-ray diffraction (XRD) mineral analysis, and the excess methane adsorption isotherms with pressure up to 50 MPa at 40 °C of 106 overmature shale samples with TOC of 0.8%-9.0% and clay content of 2%-58% that belong to Wufeng-Longmaxi formation from 10 shale gas wells in Sichuan Basin, China are experimentally investigated and analyzed. New correlations found between compositions and methane adsorption characteristic parameters guide the establishment of a composition-based methane adsorption model that the excess adsorption isotherm of shale is the content-weighted sum of equivalent unit-content excess isotherms for organic matter and clay. With this model, the differences of excess isotherms of these two compositions and the differences of clay-contribution to methane adsorption for different sublayers are disclosed. It is beneficial to improve the accuracy of shale reservoir evaluation of studied blocks under the condition of limited coring and deepening the understanding of the underlying mechanism of methane adsorption characteristics. [ABSTRACT FROM AUTHOR]