Microscopic pore structure characteristics of shale reservoir based on low-temperature argon adsorption experiments

Shale reservoirs have a strong microscopic heterogeneity and a wide pore size distribution. In this study, argon was used as the adsorbent, and argon isotherm adsorption experiments at 87 K were used to investigate the microscopic pore structure characteristics of six organic-rich shale samples taken from the Upper Ordovician Wufeng-Lower Silurian Longmaxi formations in southern Sichuan Basin. The effect of total organic carbon content on the microscopic pore structure of shale samples was also discussed. The results showed that the pore shape of organic-rich shale samples is slit-like, with an average specific surface area of 31.65 m²/g and an average pore volume of 0.062 2 cm³/g. Over 90% of the specific surface area of the shale samples was provided by micro pores and meso pores, which were less than 50 nm in size, and the 2-100 nm meso pores and macro pores comprising over 90% of the pore volume. TOC content is the main factor affecting the development of organic-rich shale microscopic pores. With the increase of organic carbon content in shale, the specific surface area and pore volume of shale increase, the micro pore ratio increases, and the fractal dimension of pore surface increases, which means that the heterogeneity of pore structure is enhanced. All these factors will enhance the methane adsorption capacity of shale.