A series of methane sorption isotherms were measured at 303 K, 313 K, 323 K, 333 K, and 343 K at pressures up to 12.0 MPa for two shale samples from the Upper Triassic Chang 7 Member in the southeastern Ordos Basin with total organic carbon content values of 5.15% and 4.76%, respectively. Both the Langmuir- and Dubinin–Radushkevich-based excess sorption models were found to well represent the excess sorption isotherms within the experimental pressure range. The maxima of absolute methane sorption capacity fitted by both models are not significantly different. In the current study, the effects of temperature and pressure on methane sorption capacity support the findings that under isothermal condition, methane sorption capacity of organic shale goes up with increasing pressure and under isobaric condition, while it goes down with increasing temperature. Good negative linear relationships between temperature and maximum sorption capacity exist both in the Langmuir and the Dubinin–Radushkevich models. In addition, a good positive linear relation exists between the reciprocal of temperature and the natural logarithm of Langmuir pressure, which indicate that temperature and pressure are really important for methane sorption capacity. The extended Langmuir and Dubinin–Radushkevich models have been improved to calculate the methane sorption capacity of shales, which can be described as a function of temperature and pressure. By means of using the two estimation algorithms established in this study, we may draw the conclusion methane sorption capacity can be obtained as a function of depth under geological reservoir. Due to the dominant effect of pressure, methane sorption capacity increases with depth initially, till it reaches a maximum value, and then decrease as a result of the influence of increasing temperature at a greater depth. Approximately, the maximum sorption capacity ranges from 400 m to 800 m.

The pores in shales are mainly on a nanometer scale, and the pore-size distribution is vital with regard to the preservation and exploitation of shale gas. This study focuses on the organic-rich lower Cambrian black shale in the Upper Yangtze Platform, South China and investigates their TOC, mineralogical composition and nanopore structure. Low-pressure N₂ and CO₂ adsorption experiments were conducted at 77.35 K and 273.15 K, respectively, and the nanopore structures were characterised by the modified Brunauer–Emmett–Teller, Dubinin–Radushkevich, t-plot, Barrett–Joyner–Halenda and density functional theory (DFT) methods. The results indicate the following. (1) The lower Cambrian shale has a high TOC content (1.77–7.23 wt%) and a high quartz content (27.7–51.6 vol%). The total specific surface area varies from 12.02 to 28.87 m²/g. Both the total specific surface area and quartz content are positively associated with the TOC content. (2) Shale samples with a higher TOC content have a greater number of micropores, resulting in more complicated nanopore structures. Micropore volumes/surface areas and non-micropore surface areas all increase with increasing TOC content, indicating that TOC is the key factor determining the nanopore structure of the lower Cambrian shale. (3) A combination of N₂ and CO₂ adsorption provides the most suitable detection range (∼0.3–60 nm) and is both highly reliable and accurate with regard to nanopore structure characterisation.

Because of the great potential for hydrocarbon generation, the Lower Cambrian Wangyinpu and Guanyintang Formations of the Jiangxi Xiuwu Basin have become the most important targets for shale-gas exploration in the Jiangxi province. We investigate the pore characteristics and main controlling factors of overmature shale using field emission-scanning electron microscopy, image-processing software (i.e., the Particles [Pores] and Crack Analysis System), X-ray diffraction, and gas-adsorption experiments. The results show that the shales have a high abundance of organic matter (OM), over maturity, and highly siliceous mineral content. The kerogen type is identified as type I. OM pores are the most developed, followed by interparticle (interP) pores and intraparticle (intraP) pores. We combine complementary image processing and gas-adsorption methods to reveal that micropores are mainly from OM pores; mesopores are from OM pores and interP pores; and macropores are from OM pores, interP pores, and intraP pores. Although the number of micropores is at a maximum, the total contribution of mesopores and macropores to the pore volume (PV) is larger than that of micropores. However, the specific surface area (SSA) is mainly from the micropores. OM content and maturity are the main controlling factors for the development of pore structures. Because of overmaturity, OM loses its potential for hydrocarbon generation and new pores cannot be produced. Gas loss leads to reservoir pressure drop, and the pores generated during the mature stage collapse and even disappear because they lack support. Therefore, PV, SSA, and porosity decrease when the OM content is more than 10%. When the OM content is less than 10%, most of the OM pores are preserved because they are protected by the skeleton particles.