Intermolecular forces that act between moisture and the atoms of the coal structure have a significant influence on methane adsorption- and desorption-induced deformation in coal. After analyzing the porous characteristics and existing forms of moisture in coal, both the adsorption-induced swelling and the desorption-induced shrinkage deformation experiments were carried out under the conditions of varying moisture content, constant temperature, and variable equilibrium pressure. Both the swelling and shrinkage volumetric strains with different coal moisture contents were fitted by Langmuir-type equations in which the fitting coefficients were functions of the moisture content. It was found that there is a lag between the swelling curve and the corresponding shrinkage curve, and a variable known as the hysteresis rate was defined to illustrate this characteristic. A mathematical model of swelling and shrinkage deformation that considers the effect of moisture content was established based on the experimental results and analysis.

The coal-rock reservoir exhibits a dual porous medium characteristic, where fractures are the primary contributor to permeability, while pore structure influences the gas adsorption properties of coal rock. Gas adsorption induces swelling in the coal matrix, leading to a reduction in fracture width and subsequently causing decreased permeability and reduced well production. Investigating the impact of geological characteristics of coal-rock on gas adsorption and desorption properties can enhance our understanding of the patterns governing changes in coal-layer production. This study focused on the 3^# coal seam in China's Qinshui Basin as its research subject. It involved an analysis of mineral composition, physical properties, gas content, and pore structure characteristics to explore the adsorption traits of different gases and conduct experimental studies on variations in gas adsorption and desorption capabilities under diverse conditions. The research findings suggest that the coal rock in the study area is primarily characterized by micropores and small pores, with well-developed larger pores and fractures. The pore connectivity is somewhat limited, and the predominant pore size ranges from 100 to 200 nm. The average permeability measures 0.198 × 10^–3 µm², while the mean specific gas content stands at 21.7 m³/t. Analysis of the isothermal adsorption curve reveals a substantial increase in adsorption when pressure falls below 3.5 MPa due to a steep slope; as pressure continues to rise, there is a gradual upward trend in adsorption until reaching 8 MPa, after which point adsorption increases slowly and stabilizes. Results from binary gas adsorption–desorption experiments indicate low desorption levels and rates for CO₂ components compared to relatively higher desorption amounts and rates for CH₄ components. Furthermore, it was observed that CO₂ has a displacement effect on CH₄; higher CO₂ concentrations are more conducive to CH₄ release and CO₂ storage.

The phenomenon of coal swelling caused by gas adsorption is well known. For Enhanced Coal Bed Methane Recovery and carbon storage, coal swelling induced by gases adsorption may cause significant reservoir permeability change. In this paper, based on the assumption that the surface energy change caused by adsorption is equal to the change in elastic energy of the coal matrix, a theoretical model is derived to describe coal swelling induced by gas adsorption in the full pressure range. The Langmuir constant, coal density, solid elastic modulus, and Poisson’s ratio are required in this model. These model parameters are easily obtained through laboratory testing. The developed model is verified by available experimental data. The results show that the presented model shows good agreement with the experimental observations of swelling. The model errors are within 14% for pure gas, and within 20% for mixed gas. It is shown that this model is able to describe coal swelling phenomena for full pressure range and different gas type including pure gas and mixed. In addition, it is also shown that the errors of the presented model and the Pan’s model are almost the same, but the presented model is solved more easily.

Unconventional natural gas development requires a deeper insight into how CH₄ and CO₂ adsorb and diffuse in the pores of coal seams. Graphene (GRA) is frequently employed in microscopic mechanism simulations on coal surfaces because its structure closely resembles that of the coal seam matrix. In this study, molecular dynamics simulations were conducted to systematically investigate the diffusion, adsorption, and desorption behaviors of CH₄ and CO₂ within the pore system of hydrated graphene under three representative temperature and pressure conditions: 190 K-6 MPa, 298 K-0.1 MPa, and 320 K-8 MPa. The results show that heatinfg and depressurization significantly enhance the diffusion ability of gas molecules and promote their desorption from the graphene surface. Low temperature and high pressure are conducive to the formation of a stable adsorption layer, and more hydrogen bond structures are formed between CO₂ and water. However, under high-temperature conditions, this ordered structure is significantly weakened. The density distribution further reveals the spatial distribution characteristics of water molecules and gases and their evolution trends with changes in temperature and pressure. This research is conducive to a deeper understanding of the multiphase behavior of coalbed methane and its regulatory mechanism, providing theoretical support for the gas storage and displacement processes.

A metal-doped modified CO oxidation catalyst with strong adsorption and water resistance for coalbed methane was prepared by the CO precipitation method. The CO ablation characteristics were tested, and the Cu Mn catalyst synthesized by metal Ce doping achieved an instantaneous ablation efficiency of 80% when in contact with CO at room temperature. By analyzing the surface crystal structure and pore characteristics, as well as by testing the ablation properties, it was found that the CO oxidation catalyst synthesized by Ce had the best effect at a precipitation temperature of 70 °C. A water-resistant CO oxidation catalyst was synthesized by adding polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). After storage at a relative humidity of 90%, it still had a CO adsorption rate of about 85%. The water-resistant CO oxidation catalyst prepared with polyvinyl alcohol (PVA) as an additive had a higher content of CeO₂ crystal nuclei, and the PVA-added CO oxidation catalyst had the best ablation characteristics. In the evaluation of the water-resistant steam ablation process, the CuMnO_x-Ce-PVA catalyst showed a significant increase in intermediate products during the stress process under water vapor conditions and a decrease in the peak value of the catalyst’s binding to water, and the catalyst has a particular inhibitory influence on the adsorption of water molecules on its surface. Due to its outstanding water resistance, the catalyst was able to retain good ablation characteristics.

China’s shale gas has undergone nearly 20 years of exploration; unconventional oil and gas geological evaluation theories and research methods have been greatly enriched, but how to quickly, conveniently, and accurately identify the sweet spots of shale gas is still puzzling many researchers. This study focuses on the black shale of the Wufeng–Longmaxi Formation in the southeastern edge of the Sichuan Basin; lithofacies classification, the relationship between lithofacies and depositional environments, and the correlation between lithofacies and shale gas–bearing capacity are discussed. At last, we have established the lithofacies classification criteria; the Wufeng–Longmaxi Formation deposited eight types of lithofacies, which the paleoenvironment during deposition evolved gradually from anaerobic environment to oxygen‐poor and oxygen‐rich environment. The black high‐carbon and high‐silicon shale lithofacies and the black carbon‐rich and silicon‐rich shale lithofacies are rich in organic matter, and they were deposited in high primary productivity, low terrigenous detritus input, and euxinic environment. The black medium‐carbon medium‐silica shale lithofacies and the black medium‐carbon and high‐silica shale lithofacies contain organic matter, which are deposited in medium primary productivity, middle terrigenous detritus input, and oxygen‐poor and low hydrodynamic environment. The gray–black low‐carbon low‐silicon clay‐rich shale lithofacies, the gray low‐carbon and high‐silicon shale lithofacies, and the gray–white low‐carbon and silicon‐rich shale lithofacies are poor in organic matter, which are deposited in a transitional environment of low primary productivity and oxygen poor–oxygen rich. In the analysis of the relationship between organic matter–rich black shale facies and sedimentary environment, it is shown that the enrichment of organic matter is positively correlated with the oxidation–reduction discrimination indicators Ni/Co, U/Th ratio of ancient oceans, and the evaluation indicators Ba _bio and Ba/Al ratios of primary productivity. Only under the favorable sedimentary geochemical conditions and good preservation conditions can deposit lithofacies sections (zones). Based on the optimization of shale gas dessert section and the drilling of horizontal wells, the optimization of favorable black shale lithofacies types and the classification of shale gas dessert section are the key to shale gas exploration. The shale gas–bearing capacity is closely related to lithofacies. Black carbon‐rich silicon‐rich shale lithofacies and black high‐carbon high‐silicon shale lithofacies have the best gas‐bearing capacity and are favorable lithofacies.