Yi Jin

Coal measure gas (CMG) is an important unconventional energy resource, and a clear understanding of its accumulation mechanisms is essential for effective exploration and development. This study investigates the coal measure strata of the Shanxi Formation in the eastern Pingdingshan mining area. An integrated approach combining geostatistical analysis, geochemical characterization, X-ray diffraction, and high-pressure mercury intrusion measurements, together with a Markov chain model, was employed to elucidate the accumulation framework and spatial organization of CMG systems. The results show that (1) the study area is characterized by a coal–mudstone–sandstone tripartite assemblage. The thickness of the main coal seam (No. 2-1) ranges from 0.65 to 12.42 m (average 5.50 m), thickening toward the central area and thinning toward the margins, and serves as the primary source rock. Mudstonethickness ranges from 5.66 to 89.91 m (average 39.67 m) in thickness and acts as an effective seal, whereas sandstone (ranging from 2.15 to 68.28 m, average 34.72 m) is preferentially developed in the central area and constitutes the main reservoir. (2) Source rocks exhibit high organic abundance and thermal maturity, whereas reservoirs typically exhibit low porosity and extremely low permeability. The coal seam exhibits a maximum vitrinite reflectance (Ro,max) ranging from 1.106% to 1.651% (average 1.461%) and high organic matter abundance. Mudstone exhibits a total organic carbon (TOC) content ranging from 2.61% to 28.00% (average 9.34%) and is dominated by type III kerogen, indicating a mature to highly mature thermal evolution stage. Coal, mudstone, and sandstone reservoirs all display low porosity and extremely low permeability characteristics. (3) Based on the Markov chain analysis, five dominant lithofacies sequences were quantitatively identified, and three CMG accumulation patterns were recognized: single-source dual-reservoir, dual-source dual-reservoir, and dual-source multi-reservoir types. These results suggest that depositional environment exerts the primary control on the spatial differentiation of CMG accumulation patterns. This study provides a geological basis for integrated source–reservoir–seal assessment and sweet-spot prediction in CMG exploration.

1. Amid the ongoing energy transition and environmental concerns, clean energy development has attracted broad attention. However, China's coal-dominated energy landscape is unlikely to undergo a f...

As one of the controlling factors of the three-dimensional (3D) fracture flow, the effect of surface contact on fluid flow behavior is usually characterized by the parameter of contact ratio. However, the difference in the shape of surface contact induces different fluid flow pathways, thereby resulting in a more complex flow process, while the influence mechanism has not been fully revealed. This study focuses on the reexamination of the effect of surface contact characteristics on complex fluid flow behaviors. For that, the origin of hydraulic tortuosity in rough fractures with contact areas was identified by theoretical derivation, and a modified permeability estimation model was established on the basis of the triple-effect model. To further clarify the control mechanism of contact shape on permeability, a novel algorithm for the generation of 3D rough-walled fractures with different contact modes (i.e., isotropic and anisotropic contacts) was developed, and a series of lattice Boltzmann simulations of the fluid flow through the generated fractures were conducted. Numerical results indicate that it is inadequate to accurately characterize the effect of contact area only by contact ratio, and the contribution degree of contact ratio to hydraulic tortuosity depends on contact mode that represented by anisotropy factor of contact area. On this basis, as an important source of the hydraulic tortuosity, the effect of surface contact was identified to be characterized by two parameters, namely, contact ratio and anisotropy factor. Finally, the validity of the modified permeability model was validated, and its generalizability was also discussed.

Carbon disulfide (CS₂) as a focus has been extensively studied in stimulating the coal macromolecular structure and pore structure. However, the desorption characteristics are not examined after CS₂ extraction, limiting an insightful understanding of the targeted stimulation mechanism of CS₂ extraction on desorption. The study further explores the effect of CS₂ extraction on methane desorption through the isothermal adsorption experiment and the desorption stage theory. From the results, CS₂ extraction induces the adsorption weakened effect and desorption enhanced effect, with a decrease in Langmuir constants a and b. By affecting key desorption pressure points, CS₂ extraction alters the dynamic desorption process, with an expansion on slow desorption stage II and fast desorption stage III and a shortening of sensitive desorption stage IV. Additionally, the increase in desorption characteristic parameters in extracted coal, including the critical desorption pressure P_cd, gas saturation β, effective pressure drop P_e, and effective desorption quantity V_e, indicates that CS₂ extraction lowers the required critical desorption condition and contributes to increasing the desorption capacity. Meanwhile, the targeted stimulation mechanism of CS₂ extraction on the dynamics of physical desorption characteristic has been further revealed. We also validate the plateau extension effect and decrement weakening effect by CS₂ extraction, promoting the conversion of adsorbed gas to free gas and prolonging the effective production process. The study provides a theoretical basis for CS₂ extraction utilization in changing the desorption characteristic and increasing CBM production.

Extracellular DNA (eDNA) has become a focus in public health, with soil recognized as a key reservoir where eDNA's mobility and stability are primarily controlled by clay minerals and organic matter. Montmorillonite (MMT) often interacts with humic acids (HA), forming MMT-HA complexes, although the molecular mechanisms behind DNA adsorption in these complexes remain unclear. Here, molecular dynamics simulations were used to examine the adsorption, diffusion, interfacial structure, and dynamics of DNA on MMT and MMT-HA complexes, revealing critical molecular interactions. Interaction energy analysis showed that DNA adsorption is energetically more favorable on MMT than on MMT-HA, as HA reduces DNA's adsorption capacity on MMT. Diffusion coefficients indicated that DNA has lower mobility on MMT than on MMT-HA. Ca²⁺ cations and water molecules bridge MMT surfaces and DNA phosphate groups, enhancing DNA adsorption on MMT, while HA occupies MMT binding sites and forms limited hydrogen bonds with DNA, thereby inhibiting adsorption. These results provide insights into the adsorption, migration, and stability of eDNA on soil clay minerals.

Coalbed methane (CBM) reservoir mass transfer performances, including adsorption/desorption, diffusion and seepage, are related to the types of intact and cataclastic coal structures. By “cataclastic coal,” we mean that coal produces fractures in different directions caused by tectonic stress and is divided into fragments along the fractures surface, but there is no significant displacement between fragments. This paper sampled coal specimens from a coal mine to investigate the dynamic behaviors of reservoir by using experiments and Lattice Boltzmann Simulation Method (LBM). The results show that Langmuir VL, specific surface areas, and pore volumes occurring at cataclastic coal seam (570–572 m) are higher than in intact coals. The dominant pore size in samples 1, 2, 3, and 4 is distributed between 2 and 10 nm, leading to increased adsorption capacity in cataclastic coal. Cataclastic coals' fractal dimension D1 is higher than in intact coal, but D2 is lower than in intact coal, which means tectonic damage causes the pore surface to become coarser and the pore structures to become homogenous. Because of increased pore volume in cataclastic coal, its dynamic diffusion coefficient is better than in intact coal, meaning the upper coal seam has beneficial gas releasing efficiency. Based on LBM simulation and tri-axial permeability experiments, it is found that cataclastic coal with developed natural fractures is characterized by high velocity of fluids, but its damage ratio of permeability is stronger than in intact coal. Finally, it summarizes the reservoir characters of Gaohe coal field and proposes that it should pay attention on the lower intact coal seam for the stimulation of CBM reservoir.