Stress Sensitivity for the Occurrence of Coalbed Gas Outbursts: A Reactive Force Field Molecular Dynamics Study

Abstract

Coalbed gas outburst processes commonly occur in ductile shear zones and release gas quantities that far exceed the maximum gas adsorption capacity of coal seams. Although outburst accidents pose a serious safety hazard, this process has long remained poorly understood at a molecular level. In this work, we use reactive force field molecular dynamics simulations to analyze the influence of stress on the mechanochemical decomposition reactions and products of coal macromolecular models. The results indicate that a maximum of reaction amounts occurs upon changing the external force for the mechanochemical reactivity of bituminous coal under working conditions. This implies that gas generation readily occurs over a suitable stresssensitive range, which can be used to qualitatively explain why coalbed gas outbursts typically occur in ductile shear zones. When a force is too large, it can cause brittle fracture and is less likely to initiate mechanochemical reactions that generate gas, whereas a too small of a force is insufficient to trigger chemical changes of the coal macromolecular structure. The anisotropic properties of coal must also be considered in terms of mechanochemical reactions. Coal molecules can generate different kinds of gases when driven by external forces in different orientations. The simulation results provide important insights into coalbed gas outburst characteristics and the anisotropic nature of coal. Only by comprehensively considering stress factors will it be possible to understand the occurring conditions of coalbed gas outbursts.

Evolution of the Hierarchical Molecular Structures of Tectonically Deformed Coals: Insights from First-Order Raman Spectra

“…As the coal deformation intensity increased, the value of A C / A Total gradually decreased (Figure ), indicating that tectonic stress could result in the dissociation of these functional groups. Further, simulative coal deformation experiments have shown that under the action of stress, oxygen functional groups (particularly carbonyl) can be dissociated into gases. − It should be noted that the average A C / A Total values of scaly coals are lower than that of wrinkle coal, which indicates that higher shear stresses are likely to facilitate the disassociation of oxygen functional groups. Furthermore, the disassociation of oxygen functional groups can also break the hydrogen bonds connected with them, thereby increasing the motion and rearrangement of aromatic structures.…”

Virtual Special Issue of Recent Research Advances in China: Unconventional Gas

“…A review by Lu et al presents a summary and perspective on efficient exploitation of CBM in China. The original research articles on this topic cover several aspects related to CBM, including gas adsorption, methane production, , numerical modeling and simulation, , pore-scale measurements, , characterization studies, , etc.…”

“…A review by Lu et al 62 presents a summary and perspective on efficient exploitation of CBM in China. The original research articles on this topic cover several aspects related to CBM, including gas adsorption, 63 methane production, 68,71 numerical modeling and simulation, 64,66 porescale measurements, 65,69 characterization studies, 67,70 etc. This VSI is part of the series of VSIs on recent advances in selected energy research areas, launched by Energy & Fuels in January 2021.…”

Characterization of Coal Particle Methane Desorption and Optimization of Desorption Model Based on Desorption Damage

“…A significant outburst of coal and gas accidents will be accompanied by energy release, which produces strong power in the period of underground mining. − Gas outburst produces a large amount of pulverized coal, and the desorption gas of pulverized coal will further facilitate the outburst. − Therefore, gas significantly influences the gestation and occurrence of gas outbursts. − As coal mining depths increase, the amount and intensity of gas emissions also increase, which will induce more gas calamities. − In addition to the high-intensity mining stage of deep coal seams, the coal has been strongly damaged many times during the coal-forming process, leading to the gas migration in the coal body and the circumstance of gas desorption–pulverization–desorption. , Consequently, studying the law of gas desorption in coal under damage conditions is crucial for understanding gas emission laws and gas flow mechanisms and predicting coal and gas outbursts. − …”