Abstract This study explored the occurrence of coal-rock dynamic disasters during the low-temperature oxidation of coalbed methane (CBM) reservoirs for different coal ranks by investigating the dynamic development of pores in coal during low-temperature oxidation. This research monitored dynamic changes in the diameters and numbers of pores in different rank coals during low-temperature oxidation using nuclear magnetic resonance (NMR) and the P-wave rock measurement system. Microscopically, by utilizing industrial component analysis technology and gas chromatography, this study determined the dynamic changes occurring in the composition of coal and the concentrations of representative gases in the low-temperature oxidation of different rank coals. By adopting a new comprehensive index K, which is a combination of the coal-rock hardness (f) and the initial velocity (△p) of a gas emission, to predict a gas outburst, the authors predicted coal-rock dynamic disaster hazards in the low-temperature oxidation of different rank coals. The experiment showed that there are similarities and differences in pore development during the low-temperature oxidation of different rank coals. The similarities are illustrated in the consistencies underlying fracture development. Specifically, in the early stage of low-temperature oxidation of coal (30–130 °C), due to the evaporation of water, the dehydration of compounds containing crystalline water and the decomposition and volatilization of volatiles, micro-pores in coal expand and connect to form meso-pores. In the late stage of oxidation (130–230 °C), the macromolecular compounds and volatiles in coal oxidize and decompose such that meso-pores expand and connect to form macro-pores and micro-fractures. However, as the metamorphic degree of the coal increases, the oxidation resistance and thermal stability of the coal improves, and the initial temperature for the development of pores with the same diameter increases. Based on the concept of the comprehensive prediction index K, the probability of a coal-rock dynamic disaster occurring in a CBM reservoir gradually increases as the oxidation temperature increases. The lower the metamorphic degree of the coal, the faster the growth rate. Therefore, the oxidation temperature at which the probability of a coal-rock dynamic disaster increases by 50% is used as the critical temperature for taking fire prevention measures, i.e., 90 °C and 130 °C for lignite and bituminous coals, respectively.

中文翻译：

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煤层气抽采过程中煤孔缝发育：对煤与瓦斯突出倾向的促进作用

摘要 本研究通过研究煤层气孔在低温氧化过程中的动态发育，探讨了不同煤级煤层气储层低温氧化过程中煤岩动力灾害的发生。这项研究使用核磁共振 (NMR) 和 P 波岩石测量系统监测了低温氧化过程中不同等级煤中孔隙直径和数量的动态变化。微观上，本研究利用工业成分分析技术和气相色谱法，确定了不同等级煤低温氧化过程中煤组成和代表性气体浓度的动态变化。通过采用新的综合指数 K，结合煤岩硬度（f）和瓦斯排放初速度（△p），预测瓦斯突出，预测了不同等级低温氧化下煤岩动力灾害危害煤。试验表明，不同煤级煤在低温氧化过程中孔隙发育有异同。裂缝发育的一致性表明了相似性。具体而言，在煤的低温氧化初期（30～130℃），由于水分的蒸发、含有结晶水的化合物的脱水和挥发分的分解挥发，煤中的微孔膨胀并连接形成中孔。在氧化后期（130-230℃），煤中的大分子化合物和挥发分发生氧化分解，使中孔扩大连通，形成大孔和微裂缝。但随着煤变质程度的增加，煤的抗氧化性和热稳定性提高，同径孔隙发育的初始温度升高。基于综合预测指标K的概念，煤层气储层发生煤岩动力灾害的概率随着氧化温度的升高而逐渐增大。煤的变质程度越低，增长速度越快。因此，将煤岩动力灾害概率增加50%的氧化温度作为采取防火措施的临界温度，即：