Abstract Revealing gas field evolution and distribution in coal seams is of great significance to coalbed methane (CBM) recovery. It is believed that gas migration in coal involves multifield coupling processes. In this study, an improved thermo-hydro-mechanical (THM) coupling model is developed to investigate the physical fields evolution during gas flow in coal. In this model, the effect of internal swelling deformation is considered to modify the conventional coal deformation equation and coal permeability model. A dynamic diffusion model is introduced to accurately characterize the dynamic evolution of gas diffusion in matrix. Besides, a new matrix porosity model is developed based on the assumption that the pore volume change equals to the matrix volume change. To reveal the gas field evolution and distribution in coal core during coal permeability test in the lab, we build two heterogeneous coal models based on numerically reconstructed method and CT scanning. With the THM model, the gas pressure distribution in the coal core is quantitatively characterized. It is found that in the heterogeneous coal core, gas streamline fluctuates in space. The gas pressure nonlinearly distributes in the coal core, rather than the linear distribution assumed when testing permeability in the lab. Aiming at the confliction between the theoretical result and the assumption used in permeability testing, we propose to improve the accuracy of lab testing result by reducing the gas pressure difference between the gas inlet and outlet.

中文翻译：

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控制非均质弹性变形煤中气体运移的热-水-力耦合

摘要 揭示煤层气田演化与分布对煤层气回收具有重要意义。据信，煤中的气体运移涉及多场耦合过程。在这项研究中，开发了一种改进的热-水-机械 (THM) 耦合模型来研究煤中气体流动过程中的物理场演化。该模型考虑了内部膨胀变形的影响，对常规煤变形方程和煤渗透率模型进行了修正。引入动态扩散模型来准确表征基质中气体扩散的动态演化。此外，基于孔隙体​​积变化等于基质体积变化的假设，建立了新的基质孔隙度模型。为揭示实验室煤渗透率测试过程中煤芯内的气田演化和分布，我们基于数值重建方法和CT扫描建立了两种非均质煤模型。使用 THM 模型，可以定量表征煤芯中的瓦斯压力分布。发现在非均质煤芯中，气体流线在空间上有波动。瓦斯压力在煤芯中呈非线性分布，而不是在实验室测试渗透率时假设的线性分布。针对渗透率测试中理论结果与假设的矛盾，提出通过减小气体进出口气压差来提高实验室测试结果的准确性。我们基于数值重建方法和CT扫描建立了两种非均质煤模型。使用 THM 模型，可以定量表征煤芯中的瓦斯压力分布。发现在非均质煤芯中，气体流线在空间上有波动。瓦斯压力在煤芯中非线性分布，而不是在实验室测试渗透率时假设的线性分布。针对渗透率测试中理论结果与假设的矛盾，提出通过减小气体进出口气压差来提高实验室测试结果的准确性。我们基于数值重建方法和CT扫描建立了两种非均质煤模型。使用 THM 模型，可以定量表征煤芯中的瓦斯压力分布。发现在非均质煤芯中，气体流线在空间上有波动。瓦斯压力在煤芯中非线性分布，而不是在实验室测试渗透率时假设的线性分布。针对渗透率测试中理论结果与假设的矛盾，提出通过减小气体进出口气压差来提高实验室测试结果的准确性。气体流线在空间中波动。瓦斯压力在煤芯中非线性分布，而不是在实验室测试渗透率时假设的线性分布。针对渗透率测试中理论结果与假设的矛盾，提出通过减小气体进出口气压差来提高实验室测试结果的准确性。气体流线在空间中波动。瓦斯压力在煤芯中非线性分布，而不是在实验室测试渗透率时假设的线性分布。针对渗透率测试中理论结果与假设的矛盾，提出通过减小气体进出口气压差来提高实验室测试结果的准确性。