考虑吸附/解吸热效应的含瓦斯煤热-流-固耦合模型及数值模拟

Gassy coal thermal-hydraulic-mechanical coupling model and numerical simulation considering adsorption/desorption thermal effect

为了研究煤吸附/解吸瓦斯热效应对煤与瓦斯突出前兆信息演化规律及互耦关系的影响,开展了煤吸附/解吸瓦斯热效应实验,建立了不同压力梯度下的煤体温度变化方程,进而构建了反映采场孔隙率与渗透率动态演化、瓦斯吸附-解吸-扩散以及能量积聚与耗散等过程的热-流-固耦合模型。以耦合模型为基础,进行了煤与瓦斯相互作用机理数值模拟。结果表明:相同压力梯度时,煤体温度和瓦斯压力自煤壁向煤层内部逐渐升高,渗透率在工作面推进方向上呈现为先减小后增大;应力集中区内,地应力主导煤体渗透率的变化,应力集中区外,煤吸附/解吸瓦斯热效应引起的热膨胀应变、游离瓦斯产生的压缩应变和吸附膨胀应变起主导作用;随瓦斯压力梯度增大,煤体温度升高,瓦斯压力增大,煤体变形增大、变形量较小,渗透率逐渐减小,渗透率的降低量随瓦斯压力梯度增大而减小,吸附/解吸热效应对煤与瓦斯相互作用关系的影响逐渐减弱。

To study the effect of adsorption and desorption thermal effect on the evolution law and mutual coupling relation of coal and gas outburst precursor information,the thermal effect experiment of coal adsorption and desorption gas was carried out.Meanwhile,the coal temperature change equation under different pressure gradients was established.And then the thermo-hydro-mechanical coupling model for the evolution of porosity and permeability,gas adsorption-desorption-diffusion and energy accumulation-dissipation was constructed.Based on the coupling model,the interaction between coal and gas was studied through numerical simulation.The results have shown that at the same pressure gradient,the coal body temperature and gas pressure gradually increase from coal wall to deep coal seam, and the permeability first decreases and then increases in the advancing direction of the working face. Also, in-situ stress dominates the change of coal permeability in the stress concentration area, while outside the stress concentration area, the thermal expansion strain caused by the thermal effect of coal adsorption/desorption gas, the compressive strain produced by the free gas and adsorption expansion strain play a leading role. With the increase of the gas pressure gradient, the temperature of coal increases, gas pressure increases, coal deformation increases, but the amount of deformation is small, and the permeability decreases gradually. The reduction of permeability gradually decreases with the increase of gas pressure gradient. And the effect of adsorption and desorption thermal effect gradually weakens on the coupling relation between coal and gas.