基于两能态吸附热理论的煤层瓦斯流动热-流-固多场耦合模型

A fully coupled thermal-hydrological-mechanical model for gas seepage based on binary-energy-state heat theory

为了研究煤层瓦斯流动过程中温度与渗流场和应力场的耦合作用变化规律,引入煤层瓦斯两能态吸附热理论,重新构建煤层温度场控制方程,推导了温度场控制方程中解吸微分热能项的理论求解方法,改进了煤层瓦斯流动的热-流-固多场耦合数学模型;从理论上阐述了煤层瓦斯流动过程中吸附解吸、应力场、温度场、渗流场相互影响的作用机制;利用该模型研究了煤层瓦斯抽采过程中煤层瓦斯流动时的煤层温度、瓦斯压力、煤层渗透率的变化规律;结合已有试验研究结果,对比验证了模型的精确性和合理性;研究结果表明,在煤层瓦斯抽采过程中,煤层温度下降的快、慢受煤层原始瓦斯含量和压力及煤层渗透率的共同影响,煤层渗透率越大,温度下降越快,煤层瓦斯压力和含量越大,温度下降越快;同时,煤层渗透率随抽采时间的增长而增加,越靠近钻孔壁面煤层渗透率增加幅度越大。

To investigate the coupling effect among coal seam temperature, gas seepage field and stress field, a temperature field controlling equation was reestablished by employing binary-energy-state theory in coal gas flow. Then, the theoretical solution of desorption differential heat term in the equation was derived as well. Finally, a fully coupled thermal-hydrological-mechanical（THM） model was improved. Based on the improved THM model, this study discussed complex interactions among adsorption, desorption, stress field, temperature field and seepage field in coal gas flow. Moreover, the THM model was used to investigate the changes of temperature, gas pressure and permeability of coal seam during gas drainage. The model results showed good agreement with the results from previous experimental studies. The results indicated that the drop-down rate of coal seam temperature was controlled by the combined effect of the original gas content, pore pressure and permeability of coal seam during gas drainage. It means that the greater the permeability of the coal seam is, the faster the dropdown rate of the temperature is. The greater the coal seam gas content and gas pressure are, the faster the temperature drops. Meanwhile, the permeability of coal seam increased with the elapsed time of drainage and the amplitude of the increase declined with the increase of the distance from borehole axis along the radial direction.