热采煤层气藏过程煤层气运移规律的数值模拟

Numerical simulation on flow rules of coal-bed methane by thermal stimulation

为得到注热开采煤层气藏过程中煤层气的流动规律,以前人实验成果为依据,结合传热学、热力学、弹性力学、渗流力学等相关理论,建立了热采煤层气藏过程中的煤层气热-固-流耦合数学模型,给出了模型中各物理场方程的弱解形式,利用有限元软件进行了单井筒热采煤层气流动规律的数值模拟,分别得出注热10 d、开采100 d后煤层温度场、应力场和气体渗流场变化规律.数值模拟结果显示,向煤层注热后,气体压力较未注热下降幅度增加,井筒气产量在开井初始阶段较未注热增量明显,一定时间后增幅减缓.由模拟结果可以得出,在开采初始阶段,气体吸热后从煤基质内表面解吸能力增强,裂缝内气体浓度增加,渗流能力增强,煤层气井筒产量增加;同时随气体的不断产出,煤层有效应力的增加和温度的降低导致煤层渗透率及孔隙度的减小,造成井筒气体产量减缓.

In order to obtain the flow rules of coal-bed methane in the process of thermal stimulation,based on predecessors＇ experimental results,combined with heat transfer,thermodynamics,elasticity mechanics,seepage mechanics and so on,the thermal-solid-fluid coupling mathematical models of coal-bed methane were established,and the weak solutions of physical field equations were given,and the finite element software was used to carry out numerical simulation of the flow rules under the condition of single well by thermal stimulation,the changing rules of temperature field,stress field and gas seepage field were drawn after 10 d thermal stimulation,and 100 d coal-bed methane mining.The numerical simulation results show that the gas pressure drop is higher than that of non-thermal stimulation,and the output of coal-bed methane is higher obviously during the beginning stage when the well is opened,after a mount of time,the increment of gas output is slow.The gas desorption ability enhanced,and the gas concentration in cracks and the seepage pressure difference increased,and the output of coal-bed methane increased after gas absorbed heat.At the same time,as the gas is exploited continuously,the permeability and pore decrease with the increment of effective stress and the fall of temperature of coal-bed,and the output of gas become slow.