多因素耦合作用和循环围压对煤岩CH_(4)渗透率的影响研究

Study on the effects of multi-factor coupling and cycling confining pressure on the permeability of CH_(4)in coal rock

煤储层渗透率受自身性质、温度、应力状态等诸多因素影响。以淮南刘庄煤矿13-1煤层为研究对象,基于CH_(4)渗透率测试,研究了体积应力、温度与气体压力耦合以及循环围压下CH_(4)渗透率的变化规律。结果表明:体积应力与气体压力耦合主要通过控制有效应力大小来影响煤岩CH_(4)渗透率,有效应力越大,渗透率越低;气体压力对CH_(4)渗透率的影响受限于体积应力,但气体压力对渗透率的影响大于体积应力;温度与气体压力耦合对CH_(4)渗透率的影响由气体压力主导,渗透率随气体压力的增大呈“U形滑梯式”下降,且“滑梯式”变化比“U”形变化更为明显;气体压力对CH_(4)渗透率的影响大于温度,且增大气体压力会降低温度对渗透率的影响;循环围压会造成煤岩孔裂隙的不可逆塑性变形,使煤中有效渗流通道减少,CH_(4)渗透率降低;第1次循环围压产生的塑性变形量最大,随循环次数增加,塑性变形量逐渐减少。

The permeability of coal reservoirs is affected by its inherent properties,temperature,stress state,etc.Taking the 13-1 coal seam of Huainan Liuzhuang Coal Mine as the research object,the variation of CH_(4)permeability under the coupling of volume stress,temperature and gas pressure,and under cyclic confining pressure were studied based on the CH_(4)permeability test.The results show that the CH_(4)permeability of coal affected by the coupling of volume stress and gas pressure mainly controlled by the effective stress,and the greater the effective stress is,the lower the permeability is.The effect of gas pressure on CH_(4)permeability is limited by volume stress,but gas pressure has a greater effect on CH_(4)permeability than volume stress.The influence of temperature and gas pressure coupling on CH_(4)permeability is dominated by gas pressure.Permeability decreases with the increase of gas pressure showing a type of“U slide”,and the“slide”change is more obvious than the“U”change.The influence of gas pressure on CH_(4)permeability is greater than that of temperature,and the increasing gas pressure will reduce the influence of temperature on permeability.The cyclic confining pressure will cause irreversible plastic deformation of the pore fractures,which reduces effective seepage channels in the coal and decreases CH_(4)permeability.The plastic deformation produced by the first cyclic confining pressure is the largest,and the amount of plastic deformation gradually decreases with the increase of the number of cycles.