初应力作用下孔隙介质升温时渗透率变化规律

为研究不同地应力作用下的油气储层热采过程中渗透率的变化规律,利用自主研制的热流固三场耦合渗流试验系统,选用难被孔隙介质吸附的氦气作为渗流气体,并考虑氦气黏度随温度和压强的变化,消除孔隙介质对渗流气体的吸附和气体黏度变化对渗透试验的影响,开展不同初始应力条件下煤岩试件升温渗透试验。结果表明:孔隙介质渗透率随温度升高先增大后减小,呈非单调非线性变化规律,并存在与初始有效应力有关的拐点温度,这是由于在拐点温度之前,温度应力小于初始有效应力,固体骨架向外膨胀,孔隙空间增大,渗透率增大,超过拐点温度后,温度应力大于初始有效应力,固体骨架向孔隙内膨胀挤占孔隙空间,渗透率降低;渗透率变化拐点温度随初始体积应力的增大而减小,温度应力升高速率随初始体积应力增加而增大。

Permeability variation law of porous media during heating process under effect of initial geostress

To reveal the rule of permeability variation during thermal recovery of oil and gas reservoirs under different ground stresses, a thermo-hydro-mechanical coupled experimental system was developed, and non-adsorbed helium was used in the experiments. The change of helium gas viscosity with temperature and pressure was considered to eliminate the influences on the infiltration experiments. A series of infiltration experiments were conducted for coal and sandstone under different temperature conditions and different initial stresses. The results indicate that with the increase of temperature, the permeability of porous medium increases firstly, and then decreases in the form of nonlinearity and non-monotone. There is a temperature of inflection point related with the initial effective stress. The mechanism is described as the following:when temperature is lower than the temperature of inflection point, temperature stress is less than the initial effective stress, pore space increases because of the outward expansion of solid skeleton, so the permeability will increase. When temperature is higher than the temperature of inflection point, temperature stress is bigger than the initial effective stress, pore space decreases because of the inward expansion of solid skeleton. In addition, the temperature of permeability variation inflection point decreases with the increase of initial volume stress, the increasing rate of temperature stress is higher when the size of the initial volume stress is bigger.