低渗透岩石在围压作用下的耦合渗流实验

Experimental study on coupled flow through low permeability rock under confining pressure

为了解有效围压对低渗透砂岩渗流性能的影响规律,利用高精度的FDES-641三轴驱替评价系统,以盐水作为渗流流体,分别采用恒速法和恒压法进行低渗透饱和砂岩在有围压耦合作用下的稳定渗流实验。结果表明:岩石渗透率随着有效围压的增加而下降,呈现非线性关系。结论为:1)当流速或压力梯度保持恒定时,随着有效围压升高,渗透率下降速率逐渐降低,渗透率比与有效围压近似呈反比关系。2)当有效围压下降时,岩石渗透率回升,但回升路径低于原始路径。3)恒速法比恒压法操作方便、精度高,有利于围压作用下的稳定渗流实验。

A steady-state flow experiment was performed to investigate the coupled flow through low permeability sandstone subjected to confining pressure. A precise triaxial testing system (FDES-641) was used to measure the flow of brine liquid through low permeability saturated rock under two different conditions, such as constant flow speed and constant pressure gradient. The experiments confirmed that the permeability of sandstone samples varies with change of the confining pressure and that the relationship is nonlinear. Under both conditions the permeability of sandstone decreases with increasing of confining pressure, but the decreasing rate of permeability becomes lower at low level of confining pressure, so that the ratio of the permeability is approximately inversely proportional to the confining pressure. During unloading of the confining pressure, the permeability of rock increases, but with lower rate in comparison with that in loading process of confining pressure. The constant flow speed condition is more easily controlled than the constant pressure gradient condition, so it is more commonly used in steady-state flow experiments.