Steady-state and unsteady-state (downstream pressure build-up) gas permeability tests were conducted on low permeability siltstone at a series of upstream pressures during the loading and unloading processes. The characteristics of downstream pressure build-up curves are analysed in detail, and the permeability is calculated based on the data in the stabilization stage. Analysing approaches with and without consideration of the sample pore volume are used to obtain the unsteady-state permeability for both the real pressure and the pseudo pressure. Findings suggest that the permeability based on the pseudo pressure is generally lower than that based on the real pressure, with their ratio ranging from 0.75 to 0.98. The sample pore volume corrected permeability is 1.42–1.51 times of that without the consideration of sample pore volume. The apparent steady-state gas permeability is higher than the sample pore volume corrected permeability due to slip flow, while its intrinsic permeability is lower as the pore pressure is smaller in the steady-state test. The permeabilities decrease with the confining pressure in the loading path especially at lower confinements, while only part of the reductions is recovered during the unloading process. Increase of pore pressure enhances permeability under low confinement conditions. Water permeability is lower than gas permeability in steady-state test due to the water-rock interaction and the residual gas inside the sample.

中文翻译：

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试验方法和加载历史对致密储层岩石渗透率的影响

在加载和卸载过程中，在一系列上游压力下对低渗透粉砂岩进行了稳态和非稳态（下游压力建立）气体渗透率测试。详细分析了下游建压曲线的特点，并根据稳定阶段的数据计算渗透率。使用考虑和不考虑样品孔隙体积的分析方法来获得真实压力和伪压力的非稳态渗透率。结果表明，基于伪压力的渗透率普遍低于基于真实压力的渗透率，其比值在0.75～0.98之间。样品孔隙体积修正渗透率是不考虑样品孔隙体积的 1.42~1.51 倍。由于滑流，表观稳态气体渗透率高于样品孔隙体积校正渗透率，而在稳态测试中，随着孔隙压力较小，其固有渗透率较低。渗透率随着加载路径中的围压而降低，特别是在较低的限制下，而在卸载过程中只有部分降低被恢复。在低约束条件下，孔隙压力的增加提高了渗透率。由于水岩相互作用和样品内部的残余气体，在稳态测试中水渗透率低于气体渗透率。渗透率随着加载路径中的围压而降低，特别是在较低的限制下，而在卸载过程中只有部分降低被恢复。在低约束条件下，孔隙压力的增加提高了渗透率。由于水岩相互作用和样品内部的残余气体，在稳态测试中水渗透率低于气体渗透率。渗透率随着加载路径中的围压而降低，特别是在较低的限制下，而在卸载过程中只有部分降低被恢复。在低约束条件下，孔隙压力的增加提高了渗透率。由于水岩相互作用和样品内部的残余气体，在稳态测试中水渗透率低于气体渗透率。