Abstract The pressure transient technique has been widely used for laboratory tests on unconventional gas reservoirs; however, it is still a time-consuming process when applying this technique to rocks of ultra-low permeability in the nano-Darcy scale. The applicability of a novel radial-flow transient technique to achieve fast and accurate permeability measurements is verified by an experimental investigation in this study. Pressure transient tests were performed on two hollow cylindrical shale specimens with different inner radii under radially convergent flow conditions; and for comparison, a solid shale core was also tested via an axial-flow transient technique. The results showed that the time required for a complete pressure pulse decay by the radial-flow test is within several hours compared to a few days by the axial-flow test. It was also found that non-uniform stress distribution along the radius of the sample is the principle factor resulting in errors in the measured permeability; and thus, samples with a small inner radius should be used to reduce the error in the measured permeability. In addition, analytical solutions are derived to interpret the lab data for permeability determination. The accuracy of the proposed technique is elucidated by the small permeability difference of less than 15% compared to the axial flow tests. The permeability error analysis indicated that the effect of compressive storage and gas sorption can be eliminated, and the error is less than 6.7% even though two large pressure pulses of 0.5 MPa were generated. The study experimentally validates that fast and accurate permeability measurements can be achieved by adopting the proposed radial-flow transient technique.

中文翻译：

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使用径向流瞬态技术对致密气藏和吸附气藏进行快速渗透率测量

摘要 压力瞬变技术已广泛应用于非常规气藏的室内试验；然而，将这种技术应用于纳米达西尺度的超低渗透率岩石仍然是一个耗时的过程。本研究中的一项实验研究验证了新型径向流瞬态技术在实现快速准确渗透率测量方面的适用性。在径向收敛流动条件下，对两个不同内半径的空心圆柱形页岩试样进行了压力瞬态试验；为了进行比较，还通过轴流瞬态技术测试了固体页岩岩心。结果表明，与轴流测试的几天相比，径向流测试完全压力脉冲衰减所需的时间在几小时内。还发现沿样品半径的非均匀应力分布是导致测量渗透率误差的主要因素；因此，应使用内径较小的样品以减少测量渗透率的误差。此外，还推导出解析解来解释渗透率测定的实验室数据。与轴流测试相比，小于 15% 的小渗透率差异说明了所提出技术的准确性。渗透率误差分析表明，压缩储存和气体吸附的影响可以消除，即使产生两个0.5 MPa的大压力脉冲，误差也小于6.7%。