This contribution presents an early-time solution for permeability evaluation in pulse-decay tests. A nonlinear governing equation for gas transport in the sample is derived considering the pressure dependence of gas compressibility and Klinkenberg slippage effect, and the early-time solution is obtained through the integral balance analysis. The permeability coefficient can be determined by the proposed solution through the pressure transients during the early-time stage of the tests, that is, before the upstream pressure pulse penetrates through the core sample and reaches the downstream side. To test the proposed solution, measurements were performed on a core sample of the Cretaceous Eagle Ford shale, Texas, USA, under different pore and confining pressures. Helium was used as the testing fluid to minimize the Joule-Thomson effect and adsorption. The experimental results show that the permeability coefficients obtained from this new solution agree well with those from the late-time solution, and prove our solution accurate and efficient for permeability evaluation. The present approach provides a good supplement to the pulse-decay method and is suitable for measurements of low-permeable rocks.

中文翻译：

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致密岩石渗透率测量的脉冲衰减法早期求解

该贡献为脉冲衰减测试中的渗透率评估提供了早期解决方案。考虑气体压缩性和Klinkenberg滑移效应的压力依赖性，推导了样品中气体输运的非线性控制方程，并通过积分平衡分析得到了早期解。渗透系数可以通过建议的解决方案通过测试早期阶段的压力瞬变来确定，即在上游压力脉冲穿透岩心样本并到达下游侧之前。为了测试建议的解决方案，在不同孔隙压力和围压下对美国德克萨斯州白垩纪 Eagle Ford 页岩的岩心样本进行了测量。氦气用作测试流体以最小化焦耳-汤姆逊效应和吸附。实验结果表明，新解得到的渗透系数与后期解得到的渗透系数吻合较好，证明了我们的解对渗透率评价的准确性和有效性。该方法为脉冲衰减法提供了很好的补充，适用于低渗透岩石的测量。