Stress-sensitive permeability (SSP) influences gas well productivity and is a crucial element influencing gas reservoir development. SSP for high-pressure fractured gas reservoirs with an initial reservoir pressure of more than 20 MPa has never been comprehensively evaluated to the best of our knowledge. SSP experiments with special procedures were designed by adopting the variable confining pressure (VCP) and variable internal pressure (VIP) methods. VCP is a test method in which the confining pressure is altered and a constant internal pressure is maintained for the experimental core holder. VIP is a test method in which the internal pressure is changed and a constant confining pressure is maintained. A four-stage curve analysis method was developed to perform regressions on semilogarithmic curves and exponential curves of experimental data. A method to evaluate the SSP was developed using stress sensitivity coefficients obtained via regressions. A calculation approach for determining the degrees of permeability damage and permeability recovery also was evaluated. In total, six matrix cores and six cores with artificial fractures from a high-pressure fractured sandstone gas reservoir were tested using the two methods. The SSP curves for high-pressure reservoirs were characterized by four-stage variation trends, which show differentiation with low-pressure reservoirs with an initial reservoir pressure less than 20 MPa. The stress sensitivity of the VCP method was stronger than that of the VIP method. The core samples mainly showed a “medium”/“medium-strong” stress sensitivity under low/high effective stress conditions. Compared with matrix cores, fractured cores showed stronger stress sensitivity owing to strong plasticity and weak elasticity. The maximum permeability damage degree reached 99.67%, and the minimum permeability recovery was only 6.9%. Our method of experimental design, four-stage curve analysis, stress sensitivity evaluation, and our overall findings can provide references for future studies on SSP in high-pressure fractured sandstone gas reservoirs.

中文翻译：

---

高压条件下基体岩心和非支撑填充裂缝的人工压裂岩心的应力敏感性渗透率

应力敏感渗透率（SSP）影响气井产能，是影响气藏开发的关键因素。据我们所知，从未对初始储层压力超过20 MPa的高压裂缝性气藏的SSP进行过全面评估。通过采用可变围压（VCP）和可变内压（VIP）方法，设计了具有特殊程序的SSP实验。VCP是一种测试方法，其中更改围压并为实验堆芯支架保持恒定的内部压力。VIP是一种改变内部压力并保持恒定围压的测试方法。开发了一种四阶段曲线分析方法以对实验数据的半对数曲线和指数曲线进行回归。利用通过回归获得的应力敏感性系数，开发了一种评估SSP的方法。还评估了确定渗透率破坏和渗透率恢复程度的计算方法。使用这两种方法，总共测试了六个基质岩心和六个来自高压裂缝性砂岩气藏的人工裂缝岩心。高压油藏的SSP曲线具有四个阶段的变化趋势，与初始油藏压力小于20 MPa的低压油藏表现出差异。VCP方法的应力敏感性比VIP方法强。核心样品在低/高有效应力条件下主要表现出“中” /“中-强”应力敏感性。与矩阵核相比，断裂的岩心由于较强的可塑性和较弱的弹性而表现出较强的应力敏感性。最大的渗透率破坏程度达到99.67％，最小的渗透率恢复率仅为6.9％。我们的实验设计方法，四阶段曲线分析，应力敏感性评估以及我们的整体研究结果可为高压裂隙砂岩气藏中的SSP研究提供参考。