Abstract: The invasion of fracturing fluid into shale formations has a significant influence on the magnitude of permeability stress sensitivity, ultimately affecting shale gas well productivity. However, there remains a lack of mature theoretical evaluation methods for the influential mechanisms and characterization of stress sensitivity in water-invaded shale. To address this, novel physical simulation experiments and theoretical characterization methods were established to investigate the influence of fracturing fluid invasion on stress sensitivity in different shale flow regions, thus clarifying the relationship between shale stress sensitivity, effective stress, and water invasion degree. Results show that the initial stress sensitivity coefficient of shale exhibits a linear positive correlation with the degree of water invasion, while showing a linear negative correlation with effective stress. When the fracture water saturation reaches 0.90, the initial stress sensitivity coefficient can increase linearly by approximately 100 %, and decrease linearly by 17.86 % under the high stress of 55 MPa, accompanied by a five-order-of-magnitude permeability loss. Furthermore, the variation rate of the initial stress sensitivity coefficient with respect to water saturation and that of stress sensitivity with respect to effective stress are linearly correlated with clay mineral content and clay water absorption capacity.

Key words: unsupported fractures, stress loading, water invasion, swelling deformation due to water invasion, stress sensitivity

摘要： 页岩压裂液侵入会影响渗透率应力敏感性大小,最终影响页岩气井产气量。但关于水侵页岩应力敏感性的影响机理及表征尚无成熟的理论评价方法。鉴于此,建立了压裂液侵入对不同流动区域的页岩应力敏感性影响的物理模拟实验和理论表征方法,明确了页岩应力敏感性关于有效应力以及水侵程度的关联。研究结果表明,页岩初始应力敏感性系数与水侵程度呈线性正相关,而应力敏感性系数和有效应力呈线性负相关。当裂缝含水饱和度为0.90时,初始应力敏感性系数可线性增长约1倍,应力敏感性系数在高应力55 MPa作用下可线性降低17.86%,其渗透率损失5个数量级。另外,初始应力敏感性系数关于含水饱和度的变化率、应力敏感性关于有效应力的变化率与黏土矿物含量、黏土矿物吸水性能存在线性关系。

关键词: 无支撑裂缝, 应力加载, 水分侵入, 水侵膨胀变形, 应力敏感性