During deep shale gas production, flowing water-based working fluid inevitably cools shale reservoirs around boreholes and some fractures, and possible extraction methods induce dynamic stresses. To understand the dynamic tensile behavior of deep anisotropic shale reservoir after water-based working fluid cooling, a split Hopkinson pressure bar was used for performing the dynamic Brazilian tests on shale samples with bedding angles of 0°, 30°, 45°, 60° and 90° after reservoir temperature realization (25–200 °C) and water cooling. The results illustrate that dynamic tensile strength of shale samples decreases gradually as reservoir temperature increases under the loading rates 100–1000 GPa/s. From room temperature to 200 °C the most strength deterioration appears on samples with the bedding angle of 90°. A dynamic tensile strength deterioration model for deep shale reservoirs after water-based working fluid cooling is proposed considering the influence of loading rate and bedding angle. Geometrical trajectories of the main failure cracks are separated into three types, i.e., fully central tensile failure, tensile-shear failure and fully shear failure (sliding of bedding planes). For samples with bedding angles of 30°, 45° and 60°, increasing reservoir temperature encourages tensile failure to change into shear failure. The roles that bedding planes play in interacting with failure crack growth are summarized as IP mode (intersecting propagation), TP mode (turning propagation) and PP mode (promoting propagation). Anisotropic dynamic tensile strength responses are systematically discussed by using thermal stress simulation in ABAQUS, microstructure analyses, crack interaction conditions and the one-dimensional stress wave propagation theory. Based on experimental observations, field implications in borehole stability and fracturing of deep shale reservoirs are proposed under medium and high loading rates. This work is instrumental in providing valuable information and technology assistance for real deep shale gas production projects.

中文翻译：

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深入了解水基工作液冷却后深层各向异性页岩储层动态拉伸行为


在深层页岩气生产过程中，流动的水基工作液不可避免地会冷却钻孔周围的页岩储层和一些裂缝，并且可能的提取方法会引起动态应力。为了了解水基工作液冷却后深层各向异性页岩储层的动态拉伸行为，采用分体式霍普金森压力棒对层理角度为0°、30°、45°、60°的页岩样品进行动态巴西试验。实现储层温度 (25–200 °C) 和水冷却后 90°。结果表明，在加载速率100~1000 GPa/s下，页岩样品的动态拉伸强度随着储层温度的升高而逐渐降低。从室温到200°C，层理角为90°的样品强度劣化最严重。考虑加载速率和层理角度的影响，提出了水基工作液冷却后深层页岩储层动态拉伸强度劣化模型。主要破坏裂纹的几何轨迹分为全中心拉伸破坏、拉剪破坏和全剪切破坏（层理面滑动）三种类型。对于层理角度为30°、45°和60°的样品，储层温度升高会促使拉伸破坏转变为剪切破坏。层理面在与失效裂纹扩展相互作用中所起的作用概括为IP模式（相交扩展）、TP模式（转动扩展）和PP模式（促进扩展）。利用ABAQUS中的热应力模拟、微观结构分析、裂纹相互作用条件和一维应力波传播理论，系统地讨论了各向异性动态拉伸强度响应。 基于实验观察，提出了中高加载速率下深层页岩储层井眼稳定性和压裂的现场影响。这项工作有助于为真正的深层页岩气生产项目提供有价值的信息和技术援助。