高温对深部储层横观各向同性页岩断裂特性的影响研究

    EFFECTS OF HIGH TEMPERATURE ON FRACTURE CHARACTERISTICS OF TRANSVERSELY ISOTROPIC SHALE IN DEEP RESERVOIRS

    • 摘要: 针对深部页岩气开发中的高温储层断裂特性演化问题,本研究基于离散元方法并结合热力学基本定律,建立了页岩断裂特性温度效应的数值表征方法,并考虑层理分布特征构建了横观各向同性页岩断裂热-力耦合数值模型,模拟了横观各向同性页岩在不同温度(23~200 ℃)和层理分布(正层理分布和上层理分布)下的断裂行为,系统分析了温度效应和层理效应对横观各向同性页岩断裂特性的协同调控机制。研究结果表明:高温诱发颗粒热膨胀与接触黏结失效,导致页岩断裂韧度近似线性衰减;层理面分布则主要通过弱面导向效应来主导断裂路径演化。正层理分布页岩断裂特性的温度效应和层理效应均强于上层理分布页岩,其断裂路径更多呈现沿层理面偏折、穿层延伸或被局部层理面引导的复合型断裂特征。上层理分布页岩相对稳定,在低层理角度和高温条件下更能维持较高韧度性能;而正层理分布页岩的层理面导控效应更强,在中高层理角度区间页岩的断裂韧度温度敏感性显著增强,高温更易诱发突变性断裂损伤。温度的升高会抑制微裂纹的穿层行为(剪切微裂纹主导)并增强层理弱面的引导效应(拉伸微裂纹主导),致使页岩断裂产生的拉伸微裂纹数量与剪切微裂纹数量之比增大。

       

      Abstract: To address the evolution of fracture characteristics in high-temperature reservoirs during deep shale gas development, this study developed a numerical method for the thermal effects on shale fracture characteristics based on the discrete element method (DEM) and fundamental thermodynamic principles, and further constructed a coupled thermo-mechanical fracture model for transversely isotropic shale by explicitly incorporating bedding distribution features. The model was used to simulate fracture processes under temperatures ranging from 23 ℃ to 200 ℃, considering two bedding configurations: front and upper bedding distributions. The study systematically analyzed the synergistic effects of temperature and bedding orientation on shale fracture characteristics. The results indicate that elevated temperatures induce thermal expansion of particles and progressive bond degradation, resulting in an approximately linear decline in fracture toughness. Bedding plane distribution plays a dominant role in guiding crack paths through weak-plane effects. Shale with front beddings exhibits stronger sensitivity to both thermal and structural factors than shale with upper beddings, leading to more complex fracture modes such as deflection along bedding planes, trans-bedding propagation, and localized mixed-mode fractures. In contrast, shale with upper beddings maintains relatively higher fracture toughness and stability under low bedding angles and high temperatures. For front bedding configurations, fracture toughness becomes significantly temperature-sensitive at medium-to-high bedding angles, where thermal effects can readily trigger abrupt structural damage. Furthermore, rising temperature suppresses the development of trans-bedding shear micro-cracks while enhancing tensile micro-cracks aligned with bedding planes. This results in an increased ratio of tensile to shear micro-cracks, indicating a shift in the dominant fracture mechanism with temperature. These findings provide new insights into the thermo-mechanical responses of transversely isotropic shale and offer theoretical support for the optimization of fracturing strategies in deep shale reservoirs.

       

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