Understanding the relationship between dynamic and static mechanical properties of organic-rich shales is crucial for successful in situ stress profile prediction and hydraulic fracturing stimulation in unconventional reservoirs. However, the relationship between dynamic and static properties remains ambiguous, considering the complex rock microstructure and subsurface stress environment. We have reported pseudotriaxial tests on a pair of outcrop Eagle Ford shale plugs, with the axial load applied perpendicular and parallel to bedding planes, to investigate the effects of intrinsic anisotropy and anisotropic stress on dynamic-static relationships. The bedding-parallel Young’s modulus is larger than the bedding-normal one dynamically and statically, whereas there exist complex relations among three static Poisson’s ratios, which are attributed to the intrinsic anisotropy induced by the lenticular texture and finely laminated alignment of kerogen. Along with a stress increment, static tests respond to superpositions of the elastic, viscoelastic, and nonelastic properties, whereas dynamic tests, with more than two orders of magnitude smaller strain amplitude, only reflect the elastic properties of rocks. As a result, the static properties characteristically exhibit more stress dependence than the dynamic properties. Moreover, the evolutions of static properties, especially two static Poisson’s ratios in the horizontal plug, are significantly influenced by the applied stress orientation with respect to the bedding plane. Lastly, we calculate four independent stiffnesses using the five static mechanical parameters with the assumption of transverse isotropy to compare with those calculated from ultrasonic velocities at different stress levels. Finally, when the deviatoric stress is approximately 20 MPa, static parameters derived from stress loading, unloading, and reloading almost intersect together. At this stress level, dynamic and static stiffnesses demonstrate a reasonable correlation with the fitting coefficient of approximately 1.4.

中文翻译：

---

富含有机物的页岩的各向异性动，静态力学性能：应力的影响

理解富含有机物的页岩的动态和静态力学性能之间的关系对于非常规油藏成功进行现场应力分布预测和水力压裂增产至关重要。但是，考虑到复杂的岩石微观结构和地下应力环境，动，静特性之间的关系仍然不明确。我们已经对一对露头的Eagle Ford页岩塞进行了伪三轴试验，轴向载荷垂直于和平行于层理平面施加，以研究固有各向异性和各向异性应力对动静关系的影响。平行于动态的床层平行杨氏模量大于正常的床层杨氏模量，而三个静态泊松比之间存在复杂的关系，这归因于由透镜状结构和干酪根的精细叠层排列引起的固有各向异性。随着应力的增加，静态测试会响应弹性，粘弹性和非弹性特性的叠加，而动态测试的应变幅度要小两个数量级，只能反映岩石的弹性特性。结果，静态特性通常比动态特性表现出更多的应力依赖性。此外，静态特性的变化，尤其是水平栓塞中两个静态泊松比的变化，受到相对于层理面施加的应力方向的显着影响。最后，我们在假定横向各向同性的前提下，使用五个静态力学参数计算了四个独立的刚度，以与在不同应力水平下根据超声波速度计算的刚度进行比较。最后，当偏应力约为20 MPa时，源自应力加载，卸载和再加载的静态参数几乎会相交。在此应力水平下，动刚度和静刚度与约1.4的拟合系数表现出合理的相关性。