Fracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result in large and disparate reductions in P and S wave velocities with negligible porosity development, which breaks the classic velocity-porosity relationship. Properly interpreting these signatures in seismic surveys from stimulated geothermal, oil, and gas reservoirs or seismogenic areas requires a rock physics model that uses realistic elastic properties of fractures. Conventional models for cracked rocks employ specific inclusion shapes such as spheroids with small aspect ratios. However, all these exhibit the same normal-to-shear compliance ratio—regardless of aspect ratio—and therefore impact the bulk and shear moduli in the same qualitative way. As such they are inadequate for describing many of the complementary evolutions of P and S wave velocities that transpire with the generation of cracks. Using a differential model of dimensionless compliances, we analyze published velocities for granite, basalt, and limestone to quantify typical compliance ratios and find that they are often different from those assumed in conventional crack models, which then affects crack density estimates. We also investigate how the total normal and shear compliances change due to certain thermo-hydro-chemo-mechanical processes that generate large crack densities, and conclude that the final ratios often still deviate from that of conventional models. Finally, we demonstrate how the model can be used to describe scatter in both P and S wave velocity-porosity trends. Implications for energy extraction and seismic monitoring are discussed.

中文翻译：

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评估由热-水-化学-机械过程损坏的低孔隙度岩石中的裂纹诱导柔顺性

裂缝几何形状、密度和分布控制低孔隙度岩石中的流体和热传输，以及它们的地震属性。整个基体中裂纹的产生会导致P和S 的大量和不同的减少孔隙度发展可忽略不计的波速度，这打破了经典的速度-孔隙度关系。在来自受激地热、石油和天然气储层或发震区的地震勘测中正确解释这些特征需要使用裂缝的真实弹性特性的岩石物理模型。裂纹岩石的传统模型采用特定的包裹体形状，例如具有小纵横比的球体。然而，所有这些都表现出相同的法向与剪切柔量比 - 无论纵横比如何 - 因此以相同的定性方式影响体积和剪切模量。因此，它们不足以描述P和S 的许多互补演化随着裂缝的产生而发生的波速。我们使用无量纲柔量的微分模型，分析了花岗岩、玄武岩和石灰石的公布速度，以量化典型的柔量比，并发现它们通常与传统裂纹模型中假设的不同，从而影响裂纹密度估计。我们还研究了总法向和剪切柔量如何因某些产生大裂纹密度的热-水-化学-机械过程而变化，并得出结论，最终比率通常仍与传统模型的比率不同。最后，我们演示了如何使用该模型来描述P和S 中的散射波速-孔隙度趋势。讨论了对能量提取和地震监测的影响。