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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Mechanical prediction of fracture aperture in layered rocks
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Mechanical prediction of fracture aperture in layered rocks

机译：层状岩石裂隙孔径的力学预测

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Two types of opening-mode fractures (joints) are commonly found in layered rocks. One is called unconfined because fracture heights are much less than the layer thickness and they behave like fractures in massive rocks. The other is called confined because the fractures terminate at the layer boundaries. We investigate the mechanical control on apertures in these systems using the theory of elasticity. An analytical solution demonstrates that the ratio of aperture to height (aspect ratio) of an unconfined fracture in a homogeneous, isotropic medium is linearly related to the average strain, the overburden stress, and the internal fluid pressure within the fracture. Numerical results based on of the finite element method (FEM) for an unconfined fracture in the central layer of a three-layer model agree with the analytical result when the fractured layer and neighboring layers have the same elastic constants. The aspect ratio of the unconfined fracture is insensitive to the ratio of Young's modulus of the fractured layer to that of the neighboring layers and to the differences in Poisson's ratios. The FEM results for confined fractures show that their aspect ratio is linearly related to the average strain, the overburden stress, and the internal fluid pressure. However, the aspect ratio increases nonlinearly with increasing fracture spacing to layer thickness ratio because of the mechanical interaction between adjacent fractures. The interaction becomes insignificant when the spacing to layer thickness ratio is >similar to 6.0. The aspect ratio of confined fractures depends on the ratio of Young's modulus of the fractured layer to that of the neighboring layers. This dependence is significant when the fracture spacing to layer thickness ratio is < 1.3; otherwise, it is negligible. In all of these cases the aspect ratio of confined fractures is insensitive to variations in Poisson's ratios. Furthermore, the FEM results predict that fracture accommodated strain measured by the traditional scan line method may slightly overestimate the average normal strain when the spacing to layer thickness ratio is
机译：在层状岩石中通常会发现两种类型的开模裂缝（缝）。一种称为无限制的，因为裂缝高度远小于层厚度，并且它们的行为就像块状岩石中的裂缝一样。另一个被称为封闭的，因为裂缝终止于层边界。我们使用弹性理论研究了这些系统中孔的机械控制。一种分析解决方案表明，均质各向同性介质中无界限裂缝的孔径与高度之比（纵横比）与平均应变，上覆应力和裂缝内部的流体压力呈线性关系。当三层模型的中间层具有相同的弹性常数时，基于有限元方法（FEM）的三层模型中心层无边界裂缝的数值结果与分析结果相符。无限制裂缝的长宽比对裂缝层的杨氏模量与相邻层的杨氏模量之比以及泊松比之差不敏感。有限裂缝的有限元分析结果表明，其纵横比与平均应变，上覆应力和内部流体压力成线性关系。然而，由于相邻裂缝之间的机械相互作用，长宽比随着裂缝间距与层厚比的增加而非线性增加。当间距与层厚度之比> 6.0时，相互作用变得不明显。受限裂缝的长宽比取决于裂缝层的杨氏模量与相邻层的杨氏模量之比。当裂缝间距与层厚之比<1.3时，这种依赖性很明显。否则，可以忽略不计。在所有这些情况下，受限裂缝的纵横比对泊松比的变化不敏感。此外，有限元分析结果预测，当间距与层厚之比小于1.0时，用传统扫描线法测得的裂缝适应应变可能会略微高估平均法向应变，而对于更大的比率可能会略微低估该应变。 [参考：56]

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