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首页> 外文期刊>Pure and Applied Geophysics >Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities
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Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities

机译：通过反转弹性波速度来量化裂隙岩石的损伤，饱和度和各向异性

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摘要

Crack damage results in a decrease of elastic wave velocities and in the development of anisotropy. Using non-interactive crack effective medium theory as a fundamental tool, we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor, average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties. Using this same tool, we show that both the anisotropy and shear-wave splitting of elastic waves can be derived. Two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation, reaching up to 60% in the dry case. Comparison with experimental data on two granites, a basalt and a marble, shows that the range of validity of the non-interactive effective medium theory model extends to a total crack density of approximately 0.5, considering symmetries up to orthorhombic. In the isotropic case, Kachanov's (1994) non-interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions. Inversions are stable and give coherent results in terms of crack density and aperture evolution. Crack density variations can be interpreted in terms of crack growth and/or changes of the crack surface contact areas as cracks are being closed or opened respectively. More importantly, the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio (and therefore aperture) with pressure, which has broader geophysical implications, in particular on fluid flow. The recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure. In the anisotropic cases—both transverse isotropic and orthorhombic symmetries were considered—anisotropy and saturation patterns were well reproduced by the modelling, and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging.
机译：裂纹损伤会导致弹性波速度的降低和各向异性的发展。使用非交互式裂纹有效介质理论作为基本工具，我们根据固体密度和流体弹性特性，根据裂纹密度张量，平均裂纹纵横比和平均裂纹织物取向来计算裂纹岩石的干弹性和湿弹性。使用相同的工具，我们表明可以导出弹性波的各向异性和剪切波分裂。考虑了两个简单的裂纹分布，其预测的各向异性主要取决于饱和度，在干燥情况下可达60％。与玄武岩和大理石这两种花岗岩的实验数据比较表明，考虑到正交晶系的对称性，非交互式有效介质理论模型的有效范围扩展到大约0.5的总裂纹密度。在各向同性的情况下，使用Kachanov（1994）的非交互式有效介质模型来反转弹性波速度并推断裂纹密度和纵横比的演变。反演是稳定的，并且在裂纹密度和孔径变化方面给出一致的结果。裂纹密度的变化可以用裂纹扩展和/或在裂纹分别闭合或打开时裂纹表面接触面积的变化来解释。更重要的是，长宽比的恢复演变显示随着压力的增加，长宽比（并因此导致孔径）呈指数下降，这对地球物理的影响尤其是流体流动具有更广泛的意义。纵横比的恢复演变也与当前的裂纹闭合力学理论相一致。在各向异性情况下（考虑了横向各向同性和正交各向异性），通过建模可以很好地再现各向异性和饱和模式，并且我们恢复的平均裂缝织物取向与原位地球物理成像是一致的。

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