Comparative review of theoretical models for elastic wave attenuation and dispersion in partially saturated rocks
Comparative review of theoretical models for elastic wave attenuation and dispersion in partially saturated rocks
复制标题
DOI：
10.1016/j.soildyn.2006.01.008
复制
发表时间：
2006-06
影响因子：
4
通讯作者：
J. Toms;T. Müller;R. Cíz;B. Gurevich
中科院分区：
文献类型：
--
作者：
J. Toms;T. Müller;R. Cíz;B. Gurevich
具有两种流体混合物的多孔岩石的饱和度（称为部分饱和度）对通过这些岩石传播的地震波具有实质性影响。特别地，部分饱和由于波引起的流体流动而导致传播波的显著衰减和分散。当通过的波在被不同流体饱和的岩石区域中引起不同的流体压力时，这种流动就产生了。由于部分流体饱和可以发生在不同的长度尺度上，由于波引起的流体流动的衰减是普遍存在的。特别是，介观流体流动，由于非均匀性发生在一个规模大于孔隙尺度，但小于波长尺度，是负责从10到1000赫兹的频率范围内的显着衰减。由于介观不均匀性的衰减和色散的大多数模型意味着流体不均匀性以周期性/规则的方式分布。在1D中，这对应于周期性交替的分层，在3D中，作为给定形状的周期性分布的夹杂物（通常是球体）。所有这些模型产生非常相似的衰减和色散估计。实验研究表明，介观非均匀性有不太理想的分布和分布本身的影响衰减和色散。因此，需要理论模型来模拟更一般和更现实的流体分布的影响。我们已经开发了两个理论模型来模拟介观流体不均匀性的随机分布的影响。第一种模型假设一种流体在被另一种流体饱和的多孔介质中形成球形夹杂物的随机系综。该模型预测的衰减和色散与三维周期分布的预测结果非常相似。对于两种分布，衰减（逆品质因数）在低频时与ω成比例。这与1D情况相反，其中随机和周期性交替分层在低频下显示不同的衰减行为。第二个模型，它假设一个三维连续分布的流体不均匀性，也预测相同的低频渐近线的衰减。然而，衰减的频率依赖性的形状是不同的。由于3D连续随机方法假设将存在不同斑块大小的分布，因此预计它更适合于模拟实验结果。需要进一步的研究，以揭示如何将随机函数与实验上重要的参数联系起来。
Saturation of porous rocks with a mixture of two fluids (known as partial saturation) has a substantial effect on the seismic waves propagating through these rocks. In particular, partial saturation causes significant attenuation and dispersion of the propagating waves, due to wave-induced fluid flow. Such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids. As partial fluid saturation can occur on different length scales, attenuation due to wave-induced fluid flow is ubiquitous. In particular, mesoscopic fluid flow due to heterogeneities occurring on a scale greater than porescale, but less than wavelength scale, is responsible for significant attenuation in the frequency range from 10 to 1000Hz. Most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a periodic/regular way. In 1D this corresponds to periodically alternating layering, in 3D as periodically distributed inclusions of a given shape (usually spheres). All these models yield very similar estimates of attenuation and dispersion. Experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion. Therefore, theoretical models are required which would simulate the effect of more general and realistic fluid distributions. We have developed two theoretical models which simulate the effect of random distributions of mesoscopic fluid heterogeneities. The first model assumes that one fluid forms a random ensemble of spherical inclusions in a porous medium saturated by the other fluid. The attenuation and dispersion predicted by this model are very similar to those predicted for 3D periodic distribution. Attenuation (inverse quality factor) is proportional to ω at low frequencies for both distributions. This is in contrast to the 1D case, where random and periodically alternating layering shows different attenuation behaviour at low frequencies. The second model, which assumes a 3D continuous distribution of fluid heterogeneities, also predicts the same low-frequency asymptote of attenuation. However, the shapes of the frequency dependencies of attenuation are different. As the 3D continuous random approach assumes that there will be a distribution of different patch sizes, it is expected to be better suited to modelling experimental results. Further research is required in order to uncover how to relate the random functions to experimentally significant parameters.