Seismoelectric wave propagation numerical modelling in partially saturated materials
Seismoelectric wave propagation numerical modelling in partially saturated materials
复制标题
DOI：
10.1093/gji/ggt198
复制
发表时间：
2013-09
影响因子：
2.8
通讯作者：
S. Warden;S. Garambois;L. Jouniaux;D. Brito;P. Sailhac;C. Bordes
中科院分区：
文献类型：
--
作者：
S. Warden;S. Garambois;L. Jouniaux;D. Brito;P. Sailhac;C. Bordes
为了更好地理解和解释在包气环境下获得的地电测量，现有的理论和适用于饱和材料的波传播模拟程序都应该扩展到部分饱和条件。在这里，我们提出了Pride方程的一个扩展，目的是在水-空气混合物的情况下考虑部分饱和的材料。这组新的方程被合并到现有的地震电波传播建模程序中，该程序最初是为分层饱和介质设计的。这种扩展既涉及机械部分，使用Biot-Gassmann理论的推广，也涉及电磁部分，对于电磁部分，介质介电常数和电导率与含水饱和度有关。利用从最近的实验室或理论研究中得出的四个不同的关系式，将动态地震电耦合写成取决于饱和度的流动电势系数的函数。在第二部分中，这一扩展程序被用来合成层状介质的地电响应，该层状介质由饱和砂岩半空间顶部的部分饱和砂层覆盖组成。随后对模拟幅度的分析表明，当浅层表现出低饱和度时，通常非常弱的界面响应(IR)可能是最好的恢复。我们还用我们的程序计算了渗流砂层和饱和砂半空间之间的毛细条纹的地电响应。我们的初步模拟结果表明，对地电红外的研究可能有助于探测到比平滑的饱和转变更好的鲜明的饱和对比度。在我们的例子中，完全饱和的砂半空间和部分饱和的浅砂层之间50%的饱和度对比产生了比饱和度逐步降低更强的IR。
To better understand and interpret seismoelectric measurements acquired over vadose environments, both the existing theory and the wave propagation modelling programmes, available for saturated materials, should be extended to partial saturation conditions. We propose here an extension of Pride's equations aiming to take into account partially saturated materials, in the case of a water-air mixture. This new set of equations was incorporated into an existing seismoelectric wave propagation modelling code, originally designed for stratified saturated media. This extension concerns both the mechanical part, using a generalization of the Biot-Gassmann theory, and the electromagnetic part, for which dielectric permittivity and electrical conductivity were expressed against water saturation. The dynamic seismoelectric coupling was written as a function of the streaming potential coefficient, which depends on saturation, using four different relations derived from recent laboratory or theoretical studies. In a second part, this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half-space. Subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response (IR) may be best recovered when the shallow layer exhibits low saturation. We also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half-space. Our first modelling results suggest that the study of the seismoelectric IR may help to detect a sharp saturation contrast better than a smooth saturation transition. In our example, a saturation contrast of 50 per cent between a fully saturated sand half-space and a partially saturated shallow sand layer yields a stronger IR than a stepwise decrease in saturation.