Fluid substitution effects on seismic anisotropy
Fluid substitution effects on seismic anisotropy
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DOI：
10.1002/2014jb011246
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发表时间：
2014-08
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影响因子：
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通讯作者：
L. Huang;R. Stewart;S. Sil;N. Dyaur
中科院分区：
文献类型：
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作者：
L. Huang;R. Stewart;S. Sil;N. Dyaur
我们推导出 HTI 和正交对称方程来分析多孔裂缝介质中的流体替代效应。推导基于各向异性加斯曼方程和线性滑移理论。我们评估了流体替代（天然气、盐水和石油）对弹性模量、速度、各向异性和方位振幅变化的影响。我们发现，在垂直于裂缝的方向上，对于气体到盐水的替代，纵波模量增加了 56%，纵波速度增加了 19%。对于平行于裂缝的方向，当孔隙度较低（5%）时，纵波速度几乎保持恒定，但如果孔隙度较高（25%），纵波速度可增加至 4%。由于两个不同方向的 P 波对流体和裂缝具有不同的敏感性，因此汤姆森参数（为 HTI 和斜方对称性定义）ε 和 δ 对流体类型和裂缝敏感。我们还发现，对于液体饱和度，δ 对孔隙度敏感，但对于气体饱和度，δ 对孔隙度不敏感。加斯曼假设（正如已经观察到的那样）剪切模量不依赖于流体。我们观察到不同流体的剪切波分裂（γ）没有变化。方位角振幅变化取决于流体类型、裂缝和孔隙度。我们观察到，盐水饱和后，低孔隙度含气砂的方位角振幅变化增加了 12%，而高孔隙度含气砂的方位角振幅变化减少了 6%。我们发现天然气替代石油的百分比变化约为天然气替代盐水情况的一半。我们推导出的方程提供了一个有用的工具来定量评估流体替代对地震各向异性的影响。
We derive equations for HTI and orthorhombic symmetries to analyze fluid substitution effects in porous fractured media. The derivations are based on the anisotropic Gassmann equation and linear slip theory. We assess the influence of fluid substitution (gas, brine, and oil) on elastic moduli, velocities, anisotropy, and azimuthal amplitude variations. We find that in the direction normal to fractures, P‐wave moduli increase as much as 56% and P‐wave velocity increases up to 19% for gas‐to‐brine substitution. For the direction parallel to fractures, P‐wave velocity remains almost constant when porosity is low (5%) but can increase up to 4% if porosity is high (25%). Since P‐waves in two different directions have different sensitivities to fluids and fractures, the Thomsen's parameters (defined for HTI and orthorhombic symmetries), ϵ and δ, are sensitive to fluid types and fractures. We also found that δ is sensitive to porosity for liquid saturation but insensitive to porosity for the case of gas saturation. Gassmann assumes (and as has been observed) that shear modulus does not depend on fluids. And we observe no changes in shear‐wave splitting (γ) for different fluids. The azimuthal amplitude variation is dependent on fluid types, fractures, and porosity. We observe up to 12% increase in azimuthal amplitude variation for low porosity gas sands after brine saturation and 6% decrease for high porosity gas sands. We find that the percentage changes in gas‐to‐oil substitution are about half that of the gas‐to‐brine case. The equations we have derived provide a useful tool to quantitatively evaluate the effects of fluid substitution on seismic anisotropy.