Seismic velocities for hydrate-bearing sediments using weighted equation
Seismic velocities for hydrate-bearing sediments using weighted equation
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DOI：
10.1029/96jb01886
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发表时间：
1996-09-10
影响因子：
3.9
通讯作者：
Dillon, WP
中科院分区：
文献类型：
--
作者：
Lee, MW;Hutchinson, DR;Dillon, WP
应用基于三相时间平均和伍德方程的加权方程来推导压缩波（P波）速度与填充孔隙空间的水合物量之间的关系。该理论准确预测了孔隙度范围为 40-80% 的海洋沉积物的 P 波速度，并提供了利用地震速度估算原位水合物含量的实用方法。剪切（S）波速是在假设水合沉积物的纵波与横波速度比与沉积物组成成分的纵波与横波速度比的加权平均值成比例的情况下推导的。在所有组成部分已知的情况下，使用多相时间平均和伍德方程的加权方程是可能的。然而，这项研究表明，修正基质速度并补偿粘土含量的三相方程足以准确预测海洋沉积物的压缩波速度。该理论应用于永久冻土样本中纵波和横波速度的实验室测量，以推断松散沉积物中的冰量。该结果与重复应用两相波散射理论获得的结果相当。该理论预测，水合沉积物的泊松比随着水合物浓度的增加和孔隙度的减小而减小。因此，底部模拟反射的振幅与偏移量 (AVO) 数据可能会显示正、负或无 AVO 异常，具体取决于沉积物中水合物的浓度。
A weighted equation based on the three-phase time-average and Wood equations is applied to derive a relationship between the compressional wave (P wave) velocity and the amount of hydrates filling the pore space. The proposed theory predicts accurate P wave velocities of marine sediments in the porosity range of 40-80% and provides a practical means of estimating the amount of in situ hydrate using seismic velocity. The shear (S) wave velocity is derived under the assumption that the P to S wave velocity ratio of the hydrated sediments is proportional to the weighted average of the P to S wave velocity ratios of the constituent components of the sediment. In the case that all constituent components are known, a weighted equation using multiphase time-average and Wood equations is possible. However, this study showed that a three-phase equation with modified matrix velocity, compensated for the clay content, is sufficient to accurately predict the compressional wave velocities for the marine sediments. This theory was applied to the laboratory measurements of the P and S wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment. The results are comparable to the results obtained by repeatedly applying the two-phase wave scattering theory. The theory predicts that the Poisson's ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases. In consequence, the amplitude versus offset (AVO) data for the bottom-simulating reflections may reveal positive, negative, or no AVO anomalies depending on the concentration of hydrates in the sediments.