Sonic waveform attenuation in gas hydrate-bearing sediments from the Mallik 2L-38 research well, Mackenzie Delta, Canada
Sonic waveform attenuation in gas hydrate-bearing sediments from the Mallik 2L-38 research well, Mackenzie Delta, Canada
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DOI：
10.1029/2001jb000556
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发表时间：
2002-05
影响因子：
--
通讯作者：
G. Guérin;D. Goldberg
中科院分区：
文献类型：
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作者：
G. Guérin;D. Goldberg
[1]Mallik 2L-38研究井钻探至加拿大麦肯齐三角洲地下1150米处，钻入了冻土层以下，甲烷水合物占据了高达80%的孔隙空间。获得了一套高质量的井下测井资料，用于现场测量这些含水合物沉积物的物性。与其他水合物沉积类似，由于孔隙空间的电绝缘和沉积物骨架的硬化，随着水合物饱和度的提高，电阻率和纵切声速数据增加。此外，声波波形显示，在观察到甲烷水合物的区段中，纵波和横波的振幅损失都很大。我们使用单极子和偶极子波形来估计压缩和剪切衰减。与由电阻率测井得到的水合物饱和度值相比，我们观察到两种衰减量都随着水合物饱和度的增加而线性增加，这对硬化沉积物是不直观的。波形的数值模拟使我们能够再现记录的波形并说明这些结果。我们还使用冻结多孔介质中的波传播模型定性地解释了含水合物沉积物中声波波形幅度的损失。我们建议对该模型进行改进和扩展，使水合物饱和度可以根据相似环境中的衰减测量进行量化，并为了解水合物与其沉积物宿主的相互作用提供了新的见解。
[1] The Mallik 2L-38 research well was drilled to 1150 m under the Mackenzie Delta, Canada, and penetrated a subpermafrost interval where methane hydrate occupies up to 80% of the pore space. A suite of high-quality downhole logs was acquired to measure in situ the physical properties of these hydrate-bearing sediments. Similar to other hydrate deposits, resistivity and compressional and shear sonic velocity data increase with higher hydrate saturation owing to electrical insulation of the pore space and stiffening of the sediment framework. In addition, sonic waveforms show strong amplitude losses of both compressional and shear waves in intervals where methane hydrate is observed. We use monopole and dipole waveforms to estimate compressional and shear attenuation. Comparing with hydrate saturation values derived from the resistivity log, we observe a linear increase in both attenuation measurements with increasing hydrate saturation, which is not intuitive for stiffening sediments. Numerical modeling of the waveforms allows us to reproduce the recorded waveforms and illustrate these results. We also use a model for wave propagation in frozen porous media to explain qualitatively the loss of sonic waveform amplitude in hydrate-bearing sediments. We suggest that this model can be improved and extended, allowing hydrate saturation to be quantified from attenuation measurements in similar environments and providing new insight into how hydrate and its sediment host interact.