Attenuation of seismic waves in methane gas hydrate‐bearing sand
Attenuation of seismic waves in methane gas hydrate‐bearing sand
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DOI：
10.1111/j.1365-246x.2005.02831.x
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发表时间：
2006
影响因子：
2.8
通讯作者：
J. Priest;A. Best;C. Clayton
中科院分区：
文献类型：
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作者：
J. Priest;A. Best;C. Clayton
利用远程地震方法的纵波（P波）和横波（S波）速度（Vp和Vs）来推断海洋沉积物中天然气水合物的分布和体积。地震方法的最新进展现在可以测量纵波和横波衰减（分别为Q1p和Q1s）。然而，由于我们对天然气水合物对物理性质影响的理解有限，对这些数据的解释存在问题。因此，开发了实验室天然气水合物共振柱，模拟砂样中甲烷天然气水合物形成的压力和温度条件，并在与海洋地震调查相关的频率和应变下测量Q1p和Q1s。研究了13个干砂（含气饱和）样品，每个样品中均匀分布着不同量的甲烷天然气水合物。结果表明，对于这些干燥样品，Q1p和Q1s对水合物饱和度高度敏感，在3%至5%的水合物饱和度之间观察到意想不到的峰值。人们认为，颗粒接触处的水合物水泥和水合物本身的纳米孔隙度增强了孔隙空间内吸收的水或自由气体的粘性喷射流动。这些结果首次揭示了甲烷天然气水合物对砂土中地震波衰减的显著影响，并为地震波的传播机制提供了新的见解。这些结果将有助于解释利用海洋地震勘探方法获得的弹性波衰减数据。
Compressional wave (P wave) and shear wave (S wave) velocities (Vp and Vs, respectively) from remote seismic methods have been used to infer the distribution and volume of gas hydrate within marine sediments. Recent advances in seismic methods now allow compressional and shear wave attenuations (Q1p and Q1s, respectively) to be measured. However, the interpretation of these data is problematic due to our limited understanding of the effects of gas hydrate on physical properties. Therefore, a laboratory gas hydrate resonant column was developed to simulate pressure and temperature conditions suitable for methane gas hydrate formation in sand specimens and the subsequent measurement of both Q1p and Q1s at frequencies and strains relevant to marine seismic surveys. 13 dry (gas saturated) sand specimens were investigated with different amounts of methane gas hydrate evenly dispersed throughout each specimen. The results show that for these dry specimens both Q1p and Q1s are highly sensitive to hydrate saturation with unexpected peaks observed between 3 and 5 per cent hydrate saturation. It is thought that viscous squirt flow of absorbed water or free gas within the pore space is enhanced by hydrate cement at grain contacts and by the nanoporosity of the hydrate itself. These results show for the first time the dramatic effect methane gas hydrate can have on seismic wave attenuation in sand, and provide insight into wave propagation mechanisms. These results will aid the interpretation of elastic wave attenuation data obtained using marine seismic prospecting methods.