Acoustic properties of gas hydrate-bearing consolidated sediments and experimental testing of elastic velocity models
Acoustic properties of gas hydrate-bearing consolidated sediments and experimental testing of elastic velocity models
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DOI：
10.1029/2008jb006160
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发表时间：
2010-02-20
影响因子：
3.9
通讯作者：
Wang, Jia S.
中科院分区：
文献类型：
--
作者：
Hu, Gao W.;Ye, Yu G.;Wang, Jia S.
尽管弹性速度(V-p、V-S)可以用来现场评估海洋天然气水合物的分布和浓度，而且现有的几个模型将水合物饱和度与声速联系起来，但由于难以确定完整的含水合物沉积物的水合物饱和度和速度，这些模型的准确性不确定。本文对含天然气水合物的固结沉积物的声学特性进行了实验研究。在一个含水人造岩心中，用时间域反射法和超声波法分别测量了天然气水合物形成过程中的水合物饱和度(S H)和声速。当水合物饱和度较低时(0%~接近10%)，声速变化不大，当水合物饱和度在10%~30%之间时，声速迅速增加。我们验证了两个常用的模型，即加权方程(WE)和Lee修正的Biot-Gassmann理论(BGTL)。在0%~40%水合物饱和度范围内，WE模型与V-p实测值吻合较好，而结合BGTL中的WE和V-p/V-S比值预测的V-P-P与实测值相对应。但是，当水合物饱和度大于30%时，BGTL更适合于预测V-p和V-S。这表明，当水合物饱和度超过30%时，天然气水合物可被视为固结沉积物基质中的一个组分。当S-h小于30%时，水合物位于孔隙流体中或部分附着在沉积物骨架上。
Although elastic velocities (V-p, V-s) can be used to assess the distribution and concentration of marine gas hydrates in situ and several existing models relate hydrate saturation to acoustic velocity, the accuracy of these models is uncertain because of the difficulty in determining hydrate saturations and velocities of intact hydrate-bearing sediments. In this paper, the acoustic properties of gas hydrate-bearing consolidated sediments were investigated experimentally. Hydrate saturation (S-h) and acoustic velocities were measured in one system by time domain reflectometry and ultrasonic methods, respectively, during gas hydrate formation and subsequent dissociation in a water-saturated artificial core. Acoustic velocities change little at low hydrate saturations (0% to similar to 10%), whereas they increase rapidly when hydrate saturation is between 10% and 30%. We verified two commonly used models, i.e., the weighted equation (WE) and the Biot-Gassmann theory modified by Lee (BGTL). In the 0% to 40% hydrate saturation range, the WE model is consistent with the measured V-p data, while a combination of the WE and the V-p/V-s ratio in the BGTL predicts V-s corresponding to the observed data. As hydrate saturation is more than 30%, however, the BGTL is more suitable for predicting both V-p and V-s. This suggests that gas hydrate may be treated as a component within a matrix of consolidated sediments when hydrate saturation exceeds 30%. However, when S-h is less than 30%, the hydrate locates in the pore fluid or partly adheres to the sediment frame.