Influence of heterogeneous hydrate distribution on the compressional wave velocity of hydrate-bearing sediment specimens
Influence of heterogeneous hydrate distribution on the compressional wave velocity of hydrate-bearing sediment specimens
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DOI：
10.1016/j.jngse.2014.11.021
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发表时间：
2015
影响因子：
--
通讯作者：
L. Yongjiang;Jianming Peng;Lina Peng;He Jiangfu;Lijia Li
中科院分区：
文献类型：
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作者：
L. Yongjiang;Jianming Peng;Lina Peng;He Jiangfu;Lijia Li
本文报告了对用孔隙中的天然气水合物代替冰纯水的样本进行的一系列压缩波速测试的结果。在这些样品中，通过将含冰样品分成高饱和度和低饱和度部分，以模拟实验室合成含水合物沉积物样品期间样品一侧的水合物积累，冰呈不均匀分布。调整高饱和度段和低饱和度段的长度来模拟合成的含水合物沉积物样品的不同程度的局部积累。采用直接和间接测量方法研究了含冰试件在5%饱和度梯度下从15%到40%的计算饱和度。采用超声波测量来确定压缩波速，结果表明，多孔样品中冰的不均匀分布显着影响含冰样品的压缩波速，特别是对于低饱和度样品。压缩波速随着高饱和度段长度的增加而增大，在30%计算饱和度时，压缩波速最大差值达到0.247 km/s（直接测量）和0.199 km/s（间接测量）。这种差异导致使用胶结理论模型的含冰样品饱和度的不确定性超过 20%。因此，水合物的不均匀分布导致含水合物沉积物样品压缩波速的测量误差较大。利用实验室数据修正后的水合物饱和度和压缩波速相应模型来解释声波测井数据和地震数据，在估算天然气水合物地层水合物饱和度时可能会出现较大误差。
This paper reports the results of a series of compressional wave velocity tests on specimens in which gas hydrate in the pores are substituted for iced pure water. In these specimens, ice is heterogeneously distributed by separating the ice-bearing sample into high- and low-saturation segments to simulate hydrate accumulation on one side of the specimen during synthesis of the hydrate-bearing sediment samples in laboratory. The length of high- and low-saturation segment was adjusted to simulate the different degrees of local accumulation of the synthesized hydrate-bearing sediment samples. The calculated saturation of the ice-bearing specimen from 15% to 40% with 5% saturation gradient was studied by the direct and indirect measurement methods. Ultrasonic measurements were performed to determine the compressional wave velocities, and results show that the heterogeneous distribution of ice in porous specimen remarkably influences the compressional wave velocity of the ice-bearing sample, especially for low-saturation samples. The compressional wave velocity increases with the increasing of the length of high saturation segment, and the maximum difference of the compressional wave velocity is up to 0.247 km/s (direct measurement) and 0.199 km/s (indirect measurement) at 30% calculated-saturation. This difference causes >20% uncertainty in the saturation of the ice-bearing sample using the Cementation Theory Model. Thus, the heterogeneous distribution of hydrate leads to a considerable measurement error for the compressional wave velocity of hydrate-bearing sediment sample. A larger error could occur during the estimation of hydrate saturation in the natural gas hydrate-bearing stratum, when the corresponding model of the hydrate saturation and compressional wave velocity corrected by the laboratory data are used to interpret the sonic logging data and seismic data.