Occurrence and structural characterization of gas hydrates associated with a cold vent field, offshore Vancouver Island
Occurrence and structural characterization of gas hydrates associated with a cold vent field, offshore Vancouver Island
复制标题
DOI：
10.1029/2005jb003900
复制
发表时间：
2005-10-20
影响因子：
3.9
通讯作者：
Dallimore, S
中科院分区：
文献类型：
--
作者：
Lu, HL;Moudrakovski, I;Dallimore, S
通过宏观观测和仪器分析（粉末X射线衍射法（PXRD）、核磁共振（NMR）和拉曼光谱）对温哥华岛近海冷喷口天然气水合物样品进行了详细研究。结果表明，在2.64 ~ 2.94 m的深度范围内，天然气水合物呈块状，在4.60 ~ 4.81 m的深度范围内，水合物呈长条状、结节状和板状，在5.48 ~ 5.68 m的深度范围内，水合物呈脉状，呈现出随深度增加水合物含量逐渐减少的趋势。所有样品由PXRD、NMR和拉曼光谱确定为结构I水合物。根据NMR和拉曼分析结果，由笼状位点上的甲烷分布确定，水合数估计为平均6.1 +/-0.2。对转化水平的估计表明，块状样品中近似78%的水是水合物，对于孔隙水合物样品，其值低至近似0.4%。结果进行了比较与合成水合物和样品从下面的永久冻土上Mallik网站的测量。合成和天然样品的甲烷含量和晶格参数的差异相对较小。还需要开展更多的工作，以解决天然水合物样品中微量气体成分的存在和不均匀性问题。
Gas hydrate samples recovered from a cold vent field offshore Vancouver Island were studied in detail both by macroscopic observations and instrumental methods (powder X-ray diffraction method (PXRD), nuclear magnetic resonance (NMR), and Raman spectroscopy). It was found that gas hydrates were massive from 2.64 to 2.94 m below seafloor (mbsf), elongated, nodular and tabular from 4.60 to 4.81 mbsf, and vein-like from 5.48 to 5.68 mbsf, showing a trend of decreasing hydrate content with increasing depth. All samples were determined to be structure I hydrate from PXRD, NMR, and Raman spectroscopies. The hydration numbers were estimated to be 6.1 +/- 0.2 on average as determined from the methane distribution over the cage sites from NMR and Raman analytical results. Estimates of conversion levels indicated that similar to 78% of the water in the massive samples was hydrate, down to a low value of similar to 0.4% for the pore hydrate samples. The results are compared with measurements on synthetic hydrates and samples recovered from below the permafrost on the Mallik site. Differences in methane content and lattice parameters for synthetic and natural samples are relatively minor. Additional work is needed to address the presence of minor gas components and the heterogeneity of natural hydrate samples.