Occurrence and structural characterization of gas hydrates associated with a cold vent field, offshore Vancouver Island.

Lu, Hailong, Moudrakovski, I., Riedel, Michael , Spence, G., Dutrisac, R., Ripmeester, J., Wright, F. and Dallimore, S. (2005) Occurrence and structural characterization of gas hydrates associated with a cold vent field, offshore Vancouver Island. Journal of Geophysical Research - Solid Earth, 110 (B10). B10204. DOI 10.1029/2005JB003900.

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Abstract

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 ∼78% of the water in the massive samples was hydrate, down to a low value of ∼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.

Document Type: Article
Keywords: Gas hydrate; cold vent; Vancouver Island
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2005JB003900
ISSN: 0148-0227
Date Deposited: 25 Nov 2015 12:21
Last Modified: 25 Nov 2015 12:21
URI: http://oceanrep.geomar.de/id/eprint/30172

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