Blake-Bahama Ridge Hydrate Assessment

1 Case Study 1 Leg 164 in the Blake-Bahama Ridge (Hydrate Assessment) 

The discussion in this section is exerpted from Leg 164 Scientific Party Report. The Ocean Drilling Program (ODP) Leg 164, represented a drilling effort in late 

Site 997 with a strong BSR on the ridge crest. Site 996 was drilled some distance away from the BSR, to investigate migration in a fault zone where methane was leaking from the rise. 

The hydrate recovered consisted of methane ( 99%), with minor to trace amounts of carbon dioxide (1.22%), ethane (86 ppmv), propane (2 ppmv), with a volumetric ratio of methane to water of 154. The chlorinity concentration (57.2 mM) of water collected indicated that the sample was a mixture of 10% pore water and 90% freshwater. The gas water ratio exceeded 170, higher than any previously reported for in situ hydrates. The C1/C2 ratio was 11,500, compared to a headspace value three times lower however, both gas ratios indicate biogenic gas. 

FIGURE 7.22a Chloride anomalies and acoustic and resistivity logs for Blake-Bahama Ridge site 994. (Paul et al., 1996. With permission.) 

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Chapter 7 discusses in situ hydrates in the oceans and permafrost. Seven key concepts are presented for hydrates in nature. These concepts are illustrated in four field case studies for hydrate assessment (Blake Bahama Ridge, Hydrate Ridge) and production (Messoyakha and Mallik, 2002). 

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