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Logging-while-drilling data acquired during the 2009 Gulf of Mexico (GoM) Gas Hydrate Joint Industry Project Leg II program combined with features observed in seismic data allow assessment of the depositional environment, geometry, and internal architecture of gas-hydrate-bearing sand reservoirs from three sites in the northern Gulf of Mexico (GoM): Walker Ridge 313, Alaminos Canyon 21, and Green Canyon 955. The site descriptions assist in the understanding of the geological development of gas-hydrate-bearing sands and in the assessment of their energy production potential. Three sand-rich units are described from the Walker Ridge site, including multiple ponded sand-bodies representing turbidite channel and associated levee and terminal lobe environments within the Terrebonne basin on the lower slope of the GoM. Older units display fewer but greater-reservoir-quality channel and proximal levee facies as compared to thinner, more continuous, and unconfined sheet-like sands that characterize the younger units, suggesting a decrease in depositional gradient with time in the basin. The three wells in the Green Canyon 955 site penetrated proximal levee sands within a previously recognized Late Pleistocene basin floor turbidite-channel-levee complex. Reservoirs encountered in GC955 exhibit thin-bedded internal structure and complex fault compartmentalization. Two wells drilled in the Alaminos Canyon 21 site tested a large, shallow, sand unit within the Diana mini-basin that exhibits steep lateral margins, non-sinuous elongate form, and flat base with hummocky upper surface. These features suggest deposition as a mass-transport deposit consisting of remobilized sand-rich turbidites or as a large basin-floor fan that was potentially eroded and buried by later-stage, mud-prone, mass-transport deposits. |
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