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The Characteristics of Gas Hydrate in Sediments Recovered from Mt. Elbert Gas Hydrate Stratigraphic Test Well, Milne Point, Alaska

Lu, Hailong 1; Moudrakovski, Igor L.1; Ripmeester, John A.1; Collett, Timothy S.2; Hunter, Robert B.3
1 Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, ON, Canada.
2 US Geological Survey, Denver, CO.
3 ASRC Energy Services, BP Exploration (Alaska), Inc., Anchorage, AK.

Two gas-hydrate-bearing core samples, BB Parr 16 (2180.58 - 2181.42 ft) and HY10 (2182.58 - 2183.00 ft), recovered from the Mount Elbert gas hydrate stratigraphic test well, Milne Point, Alaska, were examined to ascertain information on hydrate saturations, structure type, and gas composition. BB Parr 16 was kept in a pressure cell under a pressure of methane gas for 80 days and then transferred to liquid nitrogen for preservation, while HY 10 has been stored in liquid nitrogen after recovery. Gas hydrates were found to occur in the pores of medium sands with no visible hydrate identified.

The results obtained by Powder XRD, Raman and solid 13C NMR all indicate that the gas hydrates in the samples studied were all of structure I (sI) type, and the gas composition is predominantly methane.

The saturation level of gas hydrate in sediments (percent of pore volume occupied by gas hydrate) was estimated from the amount of gas released from sample when dissociated in the laboratory. It was found, that the saturation level changes from the edge to the center of both sediment cores. In BB Parr 16, it is 40% in the first 5 mm, then increases from 40 to 86% in the interval of 5-15 mm, and remains at 86% from 15 mm to the center; in HY 10, there was no hydrate in the first 2 mm, then increases from 0 to 52% in the interval of 2-17 mm, and it is almost constant at 52% from 17 mm to the center This distribution of hydrate saturation in the cores studied implies that hydrate experienced step-wise dissociation before sample preservation. Because BB Parr 16 had ever been preserved under a pressure of methane gas, the relatively high hydrate saturation in the surfacial layer of the core might have been caused by the secondary formation of methane hydrate during sample preservation.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009