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Resource-Quality Gas Hydrates Discovered in Deepwater

In a landmark discovery, high saturations of natural gas hydrates have been discovered within reservoir-quality sands in the Lower Tertiary of the Gulf of Mexico (GOM), the Office of Fossil Energy's National Energy Technology Laboratory (NETL) reported Thursday.

The NETL, in collaboration with entities that included the U.S. Geological Survey (USGS), the Minerals Management Service (MMS) and an industry research consortium led by Chevron Corp., completed a 21-day gas hydrates drilling expedition, which uncovered the first two resource-quality marine gas hydrate deposits in the world. From the middle of April until early this month, the expedition team drilled seven wells in three locations: Walker Ridge, Green Canyon and Alaminos Canyon in water depths of 4,800-6,600 feet.

Three wells were drilled 3,500 feet below the seafloor at Walker Ridge, more than 1,000 feet deeper than any previous gas hydrate research wells. Two of the three wells at Walker Ridge uncovered the high saturation levels, NETL said. Some gas hydrate concentration was found in all but one of the wells drilled, NETL said.

The discovery "is very encouraging," said USGS research leader Timothy Collett. "We consider this expedition a major shift in our understanding...What's unique about the Gulf of Mexico accumulations identified is this: it's the first time we've seen highly concentrated hydrates in conventional sand reservoirs that could be commercially producible."

The GOM Gas Hydrate Joint Industry Project (JIP) Leg II expedition follows a 2005 JIP drilling program that focused on possible drilling hazards related to gas hydrates in fine-grained sediments. The latest expedition specifically targeted systems thought to include high-quality, or thick, porous and permeable, sands.

During the expedition, gas hydrates were found at saturations ranging from 50% to more than 90% in high-quality sands. The deposits also were discovered "in close accordance with the project's pre-drill predictions, providing increased confidence in the gas hydrate exploration and appraisal technologies," said NETL.

Hydrates were found in a variety of locations, including sand reservoirs, thick sequences of fracture-filling gas hydrates in shales, and potential partially saturated gas hydrates in younger systems. These sites, said researchers, provide a wealth of opportunities for further study and data collection to enable "significant advances in understanding the nature and development of gas hydrate systems."

Gas hydrates are composed of methane gas and water, and because of their natural abundance, they could become a significant new energy source. Earlier this year the USGS reported that gas hydrates were showing increasing promise (see NGI, April 13). However, before the recent expedition, there was little proof that gas hydrates occurred in resource-quality accumulations in the marine environment.

By 2025 researchers hope to determine the amount of producible gas hydrates in the United States, and whether gas hydrates should be added as an energy option, said NETL's Ray Boswell. He said the cooperation of government, industry and academia "was critical to the successful completion of this project." The expedition, he said, was completed on time with no incidents and below the planned $11.2 million budget.

JIP Leg II used an advanced suite of logging-while-drilling tools, which provided unprecedented 3-D images of hydrate-bearing sediments, said NETL. The MMS, AOA Geophysics and Schlumberger Ltd. provided the initial appraisals of the hydrate targets, and operations also were supported by the Borehole Research Group at Lamont-Doherty Earth Observatory of Columbia University.

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