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Assessment of Technically Recoverable Gas Hydrate Resources from the North Slope of Alaska

Collett, Timothy S.1
1 US Geological Survey, Denver, CO.

The U.S. Geological Survey (USGS) has completed the first assessment of the undiscovered, technically recoverable gas-hydrate resources beneath the North Slope of Alaska. This assessment indicates the existence of technically recoverable gas-hydrate resources—that is, resources that can be discovered, developed, and produced using current technology. The assessment is based on the geologic elements used to define a Total Petroleum System (TPS), including hydrocarbon source rocks (source-rock type and maturation and hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy, petrophysical properties, seismic attribute development, and prospecting), and hydrocarbon traps (trap formation and timing). For the first time, the USGS has assessed gas hydrates, a traditionally unconventional resource with no confirmed production history, as a producible resource occurring in discrete hydrocarbon traps and structures. The approach used to assess the gas hydrate resources in northern Alaska followed standard geology-based USGS assessment methodologies developed to assess conventional oil and gas resources. In order to use the USGS conventional assessment approach on gas hydrate resources, it was documented through the analysis of three-dimensional industry-acquired seismic data that the gas hydrates on the North Slope occupy limited, discrete volumes of rock bounded by faults and downdip water contacts. The USGS conventional assessment approach also assumes that the hydrocarbon resource being assessed can be produced by existing conventional technology. The production potential of the known and seismically-inferred gas hydrate accumulations in northern Alaska has not been adequately field tested. Although verified by only limited field testing, numerical production models of gas hydrate-bearing reservoirs suggest that gas can be produced from gas hydrate with existing conventional technology. Using a geology-based assessment methodology, the USGS has estimated the total undiscovered technically recoverable natural gas resources in gas hydrates in northern Alaska. For the Northern Alaska Gas Hydrate TPS, the USGS estimates that the total undiscovered natural gas resources in gas hydrate range between 25.2 and 157.8 trillion cubic feet (TCF; 95-percent and 5-percent probabilities of greater than these amounts, respectively), with a mean estimate of 85.4 TCF.


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