--> --> Abstract: Geochemical Evidence for Gas Hydrate Occurrences in Northern Alaska, by Thomas D. Lorenson and Timothy S. Collett; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Geochemical Evidence for Gas Hydrate Occurrences in Northern Alaska

Thomas D. Lorenson1; Timothy S. Collett2

(1) USGS, Menlo Park, CA.

(2) USGS, Denver, CO.

GGas hydrate deposits are common on the North Slope of Alaska in and around the Prudhoe Bay oil field complex, however the extent of these deposits is unknown for other areas in northern Alaska. As part of a USGS-BLM-industry collaboration, well cuttings hydrocarbon gases have been collected and analyzed from industry-drilled wells on the Alaska North Slope to prospect for gas hydrate deposits. Since 1983, 33 wells have been tested from the surface down to 2500-5000 ft. from as far west as Wainwright to Prudhoe Bay in the east. Regionally, the USGS has assessed the gas hydrate resources of the North Slope and determined that there is about 85.4 TCF of technically recoverable hydrate-bound gas within three petroleum systems, the systems are defined mainly by three separate stratigraphic intervals and constrained by the physical temperatures and pressures where gas hydrate can form. Geochemical studies of known gas hydrate occurrences on the North Slope have shown a link between gas hydrate and more deeply buried conventional oil and gas deposits. The link is established when hydrocarbon gases migrate from depth and charge the reservoir rock within the gas hydrate stability zone. It is likely gases migrated into conventional traps as free gas, and were later converted to gas hydrate in response to climate cooling concurrent with permafrost formation. Results from this study indicate that thermogenic gas is present in 29 of the wells, limited evidence of thermogenic gas in four wells, and one well with no thermogenic gas. Gas migration routes are common in the North Slope including faults and widespread, continuous, shallowly dipping delta foreset sands that are potentially in contact with deeper oil and gas sources. The application of this geologic model with the geochemical evidence suggests that gas hydrate deposits may be widespread across the North Slope of Alaska.