DOI: Alaskan North Slope Gas Hydrates Hold Large U.S. Deposits of Technically Recoverable Natural Gas

November 24, 2008 // Published as a news service by IHS

Further research, including long-term production tests, are needed to demonstrate gas hydrates as an economically producible resource, said DOI.

The USGS assessment is the first resource estimate of technically recoverable natural gas hydrates, which are naturally occurring, ice-like solids in which water molecules trap natural gas molecules in a cage-like structure known as a clathrate.

The USGS estimates that the 85.4 TCF of gas accounts for 11.5% of the volume of gas within all other undiscovered, technically recoverable gas resources onshore and in the state waters of the U.S.

"Technically recoverable" means the resource can be discovered, developed and produced using current technology and industry practices.

The world currently consumes about 104 TCF of natural gas a year and the U.S. uses about 23 TCF of natural gas per year, according to the Energy Information Administration (EIA).

Other USGS assessments of undiscovered, technically recoverable natural gas resources (not gas hydrates) estimate that the Wyoming Basin holds 85 TCF; the National Petroleum Reserve in Alaska holds 73 TCF; the Western Gulf Basin in Texas holds 71 TCF; and the San Juan Basin in New Mexico and Colorado holds 50 TCF. Conventional, undiscovered, technically recoverable gas resources on the Alaskan North Slope are estimated at 119.15 TCF.

Among the various techniques for production of natural gas from gas hydrates, depressurization appears to be the most promising method, said DOI. This involves changing the pressure of the hydrate accumulation, which changes the resource from a solid state into components of gas and water that can be produced to the surface. Depressurization was the only production technique assessed in this estimate.

The area assessed in northern Alaska extends from the National Petroleum Reserve in Alaska on the west through the Arctic National Wildlife Refuge on the east and from the Brooks Range northward to the state-federal offshore boundary (located three miles north of the coastline).

Of the estimated 85.4 TCF of gas within hydrates on the Alaskan North Slope, 56% occurs on federally managed lands, 39% on lands and offshore waters managed by the state of Alaska and 4% on Native Alaskan lands. The assessment of the potential gas hydrate resources on the federally managed offshore regions of northern Alaska is being conducted by the Minerals Management Service.

The mean estimate of 85.4 TCF of gas within the gas hydrates of northern Alaska is considerably less than the 590 TCF reported in the 1995 USGS assessment of domestic natural gas hydrates. This difference is because the 1995 assessment included all volumes of gas, whereas this assessment deals only with technically recoverable gas.

Also, the 1995 assessment included offshore federal waters of Alaska, which were not included in this assessment. The approach used to assess the gas hydrate resources in northern Alaska followed current standard geology-based USGS assessment methodologies developed to assess conventional oil and gas resources, said DOI.

The research project in support of this assessment was a cooperative effort with the Bureau of Land Management (BLM), who provided the geologic and geophysical datasets of the Alaskan North Slope. Both USGS and BLM are agencies of DOI.

To learn more about USGS research on natural gas hydrates and to see results of the gas hydrate assessment in northern Alaska visit the USGS Energy Resources web site.

Source: U.S. Department of the Interior (DOI).