ASSESSMENT OF UNDISCOVERED OIL AND GAS RESOURCES IN YUKON FLATS, EAST-CENTRAL ALASKA

The U.S. Geological Survey (USGS) recently assessed the undiscovered petroleum potential of Yukon Flats, a vast and remote lowland located along the Yukon River about 550 km northeast of Anchorage. The USGS assessed an area of about 35,000 sq km, within which the major landowners are the Federal and State governments and Native groups.

Seismic reflection, gravity, and magnetics indicate that low-density sedimentary strata beneath Yukon Flats are as thick as 8 km and are underlain by Devonian to Jurassic oceanic rocks. On the basis of shallow core hole penetrations and by analogy with outcrops near Yukon Flats, the low-density strata are thought to consist mainly of Tertiary fluvial and lacustrine deposits.

Although no petroleum exploration wells have been drilled in Yukon Flats, a coalbed methane test at Fort Yukon reached a total depth of about 700 m and found small amounts of biogenic methane. Geological and geochemical data from outcrops and shallow core holes suggest that potential source rocks in Yukon Flats include Tertiary nonmarine coal, mudstone, and shale, whereas potential reservoirs include Tertiary nonmarine sandstone and conglomerate. Many potential structural and stratigraphic traps are evident on seismic profiles.

The lack of deep well penetrations in Yukon Flats contributes to considerable uncertainty in resource assessment. The USGS estimates that undiscovered, technically recoverable oil resources range from zero to almost 600 million barrels (MMBO) with a mean of 173 MMBO and that undiscovered, technically recoverable gas resources range from zero to almost 15 trillion cubic feet (TCF) with a mean of about 5.5 TCF.

For comparison, these oil quantities are much less than recent USGS estimates for the National Petroleum Reserve-Alaska (NPRA) (6,700-15,000 MMBO) and for the Arctic National Wildlife Refuge (ANWR) 1002 area (5,700-16,000 MMBO). Gas quantities for Yukon Flats are much less than estimated for NPRA (40 to 85 TCF) and are similar to those estimated for ANWR (0 to 11 TCF). The mean estimate for undiscovered, technically recoverable gas in Yukon Flats (5.5 TCF) is similar to the cumulative gas production from Cook Inlet (6.4 TCF through 2003). These comparisons suggest that Yukon Flats is unlikely to rival NPRA or ANWR in oil resources but may, like Cook Inlet, hold significant amounts of gas.