PETROLEUM POTENTIAL OF YUKON FLATS, EAST-CENTRAL ALASKA

Some Tertiary sedimentary basins in central Alaska may contain oil and gas resources that could provide energy to rural Alaska villages and mines. Among the largest of these is the Yukon Flats basin, located along the Yukon River about 550 km northeast of Anchorage and about 150 km northeast of Fairbanks. The U.S. Geological Survey (USGS) recently evaluated the geology and undiscovered petroleum potential of this basin, which covers an area of about 35,000 sq km and 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 in the Yukon Flats basin are as thick as 8 km and are underlain by higher-density Devonian to Jurassic oceanic rocks. On the basis of shallow core hole penetrations and by analogy with nearby outcrops, the low-density strata are thought to consist mainly of Tertiary fluvial and lacustrine deposits. Geological and geochemical data from outcrops and shallow core holes suggest that potential source rocks of petroleum 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 and include some traps that possibly could contain hundreds of millions of barrels of oil or billions of cubic feet of gas.

No deep petroleum exploration wells have been drilled in Yukon Flats. A coalbed methane test drilled in 2005 at Fort Yukon reached a total depth of about 700 m and found coal with small amounts of biogenic methane. Preliminary information suggests that gas production from this well would require pumping of large volumes of water from the coal.

The lack of deep wells 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. Quantities of gas at or near this mean value, if found and developed, could provide energy to villages in Yukon Flats and could be transported via pipeline to Fairbanks and other population centers.