Nick Snow
Washington Editor
WASHINGTON, DC, Oct. 30 -- An estimated 2.4 tcf of natural gas and 9.8 million bbl of natural gas liquids lie beneath eastern Oregon and Washington, the US Geological Survey reported in late October.
The figures are mean estimates of undiscovered gas resources beneath 60,000 sq miles of the two Pacific Northwest states. A USGS team conducted a geology-based assessment using the total petroleum system approach, the US Department of the Interior agency said. The work was done in 2006, but specific figures were not released until recently, a spokeswoman said.
The report said the Columbia River Basalt Group, 4,000-18,000 ft in thickness, overlies the Cretaceous Tertiary total petroleum system in the area east of the Cascade Mountains. Volcanic rock units from the Miocene epoch through the Quaternary period overlying the province's most southern part had previously limited knowledge of that area's stratigraphy and structural geology, USGS said.
Within the hypothetical Columbia basin assessment unit (AU), which covers more than 4 million acres, the assessment team estimated that 2.1 tcf of gas and 9.2 million bbl of NGL are in Tertiary rocks beneath the Columbia River basalt, according to the report. The largest undiscovered gas field within the AU holds a mean estimate of 362.9 bcf, it added.
In a second area, the hypothetical Eastern Oregon and Washington conventional gas AU covering more than 22.2 million acres, the report listed a mean estimate of 300 bcf of conventional gas and 610,000 bbl of NGL. It said the estimated mean size of the AU's largest undiscovered gas field is 78.3 bcf.
The report said that the assessment team identified a third area, the Republican Graben Gas AU, but did not quantitatively assess it.
Known to be present beneath the basalt of North-Central Oregon and Central Washington are some 5,000-10,000 ft of arkosic sandstone, mudstone, lacustrine shale, and coal, which include potential source and reservoir rocks, are. The report indicated that the province's only discovered commercial gas accumulation is the abandoned Rattlesnake Hills gas field, which produced about 1.3 bcf.
"Numerous other gas shows are known within the province, but as of 2006, there have been no new commercial accumulations found," the report said.
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