An estimated 2.4 trillion cubic feet of natural gas and 9.8 million bbl of natural gas liquids lie beneath eastern Oregon and Washington, the US Geological Survey said in late October.
The figures are mean estimates of undiscovered gas resources beneath approximately 60,000 square 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 that the Columbia River Basalt Group, ranging from 4,000 to 18,000 feet in thickness, overlies the Cretaceous Tertiary TPS in the area east of the Cascade Mountains. Volcanic rock units from the Miocene epoch through the Quaternary period overlie overlying the province's most southern part previously limited knowledge of that area's stratigraphy and structural geology, USGS said.
Within the hypothetical Columbia Basin Assessment Unit, which covers more than 4 million acres, the assessment team estimated that 2.1 Tcf of gas and 9.2 million bbl of NGLs 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 billion cubic feet, 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 NGLs. It said that 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.
It said that some 5,000-10,000 feet of arkosic sandstone, mudstone, lacustrine shale and coal which include potential source and reservoir rocks are known to be present beneath the basalt of North-Central Oregon and Central Washington. It indicated that the province's only discovered commercial gas accumulation is the abandoned Rattlesnake Hills gas field, which produced approximately 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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