GEOLOGIC ASSESSMENT OF UNDISCOVERED HYDROCARBON RESOURCES OF THE WESTERN OREGON AND WASHINGTON PROVINCE

The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered, technically recoverable oil and gas resources of the Western Oregon and Washington Province, which includes all of Oregon and Washington north of the Klamath Mountains and west of the crest of the Cascade Range. The province extends offshore to the 3-mile limit of State waters on the west and to the International Boundary in the Straits of Juan de Fuca and Canada on the north, encompassing more than 51,000 mi².

The assessment of the Western Oregon and Washington Province was geology-based and used the total petroleum system (TPS) concept. The geologic elements of a TPS include hydrocarbon source rocks (source rock maturation and hydrocarbon generation and migration), reservoir rocks (quality and distribution), and traps for hydrocarbon accumulation. Using these geologic criteria, the USGS defined two conventional TPS and one unconventional (continuous) TPS, each with one assessment unit (AU). These are (1) the Cretaceous-Tertiary TPS and the Western Oregon and Washington Conventional Gas AU; (2) the Tertiary Marine TPS and the Tertiary-Marine Gas AU; and (3) the Tertiary Coalbed Gas TPS and the Eocene Coalbed Gas AU.

Currently, the only hydrocarbon production within the province is from the Mist Gas Field in northwestern Oregon that was discovered in May 1979 and has produced about 65 billion cubic feet of gas (BCFG) from upper Eocene Cowlitz Formation reservoirs through 2008.

The USGS assessed both conventional oil and gas and continuous (unconventional) coalbed gas in the Western Oregon and Washington Province, resulting in estimated total means of 2.2 trillion cubic feet of gas (TCFG) and 15 million barrels of oil (MMBO). Within the Western Oregon-Washington Conventional Gas AU, the USGS estimated a mean volume of 454 BCFG. An estimated mean volume of 15 MMBO of conventional oil and 725 BCFG is in the Tertiary Marine AU. More than 67 percent of the gas (1.5 TCFG) is contained within the hypothetical Eocene Coalbed Gas AU. In this AU the Eocene coals serve as both source rock and reservoir.