Since 1960 the outer continental shelf off Oregon has been actively explored by petroleum companies. Initial surveys between Cape Blanco and the Columbia River established the presence of a thick Tertiary rock sequence within a framework of several composite offshore basins. Gravimeter and magnetometer results indicate the existence of more than 20,000 ft of relatively homogeneous section in Tertiary depositional centers beneath the shelf. A decrease in the amount of interbedded volcanic rock offshore has encouraged exploration of the offshore Tertiary basins.
Detailed exploratory programs, including conventional seismic, sparker, and gas-exploder surveys, reveal numerous well-defined structural trends and many large-size anomalies. Shallow core drilling and ocean-bottom sampling established a composite thickness of more than 8,000 ft of late Miocene, Pliocene, and Pleistocene deposits which are not present in the adjacent coastal area. Diagnostic foraminiferal assemblages have been found in much of the Tertiary column. Absence of overburden on submarine banks off the central and southern parts of the coast makes it possible to map the formations exposed on the ocean floor. The oldest rocks penetrated on the shelf are believed to be of middle Eocene age. Several important unconformities are recognized in the offshore stratigraphic column.
In October 1964 the Federal government offered 1,090,000 acres off Oregon and Washington for competitive oil and gas lease. The total bonus received from this sale was $35.6 million, of which $27.8 million was for leases off Oregon.
To date, eight exploratory wells have been drilled totaling 71,149 ft of hole; however, no commercial production has been reported. Many large structures remain main untested, but most lands acquired at the 1964 sale have been quitclaimed. Although source rocks are distributed throughout the section, a lack of permeable reservoirs has been discouraging. Despite the negative aspects, the writer believes that the area has much exploratory potential. Another industry exploration cycle is anticipated in the not too distant future.