Oil and Gas Exploration Offshore Central and Northern California

The regional Pacific basin from the west end of the Santa Barbara Channel north to the Oregon border includes five local offshore basins which all have embayments onshore. These are: (from south to north) the Santa Maria basin, the Salinas basin, the Bodega-Santa Cruz basin, the Point Arena basin, and the Eel River basin. In all of these, there is onshore oil or gas production in the same stratigraphic units that should have potential in the offshore, except Point Arena basin where outcropping bituminous sands have been mined. Tracts in each of these basins were sold by the federal government in 1963. Following that, 19 wells were drilled, with one or more in each basin. Data were not released until 1975. Excellent shows of tarry oil were reported in several wells, with the best shows being in the fractured Monterey (Miocene) cherts and siliceous shales. No drill-stem tests were run and pipe was not set on any well to test through perforations. Modern evaluation of the well data indicates that, in the light of present knowledge gained in drilling and testing similar Monterey zones with similar shows in the Santa Barbara Channel since these 19 wells were drilled, had pipe been set and the Monterey zones been tested through perforations, discoveries of commercial, medium-gravity oil might have been made. The principal objectives in these basins, in addition to the fractured Monterey, are Pliocene, Miocene, Oligocene, and Eocene sandstones. The offshore Santa Maria basin has optimum potential because it is considered to be an extension of present production onshore where ultimate recovery of over 900 million bbl of oil (and gas as oil equivalent) has been estimated. The offshore Salinas basin and offshore Point Arena basin are considered to have excellent potential in fractured Monterey, and the offshore Bodega-Santa Cruz basin is somewhat less prospective. The offshore Eel River basin is considered to have excellent potential for gas discoveries in the Pliocene and possibly high-gravity oil in upper Miocene rocks. All offshore areas are being actively explored in preparation for OCS Sale 53, scheduled for early 1981.