Preliminary geophysical interpretation of 1240 line miles of CDP seismic data on untested offshore California state lands between the Santa Maria River and Point Arguello has defined four prospective areas of potential hydrocarbon entrapment. Various structural and stratigraphic trend: have been delineated as important trapping mechanisms, including anticlines, faults, truncations, pinchouts and onlap. The major potential reservoir horizon is the Monterey Formation, although hydrocarbons are present in younger and possibly older rocks.
The southern portion of the Santa Maria Basin has been proven to be highly productive, both immediately adjacent onshore and offshore. Since the three-mile State zone in this study lies between these productive areas, it is perceived to have very favorable potential for future discoveries. Producing onshore trap analogs in the Upper Miocene Monterey Formation are expected to be found in this offshore area adjacent to and east of the Hosgri Fault Zone. Additional potential reservoir rocks include Upper Cretaceous, Paleogene, and younger units, Offshorer fractured quartz and opal-CT phases are believed to comprise much of the Monterey reservoir rock. Permeabilities in the Monterey Formation are reported to be as much as three darcies per foot and porosities up to 20 percent.
This preliminary study deals with the petroleum potential of the three mile zone of California Tide and Submerged lands in the Santa Maria Basin, offshore Santa Barbara County, California (Figure 1). The three mile zone, extending for a distance of about thirty miles between Point Arguello and the mouth of the Santa Maria River, has never been explored by the drill, or ever leased. Yet, it has now been established that large and prolific fields virtually surround the State area, both onshore and offshore. The several onshore fields extend from the shoreline to about twenty miles inland. Some have been producing since early 1900?s, essentially from Miocene and Pliocene age rocks, primarily from traps within asymmetric, faulted folds. The gravity of the onshore oil is generally 10W, but varies widely from about 30 degrees API to asphalt.
In the 1950?s, industry initiated preliminary offshore seismic investigations. With the general recognition and acceptance in the 1970?s that the Monterey Formation was the source for much of California?s oil, it soon became a new target. Besides being a prolific source rock, it also serves as its own reservoir. However, it was to be another thirty years before the offshore portion of the Santa Maria Basin finally came into its own. This was triggered by the discovery of the giant Point Arguello Field, by Chevron, in 1981. The discovery well was drilled on Federal Parcel P-0316, which was obtained in the 1981 OCS Lease Sale 53.The Chevron P-0316-1 discovery test is located eight and one-half miles south of Point Arguello, at the southern edge of the Santa Maria Basin, in 635 feet of water.
