Introduction to Stratigraphy and Hydrocarbon Occurrence in Oligocene and Miocene Rocks of the Santa Barbara-Ventura and Santa Maria Basins of California

Abstract The Santa Barbara-Ventura and Santa Maria basins of southern California have been of great interest to the oil industry because oil or gas has been produced from nearly all the sedimentary units ranging in age from the Cretaceous to the Pleistocene. In particular, the Neogene section of these basins is oil-rich, containing eight giant oil fields (greater than 100 million barrels) in the onshore and at least five in the offshore. In the Santa Barbara-Ventura basin the sedimentary sequence includes marine beds ranging in age from Cretaceous to Pleistocene and two nonmarine sequences of Eocene-Oligocene and Pleistocene ages. The main reservoir for hydrocarbons in this basin is the thick deep-sea sand sequence of the Pliocene and Pleistocene Pico Formation. The other important production in this basin is from reservoirs in the Miocene and, to a lesser extent, the Oligocene sequences. These reservoirs, including the nonmarine Sespe Formation and the marine Alegria, Vaqueros, Monterey, and Sisquoc Formations, are the emphasis of this core workshop. In the Santa Maria basins to the north and northwest of the Santa Barbara-Ventura basin, the Paleogene sequence is absent for the most part, and the upper Neogene sequence does not include the thick Pliocene and Pleistocene Pico Formation. In both the onshore and offshore Santa Maria basins the fractured rocks of the deep-marine Miocene Monterey Formation are the main reservoir for hydrocarbons. Another important reservoir is the upper Miocene and Pliocene marine Sisquoc Formation; both Monterey and Sisquoc cores from the Santa Maria basin are shown in this workshop. As in the Santa Barbara-Ventura basin, the pre-Monterey sedimentary sequence of the Santa Maria basins also contains minor petroleum accumulations.