History of Petroleum Exploration in California and the West Coast

KILKENNY, JOHN E., Consultant, Alhambra, CA

California's main oil and gas basins consist of the inland Sacramento and San Joaquin and the Los Angeles, Ventura, and Santa Maria basins adjacent to the coast and extending offshore.

The state's total oil production to 1991 is approximately 22.8 billion bbls. Producing formations range in age from basement Jurassic to Pleistocene, but production is mainly from thick multiple sand zones of Miocene and Pliocene age.

The first oil discovery was in the eastern Ventura basin in 1875. By the turn of the century, 22 fields, including several giants in the San Joaquin Valley, had been discovered by drilling near oil see
pages. During the next 20 years, geologists became more influential in the selection of drill sites resulting in the discovery of large anticlinal fields in all of the oil basins.

The most important event of the 1920s was the discovery of several giant oil fields in the Los Angeles basin, drilled on topographic highs suggestive of underlying anticlines. State production rapidly increased to 850,000 BOPD, or 40% of all U.S. production. The 1920s also saw micropaleontology become an important method of correlation. In 1928 the great Kettleman Hills anticline was proven productive.

The 1930s saw the advent of the reflection seismograph, responsible for the state's largest oil field (Wilmington) in the Los Angeles basin and the state's largest gas field (Rio Vista) in the Sacramento basin. A number of important fields were found under the San Joaquin Valley floor.

Geological thinking in the late 1930s and 1940s resulted in the discovery of large stratigraphic traps in the San Joaquin Valley (e.g., East Coalinga) and at Santa Maria from fractured shale, plus two new small producing basins, the Cuyama and the Salinas.

Offshore exploration, consisting of seismic work, ocean-bottom sampling, and coreholing, revealed the presence of a number of anticlines in the Ventura basin, paralleling the Santa Barbara coast. The first offshore discovery was made in 1959 on state lands followed by several major fields on federal lands in the late 1960s. The offshore Santa Maria basin was opened in the late 1970s and two giant discoveries were made including the largest domestic field since Prudhoe Bay.

Elsewhere along the West Coast, exploration in Oregon and Washington has yielded only minor gas.

California geologists continue to be optimistic about the future, but political events will play a large role in the availability of promising offshore acreage.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)