|Fig. 1: Map of California's Oil, Gas and Geothermal Fields. (Courtesy of the California Department of Conservation)|
Since the discovery of oil in California, not gold or the entertainment industry, the state has been an economic powerhouse within the United States of America and the world. The city of Los Angeles specifically owes its wealth and prominence too the oil fields located in the basin, while a pleasant climate also most likely plays a role. In the 1920s California was the nation's most productive state in terms of crude oil. The Los Angeles Basin produced one of every five barrels of crude oil in the nation. The cumulative oil production in the state is well over 3 billion barrels.  Even today California still ranks high nationally for crude oil production as the third largest, behind Texas and North Dakota. 
The geology in California's oil fields vary due to the number of different basins in the state (Fig. 1). However the general source and reservoir rocks are similar at respective ages throughout the different basins. The number one oil producing basin in California is the San Joaquin.  This basin also happens to the topic of much conversation as it is home to much of California's Monterey Formation. This formation is a Miocene age organic rich sedimentary body. The name "Monterey" is used to describe Miocene strata in California that are unusually siliceous. Other names are used for Miocene siliceous strata in some basins. Pliocene strata that are slightly siliceous have been included in the Monterey Formation sometimes. Upper Miocene (11-5.5 Ma) deposits are most extensive and are of economic significance. The Monterey strata are spread throughout California, as far south as Newport Harbor and as far north as Mendocino county and originally deposited in marine basins. All were primarily adjacent to an active continental margin. The basins the Monterey strata were deposited in varied in the details of their depositional setting.  This formation is so critical to California because it is presumed to be the source for the majority of the crude oil that is produced in California. Recently techniques have been attempted to approach the Monterey as a reservoir rock. The economic returns from producing this formation could be significant.
Estimates of undeveloped technically recoverable resources for shale oil in the Monterey and similar Santos Formation combined is 15 billion barrels.  This resource is at an average depth of 11,250 feet and has an average thickness of 1,875 feet. Techniques to identify the best strategy to produce this formation economically have not been very successful to date.  However, there are promising theories involving the injection of carbon dioxide into the formation.  The depth of the formation causes it to be less amenable to the thermal enhanced oil recovery processes used in many of California's more shallow oil fields. The carbon dioxide was tested for flooding under countercurrent and cocurrent flow regimes both above and below the minimum miscibility pressure for the carbon dioxide and the oil in place. Results indicate that immiscible countercurrent and cocurrent enhance oil recovery between 0-10% and 18-25% respectively. Under miscible conditions countercurrent and cocurrent injection of carbon dioxide increases oil recovery 25% and 10% respectively. The results give evidence that these techniques could be a technically viable strategy to produce the Monterey formation. 
Considering that public sentiment in the San Joaquin Basin continues to be positive regarding exploiting this formation we should expect California to be a strong contributer to increasing production of crude oil domestically.  The estimated resources for California's shale oil are close to three times that of the next largest, the Bakken Formation in North Dakota. With this in mind it is safe to say that California is, was, and will continue to be a state of oil.
© Tyler Scott. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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