South Mountain Oil Field
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The South Mountain Oil Field is a large and productive
oil field A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...
in Ventura County, California, in the United States, in and adjacent to the city of Santa Paula. Discovered in 1916, and having a cumulative production of over of oil, it is the 37th largest oil field in California and the second largest in Ventura County (after the Ventura field). p. 63, 166 As of the beginning of 2009, it retains 316 active wells, and has an estimated of oil remaining recoverable with current technology. Vintage Production, a subsidiary of
Occidental Petroleum Occidental Petroleum Corporation (often abbreviated Oxy in reference to its ticker symbol and logo) is an American company engaged in hydrocarbon exploration in the United States, and the Middle East as well as petrochemical manufacturing in the ...
, was the largest operator as of 2009.


Geographic setting

The oil field covers most of the north slope, the summit, and part of the south slope of topographically prominent South Mountain, southeast of Santa Paula. Adjacent to the west and southwest is the small West Mountain Oil Field and the
Saticoy Oil Field The Saticoy Oil Field is an oil and gas field in Ventura County, California, in the United States. The field is a long narrow band paralleling the Santa Clara River near the town of Saticoy. Discovered in 1955, it is one of the smaller but p ...
, which follows the north bank of the Santa Clara River. Land use is relatively unmixed, as the entire mountain is inaccessible to the public; areas not developed for oil and gas production are left in their natural state, excepting an area of orchards on Richardson Canyon Road near the north entrance to the field. Native vegetation on the mountain consists of chaparral,
coastal sage scrub Coastal sage scrub, also known as coastal scrub, CSS, or soft chaparral, is a low scrubland plant community of the California coastal sage and chaparral subecoregion, found in coastal California and northwestern coastal Baja California. It is w ...
, and oak woodlands. Elevations on the oil field range from around on the bank of the Santa Clara River to at the topmost point of South Mountain. Drainage from the mountain to the north is into the Santa Clara River and then out to the Pacific Ocean. The south slope of the mountain drains via several canyons that flow into Calleguas Creek, which empties into the Pacific via Mugu Lagoon at the western foot of the Santa Monica Mountains. The climate in the region is
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
, with cool, rainy winters and warm, rainless summers, in which the heat is moderated by frequent morning coastal low clouds and fog. Annual precipitation is around , almost all in the winter, and all in the form of rain, with occasional dustings of snow on the mountaintop in exceptionally cold winter storms. The mean annual temperature is 56 to 60 degrees Fahrenheit; freezes occur rarely. Because the terrain is almost uniformly steep and difficult, well drilling has been done on pads graded flat in areas suitably stable, and many wells are grouped and drilled directionally from these pad locations. These groups contain from 2 to 12 wells, especially on the steepest parts of the mountain near the top of the ridge.
Directional drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical bores. It can be broken down into four main groups: oilfield directional drilling, utility installation directional drilling, directional boring (horizontal dire ...
is necessary to have the well completions, deep underground, spaced in an optimal manner, rather than clustered, as they are at the surface. The total productive area of the oil field is .DOGGR, p. 532.


Geology

The South Mountain field is one of several oil fields within the Oak Ridge Anticline, a large
anticlinal Anticlinal may refer to: *Anticline, in structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. *Anticlinal, in stereochemistry, a torsion angle between 90° to 150°, and –90° to –150°; see Alkane_st ...
structure upthrown over the Oak Ridge reverse fault. Tectonic forces caused by the collision and lateral movement of the
North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...
and
Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...
s have compressed the area of the Oxnard and Ventura Basins from north to south, resulting in structural folds; oil has collected in those folds which form an anticlinal trapping mechanism. Extensive faulting is a secondary trapping mechanism, as the fault offsets have brought impermeable rock adjacent to oil-bearing formations, preventing further upward migration of hydrocarbons. pp. 24-32 pp. 12-16 Oil in the South Mountain field is found in two producing horizons, one on each side of the Oak Ridge Fault. The larger pool, and the one first to be discovered, is in the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
-age Sespe Formation, trapped in the huge anticline of which South Mountain is the surface expression. The pool north of the Oak Ridge Fault, known as the "Bridge" pool, is in the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standa ...
, and has a relatively high sulfur content, at 2.79% by weight. Oil in the Bridge pool is lighter with lower sulfur, having an average API gravity of 33. Oil in the field is relatively young, with an estimated age of about 2 million years, and likely originated in the underlying
Monterey Formation The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands ...
. The lack of free gas in the field is used as evidence for the young age of the oil; the same condition prevails at other oil fields adjacent to the Ventura Basin. Additionally, biomarkers and hydrocarbon source modeling suggest a recent origin for the oil: the Monterey Formation is a fertile source rock for hydrocarbons and continues to produce oil, which migrates upwards, filling available reservoirs over time-spans measured in hundreds of thousands to millions of years.


History, production and operations

The field was discovered in April 1916 by now-defunct Oak Ridge Oil Co., which completed the discovery well into the Sespe Formation and found oil around below ground surface. While the first well was not a huge producer, bringing in only , it was sufficient to encourage further exploration, and in the next year Oak Ridge Oil put in two more wells at shallower depths which produced approximately the same amount. Other companies attempted to exploit the field, and in July 1917 the Santa Paula Oil Company brought in a -per-day well at a depth of around 2,000 feet. Gradually the field began to sprout drilling rigs wherever stability conditions allowed. On the average, about eight new wells per year went in between 1917 and 1929. Engineering the field was a challenge, because the steep terrain was prone to landslides and mudslides during the rainy season. pp. 5-9 After 1929, due to economic conditions during the
Great Depression The Great Depression (19291939) was an economic shock that impacted most countries across the world. It was a period of economic depression that became evident after a major fall in stock prices in the United States. The economic contagio ...
(including a sharp decline in the price of oil), the pace of well development slackened; only 11 wells were drilled between 1930 and 1942, less than one per year. As the field was developed, gas pressure gradually declined, reducing the danger of blowouts, an occurrence which had been common in the early days of the field's development, and which was relatively commonplace prior to the advent of modern blowout-prevention technology. Many of the canyons on the north side of the mountain were dammed with earthen berms to form improvised sumps or catchment basins for wells which blew out in the 1920s. By 1941, gas pressure within the reservoir had declined to the point that the last freely flowing well stopped producing on its own, and needed to have a pump put in, so all the wells on the field were on the pump. At the end of 1943, the field contained 93 wells which were producing oil. In December 1955, the Bridge producing horizon was discovered, at about below ground surface in the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 In spite of the methodical early development of the field, the peak production did not occur until 1959, after the waterflood in the Sespe zone had been running for three years, and four years after the discovery of the productive Bridge zone north of the Oak Ridge Fault. In 1959 the field produced over of oil and in 1960 of natural gas. In the 1990s, the major oil companies pulled out of the field and sold their holdings to independent and smaller operators. This event mirrored a trend throughout coastal and offshore California, as the firms with large financial resources and international holdings decided to focus on easier-to-exploit oil fields elsewhere in the world.
Texaco Texaco, Inc. ("The Texas Company") is an American Petroleum, oil brand owned and operated by Chevron Corporation. Its flagship product is its Gasoline, fuel "Texaco with Techron". It also owned the Havoline motor oil brand. Texaco was an Indepe ...
, formerly the Texas Company, which had been one of the field's major operators in the 1940s, sold their holdings to Vintage Production;
Union Oil Union Oil Company of California, and its holding company Unocal Corporation, together known as Unocal was a major petroleum explorer and marketer in the late 19th century, through the 20th century, and into the early 21st century. It was headqu ...
sold many of its holdings to Torch Operating Company, which sold them to Mirada Petroleum;
Shell Oil Shell plc is a British multinational oil and gas company headquartered in London, England. Shell is a public limited company with a primary listing on the London Stock Exchange (LSE) and secondary listings on Euronext Amsterdam and the New Yor ...
sold its holdings to a Vintage Petroleum subsidiary. When
Occidental Petroleum Occidental Petroleum Corporation (often abbreviated Oxy in reference to its ticker symbol and logo) is an American company engaged in hydrocarbon exploration in the United States, and the Middle East as well as petrochemical manufacturing in the ...
acquired Vintage in 2006, they effectively took over production of most of the field, although it still runs under the Vintage banner. In 2010, there were 316 active wells remaining on the field, and 8 operators, of which Vintage Petroleum was by far the largest, with 266 wells. Mirada Petroleum had 21, and The Termo Co. had 18; several other small operators owned between 1 and 3 wells each. As a mature field, production was in a steady decline, with only pumped from the field in 2008. Average daily production had dropped to approximately for the Vintage wells, and was even less for some of the other operators.DOGGR 2009, p. 166


Notes


References

* ''California Oil and Gas Fields, Volumes I, II and III''. Vol. I (1998), Vol. II (1992), Vol. III (1982). California Department of Conservation, Division of Oil, Gas, and Geothermal Resources (DOGGR). 1,472 pp. South Mountain Oil Field information pp. 530–532. PDF file available on CD from www.consrv.ca.gov. * California Department of Conservation, Oil and Gas Statistics, Annual Report, December 31, 2008. * Keller, Margaret. ''Ventura Basin Province'', U.S. Geological Survey Digital Data Series DDS-30, Release 2, one CD-ROM, 19 p. + supporting maps, figures, and tables.
Available here
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