Oxnard Oil Field
Encyclopedia
The Oxnard Oil Field is a large and currently productive oil field
in and adjacent to the city of Oxnard
, in Ventura County, California
in the United States. Its conventional oil reserves are close to exhaustion, with only an estimated one percent of the original oil recoverable with current technology remaining: 434000 barrels (69,000.5 m³) out of an original 43.5 million. However, the reservoir includes an enormous deposit of tar sands, ultra-heavy oil classed as an unconventional petroleum reserve, and potentially containing 400 Moilbbl of oil equivalent, should it become economically feasible to extract. p. 6-8 Present operators on the field include Tri-Valley Oil & Gas Co., Anterra Energy Services, Inc., Chase Production Co., and Occidental Petroleum
through its Vintage Production subsidiary. p. 97, 122, 118, 160 As of the beginning of 2009, there were 34 active wells on the field.
, a mostly agricultural area now partially overbuilt with suburban and light industrial development from the expanding regional communities of Ventura
, Oxnard, and Camarillo
. In the vicinity of the oil field, agriculture remains the predominant land use, and oil wells, processing facilities, and associated infrastructure are interspersed with fields planted with crops such as strawberries, broccoli, and onions. Parts of the field, particularly on the west, have been given over to light industrial and commercial development as the Oxnard metropolitan area expands to the east. U.S. Highway 101 bounds the field on the north; California State Route 34
(Oxnard's East 5th Street) cuts across it from east to west, and Rice Avenue crosses it from north to south. Most of the currently active oil wells are in the eastern portion of the field, west of the intersection of 5th Street and Pleasant Valley Road. Some active wells remain west of Rice Avenue, and a group of wells using directional drilling is clustered together in a drilling island near the northeast corner of the intersection of Rose Avenue and Wooley Road. The total productive area of the field projected to the surface is 1350 acre (546 ha).
The climate in the region is Mediterranean
, 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 15 inches (381 mm), almost all in the winter, and all in the form of rain. The mean annual temperature is 56 to 60 °F (15.6 °C); freezes occur rarely.
Elevations on the field range from about 40 to 60 feet (18.3 m) above sea level. It is mostly flat, with a very gentle slope to the south-southeast; drainage is along Revolon Slough to Calleguas Creek to Mugu Lagoon, and then to the Pacific Ocean.
that occurred during the late Pliocene
. Rocks within the region are all sedimentary
and mostly marine. Oil accumulations, of which there are many in the Ventura province, mainly occur in anticlinal
settings modified by faulting; stratigraphy
is also influential in creating traps for hydrocarbons. Where the sedimentary rocks are sandstones with high porosity, and the structure and stratigraphy allow hydrocarbons to be trapped on their upward migration, oilfields are found.
As the oil field is in the center of a large flat alluvial
floodplain, there is no surface expression of any anticlinal structure capable of holding oil. Under the surface alluvium, a series relatively impermeable sedimentary units cap the petroleum-bearing formation. On top are the Pleistocene
San Pedro and Pleistocene-upper Pliocene
Santa Barbara formations; under that the Pico Sands, of Pliocene age, which contain areas of tar sands; under that, separated by an unconformity, the Monterey Formation
, of Miocene
age, which also contains tar sands (the Vaca Tar Sand); under that, again separated by an unconformity, the relatively impermeable Conejo-Topanga Formation, which caps the faulted anticlinal structure containing medium-grade oil about 6500 feet (1,981.2 m) below ground surface. This producing horizon is named the "McInnes" pool, and is in the Oligocene
-age Sespe Formation
.
The Oxnard field contains a large quantity of tar sand, a type of bitumen which is categorized as an unconventional oil deposit. The average depth below ground surface of the tar sands – both the Vaca Sand, and the Pico Sand – is about 2500 feet (762 m), and their thickness ranges from 0 to 600 feet (182.9 m), representing a total volume of 405000 acre.ft, equivalent to approximately 565 Moilbbl of oil for both units, were it possible to recover their petroleum content. Only a tiny fraction of this has been brought to the surface to date, although Tri-Valley Corporation is actively developing the unit by drilling horizontal wells through the sands and subjecting them to the cyclic steam
process. According to Tri-Valley, some of the test wells have shown production rates of 1000 oilbbl/d, and can be brought online as soon as the steam generators and storage infrastructure are in place on the field.
The quality of the oil from the lower pools is good and the gravity medium, at 24 to 38 API
, while the oil from the tar sand is extremely heavy and of poor quality, with an extraordinarily high sulfur content – API gravity of 7, viscosity of 28,000 to 33,000 centipoise, and sulfur content of between 5 and 7.5 percent by weight.
from which they were able to produce about 90 barrels (14.3 m³) of oil per day.
More adventurous drillers found deeper producing horizons with lighter oil. In 1953 and 1954 the McInnes, Lucas, and Livingston pools were brought online, producing oil of API gravity 24, 32 and 25-36 respectively. Waterflooding operations in these deeper reservoirs in the 1960s assisted production, but most wells in these horizons were abandoned as the last economically recoverable oil was extracted; a few remained as water disposal wells, as it is usually both economically and environmentally preferable to reinject wastewater back into a depleted reservoir than to treat and release it on the surface. In 2008 only two wells remained active in the deep McInnes reservoir; all the others were in the shallow tar sands.
Under the California Department of Conservation well adoption rule, Tri-Valley Oil & Gas Company acquired 20 wells formerly operated by defunct GEO Petroleum, Inc., which filed for Chapter 11 bankruptcy protection in 1998. Wells declared deserted by the State – typically due to the dissolution of the operator – are open to adoption and redevelopment under the "orphan well" rule, with the written consent of the owner of the mineral rights to the property as well as the State Department of Oil, Gas, and Geothermal Resources. In 2008 Tri-Valley began redeveloping these wells and bringing them back to production.
Oil produced in the field goes to the small (2800 barrels (445.2 m³)-per-day) Oxnard Refinery, owned by Tenby, Inc., in an unincorporated area south of Fifth Street near the eastern Oxnard city limit. This refinery also processes oil from the West Montalvo field
on the coast directly west of the Oxnard field.
Oil field
An oil field is a region with an abundance of oil wells extracting petroleum from below ground. Because the oil reservoirs typically extend over a large area, possibly several hundred kilometres across, full exploitation entails multiple wells scattered across the area...
in and adjacent to the city of Oxnard
Oxnard, California
Oxnard is the 113th largest city in the United States, 19th largest city in California and largest city in Ventura County, California, by way of population. It is located at the western edge of the fertile Oxnard Plain, and is an important agricultural center, with its distinction as the...
, in Ventura County, California
Ventura County, California
Ventura County is a county in the southern part of the U.S. state of California. It is located on California's Pacific coast. It is often referred to as the Gold Coast, and has a reputation of being one of the safest populated places and one of the most affluent places in the country...
in the United States. Its conventional oil reserves are close to exhaustion, with only an estimated one percent of the original oil recoverable with current technology remaining: 434000 barrels (69,000.5 m³) out of an original 43.5 million. However, the reservoir includes an enormous deposit of tar sands, ultra-heavy oil classed as an unconventional petroleum reserve, and potentially containing 400 Moilbbl of oil equivalent, should it become economically feasible to extract. p. 6-8 Present operators on the field include Tri-Valley Oil & Gas Co., Anterra Energy Services, Inc., Chase Production Co., and Occidental Petroleum
Occidental Petroleum
Occidental Petroleum Corporation is a California-based oil and gas exploration and production company with operations in the United States, the Middle East, North Africa, and South America...
through its Vintage Production subsidiary. p. 97, 122, 118, 160 As of the beginning of 2009, there were 34 active wells on the field.
Setting
The Oxnard Oil Field is one of several beneath the Oxnard PlainOxnard Plain
The Oxnard Plain is a large coastal plain in southwest Ventura County, California bounded by the Santa Monica Mountains, the Santa Susana Mountains, and Oak Ridge to the east, the Topatopa Mountains to the north, the Santa Clara River Valley to the northeast and the Pacific Ocean to the south and...
, a mostly agricultural area now partially overbuilt with suburban and light industrial development from the expanding regional communities of Ventura
Ventura, California
Ventura is the county seat of Ventura County, California, United States, incorporated in 1866. The population was 106,433 at the 2010 census, up from 100,916 at the 2000 census. Ventura is accessible via U.S...
, Oxnard, and Camarillo
Camarillo, California
Camarillo is a city in Ventura County, California, United States. The population was 65,201 at the 2010 census, up from 57,084 at the 2000 census. The Ventura Freeway Camarillo is a city in Ventura County, California, United States. The population was 65,201 at the 2010 census, up from 57,084 at...
. In the vicinity of the oil field, agriculture remains the predominant land use, and oil wells, processing facilities, and associated infrastructure are interspersed with fields planted with crops such as strawberries, broccoli, and onions. Parts of the field, particularly on the west, have been given over to light industrial and commercial development as the Oxnard metropolitan area expands to the east. U.S. Highway 101 bounds the field on the north; California State Route 34
California State Route 34
State Route 34 is a short state highway in the U.S. state of California.-Route description:SR 34 is part of the California Freeway and Expressway System....
(Oxnard's East 5th Street) cuts across it from east to west, and Rice Avenue crosses it from north to south. Most of the currently active oil wells are in the eastern portion of the field, west of the intersection of 5th Street and Pleasant Valley Road. Some active wells remain west of Rice Avenue, and a group of wells using directional drilling is clustered together in a drilling island near the northeast corner of the intersection of Rose Avenue and Wooley Road. The total productive area of the field projected to the surface is 1350 acre (546 ha).
The climate in the region is Mediterranean
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...
, 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 15 inches (381 mm), almost all in the winter, and all in the form of rain. The mean annual temperature is 56 to 60 °F (15.6 °C); freezes occur rarely.
Elevations on the field range from about 40 to 60 feet (18.3 m) above sea level. It is mostly flat, with a very gentle slope to the south-southeast; drainage is along Revolon Slough to Calleguas Creek to Mugu Lagoon, and then to the Pacific Ocean.
Geology
The Oxnard field is within the Ventura Basin Province of southern California. Geologically, this area is part of a structural downwarpDepression (geology)
A depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms.Structural or tectonic related:...
that occurred during the late Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. Rocks within the region are all sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
and mostly marine. Oil accumulations, of which there are many in the Ventura province, mainly occur in anticlinal
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
settings modified by faulting; stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
is also influential in creating traps for hydrocarbons. Where the sedimentary rocks are sandstones with high porosity, and the structure and stratigraphy allow hydrocarbons to be trapped on their upward migration, oilfields are found.
As the oil field is in the center of a large flat alluvial
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
floodplain, there is no surface expression of any anticlinal structure capable of holding oil. Under the surface alluvium, a series relatively impermeable sedimentary units cap the petroleum-bearing formation. On top are the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
San Pedro and Pleistocene-upper Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
Santa Barbara formations; under that the Pico Sands, of Pliocene age, which contain areas of tar sands; under that, separated by an unconformity, the Monterey Formation
Monterey Formation
The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with massive outcroppings of the formation in areas of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands...
, of Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
age, which also contains tar sands (the Vaca Tar Sand); under that, again separated by an unconformity, the relatively impermeable Conejo-Topanga Formation, which caps the faulted anticlinal structure containing medium-grade oil about 6500 feet (1,981.2 m) below ground surface. This producing horizon is named the "McInnes" pool, and is in the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
-age Sespe Formation
Sespe Formation
The Sespe Formation is a widespread fossiliferous sedimentary geologic unit in southern and south central California in the United States. It is of nonmarine origin, consisting predominantly of sandstones and conglomerates laid down in a riverine, shoreline, and floodplain environment between the...
.
The Oxnard field contains a large quantity of tar sand, a type of bitumen which is categorized as an unconventional oil deposit. The average depth below ground surface of the tar sands – both the Vaca Sand, and the Pico Sand – is about 2500 feet (762 m), and their thickness ranges from 0 to 600 feet (182.9 m), representing a total volume of 405000 acre.ft, equivalent to approximately 565 Moilbbl of oil for both units, were it possible to recover their petroleum content. Only a tiny fraction of this has been brought to the surface to date, although Tri-Valley Corporation is actively developing the unit by drilling horizontal wells through the sands and subjecting them to the cyclic steam
Steam injection (oil industry)
Steam injection is an increasingly common method of extracting heavy oil. It is considered an enhanced oil recovery method and is the main type of thermal stimulation of oil reservoirs. There are several different forms of the technology, with the two main ones being Cyclic Steam Stimulation and...
process. According to Tri-Valley, some of the test wells have shown production rates of 1000 oilbbl/d, and can be brought online as soon as the steam generators and storage infrastructure are in place on the field.
The quality of the oil from the lower pools is good and the gravity medium, at 24 to 38 API
API gravity
The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks...
, while the oil from the tar sand is extremely heavy and of poor quality, with an extraordinarily high sulfur content – API gravity of 7, viscosity of 28,000 to 33,000 centipoise, and sulfur content of between 5 and 7.5 percent by weight.
History, production and operations
The field was discovered in January 1937 by Vaca Oil Exploration Co., which drilled into tar sands about 2800 feet (853.4 m) below ground surface. In spite of the extremely viscous petroleum deposits in the producing formation, which they named after their firm – the Pliocene "Vaca" Tar Sand – they were able to produce about 50 oilbbl/d. In May of that same year they discovered tar sands in the underlying Monterey FormationMonterey Formation
The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with massive outcroppings of the formation in areas of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands...
from which they were able to produce about 90 barrels (14.3 m³) of oil per day.
More adventurous drillers found deeper producing horizons with lighter oil. In 1953 and 1954 the McInnes, Lucas, and Livingston pools were brought online, producing oil of API gravity 24, 32 and 25-36 respectively. Waterflooding operations in these deeper reservoirs in the 1960s assisted production, but most wells in these horizons were abandoned as the last economically recoverable oil was extracted; a few remained as water disposal wells, as it is usually both economically and environmentally preferable to reinject wastewater back into a depleted reservoir than to treat and release it on the surface. In 2008 only two wells remained active in the deep McInnes reservoir; all the others were in the shallow tar sands.
Under the California Department of Conservation well adoption rule, Tri-Valley Oil & Gas Company acquired 20 wells formerly operated by defunct GEO Petroleum, Inc., which filed for Chapter 11 bankruptcy protection in 1998. Wells declared deserted by the State – typically due to the dissolution of the operator – are open to adoption and redevelopment under the "orphan well" rule, with the written consent of the owner of the mineral rights to the property as well as the State Department of Oil, Gas, and Geothermal Resources. In 2008 Tri-Valley began redeveloping these wells and bringing them back to production.
Oil produced in the field goes to the small (2800 barrels (445.2 m³)-per-day) Oxnard Refinery, owned by Tenby, Inc., in an unincorporated area south of Fifth Street near the eastern Oxnard city limit. This refinery also processes oil from the West Montalvo field
West Montalvo Oil Field
The West Montalvo Oil Field is a large and productive oil field on the coast of Ventura County, California, in the United States, in and adjacent to the city of Oxnard. Discovered in 1947, it has produced approximately of oil, and retains about 2.2 million recoverable with current technology, in...
on the coast directly west of the Oxnard field.