Dos Cuadras Offshore Oil Field
Encyclopedia
The Dos Cuadras Offshore Oil Field is a large oil and gas field underneath the Santa Barbara Channel
about eight miles southeast of Santa Barbara, California
. Discovered in 1968, and with a cumulative production of over 260 million barrels of oil, it is the 24th-largest oil field within California and the adjacent waters. As it is in the Pacific Ocean outside of the 3-mile tidelands
limit, it is a federally-leased field, regulated by the U.S. Department of the Interior rather than the California Department of Conservation. It is entirely produced from four drilling platforms in the channel, which as of 2009 were operated by Dos Cuadras Offshore Resources (DCOR), LLC, a private firm based in Ventura
. A blowout
near one of these platforms – Unocal's Platform A – was responsible for the 1969 Santa Barbara oil spill that was formative for the modern environmental movement, and spurred the passage of the National Environmental Policy Act
.
, making it subject to U.S. government rather than California regulation. The four platforms are arranged in a line running from east to west, spaced one-half mile apart, with Platform Hillhouse on the east, and Platforms "A", "B", and "C" in order to the west.
A pair of undersea pipelines, one for oil and one for gas, connect the four platforms to the shore near La Conchita
. Oil and gas produced on the Dos Cuadras field are pumped about 12 miles east to the Rincon Oil & Gas Processing Plant on a hilltop adjacent to the Rincon Oil Field
, about a mile southeast of La Conchita. From there oil travels down to Ventura along Venoco's M-143 pipeline to the Ventura pump station, and then to Los Angeles area refineries by way of a TOSCO pipeline in the Santa Clara River Valley.
The ocean bottom is relatively flat in the vicinity of the field, and all platforms are in a water depth of approximately 190 feet.
anticlinal
structure which plunges at both ends, thereby forming an ideal trap for hydrocarbon
accumulation. It is part of the larger Rincon Anticlinal Trend, which includes the Carpinteria Offshore Oil Field
to the east, as well as the Rincon
, San Miguelito
, and Ventura
fields onshore. Oil is found in two formations, the Pliocene
-age Pico Formation and the underlying Miocene
Santa Margarita Formation. By far the most productive unit is the Repetto Sands portion of the Pico Formation. Only one well has produced from the Santa Margarita; all the others are in the Repetto Sands.
The Repetto Sands unit consists of layers of mudstone, siltstone, and shale, and due to its depositional environment the general grain size and porosity
increase towards the east. It is the same formation which is richly productive in the oil fields of the Los Angeles Basin, such as the Salt Lake
and Beverly Hills
fields, where it is also folded into anticlinal traps. In the Dos Cuadras field, the oil-bearing strata are at depths ranging from 500 to 4,200 feet below the sea floor, and individual strata are separated by impermeable layers of shaly
material.
Oil from the field averages API gravity
of 25, with a range from 18 to 34, which classifies as medium-grade crude. Reservoir pressure began at 750 psi, sufficient for easy pumping in the early years of field development.
in 1896, only five miles north of the Dos Cuadras field. Those wells were put in from piers in shallow water. Technology for drilling in deeper water from platforms did not come about until the middle of the 20th century.
While the existence of the field was suspected in the 1950s, the field was not discovered until 1968. Unocal and several other oil companies took out leases on the field in February 1968, and put in the first well, and the first platform, that same year. Data regarding the four platforms are as follows:
Unocal succeeded in installing the first four wells from its Platform A by January 1969, but their attempt to install the fifth well was catastrophic, and resulted in one of the most notorious environmental disasters in United States history. Because the drillers were using an insufficient length of protective casing, when the well hit a high-pressure zone in the field, it blew out, spewing enormous quantities of oil and gas into the water from the sea floor. While crews were able to cap the wellhead and relieve the pressure there, the adjacent geologic formations were not strong enough to contain the pressure, and lacking a steel protective casing, the reservoir fluid and gas ripped through the sedimentary sand layers directly on the ocean floor; the result was the 1969 Santa Barbara oil spill
of 80,000 to 100,000 barrels, which eventually coated over 40 miles of southern California coastline with oil, an ecological disaster which killed upward of 10,000 birds and numerous sea mammals and other creatures.
Following the spill, the Secretary of the Interior ended all offshore oil drilling in the Outer Continental Shelf (OCS) until measures for better oversight were put in place, which happened in 1970 with the passage of the federal National Environmental Policy Act
(NEPA), and in California, with the California Environmental Quality Act
(CEQA). Opposition to oil drilling was nothing new in Santa Barbara – local residents, led by a newspaper publisher, objected enough to the expansion of the Summerland field in the 1890s to organize a late-night derrick-destroying party near the present-day Miramar Hotel – but the spill intensified the local hostility to oil drilling to the point that few new platforms were installed, and none at all within the 3-mile limit.
After the disaster and cleanup, Unocal continued drilling wells from the two platforms that were already in place ("A" and "B", began producing from them in March 1969, and installed two more platforms ("C" and "Hillhouse"). Production from the field peaked quickly, reaching a maximum in 1971, during which year almost 28 million barrels of oil were extracted. The field experienced a gradual decline in production afterwards, approximately 8 percent per year, as is typical of fields when the reservoir pressure declines, and in the absence of secondary recovery technologies (such as water or gas injection). In 1985, Unocal tried waterflooding, and then polymer flooding, to improve production rates, and then in 1990 they began a horizontal drilling program to reach reservoirs impractical to exploit any other way.
Unocal continued to produce from the field until they sold all of their California production assets in 1996 to Nuevo Energy, as operated by Torch Energy Advisors. In 1997 Nuevo took over the operations of the four platforms directly, and in 2004 passed them on to Plains Exploration & Production
on that firm's acquisition of Nuevo. Plains only ran the platforms for a little more than four months, selling the operation to DCOR in March 2005. As of 2009, DCOR retains control of the Dos Cuadras field.
According to the Minerals Management Service (MMS), the field retains about 11.4 million barrels of oil in reserves recoverable with current technology. At the beginning of 2008, there were 145 producing oil wells distributed between the four platforms.
Santa Barbara Channel
The Santa Barbara Channel is a portion of the Pacific Ocean which separates the mainland of California from the northern Channel Islands. It is generally south of the city of Santa Barbara, and west of the city of Ventura....
about eight miles southeast of Santa Barbara, California
Santa Barbara, California
Santa Barbara is the county seat of Santa Barbara County, California, United States. Situated on an east-west trending section of coastline, the longest such section on the West Coast of the United States, the city lies between the steeply-rising Santa Ynez Mountains and the Pacific Ocean...
. Discovered in 1968, and with a cumulative production of over 260 million barrels of oil, it is the 24th-largest oil field within California and the adjacent waters. As it is in the Pacific Ocean outside of the 3-mile tidelands
Tidelands
Tidelands are the territory between the high and low water tide line of sea coasts, and lands lying under the sea beyond the low-water limit of the tide, considered within the territorial waters of a nation. The United States Constitution does not specify whether ownership of these lands rests with...
limit, it is a federally-leased field, regulated by the U.S. Department of the Interior rather than the California Department of Conservation. It is entirely produced from four drilling platforms in the channel, which as of 2009 were operated by Dos Cuadras Offshore Resources (DCOR), LLC, a private firm based in 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...
. A blowout
Blowout (well drilling)
A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed....
near one of these platforms – Unocal's Platform A – was responsible for the 1969 Santa Barbara oil spill that was formative for the modern environmental movement, and spurred the passage of the National Environmental Policy Act
National Environmental Policy Act
The National Environmental Policy Act is a United States environmental law that established a U.S. national policy promoting the enhancement of the environment and also established the President's Council on Environmental Quality ....
.
Setting
The Dos Cuadras field is one of many underneath the ocean bottom offshore of Southern California, most of which were discovered in the 1960s and 1970s. All of the field is outside of the 3-mile geographic limitTidelands
Tidelands are the territory between the high and low water tide line of sea coasts, and lands lying under the sea beyond the low-water limit of the tide, considered within the territorial waters of a nation. The United States Constitution does not specify whether ownership of these lands rests with...
, making it subject to U.S. government rather than California regulation. The four platforms are arranged in a line running from east to west, spaced one-half mile apart, with Platform Hillhouse on the east, and Platforms "A", "B", and "C" in order to the west.
A pair of undersea pipelines, one for oil and one for gas, connect the four platforms to the shore near La Conchita
La Conchita, California
La Conchita is a small unincorporated community in western Ventura County, California, on U.S. Route 101 just southeast of the Santa Barbara county line...
. Oil and gas produced on the Dos Cuadras field are pumped about 12 miles east to the Rincon Oil & Gas Processing Plant on a hilltop adjacent to the Rincon Oil Field
Rincon Oil Field
The Rincon Oil Field is a large oil field on the coast of southern California, about ten miles northwest of the city of Ventura, and about 20 miles east-southeast of the city of Santa Barbara. It is the westernmost onshore field in a series of three fields which follow the Ventura Anticline, an...
, about a mile southeast of La Conchita. From there oil travels down to Ventura along Venoco's M-143 pipeline to the Ventura pump station, and then to Los Angeles area refineries by way of a TOSCO pipeline in the Santa Clara River Valley.
The ocean bottom is relatively flat in the vicinity of the field, and all platforms are in a water depth of approximately 190 feet.
Geology
The Dos Cuadras field is a faultedGeologic fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of tectonic forces...
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...
structure which plunges at both ends, thereby forming an ideal trap for hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
accumulation. It is part of the larger Rincon Anticlinal Trend, which includes the Carpinteria Offshore Oil Field
Carpinteria Offshore Oil Field
The Carpinteria Offshore Oil Field is an oil and gas field in Santa Barbara Channel, south of the city of Carpinteria in southern California in the United States...
to the east, as well as the Rincon
Rincon Oil Field
The Rincon Oil Field is a large oil field on the coast of southern California, about ten miles northwest of the city of Ventura, and about 20 miles east-southeast of the city of Santa Barbara. It is the westernmost onshore field in a series of three fields which follow the Ventura Anticline, an...
, San Miguelito
San Miguelito Oil Field
The San Miguelito Oil Field is a large and currently productive oil field in the hills northwest of the city of Ventura in southern California in the United States. The field is close to the coastline, with U.S...
, and Ventura
Ventura Oil Field
The Ventura Oil Field is a large and currently productive oil field in the hills immediately north of the city of Ventura in southern California in the United States. It is bisected by California State Route 33, the freeway connecting Ventura to Ojai, and is about eight miles long by two across,...
fields onshore. Oil is found in two formations, the 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...
-age Pico Formation and the underlying 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...
Santa Margarita Formation. By far the most productive unit is the Repetto Sands portion of the Pico Formation. Only one well has produced from the Santa Margarita; all the others are in the Repetto Sands.
The Repetto Sands unit consists of layers of mudstone, siltstone, and shale, and due to its depositional environment the general grain size and porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
increase towards the east. It is the same formation which is richly productive in the oil fields of the Los Angeles Basin, such as the Salt Lake
Salt Lake Oil Field
The Salt Lake Oil Field is an oil field underneath the city of Los Angeles, California. Discovered in 1902, and developed quickly in the following years, the Salt Lake field was once the most productive in California; over 50 million barrels of oil have been extracted from it, mostly in the first...
and Beverly Hills
Beverly Hills Oil Field
The Beverly Hills Oil Field is a large and currently active oil field underneath part of the city of Beverly Hills, California, USA, and portions of the adjacent city of Los Angeles...
fields, where it is also folded into anticlinal traps. In the Dos Cuadras field, the oil-bearing strata are at depths ranging from 500 to 4,200 feet below the sea floor, and individual strata are separated by impermeable layers of shaly
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
material.
Oil from the field averages API gravity
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...
of 25, with a range from 18 to 34, which classifies as medium-grade crude. Reservoir pressure began at 750 psi, sufficient for easy pumping in the early years of field development.
History and production
Oil has been known in the Santa Barbara Channel since prehistoric times; the native Chumash people used tar from the numerous natural seeps as a sealant, and tar regularly washes up on the beaches from the offshore seeps. The world's first offshore oil drilling took place at the Summerland Oil FieldSummerland Oil Field
The Summerland Oil Field is an inactive oil field in Santa Barbara County, California, about four miles east of the city of Santa Barbara, within and next to the unincorporated community of Summerland...
in 1896, only five miles north of the Dos Cuadras field. Those wells were put in from piers in shallow water. Technology for drilling in deeper water from platforms did not come about until the middle of the 20th century.
While the existence of the field was suspected in the 1950s, the field was not discovered until 1968. Unocal and several other oil companies took out leases on the field in February 1968, and put in the first well, and the first platform, that same year. Data regarding the four platforms are as follows:
| Name | Installed | First production | Water depth |
|---|---|---|---|
| Platform A | September 14, 1968 | March 3, 1969 | 188 feet |
| Platform B | November 8, 1968 | July 19, 1969 | 190 feet |
| Platform Hillhouse | November 26, 1969 | July 21, 1970 | 190 feet |
| Platform C | February 28, 1977 | August 1, 1977 | 192 feet |
Unocal succeeded in installing the first four wells from its Platform A by January 1969, but their attempt to install the fifth well was catastrophic, and resulted in one of the most notorious environmental disasters in United States history. Because the drillers were using an insufficient length of protective casing, when the well hit a high-pressure zone in the field, it blew out, spewing enormous quantities of oil and gas into the water from the sea floor. While crews were able to cap the wellhead and relieve the pressure there, the adjacent geologic formations were not strong enough to contain the pressure, and lacking a steel protective casing, the reservoir fluid and gas ripped through the sedimentary sand layers directly on the ocean floor; the result was the 1969 Santa Barbara oil spill
1969 Santa Barbara oil spill
The Santa Barbara oil spill occurred in January and February 1969 in the Santa Barbara Channel, near the city of Santa Barbara in Southern California. It was the largest oil spill in United States waters at the time, and now ranks third after the 2010 Deepwater Horizon and 1989 Exxon Valdez spills...
of 80,000 to 100,000 barrels, which eventually coated over 40 miles of southern California coastline with oil, an ecological disaster which killed upward of 10,000 birds and numerous sea mammals and other creatures.
Following the spill, the Secretary of the Interior ended all offshore oil drilling in the Outer Continental Shelf (OCS) until measures for better oversight were put in place, which happened in 1970 with the passage of the federal National Environmental Policy Act
National Environmental Policy Act
The National Environmental Policy Act is a United States environmental law that established a U.S. national policy promoting the enhancement of the environment and also established the President's Council on Environmental Quality ....
(NEPA), and in California, with the California Environmental Quality Act
California Environmental Quality Act
The California Environmental Quality Act is a California statute passed in 1970, shortly after the United States federal government passed the National Environmental Policy Act , to institute a statewide policy of environmental protection...
(CEQA). Opposition to oil drilling was nothing new in Santa Barbara – local residents, led by a newspaper publisher, objected enough to the expansion of the Summerland field in the 1890s to organize a late-night derrick-destroying party near the present-day Miramar Hotel – but the spill intensified the local hostility to oil drilling to the point that few new platforms were installed, and none at all within the 3-mile limit.
After the disaster and cleanup, Unocal continued drilling wells from the two platforms that were already in place ("A" and "B", began producing from them in March 1969, and installed two more platforms ("C" and "Hillhouse"). Production from the field peaked quickly, reaching a maximum in 1971, during which year almost 28 million barrels of oil were extracted. The field experienced a gradual decline in production afterwards, approximately 8 percent per year, as is typical of fields when the reservoir pressure declines, and in the absence of secondary recovery technologies (such as water or gas injection). In 1985, Unocal tried waterflooding, and then polymer flooding, to improve production rates, and then in 1990 they began a horizontal drilling program to reach reservoirs impractical to exploit any other way.
Unocal continued to produce from the field until they sold all of their California production assets in 1996 to Nuevo Energy, as operated by Torch Energy Advisors. In 1997 Nuevo took over the operations of the four platforms directly, and in 2004 passed them on to Plains Exploration & Production
Plains Exploration & Production
Plains Exploration & Production, commonly known by its New York Stock Exchange ticker symbol , is a U.S. petroleum company based in Houston, Texas. A spin-off from Plains Resources, Inc., the company was founded in 2002. Its operations, as of 2009, were all in North America, including California,...
on that firm's acquisition of Nuevo. Plains only ran the platforms for a little more than four months, selling the operation to DCOR in March 2005. As of 2009, DCOR retains control of the Dos Cuadras field.
According to the Minerals Management Service (MMS), the field retains about 11.4 million barrels of oil in reserves recoverable with current technology. At the beginning of 2008, there were 145 producing oil wells distributed between the four platforms.