Ventura Oil Field
Encyclopedia
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 (13 km) long by two across, with the long axis aligned east to west. Discovered in 1919, and with a cumulative production of just under a billion barrels of oil as of 2008, it is the seventh-largest oil field in California, retaining approximately 50 million barrels in reserve, and had 423 wells still producing. As of 2009 it was entirely operated by Aera Energy LLC
.
and coastal sage scrub, and riparian woodland is found along the course of the Ventura River. Terrain on the hills is steep, and the roads to well pads, tanks, and other infrastructure make numerous switchbacks. Most of the field is hidden from view from the city because of the first steep range of hills. The oil field is one of several following the east-west trend of the Transverse Ranges at this point: to the west are the San Miguelito Oil Field
and the Rincon Oil Field
, and to the east, across the Santa Clara River
valley, the large South Mountain Oil Field
adjacent to Santa Paula
and the smaller Saticoy Oil Field
along the Santa Clara River east of Saticoy. To the north are the smaller Ojai and Santa Paula fields. Total productive area of the field, projected to the surface, encompasses 3410 acres (13.8 km²).
California State Route 33, which follows the route of the Ventura River through the hills and through the field, provides much of the vehicular access, and other access roads come directly from the city of Ventura to the south.
Climate in the area is Mediterranean
, with cool, rainy winters and mild, dry summers, cooled by morning coastal clouds. Elevations on the field range from about 40 feet (12.2 m) above sea level along the Ventura River to around 1200 feet (365.8 m) on the highest ridges both east and west of the river. Runoff from the oil field is into the Ventura River, although some of the eastern portions of the field drain south into the Santa Clara River.
dips steeply on both sides, with the dip angle ranging from 30 to 60 degrees, resulting in a series of rock beds resembling a long house with a gabled roof, under which oil and gas collect in abundance. Within this feature, the primary petroleum-bearing unit is the Pico Formation, a sedimentary
unit of turbidite
sands of high porosity (16 to 20 percent). Additionally, oil is found in the underlying Santa Margarita Formation. Eight different oil-bearing zones have been identified by number, 1st through 8th based on depth, with the 2nd zone the first to be discovered, in March 1919 by the Shell Oil Company. The pools range in depth from 3680 feet (1,121.7 m) to over 12000 feet (3,657.6 m), although depth within each pool varies greatly; the discovery well into the 2nd zone, which has an average depth of 5180 feet (1,578.9 m), had a total depth of only 3500 feet (1,066.8 m).
The underlying Monterey Formation
is presumed to be the source of the oil accumulations in the Ventura field, as well as the other two fields in the same geologic trend. The Monterey Formation is rich in organic matter, averaging 3-5 percent but reaching 23 percent in some areas. Oil likely migrated upwards during the late Pliocene
, becoming trapped in the folds and structural traps of the higher rocks of the anticline which form an impermeable caps. Some of the oil-bearing zones, such as the 4th and 5th, are capped by the Barnard Fault, which provides an additional structural trap. Even with the impermeable caps and structural traps, there are enough breaks in the structure for significant natural tar seeps to occur; indeed the entire region is riddled with natural seeps, and tar was used by the native Chumash peoples as a sealant for their watercraft.
Oil gravity and sulfur content is similar in all pools in the field, with an API gravity
of 29-30 and approximately 1 percent sulfur by weight.
While the field was productive from the earliest years, it had a reputation for difficulty, and challenged the technological skill of the early 20th-century drillers. The Lloyd No. 102 well, operated by the Associated Oil Company, was the deepest production well in the world in 1928, producing from a depth of 7210 feet (2,197.6 m). Later wells reached even greater depths, as drillers attempted to find the bottom of this extraordinarily productive but challenging field. Shell Oil Company's Taylor 653 reached a depth of 21500 feet (6,553.2 m), penetrating into the Miocene
age Monterey Formation
, but found no oil at those depths. Deeper reservoir oil was extremely hot; the temperature of oil in the 4th zone, discovered in 1925, and determined later to have an average depth of 9150 feet (2,788.9 m), was approximately 300 °F (148.9 °C).
Production at the field peaked in the 1950s, at which time the field became the 12th most productive in the United States. In 1954 alone the field produced over 31 million barrels of oil. As production began to decline after 1954, technologies for enhanced recovery became available. Waterflooding – the reinjection of produced water to increase reservoir pressure, allowing wells with diminishing returns to flow more freely – commenced in most zones in the late 1950s and 1960s, and continues in the present.
Aera Energy LLC
, a joint venture of ExxonMobil
and Shell Oil Co., eventually acquired the entire field, by consolidation of their predecessor company's operations and acquisition of the few remaining independent operators in the area. Their neighbor on the abutting San Miguelito and Rincon fields to the west is Vintage Petroleum, a subsidiary of Occidental Petroleum. In 2009 Aera was still producing an average of 11,600 barrels of oil a day from the field, making the company the largest oil and gas producer in Ventura County.
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 the hills immediately north of the city 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...
in southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
in the United States. It is bisected by California State Route 33
California State Route 33
State Route 33 is a north–south state highway in the U.S. state of California. SR 33 replaced part of U.S. Route 399 in 1964 during the "great renumbering" of routes. In the unincorporated sections of Kern County it is known as the West Side Highway...
, the freeway connecting Ventura to Ojai
Ojai, California
Ojai is a city in Ventura County, California, USA. It is situated in the Ojai Valley , surrounded by hills and mountains. The population was 7,461 at the 2010 census, down from 7,862 at the 2000 census.-History:Chumash Indians were the early inhabitants of the valley...
, and is about eight miles (13 km) long by two across, with the long axis aligned east to west. Discovered in 1919, and with a cumulative production of just under a billion barrels of oil as of 2008, it is the seventh-largest oil field in California, retaining approximately 50 million barrels in reserve, and had 423 wells still producing. As of 2009 it was entirely operated by Aera Energy LLC
Aera Energy LLC
Aera Energy LLC is a natural gas, oil exploration and production company jointly owned by Shell and ExxonMobil headquartered in Bakersfield, California...
.
Setting
The oil field is on and beneath the ranges of hills northwest, north and northeast of the city of Ventura. The Ventura River, flowing down from Ojai, cuts through the field, and empties into the Pacific Ocean at Ventura. Native vegetation in the hills is predominantly chaparralChaparral
Chaparral is a shrubland or heathland plant community found primarily in the U.S. state of California and in the northern portion of the Baja California peninsula, Mexico...
and coastal sage scrub, and riparian woodland is found along the course of the Ventura River. Terrain on the hills is steep, and the roads to well pads, tanks, and other infrastructure make numerous switchbacks. Most of the field is hidden from view from the city because of the first steep range of hills. The oil field is one of several following the east-west trend of the Transverse Ranges at this point: to the west are the San Miguelito Oil Field
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 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...
, and to the east, across the Santa Clara River
Santa Clara River (California)
The Santa Clara River is approximately long, located in southern California in the United States. It drains an area of the coastal mountains north of Los Angeles. The Santa Clara is one of the largest river systems along the coast of Southern California and one of only a few remaining river...
valley, the large South Mountain Oil Field
South Mountain Oil Field
The South Mountain Oil Field is a large and productive oil field 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...
adjacent to Santa Paula
Santa Paula, California
Santa Paula is a city within Ventura County, California, United States. The population was 29,321 at the 2010 census, up from 28,598 at the 2000 census...
and the smaller Saticoy Oil Field
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 productive fields found in the region after most of the...
along the Santa Clara River east of Saticoy. To the north are the smaller Ojai and Santa Paula fields. Total productive area of the field, projected to the surface, encompasses 3410 acres (13.8 km²).
California State Route 33, which follows the route of the Ventura River through the hills and through the field, provides much of the vehicular access, and other access roads come directly from the city of Ventura to the south.
Climate in the area 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 mild, dry summers, cooled by morning coastal clouds. Elevations on the field range from about 40 feet (12.2 m) above sea level along the Ventura River to around 1200 feet (365.8 m) on the highest ridges both east and west of the river. Runoff from the oil field is into the Ventura River, although some of the eastern portions of the field drain south into the Santa Clara River.
Geology
In the Ventura field, the large-scale structural feature responsible for petroleum accumulation is the Ventura Anticline, an east-west trending geologic structure 16 miles (25.7 km) long, visible in the numerous rock outcrops in the rugged topography of the area. This anticlineAnticline
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...
dips steeply on both sides, with the dip angle ranging from 30 to 60 degrees, resulting in a series of rock beds resembling a long house with a gabled roof, under which oil and gas collect in abundance. Within this feature, the primary petroleum-bearing unit is the Pico Formation, a 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....
unit of turbidite
Turbidite
Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...
sands of high porosity (16 to 20 percent). Additionally, oil is found in the underlying Santa Margarita Formation. Eight different oil-bearing zones have been identified by number, 1st through 8th based on depth, with the 2nd zone the first to be discovered, in March 1919 by the Shell Oil Company. The pools range in depth from 3680 feet (1,121.7 m) to over 12000 feet (3,657.6 m), although depth within each pool varies greatly; the discovery well into the 2nd zone, which has an average depth of 5180 feet (1,578.9 m), had a total depth of only 3500 feet (1,066.8 m).
The underlying 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...
is presumed to be the source of the oil accumulations in the Ventura field, as well as the other two fields in the same geologic trend. The Monterey Formation is rich in organic matter, averaging 3-5 percent but reaching 23 percent in some areas. Oil likely migrated upwards 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...
, becoming trapped in the folds and structural traps of the higher rocks of the anticline which form an impermeable caps. Some of the oil-bearing zones, such as the 4th and 5th, are capped by the Barnard Fault, which provides an additional structural trap. Even with the impermeable caps and structural traps, there are enough breaks in the structure for significant natural tar seeps to occur; indeed the entire region is riddled with natural seeps, and tar was used by the native Chumash peoples as a sealant for their watercraft.
Oil gravity and sulfur content is similar in all pools in the field, with an 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 29-30 and approximately 1 percent sulfur by weight.
History, production and operations
Prior to the drilling of the discovery well for the Ventura in 1919, a utility company drilled some gas wells in the area in 1903. While they reached depths of between 400 and 800 feet (243.8 m), it is not known if they produced oil. Shell Oil drilled the first well into what is now known as the 2nd Pool, in the Pico Formation, in March 1919, reaching a depth of 3498 feet (1,066.2 m).While the field was productive from the earliest years, it had a reputation for difficulty, and challenged the technological skill of the early 20th-century drillers. The Lloyd No. 102 well, operated by the Associated Oil Company, was the deepest production well in the world in 1928, producing from a depth of 7210 feet (2,197.6 m). Later wells reached even greater depths, as drillers attempted to find the bottom of this extraordinarily productive but challenging field. Shell Oil Company's Taylor 653 reached a depth of 21500 feet (6,553.2 m), penetrating into the 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 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...
, but found no oil at those depths. Deeper reservoir oil was extremely hot; the temperature of oil in the 4th zone, discovered in 1925, and determined later to have an average depth of 9150 feet (2,788.9 m), was approximately 300 °F (148.9 °C).
Production at the field peaked in the 1950s, at which time the field became the 12th most productive in the United States. In 1954 alone the field produced over 31 million barrels of oil. As production began to decline after 1954, technologies for enhanced recovery became available. Waterflooding – the reinjection of produced water to increase reservoir pressure, allowing wells with diminishing returns to flow more freely – commenced in most zones in the late 1950s and 1960s, and continues in the present.
Aera Energy LLC
Aera Energy LLC
Aera Energy LLC is a natural gas, oil exploration and production company jointly owned by Shell and ExxonMobil headquartered in Bakersfield, California...
, a joint venture of ExxonMobil
ExxonMobil
Exxon Mobil Corporation or ExxonMobil, is an American multinational oil and gas corporation. It is a direct descendant of John D. Rockefeller's Standard Oil company, and was formed on November 30, 1999, by the merger of Exxon and Mobil. Its headquarters are in Irving, Texas...
and Shell Oil Co., eventually acquired the entire field, by consolidation of their predecessor company's operations and acquisition of the few remaining independent operators in the area. Their neighbor on the abutting San Miguelito and Rincon fields to the west is Vintage Petroleum, a subsidiary of Occidental Petroleum. In 2009 Aera was still producing an average of 11,600 barrels of oil a day from the field, making the company the largest oil and gas producer in Ventura County.