Semitropic Oil Field
Encyclopedia
The Semitropic Oil Field is an oil and gas field
in northwestern Kern County
in California in the United States, within the San Joaquin Valley
. Formerly known as the Semitropic Gas Field, it was discovered by the Standard Oil Company of California in 1935, and first understood to be primarily a natural gas reservoir; however, in 1956 a much deeper oil-bearing zone was discovered. The field contains the deepest oil well ever drilled in California, at 18876 feet (5,753.4 m). p. 61. While deeper boreholes have been drilled, this is the deepest that had ever been converted into a productive oil well. It was abandoned in 1975. At the end of 2008 the field still had 56 active oil wells, most of which were owned by Occidental Petroleum
, and the field had an estimated 343,000 barrels of oil still recoverable with current technology.
and Midway-Sunset
fields; in the bottomlands, the fields are more deeply buried and harder to find, as they have no surface geological expression, such as a line of hills indicating an anticlinal
structure hiding an oil reservoir. Like many of the fields on the west side of the valley, it is an elongate dome aligned from northwest to southeast. The field is about seven miles (11 km) long by two across, at the widest point, and has a productive area of 4430 acres (17.9 km²).
The field parallels Interstate 5
about five miles (8 km) to the northeast. California State Route 46, the Paso Robles Highway, cuts across the northern extremity of the field from east to west, about 12 miles (19.3 km) east of Lost Hills
. The town of Wasco
is about eight miles (13 km) farther east along the same route. Several small abandoned oil and gas fields adjoin the Semitropic field from the southeast to the southwest, and the small Wasco Oil Field (with only three wells remaining active) is immediately adjacent to the east. The nearest large and still active oil field is the Lost Hills
field, about 13 miles (20.9 km) to the west-northwest.
Terrain in the vicinity of the oil field is almost table-flat, with elevations ranging from approximately 250 to 280 feet (85.3 m) above sea level throughout the productive region, with a very slight gradient from south to north towards the Tulare Lake
bed. The Semitropic Ridge, a gentle topographic prominence with a mean elevation of about twenty feet above the oil field, parallels the field to the southwest, separating it from Interstate 5. Climate is typical of the valley bottom in the south, which is arid. Temperatures in the summer routinely exceed 100 °F (37.8 °C) on typically cloudless days. Rain falls mainly in the winter months, and averages 5 to 6 inches (152.4 mm). Freezes occur occasionally during the winter, and the winter months are also subject to frequent dense tule fog
s, limiting visibility to near zero. Drainage from the field in generally into the irrigation canal system, but because of the flat surface gradient most rainfall soaks directly into the ground.
Land use in the vicinity of the field is predominantly agricultural, with oil and gas production, storage, and transportation infrastructure interspersed with orchards and row crops. Little native vegetation remains as all the land has been converted to agricultural use. Roads cross the region at right angles, following township, range, and section lines
, as do irrigation canals.
Underneath several hundred feet of Holocene
-age alluvium, deposited by thousands of years of runoff from the mountains that ring the Central Valley, is the Pleistocene
Tulare Formation, which forms an impermeable cap to the underlying San Joaquin Clay, the principal gas-bearing unit. This unit varies in thickness from 2,200 to 4400 feet (1,341.1 m), and has an average porosity of 28%. Drillers of early boreholes had determined that deeper formations contained oil, but since it never flowed, those prospectors guessed that the permeability of the units was insufficient for the field ever to be commercially viable. Wells drilled in 1956 and subsequent years, however, proved this wrong. Underneath the San Joaquin Clay is the Etchegoin Formation, which contains the Randolph Pool, a unit which turned out to be moderately productive. Its average depth is 7400 feet (2,255.5 m) and the oil-bearing, highly porous subunit has a thickness of about 100 feet (30.5 m). Beneath this unit are several other rock units with no oil, including 4000 feet (1,219.2 m) of the Monterey Formation
; but underneath several other rock layers yet another oil pool was found in the Oligocene
-age Vedder Sands, at a depth of 17610 feet (5,367.5 m). This unit produced from only a single well, from 1975 until it was abandoned in 1977, and was the deepest oil-producing unit ever exploited in California. Oil from this depth was light, with an API gravity
of 42, and came up with a temperature of 300 °F (148.9 °C), along with a reservoir pressure of 8,200 psi.
and then part of BP
, drilled the first well into the field in 1929, but the well was poorly placed and failed to find a commercially viable gas or oil zone. Several other firms tried the area, with mixed luck: Shell Oil drilled a well all the way to 9700 feet (2,956.6 m), but both oil and gas failed to produce, though they showed in drill cuttings; Fullerton Oil drilled seven separate holes, one of which blew out ten million cubic feet of gas per day, but then stuck shut, and had to be abandoned. Standard Oil Company finally was able to complete a gas well which was self-sustaining, and was therefore considered the discovery well for the field.
Peak gas production for the field was in 1942, and peak oil was in 1981. The field changed ownership several times in its history. Recent operators have included Pacific Energy Resources and Occidental Petroleum. Pacific Energy sold the field – which amounted to 75 wells – in October 2008 to Vintage Production, a subsidiary of Occidental. Vintage still runs the field as of early 2010.
Oil and gas field
An oil and gas field is a field, or vast reservoir, that contains both oil and natural gas.-See also:* Oil field* Natural gas field* Oil reservoir* List of oil fields* List of natural gas fields...
in northwestern Kern County
Kern County, California
Spreading across the southern end of the California Central Valley, Kern County is the fifth-largest county by population in California. Its economy is heavily linked to agriculture and to petroleum extraction, and there is a strong aviation and space presence. Politically, it has generally...
in California in the United States, within the San Joaquin Valley
San Joaquin Valley
The San Joaquin Valley is the area of the Central Valley of California that lies south of the Sacramento – San Joaquin River Delta in Stockton...
. Formerly known as the Semitropic Gas Field, it was discovered by the Standard Oil Company of California in 1935, and first understood to be primarily a natural gas reservoir; however, in 1956 a much deeper oil-bearing zone was discovered. The field contains the deepest oil well ever drilled in California, at 18876 feet (5,753.4 m). p. 61. While deeper boreholes have been drilled, this is the deepest that had ever been converted into a productive oil well. It was abandoned in 1975. At the end of 2008 the field still had 56 active oil wells, most of which were owned by 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...
, and the field had an estimated 343,000 barrels of oil still recoverable with current technology.
Setting
The Semitropic field is one of the oil and gas fields in the southern San Joaquin Valley which is underneath the bottomlands of the valley, rather than in the hills which surround it. Most of the largest fields are in the lower parts of the foothills to the mountains on either side of the valley, including monstrous reservoirs such as the Kern RiverKern River Oil Field
The Kern River Oil Field is a large oil field in Kern County in the San Joaquin Valley of California, north-northeast of Bakersfield in the lower Sierra foothills...
and Midway-Sunset
Midway-Sunset Oil Field
The Midway-Sunset Oil Field is a large oil field in Kern County, San Joaquin Valley, California in the United States. Discovered in 1894, and having a cumulative production of close to of oil at the end of 2006, it is the largest oil field in California and the third largest in the United States....
fields; in the bottomlands, the fields are more deeply buried and harder to find, as they have no surface geological expression, such as a line of hills indicating an 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 hiding an oil reservoir. Like many of the fields on the west side of the valley, it is an elongate dome aligned from northwest to southeast. The field is about seven miles (11 km) long by two across, at the widest point, and has a productive area of 4430 acres (17.9 km²).
The field parallels Interstate 5
Interstate 5
Interstate 5 is the main Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific Ocean coastline from Canada to Mexico . It serves some of the largest cities on the U.S...
about five miles (8 km) to the northeast. California State Route 46, the Paso Robles Highway, cuts across the northern extremity of the field from east to west, about 12 miles (19.3 km) east of Lost Hills
Lost Hills, California
Lost Hills is a census-designated place in Kern County, California, United States. Lost Hills is located west-northwest of Bakersfield, at an elevation of 305 feet...
. The town of Wasco
Wasco, California
Wasco is a city in the San Joaquin Valley, in Kern County, California, United States. Wasco is located northwest of Bakersfield, at an elevation of 328 feet...
is about eight miles (13 km) farther east along the same route. Several small abandoned oil and gas fields adjoin the Semitropic field from the southeast to the southwest, and the small Wasco Oil Field (with only three wells remaining active) is immediately adjacent to the east. The nearest large and still active oil field is the Lost Hills
Lost Hills Oil Field
The Lost Hills Oil Field is a large oil field in the Lost Hills Range, north of the town of Lost Hills in western Kern County, California, in the United States.-Production:...
field, about 13 miles (20.9 km) to the west-northwest.
Terrain in the vicinity of the oil field is almost table-flat, with elevations ranging from approximately 250 to 280 feet (85.3 m) above sea level throughout the productive region, with a very slight gradient from south to north towards the Tulare Lake
Tulare Lake
Tulare Lake, named Laguna de Tache by the Spanish, is a fresh-water dry lake with residual wetlands and marshes in southern San Joaquin Valley, California...
bed. The Semitropic Ridge, a gentle topographic prominence with a mean elevation of about twenty feet above the oil field, parallels the field to the southwest, separating it from Interstate 5. Climate is typical of the valley bottom in the south, which is arid. Temperatures in the summer routinely exceed 100 °F (37.8 °C) on typically cloudless days. Rain falls mainly in the winter months, and averages 5 to 6 inches (152.4 mm). Freezes occur occasionally during the winter, and the winter months are also subject to frequent dense tule fog
Tule fog
Tule fog is a thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of California's Great Central Valley. Tule fog forms during the late fall and winter after the first significant rainfall. The official time frame for tule fog to form is from November 1 to March 31...
s, limiting visibility to near zero. Drainage from the field in generally into the irrigation canal system, but because of the flat surface gradient most rainfall soaks directly into the ground.
Land use in the vicinity of the field is predominantly agricultural, with oil and gas production, storage, and transportation infrastructure interspersed with orchards and row crops. Little native vegetation remains as all the land has been converted to agricultural use. Roads cross the region at right angles, following township, range, and section lines
Public Land Survey System
The Public Land Survey System is a method used in the United States to survey and identify land parcels, particularly for titles and deeds of rural, wild or undeveloped land. Its basic units of area are the township and section. It is sometimes referred to as the rectangular survey system,...
, as do irrigation canals.
Geology
The Semitropic field resembles the other three natural gas reservoirs in the southern San Joaquin Valley – the Buttonwillow, Trico, and Paloma gas fields – in being a northwest-to-southeast trending ellipsoidal dome, with the topmost unit containing commercial quantities of gas within a geologic formation known as the San Joaquin Clay. None of this geologic structure is visible on the ground surface since the Central Valley is wide and flat, but enough wells had been drilled in the general vicinity to give early prospectors the idea that a petroleum reservoir might be nearby.Underneath several hundred feet of Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
-age alluvium, deposited by thousands of years of runoff from the mountains that ring the Central Valley, is 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 ....
Tulare Formation, which forms an impermeable cap to the underlying San Joaquin Clay, the principal gas-bearing unit. This unit varies in thickness from 2,200 to 4400 feet (1,341.1 m), and has an average porosity of 28%. Drillers of early boreholes had determined that deeper formations contained oil, but since it never flowed, those prospectors guessed that the permeability of the units was insufficient for the field ever to be commercially viable. Wells drilled in 1956 and subsequent years, however, proved this wrong. Underneath the San Joaquin Clay is the Etchegoin Formation, which contains the Randolph Pool, a unit which turned out to be moderately productive. Its average depth is 7400 feet (2,255.5 m) and the oil-bearing, highly porous subunit has a thickness of about 100 feet (30.5 m). Beneath this unit are several other rock units with no oil, including 4000 feet (1,219.2 m) of 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...
; but underneath several other rock layers yet another oil pool was found 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 Vedder Sands, at a depth of 17610 feet (5,367.5 m). This unit produced from only a single well, from 1975 until it was abandoned in 1977, and was the deepest oil-producing unit ever exploited in California. Oil from this depth was light, 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 42, and came up with a temperature of 300 °F (148.9 °C), along with a reservoir pressure of 8,200 psi.
History, production, and operations
Richfield Oil Company, ancestor of ARCOARCO
Atlantic Richfield Company is an oil company with operations in the United States as well as in Indonesia, the North Sea, and the South China Sea. It has more than 1,300 gas stations in the western part of the United States. ARCO was originally formed by the merger of East Coast-based Atlantic...
and then part of BP
BP
BP p.l.c. is a global oil and gas company headquartered in London, United Kingdom. It is the third-largest energy company and fourth-largest company in the world measured by revenues and one of the six oil and gas "supermajors"...
, drilled the first well into the field in 1929, but the well was poorly placed and failed to find a commercially viable gas or oil zone. Several other firms tried the area, with mixed luck: Shell Oil drilled a well all the way to 9700 feet (2,956.6 m), but both oil and gas failed to produce, though they showed in drill cuttings; Fullerton Oil drilled seven separate holes, one of which blew out ten million cubic feet of gas per day, but then stuck shut, and had to be abandoned. Standard Oil Company finally was able to complete a gas well which was self-sustaining, and was therefore considered the discovery well for the field.
Peak gas production for the field was in 1942, and peak oil was in 1981. The field changed ownership several times in its history. Recent operators have included Pacific Energy Resources and Occidental Petroleum. Pacific Energy sold the field – which amounted to 75 wells – in October 2008 to Vintage Production, a subsidiary of Occidental. Vintage still runs the field as of early 2010.