The Mount Poso Oil Field is a large oil and gas field in the lower foothills of the Sierra Nevada Mountains in Kern County, California

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...

. Discovered in 1926, and relatively close to exhaustion with less than three percent of its original oil remaining, it is the 21st largest field in California by total ultimate oil recovery, having a cumulative production of close to 300 Moilbbl. The current principal operator of the field is Plains Exploration & Production; 652 wells remained active at the end of 2006, while production had dwindled to 554000 barrels (88,079 m³) during that year, from a peak of over 9 million in 1981.

Setting

The oil field is in the lower Sierra Foothills, north and northeast of the city of Bakersfield, and directly north of the giant Kern River Oil Field

Kern 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...

. To the west is the large agricultural region of 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...

. Vegetation on the hills around the oil field is mostly grassland. The field is about nine miles (14 km) long and four to five miles (8 km) across, although some of the productive areas are widely separated, and even within the four named areas the pools are often discontiguous. Elevations on the field range from around 650 feet (198.1 m) at the southern boundary along Poso Creek to over 1400 feet (426.7 m) in the northeastern portion; the central area of operations, around Halfway House, is approximately 1100 feet (335.3 m) above sea level.

Access to the field is by several roads. Famoso Woody Road enters the field from the west, from its junction with California State Route 65 in the San Joaquin Valley bottom, and Granite Road crosses the field from south to north, also passing through the Kern Front field.

Other oil fields nearby, in addition the Kern River field, are the Poso Creek Oil Field to the southwest, adjacent to the San Joaquin Valley bottomland, and the Kern Front Oil Field

Kern Front Oil Field

The Kern Front Oil Field is a large oil and gas field in the lower Sierra Nevada foothills in Kern County, California. Discovered in 1912, and with a cumulative production of around of oil, it ranks 29th in size in the state, and is believed to retain approximately ten percent of its original oil...

, which is between the Poso Creek field and the Kern River field; all three of these nearby fields are in the lowest portion of the foothills as they begin to rise from the valley floor. To the southeast of Mount Poso is the Round Mountain Oil Field

Round Mountain Oil Field

The Round Mountain Oil Field is a large oil and gas field in the foothills of the Sierra Nevada Mountains, about ten miles northeast of Bakersfield, California. It is east of the giant Kern River Oil Field, one of the largest in the United States, and also close to the Mount Poso Oil Field and...

.

The climate is semi-arid, with long, hot summers and cool winters. Most precipitation falls in the winter, in the form of rain, with the amount increasing with elevation. Summertime temperatures regularly exceed 100 °F (37.8 °C).

Geology

The Mount Poso Oil Field is a complex agglomeration of petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 pools in structural and stratigraphic traps, and divided into six general areas, all of which are cut by faults, and many of which are discontinguous even within named areas. From north to south, the areas are: Dominion, the second-largest, at 790 acres (3.2 km²); Granite Canyon (130 acre (0.5260918 km²)); the Main Area, the largest, at 2335 acres (9.4 km²); West (210 acre (0.8498406 km²)); Dorsey Area (410 acres (1.7 km²)); and the Baker-Grover Area (115 acre (0.4653889 km²)). All six areas include wells in the Vedder Formation, of 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, while the Dominion and Main Areas also include wells in the more recently-discovered Freeman-Jewett Formation, 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. Source rocks are well-sorted medium grain marine sandstones of high porosity (around 35%).

The oil field is shallow, compared to other Central Valley fields, as the basement rocks are only about 3000 feet (914.4 m) below ground surface. The deepest well only goes to 3759 feet (1,145.7 m), reaching the Freeman Formation, of Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 age. Underneath the oil-bearing sedimentary formations, the basement granitic complex is of Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 age. It rises towards the east, part of the enormous Sierra Nevada Batholith

Sierra Nevada Batholith

The Sierra Nevada Batholith is a large batholith which forms the core of the Sierra Nevada mountain range in California, USA, exposed at the surface as granite....

.

Oil from the field is heavy crude, and consistent between the different areas, ranging from 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 13 to 16. Sulfur content is also consistent at approximately 0.65 percent by weight throughout the different pools.

History, production, and operations

The Mount Poso Oil Field was discovered in 1926, during an era in which many of the large California oil fields were found, especially those adjacent to the previous large discoveries which had taken place in the preceding three decades.

Shell Oil acquired the field in the 1960s, intending to subject the entire area to steam flooding, a technology which was then new, and producing impressive yields elsewhere in heavy oil fields in California, such as the Midway-Sunset and Kern River fields. In 1969, production from the field was a mere 1560 barrels (248 m³) of oil per day (BOPD); however, by the 1980s, Shell had increased production to 25000 barrels (3,974.7 m³) of oil per day, attaining a total of over 9 Moilbbl in 1981, the highest yield ever achieved from the field, and making the field the 8th-most productive in the state. In 1999, as the field appeared to be played out, they sold it to Nuevo Energy, the predecessor of 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,...

 (PXP). This firm ran the field until they sold their portion of it to Vintage Production LLC, a subsidiary of 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...

, in 2006. As of 2009, Vintage was the largest operator on the field, with numerous smaller operators still active.