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67-770: 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 large fields had already been operational for decades. At the beginning of 2009 it still contained an estimated 387,000 barrels (61,500 m) of recoverable oil out of its original 23.5 million, and had 15 wells remaining in operation. Vintage Production,

134-445: A cap rock) is a fundamental part of the trap that prevents hydrocarbons from further upward migration. A capillary seal is formed when the capillary pressure across the pore throats is greater than or equal to the buoyancy pressure of the migrating hydrocarbons. They do not allow fluids to migrate across them until their integrity is disrupted, causing them to leak. There are two types of capillary seal whose classifications are based on

201-406: A consequence, oil and natural gas are often found together. In common usage, deposits rich in oil are known as oil fields, and deposits rich in natural gas are called natural gas fields. In general, organic sediments buried in depths of 1,000 m to 6,000 m (at temperatures of 60 ° C to 150 °C) generate oil, while sediments buried deeper and at higher temperatures generate natural gas. The deeper

268-407: A few, very large offshore drilling rigs, due to the cost and logistical difficulties in working over water. Rising gas prices in the early 21st century encouraged drillers to revisit fields that previously were not considered economically viable. For example, in 2008 McMoran Exploration passed a drilling depth of over 32,000 feet (9754 m) (the deepest test well in the history of gas production) at

335-417: A gravity higher than 45 API. Gas cycling is the process where dry gas is injected and produced along with condensed liquid. 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. API gravity

402-642: A metric ton of West Texas Intermediate (39.6° API) has a volume of about 7.6 barrels. To derive the API gravity, the specific gravity (i.e., density relative to water) is first measured using either the hydrometer , detailed in ASTM D1298 or with the oscillating U-tube method detailed in ASTM D4052. Density adjustments at different temperatures, corrections for soda-lime glass expansion and contraction and meniscus corrections for opaque oils are detailed in

469-476: A relatively large sample volume and may not be suitable for highly viscous or opaque fluids. Proper cleaning and handling of the hydrometer are crucial to maintain accuracy, and for volatile liquids, special precautions may be necessary to prevent evaporation during measurement. Generally speaking, oil with an API gravity between 40 and 45° commands the highest prices. Above 45°, the molecular chains become shorter and less valuable to refineries. Crude oil

536-471: A result of changes in the structure of the subsurface from processes such as folding and faulting , leading to the formation of domes , anticlines , and folds. Examples of this kind of trap are an anticline trap, a fault trap, and a salt dome trap. They are more easily delineated and more prospective than their stratigraphic counterparts, with the majority of the world's petroleum reserves being found in structural traps. Stratigraphic traps are formed as

603-435: A result of lateral and vertical variations in the thickness, texture, porosity, or lithology of the reservoir rock. Examples of this type of trap are an unconformity trap, a lens trap and a reef trap. Hydrodynamic traps are a far less common type of trap. They are caused by the differences in water pressure, that are associated with water flow, creating a tilt of the hydrocarbon-water contact. The seal (also referred to as

670-502: A significantly higher displacement pressure such that the pressure required for tension fracturing is actually lower than the pressure required for fluid displacement—for example, in evaporites or very tight shales. The rock will fracture when the pore pressure is greater than both its minimum stress and its tensile strength then reseal when the pressure reduces and the fractures close. Unconventional (oil & gas) reservoirs are accumulations where oil and gas phases are tightly bound to

737-533: A subsidiary of Occidental Petroleum , was the primary operator on the field as of 2009. The field is long and narrow, exactly following the Oak Ridge Fault which also defines the alignment of the Santa Clara River, running from northeast to southwest. The field is approximately four miles long by one-quarter mile across, amounting to 640 productive acres total, mostly on the northwest side of

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804-405: Is an area of accumulated liquid petroleum underground in multiple (potentially linked) reservoirs, trapped as it rises to impermeable rock formations. In industrial terms, an oil field implies that there is an economic benefit worthy of commercial attention. Oil fields may extend up to several hundred kilometers across the surface, meaning that extraction efforts can be large and spread out across

871-402: Is analogous to saying that the oil which can be extracted forms within the source rock itself, as opposed to accumulating under a cap rock. Oil sands are an example of an unconventional oil reservoir. Unconventional reservoirs and their associated unconventional oil encompass a broad spectrum of petroleum extraction and refinement techniques, as well as many different sources. Since the oil

938-403: Is being pursued at a higher rate because of the scarcity of conventional reservoirs around the world. After the discovery of a reservoir, a petroleum engineer will seek to build a better picture of the accumulation. In a simple textbook example of a uniform reservoir, the first stage is to conduct a seismic survey to determine the possible size of the trap. Appraisal wells can be used to determine

1005-452: Is best to manage the gas cap effectively, that is, placing the oil wells such that the gas cap will not reach them until the maximum amount of oil is produced. Also a high production rate may cause the gas to migrate downward into the production interval. In this case, over time the reservoir pressure depletion is not as steep as in the case of solution-based gas drive. In this case, the oil rate will not decline as steeply but will depend also on

1072-426: Is called the stock tank oil initially in place . As a result of studying factors such as the permeability of the rock (how easily fluids can flow through the rock) and possible drive mechanisms, it is possible to estimate the recovery factor, or what proportion of oil in place can be reasonably expected to be produced. The recovery factor is commonly 30–35%, giving a value for the recoverable resources. The difficulty

1139-490: Is contained within the source rock, unconventional reservoirs require that the extracting entity function as a mining operation rather than drilling and pumping like a conventional reservoir. This has tradeoffs, with higher post-production costs associated with complete and clean extraction of oil being a factor of consideration for a company interested in pursuing a reservoir. Tailings are also left behind, increasing cleanup costs. Despite these tradeoffs, unconventional oil

1206-508: Is detailed in ASTM D287. The hydrometer method is a standard technique for directly measuring API gravity of petroleum and petroleum products. This method is based on the principle of buoyancy and utilizes a specially calibrated hydrometer to determine the API gravity of a liquid sample. The procedure typically involves the following steps: The hydrometer method is widely used due to its simplicity and low cost. However, it requires

1273-635: Is graduated in degrees on a hydrometer instrument. API gravity values of most petroleum liquids fall between 10 and 70 degrees. In 1916, the U.S. National Bureau of Standards accepted the Baumé scale , which had been developed in France in 1768, as the U.S. standard for measuring the specific gravity of liquids less dense than water . Investigation by the U.S. National Academy of Sciences found major errors in salinity and temperature controls that had caused serious variations in published values. Hydrometers in

1340-628: Is in the Santa Clara River floodplain it is mostly flat, with runoff going directly into the adjacent Santa Clara River which flows west toward its outlet into the Pacific Ocean between Oxnard and Ventura. The Saticoy field is within the Ventura Basin Province of southern California. Geologically, this area is part of a structural downwarp that occurred during the late Pliocene . Within the Ventura Basin are some of

1407-649: Is shared between Iran and Qatar . The second largest natural gas field is the Urengoy gas field , and the third largest is the Yamburg gas field , both in Russia . Like oil, natural gas is often found underwater in offshore gas fields such as the North Sea , Corrib Gas Field off Ireland , and near Sable Island . The technology to extract and transport offshore natural gas is different from land-based fields. It uses

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1474-413: Is that reservoirs are not uniform. They have variable porosities and permeabilities and may be compartmentalized, with fractures and faults breaking them up and complicating fluid flow. For this reason, computer modeling of economically viable reservoirs is often carried out. Geologists, geophysicists, and reservoir engineers work together to build a model that allows simulation of the flow of fluids in

1541-417: Is thus an inverse measure of a petroleum liquid's density relative to that of water (also known as specific gravity ). It is used to compare densities of petroleum liquids . For example, if one petroleum liquid is less dense than another, it has a greater API gravity. Although API gravity is mathematically a dimensionless quantity (see the formula below), it is referred to as being in 'degrees'. API gravity

1608-940: Is usually necessary to drill into the Earth's crust, although surface oil seeps exist in some parts of the world, such as the La Brea Tar Pits in California and numerous seeps in Trinidad . Factors that affect the quantity of recoverable hydrocarbons in a reservoir include the fluid distribution in the reservoir, initial volumes of fluids in place, reservoir pressure, fluid and rock properties, reservoir geometry, well type, well count, well placement, development concept, and operating philosophy. Modern production includes thermal , gas injection , and chemical methods of extraction to enhance oil recovery. A virgin reservoir may be under sufficient pressure to push hydrocarbons to

1675-545: The Petroleum Measurement Tables , details of usage specified in ASTM D1250. The specific gravity is defined by the formula below. With the formula presented in the previous section, the API gravity can be readily calculated. When converting oil density to specific gravity using the above definition, it is important to use the correct density of water, according to the standard conditions used when

1742-560: The aquatic ecosystem , which is usually a sea but might also be a river, lake, coral reef, or algal mat , the formation of an oil or gas reservoir also requires a sedimentary basin that passes through four steps: Timing is also an important consideration; it is suggested that the Ohio River Valley could have had as much oil as the Middle East at one time, but that it escaped due to a lack of traps. The North Sea , on

1809-407: The buoyancy forces driving the upward migration of hydrocarbons through a permeable rock cannot overcome the capillary forces of a sealing medium. The timing of trap formation relative to that of petroleum generation and migration is crucial to ensuring a reservoir can form. Petroleum geologists broadly classify traps into three categories that are based on their geological characteristics:

1876-671: The Blackbeard site in the Gulf of Mexico. ExxonMobil 's drill rig there had reached 30,000 feet by 2006, without finding gas, before it abandoned the site. Crude oil is found in all oil reservoirs formed in the Earth's crust from the remains of once-living things. Evidence indicates that millions of years of heat and pressure changed the remains of microscopic plants and animals into oil and natural gas. Roy Nurmi, an interpretation adviser for Schlumberger oil field services company, described

1943-483: The Oak Ridge Thrust Fault; oil migrating upwards within permeable units, in this case, encounters an impermeable barrier of rock placed there by the fault. Horizontally, the fault defines the course of the Santa Clara River and the northern base of the hills south of the river (including South Mountain), and is part of the fault complex responsible for the 1994 Northridge earthquake . The fault bounds

2010-670: The Santa Clara River. California State Route 126 parallels the field for its entire length, about one-half mile to the northwest. The large South Mountain Oil Field is adjacent on the northeast, and the Santa Clara Avenue and Oxnard oil fields are south of the river, on the north and south sides of U.S. Highway 101 respectively. Land use in the vicinity of the field is predominantly agricultural, with oil wells and associated production infrastructure interspersed between working agricultural fields and orchards. Climate in

2077-541: The U.S. had been manufactured and distributed widely with a modulus of 141.5 instead of the Baumé scale modulus of 140. The scale was so firmly established that, by 1921, the remedy implemented by the American Petroleum Institute was to create the API gravity scale, recognizing the scale that was actually being used. The formula to calculate API gravity from specific gravity (SG) is: Conversely,

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2144-410: The actual capacity. Laboratory testing can determine the characteristics of the reservoir fluids, particularly the expansion factor of the oil, or how much the oil expands when brought from the high pressure and high temperature of the reservoir to a "stock tank" at the surface. With such information, it is possible to estimate how many "stock tank" barrels of oil are located in the reservoir. Such oil

2211-449: The area. In addition to extraction equipment, there may be exploratory wells probing the edges to find more reservoir area, pipelines to transport the oil elsewhere, and support facilities. Oil fields can occur anywhere that the geology of the underlying rock allows, meaning that certain fields can be far away from civilization, including at sea. Creating an operation at an oil field can be a logistically complex undertaking, as it involves

2278-504: The deepest, the K, has an average depth of 9,035 feet (2,754 m). Shell Oil Co. drilled the discovery well for the field in May 1955, reaching a depth of 12,020 feet. Development of the Saticoy field was unusual in that the deepest producing horizons, the J and K, were the first to be discovered. All of the rest – F, G, H, and I – had been found by Shell by August 1956, and development of

2345-430: The equipment associated with extraction and transportation, as well as infrastructure such as roads and housing for workers. This infrastructure has to be designed with the lifespan of the oil field in mind, as production can last many years. Several companies, such as Hill International , Bechtel , Esso , Weatherford International , Schlumberger , Baker Hughes and Halliburton , have organizations that specialize in

2412-607: The field on the southeast; many of the oil-bearing units have been deformed so as to be aligned almost vertically, especially in the lower zones. The sedimentary units are predominantly turbidites , and are of Pleistocene and Pliocene age. From the top down, the units are the Pleistocene Santa Barbara Formation , which contains the producing horizon labeled the "Upper F Zone"; and the Upper Pliocene Pico Sand , which contains

2479-454: The field until 2002, at which time they sold their 41 remaining wells to Bentley-Simonson, who held it until April 2005, selling to Plains Exploration & Production , who operated the declining field for slightly more than a year, selling the 14 remaining active wells to their present operator, Vintage Production, in October 2006. As of 2010, there were 15 wells remaining on

2546-448: The field was quick after that. The field reached peak production in 1958 at 2.8 million barrels (450 × 10 ^  m) of oil per year. As production began its inevitable decline, Shell commenced waterflooding operations to increase reservoir pressure and dispose of produced water. Waterflooding ran from 1963 to 1968 in the G, H, I, and J zones. Shell held most of the field until 1984, at which time they sold it to Sage Energy. This

2613-494: The field, 14 active and operated by Vintage. The one other, owned by Ibsen Resource Management, Inc., had been idled. The 14 Vintage wells were each producing oil at an average rate of 8.1 barrels per day (1.29 m/d). 34°18′32″N 119°06′28″W  /  34.3088°N 119.1078°W  / 34.3088; -119.1078 Petroleum reservoir Reservoirs are broadly classified as conventional and unconventional reservoirs. In conventional reservoirs,

2680-402: The gas bubbles drive the oil to the surface. The bubbles then reach critical saturation and flow together as a single gas phase. Beyond this point and below this pressure, the gas phase flows out more rapidly than the oil because of its lowered viscosity. More free gas is produced, and eventually the energy source is depleted. In some cases depending on the geology the gas may migrate to the top of

2747-684: The globe, on land and offshore. The largest are the Ghawar Field in Saudi Arabia and the Burgan Field in Kuwait , with more than 66 to 104 billion barrels (9.5×10 m ) estimated in each. In the modern age, the location of oil fields with proven oil reserves is a key underlying factor in many geopolitical conflicts. Natural gas originates by the same geological thermal cracking process that converts kerogen to petroleum. As

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2814-525: The horizons labeled "Lower F Zone", "G Zone", "H Zone", "I Zone", "J Zone", and "K Zone." Most of the oil is between 6,000 and 9,000 feet (1,800 and 2,700 m) below ground surface. Oil is of medium gravity and low sulfur content throughout, varying little between the different producing horizons. API gravity varies from 30 to 36. The shallowest producing formation, the Upper F Zone, has an average depth of 6,350 feet (1,940 m) below ground surface, and

2881-575: The large-scale construction of the infrastructure to support oil field exploitation. The term "oilfield" can be used as a shorthand to refer to the entire petroleum industry . However, it is more accurate to divide the oil industry into three sectors: upstream ( crude oil production from wells and separation of water from oil ), midstream (pipeline and tanker transport of crude oil) and downstream ( refining of crude oil to products, marketing of refined products, and transportation to oil stations). More than 65,000 oil fields are scattered around

2948-434: The liquid sections applying extra pressure. This is present in the reservoir if there is more gas than can be dissolved in the reservoir. The gas will often migrate to the crest of the structure. It is compressed on top of the oil reserve, as the oil is produced the cap helps to push the oil out. Over time the gas cap moves down and infiltrates the oil, and the well will produce more and more gas until it produces only gas. It

3015-438: The location of oil-water contact and with it the height of the oil bearing sands. Often coupled with seismic data, it is possible to estimate the volume of an oil-bearing reservoir. The next step is to use information from appraisal wells to estimate the porosity of the rock. The porosity of an oil field, or the percentage of the total volume that contains fluids rather than solid rock, is 20–35% or less. It can give information on

3082-534: The measurement was made. The official density of water at 60 °F according to the 2008 edition of ASTM D1250 is 999.016 kg/m . The 1980 value is 999.012 kg/m . In some cases the standard conditions may be 15 °C (59 °F) and not 60 °F (15.56 °C), in which case a different value for the water density would be appropriate ( see standard conditions for temperature and pressure ). There are advantages to field testing and on-board conversion of measured volumes to volume correction. This method

3149-403: The naturally occurring hydrocarbons, such as crude oil ( petroleum ) or natural gas , are trapped by overlying rock formations with lower permeability , while in unconventional reservoirs the rocks have high porosity and low permeability, which keeps the hydrocarbons trapped in place, therefore not requiring a cap rock . Reservoirs are found using hydrocarbon exploration methods. An oil field

3216-438: The oil and form a secondary gas cap. Some energy may be supplied by water, gas in water, or compressed rock. These are usually minor contributions with respect to hydrocarbon expansion. By properly managing the production rates, greater benefits can be had from solution-gas drives. Secondary recovery involves the injection of gas or water to maintain reservoir pressure. The gas/oil ratio and the oil production rate are stable until

3283-724: The other hand, endured millions of years of sea level changes that successfully resulted in the formation of more than 150 oil fields. Although the process is generally the same, various environmental factors lead to the creation of a wide variety of reservoirs. Reservoirs exist anywhere from the land surface to 30,000 ft (9,000 m) below the surface and are a variety of shapes, sizes, and ages. In recent years, igneous reservoirs have become an important new field of oil exploration, especially in trachyte and basalt formations. These two types of reservoirs differ in oil content and physical properties like fracture connectivity, pore connectivity, and rock porosity . A trap forms when

3350-406: The placement of the well with respect to the gas cap. As with other drive mechanisms, water or gas injection can be used to maintain reservoir pressure. When a gas cap is coupled with water influx, the recovery mechanism can be highly efficient. Water (usually salty) may be present below the hydrocarbons. Water, as with all liquids, is compressible to a small degree. As the hydrocarbons are depleted,

3417-431: The preferential mechanism of leaking: the hydraulic seal and the membrane seal. A membrane seal will leak whenever the pressure differential across the seal exceeds the threshold displacement pressure, allowing fluids to migrate through the pore spaces in the seal. It will leak just enough to bring the pressure differential below that of the displacement pressure and will reseal. A hydraulic seal occurs in rocks that have

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3484-429: The pressure. As the reservoir depletes, the pressure falls below the bubble point , and the gas comes out of solution to form a gas cap at the top. This gas cap pushes down on the liquid helping to maintain pressure. This occurs when the natural gas is in a cap below the oil. When the well is drilled the lowered pressure above means that the oil expands. As the pressure is reduced it reaches bubble point, and subsequently

3551-485: The process as follows: Plankton and algae, proteins and the life that's floating in the sea, as it dies, falls to the bottom, and these organisms are going to be the source of our oil and gas. When they're buried with the accumulating sediment and reach an adequate temperature, something above 50 to 70 °C they start to cook. This transformation, this change, changes them into the liquid hydrocarbons that move and migrate, will become our oil and gas reservoir. In addition to

3618-491: The reduction in pressure in the reservoir allows the water to expand slightly. Although this unit expansion is minute, if the aquifer is large enough this will translate into a large increase in volume, which will push up on the hydrocarbons, maintaining pressure. With a water-drive reservoir, the decline in reservoir pressure is very slight; in some cases, the reservoir pressure may remain unchanged. The gas/oil ratio also remains stable. The oil rate will remain fairly stable until

3685-466: 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, almost all in the winter, and all in the form of rain. The mean annual temperature is 56 °F (13 °C) to 60 °F (16 °C); freezes occur rarely. Elevations on the field range from about 140 to 220 feet (43 to 67 m) above sea level. As it

3752-408: The reservoir pressure drops below the bubble point when critical gas saturation is reached. When the gas is exhausted, the gas/oil ratio and the oil rate drops, the reservoir pressure has been reduced, and the reservoir energy is exhausted. In reservoirs already having a gas cap (the virgin pressure is already below bubble point), the gas cap expands with the depletion of the reservoir, pushing down on

3819-409: The reservoir, leading to an improved estimate of the recoverable resources. Reserves are only the part of those recoverable resources that will be developed through identified and approved development projects. Because the evaluation of reserves has a direct impact on the company or the asset value, it usually follows a strict set of rules or guidelines. To obtain the contents of the oil reservoir, it

3886-591: The richest agricultural fields in California, made possible by the thick alluvial topsoil left by tens of thousands of years of floods from the area's river systems. The basin is filled with sedimentary layers, and cut through from northeast to southwest by the Oak Ridge Fault . In the Saticoy field, oil is trapped both in pinchouts of updipping permeable sedimentary units within units of lesser permeability, and in sedimentary units which end abruptly at

3953-410: The rock fabric by strong capillary forces, requiring specialised measures for evaluation and extraction. Unconventional reservoirs form in completely different ways to conventional reservoirs, the main difference being that they do not have "traps". This type of reservoir can be driven in a unique way as well, as buoyancy might not be the driving force for oil and gas accumulation in such reservoirs. This

4020-410: The source, the "drier" the gas (that is, the smaller the proportion of condensates in the gas). Because both oil and natural gas are lighter than water, they tend to rise from their sources until they either seep to the surface or are trapped by a non-permeable stratigraphic trap. They can be extracted from the trap by drilling. The largest natural gas field is South Pars/Asalouyeh gas field, which

4087-436: The specific gravity of petroleum liquids can be derived from their API gravity value as Thus, a heavy oil with a specific gravity of 1.0 (i.e., with the same density as pure water at 60 °F) has an API gravity of: In the oil industry, quantities of crude oil are often measured in metric tons . One can calculate the approximate number of barrels per metric ton for a given crude oil based on its API gravity: For example,

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4154-454: The structural trap, the stratigraphic trap, and the far less common hydrodynamic trap . The trapping mechanisms for many petroleum reservoirs have characteristics from several categories and can be known as a combination trap. Traps are described as structural traps (in deformed strata such as folds and faults) or stratigraphic traps (in areas where rock types change, such as unconformities, pinch-outs and reefs). Structural traps are formed as

4221-452: The surface. As the fluids are produced, the pressure will often decline, and production will falter. The reservoir may respond to the withdrawal of fluid in a way that tends to maintain the pressure. Artificial drive methods may be necessary. This mechanism (also known as depletion drive) depends on the associated gas of the oil. The virgin reservoir may be entirely semi-liquid but will be expected to have gaseous hydrocarbons in solution due to

4288-407: The water begins to be produced along with the oil, the recovery rate may become uneconomical owing to the higher lifting and water disposal costs. If the natural drives are insufficient, as they very often are, then the pressure can be artificially maintained by injecting water into the aquifer or gas into the gas cap. The force of gravity will cause the oil to move downward of the gas and upward of

4355-431: The water reaches the well. In time, the water cut will increase, and the well will be watered out. The water may be present in an aquifer (but rarely one replenished with surface water ). This water gradually replaces the volume of oil and gas that is produced out of the well, given that the production rate is equivalent to the aquifer activity. That is, the aquifer is being replenished from some natural water influx. If

4422-442: The water. If vertical permeability exists then recovery rates may be even better. These occur if the reservoir conditions allow the hydrocarbons to exist as a gas. Retrieval is a matter of gas expansion. Recovery from a closed reservoir (i.e., no water drive) is very good, especially if bottom hole pressure is reduced to a minimum (usually done with compressors at the wellhead). Any produced liquids are light-colored to colorless, with

4489-421: Was a period during which many of the major oil companies were divesting their operations in the onshore coastal portions of California, selling them to smaller independent operators, in order to focus on more profitable opportunities overseas. Sage held the field until 1990, at which time they sold it to Whiting Petroleum Corp; Whiting sold some active wells to Crimson Resource Management Corp. in 1994. Crimson ran

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