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Petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
is a
fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...
that can be drawn from beneath the earth's surface. Reservoirs of petroleum was formed through the mixture of plants, algae, and sediments in shallow seas under high pressure. Petroleum is mostly recovered from oil drilling. Seismic surveys and other methods are used to locate oil reservoirs. Oil rigs and
oil platforms An oil platform (or oil rig, offshore platform, oil production platform, and similar terms) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platf ...
are used to drill long holes into the earth to create an oil well and extract petroleum. After extraction, oil is refined to make
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
and other products such as tires and refrigerators. Extraction of petroleum can be dangerous and have led to oil spills.


Locating the oil field

Geologists and geophysicists use
seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
surveys to search for geological structures that may form oil reservoirs. The "classic" method includes making an underground
explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
nearby and observing the seismic response, which provides information about the geological structures underground. However, "passive" methods that extract information from naturally occurring seismic waves are also used. Other instruments such as
gravimeter Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest. Units of measurement Gr ...
s and
magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
s are also used in the search for petroleum. Extracting
crude oil Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
normally starts with drilling wells into an underground reservoir. When an oil well has been tapped, a geologist (known on the rig as the "mudlogger") will note its presence. Historically in the United States, in some
oil field A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presen ...
s the oil rose naturally to the surface, but most of these fields have long since been used up, except in parts of
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
. Often many wells (called ''multilateral wells'') are drilled into the same reservoir, to an economically viable extraction rate. Some wells (''secondary wells'') may pump
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
,
steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...
,
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
s or various gas mixtures into the reservoir to raise or maintain the reservoir pressure and economical extraction


Drilling

The oil well is created by drilling a long hole into the earth with an oil rig. A steel pipe (casing) is placed in the hole, to provide structural integrity to the newly drilled well bore. Holes are then made in the base of the well to enable oil to pass into the bore. Finally, a collection of valves called a "
Christmas tree A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern ...
" is fitted to the top; the valves regulate pressures and control flow. The
drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...
process comes under "upstream", one of the three main services in the oil industry, along with mid-stream and downstream.


Oil extraction and recovery


Primary recovery

During the ''primary recovery stage'', reservoir drive comes from a number of natural mechanisms. These include: natural water displacing oil downward into the well, expansion of the
associated petroleum gas Associated petroleum gas (APG), or associated gas, is a form of natural gas which is found with deposits of petroleum, either dissolved in the oil or as a free "gas cap" above the oil in the reservoir. The gas can be utilized in a number of ways ...
at the top of the reservoir, expansion of the associated gas initially dissolved in the crude oil, and gravity drainage resulting from the movement of oil within the reservoir from the upper to the lower parts where the wells are located. Recovery factor during the primary recovery stage is typically 5-15%. While the underground pressure in the oil reservoir is sufficient to force the oil (along with some associated gas) to the surface, all that is necessary is to place a complex arrangement of
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s (the
Christmas tree A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern ...
) on the well head to connect the well to a pipeline network for storage and processing. Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface; these are known as artificial lifting mechanisms.


Secondary recovery

Over the lifetime of a well, the pressure falls. At some point there is insufficient underground pressure to force the oil to the surface. After natural reservoir drive diminishes, ''secondary recovery'' methods are applied. These rely on supplying external energy to the reservoir by injecting fluids to increase reservoir pressure, hence increasing or replacing the natural reservoir drive with an artificial drive. Secondary recovery techniques increase the reservoir's pressure by water injection, gas reinjection and
gas lift Gas lift or bubble pumps use the artificial lift technique of raising a fluid such as water or oil by introducing bubbles of compressed air, water vapor or other vaporous bubbles into the outlet tube. This has the effect of reducing the hydrost ...
. Gas reinjection and lift each use associated gas,
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
or some other inert gas to reduce the density of the oil-gas mixture, and thus improve its mobility. The typical recovery factor from water-flood operations is about 30%, depending on the properties of the oil and the characteristics of the reservoir rock. On average, the recovery factor after primary and secondary oil recovery operations is between 35 and 45%.


Enhanced recovery

Enhanced, or tertiary oil recovery methods, increase the mobility of the oil in order to increase extraction. Thermally enhanced oil recovery methods (TEOR) are tertiary recovery techniques that heat the oil, reducing its viscosity and making it easier to extract. Steam injection is the most common form of TEOR, and it is often done with a
cogeneration Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time. Cogeneration is a more efficient use of fuel or heat, because otherwise- wasted heat from elec ...
plant. This type of cogeneration plant uses a
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
to generate
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...
, and the
waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utilit ...
is used to produce steam, which is then injected into the reservoir. This form of recovery is used extensively to increase oil extraction in the
San Joaquin Valley The San Joaquin Valley ( ; es, Valle de San Joaquín) is the area of the Central Valley of the U.S. state of California that lies south of the Sacramento–San Joaquin River Delta and is drained by the San Joaquin River. It comprises seven ...
, which yields a very heavy oil, yet accounts for ten percent of the United States' oil extraction. Fire flooding (In-situ burning) is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil. Occasionally,
surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...
s (
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s) are injected to alter the surface tension between the water and the oil in the reservoir, mobilizing oil which would otherwise remain in the reservoir as residual oil. Another method to reduce viscosity is
carbon dioxide flooding Carbon dioxide (CO2) flooding is a process whereby carbon dioxide is injected into oil reservoirs in order to increase output when extracting oil, especially in reservoirs where production rates have declined over time. The process was first attem ...
. Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered. In some California heavy oil fields, steam injection has doubled or even tripled the oil reserves and ultimate oil recovery. For example, see Midway-Sunset Oil Field, California's largest oilfield. Tertiary recovery begins when secondary oil recovery is not enough to continue adequate extraction, but only when the oil can still be extracted
profit Profit may refer to: Business and law * Profit (accounting), the difference between the purchase price and the costs of bringing to market * Profit (economics), normal profit and economic profit * Profit (real property), a nonpossessory inter ...
ably. This depends on the
cost In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something or deliver a service, and hence is not available for use anymore. In business, the cost may be one of acquisition, in whic ...
of the extraction method and the current price of crude oil. When prices are high, previously unprofitable wells are brought back into use, and when they are low, extraction is curtailed. The use of microbial treatments is another tertiary recovery method. Special blends of the microbes are used to treat and break down the hydrocarbon chain in oil, making the oil easy to recover. It is also more economical versus other conventional methods. In some states such as Texas, there are tax incentives for using these microbes in what is called a secondary tertiary recovery. Very few companies supply these.


Recovery rates

The amount of oil that is recoverable is determined by a number of factors, including the permeability of the rock, the strength of natural drives (the associated gas present, pressure from adjacent water or gravity),
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
of the reservoir rock, i.e. the rock storage capacity, and the viscosity of the oil. When the reservoir rocks are "tight", as in
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
, oil generally cannot flow through, but when they are permeable, as in
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...
, oil flows freely.


Estimated ultimate recovery

Although recovery of a well cannot be known with certainty until the well ceases production, petroleum engineers often determine an
estimated ultimate recovery Estimated ultimate recovery or Expected ultimate recovery (EUR) of a resource is the sum of the proven reserves Proven reserves (also called measured reserves, 1P, and reserves) is a measure of fossil fuel energy reserves, such as oil reserves, n ...
(EUR) based on decline rate projections years into the future. Various models, mathematical techniques, and approximations are used. Shale gas EUR is difficult to predict, and it is possible to choose recovery methods that tend to underestimate decline of the well beyond that which is reasonable.


Health and safety

The oil and gas extraction workforce faces unique health and safety challenges and is recognized by the
National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...
(NIOSH) as a priority industry sector in the
National Occupational Research Agenda The National Occupational Research Agenda (NORA) is a partnership program developed by the National Institute for Occupational Safety and Health (NIOSH). The program was founded in 1996 to provide a framework for research collaborations among univer ...
(NORA) to identify and provide intervention strategies regarding occupational health and safety issues. During 2003–2013, the annual rate of occupational fatalities significantly decreased 36.3%; however, the number of work-related fatalities in the U.S. oil and gas extraction industry increased 27.6%, with a total of 1,189 deaths because the size of the workforce grew during this period. Two-thirds of all worker fatalities were attributed to transportation incidents and contact with objects or equipment. More than 50% of persons fatally injured were employed by companies that service wells. Hazard controls include land transportation safety policies and
engineering controls Engineering controls are strategies designed to protect workers from hazardous conditions by placing a barrier between the worker and the hazard or by removing a hazardous substance through air ventilation. Engineering controls involve a physi ...
such as automated technologies.


See also


References

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