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Petroleum is a fossil fuel that can be drawn from beneath the Earth's surface. Reservoirs of petroleum are 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 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 and other products such as tires and refrigerators. Extraction of petroleum can be dangerous and have led to oil spills. [1]
Geologists and geophysicists use seismic surveys to search for geological structures that may form oil reservoirs. The "classic" method includes making an underground explosion 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. [2]
Other instruments such as gravimeters and magnetometers are also used in the search for petroleum. Extracting crude oil 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 fields the oil rose naturally to the surface, but most of these fields have long since been used up, except in parts of Alaska. 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, steam, acids or various gas mixtures into the reservoir to raise or maintain the reservoir pressure and economical extraction
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 " is fitted to the top; the valves regulate pressures and control flow. The drilling process comes under "upstream", one of the three main services in the oil industry, along with mid-stream and downstream.
During the primary recovery stage, reservoir drive comes from a number of natural mechanisms:
Recovery factor during the primary recovery stage is typically 5-15%. [3]
When 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 to capture oil is to place a complex arrangement of valves (the Christmas tree) on the well head and further to connect the well to a pipeline network for storage and processing. Sometimes, during primary recovery, to increase extraction rates, 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.
Over the lifetime of a well, the pressure falls. After natural reservoir drive diminishes and there is insufficient underground pressure to force the oil to the surface, 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 reinjection and lift each use associated gas, carbon dioxide or some other inert gas to reduce the density of the oil-gas mixture; improving its mobility. The typical recovery factor from water injection 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%. [3]
Enhanced, or tertiary oil recovery methods, further increase 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 plant. This type of cogeneration plant uses a gas turbine to generate electricity, and the waste heat 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, which yields a very heavy oil, yet accounts for ten percent of the United States' oil extraction.[ citation needed ] 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, surfactants (detergents) 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. [4]
Another method to reduce viscosity is carbon dioxide flooding.
Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered. [3] In some California heavy oil fields, steam injection has doubled or even tripled the oil reserves and ultimate oil recovery. [5] 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 profitably. This depends on the cost 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 microbes.[ quantify ]
The amount of recoverable oil is determined by a number of factors:
When the reservoir rocks are "tight", as in shale, oil generally cannot flow through, but when they are permeable, as in sandstone, oil flows freely.
Although recovery of a well cannot be known with certainty until the well ceases production, petroleum engineers often determine an estimated ultimate recovery (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.
The oil and gas extraction workforce faces unique health and safety challenges and is recognized by the National Institute for Occupational Safety and Health (NIOSH) as a priority industry sector in the National Occupational Research Agenda (NORA) to identify and provide intervention strategies regarding occupational health and safety issues. [6] [7] 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 such as automated technologies. [8]
In 2023, the CDC published that 470 workers had died from 2014–2019. [9]
When oil and gas are burned they release carbon dioxide into the air. Fossil fuels, such as oil, are responsible for 89% of the CO2 emissions. [10] Carbon emissions cause climate change which negatively impacts people's safety by raising sea levels and worsening weather.
Oil can also cause oil spills, which pollutes the ocean. [11]
Natural gas is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (95%) in addition to various smaller amounts of other higher alkanes. Traces of carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present. Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide. Because natural gas is odorless, odorizers such as mercaptan are commonly added to it for safety so that leaks can be readily detected.
Petroleum or crude oil, also referred to as 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 oil and petroleum products that consist of refined crude oil.
Petroleum geology is the study of the origins, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons.
An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well. Wells are created by drilling down into an oil or gas reserve and if necessary equipped with extraction devices such as pumpjacks. Creating the wells can be an expensive process, costing at least hundreds of thousands of dollars, and costing much more when in difficult-to-access locations, e.g., offshore. The process of modern drilling for wells first started in the 19th century but was made more efficient with advances to oil drilling rigs and technology during the 20th century.
Coalbed methane, coalbed gas, or coal seam gas (CSG) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, Australia, and other countries.
North Sea oil is a mixture of hydrocarbons, comprising liquid petroleum and natural gas, produced from petroleum reservoirs beneath the North Sea.
Gas reinjection is the reinjection of natural gas into an underground reservoir, typically one already containing both natural gas and crude oil, in order to increase the pressure within the reservoir and thus induce the flow of crude oil or else sequester gas that cannot be exported. This is not to be confused with gas lift, where gas is injected into the annulus of the well rather than the reservoir. After the crude has been pumped out, the natural gas is once again recovered. Since many of the wells found around the world contain heavy crude, this process increases their production. The basic difference between light crude and heavy crude is its viscosity and pumpability—the lighter the crude the easier it is to pump. Recovery of hydrocarbons in a well is generally limited to 50% and 75–80%. Recycling of natural gas or other inert gases causes the pressure to rise in the well, thus causing more gas molecules to dissolve in the oil lowering its viscosity and thereby increasing the well's output. Air is not suitable for repressuring wells because it tends to cause deterioration of the oil, thus carbon dioxide or natural gas is used to repressure the well. The term 'gas-reinjection' is also sometimes referred to as repressuring—the term being used only to imply that the pressure inside the well is being increased to aid recovery.
Induced seismicity is typically earthquakes and tremors that are caused by human activity that alters the stresses and strains on Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such as The Geysers geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009. The Human-Induced Earthquake Database (HiQuake) documents all reported cases of induced seismicity proposed on scientific grounds and is the most complete compilation of its kind.
Heavy crude oil is highly viscous oil that cannot easily flow from production wells under normal reservoir conditions.
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 is created in surrounding rock by the presence of high heat and pressure in the Earth's crust.
Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.
Enhanced oil recovery, also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise. Although the primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the chemical composition of the oil itself in order to make it easier to extract. EOR can extract 30% to 60% or more of a reservoir's oil, compared to 20% to 40% using primary and secondary recovery. According to the US Department of Energy, carbon dioxide and water are injected along with one of three EOR techniques: thermal injection, gas injection, and chemical injection. More advanced, speculative EOR techniques are sometimes called quaternary recovery.
Steam-assisted gravity drainage is an enhanced oil recovery technology for producing heavy crude oil and bitumen. It is an advanced form of steam stimulation in which a pair of horizontal wells are drilled into the oil reservoir, one a few metres above the other. High pressure steam is continuously injected into the upper wellbore to heat the oil and reduce its viscosity, causing the heated oil to drain into the lower wellbore, where it is pumped out. Dr. Roger Butler, engineer at Imperial Oil from 1955 to 1982, invented the steam assisted gravity drainage (SAGD) process in the 1970s. Butler "developed the concept of using horizontal pairs of wells and injected steam to develop certain deposits of bitumen considered too deep for mining". In 1983 Butler became director of technical programs for the Alberta Oil Sands Technology and Research Authority (AOSTRA), a crown corporation created by Alberta Premier Lougheed to promote new technologies for oil sands and heavy crude oil production. AOSTRA quickly supported SAGD as a promising innovation in oil sands extraction technology.
Carbon dioxide (CO2) flooding is a process in which carbon dioxide is injected into an oil reservoir to increase the output when extracting oil. This is most often used in reservoirs where production rates have declined due to depletion.
B3 is a major oil and gas field in the Baltic Sea. The field is located 80 km north of the Polish coastal town Rozewie. The crude oil is also referred to as Rozewie crude. Processing, drilling and accommodation is based on the jack up rig Baltic Beta located in the field. Most of the oil is shipped by tanker to the Gdańsk refinery as a part of the refinery feedstock. The associated gas is transmitted by pipeline to the combined heat and power (CHP) plant in Wladyslawowo.
Heavy oil production is a developing technology for extracting heavy oil in industrial quantities. Estimated reserves of heavy oil are over 6 trillion barrels, three times that of conventional oil and gas.
The Weyburn-Midale Carbon Dioxide Project was, as of 2008, the world's largest carbon capture and storage project. It has since been overtaken in terms of carbon capture capacity by projects such as the Shute Creek project and the Century Plant. It is located in Midale, Saskatchewan, Canada.
Fracking is a well stimulation technique involving the fracturing of formations in bedrock by a pressurized liquid. The process involves the high-pressure injection of "fracking fluid" into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants hold the fractures open.
Oil and gas reserves denote discovered quantities of crude oil and natural gas that can be profitably produced/recovered from an approved development. Oil and gas reserves tied to approved operational plans filed on the day of reserves reporting are also sensitive to fluctuating global market pricing. The remaining resource estimates are likely sub-commercial and may still be under appraisal with the potential to be technically recoverable once commercially established. Natural gas is frequently associated with oil directly and gas reserves are commonly quoted in barrels of oil equivalent (BOE). Consequently, both oil and gas reserves, as well as resource estimates, follow the same reporting guidelines, and are referred to collectively hereinafter as oil & gas.
Unconventional reservoirs, or unconventional resources are accumulations where oil and gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialized measures for evaluation and extraction.
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