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An oil well is a drillhole boring in
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
that is designed to bring
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 ...
oil
hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
to the surface. Usually some
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
is released as
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 a ...
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 that is then mounted with an extraction device such as a
pumpjack A pumpjack is the overground drive for a reciprocating piston pump in an oil well. It is used to mechanically lift liquid out of the well if there is not enough bottom hole pressure for the liquid to flow all the way to the surface. The arra ...
which allows extraction from the reserve. Creating the wells can be an expensive process, costing at least hundreds of thousands of dollars, and costing much more when in hard to reach areas, e.g., when creating offshore oil platforms. The process of modern drilling for wells first started in the 19th century, but was made more efficient with advances to oil
drilling rig A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill wat ...
s during the 20th century. Wells are frequently sold or exchanged between different oil and gas companies as an asset – in large part because during falls in price of oil and gas, a well may be unproductive, but if prices rise, even low production wells may be economically valuable. Moreover new methods, such as
hydraulic fracturing Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
(a process of injecting gas or liquid to force more oil or natural gas production) have made some wells viable. However,
peak oil Peak oil is the hypothetical point in time when the maximum rate of global oil production is reached, after which it is argued that production will begin an irreversible decline. It is related to the distinct concept of oil depletion; while ...
and
climate policy The politics of climate change results from different perspectives on how to respond to climate change. Global warming is driven largely by the emissions of greenhouse gases due to human economic activity, especially the burning of fossil fuels, ...
to fossil fuels has made fewer and fewer of these wells and expensive techniques viable. However, the large number of neglected or poorly maintained wellheads is a large environmental issue: they may leak
methane emissions Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% (360 million tons) of methane r ...
or other toxic emissions into local air, water or soil systems. This pollution often becomes worse when wells are abandoned or orphaned – where wells no longer are economically viable, and no longer are maintained by a company. A 2020 estimate by Reuters suggested that there were at least 29 million abandoned wells internationally, creating a significant source of
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and lar ...
causing climate change.


History

The ancient records of China and
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum was known as ''burning water'' in Japan in the 7th century. According to Kasem Ajram, petroleum was
distilled Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...
by the
Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...
alchemist
Muhammad ibn Zakarīya Rāzi Abū Bakr al-Rāzī (full name: ar, أبو بکر محمد بن زکریاء الرازي, translit=Abū Bakr Muḥammad ibn Zakariyyāʾ al-Rāzī, label=none), () rather than ar, زکریاء, label=none (), as for example in , or in . In m ...
(Rhazes) in the 9th century, producing chemicals such as
kerosene Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...
in the
alembic An alembic (from ar, الإنبيق, al-inbīq, originating from grc, ἄμβιξ, ambix, 'cup, beaker') is an alchemical still consisting of two vessels connected by a tube, used for distillation of liquids. Description The complete disti ...
(''al-ambiq''), and which was mainly used for
kerosene lamp A kerosene lamp (also known as a paraffin lamp in some countries) is a type of lighting device that uses kerosene as a fuel. Kerosene lamps have a wick or mantle as light source, protected by a glass chimney or globe; lamps may be used on a t ...
s. Arab and Persian chemists also distilled crude oil in order to produce
flammable A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
products for military purposes. Through
Islamic Spain Al-Andalus DIN 31635, translit. ; an, al-Andalus; ast, al-Ándalus; eu, al-Andalus; ber, ⴰⵏⴷⴰⵍⵓⵙ, label=Berber languages, Berber, translit=Andalus; ca, al-Àndalus; gl, al-Andalus; oc, Al Andalús; pt, al-Ândalus; es, ...
, distillation became available in
Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the ancient Mediterranean ...
by the 12th century. Some sources claim that from the 9th century,
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 presence ...
s were exploited in the area around modern
Baku Baku (, ; az, Bakı ) is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea and of the Caucasus region. Baku is located below sea level, which makes it the lowest lying national capital in the world a ...
,
Azerbaijan Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan, , also sometimes officially called the Azerbaijan Republic is a transcontinental country located at the boundary of Eastern Europe and Western Asia. It is a part of th ...
, to produce
naphtha Naphtha ( or ) is a flammable liquid hydrocarbon mixture. Mixtures labelled ''naphtha'' have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions ''n ...
for the
petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larges ...
. These places were described by
Marco Polo Marco Polo (, , ; 8 January 1324) was a Venetian merchant, explorer and writer who travelled through Asia along the Silk Road between 1271 and 1295. His travels are recorded in ''The Travels of Marco Polo'' (also known as ''Book of the Marv ...
in the 13th century, who described the output of those oil wells as hundreds of shiploads. When Marco Polo in 1264 visited Baku, on the shores of the
Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...
, he saw oil being collected from seeps. He wrote that "on the confines toward Geirgine there is a fountain from which oil springs in great abundance, in as much as a hundred shiploads might be taken from it at one time." In 1846, Baku (settlement Bibi-Heybat) the first ever well was drilled with percussion tools to a depth of for oil exploration. In 1846–1848, the first modern oil wells were drilled on the
Absheron Peninsula The Absheron Peninsula ( az, Abşeron yarımadası) is a peninsula in Azerbaijan. It is the location of Baku, the biggest and the most populous city of the country, and also the Baku metropolitan area, with its satellite cities Sumqayit and Khyrd ...
north-east of Baku, by Russian engineer Vasily Semyonov considering the ideas of Nikolay Voskoboynikov.
Ignacy Łukasiewicz Jan Józef Ignacy Łukasiewicz (; 8 March 1822 – 7 January 1882) was a Polish pharmacist, engineer, businessman, inventor, and philanthropist. He was one of the most prominent philanthropists in the Kingdom of Galicia and Lodomeria, crown land o ...
, a
Polish Polish may refer to: * Anything from or related to Poland, a country in Europe * Polish language * Poles, people from Poland or of Polish descent * Polish chicken *Polish brothers (Mark Polish and Michael Polish, born 1970), American twin screenwr ...
''Magdalena Puda-Blokesz''
Ignacy Łukasiewicz: ojciec światowego przemysłu naftowego, działacz polityczny i patriota, filantrop i społecznik, przede wszystkim Człowiek
''Ludwik Tomanek'', Ignacy Łukasiewicz twórca przemysłu naftowego w Polsce, wielki inicjator – wielki jałmużnik. Miejsce Piastowe: Komitet Uczczenia Pamięci Ignacego Łukasiewicza. 1928
pharmacist A pharmacist, also known as a chemist (Commonwealth English) or a druggist (North American and, archaically, Commonwealth English), is a healthcare professional who prepares, controls and distributes medicines and provides advice and instructi ...
and
petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larges ...
pioneer built one of the world's first modern oil wells in 1854 in
Polish Polish may refer to: * Anything from or related to Poland, a country in Europe * Polish language * Poles, people from Poland or of Polish descent * Polish chicken *Polish brothers (Mark Polish and Michael Polish, born 1970), American twin screenwr ...
village
Bóbrka, Krosno County Bóbrka is a village in the administrative district of Gmina Chorkówka, within Krosno County, Subcarpathian Voivodeship, in south-eastern Poland. It lies approximately south-east of Chorkówka, south-west of Krosno, and south-west of the re ...
who in 1856 built one of the world's first
oil refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...
. In North America, the first commercial oil well entered operation in
Oil Springs, Ontario Oil Springs is a village in Lambton County, Ontario, Canada, located along Former Provincial Highway 21 south of Oil City. The village, an enclave within Enniskillen Township, is the site of North America's first commercial oil well. It is home ...
in 1858, while the first offshore oil well was drilled in 1896 at the
Summerland Oil Field The Summerland Oil Field (and Summerland Offshore Oil Field) is an inactive oil field in Santa Barbara County, California, about four miles (6 km) east of the city of Santa Barbara, within and next to the unincorporated community of Summerla ...
on the California Coast. The earliest oil wells in modern times were drilled percussively, by repeatedly raising and dropping a cable tool into the earth. In the 20th century, cable tools were largely replaced with
rotary drilling A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to i ...
, which could drill boreholes to much greater depths and in less time. The record-depth Kola Borehole used a mud motor while drilling to achieve a depth of over . Until the 1970s, most oil wells were vertical, although
lithological The lithology of a Rock (geology), rock unit is a description of its physical characteristics visible at outcrop, in hand or core sample, core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain ...
and mechanical imperfections cause most wells to deviate at least slightly from true vertical (see
deviation survey In the oil industry, a deviation survey, or simply a ''survey'', is the measurement of a borehole's departure from the vertical, expressed in degrees (°). When a ''well plan'' dictates the drilling of a straight borehole, surveys are periodical ...
). However, modern
directional drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical bores. It can be broken down into four main groups: oilfield directional drilling, utility installation directional drilling, directional boring (horizontal dire ...
technologies allow for strongly deviated wells which can, given sufficient depth and with the proper tools, actually become horizontal. This is of great value as the
reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...
rocks which contain hydrocarbons are usually horizontal or nearly horizontal; a horizontal wellbore placed in a production zone has more surface area in the production zone than a vertical well, resulting in a higher production rate. The use of deviated and horizontal drilling has also made it possible to reach reservoirs several kilometers or miles away from the drilling location (extended reach drilling), allowing for the production of hydrocarbons located below locations that are either difficult to place a drilling rig on, environmentally sensitive, or populated.


Life of a well


Planning

Before a well is drilled, a geologic target is identified by a
geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
or geophysicist to meet the objectives of the well. * For a production well, the target is picked to optimize production from the well and manage reservoir drainage. * For an exploration or appraisal well, the target is chosen to confirm the existence of a viable hydrocarbon reservoir or to learn its extent. * For an injection well, the target is selected to locate the point of injection in a permeable zone, which may support disposing of water or gas and /or pushing hydrocarbons into nearby production wells. The target (the end point of the well) will be matched with a surface location (the starting point of the well), and a
trajectory A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete traj ...
between the two will be designed. There are many considerations to take into account when designing the trajectory such as the clearance to any nearby wells (anti-collision) or if this well will get in the way of future wells, trying to avoid faults if possible and certain formations may be easier/more difficult to drill at certain inclinations or azimuths. When the well path is identified, a team of geoscientists and engineers will develop a set of presumed properties of the subsurface that will be drilled through to reach the target. These properties include
pore pressure Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles ( pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometer ...
, fracture gradient, wellbore stability,
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 measure ...
, permeability,
lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
, faults, and clay content. This set of assumptions is used by a well engineering team to perform the casing design and completion design for the well, and then detailed planning, where, for example, the drill bits are selected, a BHA is designed, the
drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...
is selected, and step-by-step procedures are written to provide instruction for executing the well in a safe and cost-efficient manner. With the interplay with many of the elements in a well design and making a change to one will have a knock on effect on many other things, often trajectories and designs go through several iterations before a plan is finalised.


Drilling

The well is created by
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 ra ...
a hole 12 cm to 1 meter (5 in to 40 in) in diameter into the earth with a drilling rig that rotates a
drill string A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the Well drilling#Drill bits in mechanical drilling, drill bit. The term ...
with a bit attached. After the hole is drilled, sections of steel pipe ( casing), slightly smaller in diameter than the borehole, are placed in the hole. Cement may be placed between the outside of the casing and the borehole known as the annulus. The casing provides structural integrity to the newly drilled wellbore, in addition to isolating potentially dangerous high pressure zones from each other and from the surface. With these zones safely isolated and the formation protected by the casing, the well can be drilled deeper (into potentially more-unstable and violent formations) with a smaller bit, and also cased with a smaller size casing. Modern wells often have two to five sets of subsequently smaller hole sizes drilled inside one another, each cemented with casing. ;To drill the well * The drill bit, aided by the weight of the
drill string A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the Well drilling#Drill bits in mechanical drilling, drill bit. The term ...
above it, cuts into the rock. There are different types of drill bit; some cause the rock to disintegrate by compressive failure, while others shear slices off the rock as the bit turns. *
Drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...
, a.k.a. "mud", is pumped down the inside of the drill pipe and exits at the drill bit. The principal components of drilling fluid are usually water and clay, but it also typically contains a complex mixture of fluids, solids and chemicals that must be carefully tailored to provide the correct physical and chemical characteristics required to safely drill the well. Particular functions of the drilling mud include cooling the bit, lifting rock cuttings to the surface, preventing destabilisation of the rock in the wellbore walls and overcoming the pressure of fluids inside the rock so that these fluids do not enter the wellbore. Some oil wells are drilled with air or foam as the drilling fluid. * The generated rock " cuttings" are swept up by the drilling fluid as it circulates back to surface outside the drill pipe. The fluid then goes through "
shakers The United Society of Believers in Christ's Second Appearing, more commonly known as the Shakers, are a Millenarianism, millenarian Restorationism, restorationist Christianity, Christian sect founded in England and then organized in the Unit ...
" which strain the cuttings from the good fluid which is returned to the pit. Watching for abnormalities in the returning cuttings and monitoring pit volume or rate of returning fluid are imperative to catch "kicks" early. A "kick" is when the formation pressure at the depth of the bit is more than the hydrostatic head of the mud above, which if not controlled temporarily by closing the
blowout preventer A blowout preventer (BOP) (pronounced B-O-P, not "bop") is a specialized valve or similar mechanical device, used to seal, control and monitor oil and gas wells to prevent blowouts, the uncontrolled release of crude oil or natural gas from a w ...
s and ultimately by increasing the density of the drilling fluid would allow formation fluids and mud to come up through the annulus uncontrollably. * The pipe or
drill string A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the Well drilling#Drill bits in mechanical drilling, drill bit. The term ...
to which the bit is attached is gradually lengthened as the well gets deeper by screwing in additional 9 m (30 ft) sections or "joints" of pipe under the
kelly Kelly may refer to: Art and entertainment * Kelly (Kelly Price album) * Kelly (Andrea Faustini album) * ''Kelly'' (musical), a 1965 musical by Mark Charlap * "Kelly" (song), a 2018 single by Kelly Rowland * ''Kelly'' (film), a 1981 Canadi ...
or topdrive at the surface. This process is called making a connection. The process called "tripping" is when pulling the bit out of hole to replace the bit (tripping out), and running back in with a new bit (tripping in). Joints can be combined for more efficient tripping when pulling out of the hole by creating stands of multiple joints. A conventional triple, for example, would pull pipe out of the hole three joints at a time and stack them in the derrick. Many modern rigs, called "super singles", trip pipe one at a time, laying it out on racks as they go. This process is all facilitated by a
drilling rig A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill wat ...
which contains all necessary equipment to circulate the drilling fluid, hoist and turn the pipe, control downhole, remove cuttings from the drilling fluid, and generate on-site power for these operations.


Completion

After drilling and casing the well, it must be 'completed'. Completion is the process in which the well is enabled to produce
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
or gas. In a cased-hole completion, small holes called
perforations A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a ''perforation''. The process of creating perforations is called perfor ...
are made in the portion of the casing which passed through the production zone, to provide a path for the oil to flow from the surrounding rock into the production tubing. In open hole completion, often 'sand screens' or a 'gravel pack' is installed in the last drilled, uncased reservoir section. These maintain structural integrity of the wellbore in the absence of casing, while still allowing flow from the reservoir into the wellbore. Screens also control the migration of formation sands into production tubulars and surface equipment, which can cause washouts and other problems, particularly from unconsolidated sand formations of offshore fields. After a flow path is made, acids and fracturing fluids may be pumped into the well to
fracture Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...
, clean, or otherwise prepare and stimulate the reservoir rock to optimally produce hydrocarbons into the wellbore. Finally, the area above the reservoir section of the well is packed off inside the casing, and connected to the surface via a smaller diameter pipe called tubing. This arrangement provides a redundant barrier to leaks of hydrocarbons as well as allowing damaged sections to be replaced. Also, the smaller cross-sectional area of the tubing produces reservoir fluids at an increased velocity in order to minimize liquid fallback that would create additional back pressure, and shields the casing from corrosive well fluids. In many wells, the natural pressure of the subsurface reservoir is high enough for the oil or gas to flow to the surface. However, this is not always the case, especially in depleted fields where the pressures have been lowered by other producing wells, or in low permeability oil reservoirs. Installing a smaller diameter tubing may be enough to help the production, but artificial lift methods may also be needed. Common solutions include downhole pumps, gas lift, or surface pump jacks. Many new systems in the last ten years have been introduced for well completion. Multiple packer systems with frac ports or port collars in an all in one system have cut completion costs and improved production, especially in the case of horizontal wells. These new systems allow casings to run into the lateral zone with proper packer/frac port placement for optimal hydrocarbon recovery.


Production

The production stage is the most important stage of a well's life; when the oil and gas are produced. By this time, the oil rigs and workover rigs used to drill and complete the well have moved off the wellbore, and the top is usually outfitted with 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 ...
or production tree. These valves regulate pressures, control flows, and allow access to the wellbore in case further completion work is needed. From the outlet valve of the production tree, the flow can be connected to a distribution network of pipelines and tanks to supply the product to refineries, natural gas compressor stations, or oil export terminals. As long as the pressure in the reservoir remains high enough, the production tree is all that is required to produce the well. If the pressure depletes and it is considered economically viable, an artificial lift method mentioned in the completions section can be employed.
Workover The term workover is used to refer to any kind of oil well intervention involving invasive techniques, such as wireline, coiled tubing or snubbing. More specifically, a workover refers to the expensive process of pulling and replacing comple ...
s are often necessary in older wells, which may need smaller diameter tubing, scale or paraffin removal, acid matrix jobs, or completing new zones of interest in a shallower reservoir. Such remedial work can be performed using workover rigs – also known as ''pulling units'', ''completion rigs'' or "service rigs" – to pull and replace tubing, or by the use of
well intervention A well intervention, or well work, is any operation carried out on an oil or gas well during, or at the end of, its productive life that alters the state of the well or well geometry, provides well diagnostics, or manages the production of the wel ...
techniques utilizing
coiled tubing In the oil and gas industries, coiled tubing refers to a very long metal pipe, normally in diameter which is supplied spooled on a large reel. It is used for interventions in oil and gas wells and sometimes as production tubing in depleted g ...
. Depending on the type of lift system and wellhead a rod rig or flushby can be used to change a pump without pulling the tubing. Enhanced recovery methods such as water flooding, steam flooding, or CO2 flooding may be used to increase reservoir pressure and provide a "sweep" effect to push hydrocarbons out of the reservoir. Such methods require the use of injection wells (often chosen from old production wells in a carefully determined pattern), and are used when facing problems with reservoir pressure depletion, high oil viscosity, or can even be employed early in a field's life. In certain cases – depending on the reservoir's geomechanics – reservoir engineers may determine that ultimate recoverable oil may be increased by applying a waterflooding strategy early in the field's development rather than later. Such enhanced recovery techniques are often called " tertiary recovery".


Abandonment


Types of wells


By produced fluid

* Wells that produce
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
* Wells that produce oil ''and''
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, or * Wells that ''only'' produce natural gas. Natural gas, in a raw form known as
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 a ...
, is almost always a by-product of producing oil. The small, light gas carbon chains come out of solution as they undergo pressure reduction from the
reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...
to the surface, similar to uncapping a bottle of soda where the carbon dioxide
effervesce Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb ''fervere'' (to boil), preceded by the adverb ''ex''. It has the same lin ...
s. If it escapes into the atmosphere intentionally it is known as vented gas, or if unintentionally as fugitive gas. Unwanted natural gas can be a disposal problem at wells that are developed to produce oil. If there are no pipelines for natural gas near the
wellhead A wellhead is the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment. The primary purpose of a wellhead is to provide the suspension point and ...
it may be of no value to the oil well owner since it cannot reach the consumer markets. Such unwanted gas may then be burned off at the well site in a practice known as
production flaring Routine flaring, also known as production flaring, is a method and current practice of disposing of large unwanted amounts of associated petroleum gas (APG) during crude oil extraction. The gas is first separated from the liquids and solids d ...
, but due to the energy resource waste and environmental damage concerns this practice is becoming less common. Often, unwanted (or 'stranded' gas without a market) gas is pumped back into the reservoir with an 'injection' well for storage or for re-pressurizing the producing formation. Another solution is to convert the natural gas to a
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
fuel.
Gas to liquid Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies ex ...
(GTL) is a developing technology that converts stranded natural gas into synthetic gasoline, diesel or jet fuel through the Fischer–Tropsch process developed in World War II Germany. Like oil, such dense liquid fuels can be transported using conventional tankers or trucking to users. Proponents claim GTL fuels burn cleaner than comparable petroleum fuels. Most major international oil companies are in advanced development stages of GTL production, e.g. the
Pearl GTL The Pearl GTL is a gas to liquids (GTL) plant based in Ras Laffan, Qatar. It converts natural gas into liquid petroleum products. It is the largest GTL plant in the world. The first commercial shipment from the Pearl GTL was made on 13 June ...
plant in Qatar, scheduled to come online in 2011. In locations such as the United States with a high natural gas demand, pipelines are usually favored to take the gas from the well site to the
end consumer A consumer is a person or a group who intends to order, or uses purchased goods, products, or services primarily for personal, social, family, household and similar needs, who is not directly related to entrepreneurial or business activities. T ...
.


By location

Wells can be located: * On land, or *
Offshore Offshore may refer to: Science and technology * Offshore (hydrocarbons) * Offshore construction, construction out at sea * Offshore drilling, discovery and development of oil and gas resources which lie underwater through drilling a well * Off ...
Offshore wells can further be subdivided into * Wells with subsea wellheads, where the top of the well is sitting on the ocean floor under water, and often connected to a pipeline on the ocean floor. * Wells with 'dry' wellheads, where the top of the well is above the water on a platform or jacket, which also often contains processing equipment for the produced fluid. While the location of the well will be a large factor in the type of equipment used to drill it, there is actually little difference in the well itself. An offshore well targets a reservoir that happens to be underneath an ocean. Due to logistics, drilling an offshore well is far more costly than an onshore well. By far the most common type is the onshore well. These wells dot the Southern and Central Great Plains, Southwestern United States, and are the most common wells in the Middle East.


By purpose

Another way to classify oil wells is by their purpose in contributing to the development of a resource. They can be characterized as: * ''wildcat wells'' are drilled where little or no known geological information is available. The site may have been selected because of wells drilled some distance from the proposed location but on a terrain that appeared similar to the proposed site. Individuals who drill wildcat wells are known as '
wildcatter A wildcatter is an individual who drills wildcat wells, which are exploration oil wells drilled in areas not known to be oil fields. Notable wildcatters include Glenn McCarthy, Thomas Baker Slick Sr., Mike Benedum, Joe Trees, Clem S. Clarke, ...
s'. * ''
exploration well Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology. Exploration methods Vis ...
s'' are drilled purely for exploratory (information gathering) purposes in a new area, the site selection is usually based on seismic data, satellite surveys etc. Details gathered in this well includes the presence of hydrocarbon in the drilled location, the amount of fluid present and the depth at which oil or/and gas occurs. * ''appraisal wells'' are used to assess characteristics (such as flow rate, reserve quantity) of a proven hydrocarbon accumulation. The purpose of this well is to reduce uncertainty about the characteristics and properties of the hydrocarbon present in the field. * ''production wells'' are drilled primarily for producing oil or gas, once the producing structure and characteristics are determined. * ''development wells'' are wells drilled for the production of oil or gas already proven by appraisal drilling to be suitable for exploitation. * ''
abandoned wells Orphan, orphaned or abandoned wells are oil or gas wells that have been abandoned by fossil fuel extraction industries. These wells may have been deactivated because of economic viability, failure to transfer ownerships (especially at bankruptcy o ...
'' are wells permanently plugged in the drilling phase for technical reasons. At a producing well site, active wells may be further categorised as: * ''oil producers'' producing predominantly
liquid hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
s, but most include some
associated 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 a ...
. * ''gas producers'' producing almost entirely gaseous hydrocarbons, consisting mostly of
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
. * ''water injectors'' injecting water into the formation to maintain
reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...
pressure, or simply to dispose of water produced with the hydrocarbons because even after treatment, it would be too oily and too saline to be considered clean for dumping overboard offshore, let alone into a fresh water resource in the case of onshore wells. Water injection into the producing zone frequently has an element of reservoir management; however, often produced water disposal is into shallower zones safely beneath any fresh water zones. * ''aquifer producers'' intentionally producing water for re-injection to manage pressure. If possible this water will come from the reservoir itself. Using aquifer produced water rather than water from other sources is to preclude chemical incompatibility that might lead to reservoir-plugging precipitates. These wells will generally be needed only if produced water from the oil or gas producers is insufficient for reservoir management purposes. * ''gas injectors'' injecting gas into the reservoir often as a means of disposal or sequestering for later production, but also to maintain reservoir pressure. Lahee classification''

* ''New Field Wildcat'' (NFW) – far from other producing fields and on a structure that has not previously produced. * ''New Pool Wildcat'' (NPW) – new pools on already producing structure. * ''Deeper Pool Test'' (DPT) – on already producing structure and pool, but on a deeper pay zone. * ''Shallower Pool Test'' (SPT) – on already producing structure and pool, but on a shallower pay zone. * ''Outpost'' (OUT) – usually two or more locations from nearest productive area. * ''Development Well'' (DEV) – can be on the extension of a pay zone, or between existing wells (''Infill'').


Cost

The cost of a well depends mainly on the daily rate of the drilling rig, the extra services required to drill the well, the duration of the well program (including downtime and weather time), and the remoteness of the location (logistic supply costs). The daily rates of offshore drilling rigs vary by their capability, and the market availability. Rig rates reported by industry web serviceRigzone - Rig day rates : http://www.rigzone.com/data/dayrates/ show that the deepwater water floating drilling rigs are over twice that of the shallow water fleet, and rates for jackup fleet can vary by factor of 3 depending upon capability. With deepwater drilling rig rates in 2015 of around $520,000/day, and similar additional spread costs, a deep water well of duration of 100 days can cost around US$100 million. With high performance jackup rig rates in 2015 of around $177,000, and similar service costs, a high pressure, high temperature well of duration 100 days can cost about US$30 million. Onshore wells can be considerably cheaper, particularly if the field is at a shallow depth, where costs range from less than $4.9 million to $8.3 million, and the average completion costing $2.9 million to $5.6 million per well. Completion makes up a larger portion of onshore well costs than offshore wells, which have the added cost burden of an oil platform. The total cost of an oil well mentioned does not include the costs associated with the risk of explosion and leakage of oil. Those costs include the cost of protecting against such disasters, the cost of the cleanup effort, and the hard-to-calculate cost of damage to the company's image.


See also

*
Fracking Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
(hydraulic fracturing) *
Offshore drilling Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the te ...
*
Oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...
*
Petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larges ...


References


External links


Halliburton Technical Papers

Freemyer Industrial Pressure

Schlumberger Oilfield Glossary



"Black Gold"
''Popular Mechanics'', January 1930 - large photo article on oil drilling in the 1920s and 1930s
"World's Deepest Well"
''Popular Science'', August 1938, article on the late 1930s technology of drilling oil wells
'Ancient Chinese Drilling'
article from June 2004 CSEG Recorder

* ir-Babayev M.F. Brief history of the first drilled oil well; and the people involved - "Oil-Industry History" (USA), 2017, v.18 #1, p. 25-34 {{DEFAULTSORT:Oil Well American inventions Azerbaijani inventions Chinese inventions Drilling technology Polish inventions Russian inventions