Enhanced oil recovery
Encyclopedia
Enhanced Oil Recovery is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field
Oil field
An oil field is a region with an abundance of oil wells extracting petroleum from below ground. Because the oil reservoirs typically extend over a large area, possibly several hundred kilometres across, full exploitation entails multiple wells scattered across the area...

. Using EOR, 30-60 %, or more, of the reservoir's original oil can be extracted compared with 20-40% using primary and secondary recovery.

Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques.

How does it work?

Enhanced oil recovery is achieved by gas injection, chemical injection, microbial injection, or thermal recovery (which includes cyclic or continous steam, steam flooding
Steam injection (oil industry)
Steam injection is an increasingly common method of extracting heavy oil. It is considered an enhanced oil recovery method and is the main type of thermal stimulation of oil reservoirs. There are several different forms of the technology, with the two main ones being Cyclic Steam Stimulation and...

, and fire flooding).

Gas injection

Gas reinjection is presently the most-commonly used approach to enhanced recovery. In addition to the beneficial effect of the pressure, this method sometimes aids recovery by reducing the viscosity of the crude oil as the gas mixes with it.

Gases used include CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 or nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

. Air cannot be used to repressurize the reservoir because the oil will quickly catch on fire.

Oil displacement by carbon dioxide injection
Carbon dioxide flooding
Carbon dioxide flooding is a process whereby carbon dioxide is injected into an oil reservoir in order to increase output when extracting oil....

 relies on the phase behaviour of the mixtures of that gas and the crude, which are strongly dependent on reservoir temperature, pressure and crude oil composition. These mechanisms range from oil swelling and viscosity reduction for injection of immiscible fluids (at low pressures) to completely miscible displacement in high-pressure applications. In these
applications, more than half and up to two-thirds of the injected
CO2 returns with the produced oil and is usually re-injected into the reservoir to minimize operating costs. The remainder is trapped in the oil reservoir by various means.

Chemical injection

The injection of various chemicals, usually as dilute solutions, have been used to improve oil recovery. Injection of alkaline or caustic solutions into reservoirs with oil that has organic acids naturally occurring in the oil will result in the production of soap that may lower the interfacial tension enough to increase production. Injection of a dilute solution of a water soluble polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 to increase the viscosity of the injected water can increase the amount of oil recovered in some formations. Dilute solutions of surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s such as petroleum sulfonates or biosurfactants
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

 such as rhamnolipid
Rhamnolipid
Rhamnolipids are a class of glycolipid produced by Pseudomonas aeruginosa, frequently cited as the best characterised of the bacterial surfactants They have a glycosyl head group, in this case a rhamnose moiety, and a 3-alkanoic acid fatty acid tail.Specifically there are two main classes of...

s may be injected to lower the interfacial tension or capillary pressure that impedes oil droplets from moving through a reservoir. Special formulations of oil water and surfactant, microemulsion
Microemulsion
Microemulsions are clear, thermodynamically stable, isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons and olefins...

s, can be particularly effective in this. Application of these methods is usually limited by the cost of the chemicals and their adsorption and loss onto the rock of the oil containing formation. In all of these methods the chemicals are injected into several wells and the production occurs in other nearby wells.

Microbial injection

Microbial injection is part of microbial enhanced oil recovery
Microbial enhanced oil recovery
Microbial Enhanced Oil Recovery is a biological based technology consisting in manipulating function or structure, or both, of microbial environments existing in oil reservoirs. The ultimate aim of MEOR is to improve the recovery of oil entrapped in porous media while increasing economic profits...

 and is presently rarely used, both because of its higher cost and because the developments in this field are more recent than other techniques. Strains of microbes have been both discovered and developed (using gene mutation) which function either by partially digesting long hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 molecules, by generating biosurfactants, or by emitting carbon dioxide (which then functions as described in Gas injection above).

Three approaches have been used to achieve microbial injection. In the first approach, bacterial cultures mixed with a food source (a carbohydrate such as molasses
Molasses
Molasses is a viscous by-product of the processing of sugar cane, grapes or sugar beets into sugar. The word molasses comes from the Portuguese word melaço, which ultimately comes from mel, the Latin word for "honey". The quality of molasses depends on the maturity of the sugar cane or sugar beet,...

 is commonly used) are injected into the oil field. In the second approach, used since 1985, nutrients are injected into the ground to nurture existing microbial bodies; these nutrients cause the bacteria to increase production of the natural surfactants they normally use to metabolize crude oil underground. After the injected nutrients are consumed, the microbes go into near-shutdown mode, their exteriors become hydrophilic, and they migrate to the oil-water interface area, where they cause oil droplets to form from the larger oil mass, making the droplets more likely to migrate to the wellhead. This approach has been used in oilfields near the Four Corners and in the Beverly Hills Oil Field
Beverly Hills Oil Field
The Beverly Hills Oil Field is a large and currently active oil field underneath part of the city of Beverly Hills, California, USA, and portions of the adjacent city of Los Angeles...

 in Beverly Hills, California
Beverly Hills, California
Beverly Hills is an affluent city located in Los Angeles County, California, United States. With a population of 34,109 at the 2010 census, up from 33,784 as of the 2000 census, it is home to numerous Hollywood celebrities. Beverly Hills and the neighboring city of West Hollywood are together...

.

The third approach is used to address the problem of paraffin
Paraffin
In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the...

 components of the crude oil, which tend to separate from the crude as it flows to the surface. Since the Earth's surface is considerably cooler than the petroleum deposits (a temperature drop of 13-14 degree F per thousand feet of depth is usual), the paraffin's higher melting point causes it to solidify as it is cooled during the upward flow. Bacteria capable of breaking these paraffin chains into smaller chains (which would then flow more easily) are injected into the wellhead, either near the point of first congealment or in the rock stratum itself.

Thermal methods

In this approach, various methods are used to heat the crude oil in the formation to reduce its viscosity and/or vaporize part of the oil. Methods include cyclic steam injection, steam drive and in situ combustion. These methods improve the sweep efficiency and the displacement efficiency. Steam injection has been used commercially since the 1960s in California fields. In 2011 Solar Thermal Enhanced Oil Recovery
Solar Thermal Enhanced Oil Recovery
-Overview:Solar Thermal Enhanced Oil Recovery is a form of Thermal Enhanced Oil Recovery , a technique applied by oil producers to extract more oil from maturing oil fields. Solar EOR uses solar arrays to concentrate the sun’s energy to heat water and generate steam...

 projects were started in California and Oman
Oman
Oman , officially called the Sultanate of Oman , is an Arab state in southwest Asia on the southeast coast of the Arabian Peninsula. It is bordered by the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest. The coast is formed by the Arabian Sea on the...

, this method is similar to Thermal EOR but uses a solar array to produce the steam.

Economic costs and benefits

Adding oil recovery methods adds to the cost of oil — in the case of CO2 typically between 0.5-8.0 US$ per tonne of CO2. The increased extraction of oil on the other hand, is an economic benefit with the revenue depending on prevailing oil prices. Onshore EOR has paid in the range of a net 10-16 US$ per tonne of CO2 injected for oil prices of 15-20 US$/barrel
Barrel (unit)
A barrel is one of several units of volume, with dry barrels, fluid barrels , oil barrel, etc...

. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 90 US$/barrel, the economic benefit is about 70 US$ per tonne CO2.

Examples of current EOR projects

In Canada, a CO2-EOR project has been established by Cenovus Energy
Cenovus Energy
Cenovus Energy is an integrated oil company headquartered in Calgary, Alberta.Cenovus was formed on December 1, 2009 when Encana Corporation split into two distinct companies: one an integrated oil company , the other a pure play natural gas company . The split left Cenovus with the assets formerly...

 at the Weyburn Oil Field in southern Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

. The project is expected to inject a net 18 million ton CO2 and recover an additional 130 Moilbbl of oil, extending the life of the oil field by 25 years. There is a projected 26+ million tonnes (net of production) of CO2 to be stored in Weyburn, plus another 8.5 million tonnes (net of production) stored at the Weyburn-Midale Carbon Dioxide Project
Weyburn-Midale Carbon Dioxide Project
The Weyburn-Midale Carbon Dioxide Project is, as of 2008, the world's largest carbon capture and storage project...

, resulting in a net reduction in atmospheric CO2). That's the equivalent of taking nearly 7 million cars off the road for a year. Since CO2 injection began in late 2000, the EOR project has performed largely as predicted. Currently, some 1600 m3 (10,063 barrels) per day of incremental oil is being produced from the field.

Potential for EOR in United States

In United States, the Department of Energy (DOE) has estimated that full use of 'next generation' CO2-EOR in United States could generate an additional 240 Goilbbl of recoverable oil resources. Developing this potential would depend on the availability of commercial CO2 in large volumes, which could be made possible by widespread use of carbon capture and storage
Carbon capture and storage
Carbon capture and storage , alternatively referred to as carbon capture and sequestration, is a technology to prevent large quantities of from being released into the atmosphere from the use of fossil fuel in power generation and other industries. It is often regarded as a means of mitigating...

. For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1 Toilbbl, most of it remaining unrecoverable. The DOE estimates that if the EOR potential were to be fully realised, State and local treasuries would gain $280 billion in revenues from future royalties
Royalties
Royalties are usage-based payments made by one party to another for the right to ongoing use of an asset, sometimes an intellectual property...

, severance tax
Severance tax
Severance taxes are incurred when non-renewable natural resources are separated from a taxing jurisdiction. Industries that typically incur such taxes are oil and gas, coal, mining, and timber industries....

es, and state income taxes on oil production, aside from other economic benefits.

Environmental impacts

Enhanced oil recovery wells typically produce large quantities of brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

 at the surface. The brine may contain toxic metals and radioactive substances
Naturally occurring radioactive material
Naturally Occurring Radioactive Materials and Technologically Enhanced Naturally Occurring Radioactive Materials consist of materials, usually industrial wastes or by-products enriched with radioactive elements found in the environment, such as uranium, thorium and potassium and any of their...

, as well as being very salty. This can be very damaging to drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 sources and the environment generally if not properly controlled.

In the United States, injection well activity is regulated by the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 (EPA) and state governments under the Safe Drinking Water Act
Safe Drinking Water Act
The Safe Drinking Water Act is the principle federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency is required to set standards for drinking water quality and oversee all states, localities, and water...

. EPA has issued Underground Injection Control (UIC) regulations in order to protect drinking water sources. The regulations require well operators to reinject the brine deep underground.

See also

  • Wikiversity:Enhanced oil recovery
  • Carbon capture and storage
    Carbon capture and storage
    Carbon capture and storage , alternatively referred to as carbon capture and sequestration, is a technology to prevent large quantities of from being released into the atmosphere from the use of fossil fuel in power generation and other industries. It is often regarded as a means of mitigating...

  • Gas reinjection
    Gas reinjection
    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...

  • Injection well
    Injection well
    An injection well is a vertical pipe in the ground into which water, other liquids, or gases are pumped or allowed to flow.-Waste disposal: One application is waste water disposal, in which treated waste water is injected into the ground between impermeable layers of rocks to avoid polluting fresh...

  • Steam assisted gravity drainage
    Steam assisted gravity drainage
    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...

  • Steam injection (oil industry)
    Steam injection (oil industry)
    Steam injection is an increasingly common method of extracting heavy oil. It is considered an enhanced oil recovery method and is the main type of thermal stimulation of oil reservoirs. There are several different forms of the technology, with the two main ones being Cyclic Steam Stimulation and...

  • Water injection (oil production)
    Water injection (oil production)
    Water injection refers to the method in oil industry where water is injected back into the reservoir, usually to increase pressure and thereby stimulate production. Water injection wells can be found both on- and offshore, to increase oil recovery from an existing reservoir...

  • Solar Thermal Enhanced Oil Recovery
    Solar Thermal Enhanced Oil Recovery
    -Overview:Solar Thermal Enhanced Oil Recovery is a form of Thermal Enhanced Oil Recovery , a technique applied by oil producers to extract more oil from maturing oil fields. Solar EOR uses solar arrays to concentrate the sun’s energy to heat water and generate steam...


External links

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