Enhanced oil recovery (abbreviated EOR), also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise. Whereas primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the physical or chemical properties of the oil itself in order to make it easier to extract. When EOR is used, 30% to 60% or more of a reservoir's oil can be extracted, [1] compared to 20% to 40% using only primary and secondary recovery. [2] [3]
There are four main EOR techniques: carbon dioxide (CO2) injection, other gas injection, thermal EOR, and chemical EOR. More advanced, speculative EOR techniques are sometimes called quaternary recovery. [4] [5] [6] [7] Carbon dioxide injection, known as CO2-EOR, is the most common method. In this method, CO2 is injected into a depleted oil field and is mostly left underground.
CO2-EOR is usually performed using CO2 from naturally-occurring underground deposits. It is also sometimes performed using CO2 captured from the flue gas of industrial facilities. When EOR is done using CO2 captured from flue gas, the process can prevent some emissions from escaping. However, there is controversy over whether the overall process is beneficial for the climate. EOR operations are energy-intensive, which leads to more emissions, and further emissions are produced when the oil is burned.
EOR adds to the cost of producing oil but can be economically attractive if the price of oil is high. The U.S. Department of Energy estimates that 20 billion tons of captured CO2 could produce 67 billion barrels of economically recoverable oil. As a means of boosting domestic oil production, the US federal tax code began to include incentives for EOR in 1979.
Crude oil development and production can include up to three distinct phases: primary, secondary, and tertiary (or enhanced) recovery. During primary recovery, the natural pressure of the reservoir or gravity drive oil into the wellbore, combined with artificial lift techniques (such as pumps) which bring the oil to the surface. [1] But only about 10 percent of a reservoir's original oil in place is typically produced during primary recovery. [1] Secondary recovery techniques extend a field's productive life generally by injecting water or gas to displace oil and drive it to a production wellbore, resulting in the recovery of 20 to 40 percent of the original oil in place. [1]
Producers have attempted several tertiary, or enhanced oil recovery (EOR), techniques that offer prospects for ultimately producing 30 to 60 percent, or more, of the reservoir's original oil in place. [1]
The main classes of EOR technologies are:
In 2017, there were 374 EOR projects worldwide. Of these, 44% were CO2-EOR, 12% were other gas injection EOR, 32% were thermal EOR, 9% were chemical EOR, and 2% were other EOR methods. [8]
Gas injection or miscible flooding is presently the most-commonly used approach in enhanced oil recovery. Miscible flooding is a general term for injection processes that introduce miscible gases into the reservoir. A miscible displacement process maintains reservoir pressure and improves oil displacement because the interfacial tension between oil and gas is reduced. This refers to removing the interface between the two interacting fluids. This allows for total displacement efficiency. [9] Gases used include CO2, natural gas or nitrogen. The fluid most commonly used for miscible displacement is carbon dioxide because it reduces the oil viscosity and is less expensive than liquefied petroleum gas. [9] Oil displacement by carbon dioxide injection relies on the phase behavior of the mixtures of that gas and the crude, which are strongly dependent on reservoir temperature, pressure and crude oil composition.
Using CO2 for enhanced oil recovery was first investigated and patented in 1952. [10] The process was first commercially attempted in 1977 in Scurry County, Texas. [11] Since then, the process has become extensively used in the Permian basin region of the US and is now more recently is being pursued in many different states. [12] It is now being more actively pursued in China and throughout the rest of the world. [13] [14] [15]
Most CO2 injected in CO2-EOR projects comes from naturally occurring underground CO2 deposits. [16] Some CO2 used in EOR is captured from industrial facilities such as natural gas processing plants, using carbon capture technology. [16]
CO2 is particularly effective in reservoirs deeper than 2,000 ft., where CO2 will be in a supercritical state. [17] In high pressure applications with lighter oils, CO2 is miscible with the oil, with resultant swelling of the oil, and reduction in viscosity, and possibly also with a reduction in the surface tension with the reservoir rock. In the case of low pressure reservoirs or heavy oils, CO2 will form an immiscible fluid, or will only partially mix with the oil. Some oil swelling may occur, and oil viscosity can still be significantly reduced. [18] [19]
In these applications, between one-half and 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. Carbon dioxide as a solvent has the benefit of being more economical than other similarly miscible fluids such as propane and butane. [20]
Water-alternating-gas (WAG) injection is another technique employed in EOR. Water is used in addition to carbon dioxide. A saline solution is used here so that carbonate formations in oil wells are not disturbed. [21] [22] Water and carbon dioxide are injected into the oil well for larger recovery, as they typically have low miscibility with oil. Use of both water and carbon dioxide also lowers the mobility of carbon dioxide, making the gas more effective at displacing the oil in the well. [23] According to a study done by Kovscek, using small slugs of both carbon dioxide and water allows for quick recovery of the oil. [23] Additionally, in a study done by Dang in 2014, using water with a lower salinity allows for greater oil removal, and greater geochemical interactions. [24]
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 and thus decrease the mobility ratio. The increased heat reduces the surface tension and increases the permeability of the oil. The heated oil may also vaporize and then condense forming improved oil. Methods include cyclic steam injection, steam flooding and combustion. These methods improve the sweep efficiency and the displacement efficiency. Steam injection has been used commercially since the 1960s in California fields. [25] In solar thermal enhanced oil recovery, a solar array is used to produce the steam. [26]
Steam flooding (see sketch) is one means of introducing heat to the reservoir by pumping steam into the well with a pattern similar to that of water injection. [27] Eventually the steam condenses to hot water; in the steam zone the oil evaporates, and in the hot water zone the oil expands. As a result, the oil expands, the viscosity drops, and the permeability increases. To ensure success the process has to be cyclical. This is the principal enhanced oil recovery program in use today.
Fire flooding works best when the oil saturation and porosity are high. Combustion generates the heat within the reservoir itself. Continuous injection of air or other gas mixture with high oxygen content will maintain the flame front. As the fire burns, it moves through the reservoir toward production wells. Heat from the fire reduces oil viscosity and helps vaporize reservoir water to steam. The steam, hot water, combustion gas and a bank of distilled solvent all act to drive oil in front of the fire toward production wells. [28]
There are three methods of combustion: Dry forward, reverse and wet combustion. Dry forward uses an igniter to set fire to the oil. As the fire progresses the oil is pushed away from the fire toward the producing well. In reverse the air injection and the ignition occur from opposite directions. In wet combustion water is injected just behind the front and turned into steam by the hot rock. This quenches the fire and spreads the heat more evenly.
The injection of various chemicals, usually as dilute solutions, have been used to aid mobility and the reduction in surface tension. [29] Injection of alkaline or caustic solutions into reservoirs with oil that have organic acids naturally occurring in the oil will result in the production of soap that may lower the interfacial tension enough to increase production. [30] [31] Injection of a dilute solution of a water-soluble polymer to increase the viscosity of the injected water can increase the amount of oil recovered in some formations. Dilute solutions of surfactants such as petroleum sulfonates or biosurfactants such as rhamnolipids may be injected to lower the interfacial tension or capillary pressure that impedes oil droplets from moving through a reservoir, this is analyzed in terms of the bond number, relating capillary forces to gravitational ones. Special formulations of oil, water and surfactant, microemulsions, can be particularly effective in reducing interfacial tension. 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.
Polymer flooding consists in mixing long chain polymer molecules with the injected water in order to increase the water viscosity. This method improves the vertical and areal sweep efficiency as a consequence of improving the water/oil mobility ratio.
Surfactants may be used in conjunction with polymers and hyperbranched polyglycerols; they decrease the interfacial tension between the oil and water. [29] [32] This reduces the residual oil saturation and improves the macroscopic efficiency of the process.
Primary surfactants usually have co-surfactants, activity boosters, and co-solvents added to them to improve stability of the formulation.
Caustic flooding is the addition of sodium hydroxide to injection water. It does this by lowering the surface tension, reversing the rock wettability, emulsification of the oil, mobilization of the oil and helps in drawing the oil out of the rock.
EOR processes can be enhanced with nanoparticles in three ways: nanocatalysts, nanofluids, and nanoemulsions. Nanofluids are base fluids that contain nanoparticles in colloidal suspensions. Nanofluids perform many functions in EOR of oil fields, including pore disjoining pressure, channel plugging, interfacial tension reduction, mobility ratio, wettability alteration, and asphaltene precipitation prevention. Nanofluids facilitates disjoining pressure to remove sediment entrapped oil via aggregation at the interface. Alternatively, wettability alteration and interfacial surface tension reduction are other alternative mechanism of EOR. [33] [34]
Microbial injection is part of microbial enhanced oil recovery and is rarely used because of its higher cost and because the development is not widely accepted. These microbes function either by partially digesting long hydrocarbon molecules, by generating biosurfactants, or by emitting carbon dioxide (which then functions as described in Gas injection above). [35]
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 is commonly used) are injected into the oil field. In the second approach, used since 1985, [36] 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. [37] [ better source needed ] 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 in Beverly Hills, California.
The third approach is used to address the problem of paraffin wax components of the crude oil, which tend to precipitate as the crude flows to the surface, since the Earth's surface is considerably cooler than the petroleum deposits (a temperature drop of 9–10–14 °C per thousand feet of depth is usual).
In 2013, a technique called plasma-pulse technology was introduced into the United States from Russia. This technique can result in another 50 percent of improvement in existing well production. [38]
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. [39] 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$/barrel. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. [40] Example: With oil prices at around 90 US$/barrel, the economic benefit is about 70 US$ per tonne CO2. The U.S. Department of Energy estimates that 20 billion tons of captured CO2 could produce 67 billion barrels of economically recoverable oil. [41]
From 1986 to 2008, the quote oil production deriving from EOR has increased from 0.3% to 5%, thanks to an increasing oil demand and a reduction of oil supply. [42]
Enhanced oil recovery wells typically pump large quantities of produced water to the surface. This water contains brine and may also contain toxic heavy metals and radioactive substances. [43] This can be very damaging to drinking water sources and the environment generally if not properly controlled. Disposal wells are used to prevent surface contamination of soil and water by injecting the produced water deep underground. [44] [45]
Carbon dioxide can be captured from the flue gas of an industrial facility such as natural gas processing plant or a coal power plant. If captured CO2 is used for EOR, the process is known as carbon capture-EOR (CC-EOR) and is a form of carbon capture and storage.
There is controversy over whether carbon capture followed by enhanced oil recovery is beneficial for the climate. The EOR process is energy-intensive because of the need to separate and re-inject CO2 multiple times to minimize losses. If CO2 losses are kept at 1%, the energy required for EOR operations results in around 0.23 tonnes of CO2 emissions per tonne of CO2 sequestered. [46]
Furthermore, when the oil that is extracted using EOR is subsequently burned, CO2 is released. If these emissions are included in calculations, carbon capture with EOR is usually found to increase overall emissions compared to not using carbon capture at all. [47] If the emissions from burning extracted oil are excluded from calculations, carbon capture with EOR is found to decrease emissions. In arguments for excluding these emissions, it is assumed that oil produced by EOR displaces conventionally-produced oil instead of adding to the global consumption of oil. [47] A 2020 review found that scientific papers were roughly evenly split on the question of whether carbon capture with EOR increased or decreased emissions. [47]
The International Energy Agency's model of oil supply and demand indicates that 80% of oil produced in EOR will displace other oil on the market. [46] Using this model, it estimated that for each tonne of CO2 sequestered, burning the oil produced by conventional EOR leads to 0.13 tonnes of CO2 emissions (in addition to the 0.24 tonnes of CO2 emitted during the EOR process itself). [46]When the CO2 used in EOR is sourced from underground CO2 deposits, which is usually the case, EOR provides no climate benefit. [16]
In the US, regulations can both assist and slow down the development of EOR for use in carbon capture & utilization, as well as general oil production.
As a means of boosting domestic oil production, the US federal tax code began to include incentives for EOR in 1979, when crude oil was still under federal price controls. A 15 percent tax credit was codified with the U.S. Federal EOR Tax Incentive in 1986, and oil production from EOR using CO2 subsequently grew rapidly. [48]
In the U.S., the 2021 Infrastructure Investment and Jobs Act designates over $3 billion for a variety of CCS demonstration projects. A similar amount is provided for regional CCS hubs that focus on the broader capture, transport, and either storage or use of captured CO2. Hundreds of millions more are dedicated annually to loan guarantees supporting CO2 transport infrastructure. [49]
The Inflation Reduction Act of 2022 (IRA) updates tax credit law to encourage the use of carbon capture and storage. Tax incentives under the law provide up to $85/tonne for CO2 capture and storage in saline geologic formations or up to $60/tonne for CO2 used for enhanced oil recovery. [50] The Internal Revenue Service relies on documentation from the corporation to substantiate claims on how much CO2 is being sequestered, and does not perform independent investigations. [51] In 2020, a federal investigation found that claimants for the 45Q tax credit failed to document successful geological storage for nearly $900 million of the $1 billion they had claimed. [52]
One of the primary regulations governing EOR is the Safe Drinking Water Act of 1974 (SDWA), which gives most of the regulatory power over EOR and similar oil recovery operations to the EPA. [53] The agency in turn delegated some of this power to its own Underground Injection Control Program, [53] and much of the rest of this regulatory authority to state and tribal governments, making much of EOR regulation a localized affair under the minimum requirements of the SDWA. [53] [54] The EPA then collects information from these local governments and individual wells to ensure they follow overall federal regulation, such as the Clean Air Act, which dictates reporting guidelines for any Carbon Dioxide sequestration operations. [53] [55] Beyond the atmospheric concerns, most of these federal guidelines are to ensure that the Carbon Dioxide injection causes no major damage to America's waterways. [56] Overall, the locality of EOR regulation can make EOR projects more difficult, as different standards in different regions can slow down construction and force separate approaches to utilize the same technology. [57]
EPA has issued Underground Injection Control (UIC) regulations in order to protect drinking water sources. [58] Enhanced oil recovery wells are regulated as "Class II" wells by the EPA. The regulations require well operators to reinject the brine used for recovery deep underground in Class II disposal wells. [44]
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.
Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. Mitigation includes precombustion approaches, such as cleaning coal, and post combustion approaches, include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. These measures aim to reduce coal's impact on human health and the environment.
Heavy crude oil is highly viscous oil that cannot easily flow from production wells under normal reservoir conditions.
Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.
Carbon capture and storage (CCS) is a process by which carbon dioxide (CO2) from industrial installations is separated before it is released into the atmosphere, then transported to a long-term storage location. With CCS, the CO2 is captured from a large point source, such as a natural gas processing plant and typically is stored in a deep geological formation. Around 80% of the CO2 captured annually is used for enhanced oil recovery (EOR), a process by which CO2 is injected into partially-depleted oil reservoirs in order to extract more oil and then is largely left underground. Since EOR utilizes the CO2 in addition to storing it, CCS is also known as carbon capture, utilization, and storage (CCUS).
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.
The Shengli Oil Field is the second-largest oil field in China. Located in the delta of the Yellow River, it was discovered in 1961, and oil production began in earnest in 1964. Oil output quickly increased, peaking in 1991 at 33.55 million tons. While output has decreased since then, enhanced oil recovery techniques have maintained oil production at high levels, producing around 650,000 barrels (103,000 m3) per day.
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.
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.
Steam injection is an increasingly common method of extracting heavy crude oil. Used commercially since the 1960s, it is considered an enhanced oil recovery (EOR) 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 Steam Flooding. Both are most commonly applied to oil reservoirs, which are relatively shallow and which contain crude oils which are very viscous at the temperature of the native underground formation. Steam injection is widely used in the San Joaquin Valley of California (US), the Lake Maracaibo area of Venezuela, and the oil sands of northern Alberta, Canada.
Carbon capture and storage (CCS) is a technology that can capture carbon dioxide CO2 emissions produced from fossil fuels in electricity, industrial processes which prevents CO2 from entering the atmosphere. Carbon capture and storage is also used to sequester CO2 filtered out of natural gas from certain natural gas fields. While typically the CO2 has no value after being stored, Enhanced Oil Recovery uses CO2 to increase yield from declining oil fields.
The milestones for carbon capture and storage show the lack of commercial scale development and implementation of CCS over the years since the first carbon tax was imposed.
Hydromethanation, [hahy-droh- meth-uh-ney-shuhn] is the process by which methane is produced through the combination of steam, carbonaceous solids and a catalyst in a fluidized bed reactor. The process, developed over the past 60 years by multiple research groups, enables the highly efficient conversion of coal, petroleum coke and biomass into clean, pipeline quality methane.
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.
Solar thermal enhanced oil recovery is a form of thermal enhanced oil recovery (EOR), a technique applied by oil producers to extract more oil from maturing oil fields. Solar EOR uses solar thermal arrays to concentrate the sun's energy to heat water and generate steam. The steam is injected into an oil reservoir to reduce the viscosity, or thin, heavy crude thus facilitating its flow to the surface. Thermal recovery processes, also known as steam injection, have traditionally burned natural gas to produce steam. Solar EOR is proving to be a viable alternative to gas-fired steam production for the oil industry. Solar EOR can generate the same quality steam as natural gas, reaching temperatures up to 750 °F (399 °C) and 2,500 PSI.
Microbial Enhanced Oil Recovery (MEOR) is a biological-based technology involving the manipulation of functions or structures within microbial environments present in oil reservoirs. The primary objective of MEOR is to improve the extraction of oil confined within porous media, while boosting economic benefits. As a tertiary oil extraction technology, MEOR enables the partial recovery of the commonly residual 2/3 of oil, effectively prolonging the operational lifespan of mature oil reservoirs.
Mexico highly depends on the burning of its fossil fuels, and for the same reason, it is in its interest to look into mitigation solutions for its corresponding emissions. In the General Law on Climate Change on 2012, Mexico promised to reduce 20% of its greenhouse gas (GHG) emissions by 2020 and 50% by 2050, as well as in the Paris Agreement. 19% of this new mitigation plan will be dedicated to carbon capture and storage and specifically 10% to the energy industry.
Carbon storage in the North Sea includes programmes being run by several Northern European countries to capture carbon, and store it under the North Sea in either old oil and gas workings, or within saline aquifers. Whilst there have been some moves to international co-operation, most of the Carbon Capture and Storage (CCS) programmes are governed by the laws of the country that is running them. Because the governments have pledged net zero carbon emissions by 2050, they have to find ways to deal with any remaining CO2 produced, such as by heavy industry. Around 90% of the identified storage geologies for carbon dioxide in Europe are shared between Norway and the United Kingdom; all of the designated sites for storage are located in the North Sea.