This article will discuss the various oil and gas recovery methods, focusing mainly on tertiary or enhanced oil recovery (EOR) operations.
WHAT IS EOR?
Enhanced oil recovery (EOR), also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise.
Although the primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the chemical composition of the oil itself in order to make it easier to extract.
According to the US Department of Energy, carbon dioxide and water are injected along with one of three EOR techniques: thermal injection, gas injection, and chemical injection. More advanced, speculative EOR techniques are sometimes called quaternary recovery.
METHODS
Enhanced Oil Recovery (EOR) methods are techniques used to increase the amount of oil extracted from an oil field or reservoir. Traditional primary and secondary recovery methods can only extract about 20-40% of the original oil in place (OOIP). EOR methods aim to recover an additional 10-60% of the OOIP, depending on the reservoir and method used.
There are three primary techniques of EOR: gas injection, thermal injection, and chemical injection. Gas injection, which uses gases such as natural gas, nitrogen, or carbon dioxide (CO2), accounts for nearly 60 percent of EOR production in the United States.
Thermal injection, which involves the introduction of heat, accounts for 40 percent of EOR production in the United States, with most of it occurring in California.
Chemical injection, which can involve the use of long-chained molecules called polymers to increase the effectiveness of waterfloods, accounts for about one percent of EOR production in the United States.
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.
GAS INJECTION
Gas injection or miscible flooding is presently the most-commonly used approach in enhanced oil recovery.
Gas injection as an EOR method uses nitrogen gas (N2) or Carbon dioxide (CO2) for the miscible displacement of crude in unconventional reservoirs our mature wells. The principle for recovery is that when the gas dissolves in the oil, it reduces its viscosity, improving mobility. According to the US Department of Energy, gas injection techniques account for nearly 60% of EOR production in the United States.
READ: LPG / Gas Business Opportunities & How to Start
To successfully carry out a gas injection, CO2 pumps into the formation via injection wells. At high downhole pressures, the gas forms a miscible zone that mops up stranded oil and forces it towards the production casing of the target well. Gas injection is often alternated with water injection using a water injection pump system to further improve sweep efficiency.
Due to growing concerns about the impact of CO2 (a known greenhouse gas) on global climate change, operators may opt to use high-purity nitrogen gas. Typically, N2 is also favorable over CO2 because it has relatively inert properties that prevent downhole combustion. In addition, N2 can be generated cost-effectively from atmospheric air using a nitrogen generator skid.
THERMAL INJECTION
Thermal Injection enhanced oil recovery (also called Steam injection or steam flooding) refers to the injection of water vapor at high pressure and temperature into a well to mop up stranded oil from the reservoir following a decline in the formation pressure.
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. In 2011 solar thermal enhanced oil recovery projects were started in California and Oman, this method is similar to thermal EOR but uses a solar array to produce the steam.
- Steam flooding
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. 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
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
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.
CHEMICAL INJECTION
In chemical injection, long-chain polymers are injected into a well via a chemical injection skid to free up oil and gas molecules from remote sections of the reservoir. Chemical injection can be done alongside waterflooding. This effectively improves the recovery factor by increasing the efficacy of the surfactants for improved mobility of hydrocarbons.
The polymers utilized in this EOR process can be alkaline or micellar substances which enhance the flow of crude (sweep efficiency) by reducing the interfacial tension between the hydrocarbon molecules and water present in the reservoir.
- Polymer flooding
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. This reduces the residual oil saturation and improves the macroscopic efficiency of the process.
- Low salinity nanofluids
EOR processes can be enhanced with nanoparticles in three ways: nano catalysts, nanofluids, and nano emulsions. 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.
C02 INJECTION
In addition to these three enhanced oil recovery types, CO2 injection is also a valuable method. CO2 pumps and injection pumps are used in the carbon sequestration (i.e. C02 sequestration) process. This injection method is crucial for handling the corrosion, scaling, and potential higher temperatures that occur in re-injection. AP-610 pumps are particularly effective when it comes to CO2 pumping/injection and there is a full line of pumps available to meet your Carbon Capture, Utilization, and Storage (CCUS) needs. Here are a few examples:
Process pumps
In-line pumps
Vertical pumps
Single-stage double pumps
Split-case pumps
Barrel pumps
Packaged systems and more