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Enhanced oil recovery

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Enhanced Oil Recovery (abbreviated EOR) is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field. Using EOR, 30-60 %, or more, of the reservoir's original oil can be extracted[1] compared with 20-40%[2] using primary and secondary recovery.

Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery).

How it works

Enhanced oil recovery is achieved by gas injection, chemical injection, ultrasonic stimulation, microbial injection, or thermal recovery (which includes cyclic steam, steamflooding, and fireflooding).

Gas injection

Gas injection is presently the most-commonly used approach to enhanced recovery. A gas is injected into the oil-bearing stratum under high pressure. That pressure pushes the oil into the pipe and up to the surface. 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 commonly used include CO2, natural gas or nitrogen.

Oil displacement by carbon dioxide injection 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

Several possible methods have been proposed. Some successful applications are injection of polymers, which can either reduce the crude's viscosity or increase the viscosity of water which has also been injected to force the crude out of the stratum. Detergent-like surfactants such as rhamnolipids are injected to lower the capillary pressure that impedes oil droplets from moving through a reservoir.

Ultrasonic stimulation

It has been proposed to use high-power ultrasonic vibrations from a piezoelectric vibration unit lowered into the drillhead, to "shake" the oil droplets from the rock matrices, allowing them to move more freely toward the drillhead. This technique is projected to be most effective immediately around the drillhead.[3]

Microbial injection

Microbial injection 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 molecules, by generating biosurfactants, or by emitting carbon dioxide (which then functions as described in Gas injection above).[3]

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[4], 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.[5] 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 Beverly Hills, California.

The third approach is used to address the problem of paraffin 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),[6] 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.[7]

Thermal recovery

In this approach, various methods are used to heat the crude oil either during its flow upward in the drillhead, or in the pool, which would allow it to flow more easily toward the drillhead.

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.[8] 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$/barrel. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 130 US$/barrel, the economic benefit is about 100 US$ per tonne CO2.

Examples of current EOR projects

In Canada, a CO2-EOR project has been established by EnCana at the Weyburn Oil Field in southern Saskatchewan. The project is expected to inject a net 18 million ton CO2 and recover an additional 130 million barrels (21,000,000 m3) of oil, extending the life of the oil field by 25 years.[9] (When combusted, this extra volume of oil will produce nearly 60 million ton CO<subB>2, so in this case carbon capture and storage in combination does not result in a net reduction in atmospheric CO2). 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 billion barrels (3.8×1010 m3) 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. For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1 trillion barrels (1.6×1011 m3), 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, severance taxes, and state income taxes on oil production, aside from other economic benefits.

References

  1. ^ DOE - Fossil Energy: DOE's Oil Recovery R&D Program
  2. ^ http://www.energy.ca.gov/process/pubs/electrotech_opps_tr113836.pdf
  3. ^ "Tiny Prospectors", Chemical & Engineering News, 87, 6, p. 20
  4. ^ http://www.saione.com/aboutpdl.htm Biography of Philip Lauer
  5. ^ www.titanoilrecovery.com Titan Oil Recovery (Beverly Hills CA) webpage
  6. ^ http://www.en.allexperts.com/q/Geology-1359/2009/1/temperature-underground.htm#6 Geology Q/A website
  7. ^ WMI International, Houston TX 77092; (713) 956-4001
  8. ^ Austell, J Michael (2005). "CO2 for Enhanced Oil Recovery Needs - Enhanced Fiscal Incentives". Exploration & Production: The Oil & Gas Review -. Retrieved 2007-09-28. {{cite journal}}: Cite has empty unknown parameters: |month= and |coauthors= (help)
  9. ^ http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/2a1.pdf Department of Energy website

See also

http://www.firp.ula.ve/

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