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 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 1000 billion barrels, 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. For the climate, the CO2 released from the combustion of 240 billion barrels of oil would be on the order of 100 billion tonnes of CO2, equivalent to four times the annual global CO2 emissions.
Steam injection is an increasingly common method of extracting heavy oil. 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.
Cyclic Steam Stimulation
This method, also known as the Huff and Puff method, consists of 3 stages: injection, soaking and production. Steam is first injected into a well for a certain amount of time to heat the oil in the surrounding reservoir to a temperature at which it flows. After it is decided enough steam has been injected, the steam is usually left to "soak" for some time after (typically not more than a few days). Then oil is produced out of the same well, at first by natural flow (since the steam injection will have increased the reservoir pressure) and then by artificial lift. Production will decrease as the oil cools down, and once production reaches an economically determined level the steps are repeated again.
The process can be quite effective, especially in the first few cycles. However, it is typically only able to retrieve approximately 20% of the Original Oil in Place (OOIP), compared to steam flooding which has been reported to retrieve over 50% of OOIP. It is quite common for wells to be produced in the cyclic steam manner for a few cycles before being put on a steam flooding regime with other wells.
The mechanism was accidentally discovered by Shell while it was doing a steam flood in Venezuela and one of its steam injectors blew out and ended up producing oil at much higher rates than a conventional production well in a similar environment.
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Steam Flooding in a steam flood, sometimes known as a steam drive, some wells are used as steam injection wells and other wells produce from them. The idea is the same as with water flooding, the oil is meant to be pushed to the production wells. While more steam is needed for this method, it is typically more effective at recovering a larger portion of the oil. A form of steam flooding that has become popular in the Alberta tar sands is steam assisted gravity drainage (SAGD), in which two horizontal wells are drilled, one a few meters above the other, and steam is injected into the upper one. The idea is to reduce the viscosity of the bitumen to the point where gravity will allow gravity to pull it down into the producing well
Water injection
The water injection method used in oil production is 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. This method is used to increase oil recovery from an existing reservoir.
Water is injected for two reasons: 1. For pressure support of the reservoir (also known as voidage replacement). 2. To sweep or displace the oil from the reservoir, and push it towards an oil production well.
Normally only 30% of the oil in a reservoir can be extracted, but water injection increases that percentage (known as the recovery factor) and maintains the production rate of a reservoir over a longer period of time.
Injected Water Sources
Water produced from the reservoir (at the same time as the oil) is preferred for use as an injection fluid. Using produced water avoids the potential of causing formation damage due to incompatible fluids. Also, the produced water, being environmentally unfriendly, must be disposed of in some manner, and this method has an economic benefit. As the volumes of water being produced are not sufficient to replace all the production volumes (oil & gas), make-up water must be used to ensure that all the reservoir voidage is replaced.
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When it is ocean water, it is pumped through large pipes which extend far out into the ocean. It is collected in large basins at a seawater intake pumping station. The seawater is pressurized and passed through filters to the de-oxygenation tower.
Water injection pumps
The high pressure, high flow water injection pumps are placed near to the de-oxygenation tower and boosting pumps. They fill the bottom of the reservoir with the filtered water to push the oil towards the wells like a piston. The result of the injection is not quick, it needs time.
Water injection is used to prevent low pressure in the reservoir. The water replaces the oil which has been taken, keeping the production rate and the pressure the same over the long term. For example, if the water injection is stopped for a day, the production rate does not change, unlike with gas lifts.
| RECOVERY TECHNIQUES | |
| recovery | добыча |
| primary recovery | первичная добыча |
| secondary recovery | вторичная добыча |
| tertiary recovery | третичная добыча |
| depletion | истощение |
| well placement | расположение скважин |
| completion | закачивание скважины |
| gravity drainage | гравитационный режим пласта |
| water injection | нагнетание воды |
| waterflood(ing) recovery | добыча нефти за счет наводнения |
| gas injection | нагнетание газа в залежь; газовая репрессия |
| miscible drive | вытеснение в условиях смешиваемости фаз |
| thermal | тепловой |
| steam injection | нагнетание пар в залежь |
| sweeping (reservoir) | охват пласта вытесняющим агентом |
| air injection | нагнетание воздух в залежь |
| thermally – cracked hydrocarbon zone | создание фронта горения в пласте путем частичного сжигания нефти |
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