Steam Injection (Oil Industry) Information
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. 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 (USA), the Lake Maracaibo area of Venezuela, and the oil sands of northern Alberta (Canada).
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 recover approximately 20% of the Original Oil in Place (OOIP), compared to steam flooding, which has been reported to recover 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.
Steam Flooding
In a steam flood, sometimes known as a steam drive, some wells are used as steam injection wells and other wells are used for oil production. Two mechanisms are at work to improve the amount of oil recovered. The first is to heat the oil to higher temperatures and to thereby decrease its viscosity so that it more easily flows through the formation toward the producing wells. A second mechanism is the physical displacement employing in a manner similar to water flooding, in which oil is meant to be pushed to the production wells. While more steam is needed for this method than for the cyclic 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 oil 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 intent is to reduce the viscosity of the bitumen to the point where gravity will pull it down into the producing well.
In 2011 Laricina Energy combined solvent injection with steam injection in a process called solvent cyclic steam-assisted gravity drainage (SC-SAGD).[1] Laricina claims that combining solvents with steam reduces the overall steam oil ratio for recovery by 30%.
References
- Butler, Roger M. (1997). Thermal Recovery of Oil and Bitumen. ISBN 0-9682563-0-9.
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