The steam-cycling, or stimulation, process was discovered by accident in the Mene Grande Tar Sands, Venezuela, in 1959. During a steam-injection trial, it was decided to relieve the pressure from the injection well by backflowing the well. When this was done, a very high oil production rate was observed. Since this discovery, many fields have been placed on steam cycling.
The steam-cycling process, also known as the steam huff and puff, steam soak, or cyclic steam injection, begins with the injection of 5000 bbl to 15,000 bbl of high-quality steam. This could take a period of days to weeks to accomplish. The well is then shut in, and the steam is allowed to soak the area around the injection well. This soak period is fairly short, usually from 1 to 5 days. The injection well is then placed on production. The length of the production period is dictated by the oil production rate but could last from several months to a year or more. The cycle is repeated as many times as is economically feasible. The oil production will decrease with each new cycle.
Mechanisms of oil recovery due to this process include (1) reduction of flow resistance near the wellbore by reducing the crude oil viscosity and (2) enhancement of the solution gas drive mechanism by decreasing the gas solubility in an oil as temperature increases.
Often, in heavy-oil reservoirs, the steam stimulation process is applied to develop injectivity around an injection well. Once injectivity has been established, the steam stimulation process is converted to a continuous steam-drive process.
The oil recoveries obtained from steam stimulation processes are much smaller than the oil recoveries that could be obtained from a steam drive. However, it should be apparent that the steam stimulation process is much less expensive to operate. The cyclic steam stimulation process is the most common thermal recovery technique.19,20,24 Recoveries of additional oil have ranged from 0.21 bbl to 5.0 bbl of oil per barrel of steam injected.
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