Importance of IOR/EOR
George Stosur, who previously headed the IOR Division at the US DoE, suggested in 1991 that IOR would take off in 2000 – albeit at a modest pace initially – and then increase until about 2025. In 2025, IOR production was projected to contribute to around 40% of the total conventional light oil at peak production (see Figure 1). If this scenario still holds true, there is not much time left, and there could therefore be a serious oil shortage in the next 10 years.
Figure 1: World Crude Oil Supply (1)
The main, realistic options are carbon dioxide (CO2) and air as fluids to inject into light oil reservoirs. CO2 is available in a limited number of natural aquifers, in the US and other parts of the world. One major source is power station stack gas, supplemented by other industrial sources. A number of examples of this approach are cited in Greenhouse Issues, (2) and include the Alberta CCS project, the Weyburn lignite gasification-CO2 pipelining project and the Norwegian pilot project to pipeline CO2 out to North Sea fields. Although CO2 availability is partly an issue, its capture, separation (need for pure CO2) and pipeline costs are sufficiently high to make most projects economically marginal at best, unless significant carbon subsidies are available, or other incentives, such a ‘tax break’ for IOR, are forthcoming. Some in the industry argue that they already suffer a 10% tax disadvantage compared with the rest of British industry.
If a sufficiently long-term view is taken, for strategic reasons, or because of global warming considerations and the Kyoto Protocol, the injection of CO2 into watered-out Brownfield reservoirs on the UK Continental Shelf (UKCS), could be economic, eventually. This could be accomplished by using a ‘slow’ EOR-technique, such as miscible gravity stabilised gas injection (GSGI), over 20 to 30 years, the same as for waterflooding. The full benefit of CO2 miscibility is only possible in reservoirs at a high enough pressure, ca. 200 bar. Very high recoveries can be obtained of around 80% or more, compared with 25% to 28% of residual, using a horizontal miscible water alternating gas (WAG) process. Air injection into residual light oil reservoirs is also being considered for the North Sea, in the giant Ekofisk field. (3)
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