Short-versus Long-distance
Displacement All conventional oil recovery processes (e.g. waterflooding) operate via long-distance displacement. This is shown schematically in Figure 3. In longdistance displacement, the reservoir geology dominates, unless advantage can be taken of good conformity, dip angle, etc. Most times, this is not the case. Moreover, the pathway for the mobilised oil is hundreds of metres long before it eventually arrives at the production well. The advent of horizontal well technology has changed everything – at least, in those parts of the world where innovative technology is seen as a necessary part to achieving future success in the oil industry. The examples in Figure 3 are taken from the heavy oil and bitumens scene, which is being aggressively exploited in Canada, Venezuela and other parts of the world. The THAI process shown in Figure 4, was developed by the Improved Oil Recovery Group at the University of Bath, (6) in collaboration with the Petroleum Recovery Institute, Calgary.
Figure 3: Short and long-distance displacement processes
In ‘short-distance displacement’, mobilised oil ahead of the combustion front only has to travel a short distance to be captured by the horizontal producer well, located in the bottom of the oil layer. The production path in the reservoir is only a few metres, compared to the hundreds or thousands of metres in long-distance displacement – a simple way to maximise net present value (NPV). The THAI Process is set to be piloted at Christina Lake, Athabasca Tar Sands, Alberta, Canada, in early 2005, by Petrobank Ltd.
Figure 4: THAI Process for Heavy
Oil Recovery and Downhole Upgrading
Innovative EOR Process Technology for the North Sea
Horizontal wells have contributed huge gains in productivity, compared with vertical–vertical, or conventional well pattern arrangements. It is opportune, therefore, to capitalise on this by way of new EOR technology. It should be possible to implement short-distance displacement, or integrated horizontal wells processes in UKCS oil fields, and achieve very substantial oil recovery and economic advantage. THAI can be applied, not only in heavy oil fields in the UKCS, e.g. in Mariner and Bressay (10–14ºAPI American Petroleum Institute (°API)), but also in the medium-heavy oilfields, such as Harding, Alba, Foinhaven (ca. 20–24°API). The UKCS reserves of heavy oil are estimated to be 10 billion barrels. (7) A very sizeable resource when compared with the 20 billion or so barrels of unrecovered light oil. Oil recoveries achievable by the THAI process are consistently above 80% original oil in place (OOIP). (8)
Who is going to take the lead? Obviously, a concerted partnership is needed between oil companies, governments and the universities. Some steps are being taken in this direction through the US Interagency Task Force (ITF) Programme and also by the UK Engineering and Physical Sciences Research Council (EPSRC). However, short-term needs tend to prevail, and many good ideas are cast aside in favour of early, but often very limited, short-term gains. Business survival of course, depends on this, but if Canada can organise the necessary long-term partnerships, so too can the UK. The very survival of the UKCS oil industry depends on its ability to innovate, by way of new, advanced technology and reservoir processes. Such activity can bring unexpected bonuses, such as downhole upgrading of heavy oil (8) using the reservoir as a ‘free reactor’. To achieve similar conversions, a surface process plant to process 100,000 bbl/d would cost up to US$2 billion. This an issue that is now being seriously contemplated in the UK, owing to the lack of suitable refining conversion plant (upgrader) to handle future heavy oil production from the UKCS.
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