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Up one levelExpert Viewpoint – THAI in situ combustion
HeavyOilinfo.com spoke to Professor Malcolm Greaves, principal inventor of the THAI process for heavy oil recovery and co-inventor of the CAPRI process for downhole catalytic upgrading.
The development of THAI
Professor Greaves became involved with academic work relating to enhanced oil recovery (EOR) in 1981 when one of his PhD students at the University of Bath, UK, was researching polymer flooding. He became aware of the benefits of in situ combustion (ISC) at the first European EOR Conference in Bournemouth, UK. Subsequent discussions in the US and Canada confirmed that in situ combustion had the greatest potential as a research area, and was at that time still regarded by the oil industry as “the great hope” for heavy oil recovery.
Benefits of THAI
The THAI process can be considered as a variant of ISC, but its horizontal well arrangement provides a unique gravity and pressure drawdown geometry. Another key difference is that oil recovery occurs via a short displacement mechanism, unlike the conventional ISC process, which requires oil to move laterally 100s of meters (long-distance displacement). By comparison, THAI requires oil to move downwards, with the help of gravity, typically just 5-10 meters.
Applications of THAI
According to Greaves, THAI has a wider range of application than SAGD, but in any case, a detailed knowledge of the reservoir is essential. SAGD generally works best in relatively thick (40m) homogeneous pay zones. Laboratory simulations indicate that THAI can also be applied in such situations, but also in much thinner zones. The pilot field projects at Christina Lake are targeting a producing zone about 20m thick. It is possible that THAI will be effective down to about 6m thickness, as is common in many Saskatchewan heavy oil pools.
CAPRI in situ upgrading
CAPRI involves the addition of gravel-packed catalyst—as used in a conventional refinery—between the tubing and the horizontal wellbore. Laboratory test results have shown the technique to add 6–8 API points on top of the THAI in situ upgrades. Based on these experiments, the combination could deliver in situ upgrading to above the 22 API requirement for produced fluids that can be transported by pipeline without diluent—a major cost saving. In situ upgrading will also enable considerable savings in surface upgrading and refining costs.
