The level of in situ upgrading of heavy Wolf Lake oil achieved by CAPRI, the catalytic variant of the THAI process - 'Toe-to-Heel Air Injection', has been investigated by various analytical methods. These included gas chromatography (GC), elemental analysis, simulated distillation (SIMDIS), micro activity test (MAT), plus density and viscosity. The tests were performed on the oil produced from the CAPRI process, which was conducted in a semi-scaled 3-D combustion cell. The tests employed a standard HDS catalyst, which was "gravel packed" around the horizontal producer well, forming an annular radial inflow type reactor. Although the analytical measurements made were necessarily selective in their scope, they nevertheless provide a good indication of what the potential may be for downhole upgrading in the field. CAPRI produces a 'light oil', characterized by a low viscosity of around 60 mPas, or less. The produced oil is readily converted into gasoline and diesel fractions, with a higher conversion (FCC) than that obtained with normal virgin bitumen vacuum gas oil. Environmentally, there are also very significant potential benefits regarding in situ removal (and retention) of heavy metals, and reduction of sulphur in the oil.
Fireflooding, in situ combustion (ISC), or heavy oil air injection (HOAI) is a process whereby a combustion front is propagated through the formation, vaporizing the oil and water ahead of it. In the conventional, forward combustion, long distance displacement process (Figure 1), the vaporized oil and water are condensed in the cooler parts of the reservoir and are eventually produced from a producer well. Forward combustion burns the least desirable fraction of the oil, leaving a clean formation behind and is an efficient heat generation process. Its main draw back is that there must be sufficient mobility for the vaporized oil and water to be produced after they have condensed ahead of the combustion front. This factor, frequently leading to loss of air injectivity and consequent inability to maintain the process in a high temperature oxidation (HTO) mode, has probably been responsible for the poor performance, or failure, of many field applications of the conventional ISC process.
Short-distance displacement (Figure 1) is a concept that was made possible by the development of horizontal well technology. SAGD (steam-assisted gravity drainage) is the most well-known thermal process in this category. THAI-"Toe-to-Heel Air Injection" is an integrated horizontal wells thermal process, also fitting into the short-distance displacement category (Figure 1), but with some unique features. Briefly, there is no necessity for communication into, or displacement through, the oil layer downstream of the combustion front. Rather this is excluded by THAI, since the cold heavy oil region downstream of the combustion front provides a natural 'barrier', by virtue of its very high viscosity, as well as providing a seal around the horizontal producer well. Figure 1 illustrates the 'moving window' effect in THAI, due to the propagation of the combustion front.
