Recent technical advances in the understanding ofin situ combustion have made it worthwhile to consider this process as a serious means of recovering heavy oil. However, it mustfirst prove itself to be economically viable, particularly in comparison with steam-based recovery processes. This paper examines the factors that are necessary to make in situ combustion work in the field. including the need to ensure operation at high temperatures, optimal well layouts and spacing, and why economies of scale must be used to ensure competitive economics. Based on these requirements, an in situ combustion process is then compared to a similarlydesigned steam process and the comparative economics are discussed.
The results of this work show that in situ combustion should be laid out in a line drive pattern, based on a 10acre well spacing. Sufficient air injection capacity must be installed to best ensure high-temperature combustion, thus achieving reasonable oil produt:tion rates. It is recognised that in situ combustion has higher front-end costs than steam processes, but recovery factors for in situ combustion can be as mut:h as 60 percent higher. The cost comparison for a 20-well combustion project and a comparable steam project set in Western Canada yields a per barrel cost of $1655 for steam and $12.40 for in situ combustion.
As with any investment, the major concern with in situ combustion (ISC) is the risk and the competitive return, since it is a relatively-costly supplementary recovery process. The major economic consida-ation is risk, as in the past, this complex process has exhibited an uninspiring lack of success. It has been tried in dozens of projects over the past 40 years, but has not accounted for and still does not account for significant heavy oil production anywhere in the world1. This paper will focus on the fireflooding of heavy oil in Western Canada, where the competing process is steam injection.
In hindsight, thanks to research at the University of Calgary and elsewhere, the reasons for this lack of success are understandable. In situ combustion is far more complex than was originally thought, and it is not intuitive that there would be multiple oxidation reactions with uneven transitions. This dynamic displacement process is highly technical, with low-temperature oxidation (LTO), high temperature oxidation (HfO) and gas-phase combustion intertwined with complex organic reactions, and it is influenced by temperature and oxygen partial pressure. Also, it is possible to now benefit from the considerable amount of field experience gained on the unsuccessful projects. -If-properly operated the process does not produce difficult emulsions nor does it increase oil gravity or viscosity; all problems which have been associated with in situ combustion in Canadian heavy oil.
The economic driving force behind in situ combustion has always been the potential of a higher oil recovery than is possible from other processes. Estimates show that the capital cost of using ISC for an average Canadian heavy oil project is approximately equal to that of a steam-based process (dependent, of course, on a number of variables); however, the operating cost per bbl is less, based on this higher production rate and the lower cost of operating fuel.