Considering the present technology of surface mining, less than ten per cent of the tar sands deposits of Alberta can be exploited by surface mining methods. Recovery of oil from the remainder would necessitate the use of a suitable in situ method. This is particularly true of other tar sands deposits, such as those of Venezuela, which lie too deep to be amenable to surface mining methods.
The two principal problems encompassing in situ oil recovery methods, applied to tar sands, are, first, the lack of communication among wells, and secondly, the high viscosity of the in-place bitumen. Communication between injection and production wells can be created by fracturing, by hot gas injection, or by the use of suitable solvents. Bitumen viscosity can be lowered by the application of heat, by admixture with certain solvents, or by means of emulsifying agents. Other recovery methods that have been proposed involve underground nuclear detonations, in situ hydrogenation, conduction heating, etc.
The present paper discusses the in situ oil recovery methods, involving the above schemes, that have been applied to the tar sands of Alberta, United States of America and Venezuela. Selected field results are described. Also discussed are the above-mentioned proposed recovery schemes, which show considerable promise. The field-tested methods include the Shell Process, cyclic steam stimulation, steam flooding, forward combustion, and reverse combustion. Under favorable conditions, a few of these recovery methods have been shown to be technically feasible. One can conclude that the in situ recovery of oil the tar sands can become a reality, if favorable economic conditions exist. However, a generally applicable in situ recovery method for the tar sands is still not around the corner.