Many heavy oil formations are characterized by a bottom water sand, or a high gas saturation zone near the top. Either can have an undesirable effect on steam injection and in situ combustion response. The purpose of this paper is to present: (i) field test, (ii) laboratory model, and (iii) mathematical simulation results pertaining to bottom water or gas cap in thermal recovery processes. Some guidelines are offered for judging the suitability of a formation for one of the thermal methods.

Selected steam injection and in situ combustion projects, where a bottom water or high gas saturation zone was present, are discussed. It is shown that in a number of situations, it was possible to conduct a successful steamflood in spite of bottom water or gas zone. This was not so in some of in situ combustion projects under such conditions, where the water zone led to severe air channeling.

The laboratory model results mainly pertain to bottom water type situations in steamflooding. Results obtained by the author for tar sands, as well as those of other investigators, are discussed. A high conductivity zone near the base of the formation can serve as a means of initial heating. Subsequent steam displacement behavior would depend largely on oil viscosity and formation characteristics. One instance of a gas zone in in situ combustion is also considered.

The simulation results are those of the author, as well as other published data, concerning the effect of bottom water on cyclic steam stimulation, steamflooding, and in situ combustion response. Bottom water sand thickness is an important variable in cyclic steam stimulation, and in particular, steamflood response. In situ combustion seems to be relatively insensitive to the bottom water sand thickness, however, even small thicknesses can lead to severe air bypassing. A gas zone seems to be undesirable in the case of cyclic steaming and in situ combustion, but may be used to advantage in steam-flooding.

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