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Reservoir Characterization |
1 Institut Français du Pétrole, B.P. 311, 92506 Rueil-Malmaison Cedex, France
2 IKU Petroleum Research, N-7034 Trondheim, Norway
The objective of this paper is to demonstrate the impact of film continuity on oil recovery by gas injection under secondary conditions, e.g. when water is non-mobile. In this case two films have to be considered: a water film and an oil film. The continuity of the former is insured by the wettability conditions, whereas the continuity and stability of the latter depend on the ability of the oil phase to spread on the water substrate in the presence of a gas phase. This ability is expressed by the spreading coefficient, S, defined as a balance of the three interfacial tensions. To study the effect of wettability and spreading on the residual oil saturation obtained by gas flooding and on the capillary pressure and relative permeabilities, centrifuge, displacement and gravity drainage experiments have been performed for various wettability and spreading conditions.
It is shown that both parameters modify the flow characteristics, the residual oil saturation and the recovery kinetics. More specifically, in a water-wet porous medium, the residual oil saturation is found to be higher and the drainage capillary pressure and relative permeabilities lower when measured for a non-spreading oil than for a spreading one. For an oil-wet porous medium the impact of S is much less important. However, for the same positive spreading coefficient, although the capillary pressure threshold is almost the same in water-wet and oil-wet porous media, the recovery kinetics are essentially different, due to the different displacement mechanisms.
