The effect of wettability on foam sensitivity to crude oil in porous media

We evaluated foam-oil sensitivity in oleophilic (oil- or intermediate-wetting) media compared with hydrophilic (water-wetting) media. The porous media used were either Berea sandstone or glass microvisual cells with and without Quilon C coating (hydrophilic or oleophilic). Dynamic contact angle measurements on untreated and Quilon C-treated glass showed that the treatment makes the glass microvisual cells intermediately wet. Microvisual studies showed that foams tend to be more sensitive (less effective) to oil at residual oil saturation when the pores are intermediately wet as opposed to water-wet. These studies show that, at least for glass plates, the surfactants can adsorb and partially reverse the wettability, back towards water-wet. Coreflood tests using treated and untreated Berea sandstone rock show that the Quilon C treatment also changed the wettability of the rock away from water-wetting. In most cases the foam effectiveness was reduced in oleophilic rock over hydrophilic rock (oil-free). At residual oil saturation foam effectiveness for most foams was further reduced in oleophilic-treated rock over hydrophilic rock. This work confirms earlier suggestions that foam effectiveness may be reduced in porous media of intermediate or oleophilic wettability and that the foam effectiveness may be further reduced at residual oil saturation. Surfactant selection for field use should be made taking into account the actual reservoir conditions under which they will be used, including nature of the oil, Sor and wettability. The results of this research should provide some guidance for this purpose.