Effect of the spreading coefficient on three-phase flow in porous media

A pore-level network model has been developed to study the effect of spreading coefficients on three-phase flow through porous media. This model combines the morphological description of the pore space with pore-level displacement physics to model capillarity-controlled, immiscible gas invasion of a porous medium initially saturated with water and oil. Three displacement events are involved during gas invasion, namely, direct water drainage, direct oil drainage, and double drainage. Direct oil drainage and double drainage involve oil mobilization and consequently lead to oil recovery. Direct water drainage event is preferred over double drainage if the spreading coefficient is highly negative. The residual oil saturation to gasflood starting after a waterflood is higher for nonspreading oils than for spreading oils. In spreading oils, it is not a function of the spreading coefficient. In nonspreading oils, the residual oil saturation increases with the magnitude of the spreading coefficient. The residual oil saturation to gasflood is also a function of the initial oil saturation; it increases as the initial oil saturation increases. The increase is higher for nonspreading oils. The gas-oil capillary pressure is not a function of the liquid saturation alone, as is commonly presumed. It is a function of the spreading coefficient and the initial oil saturation, as well. (C) 1997 Academic Press.