(267g) Flow Instability Associated With Displacements Involving Wettability Alteration

Wettability can be altered in petroleum reservoirs due to injection of surfactants and changes in electrolyte concentrations or temperature. Wettability alteration, in turn, affects residual oil saturation, relative permeabilities and capillary pressure functions. Low salinity waterfloods are supposed to increase oil recovery due to wettability alteration. Decrease in residual oil saturation leads to increase in oil relative permeability and in some cases the total mobility behind the flood front. This increase in mobility can introduce instability to the flood front and affect the areal sweep and overall recovery. A viscous fingering theory is developed for these displacement processes in homogeneous porous media based on viscous fingering theory in compositional displacement. A 2-D, two-phase, multi-component, finite-difference simulator is used to study the effect of wettability alteration on the flood fronts in heterogeneous media. 1-D viscous fingering theory shows that the adverse mobility ratio at the flood front is of the order of 4 or less in typical cases. Finger tip moves at a speed of 1.5 times the shock speed (or slower). For the case of homogeneous reservoirs, 2-D simulations of low salinity water flood show development of fingers at the flood front. Fingering in the presence of heterogeneities is more severe.