Miscible and immiscible displacements in porous media.

摘要

Bypassing occurs during a flood in a porous medium when the displacing phase is more mobile than the displaced phase (fingering), when the displacing phase is lighter than the displaced phase (gravity override), or/and when there are areas with different permeability. The phenomenon leads to poor sweep efficiency, early breakthroughs and low oil recovery. To investigate mass-transfer from a bypassed region and the dependence of bypassing on injectant composition and core orientation, mass-transfer experiments and corefloods in an oil-wet core at residual oil saturation have been carried out. Oil recovery was found to be a monotonic function of gas enrichment for both types of experiments. In mass transfer experiments, diffusion and gravity are the mechanisms identified to contribute to oil extraction from the pores of a bypassed zone. In corefloods, gravity forces delay oil production for multicontact miscible mixtures.; In the literature, relative permeability dependence on the capillary number has generated much discussion. The effect of capillary number on relative permeability was experimentally investigated contacting drainage floods in a water-wet homogeneous core. The range of capillary number investigated was 10−8–10−4. The experimental data were analyzed using the JBN method. Results showed that increasing the capillary number, relative permeability values increase for all oilfloods devoid of capillary end effects. The latter is a phenomenon observed for low rates, short core samples and low viscosity ratios. It refers to the accumulation of the wetting phase at the edge of the core, distorting the saturation profiles and, hence, the relative permeability values. For all floods free from capillary end effects: (a) increase in the viscosity ratio results in increase of the relative permeability, (b) decreasing the interfacial tension leads to higher relative permeabilities and (c) increasing the flow rate leads to higher relative permeability values.