Using vorticity to quantify the relative importance of heterogeneity, viscosity ratio, gravity and diffusion on oil recovery

Abstract

The vorticity of the displacement velocity is used to derive dimensionless numbers that can be used to quantify the relative importance of viscosity ratio, gravity, diffusion/dispersion and permeability heterogeneity on secondary hydrocarbon recovery. Using this approach, a new objective measure of the impact of permeability and porosity heterogeneity on reservoir performance is obtained. This is used, in conjunction with other dimensionless numbers, to analyse the relative impact of heterogeneity, buoyancy effects, mobility ratio and dispersion on breakthrough time and recovery at 1 pore volume injected during first contact miscible gas injection. This is achieved using results obtained from detailed simulation of miscible displacements through a range of geologically realistic reservoir models. This study goes some way towards developing a unified mathematical framework to determine under which flow conditions reservoir heterogeneity becomes more important than other physical processes. We propose that comparison of these dimensionless numbers can be used to identify the key factors controlling recovery and thus assist the engineer in determining appropriate enhanced oil recovery techniques to improve recovery.