A pore-level screening study on miscible/immiscible displacements in heterogeneous models

Abstract

Abstract A comprehensive understanding of the role of reservoir heterogeneities induced by flow barriers and connate water on sweep efficiency of different EOR scenarios is rarely attended in the available literature. In this work, different miscible/immiscible EOR processes were conducted on various one-quarter five-spot glass micromodels incorporating small-scale flow barriers. Microscopic and macroscopic observations revealed the reduction of sweep efficiency, premature breakthrough of displacing fluids, the severity of fingering at displacement front which leaves a large amount of oil behind the flow barriers untouched, and significant increasing trend of oil recovery after breakthrough in the presence of flow barriers. For the range of experiments performed here, the higher oil recovery is attained by polymer, hydrocarbon solvent, surfactant and water flooding. Flow around the shale streaks is strongly influenced by capillary forces during immiscible floods. Shales on the small-scale affect oil recovery by reducing effective permeability and increasing residual oil saturation. The effect of convection is much more profound than diffusion transport mechanism during oil displacements by hydrocarbon solvent in shaly models; as well, pore-level visualizations disclosed that the presence of connate water in solvent injection process improves the recovery efficiency specifically at higher water saturations, but it acts conversely for the case of immiscible floods. The obtained results provide opportunities for possible quantifying the impact of discontinuous impermeable barriers on sweep efficiency, and identifying bypassed oil zones for future infill drilling in heterogeneous heavy oil systems.