Normal Stresses and Interface Displacement: Influence of Viscoelasticity on Enhanced Oil Recovery Efficiency

Abstract

One of chemical Enhanced Oil Recovery (EOR) methods consists in injectingaqueous solutions of polymers into the reservoir in order to improvemobility ratio between the injected fluid and the remaining oil.This "polymer flooding" process is usually only characterized withthe low shear viscosity of the injected fluid, even if these aqueoussolutions are strongly shear thinning and may show high elastic propertiesevidenced by normal stresses appearance. In order to study the mechanismsat the interface level, we develop simple model experimentationswith the goal of quantifying the influence of viscoelastic propertieson fluid displacement in a simple geometry. For this purpose, wepropose and characterize a model fluid formulation, for which elasticand viscous effects can be tuned systematically. We study then thedisplacement of a viscous oil by a Newtonian non elastic, a viscoelasticor a purely shear thinning fluid in a two dimensional flow cell.Observing the shape of the interface between aqueous fluids and displacedoil permits to appreciate viscoelasticity effects on the displacement.Using model geometries and controlled rheology fluids, we show thatviscoelastic fluids tend to better displace immiscible liquids thanNewtonian fluids and that those effects are closely related to theapparitions of normal stresses independently of shear thinning propertyor variation of interfacial tension as soon as viscous effects governthe flow.