(355b) Crude Oil – Water Interfacial Viscoelasticity in Waterflooding Performance

Waterflooding with optimized water chemistry in Enhanced Oil Recovery (EOR) has gained much interest in the last few years. Specifically, the use of low salinity brines and small amounts of surface active chemicals can improve oil recovery in waterflooding processes. Mechanisms by which these processes take place are uncertain. The focus has been on fluid-rock interactions. Not much attention has been paid to the molecular structure of the fluid-fluid interface. Crude oil-water interfaces can have a viscoelastic character affected by the adsorption of organic compounds. The brine concentration as well as surfactants may also strongly affect the fluid-fluid interfacial viscoelasticity.

In this work we present a systematic analysis of the interfacial viscoelasticity of two different oils in terms of brine concentration and a nonionic surfactant. We correlate these measurements with oil recovery in a glass etched “porous media” microfluidic device. Viscoelastic measurements are made using a shear rheometer with a DuNouy ring and constant small strain amplitude and frequency oscillations (0.5 rad/sec).

Interfacial viscoelasticity develops relatively fast in both oils, and in all cases, stabilizes at 48 hours. The interfaces are found to be at all times more elastic than viscous. The interfacial elastic storage (G') and viscous (G") moduli increase as the salt concentration decreases. A maximum in viscoelasticity is observed at 0.01% wt% of salt. Monovalent (Na⁺) and divalent (Mg²⁺) cations are used to investigate the effect of ion type; no difference is observed at low salinity. The introduction of a low amount of surfactant (100 ppm of DEM) increases the elasticity of the crude oil – water interface

Low salinity brines (0.01% salt wt%), where maximum of elasticity is observed, and high salinity brines (1.0% salt wt%) are used to displace oil in a glass etched “porous media” microfluidic device. Pressure fluctuations after breakthrough are observed in systems with high salt concentration while at low salt concentration there are no appreciable pressure fluctuations. Oil recovery increases by 5-10% with low salinity brines. By using a small amount of a nonionic surfactant with high salinity brine, oil recovery is enhanced 10% with no pressure fluctuations.

Increase in interfacial viscoelasticity can be explained in terms of electrostatic interactions formed by the double electrical layer at the water-oil interface. Elastic interfaces can sweep more efficiently the oil and reduce snap-off of oil droplets in the waterflooding. This study, along combined previous studies on solid-fluid interfaces may shed light on the mechanisms of waterflooding performance from brine chemistry.