Abstract
In this study, we have investigated the effects of brine and biosurfactant compositions on crude-oil-rock-brine interactions, interfacial tension, zeta potential, and oil recovery. The results of this study show that reduced brine salinity does not cause significant change in IFT. However, addition of biosurfactants to both high and low salinity brines resulted in IFT reduction. Also, experimental results suggest that the zeta potential of high salinity formation brine-rock interface is positive, but oil-brine interface was found to be negatively charged for all solutions used in the study. When controlled salinity brine (CSB) with low salinity and CSB with biosurfactants were injected, both the oil-brine and rock-brine interfaces become negatively charged resulting in increased water-wetness and, hence, improved oil recovery. Addition of biosurfactants to CSB further increased electric double layer expansion which invariably resulted in increased electrostatic repulsion between rock-brine and oil-brine interfaces, but the corresponding incremental oil recovery was small compared with injection of low salinity brine alone. Moreover, we found that the effective zeta potential of crude oil-brine-rock systems is correlated with IFT. The results of this study are relevant to enhanced oil recovery in which controlled salinity waterflooding can be combined with injection of biosurfactants to improve oil recovery.
Highlights
The crude-oil-rock-brine (CORB) system is a complex system that involves fluid-fluid and rock-fluid interactions and the properties of each component are fundamental to the mechanisms involved in the system
The observed change in oil may be associated with rock-fluid interaction and the improved oil recovery observed with controlled salinity brine (CSB) cannot be attributed to interfacial tension (IFT) reduction
When crude oil is present in the system alongside the formation brine the effective zeta potential becomes less positive, suggesting that crude oil-FMB interface is negatively charged
Summary
The crude-oil-rock-brine (CORB) system is a complex system that involves fluid-fluid and rock-fluid interactions and the properties of each component are fundamental to the mechanisms involved in the system. The interfacial phenomenon at the rock-fluid interface is controlled by electric double layer (EDL) effects and understanding of interactions between ions and rock surface is fundamental [2]. Reservoir fluids such as crude oil, formation brine, injection brine, and enhanced oil recovery (EOR) fluids such as surfactants are comprised of ions or polar components in one form or another. These components can have chemical interactions with the bulk solution or the rock surface. The net charge at the oil-brine and rock-brine interfaces influences the stability of water film between oil and rock surfaces based on Deryaguin-Landua-Verwey-Overbeek (DLVO) theory [6, International Journal of Geophysics
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