Water Ion Interactions at Crude Oil-water Interface - Is there a Correlation between IFT and Interfacial Rheology?

Abstract

SmartWater flooding (SWF) through the injection of optimized chemistry waters is getting good attention in recent years for improved oil recovery (IOR) and enhanced oil recovery (EOR) in carbonate reservoirs. Consequently, much of the research conducted so far in this emerging area has been limited to studying salinity and water ion interactions at carbonate rock-crude oil-water interfaces. Favorable wettability alteration has been seen to play a major role on oil recovery based on measurements such as contact angle and zeta potential; however, the other important aspect of characterizing water ion interactions at crude oil-water interface has received little attention. In this study we performed interfacial shear rheology measurements to study water ion interactions at crude oil-water interface and compared these results with the previously reported IFT data. The major objectives are to determine the impact of different water ions on the viscoelastic properties of crude oil-water interface as well as to explore the correlation between IFT and interfacial rheology. Several low salinity SmartWater recipes with varying individual ion compositions were used in these experiments. The data indicated noticeably higher IFT values for SmartWater recipes containing sulfate ions, while IFT was the lowest for SmartWater composed of magnesium ions. In contrast, SmartWater with only sodium or calcium ions displayed almost similar IFT values. Interfacial shear rheology results showed significantly higher viscous and elastic modulus for SmartWater recipes comprising of sulfate ions. The SmartWater recipes with sodium-only, calcium-only or magnesium-only ions showed comparable interfacial rheology. The transition times for the interface to become elastic-dominant from a viscous-dominant regime are found to be the lowest for sulfates-only brine followed by the sodium-only and calcium-only brines, and the highest being with magnesium-only brine. The much quicker transition times to elastic regime observed with sulfates-only brine indicates rigid skin at the interface that could potentially delay the destabilization of the interfacial film and hinder the coalescence between oil droplets. The longer transition times to elastic regime observed with magnesium-only brine shows the presence of less rigid films at the interface to promote the coalescence between oil droplets. A good correlation between IFT and the interfacial film transition times from viscous to elastic-dominant region was observed for all the brines, which confirms that similar sensitivity of water ions is reflected in both the parameters. These novel findings on the microscopic scale interactions of different water ions at crude oil-water interface pointed out the importance of magnesium and calcium ions in the SmartWater to enhance the coalescence between released oil droplets to quickly form oil bank in the reservoir for faster recovery.