Auto-Emulsification of Water at the Crude Oil/Water Interface: A Mechanism Driven by Osmotic Gradient

Abstract

This work aims at studying the origin of spontaneous emulsification occurring at the oil/water interface. This phenomenon was observed for the five crude oils tested as well as at the interface of an asphaltene toluene mixture and water. The kinetics of appearance of water micro-droplets was slowed down for increasing salt concentrations and the micro-droplet formation ceases when the chemical potential of water they contain is equal to the one of the water in the bulk solution. Nucleation events occur at the oil-water interface and at the solid surface/liquid interface: some water microdroplets are stuck together close to the oil/water interface, others grow in oil and sediment or nucleate at the oil/solid surface. This suggests the following mechanism: water molecules diffuse from the water reservoir into the oil phase, and then create droplets. These droplets are simultaneously fed by hydrosoluble "osmogeneous" species increasing the osmotic pressure, inducing an osmotic pumping of water molecules into micro-droplets WATER OIL

Evaluating physicochemical properties of crude oil as indicators of low-salinity–induced wettability alteration in carbonate minerals

“…The general trend agrees with the widely accepted premise that precipitated asphaltene can stabilize water-in-oil dispersion, probably due to the formation of an asphaltene rigid layer at the oil/water interface and its ability to provide electrostatic and steric repulsion for a repulsive disjoining pressure [62][63][64][65] . Duboue et al 49 . have found de-asphaltenated crude oil to have less microdispersion compared to the original crude oil, even though microdispersion still exists for the de-asphaltenated oil.…”

“…Some researchers relate the formation of microdispersion to the spontaneous emulsification process because ultra-low IFT or mechanical agitation is not required for this process [44][45][46][47][48][49] . Several mechanisms, including interfacial turbulence and diffusion, have been proposed to explain the spontaneous emulsification in high IFT systems (a few mN/m) 46,49 . To be consistent with the recent literature, we continue to describe such phenomena as microdispersion but examine their nature under cryo-TEM in this section.…”

Relevance of zeta potential as a tool for predicting the response of controlled salinity waterflooding in oil–water-carbonate systems

“…Irrespective of the chosen method to determine zeta potential, it is still unclear if it provides an accurate representation of the oil/water interface of interest during oil recovery. First, the stability of the interface is questionable as it may evolve during recovery, especially with the formation of water micro-droplets [21][22][23][24]. Hence, measurement of oil/water zeta potential may only represent a (a) (b) snapshot of the interface, not representative of the entire recovery process.…”

“…Also, it is unclear if the initial stabilization of the water film on rock surface is mainly related to electrostatic repulsion rather than to the presence of water micro-dispersion. Indeed, the spontaneous emulsification and growth of water-in-oil micro-droplets governed by osmotic effects occur more rapidly as the salinity is decreased [21,70,71]. The presence of solid/liquid surface in the vicinity of these structures can result in the formation of dewetting patterns on the solid surface, and their possible coalescence can be responsible of the formation of a continuous water film [68].…”

“…However, modification of many parameters can result in wettability alteration, and the most common suggested mechanisms are mineral dissolution, surface charge alteration by multi-ionic exchange, or double layer expansion [15][16][17][18][19][20]. In recent years, many studies have highlighted the importance of the oil/water interactions in impacting the LSE, especially with the spontaneous formation of water-in-oil micro-droplets [21][22][23][24], and thus on the importance of oil/water interface in the mechanism of additional recovery [25,26]. Hence, both rock/water and oil/water interactions are important to understand LSE.…”