ENCAPSULATION OF SURFACTANTS INTO SILICA NANOSIZED PARTICLES: MECHANISIM OF CONTROLLED RELEASE, LIQUID-SOLID AND LIQUID-LIQUID INTERACTIONS FOR ENHANCED OIL RECOVERY APPLICATIONS

Abstract

Removal or recovery of oil, which is either attached to a solid surface or as an emulsion in water is an ongoing challenge. Its removal and recovery could be challenging due to the strong interactions of the polar groups of oil to the charged solid surfaces. Moreover, large surface tension forces result in low mobility of the oil emulsions. To that end, surfactants could be utilized to mobilize oil. However, excess of surfactant molecules could hinder their effectiveness due to the formation of micelles or bilayers. Additionally, adsorption of surfactant molecules to the rock-solid surfaces leads to having surfactant unnecessarily wasted and results in higher costs. In this thesis, a new controlled surfactant delivery system via encapsulation of cationic and anionic surfactants into mesoporous silica nanoparticles will be described. Encapsulation of the cationic surfactant resulted in hexagonal mesoporous particles of around 50 nm in diameter. The anionic surfactant encapsulation resulted in hollow-spherical like nanoparticles. The responsive and controlled release of the surfactant molecules from the mesoporous particles was studied in simulated high salinity and high temperature conditions that are normally encountered in subsurface environment. The surfactant molecules were released from the nanosized porous particles in response to the ions present in solution and high temperature (conditions typically encountered in a reservoir). The ability of the suspension in mobilizing oil attached to a solid surface was studied via sessile drop contact angle measurements. We concluded that the release of the surfactants transforms an oil-wet surface to water-wet due to the favorable partitioning of the surfactants at the interface. Moreover, the improved interfacial properties of the nanoparticles were assessed by dynamic interfacial tension at the oil-water interface. The performance of the new system resulted in decreasing the interfacial tension up to three orders of magnitude. This reduction outweighs the performance of the bare surfactant or neat nanoparticles.