(445c) Interfacial Behavior of Surfactant-Stabilized Carbon Nanotubes in Oil-Water System

Chemical flooding with a surfactant aqueous solution is a technique used to recover oil after primary production in a reservoir is completed. The surfactant molecules modify the interfacial tension at the oil-water interface and mobilize the trapped oil. A major challenge in applying this enhanced oil recovery (EOR) technique is that a lot of the injected surfactant tends to adsorb on the reservoir surface, and cannot reach the trapped oil. While several approaches to get around this problem have been proposed, there is plenty of room for innovation and improvements. A potential solution is to provide the surfactants with an alternative surface to adsorb, for example to let the surfactants adsorb on the surface of hydrophobic nanoparticles, such as carbon nanotubes (CNT), before injecting them into the oil reservoir. The CNTs introduce hydrophobic surfaces for adsorption of the surfactants’ tails, meaning only the heads of surfactants are available for contact with the aqueous solution [1,2]. The nanoparticle can propagate through the porous medium and reach the oil-water interface, while the loss of surfactants is minimized because the hydrophilic heads of surfactants only adsorb weakly onto the rock’s surface. The surface of the surfactant-grafted CNT behaves as hydrophilic, and the CNTs stay in suspension. The CNTs are stabilized by either electrostatic repulsion from the heads of adsorbed ionic-surfactants or steric repulsion by nonionic surfactants [3]. Thus, the surfactant-particle systems are expected to travel to favored positions with minimal loss. In this study, we focus on the behavior of the surfactant-CNT systems in oil-water interface by using mesoscale dissipative particle dynamics (DPD) simulations. The surfactant used is sodium dodecyl sulfate (SDS) that is allowed to adsorb on CNTs in water. Then, the surfactant-CNT systems are inserted to the interface of oil (represented by decane) and water. The DPD model interaction parameters for SDS-CNT, water-CNT and water-DSD have been obtained previously.[4,5] The decane-water and decane CNT interactin parameters are obtained with validation of the simulation results with the interfacial tension of decane over water. It appears that SDS adsorbs stably on the CNT surface to form ad-micelles in water. When arriving at the oil-water environment, the surfactant molecules release completely from the CNT and distribute on the interface of oil-water. This result demonstrates that CNTs can be good candidates to deliver surfactant to trapped oil in EOR processes. In this presentation, we will discuss the DPD methodology and the effects of the surfactants and the nanotubes on the interfactial tension and on the mobility of the oil.

ACKNOWLEDGEMENTS

The computational support of XSEDE (CTS090017) is gratefully acknowledged.

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