Silica Nanoparticles Suspension for Enhanced Oil Recovery: Stability Behavior and Flow Visualization
Authors: Li Shidong , Hadia Nanji J , Lau Hon Chung , Torsæter Ole , Stubbs Ludger P , Ng Qi Hua 
Published: April 2018

Abstract
Oil and gas industry is witnessing a rapid increase of interest in application of nanotechnology. Since last few years, nanotechnology is being studied as an alternative enhanced oil recovery (EOR) method and laboratory experiments have shown its potential. However, the adsorption behavior of nanoparticles in porous media and underlying mechanisms for improving oil recovery are still not well understood. The objective of this study was to investigate silica nanoparticles adsorption and displacement mechanisms at the pore scale within a micromodel. Another objective was to stabilize silica nanoparticles in the presence of crude oil at a high salinity and a high temperature for a longer period of time.
A turbidity scanner was utilized to test stability of silica nanoparticles suspension in the presence of crude oil under 60°C. Turbidity stability index was used to evaluate stability of nanoparticles suspension and hydrochloric acid (HCl) was used as stabilizer to improved stability of nanoparticles suspension. The interfacial tensions (IFT) and contact angle between crude oil and the nanoparticles suspension with stabilizer were also measured. Both single-phase and two-phase flooding experiments were conducted for nanoparticles with and without stabilizer by using glass micromodels to visualize the nanoparticles adsorption and displacement behavior at the pore scale. Oil recovery was determined with image analysis to evaluate the potential of these nanoparticles for EOR applications. In addition, microscope images were taken and analyzed to investigate EOR mechanisms of nanoparticles suspension.
Results of turbidity scanner showed nanoparticles behavior changed from aggregation to sedimentation. Silica nanoparticles suspension with HCl showed much better stability than the one without HCl under 3.8 wt. % synthetic sea water and 60°C condition. Wettability alteration between crude oil and water were observed with silica nanoparticles. For single-phase visualization flooding experiments, nanoparticles suspension with a stabilizer had less adsorption than the one without a stabilizer, and it could flow through micromodel without significant plugging. Nanoparticles adsorption can alter wettability of the micromodel to more water-wet. For two-phase visualization flooding experiments, injection of silica nanoparticles suspension with a stabilizer had better EOR result under high flow rate and can increase oil recovery about 3%. Wettability alteration and emulsification were proposed as main EOR mechanisms for nanoparticles.
Silica nanoparticles stability behavior in the presence of crude oil under a high salinity and a high temperature was studied and the stability of nanoparticles suspension was quantified by using turbiscan stability index. Adding HCl as a stabilizer can reduce adsorption of nanoparticles in micromodel and avoid plugging. Enhanced oil recovery mechanisms of nanoparticles were investigated by using visualization micromodel flooding for better understanding of nanoparticles flooding.