Selection of Nanomaterials as Emulsion Stabilizers in Alkali-Polymer EOR of High-TAN Number Oil
Authors: Neubauer Elisabeth , Hincapie Rafael E. , Clemens Torsten , Cornelius Maximilian 
Published: August 2020

Abstract
The potential application of surface modified silica nanomaterials to boost the stability of oil in water emulsions created by alkali-polymer flooding has been investigated. Long-term phase behavior experiments and interfacial tension measurements are performed. We evaluate the effects of particle size and surface modification, as well the influence of the alkali type and concentration on the emulsion stability. The workflow helps understanding the fluid-fluid interactions and facilitates the selection of materials for further core-flood evaluations.
Three types of nanomaterials allowed investigating the effect of particle size (60 and 100 nm) and two different surface modifications, which differ slightly in hydrophilicity and zeta-potential. Phase-experiments were performed at 1:1 water/oil ratio using a high TAN crude-oil. Emulsion volume was recorded over 100 days and aqueous-phase composition was varied to study the effect of alkali concentration (1000−15000 ppm), particle type/concentration (0.05−5 wt.%), alkali (Na2CO3 versus K2CO3), and polymer (0 and 2000 ppm). Overall, ∼100 different combinations with triplicates were tested. IFT experiments were performed using a spinning-drop tensiometer, and results were compared at 300 min of observation.
Phase experiments revealed that surface modified nanomaterials have the ability to stabilize oil-in-water emulsions that were formed due to reaction of alkaline brine with crude-oil, supported by a low IFT in the alkali/particle system. Combination of 0.1 wt% silica particles and 3000ppm alkali produces very-long lived emulsions and outperforms the control experiments by a factor of four in terms of emulsion volume (at 100 days). The type of surface modification of the nanomaterial had a negligible effect on the volume of the stabilized emulsion. However, density and viscosity of the emulsion were influenced, which will affect fluid flow in the reservoir.
A synergistic effect of smaller size (higher effective concentration of particles) and more neutral surface charge of the modified particles resulted in emulsification of crude-oil with silica particles alone, which did not occur for the samples with larger particle size and lower zeta potential. Too high concentrations of alkali and particles resulted in destabilization of the emulsions, which may be due to charge reversal of particles and exceedance of the critical coagulation concentration. Since the viscosity of an emulsion is larger than that of the continuous phase, polymer could be required to flood the emulsion out of the reservoir. In our experiments, the addition of polymer reduced emulsion stability in the alkali-only experiments, but adding nanomaterial boosted the emulsion stability. Nano-EOR is an embryonic technology and to the best knowledge of the authors, literature data is scarce on how nanomaterials emulsify crude-oil, since most studies have been done with simple hydrocarbons such as decane. The majority of the existing literature addresses the stabilizing effect of nanoparticles on emulsions created due to the mixing of surfactants with hydrocarbons, whereas in this study we use alkali as an economically more attractive saponifying agent.