Crude oil-water interface partitioning of polyvinylpyrrolidone-coated silica nanoparticles in low-salinity brine

Highlights

• Fabricated composite nanoparticles are well-dispersed in low-salinity brine.

• Nanoparticle adsorption was initially diffusion limited.

• Low-salinity brine enhanced particle diffusion due to surface charge screening.

• Weakened electrostatic force attributes to greater interfacial coverage.

Abstract

Nanoparticles are of interest in recent oil production process due to their potential to wettability alteration, but not interfacially active at the crude oil-water interface. Stability loss in brine environment, where nanoparticles tend to aggregate, is another issue for field implementation. Hence, recent challenge is to functionalize nanoparticles that are interfacially active and still stabilized in brine. The current study fabricated and characterized the polyvinylpyrrolidone-coated silica composite nanoparticles for their interfacial activity at the crude oil-water interface. Reduction in oil-water interfacial tension was observed and more dramatic with increasing particle concentration, confirming particle adsorption performance. In low-salinity brine (2000 ppm NaCl), the composite particles remained stabilized with weakened electrostatic force between particle and crude oil surfaces, while their size was smaller due to polymer shell dehydration. These led to faster diffusion rate than in Milli-Q water, which affected the rate of change in oil-water/brine interfacial tension, with the early-stage adsorption being a diffusion-controlled in both fluids. At equivalent particle concentration, the oil-water interfacial tensions in brine were lower than those of Milli-Q water (by ∼2 mN/m), with interfacial coverage of the particles at the interface was found to be higher in the brine. Such difference is attributed to a weaker repulsive force between particle and the interface, induced by surface charge screening that is only present in brine. The study has demonstrated the potential use of polymer-coated nanoparticles as suitable additives for use in oil recovery, which can be used concurrently with low-salinity brine as a combined fluid. While both chemicals are known to construct disjoining pressure for wettability alteration, advantage of using interfacially active nanoparticles is additional mechanism to enhance oil recovery, i.e. reducing the oil-water interfacial tension, which unfunctionalized particles could not contribute.

Introduction

Chemical enhanced oil recovery (EOR) is increasingly used to extract oil from conventional and unconventional reservoirs (Hou et al., 2016; Sheng, 2015; Raffa et al., 2016; Tangparitkul et al., 2018). Improvements to oil extraction can only be made by understanding the interfacial phenomena that governs oil displacement. Chemical additives (typically surfactants) are injected to improve oil displacement by lowering the oil-water interfacial tension, changing the rock wettability, and improving oil liberation from the reservoir rock (Tangparitkul et al., 2018; Tangparitkul, 2018; He et al., 2015; Young, 1805). While surfactants are typically considered, there are drawbacks to their use including: surfactant retention in non-targeted zones; poor conformance control; and being reversible when diluted with chasing water (Kamal et al., 2017; Sukee et al., 2022; Divandari et al., 2021).

In recent years, nanoparticles have been considered as an alternative additive for EOR, especially because of the potential to improve squeeze performance and oil liberation, with the latter achieved via a disjoining pressure induced by accumulating particles (Suleimanov et al., 2011; Zhang et al., 2014; Onyekonwu and Ogolo, 2010; Sun et al., 2020). Nanoparticles can also partition at an oil-water interface, although due to an absence of amphiphilicity, this partitioning strongly depends on the wetting angle (ShamsiJazeyi et al., 2014; Binks and Lumsdon, 2000; Hodges and Tangparitkul, 2019). The particle detachment energy from an interface (i.e. ease of particle removal from a liquid-liquid interface) is succinctly described by, $\Delta E=-{\sigma }_p\pi r^2{\left(1\pm \cos \theta \right)}^2$, where ${\sigma }_p$ is the oil-water interfacial tension (without particles), $r$ the hydrodynamic radius of nanoparticle, and $\theta$ being the three-phase contact angle (Binks, 2002). For Brownian-particles, increasing $r$ and $\theta$ to 90° maximizes the detachment energy, thus particles could be considered irreversibly adsorbed, unlike surfactant molecules that reversibly exchange between the interface and bulk.

The preparation of nanoparticles combined with polymers (composite particles) has gained interest for their improved stability in harsh processing environments (Metin et al., 2011; El-Diasty and Aly, 2015; Hendraningrat and Torsæter, 2016; French et al., 2020), and also the increased interfacial activity. Often the nanoparticles are oxide-based materials and are thus inherently strongly water wetting, hence the interfacial activity and retention at an oil-water interface is poor. The hydrophobicity of polymers promotes reduced water wetting and increases the apparent contact angle of the particle for better retention at an oil-water interface. Table 1 summarizes previous studies that have considered nanoparticles at the oil-water interface for EOR application. Those nanoparticles were functionalized by various methods to improve their interfacial activity, e.g. hydrophobically modifying the surface or fabricating composite core-shell particles. However, many of the modification routes require complex synthesis steps which limits their potential use in the field. To be more feasible, facile, one-pot synthesis routes should be considered.

Yu et al. (2017) recently fabricated polymer-coated nanoparticles of polyvinylpyrrolidone (PVP) polymer and silica nanoparticles by a simple one-step adsorption method. The composite particles were found to be stable in divalent salts and strongly partitioned at air-water interfaces (Yu et al., 2018a; Yu et al., 2020; Yu et al., 2021). In the current study, the favorable interfacial properties were explored for application with crude-oil water/brine systems. With low-salinity brines known to improve oil droplet dewetting from hydrophilic/hydrophobic substrates, and our previous research having determined an optimal brine concentration of $\sim$2000 ppm NaCl (Tangparitkul et al., 2021), the current study seeks to understand the stability and interfacial activity of the composite particles in both Milli-Q water and brine of 2000 ppm NaCl. Interfacial coverages of the composite nanoparticles at the oil-water/brine interface and nanoparticle-interface interactions were also analyzed to emphasize the interfacial behavior of the composite nanoparticles in the current water/brine system.