Rheological investigation of clay-stabilized oil-in-water Pickering emulsions for potential reservoir applications

Abstract

Particle-stabilized Pickering emulsions are attracting increasing interest in oil and gas industries due to their unique rheological properties and stability. In this work, the rheological behavior of Na-montmorillonite stabilized oil-in-water (O/W) Pickering emulsions was studied under various salinities, pHs, clay concentrations and oil volume fractions. Results suggested that the Na-montmorillonite particles form a three dimensional network in water by different particle-particle interactions under specific salinity and pH values. The emulsion rheology can be explained by such clay interactions. The clay stabilized emulsion exhibits shear thinning behavior. At moderate salinities (around 0.25–5 wt% NaCl), the emulsion possesses a high viscosity of up to 100 mPa s at a shear rate of 7 s−1. Evidence suggests that a strong three dimensional clay network which connects the oil droplets is formed. The clay-droplet network possesses enough strength to withstand significant shear force, giving the emulsion a high bulk viscosity. Both too low and too high a salinity is unfavorable for maintaining a high emulsion viscosity. The gradual breakdown of the clay network with increasing shear rate accounts for the shear thinning behavior of the emulsion. The emulsion viscosity decreases with increasing pH as the clay-droplet network is more likely to form in an acidic environment. A two dimensional diagram summarizing the impact of salinity and pH on emulsion viscosity was generated. Emulsion viscosity also increases with clay concentration, but not always increases with oil volume fraction at a fixed clay concentration. The clay-stabilized emulsion shows significant elastic behavior. The clay network formed under a range of salinities and pHs is resilient to breakdown and has the ability to reform during strain, thus giving the emulsion a high elastic modulus. Our work shows that a clay-stabilized O/W emulsion system can possess high viscosity, shear thinning rheology and elasticity at high salinities and different pH of 3.3, 4.7, 6, 8, 9.5 and 11. These properties make the emulsion a potential candidate for various reservoir applications.