Pickering emulsion stabilized by organoclay and intermediately hydrophobic nanosilica for high-temperature conditions

Abstract

Pickering emulsions show great promise for many applications in the oil and gas industry. However, the thermal stability of Pickering emulsions reported thus far has been unfavorable for safe operation in the always high-temperature deep underground condition. Here we report a Pickering water-in-oil (W/O) emulsion that exhibits high temperature tolerance in the absence of any surfactant due to the synergistic effect between organoclay and silica nanoparticles (NPs) with intermediate hydrophobicity. The interaction between silica NPs and organoclay was characterized by X-ray diffraction, thermogravimetric analysis, zeta potentials, scanning electron microscopy and transmission electron microscopy. The results of gel volume and water contact angle measurement confirmed the hydrophobicity of the organoclay. The effects of varying the hydrophobicity and concentration of the silica NPs, the clay concentration of the organoclay, and the thermal-rolling temperature on the emulsion stability, droplet size, morphology, and rheology were investigated in detail. The optimal synergy for stabilizing the W/O emulsion was found to occur with 1 wt% silica NPs exhibiting intermediate hydrophobicity and 1 wt% organoclay. As expected, neither hydrophobic nor hydrophilic silica NPs could improve the emulsion stability due to inefficient adsorption at the water-oil interface. Organoclay was found to have a significant influence on the stability and rheological properties of the W/O Pickering emulsion since it dominates the formation of networks in the continuous phase due to its excellent swelling and exfoliation. The adsorption of silica NPs further enhanced the interactions between the particles and the medium, making it possible for the retainment of rheology even after thermal rolling at 220 ℃. The increase in temperature tolerance achieved through a simple and environmentally friendly method makes this Pickering emulsion applicable in potential drilling fluids for the oil and gas field.