Experimental Study of Mobility Control by Clay-Stabilized Pickering Emulsions in High-Salinity Reservoirs

Abstract

Abstract In waterflooding, achieving adequate mobility control in high-salinity reservoirs is a key challenge because polymers, the traditional mobility control agents, have poor solubility at high salinities. The objective of this work is to find an inexpensive and environmentally friendly mobility control formulation using a clay-stabilized Pickering emulsion and test its performance for waterflooding at high salinity conditions. Pickering emulsion is an emulsion that is stabilized by solid particles. Decane-in-water Pickering emulsions stabilized with clay particles (sodium montmorillonite) in NaCl brines at high salinity were prepared using a sonicator. The emulsion droplet coalescence stability was analyzed by measuring the droplet size distribution of the emulsion over time by light scattering, and creaming stability was evaluated by emulsion height visualization. A fluorescent dye was added into the clay suspension to characterize the structure of the emulsion by fluorescence imaging. The arrangement of clay particles on the oil-water interface was examined by Cyro-SEM, wherein the emulsion sample was frozen before being placed in the SEM chamber. The rheological properties of clay-stabilized Pickering emulsion under high-salinity conditions were measured with a rheometer. Flooding experiments with clay-stabilized emulsion were conducted in both a microfluidic and a sandpack apparatus to test mobility control performance of Pickering emulsions. Results show that clay particles have the ability to stabilize Pickering emulsions, which exhibit good coalescence stability at high salinities. Clay particles adsorb at the oil-water interface, thus preventing the droplets from coalescing for at least several months. Fluorescent and cryo-SEM images revealed a 3D spherical structure of emulsion droplets with clay particles arranged perpendicular to the oil-water interface. The bulk viscosity of stable emulsion with 5 vol. % oil fraction is around 100 mPa.s at a shear rate of 7 s-1. Microfluidic experiments showed that the injection of Pickering emulsion provides adequate mobility control, as evidenced by significant recovery of residual oil after waterflooding. After Pickering emulsion flooding, oil recovery factor increased from 67% (water flooding) to more than 80%. Enhanced oil recovery (EOR) mechanisms of Pickering emulsion flooding are also studied by using a microfluidic chip showing some novel and interesting phenomena. In sandpack with higher permeability, emulsion injection mobilized more than 10% residual oil after water flooding. This is the first time research on using clay-stabilized Pickering emulsion for mobility control under high-salinity conditions is reported. Results reveal that clay-stabilized Pickering emulsions exhibit good coalescence stability and promising potential for EOR at high salinity conditions. Since clay particles are naturally-occurring, they may also be an economical and environmentally friendly alternative to polymer for mobility control in a high salinity reservoir.