Self-adaptive W/O emulsion for reservoir water control: In-situ formation of high internal phase emulsion from ordinary emulsion synergistically stabilized by two surfactants of polyglycerol esters

Abstract

In many industrial applications, stable high internal phase emulsions (HIPEs) are of great value for stable dispersion and effective delivery of internal phase substances. For example, in recent years, W/O HIPEs have emerged as one of the most promising soft materials for water control in horizontal wells for enhanced oil recovery (EOR), owing to their high viscosity and the Jamin effect. However, the formation of stable W/O HIPEs under low surfactant concentrations and low-energy emulsification conditions remains a challenge. In this study, a feasible strategy is proposed to address the above technical challenges. Under mild stirring (500 rpm) condition, the paraffin oil containing 3 % (w/w) of a emulsifier blend of polyglyceryl-3-dioleate (POOC) and polyglycerol polyricinoleate (PGPR) efficiently emulsifies water to form a stable and uniformly dispersed W/O emulsion. The emulsion viscosity can be continuously tuned from low to high by varying the water-to-oil volume ratio from 1:1 to 9:1. The finally formed W/O HIPEs exhibit high viscosity (1829  mPa·s), strong viscoelasticity (tan δ = 0.19), and excellent coalescence stability (no phase separation over 30 days) at 60 °C, making them suitable for water control in EOR application. The key role of POOC + PGPR composite surfactant in the formation and stabilization of emulsions was elucidated using diffusion-ordered ¹H NMR (DOSY) spectrogram and molecular dynamics simulations.