The effect of inorganic solids on emulsion layer growth in asphaltene‐stabilized water‐in‐oil emulsions

Abstract

Oilfield emulsions are often stabilized by asphaltenes but inorganic solids can impact both emulsion stability and rag layer accumulation. In this study, the effect of inorganic solids on emulsion stability and emulsion layer growth was investigated using batch and continuous separations performed on water‐in‐oil emulsions stabilized by asphaltenes. The emulsions were prepared at 60 °C from an organic phase consisting of solids, asphaltenes, n‐heptane, and toluene and an initial water phase volume of 0.50. Three types of coarse solids were considered: 12 μm kaolin, 18–32 μm silica, and 32–63 μm silica with wettabilities ranging from 50 to 125°. In batch experiments, the coalescence rate was determined from the change in height of the free water and oil layers over time as the emulsion coalesced. In continuous experiments, emulsion layer growth was measured as the emulsion was continuously fed into a vertical separator. The data were modelled with a material balance that included a coalescence rate equation. In the absence of solids, the continuous emulsion layer growth rate and ultimate stability correlated well to batch coalescence parameters. The addition of the coarse solids at concentrations below 5 g/L accelerated coalescence rates. Above 5 g/L, the solids increased emulsion stability indicating that they form a steric barrier between the droplets. Even if the feed is below this threshold, the solids accumulate in the rag layer until the threshold is reached, the emulsion becomes stable, and the performance of the continuous separation can no longer be predicted from batch tests.