Formation and stability of W/O emulsions in presence of asphaltene at reservoir thermodynamic conditions

In-situ formation of W/O (water-in-oil) emulsion in oil reservoirs is gaining increased attention particularly for EOR purposes. In this process, asphaltic components may serve as a stabilizer for W/O emulsions, which may result in higher viscosity of injected fluid front causing improved oil recovery. In this study, the effect of temperature and pressure on the formation and stability of W/O emulsions were evaluated by a high pressure-high temperature (HP-HT) test apparatus in order to simulate as close as possible to reservoir conditions. The experimental results showed that the stability of the emulsions reduced as temperature increased from 25 to 110 degrees C. The relationship between pressure and the emulsion stability, on the other hand, is more complicated where an increase in emulsion stability was shown with pressure when it reaches a plateau at 27579.0 kPa (4000 psia) with a decrease afterwards. Based on the experimental results, different mechanisms dominate in each pressure interval. In the first pressure interval (3447.4 to 27,579.0 kPa) the break-up of the dispersed phase droplets caused by the exerted shear energy, which makes the dispersed phase droplets smaller in size, where W/O surface coverage of the asphaltene was important. In the second interval pressure (27,579.0 to 41,368.5 kPa), the reduction of emulsifier (asphaltene) due to the increased pressure in the dead oil showed a much lower stable emulsion. Thus, at pressures below 27,579.0 kPa with increased pressure, the mechanism of increased shear energy prevailed. For the pressure interval of 27,579.0 to 41,368.5 kPa though, as pressure increased, asphaltene precipitation decreased at the water/oil interface. (C) 2019 Elsevier B.V. All rights reserved.