High water content (>50%) water-in-oil (W/O) emulsions have been suggested as a drive fluid for recovery of heavy oil in high permeability reservoirs. High emulsion viscosity can provide sufficient mobility control and its oil-external nature enables a semi-miscible process while displacing crude oil. Initially crude oil itself was suggested as base oil for generating this type of emulsion, and both laboratory experiments and field pilot have demonstrated its high efficiency in recovering heavy crude. Recently used engine oil was suggested as a candidate for generating W/O emulsions for the same purpose, because of its better stability and more favorable viscosity.
In this work a stable emulsion was generated by mixing used engine oil (40%) and brine (60%) under high shear. Then this emulsion was injected into sandstone cores (400 ~ 2400 md, 0.5 or 1 ft in length) at several different rates for periods of several days, to characterize its stability and flow properties while passing through porous media. Small amounts of water breakout were observed in the emulsion effluents. Higher values of water breakout were observed in lower permeability rock, at higher injection rate, and with longer core lengths. The the emulsion was also injected into sand-packed slimtubes (~8000 md) of 3-ft and 6-ft lengths, and less than 1% of free water was observed from the effluents at moderate injection rates, verifying good stability of this emulsion passing through high-permeability porous media. Pressure drops were found to be quite stable at any constant rate of injection for all corefloods, indicating no plug-off effect from the soot particles in the emulsion.
Numerical simulations on emulsion flooding a homogeneous heavy oil reservoir were also conducted by simulating the emulsion as single-phase oil, and the breakdown of emulsion as a co-injection of water together with this oil. Results indicated significant improvement of displacement pattern and oil recovery compared to water flooding.