The formation and flow of emulsions during alkaline flooding process plays an important role for improving heavy oil recovery. In this study alkaline/surfactant (A/S) flood tests were performed in sandpacks to demonstrate the effectiveness of sweep efficiency improvement by the in-situ generated O/W emulsion. High tertiary oil recoveries were obtained in all the sandpack flood tests. Experimental results were history matched by including the mechanisms of in-situ generation and flow of O/W emulsion, as well as the chemical adsorption and the reduction of interfacial tension involved in the chemical flooding process. The decrease in local water phase permeability caused by the entrapment of emulsion droplets was modeled using the filtration theory. Both the pressure response and the oil recovery improvement were fairly matched. Field scale simulations were conducted to investigate the potential of A/S flooding for heavy oil reservoirs. Simulations showed promising results of chemical flooding for heavy oils. It was indicated that certain length of waterflooding time would benefit for the final oil recovery, and there existed an optimum chemical slug size. These laboratory results and the simulation technique are helpful in the simulation and design of field scale projects of chemical flooding for enhanced heavy oil recovery.
Both field and laboratory studies showed that caustic flood could effectively improve oil recovery for moderately viscous oils. Johnson[1] summarized four main mechanisms of oil recovery improvement by alkaline flooding: dispersion and entrainment, wettability reversal from oil-wet to water-wet, or vice versa, and emulsification and entrapment. In the case of heavy oils, the emulsification and entrapment during alkaline flooding has been recognized as the dominant mechanism [2 -4], which can efficiently improve sweep efficiency. Jennings et al.[2] demonstrated this mechanism through extensive experimental studies. Visual experiments clearly showed that the areal sweep efficiency was improved by the in-situ generated emulsions, and the oil recovery at breakthrough was doubled compared to that obtained in the waterflooding test. Core flooding tests demonstrated the increase in oil recovery and the decrease in the instantaneous water oil ratio (WOR). The mechanism was summarized as: a drastic reduction of oil/water interfacial tension (below about 0.01 mN/m) by the caustic activation of potentially surface-active organic acids in the crude oil, in-situ production of the O/W emulsions that tends to lower the mobility of the injected water and damp viscous fingering, and the diversion of the flow of injected water to give improved sweep efficiency.
Dong et al.[5 -6] reported comprehensive studies of the alkaline/surfactant (A/S) flood potential for three West Canadian heavy oils. Extensive emulsification tests, IFT measurements, micromodel experiments and sandpack flood tests were conducted. Their results showed that the IFT could be reduced to be lower than 0.01 mN/m by an alkaline solution and a very dilute concentration of surfactant, leading to easy emulsification of heavy oil in formation brine under slight interfacial disturbance. Tertiary oil recovery in sandpack flood tests reached more than 20% OOIP. Liu et al.[7] studied the synergy of alkali and surfactant in emulsifying a heavy oil in brine.
