Journal of Canadian Petroleum Technology, Vol.37, No.7, 55-62, 1998
Evaluation of emulsified solvent flooding for heavy oil recovery
Efficient secondary and tertiary recovery of heavy oil from thin reservoirs, such as those in the Lloydminster area, remains an unsolved challenge to IOR researchers. The primary recovery from these heavy oil reservoirs is generally poor (often less than 5% of original oil in place) and waterflooding is rather inefficient due to very adverse mobility ratio which results in severe viscous fingering and early water breakthrough. Thermal methods are also not viable due to excessive heat losses to the underlying and overlying formations. Non-thermal techniques involving injection of a miscible solvent are uneconomical due to the high cost of solvent in relation to the market value of the heavy oil recovered. Therefore, there is a need for novel processes designed specifically for such reservoirs. This paper presents an experimental evaluation of the use of emulsified solvents to recover heavy oil from thin reservoirs. The emulsified solvent flooding can potentially provide the high recovery efficiency of miscible solvents at a fraction of the cost. The process, if successful, would have wide application in thin heavy oil reservoirs. Commercially available emulsifiers were used to formulate solvent-in-water emulsions using natural gas condensate or petroleum naphtha as the solvent. The oil recovery potential of these emulsions was evaluated in one metre long linear sand-packs and in a three-dimensional glass-bead packed visual model. Effects of various process variables, including: solvent volume fraction; surfactant concentration; flow velocity; and oil viscosity, on oil recovery performance were experimentally evaluated. The results show that the emulsified solvent flooding provides significantly superior displacement efficiency compared to straight solvent injection and waterflooding. The mechanisms responsible for such high efficiency include: 1) reduction in oil viscosity due to dilution by the solvent; 2) mobility control provided by the trapping of emulsion droplets at pore throats; and 3) in situ emulsification of the oil being displaced. The relative importance of these mechanisms was evaluated under different conditions. An economic analysis showed that, although the process can recover a large fraction of the oil in place, it would not be profitable under current price conditions. Several novel ideas for improving the performance are suggested.