In phase behavior studies of conventional oil for chemical EOR, formation of a single phase homogeneous emulsion system can be achieved only with formulations containing relatively high concentrations of synthetic surfactant. Application of the single phase micellar emulsion in chemical EOR has not been successful economically due to high cost of surfactant and surfactant loss in the reservoir. The economic picture could be much better when this technology is applied for recovery of high TAN heavy oils which can release the required amount of surfactant (petroleum soap) in-situ upon contact with the ASP solution.
This paper describes the successful formulation of an ASP system which can generate a single phase (Winsor type IV) micellar emulsion when mixed with a viscous high TAN (2.0 mg KOH/g) heavy oil. This ASP system contains commercial HPAM and NaOH in low salinity water. The micellar emulsion system, which is thermodynamically stable under very low salinity conditions, can contain as much as 33% of crude oil before transition to a Winsor type I system with a separate excess oil phase. Viscosity of the oil-in-water micellar emulsion varies with its oil content and is generally much less than 1/10 of the parent crude oil. The petroleum acid, which is a key component in the formation of the micellar emulsion, has been successfully isolated from the crude oil. Analytical results of the acid, by means of FTIR, NMR, LC-mass-spectroscopy and elemental analysis, will be presented.
The effectiveness of this ASP system in mobilization of capillary trapped heavy oil has been demonstrated with a Berea coreflood test. To ensure that adequate mobility control was present during displacement of the viscous heavy oil, separate sand-pack tests were also conducted for selection of candidate ASP solutions based on in-situ resistance factors. As a result, excellent incremental oil recovery (67% OOIP) and outstanding production rate (30% OOIP in 1 PV) were achieved during displacement of the viscous heavy oil (10,000 mPa.s) from Berea core. Residual oil saturation of the post-test core was < 7% Pore Volume.
To our knowledge, application of micellar emulsion generated from natural petroleum soap in chemical EOR of heavy oil has not been investigated extensively. Results from this study can lead to better understanding and improvement of this chemical EOR technology for heavy oil.