Spontaneous Emulsification-A Possible Mechanism for Enhanced Oil Recovery

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Introduction Spontaneous emulsification will occur between a hydrocarbon phase and an aqueous solution of petroleum sulfonates if the sulfonate preferentially partitions into the oil phase. The displacement of residual oil, in phase. The displacement of residual oil, in laboratory core floods, at a small capillary number is significantly improved when spontaneous emulsification occurs; with the displacement efficiency being favored by high emulsion coalescence rates. The mechanism of oil mobilization in these displacements may distinct from those of miscible and immiscible processes. processes. MECHANISMS OF SPONTANEOUS EMULSIFICATION If a layer of toluene is carefully poured on top of an aqueous phase containing 3 weight-percent of a petroleum sulfonate and 1 weight-percent NaCl, the system initially consisting of two relatively clear, distinct phases is at first quiescent. After about 15 minutes, a mist of fine drops can be seen at the interface: the surface beings to twitch sporadically and an emulsion of growing proportions is observed to form. This spontaneously formed emulsion is not, however, thermodynamically stable and so it cannot be attributable to "negative" interfacial tensions. Indeed, in a matter of days, coalescence of the emulsion can be detected. Eventually, the emulsion will coalesce entirely and the two clear phases are then stable, but of different composition. The example of spontaneous emulsification/ breaking cited above is not an isolated one; many other similar systems will be defined in this paper. What makes the above process fascinating and certainly worthy of further study is that it represents a possible mechanism for tertiary oil recovery - one that appears to have been largely overlooked: one which is distinctly different from the low tension processes. It is the purpose of this paper to explore this possibility. The paper to explore this possibility. The conclusion is that residual oil can be mobilized by spontaneous emulsification. One possible mechanism is that the small oil droplets thereby mobilized may subsequently coalesce with other ganglia of residual oil, creating a local region of enhanced oil saturation. Other mechanisms of increasing the local saturation pre, however, possible. Once the local oil pre, however, possible. Once the local oil saturation is increased sufficiently the oil will be mobilized. Further coalescence can take place, and an oil bank can be formed. This place, and an oil bank can be formed. This process has been tested and the results are process has been tested and the results are reported here.