Recent studies have suggested the possibility of spontaneous emulsification as a mechanism for enhanced oi1 recovery (EOR). The discussions have however, remained essentially qualitative. A study was therefore undertaken to estimate quantitatively the contribution of spontaneous emulsification as an EOR mechanism. The tests were conducted on several bulk liquid/liquid systems as well as by displacement experiments in unconsolidated synthetic sand packs.
Spontaneous emulsification was found to be a mechanism For EOR; the estimated extra contribution to EOR due to this mechanism was found to be at least nine percentage points in laboratory scale displacement experiments. Results of tests on bulk 1iquid/liquid systems indicate that the occurrence or absence of spontaneous emulsification is correlatable with positive or negative values of partition parameter. It may be concluded that higher oil recoveries may be achieved in chemical EOR processes where interface mass transfer (and the accompanying spontaneous emulsification) occurs.
The evaluation of efficiency of residual oil mobilization through the capillary number theory (with and without spontaneous emulsification) is also discussed. Displacement tests with spontaneously emulsifying systems showed that residual oil left behind a conventional waterflood was mobilized in a range of capillary numbers much less than that which applies to low-tension waterfloods.
The improvement of oil recovery from a reservoir demands that either residual oil must not be allowed to form at all or where it occurs, it must be remobilized and then produced. It has been estimated that in a carefully selected, well-designed, good performing operation, an additional 30 – 50 percent of the oil originally in place might be recovered by EOR methods (1). Techniques for enhancing oil recovery which have shown significant promise for this remobilization include thermal methods, carbon dioxide and hydrocarbon miscible processes, and chemical flooding. Of all these, chemical flooding, although the most complex, seems to hold the most promise for EOR. although only limited data are available at present (2). Several chemically driven mobilization mechanisms are thought to occur during displacement processes. These include ultra-low interfacial tension, wettability reversal, and/or spontaneous emulsification. Although all three and other related processes can integrally be assessed. this paper is concerned only with the spontaneous emulsification aspect of the recovery processes.
Understanding the mechanisms of chemical EOR requires d combination of the disciplines of reservoir engineering and chemistry, Understanding the complex fluid-fluid-rock interaction is a chemical problem while utilizing it to improve recovery is a reservoir engineering problem. This paper is concerned with the latter and not with the former. No attempt is made to offer a chemical interpretation of the process but rather its contribution in the overall recovery process is examined.
The term "spontaneous emulsification" in its strict sense means emulsification which arises in the absence of even the slightest agitation or external disturbance (3). This distinguishes it from the sure easy emulsification where with low interfacial tension the liquids are easily emulsified by external mechanical means.