Use of Soluble Oils for Oil Recovery
Authors: Holm L.W. 
Published: December 2007

A method involving the use of soluble oils can substantially reduce the oil saturation in a reservoir below, that obtainable by waterflooding. The soluble oil, which consists essentially of hydrocarbon, surfactant, and a stabilizing agent, will spontaneously emulsify with water. Small soluble-oil slugs driven with thickened water can displace all or most of the oil in linear porous systems.

Introduction
In recent years, many new oil recovery processes have been developed in an effort to improve waterflooding or to substitute for it. These processes include placement of oil with LPG or enriched gas alcohol placement of oil with LPG or enriched gas alcohol flooding, surfactant injection, polymer solution flooding, and CO flooding. The miscible displacement methods and surfactant flooding processes were found to be capable of reducing the capillary retention forces that limit oil displacement by waterflooding. However, miscible displacement involving either LPG and gas or alcohol and water has not been profitable in most applications because of the unfavorable mobility ratio that exists between displaced and displacing phases and the large amount of solvent required. The addition of surface-active agents to the injection water has not been a profitable oil recovery method because of the high loss of the surfactant by adsorption on the pore surface of reservoir rock.
A means to combine the beneficial effects of oil miscible solvents and surface-active agents was first suggested in U. S. Patent 3,082,822 (Ref. 1); in this teaching, surface-active agents in solution with oil-soluble solvents were introduced ahead of flood water to enhance oil recovery. Later, Csaszar, described a new oil recovery process consisting of the combination of oil-soluble solvents, surface-active agents, and amphipathic solvents as a water-driven, soluble-oil flooding process. Since 1968 there have been published several studies of oil recovery by displacement with micellar solutions of hydrocarbons, surfactants, and water. These flooding materials have begun to look economically promising for secondary and tertiary oil recovery if they are driven by thickened water so that favorable mobility ratios are maintained during the flood.
The following terminology is provided to orient the reader and show the relationships among the various flooding agents associated with this type of oil-recovery process.
A micellar solution is a dispersion of surfactant in a solvent (oleic or aqueous), in which the surfactant molecules or ions are arranged in oriented aggregates. Many micellar solutions can spontaneously take up (solubilize) large amounts of water or oil to form either water-in-oil or oil-in-water microemulsions, respectively. In such cases, the internal phase is solubilized into the centers of the surfactant aggregates.
A microemulsion is a thermodynamically stable emulsion of oil and water in which the particle size of the emulsified or internal phase is less than about 0.1 microns. In the absence of color bodies, these emulsions are transparent. Microemulsions can be of the water-in-oil or of the oil-in-water type.
Soluble oils are oleic compositions that spontaneously take up (solubilize) water when mixed with it; they are specific and limited micellar solutions - that is, they will spontaneously solubilize water (not oil).
JPT
P. 1475