Oil-in-Water Emulsions and Their Flow Properties in Porous Media

Abstract

The laboratory studies described here in detail were conducted to ascertain the properties of oil-in-water emulsions and to determine if such emulsions could act as a selective plugging agent to improve oil recovery in waterfloods. Introduction In waterfloods, the rapid channeling of water from injection to producing wells through the more permeable portions of the reservoir gives low oil permeable portions of the reservoir gives low oil recovery. A number of materials, such as cement, ground leather, and ground limestone, have been used in wellbore treatments to improve injection profiles in water-injection wells, However, even if such treatments do effect a better distribution of water in the formation at the wellbore, they are unlikely to be successful because of cross-formation flow near the wellbore. A deep-penetration method should be more effective. Silica gel, rubber latex, and asphalt, have been tested as deeper-penetration plugging agents in attempts to decrease reservoir heterogeneity. The laboratory investigations described here were undertaken to determine the properties of oil-in-water emulsions and to study the flow of emulsions through porous media. Samples of core material can be considered as miniature reservoirs and the cores are heterogeneous. In our investigations we hoped to determine if oil-in-water emulsions would decrease reservoir (core) heterogeneity and improve water displacement of oil in sandstone reservoirs. Concept of Emulsion Flow in Porous Media Consider a single droplet of oil emulsion (Fig. 1) entering a pore constriction smaller than itself. It proves a radius of curvature in the leading portion proves a radius of curvature in the leading portion smaller than the radius of the portion of the drop still in the pore. Thus, the capillary pressure is greater at the front of the (drop than at the back, and pressure is required to force the droplet through. This "Jamin" effect can become appreciable as more and more emulsion droplets encounter pore constrictions. For an emulsion to be most effective, the droplets of oil in the emulsion should be slightly larger than the pore-throat constrictions in the porous medium. Emulsion droplets have a range of sizes, as do pore-throat constrictions in porous media. Thus, pore-throat constrictions in porous media. Thus, emulsification can make a relatively small volume of oil quite effective in restricting flow, provided the pore-throat constrictions are not excessively large. pore-throat constrictions are not excessively large. (Uzoigwe and Marsden recently reported on the flow of oil-in-water emulsions through glass bead packs and did not show flow restriction. Probably, packs and did not show flow restriction. Probably, the emulsion droplets were small compared with the sizes of the pore throats in the unconsolidated porous media.) As water displaces oil, fingering develops because of rock heterogeneity. When oil-in-water emulsion is injected, a greater amount of emulsion enters the more permeable zones. As this occurs, flow becomes more restricted, so water begins to flow into less permeable zones, resulting in greater sweep efficiency. permeable zones, resulting in greater sweep efficiency. Laboratory Experiments Becker states, "An emulsion is a heterogeneous system consisting of at least one immiscible liquid intimately dispersed in another in the form of droplets, whose diameters, in general, exceed 0.1 micron." JPT P. 727