Micellar-Polymer Flooding: Status And Recent Advances

Abstract

Abstract The micellar (or microemulsion) flooding process is one of the very few oil recovery methods, which have been shown to be successful in the field for recovering oil from a waterflooded reservoir. In spite of the field and laboratory successes, the process is complex to design and its economics remain a matter of concern in view of large initial investments and a high risk factor. This paper examines the micellar-polymer flooding process from the points-of-view of laboratory and field experience, as well as simulation. In particular, the authors' own laboratory work all salinity and multiple micellar slugs is described. The micellar flooding process employs a micellar solution consisting of oil, water and a surfactant as well as small amounts of other chemicals. The role of phase behaviour of such a system is examined with regard to displacement efficiency. Salinity of the brine in the fluid system used is an important factor in determining the process efficiency. The micellar slug can be broken into two, or more slugs using the phase diagram, in such a way that the individual slugs are compatible with each other, reducing the slug dissipation rate. Introduction Micellar flooding is technically the most successful chemical flooding process for waterflooded formations. It has some of the limitations of chemically-based processes, but its long-term potential for the recovery of residual (waterflood) tight oils could be comparable to that of steamflooding for heavy oil given the right economic conditions. Micellar flooding is indeed the only process that has been demonstrated successfully in the field as a tertiary recovery process for low pressure, depleted oil reservoirs. In spite of this promise, micellar flooding is only marginally economical, or even uneconomical, and is also strongly dependent on the mineral content of the reservoir rock and the composition of the interstitial water. It is a process that needs to be tailored carefully for the target reservoir. The high cost of the process is in part due to the cost of the chentica1s and the small well spacing needed - drawbacks of most chemical flooding processes. (For a discussion of the economics of the process, refer to Gogarty(l). This paper presents an assessment of the micellar flooding process in the tight of the laboratory and field data, with a view to determining its future prospects. Definitions Micellar flooding is variously known as "microemulsion flooding", "micellar-polymer flooding", and "surfactant-polymer flooding", with varying shades of meaning. Generally, the basic process consists in injecting a slug of a preflush, followed by the micellar slug proper, followed by a slug of a polymer solution, which is graded into a waterflood. Variations have been proposed, e.g. mixing the polymer with the micellar solution. The definitions given by Holm(2) help to distinguish between different types of surfactant-polymer floods. A micellar solution is a dispersion of a surfactant in an oleic or aqueous solvent. Such solutions can solubilize large amounts of water or oil to form either water-in-oil (w/o) or oil-in-water (o/w) microemulsions, respectively.