The Dual Solvent Slug Technique For Improving Injectivity Of Waterfloods
Authors: Relf J.A. , Sears J.R. 
Published: December 2007

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Abstract
In recent years secondary recovery of oil by waterflooding has become increasingly popular in Western Canada. In most cases water injection wells are completed by converting wells that were formerly used for oil production and common practice is to place these wells on injection after some form of treatment to remove wax and other deposits from the well bore.
It has been known for some time that the presence of residual oil impedes the flow of water and this is particularly significant in the area immediately surrounding the well bore. It has also been demonstrated in the past that use of a miscible displacing fluid leaves lower residual oil saturations that does an immiscible displacing medium such as water. There have been several methods proposed to achieve a reduction in residual oil saturation around water injection wells. These have mainly dealt with the use of surfactants or the injection of low viscosity hydrocarbon solvents.
Recently several articles have appeared in the literature concerning increased recovery of crude oil from formations using large solvent slugs that are mutually miscible with oil and water. These articles, based on laboratory studies on a variety of solvents, indicate that this method of recovery is technically feasible but does not appear to be economical.
This paper covers an adoption of the miscible solvent slug technique to increasing injectivity of conventional waterfloods by reduction of residual oil saturation around the well bore. Reduction is accomplished by injecting an oil-soluble solvent slug followed by a mutually miscible water-soluble solvent slug. Two alternate types of treatment are discussed, one for newly converted injection wells and the other for wells that have been performing poorly on water injection. The theory behind these treatments is discussed as well as actual case histories on successful field trials on several Alberta wells.

Introduction
Several articles have been written recently on the subject of secondary recovery by water-flooding in Western Canada. It has been stated that known recoverable oil reserves will increase by approximately 50 per cent when all secondary recovery projects now in operation or planned will be complete.