Abstract

In recent years, secondary recovery of oil by water flooding has becomeincreasingly popular in Western Canada. In most cases, water injection wellsare completed by converting wells that were formerly used for oil production;common practice is to place these wells on injection after some form oftreatment to remove wax and other deposits from the well bore.

It has been known for some time that the presence of residual oil impedesthe 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 theuse of a miscible displacing fluid leaves lower residual oil saturations thatdoes the use of 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 through the use of 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 adaptation of the miscible solvent slug technique to increasing injectivity of conventional waterfloods by a reduction of the 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 of successful field trials on several Alberta wells.

Introduction

Several articles have been written recently on the subject of secondary recovery by waterflooding 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 are completed.

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