Abstract

A novel approach was evaluated for the first time to test the effectiveness of a continuous injection of progressively decreasing chemical concentration (tapered chemical injection process) in preventing permeability impairment and sustaining injectivity improvements. The process. here referred to as "The Amflo Process" also significantly improves oil recovery beyond that obtained with conventional waterflooding. Three distinct and contiguous steps are involved in the implementation of this new process. These include; stimulation, tapered chemical injection and a continuous injection of a low concentration chemical in floodwater. Fluids employed in each of these steps are tailored to the specific reservoir being flooded to ensure technical and economic optimization.

This paper discusses the results of several laboratory tests and two preliminary field trials involving single wells. Also, a field pilot project currently being implemented in the Viking Formation of the Dodsland Field in west-central Saskatchewan to evaluate the commercial viability of this new process, is reviewed.

Introduction

Permeability reduction resulting from water sensitivity of certain reservoirs is of serious concern during waterflooding or enhanced oil recovery operations. Many oil-producing formations contain significant amounts of clays. Because of the large surface area, and high reactivity of such surfaces, the response of the formations to various recovery processes may be dominated by the reactions of clays. Thus, the success or failure of waterflooding or enhanced oil recovery operations may be controlled to a large extent by the amount and type of clays in the formations to which these recovery processes are being applied (1).

Formation damage, i.e., reduction or loss of permeability of sandstone, has been known to occur in some reservoirs upon injection of water that is less saline than connate water(2). Generally, permeability reduction can be caused by water-sensitivity resulting from pore blockage by clay swelling, clay particle migration or a combination of these effects. Permeability reduction resulting from clay swelling and methods of che1r sta.bilizat1on have been discussed by several authors (3–17). Others(18–27) have described water sensit1vity attributable to clay particle dispersion and migration. Recently, a race control procedure has been proposed (28) as an effective mechanism for fines movement control in petroleum reservoirs.

The limitations discussed above have led to the development of a new waterflood process. After extensive research, development and evaluation, the new injection process has evolved to its present form.

Results of several laboratory tests and two preliminary single well field trials are discussed. Also, comments are provided on the design of an Amflo Process pilot project currently being implemented in the Dodsland Viking field in west-central Saskatchewan.

DESCRIPTION OF THE PROCESS AND OPERATIVE MECHANISMS

The new process for improved conventional oil recovery is a tapered chemical injection process which utilizes the action of a patented acid-surfactant system to allow water injection into water-sensitive formations. Designed to specifically counteract numerous factors which have usually led to insufficient waterflooding operations, the process utilizes laboratory proven procedures that include wettability adjustment, interfacial tension lowering and wettability control to improve recovery of oil from sandstone reservoirs.

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