Abstract

The evaluation of a mobility control polymer requires that proper laboratory techniques be followed if meaningful results are to be obtained. New procedures are presented and existing procedures are reviewed to aid in the measurement of properties related to performance of Polyacrylamide solutions. In addition to mixing and filtration techniques, the measurement of polymer concentration, thermal stability, core testing, and other factors relating to mobility control in the reservoir are discussed.

References and illustrations at end of paper

Introduction

Polymers are being widely used to provide mobility control in secondary and tertiary oil recovery processes. Large quantities of polymer are required for these processes and it is imperative that adequate, but not excessive, quantities be used to insure the economic success of these processes. To accomplish this, it is necessary that sufficiently accurate laboratory core data be developed to permit optimum mobility bank design.

This paper will describe the elements of such a laboratory testing program. It will be organized into three sections:

  • Solution Preparation

  • Characterization of Polyacrylamide Solutions.

  • Polyacrylamide Behavior in Field Core Specimens.

In Section I, procedures will be given to dissolve polymers properly in stable analogs of the natural field brines. Section II continues with methods to assess the properties (screen factor, viscosity and thermal stability) of Polyacrylamide dissolved in brine. It also contains a new analytical method to determine the polymer concentrations in oil field brine. The last section describes the techniques used to measure polymer solution behavior in actual field core specimens.

The procedures presented are the results of hundreds of core tests using water soluble polymers. Although this paper is not a complete reference manual, an attempt has been made to cover many of the critical points. A topical sentence has been underlined to identify recommended standard procedures in Section I and in Section II where alternative procedures are also discussed. It is hoped that the methods presented might be considered as the first step in setting standards for resistance factor determinations.

Solution Preparation

Several techniques are available for solution preparation. They all require complete separation of particles during the initial dispersion of the sample. A satisfactory dispersion can be obtained with an ordinary laboratory magnetically driven stirrer1–2 (Recommended Standard Procedure). The dry polymer should be sprinkled uniformly onto the shoulder of a well developed vortex within 60 seconds. If dispersion is attempted over a longer time span, viscosity from dissolved polymer may prevent proper wetting. As soon as all the polymer has been added, the stirrer is slowed to a speed of 60–80 rpm to avoid mechanical degradation. After 2 or 3 hours the stirrer should be turned off. The solutions are usually allowed to stand overnight and stirred about 20 minutes before using. Homogenizers and high shear mixers will degrade the polymer and should not be used for solution preparation. All of the polymers used in this investigation are listed in Table 1. An example of the degradation produced by vigorous agitation is demonstrated with one of these polymers as indicated in Table 2.

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