Applications of Water-Soluble Polymers in the Oil Field

Abstract

Summary Water-soluble polymers commonly used in the oil field are reviewed. The properties of guar, guar derivatives, cellulose derivatives, xanthan gum, locust bean gum, starches, and synthetic polymers, especially polyacrylamides, are discussed and related to chemical structures of the polymers. Original data comparing polymer solution viscosity properties under identical conditions are presented. These data include effect of polymer concentration on solution viscosity, temperature effect on solution viscosity, viscosity in acidic solution, and polymer solution viscosity in the presence of a hemicellulase enzyme. Introduction Water-soluble polymers are used extensively in various phases of drilling, completion, workover, and production of oil and gas wells. 1,2 In spite of widespread use, the connotation "polymers" (macromolecules) still confuses many people involved in oilfield work. This confusion is due in part to the wide variety of commercially available polymers, which are generally organic and have a carbon-based structure. The lack of understanding and appreciation of polymers and their properties severely restricts the selection of the best polymer for the particular application under consideration. The purpose of this paper is to define clearly the commonly used but often misunderstood terminology. The paper defines the term polymer and distinguishes between homopolymers, copolymers, block copolymers, and graft copolymers. The chemical structures of most commonly used naturally occurring polymers, chemically modified naturally occurring polymers, and synthetic polymers are shown. Attempts are made to describe how physical and chemical properties of these organic polymers are regulated by their chemical structures. Use of these polymers in drilling, cementing, fracturing, acidizing, controlling water production, preventing sand production, clay stabilization, lost circulation, and enhanced recovery, where known, is described. Polymer Definition Ethylene gas (CH2=CH2, boiling point˜-152°F, molecular weight=28), under proper chemical conditions, will combine with hundreds or thousands of other ethylene molecules to form a solid product called polyethylene, with a molecular weight in the millions. This polymer is familiar to everyone as packaging film and can be seen at any supermarket meat counter. This conversion of ethylene to polyethylene is called polymerization - the chemical combination of many small molecules to form a very large molecule.3–6 Polymer Definition Ethylene gas (CH2=CH2, boiling point˜-152°F, molecular weight=28), under proper chemical conditions, will combine with hundreds or thousands of other ethylene molecules to form a solid product called polyethylene, with a molecular weight in the millions. This polymer is familiar to everyone as packaging film and can be seen at any supermarket meat counter. This conversion of ethylene to polyethylene is called polymerization - the chemical combination of many small molecules to form a very large molecule.3–6