Description And Use Of Polymers Used In Drilling, Workovers, And Completions

Abstract

Abstract The confusion surrounding the use of polymers in drilling, workover, and polymers in drilling, workover, and completion fluids can severely limit their effectiveness. This paper will eliminate some of this confusion by describing and comparing the polymers currently being used in the industry. The polymers covered include cellulosics, guar gum, xanthan gum, starch, polyacrylates, polyacrylamides, and maleic anhydride derivatives. This paper examines each polymer according to its molecular structure, rheology, shear, acid and temperature stabilities, and salt sensitivity. Some guidelines are included for polymer usage in the field. Introduction A quick count of materials called "polymers" in World oils 1978–1979, Guide to Drilling, Workover, and Completion Fluids, produced a list of 263 tradenames produced a list of 263 tradenames (including blends). This multiplicity of products is the main reason there is so much confusion surrounding the use of "polymer fluids". The purpose of this paper is to eliminate some of the confusion and allow the user of drilling, workover, or completion fluids to make intelligent use of the available polymers. POLYMER DEFINITION POLYMER DEFINITION One definition of a polymer is: a substance composed of giant molecules formed by the union of many simple molecules. Most substances encountered every day are covered by this definition. Some examples of these are any plastics, rubber, clothing (either synthetic or natural), wood products, and many more. In petroleum operations, many of the chemicals used could also be called polymers, including bentonite and lignosulfonates. In this paper, only the products normally considered polymers by oil field personnel will be covered. These are all organic chemicals and usually are sold as powders. Confusion is introduced by the multitude of blends on the market that contain polymers. These might be blends of two or more polymers or blends of polymers with inorganic materials, such as calcium carbonate, clays, and salts. These blends are almost always proprietary products and the manufacturer is normally products and the manufacturer is normally reluctant to divulge the composition of the blend. POLYMER USES POLYMER USES The primary uses of polymers are shown in Table 1. These uses are: filtration control, viscosity modification, flocculation, and shale stabilization. The first and major use of polymers is in filtration control, usually as a supplemental additive to bentonite or some other chemical. The amount of material used for filtration control is far greater than the amounts used for the other uses. The next use of polymers would be viscosity modification, followed by flocculation and then lastly, shale stabilization. TYPES OF POLYMERS Table 2 lists the types of polymers that are most commonly found in petroleum operations. Table 3 shows these polymers arranged according to their primary function. These polymers can be classified as synthetic or natural polymers. The natural polymers are starch, guar gum, and xanthan polymers are starch, guar gum, and xanthan gum. The synthetic gums are the cellulosics, the acrylates, the acrylamides, and the maleic anhydride derivatives.