Types of Polymers
The following is a listing of the current polymer types in use in the oilfield. Oilfield uses of the polymers are primarily in drilling fluids for rheology or fluid loss control and in wellbore stabilization. Some polymers are used in cements and fracturing fluids, in reservoir drill-in fluids and for waste management (solids flocculation).
Starch—Starch is a natural polymer produced from either corn or potatoes, but can be made from other starchy plants. It is supplied as a pregelatinized (water-dispersible) powder. Natural starch is usually treated with a preservative. Modified starches can be either cationic, anionic or nonionic, the most common drilling fluid additive being anionic.
Examples: starch, cm-starch, hp-starch, cmhp-starch
Uses: Fluid loss control for all types of mud systems, particularly useful in salt water systems. Natural starch requires a bactericide while drilling. Modified starches are used in reservoir drill-in fluids.
Guar gum—Derived from the seed of the Guar plant. Regular guar contains residue left from processing the guar bean, which can cause formation damage. HP-guar is further processed with hydroxypropyl side chains and cleaned of excess residue.
Uses: Not used in most drilling fluids (solids reactivity). Has been used in top-hole drilling for quick viscosity. HP-Guar—primary fracturing fluid viscosifier and fluid loss controller
Biopolymers—Polysaccharides manufactured from bacterial or fungal fermentation. They have extremely complex structures with high molecular weights (500 to 2 million+). Their side chains are slightly anionic.
Examples: xanthan gum, wellan gum, diutan, scleroglucan
Uses: Rheology control. Develops high, low-shear-rate viscosities for suspension and carrying capacity.
CMC—A polysaccharide linear polymer based on a plant cellulose backbone modified with carboxymethyl (CM) side chains for water dispersion. Carboxylic acid side chains are anionic. Its functionality depends on the degree of substitution (DS), the number of CM side chains, and molecular weight (MW).
Examples: High MW: Regular CMC or Hi viscosity CMC
Low MW: Low viscosity CMC
Tech grade: Usually high MW but contains up to 40% salt contamination.
PAC (polyanionic cellulose): Higher DS than regular CMC.
Uses: Fluid loss control in drilling; high MW is a bulk viscosifiers with minimal low shear-rate viscosity and minimal suspending ability.
HEC—A polysaccharide linear polymer based on a plant cellulose backbone modified with hydroxyethyl side chains. Its side chains are nonionic. Its functionality depends upon its molecular weight. Usually supplied as a high molecular weight product, >250,000.
Uses: Bulk viscosifier for high density brine fluids, such as the saturated chlorides and bromides. Not normally used in drilling fluids, but used in clear completion fluids, gravel packs, and fracturing fluids. It has no solids suspending ability.
Synthetics—A multitude of synthetic polymers can be designed in chemical manufacturing plants. The two most common synthetics in drilling fluids are the acrylates and polyacrylamides.
Acrylates—Synthetic materials manufactured from acrylic acid. Not as complex structurally as the natural polymers. Usually has a straight-chain carbon backbone but can have a multitude of different side chains, depending on the end product desired. It is usually anionic.
Examples: polyacrylates, vinyl polymers, copolymers, vinyl acetate, maleic anhydride,
Uses: Low molecular weight (<1000)—thinners, deflocculants
Medium molecular weights—fluid loss, flocculent, shale stabilizer
High molecular weights—bentonite extender, flocculent
Polyacrylamide—A copolymer of acrylic acid and acrylamide in various ratios. Usually called a partially hydrolyzed polyacrylamide (PHPA). Usually anionic for drilling fluids; can be anionic, nonionic, or cationic for use as a dewatering flocculent.
Uses: flocculants, increased bulk viscosity, shale stabilizer
Cationic polymers—A copolymer, many times with acrylates or acrylamides with ammonium (amides,amines) cationic side chains.
Uses: flocculants, Shale stabilizer