Hydrophobically Associating Polymers for Oilfield Applications

Recent developments in water-soluble hydrophobically associating polymers are examined with particular emphasis on their use for oilfield applications. These polymers have potential for use in EOR, acidizing, drilling fluids, completion fluids and profile modification. They have also been reported to selectively reduce water permeability in sandstones, and have been used as drag-reducing agents. Associating polymers are very similar to conventional water-soluble polymers used in the oil industry, except that they have a small number of hydrophobic groups incorporated into the polymer backbone. At levels of incorporation of less than 1 mol%, these hydrophobic groups can significantly change polymer performance. Factors that affect the rheology and adsorption of associating polymers are discussed. These factors include the hydrophobe type, content and distribution in the polymer, the polymer molecular weight, and the brine composition. This paper provides an evaluation of the current state of this technology. Introduction Water-soluble polymers are used in the oilfield in polymer flooding, in drilling and completion fluids, in acid stimulation treatments, as drag reducing agents and in profile modification. These water-soluble polymers are usually acrylamide copolymers, partially hydrolyzed polyacrylamide (HPAM), or biopolymers such as xanthan or guar gum. Water-soluble hydrophobically associating polymers (AP) are water-soluble polymers that contain a small number (less than one mole percent) of hydrophobic groups attached directly to the polymer backbone (Figure 1). In aqueous solutions, these hydrophobic groups can associate to minimize their exposure to the solvent, similar to the formation of micelles by a surfactant above its critical micelle concentration (CMC) (Figure 2). Polymer association can result in solution properties not available with conventional water-soluble polymers. The potential for using hydrophobically associating polymers in the oilfield was extensively reviewed in 1998. In that work, Taylor and Nasr-El-Din examined the synthesis, characterization, stability and rheology of acrylamide-based