Rheology of Hydrophobically Associating Polymers for Oilfield Applications

Water-soluble hydrophobically associating polymers are examined with particular emphasis on their rheology for oilfield applications. The incorporation of a small amount (less than 1 mol%) of hydrophobic groups into the polymer backbone of a water-soluble polymer dramatically alters the rheological properties of the resulting material. Associating polymers have potential for use in mobility control, drilling and completion fluids and profile modification. 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. The rheology of HPAM and biopolymers for enhanced oil recovery has been studied in detail. Biopolymers such as xanthan are not easily shear-degraded and are not sensitive to an increase in salinity or divalent ion concentration. As a result, they are used in drilling fluids and at high salinities. In contrast, acrylamide polymers are easily shear degraded and their viscosity is significantly reduced as salinity or divalent ion concentration increase. Acrylamide polymers are more commonly used at lower salinities, up to an equivalent of 1 wt% sodium chloride. Water-soluble hydrophobically associating polymers are water-soluble polymers that contain a small number (less than one mole %) of hydrophobic groups attached directly to the polymer backbone. 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. As a result of association, the hydrodynamic size of the polymer increases and the solution viscosity increases. Water-soluble hydrophobically associating polymers were extensively reviewed by Taylor and Nasr-El-Din in 1998. In that work, they examined the synthesis, characterization, stability and rheology of acrylamide-based associating polymers for improved oil recovery. Further studies of the rheology of associating polymers for oilfield applications have been reported since 1998. Young et al. proposed a hydrophobically modified guar gum for use in completion fluids. Audibert-Hayat et al. reported on hydrophobically modified natural polymers for use as non-damaging drilling fluids. Yabin et al. synthesized hydrophobically associating acrylamide polymers for oilfield applications and studied their solution Rheology of Hydrophobically Associating Polymers for Oilfield