Polymer Solution Rheology and Polymer Synthesis for Enhanced Oil Recovery
Enhanced Oil Recovery (EOR) is used to access the oil within oil basins that remains after traditional recovery methods are deployed. In alkali-surfactant-polymer EOR, aqueous solutions containing surfactants and high molecular weight polymers are injected into oil basins. The most common polymer used in polymer EOR is partially hydrolyzed polyacrylamide (HPAM), a copolymer of polyacrylamide and polyacrylic acid, and in aqueous solutions, HPAM is a polyelectrolyte. The presence of salts in the oil basin and in water used to make industrial injection solutions can alter the interactions of these anionic charges. By knowing the rheological behavior of polymer solutions containing ions, polymer solutions can be more specifically formulated to the conditions of various oil basins, improving recovery. In this study, shear and extensional rheology are utilized to determine the behavior of polyelectrolyte solutions and interactions between polyelectrolytes and ions in three stages. The first stage used commercial polymers, marketed for EOR, and investigated the effect of monovalent and divalent salts on solution behavior in shear. The second stage studied these same solutions under extension. It was found that all solutions, even with monovalent and divalent salts were shear thinning but strain hardening. This suggests that calcium may form complexes with the polymer. In the final stage of this study, model polyacrylamides were used; the degree of hydrolysis of the polymer was varied thereby controlling the concentration of negative charges along the polymer backbone. Shear rheometry was again used to study the behavior of these solutions in the presence of monovalent and divalent salts. Additionally, a novel physical gel was discovered, and its structure was probed using swelling studies and small-angle x-ray scattering. Overall, this project offers insight into the physical behavior of polyelectrolytes under industrially relevant conditions. The nature of polyelectrolyte interactions with multivalent salts, one of the most challenging problems in polymer physics, was probed. By relating the chemical structure of polyelectrolytes and composition of aqueous solutions to rheological behavior, predictions about the efficacy of polymer solutions for EOR can be made. This project will have a lasting impact, not only by increasing the productivity of current oil wells but also by clearly determining the nature of polyelectrolyte – ion interactions.
Erk, Purdue University.
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