The effects of mineral salts on the rheology of polymer solutions in case of Santa Cruze Reservoir (Cuba)

Abstract

This study investigates the polymer solutions used in water shut-off control of production wells and polymer flooding of Santa Cruze reservoir located in Republic of Cuba. The reservoir is characterized by early water breakthrough and therefore application of chemical reagents is required to decrease the content of produced water and gases from production wells. The aim of this study was to reveal the influence of mineral salts on the rheology of polymer solutions based on two different industrial trademarks: Seurvey R1 and Softpusher. The hydrochemical composition and physical properties of formation water samples from Santa Cruze reservoir revealed domination of sodium and potassium cations and chloride anion. The water hardness (8.3 mg-eq./L) was calculated basing on the content of calcium and magnesium cations. It was revealed that Suervey R1 has a higher viscosity, which is in consistent with its molecular mass. In general, investigation of polymer solutions, which were prepared with distilled water, shows better rheological performance than solutions based on formation water samples. This is due to sensitivity of polyacrylamide (PAA) to the ion forces of solvents. The swelling degree is maximum in case of distilled water and sharply decreases with addition of salt content. The Softpusher polyacrylamide solutions were more salt-tolerated than Seurvey R1 polyacrylamide solutions, as Softpusher PAA has less branched structures in contrast with high-molecular and more branched Seurvey R1 polymer. Increasing viscosity of dispersion medium inhibits the precipitation rate of dispersed particles. Thus, the rheology and sedimentation stability of dispersion are improved due to polyacrylamide flocculation.