Abstract
High-molecular-weight (HMW) polyacrylamide and its derivatives are widely used in oilfield applications ranging from drilling fluids, enhanced oil recovery (EOR), and treatment of oil sand tailings. In these applications the adsorption characteristics of these polymers are essential since it would affect their applicability and efficiency. In this study, adsorption of three high-molecular-weight polymers (nonionic (NPAM), partially hydrolyzed (HPAM), and sulfonated (SPAM) polyacrylamides on silica surfaces from 2% KCl) is characterized using a quartz crystal microbalance with dissipation monitoring (QCM-D) and an AFM-based colloidal probe apparatus. QCM-D measurements show that semiequilibrium for adsorption on silica surfaces is reached within 3 h. The adsorbed amount and adsorption rate are highest for NPAM and lowest for SPAM. AFM experiments revealed that after 20 min of incubation in solution, HPAM induced bridging attraction on approach (i.e., compression). On the other hand, only a weak attraction is observed in the NPAM solution. However, SPAM shows only steric repulsion on approach after 20 min of incubation commencing at a separation of around 250 nm. Significant adhesion on retraction was observed after 20 min of incubation in NPAM and HPAM. However, only slight adhesion was observed in SPAM in the same time frame. After incubation in polymer solutions for 20 h, all polymers induced steric repulsion on approach and the absence of adhesion on retraction at different separations, indicating full surface coverage and different effective hydrodynamic layer thickness (EHT). On the basis of the AFM measurements after 20 h of incubation, the EHT of the adsorbed layers in NPAM, HPAM, and SPAM is 125, 30, and 175 nm, respectively. We believe that the results in this study will lead to enhanced understanding of the polymers under investigation with respect to their use in EOR applications. Moreover, this study gives clues on the differences between the three polymers under consideration with respect to their flocculating power, which is employed in the oil sand tailings treatments.
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