Enhancing Polymer Flooding Performance in a High-Salinity Reservoir in Kazakhstan via Water Ion Modification

Abstract This study investigates enhanced oil recovery methods for high-salinity oil reservoirs with a focus on an oil Field in Kazakhstan (Field X). Conventional recovery techniques recover only a portion of the original oil in place, making polymer flooding an important EOR strategy due to its ability to improve water injection mobility and sweep efficiency. However, the extreme salinity of formation water at the field (TDS ~60,000 ppm) challenges polymer stability and effectiveness, reducing their viscosity and overall performance. Through laboratory experiments replicating reservoir conditions, this research evaluates several hydrolyzed polyacrylamide (HPAM) polymers for their suitability in high-salinity environments. Rheological behavior, thermal stability, static adsorption, and injectivity performance were assessed. Ion modification studies were also conducted, focusing on the controlled addition of Na₂SO4, CaCl₂, and MgCl₂ to evaluate the influence of individual ions without changing total salinity. Results show that precise ion management leads to considerable improvements in polymer stability and viscosity retention. The injectivity evaluation confirmed that enhanced formulations with 4×Mg2+ ions produced higher flow resistance and better viscosity retention under flow conditions. Resistance factor values significantly improved compared to the base case, confirming the positive influence of Mg2+ ions in maintaining polymer performance. In contrast, excessive Ca2+ caused polymer chain disruption and viscosity loss. Moderate sulfate addition improved viscosity, but excessive levels had the opposite effect. The best polymer which shows the lowest static adsorption and strong thermal stability at high salinity condition was selected as the most efficient polymer for the Field X. This research presents an integrated approach to polymer evaluation by combining laboratory testing with ion modification techniques, offering practical guidance for improving polymer performance in harsh reservoir environments. The findings emphasize the importance of targeted ion control in extending the operational window of polymer flooding technologies.