EFFECT OF AIR CONTENT, TEMPERATURE, AND SALINITY ON POLYMER DEGRADATION

Abstract

With rising global energy demands, the oil and gas sector is tasked with optimizing output from mature oil fields. These fields, once powered by natural pressures for primary production, now yield less due to the limitations of traditional recovery methods like gas and water drives. This necessitates a shift towards secondary and then to enhanced oil recovery (EOR) techniques for better efficiency and economic feasibility. Polymer flooding, a key EOR strategy, improves recovery using water-soluble polymers to enhance water viscosity, addressing inefficiencies such as fingering and channeling within reservoirs. While successfully boosting oil recovery worldwide, this method encounters obstacles including polymer degradation, adsorption issues, and reduced effectiveness, mainly due to the challenging conditions within reservoirs such as varying oxygen levels, temperatures, and salinity. These environmental factors critically affect the performance and success of polymer flooding. This research investigates the impact of adding specific ions to brine on polymer viscosity and stability in oil recovery processes, particularly polymer flooding. The whole experimental part of this research was divided into three steps, which are rheology test, thermal stability test and oil displacement test. During the rheology test, the difference in viscosity values of polymer solutions prepared on different brine compositions was analyzed. On the thermal stability test, the effect of air and nitrogen injection, effect of additional ions on the ability of polymer to withstand the higher temperature for the long period between 14 and 60 days can be observed. Finally, oil displacement test was conducted, with the optimized brine composition for polymer preparation, to see how the optimization of brine composition improves the recovery. It was found that while calcium chloride (CaCl2) negatively affects polymer viscosity, sodium sulfate (Na2SO4) enhances it, especially in the presence of other ions, indicating that overall salinity is a crucial factor in polymer behavior. Notably, Na2SO4 protects polymers from oxygen-induced degradation, suggesting that oxygen removal, which requires additional facilities, might not be necessary. Long-term thermal stability tests showed that polymers with added Na2SO4 are more stable and less sensitive to oxygen presence. The optimal combination of 4 doses of Na2SO4 and 2 doses of CaCl2 was identified, leading to the most stable polymer with the highest viscosity and lowest degradation. This optimal solution demonstrated improved oil recovery in displacement tests, with 4.6% of additional recovery per each injected PV, compared to 2.9%/PV for the polymer solution prepared on standard CSW, although, total recovery factor at the end of polymer flooding stage was 90% of OOIP. It happens due to negatively charged sulfate ions reducing attraction between the polymer and formation rock walls, thus maintaining polymer structure stability. These findings highlight the potential of optimized ion concentrations in enhancing polymer flooding efficiency.