Preparation and evaluation of an ultra-high temperature resistant zwitterionic polymer viscosity reducer

In this study, a new zwitterionic polymer viscosity reducer (HP-THIN) was designed to address the issue of viscosity increases in high-temperature and high-density water-based drilling fluids. HP-THIN is specifically formulated for ultra-high temperatures and optimized using the viscosity reduction index before and after thermal aging. The molecular structure, thermal stability, and viscosity-average molecular weight of HP-THIN were characterized using FTIR, TGA, and rheometric analysis using a Ubbelohde viscometer. The viscosity-reducing performance of HP-THIN was evaluated in various types of drilling fluid-based slurries at 220 °C, including fresh-water slurry, brine slurry, calcium-containing slurry, and high-density composite brine slurry. Furthermore, HP-THIN was compared to commercial viscosity reducers such as Polythin and xy-27. At optimal dosage of 0.3 wt.% at 220 °C, HP-THIN demonstrated excellent viscosity reduction rates of 86%, 72%, 73%, and 51% in fresh-water slurry, brine slurry, calcium-containing slurry, and high-density composite brine slurry, respectively. HP-THIN exhibited superior viscosity reduction index in all drilling fluid slurries, compared to Polythin exhibiting reduction index of 86%, 64%, 30% and -17.8% while xy-27 achieved reduction rates of 83.3%, 56%, 55% and 37.8%. The excellent viscosity reduction performance of HP-THIN makes it a promising candidate for practical applications in the oil and gas industry.