Comparative Study on Enhancing Oil Recovery under High Temperature and High Salinity: Polysaccharides Versus Synthetic Polymer.

The synthetic water-soluble polymer, partially hydrolyzed polyacrylamide (HPAM), has been most widely used for enhanced oil recovery (EOR); however, its poor thermal stability and weak salt tolerance impede further application in high-temperature and high-salinity oil reservoirs. To address such deficiencies, three polysaccharides, xanthan gum, diutan gum, and scleroglucan, were examined in comparison with HPAM on rheological behaviors, shearing resistance, long-term thermal stability, and core flooding test. It was found that all of these three polysaccharides were less sensitive to salinity and shearing time, while HPAM showed a monotonous decrease in viscosity with increasing monovalent cations and shearing history. After 90 days of aging at 85 °C and 10.1 × 104 mg·L-1 of total dissolved solids with 1.0 × 103 mg·L-1 of Ca2+, the viscosity of diutan gum and scleroglucan solutions nearly remained unchanged; on the contrary, the viscosity of xanthan gum and HPAM solutions drops massively. Core flooding tests at 85 °C with the same initial viscosity demonstrated that all polymers showed good transportation in porous media, and 16, 13, and 11% of oil recovery were obtained by diutan gum, scleroglucan, and xanthan gum, respectively, while only 10% was obtained from HPAM. These comparative results may underpin the potential of diutan gum and scleroglucan to be used in the EOR process in HTHS oil reservoirs.