(563e) Experimental and Theoretical Study of Viscosity Behavior of Sulfonated Partially Hydrolyzed Polyacrylamides (S-HPAM) with Long-Term Thermal Stability

With the application of polymer flooding in enhanced oil recovery, great efforts have been made in improving polyacrylamide performance with high temperature and high salinity. Here in this paper, our effort is focused on developing a novel HPAM copolymers with long term thermal stability and theoretical simulations were done to investigate the mechanism of its viscosity behavior.

By aqueous solution polymerization, temperature and salt-resistant groups were introduced into the traditional HPAM structures and a modified high temperature-resistant sulfonated polyacrylamide (termed as S-HPAM) was developed. The viscosity behavior was studied with respect to temperature, salinity, rejection rate and aging with time. Besides, molecular dynamics (MD) simulations using Gromacs software were performed to study the influence of temperature and inorganic salts on the viscosity behavior of the designed S-HPAM in solution at the atomic and molecular level.

The designed S-HPAM exhibited a relatively high temperature and salt tolerance. Aged at 95℃ in oilfield water for 180 days, the viscosity retention rate of S-HPAM demonstrated excellent thermal stability with a slight decrease in viscosity, which meant great potential in long-term thermal stability. Besides, S-HPAM showed better shear-resistant property, as the injection rate increased to 600 mL/h, higher viscosity retention rate were observed. MD simulation results indicated that the introduced temperature and salt-resistant groups brought changes of the charged groups, flexibility and intermolecular non-bonded interaction, which endowed S-HPAM with long-term thermal stability. The improved temperature resistance performance may be contributed to three factors. First, the introduced sulfonic acid group weaken the electrostatic shielding effect of salt ions on molecular chains. Second, the large side chains introduced increase the shear resistance, and the steric hindrance of side chains enhanced the hydrolysis resistance of adjacent amino groups. Furthermore, a higher non-bond interaction energy of S-HPAM lead to stronger resistance to temperature and salt ions.

The modified S-HPAM exhibited improved stability under high temperature and salinity environment and its long-term thermal stability showed great potential in the application of polymer flooding. Besides, MD simulations suggested an effective way to improve temperature resistance by tuning charged groups, side chains and non-bond interaction of polymers.