Viscosity Loss of Partially Hydrolyzed Polyacrylamide Solution Caused by Sulfide Ion

The viscosity of hydrolyzed polyacrylamide (HPAM) solution plays an important role in its sweep efficiency. However, it has been noticed that sulfide ions contained in produced water can cause viscosity loss dramatically. Scanning electron microscopy (SEM), GPC-refractive index detection, the quantum chemistry calculation and molecular dynamics simulation were conducted to reveal the mechanism better. The results show that the viscosity loss of 2000 mg/L polymer solution was above 80% when the sulfide ion was over 7 mg/L. Sulfide ions can destroy the network structure of HPAM, decrease average molecular weight and mean square radius of gyration, and widen the molecular weight distribution. The quantum chemistry calculation and molecular dynamics simulation showed that the main reason for HPAM viscosity loss was the cleavage of the main carbon chain backbone, and the coil and shrinkage of HPAM chain was the secondary reason. These results help understand the mechanism of HPAM solution viscosity loss to a certain degree.