Influence factors of apparent viscosity and molecular chain failure mechanism of polyacrylamide solution used in drilling and production

Key words:  working fluid for drilling and production  hydrolyzed polyacrylamide  apparent viscosity  metal ions  molecular chain degradation

Abstract:

The effects of several conventional ions (Na⁺、K⁺、Ca²⁺、Mg²⁺、Fe²⁺、Fe³⁺、S2-and dissolved oxygen) on the viscosity of polyacrylamide were studied, and the damage mechanism of polyacrylamide molecular chain was investigated. The results show that the above ions can reduce the viscosity of polyacrylamide aqueous solution. Divalent ions cause intramolecular polycondensation of the polymer, resulting in molecular chain shrinkage, so the influence degree is stronger than that of monovalent ions. Among them, Fe²⁺ and S2- present the most significant effect on the viscosity of the solution. S2-lead to the fracture of HPAM skeleton mainly through oxidative degradation mechanism, resulting in a significant decrease in the viscosity of HPAM solution. Ca²⁺/Mg²⁺ and Fe²⁺ show similar influence on the viscosity of the polymer gel. The divalent ions cause the intramolecular polycondensation of the polymer, the molecular chain shrinkage, and the viscosity of the polymer decreases. Fe³⁺ is mainly combined with carboxylic acid groups on the molecular chain of polyacrylamide, and it is difficult to ionize again. Macromolecular chains begin to aggregate, cross-linking flocculation reaction occurs between molecules, and the viscosity of polymer solution decreases.