Abstract: Considering the problem that reducing substances cause serious viscosity loss of hydrolytic polyacrylamide (HPAM) solution used as oil displacement agent in crude oil field,the effects of Fe²⁺ and Fe³⁺ on the zero shear viscosity,dynamic viscoelasticity and rheological performance under instant extension were qualitatively and quantitatively analyzed with laboratory physical simulation method;then the mechanism for the effect of two kinds of iron ion on the viscosity of HPAM solution was examined.Results showed that the presence of Fe²⁺ in the solution mainly causes the break of the molecular chain of HPAM via redox reaction and chemical behavior of hydrolysis,which results in significant decline of viscosity and rheological performance of the HPAM solution.Meanwhile,the presence of Fe²⁺ in the HPAM solution not only causes the elastic modulus and loss modulus both fall sharply;but also reduces the filament diameter of HPAM solution and accelerates the break of the filament.Finally,degree of entanglement between polymer molecules reduces,and the molecules become easy to flow.Effect of Fe³⁺ on the rheological performance of HPAM solution is rather small,and its main functions are flocculation and precipitation of HPAM.

Key words: hydrolytic polyacrylamide, viscosity, viscoelasticity, rheological performance