Performance characteristics of partially hydrolyzed polyacrylamide (HPAM) and crosslinked
polymer (CLP, Cr³⁺ as the cross linker) solutions have been investigated. A Brookfield viscometer,
rheometer, dynamic light scattering system, and core flow device have been used to measure the
viscosity, viscoelasticity, polymer coil dimensions, molecular configuration, flow characteristics, and
profile modification. The results show that, under conditions of high salinity and low HPAM and Cr³⁺
concentrations, cross-linking mainly occurred between different chains of the same HPAM molecule
in the presence of Cr³⁺, and a cross-linked polymer (CLP) system with a local network structure was
formed. Compared with an HPAM solution of the same concentration, the apparent viscosity of the
CLP solution increased slightly or remained almost unchanged, but its viscoelasticity (namely storage
modulus, loss modulus, and first normal stress difference) increased, and the resistance coefficient and
residual resistance coefficient increased significantly. This indicates that the CLP solution exhibits a
strong capability to divert the sequentially injected polymer flood from high-permeability zones to lowpermeability
zones in a reservoir. Under the same HPAM concentration conditions, the dimensions of
polymer coils in the CLP solution increased slightly compared with the dimensions of polymer coils in
HPAM solution, which were smaller than the rock pores, indicating that the cross-linked polymer solution
was well adapted to reservoir rocks. Core flood experiments show that at the same cost of reagent, the oil
recovery by CLP injection (HPAM-1, Cr³⁺ as the cross linker) is 3.1% to 5.2% higher than that by HPAM-
2 injection.