Deep mobile profile control agent for iron-containing reservoirs prior to salinity-based ternary flooding

To mitigate problems such as ​​injection water channeling, abrupt water breakthrough, rapid decline in oil production accompanied by an abrupt rise in water cut, and poor mobilization of matrix oil that commonly arise in low-permeability fractured reservoirs after conventional water flooding, many Chinese oilfields have implemented chemical profile modification. However, the produced water used to prepare these chemicals contains high concentrations of divalent metal cations especially Fe²⁺ which dramatically reduce the gel viscosity and thus degrade the conformance control performance. To address this issue, we developed a deep profile conformance control system tailored to the produced water from the Xingshugang block. We optimized both the type and concentration of each component in the formulation: a polymer concentration of 1000 mg/L TS1600; a chromium-based crosslinker at 130 mg/L; thiourea as an oxygen scavenger at 1000 mg/L; 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) as a metal ion chelating agent at 60 mg/L; and formaldehyde as a biocide at 100 mg/L. Laboratory tests demonstrated that, when prepared with produced water, the system forms a gel with a viscosity of 3704 mPa·s, achieves a plugging rate of 86.0%, and contributes to an enhanced oil recovery (EOR) of 17.82%. These results indicate that the proposed deep profile conformance control system exhibits excellent salt tolerance and enhanced profile modification performance in the presence of divalent metal ions.