Rheology and gelation kinetics of sulfonated polyacrylamide/Cr(III) acetate gels for water shut-off: effects of salinity, temperature, and shear.

Gel treatments are widely used as a conformance-control method to reduce excessive water production and improve sweep efficiency in oil reservoirs. Their field performance is strongly influenced by reservoir and operational conditions such as salinity, temperature, and pumping-induced shear. In this work, the gelation behavior of a sulfonated polyacrylamide/chromium(III) acetate (SPAM/Cr(III)) system was systematically investigated as a function of make-up water salinity, temperature, shear rate, and polymer/crosslinker concentrations. Steady-shear rheometry was employed to track viscosity evolution during gelation and to extract kinetic parameters, while yield-stress measurements were used to assess gelant injectivity and the mechanical integrity of the formed gels. Gelation-time results showed that increasing temperature accelerates gelation, and this effect becomes more pronounced at higher polymer and crosslinker concentrations. Shear history revealed a dual effect: raising shear rate initially enhanced gelation, but at higher shear levels gelation was hindered, mainly due to shear-induced degradation. Increasing Cr(III) acetate concentration up to 1500 ppm improved gel strength; however, further increase led to lower final viscosity and weaker gels. The apparent activation energy depended on salinity, decreasing from 113.72 kJ/mol in distilled water to 94.74 kJ/mol in seawater brine. Although the distilled-water gelant viscosity was ~ 17 times higher than that of the seawater gelant, the final gel viscosity in seawater was ~ 40 times larger than the gel formed in distilled water, consistent with yield-stress results showing substantially higher yield stress for the seawater-based gel. These findings provide practical insights for balancing injectivity and water shut-off performance of SPAM/Cr(III) gels under harsh brine conditions.