Rheological Characteristics of Sulphonated Polyacrylamide/Chromium Triacetate Hydrogels Designed forWater Shut-off

Injecting a gelation system of a polymer and a cross-linker among available methodsto reduce water in petroleum industry is widely used. In this work, a hydrogel wasprepared by cross-linking of an aqueous solution of chromium acetate (III) and thecopolymer of 2-acrylamido-2-methyl-propanesulphonic-acid sodium salt (AMPS) andacrylamide (PAMPS). The phase diagram of bottle tests showed that the minimumconcentration of copolymer for gel formation is 5500 ppm (0.55 wt%). The study ofviscoelastic behaviour of hydrogels using dynamic rheometry showed that the storagemodulus of the hydrogels increased with increased copolymer concentration andcross-linker/copolymer ratio. At low concentrations of copolymer (5500 and 7500 ppm(0.75 wt%)) there would be no effects on the elastic modulus by increasing thecross-linker/copolymer ratio. Therefore, the effect of copolymer and cross-linker concentrations on the apparent plastic viscosity (ηpl) of the gel was investigated.Increasing the solvent ionic power led to decrease in latent gel strength, in which theeffect of divalent ions is higher than monovalent ions. A numerical codification for gelstrength magnitude is suggested in the range of 10-200 1/s shear rate by usingviscometric and bottle test results. The results show that a gel with copolymer concentration of 9500 ppm (0.95 wt%) and cross-linker/copolymer ratio of 1/5 is a suitable gel in terms of gel strength and gelation time.