Abstract:

The rheological properties of xanthan (XG) /guar gum (GG) mixed solutions and their borax-crosslinked systems were investigated at a total solution concentration of 2.00 g/L. The synergistic interaction viscosification efficiency between XG and GG as well as the influence of solution composition, pH, and electrolytes (NaCl and CaCl₂) on the rheological properties were discussed. Under the studied conditions, all solution systems including pure XG, pure GG, and mixed XG/GG solutions as well as their borax-crosslinked systems behave as pseudoplastic fluids, and the rheological curves can be described by the Herschel-Bulkley and Casson models. The mixing of XG and GG exhibits a significant “synergistic viscosification effect”. When the mass fraction of XG in the two polymers (w(XG)) is 20% and 90%, maximum values of the synergistic viscosification rate (R_m) are observed, which are 42% and 34%, respectively. The XG/GG mixed solutions can be crosslinked by borax, and the crosslinking effect is enhanced with a decrease in w(XG) or an increase in borax mass concentration (ρ(B)). At w(XG)=50% and ρ(B)=1.00 g/L, the crosslinking viscosification rate (R) is up to 85%. In the studied pH range (6.2~10.0), there is no obvious change in the rheological properties for XG/GG mixed solutions, while for the borax-crosslinked systems (w(XG)=50% and ρ(B)=0.75~1.00 g/L), the apparent viscosity initially increases and then decreases, showing a maximum value at pH=9.0, and the corresponding R is up to ~107%. The addition of electrolytes (NaCl and CaCl₂) leads to a significant decrease in the viscosity for the crosslinked XG/GG/B solution (w(XG)=10% and ρ(B)=0.50 g/L), and the influence of CaCl₂ is more obvious than that of NaCl. These results may deepen the understanding of rheological behavior of XG/GG mixed solutions and provide important information for their practical applications such as in the enhanced oil recovery.

Key words: xanthan gum, guar gum, borax, synergistic interaction, crosslinking, rheology, viscosity