Low-Substitution Glycerol Etherification of Guar Gum for Reduced-Residue Fracturing Fluids

Reducing water-insoluble residues while maintaining sufficient rheological performance remains a key challenge for guar gum-based fracturing fluid thickeners. Natural guar gum (GG) is widely used in fracturing fluids, but its relatively high content of water-insoluble residues can impair permeability and reduce fracture conductivity. In this study, GG was modified by low-substitution etherification using a glycerol ether-based modifier (GMH-1) under mild alkaline reaction conditions to develop a reduced-residue thickener for fracturing fluid applications. The modification conditions were optimized through an L9 orthogonal design combined with single-factor analysis. Under the optimal conditions of 35 °C, 2.0 h, 2.0 wt % NaOH, and 0.2 wt % GMH-1, the modified product (GMGG) exhibited an apparent viscosity of 125.3 mPa·s and a water-insoluble residue content of 5.1% in a 0.6 wt % aqueous solution; in comparison, GG showed a viscosity of 89.3 mPa·s and a residue content of 12.4%. FTIR, UV-Vis spectroscopy, and elemental analysis provided indirect but consistent evidence for low-substitution chemical modification and the introduction of oxygen-containing hydrophilic groups while largely preserving the polysaccharide backbone. GMGG also showed improved rheological and thermal response behavior, suggesting that low-substitution glycerol etherification may provide a feasible route to balance residue reduction and viscosity enhancement. These results indicate the potential of this strategy for designing reduced-residue guar-based thickeners for fracturing fluids, while further molecular-level characterization is still required to determine the exact substitution pattern and mechanism.