Preparation and Rheological Behavior of Temperature-Resistant Hydroxypropyl Guar Gum Supramolecular Hydrogels Based on Dynamic Borate Ester Bonds

The increasing depth of oil wells and associated elevated formation temperatures pose significant challenges to conventional crosslinked polymer gels used in hydraulic fracturing, as viscosity degradation severely impairs proppant transport and stimulation efficiency. In this study, a thermally stable organic boron crosslinker was developed and evaluated in combination with hydroxypropyl guar gum (HPG). The rheological performance of the crosslinked gel system was systematically investigated under high-temperature shearing conditions. At a guar gum concentration of 0.5 wt% and a crosslinker-to-gum ratio of 100:0.5, the system maintains a viscosity of 500 mPa·s at 120 °C and 170 s−1, and the viscosity remains above 300 mPa·s after 60 min of continuous shearing, demonstrating outstanding thermal resistance. (For 0.3 wt% HPG, the optimal crosslinking ratio is 100:0.3; for 0.5 wt% HPG, the optimal ratio is 100:0.5). This gel formulation achieves efficient proppant transport with minimal additives. It maintains static proppant suspension for up to 48 h. After breaking, the fluid viscosity drops to approximately 5 mPa·s. With the addition of a flowback aid, surface tension can be reduced to as low as 16.29 mN/m, while the formation matrix permeability damage rate is limited to only 20.76%. Additionally, the gel features rapid breaking and low residue generation, making it highly suitable for high-temperature fracturing operations.