Supramolecular Polymer-Based Delayed Crosslinking Weighted Fracturing Fluid with a Double Network for Ultra-Deep Reservoirs

Hydraulic fracturing in ultra-deep reservoirs faces significant challenges, including high wellbore friction and inadequate thermal stability of conventional fracturing fluids. To address these issues, we developed a potassium formate-weighted fracturing fluid with delayed crosslinking, excellent friction reduction, and superior temperature resistance, using a hydrophobic associating polymer thickener and a multi-ligand organic zirconium crosslinker. The weighted fracturing fluid has a density of 1.4 g/cm3 and completes crosslinking within 300 s at 90 °C. It achieves a maximum friction reduction rate of 63.2%. Below 60 °C, the system relies on a supramolecular thickener network for low viscosity and friction reduction; above 60 °C, chemical crosslinking between the thickener and zirconium ions creates a dual-network structure that significantly enhances temperature and shear resistance. After 120 min of shearing at 200 °C and 170 s−1, the retained viscosity reaches 75.3 mPa·s. Complete gel breaking is achieved by sodium bromate via an oxidation reaction. This dual-network delayed crosslinking system successfully reconciles the conflict between low wellbore friction and high-temperature proppant-carrying capacity. This work presents a superior weighted fracturing fluid for ultra-deep reservoirs, as well as an innovative technique for their development.