Delayed crosslinking gel fracturing fluid with dually crosslinked polymer network for ultra-deep reservoir: Performance and delayed crosslinking mechanism

The gel with dually crosslinked polymer network (DPN) based on supramolecular interaction and chemical crosslinking usually has excellent temperature and shear resistance. The gel fracturing fluid with DPN will provide a new working fluid strategy for the efficient development of deep/ultra-deep oil and gas. Herein, a delayed crosslinking gel fracturing fluid with DPN is reported, which is formed by a supramolecular enhanced polymer containing catechol groups and a multisite organic zirconium delayed crosslinker. The gel breaker and cleanup additive are optimized, and the gel breaking liquid is uniform and had high surface/interface activity. The gel fracturing fluid has excellent delayed crosslinking ability, temperature resistance and shear resistance. It can be crosslinked to the hanging state within 233 s, and the residual viscosity is 71 mPa·s after shearing at 200 °C. The delayed crosslinking behavior and mechanism of gel fracturing fluid are further analyzed by viscoelastic rheological experiment and gelation kinetics calculation. Before reaching the temperature threshold of chemical crosslinking (70 °C), the system is dominated by supramolecular polymer network (SPN). After reaching 70 °C, the addition of chemical crosslinking makes SPN become DPN. The Avrami kinetic calculation results show that the gel growth mode at 70 °C changes from multi-dimensional diffusion growth to one-dimensional linear rapid growth. In addition, the final one-dimensional linear rapid growth stage of gelation is not controlled by temperature. The temperature mainly affected the multidimensional growth stage of gelation.