Preparation and Performance Evaluation of Weighted Gel Fracturing Fluid with Delayed Cross-Linking Property for Ultradeep Reservoir

Weighted gel fracturing fluid has been recognized as a crucial technology to address the challenges of abnormally high pressure and ultrahigh temperature reservoir stimulation in the deep oil and gas exploration and development process. Herein, a NaBr weighted gel fracturing fluid with delayed cross-linking properties and good temperature resistance is developed by selecting the type of weighting materials and optimizing the concentration of the fracturing fluid main agents. The results indicated that the density of the weighted gel fracturing fluid is up to 1.372 g/cm3. When both thickener and cross-linking agent concentrations reach 0.8 wt %, the fracturing fluid can meet the temperature and shear resistance requirements at 200 °C and 100 s–1. More importantly, the weighted gel exhibits significant delayed cross-linking properties, and the cross-linking is complete within 266 s. Through the multicycle strain oscillation scanning test, steady shear test, and microscopic characterization, it was confirmed that the weighted gel has exceptional self-healing properties from the macroscopic properties and microstructure, and a dense cross-linking network structure exists. In addition, the gel breaking effect of different gel breakers on the weighted gel fracturing fluid is discussed. The ammonium persulfate breaker with strong oxidation can effectively damage the weighted gel. We expect that this study can provide new ideas for the application of weighted gel fracturing fluid in abnormally high pressure and ultrahigh temperature reservoirs and provide a theoretical basis for field practice.