Development and performance evaluation of high-temperature resistant and acidic-crosslinking weighted fracturing fluid

Aiming at the problems of deep burial, high formation pressure and difficult fracturing stimulation of high-temperature deep oil and gas reservoirs, research on high-temperature resistant weighted fracturing fluid was carried out. A polymer thickener TS-700, which is resistant to high temperature and salt, and organozirconium crosslinker OZ-60, which is suitable for acid crosslinking, were independently synthesized in the laboratory, and the additive dosage was optimized to form an acidic-crosslinking fluid system with a temperature resistance of 180 ℃. The viscosity, drag reduction and delayed crosslinking of the weighted fracturing fluid were studied, and the temperature and shear resistance, sand carrying, gel-breaking, core damage and string corrosion ability were systematically evaluated. The experimental results show that the novel fluid system can be crosslinked under acidic conditions, and the crosslinking time can be controlled within 3~12 min by adjusting the dosage of crosslinker and the pH value. High temperature is conducive to the improvement of viscosity, while the addition of salt will reduce the viscosity of the base fluid. The retention viscosity of the weighted fracturing fluid formula with a density of 1.20 g/cm³ is still greater than 70 mPa·s after shearing for 120 min at 180 ℃. Weighting agent can reduce the drag reduction performance of fracturing fluid to a certain extent, but under different thickener dosages, the drag reduction rate of the weighted fracturing fluid can still reach more than 68%, which meets the requirement of effectively reducing the friction loss in long wellbores. The crosslinked fracturing fluid showed excellent sand suspension at room temperature and 100 ℃, with low proppant settling rate. The results of gel-breaking and core damage show that the crosslinked system can achieve complete gel breaking at 0.03% of the dosage of breaker, and the damage rate of gel-breaking liquid to the tight core is only 19.4%. The high-temperature and high-pressure dynamic corrosion test results show that the fully formulated fracturing fluid has a low corrosion rate on N80 and 13Cr steel, which can ensure the safety of the fracturing string in the field.