Development and Evaluation of Salt-Tolerant Green Surfactant-Based Multifunctional Fracturing Fluids Prepared by Formation Brine

This study develops a salt-tolerant, green surfactant (VES)-based fracturing fluid that uses formation brine for unconventional reservoirs. Two erucic acid-derived VESs (EDPG and VES-BC) were evaluated under varying salinity conditions. Results showed excellent salt tolerance and viscoelasticity, with EDPG achieving viscosities of 236.17 mPa·s (in Xujiahe formation water) and 271.22 mPa·s (in Ordos Basin water), while VES-BC reached 296.56 mPa·s (in Ordos Basin water). Thermal stability tests confirmed that EDPG retained 30.17 mPa·s at 120°C, and VES-BC maintained 29.66 mPa·s at 140°C. The proppant settling velocity in VES fluids (3.9×10⁻³ mm/s at 30°C) was significantly lower than that in guar gum fluids. Breaking tests identified ethylene glycol butyl ether as the optimal breaker, achieving a 0.6 h breaking time, a 1.9 mPa·s viscosity, and a residue content of less than 6.5 mg/L. Core damage was less than 10%, far below guar gum's 23.5%. Additionally, the broken fluids enhanced oil recovery, with BCF-B1 achieving a 31.2% static imbibition replacement rate and a 14.6% incremental recovery in huff-puff tests. This eco-friendly fluid reduces freshwater use, offers low formation damage, and supports sustainable unconventional reservoir development.