Preparation and characterization of in situ cured vegetable-based resin plugging agent for fracture plugging in reservoirs

Epoxy resin has been mainly used as a monomer to construct an in situ curing plugging agent in casing leakage treatment, but epoxy resin is expensive. In this study, epoxidized vegetable oil (EVO) was prepared by the modification of a soybean oil sediment (VO). A new type of high-value-added in situ curing plant-based resin plugging agent (BEVO) was successfully prepared by modifying EVO and methylhexahydrophthalic anhydride (MHHPA) with bisphenol A benzoxazine (BZ). The blending properties, curing time, curing strength, thermal stability, thermomechanical properties, rheology, and plugging performance were statistically evaluated. The experimental results showed that MHHPA and BZ with EVO build double-crosslinked structures of polyester and polyether, respectively, in the EVO/MHHPA/BZ reaction system. Curing times in the range of 120–720 min can be controlled by adjusting the amount of accelerator from 0–4 wt. %. Both elevated temperatures and increased shear rates were effective in reducing the viscosity of the BEVO reaction solution, and the monomer structure of the BEVO reaction solution was not broken over the range of shear rates from 0.1 to 100 s−1. BEVO reaction solutions with 10–20 wt. % BZ content have excellent pumpability, and a viscosity time below 100 mPa·s for more than 60 min on the viscosity–temperature curve. Meanwhile, it exhibited excellent injection and plugging performances. When the pumping rate is 8 ml/min, the pumping pressure is 0.16 and 0.4 MPa, and the breakthrough plugging pressure is more than 32.5 MPa and the stable plugging pressure is more than 18.9 MPa for the 0.5 mm steel fracture cores.