摘要
The failure of traditional acid systems to retard reaction rates has posed challenges for acid fracturing in ultra-deep carbonate reservoirs. Microencapsulated acid can address the retardation issue by targeting release at distal fractures, but existing formulations lack sufficient pressure resistance to meet operational demands, and their controlled-release mechanisms in complex environments remain unclear. This study employed emulsion polymerization to prepare high-temperature and high-pressure resistant microencapsulated acid, incorporating benzene rings via the addition reaction of N -hydroxymethyl acrylamide with isocyanate monomers containing aromatic rings to enhance thermal and pressure resistance. Trimethylolpropane tri-acrylate was used as a trifunctional crosslinker to simultaneously improve thermal stability. The effects of varying benzene ring content on the microcapsules' morphology, thermal resistance, pressure tolerance, load rate, and shear resistance were investigated, leading to the optimal product MA-TDI-2. It exhibited the highest sphericity and smoothness, with a thermal resistance of 199.4 °C, pressure resistance of 69 MPa, and shear tolerance of 170 s −1 . These properties ensure targeted release in distal fractures, occurring only at 180–200 °C and 55.2–69 MPa. Post-release, the point etching exhibited greater non-uniformity compared to the planar etching of gelled acid. Finally, the hierarchical influence of environmental factors on controlled release was determined as pressure > temperature > salinity, where high pressure directly crushes the shell to promote release, high temperature softens and enlarges shell pores to accelerate release, and high salinity causes shell shrinkage to inhibit release. The developed product and elucidated release mechanisms can advance the application of microencapsulated acid in ultra-deep acid fracturing.
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