Pressure-regulated pore structure evolution and dielectric performance enhancement in MgO/epoxy composite systems

With the surging demand for unconventional oil and gas extraction, the insulation performance of downhole high-power electric heaters has become a critical bottleneck limiting long-term stable operation. The MgO/epoxy system is an ideal option for end-sealing materials, yet the mechanism underlying the formation of cascading discharge paths and the insulation failure threshold under extreme conditions, such as in enclosed environments and micrometer-scale gap arrays (<100 μm), remains unclear. Therefore, this study prepared MgO matrices at five pressure levels (30–70 MPa), quantitatively characterized the pore size distribution via FE-SEM, injected epoxy resin to fill pores under vacuum assistance, and established a 2D one-way coupled phase-field-electrostatic model based on the Carreau-Yasuda constitutive law. Results indicate that pressing pressure regulates pore geometric features through sliding, particle rearrangement, and interparticle mechanical interlocking, thereby influencing the infiltration paths and depth of epoxy resin. Additionally, through dielectric constant gradient effects and geometric smoothing, microscopic electric field distortion is effectively mitigated, significantly enhancing the dielectric breakdown characteristics of the composite system, providing a quantitative basis for optimizing the design of end-sealing materials for high-power electric heaters.