Epoxy resin/thermally expandable microsphere composite insulation materials for deep rock in situ temperature-preserved coring: Thermal and mechanical performance study

Deep oil and gas reservoirs are typically characterized by high-temperature and high-pressure (HTHP) conditions, under which conventional coring techniques fail to preserve the in situ temperature of rock cores, thereby hindering the accurate evaluation and efficient exploitation of deep reservoirs. To address this challenge, a composite insulation system based on high-strength epoxy resin (EP) and thermally expandable microspheres (TEMs) was developed to reduce the thermal conductivity of the material. By coupling the curing process of the epoxy resin with the thermal expansion of the microspheres, the effects of foaming temperature and microsphere content on the thermal conductivity and compressive strength of the composites were systematically investigated. Composite samples with thermal conductivities of 0.085–0.205 W/(m K) and compressive strengths of 17.2–206.3 MPa were successfully fabricated. The composites retained their structural integrity under simulated high-temperature and high-pressure conditions, whereas high-pressure water infiltration increased thermal conductivity and decreased compressive strength. Numerical simulations further indicate that the optimized insulation formulation, PG13-T90, reduces core heat exchange by 84.4% under 100 MPa and 100 °C, thereby markedly enhancing the thermal preservation efficiency and reliability of in situ temperature-preserved coring (ITP-Coring) and providing essential technical support for deep hydrocarbon resource development.