Energy-driven damage constitutive model of thermal insulation materials for deep rock in-situ temperature-preserved coring

Accurate evaluation of deep oil and gas reservoirs critically depends on key properties such as rock porosity and permeability, which are significantly affected by high-temperature conditions in deep formations. In-situ temperature-preserved coring (ITP-Coring) is a prerequisite for reliable assessment of deep rock properties, with thermal insulation materials serving as its key component. This study investigates the performance variation law and damage evolution characteristics of thermal insulation materials under high-temperature and high-pressure conditions. The findings show that at elevated temperatures, the material compressive strength decreases to one-fourth to one-fifth of its value at room temperature, while the peak compressive strain increases by two to three times. Furthermore, the energy evolution and damage characteristics of the hollow glass microsphere/epoxy thermal insulation materials (HGM/EP materials) during uniaxial compression were analyzed, and an energy-driven statistical damage constitutive model was established, which effectively predicts the stress–strain behaviour of HGM/EP materials after temperature-pressure preconditioning. The correlation between initial damage d and pretreatment temperature and pressure was also examined. It was found that when the pretreatment pressure is below 100 MPa, the threshold temperature at which initial damage sharply increases is 100 °C. An initial damage evolution model considering temperature and pressure effects was established, and the relationship between damage rate, temperature, pressure and initial damage was analysed. The research results provide a theoretical basis for the application of thermal insulation materials under extreme conditions in deep ITP-Coring operations.