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 ℃. An initial damage evolution model considering temperature and pressure effects was established, and the relationship between damage rate, temperature, pressure and initial damage was analyzed. The research results provide a theoretical basis for the application of thermal insulation materials under extreme conditions in deep ITP-Coring operations.

In order to help establish a new theory of deep rock mechanics and better guide the development of deep engineering, it is crucial to develop a deep in-situ condition-preserved coring device capable of obtaining cores while maintaining their original in-situ temperature and pressure conditions. To achieve insulation functionality within a compact design, a passive insulation system must be developed for such coring devices. Considering the size constraints and thermal insulation requirements, a passive thermal insulation system combining a vacuum layer and an insulating material layer has been designed in this work. Epoxy resin was selected as the insulation material due to its high compressive strength and low thermal conductivity. The type and dosage of curing agents, as well as the curing process with epoxy resin, were optimized. The ideal resin achieved a compressive strength of 241.03 MPa and a thermal conductivity as low as 0.25 W/m·K. Additionally, it exhibited excellent thermal stability and a high decomposition temperature. Under high-temperature and high-pressure water conditions simulating deep-earth environments, the epoxy resin’s maximum water absorption was below 0.7%. The insulation layer could effectively minimize heat exchange between the core and the external environment by up to 19.01%. These findings provide a significant contribution to the advancement of passive insulation systems for deep in-situ core drilling operations.

Deep rock in-situ temperature-preserved coring is important for the exploration and development of deep resources. In addition, understanding the temperature variation laws of the core during coring is fundamental to achieving temperature-preserved coring. In this study, under the coexistence of the core and strata water inside the coring tool, we explore the factors sensitive to the temperature variation of the core during coring and propose suggestions to reduce the unevenness of core temperature. The findings indicate that at a strata temperature of 150 ℃ and a core lifting speed of 2.5 m/s, during process of lifting the passively insulated core to the ground, natural convection occurs within the coring tool due to buoyancy, circulating in a counterclockwise direction. The temperature difference of the core in the axial and radial directions is 21 and 7.7 ℃, respectively, with temperature variation rates of 21 and 308 ℃/m per unit length, respectively. The greatest decrease in temperature is observed at the outer edge of the core bottom. The natural convection of strata water results in significant temperature differences along the axis of the core, exacerbating the unevenness of core temperature. To ensure uniform core temperature, efforts should be made to minimize the space between the core and the inner tube. In addition, the use of water-blocking mechanisms should be facilitated to reduce the ingress of strata water into the coring device. During the coring process, the frequency of active thermal insulation gradually increases as the ambient temperature decreases, thereby reducing the temperature difference between the inner and outer sides of the coring device to suppress the occurrence of natural convection. These research findings have practical implications for achieving deep rock in-situ temperature-preserved coring, providing theoretical and technical guidance for the development of deep resources such as coal, geothermal energy, and oil and gas.