To establish in-situ fluidized coal mining technology and a theory of mining mechanics for deep coal resources, it is crucial to obtain a fidelity rock core that maintains deep in-situ conditions to understand the physical mechanics of deep rock. Doing so requires the development of in-situ condition-preserved coring (ICP-coring) technology. In this work, hollow glass microsphere/epoxy resin (HGM/EP) composite insulation materials with high strengths were prepared. An epoxy resin matrix with high strength and high-temperature resistance was selected from among epoxy resins cured by different curing agents. Then, a series of composite insulation materials with different HGM volume fractions were prepared. The mechanical strengths of the composites decreased with increasing HGM volume fraction. Then, thermal insulation materials suitable for different ICP-coring depths were selected. Changes in the thermal conductivities and mechanical strengths of the composites were characterized after they were subjected to high water pressure (45MPa). Verification of the applicability of the thermal insulation material under high water pressure (45MPa) conditions demonstrated that it met the working requirements for the ICP-coring device.

Intelligent drilling technologies, such as downhole signal and power transmission, can be used to measure key downhole data and obtain thermal insulation cores. This technology is of great significance for the accurate assessment of deep oil and gas resources, the reconstruction of oil and gas resource extraction systems, and the realization of efficient, intelligent and safe resource extraction. In order to meet the needs of underground communication and power supply for active thermal insulation coring, a new type of conductive center pole was innovatively designed. Using the theory of innovation problem solving (TRIZ) and axiomatic design (AD) to analyze the functional requirements of the conductive central pole, establish and solve the original design matrix. Based on the axiomatic design theory, the non-coupling matrix is decoupled by using the TRIZ solving tool, and the key indicators of the design scheme that meet the independent axiom are evaluated. In view of the contradictions and conflicts, the TRIZ solution tool was continually used to solve, optimize and obtain a design scheme with a higher comprehensive evaluation. Thus, the self-adaptive non-winding connection and power conduction of the conductive center pole was realized. Finally, the strength of the newly designed center pole was checked, and a physical prototype was made. Pre-research experiments on its conductivity and electrothermal conversion efficiency were carried out under different simulation environments to verify its conductivity. It provides innovative solutions to related problems in the field of deep insulation coring and intelligent drilling and provides effective technical means for related needs.

Analysis of core temperature variation and its influencing factors in deep rock in-situ temperature-preserved coring

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. Document Type: Original article Cited as: Yang, J., Bai, H., He, Z., Yu, B., Xie, H. Design of passive insulation system and optimization of thermal insulation material for deep in-situ condition-preserved coring. Advances in Geo-Energy Research, 2025, 15(2): 99-111. https://doi.org/10.46690/ager.2025.02.03 References D’Almeida, J., Monteiro, S. The effect of the resin/hardener ratio on the compressive behavior of an epoxy system. Polymer Testing, 1996, 15(4): 329-339. Du, U. L. 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In the extreme high-temperature (up to 150 °C) and high-pressure (up to 140 MPa) conditions of deep in situ condition-preserved coring devices, high-strength epoxy resin was selected as the insulation layer. The non-isothermal DSC method was employed at heating rates of 2.5, 5, 10, 15, and 20 °C/min, revealing that increasing the heating rate elevates curing temperatures, expands the curing range, and enhances curing rate and heat release. The curing kinetics were modeled using n-order and autocatalytic approaches, with the latter accurately describing the behavior. Optimized integration process conditions (80 °C/4 h + 150 °C/2 h + 180 °C/3 h) yielded epoxy with compressive strength of 204.47 MPa, initial thermal decomposition temperature of 345.9 °C, thermal conductivity of 0.246 W/m·K, and T_g of 193.04 °C (storage modulus 2.41 GPa at 150 °C). As insulation, it reduces rock core heat loss by 32.38% (8.78 × 10⁴ J) and active heating demand by 44 W, enhancing system stability for in situ temperature preservation.