The in-situ temperature preservation coring of deep rocks is crucial for studying the physical properties of cores under temperature and pressure sensitivity and for assessing resource reserves. Existing core sampling strategies in this field rarely consider temperature preservation, with most employing passive insulation structures based on vacuum technology. In this context, the main challenge is that current insulation technologies and methods cannot meet the requirements of extreme deep environments, necessitating innovative designs of deep in-situ insulation coring systems. The insulation system proposed in this paper integrates three subsystems, active insulation, passive insulation, and control system. The analytic hierarchy process is used to perform parametric analysis on the design of these subsystems. By combining heat transfer theory analysis with laboratory pre-research experiments, the evaluation index parameters in the analytic hierarchy process method are quantitatively assigned. This approach further integrates the experience and knowledge of engineering designers to obtain a comprehensive evaluation table of the design parameters. On the basis of the permutation and combination mathematical method, a full matrix set of all feasible conceptual design schemes is established, or the optimal solution is sought through scheme integration, coupling, decoupling, and optimization. The analytic hierarchy process analysis method, which combines theory and pre-experiments, provides a set of parametric analysis methods for conceptual design schemes of insulation coring systems. Furthermore, the optimization of conceptual design schemes through full matrix scheme combinations offers guidance for future data-driven optimization of multi-subsystem conceptual schemes.

Shallow resources are becoming increasingly depleted, deep resource exploration has become a global strategy. The design and testing of deep in-situ core samples are prerequisites for exploring deep resources; however, no in-situ condition-preserved coring and testing techniques and tools have been reported yet. Here, the first deep in-situ condition-preserved coring system (with the preservation of pressure, temperature, substance, light, and moisture) was developed that considers the effects of high water pressure and formation dynamic loads, along with an in-situ condition-preserved testing system. A pressure-preserved controller was designed, achieving the ultimate capacity of 140 MPa and 150 ℃. A temperature-preserved coring system combining active heating and passive insulation was constructed, realizing temperature preservation from room temperature to 150 ℃. Three generations of film-formation principles and methods were designed, achieving an excellent quality preserved rate, moisture preserved rate, and visible light barrier rate. Moreover, a deep in-situ condition-preserved coring system, and a simulated coring platform for large cores under in-situ environments was fabricated. A non-contact testing system was derived to cut and prepare specimens under in-situ environment and to perform non-contact non-destructive testing and true triaxial testing. The research findings can be successfully applied to deep coal and gas development, deep oil and gas resources assessment, and deep-sea sediment prospecting, achieving excellent application outcomes. This study provides important theoretical, technical and hardware support for deep in-situ rock physics and mechanics research and deep resource exploitation.

Deep oil and gas reservoirs are under high-temperature conditions, but traditional coring methods do not consider temperature-preserved measures and ignore the influence of temperature on rock porosity and permeability, resulting in distorted resource assessments. The development of in situ temperature-preserved coring (ITP-Coring) technology for deep reservoir rock is urgent, and thermal insulation materials are key. Therefore, hollow glass microsphere/epoxy resin thermal insulation materials (HGM/EP materials) were proposed as thermal insulation materials. The materials properties under coupled high-temperature and high-pressure (HTHP) conditions were tested. The results indicated that high pressures led to HGM destruction and that the materials water absorption significantly increased; additionally, increasing temperature accelerated the process. High temperatures directly caused the thermal conductivity of the materials to increase; additionally, the thermal conduction and convection of water caused by high pressures led to an exponential increase in the thermal conductivity. High temperatures weakened the matrix, and high pressures destroyed the HGM, which resulted in a decrease in the tensile mechanical properties of the materials. The materials entered the high elastic state at 150 °C, and the mechanical properties were weakened more obviously, while the pressure led to a significant effect when the water absorption was above 10%. Meanwhile, the tensile strength/strain were 13.62 MPa/1.3% and 6.09 MPa/0.86% at 100 °C and 100 MPa, respectively, which meet the application requirements of the self-designed coring device. Finally, K46-f40 and K46-f50 HGM/EP materials were proven to be suitable for ITP-Coring under coupled conditions below 100 °C and 100 MPa. To further improve the materials properties, the interface layer and EP matrix should be optimized. The results can provide references for the optimization and engineering application of materials and thus technical support for deep oil and gas resource development.

In-situ pressure-preserved coring (IPP-Coring) is considered to be the most reliable and efficient method for the identification of the scale of oil and gas resources. During IPP-Coring, because the rotation behavior of the pressure controller valve cover in different medium environments is unclear, interference between the valve cover and inner pipe may occur and negatively affect the IPP-Coring success rate. To address this issue, we conducted a series of indoor experiments employing a high-speed camera to gain greater insights into the valve cover rotation behavior in different medium environments, e.g., air, water, and simulated drilling fluids. The results indicated that the variation in the valve cover rotation angle in the air and fluid environments can be described by a one-phase exponential decay function with a constant time parameter and by biphasic dose response function, respectively. The rotation behavior in the fluid environments exhibited distinct elastic and gravitational acceleration zones. In the fluid environments, the density clearly impacted the valve cover closing time and rotation behavior, whereas the effect of viscosity was very slight. This can be attributed to the negligible influence of the fluid viscosity on the drag coefficient found in this study; meanwhile, the density can increase the buoyancy and the time period during which the valve cover experienced a high drag coefficient. Considering these results, control schemes for the valve cover rotation behavior during IPP-Coring were proposed for different layers and geological conditions in which the different drilling fluids should be used, e.g., the use of a high-density valve cover in high-pore pressure layers.