Accurately evaluating the quality and scale of deep oil and gas reservoirs is the key to effectively exploring and developing deep oil and gas resources. Changes in temperature and pressure can cause significant variations in key reservoir quality parameters, such as porosity, permeability, and saturation, leading to distortions in oil and gas reserve assessments. To addresses the technical bottleneck of the existing pressure-preserved coring systems, which has a pressure-preserved capacity not exceed 70 MPa due to the limitations of small coring space, a complex coring environment, significant disturbance during the coring process, and the difficulty in controlling coring operations, a self-sealing control principle and method for pressure-preserved coring was proposed. The sealing structural parameters of the pressure-preserved controller (PPC) under high temperature (150 ℃) were optimized through experiments and numerical simulations, the sealing failure mechanism was thoroughly revealed, and the pressure-preserved capacity of the PPC under high temperature was enhanced from 100 to 140 MPa. In addition, to achieve the temperature preservation of the core in the deep oil and gas environment, a temperature preservation system combining active and passive temperature preservation was designed and integrated into the deep oil and gas in-situ temperature pressure preserved (ITPP) coring system. Finally, the coring function and temperature pressure preserved capacity of the ITPP coring system were verified through field and laboratory tests. The results show that the developed ITPP coring system can successfully achieve the temperature pressure preserved function, and can sample oil and gas-bearing core samples with a diameter of 50 mm and a maximum length of 1000 mm from wells up to 5000 m. This study addresses the urgent need for reliable and effective pressure-preservation in deep oil and gas exploration.

The pressure relief check valve plays a pivotal role in determining the oil and gas content during deep in-situ pressure-preserved coring. Prolonged exposure to high-pressure, high-solid-content fluids in deep wells can lead to mechanical erosion of the check valve, potentially causing severe failure and a loss of sealing integrity. To withstand the typical flow conditions in shale gas wells and on the basis of an in-depth understanding of deep fluid dynamics, a check valve was designed to operate at 70 MPa pressure and relieve pressure after coring. To mitigate erosion, a coupled Computational Fluid Dynamics-Discrete Element Method model was applied to simulate fluid flow dynamics and identify regions susceptible to erosion and wear in the valve body. The findings confirmed that the proposed check valve design meets the requirements for shale gas pressure-preserved coring and testing, with erosion mainly occurring in the constricted regions of the flow path. The erosion depth was found to increase with higher inlet flow rate and mass flow rates, demonstrating a sixfold increase as the inlet flow rate rises from 10 to 30 m/s. Non-spherical particles caused significantly more erosion than spherical ones, while the erosion depth decreased with larger particle sizes, showing a 33% reduction as particle size increased from 0.02 to 0.14 mm. To avoid sealing failures caused by prolonged erosion, the constricted flow channel was redesigned to accommodate an arc-shaped structure and appropriately widened. Simulations indicated that this structure can reduce peak pressure to 69% of the original value and minimize wall impacts. The maximum erosion depth decreased by 10%, indicating the improved durability and sealing of the redesigned check valve. These results underscore the enhanced check valve’s superior erosion resistance and sealing performance, highlighting its potential for future shale gas collection and testing and providing an effective strategy to enhance the reliability and longevity of check valves.

Pressure-preserved coring is an effective means to develop deep resources. However, due to the complexity of existing pressure-preserved technology, the average success rate of pressure-preserved coring is low. In response, a novel in situ magnetically controlled self-sealing pressure-preserved coring technology for deep reserves has been proposed and validated. This innovative technology distinguishes itself from conventional methods by employing noncontact forces to replace traditional pre-tensioning mechanisms, thereby enhancing the mechanical design of pressure-preserved coring equipment and significantly boosting the fault tolerance of the technology. Here, we report on the design, theoretical calculations, experimental validation, and industrial testing of this technology. Through theoretical and simulation calculations, the self-sealing composite magnetic field of the pressure controller was optimized. The initial pre-tensioning force of the optimal magnetic field was 13.05 N. The reliability of the magnetically controlled self-sealing pressure-preserved coring technology was verified using a self-developed self-sealing pressure performance testing platform, confirming the accuracy of the composite magnetic field calculation theory. Subsequently, a magnetically controlled self-triggering pressure-preserved coring device was designed. Field pressure-preserved coring was then conducted, preliminarily verifying the technology's effective self-sealing performance in industrial applications. Furthermore, the technology was analyzed and verified to be adaptable to complex reservoir environments with pressures up to 30 MPa, temperatures up to 80 ℃, and pH values ranging from 1 to 14. These research results provide technical support for multidirectional pressure-preserved coring, thus paving a new technical route for deep energy exploration through coring.

The pressure-preserving controller is the core part of deep in-situ pressure-preserving coring (IPP-Coring) system, and its pressure-preserving capability is the key to IPP-Coring technology. To achieve a good understanding of the influence of mechanical properties of materials on the ultimate pressure-bearing capability (UPB-Capability) of the pressure-preserving controller, the IPP-Coring experimental platform was developed to test the UPB-Capability of pressure-preserving controllers of four different materials. The experimental results show that the UPB-Capability of pressure-preserving controllers with different material varies greatly. A numerical model of the pressure-preserving controller was developed to study the influences of mechanical parameters of materials on the UPB-Capability of the pressure-preserving controller after the accuracy of the numerical model is verified by experiments. The results indicate that the yield strength (YS) and Poisson's ratio (PR) of the material have little effect on the UPB-Capability of the pressure-preserving controller, whereas the elastic modulus (EM) of the material has a significant effect. A generalized model of the UPB-Capability of the pressure-preserving controller is developed to reveal the mechanism of the influence of material properties on the UPB-Capability of the pressure-preserving controllers. Considering these results, the future optimization direction of the pressure-preserving controller and material selection scheme in practical engineering applications of the pressure-preserving controller are suggested.