Le Zhao

Pressure-preserved coring enables in situ encapsulation of deep coal samples at the borehole bottom. By effectively reducing gas desorption, it supports reliable reserve assessment. Achieving reliable pressure-preserved sealing within the confined space of drilling tools remains a critical technical challenge in the field. Focusing on the pressure controller, this study investigates three key aspects: configuration design, sealing interface behavior, and structural performance. The investigation employs both theoretical modeling and laboratory experiments. First, a geometric configuration design methodology was proposed for the pressure controller using intersecting contact and tapered sealing principles. This was followed by the creation of a spatial motion interference prediction model for the assemblies. Secondly, the contact behavior of intersecting sealing interfaces was studied; analysis of the failure mechanisms showed that the design achieves a pressure-preserved capacity of about 24 MPa. Finally, laboratory tests validated the sealing performance of the pressure controller. The tests confirmed that seal ring failure is characterized by high-pressure extrusion, which is caused by an increased sealing clearance. The research findings elucidate the sealing formation mechanism of the pressure controller, establishing a theoretical foundation for advancing pressure-preserved coring technologies in coalbed methane and gas hydrate exploration and development.

Deep in situ pressure coring provides an accurate means of determining oil and gas reserve parameters. The key to achieving pressure coring at depths exceeding 5000 m lies in the ultimate bearing strength and stability of the pressure controllers. Due to the limited downhole space and the inherent technical demands of pressure coring, traditional pressure coring technology typically has an ultimate bearing pressure capacity of less than 70 MPa. The structural model of the pressure controller is designed. The stress–strain distribution of the pressure controller under external load is numerically simulated. A contact stress optimization scheme and critical sealing gap of pressure controllers are proposed. It was found that the saddle pressure controllers can ensure the fit clearance of the sealing surface and effectively control the deformation of the valve cover within 0.015 mm. The saddle pressure controllers have demonstrated an ultimate bearing strength exceeding 140 MPa, with minimal leakage. These findings have significant implications for accurate assessment of deep petroleum resources.

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 f low conditions in shale gas wells and on the basis of an in-depth understanding of deep f luid 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. Document Type: Original article Cited as: Fang, X., Li, C., Guo, D., Wang, D., Zhao, L., Xie, H. Novel structural design and anti-erosion performance evaluation of check valve applied to deep in-situ pressure-preserved coring. Advances in Geo-Energy Research, 2025, 15(3): 190-202. https://doi.org/10.46690/ager.2025.03.03

Obtaining real natural gas hydrate pressure-retaining samples is challenging, necessitating the study of in-situ condition preserved coring (ICP-Coring) technology. In this paper, we simulated the in-situ formation of natural gas hydrate using a high pressure cooling method within a self-developed formation environment simulation chamber. Drilling experiments were conducted to examine the influence of drilling parameters on low disturbance drilling processes. Our findings indicate that the feed rate of the drill pipe primarily affects the force magnitude on the drill pipe, while the rotational speed of the drill pipe significantly impacts the stability of this force, with slightly higher rotational speeds resulting in less disturbance.