Laser shock peening (LSP) and surface texturing are two valid surface modification techniques with well-studied tribological benefits. However, whether their synergistic effect can produce an enhancement effect has not been explored. This study performed on 55SiMoVA bearing steel, systematically evaluating the tribological behavior of untreated, laser shock peening-treated (LSPed), surface texturing-treated (Textured), and laser shock peening synergistic surface texturing-treated (LSPed-textured) samples through a reciprocating friction test system under the drilling fluid lubrication. The results exhibited that the LSPed-textured sample showed the best wear performance, with a 71.43% reduction in wear volume compared to the untreated sample, and were significantly better than the LSPed (42.86% reduction) and Textured (38.46% reduction) samples. The microstructure evolution induced by LSP formed a protective surface layer characterized by high hardness and residual compressive stress, enhancing the load-bearing capacity and inhibiting crack extension, thus reducing the wear volume due to abrasive and delamination wear. Furthermore, surface texturing produced a surface with positive kurtosis (Sku) and negative skewness (Ssk), and the reduced valley depth (Svk) and the valley void volume (Vvv) increased 86 times and 75 times, respectively. This surface characteristic was conducive to capturing wear debris, supporting load, and lubricating, further optimizing the interfacial friction behavior.

Downhole gas-liquid separators often face the challenge of wide operating conditions in which a wide range of gas volume fraction (GVF) and processing capacity (PC) are coupled in actual operations. To overcome the bottleneck problem that the continuity of gas core and the stability of flow field are difficult to maintain due to the failure of interstage synergy in traditional design, which leads to a significant reduction in separation efficiency, this study innovatively proposes an inter-stage coupled gas-liquid separator (IS-C-GLS) based on the sequential separation concept of "stabilization before separation, and coarse before fine". Combining numerical simulations with experimental validation, the internal flow field evolution characteristics and synergistic separation mechanisms of the IS-C-GLS were systematically investigated under the typical operating conditions of the Qinghai Oilfield (China), spanning a GVF of 20% similar to 80% and a PC of 300-700 m(3)/d. The results indicate that the IS-C-GLS exhibits excellent operating adaptability under wide working conditions based on the rigorous evaluation criteria of a separation efficiency eta > 80% and a pressure drop Delta P < 3177 kPa. Benefiting from the inter-stage synergistic effect enabled by the sequential structure, the simulated and experimental separation efficiencies remain stably above 83.5% and 80%, respectively, which highly matches the fluctuating production demands of the oilfield. By validating and analyzing the suppression mechanisms of the IS-C-GLS's inter-stage synergy against gas core breakup and flow field instability, this study provides vital theoretical and technical support for enhancing separator efficiency under complex operating conditions.

Natural gas hydrate (NGH) has emerged as a promising clean energy resource, yet its commercial exploitation faces significant challenges due to hydrate-sand cemented particles agglomeration during solid fluidization mining. These composite particles not only increase energy consumption and equipment abrasion but also pose reservoir destabilization risks, ultimately compromising extraction efficiency. To address these challenges, this study proposes a novel coupled numerical approach based on Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to systematically investigate the de-cementation mechanism. This article uses the CFD-DEM coupling method to analyze the variation laws of tangential stress and normal stress of cemented particles, and combines quantitative evaluation of de-cementation efficiency to reveal the de-cementation mechanism at different structural parameters. The results show that the de-cementation efficiencies gradually increase to 88.61% and 89.36% with the increase of do andl, respectively. While the de-cementation efficiencies gradually decrease to 81.4%, 80% and 77.78% with the increase of b, H and theta, respectively. Moreover, as duincreases, the de-cementation efficiency first increases then decreases with the peak value of 84.78%. The research presents a systematic evaluation of hydrocyclone structural parameters for de-cementation performance, offering a novel approach for enhanced in-situ hydrate-sand separation during NGH mining.

Driven by China's carbon peaking and carbon neutralization goals as well as the strategic development of deep-offshore energy resources,energy island clusters in the South China Sea are evolving from single energy-supply nodes into integrated engineering platforms that combine multi-energy coupling,energy conversion,operational support,emergency response,and long-distance replenishment.However,the existing support model dominated by nearshore home ports is constrained by long offshore distances,complex sea conditions,extended replenishment chains,and insufficient multi-stakeholder coordination,making it difficult to support large-scale and continuous operation of deep-offshore energy island clusters.This study reviews operational support models for energy islands and offshore energy hubs in China and abroad,analyzes the capability basis and limitations of ports,island-reef nodes,and frontier facilities in the South China Sea,and proposes a three-tier coordinated support system consisting of core home ports,relay hubs,and frontier support nodes.Based on support distance,water depth,task attributes,and response requirements,the proposed system divides the support space into a nearshore support layer,an offshore relay layer,and a deep-offshore frontier layer,corresponding respectively to integrated coordination,relay transfer,and near-field response functions.Scenario-based calculations indicate that the proposed system can reduce the response time for urgent spare-parts replenishment from approximately 51.5 h to 17.5 h,a decrease of about 66%,and reduce the arrival time for medical rescue from approximately 3.28 h to 1.43 h,a decrease of about 56.4%.Institutionally,this study recommends establishing the South China Sea Deep Blue Economic Comprehensive Pilot Zone as a coordination platform,while advancing standard sea-unit certification,three-dimensional layered sea-use rights,enclave-economy cooperation,and sea-air emergency coordination mechanisms.The results indicate that the three-tier coordinated support system can improve the operational efficiency,emergency response capability,and system resilience of energy island clusters in the South China Sea,providing a reference for the construction of deep-offshore energy engineering support systems in China.

To address the industry challenges of mismatched power output from gas generators and dynamic downhole load demand in drilling operations, along with the lack of scientific configuration basis for the coordinated operation of energy storage systems and traditional power generation equipment, this study conducts an in-depth optimization study on a hybrid gas-energy storage power supply system using a 50DB drilling rig as the specific research object. Historical load power data of the rig during typical operating cycles were systematically collected and analyzed. Based on this, a cost optimization model for the coordinated gas-energy storage power supply was developed, aiming to minimize the total life-cycle cost. This model innovatively integrates key economic factors, including the initial investment and long-term operation and maintenance costs of the battery energy storage system, as well as the fuel consumption and maintenance costs of the gas generator sets. The optimization objectives are the lowest overall system cost and the optimal energy storage capacity configuration. The results indicate that: ① While meeting the actual power demand, the optimal capacity of the energy storage battery is 1870 kWh, and the optimal charging/discharging power is 992 kW; ② The number of gas generator sets on site can be optimized from the original 8 to 4. This allows the units to operate stably within their high-efficiency range, increasing the average operating efficiency significantly from a maximum of 22.7% before optimization to 42.6%; ③ Under extreme working conditions with the maximum load during drilling operations, the optimally configured energy storage system can independently support the full site load for 4 hours, greatly enhancing the reliability and resilience of the power supply system.

The strengthening of the marine sector and the realization of carbon peaking and carbon neutralization goals urgently necessitates a shift in marine energy development toward deep-sea and intensive utilization.The offshore integrated energy island(OIEI)serves as an effective solution for resolving challenges in deep-sea power consumption and achieving the diversified conversion of energy forms.Based on a summary of international OIEI development models and their current status,this study reviews China's development foundation and analyzes challenges such as institutional fragmentation,technological bottlenecks,and the absence of a business closed loop.Drawing on a source-grid-load-storage-utilization integrated philosophy,the study proposes a comprehensive development model featuring energy conversion,multi-energy complementarity,and zero-carbon services.It outlines three differentiated pathways:a nearshore shared model,a mid-to-far offshore industrial fusion model,and a deep-sea off-grid model.Multi-scenario techno-economic calculations and sensitivity analysis indicate that the economic efficiencies of the three models exhibit significant nonlinear alternating evolution characteristics with increasing offshore distances,and the commercial feasibility of off-grid energy islands in the deep sea is highly dependent on the support provided by green fuel premiums and the carbon market mechanism.The study recommends leveraging marine resource endowments to formulate medium-to-long-term plans supporting OIEI development.It calls for mastering key core technologies,such as high-efficiency energy conversion and green fuel power equipment tailored for multi-scenario applications.Furthermore,the research suggests accelerating the deep cross-sector integration of energy,marine engineering,and shipping industries,as well as establishing international certification systems for green hydrogen,ammonia,and alcohols.Additionally,it proposes perfecting a commercial guarantee mechanism driven by incentive policies and carbon markets to advance the large-scale construction and high-quality development of China's OIEIs.

Solid fluidization technology is an effective method for the development of natural gas hydrate, and the key step is the de-cementation and separation of a large number of hydrate-sand cemented particles in the hydrate slurry. Natural gas hydrate reservoirs have characteristics such as anisotropy, wide saturation range, diverse occurrence forms, and cross-scale particle distribution. Therefore, it is urgent to systematically study the effect of different reservoir parameters on the de-cementation performance of a hydrocyclone. This article uses the CFD-DEM coupling method to analyze the variation laws of tangential stress and normal stress of cemented particles under different reservoir parameters, and combines quantitative evaluation of de-cementation efficiency to reveal the de-cementation mechanism. It is pointed out that hydrate-sand cemented particles are mainly subjected to normal tensile failure during the de-cementation process. This article provides a key theoretical basis and data support for the optimization design of a hydrocyclone and is conducive to promoting the green and safe development of natural gas hydrate.

The stability of underground building foundations in fractured rock masses is a critical concern in geotechnical engineering, particularly for urban projects situated in complex geological settings. In such environments, the interaction between weak planes, groundwater seepage, and in situ stress plays a decisive role in controlling deformation and failure mechanisms. This study presents a novel weak plane–seepage–stress coupling model specifically developed to evaluate the stability of underground excavations and foundation walls under these challenging conditions. Unlike conventional approaches that often assume isotropy or consider isolated factors, the proposed model integrates multiple interacting variables—including weak plane orientation, seepage coefficient, and excavation direction—to systematically assess their combined influence on stress redistribution and failure pressure. A key innovation lies in the quantitative evaluation of the permeability-sealing coefficient, which reflects the effectiveness of waterproofing measures, and its coupling with weak plane characteristics. The results demonstrate that weak planes significantly alter the surrounding stress field, inducing directional instability. The optimal excavation orientation for minimizing instability is identified within the range of 200° to 280°. Moreover, increasing δ from 0 to 1 leads to a substantial reduction in the required supporting pressure, underscoring the critical role of effective sealing and waterproofing in enhancing foundation stability. While the current model is based on a single weak plane assumption and focuses on short-term mechanical responses, it provides a foundational framework for understanding coupled instability mechanisms. Future work will extend the model to incorporate multi-set weak planes, time-dependent degradation, and dynamic excavation processes. This research offers both theoretical insights and practical guidance for optimizing geotechnical design in fractured rock environments, contributing to more resilient and sustainable underground construction.

The gradient structure can enhance the wear resistance of low carbon steel while maintaining its impact toughness through the heterogeneous synergy between the surface layer and the interior layer region. However, the conventional surface single-gradient composition structure is increasingly failing to meet the service requirements of EX30 bearing steel. Therefore, an integrated gradient structure is proposed to further enhance the wear resistance of EX30 bearing steel under oil-lubricated conditions, and the friction and wear mechanisms of the steel with this integrated gradient structure are investigated. A carbon composition gradient was formed through carburizing heat treatment, and a nanocrystalline gradient layer was further induced by laser shock peening (LSP). The results indicate that the carburizing heat treatment formed a compositional gradient layer approximately 1.5 mm thick on the material surface. The plastic deformation induced by LSP eliminated the texture of the surface layer in specific orientations, triggered intense dislocation motion, and resulted in defect features such as dislocation accumulation and slip. Ultimately, a gradient nanocrystalline layer approximately 200 mu m thick was formed. The single-composition gradient structure tends to generate localized stress concentration during reciprocating friction, leading to micro-cutting and plastic deformation. In contrast, the richer local defect characteristics and the abundance of nanograins in the integrated gradient structure promote the dispersion of surface strain over a wider stress range, significantly alleviating material damage and crack propagation caused by stress localization. Furthermore, the integrated gradient structure reduced the wear rate by 53.9 % and 54.3 % across different sliding frequencies compared to the single-gradient structure.

Solid fluidization mining is a promising method for natural gas hydrate. However, this technique involves complex downhole conditions, including pulsating flow resulting from drilling pump operations, which significantly impairs the separation efficiency of hydrocyclones. This study investigates the flow field characteristics and separation performance of both a conventional hydrocyclone separator and a novel hydrocyclone separator specifically designed for pulsating flow conditions. Using computational fluid dynamics with the Reynolds stress model and the Mixture model, simulations are conducted to analyze the velocity field, pressure distribution, phase volume fraction, and separation efficiency under both steady and pulsating flow. Results demonstrate that pulsating flow considerably disrupts the internal flow field of a conventional hydrocyclone separator, leading to a reduced separation efficiency and increased operational instability. In contrast, a novel hydrocyclone separator equipped with a spiral section and a flow-stabilizing cone effectively mitigates these disturbances. It maintains stable distributions of tangential, radial, and axial velocities, minimizes pressure fluctuations, and ensures consistent concentration profiles of hydrate and sand under pulsating conditions. As a result, the novel hydrocyclone separator achieves higher average separation efficiencies for both sand (90.74%) and hydrate (89.98%), with significantly reduced efficiency fluctuations compared with the conventional hydrocyclone separator. This study confirms that the novel hydrocyclone separator robustly handles flow instabilities, delivering an enhanced separation performance and operational reliability. The findings provide valuable insights for the optimization of downhole separation equipment in natural gas hydrate mining.

To address the unstable performance of existing downhole gas-liquid separators under 0.2-0.8 wide gas volume fraction ranges, this study proposes compact coupling separator based on inter-stage functional synergy. Through bubbles force analysis, numerical simulation and experimental verification, the separation performance and potential mechanism under different conditions are revealed. The results demonstrate: Through inter-stage functional coordination and flow field dynamic coupling, that is, flow-field stabilization before separation, and coarse separation before fine separation, the separator achieves efficient separation in a wide range of gas volume fractions. It achieves near-complete degassing at low gas volume fraction (simulation 96.6%, experiment 99.5%) and retains high-efficiency even at high gas volume fraction (simulation 74.6%, experiment 77.55%). Pressure drops characteristic and energy distribution demonstrate clear functional division between two- stages. The primary-stage consumes higher energy to generate intense swirl field, creating pronounced radial pressure gradient that drives bubbles toward the axis via centripetal force. Following flow stabilization in gravitydominated region, the secondary-stage captures and discharges residual bubbles with substantially lower energy input. Flow field analysis and efficiency data confirm that the primary-stage achieves gas pre-enrichment and flow homogenization in a strong centrifugal field, whereas the secondary-stage accomplishes fine separation under strong-weak alternating swirl. This orderly coupling and functional synergy between two- stages in their distinct mechanical environments enables strong-weak alternating swirl separator to maintain high separation performance across wide gas volume fraction ranges. This work provides a scheme with both theoretical principles and demonstrates practical engineering feasibility for downhole gas-liquid separator.

Solid fluidization mining method is a promising method to develop natural gas hydrate, in which the in-situ separation of sand and hydrate particles is a key link. However, the presence of cemented particles will increase the difficulty of sand removal, leading to a decline in the sand removal efficiency of the hydrocyclone. This paper presents an experimental and a CFD-DEM coupling numerical study to investigate the movement behavior of these particles within the swirling field. The results show that with the increase of inlet velocity, the self-rotation and revolution velocities of cemented particles exhibit an increasing trend. At the same time, the tangential velocity gradient of the flow field gradually increases, which is conducive to achieving the de-cementation dispersion of cemented particles. The average normal force on cemented particles is greater than the normal cementation force, while the average tangential force on cemented particles is much less than the tangential cementation force. As the inlet velocity increases, the de-cementation efficiency increases obviously from 34.09% to 95.45%. This research provides theoretical guidance for the design and optimization of the hydrocyclone, which is conducive to promoting the green and safe development of natural gas hydrate.

During the exploitation of low permeability oilfields, associated gas will be produced with crude oil. The intermittent pumping method leads to a large range of gas-liquid ratio of produced liquid. Although a little separator can meet the separation requirements of oil field, there are problems such as difficult operation or large structure size. Therefore, a spiral-uniflow coupled gas-liquid separator was designed in this study, and the separation mechanism, flow field characteristics and separation performance were analyzed by numerical simulation. The results show that under the action of stabilizing fluids and pre-separation of the primary-separator, the uniformity of the velocity and pressure distribution, the degree of gas-phase aggregation, the stability of the stratification interface and the separation speed of the gas-liquid two-phase of the secondary-separator are significantly improved. With the increase of gas volume fraction, the pressure drop of the separator decreases from 623kPa to 159kPa, and the separation efficiency increases first and then decreases. Under the synergistic effect of the coupling separation mechanism and the progressive gas-liquid separation, the lowest separation efficiency is still as high as 74.6%. The design goal is achieved, which provides a new design for gas-liquid separator with the wide range of inlet gas volume fractions.

Amid escalating global energy demands, the exploration of deepwater resources has become crucial for future energy supplies. Vast hydrocarbon reserves in deepwater zones are now primary targets for boosting global offshore oil and gas production. However, deepwater drilling faces significant challenges in safely and effectively managing wellbore pressure under complex geological conditions. To ensure the safety of deepwater drilling operations, Dual-Gradient Drilling (DGD) technology demonstrates unique advantages in controlling drilling fluid density and managing narrow pressure windows. This article begins with the principles, historical development, and current research status of DGD, providing a comprehensive review of ten distinct DGD methods. By comparing these technologies' application status and advantages and disadvantages, this paper delves into their performance in actual operations, addressing safety and efficiency issues in deepwater drilling. Drawing on rich historical case studies, the article summarizes the current industrial application status of DGD, looks forward to the future development potential of multi-gradient drilling, and proposes future research directions for tackling the challenges in deepwater drilling pressure control, including advanced techniques for predicting complex formation pressures, managing subsea pressures with rapid response capabilities, ensuring long-term wellbore stability and circulation, and improving the durability and maintenance of subsea equipment used in DGD.

Improving the wear resistance of cone bit bearings is crucial for enhancing bit life and drilling efficiency. This study integrates surface texture lubrication with bit floating sleeve bearings. A ring-block friction experiment was conducted under simulated drilling conditions, examining groove textures with various geometric parameters. The effects of groove texture parameters-depth, area ratio, skew angle, and width-on the tribological performance were analyzed using friction coefficient, wear amount, and surface morphology. Results indicate that optimal texture arrangements significantly enhance wear resistance. The best parameters found were a depth of 40 mu m, a texture area ratio of 10%, and an angle of 45 deg, reducing the friction coefficient by over 39%.

As the operational depth of ultra-deep wells, long horizontal wells, and large-displacement wells increases, downhole temperatures progressively rise. Under these high-temperature conditions, the issue of friction and wear between coiled tubing and casing becomes increasingly significant. However, existing studies primarily focus on room temperature conditions and neglect changes in the contact state between the two, which fails to accurately reflect their friction and wear characteristics. This study directly obtained samples from the tubing and casing materials, preserving the original contact state, and conducted friction and wear tests under various temperatures using both water-based and oil-based drilling fluids to investigate the wear mechanisms. The results indicate that under dry friction conditions at room temperature, the friction coefficient reached as high as 0.3534, leading to the formation of deep ploughing grooves on the surface. After the addition of lubricants, both the friction coefficient and surface roughness decreased, with the oil-based drilling fluid demonstrating the best lubricating effect (friction coefficient of 0.1033), primarily exhibiting abrasive wear. As the temperature increased, the friction coefficient initially decreased before slightly rising, with adhesive wear phenomena observed. When the temperature reached 160 degrees C, the wear mechanism displayed a mixed state of abrasive wear, adhesive wear, and oxidative wear. At this elevated temperature, the depth of the plastic deformation layer resulting from wear increased, accompanied by the formation of internal cracks, which further exacerbated the wear of the casing.

15CrNiMo is an essential bearing steel in the mining equipment industry. Multi-body friction significantly contributes to the premature damage of bearings made from 15CrNiMo. This paper investigates the impact of laser shock peening (LSP) on the wear behavior of a carburized layer in 15CrNiMo under multi-body friction. Analysis using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) reveals that LSP induces high-density dislocations and twins in the near-surface layer of the carburized material. Following LSP treatment, the near-surface layer (up to 200 mu m) exhibits a 26 % increase in grain quantity, a 14.3 % reduction in average grain size, and a 5.3 % increase in the proportion of large-angle grain boundaries. Additional characterization of residual stress and microhardness indicates that LSP increases surface microhardness by 20.5 % and average hardness within the 850 mu m range by 18.8 % while creating a residual stress layer approximately 1 mm thick near the surface. Scanning electron microscopy (SEM), results indicate that untreated specimens primarily experience abrasive wear, characterized by ploughing grooves and pits. In contrast, after LSP, abrasive wear decreases, and wear resistance improves, with the dominant wear mechanism shifting to adhesion among multi-body friction materials. The primary anti-wear mechanism is attributed to the nano-crystalline layer and residual stress layer induced by LSP, which effectively suppresses surface ploughing by multi-body friction materials, reduces cutting and compressive stresses during friction, and inhibits the crack formation and propagation.

This study examines the adaptive boundary control problem of flexible marine riser with internal flow coupling. The dynamic model of the flexible marine riser system with internal flow coupling is derived using the Hamiltonian principle. An analysis of internal flow's influence on the vibration characteristics of flexible marine risers is conducted. Then, for the uncertain environmental disturbance, the adaptive fuzzy logic system is introduced to dynamically approximate the boundary disturbance, and a robust adaptive fuzzy boundary control is proposed. The uniform boundedness of the closed-loop system is proved based on Lyapunov theory. The well-posedness of the closed-loop system is proved by operator semigroup theory. The proposed control's effectiveness is validated through comparison with existing control methods.

A coupled non-local thermal-hydro numerical based on the peridynamic differential operator (PDDO) is presented for simulating gas-fluid flow coupled with heat transfer of natural gas hydrate (NGH). The non-local integral replaces the governing equations for nonlinear seepage motion heat conduction. The nonlocal governing equations are resolved by employing an explicit iterative technique. This method is applied to model heat transfer in saturated NGH porous media with accompanying gas-liquid seepage. The effects of boundary pressure and temperature changes on seepage behavior are also investigated. The efficacy and precision of the established coupled model were validated by comparing the temperature field and pressure field outcomes derived from Lagrange multiplier variation analysis with the finite element findings and analytical solutions documented in previous literature. This paper introduces a different approach to numerically simulate the flow of gas and fluid, while also considering heat transfer issues.