In the process of sliding drilling in highly deviated wells and horizontal wells, cuttings accumulate at the lower side of the borehole to form a cuttings bed, which is difficult to remove. To address the difficulty of removing cuttings beds during the sliding drilling process in horizontal and highly deviated well sections, this paper proposes awe propose a vortexing cuttings removal tool (VCRT). The internal flow field model of the VCRT has been established, and the computational fluid dynamics (CFD) method is used to analyze flow field variations. The results indicate that under the sliding drilling conditions of horizontal wells, when VCRT is installed near the bit, the cuttings volume fraction at the low side of the annulus is reduced by 18% compared to the conventional cuttings removal tool (CCRT). When the VCRT is installed in the section with a cuttings bed, the cuttings volume fraction at the low side of the annulus flow fluid is reduced by 36% compared to that with the CCRT. Therefore, the approximate installation location of the tool is determined based on comparative CFD analysis of two installation positions, and it is recommended to install the VCRT in the section with the cuttings bed. This tool has been applied in an oil field in Jiangsu, China, and field tests demonstrate that at a drilling fluid flow rate of 30 L/s, the rotational speed of the rotating blade can reach 400 rev/min, the pressure drop in the VCRT field is 1.6 MPa, and the friction resistance of the drill string will be reduced by 35.90%. Through CFD analysis, the working mechanism of the VCRT and its cuttings removal efficiency are revealed. The CFD results show good agreement with experimental data, and these findings provide important theoretical support for VCRT applications.

An accurate analysis of the three-dimensional(3D)deformed configuration of a bottom-hole assembly(BHA)is critical for predicting and controlling well paths in directional drilling.Among the various numerical approaches,the weighted residual method exhibits superior performance owing to its semi-analytical nature,enabling high accuracy in handling diverse boundary conditions.In previous studies,the weighted residual method has been coupled with a dual optimization process to determine the 3D deformation and tangency point of the BHA.However,its applicability is limited by the conventional treatment of contact interactions between the BHA and wellbore wall.Specifically,stabilizer-wellbore contacts are regarded as predefined boundary con-ditions,rather than solving these contact positions as unknown variables consistent with actual downhole conditions.This limitation reduces modeling fidelity in complex down-hole environments.To address this limitation,this study enhances the optimization-based weighted residual method by introducing ant colony optimization(ACO)to solve the 3D contact problem.In the proposed framework,the bending energy of the deformed BHA is conceptualized as"food",while the contact positions and orientations of stabilizers are assigned a measure of"taste".Through this metaphor,the ACO algorithm employs artificial"ants"to explore the optimal stabilizer locations and orientations that minimize the BHA bending energy,thereby refining the computed 3D deformation.The simulation results demonstrate that integrating ACO into the previously established dual optimiza-tion framework enables the effective determination of the contact configuration between the BHA and wellbore wall.As a result,the overall accuracy of the 3D BHA deformation analysis is significantly improved.In one representative case study,the bending energy of the BHA is reduced by 55.6％compared with that obtained from the original dual-optimization method.

Ultra-deep-well drilling is performed in long, narrow wellbores with restricted borehole clearance, where drill string-wellbore interactions promote nonlinear coupling among axial, lateral, and torsional vibrations and increase fatigue-related failure risk. This study presents a beam-solid coupled modeling strategy for full-scale drill string dynamics in ultra-deep wells with restricted borehole clearance. The three-dimensional wellbore trajectory is reconstructed from survey data using the curvature-radius method. Realistic downhole boundary conditions are represented by incorporating drilling-fluid loads as well as drill string-wellbore contact. To improve full-well modeling feasibility while retaining a refined representation of the near-bit region, the upper drill pipe is modeled using beam elements, whereas the BHA is modeled using solid elements. Simulations reveal pronounced high-frequency torsional vibrations in the near-bit region, with dominant spectral peaks around 118 Hz and 198 Hz, accompanied by significant lateral whirling. The peak lateral acceleration in the BHA pendulum section reaches 177.2 g, and stress fluctuation amplitudes vary markedly along depth. In certain intervals, repeated lateral excursions trigger frequent wall contact and promote vibration propagation along the drill string in the depth direction, indicating higher vibration sensitivity in these regions. Simulated dynamic characteristics are generally consistent with surface logging data from ultra-deep drilling operations and with downhole vibration observations reported in the literature, supporting the applicability of the proposed model for vibration mitigation and drilling-parameter optimization in ultra-deep wells.

The SDTK-1 well is the first ultradeep well exceeding 10,000 m in China and Asia, undertaking the dual tasks of deep-Earth scientific exploration and oil and gas discovery. Ensuring the success of coring operations at a depth exceeding 10,000 m is of utmost importance. Due to its length exceeding 10,000 m, the coring drillstring has complex and dynamic characteristics, which made designing the coring drillstring and the predicting the maximum core length significantly challenging. In this paper, we present a maximum core length prediction method based on the dynamic analysis of the drillstring. First, we establish a dynamic model of the drillstring, and solve the dynamic characteristics of the drillstring with lengths exceeding 10,000 m by combining the Newman method and the node iteration method. Then, we study the dynamic stability of the coring bottomhole assembly (BHA) and the contact interaction between the inner and outer barrels of the coring tool. Finally, we predict the maximum core length, and on this basis, discuss the rationality of the coring BHA's structure. The results show that the core sampling ability at depths exceeding 10,000 m is closely related to the structure of the coring BHA, as well as the whirl trajectory and the maximum dynamic displacement of the outer barrel axis of the coring tool. The maximum core length mainly depends on the position of the contact points between the inner and outer barrels. The actual core length is 6.20 m, while the predicted result is 6.12 m. The coincidence rate reaches 98.7%, which proves the correctness of the method for predicting the core retrieval length by considering the dynamic contact relationship between the inner and outer barrels of the coring tool. By comparing the maximum core lengths corresponding to the three coring BHAs, it was found that the designed coring BHA structure has a more reasonable structure.

In this work, the direct kinetic method is employed to investigate the anomalous transport process of current-driven instability in the hollow cathode plume. The influences of electron Mach number, gas species, and gas flow rate on the evolution of both the electron/ion velocity distribution functions and the corresponding macroscopic quantities (bulk velocity and temperature) are carefully examined. The spatial distribution of neutral particles is determined under a conical diffusion assumption, and the role of electron-neutral classical collisions in the anomalous transport process is quantitatively evaluated. The results reveal that: (i) increasing the electron Mach number enhances particle-wave interactions, thereby accelerating the formation of electron holes, high-energy ion tails, and stronger macroscopic oscillations; (ii) lighter gas species intensify particle-wave coupling, leading to a faster and stronger non-equilibrium evolution of both electrons and ions; and (iii) a higher gas flow rate suppresses nonlinear evolution by strengthening electron-neutral classical collisions, which stabilizes the velocity distributions and reduces anomalous energy transfer from electrons to ions. These findings provide new theoretical insight into the particle-wave anomalous transport mechanism and offer valuable guidance for the design and optimization of high-performance hollow cathodes.

The phenomenon of secondary makeup in threaded joints frequently occurs during ultra-deep well drilling, indicating the presence of downhole impact torque that exceeds the initial makeup torque. This excessive torque not only complicates the breakout process of drill tool connections but also increase their susceptibility to failure, posing significant safety risks. To investigate the generation mechanism of downhole impact torque, a finite element model was developed based on a comprehensive simulation of drill string dynamics under various operating conditions. Derived from Hamilton's principle, the model was solved using a combination of Newmark method and the Successive Over-Relaxation node iteration technique to obtain the dynamic response of the drill string. A case study, using a representative drill string configuration under specified borehole conditions, was conducted to analyze the self-rotation and whirl characteristics of the Bottom Hole Assembly during stick-slip events. The results reveal that secondary makeup is primarily caused by stick-slip vibration. While the impact torque arising from the drill string self-rotation is relatively small and insufficient to induce secondary makeup, the intensified whirl motion during the slip phase of stick-slip oscillations generates a significant impact torque-reaching up to 94.6 kN m-which far exceeds the initial makeup torque. This dynamic torque is identified as the primary factor leading to secondary makeup in threaded connections. The proposed model demonstrates high predicative accuracy, with a deviation of only 5.1 % from field measured breakout torque, confirming its reliability and practical relevance.

Threaded connection loosening impairs operational safety, yet research on the mechanical mechanisms of anti-loosening is limited. This study developed a 2D axisymmetric finite element model in ABAQUS for standard, wedge-shaped self-locking, and arc-lock threads, validated it through photoelasticity experiments, and analyzed their mechanical characteristics under various preloads. Due to their unique root bevel angles, wedge-shaped self-locking and arc-lock threads exhibit altered engagement force distribution, a higher normal force at the same preload, and potentially enhanced anti-loosening frictional resistance. Notably, arc-lock connections have 9.8

The degradation of casing due to wear is a crucial factor contributing to the problems of wellbore integrity. Although the impact of wear on the burst resistance of the casing body has been extensively studied, fewer investigations have focused on the burst resistance and sealing effectiveness of worn casing connections. This is due to the complexity of their mechanical properties. The objective of this research is to evaluate how wear affects both the burst resistance and sealing effectiveness of casing connections. Three-dimensional finite element models of worn casing connections were developed to explore the relationship between burst resistance and wear depth. The findings indicate that as wear depth increases, the burst resistance of the casing connection decreases. Additionally, the effect of wear on the contact stress at the sealing interface was analyzed. The results suggest that wear exacerbates the uneven distribution of contact stress on the sealing interface. A greater wear depth leads to a significant reduction in the sealing effectiveness of the casing connection. An evaluation model for the burst resistance of worn casing connections has been developed, incorporating Murtagian’s test results and seal contact energy theory. This model accounts for sealing integrity and provides a more practical framework for assessing the burst resistance of casing connections.

The torque-tension relationship is fundamental to evaluating the performance of bolted joints. Inaccurate estimation of this relationship can result in insufficient clamping force or excessive tightening, thereby impairing the integrity and reliability of bolted joints. Although numerous analytical models have been developed for conventional threads, their applicability to diverse thread geometries is often restricted by oversimplified assumptions regarding the distribution of bearing contact pressure. In practical applications, the mechanical response of bolted joints is further complicated by frictional variability, evolving contact conditions, and service-induced effects, making accurate preload prediction challenging. Although these factors affect long-term behavior, the torque-tension relationship is primarily established during the tightening stage, where the initial contact conditions govern the subsequent mechanical behavior. To address these limitations, an analytical model is proposed wherein the bearing contact pressure is characterized by a quadratic distribution. This assumption offers a more realistic representation compared with conventional uniform or linear assumptions, while explicitly incorporating its interplay with thread geometry and friction behavior. The model is validated through three-dimensional elastic-plastic finite element analysis and controlled bolt-tightening experiments. Results show that the model achieves prediction accuracies of 98.59% for standard threads and 97.90% for arc-locking self-locking threads, showing good agreement with both numerical and experimental data. The consistent prediction performance across different thread configurations demonstrates the robustness of the quadratic pressure distribution assumption. The proposed model provides a more accurate and practically viable method for predicting the torque-tension behavior of bolted joints.

Titanium alloy drill pipes exhibit promising potential for ultra-deep well drilling due to their high specific strength and superior corrosion resistance. However, the engagement surfaces of the pin and box joints feature distinct material stiffness and surface roughness, which influence both the load bearing characteristics and sealing performance. This study establishes a 3D elastoplastic finite element model for steel-titanium heterogeneous drill pipe joints and analyzes their stress distribution under complex loading conditions. Furthermore, a sealing performance evaluation model based on microscopic leakage mechanisms is proposed, and the sealing performance of single shoulder and double shoulder drill pipe joints is comparatively analyzed. The results indicate that, compared to the NC50 single-shoulder joint, the DS50 double-shoulder joint exhibits a 12.8% improvement in sealing performance under an axial tension of 2500 kN, and a 27.6% improvement under combined loading of 2500 kN axial tension and 8 kN·m bending moment. The synergistic action of the primary and secondary shoulders enhances the sealing stability of the drill pipe joint.

Titanium alloy has promising applications in the ultra-deep well drilling field. When using titanium alloy drill pipes in composite drill strings, using titanium-steel tool joints becomes inevitable. However, the mechanical properties of such titanium-steel tool joints are not fully understood. This paper develops a three-dimensional elastic-plastic finite element model to analyze the loading characteristics of API standard tool joints with different material combinations. The analysis shows that the torsional performance of titanium-steel tool joints is significantly reduced compared to traditional steel tool joints. Based on these findings, a titanium-steel double-shoulder tool joint was designed. Its model accuracy was verified through experimental testing, and its mechanical behavior was analyzed. Results indicate that incorporating a secondary shoulder structure and adjusting the clearance of the secondary shoulder can effectively enhance the torsional performance of the tool joint. Specifically, the ultimate working torque of the titanium-steel double-shoulder tool joint (DS50-H) is 84.6 kN·m, 39.15% higher than the 60.8 kN·m torque of the titanium-steel single-shoulder tool joint (NC50). This improvement significantly enhances the tool joint’s stability under complex geological conditions.

The rapid advancement of micro/nano-electromechanical systems has brought increasing attention to gas transport phenomena at micro/nanoscales. This study investigates the non-equilibrium flow characteristics in circular micro/nanochannels using a newly developed cylindrical-coordinate discrete Boltzmann method (DBM). We first establish a novel framework for steady-state DBM implementation in cylindrical coordinates and validate the model through benchmark cases, including both pressure-driven and thermal creep flows, demonstrating its multiscale modeling capability and superior computational accuracy. Through a comprehensive comparative analysis of pressure-driven and thermal creep flows from the perspective of non-equilibrium quantities, we elucidate their fundamental distinct transport mechanisms. Furthermore, we critically examine the Onsager reciprocal relations between mass flux in thermal creep flow and heat flux induced by mechanocaloric effects, revealing new physical insights into the radial distribution patterns of velocity and heat flux fields. Finally, we provide quantitative evaluations of two key phenomena: thermomolecular pressure difference arising from thermal creep flow and thermomolecular temperature difference generated by mechanocaloric effects, systematically characterizing their dependence on the Knudsen number and boundary conditions.

The Kelvin–Helmholtz Instability (KHI) with and without external magnetic fields is computationally investigated based on the Discrete Boltzmann Method (DBM). The maximum local Knudsen number in the system is up to more than 0.06. Simultaneously, the density correction induced by the second-order Knudsen number effects near some interfaces is up to more than 10% . This work aims at the kinetic physics that occurs on the length and time scales of particle collisions, which leads to discrete/non-equilibrium effects and may contribute to the observed differences between hydrodynamic predictions and experiments. Through selecting appropriate kinetic moments, the DBM has the capability to describe flow systems ranging from continuum to early transition flow regime. The first- and second-order DBMs with different physical capabilities are constructed. The results of the two DBMs are compared, including the hydrodynamic non-equilibrium and the most relevant thermodynamic non-equilibrium behaviors. It is found that: (i) In KHI, without an external magnetic field, two competing energy transport mechanisms influence the saturation moment of the vortex. (ii) In the presence of an external magnetic field, viscous shear stress and heat flux are enhanced, while the magnetic field suppresses the KHI evolution by inhibiting vorticity transport and inducing secondary vortex structures. This results in an increased local Knudsen number and density difference. (iii) The Atwood number At further amplifies the local Knudsen number and density difference. The maximum density difference first increases and then decreases with At as it suppresses the formation of rotational discontinuities near the saturation moment.

Multi-mode Rayleigh-Taylor instability (RTI) exhibits more complex nonlinear interactions and richer multiscale interfacial dynamics than single-mode cases, resulting in fundamentally distinct thermodynamic nonequilibrium (TNE) behaviors beyond conventional hydrodynamic predictions. This study employs a multiphase discrete Boltzmann model with surface tension to examine macroscopic dynamics and TNE features of multi-mode RTI. At the macroscopic level, surface tension enhances mode coupling in the early stage, delays the onset of Kelvin-Helmholtz instability, and suppresses mixing between light and heavy fluids. Notably, within a certain range, increasing the surface tension slightly enhances disturbance amplitudes in the later stages. At the nonequilibrium level, various TNE metrics are analyzed to capture fine-scale interface structures and characterize stage-wise evolution. Among these metrics, the global average TNE strength D-TNE and heat flux strength D-3,D-1 demonstrate high sensitivity and robustness in identifying distinct evolutionary stages. The growth rate of TNE strength reveals distinct regime transitions: exponential in the linear stage, linear in the self-similar stage, and oscillatory during the turbulent mixing stage. The effects of the initial perturbation wavenumber on RTI evolution are also examined. Although bubble and spike velocities vary considerably with wavenumber, the TNE strength growth rate follows a consistent trend, underscoring its reliability as a staging indicator. These findings demonstrate that TNE-based kinetic diagnostics provide new physical insights into multi-mode RTI evolution, complementing and extending traditional hydrodynamic analysis.

The complex vibration directly affects the dynamic safety of drill string in ultra-deep wells and extra-deep wells. It is important to understand the dynamic characteristics of drill string to ensure the safety of drill string. Due to the super slenderness ratio of drill string, strong nonlinearity implied in dynamic analysis and the complex load environment, dynamic simulation of drill string faces great challenges. At present, many simulation methods have been developed to analyze drill string dynamics, and node iteration method is one of them. The node iteration method has a unique advantage in dealing with the contact characteristics between drill string and borehole wall, but its drawback is that the calculation consumes a considerable amount of time. This paper presents a dynamic simulation method of drilling string in extra-deep well based on successive over-relaxation node iterative method (SOR node iteration method). Through theoretical analysis and numerical examples, the correctness and validity of this method were verified, and the dynamics characteristics of drill string in extra-deep wells were calculated and analyzed. The results demonstrate that, in contrast to the conventional node iteration method, the SOR node iteration method can increase the computational efficiency by 48.2% while achieving comparable results. And the whirl trajectory of the extra-deep well drill string is extremely complicated, the maximum rotational speed downhole is approximately twice the rotational speed on the ground. The dynamic torque increases rapidly at the position of the bottom stabilizer, and the lateral vibration in the middle and lower parts of drill string is relatively intense.

A Discrete Boltzmann Method (DBM) with a Maxwell-type boundary condition is constructed to investigate the influence of rarefaction on laminar Shock Wave/Boundary Layer Interaction (SWBLI). Due to the complexity of compressible flow, a Knudsen number vector Kn, whose components include the local Knudsen numbers such as Knp and KnU, is introduced to characterize the local structures, where Knp and KnU are Knudsen numbers defined in terms of the density and velocity interfaces, respectively. Since first focusing on the steady state of SWBLI, the DBM considers up to the second-order Knp (rarefaction/non-equilibrium) effects. The model is validated using Mach number 2 SWBLI and the necessity of using DBM with sufficient physical accuracy is confirmed by the shock collision problem. Key findings include the following: the leading-edge shock wave increases the local density Knudsen number Knp and eventually leads to the failure of linear constitutive relations in the Navier-Stokes (N-S) model and surely also in the lower-order DBM; the non-equilibrium effect differences in regions behind the leading-edge shock wave are primarily correlated with Knq, while in the separation region are primarily correlated with KnU; the non-equilibrium quantities D2 and D4 2, as well as the viscous entropy production rate SNOMF can be used to identify the separation zone. The findings clarify various effects and main mechanisms in different regions associated with SWBLI, which are concealed in N-S model. (c) 2025 The Authors. Published by Elsevier Ltd on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Supersonic flow is a typical nonlinear, nonequilibrium, multiscale, and complex phenomenon. This paper applies discrete Boltzmann method/model (DBM) to simulate and analyze these characteristics. A Burnett-level DBM for supersonic flow is constructed based on the Shakhov-BGK model. Higher-order analytical expressions for thermodynamic nonequilibrium effects are derived, providing a constitutive basis for improving traditional macroscopic hydrodynamics modeling. Criteria for evaluating the validity of DBM are established by comparing numerical and analytical solutions of nonequilibrium measures. The multiscale DBM is used to investigate discrete/nonequilibrium characteristics and entropy production mechanisms in shock regular reflection. The findings include: (a) Compared to NS-level DBM, the Burnett-level DBM offers more accurate representations of viscous stress and heat flux, ensures non-negativity of entropy production in accordance with the second law of thermodynamics, and exhibits better numerical stability. (b) Near the interfaces of incident and reflected shock waves, strong nonequilibrium driving forces lead to prominent nonequilibrium effects. By monitoring the timing and location of peak nonequilibrium quantities, the evolution characteristics of incident and reflected shock waves can be accurately and dynamically tracked. (c) In the intermediate state, the bent reflected shock and incident shock interface are wider and exhibit lower nonequilibrium intensities compared to their final state. (d) The Mach number enhances various kinds of nonequilibrium intensities in a power-law manner D_mn∼𝙼𝚊^α. The power exponent α and kinetic modes of nonequilibrium effects m follows a logarithmic relation α∼ln (m - m_0). This research provides new perspectives and kinetic insights into supersonic flow studies.