Search Results (655)

To address the difficulty of determining the safe reserved thickness of the mining wall in the test block of the panel pillar at Tongkeng Mine, The stress of mining wall is comprehensively analyzed. Combined with numerical simulation method and field monitoring, the optimal wall thickness is determined. By differentiating each stress component, the mathematical equations governing the locations where extreme values of the stress components occur are derived, and the mathematical expressions for the extreme value positions of each stress component are further determined accordingly. Considering the geological characteristics and mining conditions of the experimental stope with panel pillars, the eastern mining wall of the test block is selected as the research object. A mining wall thickness range of 3 m to 8 m is designed, and the optimal safe reserved thickness of the mining wall is determined through numerical simulation. Based on the optimal mining wall retention thickness, stopping operations are carried out on the orebody of the experimental stope. Meanwhile, monitoring points are reasonably arranged from the upper-middle section to the middle of the mining wall, and real-time monitoring is performed on the stress variation data at each monitoring point during the entire stopping process of the test block. Theoretical analysis results show that the exact locations of the extreme values of each stress component can be accurately determined within the two-dimensional plane of the mining wall, among which the extreme value of the horizontal stress component appears at the midpoint of the mining wall thickness. Numerical simulation results indicate that both the stress and displacement of the mining wall exhibit a gradual decreasing trend with an increase in mining wall thickness. However, when the mining wall thickness exceeds 5 m, the reduction rate of stress and displacement slows down significantly, and the mining wall tends to become stable. Maintaining a mining wall thickness of 5 m in the experimental stope can generally ensure the safe recovery of the orebody. However, pronounced stress concentrations occur at the geometric corners of the mining wall, which result from stress retention caused by changes in the mining wall geometry. Meanwhile, the stress concentration in the mining wall is synchronized with that in the drilling galleries of the experimental stope, and varying degrees of failure occur in the drilling galleries at locations where stress concentration appears in the mining wall. Monitoring results show that the maximum stress borne by the drilling gallery is approximately 26 MPa, beyond which rock mass collapse and fragmentation are prone to occur. Full article

Carbon fiber reinforced polymer (CFRP) composites are widely used in many engineering applications such as aerospace, automotive, and defense industries due to their superior properties such as high specific strength, stiffness, and corrosion resistance. However, these materials require drilling, especially during assembly processes. Damage mechanisms arising during this process, such as delamination, high thrust force, and torque, negatively affect structural integrity and production quality. This study proposes a data-driven, multi-objective optimization approach to solve problems encountered during drilling in multi-walled carbon nanotube (MWCNT)-reinforced CFRP nanocomposites. The study considers the MWCNT reinforcement ratio, cutting speed, and feed rate as process parameters and examines their effects on thrust force, torque, and delamination factor. Second-degree polynomial regression-based prediction models were created using the experimental data obtained, and these models were included in the multi-objective optimization process. During the optimization phase, thrust force and torque values were simultaneously minimized, while the delamination factor was kept below the statistically determined constraint of F_d ≤ 1.054. Pareto-optimal solution sets were obtained using NSGA-II and MOPSO meta-heuristic algorithms in the solution process. The results indicate that suitable combinations of drilling parameters can be identified through Pareto-based optimization, allowing significant reductions in thrust force and torque while maintaining the delamination factor below the specified limit. The study presents a reliable optimization approach for the more efficient machining of CFRP nanocomposites. Full article

Neutron logging-while-drilling is a nuclear logging technique within the logging-while-drilling (LWD) system, characterized by high sensitivity to hydrogen formation. With the increasing complexity of well trajectories and the development of unconventional oil and gas, it has evolved from a traditional porosity measurement tool into a critical source of real-time information for geosteering and engineering decision-making. From a systems engineering perspective, this paper reviews the physical basis, tool system configuration, data processing methods, and typical engineering applications of LWD neutron logging. It discusses key technical bottlenecks and development trends. The results indicate that multiple interacting factors, including the neutron source, detector configuration, measurement geometry, environmental suppression capability, and interpretation strategy, constrain its performance. The transition from chemical neutron sources to pulsed neutron generators (PNG) represents a critical turning point, improving measurement safety and expanding the range of measurable parameters while simultaneously introducing new engineering challenges such as target material lifetime and long-term stability. Field practice further demonstrates that the main value of LWD neutron logging lies in providing real-time porosity and related information that overcomes physical limitations during drilling, supporting geosteering and real-time reservoir evaluation decisions. Based on current progress, future work will focus on enhancing the reliability of PNG-based neutron sources and developing data processing and intelligent interpretation workflows that integrate physical models with data-driven methods. Full article

Managed pressure drilling (MPD) is the core technology for developing formations with high pressure and narrow density windows. It precisely maintains the bottomhole pressure (BHP) within the safe operating window defined by formation pore pressure and fracture pressure by actively regulating the wellbore pressure profile. If pressure control becomes unstable, it can easily trigger gas kicks or lost circulation, posing a severe threat to operational safety. However, existing model predictive control (MPC) schemes have significant limitations: pure data-driven models exhibit poor generalization under complex conditions, while control algorithms based on traditional mechanistic models struggle to meet the stringent real-time requirements of field control cycles due to high-complexity numerical iteration processes. To balance control precision and real-time performance, this paper proposes a physics-informed model predictive control framework (PINC-MPC). During the training phase, physical prior knowledge such as the law of mass conservation is embedded into the neural network as constraints to construct a physically consistent deep surrogate model, enabling it to characterize complex wellbore characteristics. In the control phase, this surrogate model replaces the time-consuming numerical solving process of the mechanistic model within the MPC loop, achieving near-real-time state prediction and rolling optimization while ensuring physical fidelity. Experimental results indicate that PINC-MPC demonstrates superior control performance. Its median single-step solving time is only 16.81 ms, achieving an 11.1-fold acceleration compared to the mechanistic model-based scheme (187.3 ms). In a 5000 s full-cycle closed-loop control experiment, the total time required for the former is only 1.68 s, while the latter reaches 18.73 s, representing an efficiency improvement of approximately 91%. In terms of control accuracy, the integrated absolute error (IAE), reflecting the total deviation of the control process, significantly decreased from 63.40 MPa·s for the industrial successive linearization MPC (SLMPC) to 12.90 MPa·s, an improvement of 79.7%. Especially in extreme dynamic conditions such as simulated pump shutdowns for pipe connections and sudden gas kicks, the framework demonstrates excellent predictive ability and response efficiency. It can proactively trigger compensation actions to keep BHP fluctuations within 0.30 MPa, significantly outperforming the traditional SLMPC method. The research results prove that PINC-MPC provides an efficient, precise, and robust nonlinear control strategy for MPD systems, offering important engineering reference value for enhancing the automation level of intelligent drilling systems. Full article

The treatment of spent drilling fluids generated during the drilling of technological wells for uranium production represents an important engineering and environmental challenge associated with high energy consumption, significant waste generation, and the need for rational water use under arid regional conditions. Conventional phase separation methods based on gravitational settling and chemical–mechanical treatment are characterized by limited process controllability, long processing times, and increased consumption of reagents and energy. This study proposes an energy-efficient and reliable hydrodynamic technology for the treatment of spent drilling fluids based on the formation of controlled turbulent structures without the use of mechanical drives. The research object comprised spent drilling fluids (SDFs) generated during the drilling of technological wells for uranium production in the southern regions of the Republic of Kazakhstan and the Kyzylorda region. Experimental investigations were carried out using a laboratory–pilot hydrodynamic disperser with variations in velocity gradient, treatment time, flocculant dosage, and suspension flow rate. A mathematical model linking hydrodynamic process parameters with phase separation kinetics and energy characteristics was developed. Model calibration by weighted nonlinear least squares yielded a stable parameter set with 95% confidence intervals, and model validation demonstrated good agreement between calculated and experimental data (MAPE 8.4%; maximum relative error 11.8%). It was established that the use of a hydrodynamic disperser provides separation efficiency of up to 90–95% under optimal operating conditions while reducing specific energy consumption and maintaining stable repeated-cycle performance within the investigated operating window. Experimental results confirm that implementation of the hydrodynamic technology enables a reduction in sludge volume by 40–60%, recovery of up to 60–80% of process water, and a significant decrease in waste requiring transportation and disposal. The obtained results demonstrate the high environmental and resource-saving efficiency of the proposed technology and its suitability for scaling and industrial implementation at facilities drilling technological wells for uranium production. The developed hydrodynamic approach can be considered an effective engineering platform for creating energy-efficient and sustainable systems for drilling fluid treatment in regions with limited water resources and remote industrial infrastructure. Full article

The Xinqiao Cu-S polymetallic deposit is located in the Tongling ore concentration area of the Middle-Lower Yangtze River metallogenic belt. The orebodies consist of skarn orebodies and stratiform sulfide orebodies, but the genetic link between them remains controversial. In this study, magnetite was used as a proxy to systematically constrain the hydrothermal evolution from the intrusion to the contact zone and further to the stratiform orebodies. A representative drill hole (E603) was logged, and samples were systematically collected from the Jitou pluton outward to the contact zone. Composite samples from the 8–28 m interval were crushed and prepared as resin mounts for integrated TIMA automated mineralogy, BSE textural observation, and in situ LA-ICP-MS trace element analysis. Five types of magnetite (Mt1 to Mt5) were systematically identified. Mt1 occurs as inclusions within feldspar in the quartz monzodiorite. It exhibits typical magmatic magnetite characteristics and contains grid-like ilmenite exsolution, indicating crystallization during the late magmatic stage. Mt2 is distributed in the interstices of magmatic minerals, commonly showing hematitization and replacement of ilmenite exsolution lamellae by titanite. Its trace element geochemistry displays magmatic–hydrothermal transitional features. Mt3–Mt5 in the skarn and stratiform orebodies are paragenetic with retrograde alteration minerals (e.g., epidote, chlorite, and actinolite) and sulfides, and are characterized by low Ti, Al, and V contents and high Mg, Mn, and Sn contents, indicating a hydrothermal origin. From Mt3 to Mt5, (Ti + V) and (Al + Mn) decrease, while Zn and Mn increase, accompanied by a decrease in the (Si + Al)/(Mg + Mn) ratio. This reflects a trend of decreasing fluid temperature and progressively enhanced wall-rock buffering. The Mg-in-magnetite geothermometer yields relatively consistent results for Mt1–Mt3, but anomalously high temperatures for Mt4–Mt5. This suggests that the elevated Mg activity in the fluid, caused by reaction with carbonate wall rocks, can significantly influence the calculated temperatures. Therefore, this geothermometer should be used cautiously for magnetite in the outer skarn zone and interpreted in combination with other temperature constraints. The textures, paragenetic mineral assemblages, and trace element characteristics of magnetite collectively reveal a continuous mineralization process linking the skarn and stratiform orebodies at Xinqiao, providing robust mineralogical and geochemical evidence for the contribution of Yanshanian magmatic–hydrothermal activity to the stratiform mineralization. Full article

The current study offers a deeper understanding of the thermal behavior of AISI 420 stainless-steel drill bits during titanium alloy machining. It utilizes non-linear simulations with the finite element method (FEM) to analyze heat generation, accumulation, and dissipation. The FEM formulation displays the time-dependent temperatures for the tool and hole during the drilling process. The simulation was examined during drilling and subsequent stages, up to room temperature. The study explored a wide range of drill bit lengths (60–160 mm) and tool diameters (2–10 mm). Significant convergence of 4.1% was achieved when compared to infrared thermography data. Furthermore, increasing the tool length beyond 120 mm did not significantly increase the thermal effect. Moreover, increasing the tool diameter up to 10 mm also did not significantly increase the thermal efficiency compared to tool diameters between 2 and 5 mm based on a constant tool length. An exploratory data analysis (EDA) heatmap correlation matrix was used to examine the most efficient variables and the optimum tool geometry. The results obtained provide a clear understanding of the optimal geometry choice for steel drilling tools when used in drilling titanium alloys. Full article

The plugging of fractured gas reservoirs with severe lost circulation during oil and gas drilling and production has long been challenged by technical issues such as low plugging strength and short effective duration. This paper reports the preparation of a high-strength supramolecular gel plugging agent via micellar copolymerization based on the synergistic effects of hydrophobic association and hydrogen bonding. Systematic optimization determined the optimal synthesis formula: acrylamide (AM) 12%, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) 2%, stearyl methacrylate (SMA) 0.4%, sodium dodecyl sulfate (SDS) 1.5%, and potassium persulfate 0.3%, with a reaction temperature of 60 °C. Performance evaluations revealed that the gel possesses a controllable gelation time (120 min) and excellent viscoelastic recovery properties. At a compressive strain of 87%, the compressive stress reached 1.43 MPa while maintaining structural integrity. Swelling behavior analysis indicated that the gel follows a non-Fickian diffusion mechanism, with its swelling process governed by the synergistic interplay of water molecule diffusion and polymer network relaxation. Core plugging experiments demonstrated that the gel achieved plugging efficiencies exceeding 95% for cores with permeabilities ranging from 0.18 to 0.90 μm², with a maximum breakthrough pressure gradient of up to 11.48 MPa/m. These results highlight the gel’s efficient and broad-spectrum plugging capability for fractured lost circulation zones. This preliminary study provides experimental foundations for the material design and performance optimization of supramolecular gel-based long-lasting plugging agents for severe lost circulation gas reservoirs, and further field-scale validation is required for engineering application. Full article

When a H₂S-containing gas kick occurs during drilling, the formation fluid containing hydrogen sulfide is mixed into the drilling fluid. Drilling fluid containing hydrogen sulfide is prone to causing hydrogen embrittlement when it comes into contact with the drill string during the upward return process. However, research on the risk and timing of hydrogen embrittlement in drill pipes remains limited. This study constructed a risk area and hydrogen embrittlement time analysis model. The risk area and time of hydrogen embrittlement in the drill pipe of the Jinyue 402 well in Tarim Oilfield were analyzed using the constructed model. The results indicate that the concentration of hydrogen sulfide in the Jinyue 402 well is in the area where the corrosion rate of steel increases rapidly, and the partial pressure of hydrogen sulfide is higher than the critical partial pressure at which corrosion cracking occurs. Taking into account the pH of the drilling fluid, fluid flow rate, hydrogen sulfide partial pressure, drill pipe tensile stress, hydrogen sulfide concentration, and gas partial pressure, the high-risk area for hydrogen sulfide corrosion damage in the Jinyue 402 well is 0–1680 m. The predicted highest risk point location and hydrogen embrittlement time are at a well length of 280 m and 21 h. Further predictions were made for the hydrogen embrittlement length and time of the Tazhong 83 and Zhonggu 503 wells in the Tarim Oilfield. The maximum prediction errors for the hydrogen embrittlement position and time of the drill pipe in the three wells were 4.8% and 5.2%, respectively. This indicates that the model can be applied to wells with different geological conditions and hydrogen sulfide concentrations. Full article

Precise assessment of rock brittleness is a prerequisite for effective wellbore integrity and successful reservoir stimulation in drilling programs. To achieve precise prediction of rock brittleness index (BI), this study proposes an improved optimization algorithm for an artificial gorilla troops optimizer (GTO), called a Bernoulli Differential Evolution Gorilla Troops Optimizer (BDEGTO). In the BDEGTO, Bernoulli mapping is introduced during the population initialization process, and the differential evolution is embedded after the exploration stage of the GTO. These modifications effectively address the early-stage optimization weaknesses and the susceptibility to local optima that are commonly encountered in a traditional GTO. To evaluate the performance of the BDEGTO, comparisons are made with other optimization algorithms based on 91 datasets from 32 rock types. The results demonstrate the significant advantages of the BDEGTO over other algorithms. Furthermore, the BDEGTO is applied to the optimization process of Least Squares Boosting (LSB), Extreme Gradient Boosting (XGB), and Light Gradient Boosting Machine (LGBM). A comparison is made with Support Vector Regression (SVR), Artificial Neural Network (ANN), and Convolutional Neural Network (CNN) algorithms for predicting rock brittleness based on input parameters such as P-wave velocity (V_p), point load index (Is₅₀), and unit weight (UW). The findings indicate that BDEGTO-XGB achieves the best prediction performance for BI. Additionally, through SHapley Additive exPlanations (SHAP) analysis, it is determined that among the three input parameters, Is₅₀ has the most significant influence. These research results provide valuable guidance for the brittleness assessment of similar rocks. Full article

Real-time lithology identification while drilling is widely applied in oil and gas exploration, development drilling, geo-steering, unconventional resource extraction, well logging, and environmental monitoring, enhancing efficiency and accuracy in subsurface operations. This study investigates the frequency characteristics of rock-drilling sounds generated during drilling operations and explores their potential for real-time lithology identification. Experiments were conducted using 8 mm and 14 mm drill bits at both high and low rotational speeds on four types of rock samples: sandstone, limestone, granite, and shaly sandstone. Sound signals were recorded both within the rock and in air using high-fidelity sensors. The results reveal distinct frequency patterns for each rock type, with sandstone exhibiting dominant low-frequency energy, limestone and granite showing broader frequency bands with strong high-frequency components, and shaly sandstone displaying a mix of low- and high-frequency energy. Quadratic polynomial regression models between the Vp or Vs and the peak frequencies of the four distinct rock samples are built, and the corresponding coefficients of determination are 0.9878 and 0.9799. The study also demonstrates that drilling parameters, such as drill bit diameter and revolutions per minute (RPM), significantly influence the frequency distribution of rock-drilling sounds, with larger drill bits and higher RPMs producing broader frequency bands and stronger high-frequency energy. Comparisons between in-rock and in-air recordings show that the latter captures richer high-frequency information, though the overall trends remain consistent. These findings provide an experimental foundation for using rock-breaking sounds as a potential tool for lithology identification during drilling operations. The study highlights the importance of considering rock heterogeneity and drilling conditions when interpreting acoustic data and suggests future work to validate the method in field conditions and integrate advanced data processing techniques. Full article

Polycrystalline diamond compact (PDC) bits often experience localized heating during impact rock breaking in complex formations, resulting in reduced service life and lower drilling efficiency. An optimized structural design of PDC cutters can significantly enhance bit performance, mitigate thermal concentration, and extend operational longevity. Inspired by previous work on PDC cutter surface topography, five saw-type tooth-shaped cutter designs—featuring one to five saw-type teeth were developed. To evaluate their rock-breaking effectiveness and identify the optimum design, the impact-induced rock fragmentation processes of these cutters were compared using the finite element method. Key indicators, including cutting force, mechanical specific energy (MSE), and cutter surface temperature, were analyzed to determine the superior tooth configuration. Among the five designs, the four-saw-tooth cutter induced the most pronounced stress concentration in the rock. Its optimized number of saw-type teeth ensured full participation of all teeth in rock cutting, enabling efficient rock removal and maximizing breakage performance. Compared with other designs, this cutter exhibited the smallest fluctuations and mean cutting force. The specific mechanical energy decreased initially and then increased with the number of saw-type teeth, reaching a minimum for the four saw-type tooth design. Moreover, it showed the lowest surface temperature and the mildest temperature variation, which helps alleviate localized heating and improve wear resistance. The cutting performance of the four saw-type tooth was further influenced by cutting depth and back rake angle, with optimal values identified as 1.5 mm and 20°, respectively. Compared with a conventional cutter, the four saw-type tooth design reduced the overall surface temperature by approximately 10.69%, with temperature rise confined mainly to the grooves between adjacent saw-type teeth and no widespread thermal concentration observed, confirming its design superiority. Full-scale rock-breaking simulations demonstrated that the bit equipped with four saw-type tooth achieved greater penetration depth and required lower torque than the conventional design, indicating enhanced rock-breaking ability and higher drilling efficiency. In conclusion, the four saw-type tooth PDC cutter design offers a promising approach for developing high-performance drill bits and reducing drilling costs. Full article

Under extreme heterogeneous loading conditions in the deep sea, obtaining well-preserved and stratigraphically coherent cores is a critical challenge that requires urgent resolution. Current methods cannot directly determine the preservation of core stratigraphic information or the sampling behaviour of drill bits through experimentation. Consequently, a new evaluation method for angular velocity-based stratigraphic preservation, which is grounded in Discrete Element Method (DEM) theory, is proposed. Simulation modelling uses the Hertz–Mindlin contact model to construct a multi-scale geotechnical–drill string numerical coupling model. The drill string structure is simplified while incorporating actual geometric dimensions and material properties. By simulating and extracting particle angular velocity data under various operating conditions, a correlation is established between particle motion characteristics and the stratigraphic preservation status. Experiments were conducted on a customised drilling rig platform using specimens with deep-sea geomechanical properties consistent with the simulations. Drilling tools with multiple inner diameter specifications were configured, and multiple variable combinations of the rotational speed and feed rate were set. The degree of bedding preservation in the sampled cores was recorded synchronously. The study clarified the relationship between particle angular velocity and bedding preservation, identifying the influence patterns of parameters such as the tool inner diameter, rotational speed, and feed rate on bedding preservation. Results indicate that when the rotational speed exceeds 200 rpm and the feed rate falls below 0.018 m/s, stratigraphic distortion significantly increases; the drill bit inner diameter exhibits a non-linear negative correlation with core disturbance. This study provides theoretical underpinnings and experimental evidence for multi-parameter process optimisation in maintaining stratigraphic integrity during deep-sea submersible coring operations. Full article

With the advancement of high-end manufacturing, the application of difficult-to-machine materials such as titanium alloys and superalloys is becoming increasingly widespread. Their inherent material properties pose challenges during machining, including high cutting temperatures, rapid tool wear, and difficulty in controlling surface quality. Nanofluid minimum quantity lubrication (NFMQL) technology, as an advanced lubrication and cooling method, enhances the thermal conductivity and lubricating properties of fluids by uniformly dispersing nanoparticles in the base oil. This paper reviews the preparation methods, advanced atomization techniques, and core mechanisms of NFMQL technology. It focuses on analyzing the effectiveness of this technology in four major machining processes, turning, milling, grinding, and drilling, for typical materials such as titanium alloys, steel, and superalloys. Compared to dry cutting, conventional MQL, and poured cooling, NFMQL reduces cutting forces/torque, cutting temperatures, tool wear, and surface roughness while improving material removal rates, machining accuracy, and surface integrity. This paper concludes by summarizing the technology’s advantages, current challenges, and future research directions. Full article

Although powder metallurgy (PM) is known as a near-net-shape fabrication process, a large number of PM parts need to be machined for dimensional conformance or to produce complex geometrical features that cannot be achieved through compaction. However, due mainly to the presence of porosity, the machinability of PM steels is difficult compared to that of wrought steels and can add 20% or more to the overall fabrication cost of PM parts. Among the various measures known to improve the machinability of PM steels, the addition of machining aids, either as admixed or pre-alloyed constituents, is the most popular. Manganese sulfide (MnS) is by far the most common machinability-enhancing additive used in the PM steel industry. Although it is extremely efficient in improving the machining response of PM steels, MnS is known to have detrimental effects on mechanical properties and corrosion resistance. Thus, the use of MnS involves a compromise between obtaining good machinability at the expense of lower mechanical properties and corrosion resistance. In this study, free graphite particles are introduced as a new additive that not only noticeably improves the machinability of PM steel components but also does not affect their mechanical properties or corrosion resistance. It was found that it is possible to obtain free graphite particles in press-and-sintered PM steel components by coating graphite particles with a metallic layer. This coating prevents graphite from diffusing into the iron matrix while creating metallurgical bonds with the surrounding steel matrix during sintering. In this research, graphite particles were coated with nickel and copper through a cementation process. A heat treatment was then performed on this newly developed material to obtain a more uniform single-layer coating and achieve dimensional changes during sintering that are similar to those measured when MnS is used as a machinability enhancer. The results showed that the tensile properties as well as the fatigue resistance of components made of FC-0208-type PM steel containing admixed copper/nickel-coated graphite particles are not affected by the presence of the latter. Moreover, the corrosion resistance of the samples containing copper/nickel-coated graphite was found to be the same as that of samples without the additive, which is a significant improvement on the case where MnS is used. The performance of the newly developed additive in terms of machinability was also characterized in drilling. It was found that this new additive has an identical machinability-enhancing performance to admixed MnS. Full article