Tight oil reservoirs are characterized by low porosity, low permeability, and the development of micro-and nano-scale pore structures. Conventional depletion and water flooding methods are generally ineffective, making CO2 flooding a widely adopted approach to enhance oil recovery. The minimum miscibility pressure (MMP) is a key parameter in determining whether CO2 can achieve miscibility with crude oil. However, due to the strong heterogeneity in the wettability of tight oil reservoirs, the mechanism by which different wettability conditions affect the MMP of CO2-oil systems remains unclear. In this study, quartz nanopore models with varying wettability were constructed, and Non-Equilibrium Molecular Dynamics (NEMD) simulations were performed to calculate the MMP within nanopores. The effects of temperature, pore size, wall wettability, and crude oil composition on the MMP and CO2 storage efficiency were systematically analyzed. The results show that the MMP within nanopores is lower than that in the bulk phase. MMP increases with temperature and exhibits a non-monotonic trend with decreasing pore size-initially decreasing and then increasing. As the wettability shifts from water-wet to oil-wet, the MMP tends to increase. Due to the strong interactions between the pore wall and CO2 molecules, water-wet reservoirs are more favorable for CO2 storage and result in a lower MMP in CO2-oil systems. This study provides new insights into the microscopic miscibility mechanisms of CO2 and oil under varying wettability conditions in tight reservoirs and offers theoretical support for enhancing oil recovery and CO2 sequestration through CO2 injection in tight oil formations.

This study systematically evaluated the tribological behaviors of polycrystalline diamond compact (PDC) when paired with various materials in high temperature drilling fluid. The results demonstrated that PDC/Si3N4 exhibited excellent overall performance under high temperature, with both the coefficient of friction and wear rate being significantly lower than those at room temperature. This phenomenon was attributed to an effective wear-oxidation lubrication mechanism: high temperature promoted the formation of a composite synergistic film consisting of both oxide layer and carbonaceous material. In contrast, although PDC/steel showed reduced the coefficient of friction under high temperature, this was accompanied by an increased wear rate. The decrease in the coefficient of friction primarily originated from decreased shear strength due to material softening and improved graphitization degree within the transfer layer. However, high temperature also aggravated both oxidation processes and adhesive wear. Coupled with the corrosion induced by Cl- in the drilling fluid, multiple failure mechanisms interacted synergistically, leading to accelerated wear.

The all-metal positive displacement motor (AMPDM) is a key downhole power tool for deep well drilling, but its service life is severely limited by wear from the synergy of stator-rotor impact-sliding, abrasive particles, and drilling fluid. Conventional studies fail to address this issue as they cannot replicate AMPDM's complex impact-sliding motion and multifactor coupled wear mechanisms. This study developed a multifunctional test system to simultaneously simulate impact-sliding motion and dynamic abrasive interactions in drilling fluid, and investigated the tribological performance of a novel nitrided 38CrMoAl steel/YL10.2 cemented carbide tribo-pair. The results show that the nitrided 38CrMoAl steel/YL10.2 cemented carbide pairing reduces the friction coefficient by 75% compared with the untreated 38CrMoAl steel/YL10.2 carbide pair under identical working conditions, demonstrating that the novel tribo-pair achieves substantially enhanced tribological performance. A critical load of 600 N was identified, at which contact pressure exceeds SiO2 abrasives' compressive strength, triggering wear mechanism evolution from mild rolling abrasive wear to severe abrasive wear that increases wear volume by 175% due to deep particle embedding, and finally to oxidative wear as abrasives fragment and a protective friction oxidation film forms. Additionally, aligning rotor surface texture with abrasive sliding direction significantly reduces wear volume compared to perpendicular orientation, providing a rotor design optimization criterion. This study clarifies the coupled effect of impact load and abrasives on AMPDM wear, offering engineering guidance to extend its lifespan in deep resource exploration.

In the field of drilling engineering, the rubber screw motor adopts the cycloidal principle for drilling, and the rubber bushing will carbonize and fail when the drilling at 180°C and above. As a positive displacement motor, the cycloidal motor has high temperature and corrosion resistance, low speed, and high torque. It is used in traditional mechanical engineering fields, such as the hydraulic cycloidal motor of the hoist, while the hydraulic cycloidal motor applied in the drilling fluid field has been blank. Therefore, the cycloidal motor in drilling fluid medium is proposed in this paper, which is different from the traditional mechanical cycloidal motor in oil medium and applied in the field of high-temperature drilling engineering. Based on the clearance flow theory and energy conservation law, the mathematical model of fluid leakage of the cycloidal motor was calculated. Through Matlab programming, the cloud diagram of fluid pressure drop, clearance, and viscosity on the leakage of the cycloidal motor was calculated numerically. The characteristic curve of motor numerical calculation was compared and verified by experimental data of the OMT 160 cycloidal motor produced by Danfoss Company. A theoretical basis for selecting clearance of machining and manufacturing all-metal cycloidal motor were provided.

In deep-sea oil and gas exploitation, the reliability of mud lifting pumps directly affects the operational safety. However, the coupled operation of multiple pumps may easily induce composite faults such as abnormal vibration and excessive torque, which the conventional diagnostic methods struggle to address effectively. This article proposes an improved support vector machine (SVM) diagnostic method based on the collaborative optimization of linear discriminant analysis (LDA) and adaptive differential evolution (ADE). It uses LDA to reduce the dimensionality of the dataset and extract fault-sensitive features, and dynamically optimizes the kernel function parameters of SVM through the ADE algorithm, thereby constructing the LDA–ADE–SVM hybrid diagnostic model. To verify its effectiveness, a ten-stage centrifugal pump fluid–structure coupling model was built. Eighty-one groups of orthogonal experiments were designed to obtain 81 groups of simulation data. Compared with SVM, LDA–SVM, and LDA–PSO–SVM, the LDA–ADE–SVM achieved an accuracy of 96.30% with a calculation time of 13.93 s, outperforming the other algorithms. A dual-pump test platform was built to simulate dynamic working conditions. Fifty-four groups of orthogonal experiments were completed to collect 9294 samples, which were divided into groups at a ratio of 7:3 for comparison. The LDA–ADE–SVM showed significant advantages with an accuracy of 98.27% and a calculation time of 1028.16 s. This verifies its adaptability and robustness, providing support for offshore drilling and oil-gas development safety.

The formation of tectonic-magmatic-sedimentary processes during the Permian in the Beishan region represents a highly debated research topic along the southern margin of the Central Asian Orogenic Belt and even globally: does it mark the final subduction and amalgamation of the Paleo-Asian Ocean, or does it instead represent rifting superimposed upon an earlier orogen? New field observations combined with geochemical analyses reveal that the Liuyuan area is dominated by Early Permian basalts, associated with a rifting sedimentary sequence. During the Mid-Late Permian, gabbro-rhyolite associations were emplaced, accompanied by minor lacustrine sedimentation. The late stage was characterized by minor granitic intrusions or dikes with adakitic affinities, culminating in the emplacement of lamprophyre dikes. The basalts and gabbros in the Liuyuan area display mantle-derived geochemical signatures, with compositions intermediate between MORB and OIB. The exposed Permian basalt-rhyolite bimodal magmatic suite represents a genetically integrated rift-related rock series. Geochemical data from the Ordovician granites and schists within the belt reveal adakitic characteristics, implying that the Permian granitic rocks largely represent remelting products of these early granitic and schistose protoliths. Collectively, the lithological characteristics and magmatic associations clearly demonstrate that the tectonic setting during the Early Permian corresponded to a post-collisional extensional environment superimposed upon the early Paleozoic orogenic belt (Caledonian Huitongshan ophiolite-arc accretionary orogen), which subsequently underwent tectonic inversion to form the present-day orogenic structure. This paper proposes a theoretical model wherein the bimodal magmatic suite was generated by the upwelling of enriched asthenospheric mantle material, providing the driving mechanism for rifting. It formed within a post-collisional extensional environment developed over a complex pre-existing orogenic belt and was subsequently inverted, forming the current tectonic belt-a typical intracontinental Pyrenees-type orogeny.

To describe the dynamic bidirectional phase transformation process and non-metallic inclusions' motion behavior during electroslag fusion welding, a fully coupled mathematical model integrating electromagnetics, fluid dynamics, heat transfer, and inclusion dynamics was established, and the mechanism of inclusion removal and capture was analyzed. Experimental validation confirmed the model's accuracy, revealing the geometric characteristics and elemental composition of inclusions newly formed at the solidification front. Results indicate that newly formed inclusions in 04Cr13Ni5Mo material during ESFW have diameters below 5 mu m, primarily consisting of sulfides, chromium-aluminum-manganese composite oxides, calcium aluminum silicates, and Cr23C6 carbides. The ESFW process achieves deep metal purification with significantly enhanced inclusion removal rates (>= 95 % for 1 mu m inclusions, similar to 99 % for 10 mu m inclusions). Electrode melting rate significantly alters inclusion removal efficiency and capture location distribution by influencing flow patterns. Under the studied geometric specification, the optimal value was determined to be 2.582 kg/min. These findings provide crucial theoretical support for optimizing ESFW process parameters, enhancing fusion welding zone cleanliness, and promoting the dispersion of fine inclusions.

Soil contamination, particularly by heavy metals, poses significant environmental and public health risks. Traditional solidification/stabilization (S/S) methods, such as high-pressure jet grouting, face challenges related to inefficient remediation, slurry leakage, and uneven contaminant distribution. To address the engineering challenges identified during field applications of in-situ jet injection technology, this study proposes a novel implementation of S/S technology: pulse jet grouting. Additionally, this study employs numerical method and field experiments, utilizing a single-factor analysis approach to optimize the process parameters. Numerical and experimental results show that the accuracy of analogy method is improved by 12.3 % compared with the transfer matrix method. A set of optimized pulse grouting process parameters was established as follows: injection pressure of 3 MPa, pipeline specification of DN6, oscillation cavity length of 5.2 mm, lower nozzle diameter of 1.8 mm, injection angle of 30 degrees, injection distance of 15 mm, symmetrical nozzle arrangement, and an optimal nozzle spacing of 20 cm. Under these parameters, the scouring range reaches 8.9 cm, the stirring and mixing area extends to 14.7 cm, and the squeezing-permeation area covers 25 cm. The optimized process parameters significantly enhance performance of pulse grouting, increasing both the remediation depth of pollutants and the migration range of remediation agents. Moreover, the injection effectiveness under varying pressure conditions is notably improved. This research provides essential technical support and a theoretical foundation for the practical application of pulse grouting technology in the solidification and stabilization of heavy metal-contaminated soils.

The scientific drilling of ultradeep wells faces problems such as high-temperature and high-pressure conditions, poor surface drive feasibility, and low reliability. Therefore, it is an inevitable choice to use all-metal bottomhole power drilling tools. The key component of the all-metal positive displacement power drilling tool is its dynamic sealing structure, which determines its dynamic characteristics. In this paper, we study the working process and output characteristics of the dynamic sealing structure of the radial dynamic sealing structure of a metal roller to provide a reference for the research and development of a new type of volumetric downhole motor. Based on the metal roller radial dynamic seal structure, we establish a theoretical model of the movement and force of the roller dynamic seal working process by using the basic theory of fluid mechanics. We further optimize the optimal structural parameters to ensure the efficient operation of the motor. In addition, we establish the leakage model of roller radial dynamic seal gap based on gap flow theory. Through numerical analysis and computational fluid simulation, we obtain the influence of dynamic seal gap leakage on gap height, pressure difference between high-and low-pressure chambers, viscosity coefficient, and rotational speed. We establish a mathematical model of the dynamic output characteristics of the motor dynamic seal: The average output torque of the designed all-metal volumetric power drilling tool is 1004.16 Nm, and the output mechanical efficiency is 78.45%, which lays a certain foundation for the popularization and application of the new all-metal volumetric downhole power drilling tool.

The exploration and development of deep marine resources are faced with the problems of poor drill ability and serious wellbore instability in high temperature and high-pressure formations. The bottom hole dynamic drilling tool with low vibration characteristics is the best choice for deep well drilling. The output torque of the turbodrill is relatively small, which limits its application potential. In this study, intelligent optimization algorithms are used to improve the blade shape design to improve its output torque. Firstly, based on the moment of momentum theorem, the key blade profile parameters and range affecting the output characteristics of the turbodrill are analyzed and summarized. Subsequently, the five-order polynomial method and UG software (version 10.0) are used to complete the three-dimensional configuration of the bent-twisted blade. Then, based on the GA-LSSVM-MOPSO-TOPSIS intelligent optimization algorithm, the two-dimensional and three-dimensional modeling design parameters under the optimal hydraulic performance are optimized, and the accuracy of the intelligent optimization algorithm and parameters is verified by CFD simulation analysis. The results show that the hydraulic efficiency of only 4.9% is sacrificed, and the output torque is increased by 36.61%, which significantly improves the hydraulic performance of the turbodrill and provides guidance for the design of low-speed and high-torque turbodrills.

Downhole drilling operations expose all-metal positive displacement motors (AMPDM) to abrasives of different sizes, causing serious abrasive wear behavior. Controlling the entry of large particles into the motor by installing a filter can effectively reduce wear conditions and improve its lifespan. This study investigated the particle size effect on abrasive wear to seek an appropriate filter size for AMPDM. The multi-function tribo-tester was modified according to the actual working conditions of the stator and rotor. The tribological properties of stator material (nitrided 38CrMoAl steel) against rotor material (YL10.2 cemented carbide) were conducted using SiO2 particles with 1-500 mu m sizes in the range on a pin-on-disc tribo-tester under wet sliding-vibration conditions. The results showed more complicated friction coefficient evolution characteristics for small particles, existing two stable stages. Two critical-size values of average wear-rate and wear mechanism transformation are determined. The wear products of the tribochemical reaction were determined. The filter porosity of about 200 mu m may be an optimal selection to decrease wear. This work has developed new insights into how AMPDM responds to changing abrasive sizes and provides a proposal for controlling the entry size of abrasive particles.

Lubrication film thickness and coating wear depth are two important parameters indicating tribological condition in tribological elements. In this paper, a new ultrasonic model was proposed to measure the lubricant film thickness and the coating wear depth simultaneously. A ratio coefficient, which was constructed by dividing the echo signal reflected from the oil film layer to that reflected from the pad-coating interface, was established, and the amplitude and phase of this ratio coefficient were used to measure the film thickness and wear depth, respectively. A pre-calibration test was conducted to help eliminate the effect of the temperature and a dynamic calibration test rig was built to construct series known oil film thickness and wear depth under various temperature. The calibration tests demonstrated that the proposed ultrasonic method could measure the lubricant film thickness and coating wear depth simultaneously under varying temperature. This paper can provide an effective means to observe the evolution characteristics between lubrication and wear.

Horizontal wells jet injection has been proved to be an efficient and green in-situ remediation technology for contaminated sites in practical engineering. However, the injection mechanism has not been studied, which leads to the over dependence of injection parameters on engineering experience. In this work, horizontal well jet injection technology for in-situ remediation of contaminated sites was studied through laboratory experiments and field tests. The jet injection process was simulated through vertical submerged jet scouring of loading soil in laboratory. In addition, the field test was carried out in a contaminated site with a pollution plume area 3004.8 m. Based on the laboratory experimental results, the relationship between scour hole dimension and soil parameters and jet parameters was analysed. The remediation effect of contaminated sites within 28 days after injection was evaluated. The results showed that soil pressure will suddenly drop at the beginning of the injection, and then gradually decrease to a stable value. The dimension of the scouring hole is positively correlated with the injection pressure and average particle size of the soil, and is negatively correlated with clay content. After 21 days of horizontal well injection, the pollutant concentration in the contaminated site is lower than the standard requirement. This study provides a new method for efficient and low-cost in-situ remediation of contaminated sites.

Diamond reinforced WC based cemented carbide shows potential for hardbanding applications, with its performance hinging on the matrix's toughness, strength, and diamond holding ability. However, a comprehensive theoretical understanding of enhancing mechanical properties and controlling microstructure during pressureless infiltration remains limited. In this study, WC based cemented carbide was fabricated via pressureless infiltration, and the effects of Ni and B content variations on the bending strength and microstructural characteristics of the composites were systematically investigated. The results demonstrated that WC based cemented carbide with Cu-Zn-Mn infiltration exhibited lower bending strength compared to Cu-Mn-Ni. However, with the addition of 4 wt%Ni, its bending strength (833.4 MPa) increased by 10.3 %, reaching a level comparable to that of Cu-Mn-Ni (861.3 MPa). B was added to two distinct diamond composites formulations-60 wt%WC/40 wt%Cu-Mn-Ni and 56 wt%WC/40 wt%Cu-Zn-Mn/4 wt%Ni-with varying proportions. The diamond composites with Cu-Zn-Mn infiltration reached maximum bending strength at 0.5 wt%B content, achieving 714.2 MPa. At the same time, the diamond holding force coefficient reached 85.7 %, surpassing that of Cu-Mn-Ni composites (82.9 %). The study further identified that controlled diamond surface etching and interfacial boron carbide formation were the primary contributors to enhanced diamond holding ability.

Traditional methods for measuring the rotational speed of downhole equipment require various external power sources. This study introduces a high-performance petal-shaped triboelectric nanogenerator (PS-TENG) for monitoring rotational speed variations in downhole equipment. The PS-TENG does not require an external power supply, and through the application of Fourier and Hilbert-Huang transforms, it enables real-time monitoring of instantaneous rotational speed in downhole machinery under both constant and variable speed conditions. Moreover, the PS-TENG exhibits excellent power generation performance. With power management circuits (PMCs), the PS-TENG can charge a 100- mu F capacitor to 10 V in just 4 s at a rotational speed of 800 r/min. It can also recharge a 150-mAh lithium battery from 1.6 to 2 V within 280 s. Notably, the PS-TENG demonstrates favorable adaptability to high-humidity environments in downhole settings, and due to its soft-contact motion form, the PS-TENG has a lifespan that meets the requirements of downhole applications. In conclusion, the PS-TENG offers an innovative and efficient solution for self-powered sensing and real-time rotational speed monitoring in downhole applications.

Abrasive wear is a prevalent failure issue in the drilling environment that frequently hampers the reliability and longevity of downhole tools. This study investigated the friction and wear behavior of common drilling materials (nitrided 38 chromium-molybdenum-aluminum (38CrMoAl) steel against 10 cobalt-tungsten-carbon (10Co-WC) cemented carbide) under two conditions (with or without silicon-oxygen (SiO2) particles). The influence of abrasive particles on the coefficient of friction, wear loss, wear surface morphology, and wear mechanisms is discussed in detail. The results indicated that the dispersion of abrasive particles between the contact surfaces reduced the coefficient of friction by approximately 15-25% under loads ranging from 200 to 1,000 N, enhancing the frictional performance. However, this came at the cost of increased wear loss. The wear loss of 38CrMoAl steel increased by 60-80% in the presence of SiO2 particles. The discrepancy between wear mass (measured by weighing) and wear volume (obtained by three-dimensional surface topography) reached up to 40%, highlighting the complex interplay of particle embedding and drilling fluid adsorption. Surface topography studies showed that abrasive particles enhanced lubrication film coverage at lower loads but also induced material spalling. At higher loads (800-1,000 N), the formation of a stable lubricating film reduced wear loss by 20-30%, regardless of abrasive particles presence. Chemical analysis confirmed the generation of anti-friction oxides and chlorides on worn surfaces, while their content decreased by 15-20% due to lubrication film disruption under abrasive particle conditions. The study provides quantitative insights for optimizing downhole tool materials and operational parameters in abrasive drilling environments.

The rotor, as one of the key components of a downhole motor, directly affects the safety, cost, and efficiency of the entire drilling operation. This paper proposes an annular triboelectric sensor (ATES) for monitoring rotor faults in downhole motors, marking an innovative application of triboelectric nanogenerators in the field of downhole fault monitoring. The ATES is characterized by its simple structure, long lifespan, and high- temperature resistance, making it particularly suitable for the complex conditions of downhole environments. The ATES can also monitor radial vibrations of downhole tools in real time and, when combined with the ResNet18 algorithm, can accurately identify rotor imbalances, misalignments, and rubbing faults, achieving a classification accuracy of up to 100 %. Additionally, this paper presents an intelligent offline analysis system for downhole rotor fault diagnosis, which integrates deep learning and visualization techniques. This system efficiently identifies rotor faults and outputs visual results, providing drillers with intuitive diagnostic references, thereby significantly improving the efficiency and accuracy of fault diagnosis. Overall, the ATES offers a viable pathway for developing new downhole intelligent sensing devices and technologies.

Currently, deep drilling operates under extreme conditions of high temperature and high pressure, demanding more from subterranean power motors. The all-metal positive displacement motor, known for its robust performance, is a critical choice for such drilling. The dimensions of the PDM are crucial for its performance output. To enhance this, optimization of the motor's profile using a genetic algorithm has been undertaken. The design process begins with the computation of the initial stator and rotor curves based on the equations for a screw cycloid. These curves are then refined using the least squares method for a precise fit. Following this, the PDM's mathematical model is optimized, and motor friction is assessed. The genetic algorithm process involves encoding variations and managing crossovers to optimize objective functions, including the isometric radius coefficient, eccentricity distance parameter, overflow area, and maximum slip speed. This optimization yields the ideal profile parameters that enhance the motor's output. Comparative analyses of the initial and optimized output characteristics were conducted, focusing on the effects of the isometric radius coefficient and overflow area on the motor's performance. Results indicate that the optimized motor's overflow area increased by 6.9%, while its rotational speed reduced by 6.58%. The torque, as tested by Infocus, saw substantial improvements of 38.8%. This optimization provides a theoretical foundation for improving the output characteristics of all-metal PDMs and supports the ongoing development and research of PDM technology.

Erosion damage of clearance fits is the major factor for the failure of metal-to-metal screw motors. In this study, the slurry erosion behavior of the WC-based laser cladding layer was investigated. It aimed to explore the effect of SiO2 particle concentration on the laser cladding layer. The experimental results indicate that the WC-based laser cladding layer exhibits excellent erosion resistance across various particle concentration environments. The presence of the 'baffle effect' resulted in the cladding layer demonstrating enhanced erosion resistance, particularly at high particle concentrations. The 'baffle effect' refers to exposed WC particles hindering the movement of SiO2 particles. As SiO2 particles continuously impact the clearance material surface, much of the matrix on the cladding surface is removed. The presence of remaining WC particles on the clearance material can impede the impact of particles in the slurry. The current results aim to offer experimental support for future investigations of surface strengthening methods for metal-to-metal screw motors.