Search Results (188)

Vibration-stimulated waterflooding (VS-WF) is a promising enhanced oil recovery (EOR) method, especially for reservoirs with high-viscosity or emulsified oil. This study explores the effect of low-frequency vibration (2 Hz and 5 Hz) on oil mobilization under constant pressure and flow rate, using both crude and emulsified oil samples. Vibration significantly improves recovery by inducing stick-slip flow, lowering the threshold pressure, and enhancing oil phase permeability while suppressing the water phase flow. Crude oil recovery increased by up to 24% under optimal vibration conditions, while emulsified oil showed smaller gains due to higher viscosity. Intermittent vibration achieved similar recovery rates to continuous vibration, but with reduced energy use. Statistical analysis revealed a strong correlation between pressure fluctuations and oil production in vibration-assisted tests, but no such relationship in non-vibration cases. These results provide insight into the mechanisms behind vibration-enhanced recovery, supported by analysis of pressure and flow rate responses during waterflooding. Full article

This paper presents a comprehensive study of torsional stick–slip vibrations in rotary drilling systems through a comparison between two lumped parameter models with differing complexity: a simple two-degree-of-freedom (2-DOF) model and a complex high-degree-of-freedom (high-DOF) model. The two models are developed under identical boundary conditions and consider an identical nonlinear friction torque dynamic involving the Stribeck effect and dry friction phenomena. The high-DOF model is calculated with the Finite Element Method (FEM) to enable accurate simulation of the dynamic behavior of the drill string and accurate representation of wave propagation, energy build-up, and torque response. Field data obtained from an Algerian oil well with Measurement While Drilling (MWD) equipment are used to guide modeling and determine simulations. According to the findings, the FEM-based high-DOF model demonstrates better performance in simulating basic stick–slip dynamics, such as drill bit velocity oscillation, nonlinear friction torque formation, and transient bit-to-surface contacts. On the other hand, the 2-DOF model is not able to represent these effects accurately and can lead to inappropriate control actions and mitigation of vibration severity. This study highlights the importance of robust model fidelity in building reliable real-time rotary drilling control systems. From the performance difference measurement between low-resolution and high-resolution models, the findings offer valuable insights to optimize drilling efficiency further, minimize non-productive time (NPT), and improve the rate of penetration (ROP). This contribution points to the need for using high-fidelity models, such as FEM-based models, in facilitating smart and adaptive well control strategies in modern petroleum drilling engineering. Full article

The torsional, lateral, and axial vibrations that occur during drilling operations have negative effects on the drilling equipment. These negative effects can cause huge economic impacts, as the failure of drilling tools results in wasted materials, non-productive time, and substantial expenses for equipment repairs. Many researchers have tried to reduce these vibrations and have tested several models in their studies. In most of these models, the drill string used in oil wells behaves like a rotating torsion pendulum (mass spring), represented by different discs. The top drive (with the rotary table) and the BHA (with the drill pipes) have been considered together as a linear spring with constant torsional stiffness and torsional damping coefficients. In this article, three models with different degrees of freedom are considered, with the aim of analyzing the effect of variations in the stiffness and damping coefficients on the severity of torsional vibrations. A comparative study has been conducted between the three models for dynamic responses to parametric variation effects. To ensure the relevance of the considered models, the field data of torsional vibrations while drilling were used to support the modeling assumption and the designed simulation scenarios. The main novelty of this work is its rigorous comparative analysis of how the stiffness and damping coefficients influence the severity of torsional vibrations based on field measurements, which has a direct application in operational energy efficiency and equipment reliability. The results demonstrated that the variation of the damping coefficient does not significantly affect the severity of the torsional vibrations. However, it is highly recommended to consider all existing frictions in the tool string to obtain a reliable torsional vibration model that can reproduce the physical phenomenon of stick–slip. Furthermore, this study contributes to the improvement of operational energy efficiency and equipment reliability in fossil energy extraction processes. Full article

Rotary drilling systems with PDC bits, commonly used for drilling deep wells in the production and exploration of oil and natural gas, frequently encounter severe vibrations. These vibrations can cause significant damage to the drilling system, particularly its downhole components, leading to drilling performance inefficiencies, notably reducing the rate of penetration and incurring high costs. This paper presents a parametric study on a proposed new axial semi-active tool designed to mitigate these unwanted vibrations. The tool, an axial absorber with tunable stiffness and damping coefficients over a wide range, composed of a hybrid magnetorheological elastomer-fluid (MRE-F), is installed above the PDC bit. In this study, the lumped parameter model considering axial and torsional vibrations is followed to assess the effectiveness of including the proposed absorber in the drill-string system’s behavior and to estimate the optimal coefficient values for achieving high-efficiency drilling. The drilling system response shown in this study indicates that, with optimal axial absorber coefficient values, the bit dynamically stabilizes, and unwanted vibrations are minimized, effectively eliminating the occurrence of bit-bounce and stick–slip, even when operating at critical frequencies. The proposed semi-active control tool has been proven to significantly reduce maintenance time, reduce the costs associated with severe vibrations, extend the lifespan of bottom-hole assembly components, and achieve smoother drilling with a simple addition to the drilling system. Full article

Introduction: Robotic-assisted (RA) spine surgery enhances pedicle screw placement accuracy through real-time navigation and trajectory guidance. However, the absence of traditional direct haptic feedback by freehand instrumentation remains a concern for some, particularly in minimally invasive (MIS) procedures where direct visual confirmation is limited. During RA spine surgery, navigation systems display three-dimensional data, but factors such as registration errors, intraoperative motion, and anatomical variability may compromise accuracy. This technical note describes a visuohaptic intraoperative phenomenon observed during RA spine surgery, its underlying mechanical principles, and its utility. During pedicle screw insertion with a slow-speed automated drill in RA spine procedures, a subtle and rhythmic variation in resistance has been observed both visually on the navigation interface and haptically through the handheld drill. This intraoperative pattern is referred to in this report as a cyclical insertional torque (CIT) pattern and has been noted across multiple cases. The CIT pattern is hypothesized to result from localized stick–slip dynamics, where alternating phases of resistance and release at the bone–screw interface generate periodic torque fluctuations. The pattern is most pronounced at low insertion speeds and diminishes with increasing drill velocity. CIT is a newly described intraoperative observation that may provide visuohaptic feedback during pedicle screw insertion in RA spine surgery. Through slow-speed automated drilling, CIT offers a cue for bone engagement, which could support intraoperative awareness in scenarios where tactile feedback is reduced or visual confirmation is indirect. While CIT may enhance surgeon confidence during screw advancement, its clinical relevance, reproducibility, and impact on placement accuracy have yet to be validated. Full article

With increasing demand for high-precision motion control systems, high operational speed and load capacity are imposed with piezoelectric stick-slip actuators based on compliant mechanisms, yet their performances are often constrained by the step size and move speed. In this paper, a novel piezoelectric stick-slip actuator featuring flexure beams and a trapezoidal driving foot is proposed for high dynamic performance and load requirements. The trapezoidal structure consists of a trapezoidal driving foot to differentiate the friction in the stick and slip phases, four flexure beams for the high resonant frequency due to distributed compliance and the high load capacity due to structural geometry, and a rigid rod for motion transmission. At first, the mechanism design and the working principle are described in detail. Then, its dominant performances are predicted through finite element analysis, including the step size and the first natural frequency. On this basis, the structural parameters are optimized through the genetic algorithm. As a result, the forward displacement in the stick phase can be obtained as 4.8 $\mathsf{\mu }$m through FEA simulations, where the first natural frequency can be observed as 627 Hz. Full article

The rapid expansion of land reclamation necessitates a fundamental understanding of the strain rate effects on structured clays. While the rate effect has been widely studied in various soils, the interplay between bond structure and strain rate sensitivity remains unclear. This study investigates these mechanisms using artificially cemented kaolin (ACK) with controlled curing periods (2 and 30 days) to simulate naturally bonded clays. A series of undrained triaxial tests was conducted under low (100 kPa) and high (600 kPa) confining stresses, employing constant strain rates (0.01–5%/h) pre-peak and stepwise rate changes post-peak. The results reveal that the strain rate effects are governed by the bond structure maturity and drainage mechanisms. For the 30-day curing ACK, the pre-peak strength under low confining stress shows minimal rate sensitivity due to the rigid bond, while high confining stress induces a “negative” rate effect attributed to localised drainage along shear planes. The post-peak behaviour consistently exhibits a positive isotach-type rate effect (+3%/log-cycle) driven by viscous sliding. In contrast, the 2-day curing ACK displays negative rate effects pre-peak influenced by ongoing curing and post-peak strength reductions (−8%/log-cycle) linked to stick-slip dynamics. These findings establish a framework for predicting rate-dependent behaviour in structured clays, offering insights into land reclamation and subsequent construction work. Full article

During the drilling process, stick–slip vibrations are one of the critical causes of bottom-hole assembly (BHA) failure and reduced drilling efficiency. To address this, this study first proposes a drill-string model based on a three-dimensional nonlinear finite beam element, combined with Hamilton’s principle of virtual work, to comprehensively describe the nonlinear behavior of the drill-string system. Next, to improve computational efficiency, the model is reduced using the modal truncation method, which retains the key modes of drill-string vibrations. Based on this, a model predictive control (MPC) method is designed to eliminate stick–slip vibrations. Furthermore, the robustness of the MPC method under parameter uncertainties is also investigated. In particular, the impact of the weight on bit (WOB) on the drill bit’s torsional velocity is further considered, and an MPC angular velocity comprehensive control scheme based on the dynamic WOB (DWOB-MPC) is proposed. This scheme stabilizes the velocity of the drill bit by dynamically adjusting the WOB, thereby eliminating stick–slip vibrations. Simulation results demonstrate that both the proposed MPC and DWOB-MPC methods effectively suppress stick–slip vibrations. Notably, the DWOB-MPC method further reduces the settling time and overshoot, exhibiting superior dynamic performance. Full article

This work continues the study of a mathematical model for the motion of a mass–spring–damper system with friction. There, a two-mass model was constructed, its solvability established, the steady states investigated, and numerical simulations presented. The main interest here is in the modeling, analysis of the steady states, and simulation of a three-mass system—in particular, in the propagation of detachment or slip waves, which happen when the system transits from a stick state to a slip motion. The introduction of friction changes the problem into systems of three differential set-valued inclusions, which are mathematically and computationally very challenging. The analysis of the steady states shows the regions of stick, where there is enough frictional resistance that prevents motion. The proposed numerical methods are implemented, and the simulations show some representative types of system behavior, especially the cases of detachment waves. Some of the numerical simulations specifically support the theoretical analysis of slip initiation, reachability, and energy balance. Full article

Considering stick–slip vibration and the impact loads formed while drilling in strongly heterogeneous formations or soft–hard interbedded formations, an adaptive matching drilling load method is presented in this paper to form dynamic drilling loads to automatically adjust the applied axial load acting on the drill bit. To determine the rock-breaking mechanisms using this method, the structure of a kind of downhole tool was designed and a discrete element simulation model was established with a PDC cutter cutting heterogeneous rock. The effects of the load factor, the applied initial axial force, and the driven force on the variation in the axial force, as well as the moving displacement of the PDC cutter and the rock-breaking characteristic parameters, were studied. The failure states of the simulated rock have a positive correlation with the number of total cracks generated in the rock-breaking process, as opposed to MSE. The decrease in the reaction force suffered by the PDC cutter in the cutting direction was caused by the automatically adapting load, although there was no significant regularity in the axial direction. MSE decreased obviously under the action of the adaptive matching drilling load method so that the contacting states of the PDC cutter could be improved, thus raising the rate of penetration of the PDC bit. This study provides a feasible method for rapidly drilling in highly heterogeneous formations or soft–hard interbedded formations. Full article

The global response characteristics of rotor/stator rubbing systems are critical for the optimal design and safe operation of rotating machinery. Based on the mathematical model, numerical simulation and theoretical analysis have been widely carried out to study the regions of different responses, which have not been globally explored and evaluated by experiments with the unified parameters of a mathematical and physical model. Thus, the existence conditions of the global responses of a rubbing rotor are experimentally investigated and then quantitatively compared with theoretical solutions and dynamic simulation results. With the equivalent stiffness and the kinetic dry friction identified by the aid of a new voltage divider, the rubbing rotors are accurately tested by the new experimental technique and dynamically simulated by rigid-flexible coupling technique. From the comparison results of orbit and full spectrum, it is shown that the response characteristics of no rub motion, synchronous full annular rub, partial rub, and dry friction backward whirl obtained by experiment and dynamic simulation are in good agreement with theoretical solutions. Then, it is also concluded that all boundaries of the existence/co-existence regions of the whirling motions are proved to be valid. Moreover, stick-slip oscillation is detected in the rotor/stator testing system. Full article

Composite interfaces, particularly in joints, play a critical role in the damage resistance and durability of structures for aeronautics applications. This study investigates the use of carbon nanotube (CNT) interleaves for the co-cured joining of composite parts and its effects on fracture toughness and damage progression at the co-cured interface. CNT dispersed in a thermoset resin and partially cured into thin film interleaves at three weight concentrations (0.5% wt., 1% wt., and 2% wt.) of two discrete thicknesses (200 µ and 500 µ) were investigated. The fracture toughness of the co-cured interface with CNT interleaves in mode I and mode II loading conditions was determined through double cantilever beam and end-notched flexure tests, respectively. The results reveal that despite the occurrence of a stick–slip damage progression in mode I, the crack arrest mechanisms and forces are surprisingly predictable based on interleaf thickness. At CNT concentrations above 1% wt., there was no significant enhancement of toughening, and interleaf thickness controlled the crack arrest loads. Damage delay also occurred at the interface due to the activation of multiscale toughening mechanisms. Toughening in mode II was dominated by CNT pullout resistance and, therefore, yielded up to six-fold improvement in critical fracture toughness. These insights offer significant potential for designing joints with nanocomposites for aerospace applications, incorporating inherent toughening and damage delay mechanisms. Full article

Nowadays, the exploration of different deep subsurface energy-related natural resources (oil/gas, natural hydrogen, geothermal, among others) is gaining importance. The exploration of these deep subsurface resources can present several challenges, such as complex lithology to be drilled, high depth to be reached, and considerable rock hardness, among others. In this context, the implementation of methodologies focused on real-time operational efficiency improvement has gained attention. Mechanical specific energy (MSE), rate of penetration (ROP), and even vibrations are key indicators that can be combined and used for drilling process optimization and efficiency improvement. These indicators are linked to operational drilling mechanic parameters, such as weight on bit (WOB), rotary speed (RPM), torque (TOR), and flow rate (FLOW). Despite this, multi-objective research considering both MSE and torsional vibration (stick–slip) has been largely overlooked in drilling optimization studies. Therefore, the main objective of this paper is to analyze field data from carbonate reservoirs using a multi-objective optimization approach based on torsional vibration, by means of stick–slip and MSE analyses. The focus is to minimize MSE values and mitigate stick–slip using self-developed decision matrices which consider WOB, RPM, and FLOW as key elements. The research results demonstrated that FLOW is a crucial parameter for minimizing torsional vibrations and should be prioritized in drilling operations, also for mitigating undesirable events. The optimization process yielded optimal WOB values for each RPM range (from 100 to 180 [rev/min]) and FLOW range (from 2200 to 3900 [L/min]). The decision matrix revealed that regions with high desirability correspond to high RPM (above 120 [rev/min]), with WOB varying from 5 to 13 [tf], and FLOW rates above 2300 [L/min]. Critical drilling conditions occur when low RPM, low FLOW, and high WOB (above 13 [tf]) are applied, as these conditions and this combination of parameters are most susceptible to release severe torsional vibrations, indicating a higher risk of operational problems. Full article

Torsional vibrations pose a serious challenge in drilling operations and can lead to effects such as stick-slip phenomena, tool wear, and reduced drilling efficiency. While previous research has been conducted on torsional vibrations, there is a notable gap in comparative studies that assess the scalability of downscale models to real-world drilling conditions. This study fills this gap by systematically comparing torsional vibrations in downscale and upscale drill strings under different torque conditions at three different depths, shedding light on scaling effects in drilling vibrations. Numerical simulation was carried out taking into account non-linear interactions, damping effects, and torque variations. The laboratory set-up was for a well length of 15 m and was geometrically scaled to represent an upscale well of 450 m. Certain operational parameters such as rotation speed, torque, density, and friction coefficients were modified to keep realistic dynamic behavior, and all models were run at an identical speed of rotation to enforce consistency. The results show that both the upscale and downscale models exhibited stick-slip behavior, but differences in vibration intensity and stabilization trends point out how scaling affects torsional dynamics. Notably, the upscale bit first faced higher torsional oscillation than the set rotation speed after overcoming stick-slip before stabilizing, whereas the downscale bit went through prolonged stick-slip instability before synchronization. This study enhances the understanding of scaling effects in torsional drilling vibrations, offering a foundation for optimizing experimental setups and improving predictive modeling in drilling operations. Full article

Single and multiple pull-out properties of a nano-processed para-aramid fabric structure were investigated. The nano pull-out behavior exhibited three distinct regions, namely crimp extension, interlacement rupture, and stick-slip. Multiple yarn pull-out tests demonstrated a significantly higher pull-out force compared to single-yarn pull-out, primarily attributed to the incorporation of nanoparticles. Furthermore, it was observed that an increase in fabric length resulted in an approximately linear increase in both yarn crimp extension and pull-out force. The highest pull-out force was obtained in the nano-hexagonal boron carbide (nh-B₄C, 0.3%) para-aramid structure, followed by multiwalled carbon nanotube (MWCNT, 0.3%) para-aramids. This is because of the enhancement of filament-to-filament friction, especially in the interlacement zone of fabric, alongside the cumulative frictional interactions among the nanoparticles. Additionally, the findings highlight an improvement in crimp extension energy absorption facilitated by nanoparticle incorporation in soft fabric. Notably, the improvement in the energy absorption capacity of yarns within the fabric, without disintegration, is considered significant at this stage. These results indicate a promising potential for performance enhancement in prospective soft ballistic applications. Full article