Drilling Conditions Research Articles

Influence of drilling technology on wear evolution of impregnated diamond bits

Diamond exposed on the surface of an impregnated diamond bit (IDB) is the key to breaking rock. The exposure conditions of the diamond affect the drilling efficiency and life of the bit. However, scant attention has been directed towards investigating the diamond exposure mechanism of IDBs, particularly under varying drilling process conditions. In this study, drilling experiments were conducted on granite under rotary and rotary-percussive drilling conditions using a self-developed drilling test platform. The evolution of diamond emergence on the surface of the IDB under two drilling technology conditions was evaluated; the typical characteristics of diamond wear and their causes were discussed. The results indicate that under rotary drilling conditions, the primary evolution process of diamond on a slippery IDB surface follows the sequence of Emerging→Whole→Blunt (Flat). The exposed diamond tends to be predominantly blunt and fractured, and a slippery IDB cannot be resharpened by increasing the weight-on-bit. The evolution process of a diamond under rotary-percussive drilling conditions encompasses Emerging→Whole→Fractured→Pull out, and the diamond on the surface of the bit is primarily fractured. Diamond emerges from the matrix in the form of points, lines, and planes, with different emergence states affecting its wear and failure modes. The main form of wear in diamonds is mechanical wear, which is dominated by abrasive and fatigue wear. The proportion of fractured diamonds was notably higher under rotary-percussive conditions than in rotary drilling conditions. The tail of the diamond under rotary-percussive drilling conditions was shorter than that under rotary drilling conditions. The impact effect in rotary-percussive drilling enhances the bit-rock contact, facilitating matrix wear and diamond emergence. These results provide valuable insight for optimizing the IDB design and refining drilling technology.

Numerical validation of a novel cuttings bed impeller for extended reach horizontal wells

To reduce the risk of downhole accidents resulting from poor wellbore cleaning during the drilling of extended reach horizontal wells, a new cuttings bed impeller is developed. The performance of existing cuttings bed impellers on wellbore cleaning efficiency is analyzed by multiphase numerical simulation. Based on this analysis, a new type of cuttings bed impeller is proposed, and its key structure parameters are optimized. Its cuttings removal performance under different working conditions is verified. The results show that the spiral impellers have the highest annular velocity, promoting the movement of the cuttings bed. Increasing the rotation speed of the impeller causes the cuttings bed to move further from the low side of the wellbore, facilitating the cuttings removal. Two major improvements are introduced to the new cuttings bed impeller: a positive displacement motor that enables the self-rotation of the impeller, and the elastic contacts on the spiral blades that stir cuttings bed and reduce friction with the wellbore. The optimized parameters of the new impeller are: helix angle of 60°, 4 blades, elastic contacts arranged in crossed pattern, and self-rotation speed of 60 r/min. It is also demonstrated that the new impeller achieves satisfactory cleaning results in both rotary drilling (84.71%) and sliding drilling (71.07%) conditions. This work provides a new solution for the efficient removal of cuttings in extended reach horizontal wells.

Оптимальное проектирование профиля ствола наклонно направленной скважины в горных условиях

The well design process is closely related to the problem of determining effective drilling conditions, namely, constructing an optimal well profile in mountain conditions. The accuracy of the trajectory of the drilling tool in the rock directly depends on the operational calculation of the spatial coordinates of the well. Materials and methods. The displacement and length of the wellbore were preliminarily determined; determining the accuracy of the design well profile and deviation of the wellbore. Results and discussion. During the solution, in addition to constructing a graph of the parabolic dependence using the least squares method, graphic images of other dependences that approximate the original data were also found. Conclusion. Calculating the length of the trajectory at any part of the well and the ability to reach a given end point of drilling in a rock formation with changes in external factors is an obvious advantage of the proposed method. Resume. Based on the results of the analysis of various methods and inclinometric studies, the application of the least squares method is justified, which allows determining the estimated length of the well and promptly responding to any deviation from the optimal trajectory, calculating the shortest path without affecting the drilling speed in mountainous conditions. Suggestions for practical applications and future research directions. The application of this method in combination with existing methods for constructing an optimal well profile and verification by physical methods is proposed.

Ex-vivo parametric study of laser ablation-based drilling of cortical bone.

Frequently orthopedic surgeries require mechanical drilling processes especially for inserted biodegradable screws or removing small bone lesions. However mechanical drilling techniques induce large number of forces as well as have substantially lower material removal rates resulting in prolong healing times. This study focuses on analyzing the impact of quasi-continuous laser drilling on the bone's surface as well as optimizing the drilling conditions to achieve high material removal rates. An ex-vivo study was conducted on the cortical region of desiccated bovine bone. The laser-based drilling on the bovine bine specimens was conducted in an argon atmosphere using a number of laser pulses ranging from 100 to 15,000. The morphology of the resulting laser drilled cavities was characterized using Energy dispersive Spectroscopy (EDS) and the width and depth of the drills were measured using a laser based Profilometer. Data from the profilometer was then used to calculate material removal rates. At last, the material removal rates and laser processing parameters were used to develop a statistical model based on Design of Experiments (DOE) approach to predict the optimal laser drilling parameters. The main outcome of the study based on the laser drilled cavities was that as the number of laser pulses increases, the depth and diameter of the cavities progressively increase. However, the material removal rates revealed a decrease in value at a point between 4000 and 6000 laser pulses. Therefore, based on the sequential sum of square method, a polynomial curve to the 6th power was fit to the experimental data. The predicted equation of the curve had a p-value of 0.0010 indicating statistical significance and predicted the maximum material removal rate to be 32.10 mm3/s with 95%CI [28.3,35.9] which was associated with the optimum number of laser pulses of 4820. Whereas the experimental verification of bone drilling with 4820 laser pulses yielded a material removal rate of 33.37 mm3/s. Therefore, this study found that the carbonized layer formed due to laser processing had a decreased carbon content and helped in increasing the material removal rate. Then using the experimental data, a polymetric equation to the sixth power was developed which predicted the optimized material removal rate to occur at 4820 pulses.

Effect of solid lubricant reinforcing on drilling performance of castamide and thermal analysis

AbstractThis study addresses the pressing need for enhancing the machining performance and hole quality of castamide by investigating the effects of solid lubricant addition and drilling parameters. Castamide, a highly crystalline polyamide synthesized via anionic ring‐opening polymerization, offers superior mechanical, physical, and chemical properties compared to conventional polyamide 6. However, its machining process, particularly drilling, remains a critical challenge due to its viscoelastic nature and sensitivity to heat generation. Using experimental investigations, thrust forces, drilling temperatures, hole geometry, and quality parameters are systematically analyzed and discussed. Notably, the study introduces Kestlub, a modified version of castamide with solid lubricant, and evaluates its drilling performance, a previously unexplored area in the literature. The research employs response surface methodology to model experimental data, considering both linear and quadratic effects of drilling parameters. Additionally, the significance of each parameter is assessed using ANOVA tables and Pareto charts, offering valuable insights into optimizing the drilling process for enhanced hole quality in castamide. It found that optimal drilling conditions occur at low rotational speeds and high feed rates, but thermal damage, influenced by factors like thermal conductivity and transition temperature, affects hole geometry and burr formation.Highlights Drilling performances of solid lubricant reinforced castamides were investigated. Drilling temperatures were recorded with a thermal camera and differential scanning calorimeter and thermal gravimetric analyses were performed. Drilling properties were analyzed statistically according to the response surface method. It found that optimal drilling conditions occur at low rotational speeds and high feed rates.

Optimization of stepped hole drilling for consistent aperture in BCF/PEEK and PEEK stacks

To ensure the aperture consistency of the stepped hole in the drilling of braided carbon fiber reinforced polyether ether ketone (BCF/PEEK) and PEEK stacks, a step variation parameter method is proposed to obtain the optimum process parameters in this study. Initially, the lay-up sequence is determined by analyzing diameter differences in drilled sequences of BCF/PEEK and PEEK stacks. Concurrently, hole-wall surface morphology and damage are observed under traditional drilling conditions to define stepped hole phenomena. Subsequently, optimum step position is identified by analyzing diameter differences at various positions with variable parameters. Moreover, the influence weight of drilling parameters on diameter difference is assessed using Taguchi orthogonal array. An optimization process scheme is proposed for minimum diameter difference control. Results suggest spindle speed of 2000 r/min and feed rate of 40 mm/min for BCF/PEEK, and 5000 r/min and 30 mm/min for PEEK are optimum parameters. This method holds promise for achieving consistent apertures in other laminated composites during drilling.

Influence of spatial engagement angles on machining forces and surface roughness in turning of unidirectional CFRP

Carbon fibre-reinforced polymer (CFRP) is being widely used due to its low specific weight and outstanding mechanical properties. However, using identical machining parameters on unidirectional CFRP can lead to different results depending on the fibre orientation.Recently, a process-independent model describing the engagement conditions in oblique cutting of unidirectional CFRP has been developed, introducing the spatial angles θ0 and φ0. Since the engagement conditions of milling and drilling are complex, analogy experiments are conducted in turning with variation of the setting κrand inclination angles λs. In this study, process forces and surface roughness were measured as a function of the complete range of fibre cutting angle θ.

Logging-While-Drilling Laterolog vs. Electromagnetic Propagation Measurements: Which Is Telling the True Resistivity?

Summary The electromagnetic propagation (EMP) measurement frequently acquired with logging-while-drilling (LWD) tools in high-angle wells is sensitive to geometrical effects that can mask the true formation resistivity. Less commonly used, the LWD laterolog measurement is sometimes perceived as providing data too shallow to give a true formation resistivity (Rt). In this paper, we presents modeling and actual examples to demonstrate that the laterolog can often provide a superior resistivity measurement for formation evaluation to that of the LWD EMP tool. We examine the laterolog and EMP resistivities in several high-angle wells crossing carbonate formations in 8.5-in. and 6.125-in. hole sizes. In the 8.5-in. sections, producers and water injectors (high- and low-resistivity ranges) were evaluated. In the 6.125-in. sections, one reservoir sandwiched between two very high-resistivity layers and another borehole in a highly fractured reservoir were examined. The laterolog data were corrected for invasion using a 1D inversion of the memory data. Structure-based forward modeling was used to examine and explain the differences between the laterolog and EMP resistivity measurements. In the first example in a thick low-resistivity water reservoir, laterolog resistivity and EMP resistivity agree, showing that the two tools provide the same measurement when no geometrical effects are present. In the first part of the second example, a reservoir zone was initially drilled only with the LWD EMP resistivity measurement. The LWD laterolog was run several days later, and the resistivity data read much lower in the relogged section compared with the EMP resistivity. The laterolog 1D inversion was unable to resolve Rt because of the excessively deep invasion that occurred over the course of several days. In the second part of the second example, the laterolog resistivity showed a clear conductive invasion profile. While the deepest laterolog real-time resistivity data indicated lower resistivity than the EMP resistivity, the true resistivity, Rt (invasion-corrected 1D-inverted laterolog resistivity), matched the EMP Rt resistivity. This result validated both measurements and emphasized that the differences were due to invasion. The first two examples demonstrated that when acquired in normal drilling conditions (within 1–2 hours of drilling the section), the laterolog measurements can provide uninvaded formation resistivity even in the presence of invasion. A reservoir in another example was sandwiched between resistive layers that caused difficult-to-explain elevated EMP resistivity readings. Structural modeling reproduced the elevated behavior of the EMP data and explained the differences between resistivity measurements. This result showed that the laterolog is better suited to evaluate resistivity in thin reservoirs where there is a high-resistivity contrast to the adjacent layer. Finally, fractured reservoir examples are presented, which show that both the laterolog and EMP can be affected by the presence of fracture swarms. The examples presented in this paper demonstrate that in high-angle wells, when acquired under normal drilling conditions, invasion-corrected laterolog resistivity is often nearer to Rt than EMP resistivity. In those cases, the laterolog measurement provides data that are better inputs to water saturation calculations. Multiple examples from high-angle wells illustrate the findings.

Experimental investigation on fiber laser micro drilling of Titanium grade 5: fabrication, nature-inspired optimization and analysis through image processing

This investigation showed that micro holes were created on Titanium grade 5 substrate surface using a 30 W fiber laser. The impact of the control factors such as scan speed, frequency, number of passes and power were studied on the responses namely heat affected zone (HAZ), hole circularity (HC) and deviation in diameter (DIV). The control factors were optimized using firefly algorithm. Mathematical models were developed for each response having significant R-square value. 3D surface plots were used to examine how the control parameters affected the response. The firefly algorithm identifies the optimal conditions for micro drilling as scan speed of 210 mm s−1, frequency of 40 kHz, power of 8 W and total of 40 passes which improved experimental findings i.e. HC-0.974, DIV-37.02 μm and HAZ-19.53. After comparing the predicted values with the experimental findings, it was observed that the prediction error is lowest for HC (1.23%) followed by DIV (13.9%) and HAZ (16.9%). Image processing technique was used to convert regular images into a digital format to extract useful information.

Real-time prediction of bottom-hole circulating temperature in geothermal wells using machine learning models

Drilling high-temperature geothermal wells presents technical and economic challenges. Real-time and precise estimation of bottom-hole circulating temperature (BHCT) during geothermal drilling is crucial for maximizing the working life of drill bits and temperature-limited bottom-hole assembly (BHA) components, thereby avoiding unplanned and unnecessary bit/BHA trips. This study introduces a novel machine learning (ML) model that accurately predicts BHCT in real time, enhancing proactive temperature management and mitigating thermally induced challenges during geothermal drilling operations.An integrated thermo-hydraulic model, validated using publicly available data from the Utah FORGE field, was used to generate a large dataset that simulates the transient BHCT under typical drilling conditions. This dataset was subsequently used to train and test the prediction capability of six ML models of the BHCT, including deep neural networks (DNN), support vector machines (SVR), random forests (RF), extreme gradient boosting regressor (XGBoost), ensemble (Stacked) algorithm, and long-short term memory (LSTM) networks. It was also used to generate an understanding of the non-linear relationship between the input features and the output variable (BHCT). Resultsdemonstrate the benefits of implementing the LSTM model for reliable prediction of the BHCT and capturing its full-scale transient behavior in geothermal wells. The LSTM model stands out for its excellent generalization capability, stability, and precision in real-time estimation of BHCT across various geothermal drilling conditions, including both stationary and dynamic scenarios. This is achieved without the high computational costs associated with complex numerical models, thus preventing temperature-related drilling problems. Among the other supervised ML models, the XGBoost model can still reliably simulate the BHCT with a mean absolute error (MAE) below 1 °C during geothermal drilling at constant drilling parameters, but will show overfitting when drilling parameters change.

Rock Breaking Law Under the Condition of Multi-row Drilling of Static Crushing Agent and Its Application in Roadway Expansion

Static crushing agent (SCA) has the advantages of good safety, no harmful gas and no vibration. It is widely used in rock crushing engineering of mine or underground engineering. Aiming at the performance of static crushing agent with different water-cement ratios, based on the engineering and environmental conditions of roadway side protection in a mine of Shanxi coking coal, the stress-time curve of SCA and the fracturing law of SCA on roadway side rock under the condition of multi-row drilling were studied by means of laboratory test and numerical simulation. The results show that: the smaller the hole spacing, the better the fracturing effect of SCA, the smaller the required fracture initiation stress and penetration stress, and the existence of the free surface contributes to the development of the fracture, and the fracture around the hole extends along the direction of the incoming pressure under the peripheral pressure conditions; the porous SCA fracturing can be used for the high efficiency of underground rock fracturing projects such as rocky roadway spreading and other underground rock fracturing projects. The research results of the project provide a new method for non-blasting roadway expansion, roof picking and other rock-breaking projects in underground coal mines.

Stress relief cracking and permeability improvement by high-pressure water jet slotting to enhance coalbed methane extraction

Extracting coalbed methane (CBM) is important for energy development. Improving coal seam permeability is the key to high-efficiency CBM extraction. High-pressure water jet (HPWJ) slotting is an effective method for improving permeability. However, the mechanism by which this technology improves coal seam permeability is unclear. Therefore, in this paper, the mechanism by which HPWJ slotting causes stress relief cracking and permeability improvement to enhance CBM extraction is studied in terms of the stress relief effect and the changes in fracture field and flow field induced by HPWJ slotting. Significant changes occur in facture field and flow field. The process, coal mass stress relief → fracture development → permeability improvement → CBM extraction enhancement, is triggered by HPWJ slotting. A field experiment indicates that after HPWJ slotting, the total CBM production and its average pure quantity are 4.41 and 4.20 times those under traditional drilling conditions, suggesting that HPWJ slotting can effectively improve permeability and enhance CBM extraction. The study results have important significance for revealing the mechanism by which HPWJ slotting improves permeability and for achieving high-efficiency underground CBM extraction.

Design and dynamic characteristics of automatic vertical drilling tool

Higher performance is needed in deeper and longer horizontal wellbore drilling. In vertical drilling conditions, wellbore trajectory often be led to deviation due to objective conditions. Based on the engineering issues, this paper presents a new automatic vertical drilling tool, including the innovative design and working mechanism research. This tool working mechanism are carried out, such as the mechanics model of eccentric tube and the relationships between eccentric torque and deflection angle. The eccentric tube torque increases with the wellbore deviation angle. When wellbore deviation angle is constant, the eccentric tube torque reaches maximum value when its deflection angle is 90°. The internal flow parameters are studied by fluid field simulation, such as drilling fluid flow rate, pressure drop, and pressure distribution inside this tool during downhole drilling process. The larger the diameter of switch hole, the higher is the pressure drop around, which leads to the force on push block increasing. The drilling fluid pressure increases with higher input flow rate inside this tool. The comparison of results, the data of simulation and theoretical model calculations, verified the reliability and accuracy of research. This study has provided innovative ideas and reference for drilling tool design and wellbore trajectory control methods.

Experimental and simulation investigation on the impact performance of pneumatic hammer under varied drilling conditions

It is of great significance to reveal the influence on the output performance of pneumatic hammers under different drilling condition parameters to improve their impact efficiency used in drilling applications. In this study, Computational fluid dynamics (CFD) wisth dynamic mesh method was utilized to simulate dynamic airflow and piston movement within the hammer. User-Defined Functions (UDFs) are modified to introduce friction and varying well deviation angles. Meanwhile, a test bench of pneumatic hammer performance is designed and built to record real-time data on the piston displacement and chamber pressure within the hammer, validating the simulation results. The results show that the simulated and experimental data exhibit similar values and trends, with a maximum error of 10.92% for the impact velocity, 9.5% for the impact frequency, 8.36% for the maximum piston displacement, and 10.81% for the pressure drop, respectively. In addition, the piston motion mechanism was analyzed and the effects of well deviation angle, mass-flow rate, backpressure, restitution coefficient, and friction coefficient on the hammer's performance were investigated in detail. The results indicate that the mass-flow rate and restitution coefficient have a positive effect on increasing the piston's impact velocity and impact frequency, as well as pressure drop. In the context of directional drilling, the hammer's impact energy varies with the well deviation angle. At lower values of the friction coefficient, a clear positive correlation emerges between impact energy and deviation angle. Conversely, at larger values of the friction coefficient, a distinct biphasic behavior is observed, with the impact energy first decreasing before subsequently increasing. Furthermore, the backpressure, and friction coefficient adversely affect the hammer performance, with the backpressure being the dominant factor.

A Method for Evaluating Coalbed Methane Reservoir Productivity Considering Drilling Fluid Damage

In the process of coalbed methane development, drilling fluid and fracturing fluid cannot achieve absolute compatibility with formation. The incompatibility between the working fluid and reservoir will lead to the intrusion of working fluid into the reservoir and cause reservoir pollution. This is a very common phenomenon. There is a large amount of pulverized coal in the coal seam, and the intrusion of working liquid will be combined with the pulverized coal to form cement to block the seepage space in the reservoir. Since pressure relief and fracturing fluid backflow will be performed at the first time after fracturing, the intrusion range of the working fluid is small, generally reaching 10 m to 50 m. Compared with a conventional gas reservoir or shale gas reservoir, the working fluid loss during CBM development will seriously affect the subsequent production project and even make the gas well lose production capacity. On the other hand, in order to avoid this phenomenon, measures such as acidification or volumetric fracturing are sometimes used to improve the seepage environment near the well and near the fracture. The purpose of this study is to quantitatively evaluate the impacts of working fluid filtration and reservoir reconstruction on production. In this study, a single well productivity evaluation model and sensitivity analysis method considering drilling fluid filtration loss, fracturing fluid filtration loss, reservoir reconstruction and other processes is proposed. The formation mechanism of fluid loss during drilling and fracturing is described, and the productivity evaluation model considering fluid loss is combined with the Langmuir isothermal adsorption equation, steady-state diffusion law, Darcy’s seepage law and Duhamel convolution formation. Combined with the distribution of actual gas reservoir flow characteristics, the sensitivity of single well productivity to gas reservoir porosity, gas reservoir permeability, coal seam adsorption coefficient, working fluid filtration loss and reservoir reconstruction measures are analyzed. Through the analysis and fitting of the actual production data on site, the relationship curve can better fit the field production data, and the evaluation results are in line with the drilling and fracturing conditions at that time and the subsequent production conditions, with small errors. The obtained method is suitable for predicting the productivity of fractured vertical wells in different working conditions and provides a basis for the development and productivity prediction of CBM reservoirs in China and in international cooperation.

Numerical Simulation of Rock Breaking by Diamond Particles Under Ultra Deep Drilling Conditions

In the quest to access deeper fossil energy reserves, the past three decades have witnessed a concerted effort by scientists to develop and refine technologies capable of efficient drilling in environments characterized by high temperatures and pressures. Despite these advancements, our comprehension of the physical phenomena at play remains incomplete. A fundamental challenge pertains to the interaction between the rock and the drilling bit during drilling operations. This study delves into the influence of drilling bit pressure and rotation speed on the rock-breaking efficacy of impregnated diamonds under geostress conditions of 240 MPa and temperatures of 200℃.It juxtaposes these findings with those from rock-bit interaction experiments executed on a physical simulator, which was designed in accordance with similarity principles, in a controlled laboratory setting. Our findings indicate that for ultra-deep formations, a high Weight on Bit (WOB) coupled with a lower rotation speed results in enhanced rock cutting efficiency and a reduced rate of bit wear. Consequently, we recommend optimal drilling parameters of 8.0 to 8.5 kN for WOB and a rotational speed range of 180 to 240 rad/min. Furthermore, the study underscores the profound impact of horizontal differential stress on the rate of penetration (ROP). The insights gleaned from these tests are instrumental in refining the design of rock-breaking tools and optimizing drilling parameters, thereby augmenting the efficiency of rock breaking in challenging drilling environments.

Design and rigid body dynamics analysis of a novel retractable drill bit used in casing-while-drilling

Utilizing the Geneva drive mechanism, an inventive retractable drill bit tailored for casing-while-drilling (CwD) applications was developed. This novel design allows the lower segment of the drill bit to be swung outward through rotation, facilitating to drill a larger hole and retrieved effortlessly by raising the drill tools. An exploration into the dynamic behavior of this retractable drill bit under varying drilling conditions was undertaken, focusing on parameters such as weight-on-bit, rotation speed, friction coefficient between the drill bit and rock, and lifting force. Findings from the investigation revealed that, under conditions of 20 kN weight-on-bit, a friction coefficient of 0.3, and a rotation speed of 30 rpm, the drill bit achieved full extension within 3.8 s. Notably, the movement speed of the lower drill bit was notably influenced by weight-on-bit, the friction coefficient, and lifting force, demonstrating accelerated movement with increased values of these factors. Rotation speed, however, exhibited negligible impact on the movement of the drill bit. An indoor experimental examination mirrored the outcomes obtained through simulations. Subsequent to numerical simulations and indoor testing, a large-diameter drill bit was produced and field tested, showcasing its capability to flexibly extend and retract during drilling, achieving an average drilling speed of 1.7 m/h.

A New Design of Vibration Damping Structure for Positive Displacement Motor

Positive displacement motor (PDM) is a downhole power drilling tool, and the bottom of the drilling tool is directly connected to the drill bit. During the drilling process, the drilling tool will be directly affected by the impact load caused by the drill bit breaking the rock. Severe vibration can easily cause drill tool bearings to break and fail, threads to trip and other problems. The new PDM vibration damping structure uses wear-resistant and heat-resistant metal rubber instead of disc springs as energy-absorbing materials, and designs a "keyway type" vibration damping structure; a two-degree-of-freedom "spring - mass" model is established based on actual working conditions. , determine the basic size of the metal rubber pad based on the metal rubber stress-strain curve, and bring it into the drilling tool dynamics equation to verify that the stiffness and damping parameters of the metal rubber pad will not resonate; finally, compare the drilling conditions under different excitations in the dynamics simulation software The amount of impact the tool receives. Finally, the dynamics simulation of the new vibration-damping drilling tool under different frequency excitations was carried out in Adams simulation software, and it was concluded that in the common working environment of 6-15 Hz, the new vibration-damping drilling tool can effectively reduce the stress on the drilling tool. Impact force, the new vibration-damping drilling tool can reduce the impact force by about 40% when excited at 12 , 15 Hz . The conclusions drawn from the study have reference value for the development of long-life drilling tools and the design of drilling tool vibration damping structures.

Development of a rock-bit interaction analytical model by considering the in-situ stresses for a bottom-hole element

PDC drill bits are an important part of drilling engineering, but improper selection or design can lead to decreased performance and increased costs. Then, accurate modeling of rock-bit interaction for Oil/gas well drilling is critical. Although several mathematical models are presented for this purpose, they have not been able to present a comprehensive model for the rock-bit interaction. In-situ stresses in real drilling conditions affect the force required for rock failure. However, the models proposed so far either have not considered the effects of in-situ stresses or have assumed that the rock failure angle in the downhole conditions is equal to the one calculated in the atmospheric conditions. In this work, after reviewing the background of studies conducted on the rock and bit interaction, with an analytical method, stresses applied to the bottom hole element are examined, including stresses resulting from bit and in-situ stresses. Based on the principle of superposition, the total stress imposed on the bottom hole element is calculated to determine the angle and force of rock cutting. Finally, a novel mathematical model of rock-bit interaction in vertical and deviated oil/gas wells drilling by Considering In-Situ Stresses is presented. Also, the study compares the current model to the Nishimatsu and Xin Ling models using data from a southwest field in Iran. The results show that the simplifying assumption made by previous models leads to a significant underestimation of the failure angle and the amount of force required to the rock failure, with reductions of up to 21% and 48%, respectively, in the case of a vertical well. In an inclined well, the current model predicts cutting force at about 0.14 of that predicted by the previous model.

Ultrasonic-Assisted Grinding of Microholes Using Ultrasmall-Diameter Cemented WC Tools

Although grinding is a widely employed method for hard and brittle materials, drilling microholes requires the use of an ultrasmall-diameter grinding wheel that is difficult to fabricate and breaks easily when grinding force is applied, resulting in a high tool cost. To solve this problem, cemented WC micropins were fabricated by electrical discharge machining, and microholes were drilled using them as micro-grinding tools with the assistance of ultrasonic oscillation. The micropin tools can be employed in grinding because the convex parts of the electrical discharge craters formed on their surfaces serve as cutting edges of abrasive grains in grinding wheels. To clarify the drilling conditions necessary for ultrasmall-diameter tools to drill holes with a diameter less than 5 µm, the relationships between drilling conditions and drilling characteristics were investigated. The drilling conditions included the tool rotation speed, tool feed speed, ultrasonic oscillation amplitude, and use of grinding fluid. The drilling characteristics included the hole diameter and grinding force evolution. The investigation showed that a high tool rotation speed prevented the increase in the grinding force because of the faster grinding speed. A low tool feed speed was favorable to lower grinding force. At a high tool feed speed, most likely, the tool was fed before the workpiece material was sufficiently removed, thereby exhibiting a large grinding force. The ultrasonic oscillation amplitude had no noticeable effect on the grinding force. The hole diameter was not affected by the tool rotation speed, tool feed speed, or ultrasonic oscillation amplitude. Although the use of grinding fluid reduced the grinding force, the hole diameter increased, probably because enhanced lubrication caused the tool to slip on the workpiece surface at the beginning of drilling, resulting in an increased rotational runout. Under the favorable conditions obtained, a hole of 3.2 µm in diameter was successfully drilled in crown glass.