Drilling Performance Research Articles

Machine Learning Solution for Predicting Vibrations while Drilling the Curve Section.

The downhole vibration is one of the most crucial factors that affect downhole equipment performance and failure, besides wellbore instability. Downhole tool failure, hole problems, mechanical energy loss, and ineffective drilling performance are commonly associated with drillstring high vibration levels. The high vibration level will lead to more complications while drilling that might cause nonproductive time and extra cost. Meanwhile, the downhole sensors for detecting the drillstring vibrations add more cost to the operation. Consequently, the new solutions based on technology capabilities provide a powerful tool to integrate and interpret the drilling data for the best use of @@the data for operation performance enhancement. This study provides a successful application for utilizing the surface drilling data to automate drillstring vibration detection during the drilling curve section employing machine learning (ML) techniques. The axial, torsional, and lateral vibration modes are detected through testing four ML techniques named the @@adaptive neuro-fuzzy inference system (ANFIS), radial basis function (RBF), functional networks (FN), and support vector machines (SVMs) with real field data. The models' development was achieved by comprehensive study starting from data gathering, wrangling, statistical analysis, developing the ML models, evaluating the model prediction accuracy, and reporting the high accuracy results. The developed models were evaluated, and results showed that ANFIS and SVM models provided the highest accuracy with a coefficient of correlation (R) ranging from 0.9 to 0.99 followed by the RBF and FN models through model training and testing (R ranging from 0.82 to 0.96). Validating the models over unseen data confirmed the high accuracy prediction for the three vibration modes. Generally, the developed models provided technically accepted accuracy with R higher than 0.93 and AAPE less than 2.8% for SVM and ANFIS models while FN and RBF showed R between 0.82 and 0.95 and AAPE less than 5.7% between actual readings and predictions. Based on these results, the developed ML algorithm might be utilized as an intelligent solution to autodetect downhole vibration while drilling from surface sensor data only, which will save the downhole tool cost.

Effect of Low Gravity Solids on Weak Gel Structure and the Performance of Oil-Based Drilling Fluids.

Drilling cuttings from the rock formation generated during the drilling process are generally smashed to fine particles through hydraulic cutting and grinding using a drilling tool, and then are mixed with the drilling fluid during circulation. However, some of these particles are too small and light to be effectively removed from the drilling fluid via solids-control equipment. These small and light solids are referred to as low gravity solids (LGSs). This work aimed to investigate the effect of LGSs on the performance of oil-based drilling fluid (OBDF), such as the rheological properties, high-temperature and high-pressure filtration loss, emulsion stability, and filter cake quality. The results show that when the content of LGSs reached or even exceeded the solid capacity limit of the OBDF, the rheological parameters including the plastic viscosity, gel strength, and thixotropy of OBDF increased significantly. Furthermore, the filtration of OBDF increases, the filter cake becomes thicker, the friction resistance becomes larger, and the stability of emulsion of OBDF also decreases significantly when the concentration of LGSs reached the solid capacity limit of OBDF (6-9 wt% commonly). It was also found that LGSs with a smaller particle size had a more pronounced negative impact on the drilling fluid performance. This work provides guidance for understanding the impact mechanism of LGSs on drilling fluid performance and regulating the performance of OBDF.

A comprehensive Cosserat rod drill-string model for arbitrary well geometry that includes the dynamics of the cutting and lateral contact

In this paper, a comprehensive continuous Cosserat rod model is developed to study the dynamics of a drill-string. The model presents the following features: (1) it can simulate the 3-D dynamics of the system, including lateral, axial and torsional motion; (2) it includes damping effects by adopting a Kelvin–Voigt material; (3) it uses a velocity-independent bit-rock interaction formulation in which the forces and torques at the bit are obtained by considering the dynamics of the cutting blades and the evolution of the soil profile, which is simulated with the help of an advection equation; (4) lateral contact is also included. In this paper, two application cases are analysed. The first one deals with a vertical borehole. It includes four simulations that are used to further investigate the hypothesis that low-dimensional lumped formulations are not able to capture the dynamics of a drill-string and, while doing so, evaluate the effect of the damping in the system’s response. The predictions are compared with those given by two other models: the first one considers a 2-degrees-of-freedom (DOF) formulation, with 1-axial and 1-torsional DOF; the second one is a semi-discrete approach, with 1 DOF for the axial dynamics and a continuous formulation for the torsional one. Divergences between the predictions are found, associated with the presence of higher frequencies in the signals obtained with the Cosserat model, which reassures the hypothesis that the new continuous approach can capture aspects of the dynamics that cannot be modelled with low-dimensional representations. The efficiency of the drilling is also assessed for the simulations obtained with the new model. The highest performance was observed in those simulations where only axial oscillations occurred, while a performance drop was seen when those vibrations were accompanied by torsional stick–slip, suggesting that an optimum damping value associated with the best drilling performance could be found, were damping controllable. Finally, the second application case is used to illustrate the full potential of the new model to tackle the 3-D lateral, axial, and torsional dynamics in a curved borehole.

Influence of Electrical Parameters on the Machining Performance in the Small Hole Drilling by EDM Process

This research aims to study the influence of controlled parameters on the machining performance for small hole drilling by an electrical discharge machine. Tubular copper with an outside diameter of 1 mm was used as an electrode. JIS SKD 61 grade steel at a depth of 40 mm for machining was used as a workpiece. The experimental results show that machining speed and electrode wear drastically increased with the discharge current. The high machining performance with varied pulse on-time occurred in the range of 16 to 28 μs. The machining time and electrode wear ratio increased with a decreased pulse off-time. In addition, the lowest difference in the dimension of the entrance and exit of the drilled hole at approximately 0.030 mm appeared at the pulse off-time of 6 μs. However, the high machining speed and electrode wear ratio occurred at the low dielectric pressure of 20 kg/cm2. Furthermore, the machining performance reduced and slightly fluctuated with the varied dielectric pressure in the range of 40 to 80 kg/cm2.

Numerical analysis of the effect of temporal and/or spatial shaping on the ms/ns combined pulse laser drilling performance of alumina ceramic

Numerical analysis of the effect of temporal and/or spatial shaping on the ms/ns combined pulse laser drilling performance of alumina ceramic

Improvement of micro-EDM drilling efficiency on Inconel 625

Micro-level drilling is a crucial production technique that is utilised in many different industries. In this experimental effort, research is conducted by drilling holes 600 µm in diameter, 5 mm deep, and 9 numbers apart. Because of its exceptional mechanical properties, highest corrosion resistance, and high-temperature resistance, Inconel 625 is chosen as the working material. The optimum relevant input variables are necessary to get better efficiency of machining effectiveness on that material. The process was carried out with micro EDM while considering different processes into account. In order to identify the ideal factors, optimisation methods like Taguchi analysis was adopte. According to the findings, current is the most important procedure limitation on TWR and MRR, preceded by pulse inactive time. An ideal process factor has improved the drilling performance of micro-EDM.

Preparation of wells using an electrohydraulic drill and modeling of heat transfer processes in heat transfer elements of a heat pump

The article discusses the use of innovative electrohydraulic technology in the preparation of vertical ground heat exchangers to create heat supply using heat pumps. The discharge energy in the operating range varied E=900÷2600 J. The most economical mode of operation of the electrohydraulic installation is carried out with the following parameters: discharge voltage 30÷51 kV, capacitor bank capacity 2 µF and interelectrode distance 8÷15 mm. It is determined that the optimal energy of destruction of natural materials depends on their thickness. Based on the research, the limits of the electrophysical parameters of the approach were established, at which the concentrated destruction of hard rocks – the main stones ‒ begins. The effective amount of energy for the destruction of stones with a thickness of 53 mm is 900 J. For stones with a thickness of 78 mm, there should be 2600 J. If to increase the energy of the discharges to 1837 J, the process of complete destruction of the stones is underway. Using an electro hydraulic drill, we have prepared vertical wells up to 25 m deep. In the future, we have installed special temperature sensors along the length of the pipes, inside the well. Using a software product (Temp Keeper), data from temperature sensors are received in real time. This program allows to visually monitor temperature changes occurring at a local point. Temperature and time dependences are also obtained at coolant velocities of 0.2÷0.4 m/s. A significant decrease in the temperature in the well and at the outlet was observed at a coolant velocity of 0.35 m/s for one hour. The study conducted on the basis of the data obtained enables to achieve higher optimal drilling performance compared to conventional installations

A new approach for real-time prediction of stick–slip vibrations enhancement using model agnostic and supervised machine learning: a case study of Norwegian continental shelf

Efficient and safe drilling operations require real-time identification and mitigation of downhole vibrations like stick-slip, which can significantly diminish performance, reliability, and efficiency. This pioneering research introduces a robust machine learning approach combining model-agnostic regression techniques with Bayesian Optimized Extra Trees (BO_ET) to accurately predict stick-slip events in real-time using downhole sensor data. The model is rigorously tested and validated on a substantial offshore dataset comprising over 78,000 data points from a Norwegian continental shelf (NCS) oil field. The key input features encompassing real-time downhole and surface drilling parameters are carefully selected, including critical variables such as collar rotational speed, shock risks, annular pressure, torque, mud flow rate, drill string vibration severity, and other relevant measurements. These parameters offer significant insights into the occurrence of harmful stick-slip vibrations. Among several sophisticated machine learning models, the Extra Trees (ET) algorithm demonstrates superior performance with the lowest errors of 5.5056 revolutions per minute (r/min) Mean Absolute Error (MAE) and 9.9672 r/min Root Mean Square Error (RMSE) on out-of-sample test data. Further hyperparameter tuning of the ET algorithm via Bayesian Optimization dramatically reduces errors down to 0.002156 MAE and 0.024495 RMSE, underscoring the significant innovation and advantages of the proposed approach. By seamlessly incorporating real-time downhole sensor data and drill string mechanics, the model enables reliable identification of stick-slip events as they occur downhole. This grants opportunities to optimize critical drilling parameters including revolutions per minute (RPM), weight-on-bit (WOB), mud flow rates, and more to effectively mitigate stick-slip severity and improve the rate of penetration (ROP). Integrating the approach into automatic driller systems on offshore rigs offers immense benefits for drilling operations through substantially increased efficiency, fewer premature failures, lower costs, and significantly improved productivity and safety. Overall, this research strongly emphasizes the immense transformative potential of advanced data analytics and machine learning in enabling more efficient, economical, and sustainable drilling practices. The proposed model demonstrates clear superiority over existing methods and establishes a robust and reliable platform for real-time stick-slip prediction and mitigation, maximizing drilling performance.Graphical abstract

LABORATORY INVESTIGATION OF IMPROVING DRILLING FLUID PERFORMANCE OF WATER BASE MUD USING OILY GRAPHITE SILICATE AND NANO SILICA PARTICLES AS ADDITIVES

Drilling performance is enhanced by the use of a mud system that prevents or retards the dispersion of formation and cuttings and minimizes torque and drag on the drill string, water base drilling fluids for adaptability with environment and ease of operation. A water base drilling fluid can have a significant role in drilling operations with its desirable properties including rheology, fluid loss, coefficient of friction (CF), PH, and fluid weight. This work studies the effect of nanoparticles and oily graphite silicate on improving the properties of water-based drilling fluid in various laboratory experiments using rotary viscometer, standard filter press, lubricity meter, Ph- meter and mud balance. In addition, fluid loss control additives were used as a control to compare the obtained results from application of nanoparticles and oily graphite and understanding the various effects of their presences in experiments. The results show a positive influence in drilling performance when compared against estimated drilling rate, which can lead to substantial savings in drilling costs, were observed. Torque values in the wells tested were generally low (between 250 and 450 Amps) drilling days were reduced by more than 20% of programmed. The compound also showed cost effectiveness in stabilizing the mud properties by eliminating the need for a defoamer. Results finding also showed that these compounds can increase yield point (YP) in mud (increased from 101b/100f12 to 121b/100ft2 ), findings also indicate that oily graphite/nanoparticles can reduce drilling fluid loss in 100psi and T = 75o f about 22% (from 4.5cc to 3.5cc during 30min). Key Words: Drilling fluid, drilling performances, nano silica particles, oily graphite silicate, water base mud, fluid loss, cost effectiveness, fluid properties and drilling parameters

Hydraulic parameters optimization of two-stage PDC bit in deep formation applications

Two-stage PDC (Polycrystalline diamond compact) bit is a special drilling bit consisting of a small-diameter pilot and a large-diameter reamer. The unique rock-breaking structure is designed to improve drilling efficiency and reduce drilling costs in deep and abrasive formations. According to previous studies, the hydraulic structure of the two-stage PDC bit can significantly affect the drilling performance of removing cuttings near the bottom of the wellbore. Therefore, this research has proposed to achieve high efficiency of cuttings removal by optimizing the hydraulic structure. In this paper, the flow field at the bottom of the well near the two-stage PDC bit (Φ171.45 mm pilot + Φ215.9 mm reamer) has been numerically studied using the finite element method. As shown in the analysis results, both the flow rate of the pilot and the flow rate ratio of the pilot to the reamer increase significantly with the increase of the area ratio of the pilot nozzles to the total nozzles. The numerical data supports that the cuttings can be removed effectively from the bottom of the wellbore when the area ratio is between 0.75 and 0.80. Moreover, the cuttings can be removed effectively from the bottom of the wellbore when the mud viscosity is about 10 mPa s, the rate of penetration is between 4 and 8 m/h, the drill speed is 90 rpm, and the cuttings particle sizes is between 1 and 2 mm. Besides, increasing the pump rate can improve the cutting-carrying efficiency through the wellbore bottom. Field test results indicate that the average penetration rate of the optimized bit is increased by 47.17% and the footage of the optimized bit is increased by 95.40% compared to the equivalent formation in adjacent wells. This study can provide guidance for the optimal design of the hydraulic structure of such two-stage PDC bits.

Fly ash as an additive for controlling sagging tendency in ilmenite densified water-based mud for a highly inclined high temperature well

Sagging has a detrimental outturn on the drilling effectuation and increases the drilling risks. Drilling deviated wells and wells with high pressures and temperatures has a greater impact on the sagging occurrence. It is desirable for a drilling operator to ensure stability and maintain the suspension of weight material in the fluid throughout the drilling operation. Optimum drilling fluid design for the drilling industry aids in the effective removal of cuttings and suspension of cuttings to avoid expensive complications and maintain the stability of the well particularly for drilling highly deviated wells and wells in high-temperature harsh formations. Drilling fluid physio-chemical behavior changes because of the weighing agent separating from the liquid phase and settling down, which is referred to as sagging and is more prevalent in highly inclined wells and wells with high temperatures. Few studies are geared toward understanding and possibly mitigating the occurrence of solid sagging to improve the drilling performance, particularly in highly deviated wells and wells in high-temperature harsh formations. This study evaluates the effectiveness of fly ash buffered with an industrial standard polymer to eliminate ilmenite sag encountered with water-based drilling fluids at high-pressure high-temperature (HPHT)environments when accessing geothermal wells, extended-reach wells, and high-inclined wells. Four laboratory barrels of water-based drilling fluids were formulated for this study. Fly ash of 130 μm particle size was added to mud samples at 0, 1, 2, and 3 lb./bbl ratio. Each industrial standard polymer of 1lb./bbl was added to all four samples prepared. The influence of fly ash on drilling fluids properties was thoroughly evaluated by measuring static and dynamic sagging at vertical and inclined (300, 450, 600, 700, 800, and 900) conditions over a range of temperatures (2500F, 3000F, 3500F, and 4000F). It was observed that the inclusion of fly ash improves the sagging phenomena and the rheological behavior of the water-based mud samples to satisfy the industrial API standard value.

Amine-functionalized graphene oxide in polyamine based drilling fluids for nanosized pore plug filter cake

Water-based muds (WBM) is widely used in oil and gas wells drilling industry due to its environmental friendliness and lower operational cost implication. However, WBM drilling process has severe shale swelling problems caused by the hydration due to the shale minerals affinity to water from the WBM which reduces WBM technical performance. Thus, additives that fitted to its function should be added in WBM formulations to enhance overall drilling performance to achieve the target depth. In this study, graphene oxide (GO) is selected as the additive due to its excellent physico-chemical properties could benefit as an option to mitigate the above challenges. GO was synthesized via Modified Hummers' method where the average thickness obtained was ±46 nm. The GO additive was then modified with Octadecylamine (ODA) to alter the surface hydrophobicity. The contact angle of GO changed from 25° ± 0.5 to 98.9° ± 1.8 after the ODA modification. The hydrophobic GO (HGO) was then added in the drilling fluid formulation and the drilling fluid performance was evaluated based on filtration characteristics. The filter cake showed a thickness of 0.832 mm and a filtrate volume of 5.09 ml at 150 psi/30 min after the filtration with drilling fluid treated with HGO. The filter cake formed was the thinnest and the least filtrate volume was produced which are 30% and 20% reductions compared to drilling fluid without GO, which signify the remarkable reduction of fluid loss. On top of that, the drilling fluid with HGO demonstrated a good rheology property over wide shear rate scheme and enhanced thermal stability. Hence, GO was highly recommended as a potential fluid loss control nano-additive in drilling fluid formulation.

Synthesis and characterization of a novel functionalized silica/polyacrylamide composite for advanced water‐based drilling design

AbstractPolyacrylamide (PAM) has become a potential additive in drilling, but it has limitations in terms of viscosity, fluid loss, and bored pile stability concerns. Previous rheological studies have reported silica (SiO2) usage in PAM modification. However, there is insufficient rheological information such as plastic viscosity, apparent viscosity, yield point, and gel strength. Herein, this research investigates the effects of SiO2 in PAM with comprehensive rheological data. The morphological properties of SiO2 were analyzed. Compared with bare PAM, modified PAM demonstrated distinct chemical structures, but both were hydrophilic fluids. Moreover, an undulated trend was observed in the rheological results of all modified PAM for all concentrations of SiO2 and all the selected temperatures. However, all modified PAM showed better rheological performance than bare PAM. Consequently, 0.5 wt% SiO2 is a promising formulation for PAM modification, which can even be simulated in the performance of the bored pile drilling. For thermal stability, the rheological performance of bare PAM and modified PAM performed better at 60 and 40°C, respectively.

Knowledge, attitude, and proficiency of healthcare providers in cardiopulmonary resuscitation in a public primary healthcare setting in Qatar.

Early and effective cardiopulmonary resuscitation (CPR) increases both survival rate and post-cardiac arrest quality of life. This study aims to assess the current knowledge and ability of physicians and nurses in health centers (HCs) operated by the Primary Health Care Corporation (PHCC) in Doha, Qatar, to perform CPR. This study consists of two parts. The first part is a descriptive cross-sectional survey using an online form targeting physicians and nurses working in all HCs to assess their CPR knowledge and attitude. The second part is a direct observation of CPR drills to evaluate the skills and competencies of code blue team members in a convenient sample of 14 HCs. A multivariate model was employed to test the independent effect of explanatory variables on the total knowledge score. A total of 569 physicians and nurses responded to the survey. Only one-half (48.7%) formally received training on basic life support within the last year. Furthermore, 62.7% have tried to revive a dying person with no pulse. All the participants recognize the importance of knowing how to revive a dying adult or child as part of their job. The study showed that being a nurse was the most important predictor of a higher knowledge score in both components. Attending more resuscitation courses (3-6 courses in the last 3 years) ranked second in importance, and a longer experience in clinical practice (5-10 and >10 years) ranked third in predictive power. In addition, the direct observation of CPR drill performance revealed a satisfactory outcome. The level of CPR knowledge and skills practice among healthcare providers in PHCC is deemed satisfactory as most providers reported having performed CPR in the past. Considering that PHCC is the first step to people's healthcare in Qatar, clinical staff should be certified and assessed regularly to ensure retention of resuscitation knowledge and skills.

Robotic drilling for the Chinese Chang’E 5 lunar sample-return mission

On December 2, 2020, a 2-m class robotic drill onboard the Chinese Chang’E 5 lunar lander successfully penetrated 1 m into the lunar regolith and collected 259.72 g of samples. This paper presents the design and development, terrestrial tests, and lunar sampling results of the robotic drill. First, the system design of the robotic drill, including its engineering objectives, drill configuration, drilling and coring methods, and rotational speed determination, was studied. Subsequently, a control strategy was proposed to address the geological uncertainty and complexity of the lunar surface. Terrestrial tests were conducted to assess the sampling performance of the robotic drill under both atmospheric and vacuum conditions. Finally, the results of drilling on the lunar surface were obtained, and the complex geological conditions encountered were analyzed. The success of the Chinese Chang’E 5 lunar sample-return mission demonstrates the feasibility of the proposed robotic drill. This study can serve as an important reference for future extraterrestrial robotic regolith-sampling missions.

Influence of temperature and pH on polyacrylamide-based drilling fluid: Characterization and rheological study

Polyacrylamide (PAM) is a biodegradable polymer with good lubricity in friction reduction. However, there is insufficient guidance on the dosage of PAM and poor rheological information on the effects of temperature and pH. This study aimed to investigate the characterization of the material and rheological analysis regarding the effects of concentration, pH, and temperature of PAM. In material characterization, PAM has been shown to offer hydrophilic surfaces. In a rheological study, 1000 ppm PAM was the critical association concentration, as the rheological properties below 1000 ppm PAM were superior. This was due to the dispersion stability effect caused by the polymer concentration. Additionally, a low concentration of polymer contributes to bridging flocculation with an unstable rheological profile and low association networking. When the polymer concentration is further increased to the saturated adsorption level, the rheological profile of PAM above 1000 ppm is significantly affected as a result of the alternation from steric stabilization to depletion flocculation in a polymer system. Furthermore, the rheological performance of PAM was significantly affected by temperature and pH, showing better performance after heating to 60 °C and at pH = 10. Future studies can further develop modified PAM with specific additives at an optimized temperature and pH to investigate the rheological performance of drilling.

Drilling Optimization by Using Advanced Drilling Techniques in Buzurgan Oil Field

Efficient and cost-effective drilling of directional wells necessitates the implementation of best drilling practices and advanced techniques to optimize drilling operations. Failure to adequately consider drilling risks can result in inefficient drilling operations and non-productive time (NPT). Although advanced drilling techniques may be expensive, they offer promising technical solutions for mitigating drilling risks. This paper aims to demonstrate the effectiveness of advanced drilling techniques in mitigating risks and improving drilling operations when compared to conventional drilling techniques. Specifically, the advanced drilling techniques employed in Buzurgan Oil Field, including vertical drilling with mud motor, managed pressure drilling (MPD), rotary steerable system (RSS), and expandable liner hanger (ELH), are investigated and evaluated through case study analyses, comparing their performance to that of conventional drilling techniques. The findings indicate that vertical drilling with mud motor exhibits superior drilling performance and wellbore verticality compared to conventional rotary drilling bottom hole assemblies (BHA) for drilling the 17 ½" hole section. MPD systems employed in the 12 ¼" hole section demonstrate safe drilling operations and higher rates of penetration (ROP) than conventional drilling methods. Rotary steerable systems exhibit reduced tortuosity and achieve higher ROP when compared to mud motor usage in the 8.5" and 6" hole sections. Lastly, investigations of expandable liner hanger cases reveal subpar cement quality in the first case and liner remedial work in the second case, highlighting the successful implementation of ELH techniques in the offset field. Overall, this paper highlights the advantages of utilizing advanced drilling techniques in Buzurgan Oil Field, showcasing their ability to mitigate drilling risks and enhance drilling operations when compared to conventional drilling approaches.

Self-attention mechanism for dynamic multi-step ROP prediction under continuous learning structure

The evaluation and prediction of the rate of penetration have been long-term challenging in real-time drilling operations due to, for example, the complexity of influence parameters and uncertainties from the subsurface. In this paper, we propose a machine learning structure combining with a conceptual framework of continuous learning and a deep learning network with the self-attention mechanism to further improve the practical ROP prediction. The self-attention mechanism, also the cornerstone of the Transformer model in the recent impressive GPT3.5 and 4 (Generative Pretrained Transformer), exhibits an enhanced capability to capture the long-dependence relation within sequential data. Compared with the other commonly used recurrent neural networks, the proposed self-attention network model shows significant improvement in reliability and accuracy, especially when one tries to forward predict a long sequence of ROP. This newly presented model can predict the real-time long-term ROP value and can further improve its efficiency by adjusting the controllable drilling parameters. Moreover, the continuous learning structure allows for the extension of single well application to a field scale in a continuous manner for each network model. Field case studies demonstrate the effectiveness and stability of the newly proposed model, which reaches a higher prediction accuracy than 90% for three testing wells. Hence, the proposed structure and network model can help with predictive analysis for real-time drilling performance as an accurate and robust model.

High performance drilling of T800 CFRP composites by combining ultrasonic vibration and optimized drill structure

Drilling of high-strength T800 carbon fiber reinforced plastic (CFRP) are widely employed in current aviation industry. Drilling-induced damages frequently occur and affect not only the load carrying capacity of components but also the reliability. As one of effective methods to reduce the drilling-induced damages, advanced tool structures have been widely used. Nevertheless, it is still difficult to realize high machining accuracy and efficiency by this method. This paper compared three different drill bits to evaluate the drilling performance of T800 CFRP composites and the results showed that the dagger drill was a good choice to drill T800 CFRP considering the lowest thrust force and damages. On this basis, ultrasonic vibration was successfully imposed on dagger drill to further improve the drilling performance. The experimental results showed that ultrasonic vibration reduced the thrust force and surface roughness with a maximum decrease of 14.1 % and 62.2 % respectively. Moreover, the maximum hole diameter errors were decreased from 30 μm in CD to 6 μm in UAD. Besides, the mechanisms of force reduction and hole quality improvement by ultrasonic vibration were also revealed. The results suggest that the combination of ultrasonic vibration and dagger drill is a promising strategy for high performance drilling CFRP.

An Ultrasonic Drilling System for Fast Drilling Speed With Uncertain Load

China's first asteroid exploration project plans to use ultrasonic drilling solutions to achieve asteroid anchoring. The uncertain rock strength on the asteroid and the high and low temperatures pose challenges to the drilling speed and stability of an ultrasonic drill. Therefore, we propose a design method for the ultrasonic drilling system to tackle this issue. First, a novel percussive ultrasonic drill is designed based on theory and experiments. Then, an ultrasonic drive power with resonance frequency tracking, electrical matching, and constant amplitude control is developed to improve the adaptive ability of an ultrasonic drill in an uncertain load environment. Finally, the drilling performance of an ultrasonic drill on rocks with different compressive strengths at different temperatures is verified by experiments. Our results show that when the temperature range is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 60 to 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C and the rock strength is 200 MPa, the drilling speed is 8–28 mm/min, and the power consumption is less than 50 W, the stable working time of a single operation exceeds 2 min. Herein, we provide a technical reference for the application of ultrasonic drilling in planetary exploration.