Polycrystalline Diamond Compact Research Articles

New understandings of the applications of PDC cutters in oil and gas drilling

Today, the polycrystalline diamond compact (PDC) cutters have already reached a pretty high level of quality and are still keeping advancing. The formations drillability is positively related to the quality of PDC cutters. With advances in PDC cutters, most formations have become easy-to-drill. Years of improvements in the PDC cutter quality and the drilling techniques have also upended some long-hold knowledge and understandings about the cutter applications. PDC designs abandoned long ago are once again applicable, such as unleaching, thin diamond table, small chamfer, and non-pure diamond mix. From the perspective of saving money and environmental protection, these long-abandoned PDC designs are worth a shot, but are suggested to be used in the well-understood formations and lithologies. On the other hand, why do PDC cutters always perform poorly in challenging formations? The results revealed that this is mainly due to the irregular dynamic impacts and inefficient rock cutting, which are the primary causes of the premature failure of PDC cutters and bits. The challenging formations as well as the unknown formations in the exploratory wells still prefer the cutters with the best quality, such as pure diamond mix, thicker diamond table, deep leaching, excellent residual stress management, and the ones from the best manufacturer. In addition, how to select the right cutters depends highly on the bit failure forensics and the multi-index evaluation. The emphasis of cutter selection is on selecting the right design and the right materials for the right formations, rather than the most expensive ones.

Comparison of the relationship between hardness and wear resistance of polycrystalline diamond and cubic boron nitride

AbstractHardness is an important indicator of the wear resistance of tool materials. The study of the effect of hardness on the wear resistance of tool materials has significant practical applications. In this experimental work, a series of polycrystalline cubic boron nitride (PcBN) and diamond (PCD) compacts with different hardness are sintered under high temperature and pressure, and these samples were fashioned into turning tools, used for edge wear testing in the granite turning process. Based on the measurements above, the relationship between hardness and wear resistance in two materials with identical grain sizes (1–2 µm) was examined, and the results reveal a significant positive correlation between the hardness and wear resistance of the two materials. Remarkably, the relationship between hardness and wear resistance in two materials complies with the same type of fitting function. But incredibly, the wear resistance of the two materials exhibits inconsistency as the hardness increases. Specifically, below 40 GPa Vickers hardness, both materials exhibit comparable wear resistance. However, above 40 GPa, the difference in wear resistance between the two materials becomes more pronounced with increasing hardness. At the Vickers hardness of 70 GPa, the abrasion ratio of the PCD is approximately 3.5 times that of the PcBN, and it is anticipated that the disparity between them will continue to expand within the broader range of hardness. Further analysis reveals that the intrinsic hardness of the crystal grains significantly impacts the wear resistance of polycrystalline materials.

Dynamic response and damage behavior of impact wear for polycrystalline diamond compact under low kinetic energy impact

Polycrystalline diamond compact (PDC) cutters are the main load-bearing components in shale gas drilling, and their performance significantly affects the efficiency of shale gas extraction. One of the primary reasons for cutter failure is the dynamic impact between the rock and the cutter due to the complex geological conditions of shale gas extraction. Investigating the impact wear behavior and damage mechanisms is vital to designing superior-performing PDC structures and improving their effectiveness in engineering applications. This work investigates the kinetic response and damage behavior of PDCs under low kinetic energy impacts to explain the characteristics and mechanisms of PDC impact wear. The results show that the impact force fluctuates with impact owing to changes in the interface state. Owing to the elastic-plastic properties of PDC, 87 % of the kinetic energy is used for plastic deformation and fracture. Secondly, the contact time and kinetic energy absorption rate only relate to the impact mass. The contact time positively correlates with mass, while the kinetic energy absorption rate changes in the opposite direction. In addition, diamond fracture occurs with a low kinetic energy accumulation of only 0.059 J. Cobalt catalysis and stress effects were found to induce graphitization and carbon rehybridization jointly during impact wear. It is concluded that the PDC impact wear mechanism under low kinetic energy impact is a brittle fracture with a combination of transcrystalline fracture and intergranular fracture. This work provides referable basic research data for designing impact-wear resistant PDC structures and improving the efficiency of shale gas extraction.

Investigation of the friction and wear characteristics of polycrystalline diamond compact in a wide temperature range

The friction and wear behaviours of polycrystalline diamond compact (PDC) at temperatures ranging from room temperature to 600 °C are evaluated using a pin-on-disc high-temperature tribometer, and the microstructures and chemical compositions of the worn PDC surfaces are analysed experimentally. The results show that the friction coefficient of PDC is significantly affected by temperature; the friction coefficient decreases with increasing temperature below 200 °C and increases with increasing temperature above 200 °C; the friction coefficient is the lowest at 200 °C, with a value of 0.048. The fluctuation of the friction coefficient with temperature is related to the different synthesis results of surface deformations and tribochemical reactions during the sliding tests at different temperatures. The exfoliation of the diamond grains and Co phase from the PDC surface results in a scratched appearance on the PDC surface, which has a friction-increasing effect and dominates at temperatures above 200 °C. The cobalt oxides and graphite formed on the PDC surface can operate as solid lubricants to decrease the interfacial friction of the PDC, which has a friction-decreasing effect and dominates at temperatures below 200 °C.

Investigation on the rock-breaking performance of specially-shaped PDC cutter under confining pressure conditions

Cutter shape has a significant influence on the rock-breaking performance of drill bit. Compared with conventional Polycrystalline Diamond Compact (PDC) cutter, the emergence of specially-shaped PDC cutters (SSPCs) with different geometric shapes is of great benefit to solve the problems of low rate of penetration (ROP) and rock-breaking efficiency in deep hard and hot dry rock formations. However, the high confining pressure and high in-situ stress (HCHS) have a significant influence on the rock-breaking performance of PDC cutter which cannot be ignored. Given that the above facts, this paper selects five kinds of PDC cutters with different cutter shapes, and implements a series of cutting experiments of granite under confining pressure conditions (CPCs) and atmospheric pressure condition (APC) using a true triaxial rock cutting device. The influence of cutter profile on the rock-breaking performance of PDC cutter was studied from the perspective of cutting force, mechanical specific energy (MSE), cuttings, coarseness index (CI) and fractal dimension. The results show that the rock breaking under CPC is more difficult than that under APC, resulting in the increased cutting force and MSE. Moreover, the cuttings obtained under CPC are smaller in size and the cutting grooves are smoother. Cutter shape has a great influence on the rock-breaking efficiency of PDC cutter, the rock-breaking efficiency of axe-shaped cutter is higher, while that of stinger cutter is lower. Moreover, PDC cutters with different shapes have different sensitivities to confining pressure, and stinger cutter has the lowest sensitivity to confining pressure, in other words, confining pressure has little influence on the rock breaking process of stinger cutter. What is more, the distribution of cuttings is characterized by the fractal dimension and particle size distribution parameter from the perspective of cuttings morphology and size respectively, and they present completely opposite changing trends. The obtained results are of great significance to the optimization of cutter profile, the design of bit cutter arrangement and the drilling of deep formation.

Study on Composite Rock-Breaking Mechanism of Ultrahigh-Pressure Water Jet–PDC Cutter

Summary The drilling industry is paying increasing attention to deep and ultradeep wells because of the gradual decline and depletion of recoverable resources on the shallow surface. However, the difficulty of conventional mechanical rock-breaking grows significantly with increasing drilling depth. It has been found that the effect of a high-pressure water jet combined with a polycrystalline diamond compact (PDC) cutter is significant and can greatly increase the efficacy of rock breaking. A composite rock-breaking experimental device with a high-pressure jet was designed to carry out composite rock-breaking experiments. Meanwhile, a composite rock-breaking numerical model of high-pressure water jet-PDC cutter was created by smoothed particle hydrodynamics/finite element method (SPH/FEM). After verifying the reliability of the numerical model through experiments, the key factors, including rock stress field, cutting force, and jet field, were extracted to analyze the composite rock-breaking mechanism. The results show that the enhancing effect of jet impact on rock breaking is mainly reflected in three aspects: (1) The high-pressure water jet can create a groove and crater on the rock surface, effectively unloading the rock stress at the bottom of the well and increasing the area of rock damage; (2) PDC cutter vibration can be efficiently reduced with high-pressure jet; and (3) the rock debris in front of the cutter is cleaned in time, avoiding the waste of energy caused by the secondary cutting and reducing the temperature rise of the PDC cutter. Besides, it has been investigated how parameters like jet pressure, nozzle diameter, impact distance, and cutting depth influence the effect of jet rock breaking. The findings indicate that the best rock-breaking efficiency and economy occur at jet pressures of 30–40 MPa. Correspondingly, in terms of nozzle angle, nozzle diameter, and impact distance, the ideal ranges are 60°, 1.0–1.5 mm, and 10 mm, respectively, wherein the ideal impact distance is approximately 10 times the nozzle diameter. This research is critical for the advancement of high-pressure jet drilling technology and the design of supporting drill bits.

Performance and Formula Optimization of Graphene-Modified Tungsten Carbide Coating to Improve Adaptability to High-Speed Fluid Flow in Wellbore

In order to improve the erosion resistance of steel PDC (Polycrystalline Diamond Compact) bit under high-speed fluid flow conditions underground, it is necessary to develop a high-performance erosion-resistant coating. In this paper, laser cladding was used to prepare the new coating by modifying tungsten carbide with graphene. And the effects of tungsten carbide content and graphene content on the coating performance have been thoroughly studied and analyzed to obtain the optimal covering layer. The research results indicate that, for new coatings, 60% tungsten carbide and 0.3% graphene are the optimal ratios. After adding tungsten carbide, the hardness has significantly improved. However, when the tungsten carbide content further increases more than 30%, the increase in hardness is limited. In addition, when the content of graphene is more than 0.3%, the branched structure becomes thicker. In detail, this is a phenomenon where the segregation of Cr, Si, and W becomes very obvious again, and the segregation of Fe occurs at the Ni enrichment site. The research results contribute to the development and optimization of high-quality erosion-resistant coatings under the high-speed flow conditions in wellbore. These are of great significance for improving the efficiency of oil and gas exploration and development.

Numerical simulation study of PDC cutter rock breaking based on CT scanning to construct a rock model and apply a cohesive element to construct a discretization element

To more accurately simulate the interaction between a polycrystalline diamond compact (PDC) cutter and rock, the structural characteristics of basalt were analysed using computed tomography (CT), and a hard particle–matrix–pore three-phase rock model was established due to its structural characteristics. Three-dimensional models of the interaction between PDC cutters and rock were established by using the finite–discrete element method (FDEM). Using Voronoi diagrams to randomize the grid structure and optimize the propagation of cracks. This study revealed that a broken zone near the cutters will form during the rock breaking process, resulting in the affected area being larger than the area in contact with the formation rock. The rock breaking ability of circular cutters is stronger than that of conical cutters. When a conical cutter breaks hard particles, they are mainly striped or forced away from the rock, but circular cutters can divide hard particles into small pieces. The numerical model used in the research institute can effectively calculation results of the process of interaction between PDC cutter and rock, this proves that the application of the cohesive method to simulate rock breaking by PDC cutters is reliable.

Experimental Research on Impact Resistance Test of Polycrystalline Diamond Compact Based on Digital Image Correlation Method

In this study, the impact resistance of Polycrystalline Diamond Compact (PDC) was studied with DIT drop weight tester and high speed camera. The surface of PDC was analyzed by Digital Image Correlation (DIC). The reason of impact failure of PDC was obtained by using the surface strain field of PDC. The results show that local delamination occurs near the impact point of the polycrystalline layer. The brittle fracture occurs at the maximum tensile strain of the impact resistant composite sheet. The quantitative relationship between the surface strain and the image obtained by DIC can effectively reflect the whole process of PDC composite failure, and can reasonably explain the failure process of PDC composite, and provide scientific research methods for engineering applications.

Novel high-performance polycrystalline diamond compact enhanced using vanadium additives

Polycrystalline diamond compacts (PDCs) with varying amounts of vanadium were successfully sintered. The mechanical and thermal performance tests showed that the abrasion resistance, impact toughness, and thermal resistance increased by 69%, 202.9%, and 30 °C, respectively. The improved performance can be attributed to the solid solution formed by V8C7 with tungsten carbide (WC) as a reinforcing phase, which eliminated interfacial defects, improved residual stress, and reduced the thermal expansion coefficient. In summary, we successfully developed a novel method for fabricating high-performance PDCs to enhance abrasion resistance and thermal stability, while substantially improving impact resistance, and which have remarkable application prospects.

Effect of different base oils on the friction behaviour of polycrystalline diamond compact

AbstractThis study analysed and discussed the friction and wear properties, as well as the interface evolution behaviour of polycrystalline diamond compact (PDC) under various base oils, through conducting friction experiments on PDC/Si3N4 with different base oils. The friction and lubrication mechanism of PDC under different base oils were examined using scanning electron microscopy (SEM), x‐ray energy dispersive spectrometry (EDS), three‐dimensional white light interferometry, and Raman spectroscopy. The results of the study demonstrated that PDC exhibited the best friction and wear performance when lubricated with synthetic oil PAO, followed by castor oil. The inferior performance of paraffin oil can be attributed to its low viscosity, resulting in a lower presence of ions capable of passivating the carbon dangling bond. Consequently, paraffin oil displayed inadequate oxidation stability and increased susceptibility to oil film destruction, ultimately leading to suboptimal friction and wear characteristics. Overall, this study provides valuable insights for industrial applications, aiding in the selection of appropriate base oils as cutting fluids for PDC cutting tools and enhancing the friction and wear properties of PDC.

Tribological properties of Graphene/MoS2 combinations as lubricant additives for polycrystalline diamond compact

To investigate the tribological properties of polycrystalline diamond compact (PDC), different additives including graphene, molybdenum disulfide (MoS2), and a combination of graphene + MoS2 were utilized. The microstructure and chemical reactions of PDC were analyzed using techniques such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The focus was on the formation and degradation of the friction film. The findings revealed that both graphene + MoS2 exhibit excellent lubrication properties, forming a protective friction film on the surface of PDC. Furthermore, the combined use of graphene + MoS2 demonstrated a synergistic effect, resulting in enhanced wear resistance of PDC compared to the individual use of graphene or MoS2 alone.

Study on super impact resistant polycrystalline diamond compacts with homogeneous PCD/WC-Co interlayer

With ultra-deep wells exceeding 10,000 m, the downhole drilling environment has become increasingly harsh and challenging and poses higher and more urgent requirements for the improvement of mechanical properties of polycrystalline diamond compact (PDC) cutters. In this work, four different types of polycrystalline diamond (PCD) structures were utilized with the purpose of exploiting both the advantages of homogeneous PCD/WC-Co composites in the impact toughness and the advantages of pure PCD composites in the wear resistance. Each PCD layer was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The indentation hardness, wear resistance and impact resistance of PDC cutters were evaluated using nanoindentation instrument, vertical turret lathe and progressive drop tester, respectively. The field trials of the developed PDC cutters in the ultra-well above 8000 m were also carried out. The experimental results demonstrated that PDC cutters with homogeneous PCD/WC-Co interlayer have excellent impact resistance while the pure PCD top layer ensures the cutter's hardness and wear resistance. Through observing the cracks in the diamond layer after mechanical performance testing, it was discovered that the homogeneous PCD/WC-Co interlayer has the capability of promoting the deflection of cracks on a macroscopic level. In addition, the inclusion of WC-Co alters the fracture mode of the PCD layer from transgranular fracture to mixed-mode fracture, which well explains the toughening mechanism of PCD/WC-Co cutter. This work provides valuable insights for the development of high-quality PDC cutters, and has important significance for the further design of efficient rock-cutting materials and comprehensive improvement of the drilling performance of PDC bits.

Numerical Investigations for Rock-Breaking Process and Cutter Layout Optimization of a PDC Drill Bit with Dual-Cutter

PDC (polycrystalline diamond compact) drill bits are widely employed for rock-breaking in many industries like underground engineering and building constructions. The cutter layout would directly affect the overall performance of the drill bits. Field applications show that the staggered cutter layout strategy of dual-cutter can increase the drilling efficiency of the PDC bit. In order to explore the rock breaking mechanism of this type of drill bit, a numerical model of a dual-cutter and rock breaking with damage evolution based on a hybrid finite and cohesive element method (FCEM) has been established in this work. The model is verified through Brazilian disk tests. The rock breaking processes of this type of bit have been analyzed, including crack initiation, propagation, and the formation of rock debris. Moreover, the effects of horizontal and vertical offset of the back cutter on the MSE (mechanical special energy) have been investigated. Results demonstrate that the dual-cutter can prominently reduce the MSE compared to a single-cutter. The vertical offset of the back cutter has a minor effect on the MSE, while the horizontal offset is of great significance on the MSE. On this basis, the relationships between the MSE and both the vertical and horizontal offset coefficients have been built based on the response surface methodology (RSM). Finally, an optimized layout solution, with optimal vertical and horizontal offset coefficients of 0.641 and 0.497, is determined via the Gray Wolf algorithm.

A novel experimental setup for axial-torsional coupled vibration impact-assisted PDC drill bit drilling.

The geological conditions of hot dry rock (HDR) reservoirs are complex. The geothermal mining of HDR faces major challenges in the drilling and construction of wells, fracturing to create storage, and flowing to extract heat. Vibration impacts help improve the rock-breaking efficiency, where the axial-torsional coupled vibration impact technology can increase the bit penetration depth and reduce the stick-slip effect. To study the feasibility and efficiency of the axial-torsional-coupled vibration impact-assisted Polycrystalline Diamond Compact (PDC) bit to break high-temperature and high-pressure rocks, a new experimental setup was designed. The system includes a drilling fluid circulation system, an axial-torsional coupled impact drilling system, a formation simulation system, and a data acquisition and control system. This setup can produce a rock-breaking torque of 2000 N·m, a drilling speed of 200rpm, a weight on bit of 100kN, an axial vibration frequency of 100Hz, and a torsional vibration frequency of 50Hz. It can simulate the formation pressure of 70 MPa and the rock temperature of 400 °C. A series of rock-breaking drilling experiments were successfully conducted using this setup. The results show that the axial-torsional coupled vibration-impact assisted PDC bit has a good performance in breaking high-temperature and hard rocks, which can accelerate the application of this new technology in deep formation drilling.

Numerical and analytical models of the mechanism of torque and axial load transmission in a shock absorber for drilling oil, gas and geothermal wells

The paper proposes an improved design of a shock absorber used in drilling deep oil and gas and geothermal wells with polycrystalline diamond compact (PDC) bits. The proposed innovations successfully combat the dangerous phenomenon of self-excited vibrations, which can lead to malfunctions such as stick-slip and whirling of the drilling tool. Most conventional drill shock absorbers are designed to only absorb longitudinal vibrations, which was sufficient when using roller cutter bits for the drilling process. However, the design features of PDC bits and the phenomenon of interaction of their cutters with interlayered rocks during deep drilling impose new requirements on the properties of the drill shock absorber. To protect the downhole tool from abnormal torque values and torque oscillations, it is proposed to equip the shock absorber with a special torque transmission unit in the form of a fourteen-thread self-releasing screw pair. This unit is capable of transforming increases in external torque into increases in the force that loads the elastic element of the shock absorber. The numerical and analytical models of the mechanism of transferring external axial load and torque to the elastic element of the drill shock absorber are constructed. The distribution of contact pressures on the interacting surfaces of the screw pair and the distribution of equivalent stresses in the screw pair parts are analysed. The strength of the proposed drill shock absorber assembly was evaluated using the Huber-von Mises energy criterion. The dependence of the load transmitted to the elastic element of the shock absorber on changes in the external torque and external axial force is investigated. In general, it is determined that the external load is distributed evenly between all turns of the screw pair, and the limit state of the parts of the proposed assembly is not reached even under high-torque operating load. The obtained analytical dependencies will allow to effectively determine the required strength and stiffness of the elastic element of the drill shock absorber at the design stage. The obtained analytical results were verified using a finite element model.

Optimizing rock breaking performance: The influence of chamfer on polycrystalline diamond compact (PDC) cutters

Research on the rock-breaking performance of the Polycrystalline Diamond Compact (PDC) cutter has primarily focused on sharp cutters, often overlooking the influence of chamfer. Notably, the design of chamfer parameters has been largely unreported. In this study, we established a theoretical model of cutting force that takes chamfer into account. We analysed the primary and secondary relationships of four factors – back rake angle, depth of cut, chamfer angle, and chamfer length – on the force of the PDC cutter. This was done through a pseudo-level orthogonal level test. A numerical simulation, based on the Smooth Particle Hydrodynamic (SPH) method, was conducted to analyse the rock-breaking force and stress distribution characteristics of PDC cutters with different chamfer angles. Combined with a drop hammer impact test, we provided an optimized design of chamfer parameters. Our findings revealed that while the chamfer had a relatively minor influence on the force of the PDC cutter, it contributed to the optimal distribution of stress on the PDC cutter. This effectively protected the cutting edge and prevented early cracks and spalls of the cutter. When the chamfer angle was less than or equal to the back rake angle, the resultant force of the PDC cutter increased with the increase of the chamfer angle. However, when the chamfer angle was greater than the back rake angle, the resultant force of the PDC cutter first increased and then slightly decreased with the increase of the chamfer angle. Additionally, the resultant force of the PDC cutter increased approximately linearly with the increase of chamfer length. When the chamfer angle of the PDC cutter was between 30° and 45°, the fluctuation of the cutting force was relatively smooth, the rock-breaking process was stable, and the cutter’s impact resistance energy was relatively higher. These findings will provide valuable guidelines for the design of chamfered PDC cutters.

Structure Design of Bionic PDC Cutter and the Characteristics of Rock Breaking Processes

The rational structural design of polycrystalline diamond compact (PDC) cutters effectively enhances the performance of drill bits in rock fragmentation and extends their service life. Inspired by bionics, a bionic PDC cutter was designed, taking the mole claw toe, shark tooth, and microscopic biomaterial structures as the bionic prototypes. To verify its rock-breaking effectiveness, the finite element method was employed to compare the rock-breaking processes of the bionic cutter, triangular prism cutter, and axe cutter. The study also investigated the influence of different back rake angles, cutting depths, arc radii, and hydrostatic pressures on rock breaking using the bionic cutter. Prior to this, the accuracy of the finite element model was validated through laboratory tests. Subsequently, a drill bit incorporating all three types of cutters was constructed, and simulations of rock breaking were conducted on a full-sized drill bit. The results demonstrate that the bionic cutter exhibits superior load concentration on the rock compared to the triangular prism cutter and the axe cutter. Additionally, its arc structure facilitates the “shoveling” of the rock, making it more susceptible to breakage under tensile stress. As a result, the efficiency of the bionic cutter surpasses that of the triangular prism and axe cutters. Similarly, it exhibits minimal fluctuations and values in cutting force. As the back rake angle and cutting depth increase, the MSE and cutting force of all three cutters also increase. However, the bionic cutter consistently maintains the lowest MSE and cutting force, confirming the superiority of its bionic structural design. The MSE and cutting force of the bionic cutter fluctuate with the increase of the arc radius, and the optimal arc radius falls within the simulation range, between 21 mm and 23 mm. Compared to the other two types of cutters, bionic cutters possess a unique structure that allows for better release of internal stress within the rock, thereby ensuring higher efficiency in rock-breaking, particularly in deep geological formations. The rock breaking simulation results of full-sized drill bits show that the use of a bionic cutter can improve the drill bit’s ability to penetrate the formation, reduce the possibility of drill bit bounce during the rock breaking process, prevent the occurrence of stick-slip, improve the drilling stability, effectively improve the efficiency and service life of the drill bit during the rock breaking process, and reduce the drilling cost. It is concluded that the research results of bionic PDC cutters are helpful to the development of high-performance drill bits and the reduction of drilling costs.

Failure Forensics of Shaped PDC Cutters Using Image Analysis and Deep Learning

Summary One of the major advances in polycrystalline diamond compact (PDC) bits in the last 10 years is the global adoption of 3D-shaped PDC cutters. By manipulating the cutter shape based on the understandings of cutter–rock interaction mechanisms, the cutting efficiency and mechanical properties of PDC cutters have been greatly improved. Ongoing innovations in 3D-shaped PDC cutter technology are critical to overcoming the more and more challenging formations in ultradeep wells, such as the 10 000-m-deep wells being drilled in China. Such an important role for 3D-shaped PDC cutters in oil and gas drilling applications necessitates a complete and effective failure analysis method. However, the current International Association of Drilling Contractors (IADC) dull grading cannot fulfill this objective. It is out of date in judging the damages to PDC bits and exhibits more limitations in addressing the unique challenges presented by complicated cutter shapes. To address this issue, an intelligent recognition model for PDC bit damage identification was developed based on the image analysis technology and the YOLOv7 algorithm. More than 10,000 dull bit images were used to train and validate this intelligent recognition model, which were collected from 363 PDC bits that suffered different degrees of damage after being used to drill 185 wells in the Sinopec Shengli Oilfield. Compared to the existing models, the developed intelligent recognition model has several notable contributions. First, the developed model is capable of recognizing the damages of various shaped PDC cutters commonly used by the global bit manufacturers, enabling a more accurate assessment of the failure behaviors of shaped cutters and their bits. The detection accuracy of the developed model exceeds 80% based on the confusion matrix. The recognition results by the developed artificial intelligence (AI) model are consistent with the actual failure modes judged by experienced drilling engineers. Second, the developed AI model provides direct qualitative identification of the failure modes and failure reasons for both cutters and PDC bits rather than the quantitative evaluation of the missing diamond layer used by IADC dull grading. Furthermore, the developed model eliminates the effect of reclaimed cutters on the AI detection results based on the implicit use of spatial cues in the YOLOv7 algorithm. The intelligent recognition model developed in this work can provide reliable and valuable guidance for the post-run evaluation, the bit selection for the next run, and the iterative optimization of bit design.

Dynamic characteristic response of PDC bit vibration coupled with drill string dynamics

A thorough understanding of the rock breaking process is key to increasing the rate of penetration and reducing bit wear. Currently, many models of drill bit–rock interaction have been developed. However, these models inaccurately reflect the complex movement of polycrystalline diamond compact (PDC) bits in the well. In this study, the finite element method was used to discretize and simulate the rock removal process, and drill string nodes were taken as the boundary conditions of drill bit movement. A model combining drill string dynamics and drill bit–rock interaction was established to describe the complex dynamic behavior of a PDC bit in a well. The accuracy of the model was verified by a PDC bit drilling experiment. Then, the influences of rock type, weight on bit (WOB), rotational speed, and PDC bit blade number on PDC bit vibration characteristics were studied. Results show that drill bit vibration is stronger when drilling in rocks with high hardness and roughness, and the bit runs more smoothly with more blades. Therefore, drill bits with more blades should be used when drilling hard rocks. Bit vibration is enhanced by increasing rotational speed and WOB, but the effect of rotational speed on bit vibration is much smaller than that of WOB.