PDC Cutter Research Articles

Numerical study of the compound vertical and horizontal impact cutting with a single PDC cutter

Extensive studies have been carried out on vertical or horizontal impact cutting because they are both high-efficiency rock breaking methods, but little attention has been paid to impact cutting with simultaneous vertical and horizontal impact loads. In this work, we conducted numerical simulations to study the mechanism of compound vertical and horizontal impact (CVHI) cutting. Firstly, a finite element analysis model considering the strain rate effect was established, and the parameters of the rock were adjusted by fitting laboratory test data of granite. Then, the differences in the cutting process between conventional cutting and CHVI cutting were analyzed, and a series of simulations were conducted to research how the vertical impact load affects the cutting mode. Finally, other simulations were performed with different horizontal impact loads to reveal the reason for improving cutting efficiency. Due to the applied vertical impact load, the rock failure mode is transformed from the ductile mode into the brittle mode. Besides, the torsional impact load can speed up the cutting process by promoting the generation, propagation, and connection of cracks. Therefore, the cutting efficiency is significantly improved with the action of CVHI loads.

Effect of cobalt content on the performance of polycrystalline diamond compacts

Cobalt was an indispensable role in the damage of a PDC cutter due to its inevitable adverse thermal effect like thermal catalysis, thermal expansion and thermal oxidation in the welding and drilling process, while the quantitative studies on its serial thermal damage effect were still seldom reported. In order to understand the damage mechanism of a PDC cutter and therefore design better products, it was quite necessary to study the roles of cobalt in the PDC cutter by a quantitative means. In present study, the total cobalt content of the PCD layer of polycrystalline diamond compacts were adjusted by blending different amount of microsized cobalt powder in the mixed diamond grains and the infiltrated cobalt from the cemented carbide cylinder during the HTHP sintering process. The sintered PDC cutters were examined by XRD, SEM, EDX, vertical lathe tests, and impact tests, and it was found that the abrasive ratios of the fabricated PDC cutters were strongly dependent on the cobalt content of sintered diamond layers. The PDC cutter without adding cobalt powder exhibited the best resistance to the abrasion, while the PDC cutters sintered by adding 4% mass of cobalt powder demonstrated the worst abrasive ratio, which was the direct proof confirming that by decreasing the content of residual cobalt in the PCD layer the resistance of the PDC cutter to the abrasion would be improved significantly. A non-destructive characterization method was adopted based on the statistical calculation was proposed by using Matlab and Image-J software to quantitatively explore the relationship between the cobalt content as well as the average size of residual cobalt in the PCD layer and the abrasion performance, which opened a new technical route for the disclosure of cobalt-dependent abrasion resistance for the PDC cutter analysis. Moreover, a cobalt-rich narrow zone was found to appear in the interface of PCD/cemented carbide, which was deduced to be the main reason to cause the delamination of PCD layer from the cemented carbide. It was also interesting to find that the percentage of added cobalt powders seemed no adverse effect on the impact performance of the PDC cutters. The conclusion of present study about the cobalt role in the PDC performance was quite good for understanding the PDC damage modes and helped for the better design and fabrication of PDC.

РАЗРАБОТКА ПОРОДОРАЗРУШАЮЩЕГО ИНСТРУМЕНТА С РЕЗЦАМИ PDC

Актуальность. При разработке инструмента для бурения скважин различного назначения основными критериями оптимизации являются повышение механической скорости и его ресурса. Особенно это актуально для породоразрушающего инструмента, предназначенного для бурения в изменяющихся горно-геологических условиях глубоких и наклонных скважин. В последнее время все чаще поднимается вопрос повышения универсальности и проходки бурового инструмента. Возможности в области создания искусственных материалов позволили создать современные буровые инструменты, обладающие выдающимися характеристиками. А опыт научных исследований закономерностей работы бурового инструмента показал, что конструктивные параметры инструмента оказывают влияние на его производительность. Разработка нового бурового инструмента ведется с учетом возможностей производства и опыта последних научных исследований. В настоящее время наиболее востребованным является инструмент, армированный резцами PDC. Аномальный износ режущей кромки резцов PDC является причиной преждевременной отработки инструмента. Возможность вращения резцов PDC вокруг своей оси создает условия их равномерного износа и как следствие приводит к увеличению ресурса бурового инструмента. Цель: разработка высоко ресурсного породоразрушающего инструмента. Объекты: причины повышения износа инструмента; конструктивные параметры инструмента с вращающимися при бурении резцами. Методы: аналитические исследования, анализ. Результаты. Повышение ресурса породоразрушающего инструмента возможно при обеспечении вращения резцов PDC. Возможность размещения максимального числа вращающихся резцов достигается углом наклона торцевой поверхности долота в 45°. При этом достигается максимальное значение усилия прижатия и максимальное совпадение плоскости действия углубления долота в скважине. Для обеспечения активного вращения резцов при бурении следует повышать фрикционные характеристиками их боковой поверхности.

АНАЛИТИЧЕСКОЕ ИССЛЕДОВАНИЕ МЕХАНИКИ РАЗРУШЕНИЯ ГОРНЫХ ПОРОД РЕЗЦАМИ PDC С УЧЕТОМ ДИНАМИЧЕСКИХ ПРОЦЕССОВ РЕЗАНИЯ-СКАЛЫВАНИЯ ГОРНОЙ ПОРОДЫ И СОПРОТИВЛЕНИЯ СРЕДЫ

АНАЛИТИЧЕСКОЕ ИССЛЕДОВАНИЕ МЕХАНИКИ РАЗРУШЕНИЯ ГОРНЫХ ПОРОД РЕЗЦАМИ PDC С УЧЕТОМ ДИНАМИЧЕСКИХ ПРОЦЕССОВ РЕЗАНИЯ-СКАЛЫВАНИЯ ГОРНОЙ ПОРОДЫ И СОПРОТИВЛЕНИЯ СРЕДЫ

Определение глубины разрушения горной породы резцами PDC с учетом сопротивления среды

Определение глубины разрушения горной породы резцами PDC с учетом сопротивления среды

Comparative analysis cutting characteristics of stinger PDC cutter and conventional PDC cutter

The Stinger PDC cutter has a better performance than the conventional PDC cutter drilling for hard, interbedded and highly abrasive rocks. Although researchers have investigated the cutter's characteristic, such as impact resistance, wear resistance and cutter's life, the cutting behaviors of the Stinger PDC cutter still remains unclear. In this study, the single cutter tests were carried out with a Stinger PDC cutter and a conventional PDC cutter as comparisons. The cutting force, cuttings size, surface topography along the cutting trajectory and microscopic morphology of the fracture surface were compared and analyzed. The results show that the average cutting force of a Stinger PDC cutter is 46.14% lower than that of a conventional PDC cutter. The proportion of large cuttings (r > 2.36 mm) generated in the Stinger PDC cutter test is higher than that in the conventional PDC cutter test. In addition, the energy consumption of breaking rocks by a Stinger PDC cutter is 34.09% lower than that by a conventional PDC cutter. The cutting trajectory in the Stinger PDC cutter test has a “V” shape and the surface is relatively rough (Sa = 617.08 μm), while the conventional PDC cutter produces a “U” shape cutting trajectory and the surface is relatively smooth (Sa = 462.18 μm). Furthermore, the SEM analysis shows that the Stinger PDC cutter breaks granite mainly by tensile stress, which is different with the conventional PDC cutter by shear stress. The key findings of this work will help to reveal the rock-breaking process and mechanism with the Stinger PDC cutters.

Study of PDC drill bit crown shape for design optimization: angle of blade inclination aspect

The article studies PDC-type bit operation, in particular, the redistribution of loads on drill bit blades is simulated, depending on “cutter-rock” contact areas, which is determined by a drill bit design. This work aims at PDC bit design optimization, namely to study the effect of the blade angle to the horizontal axis on the torque generated by the bit. The study is based on the Voitanovich and Kuru’s model of Voitanovich and Kuru’s and has its core at determining the balance of forces acting on a single cutter. The scientific novelty of the work is that two areas of contact are considered for each cutter – the on the front and side surfaces. Also, it is hypothesized that the force of the reaction of the pore is directed towards the placement of heterogeneities of the rock. This approach makes it possible to consider the fluctuations of the bits due to the instability of the cutting forces, which in turn are caused by the instability of the properties of the fractured rocks (first of all, their structural heterogeneity).The spatial shape of the PDC cutter crown was studied, characterized primarily by the shape of its upper part, which in turn is characterized by the angle of inclination of the cutting part of the cutter. Contact areas for each cutter, the volume of the destroyed rock depending on the location of the cutter, as well as the loading for a single cutter, the torque for the whole blade and the bit were simulated in the work. The angles of inclination of the blade to the horizontal axis at which the minimum / maximum torques are observed are determined.Changing the inclination of the cutting part causes the redistribution of the destroyed rock volumes. This section dealt with worn-out chisels, and the load was distributed in proportion to the volume of the destroyed rock. It was found that increasing the angle of the blade causes an increase in the total torque for the bit. A method is proposed that allows optimization of the PDC bit design. An increase in the total twisting angle and the total deflection is observed for the cutters, which are most separated from the borehole face.

Numerical simulation of rock breaking by PDC bit in hot dry rocks

Penetrating through hot dry rocks for geothermal resources with high geothermal gradients, high degrees of hardness and abrasivity will be extremely difficult, and a reasonable tooth distribution is a key factor to improve its rock-breaking efficiency. In order to explore an available cutter arrangement design of PDC cutters in hot dry rock drilling, we based on elastic–plastic mechanics and rock mechanics, established a dynamic 3D numerical simulation model of rock breaking with PDC cutters by using the Drucker–Prager yield criterion as the rock strength judgment principle. On the basis of this, we studied, under the confining pressure of 60 MPa, the effects of cutting depth, temperature, back rake angle and cutting speed on the mechanical specific energy of PDC cutters. The following results were achieved. (1) When a PDC cutter cuts a rock with the speed of 0.5 m/s and the back rake angle of 5–25°, the rock destruction specific energy of the cutter decreases significantly with the rise of cutting depth, while increases first and then decreases with the increasing temperature. And the critical temperature is 200 °C. (2) When a PDC cutter cuts a rock with the speed of 0.5 m/s and the cutting depth of 1–3 mm, the rock destruction specific energy of the cutter decreases first and then increases with the increase of back rack angle. And the optimal rack angle is 20°. (3) Within the temperature range of 20–300 °C, a PDC cutter cuts a rock with the back rake angle of 5°, the rock destruction specific energy of the cutter increases with the cutting speed but decreases with the increase of cutting depth.

Shale bedding planes control rock removal behaviors of PDC cutter: Single cutter experiment

Shale bedding planes arise with the complexity of rock removal by the PDC cutters. A series of single cutter experiments were conducted to understand the effects of bedding planes of shale on chip formation behaviors. Six bedding inclinations were taken into account by recording the variation of cutting force, cutting size, topography of debris, and high-speed images. Results demonstrate that the average cutting force highly correlates with bedding inclination where a parabolic relation is observed. The maximum value of cutting force is presented while perpendicular cutting to the bedding plane. Crushing and chipping are approved to be two mechanisms of rock removal of the laminated shale. Particularly, the bedding plane controls the chip formation behaviors. While the cutting force is perpendicular to shale bedding, the crushing dominates the rock removal process in which more powder debris are created. While the cutting force is parallel to shale bedding, the chipping dominates the rock removal and more chunk-like cuttings are generated. Shear cracking along the weak bedding planes promotes chipping that is controlled by the bedding inclination. In summary, the bedding plane attributes to the variation of cutting force response, cutting size distribution, and even rock removal mechanisms.

Modeling of PDC single cutter – Poroelastic effects in rock cutting process

When cutting a saturated rock under pressure, the PDC cutter is not only fragmenting the rock matrix, but also driving the pore fluid ahead of it. Because of the solid-fluid coupling in rock, different pore pressures induced by cutter will affect rock failure and lead to different MSE. The fact that cutting process is influenced by the pore pressure response in the rock is referred to as poroelastic effects in this paper.This paper continues the research in our previous work (Chen et al., 2018) and gives more insights into the poroelastic effects during rock cutting process. The influences of rock diffusivity coefficient and cutter speed are studied. The results show that the two parameters will affect pore pressure response in rock and further affect rock failure and MSE during cutting process. Based on the results, the cutting process can be identified as three conditions: undrained, drained and a transition zone between undrained and drained condition. In undrained and drained condition, MSE will be independent of cutter speed; while in transition condition, MSE decreases with increasing cutter speed. The transition boundaries for the three conditions are given. Cavitation in intact rock during cutting process is also studied. The results show that cavitation is easy to occur when cutting a hard rock with low original pore pressure.Cutting tests were conducted on Torrey Buff sandstone and Carthage marble to verify the poroelastic effects in cutting process. A good agreement between the model results and experiments is found. In general, the results in this paper can give a good understanding on the combined influence of formation permeability, depth of cut and RPM on cutting rock during drilling.

The Use of New Wear-Resistant Materials in the Development of Two-Level Bits with a Balanced Resultant Moment at the Drilling Flight

Two-level bit with a planetary reducer is described in the article. The thrust ball bearings of the planetary reducer are supposed to be replaced by bearings with inserts from grounded -in PDC plates. The scheme of this bearing is given, the research on its bearing capacity is carried out. The results of PDC cutters’ tests for wear depending on depth and penetration in rock are also given. The test results for PDC wear resistance are given in conditions of drilling a well with standard cutters and the cutters that have undergone cryogenic-magnetic treatment. The results of tests on wear resistance of standard PDC plates, PDC plates with leached subsurface layer, and leached PDC plates, covered with additional diamond coating are given. Therefore the existing technologies allow to increase the PDC wear resistance in two-level bit by 1.7-2 times compared to the standard PDC plates. The reasons of the PDC plates chipping are considered, the link between the torque at the drill string and the probability of the PDC plates’ chip is discussed

ОПРЕДЕЛЕНИЕ ПОЛОМОК РЕЗЦОВ PDC С ПОМОЩЬЮ РЕГРЕССИОННОГО И НЕЙРОСЕТЕВОГО МОДЕЛИРОВАНИЯ

Актуальность. В процессе бурения скважин буровые долота, армированные пластинами PDC, отрабатывают свой ресурс не полностью, так как часть режущих PDC элементов выходит из строя по причине их скола, слома или потери, что в значительной степени сказывается на конечных технико-экономических показателях бурения скважин. Цель: разработка и предложение нейросетевой модели для решения проблемы определения процента поломок режущих элементов буровых долот, армированных PDC, на основе имеющихся полевых данных бурения скважин по породам VI–VIII категории по буримости. Объекты: причины, вызывающие выход из строя пластин PDC на буровых долотах в процессе бурения скважин в породах VI–VIII категории по буримости в зависимости от режимных параметров бурения. Методы. В качестве факторов для определения процента поломок использовалась нагрузка на долото (P, кН), частота его вращения (N, об/мин) и скорость бурения (V, м/час) при неизменных значениях параметров промывочной жидкости и компоновки низа бурильной колонны. Для анализа данных применялись регрессионные и нейросетевые модели различных конфигураций. Результаты. Анализ регрессионных моделей показал их непригодность из-за нелинейного характера скорости бурения при низких давлениях и высоких оборотах. Авторами предложена двухступенчатая нейросетевая модель, в которой первая нейронная сеть (Neural Network) служит для определения скорости бурения, а вторая – для прогнозирования процента поломок пластин PDC. Ошибки нейросетевого ансамбля на тестовых данных не превышают величину пригодности нелинейных моделей, равную 4,5 % для относительной ошибки и 12–15 % для максимальной величины. Предложенная нейросетевая модель может найти применение при разработке технологического регламента отработки долот, армированных резцами PDC.

Cracks imaging in linear cutting tests with a PDC cutter: Characteristics and development sequence of cracks in the rock

Imaging cracks is a direct way to learn the rock breaking mechanism beneath a PDC cutter. In this study, a series of linear cutting tests and precise observations of cracks were conducted. The formation of major cracks was captured in-situ with a high speed camera in the process of cutting rock sheets. Then the cracks under the cutting groove (subsurface cracks) were studied by reproducing the cutting groove after cutting some rock blocks and further observed by means of thin-section optical microscopy. Finally, the development sequence of the cracks and adjacent crushed zone was determined by recording the cutting process on a rock-like silica glass block. The results show that the shape of major cracks is mainly curved, both upward and downward curves were observed. The major cracks mainly initiate at the tip of the cutter when cutting sandstone and granite, while they initiate more randomly in marble. The length and angle of the subsurface cracks vary with the rocks: the subsurface cracks extend the longest in granite, while propagating more vertically in sandstone. Finally, it is determined that the major cracks initiate after the formation of crushed zone. And the initiation of major cracks will enlarge the crushed zone and lead to the initiation and propagation of the subsurface cracks. The results in this paper are expected to further reveal the rock breaking mechanism beneath a PDC cutter.

РАЗРАБОТКА И СОВЕРШЕНСТВОВАНИЕ КОНСТРУКТИВНЫХ ПАРАМЕТРОВ ДОЛОТ С РЕЗЦАМИ PDC

РАЗРАБОТКА И СОВЕРШЕНСТВОВАНИЕ КОНСТРУКТИВНЫХ ПАРАМЕТРОВ ДОЛОТ С РЕЗЦАМИ PDC

Effect of PDC cutter rake on penetration rate of wing bit drilling in variable hardness rocks

Effect of PDC cutter rake on penetration rate of wing bit drilling in variable hardness rocks

Analysis of rock cutting process with a blunt PDC cutter under different wear flat inclination angles

It is generally accepted that drilling with drag bits (Polycrystalline Diamond Compact bits) simultaneously consists of “pure cutting” and “frictional contact” processes. To date, the mechanics of rock cutting have been mostly based on the assumption that these two processes are fully independent as the influence of wear flat inclination angle (β) with respect to the cutter velocity vector (v) on the frictional contact force is often not accounted for. The specific aim of this study is to determine the effect of wear flat inclination angle on the frictional force acting on the wear flat surface of a single blunt cutter over a wide range of depths of cut (d). For this purpose, an extensive and comprehensive set of cutting experiments was performed on two sedimentary rock samples (a limestone and a sandstone) using a state-of-the-art rock cutting equipment and a unique cutter holder. The results show that the normal contact stress (σ) at the wear flat-rock interface (and therefore the normal frictional force acting on the wear flat) is dependent on the depth of cut within the elastoplastic and particularly plastic regimes of frictional contact; however, the contact stress is invariant with depth of cut within the elastic regime. Further investigations indicate that the assumption that the force acting on the wear flat surface of a blunt cutter is independent of the cutting process taking place ahead of the cutter is not valid in particular, for the large values of inclination angles.

The rock breaking mechanism analysis of rotary percussive cutting by single PDC cutter

Rotary percussive drilling technology can solve the problems of low efficiency and high cost in deep hard formation drilling effectively; it can improve drilling efficiency and reduce stick-slip vibration in order to improve transmission efficiency of WOB (weight of bit). However, the rock breaking and ROP rising (rate of penetration) mechanism are not clear enough to some extent. This paper established three-dimensional finite element model of rotary percussive cutting by single PDC cutter. The crack propagation, chip formation, damage evolution, mechanical specific energy (MSE), and other problems are discussed. The results show that the hard rock is more prone to occur brittle failure under rotary percussive cutting, the rotary percussive drilling technology can improve the stress state of the PDC cutter, better to protect the cutter and improve the drilling efficiency; the magnitude of impact amplitude should not be too large when it reaches the threshold to break rock, the impact frequency has significant influence on MSE; rotary percussive drilling technology is not suitable for soft formations. The field applications show that the use of high-frequency impactor can bring obvious ROP rising in the hard formation drilling. The results obtained in this paper can enhance the understanding of rotary percussive drilling technology and provide theoretical basis for the design of impactor.

Calibrated FEM modelling of rock cutting with PDC cutter

Complexity of bit-rock interactions and formation fracture makes rock drilling a challenging task from modelling perspective. A finite element model is developed which can plausibly capture the rock fractures while it is capable of evaluating drilling forces for various values of Rate of Penetration (ROP), bit angular velocity and cutter configuration. Firstly, experiments on a single cutter rig are performed with various drilling parameters to be compared to the proposed FE model. Prior to detailed numerical simulation, a rigorous computation test on material model characterization and the element size and type is conducted to ensure feasible and reliable simulation results. The cutting forces are analysed for different values of WOB, rake angle, initial depth of cut and cutter speed for a single-cutter linear cutting. The formation fragmentation process and computed results are comparable to laboratory tests.

Измерение нагрузки на резец PDC при стендовом бурении

Измерение нагрузки на резец PDC при стендовом бурении

Виброгаситель-калибратор

FIELD: oil and gas industry.SUBSTANCE: invention relates to support-centering elements of a drill string and can be used in drilling deep oil and gas wells. Vibration damper-calibrator includes a housing with a central hole for the flushing liquid supply to the well shaft and two connecting threads for its installation into the drill string, divided by external flushing channels into separate working sectors, each of which is equipped with pushing floating spring-loaded dampers-elements of drill string transverse oscillations extending above casing central surface, which outer surface on the side of the well wall is reinforced with wear-resistant teeth or PDC cutters for simultaneous calibration of the well shaft. In each working sector there are longitudinal grooves in the form of swallowtail, open on the side of the face and closed on the opposite side, allowing to install and movably fix in them floating insert elements with extending springs, having dimensions and configuration, congruent to the shape of slots, open ends of which are protected by covers with locking elements. Value of maximum extension of floating plug-in elements above diameter of housing is provided by selection of angle of undercut of longitudinal grooves within α=5–16°, which when selecting the side gap between inclined walls of grooves and sidewalls of floating plug-in elements allows extending springs to advance their calibrating surface to design value above diameter of housing, which can be readjusted and fixed by means of tightening ring.EFFECT: wear resistance of drilling tool.1 cl, 5 dwg