Conventional Polycrystalline Diamond Research Articles

Investigation on rock-breaking characteristics of hard sandstone by non-planar PDC cutters under high confining pressure

Due to high hardness, strong heterogeneity, and low drillability in deep formations, conventional Polycrystalline Diamond Compact (PDC) bits with planar cutters usually get bit worn, short drilling footage, and low rate of penetration (ROP) when drilling into such formations. To improve the aggression and the impact resistance of PDC bit, a series of non-planar PDC cutters have been proposed and developed by scholars and oil & gas industries. However, the in-situ stress and hydrostatic pressure significantly weaken the rock-breaking performance of PDC cutters, which is a paucity in related studies. Consequently, this paper conducts rock-cutting experiments in hard sandstones by planar cutters and three types of ridged cutters under confining pressure and atmospheric conditions. The influences of cutting parameters on the rock-breaking performances of different cutters are investigated, focused on the changes in cutting force, mechanical specific energy, and rock cuttings distribution. Additionally, visual cutting experiments are conducted to compare the differences in the rock-breaking mechanisms of different cutters. The results indicate that in-situ stress and hydrostatic pressure exert a noticeable inhibitory effect on rock fragmentation, resulting in smaller cuttings and lower rock-breaking efficiency than those under atmospheric conditions. Furthermore, compared to the three types of ridge cutters, planar cutters exhibit a lower rock-breaking efficiency. Ridged cutters, which leverage the efficient stress concentration caused by their ridges, demonstrate a higher rock-breaking performance by effective and efficient rock failure near the ridges. Additionally, under different cutting parameter conditions, each cutter have a corresponding optimal rock-breaking efficiency range. Specifically, for the triple-ridged concave cutters, the highest rock-breaking efficiency is achieved when the cutting angle is approaching 20°. As the cutting angle increases, the axe-shaped cutter exhibits the highest rock-breaking efficiency. In addition, the triple-ridged concave cutter and the axe-shaped cutter possess unique rock-breaking advantages, with the former being more stable and the latter producing larger volumes of cuttings. The selection of appropriate cutter parameters can enhance the service life and the drilling speed of PDC bits. The experimental results and optimization charts have significant implications for selection on cutter shapes and the design of hybrid-cutter parameters in deep hard formation drilling.

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.

Individualized Design and Field Application of Annular-Groove Polycrystalline Diamond Composite Bit

Summary Aiming at the problems of slow drilling speed, low service life, and poor stability of conventional polycrystalline diamond compact (PDC) bits in deep formations that are difficult to drill, a new annular-grooved PDC bit is proposed. The bit adopts discontinuous tooth arrangement to set cutters, and a circumferential annular groove around the center of the bit is set on the bit body to form a fragile convex annular ridge at the bottom of the well, improving the bit’s ability to invade the formation and its rock-breaking efficiency. Combined with the formation characteristics of Shapai 11 well and Shixi 102 well in Xinjiang Oil Field, the PDC bit crown shape, annular-groove design, cutter selection, and other aspects are designed individually, and the dynamic rock-breaking and hydraulic characteristics of the annular-groove PDC bit are simulated and analyzed. Finally, two PDC bits with different diameters are developed—a Φ215.9-mm annular-groove PDC bit and the field application bit. The field application bit results show that compared with the bit in the same layer of adjacent wells, the mechanical penetration rate of the annular-groove PDC bit is increased by 29.8–176.7%, and the footage is increased by 142.5–273.1%. It is concluded that the annular-groove PDC bit can significantly reduce the rock-breaking energy consumption of the bit and improve the mechanical rate of penetration (ROP) of the bit. At the same time, the raised annular ridge can reduce the lateral vibration of the bit and extend the service life of the bit, which will accelerate the exploration and development of deep difficult-to-drill formations. It is of positive significance to reduce drilling costs.

Polycrystalline diamond obtained in the diamond-Mo system with enhanced thermal stability sintered by HPHT

This study provides thermoanalytical data on polycrystalline diamond (PCD) sintered in the diamond-Mo system at high pressure-high temperatures (HPHT). PCD is a key material for the abrasive tool industry, given its unprecedented hardness and wear resistance, as well as its excellent thermal conductivity. These characteristics make it highly effective in drilling into rock formations and machining non-ferrous materials, such as titanium alloys. A critical issue in the performance and lifetime of polycrystalline diamond, however, is its low thermal stability, which limits its potential applications. Accordingly, PCD with enhanced thermostability was obtained in the diamond-Mo system, with resistance graphitization and oxidation around 200 °C higher than conventional PCD. The superior thermal performance seen for PCD-Mo may be due to the formation of in situ carbides (MoC and Mo2C), which inhibit the evolution of graphitization and oxidative processes.

Design of discrete-edge polycrystalline diamond tool and its cutting performance in milling Cf/SiC composites

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites are used extensively in many fields because of their superior properties, such as high specific strength and high specific modulus. However, Cf/SiC composites are typically difficult to machine materials due to their high hardness and anisotropy. Its machining easily leads to high cutting force, short tool life, and poor surface quality. The tool structure shows a significant impact on the cutting performance, which can further affect the cutting force and surface quality. In this study, a novel polycrystalline diamond (PCD) tool with discrete-edge structure was designed for milling Cf/SiC composites, which was devised with tiny microgrooves on the peripheral edge, and the geometric parameters were optimized by finite element simulation method. The cutting performance of the designed discrete-edge PCD tool in milling of Cf/SiC composites was studied. Cutting force, machined surface quality, tool wear mechanisms, and tool life were comprehensively investigated. Comparative experiments were also carried out with conventional straight-edge PCD tools by using identical cutting parameters. The cutting force when using the discrete-edge PCD tool gradually decreased with increasing cutting speed. The machined surface roughness Sa reached 3.5 μm at cutting speed of 125 m⋅min−1 with the discrete-edge tool. Surface defects in terms of fiber pullout, debonding, and cavities were reduced by the discrete-edge tool. The life of the discrete-edge PCD tool was 1.875 times that of the conventional PCD tool. The study illustrates that the cutting performance of the designed discrete-edge PCD tool is better than that of the conventional straight-edge PCD tool.

Experiments on the Novel Chord-Edge Cutter to Break Rock with Higher Efficiency and Its Field Application

Summary Aiming at the difficulty of penetration in hard-plasticity formation represented by the Mahu oil field, a new type of chord-edge cutter is proposed. Through theoretical derivation and quantitative analysis of specific unit pressure (SUP) and breaking area, the penetration and rock-breaking area of the chord-edge cutter are studied, which clarifies that the rock-breaking efficiency of the chord-edge cutter is higher than that of the conventional cutter. The first part of the laboratory experiment investigated the drilling efficiency of two mini-bits on a special sample. The results show that the chord-edge cutter mini-bit has higher efficiency than a conventional mini-bit. The second part of the laboratory experiment investigated the influence of rate of penetration (ROP), revolutions per minute (RPM), and rock types on the drilling performance of chord-edge cutter mini-bit. The data show that the chord-edge cutter is more suitable for drilling hard-plastic rocks. It also reveals that the higher the RPM, the lower the stick/slip vibration, but the RPM above a certain value will lead to an increase in lateral vibration. ROP and weight on bit (WOB) are positively correlated. And the higher the drilling speed, the higher the stick/slip vibration and lateral vibration. To verify these conclusions, a field test is carried out in the hard-plastic formation of a well in the Mahu. In this test, compared with a conventional polycrystalline diamond compact (PDC) bit, a roller-cone bit, and a hybrid bit, the chord-edge cutter bit has the best drilling effect. Further, it is found that when using the chord-edge cutter bit, the high RPM and proper control of WOB can achieve a better drilling efficiency. This rule is mutually confirmed with the conclusion of the laboratory experiment. After the above research and its implementation, it can be concluded that the novel chord-edge cutter bit can achieve the research goal of higher efficiency, which provides a new idea to overcome challenges in the hard-plastic strata.

3D Numerical Simulation of Rock Cutting of an Innovative Non-Planar Face PDC Cutter and Experimental Verification

The low rock breaking efficiency of conventional polycrystalline diamond compact (PDC) bits in hard abrasive formations prompts the development of PDC cutting elements from the planar structure to the non-planar structure. As an innovative non-planar cutter, the design and research of the three-ridged diamond element (3-RDE) cutter is still in its infancy, and its rock breaking mechanism and laws are not yet clear. In this paper, a three-dimensional (3D) finite element model of dynamic rock breaking with 3-RDE cutter has been established. The accuracy of the numerical model was verified by experimental data. Then, the difference of rock breaking mechanism between 3-RDE cutter and conventional cutter was studied. The effects of back-rake angle, cutting depth, rotational angle, and rock properties on rock breaking efficiency were also analyzed. The results show that, unlike the conventional PDC shear rock breaking cutter, the 3-RDE cutter breaks rock mainly by crushing and shearing, and the rock breaking efficiency is higher. A small back-rake angle and reasonable cutting depth contribute to improving the rock breaking efficiency; the existence of rotational angle is not conductive to the rock breaking. The field application shows that compared with the conventional cutter, the 3-RDE cutter is easier to penetrate into the formation, and is more stable with less torque required. The research results can be of benefit to the design and manufacture of 3-RDE PDC bits.

Research on working principle and cross-track cutting characteristic of the axis-tilted rock-breaking tool

Concentric-track cutting method of a conventional polycrystalline diamond compact bit makes the bit suffer from inadequate rock-penetrating capacity and severely hinders the improvement of rock-bre...

Design and test of a self-adaptive bionic polycrystalline diamond compact bit inspired by cat claw

Cats protract claws while hunting or pawing on the ground and retract to muscles when relaxing. Inspired by this behavior, and in order to solve the problem of short service life and low comprehensive drilling efficiency of polycrystalline diamond compact bits which results from its poor adaptability to soft-hard interbedded strata, a self-adaptive bionic polycrystalline diamond compact bit was designed, which can use the elastic element to adjust its back-rake angle according to the formation hardness to improve the adaptability of polycrystalline diamond compact bits. Theoretical analysis and drilling test results show that the self-adaptive bionic polycrystalline diamond compact bit has a strong adaptability to soft-hard interbedded rock strata. When drilling in soft rock, the back-rake angle is small and the rate of penetration is high; when drilling in hard rock, the angle becomes larger to reduce the abnormal damage of cutters. Thus, it can improve the integrated drilling efficiency and service life of polycrystalline diamond compact bits. In the whole drilling test, the average penetration rate of the self-adaptive bionic polycrystalline diamond compact bit increases by 10%–13% over conventional polycrystalline diamond compact bits with the same dimension and material.

Experimental study on the rock-breaking mechanism of disc-like hybrid bit

In order to solve the problems of low rate of penetration (ROP) and short service life of the bit drilling in hard formation, and further improve the performance of conventional hybrid bit, a hybrid bit, disc-like hybrid bit (DLHB) is put forward. The hybrid bit has the advantages of conventional Polycrystalline Diamond Compact (PDC) bit and disc-like roller bit. With analysis on the structural characteristics and rock-breaking mechanism of DLHB, comparison experiments on DLHB and conventional hybrid bit are conducted. The results show that pre-fracturing of the disc inserts is quite significant. The circumferential coverage of the grooved craters produced by disc insert-rows is 40% higher than conventional teeth-rows, and the dynamic load factor is much lower. Besides, ROP of DLHB is 30% higher and weight on bit (WOB) fluctuation is 15%–25% lower than the conventional one in hard formation. DLHB can make the PDC cutters and bearings more durable and it has longer service life compared with conventional hybrid bit.

Diamond-CaCO3 and diamond-Li2CO3 materials sintered using the HPHT method

Diamond-CaCO3 and diamond-Li2CO3 materials were sintered at high pressure (8.0GPa) and high temperature (2300°C) for 3min using the infiltration technique. The structure and mechanical properties of the sintered compacts were characterized. It was determined that the melts of carbonates penetrate into the diamond layer to a depth of 4.5mm. The wear resistance of the materials was measured using the free-diamond abrasive-grinding test. The wear resistance of the diamond that was sintered with CaCO3 is 33% better than that of the conventional polycrystalline diamond cutters (PDC). The wear of the diamond that was sintered with Li2CO3 also exceeds conventional PDC by 27%.

Constant Depth Scoring of Fibre Reinforced Plastic Structures to Prevent Delamination

Scoring of the outer layers of a workpiece with small engagement (ae) using circular saws is a well known method to avoid unwanted delamination of these layers, such as coatings of wooden particle boards. In edge milling fibre reinforced plastics (FRP), delamination also occurs in the top or bottom layer of the component and requires time intensive rework or scrapping of material. A combined process of scoring and milling is presented in this paper as a means to avoid delamination during machining of FRP structures such as aircraft carbon FRP parts. For the scoring process a diamond electroplated circular wheel is used. To guarantee a constant width of the scored slot, a constant depth of engagement is needed due to the shape of the grinding wheel. Therefore the profile of the scoring path on the workpiece surface is measured with respect to the machine coordinate system to correct a variation in the workpiece thickness and to compensate for uneven clamping. Next, the workpiece is scored with constant depth of engagement (ae,s < 0.5mm) and a high feed velocity of up to 16 m/min. Subsequently, the scored component is machined with a conventional polycrystalline diamond (PCD) milling tool. From experiments it is proven that a delamination-free edge is achievable even with a worn tool (cutting edge radius rn > 50μm) at an increased feed velocity (vf,m = 4.5 m/min). Without scoring, flawed workpiece edges have been obtained with cutting edge radii beyond rn > 23μm (progressive uniform wear stage) and a feed velocity of vf,m = 1.5 m/min. Hence, high performance cutting (HPC) edge milling of composites may be realized by an initial scoring step to fulfil quality requirements of the machined edges and simultaneously increase the tool life of the milling tool.

Synthesis and Characterization of Thermally Stable B-Doped Polycrystalline Diamond

In this study we report on the synthesis and characterization of thermally stable polycrystalline diamond (PCD) using Ni-based alloys catalyst as a sintering aid and the B-doped diamond powder in the infiltrating way. The samples were treated at 5.6 GPa and 1200–1480 °C for 10 min in China-type cubic high pressure apparatus. Scanning electron microscopy showed significant intergrowth of the diamond particles sintered in the presence of Ni-based alloy. X-ray diffraction showed the phase change of the samples sintered at the different temperature. Differential thermal analysis (DTA) and thermogravimetric analysis (TG) showed the sample was significantly more heat-resisting compared to conventional PCD. The results showed that the appropriate conditions of thermally stable PCD sintered were 5.6GPa and 1200–1480 °C.

Cutting Performances of Nano-Polycrystalline Diamond

Single-phase (binder-less) nano-polycrystalline diamond (NPD) has been synthesized by direct conversion sintering from graphite under high pressure and high temperature. NPD is characterized by extremely high hardness compared with single crystal diamond (SCD), even at high temperature. In addition, NPD has high wear resistance, no anisotropic mechanical properties, no cleavages, and high thermal stability. These characteristics suggest that NPD has high potential for use in precision cutting tools for various hard works. In order to evaluate the cutting performance of NPD, cutting tests for various cemented carbides were conducted under various conditions and the results compared with those of single crystal diamond (SCD) and conventional polycrystalline diamond containing metal binder (PCD). The results revealed that NPD has outstanding potential for precision cutting and processing of diverse hard and brittle materials.

Improvement of Conventional Polycrystalline Diamond Composites by Nanodiamond Incorporation

Polycristalline diamond composites (PDC) obtained by sintering of micro sized diamond particles together with silicon as binder is a conventional superhard material for high speed cutting tools. nanosized dispersed diamond particles have been recently used as precursor for a new generation of superhard composites. In the present work, PDCs were produced by sintering at high pressure and high temperature using a mixture of micro and nanosized diamond particles for optimized compactation. The values of density and hardness as well the results of X-ray diffraction suggest a plastic deformation of the larger diamond particles. The compression strength of these composites was found to be close to that of natural diamonds.

Small Holes Fabrication on Soda Glass by Self-Elastic Polycrystalline Diamond Tool

This study describes a novel process to drill small holes in brittle materials such as glass, silicon and ceramic using a self-elastic polycrystalline diamond (PCD) drilling tool. In order to improve the surface roughness and reduce crack of the small holes, a new type of self-elastic PCD drilling tool equipped with vibration absorbing materials inside the housing was developed to fabricate small holes in glass in this study. The self-elastic PCD drilling tools could absorb the mechanical force by the vibration absorbing materials while the PCD tool penetrates into the small holes. Compared to conventional PCD drilling tools, the experimental results show that high-quality small holes drilled in glass can be achieved with cracking as small as 0.02mm on the outlet surface using the self-elastic PCD drilling tool.

Cutting performance of nano-polycrystalline diamond

Nano-polycrystalline diamond (NPD) synthesized by the direct conversion sintering process from graphite under ultra-high pressure and high temperature (15–18GPa, 2100–2300°C) has a very fine texture consisting of small diamond grains (10–50nm in size) bonded directly without any binder materials. NPD has extremely high hardness, high wear resistance, no anisotropic mechanical properties, no cleavage feature, and high thermal stability, and so has high potential for precise cutting tools. To clarify this potential, we conducted cutting tests for various work materials under different conditions and compared the results with those for conventional polycrystalline diamond (PCD) and single crystal diamond (SCD) tools.The results of the cutting tests were as follows: approximately 10–20 times higher than the PCD tool on turning of Al–Si alloy, 3–5 times higher than the PCD tool on turning of cemented carbide, and more than two times higher than the SCD tool on ultra-precision cutting for binderless cemented carbide. Detailed observations of the cutting edge after the cutting tests indicated that the excellent cutting performance of the tool was the result of its isotropic feature and fine texture without any binder. These results revealed that nano-polycrystalline diamond has outstanding potential for various cutting and processing applications.

Distinctive mechanical properties of nano-polycrystalline diamond synthesized by direct conversion sintering under HPHT

The mechanical properties of nano-polycrystalline diamond (NPD) synthesized by the direct conversion of graphite under high pressure and high temperature have been investigated. Indentation hardness and bending strength tests revealed that NPD has considerably high hardness and high transverse rupture strength (TRS) at high temperature, far surpassing those of conventional polycrystalline diamond (PCD) and single-crystal diamond (SCD). The hardness remained higher than 100GPa even at 800°C, while the hardness of SCD sharply decreased to 60GPa above 300°C. The TRS remained at about 3GPa up to 1000°C, above which it showed a positive temperature dependence, while the TRS of PCD decreased rapidly at about 500°C. Wear tests using a diamond wheel indicated that the abrasive wear resistance of NPD is equivalent to those of the high wear-resistance directions on SCD, and from 10 to 50 times higher than those of PCD. These results suggest that NPD has outstanding potential for cutting tools.

Thermally stable polycrystalline diamond sintered with calcium carbonate

In this study we report on the synthesis and characterisation of thermally stable polycrystalline diamond (PCD) using CaCO 3 as a sintering aid. The diamond powder was treated at 8 ± 0.5 GPa and 2000–2200 °C for 10 min in a multi-anvil press. Scanning electron microscopy showed significant intergrowth of the diamond particles sintered in the presence of CaCO 3, which remained in the compacts in the form of aragonite and calcite as evident from X-ray diffraction data. The diamond compacts showed no drop in wear resistance, as measured using a machine test, after heat treatment up to 1200 °C in vacuum. This is significantly higher compared to conventional PCDs sintered with a metallic binder. The transmission electron microscopy (TEM) investigation of the samples was carried out in order to gain more knowledge about the role of the carbonate sintering aid in the sintering process.

Cutting performance of time-modulated chemical vapour deposited diamond coated tool inserts during machining graphite

In this investigation, two types of diamond coatings were deposited onto commercially available cemented tungsten carbide (WC-Co) tool inserts using two distinctive processes: i) conventional hot filament chemical vapour deposition (HFCVD) and ii) our recently developed time-modulated chemical vapour deposition process (TMCVD). The TMCVD process enabled the production of smaller sized diamond grains by the promotion of secondary nucleation processes occurring during the larger flow methane modulations. With the conventional HFCVD process, the methane concentration in the gas phase was kept constant during the entire diamond chemical vapour deposition (CVD) process and we labelled the resulting coating as “conventional diamond”, whereas the coating was referred to as “TMCVD diamond” when the methane content in the gas phase was time-modulated by changing its flow rate during CVD. Inserts coated employing both conventional HFCVD and TMCVD deposition process were characterized by scanning electron microscopy (SEM) and Raman spectroscopy and then were tested for turning performance using graphite as working material. For sake of comparison, polycrystalline diamond (PCD) and bare WC-Co inserts were also used for graphite turning. The different wear mechanisms have been compared and discussed in terms of diamond coating microstructure. Repeated turning tests showed that the TMCVD diamond coated inserts exhibit a better wear resistance with respect to inserts coated with conventional diamond coatings, PCD and bare WC-Co inserts.