Applications of Polycrystalline Diamond (PCD) Materials in Oil and Gas Industry

Abstract

Polycrystalline diamond possesses high hardness and wear resistance, among other superior properties, such as low coefficient of friction, high thermal conductivity, high corrosion resistance and low electrical conductivity. Some of these properties favor the application of polycrystalline diamond in oil & gas industry. PDC cutters are the primary and key components in the PDC drill bits to cut various formations. However, drilling very hard and highly abrasive formations poses a big challenge for today’s PDC drill bits. The weakness in the current technology is due to the unavoidable use of metallic catalysts to bond the diamond grains that comprise the PDC cutters in traditional high-pressure and high-temperature (HPHT) manufacturing. Development of catalyst-free PDC cutters would be a game changing technology for drill bits to potentially realize the goal of “One Run to Total Depth” in drilling technology. This chapter will cover the development and applications of both catalyst-synthesized and catalyst-free polycrystalline diamonds in oil and gas industry including latest breakthrough on ultra-HPHT manufacturing technology to make the hardest diamond on earth for drilling and completion. Besides the application of polycrystalline diamond as PDC cutters, this chapter will also cover its applications in bearing or drilling system.

1. Introduction

Polycrystalline diamond compact (PDC) drill bits are critical drilling tools for most formations in oil and gas exploration and drilling, with annual market size of more than $4.5 billion. PDC cutters are the main and critical component in PDC drill bits that cut these formations because of their excellent properties such as high hardness, thermal conductivity, impact resistance and wear resistance. PDC drill bits equipped with PDC cutters have gained widespread popularity in oil and gas drilling due to their long bit life and ability to maintain a high rate of penetration (ROP). The shearing effect caused by the fixed PDC cutter has been shown to be more effective than the crushing effect of the tooth or insert on the rollcone drill bits. Most PDC drill bits consist of a body either milled from a solid steel block or infiltrated by a metallic binder into tungsten carbide particulars. The bit body has blades, in which the actual PDC cutter is mounted in the form of flat or shaped diamond table, as well as open areas or slots where cuttings and mud streams can escape to the annulus. Figure 1 shows a typical 5−7/8″ diameter PDC bit. In Figure 1, the PDC cutters are brazed and placed on the blades. The flow pathways are used for mud and cuttings removals. However, when drilling very hard and abrasive formations, PDC drill bits on the market face very high challenges [1, 2, 3]. PDC cutters currently available on the market do not provide sufficient wear resistance, impact resistance, or thermal stability to cope with this challenging drilling environment. Low penetration rates (ROP) and short bit life have led to the use of multiple bits to drill a single interval, which is not optimal for well economy [4, 5, 6].

Figure 1.

PDC Drill bit equipped with PDC cutters.

The main weakness in the current technology comes from the unavoidable use of a metallic catalyst (typically cobalt) during the manufacturing of the PDC cutters [4]. Figure 2 shows a typical SEM microstructure of PDC cutter showing Co catalyst distribution in the diamond structure. Traditionally, PDC cutters can be manufactured at relatively low pressures and temperatures, around 5.5 GPa and 1400°C, respectively, due to metal catalysts. However, these metal binders reduce the hardness of polycrystalline diamond (PCD) materials to approximately 50−70 Gpa [7]. More seriously, when the formation or rock drilling operation generates high frictional heat, the metal catalyst binder in the PCD layer will unfavorably help the diamond turn back into graphite. In addition, the cutting and drilling process exposes the PCD material to high stresses, where PDC cutting edges with cobalt binders tend to produce microcracks and diamond particles fall/collapse when the stress is greater than the binding strength of the diamond grains in the PDC cutters at a specific temperature. The reason for this can be explained by differences in the modulus of elasticity and coefficient of thermal expansion between the cobalt metal binder and the diamond, which can lead to a mismatch between the volume change of the diamond and the binder in a high-stress and high-temperature operating environment. As a result, large stresses are created inside the PDC material, leading to early failure. Therefore, the whole drill bit industry tried to leach out the metallic binder from the diamond structure to improve the thermal stability. But this can reduce the fracture toughness of the PDC cutting structures and shorten the drill bit life. Developing a catalyst-free or binderless PDC cutter for drill bits would be an ideal and game-changing technical solution that has the potential to achieve the goal of “one run to total depth” in drilling technology.

Figure 2.

A typical SEM microstructure of conventional PDC cutters with Co.

This chapter will highlight their own research and development of binderless or catalyst-free micro polycrystalline diamond (MPD) PDC tools and related drill bit technologies in the oil and gas industry. Ultra-high pressure and ultra-high temperature (UHPHT) technologies make this possibility a reality. UHPHT technology is cutting-edge technology developed for many advanced superhard materials. Currently, the technology is mainly focused on the study of nanocrystalline diamond (NPD). However, their industrial applications are limited by small sizes and/or high costs. In Japan, researchers [8] developed a Kawai type 2–6-8 large-cavity hydrostatic pressure device that successfully achieved a high pressure of about 15 GPa when synthesizing millimeter-scale nanocrystalline PDC materials. Since then, after nearly 10 years of further development, the size of synthetic NPD has been successfully increased to the centimeter level. Larger tonnage high-pressure units are required to obtain larger sample sizes and ensure reasonable high-pressure efficiency. In anvil design, high reliability and efficiency are mainly affected by load losses during the transmission process, of which the structural design of the anvil assembly and the strength of the anvil material in the final stage are the most important. The progress of our UHPHT technologies will be introduced.

2. Diamond basic

Diamond, with a Vickers hardness of more than 100 GPa, is one of the most commonly used superhard materials for industrial applications because it has short and strong covalent bonds between carbon atoms in cubic crystal structures. It is a metastable allotrope of carbon, with atoms arranged in a modified surface-centered cube (fcc) crystal structure called a “diamond cube” or “diamond lattice.” Currently, there are two approaches, either using graphite as a starting powder, or using diamond in the industry to produce catalyst-free or binderless PCDs, and two carbon allotropes – diamond and graphite (Figure 3) will be focused on, which have very different mechanical properties from superhard and supersoft materials, respectively. Diamonds are the hardest known phases in natural and synthetic materials, with a face-centered cubic lattice (space group #227, a = 3.56679 Å). In this compact structure (density of 3.51 g/cm3), the atoms are covalently bonded to four other atoms due to sp3 orbital hybridization, with an average bond length of about 1.54 Å. Graphite has a hexagonal structure (space group #194, a = b = 2.456 Å, c = 6.696 Å), formed by stacks of layers composed of regular hexagonal carbon. Each atom of a given layer is covalently bonded to three other atoms to form a sp2 hybridization type, while the bonds between the layers are weaker, by van der Waals type. The stable form of crystalline carbon at standard temperature and pressure (STP) is graphite, while at higher temperatures and pressures above the well-known Berman-Simon line [10], the cubic form of diamond is stable. Because the diamond is processed using the high temperature and pressure technology above the Berman-Simon line, the diamond retains its unique superhard cube structure when lowered to STP. The formation of diamond from graphite is only a phase transition under HPHT, given by the following equation:

Figure 3.

Two carbon allotropes - diamond (left) and graphite (right) [9].

$${\text{C}}_{\text{graphite}}<=>{\text{C}}_{\text{diamond}}$$E1

At atmospheric pressure, the Gibbs energy change from graphite to diamond at all temperatures is greater than zero, which means that graphite is a stable phase at all temperatures at atmospheric pressure. However, since diamonds are a denser form of carbon, one would expect increased pressure to make diamond formation more likely. Both diamond powder and graphite powder can be used as raw materials to create bulky, superhard-cutting structures for drilling tools. However, the sintering mechanism is completely different, which has a great impact on the properties of the material.

Due to its extremely high hardness, diamond is widely used in industrial applications that require very high wear resistance. It can be processed as a single crystal in the form of large blocks, or as a powder for grinding, polishing, and grinding operations, or as a PDC tool, where individual grains are joined together by a high pressure and high temperature (HPHT) process. Until the 1950s, only natural diamonds could be used for niche abrasive applications. With the introduction of the HPHT process for synthetic PCDs by GE in 1955 [11], the use of synthetic diamond abrasive materials has increased dramatically. While the performance of natural diamonds varies greatly due to differences in defect density and impurity levels, the performance of synthetic or man-made diamonds is more controllable and consistent. Therefore, synthetic diamonds (grit or bulk) are the first choice for most industrial applications. Another reason is that they cost relatively little. One of the most successful tools for using synthetic diamond is the PDC cutter for oil and gas drill bits, which significantly improves drilling economy by increasing drilling speed (ROP) and tool life, as shown in Figure 4. Although PCDs have been successfully used in oil and gas drilling tools, they still suffer from catastrophic failures from time to time due to their inherent low fracture toughness compared to other cutting materials such as cemented carbide. In the course of oil and gas exploration, many different rock formations may be encountered. Some will be coarser than others, while others will consist of a mixture of hard and softer phases, which will have a significant impact on the tool when drilling. These shocks can cause micro-cracks, fragmentation, or spalling, which can seriously impair the drilling schedule. It is also thermally unstable at high temperatures, which is likely to occur during drilling, especially in hard formations. When the PDC cutter heats up due to strong rock/cutter friction during the drilling process, the expansion of the metal Co far exceeds that of the diamond grain, resulting in extensive thermal stress and further cracking.

Figure 4.

PDC drill bit applications in oil & gas exploration and drilling [9].

3. Diamond synthesis and PDC manufacturing technologies

3.1 Conventional high-pressure high-temperature (HPHT) technology

The PCD material produced using traditional HPHT technology creates a unique superhard engineering tool material with high hardness, high wear resistance, and high impact resistance. PDC drill bits equipped with PDC cutters are widely recognized in oil and gas drilling due to their long drill life and ability to maintain high penetration rates (ROP) because the shear action of the fixed cutter on penetrating rock is more effective than crushing action of the roller cone bits. There are two main pressing technologies, including belt press and cubic press, which are currently used in the production of almost all synthetic diamond powders and sintered PCDs. Other techniques also exist, but due to the small size of the samples, their use is limited to research and development. The belt press was developed in the 1950s when GE successfully synthesized historically first man-made diamond crystals. Another important HPHT press technology is cubic press technology, which was originally developed as an alternative to generating diamond synthetic conditions, but it has been becoming the primary PDC manufacturing method. Diamond sintering requires extremely high heat and extremely high pressure, and metal systems use catalytic solvents to make the sintering process more economical (Figure 5). Typically, diamonds are sintered at temperatures around 1400°C. The source of the catalytic/solvent metal can be enhanced by an in-situ process that directly adds the original diamond powder or infiltrates from the substrate in a state where the catalytic/solvent metal can flow with capillary force. The gap spacing of the diamond raw material is filled with a catalyst or solvent from the matrix, which sinters to bond adjacent diamond crystals together. Cobalt is commonly used as an adhesive phase for PDC presses.

Figure 5.

P–T phase diagram of carbon showing conventional HPHT sintering region [4].

At high temperatures and pressures, diamond-to-diamond bonding occurs, and the metal is relieved into diamond abrasive particles, which helps to catalyze the binding process. For catalytic/solvent metals to be effective, the temperature at which the carbon dissolves and re-precipitates must be reached. These temperatures typically exceed 1200°C [4, 12]. For catalytic solvent systems at active temperatures, diamonds are easily and significantly degraded to graphite at temperatures close to atmospheric pressure; that is, these extreme temperatures can cause diamonds to return to graphite. High pressure is also necessary for the success of diamond sintering. In order to maintain the stable phase of the diamond, high pressure must be maintained during the sintering process. This usually requires a pressure of about 5.5 GPa or more. In this state, the diamond is stable in the sp³ structure and can be sintered without considering the significant degradation of the diamond raw material. In the design and operation of the HPHT system, the system will reach the required pressure of 5.5 GPa and 1427°C while maximizing the life expectancy of expensive hard metal tools such as anvils and molds. PDC cutters and synthetic diamond manufacturers are constantly striving to improve the performance and cost-effectiveness of their HPHT systems so that more extreme sintering conditions can provide the next generation of high-performance drilling products. In order to achieve these high temperatures and pressures at the same time, cubic pressure technology development is the key. The cube press consists of six large pistons, each of which can provide thousands of tons of force. Each piston pushes a small tungsten carbide anvil, which in turn compresses a cubic pressure unit containing the starting material (cemented carbide and diamond powder). Once the cube is pressed to reach the desired pressure, the current generates the desired high temperature through a resistance heater embedded in the pressure unit. These conditions are maintained long enough to ensure that a complete diamond-diamond bond is formed among diamond particulates to make the diamond bulk. However, the pressure is limited to a maximum of 10 GPa because the graphite heater will be transferred to the insulated diamond and lose its heater function.

One of the challenges in improving PDC cutter performance through traditional HPHT processes is the removal of Co, a key component in the formation of a robust diamond-to-diamond bond structure during PDC cutter manufacturing but is also the main cause of these problems in drilling applications. The entire industry has been researching and improving leaching methods or other methods to reduce the adverse effects of Co. On the bright side, the removal of Co improves the thermal stability of PDC tools by reducing the tendency to graphitization at high temperatures and preventing accelerated cracking caused by the above thermal stresses. On the downside, removing the Co phase tends to reduce the fracture toughness of PDC tools. Therefore, PDC cutter suppliers often offer Co leaching at different depths depending on the application requirements. Currently, there are no “standard” tools, but a range of tool leaching designs that suit different drilling requirements. The industry’s best desire is to raise the degradation temperature from the usual 750–1200°C through cobalt leaching. Zhan et al. [4] made the thin film with a scanning electron microscope (SEM) showing what happens when the PDC sample is heated under mimic reservoir conditions. The end result is thermal failure, darkening the material when irregular cracks appear, turning the once uniform surface into something similar to the cracked mud seen at the bottom of a dry pond. There is a solution to this problem, called the deep leaching technique, which leaches most of the cobalt by immersing the PDC in the acid. But it also has its limitations, as some metals are sealed in spaces that liquids cannot reach and are left behind. The industry as a whole is researching (improving) leaching methods or other methods to further reduce the impact of cobalt. Across the industry, PDC cutters aim to be able to withstand the resulting high temperatures when cutting hard, variable formations. The industry’s rule of thumb is that high temperatures can damage PDCs above 750°C, and leaching pushes this limit up to around 1200°C. One of the emerging technologies identified as technological breakthroughs is that through UHPHT technology that can manufacture PDC cutters without the use of metal catalysts [13, 14]. In this chapter, a range of new ultra-strong catalyst-free PDC cutting materials using innovative UHPHT technology has been successfully synthesized and tested. These catalyst-free or binderless PDC cutting materials are more than twice as hard as current PDC cutting machines. As a result, new industry records for wear resistance are more than three times higher than traditional PDC cutters used in the oil and gas drilling industry. The new material also has fracture toughness close to that of metals. In addition, these catalyst-free PDC cutters do not require any expensive and time-consuming leaching process to remove the Co catalyst. With these super-strong catalyst-free PDC cutting elements on PDC drill bits, the possibility of achieving the game-changing goal of “one run to total depth”, especially in drilling, hard formations is explored.

3.2 Ultra-high pressure and ultra-high temperature (UHPHT) technology

Ultra-high pressure and ultra-high temperature technology is a cutting-edge technology. At present, the technology is mainly focused on the research of nano-polycrystalline diamond (NPD). However, their industrial applications are limited by tiny sample sizes. This chapter will introduce new UHPHT techniques to create centimeter-sized samples that are large enough for industrial and scientific applications. Expanding the sample chamber is an important goal in UHPHT device development, and its record is constantly being refreshed. In 2003, Irifune et al. successfully synthesized millimeter-scale nanocrystalline polycrystalline diamonds using a hexagonal large-cavity hydrostatic pressure device [8, 15] under high pressure conditions of about 15 GPa. After nearly 10 years of improvement, the size of synthetic NPD has been increased to the centimeter level. Large tonnage high pressure devices are required to obtain larger sample sizes and to ensure reasonable high-pressure efficiency. The high-pressure occurrence efficiency is mainly affected by the load loss in the transmission process, whether it is the mechanical structure of the assembly or the strength of the final stage of anvil material. Please refer to the reference [12] for more details in NPD development and their performance. In a combination of multi-stage loading, for the first time a two-stage loading device that is integrated directly into the first six-sided cubic pressure chamber was developed [16], eliminating the intermediate conversion process of loading by a single axis. Compared to type 2–6-8 loading based on belt press technology, tri-axial loading significantly improves the transmission efficiency of loads. The utility of a new type of superhard material, such as NPD and cubic boron nitride, depends heavily on the sample size and pressure required for bulk materials, typically around 14 GPa. Therefore, the challenge in developing a large cavity static pressure device should be to increase the pressure limit while expanding the cavity. Ultra-high-pressure technology is based on a hinge six-sided cubic press, with a single cylinder load capacity of about 50MN (5000 tons) in the centimeter cavity. On the other hand, the technology capable of producing large tonnage six-sided cubic presses is cost-effective, which will expand its range of applications. Millimeter-scale samples are still limited to the physical properties studied. The application prospect of centimeter-level samples in comprehensive physical characterization and tool device preparation is broad. Therefore, the ability to integrate the production of centimeter-level samples on a single-axis (double-sided) press and the development of centimeter-level high-pressure chambers with pressures greater than 14 GPa are of great significance for the high-pressure research and application of new superhard materials.

3.3 Shaped cutters

PDC cutters are key components of the drill bit. Most PDC cutters in drill bits have flat diamond cutting tables or layers. Recently, due to advances in cutter material development and geometry cutting technology, special-shaped PDC cutters, for example ax-shaped cutters (ASC) (Figure 6), have been warmly welcomed by drilling engineers to drill many hard and abrasive formations [17]. The shape of the PDC cutter has a great influence on the impact resistance of the component and the mechanism of cutting the formation, which greatly affects the performance of the PDC drill bit.

Figure 6.

Examples of shaped PDC cutters.

4. Catalyst-free or Binderless Micro polycrystalline diamond (MPD)

4.1 Experimental procedures and materials characterization

For the synthesis, characterization and their applications of NPD materials, see the review journal paper in [12]. This chapter will focus on our own work on the basis of micro-polycrystalline diamond (MPD) or catalyst-free polycrystalline diamond (CFPCD), based on a newly developed hinged six-sided cubic press [18]. Drilling very hard, abrasive and sandwich formations presents a significant challenge for today’s PDC drill bits. Current PDC tools on drill bits do not provide sufficient wear, impact, or thermal stability to withstand this drilling environment, resulting in low penetration rates (ROP) and short drill life. The weakness of existing PDC cutters is due to the inevitable use of cobalt catalysts to bond diamond grains manufactured by traditional HPHT techniques with a combined capacity of about 5.5 GPa and a temperature of about 1400°C. In our study, ultra-high pressure and high temperature (UHPHT) technology was developed by an innovative two-stage multiple anvil that is capable of producing ultra-high pressure of 14–35 GPa, which is three to seven times that of traditional PDC cutting machine manufacturing techniques. In addition, extreme heat from 1900–2300°C was achieved. Using this UHPHT technology, new PDC materials with super strength and no catalyst at two high pressures of 14 and 16 GPa have been successfully produced in order to study the different responses of material properties under different processing parameters. As the starting material for the experiment, the average particle size of commercially available high-purity diamond powder is 10 microns, and the particle size distribution is 8 to 12 microns. Then these diamond powders were pressed in the newly developed and innovative UHPHT press. Details of the processing can be found in the references [13]. The preparation of NPD from graphite involves a phase transition mechanism [15]. This results in a significant volume change of more than 35% due to density changes (under ambient conditions, graphite density ~ 2.25 g/cc to diamond density ~ 3.52 g/cc). Large shrinkage is known to make pressure and temperature control more unstable or difficult (heater deformation), especially under extreme HPHT conditions. On the other hand, our CFPCD synthesis or fabrication process uses diamond powders with micron, sub-micron or nanoscale grains available on the market as raw materials to solve all of the above problems and challenges, as there is no phase transition when pressing diamond powder into diamond blocks under UHPHT. As a result, the microstructure of CFPCD materials and the resulting mechanical properties are more controllable between hardness and toughness. This is important for large-scale industrial tool manufacturing applications. Essentially, this work provides a new strategy or approach to developing the next generation of super-hard or super-hard diamonds. Figure 7(a) and (b) show the typical microstructure of a PDC tool with pressures of 14-GPa and 16-GPa, respectively, showing the full detection of diamond structures without a metal binder.

Figure 7.

SEM microstructures of (a) 14-GPa CFPCD, and (b) 16-GPa CFPCD showing fully dense catalyst-free microstructure [19].

Scanning electron microscopy (SEM) was used to study the morphology and microstructure of polished samples. Samples prepared at 16 GPa and 2300^°C are characterized by transmission electron microscopy (TEM) with an acceleration voltage of 200,000 volts for microstructures at high magnifications. Figure 8 shows the HRTEM nanostructure features in a 16-GPa CFPCD material that are produced by severe plastic deformation of a single diamond grain during UHPHT. Extensive twins and stacked faults in the particles were observed. This is due to the high-pressure work hardening mechanism [13], which can greatly improve the strength of UHPHT CFPCD materials. Typically, CFPCD materials consist of a diamond skeleton consisting of micron-sized particles and an isolated Y-zone. Each micron-sized particle has a substructure of stacked nanoplates, while the Y-zone consists of NPDs embedded in turbo graphite and amorphous carbon. This unique micro-nested structure stems from the plastic deformation of the diamond particles and the mutual transformation of the diamond produced during the high temperature and high-pressure process. Crystallization defects prevent grain alignment during deformation and play a preventive role, which is conducive to its mechanical properties. In addition, during processing, the particles form plastic deformations in the substructure by squeezing the diamond particles, and the hardness is further increased due to the Hall–Petch effect [20].

Figure 8.

The HRTEM showing nanostructure features (substructure) of twin and stacking fault in grains [9].

4.2 Mechanical properties - hardness and fracture toughness

Hardness is a key performance index of materials and is mainly tested by the indentation method. The Vickers hardness indentations were performed on the polished samples of these materials under an applied load of up to 9.8 N and a dwelling time of 15 s. Figure 9(a) and (b) show the Vickers hardness (Hv) indenter before testing with a standard indenter made of a single crystal diamond, and the indenter that is damaged after pressing it into a CFCD sample, respectively. The tests were repeated on 4 different specimens and all 4 new indenters made of single crystal diamond were broken in the same pattern as shown in Figure 9(b). The study found that even when the load was increased from 1 N to 9.8 N, the Vickers indentation on the polished CFPCD sample was too small to be accurately measured. As a good comparison, standard diamond indenters remain in good shape after commercial PDC sample testing. The comparison results showed that the hardness of the CFPCD sample exceeded the Vickers hardness limit of single crystal diamond (120 GPa) and was by far the hardest material in the world. The hardness of commercial PDC materials is only about 64GPa.

Figure 9.

The optical images of single crystal diamond indenters (a) before the hardness testing and (b) after the testing on CFPCD material, showing the hardness of the CFPCD material is higher than single crystal diamond (120 GPa). Arrow in Figure 4b indicates the damage on the indenter tip [19].

The ultra-high hardness of microcrystalline diamond materials can be attributed to nanostructural defects such as stacked nanoplate layers, stacked faults, and twin microstructures caused by high-pressure hardening. A schematic diagram of the mechanism of microstructural change of pressure increase is given, as shown in Figure 10.

Figure 10.

Schematic deformation micro-mechanism of UHPHT superstrong diamond.

The fracture toughness of MPD samples has been characterized and calculated by the following equation [21].

$$K_{IC}=\xi {\left(E/H_V\right)}^{1/2}\left(P/c^{3/2}\right)\left(MPa{\text{m}}^{1/2}\right),$$E2

where ξ is the calibration constant of 0.0166 (±0.004), E is Yong’s modulus (GPa) (in the experiment Young’s modulus, 1050 GPa, is used for diamond), P is the loading force (N), and c is the length of the crack.

The K_IC of MPD prepared at 14 GPa and 1900°C is 18.7 MPa m^1/2, the highest in the world of diamond materials. This is 3.7 to 5.5 times higher than a single crystal diamond. Interestingly, microcracks are mainly generated on diamond microcrystallines and terminated at the grain boundary (Y-zone). The Y-region of the nanostructure is composed of nanocrystallines, turbo graphite, and amorphous carbon, which can significantly prevent further propagation of cracks, thereby greatly improving the fracture toughness of the prepared sample. For 16-GPa CFPCD materials, it is difficult to measure indentation fracture toughness due to the previously-mentioned indenter damage. However, other ways are explored to assess the fracture toughness of materials and will report in the future.

4.3 Wear resistance

The cutting performance of a sample is the most widely used method to evaluate the cutting performance on a turned granite log by cutting it on a CNC lathe. Granite has high hardness and abrasion resistance, as well as low thermal conductivity. The cutting parameters of the granite log turning test are as follows: cutting speed (Vc) of 100 m/min, depth of cutting (Ap) of 0.5 mm, and feed rate (f) of 0.4 mm/rpm. CFPCD and commercial PDC samples are processed into cylindrical cutting tools with a diameter of 11 mm and a height of 6 mm. G ratio is the ratio of rock loss volume to wear flat volume, which is used to evaluate the wear resistance of the material to granite. The reference HPHT cutter is also carefully selected from the best PDC cutters currently used in drilling hard formations. The wear resistance of the CFPCD and commercial PDC samples is quantified using the abrasion wear ratio, G, and the wear rate or ratio is calculated using the following equation:

$$G=\frac{V1}{V2}$$E3

Where V1 is the volume loss from granite, (mm³); V2 is the volume loss from cutting tools (mm³). The higher G means the higher wear resistance of the material.

Figure 11 shows an optical image of the cutting edge of a CFCD sample and a commercial PDC sample after cutting the granite by length of 1260 m. It can be clearly seen that the wear area of the commercial PDC sample is uneven and significantly larger than the wear area of the CFPCD sample, especially when the turning length reaches 1260 m. The study found that the average wear ratio of CFPCD samples is more than four times that of commercial PDC samples, making it the best diamond material currently used in the industry. Previously, it took a decade for PDC tools to improve their wear resistance by 30 to 50 percent. This breakthrough represents a 50-year technological leap in the development of PDC cutting machine technology. As the cutting length increases, the CFPCD sample is at a stable level because the diamond blocks do not fall off during turning granite testing. The extraordinary wear resistance of CFPCD materials is directly related to their ultra-high hardness, which is due to the fact that it is catalyst-free.

Figure 11.

Wear flats development of (a1-a3) UHPHT 16-GPa synthesized CFPCD, and (b1-b3) reference cutter [14].

4.4 Thermal stability

Thermal stability and oxidation resistance at high temperatures are important for applications of PDC cutters, especially in hard and abrasive formation drilling in the oil and gas industry. Thermal stability and oxidation resistance tests are performed at different temperatures from room temperature to 1400°C by an in-situ XRD. The in-situ X-ray diffraction (XRD) using Cu kα radiation at a wavelength of 0.15406 nm, a step rate of 0.01°/s, and a scanning range of 2θ = 10°-100°, is used to characterize the phase transition of CFPCD samples from room temperature to up to 1400°C. For comparison, commercial PDC materials were also tested. As can be seen from Figure 12(a), the initial oxidation temperature of commercial PDCs at around 806°C is harsh. On the other hand, the new CFPCD material shows no oxidation until 1400°C (Figure 12b) and is found to be even stable at 1200°C – the highest recorded in the industry, well above natural diamond (~800°C), nanoparticle diamond (~680°C), unowned diamond (~1056°C) and commercial PDC (~600°C).

Figure 12.

High-temperature in-situ XRD spectra of (a) a commercial PDC material, and (b) a 16-GPa UHPHT CFPCD material at temperatures up to 1400°C [14].

5. Conclusions and future direction

In short, ultra-strong and catalyst-free PDC cutting materials have been successfully synthesized through innovative UHPHT technologies. These new CFPCD materials set new industry records in the diamond family for hardness, toughness, abrasion resistance, and thermal stability. Using these unique properties of the new CFPCD material as a combination of PDC cutters in drill bits, can help achieve the goal of “one run to TD” game-changing drilling techniques. Future research directions (Figure 13) continue to explore much higher pressures and higher temperatures domains and produce larger size UHPHT CFPCD cutting materials in preparation for further breakthroughs in drilling technology.

Figure 13.

Future research directions for ultra-high pressure and ultra-high temperature [18].

6. Other applications

Bearings have been used in various industries in a variety of forms and shapes. They are crucial in tribology to reduce friction between objects. For oil and gas drilling operations, different types of bearings are used, from the surface to the bottom of the wellbore. There are several types of bearings in which surface-to-surface rubbing is involved, such as thrust bearings (as shown in Figure 14) and plain bearings, as shown by examples in Figure 15. In these examples, the surface-to-surface contact between the counterparts prevailed. Such types of bearings are used in drilling rotary control device (RCD), mud motors, rotary steering system (RSS), powder generating turbines, mud pulse tools, coring tools, electric submersible pumps, etc.

Figure 14.

Thrust bearings using catalyst-free and ultra-strong PCD materials [22].

Figure 15.

A downhole tool uses the new catalyst-free, ultra-strong PCD materials [23].

One of the tools is shown as an example in Figure 15. The materials of the thrust and plain bearings include bronze, brass, lead-based metal, cast iron, zirconia, tungsten carbide, silicon carbide, and PCD.

The PCD materials currently used in these applications are made of PCD grains bonded by metallic binders, such as cobalt, nickel, iron, or silicon. These metallic binders (Co, Ni, or Fe) are used as catalysts to facilitate diamond manufacturing so that the diamond grains can be obtained at traditionally high temperatures and high pressure. In the above-mentioned bearing applications, PCD materials typically outperform the rest of the materials, mainly due to their high hardness, high compression strength, high thermal conductivity, and very low coefficient of friction.

Electric Submersible Pumps (ESPs) are one of the primary artificial lift methods for oil and gas industry. The system is a complex electro-hydraulic system consisting of a centrifugal pump, a protector and an electric motor in addition to a sensory unit and a power delivery cable. The pump is used to lift well fluids to the surface. The motor converts electric power to mechanical power to drive the pump via the shaft. The power delivery cable provides a means of supplying the motor with the needed electrical power from the surface. The protector absorbs the thrust load from the pump, transmits power from the motor to the pump, equalizes motor internal and external pressures, provides/receives additional motor oil as temperature changes and prevents well fluids from entering the motor. The pump consists of stages, which are made up of impellers and diffusers. The impeller, which is rotating, adds energy to the fluid as kinetic energy, whereas the diffuser, which is stationary, converts the kinetic energy of fluids into head. The pump stages are typically stacked in series to form a multi-stage system that is contained within a pump housing. The sum of head generated by each individual stage is summative; hence, the total head developed by the multi-stage system increases from the first to the last stage. The monitoring sub/tool is installed onto the motor to measure parameters such as pump intake and discharge pressures, intake and motor oil temperature, and vibration. Measured downhole data is communicated to the surface via the power cable. The ESP industry faces two main challenges with this legacy technology: reliability and intervention cost. Low reliability is attributed to the system complexity both mechanically and electrically, compounded by the harsh operating environments. High intervention cost is a result of rig dependency of the system for deployment, retrieval and replacement. Improving reliability and developing rigless deployment are the two ongoing battle fronts that the industry is currently engaged in intensely. Both radial and thrust bearings use liquid film to prevent metal-to-metal contact. Erosion, corrosion, vibration, impact force, and heat are all detrimental to the performance of bearings. Bearing failures (Figure 16) can lead to vibration, low efficiency, broken shaft, shaft mechanical seal damage, fluid invasion to the motor, and motor electrical failure.

Figure 16.

Examples of protector thrust bearing/runner damages.

Bearings can be made of our new-generation catalyst-free, ultra-strong polycrystalline diamond (PCD) material synthesized by the novel ultra-high pressure and ultra-high temperature techniques without using any catalyst to greatly enhance the reliability of bearings used in ESPs [22].

Nomenclature

PDC

Polycrystalline diamond compact cutter

PCD

Polycrystalline diamond

CFPCD

Catalyst-free polycrystalline diamond

NPD

Nano-polycrystalline diamond

MPD

Micro-polycrystalline diamond

HPHT

High pressure and high temperature

UHPHT

Ultra high pressure and ultra high temperature

ROP

Rate of penetration

XRD

X-ray diffraction

TEM

Transmission electron microscopy

SEM

Scanning electron microscope