PDC Cutter Research Articles

Numerical Simulation Research on Cutting Rock with a PDC Cutter Assisted by an Impact Force

Extensive studies have been carried out on cutting rock with a PDC cutter, but cutting rock assisted by impact force is rarely studied. In this paper, cutting rock using conical and cylindrical PDC cutters assisted by impact force were researched with the explicit dynamic model. The laws of cutting rock using a cylindrical cutter assisted by impact force are the same as those of a conical cutter. There are thresholds of impact frequency and amplitude when they are single variables. When impact frequency is lower than the threshold frequency, the impact frequency is the dominant frequency in the frequency spectrum of weight on bit (WOB), and the amplitude of dominant frequency and removal volume decreases with the increase of impact frequency. When the impact frequency is higher than the threshold frequency, there is no dominant frequency in the frequency spectrum of WOB, and the removal volume behaves the same. When the impact force is lower than the threshold amplitude, there is no dominant frequency in the frequency spectrum of WOB, and it does not affect the removal volume but the removal volume is positively correlated with the impact amplitude. When the impact amplitude is higher than the threshold amplitude, the removal volume is also positively correlated with the impact amplitude, and the removal volume assisted by low-frequency (20 Hz and 40 Hz) impact force is higher. The frequency threshold and amplitude threshold of the conical cutter are smaller than those of the cylindrical cutter. Although the cutting depth and removal volume of the conical cutter are lower than those of the cylindrical cutter, the amplifications of cutting depth and removal volume of the conical cutter are higher than those of the cylindrical cutter when assisted by impact force.

Research on cutting track and working load of directional drilling PDC bit

Polycrystalline diamond compact bit directional drilling technology has proven to be an important means to effectively improve drilling efficiency and save drilling costs. Under the directional drilling condition of PDC bit, due to the existence of screw angle or offset mechanism, the center axis of the bit deviates from the center of the borehole, and the cutting teeth of the bit do complex alternating trajectory cutting motion at the bottomhole and the trajectory lines of the cutting teeth themselves intersect in space. (1) The kinematics analysis of directional drilling PDC bit under different working conditions was carried out, including motion analysis at the stage of sliding steering deflection and motion analysis at the stage of composite steering drilling. The kinematics equation of PDC bit under sliding steering deflection and motion space equation of PDC bit cutters at the stage of composite steering drilling were deduced respectively. (2) By establishing the calculation model of cross Angle of cutters under directional drilling conditions, the influences of transmission ratio, tooth placement, offset and deflection Angle on the cross angle are analyzed. The movement law of PDC cutters and the bottom hole morphology formed by bit are studied under directional drilling conditions. (3) Based on the digital simulation system of PDC bit rock breaking, the cutting load under the state of alternating trajectory was studied. On this basis, the cutting mechanics model of PDC bit cutters in directional drilling was established. At the same time, the accuracy of simulation analysis was verified by laboratory unit experiments. It is considered that PDC cutters can form alternate cutting path in directional drilling, which can easily invade rock and improve mechanical efficiency. The larger the intersecting angle of the cutting teeth, the more likely the rock is to form a through crack and then be broken. When the intersecting angle is 90°, the average energy consumption of rock breaking in cross cutting is reduced by about 32.9% compared with parallel cutting. The research results have improved the understanding of the rock breaking mechanism of PDC bit directional drilling, provided a new technical means for bit performance analysis and have also provided a reference for the design of new personalized bits under the discussed working conditions.

Rock-Breaking Mechanism and Parameter Optimization of Ridged Pdc Cutters

Rock-Breaking Mechanism and Parameter Optimization of Ridged Pdc Cutters

Combined finite-discrete element method for modeling the interaction between single PDC cutter and brittle rock

This paper describes a combined finite-discrete element method for simulating the interaction between single PDC cutter and brittle rock. The proposed method is capable of capturing the nucleation, propagation, branching, and coalescence of cracks as well as the contact between fragments during the cutting process. A detailed description of the method is provided. A linear Mohr-Coulomb criterion with tension cutoff is applied to identify which edge is failure based on the normal and shear stresses estimated from the triangular elements abutting from the edge. The Munjiza-NBS algorithm and Simple-Common-Plane (SCP) contact algorithm are used for the contact detection and interaction, respectively. The method is then validated against the theoretical results of Brazilian disc test and uniaxial compressive strength test. The results demonstrate that the proposed method is of high accuracy, especially before rock failure, because the cracks in the model are introduced on the fly by splitting the nodes where and when needed. Finally, several typical cases of the interaction between single PDC cutter and brittle rock are performed. The numerical results indicate that the wedging effect is significant, leading to the formation of large size chippings for brittle rock cutting.

Experimental Investigation into Mixed Tool Cutting of Granite with Stinger PDC Cutters and Conventional PDC Cutters

Experimental Investigation into Mixed Tool Cutting of Granite with Stinger PDC Cutters and Conventional PDC Cutters

Simulation study on temperature field and rock breaking characteristics of bionic PDC cutter in rotating state

In view of the problems of low rock-breaking efficiency, short service life, etc. of conventional PDC bits, a new type of coupling bionic PDC cutter was designed by taking pangolin scales, mole fingers, shark teeth and scallops as bionic prototypes. Based on the finite element method, elastic-plastic mechanics and other methods, the rock-breaking simulation model of the bionic PDC cutter is established. In the finite element software ABAQUS, the temperature-displacement coupling explicit penetration contact algorithm and explicit dynamics module are used to study the temperature field variation and rock-breaking mode of the bionic PDC cutter in the rotating state, and the simulation results are compared with those of the conventional PDC cutter. The simulation results show that the temperature transfer process of bionic PDC cutter is quite different from that of conventional PDC cutter when breaking rock; Bionic PDC cutter can effectively prevent the generation of bit mud pockets, reduce the accumulation of friction heat, avoid the generation of high temperature thermal failure and prolong the service life; Bionic PDC cutter break rock faster and break rock more thoroughly. The research shows that the bionic PDC bit has good field practicability and can be popularized and applied in the field in the future.

Experimental investigation on the PDC cutter penetration efficiency in high-temperature granite

Hot dry rock (HDR) is a renewable and clean energy resource, its efficient exploration has attracted widespread attention from scholars. However, the rock encountered during drilling is characterized by poor drillability, high abrasiveness and great hardness, which aggravates the wear of bits and increases drilling costs. To address such an issue, much research has been conducted to investigate the failure mechanism of high-temperature rocks. But most of them focused on the rock cutting process by PDC cutters and the penetration of rocks was ignored. In the present study, a series of experiments were performed to determine the penetration efficiency of PDC cutters under different temperatures and back rake angles. The penetration force and 3D topography of penetration pits were measured to analyze rock failure characteristics. Besides, uniaxial compressive experiments were carried out to study the effects of temperature on rock properties. The results indicate that as the rock is heated from 25 to 240 ℃, its properties change slightly. Analogous rock failure characteristics can be found in rock indentation process, where chipping and crushing of rocks, on following another, are presented, respectively. Moreover, the occurrence of chipping is the major contributor to the increase in penetration efficiency. The further increase in rock temperature (greater than 360 ℃) results in a sharp decrease in the strength of rocks, which is accompanied by the enhancement of rock plasticity. At his moment, the plastic failure dominates rock indentation process under different back rake angles. The induced horizontal force cannot promote brittle failure and the penetration efficiency is hard to be improved, significantly affecting the performance of conventional PDC bits in high-temperature formations. Based on the results, the low penetration efficiency at high temperatures is a major obstacle that restricts the exploration of HDR. Increasing the cutting depth should be an important target in optimizing drilling parameters and the arrangement of PDC bits.

Technological solutions for drilling a trap intrusion section on the Srednebotuobinskoe oil gas condensate field, East Siberia

One of the largest trap intrusion provinces, Siberian traps, is located in the East-Siberian Platform in Russia. A trap intrusion zone usually has abnormally low reservoir pressures and natural fractures. Consequently, trap drilling is associated with fluid losses that can be catastrophic. The section of trap intrusion is a part of a Ø 174 mm production casing section of the Srednebotuobinskoe field. The basic well design of this section also includes the Osinsky horizon, which features an abnormally high reservoir pressure zone. The latter creates incompatible with drilling conditions environment due to the presence of catastrophic loss zones in traps. Time spent on drilling a trap intrusion zone accounts for up to 30 % of the total well drilling time. The abovementioned geological issues in directional wells become the key topic in solving it. The method to resolve this issue is an integrated approach employing all the technologies and technical facilities aimed at finding a technological solution. First of all, in order to optimize the well construction cycles and reduce the complications, all the wells were classified in three categories as per the type of behavior in trap intrusion. This allowed to work out multi-level activities, that depended on severity of losses and non-operational time spent on drilling through this section. An alternative well design was developed and trialed on several wells, which showed positive results on decreasing non-productive timing. The main concept of this design was significantly different from the basic well design that was used in the past on the Srednebotuobinskoe field. The main difference was isolation of traps from the high pressure Osinsky horizon lower section with a Ø 245 mm casing string, which allowed safe splitting of two incompatible drilling zones. The economic effect of this solution allowed saving of up to 10.4 days or 15 % of the construction time in the wells of first category. These results were reviewed at the Technical Committee of the Company and agreed to implement the alternative well design on first category wells on the Srednebotuobinskoe field. In addition, for the rest of well categories the Drilling Team has produced and successfully implemented the preventative measures that allowed drilling through traps with lost circulation material. It is worth to mention that this method assumed a by-passing mud-cleaning system on the rig to allow building up a solid phase thus stemming the losses while drilling. For all the categories of the wells the Drilling team has selected and trialed different types and designs of drilling bits that would allow drilling hard rock such as dolerite section in traps with minimal number of runs. For the last five years the Drilling team together with the bit producing companies have designed a new type of PDC cutters that would allow to enhance durability as well as improve drilling speed both in dolerite formations and in overlying formations in the Production casing section. The Drilling team has also managed to reduce the number of trips associated with early bit wear decreasing them from five to two runs and create an experimental basis for drilling the entire section of the production casing in one run. From 2019 team continue looking for further solutions that would allow to improve bottomhole assembly elements balancing between durability and drilling rate in different types of formations above and below traps. A range of proposed technological solutions significantly reduced the impact on the well construction performance by preventing and reducing the downhole losses events in the section of trap intrusion on the Srednebotuobinskoe field.

Performance dynamics of pdc cutters used in breaking ductile brittle rock

The widespread application of cutting - chipping action bits with PDC cutters is held back due to the intense chipping and breakage of the latter. This article presents the results of bench-scale tests conducted to determine the values of three mutually perpendicular components of the load on sharp-edged and beveled rock-breaking cutters of 13.5 mm in diameter as well as the dynamic-response factors and mean square deviations (MSD) of these components. The forces change in time by leaps, which reflects the rock fracturing under the cutter. The MSD accepted as per-cycle amplitude is four times as low on average as the mean axial force; when a sharp-edged and a beveled cutter is used, the MSD is by 150 to 300 and by 300 to 500 % lower than the mean circumferential force.

Theoretical and simulation analysis on rock breaking mechanical properties of arc-shaped PDC bit

In order to grasp the rock breaking mechanical characteristics of arc-shaped PDC bit, and guide the optimization design of bit structure, theoretical calculation models of cutting parameters of PDC cutters were established. Taking Φ94 mm tri-wing arc-shaped PDC bit as an example, theoretical calculation results show that, with the increase of radial distance, the cutting area, cutting arc length and cutting force of cutters approximately increase first and then decrease; the maximum cutting force is concentrated on number 5 and 6 cutters, which makes these two cutters very easy to be damaged in advance. Based on this, a Φ94 mm four-wing arc-shaped PDC bit was designed, and the maximum cutting force is distributed on number 4, 5, 6 and 7 cutters, also the force value is greatly reduced, which is beneficial to the uniform wear of the cutters. At the same time, numerical simulation and field test were carried out, simulation results are in good agreement with the theoretical calculation results, and the wear conditions of the cutters in the field test are basically consistent with the theoretical and simulation results, which indicate the reliability of the theoretical calculation and the simulation results.

Numerical investigation on rock‐breaking mechanism and cutting temperature of compound percussive drilling with a single PDC cutter

AbstractCompound percussive drilling technology is a new method to improve the rock‐breaking efficiency in deep hard formation. In order to study the rock‐breaking mechanism of compound impact drilling, the thermal‐structure coupling simulation of the dynamic rock‐breaking process with a single PDC cutter was investigated by using ABAQUS software. The influence of impact parameters on the rock‐breaking performance and cutting temperature was analyzed. The results proved that the compound impact load changes the rock failure mode and improves the rock‐breaking efficiency. Compared with steady load cutting, the rock broken volume under compound impact increased by 7.5%, and the mechanical specific energy (MSE) decreased by 12.3%. As the axial impact load amplitude increases, the MSE increases gradually. With an increase in torsional impact load amplitude and impact frequency, the MSE decreases first and then increases, and the optimal torsional static load ratio is 0.3, and the optimal impact frequency is 30 Hz. In addition, the cutting temperature of the compound percussive drilling is higher than that of the steady load cutting, and it increases with the impact load amplitude and decreases with the frequency. For the three impact load waveforms—sine, triangle, and square in this paper, the rock‐breaking efficiency under the condition of sine waveform is the largest when the dynamic amplitude of the pulse force is fixed, and the cutting temperature under the condition of square waveform is the highest. Finally, based on the analysis of the rock‐breaking mechanism, a novel compound percussive drilling tool was designed and tested in the field.

3D Cutting Force Model of a Stinger PDC Cutter: Considering Confining Pressure and the Thermal Stress

3D Cutting Force Model of a Stinger PDC Cutter: Considering Confining Pressure and the Thermal Stress

Experimental research on working principle of the composite single-cone bit

The composite single-cone bit is a new structure of single-cone bit, which breaks the limitation of the one-piece cone structure of existing single-cone bit. The new bit structure makes it possible to apply PDC cutters with strong wear resistance to single cone bit. PDC cutter is more suitable for rock breaking by scraping. In this paper, rock breaking and comparative drilling experiments of composite single-cone bit are carried out. The experiments verified the working principle of the new composite bit. The effective combination of fixed and unfixed cutting structures in the new bit can form complex cross-scraping. The comparative drilling experiments show that the new composite bit has higher rock breaking efficiency than the common single-cone bit, and it is more energy-saving for cross-scraping. The application of PDC cutters can improve the wear resistance of bit cutters and prolong the service life of bit. The research results can provide basic support and reference for subsequent research on the design, development, and application of this new type of bit.

The rock breaking mechanism analysis of axial ultra-high frequency vibration assisted drilling by single PDC cutter

Axial ultra-high frequency vibration (UHFV)-assisted drilling technology that combines polycrystalline diamond compact bits and rotary ultrasonic machining technology is expected to improve rock-breaking efficiency and reduce the drilling costs of deep and ultra-deep wells. To better understand the rock-breaking mechanism under a UHFV load and provide a theoretical basis for practical engineering, this paper presents numerical modelling with the finite element method of dynamic cutting processes under different UHFV loads. The cutting force, mechanical specific energy (MSE), rock failure mode, and crack propagation process of a heterogeneous rock with natural cracks are analysed, and then compared with the steady load cutting condition. The simulation results indicate that when the excitation frequency is close to the natural frequency of the rock (approximately 25–30 kHz), the MSE and cutting force reach the minimum value. Compared with the steady load, the average cutting force and MSE under a 25 kHz UHFV load decreased by 49.4% and 28.5%, respectively. The number of cracks increased by 24.9%, while the crack volume and area reached the maximum. In addition, the shear crack ratio can be reduced under UHFV loads. The proportion of shear cracks in 25 kHz UHFV cutting was 5.3% lower than that in steady load cutting. Thus, axial UHFV-assisted drilling can effectively improve the rock-breaking efficiency by adjusting the magnitude of the excitation frequency. The results provide a theoretical basis for the new rock-breaking technology of PDC bit drilling.

Fragmentation Characteristics of Rocks Under Indentation by a Single Polycrystalline Diamond Compact Cutter

Abstract Polycrystalline diamond compact (PDC) bit accounts for the most drilling footage in the development of deep and geothermal resources. The goal of this paper is to investigate the PDC cutter-rock interaction and reveal the rock fragmentation mechanism. A series of loading and unloading tests are conducted to obtain the curves of contact force versus penetration displacement. A single practical PDC cutter is fixed on the designed clamping devices that are mounted on the servo experiment system TAW-1000 in the tests. The craters morphology and quantified data were obtained by scanning the fragmented rock specimen using a three-dimensional morphology scanner. Finally, a numerical model is established to get the stress and deformation fields of the rock under a single PDC cutter. The results show that there are two kinds of failure modes, i.e., brittle failure and plastic failure, in the loading process. Marble is more prone to brittle fracture and has the lowest specific energy, followed by shale and granite. The brittle failure in marble mainly occurs behind the cutter while that happens ahead of the cutter for shale. Curves of contact force versus penetration displacement illustrate that a cutter with a back rake angle of 40 deg has a better penetration result than that with a back rake angle of 30 deg. Enhancing loading speed has a positive effect on brittle fragmentation. The distribution of von Mises stress indicates the initiation point and direction, which has a good agreement with the experiment. The research is of great significance for optimizing the PDC bit design and increasing the rate of penetration.

Influence of solder and flux composition on thermal stability of brazed PDC cutters

ABSTRACT The process of induction brazing of diamond-carbide cutters with various silver solders and fluxes with different proportions of active substances is considered in this paper. The influence of heating during brazing on the thermal stability of polycrystalline diamond is also investigated. A methodology for testing brazed cutters is developed and the results of the wear dependence from the applied solders and the soldering mode are obtained. It is established that at hold-up time at temperature over 800°C for more than 1 min takes place destruction of the diamond plate. Due to the significant alloying of silver solders with manganese and nickel, a dependence of the solder wetting of the diamond-hard alloy cutters (DHAC) carbide substrate surface from the composition of the fluoroborate flux is found. The best results are obtained when using PV209 or PV209X flux, which have a minimum F/B ratio, i.e. with lower fluorine content. When choosing solders, preference should be given to alloys based on silver with a melting point no higher than 700°C, alloyed with manganese and nickel. It is possible to reduce the silver content in solders from 49 to 38 wt % while maintaining high properties of the brazed joints.

Research on the method of dynamic PDC cutters distribution

PDC bit design, especially the design of the crown and cutters of PDC bit, is a relatively complex analysis process, which involves many factors such as the back-dip angle, cutting depth, cutting force, cutting power and other factors of PDC cutters. At present, the traditional design methods of PDC cutters distribution are mostly based on analysis of rock breaking efficiency of single cutter, which can only reflect the working state of the single cutter under the set parameters, and cannot fully reflect the differences of different positional cutters during the cutting process. In order to solve this problem, this article proposes a dynamic method through target formation lithology characteristics. The working parameters of all the PDC cutters are analyzed in detail basing on equal wear theory and bottom hole covering theory. The working parameters include static parameters (cutting position, back dip angle, cutting depth, effective cutting area.) and dynamic parameters (cutting force, cutting power, cutting torque and cutting energy etc.). The energy required by all the PDC cutters to break rock of per volume during drilling process is taken as the target constraint condition for iterative analysis. This design method can intuitively and effectively analyse the working parameters of cutters which located bit core, nose, shoulder and gauge area, and it provides a good reference for dynamic balance design of PDC bit.

Fluid-Solid Coupling Simulation of a New Hydraulic Self-Adaptive PDC Cutter for Improving Well-Drilling Efficiency in Complex Formations

A new type of hydraulic self-adaptive PDC cutter (SAPC) is designed for controlling cutting depth of the PDC bit flexibly and reducing the harm of stick-slip vibration to drilling operation. The fluid-solid coupling movement of SAPC under different well-drilling conditions are simulated and analyzed. The results show that the up-going time of SAPC can be increased by reducing the diameter of the thin connecting pipe, increasing the diameter of the SAPC liquid-cavity, increasing the height of the cavity, increasing the liquid viscosity and increasing the initial spring force/decreasing the elasticity coefficient. Among them, reducing the diameter of thin connecting pipeline and increasing cavity diameter are the most sensitive. The up-going time can also be increased by the way of changing liquid viscosity without changing the structure of SAPC. Increasing the initial spring force and decreasing the elasticity coefficient can also increase the up-going time of the SAPC, however, the response window to the linkage force is reduced. The double-pipeline embedded SAPC can effectively reduce the volume and installation difficulty. The reasonable thin pipeline diameter is 0.2 - 0.5mm, and the thick pipeline diameter is more than 2mm, and the cavity diameter is more than 18mm. Based on the results of the numerical simulation study, the up-going time of the SAPC is designed over 1.25s, which meets the performance requirements of the hydraulic SAPC using in complex reservoir drilling, such as carbonate-sandstone reservoir.

Method of drilling process control and experimental studies of resistance forces during bits drilling with PDC cutters

A rational, theoretically proved and empirically verified control system is a condition for optimal management of the drilling process in compliance with the criteria for minimizing the cost of time and material resources. A new generation of rock-cutting tools using PDC cutters (polycrystalline diamante cutters), which are extremely effective when drilling wells for various purposes in medium-hard rocks, dictates the need to develop methods and criteria for optimal control of the drilling process using this tool.
 The paper presents an analysis of the force interaction between rock-cutting elements, face rock, and drilling mud saturated with slam, highlights the influencing factors and provides dependencies for determining the parameters of rock failure. Empirical verification of the theoretical propositions was carried out based on the data analysis from experimental bit drilling of marble with PDC cutters with a diameter of 76.2 mm, processed using the method of full factor experiment to obtain mathematical models of factors and their graphical interpretation.
 The method of controlling the drilling process based on the optimal ratio of the tool rotation frequency, axial weight and deepening per one turnover is considered, which allows determining the rock failure mode at the well bottom by indirect signs and choose the optimal values of the drilling mode parameters that correspond to the most optimal conditions in terms of achieving the maximum mechanical drilling speed in conjunction with the rational mode of rock-cutting tool operation. A scheme is presented that contains possible variants of the bit run mode and ways to recognize them by the ratio of the deepening per turnover and the rotation frequency of the rock-cutting tool.

Effective mechanical specific energy: A new approach for evaluating PDC bit performance and cutters wear

Predicting the PDC bit performance during drilling operation is important for the cost effectiveness of the operation. The majority of PDC bits are assessed based on their performance that are relative to offset wells. Determination of mechanical specific energy (MSE) in real time and compare it with the known MSE for a sharp bit to assess the bit life has been utilized by several operators in the past. However, MSE still cannot be used to predict the bit performance in exploration wells and also it cannot assess the bit efficiency in the inner and outer cones.A more precise approach needs to be devised and applied to improve the prediction of bit life and the decision when to pull the bit out of the hole. Effective mechanical specific energy (EMSE) developed in this work is a new wear and performance predictive model that is to measure the cutting efficiency based on number of cutters, which contact the rock as a function of weight on bit (WOB), rotary speed (RPM), torque, and depth of cut (DOC). This model modifies the previous MSE model by incorporating such parameters and including detailed design of the bit, number of blades, cutter density, cutter size, and cutting angle. Using this approach together with the analysis of rock hardness, a level of understanding of how the drilling variables influence the bit performance in the inner and outer cone is improved, and a convenient comparison of the bit condition in the frame of the standard bit record is achieved. This work presents a new simple model to predict the PDC cutters wear using actual data from three sections drilled in three oil wells in Libya. It is found that the obtained results are in well agreement with the actual dull grading shown in the bit record.