Diamond Compact Bits Research Articles

Prediction and Analysis of PDC Bit Wear in Conglomerate Layer with Machine Learning and Finite-Element Method

Polycrystalline diamond compact (PDC) bits experience a serious wear problem in drilling tight gravel layers. To achieve efficient drilling and prolong the bit service life, a simplified model of a PDC bit with double cutting teeth was established by using finite-element numerical simulation technology, and the rock-breaking process of PDC bit cutting teeth was simulated using the Archard wear principle. The numerical simulation results of the wear loss of the PDC bit cutting teeth, such as the caster angle, temperature, linear velocity, and bit pressure, as well as previous experimental research results, were combined into a training dataset. Then, machine learning methods for equal-probability gene expression programming (EP-GEP) were used. Based on the accuracy of the training set, the effectiveness of this method in predicting the wear of PDC bits was demonstrated by verifying the dataset. Finally, a prediction dataset was established by a Latin hypercube experiment and finite-element numerical simulation. Through comparison with the EP-GEP prediction results, it was verified that the prediction accuracy of this method meets actual engineering needs. The results of the sensitivity analysis method for the gray correlation degree show that the degree of influence of bit wear is in the order of temperature, back dip angle of the PDC cutter, linear speed, and bit pressure. These results demonstrate that when an actual PDC bit is drilling hard strata such as a conglomerate layer, after the local high temperature is generated in the formation cut by the bit, appropriate cooling measures should be taken to increase the bit pressure and reduce the rotating speed appropriately. Doing so can effectively reduce the wear of the bit and prolong its service life. This study provides guidance for predicting the wear of a PDC bit when drilling in conglomerate, adjusting drilling parameters reasonably, and prolonging the service life of the bit.

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.

Torsion and vibration reduction mechanism of roller PDC hybrid bit

In directional drilling, torque fluctuation generates a big shock when using polycrystalline diamond compact (PDC) bits, causing problems such as instability in vibration tools. This study presents a new type of composite bit with a roller on the blade. The mechanism of torsion reduction and vibration of the roller PDC hybrid bit is studied through a rock breaking experiment on the roller unit and a comprehensive drilling experiment on the composite bit. Six roller contour shapes, different pressures into the depth of the roller, six roller radial positions and the relative height of roller teeth, and PDC cutters that affect the novel hybrid torsion on bit (TOB) and weight on bit (WOB) are investigated. The equivalent friction coefficient of the roller and axial force per unit depth is used to evaluate the torsional and vibration reduction ability of the Roller. The results show that the equivalent friction coefficient of different contour Rollers is lower than that of PDC cutters, and the torsion reduction ability of the Rollers is higher than that of PDC cutters. The vibration reduction in the roller teeth in different radial positions was 1.59–9.17 times higher than that of PDC cutters, The torque of the roller PDC hybrid bit is 71.72%–98.33% of the conventional PDC bit. The roller shares 1.59%–23.06% of the WOB of the whole bit. As the cutter teeth and the PDC cutter's relative height decreases, the compound drilling torque decreases, the roller bit's weight proportion gradually increases, the torsional capacity decreases, and the damping capacity increases.

Study on Composite Design Suitable for High Hardness and Strong Abrasive Formation

PDC (Polycrystalline Diamond Compact bit) composite is the most important cutting element of petroleum bit, which performance directly affects the service effect and service life of the bit. During the drilling process, the cutter will produce a large amount of friction heat when cutting the rock, resulting in a sharp increase in the internal temperature of the cutter. When the temperature reaches a certain value, thermal wear and tear are very easy to occur, which will not only cause diamond delamination but also reduce the wear resistance of the cutter. Under the action of impact load, impact failure is more likely to occur, which greatly reduces the service life of the cutter and the rock-breaking efficiency of the drill bit. Therefore, this paper studies the composite interface suitable for high-temperature drilling through the changes of cutting tooth temperature field and stress field with different interface shapes, which shows that the non-planar interface is more suitable for improving the cutting tooth life of composite under the action of comprehensive stress field.

Technique Models Effect of Local Doglegs on Running of Completions and Casing in Hole

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202431, “RSS and Motor Directional Analysis: Modeling the Effect of Local Doglegs on Running in Hole of Completions and Casing,” by Benjamin Nobbs, SPE, Stéphane Menand, SPE, and Ngoc-Ha Dao, SPE, DrillScan, prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. Rotary steerable systems (RSS) and steerable motors pose unique challenges when modeling bottomhole-assembly (BHA) directional behavior. The complete paper presents a methodology that aims to allow the anticipation of problems such as mechanically stuck pipe or lockup situations when running in hole (RIH) casing or completion strings. Correctly evaluating the risk of BHA, casing, or completion strings being stuck or locked up when RIH can ultimately provide a template for ultimate reduction of nonproductive time. Local Doglegs and Downhole Equipment A pure rotary BHA has no ability to change its directional behavior during the run. Its directional capabilities are defined by stabilizer position and outer diameter, and, although no ability exists to control directional behavior directly, this type of BHA may be sensitive to weight on bit (WOB), mud weight, formation changes [unconfined compressive strength (UCS)], and inclination. With proper design, it is possible to design a rotary BHA that is insensitive to these parameters. A motor and turbine can operate with or without a bent housing. A bent housing imposes a small angle offset from the axis of the drillstring, with the result that two distinct modes of directional behavior occur, sliding and rotating. Because of its increased rotary speed, rotary mode is prioritized over sliding mode (ideally, 30% sliding and 70% rotating). Because a combination of these distinct drilling modes exists, the actual tortuosity may be quite different when compared with standard survey spacing (Fig. 1). A slight overgauge will be present when operating in rotating mode because of the bent sub. Much like a rotary BHA, a motor may be sensitive to operational parameters. The type of polycrystalline diamond compact bit recommended is one with a long passive gauge that is required to drill in the direction of bit tilt. An RSS can be modelled in two distinctive modes: point-the-bit and push-the-bit. A point-the-bit system operates in much the same way as a downhole motor by varying the tilt at bit. A push-the-bit system operates by applying a side force at pads that pushes against the wellbore. Both types of RSS allow continuous rotation of the drillstring and reduce the risk of differential sticking and, ultimately, stuck pipe. A point-the-bit system may operate with or without proportional steering. A push-the-bit RSS system can operate either by varying the magnitude of force or having a constant force that is varied for a set period in the desired tool-face orientation (TFO). Because of the method of activation (using pads that hit against the side of the wellbore), the local doglegs that can be induced are slightly higher.

Big Data and Machine Learning Optimize Operational Performance and Drill-Bit Design

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202243, “Use of Big Data and Machine Learning To Optimize Operational Performance and Drill-Bit Design,” by Simon Cornel, SPE, Baker Hughes, and Gonzalo Vazquez, Senex Energy, prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. Time savings and bit longevity are major challenges in coal-seam gas (CSG) unconventional fields onshore Queensland. Maximizing rate of penetration (ROP) on the basis of optimal drilling parameters was the key to tackling these issues. A formal process for optimizing performance was developed, with a focus on optimizing polycrystalline diamond compact (PDC) bit design and drilling hydraulics and developing a drillers’ road map. As a result, ROP increased from 50 to 150 m/h. Time savings of more than 150 hours for the drilling campaign was achieved. Background The drilling campaign encompassed two areas for development. Field A is a CSG acreage 45 km southwest, and Field E 30 km northeast, of Wandoan, Queensland. Eighty vertical wells would be drilled across the two fields. This would provide the opportunity to trial the data-mapping concept to increase ROP and fine-tune bit designs to improve longevity. In addition, the rig-sensor data set provided the basis for creating a machine-learning model to help improve drilling parameters during the production-drilling phase. Drilling Challenges The three primary challenges to be addressed included the following: - Economics for unconventional fields, specifically delivering time savings in order to lower the average cost per well - Control vibrations to avoid twistoffs and bottomhole-assembly fatigue - Consistent performance The benchmark for the initial project was an on-bottom ROP of 80 m/h. Therefore, the target for this campaign was to achieve an average on-bottom ROP of over 100 m/h and drilling-time savings of 1 hour per well. Methodology Bit optimization typically has been an iterative process, taking bit-record information to make assumptions about bit performance before providing recommendations for the next well. A more-detailed approach may include the use of log data (i.e., gamma ray and sonic) to estimate rock strength and overlay the depth-based well data to identify key incidents that affected performance (both positive and negative) so such incidents can be mitigated in future wells. This approach, while exhaustive, takes time to complete and is open to subjective interpretation of the engineer performing the analysis. When drilling CSG wells, typical well duration is 3–5 days. With short turn-around times between wells to analyze the data, the goal in this study was to develop an automated approach using real-time data gathered from the rig and present it to the field and rig crew in a visualized method. A two-step approach was devised in which data from the rig was used, followed by a real-time model.

Dynamic trip point categorisation using manufacturing process for polycrystalline diamond compact bits as case study

Disruptions in the manufacturing process cast substantial impacts on the consumer's centric values, cost, and overall efficiency. The ripple effect of these disruptions is observed in the whole assembly line. The proper analysis and mitigation of disruptions is the key to the proficiency of the plant and resource utilisation. The research focuses on the quantitative analysis of the impact of disruptions of the manufacturing process, which is performed by analysing the disruptive workstation dynamically. The disruptive workstations have a significant impact on succeeding and preceding workstations, which have been analysed dynamically, and accordingly, the pre-set alarm trip points are elevated. The results show that lowering the number of starts and stops decreases the number of rejections of valuable process batches that finally improve efficiency. Finally, the developed model is implemented on a polycrystalline diamond compact drill bit manufacturing plant. The results are compared with the research work of other researchers, showing a 60% reduction in the number of start/stop events, 60% reduction in downtime, while a 75% reduction in the number of rejections is noted.

Drilling Technology for Long-Offset 3D Horizontal Shale Oil Wells in the Longdong Area of the Changqing Oilfield

Ravines and gullies criss-cross the shale oil reservoirs of the Longdong Area in the Changqing Oilfield, where there are also numerous protected zones for water and forest resources, plus prime farmlands. The development of horizontal wells is greatly restrained by the topography and protection zones, and the offset of 3D horizontal wells directly affects the number of horizontal well platforms and the factory-like operation of large platforms, and affects the effective utilization of subsurface resources. Based on the analysis of the characteristics and drilling difficulties of long-offset 3D horizontal wells, the wellbore profile design was optimized, and kick-off points, azimuths, deviation angles, and well sections for eliminating offset were selected to improve the control mode of hole trajectories. In the absence of a rotary steering system, conventional positive displacement motors (PDM) and polycrystalline diamond compact (PDC) bits were upgraded. In addition, tools for reducing friction and a water-based CQSP-4 drilling fluid system suitable for long-offset horizontal shale oil wells were employed. Finally, the drilling technology for long-offset 3D horizontal shale oil wells in the Longdong Area was developed. This technology was applied to 6 3D horizontal wells with offsets over 900 m in Longdong Area. Friction torque was reduced significantly and the drilling process was safe and efficient, with good field application effect achieved. The successful application of the technology can support factory-like efficient development of the large shale oil platforms in the Longdong Area, which have multilayered systems and multiple drilling rigs. Further, it can facilitate the transformation of the drilling operation mode from single-rig and single-team to industrialized and clustered production.

Application of multi-layer denoising based on ensemble empirical mode decomposition in extraction of fault feature of rotating machinery

Aiming at the problem that the weak features of non-stationary vibration signals are difficult to extract under strong background noise, a multi-layer noise reduction method based on ensemble empirical mode decomposition (EEMD) is proposed. First, the original vibration signal is decomposed by EEMD, and the main intrinsic modal components (IMF) are selected using comprehensive evaluation indicators; the second layer of filtering uses wavelet threshold denoising (WTD) to process the main IMF components. Finally, the virtual noise channel is introduced, and FastICA is used to de-noise and unmix the IMF components processed by the WTD. Next, perform spectral analysis on the separated useful signals to highlight the fault frequency. The feasibility of the proposed method is verified by simulation, and it is applied to the extraction of weak signals of faulty bearings and worn polycrystalline diamond compact bits. The analysis of vibration signals shows that this method can efficiently extract weak fault characteristic information of rotating machinery.

Research on building the formula to determine the rate of penetration for polycrystalline diamond compact bits

Nowadays, polycrystalline diamond compact (PDC) drill bits are widely used in the oil and gas industry when drilling in soft rocks. However, parameters used for the PDC bit are usually based on the instructions of the drill manufacturer with a very wide adjustment range. Therefore, it is necessary to have a specific formula in order to determine the rate of penetration parameter (ROP) for the PDC bit in evaluating the influence of the parameters, rock mechanical properties and other parameters on the rate of penetration parameter (ROP). From there, it gives reasonable parameters and improves the design of the PDC bit to improve drilling efficiency. The article applies theoretical analysis method and Dalamber's principle to illuminate and build up the impact force model for PDC bits in the rock destruction process. From the impact force model, a formula to determine ROP for PDC bits was proposed. Finally, the authors applied the research results to the actual data obtained from the Nam Rong - Doi Moi oil field. The formula for determining the rate of penetration parameter (ROP) for the PDC bit that the authors have built has high accuracy and can be applied to many different rock.

Anti-balling Mechanism on the Non-smooth Surface of Bionic Polycrystalline diamond compact Drill Bits

Polycrystalline diamond compact (PDC) bit balling is one of the major factors that limits the penetration rate of drilling and causes bit failure in soft stratum. In order to solve the PDC bit balling problem, in this research we designs typical bionic non-smooth surfaces and analyzes the anti-adhesion mechanisms. Next, the non-smoothness characterization is extended from a two-dimensional to three-dimensional in which the area ratio and the width ratio are used to characterize lateral and longitudinal non-smoothness. Then, a comparative experiment between typical non-smooth surfaces and the smooth surface condition is carried out. The results show that the scale-like non-smooth surface has the best anti-adhesion effect and that longitudinal non-smoothness has a greater influence on mud block adhesion than lateral non-smoothness. The research results also show that after applying the principle of anti-adhesion and resistance reduction for the non-smooth surface of soil animals to the design of the flow channel of a PDC drill bit, the novel bionic anti-balling PDC bit can effectively avoid the problem of bit balling.

Experimental Research on the Process Parameters of a Novel Low-Load Drill Bit Used for 7000 m Bedrock Sampling Base on Manned Submersible

Due to the need for accurate exploration of deep-sea scientific research, drilling techniques by combining the operational advantages of the Jiaolong manned submersible is considered one of the most feasible methods for deep-sea bedrock drilling. Based on deep sea bedrock cutting model and discrete element simulation, as well as efficient drilling as the design criterion, the development of a deep sea 7000 m electromechanical coring apparatus was carried out. The outstanding feature of this technology is that the bit load produced by the drill pressure is usually within the range 100–400 N while the recommended load for diamond drilling is 1–3 KN or even more. Therefore, searching for the drilling bits that can drill in extremely hard formations with minimal load and acceptable rates of penetration and rotary speed is the necessary step to prove the feasibility of electromechanical deep-sea drilling technology. A test has been designed and constructed to examine three types of drill bits. The results of experiments show that the new low-load polycrystalline diamond compact (PDC) bit has the highest penetration length of 138 mm/15 min under a 300 N load and 250 rpm rotary speed. Finally, field tests with the Jiaolong submersible were used to conduct deep sea experiments and verify the load model, which provides theoretical and technical data on the use of a low-load core sampling drill developed specifically for a deep sea submersible.

A formation-based approach for modeling of rate of penetration for an offshore gas field using artificial neural networks

Due to the mounting concern in the oil and gas industry about creating well-designed drilling plans and efficiently drilling new wells, analysis of offset well data has received extensive attention over the past few decades. By doing this, bottom hole assemblies, drill bit for a given section, drilling fluid, and the operational parameters such as weight on bit (WOB) and drilling string rotational speed (RPM) can be accurately determined. This makes it possible to achieve the most favorable Rate of Penetration (ROP) without causing drilling problems or non-productive Time (NPT). The present paper proposes a unique formation-based Artificial Neural Networks (ANN) model of ROP, which suits deviated wells with the application of Polycrystalline Diamond Compact (PDC) bits. In this study, nine different drilling functions that account for various factors affecting ROP are considered. Unlike the conventional ANN-ROP modeling technique, which directly considers raw drilling variables as inputs into ANN, the drilling functions are considered as inputs to ANN in the proposed ANN-ROP model. The drilling functions for this study are available in literature. The proposed ANN-ROP model is trained and tested using data collected from the 12 ¼ inches drilling section, which is the most extended drilling section of these wells. Furthermore, the prediction performance of the proposed models is evaluated in various formations. The results indicate that the proposed model is able to predict drilling ROP with high accuracy with the average Absolute Percentage Error (AAPE) being 0.83% for the training wells and 4.5% for the testing wells and with the R-squared obtained being 0.97 for the training wells and 0.93 for the testing wells. The proposed formation-based ANN-ROP methodology is shown to surpass the conventional ANN-ROP in terms of both accuracy and efficiency and the principle-based methodology in terms of accuracy.

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.

An experimental study of the relationship between cutting efficiency and cuttings size in rock cutting using a PDC cutter

Rock cutting efficiency is the most common parameter used to evaluate the performance of polycrystalline diamond compact (PDC) bits. Many studies have shown that cuttings size might be used to evaluate rock breaking efficiency; however, there are few quantitative studies of the relationship between rock cutting efficiency and cuttings size in rock cutting when a PDC bit is used. Several linear cutting tests were conducted to explore the relationship between the mechanical specific energy (MSE) and cuttings size to solve this problem. The cuttings size distributions were also discussed. Then, the coarseness index (CI) was selected as the most appropriate indicator of cuttings size and its relationship with the MSE was investigated. In addition, rock cutting tests based on the Taguchi method were conducted to analyze cutting parameters such as the depth of cut (DOC), the back rake angle (θ) and the cutting speed (v) effects on the CI and MSE. The contribution of each parameter to the response was obtained. The results show that the distribution of cuttings size conforms to the Rosin–Rammler equation, and there is a significant relationship between the MSE and cuttings size. The MSE decreases with increased cuttings size, furthermore, the relationship between the MSE and the CI could be described by an exponent function. The Taguchi experiment results show that DOC and θ have significant impacts: the CI value increases with increased DOC, and the CI increases slightly with increased θ. The most influential factor on the CI is the DOC, followed by θ. However, within the range of experiments, the cutting speed has an insignificant effect on the CI value. This work is highly pertinent to better understanding of the relationship between rock cutting efficiency and cuttings size in rock cutting using a PDC cutter.

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.

Weak fault feature extraction for polycrystalline diamond compact bit based on ensemble empirical mode decomposition and adaptive stochastic resonance

Aiming at the problem of weak early fault signals of rotating machinery, a feature extraction method combining ensemble empirical mode decomposition (EEMD) and adaptive stochastic resonance (ASR) is proposed. First, the original vibration signal is decomposed into a series of intrinsic mode functions (IMF) through EEMD, and the main IMF components are selected using the correlation coefficient and the root mean square principle. Next, the selected components are reconstructed and used as the input of the ASR system based on the gray wolf algorithm. Finally, to evaluate the performance of ASR, a new evaluation index-weighted power spectrum kurtosis (WPSK) is defined. The results of experimental analysis on the simulation signals and vibration signals are used to verify the feasibility and superiority of the proposed method. Compared with the GA-SR, the proposed method increases the WPSK value by 34.5% when detecting weak signals of worn polycrystalline diamond compact bits.

3D numerical simulation study of rock breaking of the wavy PDC cutter and field verification

The structure of polycrystalline diamond compact (PDC) bits is a key factor in improving their rock-breaking efficiency. To further study the rock-breaking mechanism of the wavy PDC cutter, a 3D finite element model of the dynamic rock breaking of the PDC cutter was established, and a comparative study on the rock-breaking process of the wavy PDC cutter and the conventional PDC cutter was conducted. The results show that the wavy PDC mainly breaks the rock by ploughing and shearing, which results in a higher rock-breaking efficiency. The cutting force of the wavy PDC cutter is 6.64% lower than that of the conventional PDC cutter, and its fluctuation is obviously smaller. With an increase in back-rake angle, the cutting force, its fluctuation, and the mechanical specific energy (MSE) increase, and the optimal back-rake angle is 10°–15°.With an increase in cutting depth, the cutting force and its fluctuation in the wavy PDC cutter increase, the MSE decreases, and the optimal cutting depth is 2 mm. As the number of waves increases, the cutting force and MSE of the PDC cutter increase first and then decrease, and the greater the number of waves, the larger the fluctuation of the cutting force. The cutting temperature of the wavy PDC cutter is lower than that of the conventional cutter, it decreases with an increase in the back-rake angle and number of waves, and gradually increases with an increase in cutting depth. The main results of this work will help to reveal the process of rock breaking and the mechanism of the wavy PDC cutter, thus contributing to the achievement of a high rate of penetration and efficiency in the drilling process of hard formations with PDC bits.

Investigation of the Cross-Cutting Polycrystalline Diamond Compact Bit Drilling Efficiency

The parallel track scraping principle of conventional PDC bits largely limits the cutting efficiency and working life in deep formations. Cross-cutting polycrystalline diamond compact (PDC) bit may be an efficient drilling tool that increases the rock-breaking efficiency through both cross-cutting and alternate-cutting modes of the PDC cutter. The motion track equation of the cross-cutting PDC bit was derived by using the compound coordinate system, and the motion track was analyzed. Meanwhile, through the unit experiment and discrete element simulation, the cutting force, volume-specific load, and crack propagation were analyzed under different cutting modes. Through establishing a nonlinear dynamic model of the bit-rock system, the speed-up mechanism of the novel bit was analyzed based on rock damage, rock stress state, and motion characteristic of the bit during the rock-breaking process. Compared with unidirectional cutting, cross-cutting produces less cutting force, more brittle fracture, and a greater decrease of formation strength. The novel PDC bit can put more rock elements into a tensile stress condition than a conventional PDC bit, and the plastic energy dissipation ratio of the cross-cutting PDC bit is lower while the damage energy consumption ratio is higher than they are for conventional bits, which is beneficial to increasing the ratio of fracture failure and improving rock-breaking efficiency. Laboratory drilling tests show that the cross-cutting PDC bit can create mesh-like bottom-hole features. Drilling contrast experiments show that a mesh-like bottom-hole pattern can be obtained by using the cross-cutting PDC bit, of which the ROP is obviously higher than that of the conventional bit when drilling in sandstone or limestone formation. Meanwhile, the influence of deviation angle, weight on bit, and rock properties on cutting efficiency of the cross-cutting PDC bit are studied.

Improving drilling performance through optimizing controllable drilling parameters

The prediction of the drilling rate of penetration (ROP) is one of the key aspects of drilling optimization due to its significant role in reducing expensive drilling costs. Many variables could affect ROP, which can be classified into two general categories; controllable operational variables and uncontrollable or environmental variables. Minimizing the drilling cost can be achieved through optimizing the controllable drilling parameters. As a direct result, the drilling speed will be increased while maintaining safe practices. The primary purpose of this study is to address the simultaneous impact of controllable parameters such as weight on bit (WOB), revolutions per minute, and flow rate (FR) on the rate of penetration (ROP). Response surface methodology was applied to develop a mathematical relation between operational controllable drilling parameters and ROP. To accomplish this, actual field datasets from several wells drilled in Southern Iraq in different fields were used. The second purpose of this study was to identify all prospective optimal ranges of these controllable parameters to obtain superior drilling performance with an optimum ROP. The obtained results showed that the developed model offers a cost-effective tool for determining the maximum ROP as a function of controllable parameters with reasonable accuracy. In addition, the proposed model was used to estimate optimal combinations of controllable drilling parameters for various depths. The results have shown that FR has the most significant effect on ROP variation with a sum of squares values of 23.47. Applying high WOB does not permanently improve ROP but could result in reducing ROP for some cases. The developed mechanical specific energy model for polycrystalline diamond compact (PDC) bit with vertical and deviated wells can estimate combinations of controllable drilling parameters. The developed model can be successfully applied to predict and optimize the drilling rate when using PDC bits, hence reducing the drilling time and the associated drilling cost for future wells.