Polycrystalline Diamond Compact Research Articles

Mechanism and Data Fusion Method for Predicting Wear and Life of Polycrystalline Diamond Compact Bits Based on the Gaussian Process Regression

Mechanism and Data Fusion Method for Predicting Wear and Life of Polycrystalline Diamond Compact Bits Based on the Gaussian Process Regression

New insights on impact wear of polycrystalline diamond compact: Effect of interface state on kinetic response and damage behavior

The impact wear of polycrystalline diamond compact (PDC) cutters caused by the discontinuous cutting during the drilling process significantly affects the lifespan and efficiency of the drilling tools. Different PDC impact contact interface states are realized through the selection of impact mating materials. Understanding the effects of different interface states on the kinetic response, damage behavior and impact wear mechanism of PDC is significant in guiding the practical design of material structures with excellent impact wear resistance. Therefore, the kinetic response and damage behavior of PDC impact with different mating materials are investigated. The results show that the kinetic response and damage behavior of PDC are correlated with the mechanical properties of the mating material and physicochemical changes at the impact surface interface. Adhesion and filling resulting from strong covalent bonding and filling effects mitigate the interfacial stress and reduce the average impact force of SiC and Al2O3. Moreover, brittle fracture and filling effects increase the consumption of kinetic energy of SiO2, resulting in an energy absorption of up to 86 %. In addition, the strong covalent bonding effects exacerbated the damage to the PDC interfaces, leading to the internal fracture of diamond particles and detachment at grain boundaries. Furthermore, the filling effect formed plays a specific protective role for diamonds. However, it increases the energy absorption rate and reduces the mating material damage efficiency. In this work, the relationship between impact interface state and impact wear mechanism has been established by understanding the kinetic response, damage morphology, and structural evolution.

Research on Strength of Bilateral Support Bearing of PDC–Cone Hybrid Bit

The existing PDC (polycrystalline diamond compact)–cone hybrid bit bearing adopts a unilateral support structure, which is prone to stress concentration in the journal area, resulting in fracture and wear failure of the bearing, thus reducing the service life of the hybrid bit. In this paper, a new type of double supported bearing hybrid bit is proposed. The static strength analysis of unilateral and bilateral support bearing structures is carried out by finite element simulation, and the stress and strain distribution of the two structures under loads of 20–100 kN is obtained. Experimental devices for unilateral and bilateral support bearing structures are designed and manufactured to complete 50–100 kN static pressure loading experiments. The results show that the stress and strain of unilateral and bilateral support bearing increased linearly with the increase of load. Compared with unilateral bearing, when the load was 100 kN, the maximum Mises stress of bilateral bearing decreased from 358.80 MPa to 211.10 MPa, with a decrease of 41.16%. The maximum contact stress decreased from 415.20 MPa to 378.10 MPa, a decreased of 8.94%, and the maximum principal strain decreased from 1.101 × 10−3 to 9.71 × 10−4, a decrease of 11.81%. The axial strain in the danger zone was reduced by 14.68% and 17.35%, respectively. It is found that the contact stress of the simulation data is highly correlated with the bearing life, and the service life of the bilateral bearing bit is increased by 8.94%. The simulation data and experimental results provide data support for the production of hybrid bits with bilateral bearing support.

Preparation, wear resistance, and impact toughness of homoepitaxial diamond film deposited on polycrystalline diamond compact by HFCVD method

To minimize the detrimental effects of cobalt binder on the thermal stability of polycrystalline diamond compact (PDC) under high temperature working conditions and enhance the PDC’s properties. Hot filament chemical vapor deposition diamond coated polycrystalline diamond compact (HFCVD-PDC) was prepared by depositing homogeneous epitaxial diamond film on the polycrystalline diamond layer (PCD layer) treated with cobalt binder removal. The effect of deposition pressure on the microstructure of the diamond film was investigated, and the PDC’s wear resistance was assessed using the abrasion ratio test. The drop hammer impact test was utilized to evaluate the impact toughness of the original PDC, cobalt removal PDC, and HFCVD-PDC. The results showed that a continuous and dense nanodiamond film with a cauliflower-like structure was formed on the PDC surface at the deposition pressure of 3 kPa. The abrasion ratio of the HFCVD-PDC increased by 67.44% compared to the original PDC, and by 33.29% compared to the cobalt removal PDC. Furthermore, filling nanodiamonds into the pores of cobalt removal PDC improved its impact toughness. These findings suggest that the application of homogeneous epitaxial diamond on the PCD layer can significantly improve the PDC’s wear resistance and impact toughness.

Computational Fluid Dynamics Study on Bottom-Hole Multiphase Flow Fields Formed by Polycrystalline Diamond Compact Drill Bits in Foam Drilling

High-temperature geothermal wells frequently employ foam drilling fluids and Polycrystalline Diamond Compact (PDC) drill bits. Understanding the bottom-hole flow field of PDC drill bits in foam drilling is essential for accurately analyzing their hydraulic structure design. Based on computational fluid dynamics (CFD) and multiphase flow theory, this paper establishes a numerical simulation technique for gas-liquid-solid multiphase flow in foam drilling with PDC drill bits, combined with a qualitative and quantitative hydraulic structure evaluation method. This method is applied to simulate the bottom-hole flow field of a six-blade PDC drill bit. The results show that the flow velocity of the air phase in foam drilling fluid is generally higher than that of the water phase. Some blades’ cutting teeth exhibit poor cleaning and cooling effects, with individual cutting teeth showing signs of erosion damage and cuttings cross-flow between channels. To address these issues, optimizing the nozzle spray angle and channel design is necessary to improve hydraulic energy distribution, enhance drilling efficiency, and extend drill bit life. This study provides new ideas and methods for developing geothermal drilling technology in the numerical simulation of a gas-liquid-solid three-phase flow field. Additionally, the combined qualitative and quantitative evaluation method offers new insights and approaches for research and practice in drilling engineering.

Multi-objective optimization of Stinger PDC cutter breaking rock parameters under intrusion-cutting action using Taguchi-based gray relational analysis.

To enhance the efficiency of the Stinger Polycrystalline Diamond Compact (PDC) cutter in breaking hard rocks, this study focuses on optimizing the cutter intrusion-cutting rock breaking parameters. A numerical calculation model for the rotational breaking of granite by a Stinger PDC cutter was established. A comprehensive statistical examination was performed to assess the influence of various factors on intrusion ability (IA), tangential force (TF), and mechanical specific energy (MSE). The Taguchi method was used to determine the optimal settings for each factor, while analysis of variance was employed to assess the significance and relative impact of these factors on the target outcomes. In addition, the multi-objective function was optimized using the gray relational analysis method. The primary process parameters obtained for the various performance characteristics are the cone top angle (α), the cone top radius (r), the cutter diameter (d), the cutter back inclination angle (β), and weight on bit (P). The impact ratios of these parameters are 6.20%, 7.66%, 3.93%, 17.20%, and 65.02%, respectively. The optimal geometrical parameters are α = 60°, r = 2mm, and d = 15mm, while the optimal working parameters are β = 30° and P = 800 N. In the optimal case, IA and MSE were reduced by 55.335% and 15.809%, respectively, compared to the initial case. Despite a 15.706% increase in TF, the overall GRG increased for all three evaluation criteria, with an overall increase in efficiency of 18.229%. The results of this paper can provide guidance for the design of Stinger cutter PDC drill bits.

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

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

Relationship between sintering pressure and leach rate of polycrystalline diamond compacts (PDCs) using central composite design (CCD) modelling

The effect of sintering pressure on the microstructure, wear resistance and leachability of polycrystalline diamond (PDC) was studied using central composite design (CCD) modelling. Pressure and leachability had an inverse relationship due to reduced cobalt pool size and increased diamond contiguity with higher pressures. X-ray diffraction and X-ray fluorescence confirmed the selective removal of cobalt during leaching. The relationship between pressure and leachability was modelled as linear: Y = −1.047× + 11.139, valid within the 5–7 GPa pressure range. For a fixed temperature of 1600 °C, the optimum leach rate was 6.1 μm/h at 5 GPa. This study provided insights into optimizing PDC design and leaching processes for improved performance.

Uniaxial compressive strength prediction based on measurement while drilling data: A laboratory study

The uniaxial compressive strength is one of the most important basic parameters of rock, which is essential for surrounding rock stability analysis and support scheme design of underground engineering. At present, it is time consuming and costly to take a large amount of core samples for laboratory testing, and the mechanical properties of the cores may be affected by mining disturbance, which can easily lead to inaccurate result. The measurement while drilling (MWD) technology provides a new approach to solve the above challenge. The key to implementing this technology is to establish a correlation model between drilling parameters and rock mechanics parameters. Based on the characteristics of polycrystalline diamond compact (PDC) bits in drilling and rock breakage, this paper analyzes the mechanical state of the bit in breaking rock. A theoretical correlation model between the torque, feed force of the bit and the uniaxial compressive strength of the rock has been developed. To verify the accuracy of the theoretical model, the uniaxial compressive strength of five different types of rocks (red sandstone, green sandstone, limestone, marble and shale) was obtained through laboratory mechanical tests. The torque Mb, feed force Fb and other parameters in the drilling process of these five rocks were tested through the newly developed MWD test system. The correlation between the drilling parameters and the uniaxial compressive strength of rock was established. The results showed that the feed force Fb and torque Mb measured at five different types of rocks indicate a linear increasing trend with an increase in depth of cut h. Meanwhile, a strong linear relationship between the feed force Fb and torque Mb is evident. This paper proposes an MWD-based method to rapidly conduct the in-situ measurement of the uniaxial compressive strength of various rocks.

Cobalt removal process from PDC with ultrasonication in neutral electrolyte

Cobalt removal is considered a common method to improve the performance of polycrystalline diamond compact (PDC). To effectively reduce the pollution during the process of cobalt removal, a neutral electrolyte was used in this work to remove cobalt from PDC by electrolysis with ultrasonication. The electrode process and mass transfer model of cobalt removal in a NaCl–KCl solution were established by performing electrochemical impedance spectroscopy (EIS) measurements. Different electrode potentials and electrolytic durations were set to investigate the limits of cobalt removal in the neutral electrolyte. Cobalt removal was assessed by conducting potentiodynamic polarisation, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) measurements. The ImageJ2x image analysis software was used to study the collected spectra. The experimental results indicated that cobalt was successfully removed in the neutral electrolyte and that ultrasonication enhanced its removal. The optimal electrode potential for cobalt removal in the NaCl–KCl solution was less than 500 mV or more than 2000 mV. As the electrolysis time increased, the porosity of the PDC surface first increased to 9.4 % and then decreased to 7.2 %, and the depth of cobalt removal was up to 224 μm. Over time, the rate of cobalt removal decreased, suggesting that the efficacy of ultrasonication in promoting the cobalt removal process gradually weakened as electrolysis products continued to accumulate.

Evaluation of cobalt removal from polycrystalline diamond compact in the coupling mechanism of acid leaching and electrolysis

Polycrystalline diamond compact (PDC) is a widely used superhard material, and its thermal stability and wear resistance are the main factors determining its performance. The residual cobalt binder content in polycrystalline diamond (PCD) has a significant impact on the thermal stability and wear resistance of PDC. Therefore, cobalt removal treatment is required to improve the performance of PDC. The current cobalt removal methods mainly include acid leaching and electrolysis. This study proposes a novel coupling method that combines acid leaching and electrolysis for cobalt removal. Cobalt removal was conducted for 10 h under the conditions of electrolytic voltage of 12 V, direct current power supply current of 0.01 A, and sulfuric acid electrolyte concentration of 9.2 mol/L. The cobalt removal effect was evaluated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness and elastic modulus of PDC before and after cobalt removal were measured using nanoindentation experiments. The results indicate that the coupled electrolysis process effectively removes the cobalt phase in the PCD layer while retaining the WC phase. The hardness and elastic modulus of PDC decrease after the removal of cobalt binder, and the cobalt removal depth can reach 807 μm.

Prediction of formation abrasiveness under the action of a PDC bit based on the fractal dimension of a rock surface

During rock drilling, a drill bit will wear as it breaks the rock. However, there is no uniform grading standard for rock abrasiveness. To solve this problem, the wear mechanisms of a polycrystalline diamond compact (PDC) bit and the formation it is drilling into are analyzed in depth, and an abrasiveness evaluation method based on the fractal dimension of the rock surface topography is established. Initially, a three-dimensional digital model is generated from a scanning electron microscope image of the rock after drilling; next, an evaluation of the irregularities on the rock surface is performed using an adapted Weierstrass–Mandelbrot (W-M) function to ascertain the fractal dimensionality. Then, the microcontact characteristics of the contact surface between the formation and the PDC bit are analyzed, and the distribution of the microconvex contact points of the two-body friction pair in a region is obtained. Because the sliding friction between the drill bit and the rock produces a large amount of heat, according to the contact area formula of the friction surface and heat conduction theory, the temperature rise and overall temperature distribution of the formation and PDC bit under the condition of sliding friction are revealed, and the real contact area between the formation and the drill bit within a certain temperature range is obtained. Finally, the evaluation index of rock abrasiveness under sliding conditions is established by adopting the wear weight loss of the rock cutting tool per unit volume as the index of rock abrasiveness, and the model is verified by a microdrilling experiment. The research in this paper is highly important for improving the rock-breaking efficiency and bit service life during drilling.

Numerical investigation of rock-breaking mechanisms and influencing factors of different PDC cutters during rotary percussion drilling

While drilling deep or ultra-deep wells in hard rock formations, there are significant problems such as easy wear of drilling cutters and a low rate of penetration (ROP), and rotary percussion drilling technology is one of the essential techniques for improving drilling efficiency. However, there is currently limited research on the compatibility of rotary percussion drilling tools, polycrystalline diamond compact (PDC) cutters, and hard rock formations. Considering the motion mechanism of rotary percussion drilling tools, a three-dimensional rock-breaking numerical model was established for different cutters (planar, axe-shaped, and triple-ridged) under impact loads. Penetration depths, cutting widths, and rock-breaking volumes of different cutters under static and dynamic load coupling were analyzed. Changes in tensile, compressive, and shear stresses during the cutter rock-breaking process were compared, revealing the different cutter rock-breaking mechanisms under impact loads. The cutter rock-breaking laws under different impact amplitudes and frequencies were analyzed quantitatively, and the differences in rock-breaking effects of different cutters under various geological conditions were assessed. The results indicated that cutter penetration depth during rotary percussion drilling could be increased by 16.04% compared to that during conventional drilling. Under the same impact load, the rock-breaking effects of different cutters on hard and soft rocks exhibited similar variation patterns. The penetration depth followed the order axe-shaped > triple-ridged > planar cutters, with an average tangential order of triple-ridged < axe-shaped < planar cutters. When drilling through hard rock, the average penetration depths of planar, axe-shaped, and triple-ridged cutters were 5.57, 6.06, and 3.91 mm, respectively. The average tangential forces were 670.57, 541.76, and 347.89 N, respectively. During the transition from soft to hard rock during drilling, the tangential forces of the planar, axe-shaped, and triple-ridged cutters increased by 8.41%, 3.21%, and 2.64%, respectively. The planar cutter experienced the most significant instantaneous tangential-force change and was more prone to impact damage. Increasing the amplitude of the axial stress waves helps enhance the penetration depth of the drill bit, whereas increasing the frequency of the stress waves can reduce the intensity of fluctuations during drill-bit penetration and increase drill-bit stability. The research results provide insights into optimizing drilling cutters and engineering parameters during rotary percussion drilling.

Stick-slip vibration analysis of a coupling drilling-rock system with two delays and one delay-dependent coefficient

Drilling depths exceeding 10,000 m have recently been achieved, but the increasing depth poses challenges due to the flexible drill-string, making it more susceptible to stick-slip vibration. This vibration can lead to accidents such as excessive bit wear and tool falling into the well. Previous studies on modeling polycrystalline diamond compact (PDC) bits have focused on symmetrically distributed complete blade bits, which are not commonly used. To address this gap, this study introduces PDC bits that closely resemble the actual ones, with a structural configuration of both complete blades and part-blades symmetrically distributed. We also consider the impact of mud and rock chips on the drill bit by introducing a delay-dependent coefficient of response damping change. This study develops a stick-slip vibration model for a coupling drilling-rock system with two state-dependent delays tn1 and tn2, and one delay-dependent coefficient. Using the crossing curve method and numerical studies, we obtain different types of crossing curves reflecting the stability switching characteristics of the system in the dimensionless delay τ2τ1 space. During stick-slip vibration, τ1 mutates from 1.69 s to 2.51 s, and τ2 mutates from 1.3 s to 2.16 s, both within the stable region of the crossing curve. The critical steady state and the stable state typically cross the stable and unstable regions of the crossing curve in their respective times. Increasing the torsional damping within the range of 0.04 to 0.08 can accelerate system stabilization or delay the arrival of the critical steady state. Moreover, increasing the drive rotation speed within the range of 4 to 6 eliminates stick-slip vibration and accelerates the system towards a steady state. In conclusion, this study predicts the drill-string dynamics of a symmetrically distributed PDC bit with complete blades and part-blades. The insights gained can help minimize stick-slip vibration and provide recommendations for drilling operation parameters.

Tribological behavior of textured polycrystalline diamond compact for thrust bearings using the surface morphology of dung beetles as an inspiration

To improve the lubrication and friction characteristics of diamond thrust bearings and extend their service life, this study took inspiration from the anti-adhesion and wear-resistant properties of a dung beetle body surfaces and used laser processing to create dimples on the surface of a polycrystalline diamond compact (PDC). The spacing, diameter, and depth of the dimples were designed and optimized using an orthogonal experimental method. The wear mechanism of the textured PDC was analyzed using various microscopic characterization methods. The results showed that the bio-inspired dimple-textured PDC exhibited better tribological behavior and was an effective way to enhance the lifetime and reliability of diamond thrust bearings.

Rock-Breaking Characteristics of Three-Ribbed Ridge Nonplanar Polycrystalline Diamond Compact Cutter and Its Application in Plastic Formations

Summary To improve the penetration performance of polycrystalline diamond compact (PDC) bits in hard-to-penetrate plastic formations, the study of three-ribbed ridge nonplanar PDC cutter technology was carried out. The rock-breaking characteristics of nonplanar cutters are analyzed by comparison with conventional planar cutters and axe-shaped cutters through simulation and indoor experiments. The simulation results show that the planar cutter mainly breaks the rock by shearing and extruding, the axe-shaped cutter mainly breaks the rock by shearing, and the nonplanar PDC cutter mainly relies on its convex ridge structure to penetrate and split the rock. Nonplanar cutter has better penetration performance and cutting stability than planar cutters and axe-shaped cutters. The field test shows that the rate of penetration (ROP) and footage of the developed PDC bit with three-ribbed ridge nonplanar PDC cutters are increased by 133.66% and 176.11% compared with the conventional PDC bit in the hard-to-penetrate plastic formations. The use of nonplanar PDC cutters improves the working stability, rock-breaking efficiency, and service life of the bit. The special three-ribbed ridge structure of the nonplanar cutter has changed the interaction mode between the cutter and the rock. Its successful application in the plastic formation provides a reference for faster drilling of PDC bits in hard-to-penetrate plastic formations.

Research on the Temperature Field Distribution Characteristics of Bottomhole PDC Bits during the Efficient Development of Unconventional Oil and Gas in Long Horizontal Wells

Unconventional tight oil and gas resources, including shale oil and gas, have become the main focus for increasing reserves and production. The safe and efficient development of unconventional oil and gas is a crucial demand for the energy development strategy. Deep tight oil and gas resource development generally adopts horizontal well drilling methods. During drilling, especially in long horizontal sections, the high temperature frequently causes failures of downhole drilling tools and rotary steering tools. The temperature rises sharply during rock breaking with the drill bit. Existing wellbore heat transfer models do not fully consider the impact of heat generated by the drill bit on the wellbore temperature field. This paper aims to experimentally study the temperature rise law of the cutting tooth of the bottom polycrystalline diamond compact (PDC) bit during rock breaking. A set of evaluation devices was developed to study the temperature field distribution characteristics at the bottom of the PDC bit during rock breaking under different experimental conditions. The results indicate that the flow rate of drilling fluid, bit rotation speed, and weight on bit (WOB) significantly affect the distribution of the temperature field at the well bottom. This experimental research on the temperature field distribution characteristics at the bottom of the PDC bit during rock breaking helps reveal the heat transfer characteristics of the long horizontal section wellbore, guide the optimization of drilling parameters, and develop temperature control methods. It is of great significance for the advancement of efficient development technologies for unconventional resources in long horizontal wells.

Evaluating PDC bit-rock interaction models to investigate torsional vibrations in geothermal drilling

Polycrystalline diamond compact (PDC) bits are superior for drilling geothermal wells because of their superior drilling performance compared to conventional roller cone bits. However, the shear action of PDC bits generates detrimental vibrations during drilling. The main objective of this study was to establish a methodology to analyze and predict the stick-slip severity in hard rocks for geothermal wells. Two non-linear coupled axial-torsional bit-rock interaction (BRI) models are presented: one is based on a velocity-decaying friction model (VDF), and the other is based on a state-dependent delay friction model (SDDF). The capabilities of the two models were evaluated to assess the axial and torsional dynamic stabilities of drill stems in deep geothermal wells. The comparative analysis, along with the results from both models, were validated using geothermal well downhole data. Five distinct zones were selected for analysis, and the stick-slip severity value (SSV) was calculated using these two models (VDF and SDDF). The results from these two models for the five different zones were compared with the field data. The results indicated that VDF demonstrated superior quality when compared with field values, as the results of VDF were within the interquartile range of the observed SSV in each zone. A sensitivity analysis employing spider plots was performed for both models, considering parameters related to rock, bit, operational, and frictional aspects. In terms of the operational parameters, the weight-on-bit (WOB) and revolutions per minute (RPM) exerted the most significant influence on the SSV for both models. For the VDF model, the sensitivity analysis indicated that the frictional parameter, uniaxial compressive strength (UCS), and number of cutters (NOC) had the most pronounced impact on the SSV. In the case of the SDDF, the Intrinsic specific energy (ISE), bit diameter, and number of blades (NOB) are the key factors that predominantly affect the SSV.

Rock fragmentation mechanism of PDC cutter from the insight of cutting chips

To meet the global energy needs and demands, obtaining oil and gas resources from deep strata plays an increasingly important role in energy supply. However, it is difficult to drill since the special properties of rocks in deep formation. To further improve the breaking efficiency of polycrystalline diamond compact (PDC) bit in deep hard rock, this paper conducted several groups of experiments on cutting granite with PDC cutters. By changing the cutting depth, rake angle and linear velocity, the relationship between the mass proportion, fractal dimension and roughness index of cuttings and the mechanical specific energy (MSE) is explored, and the following conclusions are obtained: When cutting depth HC exceeds 0.8 mm, massive chips with particle size r > 2 mm begin to form and the brittle failure begins to occur, and the probability of brittle failure will increase with the further increase of cutting depth. With the increase of rake angle, more energy will be used to form new surfaces of cutting chips, resulting in a decrease in the roughness index and an increase in MSE. More massive chips will be formed with the increasing linear velocity, but MSE only decrease slightly. The variation of the fractal MSE (FMSE) that based on the fractal dimension of cutting chips is extremely consistent with the MSE. The relevant conclusions in this paper can provide some reference for the structural design of PDC bit, so as to improve the drilling efficiency in deep hard rock.

Study on Evaluation and Prediction for Shale Gas PDC Bit in Luzhou Block Sichuan Based on BP Neural Network and Bit Structure

Deep and ultra-deep shale gas resources have great potential, but well drilling faces many challenges. The Polycrystalline Diamond Compact (PDC) bit has become the primary rock-breaking instrument for oil and gas drilling. Reasonable bit structure designs can promote rock-breaking efficiency and extend service life. In this study, reverse modeling technology is used to analyze the structural characteristics of PDC bits collected in the field, and the influence of the structural characteristics of the bit at a specific interval on the rate of penetration (ROP) and drill footage is investigated using the Spearman rank correlation coefficient method. The number of blades, cutting angle of the cutters, crown rotation radius, internal cone angle, and diameter of the cutters are discovered to be the main structural characteristics that affect the ROP and footage of the bits, and the degree of influence varies depending on the formation conditions. The number of blades, crown rotation radius, inner cone angle, and cutting angle of the cutters have a significant impact on the ROP, whereas blade thickness, gauge length, gauge width, nozzle equivalent diameter have a significant impact on the bit footage. In addition, a back propagation (BP) neural network is utilized to build a prediction model of bit footage and ROP over a certain interval based on the structural characteristics of the bit. The goodness of fit of the model is greater than 85%, and its accuracy is high. Based on the usage of the bit, the evaluation and prediction of the bit can provide a reference for the structural design and optimization of the bit in a specific interval, guide the bit selection work, rationally plan the drilling operation, and reduce the drilling cost.