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Abstract

Polycrystalline diamond compact bits have been widely used in the Oil and Gas drilling industry, despite the fact that they may introduce undesired vibration into the drilling process, for example, stick-slip and bit bounce, which accelerate the failure rate and lead to higher drilling costs. First, we develop an innovative ridge-ladder-shaped polycrystalline diamond compact cutter, which has ridge-shaped cutting faces and multiple cutting edges with stepped distribution, in the hope of reducing vibration and improving drilling speed. Then, the scrape tests of ridge-ladder-shaped and general polycrystalline diamond compact cutters are carried out in a laboratory, indicating that the cutting, lateral, and longitudinal forces on ridge-ladder-shaped polycrystalline diamond compact cutters are smaller and with minor fluctuations. Due to different rock-breaking mechanisms, ridge-ladder-shaped polycrystalline diamond compact cutters have higher cutting efficiency compared to general polycrystalline diamond compact cutters, which is also verified experimentally. Finally, the drilling characteristics of a new polycrystalline diamond compact bit fitted with some ridge-ladder-shaped polycrystalline diamond compact cutters are compared to those of a general polycrystalline diamond compact bit by means of finite element simulation. The results show that introducing ridge-ladder-shaped polycrystalline diamond compact cutters can not only reduce the stick-slip vibration, bit bounce, and backward rotation of drill bits effectively, but also improve their rate of penetration.

Keywords

RLS PDC cutter reduced vibration improved drilling speed laboratory test finite element analysis

Introduction

Polycrystalline diamond compact (PDC) bit is the most common drilling tool, which interacts with rocks directly to create a passage from the ground to the bottom hole for oil and gas exploration. Statistically, PDC bits have been used for more than 90% total drilling length all over the world because of their high rock-breaking efficiency.¹ However, the service of a PDC bit is limited by the low impact resistance of its cutters.² When facing a difficult drilling formation, harmful vibrations appear, such as stick-slip and bit bounce, which have been identified as the main causes for PDC bit damage (see Figure 1) and low drilling speed,³ increasing the drilling costs significantly. One of the effective measures to overcome these problems is the optimization of the bit design, especially the structure of a PDC cutter, which usually has a cylindrical shape. Some efforts and acquired results in this field will be briefly discussed next.

Figure 1.

PDC bit damage caused by its undesired vibrations.

DiGiovanni et al.⁴ proposed a non-planar face PDC cutter with shallow recessed features, which provided lower mechanical specific energy (MSE) and a higher drilling speed, compared to a general PDC bit under the same conditions. Schlumberger developed the ONYX 360 rolling PDC cutter which helped to reduce the wear and frictional heat issues of general PDC cutters,⁵ prolonging the service life of a drill bit and improving its drilling speed. Rodriguez et al.⁶ and Pak et al.⁷ mentioned a hybrid-type bit fitted with both the general and conical PDC cutters. In the drilling process, the conical PDC cutter applies a concentrated point load to break rocks by plowing, and then the general PDC cutter creates a more efficient and durable shearing action. Crane et al.⁸ introduced a PDC cutter with an elongated ridge which fractures and shears the rock at the same time, improving the rock-breaking efficiency of drill bits. Al-Ajmi et al.⁹ developed a PDC cutter with a unique cutting structure to increase the stress concentration acting on the rock, offering more efficient cutting action than the general PDC cutter. As can be seen from this review, there is a lot of interest in the structural improvement of a drill bit, especially in the field of innovative design of PDC cutters, while most of the existing research aims to improve rock-breaking efficiency and optimize static mechanical characteristics of a full drill bit. However, research on adopting innovative PDC cutters to reduce the vibration is rarely reported in the scientific community.

This article introduces an innovative ridge-ladder-shaped (RLS) PDC cutter, which has ridge-shaped cutting faces and multiple cutting edges with stepped distribution, as shown in Figure 2. In principle, this new structure improves the stress concentration on rocks and lowers MSE, which would alleviate peeling large chunks of rocks effectively and instantaneous impact actions, reducing vibration and improving the rate of penetration (ROP). In order to verify this hypothesis, RLS PDC cutters and general PDC cutters are manufactured by using the 3D printing technique, followed by scrape tests carried out in a laboratory. Meanwhile, the rock-breaking mechanisms for both cutters are analyzed and compared with each other. In addition, the dynamic drilling behaviors of the general PDC bit and the new PDC bit fitted with some RLS PDC cutters are compared with each other by using finite element analysis.

Figure 2.

The structure of RLS PDC cutter.

Scrape experiment of a single PDC cutter

In order to evaluate the cutting mechanical properties of RLS PDC cutters, a series of laboratory tests are carried out and compared with those of general PDC cutters. First, both types of PDC cutters, with a radius of 7.5 mm, are manufactured using a 3D printing technique and C45E4 steel, as shown in Figure 3. Then, the cutters are installed onto a specialized experimental rig designed to scrape the rock, while measuring the cutting, lateral, and longitudinal forces acting on the cutter. The directions of those forces are shown in Figure 4.

Figure 3.

Experimental samples of two types of PDC cutters.

Figure 4.

A schematic defining the directions of the typical forces on a PDC cutter.

Experimental rig and principles

The experimental rig shown in Figure 5 is designed to simulate the straight scraping of a PDC cutter, where the PDC cutter is soldered to the tooth holder connected to the load cell. The shaper machine drives the PDC cutter and scrapes the rock, measuring three orthogonal forces defined in Figure 4. The resulting three-phase current signals are collected by the data acquisition system (DAQ) and displayed in the Labview system. Ultimately, the forces acting on the PDC cutter are derived according to the calibrated relationship with the current signals.

Figure 5.

A schematic (left) and photograph (right) of the experimental rig. Main components of the system include shaper, load cell, PDC cutter, rock sample, DAQ, and Labview system.

Experimental design

A key goal of the experiments is to compare the cutting mechanical properties of RLS PDC cutters with those of general PDC cutters. Therefore, both types are driven to scrape the rock with the same parameters, including the front rake of 15 degrees and the cutting depth of 3 mm. Under this condition, all the three cutting edges of RLS PDC cutters can participate in the scraping rock. Meanwhile, sandstone rock samples are utilized to avoid PDC cutter damage. Furthermore, in order to eliminate accidental errors, three PDC cutter samples in each category are selected and each PDC cutter sample scrapes the rock sample two times. Then, the six sets of the measured cutting, lateral, and longitudinal forces acting on each type of a PDC cutter are averaged to represent its cutting mechanical properties.

Experimental results

In Figure 6, an example family of time histories for the scrape experiments of RLS and general PDC cutters is presented. It can be seen that the cutting, lateral, and longitudinal forces acting on these two types of PDC cutters are always fluctuating. We selected the experimental results under the stable state (from step 200 to step 400) to calculate the average values and the root mean square (RMS) values of the three forces, which are listed in Table 1. It is important to state that step is a time scale related to the sampling frequency of DAQ.

Figure 6.

A sample of the recorded experimental time histories of the forces acting on two types of PDC cutters, where step is a time measurement. (a) The cutting force; (b) the longitudinal force; and (c) the lateral force.

Table 1.

The average and RMS values of the forces acting on RLS and general PDC cutters.

Type of force	Average value of experiment results		RMS value of experiment results
Type of force	General PDC cutter	RLS PDC cutter	General PDC cutter	RLS PDC cutter
Cutting force	196.339 N	85.241 N	84.449 N	63.505 N
Longitudinal force	290.428 N	99.314 N	131.055 N	59.931 N
Lateral force	−8.558 N	−0.034 N	15.251 N	4.896 N

RMS: root mean square; PDC: polycrystalline diamond compact; RLS: ridge-ladder shaped.

Through the comparison, it can be seen that the cutting, lateral, and longitudinal forces acting on RLS PDC cutters are less and have minor fluctuations compared to general PDC cutters, which indicates that the former has better cutting mechanical properties. Therefore, the unexpected vibration, for example, stick-slip and bit bounce, may be effectively mitigated by employing RLS PDC cutters, improving drilling speed and service life of a drill bit. Interestingly, the lateral forces acting on these two types of PDC cutters are at least 1 order of magnitude lower than the cutting and longitudinal forces, so that the lateral dynamical behaviors of any a full drill bit are ignored in subsequent research.

Rock-breaking mechanism analysis

According to the experimental conditions given in Section 2, both general and RLS PDC cutters are imposed to move with constant horizontal velocity $v_{c}$ and depth of cut $d$ . In this process, they have a cutting face of an inclination angle $θ$ with respect to the vertical direction $n$ . First, a perfectly sharp general PDC cutter is selected as the research object, the cutting behavior of which will form a notch of constant cross-section area $A^{g}$ in the horizontal direction $s$ , as shown in Figure 7(a). In the cutting process, a force $F_{c}^{g}$ is imparted by the rock on the general PDC cutter, and it can be decomposed into the cutting and longitudinal forces along parallel and normal to the rock surface, which are denoted as $F_{cs}^{g}$ and $F_{cn}^{g}$ , respectively. Meanwhile, the flat cutting face of the general PDC cutter makes the stress acting on the rock distributed along the contact region marked in red, as shown in Figure 7(b).

Figure 7.

Sketch of a sharp general PDC cutter scraping a rock on (a) longitudinal cross-section¹ and (b) lateral cross-section.

It is assumed that $F_{cs}^{g}$ and $F_{cn}^{g}$ are averaged over a much larger distance than the depth of cut $d$ . So, these two forces can be treated as being steady,^10,11 and their expressions are given by

F_{cs}^{g} = ε^{g} A^{g}, F_{cn}^{g} = ζ^{g} ε^{g} A^{g}

(1)

where $ε^{g}$ represents the amount of energy spent to crush a unit volume of rock by using general PDC cutters. $ζ^{g}$ is the ratio of its vertical to horizontal force acting on the cutting surface.

According to the geometrical relationships shown in Figure 7, the work area of a general PDC cutter on its cutting face can be given by the shaded area of Figure 8, in which $R$ represents the radius of the PDC cutter and the height of the work area is denoted as $h = d / \cos θ$ . $A^{g}$ can be obtained by projecting the work area to vertical direction, expressed as equation (2)

A^{g} = \cos θ [R^{2} \arccos (\frac{R - h}{R}) - (R - h) \sqrt{2 Rh - h^{2}}]

(2)

For a RLS PDC cutter, its ridge-shaped cutting faces and cutting edges with stepped distribution do not change the cylindrical shape of the cutter. Therefore, under the same radius, front rake, and depth of cut, RLS PDC cutters will generate a notch of the same cross-section area as the general PDC cutter, which means that $A^{I} = A^{g}$ . With reference to the cutting model of general PDC cutters, cutting force and longitudinal force imparted by rocks on RLS PDC cutters, denoted as $F_{cs}^{I}$ and $F_{cn}^{I}$ , respectively, can be expressed as

F_{cs}^{I} = ε^{I} A^{I} = ε^{I} A^{g}, F_{cn}^{I} = ζ^{I} ε^{I} A^{I} = ζ^{I} ε^{I} A^{g}

(3)

where $ε^{I}$ represents the amount of energy spent to cut a unit volume of rock by using RLS PDC cutters. $ζ^{I}$ is a number characterizing the orientation of its cutting force.

Figure 8.

Cutting face of the general PDC cutter, where the shaded area is its work area.

The experimental results given in Section 2 indicate that RLS PDC cutters have better cutting mechanical properties than general PDC cutters, which is due to the former’s special structure. As shown in Figure 9(a), the cutting edges with stepped distribution can decompose a total depth of cut $d$ into smaller chunks $d_{1}$ , $d_{2}$ , and $d_{3}$ . As illustrated in Figure 9(b), the ridge-shaped cutting face applies a concentrated load around the cusp area, so that the stress on the rock is much higher than that under the action of general PDC cutters. These two effects may lead RLS PDC cutters to remove rocks more effectively than general PDC cutters.

Figure 9.

Sketch of a sharp RLS PDC cutter scraping rock on (a) longitudinal cross-section and (b) lateral cross-section.

In order to verify the previous statement, the values of $ε^{g}$ and $ε^{I}$ are calculated and compared with each other on the basis of experimental conditions and results in Section 2. By substituting $R = 7.5 mm$ , $d = 3 mm$ , $θ = π / 12$ , $F_{cs}^{g} = 196.339 N$ , and $F_{cs}^{I} = 85.241 N$ into equations (1), (2), and (3), it can be seen that $ε^{g} = 7.69 MPa$ and $ε^{I} = 3.34 MPa$ , which indicates that RLS PDC cutters have higher cutting efficiency than general PDC cutters.

Effect of RLS PDC cutters on drilling performance

In order to obtain the performance of RLS PDC cutters under drilling conditions, the drilling behaviors of a new PDC bit fitted with some RLS PDC cutters are simulated using the finite element analysis method and are compared with those of a general PDC bit. The geometric models of the new and general PDC bits are illustrated in Figure 10(a) and (b), respectively, and their only difference is demonstrated only in their main PDC cutters, which are marked by the blue and red dotted ovals, respectively.

Figure 10.

Geometric models of two kinds of PDC bits used in simulation. (a) New PDC bit and (b) general PDC bit.

Finite element models

In this section, the finite element models of these two kinds of PDC bits drilling rocks are established by using ABAQUS software, as shown in Figure 11. Any finite element model includes three parts: reduced scale drill-string, drill bit, and rock. The reduced scale drill-string is composed of rotary table, flexible shaft, and bottom hole assembly (BHA), which are discretized using eight-node hexahedron reduced elements (C3D8R). The same element type is used for discretization of the rock. In addition, the four-node 3-D bilinear rigid quadrilateral unit (R3D4) is employed to mesh two types of PDC bits, which are modeled as discrete rigid bodies.

Figure 11.

Finite element models of the new and general PDC bits drilling rocks.

Nonlinearities of a full drill bit breaking rocks

A full drill bit breaking a rock is a complicated process and includes three main nonlinearity types,¹² for example, (i) the geometric nonlinearity caused by the large rotation and large drilling footage of a drill bit, (ii) the material nonlinearity caused by the large plastic strain to the occurrence of failure and even elimination of rock units, and (iii) the contact nonlinearity excited by the dynamic contact between the drill bit and rock, which is due to the combined action of the first two. In order to better understand the rock-breaking behaviors of a full drill bit, all the factors leading to nonlinearity should be mathematically expressed.

Dynamic model of the drill bit–rock interaction

Based on the finite element method, we set the occupying space domain of a contact system at any time $t$ as $Ω$ , and the body force, boundary force, and Cauchy stress interacting with the contact system as $b$ , $r$ , $r_{c}$ , and $σ$ , respectively. Then, the contact problem can be described by equation (4)¹³

\int_{Ω} σ δ ed Ω - \int_{Ω} b δ ud Ω - \int_{Γ_{f}} r δ edS - \int_{Γ_{c}} r_{c} δ udS + \int_{Ω} ρ a δ ud Ω = 0

(4)

where $Γ_{f}$ is the border for a given boundary force, $Γ_{c}$ is the contact boundary, $δ u$ is the virtual displacement, $δ e$ is the virtual strain, $ρ$ is the density, and $a$ is the acceleration. By discretizing space domain $Ω$ and introducing the virtual displacement field, the dynamic model describing the drill bit–rock interaction can be obtained as follows

M \overset{\cdot\cdot}{u} = p (t) + c (u, γ) - f (u, β)

(5)

where $M$ is the mass matrix, $\overset{\cdot\cdot}{u}$ is the acceleration vector, $p$ is the external force vector, $c$ is the contact force and friction vector, $f$ is the internal stress vector, $u$ is the object displacement, $γ$ is the relevant variable with the contact surface characteristics, and $β$ is the variable associated with the constitutive relation of materials.

Rock constitutive relation

The true stress–strain behavior of rock materials has obvious nonlinearities, which make numerical solution and simulation difficult. In order to balance calculation accuracy and cost, the Drucker–Prager strength criterion, which treats deviatoric stress as the primary cause of rock damage and can reflect the influence of volume stress on rock strength, is usually used to establish the constitutive model of the rock approximately,^14,15 especially in research for rock breaking of a full drill bit reported in this article. According to this criterion, the intermediate principal stress has an influence on rock damage, which is indicated by the normal stress $σ_{oct}$ and the shear stress $τ_{oct}$ on the surfaces of a regular octahedron¹⁶

τ_{oct} = τ_{0} + m σ_{oct}

(6)

where

{\begin{matrix} τ_{oct} = \frac{1}{3} \sqrt{{(σ_{1} - σ_{2})}^{2} + {(σ_{2} - σ_{3})}^{2} + {(σ_{3} - σ_{1})}^{2}} \\ σ_{oct} = \frac{1}{3} (σ_{1} + σ_{2} + σ_{3}) \\ m = - \sqrt{6} ψ, τ_{0} = \frac{\sqrt{6}}{3} k \end{matrix}

(7)

in which $σ_{1}$ , $σ_{2}$ , and $σ_{3}$ are the respective maximum principal stress, intermediate principal stress, and minimum principal stress of the rock. $k$ and $ψ$ are two material parameters relating only to the cohesion $ζ$ and the internal friction angle $φ$ , and their expressions are different for different stress Lode angle $θ_{σ}$ .

For compression hardening, $θ_{σ} = π / 6$ . In this case, $ψ$ and $k$ can be expressed as follows

ψ = \frac{2 \sin φ}{\sqrt{3} (3 - \sin φ)}, k = \frac{6 ζ \cos φ}{\sqrt{3} (3 - \sin φ)}

For tensile hardening, $θ_{σ} = - π / 6$ . In this case, the following relationship is used

ψ = \frac{2 \sin φ}{\sqrt{3} (3 + \sin φ)}, k = \frac{6 ζ \cos φ}{\sqrt{3} (3 + \sin φ)}

For shear hardening, $\tan θ_{σ} = - \sin φ / \sqrt{3}$ . In this case, $ψ$ and $k$ can be given by

ψ = \frac{\sin φ}{\sqrt{3 (3 + \sin^{2} φ)}}, k = \frac{\sqrt{3} ζ \cos φ}{\sqrt{3 + \sin^{2} φ}}

Rock damage criterion

It is known from damage mechanics that rock destruction is not a state but a process. Figure 12 shows a characteristic stress–strain curve of a rock, which indicates that there are three main stages from starting bearing load (point a) to complete damage (point d) of a rock, including a linear elastic stage (a–b), a plastic yield stage (b–c), and a damage evolution stage (c–d). In this figure, $σ_{y 0}$ and ${\bar{ε}}_{0}^{pl}$ are the respective stress and plastic strain of the rock at the beginning of damage, and ${\bar{ε}}_{f}^{pl}$ is the plastic strain of the rock when it reaches its complete damage state. Point c corresponds to the state at the onset of damage, and once beyond this point (c–d), the carrying capacity of the rock decreases obviously until complete failure. At this stage, the solid curve c–d can be viewed as the degeneration of the dotted curve c–d’ that represents the response of an undamaged rock.

Figure 12.

The stress–strain curve with rock damage evolution.

In Figure 12, the damage factor $D$ can be expressed as equation (8).¹⁷ Based on this, we can say that rock damage has two forms, one is yield stress softening $D \bar{σ}$ and the other one is the degradation of elasticity $(1 - D) E$

D = 1 - \frac{E'}{E} = {\begin{matrix} 0, (ε \leq {\bar{ε}}_{0}^{pl}) \\ 1 - \frac{σ}{\bar{σ}}, (ε > {\bar{ε}}_{0}^{pl}) \end{matrix}

(8)

where $E$ is the elasticity modulus of a rock before it experiences damage. $E'$ is the equivalent elasticity modulus of the rock during its damage evolution process. $\bar{σ}$ represents the rock stress in the absence of its damage. On the basis of equation (8), $D = 1$ corresponds to the complete failure of the rock, and at this time, rock elements begin to peel away from the matrix.

After comprehensive consideration, the plastic strain ${\bar{ε}}^{p}$ is employed as the rock damage criterion,¹⁸ which can be expressed as

{\bar{ε}}^{p} \leq {\bar{ε}}_{f}^{pl}

(9)

Boundary conditions and loading

The configuration of the FE model indicating boundary conditions and loads is shown in Figure 13, which is established on the basis of previous efforts.¹⁹ It can be seen that the lower surface of the rock is fully fixed. Meanwhile, the lateral motions of the rotary table and PDC bit are restricted and their rotations around both $x$ and $y$ axes are not allowed. In order to simulate their drilling behaviors, a constant rotational speed $Ω_{0} = 4.7 rad / s$ and a constant weight on bit (WOB) $W_{b} = 15 kN$ are imposed on the rotary table and the upper surface of the BHA, respectively. It is noted that the FE models of two kinds of PDC bits drilling rocks have identical boundary conditions and loads.

Figure 13.

Configuration diagram of boundary conditions and loads, in which $φ_{x}$ and $φ_{y}$ represent rotations around $x$ and $y$ axes, respectively.

Results and discussion

The angular velocity curves of the general and new PDC bits are shown in Figure 14. It can be seen that both kinds of PDC bits exhibit stick-slip vibration of different degrees, with repeated alternation of stick and slip phases. In the stick phase, the angular velocities of both PDC bits are equal to 0. Once they get into the slip phases, their angular velocities can be accelerated to several times higher than rotary table speed $Ω_{0}$ in a very short time, which leads to drill bit failure and a lower drilling efficiency.²⁰ Meanwhile, the stick phases of the new PDC bit are shorter than those of the general PDC bit, which indicates that the former has better continuous drilling capacity. According to the stick-slip vibration grading criterions of drilling tools shown in Table 2, which rules that the grade is higher and vibration is more serious, the stick-slip vibration of the general PDC bit is in grade 5 $(S_{1} = 1.103)$ and that of the new PDC bit is in grade 3 $(S_{1} = 0.790)$ . Therefore, it is concluded that employing RLS PDC cutters can reduce the stick-slip vibration of a full drill bit, which confirms the conclusion of the experimental data presented in Section 2.

Figure 14.

Angular velocity time history curves of the general and new PDC bits, where the black dotted line represents the angular velocity of 0 rad/s.

Table 2.

Stick-slip vibration on grading standards proposed by Baker Hughes.^21,22

Rank	Vibrational levels	Quantitative classification indexes
0	$0 \leq S_{1} < 0.2$	${\begin{matrix} S_{1} = \frac{(N_{max} - N_{min})}{2} \cdot N_{a} (Δ t = 7.5 s) \\ S_{2} = \frac{t_{bak}}{t_{total}} \times 100 % \end{matrix}$ where $N_{max}$ , $N_{min}$ , and $N_{a}$ are the maximum, minimum, and average angular velocities in a time interval $Δ t = 7.5 s$ , r/s, respectively. $t_{total}$ and $t_{bak}$ represent the total drilling time and the time consumption of backward whirling, s, respectively.
1	$0.2 \leq S_{1} < 0.4$
2	$0.4 \leq S_{1} < 0.6$
3	$0.6 \leq S_{1} < 0.8$
4	$0.8 \leq S_{1} < 1.0$
5	$1.0 \leq S_{1} < 1.2$
6	$1.2 \leq S_{1}$
7	$S_{2} > 0.1$

Interestingly, the backward rotation of the general PDC bit can be observed during its drilling process, which manifests as the rotational velocity less than 0, but this is not observed for the new PDC bit, as illustrated in Figure 14. For the general PDC bit, its backward rotation tends to cause a reversed reaction torque from the rock, which is represented as a torque greater than 0 (in the driving direction), as shown in Figure 15. For a single PDC cutter, a reversed cutting force $F_{r}$ will be formed, as shown in Figure 16. Due to a lack of support in the direction of $F_{r 2}$ , the PDC cutter is likely to fall off, which will greatly shorten the service life of a drill bit. Based on this analysis, we may safely arrive at the conclusion that the losing tooth failure of a drill bit can be alleviated to a certain extent by fitting RLS PDC cutters, reducing the drilling cost.

Figure 15.

Reaction torque acting on the general and new PDC bits from a rock, where the black dotted line represents the torque of 0 kN.m.

Figure 16.

Force diagram of a PDC cutter during backward rotation.

In addition, particular attention is given to the axial motions of both kinds of PDC bits. As can be seen from Figure 17(a), both the general and new PDC bits experience bit bounce of different degrees in the drilling process, which is characterized by the negative ROP for a short time interval. However, the bounce of the general PDC bit is more severe than that of the new PDC bit. In addition, the average ROPs of the general PDC bit and the new PDC bit are 6.428 and 6.487 mm/s, respectively, and their RMS values are 13.614 and 8.145 mm/s, respectively. Therefore, it can be said that the use of RLS PDC cutters can not only reduce the axial vibration of a full drill bit, but also improve its axial drilling speed, which is clearly demonstrated by the fact that the new PDC bit has a deeper drilling depth, as shown in Figure 17(b).

Figure 17.

Time history responses corresponding to the axial motions of the general and new PDC bits, where the black dotted line represents the drilling speed of 0 mm/s. (a) ROP and (b) footage.

Based on the above results of finite element analysis, it can be concluded that introducing RLS PDC cutters will effectively mitigate the undesired dynamic behaviors, such as stick-slip and bit bounce, which should help to prolong the service life of a drill bit and increase the efficiency of rock breaking. As a positive result, the drilling speed will have a noticeable improvement. Once again, it is important to emphasize that the primary purpose of this article was to propose a new PDC cutter structure to improve drilling performance (for example, vibration reduction and drilling speed improvement) and preliminarily demonstrating whether it reaches the expected goals or not. Therefore, this study is not involved in the processing technology of the new PDC cutter and its comprehensive influence on economic benefit, which will be further discussed in the future research.

Conclusion

We propose a RLS PDC cutter which has ridge-shaped cutting faces and multiple cutting edges with stepped distribution. This innovative cutting structure improves stress concentration acting on a rock and lowers MSE. Therefore, we hope to improve cutting efficiency and reduce instantaneous impact actions by adopting this new PDC cutter, reducing vibration, and improving the ROP.

RLS and general PDC cutters are manufactured by using the 3D printing technique and their scrape tests are carried out in a laboratory. The test results indicate that the cutting, lateral, and longitudinal forces acting on a RLS PDC cutter are smaller with less fluctuations compared to those acting on a general PDC cutter. Therefore, it can be concluded that a RLS PDC cutter has better cutting mechanical properties. In addition, it can also be concluded from test results that a RLS PDC cutter has higher cutting efficiency because of its particular rock breaking mechanism.

The drilling behavior characteristics of a new PDC bit fitted with some RLS PDC cutters are compared to those of a general PDC bit by means of finite element simulation. Simulation results show that introducing RLS cutters can reduce the stick-slip vibration, bit bounce, and backward rotation of a drill bit effectively, improving subsequently the ROP.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was financially supported by the Sichuan Science and Technology Program (No. 2019YJ0536) and the National Natural Science Foundation of China (No. 51904263).

ORCID iDs

Zhiqiang Huang

Yachao Ma

Author biographies

Dou Xie is a Doctor in the School of Mechanical Engineering, Southwest Petroleum University, Sichuan, China. His research focuses on drill-string dynamics.

Zhiqiang Huang is a Professor in the School of Mechanical Engineering, Southwest Petroleum University, Sichuan, China. His research focuses on oil and gas equipment.

Yuqi Yan is a Master Student in the School of Mechanical Engineering, Southwest Petroleum University, Sichuan, China. Her research focuses on rock mechanics.

Yachao Ma is a Lecturer in the School of Mechanical Engineering, Southwest Petroleum University, Sichuan, China. His research focuses on the structure optimization of PDC bit.

Yuan Yuan is a patent examiner in the General Machinery Section of Machinery Department, CNIPA, Sichuan, China. Her research focuses on the advanced material of PDC bit.

References

Huang

, et al. Geometry and force modeling, and mechanical properties study of polycrystalline diamond compact bit under wearing condition based on numerical analysis. Adv Mech Eng 2017; 9(6): 1–15.

Huang

Yang

, et al. The improved rock breaking efficiency of an annular-groove PDC bit. J Petrol Sci Eng 2019; 172: 425–435.

Liu

Lin

Páez Chávez

, et al. Torsional stick-slip vibrations and multistability in drill-strings. Appl Math Model 2019; 76: 545–557.

DiGiovanni

Stockey

Fuselier

, et al. Innovative non-planar face PDC cutters demonstrate 21% drilling efficiency improvement in interbedded shales and sand. In: Proceedings of IADC/SPE Drilling Conference and Exhibition, Fort Worth, TX, 4–6 March 2014, SPE No. 168000. Richardson, TX: Society of Petroleum Engineers (SPE).

Ford

. Rolling PDC cutter enhances drill bit life in Granite Wash runs, http://www.drillingcontractor.org/rolling-pdc-cutter-enhances-drill-bit-life-in-granite-wash-runs-29798 (accessed 24 July 2015).

Rodriguez

Laguna

Gomez Caselles

, et al. Durable yet aggressive conical diamond element bit increases ROP by 34% drilling difficult lower chert/conglomerate section, Ecuador. In: Proceedings of SPE Latin American and Caribbean Petroleum Engineering Conference, Quito, Ecuador, 18–20 November 2015, SPE No. 177085. Richardson, TX: Society of Petroleum Engineers (SPE).

Pak

Azar

Bits

, et al. Conical diamond element enables PDC bit to efficiently drill chert interval at high ROP replacing turbine/impregnated BHA. In: Proceedings of IADC/SPE Drilling Conference and Exhibition, Fort Worth, TX, 1–3 March 2016, SPE No. 178765. Richardson, TX: Society of Petroleum Engineers (SPE).

Crane

Zhang

Douglas

, et al. Innovative PDC cutter with elongated ridge combines shear and crush action to improve PDC bit performance. In: Proceedings of SPE Middle East Oil & Gas Show and Conference, Manama, Kingdom of Bahrain, 6–9 March 2017, SPE No. 183984. Richardson, TX: Society of Petroleum Engineers (SPE).

Al-Ajmi

Rushoud

Gohain

, et al. Innovative drill bit technology with unique geometry cutting structure sets drilling record in harsh rock application. In: Proceedings of Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, UAE, 12–15 November 2018, SPE No. 193035. Richardson, TX: Society of Petroleum Engineers (SPE).

10.

Detournay

Defourny

. A phenomenological model for the drilling action of drag bits. Int J Rock Mech Min 1992; 29(1): 13–23.

11.

Richard

Germay

Detournay

. A simplified model to explore the root cause of stick–slip vibrations in drilling systems with drag bits. J Sound Vib 2007; 305(3): 432–465.

12.

Zhu

Liu

Tong

. Analysis of reamer failure based on vibration analysis of the rock breaking in horizontal directional drilling. Eng Fail Anal 2014; 37: 64–74.

13.

Wang

Zhu

Song

, et al. Non-linear dynamic analysis of a roller cone bit-well rock system with rock-cone bit interaction. J Vib Shock 2010; 29(10): 108–112.

14.

Liebe

Willam

. Localization properties of generalized Drucker–Prager elastoplasticity. J Eng Mech 2001; 127(6): 616–619.

15.

Alejano

Bobet

. Drucker–Prager criterion. Rock Mech Rock Eng 2012; 45(6): 995–999.

16.

Zhu

Jia

. 3D mechanical modeling of soil orthogonal cutting under a single reamer cutter based on Drucker–Prager criterion. Tunn Undergr Sp Tech 2014; 41: 255–262.

17.

Lin

Lian

Meng

, et al. Finite elements method study on dynamic rock breaking in air drilling. Chin J Rock Mech Eng 2008; 27(Suppl2): 3592–3597.

18.

Zhu

Tang

Tong

. Effects of high-frequency torsional impacts on rock drilling. Rock Mech Rock Eng 2014; 47: 1345–1354.

19.

Kapitaniak

Vaziri Hamaneh

Páez Chávez

, et al. Unveiling complexity of drill-string vibrations: experiments and modelling. Int J Mech Sci 2015; 101–102: 324–337.

20.

Kovalyshen

. Understanding root cause of stick-slip vibrations in deep drilling with drag bits. Int J Nonlinear Mech 2014; 67: 331–341.

21.

Zou

, et al. Drillstring dynamics and control technologies and new progress. Petrol Eng 2006; 34(6): 7–10.

22.

Huang

Xie

, et al. Investigation of PDC bit failure base on stick-slip vibration analysis of drilling string system plus drill bit. J Sound Vib 2018; 417: 97–109.

Application of an innovative ridge-ladder-shaped polycrystalline diamond compact cutter to reduce vibration and improve drilling speed

Abstract

Keywords

Introduction

Scrape experiment of a single PDC cutter

Experimental rig and principles

Experimental design

Experimental results

Rock-breaking mechanism analysis

Effect of RLS PDC cutters on drilling performance

Finite element models

Nonlinearities of a full drill bit breaking rocks

Dynamic model of the drill bit–rock interaction

Rock constitutive relation

Rock damage criterion

Boundary conditions and loading

Results and discussion

Conclusion

Footnotes

Declaration of conflicting interests

Funding

ORCID iDs

Author biographies

References