A design method of a PDC cone combined bit with blades

Abstract

This invention relates to a design method for a blade-type PDC roller cone composite drill bit, a design method for oil and gas well drilling tools, belonging to the field of oil and gas well drilling tool and rock-breaking tool design. The method first obtains the shear strength and internal friction angle of the formation through field logging data, then determines the drill bit diameter based on drilling conditions, then determines the number of roller cones based on the drill bit diameter, then determines the radial position and radial coverage area of ​​the roller cones based on the drill bit diameter and the formation internal friction angle, and finally determines the axial tilt angle of the roller cones based on the formation shear strength value. This invention combines field test data, classification discussion, and numerical calculation to design the structural parameters of the composite drill bit roller cones, providing theoretical support for the optimized design of blade-type PDC roller cone composite drill bits, thereby improving the application range of blade-type PDC roller cone composite drill bits.

Description

Technical Field

[0001] This invention relates to a design method for a blade-type PDC roller cone composite drill bit, belonging to the field of design science for oil and gas well drilling tools and rock breaking tools. Background Technology

[0002] PDC drill bits rely on high-hardness, wear-resistant, and self-sharpening polycrystalline diamond composite plates (PDC teeth or cutting teeth) as cutting elements to shear and break rocks. PDC drill bits offer high mechanical drilling speeds, long service life, and low drilling costs in soft to medium-hard formations, making them widely used in oil and gas well drilling. In oil and gas drilling, the geological conditions of the formations are often complex. Deep formations such as shale and argillaceous sandstone, under the pressure of the overlying formation and high-density drilling fluid, not only increase in density and hardness but also transform from brittle rocks under normal pressure to ductile-brittle or ductile rocks. Furthermore, the hydraulic energy in deep well sections is severely insufficient, failing to effectively utilize hydraulic-assisted rock breaking, resulting in extremely low rock-breaking efficiency for the drill bit.

[0003] Tricone drill bits break rocks by impacting them under heavy loads. They are used in heterogeneous formations, gravel formations, and extremely heterogeneous formations. In directional and horizontal wells, the torque fluctuation of tricone drill bits is relatively small, and the bottom tool face is easy to control. However, the mechanical drilling rate of tricone drill bits is too low.

[0004] The blade-type PDC roller cone composite drill bit features one or more grooves on its blades, within which roller cones are placed. The roller cones have teeth, and the blades directly support them, eliminating the need for a toothed structure and saving valuable drill bit space. This significantly increases the thickness of the roller cone housing, effectively reducing downhole accidents caused by roller cones falling to the bottom of the well due to shell cracking or breakage. The roller cone bearings, connected by double supports, significantly improve the bearing's stress distribution, greatly increasing the bearing system's load-bearing capacity. With uniform stress distribution, the bearing's sealing ability is enhanced, extending the bearing system's lifespan and thus the drill bit's overall lifespan. However, the design of the roller cone structure in composite drill bits relies entirely on the designer's experience. Therefore, proposing a design method for blade-type PDC roller cone composite drill bits is crucial for further improving their performance and expanding their application areas.

[0005] Suppose the drill bit has a cutting plane passing through its axis and a point on the drill bit (called the axial plane or axial surface passing through that point). When the drill bit rotates around its own axis at zero drilling speed, the contour lines of the cutting elements intersect the cutting plane or axial surface to form an intersection line. This intersection line is the axial contour line of the cutting elements. The axial contour lines of all cutting elements are gathered together to form the bottom-hole radial coverage diagram of the drill bit. In this diagram, an envelope curve tangent to the axial contour lines of all cutting elements can be drawn; this is called the drill bit cutting contour line. The drill bit cutting contour line reflects the basic shape characteristics of the bottom of the well drilled by the drill bit. The drill bit body contour line is the position curve of the drill bit body reflected in the bottom-hole coverage diagram; it is an important characteristic curve of diamond drill bits. It's worth noting that the drill bit cutter wing body contour line and the cutter wing cutting contour line should not include the drill bit gauge protection section. This is derived from the definition of the cutter wing cutting contour line and body contour line. The main cutting teeth in a drill bit generally refer to cutting elements with longitudinal cutting capabilities, while the gauge protection teeth in the gauge protection section do not have longitudinal cutting capabilities. Therefore, the main cutting teeth do not include the gauge protection teeth. Thus, the cutter wing cutting contour line and body contour line should start from the drill bit center and end at the gauge protection teeth. The drill bit tooth distribution surface refers to the curved surface formed by rotating around the drill bit axis as the center of rotation and the drill bit body contour line as the radius of rotation, intersecting with the drill bit body. Summary of the Invention

[0006] To address the issue of relying solely on experience in designing the annular groove structure of existing composite drill bits, this invention proposes a design method for a blade-type PDC roller cone composite drill bit. First, formation shear strength and internal friction angle are obtained using field logging data. Then, the drill bit diameter is determined based on drilling conditions. Next, the number of roller cones is determined based on the drill bit diameter, and the cones are evenly distributed across different blades. Subsequently, the radial position and coverage area of ​​the roller cones are determined based on the drill bit diameter and formation internal friction angle. Finally, the axial tilt angle of the roller cones is determined based on the formation shear strength. This invention combines field test data, classification discussions, and numerical calculations to design the roller cone structure parameters of the composite drill bit. Its high calculation accuracy provides theoretical support for the personalized design of blade-type PDC roller cone composite drill bits, thereby expanding the applicability of blade-type PDC roller cone composite drill bits.

[0007] This invention is achieved through the following technical solutions:

[0008] 1. A design method for a blade-type PDC roller cone composite drill bit, comprising a drill body, fixed blades, roller cones, and a water hole, wherein the fixed blades have cutting teeth, the roller cones have teeth, at least one fixed blade has one or more grooves, the roller cones are disposed in the grooves, and the roller cones are rotatably connected to the fixed blades via roller cone shafts, characterized in that: the design method for the blade-type PDC roller cone composite drill bit includes the following steps:

[0009] ①The shear strength of the formation is obtained through well logging data. t c The unit is MPa, and the internal friction angle of the formation. f, The unit is °;

[0010] ② Determine the diameter of the drill bit according to the drilling conditions. D b The unit is mm;

[0011] ③According to the drill bit diameter D b The total number of compound drill bit roller cones is calculated according to formula (1). G， The unit is a single piece, and the toothed cones are set on different fixed blades according to the principle of uniform distribution;

[0012] (1)

[0013] The above formula states G This indicates the number of toothed cones in the drill bit, expressed in units of individual cones. D b The drill bit diameter is in mm.

[0014] ④ According to the drill bit diameter D b Internal friction angle of the formation f, The radial position H of the roller cone is obtained according to formula (2), with the unit being mm. The radial position of the roller cone refers to the distance from the intersection of the roller cone axis and the end face to the drill axis. The radial coverage area W of the roller cone is obtained according to formula (3), with the unit being mm. The coverage area of ​​the roller cone refers to the spatial distance occupied by the two end faces of the roller cone in the radial coverage diagram of the drill bit.

[0015] (2)

[0016] (3)

[0017] In the above formula, H represents the radial position of the roller cone, in mm, and W represents the radial coverage area of ​​the roller cone, in mm. D b This refers to the drill bit diameter, in mm. f This represents the internal friction angle within the formation, expressed in degrees (°).

[0018] ⑤ Based on the shear strength of the rock t c The axial tilt angle of the roller is calculated according to formula (4). β， The unit is °, where the roller cone axis inclination angle refers to the angle between the roller cone axis and the drill bit axis in the drill bit radial overlay diagram;

[0019] (4)

[0020] The above formula states β The axial inclination angle of the gear is expressed in degrees (°). t c Shear strength of the formation, expressed in MPa.

[0021] Existing PDC (Polydioxanone Cone) composite drill bit designs primarily rely on experience. The cones in these bits are mainly derived from the cones and shanks of ternary cone drills. Consequently, the axial tilt angle of the cones in existing composite drill bits is limited to between 56° and 60°, preventing the achievement of larger angles. Furthermore, the cutting profile of the cones is influenced by the existing cones, hindering the free design of the cone structure in composite drill bits. This invention proposes a cutter-wing type PDC composite drill bit that eliminates the shank structure of existing composite drill bits, saving limited tooth placement space on the drill bit. The cones and cone shafts can be integrated or separate. The cone shafts are connected to the cutter-wing body on both sides, and this dual-sided support significantly improves the stress distribution on the bearings, greatly increasing the bearing capacity of the bearing system. Under uniform stress distribution, the bearings' sealing ability is enhanced, extending the bearing system's lifespan and thus improving the overall lifespan of the drill bit. Due to the greatly improved flexibility of the roller cone shaft, the axial tilt angle of the blade-type PDC roller cone composite drill bit has been significantly increased, with its axial tilt angle range expanding to 50° to 75°. At the same time, the design flexibility of the roller cone cutting area coverage area of ​​the new drill bit has also been greatly improved.

[0022] The design method of the blade-type PDC roller cone composite drill bit described in this invention conducts in-depth research on the torsion reduction and vibration reduction effects of the composite drill bit. First, the formation shear strength and internal friction angle are obtained through field logging data. Then, the drill bit diameter is determined based on drilling conditions. Next, the number of roller cones is determined based on the drill bit diameter, and the roller cones are evenly distributed on different blades. Then, the radial position and coverage area of ​​the roller cones are determined based on the drill bit diameter and the formation internal friction angle. Finally, the axial tilt angle of the roller cones is determined based on the formation shear strength, and relevant calculation formulas are established to ensure that the roller cone structural parameters are the optimal parameters for the comprehensive performance of the composite drill bit. This improves the rock-breaking efficiency and service life of the composite drill bit, provides theoretical support for the personalized design of blade-type PDC roller cone composite drill bits, and thus expands the application range of blade-type PDC roller cone composite drill bits. Attached Figure Description

[0023] Figure 1 A schematic diagram and design method diagram of a blade-type PDC roller cone composite drill bit;

[0024] Figure 2 This is a schematic diagram of the roller cone structure parameters of a composite drill bit;

[0025] 1-Drill body, 2-Fixed cutter blade, 21-PDC tooth, 3-Roller cone, 31-Tooth, 32-Roller cone shaft, 4-Water hole, 5-Groove. Detailed Implementation

[0026] 1. A design method for a blade-type PDC roller cone composite drill bit, comprising a drill body, fixed blades, roller cones, and a water hole, wherein the fixed blades have cutting teeth, the roller cones have teeth, at least one fixed blade has one or more grooves, the roller cones are disposed in the grooves, and the roller cones are rotatably connected to the fixed blades via roller cone shafts, characterized in that: the design method for the blade-type PDC roller cone composite drill bit includes the following steps:

[0027] ①The shear strength of the formation is obtained through well logging data. t c The unit is MPa, and the internal friction angle of the formation. f, The unit is °;

[0028] ② Determine the diameter of the drill bit according to the drilling conditions. D b The unit is mm;

[0029] ③According to the drill bit diameter D b The total number of compound drill bit roller cones is calculated according to formula (1). G， The unit is a single piece, and the toothed cones are set on different fixed blades according to the principle of uniform distribution;

[0030] (1)

[0031] The above formula states G This indicates the number of toothed cones in the drill bit, expressed in units of individual cones. D b The drill bit diameter is in mm.

[0032] ④ According to the drill bit diameter D b Internal friction angle of the formation f, The radial position H of the roller cone is obtained according to formula (2), with the unit being mm. The radial position of the roller cone refers to the distance from the intersection of the roller cone axis and the end face to the drill axis. The radial coverage area W of the roller cone is obtained according to formula (3), with the unit being mm. The coverage area of ​​the roller cone refers to the spatial distance occupied by the two end faces of the roller cone in the radial coverage diagram of the drill bit.

[0033] (2)

[0034] (3)

[0035] In the above formula, H represents the radial position of the roller cone, in mm, and W represents the radial coverage area of ​​the roller cone, in mm. D b This refers to the drill bit diameter, in mm. f This represents the internal friction angle within the formation, expressed in degrees (°).

[0036] ⑤ Based on the shear strength of the rock t c The axial tilt angle of the roller is calculated according to formula (4). β， The unit is °, where the roller cone axis inclination angle refers to the angle between the roller cone axis and the drill bit axis in the drill bit radial overlay diagram;

[0037] (4)

[0038] The above formula states β The axial inclination angle of the gear is expressed in degrees (°). t c Shear strength of the formation, expressed in MPa.

[0039] Known compressive strength of the strata t c The pressure is 100 MPa, the internal friction angle of the formation is 30°, and the drill bit diameter is determined based on the drilling conditions. D b The diameter is 215.9 mm. Based on the formula above, the number of roller cones in this drill bit can be calculated. G There are 3 rollers, with a radial position H of 72.32 mm. The radial coverage area is... W The axial tilt angle of the roller is 27.38 mm. β It is 62.8 ° .

[0040] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A design method for a blade-type PDC roller cone composite drill bit, comprising a drill body, fixed blades, roller cones, and a water hole, wherein the fixed blades have cutting teeth, the roller cones have teeth, at least one fixed blade has one or more grooves, the roller cones are disposed in the grooves, and the roller cones are rotatably connected to the fixed blades via roller cone shafts, characterized in that: The design method for blade-type PDC roller cone composite drill bits includes the following steps: ①The shear strength of the formation is obtained through well logging data. τ c The unit is MPa, and the internal friction angle of the formation. φ, The unit is °; ② Determine the diameter of the drill bit according to the drilling conditions. D b The unit is mm; ③According to the drill bit diameter D b The total number of compound drill bit roller cones is calculated according to formula (1). G， The unit is a single piece, and the toothed cones are set on different fixed blades according to the principle of uniform distribution; （1） The above formula states G This indicates the number of toothed cones in the drill bit, expressed in units of individual cones. D b The drill bit diameter is in mm. ④ According to the drill bit diameter D b Internal friction angle of the formation φ, According to formula (2), the radial position H of the roller cone is obtained in mm. The radial position of the roller cone refers to the distance from the intersection of the roller cone axis and the end face to the drill axis. According to formula (3), the coverage area W of the roller cone is obtained in mm. The coverage area of ​​the roller cone refers to the spatial distance occupied by the two end faces of the roller cone in the radial coverage diagram of the drill bit. （2） （3） In the above formula, H represents the radial position of the roller cone, in mm, and W represents the radial coverage area of ​​the roller cone, in mm. D b This refers to the drill bit diameter, in mm. φ This represents the internal friction angle within the formation, expressed in degrees (°). ⑤ Based on the shear strength of the rock τ c The axial tilt angle of the roller is calculated according to formula (4). β， The unit is °, where the roller cone axis inclination angle refers to the angle between the roller cone axis and the drill bit axis in the drill bit radial overlay diagram; （4） The above formula states β The axial inclination angle of the gear is expressed in degrees (°). τ c Shear strength of the formation, expressed in MPa.

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