Design method of PDC (Polycrystalline Diamond Compact) drill bit scraping group

Abstract

The invention discloses a design method of a PDC (Polycrystalline Diamond Compact) drill bit scraping group, and belongs to the field of oil and gas well drill bit design science. According to the method, a rock anti-drilling characteristic experiment test is carried out by utilizing a stratum rock core to obtain compressive strength, hardness and abrasiveness grade values of stratum rock, and a calculation method of an included angle between crushing units in a scraping group is established. And then according to the included angle between the crushing units, the design distance between the crushing units is obtained through theoretical calculation, and efficient utilization of the tooth distribution space of the drill bit is ensured. And finally, calculating the radius of the invasion blade of the crushing unit in the scraping group according to the stratum hardness value. According to the design method, the problem that the scraping groups of the PDC drill bit in different stratums depend on experience design can be solved, and a basis is provided for design of the novel and efficient PDC drill bit with the scraping groups.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling tool design, and more specifically, to a design method for a PDC drill bit scraping assembly. Background Technology

[0002] Polycrystalline Diamond Compact (PDC) drill bits are crucial tools in existing underground energy drilling projects, such as those for oil and gas. They rely on high-hardness, wear-resistant, and self-sharpening superhard materials (including diamond composites, ceramics, and cemented carbide) as cutting elements to cut and break rocks, forming wellbores and establishing connections between oil and gas resources and the surface. With the rapid advancement of cutting tooth material technology, PDC drill bits are increasingly widely used in oil and gas drilling, geothermal drilling, and even underground space engineering, significantly surpassing roller cone drill bits in the total drilling footage.

[0003] The lithology of underground rock formations varies greatly. Deep formations have high rock hardness, strong abrasiveness, and poor drillability, making it difficult for drill bits to penetrate and causing rapid wear and failure. This results in frequent tripping in and out of the drill string, leading to long drilling cycles and high costs. In contrast, softer formations do not present penetration problems, resulting in high drilling efficiency. Drill bit technologies for different formations are constantly evolving, with drill bit developers continuously innovating and proposing many new technologies. Both domestic and international companies have launched customized products specifically for deep, difficult-to-drill formations, achieving good application results. For directional wells or heterogeneous formations such as mixed hard and soft formations, adaptive drill bits have been developed, incorporating depth control devices on PDC drill bits.

[0004] Suppose that the drill bit has a cutting plane passing through the drill bit axis and a certain point on the drill bit (called the axis plane or axial surface passing through that point). When the drill bit rotates around its own axis under the condition of zero drilling speed, the contour lines of the cutting elements intersect with the cutting plane or axial surface to form an intersection line. This intersection line is the axial surface contour line of the cutting elements. The axial surface contour lines of all the cutting elements are gathered together to form the bottom cover map of the drill bit. In the bottom cover map, an envelope curve tangent to the axial surface contour lines of all the 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.

[0005] Currently, the design method for drill bits based on formation lithology usually involves changing the shape of the cutting structure and the density of the cutting teeth on the drill bit, rather than changing the design method of the scraping assembly based on the characteristics of the formation to achieve efficient drilling. Summary of the Invention

[0006] To address the issue that conventional PDC drill bits rely on empirical methods of adjusting tooth density to improve their penetration capability, this invention proposes a design method for a PDC drill bit scraping assembly. Through the design of the scraping assembly, the penetration capability of drill bits in different formations can be effectively improved.

[0007] This invention is implemented as follows: A design method for a PDC drill bit scraping assembly, wherein at least one scraping assembly is provided on the drill bit body, the scraping assembly consists of two crushing units, each crushing unit including an intrusion cutting edge and an intrusion edge, the intrusion edges of the two crushing units in the scraping assembly are arranged adjacent to each other, and the design method for the PDC drill bit scraping assembly includes the following steps: Step S1: Obtain the uniaxial compressive strength of the rock based on the drill resistance test. Rock abrasiveness grade and rock plasticity coefficient The target formation temperature is obtained based on the logging technology. The included angle between the two crushing units in the scraping group is calculated using formula (1); (1) In the formula, The angle between the edges of the two crushing units in the scraping group, in degrees; This represents the uniaxial compressive strength of the rock, expressed in MPa. The grinding coefficient is dimensionless. This is the temperature coefficient, dimensionless. Grinding coefficient The value is determined according to formula (2), where the rock abrasiveness grade value is... Dimensionless; (2) Temperature coefficient The value is determined according to formula (3), where The target formation temperature is expressed in degrees Celsius. (3) Step S2: Based on the included angle and length The edge penetration distance between the two crushing units in the scraping group is calculated according to formula (4). ; (4) In the formula, The distance between the edges of the two crushing units in the scraping group is in mm; The length of the edge of the crushing unit in the scraping and cutting group, in mm; The included angle between the edges of the two crushing units in the scraping group, in degrees; Step S3: Based on the rock plasticity coefficient and the length of the intrusion The radius of the intrusion blade of the crushing unit is calculated according to formula (5). ; (5) In the formula, The radius of the intrusion blade of the crushing unit is in mm; is the rock plasticity coefficient, dimensionless; The length of the edge of the crushing unit is in mm.

[0008] The included angle between the two breaking units in the scraping group is crucial, directly affecting the penetration capability in formations of varying hardness. Current drill bit technology relies on experience to alter the penetration capability by changing the number of cutting teeth and the shape of the cutting structure, which is ineffective and can even lead to premature drill bit failure. This solution utilizes scientific calculation methods to control the penetration capability of the scraping group by changing the included angle between the adjacent penetration edges of the two breaking units in the scraping group, thereby altering the contact length between the penetration edge and the formation and the penetration direction of the penetration edge. It should be noted that when the penetration edge lengths of the two breaking units in the scraping group are inconsistent, the values ​​in formulas (4) and (5) will differ. The calculation is based on the longer of the two encroaching sides.

[0009] Preferably, the crushing unit in the scraping group is a semi-circular tooth.

[0010] In the above scheme, the crushing unit in the scraping group is a semi-circular tooth, which means that it is directly cut based on the existing circular tooth or elliptical tooth. The semi-circular tooth crushing unit is easy to process, has a mature welding process, and has high reliability.

[0011] Preferably, the shape of the edge of the breaking unit includes: a straight line, a circular arc, and a spline curve.

[0012] When the edge of the crushing unit has a complex shape, its length is calculated as the line connecting the starting point and the ending point of the edge, and the corresponding center point of the edge is the midpoint of the line connecting the starting point and the ending point of the edge.

[0013] Preferably, the two crushing units in the scraping group are arranged on the same substrate.

[0014] In the above solution, the scraping assembly is set on a scraping assembly base and then on the drill bit body, making replacement easier when a scraping assembly fails. Currently, the cutting teeth on drill bits are fixed to the drill bit by welding, which requires complex processes for replacement when damaged, and may even result in unsuccessful replacement.

[0015] As a further preferred option, the scraping assembly base and the drill bit body are connected in a replaceable manner, including bolt connection.

[0016] This invention provides a design method for a PDC drill bit scraping assembly. Based on drilling resistance tests of geological core samples, the uniaxial compressive strength, plasticity coefficient, and abrasiveness grade of the target formation are determined. The temperature of the target formation is obtained through logging. The included angle between two adjacent intrusion edges in the scraping assembly is calculated using theoretical methods. Based on the included angle and the length of the intrusion edge, the arrangement distance between the breaking units in the scraping assembly is calculated. The radius of curvature of the intrusion edge of the breaking unit is determined based on the formation plasticity coefficient. This invention, without changing the shape of the drill bit's cutting structure or the tooth density, significantly improves the drill bit's compatibility with different formations through theoretical design. When the scraping assembly is set on the substrate, it can be replaced on the drill bit in a replaceable manner, allowing for rapid replacement if the scraping assembly fails. The scraping assembly can also be set at any position on the drill bit, greatly increasing the design freedom of the drill bit. The distance calculation of the breaking units in the scraping assembly ensures the welding strength of the breaking units, preventing interference between them while making more rational use of the scraping assembly substrate space. When the scraping group forms an inverted trapezoidal rock ridge, it can cause volumetric rock fragmentation, improving rock breaking efficiency. This design method can solve the problem of relying on experience in the design of PDC drill bits, and provide theoretical support for the personalized design of this type of drill bit. Attached Figure Description

[0017] To more clearly illustrate the technical methods of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 Flowchart of the design method for PDC drill bit scraping assembly; Figure 2 This is a schematic diagram showing the arrangement of the scraping group in the radial coverage of the drill bit teeth, with a negative edge penetration angle. Figure 3 This is a schematic diagram illustrating the definition of the included angle between two adjacent sides of the crushing unit in the scraping group; Figure 4 This is a schematic diagram of the interaction between the scraping group and the rock; Figure 5 This is a schematic diagram of the edge penetration of the crushing unit in the scraping group as a spline curve; Figure 6 A schematic diagram showing a scraping assembly having a scraping assembly base and being fixed to the drill bit body by bolt fastening; Figure 7 This is a schematic diagram of rock breaking when the included angle of the crushing unit in the scraping group is positive.

[0019] The markings in the diagram are: 1—scraping group; 2—crushing unit; 3—penetrating edge; 4—edge penetration; 40—edge penetration equivalent line; 41—edge penetration start point; 42—edge penetration end point; 5—fixed cutting tooth; 6—auxiliary tooth; 10—scraping group base; 11—fastening bolt; 12—drill bit body; 20—rock. Detailed Implementation

[0020] To make the objectives, technical methods, and advantages of the embodiments of the present invention clearer, the technical methods and solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0021] like Figures 1 to 6 A design method for a PDC drill bit scraping assembly 1, wherein at least one scraping assembly 1 is provided on the drill bit body 12, the scraping assembly 1 is composed of two crushing units 2, the crushing unit 2 includes an intrusion blade 3 and an intrusion edge 4, and the intrusion edges 4 of the two crushing units 2 in the scraping assembly 1 are arranged adjacent to each other, characterized in that the design method for the PDC drill bit scraping assembly 1 includes the following steps: Step S1: Obtain the uniaxial compressive strength of the target layer rock based on the drill resistance test. Target stratum rock abrasiveness grade and rock plasticity coefficient ， The target formation temperature is obtained based on well logging techniques. The included angle between the intrusion edges 4 of the two crushing units 2 in the scraping group 1 is calculated using formula (1). (1) In the formula, The included angle between the two crushing units 2 and the edge 4 in the scraping group 1, in degrees; This represents the uniaxial compressive strength of the rock, expressed in MPa. The grinding coefficient is dimensionless. This is the temperature coefficient, dimensionless. Grinding coefficient The value is determined according to formula (2), where the rock abrasiveness grade value is... Dimensionless; (2) Temperature coefficient The value is determined according to formula (3), where The target formation temperature is expressed in degrees Celsius. (3) Step S2: Based on the included angle of the intrusion edge 4 in the scraping group 1 and length The distance between the two encroaching edges 4 in the scraping group 1 is calculated according to formula (4). ; (4) In the formula, The distance between the two intrusion edges 4 in scraping group 1 is in mm; The length of the intrusion edge 4 of the crushing unit 2 in the cutting and scraping group 1 is in mm; The included angle between the intrusion edges 4 of the two crushing units 2 in the scraping group 1, in degrees; Step S3: Based on the rock plasticity coefficient and the length of the intrusion edge 4 The radius of the intrusion blade 3 of the crushing unit 2 is calculated according to formula (5). ; (5) In the formula, The radius of the intrusion blade 3 of the crushing unit 2 is in mm; is the rock plasticity coefficient, dimensionless; The length of the intrusion edge is 4 mm.

[0022] The included angle between the breaking units 2 in the scraping group 1 is crucial, as it directly affects the penetration capability in different formations. Current drill bit technology relies on experience to alter the penetration capability of the drill bit by changing the number of cutting teeth and the shape of the cutting structure. This method is ineffective and can even cause premature drill bit failure. In this scheme, mathematical calculations are used to change the included angle between the penetration edges 4 of the two breaking units 2 in the scraping group 1, further altering the contact length between the penetration blade 3 and the formation and the penetration direction of the penetration edge 4, thereby controlling the penetration capability of the scraping group 1. When the uniaxial compressive strength of the formation is below 40 MPa, the included angle between the penetration edges 4 of the two breaking units 2 in the scraping group 1 calculated by formula (1) is negative. Please refer to... Figure 2The radial coverage diagram at the bottom of the well is shown. Here, it is defined that when the included angle of the intrusion edge 4 is negative, the distance between the starting points 41 of the intrusion edges 4 of the two breaking units 2 is greater than the distance between the ending points 42 of the two intrusion edges, meaning the direction of the resulting open space is upward; conversely, it is positive. When the formation is relatively soft, the included angle of the intrusion edge 4 is negative, the intrusion blade 3 contacts the rock 20, and the breaking unit 2 penetrates more into the formation, improving the cutting efficiency of soft formations. When the formation is relatively hard, the included angle of the intrusion edge 4 decreases, gradually becoming more vertical, or the included angle of the intrusion edge 4 becomes positive (the sharp shape formed by the intrusion blade 3 and the intrusion edge 4 faces the formation, making it easier to penetrate). The contact between the intrusion blade 3 and the rock 20 decreases, increasing the specific pressure of the scraping group 1 and improving the drill bit's penetration capability. Please refer to [link to relevant documentation]. Figure 7 .

[0023] It is worth noting that when the included angle of the intrusion edge 4 of the scraping group 1 is negative, the scraping group 1 can form a shape like this when cutting the rock. Figure 4 The inverted trapezoidal (bcfe) shown is a rock ridge with a large upper end and a small lower end. Such a rock ridge is easier to be cleared by the rotating and following auxiliary tooth 6, while reducing the workload of the adjacent fixed cutting tooth 5.

[0024] Please see Figure 2 and Figure 4 As a preferred option, the crushing unit 2 has semi-circular teeth, which are easy to process, have mature welding technology, and are highly reliable.

[0025] Please see Figure 5 Preferably, the shape of the intrusion edge 4 of the breaking unit 2 is a spline curve. In this case, the length of the intrusion edge 4 is the line connecting the starting point 41 and the ending point 42 of the intrusion edge, i.e., the equivalent line 40 of the intrusion edge. The corresponding center point of the intrusion edge 4 is the midpoint of the equivalent line 40 of the intrusion edge, i.e., the midpoints m and n of the equivalent lines 40 of the two breaking units 2 in the figure. In addition, when the intrusion edge 4 is not a straight line, the included angle between the intrusion edges 4 is the included angle between the equivalent lines 40 of the intrusion edge.

[0026] Please see Figure 6 As a preferred embodiment, the two crushing units 2 in the scraping group 1 are set on the same scraping group base 10. The scraping group 1 is set on the drill bit body 12 through the scraping group base 10 and locked by the fastening bolts 11. When a crushing unit 2 fails, it is more convenient to replace it.

[0027] As a further preferred embodiment, the scraping assembly base 10 of the scraping assembly 1 is connected to the drill bit body 12 in a replaceable manner, including bolt connection, etc.

[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A design method for a PDC drill bit scraping assembly, wherein at least one scraping assembly is provided on the drill bit body, the scraping assembly consists of two crushing units, each crushing unit including an intrusion cutting edge and an intrusion edge, the intrusion edges of the two crushing units in the scraping assembly being arranged adjacent to each other, characterized in that, The PDC drill bit scraping assembly design method includes the following steps: Step S1: Obtain the uniaxial compressive strength of the rock based on the drill resistance test. Rock abrasiveness grade and rock plasticity coefficient The target formation temperature is obtained based on the logging technology. The included angle between the two crushing units in the scraping group is calculated using formula (1); （1） In the formula, The angle between the edges of the two crushing units in the scraping group, in degrees; This represents the uniaxial compressive strength of the rock, expressed in MPa. The grinding coefficient is dimensionless. This is the temperature coefficient, dimensionless. Grinding coefficient The value is determined according to formula (2), where the rock abrasiveness grade value is... Dimensionless; （2） Temperature coefficient The value is determined according to formula (3), where The target formation temperature is expressed in degrees Celsius. （3） Step S2: Based on the included angle and length The edge penetration distance between the two crushing units in the scraping group is calculated according to formula (4). ; （4） In the formula, The distance between the edges of the two crushing units in the scraping group is in mm; The length of the edge of the crushing unit in the scraping and cutting group is in mm; The included angle between the edges of the two crushing units in the scraping group, in degrees; Step S3: Based on the rock plasticity coefficient and the length of the intrusion The radius of the intrusion blade of the crushing unit is calculated according to formula (5). ; （5） In the formula, The radius of the intrusion blade of the crushing unit is in mm; is the rock plasticity coefficient, dimensionless; The length of the edge of the crushing unit is in mm.

2. The design method of a PDC drill bit scraping assembly according to claim 1, characterized in that, The crushing unit is a semi-circular tooth.

3. The design method of a PDC drill bit scraping assembly according to claim 1, characterized in that, The shapes of the edges of the breaking elements include: straight lines, circular arcs, and spline curves.

4. The design method of a PDC drill bit scraping assembly according to claim 1, characterized in that, The two crushing units in the scraping group are set on the same substrate.

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