A flexible drill bit with friction and drag reduction functions

Abstract

The present invention belongs to the technical field of low-yield and low-efficiency drilling and completion development in offshore oil fields, and discloses a flexible drill tool short section with friction and drag reduction functions, including multiple flexible sections connected end to end in sequence; the flexible section includes a drag reduction joint, a drag reduction ball head is movably connected inside the drag reduction joint, the bottom end of the drag reduction ball head is threadedly connected to a transition joint, and the bottom end of the transition joint is threadedly connected to the top end of the drag reduction joint of the next flexible section; a plurality of positioning holes are formed through the outer wall of the drag reduction joint, and the outer wall of the drag reduction ball head is provided with positioning grooves corresponding to the positioning holes, and anti-torsion pins are inserted into the positioning holes, and the anti-torsion pins extend out of the positioning holes and are inserted into the positioning grooves. The flexible drill tool short section of the present invention reduces friction during drilling, reduces wear between the drill tool and the casing, and improves drilling efficiency. Its flexible connection method and anti-torsion design can also better adapt to complex drilling environments, providing a new solution for increasing production and tapping potential in the later stages of offshore oil field development.

Description

Technical Field

[0001] The present invention relates to the technical field of low-yield and low-efficiency drilling and completion development in offshore oil fields, and in particular to a flexible drill tool pup joint with friction and drag reduction functions. Background Art

[0002] Offshore oilfields face challenges in their later stages of development, both in terms of high water cut and high recovery rates. Conventional production-stimulation technologies are ineffective due to limitations in offshore platforms. Offshore oilfield development faces numerous challenges, creating an urgent need for efficient drilling and completion technologies. On the one hand, some offshore oilfields face challenges in their later stages of development, both in terms of high water cut and high recovery rates. Conventional production-stimulation technologies are ineffective due to limitations in offshore platforms, necessitating the effective utilization of remaining oil and the development of low-permeability and thin, poorly-permeable reservoirs near the wellbore. On the other hand, the expansion of exploration and development areas presents complex drilling and completion challenges, and the lack of mature design for flexible tool optimization necessitates specialized flexible drilling tools to address these challenges and leverage their unique advantages.

[0003] Ultra-short radius horizontal well drilling technology is suitable for the development of low-yield, low-efficiency wells and the utilization of residual oil. However, it suffers from problems such as high friction between the tubing and the wellbore wall during wellbore drilling. In particular, during sliding drilling, the pressure support and sticking resistance are severe, resulting in drill string buckling, the inability to transmit drilling pressure, and severe friction between the drill bit and the casing, causing casing wear and drill bit leakage. These problems reduce drilling efficiency and may even lead to operation suspension or dangerous accidents. At the same time, there is currently no flexible drill bit short section structure suitable for this technology and with the function of reducing friction and drag.

[0004] Therefore, the present application designs a flexible drill bit with friction and drag reduction functions to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible drill bit with friction and drag reduction function, so as to overcome the friction resistance generated between the pipe string and the well wall during drilling by the flexible tool and solve the problems existing in the prior art.

[0006] To achieve the above object, the present invention provides the following solution: The present invention provides a flexible drill sub with friction and drag reduction function, comprising multiple flexible subsegments, wherein adjacent flexible subsegments are connected end to end in sequence, and the flexible subsegments at the upper and lower ends are respectively connected to the drill pipe;

[0007] The flexible joint includes a drag-reducing joint, a drag-reducing ball head is movably connected to the drag-reducing joint, the bottom end of the drag-reducing ball head extends out of the drag-reducing joint and is threadedly connected to a transition joint, and the bottom end of the transition joint is threadedly connected to the top end of the drag-reducing joint of the next flexible joint;

[0008] A plurality of positioning holes are formed through the outer wall of the drag reduction joint, and a positioning groove corresponding to the positioning holes is provided on the outer wall of the drag reduction ball head. An anti-torsion pin is inserted into the positioning hole, and the anti-torsion pin extends out of the positioning hole and is inserted into the positioning groove.

[0009] Preferably, a plurality of protruding blocks are provided at equal intervals in the circumferential direction on the outer wall of the drag reducing joint, and the protruding blocks are spirally attached to the outer wall of the drag reducing joint.

[0010] Preferably, the size of the positioning hole is adapted to the anti-torsion pin, the diameter of the positioning groove is larger than the diameter of the anti-torsion pin, the anti-torsion pin and the positioning hole have an interference fit, and the anti-torsion pin and the positioning groove have a clearance fit.

[0011] Preferably, a first positioning head is provided at the bottom end of the drag reduction joint, and a first positioning groove corresponding to the first positioning head is provided at the top end of the transition joint, and the first positioning head is inserted and positioned in the first positioning groove.

[0012] Preferably, the drag reduction ball head includes a spherical seat movably arranged in the inner cavity of the drag reduction joint, and the positioning groove is opened on the outer wall of the spherical seat; the bottom end of the spherical seat is fixedly connected with a first connecting screw barrel, and the first connecting screw barrel extends out of the drag reduction joint and is threadedly connected to the first connecting thread arranged at the top of the transition joint.

[0013] Preferably, a sealing ring is embedded in the inner cavity of the transition joint, and the bottom end of the inner cavity of the sealing ring is in sealing and sliding connection with the top end of the spherical seat of the next flexible joint.

[0014] Preferably, a second connecting thread is provided at the top of the inner cavity of the drag reducing joint, and a second connecting barrel adapted to the second connecting thread is provided at the bottom end of the outer wall of the transition joint, and the second connecting thread is threadedly connected to the second connecting barrel.

[0015] Preferably, a limiting groove is coaxially provided in the positioning hole, an elastic retaining ring is provided in the limiting groove, and the elastic retaining ring is in limiting abutment with an end of the anti-torsion pin away from the drag-reducing ball head.

[0016] Preferably, a drag reducing ring is provided on the transition joint, and the drag reducing ring is fixed by a fixed pressure ring provided on the transition joint.

[0017] Preferably, the drag reducing ring includes a drag reducing groove arranged between the transition joint and the fixed pressure ring, a plurality of drag reducing balls are arranged in the drag reducing groove, and the outer edges of the drag reducing balls extend out of the drag reducing groove and contact the well wall.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: the present invention discloses a flexible drill tool short section with the function of reducing friction and drag, the flexible drill tool short section is composed of multiple flexible sections, these flexible sections can be connected to each other and adapt to complex drilling environments, effectively reduce the friction resistance during drilling, reduce the wear between the drill tool and the casing, and improve drilling efficiency; the flexible drill tool short section is composed of multiple flexible sections, and adjacent flexible sections are connected end to end to form a continuous, bendable drill tool structure, which increases the flexibility of the drill tool and enables it to better adapt to complex wellbore conditions; each flexible section includes a drag reducing joint, and a drag reducing ball head is movably connected inside the joint, allowing the drag reducing ball head to be fine-tuned according to changes in the wellbore during drilling, so that the flexible section can adapt to the tortuosity of the wellbore, thereby reducing the friction between the drill tool and the well wall; the bottom of the drag reducing ball head is connected to the bottom of the flexible section. The end extends out of the drag reduction joint and is connected to the transition joint by threads. The bottom end of the transition joint is then threadedly connected to the top end of the drag reduction joint of the next flexible joint, which ensures the continuity and stability of the drill bit. Different numbers of flexible joints can be adaptively selected according to usage requirements, thereby improving the applicability of the flexible drill bit short section; a number of positioning holes are opened through the outer wall of the drag reduction joint, and the outer wall of the drag reduction ball head is provided with positioning grooves corresponding to these positioning holes. After the anti-torsion pin is inserted into the positioning hole and extended out, it is inserted into the positioning groove, which not only increases the torsional strength of the drill bit, but also further limits the range of motion of the drag reduction ball head, prevents the drag reduction ball head from being separated from the drag reduction joint due to excessive torque, and can play a stabilizing role, thereby preventing the flexible drill bit short section from breaking during drilling, so that it can remain stable while maintaining flexibility, thereby improving drilling efficiency and safety.

[0019] The flexible drill bit of the present invention reduces friction during drilling, reduces wear between the drill bit and the casing, and improves drilling efficiency. Its flexible connection method and torsion-resistant design can also better adapt to complex drilling environments, providing a new solution for increasing production and tapping potential in the later stages of offshore oil field development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings that constitute part of this application are used to provide a further understanding of this application. The embodiments and descriptions of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0021] Figure 1 This is a view of the short section shaft of the flexible drilling tool with the function of reducing friction and drag of the present invention;

[0022] Figure 2 This is a schematic diagram of the flexible joint structure of the present invention;

[0023] Figure 3 This is an axial view of the drag reduction joint of the present invention;

[0024] Figure 4This is a structural schematic diagram of the drag reduction joint of the present invention;

[0025] Figure 5 This is a view of the drag reduction ball head shaft of the present invention;

[0026] Figure 6 This is an axial view of the transition joint of the present invention;

[0027] Figure 7 This is a schematic structural diagram of the transition joint of the present invention;

[0028] Figure 8 This is an axial view of a transition joint according to a second embodiment of the present invention;

[0029] Figure 9 This is a schematic structural diagram of a transition joint according to a second embodiment of the present invention;

[0030] In the figure: 1. Drag reduction joint; 2. Drag reduction ball head; 3. Transition joint; 4. Anti-torsion pin; 11. Positioning hole; 12. Protruding block; 13. First positioning head; 14. Second connecting thread; 15. Limiting groove; 16. Elastic snap ring; 21. Positioning groove; 22. Spherical seat; 23. First connecting screw; 31. First positioning groove; 32. First connecting thread; 33. Sealing groove; 34. Sealing ring; 35. Second connecting screw; 36. Drag reduction ring; 37. Fixed pressure ring; 38. Drag reduction groove; 39. Drag reduction ball. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] Reference Figures 1 to 7 As shown, this embodiment provides a flexible drill tool short section with friction and drag reduction functions, including multiple flexible sections, adjacent flexible sections are connected end to end in sequence, and the flexible sections at the upper and lower ends are respectively connected to the drill pipe;

[0035] The flexible joint includes a drag reduction joint 1, in which a drag reduction ball head 2 is movably connected. The bottom end of the drag reduction ball head 2 extends out of the drag reduction joint 1 and is threadedly connected to a transition joint 3. The bottom end of the transition joint 3 is threadedly connected to the top end of the drag reduction joint 1 of the next flexible joint.

[0036] A plurality of positioning holes 11 are formed through the outer wall of the drag reduction joint 1, and a positioning groove 21 corresponding to the positioning holes 11 is formed on the outer wall of the drag reduction ball head 2. An anti-torsion pin 4 is inserted into the positioning hole 11, and the anti-torsion pin 4 extends out of the positioning hole 11 and is inserted into the positioning groove 21.

[0037] The present invention discloses a flexible drill tool short section with the function of reducing friction and drag, the flexible drill tool short section is composed of multiple flexible sections, which can be connected to each other and adapt to complex drilling environments, effectively reduce the friction resistance during drilling, reduce the wear between the drill tool and the casing, and improve drilling efficiency; the flexible drill tool short section is composed of multiple flexible sections, and adjacent flexible sections are connected end to end to form a continuous, bendable drill tool structure, which increases the flexibility of the drill tool and enables it to better adapt to complex wellbore conditions; each flexible section includes a drag reducing joint 1, which is movably connected to a drag reducing ball head 2 inside, allowing the drag reducing ball head 2 to be fine-tuned according to changes in the wellbore during drilling, so that the flexible section can adapt to the tortuosity of the wellbore, thereby reducing the friction between the drill tool and the well wall; the bottom end of the drag reducing ball head 2 extends out of the drag reducing joint 1 and is connected to a transition The bottom end of the joint 3 and the transition joint 3 are then threadedly connected to the top end of the drag reduction joint 1 of the next flexible joint, ensuring the continuity and stability of the drill tool. Different numbers of flexible joints can be adaptively selected according to the use requirements, thereby improving the applicability of the flexible drill tool short section. A number of positioning holes 11 are penetrated through the outer wall of the drag reduction joint 1, and the outer wall of the drag reduction ball head 2 is provided with positioning grooves 21 corresponding to these positioning holes 11. The anti-torsion pin 4 is inserted into the positioning hole 11 and extended out, and then inserted into the positioning groove 21, which not only increases the torsional strength of the drill tool, but also further limits the range of motion of the drag reduction ball head 2, and can prevent the drag reduction ball head 2 and the drag reduction joint 1 from falling off due to excessive torque, and can play a stabilizing role, thereby preventing the flexible drill tool short section from breaking during the drilling process, so that it can remain stable while maintaining flexibility, thereby improving drilling efficiency and safety. The flexible drill bit of the present invention reduces friction during drilling, reduces wear between the drill bit and the casing, and improves drilling efficiency. Its flexible connection method and torsion-resistant design can also better adapt to complex drilling environments, providing a new solution for increasing production and tapping potential in the later stages of offshore oil field development.

[0038] A further optimization scheme features several protrusions 12 circumferentially and evenly spaced around the outer wall of the drag-reducing joint 1. These protrusions 12 are spirally attached to the outer wall of the joint. The spiraling direction of these protrusions 12 aligns with the drilling direction of the drill pipe, guiding the flow of drilling fluid and reducing direct contact friction between the drill tool and the wellbore wall. Furthermore, these protrusions 12 also expand the hole, reducing contact between the drill pipe and the wellbore wall, assisting the drill tool in drilling along a predetermined trajectory and further reducing drilling resistance.

[0039] In a further optimized solution, the size of the positioning hole 11 is adapted to the anti-torsion pin 4, the diameter of the positioning groove 21 is larger than the diameter of the anti-torsion pin 4, the anti-torsion pin 4 has an interference fit with the positioning hole 11, and the anti-torsion pin 4 has a clearance fit with the positioning groove 21. The interference fit of the anti-torsion pin 4 in the positioning hole 11 ensures that the pin and the positioning hole 11 are tightly fixed to prevent loosening; while the diameter of the positioning groove 21 is larger than the anti-torsion pin 4, providing a clearance fit. While torque is transmitted, it allows the drag-reducing ball head 2 to move in all directions, achieving flexible drag reduction. At the same time, the clearance fit between the anti-torsion pin 4 and the positioning groove 21 enables flexible transmission, reducing the risk of fracture of the anti-torsion pin 4 due to overtightening.

[0040] In a further optimized solution, a first positioning head 13 is provided at the bottom end of the drag reduction joint 1, and a first positioning groove 31 corresponding to the first positioning head 13 is provided at the top end of the transition joint 3. The first positioning head 13 is inserted and positioned in the first positioning groove 31. When the transition joint 3 and the drag reduction ball head 2 are threaded together, the first positioning head 13 at the bottom end of the drag reduction joint 1 is inserted and positioned in the first positioning groove 31 at the top end of the transition joint 3, making the positioning of the two more precise, improving the efficiency of drilling operations, and eliminating the concave-convex transition on the contact surface between the drag reduction joint 1 and the transition joint 3. At the same time, when the drag reduction joint 1 and the drag reduction ball head 2 move, a movable margin is provided to ensure flexible adjustment.

[0041] A further optimization scheme is that the drag reduction ball head 2 includes a spherical seat 22 movably arranged in the inner cavity of the drag reduction joint 1, and a positioning groove 21 is opened on the outer wall of the spherical seat 22; the bottom end of the spherical seat 22 is fixedly connected to a first connecting screw barrel 23, and the first connecting screw barrel 23 extends out of the drag reduction joint 1 and is threadedly connected to the first connecting thread 32 arranged at the top of the transition joint 3. The drag reduction ball head 2 consists of a spherical seat 22 and a first connecting screw 23 fixed at the bottom end of the spherical seat 22. The outer diameter of the spherical seat 22 is larger than the outer diameter of the first connecting screw 23, and the inner cavity of the drag reduction joint 1 is also larger at the top and smaller at the bottom. The large diameter of the upper end is adapted to the spherical seat 22, and the small diameter of the lower end is adapted to the first connecting screw 23, so that the drag reduction ball head 2 can be placed from the top of the drag reduction joint 1 and stuck in the drag reduction joint 1. At this time, the positioning groove 21 on the spherical seat 22 is aligned with the positioning hole 11 on the drag reduction joint 1, and the anti-torsion pin 4 can be used for connection conveniently, thereby forming a flexible and bendable whole of the drag reduction joint 1, the drag reduction ball head 2 and the transition joint 3.

[0042] As a further optimization, a sealing ring 34 is embedded in the inner cavity of the transition joint 3. The bottom end of the sealing ring 34 seals and slides with the top of the spherical seat 22 of the next flexible joint. A sealing groove 33 is provided at the bottom end of the inner cavity of the transition joint 3. A sealing ring 34 is installed in this groove. When connected, the sealing ring 34 seals against the outer wall of the spherical seat 22, preventing drilling fluid leakage, contaminating the wellbore, or affecting the transmission of drilling pressure. Furthermore, the sealing ring 34 is made of wear-resistant material, extending its service life and ensuring a more secure connection at the drag-reducing ball head 2.

[0043] In a further optimization, the top of the inner cavity of the drag reduction joint 1 is provided with a second connecting thread 14, and the bottom of the outer wall of the transition joint 3 is provided with a second connecting barrel 35 that matches the second connecting thread 14. The second connecting thread 14 is threadedly connected to the second connecting barrel 35. The drag reduction joint 1 and the transition joint 3 are threadedly connected. This dual connection enhances structural stability, resists complex downhole working conditions, and prevents the short joint from being disconnected due to the failure of a single connection.

[0044] As a further optimization, a limiting groove 15 is coaxially defined within the positioning hole 11. An elastic retaining ring 16 is disposed within the limiting groove 15 and engages with the end of the anti-torsion pin 4 that is distal to the drag-reducing ball head 2. The limiting groove 15 and the elastic retaining ring 16 are disposed within the positioning hole 11. The elastic retaining ring 16 abuts against the anti-torsion pin 4, preventing it from being dislodged from the positioning hole 11 due to vibration or impact. The elastic retaining ring 16 can be easily removed for replacement, enabling quick disassembly and replacement without remachining the positioning hole 11.

[0045] Example 2

[0046] Refer to the attached Figures 8 to 9 As shown, a drag reducing ring 36 is provided on the transition joint 3, and the drag reducing ring 36 is fixed by a fixed pressure ring 37 provided on the transition joint 3. A detachable fixed pressure ring 37 is provided on the outer wall of the transition joint 3. The outer wall of the fixed pressure ring 37 is flush with the outer wall of the transition joint 3. The drag reducing ring 36 is press-fitted between the fixed pressure ring 37 and the bottom end of the outer wall of the transition joint 3. The drag reducing ring 36 is rotatably arranged on the outer wall of the transition joint 3 and is in rolling contact with the well wall. It can convert the planar friction generated between the drill tool and the well wall during drilling into rolling friction, which can effectively reduce the frictional resistance between the drill tool and the well wall. The fixed pressure ring 37 is designed to facilitate the replacement of worn drag reducing rings 36.

[0047] To further optimize the solution, the drag reduction ring 36 includes a drag reduction groove 38 disposed between the transition joint 3 and the fixed pressure ring 37. A number of drag reduction balls 39 are disposed within the drag reduction groove 38, with the outer edges of the drag reduction balls 39 extending out of the groove 38 and contacting the wellbore wall. The drag reduction groove 38 is an arc-shaped groove disposed between the contact surfaces of the transition joint 3 and the fixed pressure ring 37. The drag reduction balls 39 are engaged in the drag reduction groove 38 and are arranged to roll. The outer edges of the drag reduction balls 39 extend out of the groove 38 and contact the wellbore wall, replacing sliding friction with rolling friction, significantly reducing the friction coefficient and energy loss. At the same time, the position of the drag reduction balls 39 can freely roll as the wellbore trajectory changes, maintaining the flexibility of the drilling tool.

[0048] In one embodiment of the present invention, the number of drag-reducing balls 39 can be selected as 36, or can be selected according to the specifications of the drilling tools and the adaptability of the specifications of the drag-reducing balls 39. These are all applicability optimizations based on the technology of this embodiment and are not limitations of the present invention.

[0049] Specific examples:

[0050] The drill string in the buildup section bears the axial force at the window opening and its own weight, while the guide screen in the horizontal section bears only its own weight. Therefore, the frictional resistance between the wellbore and the flexible drill string is evaluated only in the buildup section. The boundary conditions include lateral displacement constraint at the window opening, full constraints on the bottomhole and wellbore, and a contact friction boundary between the guide screen and the wellbore. The operating conditions are: curvature radii of 2.8m, 3.2m, and 3.6m; inclination angles of 30°, 60°, and 90°; and axial forces of 20kN, 30kN, and 40kN at the window opening.

[0051] A flexible drill string sub was selected as the research object, and a local model was established using solid elements. Loads were applied to the critical area of ​​the drill string sub in the buildup section, primarily bearing axial, lateral, and bending forces. The boundary conditions were: full constraint at the upper end and weight-on-bit at the lower end. The contact friction boundary between the wellbore and the drill string was calculated. Finite element analysis was used to account for contact between the transverse joints of the flexible drill string.

[0052] The flexible drilling tool material is initially determined to be 42CrMo, with a yield strength of 930MPa, a tensile strength of 1080MPa, and a density of 7850kg / m 3³ , Young's modulus is 210GPa, Poisson's ratio is 0.28, and hardness is 48HRC.

[0053] The finite element method was used to calculate the frictional resistance generated by the contact between the wellbore wall and the flexible drill tool under three working conditions: drilling at 30°, 60°, and 90°, with a window opening torque of 20 kN·m and an axial force of 20 kN, 30 kN, and 40 kN, respectively. Cloud diagrams of the frictional resistance generated when the wellbore wall contacts the flexible drill tool were obtained when the curvature radius was 2.8 m, 3.2 m, and 3.6 m, respectively.

[0054] Simulated data 1

[0055] Finite element calculations were performed to obtain the changes in frictional resistance and overall equivalent elastic strain when the flexible drill bit contacts the wellbore wall when the curvature radius is 2.8 m, as shown in the following figure (drilling angles of 30°, 60°, and 90° in the deflection section). The unit element in contact with the wellbore wall was analyzed, and its unit was Pa. This was converted into kN for comparison with the calculated results.

[0056] From the simulation data, it can be seen that with the increase of the drilling angle and bit pressure of the drill tool, the total friction resistance and total friction torque of the flexible drill tool increase approximately linearly. The deformation displacement is small and can be ignored. The maximum friction resistance occurs above the thread because it bears greater torque than other positions, so the friction resistance is greater.

[0057] Simulated data 2

[0058] Finite element calculations were performed to obtain the changes in frictional resistance and overall equivalent elastic strain when the flexible drill bit contacts the wellbore wall when the curvature radius is 3.2 m, as shown in the following figure (drilling angles of 30°, 60°, and 90° in the build-up section). The unit element in contact with the wellbore wall was analyzed, and its unit was Pa. This was converted into kN for comparison with the calculated results.

[0059] The simulation data show that with the increase of drilling angle and bit pressure, the total friction and total friction torque of the flexible drill tool increase approximately linearly, its deformation is negligible, and the friction distribution is relatively uniform. Compared with the other two working conditions, the friction is greater when drilling 90° in the deflection section, and the total deformation begins to break when drilling 60°. The reason is that as the friction increases, the axial force gradually increases, the constraint applied is relatively simple, and a large force may break through the string.

[0060] Simulated data 3

[0061] Finite element calculations were performed to obtain the changes in frictional resistance and overall equivalent elastic strain when the flexible drill bit contacts the wellbore wall when the curvature radius is 3.6 m. The following figure shows the results (drilling angles of 30°, 60°, and 90° in the build-up section). The contact unit with the wellbore wall was analyzed. The unit is Pa, which was converted into kN for comparison with the calculated results.

[0062] The simulation data show that as the drilling angle and bit pressure of the drill tool increase, the flexibility decreases, the torque increases, and the total friction resistance and total friction torque of the flexible drill tool increase approximately linearly. The deformation displacement is small and can be ignored. The maximum friction resistance occurs above the thread and is relatively evenly distributed. The working condition with the maximum friction resistance is when the bevel section is drilled at 90°, but no deformation occurs.

[0063] The total friction resistance and total friction torque before and after thread installation were calculated by theoretical calculation combined with finite element analysis for comparison.

[0064] Table 1 Comparison of frictional resistance before and after thread installation under different parameters

[0065]

[0066] As shown in Table 1, the friction between the flexible drill bit and the wellbore wall can be effectively reduced after adding threads. Both the friction resistance and friction torque increase with the increase of the inclination angle. The friction resistance can be better reduced by appropriately optimizing the thread size and reducing the contact area with the wellbore wall.

[0067] Simulated data 4

[0068] The finite element method was used to calculate the frictional resistance generated by the contact between the wellbore wall and the flexible drill tool under three different working conditions: drilling at 30°, 60°, and 90°, with a window opening torque of 20 kN·m and an axial force of 20 kN, 30 kN, and 40 kN, respectively. The cloud diagrams of the frictional resistance generated when the wellbore wall contacts the flexible drill tool were obtained when the curvature radius was 3.6 m.

[0069] The simulation data show that with the increase of drilling angle and bit pressure, the total friction resistance and total friction torque of the flexible drilling tool increase approximately linearly, the deformation displacement is small, the friction resistance changes evenly, and no bulge occurs.

[0070] Simulated data 5

[0071] The finite element method was used to calculate the frictional resistance generated by the contact between the wellbore wall and the flexible drill tool under three working conditions: drilling at 30°, 60°, and 90°, with a window opening torque of 20 kN·m and an axial force of 20 kN, 30 kN, and 40 kN at the window opening point. The cloud diagrams of the frictional resistance generated when the wellbore wall contacts the flexible drill tool were obtained when the curvature radius was 3.2 m.

[0072] The simulation data show that with the increase of drilling angle and bit pressure, the total friction resistance and total friction torque of the flexible drilling tool increase approximately linearly, the deformation displacement is small, the friction resistance changes evenly, and no bulge occurs.

[0073] Simulated data six

[0074] The finite element method was used to calculate the frictional resistance generated by the contact between the wellbore wall and the flexible drill tool under three different structures when drilling at 30°, 60°, and 90°, with a window opening torque of 20 kN·m and an axial force of 20 kN, 30 kN, and 40 kN, respectively. The cloud diagrams of the frictional resistance generated when the wellbore wall contacts the flexible drill tool were obtained when the curvature radius was 2.8 m.

[0075] Simulation data shows that as the wellbore inclination increases in the buildup section, total friction, equivalent elastic strain, and total deformation displacement increase. However, compared to the other two operating conditions, the friction and equivalent elastic strain generated by the flexible drill sub are at their minimums, with no bulges observed. This indicates that as flexibility decreases, the friction between the drill sub and the wellbore increases. When flexibility remains constant, increasing wellbore inclination increases the axial force and total friction torque. Comparing the curvature radii of 3.2m and 3.6m, the 2.8m curvature radius produces the lowest friction, equivalent elastic strain, and total deformation.

[0076] The total frictional resistance and total frictional torque before and after the installation of the ball bearing were compared through theoretical calculation and finite element analysis. The unit of frictional resistance in the finite element method, Pa, was converted into kN, F=P·S (S is the contact area).

[0077] Table 2 Comparison of frictional resistance before and after installation of ball bearings under different working conditions

[0078]

[0079] As shown in Table 2, the installation of ball bearings effectively reduces the friction between the drill bit sub model and the wellbore wall, and both the total frictional resistance and the total frictional resistance torque show a downward trend. However, if the axial force at the window opening point and the drilling angle are too large, slight deformation may occur due to long-term contact with the wellbore wall.

[0080] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0081] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A flexible drill bit with friction and drag reduction function, characterized by: It includes multiple flexible sections, the adjacent flexible sections are connected end to end in sequence, and the flexible sections at the upper and lower ends are respectively connected to the drill pipe; The flexible joint comprises a drag reduction joint (1), a drag reduction ball head (2) is movably connected inside the drag reduction joint (1), the bottom end of the drag reduction ball head (2) extends out of the drag reduction joint (1) and is threadedly connected to a transition joint (3), and the bottom end of the transition joint (3) is threadedly connected to the top end of the drag reduction joint (1) of the next flexible joint; The outer wall of the drag reduction joint (1) is provided with a plurality of positioning holes (11), the outer wall of the drag reduction ball head (2) is provided with positioning grooves (21) corresponding to the positioning holes (11), an anti-torsion pin (4) is inserted into the positioning hole (11), and the anti-torsion pin (4) extends out of the positioning hole (11) and is inserted into the positioning groove (21); The bottom end of the drag reduction joint (1) is provided with a first positioning head (13), the top end of the transition joint (3) is provided with a first positioning groove (31) corresponding to the first positioning head (13), and the first positioning head (13) is inserted and positioned in the first positioning groove (31); The drag-reducing ball head (2) comprises a spherical seat (22) movably arranged in the inner cavity of the drag-reducing joint (1), and the positioning groove (21) is provided on the outer wall of the spherical seat (22); a first connecting screw barrel (23) is fixedly connected to the bottom end of the spherical seat (22), and the first connecting screw barrel (23) extends out of the drag-reducing joint (1) and is threadedly connected to a first connecting thread (32) provided at the top end of the transition joint (3); The size of the positioning hole (11) is adapted to the anti-torsion pin (4), the diameter of the positioning groove (21) is larger than the diameter of the anti-torsion pin (4), the anti-torsion pin (4) and the positioning hole (11) are interference fit, and the anti-torsion pin (4) and the positioning groove (21) are clearance fit; A limiting groove (15) is coaxially provided in the positioning hole (11), an elastic snap ring (16) is provided in the limiting groove (15), and the elastic snap ring (16) is in limiting contact with an end of the anti-torsion pin (4) away from the drag-reducing ball head (2); A drag reduction ring (36) is provided on the transition joint (3), and the drag reduction ring (36) is fixed by a fixed pressure ring (37) provided on the transition joint (3); The drag reduction ring (36) includes a drag reduction groove (38) arranged between the transition joint (3) and the fixed pressure ring (37), a plurality of drag reduction balls (39) are arranged in the drag reduction groove (38), and the outer edges of the drag reduction balls (39) extend out of the drag reduction groove (38) and contact the well wall.

2. The flexible drill sub with friction and drag reduction function according to claim 1 is characterized in that: The outer wall of the drag reducing joint (1) is provided with a plurality of protruding blocks (12) at equal intervals in the circumferential direction, and the protruding blocks (12) are spirally attached to the outer wall of the drag reducing joint (1).

3. The flexible drill sub with friction and drag reduction function according to claim 1, characterized in that: A sealing ring (34) is embedded in the inner cavity of the transition joint (3), and the bottom end of the inner cavity of the sealing ring (34) is in sealing and sliding connection with the top end of the spherical seat (22) of the next flexible joint.

4. The flexible drill sub with friction and drag reduction function according to claim 1 is characterized in that: The top end of the inner cavity of the drag reducing joint (1) is provided with a second connecting thread (14), and the bottom end of the outer wall of the transition joint (3) is provided with a second connecting screw barrel (35) adapted to the second connecting thread (14), and the second connecting thread (14) is threadedly connected to the second connecting screw barrel (35).

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