Design and manufacturing methods for direct-connection gas-tight threads based on optimized bearing surface angle for bending resistance

Abstract

This invention relates to a design and manufacturing method for direct-connection gas-tight threads based on optimized bearing surface angle for bending resistance. One method for optimizing the bending resistance of direct-connection gas-tight threads based on bearing surface angle includes the following steps: S1, determining the critical section of the direct-connection thread under bending conditions: the tension side of the direct-connection thread is the critical section; S2, determining the key factors for thread tensile resistance: the bearing surface angle is the key factor determining the thread's tensile resistance. Compared to existing technologies, the technical advantages of this invention are that, through analysis and verification, it obtains the physical law that as the bearing surface angle increases, the maximum sealing contact pressure and the axial area formed by the contact increase. Applying this to products improves product performance, meeting the increasingly demanding requirements of small-diameter wells and high-curvature horizontal wells.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology. The scope of this invention is well completion technology and production casing string. Specifically, it is a bending-resistant gas-tight direct connection thread for wellbore reconstruction and oil layer suspension tailpipe and production casing. Background Technology

[0002] Direct-connect gas-tight threaded casing has the advantage of having the threaded connection end flush with the inner and outer walls of the casing, and is widely used in wellbore reconstruction for small wells and old wells, significantly reducing drilling costs for oil and gas development.

[0003] However, due to the use of a sleeve body for internal and external thread connection, the thickness of the threaded joint's tooth root wall makes it prone to thread breakage or slippage failure under bending, posing a safety hazard to field use.

[0004] The existing direct-connection gas-tight threaded connections have the following problems: 1. The performance indicators of direct-connection gas-tight threads on the domestic and international markets and those for which patents have been applied are relatively low (e.g., VAM FJL compression efficiency 23%, curvature <27° / 30m, refer to VAM product manual performance indicators), which cannot meet the drilling technology requirements of increasingly large displacement and large curvature horizontal wells with curvature ≥30° / 30m.

[0005] 2. The existing direct-connection gas-tight threaded connection structure is characterized by: one type adopting the thread profile angle specified by API 5B (200815 version), with both the bearing surface and guide surface angles being 6°, tooth height 1.35mm, and taper 1:8-1:10. The tensile and bending performance of the thread is significantly reduced, with a typical bending degree <10° / 30m. Therefore, oil fields and manufacturers rarely adopt this thread type. Summary of the Invention

[0006] The technical problem to be solved by this invention is: In view of the above problems, it is necessary to carry out the optimization design and product development of new high-performance anti-bending direct connection gas-tight threads to meet the requirements of increasingly demanding working conditions for small-diameter and high-curvature horizontal well development.

[0007] The specific technical solution of the present invention is as follows: A design method for direct-connection gas-tight threads based on optimized bearing surface angle for bending resistance includes the following steps: S1. Determine the critical section of the straight-connected thread under bending condition: The tension side of the straight-connected thread is the critical section of the straight-connected thread; S2. Key factors for determining thread tensile strength: The angle of the bearing surface is the key factor for determining thread tensile strength. S3. Determine the effect of thread bearing surface angle change on internal pressure sealing performance under bending load: By comparing the magnitude of sealing surface contact pressure and length under the same limit bending conditions and different bearing surface angles, the applicable angle range is finally determined. S4. Design the product structure of a straight-connection thread; based on the influence of the thread bearing surface angle change on the internal pressure sealing performance under the above bending load, carry out the thread structure optimization design: S5. Establish the optimization method and quantitative law of bending on seal integrity: Under the same bending load, experiments were conducted with bearing surface angles of 0, -5, -10, -15 and -20 degrees respectively to carry out comparative analysis. The law can be obtained: as the bearing surface angle increases, the maximum sealing contact pressure and the axial area formed by the contact increase. S6. Determine product parameters: Based on the above rules, determine the product parameters: the bearing surface angle of the lower thread is -17 to -20°.

[0008] In step S4, the thread structure optimization design is carried out as follows: One end of the direct-connection threaded structure is the external sealing external pressure zone a, which ensures that the thread is not penetrated under external pressure, causing the internal and external threads to separate and slip off under tension; the middle part of the direct-connection threaded structure is the thread tooth connection zone b, where both the internal and external threads are complete tooth profiles, ensuring sufficient tensile strength under tension; the other end of the direct-connection threaded structure is the internal sealing internal pressure zone c, which ensures that the internal pressure seal does not fail under bending and tensile loads. The bearing surface angle of the internal thread improves the thread's resistance to bending and tensile stress, ensuring the integrity of the internal pressure seal; The guide face angle of the internal thread is designed to prevent sticking and ensure easy engagement and prevent sticking. The pitch of the internal thread ensures the effective number of threads in the threaded connection and improves the tensile load-bearing capacity of the thread; The taper of the internal thread ensures the thread's tensile strength and engagement. The thread height of an internal thread ensures that the effective load-bearing area and the wall thickness at the tooth root do not deform under tensile and bending loads.

[0009] In step S6, the product parameters include: The guide surface angle 4 of the lower thread is 25° to 45°; The pitch of the underthread is 15-20 threads / 2.5 inches; The taper of the lower thread is 1:18.5~20.5; The tooth height of the lower thread is 0.75–1.05 mm; The inner sealing pressure zone C is a conical surface or a combination of a conical surface and a spherical surface; The sealing position is 4.5–7.5 mm from the tip of the nose.

[0010] A manufacturing method for a direct-connection gas-tight thread based on optimized bearing surface angle to resist bending is proposed. The above design method is used and the parameters are used in the manufacturing process to obtain the final product.

[0011] Compared to existing technologies, the technical advantages of this invention are as follows: Through analysis and verification, this invention reveals physical laws that increase with the angle of the bearing surface, leading to both the maximum sealing pressure and the axial area formed by the contact. Applying these laws to products improves product performance, meeting the increasingly demanding requirements of small-diameter wells and high-curvature horizontal wells. Attached Figure Description

[0012] Figure 1 This is a longitudinal sectional view of a straight-connection type thread.

[0013] Figure 2 This is a schematic diagram of the bending stress state of a straight-connected thread, where the upper part is the tension side and the lower part is the compression side.

[0014] Figure 3 This is an enlarged longitudinal sectional view of the drawn edge of a straight-connected thread.

[0015] Figure 4 yes Figure 3 Enlarged schematic diagram of the thread teeth in section B.

[0016] Figure 5 This is a schematic diagram of the stress analysis of a straight-connection thread under a bending load of 40° / 30m and a bearing surface angle of 0°. Figure a shows the thread stress distribution, figure b shows the location of the maximum stress, and figure c shows the sealing contact pressure.

[0017] Figure 6 This is a schematic diagram of the stress analysis of a straight-connection thread under a bending load of 40° / 30m and a bearing surface angle of -5°. Figure a shows the thread stress distribution, figure b shows the location of the maximum stress, and figure c shows the sealing contact pressure.

[0018] Figure 7 This is a schematic diagram of the stress analysis of a straight-connection thread under a bending load of 40° / 30m and a bearing surface angle of -10°. Figure a shows the thread stress distribution, figure b shows the location of the maximum stress, and figure c shows the sealing contact pressure.

[0019] Figure 8 This is a schematic diagram of the stress analysis of a straight-connection thread under a bending load of 40° / 30m and a bearing surface angle of -15°. Figure a shows the thread stress distribution, figure b shows the location of the maximum stress, and figure c shows the sealing contact pressure.

[0020] Figure 9This is a schematic diagram of the stress analysis of a straight-connection thread under a bending load of 40° / 30m and a bearing surface angle of -20°. Figure a shows the thread stress distribution, figure b shows the location of the maximum stress, and figure c shows the sealing contact pressure.

[0021] Figure 10 This is a schematic diagram illustrating the analysis of the sealing integrity of a straight-connected thread under bending loads of 40° / 30m with different bearing surface angles and internal thread pressure.

[0022] Figure 11 This is a reference image of a Ø139.7×7.72mm L80SS grade steel sleeve threaded connector, where image a shows the external thread and image b shows the internal thread.

[0023] Figure 12 for Figure 11 A schematic diagram of the thread morphology of the product after the second unraveling, where diagram a shows the external thread and diagram b shows the internal thread.

[0024] Figure 13 It is a physical reference diagram for internal pressure load holding and failure tests.

[0025] Figure 14 This is a schematic diagram of the internal pressure test curve.

[0026] Figure 15 This is a schematic diagram of the load recording curve for the failure test of a direct-connection threaded bending seal.

[0027] Figure 16 This is a physical reference diagram showing the morphology of the bending failure test of a direct-connection thread. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1-2 A design method for direct-connection gas-tight threads based on bearing surface angle optimization for bending resistance includes the following steps: S1. Determine the critical section for bending conditions of direct-connection thread. See Figure 1 The direct-connection gas-tight thread includes external thread 1 (the thread located on the outer surface) and internal thread 2 (the thread located on the inner surface). The thread section with the bending moment applied to the sleeve has the greatest stress. The area with the greatest stress in the section is distributed symmetrically in opposite directions at 180°, that is, it is stretched on one side and compressed on the other. The distribution of tensile and compressive stress generated by bending is shown in Equation 1. The relationship between bending moment M and pipe curvature is shown in Equation 2. (Equation 1) (Equation 2) In the formula: Dleg – curvature (dogleg), expressed in ° / 30m; D——tube outer diameter, mm; t — wall thickness, mm; —Axial stress generated on the inner surface of the tube by bending, MPa; M—Bending moment acting on the pipe, N / mm; I—Moment of inertia of the cross section .

[0030] Moment of inertia of cross section: .

[0031] For the most common tensile fracture or sealing leakage failure modes of threads, combined with Figure 2 The stress analysis shows that under bending load, the tension side of the straight-connected thread bears the main tensile stress, which is the dangerous section of the straight-connected thread.

[0032] S2. Key factors for determining thread tensile strength Based on the bending resistance principle and optimization design method of direct-connection threads, it can be seen that the failure mechanism of threads under bending load is the fracture of the tensile edge or the failure of the seal leakage. Therefore, the size of the bearing surface angle is the key factor that determines the tensile resistance of the thread.

[0033] S3. Determine the impact of the change in the thread bearing surface angle under bending load on the internal pressure sealing performance. By comparing the magnitude of the contact pressure and length of the sealing surface under the same limit bending degree (40° / 30m) and different bearing surface angles, the applicable angle range was finally determined.

[0034] S4. Design of product structure with direct-connection thread. Based on the influence of the thread bearing surface angle change under bending load on the internal pressure sealing performance, the thread structure optimization design is carried out: See Figure 3 , Figure 4 The direct-connection thread structure includes an external thread 1 and an internal thread 2, which are engaged with each other through an upper thread. One end of the direct-connection threaded structure is the external sealing external pressure zone a, which ensures that the thread is not penetrated under external pressure, causing the internal and external threads to separate and slip off under tension; the middle part of the direct-connection threaded structure is the thread tooth connection zone b, where both the internal and external threads are complete tooth profiles, ensuring sufficient tensile strength under tension; the other end of the direct-connection threaded structure is the internal sealing internal pressure zone c, which ensures that the internal pressure seal does not fail under bending and tensile loads. The bearing surface angle 3 of the internal thread 2 improves the thread's resistance to bending and tensile stress, ensuring the integrity of the internal pressure seal; The guide face angle of the internal thread 2 is 4. The thread is anti-sticking and anti-coupling, ensuring easy coupling and preventing sticking. The pitch 5 of the internal thread 2 ensures the effective number of threads in the threaded connection and improves the tensile load-bearing capacity of the thread; The thread taper 6 of the internal thread 2 ensures the thread's tensile strength and thread engagement. The thread height 7 of the internal thread 2 ensures that the effective load-bearing area of ​​the thread and the wall thickness of the tooth root do not deform under tensile and bending loads.

[0035] S5. Establish optimization methods and quantitative laws for the effect of bending on seal integrity. Based on the criterion that the thread has good sealing integrity under bending load, the sealing integrity analysis under bending load is carried out on the same thread structure size: under bending load of 40° / 30m, experiments are conducted with bearing surface angles of 0, -5, -10, -15 and -20 degrees respectively to carry out comparative analysis, and establish the optimization method and quantitative law of bending on sealing integrity.

[0036] See Figures 5-9 With a bearing surface angle of 0°, the maximum stress of the thread is 920 MPa; with a bearing surface angle of -5° to -20°, the maximum stress of the thread is 716 to 768 MPa, a reduction of 17% to 22%; with a bearing surface angle of 0 to -10°, the maximum contact pressure range of the internal pressure seal is 979 to 991 MPa; with a bearing surface angle of -15° to -20°, the maximum contact pressure range of the internal pressure seal is 1008 to 1023 MPa; the sealing performance increases significantly after the bearing surface angle is increased to above -15°.

[0037] See Figure 10 It can be seen that: when the bearing surface angle is 0° to -10°, the contact area is 175 to 180 N / mm; when the bearing surface angle is -15° to -20°, the contact area is 225 to 230 N / mm. It can be observed that: as the bearing surface angle increases, the maximum sealing contact pressure and the axial area formed by the contact increase.

[0038] Increasing the axial area reduces the force per unit area, making it less prone to damage.

[0039] S6. Determine product parameters Based on the above patterns, determine the product parameters: The bearing surface angle 3 of the lower thread is -17 to -20°, which improves the tensile and bending resistance of the joint; The guide surface angle 4 of the lower thread is 25-45°, which facilitates threading and prevents sticking. The pitch of the underthread is 15-20 threads / 2.5 inches (63.5 mm), ensuring that both the internal and external threads are complete threads, and designing and measuring the thread pitch within the effective length of the thread; The taper of the lower thread is 1:18.5~20.5, which increases the effective complete thread length and the thickness of the external thread nose; the tooth tip and tooth root are parallel generatrices, which facilitates inspection and machining; The tooth height of the lower thread is 0.75 to 1.05 mm to ensure sufficient connection bearing area; The inner sealing pressure zone C position is a conical surface or a conical surface plus a spherical surface, which is easy to process and inspect; it has good anti-sticking performance; stable sealing contact length and local high contact pressure distribution; clear and well-defined upper clamping torque curve; the sealing position is 4.5 to 7.5 mm away from the nose end, preventing bumps and damage during transportation and interlocking; it removes contaminants and debris from the sealing surface to prevent seal failure.

[0040] S7. A manufacturing method for a direct-connection gas-tight thread based on the angle optimization of the bearing surface to resist bending. Using the above design method and manufacturing with these parameters, the final product is obtained. See the specific implementation details below.

[0041] Depending on the specific working conditions, different specifications of anti-bending oil sleeve gas-tight special threaded connections can be selected. CNC machined, both internal and external threads undergo surface coating treatment. When threading, apply API thread grease evenly to both ends, and use the optimal torque to clamp the pipe body during threading, for example: A type of threaded casing material of L80 grade, with specifications of 139.7×7.72mm, for use in unconventional tight gas development. See the physical sample. Figure 11 The dimensions and functions of the thread structure are shown in Table 1; the performance indicators are shown in Table 2.

[0042] Table 1 Thread Structure and Function

[0043] Table 2 Design Verification of Performance Indicators for Direct-Connection Gas-Tight Threads Verify the final product S8. Upper and lower buckle test: Samples #1, #2, #3, and #4 did not exhibit sticking during the coupling / uncoupling test at the maximum torque specified in the design. Test data are shown in Table 3. The morphology of the samples after uncoupling is shown in [Table data missing]. Figure 12 .

[0044]

[0045] Table 3. Test data for upper and lower buckles S9. Internal pressure to failure test: Test specimen #3 was held under an internal pressure of 53.4 MPa for 30 minutes without failure. However, when the pressure was increased to 76.5 MPa, the threaded connection broke and failed. The test results are shown in Table 4.

[0046]

[0047] Table 4 Internal Pressure Failure Test See photos of the test specimens after the test. Figure 13 The pressure-time curve is shown below. Figure 14 It can be concluded that: 1) No leakage occurred during the pressure holding process of 53.4MPa as specified in API 5C3, the standard for calculating the internal pressure resistance of oil casing; 2) The internal pressure failure load of 76.5MPa is greater than the ultimate bearing capacity of the pipe body of 74.6MPa, resulting in thread stripping and leakage.

[0048] S10, Internal pressure to failure test: No internal pressure sealing failure occurred in sample #4 within a curvature range of 40° / 30m; however, leakage failure occurred at the threaded connection when the curvature was increased to 62.1° / 30m. The test results are shown in Table 5.

[0049]

[0050] Table 5 Results of internal pressure sealing test under bending load The load-time curve is shown below. Figure 15 Photos of the test specimens after the experiment are shown below. Figure 16 .

[0051] The test results show that the method of optimizing the bearing surface angle of the direct-connection thread has effectively verified that it significantly improves the thread's bending resistance and sealing capability, achieving performance indicators that surpass those of existing similar products (27° / 30m), and meeting actual needs.

[0052] For other details, please refer to the existing technology.

[0053] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A design method for optimizing bending resistance of a straight thread gas seal based on the load flank angle, characterized by: Includes the following steps: S1. Determine the critical section of the straight-connected thread under bending condition: The tension side of the straight-connected thread is the critical section of the straight-connected thread; S2. Key factors for determining thread tensile strength: The angle of the bearing surface is the key factor for determining thread tensile strength. S3. Determine the effect of thread bearing surface angle change on internal pressure sealing performance under bending load: By comparing the magnitude of sealing surface contact pressure and length under the same limit bending conditions and different bearing surface angles, the applicable angle range is finally determined. S4. Design the product structure of a straight-connection thread; based on the influence of the thread bearing surface angle change on the internal pressure sealing performance under the above bending load, carry out the thread structure optimization design: S5. Establish the optimization method and quantitative law of bending on seal integrity: Under the same bending load, experiments were conducted with bearing surface angles of 0, -5, -10, -15 and -20 degrees respectively to carry out comparative analysis. The law can be obtained: as the bearing surface angle increases, the maximum sealing contact pressure and the axial area formed by the contact increase. S6. Determine product parameters: Based on the above rules, determine the product parameters: the bearing surface angle of the lower thread is -17 to -20°.

2. The design method of straight thread gas seal thread based on load flank angle optimization for bending resistance as claimed in claim 1 wherein: In step S4, the thread structure optimization design is carried out as follows: One end of the direct-connection threaded structure is the external sealing external pressure zone a, which ensures that the thread is not penetrated under external pressure, causing the internal and external threads to separate and slip off under tension; the middle part of the direct-connection threaded structure is the thread tooth connection zone b, where both the internal and external threads are complete tooth profiles, ensuring sufficient tensile strength under tension; the other end of the direct-connection threaded structure is the internal sealing internal pressure zone c, which ensures that the internal pressure seal does not fail under bending and tensile loads. The bearing surface angle 3 of the internal thread 2 improves the thread's resistance to bending and tensile stress, ensuring the integrity of the internal pressure seal; The guide face angle of the internal thread 2 is 4. The thread is anti-sticking and anti-coupling, ensuring easy coupling and preventing sticking. The pitch 5 of the internal thread 2 ensures the effective number of threads in the threaded connection and improves the tensile load-bearing capacity of the thread; The thread taper 6 of the internal thread 2 ensures the thread's tensile strength and thread engagement. The thread height 7 of the internal thread 2 ensures that the effective load-bearing area of ​​the thread and the wall thickness of the tooth root do not deform under tensile and bending loads.

3. The design method for direct-connection gas-tight threads based on bearing surface angle optimization for bending resistance as described in claim 1, characterized in that: In step S6, the product parameters include: The guide surface angle 4 of the lower thread is 25° to 45°; The pitch of the underthread is 15-20 threads / 2.5 inches; The taper of the lower thread is 1:18.5~20.5; The tooth height of the lower thread is 0.75–1.05 mm; The inner sealing pressure zone C is a conical surface or a combination of a conical surface and a spherical surface; The sealing position is 4.5–7.5 mm from the tip of the nose.

4. A manufacturing method for a direct-connection gas-tight thread with optimized bending resistance based on bearing surface angle, characterized in that: Using the above design method and manufacturing with these parameters, the final product is obtained.

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