Method for improving over-torque resistance and air-tightness of oil casing and oil casing

Abstract

The present application relates to the technical field of oil and gas drilling and development, and relates to a method for improving the over-torque resistance and gas sealing performance of an oil casing and the oil casing, the method comprising: asymmetrically upsetting the pipe end, the wall thickness after upsetting being increased by 15% to 25% relative to the original wall thickness of the pipe body, satisfying Leu >= 2Ls, La >= Leu + b + 15mm, wherein Leu is the length of the outer thickening section, Ls is the thread make-up loss length, La is the length of the inner thickening section, and b is the length of the transition section; the angle of the transition section is controlled to be 10° to 20°, and the radius of the arc is greater than 19mm; and after heat treatment of the whole pipe, symmetric male and female threaded joints are processed at both ends. By precisely controlling the geometric matching relationship of the lengths of the upset sections, the over-torque resistance and gas sealing performance are significantly improved, and the stress concentration hidden danger of the transition section is eliminated.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling and development technology, and to a method and oil casing for improving the resistance to over-torsion and gas sealing performance of oil casing. Background Technology

[0002] In the exploration and development of oil and gas, especially in the development of unconventional wells such as ultra-deep wells, directional wells, extended reach wells, and shale gas wells, traditional API threaded joints can no longer meet the requirements for high sealing performance, high compression resistance, high over-torsion resistance, and limited annular clearance. For example, in the development of shale gas wells with large vertical displacement, casing is difficult to run due to high friction. Conventional sliding casing running methods are no longer sufficient, requiring a top drive to apply high torque to the casing and rotate it for entry. In the exploration and development of ultra-deep wells, the complex downhole conditions are unpredictable. To meet design requirements, one or two alternative casing options need to be reserved to satisfy the final design requirements. In such cases, conventional casing selection cannot meet the design requirements, mainly due to insufficient annular clearance and inadequate gas sealing performance.

[0003] To address the aforementioned issues, research and development of special threaded joints with upset pipe ends and gas-tight seals has been undertaken in this field. Among them, Chinese patent CN120844931A discloses a high-torsion-resistant sleeve gas-tight threaded joint structure, which is the closest prior art to this application. This patent forms an inner and outer double-shoulder and inner and outer double-sealing surface structure through upset pipe end formation. It employs parametric control of the upset outer diameter, thread taper, and upper thread loss length, and optimizes the shoulder height ratio, achieving a joint resistance to over-torsion torque that is more than four times that of ordinary API joints. This significantly improves the overall performance of the joint and can meet the usage requirements of some deep shale gas wells and long horizontal well sections.

[0004] However, as well depths continue to exceed 10,000 meters, the high torque and high stress conditions downhole become more demanding. The aforementioned existing technologies have revealed significant shortcomings in application. Under high torque conditions, there is a risk of thread root deformation and joint failure. Stress concentration and uncontrollable plastic deformation are prone to occur at the connection between the upsetting section and the transition section, affecting the structural integrity and sealing reliability of the joint. The wall thickness distribution and stress transmission path have not been optimized for high torque conditions, and the repair margin is insufficient, making it difficult to meet the extreme service requirements of ultra-deep wells at depths of 10,000 meters.

[0005] In response to the shortcomings of existing technologies, there is an urgent need to develop a method to improve the over-torsion resistance and gas-tightness of oil casings in order to meet the development needs of extreme well conditions such as ultra-deep wells, extended reach wells, and deep shale gas wells. Summary of the Invention

[0006] With the development of large-angle horizontal wells and directional wells, the performance requirements for joints are becoming increasingly stringent, especially in terms of sealing capacity and over-torque resistance. Ensuring that the oil casing joint maintains its sealing performance under higher over-torque conditions is crucial. Addressing the structural shortcomings of existing technologies, the present invention aims to provide a method and oil casing that improves the over-torque resistance and gas-tightness of oil casing. By asymmetric upsetting of the pipe ends and parametrically designing the relationship between the outer thickened section, the inner thickened section, the thread loss length, and the transition section length, the sealing performance, compression resistance, over-torque resistance, and limited annular space clearance of the oil casing joint are simultaneously improved.

[0007] The objective of this invention is achieved through the following methods: This invention provides a method for improving the over-torsion resistance and gas-tightness of oil casing, comprising the following steps: (1) The oil casing pipe ends are subjected to asymmetric upsetting treatment to form an outer thickened section, an inner thickened section and a transition section. After the pipe ends are upset, the wall thickness increases by 15% to 25%, and the following geometric relationship is satisfied at the same time: Leu≥2×Ls, La≥Leu+b+15, Where Leu is the length of the outer thickened section, Ls is the thread loss length, La is the length of the inner thickened section, and b is the length of the transition section; (2) The angle range of the upsetting and thickening transition section should be between 10° and 20°, the radius of the arc should be greater than 19mm, and there should be no abrupt structural changes; (3) Perform full-length heat treatment on the upset oil casing; (4) The asymmetric upset end of the oil casing with qualified heat treatment performance is rough machined, and the two ends are respectively machined to form a male end threaded joint and a female end threaded joint. The male end threaded joint and the female end threaded joint are symmetrical structures. The male end threaded joint includes an external thread, a male internal shoulder, a male external shoulder, a male internal sealing surface and a male external sealing surface; the female end threaded joint includes an internal thread, a female internal shoulder, a female external shoulder, a female internal sealing surface and a female external sealing surface, to obtain an oil casing with upset gas-tight threaded joint.

[0008] Preferably, the external thread and the internal thread are tapered threads, with the taper τ ranging from 1:16 to 1:6.

[0009] Preferably, the pitch of the external thread and the internal thread is 4 to 8 threads per inch, and the tooth height of both the external thread and the internal thread is 0.762 to 1.775 mm.

[0010] Preferably, the outer diameter Dw of the asymmetric upsetting end is designed to match the outer diameter W of the thread to meet the annular clearance requirements.

[0011] Preferably, the angle between the male inner top shoulder and the female inner top shoulder and the axis is 90°, and the angle between the male outer top shoulder and the female outer top shoulder and the axis direction is 75°.

[0012] Preferably, the upset outer diameter Dw of the outer thickening section and the upset inner diameter Di of the inner thickening section correspond to the design thread outer diameter W and d.

[0013] Another aspect of the present invention provides an oil casing obtained by the above method, comprising a casing body and asymmetric upset sections located at both ends of the body, wherein the asymmetric upset sections are respectively processed into male end threaded joints and female end threaded joints, and the male end threaded joints and female end threaded joints are symmetrical structures.

[0014] Preferably, after the male threaded connector and the female threaded connector are screwed together, the inner and outer shoulders are aligned and the inner and outer sealing surfaces of the male are interference-fitted, forming a double-sealing-surface, double-shoulder airtight structure.

[0015] Preferably, the middle section of the casing body is not upset, and the oil casing is an integral straight-connected casing without independent couplings.

[0016] The advantages and beneficial effects of this invention are: (1) This invention achieves synergistic optimization of the lengths of each segment within the upsetting section by precisely controlling the geometric relationship between the outer thickening section length Leu and the thread breakage length Ls (Leu ≥ 2×Ls), as well as the matching relationship between the inner thickening section length La and the outer thickening section length Leu and the transition section length b (La ≥ Leu + b + 15). This effectively disperses the torque load generated during thread breakage and service. When the male and female threads are screwed together and an over-torque is applied, the inner and outer double shoulders can simultaneously align and bear the load evenly, avoiding local yielding or failure caused by a single shoulder bearing all the torque.

[0017] (2) This invention provides explicit parameterized control over the transition section: the transition section angle is controlled between 10° and 20°, and the arc radius is greater than 19mm, with strict requirements for no structural abrupt changes. The limitation of these parameter ranges makes the geometric transition between the upsetting section and the pipe body smoother, effectively reducing the stress concentration factor in this area. Under extreme conditions such as high torsion and high compression, the transition section will not become a crack initiation source, significantly improving the fatigue life and operational safety of the sleeve joint.

[0018] (3) The present invention adopts an integral direct connection structure, which does not require an independent coupling. The outer diameter of the joint is close to the outer diameter of the pipe body, which is significantly smaller than that of API conventional coupling products. At the same time, through the matching design of the upset end outer diameter Dw and the thread outer diameter W, the radial dimension of the joint is minimized to the maximum extent while ensuring the joint strength, providing greater margin for the well body structure design with limited annular space gaps such as ultra-deep wells and large-displacement wells.

[0019] (4) By controlling the length of the inner thickened section to be at least greater than the sum of the outer thickened section and the transition section, the upsetting end has the capability to perform thread processing two or even three times. When the first thread fails due to wear or damage, it can be repaired and reprocessed without replacing the entire sleeve, which greatly reduces on-site maintenance costs and material waste. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the asymmetric upsetting structure of the oil casing end of the present invention; Figure 2 This is a schematic diagram of the structure of the upset gas-tight threaded joint of the oil casing of the present invention after screwing. Detailed Implementation

[0021] The oil casing and manufacturing method of an upsetting gas-tight threaded joint according to the present invention will be described in conjunction with the accompanying drawings.

[0022] A method for improving the over-torsion resistance and gas-tightness of oil casing is illustrated using an oil casing with a specification of 127×9.19mm as an example. The steps are as follows: (1) Asymmetric upsetting of pipe ends like Figure 1 As shown, the end of an oil casing with dimensions of 127×9.19mm undergoes asymmetric upsetting to form an outer thickened section, an inner thickened section, and a transition section. The wall thickness increases by 15%~25% after upsetting. Specific parameters are as follows: Upsetting end outer diameter Dw: 142~144mm; Upsetting end inner diameter Di: 102~104mm; The length of the thickened section (Leu) is 240~260mm. Transition section length b: 45~58mm; Length of the inner thickened section La: ≥300mm; And satisfy the following geometric relationship: Leu ≥ 2 × Ls, where Ls is the thread loss length, and in this embodiment Ls=120mm; La ≥ Leu + b + 15; The transition section angle is controlled at 15°, the arc radius is 19mm, and the transition section and the pipe body are smoothly connected without any structural abrupt changes.

[0023] (2) Full-length heat treatment The entire length of the upset oil casing is subjected to heat treatment. The heat treatment regime is determined according to the steel grade of the casing to ensure the consistency of mechanical properties between the casing body and the upset section.

[0024] (3) Rough machining and threading of pipe ends The asymmetric upset end of the oil casing with qualified heat treatment performance is rough machined, and the two ends are respectively machined to form a male end threaded joint and a female end threaded joint, which are symmetrical structures.

[0025] The thread parameters are as follows: Thread type: Offset trapezoidal thread; Thread taper: 1:16; Pitch: 5.08mm (i.e., 5 threads per inch); Tooth height: 1.575mm; Bearing side angle: 3°; Import side angle: 10°; The outer diameter W of the threaded connector is 140~141mm, and the inner diameter d of the threaded connector is 105~106mm; The male threaded connector includes an external thread, an internal male shoulder, an external male shoulder, an internal male sealing surface, and an external male sealing surface; the female threaded connector includes an internal thread, an internal female shoulder, an external female shoulder, an internal female sealing surface, and an external female sealing surface.

[0026] The angle between the male inner and female inner top shoulders and the axis is 90°, while the angle between the male outer and female outer top shoulders and the axis is 75°. The taper of the sealing surface along the pipe axis is 1:10.

[0027] After processing, visual inspection is carried out to ensure that there are no structural mutations.

[0028] (4) Tightening to form an airtight structure like Figure 2 As shown, the male threaded connector and the female threaded connector are screwed together with a certain torque so that the inner and outer shoulders are aligned and the inner and outer sealing surfaces reach the designed interference fit, forming a double sealing surface and double shoulder airtight structure.

[0029] For the female end, the upper deduction loss is a negative tolerance (0, -a); for the male end, the upper deduction loss is a positive tolerance (+a, 0), where a = 0.5.

[0030] Performance testing The oil casing manufactured using the method of this invention was tested for its resistance to over-torsion and its gas-tight performance.

[0031] (1) Torsional resistance test: The steel is 127x9.19mm thick, P110 grade, and API long oval thread type. The maximum upsetting torque is 9000NM. After the pipe end is upset, the over-torque torque can reach 40000NM, which is more than 4 times the over-torque capacity.

[0032] (2) Gas seal test: The sealing performance was tested under high torque conditions. The high and low pressure loading was simulated to simulate shale gas fracturing. There was no leakage and the sealing performance was good.

[0033] In summary, this invention significantly improves the over-torsion resistance and gas-tight performance of oil casing by precisely controlling the geometric matching relationship of the length of each segment of the upsetting section and the parameters of the transition section, eliminating the hidden danger of stress concentration. It is suitable for complex well conditions with limited annular space, such as ultra-deep wells, extended reach wells, and shale gas wells.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the over-torsion resistance and gas-tightness performance of oil casing, characterized in that, The steps are as follows: (1) The oil casing pipe ends are subjected to asymmetric upsetting treatment to form an outer thickened section, an inner thickened section and a transition section. After the pipe ends are upset, the wall thickness increases by 15% to 25%, and the following geometric relationship is satisfied at the same time: Leu≥2×Ls, La≥Leu+b+15mm, Where Leu is the length of the outer thickened section, Ls is the thread loss length, La is the length of the inner thickened section, and b is the length of the transition section; (2) The angle range of the upsetting and thickening transition section should be between 10° and 20°, the radius of the arc should be greater than 19mm, and there should be no abrupt structural changes; (3) Perform full-length heat treatment on the upset oil casing; (4) The asymmetric upset end of the oil casing with qualified heat treatment performance is rough machined, and the two ends are respectively machined to form a male end threaded joint and a female end threaded joint. The male end threaded joint and the female end threaded joint are symmetrical structures. The male end threaded joint includes an external thread, a male internal shoulder, a male external shoulder, a male internal sealing surface and a male external sealing surface; the female end threaded joint includes an internal thread, a female internal shoulder, a female external shoulder, a female internal sealing surface and a female external sealing surface, to obtain an oil casing with upset gas-tight threaded joint.

2. The method according to claim 1, characterized in that, The external and internal threads are tapered threads, with the taper τ ranging from 1:16 to 1:

6.

3. The method according to claim 1, characterized in that, The pitch of the external and internal threads is 4 to 8 threads per inch, and the tooth height of both external and internal threads is 0.762 to 1.775 mm.

4. The method according to claim 1, characterized in that, The outer diameter Dw of the asymmetric upsetting end is designed to match the outer diameter W of the thread to meet the requirements of the annular space clearance.

5. The method according to claim 1, characterized in that, The angle between the male inner top shoulder and the female inner top shoulder and the axis is 90°, and the angle between the male outer top shoulder and the female outer top shoulder and the axis direction is 75°.

6. The method according to claim 1, characterized in that, The upsetting outer diameter Dw of the outer thickening section and the upsetting inner diameter Di of the inner thickening section correspond to the design thread outer diameter W and d.

7. An oil casing obtained by the method according to any one of claims 1-6, characterized in that, It includes a casing body and asymmetrical upsetting sections located at both ends of the casing body. The asymmetrical upsetting sections are respectively machined into male threaded connectors and female threaded connectors, and the male threaded connectors and female threaded connectors have a symmetrical structure.

8. The oil casing according to claim 7, characterized in that, After the male threaded connector and the female threaded connector are screwed together, the inner and outer shoulders are aligned and the inner and outer sealing surfaces of the male are interference-fitted, forming a double-sealing-surface, double-shoulder airtight structure.

9. The oil casing according to claim 7, characterized in that, The middle section of the casing body is not upset, and the oil casing is an integral straight-connected casing without independent couplings.

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