Threaded joint for oil casing

Abstract

The invention provides an oil casing pipe screwed joint. The oil casing screwed joint comprises an inner screwed joint and an outer screwed joint, and the sealing part comprises a sealing cambered surface which is arranged on the peripheral side of the outer screwed joint and protrudes in the direction away from the central axis in the radial direction of the oil casing screwed joint. The composite sealing surface is arranged on the inner peripheral side of the internal thread joint and comprises a main sealing conical surface and an auxiliary sealing conical surface which are connected with each other and are sequentially arranged, the distance between the main sealing conical surface and the central axis and the distance between the auxiliary sealing conical surface and the central axis are gradually reduced, and an angle beta 1 is formed between the main sealing conical surface and the central axis; an angle beta 2 is formed between the auxiliary sealing conical surface and the central axis, and the angle beta 1 is larger than the angle beta 2. According to the technical scheme, the problems that in the prior art, an oil casing pipe threaded connector is poor in sealing stability, compression resistance and thread gluing resistance under the action of combined loads are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil pipe engineering, and in particular, to an oil casing thread joint. Background Art

[0002] With the increasingly complex development environment of oil and gas fields, more stringent requirements are put forward for the sealing performance of oil casing thread joints, that is, excellent sealing robustness and excellent compression performance can be maintained under various complex and harsh working conditions such as tension, compression, internal pressure, external pressure, bending, temperature, etc. and accidental external factors.

[0003] Standard API (American Petroleum Institute) threaded oil casings have problems such as low connection strength of thread joints, poor ability to resist combined loads, and lack of gas sealing performance due to their own design defects, and it is difficult to cope with harsh well conditions, and they are mainly used in well conditions with low requirements such as shallow wells and low-pressure wells.

[0004] Chinese Patent with Publication No. CN2575286Y discloses a utility model patent named "Oil and Casing Thread Joint". The thread of this patented technology is an improved partial trapezoidal structure, and the sealing structure adopts a structure with a cylindrical outer sealing surface and a spherical inner sealing surface. This sealing structure can maintain stable sealing performance under the stress state of oil casings. However, the structure with a spherical inner sealing surface will cause problems of difficult production, processing and detection, and since it is a line contact between the spherical surface and the cylindrical surface, not only is it easy to have poor anti-galling performance between multiple make-up and break-out operations, but also it is easy to cause accidental damage to the sealing structure.

[0005] Chinese Patent with Publication No. CN202946041U discloses a utility model patented technology named "Gas Sealing Serrated Oil Well Pipe Thread Joint Structure". This technology adopts a serrated tooth profile structure, the tooth top and tooth bottom are parallel to the thread generatrix, and the thread connection strength is relatively high, reducing the influence of external loads on the sealing performance; the sealing structure and the positioning shoulder form a wedge structure to maintain the stability of the seal. This patented technology thread joint has good connection strength and sealing performance; however, this sealing structure is close to the positioning shoulder, and its sealing performance is affected by the stress state of the positioning shoulder, and the stability of the sealing performance is not high. When the oil casing thread joint bears external loads, it is easy to have problems of poor sealing robustness. Summary of the Invention

[0006] The main object of the present invention is to provide an oil casing thread joint to solve the problems of poor sealing robustness, poor anti-compression performance, and poor anti-galling performance of the existing oil casing thread joints under the action of combined loads.

[0007] To achieve the above object, the present invention provides an oil casing thread joint. The oil casing thread joint has a central axis. The oil casing thread joint includes an internal thread joint and an external thread joint. Along the central axis, a thread portion, a first groove portion, a sealing portion, a second groove portion, and a shoulder portion are sequentially provided between the internal thread joint and the external thread joint. The thread portion includes an external thread provided on the external thread joint and an internal thread provided on the internal thread joint. The internal thread and the external thread are threadedly connected. The first groove portion and the second groove portion can store thread compound. The sealing portion includes: a sealing arc surface provided on the outer peripheral side of the external thread joint. Along the radial direction of the oil casing thread joint, the sealing arc surface protrudes in a direction away from the central axis; a composite sealing surface provided on the inner peripheral side of the internal thread joint. The composite sealing surface includes a main sealing cone surface and an auxiliary sealing cone surface connected to each other. In the direction from the pipe end of the internal thread joint to the pipe body of the internal thread joint, the main sealing cone surface and the auxiliary sealing cone surface are arranged in sequence, and the distances between the main sealing cone surface and the auxiliary sealing cone surface and the central axis gradually decrease. The main sealing cone surface has an angle β1 with the central axis, and the auxiliary sealing cone surface has an angle β2 with the central axis. The angle β1 is greater than the angle β2. When the internal thread joint and the external thread joint are screwed together, the main sealing cone surface is in sealing cooperation with the sealing arc surface. When the oil casing thread joint bears an external load, both the main sealing cone surface and the auxiliary sealing cone surface are in sealing cooperation with the sealing arc surface.

[0008] Further, the angle β1 and the angle β2 satisfy: 0.2° < angle β1 - angle β2 < 2°.

[0009] Further, the range of the angle β1 is: 4° ≤ β1 ≤ 9°; and / or, the range of the angle β2 is: 3° ≤ β2 ≤ 8°.

[0010] Further, the range of the axial length L21 of the main sealing cone surface is: 2.5 mm ≤ L21 ≤ 4 mm; and / or, the range of the axial length L22 of the auxiliary sealing cone surface is: 1 mm ≤ L22 ≤ 2.5 mm.

[0011] Further, the range of the arc radius R10 of the sealing arc surface is: 200 mm ≤ R10 ≤ 500 mm.

[0012] Further, the nose end of the external thread joint has an axial length L10, and the sealing arc surface has an axial length L11. The ratio of the axial length L11 to the axial length L10 satisfies: 0.3 ≤ L11 / L10 ≤ 0.9.

[0013] Further, when the external thread joint and the internal thread joint are screwed together, the sealing arc surface and the main sealing cone surface first come into contact at the initial contact tangent point P. The tangent point P has an axial distance L30 from the external thread. The nose end of the external thread joint has an axial length L10. The ratio of the axial distance L30 to the axial length L10 satisfies: 0.56 ≤ L30 / L10 ≤ 0.86.

[0014] Further, the nose end of the external threaded joint has an axial length L10, and the axial length L10 satisfies: 10mm≤L10≤30mm.

[0015] Furthermore, the external thread joint is provided with an outer cylindrical surface for connecting the sealing arc surface and the external thread, and the internal thread joint is provided with an inner cylindrical surface for connecting the internal thread and the main sealing cone surface. Part of the internal thread and the inner cylindrical surface and the outer cylindrical surface together form a first groove portion.

[0016] Furthermore, an inner connecting surface is provided on the internal thread joint, and the inner connecting surface is connected to the side of the auxiliary sealing cone surface away from the main sealing cone surface, and part of the sealing arc surface and the inner connecting surface form a second groove portion.

[0017] Furthermore, the inner connecting surface is a cylindrical surface; or, the inner connecting surface is a conical surface, and the angle between the inner connecting surface and the central axis ranges from 0° to 3°.

[0018] Furthermore, the shoulder portion includes: a first shoulder surface, which is arranged on the external threaded joint; a second shoulder surface, which is arranged on the internal threaded joint. When the internal threaded joint and the external threaded joint are screwed together, the first shoulder surface and the second shoulder surface are interference fit.

[0019] Further, an angle α1 is formed between the first shoulder surface and the cross section of the external threaded joint, and the angle α1 satisfies: 5°≤α1≤15°.

[0020] Further, an angle β3 is formed between the second shoulder surface and the cross section of the internal thread joint, and the angle β3 and the angle α1 satisfy: 0°≤β3-α1≤0.5°.

[0021] Further, along the central axis A, there is an axial distance L20 between the end of the main sealing cone surface close to the internal thread and the second shoulder surface, and the axial distance L20 and the axial length L21 of the main sealing cone surface satisfy: 0.1≤L21 / L20≤0.5.

[0022] Furthermore, the nose end of the external threaded joint is provided with a nose end inner surface, and an angle α2 is formed between the nose end inner surface and the central axis, and the angle α2 satisfies: 0°≤α2≤10°.

[0023] Applying the technical solution of the present invention, on the one hand, compared with the prior art in which the inner sealing surface is set as a spherical surface, the sealing arc surface of the present invention is arranged on the outer peripheral side of the external thread joint. In this way, not only can the processing difficulty be simplified, but also it is convenient for the quality inspection of the oil casing thread joint during the production stage. Moreover, both the main sealing cone surface and the auxiliary sealing cone surface are in surface contact with the sealing arc surface. In this way, the sealing contact area can be increased, and the sealing arc surface and the composite sealing surface can be uniformly stressed throughout the entire contact length, effectively dispersing the stress concentration during the tightening process. This can not only avoid the problem of poor anti-galling performance caused by multiple make-up and break-out operations, but also prevent accidental damage to the sealing part, thereby maintaining a long-term stable connection sealing effect. On the other hand, compared with the problem of poor sealing performance of the sealing structure in the prior art, in the present invention, when the oil casing thread joint bears external loads, especially compressive loads and external pressure loads, its sealing performance is further improved. Specifically, when the external thread joint and the internal thread joint are screwed and engaged, a preliminary sealing fit is formed between the main sealing cone surface and the sealing arc surface. And when the oil casing thread joint bears loads under complex working conditions, the auxiliary sealing cone surface can also participate in the sealing, and the auxiliary sealing cone surface and the sealing arc surface form a second layer of sealing, greatly increasing the sealing contact area. The design of this composite sealing structure not only improves the initial sealing performance in the unloaded state, but also when bearing external compressive loads and external pressure loads, the main sealing cone surface and the auxiliary sealing cone surface are both in sealing fit with the sealing arc surface, making the contact pressure distribution of the sealing part more uniform, and can avoid the problem of sealing failure that may be caused by pressure concentration. Thereby, the gas sealing robustness and compressive capacity of the oil casing thread joint can be enhanced, and further the sealing performance of the oil casing thread joint can be improved. At the same time, this multi-position contact sealing method also improves the gas tightness of the oil casing thread joint, and can maintain a good sealing state even under extreme combined loads. On the other hand, the sealing arc surface protrudes radially away from the central axis A of the oil casing thread joint. Since the thickness of the sealing arc surface along the axial direction decreases less than that of the sealing cone surface, the thickness of the shoulder surface of the sealing arc surface can be made larger, so that the oil casing thread joint has a higher compressive strength. Description of the Drawings

[0024] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0025] Figure 1 The structural schematic diagram of the embodiment of the oil casing thread joint of the present invention is shown;

[0026] Figure 2 Shown is Figure 1 The structural schematic diagram of the external thread joint of the oil casing thread joint of

[0027] Figure 3 shows the Figure 1 structural schematic diagram of the internal thread joint of the casing and tubing thread joint;

[0028] Figure 4 shows the Figure 2 partial enlarged view of the external thread joint;

[0029] Figure 5 shows the Figure 3 partial enlarged view of the internal thread joint;

[0030] Figure 6 shows the Figure 3 another partial enlarged view of the internal thread joint;

[0031] Figure 7 shows the Figure 1 schematic diagram of the tangent point P where the sealing arc surface of the external thread joint first contacts the main sealing cone surface of the internal thread joint;

[0032] Figure 8 shows the stress nephogram of the casing and tubing thread joint under the action of the maximum compressive load in the prior art;

[0033] Figure 9 shows the stress nephogram of the casing and tubing thread joint of the present invention under the action of the maximum compressive load;

[0034] Figure 10 shows the comparison diagram of the sealing contact pressure distribution of the casing and tubing thread joint in the prior art and the present invention under the action of external pressure and compressive load;

[0035] Figure 11 shows the comparison diagram of the sealing contact pressure distribution of the casing and tubing thread joint in the prior art and the present invention under the action of external pressure and tensile load.

[0036] Among them, the above-mentioned drawings include the following reference numerals:

[0037] 1. External thread joint; 10. Outer cylindrical surface; 11. Sealing arc surface; 12. First shoulder surface; 13. Cylindrical surface; 14. Inner surface of nose end; 2. Internal thread joint; 20. Inner cylindrical surface; 21. Inclined surface; 22. Main sealing cone surface; 23. Auxiliary sealing cone surface; 24. Inner connection surface; 25. Second shoulder surface; 30. Thread part; 31. Internal thread; 32. External thread; 40. First groove part; 50. Sealing part; 60. Second groove part; 70. Shoulder part. Detailed implementation mode

[0038] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] It should be noted that in the embodiments of the present invention, the external load refers to the multi-dimensional composite load composed of tensile load, compressive load, internal pressure load, external pressure load, bending load, etc. acting on the oil casing thread joint after the internal thread joint 2 and the external thread joint 1 are screwed together. Among them, the external pressure load refers to the pressure acting on the outer surface of the oil casing thread joint, and the internal pressure load refers to the pressure acting on the inner surface of the oil casing thread joint. If it is a large pipe string, it mainly bears the external pressure load, and the internal pipe string mainly bears the internal pressure load; the compressive load is an axial force load caused by thermal expansion due to high temperature downhole and the axial thrust applied manually during the downhole operation of the pipe string, which is common in the complex working conditions of oil casings during drilling, completion and production; the tensile load refers to the axial tensile force borne by the oil casing thread joint. During oil extraction, the tensile load is caused by the weight of the pipe string itself, the lifting of the oil casing, and the cyclic thermal expansion and contraction.

[0040] It should be noted that in the embodiments of the present invention, the nose end of the external thread joint 1 refers to the pipe end of the external thread joint 1.

[0041] It should be noted that in the embodiments of the present invention, the axial length refers to the length in the direction of the central axis, and the axial distance refers to the distance in the direction of the central axis.

[0042] Such as Figures 1 to 11As shown in the figure, an embodiment of the present invention provides an oil casing thread joint. The oil casing thread joint has a central axis A. The oil casing thread joint includes an internal thread joint 2 and an external thread joint 1. Along the central axis A, a thread portion 30, a first groove portion 40, a sealing portion 50, a second groove portion 60, and a shoulder portion 70 are sequentially arranged between the internal thread joint 2 and the external thread joint 1. The thread portion 30 includes an external thread 32 provided on the external thread joint 1 and an internal thread 31 provided on the internal thread joint 2. The internal thread 31 and the external thread 32 are threadedly connected. The first groove portion 40 and the second groove portion 60 can store thread compound. The sealing portion 50 includes: a sealing arc surface 11 provided on the outer peripheral side of the external thread joint 1. Along the radial direction of the oil casing thread joint, the sealing arc surface 11 protrudes in a direction away from the central axis A; a composite sealing surface provided on the inner peripheral side of the internal thread joint 2. The composite sealing surface includes a main sealing conical surface 22 and an auxiliary sealing conical surface 23 connected to each other. In the direction from the pipe end of the internal thread joint 2 to the pipe body of the internal thread joint 2, the main sealing conical surface 22 and the auxiliary sealing conical surface 23 are arranged in sequence, and the distances between the main sealing conical surface 22 and the auxiliary sealing conical surface 23 and the central axis A gradually decrease. The main sealing conical surface 22 has an angle β1 with the central axis A, and the auxiliary sealing conical surface 23 has an angle β2 with the central axis A. The angle β1 is greater than the angle β2. When the internal thread joint 2 and the external thread joint 1 are screwed together, the main sealing conical surface 22 is in sealing cooperation with the sealing arc surface 11. When the oil casing thread joint bears compressive loads and external pressure loads (such as pure compressive loads, compressive + internal pressure loads, compressive + external pressure loads, external pressure loads, external pressure + tensile loads, etc.), both the main sealing conical surface 22 and the auxiliary sealing conical surface 23 are in sealing cooperation with the sealing arc surface 11.

[0043] In the above technical solution, on the one hand, compared with the prior art in which the inner sealing surface is set as a spherical surface, the sealing arc surface 11 of the present invention is arranged on the outer peripheral side of the external thread joint 1. In this way, not only can the processing difficulty be simplified, but also the quality inspection of the oil casing thread joint during the production stage is facilitated. Moreover, both the main sealing cone surface 22 and the auxiliary sealing cone surface 23 are in surface contact with the sealing arc surface 11. In this way, the sealing contact area can be increased, and the sealing arc surface 11 and the composite sealing surface can be evenly stressed along the entire contact length, effectively dispersing the stress concentration during the tightening process. This can not only avoid the problem of poor anti-galling performance caused by multiple make-and-break operations, but also prevent accidental damage to the sealing part 50, thus maintaining a long-term stable connection sealing effect. On the other hand, compared with the problem of poor sealing performance of the sealing structure in the prior art, in the present invention, when the oil casing thread joint bears external loads, especially compression loads and external pressure loads, its sealing performance is further improved. Specifically, after the external thread joint 1 and the internal thread joint 2 are screwed and engaged, a preliminary sealing fit is formed between the main sealing cone surface 22 and the sealing arc surface 11. When the oil casing thread joint bears loads under complex working conditions, the auxiliary sealing cone surface 23 can also participate in the sealing, and the auxiliary sealing cone surface 23 and the sealing arc surface 11 form a second-stage seal, greatly increasing the sealing contact area. The design of this composite sealing structure not only improves the initial sealing performance in the unloaded state, but also when bearing external compression loads and external pressure loads, the main sealing cone surface 22 and the auxiliary sealing cone surface 23 are both in sealing fit with the sealing arc surface 11, making the contact pressure distribution of the sealing part 50 more uniform, and can avoid the problem of sealing failure that may be caused by pressure concentration, thereby enhancing the gas sealing robustness and compressive capacity of the oil casing thread joint, and further improving the sealing performance of the oil casing thread joint. At the same time, this multi-position contact sealing method also improves the gas tightness of the oil casing thread joint, and can maintain a good sealing state even under extreme combined loads. On the further hand, the sealing arc surface 11 protrudes radially away from the central axis A along the oil casing thread joint. Since the thickness of the sealing arc surface 11 decreases less along the axial direction compared with the sealing cone surface, the thickness of the first shoulder surface 12 of the sealing arc surface 11 can be made larger, so that the oil casing thread joint has a higher compressive strength.

[0044] Furthermore, the setting of the first groove portion 40 and the second groove portion 60 further optimizes the performance of the oil casing thread joint during operation. The first groove portion 40 and the second groove portion 60 can not only store excessive thread compound to reduce the interference of the high backpressure caused by the thread compound after making up the thread on the sealing performance, so as to improve the reliability of the thread sealing performance.

[0045] For the casing and tubing thread joint of the Chinese patent with the publication number CN202946041U, in order to achieve 100% compression performance, the tube end necking process is often required, which will lead to the problem of high production and processing costs. Therefore, in the present invention, by adopting the sealing arc surface 11, the first shoulder surface 12 of the casing and tubing thread joint can have a larger thickness value, which is beneficial to enhancing the anti-compression performance of the casing and tubing thread joint, and at the same time, the sealing arc surface 11 and the composite sealing surface have excellent sealing performance.

[0046] Preferably, in the embodiment of the present invention, after the external thread joint 1 and the internal thread joint 2 are screwed and engaged, the sealing arc surface 11 and the main sealing cone surface 22 are in interference contact, that is, the sealing arc surface 11 and the main sealing cone surface 22 are in sealing cooperation; when the casing and tubing thread joint is under the action of a compression load, both the main sealing cone surface 22 and the auxiliary sealing cone surface are in interference contact with the sealing arc surface 11, jointly constituting the sealing part 50. In this way, the sealing performance of the casing and tubing thread joint under complex working conditions can have excellent stability.

[0047] It should be noted that the radial direction of the casing and tubing thread joint is perpendicular to the central axis.

[0048] It should be noted that according to Figure 10 the comparison of the sealing contact pressure distribution between the casing and tubing thread joint of the existing patent technology and the casing and tubing thread joint of the present invention under the external pressure load and compression load shown, it can be seen that the peak value of the sealing contact pressure of the casing and tubing thread joint of the present invention is significantly lower than that of the casing and tubing thread joint of the existing patent technology, reducing the probability of fretting wear and sticking; at the same time, it can be seen that the length of the sealing contact pressure of the casing and tubing thread joint of the existing patent technology is greater than that of the existing technology, indicating that the present invention has better sealing performance; according to Figure 11 the comparison of the sealing contact pressure distribution between the casing and tubing thread joint of the existing patent technology and the casing and tubing thread joint of the present invention under the external pressure load and tensile load shown, it can be seen that the peak value of the sealing contact pressure of the casing and tubing thread joint of the present invention is significantly lower than that of the casing and tubing thread joint of the existing patent technology, reducing the probability of fretting wear and sticking; at the same time, it can be seen that the length of the sealing contact pressure of the casing and tubing thread joint of the existing patent technology is greater than that of the existing technology, indicating that the present invention has better sealing performance. Therefore, the sealing performance of the casing and tubing thread joint of the present invention under complex working conditions is more excellent than that of the casing and tubing thread joint of the existing patent technology.

[0049] As Figure 6 shown, in the embodiment of the present invention, the angle β1 and the angle β2 satisfy: 0.2° < angle β1 - angle β2 < 2°.

[0050] In the above technical scheme, by setting the above angle range, when the internal threaded joint 2 and the external threaded joint 1 are screwed together and the oil casing threaded joint is not subjected to external load, the main sealing cone surface 22 can be in contact with the sealing arc surface 11, and the auxiliary sealing cone surface 23 can be prevented from contacting the sealing arc surface 11; when the internal threaded joint 2 and the external threaded joint 1 are screwed together and the oil casing threaded joint is subjected to external load, the auxiliary sealing cone surface 23 can be fully in contact with the sealing arc surface 11, and the problem of insufficient sealing ability between the auxiliary sealing cone surface 23 and the sealing arc surface 11 can be avoided, and the problem of excessive contact pressure between the composite sealing surface and the sealing arc surface 11 can be avoided, so that the problem of micro-motion damage to the sealing surface can be avoided; therefore, the above angle range can effectively prevent excessive contact and damage to the sealing surface while ensuring that the oil casing threaded joint has excellent sealing performance.

[0051] Preferably, in an embodiment of the present invention, angle β1 - angle β2 is 0.95°.

[0052] like Figure 6 As shown, in the embodiment of the present invention, the angle β1 is in the range of 4°≤β1≤9°. By using the sealing angle in the above range, the oil casing threaded joint can have an excellent sealing distribution state and good anti-seizing performance of the sealing surface.

[0053] like Figure 6 As shown, in the embodiment of the present invention, the angle β2 is in the range of 3°≤β2≤8°.

[0054] Through the sealing angle within the above range, when subjected to a compressive load, the main sealing cone surface 22 and the auxiliary sealing cone surface 23 can both come into contact with the sealing arc surface 11, thereby jointly forming a sealing portion 50. In this way, the sealing performance of the oil casing threaded joint can have excellent stability under complex working conditions.

[0055] like Figure 5 and Figure 6 As shown, in the embodiment of the present invention, the axial length L21 of the main sealing cone surface 22 is in the range of: 2.5mm≤L21≤4mm.

[0056] In the above technical solution, the range selection of L21 can enable the main sealing cone surface 22 to effectively disperse the stress when subjected to external composite loads, thereby avoiding stress concentration at a certain point and destroying the seal. When subjected to compression loads or external pressure loads, the main sealing cone surface 22 with a suitable length can form a more uniform contact pressure distribution with the sealing arc surface 11 of the external threaded joint 1, ensuring that even under harsh working conditions, the sealing part 50 can maintain the sealing ability and structural integrity under high pressure.

[0057] like Figure 5 and Figure 6As shown, in the embodiments of the present invention, the axial length L22 of the auxiliary sealing conical surface 23 ranges from 1 mm ≤ L22 ≤ 2.5 mm.

[0058] In the above technical solution, the specific range of L22 can optimize the stress distribution of the oil casing thread joint under combined loads, effectively avoiding seal failure caused by stress concentration. When the oil casing thread joint works under complex conditions, the combined contact between the auxiliary sealing conical surface 23 and the sealing arc surface 11 not only increases the overall seal contact area, but also enables the contact pressure to be evenly distributed over a larger range, thereby greatly reducing the risk of damage to a single sealing surface due to excessive pressure and enhancing the joint's resistance to combined loads.

[0059] As Figure 4 shown, in the embodiments of the present invention, the arc radius R10 of the sealing arc surface 11 ranges from 200 mm ≤ R10 ≤ 500 mm. Among them, the sealing arc surface 11 is preferably an arc surface.

[0060] Through the above settings, the first shoulder surface 12 of the external thread joint 1 can have a relatively large thickness value, which is beneficial to enhancing the compression resistance of the oil casing thread joint (for example, under the action of the maximum compression load, the compression resistance of the oil casing thread joint of the present invention ( Figure 9 shown stress nephogram) is significantly better than that of the oil casing thread joint of the prior art ( Figure 8 shown stress nephogram)). At the same time, setting the arc radius R10 within the above range can increase the seal contact area between the sealing arc surface 11 and the composite sealing surface, so that the sealing part 50 has excellent anti-galling performance.

[0061] As Figure 4 shown, in the embodiments of the present invention, the nose end of the external thread joint 1 has an axial length L10, the sealing arc surface 11 has an axial length L11, and the ratio of the axial length L11 to the axial length L10 satisfies: 0.3 ≤ L11 / L10 ≤ 0.9.

[0062] Through the above settings, the stiffness of the sealing part 50 of the oil casing thread joint can be improved, thereby improving the seal stability performance.

[0063] As Figure 7 shown, in the embodiments of the present invention, when the external thread joint 1 and the internal thread joint 2 are screwed together, the sealing arc surface 11 and the main sealing conical surface 22 first come into contact at the initial contact tangent point P. There is an axial distance L30 between the tangent point P and the external thread 32. The nose end of the external thread joint 1 has an axial length L10, and the ratio of the axial distance L30 to the axial length L10 satisfies: 0.56 ≤ L30 / L10 ≤ 0.86.

[0064] With the above settings, by controlling the position of the tangent point P and the ratio of L30 / L10, it can be ensured that at the initial stage of screwing, the sealing arc surface 11 and the main sealing conical surface 22 can quickly establish a gentle and stable contact; and by reasonably setting the position of the tangent point P, problems such as excessive wear or unstable contact of the sealing surface caused by premature or late contact of the sealing surface can be avoided, thereby extending the service life of the threaded joint and reducing the maintenance and replacement costs caused by threaded joint failures.

[0065] It should be noted that, as Figure 7 shown, in the embodiment of the present invention, the tangent point P is located at the forefront position where the sealing arc surface 11 and the main sealing conical surface 22 intersect during the tightening process of the external threaded joint 1 and the internal threaded joint 2, that is, during the tightening process of the external threaded joint 1 and the internal threaded joint 2. The point where the sealing arc surface 11 and the main sealing conical surface 22 first come into contact.

[0066] It should be noted that, as Figure 7 shown, in the embodiment of the present invention, the axial distance L30 refers to the distance between the end of the external thread 32 facing the sealing arc surface 11 and the tangent point P in the direction of the central axis A, that is, the distance between the starting position of the external thread 32 and the tangent point P.

[0067] As Figure 4 and Figure 7 shown, in the embodiment of the present invention, based on the different specifications of the oil casing threaded joint, the nose end of the external threaded joint 1 has an axial length L10, and the axial length L10 satisfies: 10mm ≤ L10 ≤ 30mm.

[0068] Through the above settings, a better balance can be achieved between the connection strength and the sealing performance of the oil casing threaded joint.

[0069] As Figure 1 、 Figure 4 and Figure 5 shown, in the embodiment of the present invention, an external cylindrical surface 10 for connecting the sealing arc surface 11 and the external thread 32 is provided on the external threaded joint 1, and an internal cylindrical surface 20 for connecting the internal thread 31 and the main sealing conical surface 22 is provided on the internal threaded joint 2. Part of the internal thread 31, the internal cylindrical surface 20 and the external cylindrical surface 10 together enclose a first groove portion 40. In this way, the first groove portion 40 can store excessive thread compound, thereby avoiding the influence of the thread compound pressure on the sealing performance.

[0070] As Figure 1 、 Figure 4 and Figure 5As shown, in the embodiment of the present invention, the internal thread joint 2 is provided with an internal connection surface 24, which is connected to the side of the auxiliary sealing cone surface 23 away from the main sealing cone surface 22, and part of the sealing arc surface 11 and the internal connection surface 24 form a second groove portion 60. In this way, the second groove portion 60 can store excess thread compound, thereby preventing the thread compound pressure from affecting the sealing performance.

[0071] It should be noted that the first groove portion 40 and the second groove portion 60 are formed by the cooperation of the internal thread joint 2 and the external thread joint 1, and can store excess thread grease applied during the downhole operation, thereby reducing the influence of the thread grease pressure on the performance of the oil casing thread joint. In this way, there is no need to specially process the groove structure on the external thread joint 1 or the internal thread joint 2, thereby improving the processing efficiency.

[0072] Specifically, Figure 5 As shown, in an embodiment of the present invention, an inclined surface 21 for connecting the inner cylindrical surface 20 and the main sealing cone surface 22 is provided on the internal threaded joint 2, and an arc R20 is provided between the inclined surface 21 and the inner cylindrical surface 20, so that a transition connection between the inner cylindrical surface 20 and the main sealing cone surface 22 can be achieved.

[0073] Preferably, if Figure 5 As shown, in the embodiment of the present invention, the inner connecting surface 24 is a cylindrical surface.

[0074] In one embodiment, the inner connecting surface 24 is a conical surface, and the angle between the inner connecting surface 24 and the central axis A is between 0° and 3°. By setting the angle in the above range, the second groove portion 60 of the oil casing threaded joint can better accommodate excessive thread grease, and at the same time, it can avoid affecting the contact between adjacent sealing surfaces (sealing arc surface 11 and composite sealing surface).

[0075] like Figure 1 , Figure 4 and Figure 5 As shown, in an embodiment of the present invention, the shoulder portion 70 includes: a first shoulder surface 12, which is arranged on the external threaded joint 1; a second shoulder surface 25, which is arranged on the internal threaded joint 2. When the internal threaded joint 2 and the external threaded joint 1 are screwed together, the first shoulder surface 12 and the second shoulder surface 25 are interference fit.

[0076] With the above settings, the interference fit between the first shoulder surface 12 and the second shoulder surface 25 forms a shoulder portion 70. In this way, it can play the roles of screwing connection positioning and anti-compression, preventing the screwing position of the oil casing thread joint from being uncertain and preventing structural damage under high compression in extreme conditions, thereby maintaining the connection strength of the oil casing thread joint and the stability of the overall structure. Among them, when the internal thread joint 2 and the external thread joint 1 are screwed and rotated to the final position, the interference contact between the first shoulder surface 12 and the second shoulder surface 25 prompts the sealing arc surface 11, the main sealing cone surface 22 and the auxiliary sealing cone surface 23 to form a more compact sealing contact. This tight contact mechanism, especially the interference contact fit, greatly improves the robustness and reliability of the seal. Even under high-pressure gas or liquid media, it can maintain an effective sealing effect.

[0077] Furthermore, the interference fit between the first shoulder surface 12 and the second shoulder surface 25 of the shoulder portion 70 provides a clear termination mark for the screwing operation of the thread joint. The operator can judge whether the screwing reaches the ideal state by feeling the obvious damping when the first shoulder surface 12 contacts the second shoulder surface 25, thereby avoiding over-screwing or under-screwing, improving the accuracy and convenience of on-site operation, and at the same time reducing the damage of the thread joint caused by improper operation.

[0078] As Figure 4 shown, in the embodiment of the present invention, there is an angle α1 between the first shoulder surface 12 and the cross-section of the external thread joint 1, and the angle α1 satisfies: 5° ≤ α1 ≤ 15°.

[0079] Through the above settings, after the first shoulder surface 12 and the second shoulder surface 25 are in interference contact, the force on the first shoulder surface 12 can be relatively uniform, so that the oil casing thread joint has good compression performance.

[0080] It should be noted that in the embodiment of the present invention, the cross-section of the external thread joint 1 is perpendicular to the central axis A.

[0081] Specifically, in the embodiment of the present invention, a transition arc R11 is provided between the first shoulder surface 12 and the sealing arc surface 11, and the value range of the transition arc R11 satisfies: 0.6 mm ≤ R11 ≤ 2.0 mm.

[0082] As Figures 4 to 6 shown, in the embodiment of the present invention, there is an angle β3 between the second shoulder surface 25 and the cross-section of the internal thread joint 2, and the angle β3 and the angle α1 satisfy: 0° ≤ β3 - α1 ≤ 0.5°.

[0083] Through the above settings, it is possible to compensate for the increase in the interference amount on the side of the shoulder surface close to R11 caused by the necking of the pipe end of the external thread joint 1, and to compensate for the decrease in the interference amount on the side of the shoulder surface far from R11 caused by the necking of the pipe end of the external thread joint 1. In this way, the first shoulder surface 12 and the second shoulder surface 25 can be in contact with relatively uniform stress, so that the oil casing thread joint has good compression performance.

[0084] It should be noted that in the embodiment of the present invention, the cross-section of the internal thread joint 2 is perpendicular to the central axis A.

[0085] As Figure 6 shown, in the embodiment of the present invention, along the central axis A, there is an axial distance L20 between the end of the main sealing cone surface 22 close to the internal thread 31 and the second shoulder surface 25, and the axial distance L20 and the axial length L21 of the main sealing cone surface 22 satisfy: 0.1 ≤ L21 / L20 ≤ 0.5.

[0086] Through the above settings, the sealing part 50 of the oil casing thread joint can be far away from the shoulder part 70, and the stiffness of the sealing part 50 is improved. Thus, it is effectively avoided that the sealing part 50 in the sealing contact state (the sealing arc surface 11 and the composite sealing surface are in sealing contact) is affected by the stress state of the shoulder part 70. Furthermore, the sealing performance of the oil casing thread joint under complex working conditions can have excellent stability and compression performance.

[0087] As Figure 4 shown, in the embodiment of the present invention, the nose end of the external thread joint 1 is provided with a nose end inner surface 14, and there is an angle α2 between the nose end inner surface 14 and the central axis A, and the angle α2 satisfies: 0° ≤ α2 ≤ 10°.

[0088] Through the above settings, the nose end of the external thread joint 1 can be more easily deformed, that is, the axial stiffness of the nose end of the external thread joint 1 is reduced. In this way, the compression performance of the oil casing thread joint is improved, and at the same time, it is beneficial to the circumferential uniform contact deformation of the sealing part 50, so that the sealing contact pressure is evenly distributed in the circumferential direction.

[0089] In one embodiment, when α2 = 0°, that is, the nose end inner surface has both a cylindrical surface 13 ( Figure 4 the cylindrical surface 13 shown by the dotted line in

[0090] In one embodiment, when α2 = 8°, the axial stiffness of the nose end is reduced, and at the same time, the stiffness of the sealing surface is increased.

[0091] It should be noted that the present invention provides an oil casing thread joint with excellent compression performance and gas seal robustness. This thread joint still has good structural integrity and seal integrity under various complex and severe load conditions, especially has excellent sealing performance under external pressure composite conditions, and can be applied to oil and gas wells with complex geological conditions such as high temperature, high pressure, and ultra-deep depth. It is mainly used for well conditions with demanding requirements for gas seal and compression performance.

[0092] Preferably, the embodiment of the present invention uses a casing with a specification of 196.85mm×12.7mm and a steel grade of 140V. The geometric parameters of the oil casing thread joint are: pitch P = 5 threads per inch, thread taper 1:16, L10 = 21mm, L30 / L10 = 0.57, L11 / L10 = 0.60, R10 = 250, α1 = 8°, α2 = 8°, L21 = 3.5mm, L22 = 1.6mm, β3-α1 = 0.3°, L21 / L20 = 0.24. The connection strength of this oil casing thread joint can reach 7094kN, the anti-compression strength can reach 7094kN, the gas seal performance can reach above 109.1Mpa, the anti-external pressure performance can reach above 85.8Mpa, the anti-bending ability can reach above 20° / 30 meters, and it meets the requirement of no sticking during 3 make-and-break operations. At the same time, this oil casing thread joint has good operability such as threading and engaging, and has the robustness of excellent sealing performance.

[0093] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: On the one hand, compared with the prior art in which the inner sealing surface is set as a spherical surface, the present invention sets the sealing arc surface on the outer peripheral side of the external thread joint. In this way, not only can the processing difficulty be simplified, but also it is convenient for the quality inspection of the oil casing thread joint during the production stage. Moreover, both the main sealing cone surface and the auxiliary sealing cone surface are in surface contact with the sealing arc surface. In this way, the sealing contact area can be increased, and the sealing arc surface and the composite sealing surface can be uniformly stressed throughout the entire contact length, effectively dispersing the stress concentration during the tightening process. This can not only avoid the problem of poor anti-galling performance caused by multiple make-up and break-out operations, but also prevent accidental damage to the sealing part, thus maintaining a long-term stable connection sealing effect. On the other hand, compared with the problem of poor sealing performance of the sealing structure in the prior art, in the present invention, when the oil casing thread joint bears external loads, especially compressive loads and external pressure loads, its sealing performance is further improved. Specifically, when the external thread joint and the internal thread joint are screwed and engaged, a preliminary sealing fit is formed between the main sealing cone surface and the sealing arc surface. And when the oil casing thread joint bears loads under complex working conditions, the auxiliary sealing cone surface can also participate in the sealing, and the auxiliary sealing cone surface and the sealing arc surface form a second layer of sealing, greatly increasing the sealing contact area. The design of this composite sealing structure not only improves the initial sealing performance in the unloaded state, but also when bearing external compressive loads and external pressure loads, the sealing fit between the main sealing cone surface and the auxiliary sealing cone surface and the sealing arc surface makes the contact pressure distribution of the sealing part more uniform, and can avoid the problem of sealing failure that may be caused by pressure concentration. Thereby, the gas sealing robustness and compressive resistance of the oil casing thread joint can be enhanced, and further the sealing performance of the oil casing thread joint can be improved. At the same time, this multi-position contact sealing method also improves the gas tightness of the oil casing thread joint, and can maintain a good sealing state even under extreme combined loads. On the other hand, the sealing arc surface protrudes radially away from the central axis A of the oil casing thread joint. Since the thickness of the sealing arc surface decreases less along the axial direction compared with the sealing cone surface, the thickness of the shoulder surface of the sealing arc surface can be made larger, so that the oil casing thread joint has a higher compressive strength.

[0094] The foregoing is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A threaded joint for oil casing, characterized in that: The oil casing threaded joint has a central axis (A), and comprises an internal threaded joint (2) and an external threaded joint (1). Along the central axis (A), a threaded portion (30), a first groove portion (40), a sealing portion (50), a second groove portion (60) and a shoulder portion (70) are sequentially arranged between the internal threaded joint (2) and the external threaded joint (1). The threaded portion (30) comprises an external thread (32) arranged on the external threaded joint (1) and an internal thread (31) arranged on the internal threaded joint (2). The internal thread (31) and the external thread (32) are threadedly connected. The first groove portion (40) and the second groove portion (60) are capable of storing thread grease. The sealing portion (50) comprises: A sealing arc surface (11) is arranged on the outer peripheral side of the external threaded joint (1), and along the radial direction of the oil casing threaded joint, the sealing arc surface (11) protrudes in a direction away from the central axis (A); A composite sealing surface is provided on the inner circumference of the internal threaded joint (2), the composite sealing surface comprising a main sealing cone surface (22) and an auxiliary sealing cone surface (23) connected to each other, in the direction from the pipe end of the internal threaded joint (2) to the pipe body of the internal threaded joint (2), the main sealing cone surface (22) and the auxiliary sealing cone surface (23) are arranged in sequence, and the distances between the main sealing cone surface (22) and the auxiliary sealing cone surface (23) and the central axis (A) gradually decrease, and the main sealing cone surface (22) and the auxiliary sealing cone surface (23) are connected to each other. An angle β1 is formed between the central axis (A), an angle β2 is formed between the auxiliary sealing cone surface (23) and the central axis (A), and the angle β1 is greater than the angle β2. When the internal thread joint (2) and the external thread joint (1) are screwed together, the main sealing cone surface (22) and the sealing arc surface (11) are sealed together. When the oil casing thread joint is subjected to an external load, the main sealing cone surface (22) and the auxiliary sealing cone surface (23) are both sealed together with the sealing arc surface (11).

2. The oil casing threaded joint according to claim 1, characterized in that: The angle β1 and the angle β2 satisfy: 0.2°<the angle β1−the angle β2<2°.

3. The oil casing threaded joint according to claim 2, characterized in that: The angle β1 is in the range of: 4°≤β1≤9°; and / or, The range of the angle β2 is: 3°≤β2≤8°.

4. The oil casing threaded joint according to claim 1, characterized in that: The axial length L21 of the main sealing cone surface (22) is in the range of: 2.5 mm ≤ L21 ≤ 4 mm; and / or, The axial length L22 of the auxiliary sealing cone surface (23) is in the range of 1 mm ≤ L22 ≤ 2.5 mm.

5. The oil casing threaded joint according to claim 1, characterized in that: The range of the arc radius R10 of the sealing arc surface (11) is: 200mm≤R10≤500mm.

6. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The nose end of the external threaded joint (1) has an axial length L10, the sealing arc surface (11) has an axial length L11, and the ratio of the axial length L11 to the axial length L10 satisfies: 0.3≤L11 / L10≤0.

9.

7. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: When the external thread joint (1) and the internal thread joint (2) are screwed together, the sealing arc surface (11) and the main sealing cone surface (22) first come into contact at an initial contact point P, and there is an axial distance L30 between the point P and the external thread (32). The nose end of the external thread joint (1) has an axial length L10, and the ratio of the axial distance L30 to the axial length L10 satisfies: 0.56≤L30 / L10≤0.

86.

8. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The nose end of the external threaded joint (1) has an axial length L10, and the axial length L10 satisfies: 10 mm ≤ L10 ≤ 30 mm.

9. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The external thread joint (1) is provided with an outer cylindrical surface (10) for connecting the sealing arc surface (11) and the external thread (32), and the internal thread joint (2) is provided with an inner cylindrical surface (20) for connecting the internal thread (31) and the main sealing cone surface (22), and a portion of the internal thread (31) and the inner cylindrical surface (20) and the outer cylindrical surface (10) together form the first groove portion (40).

10. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The internal threaded joint (2) is provided with an internal connection surface (24), which is connected to the side of the auxiliary sealing cone surface (23) facing away from the main sealing cone surface (22), and part of the sealing arc surface (11) and the internal connection surface (24) form the second groove portion (60).

11. The oil casing threaded joint according to claim 10, characterized in that: The inner connecting surface (24) is a cylindrical surface; or, the inner connecting surface (24) is a conical surface, and the angle between the inner connecting surface (24) and the central axis (A) is in the range of 0° to 3°.

12. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The shoulder portion (70) comprises: A first shoulder surface (12) is provided on the external threaded joint (1); The second shoulder surface (25) is arranged on the internal thread joint (2). When the internal thread joint (2) and the external thread joint (1) are screwed together, the first shoulder surface (12) and the second shoulder surface (25) are interference fit.

13. The oil casing threaded joint according to claim 12, characterized in that: An angle α1 is formed between the first shoulder surface (12) and the cross section of the external threaded joint (1), and the angle α1 satisfies: 5°≤α1≤15°.

14. The oil casing threaded joint according to claim 13, characterized in that: An angle β3 is formed between the second shoulder surface (25) and the cross section of the internal thread joint (2), and the angle β3 and the angle α1 satisfy the following relationship: 0°≤β3-α1≤0.5°.

15. The oil casing threaded joint according to claim 13, characterized in that: Along the central axis (A), there is an axial distance L20 between the end of the main sealing cone surface (22) close to the internal thread (31) and the second shoulder surface (25), and the axial distance L20 and the axial length L21 of the main sealing cone surface (22) satisfy: 0.1≤L21 / L20≤0.

5.

16. The oil casing threaded joint according to any one of claims 1 to 5, characterized in that: The nose end of the external threaded joint (1) is provided with a nose end inner surface (14), and an angle α2 is formed between the nose end inner surface (14) and the central axis (A), and the angle α2 satisfies: 0°≤α2≤10°.

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