A gas seal threaded joint structure suitable for SAGD thermal recovery well pipe string connection

Abstract

The application relates to a gas seal threaded joint structure suitable for SAGD thermal recovery well pipe string connection, which comprises a male end A and a female end B, the female end B comprises female threads E with a taper, a tool withdrawal groove, a female sealing surface G and a female shoulder J, the male end A comprises male threads C with a taper, a male sealing surface F and a male shoulder H; the female sealing surface G comprises a taper surface and a cylindrical surface, the taper surface is connected with the tool withdrawal groove, and the cylindrical surface is connected with the female shoulder J; the male sealing surface F comprises an arc surface, one end of the arc surface is directly or through a cylindrical surface connected with the male threads C, the cylindrical surface is tangent to the arc surface, and the other end of the arc surface is directly connected with the male shoulder; when the male end and the female end are screwed in place, the male threads C and the female threads E are engaged with each other, the female sealing surface G and the male sealing surface F are in interference contact through the taper surface and the arc surface to realize sealing, and the male shoulder and the female shoulder are mutually abutted. Under the complex working conditions of high-temperature circulation and internal pressure circulation of the pipe string, excellent sealing integrity and structural integrity are provided for the connection of the pipe string.

Description

Technical Field

[0001] This invention relates to a sealing threaded joint structure. Background Technology

[0002] Oil sands refer to sedimentary sands rich in natural bitumen, and their extraction methods differ significantly from traditional oil extraction. The primary extraction technology is Steam Assisted Gravity Drainage (SAGD). SAGD, short for Steam Assisted Gravity Drainage, is an oil extraction method that injects steam from a vertical or horizontal well above a horizontal production well located near the bottom of the reservoir. The heated crude oil and steam condensate are then produced from the horizontal well at the bottom of the reservoir. This method offers advantages such as high oil recovery capacity, high oil-to-steam ratio, high ultimate recovery rate, reduced inter-well interference, and prevention of premature well cross-connection.

[0003] Chinese patent document application number 201410645727.5 discloses a method for exploiting heavy oil reservoirs using SAGD (Super-Action Gauge Deposition). This SAGD includes a process of producing oil using an injection-production well group, which comprises at least one pair of adjacent injection wells and production wells. The injection wells have horizontal sections located within the oil layer of the heavy oil reservoir, and the production wells have horizontal sections located within the oil layer. The horizontal sections of the injection wells are located above the horizontal sections of the production wells. Steam is injected into both the vertical wells and the injection wells, and oil is produced using the production wells. In the later stages of SAGD, vertical wells are installed at locations where steam cavities have not yet developed, and steam is injected into these vertical wells. The heat from the steam promotes the development of steam cavities in the horizontal sections, thus achieving the effect of uniform development of steam cavities in the horizontal sections.

[0004] Chinese patent document with application number 201610823190.6 discloses a 125ksi high-strength and high-toughness oil casing for heavy oil extraction using the SAGD method and its manufacturing method. After steelmaking, high-precision rolling and heat treatment, a combination of high strength and high toughness is obtained. The effect is good thermal stability, with a yield strength of not less than 800MPa at an ambient temperature of 350℃; strong resistance to external extrusion deformation, with actual crush resistance exceeding the API calculation value by more than 56%, meeting the requirements for heavy oil extraction using the SAGD method.

[0005] The two patent documents mentioned above relate to the extraction method of SAGD thermal recovery wells and the manufacturing method of 125ksi high-strength and tough oil casing for heavy oil extraction, both mentioning that the operating temperature of SAGD thermal recovery wells is above 300℃. Because the casing string used in SAGD thermal recovery wells needs to withstand cyclical alternation of high temperature and internal pressure loads, the airtightness and structural integrity of the casing string joints are subject to very high requirements. Ordinary API standard round thread and trapezoidal thread joints are no longer sufficient; special thread joints must be used to ensure sealing.

[0006] The service loads of casing joints used in SAGD thermal recovery wells are mainly temperature cycles and internal pressure cycles, so the sealing integrity at the joint is very important. The sealing surfaces of special threaded joints used in traditional oil and gas wells are all interference fits—cone-cone interference fits. After screwing, the contact pressure on the sealing surface is exponentially distributed: the peak pressure is higher only at the contact end, and lower at other locations. Even if the designed sealing surface length is relatively long, the effective length that actually achieves the sealing effect is still relatively short, and it is always at the end closer to the large cone.

[0007] If the cone-face interference fit joint sealing method is applied to SAGD thermal recovery wells, the following problems will occur: Under repeated high-temperature-low-temperature cycles, the contact parts of the sealing surface will shift with temperature fluctuations, and due to stress relaxation, the contact pressure of the sealing surface will gradually decrease, and the effective contact length of the sealing surface will gradually shorten. Under repeated thermal cycles, the contact pressure of the sealing surface will gradually decrease or even reach zero, eventually losing its sealing ability.

[0008] For the high-temperature and internal pressure circulation conditions inside the tubing of SAGD thermal recovery wells, developing a special threaded joint structure with reliable sealing has become an urgent technical problem to be solved. Summary of the Invention

[0009] The purpose of this invention is to provide a gas-tight threaded joint that provides a reliable seal and is suitable for sealing connections in the steam transport casing of SAGD thermal recovery wells.

[0010] Traditional oil and gas well threaded joints are designed based on stress, meaning that the tubing string does not undergo plastic deformation during normal service, and the internal pressure, external pressure, axial tension, compression, and bending loads it experiences are all within the elastic range of the tubing material. However, SAGD thermal recovery well tubing strings are subjected to high-temperature and internal pressure cycles, with high-temperature cycles reaching up to 350°C. These service conditions exceed the elastic range of the tubing material. Therefore, threaded joints used for steam transmission tubing strings in SAGD thermal recovery wells must adopt a strain-based design, meaning that the joint can maintain excellent sealing and structural integrity even after plastic deformation.

[0011] To achieve the above objectives, this application provides a gas-tight threaded joint structure suitable for connecting tubing in SAGD thermal recovery wells. The joint includes a female end, i.e., a symmetrical coupling structure, which mainly consists of a tapered female thread, a relief groove, a female sealing surface, and a female shoulder. The joint also includes a male end machined at the end of the tubing, which consists of a tapered male thread, a male sealing surface, and a male shoulder. When the female and male ends are tightened, the male and female threads mesh together, the male and female sealing surfaces contact each other with an interference fit, and the male and female shoulders abut against each other. The female and male ends are located at the ends of the two tubing bodies to be connected.

[0012] The female sealing surface consists of a conical surface and a cylindrical surface. The angle between the conical surface and the axis of the pipe body is θ, which is taken from Formula 1. The cylindrical surface connects to the female shoulder and plays a crucial role. It not only stores any thread grease that cannot be released after tightening, preventing the grease from becoming trapped, but also optimizes the stress distribution on the sealing surface, reducing stress concentration and helping to maintain seal integrity. The rounded corner R between the conical surface and the cylindrical surface... b The range is shown in Formula 2.

[0013] 2°≤θ≤15° (Formula 1)

[0014] 3≤R b ≤6 (Formula 2)

[0015] The axial length of the mother sealing surface is L. u The relationship between the outer diameter D of the tube and the outer diameter D is shown in Formula 3.

[0016] 0.05D≤L u ≤0.0875D (Formula 3)

[0017] The axial length of the conical surface is L t The axial length of the cylindrical surface is L. s Their relationship is shown in formulas 4 and 5.

[0018] L u =L s +L t (Formula 4)

[0019] 0.15L u ≤L s ≤0.25L u (Formula 5)

[0020] The area between the female sealing surface and the female thread is a relief groove, which stores thread grease applied during the screwing of the male and female ends. The relief groove transitions to the female sealing surface via a chamfer at a 45° angle to the pipe body axis, and the rounded corner R between the chamfer and the conical surface of the female sealing surface... k The range is shown in Formula 6.

[0021] R k ≥5(Formula 6)

[0022] The male sealing surface is composed of an arc surface or an arc surface and a cylindrical surface tangent to it. The arc surface is press-fitted with the female sealing surface. The cylindrical surface serves as a transition between the arc surface and the male thread, and is tangent to the arc surface. The end of the arc surface is a male shoulder. The axial length of the male sealing surface is L. e axial length L of the mother sealing surfaceu The relationship is shown in Formula 7.

[0023] L u <L e ≤1.3L u (Formula 7)

[0024] The axial length of the arc surface of the male sealing surface is L. r It satisfies Formula 8.

[0025] L e ≥L r (Formula 8)

[0026] After the male and female ends are screwed into place, the arc surface of the male seal and the conical surface of the female seal come into contact to create an interference fit, thereby achieving a seal. In the axial cross-sectional view formed by the interference fit, the maximum interference value in the direction perpendicular to the pipe axis (i.e., the radial direction of the pipe) is 'a'. The relationship between the maximum interference value 'a' and the outer diameter D and wall thickness 't' of the pipe is shown in Formula 9.

[0027]

[0028] The radius of the arc surface of the sealing surface is R, in mm, and is determined by formula 10.

[0029] 0<R≤192-633cosθ(Formula 10)

[0030] The female shoulder of the female end and the cylindrical surface of the female sealing surface are transitioned by a rounded corner, and the male shoulder of the male end and the arc surface of the male sealing surface are transitioned by a rounded corner. The angle β between the female shoulder of the female end and the male shoulder of the male end and the direction perpendicular to the axis satisfies the following formula 11.

[0031] 12°≤β≤18°(Formula 11)

[0032] In formula 1-11:

[0033] D: Outer diameter of the pipe containing male end A, in mm; t: Pipe wall thickness, in mm;

[0034] a: The maximum interference fit of the male and female sealing surfaces in the direction perpendicular to the pipe axis;

[0035] θ: The angle between the conical surface of the mother sealing surface and the axis of the pipe body; L u : Axial length of the female sealing surface;

[0036] L s : The axial length of the cylindrical surface of the mother sealing surface;

[0037] L t : The axial length of the conical surface of the mother sealing surface;

[0038] R b The rounded corner between the conical and cylindrical surfaces of the mother sealing surface;

[0039] R k The rounded corner of the transition between the female end relief groove and the female sealing surface (conical surface);

[0040] L e : Axial length of the male sealing surface; L r : The axial length of the arc surface of the male sealing surface;

[0041] R: The radius of the arc surface of the male sealing surface;

[0042] β: The angle between the male shoulder and the female shoulder and the direction perpendicular to the axis.

[0043] The aforementioned male and female threads are trapezoidal thread structures with a pitch of 3 to 5 teeth per inch; a taper of 1:12 to 1:18; the male thread has the same tooth height of 1.4 to 1.8 mm; the tooth tip and tooth root of both the male and female threads are parallel to the generatrix; after the male and female threads are engaged, there is a gap between the tooth tip and tooth root, and the tooth flank is an interference fit.

[0044] This application provides a design structure for the sealing surface of the special threaded joint for casing in SAGD thermal recovery wells. Under the complex working conditions of high temperature circulation and internal pressure circulation of steam transmission tubing in SAGD thermal recovery wells, it ensures that the joint does not stick during the three-times-on-off-tightening process, and provides excellent sealing integrity and structural integrity for the connection parts of the tubing. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the casing threaded joint structure for thermal recovery wells in this application;

[0046] Figure 2 This is an enlarged schematic diagram of the sealing structure of the casing threaded joint for thermal recovery wells in this application;

[0047] Figure 3 This is an enlarged schematic diagram of the sealing structure of the female end of the casing threaded joint for thermal recovery wells in this application;

[0048] Figure 4 This is an enlarged schematic diagram of the sealing structure of the male end of the casing threaded joint for thermal recovery wells in this application;

[0049] Figure 5 This is a schematic diagram of the thread engagement of the casing threaded joint for thermal recovery wells in this application. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0051] The gas-tight threaded joint structure of this embodiment includes a female end B and a male end A. The female end B (i.e., the coupling) has a symmetrical structure and includes a tapered female thread E, a relief groove, a female sealing surface G, and a female shoulder J arranged sequentially. The area between the female sealing surface G and the female thread E serves as the relief groove. The male end A includes a tapered male thread C, a male sealing surface F, and a male shoulder H arranged sequentially.

[0052] The female sealing surface G includes a conical surface and a cylindrical surface, with a rounded corner R between the conical and cylindrical surfaces. b The conical surface and the relief groove are transitioned by a chamfer at a 45° angle to the tube body axis, and the chamfer and the conical surface are rounded with a radius R. k The cylindrical surface and the female shoulder J are connected by a fillet.

[0053] The male sealing surface F includes an arc surface (radius R). One end of the arc surface transitions to the male thread C through a cylindrical surface, which is tangent to the arc surface. The other end of the arc surface directly transitions to the male shoulder through a fillet.

[0054] Male thread C and female thread E are both trapezoidal threads. The pitch of male thread C and female thread E is 3 to 5 threads per inch; the taper is 1:12 to 1:18; the tooth height of male thread C is the same, which is 1.4 to 1.8 mm; the tooth tip and tooth root of both male and female threads are parallel to the generatrix; after the male and female threads are engaged, there is a gap between the tooth tip and tooth root, and there is an interference on the tooth flank.

[0055] With male end A and female end B screwed in, male thread C and female thread E are engaged with each other. The female sealing surface C and male sealing surface F are sealed by interference contact between the conical surface and the arc surface. Male shoulder H and female shoulder J are aligned with each other.

[0056] For the setting of process parameters for each part of male terminal A and female terminal B, please refer to Formula 1-11.

[0057] The commonly used outer diameter specifications for special threaded joints used in SAGD thermal recovery wells are 177.8–298.45 mm. The structure of the casing joint for SAGD thermal recovery wells of this utility model / invention is illustrated by the following example.

[0058] Example 1

[0059] The sleeve has an outer diameter D = 219.08 mm and a wall thickness t = 8.94 mm.

[0060] The data for the female sealing surface are as follows: Based on the range of θ in Formula 1, θ = 3° is determined. Based on Formula 2, the fillet angle between the conical and cylindrical surfaces of the female sealing surface is determined to be R. b =5mm. L is calculated according to Formula 3. u The range is 10.95–19.17 mm, determine L. u= 15 mm. L is calculated according to Formula 5 s The range of s is 2.25 - 3.75 mm, and L is determined s = 3 mm. L can be calculated according to Formula 4 t = 15 - 3 = 12 mm. R is determined according to Formula 6 k = 5 mm.

[0061] The data of the male end sealing surface is as follows: L is calculated according to Formula 7 e The range of e is 15 - 19.5 mm, and L is determined e = 17 mm. The range of a calculated according to Formula 9 is: 0.26 ≤ a ≤ 0.42 mm, and a = 0.3 mm is determined. The range of the male sealing surface radius R calculated according to Formula 10 is 0 < R ≤ 158.8 mm, and R = 130 mm is determined. According to Formula 11, β = 15° is determined.

[0062] The thread parameters are as follows: The male and female threads are of trapezoidal thread structure with a pitch of 5 threads per inch for the tooth profile; the taper is 1:16; the male thread tooth height is the same, which is 1.575 mm; the tooth tops and bottoms of the male and female threads are parallel to the generatrix; after the male and female threads are engaged, there are clearances at the tooth tops and bottoms.

[0063] Example 2

[0064] A casing with an outer diameter D = 244.48 mm and a wall thickness t = 10.03 mm.

[0065] The data of the female end sealing surface is as follows: According to the θ range of Formula 1, θ = 10° is determined. The fillet between the conical surface and the cylindrical surface of the female sealing surface is determined as R according to Formula 2 b = 5 mm. L is calculated according to Formula 3 u The range of u is 12.22 - 21.39 mm, and L is determined u = 16 mm. L is calculated according to Formula 5 s The range of s is 2.4 - 4 mm, and L is determined s = 3.2 mm. L can be calculated according to Formula 4 t = 16 - 3.2 = 12.8 mm. R is determined according to Formula 6 k = 6 mm.

[0066] The data of the male end sealing surface is as follows: L is calculated according to Formula 7 e The range of e is 16 - 20.8 mm, and L is determined e = 18.5 mm. The range of a calculated according to Formula 9 is: 0.25 ≤ a ≤ 0.42 mm, and a = 0.33 mm is determined. The range of the male sealing surface radius R calculated according to Formula 10 is 0 < R ≤ 80.38 mm, and R = 40 mm is determined. According to Formula 11, β = 15° is determined.

[0067] The thread parameters are as follows: the male and female threads are trapezoidal thread structures with a pitch of 4 teeth per inch; the taper is 1:16; the male thread has the same tooth height of 1.7mm; the tooth tip and tooth root of both the male and female threads are parallel to the generatrix; after the male and female threads are engaged, there is a gap between the tooth tip and tooth root.

[0068] Although preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gas-tight threaded joint structure suitable for connecting tubing in SAGD thermal recovery wells, comprising a male end A and a female end B, characterized in that: The female end B includes a tapered female thread E, a relief groove, a female sealing surface G, and a female shoulder J arranged in sequence; the male end A includes a tapered male thread C, a male sealing surface F, and a male shoulder H arranged in sequence. The female sealing surface G includes a conical surface and a cylindrical surface. The conical surface is connected to the tool relief groove, and the cylindrical surface is connected to the female shoulder J. The male sealing surface F includes an arc surface. One end of the arc surface transitions directly or through a cylindrical surface to the male thread C. The cylindrical surface is tangent to the arc surface. The other end of the arc surface transitions directly to the male shoulder. The axial length L of the male sealing surface F e The axial length L is greater than that of the mother sealing surface G. u The radius R of the arc surface, in mm, satisfies: （10） In equation (10), θ is the angle between the conical surface of the mother sealing surface G and the axis of the joint; With the male end A and female end B screwed in, the male thread C and female thread E are engaged with each other, the female sealing surface G and the male sealing surface F are sealed by interference contact between the conical surface and the arc surface, and the male shoulder H and the female shoulder J are opposed to each other. On the axial cross-sectional view of the interference contact between the conical surface and the arc surface, the maximum interference value perpendicular to the axis of the joint pipe is 'a'. The maximum interference value 'a' satisfies the following relationship with the outer diameter D and wall thickness 't' of the pipe where the male end A is located: （9）； The axial length L of the female sealing surface G u The range is (0.05D, 0.0875D), where D is the outer diameter of the pipe containing male end A; the axial length L of the male sealing surface F. e The range is (L) u 1.3L u ), where L u This is the axial length of the mother sealing surface.

2. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The rounded corner R between the conical surface and the cylindrical surface of the mother sealing surface G. b The range is 3mm to 6mm.

3. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The relief groove and the conical surface form a chamfer at 45° to the axis of the tube body, and the rounded corner R at the transition between the chamfer and the conical surface... k Greater than 5mm.

4. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The female shoulder of the female end and the cylindrical surface of the female sealing surface are transitioned by a rounded corner, and the male shoulder of the male end and the arc surface of the male sealing surface are transitioned by a rounded corner. The angle β between the male shoulder and the female shoulder and the direction perpendicular to the axis is 12 to 18°.

5. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The θ satisfies .

6. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The axial length of the conical surface of the mother sealing surface G is L. t The axial length of the cylindrical surface is L. s , ； 。 7. The gas-tight threaded joint structure for connecting tubing in SAGD thermal recovery wells according to claim 1, characterized in that: The male thread C and the female thread E are both trapezoidal threads.

8. The gas-tight threaded joint structure for SAGD thermal recovery well tubing connection according to claim 7, characterized in that: The pitch of the male thread C and the female thread E is 3 to 5 threads per inch; the taper is 1:12 to 1:18; the tooth height of the male thread C is the same, which is 1.4 to 1.8 mm; the tooth tip and tooth root of the male and female threads are parallel to the generatrix; after the male and female threads are engaged, there is a gap between the tooth tip and the tooth root, and there is an interference on the tooth side.

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