Composite oil casing male end thread structure and machining method thereof

Abstract

The invention belongs to the field of oilfield exploitation equipment manufacturing, and relates to a composite oil casing male end thread structure and a machining method thereof.Corrosion-resistant alloy is welded to the composite pipe end through an additive manufacturing method before thread machining, the reasonable threaded connection structure size is designed, and the connection strength of a corrosion-resistant alloy layer and a base body is ensured; and a special corrosion-resistant thread structure is formed. The invention is mainly used for oil casing systems in petroleum and natural gas industries, and aims to improve the corrosion resistance, prolong the service life and reduce the exploitation cost. The solution aims at improving the durability of the oil casing under severe mining conditions and reducing the requirements for frequent replacement and repair. Compared with a traditional manufacturing method, the additive manufacturing technology can achieve more accurate material surfacing, and the machining precision and the anti-corrosion effect of the thread structure are improved.

Description

Technical Field

[0001] The invention belongs to the field of oilfield mining equipment manufacturing and relates to a composite oil casing male end thread structure and a processing method thereof. Background Art

[0002] As global oil demand continues to increase, oilfield production is gradually expanding to deeper depths and harsher environments. In these environments, tubing and casing are subjected to constant mechanical stress and erosion from corrosive fluids. Corrosion and wear of tubing and casing have long led to significant economic losses and safety hazards. The current market demands higher durability and corrosion resistance for tubing and casing, but traditional anti-corrosion measures are no longer sufficient to meet the demands of modern oilfields.

[0003] Currently, corrosion protection technologies for oil casing and tubing primarily rely on corrosion-resistant materials such as stainless steel and nickel-based alloys. However, these materials perform poorly in environments with high levels of CO₂ and H₂S, and their high cost makes them uneconomical for large-scale application. Furthermore, the production and processing of traditional corrosion-resistant materials are complex, especially when applied to complex threaded structures, leading to issues such as poor sealing and durability.

[0004] Additive manufacturing technology (including 3D printing, laser cladding, etc.) is an integrated manufacturing technology that takes into account both precise forming and high-performance forming requirements, and has gradually become an important means of advanced manufacturing. Additive manufacturing technology can solve the corrosion resistance problem existing in complex threaded structures. Chinese patent CN111872385 A discloses a local additive manufacturing method for bimetallic composite oil well pipe threaded joints. The sealing structure is processed by additive manufacturing technology to ensure that the corrosive medium in the pipe does not contact the outer pipe. Although it solves the corrosion of the medium on the pipe to a certain extent, the interface bonding strength between the additive part and the pipe end is insufficient, requiring frequent replacement and repair, and has poor durability.

[0005] Therefore, it is necessary to develop a new method for processing the male end thread of the composite oil casing to improve the corrosion resistance and durability of the oil casing and reduce the production cost. Summary of the Invention

[0006] In order to cope with the shortage of nickel resources and the corrosion challenges of the oilfield environment, composite oil casing is used, whose structure is composed of an outer layer of carbon steel and an inner layer of corrosion-resistant alloy. The outer layer of carbon steel provides the main mechanical strength and load-bearing capacity, while the inner alloy layer plays a role in corrosion protection. Considering that the threaded connection of the oil casing is most susceptible to corrosion, the present invention discloses a composite oil casing male end thread structure and a processing method thereof. The corrosion-resistant alloy is welded to the composite pipe end before thread processing by an additive manufacturing method, thereby forming a fully corrosion-resistant structure. The present invention is mainly used for oil casing systems in the oil and gas industry, aiming to improve corrosion resistance, extend service life, and reduce mining costs. The solution aims to improve the durability of oil casing under harsh mining conditions and reduce the need for frequent replacement and repair. Compared with traditional manufacturing methods, additive manufacturing technology can achieve more precise material surfacing, improve the processing accuracy and corrosion protection effect of the threaded structure.

[0007] The technical solution adopted by the present invention to solve the technical problem is:

[0008] In one aspect, the present invention provides a method for processing a composite oil casing male end thread structure, comprising the following steps:

[0009] (1) An annular groove with an included angle ɑ with the pipe axis is machined on the inner surface of one end of a composite oil casing composed of a base carbon steel layer and an inner corrosion-resistant alloy layer; in order to ensure a smooth transition and facilitate additive manufacturing processing, the included angle ɑ is 10° to 30°;

[0010] (2) machining a surfacing layer at the end of the composite oil casing after turning in step (1) by an additive manufacturing method, wherein the surfacing layer includes a transition section and an additive portion at the pipe end; the transition section is located at the annular groove and has a thickness of 1.5 to 2.5 times the thickness of the corrosion-resistant alloy layer;

[0011] (3) Cutting the cladding layer to the original composite oil casing wall thickness;

[0012] (4) Processing the male end thread structure of the outer surface of the composite oil casing after the cutting process in step (3), wherein the thread structure includes a male thread, a pipe end cylindrical surface, a male end sealing surface and a torque shoulder.

[0013] Furthermore, the thickness of the surfacing layer is the sum of the thicknesses of the basic carbon steel layer and the inner corrosion-resistant alloy layer.

[0014] Furthermore, the total length of the surfacing layer is greater than or equal to twice the length of the male end sealing surface.

[0015] Furthermore, the length of the added material portion of the tube end is 3-8 mm greater than the length of the male end sealing surface.

[0016] Furthermore, the total length of the surfacing layer is 1.8 to 3.0 times the length of the added material portion of the pipe end.

[0017] Furthermore, the surfacing layer uses a corrosion-resistant alloy material, and the corrosion-resistant alloy material is one of 316 stainless steel, nickel-based alloy, and titanium alloy.

[0018] Furthermore, the additive manufacturing method is 3D printing or laser cladding.

[0019] Another aspect of the present invention provides a composite oil casing male end thread structure, which is processed according to the processing method.

[0020] Before thread processing, the present invention uses additive manufacturing technology to weld corrosion-resistant materials on the end of the composite pipe to form a corrosion-resistant layer to resist damage to the oil casing by corrosive gases and reduce the risk of corrosion failure caused by harsh environment.

[0021] The threaded connection structure is designed with reasonable dimensions to ensure the connection strength between the corrosion-resistant alloy layer and the substrate. The special thread design of the present invention ensures the sealing of the threaded connection through a reasonable surfacing structure, reducing leakage and corrosion problems caused by improper connection.

[0022] By optimizing the thickness and shape of the cladding material, the sealing performance of the threaded connection is ensured, effectively preventing the penetration of corrosive media.

[0023] Compared with the use of all-alloy oil casing, the present invention greatly reduces the use of alloy materials and has higher cost-effectiveness.

[0024] The application of the technology of the present invention helps to extend the service life of oil casing, reduce maintenance requirements, and lower overall production costs. At the same time, it helps to improve oil field operation efficiency and minimize oil field operating costs.

[0025] The present invention contributes to the environmental protection and sustainable development of oil fields, reduces the risk of oil well leakage, and reduces the release of corrosive substances, thereby meeting the requirements of modern society for clean production.

[0026] The advantages and positive effects of the present invention are:

[0027] This invention innovatively proposes using additive manufacturing technology to weld a layer of corrosion-resistant alloy to the ends of composite oil casing before threading. This, combined with rationally designed thread connection dimensions, creates a unique, corrosion-resistant thread structure. Compared to traditional anti-corrosion materials and methods, this invention offers the following advantages:

[0028] Improved durability: By optimizing the thickness of the weld overlay, the angle ɑ between the annular groove and the pipe axis, and the thickness of the transition section, the sealing performance of the threaded connection and the connection strength between the corrosion-resistant alloy layer and the substrate are ensured, effectively preventing the infiltration of corrosive media. This improves the durability of the oil casing and tubing under harsh mining conditions and reduces the need for frequent replacement and repair.

[0029] Cost advantage: By adopting carbon steel composite materials, the proportion of nickel-based corrosion-resistant materials used is greatly reduced, thereby reducing production costs.

[0030] Improved anti-corrosion performance: Additive manufacturing technology can achieve precise surfacing of corrosion-resistant materials, avoiding corrosion failure problems in threaded connections.

[0031] Improve production efficiency: Additive manufacturing reduces complicated processing technology, improves production efficiency and shortens production cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the original composite oil casing structure;

[0033] Figure 2 This is a schematic diagram of the original composite oil casing without pipe end treatment + threaded connection structure;

[0034] Figure 3 This is a schematic diagram of the conventional pipe end treatment + threaded connection structure of the composite pipe;

[0035] Figure 4 This is a schematic diagram of the composite oil casing structure after turning in step (1) of Example 1;

[0036] Figure 5 This is a schematic diagram of the thread structure of the male end of the composite oil casing in Example 1;

[0037] Figure 6 This is a partially enlarged schematic diagram of the threaded structure of the male end of the composite oil casing in Example 1.

[0038] Figure 7 This is a partially enlarged schematic diagram of the threaded structure of the male end of the composite oil casing in Example 2.

[0039] L1: length of the added material part of the pipe end; L2: length of the male end sealing surface; L3: total length of the cladding layer; t1: thickness of the base carbon steel layer; t2: thickness of the inner corrosion-resistant alloy layer; t3: thickness of the transition section of the cladding layer; ɑ: angle of the transition section. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0041] Example 1

[0042] A method for processing a composite oil casing male end thread structure comprises the following steps:

[0043] (1) In the composite oil casing (such as Figure 1The inner surface of one end of the tube is turned to form an annular groove with an angle ɑ with the tube axis, and the resulting structure is as shown in FIG. Figure 4 As shown, the thickness of the basic carbon steel layer is t1, and the thickness of the corrosion-resistant alloy layer is t2. In order to ensure a smooth transition and facilitate additive manufacturing processing, the angle ɑ is 10° to 30°;

[0044] (2) A surfacing layer is machined on the end of the composite oil casing after turning in step (1) by laser cladding, wherein the surfacing layer includes a transition section and a pipe end material-added portion; the transition section is the annular groove, and the thickness is t3, which is between 1.5 times the thickness of the corrosion-resistant alloy layer t2 and 2.5 times the thickness of the corrosion-resistant alloy layer t2. The total length L3 of the surfacing layer is greater than or equal to twice the length L2 of the male end sealing surface, L3 is 1.8 to 3.0 times the length L1 of the pipe end material-added portion, and the thickness of the surfacing layer is the sum of the thickness of the basic carbon steel layer t1 and the thickness of the inner corrosion-resistant alloy layer t2. The length L1 of the pipe end material-added portion is 3-8 mm greater than the length L2 of the male end sealing surface. The surfacing layer is laser clad using 316L stainless steel powder (particle size 50-150 μm) in an argon gas protective environment (oxygen content <50 ppm). Process parameters: laser power 1.5kW, spot diameter 2mm, scanning speed 10mm / s, powder feed rate 3g / min, overlap rate 50%, substrate preheating 150°C. The cladding layer was air-cooled and then annealed at 600°C for 2h.

[0045] (3) Cutting the inner and outer surfaces of the composite oil casing cladding layer according to the wall thickness requirements of the original composite oil casing design structure;

[0046] (4) The outer surface of the composite oil casing after cutting treatment in step (3) is processed with a male end thread structure, wherein the thread structure includes a male thread, a pipe end cylindrical surface, a sealing surface and a torque shoulder. The thread structure is as follows: Figure 5 As shown, Figure 6 for Figure 5 A partial enlarged view of .

[0047] Example 2

[0048] The outer diameter is 88.9mm, the total wall thickness is 7.34, the outer carbon steel pipe thickness t1 is 6.45mm, the inner corrosion-resistant alloy pipe thickness t2 is 0.89mm, and the sealing surface length L2 of the male end threaded connection structure is 5mm. The composite oil casing male end thread structure prepared by the processing method described in Example 1 is obtained. The composite pipe male end pipe end additive manufacturing structure is as follows Figure 7 As shown:

[0049] The design length of L1 is 8mm, the design length of L3 is 15mm, the wall thickness of t3 is 1.5mm, and the α angle is 30°.

[0050] Comparative Example 1

[0051] The difference between the processing method and Example 1 is that no additive manufacturing is performed, and the thread structure is as follows Figure 2 shown.

[0052] Comparative Example 2

[0053] The difference between the processing method and embodiment 1 is that the additive manufacturing method is different and the surfacing layer has no transition section. Figure 3 shown.

[0054] Comparative Example 3

[0055] The only difference from Example 2 is that the angle α is 35°.

[0056] Comparative Example 4

[0057] The only difference from Example 2 is that the angle α is 8°.

[0058] The threaded composite oil casings of Example 2 and Comparative Examples 1 to 4 were respectively tested for durability (make-up and break-out test) and corrosion resistance (salt spray test). The results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] As can be seen from Table 1, the transition section design of Example 2 (α = 30°, t3 = 1.68t2) significantly improves the interface bonding strength and the sealing performance of the threaded connection, and the number of times of make-up and make-down is up to 5 times without damage. In Example 1, the thread structure prepared without additive manufacturing showed wear after 3 make-up and make-down, while the thread structure prepared by ordinary additive manufacturing in Example 2 showed wear after 2 make-up and make-down, indicating that the thread structure prepared by the additive manufacturing method of the present application can significantly improve the durability. Moreover, in Examples 3 and 4, the included angle ɑ is set to 35° and 8° respectively, and the durability is not as good as that of the present invention, indicating that the present invention improves the durability of oil casing under harsh mining conditions by optimizing the thickness of the cladding layer, the range of the included angle ɑ between the annular groove and the pipe axis, and the thickness of the transition section.

[0063] The dense cladding layer (316 stainless steel) manufactured by additive manufacturing of the present invention blocks the corrosion path and shows no corrosion after 800 hours in the salt spray test, which is 4 times higher than that of the traditional structure (Comparative Example 1). The corrosion resistance of the threaded structure prepared by ordinary additive manufacturing in Comparative Example 2, Comparative Example 3, and Comparative Example 4 with a changed angle ɑ is significantly improved.

[0064] The additively manufactured composite oil well tubular goods produced by this invention can reduce the use of corrosion-resistant materials and lower production costs. Furthermore, the improved corrosion resistance extends the service life of the tubular casing and reduces the need for frequent replacement and repair, thus possessing broad market potential. Furthermore, the environmental friendliness of this technology complies with the green production standards increasingly valued by the oil and gas industry.

[0065] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A method for processing the thread structure of the male end of a composite oil casing, characterized in that: The steps include: (1) An annular groove is machined on the inner surface of one end of a composite oil casing composed of a base carbon steel layer and an inner corrosion-resistant alloy layer, and the angle ɑ is 10° to 30° with the pipe axis; (2) machining a surfacing layer at the end of the composite oil casing after turning in step (1) by an additive manufacturing method, wherein the surfacing layer includes a transition section and an additive portion at the pipe end; the transition section is located at the annular groove and has a thickness of 1.5 to 2.5 times the thickness of the corrosion-resistant alloy layer; (3) Cutting the cladding layer to the original composite oil casing wall thickness; (4) Processing the male end thread structure of the outer surface of the composite oil casing after the cutting process in step (3), wherein the thread structure includes a male thread, a pipe end cylindrical surface, a male end sealing surface and a torque shoulder.

2. The processing method according to claim 1, characterized in that: The thickness of the surfacing layer is the sum of the thickness of the basic carbon steel layer and the inner corrosion-resistant alloy layer.

3. The processing method according to claim 1, characterized in that: The total length of the surfacing layer is greater than or equal to twice the length of the male end sealing surface.

4. The processing method according to claim 1, characterized in that: The length of the added material portion of the pipe end is 3-8 mm greater than the length of the male end sealing surface.

5. The processing method according to claim 1, characterized in that: The total length of the surfacing layer is 1.8 to 3.0 times the length of the added material portion of the pipe end.

6. The processing method according to claim 1, characterized in that: The surfacing layer uses a corrosion-resistant alloy material, and the corrosion-resistant alloy material is one of 316 stainless steel, nickel-based alloy, and titanium alloy.

7. The processing method according to claim 1, characterized in that: The additive manufacturing method is 3D printing or laser cladding.

8. A composite oil casing male end thread structure, characterized in that: The processing method according to any one of claims 1 to 6 is used.

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