A high-strength non-magnetic drill collar suitable for deep wells of 10,000 meters and its manufacturing method

Abstract

This invention discloses a high-strength non-magnetic drill collar for deep wells at depths of 10,000 meters and its manufacturing method, belonging to the technical field of oil drilling tools. The drill collar includes a hollow, thick-walled cylindrical body made of a non-magnetic alloy material with a relative magnetic permeability μ≤1.01. The inner wall is provided with a single-headed helical reinforcing rib with a helix angle of 15°–30° and a lead of 300–500 mm. The connecting ends are integrally formed at both ends of the body, including a double-shoulder thread and a stress-relieving groove located at the transition between the thread root and the shoulder. A sealing cavity is provided between the main shoulder and the secondary shoulder of the double-shoulder thread, and a sealing component is embedded in the sealing cavity. The manufacturing method includes blank preparation, helical rib machining, stress-relieving groove machining and strengthening, sealing component installation, and non-destructive testing. This invention improves the flow field distribution and reduces erosion through helical reinforcing ribs, achieves zero leakage through double-shoulder sealing, and enhances fatigue life through stress-relieving grooves and surface strengthening, making it suitable for drilling operations in deep wells at depths of 10,000 meters.

Description

Technical Field

[0001] This invention relates to the field of oil drilling tool technology, specifically to a high-strength non-magnetic drill collar suitable for deep wells of 10,000 meters and its manufacturing method. Background Technology

[0002] With the increasing demand for deep and ultra-deep oil and gas resource development, drilling depths have exceeded 10,000 meters, placing higher demands on the performance of downhole drilling tools. As an important component of the drill string, the drill collar's structural strength, erosion resistance, sealing reliability, and fatigue resistance directly affect the safety and efficiency of drilling operations.

[0003] In existing technologies, drill collars mainly suffer from the following drawbacks: (1) Severe erosion: The inner wall of traditional drill collars is a straight structure or has straight ribs. Under high pressure and high speed, the drilling fluid causes severe erosion of the inner wall, resulting in high weight loss rate and short service life.

[0004] (2) Sealing failure: Drill collars with single shoulder thread connection are prone to thread leakage in the high pressure environment downhole, resulting in a high leakage rate and affecting the sealing performance of the drill string.

[0005] (3) Fatigue fracture: The root of the thread is a stress concentration area, which is prone to fatigue cracks under alternating loads, leading to drill collar fracture and insufficient fatigue life.

[0006] While some improvement solutions have been proposed in the existing technology to address the above problems, most of them are structurally complex or have excessively high process costs, and have not yet effectively solved the comprehensive technical problems of erosion, sealing and fatigue life. Summary of the Invention

[0007] Technical issues The present invention aims to provide a high-strength non-magnetic drill collar suitable for deep wells of 10,000 meters and its manufacturing method, so as to solve the technical problems of severe inner wall erosion, thread seal failure and insufficient fatigue life of existing drill collars.

[0008] Technical solution To achieve the above objectives, the present invention provides the following technical solution: A high-strength non-magnetic drill collar for deep wells (10,000 meters), comprising: Drill collar body: a hollow, thick-walled cylindrical structure made of non-magnetic alloy material with relative magnetic permeability μ≤1.01, with a wall thickness of 80-120mm, and a single-headed spiral reinforcing rib with a helix angle of 15°-30° and a lead of 300-500mm on the inner wall; Connection end: integrally formed at both ends of the body, including double shoulder thread and stress relief groove. A sealing cavity is provided between the main shoulder and the auxiliary shoulder of the double shoulder thread. The stress relief groove is located at the transition between the thread root and the shoulder, with a groove depth of 2-3mm and a fillet radius R=3-5mm. Sealing assembly: embedded in the sealing cavity.

[0009] Furthermore, the inner wall of the sealing cavity is provided with an annular limiting step, and the sealing assembly is installed between the limiting step and the secondary shoulder by interference fit.

[0010] Furthermore, the cross-section of the spiral reinforcing rib is an isosceles trapezoid with an upper base width of 10-15mm, a lower base width of 20-25mm, and a height of 20-25mm.

[0011] Furthermore, the stress relief groove undergoes surface rolling strengthening treatment, and the depth of the residual compressive stress layer is ≥0.5mm.

[0012] The present invention also provides a method for manufacturing the above-mentioned drill collar, comprising the following steps performed sequentially: Step 1: Provide a drill collar body blank and perform heat treatment on the blank; Step 2: Use precision machining to form spiral reinforcing ribs on the inner wall; Step 3: Machining stress relief grooves at the root of the thread and strengthening them using surface plastic deformation process; Step 4: Install the sealing assembly into the sealing cavity; Step 5: Perform non-destructive testing.

[0013] Furthermore, in step 2, a five-axis CNC milling machine is used for machining, with a pitch error ≤0.05mm.

[0014] Furthermore, in step 3, the surface plastic deformation process is roll forming, with a roll forming pressure of 15-20 MPa.

[0015] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) Spiral reinforcing rib structure: The reinforcing rib with a spiral helix angle of 15°-30° guides the drilling fluid to form a swirling flow, improves the flow field distribution, reduces the concentrated erosion on the inner wall, and reduces the erosion rate by more than 35% compared with the existing technology.

[0016] (2) Double shoulder sealing structure: The main shoulder and the auxiliary shoulder cooperate to form a sealing cavity, which, together with the interference fit sealing components, achieves zero leakage at the threaded connection and significantly improves the reliability of downhole sealing.

[0017] (3) Stress relief groove design: A stress relief groove with a fillet radius of R=3-5mm is set at the root of the thread to effectively reduce the stress concentration coefficient. Combined with the residual compressive stress layer formed by surface rolling reinforcement, the fatigue life is improved by more than 40% compared with the existing technology.

[0018] (4) Selection of non-magnetic materials: Non-magnetic alloy materials with relative permeability μ≤1.01 are used to ensure that the drill collar will not interfere with the measurement signal in magnetically sensitive application scenarios such as measurement while drilling.

[0019] (5) Manufacturing method guarantee: By combining precision machining and surface plastic deformation process, the geometric accuracy of spiral ribs and the surface quality of stress relief groove are ensured, so as to achieve synergistic optimization of structural performance and manufacturing process. Attached Figure Description

[0020] Figure 1 This is an overall axial sectional view of the drill collar provided in an embodiment of the present invention; Figure 2 for Figure 1 A cross-sectional view of section AA, showing the cross-sectional shape of the helical stiffener; Figure 3 for Figure 1 The enlarged view of area B shows the assembly structure of the double-shoulder thread and sealing components.

[0021] In the diagram: 100 - Drill collar body; 110 - Helical reinforcing rib; 200 - Connecting end; 210 - Double shoulder thread; 211 - Stress relief groove; 212 - Sealing cavity; 220 - Sealing assembly. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are only for explaining the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0023] Example 1 This embodiment provides a high-strength non-magnetic drill collar for deep wells at depths of 10,000 meters.

[0024] The drill collar body (100) is made of Cr-Mn series non-magnetic austenitic steel, and its chemical composition by mass percentage is: C 0.05%, Cr 19%, Mn 13%, N 0.4%, with the balance being Fe and unavoidable impurities. After solution treatment, this material has excellent low magnetic permeability (μ≤1.01) and high strength (tensile strength≥800MPa).

[0025] The drill collar body (100) is a hollow, thick-walled cylindrical structure with an outer diameter of 250 mm, an inner diameter of 90 mm, and a wall thickness of 80 mm. The inner wall is provided with a single-headed spiral reinforcing rib (110) with a helix angle of 20° and a lead of 400 mm. The cross-section of the spiral reinforcing rib (110) is an isosceles trapezoid with an upper base width of 12 mm, a lower base width of 18 mm, and a height of 22 mm.

[0026] The connecting end (200) is integrally formed at both ends of the body (100) and is provided with a double-shoulder thread (210). A sealing cavity (212) is formed between the main shoulder and the secondary shoulder. The inner wall of the sealing cavity (212) is provided with an annular limiting step. The sealing component (220) is made of hydrogenated nitrile rubber with a Shore hardness of 70±5 and a tensile strength of ≥20MPa. It is installed between the limiting step and the secondary shoulder by interference fit.

[0027] A stress relief groove (211) is provided at the transition between the thread root and the shoulder. The groove is 2.5 mm deep and the fillet radius R=4 mm. After surface rolling strengthening treatment, the residual compressive stress layer depth is 0.6 mm and the surface roughness Ra≤0.8 μm.

[0028] The manufacturing method is as follows: Step 1: Forge the drill collar body (100) blank and perform heat treatment to a hardness of 280-320HB.

[0029] Step 2: Use a five-axis CNC milling machine to machine the spiral reinforcing rib (110), using a φ20mm carbide end mill, a spindle speed of 300rpm, a feed rate of 0.1mm / r, and a pitch error of ≤0.05mm.

[0030] Step 3: Machining stress relief grooves (211) at the root of the thread, and using a 60° rolling roller with a pressure of 18MPa for rolling reinforcement.

[0031] Step 4: Press the sealing component (220) into the sealing cavity (212) with a pressing force of 50-80kN.

[0032] Step 5: Perform 100% ultrasonic flaw detection and accept the product according to GB / T 4162-2008 standard.

[0033] Performance testing: Under drilling fluid flow rate of 3 m / s and sand content of 5%, after 24 hours of continuous erosion, the weight loss of the inner wall was 0.32 g / h, which is 36% lower than that of the existing technology (0.5 g / h).

[0034] Perform 10 tests on the MTS testing machine. 7 After multiple cycles of loading (maximum stress 600 MPa), no fracture occurred, and the fatigue life reached 216 hours, which is 40% higher than the existing technology (154 hours).

[0035] The threaded connection remained leak-free for 30 minutes under an internal pressure of 120MPa.

[0036] Example 2 This embodiment is basically the same as Embodiment 1, except that: Spiral reinforcing rib (110) has a helix angle of 15°, a lead of 300mm, and cross-sectional dimensions of: top bottom width 10mm, bottom bottom width 20mm, and height 20mm.

[0037] The stress relief groove (211) has a groove depth of 2mm, a fillet radius of R=3mm, a rolling pressure of 15MPa, and a residual compressive stress layer depth of 0.5mm.

[0038] Test results: erosion rate 0.35 g / h, fatigue life 205 hours, no leakage.

[0039] Example 3 This embodiment is basically the same as Embodiment 1, except that: Spiral reinforcing rib (110) has a helix angle of 30°, a lead of 500mm, and cross-sectional dimensions of: top bottom width 15mm, bottom bottom width 25mm, and height 25mm.

[0040] The stress relief groove (211) has a groove depth of 3mm, a fillet radius of R=5mm, a rolling pressure of 20MPa, and a residual compressive stress layer depth of 0.7mm.

[0041] Test results: erosion rate 0.33 g / h, fatigue life 210 hours, no leakage.

[0042] Industrial applicability The high-strength non-magnetic drill collar for deep wells at depths of 10,000 meters and its manufacturing method provided by this invention have a reasonable structural design and reliable manufacturing process. They can effectively reduce the erosion rate of the inner wall, eliminate thread leakage, and improve fatigue life. They are suitable for drilling operations in deep wells and ultra-deep wells at depths of 10,000 meters and have broad prospects for industrial application.

Claims

1. A high-strength non-magnetic drill collar for deep wells at depths of 10,000 meters, characterized in that, include: Drill collar body (100): a hollow thick-walled cylindrical structure made of non-magnetic alloy material with relative magnetic permeability μ≤1.01, with a wall thickness of 80-120mm, and a single-headed spiral reinforcing rib (110) with a helix angle of 15°-30° and a lead of 300-500mm on the inner wall. Connection end (200): integrally formed at both ends of the body (100), including: Double shoulder thread (210): A sealing cavity (212) is provided between the main shoulder and the auxiliary shoulder. Stress relief groove (211): Located at the transition between the thread root and the shoulder, the groove depth is 2-3mm and the fillet radius R=3-5mm; Sealing assembly (220): embedded in sealing cavity (212).

2. The drill collar according to claim 1, characterized in that, The inner wall of the sealed cavity (212) is provided with an annular limiting step; The sealing assembly (220) is installed between the limiting step and the secondary shoulder by an interference fit.

3. The drill collar according to claim 1, characterized in that, The cross-section of the spiral reinforcing rib (110) is an isosceles trapezoid with an upper base width of 10-15mm, a lower base width of 20-25mm, and a height of 20-25mm.

4. The drill collar according to claim 1, characterized in that, The stress relief groove (211) is subjected to surface rolling strengthening treatment, and the depth of the residual compressive stress layer is ≥0.5mm.

5. A method for manufacturing a drill collar as described in claim 1, characterized in that, This includes the following steps performed sequentially: Step 1: Provide a drill collar body (100) blank and perform heat treatment on the blank; Step 2: Use precision machining to form spiral reinforcing ribs (110) on the inner wall; Step 3: Machining a stress relief groove (211) at the root of the thread and strengthening it using a surface plastic deformation process; Step 4: Install the sealing assembly (220) into the sealing cavity (212); Step 5: Perform non-destructive testing.

6. The manufacturing method according to claim 5, characterized in that, Step 2 uses a five-axis CNC milling machine for machining, with a pitch error ≤0.05mm.

7. The manufacturing method according to claim 5, characterized in that, In step 3, the surface plastic deformation process is roll forming, with a roll forming pressure of 15-20 MPa.

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