A high collapse resistance oil casing with uniform strength and method of designing and manufacturing the same

Abstract

The application discloses a high-anti-extrusion oil casing with uniform strength and a design and manufacturing method thereof. The design method of the high-anti-extrusion oil casing with uniform strength comprises the following steps: S100, analysis and verification of casing extrusion mechanism, comprising steps S110-S130; S110, casing sample preparation, comprising steps S111-S113: S111, geometric size detection: taking a sample of a casing specification meeting the API anti-extrusion requirement, the sample length is more than 8 times of the nominal outer diameter, and taking the middle section of the sample length as a reference. Beneficial effects: compared with the prior art, the application produces a high-anti-extrusion oil casing on the basis of the extrusion mechanism research, and the high-anti-extrusion casing is subjected to the equal-strength high-anti-extrusion casing test verification, the geometric size control and the residual stress are significantly changed and are greater than the control value required by the conventional high-anti-extrusion casing.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology, specifically relating to a high-strength, high-strength-uniform-stretch-resistant oil casing and its design method. Background Technology

[0002] With the increasing number of deep and ultra-deep wells in the petroleum industry, the formation pressure increases with depth, requiring the wellbore to withstand higher pressure, i.e., the casing and tubing need higher resistance to compression. The typical design method for the resistance to compression of casing and tubing is the calculation formula proposed in API 5C3. This formula determines the resistance to compression of the tubing based on the nominal yield strength corresponding to the steel grade of the casing and tubing material and the ratio of the nominal outer diameter to the wall thickness; this is called the API resistance to compression. By studying and controlling the influencing parameters of resistance to compression, a resistance to compression exceeding the API specified value is called high-resistance casing and tubing. Appendix F of API 5C3 lists the main influencing factors for the resistance to compression of casing and tubing as tubing ellipticity, wall thickness non-uniformity, residual compressive stress, and the casing and tubing straightening process.

[0003] Problems with existing high-stretch-resistance oil casing design methods:

[0004] 1) According to the API extrusion strength calculation method, the main measures to improve the extrusion strength of the pipe body are to increase the yield strength of the material and the wall thickness of the pipe body, and reduce the ratio of outer diameter to wall thickness, which will increase the self-weight of the oil casing and the steel grade, and increase the use cost.

[0005] 2) The API 5C3 Appendix F's factors affecting extrusion strength are based on the KT extrusion strength calculation formula, which is derived from the statistical results of actual extrusion tests on oil casing pipes. This formula relies on the ellipticity of the pipe's geometry, wall thickness non-uniformity, residual compressive stress, and the straightening process of the oil casing pipe. Strict control over the pipe's geometry leads to a higher scrap rate and significantly increased manufacturing costs in actual production. Furthermore, it lacks analysis of the extrusion mechanism for oil casing pipes with different outer diameters and wall thicknesses, provides no specific targeted measures, and the statistical formula fails to reflect the irregularities in the cross-sectional geometry of the oil casing pipe. Treating the oil casing pipe as an ideal ellipse fails to guide actual oil casing pipe production.

[0006] 3) Patent application number CN201510088968, a low-cost, high-strength oil casing containing rare earth elements and its manufacturing method, describes a product with low production cost, high strength and toughness, uniform and fine microstructure, low residual stress, and high resistance to crushing. However, this invention does not reveal the mechanism of the high crush resistance of the oil casing; it only changes the chemical composition of the oil casing and does not provide physical verification of the oil casing's crush resistance.

[0007] 4) Patent application number CN201910222980, a corrosion-resistant, high-stretch-resistance oil casing and its preparation method. The characteristic feature is that the outer diameter ellipticity of the oil casing is ≤0.5%D, the wall thickness non-uniformity is ≤15%t, and the residual stress of the casing body is ≤100MPa; where D is the nominal diameter of the oil casing in mm, and t is the nominal wall thickness of the oil casing in mm. Controlling geometric dimensional accuracy and residual stress based on the influencing factors of stretch resistance proposed in the standard to improve stretch resistance strength results in a significant increase in production costs and offers no innovation or contribution to high-stretch-resistance design methods.

[0008] Based on the above analysis, it can be seen that the existing high-stretch-resistance oil casing design methods are: 1) based on the influencing factors and stretch-resistance calculation formula proposed by the API standard to design high-stretch-resistance oil casing; 2) controlling the chemical composition of the oil casing material to reduce production costs.

[0009] The above design method does not reveal the anti-crushing mechanism of the oil casing and cannot meet the actual needs of the oil casing and pipe. Summary of the Invention

[0010] The technical problem to be solved by this invention is: how to design a high-strength, high-strength, high-strength-resistant oil casing design method, and to design an oil casing with better performance by utilizing the anti-strength mechanism of the oil casing.

[0011] The specific plan is as follows:

[0012] A design method for a high-strength, high-strength-resistant oil casing includes the following steps:

[0013] S100, Analysis and verification of the bursting mechanism of the oil casing and tubing, including steps S110-130;

[0014] S110, Preparation of oil casing and tubing samples, including steps S111-113:

[0015] S111. Geometric dimension inspection: Take samples of the oil casing specifications that meet the API anti-extrusion requirements. The sample length is more than 8 times the nominal outer diameter. Using the middle section of the sample length as the reference, inspect the geometric dimensions of the pipe at equal intervals with the pipe diameter D as the inspection interval. Inspect at least 5 sections, and inspect at least 4 diameters and 8 wall thickness points in each section.

[0016] After inspection, the geometric dimensions were analyzed, and the ellipticity and wall thickness non-uniformity of each cross section are shown in Equations 1 and 2.

[0017] OV = 100 (Dmax - Dmin) / Dave; (Equation 1)

[0018] Where OV: ellipticity of each cross section, in percentage (%)

[0019] Dmax: The maximum measured diameter for each cross-section;

[0020] Dmin: The minimum measured diameter for each cross-section;

[0021] Dave: The average diameter measured for each cross-section;

[0022] EC=100 (tcmax - tcmin) / tcave; (Formula 2)

[0023] EC: Wall thickness non-uniformity at each cross section, in percentage.

[0024] tcmax: The maximum measured wall thickness for each cross-section;

[0025] tcmin: The minimum wall thickness measured at each cross-section;

[0026] tcave: The average wall thickness measured at each cross-section;

[0027] S112. Residual stress detection of several pipe bodies: The macroscopic residual stress of the pipe body is detected by the circumferential cutting method. The length of the pipe body is more than 2.5 times the diameter. Three diameter positions and six wall thickness points are measured on the pipe body. The geometric dimensions of the pipe body are detected according to the following residual stress calculation method.

[0028]

[0029] in,

[0030] , is the average outer diameter of the oil casing after cutting;

[0031] , is the average outer diameter of the oil casing before cutting;

[0032] σ: Residual stress in the tube body;

[0033] E: Material elastic modulus;

[0034] t; average wall thickness at measurement points;

[0035] μ: Poisson's ratio of the material;

[0036] D1, D2, D3: Diameter of the measurement point;

[0037] S113. Mechanical property testing of tube body material: Take plate-shaped tensile specimens in four quadrants of the tube body to test the mechanical properties of the material, including tensile yield strength, tensile strength and elongation. The mechanical property testing in four quadrants can reflect the changes in the mechanical properties of the tube body material during the production rolling, heat treatment and straightening process.

[0038] S120, Pipe body crush test, including steps S121-122.

[0039] S121. External pressure crushing test: Put the pipe into the external pressure crushing container, apply external pressure until the pipe is crushed and deformed, and record the pressure test curve.

[0040] S122. Geometric dimension inspection after external pressure crushing test: The outer diameter and wall thickness of the test specimen after crushing failure are inspected.

[0041] The test results show that the most severe crushing failure deformation occurred in the middle of the tube body, indicating that the crushing started from the middle of the sample tube body and began with plastic deformation under external pressure until complete crushing failure occurred.

[0042] S130, Analysis of the crushing mechanism of oil casing and tubing, including steps S131-133;

[0043] S131. Finite element modeling: The geometric dimensions are modeled based on the original outer diameter and wall thickness of the maximum deformation position of the crushed specimen in the physical test; the model is divided into four quadrants, and the material mechanical properties are assigned based on the measured mechanical properties of the material in the four quadrants; the tube body is divided into mesh elements, and at least four deformation-coordinating elements are used in the thickness direction.

[0044] The modeling is based on the measured stress-strain curves of the oil casing material in four quadrants, the structural geometry, and the length is considered to be more than 10 times the outer diameter of the pipe, taking into account the pipe end clamping and fixing effect.

[0045] S132. Finite element simulation of external pressure crushing process: The residual circumferential stress measured in step S112 of the specimen is applied to the tube body. Then, external pressure is applied until the crushing deformation of the tube body is consistent with the maximum deformation size measured after the crushing of the full-size physical test. The relative error between the external pressure load calculated by finite element and the crushing load of the physical test is compared to verify whether the finite element calculation method is accurate and reliable.

[0046] The finite element analysis results of the oil casing crushing process were compared with the simulated crushing morphology and the actual crushing morphology. It can be seen that the calculated crushing morphology is consistent with the actual crushing morphology. The calculated external pressure change curve during the crushing process is consistent with the actual crushing process curve. The relative error between the calculated value and the experimental value of the maximum external pressure during the crushing process is 0.07%, indicating that the calculation simulation of the oil casing crushing process is accurate and reliable.

[0047] S133. Analysis of the dominant factors in the crushing process: Analysis of the crushing mechanism of the oil casing and tubing shows that when the external pressure resisting crushing reaches its maximum value:

[0048] 1) The inner wall with the minimum yield strength in the first quadrant yields first;

[0049] 2) The second quadrant has the largest plastic strain where the wall thickness is smaller;

[0050] 3) The diameter at which the inner wall first yields has the largest outer diameter, and its ellipticity increases by 2.14 times compared to the original value; the wall thickness non-uniformity remains unchanged compared to the original value.

[0051] 4) After the oil casing and tubing finally underwent severe crushing plastic deformation, the material at both the major axis and minor axis positions of the ellipse yielded, exceeding the measured yield strength of the material and exhibiting severe plastic deformation exceeding the material's yield plastic strain point by 0.65%.

[0052] No yielding or significant plastic deformation occurred at any other location;

[0053] S200, high-stretch-resistant oil casing design

[0054] Based on the above analysis: increasing the yield strength of the material along the circumference of the casing can significantly improve the extrusion resistance; controlling the uniformity of material strength along the circumference of the casing can also improve the extrusion resistance. Based on this analysis, a high-extrusion-resistance casing design is carried out as follows:

[0055] The geometric ellipticity should be controlled to be ≤0.8%; wall thickness non-uniformity to be ≤10%; residual compressive stress to be ≤200MPa; and the minimum wall thickness to be more than 90% of the specified nominal wall thickness.

[0056] S300, High-Stretch-Resistant Oil Casing Verification and Evaluation

[0057] Based on the research on the crushing mechanism, a high-strength crush-resistant oil casing was produced. The results of the equal-strength high-strength crush-resistant oil casing test verified that the geometric dimension control and residual stress were significantly different from the control values ​​required for conventional high-strength crush-resistant oil casing.

[0058] A method for manufacturing a high-strength, high-strength-resistant oil casing is provided. The product parameters obtained according to the above-mentioned high-strength-uniformity, high-strength-resistant oil casing design method are used as requirements. During manufacturing, the heat treatment process is controlled to make the mechanical properties of the pipe material uniform along the circumference, thereby improving the pipe's resistance to extrusion. High extrusion resistance of the oil casing can be achieved by controlling the material strength uniformity.

[0059] A high-strength, high-strength-resistant oil casing is manufactured by the aforementioned method for manufacturing high-strength, high-strength-resistant oil casing.

[0060] Beneficial effects: Compared with the existing technology, this invention produces a high-strength oil casing based on the research of the crushing mechanism. The results of the equal strength high-strength oil casing test verified that the geometric dimension control and residual stress are significantly different and exceed the control values ​​required by conventional high-strength oil casing. Attached Figure Description

[0061] Figure 1 This is a schematic diagram illustrating the geometric dimension measurement of the present invention;

[0062] Figure 2This is a graph showing the external pressure crushing test results of the present invention.

[0063] Figure 3 This is a schematic diagram of the external pressure crushing model of the present invention (modeling of the geometric dimensions of the pipe cross-section);

[0064] Figure 4 This is a schematic diagram of the external pressure crushing model of the present invention (finite element modeling of external pressure crushing).

[0065] Figure 5 Comparison of finite element simulation of oil casing crushing and actual test (finite element simulation of crushing morphology of pipe body).

[0066] Figure 6 A comparison diagram of finite element simulation of oil casing crushing and actual test (MISES stress distribution diagram of maximum external pressure crushing value);

[0067] Figure 7 A comparison diagram of finite element simulation of oil casing crushing and actual test (equivalent plastic strain distribution diagram of maximum external pressure crushing value);

[0068] Figure 8 A comparison diagram of finite element simulation of oil casing crushing and actual test (geometric dimensions of the maximum external pressure crushing value);

[0069] Figure 9 A comparison diagram of finite element simulation of oil casing crushing and actual test (stress distribution diagram of oil casing crushing deformation under external pressure).

[0070] Figure 10 A comparison diagram of finite element simulation of oil casing crushing and actual test (equivalent plastic strain diagram of oil casing crushing deformation under external pressure).

[0071] Figure 11 Comparison of calculated loading and experimental record curves for oil casing crushing (curve of external pressure loading process in finite element simulation of oil casing crushing process);

[0072] Figure 12 A comparison chart of calculated loading and test record curves for the crushing of the oil casing (actual crushing test curve);

[0073] Figure 13 This is a graph showing the variation of the maximum external pressure resisting crushing of the oil casing.

[0074] Figure 14 This is a test record of high-strength, high-strength, anti-crushing oil casing;

[0075] Figure 15 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0076] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings.

[0077] like Figure 15 A design method for a high-strength, high-strength, and high-strength-resistant oil casing includes the following steps:

[0078] S100, Analysis and verification of the bursting mechanism of the oil casing and tubing, including steps S110-130;

[0079] S110, Preparation of oil casing and tubing samples, including steps S111-113:

[0080] S111, Geometric Dimension Inspection: Samples shall be taken from existing oil casing and tubing specifications that meet the API standards (internationally recognized design and manufacturing standards for petroleum equipment, developed by the American Petroleum Institute) for resistance to crushing. See [reference needed]. Figure 1 The sample length is 1400mm, which is 10.02 times (i.e. more than 8 times) the nominal outer diameter (139.7mm). Taking the middle section of the sample length as the reference, the geometric dimensions of the tube are measured at equal intervals (tube diameter D) at both ends. At least 5 sections are measured, and at least 4 diameters and 8 wall thickness points are measured at each section.

[0081] The measured geometric dimensions of its outer diameter are shown in Table 1;

[0082]

[0083] Table 1. Measurement unit for outer diameter of oil casing and tubing (mm)

[0084] The actual measured geometric dimensions of its wall thickness are shown in Table 2.

[0085]

[0086] Table 2. Unit for measuring wall thickness of oil casing and tubing (mm)

[0087] The analysis of ellipticity and wall thickness non-uniformity of geometric dimensions is shown in Table 3.

[0088]

[0089] Table 3 Geometric Dimension Analysis of Oil Casing and Pipe

[0090] After inspection, the geometric dimensions were analyzed, and the ellipticity and wall thickness non-uniformity of each cross section are shown in Equations 1 and 2.

[0091] OV = 100 (Dmax - Dmin) / Dave; (Equation 1)

[0092] OV: Ellipticity of each cross section, in percentage (%)

[0093] Dmax: The maximum measured diameter for each cross-section, in mm;

[0094] Dmin: The minimum diameter measured for each cross-section, in mm;

[0095] Dave: The average diameter measured for each cross-section, in mm.

[0096] EC=100 (tcmax - tcmin) / tcave; (Formula 2)

[0097] EC: Wall thickness non-uniformity at each cross section, in percentage.

[0098] tcmax: The maximum wall thickness measured at each cross-section, in mm;

[0099] tcmin: The minimum wall thickness measured at each cross-section, in mm;

[0100] tcave: The average wall thickness measured at each cross-section, in mm.

[0101] S112. Residual stress detection of several pipe bodies: The macroscopic residual stress of the pipe body is detected by the circumferential cutting method. The length of the pipe body is 350mm, which is more than 2.5 times the diameter. Three diameter positions and six wall thickness points are measured on the pipe body. The geometric dimensions of the pipe body are detected according to the following residual stress calculation method.

[0102]

[0103] in

[0104] , is the average outer diameter of the oil casing after cutting;

[0105] , is the average outer diameter of the oil casing before cutting;

[0106] σ: Residual stress in the tube, in MPa;

[0107] E: Material elastic modulus, in GPa;

[0108] t; average wall thickness at measurement points, in mm;

[0109] μ: Poisson's ratio of the material;

[0110] D1, D2, D3: Diameter of the measuring point, in mm.

[0111] The results of the circumferential residual compressive stress test of the pipe body are shown in Table 4.

[0112]

[0113] Note: The residual compressive stress on the inner surface of the tube after the slit is opened is negative.

[0114] Table 4 Results of residual stress detection in oil casing

[0115] S113. Mechanical property testing of tube body material: Plate-shaped tensile specimens are taken from the four quadrants of the tube body for mechanical property testing, including tensile yield strength, tensile strength, and elongation. The mechanical property testing in the four quadrants reflects the changes in the mechanical properties of the tube body material during production, rolling, heat treatment, and straightening. The test results are shown in Table 5.

[0116]

[0117] Table 5 Four-quadrant testing of material mechanical properties

[0118] S120, Pipe body crush test, including steps S121-122.

[0119] S121. External Pressure Crushing Test: Place the pipe body into an external pressure crushing container, apply external pressure until the pipe body is crushed and deformed, and record the pressure test curve, such as... Figure 2 .

[0120] S122. Geometric dimension inspection after external pressure crushing test: The outer diameter and wall thickness of the test sample after crushing failure are inspected, and the inspection results are shown in Table 6.

[0121]

[0122] Table 6 Geometric Dimension Inspection of Physical Crushed Specimens

[0123] The test results show that the middle position of the tube ( Figure 1 The most severe crush failure deformation occurred at the cross section M3 position, indicating that the crush failure started from the middle position of the sample tube and began with external pressure plastic deformation until complete crush failure occurred.

[0124] Given that the external pressure crush test method involves applying an external pressure load to the pipe after it has been machined and fixed at both ends, resulting in significant crush deformation in a localized area, the pipe near the clamping end is less prone to crush deformation due to the reinforcement effect of the clamping fixtures. Therefore, the structural geometry at this location cannot reflect the impact on the crush resistance (i.e., the outer diameter ellipticity and wall thickness non-uniformity of the cross-section near the clamping end are the largest compared to all measured cross-sectional dimensions, but no significant crush deformation occurs; therefore, the geometry at this location cannot reflect the impact on the pipe's crush resistance). To determine the influence of the pipe's structural geometry on its crush resistance, the outer diameter and wall thickness of the specimen after the crush test are measured. Based on the maximum change in ellipticity, the starting position of the crush deformation and the original geometry at that corresponding position are identified. This confirms that the pipe's structural geometry at this location is the main influencing factor causing the crush.

[0125] S130, Analysis of the crushing mechanism of the oil casing and tubing, including steps S131-133.

[0126] S131, Finite Element Modeling: such as Figure 3-4 The geometric dimensions are modeled based on the original outer diameter and wall thickness of the crushed specimen at the maximum deformation position in the actual test. The model is divided into four quadrants, and the mechanical properties of the material (yield, tensile, elongation) are assigned based on the measured mechanical properties of the material in the four quadrants. The tube body is divided into mesh units, and at least four deformation coordination units are used in the thickness direction to better simulate the bending deformation of the tube body during the crushing process.

[0127] The modeling is based on the measured stress-strain curves of the oil casing material in four quadrants, the structural geometry (the structural geometry of the cross-section at the maximum deformation position of the crushed sample), and the length is considered to be more than 10 times the outer diameter of the pipe, taking into account the pipe end clamping and fixing effect.

[0128] S132. Finite element simulation of external pressure crushing process: Apply the detected circumferential residual stress to each unit of the tube body; apply uniform external pressure to the effective crushed sample section of the tube body until the tube body crushes and fails, deforming to the measured outer diameter of the final crushed state of the sample.

[0129] like Figure 5-10 First, residual stress (the residual circumferential stress measured on the specimen according to step S112) is applied to the tube. Then, external pressure is applied until the tube collapses and the deformation is consistent with the maximum deformation measured after the full-size physical test. The relative error between the external pressure load calculated by finite element method and the collapse load of the physical test is compared to verify whether the finite element method is accurate and reliable.

[0130] like Figure 11-12The finite element analysis results of the casing and tubing crushing process were compared with the simulated crushing morphology and the actual crushing morphology. It was found that the calculated crushing morphology is consistent with the actual crushing morphology. Comparison of the calculated external pressure change curve and the actual crushing process curve showed that the external pressure change trend was consistent. The calculated maximum external pressure value of 199.835 MPa was consistent with the experimental value of 199.7 MPa, with a relative error of 0.07%, indicating that the calculated simulation of the casing and tubing crushing process is accurate and reliable.

[0131] S133. Analysis of the dominant factors in the crushing process: Analysis of the crushing mechanism of the oil casing and tubing shows that when the external pressure resisting crushing reaches its maximum value:

[0132] 1) The inner wall with the minimum yield strength in the first quadrant yields first;

[0133] 2) The second quadrant, with its smaller wall thickness (position O), exhibits the maximum plastic strain of 0.4259%;

[0134] 3) The diameter at which the inner wall yielding first occurred, PO, had the largest outer diameter of 141.2 mm and an ellipticity of 1.52%, which was 2.14 times higher than the original value (0.71%). The wall thickness non-uniformity of 5.32% was unchanged from the original value (5.3%).

[0135] 4) After the oil casing and casing finally underwent severe crushing plastic deformation, the material at the position of the largest major axis PO (diameter 154mm) and the position of the minor axis MN (diameter 124.1mm) of the ellipse both yielded, exceeding the measured yield strength of the material (1009MPa) and exhibiting severe plastic deformation exceeding the material's yield plastic strain point by 0.65% (the diameter and wall thickness of PO / MN both increased significantly, for example, point P increased from the original value of 12.86mm to 13.13mm).

[0136] No yielding or significant plastic deformation occurred at any other location.

[0137] S200, high-stretch-resistant oil casing design

[0138] Based on the above analysis: increasing the yield strength of the material along the circumference of the casing can significantly improve the extrusion resistance; controlling the uniformity of material strength along the circumference of the casing can also improve the extrusion resistance. Based on this analysis, a high-extrusion-resistance casing design is carried out as follows:

[0139] The geometric ellipticity should be controlled to be ≤0.8%; wall thickness non-uniformity to be ≤10%; residual compressive stress to be ≤200MPa; and the minimum wall thickness to be more than 90% of the specified nominal wall thickness.

[0140] like Figure 13 Using material homogenization design, the maximum crushing external pressure value of the oil casing was calculated according to the material stress-strain curves in Table 7. The analysis results show that the crushing strength of the oil casing is improved after material homogenization (the mechanical properties of the materials in the four quadrants are consistent).

[0141]

[0142] Table 7 Material mechanical properties and extrusion strength

[0143] By controlling the heat treatment process to homogenize the mechanical properties of the pipe material along its circumference, the pipe's resistance to extrusion can be effectively improved. High resistance to extrusion in oil casing can be achieved through homogenization control of material strength (yield strength, tensile strength, elongation).

[0144] S300, High-Stretch-Resistant Oil Casing Verification and Evaluation

[0145] Based on this study of the crushing mechanism, a high-crush-resistance oil casing was produced, such as... Figure 14 The high-strength, high-strength oil casing was tested and verified. The geometric dimensions and residual stress showed significant changes, exceeding the control values ​​required for conventional high-strength oil casings. See Table 8 for comparison.

[0146]

[0147] Table 8 Verification of the crush resistance of 139.7×12.7mm Q125 oil casing by actual crush test

[0148] By controlling the heat treatment process, the mechanical properties of the pipe material are made uniform along the circumference. This uniformity of mechanical properties along the four quadrants of the circumference means that the material's yield strength, tensile strength, and elongation are consistent.

[0149] like Figure 14 Equal strength high-strength crush-resistant oil casing was tested, and its crush resistance was verified by external pressure crushing. It achieved crush resistance strength consistent with oil casing requiring higher material mechanical properties. The performance of the high-strength crush-resistant oil casing was higher than the API specified value (142 MPa) by 40.6% and higher than the high-strength crush resistance calculation formula (KT value 174 MPa) by 14.7%. Table 8 shows that the high-strength crush-resistant oil casing with homogenized material strength significantly improves crush resistance strength.

[0150] Other details are available in existing technologies and will not be elaborated further.

[0151] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A design method for a high-strength, high-strength, high-strength-resistant oil casing, characterized in that: Includes the following steps: S100, Analysis and verification of the bursting mechanism of the oil casing and tubing, including steps S110-130; S110, Preparation of oil casing and tubing samples, including steps S111-113: S111. Geometric dimension inspection: Take samples of the oil casing specifications that meet the API anti-extrusion requirements. The sample length is more than 8 times the nominal outer diameter. Using the middle section of the sample length as the reference, inspect the geometric dimensions of the pipe at equal intervals with the pipe diameter D as the inspection interval. Inspect at least 5 sections, and inspect at least 4 diameters and 8 wall thickness points in each section. After inspection, the geometric dimensions were analyzed, and the ellipticity and wall thickness non-uniformity of each cross section are shown in Equations 1 and 2. OV = 100 (Dmax - Dmin) / Dave; (Equation 1) Where OV: ellipticity of each cross section, in percentage (%) Dmax: The maximum measured diameter for each cross-section; Dmax: The minimum measured diameter for each cross-section; Dave: The average diameter measured for each cross-section; EC=100 (tcmax - tcmin) / tcave; (Formula 2) EC: Wall thickness non-uniformity at each cross section, in percentage. tcmax: The maximum measured wall thickness for each cross-section; tcmin: The minimum wall thickness measured at each cross-section; tcave: The average wall thickness measured at each cross-section; S112. Residual stress detection of several pipe bodies: The macroscopic residual stress of the pipe body is detected by the circumferential cutting method. The length of the pipe body is more than 2.5 times the diameter. Three diameter positions and six wall thickness points are measured on the pipe body. The geometric dimensions of the pipe body are detected according to the following residual stress calculation method. ； in, , is the average outer diameter of the oil casing after cutting; , is the average outer diameter of the oil casing before cutting; σ: Residual stress in the tube; E: Material elastic modulus; t; average wall thickness at measurement points; μ: Poisson's ratio of the material; D1, D2, D3: Diameter of the measurement point; S113. Mechanical property testing of tube body material: Take plate-shaped tensile specimens in four quadrants of the tube body to test the mechanical properties of the material, including tensile yield strength, tensile strength and elongation. The mechanical property testing in four quadrants can reflect the changes in the mechanical properties of the tube body material during the production rolling, heat treatment and straightening process. S120, Pipe body crush test, including steps S121-122; S121. External pressure crushing test: Put the pipe into the external pressure crushing container, apply external pressure until the pipe is crushed and deformed, and record the pressure test curve. S122. Geometric dimension inspection after external pressure crushing test: The outer diameter and wall thickness of the test specimen after crushing failure are inspected. The test results show that the most severe crushing failure deformation occurred in the middle of the tube body, indicating that the crushing started from the middle of the sample tube body and began with plastic deformation under external pressure until complete crushing failure occurred. S130, Analysis of the crushing mechanism of oil casing and tubing, including steps S131-133; S131. Finite element modeling: The geometric dimensions are modeled based on the original outer diameter and wall thickness of the maximum deformation position of the crushed specimen in the physical test; the model is divided into four quadrants, and the material mechanical properties are assigned based on the measured mechanical properties of the material in the four quadrants; the tube body is divided into mesh elements, and at least four deformation-coordinating elements are used in the thickness direction. The modeling is based on the measured stress-strain curves of the oil casing material in four quadrants, the structural geometry, and the length is considered to be more than 10 times the outer diameter of the casing, taking into account the pipe end clamping and fixing effect. S132. Finite element simulation of external pressure crushing process: The residual circumferential stress measured in step S112 of the specimen is applied to the tube body. Then, external pressure is applied until the crushing deformation of the tube body is consistent with the maximum deformation size measured after the crushing of the full-size physical test. The relative error between the external pressure load calculated by finite element and the crushing load of the physical test is compared to verify whether the finite element calculation method is accurate and reliable. The finite element analysis results of the oil casing crushing process were compared with the simulated crushing morphology and the actual crushing morphology. It can be seen that the calculated crushing morphology is consistent with the actual crushing morphology. The calculated external pressure change curve during the crushing process is consistent with the actual crushing process curve. The relative error between the calculated value and the experimental value of the maximum external pressure during the crushing process is 0.07%, indicating that the calculation simulation of the oil casing crushing process is accurate and reliable. S133. Analysis of the dominant factors in the crushing process: Analysis of the crushing mechanism of the oil casing and tubing shows that when the external pressure resisting crushing reaches its maximum value: 1) The inner wall with the minimum yield strength in the first quadrant yields first; 2) The second quadrant has the largest plastic strain where the wall thickness is smaller; 3) The diameter at which the inner wall first yields has the largest outer diameter, and its ellipticity increases by 2.14 times compared to the original value; the wall thickness non-uniformity remains unchanged compared to the original value. 4) After the oil casing and tubing finally underwent severe crushing plastic deformation, the material at both the major axis and minor axis positions of the ellipse yielded, exceeding the measured yield strength of the material and exhibiting severe plastic deformation exceeding the material's yield plastic strain point by 0.65%. No yielding or significant plastic deformation occurred at any other location; S200, high-stretch-resistant oil casing design Based on the above analysis: increasing the yield strength of the material along the circumference of the casing can significantly improve the extrusion resistance; controlling the uniformity of material strength along the circumference of the casing can also improve the extrusion resistance. Based on this analysis, a high-extrusion-resistance casing design is carried out as follows: The geometric ellipticity should be controlled to be ≤0.8%; wall thickness non-uniformity to be ≤10%; residual compressive stress to be ≤200MPa; and the minimum wall thickness to be more than 90% of the specified nominal wall thickness. S300, High-Stretch-Resistant Oil Casing Verification and Evaluation Based on the research on the crushing mechanism, a high-strength crush-resistant oil casing was produced. The results of the equal-strength high-strength crush-resistant oil casing test verified that the geometric dimension control and residual stress were significantly different from the control values ​​required for conventional high-strength crush-resistant oil casing.

2. A method for manufacturing a high-strength, high-strength, high-strength, extrusion-resistant oil casing, characterized in that: Using the high-strength-uniformity, high-strength-resistant oil casing design method described in claim 1, and taking the product parameters obtained by this method as requirements, during manufacturing, the heat treatment process is controlled to make the mechanical properties of the pipe material uniform along the circumference, thereby improving the pipe's strength resistance to extrusion; high extrusion resistance of the oil casing can be achieved through material strength uniformity control.

3. A high-strength, high-strength, high-strength-resistant oil casing, characterized in that: The high-strength, high-strength, high-strength, high-strength-resistant oil casing is manufactured using the manufacturing method described in claim 2.

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