Ultra-high-strength and high-ductility petroleum casing and manufacturing method therefor

Abstract

Disclosed in the present invention is a petroleum casing. The petroleum casing comprises Fe and inevitable impurities, and further comprises the following chemical elements, in percentage by mass: 0.10%-0.20% of C, 0.5%-0.8% of Si, 1.9%-2.8% of Mn, 0.6%-1.5% of Cr, 0.4%-0.8% of Mo, 0.10%-0.20% of V, 0.2%-0.7% of Ni, 0.0005%-0.0050% of Ca, 0.01%-0.05% of Al, and 0.020%-0.040% of Nb. Further disclosed in the present invention is a method for manufacturing the petroleum casing. The petroleum casing of the present invention exhibits ultra-high strength and high ductility, ensuring the service safety of the petroleum casing in a complex and harsh environment of an ultra-deep well.

Description

A high-strength, high-plasticity oil casing and its manufacturing method Technical Field

[0001] This disclosure relates to a type of steel and a method for manufacturing the same, and more particularly to an oil casing and a method for manufacturing the same. Background Technology

[0002] The working environment of ultra-deep wells is complex, with high temperature and pressure, and some blocks contain thick high-pressure salt layers (high-pressure formations), which will exert complex forces such as tension, pressure, bending and torsion on the casing, making the casing extremely prone to failure.

[0003] The deformation of casing varies depending on the formation stress. Under axial tension, the casing will neck, leading to fracture. Under shear force, the casing will undergo shear deformation, also leading to fracture. When the casing has high plasticity, it undergoes minor deformation but does not fracture, maintaining the integrity of the tubing string and allowing for normal operation. However, when the casing has low plasticity, it is prone to fracture, making normal production impossible. Therefore, casing for deep and ultra-deep wells needs to possess both high strength and high plasticity.

[0004] Uniform elongation is an important indicator of plasticity. Uniform elongation refers to the maximum percentage increase in length of a specimen before fracture during a tensile test. It is a crucial parameter for measuring a material's ability to undergo plastic deformation. A higher uniform elongation indicates better plasticity, meaning the material is more capable of uniform deformation under external forces and less prone to fracture.

[0005] In the existing technology, there are relevant patent documents dedicated to improving the mechanical properties of the casing, for example:

[0006] Chinese patent document CN103194693A, published on July 10, 2013, entitled "A High-Strength, High-Toughness Oil Casing and Its Manufacturing Method," discloses a high-strength, high-toughness oil casing and its manufacturing method. This document employs a process technology of "high-frequency welding (HFW) + online heat treatment of the weld seam + thermal tension reduction + full-body heat treatment" to obtain Q125 grade oil casing.

[0007] Chinese patent document CN102296239A, published on December 28, 2011, entitled "A High-Strength Anti-Crush Oil Casing Pipeline and Its Manufacturing Method," discloses a high-strength anti-crush oil casing pipeline and its manufacturing method. The outer diameter of the pipeline is [missing information]. The wall thickness of the tubing is 10.7 mm to 12.9 mm.

[0008] Chinese patent document CN102747300A, published on October 24, 2012, entitled "A High-Strength, High-Toughness Seamless Steel Pipe for Structures and Its Manufacturing Method," discloses a high-strength, high-toughness seamless steel pipe for structures and its manufacturing method. The seamless steel pipe has a yield strength of not less than 890 MPa, a tensile strength of not less than 960 MPa, an elongation of not less than 14%, a longitudinal impact energy of not less than 120 J at -20℃, and a longitudinal impact energy of not less than 75 J at -40℃ in the welded area.

[0009] However, the aforementioned existing technologies are all limited to improving the strength, toughness, or crush resistance of the casing, without paying attention to the uniform elongation of the casing. Summary of the Invention

[0010] One of the purposes of this disclosure is to provide an oil casing that has both ultra-high strength and high plasticity (high uniform elongation), thereby ensuring the safety of the casing in the complex and harsh environment of ultra-deep wells.

[0011] To achieve the above objectives, this disclosure provides an oilfield casing that, in addition to containing Fe and unavoidable impurities, contains the following chemical elements in the following mass percentages:

[0012] C: 0.10-0.20%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.2-0.7%, preferably 0.3-0.7%, Ca: 0.0005-0.0050%, Al: 0.01-0.05%, Nb: 0.020-0.040%.

[0013] Preferably, the mass percentage content of each element in the oil casing of this disclosure is as follows:

[0014] C: 0.10-0.20%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.2-0.7%, preferably 0.3-0.7%, Ca: 0.0005-0.0050%, Al: 0.01-0.05%, Nb: 0.020-0.040%; the balance being Fe and other unavoidable impurities.

[0015] By optimizing the composition of the oil casing and employing specific manufacturing processes (especially heat treatment), a microstructure of tempered sorbite + retained austenite was achieved. Under stress during plastic deformation, the retained austenite undergoes the TRIP effect, with a large amount of stable gradient-distributed retained austenite transforming into hard martensite. The formation of martensite causes volume expansion, increasing the dislocation density in the tempered sorbite. This enhances the coordinated deformation ability between the phases, significantly improving the uniform elongation of the material and enhancing the uniform deformation capability of the casing, thus preventing casing breakage.

[0016] Preferably, in the oil casing of this disclosure, unavoidable impurities include P and S, and P ≤ 0.015% and S ≤ 0.005%.

[0017] In the technical solutions described above, both P and S are harmful impurity elements. To obtain steel with better performance and higher quality, the content of P and S should be reduced as much as possible, where technically permissible.

[0018] Preferably, the microstructure of the oil casing disclosed herein is tempered sorbite + retained austenite.

[0019] Preferably, in the oil casing of this disclosure, the area percentage of retained austenite is 6-12%.

[0020] Preferably, the yield strength of the oil casing disclosed herein is 965-1170 MPa, for example 980-1140 MPa.

[0021] Preferably, the tensile strength of the oil casing disclosed herein is ≥1034MPa, for example 1080-1210MPa.

[0022] Preferably, the uniform elongation of the oil casing disclosed herein is ≥12%.

[0023] Preferably, the 0°C transverse Charpy impact energy of the oil casing disclosed herein is ≥80J, for example 85-115J.

[0024] Another object of this disclosure is to provide a method for manufacturing oil casing. This manufacturing method is simple and facilitates the mass production of ultra-high strength and high plasticity oil casing.

[0025] To achieve the above objectives, this disclosure provides a method for manufacturing an oil casing, comprising the following steps:

[0026] - Smelting and continuous casting yield round billets;

[0027] -Piercing: Piercing the round billet to form a steel pipe;

[0028] - Rolling: The steel pipe is rolled at a final rolling temperature of 920-980℃;

[0029] - Two-phase region quenching treatment: Heat the steel pipe to the austenitizing temperature Ac3-(10-30)℃, hold for 30-60 minutes and then water quench;

[0030] -Tempering treatment;

[0031] - Thermal straightening.

[0032] In the method disclosed herein, the austenitizing temperature is controlled at Ac3-(10-30)℃, with the aim of obtaining the final tempered sorbite and retained austenite / ferrite multiphase structure, thereby ensuring a reasonable proportion of each component in the steel and improving the work hardening index of the steel.

[0033] It should be noted that in step (4), Ac3 = 910 - 203[C] 1 / 2 -15.2[Ni]+44.7[Si]+104[V]+31.5[Mo]+13.1[W], where C, Ni, Si, V, Mo and W represent their respective mass percentages; when substituting into the above formula, the values ​​before the percentage sign should be used.

[0034] Preferably, in the smelting and continuous casting steps of the manufacturing method disclosed herein, the continuous casting speed is 1.8-2.4 m / min.

[0035] Preferably, in the piercing step of the manufacturing method disclosed herein, the round blank is homogenized at 1220-1270°C and then pierced at a piercing temperature of 1150-1210°C.

[0036] Preferably, in the rolling step of the manufacturing method disclosed herein, the sizing temperature is 800-880°C.

[0037] Preferably, in the tempering step of the manufacturing method disclosed herein, the tempering temperature is 550-630°C and the holding time is 60-90 min.

[0038] The oil casing and its manufacturing method disclosed herein have the following advantages and beneficial effects:

[0039] The oil casing disclosed herein, through a reasonable composition design, possesses high strength and uniform elongation, while remaining inexpensive. This solves the problem of poor plasticity in existing high-strength casings and improves the safe service capability of the casing in downhole applications.

[0040] In some embodiments, the oil casing of this disclosure has a yield strength of 965-1170 MPa, a tensile strength of ≥1034 MPa, a uniform elongation of ≥12%, and a transverse Charpy impact energy of ≥80 J at 0°C.

[0041] In some embodiments, the oil casing of this disclosure has a yield strength of 980-1140 MPa, a tensile strength of 1080-1210 MPa, a uniform elongation of ≥12%, and a transverse Charpy impact energy of 85-115 J at 0°C.

[0042] The oil casing manufacturing method disclosed herein is simple in process and easy to mass-produce ultra-high strength and high plasticity oil casing. Detailed Implementation

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0044] In this paper, the area percentage of retained austenite was obtained by observing the microstructure using scanning electron microscopy and statistically analyzing the data using image analysis software.

[0045] In this paper, yield strength, tensile strength, and uniform elongation were determined according to GB / T 228.1-2000.

[0046] In this paper, the transverse Charpy impact energy at 0℃ was determined according to GB / T 229-2007.

[0047] The design principles of each chemical element in the oilfield casing disclosed herein are as follows:

[0048] Carbon (C): In the oil casing of this disclosure, carbon (C) is a precipitate-forming element that can improve the strength of the steel. When the mass percentage of carbon is too low, the hardenability of the steel decreases, making it difficult to simultaneously maintain high strength. When the mass percentage of carbon is too high, carbon will also form a large number of coarsening precipitates with Cr and Mo, significantly aggravating the segregation of the steel, leading to a significant decrease in plasticity and toughness. Therefore, in the oil casing of this disclosure, the mass percentage of carbon is controlled between 0.10-0.20%, for example, 0.12-0.18%.

[0049] Silicon (Si): In the oil casing of this disclosure, Si promotes carbon diffusion into austenite and inhibits the precipitation of cementite in austenite. This not only provides solid solution strengthening but also promotes carbon enrichment in austenite, improving the stability of retained austenite. When the mass percentage of Si is too low, the effect on improving the stability of retained austenite is not significant. However, the mass percentage of Si in steel should not be too high, as excessive Si will deteriorate the workability and toughness of the steel. Therefore, in the oil casing of this disclosure, the mass percentage of Si is controlled between 0.5% and 0.8%.

[0050] Manganese (Mn): In the oil casing of this disclosure, Mn is an austenite-forming element that can stabilize austenite in steel, slow down the ferrite transformation rate, reduce carbon diffusion from ferrite to austenite, and increase the amount of retained austenite, which is beneficial to improving the uniform elongation of the material. To achieve the desired microstructure control, the Mn content needs to be controlled above 1.9%. However, when the mass percentage of Mn is too high, it will significantly increase microstructure segregation in the steel, affecting the uniformity and impact properties of the hot-rolled microstructure. Therefore, in the oil casing of this disclosure, the mass percentage of Mn is controlled between 1.9% and 2.8%, for example, 2.2% to 2.8%.

[0051] Chromium (Cr): In the oil casing disclosed herein, Cr is a strong element that enhances hardenability and is also a strong precipitate-forming element. During tempering, it can precipitate precipitates, increasing the strength of the steel. However, when the mass percentage of Cr is too high, coarse precipitates (M-type precipitates) are easily formed at the grain boundaries. 23 C6 precipitates reduce toughness. When the mass percentage of Cr is too low, hardenability is poor, and sufficient toughness cannot be guaranteed. Therefore, in the oil casing of this disclosure, the mass percentage of Cr is controlled between 0.6% and 1.5%, for example, 0.9% to 1.5%.

[0052] Molybdenum (Mo): In the oil casing of this disclosure, the main role of Mo is to improve the strength and tempering stability of the steel through precipitates and solid solution strengthening. The oil casing of this disclosure has a low carbon content. When the mass percentage of Mo is too high, it has little effect on improving the steel strength, easily leading to alloy waste; when the mass percentage of Mo is too low, the strength is difficult to reach the 140ksi steel grade. Therefore, in the oil casing of this disclosure, the mass percentage of Mo is controlled between 0.4% and 0.8%.

[0053] Vanadium (V): In the oil casing of this disclosure, vanadium (V) is a typical precipitation strengthening element that can compensate for the decrease in strength caused by the reduction in carbon content. When the mass percentage of vanadium is too high, coarse vanadium (CN) is easily formed, thereby reducing toughness. Therefore, in the oil casing of this disclosure, the mass percentage of vanadium is controlled between 0.10% and 0.20%.

[0054] Nickel (Ni): In the oil casing of this disclosure, Ni can promote the formation of austenite, ensuring the presence of retained austenite in the rolled steel, which is beneficial for improving the uniform elongation of the material and enhancing its impact toughness. However, when the mass percentage of Ni is higher than 0.7%, although it can further improve austenite stability, the effect on increasing the proportion of retained austenite tends to saturate, while significantly increasing material costs; when the mass percentage of Ni is lower than 0.3%, it cannot effectively increase the proportion of retained austenite. Therefore, in the oil casing of this disclosure, the mass percentage of Ni is controlled between 0.3% and 0.7%.

[0055] Calcium (Ca): In the oil casing of this disclosure, Ca can purify molten steel and promote MnS spheroidization, thereby improving impact toughness. However, when the mass percentage content of Ca is too high, it easily forms coarse non-metallic inclusions. Therefore, in the oil casing of this disclosure, the mass percentage content of Ca is controlled between 0.0005% and 0.0050%.

[0056] Al: In the oil casing disclosed herein, Al is a traditional deoxidizing and nitrogen-fixing element that can refine grains. Considering that Al reduces the yield strength ratio of the material, its content should not be too high. Therefore, in the oil casing disclosed herein, the mass percentage content of Al is controlled between 0.01% and 0.05%.

[0057] Nb: In the oil casing of this disclosure, Nb is a grain-refining and precipitation-strengthening element that can compensate for the decrease in strength caused by the reduction in carbon content. When the mass percentage of Nb is higher than 0.040%, coarse Nb(CN) is easily formed, thereby reducing toughness. When the mass percentage of Nb is lower than 0.020%, the strengthening effect is not obvious. Therefore, in the oil casing of this disclosure, the mass percentage of Nb is controlled between 0.020% and 0.040%.

[0058] The oil casing and its manufacturing method disclosed herein will be further explained and described below with reference to specific embodiments. However, such explanation and description do not constitute an improper limitation on the technical solution of the present invention.

[0059] Examples 1-5 and Comparative Examples 1-6

[0060] The oil casings in Examples 1-5 and the control tubes in Comparative Examples 1-6 were all prepared using the following steps:

[0061] (1) Smelting and continuous casting to obtain round billets;

[0062] (2) Piercing: Piercing the round billet to form a steel pipe;

[0063] (3) Rolling: The steel pipe is rolled at a final rolling temperature of 920-980℃;

[0064] (4) Two-phase region quenching treatment: Heat the steel pipe to the austenitizing temperature Ac3-(10-30)℃, hold for 30-60 minutes and then water quench;

[0065] (5) Tempering treatment;

[0066] (6) Thermal straightening.

[0067] Table 1 lists the mass percentage of each chemical element for the oil casings of Examples 1-5 and the control tubes of Comparative Examples 1-6.

[0068] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0069] Table 2 lists the specific process parameters of the oil casing for Examples 1-5 and the control casing for Comparative Examples 1-6.

[0070] Table 2.

[0071] Samples were taken from the oil casings of Examples 1-5 and the control tubes of Comparative Examples 1-6. After polishing, the microstructure of the samples was observed by scanning electron microscopy, and the test results are listed in Table 3.

[0072] Table 3 lists the microstructure test results of the oil casing of Examples 1-5 and the control tubes of Comparative Examples 1-6.

[0073] Table 3.

[0074] As can be seen from Table 3, the microstructure of the oil casing using Examples 1-5 is tempered sorbite + retained austenite, and the area percentage of retained austenite is between 6-12%.

[0075] In addition, samples were taken again from the oil casing of Examples 1-5 and the control tubing of Comparative Examples 1-6, and the samples were subjected to performance testing. The test results are listed in Table 4. The relevant test methods are as follows:

[0076] Mechanical property testing:

[0077] Tensile test: Tensile properties at room temperature were tested according to GB / T 228.1-2000 standard.

[0078] Impact test: The transverse Charpy impact energy at 0℃ was determined according to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0079] Table 4 lists the performance test results of the oil casing of Examples 1-5 and the control casing of Comparative Examples 1-6.

[0080] Table 4.

[0081] As can be seen from Table 4 above, the yield strength of the oil casing in Examples 1-5 is all above 980 MPa, the tensile strength is all above 1080 MPa, the uniform elongation is all above 12%, and the transverse Charpy impact energy at 0℃ is all above 85 J. They have high strength and uniform elongation, which can ensure the service safety of the casing in the complex and harsh environment of ultra-deep wells.

[0082] In contrast, at least one mechanical property of the comparative sleeves in Comparative Examples 1-6 failed to meet the standard of high-strength, high-plasticity sleeves, and their overall performance was significantly inferior to that of the sleeves in the Examples.

[0083] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated herein by reference in their entirety.

[0084] While this disclosure has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the disclosure in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of this disclosure to these descriptions. Various changes in form and detail can be made by those skilled in the art, including some simple deductions or substitutions, without departing from the spirit and scope of this disclosure.

Claims

1. An oilfield casing, characterized in that, In addition to Fe and unavoidable impurities, the oil casing also contains the following chemical elements in the following mass percentages: C: 0.10-0.20%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.2-0.7%, preferably 0.3-0.7%, Ca: 0.0005-0.0050%, Al: 0.01-0.05%, Nb: 0.020-0.040%.

2. The oil casing as described in claim 1, characterized in that, The mass percentage of each element in the oil casing is as follows: C: 0.10-0.20%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.2-0.7%, preferably 0.3-0.7%, Ca: 0.0005-0.0050%, Al: 0.01-0.05%, Nb: 0.020-0.040%; the balance being Fe and unavoidable impurities.

3. The oil casing as described in claim 1 or 2, characterized in that, Unavoidable impurities include P and S, with P ≤ 0.015% and S ≤ 0.005%.

4. The oil casing as described in any one of claims 1 to 3, characterized in that, The microstructure of the oil casing is tempered sorbite plus retained austenite.

5. The oil casing as described in claim 4, characterized in that, The area percentage of the retained austenite is 6-12%.

6. The oil casing as described in any one of claims 1 to 5, characterized in that, The oil casing has a yield strength of 965-1170 MPa, for example 980-1140 MPa, a tensile strength of ≥1034 MPa, for example 1080-1210 MPa, a uniform elongation of ≥12%, and a transverse Charpy impact energy of ≥80 J at 0℃, for example 85-115 J.

7. A method for manufacturing an oil casing according to any one of claims 1 to 6, characterized in that, Includes the following steps: - Smelting and continuous casting yield round billets; -Piercing: Piercing the round billet to form a steel pipe; - Rolling: The steel pipe is rolled at a final rolling temperature of 920-980℃; - Two-phase region quenching treatment: Heat the steel pipe to the austenitizing temperature Ac3-(10-30)℃, hold for 30-60 minutes and then water quench; -Tempering treatment; - Thermal straightening.

8. The method as described in claim 7, characterized in that, In the smelting and continuous casting steps, the continuous casting speed is 1.8-2.4 m / min.

9. The method as described in claim 7 or 8, characterized in that, In the piercing step, the round blank is heated uniformly at 1220-1270℃ and then pierced at a piercing temperature of 1150-1210℃.

10. The method according to any one of claims 7 to 9, characterized in that, During the rolling process, the sizing temperature is 800-880℃.

11. The method according to any one of claims 7 to 10, characterized in that, In the tempering process, the tempering temperature is 550-630℃ and the holding time is 60-90min.

Images