High strength non-uniform load resistant oil casing and method of manufacture

Abstract

The application discloses a high-strength anti-non-uniform-load oil casing which contains Fe and inevitable impurities, and additionally contains the following chemical elements in percentage by mass: C: 0.05-0.15%; Si: 0.41-0.8%; Mn: 3-5%; Ni: 0.2-0.5%; Ca: 0.0005-0.005%; Ti: 0.01-0.04%; Al: 0.01-0.05%; Nb: 0.02-0.04%; and the microstructure is ferrite+granular bainite+residual austenite. Correspondingly, the application also discloses a manufacturing method of the high-strength anti-non-uniform-load oil casing, which comprises the following steps: smelting and continuous casting; piercing; rolling and tension reducing; two-phase zone normalizing heat treatment: heating to an austenitizing temperature Ac1+60 DEG C to Ac3-60 DEG C, keeping warm for 30-60 min and then air cooling; and hot straightening.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of pipe and its manufacturing method, especially it relates to a kind of oil casing and its manufacturing method. BACKGROUND

[0002] Shale gas is a kind of natural gas clean energy that can be exploited in shale layer, mud layer. Compared with conventional natural gas exploitation, shale gas exploitation has the difficulty of complex formation, complex fracturing and perforating process. At present, shale gas development adopts the special development technology of horizontal well + multi-stage segmented fracturing, the horizontal section is as long as 3000 meters, 15-30 segment casing perforation is carried out, then large volume hydraulic fracturing is carried out, the formation pressure is high (90-120 MPa), fracturing leads to shale crack development and formation creep, the high-strength casing used is prone to deformation, and the average casing deformation rate is more than 30%. The typical feature of such casing deformation is that the casing does not collapse, but is deformed along the radial direction under the action of uneven load of the formation. With the progress of multi-stage fracturing, the degree of casing deformation gradually increases, the bridge plug used for fracturing operation cannot pass through the deformed position, which leads to the difficulty of hydraulic fracturing, and seriously affects the recovery efficiency of shale gas.

[0003] The Chinese patent document with publication number CN101532113A, publication date September 16, 2009, and title "Anti-collapse oil casing and its manufacturing method" discloses a technical solution for obtaining an anti-collapse casing with ultra-high anti-collapse ability and excellent performance by designing and controlling texture and microstructure.

[0004] The Chinese patent document with publication number CN102296239A, publication date December 28, 2011, and title "High-strength anti-collapse oil casing string and its manufacturing method" discloses a casing string with an outer diameter size of φ141.3mm-φ142.7mm; the wall thickness of the casing string is 10.7mm-12.9mm, but it does not mention the anti-uniform external load performance.

[0005] The Chinese patent document with publication number CN104651723A, publication date May 27, 2015, and title "High anti-collapse oil casing containing rare earth and resistant to hydrogen sulfide corrosion and its production method" relates to an oil casing with a yield strength of 780-870MPa, a transverse impact value at 0℃ of ≥70J / cm 2 , which has high resistance to hydrogen sulfide corrosion and high anti-collapse performance.

[0006] The oil casings mentioned in the above patent documents all have high anti-collapse performance, but are limited to the anti-collapse performance of the casing under uniform load, and do not solve the technical problem of the anti-deformation ability of the oil casing under uneven load. SUMMARY

[0007] One of the purposes of the present application is to provide a high-strength anti-non-uniform load oil casing with a higher work hardening index and toughness and a lower yield ratio, which can significantly improve the material strength through the work hardening effect of the material when the casing is deformed by the action of the formation, thereby improving the anti-deformation ability of the casing and ensuring that the bridge plug can pass smoothly to perform fracturing operations.

[0008] In order to achieve the above-mentioned purpose, the present application provides a high-strength anti-non-uniform load oil casing containing Fe and inevitable impurities, and further containing the following chemical elements with the mass percentage as follows:

[0009] C: 0.05-0.15%; Si: 0.4-0.8%; Mn: 3-5%; Ni: 0.2-0.5%; Ca: 0.0005-0.005%; Ti: 0.01-0.04%; Al: 0.01-0.05%; Nb: 0.02-0.04%; the balance being Fe and inevitable impurities.

[0010] The microstructure thereof is ferrite + granular bainite + residual austenite.

[0011] Further, the present application provides a high-strength anti-non-uniform load oil casing, each chemical element of which has the mass percentage as follows:

[0012] C: 0.05-0.15%; Si: 0.4-0.8%; Mn: 3-5%; Ni: 0.2-0.5%; Ca: 0.0005-0.005%; Ti: 0.01-0.04%; Al: 0.01-0.05%; Nb: 0.02-0.04%; the balance being Fe and inevitable impurities.

[0013] The high-strength anti-non-uniform load oil casing described in the present application controls the mixed structure of ferrite, granular bainite and residual austenite through reasonable component design and heat treatment process, improves the work hardening index n, significantly improves the anti-deformation ability of the casing under non-uniform load, and at the same time obtains good strength and toughness.

[0014] Specifically, the design principle of each chemical element in the high-strength anti-non-uniform load oil casing described in the present application is as follows:

[0015] C: In the high-strength anti-non-uniform load oil casing according to the present application, the C element is a precipitate forming element, which can improve the strength of the steel. It should be noted that when the content of the C element is less than 0.05%, the hardenability of the steel is reduced, and at the same time, it is difficult to ensure the strength of the steel. When the content of the C element is higher than 0.15%, the formation of ferrite structure is inhibited, and the toughness of the steel is significantly reduced. In addition, the C element can also form a large amount of coarse precipitates with Cr and Mo elements, and significantly aggravate the segregation of the steel, resulting in a significant reduction in toughness. Therefore, in the high-strength anti-non-uniform load oil casing according to the present application, the mass percentage of the C element is limited to 0.05-0.15%.

[0016] Si: In the high-strength anti-non-uniform load oil casing according to the present application, the Si element promotes the diffusion of carbon into austenite, inhibits the precipitation of cementite in austenite, not only plays a solid solution strengthening role, but also can promote the enrichment of carbon in austenite, and at the same time improve the stability of residual austenite. However, it should be noted that the addition amount of Si element in the steel should not be too high, too high Si element will deteriorate the workability and toughness of the steel; at the same time, the addition amount of Si element should not be too low, when the mass percentage of Si element is less than 0.4%, the effect of improving the stability of residual austenite is not obvious. Therefore, in the high-strength anti-non-uniform load oil casing according to the present application, the mass percentage of Si element is controlled between 0.4-0.8%.

[0017] Mn: In the high-strength anti-non-uniform load oil casing according to the present application, the Mn element is an austenite forming element, which not only can stabilize the austenite in the steel, but also can slow down the transformation rate of ferrite and reduce the carbon diffusion from ferrite to austenite; at the same time, the number of residual austenite is increased, which is beneficial to improve the work hardening effect of the material. In the present application, in order to achieve the effect of structure control, the content of Mn element needs to be controlled at more than 3%. It should be noted that when the content of Mn element is greater than 5%, the organization segregation in the steel will be significantly increased, which will have a significant impact on the uniformity of hot rolling structure and impact performance. Therefore, in the high-strength anti-non-uniform load oil casing according to the present application, the mass percentage of Mn element is limited to 3-5%.

[0018] Ni: In the high-strength anti-non-uniform load oil casing according to the present application, the Ni element can promote the formation of austenite structure, so as to ensure that there is residual austenite structure in the rolled steel, which is beneficial to improve the work hardening index of the material. It should be noted that when the content of Ni is higher than 0.5%, the cost is higher and the effect of increasing the proportion of austenite is not obvious; at the same time, when the content of Ni element is less than 0.2%, the proportion of residual austenite cannot be effectively increased. Therefore, in the high-strength anti-non-uniform load oil casing according to the present application, the mass percentage of Ni element is controlled between 0.2-0.5%.

[0019] Ca: Ca can purify the liquid steel, promote MnS spheroidization, and improve impact toughness, but excessive content is prone to form coarse non-metallic inclusions. Therefore, in the high-strength anti-non-uniform load oil casing provided by the application, the mass percentage of Ca element is controlled to be 0.0005-0.005%.

[0020] Ti: In the high-strength anti-non-uniform load oil casing provided by the application, Ti element is a strong carbonitride forming element, which can significantly refine austenite grains and compensate for the decrease in strength caused by the decrease in carbon content. It should be noted that when the content of Ti element is higher than 0.04%, coarse TiN is prone to be formed, which significantly reduces the toughness of the material. Therefore, in the high-strength anti-non-uniform load oil casing provided by the application, the mass percentage of Ti element is controlled to be 0.01-0.04%.

[0021] Al: In the high-strength anti-non-uniform load oil casing provided by the application, Al element is a traditional deoxidizing and nitrogen-fixing element, which can refine grains. It should be noted that the content of Al element should not be too high, because when the content of Al element is too high, the yield ratio of the material will be significantly reduced. Therefore, in the high-strength anti-non-uniform load oil casing provided by the application, the mass percentage of Al element is limited to be 0.01-0.05%.

[0022] Nb: In the high-strength anti-non-uniform load oil casing provided by the application, Nb element is a grain refining and precipitation strengthening element, which can compensate for the decrease in strength caused by the decrease in carbon content. When the content of Nb element is higher than 0.04%, coarse Nb(CN) is prone to be formed, thereby reducing the toughness. At the same time, when the content of Nb element is lower than 0.02%, the strengthening effect is not obvious. Therefore, in the high-strength anti-non-uniform load oil casing provided by the application, the mass percentage of Nb element is limited to be 0.02-0.04%.

[0023] Further, in the high-strength anti-non-uniform load oil casing provided by the application, it further contains at least one of the following: 0

[0024] In the preferred embodiment of the application, at least one of Cr, Mo and V can be added.

[0025] wherein:

[0026] Cr: Cr element is an element that can significantly improve the hardenability and is a strong precipitate forming element, which can precipitate precipitates during the cooling phase change process, thereby improving the strength of the steel. It should be noted that when the content of Cr element is higher than 1%, coarse M 23C6 precipitates, reducing toughness. Therefore, in the high-strength anti-uniform load oil casing described in the present application, the mass percentage of Cr element can be limited to 0 < Cr < 1%.

[0027] Mo: Mo element mainly improves the strength and stability of the steel during the cooling phase transition through precipitates and solid solution strengthening. In the present application, when the Mo element content is higher than 0.5%, it is difficult to significantly improve the strength of the steel, and it is easy to cause waste of alloy. Therefore, in the high-strength anti-uniform load oil casing described in the present application, the mass percentage of Mo element can be limited to 0 < Mo < 0.5%.

[0028] V: V element is a typical precipitate strengthening element, which can make up for the decrease in strength caused by the decrease in carbon content. However, when the content of V element is higher than 0.15%, coarse V(CN) is easily formed, thereby reducing toughness. Therefore, in the high-strength anti-uniform load oil casing described in the present application, the mass percentage of V element can be limited to 0 < V < 0.15%.

[0029] Further, in the high-strength anti-uniform load oil casing described in the present application, among the other unavoidable impurities, P < 0.015%; S < 0.005%.

[0030] In the high-strength anti-uniform load oil casing described in the present application, the main impurity elements are P and S, and it is desirable to have as low content as possible under the technical conditions. In some embodiments, P < 0.015% and S < 0.005% can be controlled.

[0031] Further, in the anti-uniform load casing described in the present application, the volume fraction of granular bainite is 6-10%.

[0032] Further, in the anti-uniform load casing described in the present application, the volume fraction of residual austenite is 8-20%.

[0033] Further, in the anti-uniform load casing described in the present application, the yield strength is 758-965 MPa, the tensile strength is > 930 MPa, the yield strength ratio is < 0.85, the elongation is > 35%, the uniform elongation is > 20%, the 0℃ transverse Charpy impact energy is > 60J, the work hardening index n is > 0.15, and the yield strength is increased by more than 30% after 5% deformation of the material.

[0034] Correspondingly, another object of the present application is to provide a manufacturing method of the high-strength anti-non-uniform load oil casing, and the high-strength anti-non-uniform load oil casing manufactured by the manufacturing method has high strength, toughness, uniform elongation rate and work hardening index, and is low in cost, thereby solving the poor anti-non-uniform load deformation capacity of the casing in the prior art, improving the pressure resistance of the casing in use in a well, and meeting the demand for high-strength casing in the oil field exploitation field.

[0035] In order to achieve the above object, the present application provides the above-mentioned manufacturing method of the high-strength anti-non-uniform load oil casing, which comprises the following steps:

[0036] (1) smelting and continuous casting;

[0037] (2) piercing;

[0038] (3) rolling and tension reducing;

[0039] (4) two-phase zone normalizing heat treatment: the steel pipe is heated to an austenitizing temperature Ac1+60℃ to Ac3-60℃, and is air-cooled after being kept for 30-60 min; wherein Ac1=723-10.7Mn-16.9Ni+29.1Si+16.9Cr; Ac3=910-203C-15.2Ni+44.7Si+104V+31.5Mo; in the formula, the numerical values of each chemical element before the mass percentage content percentage sign are substituted; 1 / 2

[0040] (5) hot straightening.

[0041] In the manufacturing method, by adopting the specific two-phase zone normalizing heat treatment process matched with the element content, a mixed structure of ferrite, granular bainite and residual austenite is obtained, the work hardening index n is improved, and the anti-deformation capacity of the oil casing under non-uniform load is improved.

[0042] Further, in the step (1) of the manufacturing method of the high-strength anti-non-uniform load oil casing, the continuous casting pulling speed is controlled to be 1.6-2.0 m / min.

[0043] Further, in the step (2) of the manufacturing method of the high-strength anti-non-uniform load oil casing, the round billet is soaked at 1220-1270℃, and then is pierced, and the piercing temperature is 1150-1200℃.

[0044] Further, in the step (3) of the manufacturing method of the high-strength anti-non-uniform load oil casing, the finish rolling temperature is controlled to be 920-980℃.

[0045] ​Further, the manufacturing method of the high-strength anti-non-uniform load oil casing according to the present application has the following advantages and beneficial effects:

[0046] The high-strength anti-non-uniform load oil casing and the manufacturing method thereof according to the present application have the following advantages and beneficial effects:

[0047] The present application solves the problem of poor anti-non-uniform load deformation capacity of the casing in the prior art by reasonably designing the components, so that the high-strength anti-non-uniform load casing according to the present application has high strength, toughness, uniform elongation rate, and work hardening index, and is low in cost, thereby improving the pressure resistance of the casing in use in the well and meeting the demand for high-strength casing in the oil field exploitation field.

[0048] Correspondingly, the present application adopts a specific intercritical annealing heat treatment matched with the element content in the manufacturing process, so that a mixed structure of ferrite, granular bainite, and residual austenite is obtained, the work hardening index n is improved, and finally the anti-deformation capacity of the casing under non-uniform load is improved, and good strength-toughness matching is obtained.

[0049] In some embodiments, the high-strength anti-non-uniform load oil casing according to the present application has a yield strength of 758-965 MPa, a tensile strength ≥930 MPa, a yield strength ratio ≤0.85, an elongation rate ≥35%, a uniform elongation rate ≥20%, a 0℃ transverse Charpy impact energy ≥60 J, a work hardening index n ≥0.15, and a yield strength increase of more than 30% after 5% deformation of the material. DETAILED DESCRIPTION

[0050] The high-strength anti-non-uniform load oil casing and the manufacturing method thereof according to the present application will be further explained and described below in conjunction with specific examples, but the explanation and description do not constitute undue limitations on the technical solutions of the present application.

[0051] Examples 1-6 and Comparative Examples 1-8

[0052] The high-strength anti-non-uniform load oil casing of Examples 1-6 and the oil casing of Comparative Examples 1-8 are prepared by the following steps:

[0053] (1) Smelting and continuous casting: smelting and continuous casting, wherein the continuous casting speed can be controlled to be 1.6-2.0 m / min in some embodiments to obtain a round billet. The mass percentage of chemical elements of each example and comparative example is listed in Table 1.

[0054] (2) Piercing: the round billet is soaked at 1220-1270℃, and then pierced after soaking, with a piercing temperature of 1150-1200℃.

[0055] (3) Rolling and tension reducing: the final rolling temperature is controlled to be 920-980℃, and tension reducing is performed after the final rolling, and the temperature is 900-950℃;

[0056] (4) Two-phase region normalizing heat treatment: the steel pipe is heated to the austenitizing temperature Ac1+60℃ to Ac3-60℃, and is kept for 30-60min, and then is air cooled; wherein Ac1=723-10.7Mn-16.9Ni+29.1Si+16.9Cr; Ac3=910-203C 1 / 2 -15.2Ni+44.7Si+104V+31.5Mo; wherein each chemical element in the formula is substituted by the value before the mass percentage of the chemical element.

[0057] (5) Hot straightening.

[0058] It should be noted that the high-strength anti-non-uniform load oil casing of examples 1-6 described in the application is prepared by the above steps, and the chemical composition and related process parameters meet the design specification control requirements of the application. The oil casing of comparative examples 1-8 is also prepared by the above process, but the chemical composition and / or related process parameters of the oil casing of comparative examples 1-8 do not meet the design requirements of the application.

[0059] Table 1 lists the mass percentage of the chemical elements of the high-strength anti-non-uniform load oil casing of examples 1-6 and the oil casing of comparative examples 1-8.

[0060] Table 1. (wt%, the balance is Fe and other unavoidable impurities except P and S)

[0061]

[0062]

[0063] Table 2 lists the specific process parameters of the high-strength anti-non-uniform load casing of examples 1-6 and the oil casing of comparative examples 1-8.

[0064] Table 2.

[0065]

[0066] The high-strength anti-non-uniform load casing of examples 1-6 and the oil casing of comparative examples 1-8 prepared finally are sampled respectively, and the microstructure is observed by optical microscope after polishing the sample, and the test results are listed in Table 3.

[0067] Table 3.

[0068]

[0069]

[0070] The high strength anti-uniform load casing of examples 1-6 and the oil casing of comparative examples 1-8 were sampled respectively, and the performance was detected, and the detection results were listed in table 4. Among them:

[0071] (1) Yield strength, tensile strength, elongation, uniform elongation, according to GB / T 228.1-2000 standard.

[0072] (2) 0 ℃ transverse impact energy, according to GB / T 229-2007 "metal material charpy pendulum impact test method" standard.

[0073] (3) Yield strength after deformation 5%, work hardening index n, according to GB / T 228.1-2000 standard.

[0074] Table 4 lists the test results of the high strength anti-uniform load casing of examples 1-6 and the oil casing of comparative examples 1-8.

[0075] Table 4.

[0076]

[0077]

[0078] As can be seen from table 4, the performance of each embodiment of the present application can meet: yield strength is 760-930 MPa, tensile strength ≥ 950 MPa, yield strength ratio < 0.85, elongation ≥ 37%, uniform elongation ≥ 21.5%, 0 ℃ transverse charpy impact energy > 76 J, the yield strength of the material after deformation 5% is increased by more than 30%. Therefore, each embodiment of the present application is very suitable for making high strength anti-uniform load casing.

[0079] On the contrary, in comparative examples 1 and 2, Mn exceeds the range defined in the present application, in comparative examples 3 and 4, C and Si components exceed the range defined in the present application, in comparative examples 5 and 6, Ni exceeds the range defined in the present application, in comparative examples 7 and 8, the intercritical normalizing heat treatment temperature exceeds the range defined in the present application, so that at least one mechanical property of the oil casing of comparative examples 1-8 fails to reach the standard of the high strength anti-uniform load casing described in the present application, and the comprehensive performance is not as good as the high strength anti-uniform load casing of each embodiment in the present application.

[0080] It should be noted that the scope of protection of the present application is not limited to the embodiments given in the present application file, all prior art that does not contradict the scheme of the present application, including but not limited to prior patent documents, prior published publications, prior public use, etc., can be included in the scope of protection of the present application.

[0081] Furthermore, the combination of the technical features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments of the present application, and all the technical features described in the present application can be freely combined or integrated in any manner, unless contradictory.

[0082] It should also be noted that the above only lists specific embodiments of the present application, and obviously the present application is not limited to the above embodiments, and there are many similar changes. All variations directly derived or thought of by those skilled in the art from the content disclosed by the present application shall fall within the protection scope of the present application.

Claims

1. A high strength, non-uniform load resistant oil casing characterized by, The mass percentage of each chemical element is: C: 0.05-0.15%; Si: 0.4-0.8%; Mn: 3-5%; Ni: 0.2-0.5%; Ca: 0.0005-0.005%; Ti: 0.01-0.04%; Al: 0.01-0.05%; Nb: 0.02-0.04%; the balance being Fe and inevitable impurities; The microstructure thereof is ferrite + granular bainite + residual austenite; The performance of the oil casing satisfies: yield strength is 758-965 MPa, tensile strength ≥930 MPa, yield strength ratio ≤0.85, elongation ≥35%, uniform elongation ≥20%, 0℃ transverse Charpy impact energy ≥60J, work hardening index n ≥0.15, yield strength is increased by more than 30% after material deformation of 5%.

2. The high strength non-uniform load resistant oil casing of claim 1 wherein, It also contains at least one of the following: 0＜Cr≤1％； 0 0＜V≤0.15％。 3. The high strength non-uniform load resistant oil casing of Claim 1, wherein, Among the inevitable impurities, P ≤0.015%, S ≤0.005%.

4. The high strength non-uniform load resistant oil casing of Claim 1 wherein, The volume fraction of the granular bainite is 6-10%.

5. The high strength non-uniform load resistant oil casing of Claim 1 wherein, The volume fraction of the residual austenite is 8-20%.

6. A method of manufacturing a high-strength, non-uniform load resistant oil casing according to any one of claims 1-5, characterized in that, The method comprises the following steps: (1) smelting and continuous casting; (2) piercing; (3) rolling and tension reducing; (4) two-phase region normalizing heat treatment: heating to austenitizing temperature Ac1+60°C to Ac3-60°C, holding for 30-60 min and then air cooling; wherein Ac1=723-10.7Mn-16.9Ni+29.1Si+16.9Cr; Ac3=910-203C 1 / 2 -15.2Ni+44.7Si+104V+31.5Mo; in the formula, each chemical element substitutes the value before its mass percentage content for the percentage sign; (5) hot straightening.

7. The production method according to claim 6, wherein In step (1), the continuous casting speed is controlled to be 1.6-2.0 m / min.

8. The production method according to claim 6, wherein In step (2), the round billet is soaked at 1220-1270℃, and then pierced, and the piercing temperature is 1150-1200℃.

9. The production method according to claim 6, wherein In step (3), the final rolling temperature is controlled to be 920-980℃.

10. The production method according to claim 6, wherein In step (3), the tension reducing temperature is 900-950℃.

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