High-strength non-uniform load-resistant oil casing and manufacturing method thereof

Abstract

The invention discloses a high-strength and non-uniform load-resistant petroleum casing pipe, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.05-0.15% of C, 0.05-0.15% of Cr, 0.05-0.15% of Mo, 0.05-0.15% of Ni, 0.05-0.15% of Mo and the balance of Fe. 0.41 to 0.8 percent of Si; mn: 3-5%; 0.2 to 0.5 percent of Ni; 0.0005 to 0.005% of Ca (calcium); 0.01 to 0.04 percent of Ti; 0.01 to 0.05 percent of Al; 0.02 to 0.04 percent of Nb; the microstructure of the steel plate is ferrite, granular bainite and retained austenite. Correspondingly, the invention further discloses a manufacturing method of the high-strength and non-uniform load resistant petroleum casing pipe, and the manufacturing method comprises the steps of smelting and continuous casting; punching holes; rolling and tension reducing; two-phase region normalizing heat treatment: heating to an austenitizing temperature Ac1 + 60 DEG C to Ac3-60 DEG C, preserving heat for 30-60 minutes, and then cooling in air; and hot straightening.

Description

Technical Field

[0001] The invention relates to a pipe and a manufacturing method thereof, in particular to a petroleum casing and a manufacturing method thereof. Background Art

[0002] Shale gas is a kind of natural gas clean energy that can be mined in shale layers and mud layers. Compared with conventional natural gas mining, shale gas mining has difficulties such as complex formations and complex fracturing and perforation processes. At present, shale gas development adopts a special development process of horizontal wells + multi-stage fracturing. The horizontal section is as long as 3,000 meters, and 15-30 sections of casing perforation are carried out, followed by large-volume hydraulic fracturing. The formation pressure is high (90-120MPa). Fracturing causes the development of shale cracks and formation creep. The high-strength casing used is very easy to deform, and the average casing deformation rate reaches more than 30%. The typical feature of this casing deformation is that the casing is not squeezed, but deformed radially due to the uneven load of the formation. With the progress of multi-stage fracturing, the degree of casing deformation gradually increases, and the bridge plug used for fracturing operations cannot pass through the deformed position, making it difficult to perform hydraulic fracturing, which seriously affects the recovery efficiency of shale gas.

[0003] A Chinese patent document with publication number CN101532113A and publication date September 16, 2009, entitled “Anti-collapse petroleum casing and manufacturing method thereof” discloses a technical solution for obtaining an anti-collapse casing with ultra-high collapse resistance and excellent performance through texture and microstructure design and control.

[0004] The Chinese patent document with publication number CN102296239A and publication date December 28, 2011, entitled “A high-strength, collapse-resistant petroleum casing string and its manufacturing method” discloses that the outer diameter of the string is φ141.3mm to φ142.7mm; the wall thickness of the string is 10.7mm to 12.9mm, but it does not mention the performance of resisting non-uniform external loads.

[0005] The Chinese patent document with publication number CN104651723A and publication date May 27, 2015, entitled "A rare earth-containing, hydrogen sulfide-resistant, high-collapse-resistant oil casing and its production method", involves oil casing with a yield strength of 780-870MPa and a lateral impact value of ≥70J / cm at 0°C. 2 , with the characteristics of high resistance to hydrogen sulfide corrosion and high anti-collapse performance.

[0006] Although the oil casings mentioned in the above patent documents all have high anti-collapse performance, they are all 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 non-uniform load. Summary of the invention

[0007] One of the purposes of the present invention is to provide a high-strength oil casing that can resist non-uniform loads, has a high work hardening index and toughness, and a low yield strength ratio. When the casing is deformed due to the action of the formation, the work hardening effect of the material can significantly improve the material strength, thereby improving the casing's ability to resist deformation and ensuring that the bridge plug can pass smoothly for fracturing operations.

[0008] In order to achieve the above object, the present invention provides a high-strength non-uniform load resistant petroleum casing, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[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%;

[0010] Its microstructure is ferrite + granular bainite + retained austenite.

[0011] Furthermore, the present invention provides a high-strength non-uniform load-resistant petroleum casing, the mass percentage of each chemical element of which is:

[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 is Fe and inevitable impurities.

[0013] The high-strength non-uniform load resistant petroleum casing of the present invention 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 deformation resistance of the casing under non-uniform load, and obtains good strength and toughness.

[0014] Specifically, the design principles of the chemical elements in the high-strength non-uniform load-resistant petroleum casing of the present invention are:

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

[0016] Si: In the high-strength non-uniform load resistant petroleum casing described in the present invention, the Si element promotes the diffusion of carbon into austenite and inhibits the precipitation of cementite in austenite, which not only plays a role in solid solution strengthening, but also promotes the enrichment of carbon in austenite, while improving the stability of residual austenite. However, it should be noted that the amount of Si element added to the steel should not be too high, as too high Si element will deteriorate the processability and toughness of the steel; at the same time, the amount of Si element added 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 non-uniform load resistant petroleum casing described in the present invention, the mass percentage of Si element is controlled between 0.4-0.8%.

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

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

[0019] Ca: Ca can purify molten steel, promote MnS spheroidization, and improve impact toughness, but when the content is too high, it is easy to form coarse non-metallic inclusions. Based on this, in the high-strength non-uniform load-resistant petroleum casing of the present invention, the mass percentage of Ca element is controlled to be 0.0005-0.005%.

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

[0021] Al: In the high-strength non-uniform load resistant oil casing of the present invention, Al is a traditional deoxidation and nitrogen fixation element, which can refine the grains. It should be noted that the Al content should not be too high. When the Al content is too high, the material yield ratio will be significantly reduced. Therefore, in the high-strength non-uniform load resistant oil casing of the present invention, the mass percentage of Al is limited to between 0.01-0.05%.

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

[0023] Furthermore, the high-strength non-uniform load resistant petroleum casing of the present invention also contains at least one of the following items: 0<Cr≤1%; 0<Mo≤0.5%; 0<V≤0.15%.

[0024] In a preferred embodiment of the present invention, at least one of Cr, Mo and V may be added.

[0025] in:

[0026] Cr: Cr is an element that strongly improves hardenability and is also a strong precipitate-forming element. It can precipitate precipitates during the cooling phase transformation process to improve the strength of steel. It should be noted that when the Cr content is higher than 1%, coarse M is easily precipitated at the grain boundary. 23C6 precipitates reduce toughness. Therefore, in the high-strength non-uniform load-resistant petroleum casing of the present invention, the mass percentage of Cr element can be limited to 0<Cr≤1%.

[0027] Mo: Mo element mainly improves the strength of steel and the stability during cooling phase transformation through precipitation and solid solution strengthening. The carbon content of the present invention is relatively low, and when the Mo element content is higher than 0.5%, it is difficult to have a significant effect on improving the strength of steel, which is easy to cause alloy waste. Therefore, in the high-strength non-uniform load-resistant oil casing described in the present invention, the mass percentage of the Mo element can be limited to 0<Mo≤0.5%.

[0028] V: V is a typical precipitation strengthening element, which can make up for the decrease in strength caused by the decrease in carbon content. However, when the content of V is higher than 0.15%, it is easy to form coarse V (CN), thereby reducing toughness. Therefore, in the high-strength non-uniform load-resistant petroleum casing of the present invention, the mass percentage of V element can be limited to 0<V≤0.15%.

[0029] Furthermore, in the high-strength non-uniform load resistant petroleum casing of the present invention, among the other inevitable impurities, P≤0.015%; S≤0.005%.

[0030] In the high-strength non-uniform load resistant petroleum casing of the present invention, the main impurity elements are P and S. Under the condition that technical conditions permit, it is hoped that the content of P and S is as low as possible. In some embodiments, P can be controlled to be ≤ 0.015% and S ≤ 0.005%.

[0031] Furthermore, in the non-uniform load resistant casing of the present invention, the volume phase ratio of the granular bainite is 6-10%.

[0032] Furthermore, in the non-uniform load resistant casing of the present invention, the volume ratio of the retained austenite is 8-20%.

[0033] Furthermore, the yield strength of the non-uniform load resistant casing described in the present invention is 758-965MPa, the tensile strength is ≥930MPa, the yield strength ratio is ≤0.85, the elongation is ≥35%, the uniform elongation is ≥20%, the 0°C 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 the material is deformed by 5%.

[0034] Accordingly, another object of the present invention is to provide a method for manufacturing a high-strength non-uniform load resistant oil casing, wherein the high-strength non-uniform load resistant oil casing manufactured by the manufacturing method has high strength, toughness, uniform elongation and work hardening index, and is low in cost. Thus, the problem of poor deformation resistance of casings against non-uniform loads in the prior art can be solved, the pressure resistance of casings used underground can be improved, and the demand for high-strength casings in the field of oil field exploitation can be met.

[0035] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned high-strength non-uniform load-resistant petroleum casing, which comprises the steps of:

[0036] (1) Smelting and continuous casting;

[0037] (2) Perforation;

[0038] (3) rolling and tension reducing;

[0039] (4) Two-phase normalizing heat treatment: Heat the steel pipe to the austenitizing temperature Ac1+60℃ to Ac3-60℃, keep warm for 30-60min and then air cool; where Ac1=723-10.7Mn-16.9Ni+29.1Si+16.9Cr; Ac3=910-203C 1 / 2 -15.2Ni+44.7Si+104V+31.5Mo; each chemical element in the formula is substituted into the value before the percentage sign of its mass percentage content;

[0040] (5) Thermal straightening.

[0041] In the manufacturing method described in the present invention, a mixed structure of ferrite, granular bainite and residual austenite is obtained by adopting a specific two-phase zone normalizing heat treatment process adapted to the element composition content, thereby improving the work hardening index n and enhancing the deformation resistance of the oil casing under non-uniform loads.

[0042] Furthermore, in the method for manufacturing the high-strength non-uniform load-resistant petroleum casing of the present invention, in step (1), the continuous casting speed is controlled to be 1.6-2.0 m / min.

[0043] Furthermore, in the manufacturing method of the high-strength non-uniform load-resistant petroleum casing of the present invention, in step (2), the round billet is heated at 1220-1270°C and then perforated, and the perforation temperature is 1150-1200°C.

[0044] Furthermore, in the method for manufacturing the high-strength non-uniform load resistant petroleum casing of the present invention, in step (3), the final rolling temperature is controlled to be 920-980°C.

[0045] Furthermore, in the method for manufacturing the high-strength non-uniform load resistant petroleum casing of the present invention, in step (3), the temperature of tension reduction is 900-950°C.

[0046] The high-strength non-uniform load-resistant petroleum casing and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0047] From the perspective of component design, the present invention adopts reasonable component design to make the high-strength non-uniform load resistant casing of the present invention have higher strength, toughness, uniform elongation and work hardening index, and low cost, thereby solving the problem of poor non-uniform load deformation resistance of casing in the prior art, improving the pressure resistance of casing used underground, and meeting the demand for high-strength casing in the field of oil field exploitation.

[0048] Accordingly, in the manufacturing process, the present invention adopts a specific two-phase region normalizing heat treatment adapted to the element composition content, thereby obtaining a mixed structure of ferrite, granular bainite and residual austenite, improving the work hardening index n, and ultimately improving the deformation resistance of the casing under non-uniform loads, while obtaining a good strength-toughness match.

[0049] In some embodiments, the high-strength non-uniform load-resistant petroleum casing of the present invention has a yield strength of 758-965MPa, a tensile strength ≥930MPa, a yield strength ratio ≤0.85, an elongation ≥35%, a uniform elongation ≥20%, a 0°C transverse Charpy impact energy ≥60J, a work hardening index n≥0.15, and the yield strength increases by more than 30% after the material is deformed by 5%. DETAILED DESCRIPTION

[0050] The high-strength non-uniform load resistant petroleum casing and the manufacturing method thereof of the present invention will be further explained and illustrated in conjunction with specific embodiments below. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

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

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

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

[0054] (2) Punching: The round billet is heated at 1220-1270°C and then pierced. The piercing temperature is 1150-1200°C.

[0055] (3) Rolling and tension reduction: The final rolling temperature is controlled at 920-980°C, and tension reduction is performed after final rolling at a temperature of 900-950°C;

[0056] (4) Two-phase normalizing heat treatment: Heat the steel pipe to the austenitizing temperature Ac1+60℃ to Ac3-60℃, keep warm for 30-60min and then air cool; where 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, substitute each chemical element with the value before the percentage sign of its mass percentage.

[0057] (5) Thermal straightening.

[0058] It should be noted that the high-strength non-uniform load resistant oil casings of Examples 1-6 of the present invention are all manufactured by the above steps, and their chemical compositions and related process parameters meet the control requirements of the design specifications of the present invention. The oil casings of Comparative Examples 1-8 are also manufactured by the above process flow, but the chemical compositions and / or related process parameters of the oil casings of Comparative Examples 1-8 do not meet the design requirements of the present invention.

[0059] Table 1 lists the mass percentages of chemical elements of high-strength non-uniform load resistant petroleum casings of Examples 1-6 of the present invention and petroleum casings of Comparative Examples 1-8.

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

[0061]

[0062]

[0063] Table 2 lists the specific process parameters of the high-strength non-uniform load resistant casings of Examples 1-6 and the petroleum casings of Comparative Examples 1-8.

[0064] Table 2.

[0065]

[0066] The high-strength non-uniform load resistant casings of Examples 1-6 and the petroleum casings of Comparative Examples 1-8 were sampled respectively. After polishing, the microstructures of the samples were observed using an optical microscope. The test results are listed in Table 3.

[0067] Table 3.

[0068]

[0069]

[0070] The high-strength non-uniform load resistant casings of Examples 1-6 and the petroleum casings of Comparative Examples 1-8 were sampled and tested for performance, and the test results are listed in Table 4. Among them:

[0071] (1) Yield strength, tensile strength, elongation and uniform elongation are measured in accordance with GB / T 228.1-2000.

[0072] (2) 0℃ transverse impact energy: carried out in accordance with GB / T 229-2007 “Charpy pendulum impact test method for metallic materials”.

[0073] (3) The yield strength and work hardening index n after 5% deformation are in accordance with GB / T 228.1-2000.

[0074] Table 4 lists the test results of the high-strength non-uniform load resistant casings of Examples 1-6 and the petroleum casings of Comparative Examples 1-8.

[0075] Table 4.

[0076]

[0077]

[0078] It can be seen from Table 4 that the performance of each embodiment of the present invention can meet the following requirements: yield strength of 760-930MPa, tensile strength ≥950MPa, yield strength ratio <0.85, elongation ≥37%, uniform elongation ≥21.5%, 0°C transverse Charpy impact energy >76J, and yield strength increased by more than 30% after material deformation of 5%. This shows that each embodiment of the present case is very suitable for making high-strength non-uniform load-resistant casing.

[0079] On the other hand, in the comparative examples, the Mn content in comparative examples 1 and 2 exceeds the range defined in the present invention, the C and Si components in comparative examples 3 and 4 exceed the range defined in the present invention, the Ni content in comparative examples 5 and 6 exceeds the range defined in the present invention, and the two-phase region normalizing heat treatment temperature in comparative examples 7 and 8 exceeds the range defined in the present invention, so that at least one mechanical property of the petroleum casing of comparative examples 1-8 fails to meet the standard of the high-strength non-uniform load resistant casing described in the present invention, and the comprehensive performance is not as good as the high-strength non-uniform load resistant casing in each embodiment of the present invention.

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

[0081] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

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

Claims

1. A high-strength non-uniform load-resistant petroleum casing containing Fe and inevitable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: 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%; Its microstructure is ferrite + granular bainite + retained austenite.

2. The high-strength non-uniform load resistant petroleum casing according to claim 1, characterized in that: 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 is Fe and inevitable impurities.

3. The high-strength non-uniform load resistant petroleum casing according to claim 1 or 2, characterized in that: It also contains at least one of the following: 0＜Cr≤1％； 0<Mo≤0.5%; 0＜V≤0.15％。 4. The high-strength non-uniform load resistant petroleum casing according to claim 1 or 2, characterized in that: Among the inevitable impurities, P ≤ 0.015% and S ≤ 0.005%.

5. The high-strength non-uniform load resistant petroleum casing according to claim 1 or 2, characterized in that: The volume phase ratio of the granular bainite is 6-10%.

6. The high-strength non-uniform load resistant petroleum casing according to claim 1 or 2, characterized in that: The volume ratio of the retained austenite is 8-20%.

7. The high-strength non-uniform load resistant petroleum casing according to claim 1 or 2, characterized in that: Its performance meets at least one of the following items: yield strength is 758-965MPa, tensile strength ≥930MPa, yield strength ratio ≤0.85, elongation ≥35%, uniform elongation ≥20%, 0℃ transverse Charpy impact energy ≥60J, work hardening index n≥0.15, and the yield strength increases by more than 30% after the material is deformed by 5%.

8. A method for manufacturing a high-strength non-uniform load resistant petroleum casing as claimed in any one of claims 1 to 7, characterized in that: Includes steps: (1) Smelting and continuous casting; (2) Perforation; (3) rolling and tension reducing; (4) Two-phase normalizing heat treatment: heat to austenitizing temperature Ac1+60℃ to Ac3-60℃, keep warm for 30-60min and then air cool; where Ac1=723-10.7Mn-16.9Ni+29.1Si+16.9Cr; Ac3=910-203℃ 1 / 2 -15.2Ni+44.7Si+104V+31.5Mo; each chemical element in the formula is substituted into the value before the percentage sign of its mass percentage content; (5) Thermal straightening.

9. The manufacturing method according to claim 8, characterized in that: In step (1), the continuous casting speed is controlled to be 1.6-2.0 m / min.

10. The manufacturing method according to claim 8, characterized in that: In step (2), the round billet is heated at 1220-1270°C and then pierced at a piercing temperature of 1150-1200°C.

11. The manufacturing method according to claim 8, characterized in that: In step (3), the final rolling temperature is controlled to be 920-980°C.

12. The manufacturing method according to claim 8, characterized in that: In step (3), the temperature of the stretch reduction is 900-950°C.

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