A casing pipe for heavy oil thermal recovery and its preparation method

Abstract

The present invention discloses a casing for heavy oil thermal recovery and its preparation method, which relates to the technical field of oil casings. The casing comprises chemical components with the following mass contents: C 0.15 - 0.25%, Si 0.8 - 0.95%, Mn 0.8 - 1%, Cr 1.15 - 1.3%, Mo 0.1 - 0.17%, V 0.03 - 0.1%, RE 0.001 - 0.004%, Al 0.01 - 0.03%, Ca 0.012 - 0.025%, P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities. The yield strength of this casing at room temperature can meet the requirements of different steel grades, and it has a sufficiently large uniform elongation rate and Charpy impact toughness. The yield strength at 350°C decreases by no more than 16% of the yield strength at room temperature, and it is applicable to heavy oil steam thermal recovery wells.

Description

Technical Field

[0001] The present invention relates to the technical field of oil casing, and particularly to a heavy oil thermal recovery casing and a preparation method thereof. Background Art

[0002] Heavy oil accounts for a large proportion of oil and gas resources in China. The exploitation of heavy oil usually takes cyclic steam stimulation heating as the main method, and the cyclic steam temperature is as high as 350°C. The casing damage caused by the repeated cyclic temperature change is very serious, including casing body deformation, necking, disconnection, and thread joint disengagement. The casing damage of thermal recovery wells generally exceeds 30%, and in some blocks, it even reaches 50% - 70%. The previous design of the casing string for heavy oil thermal recovery wells was mainly based on stress, mainly considering the strength index of the material; however, under the conditions of heavy oil thermal recovery, there are creep and stress relaxation phenomena in the casing material, and at the same time, plastic strain fatigue phenomena will occur during the thermal cycle. Due to the lack of full consideration of these factors, the performance of existing products is difficult to meet the performance and quality requirements of the casing for heavy oil thermal recovery working conditions, which is the fundamental reason for the serious casing damage of thermal recovery wells.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] Based on the above deficiencies of the existing technology, the purpose of the present invention is to provide a heavy oil thermal recovery casing with high strength and sufficient elongation to meet the heavy oil steam cyclic stimulation exploitation at 350°C and a preparation method thereof.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a heavy oil thermal recovery casing is provided. By mass percentage, the heavy oil thermal recovery casing comprises the following chemical components:

[0007] C 0.15% - 0.25%, Si 0.80% - 0.95%, Mn 0.80% - 1.00%, Cr 1.15% - 1.30%, Mo 0.10% - 0.17%, V 0.03% - 0.10%, RE 0.001% - 0.004%, Al 0.010% - 0.030%, Ca 0.012% - 0.025%, P≤0.015%, S≤0.005%, N≤0.005%, O + H + N≤0.007%, and the balance is Fe and unavoidable impurities.

[0008] Optionally, by mass percentage, the heavy oil thermal recovery casing comprises the following chemical components:

[0009] C 0.15% - 0.17%, Si 0.80% - 0.87%, Mn 0.80% - 0.85%, Cr 1.15% - 1.18%, Mo 0.10% - 0.12%, V 0.03% - 0.05%, RE 0.001% - 0.002%, Al 0.010% - 0.014%, Ca 0.012% - 0.015%, P ≤ 0.011%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

[0010] Optionally, by mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components:

[0011] C 0.18% - 0.19%, Si 0.85% - 0.89%, Mn 0.86% - 0.89%, Cr 1.19% - 1.22%, Mo 0.11% - 0.13%, V 0.05% - 0.07%, RE 0.002% - 0.003%, Al 0.015% - 0.019%, Ca 0.016% - 0.018%, P ≤ 0.012%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

[0012] Optionally, by mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components:

[0013] C 0.20% - 0.22%, Si 0.90% - 0.94%, Mn 0.91% - 0.95%, Cr 1.20% - 1.24%, Mo 0.13% - 0.14%, V 0.06% - 0.08%, RE 0.003%, Al 0.020% - 0.022%, Ca 0.017% - 0.021%, P ≤ 0.011%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

[0014] Optionally, by mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components:

[0015] C 0.23% - 0.25%, Si 0.91% - 0.95%, Mn 0.97% - 1.00%, Cr 1.25% - 1.30%, Mo 0.15% - 0.17%, V 0.08% - 0.10%, RE 0.003% - 0.004%, Al 0.024% - 0.030%, Ca 0.020% - 0.025%, P ≤ 0.010%, S ≤ 0.003%, N ≤ 0.004%, O + H + N ≤ 0.006%, and the balance is Fe and unavoidable impurities.

[0016] In the second aspect of the present invention, a method for preparing a casing for heavy oil thermal recovery is provided, which includes the steps of:

[0017] After batching, smelting, and continuous casting according to the chemical composition of the casing for heavy oil thermal recovery as described above in the present invention, a continuous casting billet is obtained;

[0018] After hot piercing and hot continuous rolling of the continuous casting billet, a tube blank is obtained;

[0019] After quenching and tempering heat treatment and hot straightening of the tube blank, thread processing is carried out to obtain the casing for heavy oil thermal recovery.

[0020] Optionally, the step of obtaining a continuous casting billet after smelting and continuous casting specifically includes:

[0021] The raw materials obtained by batching are successively subjected to oxygen blowing converter smelting, feeding RE wire, secondary refining, vacuum degassing, and feeding Si - Ca wire for modifying treatment of inclusions to obtain molten steel;

[0022] The molten steel is cast into a rod - shaped continuous casting billet.

[0023] Optionally, the step of obtaining a tube blank after hot piercing and hot continuous rolling of the continuous casting billet specifically includes:

[0024] The continuous casting billet is heated in a heating furnace to 1180 - 1230 °C, held for 90 - 120 min, then hot pierced at a temperature of 1170 - 1200 °C and hot continuously rolled at a temperature of 950 - 1150 °C, and after cooling, a tube blank is obtained.

[0025] Optionally, the step of obtaining the casing for heavy oil thermal recovery after quenching and tempering heat treatment, hot straightening, and then thread processing specifically includes:

[0026] In a protective atmosphere furnace, the tube blank is heated at a temperature of 750 - 800 °C, held for 40 - 60 min, then cooled by internal and external water spraying at a cooling rate of 20 - 30 °C / s, then tempered at a temperature of 680 - 710 °C for 90 - 120 min and water-cooled, then hot straightened at a temperature of 600 - 650 °C and water-cooled, and after threading, the heavy oil thermal recovery casing is obtained.

[0027] Optionally, the steps of subjecting the tube blank to quenching and tempering heat treatment, hot straightening and then threading to obtain the heavy oil thermal recovery casing specifically include:

[0028] In a protective atmosphere furnace, the tube blank is heated at a temperature of 890 - 910 °C, held for 40 - 60 min, then cooled by internal and external water spraying at a cooling rate of 20 - 30 °C / s, then tempered at a temperature of 650 - 690 °C for 90 - 120 min and water-cooled, then hot straightened at a temperature of 600 - 650 °C and water-cooled, and after threading, the heavy oil thermal recovery casing is obtained.

[0029] Beneficial effects: The heavy oil thermal recovery casing provided by the present invention can respectively meet the requirements of steel grades of 80 ksi, 90 ksi, 100 ksi, and 110 ksi for room temperature yield, and has a sufficiently large uniform elongation and Charpy impact toughness, that is, the yield strength at room temperature is greater than 552 - 758 MPa, the tensile strength is greater than 655 - 862 MPa, the total elongation is greater than or equal to 25%, the uniform elongation is greater than or equal to 15%, and the Charpy impact toughness at 0 °C is greater than or equal to 120 J. In addition, for the heavy oil thermal recovery casing provided by the invention, the yield strength at 350 °C decreases by no more than 16% of the room temperature yield strength. The heavy oil thermal recovery casing provided by the invention can meet the requirements of the casing strength, plasticity and strain fatigue life for heavy oil steam thermal recovery wells at 350 °C. Detailed embodiments

[0030] The present invention provides a heavy oil thermal recovery casing and a preparation method thereof. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] An embodiment of the present invention provides a heavy oil thermal recovery casing. Among them, by mass percentage, the heavy oil thermal recovery casing includes the following chemical components:

[0033] C 0.15%~0.25%, Si 0.80%~0.95%, Mn 0.80%~1.00%, Cr 1.15%~1.30%, Mo 0.10%~0.17%, V 0.03%~0.10%, RE 0.001%~0.004%, Al 0.010%~0.030%, Ca 0.012%~0.025%, P≤0.015%, S≤0.005%, N≤0.005%, O+H+N≤0.007%, and the balance is Fe and unavoidable impurities.

[0034] RE is a rare earth element. In some specific embodiments, RE may be Ce (cerium).

[0035] In an embodiment of the present invention, a low carbon content is employed, along with microalloying with Si, Mn, Cr, and V, along with a small amount of Mo and rare earth (RE) elements, to control harmful elements such as P, S, O, H, and N in the steel. Al and Si-deoxidized killed steel is used, and the molten steel is treated with Ca to achieve the comprehensive performance requirements of heavy oil thermal recovery casing, balancing strength and uniform elongation. The heavy oil thermal recovery casing provided by the present invention can meet the room temperature yield strength requirements of 80 ksi, 90 ksi, 100 ksi, and 110 ksi steel grades, respectively, and exhibit sufficiently high uniform elongation and Charpy impact toughness, namely, room temperature yield strength greater than 552-758 MPa, tensile strength greater than 655-862 MPa, total elongation greater than 25%, uniform elongation greater than or equal to 15%, and Charpy impact toughness greater than or equal to 120 J at 0°C. Furthermore, the yield strength of the heavy oil thermal recovery casing provided by the present invention at 350°C does not drop by more than 16% of the room temperature yield strength. The heavy oil thermal recovery casing provided by the invention can meet the requirements of heavy oil steam thermal recovery wells on casing strength, plasticity and strain fatigue life.

[0036] C is the main strengthening element in steel. A low C content is detrimental to improving the hardenability and strength of the steel, while a high C content is detrimental to the plasticity and toughness of the steel. Taking all factors into consideration, the C content should be controlled within the range of 0.15% to 0.25%.

[0037] Si is mainly used to improve strength, oxidation resistance and thermal fatigue resistance. Taking all factors into consideration, it is best to control the content within the range of 0.80% to 0.95%.

[0038] Mn is mainly used to improve the hardenability of steel, thereby increasing strength, but too high a content will increase the tendency of segregation. Taking all factors into consideration, it is best to control it within the range of 0.80% to 1.00%.

[0039] Cr is mainly used to improve the hardenability of steel, thereby enhancing strength, oxidation resistance and corrosion resistance. However, if its content is too high, the cost will increase. Considering comprehensively, it is advisable to control it within the range of 1.15% - 1.30%.

[0040] Mo is mainly used to improve the hardenability of steel to enhance strength and tempering stability, and at the same time improve corrosion resistance. However, if its content is too high, the cost will increase. Considering comprehensively, it is advisable to control it within the range of 0.10% - 0.17%.

[0041] When V is added to steel, it forms VC and VN with C and N in the steel respectively, which has the effect of hindering the growth of austenite grains and refining grains, thereby enhancing strength and toughness. Considering comprehensively, it is advisable to control it within the range of 0.03% - 0.10%.

[0042] Adding a small amount of RE (rare earth elements) can play roles such as purifying molten steel, modifying inclusions, and alloying, which is beneficial to improving the strength, plasticity and toughness of steel. If the content is too low, the due effect cannot be achieved; if the content is too high, new inclusions are easily formed and the cost increases. Considering comprehensively, it is advisable to control it within the range of 0.001% - 0.004%.

[0043] Al is an important deoxidizer. It forms oxides with oxygen to play a deoxidizing role, and forms nitrides with nitrogen to partially eliminate the adverse effects of N. At the same time, it plays a role in refining grains, enhancing strength and toughness. To ensure the N control effect, it is planned to control Al / N ≥ 2 (that is, the mass percentage content ratio of Al to N is greater than or equal to 2). Considering comprehensively, it is advisable to control it within the range of 0.010% - 0.030%.

[0044] Ca: It can improve the properties and morphology of inclusions, thereby enhancing the plasticity, toughness and corrosion resistance of steel. To ensure the inclusion shape control and deformation effect, it is planned to control (that is, the mass percentage content ratio of Ca to S is greater than or equal to 2). Considering comprehensively, it is advisable to control it within the range of 0.012% - 0.025%.

[0045] P is a harmful element, which mainly affects the plasticity and toughness of steel. Considering comprehensively, it is advisable to control P ≤ 0.015% (that is, the mass content of P is less than or equal to 0.015%).

[0046] S is a harmful element, which mainly affects the plasticity and toughness of steel. Considering comprehensively, it is advisable to control S ≤ 0.005% (that is, the mass content of S is less than or equal to 0.005%).

[0047] O is a harmful element, mainly affecting the plasticity and toughness of steel. H is a harmful element, mainly affecting the plasticity and toughness of steel. N is a harmful element, mainly affecting the strain aging property of the plasticity and toughness of steel. Considering comprehensively, it is advisable to control N ≤ 0.005% (i.e., the mass content of N is less than or equal to 0.005%). And control O + H + N ≤ 0.007% (i.e., the total mass content of O, H and N is less than or equal to 0.007%).

[0048] In some embodiments, by mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components:

[0049] C 0.15% - 0.17%, Si 0.80% - 0.87%, Mn 0.80% - 0.85%, Cr 1.15% - 1.18%, Mo 0.10% - 0.12%, V 0.03% - 0.05%, RE 0.001% - 0.002%, Al 0.010% - 0.014%, Ca 0.012% - 0.015%, P ≤ 0.011%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

[0050] In this embodiment, the yield strength level of the casing for heavy oil thermal recovery can reach the requirement of 80 ksi. Among them, at room temperature, the yield strength is 597 - 605 MPa, the tensile strength is 694 - 703 MPa, the yield ratio is 0.86, the total elongation rate is 30%, and the uniform elongation rate is 19%; the Charpy V-notch impact toughness at 0 °C is 122 - 126 J; at 350 °C, the yield strength is 507 - 514 MPa, the tensile strength is 611 - 619 MPa, the total elongation rate is 35%, and the uniform elongation rate is 23%. The decrease in yield strength at 350 °C does not exceed 16% of the yield strength at room temperature, which can meet the requirement that the casing can withstand large uniform plastic deformation and plastic strain fatigue during the heavy oil thermal recovery process without early failure, and meet the requirements of the casing strength, plasticity and strain fatigue life for heavy oil steam thermal recovery wells at 350 °C.

[0051] In some embodiments, by mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components:

[0052] C 0.18% - 0.19%, Si 0.85% - 0.89%, Mn 0.86% - 0.89%, Cr 1.19% - 1.22%, Mo 0.11% - 0.13%, V 0.05% - 0.07%, RE 0.002% - 0.003%, Al 0.015% - 0.019%, Ca 0.016% - 0.018%, P ≤ 0.012%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

[0053] In this embodiment, the yield strength level of the heavy oil thermal recovery casing can meet the 90 ksi requirement. At room temperature, the yield strength is 668-674 MPa, the tensile strength is 768-775 MPa, the yield strength ratio is 0.87, the total elongation is 29%, and the uniform elongation is 18%. The Charpy V-notch impact toughness at 0°C is 133-136 J. At 350°C, the yield strength is 568-573 MPa, the tensile strength is 676-782 MPa, the total elongation is 34%, and the uniform elongation is 23%. The yield strength at 350°C does not drop by more than 16% of the room temperature yield strength, ensuring that the casing can withstand significant uniform plastic deformation and plastic strain fatigue without premature failure during heavy oil thermal recovery, thus meeting the strength, plasticity, and strain fatigue life requirements of casing in 350°C heavy oil steam thermal recovery wells.

[0054] In some embodiments, the heavy oil heat utilization casing comprises the following chemical components, calculated by weight percentage:

[0055] C 0.20%~0.22%, Si 0.90%~0.94%, Mn 0.91%~0.95%, Cr 1.20%~1.24%, Mo 0.13%~0.14%, V 0.06%~0.08%, RE 0.003%, Al 0.020%~0.022%, Ca 0.017%~0.021%, P≤0.011%, S≤0.003%, N≤0.005%, O+H+N≤0.007%, and the balance is Fe and unavoidable impurities.

[0056] In this embodiment, the yield strength level of the heavy oil thermal recovery casing can meet the 100 ksi requirement. At room temperature, the yield strength is 738-745 MPa, the tensile strength is 839-847 MPa, the yield strength ratio is 0.88, the total elongation is 28%, and the uniform elongation is 17%. The Charpy V-notch impact toughness at 0°C is 129-132 J. At 350°C, the yield strength is 627-633 MPa, the tensile strength is 738-745 MPa, the total elongation is 33%, and the uniform elongation is 21%. The yield strength at 350°C does not drop by more than 16% of the room temperature yield strength, ensuring that the casing can withstand significant uniform plastic deformation and plastic strain fatigue without premature failure during heavy oil thermal recovery, thus meeting the strength, plasticity, and strain fatigue life requirements of casing in 350°C heavy oil steam thermal recovery wells.

[0057] In some embodiments, the heavy oil heat utilization casing comprises the following chemical components, calculated by weight percentage:

[0058] C 0.23% - 0.25%, Si 0.91% - 0.95%, Mn 0.97% - 1.00%, Cr 1.25% - 1.30%, Mo 0.15% - 0.17%, V 0.08% - 0.10%, RE 0.003% - 0.004%, Al 0.024% - 0.030%, Ca 0.020% - 0.025%, P≤0.010%, S≤0.003%, N≤0.004%, O + H + N≤0.006%, and the balance is Fe and unavoidable impurities.

[0059] In this embodiment, the yield strength level of the casing used for heavy oil thermal recovery can reach the requirement of 110 ksi. Among them, at room temperature, the yield strength is 806 - 811 MPa, the tensile strength is 906 - 911 MPa, the yield ratio is 0.89, the total elongation rate is 27%, and the uniform elongation rate is 16%; the Charpy V-notch impact toughness at 0 °C is 124 - 127 J; at 350 °C, the yield strength is 685 - 689 MPa, the tensile strength is 797 - 802 MPa, the total elongation rate is 32%, and the uniform elongation rate is 20%. The decrease in yield strength at 350 °C does not exceed 16% of the yield strength at room temperature, which can meet the requirement that the casing can withstand large uniform plastic deformation and plastic strain fatigue during the heavy oil thermal recovery process without early failure, and meet the requirements of the casing strength, plasticity, and strain fatigue life for heavy oil steam injection wells at 350 °C.

[0060] The present invention develops a manufacturing process matching the above-mentioned chemical components in proportion. Specifically, through steelmaking (including secondary refining, vacuum degassing, Ca treatment), continuous casting, hot continuous rolling in the austenite region, quenching and tempering heat treatment, hot straightening, non-destructive testing and other processes, the material can obtain a fine and uniform microstructure to achieve a reasonable match between the strength, plasticity, and toughness of the casing. Specifically, the embodiment of the present invention also provides a preparation method for the casing used for heavy oil thermal recovery, including the following steps:

[0061] S1. After batching, smelting, and continuous casting according to the chemical composition of the casing for heavy oil thermal recovery as described in the embodiment of the present invention, a continuous casting billet is obtained;

[0062] S2. After hot piercing and hot continuous rolling of the continuous casting billet, a tube blank is obtained;

[0063] S3. After quenching and tempering heat treatment and hot straightening of the tube blank, thread processing is carried out to obtain the casing for heavy oil thermal recovery.

[0064] The chemical composition design and manufacturing process cooperation of the embodiment of the present invention have the effects of both improving strength and improving plasticity and toughness.

[0065] The preparation method of the present invention uses a casing for the heavy oil heat of the above chemical components, obtaining the expected organizational structure and performance, fully exerting the performance of the heavy oil heat - using casing, having a relatively low cost, and the process parameters in the manufacturing process are easy to control, and the performance of the obtained heavy oil heat - using casing is stable.

[0066] In step S1, in some embodiments, after smelting and continuous casting, the steps of obtaining a continuous casting billet specifically include:

[0067] The raw materials obtained by batching are successively subjected to oxygen - blown converter smelting, feeding RE wire, secondary refining, vacuum degassing, and feeding Si - Ca wire for inclusion modification treatment to obtain molten steel;

[0068] The molten steel is cast into a rod - shaped continuous casting billet (electromagnetic stirring and soft reduction technology can be used during continuous casting to control segregation in the continuous casting billet).

[0069] In step S2, in some embodiments, after hot piercing and hot continuous rolling of the continuous casting billet, the steps of obtaining a tube blank specifically include:

[0070] The continuous casting billet is heated in a heating furnace to 1180 - 1230 °C, held for 90 - 120 min, then hot - pierced at a temperature of 1170 - 1200 °C and hot - continuously rolled at a temperature of 950 - 1150 °C, and after cooling (such as air - cooling), a tube blank is obtained (specifically, it can be sawed to an appropriate length to obtain the tube blank).

[0071] In step S3, in some embodiments, for the 80 ksi steel grade, the steps of subjecting the tube blank to quenching and tempering heat treatment, hot straightening, and then threading to obtain the heavy oil heat - using casing specifically include:

[0072] In a protective atmosphere furnace, the tube blank is heated at a temperature of 750 - 800 °C, held for 40 - 60 min, and then cooled by internal and external water spraying at a cooling rate of 20 - 30 °C / s to obtain a martensite + a small amount of ferrite structure; then tempered at a temperature of 680 - 710 °C for 90 - 120 min and water - cooled (water - cooling after tempering to avoid possible temper brittleness) to obtain a tempered sorbite + a small amount of ferrite structure, and then hot - straightened at a temperature of 600 - 650 °C and water - cooled, and after threading, the heavy oil heat - using casing is obtained.

[0073] In some embodiments, for the 90 ksi, 100 ksi, and 110 ksi steel grades, the steps of subjecting the tube blank to quenching and tempering heat treatment, hot straightening, and then threading to obtain the heavy oil heat - using casing specifically include:

[0074] In a protective atmosphere furnace, the tube blank is heated at a temperature of 890 - 910°C, held for 40 - 60 minutes, and then cooled by spraying water inside and outside at a cooling rate of 20 - 30°C / s to obtain a martensite structure; then tempered at a temperature of 650 - 690°C for 90 - 120 minutes and water-cooled (water-cooling after tempering is to avoid possible temper brittleness) to obtain a tempered sorbite structure, and then hot straightened at a temperature of 600 - 650°C and water-cooled. After threading, the heavy oil thermal recovery casing is obtained.

[0075] Specifically, according to actual requirements, API standard threads or special threads can be processed at both ends of the pipe section, and magnetic particle inspection is carried out on the threads.

[0076] The present invention will be further described below through specific embodiments.

[0077] Table 1. Chemical composition of the heavy oil thermal recovery casing in Examples 1 - 12

[0078]

[0079] In Table 1 of Examples 1 - 12, the content of each component is in mass percentage, and the balance to 100% is Fe and inevitable impurities.

[0080] Example 1

[0081] Steelmaking: According to the composition of the heavy oil thermal recovery casing in Example 1 shown in Table 1, batching is carried out, and then it successively undergoes oxygen blowing converter steelmaking, feeding Ce wire, secondary refining, vacuum degassing, and feeding Si-Ca wire to control the shape and transformation of inclusions to obtain molten steel;

[0082] Continuous casting: The molten steel is cast into a rod-shaped continuous casting billet, and electromagnetic stirring and soft reduction technologies are used during continuous casting to control the segregation in the continuous casting billet;

[0083] Piercing and hot continuous rolling: The continuous casting billet is heated in a rotary hearth furnace, the furnace temperature is 1200°C, and the heating time is 120 minutes. Then it is hot pierced at a temperature of 1170°C and hot continuously rolled at a temperature of 950 - 1150°C (the starting rolling temperature is 1150°C, and the final rolling temperature is 950°C). After air cooling, it is sawed to a preset length to obtain a tube blank;

[0084] Quenching and tempering heat treatment, hot straightening: Adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high-temperature tempering. In the protective atmosphere furnace, heat the tube blank at a temperature of 780 °C, hold for 60 min, then perform internal and external water spray cooling at a cooling rate of 30 °C / s to obtain a martensite + small amount of ferrite structure; then perform tempering at a temperature of 700 °C, with a tempering time of 120 min, to obtain a fine and uniform tempered sorbite + small amount of ferrite structure, and cool with water after tempering; then perform hot straightening at a temperature of 650 °C and cool with water; after thread processing, obtain the casing for heavy oil heat.

[0085] Example 2

[0086] Steelmaking: The difference from Example 1 is only that the ingredients are prepared according to the composition of the casing for heavy oil heat in Example 2 shown in Table 1;

[0087] Continuous casting: The same as Example 1;

[0088] Piercing and hot continuous rolling: The same as Example 1;

[0089] Quenching and tempering heat treatment, hot straightening: The same as Example 1.

[0090] Example 3

[0091] Steelmaking: The difference from Example 1 is only that the ingredients are prepared according to the composition of the casing for heavy oil heat in Example 3 shown in Table 1;

[0092] Continuous casting: The same as Example 1;

[0093] Piercing and hot continuous rolling: The same as Example 1;

[0094] Quenching and tempering heat treatment, hot straightening: The same as Example 1.

[0095] Example 4

[0096] Steelmaking: The difference from Example 1 is only that the ingredients are prepared according to the composition of the casing for heavy oil heat in Example 4 shown in Table 1;

[0097] Continuous casting: The same as Example 1;

[0098] Piercing and hot continuous rolling: The same as Example 1;

[0099] Quenching and tempering heat treatment, hot straightening: Using a protective atmosphere furnace for heating, a heat treatment process of quenching + high-temperature tempering. In the protective atmosphere furnace, the tube blank is heated at a temperature of 900 °C for 60 min, then cooled by internal and external water spraying at a cooling rate of 30 °C / s to obtain a martensite structure; then tempered at a temperature of 685 °C for 120 min to obtain a fine and uniform tempered sorbite structure, and water-cooled after tempering; then hot straightened at a temperature of 630 °C and water-cooled; after threading, the heavy oil thermal recovery casing is obtained.

[0100] Example 5

[0101] Steelmaking: The difference from Example 4 is only that the ingredients are prepared according to the composition of the heavy oil thermal recovery casing in Example 5 shown in Table 1;

[0102] Continuous casting: The same as Example 4;

[0103] Piercing and hot continuous rolling: The same as Example 4;

[0104] Quenching and tempering heat treatment, hot straightening: The same as Example 4.

[0105] Example 6

[0106] Steelmaking: The difference from Example 4 is only that the ingredients are prepared according to the composition of the heavy oil thermal recovery casing in Example 6 shown in Table 1;

[0107] Continuous casting: The same as Example 4;

[0108] Piercing and hot continuous rolling: The same as Example 4;

[0109] Quenching and tempering heat treatment, hot straightening: The same as Example 4.

[0110] Example 7

[0111] Steelmaking: The difference from Example 1 is only that the ingredients are prepared according to the composition of the heavy oil thermal recovery casing in Example 7 shown in Table 1;

[0112] Continuous casting: The same as Example 1;

[0113] Piercing and hot continuous rolling: The same as Example 1;

[0114] Quenching and tempering heat treatment, hot straightening: Using a protective atmosphere furnace for heating, a heat treatment process of quenching + high-temperature tempering. In the protective atmosphere furnace, the tube blank is heated at a temperature of 900 °C for 60 min, then cooled by internal and external water spraying at a cooling rate of 30 °C / s to obtain a martensite structure; then tempered at a temperature of 670 °C for 120 min to obtain a fine and uniform tempered sorbite structure, and water-cooled after tempering; then hot straightened at a temperature of 610 °C and water-cooled; after threading, the heavy oil thermal recovery casing is obtained.

[0115] Example 8

[0116] Steelmaking: The difference from Example 7 is only that the ingredients are proportioned according to the composition of the heavy oil heat - resistant casing shown in Table 1 for Example 8;

[0117] Continuous casting: The same as Example 7;

[0118] Piercing and hot continuous rolling: The same as Example 7;

[0119] Quenching and tempering heat treatment, hot straightening: The same as Example 7.

[0120] Example 9

[0121] Steelmaking: The difference from Example 7 is only that the ingredients are proportioned according to the composition of the heavy oil heat - resistant casing shown in Table 1 for Example 9;

[0122] Continuous casting: The same as Example 7;

[0123] Piercing and hot continuous rolling: The same as Example 7;

[0124] Quenching and tempering heat treatment, hot straightening: The same as Example 7.

[0125] Example 10

[0126] Steelmaking: The difference from Example 1 is only that the ingredients are proportioned according to the composition of the heavy oil heat - resistant casing shown in Table 1 for Example 10;

[0127] Continuous casting: The same as Example 1;

[0128] Piercing and hot continuous rolling: The same as Example 1;

[0129] Quenching and tempering heat treatment, hot straightening: Adopt the heat treatment process of heating in a protective atmosphere furnace, quenching + high - temperature tempering. In the protective atmosphere furnace, the tube blank is heated at a temperature of 900 °C, held for 60 min, and then cooled by spraying water inside and outside at a cooling rate of 30 °C / s to obtain a martensite structure; then tempered at a temperature of 655 °C for 120 min to obtain a fine and uniform tempered sorbite structure, and water - cooled after tempering to avoid possible temper brittleness; then hot - straightened at a temperature of 600 °C and water - cooled; after threading, the heavy oil heat - resistant casing is obtained.

[0130] Example 11

[0131] Steelmaking: The difference from Example 10 is only that the ingredients are proportioned according to the composition of the heavy oil heat - resistant casing shown in Table 1 for Example 11;

[0132] Continuous casting: The same as Example 10;

[0133] Piercing and hot continuous rolling: same as Example 10;

[0134] Quenching and tempering heat treatment, hot straightening: same as Example 10.

[0135] Example 12

[0136] Steelmaking: The only difference from Example 10 is that the ingredients are proportioned according to the composition of the casing for heavy oil heat used in Example 12 shown in Table 1;

[0137] Continuous casting: same as Example 10;

[0138] Piercing and hot continuous rolling: same as Example 10;

[0139] Quenching and tempering heat treatment, hot straightening: same as Example 10.

[0140] The tensile property tests at room temperature and 350 °C were respectively carried out on the casings for heavy oil heat used prepared in Examples 1 - 12, including yield strength test, tensile strength test, total elongation test, uniform elongation test and Charpy V-notch impact toughness test at 0 °C. The results are shown in Table 2 and Table 3 as follows.

[0141] Table 2. Room temperature tensile properties and impact toughness at 0 °C of the casings for heavy oil heat used prepared in Examples 1 - 12

[0142]

[0143] Table 3. Tensile properties of the casings for heavy oil heat used prepared in Examples 1 - 12 at 350 °C

[0144]

[0145] In the table, 80SH, 90SH, 100SH, and 110SH respectively correspond to the casings with steel grades of 80 ksi, 90 ksi, 100 ksi, and 110 ksi.

[0146] The above results show that the casings for heavy oil heat used provided by the present invention have excellent comprehensive properties, specifically as follows:

[0147] For the 80SH casing for heavy oil heat used, at room temperature, the yield strength is 597 - 605 MPa, the tensile strength is 694 - 703 MPa, the yield ratio is 0.86, the total elongation rate is 30%, the uniform elongation rate is 19%, and the Charpy V-notch impact toughness at 0 °C is 122 - 126 J.

[0148] For the casing used in 90SH heavy oil thermal recovery, at room temperature, the yield strength is 668 - 674 MPa, the tensile strength is 768 - 775 MPa, the yield ratio is 0.87, the total elongation is 29%, the uniform elongation is 18%, and the Charpy V-notch impact toughness at 0 °C is 133 - 136 J.

[0149] For the casing used in 100SH heavy oil thermal recovery, at room temperature, the yield strength is 738 - 745 MPa, the tensile strength is 839 - 847 MPa, the yield ratio is 0.88, the total elongation is 28%, the uniform elongation is 17%, and the Charpy V-notch impact toughness at 0 °C is 129 - 132 J.

[0150] For the casing used in 110SH heavy oil thermal recovery, at room temperature, the yield strength is 806 - 811 MPa, the tensile strength is 906 - 911 MPa, the yield ratio is 0.89, the total elongation is 27%, the uniform elongation is 16%, and the Charpy V-notch impact toughness at 0 °C is 124 - 127 J.

[0151] For the casings of each steel grade used in heavy oil thermal recovery, at 350 °C compared with at room temperature, the yield strength decreases by about 15%, the tensile strength decreases by about 12%, meeting the requirement of the relevant standard that the strength decrease does not exceed 20%. The yield ratio further decreases, the total elongation and the uniform elongation increase, and the use safety is improved. It can meet the requirements of heavy oil steam thermal recovery wells for the casing strength, plasticity and strain fatigue life.

[0152] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A casing for thermal recovery of heavy oil, characterized in that, By mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components: C 0.15% - 0.25%, Si 0.80% - 0.95%, Mn 0.80% - 1.00%, Cr 1.15% - 1.30%, Mo 0.10% - 0.17%, V 0.03% - 0.10%, RE 0.001% - 0.004%, Al 0.010% - 0.030%, Ca 0.012% - 0.025%, P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

2. The heavy oil thermal recovery casing according to claim 1, characterized in that, By mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components: C 0.15% - 0.17%, Si 0.80% - 0.87%, Mn 0.80% - 0.85%, Cr 1.15% - 1.18%, Mo 0.10% - 0.12%, V 0.03% - 0.05%, RE 0.001% - 0.002%, Al 0.010% - 0.014%, Ca 0.012% - 0.015%, P ≤ 0.011%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

3. The casing for heavy oil thermal recovery according to claim 1, characterized in that, By mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components: C 0.18% - 0.19%, Si 0.85% - 0.89%, Mn 0.86% - 0.89%, Cr 1.19% - 1.22%, Mo 0.11% - 0.13%, V 0.05% - 0.07%, RE 0.002% - 0.003%, Al 0.015% - 0.019%, Ca 0.016% - 0.018%, P ≤ 0.012%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

4. The heavy oil thermal recovery casing according to claim 1, characterized in that, By mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components: C 0.20% - 0.22%, Si 0.90% - 0.94%, Mn 0.91% - 0.95%, Cr 1.20% - 1.24%, Mo 0.13% - 0.14%, V 0.06% - 0.08%, RE 0.003%, Al 0.020% - 0.022%, Ca 0.017% - 0.021%, P ≤ 0.011%, S ≤ 0.003%, N ≤ 0.005%, O + H + N ≤ 0.007%, and the balance is Fe and inevitable impurities.

5. The casing for heavy oil thermal recovery according to claim 1, characterized in that, By mass percentage, the casing for heavy oil thermal recovery comprises the following chemical components: C 0.23% - 0.25%, Si 0.91% - 0.95%, Mn 0.97% - 1.00%, Cr 1.25% - 1.30%, Mo 0.15% - 0.17%, V 0.08% - 0.10%, RE 0.003% - 0.004%, Al 0.024% - 0.030%, Ca 0.020% - 0.025%, P ≤ 0.010%, S ≤ 0.003%, N ≤ 0.004%, O + H + N ≤ 0.006%, and the balance is Fe and unavoidable impurities.

6. A preparation method of a casing pipe for heavy oil thermal recovery, characterized in that, Including the steps of: After batching, smelting, and continuous casting according to the chemical composition of the casing for heavy oil thermal recovery described in any one of claims 1 - 5, a continuous casting billet is obtained; After hot piercing and hot continuous rolling of the continuous casting billet, a tube blank is obtained; After quenching and tempering heat treatment and hot straightening of the tube blank, threading is carried out to obtain the casing for heavy oil thermal recovery.

7. The preparation method according to claim 6, characterized in that, The steps of obtaining a continuous casting billet after smelting and continuous casting specifically include: The raw materials obtained by batching are successively passed through an oxygen blowing converter for smelting, feeding RE wire, refining outside the furnace, vacuum degassing, and feeding Si - Ca wire for modifying inclusions to obtain molten steel; The molten steel is cast into a rod - shaped continuous casting billet.

8. The preparation method according to claim 6, characterized in that, The steps of obtaining a tube blank after hot piercing and hot continuous rolling of the continuous casting billet specifically include: The continuous casting billet is heated in a heating furnace to 1180 - 1230 °C and held for 90 - 120 min, then hot pierced at a temperature of 1170 - 1200 °C and hot continuously rolled at a temperature of 950 - 9. The preparation method according to claim 6, characterized in that, ​ ​ 10. The preparation method according to claim 6, characterized in that, ​ ​

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