Petroleum casing as well as preparation method and application thereof

Abstract

The invention discloses a petroleum casing pipe and a preparation method and application thereof, and relates to the technical field of petroleum casing pipes, and the petroleum casing pipe comprises the following chemical components in percentage by mass: 0.25%-0.32% of C, 0.55%-0.70% of Si, 1.25%-1.40% of Mn, 0%-0.020% of P, 0%-0.010% of S, 0.0005%-0.0020% of RE, less than 0.0010% of B, 0.015%-0.035% of Al, and the balance of Fe and inevitable impurities. The oil casing steel grade is 60 ksi and 65 ksi, the yield strength is 414-621 MPa, the tensile strength is larger than or equal to 552 MPa, and the transverse Charpy impact toughness at the temperature of 0 DEG C is larger than or equal to 40 J. When the oil casing steel grade is used as a surface casing instead of a J55 steel grade casing, the wall thickness and weight can be reduced, and the oil and gas development cost can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum casing, and in particular to a petroleum casing and a preparation method and application thereof. Background Art

[0002] In the process of oil and gas development, a large number of surface casings are used, especially J55 steel grade casings. At present, when J55 steel grade casings are used as surface casings for oil and gas development, the cost of oil and gas development is still high. Therefore, it will be of great significance to develop a high-strength oil casing that takes into account toughness and economy to further reduce the cost of oil and gas development.

[0003] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0004] Based on the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a petroleum casing and a preparation method and application thereof, aiming to solve the problem that the cost of oil and gas development is still high when J55 steel grade casing is used as surface casing for oil and gas development.

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

[0006] The first aspect of the present invention provides a petroleum casing, wherein the petroleum casing comprises the following chemical components by mass percentage:

[0007] C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0%~0.020%, S0%~0.010%, RE 0.0005%~0.0020%, B<0.0010%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

[0008] Optionally, the petroleum casing comprises the following chemical components by mass percentage:

[0009] C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0.015%~0.020%, S 0.005%~0.010%, RE 0.0005%~0.0020%, B 0%~0.0009%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

[0010] Optionally, the petroleum casing comprises the following chemical components by mass percentage:

[0011] C 0.29%~0.32%, Si 0.55%~0.62%, Mn 1.25%~1.31%, P 0.018%~0.020%, S 0.008%~0.010%, RE 0.0005%~0.0010%, Al 0.015%~0.020%, and the balance is Fe and unavoidable impurities.

[0012] Optionally, the petroleum casing comprises the following chemical components by mass percentage:

[0013] C 0.25%~0.28%, Si 0.65%~0.70%, Mn 1.34%~1.40%, P 0.015%~0.017%, S 0.005%~0.007%, RE 0.0015%~0.0020%, B 0.0007%~0.0009%, Al0.027%~0.035%, and the balance is Fe and unavoidable impurities.

[0014] A second aspect of the present invention provides a method for preparing a petroleum casing, which comprises the following steps:

[0015] According to the present invention, the chemical components of the petroleum casing as described above are mixed, smelted, and continuously cast to obtain a continuous casting billet;

[0016] The continuous casting billet is subjected to soaking, hot piercing and hot continuous rolling to obtain a tube billet;

[0017] The tube blank is subjected to heat straightening and then thread processing to obtain the petroleum casing.

[0018] Optionally, the temperature used for the equalization is 1170-1220° C., and the time used for the equalization is 90-120 min.

[0019] Optionally, the temperature used for the thermal perforation is 1140-1190°C.

[0020] Optionally, after hot rolling, a cooling step is further included before obtaining the tube blank;

[0021] The temperature of the hot rolling is 850-1150°C, and the final rolling temperature is controlled to be 850-900°C.

[0022] Optionally, after the tube blank is heat straightened and before the thread processing is performed, a water cooling step is also included;

[0023] The temperature of the heat straightening is 600-650°C.

[0024] The third aspect of the present invention provides an application of the petroleum casing as described above and / or the petroleum casing prepared by the preparation method as described above in replacing J55 steel grade casing as surface casing for oil and gas development.

[0025] Beneficial effects: The steel grade of the oil casing provided by the present invention is 60ksi and 65ksi, the yield strength is 414-621MPa, the tensile strength is greater than or equal to 552MPa, and the transverse Charpy impact toughness at 0°C is greater than or equal to 40J. It can be seen that the strength of the oil casing provided by the present invention is higher than that of the J55 steel grade oil casing (yield strength 379-552MPa). Therefore, when the oil casing provided by the present invention, which has high strength and takes both toughness and economy into consideration, is used as a surface casing instead of the J55 steel grade oil casing, the casing wall thickness can be reduced, the casing column weight can be reduced, and the oil and gas development cost can be further reduced. DETAILED DESCRIPTION

[0026] The present invention provides a petroleum casing and a preparation method and application thereof. To make the purpose, technical solution and effect of the present invention clearer and more specific, 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.

[0027] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] An embodiment of the present invention provides a petroleum casing, wherein the petroleum casing comprises the following chemical components in terms of mass percentage:

[0029] C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0%~0.020%, S0%~0.010%, RE 0.0005%~0.0020%, B<0.0010%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

[0030] RE is a rare earth element. In some specific embodiments, RE may be Ce (cerium).

[0031] In the embodiment of the present invention, fewer types of chemical elements are used. Specifically, medium-low C content, Mn, Si, and trace rare earth (RE) elements are added. A small amount of B element can also be added, and Al and Si fully deoxidized calm steel is used to achieve a casing that takes into account strength, toughness and economy. The oil casing provided by the present invention has a steel grade of 60ksi and 65ksi, a yield strength of 414-621MPa, a tensile strength of greater than or equal to 552MPa, and a transverse Charpy impact toughness of greater than or equal to 40J at 0°C. The strength of the oil casing provided by the present invention is higher than that of J55 steel grade oil casing (55ksi steel grade, yield strength of 379-552MPa, tensile strength of greater than or equal to 517MPa, and transverse Charpy impact toughness of greater than or equal to 20J at 0°C). Therefore, when the oil casing provided by the present invention, which has high strength and takes both toughness and economy into consideration, is used as a surface casing in oil and gas development instead of J55 steel grade oil casing, the casing wall thickness can be reduced, the casing column weight can be reduced, and the oil and gas development cost can be further reduced while ensuring the same pressure bearing capacity of the casing column. That is, the present invention intends to adopt a solution of appropriately improving the casing strength level and reducing the casing wall thickness to replace the J55 steel grade casing with lower strength and thicker wall thickness without significantly increasing the casing manufacturing cost per unit weight, so as to reduce the casing weight and oil and gas development costs.

[0032] Among them, C (carbon) is the main strengthening element in steel. Using medium and low carbon is conducive to taking into account both the strength and plasticity of steel. However, too low carbon content is not conducive to improving the hardenability of steel and the strength of steel; too high carbon content is not conducive to improving the plasticity of steel. Considering comprehensively, it is advisable to control it within the range of 0.25% to 0.32%.

[0033] Si (silicon) is mainly used to improve the strength of steel. Taking all factors into consideration, it is advisable to control it within the range of 0.55% to 0.70%.

[0034] Mn (manganese) is mainly used to improve the hardenability of steel and thus improve its strength. If the content is too low, it will not play the role it should play, and if the content is too high, it will increase the tendency of segregation. Taking all factors into consideration, it is advisable to control it within the range of 1.25% to 1.40%.

[0035] B (boron): Adding trace amounts of B elements can improve the hardenability of steel, thereby further improving the strength of steel. Taking all factors into consideration, it is advisable to control B < 0.0010% (i.e., the mass percentage of B is less than 0.0010%).

[0036] RE (rare earth element) has multiple functions of purifying molten steel, refining grains, modifying inclusions, and alloying. It is advisable to control it within the range of 0.0005% to 0.0020%.

[0037] Al (aluminum) forms fine and evenly distributed oxides with oxygen, which can refine the grains and improve the strength and toughness. It is also an important deoxidizer. Taking all factors into consideration, it is advisable to control the content within the range of 0.015% to 0.035%.

[0038] P (phosphorus) is a harmful element that mainly affects the plasticity and toughness of steel. It is advisable to control P ≤ 0.020% (i.e. the mass content of P is less than or equal to 0.020%).

[0039] S (sulfur) is a harmful element that mainly affects the plasticity and toughness of steel. It is advisable to control S ≤ 0.010% (i.e., the mass content of S is less than or equal to 0.020%).

[0040] In some embodiments, the petroleum casing comprises the following chemical components by mass percentage:

[0041] C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0.015%~0.020%, S 0.005%~0.010%, RE 0.0005%~0.0020%, B 0%~0.0009%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

[0042] At present, there is no D60 steel grade oil casing in the API (American Petroleum Institute) standard and relevant standards of my country, and the M65 steel grade oil casing with both strength, toughness and economy is rarely used. In this embodiment, the yield strength level of the oil casing provided can reach D60 steel grade oil casing and M65 steel grade oil casing respectively, wherein the yield strength of D60 steel grade oil casing is 414-586MPa (corresponding to 60-85ksi), the tensile strength is greater than or equal to 552MPa, and the transverse Charpy impact toughness at 0℃ is greater than or equal to 40J; the yield strength of M65 steel grade oil casing is 448-621MPa (corresponding to 65-90ksi), the tensile strength is greater than or equal to 586MPa, and the transverse Charpy impact toughness at 0℃ is greater than or equal to 60J. The strength and toughness are better than J55 steel grade oil casing. The petroleum casing provided by the present invention has not only high strength but also good toughness, and can replace the J55 steel grade surface casing currently in large quantities, thereby reducing the cost of oil and gas development.

[0043] In some embodiments, the petroleum casing comprises the following chemical components by mass percentage:

[0044] C 0.29%~0.32%, Si 0.55%~0.62%, Mn 1.25%~1.31%, P 0.018%~0.020%, S 0.008%~0.010%, RE 0.0005%~0.0010%, Al 0.015%~0.020%, and the balance is Fe and unavoidable impurities.

[0045] In this embodiment, the oil casing is specifically D60 steel grade oil casing (steel grade 60ksi), whose yield strength is 461-468MPa, tensile strength is 608-617MPa, elongation is 29%, longitudinal Charpy V-notch impact toughness at 0°C is 63-69J, and transverse Charpy V-notch impact toughness at 0°C is 44-49J.

[0046] In some embodiments, the petroleum casing comprises the following chemical components by mass percentage:

[0047] C 0.25%~0.28%, Si 0.65%~0.70%, Mn 1.34%~1.40%, P 0.015%~0.017%, S 0.005%~0.007%, RE 0.0015%~0.0020%, B 0.0007%~0.0009%, Al0.027%~0.035%, and the balance is Fe and unavoidable impurities.

[0048] In this embodiment, the oil casing is specifically an M65 steel grade oil casing (steel grade is 65ksi), whose yield strength is 498-503MPa, tensile strength is 646-653MPa, elongation is 28%, longitudinal Charpy V-notch impact toughness at 0°C is 83-88J, and transverse Charpy V-notch impact toughness at 0°C is 64-68J.

[0049] When the outer diameter and pressure bearing capacity are the same, the casing strength σ is inversely proportional to the wall thickness t, and has the following relationship: σ 1 t 1 =σ 2 t 2 Therefore, when D60 steel grade oil casing is used instead of J55 steel grade oil casing as surface casing, the wall thickness can be reduced by 8.3%; when M65 steel grade oil casing is used instead of J55 steel grade oil casing as surface casing, the wall thickness can be reduced by 15.4%. The reduction of casing wall thickness can reduce the weight of casing string, thus significantly reducing the cost of oil and gas production.

[0050] The present invention develops a manufacturing process that matches the chemical composition with the above-mentioned proportion content, mainly through processes such as steelmaking, continuous casting, hot rolling in the austenite zone, and hot straightening, so that the material obtains a fine and uniform pearlite + ferrite microstructure to achieve a reasonable match between the strength and plastic toughness of the casing, so that the casing has excellent comprehensive performance. Specifically, an embodiment of the present invention provides a method for preparing a petroleum casing, which includes the following steps:

[0051] S1. The chemical composition of the petroleum casing according to the present invention is mixed, smelted and continuously cast to obtain a continuous casting billet;

[0052] S2, subjecting the continuous casting billet to soaking, hot piercing, and hot continuous rolling to obtain a tube billet;

[0053] S3, performing heat straightening on the tube blank and then thread processing to obtain the petroleum casing.

[0054] The chemical composition design and manufacturing process of the embodiment of the present invention have the effect of improving strength and improving plastic toughness. The preparation method of the present invention is aimed at the oil casing of the above chemical composition, and the expected organizational structure and performance are obtained, and the performance of the oil casing is fully exerted, and the process parameters in the process are easy to control. The obtained oil casing has stable performance, the steel grade is 60ksi and 65ksi, the yield strength is 414-621MPa, the tensile strength is greater than or equal to 552MPa, and the transverse Charpy impact toughness at 0°C is greater than or equal to 40J. The strength is higher than that of J55 steel grade oil casing (yield strength is 379-552MPa), and it can replace the J55 steel grade surface casing currently used in large quantities. That is, by appropriately improving the strength, the casing wall thickness can be reduced, thereby reducing the weight of the casing column and reducing the cost of oil and gas development.

[0055] In step S2, in some embodiments, the temperature used for the equalization is 1170-1220°C (for example, it can be 1170°C, 1180°C, 1190°C, 1200°C, 1210°C or 1220°C, etc.); the time used for the equalization is 90-120 min (for example, it can be 90 min, 100 min, 110 min or 120 min, etc.).

[0056] In some embodiments, the temperature used for the thermal perforation is 1140-1190° C. (for example, it may be 1140° C., 1150° C., 1160° C., 1170° C., 1180° C., or 1190° C., etc.).

[0057] In some embodiments, after hot rolling, a cooling step (for example, air cooling or wind cooling) is further included before obtaining the tube blank.

[0058] In some embodiments, the hot rolling temperature is 850-1150°C, and the final rolling temperature is controlled to be 850-900°C.

[0059] In step S3, in some embodiments, after the tube blank is hot straightened and before the thread processing is performed, a water cooling step is also included.

[0060] In some embodiments, the temperature of the heat straightening is 600-650° C. (for example, 600° C., 610° C., 620° C., 630° C., 640° C., or 650° C., etc.).

[0061] In step S3, API standard threads or special threads can be processed.

[0062] The embodiment of the present invention also provides an application of the oil casing of the present invention as described above and / or the oil casing prepared by the preparation method of the present invention as described above to replace the J55 steel grade casing as the surface casing of oil and gas development. The present invention utilizes the high strength of the above oil casing to replace the J55 steel grade casing as the surface casing, which can reduce the casing wall thickness, reduce the weight of the casing column, and reduce the cost of oil and gas development.

[0063] The present invention will be further described below by means of specific examples.

[0064] Table 1 Chemical composition of the oil casing in Examples 1-6

[0065]

[0066] In Examples 1-6 of Table 1, the content of each chemical component is in mass percentage, and the remainder to 100% is Fe and unavoidable impurities.

[0067] Example 1

[0068] This embodiment provides a method for preparing a D60 steel grade petroleum casing, comprising the following steps:

[0069] Steelmaking: According to the chemical composition of the D60 steel grade petroleum casing of Example 1 shown in Table 1, the ingredients are prepared, and then the steel is successively subjected to oxygen-blown converter steelmaking, Ce wire feeding, external refining and vacuum degassing to obtain molten steel.

[0070] Continuous casting: The molten steel is cast into rod-shaped continuous casting billets.

[0071] Soaking, piercing and hot rolling: The rod-shaped continuous casting billet is soaked in a ring heating furnace with a heating furnace temperature of 1200°C and a heating time of 120 minutes; then hot pierced at 1160°C, hot rolled at 880°C to 1150°C, with the initial rolling temperature at 1150°C and the final rolling temperature controlled at 880°C, then air-cooled and sawed to a suitable length to obtain a tube billet (whose metallographic structure is: pearlite + ferrite microstructure).

[0072] Hot straightening: The tube is hot straightened at 650°C and then water cooled.

[0073] Thread processing: Process API standard threads or special threads on the pipe blank.

[0074] Example 2

[0075] This embodiment provides a method for preparing a D60 steel grade petroleum casing, comprising the following steps:

[0076] Steelmaking: According to the chemical composition of the D60 steel grade petroleum casing of Example 2 shown in Table 1, the ingredients are prepared, and then oxygen-blown converter steelmaking, Ce wire feeding, external refining and vacuum degassing are carried out in sequence to obtain molten steel.

[0077] Continuous casting: Same as Example 1.

[0078] Heat soaking, piercing and hot rolling: same as in Example 1.

[0079] Thermal straightening: Same as Example 1.

[0080] Thread processing: same as Example 1.

[0081] Example 3

[0082] This embodiment provides a method for preparing a D60 steel grade petroleum casing, comprising the following steps:

[0083] Steelmaking: According to the chemical composition of the D60 steel grade petroleum casing of Example 3 shown in Table 1, the ingredients are prepared, and then the steel is successively subjected to oxygen-blown converter steelmaking, Ce wire feeding, external refining and vacuum degassing to obtain molten steel.

[0084] Continuous casting: Same as Example 1.

[0085] Heat soaking, piercing and hot rolling: same as in Example 1.

[0086] Thermal straightening: Same as Example 1.

[0087] Thread processing: same as Example 1.

[0088] Example 4

[0089] This embodiment provides a method for preparing an M65 steel grade petroleum casing, comprising the following steps:

[0090] Steelmaking: According to the chemical composition of the M65 steel grade petroleum casing of Example 4 shown in Table 1, the ingredients are prepared, and then oxygen-blown converter steelmaking, Ce wire feeding, external refining and vacuum degassing are carried out in sequence to obtain molten steel.

[0091] Continuous casting: The molten steel is cast into rod-shaped continuous casting billets.

[0092] Soaking, piercing and hot rolling: The rod-shaped continuous casting billet is soaked in a ring heating furnace with a heating furnace temperature of 1200°C and a heating time of 120 minutes, then hot-pierced at 1160°C, hot-rolled at 860°C to 1150°C, with the initial rolling temperature at 1150°C and the final rolling temperature at 860°C, then air-cooled and sawed to a suitable length to obtain a tube billet (whose metallographic structure is: pearlite + ferrite microstructure).

[0093] Hot straightening: The tube is hot straightened at 600°C and then water cooled.

[0094] Thread processing: Process API standard threads or special threads on the pipe blank.

[0095] Example 5

[0096] This embodiment provides a method for preparing an M65 steel grade petroleum casing, comprising the following steps:

[0097] Steelmaking: According to the chemical composition of the M65 steel grade petroleum casing of Example 5 shown in Table 1, the ingredients are prepared, and then oxygen-blown converter steelmaking, Ce wire feeding, external refining and vacuum degassing are carried out in sequence to obtain molten steel.

[0098] Continuous casting: Same as Example 4.

[0099] Heat soaking, piercing and hot rolling: same as Example 4.

[0100] Thermal straightening: same as Example 4.

[0101] Thread processing: same as Example 4.

[0102] Example 6

[0103] This embodiment provides a method for preparing an M65 steel grade petroleum casing, comprising the following steps:

[0104] Steelmaking: The chemical composition of the M65 steel grade petroleum casing of Example 6 shown in Table 1 is used for batching, and then steelmaking in an oxygen-blown converter, Ce wire feeding, refining outside the furnace and vacuum degassing are carried out in sequence to obtain molten steel.

[0105] Continuous casting: Same as Example 4.

[0106] Heat soaking, piercing and hot rolling: same as Example 4.

[0107] Thermal straightening: same as Example 4.

[0108] Thread processing: same as Example 4.

[0109] The oil casings prepared in Examples 1-6 were subjected to yield strength test, tensile strength test, elongation test and Charpy V-notch impact toughness test at 0°C, respectively. The results are shown in Table 2.

[0110] Table 2. Properties of the oil casing prepared in Examples 1-6

[0111]

[0112] It can be seen that the D60 and M65 steel grade oil casing provided in the embodiment have excellent comprehensive properties, wherein the room temperature yield strength of the D60 steel grade oil casing is 461-468 MPa, the tensile strength is 608-617 MPa, the elongation is 29%, and the transverse Charpy impact toughness at 0°C is 44-49 J; the room temperature yield strength of the M65 steel grade oil casing is 498-503 MPa, the tensile strength is 646-653 MPa, the elongation is 28%, and the transverse Charpy impact toughness at 0°C is 64-68 J.

[0113] If D60 steel-grade casing is used to replace J55 steel-grade casing with a specification of 244.48mm×8.94mm (i.e., an outer diameter of 244.48mm and a wall thickness of 8.94mm) as the surface casing for oil and gas development, the wall thickness can be reduced to 8.20mm while the strength (or pressure-bearing capacity) remains unchanged, reducing the wall thickness by about 8.3% and the steel weight by about 8.0%, thereby significantly reducing the cost of oil and gas development.

[0114] If the M65 steel-grade casing (outer diameter 244.48mm, wall thickness 7.92mm) with a specification of 244.48mm×7.92mm is used instead of the J55 steel-grade casing (outer diameter 244.48mm, wall thickness 8.94mm) with a specification of 244.48mm×8.94mm as the surface casing for oil and gas development, the strength will increase by about 4.7%, the wall thickness will be reduced by about 11.4%, and the steel weight will be reduced by about 11.0%, thereby significantly reducing the cost of oil and gas development.

[0115] It can be seen that the use of the D60 and M65 steel grade petroleum casings of the present invention to replace the J55 steel grade petroleum casings of the same outer diameter has a smaller wall thickness and a lower weight, and has obvious economic benefits.

[0116] In summary, the present invention provides a petroleum casing and a preparation method and application thereof, wherein the steel grade of the petroleum casing is 60ksi and 65ksi, the yield strength is 414-621MPa, the tensile strength is greater than or equal to 552MPa, and the transverse Charpy impact toughness at 0°C is greater than or equal to 40J. The strength of the petroleum casing provided by the present invention is higher than that of J55 steel grade petroleum casing (yield strength is 379-552MPa), therefore, when the petroleum casing provided by the present invention with high strength and taking into account toughness is used as a surface casing instead of J55 steel grade casing, the wall thickness can be reduced and the weight can be reduced, thereby further reducing the cost of oil and gas development.

[0117] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A petroleum casing, characterized in that: Measured by mass percentage, the petroleum casing includes the following chemical components: C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0%~0.020%, S0%~0.010%, RE 0.0005%~0.0020%, B<0.0010%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

2. The oil casing according to claim 1, characterized in that: Measured by mass percentage, the petroleum casing includes the following chemical components: C 0.25%~0.32%, Si 0.55%~0.70%, Mn 1.25%~1.40%, P 0.015%~0.020%, S 0.005%~0.010%, RE 0.0005%~0.0020%, B 0%~0.0009%, Al 0.015%~0.035%, and the balance is Fe and unavoidable impurities.

3. The oil casing according to claim 1, characterized in that: Measured by mass percentage, the petroleum casing includes the following chemical components: C 0.29%~0.32%, Si 0.55%~0.62%, Mn 1.25%~1.31%, P 0.018%~0.020%, S 0.008%~0.010%, RE 0.0005%~0.0010%, Al 0.015%~0.020%, and the balance is Fe and unavoidable impurities.

4. The oil casing according to claim 1, characterized in that: Measured by mass percentage, the petroleum casing includes the following chemical components: C 0.25%~0.28%, Si 0.65%~0.70%, Mn 1.34%~1.40%, P 0.015%~0.017%, S 0.005%~0.007%, RE 0.0015%~0.0020%, B 0.0007%~0.0009%, Al 0.027%~0.035%, and the balance is Fe and unavoidable impurities.

5. A method for preparing a petroleum casing, characterized in that: The steps include: After batching, smelting and continuous casting of the chemical composition of the petroleum casing according to any one of claims 1 to 4, a continuous casting billet is obtained; The continuous casting billet is subjected to soaking, hot piercing and hot continuous rolling to obtain a tube billet; The tube blank is subjected to heat straightening and then thread processing to obtain the petroleum casing.

6. The preparation method according to claim 5, characterized in that: The temperature used for the equalization is 1170-1220° C., and the time used for the equalization is 90-120 min.

7. The preparation method according to claim 5, characterized in that: The temperature used for the thermal perforation is 1140-1190°C.

8. The preparation method according to claim 5, characterized in that: After hot rolling, a cooling step is also included before obtaining the tube blank; The temperature of the hot rolling is 850-1150°C, and the final rolling temperature is controlled to be 850-900°C.

9. The preparation method according to claim 5, characterized in that: After the tube blank is heat straightened and before the thread processing is performed, a water cooling step is also included; The temperature of the heat straightening is 600-650°C.

10. Use of the petroleum casing according to any one of claims 1 to 4 and / or the petroleum casing prepared by the preparation method according to any one of claims 5 to 9 in replacing J55 steel grade casing as surface casing for oil and gas development.

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