Deep gas reservoir development with high strength casing and casing steel and method of manufacture

Abstract

The application discloses a high-strength casing for deep oil and gas reservoir exploitation, which is composed of the following raw material components in percentage by mass: C: 0.27%-0.30%, Si: 0%-0.2%, Mn: 0%-0.45%, Cr: 1.0%-1.5%, Mo: 0.5%-0.8%, Nb: 0.05%-0.08%, V: 0.02%-0.03%, Ti: 0.01%-0.05%, Al: 0.01%-0.04%, Ca: 0.001%-0.003%, N: 0%-0.0003%, B: 0.0008%-0.001%, RE: 0.02%-0.05%, P content is not more than 0.008%, S content is not more than 0.003%, and the balance is Fe, and the total of the content of the above raw materials is 100%. The application further discloses a preparation method of the casing steel and a manufacturing method of the high-strength casing. The high-strength casing produced by the component system and the manufacturing method has good matching of strength and toughness, excellent anti-collapse performance, and good stress corrosion resistance, and can meet the requirements of high-strength casing with high anti-collapse strength and stress corrosion resistance in the exploitation of unconventional oil and gas resources such as deep shale oil and gas, deep wells or ultra-deep wells.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline technology for oil and gas exploration and development, and relates to high-strength casing for deep oil and gas reservoir development. This invention also relates to the manufacturing method of the above-mentioned casing steel and the manufacturing method of casing using the steel. Background Technology

[0002] In recent years, domestic oil and gas resource development and production have expanded from deep to ultra-deep formations and from conventional to unconventional formations. The efficient and safe development of deep, ultra-deep, and deep unconventional oil and gas resources has become a key focus and hot topic in current and future oil and gas exploration and development. However, with the continuous increase in wellbore depth, the stress state of the downhole tubing becomes more complex and variable, placing new demands on the strength, toughness, and stress resistance of high-strength casing materials. Furthermore, downhole tubing often encounters formations containing hydrogen sulfide gas, further increasing the failure risk of high-strength casing during downhole service. Therefore, in the production of deep, ultra-deep, and deep unconventional oil and gas resources, the application of high-strength casing with both high stress resistance and stress corrosion resistance is of great engineering significance in reducing the failure risk of downhole tubing. Summary of the Invention

[0003] The purpose of this invention is to provide a high-strength casing for deep oil and gas reservoir development, which has the characteristics of high extrusion strength and stress corrosion resistance.

[0004] The technical solution adopted in this invention is that high-strength casing is used in the development of deep oil and gas reservoirs, and is composed of the following raw material components by mass percentage: C: 0.27%–0.30%, Si: 0%–0.2%, Mn: 0%–0.45%, P: 0%–0.008%, S: 0%–0.003%, Cr: 1.0%–1.5%, Mo: 0.5%–0.8%, Nb: 0.05%–0.08%, V: 0.02%–0.03%, Ti: 0.01%–0.05%, Al: 0.01%–0.04%, Ca: 0.001%–0.003%, N: 0%–0.0003%, B: 0.0008%–0.001%, RE: 0.02%–0.05%, with the balance being Fe. The total content of all the above raw materials is 100%.

[0005] The invention is further characterized by: RE is a mixed rare earth element composed of 48%–52% La, 38%–42% Ce, and 8%–12% Nd, with the total content of each rare earth element being 100%.

[0006] The mass percentages of Cr, Mo, and B elements satisfy 2.7% ≤ Cr + Mo + 1500 × B ≤ 3.5%.

[0007] The mass percentages of Nb, V, and Ti elements satisfy Nb+V+Ti≥1.11%.

[0008] Another technical solution adopted in this invention is a method for preparing high-strength casing steel, which is specifically carried out according to the following steps: Step 1: Add scrap steel to the pre-smelted pig iron molten iron to form molten steel, wherein the pig iron molten iron accounts for 70% to 80% of the molten steel mass, and the scrap steel accounts for 20% to 30%; Step 2: The molten steel is subjected to ladle refining, vacuum degassing, argon stirring and inclusion modification treatment in sequence to obtain pure molten steel; Step 3: The pure molten steel is continuously cast into steel billets under the protection of argon gas.

[0009] Another technical solution adopted in this invention is a method for preparing a high-strength sleeve, which is specifically carried out according to the following steps: Step 1: The prepared molten steel is continuously cast into steel pipe billets under the protection of argon gas. After the steel pipe billets cool, the continuous steel pipe billets are cut into the required lengths.

[0010] Step 2: Heat the cut steel pipe billet and use a piercing mill to pierce the heated steel pipe billet to form a rough tube. Then, use a continuous rolling mill to process the rough tube into a blank tube and reduce the diameter of the blank tube to the required specifications. Then, use a hot flying saw to cut the reduced diameter blank tube to the specified length. Finally, air cool the cut blank tube to room temperature on a cooling bed. Step 3: The cooled tube blank is heated in a medium-frequency induction heating furnace and kept at a constant temperature for a period of time. Then, the entire tube body is quenched using an internal spray and external quenching system. After quenching, the tube blank is tempered in a medium-frequency induction heating furnace. Then, the tempered tube blank is air-cooled to below 300°C on a cooling bed and then water-cooled to room temperature. Step 4: The heat-treated tube blank is sent into a walking beam furnace to heat it and hold it at that temperature for a period of time. Then, the entire tube body is quenched using an internal spray and external quenching system. After that, the quenched tube blank is sent into a walking beam furnace for tempering. After tempering, the residual heat from the tempering process is used for hot straightening to obtain the original tube blank. The temperature of the tube blank during straightening is controlled to be no less than 450℃.

[0011] This manufacturing method is also characterized by: In step 2, during the continuous casting process, a crystallizer and end electromagnetic stirring are used to control the superheat of the molten steel during pouring to be no more than 30°C, while the cooling temperature of the steel pipe billet is no less than 950°C.

[0012] In step 3, the continuous rolling mill unit is a PQF three-roll continuous rolling mill unit. During the reduction, a hot tension reduction unit is used. The hot rolling temperature range of the hot tension reduction mill is 900℃~980℃, and the cross-sectional area ratio of the billet before and after hot tension reduction is not less than 1.3. The residual heat temperature of the billet after hot tension reduction is not less than 850℃.

[0013] In step 4, before quenching, the medium-frequency induction heating furnace heats the cooled tube blank to 900℃~930℃, and the temperature is controlled for 2 minutes to 5 minutes. During tempering, the medium-frequency induction heating furnace heats the tube blank to 700℃~750℃, and the temperature is controlled for 5 minutes to 10 minutes.

[0014] In step 5, before quenching, the tube blank is heated to 850℃~880℃ in a walking beam furnace and held for 30 minutes~45 minutes. During tempering, the tube blank is heated to 650℃~700℃ in a walking beam furnace and held for 60 minutes~90 minutes.

[0015] The beneficial effects of this invention are: The high-strength casing produced using the component system and manufacturing method provided by this invention has a good balance of strength and toughness, excellent resistance to crushing, and good resistance to stress corrosion. It can meet the requirements of high-strength casing with both high crushing strength and resistance to stress corrosion in the exploitation of unconventional oil and gas resources such as deep shale oil and gas, deep wells, or ultra-deep wells. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments.

[0017] The deep oil and gas reservoir development involved in this invention utilizes high-strength casing, which is composed of the following raw material components by mass percentage: C: 0.27%–0.30%, Si: 0%–0.2%, Mn: 0%–0.45%, Cr: 1.0%–1.5%, Mo: 0.5%–0.8%, Nb: 0.05%–0.08%, V: 0.02%–0.03%, Ti: 0.01%–0.05%, Al: 0.01%–0.04%, Ca: 0.001%–0.003%, N: 0%–0.0003%, B: 0.0008%–0.001%, RE: 0.02%–0.05%, with P content controlled to be no more than 0.008% and S content no more than 0.003%, the balance being Fe. The total content of all the above raw materials is 100%.

[0018] RE is a mixed rare earth element composed of 48%–52% La, 38%–42% Ce, and 8%–12% Nd, with the total content of each rare earth element being 100%.

[0019] The mass percentages of Cr, Mo, and B elements in the raw material composition satisfy 2.7%≤Cr+Mo+1500×B≤3.5%.

[0020] The mass percentages of Nb, V, and Ti elements in the raw material composition satisfy Nb+V+Ti≥1.11%.

[0021] Explanation of alloy composition selection in this invention: C: Carbon is a major solid solution strengthening element, capable of forming strengthening phases with various alloys and improving the strength of steel. Too low a carbon content makes it difficult to achieve the required high strength and high toughness, while too high a carbon content negatively impacts the toughness and corrosion resistance of the steel. Therefore, in this invention, the carbon (C) content is designed to be in the range of 0.27% to 0.30%.

[0022] Si: Silicon mainly functions as a deoxidizer, and an appropriate amount of silicon can dissolve in ferrite to increase the yield strength of steel. Therefore, to achieve the purpose of this invention, its content is limited to 0%–0.2%.

[0023] Mn: Manganese can improve the hardenability and strength of steel, but when the content is too high, it can easily increase the banded structure of steel pipes during hot rolling, affecting the uniformity, toughness and corrosion resistance of the steel pipe structure. To achieve the purpose of the invention, the design range is 0% to 0.45%.

[0024] P and S: Sulfur and phosphorus are harmful elements in steel. The lower their content, the better for the toughness and corrosion resistance of steel. Therefore, P is limited to 0% to 0.008% and S to 0% to 0.003% to ensure improved toughness and corrosion resistance of steel.

[0025] Cr: Chromium can improve the hardenability of steel, is a strong carbide-forming element, and can increase the strength of steel. However, if the content is too high, coarse chromium will precipitate during tempering. 23 C6 type carbides reduce the toughness and corrosion resistance of steel. To achieve the purpose of the invention, the chromium content is controlled between 1.0% and 1.5%.

[0026] Mo: Molybdenum is a strong carbide-forming element, which can improve the fine-grain strengthening effect and tempering stability of steel. However, the carbides formed by molybdenum are irreversible hydrogen traps, which are beneficial to improving the hydrogen embrittlement and stress corrosion cracking performance of pipes. Therefore, the content of molybdenum is controlled between 0.5% and 0.8% in this invention.

[0027] Nb: Niobium has the effect of refining grains and precipitation strengthening, which can improve the hardenability, toughness and tempering stability of steel, and make up for the strength problem caused by the reduction of carbon content. At the same time, it forms C and N carbides to form hydrogen traps. Therefore, this invention controls its content to be between 0.05% and 0.08%.

[0028] Vanadium (V) is a strong carbide-forming element that refines grains and can form carbides to improve the tempering stability of steel. However, excessively high vanadium content can lead to coarse carbides and reduced corrosion resistance. Therefore, this invention controls its content to be between 0.02% and 0.03%.

[0029] Ti: Titanium is a strong carbide-forming element, which can refine grains and improve strength and toughness. It can form compounds such as titanium carbide with nitrogen and carbon, forming irreversible hydrogen traps, which improves the tempering stability and corrosion resistance of steel. Therefore, this invention controls its content to be between 0.01% and 0.05%.

[0030] Al: Aluminum is a deoxidizing and nitrogen-fixing element that can refine grains and improve corrosion resistance. In this invention, its content is controlled at 0.01% to 0.04%.

[0031] Ca: Calcium can refine grains and alter the composition, quantity, and morphology of non-metallic inclusions, which is highly beneficial for improving the toughness and corrosion resistance of steel. To achieve the purpose of this invention, the Ca content is designed to range from 0.001% to 0.003%.

[0032] Nitrogen (N) in steel can form dispersed precipitates with elements such as Nb, V, and Ti, which not only helps refine the grain structure and promotes dispersion strengthening, but also acts as a hydrogen trap to improve resistance to hydrogen embrittlement. To achieve the purpose of this invention, the N content is designed to be 0%–0.0003%.

[0033] B: Boron can improve the hardenability, high-temperature strength, and grain boundary strengthening of steel, thereby improving the strength, toughness, and resistance to stress corrosion. However, when the boron content in steel exceeds 0.003%, "boron embrittlement" easily occurs, reducing performance. To achieve the purpose of this invention, the content is controlled within the range of 0.0008% to 0.001%.

[0034] RE: Rare earth elements not only possess strong desulfurization and deoxidation capabilities, purifying molten steel, but also control inclusion morphology and carbides, improve grain boundaries, and inhibit localized weakening, thereby enhancing the toughness and stress corrosion resistance of steel. To achieve the invention's objectives, the content is controlled within the range of 0.02% to 0.05%.

[0035] The present invention relates to a method for manufacturing high-strength casing for deep oil and gas reservoir development, which is implemented according to the following steps: Example 1: Step 1: Add 30% scrap steel to 70% pre-smelted pig iron molten iron, then smelt it in a top-and-bottom blown converter. The molten steel is then vacuum degassed and stirred with argon to reduce the gas content, especially O, H, and N. The proportions of each element in the molten steel are adjusted through ladle refining, and Ca treatment is performed to modify inclusions, forming primary molten steel. The designed chemical composition of the molten steel is as follows (mass percentage): C: 0.27%; Si: 0.19%; Mn: 0.45%; P: 0.005%; S: 0.002%; Cr: 1.45%; Mo: 0.5%; Nb: 0.08%; V: 0.02%; Ti: 0.03%; Al: 0.035%; Ca: 0.001%; ​​N: 0.0003%; B: 0.001%; ​​RE: 0.05%; balance Fe, where RE is a mixture of 48% La, 42% Ce, and 10% Nd rare earth elements. .

[0036] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ330mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 3-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 25°C during pouring and to control the cooling temperature of the continuously cast billet to be greater than 980°C, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0037] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1250℃, the piercing temperature is 1200℃, and the final rolling temperature is 1050℃. After that, the blank is fed into a hot tension reducing mill to reduce the diameter to a billet of Φ139.7*12.7mm. A hot flying saw is used to cut the reduced billet into 11-meter-long billets. Subsequently, the cut billets are air-cooled to room temperature on a cooling bed. The hot rolling temperature of the hot tension reducing mill is 950℃, and the ratio of the cross-sectional area of ​​the steel pipe before and after hot tension reducing is 1.38. The residual heat temperature of the billet after hot tension reducing is 855℃.

[0038] Step 4: The cooled tube blank is heated to 900℃ using a multi-stand medium-frequency induction heating furnace and kept at a constant temperature for 5 minutes. Then, the entire tube body is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 735℃ using a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 8 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0039] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 870℃ for 35 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is reheated to 675℃ in the walking beam furnace and held for 80 minutes for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 590℃, and the outlet temperature is controlled at 520℃, ultimately yielding a Φ139.7*12.7mm specification 140ksi grade oil casing.

[0040] Example 2: Step 1: Add 20% scrap steel to the pre-melted 80% pig iron molten iron, and then smelt it in a top and bottom blowing converter. The smelted molten steel is then vacuum degassed and stirred with argon to reduce the gas content, especially the O, H and N content. The proportion of each element in the molten steel is adjusted by ladle refining, and Ca treatment is carried out to modify the inclusions, forming primary molten steel. The target chemical composition (mass percentage) for the molten steel is as follows: C: 0.30%; Si: 0.18%; Mn: 0.40%; P: 0.004%; S: 0.002%; Cr: 1.05%; Mo: 0.75%; Nb: 0.06%; V: 0.03%; Ti: 0.02%; Al: 0.015%; Ca: 0.001%; ​​N: 0.0002%; B: 0.0008%; RE: 0.02%; with the balance being Fe, where RE is a mixture of 52% La, 40% Ce, and 8% Nd rare earth elements.

[0041] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ400mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 2.7-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 29°C during pouring and to control the cooling temperature of the continuously cast billet to be greater than 970°C, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0042] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1260℃, the piercing temperature is 1210℃, and the final rolling temperature is 1070℃. After that, the blank is fed into a hot tension reducing mill to reduce the diameter to a billet of Φ177.8*12.68mm. A hot flying saw is used to cut the reduced billet to a length of 10.5 meters. Subsequently, the cut billet is air-cooled to room temperature on a cooling bed. The hot rolling temperature of the hot tension reducing mill is 980℃, and the cross-sectional area ratio of the steel pipe before and after hot tension reducing is 1.35. The residual heat temperature of the billet after hot tension reducing is 880℃.

[0043] Step 4: The hot-stretched tube blank is heated to 920℃ using a multi-stand medium-frequency induction heating furnace and kept at that temperature for 3 minutes. Then, the entire tube is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 700℃ in a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 10 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0044] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 880℃ for 40 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is sent back into the walking beam furnace for reheating to 690℃ and held for 65 minutes for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 600℃, and the outlet temperature is controlled at 540℃, ultimately yielding a finished 140ksi grade oil casing with a diameter of Φ177.8*12.68mm.

[0045] Example 3: Step 1: Add 25% scrap steel to the pre-melted 75% pig iron molten iron, and then smelt it in a top and bottom blowing converter. The molten steel is then vacuum degassed and stirred with argon to reduce the gas content. The proportions of various elements in the molten steel, especially the contents of O, H and N, are adjusted through ladle refining. At the same time, Ca treatment is carried out to modify inclusions, forming primary molten steel. The designed chemical composition of the molten steel is as follows (mass percentage): C: 0.28%; Si: 0.19%; Mn: 0.40%; P: 0.004%; S: 0.003%; Cr: 1.30%; Mo: 0.65%; Nb: 0.07%; V: 0.03%; Ti: 0.02%; Al: 0.015%; Ca: 0.002%; N: 0.0003%; B: 0.0009%; RE: 0.035%; balance Fe, where RE is a mixture of rare earth elements: 50% La, 38% Ce, and 12% Nd.

[0046] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ350mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 3.7-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 28°C during pouring and to control the cooling temperature of the continuously cast billet to be greater than 960°C, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0047] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1275℃, the piercing temperature is 1215℃, and the final rolling temperature is 1085℃. The blank tube is then fed into a hot tension reducing mill to reduce the diameter to a billet of Φ244.48*11.99mm. A hot flying saw is used to cut the reduced billet to a length of 11 meters. Subsequently, the cut billet is air-cooled to room temperature on a cooling bed. The hot rolling temperature of the hot tension reducing mill is 960℃, the cross-sectional area ratio of the steel pipe before and after hot tension reducing is 1.36, and the residual heat temperature of the billet after hot tension reducing is 890℃.

[0048] Step 4: The hot-stretched tube blank is heated to 930℃ using a multi-stand medium-frequency induction heating furnace and kept at that temperature for 3 minutes. Then, the entire tube body is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 750℃ in a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 5 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0049] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 880°C for 30 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is reheated to 650°C and held for 90 minutes in the walking beam furnace for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 560°C, and the outlet temperature is 480°C, ultimately yielding Φ244.48*11.99mm 140ksi grade oil casing.

[0050] Example 4: Step 1: Add 20% scrap steel to 80% pre-smelted pig iron molten iron, and then smelt it in a top-and-bottom blown converter. The molten steel is then vacuum degassed and stirred with argon to reduce the gas content, especially O, H, and N. The proportions of each element in the molten steel are adjusted through ladle refining, and Ca treatment is performed to modify inclusions, forming primary molten steel. The designed chemical composition of the molten steel is as follows (mass percentage): C: 0.29%; Si: 0.18%; Mn: 0.35%; P: 0.003%; S: 0.001%; ​​Cr: 1.00%; Mo: 0.50%; Nb: 0.05%; V: 0.02%; Ti: 0.05%; Al: 0.01%; Ca: 0.002%; N: 0.0001%; ​​B: 0.0008%; RE: 0.03%; the balance being Fe, where RE is a mixture of 50% La, 40% Ce, and 10% Nd rare earth elements.

[0051] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ330mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 2.6-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 30°C during pouring and to control the cooling temperature of the continuously cast billets to be greater than 950°C, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0052] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated steel pipe billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1260℃, the piercing temperature is 1215℃, and the final rolling temperature is 1075℃. The blank is then fed into a hot tension reducing mill to reduce the diameter to a billet of Φ139.7*10.54mm. A hot flying saw is used to cut the reduced diameter billet to a length of 11 meters. Subsequently, the cut billet is air-cooled to room temperature on a cooling bed. The hot rolling temperature of the hot tension reducing mill is 915℃, the cross-sectional area ratio of the steel pipe before and after hot tension reducing is 2.33, and the residual heat temperature of the billet after hot tension reducing is 850℃.

[0053] Step 4: The hot-stretched tube blank is heated to 905℃ using a multi-stand medium-frequency induction heating furnace and kept at that temperature for 2 minutes. Then, the entire tube is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 700℃ in a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 5 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0054] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 850°C for 30 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is reheated to 655°C in the walking beam furnace and held for 60 minutes for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 565°C, and the outlet temperature is controlled at 460°C, ultimately yielding Φ139.7*10.54mm 140ksi grade oil casing.

[0055] Example 5: Step 1: Add 30% scrap steel to 70% pre-smelted pig iron molten iron, and then smelt it in a top-and-bottom blown converter. The molten steel is then vacuum degassed and stirred with argon gas to reduce the gas content, especially O, H, and N. The proportions of each element in the molten steel are adjusted through ladle refining, and Ca treatment is performed to modify inclusions, forming primary molten steel. The designed chemical composition of the molten steel is as follows (mass percentage): C: 0.28%; Si: 0.17%; Mn: 0.40%; P: 0.003%; S: 0.002%; Cr: 1.18%; Mo: 0.80%; Nb: 0.06%; V: 0.02%; Ti: 0.04%; Al: 0.030%; Ca: 0.001%; ​​N: 0.0002%; B: 0.001%; ​​RE: 0.02%; balance Fe, where RE is a mixture of 48% La, 40% Ce, and 12% Nd rare earth elements.

[0056] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ350mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 3.7-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 26℃ during pouring and to control the cooling temperature of the continuously cast billet to be greater than 980℃, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0057] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1270℃, the piercing temperature is 1240℃, and the final rolling temperature is 1100℃. The blank tube is then fed into a hot tension reducing mill to reduce the diameter to a billet of Φ177.8*13.72mm. Then, a hot flying saw is used to cut the reduced billet to a length of 10 meters. Subsequently, the cut billets are air-cooled to room temperature on a cooling bed. The hot rolling inlet temperature of the hot tension reducing mill is 945℃, the cross-sectional area ratio of the steel pipe before and after hot tension reducing is 1.79, and the residual heat temperature of the billet after hot tension reducing is 865℃.

[0058] Step 4: The hot-stretched tube blank is heated to 925℃ using a multi-stand medium-frequency induction heating furnace and kept at that temperature for 3 minutes. Then, the entire tube is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 745℃ in a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 8 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0059] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 875°C for 40 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is reheated to 670°C in the walking beam furnace and held for 75 minutes for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 600°C, and the outlet temperature is 520°C, ultimately yielding Φ177.8*13.72mm 140ksi grade oil casing.

[0060] Example 6: Step 1: Add 25% scrap steel to the pre-smelted 75% pig iron molten iron, and then smelt it in a top-and-bottom blown converter. The molten steel is then vacuum degassed and stirred with argon gas to reduce the gas content, especially O, H, and N. The proportions of each element in the molten steel are adjusted through ladle refining, and Ca treatment is performed to modify inclusions, forming primary molten steel. The designed chemical composition of the molten steel is as follows (mass percentage): C: 0.27%; Si: 0.20%; Mn: 0.45%; P: 0.004%; S: 0.001%; ​​Cr: 1.49%; Mo: 0.50%; Nb: 0.08%; V: 0.03%; Ti: 0.01%; Al: 0.040%; Ca: 0.003%; N: 0.0003%; B: 0.0009%; RE: 0.04%; the balance being Fe, where RE is a mixture of 51% La, 41% Ce, and 8% Nd rare earth elements. .

[0061] Step 2: After the chemical composition and temperature of the molten steel meet the design requirements, the molten steel is continuously cast into φ400mm steel pipe billets under argon protection. After cooling, the continuous billets are cut into 3.2-meter lengths. During the continuous casting process, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel to be less than 30°C during pouring and to control the cooling temperature of the continuously cast billet to be greater than 965°C, so as to avoid secondary oxidation of the molten steel and cracking of the billet surface.

[0062] Step 3: The cut steel pipe billet is fed into an annular heating furnace for heating. A piercing mill is used to pierce the heated billet to form a rough tube. Then, a PQF three-roll continuous rolling mill is used to process the rough tube into a blank. The heating temperature of the annular heating furnace is 1300℃, the piercing temperature is 1250℃, and the final rolling temperature is 1150℃. The blank tube is then fed into a hot tension reducing mill to reduce the diameter to a billet of Φ244.48*13.84mm. A hot flying saw is used to cut the reduced billet to a length of 10 meters. Subsequently, the cut billets are air-cooled to room temperature on a cooling bed. The hot rolling temperature of the hot tension reducing mill is 975℃, the cross-sectional area ratio of the steel pipe before and after hot tension reducing is 1.43, and the residual heat temperature of the billet after hot tension reducing is 900℃.

[0063] Step 4: The hot-stretched tube blank is heated to 910℃ using a multi-stand medium-frequency induction heating furnace and kept at a constant temperature for 4 minutes. Then, the entire tube body is quenched using an internal spray and external quenching system. The quenched tube blank is then heated to 710℃ in a multi-stand medium-frequency induction heating furnace for tempering, with the time controlled at about 10 minutes. After that, the tempered tube blank is air-cooled to 300℃ on a cooling bed, and then cooled to room temperature in a water tank in preparation for the subsequent secondary tempering heat treatment.

[0064] Step 5: The heat-treated billet is fed into a walking beam furnace and heated to 880℃ for 45 minutes. Then, the entire billet is quenched using an internal spray and external quenching system. Next, the quenched billet is reheated to 700℃ in the walking beam furnace and held for 90 minutes for tempering. After exiting the furnace, the billet is hot-straightened using its residual heat. The inlet temperature of the straightener is 630℃, and the straightening temperature is controlled at 540℃, ultimately yielding Φ244.48*13.84mm 140ksi grade oil casing.

[0065] The performance of the casing blanks prepared in Examples 1 to 6 was tested, and the specific test results are as follows: Example 1: The casing prepared in Example 1 has an average yield strength Rt0.7 of 975 MPa, an average tensile strength Rm of 1068 MPa, an average elongation of 27.6%, an average transverse impact energy of 133 J at -10℃, a grain size of 10.5-11, a hardness range of 35-36 HRC, and a measured extrusion strength of 195.6 MPa for a 4-meter-long casing section, which is 22% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not break after 720 hours of being subjected to a stress of 841 MPa using the four-point bending method.

[0066] Example 2: In Example 2, the casing produced had an average yield strength Rt0.7 of 1015 MPa, an average tensile strength Rm of 1095 Pa, an average elongation of 25.6%, an average transverse impact energy of 127 J at -10℃, a grain size of 10.0–10.5, a hardness range of 35–36 HRC, and a measured extrusion strength of 141.4 MPa for a 4-meter-long casing section, which is 31% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not fracture after 720 hours of being subjected to a stress of 862 MPa using the four-point bending method.

[0067] Example 3: In Example 3, the casing produced had an average yield strength Rt0.7 of 970 MPa, an average tensile strength Rm of 1025 Pa, an average elongation of 28.0%, an average transverse impact energy of 122 J at -10℃, a grain size of 10.0–10.5, a hardness range of 35–36 HRC, and a measured extrusion strength of 58.6 MPa for a 4-meter-long casing section, which is 44.3% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not fracture after 720 hours of being subjected to a stress of 825 MPa using the four-point bending method.

[0068] Example 4: In Example 4, the casing produced had an average yield strength Rt0.7 of 1030 MPa, an average tensile strength Rm of 1090 Pa, an average elongation of 24.6%, an average transverse impact energy of 114 J at -10℃, a grain size of 10.0–10.5, a hardness range of 35–36 HRC, and a measured extrusion strength of 145.1 MPa for a 4-meter-long casing section, which is 20.4% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not fracture after 720 hours of being subjected to a stress of 876 MPa using the four-point bending method.

[0069] Example 5: In Example 5, the casing produced had an average yield strength Rt0.7 of 990 MPa, an average tensile strength Rm of 1065 Pa, an average elongation of 26.4%, an average transverse impact energy of 118 J at -10℃, a grain size of 10.0–10.5, a hardness range of 34–36 HRC, and a measured extrusion strength of 153.5 MPa for a 4-meter-long casing section, which is 21.8% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not fracture after 720 hours of being subjected to a stress of 842 MPa using the four-point bending method.

[0070] Example 6: In Example 6, the casing produced had an average yield strength Rt0.7 of 1010 MPa, an average tensile strength Rm of 1070 Pa, an average elongation of 25.1%, an average transverse impact energy of 117 J at -10℃, a grain size of 10.0–10.5, a hardness range of 34–36 HRC, and a measured extrusion strength of 77.8 MPa for a 4-meter-long casing section, which is 28.4% higher than the calculated value of API 5C3 standard. Under an H2S partial pressure of 0.1 MPa at 100℃, the casing did not fracture after 720 hours of being subjected to a stress of 859 MPa using the four-point bending method.

[0071] Tests have shown that the high-strength casing produced according to the component system and manufacturing method provided by this invention has good strength and toughness matching, excellent crush resistance and good stress corrosion resistance.

Claims

1. High-strength casing is used in the development of deep oil and gas reservoirs, characterized in that: The following raw materials are composed according to mass percentage. composition: C: 0.27%–0.30%, Si: 0%–0.2%, Mn: 0%–0.45%, Cr: 1.0%–1.5%, Mo: 0.5%–0.8%, Nb: 0.05%–0.08%, V: 0.02%–0.03%, Ti: 0.01%–0.05%, Al: 0.01%–0.04%, Ca: 0.001%–0.003%, N: 0%–0.0003%, B: 0.0008%–0.001%, RE: 0.02%–0.05%, with P content controlled to be no more than 0.008% and S content no more than 0.003%, the balance being Fe. The total content of all the above raw materials is 100%.

2. The method of using high-strength casing for deep oil and gas reservoir development according to claim 1, characterized in that, The RE is a mixed rare earth element composed of 48%–52% La, 38%–42% Ce and 8%–12% Nd, with the total content of each rare earth element being 100%.

3. The method of using high-strength casing for deep oil and gas reservoir development according to claim 1, characterized in that, The mass percentages of Cr, Mo, and B elements satisfy 2.7% ≤ Cr + Mo + 1500 × B ≤ 3.5%.

4. The method of using high-strength casing for deep oil and gas reservoir development according to claim 1, characterized in that, The mass percentages of Nb, V, and Ti elements satisfy Nb+V+Ti≥1.11%.

5. The method for preparing high-strength casing steel according to the composition described in claims 1 to 4, characterized in that, The specific steps are as follows: Step 1: Add scrap steel to the pre-smelted pig iron molten iron to form molten steel, wherein the pig iron molten iron accounts for 70% to 80% of the molten steel mass, and the scrap steel accounts for 20% to 30%; Step 2: The molten steel is subjected to ladle refining, vacuum degassing, argon stirring and inclusion modification treatment in sequence to obtain pure molten steel; Step 3: The pure molten steel is continuously cast into steel billets under the protection of argon gas.

6. The method for manufacturing high-strength casing using high-strength casing steel in deep oil and gas reservoir development according to claim 5, characterized in that, The specific steps are as follows: Step 1: The prepared molten steel is continuously cast into steel pipe billets under the protection of argon gas. After the steel pipe billets cool, the continuous steel pipe billets are cut into the required lengths. Step 2: Heat the cut steel pipe billet and use a piercing mill to pierce the heated steel pipe billet to form a rough tube. Then, use a continuous rolling mill to process the rough tube into a blank tube and reduce the diameter of the blank tube to the required specifications. Then, use a hot flying saw to cut the reduced diameter blank tube to the specified length. Finally, air cool the cut blank tube to room temperature on a cooling bed. Step 3: The cooled tube blank is heated in a medium-frequency induction heating furnace and kept at a constant temperature for a period of time. Then, the entire tube body is quenched using an internal spray and external quenching system. After quenching, the tube blank is tempered in a medium-frequency induction heating furnace. Then, the tempered tube blank is air-cooled to below 300°C on a cooling bed and then water-cooled to room temperature. Step 4: The heat-treated tube blank is sent into a walking beam furnace to heat it and hold it at that temperature for a period of time. Then, the entire tube body is quenched using an internal spray and external quenching system. After that, the quenched tube blank is sent into a walking beam furnace for tempering. After tempering, the residual heat from the tempering process is used for hot straightening to obtain the original tube blank. The temperature of the tube blank during straightening is controlled to be no less than 450℃.

7. The method for manufacturing high-strength casing for deep oil and gas reservoir development according to claim 5, characterized in that, In the continuous casting process described in step 2, a crystallizer with end electromagnetic stirring is used to control the superheat of the molten steel during pouring to be no more than 30°C, while the cooling temperature of the steel tube billet is no less than 950°C.

8. The method for manufacturing high-strength casing for deep oil and gas reservoir development according to claim 5, characterized in that, The heating temperature of the annular heating furnace in step 3 is 1250℃~1300℃, the piercing temperature of the piercing mill is 1200~1250℃, the continuous rolling mill is a PQF three-roll continuous rolling mill, the final rolling temperature during rolling is 1050~1150℃, the diameter reduction is carried out using a hot tension reduction mill, wherein the hot rolling temperature range of the hot tension reduction mill is 900℃~980℃, and the cross-sectional area ratio of the billet before and after hot tension reduction is not less than 1.3, and the residual heat temperature of the billet after hot tension reduction is not less than 850℃.

9. The method for manufacturing high-strength casing for deep oil and gas reservoir development according to claim 5, characterized in that, In step 4, before quenching, the medium-frequency induction heating furnace heats the cooled tube blank to 900℃~930℃, and the temperature is controlled for 2 minutes to 5 minutes. During tempering, the medium-frequency induction heating furnace heats the tube blank to 700℃~750℃, and the temperature is controlled for 5 minutes to 10 minutes.

10. The method for manufacturing high-strength casing for deep oil and gas reservoir development according to claim 5, characterized in that, In step 5, before quenching, the tube blank is heated to 850℃~880℃ in a walking beam furnace and held for 30 minutes~45 minutes. During tempering, the tube blank is heated to 650℃~700℃ in a walking beam furnace and held for 60 minutes~90 minutes.