Preparation method of 125ksi high-strength anti-fatigue thermal recovery casing in supercritical steam environment

Abstract

The invention discloses a preparation method of a 125ksi high-strength anti-fatigue thermal recovery casing in a supercritical steam environment, and belongs to the technical field of material metallurgy. The steel comprises the following chemical components in percentage by mass: 0.20-0.27% of C, 0.17-0.35% of Si, 0.35-0.50% of Mn, 0.005-0.040% of Al, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 0.90-1.30% of Cr, 0.4-0.7% of Mo, 0.05-0.07% of V, less than or equal to 0.20% of Cu, less than or equal to 0.25% of Ni and the balance of Fe and trace impurities, and the total mass fraction is 100%. The preparation process comprises the following steps: smelting; a rolling process; and the heat treatment process comprises quenching and tempering. The 125ksi high-strength anti-fatigue thermal recovery casing pipe disclosed by the invention has stable mechanical properties and good toughness in a supercritical steam environment at 350 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of materials metallurgy technology, and in particular relates to a method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment. Background Technology

[0002] Due to its high viscosity and poor fluidity, heavy oil requires thermal extraction technologies (such as steam injection, steam-driven processes, and SAGD) for economical development. These processes involve injecting high-temperature (200-350℃) and high-pressure (>16MPa) steam into the formation, posing multiple challenges to the downhole casing, including thermal stress cycles, creep deformation, and hydrogen sulfide / carbon dioxide corrosion. Traditional casing materials (N80, P110) are prone to strength degradation and sealing failure under prolonged high temperatures, and their resistance to crushing is insufficient. Currently, domestic heavy oil thermal recovery typically uses 80ksi, 90ksi, 100ksi, and 110ksi steel grades. With the commissioning of my country's first large-scale extra-heavy oil thermal recovery field and the development of heavy oil into deeper formations, heavy oil thermal recovery places higher demands on high-grade, thermally stable, strong, and tough pipe materials.

[0003] This application utilizes a rational Cr-Mo-V alloy composition, resulting in casing that exhibits both high strength and good toughness. The yield strength at 350℃ decreases by less than 20% compared to its yield strength at room temperature, demonstrating excellent thermal stability and stable high-temperature mechanical properties. This allows the material to withstand heavy oil thermal recovery gas injection operations in a 350℃ supercritical steam environment. Furthermore, the material exhibits good dimensional stability and strong resistance to deformation.

[0004] After searching, three patent documents were found to be most relevant to the technology of this invention, the details of which are described below:

[0005] A search revealed a similar background technology: "A method for manufacturing 125ksi grade heavy oil thermal recovery well steel pipe" (patent application number: 202410082857.6). The differences between this invention and the present invention are: in terms of composition design, this invention adopts a Cr-Mo-V microalloying design concept, while the searched similar patent adopts a Cr-Mo-trace Ti-trace Nb-trace B design concept, resulting in different chemical compositions for the designed steel grade; furthermore, the heat treatment regimes are also different. This invention is mainly applied in a supercritical steam environment, focusing on the design and development of technical indicators such as high-temperature tensile strength, elastic modulus, and coefficient of linear expansion, which differs from the high crush resistance technical requirements of the searched patent.

[0006] A search revealed a similar patent: "A Specialized Oil Casing for Rare Earth Heavy Oil Thermal Recovery Wells and Its Production Method" (Patent Application No.: 201310409200.8). The differences between this patent and the one in this invention are: In terms of composition design, this invention adopts a Cr-Mo-V microalloying design concept, while the similar patent uses a Cr-Mo-BV design concept, resulting in different chemical compositions of the designed steel. Furthermore, the heat treatment process is also different. This patent has a yield strength of 800–900 MPa, a tensile strength ≥880 MPa, and a steel grade of 115 ksi. At 350℃, the yield strength is ≥700 MPa, and the average linear thermal expansion coefficient is ≤16×10⁻⁶, which differs from the performance indicators of this patent.

[0007] A search revealed similar background technologies, including: "Seamless steel pipes for high-temperature 95ksi grade fire-driven heavy oil thermal recovery and manufacturing method (patent application number: 201911049497.5)". The differences between this invention and the present invention are: in terms of composition design, the present invention adopts a Cr-Mo-V microalloying design concept, while the searched similar patent adopts a Cr-Mo-Ni-VW-Ti design concept, resulting in different chemical composition designs; the steel grade is 95ksi, and the technical requirements are different; furthermore, the production processes are different, with the searched patent mainly used for fire-driven heavy oil thermal recovery, while this invention is used for heavy oil thermal recovery in a critical steam environment. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam conditions. After heat treatment and tempering, the material exhibits a yield strength of 862MPa–1068MPa, tensile strength ≥931MPa, elongation ≥19%, full-size transverse impact strength ≥80J at 0℃, and full-size longitudinal impact strength ≥120J at 0℃; at 350℃, the yield strength is ≥830MPa, and the axial average linear expansion coefficient should be ≤1.40×10⁻⁶. -5 The material's mechanical properties change by ≤20% at both room temperature and 350℃, with an elastic modulus ≤190GPa at 350℃. The 125ksi high-strength, fatigue-resistant thermal recovery casing exhibits stable mechanical properties and good toughness under supercritical steam conditions at 350℃. It meets the requirements for seamless casing technology in heavy oil thermal recovery under supercritical steam environments.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] This invention discloses a method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam conditions. The 125ksi steel-grade heavy oil thermal recovery casing has the following chemical composition by mass percentage: C 0.20–0.27%, Si 0.17–0.35%, Mn 0.35–0.50%, Al 0.005–0.040%, P ≤ 0.015%, S ≤ 0.003%, Cr 0.90–1.30%, Mo 0.4–0.7%, V 0.05–0.07%, Cu ≤ 0.20%, and Ni ≤ 0.25%, with the remainder being Fe and trace impurities, totaling 100% by mass. The preparation process includes:

[0011] Smelting process: Hot metal pretreatment → Converter smelting → LF refining → VD degassing → Round billet continuous casting; wherein:

[0012] The incoming molten iron undergoes pretreatment, employing the KR stirring method for desulfurization, removing over 90% of the sulfur content, resulting in a sulfur content as low as 0.020% for the converter steelmaking process. Simultaneously, oxygen is blown from the converter top, while nitrogen and argon are blown into the bottom for re-blowing and stirring, achieving smelting goals such as dephosphorization, desulfurization, suitable tapping carbon, tapping temperature, and low oxygen content. A single-slag process is used, with the final slag basicity controlled at 3.0. The endpoint control targets are: P≤0.012% and S≤0.004%. During the LF ladle refining process, an appropriate amount of calcium wire is fed in, followed by soft blowing for 10-15 minutes. The LF ladle refining process completes metallurgical functions such as deoxidation, desulfurization, composition control, temperature control, and inclusion control, with a soft blowing time of 8-10 minutes. VD Vacuum degree ≤0.10KPa, deep vacuum time 12min~15min, further reduce inclusions and oxygen content in steel through soft blowing and killing. After treatment, [S] can be controlled to 0.003%, hydrogen content as low as 2ppm, [O] content as low as 20ppm, [N] content as low as 60ppm, inclusions ∑I=A+B+C+D less than 6.0 grade, individual items less than 1.5 grade; the continuous casting process adopts protective casting, electromagnetic stirring and end electromagnetic stirring process, the superheat of molten steel is controlled within 15~30℃, constant casting speed control process is adopted, the starting casting speed is 0.5m / s, the horizontal fixed casting speed is controlled at 1.4~1.7m / min, which can improve the quality of continuous casting billet, and the billet is stacked for slow cooling;

[0013] Rolling process: Round billet → sawing → heating → piercing → tube rolling → tension reduction → cooling bed cooling; where:

[0014] The billet heating temperature is 1200℃~1260℃; the round billet piercing temperature is 1220℃~1270℃; the steel pipe rolling temperature is 1050℃~1150℃; the final rolling temperature is ≥800℃; a descaling device is installed before the continuous rolling entrance, and the surface iron oxide scale of the incoming tube needs to be cleaned.

[0015] Heat treatment process: quenching + tempering; (1) The quenching temperature is 870℃-890℃. The seamless steel pipe is raised to the quenching temperature at a rate of 35℃ / min and held for 30min-45min. After the holding time is reached, the oil pipe is quickly taken out of the furnace and then water-cooled. The internal spray flow rate of the cooling water is controlled at 580±50m3 / h, the external spray flow rate is 1600±50m3 / h, and the external spray and internal spray time is 10-12s. The pipe body temperature after cooling should be lower than 100℃ to ensure that the oil pipe can be cooled. (1) Obtain more than 50% martensite structure, and it is not easy to have quenching cracks; (2) Open all the burners of the tempering furnace and use pulse control burners to make the flame burn completely. When the temperature inside the furnace rises to 400℃, put the seamless steel pipe after quenching into the tempering furnace to ensure the uniformity of the tempering temperature of the pipe body. Then raise the seamless steel pipe to 580℃~630℃ at a speed of 15℃ / min. Start timing after the seamless steel pipe reaches the temperature. The holding time is 30~45min.

[0016] The steel pipe, with its temperature reduced to between 450℃ and 530℃, is fed into a roller straightener for temperature straightening. Then, the steel pipe is fed into a walking beam cooling bed for natural cooling. Finally, the steel pipe is fed into a gang saw for cut to length.

[0017] Furthermore, the wall thickness is ≥6mm, and the dephosphorization water pressure ranges from 10 to 16MPa.

[0018] Furthermore, the chemical composition of the 125ksi grade heavy oil thermal recovery casing, by mass percentage, is as follows: C 0.25%, Si 0.28%, Mn 0.43%, Al 0.018%, P 0.008%, S 0.003%, Cr 1.10%, Mo 0.58%, V 0.056%, Cu 0.005%, and Ni 0.043%, with the remainder being Fe and trace impurities, totaling 100% by mass.

[0019] Furthermore, the chemical composition of the 125ksi grade heavy oil thermal recovery casing, by mass percentage, is as follows: C 0.23%, Si 0.26%, Mn 0.37%, Al 0.023%, P 0.012%, S 0.002%, Cr 1.13%, Mo 0.52%, V 0.062%, Cu 0.008%, and Ni 0.062%, with the remainder being Fe and trace impurities, totaling 100% by mass.

[0020] Furthermore, the chemical composition of the 125ksi grade heavy oil thermal recovery casing, by mass percentage, is as follows: C 0.24%, Si 0.27%, Mn 0.40%, Al 0.021%, P 0.010%, S 0.003%, Cr 1.09%, Mo 0.52%, V 0.059%, Cu 0.006%, and Ni 0.058%, with the remainder being Fe and trace impurities, totaling 100% by mass.

[0021] Furthermore, the chemical composition of the 125ksi grade heavy oil thermal recovery casing, by mass percentage, is as follows: C 0.25%, Si 0.26%, Mn 0.42%, Al 0.026%, P 0.009%, S 0.002%, Cr 1.12%, Mo 0.53%, V 0.061%, Cu 0.008%, and Ni 0.083%, with the remainder being Fe and trace impurities, totaling 100% by mass.

[0022] Furthermore, after heat treatment and tempering, the mechanical properties should meet the following requirements: yield strength 862MPa~1068MPa, tensile strength ≥931MPa, elongation ≥19%, full-size transverse impact ≥80J at 0℃, full-size longitudinal impact ≥120J at 0℃; yield strength at 350℃ ≥830MPa, and axial average linear expansion coefficient ≤1.40×10⁻⁶. -5 The material's mechanical properties change by ≤20% at room temperature and 350℃, and its elastic modulus at 350℃ is ≤190GPa. The 125ksi high-strength fatigue-resistant thermal recovery casing has stable mechanical properties and good toughness in a 350℃ supercritical steam environment.

[0023] This material primarily employs a Cr-Mo-V rare-earth microalloying design. C, the main carbide-forming element, ensures the material's strength; however, excessive C content reduces impact toughness, thus the C content is controlled between 0.20% and 0.27%. Mn plays a role in solid solution strengthening while also improving the steel's toughness; it is a weak carbide element. P and S are harmful elements; low P content ensures stable high toughness, while low S content reduces the formation of MnS inclusions, preventing chemical segregation and grain boundary weakening. Cr can improve… The steel has good hardenability and a certain degree of tempering resistance; Mo can improve the hot strength of steel by strengthening α solid solution. Considering the high cost of molybdenum and to fully utilize its effective role, the composition is controlled at 0.4-0.7%; V is a grain-refining element that improves the strength and toughness of steel and reduces its overheating sensitivity. The precipitation strengthening effect of V in Cr-Mo steel is further enhanced, and the solid solution strengthening effect of Mo is more significant, which is beneficial to improving the heat resistance of steel; V is beneficial to reducing the coefficient of thermal expansion of steel, so the vanadium content is controlled at 0.05-0.07%.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] 1. A high-strength, fatigue-resistant thermal recovery casing with 125 ksi in a supercritical steam environment, which, through Cr-Mo-V rare earth microalloying, gives the material 125 ksi mechanical properties while also providing high toughness, and exhibits stable mechanical properties, thermal stability, and heat resistance in a 350℃ supercritical steam environment.

[0026] 2. The material exhibits stable mechanical properties, thermal stability, and heat resistance in a supercritical steam environment at 350℃, demonstrating excellent high-strength fatigue resistance. Detailed Implementation

[0027] The following are specific embodiments of the present invention.

[0028] The steel smelting process is as follows: hot metal pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting. The chemical composition of each example was analyzed, and the chemical composition is shown in Table 1.

[0029] Table 1. Percentage of chemical composition (by weight %) for each example

[0030]

[0031] The steel rolling process includes round billet → sawing → heating → piercing → tube rolling → tension reduction → cooling on a cooling bed. The billet heating temperature is 1220℃~1270℃. At this temperature, all alloying elements can be completely dissolved and diffused uniformly without overheating the billet. Controlling the maximum billet heating temperature to 1260℃ can reduce grain coarsening in the cast billet. The piercing temperature of the round billet is 1220℃~1270℃, and the tube rolling temperature is 1050℃~1150℃. Within this temperature range, the steel has good plasticity, good piercing bite, and is easy to deform, ensuring the quality of the inner and outer surfaces of the steel tube. The final rolling temperature is guaranteed to be ≥800℃. A high final rolling temperature is equivalent to normalizing the steel tube, which can uniformly refine the microstructure. The specific rolling processes of each embodiment are shown in Table 2.

[0032] Table 2 Examples of Rolling Processes

[0033]

[0034] The chemical and mechanical properties test results of each embodiment are shown in Table 3. The material has high yield strength and tensile strength, as well as high plasticity, and has excellent comprehensive mechanical properties.

[0035] Table 3. Mechanical performance test results for each embodiment.

[0036]

[0037] The test results of non-metallic inclusions and grain size in each embodiment are shown in Table 5. The steel has low inclusion content and high material purity.

[0038] Table 4. Test results of non-metallic inclusions and grain size in each embodiment.

[0039]

[0040]

[0041] The test results of the axial average linear expansion coefficient of each embodiment at 50℃~350℃ are shown in Table 5. The experimental linear expansion coefficient of each embodiment is ≤1.4×10 -5 / ℃. The low coefficient of linear expansion indicates that the casing exhibits good dimensional stability and strong resistance to deformation in a supercritical steam environment at 350℃.

[0042] Table 5. Test results of axial average linear expansion coefficient from 50℃ to 350℃

[0043]

[0044] The high-temperature mechanical property test results of each embodiment at 350℃ are shown in Table 6. The high-temperature mechanical properties of the material at 350℃ meet the key high-temperature resistance requirements of 25ksi steel grade thermal recovery well pipe. The yield strength at 350℃ decreases by less than 20% compared to the yield strength at room temperature, indicating that the material has good thermal stability and stable high-temperature mechanical properties, and can withstand the working scenarios of heavy oil thermal recovery gas injection in a 350℃ supercritical steam environment.

[0045] Table 6. Test results of mechanical properties at 350℃

[0046]

[0047]

[0048] The test results above show that the 125ksi high-strength fatigue-resistant thermal recovery casing and its preparation method under supercritical steam environment of the present invention exhibit excellent mechanical properties after heat treatment and tempering. While possessing high strength, the material also maintains good toughness. The yield strength at 350℃ decreases by less than 20% compared to the yield strength at room temperature, indicating good thermal stability and stable high-temperature mechanical properties. It can withstand the working conditions of heavy oil thermal recovery gas injection in a 350℃ supercritical steam environment. Simultaneously, the material exhibits good dimensional stability and strong resistance to deformation.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment, characterized in that, The chemical composition (mass percentage) of the 125ksi grade heavy oil thermal recovery casing is as follows: C 0.20–0.27%, Si 0.17–0.35%, Mn 0.35–0.50%, Al 0.005–0.040%, P≤0.015%, S≤0.003%, Cr 0.90–1.30%, Mo 0.4–0.7%, V 0.05–0.07%, Cu≤0.20%, and Ni≤0.25%, with the remainder being Fe and trace impurities, totaling 100% by mass. Its preparation process includes: Smelting process: Hot metal pretreatment → Converter smelting → LF refining → VD degassing → Round billet continuous casting; wherein: The incoming molten iron undergoes pretreatment, employing the KR stirring method for desulfurization, removing over 90% of the sulfur content, resulting in a sulfur content as low as 0.020% for the converter steelmaking process. Simultaneously, oxygen is blown from the converter top, while nitrogen and argon are blown into the bottom for re-blowing and stirring, achieving smelting goals such as dephosphorization, desulfurization, suitable tapping carbon, tapping temperature, and low oxygen content. A single-slag process is used, with the final slag basicity controlled at 3.

0. The endpoint control targets are: P≤0.012% and S≤0.004%. During the LF ladle refining process, an appropriate amount of calcium wire is fed in, followed by soft blowing for 10-15 minutes. The LF ladle refining process completes metallurgical functions such as deoxidation, desulfurization, composition control, temperature control, and inclusion control, with a soft blowing time of 8-10 minutes. VD Vacuum degree ≤0.10KPa, deep vacuum time 12min~15min, further reduce inclusions and oxygen content in steel through soft blowing and killing. After treatment, [S] can be controlled to 0.003%, hydrogen content as low as 2ppm, [O] content as low as 20ppm, [N] content as low as 60ppm, inclusions ∑I=A+B+C+D less than 6.0 grade, individual items less than 1.5 grade; the continuous casting process adopts protective casting, electromagnetic stirring and end electromagnetic stirring process, the superheat of molten steel is controlled within 15~30℃, constant casting speed control process is adopted, the starting casting speed is 0.5m / s, the horizontal fixed casting speed is controlled at 1.4~1.7m / min, which can improve the quality of continuous casting billet, and the billet is stacked for slow cooling; Rolling process: Round billet → sawing → heating → piercing → tube rolling → tension reduction → cooling bed cooling; where: The billet heating temperature is 1200℃~1260℃; the round billet piercing temperature is 1220℃~1270℃; the steel pipe rolling temperature is 1050℃~1150℃; the final rolling temperature is ≥800℃; a descaling device is installed before the continuous rolling entrance, and the surface iron oxide scale of the incoming tube needs to be cleaned. Heat treatment process: quenching + tempering; (1) The quenching temperature is 870℃-890℃. The seamless steel pipe is raised to the quenching temperature at a rate of 35℃ / min and held for 30min-45min. After the holding time is reached, the oil pipe is quickly taken out of the furnace and then water-cooled. The internal spray flow rate of the cooling water is controlled at 580±50m3 / h, the external spray flow rate is 1600±50m3 / h, and the external spray and internal spray time is 10-12s. The pipe body temperature after cooling should be lower than 100℃ to ensure that the oil pipe can be cooled. (1) Obtain more than 50% martensite structure, and it is not easy to have quenching cracks; (2) Open all the burners of the tempering furnace and use pulse control burners to make the flame burn completely. When the temperature inside the furnace rises to 400℃, put the seamless steel pipe after quenching into the tempering furnace to ensure the uniformity of the tempering temperature of the pipe body. Then raise the seamless steel pipe to 580℃~630℃ at a speed of 15℃ / min. Start timing after the seamless steel pipe reaches the temperature. The holding time is 30~45min. The steel pipe, with its temperature reduced to between 450℃ and 530℃, is fed into a roller straightener for temperature straightening. Then, the steel pipe is fed into a walking beam cooling bed for natural cooling. Finally, the steel pipe is fed into a gang saw for cut to length.

2. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, The wall thickness is ≥6mm, and the dephosphorization water pressure range is 10~16MPa.

3. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, The chemical composition (mass percentage) of the 125ksi grade heavy oil thermal recovery casing is as follows: C 0.25%, Si 0.28%, Mn 0.43%, Al 0.018%, P 0.008%, S 0.003%, Cr 1.10%, Mo 0.58%, V 0.056%, Cu 0.005%, and Ni 0.043%, with the remainder being Fe and trace impurities, totaling 100% by mass.

4. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, The chemical composition (mass percentage) of the 125ksi grade heavy oil thermal recovery casing is as follows: C 0.23%, Si 0.26%, Mn 0.37%, Al 0.023%, P 0.012%, S 0.002%, Cr 1.13%, Mo 0.52%, V 0.062%, Cu 0.008%, and Ni 0.062%, with the remainder being Fe and trace impurities, totaling 100% by mass.

5. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, The chemical composition (mass percentage) of the 125ksi grade heavy oil thermal recovery casing is as follows: C 0.24%, Si 0.27%, Mn 0.40%, Al 0.021%, P 0.010%, S 0.003%, Cr 1.09%, Mo 0.52%, V 0.059%, Cu 0.006%, and Ni 0.058%, with the remainder being Fe and trace impurities, totaling 100% by mass.

6. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, The chemical composition (mass percentage) of the 125ksi grade heavy oil thermal recovery casing is as follows: C 0.25%, Si 0.26%, Mn 0.42%, Al 0.026%, P 0.009%, S 0.002%, Cr 1.12%, Mo 0.53%, V 0.061%, Cu 0.008%, and Ni 0.083%, with the remainder being Fe and trace impurities, totaling 100% by mass.

7. The method for preparing a 125ksi high-strength fatigue-resistant thermal recovery casing under supercritical steam environment according to claim 1, characterized in that, After heat treatment and tempering, the mechanical properties meet the following requirements: yield strength 862MPa~1068MPa, tensile strength ≥931MPa, elongation ≥19%, full-size transverse impact ≥80J at 0℃, full-size longitudinal impact ≥120J at 0℃; yield strength at 350℃ ≥830MPa, and axial average linear expansion coefficient ≤1.40×10 -5 The material's mechanical properties change by ≤20% at room temperature and 350℃, and its elastic modulus at 350℃ is ≤190GPa. The 125ksi high-strength fatigue-resistant thermal recovery casing has stable mechanical properties and good toughness in a 350℃ supercritical steam environment.

Images