High-strength heat-resistant casing for heavy oil development and its manufacturing method

Abstract

The present disclosure provides a heat-resistant casing for heavy oil development, which contains the following weight percent: C: 0.08-0.19%, Si: 0.1-0.4%, Mn: 1.0-1.8%, Cr: 1-2%, Mo: 0.1-0.4%, W: 0.1-0.5%, V: 0.01-0.15%, Al: 0.01-0.05%, N: 0.008% or less, Fe and unavoidable impurities, and the heat-resistant casing does not contain Ti and Nb. The oil casing of the present disclosure has good high-temperature strength and creep resistance, and meets the requirements for use of the casing in the high-temperature environment of heavy oil development, particularly the requirements for the performance of the casing in heavy oil development using steam flooding. The present invention further provides a method for manufacturing the heat-resistant casing for heavy oil development.

Description

[Technical Field]

[0001] The present disclosure relates to a heat-resistant casing, particularly a high-strength heat-resistant casing for heavy oil development, and a method for manufacturing the same. [Background technology]

[0002] As the oil industry continues to develop and petroleum consumption continues to increase, heavy oil has become a major production source for many domestic and international oil companies. Heavy oil recovery methods are typically divided into two categories: steam soaking and steam flooding. Water steam soaking refers to a heavy oil recovery method that combines three processes: steam injection, soaking, and production. Steam flooding involves continuously injecting steam through a steam injection well with a suitable well pattern to form a steam zone around the injection well. The injected steam heats the underground crude oil, which is then pumped to surrounding production wells for production. Before the 1990s, heavy oil development in China mainly relied on steam soaking wells. However, heavy oil development using steam soaking recovery technology in the domestic petroleum industry has generally entered a high-cycle and subsequent recovery phase. The formation pressure has decreased, leading to a deterioration in development effectiveness and a decline in production. By adopting the steam flooding method for heavy oil development, it can effectively improve the yield in the heavy oil field that has entered the high-cycle recovery stage, and can also exert outstanding effects on heavy oil production.

[0003] Additionally, the shift in heavy oil recovery methods from steam soaking wells to steam flooding wells has increased the demand for heat-resistant casings. Unlike the low-temperature operating conditions of typical oil and gas development, steam flooding heavy oil development is characterized by temperatures of 350°C, steam pressures of 17 MPa, and long-term use. Casings undergo cyclic stress changes caused by temperature increases and decreases during long-term use, and creep deformation occurs in high-temperature environments. To address the problem of casing loss due to insufficient mechanical properties or material creep in high-temperature environments, heat-resistant casings must have good high-temperature mechanical properties and creep resistance.

[0004] China Patent Application Publication No. 200810204727.6 discloses a steel for heat-resistant casings having the following composition by weight: 0.2-0.30% C, 0.10-0.3% Si, 0.4-1.0% Mn, 0.5-1.5% Cr, 0.1-0.5% W, with the balance being Fe and unavoidable impurities. The method for producing the steel for heat-resistant casings includes the following steps: smelting, casting, and hot rolling the steel according to the composition to form a seamless steel pipe; heating the seamless steel pipe to a temperature range of 820°C to 920°C and holding it for 30-60 minutes to fully austenitize it; quenching; and tempering the quenched pipe by uniformly heating it to a temperature range of 580°C to 720°C and holding it for 30-90 minutes.

[0005] China Patent Application Publication No. 201710469926.9 discloses a seamless steel pipe, its manufacturing method, and a heavy oil heat recovery casing. The seamless steel pipe contains, by weight percent, 0.20-0.30% C, 0.20-0.60% Si, 0.50-1.20% Mn, P≦0.015%, S≦0.003%, Cr: 0.80-1.30%, Mo: 0.30-0.70%, Ti: 0.005-0.02%, Ni≦0.10%, Al: 0.01-0.05%, and the remainder being iron (Fe) and unavoidable impurities. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure aims to provide a high-strength, heat-resistant casing for heavy oil development and a method for manufacturing the same. The oil casing of the present disclosure has good high-temperature strength and creep resistance, and meets the requirements for casing performance in the high-temperature environment of heavy oil development, particularly in heavy oil development using steam flooding.

[0007] The ambient temperature of heavy oil development is relatively high, generally reaching 350°C, so the casing must have good high-temperature mechanical properties and creep resistance to prevent casing loss due to insufficient mechanical properties or material creep in high-temperature environments. The general design concept is to add alloying elements such as Cr, Mo, and W, which bring about solid-solution strengthening, to improve the bonding strength between matrix atoms, thereby increasing the strength of the material in high-temperature environments and forming a microstructure favorable for creep resistance.

[0008] Steel grain size also has a significant impact on creep resistance. Continued creep allows for more grain boundary sliding and diffusion, which can lead to the initiation and growth of voids and cracks along the grain boundaries, ultimately resulting in material failure. Compared to fine-grained materials, coarse-grained materials have a smaller total grain boundary area, less deformation due to grain boundary sliding, a lower creep rate, and a higher creep rupture limit. Therefore, increasing the grain size can improve the material's creep resistance. However, conventional heat-resistant casings typically use an offline quenching and tempering process, where the casing is cooled to room temperature after hot rolling and then re-austenitized in a quenching furnace, followed by quenching and tempering. This heat treatment process significantly refines the grain size, resulting in reduced creep resistance. [Means for solving the problem]

[0009] In an embodiment of the present disclosure, an online controlled cooling technology is adopted, which differs from conventional techniques. The casing is quenched online directly after hot rolling, eliminating the offline quenching process. On the other hand, when the casing is quenched online using the residual heat from hot rolling, the original coarse grains from hot rolling are preserved, thereby solving the grain refinement problem that occurs when quenching an austenitized casing in a conventional offline heat treatment process, and improving the creep resistance of the material. However, when the casing is quenched directly after hot rolling, the grain distortion stores high energy, making it prone to cracking during the quenching process. Therefore, in an embodiment of the present disclosure, the types and amounts of alloying elements such as C, Mn, Cr, Mo, and W in the heat-resistant casing are optimized in combination with the characteristics of the online controlled cooling process to prevent cracking and stress concentration in the tube, ensuring safe production and stable quality. Because the precipitation of alloying elements such as Ti and Nb leads to grain refinement, Ti and Nb are not added in this application.

[0010] A first aspect of the present disclosure provides a heat-resistant casing for heavy oil development containing, in weight percent, the following elements: C: 0.08-0.19%, Si: 0.1-0.4%, Mn: 1.0-1.8%, Cr: 1-2%, Mo: 0.1-0.4%, W: 0.1-0.5%, V: 0.01-0.15%, Al: 0.01-0.05%, N≦0.008%, Fe and unavoidable impurities, but not containing Ti and Nb.

[0011] Another aspect of the present disclosure provides a heat-resistant casing for heavy oil development containing, in weight percent, the following elements: C: 0.08-0.19%, Si: 0.1-0.4%, Mn: 1.0-1.8%, Cr: 1-2%, Mo: 0.1-0.4%, W: 0.1-0.5%, V: 0.01-0.15%, Al: 0.01-0.05%, N≦0.008%, with the balance being Fe and unavoidable impurities.

[0012] The elements in the heat-resistant casing preferably further satisfy the following: C: 0.1 to 0.16%, Si: 0.15 to 0.35%, Mn: 1 to 1.6%, Cr: 1 to 1.5%, Mo: 0.15 to 0.4%, W: 0.2 to 0.5%, V: 0.05 to 0.12%, and Al: 0.015 to 0.035%.

[0013] The unavoidable impurities include P and S, and it is preferable that P≦0.015% and S≦0.005% by weight are satisfied.

[0014] The unavoidable impurities preferably further satisfy P≦0.013% and S≦0.003%.

[0015] The design concepts of each chemical element in the high-strength heat-resistant casing provided by the present disclosure are as follows:

[0016] C: C is an element that forms carbides and can increase the strength of steel. If the C content is less than 0.08 wt%, the hardenability of the steel decreases, resulting in a decrease in the strength and toughness of the steel. On the other hand, if the C content exceeds 0.19 wt%, the steel becomes more susceptible to quench cracking, making it more likely to occur during online quenching. In order to meet the high strength requirements of oil casing, the technical solution of the present disclosure requires that the C content be controlled to 0.08-0.19 wt%.

[0017] Si: Si dissolves in ferrite and can increase the yield strength of steel, but the Si content should not be too high. If the Si content is too high, the workability and toughness of the steel will deteriorate, and if the Si content is less than 0.1 wt%, the oil casing will be prone to oxidation, so the Si content should be controlled to 0.10 to 0.40 wt%.

[0018] Mn: Mn is an austenite-forming element and improves the high-temperature mechanical properties of steel through its solid-solution strengthening effect in steel. In the steel grade system for the high-strength heat-resistant casing according to the present disclosure, if the Mn content is less than 1 wt%, the hardenability of the steel is significantly reduced, the solid-solution strengthening effect is weakened, and high-temperature strength is reduced. However, if the Mn content exceeds 1.8 wt%, compositional segregation occurs, making quench cracking more likely to occur. Therefore, in the technical solution of the present disclosure, the Mn content is controlled to 1 to 1.8 wt%.

[0019] V: V is a typical precipitation strengthening element, which can compensate for the strength loss caused by the reduction of carbon. If the V content is less than 0.01%, the strengthening effect is not obvious, and if the V content exceeds 0.15%, coarse V(CN) is easily formed, which reduces toughness.

[0020] Mo: Mo mainly improves the strength and tempering stability of steel through carbide and solid solution strengthening. In the technical solution of the present disclosure, if the Mo content exceeds 0.4 wt%, quench cracking is likely to occur. If the Mo content is below 0.1 wt%, the strength of the oil casing cannot meet the high strength requirements. Based on this, in the present disclosure, the Mo content is controlled to be 0.1 to 0.4 wt%.

[0021] Cr: Cr is a strong element for improving hardenability and a strong carbide-forming element, which has obvious solid solution strengthening and precipitation strengthening effects in steel, and can improve the high-temperature mechanical properties of steel. However, if the Cr content exceeds 2%, coarse M 23 C6 carbide is likely to precipitate at grain boundaries, reducing toughness and making quench cracking more likely. If the Cr content is less than 1%, the high-temperature mechanical properties are insufficient.

[0022] W: Solid solution strengthening by W increases the bonding force between matrix atoms and can improve the strength of the material in high-temperature environments. If the weight percentage of W is greater than 0.5 wt%, the strengthening effect is not obvious, resulting in waste of alloy. If the W content is less than 0.1 wt%, the high-temperature mechanical properties of the steel cannot be improved. In this disclosure, it is desirable to control the W content to be 0.1-0.5 wt%.

[0023] Al: Al is a good deoxidizing and nitrogen fixing element, and the Al content is suitably 0.01 to 0.05%.

[0024] N: N is an impurity, and its content is reduced as much as possible depending on the process conditions.

[0025] A second aspect of the present disclosure provides a method for producing a pharmaceutical composition comprising the steps of: Smelting process: A process of blending the chemical components of the high-strength heat-resistant casing for heavy oil development described above to obtain raw materials, and smelting the raw materials to obtain billets; Continuous casting step: a step of continuously casting the billet to obtain a round billet; Piercing step: a step of heating and piercing the round billet; Rolling step: a step of rolling the perforated round billet; Sizing step: a step of sizing the final rolled round billet to obtain a casing; a controlled cooling step: controlling the temperature of the casing body before cooling to 850-900°C, and using an online controlled cooling device to spray-cool the outer surface of the casing with water, controlling the amount of cooling water so that the cooling rate is 20-40°C / sec when the inner wall temperature of the casing body is 500-900°C, and the cooling rate is 30-50°C / sec when the inner wall temperature of the casing body is below 500°C, and the final cooling temperature is 50°C or less; A heat treatment step: a step of subjecting the casing to a tempering heat treatment after cooling it to room temperature; and Straightening step: a step of straightening the casing The present invention provides a method for manufacturing a high-strength heat-resistant casing for heavy oil development having the above-mentioned properties.

[0026] In the continuous casting step, it is preferable that the superheat of the molten steel is controlled to be less than 40° C., and the continuous casting speed is 2.0 to 2.4 m / min.

[0027] In the piercing step, the round billet is heated and pierced in a tube furnace at 1200 to 1260°C, and the piercing temperature is preferably 1120 to 1200°C.

[0028] In the rolling step, the final rolling temperature is preferably controlled to be 980 to 1080°C.

[0029] In the sizing step, the sizing temperature is preferably 920 to 960°C.

[0030] In the heat treatment step, the tempering temperature is preferably 600 to 700° C. and the holding time is preferably 50 to 80 minutes.

[0031] In the straightening step, the straightening temperature is preferably 400 to 500°C.

[0032] The manufacturing method of the high-strength heat-resistant casing provided by the present disclosure is carried out by adopting online quenching and tempering heat treatment, which makes the steel have higher high-temperature strength and better creep resistance. The process operation is simple and easy to realize large-scale production and manufacturing, which has great economic benefits.

[0033] The casing microstructure provided by this disclosure is tempered sorbite with a grain size rating of less than 6 according to ASTM E112.

[0034] The heat-resistant casing of a steel grade exceeding 110 ksi produced according to the manufacturing method provided by the present disclosure has a yield strength of 758 to 1069 MPa, a tensile strength of 862 MPa or more, an elongation of 18% or more, a T-direction Charpy impact energy of 60 J or more at 0°C, a high-temperature yield strength of 700 MPa or more at 350°C, and a creep rate of 1.5 × 10 -6% / sec or less, which satisfies the requirements for casing performance in the high-temperature environment of heavy oil development. [Brief explanation of the drawings]

[0035] [Figure 1] 1 shows a metal structure of embodiment A3 of the present disclosure. [Figure 2] 1 shows the metal structure of Comparative Example B3 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0036] Although embodiments of the present disclosure will be described with reference to the following specific embodiments, other advantages and benefits of the present disclosure will be readily apparent to those skilled in the art from the disclosure herein. Although the specification of the present disclosure is described in connection with preferred embodiments, this does not mean that the features of the present disclosure are limited solely to these embodiments. Rather, the description of the present disclosure in connection with the embodiments is intended to encompass other options or modifications that become possible based on the claims of the present disclosure. The following description includes many specific details to provide a thorough understanding of the present disclosure. The present disclosure may be practiced without these details. Additionally, some specific details will be omitted to avoid distracting or obscuring the focus of the present disclosure.

[0037] An embodiment of the present disclosure provides a high-strength heat-resistant casing for heavy oil development containing the following elements in weight percent: C: 0.08-0.19%, Si: 0.1-0.4%, Mn: 1.0-1.8%, Cr: 1-2%, Mo: 0.1-0.4%, W: 0.1-0.5%, V: 0.01-0.15%, Al: 0.01-0.05%, N≦0.008%, Fe and unavoidable impurities, but not containing Ti and Nb.

[0038] Another embodiment of an aspect of the present disclosure provides a high-strength heat-resistant casing for heavy oil development comprising, in weight percent, the following elements: C: 0.08-0.19%, Si: 0.1-0.4%, Mn: 1.0-1.8%, Cr: 1-2%, Mo: 0.1-0.4%, W: 0.1-0.5%, V: 0.01-0.15%, Al: 0.01-0.05%, N≦0.008%, and the balance being Fe and unavoidable impurities.

[0039] Correspondingly, the present disclosure further provides a method for manufacturing the above high-strength heat-resistant casing, comprising the following steps: smelting, continuous casting, piercing, rolling, sizing, controlled cooling, heat treatment, and straightening.

[0040] In the method for producing a high-strength heat-resistant casing according to the present disclosure, it is preferable that in the continuous casting step, the superheat of the molten steel is controlled to be less than 40°C, the continuous casting speed is 2.0 to 2.4 m / min, and a round billet is obtained. The round billet is heated and pierced in a tube furnace at 1200 to 1260°C, with the piercing temperature being 1120 to 1200°C. The final rolling temperature is controlled to be 980 to 1080°C, and the final-rolled round billet is sized at a sizing temperature of 920 to 960°C to obtain a casing. The sized casing is cooled by a controlled cooling device, and the temperature of the casing body before cooling is 850 to 900°C. The outer surface of the casing is cooled by water spray using an online controlled cooling device. In order to reduce the residual stress on the inner and outer walls, the cooling rate is 20 to 40°C / second when the inner wall temperature of the casing body is 500 to 900°C, and the cooling rate is 30 to 50°C / second when the inner wall temperature of the casing body is below 500°C. The amount of cooling water is controlled so that the final cooling temperature is 50°C or less.

[0041] After the casing is cooled to room temperature, it is subjected to a tempering heat treatment, preferably at a tempering temperature of 600 to 700°C and for a holding time of 50 to 80 minutes. Finally, the casing is heat straightened at 400 to 500°C.

[0042] According to the present disclosure, it is possible to manufacture a heat-resistant casing having good high-temperature mechanical properties and a steel grade exceeding 110 ksi.

[0043] The high-strength heat-resistant casing provided by this disclosure utilizes the residual heat of the hot-rolled steel pipe for quenching, eliminating the offline quenching process. Manufacturing the heat-resistant casing using the online quenching and tempering heat treatment process improves the casing's high-temperature mechanical properties and creep resistance, while also improving production efficiency, reducing production costs and energy consumption and achieving green manufacturing.

[0044] The present disclosure will be described in more detail below according to embodiments. Embodiments A1 to A7 are embodiments of the high-strength heat-resistant casing for heavy oil development provided by the present disclosure, and B1 to B4 are comparative examples.

[0045] The casings of the embodiments A1 to A7 and the comparative examples B1 to B4 are manufactured according to the following steps. (1) Smelting: Control the weight percentage of each chemical element in embodiments A1 to A7 and comparative examples B1 to B4 according to Table 1. (2) Continuous casting: A round billet is obtained by continuous casting, and the superheat of the molten steel is controlled to be less than 40°C, and the continuous casting speed is 2.0 to 2.4 m / min. (3) Piercing: The round billet that has undergone the continuous casting process is heated in a tube furnace at 1200 to 1260°C and pierced, with the piercing temperature being 1120 to 1200°C. (4) Rolling: The pierced round billet is rolled, and the final rolling temperature is controlled to be 980 to 1080°C. (5) Sizing: The round billet that has undergone final rolling is sized to obtain a casing, and the sizing temperature is controlled to be 920 to 960°C. (6) Controlled cooling: Except for Comparative Example B3, the temperature of the casing body before cooling is controlled to be 850-900°C, and the cooling rate is 20-40°C / sec when the inner wall temperature of the casing body is 500-900°C, and the cooling rate is 30-50°C / sec when the inner wall temperature of the casing body is below 500°C, and the amount of cooling water is controlled to cool to a temperature of 50°C or less. Comparative Example 3 employs a conventional offline quenching process, specifically, heating to 900°C, holding for 40 minutes, followed by water quenching, tempering at 650°C, and holding for 60 minutes. (7) Heat treatment: The casing is tempered at 600 to 700°C and held for 50 to 80 minutes. (8) Straightening: The casing is thermally straightened at 400-500°C.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] As can be seen from Table 3, the casings of the above-mentioned embodiments A1 to A7 have a yield strength of 810 to 1050 MPa, a tensile strength of 862 MPa or more, an elongation of 18% or more, a T-direction Charpy impact energy at 0°C of 60 J or more, a high-temperature yield strength at 350°C of 700 MPa or more, and a creep rate of 1.5 × 10 -6 % / sec or less, which satisfies the requirements for casing performance in the high-temperature environment of heavy oil development.

[0050] The carbon content of Comparative Example B1 exceeds the range defined in the technical solution of the present disclosure. Although the strength meets the requirements, quench cracks occur during the manufacturing process, resulting in manufacturing defects. W is not added to Comparative Example B2. The components of Comparative Example B3 do not exceed the range defined in the technical solution of the present disclosure, but a controlled cooling process is not used after rolling. (That is, the second aspect of the present disclosure, which includes a controlled cooling process in the manufacturing method of a high-strength heat-resistant casing for heavy oil development, specifically includes the following steps: the pre-cooling temperature of the casing body is controlled to 850-900°C, and the outer surface of the casing is cooled with water spray using a controlled cooling device. When the inner wall temperature of the casing body is 500-900°C, the cooling rate is 20-40°C / s, and when the inner wall temperature of the casing body is below 500°C, the cooling rate is 30-50°C / s, and the amount of cooling water is controlled so that the final cooling temperature is 50°C or less.) The metal structures of A3 and B3 are shown in Figures 1 and 2, respectively. The grain structure in Figure 1 is coarse, which is advantageous for improving creep resistance. On the other hand, the grains in Figure 2 are fine, with a grain size rating of 8, which means poor creep resistance. The Cr content of Comparative Example B4 exceeds the range defined in the technical solution of the present disclosure, and Comparative Example B4 does not contain Mo. In particular, at least one of the mechanical properties of the casings of Comparative Examples B2 to B4 does not meet the requirements for good high-temperature strength and creep resistance.

Claims

1. The following elements in weight percent: C: 0.08-0.19%; Si: 0.1-0.4%; Mn: 1.0-1.8%; Cr: 1-2%; Mo: 0.1-0.4%; W: 0.1-0.5%; V: 0.01-0.15%; Al: 0.01-0.05%; N≦0.008% Including, The balance is Fe and unavoidable impurities. A heat-resistant casing for heavy oil development, The unavoidable impurities include P and S, and satisfy the following weight percentages: P≦0.015% and S≦0.005%; The heat-resistant casing is a heat-resistant casing for heavy oil development, having a grain size rating of less than 6 according to ASTM E112.

2. The above elements further include C: 0.1-0.16%; Si: 0.15-0.35%; Mn: 1-1.6%; Cr: 1-1.5%; Mo: 0.15-0.4%; W: 0.2-0.5%; V: 0.05-0.12%; Al: 0.015-0.035% The heat-resistant casing for heavy oil development according to claim 1, which satisfies the above.

3. 3. The heat-resistant casing for heavy oil development according to claim 1 or 2, wherein the unavoidable impurities further satisfy P≦0.013% and S≦0.003%.

4. 3. The heat-resistant casing for heavy oil development according to claim 1 or 2, wherein the heat-resistant casing has a microstructure of tempered sorbite.

5. The heat-resistant casing has a yield strength of 758 to 1069 MPa, a tensile strength of 862 MPa or more, an elongation of 18% or more, a T-direction Charpy impact energy of 60 J or more at 0°C, a high-temperature yield strength of 700 MPa or more at 350°C, and a creep rate of 1.5 × 10 －６ 3. The heat-resistant casing for heavy oil development according to claim 1 or 2, wherein the heat resistance is % / sec or less.

6. The following steps: Smelting step: A step of blending the chemical components of the heat-resistant casing for heavy oil development according to claim 1 or 2 to obtain a raw material, and smelting the raw material to obtain a billet; Continuous casting step: a step of continuously casting the billet to obtain a round billet; Piercing step: a step of heating and piercing the round billet; Rolling step: a step of rolling the pierced round billet; Sizing step: a step of sizing the final rolled round billet to obtain a casing; Controlled cooling step: controlling the temperature of the casing body before cooling to 850-900°C, and using a controlled cooling device to spray water onto the outer surface of the casing, controlling the amount of cooling water so that the cooling rate is 20-40°C / sec when the inner wall temperature of the casing body is 500-900°C, and the cooling rate is 30-50°C / sec when the inner wall temperature of the casing body is below 500°C, and the final cooling temperature is 50°C or less; A heat treatment step: a step of cooling the casing to room temperature and then subjecting it to a tempering heat treatment; and Straightening step: a step of straightening the casing A method for manufacturing a heat-resistant casing for heavy oil development.

7. 7. The method according to claim 6, wherein in the continuous casting step, the superheat of the molten steel is controlled to be less than 40°C, and the continuous casting speed is 2.0 to 2.4 m / min.

8. The manufacturing method according to claim 6, wherein in the piercing step, the round billet is heated and pierced in a tube furnace at 1200 to 1260°C, and the piercing temperature is 1120 to 1200°C.

9. The method according to claim 6, wherein the final rolling temperature in the rolling step is controlled to be 980 to 1080°C.

10. The method according to claim 6, wherein the sizing temperature in the sizing step is 920 to 960°C.

11. The manufacturing method according to claim 6, wherein in the heat treatment step, the tempering temperature is 600 to 700°C and the holding time is 50 to 80 minutes.

12. The manufacturing method according to claim 6, wherein the straightening temperature in the straightening step is 400 to 500°C.

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