Casing pipe for unconventional oil and gas development as well as preparation method and application of casing pipe

Abstract

The invention discloses a casing pipe for unconventional oil and gas development and a preparation method and application thereof, and relates to the technical field of oil casing pipes. The sleeve comprises the following chemical components in percentage by mass: 0.2 to 0.3 percent of C, 0.17 to 0.37 percent of Si, 0.9 to 1.15 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, 0.30 to 0.45 percent of Cr, 0.30 to 0.45 percent of Ni, 0.4 to 0.6 percent of Mo, 0.3 to 0.45 percent of Cu, 0.03 to 0.1 percent of Nb, 0.01 to 0.05 percent of Ti, 0.001 to 0.005 percent of RE, 0.01 to 0.030 percent of Al, 0.01 to 0.03 percent of Ca, less than or equal to 0.005 percent of N, less than or equal to 0.008 percent of O + H + N and the balance of Fe and other inevitable impurities, and has the characteristics of high strength, high plasticity and toughness and high corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of oil casing, and in particular to a casing for unconventional oil and gas development, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous growth of the global demand for energy, the development of unconventional oil and gas resources has received increasing attention. In the process of unconventional oil and gas exploitation such as shale oil and gas and tight oil and gas, there are more and more special structure wells such as directional wells and extended reach wells. Moreover, most oil and gas wells need stimulation and transformation. Due to the complex reservoir geological conditions and harsh operation processes, the casing will be subjected to large non-uniform loads, formation displacements, alternating stresses, etc. Under such complex working conditions, traditional casings often deform due to insufficient strength and poor strain capacity. Seriously, the deformation reaches 30% - 50%, resulting in the bridge plug not being seated in place, reducing the number of fracturing stages, decreasing the single-well production, shortening the life of the oil and gas well. When the casing deformation is serious, the plugging operation cannot be completed, and even the wellbore integrity fails.

[0003] The traditional casing string design method is stress-based design, that is, it is required that the working stress is lower than the material yield strength, that is, plastic deformation of the casing (string) is not allowed during use. However, in fact, due to the changes in wellbore curvature and azimuth, the wellbore trajectory is in an irregular spatial shape. Coupled with the implementation of stimulation measures such as fracturing transformation, local plastic deformation of the casing will occur. This puts forward requirements for the plastic deformation capacity (yield ratio, uniform elongation rate) of the casing, that is, the plastic deformation of the casing needs to be controlled within an allowable range to ensure the safe use of the deformed casing. That is, a strain-based casing (string) design is adopted, which also puts forward the development and application of high-strength and large-strain casings.

[0004] So far, except for the large-strain casings used in heavy oil steam stimulation wells, there are few reports on the application of large-strain casings internationally. For casings with steel grades N80 and below, although the strain-based casing string design method is not adopted and no requirements are put forward for the strain performance of the casing, due to their low strength and high elongation rate (including uniform elongation rate), most casings can easily meet the requirements for the large-strain performance of the casing by the strain-based casing string design method. However, for casings with steel grades P110 and above, due to the phenomenon that their strength is inversely proportional to plasticity and toughness, it is often difficult to meet the requirements simultaneously. In fact, a large part of the yield ratio of casings with steel grades P110 and above exceeds 0.93, and some even reach 0.98. An excessive yield ratio will lead to a significant decrease in the uniform plastic deformation ability of the material and a serious reduction in the use safety. According to relevant research results and engineering experience, it is proposed to control the yield ratio of the casing below 0.93 or even lower to meet the need for the safe use of the casing string by the strain-based design method. In addition, during the process of unconventional oil and gas development, due to CO 2 、Cl- , the presence of sulfate-reducing bacteria (SRB) is often accompanied by certain corrosion. Therefore, there is an urgent need to develop a casing for unconventional oil and gas development that combines high strength, large strain, and corrosion resistance.

[0005] Therefore, the existing technology still needs to be improved and developed. SUMMARY OF THE INVENTION

[0006] Based on the above deficiencies of the existing technology, the purpose of the present invention is to provide a casing for unconventional oil and gas development, its preparation method and application, aiming to provide a casing for unconventional oil and gas development with high strength, large strain, and corrosion resistance, so as to solve the problems of insufficient plastic toughness and corrosion resistance of existing high-strength casings.

[0007] The technical solution of the present invention is as follows:

[0008] In the first aspect of the present invention, there is provided a casing for unconventional oil and gas development, wherein, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0009] C 0.20% - 0.30%, Si 0.17% - 0.37%, Mn 0.90% - 1.15%, P ≤ 0.012%, S ≤ 0.003%, Cr 0.30% - 0.45%, Ni 0.30% - 0.45%, Mo 0.40% - 0.60%, Cu 0.30% - 0.45%, Nb 0.03% - 0.10%, Ti 0.01% - 0.05%, RE 0.001% - 0.005%, Al 0.010% - 0.030%, Ca 0.010% - 0.030%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0010] Optionally, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0011] C 0.20% - 0.22%, Si 0.17% - 0.25%, Mn 0.90% - 0.96%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.30% - 0.33%, Ni 0.30% - 0.33%, Mo 0.40% - 0.43%, Cu 0.30% - 0.32%, Nb 0.03% - 0.04%, Ti 0.01% - 0.02%, RE 0.001% - 0.002%, Al 0.010% - 0.016%, Ca 0.010% - 0.014%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0012] Optionally, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0013] C 0.23% - 0.25%, Si 0.23% - 0.27%, Mn 0.99% - 1.01%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.34% - 0.37%, Ni 0.34% - 0.38%, Mo 0.44% - 0.46%, Cu 0.33% - 0.35%, Nb 0.05% - 0.06%, Ti 0.02% - 0.03%, RE 0.001% - 0.002%, Al 0.015% - 0.019%, Ca 0.015% - 0.017%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0014] Optionally, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0015] C 0.25% - 0.26%, Si 0.28% - 0.31%, Mn 1.05% - 1.07%, P ≤ 0.012%, S ≤ 0.003%, Cr 0.36% - 0.39%, Ni 0.36% - 0.39%, Mo 0.49% - 0.51%, Cu 0.34% - 0.36%, Nb 0.06% - 0.07%, Ti 0.03%, RE 0.002% - 0.003%, Al 0.018% - 0.024%, Ca 0.018% - 0.020%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0016] Optionally, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0017] C 0.25% - 0.27%, Si 0.21% - 0.24%, Mn 1.09% - 1.11%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.40% - 0.42%, Ni 0.40% - 0.42%, Mo 0.54% - 0.56%, Cu 0.39% - 0.41%, Nb 0.07% - 0.08%, Ti 0.03% - 0.04%, RE 0.003% - 0.004%, Al 0.021% - 0.025%, Ca 0.022% - 0.025%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0018] Optionally, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0019] C 0.28% - 0.30%, Si 0.29% - 0.37%, Mn 1.13% - 1.15%, P ≤ 0.012%, S ≤ 0.002%, Cr 0.43% - 0.45%, Ni 0.43% - 0.45%, Mo 0.58% - 0.60%, Cu 0.43% - 0.45%, Nb 0.09% - 0.10%, Ti 0.04% - 0.05%, RE 0.004% - 0.005%, Al 0.026% - 0.030%, Ca 0.026% - 0.030%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0020] In a second aspect of the present invention, a method for preparing a casing for unconventional oil and gas development is provided, which includes the following steps:

[0021] After batching, smelting, and continuous casting according to the chemical components of the casing for unconventional oil and gas development as described above in the present invention, a continuous casting billet is obtained;

[0022] After hot piercing and hot continuous rolling of the continuous casting billet, a tube blank is obtained;

[0023] After quenching and tempering heat treatment, hot straightening, stress relief tempering of the tube blank, threading is carried out to obtain the casing for unconventional oil and gas development.

[0024] Optionally, the step of obtaining a tube blank after hot piercing and hot continuous rolling of the continuous casting billet specifically includes:

[0025] The continuous casting billet is heated in a heating furnace to 1200 - 1230 °C, held for 90 - 120 min, then hot pierced at a temperature of 1170 - 1200 °C and hot continuously rolled at a temperature of 950 - 1150 °C, and after cooling, a tube blank is obtained.

[0026] Optionally, the step of obtaining the casing for unconventional oil and gas development after quenching and tempering heat treatment, hot straightening, stress relief tempering of the tube blank and then threading specifically includes:

[0027] In a protective atmosphere furnace, the tube blank is heated at a temperature of 890 - 910 °C, held for 50 - 70 min, then cooled by internal and external water spraying at a cooling rate of ≥ 30 °C / s, and then tempered at a temperature of 560 - 660 °C for 90 - 120 min and then water cooled;

[0028] After hot straightening at a temperature of 510 - 610°C and then water cooling, and then stress relief tempering by holding at a temperature of 510 - 610°C for 90 - 120 minutes followed by water cooling, threading is carried out to obtain the casing for unconventional oil and gas development.

[0029] In the third aspect of the present invention, there is provided an application of the casing for unconventional oil and gas development as described above in the present invention, or the casing for unconventional oil and gas development prepared by the preparation method as described above in the present invention in unconventional oil and gas development.

[0030] Beneficial effects: The casing provided by the present invention is a high-strength and large-strain casing for unconventional oil and gas development, having excellent comprehensive properties such as strength, plasticity, toughness, and corrosion resistance. The minimum yield strengths reach steel grades of 110 ksi, 125 ksi, 130 ksi, 140 ksi, and 150 ksi respectively. The room temperature yield strength is 867 - 1132 MPa, the tensile strength is 1020 - 1217 MPa, the yield ratio is 0.85 - 0.93, the total elongation rate is 20% - 28%, the uniform elongation rate is 10% - 18%, the transverse Charpy V-notch impact toughness at 0°C is 82 - 126 J, and the corrosion rate is 0.46 - 0.54 mm / a (the corrosion rate of the API standard oil casing of the corresponding steel grade is 0.60 - 0.70 mm / a), which is reduced by about 23%, and can meet the requirements of unconventional oil and gas development for high-strength and large-strain casings. Specific embodiments

[0031] The present invention provides a casing for unconventional oil and gas development, its preparation method and application. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0033] An embodiment of the present invention provides a casing for unconventional oil and gas development. Among them, by mass percentage, the casing for unconventional oil and gas development includes the following chemical components:

[0034] C: 0.20% - 0.30%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.15%, P ≤ 0.012%, S ≤ 0.003%, Cr: 0.30% - 0.45%, Ni: 0.30% - 0.45%, Mo: 0.40% - 0.60%, Cu: 0.30% - 0.45%, Nb: 0.03% - 0.10%, Ti: 0.01% - 0.05%, RE: 0.001% - 0.005%, Al: 0.010% - 0.030%, Ca: 0.010% - 0.030%, N ≤ 0.005%, O + H + N ≤ 0.008%, the balance being Fe and other inevitable impurities.

[0035] Among them, RE is a rare earth element. In some specific embodiments, RE can be Ce (cerium).

[0036] The present invention intends to adopt medium - low C, add alloying element Mn, add a small amount of multiple elements such as Cr, Ni, Mo, and Cu, carry out Nb - Ti complex micro - alloying, and can also add trace RE elements, control harmful elements such as P, S, O, H, and N in the steel, perform Al - Si full deoxidation, and carry out Ca treatment on the molten steel to ensure meeting the requirements of the casing strength, toughness, large - strain performance (yield - strength ratio, uniform elongation rate), and corrosion resistance based on the strain casing string design method. The casing provided by the present invention is a casing for high - strength large - strain unconventional oil and gas development, having excellent comprehensive properties such as strength, plasticity, toughness, and corrosion resistance (that is, high strength, good plasticity and toughness, and strong corrosion resistance). The minimum yield strength reaches steel grades of 110 ksi, 125 ksi, 130 ksi, 140 ksi, and 150 ksi respectively. The room - temperature yield strength is 867 - 1132 MPa, the tensile strength is 1020 - 1217 MPa, the yield - strength ratio is 0.85 - 0.93, the total elongation rate is 20% - 28%, the uniform elongation rate is 10% - 18%, the transverse Charpy V - notch impact toughness at 0 °C is 82 - 126 J, and the corrosion rate is 0.46 - 0.54 mm / a (the corrosion rate of API standard oil casings of corresponding steel grades is 0.60 - 0.70 mm / a), a reduction of about 23%, which can meet the requirements of unconventional oil and gas development for high - strength large - strain casings. The high - strength large - strain casing provided by the present invention has a long service life and high reliability, can effectively reduce the number of operations such as well repair and pipe replacement caused by casing damage, reduce the production cost, improve the efficiency and economic benefits of unconventional oil and gas development, and has significant market competitiveness and promotion and application value.

[0037] Among them, C (carbon) is the main strengthening element in steel. Using medium and low carbon is beneficial to improving the plasticity and toughness of steel, but too low carbon content is not conducive to improving the hardenability of steel and is not beneficial to increasing the strength of steel; too high carbon content is not beneficial to improving the plasticity and toughness of steel. Considering comprehensively, it is advisable to control it within the range of 0.20% - 0.30%.

[0038] Si (silicon) is a common element in steel and is also an important deoxidizer. It is advisable to control it within the range of 0.17% - 0.37%.

[0039] Mn (manganese) is dissolved in steel, used to improve the hardenability of steel and thus increase the strength, and has little influence on the yield ratio. At the same time, in order to reduce segregation, considering comprehensively, it is advisable to control it within the range of 0.90% - 1.15%.

[0040] Cr (chromium) is dissolved in steel, used to improve the hardenability and tempering stability of steel, thereby increasing the strength and corrosion resistance of steel, but too high content will increase the cost. Considering comprehensively, it is advisable to control it within the range of 0.30% - 0.45%.

[0041] Ni (nickel) is dissolved in steel, used to improve the hardenability of steel and thus increase the strength. Its addition can also improve the plasticity and toughness of steel and improve the hot working process performance of Cu-containing steel. But too high content will increase the cost. Considering comprehensively, it is advisable to control it within the range of 0.30% - 0.45%.

[0042] Mo (molybdenum) is dissolved in steel, used to improve the hardenability and tempering stability of steel, make up for the adverse effect of lower Cr content on hardenability, thereby increasing the strength of steel. At the same time, adding Mo can inhibit the segregation of Mn and P, improve the uniformity, improve the temper brittleness and corrosion resistance of steel. When Mo / P ≥ 15 (that is, the mass percentage ratio of Mo to P is greater than or equal to 15), the effect is better, but too high content will increase the cost. Considering comprehensively, it is advisable to control it within the range of 0.40% - 0.60%.

[0043] Cu (copper) is mainly used to improve the corrosion resistance of steel, and can also improve the hardenability and strength of steel, but too high content will also cause Cu brittleness. Considering comprehensively, it is advisable to control it within the range of 0.30% - 0.45%.

[0044] Nb (niobium) is added to steel to form NbC and NbN with C and N in steel respectively, which has the function of hindering the growth of austenite grains and refining grains, thereby increasing the strength and toughness. But too high content will form too many carbon and nitrogen compounds, increasing the brittleness of steel and causing cost increase. Considering comprehensively, it is advisable to control it within the range of 0.03% - 0.10%.

[0045] Adding Ti (titanium) to steel has the effects of deoxidation and nitrogen fixation. It forms TiC and TiN with C and N in the steel respectively, which can hinder the growth of austenite grains and refine the grains, thereby improving strength and toughness. However, if the content is too high, excessive carbon and nitrogen compounds will be formed, increasing the brittleness of the steel and leading to increased costs. Considering comprehensively, it is advisable to control it within the range of 0.01% - 0.05%.

[0046] In the embodiments of the present invention, Nb-Ti composite microalloying is adopted, which can obtain better strengthening and toughening effects than adding Nb and Ti alone, making the casing have good strength and toughness.

[0047] RE (rare earth elements) has multiple functions such as purifying molten steel, refining grains, modifying inclusions, and alloying, thereby improving the strength, toughness and corrosion resistance of steel. Considering comprehensively, it is advisable to control it within the range of 0.001% - 0.005%. In the embodiments of the present invention, the addition of Cr, Mo, Cu, and RE and their synergistic effects improve the corrosion resistance of the casing and reduce the strength loss and failure risk caused by corrosion.

[0048] Al (aluminum) combines with oxygen or nitrogen to form fine and uniformly distributed oxides or nitrides, which can play a role in refining grains and simultaneously improving strength and toughness. It is also an important deoxidizer and nitrogen fixer. However, too much content will affect the hot working performance of the steel. Considering comprehensively, it is advisable to control it within the range of 0.010% - 0.030%.

[0049] Adding Ca (calcium) to steel can improve the properties and morphology of inclusions, thereby improving the plasticity, toughness and corrosion resistance of the steel. The effect is better when Ca / S≥2 (that is, the mass percentage content ratio of Ca to S is greater than or equal to 2). Considering comprehensively, it is advisable to control it within the range of 0.010% - 0.030%.

[0050] P (phosphorus) is a harmful element, mainly affecting the plasticity, toughness and corrosion resistance of steel. It is advisable to control P≤0.012% (that is, the mass content of P is less than or equal to 0.012%).

[0051] S (sulfur) is a harmful element, mainly affecting the plasticity, toughness and corrosion resistance of steel. It is advisable to control S≤0.003% (that is, the mass content of S is less than or equal to 0.003%).

[0052] O (oxygen), H (hydrogen), and N (nitrogen) are harmful elements, mainly affecting the plasticity, toughness and corrosion resistance of steel. Considering comprehensively, it is advisable to control O + H + N≤0.008%. Considering that N has a great influence on the strain aging performance of steel, it is advisable to control N≤0.005% (that is, the mass content of N is less than or equal to 0.005%).

[0053] In some embodiments, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0054] C 0.20% to 0.22%, Si 0.17% to 0.25%, Mn 0.90% to 0.96%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.30% to 0.33%, Ni 0.30% to 0.33%, Mo 0.40% to 0.43%, Cu 0.30% to 0.32%, Nb 0.03% to 0.04%, Ti 0.01% to 0.02%, RE 0.001% to 0.002%, Al 0.010% to 0.016%, Ca 0.010% to 0.014%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0055] In this embodiment, the yield strength level of the casing for unconventional oil and gas development can meet the requirement of 110 ksi, with a yield strength of 867 - 872 MPa, a tensile strength of 1020 - 1026 MPa, a yield ratio of 0.85, a total elongation rate of 28%, a uniform elongation rate of 18%, a transverse Charpy V-notch impact toughness at 0 °C of 123 - 126 J, and a corrosion rate of 0.46 mm / a (i.e., 0.46 mm per year).

[0056] In some embodiments, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0057] C 0.23% to 0.25%, Si 0.23% to 0.27%, Mn 0.99% to 1.01%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.34% to 0.37%, Ni 0.34% to 0.38%, Mo 0.44% to 0.46%, Cu 0.33% to 0.35%, Nb 0.05% to 0.06%, Ti 0.02% to 0.03%, RE 0.001% to 0.002%, Al 0.015% to 0.019%, Ca 0.015% to 0.017%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0058] In this embodiment, the yield strength level of the casing for unconventional oil and gas development can meet the requirement of 125 ksi, with a yield strength of 960 - 967 MPa, a tensile strength of 1091 - 1099 MPa, a yield ratio of 0.88, a total elongation rate of 25%, a uniform elongation rate of 15%, a transverse Charpy V-notch impact toughness at 0 °C of 115 - 119 J, and a corrosion rate of 0.48 mm / a (i.e., 0.48 mm per year).

[0059] In some embodiments, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0060] C 0.25% - 0.26%, Si 0.28% - 0.31%, Mn 1.05% - 1.07%, P ≤ 0.012%, S ≤ 0.003%, Cr 0.36% - 0.39%, Ni 0.36% - 0.39%, Mo 0.49% - 0.51%, Cu 0.34% - 0.36%, Nb 0.06% - 0.07%, Ti 0.03%, RE 0.002% - 0.003%, Al 0.018% - 0.024%, Ca 0.018% - 0.020%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0061] In this embodiment, the yield strength level of the casing for unconventional oil and gas development can meet the requirement of 130 ksi, the yield strength is 993 - 998 MPa, the tensile strength is 1116 - 1123 MPa, the yield ratio is 0.89, the total elongation is 24%, the uniform elongation is 14%, the transverse Charpy V-notch impact toughness at 0 °C is 104 - 107 J, and the corrosion rate is 0.49 mm / a (i.e., 0.49 mm per year).

[0062] In some embodiments, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0063] C 0.25% - 0.27%, Si 0.21% - 0.24%, Mn 1.09% - 1.11%, P ≤ 0.011%, S ≤ 0.003%, Cr 0.40% - 0.42%, Ni 0.40% - 0.42%, Mo 0.54% - 0.56%, Cu 0.39% - 0.41%, Nb 0.07% - 0.08%, Ti 0.03% - 0.04%, RE 0.003% - 0.004%, Al 0.021% - 0.025%, Ca 0.022% - 0.025%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0064] In this embodiment, the yield strength level of the casing for unconventional oil and gas development can meet the requirement of 140 ksi, the yield strength is 1057 - 1063 MPa, the tensile strength is 1162 - 1168 MPa, the yield ratio is 0.91, the total elongation is 22%, the uniform elongation is 12%, the transverse Charpy V-notch impact toughness at 0 °C is 93 - 98 J, and the corrosion rate is 0.51 mm / a (i.e., 0.51 mm per year).

[0065] In some embodiments, by mass percentage, the casing for unconventional oil and gas development comprises the following chemical components:

[0066] C 0.28% - 0.30%, Si 0.29% - 0.37%, Mn 1.13% - 1.15%, P ≤ 0.012%, S ≤ 0.002%, Cr 0.43% - 0.45%, Ni 0.43% - 0.45%, Mo 0.58% - 0.60%, Cu 0.43% - 0.45%, Nb 0.09% - 0.10%, Ti 0.04% - 0.05%, RE 0.004% - 0.005%, Al 0.026% - 0.030%, Ca 0.026% - 0.030%, N ≤ 0.005%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0067] In this embodiment, the yield strength level of the casing for unconventional oil and gas development can meet the requirement of 150 ksi, with a yield strength of 1127 - 1132 MPa, a tensile strength of 1212 - 1217 MPa, a yield ratio of 0.93, a total elongation rate of 20%, a uniform elongation rate of 10%, a transverse Charpy V-notch impact toughness at 0 °C of 82 - 87 J, and a corrosion rate of 0.54 mm / a (i.e., 0.54 mm per year).

[0068] The present invention develops a manufacturing process matching the above-mentioned chemical components in proportion. Mainly through steelmaking (including secondary refining and vacuum degassing), continuous casting, hot tandem rolling in the austenite region, quenching and tempering heat treatment, hot straightening, stress relief tempering (also known as stress elimination tempering), etc., the material obtains a fine and uniform tempered sorbite microstructure to achieve a reasonable match of the strength, plasticity, toughness, and corrosion resistance of the material; in order to control the yield strength, the finishing rolling temperature is appropriately increased, a higher hot straightening temperature is adopted, and measures such as stress relief tempering are taken. Specifically, the embodiment of the present invention also provides a preparation method for the casing for unconventional oil and gas development, which includes the following steps:

[0069] S1. After batching, smelting, and continuous casting according to the chemical components of the casing for unconventional oil and gas development as described above in the present invention, a continuous casting billet is obtained;

[0070] S2. After hot piercing and hot tandem rolling of the continuous casting billet, a tube blank is obtained;

[0071] S3. After quenching and tempering heat treatment, hot straightening, and stress relief tempering of the tube blank, thread processing is carried out to obtain the casing for unconventional oil and gas development.

[0072] The casing prepared by the preparation method provided by the present invention is a high-strength and large-strain casing for unconventional oil and gas development, and has excellent comprehensive properties such as strength, plasticity, toughness and corrosion resistance. The minimum yield strength reaches 110ksi, 125ksi, 130ksi, 140ksi and 150ksi steel grades respectively, the room temperature yield strength is 867-1132MPa, the tensile strength is 1020-1217MPa, the yield strength ratio is 0.85-0.93, the total elongation is 20%-28%, the uniform elongation is 10%-18%, the transverse Charpy V-notch impact toughness at 0°C is 82-126J, and the corrosion rate is 0.46-0.54mm / a (the corrosion rate of the API standard oil casing of the corresponding steel grade is 0.60-0.70mm / a), which is reduced by about 23%, and can meet the demand for high-strength and large-strain casing in unconventional oil and gas development. The preparation method provided by the present invention includes improving purity, hot rolling, controlled rolling and controlled cooling, and reasonable heat treatment to control the organizational morphology, so that the casing can obtain high strength, high toughness, good large strain performance and corrosion resistance. When subjected to complex loads, it can undergo large plastic deformation without breaking, and effectively adapt to working conditions such as stratum displacement in unconventional oil and gas production, as follows:

[0073] In step S1, in some embodiments, after smelting and continuous casting, the step of obtaining the continuous casting billet specifically includes:

[0074] The raw materials obtained by batching are smelted in an electric furnace or an oxygen-blown converter, fed with Si-Ca wire (to perform a denaturation treatment on inclusions), refined outside the furnace, and vacuum degassed to obtain molten steel (containing the above chemical components);

[0075] The molten steel is cast into a rod-shaped continuous casting billet (electromagnetic stirring and soft reduction techniques are used during the continuous casting process to control the center segregation of the continuous casting billet).

[0076] In step S2, in some embodiments, the step of obtaining a tube billet after hot piercing and hot rolling the continuous casting billet specifically includes:

[0077] The continuous casting billet is heated to 1200-1230° C. in a heating furnace, kept warm for 90-120 minutes, then hot-pierced at 1170-1200° C., hot-rolled at 950-1150° C., cooled (e.g., air-cooled), and sawed to a suitable length to obtain a tube billet.

[0078] In this step, adopting a higher final rolling temperature is beneficial to obtaining a lower yield strength ratio and a larger uniform plastic deformation elongation.

[0079] In step S3, in some embodiments, the tube blank is subjected to quenching and tempering heat treatment, heat straightening, and stress relief tempering, and then thread processing is performed to obtain the casing for unconventional oil and gas development, and the steps specifically include:

[0080] In a protective atmosphere furnace, the tube blank is heated at a temperature of 890 - 910 °C, held for 50 - 70 min, then cooled by internal and external water spraying at a cooling rate of greater than or equal to 30 °C / s, and then tempered at a temperature of 560 - 660 °C for 90 - 120 min and then water-cooled (water-cooling after tempering to avoid possible temper brittleness) to obtain fine and uniform tempered sorbite with a grain size of greater than or equal to grade 8;

[0081] After hot straightening at a temperature of 510 - 610 °C and then water-cooling, and then held at a temperature of 510 - 610 °C for 90 - 120 min for stress-relieving tempering and then water-cooled (in order to reduce the influence of residual stress on the casing performance, tempering and water-cooling are carried out after hot straightening), thread machining is carried out to obtain the casing for unconventional oil and gas development.

[0082] In the present invention, the addition of Cr, Mo, Cu, and RE and their synergistic effects enable the casing to have good corrosion resistance, while pure steel smelting, segregation control, heat treatment microstructure state, and residual stress regulation further improve the corrosion resistance of the casing. The combination of chemical composition and process effectively enhances the corrosion resistance of the casing and reduces the strength loss and failure risk caused by corrosion. When thread machining is carried out, API (American Petroleum Institute) standard threads or special threads can be machined on the pipe section, and magnetic particle inspection is carried out on the threads.

[0083] The embodiment of the present invention also provides a casing for unconventional oil and gas development as described above in the embodiments of the present invention, or the application of the casing for unconventional oil and gas development as described above in the embodiments of the present invention in unconventional oil and gas development. The unconventional oil and gas development includes but is not limited to shale oil and gas development and tight oil and gas development.

[0084] The present invention will be further described below through specific embodiments.

[0085] Table 1. Chemical compositions of the casings for unconventional oil and gas development in Examples 1 - 6

[0086]

[0087]

[0088] Table 2. Chemical compositions of the casings for unconventional oil and gas development in Examples 7 - 15

[0089]

[0090] In Table 1 and Table 2, in Examples 1 - 15, the contents of each chemical component are mass percentages, and the balance to 100% is Fe and unavoidable impurities.

[0091] Example 1

[0092] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0093] Steelmaking: According to the chemical composition of the casing for unconventional oil and gas development in Example 1 shown in Table 1, batching is carried out, and then molten steel is obtained through oxygen blowing converter steelmaking, feeding Si-Ca wire, refining outside the furnace, and vacuum degassing.

[0094] Continuous casting: The molten steel is cast into a rod-shaped continuous casting billet, and electromagnetic stirring and soft reduction technologies are used during the continuous casting process to control the center segregation of the continuous casting billet.

[0095] Piercing and hot continuous rolling: The continuous casting billet is heated in a ring heating furnace at a furnace temperature of 1215 °C and a heating time of 120 min, then hot piercing is carried out at a temperature of 1180 °C, hot continuous rolling is carried out at a temperature of 950 - 1150 °C (the starting rolling temperature is 1150 °C, and the final rolling temperature is 950 °C), and then air cooling (i.e., air cooling) is carried out, and it is sawed to an appropriate length to obtain a tube blank.

[0096] Quenching and tempering heat treatment, hot straightening: Using a protective atmosphere furnace heating, quenching + high-temperature tempering heat treatment process, the tube blank is heated at a temperature of 900 °C, after holding for 50 min, internal and external water spraying cooling is carried out at a cooling rate of 30 °C / s, and then tempering is carried out at a temperature of 650 °C for 90 min and then water cooled;

[0097] Hot straightening is carried out at a temperature of 600 °C and then water cooled, and then stress relief tempering is carried out by holding at a temperature of 600 °C for 90 min and then water cooled, and thread processing is carried out to obtain the casing for unconventional oil and gas development.

[0098] Example 2

[0099] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0100] Steelmaking: The difference from Example 1 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 2 shown in Table 1.

[0101] Continuous casting: The same as Example 1.

[0102] Piercing and hot continuous rolling: The same as Example 1.

[0103] Quenching and tempering heat treatment, hot straightening: The same as Example 1.

[0104] Example 3

[0105] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0106] Steelmaking: The only difference from Example 1 is that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 3 shown in Table 1.

[0107] Continuous casting: The same as Example 1.

[0108] Piercing and hot continuous rolling: The same as Example 1.

[0109] Quenching and tempering heat treatment, hot straightening: The same as Example 1.

[0110] Example 4

[0111] This example provides a preparation method for a casing for unconventional oil and gas development, including the following steps:

[0112] Steelmaking: The only difference from Example 1 is that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 4 shown in Table 1.

[0113] Continuous casting: The same as Example 1.

[0114] Piercing and hot continuous rolling: The same as Example 1.

[0115] Quenching and tempering heat treatment, hot straightening: Using a protective atmosphere furnace for heating, a heat treatment process of quenching + high-temperature tempering, heating the tube blank at a temperature of 900 °C, after holding for 60 min, cooling by spraying water inside and outside at a cooling rate of 30 °C / s, and then tempering at a temperature of 620 °C for 100 min and then water cooling;

[0116] Hot straightening at a temperature of 570 °C and then water cooling, and then holding at a temperature of 570 °C for 100 min for stress relief tempering and then water cooling, and threading to obtain the casing for unconventional oil and gas development.

[0117] Example 5

[0118] This example provides a preparation method for a casing for unconventional oil and gas development, including the following steps:

[0119] Steelmaking: The only difference from Example 4 is that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 5 shown in Table 1.

[0120] Continuous casting: The same as Example 4.

[0121] Piercing and hot continuous rolling: The same as Example 4.

[0122] Quenching and tempering heat treatment, hot straightening: The same as Example 4.

[0123] Example 6

[0124] This example provides a preparation method for a casing for unconventional oil and gas development, including the following steps:

[0125] Steelmaking: The difference from Example 4 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 6 shown in Table 1.

[0126] Continuous casting: The same as Example 4.

[0127] Piercing and hot continuous rolling: The same as Example 4.

[0128] Quenching and tempering heat treatment, hot straightening: The same as Example 4.

[0129] Example 7

[0130] This example provides a preparation method for a casing for unconventional oil and gas development, including the following steps:

[0131] Steelmaking: The difference from Example 1 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 7 shown in Table 2.

[0132] Continuous casting: The same as Example 1.

[0133] Piercing and hot continuous rolling: The same as Example 1.

[0134] Quenching and tempering heat treatment, hot straightening: Using a protective atmosphere furnace for heating, a heat treatment process of quenching + high-temperature tempering, heating the tube blank at a temperature of 900 °C, after holding for 60 min, performing internal and external water spraying cooling at a cooling rate of 30 °C / s, and then tempering at a temperature of 610 °C for 110 min followed by water cooling;

[0135] Performing hot straightening at a temperature of 560 °C followed by water cooling, then holding at a temperature of 560 °C for 110 min for stress relief tempering followed by water cooling, and performing thread processing to obtain the casing for unconventional oil and gas development.

[0136] Example 8

[0137] This example provides a preparation method for a casing for unconventional oil and gas development, including the following steps:

[0138] Steelmaking: The difference from Example 7 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 8 shown in Table 2.

[0139] Continuous casting: The same as Example 7.

[0140] Piercing and hot continuous rolling: The same as Example 7.

[0141] Quenching and tempering heat treatment, hot straightening: The same as Example 7.

[0142] Example 9

[0143] This embodiment provides a preparation method for a casing used in unconventional oil and gas development, comprising the following steps:

[0144] Steelmaking: The difference from Embodiment 7 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Embodiment 9 shown in Table 2.

[0145] Continuous casting: The same as Embodiment 7.

[0146] Piercing and hot continuous rolling: The same as Embodiment 7.

[0147] Quenching and tempering heat treatment, hot straightening: The same as Embodiment 7.

[0148] Embodiment 10

[0149] This embodiment provides a preparation method for a casing used in unconventional oil and gas development, comprising the following steps:

[0150] Steelmaking: The difference from Embodiment 1 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Embodiment 10 shown in Table 2.

[0151] Continuous casting: The same as Embodiment 1.

[0152] Piercing and hot continuous rolling: The same as Embodiment 1.

[0153] Quenching and tempering heat treatment, hot straightening: The heat treatment process of heating in a protective atmosphere furnace, quenching + high-temperature tempering is adopted. The tube blank is heated at a temperature of 900 °C, held for 70 min, then cooled by spraying water inside and outside at a cooling rate of 30 °C / s, and then tempered at a temperature of 590 °C for 120 min and then water-cooled;

[0154] Hot straightening is carried out at a temperature of 540 °C and then water-cooled, and then stress relief tempering is carried out by holding at a temperature of 540 °C for 120 min and then water-cooled, and thread processing is carried out to obtain the casing for unconventional oil and gas development.

[0155] Embodiment 11

[0156] This embodiment provides a preparation method for a casing used in unconventional oil and gas development, comprising the following steps:

[0157] Steelmaking: The difference from Embodiment 10 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Embodiment 11 shown in Table 2.

[0158] Continuous casting: The same as Embodiment 10.

[0159] Piercing and hot continuous rolling: The same as Embodiment 10.

[0160] Quenching and tempering heat treatment, hot straightening: The same as Embodiment 10.

[0161] Embodiment 12

[0162] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0163] Steelmaking: The difference from Example 10 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 12 shown in Table 2.

[0164] Continuous casting: The same as Example 10.

[0165] Piercing and hot continuous rolling: The same as Example 10.

[0166] Quenching and tempering heat treatment, hot straightening: The same as Example 10.

[0167] Example 13

[0168] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0169] Steelmaking: The difference from Example 1 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 13 shown in Table 2.

[0170] Continuous casting: The same as Example 1.

[0171] Piercing and hot continuous rolling: The same as Example 1.

[0172] Quenching and tempering heat treatment, hot straightening: Adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high-temperature tempering.

[0173] Heat the tube blank at a temperature of 900 °C, keep it warm for 70 min, then cool it by spraying water inside and outside at a cooling rate of 30 °C / s, and then temper it at a temperature of 570 °C for 120 min and then water-cool it;

[0174] Perform hot straightening at a temperature of 520 °C and then water-cool it, then keep it at a temperature of 520 °C for 120 min for stress relief tempering and then water-cool it, and perform thread processing to obtain the casing for unconventional oil and gas development.

[0175] Example 14

[0176] This embodiment provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0177] Steelmaking: The difference from Example 13 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 14 shown in Table 2.

[0178] Continuous casting: The same as Example 13.

[0179] Piercing and hot continuous rolling: The same as Example 13.

[0180] Quenching and tempering heat treatment, hot straightening: The same as in Example 13.

[0181] Example 15

[0182] This example provides a method for preparing a casing for unconventional oil and gas development, including the following steps:

[0183] Steelmaking: The difference from Example 13 is only that batching is carried out according to the chemical composition of the casing for unconventional oil and gas development in Example 15 shown in Table 2.

[0184] Continuous casting: The same as in Example 13.

[0185] Piercing and hot continuous rolling: The same as in Example 13.

[0186] Quenching and tempering heat treatment, hot straightening: The same as in Example 13.

[0187] The casings for unconventional oil and gas development prepared in Examples 1 - 15 were respectively subjected to yield strength test, tensile strength test, total elongation test, uniform elongation test, transverse Charpy V-notch impact toughness test at 0 °C, and corrosion rate test. The results are shown in Table 3.

[0188] Table 3. Performance of the casings for unconventional oil and gas development in Examples 1 - 15

[0189]

[0190] Among them, the test conditions for the corrosion rate are: (temperature is 60 °C, carbon dioxide pressure is Pco 2 = 0.25 MPa, chloride ion (Cl-) content is 30000 mg / L, and SRB content is 100000 cells / mL).

[0191] From the above test results, it can be seen that the high-strength and large-strain casings for unconventional oil and gas development of the present invention have excellent comprehensive properties such as strength, plasticity, toughness, and corrosion resistance. The room-temperature yield strength is 867 MPa - 1132 MPa, the tensile strength is 1020 MPa - 1217 MPa, the yield ratio is 0.85 - 0.93, the total elongation is 20% - 28%, the uniform elongation is 10% - 18%, the transverse Charpy V-notch impact toughness at 0 °C is 82 J - 126 J, and the corrosion rate is 0.46 mm / a - 0.54 mm / a (the corrosion rate of the API standard oil casing of the corresponding steel grade is 0.60 mm / a - 0.70 mm / a), which is reduced by about 23%. It can meet the requirements of unconventional oil and gas development for high-strength and large-strain casings.

[0192] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or modifications can be made according to the above description, and all such improvements and modifications shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A casing for unconventional oil and gas development, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.20%~0.30%, Si 0.17%~0.37%, Mn 0.90%~1.15%, P≤0.012%, S≤0.003%, Cr 0.30%~0.45%, Ni 0.30%~0.45%, Mo 0.40%~0.60%, Cu 0.30%~0.45%, Nb 0.03%~0.10%, Ti 0.01%~0.05%, RE 0.001%~0.005%, Al 0.010%~0.030%, Ca 0.010%~0.030%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

2. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.20%~0.22%, Si 0.17%~0.25%, Mn 0.90%~0.96%, P≤0.011%, S≤0.003%, Cr 0.30%~0.33%, Ni 0.30%~0.33%, Mo 0.40%~0.43%, Cu 0.30%~0.32%, Nb 0.03%~0.04%, Ti 0.01%~0.02%, RE 0.001%~0.002%, Al 0.010%~0.016%, Ca 0.010%~0.014%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

3. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.23%~0.25%, Si 0.23%~0.27%, Mn 0.99%~1.01%, P≤0.011%, S≤0.003%, Cr 0.34%~0.37%, Ni 0.34%~0.38%, Mo 0.44%~0.46%, Cu 0.33%~0.35%, Nb 0.05%~0.06%, Ti 0.02%~0.03%, RE 0.001%~0.002%, Al 0.015%~0.019%, Ca 0.015%~0.017%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

4. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.25%~0.26%, Si 0.28%~0.31%, Mn 1.05%~1.07%, P≤0.012%, S≤0.003%, Cr 0.36%~0.39%, Ni 0.36%~0.39%, Mo 0.49%~0.51%, Cu 0.34%~0.36%, Nb 0.06%~0.07%, Ti 0.03%, RE 0.002%~0.003%, Al 0.018%~0.024%, Ca0.018%~0.020%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

5. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.25%~0.27%, Si 0.21%~0.24%, Mn 1.09%~1.11%, P≤0.011%, S≤0.003%, Cr 0.40%~0.42%, Ni 0.40%~0.42%, Mo 0.54%~0.56%, Cu 0.39%~0.41%, Nb 0.07%~0.08%, Ti 0.03%~0.04%, RE 0.003%~0.004%, Al 0.021%~0.025%, Ca 0.022%~0.025%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

6. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development includes the following chemical components by mass percentage: C 0.28%~0.30%, Si 0.29%~0.37%, Mn 1.13%~1.15%, P≤0.012%, S≤0.002%, Cr 0.43%~0.45%, Ni 0.43%~0.45%, Mo 0.58%~0.60%, Cu 0.43%~0.45%, Nb 0.09%~0.10%, Ti 0.04%~0.05%, RE 0.004%~0.005%, Al 0.026%~0.030%, Ca 0.026%~0.030%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other inevitable impurities.

7. A method for preparing casing for unconventional oil and gas development, characterized in that: The steps include: After batching, smelting and continuous casting of the chemical composition of the casing for unconventional oil and gas development according to any one of claims 1 to 6, a continuous casting billet is obtained; The continuous casting billet is subjected to hot piercing and hot continuous rolling to obtain a tube billet; The tube blank is subjected to tempering heat treatment, heat straightening, stress relief tempering, and then thread processing to obtain the casing for unconventional oil and gas development.

8. The preparation method according to claim 7, characterized in that: After hot piercing and hot rolling the continuous casting billet, the steps of obtaining a tube billet specifically include: The continuous casting billet is heated to 1200-1230° C. in a heating furnace, kept warm for 90-120 minutes, then hot-pierced at 1170-1200° C., hot-rolled at 950-1150° C., and cooled to obtain a tube billet.

9. The preparation method according to claim 7, characterized in that: After subjecting the tube blank to quenching and tempering heat treatment, heat straightening, and stress relief tempering, thread processing is performed to obtain the casing for unconventional oil and gas development, the steps specifically include: In a protective atmosphere furnace, the tube blank is heated at a temperature of 890-910° C., kept at this temperature for 50-70 minutes, and then cooled by spraying water inside and outside at a cooling rate of 30° C. / s or more, and then tempered at a temperature of 560-660° C. for 90-120 minutes and then water-cooled; The casing is straightened at a temperature of 510 to 610° C. and then water-cooled. The casing is then kept at a temperature of 510 to 610° C. for 90 to 120 minutes for stress relief tempering and water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

10. Use of a casing for unconventional oil and gas development as claimed in any one of claims 1 to 6, or a casing for unconventional oil and gas development prepared by the preparation method as claimed in any one of claims 7 to 9 in unconventional oil and gas development.

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