A casing for unconventional oil and gas development and its preparation method and application

Abstract

The present invention discloses a casing for unconventional oil and gas development, a preparation method, and applications thereof, relating to the technical field of petroleum casing. The casing comprises the following chemical components by weight: C 0.2-0.3%, Si 0.17-0.37%, Mn 0.9-1.15%, P ≤ 0.012%, S ≤ 0.003%, Cr 0.30-0.45%, Ni 0.30-0.45%, Mo 0.4-0.6%, Cu 0.3-0.45%, Nb 0.03-0.1%, Ti 0.01-0.05%, RE 0.001-0.005%, Al 0.01-0.030%, Ca 0.01-0.03%, N ≤ 0.005%, O+H+N ≤ 0.008%, with the balance being Fe and other unavoidable impurities. The casing has the characteristics of high strength, high plasticity and toughness, and strong corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum 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 global energy demand, the development of unconventional oil and gas resources has received increasing attention. In the production of unconventional oil and gas, such as shale oil and gas and tight oil and gas, the number of special well structures such as directional wells and extended reach wells is increasing. Most oil and gas wells require production stimulation. Due to the complex reservoir geology and harsh operating procedures, the casing is subjected to large non-uniform loads, formation displacement, and alternating stresses. Under these complex working conditions, traditional casing often deforms due to insufficient strength and poor strain capacity. In severe cases, deformation can reach 30% to 50%, resulting in the inability to set bridge plugs, a reduction in the number of fracturing stages, lower well production, and shortened well life. Severe casing deformation can make drilling and plugging impossible and even lead to wellbore integrity failure.

[0003] The traditional casing string design method is stress-based, which requires the working stress to be lower than the material yield strength, that is, the casing (string) is not allowed to undergo plastic deformation during use. However, in reality, due to changes in wellbore curvature and azimuth, the wellbore trajectory has an irregular spatial shape. In addition, the implementation of production-enhancing measures such as fracturing stimulation will cause local plastic deformation of the casing. This puts forward requirements for the plastic deformation capacity (yield strength ratio, uniform elongation) of the casing. In other words, the plastic deformation of the casing needs to be controlled within the allowable range to ensure the safe use of the deformed casing. In other words, the casing (string) design based on strain is adopted, which also proposes the development and application of high-strength and high-strain casing.

[0004] To date, with the exception of high-strain casing used in heavy oil steam thermal recovery wells, there have been few reports on the application of high-strain casing internationally. For N80 and below steel grade casing, although strain-based casing string design methods have not been adopted and no requirements for casing strain performance have been set, due to their low strength and high elongation (including uniform elongation), most casing can easily meet the high-strain performance requirements of the strain-based casing string design method. However, for P110 and above steel grade casing, due to the trade-off between strength and plasticity and toughness, it is often difficult to meet all the requirements simultaneously. In fact, a large portion of P110 and above steel grade casing has a yield ratio exceeding 0.93, with some even reaching 0.98. Excessively high yield ratios can significantly reduce the material's uniform plastic deformation capacity and seriously reduce its safety in use. Based on relevant research results and engineering experience, it is proposed to control the yield ratio of casing to below 0.93 or even lower to meet the requirements of the strain-based design method for casing string safety. In addition, during unconventional oil and gas development, due to the influence of CO2, Cl -The presence of sulfate-reducing bacteria (SRB) is often accompanied by a certain degree of corrosion. Therefore, there is an urgent need to develop a casing for unconventional oil and gas development that has 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-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a casing for unconventional oil and gas development, and a preparation method and application thereof, aiming to provide a casing for unconventional oil and gas development with high strength, large strain and corrosion resistance, so as to solve the problem of insufficient plasticity and corrosion resistance of existing high-strength casing.

[0007] The technical solutions of the present invention are as follows:

[0008] A first aspect of the present invention provides a casing for unconventional oil and gas development, wherein the casing for unconventional oil and gas development comprises the following chemical components, calculated by weight percentage:

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

[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 unavoidable impurities.

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

[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 unavoidable impurities.

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

[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%, Ca0.018%~0.020%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other unavoidable impurities.

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

[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 unavoidable impurities.

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

[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] A second aspect of the present invention provides a method for preparing a casing for unconventional oil and gas development, comprising the following steps:

[0021] After the chemical composition of the casing for unconventional oil and gas development as described above is prepared, smelted and continuously casted, a continuous casting billet is obtained;

[0022] The continuous casting billet is subjected to hot piercing and hot continuous rolling to obtain a tube billet;

[0023] 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.

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

[0025] 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.

[0026] Optionally, the steps of subjecting the tube blank to quenching and tempering heat treatment, heat straightening, and stress relief tempering, and then threading the tube to obtain the casing for unconventional oil and gas development specifically include:

[0027] 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;

[0028] 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 then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0029] The third aspect of the present invention provides a casing for unconventional oil and gas development as described above, or the use of the casing for unconventional oil and gas development prepared by the preparation method as described above in unconventional oil and gas development.

[0030] Beneficial effects: The casing provided by the present invention is a high-strength and high-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 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 high-strain casing in unconventional oil and gas development. DETAILED DESCRIPTION

[0031] The present invention provides a casing for unconventional oil and gas development, a method for manufacturing the casing, and its application. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

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

[0033] An embodiment of the present invention provides a casing for unconventional oil and gas development, wherein the casing for unconventional oil and gas development comprises the following chemical components, calculated by weight percentage:

[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%, and the balance is Fe and other inevitable impurities.

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

[0036] The present invention proposes to use medium-low C, add the alloying element Mn, add a small amount of Cr, Ni, Mo, Cu elements, Nb, Ti composite microalloying, and also add trace RE elements to control harmful elements such as P, S, O, H, N in the steel, fully deoxidize Al-Si, and treat the molten steel with Ca to ensure that the requirements of the strain-based casing string design method for casing strength, toughness, large strain performance (yield strength ratio, uniform elongation), and corrosion resistance are met. The casing provided by the present invention is a high-strength and high-strain casing for unconventional oil and gas development. It has excellent comprehensive properties such as strength, plasticity, toughness and corrosion resistance (i.e., high strength, good plasticity and toughness, and strong 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 API standard oil casing of the corresponding steel grade is 0.60-0.70mm / a), which is reduced by about 23%. Therefore, it can meet the demand for high-strength and high-strain casing in unconventional oil and gas development. The high-strength and high-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 due to casing damage, reduce mining costs, and improve the efficiency and economic benefits of unconventional oil and gas development. It has significant market competitiveness and promotion and application value.

[0037] Carbon (C) is the primary strengthening element in steel. Using medium- to low-carbon content improves the steel's plasticity and toughness. However, too low a carbon content is detrimental to improving the steel's hardenability and strength, while too high a carbon content is detrimental to improving the steel's plasticity and toughness. Taking all factors into consideration, the carbon content should be controlled within the range of 0.20% to 0.30%.

[0038] Silicon (Si) is a common element in steel and is also an important deoxidizer. Its content should be controlled within the range of 0.17% to 0.37%.

[0039] Mn (manganese) is dissolved in steel to improve the hardenability of steel and thus increase its strength with little effect on the yield ratio. At the same time, in order to reduce segregation, it is best to control it within the range of 0.90% to 1.15% based on comprehensive considerations.

[0040] Cr (chromium) is dissolved in steel to improve its hardenability and tempering stability, thereby increasing its strength and corrosion resistance. However, excessive Cr content increases costs. Taking all factors into consideration, it is best to control the Cr content within the range of 0.30% to 0.45%.

[0041] Nickel (Ni) dissolves in steel to improve its hardenability and thus strength. Its addition also increases its plasticity and toughness, and improves the hot working properties of Cu-containing steels. However, excessive Ni content increases costs. Taking all factors into consideration, it is advisable to keep Ni content within the range of 0.30% to 0.45%.

[0042] Mo (molybdenum) is dissolved in steel to improve the hardenability and tempering stability of the steel, compensating for the adverse effect of low Cr content on hardenability, thereby improving the strength of the steel. At the same time, adding Mo can inhibit the segregation of Mn and P, improve uniformity, and improve the temper brittleness and corrosion resistance of the steel. The effect is better when Mo / P ≥ 15 (i.e., the ratio of Mo mass percentage to P mass percentage is greater than or equal to 15), but too high a content will increase the cost. Taking all factors into consideration, it is advisable to control it within the range of 0.40% to 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. However, too high a content can also cause Cu embrittlement. Taking all factors into consideration, it is advisable to control it within the range of 0.30% to 0.45%.

[0044] Niobium (Nb) is added to steel to form NbC and NbN with C and Nb, respectively. This inhibits austenite grain growth and refines the grains, thereby improving strength and toughness. However, excessive Niobium content can form excessive carbon and nitrogen compounds, increasing the brittleness of the steel and leading to increased costs. Taking all factors into consideration, the Niobium content should be controlled within the range of 0.03% to 0.10%.

[0045] Titanium (Ti) is added to steel to deoxidize and fix nitrogen. It reacts with carbon and nitrogen in the steel to form TiC and TiN, respectively, which hinders the growth of austenite grains and refines the grains, thereby improving strength and toughness. However, excessive content will form excessive carbon and nitrogen compounds, increasing the brittleness of the steel and leading to increased costs. Taking all factors into consideration, the Ti content should be controlled within the range of 0.01% to 0.05%.

[0046] The embodiment of the present invention adopts Nb-Ti composite microalloying, which can achieve better strengthening and toughening effects than adding Nb or Ti alone, so that the casing has good strength and toughness.

[0047] Rare earth elements (RE) have multiple functions, including purifying molten steel, refining grains, modifying inclusions, and alloying, thereby improving the steel's strength, toughness, and corrosion resistance. Taking all factors into consideration, the ideal concentration should be controlled within the range of 0.001% to 0.005%. The addition of Cr, Mo, Cu, and RE in the embodiments of the present invention, and their synergistic effect, enhances the corrosion resistance of the casing and reduces strength loss and failure risk caused by corrosion.

[0048] Al (aluminum) combines with oxygen or nitrogen to form fine, evenly distributed oxides or nitrides, which can refine grains and improve strength and toughness. It is also an important deoxidizer and nitrogen fixer. However, excessive content can affect the hot working properties of steel. Taking all factors into consideration, it is best to control the content within the range of 0.010% to 0.030%.

[0049] Adding Ca (calcium) to steel can improve the properties and morphology of inclusions, thereby enhancing the steel's plasticity, toughness, and corrosion resistance. The effect is best achieved when Ca / S ≥ 2 (i.e., the ratio of the mass percentage of Ca to the mass percentage of S is greater than or equal to 2). Taking all factors into consideration, the content should be controlled within the range of 0.010% to 0.030%.

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

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

[0052] O (oxygen), H (hydrogen), and N (nitrogen) are harmful elements that primarily affect the plasticity, toughness, and corrosion resistance of steel. Taking all factors into consideration, it is recommended to control O+H+N to ≤ 0.008%. Considering the significant impact of N on the strain aging properties of steel, it is recommended to control N to ≤ 0.005% (i.e., the N content by mass is less than or equal to 0.005%).

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

[0054] 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 unavoidable impurities.

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

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

[0057] 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 unavoidable impurities.

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

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

[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%, Ca0.018%~0.020%, N≤0.005%, O+H+N≤0.008%, and the balance is Fe and other unavoidable 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 strength 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, the casing for unconventional oil and gas development comprises the following chemical components, calculated by weight percentage:

[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 unavoidable 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 strength 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, the casing for unconventional oil and gas development comprises the following chemical components, calculated by weight percentage:

[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, the yield strength is 1127-1132 MPa, the tensile strength is 1212-1217 MPa, the yield strength ratio is 0.93, the total elongation is 20%, the uniform elongation is 10%, the transverse Charpy V-notch impact toughness at 0°C is 82-87 J, and the corrosion rate is 0.54 mm / a (i.e., 0.54 mm per year).

[0068] The present invention develops a manufacturing process that matches the chemical composition of the above-mentioned proportion and content, mainly through steelmaking (including refining outside the furnace, vacuum degassing), continuous casting, hot rolling in the austenite zone, tempering heat treatment, hot straightening, stress relief tempering (also known as stress relief tempering) and other processes, so that the material obtains a fine and uniform tempered bainite microstructure to achieve a reasonable match of material strength, plasticity, toughness and corrosion resistance; in order to control the yield strength, the final rolling temperature is appropriately increased, a higher hot straightening temperature is adopted, and stress relief tempering and other measures are adopted. Specifically, an embodiment of the present invention also provides a method for preparing casing for unconventional oil and gas development, which includes the following steps:

[0069] S1. According to the chemical composition of the casing for unconventional oil and gas development as described above, the raw materials are mixed, smelted, and continuously cast to obtain a continuously cast billet;

[0070] S2, hot piercing and hot rolling the continuous casting billet to obtain a tube billet;

[0071] S3. After performing quenching and tempering heat treatment, heat straightening, and stress relief tempering on the tube blank, thread processing is performed 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 high-strain casing for unconventional oil and gas development. It 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 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 high-strain casing in unconventional oil and gas development. The preparation method provided by the present invention involves improving purity, hot rolling with controlled cooling, and proper heat treatment to control microstructure, resulting in casing with high strength, high toughness, excellent high-strain properties, and corrosion resistance. Under complex loads, it can undergo significant plastic deformation without breaking, effectively adapting to conditions such as stratum displacement in unconventional oil and gas production. The details are 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 modify the 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 technology 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 continuously cast 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 sawn to a suitable length to obtain a tube billet.

[0078] In this step, adopting a higher finishing 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 threaded to obtain the casing for unconventional oil and gas development, specifically comprising:

[0080] 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 greater than or equal to 30° C. / s. Then, the tube blank is tempered at a temperature of 560-660° C. for 90-120 minutes and then water-cooled (water cooling after tempering is to avoid possible temper brittleness) to obtain fine and uniform tempered bainite with a grain size greater than or equal to level 8;

[0081] After hot straightening at a temperature of 510-610°C, the casing is water-cooled. Then, the casing is kept at a temperature of 510-610°C for 90-120 minutes for stress relief tempering and water-cooling (in order to reduce the influence of residual stress on the performance of the casing, tempering and water cooling are performed after hot straightening), and thread processing is performed to obtain the casing for unconventional oil and gas development.

[0082] In this invention, the addition of Cr, Mo, Cu, and RE, and their synergistic effect, imparts excellent corrosion resistance to the casing. Furthermore, clean steel smelting, segregation control, heat treatment microstructure, and residual stress regulation further enhance the casing's corrosion resistance. This coordinated chemical composition and process effectively enhance the casing's corrosion resistance, reducing strength loss and failure risk caused by corrosion. Threading can be performed on the pipe sections to achieve API (American Petroleum Institute) standard or special threads, and the threads can undergo magnetic particle inspection.

[0083] Embodiments of the present invention also provide a casing for unconventional oil and gas development as described above, or use of the casing for unconventional oil and gas development as described above in unconventional oil and gas development. 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 with reference to specific examples.

[0085] Table 1 Chemical composition of casing for unconventional oil and gas development in Examples 1-6

[0086]

[0087]

[0088] Table 2 Chemical composition of casing for unconventional oil and gas development in Examples 7-15

[0089]

[0090] In Table 1 and Table 2, in Examples 1-15, the content of each chemical component is in percentage by mass, and the remainder to 100% is Fe and unavoidable impurities.

[0091] Example 1

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

[0093] Steelmaking: The raw materials were prepared according to the chemical composition of the casing for unconventional oil and gas development of Example 1 shown in Table 1. The steel was then subjected to oxygen-blown converter steelmaking, Si-Ca wire feeding, off-furnace refining, and vacuum degassing to obtain molten steel.

[0094] Continuous casting: The molten steel is cast into rod-shaped continuous casting billets. Electromagnetic stirring and soft reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0095] Piercing and hot rolling: The continuous casting billet is heated in a ring heating furnace with a heating furnace temperature of 1215°C and a heating time of 120 minutes. Then, hot piercing is performed at a temperature of 1180°C, and hot rolling is performed at a temperature of 950-1150°C (the initial rolling temperature is 1150°C and the final rolling temperature is 950°C). Then, air cooling is performed (i.e., air cooling), and sawing is performed to a suitable length to obtain a tube billet.

[0096] Tempering heat treatment and hot straightening: adopting the heat treatment process of protective atmosphere furnace heating, quenching + high temperature tempering, the tube blank is heated at a temperature of 900°C, kept at this temperature for 50 minutes, and then cooled by internal and external water spraying at a cooling rate of 30°C / s, and then tempered at a temperature of 650°C for 90 minutes and then water-cooled;

[0097] The casing is straightened at 600° C. and then water-cooled. The casing is then kept at 600° C. for 90 minutes for stress relief tempering and then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0098] Example 2

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

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

[0101] Continuous casting: Same as Example 1.

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

[0103] Tempering heat treatment and heat straightening: same as in Example 1.

[0104] Example 3

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

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

[0107] Continuous casting: Same as Example 1.

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

[0109] Tempering heat treatment and heat straightening: same as in Example 1.

[0110] Example 4

[0111] This embodiment provides a method for preparing casing for unconventional oil and gas development, comprising the following steps:

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

[0113] Continuous casting: Same as Example 1.

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

[0115] Tempering heat treatment and hot straightening: adopting the heat treatment process of protective atmosphere furnace heating, quenching + high temperature tempering, the tube blank is heated at a temperature of 900°C, kept at this temperature for 60 minutes, and then cooled by internal and external water spraying at a cooling rate of 30°C / s, and then tempered at a temperature of 620°C for 100 minutes and then water-cooled;

[0116] The casing is straightened at 570° C. and then water-cooled. The casing is then kept at 570° C. for 100 minutes for stress relief tempering and then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0117] Example 5

[0118] This embodiment provides a method for preparing casing for unconventional oil and gas development, comprising the following steps:

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

[0120] Continuous casting: same as Example 4.

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

[0122] Tempering heat treatment and heat straightening: same as in Example 4.

[0123] Example 6

[0124] This embodiment provides a method for preparing casing for unconventional oil and gas development, comprising the following steps:

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

[0126] Continuous casting: same as Example 4.

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

[0128] Tempering heat treatment and heat straightening: same as in Example 4.

[0129] Example 7

[0130] This embodiment provides a method for preparing casing for unconventional oil and gas development, comprising the following steps:

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

[0132] Continuous casting: Same as Example 1.

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

[0134] Tempering heat treatment and hot straightening: adopting the heat treatment process of protective atmosphere furnace heating, quenching + high temperature tempering, the tube blank is heated at a temperature of 900°C, kept at this temperature for 60 minutes, and then cooled by internal and external water spraying at a cooling rate of 30°C / s, and then tempered at a temperature of 610°C for 110 minutes and then water-cooled;

[0135] The casing is straightened at 560° C. and then water-cooled. The casing is then kept at 560° C. for 110 minutes for stress relief tempering and then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0136] Example 8

[0137] This embodiment provides a method for preparing casing for unconventional oil and gas development, comprising the following steps:

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

[0139] Continuous casting: same as Example 7.

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

[0141] Tempering heat treatment and heat straightening: same as Example 7.

[0142] Example 9

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

[0144] Steelmaking: The only difference from Example 7 is that the ingredients are prepared according to the chemical composition of the casing for unconventional oil and gas development of Example 9 shown in Table 2.

[0145] Continuous casting: same as Example 7.

[0146] Piercing and hot rolling: same as in Example 7.

[0147] Tempering heat treatment and heat straightening: same as Example 7.

[0148] Example 10

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

[0150] Steelmaking: The only difference from Example 1 is that the ingredients are prepared according to the chemical composition of the casing for unconventional oil and gas development of Example 10 shown in Table 2.

[0151] Continuous casting: Same as Example 1.

[0152] Piercing and hot rolling: same as in Example 1.

[0153] Tempering heat treatment and hot straightening: adopting the heat treatment process of protective atmosphere furnace heating, quenching + high temperature tempering, the tube blank is heated at 900℃, kept at this temperature for 70 minutes, and then cooled by internal and external water spray at a cooling rate of 30℃ / s, and then tempered at 590℃ for 120 minutes and then water-cooled;

[0154] The casing is straightened at 540° C. and then water-cooled. The casing is then kept at 540° C. for 120 minutes for stress relief tempering and then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0155] Example 11

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

[0157] Steelmaking: The only difference from Example 10 is that the ingredients are prepared according to the chemical composition of the casing for unconventional oil and gas development of Example 11 shown in Table 2.

[0158] Continuous casting: same as Example 10.

[0159] Piercing and hot rolling: same as Example 10.

[0160] Tempering heat treatment and heat straightening: same as Example 10.

[0161] Example 12

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

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

[0164] Continuous casting: same as Example 10.

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

[0166] Tempering heat treatment and heat straightening: same as Example 10.

[0167] Example 13

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

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

[0170] Continuous casting: Same as Example 1.

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

[0172] Tempering heat treatment and heat straightening: adopt protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process,

[0173] The tube blank is heated at 900°C, kept at this temperature for 70 minutes, and then cooled by spraying water inside and outside at a cooling rate of 30°C / s, and then tempered at 570°C for 120 minutes and then water-cooled;

[0174] The casing is straightened at 520° C. and then water-cooled. The casing is then kept at 520° C. for 120 minutes for stress relief tempering and then water-cooled. The casing is threaded to obtain the casing for unconventional oil and gas development.

[0175] Example 14

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

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

[0178] Continuous casting: Same as Example 13.

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

[0180] Tempering heat treatment and heat straightening: same as Example 13.

[0181] Example 15

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

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

[0184] Continuous casting: Same as Example 13.

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

[0186] Tempering heat treatment and heat straightening: same as Example 13.

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

[0188] Table 3. Properties of casing for unconventional oil and gas development in Examples 1-15

[0189]

[0190] The test conditions for the corrosion rate are as follows: (temperature of 60° C., carbon dioxide pressure of Pco2=0.25 MPa, chloride ion (Cl-) content of 30,000 mg / L, and SRB content of 100,000 / mL).

[0191] The test results indicate that the high-strength, high-strain casing for unconventional oil and gas development of the present invention exhibits excellent comprehensive properties, including strength, ductility, toughness, and corrosion resistance. The casing exhibits room-temperature yield strength of 867 MPa to 1132 MPa, tensile strength of 1020 MPa to 1217 MPa, yield strength ratio of 0.85 to 0.93, total elongation of 20% to 28%, uniform elongation of 10% to 18%, transverse Charpy V-notch impact toughness of 82 J to 126 J at 0°C, and corrosion rate of 0.46 mm / a to 0.54 mm / a (compared to the corrosion rate of API standard oil casing of the corresponding steel grade of 0.60 mm / a to 0.70 mm / a), representing a reduction of approximately 23%. This material meets the demand for high-strength, high-strain casing in unconventional oil and gas development.

[0192] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A casing for unconventional oil and gas development, characterized in that: The casing for unconventional oil and gas development comprises the following chemical compositions, calculated by mass percentage: C 0.20%~0.30%, Si 0.17%~0.37%, Mn 0.90%~1.15%, P≤0.012%, S≤0.003%, Cr0.30%~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 is Fe and other unavoidable impurities; The casing for unconventional oil and gas development has a room temperature yield strength of 867 to 1132 MPa, a tensile strength of 1020 to 1217 MPa, a yield strength ratio of 0.85 to 0.93, a total elongation of 20% to 28%, a uniform elongation of 10% to 18%, a transverse Charpy V-notch impact toughness of 82 to 126 J at 0°C, and a corrosion rate of 0.46 to 0.54 mm / a.

2. The casing for unconventional oil and gas development according to claim 1, characterized in that: The casing for unconventional oil and gas development comprises the following chemical compositions, calculated by mass percentage: C 0.20%~0.22%, Si 0.17%~0.25%, Mn 0.90%~0.96%, P≤0.011%, S≤0.003%, Cr0.30%~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%, 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 comprises the following chemical compositions, calculated by mass percentage: C 0.23%~0.25%, Si 0.23%~0.27%, Mn 0.99%~1.01%, P≤0.011%, S≤0.003%, Cr0.34%~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%, 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 comprises the following chemical compositions, calculated by mass percentage: C 0.25%~0.26%, Si 0.28%~0.31%, Mn 1.05%~1.07%, P≤0.012%, S≤0.003%, Cr0.36%~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%, 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 comprises the following chemical compositions, calculated by mass percentage: C 0.25%~0.27%, Si 0.21%~0.24%, Mn 1.09%~1.11%, P≤0.011%, S≤0.003%, Cr0.40%~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%, 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 comprises the following chemical compositions, calculated by mass percentage: C 0.28%~0.30%, Si 0.29%~0.37%, Mn 1.13%~1.15%, P≤0.012%, S≤0.002%, Cr0.43%~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%, the balance is Fe and other inevitable impurities.

7. A method for preparing a casing for unconventional oil and gas development according to any one of claims 1 to 6, characterized in that: The steps include: The chemical composition of the casing for unconventional oil and gas development according to any one of claims 1 to 6 is subjected to batching, smelting, and continuous casting to obtain a continuous casting billet; 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 The steps of subjecting the tube blank to quenching and tempering heat treatment, heat straightening, and stress relief tempering, and then threading the tube to obtain the casing for unconventional oil and gas development 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 then 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 according to any one of claims 1 to 6, or a casing for unconventional oil and gas development prepared by the preparation method according to any one of claims 7 to 9 in unconventional oil and gas development.

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