Iron-based shape memory alloy oil casing and preparation method thereof

Abstract

The invention belongs to the technical field of oil well pipe manufacturing in the petroleum and natural gas industry, and discloses an iron-based shape memory alloy petroleum casing pipe and a preparation method thereof.The preparation method comprises the steps that a round pipe blank is prepared through smelting, continuous casting and forging; the round pipe blank is perforated; performing pipe rolling on the perforated round pipe blank; cooling the rolled round tube blank; carrying out heat treatment on the cooled round tube blank; and carrying out hot straightening on the round tube blank subjected to heat treatment to obtain a finished product. According to the invention, the shape memory alloy is used as the material of the oil casing, the shape memory ability and the recovery stress of the alloy are improved through the element composition design of the material alloy, the yield of the casing is improved, and when the casing deforms due to non-uniform load of a stratum, steam with the temperature of more than 300 DEG C is injected into the underground casing, so that the deformation of the casing is reduced. The deformed casing can be restored to a certain extent, so that the problem that subsequent operation tools cannot smoothly pass through for operation due to deformation of the casing of a shale gas well is solved, and the development efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil well pipe manufacturing in the petroleum and natural gas industry, and in particular relates to an iron-based shape memory alloy oil casing and a preparation method thereof. Background Art

[0002] The shale gas reservoirs in Sichuan and Chongqing are characterized by deep reservoirs, high formation pressure, complex natural fractures, long horizontal sections of shale gas wells, high fracturing operation pressure, large fracturing fluid displacement, and long operation cycles. The pipe string is subjected to complex forces. At the same time, affected by the active geological movement in the region, the damage problem of the production casing string is very serious. According to the survey and analysis, the damage to the production casing is mainly caused by the casing being squeezed or flattened, which makes it impossible to lower the bridge plug and other tools for subsequent operations, delaying the subsequent fracturing construction and production, causing huge time and economic losses, and affecting the construction of shale gas development capacity. At present, the treatment of shale gas well casing damage often uses a relatively extensive method, that is, the casing that has been squeezed or flattened is blasted open by explosives in the well. Although this solves the problem of smooth lowering of subsequent tools, it also causes the explosion of the casing body of this section. During oil and gas production, part of the oil and gas resources passing through this area will re-enter the formation along the cracks in the casing, seriously affecting the production of a single well.

[0003] The Chinese patent with publication number CN 112708730 B discloses "an ultra-high collapse-resistant oil casing and its manufacturing method", with a yield strength of 965-1173MPa, a tensile strength of ≥1034MPa, an elongation of ≥20%, a 0℃ transverse Charpy impact energy of ≥120J, and collapse resistance performance exceeding the API standard by more than 25%. The Chinese patent with publication number CN 113637892 B discloses "a high-strength collapse-resistant oil casing and its manufacturing method", with a collapse resistance of more than 55MPa in the Φ244.48mm×11.99mm specification, which exceeds the API standard requirement by more than 40%. Although various types of highly resistant casings have been developed and put into use, the casing damage rate of shale gas horizontal wells is still high. The main reason is that casing damage is mainly caused by non-uniform loads caused by stratum migration, and the casing collapse strength is tested under uniform loads. Under non-uniform loads, the casing collapse strength will drop significantly. At the same time, since the stress generated during stratum migration will be infinite, and the improvement of casing collapse strength is limited, it is far from enough to reduce the probability of casing damage by simply improving the casing collapse resistance. Therefore, it is a very good means of casing change control to develop a casing with deformation recovery ability. When the casing is deformed during stratum migration, the casing deformation can be partially recovered by external excitation, so that subsequent operating tools can pass smoothly.

[0004] Shape memory alloy materials are widely used in aerospace, biology, construction and other fields due to their unique shape memory effect, superelasticity, wear resistance and biocompatibility. Therefore, when developing oil casing based on shape memory alloy, especially in the horizontal section of shale gas wells, when the casing is crushed or flattened, the casing shape can be restored to a certain extent by injecting steam for heating, which does not affect the subsequent insertion of tools, and also reduces the cost of treatment after casing deformation, significantly improving the development efficiency of shale gas wells.

[0005] However, there are currently no mature products of shape memory alloys used in the oil and gas drilling and production field. Due to the different service performance requirements of components and materials in different application scenarios, especially for shape memory alloy casings, there are no precedents to follow from material design to tube rolling process and product heat treatment technology, and copying mature materials used in other fields will not meet the comprehensive performance requirements.

[0006] In summary, there is an urgent need to develop a shape memory alloy casing with high yield strength and anti-collapse performance and a certain deformation recovery ability, so that the casing can be used in the harsh service conditions of shale gas wells and reduce the occurrence of casing damage accidents. Summary of the invention

[0007] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to solve the current situation that there is no mature shape memory alloy petroleum pipe, and to provide an iron-based shape memory alloy petroleum casing and a preparation method thereof, so as to solve the problem that shale gas wells cannot smoothly pass subsequent operating tools due to casing deformation, thereby improving development efficiency. When the casing is deformed due to non-uniform formation load, by injecting steam above 300°C into the downhole casing, the deformed casing can be restored to a certain extent.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] An iron-based shape memory alloy petroleum casing, characterized in that the chemical elements in the petroleum casing, by weight percentage, include Mn: 25-33%, Si: 5.2-6.0%, Cr: 5.8-9.2%, Ni: 5.3-7.5%, Nb: 0.32-0.46%, V: 0.01-0.04%, N: 0.01-0.04%, C≤0.2%, P≤0.01%, S≤0.01%, and the rest are Fe and unavoidable impurities.

[0010] Furthermore, the microstructure of the oil casing is tempered martensite.

[0011] Furthermore, the room temperature tensile properties of oil casing are: R t0.6 758-908MPa, R m≥1013MPa, elongation ≥20%;

[0012] Impact properties of oil casing at -20℃: transverse A kv ≥100 joules, longitudinal A kv ≥120 joules;

[0013] The room temperature anti-extruded strength of petroleum casing is ≥138MPa, the residual stress is ≤40MPa, and the deformation recovery rate at 300℃ is ≥60%.

[0014] On the other hand, the present invention discloses a method for preparing an iron-based shape memory alloy petroleum casing, comprising the following steps:

[0015] Prepare round tube billets by smelting, continuous casting and forging;

[0016] Punching the round tube blank;

[0017] Rolling the perforated round tube billet;

[0018] Cooling the round tube billet after tube rolling;

[0019] Heat treating the cooled round tube blank;

[0020] The heat-treated round tube billet is heat-straightened to obtain a finished product.

[0021] Further, the round tube blank is perforated, including:

[0022] The round tube billet is pierced by a two-time piercing process, with the initial piercing temperature of 2030-2100°C, the final piercing temperature of 1550-1600°C, the final piercing plug outer diameter of 1.2 times the initial piercing plug outer diameter, and the running speed of the piercing mandrel of 10m / s.

[0023] Further, the perforated round tube blank is rolled, including:

[0024] The starting rolling temperature of the tube is 1300-1350℃, and the final rolling temperature is 1100-1150℃.

[0025] Furthermore, the perforated round tube blank is subjected to tube rolling, which further comprises:

[0026] The round tube billet after final rolling is kept at 1150°C for 30 minutes;

[0027] The round tube billet after heat preservation is subjected to tension reduction, and the temperature of tension reduction is 1150°C and the time is 30 minutes.

[0028] Further, the round tube billet after tube rolling is cooled, including:

[0029] The rolled round tube is fed into a 1150°C annular furnace and cooled to room temperature at a rate of 10°C / s.

[0030] Further, the cooled round tube blank is heat treated, including:

[0031] The cooled round tube billet is subjected to two-stage solution treatment: after being kept at 1120-1150°C for 1.5h, it is kept at 1080-1100°C for 2.5h;

[0032] The round tube billet after two-stage solution treatment is subjected to aging treatment: keeping at 850-900℃ for 3h, and then air cooling to room temperature;

[0033] The round tube billet after aging treatment is tempered: the tempering temperature is 200-250℃.

[0034] Further, the heat-treated round tube blank is subjected to heat straightening, including:

[0035] The temperature of heat straightening is controlled to be 200℃;

[0036] Straightening force according to the model set up,

[0037] Where F is the straightening force; D is the outer diameter of the round tube; t is the wall thickness of the round tube; d is the inner diameter of the round tube; F 0 is the initial value of the straightening force.

[0038] Technical effects and advantages of the present invention:

[0039] 1. The present invention uses shape memory alloy as the material of the oil casing. When the casing is deformed during formation migration, the casing deformation can be partially restored by external excitation means, so that subsequent operating tools can pass smoothly, solving the problem that the casing loss rate of shale gas horizontal wells is still high.

[0040] 2. In the design of the alloy element composition of the material, the present invention improves the shape memory ability and recovery stress of the alloy by reasonably controlling the element content of V and N, and improves the yield rate of the casing by controlling the content of elements such as P, S, and C.

[0041] 3. The present invention adopts a two-perforation process to control the outer diameter of the final perforation plug to 1.2 times the outer diameter of the initial perforation plug, which effectively prevents the sleeve from deforming and recovering during perforation; secondly, the present invention combines the characteristics of shape memory alloys and reasonably sets process parameters such as tube rolling, tension reduction, cooling, and heat treatment to effectively ensure the one-time forming and quality stability of the tube body.

[0042] 4. The present invention proposes a thermal straightening force calculation model This ensures that the tube body will not recover from deformation during the heat straightening process.

[0043] 5. The tensile properties of the sleeve prepared by the present invention are R t0.6 758-908MPa, R m ≥1013MPa, elongation ≥20%, -20℃ impact performance is transverse A kv ≥100 joules, longitudinal A kv ≥120 joules, anti-external collapse strength ≥138MPa, residual stress ≤40MPa, deformation recovery rate at 300℃ ≥60%, which meets the use requirements of oil casing, can realize large-scale production and manufacturing, and has good economic benefits.

[0044] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a flow chart of a method for preparing an iron-based shape memory alloy petroleum casing. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] In order to overcome the defects of the above-mentioned prior art, the present invention provides an iron-based shape memory alloy petroleum casing. The chemical elements in the petroleum casing include, by weight percentage, Mn: 25-33%, Si: 5.2-6.0%, Cr: 5.8-9.2%, Ni: 5.3-7.5%, Nb: 0.32-0.46%, V: 0.01-0.04%, N: 0.01-0.04%, C≤0.2%, P≤0.01%, S≤0.01%, and the rest are Fe and unavoidable impurities.

[0048] It should be noted that the iron-based shape memory alloy oil casing of the present invention includes a 110ksi grade iron-based shape memory alloy oil casing, which is designed with iron-based components, and takes into account the economy, easy processing and deformation memory recovery ability of the casing through the reasonable proportion of Mn, Si, Cr, Ni, Nb, V, N, and C elements. In the iron-based shape memory alloy oil casing of the present invention, the design principles of each chemical element are as follows:

[0049] Mn: Mn content affects the M S (start of martensitic transformation) point and T n (antiferromagnetic transition temperature) point has an important influence, M s As the Mn content increases, T n It increases with the increase of Mn content. n >M s When the Mn content is too low, the γ phase will be stabilized and it will be unfavorable for the formation of ε martensite; when the Mn content is too low, α′ martensite is easily generated at the intersection of stress-induced ε martensite sheets, making atomic movement irreversible and reducing the shape recovery rate of the alloy. In order to ensure the strength and deformation recovery requirements of the alloy, and at the same time ensure the structural stability at the alloy perforation and rolling temperature, the mass percentage content of the Mn element in the oil casing is controlled to 28-33%.

[0050] Si: The addition of Si can reduce the stacking fault energy of austenite, making it easy to induce the ε martensite phase, promote the γ-ε phase transformation, and reduce the critical stress of the ε martensite formation. Therefore, as the Si content increases, the shape memory effect of the alloy increases. When the Si content exceeds a certain level, the plasticity of the alloy will decrease, the brittleness will increase, and it will be unfavorable for processing and forming. In order to ensure the shape memory ability and plasticity of the oil casing, the mass percentage content of the Si element in the oil casing is controlled at 5.2-6.0% in the present invention.

[0051] Cr: The addition of Cr can significantly improve the corrosion resistance of the alloy, strengthen the γ phase, and increase the critical stress of slip. It can promote the γ-ε phase transformation during deformation, and reduce slip while also improving the shape memory effect. However, if the Cr content is too high, it is easy to generate brittle α′ phase, which reduces the plasticity of the alloy and further affects the processing performance of the alloy. In order to ensure the corrosion resistance and processability of the alloy, the mass percentage content of the Cr element in the oil casing is controlled to 5.8-9.2% in the present invention.

[0052] Ni: Ni element strongly affects the distribution of stacking faults. With the increase of Ni content, the density of ε martensite and stacking faults decreases, which is conducive to the nucleation of ε martensite. At the same time, the addition of Ni can inhibit the appearance of α′ phase caused by the addition of Cr, which is used to improve the processing performance. However, because Ni can stabilize the γ phase and reduce the M s In order to ensure the processability and shape memory ability of the alloy, the mass percentage content of the Cr element in the petroleum casing is controlled within 5.3-7.5%.

[0053] C: The C element mainly improves the shape memory effect by solid solution strengthening the austenite matrix, but too high a C content will reduce the corrosion resistance of the alloy and reduce the chemical uniformity, which is not conducive to the industrial application of the alloy. In order to ensure the corrosion resistance and industrial application of the alloy, the mass percentage content of the C element in the oil casing is controlled within 0.2% in the present invention.

[0054] Nb: Nb element mainly improves the shape memory effect of the alloy by forming fine dispersed NbC precipitation with carbon in the alloy, but Nb has little effect on the shape memory effect when it exists alone. However, sometimes the generation of α′ martensite will inhibit the generation of ε martensite and weaken the recovery characteristics of the alloy. Since the mass percentage content of C element in the alloy is within 0.2%, in order to achieve the optimal ratio with C element and thus improve the recovery ability of the alloy, the mass percentage content of Nb element in the oil casing is controlled to 0.32-0.46% in the present invention.

[0055] V, N: The addition of a small amount of V and N elements can generate fine dispersed VN, NbN, and VC, and improve the shape memory effect and recovery stress of the alloy. The present invention controls the V and N contents in the oil casing to 0.01-0.04%.

[0056] P, S: P and S are unavoidable harmful elements in alloy steel, which have a bad influence on the toughness and corrosion resistance of the alloy. The present invention controls the mass percentage content of P and S elements in the petroleum casing to ≤0.01%.

[0057] In some embodiments of the present invention, the microstructure of the petroleum casing is tempered martensite.

[0058] In some embodiments of the present invention, the room temperature tensile properties of the petroleum casing are: t0.6 758-908MPa, R m ≥1013MPa, elongation ≥20%;

[0059] Impact properties of oil casing at -20℃: transverse A kv ≥100 joules, longitudinal A kv ≥120 joules;

[0060] The room temperature anti-extruded strength of petroleum casing is ≥138MPa, the residual stress is ≤40MPa, and the deformation recovery rate at 300℃ is ≥60%.

[0061] On the other hand, Figure 1 As shown, the present invention discloses a method for preparing an iron-based shape memory alloy petroleum casing, comprising the following steps:

[0062] Prepare round tube billets by smelting, continuous casting and forging;

[0063] Punching the round tube blank;

[0064] Rolling the perforated round tube billet;

[0065] Cooling the round tube billet after tube rolling;

[0066] Heat treating the cooled round tube blank;

[0067] The heat-treated round tube billet is heat-straightened to obtain a finished product.

[0068] In some embodiments of the present invention, perforating a round tube blank comprises:

[0069] The round tube billet is pierced by a two-time piercing process, with the initial piercing temperature of 2030-2100°C, the final piercing temperature of 1550-1600°C, the final piercing plug outer diameter of 1.2 times the initial piercing plug outer diameter, and the running speed of the piercing mandrel of 10m / s.

[0070] In some embodiments of the present invention, the perforated round tube blank is subjected to tube rolling, comprising:

[0071] The starting rolling temperature of the tube is 1300-1350℃, and the final rolling temperature is 1100-1150℃.

[0072] In some embodiments of the present invention, the method of rolling the perforated round tube blank further comprises:

[0073] The round tube billet after final rolling is kept at 1150°C for 30 minutes;

[0074] The round tube billet after heat preservation is subjected to tension reduction, and the temperature of tension reduction is 1150°C and the time is 30 minutes.

[0075] In some embodiments of the present invention, cooling the round tube blank after tube rolling comprises:

[0076] The rolled round tube is fed into a 1150°C annular furnace and cooled to room temperature at a rate of 10°C / s.

[0077] In some embodiments of the present invention, the cooled round tube blank is heat treated, comprising:

[0078] The cooled round tube billet is subjected to two-stage solution treatment: after being kept at 1120-1150°C for 1.5h, it is kept at 1080-1100°C for 2.5h;

[0079] The round tube billet after two-stage solution treatment is subjected to aging treatment: keeping at 850-900℃ for 3h, and then air cooling to room temperature;

[0080] The round tube billet after aging treatment is tempered: the tempering temperature is 200-250℃.

[0081] In some embodiments of the present invention, heat straightening is performed on the heat-treated round tube blank, comprising:

[0082] The temperature of heat straightening is controlled to be 200℃;

[0083] Straightening force according to the model set up,

[0084] F is the straightening force; D is the outer diameter of the tube; t is the wall thickness of the tube; d is the inner diameter of the tube; F 0 is the initial value of the straightening force, which can be taken as 20kN.

[0085] In order to better illustrate the solutions of the present invention, the following examples are also provided.

[0086] Example 1

[0087] The casing specification is Φ139.7mm×12.7mm and is manufactured in the following steps:

[0088] S1: Smelting, continuous casting and forging according to the alloy element composition of 0.15% C, 5.5% Si, 30% Mn, 7% Cr, 7% Ni, 0.45% Nb, 0.025% V, and 0.03% N to obtain a round tube billet.

[0089] S2: The round tube billet is pierced by a two-time piercing process. The initial piercing temperature is set to 2050°C, followed by the final piercing. The final piercing temperature is 1600°C. The outer diameter of the final piercing plug is 1.2 times the outer diameter of the initial piercing plug. The running speed of the piercing mandrel is 10m / s.

[0090] S3: The pierced round tube billet is rolled, the starting rolling temperature is 1300°C, the final rolling temperature is 1150°C, and after the final rolling, it is kept in a ring furnace at a temperature of 1150°C for 30 minutes, and then tension reduction is performed.

[0091] S4: The round tube billet after tension reduction is sent into an annular furnace with a temperature of 1150°C, and the cooling rate of the annular furnace is controlled to be 10°C / s, and the round tube billet is cooled to room temperature along with the furnace.

[0092] S5: The round tube billet cooled to room temperature is heat treated at 1140°C for 1.5 hours, and then at 1080°C for 2.5 hours for secondary solution treatment. After solution treatment, the temperature is lowered to 850°C for 3 hours of aging treatment, and then air-cooled to room temperature for tempering, and the tempering temperature is 250°C.

[0093] S6: The heat-treated round tube is straightened at 200°C. The straightening force is based on the model. Set it to 498.6kN and get the finished product.

[0094] Five sleeves were randomly selected from five different batches of finished products. X-ray residual stress analysis was first performed, and then samples were taken for chemical composition analysis, room temperature tensile property test, -20℃ Charpy impact test and room temperature anti-external collapse strength test. The chemical composition test results of the five sleeves are shown in Table 1: C: 0.13-0.15%, Si: 5.4-5.5%, Mn: 30-30.5%, P: 0.003-0.005%, S: 0.005-0.008%, Cr: 7.1-7.3%, Ni: 6.8-7.0%, Nb: 0.43-0.44%, V: 0.025-0.027%, N: 0.03-0.033%.

[0095] Table 1 Experimental results of chemical composition of casing pipe in Example 1 (wt%)

[0096] Sample No. C Si Mn P S Cr Ni Nb V N 1 0.13 5.5 30 0.005 0.007 7.3 7.0 0.44 0.025 0.032 2 0.14 5.5 30.2 0.003 0.007 7.1 6.8 0.43 0.027 0.03 3 0.13 5.4 30.5 0.006 0.008 7.3 7.0 0.43 0.027 0.033 4 0.15 5.5 30 0.005 0.006 7.3 6.9 0.44 0.025 0.031 5 0.14 5.5 30.2 0.005 0.005 7.2 7.0 0.44 0.025 0.033

[0097] The mechanical properties test results of the five sleeves are shown in Table 2. The room temperature tensile properties are: R t0.6 822-868MPa, R m 1070-1123MPa, elongation ≥22%;

[0098] The impact performance of oil casing at -20℃ is: transverse Akv≥120 joules, longitudinal Akv≥140 joules;

[0099] The anti-external collapse strength of petroleum casing is ≥150MPa and the residual stress is ≤40MPa.

[0100] Table 2 Mechanical properties test results of casing in Example 1

[0101]

[0102] Five finished casings with a length of 1 m were cut and their outer diameters were measured respectively. Then, a compressive load was applied to each casing to flatten it. The flattened casing was heated to 300°C in a heating furnace and kept warm for 30 minutes. It was then cooled with the furnace and its outer diameter after heating was measured. The measurement results are shown in Table 3. The deformation recovery rate of the finished casing at 300°C is ≥63.2%.

[0103] Table 3 Casing deformation capacity recovery test results of Example 1

[0104]

[0105] Example 2

[0106] The casing specification is Φ244.48mm×11.99mm and is manufactured in the following steps:

[0107] S1: Smelting, continuous casting and forging according to the alloy element composition of 0.2% C, 6.0% Si, 33% Mn, 9.2% Cr, 7.5% Ni, 0.45% Nb, 0.04% V, and 0.04% N to obtain a round tube billet.

[0108] S2: The round tube billet is pierced by a two-time piercing process. The initial piercing temperature is set to 2030°C, followed by the final piercing. The final piercing temperature is 1550°C. The outer diameter of the final piercing plug is 1.2 times the outer diameter of the initial piercing plug. The running speed of the piercing mandrel is 10m / s.

[0109] S3: The pierced round tube billet is rolled, the starting rolling temperature is 1300°C, the final rolling temperature is 1100°C, and after the final rolling, it is kept in a ring furnace at a temperature of 1150°C for 30 minutes, and then tension reduction is performed.

[0110] S4: The round tube billet after tension reduction is sent into an annular furnace with a temperature of 1150°C, and the cooling rate of the annular furnace is controlled to be 10°C / s, and the round tube billet is cooled to room temperature along with the furnace.

[0111] S5: The round tube billet cooled to room temperature is heat treated at 1120°C for 1.5 hours, and then at 1080°C for 2.5 hours for secondary solution treatment. After solution treatment, the temperature is lowered to 850°C for 3 hours of aging treatment, and then air-cooled to room temperature for tempering, and the tempering temperature is 200°C.

[0112] S6: The heat-treated round tube is straightened at 200°C. The straightening force is based on the model. Set it to 626.64kN and get the finished product.

[0113] Five sleeves were randomly selected from five different batches of finished products. X-ray residual stress analysis was first performed, and then samples were taken for chemical composition analysis, room temperature tensile property test, -20℃ Charpy impact test and room temperature anti-external collapse strength test. The chemical composition test results of the five sleeves are shown in Table 4: C: 0.18-0.20%, Si: 5.9-6.0%, Mn: 32.6-32.9%, P: 0.003-0.005%, S: 0.005-0.006%, Cr: 8.8-9.1%, Ni: 7.3-7.4%, Nb: 0.43-0.44%, V: 0.035-0.036%, N: 0.031-0.037%.

[0114] Table 4 Experimental results of chemical composition of casing in Example 2 (wt%)

[0115] Sample No. C Si Mn P S Cr Ni Nb V N 1 0.20 5.9 32.8 0.002 0.005 9.1 7.3 0.44 0.036 0.036 2 0.19 5.9 32.9 0.003 0.005 9.1 7.3 0.44 0.035 0.031 3 0.20 5.9 32.9 0.003 0.006 8.8 7.4 0.43 0.033 0.032 4 0.18 6.0 32.6 0.004 0.004 9.0 7.3 0.43 0.036 0.034 5 0.19 6.0 32.9 0.004 0.005 9.1 7.4 0.44 0.035 0.037

[0116] The mechanical properties test results of the five sleeves are shown in Table 5. The room temperature tensile properties are: R t0.6 811-835MPa, R m 1066-1088MPa, elongation ≥22%;

[0117] Impact properties of oil casing at -20℃: transverse A kv ≥109 joules, longitudinal A kv ≥125 joules;

[0118] The anti-external collapse strength of petroleum casing is ≥140MPa and the residual stress is ≤17MPa.

[0119] Table 5 Mechanical properties test results of casing in Example 2

[0120]

[0121] Five finished casings with a length of 1 m were cut and their outer diameters were measured respectively. Then, a compressive load was applied to each casing to flatten it. The flattened casing was heated to 300°C in a heating furnace and kept warm for 30 minutes. It was then cooled with the furnace and its outer diameter after heating was measured. The measurement results are shown in Table 6. The deformation recovery rate of the finished casing at 300°C is ≥61.5%.

[0122] Table 6 Casing deformation capacity recovery test results of Example 2

[0123]

[0124] Example 3

[0125] The casing specification is Φ139.7mm×12.7mm and is manufactured in the following steps:

[0126] S1: Smelting, continuous casting and forging according to the alloy element composition of 0.1% C, 5.2% Si, 25.4% Mn, 5.88% Cr, 5.35% Ni, 0.32% Nb, 0.018% V, and 0.012% N to obtain a round tube billet.

[0127] S2: The round tube billet is pierced by a two-time piercing process. The initial piercing temperature is set to 2070°C, followed by the final piercing. The final piercing temperature is 1580°C. The outer diameter of the final piercing plug is 1.2 times the outer diameter of the initial piercing plug. The running speed of the piercing mandrel is 10m / s.

[0128] S3: The pierced round tube billet is rolled, with the starting rolling temperature being 1340°C and the final rolling temperature being 1140°C. After the final rolling, the billet is kept in a ring furnace at a temperature of 1150°C for 30 minutes, and then tension reduction is performed.

[0129] S4: The round tube billet after tension reduction is sent into an annular furnace with a temperature of 1150°C, and the cooling rate of the annular furnace is controlled to be 10°C / s, and the round tube billet is cooled to room temperature along with the furnace.

[0130] S5: The round tube billet cooled to room temperature is heat treated at 1150°C for 1.5 hours, and then at 1090°C for 2.5 hours for secondary solution treatment. After solution treatment, the temperature is lowered to 900°C for aging treatment for 3 hours, and then air-cooled to room temperature for tempering, and the tempering temperature is 240°C.

[0131] S6: The heat-treated round tube is straightened at 200°C. The straightening force is based on the model. Set it to 498.6kN and get the finished product.

[0132] Five sleeves were randomly selected from five different batches of finished products. X-ray residual stress analysis was first performed, and then samples were taken for chemical composition analysis, room temperature tensile properties test, -20℃ Charpy impact test and room temperature anti-external collapse strength test. The chemical composition test results of the five sleeves are shown in Table 7: C: 0.12-0.13%, Si: 5.2-5.3%, Mn: 25.4-25.6%, P: 0.001-0.003%, S: 0.002-0.004%, Cr: 5.86-5.88%, Ni: 5.33-5.35%, Nb: 0.32-0.33%, V: 0.015-0.018%, N: 0.011-0.013%.

[0133] Table 7 Experimental results of chemical composition of casing in Example 3 (wt%)

[0134] Sample No. C Si Mn P S Cr Ni Nb V N 1 0.12 5.2 25.6 0.002 0.003 5.86 5.33 0.33 0.016 0.011 2 0.13 5.3 25.6 0.002 0.002 5.88 5.35 0.32 0.015 0.011 3 0.12 5.2 25.5 0.001 0.003 5.88 5.37 0.33 0.018 0.012 4 0.13 5.2 25.4 0.002 0.004 5.86 5.35 0.33 0.016 0.013 5 0.12 5.2 25.4 0.003 0.003 5.86 5.33 0.33 0.016 0.011

[0135] The mechanical properties test results of the five sleeves are shown in Table 8. The room temperature tensile properties are: R t0.6 762-773MPa, R m 1016-1022MPa, elongation ≥21%;

[0136] Impact properties of oil casing at -20℃: transverse A kv ≥101 joules, longitudinal A kv ≥120 joules;

[0137] The anti-external collapse strength of petroleum casing is ≥140MPa and the residual stress is ≤11MPa.

[0138] Table 8 Mechanical properties test results of casing in Example 3

[0139]

[0140] Five finished casing pipes with a length of 1 m were cut and their outer diameters were measured respectively. Then, a compressive load was applied to each casing pipe to flatten it. The flattened casing pipe was heated to 300°C in a heating furnace and kept warm for 30 minutes. Then, it was cooled with the furnace and the outer diameter value after heating was measured. The measurement results are shown in Table 9. The deformation recovery rate of the finished casing pipe at 300°C is ≥61.5%.

[0141] Table 9 Casing deformation capacity recovery test results of Example 3

[0142]

[0143] In summary, the present invention uses shape memory alloy as the material of petroleum casing. When designing the alloy element composition, the shape memory ability and recovery stress of the alloy are improved by reasonably controlling the element content of V and N. The casing yield rate is improved by controlling the content of elements such as P, S, and C. The tensile performance R of the obtained casing is t0.6 758MPa~908MPa, R m ≥1013MPa, elongation ≥20%, -20℃ impact performance is transverse A kv ≥100 joules, longitudinal A kv ≥120 joules, anti-external collapse strength ≥138MPa, residual stress ≤40MPa, deformation recovery rate at 300℃ ≥60%, which meets the use requirements of oil casing, can realize large-scale production and manufacturing, and has good economic benefits.

[0144] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An iron-based shape memory alloy petroleum casing, characterized in that: The chemical elements in the oil casing include, by weight percentage, Mn: 25-33%, Si: 5.2-6.0%, Cr: 5.8-9.2%, Ni: 5.3-7.5%, Nb: 0.32-0.46%, V: 0.01-0.04%, N: 0.01-0.04%, C≤0.2%, P≤0.01%, S≤0.01%, and the rest are Fe and unavoidable impurities.

2. The iron-based shape memory alloy petroleum casing according to claim 1, characterized in that: The microstructure of the oil casing is tempered martensite.

3. The iron-based shape memory alloy petroleum casing according to claim 1, characterized in that: The room temperature tensile properties of the oil casing are: t0.6 758-908MPa, R m ≥1013MPa, elongation ≥20%; The impact performance of the oil casing at -20℃ is: transverse A kv ≥100 joules, longitudinal A kv ≥120 joules; The room temperature anti-external collapse strength of the petroleum casing is ≥138MPa, the residual stress is ≤40MPa, and the deformation recovery rate at 300°C is ≥60%.

4. A method for preparing an iron-based shape memory alloy petroleum casing, characterized in that: The following steps are involved: Prepare round tube billets by smelting, continuous casting and forging; Punching the round tube blank; Rolling the perforated round tube blank; Cooling the round tube billet after tube rolling; heat treating the cooled round tube blank; The heat-treated round tube blank is heat-straightened to obtain a finished product.

5. The method for preparing an iron-based shape memory alloy petroleum casing according to claim 4, characterized in that: The perforating of the round tube blank comprises: The round tube billet is pierced by a two-time piercing process, the initial piercing temperature is 2030-2100°C, the final piercing temperature is 1550-1600°C, the final piercing plug outer diameter is 1.2 times the initial piercing plug outer diameter, and the running speed of the piercing mandrel is 10m / s.

6. The method for preparing an iron-based shape memory alloy petroleum casing according to claim 4, characterized in that: The method of rolling the perforated round tube blank comprises: The starting rolling temperature of the tube is 1300-1350℃, and the final rolling temperature is 1100-1150℃.

7. The method for preparing an iron-based shape memory alloy petroleum casing according to claim 6, characterized in that: The method of rolling the perforated round tube billet further comprises: The round tube billet after final rolling is kept at 1150° C. for 30 minutes; The round tube billet after heat preservation is subjected to tension reduction, and the temperature of tension reduction is 1150° C. and the time is 30 minutes.

8. The method for preparing an iron-based shape memory alloy petroleum casing according to claim 4, characterized in that: The step of cooling the round tube billet after tube rolling comprises: The rolled round tube is fed into a 1150°C annular furnace and cooled to room temperature at a rate of 10°C / s.

9. The method for preparing an iron-based shape memory alloy petroleum casing according to claim 4, characterized in that: The heat treatment of the cooled round tube blank comprises: The cooled round tube billet is subjected to two-stage solution treatment: after being kept at 1120-1150°C for 1.5h, it is kept at 1080-1100°C for 2.5h; The round tube billet after two-stage solution treatment is subjected to aging treatment: keeping at 850-900℃ for 3h, and then air cooling to room temperature; The round tube billet after aging treatment is tempered: the tempering temperature is 200-250℃.

10. A method for preparing an iron-based shape memory alloy petroleum casing according to any one of claims 4 to 9, characterized in that: The step of heat straightening the heat-treated round tube blank comprises: The temperature of heat straightening is controlled to be 200℃; Straightening force according to the model set up, Among them, F is the straightening force; D is the outer diameter of the round tube; t is the wall thickness of the round tube; d is the inner diameter of the round tube; F0 is the initial value of the straightening force.

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