A high-toughness long-life steel for a perforating gun tube for ultra-deep wells and a method and heat treatment process for producing a perforating gun tube

Abstract

This invention provides a high-strength, long-life steel for perforating gun barrels in ultra-deep wells, along with a method for producing the perforating gun barrel and a heat treatment process. The steel composition is C, Si, Mn, Cr, Mo, Ni, Al, Nb, V, P, S, N, T, and Fe. Compared to existing technologies, this invention uses steel with the above-mentioned design composition and a matching heat treatment and production method. The heat treatment process includes stepped quenching and tempering. The resulting perforating gun barrel has a yield strength ≥1172 MPa, tensile strength ≥1241 MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100 J, and a service life ≥72 hours at 200℃. This meets the more stringent requirements for use in deep and ultra-deep well environments.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel and relates to a high-strength, high-toughness, long-life steel for perforating gun barrels in ultra-deep wells, as well as a method for producing perforating gun barrels and a heat treatment process. The perforating gun barrels produced have a long service life, with a yield strength ≥1172MPa, tensile strength ≥1241MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100J, and service life ≥72h at 200℃, meeting the requirements of more demanding deep and ultra-deep well environments. Background Technology

[0002] my country is the second largest oil consumer and the third largest natural gas consumer. With the rapid growth of my country's energy demand, the country has increased its development efforts in areas with complex geological conditions. Meanwhile, 73% of my country's proven oil and gas reserves are deep-seated. The Tarim Basin and the Sichuan Basin are my country's two richest deep-seated oil and gas basins, characterized by high resource abundance, large scale, and large overall reserves. However, they are also characterized by deep burial strata and extremely complex geological structures, presenting many world-class exploration and development challenges.

[0003] When the well depth reaches 8km or more, the bottom hole temperature is generally above 200℃. During perforation gun operation, pipe rupture or breakage can cause serious construction accidents such as stuck wells. Therefore, ultra-deep well oil and gas extraction requires the gun casing to have stronger resistance to axial loads, crushing, and internal pressure. Emphasis is placed on the casing having superior comprehensive mechanical properties; the requirements for casing use are increased strength and increased toughness.

[0004] Currently, the yield strength of materials used in perforating guns is below 1100 MPa, and their maximum operating depth is around 8 km. Furthermore, they suffer from poor resistance to crushing, easy failure, and short service life. Therefore, it is necessary to develop new materials with higher strength and toughness to meet the requirements for perforating gun barrels used in deep well operations at depths of 9 km or even greater, thereby improving the strategic security of my country's oil and gas equipment.

[0005] Patent CN102747289A, published on October 24, 2012, discloses an ultra-high strength oil casing steel, an oil casing, and a manufacturing method thereof. Its composition and weight percentages are: C 0.25–0.36%; Si 0.10–0.50%; Mn 0.2–0.8%; P ≤0.013%; S ≤0.003%; Cr 0.8–1.4%; Mo 0.60–1.0%; Al 0.01–0.04%; Ca 0.001–0.006%; and one of V 0–0.10%; Nb 0–0.08%; Ti 0–0.05%, with Fe as the balance. This patent employs a low-Mn, high-Mo composition design, achieving a yield strength of 1180 MPa, but its impact toughness is relatively low, with a full-size cross-section impact strength ≥60 J. Furthermore, it does not describe its pressure resistance, high temperature resistance, and operating environment, and therefore cannot meet the requirements for use of perforation gun barrels in ultra-deep wells.

[0006] A patent published on March 11, 2022, with authorization announcement number CN216008465U, discloses a seamless steel pipe for a multi-layer composite perforating gun, addressing the problems of existing seamless steel pipes, which are typically single-layer structures, resulting in low strength and poor impact resistance. This patent focuses on the multi-layer composite process and technology of the steel pipe, without optimizing the material composition. Furthermore, the steel's relatively low strength makes it unsuitable for ultra-deep well environments.

[0007] Patent CN103614631A, published on March 5, 2014, discloses a rare-earth-containing perforating gun barrel material and its preparation method. The composition and weight percentages are: C 0.25%–0.30%, Si 0.20%–0.35%, Mn 1.0%–1.20%, P ≤0.020%, S ≤0.010%, Cr 0.80%–1.05%, Mo 0.15%–0.25%, Al 0.015%–0.04%, and rare earth element La 0.01%–0.03%, with the remainder being Fe and impurities. This patent improves the toughness of steel through the modification and alloying effects of rare earth elements, but its relative strength is low, making it unsuitable for use in perforating gun barrels for ultra-deep wells.

[0008] Existing technologies for perforating guns in ultra-deep wells have limitations such as low yield strength and lack of high-temperature service life, failing to meet the more stringent requirements for use in deep and ultra-deep well environments. Summary of the Invention

[0009] The purpose of this invention is to provide a high-strength, high-toughness, long-life steel for perforating gun barrels in ultra-deep wells. Through composition design and matching, a steel suitable for producing perforating gun barrels is obtained.

[0010] Another objective of this invention is to provide a method and heat treatment process for producing perforating gun barrels. The perforating gun barrels are produced using the aforementioned high-strength, high-toughness, long-life steel for ultra-deep wells. Based on the steel composition, a suitable production process and heat treatment process are designed and matched. The resulting perforating gun barrel product has a yield strength ≥1172MPa, tensile strength ≥1241MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100J, and service life ≥72h at 200℃, meeting the requirements for use in more demanding deep and ultra-deep well environments.

[0011] The specific technical solution of this invention is as follows:

[0012] A high-strength, high-toughness, long-life steel for perforating gun barrels in ultra-deep wells comprises the following components by weight percentage:

[0013] C 0.33%–0.38%, Si 0.25%–0.35%, Mn 1.20%–1.40%, Cr 1.10%–1.40%, Mo 0.35%–0.45%, Ni 0.60%–1.00%, Al 0.020%–0.035%, Nb 0.025–0.035%, V 0.06–0.10%, P≤0.015%, S≤0.010%, N≤0.0080%, TO≤0.0020%, with the remainder being Fe and other unavoidable impurities.

[0014] The steel used for the high-strength, high-toughness, long-life ultra-deep well perforation gun barrel also meets the following composition requirements: 500≤Q value≤550.

[0015] Q value=1300×(%C-0.079×%Cr-0.13×%Nb-0.24×%V)

[0016] +35×%Cr+160×%Si+85×%Mn+50×%Mo.

[0017] The steel used for the high-strength, high-toughness, long-life perforation gun barrel for ultra-deep wells also meets the following requirements: R value ≥ 70;

[0018] R value

[0019] =30×%Ni+15×%Mo+20×%V+25×%Nb+22×%Mn-12×%Si×%Mn+18×%Cr-10×%Cr×%C.

[0020] When calculating using the above formula, the index value of each element = the content of that element in the steel × 100.

[0021] The present invention provides a heat treatment process for producing perforating gun barrels, which uses the above-mentioned high-strength, high-toughness, long-life perforating gun barrel steel for ultra-deep wells to produce perforating gun barrels. The heat treatment process includes stepped quenching and tempering.

[0022] The stepped quenching process specifically involves: heating the steel pipe to a heating temperature T1 of 900–930°C, holding it at that temperature for t1, and then water cooling it; then heating the steel pipe to a heating temperature T2 of 860–890°C, holding it at that temperature for t2, and then water cooling it.

[0023] The heat preservation time t1 is determined by the steel pipe wall thickness S and the heating temperature T1, and 150+S / 2-T1 / 8≤t1≤170+S / 2-T1 / 8;

[0024] The heat preservation time t2 is determined by the steel pipe wall thickness S and the heating temperature T2, and 150+S / 2-T2 / 8≤t2≤170+S / 2-T2 / 8;

[0025] Preferably, heating the steel pipe to a heating temperature T1 900~930℃ means heating it to a temperature T1 900~930℃ at a rate of 10~30℃ / min;

[0026] Preferably, heating the steel pipe to a heating temperature T2 860~890℃ means heating it to a temperature T2 860~890℃ at a rate of 10~30℃ / min;

[0027] The tempering process specifically involves heating the steel pipe to a heating temperature T3 of 520–560°C, holding it at that temperature for t3, and then water-cooling or air-cooling it.

[0028] The heat preservation time t3 is determined by the steel pipe wall thickness S and the heating temperature T3, and 220+2×S-T3 / 4≤t3≤250+2×S-T3 / 4;

[0029] Preferably, heating the steel pipe to a heating temperature T3 520~560℃ means heating it to a heating temperature T3 520~560℃ at a rate of 10~30℃ / min;

[0030] The units are: t1, t2, t3 in min, S in mm, and T1, T2, T3 in °C. When calculating the above formulas, simply substitute the data before the units into the formulas.

[0031] The water cooling method described in this invention uses water at room temperature (25°C) to cool to room temperature.

[0032] This invention provides a method for producing perforating gun barrels, utilizing the aforementioned high-strength, high-toughness, long-life steel for ultra-deep well perforating gun barrels and employing the aforementioned heat treatment process. The specific production method includes the following process flow:

[0033] Smelting → LF furnace refining → RH or VD vacuum degassing → continuous casting → heating → rolling / forging → round bar → tube threading → sizing → heat treatment process → finishing → packaging and warehousing.

[0034] The smelting process includes an arc furnace or converter, preferably an electric arc furnace: oxygen is determined before tapping, and slag discharge is strictly controlled during the tapping process.

[0035] LF furnace refining: C, Si, Mn, Cr, Mo, Ni, V, Nb and other elements are adjusted to target values;

[0036] The RH or VD vacuum degassing: pure degassing time ≥ 15 minutes, ensuring that the [H] content after vacuum treatment is ≤ 1.5 ppm;

[0037] The continuous casting process involves obtaining continuously cast billets / ingots, wherein the target temperature of the molten steel in the ladle is controlled at 10–40°C above the liquidus temperature, and round billets / square billets are continuously cast.

[0038] The produced perforating gun barrels have a yield strength ≥1172MPa, tensile strength ≥1241MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100J, and service life ≥72h at 200℃.

[0039] The design concept of this invention is as follows:

[0040] Carbon (C): Carbon is the cheapest strengthening element in steel. Each 0.1% increase in dissolved C can increase strength by 400–450 MPa. C forms precipitates with alloying elements in steel, resulting in precipitation strengthening. C significantly improves hardenability, making it easier to obtain martensitic structure in the core during oil well tubing preparation. However, as its content increases, plasticity and toughness decrease, and high C content is detrimental to corrosion resistance. Therefore, the C content is controlled at 0.33%–0.38%.

[0041] Si: Si is an effective solid solution strengthening element in steel, increasing its strength and hardness. Si also acts as a deoxidizer during steelmaking. However, Si tends to segregate at austenite grain boundaries, reducing grain boundary bonding and causing brittleness. Furthermore, Si easily causes elemental segregation in steel. Therefore, the Si content is controlled between 0.25% and 0.35%.

[0042] Mn: Mn can play a solid solution strengthening role, but its solid solution strengthening ability is weaker than that of Si. Mn is an austenite stabilizing element that can significantly improve the hardenability of steel and reduce decarburization. Mn combined with S can prevent hot brittleness caused by S. However, excessive Mn will reduce the plasticity of steel. Therefore, the Mn content should be controlled between 1.20% and 1.40%.

[0043] Cr: Cr is a carbide-forming element. Cr can improve the hardenability and strength of steel, but it easily causes temper brittleness. Cr can improve the oxidation resistance and corrosion resistance of steel, but excessive Cr content will increase crack susceptibility. The Cr content should be controlled between 1.10% and 1.40%.

[0044] Mo: Mo primarily improves the hardenability and heat resistance of steel. Mo dissolved in the matrix helps maintain high stability of the steel's microstructure during tempering and effectively reduces the segregation of impurity elements such as P, S, and As at grain boundaries, thereby improving the steel's toughness and reducing temper brittleness. Mo reduces the stability of M7C3; when the Mo content is high, acicular Mo2C will form, leading to a reduction in the Mo content in the matrix. Mo can improve the strength of steel through the combined effects of solid solution strengthening and precipitation strengthening, and it can also alter the steel's toughness by changing the precipitation of carbides. Therefore, the Mo content should be controlled between 0.35% and 0.45%.

[0045] Ni: Ni can form an infinitely miscible solid solution with Fe. It is an austenite stabilizing element, expanding the phase region, increasing the stability of supercooled austenite, shifting the C-curve to the right, and improving the hardenability of steel. Ni can refine the width of martensite laths, increasing strength. Ni significantly lowers the ductile-brittle transition temperature of steel and improves low-temperature toughness. The Ni content should be controlled between 0.60% and 1.00%.

[0046] Al: Al is the main deoxidizer in steelmaking. Al combines with N to form finely dispersed AlN, which maintains a coherent relationship with the matrix. This strengthens and refines the microstructure, increases resistance to fatigue crack initiation and propagation, and thus improves the endurance strength of steel. The Al content is controlled between 0.020% and 0.035%.

[0047] Nb / V: Both Nb and V are strong C and N compound-forming elements. Nb(C, N) and V(C, N) are finely dispersed and coherent with the matrix, thus strengthening and refining the microstructure. Strengthening the matrix increases resistance to fatigue crack initiation and propagation, thereby improving fatigue strength. The Nb and V contents are controlled at 0.025–0.035% and 0.06–0.10%, respectively.

[0048] TO and N: TO forms oxide inclusions in steel, so TO should be controlled to ≤0.0020%; N can form fine precipitates with nitride-forming elements in steel to refine the microstructure, but at the same time, Fe4N is precipitated, which reduces the processing performance. Therefore, N should be controlled to within 0.0080%.

[0049] In this invention, Cr is the main carbide precipitation element. V and Nb also consume C to form VC and NbC nanoscale precipitation, effectively strengthening the matrix. In the steel of this invention, the C consumed to form the Cr precipitation phase is 0.079 × %Cr. Sufficient precipitation of Nb and V is necessary to ensure optimal strength and toughness; the carbon consumed to form the V and Nb precipitation phases is 0.13 × %Nb + 0.24 × %V. Sufficient C is needed for solid solution to ensure strength; therefore, the solid solution C content should be %C - 0.079 × %Cr - 0.13 × %Nb - 0.24 × %V. The addition of strengthening elements Cr, Si, Mn, and Mo further enhances strength. The strength contribution coefficients of these four elements are 35, 160, 85, and 50, respectively. Therefore, the comprehensive strength determination factor of the steel is Q = 1300 × (%C - 0.079 × %Cr - 0.13 × %Nb - 0.24 × %V).

[0050] +35%Cr + 160%Si + 85%Mn + 50%Mo. To ensure strength and plasticity, 500 ≤ Q ≤ 550.

[0051] V and Nb effectively refine grains and microstructure, improving the toughness of the material. Mo is beneficial for improving tempering stability, thus enhancing toughness. Ni effectively improves and enhances the toughness of the matrix. Therefore, the contribution coefficients of these four elements to toughness are 20, 25, 15, and 30, respectively. Mn and Cr promote phase transformation, which can refine the microstructure and improve toughness. However, the interaction between Mn and Si exacerbates segregation, leading to a decrease in toughness. Therefore, their coefficients are 22 and -12, respectively. The interaction between Cr and C easily forms coarse carbides, resulting in a decrease in toughness. Therefore, their contribution coefficients to toughness are 18 and -10, respectively. Furthermore, since this invention imposes maximum content limits on P and S, the harmful effects of trace amounts of P and S on toughness are ignored. Therefore, the toughness determination factor R value of steel is...

[0052] =30×%Ni+15×%Mo+20×%V+25×%Nb+22×%Mn-12×%Si×%Mn+18×%Cr-10×%Cr×%C≥70.

[0053] This invention provides a high-strength, long-life perforating gun barrel for ultra-deep wells. Manufactured using steel with the aforementioned design composition and matching heat treatment and production methods, the resulting perforating gun barrel exhibits a yield strength ≥1172 MPa, tensile strength ≥1241 MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100 J, and a service life ≥72 hours at 200℃. This meets the stringent requirements for use in deeper and ultra-deep well environments. Attached Figure Description

[0054] Figure 1 This is a typical microstructure of the product of this invention after heat treatment. Detailed Implementation

[0055] The present invention will be further described below with reference to embodiments and comparative examples.

[0056] Examples 1-3

[0057] A high-strength, high-toughness, long-life steel for perforating gun barrels in ultra-deep wells comprises the following composition by mass percentage: as shown in Table 1. The balance not shown in Table 1 is Fe and other unavoidable impurities.

[0058] Table 1. Steel composition (wt%) for each embodiment and comparison.

[0059]

[0060]

[0061] Comparative Examples 1-3

[0062] A steel for a perforating gun barrel comprises the following composition by mass percentage as shown in Table 1, where the balance not shown in Table 1 is Fe and other unavoidable impurities.

[0063] The production process of perforating gun barrels using the steel provided in the above embodiments and comparative examples specifically includes the following steps:

[0064] Electric arc furnace smelting → LF furnace refining → RH or VD vacuum degassing → continuous casting → heating → rolling / forging → round bar → finishing → heating → tube threading → sizing → heat treatment process → finished product → packaging and warehousing.

[0065] Electric arc furnace smelting: oxygen is determined before tapping, and slag discharge is strictly controlled during the tapping process;

[0066] LF furnace refining: C, Si, Mn, Cr, Mo, Ni, V, Nb and other elements are adjusted to target values;

[0067] The RH or VD vacuum degassing: pure degassing time ≥ 15 minutes, ensuring that the [H] content after vacuum treatment is ≤ 1.5 ppm;

[0068] The continuous casting process involves obtaining continuously cast billets / ingots, wherein the target temperature of the molten steel in the ladle is controlled at 10–40°C above the liquidus temperature, and round billets / square billets are continuously cast.

[0069] The heat treatment process specifically includes stepped quenching and tempering, as detailed below:

[0070] The stepped quenching process specifically involves heating the steel pipe to T1 900-930℃ at a rate of 10-30℃ / min, holding it at that temperature for t1, and then water cooling it; and heating the steel pipe to T2 860-890℃ at a rate of 10-30℃ / min, holding it at that temperature for t2, and then water cooling it.

[0071] The heat preservation time t1 is determined by the steel pipe wall thickness S and the heating temperature T1, and 150+S / 2-T1 / 8≤t1≤170+S / 2-T1 / 8;

[0072] The heat preservation time t2 is determined by the steel pipe wall thickness S and the heating temperature T2, and 150+S / 2-T2 / 8≤t2≤170+S / 2-T2 / 8;

[0073] The tempering process specifically involves heating the steel pipe to T3 520-560℃ at a rate of 10-30℃ / min, holding it at that temperature for t3, and then water-cooling or air-cooling it.

[0074] The heat preservation time t3 is determined by the steel pipe wall thickness S and the heating temperature T3, and 220+2×S-T3 / 4≤t3≤250+2×S-T3 / 4;

[0075] The units are: t1, t2, t3 in min, S in mm, and T1, T2, T3 in °C. When calculating the above formulas, simply substitute the data before the units into the formulas.

[0076] The heat treatment process parameters for each embodiment and comparative example are shown in Table 2.

[0077] Table 2 Heat treatment process parameters for each embodiment and comparative example steel

[0078]

[0079]

[0080] The performance testing methods for the steel pipes produced in the above embodiments and comparative examples are as follows:

[0081] Organization: After heat treatment of the tube blank, samples are taken from the finished product for metallographic and grain size analysis.

[0082] Performance: After heat treatment of the tube blank, tensile, impact, and fatigue specimens were taken from the finished product for mechanical property tests. The mechanical properties are shown in Table 3. The tests were conducted in accordance with GB / T 228.1 and GB / T 229.

[0083] Table 3. List of mechanical property test results for embodiments and comparative examples of the present invention.

[0084]

[0085]

[0086] The items underlined above do not meet the requirements of this invention.

[0087] The chemical composition and production methods of the steels in Examples 1-3 were appropriately controlled, resulting in steels with good strength, plasticity, toughness, and service life. Comparative Example 1 had an unsuitable chemical composition, leading to excessively low material strength, insufficient plasticity, toughness, and fatigue performance; improper heat treatment resulted in unsatisfactory overall performance. Comparative Example 3 had an unreasonable composition; even when produced according to the heat treatment process of this invention, its performance could not meet the requirements of this invention. Comparative Example 2 had a reasonable composition design, but improper heat treatment resulted in insufficient material strength, toughness, and fatigue performance.

Claims

1. A type of steel for high-strength, high-toughness, long-life perforation gun barrels in ultra-deep wells, characterized in that, The high-strength, long-life steel for perforating gun barrels in ultra-deep wells comprises the following components by mass percentage: C 0.33%-0.38%, Si 0.25%-0.35%, Mn 1.20%-1.40%, Cr 1.10%-1.40%, Mo 0.35%-0.45%, Ni 0.60%-1.00%, Al 0.020%-0.035%, Nb 0.025-0.035%, V 0.06-0.10%, P≤0.015%, S≤0.010%, N≤0.0080%, TO≤0.0020%, with the remainder being Fe and other unavoidable impurities; The steel used for the high-strength, high-toughness, long-life ultra-deep well perforation gun barrel also meets the following composition requirements: 500≤Q value≤550. Q value=1300×(%C-0.079×%Cr-0.13×%Nb-0.24×%V)+35×%Cr+160×%Si+85×%Mn+50×%Mo; The steel used for the high-strength, high-toughness, long-life ultra-deep well perforation gun barrel also meets the following requirements: R value ≥ 70; R value=30×%Ni+15×%Mo+20×%V+25×%Nb+22×%Mn-12×%Si×%Mn+18×%Cr-10×%Cr×%C.

2. A heat treatment process for producing perforating gun barrels, characterized in that, The heat treatment process for producing the perforating gun barrel utilizes the high-strength, high-toughness, long-life steel for ultra-deep well perforating gun barrels as described in claim 1. The heat treatment process includes stepped quenching and tempering.

3. The heat treatment process according to claim 2, characterized in that, The stepped quenching process specifically involves: heating the steel pipe to a heating temperature T1 of 900-930℃, holding it for t1, and then water cooling; then heating the steel pipe to a heating temperature T2 of 860-890℃, holding it for t2, and then water cooling.

4. The heat treatment process according to claim 3, characterized in that, The heat preservation time t1 is determined by the steel pipe wall thickness S and the heating temperature T1, and 150+S / 2-T1 / 8≤t1≤170+S / 2-T1 / 8.

5. The heat treatment process according to claim 3 or 4, characterized in that, The heat preservation time t2 is determined by the steel pipe wall thickness S and the heating temperature T2, and 150+S / 2-T2 / 8≤t2≤170+S / 2-T2 / 8.

6. The heat treatment process according to claim 2, characterized in that, The tempering process specifically involves heating the steel pipe to T3520-560℃, holding it at that temperature for t3, and then water-cooling or air-cooling it.

7. The heat treatment process according to claim 6, characterized in that, The heat preservation time t3 is determined by the steel pipe wall thickness S and the heating temperature T3, and 220+2×S-T3 / 4≤t3≤250+2×S-T3 / 4.

8. The heat treatment process according to any one of claims 2, 3, 4, 6, and 7, characterized in that, The produced perforating gun barrels have a yield strength ≥1172MPa, tensile strength ≥1241MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100J, and service life ≥72h at 200℃.

9. The heat treatment process according to claim 5, characterized in that, The produced perforating gun barrels have a yield strength ≥1172MPa, tensile strength ≥1241MPa, elongation A ≥15%, reduction of area Z ≥53%, room temperature impact energy KU2 ≥100J, and service life ≥72h at 200℃.

10. A method for producing a perforating gun barrel, using the high-strength, high-toughness, long-life steel for ultra-deep well perforating gun barrels as described in claim 1, wherein the method for producing the perforating gun barrel comprises the following process flow: Smelting → LF furnace refining → RH or VD vacuum degassing → continuous casting → heating → rolling / forging → round bar → tube threading → sizing → heat treatment process → finishing → packaging and warehousing.

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