A steel for drill collar suitable for drilling and mining in an acid oil and gas field

Abstract

This invention relates to a drill collar steel suitable for drilling and production in acidic oil and gas fields. Its composition, by mass percentage, is as follows: C: 0.01-0.06%, Mn: 20.3-21.7%, Cr: 18.0-20.0%, Mo: 0.5%-3.5%, Ni: 1.4-4.5%, N: 0.6-2.2%, Cu: 1.15-1.84%, Nb: 0.38-0.82%, with the balance being Fe and unavoidable impurities. Furthermore, Cu and Nb satisfy ([Cu] / 63.5) / ([Nb] / 92.9) = 2.56-5.17, where [Cu] and [Nb] represent the mass percentage content of Cu and Nb in the steel, respectively.

Description

Technical Field

[0001] This invention relates to a drill collar steel suitable for drilling and production in acidic oil and gas fields. This drill collar steel not only has mechanical properties equal to or higher than those of traditional drill collar steel, but also has excellent anti-SSC properties, making it particularly suitable for use in drilling and production processes in acidic oil and gas fields. Background Technology

[0002] Drill collars are a major component of the drill string. In oil and gas drilling, magnetic compasses or instruments are typically used for positioning. To avoid interference with positioning, non-ferromagnetic drill collars are required. Simultaneously, to provide drilling pressure to the drill bit and improve the rigidity of the drill string, drill collars need excellent strength and toughness. Drilling operations often encounter electrochemical corrosion and pitting corrosion, requiring drill collar materials to have excellent corrosion resistance. In summary, existing drill collar materials have relatively high costs due to the stringent requirements for various properties; therefore, it is desirable for drill collar materials to have the longest possible service life.

[0003] However, during drilling and production in acidic oil and gas fields, the working environment is accompanied by high concentrations of H2S. Working under high H2S conditions for extended periods will cause sulfide stress cracking (SSC) in the drill collars, often resulting in drill collar cracking, fracture failure, short service life, and high drilling and production costs.

[0004] Based on the above problems, the inventors of this invention aim to provide a drill collar material that can effectively resist sulfide stress cracking, extend its stable and reliable service time in the drilling and production process of acidic oil and gas fields, and reduce drilling and production costs. Summary of the Invention

[0005] This invention provides a drill collar steel suitable for drilling and production in acidic oil and gas fields. This drill collar steel not only has mechanical properties equal to or higher than those of traditional drill collar steel, but also has excellent anti-SSC properties. When used in the drilling and production process of acidic oil and gas fields, it is not easy to crack or break, and has stable working performance and reliable service time, which can effectively reduce drilling and production costs.

[0006] The technical objective of this invention is achieved through the following means.

[0007] The purpose of this invention is to provide a drill collar steel suitable for drilling and production in acidic oil and gas fields. Its composition, by mass percentage, is: C: 0.01-0.06%, Mn: 20.3-21.7%, Cr: 18.0-20.0%, Mo: 0.5%-3.5%, Ni: 1.4-4.5%, N: 0.6-2.2%, Cu: 1.15-1.84%, Nb: 0.38-0.82%, with the balance being Fe and unavoidable impurities. Furthermore, Cu and Nb satisfy ([Cu] / 63.5) / ([Nb] / 92.9) = 2.56-5.17, where [Cu] and [Nb] represent the mass percentage content of Cu and Nb in the steel, respectively.

[0008] The composition design principle of this invention will be introduced below.

[0009] C: Carbon is one of the most important austenite-forming elements. This invention aims to obtain a fully austenitic structure to ensure the paramagnetism of the material; therefore, a certain carbon content is required. Furthermore, the addition of carbon helps improve the strength of steel, which is crucial for ensuring its strength properties. However, excessive carbon content easily leads to carbide formation, resulting in a decrease in the corrosion resistance of the steel. Therefore, considering the metallographic structure, strength, and corrosion resistance of this invention, the carbon content in the steel is set at 0.01-0.06%.

[0010] Mn: In this invention, manganese is a crucial element. It helps ensure the strength of the steel and stabilizes the austenitic structure. Simultaneously, only a sufficiently high manganese content can ensure adequate nitrogen dissolves into the steel, thereby ensuring a sufficiently high nitrogen content to replace nickel with nitrogen and reduce steel costs. However, excessive manganese content will lead to a deterioration in the corrosion resistance of the steel. Considering the metallographic structure, strength, and corrosion resistance of this invention, the manganese content in the steel is set at 20.3-21.7%.

[0011] Cr: Chromium can stabilize the austenitic structure of steel. On the other hand, its most important role is to ensure that the steel has sufficient corrosion resistance. However, excessive chromium will lead to a decrease in the processing performance of the steel and a deterioration in its toughness. Taking into account the metallographic structure, corrosion resistance, processing performance, toughness and other characteristics of this invention, the chromium content in the steel is set at 18.0-20.0%.

[0012] Mo: Molybdenum is an important element that ensures the excellent corrosion resistance of steel. It also significantly improves strength; however, excessive molybdenum content will deteriorate the processing performance of the steel. Considering both the corrosion resistance and processing performance of this invention, the molybdenum content in the steel is set at 0.5%-3.5%.

[0013] Ni: Nickel is an important element for improving the corrosion resistance of steel and is crucial for maintaining austenitic stability. However, nickel resources are becoming increasingly scarce, and its price remains high. Therefore, this invention uses a high-manganese, high-nitrogen approach to replace nickel. Based on corrosion resistance considerations and cost control, this invention sets the nickel content in the steel to 1.4-4.5%.

[0014] Nitrogen (N): The addition of nitrogen helps maintain austenite stability and is an element that improves strength and ensures corrosion resistance. Increasing the amount of manganese added can increase the solubility of nitrogen in the steel matrix, thus allowing manganese and nitrogen to replace most of the nickel. However, excessive nitrogen content makes addition difficult and easily forms pores in the steel matrix, affecting various properties of the steel. Based on the requirements of metallographic structure, strength, and corrosion resistance, this invention sets the nitrogen content in the steel to 0.6-2.2%.

[0015] Cu: Copper is an austenite-forming element, which helps ensure that the steel has an austenitic matrix, thereby improving its strength and ensuring that the steel has non-magnetic properties. The addition of copper will significantly improve the corrosion resistance of the steel. However, excessive copper will cause the processing characteristics of the steel to drop sharply. Taking into account the microstructure, non-magnetism, strength, corrosion resistance and processability of the steel, the present invention sets the copper content in the steel to 1.15-1.84%.

[0016] Niobium (Nb) is an element that improves the hardenability of steel and can stabilize austenite to ensure the paramagnetic properties of steel. Niobium can form carbides, nitrides, etc., refine grains, and significantly improve the strength of steel. However, excessive niobium content will lead to increased costs and decreased machinability. Taking into account the microstructure, strength, and machinability of the steel in this invention, the niobium content in the steel is set at 0.38-0.82%.

[0017] The value of ([Cu] / 63.5) / ([Nb] / 92.9): As described in the background section, existing drill collar materials are easily affected by H2S when working in acidic oil and gas fields, resulting in cracks or even fractures. This leads to a short effective service life, poor operational stability, and high drilling and production costs. Through repeated experiments, the inventors of this invention discovered that by synergistically controlling the content of Cu and Nb, the anti-SSC properties of the steel can be effectively improved. This prevents sulfide stress cracking caused by high concentrations of H2S when working in acidic oil and gas fields, ensuring excellent service life of the drill collar, extending the time for reliable and stable operation, and effectively reducing drilling and production costs. The inventors of this invention have confirmed that the range of Cu and Nb content that ensures excellent anti-SSC properties in the steel is defined as ([Cu] / 63.5) / ([Nb] / 92.9) = 2.56-5.17.

[0018] In this invention, unavoidable impurity elements can be listed as such as P, S, O, H, etc. These elements are common elements in steel, introduced by raw materials and cannot be completely removed. The lower the content of impurity elements, the better the performance of the corresponding steel, but the higher the production cost of the steel. Taking into account both performance and cost, the content of P and S in this invention is controlled below 0.01%, and the content of O and H is not higher than 50 ppm.

[0019] As a non-limiting description, the steel used for drill collars in acidic oil and gas fields according to the present invention has a yield strength of 995 MPa or higher, a tensile strength of 1075 MPa or higher, an elongation of not less than 20%, a reduction of area of ​​not less than 50%, a room temperature impact energy of not less than 90 J, and a relative permeability of μ. r ≤1.005.

[0020] The drill collar steel of this invention, suitable for drilling and production in acidic oil and gas fields, exhibits excellent resistance to SSC (Self-Strain Crack). According to Method A of NACETM0177-2016, a sample of the drill collar steel (φ6.35mm × 25.4mm) was immersed in a test solution. The test solution was prepared by adding acetic acid and sodium acetate to a 5wt.% NaCl aqueous solution to adjust the pH to 3.5, with a solution temperature of 25°C, an atmosphere of CO2: 0.95 atm, and H2S: 0.05 atm. A load of 90% of the yield strength was applied, and no cracks were observed after immersion in the solution for 720 hours.

[0021] As another aspect of the present invention, the present invention also provides the application of the aforementioned drill collar steel suitable for drilling and production in acidic oil and gas fields. Since the drill collar steel of the present invention has excellent mechanical properties in addition to those of traditional drill collar steel, it also has excellent anti-SSC properties and can effectively resist stress cracking caused by H2S under high humidity and high H2S concentration conditions. Therefore, the drill collar steel of the present invention is particularly suitable for drilling and production in acidic oil and gas fields.

[0022] By way of non-limiting description, the method for preparing drill collar steel suitable for drilling and production in acidic oil and gas fields according to the present invention can be prepared by traditional smelting and casting, or by electroslag remelting.

[0023] As a non-limiting description, the steel for drill collars of the present invention, applicable to drilling and production in acidic oil and gas fields, preferably includes a primary hot working step after the billet is prepared. The hot working can be rough rolling, forging, etc. The corresponding dimensions are obtained through the primary hot working. Before the primary hot working, a homogenization treatment step is preferably included. The homogenization temperature is 1150-1250°C and the duration is 2-5 hours. After the homogenization treatment, the primary hot working is performed directly.

[0024] As a non-limiting description, after the above-mentioned primary heat treatment, it is preferable to perform a solution treatment at 1000-1150°C for 2-4 hours.

[0025] As a non-limiting description, after the above solution treatment, it is preferable to perform secondary hot working strengthening, such as finishing rolling at 500-800°C with a total reduction of 15-65%, or extrusion or forging at 500-800°C with a total reduction of area of ​​10-70%.

[0026] The beneficial effects of this invention are as follows.

[0027] This invention, through compositional optimization, yields drill collar steel with excellent strength, toughness, and plasticity. Its mechanical properties meet or exceed those of traditional drill collar steel, effectively fulfilling the mechanical performance requirements of drill collars during drilling and production. By controlling its composition, this steel achieves an austenitic matrix structure, is a non-magnetic material, and has a relative permeability μ. r With a concentration ≤1.005, it will not interfere with exploration instruments during drilling and production. In particular, by adding Cu and Nb and synergistically controlling their contents, the steel for drill collars obtained by this invention has excellent resistance to sulfide stress cracking. It will not crack or fail even after long-term operation under high concentration H2S conditions, and has excellent service life and stable long-term working capability. This makes the steel of this invention particularly suitable for drilling and production in acidic oil and gas fields, and can significantly reduce drilling and production costs. Detailed Implementation

[0028] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed explanation is provided in conjunction with specific experimental examples.

[0029] The molten steel was smelted according to the design composition and cast into ingots. The contents of P and S were controlled at 0.008±0.001% and the contents of O and H were 40ppm±5ppm respectively. The dimensions of the steel ingots were 1000mm long × 400mm wide × 400mm high. The specific composition is shown in Table 1, where k=([Cu] / 63.5) / ([Nb] / 92.9). Two steel ingots of the above dimensions were cast for test serial numbers 1, 2 and 3, and were named test serial numbers 1-1, 1-2, 2-1, 2-2, 3-1 and 3-2 respectively.

[0030] Tests 1-2, 2-2, and 3-2 were prepared as finished products in the form of cast ingots. The remaining test samples were homogenized at 1200℃ for 2.5 hours, then hot-forged into round bars with a diameter of 350 mm. The bars were then solution-treated at 1110℃ for 2 hours, and then air-cooled to 700℃. The round bars were then forged to achieve a cross-sectional area reduction rate of 60%, resulting in finished bar products.

[0031] Various performance tests were conducted on the finished bars. The yield strength, tensile strength, elongation, and reduction of area were tested according to GB / T228.1-2021, the impact energy test was conducted according to GB / T229-2020, and the relative permeability test was conducted according to GB / T 35690-2017. The SSC resistance was tested according to Method A in NACE TM0177-2016. The sample (φ6.35mm×25.4mm) was immersed in the test solution, which was prepared by adding acetic acid and sodium acetate to a 5wt.% NaCl aqueous solution to adjust the pH of the test solution to 3.5, the liquid temperature was 25℃, and the atmosphere was CO2: 0.95atm and H2S: 0.05atm. 90% of the yield strength (based on the yield strength obtained from sampling and testing on the same bar) was used as the load stress. After immersion in the impregnation solution for 720 hours, the presence of cracks was observed.

[0032] Table 1: Composition of various steels, %, balance is Fe.

[0033]

[0034] The results of various tests on the steel samples numbered 1 to 14 above are shown in Table 2.

[0035] Table 2: Properties of various steels.

[0036]

[0037] The above-mentioned inventive examples and comparative examples will be further analyzed and explained below with reference to Tables 1-2.

[0038] All test numbers 1-7 in Table 1 meet the composition requirements of this invention; therefore, test numbers 1-7 are inventive examples of this invention. The test results clearly show that the steel with the compositions of test numbers 1-7 meets the requirements of this invention in terms of yield strength, tensile strength, elongation, reduction of area, impact energy, and relative permeability. In particular, no cracks were found after testing according to NACE TM0177-2016, confirming that the steel with the compositions of this invention has excellent SSC resistance.

[0039] In Table 2, test numbers 1-2, 2-2, and 3-2 represent performance tested under as-cast conditions, while test numbers 1-1, 2-1, and 3-1, with the same composition, represent samples after strengthening deformation. It is evident that their yield strength and tensile strength have increased, while elongation, reduction of area, and toughness have decreased to some extent, but remain within the range required by this invention. The tests confirm that steel with the composition of this invention, whether in the as-cast or strengthened deformation state, can meet all the performance requirements of this invention; the only difference is the shift in performance focus between strength and ductility / toughness. Users can choose between the as-cast or strengthened deformation state based on their actual performance needs.

[0040] Tests 8, 9, 10, and 11 adjusted the Cu and Nb content of tests 1, 2, 3, and 4, respectively. Although the Cu and Nb content still met the requirements of this invention after adjustment, the value of k[([Cu] / 63.5) / ([Nb] / 92.9)] was not within the range required by the invention. The test results showed that although the strength, plasticity, toughness, and magnetic properties of tests 8, 9, 10, and 11 met the requirements of this invention, cracks appeared after testing according to the requirements of NACE TM0177-2016, confirming that the above steel has poor anti-SSC properties and cannot meet the requirements for long-term stable operation in acidic oil and gas field conditions.

[0041] Tests 12 and 13 omitted Cu and Nb from tests 5 and 6, respectively. The results showed that the yield strength and tensile strength decreased, failing to meet the requirements of the present invention of a yield strength of 995 MPa or higher and a tensile strength of 1075 MPa or higher. Furthermore, due to the lack of Cu or Nb, the synergistic effect of Cu and Nb could not be utilized. Finally, after testing, its anti-SSC properties were found to be poor, failing to meet the requirements of the present invention.

[0042] Test No. 14 omitted Cu and Nb from Test No. 7. The results showed that its yield strength and tensile strength decreased, failing to meet the requirements of the present invention of a yield strength of 995 MPa or more and a tensile strength of 1075 MPa or more. Furthermore, due to the lack of Cu and Nb, the synergistic effect of Cu and Nb could not be utilized. Finally, after testing, its anti-SSC properties were found to be poor, failing to meet the requirements of the present invention.

[0043] It is easy to see from the above invention examples and comparative examples that by synergistically adding Cu and Nb and controlling the content relationship of Cu and Nb within the appropriate range, drill collar steel with the required strength, plasticity, toughness, and relative magnetic permeability can be obtained. Most importantly, this steel has excellent anti-SSC properties, which can meet the requirements of long-term stable operation under acidic oil and gas field conditions, has excellent service life, and can effectively control drilling and production costs.

[0044] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A type of steel for drill collars suitable for drilling and production in acidic oil and gas fields, characterized in that, The steel used for the drill collar has the following composition by mass percentage: C: 0.01-0.06%, Mn: 20.3-21.7%, Cr: 18.0-20.0%, Mo: 0.5%-3.5%, Ni: 1.4-4.5%, N: 0.6-2.2%, Cu: 1.15-1.84%, Nb: 0.38-0.82%, with the balance being Fe and unavoidable impurities. Furthermore, Cu and Nb satisfy ([Cu] / 63.5) / ([Nb] / 92.9) = 2.56-5.17, where [Cu] and [Nb] represent the mass percentage content of Cu and Nb in the steel, respectively.

2. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to claim 1, characterized in that, The yield strength of the steel used for the drill collar is above 995 MPa.

3. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to any one of claims 1-2, characterized in that, The tensile strength of the steel used for the drill collar is above 1075 MPa.

4. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to any one of claims 1-2, characterized in that, The elongation of the steel used for the drill collar is not less than 20%.

5. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to any one of claims 1-2, characterized in that, The section reduction rate of the steel used for the drill collar is not less than 50%.

6. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to any one of claims 1-2, characterized in that, The room temperature impact energy of the steel used for the drill collar is not less than 90J.

7. The drill collar steel suitable for drilling and production in acidic oil and gas fields according to any one of claims 1-2, characterized in that, The relative magnetic permeability μ of the steel used for the drill collar r ≤1.

005.

8. The use of the drill collar steel according to any one of claims 1-7 for drilling and production in acidic oil and gas fields, characterized in that, The steel used for drill collars in acidic oil and gas fields is used in such fields.

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