Biological-corrosion-resistant steel for deep SEW oil casing and preparation method of biological-corrosion-resistant steel

Abstract

The invention belongs to the technical field of oil well pipe preparation, and particularly discloses biological-corrosion-resistant steel for a deep SEW oil casing and a preparation method of the biological-corrosion-resistant steel for the deep SEW oil casing, and the biological-corrosion-resistant steel for the deep SEW oil casing comprises the following chemical components: 0.30-0.50% of C, 0.20-0.30% of Si, 2.0-3.5% of Mn, less than or equal to 0.012% of P, less than or equal to 0.005% of S, 0.10-0.30% of La, 0.35-0.50% of Mo, 0.02-0.04% of Al, 0.02-0.05% of Nb + V + Ti, 0.50-1.50% of Cu, 0.05-0.20% of Ni and the balance of Fe and inevitable impurities. The preparation method comprises the working procedures of heating, rolling, cooling and coiling. The steel for the SEW petroleum casing pipe is excellent in mechanical property and biological corrosion resistance, and meets the performance requirements of the steel for the deep petroleum casing pipe.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil well pipe preparation, and particularly relates to a steel for deep SEW oil casing resistant to biological corrosion and a preparation method thereof. Background Art

[0002] Microbiological corrosion is a phenomenon in which the life activities of microorganisms and their metabolites directly or indirectly accelerate the corrosion process of metal materials, and it can occur in almost all environments such as soil, fresh water, seawater, and oilfield systems. Microbiological corrosion is an important cause of the corrosion failure of oil casings. The growth, metabolism, and reproduction of other microorganisms such as sulfate-reducing bacteria (SRB) and saprophytic bacteria will cause the failure of oil casings and the blockage of injection wells, resulting in potential safety risks during oil production and transportation; therefore, it is of great significance to develop a steel for deep SEW oil casing resistant to biological corrosion.

[0003] As a rare earth element, La has high chemical stability and will react with the metabolites produced by certain corrosive microorganisms, thereby inhibiting the corrosion effect of these products on metals. La has a strong toxic effect on microorganisms such as sulfate-reducing bacteria (SRB) and saprophytic bacteria, and this toxic effect will cause these microorganisms to lose their activity in the environment, thereby reducing their role in the corrosion process.

[0004] Cu and its derivatives play an antibacterial role through a variety of mechanisms, including changing the cell membrane potential, causing oxidative stress, direct toxicity, reducing surface adhesion, and enhancing antibacterial performance with the increase of copper content, etc., and can effectively inhibit the growth of microorganisms such as sulfate-reducing bacteria (SRB) and saprophytic bacteria, thereby effectively reducing the possibility of microbiological corrosion.

[0005] The present invention further ensures the safety of oil and gas exploitation through the inhibitory effect of La and Cu ions on microorganisms and the inhibitory effect on microbiological corrosion through supersaturated copper precipitation. Summary of the Invention

[0006] The purpose of the present invention is to provide a steel for deep SEW oil casing resistant to biological corrosion and a preparation method thereof. The provided steel for SEW casing has excellent mechanical properties and good biological corrosion resistance, meeting the performance requirements of steel for deep oil casing.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: A steel for deep SEW oil casing resistant to biological corrosion, with its chemical composition and mass percentage being: C: 0.30 - 0.50%, Si: 0.20 - 0.30%, Mn: 2.0 - 3.5%, P ≤ 0.012%, S ≤ 0.005%, La: 0.10 - 0.30%, Mo: 0.35 - 0.50%, Al: 0.02 - 0.04%, Nb + V + Ti: 0.02 - 0.05%, Cu: 0.50 - 1.50%, Ni: 0.05 - 0.20%, and the balance being Fe and inevitable impurities.

[0008] Furthermore, the thickness specification of the steel for SEW casing in the present invention is 6 - 12 mm.

[0009] Furthermore, the hot-rolled microstructure of the steel for SEW casing in the present invention is ferrite and pearlite; its yield strength is 500 - 600 MPa, tensile strength is 650 - 750 MPa, and elongation is ≥ 20%.

[0010] Furthermore, the microstructure of the steel for SEW casing in the present invention after quenching + tempering heat treatment is tempered sorbite, with its yield strength ≥ 860 MPa, tensile strength ≥ 930 MPa, elongation ≥ 15%, and Charpy transverse impact energy ≥ 60 J.

[0011] Furthermore, the process parameters of the quenching + tempering heat treatment in the present invention are: quenching holding temperature 900 - 960 °C, quenching holding time 40 - 50 min; tempering holding temperature 600 - 630 °C, tempering holding time 80 - 100 min.

[0012] Furthermore, after the steel for SEW casing in the present invention is quenched + tempered, the maximum pitting depth ≤ 3.0 μm after being corroded in sulfate-reducing bacteria (SRB) corrosion solution for 14 days.

[0013] The preparation method of the steel for deep SEW oil casing resistant to biological corrosion in the present invention includes heating, rolling, cooling, and coiling processes.

[0014] Preferably, in the rolling process of the present invention, 7 - 8 passes of rolling are adopted, the starting rolling temperature is 1240 - 1260 °C, and the thickness after rolling is 8 - 13 mm.

[0015] Preferably, in the cooling and coiling processes of the present invention, laminar flow cooling is adopted, the laminar flow cooling rate ≤ 15 °C / s, and the coiling temperature is 720 - 780 °C.

[0016] The beneficial effects of adopting the above technical solutions are as follows: Through the combined action of Cu and La, the present invention obtains a steel for deep SEW oil casings with excellent biocorrosion resistance performance, which can effectively reduce microbial corrosion, thereby reducing the leakage of oil pipelines and the blockage of injection wells, and ensuring the smooth progress of oil and gas exploitation. The method of the present invention has low cost and simple production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the metallographic structure diagram of the steel for SEW oil casings in Example 1; Figure 2 It is the metallographic structure diagram of the steel for SEW oil casings after heat treatment in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The technical solutions of the present invention will be further described in detail below through examples.

[0019] The chemical composition and mass percentage content of the steel for deep SEW oil casings with biocorrosion resistance provided by the present invention are: C: 0.30 - 0.50%, Si: 0.20 - 0.30%, Mn: 2.0 - 3.5%, P ≤ 0.012%, S ≤ 0.005%, La: 0.10 - 0.30%, Mo: 0.35 - 0.50%, Al: 0.02 - 0.04%, Nb + V + Ti: 0.02 - 0.05%, Cu: 0.50 - 1.50%, Ni: 0.05 - 0.20%, and the balance is Fe and inevitable impurities. The chemical composition and mass percentage content of the steel for oil casings in each example and comparative example are shown in Table 1.

[0020] Table 1 Chemical composition and content of the steel for SEW casings in each example and comparative example (wt%)

[0021] The production methods of the steel for SEW oil casings in each example and comparative example include: billet heating, rolling, cooling, and coiling processes; the control of key processes is as follows: (1) Rolling: 7 - 8 passes of rolling are adopted, the starting rolling temperature is 1240 - 1260 °C, and the thickness after rolling is 8 - 13 mm; (2) Cooling and coiling: laminar cooling is adopted, the laminar cooling rate ≤ 15 °C / s, and the coiling temperature is 720 - 780 °C.

[0022] The parameter controls of the rolling, cooling, and coiling processes in each example and comparative example are shown in Table 2.

[0023] Table 2 Parameters of the rolling, cooling, and coiling processes in each example and comparative example

[0024] The metallographic structure of the hot-rolled SEW oil casing steel in Example 1 is shown in Figure 1 ; It can be seen from Figure 1 that its microstructure is ferrite and pearlite. The metallographic structures of the hot-rolled SEW oil casing steels in the remaining examples and comparative examples are the same as those in Example 1 and will not be shown one by one.

[0025] The mechanical properties of the hot-rolled SEW oil casing steels in each example and comparative example are shown in Table 3.

[0026] Table 3 Mechanical properties of the hot-rolled casing steels in each example and comparative example

[0027] The SEW oil casing steels obtained in each example and comparative example are subjected to quenching at 900 - 960 °C + tempering at 600 - 630 °C to obtain SEW oil casings. The heat treatment process parameters of each example and comparative example are shown in Table 4.

[0028] Table 4 Heat treatment process parameters of each example and comparative example

[0029] The metallographic structure of the SEW casing steel obtained in Example 1 after quenching + tempering heat treatment is shown in Figure 2 ; It can be seen from Figure 2 that its microstructure is tempered sorbite. The metallographic structures of the SEW casing steels in the remaining examples and comparative examples after quenching + tempering heat treatment are the same as those in Example 1 and will not be shown one by one.

[0030] The mechanical properties of the SEW oil casing steels in each example and comparative example after heat treatment, and the test results of the maximum pitting depth after 14 days of corrosion in the sulfate-reducing bacteria (SRB) corrosion solution are shown in Table 5.

[0031] Table 5 Test results of the SEW oil casing steels in each example and comparative example

[0032] It can be seen from Table 5 that the SEW casing steel provided by the present invention has excellent mechanical properties and good biocorrosion resistance.

Claims

1. A steel for deep SEW oil casing resistant to biological corrosion, characterized in that, The chemical composition and mass percentage of the steel for SEW casing are as follows: C: 0.30 - 0.50%, Si: 0.20 - 0.30%, Mn: 2.0 - 3.5%, P ≤ 0.012%, S ≤ 0.005%, La: 0.10 - 0.30%, Mo: 0.35 - 0.50%, Al: 0.02 - 0.04%, Nb + V + Ti: 0.02 - 0.05%, Cu: 0.50 - 1.50%, Ni: 0.05 - 0.20%, and the balance is Fe and inevitable impurities.

2. The steel for deep SEW oil casing resistant to biological corrosion according to claim 1, wherein, The thickness specification of the steel for SEW casing is 6 - 12 mm.

3. The steel for deep SEW oil casing resistant to biological corrosion according to claim 1 or 2, characterized in that, The hot-rolled metallographic structure of the steel for SEW casing is ferrite and pearlite structure, with a yield strength of 500 - 600 MPa, a tensile strength of 650 - 750 MPa, and an elongation rate of ≥20%.

4. The steel for deep SEW oil casing resistant to biological corrosion according to claim 1 or 2, characterized in that, The structure of the steel for SEW casing after quenching + tempering heat treatment is tempered sorbite, with a yield strength of ≥860 MPa, a tensile strength of ≥930 MPa, an elongation rate of ≥15%, and a Charpy transverse impact energy of ≥60 J.

5. The steel for deep SEW oil casing resistant to biological corrosion according to claim 1 or 2, characterized in that, After the steel for SEW casing is quenched + tempered, the maximum pitting depth is ≤3.0 μm after being corroded in a sulfate-reducing bacteria (SRB) corrosion solution for 14 days.

6. A preparation method of the steel for deep SEW oil casing resistant to biological corrosion according to any one of claims 1-5, characterized in that, It includes heating, rolling, cooling, and coiling processes.

7. The preparation method of a steel for deep SEW oil casing resistant to biological corrosion according to claim 6, characterized in that, For the rolling process, 7 - 8 passes of rolling are adopted, the starting rolling temperature is 1240 - 1260 °C, and the thickness after rolling is 8 - 13 mm.

8. The preparation method of a steel for deep SEW oil casing resistant to biological corrosion according to claim 6, characterized in that For the cooling and coiling processes, laminar cooling is adopted, the laminar cooling rate is ≤15 °C / s, and the coiling temperature is 720 - 780 °C.

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