High-strength oil casing pipe resistant to CO2 and microbial corrosion and manufacturing method of high-strength oil casing pipe

Abstract

The high-strength oil casing comprises the following chemical components in percentage by weight: 0.06 to 0.20 percent of C, 0.1 to 1.0 percent of Si, 0.10 to 2.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.007 percent of S, 1.5 to 7.0 percent of Cr, 0.5 to 3.5 percent of Ni, 0.3 to 3.5 percent of Cu, 0.1 to 3.5 percent of Mo, 0.02 to 0.15 percent of Nb, 0.01 to 0.20 percent of V, 0.2 to 3.0 percent of Al, 0.0010 to 0.008 percent of B, 0.10 to 0.75 percent of RE and the balance of Fe and inevitable impurities, the RE comprises La and Ce, and the sum of [La] and [Ce] is more than or equal to 0.07 percent and less than or equal to 0.35 percent. The obtained oil casing can reach the strength level of 110 ks-125 ksi, has excellent resistance to corrosion of microorganisms such as CO2, sulfate reducing bacteria (SRB) and saprophytic bacteria (TGB), has the yield strength of 758-1034 MPa, and has the full-size impact energy at 0 DEG C of more than or equal to 80 J; the temperature is 40 DEG C, the CO2 partial pressure is 2.0 MPa, 50000 pieces / ml of sulfate reducing bacteria and 20000 pieces / ml of saprophytic bacteria are contained, the test time is 300 h, the uniform corrosion rate of the oil casing is smaller than or equal to 0.0211 mm / a, and the spot corrosion rate of the oil casing is smaller than or equal to 0.0415 mm / a.

Description

Technical Field

[0001] This invention belongs to the field of oil casing and tubing used in oil and gas field development and its manufacturing, specifically relating to a high-strength oil casing and tubing resistant to CO2 and microbial corrosion and its manufacturing method. Background Technology

[0002] Water injection is a common and efficient technique in oil and gas field production. Water injection wells maintain or restore reservoir pressure by injecting water into the oil layer, providing a strong driving force and thus increasing the extraction rate and recovery rate. In shale gas well production, a mixture of water, sand, and chemicals is injected underground under high pressure through boreholes to fracture the shale layer, creating larger and more numerous fractures and releasing the oil or natural gas reserves. For convenience and economic reasons, river and lake water near oil fields is used extensively, and produced water is frequently reinjected for repeated operations. Generally, river and lake water, as well as produced water, contain high levels of microorganisms, especially sulfate-reducing bacteria and iron bacteria. These microorganisms, through biofilms attached to material surfaces, directly or indirectly accelerate the corrosion or damage of metallic materials through their life activities and metabolic products. Furthermore, many associated gases in oil and gas fields used for water injection contain corrosive CO2 gas, which can cause localized corrosion and perforation of the casing. The corrosion problem caused by the coupled effects of CO2 and microorganisms leads to frequent casing rupture accidents in oil and gas fields. With the continuous development of oil and gas extraction, the depth of oil and gas wells using water injection technology is constantly increasing, and the formation pressure is also increasing, placing higher and higher demands on the steel grade of oil casing and tubing. Therefore, the oil and gas field industry urgently needs to obtain a high-grade oil casing and tubing product resistant to CO2-SRB corrosion.

[0003] Chinese patent CN101289730B discloses a method for manufacturing a 110ksi high-strength, CO2-resistant oil casing and the oil casing obtained using this method. Its chemical composition is: C: 0.15–0.25%, Si: 0.2–1.0%, Mn: 0.20–1.0%, Cr: 12.0–14.0%, Ni: 0.5–1.5%, Mo: 0.2–1.0%, N: 0.03–0.10%, with the remainder being Fe and unavoidable impurities. This method yields an oil casing that is resistant to CO2 and chloride ion corrosion at temperatures exceeding 150℃ and achieves a strength equivalent to 110ksi steel. This oil casing exhibits excellent CO2 corrosion resistance but lacks resistance to SRB corrosion.

[0004] Chinese patent CN 107619994A discloses "a seamless pipeline resistant to CO2 / H2S and sulfate-reducing bacteria corrosion and its manufacturing method," with the following chemical composition: C: 0.03-0.10%, Si: 0.1-0.5%, Mn: 0.10-1.5%, Cr: 1.0-4.0%, Ni: 0.1-1.5%, Cu: 0.15-2.0%, Mo: 0.05-0.4%, Ti: 0.01-0.05%, RE: 0.05-0.1%, with the remainder being Fe and unavoidable impurities. The pipeline obtained by this invention exhibits excellent resistance to CO2-H2S-SRB corrosion, but its strength does not meet the requirements for 110ksi-125ksi steel grades.

[0005] Canadian patent CA02872342 discloses a "high-strength stainless steel seamless oil casing and its manufacturing method," producing a high-strength stainless steel oil well casing with a wall thickness exceeding 25.4 mm and a yield strength of 110 ksi (758 MPa) or higher. This casing exhibits excellent strength, toughness, and corrosion resistance. Its chemical composition is: C: 0.005–0.06%, Si: 0.05–0.50%, Mn: 0.20–1.8%, Cr: 15.5–18.0%, Ni: 1 The composition is 0.5–5.0%, V: 0.02–0.2%, Al: 0.002–0.05%, N: 0.01–0.15%, Mo: 1.0–3.5%, W > 3.0%, Cu < 3.5%, and satisfies the following relationships: Cr + 0.65Ni + 0.60Mo + 0.30W + 0.55Cu - 20C ≥ 19.5, Cr + Mo + 0.50W + 0.30Si - 43.5C - 0.4Mn - Ni - 0.3Cu - 9N ≥ 11.5. This patent obtains a product resistant to 230℃, CO2, and Cl. - It is a high-strength, high-toughness seamless steel pipe with excellent corrosion resistance, yield strength above 110 ksi (758 MPa), and impact toughness (-10℃) above 40 J. However, it does not have resistance to SRB corrosion.

[0006] A comparison with existing patents reveals that there are currently no oil casings with excellent resistance to CO2-SRB corrosion and a strength level of 110ksi-125ksi. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength oil casing resistant to CO2 and microbial corrosion, and its manufacturing method. The resulting oil casing can achieve a strength level of 110ksi-125ksi and has excellent resistance to CO2 and microbial corrosion such as sulfate-reducing bacteria (SRB) and saprophytic bacteria (TGB). Its yield strength is 758-1034MPa, and its full-size impact energy at 0℃ is ≥80J. Under the following conditions: temperature 40℃, CO2 partial pressure 2.0MPa, 50,000 / ml sulfate-reducing bacteria, 20,000 / ml saprophytic bacteria, and test time 300h, the uniform corrosion rate of the oil casing is ≤0.0211mm / a, and the pitting corrosion rate is ≤0.0415mm / a.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A high-strength oil casing resistant to CO2 and microbial corrosion has the following chemical composition by weight percentage: C: 0.06–0.20%, Si: 0.1–1.0%, Mn: 0.10–2.5%, P≤0.015%, S≤0.007%, Cr: 1.5–7.0%, Ni: 0.5–3.5%, Cu: 0.3–3.5%, Mo: 0.1–3.5%, Nb: 0.02–0.15%, V: 0.01–0.20%, Al: 0.2–3.0%, B: 0.0010–0.008%, RE: 0.10–0.75%, with the balance including Fe and unavoidable impurities, wherein RE contains La and Ce, and simultaneously satisfies: 0.07% ≤ [La] + [Ce] ≤ 0.35%.

[0010] Furthermore, the balance consists of Fe and other unavoidable impurities.

[0011] The microstructure of the oil casing of the present invention is tempered sorbite, with copper-rich phases dispersed throughout the microstructure.

[0012] The oil casing of the present invention has a yield strength of 758-1034 MPa and a full-size impact energy of ≥80 J at 0℃. The test conditions are: temperature 40℃, CO2 partial pressure 2.0 MPa, 50,000 sulfate-reducing bacteria / ml, 20,000 saprophytic bacteria / ml, and test time 300 h. The uniform corrosion rate of the oil casing is ≤0.0201 mm / a and the pitting corrosion rate is ≤0.0415 mm / a.

[0013] In the chemical composition design of the high-strength oil casing resistant to CO2 and microbial corrosion described in this invention:

[0014] C: Carbon is an essential component for ensuring the room temperature strength and hardenability of steel pipes. If the carbon content is below 0.06%, the hardenability is low, the strength is difficult to guarantee, and the toughness will also decrease. The carbon content should not be too high. This invention uses an online quenching process, which makes the material more susceptible to deformation stress and more prone to quenching cracks than conventional offline quenching processes. Therefore, the carbon content in this invention is controlled between 0.06% and 0.20%.

[0015] Si: Si is an important deoxidizer in the steelmaking process. In addition, Si can improve high-temperature oxidation resistance and acid resistance. To ensure the deoxidation effect of the steel, the Si content needs to be maintained at ≥0.1%, but excessive content will reduce the toughness and plasticity of the steel. Therefore, in this invention, the Si content is controlled between 0.1% and 1.0%.

[0016] Mn: Mn expands the austenite phase region, which can improve the hardenability of steel. However, Mn is prone to segregation during solidification, affecting the toughness of steel. When the Mn content is less than 0.10%, the hardenability of steel decreases significantly; when the Mn content is greater than 2.5%, compositional segregation easily occurs, leading to quenching cracks. Therefore, in this invention, the Mn content is controlled between 0.10% and 2.5%.

[0017] P: P is a harmful element that reduces resistance to CO2 corrosion and also has an adverse effect on hot working properties. If the P content is greater than 0.015%, the corrosion resistance cannot meet the requirements of the CO2 environment. Therefore, this invention controls the P content to ≤0.015%.

[0018] Sulfur (S): Sulfur is a harmful element that reduces hot working properties and adversely affects impact toughness. If the S content exceeds 0.007%, steel pipes cannot be manufactured normally. Therefore, this invention controls the S content to ≤0.007%, and more preferably, controls the S content to ≤0.005%.

[0019] Cr: Cr can significantly improve the resistance of steel to both localized and uniform CO2 corrosion. When the Cr content is less than 1.5%, excellent CO2 corrosion resistance cannot be guaranteed. However, higher Cr content is not always better, because the segregation of Cr carbides at grain boundaries can easily lead to a decrease in the corrosion resistance of the steel. Therefore, this invention controls the Cr content between 1.5% and 7.0%.

[0020] Ni: Ni can significantly improve the performance of passivation films and enhance the corrosion resistance of steel. Furthermore, the synergistic effect of Ni and Cu allows Ni to reduce the interfacial energy between the Cu-rich nanophase and the matrix, lowering the critical nucleation energy of Cu-rich particles, thereby significantly increasing the density of nanoparticles and enhancing the steel's resistance to microbial corrosion and its strengthening properties. Ni can also improve the cracking problem of steel billets and reduce the tendency of TMCP to form cracks. Therefore, this invention controls the Ni content to be between 0.5% and 3.5%.

[0021] Cu: Cu is a key alloying element in this invention and is essential for ensuring resistance to microbial corrosion. Cu is uniformly dispersed in the matrix as a copper-rich phase. Under service conditions, copper ions can continuously dissolve and adsorb onto the steel surface, preventing sulfate-reducing bacteria from adsorbing and growing on the steel surface, thus exerting a bactericidal effect. The synergistic effect of Cu and Ni: Ni reduces the interfacial energy between the Cu-rich nanophase and the matrix, lowering the critical nucleation energy of the Cu-rich particles, thereby significantly increasing the density of the nanoparticles and enhancing the steel's resistance to microbial corrosion. It exists in the corrosion product film in the form of cuprous oxide (Cu₂O and CuO), enhancing the film's density and ion barrier properties, and improving CO₂ corrosion resistance. However, excessive Cu can lead to the precipitation of coarse copper-rich phases, affecting impact toughness and hot working properties. Therefore, the Cu content in this invention is controlled at 0.3–3.5%.

[0022] Mo: Mo can improve the strength of steel through carbide and solid solution strengthening, and also effectively increase the steel's resistance to pitting corrosion. When the Mo content is less than 0.1%, the strengthening effect and pitting corrosion resistance are relatively weak; when the Mo content is greater than 3.5%, quenching cracks are easily generated in the TMCP process. Therefore, this invention controls the Mo content to be between 0.1% and 3.5%.

[0023] Nitrogen (Nb): Nitrogen is a relatively strong strengthening element that can improve the strength of steel through precipitation strengthening. Furthermore, Nb precipitates form numerous nucleation sites, thereby refining the austenite grains and improving the toughness of the steel. When the Nb content is less than 0.02%, the strengthening effect is not significant; when the Nb content is greater than 0.15%, the precipitates are more numerous and coarser, affecting the toughness and corrosion resistance of the steel. Therefore, this invention controls the Nb content between 0.02% and 0.15%.

[0024] V: V is a typical precipitation strengthening element that can improve the strength of steel. When the V content is less than 0.01%, the strengthening effect is not obvious; when the V content is greater than 0.20%, there are more and coarser precipitates, which affect the toughness and corrosion resistance of the steel. Therefore, this invention controls the V content to be between 0.01% and 0.20%.

[0025] Al: The addition of Al element, existing in the form of Al oxide in the corrosion products, intertwines with the Cr and Cu product film particles, filling the spaces between the particles, enhancing the density and ion barrier properties of the corrosion product film, and improving CO2 corrosion resistance. Therefore, the Al content in this invention is controlled at 0.2% to 3.0%.

[0026] Boron (B): Boron is an element that significantly improves the hardenability of steel. When the B content is less than 0.0010%, the effect on improving hardenability is not obvious; when the B content is greater than 0.008%, it is easy to form the brittle BN phase. Therefore, this invention controls the B content to be between 0.0010% and 0.008%.

[0027] RE (refined iron): RE can effectively improve the toughness and CO2 corrosion resistance of steel, while La (La) and Ce (Ce) can effectively enhance the steel's resistance to microbial corrosion. However, excessive RE, La, and Ce content should be avoided, as it can lead to the formation of numerous coarse inclusions, affecting the steel's toughness and corrosion resistance. Therefore, this invention recommends controlling the RE content to 0.10–0.75% (where 0.07% ≤ [La] + [Ce] ≤ 0.35%).

[0028] Overall, this invention adopts the design concept of the above-mentioned components:

[0029] 1. CO2 Corrosion Resistance: Based on the synergistic effect of novel corrosion product enrichment, the density and ion barrier properties of the corrosion product film are improved, enhancing the protective performance of the substrate. This invention simultaneously adds Cr, Cu, and Al. Cr, Cu, and Al all exhibit strong enrichment effects within the corrosion product film. Cr exists in the corrosion products in the forms of Cr₂O₃, Cr(OH)₃, and Cr(OH)O; Cu exists in the corrosion product film in the form of cuprous oxide (Cu₂O and CuO); and Al exists in the corrosion products in the form of Al oxide. The product film particles formed by Cr, Cu, and Al are interwoven and fill the spaces between particles, enhancing the density and ion barrier properties of the corrosion product film, thereby improving the corrosion resistance of the oil casing in a CO₂ environment.

[0030] 2. Resistance to Microbial Corrosion: Through the synergistic effect of Ni and Cu, Ni reduces the interfacial energy between the Cu-rich nanophase and the matrix, lowering the critical nucleation energy of the Cu-rich precipitates, thereby significantly increasing the density of Cu nanophases and enhancing the steel's resistance to microbial corrosion. Furthermore, RE plays a role in improving CO2 corrosion resistance, and the La and Ce in RE have a toxic effect on sulfate-reducing bacteria (SRB) and saprophytic bacteria (TGB). Therefore, further adding RE to enhance CO2 corrosion resistance, while controlling the total amount of La and Ce added, can improve both CO2 corrosion resistance and microbial corrosion resistance in the oil casing.

[0031] 3. High strength performance: In addition to adding microalloying elements to increase strength, the synergistic precipitation effect of Ni and Cu can further enhance the precipitation strengthening effect and ensure the high strength performance of the product.

[0032] The manufacturing method of the high-strength oil casing resistant to CO2 and microbial corrosion according to the present invention includes the following steps:

[0033] 1) Smelting and casting

[0034] The above-mentioned components are smelted and cast into ingots, and then forged or rolled into tube blanks;

[0035] 2) Heating, piercing, and continuous rolling

[0036] The billet is heated to 1220–1280℃ for 3–4 hours; the piercing temperature is 1170–1250℃; the final rolling temperature is 900–970℃; and finally, the billet is reduced in diameter by tension to form a rough tube.

[0037] 3) Control cooling

[0038] Ensure the tube temperature is ≥870℃ before cooling, and cool it to room temperature at a cooling rate of 20~60℃ / s.

[0039] 4) Tempering

[0040] Tempering temperature 530~630℃, tempering time 40~60min, to obtain finished oil casing.

[0041] Preferably, in step 3), the cooling process uses water cooling.

[0042] The TMCP process used in this invention is relatively mature in plate steel, but controlling the cooling of steel pipes due to their special shape has always been a major challenge in the industry. Existing technologies can already produce C-Mn carbon steel oil casing using the TMCP process, but the oil casing design described in this invention includes elements such as Cr, Cu, and rare earth elements (RE). The steel's microstructure becomes more complex due to the greater influence of cooling, making it difficult to produce on a TMCP platform. This invention, on the one hand, enhances the deformation-induced phase transformation effect; on the other hand, it reduces the risk of grain growth by minimizing repeated heating, and the grain refinement significantly improves strength, toughness, and corrosion resistance.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] This invention improves the corrosion resistance of the casing by adding Cr, Cu, and Al elements. The resulting product film particles interweave and fill the spaces between particles, enhancing the density and ion barrier properties of the corrosion product film, thus improving the corrosion resistance of the casing in a CO2 environment. Furthermore, the synergistic effect of Ni and Cu is utilized. Ni reduces the interfacial energy between the Cu-rich nanophase and the matrix, lowering the critical nucleation energy of the Cu-rich precipitates, thereby significantly increasing the density of the Cu nanophase and enhancing the steel's resistance to microbial corrosion and its strength. Moreover, by controlling the amount of rare earth elements added, the casing not only gains resistance to CO2 corrosion but also improved resistance to microbial corrosion. While achieving a strength level of 110ksi-125ksi for the oil casing, it also possesses excellent resistance to corrosion from CO2 and microorganisms such as sulfate-reducing bacteria (SRB) and saprophytic bacteria (TGB). Its yield strength is 758-1034MPa, and its full-size impact energy at 0℃ is ≥80J. Under the following conditions: temperature 40℃, CO2 partial pressure 2.0MPa, 50,000 / ml sulfate-reducing bacteria, 20,000 / ml saprophytic bacteria, and test time 300h, the uniform corrosion rate of the oil casing is ≤0.0211mm / a, and the pitting corrosion rate is ≤0.0415mm / a.

[0045] In terms of process design, this invention employs the TMCP process, utilizing the residual heat after rolling for direct quenching, which further strengthens the tubes through deformation-induced phase transformation. In contrast, traditional oil casing manufacturing processes employ offline quenching followed by tempering heat treatment after tube rolling. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments.

[0047] The chemical composition of the steel in this embodiment of the invention is shown in Table 1, with the balance including Fe and unavoidable impurities; the specific process parameters are shown in Table 2.

[0048] The results of the embodiments and comparative examples of the present invention are shown in Table 3.

[0049] The yield strength test data is obtained by machining the manufactured oil casing into API arc-shaped specimens, testing them according to API standards, and taking the average value.

[0050] The 0℃ full-size impact energy data is obtained by taking a 10*10*55 full-size V-type impact specimen from the manufactured oil casing, testing it according to GB / T 229 standard, and taking the average value.

[0051] The corrosion test was conducted in an environment where CO2 and SRB coexisted. The oil casing samples of the embodiments and comparative examples of the present invention were immersed in the container liquid at a temperature of 40°C, a CO2 partial pressure of 2.0 MPa, a sulfate-reducing bacteria concentration of 50,000 CFU / ml, a saprophytic bacteria concentration of 20,000 CFU / ml, and a test time of 300 h. The uniform corrosion rate was calculated by comparing the sample weights before and after the test, and the pitting corrosion rate was calculated by cross-sectional analysis of the pitting pits.

[0052] As can be seen from Table 3, the oil casing obtained by the present invention has a yield strength of 758-1034 MPa, a full-size impact energy of ≥80 J at 0℃, a uniform corrosion rate of ≤0.0211 mm / a, and a pitting corrosion rate of ≤0.0415 mm / a.

[0053] Comparative Example 1 had a low carbon content, and both Cu and Ni contents were low, resulting in a casing strength that did not meet the requirements.

[0054] Comparative Example 2 had a lower Cr content and a higher RE content, and its corrosion resistance did not meet the requirements.

[0055] Comparative Example 3: The Cu content is low, and the corrosion resistance does not meet the requirements.

[0056] Comparative Example 4: The content of C, Cr and Nb is low, and the strength and corrosion resistance do not meet the requirements.

[0057]

[0058]

[0059]

Claims

1. A high-strength oil casing resistant to CO2 and microbial corrosion, wherein the chemical composition by weight percentage is: C: 0.06-0.20%, Si: 0.1-1.0%, Mn: 0.10-2.5%, P≤0.015%, S≤0.007%, Cr: 1.5-7.0%, Ni: 0.5-3.5%, Cu: 0.3-3.5%, Mo: 0.1-3.5%, Nb: 0.02-0.15%, V: 0.01-0.20%, Al: 0.2-3.0%, B: 0.0010-0.008%, RE: 0.10-0.75%, with the balance including Fe and unavoidable impurities, wherein RE contains La and Ce, and simultaneously satisfies: 0.07%≤[La]+[Ce]≤0.35%.

2. The high-strength oil casing resistant to CO2 and microbial corrosion as described in claim 1, characterized in that, The composition of the oil casing contains S ≤ 0.005%.

3. The high-strength oil casing resistant to CO2 and microbial corrosion as described in claim 1 or 2, characterized in that, The balance consists of Fe and other unavoidable impurities.

4. The high-strength oil casing resistant to CO2 and microbial corrosion as described in claim 1, 2, or 3, characterized in that, The microstructure of the oil casing is tempered sorbite, with copper-rich phases dispersed throughout the structure.

5. The high-strength oil casing resistant to CO2 and microbial corrosion as described in claim 1, 2, 3, or 4, characterized in that, The oil casing has a yield strength of 758–1034 MPa and a full-size impact energy of ≥80 J at 0℃. Under the following conditions: temperature 40℃, CO2 partial pressure 2.0 MPa, 50,000 sulfate-reducing bacteria / ml, 20,000 saprophytic bacteria / ml, and test time 300 h, the uniform corrosion rate of the oil casing is ≤0.0201 mm / a, and the pitting corrosion rate of the oil casing is ≤0.0415 mm / a.

6. The method for manufacturing a high-strength oil casing resistant to CO2 and microbial corrosion as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Smelting and casting The components are smelted and cast into ingots according to the composition of claim 1, 2 or 3, and then forged or rolled into tube blanks. 2) Heating, piercing, and continuous rolling The billet is heated to 1220–1280℃ for 3–4 hours; the piercing temperature is 1170–1250℃; the final rolling temperature is 900–970℃; and finally, the billet is reduced in diameter by tension to form a rough tube. 3) Control cooling Ensure the tube temperature is ≥870℃ before cooling, and cool it to room temperature at a cooling rate of 20~60℃ / s. 4) Tempering Tempering temperature 530~630℃, tempering time 40~60min, to obtain finished oil casing.

7. The manufacturing method as described in claim 6, characterized in that, In step 3), water cooling is used for the cooling process.

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