Coiled tubing for acidification operation and preparation method thereof

Abstract

The invention provides a continuous pipe for acidification operation and a preparation method thereof. The continuous pipe for acidification operation comprises the following components in percentage by weight: less than or equal to 0.12% of C, 0.35-0.65% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.20-0.40% of Si, 0.70-1.10% of Cr, 0.04-0.10% of Sb, 0.25-0.45% of Cu, less than or equal to 0.2% of Sn, less than or equal to 0.2% of inevitable impurity elements and the balance of Fe. The continuous pipe is excellent in corrosion resistance, high in crack resistance, long in service life in the acidification operation process, high in service safety, capable of meeting the acidification operation requirement of an oil field, wide in market requirement, high in competitiveness and wide in market prospect, and the price of the continuous pipe is not obviously increased compared with a conventional continuous pipe.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and natural gas pipeline materials, and in particular, to a coiled tubing for acidizing operation and a preparation method thereof. Background Art

[0002] Coiled tubing (CT) is a new type of oil and gas pipeline material with a single length of up to several kilometers. This type of material has high mechanical strength, good plasticity, and certain corrosion resistance. Coiled tubing technology has technical advantages and operation advantages such as high efficiency, low cost, wide operation range, and small floor area, and plays an increasingly important role in oil and gas field exploration, development, operation, and production enhancement, with broad application prospects.

[0003] Acidizing operation is to inject acid solution into the formation to dissolve some minerals in the formation rock or the blockages in pores and fractures, causing fractures and unevenness on the rock surface, so as to increase the diameter of the penetration pores in the oil and gas reservoir, thereby effectively improving the penetration channels of the oil and gas reservoir and achieving production increase. At present, the process of using coiled tubing for acidizing operation has been relatively mature. However, the acid solution used in the acidizing operation site is usually an aqueous hydrochloric acid solution with a mass concentration of 10-15%. The coiled tubing contacts with other metal tubing or casing in the wellbore and forms a circuit in the acid solution to occur an oxidation-reduction reaction, resulting in the electrochemical corrosion of the active metals in the coiled tubing. In addition, the coiled tubing serves in an acidic working medium for a long time, and the iron element in the coiled tubing is corroded by the acid and undergoes a displacement reaction to become ferrous ions, which are then oxidized to form iron oxide. During the acidizing fluid drainage process, affected by multiple factors such as corrosion and erosion, the wall thickness of the coiled tubing rapidly decreases, and the material itself is prone to hydrogen embrittlement fracture, resulting in a significant reduction in its service life. In recent years, there have been many quality objections due to the short-term failure and inability to serve of the tubing caused by acidizing operations, seriously affecting the safety of oilfield production and unable to meet the requirements of oilfield quality improvement and efficiency increase. Summary of the Invention

[0004] The main purpose of the present invention is to provide a coiled tubing for acidizing operation and a preparation method thereof to solve the problem of short service life of the coiled tubing during the acidizing operation in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a coiled tubing for acidizing operation. By weight percentage, its material includes the following components: C≤0.12%, Mn 0.35-0.65%, P≤0.035%, S≤0.035%, Si 0.20-0.40%, Cr 0.70-1.10%, Sb 0.04-0.10%, Cu 0.25-0.45%, Sn≤0.2%, the total sum of inevitable impurity elements≤0.2%, and the rest is Fe.

[0006] Further, by weight percentage, its materials include the following components: C 0.03 - 0.12%, Mn 0.35 - 0.45%, P ≤ 0.015%, S ≤ 0.005%, Si 0.30 - 0.40%, Cr 0.80 - 1.10%, Sb 0.05 - 0.10%, Cu 0.30 - 0.40%, Sn 0.08 - 0.13%, the total sum of inevitable impurity elements ≤ 0.1%, and the balance is Fe.

[0007] Further, the total weight percentage of Cr, Cu and Sn ≥ 1.3%.

[0008] Further, the yield strength of the coiled tubing is 522 - 620 MPa, the tensile strength ≥ 601 MPa, the elongation ≥ 20%, and the hardness ≤ 22 HRC; and / or the uniform corrosion weight loss rate of the coiled tubing in a hydrochloric acid aqueous solution at 70 °C and a mass concentration of 15% < 10 mm / a.

[0009] According to another aspect of the present invention, there is provided a method for preparing coiled tubing for acidizing operations, including the following steps: Step S1, according to the component ratio, after mixing each component raw material, successively carry out smelting, casting and hot rolling to obtain a coiled sheet; Step S2, longitudinally shear the coiled sheet to obtain a steel strip; then butt-weld the steel strip and perform a first heat treatment on the butt weld to obtain a butt-welded steel strip; Step S3, successively carry out forming and longitudinal welding on the butt-welded steel strip and perform a second heat treatment on the longitudinal weld to obtain a pipe string; Step S4, perform a third heat treatment on the pipe string to obtain coiled tubing for acidizing operations.

[0010] Further, in Step S1, the smelting includes first smelting and second smelting carried out successively, the temperature of the first smelting is 1600 - 1700 °C, and the temperature of the second smelting is 1550 - 1650 °C; and / or the hot rolling includes first hot rolling and second hot rolling carried out successively, the temperature of the first hot rolling is 1000 - 1060 °C, and the temperature of the second hot rolling is 840 - 890 °C.

[0011] Further, in Step S2, after processing the end of the steel strip into a first groove, then carry out butt welding, the first groove is of I type, V type or U type; and / or the butt welding adopts one or more of friction stir welding, laser welding protected by inert gas, argon arc welding and plasma welding protected by inert gas; preferably, the butt welding adopts argon arc welding or plasma welding protected by argon gas.

[0012] Further, in Step S2, the first heat treatment includes quenching and tempering treatments carried out successively, the temperature of quenching is 850 - 950 °C, and the time is 5 - 15 min; the temperature of tempering is 500 - 550 °C, and the time is 5 - 10 min.

[0013] Further, in step S3, the longitudinal side surface of the butt steel strip is processed into a second bevel for forming; preferably, the second bevel is of type I, and the forming method is UO forming or JCO forming; and / or the longitudinal welding adopts one or more of high-frequency induction welding, plasma welding, and laser welding; preferably, the longitudinal welding adopts laser welding; and / or the temperature of the second heat treatment is 900-960°C, and the time is 5-10 min.

[0014] Further, in step S4, the temperature of the third heat treatment is 590-750°C, and the time is 5-20 min.

[0015] For the coiled tubing for acidizing operation of the present invention, by controlling C, Mn, P, S, Si, Cr, Sb, Cu, and Sn within a specific content range, and the synergistic cooperation among the components is beneficial to forming a dense film on the surface of the steel-based tubing, increasing the electrode potential of α-Fe, reducing the corrosion rate of the tubing by hydrochloric acid and electrochemical reactions, slowing down the thinning of the tubing wall thickness, improving the hydrochloric acid corrosion resistance and electrochemical corrosion resistance of the tubing, and at the same time being beneficial to improving the crack resistance of the tubing. Thus, on the basis of meeting the mechanical property requirements, the service life of the coiled tubing during the acidizing operation can be extended, the service safety can be improved, and the requirements of oilfield acidizing operations can be met. In addition, compared with conventional coiled tubing, the price of the coiled tubing for acidizing operation of the present invention does not increase significantly, has a wide market demand, strong competitiveness, and broad market prospects. Description of the Drawings

[0016] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0017] Figure 1 Shows the SEM photograph of the base metal structure of the coiled tubing for acidizing operation according to Embodiment 1 of the present invention. Detailed Embodiments

[0018] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0019] Term Explanation:

[0020] Yield strength: The yield limit when a metal material exhibits a yield phenomenon.

[0021] Tensile strength: Refers to the critical value at which a metal transitions from uniform plastic deformation to local concentrated plastic deformation, and is also the maximum load-bearing capacity of the metal under static tensile conditions.

[0022] Elongation: The percentage of the elongation of the gauge length after the specimen fractures to the original gauge length.

[0023] Hardness: The ability of a material to locally resist the penetration of a hard object into its surface.

[0024] Uniform corrosion weight loss rate: Under the condition that the entire metal surface in contact with the environment corrodes at almost the same rate, the weight of the metal material lost per unit area per unit time.

[0025] UO forming: A production process in which the pre-bent steel plate is first pressed into a U shape in a U-forming machine, then pressed into an O shape in an O-forming machine, and the O-shaped tube is welded and then subjected to diameter expansion processing.

[0026] JCO forming: A production process in which the steel plate is milled (or planed) and then pre-bent along the longitudinal edge, and then formed in the order of J-shaped - C-shaped - O-shaped.

[0027] As described in the background art of the present invention, there is a problem of short service life of coiled tubing during acidizing operations in the prior art. To solve the above problems, in a typical embodiment of the present invention, a coiled tubing for acidizing operations is provided. By weight percentage, its material includes the following components: C ≤ 0.12%, Mn 0.35 - 0.65%, P ≤ 0.035%, S ≤ 0.035%, Si 0.20 - 0.40%, Cr 0.70 - 1.10%, Sb 0.04 - 0.10%, Cu 0.25 - 0.45%, Sn ≤ 0.2%, the total sum of inevitable impurity elements ≤ 0.2%, and the rest is Fe.

[0028] Based on conventional steel-based pipe materials, the present invention specifically defines the added elements. Among them, the Cr element can form a solid solution with α-Fe and can increase the electrode potential of α-Fe, thereby playing a role in inhibiting the anodic reaction and reducing electrochemical corrosion. Moreover, Cr can form a dense oxide film on the surface of the steel to improve the corrosion resistance of the steel and the mechanical properties of the steel at normal and high temperatures. Controlling the content of Cr within the scope of the present invention can not only improve the corrosion resistance of the steel and inhibit the electrochemical reaction under acidic conditions, but also save costs.

[0029] The inventors unexpectedly found during the experiment that when the Sb element is used as an alloying element, it can partially dissolve in iron. In strong acid and strong alkali solutions, Sn will react on the material surface, and by generating a SnO2 layer, it can prevent the contact between Fe and strong acid, thus being beneficial to improving the corrosion resistance of the steel-based pipe. Considering that Sb will form a low-melting eutectic compound with sulfur and segregate at the grain boundaries, thereby reducing the intergranular bonding force and weakening the grain boundaries, showing temper brittleness. Therefore, the content of Sb in the present invention is controlled at 0.04 - 0.10%.

[0030] The Cu element can be precipitated dispersedly on the surface of the steel, and can promote the formation of a dense oxide film on the steel surface. In addition, a small amount of Cu dissolved in α-Fe can increase the electrode potential of α-Fe, thereby reducing electrochemical corrosion. The inventor unexpectedly found during the experiment that when the Cu content in the steel is less than 0.25%, the corrosion resistance of the steel is poor; when the Cu content in the steel is greater than 0.45%, the steel has a hot brittleness phenomenon. Therefore, the Cu content in the present invention is controlled within 0.25 - 0.45%.

[0031] The Mn element has a desulfurization effect, can react with S to form MnS with a relatively high melting point, which is beneficial to preventing S from reacting with Fe to form FeS with a relatively low melting point, and is also beneficial to changing the film-like distribution of FeS into a spherical distribution. MnS can maintain the spherical distribution unchanged after hot working, which is beneficial to avoiding linear cracks in the steel, thereby improving the crack resistance of the steel. When the Mn content in the steel is less than 0.35%, the crack resistance of the steel is poor; when the Mn content in the steel is greater than 0.65%, the production cost is relatively high. Therefore, the Mn content in the present invention is controlled within 0.35 - 0.65%.

[0032] The addition of the Sn element is beneficial to forming an outer film of SnO2 on the steel surface. While hindering the corrosion of the steel material, it can play a role in inhibiting anodic dissolution, thereby being beneficial to improving the acid corrosion resistance and electrochemical corrosion resistance of the steel. Considering that Sn is a low-melting-point element with a melting point of only 232°C, it is easy to precipitate along the grain boundaries to form a Sn-rich brittle phase. When the Sn content is too high, it will have an adverse effect on the high-temperature plasticity of the continuous casting billet, the toughness of the steel plate, and the surface quality. Therefore, the Sn content in the present invention is controlled below 0.2%.

[0033] By controlling the contents of C, Mn, P, S, Si, Cr, Sb, Cu, and Sn within a specific range, the components cooperate synergistically in the present invention, which is beneficial to forming a dense film on the surface of the steel-based pipe, increasing the electrode potential of α-Fe, reducing the corrosion rate of the pipe caused by hydrochloric acid and electrochemical reactions, slowing down the thinning of the pipe wall thickness, improving the hydrochloric acid corrosion resistance and electrochemical corrosion resistance of the pipe, and at the same time being beneficial to improving the crack resistance of the pipe. Thus, on the basis of meeting the mechanical property requirements, the service life of the coiled tubing during the acidizing operation can be extended. In addition, while ensuring the corrosion resistance and crack resistance of the pipe, the present invention specifically controls the content of precious metal components. Compared with conventional coiled tubing, the price of the coiled tubing for acidizing operation in the present invention does not increase significantly, has a wide market demand, strong competitiveness, and has a broad market prospect.

[0034] In a preferred embodiment, by weight percentage, the coiled tubing material for acidizing operations comprises the following components: C 0.03 - 0.12%, Mn 0.35 - 0.45%, P ≤ 0.015%, S ≤ 0.005%, Si 0.30 - 0.40%, Cr 0.80 - 1.10%, Sb 0.05 - 0.10%, Cu 0.30 - 0.40%, Sn 0.08 - 0.13%, the total sum of inevitable impurity elements ≤ 0.1%, and the balance is Fe. Under the above conditions, the corrosion resistance, crack resistance of the tubing can be further improved, and the cost can be further reduced, thus being more conducive to improving the service life of the coiled tubing of the present invention and enhancing the market competitiveness.

[0035] In order to further improve the synergistic strengthening effect of each component, and thus be more conducive to improving the acid corrosion resistance and electrochemical corrosion resistance of the coiled tubing, in a preferred embodiment, the total weight percentage of Cr, Cu and Sn ≥ 1.3%.

[0036] As described above, on the basis of meeting the mechanical property requirements, the coiled tubing prepared by the present invention has the advantages of good corrosion resistance and good anti-brittle cracking property. Specifically, in a preferred embodiment, the yield strength of the coiled tubing is 522 - 620 MPa, the tensile strength ≥ 601 MPa, the elongation ≥ 20%, and the hardness ≤ 22 HRC. Preferably, the yield strength of the coiled tubing is 551 - 620 MPa, the tensile strength ≥ 607 MPa, the elongation ≥ 22%, and the hardness ≤ 22 HRC. Under the above conditions, the mechanical properties of the coiled tubing of the present invention are better, and the safety during acidizing operations is higher. In a preferred embodiment, the uniform corrosion weight loss rate of the coiled tubing in a hydrochloric acid aqueous solution at 70°C and a mass concentration of 15% < 10 mm / a. Under the above conditions, the coiled tubing of the present invention has better corrosion resistance, anti-brittle cracking property, better comprehensive performance and longer service life.

[0037] In another typical embodiment of the present invention, a method for preparing the above-mentioned coiled tubing for acidizing operations of the present invention is further provided, comprising the following steps: Step S1, according to the component ratio, after mixing each component raw material, smelting, casting and hot rolling are carried out in sequence to obtain a coiled sheet; Step S2, longitudinally shear the coiled sheet to obtain a steel strip; then butt-weld the steel strip and perform a first heat treatment on the butt weld to obtain a butt steel strip; Step S3, perform forming and longitudinal welding on the butt steel strip in sequence, and perform a second heat treatment on the longitudinal weld to obtain a pipe string; Step S4, perform a third heat treatment on the pipe string to obtain the coiled tubing for acidizing operations.

[0038] In the present invention, first, according to the component ratio of the coiled tubing, the raw material components are mixed, and then smelting, casting, and hot rolling are carried out in sequence to obtain a coiled sheet with uniform structure and appropriate thickness. Next, the coiled sheet is longitudinally cut into steel strips of a certain width, the steel strips are butt-welded, butt-welded to the target fixed length, and the butt weld is subjected to the first heat treatment to refine the grains in the weld zone, thereby improving the structure of the butt weld. Then, after the butt-welded steel strips are formed, longitudinal welding is carried out, and the longitudinal weld is subjected to the second heat treatment to make the longitudinal weld, the heat-affected zone, and the coiled tubing base material have uniform structures. Finally, the pipe string is subjected to the third heat treatment. After the whole pipe heat treatment, the residual stress is eliminated, thereby improving the mechanical properties of the whole pipe. The preparation method of the present invention can effectively control the grain size in the weld zone, refine the grains in the weld zone and the base material, and improve the strength of the pipe material. The prepared coiled tubing for acidizing operation has excellent corrosion resistance, uniform structure, and high mechanical strength.

[0039] In a preferred embodiment, in step S1, the smelting includes the first smelting and the second smelting carried out in sequence. The temperature of the first smelting is 1600-1700°C, and the temperature of the second smelting is 1550-1650°C. Under the above conditions, through the refining process of secondary remelting, it is more conducive to removing harmful impurities and adding trace alloy elements, further reducing the content of elements such as P and S, obtaining a metal blank with more uniform composition. At the same time, the crystallization structure of the metal blank can be further improved, thereby obtaining a coiled tubing material with better mechanical properties. In a preferred embodiment, the hot rolling includes the first hot rolling and the second hot rolling carried out in sequence. The temperature of the first hot rolling is 1000-1060°C, and the temperature of the second hot rolling is 840-890°C. Under the above conditions, the two-stage hot rolling is conducive to gradually obtaining a coiled sheet with the target thickness, the structure in the material is more uniform, and the grains are more refined, which is more conducive to improving the mechanical properties of the coiled tubing. Controlling the temperatures of the first hot rolling and the second hot rolling within the above ranges is more conducive to the plastic deformation of the coiled tubing, and further can effectively reduce phenomena such as cracking or edge cracking during the rolling process, and is more conducive to maintaining the uniformity of the material structure.

[0040] In order to facilitate the actual operation of the butt welding and further improve the efficiency and quality of the butt welding, in a preferred embodiment, in step S2, after the end of the steel strip is processed into the first groove, butt welding is carried out. The first groove is of I type, V type or U type. In order to further reduce internal defects such as pores and inclusions in the butt weld and further improve the corrosion resistance of the coiled tubing, in a preferred embodiment, the butt welding adopts one or more of friction stir welding, laser welding protected by inert gas, argon arc welding, and plasma welding protected by inert gas; preferably, the butt welding adopts argon arc welding or plasma welding protected by argon gas. The inert gas used can be of conventional types in the art, such as nitrogen, argon, helium, etc. Under the above conditions, the prepared coiled tubing has better corrosion resistance and higher production efficiency.

[0041] In a preferred embodiment, in step S2, the first heat treatment includes quenching and tempering treatments performed successively. The quenching temperature is 850 - 950 °C, and the time is 5 - 15 min; the tempering temperature is 500 - 550 °C, and the time is 5 - 10 min. Under the above conditions, the grains of the butt weld are finer, the structure is more uniform, the mechanical properties of the weld are better, and further, the mechanical properties of the coiled tubing can be improved.

[0042] For the purpose of making the longitudinal welding forming effect better and the mechanical properties of the longitudinal weld more stable, in a preferred embodiment, in step S3, the longitudinal side of the butt steel strip is processed into a second groove for forming; preferably, the second groove is of type I, and the forming method is UO forming or JCO forming. Under the above conditions, the forming quality of the steel strip is more stable. To further improve the longitudinal welding efficiency, in a preferred embodiment, the longitudinal welding uses one or more of high-frequency induction welding, plasma welding, and laser welding; preferably, the longitudinal welding uses laser welding. To further reduce internal defects such as pores and inclusions in the longitudinal weld, and thus further improve the corrosion resistance of the pipe, in a preferred embodiment, an inert gas with a purity ≥ 99.99% is used as the shielding gas throughout the longitudinal welding process. The inert gas can be of the conventional types in the art, such as nitrogen, argon, helium, etc.

[0043] In a preferred embodiment, in step S3, the temperature of the second heat treatment is 900 - 960 °C, and the time is 5 - 10 min. Under the above conditions, the grains of the longitudinal weld are finer, the structure is more uniform, and the mechanical properties of the obtained coiled tubing are better. In a preferred embodiment, after the second heat treatment of the longitudinal weld, it further includes a step of sizing the pipe string to obtain coiled tubing of a certain specification.

[0044] In a preferred embodiment, in step S4, the temperature of the third heat treatment is 590 - 750 °C, and the time is 5 - 20 min. Under the above conditions, the grains of the entire pipe body are finer, the structure is more uniform, and the mechanical strength of the prepared coiled tubing is better. If the heat treatment temperature is too high, the grains are larger, resulting in a serious decline in the mechanical properties of the material. If the heat treatment temperature is too low, the effect of stress relief is small, and stress concentration during subsequent use will cause material corrosion and cracking.

[0045] Typically but not limited to, in the coiled tubing for acidizing operations, the weight percentage of Cr is 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, 1.07%, 1.08%, 1.10% or a range value composed of any two of these values; the weight percentage of Cu is 0.25%, 0.29%, 0.30%, 0.31%, 0.35%, 0.40%, 0.45% or a range value composed of any two of these values; the weight percentage of Sn is 0.05%, 0.08%, 0.10%, 0.12%, 0.13%, 0.15%, 0.20% or a range value composed of any two of these values.

[0046] Typically but not limited to, in step S1, the temperature of the first smelting is 1600°C, 1620°C, 1640°C, 1660°C, 1680°C, 1700°C or a range value composed of any two of these values; the temperature of the second smelting is 1550°C, 1570°C, 1590°C, 1600°C, 1620°C, 1640°C, 1650°C or a range value composed of any two of these values; the temperature of the first hot rolling is 1000°C, 1020°C, 1040°C, 1060°C or a range value composed of any two of these values; the temperature of the second hot rolling is 840°C, 850°C, 860°C, 880°C, 890°C or a range value composed of any two of these values.

[0047] Typically but not limited to, in step S2, the quenching temperature is 850°C, 870°C, 890°C, 900°C, 910°C, 930°C, 950°C or a range value composed of any two of these values; the quenching time is 5 min, 7 min, 9 min, 10 min, 12 min, 14 min, 15 min or a range value composed of any two of these values; the tempering temperature is 500°C, 520°C, 540°C, 550°C or a range value composed of any two of these values; the tempering time is 5 min, 7 min, 8 min, 9 min, 10 min or a range value composed of any two of these values.

[0048] Typically but not limited to, in step S3, the temperature of the second heat treatment is 900°C, 920°C, 940°C, 960°C or a range value composed of any two of these values; the time of the second heat treatment is 5 min, 7 min, 8 min, 9 min, 10 min or a range value composed of any two of these values.

[0049] Typically but not limited to, in step S4, the temperature of the third heat treatment is 590°C, 600°C, 650°C, 700°C, 750°C, or a range value composed of any two of these values; the time of the third heat treatment is 5 min, 7 min, 8 min, 9 min, 11 min, 13 min, 15 min, 17 min, 19 min, 20 min, or a range value composed of any two of these values.

[0050] The following further describes the present application in detail with specific embodiments, which should not be construed as limiting the scope claimed by the present application.

[0051] Embodiment 1

[0052] The chemical composition of the coiled tubing for acidizing operations is shown in Table 1.

[0053] In step S1, according to the component ratio of the coiled tubing for acidizing operations, each component raw material is mixed, and the first smelting is carried out in a vacuum oxygen blowing decarburization refining furnace at a temperature of 1650°C. Then, the second smelting is carried out in a ladle refining furnace at a temperature of 1650°C. Next, the obtained molten steel is cast into a continuous casting billet, and the billet is cast into a slab with a thickness of 200 mm by using continuous casting technology and applying electromagnetic stirring control, and then controlled cooling is carried out. Secondly, the slab is subjected to the first hot rolling at 1030°C and the second hot rolling at 850°C to obtain a hot rolled sheet with a thickness of 4 mm. The hot rolled sheet is subjected to front-segment concentrated laminar cooling at a cooling rate of 25°C / s, and then coiled at a controlled temperature of 600°C to obtain a coiled sheet with a length exceeding 400 meters.

[0054] In step S2, a slitting machine is used to cut the coiled sheet into steel strips with a width of 112 mm. The ends of the front and rear steel strips are processed into 45° bevels, and an I-shaped groove is opened on the bevel. The bevels of the front and rear steel strips are butt-welded by argon arc welding. After the butt weld cools, the surface of the butt weld is ground and cleaned. After welding, the butt weld is heated to 900°C, held for 10 min, water-cooled, and then subjected to a tempering treatment at 500°C for 8 min.

[0055] In step S3, the side of the butt-welded steel strip is planed into an I-shaped groove by milling, the width of the steel strip and the perpendicularity of the plate edge are accurately controlled, the steel strip is formed by the UO forming method, and under the condition that the protective gas is an inert gas with a purity ≥99.99%, the formed pipe string is longitudinally welded by laser welding technology. The longitudinal weld is heat-treated at 920°C for 8 min, and a certain amount of deformation is applied to the longitudinal weld of the pipe by using a sizing roll in a sizing manner, and then air-cooled. Finally, a pipe string with a longitudinal weld being a straight seam, a pipe diameter of Φ38.1 mm, and a wall thickness of 4.0 mm is welded.

[0056] Step S4: Heat the entire pipe body of the coiled tubing for acidizing operations to 700 °C using medium-frequency induction heating, hold for 8 minutes, then rapidly cool to room temperature, and finally wind it on a reel to form a coiled tubing for acidizing operations in a disk shape with a production length of 4000 m for convenient transportation.

[0057] The SEM photos of the base metal structure of the coiled tubing for acidizing operations are shown in Figure 1 .

[0058] Example 2

[0059] The chemical composition of the coiled tubing for acidizing operations is shown in Table 1.

[0060] Step S1: Mix the raw material components according to the component ratio of the coiled tubing for acidizing operations, conduct the first smelting in a vacuum oxygen decarburization refining furnace at a temperature of 1640 °C, then conduct the second smelting in a ladle refining furnace at a temperature of 1580 °C. Next, pour the obtained molten steel into a continuous casting billet, use continuous casting technology and apply electromagnetic stirring control to cast the billet into a slab with a thickness of 200 mm, and control the cooling. Secondly, conduct the first hot rolling of the slab at 1030 °C and the second hot rolling at 850 °C to obtain a hot rolled sheet with a thickness of 4 mm. Conduct the front-section concentrated laminar cooling of the hot rolled sheet at a cooling rate of 25 °C / s, and then control the temperature to 580 °C for coiling to obtain a coiled sheet with a length exceeding 400 m.

[0061] Step S2: Use a slitting line to cut the coiled sheet into steel strips with a width of 153 mm, process the ends of the front and rear steel strips into 45° bevels, and open a type I groove on the bevel. Use argon arc welding to butt-weld the bevels of the front and rear steel strips. After the butt weld cools, grind and clean the surface of the butt weld. After welding, heat the butt weld to 880 °C, hold for 10 minutes, cool it with water, and then conduct a tempering treatment at 500 °C for 8 minutes.

[0062] Step S3: Use a milling method to plane the side of the butt-welded steel strip into a type I groove, precisely control the width of the steel strip and the perpendicularity of the plate edge, use the UO forming method to form the steel strip, and under the condition that the protective gas is an inert gas with a purity ≥ 99.99%, use laser welding technology to longitudinally weld the formed pipe column, conduct a heat treatment of the longitudinal weld at 920 °C for 8 minutes, and use an extrusion roller to apply a certain amount of deformation to the longitudinal weld of the pipe material by sizing, and then air-cool it. Finally, weld it into a pipe column with a longitudinal weld being a straight seam, a pipe diameter of Φ50.8 mm, and a wall thickness of 4.0 mm.

[0063] Step S4: Heat the entire pipe body of the pipe column to 650 °C using medium-frequency induction heating, hold for 10 minutes, then rapidly cool to room temperature, and finally wind it on a reel to form a coiled tubing for acidizing operations in a disk shape with a production length of 4000 m for convenient transportation.

[0064] Examples 3 to 8

[0065] The difference from Example 1 is only that the components are different, as shown in Table 1.

[0066] Examples 9 to 10

[0067] The difference from Example 1 is only that in step S1, the temperatures of smelting and hot rolling are different, as detailed in Table 2.

[0068] Example 11

[0069] The difference from Example 1 is only that

[0070] the first groove is V-shaped, and friction stir welding is used for butt welding,

[0071] the second groove is I-shaped, and the forming method is JCO forming; high-frequency induction welding is used for longitudinal welding.

[0072] Example 12

[0073] The difference from Example 1 is only that

[0074] the first groove is U-shaped, and laser welding with inert gas protection is used for butt welding,

[0075] the second groove is I-shaped, and the forming method is JCO forming; plasma welding is used for longitudinal welding.

[0076] Examples 13 to 14

[0077] The difference from Example 1 is only that the parameters of the first heat treatment, the second heat treatment, and the third heat treatment are different, as detailed in Table 3.

[0078] Comparative Example 1

[0079] The difference from Example 1 is that it only undergoes the first smelting and does not undergo the second smelting.

[0080] Test the dimensions, mechanical properties, and corrosion resistance of the coiled tubes of the above examples and comparative examples. The dimensions are shown in Table 2, and the test results of the mechanical properties and corrosion resistance are shown in Table 4.

[0081] Test method:

[0082] Yield strength, tensile strength, elongation: Conduct a tensile test according to GB / T 228.1-2021 to obtain the yield strength, tensile strength, and elongation;

[0083] Hardness: Conduct a Vickers hardness test according to GB / T 4340.1-2009;

[0084] Hydrochloric acid corrosion test: A 24-hour full-immersion corrosion test was carried out in an aqueous hydrochloric acid solution at 70°C with a mass concentration of 15%.

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089] Table 3

[0090]

[0091]

[0092] Table 4

[0093]

[0094] As can be seen from the above, compared with the comparative examples, the continuous pipes for acidizing operations in each embodiment of the present invention have higher yield strength, tensile strength, higher hardness, and lower uniform corrosion weight loss rate, indicating better mechanical properties, better hydrochloric acid corrosion resistance and electrochemical corrosion resistance, and better crack resistance. Therefore, it is more conducive to extending the service life of the continuous pipe during the acidizing operation, improving service safety, and meeting the requirements of oilfield acidizing operations. Generally speaking, by using the method provided by the present invention, the corrosion rate of hydrochloric acid and electrochemistry on the continuous pipe during the acidizing operation is slow, the continuous pipe has good crack resistance, long service life, high service safety, and there is no obvious increase in price, wide market demand, and strong competitiveness.

[0095] In addition, it can be seen that when each process parameter is within the preferred range of the present invention, the mechanical properties of the continuous pipe during the acidizing operation are better and the corrosion resistance is better.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coiled tubing for acidizing operations, characterized in that, By weight percentage, its materials include the following components: C ≤ 0.12%, Mn 0.35 - 0.65%, P ≤ 0.035%, S ≤ 0.035%, Si 0.20 - 0.40%, Cr 0.70 - 1.10%, Sb 0.04 - 0.10%, Cu 0.25 - 0.45%, Sn ≤ 0.2%, the total sum of inevitable impurity elements ≤ 0.2%, and the rest is Fe.

2. The coiled tubing for acidizing operation according to claim 1, wherein, By weight percentage, its materials include the following components: C 0.03 - 0.12%, Mn 0.35 - 0.45%, P ≤ 0.015%, S ≤ 0.005%, Si 0.30 - 0.40%, Cr 0.80 - 1.10%, Sb 0.05 - 0.10%, Cu 0.30 - 0.40%, Sn 0.08 - 0.13%, the total sum of inevitable impurity elements ≤ 0.1%, and the rest is Fe.

3. The coiled tubing for acidizing operations according to claim 1 or 2, characterized in that, The total weight percentage of Cr, Cu and Sn ≥ 1.3%.

4. The coiled tubing for acidizing operation according to any one of claims 1 to 3, characterized in that The yield strength of the coiled tubing is 522 - 620 MPa, the tensile strength ≥ 601 MPa, the elongation ≥ 20%, and the hardness ≤ 22 HRC; and / or The uniform corrosion weight loss rate of the coiled tubing in a hydrochloric acid aqueous solution at 70°C with a mass concentration of 15% < 10 mm / a.

5. The preparation method of the coiled tubing for acidizing operation according to any one of claims 1 to 4, characterized in that, It includes the following steps: Step S1, according to the component ratio, after mixing each component raw material, smelting, casting and hot rolling are carried out in sequence to obtain a coiled sheet; Step S2, longitudinally shear the coiled sheet to obtain a steel strip; then butt-weld the steel strip and perform the first heat treatment on the butt weld to obtain a butt steel strip; Step S3, form and longitudinally weld the butt steel strip in sequence and perform the second heat treatment on the longitudinal weld to obtain a pipe string; Step S4, perform the third heat treatment on the pipe string to obtain the coiled tubing for acidizing operation.

6. The preparation method according to claim 5, characterized in that, In the said step S1, The smelting includes the first smelting and the second smelting carried out in sequence, the temperature of the first smelting is 1600 - 1700°C, and the temperature of the second smelting is 1550 - 1650°C; and / or The hot rolling includes the first hot rolling and the second hot rolling carried out in sequence, the temperature of the first hot rolling is 1000 - 1060°C, and the temperature of the second hot rolling is 840 - 890°C.

7. The preparation method according to claim 5 or 6, characterized in that, In the said step S2, After processing the end of the steel strip into a first groove, then carry out the butt-weld, and the first groove is of I type, V type or U type; and / or The butt-weld adopts one or more of friction stir welding, laser welding protected by inert gas, argon arc welding and plasma welding protected by inert gas; preferably, the butt-weld adopts argon arc welding or plasma welding protected by argon gas.

8. The preparation method according to any one of claims 5 to 7, characterized in that, In the said step S2, The first heat treatment includes quenching and tempering treatments carried out in sequence, the temperature of quenching is 850 - 950°C, and the time is 5 - 15 min; the temperature of tempering is 500 - 550°C, and the time is 5 - 10 min.

9. The preparation method according to any one of claims 5 to 8, characterized in that, In the said step S3, The longitudinal side of the docking steel strip is processed into a second bevel for the forming; preferably, the second bevel is of type I, and the forming method is UO forming or JCO forming; and / or The longitudinal welding adopts one or more of high-frequency induction welding, plasma welding and laser welding; preferably, the longitudinal welding adopts laser welding; and / or The temperature of the second heat treatment is 900 - 960 °C, and the time is 5 - 10 min.

10. The preparation method according to any one of claims 5 to 9, characterized in that, In the step S4, the temperature of the third heat treatment is 590 - 750 °C, and the time is 5 - 20 min.

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