Steel, coiled tubing and preparation method and application of coiled tubing

Abstract

The invention relates to the technical field of petroleum and natural gas pipes, and discloses steel, a continuous pipe and a preparation method and application of the continuous pipe. Based on the total weight of the steel, the steel comprises the following elements in percentage by weight: 95.236 to 97.23 percent of Fe, 0.12 to 0.17 percent of C, 0.2 to 0.45 percent of Si, 1.3 to 1.8 percent of Mn, 0.25 to 0.4 percent of Cu, 0.4 to 0.7 percent of Cr, 0.15 to 0.4 percent of Ni, 0.25 to 0.6 percent of Mo, 0.05 to 0.1 percent of V, 0.02 to 0.05 percent of Ti, 0.03 to 0.06 percent of Nb, not higher than 0.01 percent of P, not higher than 0.004 percent of S and not higher than 0.02 percent of rare earth elements. The microscopic structure of the steel comprises ferrite and martensite; based on the total volume of the steel, the volume fraction of martensite in the steel is 8-30% by volume. Based on the steel raw material and an improved preparation process matched with the steel raw material, the ultrahigh-strength CT150-CT170 continuous pipe product can be prepared, and the exploration and development use requirements of deep wells, ultra-deep wells and ultra-long horizontal wells can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum and natural gas pipes, and in particular to a steel material, a continuous pipe, and a preparation method and application thereof. Background Art

[0002] Coiled Tubing is also called flexible tubing, serpentine tubing or coiled tubing. It is a new type of oil pipe with no threaded connection and a single length of several thousand meters made of high-performance metal materials through continuous forming and welding process. The finished product is wound on a reel for transportation and delivery. The end of the coiled tubing can carry different operating tools to be continuously lowered into the oil and gas well and quickly pulled out. It is used in oil and gas field well repair, logging, drilling, completion, oil and gas transportation and other operating fields, and is called "universal pipe".

[0003] Coiled tubing is a key equipment for developing unconventional wells such as deep wells, ultra-deep wells, and shale gas wells. With the in-depth development of domestic deep oil and gas resources and unconventional oil and gas resources such as shale gas, the number and depth of ultra-deep wells and ultra-long horizontal wells above 8,500 meters have increased rapidly. At the same time, the development of 10,000-meter deep wells has been included in the key research projects of oilfield units. The oilfield has put forward higher requirements on the strength, descent depth, compressive resistance and bending fatigue life of coiled tubing.

[0004] CN107419195A discloses a high-strength and high-fatigue-life coiled tubing for deep wells and a manufacturing method thereof. The coiled tubing is a CT130 steel grade coiled tubing with a yield strength of 130 ksi. Under the condition of a load safety factor of 1.25, the theoretical insertion depth of the CT130 steel grade coiled tubing is 9131 meters, which can no longer meet the requirements of the oil field for the insertion depth and coiled tubing performance.

[0005] The metallographic structure of existing continuous tubes is limited to ferrite, pearlite and bainite. It is very difficult to develop higher strength continuous tubes (such as ultra-high strength continuous tubes with steel grades of 150ksi and above) by relying solely on alloying, rolling, cooling, deformation and other strengthening methods. In addition, since the steel strips used for ultra-high strength continuous tubes have high strength, high hardness, high forming resistance, high springback ability during forming, and high hardness of burrs outside the weld, conventional manufacturing processes can no longer meet the requirements for the manufacture of ultra-high strength continuous tubes with steel grades of 150ksi and above.

[0006] Therefore, there is an urgent need to provide a new type of continuous pipe product and related preparation materials and production processes that can meet the development requirements of deep wells, ultra-deep wells and ultra-long horizontal wells. Summary of the invention

[0007] Aiming at the problem that the existing coiled pipes are unable to meet the requirements of exploration, development and use of deep wells, ultra-deep wells and ultra-long horizontal wells in terms of strength, pressure bearing capacity and lowering depth due to the increase in vertical well depth and horizontal well length, the present invention provides a steel material, a coiled pipe and a preparation method and application thereof.

[0008] In order to achieve the above object, the first aspect of the present invention provides a steel material, which comprises, based on the total weight of the steel material, 95.236-97.23 wt% of Fe, 0.12-0.17 wt% of C, 0.2-0.45 wt% of Si, 1.3-1.8 wt% of Mn, 0.25-0.4 wt% of Cu, 0.4-0.7 wt% of Cr, 0.15-0.4 wt% of Ni, 0.25-0.6 wt% of Mo, 0.05-0.1 wt% of V, 0.02-0.05 wt% of Ti, 0.03-0.06 wt% of Nb, not more than 0.01 wt% of P, not more than 0.004 wt% of S and not more than 0.02 wt% of rare earth elements;

[0009] The microstructure of the steel comprises ferrite and martensite; based on the total volume of the steel, the volume fraction of martensite in the steel is 8-30 volume %.

[0010] A second aspect of the present invention provides a method for preparing a coiled tube, comprising:

[0011] (1) longitudinally shearing the coil into strips to obtain a steel strip; then welding and extending the steel strip to obtain an extended steel strip;

[0012] (2) forming, welding and post-processing the extended steel strip to obtain a continuous tube;

[0013] Wherein, the material of the rolled plate is the steel material described in the first aspect above.

[0014] The third aspect of the present invention provides a continuous tube produced by the method described in the second aspect.

[0015] A fourth aspect of the present invention provides use of the coiled tubing described in the third aspect in oil and gas exploration.

[0016] Through the above technical scheme, the steel with specific chemical composition and microstructure provided by the present invention has excellent comprehensive mechanical properties, especially has the advantages of high yield strength, high tensile strength, good elongation and good welding performance. Compared with existing steels, it can better meet the material performance requirements of continuous pipes for deep wells, ultra-deep wells and ultra-long horizontal wells; based on the steel raw material and the improved preparation process matched therewith, the present invention can prepare ultra-high strength CT150-CT170 continuous pipe products with yield strengths of 150ksi, 160ksi and 170ksi respectively, which have excellent performance in strength, pressure bearing capacity and penetration depth, and can meet the use requirements of oil and gas development in 10,000-meter deep wells. DETAILED DESCRIPTION

[0017] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0018] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0019] A first aspect of the present invention provides a steel material, which comprises, based on the total weight of the steel material, 95.236-97.23 wt% of Fe, 0.12-0.17 wt% of C, 0.2-0.45 wt% of Si, 1.3-1.8 wt% of Mn, 0.25-0.4 wt% of Cu, 0.4-0.7 wt% of Cr, 0.15-0.4 wt% of Ni, 0.25-0.6 wt% of Mo, 0.05-0.1 wt% of V, 0.02-0.05 wt% of Ti, 0.03-0.06 wt% of Nb, not more than 0.01 wt% of P, not more than 0.004 wt% of S, and not more than 0.02 wt% of rare earth elements;

[0020] The microstructure of the steel comprises ferrite and martensite; based on the total volume of the steel, the volume fraction of martensite in the steel is 8-30 volume %.

[0021] In the present invention, the elemental composition of the steel can be measured by a direct reading spectrometer, and the microstructure and content can be measured by a metallographic microscope and an image analysis system.

[0022] According to the present invention, preferably, based on the total weight of the steel, the steel comprises, in terms of elements, 95.386-97.021 wt % of Fe, 0.12-0.17 wt % of C, 0.22-0.43 wt % of Si, 1.35-1.78 wt % of Mn, 0.28-0.38 wt % of Cu, 0.43-0.68 wt % of Cr, 0.18-0.37 wt % of Ni, 0.26-0.58 wt % of Mo, 0.05-0.09 wt % of V, 0.02-0.045 wt % of Ti, 0.035-0.055 wt % of Nb, not more than 0.01 wt % of P, not more than 0.003 wt % of S and not more than 0.018 wt % of rare earth elements; and based on the total volume of the steel, the volume fraction of martensite in the steel is 10-30 vol %.

[0023] According to the present invention, preferably, the rare earth elements include La, Ce and Eu.

[0024] According to the present invention, in the steel material, preferably, the weight ratio of La:Ce:Eu is 1:(1.3-2.5):(0.5-1).

[0025] The steel material of the present invention contains, in addition to the above-mentioned elements, also impurity elements which are negligible and have no effect on the properties of the steel material.

[0026] According to the present invention, preferably, the average grain size of the steel is 10.5-13 μm.

[0027] In the present invention, the grain of steel refers to the crystal with uniform arrangement of atoms inside the steel but irregular shape. In the crystallization process, small crystals developed through the generation of crystal nuclei (crystallization centers) and crystal growth have irregular shapes because adjacent crystals collide with each other during growth. The grain size of steel can be measured by the comparison method in GB / T 6394-2002 (Method for Determination of Average Grain Size of Metals).

[0028] In the present invention, the steel contains the above specific element composition and has a specific microstructure and content, which can play a synergistic role, so that the steel has the performance advantages of high yield strength, high tensile strength and good elongation. When the element composition, microstructure and content are not within the above-defined range, the steel that meets the performance parameters of the present invention cannot be obtained.

[0029] According to the present invention, the steel material has a high yield strength. Preferably, the yield strength of the steel material is 850-1080 MPa, and more preferably 890-1050 MPa.

[0030] In the present invention, the yield strength of the steel is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0031] According to the present invention, the tensile strength of the steel is high. Preferably, the tensile strength of the steel is 1080-1260 MPa, and more preferably 1100-1230 MPa.

[0032] In the present invention, the tensile strength of the steel is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0033] According to the present invention, the steel has good elongation. Preferably, the elongation of the steel is ≥ 12%, and more preferably 13-16%.

[0034] In the present invention, the elongation of the steel material is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0035] According to the present invention, the steel has a moderate hardness. Preferably, the hardness of the steel is ≤ 43 HRC, and more preferably 36-41 HRC.

[0036] In the present invention, the Rockwell hardness of the steel is measured by the method specified in GB / T 230.1-2018 (Rockwell hardness test for metallic materials Part 1: Test method).

[0037] The steel provided by the present invention can be obtained by refining at 1500-1680° C. through conventional steelmaking processes. For example, molten iron is used as the main raw material for pre-desulfurization treatment, and then smelting in a top-bottom combined blowing converter, LF heating desulfurization, VD vacuum decarburization, and Ca treatment to obtain molten steel meeting the above element composition (containing 95.236-97.23% by weight of Fe, 0.12-0.17% by weight of C, 0.2-0.45% by weight of Si, 1.3-1.8% by weight of Mn, 0.25-0.4% by weight of Cu, 0.4-0. 7 wt% Cr, 0.15-0.4 wt% Ni, 0.25-0.6 wt% Mo, 0.05-0.1 wt% V, 0.02-0.05 wt% Ti, 0.03-0.06 wt% Nb, not more than 0.01 wt% P, not more than 0.004 wt% S and not more than 0.02 wt% rare earth elements), continuously casting, rolling and cooling molten steel to obtain the steel material.

[0038] In the process of preparing the steel material, the continuous casting may adopt conventional processes and parameters for continuously pouring molten steel, and the present invention has no particular limitation on this.

[0039] In the process of preparing the steel material, before the rolling, the slab obtained by continuous casting of molten steel is heated to 1160-1250° C., which is beneficial to the subsequent rolling deformation.

[0040] In the process of preparing the steel, the rolling includes rough rolling and finish rolling carried out in sequence, and preferably the rolling is carried out by a thermomechanical controlled rolling process (TMCP). Preferably, the starting rolling temperature of the rough rolling is 1160-1250°C, and the final rolling temperature is 980-1060°C; the starting rolling temperature of the finish rolling is 980-1010°C, and the final rolling temperature is 850-900°C.

[0041] In the process of preparing the steel, the rolled slab (steel plate) is cooled to 400-550°C, preferably at a cooling rate of 30-40°C / s, which can make the steel structure more uniform and further refine the grains. Preferably, the cooling adopts front-stage laminar cooling.

[0042] The steel provided by the present invention has high yield strength, high tensile strength, suitable hardness and good elongation. Compared with the existing continuous pipe steel, the organizational design is significantly improved, and the mechanical properties are significantly improved. Its strength and cleanliness can better meet the requirements of deep wells, ultra-deep wells and ultra-long horizontal wells for the depth of pipe insertion, pressure bearing performance and fatigue resistance.

[0043] A second aspect of the present invention provides a method for preparing a coiled tube, comprising:

[0044] (1) longitudinally shearing the coil into strips to obtain a steel strip; then welding and extending the steel strip to obtain an extended steel strip;

[0045] (2) forming, welding and post-processing the extended steel strip to obtain a continuous tube;

[0046] Wherein, the material of the rolled plate is the steel material described in the first aspect above.

[0047] According to the present invention, in step (1), the preparation process of the rolled plate may include: using molten iron as the main raw material for pre-desulfurization treatment, and performing top and bottom combined blowing converter smelting (1500-1680°C), LF heating desulfurization, VD vacuum decarburization, and Ca treatment to obtain molten steel meeting the elemental composition of the steel material described in the first aspect of the present invention (containing 95.236-97.23% by weight of Fe, 0.12-0.17% by weight of C, 0.2-0.45% by weight of Si, 1.3-1.8% by weight of Mn , 0.25-0.4 wt% Cu, 0.4-0.7 wt% Cr, 0.15-0.4 wt% Ni, 0.25-0.6 wt% Mo, 0.05-0.1 wt% V, 0.02-0.05 wt% Ti, 0.03-0.06 wt% Nb, not more than 0.01 wt% P, not more than 0.004 wt% S and not more than 0.02 wt% rare earth elements), continuously casting, rolling, cooling and coiling the molten steel to obtain the coil.

[0048] According to the present invention, the continuous casting may adopt conventional processes and parameters for continuously pouring molten steel, and the present invention has no particular limitation on this.

[0049] According to the present invention, preferably, the thickness of the slab obtained by continuous casting is 100-220 mm, which is beneficial to the control of subsequent rolling heating and rolling deformation.

[0050] According to the present invention, preferably, before the rolling, the slab is heated to 1160-1250° C. to facilitate subsequent rolling deformation.

[0051] According to the present invention, the rolling comprises rough rolling and finish rolling performed sequentially, and preferably the rolling is performed using a thermomechanical controlled rolling process (TMCP).

[0052] In the present invention, preferably, the starting rolling temperature of the rough rolling is 1160-1250°C, and the finishing rolling temperature is 980-1060°C.

[0053] Preferably, the thickness of the slab after rough rolling is controlled to be 40-65 mm.

[0054] In the present invention, preferably, the start rolling temperature of the finish rolling is 980-1010°C, and the final rolling temperature is 850-900°C.

[0055] Preferably, the thickness of the slab after finish rolling is controlled to be 3-8 mm.

[0056] According to the present invention, the rolled slab (steel plate) is cooled to 400-550°C, preferably at a cooling rate of 30-40°C / s, which can make the steel structure more uniform and further refine the grains. Preferably, the cooling is performed by front-stage laminar cooling.

[0057] According to the present invention, preferably, the coiling temperature is 400-550°C.

[0058] According to the present invention, after the rolled steel plate is coiled, it is placed in an insulation pit for slow cooling to reduce the performance fluctuation caused by the different cooling rates between the inner ring and the outer ring, thereby obtaining the coiled plate.

[0059] According to the present invention, the thickness of the rolled plate is 3-8 mm.

[0060] According to the present invention, in the above step (1), the surface of the coil is sandblasted before the longitudinal shearing and stripping, so that the surface of the coil is smooth and free of oxide scale residue. The raw steel used in the present invention has a high content of elements such as C, Si, Ni, and Cu, which will promote the formation of iron oxide scale, resulting in thicker iron oxide scale on the surface of the steel plate after rolling. In this case, if the conventional pickling process is used to remove the surface oxide scale of the coil, the pickling efficiency and the surface quality of the coil after pickling are difficult to guarantee. The residual oxide scale is easy to cause weld inclusions in the subsequent welding process, resulting in welding defects. At the same time, since the raw steel used in the present invention is of ultra-high strength grade and is sensitive to hydrogen-induced cracking, pickling will increase the risk of hydrogen-induced cracking of the subsequent pipe. The surface sandblasting can not only remove the oxide scale on the surface of the coil with high quality, but also generate compressive stress on the surface of the coil, which is beneficial to prevent the initiation of fatigue cracks on the surface of the prepared continuous pipe and improve the bending fatigue life of the continuous pipe.

[0061] According to the present invention, the surface sandblasting treatment preferably adopts a water-washing sandblasting process, including unwinding, straightening and leveling, primary water washing, sandblasting, secondary water washing, drying, electrostatic oiling and winding in sequence. The present invention has no particular limitation on the process parameters used in the implementation of the water-washing sandblasting, as long as the surface oxide scale of the coil can be fully removed. Preferably, the surface sandblasting treatment makes the surface roughness (Ra) of the coil be 3.6-4.4μm.

[0062] According to the present invention, in the above step (1), conventional equipment and processes can be used for the longitudinal slitting, and the present invention has no particular limitation thereto. Preferably, the longitudinal slitting is used to shear and split the coil into multiple steel strips with a width of 130-440 mm.

[0063] According to the present invention, in the above step (1), the steel strip is connected to the target length (i.e., the length of the continuous pipe) by the welding connection to obtain a lengthened steel strip. Preferably, the welding connection adopts the method of oblique welding butt joint, the ends of the two front and rear steel strips to be welded are beveled at 40°-50°, the beveled end faces are processed into U-shaped grooves and assembled and spliced.

[0064] According to the present invention, in the above step (1), the welding extension preferably adopts the welding method of "plasma wire welding for base + argon arc welding for cover", and the welding is carried out under a protective atmosphere. The present invention has no special restrictions on the process parameters used in the implementation of the welding extension, as long as the strength of the butt weld can be as strong or super strong as that of the parent material. In addition, it is required to ensure that the front and back welds of the butt weld are full during the welding process, leaving enough deformation for the subsequent weld processing steps.

[0065] According to the present invention, the above step (1) further includes performing a thermal deformation treatment on the extended weld obtained after the welding extension to optimize the weld structure and refine the weld grain. The thermal deformation treatment includes: heating the extended weld to 860-980°C, keeping the temperature for 10-30s, and then forging the extended weld at a pressure of 8-20MPa.

[0066] According to a preferred embodiment of the present invention, the extended weld is preferably subjected to two consecutive thermal deformation treatments, the process comprising: heating the extended weld to 860-980°C, keeping it warm for 10-30s, then forging the weld excess height with a pressure of 8-20MPa, and spray cooling it to room temperature; then heating the extended weld again to 860-980°C, keeping it warm for 10-30s, then forging the weld excess height with a pressure of 8-20MPa. After the above-mentioned thermal deformation treatment is completed, the weld is wrapped with asbestos for insulation to achieve slow cooling of the weld, so as to improve the joint toughness of the extended steel strip. After the weld is cooled to below 150°C, the insulation asbestos is removed, and the weld area is ground and non-destructively tested.

[0067] According to the present invention, in the above step (2), the extended steel strip is milled and heated in sequence before forming.

[0068] In the present invention, the burrs on the side of the steel strip produced by longitudinal shearing are removed by edge milling, the width of the extended steel strip is accurately controlled, and the side of the extended steel strip is processed into an I-shaped groove.

[0069] In the present invention, since the raw steel material used is of ultra-high strength grade, the steel strip and the extended steel strip formed thereby have ultra-high strength and correspondingly high hardness, which makes continuous high-stability forming difficult and causes great wear on the forming rollers during forming. In order to extend the service life of the forming rollers and ensure the high precision of continuous high-stability forming, the extended steel strip is heated before forming, which is beneficial to reduce the wear of the forming rollers, and the designed heating temperature will not affect the structure and performance of the steel strip. Preferably, the extended steel strip is heated by induction heating, and the heating temperature is 160-200°C.

[0070] According to the present invention, in the above step (2), the forming can adopt a conventional forming method in the art, for example, a composite forming method of row roller forming + roller type forming, wherein the front section adopts row roller forming and the rear section adopts roller type forming. According to a preferred embodiment of the present invention, on the basis of the existing composite forming method of row roller forming + roller type forming, a set of edge pressing rollers is added before the forming rollers of the fine forming, which can improve the stability of the continuous forming, and at the same time, two sets of sizing rollers are added when the extended steel strip after subsequent forming is completed for welding. Since the steel strip and the extended steel strip used in the present invention have ultra-high strength, high forming resistance, and high rebound ability during forming, the added two sets of sizing rollers can prevent the rebound of the extended steel strip after forming, as well as weld cracking or poor welding caused by rebound.

[0071] According to the present invention, in the above step (2), the formed extended steel strip is welded to obtain a pipe body. According to a preferred embodiment of the present invention, high-frequency induction welding is used for the welding, and the skin effect and proximity effect of the high-frequency current are utilized to make the current highly concentrated on the side to be welded, and the pipe body is obtained by extrusion welding under the action of the extrusion roller. Preferably, the conditions of the high-frequency induction welding include: a power supply frequency of 300-450kHz, an input power of 150-300kW, a welding pressure of 100-300MPa, a welding temperature of 1130-1350℃, an extrusion amount of the weld of 1.5-3.5mm, an opening angle θ of 4°-12°, and a welding speed of 3-26m / min. During the implementation process, the welding parameters can be adjusted according to the diameter and wall thickness of the continuous pipe to be prepared and the strength of the raw steel strip.

[0072] According to the present invention, in the above step (2), the welding is performed under a protective atmosphere, such as nitrogen, argon, etc.

[0073] According to the present invention, in the above step (2), since the steel strip and the extended steel strip used in the present invention have ultra-high strength and correspondingly high hardness, the burr formed by the welding slag extruded from the weld is also of high hardness, which causes serious wear on the scraper, resulting in a decrease in scraping accuracy of the scraper. Conventional use of one scraper cannot meet the burr removal requirements in the continuous pipe preparation method of the present invention. For this reason, the present invention uses a plurality of scrapers to work in turn. According to a preferred embodiment of the present invention, three scrapers are installed simultaneously in the burr removal device, and the first scraper is used to scrape the burrs first. When the burrs cause serious wear on the scraper, resulting in a decrease in scraping accuracy, the second scraper is activated, and the second scraper and the burr scraping position are quickly adjusted. When the second scraper scrapes the burrs to the best state of being flush with the outer surface of the pipe body, the first scraper is raised away from the burrs, and the second scraper takes over the first scraper to remove the burrs. Remove the old scraper at the position of the first scraper and install a new scraper for standby use. If the scraping accuracy of the second scraper is insufficient, use the first scraper to take over the burr removal. The first scraper and the second scraper work alternately to complete the burr removal of all welds. The third scraper is used as a backup. In case of emergencies and the blade cannot be replaced in time, the third scraper is put into scraping work. Through the above method, the continuity and high quality of the burr removal of the 10,000-meter continuous pipe weld can be achieved. After the burrs are removed, the outer surface of the weld maintains a smooth transition with the mother body of the pipe body.

[0074] According to the present invention, in the above step (2), the post-treatment includes sequentially performing heat treatment of the weld and heat treatment of the pipe body.

[0075] In the present invention, the weld heat treatment includes: heating the formed weld obtained after forming and welding to 880-960°C, forging the formed weld with a pressure of 8-20MPa, then air cooling to 150-350°C, and finally water cooling to room temperature. By performing weld heat treatment on the weld of the pipe body welded after forming, the weld structure can be refined, the weld hardness can be reduced, and the weld performance can be improved.

[0076] Preferably, in the weld heat treatment, the forging uses an extrusion shape-retaining roller made of copper alloy.

[0077] In the present invention, the heat treatment of the tube body includes: heating the tube body obtained after forming and welding to 500-720°C as a whole, then cooling it to 250-350°C at a cooling rate of 10-20°C / s, and finally cooling it to room temperature with water. By heat treating the tube body welded after forming, it is possible to control the tube body structure, decompose the martensite structure, and control the structure to be mainly "ferrite + tempered troostite", thereby improving the toughness of the tube body and reducing the residual stress of the weld and the tube body during the preparation process.

[0078] In the present invention, room temperature refers to 10-30°C.

[0079] According to the present invention, after the coiled tube is prepared, it is coiled and pressure tested. Specifically, an anticorrosive agent is applied to the surface of the prepared coiled tube, the coiled tube is wound on a drum using a continuous coiler, and cut after reaching the target length. The entire coiled tube is subjected to a hydrostatic pressure test, and an ultra-high strength coiled tube of the required length is obtained after the pressure test is qualified.

[0080] The third aspect of the present invention provides a continuous tube produced by the method described in the second aspect.

[0081] According to the present invention, the coiled tube has the characteristic of high yield strength. The yield strength of the coiled tube is 1034-1240 MPa, and three levels of ultra-high strength coiled tube products of 150 ksi, 160 ksi and 170 ksi can be provided.

[0082] In the present invention, the yield strength of the coiled tube is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0083] According to the present invention, the tensile strength of the coiled tube is high, and the tensile strength of the coiled tube is 1068-1275 MPa.

[0084] In the present invention, the tensile strength of the coiled tube is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0085] According to the present invention, the continuous tube has good elongation, and the elongation of the continuous tube is ≥13%, preferably 15-20%.

[0086] In the present invention, the elongation of the coiled tube is measured by the method specified in GB / T 228.1-2021 (Tensile test of metallic materials Part 1: Room temperature test method).

[0087] According to the present invention, the coiled tube has a moderate hardness, which is ≤43HRC, and more preferably 33-41HRC.

[0088] In the present invention, the hardness of the coiled tube is measured by the method specified in GB / T 230.1-2018 (Rockwell hardness test for metallic materials Part 1: Test method).

[0089] The coiled pipe provided by the present invention has high yield strength, excellent resistance to internal and external pressure, and high fatigue life, and can well meet the exploration and development requirements of deep wells, ultra-deep wells, and ultra-long horizontal wells. Preferably, according to different use requirements, the outer diameter of the coiled pipe can be 44.5-139.7 mm, the wall thickness can be 3-8 mm, and the length can be 100-12000 m.

[0090] The fourth aspect of the present invention provides the application of the coiled tubing described in the third aspect in oil and gas exploration, especially in the completion (perforating, fracturing, drilling and grinding, switching sleeves), logging and well repair operations of deep wells, ultra-deep wells and ultra-long horizontal wells.

[0091] The present invention will be described in detail below by way of examples. In the following examples and comparative examples, unless otherwise specified, all materials used are common commercially available products.

[0092] Example 1

[0093] (1-1) Using molten iron as the main raw material for pre-desulfurization treatment, after top and bottom combined blowing converter smelting (1560-1600°C), LF heating desulfurization, VD vacuum decarburization, Ca treatment and other conventional steps, the composition and content of the obtained molten steel meet the composition of steel S1 in Table 1, and the steel can be tapped, and the molten steel is poured into a continuous casting billet to obtain a slab with a thickness of 120 mm;

[0094] (1-2) heating the slab to 1220°C, rolling the slab using a roll mill through a thermomechanical controlled rolling process, firstly performing rough rolling (start rolling temperature of 1200°C, final rolling temperature of 1050°C), the thickness of the slab after rough rolling is 51 mm, then performing finish rolling (start rolling temperature of finish rolling is 1000°C, final rolling temperature is 890°C), the thickness of the slab after finish rolling is 4.8 mm;

[0095] (1-3) The steel plate obtained after rolling was subjected to front-stage laminar cooling at a cooling rate of 36°C / s and a coiling temperature of 475°C. After the steel plate was coiled, it was placed in a holding pit for slow cooling to obtain a coil (thickness of 4.8 mm) having a "ferrite + martensite" dual-phase structure; the steel material of the coil was denoted as S1, and the composition and content of S1 in terms of elements are shown in Table 1;

[0096] The average grain size of S1 is 13 μm, and the microstructure is ferrite and martensite. The volume fraction of martensite in S1 is 30 volume % based on the total volume of S1.

[0097] S1 has a yield strength of 1045MPa, a tensile strength of 1230MPa, an elongation of 13%, and a hardness of 37HRC;

[0098] (2-1) The coil is unrolled, straightened, leveled, washed once, sandblasted, washed twice, dried, electrostatically oiled, and rolled up in sequence. After the surface sandblasting treatment, the surface roughness (Ra) of the coil is 4.1 μm;

[0099] (2-2) The above-mentioned coiled plate after sandblasting is cut into multiple steel strips with a width of 157 mm by a slitting machine according to the specification requirements of Φ50.8×4.8 mm continuous pipe;

[0100] (2-3) The above steel strips are connected into extended steel strips by the method of oblique welding, the ends of the front and rear steel strips to be welded are beveled at 45 degrees, the beveled end faces are processed into U-shaped grooves and assembled and spliced; the welding method of "plasma wire welding for base laying + argon arc welding for cover laying" is adopted, and the front and back weld seams of the butt weld are ensured to be full during the welding process;

[0101] The weld is quickly heated to 960°C, kept warm for 15 seconds, and then forged with a pressure of 16MPa, and spray-cooled to room temperature; the weld is then heated again to 900°C, kept warm for 15 seconds, and then forged with a pressure of 16MPa; the weld is then wrapped with asbestos for insulation, and after the weld cools to below 150°C, the insulation asbestos is removed, and the weld area is ground and non-destructively tested;

[0102] (3-1) milling the edge of the extended steel strip, and processing the side of the extended steel strip into an I-shaped groove; rapidly induction heating the extended steel strip after the edge milling to 190° C., and adopting a composite forming method of row roller forming + roller forming, wherein the front section adopts row roller forming and the rear section adopts roller forming, so as to achieve continuous and highly stable forming of the extended steel strip;

[0103] (3-2) High-frequency induction welding is used to weld the formed extended steel strip; during the welding process, continuous nitrogen is applied to the welding surface for gas protection, the power supply frequency is controlled to be 400kHz, the input power is 250kW, the welding pressure is 160MPa, the welding temperature is 1280℃, the extrusion amount of the weld is 2.3mm, the opening angle θ is controlled at 5°, and the welding speed is 24m / min; at the same time, a burr removal device (three scrapers are installed, two are open and one is spare) is used to scrape and remove the weld burrs, and a straight seam pipe body with an outer diameter of Φ50.8mm and a wall thickness of 4.8mm is obtained by welding;

[0104] The weld seam was heated to 960°C by high-frequency induction heating, and two sets of aluminum-copper alloy extrusion and shape-keeping rollers were used to forge the weld seam at an extrusion pressure of 12 MPa, and then air-cooled to 280°C and finally water-cooled to room temperature.

[0105] The tube body was rapidly heated to 580°C by medium frequency induction heating, then cooled to 320°C at a cooling rate of 14°C / s, and finally water-cooled to room temperature to adjust the microstructure to a microstructure dominated by "ferrite + tempered troostite" to obtain a continuous tube (denoted as T1).

[0106] The surface of the cooled coiled tube T1 is coated with an anticorrosive agent, and the coiled tube T1 is wound on a drum using a continuous coiler and cut after reaching the target length; a 177.0MPa hydrostatic pressure test is performed on the entire coiled tube T1, and the pressure drop after maintaining the pressure for 15 minutes is less than 1.4MPa, indicating that the pressure test is qualified, and a CT170 (Φ50.8×4.8mm) coiled tube is obtained.

[0107] The main performance indicators of the obtained CT170 (Φ50.8×4.8mm) continuous tube T1 are shown in Table 2.

[0108] Example 2

[0109] (1-1) Using molten iron as the main raw material for pre-desulfurization treatment, after top and bottom combined blowing converter smelting (1560-1600°C), LF heating desulfurization, VD vacuum decarburization, Ca treatment and other conventional steps, the composition and content of the obtained molten steel meet the composition of steel S2 in Table 1, and the steel can be tapped, and the molten steel is poured into a continuous casting billet to obtain a slab with a thickness of 120 mm;

[0110] (1-2) heating the slab to 1220°C, rolling the slab using a roll mill through a thermomechanical controlled rolling process, firstly performing rough rolling (start rolling temperature of 1200°C, final rolling temperature of 1050°C), the thickness of the slab after rough rolling is 51 mm, then performing finish rolling (start rolling temperature of finish rolling is 1000°C, final rolling temperature is 890°C), the thickness of the slab after finish rolling is 4.8 mm;

[0111] (1-3) The steel plate obtained after rolling was subjected to front-stage laminar cooling at a cooling rate of 36°C / s and a coiling temperature of 490°C. After the steel plate was coiled, it was placed in a heat preservation pit for slow cooling to obtain a coil (thickness of 4.8 mm) having a "ferrite + martensite" dual-phase structure; the steel material of the coil was denoted as S2, and the composition and content of S2 in terms of elements are shown in Table 1;

[0112] The average grain size of S2 is 12.5 μm, and the microstructure is ferrite and martensite. Based on the total volume of S2, the volume fraction of martensite in S2 is 28 volume %;

[0113] S2 has a yield strength of 985MPa, a tensile strength of 1160MPa, an elongation of 14%, and a hardness of 36HRC;

[0114] (2-1) The coil is unrolled, straightened, leveled, washed once, sandblasted, washed twice, dried, electrostatically oiled, and rolled up in sequence. After the surface sandblasting treatment, the surface roughness (Ra) of the coil is 4.0 μm;

[0115] (2-2) The above-mentioned coiled plate after sandblasting is cut into multiple steel strips with a width of 157 mm by a slitting machine according to the specification requirements of Φ50.8×4.8 mm continuous pipe;

[0116] (2-3) The above steel strips are connected into extended steel strips by the method of oblique welding, the ends of the front and rear steel strips to be welded are beveled at 45 degrees, the beveled end faces are processed into U-shaped grooves and assembled and spliced; the welding method of "plasma wire welding for base laying + argon arc welding for cover laying" is adopted, and the front and back weld seams of the butt weld are ensured to be full during the welding process;

[0117] The weld is quickly heated to 950°C, kept at this temperature for 15 seconds, and then the weld excess height is forged with a pressure of 15MPa, and then spray-cooled to room temperature; the weld is then reheated to 890°C, kept at this temperature for 15 seconds, and then the weld excess height is forged with a pressure of 15MPa; the weld is then wrapped with asbestos for insulation, and after the weld cools to below 150°C, the insulation asbestos is removed, and the weld area is ground and non-destructively tested;

[0118] (3-1) milling the edge of the extended steel strip and processing the side of the extended steel strip into an I-shaped groove; rapidly induction heating the extended steel strip after the edge milling to 170° C. and adopting a composite forming method of row roller forming + roller forming, wherein the front section adopts row roller forming and the rear section adopts roller forming, so as to achieve continuous and highly stable forming of the extended steel strip;

[0119] (3-2) High-frequency induction welding is used to weld the formed extended steel strip; during the welding process, continuous nitrogen is applied to the welding surface for gas protection, the power supply frequency is controlled to be 380kHz, the input power is 230kW, the welding pressure is 140MPa, the welding temperature is 1260℃, the extrusion amount of the weld is 2.3mm, the opening angle θ is controlled at 6°, and the welding speed is 24m / min; at the same time, a burr removal device (three scrapers are installed, two are open and one is spare) is used to scrape and remove the weld burrs, and a straight seam pipe body with an outer diameter of Φ50.8mm and a wall thickness of 4.8mm is obtained by welding;

[0120] The weld seam was heated to 950°C by high-frequency induction heating, and two sets of aluminum-copper alloy extrusion and shape-keeping rollers were used to forge the weld seam at an extrusion pressure of 12 MPa, and then air-cooled to 270°C and finally water-cooled to room temperature.

[0121] The tube body was rapidly heated to 610°C by medium frequency induction heating, then cooled to 340°C at a cooling rate of 16°C / s, and finally water-cooled to room temperature. The microstructure was adjusted to a microstructure mainly composed of "ferrite + tempered troostite" to obtain a continuous tube (denoted as T2).

[0122] The surface of the cooled coiled tube T2 is coated with an anticorrosive agent, and the coiled tube T2 is wound on a drum using a continuous coiler and cut after reaching the target length; a 166.8MPa hydrostatic pressure test is performed on the entire coiled tube T2, and the pressure drop after maintaining the pressure for 15 minutes is less than 1.4MPa, indicating that the pressure test is qualified, and a CT160 (Φ50.8×4.8mm) coiled tube is obtained.

[0123] The main performance indicators of the obtained CT160 (Φ50.8×4.8mm) continuous tube T2 are shown in Table 3.

[0124] Example 3

[0125] (1-1) Using molten iron as the main raw material for pre-desulfurization treatment, after top and bottom combined blowing converter smelting (1560-1600°C), LF heating desulfurization, VD vacuum decarburization, Ca treatment and other conventional steps, the composition and content of the obtained molten steel meet the composition of steel S3 in Table 1, and the steel can be tapped, and the molten steel is poured into a continuous casting billet to obtain a slab with a thickness of 130 mm;

[0126] (1-2) heating the slab to 1200° C. and rolling the slab using a roll mill through a thermomechanical controlled rolling process, firstly performing rough rolling (start rolling temperature of 1200° C., final rolling temperature of 1050° C.), the thickness of the slab after rough rolling is 54 mm, then performing finish rolling (start rolling temperature of finish rolling is 990° C., final rolling temperature is 880° C.), the thickness of the slab after finish rolling is 5.2 mm;

[0127] (1-3) The steel plate obtained after rolling was subjected to front-stage laminar cooling at a cooling rate of 38°C / s and a coiling temperature of 510°C. After the steel plate was coiled, it was placed in a holding pit for slow cooling to obtain a coil (thickness of 5.2 mm) having a "ferrite + martensite" dual-phase structure; the steel material of the coil was denoted as S3, and the composition and content of S3 in terms of elements are shown in Table 1;

[0128] The average grain size of S3 is 12 μm, and the microstructure is ferrite and martensite. The volume fraction of martensite in S3 is 25 volume % based on the total volume of S3.

[0129] S3 has a yield strength of 890MPa, a tensile strength of 1100MPa, an elongation of 15%, and a hardness of 35HRC;

[0130] (2-1) The coil is unrolled, straightened, leveled, washed once, sandblasted, washed twice, dried, electrostatically oiled, and rolled up in sequence. After the surface sandblasting treatment, the surface roughness (Ra) of the coil is 3.9 μm;

[0131] (2-2) The above-mentioned surface-sandblasted coil is cut into multiple steel strips with a width of 186 mm by a slitting machine according to the specification requirements of Φ60.3×5.2 mm continuous pipe;

[0132] (2-3) The above steel strips are connected into extended steel strips by the method of oblique welding, the ends of the front and rear steel strips to be welded are beveled at 45 degrees, the beveled end faces are processed into U-shaped grooves and assembled and spliced; the welding method of "plasma wire welding for base laying + argon arc welding for cover laying" is adopted, and the front and back weld seams of the butt weld are ensured to be full during the welding process;

[0133] The weld is quickly heated to 940°C, kept warm for 15 seconds, and then the weld excess height is forged with a pressure of 14MPa, and then spray-cooled to room temperature; the weld is then reheated to 880°C, kept warm for 15 seconds, and then the weld excess height is forged with a pressure of 14MPa; the weld is then wrapped with asbestos for insulation, and after the weld temperature cools to below 150°C, the insulation asbestos is removed, and the weld area is ground and non-destructively tested;

[0134] (3-1) milling the edge of the extended steel strip, and processing the side of the extended steel strip into an I-shaped groove; rapidly induction heating the extended steel strip after the edge milling to 160° C., and adopting a composite forming method of row roller forming + roller forming, wherein the front section adopts row roller forming and the rear section adopts roller forming, so as to achieve continuous and highly stable forming of the extended steel strip;

[0135] (3-2) High-frequency induction welding is used to weld the formed extended steel strip; during the welding process, continuous nitrogen is applied to the welding surface for gas protection, the power supply frequency is controlled to be 360KHz, the input power is 200kW, the welding pressure is 130MPa, the welding temperature is 1240℃, the extrusion amount of the weld is 2.3mm, the opening angle θ is controlled at 8°, and the welding speed is 23m / min; at the same time, a burr removal device (three scrapers are installed, two are open and one is spare) is used to scrape and remove the weld burrs, and a straight seam pipe body with an outer diameter of Φ60.3mm and a wall thickness of 5.2mm is obtained by welding;

[0136] The weld seam was heated to 940°C by high-frequency induction heating, and two sets of aluminum-copper alloy extrusion and shape-keeping rollers were used to forge the weld seam at an extrusion pressure of 11 MPa, followed by air cooling to 270°C and finally water cooling to room temperature.

[0137] The tube body was rapidly heated to 630°C by medium frequency induction heating, then cooled to 340°C at a cooling rate of 16°C / s, and finally water-cooled to room temperature. The microstructure was adjusted to a microstructure dominated by "ferrite + tempered troostite" to obtain a continuous tube (denoted as T3).

[0138] The surface of the cooled coiled tube T3 is coated with an anticorrosive agent, and the coiled tube T3 is wound on a drum using a continuous coiler and cut after reaching the target length; a 142.7MPa hydrostatic pressure test is performed on the entire coiled tube T3, and the pressure drop after maintaining the pressure for 15 minutes is less than 1.4MPa, indicating that the pressure test is qualified, and a CT150 (Φ60.3×5.2mm) coiled tube is obtained.

[0139] The main performance indicators of the obtained CT150 (Φ60.3×5.2mm) continuous tube T3 are shown in Table 4.

[0140] Comparative Example 1

[0141] (1-1) Using molten iron as the main raw material for pre-desulfurization treatment, after top and bottom combined blowing converter smelting (1560-1600°C), LF heating desulfurization, VD vacuum decarburization, Ca treatment and other conventional steps, the composition and content of the obtained molten steel meet the composition of steel D1 in Table 1, and the steel can be tapped, and the molten steel is poured into a continuous casting billet to obtain a slab with a thickness of 120 mm;

[0142] (1-2) heating the slab to 1220°C, rolling the slab using a roll mill through a thermomechanical controlled rolling process, firstly performing rough rolling (start rolling temperature of 1200°C, final rolling temperature of 1050°C), the thickness of the slab after rough rolling is 51 mm, then performing finish rolling (start rolling temperature of finish rolling is 990°C, final rolling temperature is 880°C), the thickness of the slab after finish rolling is 5.2 mm;

[0143] (1-3) The steel plate obtained after rolling is subjected to front-stage laminar cooling at a cooling rate of 36°C / s and a coiling temperature of 475°C. After the steel plate is coiled, it is placed in a heat preservation pit for slow cooling to obtain a coil (thickness of 5.2 mm) having a "ferrite + martensite" dual-phase structure; the steel material of the coil is denoted as D1, and the composition and content of D1 in terms of elements are shown in Table 1;

[0144] The average grain size of D1 is 12 μm, and the microstructure is ferrite and martensite. The volume fraction of martensite in D1 is 25 volume % based on the total volume of D1.

[0145] D1 has a yield strength of 925MPa, a tensile strength of 1060MPa, an elongation of 15%, and a hardness of 35HRC;

[0146] Using the coil obtained in the above step (1-3), a continuous tube was prepared according to the method and parameters of steps (2-1) to (3-2) in Example 1 to obtain a continuous tube (denoted as DT1).

[0147] The surface of the cooled coiled tube DT1 was coated with an anticorrosive agent, and the coiled tube T3 was wound on a drum using a continuous coiler and cut off after reaching the target length. The whole coiled tube DT1 was subjected to a hydrostatic pressure test. When the pressure was increased to 101.2MPa, the tube cracked and failed at the weld position, which did not meet the design requirement of 142.7MPa. The hydrostatic test failed. The main performance indicators of the obtained Φ60.3×5.2mm coiled tube DT1 are shown in Table 4.

[0148] Comparative Example 2

[0149] (1-1) Using molten iron as the main raw material for pre-desulfurization treatment, after top and bottom combined blowing converter smelting (1560-1600°C), LF heating desulfurization, VD vacuum decarburization, Ca treatment and other conventional steps, the composition and content of the obtained molten steel meet the composition of steel D2 in Table 1, and the steel can be tapped, and the molten steel is poured into a continuous casting billet to obtain a slab with a thickness of 120 mm;

[0150] (1-2) heating the slab to 1220°C, rolling the slab using a roll mill through a thermomechanical controlled rolling process, firstly performing rough rolling (start rolling temperature of 1200°C, final rolling temperature of 1050°C), the thickness of the slab after rough rolling is 51 mm, then performing finish rolling (start rolling temperature of finish rolling is 990°C, final rolling temperature is 880°C), the thickness of the slab after finish rolling is 5.2 mm;

[0151] (1-3) The steel plate obtained after rolling is water-cooled to 520° C. and coiled to obtain a coil (5.2 mm thick) having a dual-phase structure of “ferrite + bainite”; the steel material of the coil is denoted as D2, and the composition and content of D2 in terms of elements are shown in Table 1;

[0152] The average grain size of D2 is 12 μm, and the microstructure is ferrite and bainite;

[0153] The yield strength of D2 is 1040MPa, the tensile strength is 1065MPa, the elongation is 13.5%, and the hardness is 35.5HRC;

[0154] Using the coil obtained in the above step (1-3), a continuous tube was prepared according to the method and parameters of steps (2-1) to (3-2) in Example 1 to obtain a continuous tube (denoted as DT2).

[0155] The surface of the cooled coiled tube DT2 is coated with an anticorrosive agent, and the coiled tube T3 is wound on a drum using a continuous coiler and cut after reaching the target length. The whole coiled tube DT2 is subjected to a 142.7MPa hydrostatic test, and the pressure drop after 15 minutes of pressure maintenance is less than 1.4MPa, indicating that the pressure test is qualified. The main performance indicators of the obtained Φ60.3×5.2mm coiled tube DT2 are shown in Table 4.

[0156] Table 1

[0157]

[0158] Table 2

[0159]

[0160] Note: The qualified condition of the water pressure test of CT170 is: the pressure drop of 177MPa for 15min is less than 1.4MPa;

[0161] The depth of the well is the theoretical depth with a safety factor of 1.25.

[0162] Table 3

[0163]

[0164] Note: The qualified condition of the water pressure test of CT160: the pressure drop is less than 1.4MPa when the pressure is maintained at 166.8MPa for 15min;

[0165] The depth of the well is the theoretical depth with a safety factor of 1.25.

[0166] Table 4

[0167]

[0168] Note: The qualified condition of the water pressure test of CT150: the pressure drop is less than 1.4MPa when the pressure is maintained at 142.7MPa for 15min;

[0169] The depth of the well is the theoretical depth with a safety factor of 1.25.

[0170] It can be seen from the steel performance data obtained in the above embodiments and comparative examples and Tables 1 to 4 that the steel provided by the present invention has high yield strength, high tensile strength and high elongation. Based on the steel provided by the present invention, ultra-high strength CT150, CT160 and CT170 continuous pipe products with yield strengths of 150ksi, 160ksi and 170ksi can be prepared, which have the characteristics of high strength and excellent resistance to internal and external pressures, and can meet the use requirements of 10,000-meter deep well oil and gas development. In contrast, the expansion, flattening and water pressure tests of the continuous pipe product DT1 made from the steel prepared in Comparative Example 1 were all unqualified, and the mechanical properties of the continuous pipe product DT2 made from the steel prepared in Comparative Example 2 could not meet the requirements of CT150 grade products.

[0171] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A steel material, characterized in that: The steel comprises, in terms of elements, 95.236-97.23 wt % of Fe, 0.12-0.17 wt % of C, 0.2-0.45 wt % of Si, 1.3-1.8 wt % of Mn, 0.25-0.4 wt % of Cu, 0.4-0.7 wt % of Cr, 0.15-0.4 wt % of Ni, 0.25-0.6 wt % of Mo, 0.05-0.1 wt % of V, 0.02-0.05 wt % of Ti, 0.03-0.06 wt % of Nb, not more than 0.01 wt % of P, not more than 0.004 wt % of S, and not more than 0.02 wt % of rare earth elements, based on the total weight of the steel; The microstructure of the steel comprises ferrite and martensite; based on the total volume of the steel, the volume fraction of martensite in the steel is 8-30 volume %.

2. The steel material according to claim 1, wherein: The steel comprises, in terms of elements, 95.386-97.021 wt% of Fe, 0.12-0.17 wt% of C, 0.22-0.43 wt% of Si, 1.35-1.78 wt% of Mn, 0.28-0.38 wt% of Cu, 0.43-0.68 wt% of Cr, 0.18-0.37 wt% of Ni, 0.26-0.58 wt% of Mo, 0.05-0.09 wt% of V, 0.02-0.045 wt% of Ti, 0.035-0.055 wt% of Nb, not more than 0.01 wt% of P, not more than 0.003 wt% of S, and not more than 0.018 wt% of rare earth elements, based on the total weight of the steel; The volume fraction of martensite in the steel is 10-30 volume % based on the total volume of the steel.

3. The steel material according to claim 1 or 2, wherein: The rare earth elements include La, Ce and Eu; The weight ratio of La:Ce:Eu is 1:(1.3-2.5):(0.5-1).

4. The steel material according to claim 1 or 2, wherein: The average grain size of the steel is 10.5-13 μm.

5. The steel material according to claim 1 or 2, wherein: The yield strength of the steel is 850-1080MPa; And / or, the tensile strength of the steel is 1080-1260 MPa; and / or, the elongation of the steel is ≥12%; And / or, the hardness of the steel is ≤43HRC.

6. A method for preparing a continuous tube, comprising: (1) Slitting the coil into strips to obtain steel strips; Then, the steel strip is welded and extended to obtain an extended steel strip; (2) forming, welding and post-processing the extended steel strip to obtain a continuous tube; Wherein, the material of the rolled plate is the steel material described in any one of claims 1-5.

7. The method according to claim 6, wherein: In step (1), the thickness of the rolled plate is 3-8 mm.

8. The method according to claim 6 or 7, wherein: In step (1), before the longitudinal shearing and slitting, the surface of the coil is sandblasted; The surface sandblasting treatment makes the surface roughness Ra of the rolled plate be 3.6-4.4 μm.

9. The method according to claim 6 or 7, wherein: In step (1), the welding extension is carried out by means of oblique butt welding, and the end portion of the steel strip to be welded is beveled to 40°-50° and a U-shaped groove is processed.

10. The method according to claim 6 or 7, wherein: Step (1) further comprises performing a thermal deformation treatment on the extended weld obtained after the welding extension; The thermal deformation treatment includes: heating the extended weld to 860-980° C., keeping the temperature for 10-30 seconds, and then forging the extended weld at a pressure of 8-20 MPa.

11. The method according to claim 6 or 7, wherein: In step (2), the welding conditions include: temperature of 1130-1350°C; weld extrusion of 1.5-3.5 mm; opening angle θ of 4°-12°; and welding speed of 3-26 m / min.

12. The method according to claim 6 or 7, wherein: In step (2), the post-treatment includes sequentially performing heat treatment of the weld and heat treatment of the pipe body; The weld heat treatment comprises: heating the formed weld obtained after forming and welding to 880-960° C., forging the formed weld with a pressure of 8-20 MPa, then air cooling to 150-350° C., and finally water cooling to room temperature; The tube heat treatment comprises: heating the tube obtained after forming and welding to 500-720° C., then cooling it to 250-350° C. at a cooling rate of 10-20° C. / s, and finally cooling it to room temperature with water.

13. A coiled tube obtained by the method according to any one of claims 6 to 12.

14. The coiled tube according to claim 13, wherein: The yield strength of the coiled tube is 1034-1240 MPa; And / or, the tensile strength of the coiled tube is 1068-1275 MPa; and / or, the elongation of the coiled tube is ≥13%; And / or, the hardness of the coiled tube is ≤43HRC.

15. Use of the coiled tube according to claim 13 or 14 in oil and gas exploration.

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