A sulfur-lead composite steel bar and its preparation method, a steel pipe and a soluble structural component

Abstract

This application discloses a sulfur-lead composite steel rod and its preparation method, as well as a steel pipe and soluble structural components, solving the technical problem that soluble bridge plugs in the prior art do not meet the high-pressure maintenance requirements of deep wells. The steel rod comprises the following chemical composition in parts by mass: Fe: 90-97.5 parts, C≤0.6 parts; S: 0.1-0.6 parts, Mn: 0.50-3.00 parts, Pb: 0.2-0.3 parts, O: 0.0010-0.0200 parts; the steel rod has composite inclusions; the composite inclusions include an inner core and a continuous or discontinuous outer shell distributed around the inner core, the inner core including manganese sulfide particles, and the outer shell including first lead particles; the steel rod includes a first region, a second region, and a third region arranged sequentially from the inside out; the average equivalent diameter of the composite inclusions in the first region is larger than that in the second region; the number of composite inclusions per square millimeter in any cross-section of the third region is greater than that in the second region. The sulfur-lead composite steel rod provided by this application has high strength and meets the high-pressure maintenance requirements of deep wells.

Description

Technical Field

[0001] This application belongs to the field of soluble materials technology, specifically relating to a sulfur-lead composite steel rod and its preparation method, a steel pipe and soluble structural components. Background Technology

[0002] Dissolvable structural components, such as dissolvable bridge plugs, are core functional parts of downhole fracturing tools. These components perform the task of isolating formations and directional reservoir stimulation during staged fracturing in oil and gas wells. Dissolvable structural components must maintain their structural integrity in the high-pressure downhole environment to ensure the reliability of fracturing operations. After fracturing is completed, the component must undergo controlled dissolution according to predetermined requirements to maintain the full-bore condition of the wellbore, thereby ensuring the smooth implementation of subsequent production operations.

[0003] Existing soluble structural components are mainly made of magnesium alloy or aluminum alloy. Although these materials have solubility properties, China's shallow surface oil and gas resources have been fully developed. Oil and gas development at depths of 4,000 meters or even deeper has become the mainstream extraction depth. When operating in deep underground layers, such as when the operating depth reaches 4,000 meters, the temperature of the rock formation reaches 150°C. Non-ferrous metal alloys are not strong enough to meet the pressure holding requirements of deep wells and cannot maintain effective sealing function. Summary of the Invention

[0004] To address the technical problem that magnesium-aluminum alloys currently lack sufficient strength at deep high temperatures, thus failing to meet high-pressure holding requirements, this application provides a sulfur-lead composite steel bar and its preparation method, as well as a steel pipe and soluble structural components.

[0005] In a first aspect of this application, a sulfur-lead composite steel rod is provided, wherein the sulfur-lead composite steel rod comprises the following chemical components in parts by mass: Fe: 90 parts to 97.5 parts, C ≤ 0.6 parts; S: 0.1 parts to 0.6 parts, Mn: 0.50 parts to 3.00 parts, Pb: 0.2 parts to 0.3 parts, O: 0.0010 parts to 0.0200 parts; The sulfur-lead composite steel bar has composite inclusions; the composite inclusions include an inner core and a continuous or discontinuous outer shell distributed around the inner core, the inner core including manganese sulfide particles, and the outer shell including first lead particles; The sulfur-lead composite steel rod includes a first region, a second region, and a third region. The second region and the third region are both annular cylindrical in shape. Along the direction from the inside to the outside, the second region and the third region are sequentially nested outside the first region. The first region, the second region, and the third region are all distributed with multiple composite inclusions. The average equivalent diameter of the composite inclusions in the first region is greater than the average equivalent diameter of the composite inclusions in the second region; the number of composite inclusions per square millimeter in any cross section of the third region is greater than the number of composite inclusions per square millimeter in any cross section of the second region.

[0006] In some embodiments, in the sulfur-lead composite steel bar, the volume fraction of the first region is 15% to 25%, and the volume fraction of the third region is 20% to 30%.

[0007] In some embodiments, the average equivalent diameter of the composite inclusions in the first region is greater than the average equivalent diameter of the composite inclusions in the three regions; The average equivalent diameter of the composite inclusions in the first region is 3 μm to 10 μm; the average equivalent diameter of the composite inclusions in the second region is 3 μm to 8 μm; and the average equivalent diameter of the composite inclusions in the third region is 3 μm to 7 μm.

[0008] In some embodiments, the number of composite inclusions per square millimeter in any cross section of the first region is greater than the number of composite inclusions per square millimeter in any cross section of the second region; The number of composite inclusions per square millimeter in any cross-section of the first region is 2,000 to 5,000; the number of composite inclusions per square millimeter in any cross-section of the second region is 2,000 to 4,000; and the number of composite inclusions per square millimeter in any cross-section of the third region is 2,000 to 5,000.

[0009] In some embodiments, the equivalent aspect ratio of the composite inclusion is greater than 5.

[0010] In some embodiments, the number of composite inclusions with an equivalent diameter of 3μm to 10μm in the first region accounts for 80% to 90%.

[0011] In a second aspect of this application, a method for preparing a sulfur-lead composite steel rod as described in the first aspect is provided, comprising: Molten steel is obtained, wherein the molten steel comprises the following chemical components in parts by mass: Fe: 90 parts to 97.5 parts, C ≤ 0.6 parts; S: 0.1 parts to 0.6 parts, Mn: 0.50 parts to 3.00 parts, Pb: 0.2 parts to 0.3 parts, O: 0.0010 parts to 0.0200 parts; The molten steel is continuously cast to obtain a steel billet; wherein, during the continuous casting process, the superheat is 40℃~50℃; The steel billet is sequentially heated, rough-rolled, and finish-rolled to obtain a sulfur-lead composite steel bar; the finish rolling includes multiple rolling passes, with a reduction rate of 5% to 15% per pass.

[0012] In some embodiments, during the continuous casting process, the cooling intensity of the crystallizer is 1650 L / min to 1750 L / min, and the cooling intensity of the secondary cooling zone is 0.3 L / kg to 0.5 L / kg.

[0013] In a third aspect of this application, a soluble steel pipe is provided, which is formed by perforation of a sulfur-lead composite steel bar as described in the first aspect, or by perforation of a sulfur-lead composite steel bar prepared by the preparation method of the second aspect.

[0014] In a fourth aspect of this application, a soluble structural component is provided, which is formed by perforation of a sulfur-lead composite steel rod as described in the first aspect, or by perforation of a sulfur-lead composite steel rod prepared by the preparation method of the second aspect, or by preparation of a soluble steel tube as described in the third aspect.

[0015] According to the sulfur-lead composite steel rod provided in the embodiments of this application, the sulfur-lead composite steel rod contains a large amount of iron, belonging to iron-based materials, and its strength is higher than that of magnesium-aluminum materials used in traditional soluble bridge plugs. Furthermore, 0.50 to 3.00 parts of manganese are added to the sulfur-lead composite steel rod, which can improve the strength of the sulfur-lead composite steel rod to a certain extent. Therefore, the sulfur-lead composite steel rod provided in this application has higher strength than soluble structural components made of traditional magnesium-aluminum materials. Soluble structural components such as soluble bridge plugs made using this high-strength sulfur-lead composite steel rod have high strength, can withstand the high-pressure environment downhole, and maintain effective sealing function.

[0016] Because 0.50 to 3.00 parts of manganese, 0.1 to 0.6 parts of sulfur, and 0.2 to 0.3 parts of lead are added to the sulfur-lead composite steel rod, a composite inclusion is formed within the rod, consisting of a manganese sulfide core and a first lead particle shell. In this composite inclusion, some manganese sulfide is exposed outside the shell, allowing it to react with the corrosive hydrochloric acid to form hydrogen sulfide. The generated H₂S dissolves rapidly in the hydrochloric acid, and the hydrogen sulfide or HS⁻ in the hydrochloric acid strongly adsorbs onto the surface of the first lead particle shell, significantly reducing the overpotential for hydrogen evolution on the surface of the first lead particle. This forms a galvanic cell within the sulfur-lead composite steel rod, with the first lead particle acting as the cathode, where the hydrogen evolution reaction can easily occur. The iron matrix acts as the anode, undergoing a reduction and dissolution reaction, thereby improving the dissolution efficiency of the sulfur-lead composite steel rod.

[0017] Because the average equivalent diameter of the composite inclusions in the first region is larger than that in the second region, meaning the composite inclusions at the core of the steel bar are larger, the core (i.e., the first region) of the sulfur-lead composite steel bar will form the inner surface of the billet after subsequent reaming. Therefore, the large size of the composite inclusions on the inner surface of the billet implies large manganese sulfide particles within the composite inclusions. After the billet is processed into a soluble structural component and sealed in the well, hydrochloric acid is injected into the wellbore. Since the inner and outer surfaces of the soluble structural component come into rapid contact with the hydrochloric acid, the large size of the manganese sulfide particles on both surfaces prolongs the time for the manganese sulfide particles to continuously supply hydrogen sulfide, allowing the hydrogen evolution reaction to continue on the surface of the first lead particles, thereby increasing the electrochemical corrosion process of the inner surface.

[0018] Since the number of composite inclusions per square millimeter in any cross section of the third region is greater than that in any cross section of the second region, this means that there are more composite inclusions on the outer surface of the steel bar. After the sulfur-lead composite steel bar is subsequently expanded to form a tube blank, the outer surface of the steel bar will become the outer surface of the tube blank. Therefore, the large number of composite inclusions on the outer surface of the tube blank can increase the electrochemical corrosion sites and improve the initial corrosion rate of the material's outer surface.

[0019] As can be seen from the above, the sulfur-lead composite steel bar provided in this application has large composite inclusions in the first region and a large number of composite inclusions in the third region, thereby increasing the corrosion rate of the inner and outer surfaces of the tube blank, making the parts of the tube blank in contact with hydrochloric acid dissolve in all directions, accelerating the dissolution process of the material, increasing the dissolution rate of soluble structural parts, and saving alloys and reducing production costs. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0022] Figure 1 The diagram shows the process steps of a method for preparing a sulfur-lead composite steel rod provided in this application.

[0023] Figure 2 A metallographic image of the sulfur-lead composite steel bar of Embodiment 1 of this application is shown. Detailed Implementation

[0024] To enable those skilled in the art to more clearly understand this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges between 1 and 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including" and "contains" used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship. "And / or" indicates that multiple situations can exist individually or simultaneously. Expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0026] According to the first aspect of this application, a sulfur-lead composite steel bar is provided. This steel bar still has good strength at depths exceeding 4,000 meters, which can meet the pressure holding requirements of deep wells. At the same time, it has a fast dissolution rate and high corrosion efficiency. When it is made into a soluble bridge plug soluble structural component, it can achieve a full-bore state of the wellbore.

[0027] The sulfur-lead composite steel rod provided in this application embodiment comprises the following chemical components in parts by mass: Fe: 90-97.5 parts, C ≤ 0.6 parts; S: 0.1-0.6 parts, Mn: 0.50-3.00 parts, Pb: 0.2-0.3 parts, O: 0.0010-0.0200 parts. The steel rod has composite inclusions, which include an inner core and a continuous or discontinuous outer shell distributed around the inner core. The inner core includes manganese sulfide particles, and the outer shell includes first lead particles. The steel rod includes a first region, a second region, and a third region. The second and third regions are both annular, and along the direction from the inside out, the second and third regions are sequentially nested outside the first region. Multiple composite inclusions are distributed in each of the first, second, and third regions. The average equivalent diameter of the composite inclusions in the first region is greater than that in the second region; the number of composite inclusions per square millimeter in any cross-section of the third region is greater than that in any cross-section of the second region. The mass fraction of Fe is 90 to 97.5 parts, for example, 90% to 97.5%. Since the steel rod is an iron-based material, and iron has a high melting point of 1539℃ and higher strength than aluminum and magnesium, bridge plugs or sleeves made of sulfur-lead composite steel rods can still meet the pressure-maintaining requirements of deep wells under high temperatures. During the hydrochloric acid dissolution process, the iron matrix acts as the anode, undergoing an oxidation-dissolution reaction to eliminate soluble structural components, achieving full-bore wellbore penetration.

[0028] Sulfur is added to the steel rod, and it combines with manganese in the steel to form manganese sulfide. A portion of this manganese sulfide has lead distributed on its outer surface, forming a composite inclusion, while the remainder exists as a single inclusion. For the composite inclusion, the core manganese sulfide particles can react chemically with acid to form hydrogen sulfide. This hydrogen sulfide product dissolves rapidly in hydrochloric acid. Firstly, hydrogen sulfide strongly adsorbs onto the surface of the first lead particle in the outer shell. Through electrochemical desorption and regeneration, the surface overpotential of the first lead particle is significantly reduced, allowing the hydrogen evolution reaction to easily occur on the cathode first lead particle surface, improving the material's dissolution efficiency. Secondly, hydrogen sulfide can interfere with the complete formation of the PbCl2 protective film on the cathode first lead particle, relieving the inhibition of mass transfer by the PbCl2 protective film and thus promoting the hydrogen evolution reaction on the cathode first lead particle. Thirdly, hydrogen sulfide can diffuse to the iron anode surface and react with Fe²⁺ to form a ferrous sulfide (FeS) film. This porous film can disrupt the passivation or dissolution balance on the iron surface, further promoting the dissolution of the iron anode. Adding manganese to steel allows most of the manganese to combine with sulfur to form manganese sulfide, while some manganese can increase the strength of the steel bar, further meeting the high-temperature pressure holding requirements of deep wells.

[0029] When lead is added to steel, most of the lead, i.e., the first lead particles, are distributed on the outer surface of the manganese sulfide particles. This distribution pattern of the first lead particles and manganese sulfide particles makes them the main component of composite inclusions. The first lead particles can act as cathodes, where hydrogen evolution occurs on their surface, promoting the dissolution of the steel rod. At the same time, the first lead particles are good conductors, providing a perfect channel for the flow of electrons from the anode to its own cathode, further improving the dissolution efficiency of the steel rod.

[0030] The composite inclusions are irregularly shaped and not strictly spherical. The equivalent diameter is the diameter corresponding to a spherical particle of the same volume that represents the irregular composite inclusion. The average equivalent diameter of the composite inclusions in the first region is the average of the equivalent diameters of multiple composite inclusions in the first region. Similarly, the average equivalent diameter of the composite inclusions in the second region is the average of the equivalent diameters of multiple composite inclusions in the second region; and the average equivalent diameter of the composite inclusions in the third region is the average of the equivalent diameters of multiple composite inclusions in the third region.

[0031] For ease of explanation, the average equivalent diameter of the composite inclusions in the first region is named the first diameter, the average equivalent diameter of the composite inclusions in the second region is named the second diameter, and the average equivalent diameter of the composite inclusions in the third region is named the third diameter.

[0032] Soluble structural components are generally tubular, such as sleeves, bridge plugs, or metal parts of the bridge plug itself. The first region, the second region, and the third region are arranged sequentially along the axis outward. Therefore, during the process of forming a tube blank by expanding the hole of the steel bar, the first region, which is the core of the steel bar, becomes the inner surface of the tube blank, and the third region, which is the part of the steel bar near the outer periphery, becomes the outer surface of the tube blank.

[0033] The first diameter is larger than the second diameter, which means that the composite inclusions in the first region are larger. Therefore, after the tube blank is made, the size of the composite inclusions near the inner surface of the tube blank will also be larger than that of other parts. This results in larger core manganese sulfide particles in the composite inclusions, which can increase the dissolution time of the core manganese sulfide particles, so as to provide a continuous supply of hydrogen sulfide to the cathode shell (first lead particle). This allows the first lead particle of the cathode to continuously undergo hydrogen evolution reaction, promoting the accelerated dissolution of the iron matrix. At the same time, hydrogen sulfide can also diffuse to the iron anode surface and react with Fe²⁺ to destroy the passivation or dissolution equilibrium ferrous sulfide (FeS) film on the iron surface, further promoting the dissolution of the iron anode.

[0034] In addition, the large size of the composite inclusions in the first region may cause pits left by the detachment of composite inclusions on the inner surface of the tube blank formed by the expansion hole, or protrusions of composite inclusions on the outer circumference. These pits and protrusions will increase the roughness of the inner surface of the tube blank, further promote the dissolution of the iron matrix, and improve the corrosion efficiency of soluble structural parts.

[0035] The number of composite inclusions per square millimeter in any cross section of the third region is greater than that in any cross section of the second region. This means that there are more composite inclusions in the third region. Therefore, after the tube blank is made, the number of composite inclusions near the outer surface of the tube blank will also be greater. This can increase the electrochemical corrosion sites and promote the initial dissolution efficiency of the outer surface.

[0036] In some embodiments, in the sulfur-lead composite steel bar, the volume fraction of the first region can be 15%~25%, for example 17%, 19%, 20%, 22%, 23%, or 24%, and the volume fraction of the third region can be 20%~30%, for example 22%, 23%, 25%, 27%, 28%, or 29%. Controlling the volume fractions of the first and third regions ensures that, after forming the tube blank, large-sized composite inclusions are distributed within a certain thickness range on both the inner and outer surfaces of the tube blank, thus guaranteeing corrosion efficiency on both the inner and outer surfaces. In other embodiments, the volume fraction of the first region can also exceed 25% or be less than 15%, for example 30% or 10%, and the volume fraction of the third region can also exceed 30% or be less than 20%, for example 35% or 15%, also achieving corrosion dissolution of soluble structural components.

[0037] In some embodiments, the average equivalent diameter of the composite inclusions in the first region can be 3 μm to 10 μm, that is, the first diameter is 3 μm to 10 μm, for example, the first diameter is 4 μm, 5 μm, etc. This ensures that the size of the manganese sulfide particles in the composite inclusions is relatively large, ensuring a continuous supply of hydrogen sulfide, improving the high-speed hydrogen evolution reaction at the first lead particle of the cathode, and improving corrosion efficiency. In other embodiments, the average equivalent diameter of the composite inclusions in the first region can also not exceed 3 μm, for example, 2 μm, which can also achieve corrosion dissolution of soluble structural components.

[0038] It should be explained that while the average equivalent diameter of all composite inclusions in the first region is greater than or equal to 3 micrometers, there are still composite inclusions with an equivalent diameter less than 3 micrometers within the first region. In some embodiments, the proportion of composite inclusions with an equivalent diameter of 3 μm to 10 μm in the first region can be 80% to 90%, such as 83%, 84%, 86%, 87%, or 89%. For composite inclusions, a larger equivalent diameter results in larger core manganese sulfide particles, which can continuously supply hydrogen sulfide. However, in production, if the size of the composite inclusions is too large, it will reduce the overall number of composite inclusions. During hydrochloric acid corrosion, although the local corrosion efficiency is very high, it may, to some extent, slow down the overall dissolution rate. Increasing the number of composite inclusions with an equivalent diameter of 3 μm to 10 μm can improve both local and overall corrosion efficiency. In other embodiments, the proportion of composite inclusions with an equivalent diameter of 3 μm to 10 μm in the first region can also be less than 80%, such as 75%.

[0039] In some embodiments, the average equivalent diameter of the composite inclusions in the second region can be 3μm to 8μm, such as 4μm, 5μm, or 6μm; the average equivalent diameter of the composite inclusions in the third region can be 3μm to 7μm, such as 4μm, 5μm, or 6μm. In some embodiments, the proportion of composite inclusions with an equivalent diameter of 3μm to 10μm in both the second and third regions can be 80% to 90%, such as 83%, 84%, 86%, 87%, or 89%. In other embodiments, the proportion of composite inclusions with an equivalent diameter of 3μm to 10μm in both the second and third regions can be less than 80%, such as 78%, while still achieving corrosion dissolution of the soluble structural components.

[0040] In some embodiments, the steel bar may also have individual inclusions, which may be manganese sulfide inclusions, and the first region, second region, and third region may all have individual inclusions distributed thereon. In the sulfur-lead composite steel bar, manganese sulfide, formed by the combination of sulfur and manganese, partly forms composite inclusions, and partly exists as individual inclusions.

[0041] For manganese sulfide inclusions present as individual inclusions in sulfur-lead composite steel bars, during hydrochloric acid corrosion, in addition to the aforementioned chemical reaction with the acid, the manganese sulfide inclusions can also act as cathodes, with the steel substrate as an anode, resulting in electrochemical corrosion and improving the corrosion efficiency of the steel bar. In other words, in the portions of the steel containing individual inclusions, electrochemical corrosion occurs locally with manganese sulfide acting as the cathode and the steel substrate as the anode; in the portions containing composite inclusions, manganese sulfide primarily undergoes chemical reaction corrosion, with lead particles acting as the cathode and the steel substrate as the anode, resulting in electrochemical corrosion.

[0042] In some embodiments, the first region contains both composite inclusions and monomeric inclusions, and the second region also contains both composite inclusions and monomeric inclusions. In the first region, the proportion of composite inclusions in all inclusions (the sum of monomeric inclusions and composite inclusions) can be 60% to 80%, such as 63%, 65%, 67%, 68%, 70%, 72%, 75%, 78%, or 79%. In the second and third regions, the proportion of composite inclusions in the inclusions (the sum of monomeric inclusions and composite inclusions) can also be 60% to 80%, such as 63%, 65%, 67%, 68%, 70%, 72%, 75%, 78%, or 79%.

[0043] Individual inclusions can undergo both chemical corrosion and act as cathodes, resulting in rapid consumption. Once depleted, the corrosion rate slows down. In contrast, manganese sulfide particles in composite inclusions are consumed only through chemical corrosion. The lead particles, acting as cathodes, prolong the consumption time of the manganese sulfide particles, thus increasing the duration of electrochemical corrosion. Consequently, the corrosion efficiency at locations with composite inclusions is higher than that at locations with individual inclusions. A higher proportion of composite inclusions in the first region increases the corrosion efficiency of the steel matrix and accelerates the dissolution process of soluble structural components. Similarly, a higher proportion of composite inclusions in the second region also increases the corrosion efficiency of the steel matrix and accelerates the dissolution process of soluble structural components.

[0044] In other embodiments, the proportion of composite inclusions in all inclusions in the first region may be less than 60% or greater than 80%, for example, 55% or 88%; of course, the proportion of composite inclusions in the inclusions in the second and third regions may be less than 60% or greater than 80%, for example, 55% or 88%, which can also achieve corrosion dissolution of soluble structural components.

[0045] In some embodiments, the equivalent aspect ratio of both composite inclusions and monomeric inclusions can be greater than 5. The equivalent aspect ratio refers to the ratio of the equivalent length of an inclusion (composite inclusions and monomeric inclusions) to its equivalent width. The equivalent length typically refers to the maximum projected length of the inclusion observed under a microscope. The equivalent width refers to the diameter of a circle whose two-dimensional projected area of ​​the inclusion on the metallographic sample surface is equal to that of the inclusion. During rolling, composite inclusions and monomeric inclusions generally extend along the rolling direction, that is, along the axial direction of the steel bar, appearing as thin strips. A large equivalent aspect ratio means that the inclusions are relatively long, making it easier to form grooves extending along the axial direction of the billet during hydrochloric acid corrosion. After the grooves are fully connected, the structure of the soluble component is more likely to collapse, increasing corrosion efficiency. In other embodiments, the equivalent aspect ratio of both composite inclusions and monomeric inclusions can be less than 5, for example, an equivalent aspect ratio of 4, which can still achieve the dissolution of the soluble component.

[0046] In some embodiments, the number of composite inclusions per square millimeter in any cross-section of the first region is greater than the number of composite inclusions per square millimeter in any cross-section of the second region. The composite inclusion density in the first region is greater than that in the second region. Therefore, during the hydrochloric acid etching process, the first region can provide more corrosion sites, accelerating the dissolution efficiency of the first region while reducing alloy costs.

[0047] In some embodiments, the number of composite inclusions per square millimeter in any cross-section of the first region of the steel bar can be 2000 to 5000; the number of composite inclusions per square millimeter in any cross-section of the second region can be 2000 to 4000; and the number of composite inclusions per square millimeter in any cross-section of the third region can be 2000 to 5000. The first and third regions have a high number of composite inclusions and numerous corrosion sites, resulting in rapid material dissolution and potentially reducing alloy costs.

[0048] In some embodiments, the steel bar may also have a plurality of second lead particles, which are arranged alternately with the composite inclusions. The number of second lead particles per square millimeter of any cross section of the steel bar may be 1,000 to 2,000. The average equivalent circular diameter of the second lead particles may be 2 μm to 3 μm, and the equivalent aspect ratio of the second lead particles may be 2 to 4.

[0049] In some embodiments, when the mass fraction of C is 0.20 to 0.60 parts, the banding grade of the soluble steel bar can be greater than or equal to grade 3. For example, a carbon mass fraction of 0.20% to 0.60% indicates that the steel bar is a medium-carbon steel bar with a high carbon content, a banding grade greater than or equal to grade 3, and a high banding defect grade. Therefore, the microstructure of the steel bar contains both ferrite and pearlite, and the ferrite and pearlite exhibit an alternating arrangement along the perpendicular rolling direction. In this case, if there are no composite inclusions or single inclusions in a local area, the ferrite and pearlite can form a micro-coupled cell. Specifically, ferrite can act as the anode and pearlite as the cathode, forming a micro-coupled cell to accelerate the dissolution rate of the material. Pearlite includes ferrite lamellae and cementite lamellae, which are also arranged alternately. Therefore, in a more localized area, the ferrite lamellae and cementite lamellae can act as the anode and cathode, respectively, to form a micro-coupled cell and accelerate the dissolution rate of the material. It should be noted that the banded structure rating can be determined according to GB / T 34474-2025 Evaluation of Banded Structure in Steel.

[0050] When the mass fraction of carbon is less than 0.2 parts, for example, when the carbon content is less than 0.20%, the microstructure of the steel matrix is ​​basically ferrite. In this case, the ferrite mainly acts as the anode, which can form a micro-couple cell with the first lead particle (cathode) or with the single inclusion (cathode), thus accelerating the dissolution rate of the material.

[0051] In some embodiments, the chemical composition of the steel bar may also include tin, with the mass fraction of Sn being 0.05 to 0.2 parts, for example, 0.05% to 0.2%. Tin can be elemental particles segregated at the grain boundaries. After the oil well production pressurization is completed, hydrochloric acid with a concentration of 10% to 20% is injected into the oil production passage. The hydrochloric acid first diffuses at the grain boundaries, and a potential difference is formed between the Sn particles at the grain boundaries and the ferrite. Sn acts as the cathode, and the ferrite acts as the anode, resulting in an electrochemical reaction that promotes the rapid dissolution of ferrite grains in the hydrochloric acid environment. Since some Sn exists in a liquid state, Sn will spread and wet at the grain boundaries due to surface tension and wettability, forming a gapless and tight contact with the iron matrix. The electron transfer efficiency from the ferrite anode to the liquid tin is close to 100%, eliminating the electron transfer limitation of "electrode contact resistance" in the solid state. This allows the "Fe dissolution-electron transfer-hydrogen evolution" cycle to reach a nearly unobstructed and highly efficient state, significantly improving the corrosion rate of ferrite grains.

[0052] The chemical composition of the steel bar may also include impurity elements, such as Cu, Ni, Cr, Mo, Pb, Al, N, etc., which will not be elaborated in this application.

[0053] Based on the same technical concept as the first aspect, the second aspect of this application provides a method for preparing a sulfur-lead composite steel rod, which can produce the sulfur-lead composite steel rod of the first aspect.

[0054] Please see Figure 1 The preparation method provided in this application includes the following steps 201, 202 and 203: Step 201: Obtain molten steel, which comprises the following chemical components in parts by mass: Fe: 90 parts to 97.5 parts, C ≤ 0.6 parts; S: 0.1 parts to 0.6 parts, Mn: 0.50 parts to 3.00 parts, Pb: 0.2 parts to 0.3 parts, O: 0.0010 parts to 0.0200 parts; Step 202: Continuously cast the molten steel to obtain a steel billet; Step 203: The steel billet is heated, rough rolled, and finish rolled in sequence to obtain sulfur-lead composite steel bar.

[0055] For step 201, molten steel can be obtained by the following method.

[0056] Iron ore or scrap steel is selected as the smelting substrate, or molten iron can be used to achieve an Fe content of 90% to 97.5%. Then, steelmaking is carried out in a converter or electric furnace, followed by LF refining and VD refining to obtain molten steel.

[0057] During the steelmaking process, slag is formed by batching and the sulfur (S) content is controlled within the range of 0~0.08%. At the end of steelmaking, carbon (C) is ≤0.03%, and the temperature can be 1590℃~1620℃. At the tapping stage, lime, fluorite, silicon carbide, refining slag, quartz sand, and other slag materials, as well as deoxidizers such as aluminum ingots, are added. The total amount of slag materials and deoxidizers is 500kg~1500kg.

[0058] Adding ferromanganese and ferrosilicon during the LF refining process can achieve the required levels of Mn and Si. Slag formation is performed during LF refining, and lime and fluorite are added based on the slag condition of the LF furnace and the sulfur content of the steel tapped from the converter to ensure good slag fluidity. Sulfurization is also carried out, resulting in a sulfur content of 0.1-0.6% at the end of LF refining. After the VD refining process, high-flow-rate bottom blowing is used, and lead alloy is added to achieve a Pb content of 0.2%-0.3% and a sulfur content of 0.1%-0.5%. After VD refining, the process is switched to the soft blowing station with a covering agent for soft blowing (argon flow rate can be 80NL / min or 90NL / min, etc.). The molten steel must not be exposed during surface creep, and the soft blowing time can be 8-15 minutes, for example, 10 or 12 minutes.

[0059] For step 202, continuous casting is a key process for controlling the size of composite inclusions. In some embodiments, the superheat during continuous casting can be 40°C to 50°C, such as 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 48°C, 49°C, etc. A superheat of 40°C to 50°C, with higher superheat, reduces the cooling rate, prolongs local solidification time, promotes the enrichment of sulfur and manganese in the core, and allows sufficient time for manganese sulfide to grow, thereby forming coarse manganese sulfide particles in the core and resulting in a high density of composite inclusions in the core. In other embodiments, the superheat can be greater than 50°C, such as 53°C, which also forms coarse and high-density manganese sulfide particles.

[0060] In some embodiments, during continuous casting, the cooling intensity of the crystallizer can be 1650 L / min to 1750 L / min, for example, 1670 L / min, 1680 L / min, 1690 L / min, 1700 L / min, 1720 L / min, 1730 L / min, or 1740 L / min; the cooling intensity of the secondary cooling zone can be 0.3 L / kg to 0.5 L / kg, for example, 0.33 L / kg, 0.35 L / kg, 0.38 L / kg, 0.40 L / kg, 0.42 L / kg, 0.45 L / kg, 0.47 L / kg, 0.48 L / kg, or 0.49 L / kg. In the formed steel billet, the outer surface of the billet corresponds to the third region, and the core of the billet corresponds to the first region. In the crystallizer, a primary billet shell is formed, corresponding to the third region of the steel bar. Controlling the crystallizer's low cooling rate of 1650 L / min to 1750 L / min promotes the formation of coarse composite inclusions in the third region. Subsequent hot rolling with multiple passes and low reduction rates breaks down these inclusions, increasing their quantity. This results in a higher number of inclusions per square millimeter in any cross-section of the third region compared to the second region. The second cooling zone primarily cools the unsolidified liquid core within the billet. Using a low cooling rate of 0.3 L / kg to 0.5 L / kg, this promotes the formation of coarse composite inclusions in the first region, ensuring that the average equivalent diameter of the inclusions in the first region is greater than that in the second region.

[0061] During solidification, the steel matrix solidifies first, forming manganese sulfide at the dendrite sites. While manganese sulfide is forming, phosphorus (Pb) remains liquid. Finally, the Pb particles (the first lead particles) in the gaps between the manganese sulfide and the steel matrix solidify and distribute on the surface of the manganese sulfide particles, forming composite inclusions. Simultaneously, a very small amount of Pb, the second lead particles, will be distributed in the iron matrix but not on the surface of the manganese sulfide particles.

[0062] In some embodiments, continuous casting can also employ intermediate-stage electromagnetic stirring (M-EMS) and final-stage electromagnetic stirring (F-EMS). The billet casting speed can be 1 m / min to 2.0 m / min, for example, 1.2 m / min, 1.4 m / min, or 2.0 m / min. The frequency of the intermediate-stage electromagnetic stirring can be 4 Hz to 6 Hz, and the current can be 300 A to 400 A. The frequency of the final-stage electromagnetic stirring can be 10 Hz to 15 Hz, and the current can be 100 A to 150 A. Using electromagnetic stirring can break up excessively large composite inclusions in the core to a certain extent, thereby increasing the quantity and size of composite inclusions in the first region of the sulfur-lead composite steel bar.

[0063] For step 203, sulfur-lead composite steel bars can be obtained through heating, rough rolling, and finish rolling. In some embodiments, the heating temperature can be 1100℃~1160℃, for example 1150℃, the heating time can be 1.5h~3h, for example 2h or 2.5h, the rough rolling start temperature can be 1080℃~1150℃, for example 1090℃ or 1100℃, and the rolling speed can be 0.1 s. -1 ~1s -1 Controlling the heating temperature can prevent as-cast MnS from remelting or melting off.

[0064] In some embodiments, finishing rolling may include multi-pass rolling, with a reduction rate of 5% to 15% per pass. Multi-pass rolling may be four-pass rolling, five-pass rolling, or six-pass rolling. In some embodiments, the finishing rolling temperature may be 1000°C to 1010°C, followed by air cooling.

[0065] By controlling the low reduction rate in multiple passes and coordinating it with the final rolling temperature, the rolling process is kept within a relatively high plasticity range, ensuring that the MnS in the core is sufficiently elongated and not easily broken, so as to obtain the required density and size of the composite inclusions in the first region. Using a low reduction rate of 5% to 15% in each pass can increase the deformation of the outer periphery, thereby crushing the composite inclusions in the outer periphery, i.e., the third region, and increasing the density of the composite inclusions in the third region.

[0066] In some embodiments, the mass fraction of C can be 0.20 to 0.60 parts, and the finishing rolling temperature can be between 800°C and 950°C. This allows for the formation of a large number of dislocation nucleation sites for ferrite formation in the two-phase region. Based on this, a post-rolling cooling rate of 10°C / s to 50°C / s is matched to ensure that ferrite strips preferentially precipitate at the dislocations in the manganese-poor region, while carbon is discharged to the manganese-rich region. The enriched region is transformed into pearlite lamellars, forming a banded structure with a banded structure grade greater than or equal to 3.

[0067] Based on the same technical concept as the first aspect, the third aspect of this application provides a soluble steel pipe.

[0068] The soluble steel pipe can be manufactured by piercing a steel bar according to the first method, or by piercing a sulfur-lead composite steel bar prepared by the second method; this application makes no limitation on this. Piercing includes sequentially arranged processes of heating, piercing, rolling, sizing, and straightening, thereby obtaining a seamless soluble steel pipe.

[0069] Based on the same technical concept as the first aspect, the fourth aspect of this application provides a soluble structural component. This soluble structural component can be manufactured by perforating a steel bar as described in the first aspect, or by perforating a sulfur-lead composite steel bar prepared by the method of the second aspect, or by preparing a soluble steel pipe as described in the third aspect.

[0070] The soluble structural component can be a sleeve, a bridge plug, or a metal part of a bridge plug.

[0071] Generally, a bridge plug may include a central tube, anchor tiles, upper climbing teeth, lower climbing teeth, and a sealing plate. At least one of the central tube, anchor tiles, upper climbing teeth, and lower climbing teeth is machined from a soluble steel tube. When hydrochloric acid dissolves the bridge plug, it first contacts the inner and / or outer surfaces of the metal parts. The bridge plug described above is merely a simple example, mainly to illustrate that the metal parts of the bridge plug are tubular. The bridge plug itself is prior art; for more details, please refer to prior art disclosures, which will not be elaborated upon in this application.

[0072] Steel bars can be pierced to form tubing. Specifically, the piercing process can be performed as follows: sulfur-lead composite steel bars are sequentially heated, pierced, rolled, sizing, and straightened to obtain seamless tubing. This seamless tubing can then be used as the blank for bridge plugs, and after being length-determined, assembled to form bridge plugs. Further details on the piercing process can be found in existing technologies; more information will not be elaborated further here.

[0073] The preparation method of the sulfur-lead composite steel bar provided in this application will be further described below with reference to specific embodiments.

[0074] Examples 1 to 5 Examples 1 to 5 provide methods for preparing sulfur-lead composite steel bars, comprising the following steps: The steel is produced by converter smelting, LF refining, and VD refining. The chemical composition of the steel is shown in Table 1, with the remainder being Fe and unavoidable impurities. The molten steel is continuously cast into billets, which are then heated, rough-rolled, and finish-rolled to obtain bars. The process parameters for each step are shown in Tables 2, 3, and 4.

[0075] Table 1 Chemical composition of molten steel Table 2 Continuous casting process parameters Table 3 Heating and rough rolling process parameters Table 4 Reduction rate for each pass in finishing rolling Table 5 Table 6 Table 7 Samples were taken from the inner core (corresponding to the first region), the half-radius point (corresponding to the second region), and the outer peripheral surface (corresponding to the third region) of the steel rods prepared in Examples 1 to 5, and observed under a scanning electron microscope. The size of the composite inclusions and the number per square millimeter were counted using the Feature function of the scanning electron microscope, as shown in Tables 6, 7, and 8.

[0076] Samples of the steel bars prepared in Examples 1 to 5 were taken and their mechanical properties were tested according to the "SY / T 6998-2022 Test Method for Mechanical Properties of Metallic Materials for Soluble Bridge Plugs in Shale Gas". The mechanical properties are shown in Table 8. Samples with a diameter of 10 mm and a length of 50 mm were machined from the steel bars prepared in Examples 1 to 5 at the inner core (corresponding to the first region), half the radius (corresponding to the second region), and the outer peripheral surface (corresponding to the third region). These samples were placed in hydrochloric acid for corrosion testing, and the results are shown in Table 9.

[0077] Table 8 Table 9 As can be seen from the data in Table 9, manganese, sulfur and lead were added to the steel bars in Examples 1 to 5 of this application, and the corrosion rate in hydrochloric acid was not less than 0.84 mm / day. This means that adding manganese, sulfur and lead can increase the dissolution rate of the steel pipe.

[0078] As shown in Table 5, in the sulfur-lead composite steel bars provided in each embodiment, the average equivalent diameter of the composite inclusions in the first region is greater than that in the second and third regions. As shown in Table 6, the density of the composite inclusions in the first region is greater than that in the second and third regions. This means that the first region has the highest density and the largest average equivalent diameter of the composite inclusions, thus determining that the first region has the highest dissolution rate under hydrochloric acid conditions. As shown in Table 9, the dissolution rate in the first region is higher than that in the second and third regions in each embodiment. This proves that the location with the highest density and largest size of the composite inclusions does indeed have the highest dissolution rate. Therefore, during the dissolution process of the pipe fittings in the hydrochloric acid environment of the oil well, the inner surface dissolves the fastest.

[0079] As shown in Tables 5 and 6, the average equivalent diameter of the composite inclusions in the second and third regions is comparable. However, the density (number per square millimeter) of the composite inclusions in the third region is higher than that in the second region, resulting in a higher dissolution rate in the second region. Table 9 shows that the dissolution rate in the third region is higher than that in the second region in all embodiments. This demonstrates that locations with higher composite inclusion density exhibit faster dissolution rates. Therefore, during the dissolution process of pipe fittings in the hydrochloric acid environment of oil wells, the outer surface dissolves faster, which can promote the initial dissolution rate of soluble structural components.

[0080] Figure 2 The metallographic image of the sulfur-lead composite steel bar of Embodiment 1 of this application is shown. As can be seen from the figure, for low carbon steel, the microstructure of the steel bar includes ferrite (dark part) and pearlite (white part), of which ferrite is the main microstructure and its volume fraction is much larger than that of pearlite. During hydrochloric acid corrosion, ferrite dissolves as the anolyte.

[0081] The sulfur-lead composite steel bar, its preparation method, steel pipe, and soluble structural component provided in this application have at least the following advantages: (1) Sulfur, manganese and lead elements are added to steel to form a composite inclusion with manganese sulfide particles in the core and lead particles in the shell. In this way, hydrogen sulfide formed by the reaction of manganese sulfide and hydrochloric acid during corrosion can be adsorbed on the surface of lead particles. The sulfur-containing species itself becomes the active center of hydrogen evolution reaction, replacing the original pure Pb metal sites and improving corrosion efficiency.

[0082] (2) The composite inclusions in the inner core of the control steel rod have a larger average equivalent diameter. After forming the bridge plug part, the composite inclusions on the inner wall of the bridge plug part have a larger average equivalent diameter. The manganese sulfide in the large-diameter composite inclusions is also large, so that hydrogen sulfide can be provided for a long time during the contact with hydrochloric acid, thereby maintaining a long-term high corrosion efficiency.

[0083] (3) Controlling the high cooling degree, the low cooling intensity of the crystallizer and the low cooling intensity of the secondary cooling zone makes the composite inclusions in the inner core (first area) of the steel bar larger and more numerous, thereby ensuring the initial corrosion efficiency of the bridge plug parts and improving the overall corrosion efficiency.

[0084] (4) Control the small reduction rate of hot rolling multiple passes to crush the composite inclusions in the third region, increase the number of composite inclusions in the third region, increase the number of corrosion points, thereby improving the corrosion efficiency of the outer peripheral surface of the bridge plug and improving the overall dissolution rate.

[0085] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A sulfur-lead composite steel bar, characterized in that, The sulfur-lead composite steel bar comprises the following chemical composition by mass fraction: Fe: 90%~97.5%, C≤0.6%; S: 0.1%~0.6%, Mn: 0.50%~3.00%, Pb: 0.2%~0.3%, O: 0.0010%~0.0200%; The sulfur-lead composite steel bar has composite inclusions; the composite inclusions include an inner core and a continuous or discontinuous outer shell distributed around the inner core, the inner core including manganese sulfide particles, and the outer shell including first lead particles; The sulfur-lead composite steel rod includes a first region, a second region, and a third region. The second region and the third region are both annular cylindrical in shape. Along the direction from the inside to the outside, the second region and the third region are sequentially nested outside the first region. The first region, the second region, and the third region are all distributed with multiple composite inclusions. The average equivalent diameter of the composite inclusions in the first region is greater than the average equivalent diameter of the composite inclusions in the second region; the number of composite inclusions per square millimeter in any cross section of the third region is greater than the number of composite inclusions per square millimeter in any cross section of the second region.

2. The sulfur-lead composite steel bar according to claim 1, characterized in that, In the sulfur-lead composite steel bar, the volume fraction of the first region is 15% to 25%, and the volume fraction of the third region is 20% to 30%.

3. The sulfur-lead composite steel bar according to claim 1, characterized in that, The average equivalent diameter of the composite inclusions in the first region is greater than the average equivalent diameter of the composite inclusions in the three regions; The average equivalent diameter of the composite inclusions in the first region is 3 μm to 10 μm; the average equivalent diameter of the composite inclusions in the second region is 3 μm to 8 μm; and the average equivalent diameter of the composite inclusions in the third region is 3 μm to 7 μm.

4. The sulfur-lead composite steel bar according to any one of claims 1-3, characterized in that, The number of composite inclusions per square millimeter in any cross section of the first region is greater than the number of composite inclusions per square millimeter in any cross section of the second region; The number of composite inclusions per square millimeter in any cross-section of the first region is 2,000 to 5,000; the number of composite inclusions per square millimeter in any cross-section of the second region is 2,000 to 4,000; and the number of composite inclusions per square millimeter in any cross-section of the third region is 2,000 to 5,000.

5. The sulfur-lead composite steel bar according to any one of claims 1-3, characterized in that, The equivalent aspect ratio of the composite inclusion is greater than 5.

6. The sulfur-lead composite steel bar according to any one of claims 1-3, characterized in that, In the first region, the number of composite inclusions with an equivalent diameter of 3μm to 10μm accounts for 80% to 90%.

7. A method for preparing a sulfur-lead composite steel rod according to any one of claims 1-6, characterized in that, include: Molten steel is obtained, wherein the molten steel comprises the following chemical composition in parts by mass: Fe: 90%~97.5%, C≤0.6%; S: 0.1%~0.6%, Mn: 0.50%~3.00%, Pb: 0.2%~0.3%, O: 0.0010%~0.0200%; The molten steel is continuously cast to obtain a steel billet; wherein, during the continuous casting process, the superheat is 40℃~50℃; during the continuous casting process, the cooling intensity of the crystallizer is 1650 L / min~1750 L / min, and the cooling intensity of the secondary cooling zone is 0.3 L / kg~0.5 L / kg; The steel billet is sequentially heated, rough-rolled, and finish-rolled to obtain a sulfur-lead composite steel bar; the finish rolling includes multiple rolling passes, with a reduction rate of 5% to 15% per pass.

8. A soluble steel pipe, characterized in that, The sulfur-lead composite steel rod is formed by perforation using any one of claims 1-6, or by perforation using the method for preparing the sulfur-lead composite steel rod as described in claim 7.

9. A soluble structural component, characterized in that, The sulfur-lead composite steel bar is formed by piercing according to any one of claims 1-6, or by piercing according to the method for preparing sulfur-lead composite steel bars according to claim 7, or by preparing the soluble steel pipe according to claim 8.

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