Anti-corrosion short section of oil casing pipe

Abstract

The invention discloses an oil casing anti-corrosion short section which comprises an anti-corrosion barrel, a plurality of spring pieces are arranged at one end of the anti-corrosion barrel, one ends of the spring pieces are arranged in the circumferential direction of the anti-corrosion barrel, and an anti-corrosion cylindrical ball is correspondingly arranged at the other end of each spring piece. The device is easy to install, does not need to be maintained, and can protect the oil pipe and the sleeve from corrosion at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield corrosion and protection, and in particular relates to an oil casing anti-corrosion short joint. Background Art

[0002] During oilfield development and production, the formation water has a high mineralization degree and contains strong electrolytes such as carbon dioxide, sulfide, oxygen, carbonate anaerobic bacteria, etc., which are highly corrosive to downhole oil pipes and casings. At the same time, the produced liquid and gas also have a serious corrosive effect on the downhole oil casing. Especially when it is found that the water content of the well is high during development and production, measures need to be taken to drain the water. According to the existing drainage technology of the oil field, there are four drainage technologies: electric pump drainage, continuous tubing natural gas lift drainage, continuous tubing + gas lift valve natural gas lift drainage, and continuous tubing short-term nitrogen gas lift drainage. The latter three gas lift drainage technologies have relatively small corrosion risks faced by oil casing due to the use of packers with better sealing performance. However, electric pump drainage lacks effective anti-corrosion measures and mainly faces four risks. One is that the double leather cup packer used is not sealed, so that the entire wellbore is in a formation water environment. Second, the formation water contains corrosive substances such as carbon dioxide and chlorides, which put the production tubing in a severe corrosive environment. Third, not all tubing and casing in the drainage wells are made of materials with good corrosion resistance. According to investigations, the casing and tubing of some wells are made of carbon steel, which is very prone to corrosion. For example, the carbon steel tubing used in the Yaha 2 well (carbon dioxide partial pressure is 0.20-0.31MPa) is severely corroded. Figure 1 As shown; Fourth, from the results of indoor evaluation tests, carbon steel corrodes most severely at 90°C, such as Figure 2 As shown in the figure, the on-site oil pipe corrosion situation also verifies this point. The carbon steel oil pipe of the YH23-1-22 well has been seriously corroded after serving for 3 years. The temperature of the most serious well section is 89~96℃. Figure 3 shown.

[0003] according to Figure 2 The corrosion rate of medium carbon steel at 90℃ is used to predict the life of the casing of multiple electric pump drainage wells. It is expected that the remaining wall thickness of the casing will not be able to meet the requirements of anti-external collapse from 2029 to 2030, and there is a risk of collapse. At the same time, the casing in the middle of the wellbore (formation temperature is within 90℃) will face a very serious corrosion risk and is more prone to corrosion perforation.

[0004] Therefore, it is necessary to develop a tool that can protect the oil casing and can withstand high temperatures, especially temperatures above 90°C, and can be used in the middle of the wellbore.

[0005] According to the data investigation, there are two types of anti-corrosion short joints for oil pipes. One is to cast the sacrificial anode material on the short joint and connect it to the oil pipe. Figure 4 This structure can prevent tubing corrosion, but cannot prevent casing corrosion.

[0006] The other is a tool similar to the casing centralizer structure but made of heat-resistant anode material, also known as a heat-resistant anode protection casing tool. It is installed on the oil pipe, but is insulated from the oil pipe and is electrically connected to the casing through a spring sheet. Figure 5 As shown, the main principle of the tool is to prevent casing corrosion by electrically connecting the spring sheet to the casing. It has been used in the Changqing Oilfield many times. The tool can effectively prevent corrosion of the inner wall of the casing, but cannot prevent corrosion of the oil pipe. At the same time, the spring sheet of the tool can easily scratch the well wall.

[0007] Currently, there is no existing tool that can prevent corrosion of both the outer wall of the oil pipe and the inner wall of the casing. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide an oil casing anti-corrosion short joint for simultaneously solving the technical problem of corrosion of the outer wall of the oil pipe and the inner wall of the casing in view of the above-mentioned deficiencies in the prior art.

[0009] The present invention adopts the following technical solutions:

[0010] A corrosion-resistant short joint for oil casing, characterized in that it includes an anti-corrosion tube, one end of which is provided with a spring sheet, the spring sheets include multiple spring sheets, one end of the multiple spring sheets is arranged along the circumference of the anti-corrosion tube, and the other end of each spring sheet is correspondingly provided with an anti-corrosion cylindrical ball as an anode material. When formation water is used as an electrolyte solution, it is electrically connected with the casing and the oil pipe as cathode materials.

[0011] Specifically, the interior of the anti-corrosion cylindrical ball is a dovetail structure corresponding to the end of the spring sheet, and the diameter of the anti-corrosion cylindrical ball is 10 to 15 mm.

[0012] Specifically, a through groove is arranged on the outer side of the anti-corrosion tube along the longitudinal direction of the anti-corrosion tube.

[0013] Furthermore, the width of the through groove is 5-10 mm, and the inner diameter of the through groove is the outer diameter of the oil pipe body.

[0014] Specifically, the anti-corrosion tube is a conical structure, the spring sheet is connected to the anti-corrosion tube through a conical sleeve, and the taper of the anti-corrosion tube and the conical sleeve is 1: (16-4).

[0015] Furthermore, the height of the conical sleeve is 30 to 50 mm, the minimum wall thickness of the anti-corrosion tube is 5 to 10 mm, and the length is 200 to 300 mm.

[0016] Specifically, the anti-corrosion cylinder is a cylindrical structure, and the spring sheet and the anti-corrosion cylinder are an integrated structure.

[0017] Furthermore, the wall thickness of the anti-corrosion tube is 5 to 10 mm, and the length of the anti-corrosion tube is 20 to 50 mm shorter than the length of the coupling.

[0018] Specifically, the number of the spring pieces is 4 to 12, and the shape of the spring pieces is a rectangular strip structure or a fan-shaped structure.

[0019] Specifically, calculated by mass percentage, the anti-corrosion cylinder is prepared by 4% to 8% Zn, 0.02% to 0.03% In, 0.05% to 1.5% Mg, 0.01% to 0.06% Al, 0.041% to 0.212% Si, Fe content ≤ 0.15%, and 0.2 to 0.6% Bi.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] The present invention discloses an oil casing anti-corrosion pup joint, which uses the oil casing anti-corrosion pup joint as an anode material, and the casing and the oil pipe as cathode materials. When formation water is used as an electrolyte solution, the oil casing anti-corrosion pup joint is in contact with the oil pipe and the casing at the same time to be electrically connected, thereby effectively protecting the oil casing. The invention has a flexible structure, is simple to construct and install, does not require maintenance, and can simultaneously protect the oil pipe and the casing from corrosion.

[0022] Furthermore, the conical sleeve is sleeved on the small end of the conical anti-corrosion tube. As it gradually corrodes in the formation water downhole, the conical sleeve continues to descend and fully contacts the anti-corrosion tube and the casing, preventing the conical sleeve from continuously corroding and dissolving at the same position of the anti-corrosion tube, thereby reducing the wall thickness of the anti-corrosion tube and affecting the corrosion effect. At the same time, in the later stage of corrosion, the oil pipe coupling will prevent the anti-corrosion tube from continuing to slide down.

[0023] Furthermore, the use of aluminum alloy sacrificial anode material does not require any external power supply, which enhances its wide application. At the same time, it has little or no interference with the stray current generated by adjacent structures, and the material cost is very low. The output current of the sacrificial anode material has a certain self-regulating ability, and the protection current is evenly distributed with high utilization rate.

[0024] In summary, the present invention can prevent both the outer wall of the oil pipe and the inner wall of the casing from being corroded during mining operations, and has temperature resistance, a simple structure, and is easy to process, install, and operate.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the carbon steel corrosion morphology in Yaha 2 Well;

[0027] Figure 2 This is a schematic diagram of the corrosion rate of carbon steel at different temperatures;

[0028] Figure 3 This is a schematic diagram of the corrosion morphology of the carbon steel oil pipe in the YH23-1-22 well at a temperature of 89℃~96℃;

[0029] Figure 4 This is a schematic diagram of an existing oil pipe anti-corrosion short joint;

[0030] Figure 5 This is a schematic diagram of a heat-resistant anode protection casing tool;

[0031] Figure 6 Schematic diagram of the morphology of aluminum anode before and after corrosion at 95°C, where (a) is the aluminum alloy anode coupon before corrosion, (b) is the aluminum alloy anode coupon after corrosion, and (c) is the aluminum alloy anode coupon and carbon steel coupon after corrosion;

[0032] Figure 7 Schematic diagram of the integrated oil casing anti-corrosion short joint of the present invention, wherein (a) is a top view and (b) is a front view;

[0033] Figure 8 It is a schematic diagram of the through slot;

[0034] Fig. 9 It is a schematic diagram of the split type oil casing anti-corrosion short joint of the present invention.

[0035] Among them: 1. Anti-corrosion cylinder; 2. Spring sheet; 3. Anti-corrosion cylindrical ball; 4. Through groove; 5. Conical sleeve; 6. Upper joint; 7. Upper pressure cap; 8. Center tube; 9. Inner and outer alloy layers; 10. Lower pressure cap; 11. Lower joint; 12. Coupling; 13. Insulating pad; 14. Fixing card; 15. Fixing sleeve; 16. Anode; 17. Spring sheet; 18. Fixing ring. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, in the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0040] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0041] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0042] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0043] See also Figure 7 and Figure 8 An embodiment of the present invention is an integrated oil casing anti-corrosion short section, comprising an anti-corrosion tube 1, a spring sheet 2 and an anti-corrosion cylindrical ball 3; the spring sheet 2 is circumferentially arranged along one end of the anti-corrosion tube 1, and the anti-corrosion cylindrical ball 3 is correspondingly arranged at the end of each spring sheet 2.

[0044] The anti-corrosion cylinder 1 is a cylindrical structure, the wall thickness of the anti-corrosion cylinder 1 is 5-10 mm, the spring sheet 2 and the anti-corrosion cylinder 1 are processed as one piece, and the thickness of the spring sheet 2 is consistent with that of the anti-corrosion cylinder.

[0045] The number of the spring sheets 2 is 4 to 12. To ensure that they can fully contact the casing, the spring sheets 2 are evenly distributed along the circumference of the anti-corrosion tube 1 and can be expanded under the buoyancy of the formation water to just contact the casing.

[0046] The spring sheet 2 is in the shape of a rectangular strip or a fan-shaped structure, and the end of the spring sheet 2 is a dovetail structure.

[0047] The anti-corrosion cylindrical ball 3 is cylindrical in shape and has a dovetail structure inside, which fits well with the spring sheet 2. The length of the anti-corrosion cylindrical ball 3 is the same as the dovetail length at the end of the spring sheet 2. The outside of the anti-corrosion cylindrical ball 3 is spherical with a cross-sectional diameter of 10 to 15 mm, which can avoid scratches inside the well and can be installed on the spring sheet 2 before use.

[0048] To ensure that the spring sheet 2 can fully contact the casing in the formation water, the length of the spring sheet 2 is 5 to 20 mm greater than the gap between the oil and the casing ring.

[0049] When the integral anti-corrosion short section of the oil casing of the present invention is sleeved on the oil pipe coupling, its inner diameter is equal to the outer diameter of the oil pipe coupling. For the convenience of operation, the length of the anti-corrosion tube 1 is 20 to 50 mm less than the length of the coupling. When the integral anti-corrosion short section of the oil casing is sleeved on the oil pipe body, for the convenience of installation, a longitudinally arranged through groove 4 is processed in the anti-corrosion tube in the integral anti-corrosion short section of the oil casing. Figure 8 As shown, the width of the through groove 4 is 5 to 10 mm, and the inner diameter of the through groove 4 is the outer diameter of the oil pipe body. In order to reduce the processing steps, the through groove can be omitted and the oil pipe can be directly installed from the external threaded end, and the length of the anti-corrosion tube 1 can be appropriately increased, preferably to a length of 200 to 300 mm.

[0050] See also Fig. 9 Another embodiment of the present invention is a split oil casing anti-corrosion short section, including an anti-corrosion tube 1, a tapered sleeve 5, a spring sheet 2 and an anti-corrosion cylindrical ball 3. The anti-corrosion tube 1 is a tapered structure, and the spring sheet 2 is circumferentially arranged along one end of the anti-corrosion tube 1. The anti-corrosion tube 1 is provided with a tapered sleeve 5 for connecting the spring sheet 2, and the anti-corrosion cylindrical ball 3 is correspondingly arranged at the end of each spring sheet 2.

[0051] The taper range of the anti-corrosion cylinder 1 and the tapered sleeve 5 is 1:(16-4), and the tapers of the two are consistent.

[0052] The conical sleeve 5 can just be put on the small end of the anti-corrosion tube 1. The height of the conical sleeve 2 is 30-50 mm. As it gradually corrodes in the formation water downhole, the conical sleeve 2 continues to descend and can fully contact the anti-corrosion tube 1 and the casing at the same time, preventing the conical sleeve 2 from continuously corroding and dissolving at the same position of the anti-corrosion tube 1, thereby reducing the wall thickness of the anti-corrosion tube 1 and affecting the corrosion effect. At the same time, in the later stage of corrosion, the oil pipe coupling will prevent the anti-corrosion tube 1 from continuing to slide down.

[0053] The design of the spring sheet 2 and the anti-corrosion cylindrical ball 3 is the same as the integral type; the conical sleeve 5 and the spring sheet 2 are processed as one piece, and the anti-corrosion cylindrical ball 3 is installed on the spring sheet 2 before use.

[0054] When the split type oil casing anti-corrosion nipple of the present invention is used, the conical sleeve 5 (including the spring sheet 2 and the anti-corrosion cylindrical ball 3) is first installed on the male end, and then the anti-corrosion tube 1 is installed.

[0055] The inner diameter of the anti-corrosion tube 1 is equivalent to the inner diameter of the oil pipe. The through groove 4 is processed as needed. The requirements are the same as those of the integral oil casing anti-corrosion short section. The minimum wall thickness of the anti-corrosion tube 1 is 5-10 mm and the length is 200 mm-300 mm.

[0056] The outer diameter of the tapered sleeve 5 is 5 to 15 mm larger than the inner diameter at the minimum point.

[0057] The present invention provides a method for using an oil casing anti-corrosion short joint. For carbon steel oil casing near the 90°C temperature range, after calculating its corrosion rate, it can be used for 500 meters near the well depth of 90°C. If an integral oil casing anti-corrosion short joint installed at a coupling is used, one is used for each 500-meter oil pipe, and 50 are needed for a single well. If an oil casing anti-corrosion short joint installed at a pipe body is used, one is used for two oil pipes, and 25 are needed for a single well.

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0059] There are many corrosion mechanisms for oil casing, but the most common ones are electrochemical corrosion, chemical corrosion, bacterial corrosion, hydrogen embrittlement and scaling corrosion. Among them, electrochemical corrosion is the most common (accounting for about 45% according to incomplete statistics). Generally speaking, electrochemical corrosion requires the following conditions, that is, there must be different metals and conductive electrolytes. These two conditions are easy to meet, mainly because the composition of the pipe string, the pipe string and the coupling, and even the same root is not exactly the same, so it is easy to meet the first condition. As for the second condition, it is easy to meet when there is highly mineralized formation water.

[0060] There are many ways to prevent metal corrosion. Through the analysis of electrochemical corrosion, sacrificial anode to cathodic protection is an important and commonly used protection method. The principle is that the metal has a corresponding electrode potential in an electrolyte solution (such as formation water), and different metals have different electrode potentials in the same electrolyte. Two different metals have a potential difference in the same electrolyte solution, forming an electric current. The place where the current flows out is called the anode, and the place where the current flows in is called the cathode. Because the current flows into the cathode, it is protected, and the metal material is anti-corrosion. Therefore, the idea of ​​the invention is to design the tool as the anode material, and the casing and oil pipe as the cathode material. When the formation water is used as the electrolyte solution, the designed tool can be in contact with the oil pipe and casing at the same time to be electrically connected, which can effectively protect the oil casing.

[0061] 1.1 Chemical composition of materials

[0062] For aluminum alloy sacrificial anodes, the chemical composition, i.e. the type and content of alloying elements, is the most important factor affecting the performance of the anode. In the existing aluminum alloy sacrificial anodes, the main alloying elements are Zn, In, Sn, Ga, Mg, Ti, Bi, Si, Re, Ba, etc.; in addition, there may be some impurity elements in the alloy, such as Fe, Cu, Mn, etc. The commonly used activation elements are mainly: Zn, In, Sn, Bi, Ga, Mg, etc. These elements all shift the potential of the aluminum alloy negatively to a certain extent, improving the current efficiency of the anode dissolution. The main function of elements such as Ti, Zr, B, N, and Re is to refine the grains.

[0063] Zn is the most important alloying element for preparing aluminum alloy sacrificial anodes. The presence of Zn promotes the generation of ZnAl2O4, increases the defects in the protective layer, and together with other alloying elements (In, Sn, Bi), effectively reduces the stability of the oxide film on the surface of pure aluminum, thereby obtaining the necessary performance of the sacrificial anode. Zinc, as the main alloying element of aluminum alloy anodes, makes aluminum anodes have the following main characteristics: easy alloying, uniform composition; negative potential shift of 0.1 to 0.3V; easy activation, and the product is easy to fall off. The recommended Zn content in the present invention is 4% to 8%.

[0064] In can slow down the pitting of aluminum anode and make the surface corrosion more uniform. Indium has very low solubility in aluminum. Controlling it in the range of 0.02-0.03% can effectively improve the activity of aluminum and shift its potential negatively. Adding a small amount of indium can reduce the alloy potential by about 0.4 volts and significantly improve the current efficiency. However, when it is higher than 0.03%, self-corrosion increases and the efficiency decreases significantly. At the same time, indium can also inhibit the adverse effects of harmful impurities such as Fe, Si, and Cu on aluminum anode. The recommended In content in the present invention is 0.02% to 0.03%.

[0065] The solubility of Mg in Al is 1.5% at room temperature. In the ternary alloy, the addition of Mg helps to improve the cathodic protection characteristics of the alloy. To obtain the desired performance, the key is to control the maximum concentration of Mg, because excessive Mg easily reacts with Al to form an intermediate product Mg3Al2 with anode characteristics. This intermediate product will cause intergranular corrosion and is not conducive to improving current efficiency. Other research results have also confirmed that Mg can change the microstructure of the aluminum alloy anode, which is beneficial to its uniform dissolution and polarization properties, thereby improving the cathodic protection performance. The recommended Mg content in the present invention is 0.05% to 1.5%.

[0066] Adding a small amount of Ti to the Al alloy can form TiAl3 with a high melting point, and TiAl3 will form a large number of fine grains before the alloy crystallizes and acts as a foreign nucleus, thereby refining the aluminum alloy grains and solid solution structure, making the alloy elements dissolve evenly and improving the capacitance and current efficiency, and reducing intergranular corrosion and casting hot cracking. Therefore, the surface dissolution state of the aluminum anode with titanium added is better when used at high temperatures. The Al content recommended in the present invention is 0.01% to 0.06%.

[0067] The main function of element B is to refine the grains. Its solid solubility in aluminum is very small. The maximum solid solubility is only 0.022% at 660°C, and it will decrease with decreasing temperature. By continuously testing the polarization curve, it can be concluded that the boron content should be controlled in the range of 0.01-0.1%, among which the mass ratio of Ti / B is controlled in the range of 3-5, and the polarization curve obtained is the best.

[0068] When the Si content is between 0.041% and 0.212%, it helps to reduce galvanic corrosion, reduce the anode potential to a certain extent, and improve the cathodic protection characteristics; while the presence of too much Si will have the opposite effect, causing non-uniform corrosion and increasing the tendency of galvanic corrosion.

[0069] When the Fe content is high, FeAl3 will be formed, which will increase the tendency of pitting corrosion, thereby reducing the cathodic protection characteristics. In the anode prepared with 99% Al, Fe can prevent In from diffusing into Al and forming the Al-In alloy surface, so that In cannot play an activation role. However, the presence of a small amount of Fe is beneficial, especially in Al-Zn-In alloys, it can improve the tendency of galvanic corrosion. In the present invention, the recommended Fe content is ≤0.15%.

[0070] In addition to being an activator, Bi can also be added to aluminum alloy anodes with other elements as activators to help improve the cathodic protection performance. Expensive heat treatment can be avoided by adding a small amount of Bi to the Al-Zn-Sn alloy. The role of Bi is to increase the solubility of Sn in Al and refine the grains by expanding the Al lattice. Compared with other anodes that require heat treatment, the cathodic protection performance is improved. The present invention recommends a Bi content of 0.2 to 0.6%.

[0071] 1.2 Electrochemical performance

[0072] The material has the recommended chemical composition as above, and the remaining chemical composition is Al. The main elements are Al-Zn-In-Mg-Ti-B. Through continuous laboratory practice, the typical composition is Al-5Zn-0.02In-1.0Mg-0.04Ti-0.014B-0.15Si-0.15Fe-0.3Bi. Its electrochemical performance test is as follows:

[0073] Table 1 Electrochemical properties of Al-5Zn-0.02In-1.0Mg-0.04Ti-0.014B-0.15Si-0.15Fe-0.3Bi

[0074]

[0075] 1.3 Temperature resistance

[0076] In a corrosive environment with a temperature of 95°C, a pH value of 5.5, and formation water as the corrosive medium, the test lasted for 6 hours. The material was made into hanging pieces with carbon steel material (oil casing material), and connected with metal nuts and placed in the above corrosive environment. Figure 6 It can be seen that at 95°C, slight pitting corrosion occurred on the surface of the aluminum alloy anode material, but it played a good protective role on the carbon steel coupons.

[0077] 1.4 Smelting process

[0078] The basic requirements for aluminum alloy materials during smelting are: shorten the smelting time as much as possible, accurately control the chemical composition, and minimize smelting losses. The correctness of the smelting process is closely related to the quality of the ingot and the quality of post-processing. Therefore, developing a suitable smelting process is crucial to reducing casting defects such as component segregation and shrinkage holes and improving the quality of the ingot.

[0079] After a large number of experiments, the addition forms of various alloying elements in aluminum alloys and zinc alloys, smelting temperature and time, selection of refining agents, etc. were determined, and the matters that should be paid attention to during the smelting process were clarified:

[0080] (1) Since the melting point of the alloying element Ti is as high as 1648°C, the alloying elements Ti and B considered in this experiment are added in the form of TiO2 and B2O3 to reduce the addition temperature of the alloying elements.

[0081] According to the alloy formula, weigh various alloy elements and wrap them tightly with aluminum foil. Set the temperature of the resistance furnace at 760℃, heat the aluminum ingot with the furnace until it is completely melted, press it into the molten aluminum water at different temperatures according to the melting points of each alloy element, stir it several times, and lightly sprinkle a layer of charcoal powder on the surface to prevent metal oxidation and reduce burning loss. After standing in the furnace for 10 minutes, add the refining agent ZnCl2, stir gently to mix evenly, drain with carbon rods after slagging, cast in a cast iron mold, and cool naturally (before using the mold, apply graphite on its surface to prevent the ingot from sticking to the mold).

[0082] (2) Notes:

[0083] a. Use carbon rods to stir thoroughly before pouring to reduce component segregation;

[0084] b. When the charge is fully melted in the crucible and the melt temperature reaches the melting temperature, add ZnCl2 to the melt, stir and refine, and remove the large amount of oxide slag floating on the surface of the melt. The slag removal should be smooth to prevent the slag from being drawn into the melt. The slag removal should be thorough, because the presence of slag will increase the gas content of the melt and dirty the metal;

[0085] c. There is a burnout of metal elements during the smelting process, so the amount of raw materials to be weighed should be calculated based on the burnout rate of different alloys;

[0086] d. During casting, ensure that the metal liquid is continuously and smoothly injected into the mold;

[0087] e. Mark the alloy name on the cast ingot to avoid confusion.

[0088] The main raw materials and purity of the laboratory are as follows for reference:

[0089] Table 2 Main materials used in the experiment

[0090]

[0091] Example

[0092] At a well depth of 2200m to 2700m, install the oil casing anti-corrosion nipple in 273.05mm×11.43mm 140V BC casing and 88.90mm×6.45mmP110 tubing. The options are as follows:

[0093] (1) Integral oil casing anti-corrosion short section installed at the coupling

[0094] The inner diameter of the anti-corrosion cylinder is 114.3mm (outer diameter of the oil pipe coupling), the thickness is 5mm, the outer diameter is 124.3mm, the length is 100mm, the number of spring leaves is 12, the length is 80mm, the thickness is also 5mm, the fan-shaped uniform distribution, the end is a dovetail structure, and the cross-sectional diameter of the anti-corrosion cylindrical ball is 12mm.

[0095] (2) Split oil casing anti-corrosion short section installed on the pipe body

[0096] The taper of the conical anti-corrosion cylinder and the conical sleeve is 1:5, the inner diameter of the conical anti-corrosion cylinder is 88.9mm, the minimum wall thickness is 5mm, the small end diameter is 98.9mm, the length is 300mm, the height of the conical sleeve is 30mm, the outer diameter is 118.9mm, the number of spring leaves is 8, the length is 80mm, the strips are evenly distributed, the end is a dovetail structure, and the cross-sectional diameter of the anti-corrosion cylindrical ball is 10mm.

[0097] In summary, the present invention provides an oil casing anti-corrosion short joint, which adopts aluminum alloy sacrificial anode material, does not require any external power supply, and enhances its wide application. At the same time, it has little or no interference to the stray current generated by the adjacent structures; and the material cost is very low, the output current of the sacrificial anode material has a certain self-regulating ability, the protection current is evenly distributed, and the utilization rate is high; the design of the oil casing anti-corrosion short joint is flexible in structure, simple in construction and installation, and does not require maintenance, and can simultaneously protect the oil pipe and casing from corrosion.

[0098] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An oil casing anti-corrosion short joint, characterized in that: The invention comprises an anti-corrosion tube (1), one end of which is provided with a spring sheet (2), the spring sheet (2) comprising a plurality of spring sheets (2), one end of the plurality of spring sheets (2) being arranged along the circumference of the anti-corrosion tube, and the other end of each spring sheet (2) being correspondingly provided with an anti-corrosion cylindrical ball (3) as an anode material, which is electrically connected with a casing and an oil pipe as cathode materials when formation water is used as an electrolyte solution.

2. The oil casing anti-corrosion nipple according to claim 1, characterized in that: The interior of the anti-corrosion cylindrical ball (3) is a dovetail structure corresponding to the end of the spring sheet (2), and the diameter of the anti-corrosion cylindrical ball (3) is 10 to 15 mm.

3. The oil casing anti-corrosion nipple according to claim 1, characterized in that: A through groove (4) is arranged on the outer side of the anti-corrosion cylinder (1) along the longitudinal direction of the anti-corrosion cylinder.

4. The oil casing anti-corrosion nipple according to claim 3, characterized in that: The width of the through groove (4) is 5 to 10 mm, and the inner diameter of the through groove (4) is the outer diameter of the oil pipe body.

5. The oil casing anti-corrosion nipple according to claim 1, characterized in that: The anti-corrosion cylinder (1) is of a conical structure, the spring sheet (2) is connected to the anti-corrosion cylinder (1) via a conical sleeve (5), and the taper range of the anti-corrosion cylinder (1) and the conical sleeve (5) is 1:(16-4).

6. The oil casing anti-corrosion nipple according to claim 5, characterized in that: The height of the conical sleeve (2) is 30 to 50 mm, the minimum wall thickness of the anti-corrosion tube (1) is 5 to 10 mm, and the length is 200 to 300 mm.

7. The oil casing anti-corrosion nipple according to claim 1, characterized in that: The anti-corrosion cylinder (1) is a cylindrical structure, and the spring sheet (2) and the anti-corrosion cylinder (1) are an integrated structure.

8. The oil casing anti-corrosion nipple according to claim 7, characterized in that: The wall thickness of the anti-corrosion tube (1) is 5 to 10 mm, and the length of the anti-corrosion tube (1) is 20 to 50 mm shorter than the length of the coupling.

9. The oil casing anti-corrosion nipple according to claim 1, characterized in that: The number of the spring sheets (2) is 4 to 12, and the shape of the spring sheets (2) is a rectangular strip structure or a fan-shaped structure.

10. The oil casing anti-corrosion nipple according to any one of claims 1 to 9, characterized in that: Calculated by mass percentage, the anti-corrosion cylinder (1) is prepared by using 4% to 8% Zn, 0.02% to 0.03% In, 0.05% to 1.5% Mg, 0.01% to 0.06% Al, 0.041% to 0.212% Si, Fe content ≤ 0.15%, and 0.2% to 0.6% Bi.

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