Aluminum-based zinc-based composite sacrificial anode resistant to high-temperature oil well environment

Abstract

The application discloses a high-temperature-resistant aluminum-zinc-based composite sacrificial anode in an oil well environment and a preparation method thereof, wherein the composite sacrificial anode is provided with an aluminum-based sacrificial anode as an inner layer anode and a zinc-based sacrificial anode as an outer layer anode; the aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, and the zinc-based sacrificial anode is zinc-aluminum-magnesium. The sacrificial anode has superior performance and excellent electrochemical performance in the environment of high-temperature oil well produced liquid, has higher electric capacity and current efficiency, and the alloy surface dissolves uniformly without local serious corrosion holes, so that the electrochemical protection of downhole oil and gas facilities is suitable, and the purpose of corrosion control is achieved.

Description

Technical Field

[0001] This invention relates to the field of corrosion control technology for marine engineering and energy equipment, and in particular to an aluminum-zinc composite sacrificial anode resistant to high-temperature oil well environments. Background Technology

[0002] With the increasing demands of oil and gas resource development, more and more corrosion problems in oil and gas working environments need to be addressed. The working environment in thermal recovery blocks of oilfields is harsh, characterized by strong corrosiveness, high temperature, high pressure, and high-temperature, high-pressure mixed fluids, often accompanied by corrosive gases such as CO2 and H2S. Electrochemical corrosion of the tubing in thermal recovery wells is severe, easily leading to tubing perforation, leakage, and annular pressure, resulting in wellbore integrity failure and affecting normal development and production. Corrosion inhibitors, however, have poor temperature resistance and are ineffective in high-temperature environments.

[0003] Sacrificial anode technology has good applicability in corrosion control of thermal oil wells. Among them, sacrificial anodes are widely used in marine environments due to their advantages such as negative driving potential, large capacitance, good anodic dissolution activity, high current efficiency, and long service life. However, research in certain special application areas, such as high-temperature oil and gas wells and oily wastewater environments, is still not mature and complete. Under field oil and gas well conditions, traditional aluminum-based sacrificial anodes (such as aluminum-zinc-indium and aluminum-zinc-silicon systems) perform poorly in high-salinity, highly corrosive oil and water media and high-temperature environments. Severe pitting occurs on the anode surface, current efficiency decreases, and oil well production equipment is not effectively protected, leading to an urgent need to develop sacrificial anode materials for high-temperature oil and gas well operating environments.

[0004] Zinc alloys are commonly used anode materials, possessing advantages such as abundant resources, simple manufacturing processes, and excellent electrochemical performance. Furthermore, zinc alloys have a low melting point, good fluidity, and are corrosion-resistant in the atmosphere. However, the environmental medium and temperature significantly affect the electrochemical performance of zinc-based sacrificial anodes during use. For example, in high-temperature seawater environments above 70°C, the potential of a conventional zinc anode relative to the protected steel material reverses, resulting in the steel material no longer being protected and instead experiencing accelerated corrosion. The application of ordinary zinc alloys in high-temperature environments is limited; therefore, the development of zinc-based sacrificial anodes suitable for thermal oil wells primarily requires addressing the electrode operating potential issue.

[0005] Due to the high temperatures and harsh environment in downhole environments, conventional aluminum-based and zinc-based sacrificial anodes perform poorly under these conditions, easily exhibiting intergranular corrosion, low current efficiency, and shortened anode lifespan. Therefore, it is necessary to develop new sacrificial anodes suitable for high-temperature and highly corrosive downhole environments.

[0006] Considering capacitance and service life, aluminum-based sacrificial anodes are suitable for high-temperature downhole environments. However, their electrochemical activity is relatively low, easily leading to local passivation and low current efficiency. Therefore, it is necessary to first develop aluminum-based sacrificial anodes suitable for high-temperature downhole environments. Furthermore, in the electrochemical protection system composed of the sacrificial anode and the protected metal, a large cathode current is required initially to polarize the cathode surface and form a stable protective film to reduce the cathodic protection maintenance current. Therefore, it is necessary to develop composite anodes to meet the cathodic protection current output requirements at different stages. Currently, the commonly used outer activation anode of sacrificial anodes is magnesium-based. However, its activity is too high in high-temperature produced fluid environments, and the time required to generate an initial stable polarization state inevitably increases the time required for the outer anode system, which is difficult to achieve in the confined space of an oil well. Therefore, it is necessary to develop composite sacrificial anodes suitable for high-temperature produced fluid environments. Summary of the Invention

[0007] In order to solve the problems of low current efficiency, short service life and passivation of traditional sacrificial anodes in high temperature, high pressure, high mineralization and strong corrosion environments, this invention provides an aluminum-zinc composite sacrificial anode suitable for high temperature oil well environments and high temperature and high corrosion gasoline well environments.

[0008] To achieve the above-mentioned objective, this invention provides an aluminum-based and zinc-based composite sacrificial anode for use in high-temperature oil well environments. The composite sacrificial anode has an aluminum-based sacrificial anode as the inner anode and a zinc-based sacrificial anode as the outer anode. The aluminum-based sacrificial anode contains aluminum, zinc, indium, tin, gallium, and bismuth, while the zinc-based sacrificial anode contains zinc, aluminum, and magnesium.

[0009] The aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, with the following specific composition and mass percentage: Al content 92-98%, Zn content 1-5%, In content 0.01-0.06%, Ga content 0.01-0.06%, Sn content 0.01-0.12%, and Bi content 0.08-0.22%. The zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Zn content 98-99.9%, Al content 0.2-0.6%, and Mg content 0.03-0.18%.

[0010] Preferably, the aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, with the following specific composition and mass percentage: Al content 95-96%, Zn content 3-4%, In content 0.02-0.05%, Ga content 0.02-0.05%, Sn content 0.02-0.1%, and Bi content 0.1-0.2%. The zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Zn content 99.35-99.65%, Al content 0.3-0.5%, and Mg content 0.05-0.15%.

[0011] Preferably, the aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, and its specific composition and mass percentage are: Zn content 4.0%, In content 0.035%, Ga content 0.02%, Sn content 0.03%, Bi content 0.1%, and Al as the balance; The zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are as follows: Al content 0.35%, Mg content 0.079%, and Zn as the balance.

[0012] To better achieve the above-mentioned objectives, the present invention also provides a method for preparing a composite sacrificial anode, which includes the following steps: Step S1: Place aluminum ingots and zinc ingots with a mass ratio of 24:0.5-3 into a crucible and heat to 700℃-800℃. After they are completely melted, stir to disperse them evenly. Quickly press a small amount of elements In, Ga, Sn, and Bi wrapped in aluminum foil into the melt and stir to disperse them evenly. Keep the temperature at 700℃-800℃ for 0.8-1.5 hours. Stir intermittently during the holding period. Preferably, stir once every 15-25 minutes during the holding period, and the stirring time is 2-4 minutes. Step S2: After the heat preservation is completed, the melt is cooled to 620℃-660℃, the oxide layer on the upper layer of the melt is removed, and then it is poured into a preheated mold. After cooling at room temperature, it is taken out to obtain the inner anode. Step S3: Using the inner anode obtained in step S2 as the core, heat the resistance furnace to 620℃-680℃, and add zinc, aluminum and magnesium metal elements according to the weight percentage into the mold so that the outer layer of the inner anode is coated with zinc-aluminum-magnesium outer anode, forming the composite sacrificial anode.

[0013] The entire preparation process described above utilizes high-purity argon gas for protection, ensuring precise composition control. Furthermore, after obtaining the composite sacrificial anode in step S3 of the preparation method, a nano-surface treatment can be performed using mechanical grinding. Specifically, bearing steel balls are used as projectiles, and the driving device vibrates at a frequency of 20-50 Hz. The composite sacrificial anode surface is treated under vacuum conditions for 15-30 minutes. This surface mechanical grinding technology can obtain a special structure on the zinc-aluminum-magnesium alloy surface, characterized by nanocrystalline surfaces and a gradient increase in grain size along the thickness direction. This surface nano-treatment not only refines the grains but also increases the grain boundary volume ratio of the nanocrystalline layer, leading to a faster electrochemical reaction rate. This effectively improves the electrochemical activity of the surface alloy and enhances the driving current during the initial operation of the composite sacrificial anode. In addition, this surface structure also makes the anode surface corrosion more uniform, inhibits localized corrosion, and improves the overall performance of the anode.

[0014] The beneficial effects of this invention are: the sacrificial anode of this invention can exhibit superior performance and excellent electrochemical performance in the environment of high-temperature oil well produced fluid, with high capacitance and current efficiency, uniform dissolution on the alloy surface, no localized severe corrosion pores, and is suitable for electrochemical protection of downhole oil and gas facilities to achieve the purpose of corrosion control. Attached Figure Description

[0015] Figure 1 The working potential of the aluminum-zinc composite sacrificial anode in the produced fluid of an oil well at 80℃ changes over time in the experimental example.

[0016] Figure 2 The capacitance of the aluminum-zinc composite sacrificial anode in the produced fluid of an oil well at 80°C is given in the experimental example.

[0017] Figure 3 The current efficiency of the aluminum-zinc composite sacrificial anode in the produced fluid of an oil well at 80°C is shown in the experimental example.

[0018] Figure 4 These are the front and back morphology images of the outer zinc-based anodic corrosion in the experimental example.

[0019] Figure 5 These are the front and back morphology images of the inner aluminum-based substrate after anodic corrosion in the experimental example. Detailed Implementation

[0020] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0021] Example 1 This invention provides an aluminum-based and zinc-based composite sacrificial anode for use in high-temperature oil well environments. The composite sacrificial anode uses an aluminum-based sacrificial anode as the inner anode and a zinc-based sacrificial anode as the outer anode. The inner aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, and its specific composition and mass percentage are: Zn content 4.0%, In content 0.035%, Ga content 0.02%, Sn content 0.03%, Bi content 0.1%, and Al as the balance; The outer zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Al content 0.35%, Mg content 0.079%, and Zn as the balance.

[0022] Example 2 This invention provides an aluminum-based and zinc-based composite sacrificial anode for use in high-temperature oil well environments. The composite sacrificial anode uses an aluminum-based sacrificial anode as the inner anode and a zinc-based sacrificial anode as the outer anode. The inner aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, and its specific composition and mass percentage are: Zn content 3%, In content 0.05%, Ga content 0.05%, Sn content 0.1%, Bi content 0.2%, and Al as the balance; The outer zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Al content 0.5%, Mg content 0.15%, and Zn as the balance.

[0023] Example 3 This invention provides an aluminum-based and zinc-based composite sacrificial anode for use in high-temperature oil well environments. The composite sacrificial anode uses an aluminum-based sacrificial anode as the inner anode and a zinc-based sacrificial anode as the outer anode. The inner aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, with the following specific composition and mass percentage: Zn content 5%, In content 0.06%, Ga content 0.03%, Sn content 0.08%, Bi content 0.22%, and Al as the balance; The outer zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Al content 0.3%, Mg content 0.05%, and Zn as the balance.

[0024] Example 4 The aluminum-based sacrificial anode is aluminum-zinc-indium-tin-gallium-bismuth, and its specific composition and mass percentage are as follows: Zn content 1%, In content 0.01%, Ga content 0.06%, Sn content 0.01%, Bi content 0.08%, and Al as the balance; The zinc-based sacrificial anode is zinc-aluminum-magnesium, and its specific composition and mass percentage are: Al content 0.2%, Mg content 0.03%, and Zn as the balance.

[0025] Example 5 This invention provides a method for preparing an aluminum-based and zinc-based composite sacrificial anode resistant to high-temperature oil well environments, the method comprising the following steps: Step S1: Place 24:1 aluminum ingots and zinc ingots into a crucible, and place the crucible in a resistance furnace and heat it to 750°C. After it is completely melted, stir it with a stirring rod for 2 minutes to disperse it evenly. Quickly press a small amount of elements In, Ga, Sn, and Bi wrapped in aluminum foil into the melt, and stir it with a graphite stirring rod for 3 minutes to disperse it evenly. Then keep it at 750°C for 1 hour, stirring it once every 20 minutes for 3 minutes. Step S2: After the heat preservation is completed, the melt is cooled to 650°C. The oxide layer on the top of the melt is removed with a slag scraper and poured into a mold preheated to 200°C. After cooling to room temperature, it is taken out and the inner anode is obtained. Step S3: Using the inner anode obtained in step S2 as the core, when the resistance furnace is heated to 650°C, zinc, aluminum, and magnesium metal elements are added to the mold according to the weight percentage, so that the outer layer of the inner anode is coated with a zinc-aluminum-magnesium outer anode, forming a composite sacrificial anode; wherein, the ratio of aluminum ingots to zinc ingots, and the mass ratio of the mixed mass of zinc, aluminum, and magnesium metal elements to the mass of the inner anode are determined by the elements of the final composite sacrificial anode and the losses in the smelting process; Step S4: Perform nano-surface treatment on the composite sacrificial anode from step S3 using mechanical grinding; bearing steel balls can be used as projectiles, the vibration frequency of the driving device is 50Hz, and the surface of the composite sacrificial anode is treated under vacuum conditions for 15 minutes.

[0026] The aluminum-based zinc-based composite sacrificial anodes for high-temperature oil well environments mentioned in Examples 1-5 can be prepared using the method described in this embodiment.

[0027] Experimental Example The electrochemical protection performance of the outer zinc-aluminum-magnesium anode and the inner aluminum-zinc-indium-tin-gallium-bismuth anode of the high-temperature resistant aluminum-zinc composite sacrificial anode obtained in Example 1 was tested according to the standard test method specified in GB / T 17848-1999.

[0028] In a high-temperature, high-salinity (18984 mg / L), CaCl2-water type oilfield produced fluid environment at 80℃, the open-circuit potential of the outer zinc-aluminum-magnesium anode was tested to be -1.042V (relative to a saturated calomel electrode), which ranges from -0.99V to -1.05V (see...). Figure 1It can be seen that the high-temperature resistant zinc-based anode developed did not exhibit potential reversal. Figure 2 The actual capacitance is displayed as 727.5 A•h / Kg, which is greater than 720 A•h / kg, and the current efficiency exceeds 85% (see...). Figure 3 ).Depend on Figure 4 It is evident that the outer anodic dissolution morphology is extremely uniform, and the corrosion products are relatively easy to detach, which can well meet the performance requirements of sacrificial anodes in high-temperature downhole environments; Similarly, in a high-temperature, high-mineralization (18984 mg / L), CaCl2-water type oilfield produced fluid environment at 80℃, the open-circuit potential of the inner aluminum-zinc-indium-tin-gallium-bismuth anode is -1.062 V (relative to a saturated calomel electrode), which ranges from -1.01 V to -1.046 V (relative to a saturated calomel electrode) (see...). Figure 1 ), Figure 3 Its actual capacitance is 2332 A·h / Kg, which is greater than 2000 A·h / kg, and its current efficiency reaches 80.3% (see...). Figure 3 (), exceeding 75%. By Figure 5 It is evident that the corrosion dissolution morphology on the inner anode surface is relatively uniform, the corrosion products are easily detached, and there are no localized corrosion pits, which well meets the performance requirements of sacrificial anodes for high-temperature downhole environments.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum-based and zinc-based composite sacrificial anode suitable for high-temperature oil well environments, characterized in that, The composite sacrificial anode uses an aluminum-based sacrificial anode as the inner anode and a zinc-based sacrificial anode as the outer anode.

2. The composite sacrificial anode according to claim 1, characterized in that, The aluminum-based sacrificial anode contains aluminum, zinc, indium, tin, gallium, and bismuth, while the zinc-based sacrificial anode contains zinc, aluminum, and magnesium.

3. The composite sacrificial anode according to claim 2, characterized in that, The specific composition and mass percentage of the aluminum-based sacrificial anode are as follows: Al content 92-98%, Zn content 1-5%, In content 0.01-0.06%, Ga content 0.01-0.06%, Sn content 0.01-0.12%, and Bi content 0.08-0.22%. The specific composition and mass percentage of the zinc-based sacrificial anode are as follows: Zn content 98-99.9%, Al content 0.2-0.6%, and Mg content 0.03-0.18%.

4. The composite sacrificial anode according to claim 2, characterized in that, The specific composition and mass percentage of the aluminum-based sacrificial anode are as follows: Al content 95-96%, Zn content 3-4%, In content 0.02-0.05%, Ga content 0.02-0.05%, Sn content 0.02-0.1%, and Bi content 0.1-0.2%. The specific composition and mass percentage of the zinc-based sacrificial anode are as follows: Zn content 99.35-99.65%, Al content 0.3-0.5%, and Mg content 0.05-0.15%.

5. The composite sacrificial anode according to claim 2, characterized in that, The specific composition and mass percentage of the aluminum-based sacrificial anode are as follows: Zn content 4.0%, In content 0.035%, Ga content 0.02%, Sn content 0.03%, Bi content 0.1%, and Al as the balance; The specific composition and mass percentage of the zinc-based sacrificial anode are as follows: Al content 0.35%, Mg content 0.079%, and Zn as the balance.

6. The method for preparing the composite sacrificial anode according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Step S1: Heat the crucible containing aluminum and zinc ingots to 700℃-800℃. After they are completely melted, stir to disperse them evenly. Quickly press the elements In, Ga, Sn, and Bi into the melt, stir to disperse them evenly, and keep it at 700℃-800℃ for 0.8-1.5 hours with intermittent stirring. Step S2: After the heat preservation is completed, the melt is cooled to 620℃-660℃, the oxide layer on the upper layer of the melt is removed, and then it is poured into a preheated mold. After cooling at room temperature, it is taken out to obtain the inner anode. Step S3: Using the inner anode obtained in step S2 as the core, heat the resistance furnace to 620℃-680℃, and add zinc, aluminum and magnesium metal elements according to the weight percentage to the mold so that the outer layer of the inner anode is coated with zinc-aluminum-magnesium outer anode to form the composite sacrificial anode.

7. The method for preparing the composite sacrificial anode according to claim 6, characterized in that, In the preparation method, after obtaining the composite sacrificial anode in step S3, a nano-surface treatment is performed by mechanical grinding.

8. The method for preparing the composite sacrificial anode according to claim 7, characterized in that, The nano-surface treatment specifically involves using bearing steel balls as projectiles to treat the surface of the composite sacrificial anode under vacuum conditions for 15-30 minutes.

9. The method for preparing the composite sacrificial anode according to claim 6, characterized in that, The mass ratio of aluminum ingots to zinc ingots in step S1 is 24:0.5-3.

10. The method for preparing the composite sacrificial anode according to claim 6, characterized in that, In step S1, the mixture is stirred once every 15-25 minutes during the heat preservation period, with a stirring time of 2-4 minutes.

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