Multi-stage opening long-acting packing device and method based on metal-cement sheath sealing

Abstract

According to the multi-stage opening long-acting packing device and method based on metal-cement sheath sealing, in the well cementation process of different opening times, when a casing pipe is tripped into different positions of a shaft, CO2 is injected or in the long-term storage process, when annulus pressure occurs in the shaft, according to the storage position and integrity analysis of the shaft, the sealing time of the casing pipe is shortened, and the sealing time of the casing pipe is shortened. A pre-embedded device on the upper portion of the leakage position is selected, the low-melting-point alloy is melted in the mode of injecting high-temperature steam, meanwhile, thermal expansion fluid drives the low-melting-point alloy to be squeezed into the sealing integrity failure position, and then the low-melting-point alloy flows into a micro annular space or a micro crack to achieve material blocking. The expansion effect in the solidification process of the low-melting-point alloy is used for achieving mechanical plugging on part of microfractures, so that a corresponding well barrier is established, and the sealing integrity of a shaft is guaranteed. And as time goes on, the corrosion effect of a bottom shaft is considered, when the annulus belt pressure occurs again, the pre-embedded devices at different positions are started in multiple stages, and the sealing integrity is guaranteed.

Description

Technical Field

[0001] This application relates to the technical field of geological storage of CO 2 specifically to a pre-buried sealing device based on a metal-cement sheath sealing mechanism and a multi-stage opening method. Background Art

[0002] CO 2 Geological storage is a technology that can effectively mitigate the global greenhouse effect, and the wellbore integrity of the storage system is the key to ensuring the success of this technology. During the implementation of CCUS projects, CO 2 is injected into the wellbore in the form of fluid from the ground and then enters the formation along the wellbore, achieving long-term geological storage while increasing production and recovery rate. However, when CO 2 is stored, the failure of wellbore integrity is one of the most likely leakage paths for CO 2 storage projects, and the test results at more and more engineering sites have also confirmed this point. It can be seen that the development of cracks in the cement sheath inside the wellbore and the failure of wellbore integrity lead to the leakage of CO 2 along the wellbore, which is the main reason for the failure of CO 2 storage in CCUS projects. A large number of engineering practices and research results show that during the implementation of CCUS projects, once CO 2 leaks, it will not only seriously threaten the safety of personnel and cause risks such as asphyxiation, but also have a significant impact on the surrounding environment, including environmental problems such as soil acidification, groundwater pollution, and exacerbation of climate change.

[0003] Regarding the process of CO 2 injection and storage, many scholars have conducted a lot of research on the factors causing the failure of wellbore integrity. Gaodeli [1] , Xuelin Dong [2] et al. showed in their research on the injection process of CO 2 that the changes in pressure and temperature inside the wellbore are the main reasons for the failure of wellbore integrity. During injection, CO 2 is usually in a liquid state and has a very low temperature. When the temperature difference between the wellbore fluid and the formation increases, the cracks at the cement sheath interface will expand and increase, easily causing the failure of wellbore integrity. And with the increase of the CO 2 injection rate, the failure of the cement sheath becomes more serious. Zhang Zhichao, Bai Mingxing [3] et al. showed in their research on CO 2 storage that when the concentration of stored CO 2 is too high and the formation temperature is too high, the corrosion of the cement sheath by CO 2 will be more serious, resulting in cracks in the cement sheath and the failure of wellbore integrity. The above research shows that in the process of CO 2 injection and storage, the problem of wellbore integrity is crucial.

[0004] To address wellbore integrity issues, many scholars have conducted research on CO 2 geological sequestration and proposed some methods to protect wellbore integrity and prevent CO 2 gas leakage. Dong Zhengliang et al. [4] proposed a multi-stage sealing structure and sealing method for preventing wellbore gas leakage (Patent No.: CN202211225107.7). This method realizes different sealing effects by setting three sealing sections, and different sealing materials can be set for each sealing section. Li Yang et al. [5] proposed a method and system for improving wellbore integrity by using thermal insulation materials (Patent No.: CN202310457988.3). This method fixes the thermal insulation materials on the inner wall of the casing to prevent low-temperature shrinkage and improve the integrity of the casing system, and is applicable to projects such as oil and gas, geothermal energy, and CO 2 storage. Li Yang et al. [6] proposed a method and system for improving wellbore integrity by heating sleeves (Patent No.: CN202310459737.9). This method prevents the shrinkage of the casing caused by low temperature by heating the casing, improves the integrity of the wellbore system, and is applicable to projects such as CO 2 storage and gas storage caverns.

[0005] In summary, the previous research on devices has the following deficiencies: (1) The previous research only considered the damage to wellbore integrity caused by temperature changes, and did not consider the effects of external adverse loads, geological changes, and cement sheath corrosion. When facing these problems, there are no reasonable repair measures for the damage to the cement sheath. (2) The previous research devices require complex construction processes and consume a large amount of time cost. When CO 2 leaks along the wellbore, the leakage situation cannot be remedied in time. If the wellbore integrity is not repaired in time, it is easy to cause a large amount of CO 2 leakage and cause more serious consequences. (3) The previous research devices consume a large amount of construction costs and also cause certain environmental pollution during the secondary construction process, which is not conducive to environmental protection.

[0006] Aiming at the problem of easy leakage of CO 2 in CCUS projects, a pre-embedded sealing device and multi-stage opening method based on the metal-cement sheath sealing mechanism are designed and developed. When the sealing integrity of the CCUS well fails and CO 2 leaks occur, by injecting heat into the wellbore, based on the mechanism of material and mechanical plugging, the effective plugging of the damaged cement sheath can be realized, a corresponding well barrier can be established, effectively preventing gases such as CO 2 from leaking along the wellbore, ensuring the safety of personnel operations, extending the life cycle of the well, and ensuring CO2 Sealing quality.

[0007] Citation

[0008] [1] Gaodeli, Liu Kui, Wang Yanbin, et al. Some research progress on the mechanical mechanism of wellbore integrity failure and design control technology in shale gas wells [J]. Acta Petrolei Sinica, 2022, 43(12): 1798 - 1812.

[0009] [2] Xuelin Dong, Zhiyin Duan, Deli Gao, Assessment on the cement integrity of CO 2 injection wells through a wellbore flow model and stress analysis, Journal of Natural Gas Science and Engineering, 2020, 74, 103097.

[0010] [3] Zhang Zhichao, Bai Mingxing, Chen Qiaozhen. Influence factors of corrosion behavior of CO 2 storage wellbores [J]. Corrosion & Protection, 2021, 42(04): 54 - 57 + 61.

[0011] [4] Dong Zhengliang, Yin Fuping, Liu Xiaobo, et al. A multi - stage sealing structure and sealing method for preventing gas leakage from wellbores [P]. Sichuan Province: CN202211225107.7, 2023 - 01 - 06.

[0012] [5] Li Yang, Liu Luoyun, Guo Zixian, et al. A method and system for improving wellbore integrity through thermal insulation materials [P]. Sichuan Province: CN202310457988.3, 2023 - 09 - 19.

[0013] [6] Li Yang, Guo Zixian, Dong Jingnan, et al. A method and system for improving wellbore integrity through a heating sleeve [P]. Sichuan Province: CN202310459737.9, 2023 - 07 - 07. Summary of the Invention

[0014] In order to overcome the above - mentioned difficulties, the present invention provides a pre - embedded sealing device and a multi - stage opening method based on the metal - cement sheath sealing mechanism. The device includes:

[0015] Casing nipple body: It includes the main casing nipple of the device. Threads are provided on both the upper and lower sides of the casing nipple, which can be directly connected to the casing string. The low-melting-point alloy system and the drive system can be fixed on the casing nipple body. At the same time, 4 symmetrical openings are provided on the casing body as drive channels.

[0016] Low-melting-point alloy system: It includes an alloy cavity sleeve outside the casing, a fixing ring, and a low-melting-point alloy. The type of alloy can be selected according to the location where the device is lowered, such as bismuth-tin alloy (melting point: 138 °C), bismuth-silver alloy (melting point: 178 °C), or other types of alloys. Part of it is sealed in the drive channel, that is, the built-in alloy, and part of it is stored in the container composed of the alloy cavity sleeve and the casing, that is, the external alloy. The built-in alloy is connected to the external alloy through the holes in the drive channel of the casing body.

[0017] Drive system: It includes a thermal expansion fluid, a drive device, and a pressure stabilizing device. Among them, the thermal expansion fluid is mainly dimethyl silicone oil, which will expand rapidly when heated, pushing the drive rod to move up and down in the drive channel; the drive device mainly includes a drive channel and a drive rod. Under the action of the thermal expansion fluid, the alloy melts and the drive rod will advance forward under the action of pressure, driving the low-melting-point alloy (liquid state after high temperature) to continuously flow out of the casing nipple; the pressure stabilizing device mainly includes a stop block, a spring, and a stop block rotating shaft. After the thermal drive fluid drives the liquid low-melting-point alloy to a certain position, the pressure stabilizing device locks, making the drive rod unable to be pushed back, and the stop block, spring, and stop block rotating shaft jointly fix the drive rod to prevent the liquid low-melting-point alloy from flowing back.

[0018] When it is detected that there is annular pressure in the cement sheath, crack propagation, or CO 2 channeling occurs, this device can be activated. The activation method of this device is as follows:

[0019] First step: According to the actual situation of different runs in the wellbore, the device is set on the casing and lowered into the wellbore together with the casing for pre-embedding. During the long-term sealing process, when it is found that there is annular pressure in the cement sheath or CO 2 carbon escapes, the devices at different positions are heated according to the damage conditions of the cement sheath in different formations to achieve the effect of multi-stage activation.

[0020] Second step: When it is detected that there is annular pressure in the cement sheath or gas channeling occurs, insert the heating tubing into the corresponding position and inject hot steam into the tubing. The high-temperature steam enters the wellbore through the holes provided on the tubing and heats the entire device through high-temperature heat conduction. 2 phenomenon, insert the heating tubing into the corresponding position and inject hot steam into the tubing. The high-temperature steam enters the wellbore through the holes provided on the tubing and heats the entire device through high-temperature heat conduction.

[0021] Step 3: After the device is heated, the internal alloy and the external alloy turn into liquid state. The volume of the thermally expandable fluid starts to expand and pushes the drive rod to squeeze the liquid low-melting-point alloy. The external liquid low-melting-point alloy is squeezed into the micro-annular gap and micro-fractures of the cement sheath, and the internal low-melting-point alloy plays a supplementary role, thereby achieving material plugging and mechanical plugging of the cement sheath.

[0022] Step 4: After the entire device stabilizes, stop injecting steam and remove the tubing. At this time, the stopper, spring, and stopper rotating shaft in the drive system jointly fix the drive rod to prevent the low-melting-point alloy from flowing back after the drive rod loses driving force, and enable the low-melting-point alloy to solidify stably between the casing and the cement sheath, ultimately achieving the repair work of the cement sheath.

[0023] And so on. When cracks appear in the cement sheath in formations at different depths, the method of injecting hot steam into the tubing can be adopted to heat the device at the corresponding formation position to repair the cement sheath in different formations, so as to achieve the purpose of multi-stage opening.

[0024] In the example of this application, the gas in the tubing should have a small specific heat capacity to improve the heating efficiency. The thermally expandable fluid should have a large coefficient of thermal expansion. Dimethyl silicone oil can be selected to facilitate pushing the drive rod and squeezing the low-melting-point alloy into the cement sheath. The low-melting-point alloy used is a bismuth-based alloy. According to the different positions of the device, bismuth-tin alloy, bismuth-silver alloy, etc. can be selected. The alloy can be quickly melted after being heated to facilitate the drive rod to push. The alloy used should have high strength and is not easily damaged after condensation.

[0025] In the example of this application, according to the actual fracturing parameters in the project and the actual size of the casing, the size and length parameters of the low-melting-point alloy can be optimized.

[0026] In the example of this application, considering the need for long-term sealing process, the number of devices in the wellbore can be optimized. At the same time, based on the installation position optimization method, the positions of multiple packers are optimized. According to different gas channeling situations in the wellbore, multi-stage opening of the devices can be achieved. 2

[0027]

[0027] Other features, advantages and process flows of the example of this application will be described in detail in the subsequent specific implementation part. Description of the Drawings

[0028] The drawings are used to provide a further understanding of the example of this application, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the example of this application, but do not constitute a limitation to the example of this application. In the drawings:

[0029] Figure 1Schematically shows the main schematic diagram of the embedded packer device and the multi-stage opening method based on the metal-cement ring sealing mechanism according to the embodiments of the present application.

[0030] Figure 2 Schematically shows the exploded view of the embedded packer device and the multi-stage opening method based on the metal-cement ring sealing mechanism according to the embodiments of the present application.

[0031] Figure 3 Schematic diagram for device embedding.

[0032] Figure 4 Steps for device startup. (a) Embedded device; (b) Cement ring rupture detected and tubing run in; (c) Heat steam startup device injected into the tubing, and the driving rod extrudes the low-melting-point alloy to repair the cement ring. (d) Tubing removed and heating stopped to complete the repair of the cement ring.

[0033] Reference numerals

[0034] Number Device Name Number Device Name 1 Body Casing Nipple 8 Block Cover Plate 2 Expansion Oil Sleeve 9 Drive Rod 3 Alloy Chamber Sleeve 10 Spring 4 Fixed Ring 11 Block Rotating Shaft 5 Low Melting Point Alloy 12 Bolt 6 Thermal Expansion Fluid 13 Block 7 Drive Channel Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the embodiments of the present application, and are not used to limit the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0036] The CCUS project is an important way to achieve "dual carbon". The injection and long-term geological sequestration of CO 2 are important stages to ensure the successful implementation of the CCUS project. However, engineering practices have shown that during the injection and long-term geological sequestration of CO 2 it is easy to leak along the wellbore, which will lead to a large amount of CO 2, which will not only seriously threaten personal safety, causing risks such as asphyxiation, but also have a significant impact on the surrounding environment, including environmental problems such as soil acidification, groundwater pollution, and exacerbating climate change. In response to the above problems, a buried isolation device and a multi-stage opening method based on the metal-cement ring sealing mechanism are designed and developed. The device can be placed at different positions in the entire wellbore by the buried method, and can be opened in multiple stages at multiple positions according to the actual gas leakage situation by injecting high-temperature steam. After opening, the low-melting-point alloy will melt under heating conditions and expand during the solidification process. The device uses the method of pressurizing the thermal expansion fluid to push the liquid low-melting-point alloy fluid to plug the micro-annular gaps and micro-fractures in the cement ring with materials and mechanics, realizing the effective plugging of the cement ring with failed sealing integrity, establishing a corresponding well barrier, and effectively preventing the leakage of gases such as CO 2 and other gases along the wellbore, ensuring the safety of personnel operations, extending the life cycle of the well, and ensuring the CO 2 sealing quality.

[0037] In the example of this application, a buried isolation device and a multi-stage opening method based on the metal-cement ring sealing mechanism are provided for CO 2 sealing to protect the integrity of the wellbore. The device is lowered into the wellbore by the buried method and is sealed at different positions in the wellbore after cementing. After the annulus pressure appears, it can be opened by injecting heat at the bottom of the well to melt the low-melting-point alloy outside the casing, realizing material plugging and mechanical plugging of the cement ring, forming a corresponding well barrier, and ensuring the sealing integrity of the wellbore.

[0038] The device includes:

[0039] Casing nipple body: It includes the main casing nipple of the device. Threads are arranged on both the upper and lower sides of the casing nipple, which can be directly connected to the casing string, and the low-melting-point alloy system and the drive system can be fixed on the nipple body. At the same time, 4 symmetric openings are provided on the casing nipple body as drive channels.

[0040] Low-melting-point alloy system: It includes an alloy cavity sleeve outside the casing, a fixing ring, and a low-melting-point alloy. The type of alloy can be selected as bismuth-tin alloy (melting point: 138 °C), bismuth-silver alloy (melting point: 178 °C) or other types of alloys according to the device's installation position. Part of the alloy is sealed in the drive channel, that is, the built-in alloy, and part is stored in the container composed of the alloy cavity sleeve and the casing nipple, that is, the external alloy. The built-in alloy and the external alloy are connected through the holes in the drive channel.

[0041] Drive system: It includes a thermal expansion fluid, a driving device, and a pressure stabilizing device. The thermal expansion fluid is mainly dimethyl silicone oil, which will expand rapidly when heated, pushing the driving rod to move up and down in the driving channel; the driving device mainly includes a driving channel and a driving rod. Under the action of the thermal expansion fluid, it will push the driving rod to advance forward in the driving channel, driving the low melting point alloy (liquid state after high temperature) to continuously flow out of the casing nipple; the pressure stabilizing device includes a stop block, a spring, and a stop block rotating shaft. After the thermal driving fluid drives the liquid low melting point alloy to a certain position, the pressure stabilizing device locks, making the driving rod unable to be pushed back. The stop block, spring, and stop block rotating shaft jointly fix the driving rod to prevent the liquid low melting point alloy from flowing back.

[0042] The method includes:

[0043] During the cementing process of different trips, the device is lowered into different positions of the wellbore along with the casing, and CO 2 Or during the long-term storage process, when there is annulus pressure in the wellbore, according to the storage position and wellbore integrity analysis, select the embedded device above the leakage position. By injecting high-temperature steam, the low melting point alloy is melted, and at the same time, the thermal expansion fluid drives the low melting point alloy to squeeze into the position where the sealing integrity fails, and then flows into the micro-annulus or micro-fractures to achieve material plugging. Utilize the expansion effect during the solidification process of the low melting point alloy to achieve mechanical plugging for some micro-fractures, thereby establishing a corresponding well barrier to ensure the sealing integrity of the wellbore. In addition, over time, considering the corrosion effect of the bottom wellbore, when annulus pressure appears again, the embedded devices at different positions can be opened in multiple stages to further ensure the sealing integrity of the entire well.

[0044] Figure 1 , Figure 2 jointly presented a schematic structural diagram of an embedded packer device based on the metal-cement sheath sealing mechanism according to an example of the present application. As Figure 1 , Figure 2 shown in the example of the present application, an embedded packer device based on the metal-cement sheath sealing mechanism and a multi-stage opening method are provided.

[0045] The device includes:

[0046] Casing nipple body: It includes the main casing nipple 1 of the device. Threads are arranged on both the upper and lower sides of the casing nipple, which can be directly connected to the casing string, and it is convenient to fix the low melting point alloy system and the drive system on the casing nipple body. At the same time, 4 symmetric openings are opened around the casing as the driving channel 7.

[0047] Low melting point alloy system: It includes an alloy cavity sleeve 3 outside the casing, a fixing ring 4, and a low melting point alloy 5. The type of alloy can be selected as bismuth-tin alloy (melting point: 138 °C), bismuth-silver alloy (melting point: 178 °C), or other types of alloys according to the device setting position. Part of it is sealed in the driving channel 7, namely the built-in alloy, and part is stored in the container composed of the alloy cavity sleeve 3 and the casing nipple 1, namely the external alloy. The built-in alloy is connected to the external alloy through the opening of the driving channel 7 on the casing body.

[0048] Driving system: It includes a thermal expansion fluid 6, a driving device, and a pressure stabilizing device. Among them, the thermal expansion fluid 6 is mainly dimethyl silicone oil, and its volume will expand rapidly when heated, pushing the driving rod to move up and down in the driving channel 7; the driving device mainly includes a driving channel 7 containing alloy and a driving rod 9. Under the action of the thermal expansion fluid 6, the driving rod 9 will be pushed forward under pressure, driving the low melting point alloy (liquid state after high temperature) to continuously flow out of the casing nipple; the pressure stabilizing device mainly includes a stop block 13, a spring 10, and a stop block rotating shaft 11. After the thermal driving fluid drives the liquid low melting point alloy to a certain position, the pressure stabilizing device locks, making the driving rod unable to be pushed back, and the stop block 13, the spring 10, and the stop block rotating shaft 11 jointly fix the driving rod to prevent the liquid low melting point alloy 5 from flowing back.

[0049] The embedding method and opening method of this device are as follows:

[0050] First step: Set this device on the casing and lower it into the formation together with the casing for embedding as Figure 3 shown. During embedding, different numbers of devices can be embedded in different runs according to different conditions of different formations. During long-term sealing, it is found that during the process of annulus pressure build-up or CO 2 carbon escape inside the cement sheath, heat different positions of the devices according to the damage conditions of the cement sheath in different formations to achieve the effect of multi-stage opening.

[0051] Second step: When it is detected that there is annulus pressure build-up in the cement sheath or CO 2 gas channeling occurs, insert the heating oil pipe into the corresponding position and inject hot steam to heat the entire device through the hot steam. After the device is heated, the volume of the thermal expansion fluid 6 in the expansion oil sleeve 2 and the main casing nipple 1 expands, and the low melting point alloy 5 turns into a liquid state.

[0052] Third step: At this time, the expanded thermal fluid 6 expands in volume and pushes the driving rod 9 in the driving channel 7. The driving rod 9 drives the liquid low melting point alloy 5. The external alloy first enters the micro-annulus and micro-fractures of the cement sheath to achieve material plugging and mechanical plugging of the cement sheath. Subsequently, the built-in alloy timely replenishes the external alloy, finally reducing the crack width inside the cement sheath and making the cement sheath more dense.

[0053] Step 4: After the cracks are stabilized, stop injecting hot steam, remove the tubing, and stop heating. The stopper 13, spring 10, and stopper rotating shaft 11 jointly fix the driving rod 9 to prevent the liquid low-melting-point alloy 5 from flowing back, enabling the liquid alloy to solidify stably, and finally realizing the repair of the cement sheath.

[0054] The entire technological process of this device is as Figure 4 shown;

[0055] Through the above technical solution, the thermal expansion fluid system and the low-melting-point alloy system are heated together, causing the fluid to expand and push the low-melting-point alloy into the micro-annular gaps and micro-fractures of the cement sheath through the driving rod in the driving system, thereby achieving material plugging and mechanical plugging of the cement sheath. Through the combined action of material plugging and mechanical plugging, the density of the cement sheath can be greatly enhanced, and the cracks inside the cement sheath can be reduced. By adopting the above technical solution, the integrity of the wellbore can be maintained. When cracks appear in the cement sheath, the range of the cracks can be reduced by heating, avoiding the escape of CO 2 When the cement sheath is affected by external factors (such as CO 2 erosion, formation activities) resulting in the development of cracks in the cement sheath and the destruction of the wellbore integrity, the above device can also be used to treat the cracks inside the cement sheath. This device effectively avoids a large amount of construction costs caused by repairing the wellbore, and can timely take repair measures for the cracks inside the cement sheath, avoiding missing the best opportunity for repairing the wellbore due to time issues and preventing the escape of CO 2 According to the size of the wellbore and the relevant parameters of the casing (such as wall thickness, diameter, length, etc.), as well as the actual fracturing parameters in the project, the thickness, length, and other parameters of the low-melting-point alloy can be flexibly adjusted. Considering the needs of the long-term geological storage process of CO 2 the number of inner sleeves of this packer device is optimized, and at the same time, the positions of multiple packer devices can be optimized based on the installation position optimization method to form a packer device that can be opened in multiple stages.

[0056] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or elements inherent to such process, method, commodity or device. Without further limitations, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, commodity or device including the element.

[0057] The above are only examples of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A multi-stage opening long-term isolation device based on metal-cement ring seal, characterized by: include: Casing nipple body: including the casing nipple; the upper and lower sides of the casing nipple are both provided with threads, which are directly connected to the casing string, and the low melting point alloy system and the driving system are fixed on the casing nipple body, and four symmetrical openings are provided on the casing nipple body as driving channels; Low melting point alloy system: including alloy cavity sleeve, fixing ring and low melting point alloy outside the casing; the type of alloy is selected from bismuth-tin alloy, bismuth-silver alloy or other types of alloy according to the position of the device; a part is sealed in the driving channel, i.e., built-in alloy, and a part is stored in a container composed of alloy cavity sleeve and casing, i.e., external alloy; the built-in alloy and the external alloy are connected through the hole of the driving channel on the casing body; Driving system: including thermal expansion fluid, driving device, and voltage stabilizing device; the thermal expansion fluid is dimethyl silicone oil, which will expand rapidly after being heated, and push the driving rod to move up and down in the driving channel; the driving device includes a driving channel and a driving rod; under the action of the thermal expansion fluid, the driving rod will move forward under the action of pressure, driving the low-melting-point alloy to continuously flow outside the short section of the casing; the voltage stabilizing device includes a block, a spring and a block shaft. After the driving rod pushes the liquid low-melting-point alloy to a certain position, the voltage stabilizing device is locked, so that the driving rod cannot be pushed back, and the block, spring and block shaft jointly fix the driving rod to prevent the liquid low-melting-point alloy from flowing back.

2. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: The low melting point alloy should have the characteristics of low melting point and high strength. The low melting point alloy can be a bismuth-based alloy; bismuth-tin alloy, bismuth-silver alloy and other types of alloys can be selected according to different insertion positions.

3. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: In the low-melting-point alloy system, the thickness and length of the alloy are dynamically adjusted according to the specifications of the casing and the size of the wellbore. The thickness and length of the low-melting-point alloy in the isolation device are optimized according to the actual fracturing parameters in the project.

4. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: The driving system has driving properties, and the holes in the sleeve should be kept smooth so that the thermal expansion fluid can easily push the driving rod to move; when the heating is stopped, the block, spring, and block shaft jointly fix the driving rod to prevent the liquid low-melting-point alloy from flowing back, so that the liquid low-melting-point alloy can solidify stably.

5. The multi-stage opening long-term isolation device based on metal-cement ring seal according to claim 1 is characterized in that: Dimethyl silicone oil is selected as the thermal expansion fluid.

6. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: When the device is pre-buried, one or more pre-buried devices are lowered into different openings respectively, but the temperature of the stratum into which they are lowered cannot exceed 75% of the liquefaction temperature of the low-melting-point alloy; when the cement sheath of the corresponding opening at the corresponding depth is damaged, the devices at different positions are started to achieve a multi-stage opening effect to protect the integrity of the cement sheath itself.

7. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: Considering the needs of long-term CO2 storage process, the number of devices in the wellbore is optimized; based on the installation position, the positions of multiple isolation devices are optimized, and the multi-stage opening of the devices is achieved according to the gas blowby conditions at different positions in the wellbore.

8. The multi-stage opening long-term isolation device based on metal-cement ring sealing according to claim 1 is characterized in that: The method of opening the device is as follows: Step 1: According to the actual situation of different wellbore opening times, the device is installed on the casing and buried underground with the casing to achieve pre-embedding; during the long-term sealing process, it is found that the annular space pressure is generated inside the cement ring. After the CO2 carbon escapes, the devices at different positions are heated according to the damage of the cement ring in different formations to achieve the effect of multi-stage opening; Step 2: When annular pressure or CO2 blowby is detected in the cement sheath, the oil pipe used for heating is extended into the corresponding position and hot steam is injected to heat the entire device; Step 3: After being heated, the internal low-melting-point alloy melts and turns into liquid, the volume of the thermal expansion fluid expands and pushes the driving rod to squeeze the low-melting-point alloy; the external low-melting-point alloy flows into the cracks in the cement sheath, and the internal low-melting-point alloy supplements the external alloy to achieve material and mechanical plugging of the cement sheath; Step 4: After the entire device is stable, stop heating; the block, spring, and shaft in the drive system jointly fix the drive rod to prevent the low-melting-point alloy from flowing back after the drive rod loses driving force, and allow the low-melting-point alloy to solidify stably, ultimately completing the cement ring repair work.

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