A wellbore cleanout string and method

Abstract

The application discloses a wellbore cleaning pipe column and method, aiming at overcoming the technical problem that the existing wellbore cleaning technology of the easy-leaking well cannot establish effective circulation to remove the pollutants in the wellbore. The wellbore cleaning pipe column integrates a temporary plugging well cleaning device, a wall scraping device and a through well device, and is connected with a drill pipe to form an effective wellbore cleaning system. The wellbore cleaning method is realized based on the wellbore cleaning pipe column, and through the positive circulation well cleaning, the pollutants in the wellbore are completely washed out by using the well killing fluid until the liquid properties at the inlet and outlet are consistent, and the cleaning quality is improved. The application not only improves the efficiency and safety of the wellbore cleaning, reduces the operation cost, but also reduces the influence on the environment, and provides an efficient and environment-friendly wellbore cleaning solution for oil and gas field development.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to a wellbore cleaning string and method. Background Technology

[0002] Carbonate reservoirs, with their unique geological structures and intricate networks of fractures and caverns, occupy a crucial position in oil and gas field development. These natural porous structures not only provide storage space for oil and gas but also present development challenges due to their high heterogeneity. In particular, wells in carbonate reservoirs prone to leakage are susceptible to severe loss of circulation during well workover operations, making it difficult to establish normal circulation during downhole operations and resulting in challenging wellbore cleaning. Therefore, efficient wellbore cleaning technology is crucial for wells prone to leakage. It effectively removes blockages such as wax and asphalt generated during wellbore cleaning and wall scraping that float on top of the kill fluid. These substances can obstruct the running of completion tubing and easily clog the flow channels of electric pumps (EPBs) and sucker pumps. By cleaning the wellbore, these blockages, such as wax and asphalt, can be removed from the kill fluid, ensuring the normal running of completion tubing and preventing blockages in EPBs and sucker pumps.

[0003] While wellbore cleaning technology is crucial, current industry practices primarily rely on traditional mechanical scraping methods, which have several limitations. For example, cleaning is often incomplete and operations are costly. In wells prone to leakage, traditional methods struggle to establish effective circulation, preventing the cleaning fluid from fully circulating and removing contaminants from the wellbore, thus increasing operational risks and the potential for environmental pollution. Furthermore, due to the high content of asphaltenes in some carbonate reservoirs, the scraping process during well workover generates large amounts of asphaltenes that float on top of the kill fluid. However, severe well leakage prevents circulation, hindering the removal of these asphaltenes. This not only impacts production but also increases the risk of obstruction during well completion string installation.

[0004] In order to overcome the limitations of existing technologies and improve the efficiency and safety of wellbore cleaning for wells prone to leakage, there is an urgent need for a wellbore cleaning string and method that can effectively solve the problem of wellbore cleaning for wells prone to leakage, so as to achieve efficient and environmentally friendly wellbore cleaning operations, reduce operating costs, reduce environmental impact, and at the same time improve the production efficiency and safety of oil and gas wells. Summary of the Invention

[0005] The purpose of this invention is to provide a wellbore cleaning string and method to overcome the shortcomings of existing wellbore cleaning technologies for easily leaking wells, which cannot establish effective circulation to remove contaminants from the wellbore.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A wellbore cleaning string includes drill pipe, a temporary plugging and cleaning device, a wall scraping device, and a well cleaning device; The upper end of the drill pipe is connected to the drill pipe control device, and the lower end is connected to the temporary plugging and washing device, the wall scraping device and the well cleaning device. The well cleaning device is connected to the lowest end of the drill pipe, the wall scraping device is arranged above the well cleaning device, and the temporary plugging and washing device is arranged above the wall scraping device. An annular space is formed between the production casing and the drill pipe. The upper end of the production casing is fixed to the wellhead, and the lower end extends to the depth required for operation. The production casing allows the drill pipe and its connected temporary plugging and flushing devices, wall scraping devices, and well cleaning devices to pass through.

[0007] The temporary plugging and well washing device includes a circulation valve, a packer, and a ball seat. The circulation valve is located above the packer, the packer is located above the ball seat, and the ball seat is located above the wall scraping device.

[0008] The wall scraping device includes a wall scraper, and the outer cylinder of the wall scraper is equipped with a scraper mechanism.

[0009] Well-clearing equipment includes a grinding shoe.

[0010] A wellbore cleaning method, based on a wellbore cleaning tubing string, includes the following steps: Remove the original tubing from the wellbore and install a wellbore cleaning tubing. The configured well cleaning string is lowered into the well to the required position for operation. Set the packer, drop the ball to plug the wellbore and clean the tubing string; Inject kill fluid into the sealed wellbore cleaning string to perform well washing; After the well cleaning work is completed, pressure is applied to knock down the ball seat, unseal the wellbore, clean the tubing string, and pull it out of the wellbore.

[0011] The configured wellbore cleaning string is lowered into the wellbore to the required position, including: The configured well cleaning string is lowered into the well. If obstruction or jamming occurs during the lowering of the wellbore, flushing should be performed until the tubing is freed. After descending to the required position, adjust the tubing column to the set position.

[0012] The well access device in the tubing string is positioned 1-1.5m from the bottom of the well.

[0013] Wellbore cleaning string sealing, including: Use a temporary plugging and well-washing device to seal the inside of the drill pipe below the packer, the annular space between the production casing and the drill pipe, and the production formation; Pressure was applied from the wellhead into the annular space between the production casing and the drill pipe to verify the sealing effect.

[0014] A wellbore cleaning method further includes: If the verification shows that the sealing effect is not up to standard, the position of the temporary plugging and well washing device will be readjusted and pressure will be applied again to verify the sealing effect.

[0015] Injecting kill fluid into the sealed wellbore cleaning string to perform well washing work includes: Inject kill fluid into the drill pipe of the sealed wellbore cleaning string; Detect the fluidity of the kill fluid when it enters and when it exits; Stop washing the well when the properties of the kill fluid entering the well are the same as those when it exits the well.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: A wellbore cleaning string is designed to improve the efficiency and safety of wellbore cleaning in oil and gas field development, particularly for wells prone to leakage. This string integrates a temporary plugging and cleaning device, a wall scraping device, and a well cleaning device, effectively increasing the efficiency of wellbore cleaning operations. This integrated design simplifies the workflow, reduces the need for multiple well runs, and thus lowers operating costs. The temporary plugging and cleaning device effectively isolates the drill pipe below the packer, the annular space between the production casing and the drill pipe, and the space above the packer, reducing kill fluid loss and environmental pollution risks, while simultaneously improving the production efficiency and safety of oil and gas wells. Furthermore, this string is particularly suitable for wells prone to leakage under complex geological conditions, adapting to different wellbore conditions and enhancing the flexibility and adaptability of cleaning operations.

[0017] A wellbore cleaning method employs a positive circulation well-washing approach, ensuring that the kill fluid completely replaces contaminants within the wellbore until the inlet and outlet fluid properties are consistent, significantly improving cleaning quality. Effective isolation and pressure control reduce the risk of safety accidents such as well blowouts, enhancing the safety of downhole operations. It reduces the need for multiple downhole operations, lowering operating costs and improving the economic efficiency of oil and gas wells. Furthermore, it reduces kill fluid leakage, mitigating environmental impact and making the method more environmentally friendly and compliant with environmental protection requirements. Through these methods, this invention provides an efficient and environmentally friendly wellbore cleaning solution for oil and gas field development. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a well cleaning tubing structure according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram showing the circulation direction of the kill fluid in the wellbore cleaning string in an embodiment of the present invention.

[0020] Figure 3 This is a flowchart of a well cleaning method according to an embodiment of the present invention.

[0021] In the diagram, 1 is the drill pipe; 2 is the production casing; 3 is the circulation valve; 4 is the packer; 5 is the ball seat; 6 is the wall scraper; 7 is the grinding shoe; and 8 is the reservoir. Detailed Implementation

[0022] Carbonate reservoirs, with their unique geological structures and intricate networks of fractures and caverns, occupy a crucial position in oil and gas field development. These natural porous structures not only provide storage space for oil and gas but also present development challenges due to their high heterogeneity. In particular, wells in carbonate reservoirs prone to leakage are susceptible to severe loss of circulation during well workover operations, making it difficult to establish normal circulation during downhole operations and resulting in challenging wellbore cleaning. Therefore, efficient wellbore cleaning technology is crucial for wells prone to leakage. It effectively removes blockages such as wax and asphalt generated during wellbore cleaning and wall scraping that float on top of the kill fluid. These substances can obstruct the running of completion tubing and easily clog the flow channels of electric pumps (EPBs) and sucker pumps. By cleaning the wellbore, these blockages, such as wax and asphalt, can be removed from the kill fluid, ensuring the normal running of completion tubing and preventing blockages in EPBs and sucker pumps.

[0023] While wellbore cleaning technology is crucial, current industry practices primarily rely on traditional mechanical scraping methods, which have several limitations. For example, cleaning is often incomplete and operations are costly. In wells prone to leakage, traditional methods struggle to establish effective circulation, preventing the cleaning fluid from fully circulating and removing contaminants from the wellbore, thus increasing operational risks and the potential for environmental pollution. Furthermore, due to the high content of asphaltenes in some carbonate reservoirs, the scraping process during well workover generates large amounts of asphaltenes that float on top of the kill fluid. However, severe well leakage prevents circulation, hindering the removal of these asphaltenes. This not only impacts production but also increases the risk of obstruction during well completion string installation.

[0024] In order to overcome the limitations of existing technologies and improve the efficiency and safety of wellbore cleaning for wells prone to leakage, there is an urgent need for a wellbore cleaning string and method that can effectively solve the problem of wellbore cleaning for wells prone to leakage, so as to achieve efficient and environmentally friendly wellbore cleaning operations, reduce operating costs, reduce environmental impact, and at the same time improve the production efficiency and safety of oil and gas wells.

[0025] This application proposes a wellbore cleaning string and method suitable for complex geological conditions such as carbonate reservoirs and easily leaking wells. By designing the string structure and cleaning process, it can effectively remove gum, bituminous substances and other debris from the wellbore, prevent well kill fluid loss, and improve the development efficiency of oil and gas wells.

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" 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 an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0028] Please refer to Figure 1 As shown, a wellbore cleaning string is provided in a specific embodiment of the present invention, including a drill pipe 1 and a temporary plugging and cleaning device, a wall scraping device, and a well cleaning device. The drill pipe 1 serves as the main structure connecting the various cleaning devices and simultaneously delivers kill fluid to form a cleaning cycle. The production casing 2 and the drill pipe form an annular space, allowing the kill fluid to circulate while maintaining the wellbore structure, bearing formation pressure, and preventing wellbore collapse. The upper end of drill pipe 1 is connected to the drill pipe control device, and the lower end is connected to a temporary plugging and washing device, a wall scraping device and a well cleaning device. The well cleaning device is connected to the lowest end of drill pipe 1, the wall scraping device is arranged above the well cleaning device, and the temporary plugging and washing device is arranged above the wall scraping device. An annular space is formed between the production casing 2 and the drill pipe 1. The upper end of the production casing 2 is fixed to the wellhead, and the lower end extends to the depth required for operation. The production casing 2 allows the drill pipe 1 and its connected temporary plugging and flushing device, wall scraping device and well cleaning device to pass through.

[0029] Temporary plugging and well-washing devices are used to seal the inside of the drill pipe below the packer, the annular space between the production casing and the drill pipe, and the producing formation, preventing well-killing fluid loss, ensuring effective circulation of the well-killing fluid within the wellbore, and improving well-washing efficiency. Wall-scraping devices are used to remove asphalt and other debris adhering to the casing wall. Well-cleaning devices are used to grind away hard asphalt and other debris encountered during well-cleaning.

[0030] Specifically, the temporary plugging and well-washing device includes a circulation valve 3, a packer 4, and a ball seat 5. The circulation valve 3 is located above the packer 4, connecting the inner and outer spaces of the drill pipe 1. The packer 4 is located above the ball seat 5, which is located above the wall-scraping device. The wall-scraping device includes a wall scraper 6, with a scraping mechanism installed on its outer cylinder. The well-clearing device includes a grinding shoe 7.

[0031] It should be noted that the grinding shoe 7 is located at the bottom of the tubing string and is connected to other tools above it via the drill pipe 1. It is used to grind hard, rubbery, asphalt and other debris encountered during well cleaning. Flat-bottomed grinding shoes, spherical grinding shoes, etc. can be selected.

[0032] The wall scraper 6 is located above the grinding shoe 7 and is connected via the drill rod 1. It is used for casing scraping operations to remove the gum, asphalt, and other debris adhering to the casing wall. A rotary wall scraper can be used, with a retractable scraper mechanism on its outer cylinder.

[0033] The ball seat 5 is located above the scraper 6 and below the packer 4, and is used to seal the inside of the drill pipe 1 during well washing to create a kill fluid circulation.

[0034] The packer 4 is located above the ball seat 5 and below the circulation valve 3. It is used to seal the producing zone from the upper casing during well washing to prevent the loss of kill fluid. The packer 4 can be an RTTS packer.

[0035] The circulation valve 3 is located above the packer and is used to connect the annular space formed between the drill pipe 1, the production casing 2, and the drill pipe 1 after the packer is set and the ball seat 5 is temporarily plugged. This meets the requirements of high-volume well washing. The circulation valve 3 can be a conventional circulation valve, a perforated screen, etc.

[0036] Reference Figure 3 As shown, another specific embodiment of the present invention provides a wellbore cleaning method, which is based on a wellbore cleaning tubing string and includes the following steps: S101, Remove the original tubing string from the wellbore and install a wellbore cleaning tubing string; S102, Lower the configured well cleaning string into the well to the required position for operation; S103, setting packer, ball-dropping plugging wellbore cleaning tubing string; S104, inject kill fluid into the sealed wellbore cleaning string to perform well washing; S105, after the well washing work is completed, the ball seat is being pressed down to release the wellbore cleaning string and pull it out of the wellbore.

[0037] In S101, all tubing strings in the original wellbore are retrieved, including flowing tubing strings, submersible pump tubing strings, and gas lift tubing strings. Afterwards, a wellbore cleaning tubing string integrating well cleaning, wall scraping, and temporary plugging is installed on the surface and lowered into the well.

[0038] S102 involves lowering the configured wellbore cleaning string into the wellbore to the required operational position, including: The configured well cleaning string is lowered into the well. If obstruction or jamming occurs during the lowering of the wellbore, flushing should be performed until the tubing is freed. After descending to the required position, adjust the tubing column to the set position.

[0039] The setting position should ensure that the grinding shoe is as close to the bottom of the well as possible; this can be achieved by placing the well access device in the tubing string 1-1.5 meters from the bottom of the well. After the well cleaning tubing string is lowered to the set position, a clamp is used to secure the tubing string to the wellhead, preventing it from sliding down or shifting due to its own weight.

[0040] Among them, the S103 setting packer and ball-dropping plugging wellbore cleaning string include: Use a temporary plugging and well-washing device to seal the inside of the drill pipe below the packer, the annular space between the production casing and the drill pipe, and the production formation; Pressure was applied from the wellhead into the annular space between the production casing and the drill pipe to verify the sealing effect.

[0041] First, the packer is set according to the packer operating procedures to seal the annular space between the production casing and the drill pipe. Next, a steel ball is inserted into the drill pipe; the ball will fall into the corresponding position in the ball seat to seal the inside of the drill pipe. After the steel ball is positioned, the annulus is back-pressurized to the preset pressure value to complete the sealing verification process. This preset pressure value needs to be set specifically according to different equipment. Through the packer setting and ball insertion temporary plugging operations, effective sealing is ensured between the upper and lower parts of the packer, thereby preventing leakage of kill fluid during well flushing.

[0042] If the verification shows that the sealing effect is not up to standard, the position of the temporary plugging and well washing device will be readjusted and pressure will be applied again to verify the sealing effect.

[0043] S104 involves injecting kill fluid into the sealed wellbore cleaning string to perform well washing, including: Inject kill fluid into the drill pipe of the sealed wellbore cleaning string; Detect the fluidity of the kill fluid when it enters and when it exits; Stop washing the well when the properties of the kill fluid entering the well are the same as those when it exits the well.

[0044] Kill fluid is injected through the internal channels of the drill pipe. The kill fluid then flows through a circulation valve from inside the drill pipe into the annular space formed by the production casing and the drill pipe, creating a positive circulation. This cleans the asphalt and gum material in the annular space. The flow direction of the kill fluid during positive circulation cleaning is as follows: Figure 2 As shown, a positive circulation method is used to clean the annular space between the drill pipe and casing to remove the asphaltene and gum deposits. Simultaneously, fluidity testing is performed at the inlet and outlet of the kill fluid. When the fluidity at the inlet and outlet is consistent, the well cleaning is considered complete. This process ensures that the asphaltene and gum deposits in the annular space between the drill pipe and casing are thoroughly cleaned, effectively achieving wellbore cleanliness.

[0045] Finally, after S105, the wellbore cleaning string is unsealed and pulled out of the wellbore. The ball seat is removed, the packer is unsealed, and the wellbore cleaning string is pulled out. The annulus passage between the drill pipe and casing is closed, and positive pressure is applied to the drill pipe. By cutting the shear pin of the ball seat, the ball seat is knocked down, restoring the connection between the upper and lower parts of the packer and ensuring pressure balance between the upper and lower parts of the packer, thus facilitating subsequent string lifting operations. After the ball seat is knocked down, the string is lifted to unseal the packer. After the packer is unsealable, the wellbore cleaning string is pulled out, and completion strings, including but not limited to flowing strings, submersible pump strings, and gas lift strings, are run according to production needs.

[0046] Another specific embodiment of the present invention provides a specific application scenario for a wellbore cleaning string and method. Taking a carbonate rock oil well in a western oilfield as the target well, with a depth of 6598.2m, it is an open-hole completion. The well adopts a three-section wellbore structure: the first section uses 273.05mm casing to a depth of 1500m; the second section uses 200.03mm casing to a depth of 6559.13m; and the third section uses a 168.30mm drill bit to a depth of 6598.20m. Before operation, a pump was used to dilute the fluid, resulting in a production fluid with an asphaltene content of 11.85% and a gum content of 3.52%. To increase the production of well HA X, it was decided to implement an electric submersible pump (ESP) operation. The formation pressure of this well is 69.19 MPa, the oil layer depth is 6578.70 m, and the formation pressure coefficient is 1.07. Considering the safety factor, the designed kill fluid density is 1.12 g / cm3. During the removal of the original well string, the volume of the string was removed, and the kill fluid volume was 6 cubic meters per hour. The annular fluid level was stable at about 600 m. A large amount of asphalt was adhered to the outer wall of the removed original well string. It was determined that a large amount of asphalt was adhered to the casing wall. Since the fluid level in this well is about 600 m, the large amount of asphalt produced by scraping the wall will float on top of the kill fluid and be difficult to circulate out of the wellbore. This will not only cause the completion string to not be lowered in place, but also affect the normal production operation of the ESP and the pump inspection cycle.

[0047] according to Figure 1 The wellbore cleaning tubing configuration shown connects various tools and lowers them into the well. The tubing is adjusted to ensure that the depth of each tool is within the design range. The upper end of the circulation valve 3 is connected to the drill pipe 1, and the lower end is connected to the RTTS packer 4. The lower end of the RTTS packer 4 is connected to the ball seat 5. The lower end of the ball seat 5 is connected to the wall scraper 6 via the drill pipe 1. The lower end of the wall scraper 6 is connected to the grinding shoe 7 via the drill pipe 1. The RTTS packer has an inner diameter of 59mm and an outer diameter of 170mm. The ball seat has an inner diameter of 25-58mm and is equipped with four shear pins, each with a shear value of 7MPa. The wall scraper has an inner diameter of 30mm and an outer diameter of 165mm. The grinding shoe has an outer diameter of 150mm.

[0048] During the process of running in the string, if there is resistance or sticking, flushing shall be carried out until the string is released from sticking.

[0049] After the string is run to the designed depth, adjust the string depth to ensure that the mill shoe is as close as possible to the bottom hole. The specific depth is 6597m, and the depth of the artificial bottom hole is 6598.20m.

[0050] Pick up the string and rotate it clockwise for 8 - 12 turns, then lower the string and apply a pressure of 80 - 100KN to set the RTTS packer 4. Drop a 34mm steel ball into drill pipe 1. After the steel ball seats, pump 20MPa pressure into the annulus between drill pipe 1 and casing 2 to test the seal of the RTTS packer 4. If the pressure drop is less than 0.5MPa after stabilizing for 30min, it is qualified. After the RTTS packer 4 is set and the ball is dropped for temporary plugging, effective isolation between the upper part and the lower part of the RTTS packer 4 can be achieved, avoiding the loss of kill fluid.

[0051] Inject kill fluid with a density of 1.12g / cm3 through the internal channel of drill pipe 1. After flowing to the circulation valve 3, it flows into the annulus between drill pipe 1 and casing 2 through the channel of the circulation valve 3 and returns to the surface. Stop flushing when the fluid properties at the inlet and outlet are the same. This process can completely wash out the asphaltenes in the annulus between drill pipe 1 and casing 2, effectively achieving wellbore cleaning. In well HA X, a total of 20 cubic meters of asphaltenes have been washed out.

[0052] Close the annulus channel between drill pipe 1 and casing 2. Gradually pump pressure in drill pipe 1 to 28MPa in stages to cut off the shear pin of the ball seat 5, knock down the ball seat, and restore the connection between the upper part and the lower part of the RTTS packer 4, ensuring the pressure balance above and below the rubber cylinder, thus facilitating the subsequent operation of picking up the string. After the ball seat 5 is knocked down, pick up the string to release the RTTS packer 4. After the RTTS packer 4 is released, pull out the wellbore cleaning string.

[0053] Finally, run in the submersible electric pump completion string according to production requirements.

[0054] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and do not limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A wellbore cleaning tubing string, comprising a production casing (2), characterized in that, It also includes drill pipe (1) and a temporary plugging and washing device, a wall scraping device, and a well cleaning device; The upper end of the drill pipe (1) is connected to the drill pipe control device, and the lower end is connected to a temporary plugging and washing device, a wall scraping device and a well-clearing device. The well-clearing device is connected to the lowest end of the drill pipe (1), the wall scraping device is arranged above the well-clearing device, and the temporary plugging and washing device is arranged above the wall scraping device. An annular space is formed between the drill pipe (1) and the production casing (2). The upper end of the production casing (2) is fixed to the wellhead, and the lower end extends to the depth required for operation. The production casing (2) allows the drill pipe (1) and its connected temporary plugging and washing device, wall scraping device and well cleaning device to pass through.

2. The wellbore cleaning tubing string according to claim 1, characterized in that, The temporary plugging and well washing device includes a circulation valve (3), a packer (4) and a ball seat (5). The circulation valve (3) is located above the packer (4), the packer (4) is located above the ball seat (5), and the ball seat (5) is located above the wall scraping device.

3. The wellbore cleaning tubing string according to claim 1, characterized in that, The wall scraping device includes a wall scraper (6), and a scraper mechanism is provided on the outer cylinder of the wall scraper (6).

4. The wellbore cleaning tubing string according to claim 1, characterized in that, The well-drilling device includes a grinding shoe (7).

5. A wellbore cleaning method, characterized in that, A wellbore cleaning string based on any one of claims 1 to 4 includes the following steps: Remove the original tubing from the wellbore and install a wellbore cleaning tubing. The configured well cleaning string is lowered into the well to the required position for operation. Set the packer, drop the ball to plug the wellbore and clean the tubing string; Inject kill fluid into the sealed wellbore cleaning string to perform well washing; After the well cleaning work is completed, pressure is applied to knock down the ball seat, unseal the wellbore, clean the tubing string, and pull it out of the wellbore.

6. The wellbore cleaning method according to claim 5, characterized in that, The step of lowering the configured wellbore cleaning string into the wellbore to the required operational position includes: The configured well cleaning tubing string is lowered into the well. If obstruction or jamming occurs during the lowering of the wellbore, flushing should be performed until the tubing is freed. After descending to the required position, adjust the tubing column to the set position.

7. A wellbore cleaning method according to claim 6, characterized in that, The designated position is 1-1.5m from the bottom of the well when the well access device in the tubing string is located.

8. A wellbore cleaning method according to claim 5, characterized in that, The wellbore cleaning string includes: Use a temporary plugging and well-washing device to seal the inside of the drill pipe below the packer, the annular space between the production casing and the drill pipe, and the production formation; Pressure was applied from the wellhead into the annular space between the production casing and the drill pipe to verify the sealing effect.

9. A wellbore cleaning method according to claim 8, characterized in that, Also includes: If the verification shows that the sealing effect is not up to standard, the position of the temporary plugging and well washing device will be readjusted and pressure will be applied again to verify the sealing effect.

10. A wellbore cleaning method according to claim 5, characterized in that, The well-washing process, which involves injecting kill fluid into the sealed wellbore cleaning string, includes: Inject kill fluid into the drill pipe of the sealed wellbore cleaning string; Detect the fluidity of the kill fluid when it enters and when it exits; Stop washing the well when the properties of the kill fluid entering the well are the same as those when it exits the well.

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