A spin flow casing repair fishing tool and method of use

Abstract

The present application belongs to the technical field of oil exploitation well repair, and particularly relates to a cyclone type casing repair fishing tool and a use method. The cyclone type casing repair fishing tool comprises, in sequence, a milling shoe, a cyclone milling column, a fishing barrel, a centralizing milling column, a drill cuttings recovery barrel, a centralizer and a drill pipe. The milling shoe is used for milling and cutting the reduced diameter and broken casing skin between the oil pipe and the casing annulus, small dropped objects, and introducing the stuck pipe column into the hollow of the milling shoe; the cyclone milling column is used for milling the reduced diameter casing and expanding the casing passage; the fishing barrel is used for sticking the stuck pipe column introduced by the milling shoe; the centralizing milling column is used for centralizing the milling shoe along the center line of the wellbore and cutting the damaged casing skin; and the drill cuttings recovery barrel is used for fishing the cuttings. The present application opens the casing passage while milling and repairing the damaged casing, fishes the stuck pipe column, and collects the cuttings of the milling and cutting by the drill cuttings recovery barrel, thereby avoiding the risk of cutting sticking and improving the cutting construction efficiency.

Description

Technical Field

[0001] This invention belongs to the field of oil well repair technology, and specifically relates to a vortex casing repair and retrieval tool and its usage method. Background Technology

[0002] Casing is widely used to fix the wellbore of oil, gas, and water wells or to isolate formation fluids to prevent wellbore collapse, ensure well safety, and facilitate drilling and resource extraction. However, due to factors such as engineering construction, environmental corrosion, fault activity, and changes in geostress, downhole casing often suffers damage such as rupture, deformation, perforation, and misalignment. This results in a reduced casing diameter, preventing large-diameter tools from passing through and thus impacting production.

[0003] There is a large number of damaged wells in oilfields across the country. In particular, wells with damaged casing sections and stuck tubing account for one-third of the damaged wells. These wells cannot be flushed with sand or subjected to general basic production enhancement measures. They are all in a state of shutdown or abandonment, resulting in idle assets and affecting production. Drilling replacement wells requires a large investment and the production is not high, which does not meet the investment requirements.

[0004] Because most wells with casing damage have their production tubing jammed by the broken casing, repair and production operations are impossible, making casing repair and retrieval extremely difficult. Currently, there are two main repair techniques for wells with casing damage causing tubing jamming:

[0005] (1) Use a grinding shoe to grind the damaged section of the pipe that is stuck, and then repair the casing. The grinding speed is slow, and the fragments generated by grinding fall down and cause the lower pipe to get stuck again, making it difficult to retrieve.

[0006] (2) First, the casing is milled to repair the damaged section of the well, and then the fishing tool is run down to fish out the tubing string. Due to the damage to the casing, the milling operation often gets stuck, causing secondary downhole accidents. The operation is slow due to the alternating cycle.

[0007] In summary, existing technologies for handling casing damage and stuck tubing can damage the stuck tubing during casing repair, prevent simultaneous retrieval, and prevent the complete removal of abrasive debris from the wellbore. This can lead to secondary jamming of the downhole tubing after the debris settles, making it impossible to release. In some wells, small downhole objects can cause the tubing to become stuck due to various reasons. Summary of the Invention

[0008] To address the aforementioned problems, the purpose of this invention is to provide a vortex-type casing repair and retrieval tool and its usage method, which can retrieve stuck casing while repairing the casing, and collect milling debris, avoiding debris jamming the drill and repeated cutting of rock cuttings, thereby improving cutting and construction efficiency.

[0009] The technical solution of this invention is as follows:

[0010] This invention provides a vortex casing repair and retrieval tool, comprising a milling shoe, a vortex milling column, a retrieval cylinder, a centralizing milling column, a cuttings recovery cylinder, a centralizer, and a drill pipe connected in sequence.

[0011] Furthermore, the milling shoe is used to mill and cut the reduced diameter and broken casing skin and small debris between the oil pipe and the casing annulus, and to guide the stuck pipe column into the hollow of the milling shoe;

[0012] Furthermore, the swirl milling column is used for milling reduced-diameter sleeves and expanding the sleeve channel;

[0013] Furthermore, the scooping cylinder is used to hold the stuck tube column introduced by the milling shoe;

[0014] Furthermore, the aforementioned straightening milling column is used to straighten the milling shoe along the wellbore centerline during milling, while simultaneously cutting the damaged casing.

[0015] Furthermore, the drill cuttings recovery cylinder is used to retrieve the cuttings from milling and grinding operations.

[0016] Furthermore, the milling shoe is fixedly connected to the swirl milling column; the milling shoe is hollow inside, with a concave bottom in the shape of a cone, and the concave surface has an arc of 160~170°.

[0017] Furthermore, alloy pillars are vertically embedded in the bottom of the tube wall of the milling shoe, with the end face of the alloy pillars flush with the end face of the tube wall, and alloy particles are welded onto their end faces.

[0018] Furthermore, the swirl milling column is cylindrical, with multiple spiral alloy strips on its outer surface, and spiral grooves I are left between adjacent alloy strips.

[0019] Furthermore, the scooping cylinder includes a scooping cylinder body and a built-in floating windowed scooping cylinder. The two ends of the scooping cylinder body are threadedly connected to a vortex milling column and a straightening milling column, respectively. Shoulders are provided at the upper and lower ends of the scooping cylinder body. The built-in floating windowed scooping cylinder is placed between the two shoulders. The built-in floating windowed scooping cylinder is a tube. Multiple trapezoidal window tongues are provided on the outer wall of the tube. The window tongues of the trapezoidal window tongues are inclined inward into the tube.

[0020] Furthermore, the straightening milling column is cylindrical, with multiple spiral grooves II on the outer surface of one end connected to the scooping cylinder, and the other end is a milling column without spiral grooves II.

[0021] Furthermore, the drill pipe is an 18° slope drill pipe.

[0022] Furthermore, the centralizer is a vortex sleeve centralizer with a diameter 6mm smaller than the inner diameter of the sleeve.

[0023] Furthermore, the present invention also provides a method for using a vortex-type casing repair and retrieval tool, comprising the following steps:

[0024] S1: Determine the location of the casing damage and the location of the pipe jamming point;

[0025] S2: Lower the vortex-type casing repair and retrieval tool, and use the milling shoe to perform milling operations on the stuck pipe string;

[0026] S3: Retrieve the stuck tubing from the well. The specific process is as follows:

[0027] After milling and cutting the reduced diameter and broken casing skin, small parts, and other debris between the tubing and casing annulus, the stuck tubing string is sequentially introduced into the hollow of the milling shoe and into the retrieval cylinder. The trapezoidal window tongue of the built-in floating window retrieval cylinder is used to lock the stuck tubing string, thereby achieving the retrieval of the stuck tubing string.

[0028] S4: While retrieving the stuck casing in step S3, the damaged area of ​​the downhole casing is repaired. The specific process is as follows:

[0029] While the milling mill is cutting, the vortex milling column and the straightening milling column form a two-stage milling column to further mill the reduced diameter casing and expand the casing channel. Then, the milling chips are retrieved through the cutting chip recovery cylinder. At the same time, the straightening milling column and the straightener form a two-stage straightening to ensure that the tool moves along the center line of the casing and prevents deviation.

[0030] The technical advantages of this invention are as follows:

[0031] 1. This invention employs a milling shoe and a vortex milling column to work simultaneously, performing casing repair while retrieving the stuck pipe column, thus solving the problem that casing repair and retrieval cannot be carried out simultaneously in existing technologies and improving construction efficiency.

[0032] 2. This invention uses a milling shoe with a concave bottom, which can effectively mill and cut the reduced diameter and broken casing between the oil pipe and the casing annulus, and guide the stuck pipe into the retrieval cylinder to realize the retrieval operation.

[0033] 3. The present invention uses a drill cuttings recovery cylinder to collect the cuttings from milling and grinding, thus avoiding the risk of cuttings getting stuck in the drill string and solving the problem of milling and grinding debris settling and causing secondary blockage of the tubing. At the same time, it avoids repeated cutting of cuttings downhole.

[0034] 4. This invention uses a two-stage milling column consisting of a vortex milling column and a straightening milling column to sequentially mill the reduced diameter sleeve and the enlarged sleeve channel, resulting in high milling efficiency.

[0035] 5. This invention employs a two-stage straightening tool consisting of a straightening milling column and a straightening device to ensure that the tool advances along the centerline of the casing, preventing deviation and ensuring the smooth completion of casing repair operations, thus avoiding downhole accidents caused by drilling through the casing.

[0036] The following will provide further explanation in conjunction with the accompanying drawings. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a vortex-type casing repair and retrieval tool according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the milling shoe and vortex milling column structure according to an embodiment of the present invention;

[0039] Figure 3 This is a cross-sectional view of the milled shoe tube wall according to an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the scooping tube structure according to an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the upright milling column structure according to an embodiment of the present invention;

[0042] Reference numerals: 1-milling shoe; 11-alloy column; 12-alloy particles; 2-vortex milling column; 21-spiral groove I; 22-alloy strip; 3-scooping cylinder; 30-built-in floating windowed scooping cylinder; 31-scooping cylinder body; 32-trapezoidal window tongue; 4-centralizing milling column; 41-milling column; 42-spiral groove II; 5-drill cuttings recovery cylinder; 6-centralizer; 7-drill rod. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0044] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] There is a large number of damaged casing wells in oilfields across the country, especially wells with damaged casing sections and stuck tubing, which account for one-third of all damaged casing wells. These wells cannot be flushed with sand or subjected to general basic production enhancement measures, and are therefore either shut down or abandoned, resulting in idle assets and impacting production. Drilling replacement wells requires a large investment, and the production output is not high, which does not meet investment requirements. In order to improve the overall efficiency of oilfield development, this invention provides a vortex-type casing repair and retrieval tool. Using this tool can effectively extend the production life of oil and water wells, increase the utilization rate of oil, gas and water wells, and has good economic benefits such as low overhaul investment and the ability to restore production capacity.

[0046] Example 1

[0047] like Figure 1As shown, the present invention provides a vortex casing repair and retrieval tool, comprising a milling shoe 1, a vortex milling column 2, a retrieval cylinder 3, a centralizing milling column 4, a drill cuttings recovery cylinder 5, a centralizer 6, and a drill rod 7 connected in sequence.

[0048] In practical use, the milling shoe 1 of this invention is used to mill and cut the reduced diameter and broken casing skin and small debris between the tubing and casing annulus, and to introduce the stuck tubing into the hollow of the milling shoe. The stuck tubing is not damaged when milling the tubing and casing annulus. The vortex milling column 2 is used to mill the reduced diameter casing and expand the casing channel. The retrieval cylinder 3 is used to hold the stuck tubing introduced by the milling shoe 1 for retrieval. The straightening milling column 4 is used to straighten the milling shoe 1 to mill along the wellbore centerline, and can also cut the damaged casing skin a second time. While milling and repairing the damaged casing, the casing channel is opened to retrieve the stuck tubing. The drill cuttings recovery cylinder 5 is used to retrieve the cuttings from the milling. It can retrieve the cuttings that the external retrieval cup cannot carry out, and bring the cuttings out of the wellbore through backwashing, avoiding the risk of cuttings getting stuck and improving the cutting efficiency. The function of the straightener 6 is secondary straightening to ensure that the milled casing does not change its trajectory.

[0049] Example 2

[0050] Based on Example 1, such as Figure 2 As shown, the milling shoe 1 is further fixedly connected to the swirl milling column 2; the milling shoe 1 is hollow inside, and the bottom is concave in a conical shape with a concave arc of 160~170°.

[0051] Furthermore, such as Figure 3 As shown, alloy pillars 11 are vertically embedded in the bottom of the tube wall of the milling shoe 1. The end face of the alloy pillars 11 is flush with the end face of the tube wall, and alloy particles 12 are welded on their end faces.

[0052] The alloy pillar 11 is made by first drilling a 4-6mm hole in the bottom of the milling shoe 1 tube wall, then inserting the alloy pillar, and then welding alloy particles on the surface. The total thickness of the alloy pillar and alloy particles reaches 6-8mm. The hollow part of the milling shoe 1 serves as a channel with a diameter of 62-75mm. The main function of the concave surface is to hold the sleeve or oil pipe inside the milling surface and prevent it from going out. The sleeve or oil pipe can pass through the middle channel of the milling process to the inner cavity of the tool to control the milling trajectory and cut and mill the damaged sleeve.

[0053] Furthermore, the alloy particles and alloy pillars are made of high-strength alloy with a hardness of 90 HRA. By using embedded alloy pillars, the strength of cutting and milling is greatly improved, preventing the problems of insufficient force and detachment when using alloy particles alone.

[0054] Furthermore, such as Figure 2As shown, the swirl milling column 2 is cylindrical, with multiple spiral alloy strips 22 on its outer surface, and spiral grooves Ⅰ21 are left between adjacent alloy strips 22.

[0055] The alloy strip is a 40mm wide alloy strip laid in a 15-20 degree spiral shape on the outer diameter. It is used for recutting and milling the casing to expand the diameter. A spiral groove I with a width of 15-20mm and a depth of 3-5mm is left between the alloy strips. The spiral groove does not contain alloy. It is used to return the circulating fluid and the debris generated by the grinding shoe. The advantage of the spiral groove is that the debris will not get stuck in the drill during rotation. The channel between them is greater than 75mm to ensure the passage of the oil pipe and casing skin and improve the wear resistance.

[0056] Furthermore, such as Figure 4 As shown, the scooping cylinder 3 includes a scooping cylinder body 31 and a built-in floating windowed scooping cylinder 30. The two ends of the scooping cylinder body 31 are threadedly connected to the swirl milling column 2 and the straightening milling column 4, respectively. The upper and lower ends of the scooping cylinder body 31 are respectively provided with shoulders. The built-in floating windowed scooping cylinder 30 is placed between the two shoulders. The built-in floating windowed scooping cylinder 30 is a tube. The outer wall of the tube is provided with multiple trapezoidal window tongues 32. The window tongues of the trapezoidal window tongues 32 are inclined inward into the tube.

[0057] The tube is placed on the shoulder and can move up and down and rotate freely. A trapezoidal window tongue 32 is distributed every 120 degrees along the outer wall of the tube. Preferably, the trapezoidal window tongue is 20mm wide at the top, 30mm wide at the bottom, and 25mm high, and extends inward by 5-8mm.

[0058] Furthermore, such as Figure 1 As shown, the trapezoidal window tongue has three layers machined vertically along the axial direction. If the tubing or a large piece of casing enters the built-in floating window retrieval tube, the coupling will be locked on the trapezoidal window tongue. The three layers ensure that it will not fall down and will be brought out of the wellbore when the drill string is pulled out. The purpose of the built-in floating window retrieval tube's vertical movement and free rotation is to prevent the tubing from being twisted and broken by milling rotation after the fallen object is retrieved.

[0059] Furthermore, such as Figure 5 As shown, the straightening milling column 4 is cylindrical, with multiple spiral grooves II 42 on the outer surface of one end connected to the scooping cylinder 3, and the other end is a milling column 41 without spiral grooves II.

[0060] The milling column 4 with a spiral groove II 42 has no alloy on it, and its function is to perform a second milling of the sleeve from all directions. The milling column 41 without the spiral groove II serves to straighten the sleeve. The surface of the milling edge formed on the milling column 4 is welded with an alloy layer to increase the wear resistance of the surface during milling and increase its service life.

[0061] Furthermore, the drill cuttings recovery cylinder 5 includes a recovery cylinder body and an inner tube. The recovery cylinder body is threadedly connected between the centralizing milling column 4 and the centralizer 6. The inner tube is disposed inside the recovery cylinder body, with one end fixedly connected to the centralizing milling column 4, forming a closed annular structure at the lower end between the inner tube and the recovery cylinder body. During reverse circulation, large pieces of grinding debris fall into the annular structure as they sink, achieving the purpose of retrieval. Preferably, the inner tube is a 4m long pipe.

[0062] In actual use, the preferred choice is the 18° inclined drill pipe 7. During the process of lowering and pulling the tool into and out of the wellbore, the 18° inclined drill pipe can reduce the frictional resistance between the drill pipe joint and the casing, and prevent the drill from getting stuck.

[0063] Furthermore, the centralizer 6 is a vortex sleeve centralizer, with a diameter 6mm smaller than the inner diameter of the sleeve.

[0064] The diameter of this swirl sleeve centralizer is relatively large, 6mm smaller than the inner diameter of the sleeve. It only serves as a forced centralizer and does not have a milling or cutting function. The swirl groove is relatively wide, 40-50mm, and also relatively deep, about 30-40mm.

[0065] A method for using a vortex-type casing repair and retrieval tool includes the following steps:

[0066] S1: Determine the location of the casing damage and the location of the pipe jamming point;

[0067] S2: Lower the vortex-type casing repair and retrieval tool, and milling shoe 1 performs milling operation on the stuck pipe string;

[0068] S3: Retrieve the stuck tubing from the well. The specific process is as follows:

[0069] After milling the tubing and casing annulus between the tubing and casing, the narrowed and broken casing skin, small falling objects, and the stuck tubing string are milled and cut, the stuck tubing string is sequentially introduced into the hollow of the milling shoe and into the retrieval cylinder 3. The trapezoidal window tongue of the built-in floating window retrieval cylinder 30 set in the retrieval cylinder 3 is used to lock the stuck tubing string, thereby realizing the retrieval of the stuck tubing string.

[0070] S4: While retrieving the stuck casing in step S3, the damaged area of ​​the downhole casing is repaired. The specific process is as follows:

[0071] While the milling shoe 1 is milling and cutting, the vortex milling column 2 and the straightening milling column 4 form a two-stage milling column to further mill the reduced diameter casing and expand the casing channel. Then, the milling and cutting debris is retrieved through the drill cuttings recovery cylinder 5. At the same time, the straightening milling column 4 and the straightener 6 form a two-stage straightening to ensure that the tool moves along the center line of the casing and prevents deviation.

[0072] The tool of this invention opens the casing passage while milling and repairing damaged casing, retrieving stuck tubing. Large pieces of casing skin generated during milling cannot be carried out of the wellbore by direct circulation; they are retrieved via a reverse circulation internal chip container. A two-stage hollow milling column ensures thorough milling and cutting of the reduced-diameter casing. Two-stage centralizers ensure the drill string advances along the casing centerline, preventing deviation. This achieves the simultaneous repair of casing and opening of the passage, retrieval of damaged and stuck tubing, and recovery of milling debris, avoiding the risk of stuck drill bits due to debris and the low efficiency of repeated cutting of debris.

[0073] This invention reduces the complexity of casing repair in such wells, avoids downhole accidents leading to project failure, and improves the success rate of casing-damaged well repair. It enables these wells to resume production and allows for general basic production enhancement measures. The overall success rate of casing-damaged well repair reaches 80%. Through research and application of casing-damaged well repair technology, a systematic casing-damaged well repair technology for the Yumen Oilfield can be developed, providing guidance for future casing-damaged well remediation projects.

[0074] Example 3

[0075] This example illustrates a practical application of the above embodiments: During pump inspection at well Q2-76, a stuck casing was discovered. Analysis of the stuck point indicated it was around 3640m. The inner diameter of this section of casing was 224mm, and the downhole production tubing was 73mm. Given the absence of any falling debris or wax, the stuck drill string was determined to be due to casing damage. During reverse drilling to 3600m, casing damage was discovered. Using a standard casing milling tool resulted in no progress, causing the casing milling shoe alloy to fall into the well. This complicated the casing repair and retrieval process, halted construction, and threatened to render the well project unusable. After research, it was decided to use this tool to process and manufacture a 205mm outer diameter vortex concave bottom hollow grinding, support, and retrieval drilling tool. Through two drilling and grinding processes, two tubing sections were retrieved using the built-in windowed retrieval cylinder, and 1.2 kg of ground casing fragments were retrieved using the built-in drill cuttings container. This prevented the fragments from falling and causing secondary stuck drill bits, which played a decisive role in the successful casing repair and retrieval of the well, saving the well and preventing the well project from being scrapped.

[0076] The tool of this invention is applicable to wells where the casing in the vertical section is damaged and the tubing string is stuck, allowing for simultaneous casing repair and retrieval, as well as wells where small objects have become stuck in the tubing string.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A vortex-type casing repair and retrieval tool, characterized in that: It includes a milling shoe (1), a vortex milling column (2), a scooping cylinder (3), a straightening milling column (4), a drill cuttings recovery cylinder (5), a straightener (6), and a drill rod (7) connected in sequence. The milling shoe (1) is used to mill and cut the reduced diameter and broken casing skin and small falling objects between the oil pipe and the casing annulus, and to introduce the stuck pipe column into the hollow of the milling shoe; The milling shoe (1) is hollow inside, with a concave bottom in the shape of a cone, and the concave surface arc is 160~170°. The aforementioned swirl milling column (2) is used for milling reduced-diameter sleeves and expanding sleeve channels; The scooping tube (3) is used to hold the stuck tube column introduced by the milling shoe (1); The scooping cylinder (3) includes a scooping cylinder body (31) and a built-in floating windowed scooping cylinder. The two ends of the scooping cylinder body (31) are threadedly connected to the swirl milling column (2) and the straightening milling column (4) respectively. The upper and lower ends of the scooping cylinder body (31) are respectively provided with shoulders. The built-in floating windowed scooping cylinder is placed between the two shoulders. The built-in floating windowed scooping cylinder is a tube. The outer wall of the tube is provided with multiple trapezoidal window tongues (32). The window tongues of the trapezoidal window tongues (32) are inclined inward into the tube. The straightening milling column (4) is used to straighten the milling shoe (1) along the center line of the wellbore and cut the damaged casing at the same time; The drill cuttings recovery cylinder (5) is used to retrieve the cuttings from milling and grinding.

2. The vortex-type casing repair and retrieval tool according to claim 1, characterized in that: The milling shoe (1) is fixedly connected to the vortex milling column (2).

3. The vortex-type casing repair and retrieval tool according to claim 1, characterized in that: The bottom of the milling shoe (1) is vertically inlaid with alloy pillars (11), the end face of the alloy pillars (11) is flush with the end face of the pipe wall, and alloy particles (12) are welded on their end faces.

4. The vortex-type casing repair and retrieval tool according to claim 1, characterized in that: The swirl milling column (2) is cylindrical, with multiple spiral alloy strips (22) on its outer surface, and spiral grooves (21) are left between adjacent alloy strips (22).

5. The vortex-type casing repair and retrieval tool according to claim 1 or 2, characterized in that: The straightening milling column (4) is cylindrical, with multiple spiral grooves II (42) on the outer surface of one end connected to the scooping cylinder (3), and the other end is a milling column (41) without spiral grooves II.

6. The vortex-type casing repair and retrieval tool according to claim 1, characterized in that: The drill rod (7) is an 18° slope drill rod.

7. The vortex-type casing repair and retrieval tool according to claim 1, characterized in that: The centralizer (6) is a vortex sleeve centralizer with a diameter 6-8 mm smaller than the inner diameter of the sleeve.

8. The method of using the vortex-type casing repair and retrieval tool according to any one of claims 1-7, characterized in that: Includes the following steps S1: Determine the location of the casing damage and the location of the pipe jamming point; S2: Lower the vortex-type casing repair and retrieval tool, and milling shoe (1) perform milling operation on the stuck pipe string; S3: Retrieve the stuck tubing from the well. The specific process is as follows: After milling and cutting the reduced diameter and broken casing skin and small parts between the tubing and the casing annulus, the stuck pipe string is sequentially introduced into the hollow of the milling shoe and the retrieval cylinder (3). It is then stuck by the trapezoidal window tongue (32) of the built-in floating window retrieval cylinder (3), thereby realizing the retrieval of the stuck pipe string. S4: While retrieving the stuck casing in step S3, the damaged area of ​​the downhole casing is repaired. The specific process is as follows: While the milling shoe (1) is milling and cutting, the vortex milling column (2) and the straightening milling column (4) form a two-stage milling column to further mill the reduced diameter casing and expand the casing channel. Then, the milling and cutting debris is retrieved by the cutting chip recovery cylinder (5). At the same time, the straightening milling column (4) and the straightener (6) form a two-stage straightening to ensure that the tool moves along the center line of the casing and prevents deviation.

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