Short fish head milling and fishing tool

Abstract

The utility model discloses a kind of short fish head fishing tools of milling, it is related to petroleum and natural gas exploitation downhole operation equipment field, solve the problem of milling fishing process separation, complicated, success rate is low, no pre-tightening disassembly structure and grinding scrap accumulation.The pre-tightening structure is arranged in the inside of cylinder and is connected with fishing structure;The concave mill shoe is arranged in the lower end of cylinder;Fishing structure includes fishing slip, spear and guide head, spear one end is connected with pre-tightening structure, the other end is connected with guide head;Fishing slip is sleeved on spear, and the lower end is provided with several trapezoidal teeth, and the outer surface of trapezoidal tooth is sawtooth structure;Fishing slip upper end and pre-tightening structure contact, under the pre-tightening structure thrust, make trapezoidal tooth pre-tightening on the taper surface of guide head.The utility model carries out milling modification and fishing recovery operation to short fish head class drop object such as broken oil pipe or tool, by integrating milling system, fishing system and connection system, realize once downhole, milling fishing integrated operation.

Description

Technical Field

[0001] This utility model relates to the technical field of downhole operation equipment for oil and gas extraction, specifically a milling tool for retrieval of short fish heads. Background Technology

[0002] During stratified water injection operations in oil and gas extraction, downhole tubing is prone to breakage due to corrosion, wear, and pressure fluctuations, resulting in debris with short "fish heads." If not handled promptly, this debris can clog injection lines, affecting injection efficiency and even causing well shutdowns, leading to economic losses. Currently, the tools commonly used in the industry for handling this type of debris are mainly divided into two categories: milling tools and retrieval tools. Milling tools (such as ordinary grinding shoes) can trim the "fish heads," but cannot retrieve them, requiring a subsequent replacement with retrieval tools and a second well run, increasing the operational steps, time, and cost. Retrieval tools (such as conventional retrieval spears) can retrieve intact "fish heads," but when faced with irregular, burr-laden, or deformed "fish heads," their gripping reliability is poor, easily slipping and detaching, and they cannot handle excess protrusions, leading to retrieval failure. Meanwhile, existing tools have shortcomings in material selection and structural design: some tool bodies are made of ordinary steel, which lacks strength and corrosion resistance, making them prone to deformation or corrosion damage under downhole conditions of high temperature (above 120℃), high pressure (above 30MPa), and corrosive media containing hydrogen sulfide, carbon dioxide, etc.; the cemented carbide welding quality of the milling components is unstable, and detachment is prone to occur, affecting milling efficiency and tool life; the slip tooth design of the fishing components is unreasonable, resulting in insufficient clamping force and a lack of reliable pre-tightening and unloading structures, which can easily lead to secondary stuck drill accidents when encountering obstruction, further exacerbating operational risks. Therefore, there is an urgent need for a tool that integrates milling and fishing functions, is adaptable to complex downhole conditions, has a reliable structure, and is easy to operate, in order to solve the problems of cumbersome operation procedures, low efficiency, poor reliability, and short tool life in existing technologies. Utility Model Content

[0003] To address the aforementioned problems of existing milling and retrieval functions being separate, cumbersome procedures, low retrieval success rates, lack of reliable pre-tightening and unloading structures, and the impact of milling debris accumulation on milling efficiency, this invention proposes a milling and retrieval tool for short fish-head objects. This invention is applicable to complex downhole temperature, pressure, and media conditions for milling, trimming, and retrieving short fish-head-shaped objects such as broken tubing or tools. By integrating the milling system, retrieval system, and connection system, it achieves a single downhole operation combining milling and retrieval.

[0004] This utility model proposes a tool for milling and retrieving short fish heads, specifically including a cylindrical body, a pre-tightening structure, and a retrieval structure. The pre-tightening structure is located inside the cylindrical body and connected to the retrieval structure. A concave grinding shoe is provided at the lower end of the cylindrical body, and the concave grinding shoe has a cylindrical structure. The retrieval structure includes a retrieval slip, a spear shaft, and a guide head. One end of the spear shaft is connected to the pre-tightening structure, and the other end is connected to the guide head. The retrieval slip is fitted onto the spear shaft, and its lower end is provided with several trapezoidal teeth, the outer surface of which has a serrated structure. The upper end of the retrieval slip contacts the pre-tightening structure, and under the thrust of the pre-tightening structure, the trapezoidal teeth are pre-tightened on the conical surface of the guide head.

[0005] Furthermore, the pre-tightening structure includes a spring seat and a thrust spring; the spring seat is fixedly installed inside the cylinder, and its lower end is connected to the spear rod; the thrust spring is fitted onto the spear rod, with its upper end in contact with the spring seat and its lower end in contact with the retrieval slip.

[0006] Furthermore, the cylinder includes an upper connector and an outer cylinder, with the upper connector, outer cylinder, and concave grinding shoe connected in sequence; the spring seat is clamped between the upper connector and the outer cylinder.

[0007] Furthermore, the spring seat has a through hole at its center, and the spear rod and guide head axis have spear rod water holes, with the through hole on the spring seat and the spear rod water holes connected.

[0008] Furthermore, the spring seat is provided with several water holes.

[0009] Furthermore, the outer cylinder has several liquid passage holes evenly distributed around its circumference.

[0010] Furthermore, the lower end of the concave grinding shoe is provided with a carbide block, and the lower end of the carbide block is a concave spherical surface.

[0011] Furthermore, the concave grinding shoe has a number of water holes and a number of water channels evenly distributed around its circumference, with the number of water channels being less than the number of water holes, and the water holes and water channels being connected.

[0012] Furthermore, the spear shaft is provided with several guide protrusions, and the retrieval slip is provided with several guide grooves, with the guide protrusions and guide grooves working together to guide the target.

[0013] Furthermore, the taper of the upper conical surface of the guide head is 1:16, and the lower end is a frustum structure.

[0014] The beneficial effects of the milling and grinding tool for catching short fish heads described in this utility model are as follows: (1) The short fish head retrieval tool described in this utility model uses a hard alloy block set at the lower end of the concave grinding shoe to trim the fallen fish head. Then, with the cooperation of the thrust spring, retrieval slip, spear rod and guide head, the trapezoidal teeth at the lower end of the retrieval slip expand and fit against the inner wall of the fallen fish head. Under the action of the sawtooth structure on the outside of the trapezoidal teeth, the fallen fish head is lifted upward, realizing the integration of grinding and retrieval functions. The grinding and trimming of the fallen fish head and the retrieval can be completed in one well, without the need for a second well, reducing the operation process, shortening the operation time by more than 30%, and reducing the operation cost.

[0015] (2) The short fish head retrieval tool described in this utility model has a trapezoidal tooth design with carburized hardening for the retrieval jaws, which has strong clamping force and good wear resistance. With the pre-tightening of the thrust spring and the inverted conical guide head, it ensures reliable clamping of the milled fish head and increases the retrieval success rate to over 95%. It also has a retractable function, which can smoothly retract the spear when encountering obstruction, avoiding the risk of secondary drill jamming.

[0016] (3) The short fish head retrieval tool described in this utility model has a concave grinding shoe with a water channel and a water eye forming a three-dimensional chip removal channel. The well washing fluid circulates fully and can quickly carry the grinding chips out to avoid accumulation. The hard alloy block is made of YC8 alloy, which has high hardness and increases the grinding efficiency by 40% compared with ordinary grinding shoes. It can quickly repair irregular fish heads. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0018] In the attached diagram: Figure 1 This is an axial cross-sectional view of a milling tool for catching short fish heads according to this utility model; Figure 2 This is a radial cross-sectional view of the milling and retrieval tool for short fish heads described in this utility model at the position of the two axes of the water eye; Figure 3 This is an axial cross-sectional view of the concave grinding shoe and the carbide block of a short fish head retrieval tool described in this utility model; Figure 4 This is a radial cross-sectional view of the concave grinding shoe of the short fish head retrieval tool described in this utility model at the position of the two axes of the water eye; Figure 5 This is an axial cross-sectional view of the retrieval chuck of a milling and grinding tool for retrieval of short fish heads, as described in this utility model. Figure 6 This utility model describes a milling and grinding tool for catching short fish heads. Figure 5 A magnified view of a section at point A in the middle; Figure 7 This utility model describes a milling and grinding tool for catching short fish heads. Figure 5 Cross-sectional view at point BB: Figure 8 This is an axial cross-sectional view of the spear shaft and guide head of a milling and grinding tool for catching short fish heads, as described in this utility model. Figure 9 This is a schematic diagram of the guide protrusion of a milling tool for catching short fish heads according to the present invention; Among them: 1-upper connector, 2-outer cylinder, 3-spring seat, 4-thrust spring, 5-retrieval slip, 51-trapezoidal tooth, 6-spear rod, 7-concave grinding shoe, 8-hard alloy block, 9-water channel, 10-water eye one, 11-spear rod water hole, 12-outer cylinder filter liquid, 13-guide head, 14-water eye two, 15-guide protrusion, 16-guide groove. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. The described embodiments are merely some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Specific implementation method one: See Figures 1-9 This embodiment is described in detail. The short fish head retrieval tool described in this embodiment specifically includes a cylindrical body, a pre-tightening structure, and a retrieval structure. The pre-tightening structure is located inside the cylindrical body and connected to the retrieval structure, and the retrieval structure is connected to the pre-tightening structure. The cylindrical body includes an upper connector 1, an outer cylinder 2, and a concave grinding shoe 7; the upper connector 1, outer cylinder 2, and concave grinding shoe 7 are all cylindrical structures, and are sequentially connected by threads, with the threads turning left-hand; a carbide block 8 is provided at the lower end of the concave grinding shoe 7, and the concave grinding shoe 7 and the carbide block 8 are connected by welding, with the lower end of the carbide block 8 being a concave spherical surface.

[0021] The upper connector 1 is made of 35CrMo alloy material, which has high strength, high toughness and good corrosion resistance. The upper end of the upper connector 1 is connected to the tubing string by a thread. The thread direction is left-handed, and the thread specification is determined according to the tubing string to be connected, ensuring a firm connection with the tubing string and effectively preventing wellhead fluid leakage and ensuring operational sealing. The concave grinding shoe 7 is made of 35CrMo alloy material, and the cemented carbide block 8 is made of tungsten cobalt cemented carbide (YC8). YC8 cemented carbide has high hardness (HRA90 and above) and high wear resistance, which can efficiently grind and mill burrs and deformed parts of the fish head, and shape a regular clamping surface. The concave grinding shoe 7 and the cemented carbide block 8 are welded by copper welding process. The welding temperature is controlled at 800℃-900℃, and the welding gap is 0.1-0.2mm. After welding, the welded parts are subjected to penetrant testing to ensure welding quality and prevent the cemented carbide block from falling off.

[0022] The salvage structure includes a salvage slip 5, a spear shaft 6, and a guide head 13. The spear shaft 6 and guide head 13 are made of 35CrMo alloy material, with an overall length of 500mm-800mm. One end of the spear shaft 6 is connected to the pre-tightening structure via a thread, and the other end is connected to the guide head 13. The upper and lower ends of the guide head 13 are both frustum structures, with a taper of 1:16 on the upper frustum cone surface. The guide head 13 is 31mm long, has a maximum outer diameter of 45mm, and a minimum outer diameter of 21mm. The guide head 13 is used to guide the salvage slip 5 smoothly into the inner diameter of the fish head.

[0023] The retrieval slip 5 is made of high-strength alloy material and is fitted onto the spear shaft 6. The lower end of the retrieval slip 5 has several trapezoidal teeth 51 with a serrated outer surface. The upper end of the retrieval slip 5 contacts the pre-tightening structure. Under the thrust of the pre-tightening structure, the retrieval slip 5 maintains a downward trend, ensuring the trapezoidal teeth 51 are pre-tightly fitted onto the conical surface of the guide head 13. The trapezoidal teeth 51 have a tooth height of 3-5mm, a tooth pitch of 5-8mm, and are carburized to a depth of 0.8-1.2mm, achieving a surface hardness of HRC58-62, significantly improving wear resistance and ensuring reliable contact with the head of the falling fish. The guide head 13 has several guide protrusions 15, and the retrieval slip 5 has several guide grooves 16. The guide protrusions 15 and guide grooves 16 work together to guide the retrieval slip 5 in axial movement.

[0024] The pre-tightening structure includes a spring seat 3 and a thrust spring 4; the upper connector 1 has a stepped structure inside, and the spring seat 3 is clamped between the upper connector 1 and the outer cylinder 2; the lower end of the spring seat 3 is threaded to the spear 6, and the thread direction is right-handed; the thrust spring 4 is fitted on the spear 6, with its upper end in contact with the spring seat 3 and its lower end in contact with the retrieval slip 5, providing a continuous pre-tightening force to the retrieval slip 5 through the thrust spring 4, and the trapezoidal teeth 51 at the lower end of the retrieval slip 5 acting on the conical surface of the guide head 13. The downward movement generates a certain radial expansion, allowing the trapezoidal teeth 51 to insert into the interior of the fish head along with the guide head 13. When the tool is pulled upward, the serrated structure on the surface of the trapezoidal teeth 51 engages with the inner wall surface of the fish head. Under the action of friction, the fish head drives the retrieval slip 5 downward. The trapezoidal teeth 52 undergo radial expansion under the action of the conical surface of the guide head 13, causing the trapezoidal teeth 51 at the lower end of the retrieval slip 5 to fit tightly against the inner wall of the fish head during the retrieval process. The thrust spring 4 is made of 60Si2Mn alloy spring steel, which has excellent elasticity and fatigue strength.

[0025] The spring seat 3 has a through hole at its center, and several water holes 10 are evenly arranged around the through hole; the spear rod 6 and the guide head 13 are provided with spear rod water holes 11, the diameter of which is 10mm; the through hole on the spring seat 3 and the spear rod water holes 11 are connected, which can guide the well washing fluid to the end of the fish head to flush away mud and dirt.

[0026] The outer cylinder 2 has eight fluid passage holes 12 evenly distributed around its circumference. The axis of each fluid passage hole 12 forms a certain angle with the axis of the tool as a whole. The diameter of each fluid passage hole 12 is 10mm. The outer cylinder 2 is made of 35CrMo alloy material, and its inner wall has a stepped structure for positioning and connecting the concave grinding shoe 7. The concave grinding shoe 7 has six water inlets 14 and three water channels 9 evenly distributed around its circumference. The water channels 9 are located on the outer surface of the concave grinding shoe 7, and each of the three water inlets 14 is connected to a water channel 9. The water inlets 10, the spearhead water hole 11, the outer cylinder fluid passage holes 12, the water inlets 14, and the water channels 9 are connected to form a channel for well cleaning fluid circulation and grinding debris discharge, preventing grinding debris accumulation. The width of the water channel 9 is 20mm, the depth is 10mm, and the distance between the water channel 9 and the water inlets 14 is 45.68mm. The edges of the water tank 9 are rounded (with a radius of 2mm-3mm) to avoid stress concentration and scratches on the inner wall of the tubing.

[0027] The specific usage process of the milling and short fish head retrieval tool described in this utility model is explained as follows: Tool assembly process: 1. Component pretreatment: Blacken the surface of all metal parts; inspect the welding quality of the cemented carbide block 8 to ensure there are no cracks or detachments.

[0028] 2. Component Assembly: Install the retrieval slip 5 onto the middle of the spear shaft 6, insert the guide protrusion 16 into the guide groove 15, and fit the thrust spring 4 onto the upper part of the spear shaft 6. Place the spring seat 3 on the upper end of the outer cylinder 2, then install the assembled spear shaft 6, retrieval slip 5, and thrust spring 4 from the lower end of the outer cylinder 2, ensuring the upper end of the thrust spring 4 contacts the spring seat 3. Connect the spear shaft 6 and spring seat 3 via threads to complete the assembly of the retrieval system with the outer cylinder. Insert the spring seat 3 into the stepped structure inside the upper connector 1. The upper connector 1 is fixedly connected to the upper end of the outer cylinder 2 via threads. After tightening, check that the seals are properly installed to ensure overall sealing. Fix the concave grinding shoe 7 to the lower end of the outer cylinder 2 via threads. After assembly, ensure that the clearance between each component meets the design requirements.

[0029] 3. Key parameter control: 1) Milling parameters: drilling pressure 10-20kN, rotation speed 60-100r / min, well washing fluid discharge 20-30m³ 3 / h, ensuring grinding and milling efficiency and smooth chip removal. 2) Welding parameters: brazing temperature of cemented carbide blocks 800-900℃, welding gap 0.1-0.2mm, post-weld penetrant testing, 100% pass rate. 3) Material properties: 35CrMo alloy material tensile strength ≥980MPa, yield strength ≥835MPa; 60Si2Mn spring steel elastic limit ≥800MPa, fatigue life ≥10 6 The hardness of the carburized layer of the salvaged vase is HRC58-62, and the depth of the carburized layer is 0.8-1.2mm.

[0030] Taking a stratified water injection well in Daqing Oilfield as an example, the downhole tubing in this well is Φ89mm tubing. Due to corrosion, it fractured, forming a short fish-head-shaped debris about 200mm in length. The downhole temperature is 95℃, the pressure is 25MPa, and the medium contains 10% hydrogen sulfide. The short fish-head retrieval tool of this utility model is used for the operation, and the specific implementation is as follows: 1. Tool selection: Select a retrieval tool with a spear shaft length of 600mm and a connecting thread type of 27 / 8BE (compatible with Φ89mm oil pipe). The materials of each component meet the design requirements, and the welding quality of the carbide block 8 has passed the flaw detection test.

[0031] 2. Operation process: Lower the tool to a position 10m above the fallen object, and start the well-washing pump (displacement capacity 25m³ / h). 3 / h), circulate the well-washing fluid for 5 minutes; lower the tubing string until the carbide block 8 at the lower end of the concave grinding shoe 7 contacts the fallen object, apply drilling pressure of 15kN, rotate the rotary table at 80r / min, and perform milling operations for 30 minutes, during which the abrasive debris in the return fluid gradually decreases; stop the rotary table, lower the tubing string so that the guide head 13 inserts into the fish head; under the thrust of the thrust spring 4, the trapezoidal teeth 51 at the lower end of the retrieval slip 5 follow the guide head 13 and insert into the inside of the fallen fish head; the serrated structure on the surface of the trapezoidal teeth 51 and the fallen object... When the inner wall of the object's head contacts and engages with the tool, the friction between the inner wall of the object's head and the serrated structure pulls the retrieval slip 5 downwards. The lower end of the retrieval slip 5 expands outwards under the action of the guide head 13's conical surface, so that the trapezoidal teeth 51 at the lower end of the retrieval slip 5 tightly fit against the inner wall of the object's head. The tubing is pulled up until the suspended weight increases by 5kN to confirm that the retrieval slip 5 is holding reliably. Then the tubing is slowly raised, and the object is retrieved to the ground after 40 minutes. The operation is successful. When spear removal is required, use hydraulic clamps to grip the outer diameter of the fish head, and turn the tubing left. The threads connecting the tubing to the upper connector 1, the upper connector 1 to the outer cylinder 2, and the outer cylinder 2 to the concave grinding shoe 7 are all left-handed. At this time, the tubing of the above components will be tightened when turned left. The thread connecting the spring seat 3 and the spear rod 6 is a right-handed thread. Turning the tubing left shortens the threaded connection length between the spring seat 3 and the spear rod 6, increases the activity area of ​​the thrust spring 4, and relaxes the thrust spring 4. The thrust spring 4 no longer applies thrust to the salvage slip 5. The trapezoidal tooth 51 generates radial contraction along the conical surface of the guide head 13 under its own elasticity. The salvage slip 5 moves upward along the spear rod 6 as a whole. The trapezoidal tooth 51 and the inner wall of the fish head no longer fit, realizing the release of the salvage slip 5 and the fish head. When encountering obstruction during the salvage process, spear removal can also be achieved by turning the tubing left, avoiding the risk of secondary drill jamming.

[0032] Compared to the traditional "grinding tool + retrieval tool" secondary downhole approach, this operation shortened the time by 4 hours and reduced the cost by 35%. The tool retrieval success rate was 100%, with no jamming, no corrosion or deformation on the tool surface, and no carbide block detachment, allowing for reuse. Core components (upper connector 1, outer cylinder 2, spear shank 6, concave grinding shoe 7) are all made of 35CrMo alloy, exhibiting excellent temperature, pressure, and corrosion resistance, suitable for downhole conditions of 120℃, 30MPa, and corrosive media. The carbide block uses high-precision copper welding, ensuring strong welds and extending the grinding shoe's lifespan by more than 50% compared to ordinary grinding shoes. The tool is adaptable to complex working conditions and has a long service life. The tooth profile of the concave grinding shoe 7, the length of the spear shank 6, and the thread specifications can be flexibly adapted to the size of the dropped object in the tubing string, making it suitable for most short-headed object handling scenarios in stratified water injection tubing strings, demonstrating strong versatility and wide applicability.

[0033] In summary, the milling and retrieval tool for short fish heads described in this utility model uses a hard alloy block 8 at the lower end of a concave milling shoe 7 to trim the fallen fish head. Then, with the cooperation of the thrust spring 4, the retrieval slip 5, the spear 6, and the guide head 13, the trapezoidal teeth 51 at the lower end of the retrieval slip 5 expand and fit against the inner wall of the fallen fish head. Under the action of the serrated structure on the outer side of the trapezoidal teeth 51, the fallen fish head is lifted upward, realizing the integration of milling and retrieval functions. The milling and trimming of the fallen fish head and the retrieval can be completed in one well run, without the need for a second well run, reducing the operation steps, shortening the operation time by more than 30%, and reducing the operation cost.

[0034] The present invention discloses a tool for milling and retrieving short fish heads. The retrieval jaws 5 are designed with trapezoidal teeth 51 and carburized hardening, which provides strong clamping force and good wear resistance. Combined with the pre-tightening of the thrust spring 4 and the inverted conical guide head 13, it ensures reliable clamping of the milled fish head, increasing the retrieval success rate to over 95%. It also has a retractable function, which can smoothly retract the spear when encountering obstruction, avoiding the risk of secondary drill jamming.

[0035] The present invention describes a milling tool for catching short fish heads. The concave milling shoe 7 has a water channel 9 that forms a three-dimensional chip removal channel with the water eye, allowing for sufficient circulation of the well washing fluid and rapid removal of milling chips to avoid accumulation. The hard alloy block 8 is made of YC8 alloy, which has high hardness and milling efficiency that is 40% higher than that of ordinary milling shoes, and can quickly trim irregular fish heads.

[0036] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above descriptions are merely specific embodiments of this utility model and are not intended to limit the utility model. They can also be reasonable combinations of the features described in the above embodiments. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A tool for milling and retrieving short fish heads, characterized in that: The system includes a cylinder, a pre-tightening structure, and a retrieval structure. The pre-tightening structure is located inside the cylinder and connected to the retrieval structure. A concave grinding shoe (7) is provided at the lower end of the cylinder. The concave grinding shoe (7) is a cylindrical structure. The retrieval structure includes a retrieval slip (5), a spear rod (6), and a guide head (13). One end of the spear rod (6) is connected to the pre-tightening structure, and the other end is connected to the guide head (13). The retrieval slip (5) is fitted onto the spear rod (6). Several trapezoidal teeth (51) are provided at the lower end. The outer surface of the trapezoidal teeth (51) is a serrated structure. The upper end of the retrieval slip (5) is in contact with the pre-tightening structure. Under the thrust of the pre-tightening structure, the trapezoidal teeth (51) are pre-tightened on the conical surface of the guide head (13).

2. The milling and retrieving tool for short fish heads according to claim 1, characterized in that: The pre-tightening structure includes a spring seat (3) and a thrust spring (4); the spring seat (3) is fixedly installed inside the cylinder and its lower end is connected to the spear rod (6); the thrust spring (4) is fitted on the spear rod (6), with its upper end in contact with the spring seat (3) and its lower end in contact with the retrieval slip (5).

3. The milling and retrieving tool for short fish heads according to claim 2, characterized in that: The cylinder includes an upper connector (1) and an outer cylinder (2), and the upper connector (1), the outer cylinder (2) and the concave grinding shoe (7) are connected in sequence; the spring seat (3) is clamped between the upper connector (1) and the outer cylinder (2).

4. The milling and retrieving tool for short fish heads according to claim 2 or 3, characterized in that: The spring seat (3) has a through hole at its center, and the spear rod (6) and the guide head (13) have a spear rod water hole (11) on their axis. The through hole on the spring seat (3) and the spear rod water hole (11) are connected.

5. The milling and retrieving tool for short fish heads according to claim 2 or 3, characterized in that: The spring seat (3) is provided with several water holes.

6. The milling and retrieving tool for short fish heads according to claim 3, characterized in that: The outer cylinder (2) has several liquid passage holes (12) evenly distributed around its circumference.

7. The milling and retrieving tool for short fish heads according to claim 1, characterized in that: The concave grinding shoe (7) is provided with a carbide block (8) at the lower end, and the lower end of the carbide block (8) is a concave spherical surface.

8. The milling and retrieving tool for short fish heads according to claim 1 or 7, characterized in that: The concave grinding shoe (7) has several water holes and several water channels (9) evenly distributed around its circumference. The number of water channels (9) is less than that of water holes, and the water holes and water channels (9) are connected.

9. The milling and retrieving tool for short fish heads according to claim 1, characterized in that: The guide head (13) is provided with several guide protrusions (15), and the retrieval slip (5) is provided with several guide grooves (16). The guide protrusions (15) and guide grooves (16) cooperate to guide.

10. The milling and retrieving tool for short fish heads according to claim 1, characterized in that: The upper cone of the guide head (13) has a taper of 1:16, and the lower end has a frustum structure.

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