Milling shoe for bridge plug

Abstract

The invention discloses a milling shoe for a bridge plug, and belongs to underground operation equipment. The milling shoe comprises a milling shoe body, a power mechanism and a plurality of cutting elements, all the cutting elements are divided into two types including movable cutting elements and fixed cutting elements, the movable cutting elements are movably arranged on the lower end face of the milling shoe body and can move in the radial direction of the milling shoe body, and the fixed cutting elements are arranged on the lower end face of the milling shoe body. The fixed cutting element is fixed to the lower end face of the milling shoe body, and the power mechanism is used for driving the movable cutting element to reciprocate in the radial direction of the milling shoe body. The two cutting elements form staggered scratches on the bridge plug, strip-shaped scrap iron generated in the grinding and washing process is easily broken at the staggered points, so that the length of the scrap iron is reduced, the scrap iron is prevented from forming rolled scraps, the generated scrap iron is not prone to being mutually wound, the drill jamming risk is reduced, and meanwhile, compared with granular scrap iron, the scrap iron is not prone to being damaged. The scrap iron is still in a strip shape, the size is obviously larger, abrasion to cutting elements is reduced, and the service life of the milling shoe can be prolonged.

Description

Technical Field

[0001] The invention belongs to downhole operation equipment, in particular to downhole grinding equipment, specifically a grinding shoe for a bridge plug. Background Art

[0002] A bridge plug is a downhole separation device used to axially divide a wellbore into distinct sections, facilitating staged fracturing in each section and ultimately increasing production. After the fracturing operation is completed, the oil and gas pathways between the sections need to be connected. Therefore, all bridge plugs must be drilled out, requiring the use of a grinding shoe. A grinding shoe is a commonly used downhole grinding tool, equipped with a grinding element on its lower end surface to abut and grind against the bridge plug.

[0003] At present, there are many kinds of grinding shoes. Figure 1 As shown, some mills have carbide particles welded on the end face of the mill body. During the rotation of the mill, the carbide particles continuously rub against the bridge plug to produce tiny iron chips. The iron chips produced by this type of mill are small in size and easily follow the outer wall of the circulating fluid, with a low risk of drill jamming. However, the grinding rate is low and the mill itself wears out more and has a short lifespan. Therefore, a single mill can grind a small number of bridge plugs, while each well often has dozens of bridge plugs that need to be ground. This requires frequent lifting of the tubing to replace the mill, significantly increasing the operation time and poor economic efficiency. Some mills weld carbide columns on the end face of the mill body according to a certain pattern. When in use, these carbide columns are inserted into the bridge plug. When the mill rotates, the carbide columns cut the bridge plug to form wire-like iron chips. In this way, the grinding time is significantly shortened and the life of the mill is significantly increased. However, the iron chips are longer in size and are prone to coiled iron chips, such as Figure 2 As shown, these iron chips easily become entangled and deposited in the wellbore, leading to drill sticking. To address this, some mills combine the features of the first two types of mills. Carbide pillars are placed on the lower end of the mill to quickly cut the mill and increase the grinding rate. Meanwhile, crushed carbide particles are randomly arranged on the back of the carbide pillars to further grind the strand-like iron chips, ultimately forming small iron chip particles. This combination achieves a high grinding rate and reduces the risk of drill sticking, but it still poses the problem of severe wear of the carbide particles, resulting in a shorter lifespan for individual mills. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a grinding shoe for a bridge plug. The grinding shoe of the present invention is provided with two cutting elements. When the grinding shoe rotates, the two cutting elements form staggered scratches on the bridge plug. The iron chips are easily broken at the scratches, thereby significantly shortening the length of the iron chips, achieving the purpose of reducing the size of the wire-shaped iron chips, and at the same time avoiding the problem of excessive wear and short service life of the grinding shoe itself caused by excessive grinding of the iron chips.

[0005] In order to achieve the above object, the solution provided by the present invention is as follows: A grinding shoe for a bridge plug, comprising: The grinding shoe body is provided with an axially extending blind hole, a water return groove on the outer wall, and a water hole connected to the blind hole on the lower end surface; A plurality of cutting elements are arranged circumferentially on the lower end surface of the mill shoe body. The cutting elements are divided into two categories: movable cutting elements and fixed cutting elements. The movable cutting elements are movably arranged on the lower end surface of the mill shoe body and can move radially along the mill shoe body. The fixed cutting elements are fixed on the lower end surface of the mill shoe body. The power mechanism is used to drive the movable cutting element to move back and forth along the radial direction of the grinding shoe body.

[0006] As a specific embodiment of the present invention, the power mechanism includes: A rotating shaft is arranged axially along the blind hole, and a cam is fixed on one end of the rotating shaft close to the lower end surface of the grinding shoe body; A centralizer fixed in a blind hole is used to centralize the rotating shaft; The screw motor located in the blind hole is used to drive the shaft to rotate; T-shaped slots located on the side wall of the mill shoe body and arranged radially along the mill shoe body; A linear groove is located on the lower end surface of the mill shoe body and is arranged radially along the mill shoe body, and the linear groove is connected to the T-slot; The T-slide block with clearance fit between the T-slot and the linear slot is used to carry the movable cutting element; A spring is used to push the T-shaped slider to move radially inward along the grinding shoe body and abut against the annular outer wall of the cam.

[0007] As a specific embodiment of the present invention, there are an even number of cutting elements, wherein the number of movable cutting elements is equal to the number of fixed cutting elements, and the two are alternately distributed on the lower end surface of the grinding shoe body.

[0008] Furthermore, the movable cutting elements are arranged in a circular array along the main body of the mill shoe. Each movable cutting element is equipped with a T-slot, T-slider, linear slot, and spring. The outer annular wall of the cam is decorated with an array of protrusions equal to the number of movable cutting elements. This helps reduce eccentric forces on the rotating shaft and centralizer, extending the life of the equipment.

[0009] Furthermore, the linear groove connects the inside and outside of the blind hole, and the proximal end of the T-slot is located outside the proximal end of the linear groove. In this way, the linear groove can be used as a movable water hole. When the T-shaped slider slides in the linear groove, it changes the water output of each water hole, thereby frequently disturbing the fluid between the mill shoe and the bridge plug, avoiding the formation of dead zones.

[0010] In one embodiment of the present invention, the movable cutting element includes multiple cutting edges, each of which is a pyramid (also known as a square pyramid or an angular pyramid). This helps reduce resistance when the movable cutting element moves in different directions within the bridge plug. Furthermore, the pyramid's tapered diameter allows its sidewalls to strongly squeeze the generated iron chips, facilitating their breakage.

[0011] In one embodiment of the present invention, when the grinding shoe body is positioned vertically with the cutting elements facing downward, the lower end of the fixed cutting element's cutting edge is higher than the lower end of the movable cutting element's cutting edge. This allows the movable cutting element to penetrate deeper into the bridge plug during grinding than the fixed cutting element does. Chips generated by the fixed cutting element are inevitably broken off at the intersection of the scratches, reducing the chance of chip curling.

[0012] As a specific embodiment of the present invention, the fixed cutting element adopts a cutting edge with a negative rake angle.

[0013] Beneficial effects: The present invention is provided with two cutting elements, wherein the fixed cutting element rotates with the mill shoe body to form approximately circular scratches on the bridge plug body, and the movable cutting element rotates with the mill shoe body and moves radially along the mill shoe body to form approximately petal-shaped scratches on the bridge plug. The scratches of the two cutting elements are staggered with each other, and the formed wire-like iron chips are easily broken at the intersection point, thereby reducing the length of the iron chips and avoiding the formation of curled chips. The iron chips produced in this way are not easy to entangle with each other, reducing the risk of drill jamming. At the same time, compared with granular iron chips, this iron chip is still in the form of wire strips and is obviously larger in size, which reduces the wear on the cutting elements and helps to increase the life of the mill shoe. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of two types of grinding shoes in the prior art; Figure 2 It is a schematic diagram of a scroll; Figure 3 It is a structural schematic diagram of a specific embodiment of the present invention; Figure 4 yes Figure 3 A schematic structural diagram of the lower end surface of the middle grinding shoe body; Figure 5 yes Figure 3 Schematic diagram of the structure with the lower end face of the middle grinding shoe main body removed; Figure 6 yes Figure 5 Schematic diagram of the structure of the middle grinding shoe after removing the T-shaped slider, rotating shaft and cam; Figure 7 yes Figure 5 Schematic diagram of the combined structure of the rotating shaft and the cam; Figure 8 yes Figure 5 Schematic diagram of the combined structure of the middle T-shaped slider and the movable cutting element; Figure 9 yes Figure 8 Schematic diagram of the structure of the middle pyramid; Figure 10 yes Figure 3 Schematic diagram of the state of the fixed cutting element cutting the bridge plug; In the figure: grinding shoe body 100; blind hole 110; return water groove 120; water eye 130; cutting element 200; movable cutting element 210; pyramid 211; fixed cutting element 220; rotating shaft 310; cam 320; T-slot 330; linear slot 340; T-slide block 350; and centralizer 360. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0016] Please refer to Figures 3 to 9 , which shows the structure of a specific embodiment of a mill shoe for a bridge plug according to the present invention. The mill shoe for a bridge plug according to the present invention comprises a mill shoe body 100 and cutting elements 200. There are a plurality of cutting elements 200, which are circumferentially distributed on the lower end surface of the mill shoe body 100 and are used to cut the bridge plug. A connecting portion is provided at the upper end of the mill shoe body 100 for connection to the upper pipe string. An axially extending blind hole 110 is provided within the mill shoe body 100. A water hole 130 is provided on the lower end surface of the mill shoe body 100, communicating with the blind hole 110 within the mill shoe body 100. A water return groove 120 is provided on the outer wall of the mill shoe body 100. During use, liquid is introduced into the pipe string on the ground and the pipe string is rotated. The cutting elements 200 abut the bridge plug and rotate with the upper pipe string, continuously cutting the bridge plug and generating iron chips. Simultaneously, liquid is ejected through the blind hole 110 and the water hole 130, cooling the cutting elements 200 and carrying the iron chips to the surface to prevent drill bit sticking. These are conventional configurations of existing grinding shoes. The number of water holes 130, the shape and number of return water grooves 120, etc. can be determined according to needs and will not be described in detail here.

[0017] The present invention improves upon existing mill shoes. The cutting elements 200 of the present invention are divided into two categories: a movable cutting element 210 and a fixed cutting element 220. The movable cutting element 210 is movably disposed on the lower end surface of the mill shoe body 100 and is capable of radial movement, while the fixed cutting element 220 is fixed to the lower end surface of the mill shoe body 100. The mill shoe of the present invention also includes a power mechanism for driving the movable cutting element 210 to reciprocate radially along the mill shoe body 100. During use, the grinding shoe body 100 rotates synchronously with the upper pipe column, and the fixed cutting element 220 forms an approximately circular scratch on the bridge plug body. The movable cutting element 210 rotates with the upper pipe column and also moves back and forth radially along the grinding shoe body 100 driven by the power mechanism, thereby forming approximately petal-shaped scratches on the bridge plug. In this way, the scratches of the movable cutting element 210 and the fixed cutting element 220 are intertwined with each other, and the formed wire-like iron chips are easily broken at the intersection point, thereby reducing the length of the iron chips and avoiding the formation of curled chips. The iron chips generated in this way are not easy to entangle with each other, reducing the risk of drill jamming. At the same time, compared with granular iron chips, this iron chip is still in the form of wire strips and is obviously larger in size, which reduces the wear on the cutting element 200 and helps to increase the life of the grinding shoe.

[0018] The fixed cutting element 220 of the present invention can adopt the cutting element 200 commonly used in existing grinding shoes, such as Figure 4 As shown, the fixed cutting element 220 includes a plurality of cutting edges, and the lower end of each cutting edge is V-shaped, so as to facilitate the penetration into the bridge plug when the grinding shoe body 100 is subjected to axial pressure. There are many specific forms of cutting edges. For example, its rake angle can be negative, positive or zero. In some embodiments, a cutting edge with a negative rake angle is selected, such as Figure 10 As shown in the figure, after the chips are generated, they are strongly squeezed by the cutting edge's rake face (the surface that the cutting edge directly contacts during cutting). This squeeze makes the chips more likely to break at mechanically weak points, such as scratch intersections. A larger negative rake angle increases the stronger the rake face's squeezing effect on the chips, making them more conducive to chip breakage. However, under the same axial pressure, the depth of the cutting edge's penetration into the bridge plug decreases with increasing angle, resulting in a decrease in cutting rate. Therefore, a smaller angle, such as 18°, is generally chosen.

[0019] The movable cutting element 210 of the present invention rotates around the grinding shoe body 100 and moves radially along the grinding shoe body 100 when in use. In some embodiments, the cutting edge of the movable cutting element 210 is a pyramid 211, such as Figure 8 and Figure 9As shown, each movable cutting element 210 includes a plurality of pyramids 211 arranged in an array. The top of each pyramid 211 is a sharp point, facilitating insertion into the bridge plug. The base of the pyramid 211 can be a regular hexagon, a regular octagon, or the like. Thus, the sidewalls of the pyramid 211 have multiple sharp edges, facilitating movement in various directions within the bridge plug to form scratches. Simultaneously, the pyramid 211 gradually tapers in diameter from the base to the point, and its sidewalls exert strong pressure on the generated iron chips, thereby facilitating the breaking of the iron chips cut by the movable cutting element 210. Furthermore, in some embodiments, the grinding shoe body 100 is arranged vertically, with the cutting element 200 facing downward. The lower end of the cutting edge of the fixed cutting element 220 is higher than the lower end of the cutting edge of the movable cutting element 210. During grinding, the depth of penetration of the movable cutting element 210 into the bridge plug is greater than the depth of penetration of the fixed cutting element 220 into the bridge plug. Thus, the iron chips generated by the fixed cutting element 220 are inevitably broken at the intersection of the scratches, reducing the probability of chip curling.

[0020] In the present invention, the power mechanism is used to drive the movable cutting element 210 to move back and forth along the radial direction of the mill shoe body 100. In some embodiments, the power mechanism includes a rotating shaft 310, a cam 320, a T-slot 330, a linear slot 340, a T-slide 350, a straightener 360, a screw motor (not shown in the figure) and a spring (not shown in the figure). The rotating shaft 310 is arranged axially along the blind hole 110, and the straightener 360 is used to straighten the rotating shaft 310 so that it is located on the center line of the blind hole 110. The cam 320 is fixed to one end of the rotating shaft 310 close to the lower end face of the mill shoe body 100; the screw motor is a commonly used component in existing drilling equipment, which uses liquid impulse to rotate the screw, thereby outputting torque. The specific structure is not described in detail here. The screw motor of the present invention is located in the blind hole 110, and is used to drive the rotating shaft 310 to rotate, thereby driving the cam 320 to rotate; the T-slot 330 is located on the side of the mill shoe body 100. The linear groove 340 is located on the lower end surface of the mill shoe body 100 and is arranged radially along the mill shoe body 100. The linear groove 340 is connected to the T-slot 330. The T-slot 350 is clearance-matched with the T-slot 330 and the linear groove 340. Therefore, it can slide along the T-slot 330 and the linear groove 340, thereby driving the movable cutting element 210 to move radially along the mill shoe body 100. The spring is used to push the T-slot 350 to move radially inward along the mill shoe body 100 and abut the annular outer wall of the cam 320. Therefore, under the cooperation of the spring, when the cam 320 rotates, the movable cutting element 210 will reciprocate radially along the mill shoe body 100.

[0021] In some embodiments, there are an even number of cutting elements 200, and the number of movable cutting elements 210 and fixed cutting elements 220 is equal, for example Figure 3As shown, there are six cutting elements 200, of which three are movable cutting elements 210 and the remaining are fixed cutting elements 220. The movable cutting elements 210 and the fixed cutting elements 220 are alternately distributed on the lower end surface of the grinding shoe body 100. The movable cutting elements 210 are arranged in an annular array along the grinding shoe body 100. Each movable cutting element 210 is equipped with a T-slot 330, a T-slider 350, a linear slot 340 and a spring. The annular outer wall of the cam 320 is provided with a plurality of protrusions arranged in an annular array. The number of protrusions is equal to the number of movable cutting elements 210. Figure 5 and Figure 7 As shown, at the same time, the forces exerted by the various protrusions on the various T-sliders 350 are closer, reducing the eccentric force on the rotating shaft 310 during operation, which helps reduce the eccentric force on the stabilizer 360 and thus prolong its life. Furthermore, in some embodiments, the linear groove 340 connects the inside and outside of the blind hole 110, and the proximal end (the end closest to the center) of the T-slot 330 is located outside the proximal end of the linear groove 340. In this way, the linear groove 340 can serve as a movable water hole. During movement, the T-slide 350 changes the flow area of ​​the movable water hole, causing the water volume in each water hole 130 to continuously change, thereby frequently disturbing the fluid between the cutting element 200 and the bridge plug, reducing dead zones, and helping to promptly flush generated iron chips out of the grinding shoe area, preventing iron chips from being trapped and increasing the risk of cross-entanglement.

[0022] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in the embodiments of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A grinding shoe for a bridge plug, characterized in that: include: A mill shoe body (100), wherein the mill shoe body (100) is provided with an axially extending blind hole (110), an outer wall thereof is provided with a water return groove (120), and a lower end surface thereof is provided with a water hole (130) in communication with the blind hole (110); A plurality of cutting elements (200) are circumferentially arranged on the lower end surface of the mill shoe body (100), and the cutting elements (200) are divided into two categories, namely, movable cutting elements (210) and fixed cutting elements (220), wherein the movable cutting elements (210) are movably arranged on the lower end surface of the mill shoe body (100) and can move in the radial direction of the mill shoe body (100), and the fixed cutting elements (220) are fixed on the lower end surface of the mill shoe body (100); A power mechanism is used to drive the movable cutting element (210) to reciprocate along the radial direction of the grinding shoe body (100).

2. A mill shoe for a bridge plug according to claim 1, characterized in that: The power mechanism comprises: a rotating shaft (310) arranged axially along the blind hole (110), a cam (320) being fixed to one end of the rotating shaft (310) close to the lower end surface of the grinding shoe body (100); a centralizer (360) fixed in the blind hole (110) for centralizing the rotating shaft (310); A screw motor located in the blind hole (110) is used to drive the rotating shaft (310) to rotate; a T-shaped slot (330) located on the side wall of the mill shoe body (100) and arranged radially along the mill shoe body (100); a linear groove (340) located on the lower end surface of the mill shoe body (100) and arranged radially along the mill shoe body (100), the linear groove (340) being in communication with the T-shaped groove (330); A T-shaped sliding block (350) that is clearance-matched with the T-shaped slot (330) and the linear slot (340), and is used to carry the movable cutting element (210); A spring for pushing the T-shaped slider (350) to move radially inward along the grinding shoe body (100) and abut against the annular outer wall of the cam (320).

3. A mill shoe for a bridge plug according to claim 2, characterized in that: There is an even number of the cutting elements (200), wherein the number of the movable cutting elements (210) is equal to the number of the fixed cutting elements (220), and the two are alternately distributed on the lower end surface of the grinding shoe body (100).

4. A mill shoe for a bridge plug according to claim 3, characterized in that: The movable cutting elements (210) are arranged in an annular array along the grinding shoe body (100), and each movable cutting element (210) is respectively equipped with a T-slot (330), a T-sliding block (350), a linear slot (340) and a spring. The annular outer wall of the cam (320) is provided with a number of protrusions in an annular array equal to the number of the movable cutting elements (210).

5. A mill shoe for a bridge plug according to claim 4, characterized in that: The linear groove (340) connects the inside and outside of the blind hole (110), and the proximal end of the T-shaped groove (330) is located outside the proximal end of the linear groove (340).

6. The mill shoe for bridge plug according to claim 1, characterized in that: The movable cutting element (210) comprises a plurality of cutting edges, and each cutting edge is a pyramid (211).

7. A mill shoe for a bridge plug according to any one of claims 1 to 6, characterized in that: When the grinding shoe body (100) is arranged vertically and the cutting element (200) faces downward, the lower end of the cutting edge of the fixed cutting element (220) is higher than the lower end of the cutting edge of the movable cutting element (210).

8. A mill shoe for a bridge plug according to any one of claims 1 to 6, characterized in that: The fixed cutting element (220) adopts a cutting edge with a negative rake angle.

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