Mechanical safety joint for drill string

Abstract

According to the mechanical safety connector for the drill column, in the safety connector, an upper connector is of a cylindrical structure, a bearing assembly is rotationally connected to a second cylinder, a spline housing is in threaded connection with the interior of the second cylinder, the outer surface of the middle section of the spline housing is provided with a polygonal structure with a fillet, and a left-handed nut is axially and slidably arranged on the spline housing in a sleeving mode; the inner surface of the left-handed nut is provided with a polygonal structure with a fillet, the outer surface of the left-handed nut is provided with a left-handed trapezoidal male buckle, and the left-handed nut and the spline sleeve form a spline assembly in which the left-handed nut and the spline sleeve cannot rotate relatively; the lower connector is sleeved outside the retaining ring, the second barrel and the spline sleeve, the upper end of the lower connector abuts against the lower end of the standby sleeve, the inner surface of the lower connector is provided with a left-handed trapezoidal female buckle used for being in threaded connection with the left-handed trapezoidal male buckle, and the anti-rotation shear pin is connected with the lower connector and the spline sleeve to prevent the lower connector and the spline sleeve from rotating relatively and limiting in the axial direction. The safety joint does not need to consider a neutral point problem and is high in construction efficiency and success rate.

Description

Technical Field

[0001] The present invention relates to the technical fields of drilling, well workover, and well logging, and particularly relates to a mechanical safety joint for a drill string. Background Art

[0002] A safety joint is a special tool widely used in the fields of drilling, well workover, well logging, etc. to protect the drill string. It can be connected to the required part of the drill string used according to the operating conditions. Under normal circumstances, it will not affect the operation of the drill string. However, if the drill string gets stuck downhole and cannot be released, the safety joint can be reversed and released by back-off, and the drill string above the sticking point can be lifted out of the wellbore for further accident handling.

[0003] Common safety joints are mainly divided into two types according to the principle of back-off and release: mechanical type and hydraulic type. There are various structural forms of mechanical safety joints. Some have directly reverse-threaded connections between the upper and lower joints for forward rotation and back-off, and some have the upper and lower joints fixed by pins and rely on the sliding of sliding keys in the sliding grooves for back-off. Hydraulic safety joints are mostly ball-drop type, which form a pressure difference by sending the ball to the ball seat by drilling fluid to hold pressure, and push the piston to cut the safety pin to achieve the purpose of reversing and releasing the upper and lower joints.

[0004] During the use of common mechanical safety joints, since the frictional resistance of the drill string at various depths along the wellbore is random, especially in the case of large well inclination or non-smooth wellbore trajectory, the frictional resistance is more uncontrollable, which will cause the position of the neutral point to change and be not easy to adjust. At this time, if the operating personnel lack experience, the neutral point cannot be accurately adjusted to the safety joint during back-off, and the safety joint may be back-off under tension or compression, thus unable to ensure smooth back-off and release, and further increasing the difficulty of handling stuck-pipe accidents. In addition, for the safety joint connected by reverse threads, after operations such as tightening, the shoulders where the upper and lower joints are combined will be tightly stuck, which will also make it difficult to back off the safety joint. When the conventional mechanical safety joint is reversed and released, the operating personnel need to adjust the neutral point to the safety joint according to experience so that it is not under tensile or compressive load to successfully complete forward rotation and back-off. However, in some wellbores with large well inclination or non-smooth wellbore trajectory, due to the large frictional resistance of the wellbore wall, it is difficult to accurately adjust the neutral point to the safety joint, resulting in the safety joint being possibly back-off under tensile or compressive state, so that the threads are pressed dead, unable to back off, and unable to release.

[0005] The above information disclosed in the background art section is only used to enhance the understanding of the background of the present invention, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0006] The object of the present invention is to provide a mechanical safety joint for a drill string, which is a mechanical safety joint without a neutral point that has a simple structure, is safe and reliable in use, does not require operation experience, and does not need to consider the adjustment problem of the neutral point. It is beneficial to improve the success rate of safe release after sticking, and has a very wide range of applications.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A mechanical safety joint for a drill string of the present invention includes:

[0009] An upper sub, which has a cylindrical structure. The cylindrical structure includes a first cylinder body with a first outer diameter and a second cylinder body with a second outer diameter. The second cylinder body extends coaxially from the lower end of the first cylinder body and the second outer diameter is smaller than the first outer diameter. A step is formed at the connection between the second cylinder body and the first cylinder body;

[0010] A bearing assembly, which is rotatably connected to the second cylinder body. The bearing assembly includes,

[0011] A bearing sleeve, which is axially sleeved on the second cylinder body rotatably,

[0012] Ball bearings, which are arranged in the annular gap formed by the step and the inner and outer shoulders of the bearing sleeve,

[0013] A spare sleeve, which is axially sleeved on the second cylinder body rotatably. The ball bearings, the bearing sleeve and the spare sleeve sleeved on the second cylinder body in sequence form a bearing assembly;

[0014] A check ring, which is threadedly connected to the second cylinder body to axially limit the bearing assembly. The check ring is tightened and fixed by an anti-back-off nail;

[0015] A spline assembly, which includes,

[0016] A spline sleeve, which is threadedly connected inside the second cylinder body. The outer surface of the middle section of the spline sleeve is provided with a polygon structure with a chamfered corner,

[0017] A left-handed nut, which is axially slidably sleeved on the spline sleeve. The inner surface of the left-handed nut is provided with a polygon structure with a chamfered corner, and the outer surface of the left-handed nut is provided with a left-handed trapezoidal male thread. The left-handed nut and the spline sleeve form a spline assembly that cannot rotate relative to each other;

[0018] A release assembly, which includes,

[0019] A lower sub, which is sleeved outside the check ring, the second cylinder body and the spline sleeve, and the upper end of the lower sub abuts against the lower end of the spare sleeve. The inner surface of the lower sub is provided with a left-handed trapezoidal female thread for threadedly connecting the left-handed trapezoidal male thread,

[0020] An anti-rotation shear pin, which connects the lower sub and the spline sleeve to prevent relative rotation between the two and axially limit them.

[0021] In the described mechanical safety joint for drill string, pressure is transmitted from the lower sub through the bearing assembly to the upper sub.

[0022] In the described mechanical safety joint for drill string, an external chamfered slope is provided at the lower end of the spare sleeve away from the bearing sleeve, and an internal chamfered slope is provided at the upper end of the lower sub, and the internal chamfered slope abuts against the external chamfered slope.

[0023] In the described mechanical safety joint for drill string, an O-ring seals and connects the lower sub and the spline sleeve.

[0024] In the described mechanical safety joint for drill string, the tubular structure has a hollow channel with variable diameter.

[0025] In the described mechanical safety joint for drill string, the bearing sleeve includes a sleeve body sleeving the second cylinder and an extension portion extending from the sleeve body towards the first cylinder.

[0026] In the described mechanical safety joint for drill string, a spring and a snap ring are sleeved on the spline sleeve to axially limit the left-handed nut.

[0027] In the described mechanical safety joint for drill string, the polygonal structure includes a quadrilateral spline.

[0028] In the described mechanical safety joint for drill string, the upper sub, the bearing sleeve, the spare sleeve, the back-off ring, the lower sub, the spline sleeve and the left-handed nut are all tubular structures with a common central axis.

[0029] In the described mechanical safety joint for drill string, the connection between the upper sub and the spline sleeve is a drill pipe or tubing thread connection.

[0030] In the above technical solution, a mechanical safety joint for drill string provided by the present invention has the following beneficial effects: The mechanical safety joint for drill string is simple to operate, safe and reliable. When back-off operation is carried out, the sensitive needle of the weight indicator does not show any swinging phenomenon; It is not necessary to accurately adjust the neutral point to the tool to safely back off and release, avoiding the situation that it is easy to be pressed to death and unable to back off during the back-off of the conventional safety joint, improving the success rate of releasing the safety joint, and providing favorable conditions for the next workover treatment.

[0031] It reduces the experience requirement for operators to accurately determine the neutral point, saves a lot of time spent on adjusting the neutral point, and greatly improves the construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic structural diagram of a mechanical safety joint for a drill string provided by an embodiment of the present invention.

[0034] Figure 2 For Figure 1 the A - A cross - sectional structural diagram of a mechanical safety joint for a drill string provided by an embodiment of the present invention. Detailed implementation manners

[0035] To make the purposes, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0040] In the present invention, unless otherwise clearly specified and defined, the terms such as "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0042] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] See Figure 1-2 As shown, in one embodiment, a mechanical safety joint for a drill string of the present invention includes

[0044] An upper sub 1, which has a cylindrical structure. The cylindrical structure includes a first cylinder body with a first outer diameter and a second cylinder body with a second outer diameter. The second cylinder body extends coaxially from the lower end of the first cylinder body and the second outer diameter is smaller than the first outer diameter. A step is formed at the connection between the second cylinder body and the first cylinder body.

[0045] A bearing assembly, which is rotatably connected to the second cylinder body. The bearing assembly includes

[0046] A bearing sleeve 3, which is axially sleeved on the second cylinder body rotatably.

[0047] Ball bearings 2, which are arranged in the annular gap formed by the step and the inner and outer shoulders of the bearing sleeve 3.

[0048] A spare sleeve 4, which is axially sleeved on the second cylinder body rotatably. The ball 2, the bearing sleeve 3 sleeved on the second cylinder body in sequence and the spare sleeve 4 form a bearing assembly;

[0049] A check ring 5, which is threadedly connected to the second cylinder body to axially limit the bearing assembly, and the check ring 5 is fastened and fixed via an anti-rotation nail 6;

[0050] A spline assembly, which includes

[0051] A spline sleeve 10, which is threadedly connected inside the second cylinder body. The outer surface of the middle section of the spline sleeve 10 is provided with a polygon structure with rounded chamfers;

[0052] A left-handed nut 11, which is axially slidably sleeved on the spline sleeve 10. The inner surface of the left-handed nut 11 is provided with a polygon structure with rounded chamfers. The outer surface of the left-handed nut 11 is provided with a left-handed trapezoidal male thread. The left-handed nut 11 and the spline sleeve 10 form a spline assembly where the two cannot rotate relative to each other;

[0053] A releasing assembly, which includes

[0054] A lower sub 7, which is sleeved outside the check ring 5, the second cylinder body and the spline sleeve 10, and the upper end of the lower sub 7 abuts against the lower end of the spare sleeve 4. The inner surface of the lower sub 7 is provided with a left-handed trapezoidal female thread for threadedly connecting the left-handed trapezoidal male thread;

[0055] An anti-rotation shear pin 12, which connects the lower sub 7 and the spline sleeve 10 to prevent relative rotation between the two and axially limit them.

[0056] In a preferred embodiment of the mechanical safety joint for a drill string described above, pressure is transmitted from the lower sub 7 to the upper sub 1 via the bearing assembly.

[0057] The mechanical safety joint for a drill string is installed on the operation pipe string such as in drilling, workover, logging, etc. When in use, the positive torque during forward rotation and reverse threading is borne by the spline assembly, the tensile and compressive loads during forward rotation and reverse threading are borne by the bearing assembly, and forward rotation and reverse threading are achieved through reverse threads. It is not necessary to accurately adjust the neutral point to the safety joint, and forward rotation and reverse threading can be carried out safely and reliably, and releasing can be carried out smoothly, creating conditions for the subsequent downhole accident treatment.

[0058] In a preferred embodiment of the mechanical safety joint for a drill string described above, the lower end of the spare sleeve 4 away from the bearing sleeve 3 is provided with an outer chamfered inclined surface, and the upper end of the lower sub 7 is provided with an inner chamfered inclined surface, and the inner chamfered inclined surface abuts against the outer chamfered inclined surface.

[0059] In a preferred embodiment of the mechanical safety joint for a drill string described above, an O-ring 13 is used to seal and connect the lower sub 7 and the spline sleeve 10.

[0060] In a preferred embodiment of the mechanical safety joint for a drill string, the tubular structure has a stepped hollow channel.

[0061] In a preferred embodiment of the mechanical safety joint for a drill string, the bearing sleeve 3 includes a sleeve body sleeving the second cylinder and an extension portion extending from the sleeve body towards the first cylinder.

[0062] In a preferred embodiment of the mechanical safety joint for a drill string, the spring 9 and the snap ring 8 are sleeved on the spline sleeve 10 to axially limit the left-handed nut 11.

[0063] In a preferred embodiment of the mechanical safety joint for a drill string, the polygonal structure includes a quadrilateral spline.

[0064] In a preferred embodiment of the mechanical safety joint for a drill string, the upper joint 1, the bearing sleeve 3, the spare sleeve 4, the back-off ring 5, the lower joint 7, the spline sleeve 10 and the left-handed nut 11 are all tubular structures with a common central axis.

[0065] In a preferred embodiment of the mechanical safety joint for a drill string, a drill pipe or tubing thread connection is provided between the upper joint 1 and the spline sleeve 10.

[0066] In one embodiment, the mechanical safety joint mainly consists of a bearing assembly, a spline assembly, a releasing assembly, etc. During use, the safety joint is installed at a predetermined position on the pipe string for various construction operations such as drilling, workover, logging, and testing. When a sticking or burying accident occurs to the pipe string downhole, if the pipe string cannot be released by means such as circulation, shock, or pulling, it is necessary to unscrew the thread at the safety joint and lift all the pipe string above the sticking point to the ground for further treatment of the stuck pipe string. During operation, there is no need to precisely adjust the position of the tool neutral point. Apply a downward pressure of 3 - 5t. The inner chamfered inclined surface at the upper end of the lower joint 7 abuts against the outer chamfered inclined surface at the lower end of the spare sleeve 4. The downward pressure is transmitted through the lower joint 7 and the spare sleeve 4 to the bearing assembly. At this time, rotate the pipe string clockwise to reverse the thread. The anti-rotation shear pin 12 is sheared off, and the left-handed thread connection between the lower joint 7 and the spline sleeve 10 is slowly unscrewed under the state of no pressure.

[0067] In one embodiment, a mechanical safety joint for a drill string includes

[0068] an upper joint 1, which is a tubular structure for connecting the drill string. The tubular structure includes a first cylinder with a first outer diameter and a second cylinder with a second outer diameter. The second cylinder coaxially extends from the lower end of the first cylinder and the second outer diameter is smaller than the first outer diameter. A step is formed at the connection between the second cylinder and the first cylinder. The tubular structure has a stepped hollow channel;

[0069] A bearing assembly is rotatably connected to the second cylinder body. The bearing assembly includes

[0070] A bearing sleeve 3 is axially sleeved on the second cylinder body rotatably. Further, the bearing sleeve 3 includes a sleeve body sleeving the second cylinder body and an extension portion extending from the sleeve body towards the first cylinder body.

[0071] Ball bearings 2 are arranged in the annular gap formed by the step and the inner and outer shoulders of the bearing sleeve 3.

[0072] A spare sleeve 4 is axially sleeved on the second cylinder body rotatably. The ball bearings 2, the bearing sleeve 3 sleeving the second cylinder body in sequence, and the spare sleeve 4 constitute the bearing assembly. An outer chamfered inclined surface is provided at the lower end of the spare sleeve 4 away from the bearing sleeve 3.

[0073] A retaining ring 5 is threadedly connected to the second cylinder body to axially limit the bearing assembly. The retaining ring 5 is tightened and fixed via an anti-loosening nail 6.

[0074] A spline assembly includes

[0075] A spline sleeve 10 is threadedly connected inside the second cylinder body. A polygonal structure is provided on the outer surface of the middle section of the spline sleeve 10 and rounded corners are provided.

[0076] A left-handed nut 11 is axially slidably sleeved on the spline sleeve 10. A polygonal structure is provided on the inner surface of the left-handed nut 11 and rounded corners are provided. A left-handed trapezoidal male thread is provided on the outer surface of the left-handed nut 11. The left-handed nut 11 and the spline sleeve 10 constitute a spline assembly where the two cannot rotate relative to each other.

[0077] A spring 9 and a snap ring 8 are sleeved on the spline sleeve 10 to axially limit the left-handed nut 11.

[0078] A releasing assembly includes

[0079] A lower sub 7 is sleeved outside the retaining ring 5, the second cylinder body, and the spline sleeve 10. The upper end of the lower sub 7 abuts against the lower end of the spare sleeve 4. A left-handed trapezoidal female thread for threadedly connecting the left-handed trapezoidal male thread is provided on the inner surface of the lower sub 7. Further, an inner circular inclined surface is provided at the upper end of the lower sub 7.

[0080] An anti-rotation shear pin 12 connects the lower sub 7 and the spline sleeve 10 to prevent relative rotation between the two and axially limit them.

[0081] An O-ring 13 seals and connects the lower sub 7 and the spline sleeve 10.

[0082] When operating the mechanical safety joint for the drill string, press down the pipe string. The pressure can be transmitted through the lower sub, via the bearing assembly, to the upper sub 1 and the pipe string connected thereto, so that the left-handed thread connection between the left-handed nut 11 and the lower sub 7 is not under pressure during left-handed reverse threading, and thus the situation of thread jamming and unable to reverse thread will not occur. The spline assembly bears the positive torque during left-handed reverse threading and also prevents the relative rotation between the left-handed nut 11 and the spline sleeve 10, which would otherwise prevent reverse threading. The designed release assembly cuts the anti-rotation shear pin 12 by rotating the pipe string to the right and forward. Continuing to rotate the pipe string to the right and forward, the left-handed trapezoidal thread connection between the left-handed nut 11 and the middle section of the inner cylinder of the lower sub 7 is slowly reversed to complete the release action.

[0083] In one embodiment, the connection between the upper sub 1 and the spline sleeve 10 is a drill pipe or tubing thread connection, which has the functions of sealing, tensile (compressive) resistance, and torque transmission. The outer circle of the middle part of the upper sub 1 is axially sleeved with a bearing sleeve 3 and a spare sleeve 4 in sequence. The ball 2 is installed in the annular gap formed by the inner and outer shoulders of the upper sub 1 and the bearing sleeve, which plays the role of supporting and reducing the rotational resistance between the bearing sleeve 3, the spare sleeve 4, and the upper sub 1. The bearing sleeve 3, the spare sleeve 4, and the ball 2 form a bearing assembly. Under the action of the ball, the bearing assembly can rotate at the lower end of the upper sub 1. The anti-backlash ring 5 is threadedly connected to the upper sub 1 and is used for the axial limit of the bearing assembly. The axial position requirement is that it cannot prevent the free rotation of the bearing assembly. Then, the anti-backlash nail 6 for drilling and punching is tightened and fixed to prevent the anti-backlash ring from loosening and backing off.

[0084] In one embodiment, the outer surface of the middle section of the spline sleeve 10 is designed as a polygon and rounded at the corners. The inner surface of the left-handed nut 11 is also designed as a polygon and rounded at the corners. The two form a spline assembly. The left-handed nut 11 is sleeved on the spline sleeve 10, and the two cannot rotate relative to each other and can transmit torque through the quadrilateral spline. The left-handed nut 11 can axially slide on the spline sleeve and is axially limited by the spring 9 and the snap ring 8. The outer surface of the left-handed nut 11 is a left-handed trapezoidal male thread, which is threadedly connected to the left-handed trapezoidal female thread in the middle section of the inner cylinder of the lower sub 7. The two, together with the anti-rotation shear pin 12, form a release assembly. The lower sub 7 is sleeved outside the anti-backlash ring, the lower end of the upper sub 1, and the spline sleeve. The inner circular inclined surface at the upper end of the lower sub abuts against the outer circular inclined surface at the lower end of the spare sleeve. The relative rotation between the lower sub and the spline sleeve is prevented by the anti-rotation shear pin 12, and the axial limit is also achieved. At the same time, the lower sub and the spline sleeve are sealed by an O-ring 13.

[0085] When the work string is run in, the mechanical safety joint without a neutral point can be connected to different positions of the string according to specific conditions. When a sticking accident occurs to the drill string below the safety joint and the stuck pipe cannot be released by means such as moving the string, circulating drilling fluid or workover fluid, or jarring, and it is necessary to discard the lower string, apply a downward pressure of 3 - 5t. The inner circular inclined surface at the upper end of the lower sub abuts against the outer circular inclined surface at the lower end of the spare sleeve. At this time, rotate the string clockwise. The anti-rotation shear pin 12 is sheared off. Continue to rotate clockwise, and the left-handed thread connection between the lower sub 7 and the left-handed nut 11 starts to back off until the lower sub 7 and the left-handed nut 11 are completely disengaged. For safety reasons, the cumulative number of effective back-off turns should not be less than 20 turns, and the number of turns is accumulated in three operations. Under normal circumstances, when using the rotary table to back off, after rotating clockwise for several turns, release the rotary table, and the rotary table should hardly rotate back. If the rotation back is serious, it may be that the tool is not pressed or is pressed too much, and adjustments should be made at this time. This is also an advantage highlight different from conventional tools. After the back-off is completed, lift the string, and the upper sub 1 together with the ball 2, bearing sleeve 3, spare sleeve 4, anti-back-off ring 5, anti-back-off pin 6, snap ring 8, spring 9, and spline sleeve 10 can be lifted out of the wellbore to complete the releasing operation of the stuck string.

[0086] The mechanical safety joint in this embodiment makes up for the defects of the existing safety joints, does not require operation experience, does not need to consider the adjustment problem of the neutral point, is simple to operate, safe and reliable, has a wide range of applications, and greatly improves the efficiency and success rate of retrieving the work string.

[0087] Finally, it should be noted that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0088] Only some exemplary embodiments of the present invention have been described by way of illustration above. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A mechanical safety joint for a drill string, characterized in that, It includes an upper sub, which is of a tubular structure. The tubular structure includes a first cylinder body with a first outer diameter and a second cylinder body with a second outer diameter. The second cylinder body extends coaxially from the lower end of the first cylinder body and the second outer diameter is smaller than the first outer diameter. A step is formed at the connection between the second cylinder body and the first cylinder body; a bearing assembly, which is rotatably connected to the second cylinder body. The bearing assembly includes a bearing sleeve, which is axially sleeved on the second cylinder body rotatably, ball bearings, which are arranged in an annular gap formed by the step and the inner and outer shoulders of the bearing sleeve, a spare sleeve, which is axially sleeved on the second cylinder body rotatably. The ball bearings, the bearing sleeve and the spare sleeve sleeved on the second cylinder body in sequence form the bearing assembly; a retaining ring, which is threadedly connected to the second cylinder body to axially limit the bearing assembly. The retaining ring is tightened and fixed via an anti-loosening nail; a spline assembly, which includes a spline sleeve, which is threadedly connected inside the second cylinder body. The outer surface of the middle section of the spline sleeve is provided with a polygon structure with a chamfered fillet, a left-handed nut, which is axially slidably sleeved on the spline sleeve. The inner surface of the left-handed nut is provided with a polygon structure with a chamfered fillet. The outer surface of the left-handed nut is provided with a left-handed trapezoidal male thread. The left-handed nut and the spline sleeve form a spline assembly in which the two cannot rotate relative to each other; a releasing assembly, which includes a lower sub, which is sleeved outside the retaining ring, the second cylinder body and the spline sleeve, and the upper end of the lower sub abuts against the lower end of the spare sleeve. The inner surface of the lower sub is provided with a left-handed trapezoidal female thread for threadedly connecting the left-handed trapezoidal male thread, an anti-rotation shear pin, which connects the lower sub and the spline sleeve to prevent relative rotation between the two and axially limit them.

2. The mechanical safety joint for a drill string according to claim 1, characterized in that, The pressure is transmitted to the upper sub through the lower sub via the bearing assembly.

3. The mechanical safety joint for a drill string according to claim 1, characterized in that, The lower end of the spare sleeve away from the bearing sleeve is provided with an external chamfered bevel, and the upper end of the lower sub is provided with an internal chamfered bevel. The internal chamfered bevel abuts against the external chamfered bevel.

4. The mechanical safety joint for a drill string according to claim 1, characterized in that, An O-ring seals and connects the lower sub and the spline sleeve.

5. The mechanical safety joint for a drill string according to claim 1, characterized in that, The tubular structure has a hollow channel with variable diameter.

6. The mechanical safety joint for a drill string according to claim 1, characterized in that, The bearing sleeve includes a sleeve body sleeving the second cylinder body and an extension portion extending from the sleeve body towards the first cylinder body.

7. The mechanical safety joint for a drill string according to claim 1, characterized in that, A spring and a circlip are sleeved on the spline sleeve to axially limit the left-handed nut.

8. The mechanical safety joint for a drill string according to claim 1, characterized in that, The polygon structure includes a quadrilateral spline.

9. The mechanical safety joint for a drill string according to claim 1, characterized in that, The upper sub, the bearing sleeve, the spare sleeve, the retaining ring, the lower sub, the spline sleeve and the left-handed nut are all tubular structures with a common central axis.

10. The mechanical safety joint for a drill string according to claim 1, characterized in that, The connection between the upper sub and the spline sleeve is a drill pipe or tubing thread connection.

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