A gap grabber, design method, grabbing method and system

Abstract

This invention discloses a notch retrieval device, its design method, retrieval technique, and system, belonging to the field of drilling machinery engineering. The method first analyzes the retrieval resistance under different sediment conditions through theoretical calculations, providing a scientific basis for the load-bearing capacity design of the retrieval device. Then, a novel notch retrieval device is designed and optimized, its core components including a connector that can be connected to the drill pipe, a shell, a central tube, and a pressure-bearing platform with a unique rotational locking function. This retrieval device can reliably grip and release the drill string, and can also apply torque to the fallen drill string to aid in unsticking. Simultaneously, its central tube structure facilitates the formation of a closed-loop circulation channel. The accompanying retrieval technique clarifies a standardized process of first cleaning the sediment, then connecting the connector, and finally circulating the unsticking mechanism. This invention achieves synergy between the design, optimization, and construction of the retrieval device, significantly improving the reliability, unsticking capability, and operational efficiency of deep well drill string retrieval.

Description

Technical Field

[0001] This invention relates to the field of drilling machinery engineering technology, and in particular to a gap fishing device, its design method, fishing method and system. Background Technology

[0002] As coal mining progresses to deeper levels, higher demands are placed on the safety, efficiency, and mechanization of well construction technology. Drilling methods, with their advantages of allowing workers to operate on the surface, providing a favorable working environment, and producing high-quality wells, have demonstrated significant advantages in deep well construction. However, when drilling into formations such as the Western Jurassic, there is a risk of increased drill string vibration and drill pipe breakage, leading to the drill bit falling to the bottom of the well. How to quickly and reliably retrieve fallen drill strings has become a key technical challenge for reducing non-productive working hours and controlling project costs.

[0003] Currently, for retrieval of drill strings from drilling rigs, various retrieval devices such as rotary resetting expanders and flip-block chucks have been publicly disclosed and used. These devices can achieve deep well retrieval and lifting functions to a certain extent, but they still have significant limitations: First, existing retrieval devices generally lack the ability to effectively apply torsional force to fallen drill strings. When the drill bit is stuck with sediment or too tightly against the well wall, it is difficult to loosen the drill string by rotation, resulting in insufficient unblocking capability. Second, their structural sealing is usually poor, making it difficult to form an effective closed flow channel inside the drill pipe during retrieval. This hinders the use of forward and reverse circulation mud to clean sediment from key areas and balance pressure, thus reducing the success rate of obstacle removal and unblocking. Finally, the lifting capacity of existing designs is limited, and the load-bearing capacity assessment and design basis under complex well conditions (such as large sediment accumulation) are insufficient, limiting their applicability in harsher and more complex field operations and increasing the risk of retrieval failure.

[0004] Therefore, there is an urgent need to develop a retrieval tool and its supporting methods that have stronger unblocking capabilities, better sealing and circulation performance, and whose structural design is based on accurate working condition load capacity assessment, so as to improve the reliability, safety and efficiency of drill string retrieval in deep drilling. Summary of the Invention

[0005] The main objective of this invention is to provide a gap-finding tool and its retrieval method, which aims to solve existing technical problems.

[0006] To achieve the above objectives, the present invention provides a notch fishing tool, comprising: a connector assembly for connecting to a transition drill pipe; A housing connected to the connector assembly; a central tube, at least partially disposed inside the housing; A pressure-bearing platform is disposed inside the outer shell, located below the central tube; By rotating the notch retrieval device, the pressure-bearing platform can be engaged or separated from the force-bearing plane of the fallen drill bit, thereby achieving grabbing or release.

[0007] Furthermore, the pressure-bearing platform is configured as follows: When the notch retriever is rotated in the first direction, the pressure-bearing platform can be tightly connected to the lower drilling tool; when the notch retriever is rotated in the second direction opposite to the first direction, the notch retriever can be recovered from the lower drilling tool without damage.

[0008] Furthermore, after the pressure-bearing platform is combined with the lower drilling tool, the notch retrieval device can be rotated in the first direction to apply torque to the lower drilling tool.

[0009] Furthermore, it also includes an upper wing plate and an inner wing plate disposed between the outer shell and the central tube, for reducing stress concentration of the salvage device at the variable cross-section in the vertical direction.

[0010] Furthermore, the lower end of the central tube extends beyond the pressure-bearing platform to align and correct the position of the retrieval device during the lowering process, and to form a closed liquid column channel inside the drill rod after engaging with the dropped drill bit.

[0011] A design optimization method for a gap fishing device, used to design a gap fishing device as described above, includes the following steps: S1. Assess the retrieval carrying capacity: Calculate the total resistance that the target drill bit needs to overcome under different working conditions, including at least: no slag removal, removal of overlying sediment, and removal of overlying and bottom sediment; the calculation of total resistance is based on theoretical analysis of sediment distribution and forces. S2. Determine the target working condition and lifting force: Based on the calculation results of step S1, determine the target working condition for the salvage operation, and determine the design lifting capacity required by the salvage device based on the total resistance under this working condition. S3. Structural Design and Optimization: Based on the design enhancement capability determined in step S2, the initial structural design of the gap retrieval device is carried out, and simulation methods, including finite element analysis, are used to optimize the strength, stiffness and fatigue of the structure until the preset design indicators are met.

[0012] Furthermore, in step S1, the total resistance under the condition of not removing slag includes the buoyant weight of the overlying sediment, the contact adsorption force between the drill bit and the sediment, the frictional resistance, the pressure of the overlying mud, the buoyant weight of the sediment at the connection between the advanced drill and the reamer, and the total weight of the drill bit and the drill rod.

[0013] Furthermore, in step S1, the total resistance under the condition of removing overlying sediment includes the contact adsorption force between the drill bit and the sediment, frictional resistance, the weight of the mud in the drill pipe, the buoyancy weight of the sediment at the connection between the pre-drill and the reamer, and the total weight of the drill bit and the drill pipe.

[0014] A method for retrieving drilling bits using a drilling method, employing a notch retriever as described above, includes the following steps: A. Preparation for cleaning: Lower the cleaning pipe to the area of ​​the overlying sediment above the fallen drill bit, and remove at least part of the overlying sediment by reverse circulation suction. B. Lowering and docking: Lower the notch retrieval device to near the falling drill bit. During the rotational lowering process, sense the change in torque until the pressure-bearing platform contacts the force-bearing plane of the drill bit and generates a predetermined torque, thus completing the docking. C. Open up mud channels: Try to open up mud transport channels inside and outside the drill pipe through positive circulation and / or reverse circulation; D. Unjamming and Lifting: Operate the gap retrieval device by pulling, rotating, or pulling and rotating simultaneously until the pulling force monitored on the ground is basically consistent with the buoyancy of the drill bit and drill rod. After confirming that the gap is unjammed, lift the drill bit to the ground.

[0015] A system for retrieving drilling bits in a drilling method includes: a notch retriever as described above; Sludge removal pipes are used to remove overlying sediment from the wellbore before retrieval operations.

[0016] The beneficial effects of this invention are reflected in: This invention, through a unique design combining a pressure-bearing platform and rotary operation, enables this retrieval device to not only reliably engage and non-destructively disengage from fallen drill strings, but also to continue applying controllable torque to the drill strings after engagement. This function can be directly used to loosen stuck rocks and disrupt dense sediment structures, greatly enhancing mechanical unblocking capabilities. The extended design of the central tube, after engagement with the drill bit, forms a closed liquid column inside the drill pipe, providing an ideal channel for implementing forward or reverse circulation. This facilitates further removal of residual sediment at the bottom of the well and in crevices through circulating mud or clean water during critical retrieval stages, balancing internal and external pressures and effectively solving the problems of poor sealing and poor circulation in existing retrieval devices, creating favorable conditions for successful retrieval.

[0017] This invention designs a method for assessing the carrying capacity of retrieval operations based on a sediment distribution theory model. Through systematic mechanical analysis of three typical operating conditions—"no sediment removal," "removal of overlying sediment," and "removal of overlying and bottom sediment"—the resistance to be overcome at different sediment removal stages is quantified. This method guides designers to select a reasonable target operating condition (usually "removal of overlying sediment") for the structural design of the retrieval device, providing a clear and scientific theoretical basis for the design of the retrieval device's lifting capacity. This avoids insufficient capacity or over-design, ensuring the safety, redundancy, and economy of retrieval operations.

[0018] This invention integrates "assessment-design-construction" into a standardized and streamlined salvage method. This method clearly specifies the operational sequence: first, clearing the overlying sediment; then, attempting to open the mud channel; and finally, using a specialized salvage tool for rotational unblocking and lifting. This step-by-step method, based on operational condition analysis, systematically reduces operational resistance, fully utilizes the structural advantages of the salvage tool, and makes the entire salvage process more controllable and efficient, significantly improving the overall salvage success rate under complex well conditions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the notch retrieval device of the present invention; Figure 2 For the present invention Figure 1 Schematic diagram of the cross-sectional structure at point 1-1; Figure 3 For the present invention Figure 1 Schematic diagram of the cross-sectional structure at points 1-2 in the middle; Figure 4 This is a schematic diagram of the design optimization method for the notch retrieval device of the present invention; Figure 5 This is a schematic diagram of the falling drill bit structure and the covering sediment of the present invention; Figure 6 Different sediment distribution states are shown in the preparatory work before salvage according to the present invention. Figure 7 This invention describes the on-site operation process for retrieving a fallen drill bit using a notch retrieval device. Figure 8 This is a schematic diagram of the falling drill bit structure and the covering slag under one working condition of the present invention; Figure 9 This is a schematic diagram of the falling drill bit structure and the covering slag under one working condition of the present invention; Figure 10 This is a schematic diagram of the falling drill bit structure and the covering slag under three working conditions of the present invention; Figure 11 This is a schematic diagram illustrating the lifting capacity of the drilling rig and the lifting capacity of the retrieval device under different working conditions according to the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Notch retrieval device; 101. Connector jaw clip; 102. Connector pipe; 103. Upper wing plate; 104. Outer shell; 105. Central pipe; 106. Pressure-bearing platform; 107. Inner wing plate.

[0021] 2. Upper counterweight; 3. Guide; 4. Lower counterweight; 5. Reamer bit; 6. Advance drill bit; 7. Overlying sludge; 8. Sludge floating at the connection of the advance reamer bit; 9. Bottom sludge; 10. Sludge cleaning pipe. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Salvage device load-bearing capacity assessment Ignoring rock jamming, we only consider the impact of settling mud and sand on the drill bit. Assuming all sand and rock cuttings (collectively referred to as "sludge") in the drilling mud settle to the bottom, the sand-containing volume in the shaft drilling mud is:

[0024] Where: V1 is the sand-bearing volume in the deep well mud; R0 is the rough diameter of the wellbore; h0 is the depth of the drill bit; C S This refers to the sand content (volume ratio).

[0025] Estimation of the gap volume between the drill bit and the surrounding rock:

[0026] In the formula: V2 is the gap volume between the drill bit and the surrounding rock; R1 is the diameter of the reamer; R2 is the rough diameter of the wellbore at the bottom of the reamer; R3 is the bottom diameter of the reamer; R4 is the diameter of the connection between the reamer and the advance drill; R5 is the rough diameter of the wellbore at the advance drill position; R6 is the diameter of the advance drill; h1 is the height of the reamer body; h2 is the height of the reamer cone; h3 is the height of the connection between the reamer and the advance drill; h4 is the height of the advance drill.

[0027] Taking the drilling parameters of a certain drilling method in Inner Mongolia as an example, the volume of sand can completely fill the gap between the drill bit and the surrounding rock, that is, V1 > V2.

[0028] This volume of sand can additionally cover the wellbore height (overlying sediment thickness) h5 by:

[0029] The additional lifting force required to lift the drill pipe is caused by the following adverse factors: 1. Float weight of the overlying sediment (G) s

[0030] In the formula: ρ s ρ is the buoyant density of the sediment; g is the gravitational force exerted on each kilogram of mass.

[0031] 2. Contact Adsorption Force

[0032]

[0033] In the formula: A c τ is the vertical contact area between the drill bit and the sediment; a The adhesion force between the drill bit and the sediment per unit contact area.

[0034] 3. Frictional resistance F f

[0035]

[0036]

[0037] In the formula: A l The contact area between the drill bit and the sediment, i.e., its lateral surface area; N is the normal contact force between the drill bit and the sediment; P is the lateral contact force between the drill bit and the sediment. mud The compressive stress exerted on the side of the drill bit by the sediment due to its own buoyancy; μ mud The coefficient of friction between the sediment and the side of the drill bit.

[0038] 4. Overlying mud pressure F mud (Due to the presence of sediment at the top of the reamer, there is no flow path for the upper mud during the lifting process.)

[0039] In the formula: ρ mud V is the mud density; V is the wellbore volume.

[0040] 5. Gravity G of mud inside the drill pipe mud (Because sediment at the bottom of the drill bit blocks the flow path of the drilling mud inside the drill pipe, during the initial stage of retrieval, the drilling mud inside the drill pipe is lifted with drilling. As the drill bit leaves the bottom of the well, the drilling mud inside the drill pipe can easily connect with the drilling mud outside the drill pipe through the space at the bottom of the drill bit. This force is gradually relieved as the drill bit is lifted.)

[0041] In the formula: r is the inner diameter of the drill pipe.

[0042] 6. Buoyancy weight G of sediment at the connection between the advanced and reaming drill bit sand

[0043] Operating Condition 1, Most Unfavorable State: No Slag Removal Please see Figure 8 The total resistance is the sum of adverse factors 1, 2, 3, 4, and 6, and the weight of the drill bit and drill pipe. In the formula: G f This represents the total weight of the drill bit and drill rod.

[0044] If salvage operations are carried out, the tensile force F0 that the salvage device will withstand is: In the formula: G d This refers to the weight of the drill pipe.

[0045] Working condition 2: Removal of overlying sediment Please see Figure 9 Because the sediment at the top of the reamer is removed, there is a flow path for the drilling mud at the top of the reamer during the lifting process. Therefore, the total resistance is the sum of the above-mentioned adverse factors 2, 3, 5, and 6 plus the weight of the drill bit and drill rod:

[0046] During the salvage operation, the salvage device was subjected to a tensile force of:

[0047] Operating Condition 3: Removal of overburden and bottom sediment Through on-site operations, a solution for removing bottom sediment from the wellbore using both forward and reverse circulation methods will be proposed to relieve the sediment's confinement to the bottom of the drill bit. The specific implementation plan is as follows: Figure 10 As shown.

[0048] If the constraint at the bottom of the drill bit is released, the mud inside the drill pipe and the mud outside the drill bit form a connected body. Compared with condition 2, unfavorable factor 5 is eliminated. Due to the removal of sediment at the bottom of the well, most of the sediment at the connection between the advance and reaming drills and the part where the drill bit is separated from the surrounding rock is removed due to gravity and flow effects. At this time, the total resistance is the sum of the weight of the drill bit and the drill pipe. F t =G f During the salvage operation, the salvage device was subjected to the following tensile force: F0=F t -G d If the drill bit cannot be lifted, it is due to other reasons, such as stuck rock.

[0049] Based on the above calculation method, the load-bearing capacity of the salvage device under different working conditions can be obtained.

[0050] Taking a drilling bit retrieval operation in Inner Mongolia as an example, the parameters were calculated using the above formula to obtain the load-bearing capacity requirements of the retrieval device under different operating conditions: Operating Condition 1 Operating Condition 2 Operating condition 3, such as Figure 11 As shown in the figure, the load-bearing capacity requirement of the retrieval device in condition 1 is two orders of magnitude higher than that in conditions 2 and 3, illustrating the importance of cleaning the overlying sediment.

[0051] Based on the calculation results, the design, manufacturing and optimization of the retrieval device were carried out according to the lifting force required for working condition 2. In terms of construction process, the top sediment was first cleaned, and then the sediment at the bottom of the well was cleaned as much as possible through forward and reverse circulation. Finally, the retrieval device was used to retrieve the dropped drill bit.

[0052] Example 1: This invention provides a notch retrieval tool, which yields... Figure 1-3 The structure of the notch retrieval device is shown. 1-The notch retrieval device consists of 101-joint toothed insert, 102-joint tube, 103-upper wing plate, 104-outer shell, 105-central tube, 106-pressure bearing platform, and 107-inner wing plate.

[0053] Among them, 101-connector jaw clip and 102-connector tube assembly are connected to the transition drill pipe (not shown in the figure).

[0054] The upper wing plate (103) and the inner wing plate (107) can reduce stress concentration at the variable cross-section of the salvage device in the vertical direction.

[0055] 104 - The outer shell provides a load transfer medium for the 106 - pressure platform.

[0056] The 105-center tube can be used to align and correct the lowering position of the retrieval device. On the other hand, when the retrieval device is fully engaged with the dropped drill bit, it forms a closed liquid column in the drill pipe, which is conducive to the use of forward and reverse circulation to open up the mud transport channels inside and outside the drill pipe when lifting the drill bit, and facilitates the circulation of mud, water and other operations.

[0057] The 106-pressure platform is the part that directly bears the force when lifting the drill bit. The connection between it and the 104-outer shell is rounded to alleviate stress concentration. Its functions are as follows: 1. By rotating the retrieval device counterclockwise (viewed from directly above the retrieval device), the lower drill string is tightly connected to the 106-pressure platform; 2. By rotating the retrieval device clockwise (viewed from directly above the retrieval device), the retrieval device can be retrieved without damage; 3. When the lower drill string is pressed on the 106-pressure platform, continuing to rotate the retrieval device counterclockwise (viewed from directly above the retrieval device) can apply torque to the lower drill string. This is beneficial for changing the position of stuck rocks when the drill string encounters them, making it easier to lift the drill bit in later operations. It also helps to break the dense state of sediment between the drill bit and the surrounding rock, increasing the possibility of mud penetrating the space inside and outside the drill pipe during forward and reverse circulation.

[0058] Example 2: The present invention also provides a design optimization method for a notch retrieval device, used to design a notch retrieval device as described above, comprising the following steps: Based on the depth and flow rate of the mud at the site and the shortcomings of the existing salvage equipment, the functions of the salvage equipment, such as grabbing, positioning, corrosion prevention and impact resistance, are defined, and quantitative indicators are set for each function.

[0059] S1: Based on the existing salvage device structure and the on-site working conditions, design the initial salvage device structure according to the functional requirements of the salvage device, and draw the CAD drawings of the salvage device. S2: Based on the CAD drawings, create parametric 3D models for each component in Solidworks, complete the assembly and fit, and perform motion interference checks. Then export the STEP file and each view for subsequent drawing. S3: Import STEP into Hypermesh, perform geometry cleanup, and use a hybrid tetrahedral and hexahedral mesh. Set fine meshes for stress concentration areas such as holes and chamfers to ensure that the mesh quality meets the requirements and output an Abaqus-compatible .inp file. S4: Subsequently, define the material elasticity in Abaqus. Plastic constitutive model, with fixed constraints, distributed hydrodynamic pressure and point / surface loads, is used to perform finite element solutions for static, impact and fatigue conditions, respectively. Equivalent stress, displacement and strain energy cloud maps are extracted and compared with design parameters (maximum stress ≤ 0.8 times the material yield strength, displacement ≤ 5 mm, fatigue safety factor ≥ 1.5).

[0060] S5: If stress exceeds the limit, start Abaqus topology optimization, set the goal of minimizing mass and maximizing stiffness, obtain the density distribution map while maintaining assembly constraints, and increase the plate thickness, set reinforcing ribs, fillet corners or replace high-strength materials locally in weak parts according to the results. Re-mesh and perform finite element analysis, iterate until all working conditions meet the requirements. If the load-bearing requirements can be met, proceed to S6. S6: Finally, based on the final structure, output complete two-dimensional engineering drawings, assembly exploded views, dimensional tolerances, surface roughness and welding symbols, compile a bill of materials (BOM) and processing technology cards (CNC machining, welding, heat treatment, corrosion protection), formulate quality inspection specifications (dimensions, non-destructive testing, mechanical properties), and deliver CAD, STEP, BOM, process cards and inspection report templates to the processing plant for plate cutting, punching, rounding, welding and surface treatment. After assembly and debugging, it can be put into use.

[0061] Example 3: The present invention also provides a method for retrieving drilling bits used in well sinking, such as... Figure 5 This is a schematic diagram of a falling drill bit structure and covered sediment according to an embodiment of the present invention. It consists of 2-upper counterweight, 3-guide, 4-lower counterweight, 5-reaming drill bit, 6-advancing drill bit, 7-overlapping sediment, 8-advancing, sediment floating part of the reaming drill connection, 9-bottom sediment, and 10-slag cleaning pipe.

[0062] Among them, counterweight blocks are often installed in the 2-upper counterweight and 4-lower counterweight to increase the overall weight of the drill bit.

[0063] 3- The guide acts to stabilize the drill bit and reduce wellbore deviation.

[0064] 5- The reaming drill bit is the main rock-breaking component in reaming operations.

[0065] 6- The advanced drill bit can crush the sedimentary rock debris in the advanced drilling process and play a certain guiding role.

[0066] 7-The overlying sediment covers the upper part of the 5-reaming drill bit. As analyzed above, this is the main area where sand and rock debris settle in the mud, and it is also one of the main reasons why the drill bit is difficult to retrieve.

[0067] 8- The secondary area where the sediment at the junction of the advanced and enlarged boreholes is composed of sand and rock debris is one of the areas with a high risk of rock jamming.

[0068] 9- Bottom sediment and 8- Pre-drilling and reaming drill joints obstruct the flow of mud inside and outside the drill rod, making them one of the more difficult areas to clean during the cleaning operation.

[0069] 10-The slag removal pipe is suspended above the 5-reaming drill bit via the drill rod, and reverse circulation is used to extract 7-overlapping slag.

[0070] Figure 6 Different sediment distribution states are shown in the pre-salvage preparation work according to an embodiment of the present invention: S1: Initial state before slag removal. At this time, the slag is distributed above the reamer, between the advanced reamer and the surrounding rock, in the middle area of ​​the advanced reamer, and at the bottom of the advanced reamer. S2: Most of the slag on top of 7 is sucked out through the 10-slag removal pipe, at which point most of the resistance that restricts the drill bit's lifting is removed; S3: On-site, the mud channels inside and outside the drill pipe are opened through forward and reverse circulation, further removing the constraint on the drill bit at the bottom of the well.

[0071] The gap-finding method generally consists of four steps: Please refer to [link / reference]. Figure 7 , S1: Lower the 10-slag removal pipe to the 7-overlapping sludge area above the 5-reaming drill bit, and absorb the 7-overlapping sludge through reverse circulation, then raise the 10-slag removal pipe; S2: When lowering the 1-notch retrieval tool to near the top of the drill bit, rotate it while lowering it until torque is generated. Continue lowering it to the 106-pressure bearing platform and the lower drill bit force plane (not shown in the figure). Rotate the 1-notch retrieval tool until the torque increases, then the retrieval tool is considered to have reached the designated position.

[0072] S3: Try using forward and reverse circulation to open up the mud transport channels inside and outside the drill pipe. Observe the drill pipe lifting force on the ground. When the lifting force drops significantly, it means that the mud transport channels inside and outside the drill pipe have been opened.

[0073] S4: Depending on the situation on site, move the bottom drill bit structure on the ground by lifting, rotating, or lifting and rotating simultaneously. When the lifting force measured on the ground is the same as the buoyancy of the drill bit and drill rod, it is considered that the drill bit has been unstuck. At this time, continue to lift the drill bit and disassemble the drill rod until the drill bit is retrieved to the ground.

[0074] Example 4: A retrieval system for drilling drill bits, comprising the notch retrieval device 1 as described above; Slag removal pipe 10 is used to remove the overlying slag inside the wellbore before retrieval operations.

[0075] It should be noted that if the embodiments of the present invention involve directional indicators such as (up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0076] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied. Furthermore, "multiple" refers to two or more. Moreover, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gap grabber, characterized in that, include: Connector assembly for connection to transition drill pipe; A housing (104) is connected to the connector assembly; a central tube (105) is at least partially disposed inside the housing (104); The pressure-bearing platform (106) is disposed inside the outer shell (104) and located below the central tube (105); By rotating the notch retrieval device (1), the pressure-bearing platform (106) can be combined with or separated from the force-bearing plane of the fallen drill bit, so as to achieve grabbing or release.

2. The gap grab of claim 1, wherein, The pressure-bearing platform (106) is configured as follows: When the notch retrieval device (1) is rotated in the first direction, the pressure-bearing platform (106) can be tightly connected with the lower drilling tool; When the notch retriever (1) is rotated in a second direction opposite to the first direction, the notch retriever (1) can be retrieved from the lower drill string without damage.

3. The gap grab of claim 2, wherein, After the pressure-bearing platform (106) is combined with the lower drill bit, the notch retrieval device (1) continues to rotate in the first direction, which can apply torque to the lower drill bit.

4. The gap grab of claim 1, wherein, It also includes an upper wing plate (103) and an inner wing plate (107) disposed between the outer shell (104) and the central tube (105) to reduce stress concentration of the salvage device at the variable cross section in the vertical direction.

5. The gap grabber of claim 1, wherein, The lower end of the central tube (105) extends beyond the pressure-bearing platform (106) to align and correct the position of the retrieval device during the lowering process, and to form a closed liquid column channel inside the drill rod after being combined with the dropped drill bit.

6. A method for design optimization of a gap grabber for designing a gap grabber according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Assess the retrieval carrying capacity: Calculate the total resistance that the target drill bit needs to overcome under different working conditions, including at least: no slag removal, removal of overlying sediment, and removal of overlying and bottom sediment; the calculation of total resistance is based on theoretical analysis of sediment distribution and forces. S2. Determine the target working condition and lifting force: Based on the calculation results of step S1, determine the target working condition for the salvage operation, and determine the design lifting capacity required by the salvage device based on the total resistance under this working condition. S3. Structural Design and Optimization: Based on the design enhancement capability determined in step S2, the initial structural design of the gap retrieval device is carried out, and simulation methods, including finite element analysis, are used to optimize the strength, stiffness and fatigue of the structure until the preset design indicators are met.

7. The design optimization method of a gap grab according to claim 6, wherein, In step S1, the total resistance under the condition of not removing slag includes the buoyant weight of the overlying sediment, the contact adsorption force between the drill bit and the sediment, the frictional resistance, the pressure of the overlying mud, the buoyant weight of the sediment at the connection between the advanced drill and the reamer, and the total weight of the drill bit and drill rod.

8. The design optimization method of a gap grab according to claim 6, wherein, In step S1, the total resistance under the condition of removing overlying sediment includes the contact adsorption force between the drill bit and the sediment, frictional resistance, the weight of the mud in the drill pipe, the buoyancy weight of the sediment at the connection between the pre-drilling and reaming drill, and the total weight of the drill bit and drill pipe.

9. A method for retrieving drilling bits used in well drilling, characterized in that, The use of the notch retrieval device (1) as described in any one of claims 1-5 includes the following steps: A. Preparation for cleaning: Lower the cleaning pipe (10) to the area of ​​the overlying sediment above the fallen drill bit, and remove at least part of the overlying sediment by reverse circulation suction; B. Lowering and docking: Lower the notch retrieval device (1) to near the falling drill bit. During the rotational lowering process, sense the change in torque until the pressure-bearing platform (106) contacts the force-bearing plane of the drill bit and generates a predetermined torque, thus completing the docking. C. Open up mud channels: Try to open up mud transport channels inside and outside the drill pipe through positive circulation and / or reverse circulation; D. Unblocking and Lifting: Operate the notch retrieval device (1) by pulling, rotating, or pulling and rotating simultaneously until the pulling force monitored on the ground is basically consistent with the buoyancy of the drill bit and drill rod. After confirming that the notch is unblocked, lift the drill bit to the ground.

10. A system for retrieving drilling bits used in well sinking, characterized in that, include: The gap retrieval device (1) as described in any one of claims 1-5; The slag removal pipe (10) is used to remove the overlying slag inside the wellbore before the salvage operation.

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