Dual tube coring tool

Abstract

The utility model provides a kind of double-tube drilling tool for core sampling, including drill cylinder, variable buckle joint, drill bit, heart tube and buffer assembly.Drill cylinder upper end is connected drill pipe by variable buckle joint, bottom end thread connection replaceable hollow drill bit;Heart tube is coaxially arranged in drill cylinder, and its top end is connected variable buckle joint by rotating assembly, to realize that heart tube is relatively stationary or low-speed rotation when drill cylinder rotates, reduce core disturbance.Heart tube is embedded transparent lining pipe assembly, and lining pipe bottom end is equipped with bud-shaped blocking ring to prevent core from falling out, and top end is pushed by telescopic rod to take core.Buffer assembly is made of spring, thrust ring and buffer pad, and is arranged in the gap cooperation between heart tube bottom and drill cylinder, to absorb drilling impact and core fracture recoil force.Drill cylinder and heart tube form annular cavity communication drainage hole and drainage hole, to realize drilling fluid circulation and fluid guide discharge.The double-tube drilling tool for core sampling provided by the utility model can significantly improve core integrity and coring rate, and reduce maintenance cost.

Description

Technical Field

[0001] This utility model belongs to the field of drilling tool technology, specifically relating to a double-tube drill for core sampling. Background Technology

[0002] In the field of geological exploration, core sampling is a crucial step in obtaining information on the physical properties, structural characteristics, and resource distribution of underground rock strata. Current technologies generally employ a dual-tube design for core drilling tools. The outer tube (drill barrel) forms the core channel by rotating and breaking up the rock, while the inner tube (core tube) is used to contain and protect the core.

[0003] In existing technologies, traditional drilling tools generate instantaneous impact loads when the drill bit encounters hard rock interlayers, uneven hole bottoms, or core blockages during drilling. Because existing drilling tools lack targeted buffer structures, the impact force is directly transmitted to the core tube and the internal core, easily causing core root fracture or damage to internal components, further affecting core recovery rates. Furthermore, the core tube and drill barrel inner wall of existing drilling tools are mostly designed for rigid contact, making the core prone to breakage due to frictional resistance or jamming during extraction. In addition, traditional core extraction methods rely on manual hammering, which can easily cause secondary damage to the core and is inefficient.

[0004] Therefore, a dual-tube drill string for core sampling is proposed to address the current shortcomings. Utility Model Content

[0005] This utility model provides a dual-tube drilling tool for core sampling, which aims to solve the problems of low core recovery rate, poor core integrity, time-consuming maintenance, and high extraction difficulty caused by existing dual-tube drilling tools, such as core fracture due to lack of effective buffering of impact load, complex core extraction operation and easy detachment, and fluid pressure interference affecting the recovery rate.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is: to provide a dual-tube drill bit for core sampling, comprising:

[0007] The drill barrel has a threaded connection to a variable thread connector at its upper end and a threaded connection to a drill bit at its lower end.

[0008] The core tube is coaxially disposed inside the drill barrel, and its upper end is rotatably connected to the variable thread connector via a rotating assembly.

[0009] A buffer assembly is disposed at the bottom of the drill barrel, and the top end of the buffer assembly is fitted with the bottom end of the core tube with a clearance.

[0010] The liner assembly includes a liner coaxially disposed inside the heart tube and a telescopic rod fixed to the top end of the heart tube, wherein the telescopic end of the telescopic rod abuts against the top of the liner.

[0011] The blocking ring is fixedly installed at the bottom of the liner and is used to constrain the entry posture of the core.

[0012] Preferably, the variable-thread connector has a drainage hole in the middle circumferential direction that communicates with its interior, and the drainage hole communicates with the annular cavity between the drill barrel and the core tube.

[0013] The high-pressure drilling fluid pumped into the drill pipe is directly diverted through the drainage hole to the annular cavity between the drill barrel and the core tube, establishing an external circulation channel. This prevents the drilling fluid from directly scouring the core and isolates the core from the risk of erosion by high-pressure fluid. At the same time, the coolant flows down along the annular cavity to cool the drill bit and carries cuttings back up. The fluid around the core inside the liner is discharged through the guide channel, the core tube drain hole, and the annular cavity. This dual channel maintains the fluid balance at the bottom of the hole and significantly reduces the interference of fluid pressure on the core extraction process.

[0014] Preferably, the bottom of the variable-thread connector is provided with a mounting cavity, and the rotating assembly includes a set of bearings arranged at intervals along the axis within the mounting cavity, and the top end of the heart tube is interference-fitted with the inner ring of the bearings through a connecting shaft.

[0015] By using a dual-bearing axially spaced arrangement and an interference fit connecting shaft, the core tube can maintain a near-zero speed when the drill barrel rotates at high speed, eliminating friction between the core and the tube wall. At the same time, the spacing between the dual bearings forms an anti-sway torque, suppressing the core tube swaying caused by bottom hole vibration and maintaining the core entering the channel in a straight line.

[0016] Preferably, the buffer assembly includes a fixed ring, a spring, and a thrust ring. The fixed ring is fixedly connected to the lower inner wall of the drill barrel. An annular buffer pad is embedded on the upper surface of the fixed ring. The spring is circumferentially distributed on the upper surface of the annular buffer pad and its upper end is connected to the thrust ring.

[0017] The spring-buffer pad dual-stage energy absorption structure maintains a precise gap of 0.5-2mm between the thrust ring and the bottom of the core tube, ensuring that the core tube is in a non-contact suspended state during normal drilling, thus preventing vibration transmission. At the same time, when encountering impact loads, the core tube presses down on the thrust ring, thereby compressing the circumferential spring and deforming the annular buffer pad to simultaneously absorb axial impacts and high-frequency vibrations, protecting the brittle rock core structure.

[0018] Preferably, the gap between the upper surface of the thrust ring and the bottom end of the core tube is 0.5-2mm, the inner wall of the drill barrel is provided with an axially extending sliding groove, and the outer edge of the thrust ring and the sliding groove form a sliding pair.

[0019] By controlling the gap (0.5-2mm) and guiding the sliding groove, the core tube is kept suspended without friction during normal drilling, preventing vibration from being transmitted to the core. The sliding groove constrains the thrust ring to move only along the drill pipe axis. When an impact occurs, the core tube is vertically pressed down by the spring, preventing off-center loading and jamming, and ensuring efficient transmission of buffer force.

[0020] Preferably, the blocking ring includes a plurality of blocking petals evenly distributed circumferentially along the axis of the liner, and the root of each blocking petal is fixed to the bottom end of the liner.

[0021] The circumferentially distributed blocking petals allow the core to be pushed open as it ascends, and then the rear blocking petals elastically reset and close, forming a bud-like locking structure to prevent the core from falling out during drilling. At the same time, the arc-shaped petals disperse contact stress, protect the integrity of the brittle core surface, and greatly improve the recovery rate of cores from fractured formations.

[0022] Preferably, the free end of the blocking petals is curved in an arc towards the axis of the liner tube, and multiple blocking petals close to form a bud-like constraint structure in a natural contraction state.

[0023] The bud-like closed structure formed by the blocking petals creates a gradually narrowing entrance. When the core enters, the blocking petals slide and open in the direction of the hole to avoid scratching the head of the core. At the same time, the structure closes after the core has passed through, completely preventing the core from falling out when the drill is lifted.

[0024] Preferably, the radius of curvature R of the blocking lobe satisfies: R = k·D, where D is the inner diameter of the liner and k is a curvature coefficient of 0.25-0.35.

[0025] Preferably, the liner is a transparent tube made of polycarbonate.

[0026] The installation of the liner allows for direct downhole observation of the core bedding structure and recovery rate, eliminating the need for pre-inspection steps.

[0027] Preferably, the inner wall of the liner has multiple guide grooves axially connected to the core tube, and the top of the core tube has multiple drainage holes connected to the annular cavity.

[0028] By using the flow channels and drainage holes, the fluid (water / mud) around the core inside the liner is guided into the core tube through the flow channels, avoiding the fluid pressure from damaging the original structure of the core. At the same time, the fluid flows into the main channel of the drilling fluid in the annular cavity through the drainage hole at the top of the core tube, avoiding mutual interference between the internal and external circulation systems. Moreover, the axial flow channel design allows the fluid containing debris to be discharged smoothly, solving the risk of core blockage and failure.

[0029] The dual-tube drilling tool for core sampling provided by this utility model has the following advantages compared with the prior art:

[0030] A rotating assembly is used to achieve relative motion separation between the core and the drill barrel. The core is rotatably connected to a variable thread joint via bearings. When the drill barrel rotates during drilling, the core can remain relatively stationary or rotate at a low speed, significantly reducing mechanical friction and disturbance between the core and the drill pipe wall during drilling, effectively improving core recovery rate and integrity.

[0031] A buffer structure is incorporated to enhance impact resistance. The buffer assembly, through the cooperation of a fixed ring, a spring, and a thrust ring, utilizes the compression deformation of the spring and the elastic deformation of the annular buffer pad to absorb impact loads during drilling and the counter-impact force when the core fractures, preventing core breakage or damage to internal components. It is particularly suitable for the protection of brittle cores.

[0032] The liner assembly and the retaining ring work together to optimize core constraint and observation functions. The liner is made of transparent polycarbonate, which facilitates direct on-site observation of core integrity and recovery rate. The retaining ring has a circumferentially distributed, closable retaining valve structure that opens to allow the core to pass through when it enters, and automatically returns to a closed state after it has passed through. This effectively constrains the core's posture to prevent it from tilting or falling off, and also prevents the core from falling out during the lifting process, thus improving core recovery efficiency and integrity.

[0033] The guide groove on the inner wall of the liner is connected to the drain hole of the core tube to form a fluid discharge channel, which allows the fluid entering the gap between the core and the liner or the core to be smoothly discharged into the annular cavity and return with the drilling fluid, reducing the impact of fluid pressure on the stability of the core and ensuring the smooth entry and preservation of the core. Attached Figure Description

[0034] Figure 1 A schematic diagram of the structure of the dual-tube drill bit for core sampling provided in this embodiment of the utility model;

[0035] Figure 2 A cross-sectional structural schematic diagram of a dual-tube drill for core sampling provided in an embodiment of this utility model;

[0036] Figure 3 yes Figure 2 A magnified view of point A in the dual-tube drill string for core sampling provided in the embodiment;

[0037] Figure 4 This is a schematic diagram of the main structure of a dual-tube drill bit for core sampling provided in an embodiment of the present invention;

[0038] Figure 5 yes Figure 4 A cross-sectional view of section BB in the twin-tube drill string for core sampling provided in the embodiment;

[0039] Figure 6 yes Figure 5 A magnified view of point C in the dual-tube drill string for core sampling provided in the embodiment;

[0040] Figure 7 yes Figure 5 A magnified view of point D in the dual-tube drill bit for core sampling provided in the embodiment.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1. Drill barrel; 101. Sliding groove;

[0043] 2. Variable thread connector; 201. Drainage hole; 202. Mounting cavity;

[0044] 3. Drill bit;

[0045] 4. Heart tube; 401. Drainage port;

[0046] 5. Rotating components; 501. Bearings;

[0047] 6. Buffer assembly; 601. Fixing ring; 602. Spring; 603. Thrust ring; 604. Annular buffer pad;

[0048] 7. Liner assembly; 701. Liner; 7011. Guide channel; 702. Telescopic rod;

[0049] 8. Blocking ring; 801. Blocking flap;

[0050] 9. Annular cavity; 10. Connecting shaft. Detailed Implementation

[0051] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0052] Please refer to the following: Figures 1 to 6 The present invention describes a dual-tube core sampling drill bit. The dual-tube core sampling drill bit includes a drill barrel 1, which is a hollow cylindrical structure open at both ends, forming the outer shell of the drill bit and the drilling components. A variable-thread connector 2 is threaded to the upper end of the drill barrel 1, enabling quick connection and diameter adaptation between the drill rod and the drill bit. A drill bit 3 is threaded to the bottom end of the drill barrel 1. A core tube 4, also a tubular structure, is coaxially arranged inside the drill barrel 1, forming a core receiving cavity to receive and protect the core. The upper end of the core tube 4 is rotatably connected to the variable-thread connector 2 via a rotating assembly 5. The bottom of the variable-thread connector 2 has an installation cavity 202. The rotating assembly 5 includes a set of bearings 501 spaced along the axis within the installation cavity 202. The top end of the core tube 4 is interference-fitted with the inner ring of the bearings 501 via a connecting shaft 10. The buffer assembly 6 is located at the bottom of the drill barrel 1, and the top of the buffer assembly 6 is in clearance fit with the bottom of the core tube 4; the liner assembly 7 includes a liner 701 coaxially disposed inside the core tube and a telescopic rod 702 fixed at the top of the core tube 4, and the telescopic end of the telescopic rod 702 abuts against the top of the liner 701; the blocking ring 8 is fixedly installed at the bottom of the liner 701 to constrain the core entry posture.

[0053] In this embodiment, the drill bit 3 can be a diamond drill bit, installed at the bottom of the drill barrel 1, to directly break the rock at the bottom of the hole, form a core column, and guide the core into the core tube 4. The drill bit 3 has a hollow cylindrical structure and is threadedly connected to the drill barrel 1.

[0054] The detachable drill bit 3 allows for quick on-site disassembly and replacement, significantly reducing maintenance time. Meanwhile, the drill bit 3 adopts a hollow cylindrical design, forming a core-accommodating channel inside. This allows the core to form along the center of the drill bit 3 and enter the liner 701 inside the drill barrel 1 during drilling, facilitating the collection and extraction of the core and reducing friction between the core and the external environment during drilling, thus protecting the integrity of the core.

[0055] When implementing, refer to Figure 3 and Figure 6 As shown, the relative rotation between the core tube 4, the variable thread connector 2, and the drill barrel 1 is achieved through the rotating assembly 5. When the drill barrel 1 rotates during drilling, the core tube 4 can remain relatively stationary or rotate at a low speed, reducing mechanical disturbance to the core and improving the core recovery rate and integrity.

[0056] The variable thread connector 2 has a drainage hole 201 in the middle circumferential direction that communicates with its interior. During implementation, the outer diameter of the core tube 4 is smaller than the inner diameter of the drill barrel 1 to form an annular cavity 9. The drainage hole 201 communicates with the annular cavity 9 between the drill barrel 1 and the core tube 4. The drilling fluid pumped into the drill pipe can be introduced into the annular cavity 9 through the drainage hole 201.

[0057] Reference Figures 5 to 7 As shown, the buffer assembly 6 is located at the bottom of the drill barrel 1, and the top of the buffer assembly 6 is fitted with the bottom of the core tube 4 with a clearance.

[0058] The buffer assembly 6 includes a fixed ring 601, a spring 602 and a thrust ring 603. The fixed ring 601 is fixedly connected to the lower inner wall of the drill barrel 1. An annular buffer pad 604 is embedded on the upper surface of the fixed ring 601. The spring 602 is evenly distributed circumferentially on the upper surface of the annular buffer pad 604 and its upper end is connected to the thrust ring 603.

[0059] The gap between the upper surface of the thrust ring 603 and the bottom end of the core tube 4 is 0.5-2mm. The inner wall of the drill barrel 1 is provided with an axially extending sliding groove 101. The outer edge of the thrust ring 603 and the sliding groove 101 form a sliding pair.

[0060] The thrust ring 603 supports the bottom of the core tube 4 upwards, providing axial buffering at the bottom of the core tube 4, absorbing the impact load during drilling, and preventing severe vibration from damaging the core or internal components.

[0061] Meanwhile, the thrust ring 603 maintains a small gap with the bottom of the core tube 4 and does not contact under normal working conditions. When an impact occurs or the core is blocked, the core tube 4 moves down to compress the spring 602, thus preventing damage to the core tube 4 or the liner tube 701.

[0062] Furthermore, when core extraction is required, the drill string is raised, causing the core root to fracture from the un-drilled rock below. At this moment, the impact force generated during the fracture is transmitted through the core tube 4. The impact force pushes the thrust ring 603 downwards, compressing the spring 602. The compression of the spring 602 and the elastic deformation of the annular buffer pad 604 together absorb the impact energy, effectively buffering the impact force and preventing the core from fracturing at the root. This is especially effective for brittle cores, protecting their integrity.

[0063] The liner assembly 7 includes a liner 701 coaxially disposed inside the core tube 4 and a telescopic rod 702 fixed to the top of the core tube 4. The liner 701 is used to directly contain and preserve the core sample. In this embodiment, the liner 701 is a transparent tube made of polycarbonate material, which facilitates direct observation of the core integrity and recovery rate on site.

[0064] The telescopic end of the telescopic rod 702 abuts against the top of the liner 701. In the initial state, the telescopic rod 702 is in a retracted state and its telescopic end abuts against the liner 701. When the core is removed from the core tube 4, the slow extension of the telescopic rod 702 pushes the liner 701, pushing the core along with the liner 701 out of the core tube 4, which facilitates the extraction and subsequent processing of the core.

[0065] Furthermore, refer to Figure 3 The inner wall of the liner 701 has multiple guide grooves 7011 axially opened to communicate with the core tube 4, and the top of the core tube 4 has multiple drain holes 401 communicating with the annular cavity 9.

[0066] Fluids (water, mud) entering between the liner 701 and the core or within the core can flow smoothly into the core tube 4 and be discharged through the drain hole 401, reducing the interference of fluid pressure on core extraction.

[0067] Reference Figure 2 and Figure 7 As shown, the blocking ring 8 is fixedly installed at the bottom of the liner 701 to constrain the core's entry posture and prevent the core from tilting or breaking. At the same time, the blocking ring 8 can ensure the lifting of the core inside the liner 701 and prevent the core from falling out of the liner 701.

[0068] Specifically, the blocking ring 8 includes multiple blocking petals 801 evenly distributed circumferentially along the axis of the liner 701, with the root of each blocking petal 801 fixed to the bottom end of the liner 701.

[0069] The free end of the blocking petal 801 is curved in an arc towards the axis of the liner 701. In the natural contraction state, multiple blocking petals 801 close to form a bud-like constraint structure.

[0070] The radius of curvature R of the blocking lobe 801 satisfies: R = k·D, where D is the inner diameter of the liner 701 and k is a curvature coefficient of 0.25-0.35.

[0071] When the core enters the liner 701 from the drill bit 3, the top of the core squeezes the blocking petals 801 from bottom to top, thus opening the multiple bud-shaped blocking petals 801. After the core passes through the obstruction of the blocking petals 801, the multiple blocking petals 801 return to the bud shape, thereby preventing the core from falling out of the liner 701, improving the efficiency of core sampling, and enhancing the integrity of the core sample.

[0072] In this embodiment, the bearing 501 is a deep groove ball bearing, the liner 701 is a PC-50 polycarbonate tube, and the telescopic rod 702 is an electric telescopic rod of model Linak MD50-50-1000.

[0073] In specific implementation of this utility model:

[0074] 1) Drilling and connection:

[0075] The variable thread connector 2 of the drill string is quickly connected to the bottom of the drill string via threads.

[0076] Based on geological conditions and drilling requirements, select a suitable diamond drill bit 3 and install it at the bottom of the drill barrel 1 via threads.

[0077] A liner 701 is placed inside the heart tube 4. The blocking ring 8 at the bottom of the liner 701 (composed of multiple centripetally curved blocking valves 801) is in a naturally contracted "bud-like" closed state.

[0078] The assembled core tube 4 is inserted into the drill barrel 1, so that the connecting shaft 10 at the upper end of the core tube 4 is rotatably connected to the mounting cavity 202 at the lower part of the variable thread connector 2 through the rotating component 5.

[0079] The bottom end of the heart tube maintains a small initial gap (0.5-2mm) with the upper surface of the thrust ring 603 of the buffer assembly 6.

[0080] Finally, the drill string was lowered to the designated sampling position at the bottom of the hole.

[0081] 2) Drilling and core formation:

[0082] The drilling rig drives the drill rod to rotate, which in turn drives the drill barrel 1 and the drill bit 3 at its bottom to rotate at high speed. The drill bit 3 breaks the rock at the bottom of the hole and forms a core column.

[0083] Drilling fluid circulation: High-pressure drilling fluid is pumped in from inside the drill pipe, flows through the drainage hole 201 in the middle of the variable thread connector 2, and enters the annular cavity 9 formed between the inner wall of the drill barrel 1 and the outer wall of the core tube 4.

[0084] The drilling fluid flows downward along the annular cavity 9 and reaches the bottom of the drill bit 3, where it cools the drill bit, lubricates the borehole wall, and carries rock cuttings back upward.

[0085] Core entry: Guided by drill bit 3, the formed core column enters upward into the core receiving channel inside drill bit 3 and liner 701.

[0086] The top of the core first contacts and pushes open the blocking valve 801, causing it to open outwards, allowing the core to smoothly enter the liner 701. After the core passes through, the blocking valve 801, under its own elasticity and structural action, can return to the "bud-like" closed state, preventing the core that has entered from falling out downwards.

[0087] Fluid discharge: The fluid (water, mud) entering between the liner 701 and the core, or within the core, flows into the gap between the core tube 4 and the liner 701 through the axially opened guide groove 7011 on the inner wall of the liner 701, and then flows upward. After reaching the drain hole 401 at the top of the core tube 4, the fluid is discharged into the annular cavity 9, and finally returns to the surface with the circulating drilling fluid, effectively reducing the interference of fluid pressure on the core extraction process.

[0088] Meanwhile, the drill barrel 1 is rotating at high speed. At this time, the core tube 4 is kept relatively stationary or rotates at low speed with the variable thread joint 2 / drill rod through the rotating component 5. This significantly reduces the mechanical disturbance, friction and wear caused by the rotation to the core column, which is the core mechanism to improve the core recovery rate and integrity.

[0089] 3) Shock buffering:

[0090] During drilling, encountering hard rock interlayers, fracture zones, or uneven bottom surfaces can generate impact loads.

[0091] The impact force is transmitted through the drill barrel 1 and the drill bit 3, causing axial vibration of the core tube 4.

[0092] Under normal circumstances, the thrust ring 603 maintains a small gap with the bottom end of the heart tube 4 and does not contact it.

[0093] When the downward impact force is too great or the core is blocked in the liner 701, causing the core tube 4 to move downward, the bottom end of the core tube 4 contacts and presses the thrust ring 603.

[0094] The thrust ring 603 moves downward, compressing the spring 602 and causing the annular buffer pad 604 to undergo elastic deformation, together absorbing the impact energy and protecting the core tube 4, liner tube 701 and internal rock core from severe vibration damage.

[0095] 4) Core Acquisition Completion and Enhancement:

[0096] Once the core of the predetermined length has entered the liner 701, drilling is stopped, and then the entire drill string is slowly lifted.

[0097] The core root (bottommost part) fractured with the bedrock below that had not been drilled.

[0098] Root fracture impact buffer: The upward counter-impact force generated at the moment of fracture acts on the bottom of the core and is transmitted to the liner 701 and core tube 4 through the blocking ring 8, thereby pushing the core tube 4 to move downward relative to the drill pipe 1.

[0099] The bottom end of the core tube 4 impacts the thrust ring 603, pushing it downwards. The thrust ring 603 compresses the spring 602 downwards and squeezes the annular buffer pad 604. The compression deformation of the spring 602 and the elastic deformation of the buffer pad 604 together absorb the impact energy generated by the fracture at the root of the core, effectively preventing the brittle core from fracturing at the root and protecting the integrity of the core end.

[0100] The closed state of the blocking ring 8 ensures that the core will not fall off the bottom of the liner 701 during the lifting process, and the drill string is lifted to the surface with the drill string.

[0101] 5) Core extraction:

[0102] 5.1 Remove the drilling tools.

[0103] Unscrew the variable thread connector 2 at the top of the drill barrel 1 and remove the inner core tube 4.

[0104] Operate the telescopic rod 702, slowly drive the telescopic end of the telescopic rod 702 to extend, and push the top of the liner 701 downward.

[0105] The liner 701, along with the core sample completely encased inside, was smoothly pushed out from the bottom of the core tube 4.

[0106] Because the liner 701 is made of transparent polycarbonate, the integrity and recovery rate of the internal core can be directly observed on site.

[0107] If it is necessary to preserve the sample, the liner 701 containing the core can be directly sealed, marked and transported.

[0108] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A double-tube drill string for core sampling, characterized in that, include: The drill barrel has a threaded connection to a variable thread connector at its upper end and a threaded connection to a drill bit at its lower end. The core tube is coaxially disposed inside the drill barrel, and the upper end of the core tube is rotatably connected to the variable thread connector via a rotating assembly. A buffer assembly is disposed at the bottom of the drill barrel, and the top end of the buffer assembly is fitted with the bottom end of the core tube with a clearance. The liner assembly includes a liner coaxially disposed inside the heart tube and a telescopic rod fixed to the top end of the heart tube, wherein the telescopic end of the telescopic rod abuts against the top of the liner. The blocking ring is fixedly installed at the bottom of the liner and is used to constrain the entry posture of the core.

2. The dual-tube drill bit for core sampling as described in claim 1, characterized in that: The variable-thread connector has a drainage hole in the middle circumferential direction that communicates with its interior. The drainage hole is connected to the annular cavity between the drill barrel and the core tube.

3. The dual-tube drill string for core sampling as described in claim 1, characterized in that: The bottom of the variable-thread connector is provided with a mounting cavity, and the rotating assembly includes a set of bearings arranged at intervals along the axis in the mounting cavity. The top end of the heart tube is interference-fitted with the inner ring of the bearings through a connecting shaft.

4. The dual-tube drill bit for core sampling as described in claim 1, characterized in that, The buffer assembly includes a fixed ring, a spring, and a thrust ring. The fixed ring is fixedly connected to the lower inner wall of the drill barrel. An annular buffer pad is embedded on the upper surface of the fixed ring. The spring is circumferentially distributed on the upper surface of the annular buffer pad and its upper end is connected to the thrust ring.

5. The dual-tube drill bit for core sampling as described in claim 4, characterized in that: The gap between the upper surface of the thrust ring and the bottom end of the core tube is 0.5-2mm. The inner wall of the drill barrel is provided with an axially extending sliding groove. The outer edge of the thrust ring and the sliding groove form a sliding pair.

6. The dual-tube drilling tool for core sampling as described in claim 1, characterized in that: The blocking ring includes multiple blocking petals evenly distributed circumferentially along the axis of the liner, with the root of each blocking petal fixed to the bottom end of the liner.

7. The dual-tube drill string for core sampling as described in claim 6, characterized in that: The free end of the blocking petals is curved in an arc towards the axis of the liner tube. In the natural contraction state, multiple blocking petals close to form a bud-like constraint structure.

8. The dual-tube drilling tool for core sampling as described in claim 7, characterized in that: The radius of curvature R of the blocking lobe satisfies: R = k·D, where D is the inner diameter of the liner and k is a curvature coefficient of 0.25-0.

35.

9. The dual-tube drilling tool for core sampling as described in claim 1, characterized in that: The liner is a transparent tube made of polycarbonate.

10. The dual-tube drill string for core sampling as described in claim 9, characterized in that: The inner wall of the liner has multiple axially formed guide grooves that communicate with the core tube, and the top of the core tube has multiple drainage holes that communicate with the annular cavity.

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