A drilling system and method for preventing wellbore instability during drilling through goaf areas.

Abstract

This invention relates to a drilling system and method for preventing wellbore instability during drilling through goaf areas, belonging to the field of drilling machinery technology. The objective is to provide a drilling system that effectively prevents wellbore instability during drilling through goaf areas. The technical solution includes a motor, a reducer, a clutch, a square drill pipe, a rotary table, a transmission rod, a drill pipe, a guide rod, and a drill bit. The motor is connected to the upper end of the square drill pipe via the clutch and reducer. The lower end of the square drill pipe passes through the rotary table and is connected to a first universal coupling. The first universal coupling is connected to the upper end of the transmission rod via a universal joint. The lower end of the transmission rod is connected to a second universal coupling via a cross bar. The lower end of the second universal coupling is connected to the upper end of the drill pipe via a flange. A rubber sheet is connected to the lower end of the drill pipe, and a solution damper is connected below the rubber sheet. The lower end of the solution damper is connected to the upper end of the guide rod, and the lower end of the guide rod is connected to the drill bit. This invention is used for drilling through goaf areas.

Description

Technical Field

[0001] This invention relates to a drilling system and method for preventing wellbore instability during drilling through goaf areas, belonging to the field of drilling machinery technology. Background Technology

[0002] During drilling through goaf areas, the uneven geological conditions make the drill bit susceptible to vibration. Furthermore, the high shear resistance and discontinuous rock-breaking process cause significant fluctuations in the drill bit's rotational torque, accelerating the breakage, detachment, and wear of the composite cutting surfaces. This also causes the drilling direction to deviate from the target trajectory, leading to wellbore instability. These problems require specialized technical solutions. Therefore, this invention proposes a drilling system and method to prevent wellbore instability during drilling through goaf areas, further improving mining efficiency and safety. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a drilling system and method that can effectively prevent wellbore instability during drilling through goaf areas.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a drilling system for preventing wellbore instability during drilling through goaf areas, comprising a motor, a reducer, a clutch, a square drill rod, a rotary table, a transmission rod, a drill rod, a guide rod, and a drill bit. The motor is connected to the upper end of the square drill rod via the clutch and the reducer. The lower end of the square drill rod passes through the rotary table and is connected to a first universal coupling. The first universal coupling is connected to the upper end of the transmission rod via a universal joint. The lower end of the transmission rod is connected to a second universal coupling via a cross bar. The lower end of the second universal coupling is connected to the upper end of the drill rod via a flange. A rubber sheet is connected to the lower end of the drill rod. A solution damper is connected below the rubber sheet. The lower end of the solution damper is connected to the upper end of the guide rod via a connector. The lower end of the guide rod is connected to the drill bit.

[0005] The drill bit includes an installation section, a connecting section, and a cutting section. The installation section has a loading and unloading groove for connecting to a guide rod. The connecting section connects the installation section and the cutting section, and is equipped with a vibration-damping drilling directional device. The cutting section has multiple blades evenly distributed around its periphery. Each blade is equipped with cutting teeth and pointed conical teeth. A chip removal groove is provided between two adjacent blades. The delivery pipe is located at the central axis of the drill bit and runs through the drill bit from top to bottom. An anti-backflow device is installed in the upper part of the delivery pipe. Multiple water holes are opened on the bottom surface of the cutting section. Each water hole is connected to the delivery pipe through a secondary pipe. Each blade has an auxiliary water hole with an inwardly inclined outlet on its inner side. Each auxiliary water hole is also connected to the delivery pipe through a secondary pipe. A nozzle is installed in each water hole and auxiliary water hole.

[0006] Furthermore, the anti-vibration drilling directional device includes a housing, a sensor, a spring shock absorber, and a wireless transmission device. The housing has an inner cavity, in which the sensor is fixed. The wireless transmission device is fixed to the top of the housing and surrounded by a rubber protective sleeve. The sensor and the wireless transmission device are connected. A spring shock absorber is installed at the bottom of the housing, with its bottom in close contact with the drill bit connection section. A stabilizing cover is installed outside the spring shock absorber.

[0007] Furthermore, a stabilizing cover is provided on the outside of the spring shock absorber. The upper end of the stabilizing cover is fixed to the outer shell of the anti-vibration drilling directional device, and the lower end is in close contact with the connecting section of the drill bit.

[0008] Furthermore, the anti-backflow device includes a valve body, a valve cover, a support ring, a valve disc, and a spring. The two valve covers are respectively fixed at the upper and lower ends of the valve body. The support ring is located inside the valve body, with its lower end fixed to the valve cover and its upper end supporting the spring. The valve disc is fixed to the spring, and the top of the valve disc cooperates with the valve seat located inside the valve body. A guide device is also provided between the valve disc and the support ring.

[0009] Furthermore, the number of blades is four.

[0010] Furthermore, the cutting teeth and conical teeth on the blade are multiple, with the multiple cutting teeth arranged in a row from top to bottom, and the multiple conical teeth also arranged in a row from top to bottom.

[0011] Furthermore, both the cutting teeth and the pointed conical teeth protrude 2 cm from the blade surface.

[0012] Furthermore, the blade is helical in shape.

[0013] Furthermore, the chip removal groove is streamlined, and its cross-sectional area gradually increases from bottom to top.

[0014] A drilling method for preventing wellbore instability during drilling through goaf areas includes the following steps:

[0015] S1. Determine the location, depth, and angle of the borehole based on geological survey data, ensuring that the deviation between the borehole location and the designed location does not exceed 0.5m;

[0016] S2. Select a drilling fluid formula that is suitable for the formation characteristics and drill using the drilling system described in claim 1 to prevent wellbore instability during drilling through goaf areas. The drilling pressure is 20-50KN and the rotation speed is 30r / min. During the drilling process, the drilling trajectory is continuously monitored by the anti-vibration drilling directional device. If the deviation between the drilling trajectory and the design trajectory exceeds the allowable range, the trajectory is corrected in time until the deviation between the drilling trajectory and the design trajectory returns to the allowable range.

[0017] S3. When drilling close to the goaf, reduce the drilling speed to 25 r / min to reduce the impact and damage to the well wall;

[0018] S4. After passing through the goaf, restore the rotation speed to 30 r / min until drilling is completed;

[0019] S5. After drilling is completed, cementing operations are carried out to reinforce the well wall.

[0020] Compared with the prior art, the present invention has the following beneficial effects.

[0021] 1. In this invention, the solution damper is filled with a viscous liquid. When subjected to external impact during drilling, the fluid flows within the damper's internal cavity, generating damping force and thus consuming vibration energy. Subsequently, when the vibration is transmitted to the rubber sheet, the rubber sheet deforms, absorbing some of the vibration energy. In this way, the solution damper and the rubber sheet provide a dual damping effect, effectively mitigating drill bit vibration and preventing wellbore instability. Furthermore, it reduces the system's resonant frequency, thereby minimizing the occurrence of resonance phenomena.

[0022] 2. In this invention, four blades are evenly distributed on the drill bit. The four-blade design is relatively simple and simplifies the operation process. In addition, the four-blade design can effectively disperse the cutting force during drilling, making the load on each blade more uniform, enabling it to maintain high cutting efficiency and drill deeper, thereby improving the overall efficiency of drilling operations, reducing vibration and wear, and improving the stability and service life of the drill bit. Furthermore, the four-blade design can usually provide a large area of ​​chip removal space, improving the efficiency of cooling the drill bit.

[0023] 3. In this invention, auxiliary water holes are provided on the inner side of the cutter blade, and nozzles are installed in the auxiliary water holes. On the one hand, this can more effectively spray drilling fluid to the bottom of the well and the surface of the drill bit, enhance the flushing effect of the drilling fluid on the bottom of the well, help remove rock cuttings on the cutting teeth, keep the drill bit surface clean, and reduce the risk of stuck drill bit. On the other hand, it can also more effectively cool and lubricate the cutting teeth, which helps to reduce the wear of the cutting teeth caused by high temperature and friction, and extend the service life of the drill bit. Thirdly, it can form a high-pressure jet, reduce the cutting load of the drill bit, improve drilling efficiency, and also change the flow direction of the drilling fluid, thereby reducing the vibration of the drill bit to a certain extent, which helps to improve the stability and cutting accuracy of the drill bit.

[0024] 4. The present invention installs an anti-backflow device in the delivery pipeline, which can prevent drilling fluid backflow from causing the mudstone and shale to expand and squeeze the well wall, resulting in a narrowing phenomenon. It also avoids the pressure difference and shear force generated by drilling fluid backflow from acting on the well wall rock, causing formation fracturing, affecting well wall stability, or causing a large amount of drilling fluid loss and formation contamination. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below.

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] Figure 2 This is a schematic diagram of the drill bit structure in this invention.

[0028] Figure 3 This is a schematic diagram of the anti-vibration drilling directional device in this invention.

[0029] Figure 4 This is a schematic diagram of the anti-backflow device in this invention.

[0030] In the diagram: 1 is the motor, 2 is the reducer, 3 is the clutch, 4 is the first universal coupling, 5 is the transmission rod, 6 is the flange, 7 is the drill pipe, 8 is the connecting part, 9 is the guide rod, 10 is the drill bit, 11 is the second universal coupling, 13 is the square drill pipe, 14 is the rotary table, 15 is the universal joint, 16 is the cross rod, 17 is the rubber sheet, 18 is the solution shock absorber, 101 is the loading and unloading groove, 102 is the anti-vibration drilling directional device, 103 is the pointed bevel tooth, 104 is the cutting tooth, 106 is the cutter blade, and 109 is the delivery pipe. 110 is the chip removal groove, 111 is the water inlet, 112 is the auxiliary water inlet, 113 is the connecting section, 114 is the installation section, 115 is the anti-backflow device, 116 is the cutting section, 121 is the wireless transmission device, 122 is the inner cavity, 123 is the sensor, 124 is the spring shock absorber, 125 is the stabilizing cover, 127 is the outer shell, 128 is the rubber protective sleeve, 131 is the valve body, 132 is the valve cover, 133 is the support ring, 134 is the valve disc, 135 is the spring, 136 is the valve seat, and 137 is the guide device. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The present invention provides the following embodiments.

[0033] like Figure 1As shown, the present invention discloses a drilling system for preventing wellbore instability during drilling through goaf areas, comprising a motor 1, a reducer 2, a clutch 3, a square drill rod 13, a rotary table 14, a transmission rod 5, a drill rod 7, a guide rod 9, and a drill bit 10. The motor 1 is connected to the upper end of the square drill rod 13 through the reducer 2 and the clutch 3. The lower end of the square drill rod 13 passes through the rotary table 14 and is connected to a first universal coupling 4. The first universal coupling 4 is connected to the upper end of the transmission rod 5 through a universal joint 15. The lower end of the transmission rod 5 is connected to a second universal coupling 11 through a cross rod 16. The lower end of the second universal coupling 11 is connected to the upper end of the drill rod 7 through a flange 6. A rubber sheet 17 is connected to the lower end of the drill rod 7. A solution damper 18 is connected below the rubber sheet 17. The lower end of the solution damper 18 is connected to the upper end of the guide rod 9 through a connector 8. The lower end of the guide rod 9 is connected to the drill bit 10.

[0034] like Figure 2 As shown, the drill bit 10 includes an installation section 114, a connecting section 113, and a cutting section 116. The installation section 114 has a loading / unloading groove 101 connected to the guide rod 9. The connecting section 113 connects the installation section 114 and the cutting section 116 together, and a vibration-damping drilling directional device 102 is installed on the connecting section 113. Multiple blades 106 are evenly distributed around the periphery of the cutting section 116. Each blade 106 is provided with cutting teeth 104 and pointed conical teeth 103. A chip removal groove 110 is provided between two adjacent blades 106. A feed pipe... The channel 109 is located at the central axis of the drill bit 10 and runs through the drill bit 10 vertically. An anti-backflow device 115 is installed in the upper part of the delivery channel 109. Multiple water holes 111 are opened on the bottom surface of the cutting section 116. Each water hole 111 is connected to the delivery channel 109 through a secondary channel. Each blade 106 has an auxiliary water hole 112 with an inwardly inclined outlet on its inner side. Each auxiliary water hole 112 is also connected to the delivery channel 109 through a secondary channel. A nozzle is installed in each water hole 111 and auxiliary water hole 112.

[0035] The aforementioned drill bit 10 comprises a hydraulic system consisting of a delivery pipe 109, a secondary pipe, a water inlet 111, an auxiliary water inlet 112, and a chip removal groove 110. When the hydraulic impact pressure reaches a certain value, the system assists the drill bit 10 in breaking rock formations. The nozzles installed at the water inlet 111 and the auxiliary water inlet 112 are both made of boron carbide, and the nozzle interface features a perforated wrench design, providing a certain degree of anti-loosening performance.

[0036] The nozzles inside the auxiliary water eye 112 can further optimize drilling parameters by adjusting the injection angle and flow rate.

[0037] The solution-based shock absorber is filled with silicone oil, a viscous liquid. When subjected to external impact during drilling, the fluid flows within the shock absorber's internal cavity, generating damping force and thus consuming vibration energy. Subsequently, when the vibration is transmitted to the rubber sheet, the rubber sheet deforms, absorbing some of the vibration energy. In this way, the solution-based shock absorber and the rubber sheet provide a dual damping effect, effectively mitigating drill bit vibration, preventing wellbore instability, and reducing the breakage, detachment, and wear of the composite material on the cutting teeth 104, thereby improving rock-breaking efficiency.

[0038] like Figure 3 As shown, the anti-vibration drilling directional device 102 includes a housing 127, a sensor 123, a spring shock absorber 124, and a wireless transmission device 121. The housing 127 has an inner cavity 122. The sensor 123 is fixed in the inner cavity 122. The wireless transmission device 121 is fixed on the top of the housing 127 and is surrounded by a rubber protective sleeve 128. The sensor 123 and the wireless transmission device 121 are connected. The bottom of the housing 127 is provided with a spring shock absorber 124, and the bottom of the spring shock absorber 124 is in close contact with the connecting section 113 of the drill bit 10.

[0039] The spring shock absorber 124 is provided with a stabilizing cover 125. The upper end of the stabilizing cover 125 is fixed to the outer shell 127 of the anti-vibration drilling directional device 102, and the lower end is in close contact with the connecting section 113 of the drill bit 10.

[0040] The spring damper 124 is a torque spring damper.

[0041] The anti-vibration drilling directional system 102 employs electromagnetic wave wireless transmission. Sensor 123 collects downhole measurement data, loads this data onto an electromagnetic carrier signal, and transmits this carrier signal via wireless transmission device 121 (electromagnetic wave transmitter). Receivers at the surface or wellhead receive the electromagnetic signal, convert it into an electrical signal, decode it, and reconstruct the original measurement data. This transmission method offers advantages such as being unaffected by drilling media, high transmission speed, and long transmission distance. The surface receiving system monitors downhole conditions by measuring changes in the potential difference between two points, adjusting the drill bit's drilling direction in real time to prevent wellbore instability caused by deviations in the drilling direction.

[0042] like Figure 4As shown, the anti-backflow device 115 includes a valve body 131, a valve cover 132, a support ring 133, a valve disc 134, and a spring 135. The two valve covers 132 are respectively fixed to the upper and lower ends of the valve body 131. The support ring 133 is disposed inside the valve body 131, with its lower end fixed to the valve cover 132 and its upper end supporting the spring 135. The valve disc 134 is fixed to the spring 135. The top of the valve disc 134 cooperates with the valve seat 136 disposed inside the valve body 131. A guide device 137 is also provided between the valve disc 134 and the support ring 133.

[0043] If drilling fluid backflow causes formation fracturing, a large amount of drilling fluid will rush into the formation fractures, causing a rapid drop in the fluid column pressure inside the well and leading to wellbore instability. Furthermore, the stress state around the wellbore will change; the pressure support originally provided by the drilling fluid may weaken due to formation fracturing, resulting in micro-cracks or plastic deformation in the wellbore, thereby reducing the wellbore's load-bearing capacity. The anti-backflow device 115 can block drilling fluid backflow, effectively reducing drilling fluid penetration into the formation.

[0044] The number of blades 106 is four.

[0045] The blade 106 has multiple cutting teeth 104 and multiple conical teeth 103, with the multiple cutting teeth 104 arranged in a row from top to bottom, and the multiple conical teeth 103 also arranged in a row from top to bottom.

[0046] The tooth arrangement scheme should ensure that the spacing between the cutting teeth 104 is reasonable and evenly distributed, avoiding excessive density or sparseness that could lead to poor cutting effect or excessive wear of the cutting teeth 104. The tooth density should be arranged from low to high. Based on the formation characteristics and drilling parameters, the cutting amount that each cutting tooth 104 should bear should be calculated. Then, the radial arrangement formula of the cutting teeth 104 should be derived according to the principle of equal cutting to ensure that the spacing between the cutting teeth 104 is reasonable.

[0047] Both the cutting tooth 104 and the conical tooth 103 protrude 2 cm from the surface of the blade 106. The cutting tooth 104 first contacts the rock or formation and performs cutting operations, reducing phenomena such as drill bit torsional vibration caused by cutting forces. During the cutting process, the blade 106 supports and protects the cutting tooth 104. The cutting tooth 104 and the conical tooth 103 cooperate to complete the cutting task, effectively releasing the bottom hole pressure. The cutting tooth 104 is responsible for the initial cutting operation, while the conical tooth 103 is responsible for subsequent auxiliary cutting and controlling the depth of penetration. Efficient cooperation helps to reduce drilling time, improve drilling efficiency, and thus reduce the time the wellbore is exposed to unstable conditions.

[0048] The blade 106 is helical in shape.

[0049] The crown section of the cutter wing 106 can be viewed as a rotating surface composed of smooth curves arranged around the drill bit's centerline. It employs a straight-arc-straight-line design, which helps achieve a smooth transition from the crown tip to the gauge, avoiding premature damage to localized cutting teeth caused by stress concentration. Within the cutter wing 106, the working surface consists of an inner cone and an arc surface. The inner cone is located inside the cutting section 116 of the drill bit 10, close to the centerline of the drill bit 10. The straight sections of the crown are typically located at both ends of the cutter wing 106, providing stable cutting force and guiding performance. The straight section design allows the drill bit 10 to maintain a stable cutting path during cutting, reducing yaw and vibration. The arc sections located between the straight sections are the core of the crown shape. The arc section design allows the drill bit 10 to better adapt to changes in the formation during cutting, improving rock-breaking efficiency and drilling speed. This contour design helps optimize the drill bit's cutting performance and drilling efficiency.

[0050] The chip removal groove 110 is streamlined, which can reduce the generation of vortices and stagnant areas on the drill bit surface. Following the law of decreasing pressure gradient within the chip removal groove 110, its cross-sectional area gradually increases from bottom to top. The existence of pressure difference enables the drill bit 10 to have a better cleaning effect and is also conducive to the timely discharge of rock cuttings. At the same time, it can cool the drill bit 10 over a large area.

[0051] The width of the chip removal groove 110 is related to the diameter and rotational speed of the drill bit 10. Its shape is streamlined, and the calculation formula is: W = (πdn) / (60 × 1000), where W is the width of the chip removal groove 110, d is the diameter of the drill bit 10, and n is the rotational speed of the drill bit 10. The length of the chip removal groove 110 is usually related to the volume of chips removed, the radius of the drill bit 10, and the drilling speed, and the calculation formula is: L = V / (πr 2 v), where: L is the length of the chip removal groove 110, V is the volume of chip removal, r is the radius of the drill bit 10, and v is the drilling speed; the maximum cross-sectional area Smax of the chip removal groove 110 is determined as: Smax = Q / Va, where: Smax is the maximum cross-sectional area of ​​the chip removal groove 110, Q is the actual discharge rate, and Va is the minimum annular return velocity. Parameters can be adjusted according to actual conditions to achieve the best drilling effect, avoid mud cake formation, and prevent wellbore instability.

[0052] This invention discloses a drilling method for preventing wellbore instability during drilling through goaf areas, comprising the following steps:

[0053] S1. Determine the location, depth, and angle of the borehole based on geological survey data, ensuring that the deviation between the borehole location and the designed location does not exceed 0.5m;

[0054] S2. Select a drilling fluid formula suitable for the formation characteristics and drilling system as described in claim 1 to prevent wellbore instability during drilling through goaf areas. The drilling pressure is 20-50 KN and the rotation speed is 30 r / min. During drilling, the drilling trajectory is continuously monitored by the anti-vibration drilling directional device 102. If the deviation between the drilling trajectory and the design trajectory exceeds the allowable range, the trajectory is corrected in time until the deviation between the drilling trajectory and the design trajectory returns to the allowable range. When correcting the trajectory, the data fed back to the ground by the anti-vibration drilling directional device 102 is used to correct the trajectory by tripping the drill string and running it down.

[0055] S3. When drilling close to the goaf, reduce the drilling speed to 25 r / min to reduce the impact and damage to the well wall;

[0056] S4. After passing through the goaf, restore the rotation speed to 30 r / min until drilling is completed;

[0057] S5. After drilling is completed, cementing operations are carried out to reinforce the well wall.

[0058] During the drilling process, drilling fluid flows into the drill bit 10 through the pipeline to clean the cutter wings 106, cool the drill bit 10, carry rock cuttings back up, prevent the formation of mud cake, and improve the stability of the well wall.

[0059] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A drilling system for preventing wellbore instability during drilling through goaf areas, comprising a motor (1), a reducer (2), a clutch (3), a square drill rod (13), a rotary table (14), a transmission rod (5), a drill rod (7), a guide rod (9), and a drill bit (10), wherein the motor (1) is connected to the upper end of the square drill rod (13) via the reducer (2) and the clutch (3), characterized in that: The lower end of the square drill rod (13) passes through the turntable (14) and is connected to the first universal coupling (4). The first universal coupling (4) is connected to the upper end of the transmission rod (5) through the universal joint (15). The lower end of the transmission rod (5) is connected to the second universal coupling (11) through the cross rod (16). The lower end of the second universal coupling (11) is connected to the upper end of the drill rod (7) through the flange (6). The lower end of the drill rod (7) is connected to a rubber sheet (17). A solution damper (18) is connected below the rubber sheet (17). The lower end of the solution damper (18) is connected to the upper end of the guide rod (9) through the connector (8). The lower end of the guide rod (9) is connected to the drill bit (10). The drill bit (10) includes an installation section (114), a connecting section (113), and a cutting section (116). The installation section (114) has a loading and unloading groove (101) connected to the guide rod (9). The connecting section (113) connects the installation section (114) and the cutting section (116) together, and a vibration-damping drilling directional device (102) is installed on the connecting section (113). Multiple cutter wings (106) are evenly distributed around the cutting section (116). Each cutter wing (106) is provided with cutting teeth (104) and pointed conical teeth (103). A chip removal groove (110) is provided between two adjacent cutter wings (106). The conveying pipe (10) 9) Located at the central axis of the drill bit (10) and running through the drill bit (10) vertically, and the upper part of the conveying pipe (109) is equipped with an anti-backflow device (115). Multiple water holes (111) are opened on the bottom surface of the cutting section (116). Each water hole (111) is connected to the conveying pipe (109) through a secondary pipe set inside the cutting section (116). Each blade (106) has an auxiliary water hole (112) with an inwardly inclined outlet on its inner side. Each auxiliary water hole (112) is also connected to the conveying pipe (109) through a secondary pipe. Each water hole (111) and auxiliary water hole (112) is equipped with a nozzle. The anti-vibration drilling directional device (102) includes a housing (127), a sensor (123), a spring shock absorber (124), and a wireless transmission device (121). The housing (127) has an inner cavity (122). The sensor (123) is fixed in the inner cavity (122). The wireless transmission device (121) is fixed on the top of the housing (127) and is surrounded by a rubber protective sleeve (128). The sensor (123) and the wireless transmission device (121) are connected. A spring shock absorber (124) is provided at the bottom of the housing (127). The bottom of the spring shock absorber (124) is in close contact with the connecting section (113) of the drill bit (10). The backflow prevention device (115) includes a valve body (131), a valve cover (132), a support ring (133), a valve disc (134), and a spring (135). The two valve covers (132) are fixed at the upper and lower ends of the valve body (131), respectively. The support ring (133) is located inside the valve body (131), with its lower end fixed on the valve cover (132) and its upper end supporting the spring (135). The valve disc (134) is fixed on the spring (135), and the top of the valve disc (134) cooperates with the valve seat (136) located inside the valve body (131). A guide device (137) is also provided between the valve disc (134) and the support ring (133).

2. The drilling system for preventing wellbore instability during drilling through goaf areas according to claim 1, characterized in that: The spring damper (124) is provided with a stabilizing cover (125) on the outside. The upper end of the stabilizing cover (125) is fixed on the outer shell (127) of the anti-vibration drilling directional device (102), and the lower end is close to the connecting section (113) of the drill bit (10).

3. A drilling system for preventing wellbore instability during drilling through goaf areas according to claim 1 or 2, characterized in that: The number of blades (106) is four.

4. The drilling system for preventing wellbore instability during drilling through goaf areas according to claim 1, characterized in that: The blade (106) has multiple cutting teeth (104) and multiple conical teeth (103). The multiple cutting teeth (104) are arranged in a row from top to bottom, and the multiple conical teeth (103) are also arranged in a row from top to bottom.

5. A drilling system for preventing wellbore instability during drilling through goaf areas according to claim 4, characterized in that: Both the cutting teeth (104) and the conical teeth (103) protrude 2 cm from the surface of the blade (106).

6. The drilling system for preventing wellbore instability during drilling through goaf areas according to claim 1, characterized in that: The blade (106) is helical in shape.

7. A drilling system for preventing wellbore instability during drilling through goaf areas according to claim 1, characterized in that: The chip removal groove (110) is streamlined and its cross-sectional area gradually increases from bottom to top.

8. A drilling method for preventing wellbore instability during drilling through goaf areas, characterized in that... Includes the following steps: S1. Determine the location, depth, and angle of the borehole based on geological survey data, ensuring that the deviation between the borehole location and the designed location does not exceed 0.5m; S2. Select a drilling fluid formula that is suitable for the formation characteristics and drill using the drilling system described in claim 1 to prevent wellbore instability during drilling through goaf areas. The drilling pressure is 20-50KN and the rotation speed is 30r / min. During the drilling process, the drilling trajectory is continuously monitored by the anti-vibration drilling directional device (102). If the deviation between the drilling trajectory and the design trajectory exceeds the allowable range, the trajectory is corrected in time until the deviation between the drilling trajectory and the design trajectory returns to the allowable range. S3. When drilling close to the goaf, reduce the drilling speed to 25 r / min to reduce the impact and damage to the well wall; S4. After passing through the goaf, restore the rotation speed to 30 r / min until drilling is completed; S5. After drilling is completed, cementing operations are carried out to reinforce the well wall.

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