Coal seam hydraulic cavity construction method

Abstract

The application discloses a coal seam hydraulic cavity construction method and belongs to the technical field of gas extraction drilling construction in a coal mine underground. The method adopts an integrated cavity drilling bit integrating a self-rotation cavity forming device and a pressure response type water flow switching mechanism, and through a three-section type process of low-pressure drilling, high-pressure cavity forming and reset drilling, the water supply pressure is controlled in stages to realize integrated operation. When the pressure is high, the water flow drives the nozzle to rotate and revolve with the integrated cavity drilling bit, spiral water jets are formed to wash along the coal seam bedding, and the coal seam hardness is graded to adjust the pressure and the inclination angle is adapted to the nozzle angle parameter. The application principle is scientific, the drilling tool does not need to be replaced, the cavity volume range is greatly improved, the construction efficiency is greatly improved, and the problems of small washing range, poor coal breaking effect and complex process of the traditional hydraulic cavity forming process are solved.

Description

Technical Field

[0001] This invention belongs to the field of underground gas drainage drilling construction technology in coal mines, specifically relating to a method for hydraulic cavity creation in coal seams. Background Technology

[0002] Pre-drainage of coal seam gas through drilling is a fundamental technical measure for preventing gas disasters. To further improve the gas extraction effect of boreholes, many mines adopt hydraulic cavity drilling to increase the coal output from the boreholes, thereby increasing the permeability of the coal seam.

[0003] However, currently used hydraulic cavity-forming devices and construction methods have significant drawbacks: First, the cavity-forming devices use fixed nozzles, resulting in a fixed high-pressure water jet scouring direction, a small scouring range, and low coal breaking efficiency; second, the cavity-forming devices and drill bits are mostly separate structures, making installation and disassembly cumbersome; and third, the process parameters are not optimized according to the coal seam geological conditions, leading to unstable cavity-forming effects and hindering subsequent gas extraction. The applicant has proposed an integrated cavity-forming drill bit with a self-rotating nozzle, a wide scouring range, adaptability to coal seams with different dip angles, and good coal breaking effect, but it lacks supporting standardized construction methods, preventing the full realization of its technical advantages. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a pure retreating hydraulic cavity-making method for coal seams. This method employs an integrated cavity-making drill bit that combines a self-rotating cavity-making device and a pressure-responsive water flow switching mechanism. The construction steps involve "drilling to the final hole first, then retreating to create the cavity." Drill cuttings are discharged directly from the borehole opening without passing through the already constructed cavity-making section, completely solving the problem of drill cuttings accumulation and blockage in forward-moving cavity-making methods. Furthermore, by combining the technical advantages of a self-rotating nozzle, the method significantly improves cavity-making efficiency and construction safety.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for hydraulic cavity creation in coal seams, employing an integrated cavity-creating drill bit that combines a self-rotating cavity-creating device and a pressure-responsive water flow switching mechanism, includes the following steps: S1. Low-pressure drilling to the designed final hole position: Low-pressure water flow is introduced into the integrated cavity drilling bit. The drilling machine drives the integrated cavity drilling bit to rotate and drill. The low-pressure water flow flows out through the front end of the drill bit to achieve cooling and chip removal until the designed final hole position is reached. S2. Drill backward to the designated position to perform the first high-pressure cavity creation: After drilling backward to the target coal seam section at the designated position, increase the water supply pressure to the set value. The pressure-responsive water flow switching mechanism automatically closes the water flow channel at the front end of the drill bit. The high-pressure water flow drives the nozzle of the self-rotating cavity creation device to rotate. At the same time, the nozzle revolves with the drill bit body. The high-pressure water jet washes the coal body to form a cavity. S3. Maintain high-pressure water flow during drill retraction: After high-pressure hole creation at the first location, create only one short hole and quickly withdraw the entire integrated hole-creation drill bit from the borehole. Alternatively, after high-pressure cavity creation at the first location, maintain high-pressure water and quickly retract the drill to the next cavity creation location. Repeat step S2 to create cavities at multiple points intermittently. After all cavities are created, quickly retract the drill until the integrated cavity creation drill bit exits the borehole. Alternatively, maintain high-pressure water flow while slowly retracting the drill bit and continuously creating a cavity until the set cavity creation termination position is reached, creating a long cavity. Then, quickly retract the drill bit until the integrated cavity-creating drill bit is removed from the borehole.

[0006] Furthermore, the integrated cavity-making drill bit includes a drill bit body with its center line arranged along the front-rear direction. Several cutting teeth are fixedly provided at the front end of the drill bit body. The drill bit body has a central hole with an open rear end inside. The central hole has an internal thread section for connecting with the drill rod, a self-rotating cavity-making device, and a water flow switching mechanism arranged sequentially from back to front. Two circular mounting grooves are symmetrically provided on the drill bit body. The bottom of the circular mounting groove has a mounting hole communicating with the central hole. The self-rotating cavity-creating device includes an internal transmission assembly, two nozzles, and an axial fixing assembly. The internal transmission assembly includes a mounting cylinder and a power shaft. The mounting cylinder is coaxially installed in the central hole of the drill bit body. The axis of the power shaft is arranged along the radial direction of the mounting cylinder. The mounting cylinder has two centrally symmetrical bearing mounting grooves. Both ends of the power shaft are rotatably connected to the two bearing mounting grooves through ball bearings. The axial rear end face of the mounting cylinder has an installation port communicating with the bearing mounting grooves. An impeller located inside the mounting cylinder is fixed on the power shaft. The power shaft has a hollow tube structure. A water inlet hole is opened between two adjacent blades of the impeller, passing through the power shaft. The water inlet hole communicates with the shaft hole of the power shaft and the central hole of the drill bit body. Both ends of the power shaft are provided with a first circumferential fixed connection structure. The water inlet hole communicates with the first circumferential fixed connection structure through the shaft hole of the power shaft. The nozzle is installed in the circular mounting groove of the drill bit body. The inner end of the nozzle is provided with a second circumferential fixed connection structure. The second circumferential fixed connection structure is coaxially connected and driven by the first circumferential fixed connection structure at the radial outer end of the power shaft. A first high-pressure sealing ring is provided between the outer circle of the nozzle and the inner wall of the circular mounting groove. The outer end of the nozzle is provided with at least one nozzle that is inclined to the nozzle axis.

[0007] Furthermore, the axial fixing assembly includes a thrust bearing and a clamping cap; the thrust bearing is sleeved on the outer circle of the nozzle, and the clamping cap is fixedly connected to the opening edge of the circular mounting groove of the drill bit body by screws, thereby axially fixing the thrust bearing and the nozzle in the circular mounting groove.

[0008] Furthermore, the water flow switching mechanism includes a sliding plug, a compression spring, and a sealing sleeve; the sliding plug and the sealing sleeve are coaxially installed at the front section of the central hole of the drill bit body, and the sealing sleeve is located in front of the sliding plug; the rear end of the sliding plug is open and the front end is closed, while the sealing sleeve is open at both ends; the outer circle of the front end of the sliding plug is provided with a first conical sealing surface that is smaller at the front and larger at the rear, and the inner circle of the rear port of the sealing sleeve is provided with a second conical sealing surface that is smaller at the front and larger at the rear and matches the first conical sealing surface; The front half of the sliding plug has a permeable first low-pressure water hole along the radial direction. The outer diameter of the front half of the sliding plug is smaller than that of the rear half and an annular step is formed at the junction. A compression spring is sleeved on the front half of the sliding plug. The front end of the compression spring is pressed against the rear end of the sealing sleeve, and the rear end of the compression spring is pressed against the front end of the annular step. The outer circumference of the sealing sleeve is provided with a second high-pressure sealing ring that seals with the inner circumference of the center hole of the drill bit body. The outer circumference of the sealing sleeve is provided with an annular water passage groove that communicates with the water outlet at the front end of the drill bit body. The sealing sleeve is provided with a second low-pressure water hole that connects the annular water passage groove with the inner cavity of the sealing sleeve.

[0009] Further, step S1 specifically involves: connecting the integrated cavity-making drill bit to the drill rod via the internal threaded section at the rear end, and connecting the other end of the drill rod to the drilling rig and high-pressure water pump; introducing low-pressure water at a pressure of 2-5 MPa into the drill rod; the drilling rig driving the drill rod and the integrated cavity-making drill bit to rotate at a speed of 100-300 r / min; the cutting teeth at the front end of the drill bit breaking the coal body for drilling; after the low-pressure water enters the central hole of the drill bit body, under the action of the compression spring, the rear end of the sliding plug is pressed against the axial front end face of the mounting cylinder, the first conical sealing surface separates from the second conical sealing surface, and the low-pressure water sequentially passes through the inside of the sliding plug, the first low-pressure water hole, the conical channel formed by the separation of the first and second conical sealing surfaces, the inside of the sealing sleeve, the second low-pressure water hole, and the annular water passage, and finally flows out from the water outlet at the front end of the drill bit body, cooling the cutting teeth and discharging the drill cuttings outside the borehole; the drilling speed is controlled at 0.3-1 m / min, and the drilling speed is adjusted according to the hardness of the coal seam.

[0010] Further, step S2 is specifically as follows: After retracting the drill to the target coal seam section, stop drilling and keep the drill bit position unchanged; increase the water supply pressure of the high-pressure water pump to 10 - 40 MPa and the flow rate to 50 - 200 L / min. The impact force of the high-pressure water flow acting on the rear end of the sliding plug is greater than the elastic force of the compression spring, pushing the sliding plug to move axially forward, making the first conical sealing surface and the second conical sealing surface press-fit to achieve sealing cooperation, and closing the channel leading to the water outlet at the front end of the drill bit body; all the high-pressure water flow enters the shaft hole of the power shaft through the water inlet hole. Part of the water flow impacts the blades of the impeller, causing the impeller to drive the power shaft to rotate around its own axis. Then, through the transmission of the first circumferential fixed connection structure and the second circumferential fixed connection structure, the nozzle head rotates at a speed of 30 - 120 r / min; another part of the water flow enters the nozzle head through the shaft hole of the power shaft and sprays out at a high speed from the inclined nozzle; at the same time, the drilling rig drives the drill bit body to rotate around the hole at a speed of 20 - 60 r / min, making the high-pressure water jet form a spiral scouring trajectory and crushing the coal body along the coal seam bedding direction to form a cavity; Further, in step S2, the cavitation time for a single cavity is 10 - 30 min, and the cavitation diameter is controlled to be 0.8 - 1.5 m; during the cavitation process, the drill pipe is axially moved 0.3 - 1.2 m every 3 - 8 min to expand the axial range of the cavity; Further, in step S2, the water supply pressure is adjusted according to the classification of the coal seam hardness coefficient: when the coal seam hardness coefficient f ≤ 1, the water supply pressure is 10 - 20 MPa; when 1 < f ≤ 2, the water supply pressure is 20 - 30 MPa; when f > 2, the water supply pressure is 30 - 40 Mpa; Further, in step S2, the inclination angle of the nozzle of the nozzle head is adjusted according to the angle between the borehole axis and the coal seam dip angle. The inclination angle range of the nozzle is 15° - 60°: when the angle is 0° - 15°, the inclination angle of the nozzle head is 45° - 60°; when the angle is 15° - 30°, the inclination angle is 30° - 45°; when the angle is greater than 30°, the inclination angle is 15° - 30°.

[0011] Further, step S3 is specifically as follows: Keep the high-pressure water supply and the rotation of the drill bit around the hole unchanged. The high-pressure water flow continuously pushes the sliding plug and the plug sleeve to maintain sealing cooperation, and the nozzle head continuously rotates and sprays out high-pressure water jets; If the single-cavity rapid drill retraction method is adopted: After the first high-pressure cavitation is completed, quickly retract the drill backward at a speed of 1 - 2 m / s until the integral cavitation drill bit completely exits the borehole. During the drill retraction process, the high-pressure water flow continuously scours and cleans the borehole wall; If a multi-point intermittent cavity-making method is adopted: After the first high-pressure cavity-making is completed, quickly retreat the drill bit 3-5m at a speed of 1-2m / s, stop retreating the drill bit after reaching the next cavity-making position, and repeat step S2 to construct the next cavity; after each cavity-making is completed, maintain high-pressure water supply and slowly move the drill rod back and forth along the length of the borehole to remove all the residual coal dust in the cavity before retreating to the next cavity-making position; after all cavities are completed, quickly retreat the drill bit at a speed of 1-2m / s until the drill bit is completely withdrawn from the borehole; If the continuous cavity-making method is adopted: after the first high-pressure cavity-making is completed, the drill is slowly retracted at a uniform speed of 0.1-0.3 m / min, and continuous cavity-making is carried out while retracting. The high-pressure water jet continuously scours the coal body to form a continuous long expansion section; after each cavity-making of 5-10 m, the retraction is stopped, and high-pressure water supply is maintained for 2-3 minutes for centralized slag removal, and then the retraction cavity-making continues; after reaching the set cavity-making termination position, the drill is quickly retracted at a speed of 1-2 m / s until the drill bit is completely withdrawn from the borehole.

[0012] Using the above technical solution, the specific functions of each component in this invention are as follows: Drill bit body: As the basic carrier of the entire drill bit, it supports the cutting teeth, the self-rotating cavity-making device and the water flow switching mechanism; the rear internal thread section is used to connect with the drill rod threadedly, transmitting the torque and axial force of the drill rod; the front cutting teeth are used to break the coal body to realize drilling.

[0013] Center hole: Serves as the main water flow channel inside the drill bit, and also provides installation space for various internal components.

[0014] Mounting sleeve: Provides mounting reference and sealing space for the power shaft, impeller and ball bearing, isolates high-pressure water flow from the inner wall of the drill bit body, and ensures that the water flow impacts the impeller in a directional manner.

[0015] Power shaft: It has dual functions of transmission and water delivery. On the one hand, it transmits the torque of the impeller to drive the nozzle to rotate. On the other hand, it serves as a high-pressure water flow channel to deliver water into the nozzle.

[0016] Ball bearings: support the radial rotation of the power shaft, reduce rotational friction resistance, and ensure the stability of the power shaft at high speed.

[0017] Impeller: It converts the kinetic energy of the high-pressure water flow into mechanical energy, rotates under the impact of the water flow and drives the power shaft to rotate, and is the power source for the nozzle's rotation.

[0018] Water inlet: Connects the central hole of the drill bit body to the shaft hole of the power shaft, guiding high-pressure water flow into the interior of the power shaft.

[0019] The first and second circumferential fixed connection structures enable circumferential transmission and coaxial connection between the power shaft and the nozzle, ensuring reliable transmission of torque and water flow.

[0020] Nozzle: High-pressure water jets are sprayed from tilted nozzles to scour the coal body. The nozzles rotate to expand the scouring range of the water jets and improve the coal breaking and cavity creation effect.

[0021] First high-pressure sealing ring: seals the fit gap between the nozzle and the circular mounting groove to prevent high-pressure water leakage and ensure jet pressure.

[0022] Nozzle: Converts high-pressure water flow into high-speed water jet. The inclined setting allows the jet to scour weak surfaces such as coal seam bedding and joints, enhancing coal breaking ability.

[0023] Thrust bearing: It bears the axial reaction force on the nozzle during operation, ensuring smooth rotation of the nozzle and preventing axial movement.

[0024] Pressure cap: It is fixed to the drill bit body with screws to achieve axial positioning of the nozzle and thrust bearing and prevent the nozzle from falling off.

[0025] Mounting port: Located at the rear end of the mounting cylinder, it is used for assembling the power shaft and ball bearing, reducing the difficulty of component installation.

[0026] Sliding plug: It works with a compression spring to automatically switch the water flow channel according to the water supply pressure; the first conical sealing surface at the front end works with the sealing sleeve to achieve a reliable seal under high pressure.

[0027] Compression spring: Provides a restoring force for the sliding plug, keeping the front water flow channel open under low pressure, and being compressed to close the channel under high pressure.

[0028] The sealing sleeve, in conjunction with the sliding plug, forms a sealing pair and guides low-pressure water to the front outlet through the annular water passage and the second low-pressure water hole.

[0029] The second high-pressure sealing ring seals the gap between the sealing sleeve and the center hole of the drill bit body, preventing water leakage.

[0030] Annular water passage: An annular water flow channel is formed on the outer circle of the sealing sleeve to ensure that low-pressure water can flow evenly to each front outlet.

[0031] Front outlet: Water is discharged at low pressure to cool the cutting teeth and remove drill cuttings from the borehole.

[0032] In summary, compared with the prior art, the present invention has the following beneficial effects: 1. This invention's hydraulic cavity-creating drill bit enables integrated low-pressure drilling and high-pressure water jet cavity creation during gas drainage drilling in coal mines. The pressure-responsive water flow switching mechanism automatically switches between low-pressure drilling and high-pressure cavity creation, eliminating the need to change drill bits mid-operation and resulting in high construction efficiency. Under low water pressure, water is supplied to the drill bit for normal drilling. Under high water pressure and high flow rate, the water flow channel at the drill bit is automatically closed, and the high-pressure water is ejected through the nozzle on the self-rotating cavity-creating device to flush and create cavities in the surrounding coal seam.

[0033] 2. The nozzle of this invention is installed perpendicular to the axis of the cavity-making device at the outer end of the power shaft, and the nozzle of the nozzle is inclined. While the hydraulic cavity-making drill revolves around its own axial axis, the high-pressure water flow drives the impeller to rotate, which in turn drives the power shaft and the nozzle to rotate around their own axes. This increases the scouring range of the high-pressure water jet and allows it to scour along weak surfaces such as coal seam bedding and joints as much as possible, resulting in good coal breaking effect and large coal output. It has a particularly good cavity-making effect in cross-layer drilling sections of coal seams.

[0034] 3. This invention uses a high-flow, high-pressure water jet to impact the impeller and make it rotate, and then drives the nozzle to rotate through a transmission mechanism. It does not require additional power, has a compact structure, and high reliability. At the same time, by tilting the nozzle outlet at a certain angle, it effectively solves the technical problems of small scouring range and poor coal breaking and hole-making effect of traditional fixed nozzles.

[0035] 4. Establish a graded water supply pressure system based on coal seam hardness and a nozzle angle adjustment method based on coal seam dip angle. Standardize process parameters, ensure stable and reliable cavity-forming effect, and effectively reduce the incidence of accidents such as blowholes and hole collapses. Attached Figure Description

[0036] Figure 1 This is a three-dimensional structural diagram of the cavity-making drill bit used in this invention; Figure 2 This is an axial sectional view of the overall structure of the cavity-making drill bit used in this invention; Figure 3 This is an axial sectional view of the drill bit body; Figure 4 This is a three-dimensional structural diagram of the mounting cylinder. Figure 5 It is a three-dimensional structural diagram of the power shaft and impeller; Figure 6 This is a schematic diagram of the three-dimensional structure of the nozzle; Figure 7 This is a three-dimensional structural diagram of the sliding plug; Figure 8 This is a three-dimensional structural diagram of the sealing sleeve.

[0037] Explanation of reference numerals in the attached figures: 1-Drill bit body; 2-Cutting teeth; 3-Center hole; 4-Internal thread section; 5-Nozzle; 6-Circular mounting groove; 7-Mounting hole; 8-Mounting sleeve; 9-Drive shaft; 10-Bearing mounting groove; 11-Ball bearing; 12-Impeller; 13-Water inlet; 14-First circumferential fixed connection structure; 15-Second circumferential fixed connection structure; 16-First high-pressure sealing ring; 17-Nozzle; 18-Sliding plug; 19-Compression spring; 20-Sealing sleeve; 21-First conical sealing surface; 22-Second conical sealing surface; 23-First low-pressure water hole; 24-Annular step; 25-Front end outlet; 26-Annular water passage groove; 27-Second low-pressure water hole; 28-Thrust bearing; 29-Pressure cap; 30-Screw; 31-Mounting port; 32-Second high-pressure sealing ring. Detailed Implementation

[0038] like Figures 1-8 As shown, the integrated cavity-making drill bit structure adopted in this invention is as follows: it includes a drill bit body 1 with its center line arranged in the front-to-back direction, a number of cutting teeth 2 fixedly provided at the front end of the drill bit body 1, a central hole 3 with an open rear end inside the drill bit body 1, and an internal thread section 4, a self-rotating cavity-making device and a water flow switching mechanism arranged sequentially from back to front in the central hole 3 of the drill bit body 1, and the internal thread section 4 is used for threaded connection with the drill rod.

[0039] The self-rotating cavity-making device includes an internal transmission assembly, two nozzles 5, and an axial fixing assembly. Two circular mounting grooves 6 are symmetrically arranged on the drill bit body 1, and the bottom of each circular mounting groove 6 has a mounting hole 7 that communicates with the central hole 3 of the drill bit body 1.

[0040] The internal transmission assembly includes a mounting cylinder 8 and a drive shaft 9. The mounting cylinder 8 is coaxially installed in the central hole 3 of the drill bit body 1. The axis of the drive shaft 9 is arranged radially along the mounting cylinder 8. Two centrally symmetrical bearing mounting grooves 10 are provided on the mounting cylinder 8. The two ends of the drive shaft 9 are rotatably connected to the two bearing mounting grooves 10 by ball bearings 11. An impeller 12 is fixedly mounted on the drive shaft 9 and located inside the mounting cylinder 8. The drive shaft 9 has a hollow tube structure. A water inlet hole 13 is provided between two adjacent blades of the impeller 12, passing through the drive shaft 9. The water inlet hole 13 connects the shaft hole of the drive shaft 9 with the central hole 3 of the drill bit body 1. Both ends of the drive shaft 9 are provided with a first circumferential fixed connection structure 14, and the water inlet hole 13 communicates with the first circumferential fixed connection structure 14 through the shaft hole of the drive shaft 9.

[0041] The nozzle 5 is installed in the circular mounting groove 6 of the drill bit body 1. A second circumferential fixing connection structure 15 is provided at the inner end of the nozzle 5. This second circumferential fixing connection structure 15 is coaxially connected to and drives the first circumferential fixing connection structure 14 at the radially outer end of the power shaft 9, enabling the inner port of the nozzle 5 to communicate with the shaft hole of the power shaft 9 and to drive synchronously. A first high-pressure sealing ring 16 is provided between the outer circle of the nozzle 5 and the inner wall of the circular mounting groove 6 of the drill bit body 1. At least one nozzle 17 is provided at the outer end of the nozzle 5. An axial fixing assembly axially fixes the two nozzles 5 into their respective circular mounting grooves 6.

[0042] The water flow switching mechanism is coaxially installed in the front section of the central hole 3 of the drill bit body 1. It is used to open the water flow channel to the cutting teeth 2 when the water supply is low pressure, and close the water flow channel to the cutting teeth 2 when the water supply is high pressure, so that the high pressure water flow enters the shaft hole of the power shaft 9 and the inside of the nozzle 5 through the water inlet hole 13 in sequence, and finally sprays out from the nozzle 17 at the outer end of the nozzle 5.

[0043] The water flow switching mechanism includes a sliding plug 18, a compression spring 19, and a sealing sleeve 20. The sliding plug 18 and the sealing sleeve 20 are coaxially installed at the front of the central hole 3 of the drill bit body 1. The sealing sleeve 20 is located in front of the sliding plug 18. The rear end of the sliding plug 18 is open and the front end is closed. The sealing sleeve 20 is open at both ends. The outer circle of the front end of the sliding plug 18 is provided with a first conical sealing surface 21 that is smaller at the front and larger at the rear. The inner circle of the rear port of the sealing sleeve 20 is provided with a second conical sealing surface 22 that is smaller at the front and larger at the rear and matches the first conical sealing surface 21. The front half of the sliding plug 18 has a through first low-pressure water hole 23 in the radial direction. The outer diameter of the front half of the sliding plug 18 is smaller than the outer diameter of the rear half and forms an annular step 24 at the junction. The compression spring 19 is sleeved on the front half of the sliding plug 18. The front end of the compression spring 19 is pressed against the annular surface of the rear end of the sealing sleeve 20, and the rear end of the compression spring 19 is pressed against the front end of the annular step 24.

[0044] The outer rear side of the sealing sleeve 20 is provided with a second high-pressure sealing ring 32 that seals with the inner circle of the center hole 3 of the drill bit body 1. The outer front side of the sealing sleeve 20 is provided with an annular water passage groove 26 that communicates with the water outlet 25 at the front end of the drill bit body 1. The sealing sleeve 20 is provided with a second low-pressure water hole 27 that connects the annular water passage groove 26 with the inner cavity of the sealing sleeve 20.

[0045] When the compression spring 19 is in its freely extended state or when water is supplied at low pressure, the rear end of the sliding plug 18 is pressed against the axial front end face of the mounting cylinder 8 under the action of the spring force of the compression spring 19. The low-pressure water flows sequentially through the interior of the sliding plug 18, the first low-pressure water hole 23, the front half of the sliding plug 18, the conical channel formed by the separation of the first conical sealing surface 21 and the second conical sealing surface 22, the interior of the sealing sleeve 20, the second low-pressure water hole 27, and the annular water passage 26, and finally flows out from the front outlet 25 of the drill bit body 1. When water is supplied at high pressure, the water flow impact force is greater than the spring force of the compression spring 19, which pushes the sliding plug 18 to move axially forward, so that the first conical sealing surface 21 and the second conical sealing surface 22 are pressed together to achieve a sealing fit, and the water outlet 25 leading to the front end of the drill bit body 1 is closed.

[0046] The first circumferential fixed connection structure 14 is a regular polygonal groove, and the second circumferential fixed connection structure 15 is a regular polygonal boss that inserts into the regular polygonal groove. In this embodiment, the regular polygon is a regular hexagon to ensure the reliability and coaxiality of the circumferential transmission.

[0047] The axial fixing assembly includes a thrust bearing 28 and a clamping cap 29. The thrust bearing 28 is sleeved on the outer circle of the nozzle 5, and the clamping cap 29 is fixedly connected to the opening edge of the circular mounting groove 6 of the drill bit body 1 by screws 30, thus axially fixing the thrust bearing 28 and the nozzle 5 in the circular mounting groove 6 of the drill bit body 1. The thrust bearing 28 is used to bear the axial load when the nozzle 5 is working, ensuring that the nozzle 5 rotates smoothly.

[0048] The mounting cylinder 8 has an installation port 31 on its axial rear end face that communicates with the bearing mounting groove 10. The two installation ports 31 are used to facilitate the installation of the power shaft 9 into the bearing mounting groove 10, reducing the assembly difficulty.

[0049] Nozzle 17 is at least one spray hole that is inclined to the axis of nozzle 5 at the outer end of nozzle 5. In this embodiment, each nozzle 5 has one inclined spray hole at its outer end with an inclination angle of 15°-45°, which can be adjusted according to the dip angle of the coal seam so that the water jet can scour along the bedding direction of the coal seam as much as possible.

[0050] The specific implementation of the coal seam hydraulic cavity creation construction method of the present invention is illustrated in detail by the following three embodiments.

[0051] Example 1: Multi-point intermittent retreating cavity construction in soft coal seams (f=0.8) S1. Low-pressure drilling to the designed final hole position: Connect the integrated cavity-making drill bit to the drill rod via the internal thread section 4 at the rear end. The other end of the drill rod is connected to the drilling rig and high-pressure water pump. A low-pressure water flow of 3MPa is introduced into the drill rod. The drilling rig drives the drill rod and the integrated cavity-making drill bit to rotate at a speed of 200r / min. The cutting teeth 2 at the front end of the drill bit break the coal body for drilling. After the low-pressure water enters the central hole 3 of the drill bit body 1, under the elastic force of the compression spring 19, the rear end of the sliding plug 18 presses against the axial front end face of the mounting cylinder 8, and the first conical sealing surface 21 separates from the second conical sealing surface 22. The low-pressure water sequentially passes through the interior of the sliding plug 18, the first low-pressure water hole 23, the conical channel formed by the separation of the first conical sealing surface 21 and the second conical sealing surface 22, the interior of the sealing sleeve 20, the second low-pressure water hole 27, and the annular water passage 26, and finally flows out from the water outlet 25 at the front end of the drill bit body 1, cooling the cutting teeth 2 and discharging drill cuttings outside the borehole. The drilling speed is controlled at 0.8 m / min, and drilling continues until the designed final hole position of 350 m.

[0052] S2. Retreat to the designated position for the first high-pressure cavity creation: Retreat to the target coal seam section at 340m, stop drilling and keep the drill bit position unchanged. Increase the water supply pressure of the high-pressure water pump to 15MPa and the flow rate to 120L / min. The impact force of the high-pressure water flow on the rear end of the sliding plug 18 is greater than the elastic force of the compression spring 19, pushing the sliding plug 18 axially forward, so that the first conical sealing surface 21 and the second conical sealing surface 22 press together to achieve a sealing fit, sealing the channel to the water outlet 25 at the front end of the drill bit body 1. All the high-pressure water flow enters the shaft hole of the power shaft 9 through the water inlet 13. Part of the water flow impacts the blades of the impeller 12, causing the impeller 12 to drive the power shaft 9 to rotate around its own axis. Then, through the transmission of the first circumferential fixed connection structure 14 and the second circumferential fixed connection structure 15, it drives the nozzle 5 to rotate at a speed of 80r / min; the other part of the water flow enters the interior of the nozzle 5 through the shaft hole of the power shaft 9 and is ejected at high speed from the inclined nozzle 17. Simultaneously, the drilling rig drives the drill bit body 1 to revolve at a speed of 40 r / min, causing the high-pressure water jet to form a spiral scouring trajectory, breaking the coal body along the coal seam bedding direction to form cavities. The creation time for a single cavity is 20 minutes, and the cavity diameter is controlled at 1.2 m. During the cavity creation process, the drill rod is moved axially by 0.8 m every 5 minutes to expand the axial range of the cavity.

[0053] S3. Maintain high-pressure water flow during drill retraction: Keep the high-pressure water supply and drill bit rotation constant. The high-pressure water flow continuously pushes the sliding plug 18 and sealing sleeve 20 to maintain a sealed fit. The nozzle 5 continues to rotate and spray high-pressure water jets. A multi-point intermittent cavity-building method is adopted: After the first high-pressure cavity is built, quickly retract the drill bit 4 meters at a speed of 1.5 m / s. After reaching the next cavity-building position, stop retracting the drill bit and repeat step S2 to construct the next cavity. After each cavity is built, maintain the high-pressure water supply and slowly move the drill rod back and forth along the length of the borehole to remove all residual coal dust from the cavity before retracting to the next cavity-building position. After all cavities are built, quickly retract the drill bit at a speed of 1.5 m / s until the drill bit is completely withdrawn from the borehole.

[0054] Example 2: Continuous Retreat Hole Creation Construction in Medium-Hard Coal Seams (f=1.5) The difference between this embodiment and Embodiment 1 is that: S1. Low-pressure drilling stage: water supply pressure is 4MPa, drill bit speed is 250r / min, and drilling speed is 0.5m / min; S2. First high-pressure cavity-building stage: water supply pressure is 25MPa, flow rate is 150L / min, nozzle rotation speed is 100r / min, drill bit revolution speed is 50r / min, cavity-building time is 15min; S3. Drill Retraction Stage: A continuous cavity-making method is adopted. After the first high-pressure cavity-making is completed, the drill is slowly retracted at a uniform speed of 0.2 m / min, and continuous cavity-making is carried out while retracting. The retraction is stopped after every 8 m of cavity-making, and high-pressure water supply is maintained for 2.5 min for centralized slag removal. Then the retraction cavity-making continues. After reaching the set cavity-making termination position of 280 m, the drill is quickly retracted at a speed of 1.5 m / s until the drill bit is completely withdrawn from the borehole.

[0055] Example 3: Single-cavity rapid retreating cavity creation construction in hard coal seams (f=2.5) The difference between this embodiment and Embodiment 1 is that: S1. Low-pressure drilling stage: water supply pressure is 5MPa, drill bit speed is 300r / min, and drilling speed is 0.3m / min; S2. First high-pressure cavity-building stage: water supply pressure is 35MPa, flow rate is 180L / min, nozzle rotation speed is 120r / min, drill bit revolution speed is 60r / min, cavity-building time is 30min, and cavity diameter is controlled at 0.8m; S3. Drill withdrawal stage: The single-hole rapid drill withdrawal method is adopted. After the first high-pressure hole creation is completed, the drill is withdrawn rapidly at a speed of 2m / s until the integrated hole creation drill bit is completely withdrawn from the borehole. During the drill withdrawal process, the high-pressure water flow continuously flushes and cleans the borehole wall.

[0056] During drilling operations using low-pressure water supply, some water will be sprayed out through nozzle 5. Since nozzle 5 is very close to the front end of the drill bit, the water sprayed out through nozzle 5 also serves to cool the drill bit and remove slag, without affecting normal drilling operations.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing hydraulic cavity creation in coal seams, characterized in that: The operation utilizes an integrated cavity-creating drill bit that incorporates a self-rotating cavity-creating device and a pressure-responsive water flow switching mechanism, and includes the following steps: S1. Low-pressure drilling to the designed final hole position: Low-pressure water flow is introduced into the integrated cavity drilling bit. The drilling machine drives the integrated cavity drilling bit to rotate and drill. The low-pressure water flow flows out through the front end of the drill bit to achieve cooling and chip removal until the designed final hole position is reached. S2. Drill backward to the designated position to perform the first high-pressure cavity creation: After drilling backward to the target coal seam section at the designated position, increase the water supply pressure to the set value. The pressure-responsive water flow switching mechanism automatically closes the water flow channel at the front end of the drill bit. The high-pressure water flow drives the nozzle of the self-rotating cavity creation device to rotate. At the same time, the nozzle revolves with the drill bit body. The high-pressure water jet washes the coal body to form a cavity. S3. Maintain high-pressure water flow during drill retraction: After high-pressure hole creation at the first location, create only one short hole and quickly withdraw the entire integrated hole-creation drill bit from the borehole. Alternatively, after high-pressure cavity creation at the first location, maintain high-pressure water and quickly retract the drill to the next cavity creation location. Repeat step S2 to create cavities at multiple points intermittently. After all cavities are created, quickly retract the drill until the integrated cavity creation drill bit exits the borehole. Alternatively, maintain high-pressure water flow while slowly retracting the drill bit and continuously creating a cavity until the set cavity creation termination position is reached, creating a long cavity. Then, quickly retract the drill bit until the integrated cavity-creating drill bit is removed from the borehole.

2. The method for constructing hydraulic cavity creation in coal seams according to claim 1, characterized in that: The integrated cavity-making drill bit includes a drill bit body with its center line arranged along the front-rear direction. Several cutting teeth are fixedly provided at the front end of the drill bit body. The drill bit body has a central hole with an open rear end inside. The central hole has an internal thread section for connecting with the drill rod, a self-rotating cavity-making device, and a water flow switching mechanism arranged sequentially from back to front. Two circular mounting grooves are symmetrically provided on the drill bit body. The bottom of the circular mounting groove has a mounting hole communicating with the central hole. The self-rotating cavity-creating device includes an internal transmission assembly, two nozzles, and an axial fixing assembly. The internal transmission assembly includes a mounting cylinder and a power shaft. The mounting cylinder is coaxially installed in the central hole of the drill bit body. The axis of the power shaft is arranged along the radial direction of the mounting cylinder. The mounting cylinder has two centrally symmetrical bearing mounting grooves. Both ends of the power shaft are rotatably connected to the two bearing mounting grooves through ball bearings. The axial rear end face of the mounting cylinder has an installation port communicating with the bearing mounting grooves. An impeller located inside the mounting cylinder is fixed on the power shaft. The power shaft has a hollow tube structure. A water inlet hole is opened between two adjacent blades of the impeller, passing through the power shaft. The water inlet hole communicates with the shaft hole of the power shaft and the central hole of the drill bit body. Both ends of the power shaft are provided with a first circumferential fixed connection structure. The water inlet hole communicates with the first circumferential fixed connection structure through the shaft hole of the power shaft. The nozzle is installed in the circular mounting groove of the drill bit body. The inner end of the nozzle is provided with a second circumferential fixed connection structure. The second circumferential fixed connection structure is coaxially connected and driven by the first circumferential fixed connection structure at the radial outer end of the power shaft. A first high-pressure sealing ring is provided between the outer circle of the nozzle and the inner wall of the circular mounting groove. The outer end of the nozzle is provided with at least one nozzle that is inclined to the nozzle axis.

3. The method for constructing hydraulic cavity creation in coal seams according to claim 2, characterized in that: The axial fixing assembly includes a thrust bearing and a clamping cap; the thrust bearing is sleeved on the outer circle of the nozzle, and the clamping cap is fixedly connected to the opening edge of the circular mounting groove of the drill bit body by screws, thereby axially fixing the thrust bearing and the nozzle in the circular mounting groove.

4. The coal seam hydraulic cavity creation construction method according to claim 2, characterized in that: The water flow switching mechanism includes a sliding plug, a compression spring, and a sealing sleeve; the sliding plug and the sealing sleeve are coaxially installed at the front section of the central hole of the drill bit body, and the sealing sleeve is located in front of the sliding plug; the rear end of the sliding plug is open and the front end is closed, and the sealing sleeve is open at both ends; the outer circle of the front end of the sliding plug is provided with a first conical sealing surface that is smaller at the front and larger at the rear, and the inner circle of the rear port of the sealing sleeve is provided with a second conical sealing surface that is smaller at the front and larger at the rear and matches the first conical sealing surface; The front half of the sliding plug has a permeable first low-pressure water hole along the radial direction. The outer diameter of the front half of the sliding plug is smaller than that of the rear half and an annular step is formed at the junction. A compression spring is sleeved on the front half of the sliding plug. The front end of the compression spring is pressed against the rear end of the sealing sleeve, and the rear end of the compression spring is pressed against the front end of the annular step. The outer circumference of the sealing sleeve is provided with a second high-pressure sealing ring that seals with the inner circumference of the center hole of the drill bit body. The outer circumference of the sealing sleeve is provided with an annular water passage groove that communicates with the water outlet at the front end of the drill bit body. The sealing sleeve is provided with a second low-pressure water hole that connects the annular water passage groove with the inner cavity of the sealing sleeve.

5. The method for constructing hydraulic cavity creation in coal seams according to claim 4, characterized in that: Step S1 is as follows: Connect the integrated cavity-making drill bit to the drill rod via the internal thread section at the rear end, and connect the other end of the drill rod to the drilling rig and high-pressure water pump; introduce low-pressure water at a pressure of 2-5 MPa into the drill rod, and the drilling rig drives the drill rod and the integrated cavity-making drill bit to rotate at a speed of 100-300 r / min. The cutting teeth at the front end of the drill bit break the coal body for drilling; after the low-pressure water enters the central hole of the drill bit body, under the action of the compression spring, the rear end of the sliding plug is pressed against the axial front end face of the mounting cylinder, the first conical sealing surface separates from the second conical sealing surface, and the low-pressure water flows sequentially through the inside of the sliding plug, the first low-pressure water hole, the conical channel formed by the separation of the first and second conical sealing surfaces, the inside of the sealing sleeve, the second low-pressure water hole, and the annular water passage, and finally flows out from the water outlet at the front end of the drill bit body, cooling the cutting teeth and discharging the drill cuttings outside the borehole; the drilling speed is controlled at 0.3-1 m / min, and the drilling speed is adjusted according to the hardness of the coal seam.

6. The coal seam hydraulic cavity creation construction method according to claim 4, characterized in that: Step S2 is specifically as follows: After retracting the drill to the target coal seam section, stop drilling and keep the drill bit position unchanged; increase the water supply pressure of the high-pressure water pump to 10 - 40 MPa and the flow rate to 50 - 200 L / min. The impact force of the high-pressure water flow acting on the rear end of the sliding plug is greater than the elastic force of the compression spring, pushing the sliding plug to move axially forward, making the first conical sealing surface and the second conical sealing surface press-fit to achieve sealing cooperation, and closing the channel leading to the water outlet at the front end of the drill bit body; all the high-pressure water flows enter the shaft hole of the power shaft through the water inlet hole. Part of the water flow impacts the blades of the impeller, causing the impeller to drive the power shaft to rotate around its own axis. Then, through the transmission of the first circumferential fixed connection structure and the second circumferential fixed connection structure, the spray head rotates at a speed of 30 - 120 r / min; another part of the water flow enters the inside of the spray head through the shaft hole of the power shaft and sprays out at a high speed from the inclined nozzle; at the same time, the drill rig drives the drill bit body to rotate around the axis at a speed of 20 - 60 r / min, making the high-pressure water jet form a spiral scouring trajectory and breaking the coal body along the coal bedding direction to form a cave.

7. The method for constructing hydraulic cavity creation in coal seams according to claim 6, characterized in that: In step S2, the cavitation time for a single cave is 10 - 30 min, and the cavitation diameter is controlled to be 0.8 - 1.5 m; during the cavitation process, the drill pipe is axially moved 0.3 - 1.2 m every 3 - 8 min to expand the axial range of the cave.

8. The method for constructing hydraulic cavity creation in coal seams according to claim 7, characterized in that: In step S2, adjust the water supply pressure according to the classification of the coal seam hardness coefficient: when the coal seam hardness coefficient f ≤ 1, the water supply pressure is 10 - 20 MPa; when 1 < f ≤ 2, the water supply pressure is 20 - 30 MPa; when f > 2, the water supply pressure is 30 - 40 Mpa.

9. The method for constructing hydraulic cavity creation in coal seams according to claim 8, characterized in that: In step S2, adjust the inclination angle of the spray head nozzle according to the angle between the borehole axis and the coal seam dip angle. The inclination angle range of the nozzle is 15° - 60°: when the angle is 0° - 15°, the inclination angle of the spray head is 45° - 60°; when the angle is 15° - 30°, the inclination angle is 30° - 45°; when the angle is greater than 30°, the inclination angle is 15° - 30°.

10. The coal seam hydraulic cavity creation construction method according to claim 4, characterized in that: Step S3 is specifically as follows: Keep the high-pressure water supply and the state of the drill bit rotation around the axis unchanged. The high-pressure water flow continuously pushes the sliding plug and the sealing sleeve to maintain the sealing cooperation, and the spray head continuously rotates and sprays out the high-pressure water jet. If the single-cave rapid drill retraction method is adopted: After the first high-pressure cavitation is completed, quickly retract the drill backward at a speed of 1 - 2 m / s until the integrated cavitation drill bit completely exits the borehole. During the drill retraction process, the high-pressure water flow continuously scours and cleans the borehole wall. If the multi-point intermittent cavitation method is adopted: After the first high-pressure cavitation is completed, quickly retract the drill backward at a speed of 1 - 2 m / s for 3 - 5 m. Stop the drill retraction when reaching the next cavitation position, and repeat step S2 to construct the next cave; after each cave cavitation is completed, keep the high-pressure water supply and slowly reciprocate the drill pipe along the length direction of the borehole to discharge all the residual coal chips in the cave, and then retreat to the next cavitation position; after all the cavitations are completed, quickly retract the drill backward at a speed of 1 - 2 m / s until the drill bit completely exits the borehole. If the continuous cavity-making method is adopted: after the first high-pressure cavity-making is completed, the drill is slowly retracted at a uniform speed of 0.1-0.3 m / min, and continuous cavity-making is carried out while retracting. The high-pressure water jet continuously scours the coal body to form a continuous long expansion section; after each cavity-making of 5-10 m, the retraction is stopped, and high-pressure water supply is maintained for 2-3 minutes for centralized slag removal, and then the retraction cavity-making continues; after reaching the set cavity-making termination position, the drill is quickly retracted at a speed of 1-2 m / s until the drill bit is completely withdrawn from the borehole.

Images