A pressure-balanced anti-collapse drilling system for directional long boreholes in coal mines

Abstract

This invention relates to a pressure-balanced anti-collapse drilling system for directional long boreholes in coal mines, belonging to the field of coal mine safety technology. It includes a drilling rig, drill rod, bottom-hole power drilling tool, bottom-hole parameter measurement and control device, borehole sealing device, pressure control system, gas-water separation device, solids control device, borehole cleaning fluid circulation device, and mud pump. This invention dynamically controls the return flow rate of the borehole cleaning fluid during drilling to establish annular pressure within the borehole, thereby balancing formation pressure and providing effective support for the borehole wall to achieve mechanical anti-collapse. Simultaneously, under the action of positive pressure differential, high-quality borehole cleaning fluid forms a dense mud cake on the borehole wall, protecting the borehole wall from scouring disturbances and hydration effects to achieve chemical collapse prevention. Through the combined action of mechanical and chemical methods, it prevents borehole wall collapse, reduces the risk of accidents within the borehole, improves the safety and construction efficiency of directional long borehole construction, and enhances the applicability of underground directional drilling technology.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety technology and relates to a pressure balance anti-collapse drilling system for directional long boreholes in coal mines. Background Technology

[0002] Shallow coal resources are becoming increasingly depleted. As coal mining progresses into deeper areas, coal seams exhibit increasingly pronounced characteristics of high ground stress, strong gas adsorption, and low permeability, leading to significant changes in the mining environment. Under the influence of mining disturbances, the intensity and frequency of coal and gas outbursts and rock bursts are showing a marked upward trend, seriously threatening coal mine production safety and energy security. To address deep coal seam dynamic hazards, the industry has invested considerable effort in developing technologies such as fracturing and permeability enhancement based on directional long-bore drilling, making it possible to achieve advanced, remote, efficient, and precise regional control of coal and rock dynamic hazards. However, the directional drilling process, which forms the foundation of these technologies, has encountered a technical bottleneck in its application to deep coal seams—the stability of the borehole walls in soft coal seams under high ground stress conditions. This results in high accident risks, low borehole formation rate, and low borehole efficiency during directional drilling construction, severely restricting the application of deep coal seam dynamic hazard control technologies.

[0003] Currently, methods to improve borehole stability include point grouting to enhance surrounding rock strength, casing protection to strengthen borehole support, and pneumatic directional drilling to reduce the scouring and disturbance of the borehole wall by the washing fluid. These methods have improved borehole success rate and stability to some extent and have been tested extensively in the field. However, these methods have drawbacks such as complex grouting and solidification processes, difficulties in casing recovery, poor pneumatic slag removal, and low rock drilling efficiency. Existing processes lack simplicity and universality. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a pressure balance anti-collapse drilling system for directional long boreholes in coal mines, which effectively prevents borehole wall collapse during directional drilling construction, thereby reducing the frequency of accidents such as stuck drill and improving the borehole formation rate and efficiency.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A pressure-balanced anti-collapse drilling system for directional long boreholes in coal mines includes a drilling rig, drill rod, bottom hole power drilling tool, bottom hole parameter measurement device while drilling, borehole sealing device, pressure control system, gas-water separation device, solids control device, hole washing fluid circulation device, and mud pump. The drilling rig, drill rod and bottom hole power drill are connected in sequence. The bottom hole power drill uses high-pressure hole washing fluid as power to drive the drill bit to break the rock. The bottom hole parameter measurement device is installed on the drill pipe and is used to measure and display the bottom hole parameters; The borehole opening is equipped with a sealing pipe, one end of which is sealed inside the coal seam, and the other end is connected to the borehole sealing device. The borehole sealing device is used to seal the borehole annulus, so that the washing fluid can only flow out from the outlet of the borehole sealing device. The pressure control system is connected to the outlet of the wellhead sealing device through the slag discharge pipe. It serves as a sedimentation buffer device for the returned washing fluid, collects and temporarily stores large rock cuttings in the washing fluid, and is used to automatically control the outlet flow rate of the washing fluid to stabilize the borehole annulus pressure at the target value. The gas-liquid separator is connected to the pressure control system and uses a negative pressure pipeline to draw out the returned gas, thus achieving gas-liquid separation. The solid control device is connected to the gas-liquid separator and is used to separate solid particles in the hole washing liquid through physical action, while retaining useful components. The hole cleaning fluid circulation device is used to precipitate and prepare slurry of the purified hole cleaning fluid; The mud pump is used to pressurize the hole-washing fluid in the hole-washing fluid circulation device to the working pressure and flow rate required to drive the bottom hole power drill bit, and to transport the hole-washing fluid through the drill pipe to drive the bottom hole power drill bit.

[0006] Furthermore, the bottom hole parameter measurement while drilling device includes a measuring device and an operating system; the measuring device includes various data sensors installed in the drill rod behind the bottom hole power drill bit, used to measure drilling trajectory parameters, bottom hole drilling engineering parameters and bottom hole geological parameters, and send them to the operating system; the operating system has table or graph display function, used to display measurement data in real time, and provide data support for drilling trajectory control and pressure closed-loop control.

[0007] Furthermore, the orifice sealing device includes a four-way housing and a sealing core; the four-way housing connects the sealing pipe and the slag discharge pipe; the sealing core fits against the drill rod passing through its central hole to achieve an inner wall seal of the borehole annulus; the other end of the slag discharge pipe is divided into three passages by a valve, two of which are connected to the pressure control system and the other is connected to the gas-water separator.

[0008] Furthermore, the pressure control device includes a pressurized slag discharge device, a pressure control valve, and a control system; the pressurized slag discharge device is located between the slag discharge pipe and the inlet of the pressure control valve; the pressure control valve adjusts the discharge flow rate to control the annular pressure by adjusting the valve opening; the control system includes a measuring device and a control unit, the measuring device is located near the bottom-of-hole motor, measures the annular pressure near the drill bit, and transmits the measured pressure to the control unit, the control unit automatically adjusts the valve opening according to the measured pressure to achieve closed-loop control of the annular pressure.

[0009] Furthermore, the pressurized cuttings removal device includes two containers capable of withstanding controlled drilling pressure, and a pressure measuring device, a flushing device, a safety relief valve, and a pressure compensation valve respectively installed on the two containers. The containers are used to settle large-diameter drill cuttings, and each container has a drain port for discharging the hole-washing fluid. The pressure measuring device is used to measure the pressure value inside the container in real time. The flushing device is used to flush the cuttings when they become blocked. The safety relief valve opens to release pressure when the pressure inside the container exceeds the equipment's safety value. The pressure compensation valve is connected to a pressure compensation pipeline and is used to fill the container with liquid after all the drill cuttings have been discharged, so that the pressure inside the container reaches the controlled pressure target value and maintains stable pressure inside the hole.

[0010] Furthermore, the solids control device includes a two-stage purification device and a transfer pump; the input end of the first-stage purification device is connected to the pressure control system, and it separates coarser drill cuttings from the hole washing fluid through sieving, with large drill cuttings being discharged from the sieve, and the hole washing fluid containing fine particles entering the underflow storage tank; the second-stage purification device separates fine particles from the hole washing fluid through swirling, with the particulate matter being discharged from the underflow, and the cleaned hole washing fluid entering the hole washing fluid circulation device; the transfer pump is used to pump the hole washing fluid in the underflow storage tank into the second-stage purification device.

[0011] Furthermore, the hole washing liquid circulation device includes a sedimentation tank, a water pump, and a slurry mixing device; the sedimentation tank is connected to a solids control device and is used to precipitate and separate the small solid phases in the hole washing liquid; the water pump is used to pump the hole washing liquid in the sedimentation tank into the slurry mixing device; the slurry mixing device is equipped with a stirring device for uniformly mixing the hole washing liquid materials.

[0012] Furthermore, it also includes a reinjection device, which is connected to the pressure control system. When the pump is stopped or the circulation pipeline is switched, if the annular pressure is less than the target value, the pressure control system will reinject the liquid into the annular space through the reinjection device to maintain the annular pressure.

[0013] The beneficial effects of this invention are as follows: By dynamically controlling the return flow rate of the flushing fluid during drilling, this invention establishes annular pressure within the borehole, thereby balancing formation pressure and providing effective support for the borehole wall to achieve mechanical anti-collapse. Simultaneously, under the action of positive pressure differential, the high-quality flushing fluid forms a dense mud cake on the borehole wall, protecting it from scouring disturbances and hydration effects, thus achieving chemical collapse prevention. Through the combined effects of mechanical and chemical methods, this invention prevents borehole wall collapse, reduces the risk of borehole accidents, improves the safety and construction efficiency of downhole directional drilling, and enhances the applicability of downhole directional drilling technology.

[0014] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 Structural diagram of a pressure balance anti-collapse drilling system for directional long boreholes in underground coal mines; Figure 2 Here is a structural diagram of the orifice sealing device; Figure 3 This is a structural diagram of the pressure control device.

[0016] Reference numerals: 1-bottom hole power drilling tool, 2-bottom hole parameter measurement device while drilling, 3-sealing section, 4-sealing pipe, 5-holehead sealing device, 6-drill rod, 7-drilling rig, 8-mud pump, 9-slag discharge pipe, 10-pressure control system, 11-reinjection device, 12-gas-water separator, 13-solids control device, 14-sedimentation tank, 15-slurry discharge pipeline, 16-slurry mixing tank, 17-mixing device, 18-slurry inlet pipeline, 19-negative pressure pipeline, 51-four-way housing, 52-sealing core. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0018] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0019] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0020] Example 1: like Figure 1-3 As shown, the present invention provides a pressure balance anti-collapse drilling system for directional long boreholes in coal mines, including a bottom hole power drill bit 1, a bottom hole parameter measurement device 2 and system, a drill rod 6, a borehole annulus, a sealing pipe 4, a borehole sealing device 5, a pressure control system 10, a reinjection device 11, a gas-water separation device 12, a solids control device 13, a hole washing fluid circulation device, a mud pump 8, and a directional drilling rig 7.

[0021] The bottom hole power drill 1 uses high-pressure flushing fluid provided by a mud pump truck to power the drill bit for rock breaking. The drilling trajectory is controlled by adjusting the tool face angle of the bottom hole power drill 1. The drill rod 6 connects the drill string, transmitting drilling torque and thrust, conveying flushing fluid, and transmitting measurement data. The borehole annulus is the channel between the drill rod 6 and the borehole wall or sealing pipe 4, allowing flushing fluid to flow and drill cuttings to return. One end of the sealing pipe 4 is securely sealed inside the coal seam, while the other end has an interface for connection to the borehole sealing device 5. The borehole sealing device 5 is installed at the outer end of the sealing pipe 4, through which the drill rod 6 passes, sealing the borehole annulus and ensuring that flushing fluid can only flow out from its discharge port, preventing leakage along the outer wall of the drill rod 6. The pressure control system 10 consists of a pressure control device and an operating system. The pressure control system 10 controls the flushing fluid outlet flow rate to increase the borehole annulus pressure, while the operating system automatically controls the pressure control device to stabilize the borehole annulus pressure at the target value. One end of the slag discharge pipe 9 is connected to the outlet of the orifice sealing device 5, and the other end is connected to the pressure control system 10. It serves as a sedimentation buffer device for the returned washing fluid, collecting and temporarily storing large rock fragments in the washing fluid to prevent clogging of the pressure control system 10. It also achieves smooth slag discharge under stable annular pressure conditions by switching the slag discharge device.

[0022] The reinjection device 11 is connected to the pressure control system 10. When the pump is stopped or the circulation pipeline is switched, if the annular pressure is less than the target value, the liquid is reinjected into the annular space through the reinjection device 11 to maintain the annular pressure.

[0023] The inlet of the gas-liquid separator 12 is connected to the outlet of the pressure control system 10, and the outlet is connected to the inlet of the solids control device 13. The gas-liquid separator 12 is also connected to a negative pressure pipeline 19, which is used to draw back the gas by negative pressure to achieve gas-liquid separation, and then input the separated liquid into the solids control device 13. The solids control device 13 separates the solid particles in the flushing liquid by physical action, retaining the useful components.

[0024] The hole washing liquid circulation device includes a sedimentation tank 14, a water pump, and a slurry mixing tank 16. After the hole washing liquid flows out of the solid control device 13, it enters the sedimentation tank 14 for further sedimentation and separation of the small solid phases. The water pump pumps the hole washing liquid in the sedimentation tank 14 into the slurry mixing device. The slurry mixing tank 16 is equipped with a stirring device 17 for uniform mixing of the hole washing liquid materials.

[0025] The mud pump 8 pressurizes the washing fluid in the hole-washing fluid circulation device to the working pressure and flow rate required to drive the power drilling tool at the bottom of the hole. The directional drilling rig 7 provides the driving force for drilling.

[0026] Furthermore, the sealing pipe 4 can withstand external pressure no less than the maximum grouting pressure. After the multi-stage sealing pipes are connected, they are lowered into the hole. The annular space between the sealing pipe 4 and the hole wall is completely filled with sealing material to form the sealing section 3. The grouting pressure during annular filling is no less than 1.5 MPa. After the sealing material reaches the design strength, the sealing quality is tested by pressure testing. The test pressure is no less than 1.5 times the maximum control pressure. If the pressure drop is no less than 0.15 MPa after stabilizing the pressure for 30 minutes and there is no leakage around the hole opening, the sealing quality is qualified. If the sealing quality is unqualified, reinforcement measures or re-drilling are required.

[0027] Furthermore, such as Figure 2 As shown, the orifice sealing device 5 includes a four-way housing 51 and a sealing core 52. The four-way housing 51 connects the sealing pipe and the slag discharge pipe 9, and houses the sealing core. The cleaning fluid, carrying drill cuttings, flows back from the borehole into the four-way housing and is discharged through the slag discharge pipe 9 to the pressure control system 10. The sealing core is tightly fitted to the drill rod 6, which passes through its central hole, sealing the cleaning fluid within the four-way housing 51 and preventing leakage along the outer wall of the drill rod 6, thus achieving an inner wall seal of the borehole annulus. The sealing core is coupled to the four-way housing, allowing it to rotate with the drill string, avoiding severe friction between the drill rod and the sealing core.

[0028] Furthermore, the pressure control system 10 includes a pressurized slag discharge device, a pressure control valve, and a control system. The pressurized slag discharge device is installed between the slag discharge pipe 9 and the inlet of the pressure control valve. The pressure control valve regulates the discharge flow rate to control the annular pressure by adjusting the valve opening. The control system includes a measuring device and a control program. The measuring device is installed near the bottom-of-hole motor to measure the annular pressure near the drill bit and transmits the measured pressure to the control program. The program controls the automatic adjustment of the valve opening to achieve closed-loop control of the annular pressure.

[0029] The pressurized cuttings removal device includes two containers capable of withstanding controlled drilling pressure, and pressure measuring devices, flushing devices, safety relief valves, and pressure compensation valves installed on the two containers respectively. Drilling fluid carrying cuttings flows out from the outlet of the four-way housing 51 of the borehole sealing device 5 through the cuttings removal pipe 9, and is then divided into three paths by valves. Two paths are connected to the pressure control valves, and the third path is an emergency path directly discharged to the borehole cleaning fluid purification device. These valves can be manually or electrically controlled. After the drilling fluid carrying cuttings enters the pressurized cuttings removal device containers, large-diameter cuttings settle at the bottom of the containers, while small-diameter cuttings remain suspended in the borehole cleaning fluid and are discharged with the fluid through the drain port on the containers into subsequent pipelines. The pressurized cuttings removal device provides a means of observing or detecting the internal conditions, accurately determining the cuttings deposition within the containers. When the cuttings deposition exceeds the drain port, the inlet valve at the front end and the outlet valve at the rear end of the containers are closed, and the cuttings removal valve at the bottom of the containers is opened to remove the cuttings. If blockage occurs during the slag removal process, a flushing device can be used to flush and remove the slag. After all drill cuttings are removed, close the bottom slag removal valve and open the pressure compensation valve to fill the container with liquid so that the internal pressure reaches the target pressure value, reducing pressure fluctuations caused by the container being empty during slag removal switching. Pressure measuring instruments can measure the pressure inside the container in real time. The safety relief valve automatically opens to release pressure when the pressure inside the container exceeds the equipment's safety value, ensuring operational safety. The pressure compensation valve connects to the pressure compensation pipeline, allowing for the injection of a constant pressure fluid into the borehole when connecting drill pipes or temporarily stopping drilling, maintaining stable borehole pressure.

[0030] Furthermore, the solids control device includes a two-stage purification system and a transfer pump. The hole-cleaning fluid, carrying drill cuttings, is discharged from the outlet of the pressure control valve to the first-stage purification system. The first-stage purification system separates coarser drill cuttings from the hole-cleaning fluid through sieving, with large drill cuttings being discharged from the sieve. The hole-cleaning fluid containing fine particles enters the underflow storage tank. The transfer pump pressurizes the hole-cleaning fluid entering the storage tank and pumps it into the second-stage purification system. The second-stage purification system separates fine particles from the hole-cleaning fluid through swirling, with the particles being discharged from the underflow. The cleaned hole-cleaning fluid then enters the hole-cleaning fluid circulation system.

[0031] Furthermore, the hole washing fluid circulation device includes a sedimentation tank 14, a water pump, and a slurry mixing tank 16. The hole washing fluid enters the sedimentation tank 14 from the outlet of the solids control device 13. The water pump pumps the hole washing fluid in the sedimentation tank 14 into the slurry mixing tank through the slurry pouring pipeline 15. The slurry mixing tank 16 is equipped with a stirring device 17 to mix the hole washing fluid material and water in a proportional manner.

[0032] Furthermore, the bottom hole parameter measurement-while-drilling device 2 includes a measuring device and an operating system. The measuring device integrates various data sensors installed within the drill rod 6 behind the bottom hole power drill bit 1, used to measure drilling trajectory parameters, bottom hole drilling engineering parameters (including but not limited to drilling pressure, water pressure inside and outside the drill rod, torque, and flow rate), and bottom hole geological parameters (including but not limited to natural gamma and resistivity). The operating system has table or graphical display functions, allowing real-time display of measurement data for the operator to read, providing data support for drilling trajectory control and pressure closed-loop control.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A pressure-balanced anti-collapse drilling system for directional long boreholes in coal mines, characterized in that: This includes drilling rigs, drill pipes, bottom hole power drilling tools, bottom hole parameter measurement and control devices, wellhead sealing devices, pressure control systems, gas-water separation devices, solids control devices, hole washing fluid circulation devices, and mud pumps. The drilling rig, drill rod and bottom hole power drill are connected in sequence. The bottom hole power drill uses high-pressure flushing fluid as power to drive the drill bit to break the rock. The bottom hole parameter measurement device is installed on the drill pipe and is used to measure and display the bottom hole parameters; The borehole opening is equipped with a sealing pipe, one end of which is sealed inside the coal seam, and the other end is connected to the borehole sealing device. The borehole sealing device is used to seal the borehole annulus, so that the washing fluid can only flow out from the outlet of the borehole sealing device. The pressure control system is connected to the outlet of the wellhead sealing device through the slag discharge pipe. It serves as a sedimentation buffer device for the returned washing fluid, collects and temporarily stores large rock cuttings in the washing fluid, and is used to automatically control the outlet flow rate of the washing fluid to stabilize the borehole annulus pressure at the target value. The gas-liquid separator is connected to the pressure control system and uses a negative pressure pipeline to draw out the returned gas, thus achieving gas-liquid separation. The solid control device is connected to the gas-liquid separator and is used to separate solid particles in the hole washing liquid through physical action, while retaining useful components. The hole cleaning fluid circulation device is used to precipitate and prepare slurry of the purified hole cleaning fluid; The mud pump is used to pressurize the hole-washing fluid in the hole-washing fluid circulation device to the working pressure and flow rate required to drive the bottom hole power drill bit, and to transport the hole-washing fluid through the drill pipe to drive the bottom hole power drill bit.

2. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: The bottom hole parameter measurement while drilling device includes a measuring device and an operating system. The measuring device includes various data sensors installed in the drill rod behind the bottom hole power drill bit, used to measure drilling trajectory parameters, bottom hole drilling engineering parameters, and bottom hole geological parameters, and send them to the operating system. The operating system has table or graph display functions to display the measurement data in real time, providing data support for drilling trajectory control and pressure closed-loop control.

3. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: The orifice sealing device includes a four-way housing and a sealing core; the four-way housing connects the sealing pipe and the slag discharge pipe; the sealing core fits against the drill rod passing through its central hole to achieve an inner wall seal of the borehole annulus; the other end of the slag discharge pipe is divided into three passages by a valve, two of which are connected to the pressure control system and the other is connected to the gas-water separator.

4. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: The pressure control device includes a pressurized slag discharge device, a pressure control valve, and a control system. The pressurized slag discharge device is located between the slag discharge pipe and the inlet of the pressure control valve. The pressure control valve adjusts the discharge flow rate to control the annular pressure by adjusting the valve opening. The control system includes a measuring device and a control unit. The measuring device is located near the bottom hole motor and measures the annular pressure near the drill bit. The measured pressure is transmitted to the control unit, which automatically adjusts the valve opening according to the measured pressure to achieve closed-loop control of the annular pressure.

5. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 4, characterized in that: The pressurized cuttings removal device includes two containers capable of withstanding controlled drilling pressure, and a pressure measuring device, a flushing device, a safety relief valve, and a pressure compensation valve installed on the two containers respectively. The containers are used to settle large-diameter drill cuttings, and each container has a drain port for discharging the hole-washing fluid. The pressure measuring device is used to measure the pressure value inside the container in real time. The flushing device is used to flush out the cuttings when they become blocked. The safety relief valve opens to release pressure when the pressure inside the container exceeds the equipment's safety value. The pressure compensation valve is connected to a pressure compensation pipeline and is used to fill the container with liquid after all the drill cuttings have been discharged, so that the pressure inside the container reaches the controlled pressure target value and maintains stable pressure inside the hole.

6. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: The solids control device includes a two-stage purification unit and a transfer pump. The input end of the first-stage purification unit is connected to the pressure control system. It separates coarser drill cuttings from the cleaning fluid through sieving, with large drill cuttings being discharged from the sieve, and the cleaning fluid containing fine particles entering the underflow tank. The second-stage purification unit separates fine particles from the cleaning fluid through swirling, with the particles being discharged from the underflow, and the cleaned cleaning fluid entering the cleaning fluid circulation device. The transfer pump is used to pump the cleaning fluid from the underflow tank into the second-stage purification unit.

7. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: The hole washing fluid circulation device includes a sedimentation tank, a water pump, and a slurry mixing device; the sedimentation tank is connected to a solids control device and is used to separate the small solid phases in the hole washing fluid by sedimentation; the water pump is used to pump the hole washing fluid in the sedimentation tank into the slurry mixing device; the slurry mixing device is equipped with a stirring device for uniformly mixing the hole washing fluid materials.

8. The coal mine underground directional long borehole pressure balance anti-collapse drilling system according to claim 1, characterized in that: It also includes a reinjection device, which is connected to the pressure control system. When the pump is stopped or the circulation pipeline is switched, if the annular pressure is less than the target value, the pressure control system will reinject the liquid into the annular space through the reinjection device to maintain the annular pressure.

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