A method for mining coal based on roof horizontal well sidetracking hole

Abstract

The application discloses a kind of based on roof horizontal well side drilling hole's with mining filling coal mining method, this method includes: in coal seam roof strata construction horizontal well, on the ground crushing coal gangue makes filling slurry, working face mining to certain distance after, from the ground roof horizontal well shaft side drilling hole forms first side drilling branch passage, from the ground well mouth injection filling slurry, the goaf formed after filling hydraulic support;Pumping bridge plug into casing, block first side drilling branch passage;Multiple side drilling hole drilling, filling and blocking are repeated to be operated, realize the filling of entire working face goaf.The application can realize with mining filling control sinking in the process of coal mining, solve goaf settlement and other problems.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof. Background Technology

[0002] Currently, underground mining remains the primary method of coal mining. Coal mining creates goaf areas, altering the geological structure and leading to surface subsidence and ground fissures. This not only poses safety hazards to buildings in mining areas but also damages farmland, causing a series of ecological and safety problems. Backfilling is one way to address overburden subsidence in mining areas. However, currently, backfilling and coal mining are independent processes. Backfilling operations require a complete halt to coal mining, resulting in long waiting times and hindering mining efficiency. Especially in recent years, the mechanization and automation of coal mining have significantly improved, leading to increased mining efficiency and placing higher demands on backfilling technology.

[0003] The paper "Ecological Coal Mining Method of Horizontal Long Drill Hole with Casing in Coal Seam Roof for On-the-Go Mining and Backfilling" (CN202110423554.2) discloses a method that utilizes a horizontal long drill hole in the casing of the coal seam roof as a filling channel for backfill paste. During the mining of the working face, the immediate roof collapses as the mining progresses. When the immediate roof collapses and the front end of the casing is exposed in the goaf, backfill paste is injected into the goaf. This method provides a new approach to on-the-go filling in coal mines, but it also faces challenges such as the inability to expose the casing when the roof cannot collapse and the difficulty of casing cutting operations behind hydraulic supports. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a coal mining method based on horizontal well side boreholes in the roof, so as to achieve controlled subsidence during coal mining and solve problems such as subsidence in goaf areas.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for coal mining with simultaneous mining and backfilling based on horizontal well side boreholes in the roof includes the following steps: Step 1: Construct a horizontal well in the roof strata of the coal seam, and then run casing and cement the well. Step 2, making filling slurry from crushed coal gangue: Coal gangue produced during coal mining is crushed, screened, and mixed with wastewater to make filling slurry; Step 3, working face back mining, drilling holes towards the lower coal seam in the horizontal shaft: After the working face has been back mined for 5-10m, the side drilling guide tool is lowered from the horizontal shaft opening to the predetermined depth. The side drilling guide tool is oriented vertically downward by gravity. Then the side drilling flexible drill bit is lowered. Under the guidance of the side drilling guide tool, the side drilling flexible drill bit is oriented vertically downward to drill into the side drilling hole until it communicates with the goaf behind the hydraulic support, forming the first side drilling branch. Then drilling is stopped and the side drilling flexible drill bit and the side drilling guide tool are pulled out. Step 4: The filling slurry prepared in step 2 is injected into the horizontal well through the surface pump. The filling slurry enters the goaf through the horizontal well shaft and the first side drilling branch to fill the goaf. Step 5: After the first side drilling branch is filled to the predetermined volume, a bridge plug is pumped into the casing by cable delivery. When the cable is energized, the bridge plug expands and sets, sealing the channel of the first side drilling branch. Step 6: Repeat steps 3 to 5 to drill, fill and seal multiple side drilling branches in sequence to complete the filling of the goaf of the entire working face.

[0007] The present invention also includes the following technical features: Specifically, in step 1, the horizontal well is 3-5m away from the top of the coal seam, and the length of the horizontal section of the horizontal well covers at least one working face.

[0008] Specifically, in step 1, when the coal seam depth is ≤300m, the horizontal well adopts a two-stage well structure. In the first stage, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second stage, the well is drilled into a vertical section, a directional section, and a horizontal section. The cementing in the second stage adopts a combined casing, with fiberglass casing in the horizontal section and steel casing in the vertical section. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to set for 48 hours.

[0009] Specifically, in step 1, when the coal seam depth is greater than 300m, the horizontal well adopts a three-section wellbore structure. In the first section, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second section, after drilling to the landing point, steel casing is run and cement is injected to cement the well. In the third section, the horizontal section is drilled. The cementing of the third section adopts a combined casing. Fiberglass casing is used in the horizontal section and steel casing is used in the vertical section. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to solidify for 48 hours.

[0010] Specifically, in step 2, the particle size of the crushed and screened material is no greater than 4 mm, and the density of the filling slurry is 1.15-1.20 g / cm³. 3 .

[0011] Specifically, in step 3, the side-drilling directional tool includes a safety release, a centralizer, a rotary directional sub, a bottom packer, and a guide head connected in sequence. The safety release mechanism is connected to the tubing via a pin; the centralizer ensures that the side-drilling guide tool remains in the middle of the casing during the lowering process; the rotary directional sub includes an intermediate shaft and an upper rotary bearing, a gravity eccentric guide, and a lower rotary bearing sequentially mounted on the intermediate shaft, the upper and lower rotary bearings enabling the gravity eccentric guide to rotate around the intermediate shaft; the bottom packer is a mechanical packer, which is released by lifting and set by lowering.

[0012] Specifically, the intermediate shaft is provided with a central channel, and the side wall of the gravity eccentric guide is provided with a vertically downward guide opening, which is connected to the central channel of the intermediate shaft, so that the side-drilling flexible drill bit can pass through the central shaft and drill through the guide opening; the gravity eccentric guide is an eccentric structure, and the material density at its guide opening is greater than the material density on the other side so that the guide opening side can always point downward under the action of gravity.

[0013] Specifically, the side-drilling flexible drill bit includes a connector, a flexible drill rod, and a drill bit connected in sequence; the connector can be connected to the upper drill bit; the flexible drill rod is composed of multiple flexible short sections connected in sequence, a single flexible short section can achieve a rotation of 3°-5°, and multiple flexible short sections connected together can achieve a rotation from horizontal to vertical; the drill bit is a PDC drill bit.

[0014] Specifically, in step 3, after the side-drilling guide tool is connected to the tubing, it is lowered into the horizontal well to a predetermined depth through the tubing, and the bottom packer is set by pressurizing through the surface drilling rig or workover rig; the side-drilling flexible drill string is lowered into the tubing to the side-drilling guide tool.

[0015] Specifically, in step 5, the bridge plug setting position is 2-5m away from the opening of the first side drill branch.

[0016] Compared with the prior art, the present invention has the following technical effects: (1) The present invention can realize the simultaneous operation of coal mining and goaf filling, avoid the impact of filling operation on coal mining operation, and can deal with goaf in a timely manner to solve the problem of ground subsidence, thereby avoiding the problems of damage to ground buildings, damage to surface ecological environment and damage to farmland caused by it.

[0017] (2) The present invention relies on the horizontal wells and side drill holes in the coal seam roof as filling channels, which can ensure the certainty of the filling channel and filling point location and improve the reliability of goaf filling.

[0018] (3) In this invention, the vertical section of the top plate horizontal well is cemented with steel casing and the horizontal section is cemented with fiberglass casing, which can ensure the durability of the vertical section and the convenience of side-drilling construction of the horizontal section of the horizontal well.

[0019] (4) The present invention adopts flexible drilling tool rotary drilling technology, with small casing window length and small radius of curvature, which can ensure safe and efficient construction of side-drilled holes. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of horizontal well drilling in the coal seam roof strata according to the present invention; Figure 3 This is a schematic diagram of the side-drilling guide tool being lowered and the packer being set in place according to the present invention; Figure 4 This is a schematic diagram of the side-drilling flexible drill bit being lowered and the side-drilling borehole of the present invention; Figure 5 This is a schematic diagram of the structure of the side-drilling guide tool string of the present invention; Figure 6 This is a cross-sectional view of the rotationally oriented short section of the present invention; Figure 7 This is a schematic diagram of the flexible side-drilling tool of the present invention; Figure 8 This is a schematic diagram comparing (a) the side-drilling branch of the present invention with (b) the side-drilling branch of a conventional screw drill bit; Figure 9 This is a schematic diagram of the side-drilled hole grouting filling of the present invention.

[0021] The meanings of the labels in the diagram are as follows: 1-Target coal seam; 2-Coal seam roof strata; 3-Coal seam overlying strata; 4-Coal seam floor strata; 5-Hydraulic support; 6-Collapsed direct roof; 7-Horizontal well in coal seam roof strata; 8-Side drilling guide tool; 9-Side drilling flexible drill string; 10-Tubing; 11-Upper drill string; 12-Side drilling borehole; 13-Filling slurry; 81-Safety release; 82-Center; 83-Rotary directional sub; 84-Bottom packer; 85-Guiding head; 831-Upper rotary bearing; 832-Gravity eccentric guide; 833-Lower rotary bearing; 91-Safety joint; 92-Flexible sub; 93-Drill bit. Detailed Implementation

[0022] This invention provides a method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps: Step 1: Construct a horizontal well in the roof strata of the coal seam: Horizontal wells should be constructed within 3-5 meters of the top surface of the coal seam, and the horizontal section of the well should cover at least one working face. Figure 2This is a schematic diagram of a horizontal well drilling in the coal seam roof strata. From top to bottom, the layers are: 3 overlying strata of the coal seam roof, 2 coal seam roof strata, 1 target coal seam to be mined, and 4 coal seam floor strata. The horizontal well 7 in the coal seam roof strata is located in the 2 coal seam roof strata. The hydraulic support 5 provides temporary support for the goaf. There is a collapsed direct roof 6 in the goaf.

[0023] When the coal seam depth is ≤300m, the horizontal well adopts a two-stage wellbore structure. In the first stage, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second stage, the well is drilled into a vertical section, a directional section, and a horizontal section. During the construction of the horizontal section, drilling-while-drilling edge detection technology is used to detect the rock strata in real time and ensure that the distance between the horizontal well trajectory and the top surface of the coal seam is 3-5m. The cementing of the second stage adopts a combined casing, that is, the horizontal section uses fiberglass casing and the vertical section uses steel casing. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to solidify for 48 hours. When the coal seam depth is greater than 300m, the horizontal well adopts a three-section wellbore structure. In the first section, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second section, after drilling to the landing point, steel casing is run and cement is injected to cement the well. In the third section, the horizontal section is drilled. During the construction process, drilling-while-probing technology is used to detect the rock strata in real time and ensure that the distance between the horizontal well trajectory and the top surface of the coal seam is 3-5m. The cementing of the third section adopts a combined casing, that is, the horizontal section uses fiberglass casing and the vertical section uses steel casing. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to solidify for 48 hours.

[0024] After cementing the well with casing, drill pipe with centralizer is used to clear accumulated rock cuttings from the hole and ensure unobstructed borehole.

[0025] Step 2: Ground crushing of coal gangue to prepare filling slurry: Coal gangue produced during coal mining is crushed and screened to a particle size not exceeding 4mm. It is then mixed with wastewater to form a slurry with a density of approximately 1.15-1.20 g / cm³. 3 .

[0026] The particle size of the crushed and screened material is no greater than 4mm to ensure that the filling slurry does not settle or delaminate during transportation.

[0027] Step 3: After the working face has been back-mined to a certain distance, drill a side borehole from the horizontal shaft of the surface roof: Commence working face mining. After mining 5-10m from the working face, lower the side-drilling guide tool from the top horizontal wellhead to the predetermined depth. Figure 3As shown, the tubing 10, carrying a sidetracking guide tool 8, is lowered into the casing, where the casing is used for cementing and adhering tightly to the inner wall of the horizontal well. The surface drilling rig or workover rig is raised and lowered to set the bottom packer. The sidetracking guide tool is oriented vertically downwards by gravity. A flexible sidetracking tool is lowered into the tubing, and guided by the sidetracking guide tool, it is oriented vertically downwards. The surface drilling rig applies pressure and rotates the drill until it reaches the goaf behind the hydraulic support, at which point drilling stops, forming the first sidetracking branch. The flexible sidetracking tool is then retrieved, the tubing is raised to release the packer, and the sidetracking guide tool is retrieved. Specifically, as shown... Figure 4 As shown, the upper drill string 11 is connected to the side drilling flexible drill string 9 and is lowered into the tubing 10. Under the guidance of the side drilling guide tool, it achieves vertical downward orientation and drills to obtain the side drilling hole 12.

[0028] Among them, the structure of the side-drilling guide tool is as follows Figure 5 As shown, the side-drilling directional tool includes a safety release 81, a centralizer 82, a rotary directional sub 83, a bottom packer 84, and a guide head 85.

[0029] Among them, the safety release tool 81 is used to release the tool by lifting it from the surface in the event of a downhole accident such as a stuck tool string. It is connected to the tubing by a pin. When a downhole accident occurs and the tool needs to be released, the upper tubing is pulled to shear the pin, thus releasing the tool.

[0030] The centralizer 82 is used to ensure that the tool remains in the middle of the casing during the insertion process.

[0031] The rotary directional sub 83 serves two purposes: first, it achieves orientation under gravity, ensuring the guiding tool always points downwards; second, it orients the flexible drill string vertically downwards, enabling vertical downward side-drilling. The structure of the rotary directional sub 83 is as follows: Figure 6 As shown, its structure includes an upper rotary bearing 831, a gravity eccentric guide 832, a lower rotary bearing 833, and an intermediate shaft. The upper rotary bearing 831 and the lower rotary bearing 833 enable the gravity eccentric guide 832 to rotate around the intermediate shaft. The gravity eccentric guide 832 is an eccentric design, with one side of the opening (guide port) made of a high-density material and the other side made of a low-density material. After the eccentric tool is lowered, the opening (guide port) side always faces downwards under the action of gravity.

[0032] The bottom packer 84 is a mechanical packer, which is released by lifting and set by lowering.

[0033] The guide head 85 is used to guide the tool during its insertion into the well.

[0034] The sidetracking directional tool is used as follows: After connecting the sidetracking directional tool to the tubing, it is lowered into the horizontal well to the predetermined depth through the tubing. The rotary directional sub should avoid the casing coupling. The bottom packer is set by pressurizing the surface drilling rig or workover rig. The rotary directional sub has upper and lower rotary bearings on both sides. The directional sub rotates under gravity, causing the guide ramp and guide opening to point vertically downwards.

[0035] Among them, flexible drill bit structures such as Figure 7 As shown, its structure comprises a connector 91, a flexible drill pipe 92, and a drill bit 93. The connector 91 is used to connect to the upper drilling tool. The flexible drill pipe consists of multiple flexible short sections connected in sequence; a single section can achieve a rotation of 3°-5°, and multiple sections connected together can achieve a rotation from horizontal to vertical. The drill bit is a conventional PDC drill bit.

[0036] This method combines side-drilling guide tools and flexible drill strings. By utilizing the flexibility of the drill string's ability to bend in any direction, and combining it with the guiding function of the side-drilling guide tool, it can achieve the goal of drilling side-drilled holes downwards. On the other hand, relying on the strong turning ability of the flexible drill string, it can significantly reduce the turning radius of the side-drilling (referring to the radius of curvature when the tool turns from horizontal to vertical). This allows multiple side-drilled holes to be drilled downwards within the horizontal wellbore, which can be used simultaneously for filling slurry, improving filling efficiency and reducing the resistance to the flow of filling slurry.

[0037] Taking a horizontal wellbore trajectory 5m vertically from the top of the coal seam as an example, assuming the borehole trajectory is horizontal before directional drilling, and calculating with a directional drilling intensity of 2° / 6m, the length of the side-drilled hole entering the coal seam needs to be at least 39 meters. Given a fixed horizontal section length, the number of side-drilled holes that can be constructed is small, and the length of ineffective holes in the roof strata of the coal seam is large. Figure 8 (b)

[0038] If the side-drilling guide tool and flexible drill string of this invention are used, the turning radius of the borehole can be controlled within 5m. In the horizontal section of a horizontal well in the coal seam roof, multiple branch holes can be drilled downwards into the coal seam. Given the same length of the horizontal section of the well, the number of side-drilled holes can be significantly increased, improving the efficiency of filling slurry transport, and reducing the length of ineffective holes drilled in the coal seam roof strata. Figure 8 (a)

[0039] Step 4: Inject filling slurry from the surface wellhead to fill the goaf formed behind the hydraulic supports. A surface pumping station is used to inject the filling slurry prepared in step 2 into the horizontal well. The slurry passes through the horizontal wellbore and the first side-drilling branch before entering the goaf to fill it. The pumping rate is determined based on the injection capacity of the surface injection pump. Figure 9As shown, the filling slurry 13 is filled into the goaf of the hydraulic support to provide support for the upper rock strata.

[0040] Step 5: After the first side drilling branch is filled to the predetermined volume, a bridge plug is pumped into the casing using a cable delivery method. When the cable is energized, the bridge plug expands and sets, sealing the channel of the first side drilling branch. The setting position of the bridge plug is 2-5m away from the opening of the first side drilling branch.

[0041] Step 6: Repeat steps 3 to 5 to drill, fill and seal multiple side drilling branches in sequence to complete the filling of the goaf of the entire working face.

[0042] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0043] Example: To control surface subsidence caused by coal mining, a coal mine in northern Shaanxi decided to adopt a mining-and-filling process. The target coal seam has an average burial depth of 260m, an average thickness of 3.3m, and a target working face width of 200m and a length of 1000m. The mining-and-filling method based on horizontal well side-drilling holes in the roof, as described in this invention, was applied to the backfilling operation after mining.

[0044] Step 1: Construct a horizontal well in the roof strata of the coal seam: To cover one working face, the horizontal section of the well is designed to be 1000m long. Due to the shallow coal seam, a two-stage wellbore structure is adopted for the horizontal well. To ensure the slurry injection discharge rate, large-diameter drilling is used. The first stage uses a φ444.5mm drill bit to drill through the surface aquifer and loose layer, reaching a depth of 30m depending on the formation conditions. After the first stage drilling is completed, a φ339.7mm steel casing is run in, cement is injected to solidify the borehole, and the cement is returned to the surface and allowed to set for 48 hours. The second stage uses a φ311.1mm drill bit and employs drilling-while-probing technology to construct the horizontal section of the well to the designed depth within the roof strata 3-5m from the top of the coal seam. After the second stage drilling is completed, a casing with an outer diameter of φ244.5mm is run in. Fiberglass casing is used for the horizontal section, while steel casing is used for the vertical and directional sections. After the casing is run in, cement is injected to solidify the borehole, and the cement is returned to the surface and allowed to set for 48 hours.

[0045] Step 2: Ground crushing of coal gangue to prepare filling slurry: Solid waste generated from coal mining is crushed and screened to a particle size no larger than 4mm. Then, wastewater and tailings fine particles and granular solids are mixed to form a slurry with a density of approximately 1.15-1.20 g / cm³. 3 .

[0046] Step 3: After the working face has been back-mined to a certain distance, drill a side borehole from the horizontal shaft of the surface roof: The working face extraction begins. After 10m of extraction, a sidetracking directional tool is lowered from the top horizontal wellhead to the predetermined depth. The surface drilling rig or workover rig applies pressure to set the bottom packer. The sidetracking directional tool is then oriented vertically downwards by gravity. A flexible sidetracking tool is lowered into the tubing, and guided by the directional tool, it is oriented vertically downwards. The surface drilling rig applies pressure and rotates to drill the sidetracking borehole until it reaches the first sidetracking branch, connecting with the goaf behind the hydraulic support. Drilling is then stopped, and the flexible sidetracking tool is retrieved.

[0047] Raise the tubing to release the packer, and raise the sidetracking guide tool 3m. The surface drilling rig or workover rig applies pressure to set the bottom packer. Run the flexible sidetracking tool into the tubing. Guided by the sidetracking guide tool, the flexible sidetracking tool is oriented vertically downwards. The surface drilling rig applies pressure and rotates the drill until it communicates with the goaf behind the hydraulic support, then stops drilling. Pull out the flexible sidetracking tool, raise to release the packer, and pull out the sidetracking guide tool. This completes the construction of both sidetracking branches.

[0048] Step 4: Inject filling slurry from the surface wellhead to fill the goaf formed behind the hydraulic support.

[0049] The filling slurry prepared in step 2 is pumped into the horizontal well using a surface pump. The side-drilled borehole in step 3 serves as the channel for the filling slurry to enter the goaf area behind the support structure from the horizontal wellbore. The pumping rate is 3m³ / h. 3 / min.

[0050] Step 5: After filling to the predetermined volume through the two side-drilling branches, a bridge plug is pumped into the casing via cable delivery. When the cable is energized, the bridge plug expands and seals to the left, blocking the side-drilling branch channel. The bridge plug setting position is 5m from the opening position of the side-drilling branch hole.

[0051] Step 6: Repeat steps 3 to 5 to fill the goaf of the entire working face.

Claims

1. A method for coal mining with simultaneous mining and filling based on horizontal well side-drilled holes in the roof, characterized in that, Includes the following steps: Step 1: Construct a horizontal well in the roof strata of the coal seam, and then run casing and cement the well. Step 2, making filling slurry from crushed coal gangue: Coal gangue produced during coal mining is crushed, screened, and mixed with wastewater to make filling slurry; Step 3, working face back mining, drilling holes towards the lower coal seam in the horizontal shaft: After the working face has been back mined for 5-10m, the side drilling guide tool is lowered from the horizontal shaft opening to the predetermined depth. The side drilling guide tool is oriented vertically downward by gravity. Then the side drilling flexible drill bit is lowered. Under the guidance of the side drilling guide tool, the side drilling flexible drill bit is oriented vertically downward to drill into the side drilling hole until it communicates with the goaf behind the hydraulic support, forming the first side drilling branch. Then drilling is stopped and the side drilling flexible drill bit and the side drilling guide tool are pulled out. Step 4: The filling slurry prepared in step 2 is injected into the horizontal well through the surface pump. The filling slurry enters the goaf through the horizontal well shaft and the first side drilling branch to fill the goaf. Step 5: After the first side drilling branch is filled to the predetermined volume, a bridge plug is pumped into the casing by cable delivery. When the cable is energized, the bridge plug expands and sets, sealing the channel of the first side drilling branch. Step 6: Repeat steps 3 to 5 to drill, fill and seal multiple side drilling branches in sequence to complete the filling of the goaf of the entire working face. In step 1, when the coal seam depth is ≤300m, the horizontal well adopts a two-stage well structure. In the first stage, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second stage, the well is drilled into a vertical section, a directional section, and a horizontal section. The cementing of the second stage adopts a combined casing. The horizontal section uses fiberglass casing and the vertical section uses steel casing. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to set for 48 hours. In step 1, when the coal seam depth is greater than 300m, the horizontal well adopts a three-section wellbore structure. In the first section, after drilling to the surface aquifer, casing is run and cement is injected to cement the well, and the cement returns to the surface. In the second section, after drilling to the landing point, steel casing is run and cement is injected to cement the well. In the third section, the horizontal section is drilled. The cementing of the third section adopts a combined casing. Fiberglass casing is used in the horizontal section and steel casing is used in the vertical section. After the casing is run to the predetermined depth, cement is injected from the surface to cement the well, and the cement returns to the surface and is allowed to set for 48 hours. In step 3, the side-drilling directional tool includes a safety release, a stabilizer, a rotary directional sub, a bottom packer, and a guide head connected in sequence. The safety release mechanism is connected to the tubing via a pin; the centralizer ensures that the side-drilling guide tool remains in the middle of the casing during the lowering process; the rotary directional sub includes an intermediate shaft and an upper rotary bearing, a gravity eccentric guide, and a lower rotary bearing sequentially mounted on the intermediate shaft, the upper and lower rotary bearings enabling the gravity eccentric guide to rotate around the intermediate shaft; the bottom packer is a mechanical packer, which is released by lifting and set by lowering.

2. The method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof as described in claim 1, characterized in that, In step 1, the horizontal well is 3-5m away from the top of the coal seam, and the length of the horizontal section of the horizontal well covers at least one working face.

3. The method for coal mining based on horizontal well side-drilled boreholes in the roof as described in claim 1, characterized in that, In step 2, the particle size of the crushed and screened material is no greater than 4 mm, and the density of the filling slurry is 1.15-1.20 g / cm³. 3 .

4. The method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof as described in claim 1, characterized in that, The intermediate shaft is provided with a central channel, and the side wall of the gravity eccentric guide is provided with a vertically downward guide opening, which is connected to the central channel of the intermediate shaft, so that the side-drilling flexible drill bit can pass through the central shaft and drill through the guide opening; the gravity eccentric guide is an eccentric structure, and the material density at its guide opening is greater than the material density on the other side, so as to ensure that the guide opening side always points downward under the action of gravity.

5. The method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof as described in claim 1, characterized in that, The side-drilling flexible drilling tool includes a connector, a flexible drill rod, and a drill bit connected in sequence; the connector can be connected to the upper drilling tool; the flexible drill rod is composed of multiple flexible short sections connected in sequence, a single flexible short section can achieve a rotation of 3°-5°, and multiple flexible short sections connected together can achieve a rotation from horizontal to vertical; the drill bit is a PDC drill bit.

6. The method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof as described in claim 4, characterized in that, In step 3, after the side-drilling guide tool is connected to the tubing, it is lowered into the horizontal well to a predetermined depth through the tubing, and the bottom packer is set by pressurization through the surface drilling rig or workover rig; the side-drilling flexible drill string is lowered into the tubing to the side-drilling guide tool.

7. The method for coal mining with simultaneous mining and filling based on horizontal well side boreholes in the roof as described in claim 1, characterized in that, In step 5, the bridge plug setting position is 2-5m away from the opening of the first side drill branch.

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