CN113107589B - Advanced pre-drainage method for coal seam roof aquifer ground - Google Patents
Advanced pre-drainage method for coal seam roof aquifer ground Download PDFInfo
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- CN113107589B CN113107589B CN202110400827.1A CN202110400827A CN113107589B CN 113107589 B CN113107589 B CN 113107589B CN 202110400827 A CN202110400827 A CN 202110400827A CN 113107589 B CN113107589 B CN 113107589B
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F16/00—Drainage
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/30—Specific pattern of wells, e.g. optimizing the spacing of wells
- E21B43/305—Specific pattern of wells, e.g. optimizing the spacing of wells comprising at least one inclined or horizontal well
Abstract
The invention relates to a coal seam roof aquifer ground advanced pre-drainage method, which comprises the following steps: constructing a ground multi-branch upward-tilting horizontal well, wherein each branch hole of the upward-tilting horizontal well penetrates through an enriched water area of a roof aquifer; constructing a large diameter drainage well leading to a water-containing enrichment and collection area of the top plate, wherein the large diameter drainage well is communicated with the upward-tilting horizontal well; and (3) putting a drainage device into the large-diameter drainage well, and performing drainage treatment by using the drainage device. The method can overcome the defects of the existing water damage treatment technology about the roof of the coal seam, can completely remove hidden dangers of the roof aquifer of the coal seam to be mined before the regional coal mine is not built, ensures that the whole coal mine has no roof water damage influence in the period from well building to well closing, and realizes safe, efficient and continuous mining of the coal seam.
Description
Technical Field
The invention relates to a pre-drainage method, belongs to the technical field of coal mine water damage prevention and control, and particularly relates to a coal seam roof aquifer ground advanced pre-drainage method.
Background
Water damage is one of factors influencing coal mine safety exploitation, especially in the coal mine exploitation period of water-rich areas, if water damage occurs, rescue difficulty and time consumption are high, the production recovery time of a mine is long, and serious life and property loss can be caused, so that advanced water damage treatment for the coal mine areas is a key work for guaranteeing coal mine safety and high-efficiency continuous exploitation. The water source for generating water damage during the coal mining mainly comes from two aspects, namely, the water-bearing rock stratum is enriched on the coal seam roof, the coal seam tunneling process generates caving zones or disturbance cracks, so that the coal seam roof generates water guide channels, and a tunneling coal seam roadway water damage flooding well is caused; secondly, the high-pressure water-bearing stratum of the coal bed bottom plate is subjected to a coal bed tunneling process, so that the covering pressure of the water-bearing stratum is reduced, the original stress balance state is damaged, and a disturbance fracture water guide channel is generated, so that the coal mine water damage floods the well.
At present, two main methods are adopted for treating the water damage of the high-pressure water-bearing rock stratum of the coal seam floor, namely, drilling multi-branch horizontal directional holes along the water bearing stratum in the coal mine well, drilling each branch hole to the designed hole depth, and then injecting pure cement or mixed slurry of fly ash and cement and the like to replace and seal the water source of the water bearing stratum; secondly, drilling multiple branch horizontal wells along an aquifer is implemented on the ground of a coal mine area, drilling each branch hole to the designed well depth, then implementing injection of pure cement or mixed slurry of fly ash and cement and the like, replacing and plugging a water source of the aquifer, wherein the implementation of the first method is limited by underground space of the coal mine, meanwhile, the underground working environment of the coal mine is poorer, the second method is obviously superior to the first method, the implementation working space is larger, the implementation is convenient and quick, and the water hazard treatment work of a coal seam bottom plate before the coal mine of the area is not built can be completely realized by means of geological data such as seismic exploration and the like.
At present, the method mainly comprises the steps of drilling multi-branch horizontal directional holes along a water-bearing layer of a coal seam roof in a coal mine, enabling each branch directional hole to penetrate through a water-rich area to realize drainage of water-bearing layer enriched water, and although the method can remove hidden danger of water damage of the coal seam roof, the method is limited in underground space of the coal mine, workers and underground working environments are poor, particularly, for high-pressure water-bearing layer of the coal seam roof, during the process of drilling the coal seam underground in a directional mode to penetrate through the high-pressure water-rich area, the enriched water is sprayed out along the directional holes at high pressure, accidents such as injury of people or water flooding equipment are caused, and meanwhile, the method is difficult to realize the hidden danger control work of the coal seam mining working face roof before the coal mine is built, so that the working face of the coal seam to be mined is planned to stop tunneling, and tunneling work can be performed after the threat of water damage of the coal seam roof is relieved, and continuous mining of the coal mine is difficult to ensure.
Disclosure of Invention
The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.
The invention mainly aims to solve the technical problems in the prior art, and provides a coal seam roof aquifer ground advanced pre-drainage method, which can overcome the defects of the existing coal seam roof water damage treatment technology, completely remove hidden dangers of the roof aquifer of a coal seam to be mined before a regional coal mine is built, ensure that the whole coal mine is free from roof water damage influence during the period from well building to well closing, and realize safe, efficient and continuous mining of the coal seam.
In order to solve the problems, the scheme of the invention is as follows:
a coal seam roof aquifer ground advanced pre-drainage method comprises the following steps:
constructing a ground multi-branch upward-tilting horizontal well, wherein each branch hole of the upward-tilting horizontal well penetrates through an enriched water area of a roof aquifer;
constructing a large diameter drainage well leading to a water-containing enrichment and collection area of the top plate, wherein the large diameter drainage well is communicated with the upward-tilting horizontal well;
and (3) putting a drainage device into the large-diameter drainage well, and performing drainage treatment by using the drainage device.
Preferably, in the method for advanced pre-drainage of the coal seam roof aquifer ground, a large-diameter drainage well surface layer sleeve (4), a large-diameter drainage well technical sleeve (5) and a large-diameter drainage well three-opening large-size steel screen pipe (6) are sequentially arranged at the bottom of the large-diameter drainage well from outside to inside; the upward-tilting horizontal well is communicated with the large-diameter drainage well through the three-opening large-size steel screen pipe (6).
Preferably, in the above method for advanced pre-drainage of the water-bearing layer of the roof of the coal seam, the center of the large-diameter drainage well is located at the midpoint of the connecting line between the landing point and the sidetracking point of the inclined horizontal well; the landing point is the landing point of the deflecting section of the upward-tilting horizontal well at the bottom of the roof aquifer, and the sidetracking point is the starting point of the branch hole of the upward-tilting horizontal well.
Preferably, in the method for pre-dredging the water in advance on the ground of the water-bearing layer of the coal seam roof, all branch holes of the multi-branch upward-inclined horizontal well are drilled from the same side drilling point, and all branch holes are a plurality of upward-inclined branch holes obtained by increasing well inclination and adjusting azimuth drilling from the side drilling point.
Preferably, in the above method for advanced pre-drainage of the water-bearing layer ground of the coal seam roof, the multi-branch upward-tilting horizontal well adopts a three-well design, wherein a drill bit with a diameter of 349.25mm is drilled into the stable bedrock for 5m, a sleeve with a diameter of 273.05mm is placed into the drill bit, and the well cementation pure cement slurry is returned to the ground; drilling a drill bit with the diameter of phi 222.25mm for the secondary main hole design to a design horizontal landing point at the bottom of a roof aquifer, putting a technical sleeve with the diameter of phi 200.03mm into the drill bit, and returning the well cementation pure cement slurry to the ground; a three-hole main hole design phi 152.4mm drill bit drills horizontally from a landing point to a side drilling point at about 5m along the bottom of a roof aquifer; and all branch holes of the upward inclined horizontal well are drilled from the same sidetrack point side drill to form multi-branch horizontal branch holes.
Preferably, in the method for advanced pre-drainage of the coal seam roof aquifer ground, the large-diameter drainage well is drilled below a transition layer top interface below the roof aquifer.
Preferably, in the method for advanced pre-drainage of the coal seam roof aquifer ground, a reverse soluble bridge plug which is easy to dissolve in alkaline liquid is arranged at the front end of a branch hole of the multi-branch upward-tilting horizontal well; after the bridge plugs are drilled through the large-diameter drainage well, alkaline materials are added into the circulating drilling fluid to dissolve the bridge plugs at the front ends of the horizontal holes of the upward-inclined branches.
Preferably, in the foregoing method for advanced pre-drainage of the water level ground of the roof of the coal seam, the large-diameter drainage well adopts a three-well deep structure, wherein: the first drilling adopts a small-size phi 152.4mm drill bit to drill pilot holes along the vertical central axis between the landing point of the second main hole and the third side drilling point of the multi-branch upward-tilting horizontal well, so that the pilot holes are communicated with the multi-branch horizontal well, the pilot holes are positioned at 1m on the top interface of the top plate aquifer, drillable bridge plugs are placed in the pilot holes to seal, and the normal circulation operation of the subsequent large-diameter well graded reaming drilling is ensured; the method comprises the steps of firstly carrying out grading drilling to stabilize bedrock, carrying out well diameter expansion to 900mm, putting in a phi 720mm surface sleeve, returning well cementation pure cement slurry to the ground, secondly carrying out grading expansion to the top interface of a roof water-bearing layer, carrying out well diameter expansion to 650mm, putting in a phi 540mm technical sleeve, returning well cementation pure cement slurry to the ground, carrying out grading reaming drilling to the position 5m below the top interface of a transition layer below the roof water-bearing layer after three-step drilling through bridge plugs, designing a water storage bin, wherein the depth of the water storage bin can be determined according to actual conditions, but ensuring that the thickness of the bottom surface of the water storage bin is not less than 3m from the top interface of the coal seam, carrying out grading expansion to 500mm, adding sodium carbonate into circulating drilling fluid to adjust the pH value of the drilling fluid to be alkaline, dissolving the bridge plugs at the front ends of all upward inclined branch horizontal holes, enabling water enriched in the roof water-bearing layer to enter a large-diameter well, carrying out pumping the discharge capacity of the circulating fluid, washing the sediment in the large-diameter drainage well, and then putting down a large-size phi 460mm steel screen into the bottom hole.
Thus, the present invention has the following advantages over the prior art: (1) The threat of water damage to the roof of the coal seam can be treated before the coal mine is built, namely, the threat of water damage to the roof of the coal seam is treated in advance on the ground; (2) The water damage treatment construction environment of the coal seam floor is transferred from underground coal mine to the ground, so that the working construction environment of workers is more friendly; (3) The drilled branches are blocked by adopting the soluble bridge plug, so that the influence of formation water on the performance of drilling fluid can be avoided, and meanwhile, the bridge plug is dissolved after drilling is finished, so that the process of milling the bridge plug is avoided; (4) According to earthquake and other prospecting geological data of a coal mine area, the method for controlling water damage by drilling and grouting along the water-bearing rock stratum of the coal seam floor by combining the ground multi-branch horizontal directional well can completely eliminate the water damage threat of the roof and the floor of the coal seam to be mined before the coal mine is not built in the whole area, namely realize regional water damage control of the coal mine, ensure that no water damage influence exists during the period from well building to well closing of the whole coal mine, and realize safe and efficient continuous mining of the coal seam.
Drawings
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the disclosure.
FIG. 1 is a schematic illustration of a vertical well bore structure of the present invention.
FIG. 2 is a schematic illustration of a horizontal projection well location and well trajectory deployment of the present invention.
FIG. 3 is a partially enlarged view of a horizontal projection well location and well trajectory deployment schematic of the present invention.
Embodiments of the present invention will be described with reference to the accompanying drawings.
In the figure, a multi-branch upward-tilting horizontal well surface casing 1, a multi-branch upward-tilting horizontal well technical casing 2, a multi-branch upward-tilting horizontal well three-opening small-size steel screen pipe 3, a large-diameter drainage well surface casing 4, a large-diameter drainage well technical casing 5, a large-diameter drainage well three-opening large-size steel screen pipe 6, a submersible pump 7, a drainage pipe 8, a roof aquifer 9, a transition layer 10, a coal seam 11, a hanger 12, a landing point 13 and a sidetracking point 14.
Detailed Description
Examples
Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
As shown in FIG. 1, in the method for advanced pre-drainage of the water-bearing layer of the roof of the coal seam according to the embodiment, a ground multi-branch upward-tilting horizontal well and a large-diameter drainage well are drilled, a high-power large-lift submersible pump is arranged in the large-diameter well, and roof-enriched water flowing through a three-opening sieve tube of the multi-branch upward-tilting horizontal well is discharged from the bottom of the large-diameter drainage well to the ground for utilization, so that advanced pre-drainage of the water-bearing layer of the roof of the coal seam is realized.
The three-well-body structure is designed in the ground multi-branch upward-tilting horizontal well, a drill bit with the design phi 349.25mm is drilled into a stable bedrock for 5m, a surface sleeve with the diameter phi 273.05mm is placed, well cementation pure cement slurry is returned to the ground, a drill bit with the design phi 222.25mm is directionally drilled to a design horizontal landing point at the bottom of a roof aquifer, a technical sleeve with the diameter phi 200.03mm is placed, well cementation pure cement slurry is returned to the ground, a drill bit with the design phi 152.4mm is horizontally drilled from the landing point along the bottom of the roof aquifer for about 5m, namely a side drilling point, all three branch holes are drilled from the same side drilling point side drilling to obtain multi-branch horizontal branch holes, the success rate of side drilling can be controlled efficiently, and meanwhile, the side drilling data of the branch holes on the side drilling point can be used for reference, and the success or not of the side drilling of the branch holes can be monitored conveniently and rapidly in real time.
Each branch hole starts to increase well inclination from a side drilling point, a plurality of upward inclined branch holes are drilled by adjusting azimuth, the hole distribution distance of the horizontal plane of each plurality of upward inclined branch holes is about 30-45 m, each branch hole is designed to penetrate through an enriched water area of a roof water-bearing layer, each branch hole is drilled to a designed depth, a three-opening small-size high-pressure resistant phi 130mm steel screen pipe is arranged, pure cement injection well cementation is not needed, a three-opening small-size steel screen pipe is not arranged between a landing point and the side drilling point, a reverse soluble bridge plug which is easy to dissolve in alkaline liquid is arranged at the foremost end (near the vertical shaft) of each branch hole, the water pressure in each branch hole is larger, the bridge plug is tightly set, so that the drilling liquid performance of the drilling process of the next branch hole is not influenced by water in the roof water-bearing layer of the branch Kong Shufang, and the designed plurality of branch holes are drilled in a pushing manner. The large-size steel screen pipe is arranged between the landing point and the side drilling point underground through the large-diameter drainage hole, so that the space between the landing point and the side drilling point must be ensured without arranging the three-opening small-size steel screen pipe between the landing point and the side drilling point, and the large-size steel screen pipe is conveniently arranged under the side drilling point.
The large-diameter drainage well adopts a three-open well deep structure, and firstly adopts a small-size phi 152.4mm drill bit to drill pilot holes along a vertical central axis between a second-open main hole landing point and a third-open side drilling point of the multi-branch upward-inclined horizontal well, so that the communication between the pilot holes and the multi-branch horizontal well is realized, the pilot holes are positioned at 1m on the top interface of a roof water-bearing layer, and drillable bridge plugs are put into the pilot holes to seal the pilot holes, thereby ensuring the normal circulation operation of the subsequent large-diameter well in the step reaming drilling. The method comprises the steps of firstly carrying out grading drilling to stabilize bedrock, carrying out well diameter expansion to 900mm, putting in a phi 720mm surface sleeve, returning well cementation pure cement slurry to the ground, secondly carrying out grading expansion to the top interface of a roof aquifer, carrying out well diameter expansion to 650mm, putting in a phi 540mm technical sleeve, returning well cementation pure cement slurry to the ground, carrying out grading reaming drilling to the position 5m below the top interface of a transition layer below the roof aquifer after three-step drilling through bridge plugs, designing a water storage bin, wherein the depth of the water storage bin can be determined according to actual conditions, but ensuring that the thickness of the bottom surface of the water storage bin is not less than 3m from the top interface of the coal seam, carrying out grading expansion to 500mm, adding sodium carbonate into circulating drilling fluid to adjust the pH value to be alkaline, dissolving the bridge plugs at the front ends of all upward inclined branch horizontal holes, enabling water enriched in the roof aquifer to enter a large-diameter well, carrying out pumping capacity adjustment of the circulating fluid, washing the sediment in the large-diameter drainage well, putting in a large-size steel screen pipe to the bottom well, and hanging the large-size steel screen pipe at the bottom through the large-diameter suspension sleeve pipe.
The flow of this embodiment is described in detail below with reference to fig. 1-2. The ground advanced pre-drainage method for the water bearing layer of the coal seam roof of the embodiment comprises the following steps:
(1) Determining the roof layer of the coal seam to be drained according to the earthquake and other prospecting geological data of the earlier coal mine area, performing well position deployment of a ground multi-branch upward-tilting horizontal well and a large-diameter well, determining specific relative position coordinates of all well heads, and performing well structure and track design of all wells.
(2) The method comprises the steps of implementing ground multi-branch upward-tilting horizontal well drilling, adopting a three-open-well structure, drilling a plurality of upward-tilting branch holes by adopting a phi 349.25mm drill bit, drilling a stable bedrock 5m, lowering a phi 273.05mm surface sleeve 1, returning well cementation pure cement slurry to the ground, directionally drilling a second open-main hole to the bottom of a designed horizontal landing point 13 at the top plate aquifer 9 by adopting a phi 222.25mm drill bit, lowering a phi 200.03mm technical sleeve 2, returning well cementation pure cement slurry to the ground, horizontally drilling a side drilling point 14 which is approximately 5m along the bottom of the top plate aquifer 9 by adopting a phi 152.4mm drill bit from the landing point 13, starting increasing well inclination, adjusting azimuth, drilling a plurality of upward-tilting branch holes, drilling a plurality of upward-tilting branch hole horizontal plane distribution holes (shown in a figure 2), designing an enriched water area of each branch hole to penetrate through the top plate aquifer 9, drilling each branch hole to a designed depth, lowering a steel screen 3 with a three-opening small size to be free of pure cement, not lowering a steel screen 3 between the landing point 13 and the side drilling point 14, and the three-opening small size being required to be in the depth, and the water-jet plugging performance of the drilling plug being tightly sealed by the top plate 62 when drilling the three-opening branches is designed to be more than the top plate water-tilting.
(3) And the large-diameter drainage well is drilled, the large-diameter drainage well adopts a three-hole structure, a small-size phi 152.4mm drill bit is firstly adopted to drill pilot holes along the vertical central axis between the two-hole landing points 13 and the three-hole side drilling points 14 of the multi-branch upward-tilting horizontal well, the communication of the pilot holes and the multi-branch upward-tilting horizontal well is realized, the position 1m below the top interface of the roof aquifer 9 is positioned, and the drillability bridge plug is plugged in the large-diameter drainage well, so that the normal circulation operation of the subsequent large-diameter drainage well graded reaming drilling is ensured. After the pilot hole penetrates through the aquifer, the pilot hole is communicated with the multi-branch upward-inclined horizontal hole, and the drillable bridge plug is lowered, so that the pilot hole above the top interface of the aquifer of the coal seam roof is temporarily closed, the drilling fluid circulation of the subsequent normal drilling process of the pilot hole into the large-diameter drainage well through grading reaming can be ensured to be normal, and the reaming is finished, so that the bridge plug is penetrated. The method comprises the steps of firstly carrying out grading drilling to stabilize bedrock, carrying out well diameter expansion to 900mm, putting down a phi 720mm surface sleeve 4, carrying out well cementation pure cement slurry to the ground, secondly carrying out grading expansion to the top interface of a roof aquifer 9, carrying out well diameter expansion to 650mm, putting down a phi 540mm technical sleeve 5, carrying out well cementation pure cement slurry to the ground, carrying out grading reaming drilling to the position 5m below the top interface of a transition layer 10 below the roof aquifer 9 after three-step drilling through bridge plugs, wherein the specific water sump depth can be determined according to practical conditions, but ensuring that the thickness of the water sump bottom surface is not less than 3m from the top interface of a coal seam 11, carrying out three-step well diameter expansion to 500mm, then adding sodium carbonate into circulating drilling fluid to adjust the pH value of the drilling fluid to be alkaline, dissolving the bridge plugs at the front ends of the inclined branch horizontal holes, enabling water flow enriched in the roof aquifer 9 to enter a large-diameter drainage well through each branch hole, carrying out discharge capacity adjustment by a slurry pump of the circulating drilling fluid, washing large-diameter drainage well, carrying out sediment sedimentation in the large-size steel screen, and then putting down large-size phi 460mm steel screen 6 to the bottom well, and carrying out large-size steel screen 6 to the bottom through the large-size hanger 12 at the top end of the sleeve 5.
(4) The water-saving type sand and gravel sediment device is characterized in that a large-power and large-lift submersible pump 7, a waterproof cable, a drainage pipeline 8 and the like are installed and connected in a large-diameter drainage well, enriched water flowing through a top plate water-bearing layer 9 in a multi-branch upward-tilting type horizontal well three-opening screen pipe 3 is discharged to the ground from a water sump at the bottom of the large-diameter drainage well by the submersible pump 7, so that the advanced pre-drainage of the ground of the top plate water-bearing layer 9 of a coal seam 11 is realized, the submersible pump 7 is placed in a water storage sump, the placed depth is 2m away from the bottom of the well, and the remaining 2m space is used for sand and gravel sediment.
As can be seen from the above description, the embodiment can realize the treatment of the water damage threat of the roof of the coal seam before the coal mine is built, namely, the water damage threat of the roof of the coal seam is treated on the ground in advance; according to the embodiment, the water damage treatment construction environment of the coal seam floor is transferred from underground coal mines to the ground, so that the working construction environment of workers is more friendly; the drilled branches are blocked by the soluble bridge plug, so that the influence of formation water on the performance of drilling fluid can be avoided, meanwhile, the bridge plug is dissolved after drilling is finished, and the process of milling the bridge plug is avoided; according to earthquake and other prospecting geological data of a coal mine area, the method for controlling water damage by drilling and grouting along the water-bearing rock stratum of the coal seam floor by combining the ground multi-branch horizontal directional well can completely eliminate the threat of water damage on the top and bottom of the coal seam to be mined before the coal mine is not built in the whole area, namely realize regional water damage control of the coal mine, ensure that no water damage influence exists during the period from well building to well closing of the whole coal mine, and realize safe, efficient and continuous mining of the coal seam.
Note that references in the specification to "one embodiment," "an embodiment," "example embodiments," "some embodiments," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. The method for advanced pre-drainage of the ground of the water-bearing layer of the roof of the coal seam is characterized by comprising the following steps:
constructing a ground multi-branch upward-tilting horizontal well, wherein each branch hole of the upward-tilting horizontal well penetrates through an enriched water area of a roof aquifer;
constructing a large diameter drainage well leading to a water-containing enrichment and collection area of the top plate, wherein the large diameter drainage well is communicated with the upward-tilting horizontal well;
a drainage device is arranged in the large-diameter drainage well, and drainage treatment is carried out by using the drainage device;
a large-diameter drainage well surface layer sleeve (4), a large-diameter drainage well technical sleeve (5) and a large-diameter drainage well three-opening large-size steel screen pipe (6) are sequentially arranged at the bottom of the large-diameter drainage well from outside to inside; the upward-tilting horizontal well is communicated with a large-diameter drainage well through the three-opening large-size steel screen pipe (6);
the center of the large-diameter drainage well is positioned on the midpoint of the connecting line of the landing point and the sidetracking point of the upward-inclined horizontal well; the landing points are landing points of the deflecting section of the upward-tilting horizontal well at the bottom of the roof aquifer, and the side drilling points are starting points of branch holes of the upward-tilting horizontal well;
all branch holes of the multi-branch upward-tilting horizontal well are drilled from the same side drilling point, and each branch hole is a plurality of upward-tilting branch holes obtained by increasing well inclination and adjusting azimuth drilling from the side drilling point;
the multi-branch upward-tilting horizontal well adopts a three-open well design, wherein a drill bit with the diameter of 349.25mm is drilled into a stable bedrock for 5m, a surface sleeve with the diameter of 273.05mm is placed in the drill bit, and well cementation pure cement slurry is returned to the ground; drilling a drill bit with the diameter of phi 222.25mm for the secondary main hole design to a design horizontal landing point at the bottom of a roof aquifer, putting a technical sleeve with the diameter of phi 200.03mm into the drill bit, and returning the well cementation pure cement slurry to the ground; a three-hole main hole design phi 152.4mm drill bit drills horizontally from a landing point to a side drilling point at about 5m along the bottom of a roof aquifer; and all branch holes of the upward inclined horizontal well are drilled from the same sidetrack point side drill to form multi-branch horizontal branch holes.
2. The method for advanced pre-drainage of the ground surface of a roof aquifer of a coal seam of claim 1, wherein the large-diameter drainage well is drilled below a transition layer roof interface below the roof aquifer.
3. The method for advanced pre-drainage of the ground of the aquifer of the roof of the coal seam according to claim 1, wherein a reverse soluble bridge plug which is easy to dissolve in alkaline liquid is put into the front end of a branch hole of the multi-branch upward-inclined horizontal well; after the bridge plugs are drilled through the large-diameter drainage well, alkaline materials are added into the circulating drilling fluid to dissolve the bridge plugs at the front ends of the horizontal holes of the upward-inclined branches.
4. The method for advanced pre-drainage of the ground surface of the aquifer of the roof of the coal seam according to claim 1, wherein the large-diameter drainage well adopts a three-well deep structure, and wherein: the first drilling adopts a small-size phi 152.4mm drill bit to drill pilot holes along the vertical central axis between the landing point of the second main hole and the third side drilling point of the multi-branch upward-tilting horizontal well, so that the pilot holes are communicated with the multi-branch horizontal well, the pilot holes are positioned at 1m on the top interface of the top plate aquifer, drillable bridge plugs are placed in the pilot holes to seal, and the normal circulation operation of the subsequent large-diameter well graded reaming drilling is ensured; the method comprises the steps of firstly carrying out grading drilling to stabilize bedrock, carrying out well diameter expansion to 900mm, putting in a phi 720mm surface sleeve, returning well cementation pure cement slurry to the ground, secondly carrying out grading expansion to the top interface of a roof water-bearing layer, carrying out well diameter expansion to 650mm, putting in a phi 540mm technical sleeve, returning well cementation pure cement slurry to the ground, carrying out grading reaming drilling to the position 5m below the top interface of a transition layer below the roof water-bearing layer after three-step drilling through bridge plugs, designing a water storage bin, wherein the depth of the water storage bin can be determined according to actual conditions, but ensuring that the thickness of the bottom surface of the water storage bin is not less than 3m from the top interface of the coal seam, carrying out grading expansion to 500mm, adding sodium carbonate into circulating drilling fluid to adjust the pH value of the drilling fluid to be alkaline, dissolving the bridge plugs at the front ends of all upward inclined branch horizontal holes, enabling water enriched in the roof water-bearing layer to enter a large-diameter well, carrying out pumping the discharge capacity of the circulating fluid, washing the sediment in the large-diameter drainage well, and then putting down a large-size phi 460mm steel screen into the bottom hole.
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