A drainage hole for draining karst water in thick layers of coal seam floor and its construction method

Abstract

The present invention discloses a water collection and drainage borehole and a construction method for dewatering a thick karst water layer at the bottom of a coal seam, including: Step 1: Determine the target water level drawdown S of water drainage and pressure reduction 降 and the safety water pressure P 安 ; Step 2: Set the position of the water collection and drainage borehole group; a water collection and drainage borehole group includes a main water collection and drainage borehole and N water collection and drainage branch boreholes; according to the target water level drawdown S determined in Step 1 降 , set the trajectory of the directional deviation section of the water collection and drainage borehole group. There is an underground roadway within a radius of 15 to 50 m of the trajectory of the directional deviation section, and the elevation of the underground roadway is less than the water level elevation after reaching the dewatering target, that is, H 巷 < H 水 - S 降 , H 巷 roadway elevation, m; H 水 water level elevation of the thick karst aquifer before dewatering, m; the water collection and drainage borehole group is arranged along the working face strike and extends towards the cutting hole direction of the working face. The water collection and drainage borehole of the present invention dewater the aquifer in the form of a "water collection corridor", and multiple water collection and drainage branches jointly form a long and wide dewatering area, eliminating the local high water level formed by the inhomogeneity of the aquifer in the underground water discharge hole.

Description

Technical Field

[0001] The invention belongs to the technical field of drainage and pressure reduction of coal mine floor aquifers, and relates to a drainage hole for draining karst water in a thick layer of a coal seam floor and a construction method. Background Art

[0002] Ordovician and Cambrian limestones are commonly developed at the base of coal seams in my country, which are extremely thick karst aquifers with a thickness generally greater than 500m. After decades of high-intensity mining, the shallow coal resources in my country's North China coalfields have gradually dried up, and most mines have moved to deep mining. Some mines have mined at depths of up to a thousand meters, and the main mining coal seams are close to the Ordovician and Cambrian thick karst aquifers. Under the deep high ground stress, high temperature, high water pressure and high-intensity mining disturbance, the threat of floor water inrush faced by coal seam mining is even more severe. The vast majority of major floor water inrush disasters in my country are related to the Ordovician and Cambrian limestone aquifers.

[0003] At present, the main technologies for preventing and controlling water hazards in the thick limestone floor of deep mining are grouting and drainage and pressure reduction. Grouting and water blocking is to transform a certain thickness of Ordovician or Cambrian limestone aquifer into an aquiclude by drilling and grouting from the ground or underground. Due to the large thickness of limestone, uneven karst development, and the difficulty in controlling the diffusion range of grouting, the transformation effect of thick limestone aquifers is often worse than that of thin limestone. Usually, after the working face is formed, drainage holes are constructed to reduce water pressure, and then mining is carried out under pressure, that is, the "blocking and drainage combined" water prevention and control mode. Drainage and pressure reduction is an important means of preventing and controlling water in the floor of coal mines. During the excavation and mining process, drainage holes are constructed to discharge water from the thick limestone aquifer in the floor. Mining is carried out after the limestone water pressure is reduced to a safe water pressure, which can fundamentally eliminate the hidden danger of water inrush and achieve inherent safety. Drainage and pressure reduction is the most effective water prevention and control method for water mining of high-pressure limestone in the floor.

[0004] At present, the problems and disadvantages of hydrophobic pressure reduction technology are:

[0005] (1) Drainage and pressure reduction drilling needs to be carried out after the working face tunnel is formed. Construction under high water pressure poses huge safety hazards, including the potential risk of water inrush from hidden structures that may be exposed during excavation and the safety hazard of spray holes when constructing drainage holes under high water pressure.

[0006] (2) The thick limestone aquifers at the base generally have weak hydraulic connections on the plane, well-developed vertical fractures, and may be separated into multiple hydrogeological units by water-blocking faults. The underground drainage boreholes are in short-line contact with the aquifer and the invalid section (from the opening to the exposure) is long. The probability of exposing the vertical fractures of the aquifer is low. The drainage of a single borehole forms a high-angle drop funnel. To achieve regional drainage, a large number of boreholes need to be intensively constructed to increase the drainage volume and efficiency. If the drainage volume is large, a special drainage tunnel needs to be constructed for drainage. Therefore, the drainage and pressure reduction project is large and the cycle is long.

[0007] (3) During the mining process of the working face, the drainage holes in the two tunnels need to be grout-closed, and the water level will gradually recover. Although the drainage holes in the deep rock tunnels in the mining area are kept drained, the drainage range is limited. With the closure of the working face, the water pressure of the floor of the goaf will gradually increase. When it exceeds the safe water pressure, it will break through the floor waterproof layer and cause water inrush from the floor of the goaf. At this time, the water inrush channel is unclear and it is very difficult to find, which brings great difficulties to disaster management. For example, the large-scale water inrush accident of the old kiln floor of Xinan Coal Mine occurred on October 25, 2021. Therefore, it is very necessary to maintain continuous drainage and pressure reduction.

[0008] To this end, the present invention aims at the above problems and shortcomings, through intensive research and design, and integrating many years of experience and achievements in related professions, to research and design a collection and drainage hole for draining thick karst water in the bottom plate of the coal seam, so as to overcome the above defects. Summary of the invention

[0009] The purpose of the present invention is to provide a drainage hole and construction method for draining karst water in thick layers of coal seam bottom plate, and to solve the problems existing in the prior art: (1) safety issues in the construction of underground drainage holes under high water pressure; (2) large workload and long cycle in the intensive construction of drainage holes; (3) continuous drainage problem after the working face is mined.

[0010] The technical solution adopted by the present invention is:

[0011] A drainage hole for draining karst water in a thick layer of coal seam floor, comprising:

[0012] Step 1: Determine the target water level drop S for decompression 降 and safety water pressure P 安 ;

[0013] Step 2: Set the location of the collection and sparseness hole group; a collection and sparseness hole group includes a collection and sparseness main hole and N collection and sparseness branch holes;

[0014] According to the target water level drawdown S determined in step 1 降 , set the directional deflection section trajectory of the collection and drainage hole group, there is an underground tunnel within the radius of 15 to 50m of the directional deflection section trajectory, and the elevation of the underground tunnel is lower than the water level elevation after the drainage and drainage target is reached, that is, H 巷 <H 水 -S 降 , H 巷 Lane elevation, m; H 水 The water level elevation of the thick karst aquifer before drainage, m;

[0015] The collection and distribution hole group is arranged along the direction of the working face and extends towards the cutting direction of the working face;

[0016] If the width of the working face is less than 110m, two collecting and distributing branch holes are arranged, located at a horizontal distance of 15 to 25m on the outside of the two lanes of the working face;

[0017] If the width of the working face is greater than 110m, three collecting and draining branch holes are arranged, one collecting and draining branch hole is arranged below the central axis of the working face, and one collecting and draining branch hole is arranged on the outside of the two tunnels at a horizontal distance of 15 to 25m respectively.

[0018] Optionally, for water-bearing plots divided by water-blocking faults outside the drainage mining area, the drainage branch holes are obliquely intersected with the water-blocking faults, with an intersection angle of 60 to 90°.

[0019] Optionally, the safety water pressure P 安 According to formula (1), we can get:

[0020] P 安 =Ts(H 隔 -H 破 ) / A (1);

[0021] Where: P 安 is the safety water pressure, MPa; Ts is the critical water inrush coefficient, which is taken according to the data of mine water inrush events. If there is no data, it is taken as 0.06~0.1MP / a; H 隔 is the minimum thickness of the impermeable rock layer, m; H 破 is the depth of floor damage caused by mining, which is determined based on the measured data of the mine. If there is no data, it is taken as 18 to 25 m. A is the safety factor, which is taken as 1.2.

[0022] Optionally, the water level drop S 降 According to formula (2), we can get:

[0023] S 降 =100(P 水 -P 安 ) (2);

[0024] Where: S 降 is the target water level drawdown, m; P 水 is the maximum water pressure, MPa.

[0025] A method for constructing a collection and drainage hole for draining karst water in a thick layer on a coal seam floor is provided, and any collection and drainage hole for draining karst water in a thick layer on a coal seam floor described in the present invention is constructed.

[0026] Optional, including:

[0027] Step 1: Construction of the main drilling hole; Directional drilling from the ground to 40 to 60 meters below the thick karst aquifer, insert the casing, and the bottom of the main drilling hole is inclined by 80 to 95 degrees;

[0028] Step 2: Construct branch holes; the branch holes are drilled at a depth of 40 to 80 m below the thick karst aquifer; the first branch hole is drilled directly from the bottom of the casing to the designed position, and the second or third branch hole is drilled to the designed position after a window is opened in the casing and side-drilled.

[0029] Optionally, the terminal hole of the collecting and draining branch hole should exceed the distance L, m of the cut eye; or pass through all water-blocking faults;

[0030] L=H 破 ×tanβ+30;

[0031] Where: β is the bottom plate failure boundary angle.

[0032] Optionally, the method further includes step 3: constructing a drainage tunnel to expose the casing;

[0033] The drainage tunnel is constructed by opening a stone gate from the permanent main tunnel. The upper limit elevation of the drainage tunnel is calculated according to the following formula. The casing is designed to be 30 to 50 meters away from the main tunnel. The drainage tunnel is constructed until the casing is exposed.

[0034] H 巷 <H 水 -S 降 .

[0035] Optionally, the method further includes step 4: separating and water stopping inside the casing; placing two sections of packers inside the casing, each of which is 20 to 30 meters above and below the position where the casing is exposed by water discharge.

[0036] Step 5: Install the water discharge device to discharge water; install the water discharge valve, blowout preventer and pressure gauge on the casing in the drainage tunnel, connect them to the drainage pipe system, and discharge the water from the thick karst aquifer.

[0037] Optionally, the drainage of the thick karst aquifer water should meet the water pressure P of the water outlet in the drainage tunnel, MPa;

[0038] P<P 安 -ΔH / 100;

[0039] ΔH, the difference between the drainage tunnel elevation and the coal seam elevation, m.

[0040] The beneficial effects of the present invention are

[0041] (1) The collection and drainage branches drain the limestone aquifer in the form of a "water collection corridor". Multiple collection and drainage branches form a long and wide drainage area, replacing the "well"-like drainage funnel formed by the underground drainage holes. At the same time, the collection and drainage branches can penetrate the water-isolating faults and connect multiple closed hydrogeological units to achieve large-scale drainage. The water level of the limestone aquifer can be reduced flatly, eliminating the local high water level formed by the underground drainage holes due to the heterogeneity of the limestone aquifer.

[0042] (2) Drilling holes on the ground can be carried out before coal tunnel excavation. On the one hand, before the installation of the water discharge device, the high-pressure water is blocked by the packer, and the installation process is not carried out under high water pressure conditions. On the other hand, the water in the limestone aquifer is discharged in advance to reduce the water pressure. The advanced exploration drilling holes in the coal tunnel excavation process are constructed under safe water pressure, which solves the safety problem of construction under high water pressure underground.

[0043] (3) The drainage and branch holes are all effective in depth. The permanent main tunnel is used for drainage, which reduces the amount of drilling and drainage tunnel engineering. The drainage and branch hole construction and tunnel excavation do not occupy the same space, avoiding the impact of cross-construction and shortening the period for completing drainage and pressure reduction work.

[0044] (4) The drainage port is located in the permanent main tunnel and is not affected by mining. After the working face is mined, it can still maintain effective drainage and pressure reduction to prevent the water level from rising and breaking through the bottom of the goaf and causing water inrush disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the cross section of the thick karst aquifer in the coal seam floor;

[0046] Figure 2 It is a schematic diagram of the collection and distribution holes in the thick karst aquifer on the bottom plate of the working face;

[0047] Figure 3 This is a schematic diagram of the side drilling with a whipstock window;

[0048] Figure 4 It is a schematic diagram of the casing separation water stop and water discharge device in the drainage tunnel;

[0049] Figure 5 It is the plan view of the arrangement of the collection and distribution holes when there are multiple water-blocking faults;

[0050] The symbols in the figure represent:

[0051] 1-hugely thick karst aquifer, 2-main collection and drainage hole, 3-branch collection and drainage hole, 4-coal seam, 5-water-isolating fault, 6-permanent tunnel, 7-drainage tunnel, 8-casing, 9-geological flower pipe, 10-working face, 11-whipstock; 12-drill bit, 13-upper packer, 14-lower packer, 15-drill pipe, 16-pressure gauge, 17-blowout preventer, 18-drain valve, 19-drainage pipeline. DETAILED DESCRIPTION

[0052] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] The thick karst aquifer 1 mentioned in the present invention is a karst aquifer, which is a phenomenon of soluble rock dissolution. The caves formed after the dissolution contain water, which is the aquifer.

[0054] A water-blocking fault is a fault zone formed when rock strata are dislocated due to crustal movement. The broken rocks in the fault zone are turned into mud, and the water content and water conductivity deteriorate, dividing the aquifer into multiple hydrological units without hydraulic connection.

[0055] Permanent tunnel 6 is a passage used for a long time during mine production, including tunnels used for ventilation, transportation, pedestrian traffic, etc.

[0056] The drainage lane 7 is a drainage lane specially constructed for draining water from the aquifer. In the present invention, it refers to a lane specially used for exposing the casing of the collecting and drainage holes and installing a drainage device to carry out drainage work.

[0057] Part 1: The arrangement scheme of the drainage hole for draining the thick karst water in the coal seam floor of the present invention includes:

[0058] Step 1: Determine the target water level drop (S 降 ) and safety water pressure (P 安 ).

[0059] P 安 =Ts(H 隔 -H 破 ) / A (1);

[0060] Where: P 安 is the safety water pressure, MPa; Ts is the critical water inrush coefficient, which is taken according to the data of mine water inrush events. If there is no data, it is 0.06-0.1MP / a; if there is a broken floor with developed faults, it is 0.06MPa / m; if there is a complete floor, it is 0.1MPa / m; H 隔 is the minimum thickness of the impermeable rock layer, m; H 破 It is the depth of floor damage caused by mining, which is determined based on the measured data of the mine. If there is no data, it is taken as 18 to 30 m. A is the safety factor, which is generally taken as 1.2.

[0061] S 降 =100(P 水 -P 安 ) (2);

[0062] Where: S 降 is the target water level drawdown, m; P 水 is the maximum water pressure, MPa, which is the three-year average maximum water pressure of the Changguan hole in the thick limestone aquifer in the drainage area.

[0063] Hydrodegassing and pressure reduction is the process of releasing water from aquifers by drilling holes to lower the water level to below the safe water head.

[0064] Step 2: Design the hole group

[0065] Combination Figure 1 A collection and sparseness hole group includes a collection and sparseness main hole 2 and N collection and sparseness branch holes 3.

[0066] According to the target drawdown determined in step 1, the directional deflection section (i.e. casing section) trajectory of the collection and drainage hole group is designed. There should be an underground permanent tunnel 6 within a radius of 15 to 50 m within the casing section trajectory, and the elevation of the permanent tunnel 6 should be less than the target of achieving the drainage and drainage (safety water pressure P 安 ) after the water level, that is, H 巷 <H 水 -S 降 , H 巷 Permanent tunnel elevation, m; H 水 The water level elevation of the thick karst aquifer before drainage, m. If the permanent tunnel 6 is less than 15m away from the casing section trajectory, it may pose a safety threat to the permanent tunnel 6 during the drilling process; if the permanent tunnel 6 is more than 50m away from the casing section trajectory, the constructed drainage tunnel 7 may not be able to expose the casing 8 due to the limitation of directional accuracy, so it needs to be set within this range. For the drainage of the thick karst aquifer 1 water of the working face 10, the drainage hole group is arranged along the working face strike and extends in the direction of the 10 cut of the working face. The number of boreholes is arranged according to the width of the working face 10: if the width of the working face 10 is less than 110m, two drainage branch holes 3 are arranged, which are located at a horizontal distance of 15 to 25m on the outside of the two tunnels of the working face 10; if the width of the working face 10 is greater than 110m, three drainage branch holes 3 are arranged, one drainage branch hole 3 is arranged below the central axis of the working face 10 strike, and one drainage branch hole 3 is arranged at a horizontal distance of 15 to 25m on the outside of the two tunnels.

[0067] For water-bearing plots divided by water-blocking faults outside the drainage mining area, the drainage branch holes 3 are obliquely intersected with the water-blocking faults, with an intersection angle of 60 to 90°.

[0068] The design of the borehole can be designed separately according to whether the drainage area is arranged at the working face or outside the mining area. For the Cambrian or Ordovician thick limestone aquifers, they are generally moderately to strongly water-rich, or even extremely water-rich. For the drainage of the thick aquifers under the working face, the boreholes can also be arranged according to the width of the working face. Under the existing technical conditions in my country, the width of the working face is generally 100 to 300m, and the drainage target can also be achieved according to the modified plan. For the thick limestone water-bearing blocks blocked by water-blocking faults, it is necessary to drill through all water-blocking faults.

[0069] The second part, the method for constructing a collection and drainage hole for draining karst water in a thick layer of a coal seam floor of the present invention comprises:

[0070] Step 1: Construction of main collection and drainage hole 2

[0071] Combination Figure 1 The drill bit 12 is directionally drilled from the ground to 40 to 60 meters below the thick karst aquifer, and the casing is lowered into the cementing well to isolate the upper stratum. The bottom of the main hole 2 is inclined by 80 to 95 degrees.

[0072] Select primary or secondary casing according to the thickness of the loose layer. Specifically: when the thickness of the loose layer is less than or equal to 20m, the wall protection pipe is used under the loose layer, and cementing is not required. The main gathering and sparsely distributed hole adopts primary casing with a casing diameter of 244.5mm~mm244.5mm; when the thickness of the loose layer is greater than 20m, the main gathering and sparsely distributed hole is equipped with a primary casing in the loose layer section with a diameter of 355~mm244.5mm, cement cementing, and the secondary casing is installed after the bedrock section is drilled to the designed position. The secondary casing has a diameter of 244.5mm~177.8mm.

[0073] Step 2: Construction of collection and distribution branch holes 3

[0074] The branch hole 3 is drilled at a depth of 40 to 80 m below the thick karst aquifer. The distance L that the terminal hole of the branch hole 3 should exceed the cut hole is calculated as follows:

[0075] L=H 破 ×tanβ+30;

[0076] Where: β is the bottom plate failure boundary angle.

[0077] Or penetrate all the impermeable faults (for extremely thick limestone aquifers divided by drainage impermeable faults).

[0078] The first collecting and draining branch hole 3 is directly drilled from the bottom of the casing 8 to the designed position, and the second and third branch holes are drilled to the designed positions after opening windows and side drilling in the casing 8 using the whipstock 11.

[0079] After each branch hole 3 is completed, a geological flower pipe 9 is lowered, and then the hole is washed and water is pressed to increase permeability. When washing the hole, clean water is used to complete 3 to 5 cycles. When water is pressed to increase permeability, the hole pressure is 1.5 to 2 times the maximum water pressure. The second and third branch holes should have the whipstock 11 recovered after the hole washing and water pressure increase permeability are completed.

[0080] Step 3: Exposing the casing in the drainage tunnel

[0081] To ensure the safety of the permanent tunnel 6 during the drilling of the main collection and drainage hole 2, the casing 8 is designed to be 30 to 50 meters away from the main tunnel. The drainage tunnel 7 is constructed by opening the stone gate of the permanent tunnel 6. The upper limit elevation of the drainage tunnel 7 is calculated according to the following formula. The drainage tunnel 7 is constructed until the casing 8 is exposed.

[0082] H 巷 <H 水 -S 降 .

[0083] Step 4: Separation and water stop inside the casing

[0084] Two packers are placed inside the casing 8, 20 to 30 m above and below the position where the casing is exposed by drainage.

[0085] The upper packer 13 is located above the drainage tunnel, and the lower packer 14 is located below. After the packers are connected with the drill pipe 15, they are sent into the casing 8, and then pressurized to make the capsule on the packer expand and get stuck in the casing to achieve water stopping.

[0086] Step 5: Install the water discharge device to discharge water

[0087] A hole is cut in the casing 8 in the drainage lane 7, and drainage devices such as a drainage valve 18, a blowout preventer 17 and a pressure gauge 16 are installed, and connected to the drainage pipeline 19 system.

[0088] After the water release device is installed, the packer is depressurized and taken out using the drill pipe 15.

[0089] Open the drain valve 18 to drain the limestone aquifer water. The water pressure (P) at the drain outlet in the drain tunnel 7 should be drained to P<P 安 -ΔH / 100. P——water pressure at the drainage tunnel outlet; ΔH——the difference between the drainage tunnel elevation and the coal seam elevation, m.

[0090] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0091] Embodiment 1:

[0092] A mine in Yuzhou Coalfield mines the lower coal group. The maximum buried depth of the coal seam is 918m. The distance between the coal seam floor and the Cambrian thick limestone aquifer is about 70m. The coal seam floor aquiclude is subjected to a water pressure of 9.7MPa, and the water inrush coefficient is greater than 0.1MPa / m, which does not meet the requirements of the floor water control in the "Detailed Rules for Coal Mine Water Control". In order to eliminate the threat of limestone water damage on the roof of the main mining coal seam, the mine organized and implemented the floor water control measures of "floor grouting reinforcement + underground drainage holes". However, with the mining going deeper, the water pressure is getting higher and higher. There are huge safety risks in the construction of grouting holes and drainage holes. The water control project is large in quantity and long in cycle. The working face needs 3 to 5 years of preparation time. Water control seriously restricts the mining and excavation succession. At the same time, after the shallow working face is mined, all drainage holes are closed, and the water level recovery poses a risk of water inrush from the floor of the goaf. To this end, this technology is used to drain and depressurize the thick Cambrian limestone aquifer on the floor, and pressurized mining is carried out after the safe water pressure is reached. The specific implementation method is as follows:

[0093] Step 1: Determine the target water level drop (S 降 ) and safety water pressure (P 安 ).

[0094] P 安 =Ts(H 隔 -H 破 ) / A (1);

[0095] Where: Ts is the critical water inrush coefficient. The fault is not developed in this mine and the floor is intact, so it is 0.1MPa / m; H隔 is the minimum thickness of the impermeable rock layer, which is taken as 70m; H 破 is the mining floor damage depth, which is 21m according to the measured data of the mine; A is the safety factor, which is 1.2. The safe water pressure P is calculated. 安 =4.1MPa;

[0096] S 降 =100(P 水 -P 安 ) (2);

[0097] Where: P 水 is the maximum water pressure, which is 9.7 MPa. The target water level drop S is calculated. 降 =560m;

[0098] Step 2: Design the hole group

[0099] like Figure 2 The width of the drainage and pressure reduction working face is 120m, so a drainage hole group is designed, including 3 drainage branch holes 3.

[0100] Step 3: Construction of the main drainage hole

[0101] The thickness of the loose layer in this mining area was selected to be 288m. The main gathering and drainage hole 2 adopted a secondary casing structure with a primary casing diameter of 244.5mm. It was lowered to 15m below the loose layer and cemented. After drilling to 50m below the Cambrian limestone, the bottom of the well was inclined at 90°, and a secondary casing with a diameter of 177.8mm was lowered and cemented to complete the construction of the main gathering and drainage hole 2.

[0102] Step 4: Construction of branch holes

[0103] The branch hole 3 is drilled at a depth of 60m below the limestone aquifer, and the branch hole 3 is parallel to the direction of the working face 10. The distance L of the terminal hole of the branch hole 3 beyond the cut eye is calculated according to the following formula, and the result is L = 53m;

[0104] L=H 破 ×tanβ+30;

[0105] Where: β is the bottom plate failure boundary angle, which is 78°.

[0106] First, construct the middle collecting and draining branch hole 3, and after completion, wash the hole with clean water for 3 cycles, and use 2 times the hydrostatic pressure of the hole mouth to pressurize the water to increase the permeability. Then, insert the whipstock 11 in the casing 8 at the positions 40m and 80m away from the bottom of the casing, respectively. Figure 3 , use the whipstock 11 to side-drill and construct the other two collecting and draining branch holes 3, wash the holes with clean water for 3 cycles, and use 2 times the hydrostatic pressure at the hole mouth to pressurize and increase permeability.

[0107] Step 5: Exposing the casing in the drainage tunnel

[0108] The drainage roadway 7 is constructed by driving a crossheading from the permanent roadway 6 (the district track main roadway in this example). The elevation of the drainage roadway 7 is calculated to be less than -542 m according to the following formula. A crossheading is driven at the -750 m elevation of the district track main roadway to construct the drainage roadway for 50 m to expose the casing 8.

[0109] H 泄 <H 水 -S 降 =18 - 560 = -542 m;

[0110] Where: H 泄 is the elevation of the drainage roadway, m; H 水 is the elevation of the highest water level, m.

[0111] Step Six: Separating and water-stopping inside the casing

[0112] As shown in Figure 4 , lower two packers inside the casing 8. After connecting the packers with the drill pipe 15, send them into the casing 8. The upper and lower packers are respectively 25 m away from the top and bottom of the drainage roadway 7. Apply pressure to make the capsules on the packers expand and get stuck inside the casing 8 to achieve water-stopping.

[0113] Step Seven: Installing the water discharge device to discharge water

[0114] As shown in Figure 4 , cut an opening in the casing 8 inside the drainage roadway 7, and install water discharge devices such as the water discharge valve 18, the blowout preventer 17, and the pressure gauge 16, and connect them to the drainage pipeline 19 system.

[0115] After the installation of the water discharge device is completed, relieve the pressure on the packer and remove it using the drill pipe 15.

[0116] Open the water discharge valve 18 to drain the water in the limestone aquifer. The measured initial water discharge flow rate is 450 m 3 / h, the water pressure is 7.7 MPa. As the water discharge time increases, the water discharge volume is basically stable at 60 m 3 / h, the water pressure is 1.8 MPa, and the drawdown is 590 m, meeting the conditions for mining with pressure.

[0117] The present invention successfully exposes the water storage space of the extremely thick limestone aquifer by using the gathering and drainage holes, completes the dewatering and pressure reduction work before the driving of the working face roadway, and provides safety guarantee for the safe driving of the coal roadway; replaces the underground water discharge holes, reduces the engineering quantity of the water discharge holes by 5200 m. After the roadway is formed, only geophysical prospecting and drilling verification are required, and then the working face can be mined after the installation is completed, greatly reducing the preparation time of the working face; maintains the dewatering and pressure reduction during the mining process of the working face, eliminating the threat of water inrush from the goaf.

[0118] Embodiment Two:

[0119] In 2017, a coal mine in Huainan Coalfield suffered a major water inrush accident caused by a hidden collapse column in the floor of the working face bottom pumping tunnel and connecting tunnel. The water inrush was caused by the Ordovician limestone aquifer, and the instantaneous water inrush volume reached 14,500 m 3 / h, exceeding the mine's drainage capacity, causing part of the mine to be flooded. After a period of water gushing, the water volume gradually stabilized. It was calculated that the underground drainage volume was about 500-600m 3 / h. At the same time, the water level of the Ordovician limestone water in this mine and the neighboring mines dropped sharply, with the maximum drop of 353.48m to 387.32m. After completing the water blocking work, in order to completely eliminate the threat of Ordovician limestone water, it was decided to drain and reduce the pressure of the Ordovician limestone aquifer outside the mining area. Since the tunnel development in the drainage area has not yet been carried out, and the exploration has found that there are many hidden water-isolating faults, the regional Ordovician limestone aquifer is divided into multiple water level geological units. For this reason, this technology is used to drain and reduce the pressure of the thick Ordovician limestone aquifer on the bottom plate.

[0120] Step 1: Determine the target water level drop (S 降 ) and safety water pressure (P 安 ).

[0121] P 安 =Ts(H 隔 -H 破 ) / A (1)

[0122] Where: Ts is the critical water inrush coefficient. The mine has developed faults and the coefficient is 0.06MPa / m; H 隔 is the minimum thickness of the impermeable rock layer, which is 125.6 m; H 破 is the mining floor damage depth, which is 23.6m according to the measured data of the mine; A is the safety factor, which is 1.4. The safe water pressure P is calculated. 安 =4.4MPa;

[0123] S 降 =100(P 水 -P 安 )

[0124] Where: P 水 is the maximum water pressure, which is 9.4 MPa. The target water level drop S is calculated. 降 =500m;

[0125] Step 2: Design the hole group

[0126] like Figure 5 There are three water-blocking faults in the drainage area. Three drainage branch holes 3 are designed to form a drainage hole group. The extension direction of the drainage branch holes is at an angle of 60 to 90 degrees with the fault strike.

[0127] Step 3: Construction of main collection and drainage hole 2

[0128] The thickness of the loose layer in this mining area is 283m. The main gathering and drainage hole 2 adopts a secondary casing structure. The diameter of the primary casing is 244.5mm. It is drilled down to 283m and cemented. After drilling 40m below the Ordovician limestone, the bottom of the well is inclined at 88°. The secondary casing with a diameter of 177.8mm is lowered and cemented to complete the construction of the main gathering and drainage hole 2.

[0129] Step 4: Construction of collection and distribution branch holes 3

[0130] The branch hole 3 was drilled to a depth of 80m below the limestone aquifer, passing through all the impermeable faults and completely exposing all the thick limestone aquifer blocks divided by the impermeable faults.

[0131] First, the middle collecting and draining branch hole 3 was constructed, and after completion, the hole was washed with clean water for 3 cycles, and water pressure was used to increase permeability with 2 times the hydrostatic pressure at the hole mouth. Then, the whipstock 11 was lowered at the positions 50m and 100m away from the bottom of the casing, and the other two collecting and draining branch holes 3 were constructed by side drilling. The holes were washed with clean water for 3 cycles, and water pressure was used to increase permeability with 2 times the hydrostatic pressure at the hole mouth.

[0132] Step 5: Exposing the casing in the drainage tunnel

[0133] According to the following formula, the elevation of the drainage tunnel is less than -540m. The borehole is exposed by digging the drainage tunnel from the -650m horizontal tunnel underground at a distance of 31m from the borehole casing. An orifice device is installed to connect the drainage pipeline to drain the Ordovician gray aquifer and lower the water level of the Ordovician gray water.

[0134] H 泄 <H 水 -S 降 =-40-500 = -540m;

[0135] Where: H 泄 H is the elevation of the drainage tunnel, m; 水 is the highest water level elevation, m.

[0136] Step 6: Separation and water stopping inside the casing

[0137] Two packers are placed in the casing 8, and after the packers are connected with the drill pipe 15, they are put into the casing, and the upper and lower packers are 20m away from the top and bottom of the drainage tunnel respectively. Pressurization makes the capsule on the packer expand and get stuck in the casing to stop water.

[0138] Step 7: Install the water discharge device to discharge water

[0139] A hole is cut in the casing in the drainage lane 7, and drainage devices such as drainage valve 18, blowout preventer 17 and pressure gauge 16 are installed, and connected to the drainage pipeline 19 system.

[0140] After the water release device is installed, the packer is depressurized and taken out using the drill pipe.

[0141] Open the water release valve 18 to release the limestone aquifer water. The measured initial water release flow is 50m 3 / h, water pressure 6.2MPa, with the increase of water discharge time, the water discharge volume is basically stable at 30m 3 / h, water pressure 1.0MPa, depth reduction 520m, achieving the dewatering target.

[0142] The above is a detailed discussion of the best embodiment in conjunction with the accompanying drawings, which is not intended to limit the present invention. The specific technical features described above can be combined in any suitable form without contradiction, and the present invention does not go into details one by one. Any person skilled in the art may adopt simple modifications or modifications such as arbitrary combination or equivalent replacement of the technical solution without departing from the scope of the technical solution, which does not affect the essence of the technical solution and still belongs to the protection scope of the technical solution represented by the embodiments of the present invention.

Claims

1. A method for constructing a drainage hole for draining karst water in a thick layer of coal seam floor. It is characterized in that The collection and drainage holes for draining the thick karst water in the coal seam floor include: Step A: Determine the target water level drop depth for drainage and pressure reduction and safety water pressure ; Step B: Set the location of the collection and distribution hole group; A collection and distribution hole group includes a collection and distribution main hole and N collection and distribution branch holes; According to the target water level drop determined in step A , set the directional deflection section trajectory of the collection and drainage hole group, there is an underground tunnel within a radius of 15 to 50m within the directional deflection section trajectory, and the elevation of the underground tunnel is lower than the water level elevation after the drainage and drainage target is reached, that is, , Lane elevation, m; The water level elevation of the thick karst aquifer before drainage is m; the drainage hole group is arranged along the working face and extends to the direction of the cutting eye of the working face; if the width of the working face is less than 110m, two drainage branch holes are arranged, which are located at a horizontal distance of 15 to 25m on the outside of the two tunnels of the working face; if the width of the working face is greater than 110m, three drainage branch holes are arranged, one drainage branch hole is arranged below the central axis of the working face, and one drainage branch hole is arranged at a horizontal distance of 15 to 25m on the outside of the two tunnels; Construction methods include: Step 1: Construction of the main drilling hole; Directional drilling from the ground to 40 to 60 meters below the thick karst aquifer, insert the casing, and the bottom of the main drilling hole is inclined by 80 to 95 degrees; Step 2: Construction of collecting and draining branch holes; the collecting and draining branch holes are drilled at a depth of 40 to 80 meters below the thick karst aquifer; the first collecting and draining branch hole is drilled directly from the bottom of the casing to the designed position, and the second or third branch hole is drilled to the designed position after opening a window in the casing and side-drilling; Step 3: Construct the drainage tunnel to expose the casing; the drainage tunnel is constructed by opening a stone gate in the permanent main tunnel. The upper limit elevation of the drainage tunnel is calculated according to the following formula. The casing is designed to be 30 to 50 meters away from the main tunnel. The drainage tunnel is constructed until the casing is exposed; ； Step 4: Separate and seal the casing; install two packers in the casing, 20 to 30 meters above and below the position where the casing is exposed by water discharge; Step 5: Install the water discharge device to discharge water; install the water discharge valve, blowout preventer and pressure gauge on the casing in the drainage tunnel, connect them to the drainage pipe system, and discharge the water from the thick karst aquifer.

2. The method for constructing a collection and drainage hole for draining karst water in a thick layer of coal seam floor according to claim 1, It is characterized in that For water-bearing plots divided by water-blocking faults outside the drainage mining area, the drainage branch holes are obliquely intersected with the water-blocking faults, with an intersection angle of 60 to 90°.

3. The method for constructing a collection and drainage hole for draining karst water in a thick layer of a coal seam floor according to claim 1 or 2, It is characterized in that The safety water pressure According to formula (1), we can get: （1）； Where: is the safety water pressure, MPa; Ts is the critical water inrush coefficient, which is determined based on the data of mine water inrush events. If there is no data, it is 0.06-0.1MP / m; is the minimum thickness of the impermeable rock layer, m; is the depth of floor damage caused by mining, which is determined based on the measured data of the mine. If there is no data, it is taken as 18 to 25 m. A is the safety factor, which is taken as 1.

2.

4. The method for constructing a collection and drainage hole for draining karst water in a thick layer of coal seam floor according to claim 1 or 2, It is characterized in that The target water level drawdown According to formula (2), we can get: （2）； Where: is the target water level drawdown, m; is the maximum water pressure, MPa.

5. The method for constructing a collection and drainage hole for draining karst water in a thick layer of coal seam floor according to claim 1 or 2, It is characterized in that The terminal hole of the collecting and sparse branch hole should exceed the distance of the cut eye. , m; or through all water-isolating faults; ； Where: β is the bottom plate failure boundary angle.

6. The method for constructing a collection and drainage hole for draining karst water in a thick layer of coal seam floor according to claim 1 or 2, It is characterized in that The drainage of the thick karst aquifer water should meet the water pressure P, MPa of the drainage tunnel outlet; ； ΔH, the difference between the drainage tunnel elevation and the coal seam elevation, m.

Images