Advanced diversion and prevention methods for complex water hazards in the roof of coal seams in close proximity

Abstract

This invention provides a method for preventing and controlling combined water hazards in the roof of a nearby coal seam. This method utilizes the water-conducting properties of the caving zone after the upper coal seam is mined, employing a combined upward and downward drainage approach to eliminate the difficulty of drilling complete boreholes in fractured strata. By leaving drainage boreholes in suspected water accumulation areas of the upper coal seam goaf underground, it ensures that newly replenished water in the goaf can flow smoothly after drainage from the surface drainage holes. This invention can eliminate the threat of combined water hazards from the aquifer in the lower coal seam mining area and water accumulation in the upper coal seam goaf during the mining process, ensuring safe mining operations.

Description

Technical Field

[0001] This invention belongs to the field of mine water control technology, and relates to a method for preventing and controlling complex water hazards, specifically a method for preventing and controlling complex water hazards in the roof of a coal seam in close proximity. Background Technology

[0002] After the upper coal seam of a closely spaced coal group is mined, local water accumulation may occur due to the non-coordinated deformation of the strata. Simultaneously, the aquitard between the coal seam and the main aquifer may re-close under long-term soaking, resulting in the mining of the lower coal seam often facing the threat of three types of water hazards simultaneously: roof aquifers, inter-layer separation water, and water accumulation in the overlying goaf, forming a complex water disaster hazard. Conventional water control methods utilize underground boreholes to drain roof aquifers or separation water, reducing local water accumulation in inter-layer separation and in areas with abnormally high water levels within the aquifer, thereby achieving peak and valley leveling and ensuring a relatively stable water inflow during the working face mining process.

[0003] However, under the condition that the upper coal seam of a closely spaced coal seam group has already been mined, the overlying strata of the coal seam are relatively fractured, making underground drilling difficult, resulting in an extremely low borehole success rate. Furthermore, the borehole trajectory is affected by fractures in the strata, making it difficult to accurately reach the designed location. Simultaneously, the continuous replenishment of the goaf by the aquifer prevents water from being drained. In addition, due to the influence of fractured strata, the exploration of water accumulation between overlying layers and aquifer-rich anomaly zones is also difficult, and the area that can be revealed by inclined underground boreholes is extremely limited, resulting in poor overall drainage effectiveness. Therefore, for complex water hazards in the roof of the lower coal seam group during mining of closely spaced coal seams, the common approach is to passively add drainage systems. This not only wastes the resources allocated to drainage systems but also fails to completely prevent roof collapse accidents. Summary of the Invention

[0004] In view of the defects and deficiencies of the existing technology, the purpose of this invention is to provide a method for the advanced diversion and prevention of complex water hazards in the roof of coal mining in close proximity to coal seams, which solves the technical problems of the inability to detect water hazards between aquifers and inter-layer separation and the incomplete drainage of water accumulation in goaf in the existing technology.

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

[0006] A method for preventing and controlling complex water hazards in the roof of a nearby coal seam mining operation, comprising the following steps:

[0007] Step 1: Identify the potential water accumulation area in the overlying goaf: Based on the undulation of the coal seam revealed during the mining of the upper coal group, select the lowest local point and delineate it as the potential water accumulation area in the overlying goaf.

[0008] Step 2, constructing underground drainage holes: Select a suitable location as the drilling site in the working face roadway of the lower coal group near the potential water accumulation area of ​​the overlying goaf. Construct underground drainage holes in the selected drilling site area. The underground drainage holes need to cover the potential water accumulation area of ​​the overlying goaf. After the final position of the underground drainage hole enters the bottom plate of the upper coal group mining, enlarge the hole and install a water-stopping casing. After ensuring that the water-stopping casing is well consolidated, install the orifice gate valve and U-shaped pipe in sequence at the orifice opening, and open the orifice gate valve to continuously drain the water accumulation in the overlying upper coal group goaf.

[0009] Step 3, Install surface drainage holes: Calculate and obtain the radius of influence R of the aquifer in the lower coal mining area using Formula I, then take half of the radius of influence R of the aquifer in the lower coal mining area as the spacing r between two adjacent surface drainage holes; Formula I is as follows:

[0010]

[0011] R represents the radius of influence of the aquifer in the lower coal mining area, in meters.

[0012] S w This indicates the average drawdown of the stable section, in meters (m).

[0013] H0 represents the initial water level of the aquifer in the lower coal mining area, in meters.

[0014] K represents the permeability coefficient of the aquifer in the lower coal mining area, in m / d.

[0015] Step 4, construct surface drainage holes: construct surface drainage holes at the location corresponding to the suspected water accumulation area in the upper coal seam, and lay out the surface drainage holes on both sides of the working face according to the interval r determined in Step 3, until the influence range can cover the entire working face of the lower coal seam; after the surface drainage holes enter the caving zone of the upper coal seam, install water-stopping casings in the strata above the aquifer in the mining area of ​​the lower coal seam and cement them.

[0016] Step 5, lowering the guide pipe: Lower the guide pipe into the constructed ground drainage hole. During the lowering process, seal the pipe opening and use the pressure difference of the pipe wall during water flow to smoothly lower the guide pipe to the bottom of the hole; the upper outer side of the guide pipe is covered with a self-expanding rubber bucket.

[0017] Step 6, lowering the water level observation device: lower the water level observation device into the ground drainage hole, and install a double-threaded sealing cap at the opening of the ground drainage hole; the double-threaded sealing cap has internal threads and external threads, the internal threads are used to connect the water-stop sleeve, and the external threads are used to connect the guide pipe. A cable passage pipe is left in the center of the inner diameter of the double-threaded sealing cap for the cable of the water level observation device to pass through.

[0018] Step 7, Drainage and Diversion: Using surface drainage holes, groundwater from the aquifer in the lower coal mining area is allowed to enter the upper coal goaf along the boreholes, further enter the mine through underground drainage holes, and finally be discharged by the underground drainage system.

[0019] The present invention also has the following technical features:

[0020] Step 8, Treatment of blocked ground drainage holes: If the water level in the ground drainage hole rises, it indicates that the ground drainage hole has collapsed and become blocked. Then, remove the water level monitoring device inside the hole and use a ground drilling rig to perform hole drilling until the ground drainage hole resumes the phenomenon of air suction and water discharge.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] (I) This invention fully utilizes the water-conducting properties of the caving zone after the upper coal seam is mined, employing a combined upper and lower drainage method to eliminate the problem of incomplete drilling in fractured strata. By leaving drainage boreholes in suspected water accumulation areas of the upper coal seam goaf underground, it ensures that newly replenished water in the goaf can flow smoothly after the surface drainage holes have been drained. This invention can eliminate the threat of combined water hazards from the aquifer in the lower coal seam mining area and water accumulation in the upper coal seam goaf during the mining process, ensuring safe mining of the working face.

[0023] (II) The present invention inserts a water-stopping sleeve into the underground water drainage borehole and installs a U-shaped pipe at the borehole opening, which can prevent secondary accidents caused by air leakage in the water drainage borehole and spontaneous combustion of coal.

[0024] (III) The present invention uses a PVC guide pipe in the ground drainage hole to ensure that the borehole will not be blocked due to the collapse of the broken strata, thus ensuring a continuous drainage effect.

[0025] (IV) The present invention adopts a double-threaded sealing cap at the orifice and a self-expanding rubber barrel structure inside the orifice, plus an automatic water level monitoring mode, and uses the dynamic water level to scientifically identify the blockage of the orifice, thereby avoiding secondary disasters such as spontaneous combustion of coal caused by air suction from the ground during drilling. Attached Figure Description

[0026] Figure 1 Plan layout of advanced diversion boreholes for complex water hazards in the roof of the lower coal seam in close proximity; Figure 1 In the middle: the orange-red lines represent the contour lines of the coal seam floor.

[0027] Figure 2 A schematic cross-sectional view of the advanced diversion borehole for the complex water hazard in the roof of the lower coal seam during close-range coal mining; Figure 2 In the middle: the blue lines represent water level lines, and the blue arrows indicate the direction of water flow.

[0028] Figure 3A schematic diagram of the connection structure of the stop sleeve, orifice gate valve and U-tube.

[0029] Figure 4 A schematic diagram of the connection structure of the double-threaded sealing cap, the guide tube, and the self-expanding rubber bucket; Figure 4 In the middle: the blue lines represent water level lines, and the blue arrows indicate the direction of water flow.

[0030] Figure 5 This is a schematic diagram of the structure of a ground drainage hole; Figure 5 (b) is Figure 5 A-A' section view of (a) in the middle.

[0031] The meanings of the labels in the diagram are as follows: 1-Underground drainage hole, 2-Surface drainage hole, 3-Upper coal goaf, 4-Lower coal working face roadway, 5-Aquifer in the lower coal mining area, 6-Water barrier, 7-Upper coal, 8-Lower coal, 9-Upper coal caving zone, 10-Upper coal water-conducting fracture zone, 11-Water-stop sleeve, 12-Orifice gate valve, 13-U-tube, 14-Water level monitoring device, 15-Double threaded sealing cap, 16-Drainage pipe, 17-Self-expanding rubber bucket.

[0032] The technical solution of the present invention will be further described below with reference to the embodiments. Detailed Implementation

[0033] It should be noted that all components, devices, and systems used in this invention, unless otherwise specified, are those known in the art. For example, the water level monitoring device 14 is a conventional water level monitoring device known in the prior art. The downhole drainage system is a conventional downhole drainage system known in the prior art.

[0034] The research background of this invention is as follows: Figure 3 As shown, during mining operations in a coal mine, after mining the upper coal seam 7, preparations are underway to mine the lower coal seam 8. During the mining of the upper coal seam 7, although the water-conducting fracture zone 10 of the upper coal seam reached the bottom of the aquifer 5 in the mining area of ​​the lower coal seam under the roof, the four-year interval between the two working faces meant that the fractures in the broken aquitard 6 within the fracture zone had largely closed. This resulted in some water accumulation in the upper coal seam goaf 3, and the aquifer 5 in the overlying lower coal seam mining area became water-rich again. Therefore, the lower coal seam working face faces the threat of water accumulation in the upper coal seam goaf 3 and water hazard from the aquifer 5 in the mining area of ​​the lower coal seam under the roof. Based on the above situation, this invention proposes a method for the advanced diversion and prevention of complex water hazards in the roof of the lower coal seam mining area in close proximity, as detailed in the embodiments.

[0035] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0036] Example:

[0037] This embodiment provides a method for advance diversion and prevention of complex water hazards in the roof of coal seam mining at close range, such as... Figures 1 to 5 As shown, the method specifically includes the following steps:

[0038] Step 1: Identify potential water accumulation areas in the overlying goaf:

[0039] Based on the contour lines of the bottom plate of the Upper Coal Group 7 and the measurement data of the coal cutting machine during the mining of Upper Coal Group 7, it was determined that the local low point in the Upper Coal Group Goaf 3 is located in the middle of the working face, and this area was identified as the potential water accumulation area of ​​the overlying goaf.

[0040] Step 2: Construct drainage holes in the well:

[0041] Near the potential water accumulation area in the overlying goaf, a suitable location is selected in the roadway 4 of the lower coal face as the drilling site. Underground drainage holes 1 are constructed in the selected drilling site area. These drainage holes 1 must cover the potential water accumulation area in the overlying goaf. The number of boreholes constructed in each drilling site is dynamically adjusted based on the on-site water output (generally three boreholes are constructed). During drilling, the drilling pressure is recorded and rock powder is collected every 2 meters. When a significant increase in drilling pressure occurs, causing the drill to jam, and the rock powder contains mudstone from the upper coal goaf 3, fire-fighting foam, or yellow mud, it is considered that the borehole has entered the upper coal goaf 3. Drilling continues until the final borehole position is at least 4 meters above the mining floor of the upper coal 7. Then, the hole is enlarged and a water-stopping sleeve 11 is inserted. After ensuring that the water-stopping sleeve 11 is well fixed, the orifice gate valve 12 and U-shaped pipe 13 are installed in sequence at the orifice opening, and the orifice gate valve 12 is opened to continuously drain the accumulated water in the overlying coal goaf 3.

[0042] As a specific solution in this embodiment, the inner diameter of the underground drainage hole 1 is 153mm, the inner diameter of the water-stopping sleeve 11 is 127mm, the upper part of the water-stopping sleeve 11 enters the upper coal goaf 3 and this section is a perforated pipe, the lower part of the water-stopping sleeve 11 is buried in the stratum and this section is a seamless steel pipe, and cement grout is used to solidify the seamless steel pipe section.

[0043] Step 3: Based on the radius of influence of the aquifer in the next coal mining area, deploy surface drainage holes:

[0044] Based on the hydrogeological data of the main water-bearing aquifers in the mine, the influence radius during surface water discharge is determined using the formula for calculating the influence radius of unconfined aquifers (Kusagin formula), as shown below:

[0045]

[0046] R represents the radius of influence of the aquifer in the lower coal mining area, in meters.

[0047] Sw represents the average drawdown of the stable section, in meters (m).

[0048] H0 represents the initial water level of the aquifer in the lower coal mining area, in meters.

[0049] K represents the permeability coefficient of the aquifer in the lower coal mining area, in m / d.

[0050] In this embodiment, the thickness of the aquifer 5 in the lower coal mining area is 85m, and H0 = 85m is selected. Previous pumping tests have yielded a permeability coefficient K = 0.4517m / d for the aquifer 5 in the lower coal mining area. The maximum drawdown of the aquifer 5 in the lower coal mining area, monitored during the maximum water inflow at the working face, is 35m. Therefore, Sw = 34m is determined, and R = 676m is finally calculated (it should be noted that the calculation using Formula I is dimensionless). To ensure the effective drainage of the aquifer, the drawdown funnels of two adjacent surface drainage holes 2 must be superimposed to ensure their final drawdown. Therefore, the final distance r between two adjacent surface drainage holes 2 is determined to be half the radius of influence of the aquifer in the lower coal mining area, i.e., 338m.

[0051] Step 4, constructing drainage holes on the construction surface:

[0052] Construct ground drainage holes 2 at the location of the suspected water accumulation area in the upper coal group 7, and lay ground drainage holes 2 on both sides of the working face at intervals of r=338m until the influence range can cover the entire working face of the lower coal group 8.

[0053] As a specific embodiment, the surface drainage hole 2 adopts a two-section structure, with an upper diameter of 311mm and a lower diameter of 133mm. The reasons for adopting the two-section structure in this embodiment are: firstly, for safety, segmented cementing can prevent wellbore collapse and control formation pressure; secondly, for layered isolation, preventing cross-flow of fluids from different formations; and thirdly, to adapt to complex geology, flexibly adjusting parameters according to the characteristics of formations at different depths.

[0054] As a specific solution in this embodiment, during the construction process, the drilling jamming and drilling fluid leakage should be recorded every 2m of construction. When obvious drilling jamming and drilling fluid leakage occur, and air suction occurs, the surface drainage hole 2 has entered the upper coal caving zone 9. Continue construction to ensure that the surface drainage hole 2 enters the upper coal caving zone 9 by more than 5m. In the loose strata above the aquifer 5 in the main lower coal mining area, the water-stopping casing 11 is installed and cemented.

[0055] As a specific solution in this embodiment, the material of the water-stop sleeve 11 should be a seamless steel pipe with a wall thickness of 15mm or more and a diameter of 219mm, with threads left on the inner side of the orifice.

[0056] Step 5, insert the drainage tube:

[0057] A guide pipe 16 is lowered into the constructed ground drainage hole 2. The guide pipe 16 is made of PVC material. The pipe opening is closed during the lowering process of the guide pipe 16. The pressure difference of the pipe wall during the water flow process allows the guide pipe 16 to be smoothly lowered to the bottom of the hole. A self-expanding rubber bucket 17 is fitted on the upper outer side of the guide pipe 16.

[0058] As a specific embodiment, the diameter of the guide pipe 16 needs to be at least 10 mm smaller than the diameter of the ground drainage hole 2. In this embodiment, the diameter of the guide pipe 16 is 98 mm.

[0059] As a specific embodiment, the lower part (aquifer section) of the diversion pipe 16 is a perforated pipe, and the upper part (seamless steel pipe section) of the diversion pipe 16 is a solid pipe. The solid pipe has a non-porous structure, which can prevent the migration of pollutants or interference with the strata. When used in conjunction with the perforated pipe, it can adapt to complex geological and engineering needs.

[0060] As a specific embodiment, the self-expanding rubber bucket 17 is made of water-expanding rubber (based on butyl rubber, neoprene rubber, or EPDM rubber, with added sodium polyacrylate resin), polyurethane-based composite material, water-absorbing resin composite polymer (made by mixing sodium polyacrylate resin with thermoplastic elastomer or polyethylene), or modified cellulose material (e.g., carboxymethyl cellulose). In this embodiment, the self-expanding rubber bucket 17 can achieve a volume expansion of 100% to 500%, and after expansion, it has certain compressive and shear resistance, does not decompose under long-term immersion, and has good durability.

[0061] Step 6: Lower the water level monitoring device.

[0062] The water level monitoring device 14 is lowered into the ground drainage hole 2. A double-threaded sealing cap 15 is installed at the opening of the ground drainage hole 2, and the cable of the water level monitoring device 14 is passed out through the center hole of the double-threaded sealing cap 15. The double-threaded sealing cap 15 has an inner and outer double thread structure, which is screwed and fixed to the inner threads of the water-stop sleeve 11 and the guide pipe 16, respectively. A cable passage is left in the center of the inner diameter of the double-threaded sealing cap 15 for the cable of the water level monitoring device 14 to pass through.

[0063] Step 7, Drainage and Diversion:

[0064] By utilizing the surface drainage hole 2, groundwater from the aquifer 5 in the lower coal mining area enters the upper coal goaf 3 along the borehole, further enters the mine through the underground drainage hole 1, and is finally discharged by the underground drainage system.

[0065] Step 8: Clogging of ground drainage holes:

[0066] If the water level in the ground drainage hole 2 rises, it indicates that the ground drainage hole 2 has collapsed and blocked. In this case, the water level observation device 14 inside the hole is removed, and a ground drilling rig is used to perform a hole-penetrating operation until the ground drainage hole 2 resumes the phenomenon of air suction and water discharge.

Claims

1. A method for preventing and controlling complex water hazards in the roof of a coal seam in close proximity during mining, characterized in that, The method specifically includes the following steps: Step 1: Identify potential water accumulation areas in the overlying goaf: Based on the coal seam undulations revealed during the mining of the upper coal group, the lowest local point was selected and delineated as the potential water accumulation area of ​​the overlying goaf. Step 2: Construct drainage holes in the well: In the lower coal face roadway (4) near the potential water accumulation area of ​​the overlying goaf, a suitable location is selected as the drilling site. In the selected drilling site area, the underground drainage hole (1) is constructed. The underground drainage hole (1) needs to cover the potential water accumulation area of ​​the overlying goaf. After the final hole position of the underground drainage hole (1) enters the bottom plate of the upper coal (7), the hole is enlarged and a water-stopping sleeve (11) is installed. After ensuring that the water-stopping sleeve (11) is well consolidated, the orifice gate valve (12) and U-shaped pipe (13) are installed in sequence at the orifice opening, and the orifice gate valve (12) is opened to continuously drain the water accumulation in the overlying upper coal goaf (3). Step 3, Install ground drainage holes: Formula I was used to calculate and obtain the radius of influence of the aquifer in the lower coal mining area. R Then, the radius of influence of the aquifer in the coal mining area was taken. R Half of the distance is used as the spacing between two adjacent ground drainage holes. r Formula I is as follows: Formula I; R Indicates the radius of influence of the aquifer in the lower coal mining area; S w This indicates the average drawdown of the stable section; H 0 indicates the initial water level of the aquifer in the lower coal mining area; K This represents the permeability coefficient of the aquifer in the lower coal mining area; Step 4, constructing drainage holes on the construction surface: Construct surface drainage holes (2) at the location of the suspected water accumulation area in the upper coal group (7), and construct them at the intervals determined in step three. r Surface drainage holes (2) are set up on both sides of the working face until the influence range can cover the entire working face of the lower coal group (8); after the surface drainage holes (2) enter the upper coal group caving zone (9), water-stopping casing (11) is installed in the stratum above the aquifer (5) in the mining area of ​​the lower coal group and cemented. Step 5, insert the drainage tube: A guide pipe (16) is lowered into the constructed ground drainage hole (2). The pipe opening is closed during the lowering process of the guide pipe (16). The guide pipe (16) is lowered smoothly to the bottom of the hole by utilizing the pressure difference of the pipe wall during the water flow. A self-expanding rubber bucket (17) is fitted on the upper outer side of the guide pipe (16). Step 6: Lower the water level monitoring device. The water level observation device (14) is lowered into the ground drainage hole (2), and a double threaded sealing cap (15) is installed at the opening of the ground drainage hole (2). The double threaded sealing cap (15) has an internal thread and an external thread. The internal thread is used to connect the water-stop sleeve (11), and the external thread is used to connect the guide pipe (16). A through pipe is left in the center of the inner diameter of the double threaded sealing cap (15) for the cable of the water level observation device (14) to pass through. Step 7, Drainage and Diversion: By using the surface drainage hole (2), the groundwater in the aquifer (5) of the lower coal mining area enters the upper coal goaf (3) along the borehole, and further enters the underground through the underground drainage hole (1), and is finally discharged by the underground drainage system.

2. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step two, the upper part of the water-stopping sleeve (11) enters the upper coal goaf area (3), the upper part of the water-stopping sleeve (11) is a perforated pipe; the lower part of the water-stopping sleeve (11) is buried in the stratum; the lower part of the water-stopping sleeve (11) is a seamless steel pipe, and cement grout is used to solidify the seamless steel pipe section.

3. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step two, during the construction of the drainage hole (1) in the well, the drilling pressure is recorded and rock powder is taken after each construction distance. When the drilling pressure increases significantly and the drill gets stuck, and the rock powder contains mudstone from the upper coal goaf (3), fire-fighting foam, or yellow mud, it is considered that the borehole has entered the upper coal goaf (3). Continue drilling until the final hole position enters the upper coal (7) mining floor.

4. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step four, the ground drainage hole (2) is drilled using a two-stage structure.

5. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step four, during the construction process, the drilling jamming and drilling fluid leakage should be recorded once every construction distance. When there is obvious drilling jamming, almost all drilling fluid leakage and air suction, the ground drainage hole (2) has entered the upper coal caving zone (9); continue construction until the ground drainage hole (2) enters the upper coal caving zone (9).

6. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step four, the material of the water-stop sleeve (11) is a seamless steel pipe with a wall thickness of 15 to 50 mm.

7. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step five, the guide tube (16) is made of polyvinyl chloride.

8. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, In step five, the lower part of the guide pipe (16) enters the aquifer (5) of the lower coal mining area and is a perforated pipe, while the upper part of the guide pipe (16) is a seamless steel pipe and is a solid pipe.

9. The method for advance diversion and prevention of complex water hazards in the roof of closely spaced coal seams as described in claim 1, characterized in that, It also includes step eight, treatment of blockage of ground drainage hole: if the water level in ground drainage hole (2) rises, it indicates that the ground drainage hole (2) has collapsed and blocked. Then, the water level observation device (14) in the hole is removed, and a ground drilling machine is used to carry out through hole operation until the ground drainage hole (2) reappears to suck air and drain water.

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