A method for transferring and storing water resources by using coal mining fissures and loess

Abstract

The present invention belongs to the technical field of coal mining, and particularly relates to a method for transferring and storing water resources by using the loess in coal mining fissures. The present invention innovatively utilizes the sectional property of the hydrogeological characteristics of the thick loess caused by coal mining. The deep loess section is mainly affected by the water-conducting fissures in coal mining, and the loess has the effect of inhibiting the development of water-conducting fissures. After reaching a certain range, a relatively good weak fissure section will be formed. The mining-induced fissures in the loess can be detected by micro-resistivity scanning imaging logging. In the weak fissure section, the fissures are relatively easy to be reformed. By grouting, a relatively water-resistant layer can be reformed, causing the overlying fissured loess to store water during the rainy season, which can continuously heal and increase the water-holding capacity of the loess. The reformed pore-fissure dual medium has good infiltration effect of atmospheric precipitation and water-holding capacity, providing a good recharge source for the water storage of the underlying strata. In this way, the mining area can achieve self-sufficiency in available water resources, reduce the acquisition of precious surface water, and at the same time protect the local fragile ecological environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mining, and particularly relates to a method for transferring and storing water resources by using coal mining fissure loess. Background Art

[0002] In China, coal resources are rich in the loess-covered areas, but water resources are scarce, and the loess-covered mining areas generally lack available water resources. Therefore, water storage in the loess-covered mining areas is an important guarantee for coal resource mining. The main methods to solve this problem in the past include water storage and supply methods in goafs, transfer and storage of aquifers before coal mining, and re-construction of water-resisting layers, etc., but there are still the following problems:

[0003] 1) When using water storage in goafs, water resources enter the mining system and are inevitably polluted to varying degrees, and the cost of treating water resource pollution is high.

[0004] 2) The main object of transfer and storage of aquifers before coal mining is the groundwater overlying the coal seam. However, due to poor infiltration conditions in the loess-covered areas, the groundwater overlying the coal seam is limited, so the amount of transfer and storage is very limited.

[0005] 3) The fracture network generated by coal mining is relatively complex, and the natural self-healing time of the water-resisting layer is too long. When artificially reconstructing the water-resisting layer, the grouting volume is large and the cost is high.

[0006] In addition, the water resource storage in the coal mining area also has certain hidden dangers of water disasters for coal mining. The previous water storage methods are mainly beside the coal mining face, with a higher risk coefficient. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above problems existing in the traditional technology, and provide a method for transferring and storing water resources by using coal mining fissure loess.

[0008] To achieve the above technical purpose and reach the above technical effect, the present invention is realized through the following technical solutions:

[0009] A method for transferring and storing water resources by using coal mining fissure loess, comprising the following steps:

[0010] S1. Select an area with a loess thickness > 30m as the water resource transfer and storage area;

[0011] S2. Before coal mining, design a coal mining face;

[0012] S3. Conduct coal mining in the coal mining face. After coal mining, plant herbaceous and shrubby vegetation on the ground corresponding to the coal mining face;

[0013] S4. Wait for the coal mining area to stabilize after coal mining;

[0014] S5. Implement the first directional borehole in the underground roadway. The horizontal section of the first directional borehole penetrates the overlying loess layer of the coal mining face described in step S2. The buried depth of the horizontal section of the first directional borehole shall be X, and the value of the buried depth X is determined by the micro-resistivity scanning imaging logging results obtained from the surface exploration borehole.

[0015] S6. After the directional drilling is completed, grouting is carried out. The injected grout is cement slurry, and the water-cement ratio is 1:1 to 1:2 until the entire borehole is filled.

[0016] S7. Based on the directional borehole in step S5, offset upward by a borehole radius and re-implement the second directional borehole.

[0017] S8. Install a filter pipe in the re-implemented second directional borehole that can allow the water in the loess to seep into the second directional borehole.

[0018] S9. Repeat steps S5 to S8 to implement multiple third directional boreholes above the coal mining face. The horizontal spacing between the horizontal sections of the third directional boreholes ≤ 20m.

[0019] S10. Set up an underlying aquifer recharge system at the underground starting point of the third directional borehole. The underlying aquifer recharge system includes a sedimentation tank, a water pump, and a recharge borehole. The sedimentation tank stores and precipitates the intercepted water in the directional borehole to remove rock debris. The water pump is used to pump the clean water in the sedimentation tank into the recharge borehole.

[0020] S11. During the rainy season, collect the infiltrated water resources from the loess area and inject them into the underlying aquifer of the coal seam, achieving the purpose of water resource storage. When the water pressure of the coal seam floor aquifer is equal to the critical water pressure, stop the borehole recharge. The calculation method of the critical water pressure P is shown in formula (I):

[0021] P = M × T (I)

[0022] Wherein, M is the distance from the aquifer to the coal seam, with the unit of m; T is the critical water inrush coefficient, with the unit of MPa / m.

[0023] Furthermore, in step S2, through the design of the coal mining face, the surface elevations of the open-off cut and the end line in the coal mining face are greater than the surface elevations of other areas of the coal mining face.

[0024] Furthermore, in step S4, through coal mining subsidence observation, observe once a day. When the change amplitude of 10 consecutive observations is less than 0.01m, it is considered that the subsidence is stable.

[0025] Furthermore, in step S5, the micro-resistivity scanning imaging logging results refer to: in the two-thirds section of the deep loess exposed by the borehole, detect the fissures once every 1m, and the buried depth of the loess section with the smallest fissure density is X.

[0026] Further, in step S5, the horizontal section of the first directional borehole has the same orientation as the coal mining face, and the length of the horizontal section is greater than the length of the coal mining face along its strike.

[0027] Further, in step S10, the recharge borehole is a borehole drilled vertically downward from the underground mine, and the drilling is stopped when the first aquifer below 15 m of the coal seam floor is exposed. This aquifer is denoted as the underlying aquifer of the coal seam.

[0028] Further, in step S10, a casing for water stop is installed above the underlying aquifer of the coal seam, and a filter pipe is installed at the location of the underlying aquifer of the coal seam. The recharge borehole can inject the pumped water into the underlying aquifer of the coal seam through the casing and the filter pipe.

[0029] Further, in step S11, the value of T ranges from 0.06 to 0.10 MPa / m.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention comprehensively considers that after coal mining in the loess-covered mining area, the loess forms a dual medium of pores and fractures. The pores have a certain water-holding capacity, and the fractures have good water conductivity. After normal mining, the dual medium of the loess shows a negative effect on water resource storage, that is, water resource loss is caused by the water conductivity of the fracture medium during the rainy season, and the pore medium does not reach a saturated state and cannot continuously supply water resources during the dry season. By innovatively utilizing the sectional characteristics of the hydrogeological properties of the relatively thick loess caused by coal mining, that is, the shallow loess section has good water conductivity due to the tensile action of mining and is suitable as the infiltration layer for atmospheric precipitation (according to the theory of active earth pressure, this range is about 10 m, exactly one-third of the shallow part of the 30-m-thick loess). The deep loess section is mainly affected by the water-conducting fractures in coal mining, and the loess has an inhibitory effect on the development of water-conducting fractures. After reaching a certain range, a relatively good weak fracture section will be formed. The mining-induced fractures in the loess can be detected by micro-resistivity scanning imaging logging. In the weak fracture section, the fractures are relatively easy to be transformed. By grouting, a relatively water-resistant layer can be transformed, causing the overlying fractured loess to store water during the rainy season, which can continuously heal and increase the water-holding capacity of the loess. The transformed pore-fracture dual medium has good infiltration effect of atmospheric precipitation and water-holding capacity, providing a good recharge source for water storage in the underlying strata.

[0032] 2. In the coal mining subsidence area of the coal mining face of the present invention, due to the relatively high starting cut and end line, after precipitation, the water converges towards the coal mining compacted area, avoiding the loss of a large amount of water resources through the starting cut and end line that are not easy to reinforce. At the same time, with the supporting surface vegetation, the water storage effect during the rainy season is better.

[0033] 3. By using the mining-induced fractured loess to transfer and store water resources, the mining area of the present invention realizes self-sufficiency in available water resources, reduces the acquisition of precious surface water, and at the same time protects the local fragile ecological environment.

[0034] Of course, it is not necessary for any product implementing the present invention to achieve all of the above advantages simultaneously. Specific Embodiments

[0035] The technical solutions will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative work fall within the scope of protection of the present invention.

[0036] The present invention provides a method for transferring and storing water resources by using loess in coal mining fissures, which is characterized by including the following steps:

[0037] S1. Select an area with a loess thickness > 30 m as the water resource transfer and storage area.

[0038] S2. Before coal mining, design the coal mining face. Through the design of the coal mining face, the surface elevation of the open-off cut and the end line in the coal mining face is greater than that of other areas in the coal mining face.

[0039] S3. Carry out coal mining in the coal mining face. After coal mining, plant herbaceous and shrubby vegetation on the ground corresponding to the coal mining face.

[0040] S4. Wait for the coal mining area to stabilize after coal mining; through coal mining settlement observation, observe once a day. When the change amplitude of 10 consecutive observations is less than 0.01 m, it is considered that the settlement is stable.

[0041] S5. Implement the first directional borehole in the underground roadway. The horizontal section of the first directional borehole penetrates the overlying loess layer of the coal mining face described in step S2. The buried depth of the horizontal section of the first directional borehole should be X, and the value of the buried depth X is determined by the micro-resistivity scanning imaging logging results implemented in the surface exploration borehole. The micro-resistivity scanning imaging logging results refer to: in the two-thirds section of the deep loess exposed by the borehole, detect the fissures once every 1 m, and the buried depth of the loess section with the minimum fissure density is X. The trend of the horizontal section of the first directional borehole is the same as that of the coal mining face, and the length of the horizontal section is greater than the strike length of the coal mining face.

[0042] S6. After the directional borehole is drilled, grouting is carried out. The injected slurry is cement slurry, and the water-cement ratio is 1:1 to 1:2 until the entire borehole is filled.

[0043] S7. Based on the directional borehole in step S5, shift upward by a borehole radius and re-implement the second directional borehole.

[0044] S8. Install a filter pipe in the re-implemented second directional borehole that can allow the underwater in the loess to seep into the second directional borehole.

[0045] S9. Repeat steps S5 to S8 to implement multiple third directional boreholes above the coal mining face. The horizontal spacing between the horizontal sections of the third directional boreholes ≤ 20 m.

[0046] S10. Set up an underlying aquifer recharge system at the underground starting point of the third directional borehole. The underlying aquifer recharge system includes a sedimentation tank, a water pump, and a recharge borehole. The sedimentation tank stores and precipitates the intercepted water in the directional borehole to remove rock debris. The water pump is used to pump the clean water in the sedimentation tank into the recharge borehole. The recharge borehole is a borehole drilled vertically downward from the underground mine until it exposes the first aquifer 15 m below the coal seam floor. This aquifer is denoted as the underlying aquifer of the coal seam. A casing for water stoppage is installed above the underlying aquifer of the coal seam, and a filter pipe is installed at the underlying aquifer of the coal seam. The recharge borehole can inject the pumped water into the underlying aquifer of the coal seam through the casing and the filter pipe.

[0047] S11. During the rainy season, collect the infiltrated water resources from the loess area and inject them into the underlying aquifer of the coal seam to achieve the purpose of water resource storage. When the water pressure of the aquifer at the coal seam floor is equal to the critical water pressure, stop the borehole recharge. The calculation method of the critical water pressure P is shown in formula (I):

[0048] (I)

[0049] where M is the distance from the aquifer to the coal seam, in m. T is the critical water inrush coefficient, in MPa / m. The value of T is 0.06 - 0.10 MPa / m.

[0050] The relevant specific embodiments of the present invention are as follows:

[0051] Embodiment 1

[0052] This embodiment takes a loess plateau area rich in coal resources but lacking in water resources as the object. A large amount of water resources are required during the coal development process in this loess plateau area and cannot be guaranteed. In order to transfer and store water resources using the fractured loess formed during coal mining while mining coal resources, the specific steps are as follows:

[0053] Step 1: Select an area with a loess thickness greater than 30 m as the water resource transfer and storage area, and the total loess thickness is 63 m.

[0054] Step 2: Before coal mining, design the layout of the coal mining face. Through the design of the coal mining face, the surface elevations of the starting cut and the end line of the coal mining face are greater than those of other areas of the coal mining face. Through this design, only a small amount of atmospheric precipitation enters the goaf through the starting cut and the end line, and most of the rest converges towards the compacted area in the middle of the coal mining face.

[0055] Step 3: Coal mining is carried out in the coal mining face. After coal mining, herbaceous and shrub vegetation is planted on the ground corresponding to the coal mining face, and the planting of the vegetation enables better conservation of water resources.

[0056] Step 4: Wait for the coal mining area to stabilize after coal mining. Through coal mining subsidence observation, it is observed once a day. When the change amplitude of 10 consecutive observations is less than 0.01 m, it is considered that the subsidence has reached stability. The observation results show that the coal mining area reaches subsidence stability after 297 days.

[0057] Step 5: Directional drilling is implemented in the underground roadway. The horizontal section of the directional drilling passes through the overlying loess layer of the coal mining face described in Step 2, and the buried depth of the horizontal section should be X = 38 m. The value of the buried depth X is determined by the micro-resistivity scanning imaging logging results implemented in the ground exploration borehole. The micro-resistivity scanning imaging logging results refer to: in the two-thirds section of the deep loess exposed by the borehole, fractures are detected once every 1 m, and the buried depth of the loess section with the smallest fracture density is X. In addition, the trend of the horizontal section of the directional drilling is consistent with the trend of the coal mining face, and the length of the horizontal section is greater than the strike length of the coal mining face.

[0058] Step 6: Grout after the directional drilling is completed. The injected grout is cement slurry, and the water-cement ratio is 1:2 until the entire borehole is filled.

[0059] Step 7: Offset upward by a borehole radius based on the directional drilling in Step 5 and re-implement directional drilling.

[0060] Step 8: Lower a filter pipe into the re-implemented directional drilling to allow the water in the loess to infiltrate into the directional drilling.

[0061] Step 9: Repeat Steps 5 to 8 to implement multiple directional drillings above the coal mining face. The horizontal spacing between the horizontal sections of the directional drillings is 20 m.

[0062] Step 10: Set up an underlying aquifer recharge system at the underground starting point of the directional drilling. The recharge system includes a sedimentation tank, a water pump, and a recharge borehole. The sedimentation tank stores and precipitates the intercepted water in the directional drilling to remove rock debris. The water pump is used to pump the clean water body in the sedimentation tank into the recharge borehole. The recharge borehole is a borehole vertically drilled downward from the mine underground until it exposes the first aquifer more than 15 m below the coal seam floor (at 25 m below the coal seam floor). Casing is installed above and below the aquifer for water sealing, and a filter pipe is installed at the aquifer to inject the pumped water into the aquifer.

[0063] Step Eleven: During the rainy season, collect the infiltrated water resources from the loess area and inject them into the aquifer underlying the coal seam to achieve the purpose of water resource storage. When the water pressure in the aquifer at the coal seam floor is equal to the critical water pressure, stop borehole recharge. The critical water pressure is calculated by the formula P = M × T = 1.5 MPa, where M = 25 m is the distance from the aquifer to the coal seam. T is the critical water inrush coefficient, taking 0.06 MPa / m.

[0064] By using the mining-induced fractures to transfer and store water resources in the loess, the mining area has achieved self-sufficiency in available water resources, reduced the acquisition of precious surface water, and protected the local fragile ecological environment.

[0065] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for transferring and storing water resources by using coal mining fissure loess, characterized in that, It includes the following steps: S1. Select an area with a loess thickness > 30 m as the water transfer and storage area; S2. Before coal mining, design the coal mining face; S3. Conduct coal mining at the coal mining face. After coal mining, plant herbaceous and shrubby vegetation on the ground corresponding to the coal mining face; S4. Wait for the coal mining area to stabilize after coal mining; S5. Implement the first directional borehole in the underground roadway. The horizontal section of the first directional borehole penetrates the overlying loess layer of the coal mining face described in step S2; the buried depth of the horizontal section of the first directional borehole should be X, and the value of the buried depth X is determined by the micro-resistivity scanning imaging logging results implemented in the ground exploration borehole; S6. After the directional borehole is drilled, grout is injected; the injected grout is cement slurry, and the water-cement ratio is 1:1 to 1:2 until the entire borehole is filled; S7. Offset upward by a borehole radius based on the directional borehole in step S5, and re-implement the second directional borehole; S8. Install a filter pipe in the re-implemented second directional borehole that can allow the water in the loess to seep into the second directional borehole; S9. Repeat steps S5 to S8 to implement multiple third directional boreholes above the coal mining face; the horizontal spacing between the horizontal sections of the third directional boreholes ≤ 20 m; S10. Set up an underlying aquifer recharge system at the underground starting point of the third directional borehole; the underlying aquifer recharge system includes a sedimentation tank, a water pump, and a recharge borehole; the sedimentation tank stores and precipitates the intercepted water in the directional borehole to remove rock debris; the water pump is used to pump the clean water in the sedimentation tank into the recharge borehole; S11. During the rainy season, collect the infiltrated water resources from the loess area and inject them into the underlying aquifer of the coal seam. When the water pressure of the aquifer at the coal seam floor is equal to the critical water pressure, stop borehole recharge; the calculation method of the critical water pressure P is shown in formula (I): P = M × T( I ) where M is the distance from the aquifer to the coal seam, in m; T is the critical water inrush coefficient, in MPa / m.

2. The method for transferring and storing water resources by using coal mining fissure loess according to claim 1, wherein: In step S2, through the design of the coal mining face, the surface elevations of the open-off cut and the end line in the coal mining face are greater than the surface elevations of other areas of the coal mining face.

3. The method for transferring and storing water resources by using coal mining fissure loess according to claim 1, wherein: In step S4, through coal mining subsidence observation, observe once a day. When the change amplitude of 10 consecutive observations is less than 0.01 m, it is considered that the subsidence is stable.

4. The method for transferring and storing water resources by using coal mining fissure loess according to claim 1, characterized in that: In step S5, the micro-resistivity scanning imaging logging results refer to: in the two-thirds section of the deep loess exposed by the borehole, detect fractures once every 1 m, and the buried depth of the loess section with the smallest fracture density is X.

5. The method for transferring and storing water resources by using coal mining fissure loess according to claim 1, wherein: In step S5, the horizontal section of the first directional borehole has the same orientation as the coal mining face, and the horizontal section length is greater than the strike length of the coal mining face.

6. The method for transferring and storing water resources using coal mining fracture loess according to claim 1, characterized in that: In step S10, the recharge borehole is a borehole vertically drilled downward from the mine underground until it exposes the first aquifer more than 15 m below the coal seam floor, and this aquifer is recorded as the underlying aquifer of the coal seam.

7. The method for transferring and storing water resources by using coal mining fissure loess according to claim 6, characterized in that: In step S10, a water-stop casing is installed above the underlying aquifer of the coal seam, and a filter pipe is installed at the underlying aquifer of the coal seam. The recharge borehole can inject the pumped water into the underlying aquifer of the coal seam through the casing and the filter pipe.

8. The method for transferring and storing water resources by using coal mining fissure loess according to claim 1, wherein: In step S11, the value of T is 0.06 - 0.10 MPa / m.