Methods for preventing and controlling water hazards in close-range coal seams

Abstract

The present invention proposes a method for preventing and controlling water hazards in a close-range coal seam. The method comprises the following steps: A) the close-range coal seam includes an upper coal seam and a lower coal seam. Based on the geological conditions and hydrogeological conditions of the close-range coal seam mining working face, it is determined that the overburden above the close-range coal seam has a hard rock layer that needs to be fractured, and the overburden is an aquifer that needs to be prevented and controlled; B) a tunnel is opened in the upper coal seam, and a fracturing borehole is opened from the tunnel to penetrate the hard rock layer; C) a drainage borehole is opened from the tunnel to the aquifer, and the drainage borehole penetrates the hard rock layer; D) the water in the aquifer is drained into the tunnel by using the drainage borehole, and the water drained into the tunnel is led into the fracturing borehole, so as to implement hydraulic fracturing on the hard rock layer. Therefore, the method for preventing and controlling water hazards in a close-range coal seam according to the present invention can save water resources, reduce production costs, and avoid the occurrence of working face frame crushing accidents and water hazards.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, and in particular to a method for preventing and controlling water damage in a close-range coal seam. Background Art

[0002] When there are thick and hard rock layers in the roof of the coal seam, if the upper coal seam does not collapse during mining, the mining of the lower coal seam at a close distance may cause fractures, resulting in strong mining pressure, causing serious fractures in the roof rock layer and the formation of larger crack channels. Especially when there is a water-rich aquifer above the hard rock layer, the violent collapse of the hard rock layer will inevitably cause the mining-induced cracks to communicate with the aquifer, causing instantaneous water inrush from the aquifer. If prevention and control measures are not timely, casualties are likely to occur. Summary of the invention

[0003] The present invention is based on the inventor's discovery and understanding of the following facts and problems: when there is an aquifer with strong water richness above the hard rock stratum, when the close coal seam is mined (especially when the lower group of coal seams are mined), the hard rock stratum is prone to collapse violently under the pressure of the aquifer and cause mining-induced cracks to communicate with the aquifer, causing instantaneous water inrush from the aquifer. If prevention and control measures are not timely, casualties may easily occur.

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a method for preventing and controlling water damage in a close-range coal seam.

[0005] The method for preventing and controlling water damage in a close-range coal seam according to an embodiment of the present invention comprises the following steps:

[0006] A) The close-range coal seam includes an upper coal seam and a lower coal seam. Based on the geological conditions and hydrogeological conditions of the close-range coal seam mining working face, it is determined that the overburden layer above the close-range coal seam has a hard rock layer that needs to be fractured, and the overburden layer is an aquifer that needs to be prevented and controlled;

[0007] B) opening a tunnel in the upper coal seam, and opening a fracturing borehole through the hard rock layer from the tunnel;

[0008] C) opening a drainage borehole from the tunnel to the aquifer, wherein the drainage borehole penetrates the hard rock formation;

[0009] D) draining water from the aquifer into the tunnel using a drainage borehole, and using the water drained into the tunnel to flow into the fracturing borehole, so as to hydraulically fracture the hard rock formation.

[0010] Therefore, the close-range coal seam water hazard prevention and control method according to the embodiment of the present invention can save water resources, reduce production costs, and avoid the occurrence of working face frame crushing accidents and water hazard accidents.

[0011] In some embodiments, in step A), the uniaxial compressive strength of the hard rock layer is greater than or equal to 30 MPa, the thickness of the hard rock layer in the vertical direction is greater than or equal to 5 m, and the distance between the hard rock layer and the upper coal seam is greater than The distance between the hard rock layer and the lower coal seam is less than or equal to Wherein m1 is the thickness of the upper coal seam, m2 is the thickness of the lower coal seam, k1 is the rock expansion coefficient of the roof of the upper coal seam, and k2 is the rock expansion coefficient of the roof of the lower coal seam.

[0012] In some embodiments, in step A), the height of the water-conducting fracture zone during mining of the lower group of coal seams is determined based on the geological conditions and hydrogeological conditions of the nearby coal seam mining working face, and the distance between the aquifer to be prevented and controlled and the lower group of coal seams is less than or equal to the determined height of the water-conducting fracture zone during mining of the lower group of coal seams.

[0013] In some embodiments, in step B),

[0014] The number of the lanes is two, and the two lanes are located at two ends of the upper coal seam in the first horizontal direction;

[0015] The number of the fracturing boreholes is multiple, and the distance between two adjacent fracturing boreholes in the same tunnel in the extension direction of the tunnel is between 25m and 35m;

[0016] Optionally, the distance between two adjacent fracturing boreholes in the same tunnel in the extension direction of the tunnel is 30 m.

[0017] In some embodiments, in step B),

[0018] The inclination angle of the fracturing borehole is greater than or equal to 20° and less than or equal to 30°;

[0019] In a horizontal plane, an angle between a projection of the fracturing borehole and a projection of the tunnel is greater than or equal to 25° and less than or equal to 70°.

[0020] In some embodiments, in step C),

[0021] The ratio of the number of the drainage boreholes to the number of the fracturing boreholes is 1:(8-12);

[0022] The inclination angle of the drainage borehole is greater than or equal to 50° and less than or equal to 75°;

[0023] In the horizontal plane, the angle between the projection of the drainage borehole and the projection of the tunnel is 90°;

[0024] Optionally, the ratio of the number of the drainage boreholes to the number of the fracturing boreholes is 1:10.

[0025] In some embodiments, in step D), the fracturing borehole includes multiple hard rock formation sections, each of the hard rock formation sections is located in the hard rock formation, the middle position of each of the hard rock formation sections is a fracturing section, the water body flows to the fracturing section in the fracturing borehole to perform hydraulic fracturing on the hard rock formation, the length of each of the hard rock formation sections in the up and down directions is greater than or equal to 5m, and the length of each of the fracturing sections in the extension direction of the fracturing borehole is greater than or equal to 1m and less than or equal to 2m.

[0026] In some embodiments, in step D), a water pump and a water injection pipe are used to inject water into the water body at P c Mpa starting pressure to implement hydraulic fracturing on the hard rock formation, P c MPa=(-σ1+3σ3+σ t +1.21×10 6 q 1.75 d -4.75 l+0.01h)MPa, where σ1 is the maximum principal stress of the hard rock formation, σ3 is the minimum principal stress of the hard rock formation, σ t is the tensile strength of the hard rock formation, q is the injection flow rate of the water injection pipe, d is the inner diameter of the water injection pipe, l is the length of the water injection pipe, and h is the height between the water outlet of the water injection pipe and the water inlet of the fracturing section.

[0027] The method for preventing and controlling water damage in a close-range coal seam according to an embodiment of the present invention further includes step E), wherein step E includes:

[0028] E-1) opening a test borehole in the tunnel that penetrates the hard rock formation, the test borehole being parallel to one of the plurality of fracturing boreholes, the test borehole being at a preset distance from the one of the plurality of fracturing boreholes in the extension direction of the tunnel, and the ratio of the number of the test boreholes to the number of the fracturing boreholes being 1:(8-12);

[0029] E-2) when hydraulic fracturing is performed on said one of the plurality of fracturing boreholes, detecting a first water pressure and a first water inflow in said test borehole;

[0030] E-3) performing a second hydraulic fracturing on said one of the plurality of said fracturing boreholes, and detecting a second water pressure and a second water inflow in said test borehole, and if said second water pressure and said second water inflow reach preset values ​​respectively, it is determined that said hard rock formation has achieved a fracturing effect and the prevention and control of said aquifer is achieved;

[0031] Optionally, the distance between the inspection borehole and one of the multiple fracturing boreholes in the extension direction of the tunnel is 3 m, and the ratio of the number of the inspection boreholes to the number of the fracturing boreholes is 1:10.

[0032] In some embodiments, in step E), if the second water pressure reaches the injection pressure of one of the multiple fracturing boreholes, and the second water inflow increases to more than 1.5 times the first water inflow, it is determined that the hard rock formation has achieved the fracturing effect and the prevention and control of the aquifer is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 2 is a front view of a fracturing borehole and a water drainage borehole according to an embodiment of the present invention.

[0034] Figure 2 2 is a front view of a fracturing borehole and a water drainage borehole according to an embodiment of the present invention.

[0035] Figure 3 1 is a top view of a fracturing borehole and a water drainage borehole according to an embodiment of the present invention.

[0036] Reference numerals:

[0037] Overburden stratum 1, weak rock stratum 1, hard rock stratum 2, aquifer 3, close-range coal seam 4, upper group coal seam 41, tunnel 411 and lower group coal seam 42, fracturing borehole 5, fracturing section 51, drainage borehole 6, inspection borehole 7. DETAILED DESCRIPTION

[0038] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0039] The following describes the method for preventing and controlling water damage in a close distance coal seam according to an embodiment of the present invention with reference to the accompanying drawings. Figures 1 to 3 As shown, the method for preventing and controlling water damage in a close-range coal seam according to an embodiment of the present invention comprises the following steps:

[0040] A) The close-range coal seam 4 includes an upper group coal seam 41 and a lower group coal seam 42. Based on the geological conditions and hydrogeological conditions of the mining working face of the close-range coal seam 4, it is determined that the overburden layer 1 above the close-range coal seam 4 has a hard rock layer 2 that needs to be fractured, and above the overburden layer 1 is an aquifer 3 that needs to be prevented and controlled.

[0041] B) A tunnel 411 is opened in the upper coal seam 41, and a fracturing borehole 5 is opened from the tunnel 411 to penetrate the hard rock layer 2.

[0042] C) A drainage borehole 6 leading to the aquifer 3 is opened from the tunnel 411, and the drainage borehole 6 penetrates the hard rock layer 2.

[0043] D) Using the drainage borehole 6 to drain the water in the aquifer 3 to the tunnel 411, and using the water drained into the tunnel 411 to pass into the fracturing borehole 5, so as to implement hydraulic fracturing on the hard rock layer 2.

[0044] The present invention is based on the inventor's discovery and understanding of the following facts and problems: when there is an aquifer with strong water richness above the hard rock stratum, when the close coal seam is mined (especially when the lower group of coal seams are mined), the hard rock stratum is prone to collapse violently under the pressure of the aquifer and cause mining-induced cracks to communicate with the aquifer, causing instantaneous water inrush from the aquifer. If prevention and control measures are not timely, casualties may easily occur.

[0045] According to the method for preventing and controlling water damage in a close-range coal seam according to an embodiment of the present invention, a fracturing borehole 5 connected to a tunnel 411 is arranged in a hard rock layer 2, thereby hydraulic fracturing can be carried out by passing water into the fracturing borehole 5, so as to break the hard rock layer 2, thereby preventing the hard rock layer 2 from drastically collapsing, reducing the intensity of the mine pressure manifestation of the close-range coal seam 4, and avoiding the occurrence of a frame crushing accident on the working face. A drainage borehole 6 connected to the tunnel 411 is arranged in the aquifer 3, thereby a part of the water in the aquifer 3 can be drained to the tunnel 411, thereby reducing the water pressure of the water layer of the aquifer 3, reducing the intensity of water inrush, and further reducing the intensity of the mine pressure manifestation of the hard rock layer 2, while reducing the height of the water-conducting fracture zone, and avoiding water damage accidents. And using the water discharged into the tunnel 411 as a water source for hydraulic fracturing of the hard rock layer 2 can reduce the waste of water resources and reduce production costs.

[0046] Therefore, the close-range coal seam water hazard prevention and control method according to the embodiment of the present invention can save water resources, reduce production costs, and avoid the occurrence of working face frame crushing accidents and water hazard accidents.

[0047] like Figures 1 to 3 As shown, the method for preventing and controlling water damage in a close distance coal seam according to an embodiment of the present invention comprises step A), step B), step C), step D) and step E).

[0048] In step A), the close-range coal seam 4 includes an upper coal seam 41 and a lower coal seam 42, and the upper coal seam 41 is located above the lower coal seam 42. Based on the geological conditions and hydrogeological conditions of the mining working face of the close-range coal seam 4, it is determined that the overburden stratum 1 above the close-range coal seam 4 has a hard rock stratum 2 that needs to be fractured, and above the overburden stratum 1 is an aquifer 3 that needs to be prevented and controlled. Specifically, the hard rock stratum 2 that needs to be fractured has a preset distance from the nearby coal seam 4 (upper group coal seam 41 and lower group coal seam 42) in the up and down directions, thereby it can be determined that the hard rock stratum 2 is the hard rock stratum 2 that needs to be fractured, thereby preventing fracture when mining the nearby coal seam 4; the aquifer 3 that needs to be prevented and controlled is an aquifer 3 with medium or higher water richness, and the aquifer 3 has a preset distance from the nearby coal seam 4 (lower group coal seam 42), thereby it can be determined that the aquifer 3 is the aquifer 3 that needs to be prevented and controlled, thereby preventing the aquifer 3 from compressing the hard rock stratum 2 when mining the nearby coal seam 4, causing the hard rock stratum 2 to collapse violently and causing the mining-induced cracks to communicate with the aquifer 3. Preventing and controlling the aquifer 3 can prevent the occurrence of instantaneous water inrush from the aquifer 3, thereby reducing casualties.

[0049] In some embodiments, the hard rock formation 2 to be fractured satisfies the following conditions:

[0050] The uniaxial compressive strength of the hard rock layer 2 is greater than or equal to 30 MPa, and the thickness of the hard rock layer 2 in the vertical direction is greater than or equal to 5 m. The distance between the hard rock layer 2 and the upper coal layer 41 in the vertical direction is greater than The distance between the hard rock layer 2 and the lower coal layer 42 in the vertical direction is less than or equal to Wherein, m1 is the thickness of the upper coal seam 41, m2 is the thickness of the lower coal seam 42, k1 is the rock expansion coefficient of the roof of the upper coal seam 41, and k2 is the rock expansion coefficient of the roof of the lower coal seam 42. If it is determined that the hard rock layer 2 above the close-up coal seam 4 meets the above conditions, it means that when mining the lower coal seam 42, the hard rock layer 2 may experience strong mine pressure, and the hard rock layer 2 needs to be fractured to prevent the hard rock layer 2 from experiencing strong mine pressure when mining the close-up coal seam 4, resulting in serious rupture of the roof rock layer and the formation of larger crack channels. Figure 1 and Figure 2 As shown by arrow B in FIG.

[0051] For example, the thickness m1 of the upper coal seam 41 is 5 m, the thickness m2 of the lower coal seam 42 is 10 m, and the rock expansion coefficient k1 of the top plate of the upper coal seam 41 and the rock expansion coefficient k2 of the top plate of the lower coal seam 42 are both 1.3. is 16.67m, If the distance between the hard rock layer 2 and the upper coal seam 41 in the vertical direction is greater than 16.67m, and the distance between the hard rock layer 2 and the lower coal seam 42 in the vertical direction is less than or equal to 50m, the hard rock layer 2 needs to be fractured.

[0052] In some embodiments, the height of the water-conducting fracture zone during mining of the lower coal seam 42 is determined according to the geological conditions and hydrogeological conditions of the mining working face of the close-range coal seam 4. For example, the height of the water-conducting fracture zone during mining of the lower coal seam 42 is calculated by analogy measurement and empirical formula.

[0053] The distance between the aquifer 3 to be prevented and controlled and the lower coal seam 42 is less than or equal to the height of the water-conducting fracture zone when the lower coal seam 42 is mined. If the aquifer 3 is not prevented and controlled, water damage will easily occur when the lower coal seam 42 is mined. Therefore, preventing and controlling the aquifer 3 can avoid water damage accidents.

[0054] In step B), a tunnel 411 is opened in the upper coal seam 41, and based on the thickness and structural characteristics of the hard rock layer 2, a fracturing borehole 5 is opened in the tunnel 411 to penetrate the hard rock layer 2. Thus, a water pump and other hydraulic fracturing equipment can be arranged in the tunnel 411, so as to hydraulically fracture the hard rock layer 2 through the fracturing borehole 5.

[0055] In some embodiments, the number of tunnels 411 is two, and the two tunnels 411 are located at both ends of the upper coal seam 41 in the first horizontal direction. The two tunnels 411 can use the tape chute and the track chute at both ends of the upper coal seam 41, thereby reducing the construction workload. Figures 1 to 3 As shown by arrow A in FIG. 4 , for example, two tunnels 411 are located at both ends of the upper coal seam 41 in the left-right direction.

[0056] There are multiple fracturing boreholes 5, and the distance between two adjacent fracturing boreholes 5 in the same tunnel 411 in the extension direction of the tunnel 411 is between 25m and 35m. The extension direction of the tunnel 411 can be the front-to-back direction, such as Figure 3 As shown by arrow C in FIG. 4 , for example, the distance between two adjacent fracturing boreholes 5 in the same tunnel 411 in the front-to-rear direction is between 25 m and 35 m.

[0057] Optionally, the distance between two adjacent fracturing boreholes 5 in the same tunnel 411 in the extension direction of the tunnel 411 is 30 m.

[0058] like Figure 1 and Figure 2As shown, in some embodiments, the inclination angle of the fracturing borehole 5 is greater than or equal to 20° and less than or equal to 30°, that is, the angle between the extension direction of the fracturing borehole 5 and the horizontal plane is greater than or equal to 20° and less than or equal to 30°. The inclination angle of the fracturing borehole 5 is greater than or equal to 20° and less than or equal to 30°, which can facilitate the hydraulic fracturing of the hard rock formation 2 through the fracturing borehole 5.

[0059] like Figure 3 As shown, in the horizontal plane, the angle between the projection of the fracturing borehole 5 and the projection of the tunnel 411 is greater than or equal to 25° and less than or equal to 70°. The angle between the projection of the fracturing borehole 5 and the projection of the tunnel 411 in the horizontal plane can be determined according to actual conditions, so as to evenly perform hydraulic fracturing on the hard rock formation 2.

[0060] In step C), a drainage borehole 6 leading to the aquifer 3 is opened from the tunnel 411 , and the drainage borehole 6 penetrates the hard rock layer 2 .

[0061] The ratio of the number of drainage boreholes 6 to the number of fracturing boreholes 5 is 1:(8-12), that is, the water discharged through one drainage borehole 6 can provide water source for multiple fracturing boreholes 5 for hydraulic fracturing.

[0062] Optionally, the ratio of the number of drainage boreholes 6 to the number of fracturing boreholes 5 is 1:10.

[0063] like Figure 1 and Figure 2 As shown, in some embodiments, the inclination angle of the drainage water borehole 6 is greater than or equal to 50° and less than or equal to 75°. That is, the angle between the extension direction of the drainage water borehole 6 and the horizontal plane is greater than or equal to 50° and less than or equal to 75°. The inclination angle of the drainage water borehole 6 is greater than or equal to 50° and less than or equal to 75°, which can facilitate the drainage of water in the aquifer 3 through the drainage water borehole 6.

[0064] like Figure 3 As shown, in the horizontal plane, the angle between the projection of the drainage borehole 6 and the projection of the tunnel 411 is 90°. This can reduce the length of the drainage borehole 6, thereby reducing the construction workload.

[0065] In step D), the water in the aquifer 3 is drained to the tunnel 411 by using the drainage borehole 6, so that the water pressure of a part of the aquifer 3 can be reduced in advance by using the drainage borehole 6, the water inrush intensity can be reduced, the accumulation of stratum water can be weakened, and the pressure of the hard rock layer 2 can be further reduced, and the height of the water-conducting fracture zone can be reduced.

[0066] The water discharged into the tunnel 411 is led into the fracturing borehole 5 to hydraulically fractur the hard rock stratum 2. The water discharged into the tunnel 411 is used as a water source for hydraulically fracturing the hard rock stratum 2, so that the water in the aquifer 3 can be reused, which can reduce the waste of water resources and reduce production costs. Hydraulic fracturing is performed on the hard rock stratum 2 to break the hard rock stratum 2, so that the hard rock stratum 2 will not collapse violently, the mine pressure intensity of the close-range coal seam 4 is reduced, and the frame crushing accident of the working face is avoided.

[0067] like Figure 1 and Figure 2 As shown, in some embodiments, the fracturing borehole 5 includes a plurality of hard rock formation 2 sections, each of which is located in the hard rock formation 2, and the middle position of each hard rock formation 2 section is a fracturing section 51, and water is passed to the fracturing section 51 in the fracturing borehole 5 to hydraulically fracture the hard rock formation 2. Specifically, at both ends of the closed fracturing section 51, water with a certain pressure is passed into the closed fracturing section 51 to fractur the hard rock formation 2 near the fracturing section 51, thereby completing the hydraulic fracturing of the hard rock formation 2. After the fracturing section 51 in the fracturing borehole 5 is hydraulically fractured, the portion of the drainage water borehole 6 above the hard rock formation 2 is blocked, and the portion of the drainage water borehole 6 located in the hard rock formation 2 is hydraulically fractured.

[0068] The length of each hard rock layer 2 in the vertical direction is greater than or equal to 5m, and the length of each fracturing segment 51 in the extension direction of the fracturing borehole 5 is greater than or equal to 1m and less than or equal to 2m. Hydraulic fracturing of the fracturing segment 51 with a length greater than or equal to 1m and less than or equal to 2m can better break the hard rock layer 2.

[0069] like Figure 2 As shown, if the hard rock layer 2 includes a weak interlayer 11 with a thickness greater than 5 m in the vertical direction, the fracturing stage 51 crosses (is not located in) the weak interlayer 11 .

[0070] In some embodiments, a water pump and a water injection pipe are used to inject water into the water body at P c The hydraulic fracturing of hard rock formation 2 is carried out with a starting pressure of Mpa, P c MPa=(-σ1+3σ3+σ t +1.21×10 6 q 1.75 d -4.75 l+0.01h)MPa, where σ1 is the maximum principal stress of hard rock layer 2, σ3 is the minimum principal stress of hard rock layer 2, σ tis the tensile strength of the hard rock formation 2, q is the injection flow rate of the water injection pipe, d is the inner diameter of the water injection pipe, l is the length of the water injection pipe, and h is the height between the water outlet of the water injection pipe and the water inlet of the fracturing section 51. Specifically, the water outlet of the water injection pipe is connected to the water inlet of the fracturing section 51 through a fracturing joint so as to perform hydraulic fracturing on the fracturing section 51, and the water outlet of the water injection pipe and the water inlet of the fracturing section 51 have a certain height, as shown in P c The starting pressure of Mpa can better fractur the hard rock formation 2.

[0071] For example, σ1 is 11.5 MPa, σ3 is 6.5 MPa, and σ t is 5MPa, q is 5L / s, d is 75mm, l is 100m, h is 5m, then P c Mpa is 15.56Mpa, that is, the water body performs hydraulic fracturing on the hard rock layer 2 with a starting pressure of 15.56Mpa.

[0072] Step E) includes step E-1), step E-2) and step E-3).

[0073] In step E-1), a test borehole 7 penetrating the hard rock layer 2 is opened in the tunnel 411, the test borehole 7 is parallel to one of the multiple fracturing boreholes 5, and there is a preset distance between the test borehole 7 and the one of the multiple fracturing boreholes 5 in the extension direction of the tunnel 411, and the ratio of the number of test boreholes 7 to the number of fracturing boreholes 5 is 1:(8-12). Specifically, the distance between the test borehole 7 and the one of the multiple fracturing boreholes 5 in the extension direction of the tunnel 411 is 3m.

[0074] Optionally, the ratio of the number of inspection boreholes 7 to the number of fracturing boreholes 5 is 1:10.

[0075] In step E-2), when hydraulic fracturing is performed on one of the plurality of fracturing boreholes 5, the first water pressure and the first water inflow in the test borehole 7 are detected;

[0076] In step E-3), a second hydraulic fracturing is performed on one of the multiple fracturing boreholes 5, and the second water pressure and the second water inflow in the test borehole 7 are detected. If the second water pressure and the second water inflow reach the preset values ​​respectively, it is determined that the hard rock layer 2 has achieved the fracturing effect and the prevention and control of the aquifer 3 is realized.

[0077] In step E), a test borehole 7 is set up and any one of the multiple fracturing boreholes 5 is tested. The fracturing effect can be determined by comparing the numerical changes of the first water pressure and the second water pressure in the test borehole 7, and the numerical changes of the first water inflow and the second water inflow. If the fracturing effect is not achieved, the hard rock formation 2 can be hydraulically fractured again.

[0078] In some embodiments, in step E), if the second water pressure reaches the injection pressure of one of the multiple fracturing boreholes 5, and the second water inflow increases to more than 1.5 times the first water inflow, it is determined that the hard rock layer 2 has achieved the fracturing effect and the prevention and control of the aquifer 3 is achieved, thereby preventing water disasters from occurring in the nearby coal seam 4.

[0079] For example, the first water inflow of the test borehole 7 is 5m 3 / h. As hydraulic fracturing increases the cracks in the rock mass, the second water inflow increases to 7.5m 3 / h or above, it proves that the hydraulic fracturing effect is good.

[0080] After completing the hydraulic fracturing of the hard rock formation 2, when the working face of the upper coal seam 41 is mined, when the pressure gauge on the upper support of the upper coal seam 41 detects that the hard rock formation 2 is broken at the set position of the fracturing section 51, it can also indicate that the hydraulic fracturing of the hard rock formation 2 has achieved the fracturing effect.

[0081] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0082] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0083] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0084] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0085] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0086] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preventing and controlling water damage in a close-range coal seam, characterized in that: The following steps are involved: A) The close-range coal seams include upper coal seams and lower coal seams. Based on the geological conditions and hydrogeological conditions of the close-range coal seam mining working face, it is determined that the overburden layer above the close-range coal seams has a hard rock layer that needs to be fractured, and the overburden layer is an aquifer that needs to be prevented and controlled; B) opening a tunnel in the upper coal seam and opening a fracturing borehole through the hard rock layer from the tunnel; C) opening a drainage borehole from the tunnel to the aquifer, wherein the drainage borehole penetrates the hard rock formation; D) draining water from the aquifer into the tunnel using a drainage borehole, and using the water drained into the tunnel to flow into the fracturing borehole, so as to perform hydraulic fracturing on the hard rock formation; In step A), the height of the water-conducting fracture zone during mining of the lower group of coal seams is determined based on the geological conditions and hydrogeological conditions of the nearby coal seam mining working face, and the distance between the aquifer to be controlled and the lower group of coal seams is less than or equal to the determined height of the water-conducting fracture zone during mining of the lower group of coal seams.

2. The method for preventing and controlling water damage in a close-range coal seam according to claim 1, characterized in that: In step A), the uniaxial compressive strength of the hard rock layer is greater than or equal to 30 MPa, the thickness of the hard rock layer in the vertical direction is greater than or equal to 5 m, and the distance between the hard rock layer and the upper coal seam is greater than , the distance between the hard rock layer and the lower coal seam is less than or equal to ,in is the thickness of the upper coal seam, is the thickness of the lower coal seam, is the rock expansion coefficient of the upper coal seam roof, is the rock expansion coefficient of the roof of the lower coal seam.

3. The method for preventing and controlling water damage in a close-range coal seam according to claim 1, characterized in that: In step B), The number of the lanes is two, and the two lanes are located at two ends of the upper coal seam in the first horizontal direction; The number of the fracturing boreholes is multiple, and the distance between two adjacent fracturing boreholes in the same tunnel in the extension direction of the tunnel is between 25m and 35m; Optionally, the distance between two adjacent fracturing boreholes in the same tunnel in the extension direction of the tunnel is 30 m.

4. The method for preventing and controlling water damage in a close distance coal seam according to claim 3 is characterized in that: In step B), The inclination angle of the fracturing borehole is greater than or equal to 20° and less than or equal to 30°; In a horizontal plane, an angle between a projection of the fracturing borehole and a projection of the tunnel is greater than or equal to 25° and less than or equal to 70°.

5. The method for preventing and controlling water damage in a close distance coal seam according to claim 1, characterized in that: In the step C), The ratio of the number of drainage boreholes to the number of fracturing boreholes is 1:(8-12); The inclination angle of the drainage borehole is greater than or equal to 50° and less than or equal to 75°; In the horizontal plane, the angle between the projection of the drainage borehole and the projection of the tunnel is 90°; Optionally, the ratio of the number of the drainage boreholes to the number of the fracturing boreholes is 1:

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6. The method for preventing and controlling water damage in a close distance coal seam according to claim 1, characterized in that: In step D), the fracturing borehole includes a plurality of hard rock formation sections, each of the hard rock formation sections is located in the hard rock formation, the middle position of each of the hard rock formation sections is a fracturing section, the water body flows to the fracturing section in the fracturing borehole so as to hydraulically fracture the hard rock formation, the length of each of the hard rock formation sections in the vertical direction is greater than or equal to 5m, and the length of each of the fracturing sections in the extension direction of the fracturing borehole is greater than or equal to 1m and less than or equal to 2m.

7. The method for preventing and controlling water damage in a close distance coal seam according to claim 6, characterized in that: In step D), the water body is pumped with a water pump and a water injection pipe. P c Mpa starting pressure to implement hydraulic fracturing on the hard rock formation, P c MPa = (- σ 1+3 σ 3+ σ t +1.21×10 6 q 1.75 d -4.75 l +0.01h)MPa, where σ 1 is the maximum principal stress of the hard rock formation, σ 3 is the minimum principal stress of the hard rock formation, σ t is the tensile strength of the hard rock formation, q is the water injection flow rate of the water injection pipe, d is the inner diameter of the water injection pipe, l is the length of the water injection pipe, h It is the height between the water outlet of the water injection pipe and the water inlet of the fracturing section.

8. The method for preventing and controlling water damage in a close distance coal seam according to claim 1, characterized in that: The step also includes step E), wherein the step E includes: E-1) opening a test borehole in the tunnel that penetrates the hard rock formation, the test borehole being parallel to one of the plurality of fracturing boreholes, the test borehole being at a preset distance from the one of the plurality of fracturing boreholes in the extension direction of the tunnel, and the ratio of the number of the test boreholes to the number of the fracturing boreholes being 1:(8-12); E-2) when hydraulic fracturing is performed on said one of the plurality of fracturing boreholes, detecting a first water pressure and a first water inflow in said test borehole; E-3) performing a second hydraulic fracturing on said one of the plurality of fracturing boreholes, and detecting a second water pressure and a second water inflow in said test borehole, and if said second water pressure and said second water inflow reach preset values ​​respectively, it is determined that said hard rock formation has achieved a fracturing effect and prevention and control of said aquifer is achieved; Optionally, the distance between the inspection borehole and one of the multiple fracturing boreholes in the extension direction of the tunnel is 3 m, and the ratio of the number of the inspection boreholes to the number of the fracturing boreholes is 1:

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9. The method for preventing and controlling water damage in a close distance coal seam according to claim 8, characterized in that: In step E), if the second water pressure reaches the injection pressure of one of the multiple fracturing boreholes and the second water inflow increases to more than 1.5 times the first water inflow, it is determined that the hard rock formation has achieved the fracturing effect and the prevention and control of the aquifer is achieved.

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