A method for protecting a working face along a seam affected by mining

Abstract

This invention discloses a method for protecting in-seam boreholes in working faces affected by mining activities. The method includes: measuring the rock mechanics parameters of each stratum in the roadway roof to determine the location and thickness of the subcritical roof strata; obtaining the width of the plastic zone of the coal seam in the working face roadway under the influence of mining activities in adjacent working faces through numerical simulation; constructing in-seam boreholes in the working face roadway to increase the initial sealing depth and sealing depth of the boreholes; performing hydraulic fracturing to weaken the roof in both adjacent working face roadways and the working face roadway to reduce the peak bearing stress of the coal seam in the working face under the influence of mining activities in adjacent working faces; lowering the extraction negative pressure of the in-seam boreholes in the working face roadway after the adjacent working face has been mined; inspecting the in-seam boreholes and performing secondary sealing on leaking boreholes. This invention effectively reduces the damage to the in-seam boreholes in the working face caused by mining activities in adjacent working faces, ensures the extraction effect of the in-seam boreholes in the mining face, reduces the gas content of the coal seam in the working face, and ensures safe production in the mining face.

Description

Technical Field

[0001] This invention relates to a method for protecting boreholes along the working face affected by mining activities, belonging to the field of coal mine gas extraction technology. Background Technology

[0002] Gas disasters are one of the major hazards threatening mine production. Gas control in longwall mining faces is the main method to ensure efficient and safe mine production. Currently, high-gas and outburst-prone mines in my country mainly use in-seam borehole pre-drainage of gas from longwall mining faces. During the mining process of adjacent working faces, high support stress is generated in the working face. Under the influence of high support stress, the coal face is damaged, and a large plastic zone is formed in the coal wall of the roadway. This causes more fractures to develop near the in-seam borehole, thereby compromising the airtightness of the borehole seal and resulting in poor drainage effect of the in-seam borehole.

[0003] In existing literature, the paper (Hu Shengyong. Seepage characteristics of coal and rock around gas drainage boreholes and powder plugging mechanism [D]. China University of Mining and Technology, 2014.) considers the influence of the disturbance caused by the sequential excavation of roadways and boreholes, studies the flow characteristics of gas and air in the surrounding rock, and directly reveals the gas leakage mechanism of the borehole. The paper (Yao Xiangrong, Cheng Gonglin, Shi Biming. Instability analysis and borehole forming method of gas drainage boreholes in deep surrounding rock with weak structure [J]. Journal of Coal Science and Technology, 2010, 35(12):2073-2081.) uses FLAC 3D The software numerically simulated the extraction boreholes in the return airway of Dingji Coal Mine, and calculated the variation law of the plastic zone around the borehole. Existing protection measures for in-seam boreholes mostly focus on increasing borehole strength, without studying how to change the roof lithology and reduce mining support stress. Summary of the Invention

[0004] To address the aforementioned problems with in-seam boreholes affected by mining activities, this invention provides a method for protecting in-seam boreholes in working faces affected by mining activities. This method systematically considers aspects such as borehole sealing parameters, hydraulic fracturing to weaken the roof and reduce support stress, and secondary borehole sealing, thereby ensuring the gas extraction effect of in-seam boreholes affected by mining activities.

[0005] This invention proposes a method for protecting boreholes along the bedding plane in working faces affected by mining. The method mainly involves studying the stress distribution law of mining support to guide the sealing parameters, weakening the roof through hydraulic fracturing to reduce the peak stress and influence range of mining support, thereby reducing borehole damage, and performing secondary sealing on locally damaged boreholes to ensure the extraction effect of boreholes along the bedding plane.

[0006] This invention provides a method for protecting boreholes along the bedding plane in working faces affected by mining activities, comprising the following: (1) The rock mechanics parameters of each rock layer in the roadway roof were measured to determine the location and thickness of the sub-key rock layer in the roof. Based on the rock mechanics parameters of the roof rock layer, the width of the plastic zone of the coal body in the roadway under the influence of mining in the adjacent working face was obtained by numerical simulation. (2) In this working face roadway, drill along the bedding plane, increase the initial sealing depth and sealing depth of the borehole, the initial sealing depth of the borehole exceeds the length of the side anchor bolt, and the sealing depth of the borehole exceeds the width of the plastic zone of the coal body under the influence of mining. Specifically, the initial sealing depth of the borehole increased from 2-4m to 7-9m, and the sealing depth increased from 14-16m to 19-21m; (3) Perform segmented hydraulic fracturing to weaken the roof in adjacent working face roadways and this working face roadways, reduce the peak bearing stress of the coal body in this working face under the influence of mining in adjacent working faces, and reduce the width of the plastic zone of the coal body in this working face. (4) After the adjacent working face is mined, the extraction negative pressure of the borehole in the roadway of this working face is appropriately reduced; the extraction concentration of the borehole in the roadway is tested (if the concentration drops too much, it means that there is a gas leak), and the leaking borehole is sealed a second time.

[0007] Furthermore, the rock mechanics parameters of each rock layer in the tunnel roof include thickness, density, tensile strength, shear modulus, bulk modulus, cohesion, and internal friction angle, which determine the location and thickness of the subcritical layer.

[0008] Furthermore, FLAC was applied based on the rock mechanical parameters of each rock layer in the tunnel roof. 3D The software performs numerical simulations to obtain the width of the plastic zone of the coal seam in the roadway of this working face under the influence of mining activities in adjacent working faces.

[0009] Furthermore, the hydraulic fracturing boreholes form an angle with the plane of the roadway roof (two fracturing boreholes can be selected according to the actual conditions of the mine), with an angle range of 60~80°. The borehole spacing is 10~15m, the borehole diameter is 75mm, and the borehole construction length is designed to exceed the subcritical layer by 1~2m. During construction, the location of the subcritical layer section is recorded in detail. Fracturing is performed every 2~3m in the fracturing section until the entire subcritical layer section is fractured. The water injection fracturing sequence is from the inside out, i.e., the reverse fracturing method. The fracturing time for each time is based on the water output of the adjacent borehole and the fracturing time is not less than 20min. After hydraulic fracturing of the roadway roof, the stress peak of the coal body of this working face under the action of the adjacent working face mining can be reduced, thereby reducing the range of the plastic zone of the coal body of this working face.

[0010] Furthermore, after the adjacent working face is mined, the negative pressure of the in-seam boreholes in this working face affected by mining is adjusted to -10~-5 kPa, referring to the negative pressure requirements for depressurization gas drainage.

[0011] Furthermore, the gas extraction concentration of the boreholes along the bedding plane was tested. For boreholes with a gas extraction concentration below 10%, a smaller diameter sealing pipe was used in conjunction with two plugs and one injection bag for secondary sealing of the borehole. The sealing depth exceeded the first sealing depth by 3-5 meters. The diameter of the sealing pipe for the second sealing was determined based on the diameter of the sealing pipe for the first sealing, and was approximately 10 mm smaller than the diameter of the sealing pipe for the first sealing.

[0012] The beneficial effects of this invention are: This invention can effectively reduce the damage to the boreholes along the seam of the working face caused by mining activities in adjacent working faces, ensure the extraction effect of the boreholes along the seam of the working face, effectively reduce the gas content of the coal seam of the working face, and ensure safe production of the working face. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the combination of hydraulic fracturing weakening boreholes and in-seam boreholes in an embodiment of the present invention; Figure 2 for Figure 1 Top view of the sealing section of the borehole in the middle bedding layer; Figure 3 This is a schematic diagram of secondary sealing of the borehole in an embodiment of the present invention; Figure 4 This is a block diagram of the process flow of the present invention.

[0014] In the diagram: 1. In-seam borehole; 2. First sealing bag of the borehole sealer; 3. Second sealing bag of the borehole sealer; 4. Side anchor bolt; 5. Plastic zone; 6. Original coal body; 7. Adjacent working face roadway; 8. This working face roadway; 9. First hydraulic fracturing borehole; 10. Second hydraulic fracturing borehole; 11. Third hydraulic fracturing borehole; 12. Subcritical stratum; 13. Fracturing line; 14. Secondary sealing pipe; 15. First sealing bag of the secondary sealing borehole sealer; 16. Second sealing bag of the secondary sealing borehole sealer. Detailed Implementation

[0015] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, an embodiment of the present invention will be further described below with reference to the accompanying drawings. Many implementation details of the present invention are set forth in the following description, but those skilled in the art can implement it in other ways without departing from the spirit of the present invention. Other embodiments obtained by those skilled in the art without inventive effort are all within the scope of protection of the present invention. Example

[0016] A method for protecting boreholes along the bedding plane in a working face affected by mining activities includes the following steps: Determine the rock mechanics parameters of each rock layer in the roadway roof, including thickness, density, tensile strength, shear modulus, bulk modulus, cohesion, and internal friction angle, to determine the thickness and location of the subcritical layer;

[0017] Based on the rock mechanics parameters given in Table 1, such as thickness, density, shear modulus, bulk modulus, cohesion, and internal friction angle of each rock layer in the tunnel roof, FLAC was applied. 3D The software performs numerical simulation to obtain the width of the plastic zone of the coal seam in the roadway of this working face under the influence of mining in the adjacent working face (18m). In this working face roadway, borehole 1 is drilled along the bedding plane. The borehole sealing pipe diameter is 63mm. The initial sealing depth exceeds the length of the side anchor bolt, meaning the depth of the first sealing bag 2 must exceed the length of the side anchor bolt 4 (2.5m). The borehole sealing depth exceeds the width of the plastic zone of the coal seam in this working face roadway, meaning the depth of the second sealing bag 3 must exceed the width of the plastic zone 5 (8m), and ensure that the second sealing bag 3 enters the original coal seam 6. Figure 1 and 2 As shown.

[0018] like Figure 1 As shown, a first hydraulic fracturing borehole 9 and a second hydraulic fracturing borehole 10, or a first hydraulic fracturing borehole 9 and a third hydraulic fracturing borehole 11, are arranged in the adjacent working face roadway 7 and the current working face roadway 8 (the conditions of each mine are different; the roof cutting method that can be implemented in the mine is adopted). The angle between the hydraulic fracturing borehole and the roadway roof plane is 80°, the borehole spacing is 10m, the borehole diameter is 75mm, and the borehole construction length is in accordance with the range of more than 12 subcritical layers. The design is carried out within a 1m radius. During construction, the location of the subcritical layer borehole is recorded in detail. Fracturing is performed every 2m in the fracturing section to form a fracturing line 13 until the entire subcritical layer borehole section is fractured. The water injection fracturing sequence is from the inside out, i.e., the reverse fracturing method. The fracturing time for each fracturing is based on the water output of the adjacent borehole and the fracturing time is not less than 20 minutes. Hydraulic fracturing weakens the roof of the coal body above this working face, reduces the peak stress of the mining support in the adjacent working face, and reduces the range of the plastic zone of the coal body in this working face.

[0019] After the adjacent working face is mined, the negative pressure of the in-seam boreholes in this working face affected by the mining is adjusted to -10~-5 kPa, referring to the negative pressure requirements for depressurization gas drainage.

[0020] The gas extraction concentration of the boreholes along the bedding plane is tested. For boreholes with a gas extraction concentration of less than 10%, secondary sealing is performed. This is done by using a secondary sealing pipe 14 with a smaller diameter (32mm) and two plugs and one injection bag for secondary sealing. The first bag 15 of the secondary sealing device is located inside the first sealing pipe, and the second bag 16 of the secondary sealing device extends 3m beyond the depth of the second bag 3 of the first sealing device.

[0021] This embodiment provides a method for protecting working faces affected by mining through in-seam borehole drilling (see flowchart). Figure 4 As shown in the figure, firstly, the rock mechanics parameters of each stratum in the roof of the roadway are measured to determine the location and thickness of the subcritical strata. Then, based on the rock mechanics parameters of the roof strata, numerical simulation is used to study the width of the plastic zone of the coal body in this working face roadway under the influence of mining in the adjacent working face. Next, in-seam boreholes are drilled in this working face roadway, increasing the initial sealing depth and sealing depth of the boreholes. The initial sealing depth exceeds the length of the side anchor bolts, and the sealing depth exceeds the width of the plastic zone of the coal body under the influence of mining. Next, segmented hydraulic fracturing is performed in the adjacent working face roadway and this working face roadway to weaken the roof, reduce the peak bearing stress of the coal body in this working face under the influence of mining in the adjacent working face, thereby reducing the width of the plastic zone of the coal body in this working face. Next, after the adjacent working face is mined, the extraction negative pressure of the in-seam boreholes in this working face roadway is appropriately reduced. Finally, the extraction concentration of the in-seam boreholes is tested, and the leaking boreholes are sealed a second time. This invention effectively reduces the damage to the boreholes along the seam of the working face caused by mining activities in adjacent working faces, ensures the extraction effect of the boreholes along the seam of the longwall mining face, can effectively reduce the gas content of the coal seam of the working face, and ensure safe production of the longwall mining face.

Claims

1. A method for protecting boreholes along the bedding plane in a working face affected by mining, characterized in that... Includes the following: (1) The rock mechanics parameters of each rock layer in the roadway roof were measured to determine the location and thickness of the sub-key rock layer in the roof. Based on the rock mechanics parameters of the roof rock layer, the width of the plastic zone of the coal body in the roadway under the influence of mining in the adjacent working face was obtained by numerical simulation. (2) In this working face roadway, drill along the bedding plane, increase the initial sealing depth and sealing depth of the borehole, the initial sealing depth of the borehole exceeds the length of the side anchor bolt, and the sealing depth of the borehole exceeds the width of the plastic zone of the coal body under the influence of mining. (3) Perform segmented hydraulic fracturing to weaken the roof in adjacent working face roadways and this working face roadways, reduce the peak bearing stress of the coal body in this working face under the influence of mining in adjacent working faces, and reduce the width of the plastic zone of the coal body in this working face. (4) After the adjacent working face is mined, the negative pressure of the extraction of the boreholes along the roadway of this working face is reduced; the extraction concentration of the boreholes along the roadway is tested, and the leaking boreholes are sealed a second time.

2. The method for protecting working faces affected by mining operations through borehole drilling according to claim 1, characterized in that: In step (1), the rock mechanics parameters of each rock layer in the roadway roof include thickness, density, tensile strength, shear modulus, bulk modulus, cohesion, internal friction angle, and the location and thickness of the subcritical layer.

3. The method for protecting working faces affected by mining operations through borehole drilling according to claim 1, characterized in that: In step (1), FLAC is applied based on the rock mechanics parameters of each rock layer in the tunnel roof. 3D The software performs numerical simulations to obtain the width of the plastic zone of the coal seam in the roadway of this working face under the influence of mining activities in adjacent working faces.

4. The method for protecting working faces affected by mining operations by drilling along the bedding plane as described in claim 1, characterized in that: In step (2), the initial sealing depth of the borehole is increased from 2~4m to 7~9m, and the sealing depth is increased from 14~16m to 19~21m.

5. The method for protecting working faces affected by mining operations by drilling along the bedding plane as described in claim 1, characterized in that: In step (3), the hydraulic fracturing boreholes form an angle of 60-80° with the plane of the roadway roof. The borehole spacing is 10-15m, the borehole diameter is 75mm, and the borehole construction length is designed to exceed the subcritical layer by 1-2m. During construction, the location of the subcritical layer is recorded in detail. Fracturing is performed every 2-3m in the fracturing section until the entire subcritical layer section is fractured. The water injection fracturing sequence is from the inside to the outside, i.e., the reverse fracturing method. The fracturing time for each time is based on the water output of the adjacent borehole and the fracturing time is not less than 20min. After hydraulic fracturing of the roadway roof, the stress peak value of the coal body of this working face under the action of the adjacent working face mining can be reduced, thereby reducing the range of the plastic zone of the coal body of this working face.

6. The method for protecting working faces affected by mining operations through borehole drilling according to claim 1, characterized in that: In step (4), after the adjacent working face is mined, the extraction negative pressure is adjusted to -10~-5 kPa.

7. The method for protecting working faces affected by mining operations by drilling along the bedding plane as described in claim 1, characterized in that: In step (4), the gas extraction concentration of the borehole is tested. For boreholes with a gas extraction concentration of less than 10%, a smaller diameter sealing pipe is used in conjunction with two plugs and one injection bag to perform secondary sealing of the borehole. The sealing depth exceeds the first sealing depth by 3 to 5 m.

8. The method for protecting working faces affected by mining operations through borehole drilling according to claim 7, characterized in that: The diameter of the sealing tube for the second sealing is determined based on the diameter of the sealing tube for the first sealing, and is 10mm smaller than the diameter of the sealing tube for the first sealing.

Images