A gas control method for a coal mining face during an initial mining period

Abstract

The application discloses a gas control method for a coal mining face during initial mining, and specifically comprises the following steps: step 1, drilling a hole after the coal mining face is formed; step 2, drilling a first drill field and a second drill field on a side of the coal mining face close to a track; step 3, drilling a roof borehole in the first drill field and drilling a roof borehole in the second drill field; step 4, drilling a cut-eye vertical borehole from a cut-eye vertical coal seam roof; and step 5, pre-splitting and blasting the roof on a coal wall side of the coal mining face when the coal mining face is mined, and damaging the coal seam roof of a goaf. The application has the advantages that the problem of underdeveloped roof fissures is solved, the gas safety during initial mining of the coal mining face is ensured, and the gas extraction effect of the roof borehole during initial mining of the coal mining face is improved.

Description

Technical Field

[0001] This invention relates to the field of gas control technology, specifically to a method for controlling gas during the initial mining stage of a coal face. Background Technology

[0002] The initial mining period of a coal face refers to the time from the start of mining the cut-off head to the initial collapse of the old roof. During the initial mining period, the roof collapse in the goaf is insufficient, and the goaf fissures are not well developed. Conventional gas extraction methods such as goaf pipe burial, roof drilling, and high-pressure extraction roadways are ineffective. After the initial pressure is applied to the fully mechanized mining face, the roof collapses over a large area, instantly squeezing out the gas accumulated in the goaf and the depressurized gas in adjacent layers, causing abnormal gas outbursts and easily leading to gas accidents.

[0003] The initial mining stage of a fully mechanized longwall face is a crucial phase in the "ventilation, gas control, and fire prevention" work for coal and gas outburst mines and high-gas mines. Currently, most methods for managing gas during the initial mining stage involve drilling through high-level drainage roadways, low-level high-level drainage roadways, and tail roadways to address the gas problem. For example, Chinese invention patent document CN108506037A discloses a method for decompression gas extraction using a group of high-level directional boreholes in the roof of a coal mining face, used to reduce gas concentration in the upper corner of the working face and in the return airflow. However, the above methods and the technical solutions disclosed in the patent are not applicable to working faces with dedicated gas control roadways, and can still easily lead to abnormal gas outbursts and gas accidents. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to ensure gas safety during the initial mining phase of a coal face.

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

[0006] A method for controlling gas during the initial mining stage of a coal face includes the following steps:

[0007] Step 1: After the coal mining face is formed, multiple exploratory boreholes are drilled from the working face and the track towards the roof of the coal seam to investigate the lithology of the roof of the coal seam and determine the height and range of the caving zone, fracture zone, and bending subsidence zone after the working face is mined.

[0008] Step 2: Construct the first and second drilling sites on the side of the track closest to the working face;

[0009] Step 3: Drill holes in the roof of the first drilling site to the goaf caving zone and fracture zone above the coal seam roof; drill holes in the roof of the second drilling site to the goaf fracture zone above the coal seam roof.

[0010] Step 4: Before the working face is mined, a vertical drilling hole is constructed from the cut-in vertically to the top of the coal seam roof to the position above the final hole of the roof drilling hole constructed in the first drilling site, to increase the connection channel between the roof drilling hole and the goaf behind the frame.

[0011] Step 5: During the mining of the working face, pre-splitting blasting is carried out on the roof of the coal face; the roof of the coal seam in the goaf is damaged to increase the connection between the roof borehole and the goaf behind the support.

[0012] This invention solves the problem of underdeveloped roof cracks, ensuring that the gas accumulated in the goaf behind the support can be extracted through roof boreholes. This not only ensures gas safety during the initial mining period of the coal face, but also improves the extraction effect of roof boreholes during the initial mining period of the coal face.

[0013] Preferably, the length, width, and height of the first drilling site and the second drilling site in step 2 are 5m, 4m, and 3.5m, respectively.

[0014] Preferably, in step 2, the first drilling site is 58m away from the cut-out, and the second drilling site is 108m away from the cut-out.

[0015] Preferably, in step 3, the top plate boreholes of the first drilling site are arranged in three rows, with the final position of the top plate boreholes located 5-15m above the coal seam roof in the vertical direction and 15-52m from the track in the horizontal direction.

[0016] Preferably, the specific construction steps of the vertical drilling of the cut-eye in step 4 are as follows: Before the working face is mined, two vertical drilling holes are constructed every 3m vertically to the top of the coal seam at a position 15-52m from the cut-eye to the track, for a total of 24 vertical drilling holes. The depth of the vertical drilling holes is 17m and the diameter is 113mm. After the drilling is completed, the hole opening is sealed for 1m with a 3-inch sealing pipe and left open.

[0017] Preferably, the specific pre-splitting blasting steps in step 5 are as follows: a blasting hole is drilled on the roof of the coal seam every 3.2m of retreat to carry out a pre-splitting blast.

[0018] Preferably, each blasting hole is constructed from the front of the working face, close to the coal wall, and perpendicular to the top of the coal seam. One blasting hole is constructed every 3m, and 60 blasting holes are constructed each time.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention solves the problem of underdeveloped roof cracks, ensuring that the gas accumulated in the goaf behind the support can be extracted through roof boreholes. This not only ensures gas safety during the initial mining period of the coal face, but also improves the extraction effect of roof boreholes during the initial mining period of the coal face. Attached Figure Description

[0021] Figure 1This is a schematic diagram illustrating the working principle of step 1 in an embodiment of the present invention;

[0022] Figure 2 for Figure 1 Sectional view of AA;

[0023] Figure 3 for Figure 1 A cross-sectional view of BB. Detailed Implementation

[0024] To facilitate understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will now be further described in conjunction with the accompanying drawings.

[0025] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0026] In this application, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited.

[0027] See Figures 1 to 3 This embodiment discloses a method for controlling gas during the initial mining stage of a coal face, including the following steps:

[0028] Step 1: After the coal mining face 1 is formed, multiple exploratory boreholes are drilled from the working face 1 and the track 2 toward the coal seam roof to investigate the lithology of the coal seam roof and determine the height and range of the caving zone, fracture zone, and bending subsidence zone after the working face is mined.

[0029] Step 2: Construct the first drilling site 8 and the second drilling site 9 on the side of the track 2 closest to the working face 1. The first drilling site 8 is 58m away from the cut-in hole, and the second drilling site 9 is 108m away from the cut-in hole. The length, width and height of the first drilling site 8 and the second drilling site 9 are 5m, 4m and 3.5m respectively.

[0030] Step 3: Drill hole 3 in the roof at the first drilling site 8 to the goaf caving zone and fracture zone above the coal seam roof, and drill hole 3 in the roof at the second drilling site 9 to the goaf fracture zone above the coal seam roof.

[0031] In this embodiment, the roof borehole 3 is drilled in the first drilling site 8 to the goaf caving zone and fracture zone 5-15m above the coal seam roof, and the roof borehole 3 is drilled in the second drilling site 9 to the goaf fracture zone 15-25m above the coal seam roof. The roof borehole 3 is connected to the goaf 7 behind the support through the fracture.

[0032] In this embodiment, considering that the roof collapse was not timely and fractures were not well developed during the initial mining stage of working face 1, the optimal area for gas extraction from the roof borehole 3 on the first drilling site 8 is 5-15m above the vertical coal seam roof in the vertical direction, and 15-52m away from the track 2 in the horizontal direction. During the initial mining period of the working face, the initial pressure step distance of the old roof at the test site under normal conditions is 35m, and the periodic pressure step distance is 18m. The initial extraction period of the roof borehole 3 on the first drilling site 8 has ended. The final position of the roof borehole 3 on the second drilling site 9 is 15-25m above the vertical coal seam roof in the vertical direction, and is used for gas extraction during the normal mining period of the working face.

[0033] Specifically, in Drilling Site 8, 24 roof boreholes (B3) with a depth of 70-85m and a diameter of 133mm were constructed, arranged in 3 rows with an average of 8 boreholes per row. The vertical positions of the final boreholes in each row were 5m, 10m, and 15m above the coal seam roof, respectively. After all the roof boreholes were completed, casings were installed and the boreholes were sealed as required. During the mining operation, the drainage system was connected for extraction. In Drilling Site 9, 15 roof boreholes (B3) with a depth of 95-105m and a diameter of 133mm were constructed, arranged in 3 rows with an average of 5 boreholes per row. The vertical positions of the final boreholes in each row were 15m, 20m, and 25m above the coal seam roof, respectively. After all the roof boreholes were completed, casings were installed and the boreholes were sealed as required. During the mining operation of Working Face 1, the drainage system was connected for extraction.

[0034] Step 4: Before the mining of working face 1, construct vertical borehole 4 from the cut-in vertically to the top of the coal seam to increase the connection between the top borehole 3 and the goaf 7 behind the support.

[0035] The specific construction steps of the vertical borehole 4 are as follows: Before the working face 1 is mined, two vertical boreholes 4 are constructed every 3m vertically to the top of the coal seam at a position 15-52m from the cut-in to the track 2. At the position corresponding to the final horizontal direction of the top borehole 3, a total of 24 vertical boreholes 4 are constructed. The depth of the vertical borehole 4 is 17m and the diameter is 113mm. After the borehole construction is completed, the borehole opening is sealed for 1m with a 3-inch sealing pipe and left open.

[0036] Step 5: During the mining of working face 1, pre-splitting blasting is carried out on the roof of the coal face 1; the roof of the coal seam in the goaf is destroyed, and the connection channel between the roof borehole 3 and the goaf 7 behind the support is increased. Specifically, a blasting hole 5 is drilled on the roof of the working face every 3.2m retreat to carry out a pre-splitting blast; the roof of the coal seam is destroyed, causing the roof of the coal seam to collapse prematurely after entering the goaf 7 behind the support.

[0037] Each blasting hole 5 is constructed from the front of the working face support 6, close to the coal wall and perpendicular to the top of the coal seam. One blasting hole is constructed every 3m, and 60 blasting holes 5 are constructed each time.

[0038] Specifically, a pneumatic hammer was used in conjunction with a 38mm drill bit for drilling, with a hole depth of 2m and a charge of 0.6-1.0kg per hole. The sealing length must not be less than 1m. Class III coal mine permissible emulsion explosives were used, with millisecond delay electric detonators and forward initiation. Each operation involved 60 blasting holes, and the entire working face was divided into upper, middle, and lower sections for blasting in stages until the old roof collapsed and the initial mining phase ended. During the initial mining phase of the test working face, the average daily retreat was 2.5m, with a total of 11 pre-splitting blasts.

[0039] In this embodiment, the method described above is used to specifically reduce the vertical position of the roof boreholes and increase the number of roof boreholes 3, based on the lithology of the coal seam roof and the roof management situation during the mining of the working face. Before the mining of the working face 1, the vertical drilling holes 4 from the cutting eye construction to the vicinity of the final hole point of the roof boreholes 3 are increased to form a connecting channel between the roof boreholes 3 and the goaf 7 behind the support. During the mining of the working face 1, pre-splitting blasting is carried out periodically on the roof construction blasting holes 5 on the side of the working face 1 to destroy the roof of the coal seam in the goaf, further increasing the connecting channel between the roof boreholes 3 and the goaf 7 behind the support. This solves the problem of underdeveloped roof fractures and ensures that the gas accumulated in the goaf 7 behind the support can be extracted through the roof boreholes 3. This not only ensures gas safety during the initial mining of the coal face but also improves the extraction effect of the roof boreholes 3 during the initial mining of the coal face.

[0040] The above method was tested on a test working face in a coal mine. During the initial pressure test, the gas extraction rate of the working face exceeded 68%, and the gas concentration in the return air did not exceed 0.3% during the initial mining period, ensuring gas safety during the initial mining phase. Before the collapse of the direct roof during the initial mining period, the low-level roof boreholes mainly communicated with the goaf through vertical coal seam boreholes constructed in the cut-off section, resulting in stable gas extraction. After the collapse of the direct roof, the natural fissures between the low-level roof boreholes and the goaf gradually developed, leading to fluctuations in the gas extraction volume, but generally an upward trend. After the collapse of the old roof, the gas extraction volume from the roof boreholes increased rapidly, and the working face entered the normal extraction stage. During the initial mining period of the test working face, pre-splitting blasting was implemented on the roof side of the coal face, causing the direct roof to collapse 3.8m earlier. This increased the natural fissures between the goaf and the low-level roof boreholes, effectively promoting gas extraction from the goaf through the low-level roof boreholes.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0042] The above embodiments are merely examples of implementation methods of the invention. The scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for controlling gas during the initial mining stage of a coal face, characterized in that: Specifically, the steps include the following: Step 1: After the coal mining face is formed, multiple exploratory boreholes are drilled from the working face and the track towards the roof of the coal seam to investigate the lithology of the roof of the coal seam and determine the height and range of the caving zone, fracture zone, and bending subsidence zone after the working face is mined. Step 2: Construct the first and second drilling sites on the side of the track closest to the working face; Step 3: Drill holes in the roof of the first drilling site to the goaf caving zone and fracture zone above the coal seam roof; drill holes in the roof of the second drilling site to the goaf fracture zone above the coal seam roof. Step 4: Before the working face is mined, a vertical drilling hole is constructed from the cut-in vertically to the top of the coal seam roof to the position above the final hole of the roof drilling hole constructed in the first drilling site, to increase the connection channel between the roof drilling hole and the goaf behind the frame. Step 5: During the longwall mining, pre-splitting blasting is carried out on the roof of the coal face. Damage the roof of the coal seam in the goaf area and increase the connection between the roof borehole and the goaf area behind the support structure; In step 3, the top plate boreholes of the first drilling site are arranged in 3 rows. The vertical direction of the final position of the top plate borehole is 5 to 15m above the top of the coal seam, and the horizontal direction is 15 to 52m away from the track. The specific construction steps for the vertical drilling of the cut-in face in step 4 are as follows: Before the working face is mined, two vertical drilling holes are constructed every 3 meters vertically to the top of the coal seam at a position 15-52m from the cut-in face. A total of 24 vertical drilling holes are constructed. The depth of the vertical drilling holes is 17m and the diameter is 113mm. After the drilling is completed, the hole opening is sealed for 1m with a 3-inch sealing pipe and left open.

2. The method for controlling gas during the initial mining stage of a coal face according to claim 1, characterized in that: The length, width, and height of the first and second drilling sites in step 2 are 5m, 4m, and 3.5m, respectively.

3. The method for controlling gas during the initial mining stage of a coal face according to claim 1, characterized in that: In step 2, the first drilling site is 58m away from the cut-in point, and the second drilling site is 108m away from the cut-in point.

4. The method for controlling gas during the initial mining stage of a coal face according to claim 1, characterized in that: The specific pre-splitting blasting steps in step 5 are as follows: a blasting hole is drilled on the roof of the coal seam every 3.2m of retreat to carry out a pre-splitting blast.

5. A method for controlling gas during the initial mining stage of a coal face according to claim 4, characterized in that: Each blasting hole was constructed from the front of the working face, close to the coal wall, and perpendicular to the top of the coal seam. One blasting hole was constructed every 3 meters, and a total of 60 blasting holes were constructed each time.

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