A full-life-cycle gas drainage method for coal seam strike boreholes

Abstract

The object of the present invention is to provide a full-life-cycle gas drainage method for coal seam strike boreholes, belonging to the technical field of coal mine underground coal seam gas extraction. Specifically, before the driving of the return airway and the conveyor airway in the working face, a boundary connection roadway is constructed near the planned stop line of the working face, and parallel long boreholes running through the entire strike of the working face are constructed in the roadway to achieve the advance pre-drainage of the coal seam during the driving of the return airway and the driving airway in the working face, shortening the time cycle of extraction-driving-mining. When the working face is arranged and starts to be mined, the boreholes are closed and the boundary connection roadway is blocked. After the end of the borehole is cut off by the shearer, the borehole is transformed into a drainage borehole to continue discharging gas into the mining space, further reducing the gas content until the end of the working face mining, and the life cycle of borehole drainage terminates. The present invention can ensure the continuous gas drainage during the full life cycle of the borehole, so as to realize the efficient and continuous treatment of the coal seam gas.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam gas drainage in coal mines, and particularly relates to a full-life cycle control method for pre-draining gas in advance through strike boreholes in the coal seam and continuously discharging gas during the coal mining process. Background Art

[0002] Gas pre-drainage mainly adopts borehole pre-drainage, which pre-drains the gas in the coal seam before the working face is mined. By constructing in-seam boreholes in advance to pre-drain the gas in the coal seam in coal mines, the gas content in the coal seam can be reduced, which is the fundamental measure to prevent coal mine gas accidents such as gas outburst, gas overrun, and gas explosion. The pre-drainage of in-seam gas is the key work for gas control in high-gas coal mines. At present, the longwall working face layout method is adopted for the coal mining methods of most working faces in the country. Most coal mines generally adopt unilateral parallel boreholes, bilateral parallel cross boreholes, and fan-shaped boreholes for the pre-drainage method of in-seam gas. There are also some coal mines that adopt the method of regional pre-drainage with kilometer directional boreholes. Due to the uneven construction and control technology levels of boreholes, the pre-drainage time in advance of conventional in-seam pre-drainage boreholes is limited, and the service life of the boreholes is short, resulting in the ineffective release of the continuous and efficient gas drainage capacity of the boreholes, the inability to guarantee the drainage time, which restricts the process of the in-seam drainage compliance evaluation work to a certain extent, affects the gas control effect, and is difficult to meet the large-scale mechanized mining technology. Therefore, in order to solve the above problems, it is necessary to conduct pre-drainage in advance before the crossheading is driven, and at the same time ensure that the boreholes are not affected by the cutting of the shearer during the coal mining process, so as to ensure the continuous gas drainage throughout the life cycle of the boreholes, thereby realizing the efficient and continuous control of in-seam gas. Summary of the Invention

[0003] In order to achieve the above object, the invention provides a full-life cycle gas drainage and discharge method for coal seam strike boreholes, which prolongs the pre-drainage time of gas in advance, increases the gas discharge function of the boreholes, avoids the damage to the borehole shape and drainage capacity caused by coal seam cutting during the coal mining process, and realizes the efficient and continuous drainage effect of the boreholes throughout the life cycle.

[0004] Specifically, before the return airway and the conveyor airway of the working face are driven, a boundary connection roadway is constructed near the planned stopping line of the working face, and parallel long boreholes running through the entire strike of the working face are constructed in the roadway to realize the pre-drainage in advance of the in-seam gas during the driving of the return airway and the driving airway of the working face, shortening the time cycle of drainage-driving-mining; when the working face is arranged and starts to be mined, the boreholes are closed and the boundary connection roadway is blocked. After the end of the borehole is cut off by the shearer, the borehole is transformed into a discharge borehole, and continues to discharge gas into the mined space, further reducing the gas content until the coal mining of the working face is completed and the drainage life cycle of the borehole ends.

[0005] Specifically, it includes the following steps:

[0006] First step: Construct a boundary connection roadway that runs through the return air crossheading and the conveyor crossheading at the stopping line position of the coal mining face. Install a regulating air door at one end of the boundary connection roadway near the return air crossheading for air volume regulation in the boundary connection roadway.

[0007] Second step: Use a drill rig to enter the boundary connection roadway from the conveyor crossheading entrance, and drill strike holes from the inner side of the boundary connection roadway into the coal seam for pre-draining coal seam gas in advance and automatically discharging gas during coal mining.

[0008] Third step: Lay the gas extraction pipeline in the return airway through the return air crossheading to the boundary connection roadway, and connect the strike holes for advanced combined extraction. Among them, install a first high-pressure stop valve at the front end of each strike hole connected to the gas extraction pipeline in the boundary connection roadway, and install a second high-pressure stop valve at the front end of the gas extraction pipeline in the boundary connection roadway when it is connected to the gas extraction pipeline in the return air crossheading. The second high-pressure stop valve is located in the return air crossheading. Open the first high-pressure stop valve and the second high-pressure stop valve, and the strike holes start to pre-drain the gas in the coal seam. As the return air crossheading and the conveyor crossheading are normally driven, the extraction state of the strike holes is not affected.

[0009] Fourth step: Conduct gas extraction compliance evaluation in stages. When the gas extraction in the entire coal mining face meets the requirements, install airtight devices at both ends of the connection roadway to seal the connection roadway.

[0010] Fifth step: Before the coal mining face is mined, close the second high-pressure stop valve to stop the hole extraction. During the normal advancement of the coal mining face, the end hole of the strike hole is cut off by the shearer, and the coal mining face is connected to the strike hole. The coal seam gas continues to be naturally discharged to the coal mining face along the strike hole channel, further reducing the coal seam gas content and realizing gas drainage while mining.

[0011] Sixth step: According to the gas emission situation during coal mining, natural emission or enhanced extraction of the strike holes can be selected and implemented in accordance with the fourth step to ensure the safe completion of coal mining in the working face.

[0012] Furthermore, the diameter of the strike holes described in the second step is not less than 73 mm.

[0013] Furthermore, the construction of the strike holes from the inner side of the boundary connection roadway into the coal seam in the second step includes the following steps: Open holes at equal intervals on the inner side of the boundary connection roadway, construct strike holes, the strike holes reach 15 m in front of the cutting eye position, and the two strike holes at both ends of the boundary connection roadway are 15 m away from the inner roadway side of the return air crossheading and the conveyor crossheading respectively, and penetrate and cover the entire strike length of the coal mining face.

[0014] Furthermore, the spacing of the strike holes is the same as the coal seam gas extraction radius, generally 3 - 5 m.

[0015] Furthermore, after the heading boreholes are constructed, the holes are sealed in the "two-block-one-injection" method, and the sealing length is not less than 15 m.

[0016] Furthermore, during the normal advancement of the coal mining face in the fifth step, before encountering the hidden danger of gas overrun in the local coal seam gas enrichment area, when the heading boreholes are sealed with cement mortar with a sealing length of not less than 10 m at the cut-off position of the heading boreholes, the second high-pressure cut-off valve is opened for enhanced gas extraction, and the coal seam gas content in the gas enrichment area is rapidly reduced through the negative pressure of the gas extraction pipeline in the return air heading.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. This technology overcomes the problem of imbalance between gas extraction and heading in the process of heading along the gateway. Gas pre-extraction for the entire working face can be started during the driving of the return air heading and the conveyor heading of the working face, realizing that the borehole construction, pre-extraction and gateway driving work do not interfere with each other in terms of space and time, greatly shortening the mining and tunneling connection time of the working face, and achieving the effect of extracting while driving in the coal seam.

[0019] 2. This technology overcomes the problem of imbalance between gas extraction and mining in the process of coal mining in the working face. By utilizing the advantage of the shearer cutting the borehole to open the end of the final hole, the heading borehole is transformed from the pre-extraction function to the drainage function. Along with the advancement of the working face, the borehole is gradually opened from the final hole section to the opening end, achieving the effect of discharging while mining in the coal seam.

[0020] 3. The heading boreholes arranged by this technology penetrate the entire coal mining face and are consistent with the coal seam strike, improving the borehole formation rate, reducing the required number of boreholes, avoiding cumbersome work such as moving the drilling rig and adjusting the borehole angle during the construction process, and greatly improving the borehole utilization rate.

[0021] 4. This technology only requires laying the gas extraction pipeline at the shutdown position of the working face, without laying the gas extraction pipeline along the gateway of the working face. This not only effectively reduces the negative pressure loss along the gas extraction pipeline, but also greatly saves the operation project such as pipeline installation, with significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the layout plan of the heading borehole advanced pre-extraction in the coal mining face provided by the present invention;

[0023] Figure 2 It is the layout plan of the heading borehole discharging while mining in the coal mining face provided by the present invention;

[0024] Figure 3 It is the layout plan of the enhanced gas extraction of the borehole in the gas enrichment area of the coal mining face provided by the present invention;

[0025] Figure 4 It is the curve graph of the natural gas emission volume change of the parallel cross boreholes in the embodiment of the present invention;

[0026] Figure 5 This is the curve graph of the gas emission change along the long borehole in the embodiment of the present invention;

[0027] Figure 6 This is the comparison graph of the cumulative pure gas extraction amount per 100-meter borehole in the embodiment of the present invention;

[0028] In the figure: 1 - mining face; 2 - stopping line; 3 - return airway; 4 - conveyor airway; 5 - boundary connection roadway; 6 - regulating air door; 7 - strike borehole; 8 - inside of the boundary connection roadway; 9 - cutting hole; 10 - inner roadway side of the return airway; 11 - inner roadway side of the conveyor airway; 12 - borehole spacing; 13 - first high-pressure stop valve; 14 - second high-pressure stop valve; 15 - extraction pipeline in the boundary connection roadway; 16 - extraction pipeline in the return airway; 17 - sealing device; 18 - coal seam gas enrichment area; 19 - grouting plugging with cement mortar. Detailed implementation manners

[0029] In combination with the accompanying drawings, the present invention will be further described.

[0030] As shown in the figure, a full-life-cycle gas drainage method for coal seam strike boreholes includes the following steps:

[0031] 1. Construct a boundary connection roadway 5 that runs through the return airway 3 and the conveyor airway 4 at the position of the stopping line 2 of the mining face 1, and set a regulating air door 6 at one end of the boundary connection roadway 5 close to the return airway 3 for regulating the air volume in the boundary connection roadway.

[0032] 2. Use a ZDY6200D drill to enter the boundary connection roadway 5 from the conveyor airway entrance, and construct a strike borehole 7 towards the coal seam inside the boundary connection roadway 8. The borehole diameter is not less than 73 mm, which is used for pre-draining the coal seam gas in advance and automatically discharging the gas during mining.

[0033] Furthermore, drill holes at equal intervals inside the boundary connection roadway 8 to construct strike boreholes, and the borehole length reaches 15 m in front of the cutting hole 9; the distances between the two strike boreholes at both ends of the boundary connection roadway from the inner roadway side 10 of the return airway and the inner roadway side 11 of the conveyor airway are both 15 m, and the entire strike length of the mining face is covered.

[0034] Furthermore, the borehole spacing 12 is the same as the coal seam gas extraction radius, generally choosing 3 - 5 m.

[0035] Furthermore, after the construction of the strike boreholes is completed, the hole sealing is carried out by the two-block-one-injection method, and the hole sealing length is not less than 15 m.

[0036] 3. Lay the extraction pipeline in the return airway through the return airway to the inside of the boundary connection roadway, and connect the strike boreholes for advanced combined extraction.

[0037] Further, a first high-pressure cut-off valve 13 is provided at the front end of each borehole connected to the extraction pipeline 15 of the boundary crossheading, and a second high-pressure cut-off valve 14 is provided at the front end of the extraction pipeline of the boundary crossheading when it is connected to the extraction pipeline 16 of the return air crossheading. The second high-pressure cut-off valve is located in the return air crossheading.

[0038] Further, open the first high-pressure cut-off valve and the second high-pressure cut-off valve, and the strike boreholes start to pre-drain the gas in the coal seam. As the return air crossheading and the conveyor crossheading are normally driven, the extraction state of the strike boreholes is not affected.

[0039] 4. Conduct gas extraction compliance evaluation in stages. When the gas extraction in the entire mining face meets the requirements, install airtight devices 17 at both ends of the crossheading to seal the crossheading.

[0040] 5. Before the mining face is mined, close the second high-pressure cut-off valve to stop borehole extraction. During the normal advancement of the mining face, the end of the borehole is cut off by the shearer, and the mining face is connected to the strike boreholes. The coal seam gas continues to be naturally discharged to the mining face along the borehole channel, further reducing the coal seam gas content and realizing gas drainage while mining.

[0041] Further, before encountering the hidden danger of gas overrun in the local coal seam gas enrichment area 18 during the advancement of the mining face, when plugging 19 the borehole with cement mortar with a plugging length of not less than 10 m at the borehole cutting position, open the second high-pressure cut-off valve for enhanced extraction, and quickly reduce the coal seam gas content in the gas enrichment area through the negative pressure of the extraction pipeline in the return air crossheading.

[0042] 6. According to the gas emission situation of the working face during mining, the natural discharge or enhanced extraction of the strike boreholes can be selected and implemented according to step 4 to ensure the safe mining of the working face.

[0043] Embodiment

[0044] In order to test the gas extraction effect of the long strike boreholes in the coal seam, a test on the gas extraction effect of the long strike boreholes was carried out in the 2308 working face of the third mining area of Mingxin Coal Mine, and a comparison of the effects was made with the parallel cross boreholes in the coal seam of the adjacent 2306 working face in the same mining area.

[0045] The average strike length of the working face in the third mining area is 1000 m, the average width is 200 m, the designed borehole spacing is 5 m, the plugging length is 15 m, and the gas pre-drainage width on each side of the roadway is 15 m. According to the width of the working face, the designed length of the parallel cross boreholes in the 2306 working face is 110 m, and the actual unilateral borehole control width is 100 m; the designed length of the long strike boreholes in the 2308 working face is 985 m.

[0046] 1. Borehole effective utilization rate and engineering comparison

[0047] 1.1 Borehole effective utilization rate

[0048] Before the formation of the 2308 working face in the third mining area, boundary connecting roadways as shown were constructed near the stop line, and then strike boreholes were drilled at a hole spacing of 5 m. After the drilling was completed, the holes were connected for pre-drainage, and at the same time, the driving operation of the crossheading in the working face and the investigation of the gas drainage effect were carried out. Figure 1 Then the effective drainage utilization rates of the boreholes in the two cases are respectively:

[0049] η2306=(100 - 15) / 110 = 77.3%;

[0050] η2308=(985 - 15) / 985 = 98.5%;

[0051] η2308=(985 - 15) / 985 = 98.5%;

[0052] Under the same conditions, through calculation, the effective utilization rate of the strike long boreholes is 1.27 times that of the parallel cross boreholes.

[0053] According to the strike and dip lengths of the working face, hole spacing, and gas pre-drainage width, the total number of boreholes constructed in the 2306 and 2308 working faces are respectively:

[0054] N2306=[(1000 - 15) / 5]×2 = 394;

[0055] N2308=[200 - 2×15] / 5 = 34;

[0056] Then, according to the length of a single borehole, the total lengths of the boreholes constructed in the two working faces can be calculated as follows:

[0057] L2306 = 394×110 = 43340 m;

[0058] L2308 = 34×985 = 33490 m;

[0059] It can be seen that the engineering quantity of the borehole construction for gas control in the 2308 working face is only 77.27% of that of the parallel cross boreholes in the 2306 working face. Obviously, the strike long boreholes are more economical in engineering.

[0060] 1.2 Comparison of Borehole Construction Time

[0061] The average construction time of a single pre-drainage borehole in the 2306 working face is 1.5 shifts / hole, including the operation of moving the machine and sealing the hole. Then, 394 boreholes require 591 shifts; the average construction time of the in-seam strike long boreholes in the 2308 working face is 10 shifts / hole, including the operation of moving the machine and sealing the hole. Then, 34 boreholes require 340 shifts. In the same comparison situation, the time required for the construction of the strike long boreholes is only 57% of the original.

[0062] 2. Study on the Decay Law of the Natural Gas Emission Quantity from Boreholes

[0063] In order to study the attenuation law of natural gas emission from long boreholes along the strike and parallel cross boreholes, an investigation on the attenuation of natural gas emission from boreholes was carried out in the 2306 and 2308 working faces. The variation law of natural gas emission from the parallel cross boreholes investigated in 2306 is as follows Figure 4 .

[0064] From Figure 4 the fitting curve, it can be obtained that the law of natural gas emission from parallel cross boreholes is:

[0065] q t = 41.24e -0.562t ;

[0066] where: q t - Gas flow rate during the emission of a 100 - meter borehole after t days, L / min·100m;

[0067] t - Self - drainage gas time of the borehole, d;

[0068] Among them, the correlation coefficient R = 97%.

[0069] The variation law of natural gas emission from the long borehole along the strike in the 2308 working face is as follows Figure 5 .

[0070] From Figure 5 it can be obtained that the law of natural gas emission from the long borehole along the strike is:

[0071] q t = 53.413e -0.256t ;

[0072] where: q t - Gas flow rate during the emission of a 100 - meter borehole after t days, L / min·100m;

[0073] t - Self - drainage gas time of the borehole, d;

[0074] Among them, the correlation coefficient R = 98.59%.

[0075] From the above two formulas, it can be seen that the average attenuation coefficient of natural gas emission from the boreholes in the parallel cross - section of the 2306 working face is 0.562 d -1 , and the initial gas flow rate of a 100 - meter borehole is 41.24 L / min·100m; after the construction of the long borehole along the strike in the 2308 working face, the attenuation of natural gas emission from the boreholes is slower, and the average attenuation coefficient is 0.256 d -1 ; the initial gas flow rate of a 100 - meter borehole is 53.413 L / min·100m. The natural gas emission attenuation coefficient of the long borehole along the strike is 38% of that of the ordinary short borehole, and the initial flow rate of a 100 - meter borehole is 1.29 times that of the original. In the same time, the gas extraction volume of the long borehole along the strike is larger, and the time to meet the extraction standard is shortened.

[0076] 3. Investigation of Gas Drainage Volume per 100-meter Borehole

[0077] Through the investigation of the gas pre-drainage effect of the coal seam in working faces 2306 and 2308, after data collation, a comparison chart of the cumulative gas drainage volume per 100-meter borehole is obtained, as Figure 6 shown. It can be seen from the comparison chart that at 60 days of gas drainage, the cumulative gas drainage volume per 100-meter borehole of parallel cross boreholes is 130 m³, and that of strike long boreholes is 185 m³; after 60 days, with the attenuation of gas emission, the difference between the two is about 70 m³ at the same time. After calculation, the gas drainage efficiency of strike long boreholes is about 1.4 times that of parallel cross boreholes.

Claims

1. A full-life-cycle gas drainage method for coal seam strike boreholes, characterized in that: It includes the following steps: In the first step, a boundary connection roadway running through the return airway and the conveyor airway is constructed at the stop line position of the coal face. An adjusting air door is installed at one end of the boundary connection roadway close to the return airway for air volume adjustment in the boundary connection roadway; In the second step, a drilling rig is used to enter the boundary connection roadway from the conveyor airway opening, and strike holes are drilled into the coal seam from the inside of the boundary connection roadway for pre-drainage of coal seam gas in advance and automatic gas drainage during coal mining; In the third step, the gas drainage pipeline in the return airway main roadway is laid through the return airway to the inside of the boundary connection roadway and connected to the strike holes for advanced combined drainage; among them, a first high-pressure stop valve is installed at the front end of each strike hole connected to the gas drainage pipeline in the boundary connection roadway, and a second high-pressure stop valve is installed at the front end of the gas drainage pipeline in the boundary connection roadway when it is connected to the gas drainage pipeline in the return airway. The second high-pressure stop valve is located in the return airway; the first high-pressure stop valve and the second high-pressure stop valve are opened, and the strike holes start to pre-drain the gas in the coal seam. As the return airway and the conveyor airway are normally driven, the gas drainage state of the strike holes is not affected; In the fourth step, the gas drainage compliance assessment is carried out in stages. When the gas drainage of the entire coal face meets the requirements, airtight devices are installed at both ends of the connection roadway to seal the connection roadway; In the fifth step, before the coal face is mined, the second high-pressure stop valve is closed to stop the drilling gas drainage. During the normal advancement of the coal face, the end hole of the strike hole is cut off by the shearer, and the coal face is connected to the strike hole. The coal seam gas continues to be naturally discharged to the coal face along the strike hole channel, further reducing the coal seam gas content and realizing gas drainage while mining; In the sixth step, according to the gas outburst situation during coal mining, natural discharge or enhanced drainage of the strike holes can be selected and implemented according to the fourth step to ensure the safe end of coal mining in the working face.

2. The full-life-cycle gas drainage method for coal seam strike boreholes according to claim 1, wherein: The diameter of the strike hole described in the second step is not less than 73 mm.

3. The full-life-cycle gas drainage method for coal seam strike boreholes according to claim 1, characterized in that: The construction of the strike hole from the inside of the boundary connection roadway into the coal seam described in the second step includes the following steps: holes are opened at equal intervals on the inside of the boundary connection roadway, and strike holes are constructed. The strike holes reach 15 m in front of the cut-through position. The distances between the two strike holes at both ends of the boundary connection roadway from the inner roadway rib of the return airway and the inner roadway rib of the conveyor airway are 15 m respectively, and the entire strike length of the coal face is covered.

4. A full-life-cycle gas drainage method for coal seam strike boreholes according to claim 3, characterized in that: The spacing of the strike holes is the same as the coal seam gas drainage radius.

5. A full-life-cycle gas drainage method for coal seam strike boreholes according to claim 3, characterized in that: After the strike holes are constructed, the two-block-one-injection method is used for hole sealing, and the hole sealing length is not less than 15 m.

6. The full-life-cycle gas drainage method for coal seam strike boreholes according to claim 1, characterized in that: During the normal advancement of the coal face described in the fifth step, before encountering the hidden danger of gas overrun in the local coal seam gas enrichment area, when the strike hole is blocked with cement mortar with a hole sealing length of not less than 10 m at the cut-off position of the strike hole, the second high-pressure stop valve is opened for enhanced drainage, and the coal seam gas content in the gas enrichment area is quickly reduced through the negative pressure of the gas drainage pipeline in the return airway.

Images