Coal bed gas outburst prevention system and outburst prevention method

Abstract

The application discloses a coal bed gas outburst prevention system and an outburst prevention method, which comprise an injection hole, an extraction hole and a monitoring hole arranged in a coal bed; a negative pressure pump which is communicated with the extraction hole and is configured to extract gas in the coal bed; a nitrogen storage bottle which is communicated with the injection hole and is configured to inject nitrogen into the injection hole to displace the gas; a valve which is arranged between the nitrogen storage bottle and the injection hole and is configured to control the amount of nitrogen injected by the nitrogen storage bottle into the injection hole; a monitor which is installed in the monitoring hole and is configured to monitor concentration information and pressure information of the gas in the coal bed; and a computer which is in communication connection with the valve and the monitor and is configured to control the amount of nitrogen injected by the valve into the injection hole and the amount of gas extracted by the negative pressure pump based on the concentration information and the pressure information of the gas.

Description

Technical Field

[0001] This invention relates to the field of underground coalbed methane extraction technology, and in particular to a coalbed methane outburst prevention system and method. Background Technology

[0002] my country possesses abundant coalbed methane resources, and its development is of great significance in alleviating the current shortage of oil and gas resources, reducing the severity of mine disasters, and decreasing greenhouse gas emissions. During gas injection and displacement, gas extraction efficiency increases with increasing injection pressure. However, due to the need to inject large amounts of gas to displace the methane, the pressure in the coal seam surrounding the injection hole has already increased to a certain level. Furthermore, given the widespread risk of gas outbursts in Chinese coal mines, further increasing the injection pressure at this point could worsen the stress conditions of the coal seam, potentially leading to coal and gas outbursts and other disasters, resulting in loss of life and property.

[0003] In geologically complex environments with numerous geological structures, the distribution of ground stress, gas distribution, and load conditions vary significantly as the working face advances. Therefore, it is necessary to use certain detection methods to predict the gas conditions in unknown areas in advance, thereby reducing the potential dangers posed by high-gas mines. Summary of the Invention

[0004] This solution addresses the problems and needs raised above by proposing a coalbed methane outburst prevention system and method. Due to the adoption of the following technical features, it can achieve the above-mentioned technical objectives and bring about several other technical benefits.

[0005] One object of the present invention is to provide a coalbed methane outburst prevention system, comprising:

[0006] Injection holes, extraction holes, and monitoring holes are drilled in the coal seam;

[0007] A negative pressure pump, connected to the extraction hole, is configured to extract gas from the coal seam;

[0008] A nitrogen storage cylinder, connected to the injection port, is configured to inject nitrogen gas into the injection port to displace the gas.

[0009] A valve is disposed between the nitrogen storage cylinder and the injection port, and is configured to control the amount of nitrogen gas injected from the nitrogen storage cylinder into the injection port;

[0010] The monitor, installed in the monitoring hole, is configured to monitor the concentration and pressure information of methane in the coal seam;

[0011] A computer, communicatively connected to the negative pressure pump, valve, and monitor, is configured to control the amount of nitrogen injected into the injection hole by the valve and the amount of gas extracted by the negative pressure pump based on gas concentration and pressure information.

[0012] In this technical solution, a computer controls the valve to open and inject nitrogen into the injection hole. After the nitrogen is injected into the coal seam, it displaces the gas located within the coal seam. The displaced gas is then extracted through the extraction hole by a negative pressure pump. During this process, a monitor continuously monitors the concentration and pressure information of the gas in the coal seam. Multiple hole units are set along the extension direction of the return airway and / or transport airway of the coal seam. Each hole unit includes an injection hole, an extraction hole, and a monitoring hole. The computer obtains the initial gas pressure P0 and the initial gas content Q0 based on the gas concentration and gas pressure information obtained by the monitor in each hole unit. Based on the initial gas pressure P0 and the initial gas content Q0, the predicted gas pressure P′ at the (n+1)th point is calculated. n+1 And predicting gas content Q′ n+1 Let n be a positive integer; determine the predicted gas content Q′ at the (n+1)th location. n+1 If the ratio of the nitrogen content to the initial gas content Q0 is less than or equal to 1, stop injecting nitrogen into the injection hole; otherwise, proceed to the next step; continue to determine the predicted gas pressure P′ at the (n+1)th point. n+1 If the ratio of nitrogen to the initial gas pressure P0 is less than or equal to 1, stop injecting nitrogen into the injection hole; otherwise, proceed to the next step. Calculate the gas outburst situation at each point using the gas outburst tendency index F, and determine if the gas outburst tendency index F at each point is greater than or equal to 1.4. If it is less than 1.4, increase the nitrogen pressure level in the injection hole and recalculate the gas outburst tendency index F until it is greater than or equal to 1.4, then proceed to the next step. Continue to determine if the gas outburst tendency index F is greater than or equal to 2.0. If it is greater than or equal to 2.0, stop injecting nitrogen into the injection hole; otherwise, maintain the current nitrogen injection pressure level. Firstly, by drilling holes and deploying monitors in the coal seam, this system achieves the goals of injecting nitrogen to displace and extract gas, and predicting the risk of gas outbursts in the unmined portion of the coal seam. Secondly, this system improves the operational safety level of on-site gas injection and gas extraction. The staggered drilling on both sides increases the efficiency of underground gas extraction, while appropriate injection pressure increases the concentration of extracted gas, thereby increasing its usability. Finally, the use of multi-parameter monitoring to prevent gas outbursts enhances the predictive sensitivity on the basis of existing outburst prevention methods, which is beneficial to improving the extraction work and safety level of underground gas injection and gas displacement.

[0013] In addition, the coalbed methane outburst prevention system and method according to the present invention may also have the following technical features:

[0014] In one example of the invention, the monitor includes:

[0015] A gas concentration monitor is configured to monitor the concentration of gas in coal seams.

[0016] The gas pressure monitor is configured to monitor the pressure information of gas in the coal seam.

[0017] In one example of the invention, a pressure gauge is also included.

[0018] Installed between the valve and the injection port, configured to monitor the pressure of nitrogen gas injected from the valve toward the injection port.

[0019] In one example of the present invention, a plurality of hole units are spaced apart along the extension direction of the return airway and / or transport airway of the coal seam, each hole unit being formed by the injection hole, the extraction hole and the monitoring hole spaced apart along the extension direction and in a depth direction perpendicular to the extension direction.

[0020] In one example of the present invention, the orifice unit includes: an injection orifice, four extraction orifices and four monitoring orifices, wherein the injection orifice is located at the center of the orifice unit, the four extraction orifices are located on both sides of the injection orifice in the extension direction and depth direction, and the monitoring orifices are located at the remaining four corner positions.

[0021] In one example of the present invention, in the hole unit, the distance between two adjacent holes is 0.6m to 0.8m.

[0022] In one example of the invention, the orifice unit comprises a plurality of orifices and is spaced apart along the extension direction of the return air tunnel and / or transport tunnel.

[0023] In one example of the present invention, the diameter of the injection hole, the extraction hole and the monitoring hole are all 100 mm, and the depth of the injection hole, the extraction hole and the monitoring hole are all 20 to 60 m.

[0024] Another object of the present invention is to provide a method for preventing coalbed methane outbursts as described above, characterized by comprising the following steps:

[0025] S10: Open the valve of the coalbed methane anti-outburst system to inject pressurized nitrogen into the coal seam, and at the same time, the gas in the extraction hole is extracted by the negative pressure pump. During this process, the gas concentration and gas pressure information are monitored by the monitor located in the monitoring hole. Multiple hole units are set along the extension direction of the return airway and / or transport roadway of the coal seam. Each hole unit includes an injection hole, an extraction hole and a monitoring hole.

[0026] S20: Based on the gas concentration and gas pressure information obtained from the monitors in each well unit, obtain the initial gas pressure P0 and initial gas content Q0, and calculate the predicted gas pressure P′ at the (n+1)th point based on the initial gas pressure P0 and initial gas content Q0. n+1 And predicting gas content Q′n+1 n is a positive integer;

[0027] S30: Determine the predicted gas content Q′ at the (n+1)th point. n+1 Check if the ratio of nitrogen to the initial gas content Q0 is less than or equal to 1. If it is not less than or equal to 1, stop injecting nitrogen into the injection hole; otherwise, proceed to the next step.

[0028] S40: Continue to determine the predicted gas pressure P′ at the (n+1)th point. n+1 Check if the ratio of nitrogen to the initial gas pressure P0 is less than or equal to 1. If it is not less than or equal to 1, stop injecting nitrogen into the injection port; otherwise, proceed to the next step.

[0029] S50: Calculate the gas outburst situation at each point using the gas outburst tendency index F, and determine whether the gas outburst tendency index F at each point is greater than or equal to 1.4. If it is less than 1.4, increase the nitrogen pressure level in the injection hole and recalculate the gas outburst tendency index F until the gas outburst tendency index F is greater than or equal to 1.4, then proceed to the next step; wherein, the calculation formula for the gas outburst tendency index F is as follows:

[0030] F = P' n+1 / P0+Q′ n+1 / Q0

[0031] S60: Continue to determine whether the gas outburst tendency index F is greater than or equal to 2.0. If it is greater than or equal to 2.0, stop injecting nitrogen into the injection hole; otherwise, maintain the current nitrogen injection pressure level.

[0032] In one example of the present invention, the predicted gas pressure P′ at the (n+1)th point n+1 And predicting gas content Q′ n+1 The calculation formula is as follows:

[0033]

[0034]

[0035] In the formula, P n Let P' be the measured gas pressure at point n, a be the prediction sensitivity coefficient, and P' be the gas pressure at point n. n For the predicted gas pressure at the nth point, Q n Let Q′ be the measured gas content at the nth point. n Let n be the predicted gas content at the nth location.

[0036] The preferred embodiments of the invention will be described in more detail below with reference to the accompanying drawings, so as to facilitate an understanding of the features and advantages of the invention. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. The drawings are merely illustrative of some embodiments of the present invention and are not intended to limit the scope of the present invention to all embodiments.

[0038] Figure 1 This is a schematic diagram of the structure of a coalbed methane anti-outburst system according to an embodiment of the present invention;

[0039] Figure 2 A top view of a coal seam according to an embodiment of the present invention;

[0040] Figure 3 This is a logic diagram illustrating the working method of a coalbed methane anti-outburst system according to an embodiment of the present invention.

[0041] List of reference numerals in the attached diagram:

[0042] Coalbed methane outburst prevention system 100;

[0043] Injection hole 101;

[0044] Extraction hole 102;

[0045] Monitoring hole 103;

[0046] Negative pressure pump 104;

[0047] Nitrogen storage bottle 105;

[0048] Valve 106;

[0049] Monitor 107;

[0050] Computer Science 108;

[0051] Pressure gauge 109;

[0052] Hole unit 110;

[0053] Gas cylinder 111;

[0054] Coal seam 200;

[0055] Working face 210;

[0056] Huifengping Lane 220;

[0057] Transport level roadway 230;

[0058] Extension direction Y;

[0059] Depth direction S. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0061] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0062] According to a first aspect of the present invention, a coalbed methane outburst prevention system 100, such as Figure 1 and Figure 2 As shown, it includes:

[0063] Injection hole 101, extraction hole 102 and monitoring hole 103 are opened in the coal seam; injection hole 101, extraction hole 102 and monitoring hole 103 are all drilled along the thickness direction H of the coal seam, wherein the thickness direction H is perpendicular to the extension direction Y and the depth direction S.

[0064] A negative pressure pump 104 is connected to the extraction hole 102 and is configured to extract gas from the coal seam; for example, gas is collected through a gas cylinder 111.

[0065] A nitrogen storage cylinder 105 is connected to the injection port 101 and is configured to inject nitrogen gas into the injection port 101 to displace the gas.

[0066] A valve 106 is disposed between the nitrogen storage bottle 105 and the injection port 101, and is configured to control the amount of nitrogen gas injected from the nitrogen storage bottle 105 into the injection port 101;

[0067] The monitor 107 is installed in the monitoring hole 103 and is configured to monitor the concentration and pressure information of gas in the coal seam.

[0068] Computer 108 is communicatively connected to the negative pressure pump 104, valve 106 and monitor 107, and is configured to control the amount of nitrogen injected into the injection port 101 by valve 106 and the amount of gas extracted by negative pressure pump 104 based on gas concentration and pressure information.

[0069] The computer 108 controls the valve 106 to open and inject nitrogen into the injection hole 101. After the nitrogen is injected into the coal seam, it displaces the gas located in the coal seam, and the displaced gas is extracted through the extraction hole 102 by the negative pressure pump 104. During this process, the monitor 107 monitors the concentration and pressure information of the gas in the coal seam in real time. Multiple hole units 110 are set along the extension direction Y of the return airway 220 and / or transport roadway 230 of the coal seam. Each hole unit 110 includes an injection hole 101, an extraction hole 102, and a monitoring hole 103. The computer obtains the initial gas pressure P0 and the initial gas content Q0 based on the gas concentration and gas pressure information obtained by the monitor 107 in each hole unit 110, and calculates the predicted gas pressure P′ at the (n+1)th point based on the initial gas pressure P0 and the initial gas content Q0. n+1 And predicting gas content Q′ n+1 Let n be a positive integer; determine the predicted gas content Q′ at the (n+1)th location. n+1 If the ratio of nitrogen to the initial gas content Q0 is less than or equal to 1, then stop injecting nitrogen into injection hole 101; otherwise, proceed to the next step; continue to determine the predicted gas pressure P′ at the (n+1)th point. n+1If the ratio of nitrogen to the initial gas pressure P0 is less than or equal to 1, then stop injecting nitrogen into injection hole 101; otherwise, proceed to the next step. Calculate the gas outburst situation at each point using the gas outburst tendency index F, and determine if the gas outburst tendency index F at each point is greater than or equal to 1.4. If it is less than 1.4, increase the nitrogen pressure level in injection hole 101 and recalculate the gas outburst tendency index F until it is greater than or equal to 1.4, then proceed to the next step. Continue to determine if the gas outburst tendency index F is greater than or equal to 2.0. If it is greater than or equal to 2.0, then stop injecting nitrogen into injection hole 101. Nitrogen is used; otherwise, the current nitrogen injection pressure level is maintained. Firstly, by drilling holes and deploying monitors 107 in the coal seam, this system achieves the goal of injecting nitrogen to displace and extract gas in the coal seam, and predicting the risk of gas outbursts in the unmined portion of the coal seam. Secondly, this system improves the operational safety level of on-site gas injection and gas extraction. The staggered drilling extraction on both sides improves the efficiency of underground gas extraction, while appropriate injection pressure increases the concentration of extracted gas, enhancing its usability. Finally, using multi-parameter monitoring to prevent gas outbursts enhances the predictive sensitivity on the basis of existing outburst prevention measures, which is beneficial for improving the underground gas injection and gas extraction work and safety level.

[0070] In one example of the present invention, the monitor 107 includes:

[0071] A gas concentration monitor is configured to monitor the concentration of gas in coal seams.

[0072] A gas pressure monitor is configured to monitor the pressure information of gas in coal seams.

[0073] Monitoring gas concentration and gas pressure parameters to prevent gas outbursts can enhance the sensitivity of prediction on the basis of the original outburst prevention, which is conducive to improving the extraction and safety level of downhole gas injection to drive out gas.

[0074] In one example of the invention, a pressure gauge 109 is also included.

[0075] Installed between the valve 106 and the injection port 101, configured to monitor the pressure of nitrogen gas injected from the valve 106 toward the injection port 101;

[0076] In other words, the pressure gauge 109 can monitor in real time the pressure of nitrogen gas injected into the injection hole 101 from the nitrogen storage cylinder 105, thus facilitating more intuitive observation.

[0077] In one example of the present invention, a plurality of hole units 110 are provided at intervals along the extension direction Y of the return airway 220 and / or transport roadway 230 of the coal seam. Each hole unit 110 is formed by the injection hole 101, the extraction hole 102 and the monitoring hole 103 being provided at intervals along the extension direction Y and the depth direction S perpendicular to the extension direction Y.

[0078] In other words, an array of boreholes is drilled into the coal seam, and each borehole is defined as an injection hole 101, a extraction hole 102, and a monitoring hole 103. By arranging the above-mentioned hole units 110 in an array, it is easier to open the boreholes. At the same time, since the spacing between each borehole is equal, the influence between gas extraction, nitrogen injection, and gas monitoring can be optimized and balanced.

[0079] In one example of the present invention, the orifice unit 110 includes: an injection orifice 101, four extraction orifices 102 and four monitoring orifices 103, wherein the injection orifice 101 is located at the center of the orifice unit 110, the four extraction orifices 102 are located on both sides of the injection orifice 101 in the extension direction Y and the depth direction S, and the monitoring orifices 103 are located at the remaining four corner positions.

[0080] In short, the four monitoring holes 103 are located at the four corners, and the extraction holes 102 are located directly above, below, to the left and to the right of the injection holes 101. This structural arrangement allows the injection holes 101 in each hole unit 110 to achieve the best displacement effect and maximize the extraction of gas from the coal seam.

[0081] In one example of the present invention, in the hole unit 110, the distance between two adjacent holes is 0.6m to 0.8m;

[0082] After repeated experiments, the optimal displacement, extraction, and monitoring effects were achieved when the array spacing between the pore units 110 was 0.6-0.8m.

[0083] In one example of the present invention, the orifice unit comprises a plurality of orifices and is spaced apart along the extension direction Y of the return air passage 220 and / or transport passage 230;

[0084] By setting up multiple borehole units 110, the coal seam can be monitored step by step, thereby predicting the risk of gas outburst in the unmined part of the coal seam.

[0085] In one example of the present invention, the diameter of the injection hole 101, the extraction hole 102 and the monitoring hole 103 are all 100 mm, and the depth of the injection hole 101, the extraction hole 102 and the monitoring hole 103 are all 20 to 60 m.

[0086] According to a second aspect of the present invention, a method for preventing coalbed methane outbursts using the coalbed methane outburst prevention system 100 as described above is provided. Figure 3 As shown, it includes the following steps:

[0087] S10: Open valve 106 of coalbed methane anti-outburst system 100 to inject pressurized nitrogen into the coal seam, while negative pressure pump 104 extracts methane from extraction hole 102. During this process, monitor 107 located in monitoring hole 103 monitors methane concentration and methane pressure information. Multiple hole units 110 are set along the extension direction Y of return airway 220 and / or transport airway 230 of the coal seam, wherein each hole unit 110 includes injection hole 101, extraction hole 102 and monitoring hole 103.

[0088] S20: Based on the gas concentration and gas pressure information obtained by the monitor 107 in each well unit 110, obtain the initial gas pressure P0 and initial gas content Q0, and calculate the predicted gas pressure P′ at the (n+1)th point based on the initial gas pressure P0 and initial gas content Q0. n+2 And predicting gas content Q′ n+2 n is a positive integer;

[0089] S30: Determine the predicted gas content Q′ at the (n+1)th point. n+1 If the ratio of nitrogen to the initial gas content Q0 is less than or equal to 1, then stop injecting nitrogen into injection port 101; otherwise, proceed to the next step.

[0090] S40: Continue to determine the predicted gas pressure P′ at the (n+1)th point. n+1 If the ratio of nitrogen to the initial gas pressure P0 is less than or equal to 1, then stop injecting nitrogen into injection port 101; otherwise, proceed to the next step.

[0091] S50: Calculate the gas outburst situation at each point using the gas outburst tendency index F, and determine whether the gas outburst tendency index F at each point is greater than or equal to 1.4. If it is less than 1.4, increase the nitrogen pressure level in injection hole 101 and recalculate the gas outburst tendency index F until the gas outburst tendency index F is greater than or equal to 1.4, then proceed to the next step; wherein, the calculation formula for the gas outburst tendency index F is as follows:

[0092] F = P' n+41 / P0+Q′ n+1 / Q0

[0093] S60: Continue to determine whether the gas outburst tendency index F is greater than or equal to 2.0. If it is greater than or equal to 2.0, stop injecting nitrogen into injection hole 101. Otherwise, maintain the current nitrogen injection pressure level.

[0094] Firstly, this method, by drilling holes and deploying monitors 107 in the coal seam, achieves the goals of nitrogen injection to displace and extract gas within the coal seam, and predicts the risk of gas outbursts in the unmined portion of the coal seam. Secondly, this method improves the operational safety level of on-site gas injection and gas extraction. The staggered drilling on both sides increases the efficiency of underground gas extraction, while appropriate injection pressure increases the concentration of extracted gas, enhancing its usability. Finally, using multi-parameter monitoring to prevent gas outbursts enhances the predictive sensitivity on top of existing outburst prevention methods, thus improving the safety and efficiency of underground gas injection and gas extraction.

[0095] In one example of the present invention, the predicted gas pressure P′ at the (n+1)th point n+1 And predicting gas content Q′ n+1 The calculation formula is as follows:

[0096]

[0097]

[0098] In the formula, P n Let P' be the measured gas pressure at point n, a be the prediction sensitivity coefficient (0.5–0.7 based on actual values ​​at the well site, preferably 0.5 in this invention), and P′ be the gas pressure at point n. n For the predicted gas pressure at the nth point, Q n Let Q′ be the measured gas content at the nth point. n Let n be the predicted gas content at the nth location.

[0099] Specific Cases

[0100] The extraction drilling operation employs a two-sided staggered drilling method, including drilling holes at 0.6-0.8m, 1.2-1.4m, and 1.8-2m heights from the initial gas injection line in the intake airway, with a spacing of 0.6m and a length of 20-30m (approximately half the working face length). Then, in the return airway, starting 0.6m from the initial point, drilling holes at 0.6-0.8m, 1.2-1.4m, and 1.8-2m heights, with a spacing of 0.6m and a length of 20-60m (approximately half the working face length), are conducted at the same locations. The specific drilling layout method is as follows: a unit of nine holes is formed by three holes in the vertical direction and three consecutive holes in the horizontal direction. The construction sequence is to start drilling from the starting point of the air intake roadway. Depending on the location, purpose and the instruments deployed, the holes are divided into injection holes 101, extraction holes 102 and monitoring holes 103. The outburst prevention is completed according to the above-mentioned outburst prevention method.

[0101] Based on the aforementioned gas pressure monitoring boreholes and gas concentration monitoring boreholes, gas pressure and gas content data within 10.8m of the starting point can be obtained, namely P1, P2, P3...P 24 Q1, Q2, Q3...Q 24 First, the initial data for this section are the gas content and injection pressure. Then, the gas outburst prediction calculation is performed using the following formula:

[0102]

[0103]

[0104]

[0105]

[0106] In the formula, P n Let P' be the measured gas pressure at point n, a be the prediction sensitivity coefficient (0.5–0.7 based on actual values ​​at the well site, preferably 0.5 in this invention), and P′ be the gas pressure at point n. n For the predicted gas pressure at the nth point, Q n Let Q′ be the measured gas content at the nth point. n Let P0 be the predicted gas content at the nth point, and let Q0 be the initial gas pressure and initial gas content, respectively.

[0107] Preferably, the diameter of the aforementioned boreholes is 100 mm, the depth is 20–60 m, and the length is preferably half the length of the working face. The plugging device and the gas injection pipe with pressure gauge 109 are placed in the gas injection borehole, the plugging device and the extraction hose are placed in the gas extraction borehole, the gas concentration monitor is placed in the gas monitoring borehole, and the gas pressure gauge is placed in the gas pressure borehole.

[0108] Open the gas injection valve 106 to begin injecting pressurized nitrogen into the coal seam. The initial gas injection pressure is set to the first level of 0.40 MPa. Gas injection begins, and at the same time, the gas pump is used to extract gas from the gas extraction boreholes around the gas injection borehole at a negative pressure of 10-15 kPa. The gas collection pipeline connected to the extraction hose transports the extracted gas to the gas tank for further enrichment and utilization.

[0109] During the extraction operation, the data measured by the gas concentration monitor is transmitted to computer 108 via optical fiber. The average value of the data measured in the first six borehole units, a total length of 10.8m from the starting point, is used as the initial value, namely Q0 and P0.

[0110] Based on the aforementioned gas outburst prevention method, the outburst risk in unmined coal seam areas is predicted using the coal seam gas outburst tendency index F. If the coal seam is determined to have no outburst risk, the gas injection pressure level is increased; if it is determined to have an outburst risk, the gas injection pressure level is decreased. Specifically, if F ≥ 2, gas injection is immediately stopped.

[0111] The foregoing description, with reference to preferred embodiments, details an exemplary implementation of the coalbed methane outburst prevention system 100 and its working method proposed in this invention. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of this invention, and various combinations can be made to the various technical features and structures proposed in this invention without exceeding the protection scope of this invention, which is determined by the appended claims.

Claims

1. A method for preventing outburst of coal bed gas in a coal bed gas outburst prevention system, characterized by, The coal bed gas outburst prevention system comprises: An injection hole (101), an extraction hole (102) and a monitoring hole (103) formed in a coal bed; A negative pressure pump (104) connected with the extraction hole (102) and configured to extract gas in the coal bed; A nitrogen storage bottle (105) connected with the injection hole (101) and configured to inject nitrogen into the injection hole (101) to displace the gas; A valve (106) arranged between the nitrogen storage bottle (105) and the injection hole (101) and configured to control the amount of nitrogen injected by the nitrogen storage bottle (105) into the injection hole (101); A monitor (107) installed in the monitoring hole (103) and configured to monitor the concentration information and pressure information of the gas in the coal bed; A computer (108) in communication connection with the negative pressure pump (104), the valve (106) and the monitor (107) and configured to control the amount of nitrogen injected by the valve (106) into the injection hole (101) and the amount of gas extracted by the negative pressure pump (104) based on the concentration information and pressure information of the gas; The outburst prevention method comprises the following steps: S10: opening the valve (106) of the coal bed gas outburst prevention system (100) to inject pressurized nitrogen into the coal bed, and simultaneously extracting the gas in the extraction hole (102) by the negative pressure pump (104), wherein the gas concentration information and gas pressure information are monitored by the monitor (107) located in the monitoring hole (103) during the process; wherein a plurality of hole units (110) are arranged along the extension direction (Y) of the return air roadway (220) and / or the transportation roadway (230) of the coal bed, and each hole unit (110) comprises an injection hole (101), an extraction hole (102) and a monitoring hole (103); S20: obtaining an initial gas pressure based on the gas concentration information and the gas pressure information obtained by the monitor (107) in each hole unit (110) P 0 and the initial gas content Q 0 , and calculating a predicted gas pressure P 0 and a predicted gas content Q 0 at the first point based on the initial gas pressure n+1 and the initial gas content and the predicted gas content , n is a positive integer; S30: judging whether the ratio of the predicted gas content of the first point to the initial gas content is less than or equal to 1, if not, stopping injecting nitrogen into the injection hole (101); otherwise, executing the next step. n+1 Q 0 ​​​ S40: Continue to determine whether the ratio of the predicted gas pressure of the point to the initial gas pressure is less than or equal to 1, if not, stop injecting nitrogen into the injection hole (101); otherwise, execute the next step. n+1 P 0 S40: Continue to determine whether the ratio of the predicted gas pressure of the point to the initial gas pressure is less than or equal to 1, if not, stop injecting nitrogen into the injection hole (101); otherwise, execute the next step.​​ S50: calculating a gas outburst tendency index of each point F calculating the gas outburst situation of each point and judging the gas outburst tendency index of each point F whether it is greater than or equal to 1.4, if less than 1.4, increasing the level of nitrogen pressure in the injection hole (101) and recalculating the gas outburst tendency index F， until the gas outburst tendency index F satisfies greater than or equal to 1.4, executing the next step; wherein the calculation formula of the gas outburst tendency index F is as follows: ； S60: Continue to judge the gas outburst tendency index F whether greater than or equal to 2.0, if greater than or equal to 2.0, stop injecting nitrogen into the injection hole (101), otherwise, maintain the current nitrogen injection pressure level.

2. The outburst prevention method of the coal bed gas outburst prevention system according to claim 1, wherein the monitor (107) comprises: A gas concentration monitor configured to monitor the concentration information of the gas in the coal bed; A gas pressure monitor configured to monitor the pressure information of the gas in the coal bed.

3. The outburst prevention method of the coal bed gas outburst prevention system according to claim 1, further comprising: A pressure gauge (109) installed between the valve (106) and the injection hole (101) and configured to monitor the pressure of the nitrogen injected by the valve (106) towards the injection hole (101).

4. The outburst prevention method of the coal bed gas outburst prevention system according to claim 1, wherein a plurality of hole units (110) are arranged at intervals along the extension direction (Y) of the return air roadway (220) and / or the transportation roadway (230) of the coal bed, and each hole unit (110) is formed by the injection hole (101), the extraction hole (102) and the monitoring hole (103) arranged at intervals along the extension direction (Y) and a depth direction (S) perpendicular to the extension direction (Y).

5. The outburst prevention method of the coal bed gas outburst prevention system according to claim 4, wherein ​ ​ ​ The hole unit (110) comprises one injection hole (101), four extraction holes (102) and four monitoring holes (103), wherein the injection hole (101) is located at the center position of the hole unit (110), the four extraction holes (102) are located on both sides of the injection hole (101) in the extension direction (Y) and the depth direction (S), and the monitoring holes (103) are located at the remaining four corner positions.

6. The outburst prevention method of the coal bed gas outburst prevention system according to claim 4, characterized in that, In the hole unit (110), the distance between two adjacent holes is 0.6-0.8 m.

7. The outburst prevention method of the coal bed gas outburst prevention system according to claim 4, characterized in that, The hole unit (110) comprises a plurality of hole units, which are arranged at intervals along the extension direction (Y) of the return air roadway (220) and / or the transportation roadway (230).

8. The outburst prevention method of the coal bed gas outburst prevention system according to claim 1, characterized in that, The diameters of the injection hole (101), the extraction hole (102) and the monitoring hole (103) are all 100 mm, and the depths of the injection hole (101), the extraction hole (102) and the monitoring hole (103) are all 20-60 m.

9. The outburst prevention method of the coal bed gas outburst prevention system according to claim 1, characterized in that, No. n+1 Predicted gas pressure at each point and predicting gas content The calculation formula is as follows: ； In the formula, P n is n The measured gas pressure of the point, is the predicted sensitive coefficient, is the predicted gas pressure of the first n point, is the measured gas content of the first n point, is the predicted gas content of the first n point.

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