Method for judging spontaneous combustion dangerous area of pressure relief drilling coal in rock burst coal seam

Abstract

The invention discloses a method for judging a coal spontaneous combustion dangerous area of a pressure relief drill hole of a rock burst coal seam, and relates to the technical field of coal spontaneous combustion fire monitoring and prevention, and the method comprises the following steps: obtaining an internal pressure value, a coal body temperature, a roadway pressure value and an oxygen concentration of the pressure relief drill hole; calculating the internal and external pressure difference of the pressure relief drill holes according to the internal pressure value and the roadway pressure value, judging whether an air leakage seepage condition exists or not, monitoring the occurrence time and concentration of SF6 gas at the drill holes and fractures, and calculating the minimum air leakage rate between the pressure relief drill holes; the air leakage range of the pressure relief drilling area is obtained based on the SF6 gas concentration and the air leakage rate; simulation is conducted by combining the internal and external pressure difference, the coal body temperature, the oxygen concentration and the air leakage range with Fluent software, and the coal body spontaneous combustion dangerous area around the pressure relief drill hole is divided. According to the method, precise judgment of the spontaneous combustion dangerous area of the coal body around the pressure relief drill hole is realized through combination of field conditions and software simulation.

Description

Technical Field

[0001] The invention relates to the technical field of coal spontaneous combustion fire monitoring and prevention, and more particularly to a method for determining a coal spontaneous combustion hazard zone in a pressure relief drilling hole of an impact ground pressure coal seam. Background Art

[0002] At present, deep coal seam mining is affected by high ground stress and strong disturbance, which can easily lead to rock burst accidents. The application of pressure relief drilling can effectively release the harmful elastic properties accumulated in the coal rock mass, but its pressure relief mechanism will also cause the integrity of the coal body around the borehole to be destroyed, forming an annular crushing zone similar to a loosening circle in the radial direction, which is manifested as widespread distribution of cracks in this area, and the influence of mining disturbance will further aggravate their development and expansion, causing the boreholes to penetrate each other, forming a pressure relief borehole fracture zone.

[0003] In the pressure relief drilling technology for preventing and controlling coal seam impact ground pressure, the boreholes are generally arranged in the entrance and return tunnels of coal seam mining. The airflow is sufficient and can easily penetrate into the boreholes gradually under the action of the pressure difference, forming a microcirculation inside the boreholes and at the same time diffuse to the surrounding boreholes with the help of cracks. The coal body is in contact with oxygen for a long time, resulting in oxidation. The heat released by the reaction accumulates continuously, forcing its temperature to rise, which increases the risk of spontaneous combustion of the coal body in the cracks of the pressure relief drilling hole.

[0004] Therefore, it is necessary to determine the influence range of the fracture field and oxygen field in the pressure relief drilling area, and then accurately divide the risk area of ​​spontaneous combustion of coal in the pressure relief drilling area, so as to take efficient fire prevention and extinguishing measures for targeted prevention and control, so as to ensure the safe production of the mine. Summary of the invention

[0005] In view of this, the present invention provides a method for determining the risk zone of spontaneous combustion of coal in a pressure-relief drilling hole in a rock burst coal seam. According to the characteristics of severe fissure development, complex air leakage and different oxygen distribution in the pressure-relief drilling hole area, the method can accurately determine the risk zone of spontaneous combustion of coal around the pressure-relief drilling hole, so as to guide the targeted prevention and control of spontaneous combustion of coal in the pressure-relief drilling hole, and reduce the spontaneous combustion accidents of coal seams induced by drilling leakage in the process of preventing and controlling rock burst in deep mining mines.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for determining a spontaneous combustion hazard zone of pressure relief drilling coal in a rock burst coal seam, comprising:

[0008] S1: Obtain the internal pressure value of the pressure relief borehole, coal body temperature, tunnel pressure value and oxygen concentration;

[0009] S2: Calculate the internal and external pressure difference of the pressure relief borehole according to the internal pressure value and the tunnel pressure value, and determine whether there is a condition for air leakage and seepage. If there is a condition for air leakage and seepage, enter S3;

[0010] S3: monitor the appearance time and concentration of SF6 gas at the boreholes and cracks, and calculate the minimum air leakage rate between the pressure relief boreholes;

[0011] S4: The leakage range of the pressure relief drilling area is obtained based on the SF6 gas concentration and leakage rate;

[0012] S5: The internal and external pressure difference, coal body temperature, oxygen concentration and air leakage range are used in combination with Fluent software to perform simulation, and the coal body spontaneous combustion risk area around the pressure relief borehole is divided based on the oxygen concentration.

[0013] Preferably, S1 specifically includes: installing a bundle pipe at each pressure relief drilling detection point, and using a handheld digital pressure gauge to measure the tunnel pressure at the buried bundle pipe and the internal pressure of the pressure relief drilling hole respectively; immediately inserting the casing device into the borehole after the pressure relief drilling construction is completed, and extracting and monitoring the oxygen concentration and coal temperature inside the pressure relief drilling hole through the built-in suction device and thermometer of the casing device.

[0014] Preferably, the calculation of the internal and external pressure difference of the pressure relief borehole specifically includes:

[0015] P i =p h -p k ;

[0016] Among them, P i is the pressure difference between the inside and outside of the pressure relief borehole, p h is the tunnel pressure value, p k It is the internal pressure value of the pressure relief borehole.

[0017] Preferably, in S2, whether the borehole can leak air is determined based on whether the pressure difference between the inside and outside of the pressure relief borehole is greater than a preset pressure difference threshold; if so, it is determined that the airflow in the tunnel here can enter the pressure relief borehole under the action of ventilation positive pressure, and the primary condition for coal spontaneous combustion is met, then the process goes to S3; if not, it is determined that the pressure relief borehole here does not have the conditions for air leakage to occur, and no further judgment on coal spontaneous combustion is required.

[0018] Preferably, in S3, a portable SF6 measuring instrument is used to detect the SF6 concentration in the tunnel, and the SF6 concentration in the tunnel environment is recorded; when SF6 release begins, a small underground vacuum pump is used to continuously extract gas from the pressure relief borehole in the study area to the portable SF6 measuring instrument for mining for analysis, with a gas measurement interval of 2 min / time, and a continuous detection time of 30 minutes or until the difference between the detected SF6 concentration value and the environmental concentration value is less than 3 ppm; the time and component concentration of SF6 detection are recorded, and the minimum air leakage rate is calculated by the relative position of the SF6 release point and the receiving point and the first detection time, as calculated by the following formula:

[0019]

[0020] Where V is the minimum air leakage rate, L is the air leakage distance, and t is the time when SF6 gas is first detected in the corresponding borehole.

[0021] Preferably, S4 specifically includes: judging whether there are mutually connected air leakage channels between the boreholes through the SF6 concentration detection result, judging the flow direction of the airflow between the cracks in combination with the air leakage rate, and determining the air leakage distance of the pressure relief drilling area according to the release point and the farthest receiving point where SF6 is detected, thereby determining the air leakage range.

[0022] Preferably, based on the air leakage range, numerical simulation is performed using Fluent software to obtain the oxygen concentration distribution in the air leakage area, and the air leakage seepage in the pressure relief drilling area in the numerical simulation satisfies Darcy's law.

[0023] Preferably, the division of the coal spontaneous combustion danger zone around the pressure relief borehole specifically includes: determining the area formed by each position where the corresponding oxygen concentration is less than the first concentration threshold or greater than the second concentration threshold as a safe area; determining the area formed by each position where the corresponding oxygen concentration is greater than the first concentration threshold and less than the second concentration threshold as an oxidation warming zone, corresponding to the range of the coal spontaneous combustion danger zone; wherein the first concentration threshold is less than the second concentration threshold.

[0024] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses a method for determining the coal spontaneous combustion hazard zone of the pressure relief drilling hole in the impact ground pressure coal seam, and the beneficial effects are: based on the actual working conditions of the pressure relief drilling hole in the deep coal seam, the pressure difference, oxygen concentration and temperature of the drilling hole are detected on site, and the tracer gas SF6 is used to determine the air leakage between the drilling holes in the fracture area, and at the same time, the Fluent software is used to simulate the drilling hole leakage process, so that the obtained oxygen distribution results cover the entire area, making the pressure relief drilling hole area transparent, overcoming the disadvantages of the limited monitoring range of the traditional bundle tube; on the basis of the on-site test of the pressure relief drilling hole leakage range, further, combined with the numerical simulation results of the drilling hole leakage area to divide the coal spontaneous combustion hazard range. The compensation space formed by the drilling hole is regarded as a small tunnel, and the coal spontaneous combustion hazard zone division standard is: the oxygen concentration between 8% and 18% is the oxidation warming zone, that is, there is a risk of spontaneous combustion of coal. The problem of unclear air leakage patterns and oxygen concentration distribution in the fracture areas of pressure relief boreholes, and complex and difficult-to-detect natural hazards of coal were overcome, and accurate, reasonable and comprehensive judgment of the risk areas of coal spontaneous combustion in pressure relief boreholes was achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 A diagram of the method steps provided by the present invention;

[0027] Figure 2 Schematic diagram of the pressure relief drilling hole and SF6 measuring point provided by the present invention;

[0028] Figure 3 A schematic diagram of a numerical simulation model provided by the present invention;

[0029] Figure 4 This is the oxygen concentration field diagram of the numerical simulation of the pressure relief drilling air leakage process of the present invention;

[0030] Figure 5 It is a lateral distribution gradient diagram of oxygen concentration in the process of air leakage in the pressure relief drilling hole numerically simulated by the present invention;

[0031] Figure 6 It is a longitudinal distribution gradient diagram of oxygen concentration in the process of air leakage in the pressure relief drilling hole numerically simulated by the present invention;

[0032] Figure 7 This is a schematic diagram of the method for determining the spontaneous combustion hazard zone provided by the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The embodiment of the present invention discloses a method for determining a spontaneous combustion hazard zone of a pressure relief drilling coal seam. Figure 1 As shown, including:

[0035] S1: Obtain the internal pressure value of the pressure relief borehole, coal body temperature, tunnel pressure value and oxygen concentration;

[0036] S2: Calculate the internal and external pressure difference of the pressure relief borehole according to the internal pressure value and the tunnel pressure value to determine whether there is a condition for air leakage and seepage. If there is a condition for air leakage and seepage, enter S3;

[0037] S3: Monitor the appearance time and concentration of SF6 gas in the boreholes and cracks, and calculate the minimum air leakage rate between the pressure relief boreholes;

[0038] S4: The leakage range of the pressure relief drilling area is obtained based on the SF6 gas concentration and leakage rate;

[0039] S5: The internal and external pressure difference, coal temperature, oxygen concentration and air leakage range are simulated with Fluent software, and the coal spontaneous combustion risk area around the pressure relief borehole is divided based on the oxygen concentration.

[0040] In step S1, only the local oxygen concentration in the borehole can be obtained through the bundle tube monitoring. Therefore, the oxygen field distribution inside the borehole and the coal body around the borehole is supplemented and analyzed through numerical simulation by Fluent software to fully grasp the oxygen concentration values ​​at various positions in the pressure relief borehole area.

[0041] In a specific embodiment, the air leakage channels formed by the development and penetration of cracks between boreholes are analyzed by SF6 concentration and air leakage rate, the seepage direction of the gas inside the borehole is determined, and the air leakage range of the pressure relief borehole area is obtained;

[0042] In a specific embodiment, S1 specifically includes: installing a bundle pipe at each pressure relief borehole detection point, and using a handheld digital pressure gauge to measure the tunnel pressure at the buried bundle pipe and the internal pressure of the pressure relief borehole respectively; immediately after the pressure relief borehole construction is completed, the casing device is deeply inserted into the borehole, and the built-in suction device and thermometer of the casing device are used to extract and monitor the oxygen concentration and coal temperature inside the pressure relief borehole.

[0043] In a specific embodiment, calculating the internal and external pressure difference of the pressure relief borehole specifically includes:

[0044] P i =p h -p k ;

[0045] Among them, P i is the pressure difference between the inside and outside of the pressure relief borehole, p h is the tunnel pressure value, p k It is the internal pressure value of the pressure relief borehole.

[0046] In a specific embodiment, in S2, it is determined whether the borehole can leak air according to whether the pressure difference inside and outside the pressure relief borehole is greater than the preset pressure difference threshold; if so, it is determined that the airflow in the tunnel here can enter the pressure relief borehole under the action of positive ventilation pressure, and the primary condition for coal spontaneous combustion is met, and then S3 is entered; if not, it is determined that the pressure relief borehole here does not have the conditions for air leakage to occur, and no further judgment on coal spontaneous combustion is required. In S2, if the pressure difference inside and outside the pressure relief borehole is greater than 0, it indicates that there is positive ventilation pressure, which can provide a driving force for the diffusion of tunnel air into the coal body in the fissure area of ​​the borehole; further, the air leakage intensity of boreholes in different areas can be judged according to the size of the wind pressure difference, which is characterized in that: the larger the wind pressure difference, the stronger the driving effect on the diffusion of wind flow, indicating that the air leakage at the detected borehole is more serious.

[0047] In a specific embodiment, a portable SF6 measuring instrument is used in S3 to detect the SF6 concentration in the tunnel and record the SF6 concentration in the tunnel environment; when SF6 release begins, a small underground vacuum pump is used to continuously extract gas from the pressure relief borehole in the study area to the portable SF6 measuring instrument for mining for analysis. The gas measurement interval is 2 min / time, and the continuous detection time is 30 minutes or the difference between the detected SF6 concentration value and the environmental concentration value is less than 3 ppm; the time and component concentration of SF6 detection are recorded, and the minimum air leakage rate is calculated by the relative position of the SF6 release point and the receiving point and the first detection time, and is calculated as follows:

[0048]

[0049] Among them, V is the minimum air leakage rate, L is the air leakage distance, and t is the time when SF6 gas is first detected in the corresponding borehole. In S3, the pressure relief borehole area with positive ventilation pressure is tested for air leakage; a group of pressure relief boreholes arranged in a row are selected as the test object. Considering the faster gas diffusion rate on the downwind side of the tunnel, the SF6 tracer gas release device is installed in the middle and upper boreholes, and the remaining boreholes are used as receiving monitoring points.

[0050] In a specific embodiment, S4 specifically includes: judging whether there are mutually connected air leakage channels between the boreholes through the SF6 concentration detection results, judging the flow direction of the airflow between the cracks in combination with the air leakage rate, and determining the air leakage distance of the pressure relief drilling area based on the release point and the farthest receiving point where SF6 is detected, thereby determining the air leakage range.

[0051] The SF6 concentration test results are used to determine whether there are mutually connected air leakage channels between the boreholes. The air leakage rate is combined to determine the flow direction of the air flow between the cracks. The direction with the larger air leakage rate is determined as the seepage direction of the gas inside the borehole.

[0052] In a specific embodiment, based on the air leakage range, numerical simulation is performed using Fluent software to obtain the oxygen concentration distribution in the air leakage area to make up for the shortcomings of bundle tube monitoring. At the same time, the oxygen concentration detection in S1 can also verify the numerical simulation results. In the numerical simulation, the air leakage seepage in the pressure relief drilling area satisfies Darcy's law, and the calculation formula is as follows:

[0053]

[0054] In the formula, k g is the gas permeability of the coal sample, μ g is the dynamic viscosity coefficient of the gas, h is the length of the coal sample, and p g1 、p g2 are the gas pressure at the inlet and outlet of the coal sample, q g2 is the gas flow rate at the outlet, ρ0 is the atmospheric pressure, and A is the cross-sectional area of ​​the coal rock mass.

[0055] The model obtained by numerical simulation using Fluent software includes the drilling area, coal seam and tunnel area. The model size is consistent with the actual value. The two sides of the tunnel are set as air inlet and outlet, the internal drilling hole is the air inlet, and the other boundaries of the model are uniformly set as wall. The coal seam porosity is set to 1e-12.

[0056] In a specific embodiment, dividing the coal spontaneous combustion danger zone around the pressure relief borehole specifically includes: determining the area formed by each position where the corresponding oxygen concentration is less than a first concentration threshold or greater than a second concentration threshold as a safe area; determining the area formed by each position where the corresponding oxygen concentration is greater than the first concentration threshold and less than the second concentration threshold as an oxidation warming zone, corresponding to the range of the coal spontaneous combustion danger zone; wherein the first concentration threshold is less than the second concentration threshold.

[0057] In Example 1: Implementation Background 2202 The coal seam of the working face is buried at a depth of about 780m, which belongs to deep mining and has a strong impact tendency. Therefore, a number of pressure relief boreholes are arranged in the auxiliary transportation chute of the working face to alleviate the harm caused by impact ground pressure. The boreholes are arranged at a spacing of 1m, a hole diameter of 0.15m, a depth of 20m, and a height of 1.5m from the floor. Figure 2 As shown. The cracks around the borehole generated during the decompression process continue to develop and penetrate, resulting in the formation of a large number of air leakage channels. The tunnel airflow seeps into the borehole and around it under the action of positive pressure, providing oxygen supply for coal spontaneous combustion. Through bundle tube monitoring, it was found that the local oxygen concentration in the decompression borehole fluctuated between 14.74% and 19.88%, and the risk of spontaneous combustion was high. In order to ensure the safe production of the mine, it is necessary to accurately define the risk range of coal spontaneous combustion in the decompression drilling area so as to take targeted fire prevention and extinguishing measures for effective prevention and control.

[0058] Detect the internal pressure of the pressure relief borehole, tunnel pressure value, coal body temperature and oxygen concentration; install bundle pipes at the measuring points of 1~6# pressure relief boreholes, and use a handheld digital pressure gauge to measure the tunnel pressure and the internal pressure of the pressure relief borehole where the bundle pipes are buried, with a measuring depth of 3m in the hole; install the casing deep into the borehole, and use a vacuum pump to pre-extract the gas inside the borehole for 2 minutes. After the residual gas inside the bundle pipe is exhausted, the gas inside the borehole is extracted into the gas sample bag through the vacuum pump, and the oxygen concentration in each borehole is detected by the on-site gas chromatograph, and the temperature change inside the borehole is monitored by the built-in thermometer.

[0059] The pressure value measured by S1 is used to calculate the pressure difference between the inside and outside of the borehole to determine whether the borehole has the conditions for air leakage and seepage. The wind pressure difference values ​​of each borehole measuring point in this embodiment are shown in Table 1. The pressure inside the six pressure relief holes is significantly lower than the tunnel pressure, and the pressure difference between the inside and outside is similar, ranging from 13.57 to 19.69 Pa. This pressure difference can provide a driving force for the diffusion of gas from the tunnel to the coal body in the borehole fracture area, which is a key factor leading to its air leakage flow field distribution and oxygen supply.

[0060] Table 1 Wind pressure difference values ​​at each drilling point

[0061]

[0062] Considering that the gas diffusion speed is faster on the downwind side of the tunnel, the third borehole SF6 release point is selected, such as Figure 2 As shown, the release point is the 4# position, and the remaining boreholes are monitoring points.

[0063] The SF6 portable measuring instrument was used to detect the SF6 concentration in the tunnel, and the SF6 concentration in the tunnel environment was recorded. The release flow rate was set to 100 mL / min, and the SF6 gas cylinder was opened for release. The release time was 10 min. A small underground vacuum pump was used to continuously extract gas from the pressure relief borehole in the study area to the mining SF6 portable measuring instrument for analysis. The gas measurement interval was 2 min / time, and the continuous detection time was 30 minutes or the difference between the detected SF6 concentration value and the environmental concentration value was less than 3 ppm. The time and component concentration of SF6 were detected, and the leakage rate was calculated, as shown in Table 2.

[0064] Table 2 SF6 time and component concentration

[0065]

[0066] Determine the air leakage channel, gas seepage direction and air leakage range between boreholes; from the monitoring record of step S4, it can be seen that SF6 was first detected on the downwind side of the SF6 release point, which took about 2 minutes; when the release time was 6 minutes, SF6 was detected at the 5# measuring point on the upwind side, but the concentration was relatively small, and SF6 was never detected at the 6# pressure relief hole. In addition, the air leakage rate on the downwind side is generally higher than that on the upwind side, which indicates that there are mutually conductive cracks in the pressure relief borehole area, and the main air leakage direction is consistent with the air flow direction of the roadway. According to the air leakage test, the air leakage distance of the crack field of the pressure relief borehole in the 2202 working face roadway can reach 3m.

[0067] Fluent software was used to simulate the air leakage process of the tunnel air flow into the pressure relief borehole during the normal mining process of the working face, and the oxygen field distribution of the coal body inside and around the borehole was analyzed. The model includes the borehole area, coal seam and tunnel area. The model size is set to the actual size, including: the tunnel width is 5m, the length is simplified to 25m, and the height is 4.5m; the average height of the coal seam is 6.7m, and the depth is simplified to 70m; the borehole diameter is 0.15m, the depth is 20m, the height is 1.5m, and the spacing is 1m. The two sides of the tunnel are set as air inlets and outlets, and the internal borehole is the air inlet. The other boundaries of the model are uniformly set as walls. Among them, the coal seam porosity is set to 1e-12, such as Figure 3 shown.

[0068] The oxygen concentration field cloud map of the pressure relief drilling area in the 2202 working face tunnel is as follows Figure 4-6 As shown in the figure, the oxygen gas concentration tends to decrease with the increase of drilling depth, and its fluctuation range is close to the roadway side, and the fluctuation area accounts for about 1 / 3 of the entire coal seam. At the drilling height, the oxygen mass fraction at the borehole mouth is 17%, and the oxygen distribution pattern among the 6 boreholes is similar. When the drilling depth is 20m, the oxygen mass fraction is 8%; at the top of the roadway, the highest oxygen mass fraction is 14%,

[0069] According to the numerical simulation results, the oxygen concentration is divided into the coal spontaneous combustion danger zone around the pressure relief borehole. The area formed at each position where the oxygen concentration is greater than the first concentration threshold and less than the second concentration threshold is determined as the oxidation warming zone, which corresponds to the range of the coal spontaneous combustion danger zone, such as Figure 7 shown.

[0070] Among them, in the embodiment of the present disclosure, the first concentration threshold is 8% and the second concentration threshold is 18% as an example for explanation. According to the simulation results and the judgment method, the oxygen concentration fields between the boreholes overlap with each other. A single pressure relief borehole in the fracture area will form an elliptical danger range centered on itself, 0.63m above and below, and about 20m deep. When multiple pressure relief boreholes are arranged at a spacing of 1m, the danger ranges between the boreholes overlap with each other, forming a coal spontaneous combustion danger zone in the middle part of the coal seam.

[0071] The method for determining the risk zone for spontaneous combustion of coal in a pressure relief borehole based on impact ground pressure coal seams in the disclosed embodiment divides the risk zone for spontaneous combustion of coal around the pressure relief borehole by detecting the pressure difference between the inside and outside of the pressure relief borehole, the oxygen concentration and the air leakage law, and combining the numerical simulation results. Thus, a comprehensive and accurate determination of the risk zone for spontaneous combustion of coal around the pressure relief borehole in the coal seam is achieved, and the risk range for spontaneous combustion of coal around the borehole is determined. Further, prevention work can be done in advance according to the division results, which has important guiding significance for reducing the hidden dangers of spontaneous combustion of coal in pressure relief boreholes in impact ground pressure coal seams.

[0072] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0073] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams, characterized in that: include: S1: Obtain the internal pressure value of the pressure relief borehole, coal body temperature, tunnel pressure value and oxygen concentration; S2: Calculate the internal and external pressure difference of the pressure relief borehole according to the internal pressure value and the tunnel pressure value, and determine whether there is a condition for air leakage and seepage. If there is a condition for air leakage and seepage, enter S3; S3: monitor the appearance time and concentration of SF6 gas at the boreholes and cracks, and calculate the minimum air leakage rate between the pressure relief boreholes; S4: The leakage range of the pressure relief drilling area is obtained based on the SF6 gas concentration and leakage rate; S5: The internal and external pressure difference, coal body temperature, oxygen concentration and air leakage range are used in combination with Fluent software to perform simulation, and the coal body spontaneous combustion risk area around the pressure relief borehole is divided based on the oxygen concentration.

2. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1 is characterized in that: The S1 specifically includes: installing a bundle pipe at each pressure relief borehole detection point, and using a handheld digital pressure gauge to measure the tunnel pressure at the buried bundle pipe and the internal pressure of the pressure relief borehole respectively; immediately after the pressure relief borehole construction is completed, the casing device is deeply inserted into the borehole, and the internal oxygen concentration and coal temperature of the pressure relief borehole are extracted and monitored through the built-in suction device and thermometer of the casing device.

3. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1 is characterized in that: The calculation of the internal and external pressure difference of the pressure relief borehole specifically includes: P i =p h -p k ; Among them, P i is the pressure difference between the inside and outside of the pressure relief borehole, p h is the tunnel pressure value, p k It is the internal pressure value of the pressure relief borehole.

4. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1 is characterized in that: In S2, whether the borehole can leak air is determined based on whether the pressure difference between the inside and outside of the pressure relief borehole is greater than a preset pressure difference threshold; if so, it is determined that the airflow in the tunnel here can enter the pressure relief borehole under the action of the positive ventilation pressure, and the primary condition for spontaneous combustion of coal is met, and then the process goes to S3; if not, it is determined that the pressure relief borehole here does not have the conditions for air leakage to occur, and no further judgment on spontaneous combustion of coal is required.

5. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1, characterized in that: In the S3, a portable SF6 measuring instrument is used to detect the SF6 concentration in the tunnel, and the SF6 concentration in the tunnel environment is recorded; when SF6 release begins, a small underground vacuum pump is used to continuously extract gas from the pressure relief borehole in the study area to the mining SF6 portable measuring instrument for analysis. The gas measurement interval is 2 minutes / time, and the continuous detection time is 30 minutes or the difference between the detected SF6 concentration value and the environmental concentration value is less than 3ppm; the time and component concentration of SF6 are recorded, and the minimum air leakage rate is calculated by the relative position of the SF6 release point and the receiving point and the first detection time, which is calculated as follows: Where V is the minimum air leakage rate, L is the air leakage distance, and t is the time when SF6 gas is first detected in the corresponding borehole.

6. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 5, characterized in that: The S4 specifically includes: judging whether there are mutually connected air leakage channels between the boreholes through the SF6 concentration detection results, judging the flow direction of the airflow between the cracks in combination with the air leakage rate, and determining the air leakage distance of the pressure relief borehole area based on the release point and the farthest receiving point where SF6 is detected, thereby determining the air leakage range.

7. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1, characterized in that: Based on the air leakage range, numerical simulation was performed using Fluent software to obtain the oxygen concentration distribution in the air leakage area. In the numerical simulation, the air leakage seepage in the pressure relief drilling area satisfies Darcy's law.

8. The method for determining the spontaneous combustion hazard zone of pressure relief drilling coal in rock burst coal seams according to claim 1, characterized in that: The division of the coal spontaneous combustion danger zone around the pressure relief borehole specifically includes: determining the area formed by each position where the corresponding oxygen concentration is less than the first concentration threshold or greater than the second concentration threshold as a safe area; determining the area formed by each position where the corresponding oxygen concentration is greater than the first concentration threshold and less than the second concentration threshold as an oxidation warming zone, corresponding to the range of the coal spontaneous combustion danger zone; wherein the first concentration threshold is less than the second concentration threshold.

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