Method and system for monitoring and analyzing overlying strata fracture condition of working face of middle coal seam

Abstract

The invention relates to the technical field of coal mine safety monitoring, in particular to a method and system for monitoring and analyzing the overlying strata fracture condition of a working face of a medium coal seam. According to the footage stage of the working face, the mining process of the working face is divided into an initial advancing stage, a stable advancing stage and an ending advancing stage; and according to the footage stage, dynamically arranging a ground monitoring unit and an underground monitoring unit in the acquisition area, acquiring monitoring data of each monitoring time point, and analyzing and judging the penetration degree grade of the overlying strata fracture. According to the method, correlation analysis can be performed on the overlying strata fissures from three aspects through the representation penetration degree, the stress penetration degree and the gas penetration degree, so that whether the penetration condition exists in the overlying strata fissures or not is accurately judged, the comprehensiveness and accuracy of overlying strata fissure analysis are improved, and subsequent corresponding treatment according to the penetration condition is facilitated; according to the method, the penetration degree grades of the overlying strata fractures are divided into complete penetration, partial penetration and non-penetration, and prevention and control measures are matched according to the penetration degree grades.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mine safety monitoring, in particular to a method and system for monitoring and analyzing fissure conditions of overburden rock in a medium coal seam working face. BACKGROUND

[0002] In the process of mining in a medium coal seam working face, the influence of overburden rock working face advancement will gradually evolve into a process of immediate roof caving, fissure development, and basic roof bending and subsidence. The fissures formed by the overburden rock are not only the core channels for air leakage in the goaf and spontaneous combustion of residual coal, but also may even cause roof instability and harmful gas accumulation, etc. Therefore, accurate monitoring and analysis of the fissure conditions of the overburden rock is a key link in ensuring the safety of coal mine production.

[0003] Existing monitoring and analysis of overburden rock fissures mostly use ground microseismic monitoring or underground borehole peeping monitoring. However, single ground monitoring cannot accurately capture the structural characteristics of the lower part of the overburden rock fissures, and single underground monitoring cannot associate the microseismic of the mine with the underground data, thus leading to incomplete monitoring of the overburden rock fissures and easy misjudgment.

[0004] Meanwhile, the existing monitoring units are all fixedly laid out without considering the differences in overburden rock movement at different footage stages of the working face. For example, fissures change frequently in the initial advancement period and the end advancement period, requiring high-frequency monitoring; fissures change smoothly in the stable advancement period, without the need for excessive monitoring; and if a fixed layout density is used, the monitoring cost will be increased.

[0005] In addition, the existing technology relies on the data of borehole peeping and the data of underground stress-displacement sensor monitoring for analysis of the fissure penetration degree. However, this way has too single data dimension, and some overburden rock fissures may not be fully reflected from the above data, thus reducing the accurate determination of the connectivity of the fissures. SUMMARY

[0006] The present application solves the above technical problems. The present application uses the following technical solution: a method for monitoring and analyzing fissure conditions of overburden rock in a medium coal seam working face, comprising: obtaining basic parameters of the coal seam working face, determining a data collection boundary on the ground and underground based on the basic parameters, and demarcating a monitoring collection area.

[0007] According to the footage stage of the working face, the working face mining process is divided into three stages: the initial advancement period, the stable advancement period, and the end advancement period; and according to the footage stage, the ground monitoring units and the underground monitoring units are dynamically laid out in the collection area. After the working face advances to a preset distance, monitoring data at each monitoring time point is collected.

[0008] Screening out monitoring data associated with the working face overburden rock; the screened monitoring data is subjected to spatial verification and time alignment, and the apparent penetration, stress penetration and gas penetration of the working face overburden rock crack are analyzed.

[0009] Based on the analysis results of the apparent penetration, stress penetration and gas penetration, the penetration grade of the overburden rock crack is determined, and the corresponding fire prevention and extinguishing measures are matched through the penetration grade.

[0010] Further, the basic parameters of the coal seam working face are obtained, and the data acquisition boundary of the ground and underground is determined based on the basic parameters, and the monitoring collection area is demarcated, specifically including: the basic parameters of the working face include the working face strike length, inclination length, mining height and expected footage speed.

[0011] The data acquisition boundary of the ground covers the preset length of the projection outer edge of the working face.

[0012] The data acquisition boundary of the underground is a closed area formed by the upper and lower lanes of the working face, the open-off cut and the stop mining line.

[0013] Further, the acquisition method of the monitoring data includes: the monitoring data includes surface subsidence data and underground monitoring data; wherein the surface subsidence data includes collecting surface microseismic events, surface microseismic coordinates and microseismic energy through a microseismic sensor.

[0014] The acquisition and processing method of the underground monitoring data includes: obtaining the original image of the crack through a borehole peep instrument.

[0015] A feature extraction method based on image edge detection and morphological analysis is adopted to extract the length, strike and bifurcation characteristics of the crack.

[0016] The stress value and displacement data of the overburden rock are collected through a stress-displacement sensor.

[0017] The gas concentration data in the goaf are collected through a gas sensor.

[0018] Further, the division standard of the working face footage stage is: the stage from the start of footage in the open-off cut to the first preset footage distance is defined as the initial advancing period.

[0019] The stage of working face footage to the second preset footage distance from the stop mining line is defined as the end advancing period.

[0020] The footage stage between the initial advancing period and the end advancing period is defined as the stable advancing period.

[0021] Further, the specific way of spatial verification is to calibrate the vertical coordinate (Z coordinate) of the surface microseismic event based on the crack position obtained by the underground borehole peep.

[0022] The specific way of time alignment is: taking the working face footage distance as the time correlation reference, constructing a footage-time coordinate system (taking the working face footage distance as the X axis and time as the Y axis), and mapping the surface microseismic data, overburden stress value data and gas concentration data to the coordinate system to realize the alignment in the time dimension.

[0023] Further, the analysis method of the overburden fracture appearance throughness is: counting the number of fracture intersection points in a single borehole observation section, denoted as node number; counting the number of interconnected fracture sections in a single borehole observation section; calculating the ratio of the number of bifurcations of a single fracture to the length of the fracture, denoted as bifurcation coefficient; and calculating the standard deviation of the angle between the strike of all fractures in a single observation section and the working face, denoted as fracture strike consistency.

[0024] The ratio of the number of interconnected fractures in a single observation section to the total number of fractures is multiplied by the correction coefficient of the fracture strike consistency to obtain the appearance throughness.

[0025] The appearance throughness level is determined based on the combination of the appearance throughness and the bifurcation coefficient: if the appearance throughness is not lower than a first appearance throughness threshold value and the bifurcation coefficient is not lower than a first bifurcation coefficient threshold value, the appearance is determined to be high throughness.

[0026] If the appearance throughness is lower than the first appearance throughness threshold value and not lower than a second appearance throughness threshold value, and the bifurcation coefficient is lower than the first bifurcation coefficient threshold value and not lower than a second bifurcation coefficient threshold value, the appearance is determined to be medium throughness.

[0027] If the appearance throughness is lower than the second appearance throughness threshold value and the bifurcation coefficient is lower than the second bifurcation coefficient threshold value, the appearance is determined to be low throughness.

[0028] Further, the analysis method of the overburden fracture stress throughness is: using the K-means clustering algorithm to perform clustering processing on the surface microseismic information, calculating the cluster center coordinates, the total cluster energy and the cluster event density of each cluster.

[0029] If the cluster event density of a certain cluster is greater than or equal to a set event density threshold value, and the total cluster energy is greater than or equal to a first set energy total threshold value, the region corresponding to the cluster is determined to be an overburden fracture dense region, and the coordinates of the region are taken as the ground microseismic coordinates.

[0030] If the stress change value monitored by the stress sensor exceeds a set stress change threshold value, and the stress change state duration exceeds a stress duration threshold value, the region is determined to be a stress relief zone, and the coordinates of the region are taken as the underground pressure relief coordinates.

[0031] If the displacement rate of the stress relief zone displacement sensor exceeds the displacement rate increase threshold, and the cluster energy sum of the corresponding position of the region is greater than or equal to the second set energy sum threshold, it is verified that the region has stress penetration.

[0032] The ratio of the vertical projection overlap area of the ground microseismic coordinates and the downhole pressure relief coordinates to the total area of the fracture dense area is taken as the stress penetration degree, and the stress connectivity degree is judged according to the stress connectivity degree, wherein: if the stress connectivity degree is not lower than the first stress connectivity threshold, it is judged as stress high connectivity.

[0033] If the stress connectivity degree is lower than the first stress connectivity threshold and not lower than the second stress connectivity threshold, it is judged as stress medium connectivity.

[0034] If the stress connectivity degree is lower than the second stress connectivity threshold, it is judged as stress low connectivity.

[0035] Further, the analysis method of the overburden rock fracture gas penetration degree is: extracting the oxygen concentration change amount monitored by the gas sensor in the buried pipe in the goaf, if the oxygen concentration change amount exceeds the set concentration change threshold, and the position of the gas sensor in the footage-time coordinate system deviates from the space-time projection of the region judged to have stress penetration by less than the preset deviation threshold, it is judged that the position has gas penetration.

[0036] Further, the judgment method of the overburden rock fracture penetration degree is: if the overburden rock fracture satisfies the appearance high penetration degree, the stress high connectivity degree, and the oxygen concentration change amount exceeds the gas concentration change threshold at the same time, it is judged as completely penetrated.

[0037] If the overburden rock fracture satisfies the appearance low connectivity degree, the stress low connectivity degree, and the oxygen concentration change amount does not exceed the gas concentration baseline threshold at the same time, it is judged as not penetrated.

[0038] Except for completely penetrated and not penetrated, other cases are judged as partially penetrated.

[0039] Further, the present application also provides a coal seam working face overburden rock fracture condition monitoring and analysis system, comprising: a region division module for determining the data acquisition boundaries of the ground and underground according to the basic parameters of the coal seam working face, and forming an acquisition region.

[0040] A monitoring layout module dynamically lays out ground and underground monitoring units in the acquisition region according to the footage stage of the working face.

[0041] An overburden rock fracture data monitoring module obtains monitoring data at each monitoring time point after the working face advances a preset distance, the monitoring data including surface subsidence data and underground monitoring data, and the monitoring data is data cleaned to determine the surface subsidence data and underground monitoring data related to the working face overburden.

[0042] The overburden rock crack analysis module spatially verifies and time-aligns the surface subsidence data and the underground monitoring data, and analyzes the surface appearance penetration, stress penetration and gas penetration of the overburden rock crack of the working face; the penetration grade of the overburden rock crack is determined through the three groups of penetrations, and the penetration grade is divided into complete penetration, partial penetration and non-penetration.

[0043] The measure matching module matches the corresponding fire prevention and extinguishing measures through the penetration grade.

[0044] The beneficial effects of the system are as follows: 1. The ground monitoring unit and the underground monitoring unit are cooperatively laid out, so that the overburden rock crack is analyzed through the double data of the ground and the underground. The ground microseism can capture the microseismic event of the crack zone, the underground borehole peephole can accurately measure the crack condition of the caving zone, and the ground and the underground monitoring modes are complementary and fully cover the overburden rock crack in the whole space. Meanwhile, the vertical coordinates of the ground microseismic event are calibrated based on the measured crack position of the underground borehole peephole, so as to eliminate the possible spatial deviation of the ground and the underground. Meanwhile, the ground microseism, underground stress and gas data are uniformly mapped to the same time dimension based on the working face footage-time coordinate system, so as to avoid the data mismatch caused by time misplacement.

[0045] 2. According to the overburden rock crack development characteristics in the initial advancing period, the stable advancing period and the tailing advancing period of the working face, the monitoring unit layout density is dynamically adjusted: the initial and tailing periods are densely laid out to ensure the capture of the rapid change of the crack; the stable period is sparsely laid out to reduce redundant monitoring. The above monitoring unit layout modes according to the mining stage ensure the monitoring accuracy in the initial and tailing periods, and reduce the monitoring cost in the stable period.

[0046] 3. The overburden rock crack is correlated and analyzed from three aspects of the surface appearance penetration, the stress penetration and the gas penetration, so as to accurately determine whether the overburden rock crack is penetrated, increase the comprehensiveness and accuracy of the overburden rock crack analysis, and facilitate the subsequent corresponding treatment according to the penetration condition. The surface appearance penetration quantifies the intuitive connectivity through the crack node number and the bifurcation system; the stress penetration quantifies the stress-related connectivity through the spatial overlap of the microseismic fracture dense area and the stress relief area; and the gas penetration quantifies the functional connectivity through the oxygen concentration change and carbon monoxide verification.

[0047] 4. The penetration grade of the overburden rock crack is divided into complete penetration, partial penetration and non-penetration, and the corresponding prevention and control measures are matched according to the above three penetration grades. BRIEF DESCRIPTION OF DRAWINGS

[0048] The application is further illustrated by the accompanying drawings, but the embodiments in the drawings do not constitute any limitation to the application, and other embodiments can be obtained by the drawings below without creative labor for those skilled in the art.

[0049] Fig. 1 is a flow chart of the method for monitoring and analyzing the overburden fissure condition of the coal seam working face in the application.

[0050] Fig. 2 is a flow chart for determining the penetration degree of the overburden fissure. DETAILED DESCRIPTION

[0051] The embodiments of the application are described in detail below. The embodiments described below are exemplary and are only used to explain the application and cannot be understood as a limitation to the application. The specific techniques or conditions not mentioned in the embodiments are performed according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0052] Reference Figs. 1-2 A method for monitoring and analyzing the overburden fissure condition of the coal seam working face, comprising: S100, obtaining the basic parameters of the coal seam working face, determining the data collection boundary of the ground and underground based on the basic parameters, and demarcating the monitoring collection area; specifically comprising: the basic parameters of the working face include the length of the working face, the length of the inclination, the mining height, and the expected footage speed.

[0053] The data collection boundary of the ground covers the preset length of the projection outer edge of the working face. Since the overburden fissure exists not only in the rock layer directly above the working face during the mining process of the coal seam, but also in the rock layer within the preset length of the outer edge of the working face, the fissure and microseismic data exist, so the data collection boundary needs to cover the preset length of the outer edge when it is determined.

[0054] It should be noted that the preset length of the outer edge needs to be determined comprehensively according to the length of the working face, the length of the inclination, the mining height, and the expected footage speed, and the preset length of the outer edge is positively correlated with the basic parameters. In actual engineering, the preset length of the outer edge is usually designed and set according to the experience of engineering personnel. For example, the length of the working face is 1200 meters, the length of the inclination is 200 meters, the mining height is 2.5 meters, and the footage speed is 6.4 meters per day, and the preset length of the outer edge is set to 35 meters.

[0055] The data collection boundary of the underground is a closed area formed by the working face upper and lower roadways, the open-off cut, and the stop mining line.

[0056] S200, according to the footage stage of the working face, the working face mining process is divided into three stages of initial advancing period, stable advancing period and end advancing period; according to the footage stage, the ground monitoring unit and the underground monitoring unit are dynamically arranged in the collection area, and after the working face advances to a preset distance, the monitoring data of each monitoring time point is collected.

[0057] S210, the division standard of the working face footage stage is that the stage from the start of the open-off cut to the first preset footage distance is defined as the initial advancing period.

[0058] The stage of advancing the working face to the second preset footage distance from the stopping line is defined as the end advancing period.

[0059] The footage stage between the initial advancing period and the end advancing period is defined as the stable advancing period.

[0060] Because the overburden crack changes frequently in the early and late stages of coal mining, and the crack development is relatively stable in the middle stage of mining, the working face mining is divided into three mining periods in the application, and different monitoring strategies are adopted in different mining periods, that is, the arrangement density of the ground monitoring unit and the underground monitoring unit is adjusted in different mining periods, which not only ensures the accuracy of the working face crack monitoring, but also reduces unnecessary monitoring cost.

[0061] The monitoring data acquisition method of the application is to collect and analyze the monitoring data after the working face advances to a certain stage in different mining periods, so that the overburden crack analysis can be carried out in different mining stages of the working face, and the real-time and accuracy of the analysis of the application is increased. For example, the preset distance of the initial advancing period is 10 meters, that is, the monitoring data is collected when the initial advancing period advances 10 meters, the preset distance of the stable advancing period is 30 meters, that is, the monitoring data is collected when the stable advancing period advances 30 meters, and the preset distance of the end advancing period is 5 meters, that is, the monitoring data is collected when the stable advancing period advances 5 meters.

[0062] S220, the monitoring data acquisition method comprises: the monitoring data comprises surface subsidence data and underground monitoring data; wherein the surface subsidence data comprises collecting surface microseismic events, surface microseismic coordinates and microseismic energy through a microseismic sensor.

[0063] S221, the acquisition and processing method of the underground monitoring data comprises: acquiring a crack original image through a borehole viewer.

[0064] S222, a feature extraction method based on image edge detection and morphological analysis is used to extract the length, direction and bifurcation characteristics of the crack.

[0065] S223, the stress value and displacement data of the overburden are collected through a stress-displacement sensor.

[0066] S224, collecting goaf gas concentration data by the gas sensor. The goaf gas concentration data specifically includes oxygen concentration, carbon monoxide concentration and gas concentration.

[0067] The present application adopts the way of on-well and down-well collaborative data collection to comprehensively analyze the working face overburden rock fissure, prevents deviation caused by single data analysis, and misjudgment; the present application obtains the development of the fissure through fissure original image analysis, reflects the pressure condition of the overburden rock through the pressure and displacement of the overburden rock, reflects whether there is a leakage passage in the goaf through the gas concentration data, and through the collaborative analysis of the above multi-dimensional data, whether the overburden rock fissure has an impact on the safety of the working face can be analyzed.

[0068] For example, the microseismic sensor is arranged at 35 meters outside the working face projection, the interval is 20 meters, and the number is greater than 5; the borehole peephole instrument is arranged in the borehole drilled from the working face to the goaf, one borehole is arranged every 8 meters, the hole depth is greater than 20 meters, and the borehole inclination is 15-30 degrees; the stress-displacement sensor is arranged on the roof of the working face and the upper and lower roadways, and is arranged at a distance of 5 meters from the open-off cut, and 10 stress-displacement sensors are evenly arranged on the roof of the working face and the upper and lower roadways at an interval of 5 meters; the gas sensor is arranged in the form of a buried bundle tube in the goaf, one gas sensor is arranged on the bundle tube every 3 meters, the number is greater than 8, and as the working face advances, the innermost sensor in the goaf is synchronously migrated.

[0069] In the stable advancing period, the interval of the microseismic sensor is 30 meters, and the rest of the arrangement parameters are the same; the interval of the borehole peephole instrument is 10 meters, and the rest of the arrangement parameters are the same; the interval of the stress-displacement sensor is 10 meters, and the rest of the arrangement parameters are the same; the interval of the gas sensor is 5 meters, and the rest of the arrangement parameters are the same.

[0070] The arrangement parameters of the monitoring unit in the finishing advancing period are the same as those in the initial advancing period, which will not be described in detail here.

[0071] S300, screening out monitoring data associated with the working face overburden rock; performing spatial verification and time alignment on the screened monitoring data, and analyzing the surface penetration degree, stress penetration degree and gas penetration degree of the working face overburden rock fissure; the present application comprehensively analyzes the above three penetration degrees, and then comprehensively analyzes the penetration of the overburden rock fissure from different dimensions, prevents one-sidedness of single monitoring analysis method, and increases the comprehensiveness and accuracy of the analysis of the present application.

[0072] Since the present application adopts the way of correlating the ground and down-well data for comprehensive analysis, the ground and down-well data need to be verified in spatial position and aligned in time, so that the present application can accurately analyze the related monitoring data of the same event on the ground and in the down-well.

[0073] S310, the specific way of the space verification is: taking the crack position obtained by the borehole peep as the reference, the vertical coordinate (Z coordinate) of the surface microseismic event is calibrated; when the overburden rock under the well produces a crack, the surface will definitely have a microseismic event, so it is necessary to verify the longitudinal coordinate of the surface microseismic with the crack position obtained by the borehole.

[0074] S311, the specific way of the time alignment is: taking the working face footage distance as the time correlation reference, constructing a footage-time coordinate system (taking the working face footage distance as the X axis and the time as the Y axis), and mapping the surface microseismic data, overburden stress value data and gas concentration data to the coordinate system to realize the alignment in the time dimension. The way of time alignment is convenient to obtain the data at each monitoring time point after the working face footage reaches the preset distance, and increases the intuitiveness and convenience of data acquisition.

[0075] S320, the analysis way of the overburden crack appearance through degree is: counting the number of crack intersection points in a single borehole observation section, which is recorded as the node number; counting the number of cracks connected to each other in a single borehole observation section; calculating the ratio of the number of bifurcations of a single crack to the crack length, which is recorded as the bifurcation coefficient; and calculating the standard deviation of the angle between the strike of all cracks in a single observation section and the working face, which is recorded as the crack strike consistency.

[0076] The specific acquisition and calculation process of the crack strike consistency is as follows: first, the borehole peep instrument is used to obtain the image of the hole wall development diagram in the observation section, the image edge detection algorithm is used to identify the crack boundary in the image, and the morphological analysis is used to refine the identification result of the crack to obtain the crack center line.

[0077] Second, the least square method is used to linearly fit the crack center line into a straight line, and the fitting straight line has an inclination angle in the image coordinate system. Since the borehole is vertical or inclined, the hole wall image is a development diagram of a cylindrical surface. Therefore, the inclination angle in the image coordinate system needs to be converted to the strike angle in the real geographical coordinate system through geometric transformation.

[0078] Third, the working face strike angle is determined at the beginning of the working face design or operation, which is a known fixed value. For each crack, the minimum angle between its strike angle and the working face strike angle is taken as the angle between the strike of the crack and the working face. The crack strike consistency is the standard deviation of all the angles between the strikes of the cracks and the working face.

[0079] The smaller the crack strike consistency is, the closer the angles between the development directions of all the cracks and the working face strike are to the average value, that is, the strike of the cracks is highly consistent, the development regularity is strong, and it is likely to be formed by the working face mining.

[0080] The greater the consistency of the crack direction, the more chaotic the crack development direction is. Some are parallel to the working face, some are vertical, and the consistency is very poor. It may be affected by the original geological structure or other random factors.

[0081] The ratio of the number of interconnected fractures to the total number of fractures in a single observation section multiplied by the correction coefficient of fracture trend consistency is taken as the apparent penetration. The analytical formula for the apparent penetration is: ,in Indicates the consistency of crack direction, It indicates the influence degree of fracture trend consistency. The product of the above two is the correction coefficient of fracture trend consistency.

[0082] Among them, in the calculation of the apparent permeability of overburden fractures, the influence degree of fracture strike consistency is a parameter used to quantify the actual weight of the effect of fracture strike consistency on the effective connectivity of overburden fractures. Its essence is to adjust the importance of fracture strike consistency in the determination of apparent permeability according to the specific mining conditions, safety risk level and monitoring objectives of the middle coal seam working face, so as to avoid distortion of the determination results under different working conditions due to fixed weights. For example, in high-gas mines, the fracture strike along the direction of gas migration is more critical, and the influence degree of fracture strike consistency can be set to 0.8-1.0 to strengthen the influence of strike consistency; in low-gas mines, the influence degree of fracture strike consistency can be set to 0.5-0.7 to reduce its weight and flexibly adapt to different working conditions.

[0083] The borehole peephole monitor monitors the area of ​​observation segments, with a single segment used as the statistical unit. This ensures spatially focused data collection and prevents the mixing of data from observation segments at different depths and with different lithologies, which could distort the judgment of fracture connectivity in a specific area. For example, within the same borehole, shallow observation segments may have dense and connected fractures, while deeper observation segments may have sparse and isolated fractures. Separate statistics can accurately pinpoint differences in fracture connectivity at different depths.

[0084] By counting the number of nodes (crack intersections) and the number of interconnected crack segments, it can be directly reflected whether the cracks form a network connection. The more nodes there are and the higher the proportion of interconnected crack segments, it means that the cracks do not exist in isolation, but have formed an interconnected network, which provides a structural basis for subsequent judgment of whether there are air leakage / harmful gas migration channels.

[0085] The bifurcation coefficient is a measure of the branching density of the fissure. The more branches there are, the more complex the channels are, which intuitively reflects the extension ability and expansion potential of the fissure. The higher the bifurcation coefficient, the easier it is for the fissure to generate new branches during development, further expanding the connectivity range.

[0086] The fissure trend consistency degree (standard deviation of the angle between the fissure trend and the working face trend) can exclude the interference of a large number of fissures with a disordered trend. If the fissure trend difference is large (the standard deviation is high), even if the proportion of the mutually connected fissure segments is high, the fissure may not form an effective connected channel due to the dispersed trend. By using the fissure trend consistency degree correction coefficient, the effective connectivity of the fissure network can be more objectively measured, and the disordered fissure group can be avoided from being mistakenly judged as a high-penetration network.

[0087] As one of the core dimensions for determining the grade of the overburden rock fissure penetration, the appearance penetration degree is calculated and analyzed by means of multi-dimensional disassembly and quantification of the fissure shape, structure and trend, so as to accurately describe the intuitive connected state of the fissure, provide a reliable visual basis for determining the overall penetration degree in combination with the stress and gas dimensions, and avoid the subjective bias caused by relying on experience observation.

[0088] The appearance penetration degree is determined based on the combination of the appearance penetration degree and the bifurcation coefficient: if the appearance penetration degree is not lower than the first appearance penetration threshold, and the bifurcation coefficient is not lower than the first bifurcation coefficient threshold, the appearance high-penetration degree is determined.

[0089] If the appearance penetration degree is lower than the first appearance penetration threshold and not lower than the second appearance penetration threshold, and the bifurcation coefficient is lower than the first bifurcation coefficient threshold and not lower than the second bifurcation coefficient threshold, the appearance medium-penetration degree is determined.

[0090] If the appearance penetration degree is lower than the second appearance penetration threshold, and the bifurcation coefficient is lower than the second bifurcation coefficient threshold, the appearance low-penetration degree is determined.

[0091] In the present application, the specific considerations for determining the grade of the appearance penetration degree based on the combination of the appearance penetration degree and the bifurcation coefficient are as follows: first, the appearance penetration degree can reflect the connected size and effectiveness of the current fissure, but cannot reflect the dynamic development potential of the fissure; for example, the appearance penetration degree of a certain observation section meets the standard, but the bifurcation coefficient is extremely low, which indicates that there is connectivity at present, but the fissure has almost no ability to derive new branches, and it is difficult to expand the penetration range in the future; if the appearance penetration degree is only used to determine the high-penetration degree, the risk will be overestimated.

[0092] Secondly, the bifurcation coefficient can quantify the expansion activity of the fissure, but it also has defects when used alone; for example, if the bifurcation coefficient is high, but the appearance penetration degree is low, it indicates that the fissure is active, but an effective connected network has not been formed at present, and it is only a high-bifurcation fissure in isolation; if the bifurcation coefficient is only used to determine the high risk, it will cause a misjudgment.

[0093] Finally, the combination of the two forms a double-dimensional judgment logic for the connected state of the current fissure and the future development potential, which not only ensures the accurate identification of the high-connected network that has been formed, but also avoids the misjudgment of the connected fissure with no expansion potential or the fissure with potential but not connected, and realizes the comprehensive evaluation of the appearance penetration state of the fissure.

[0094] The specific setting process of the first apparent penetration threshold, the second apparent penetration threshold, the first bifurcation coefficient threshold and the second bifurcation coefficient threshold among the above is as follows: first, the distribution range of the apparent penetration and the bifurcation coefficient in the high-risk connected area (apparent high penetration), the medium-risk connected area (apparent medium penetration) and the low-risk connected area (apparent low penetration) in the historical cases is respectively counted, for example, the apparent penetration of the high-risk area is mostly concentrated in 0.5-0.8, and the bifurcation coefficient is mostly concentrated in 0.3-0.5; the apparent penetration of the medium-risk area is mostly concentrated in 0.3-0.5, and the bifurcation coefficient is mostly concentrated in 0.1-0.3; the apparent penetration of the low-risk area is mostly concentrated in 0-0.3, and the bifurcation coefficient is mostly concentrated in 0-0.1.

[0095] Secondly, the threshold is preliminarily set based on the distribution range, and the lower limit of the high-risk area is taken as the first threshold, for example, the first apparent penetration threshold is 0.5, and the first bifurcation coefficient threshold is 0.3; the lower limit of the medium-risk area is taken as the second threshold, for example, the second apparent penetration threshold is 0.3, and the second bifurcation coefficient threshold is 0.1.

[0096] Thirdly, field trial monitoring and threshold verification are carried out, in the initial advancing period of the current working face, trial determination is carried out according to the preliminarily set threshold, and at the same time, the data of the underground stress-displacement sensor (for verifying whether the fracture actually affects the stress) and the gas sensor (for verifying whether there is air leakage) are combined to determine whether the threshold is reasonable, for example, if the area with apparent high penetration is determined according to the preliminary threshold, the stress sensor does not monitor obvious pressure relief, and the gas concentration is not abnormal, then the first threshold needs to be lowered, for example, the first apparent penetration threshold is reduced to 0.45.

[0097] Fourthly, the threshold is optimized and finally determined, after the trial monitoring period ends, the matching rate of the threshold determination result and the actual safety risk is counted, if the matching rate is greater than or equal to 90%, the threshold is determined as the corresponding final threshold; if the matching rate is insufficient, the steps from the first step to the third step are repeated until the threshold can accurately correspond to the actual risk, and finally the threshold system of the first apparent penetration threshold, the second apparent penetration threshold, the first bifurcation coefficient threshold and the second bifurcation coefficient threshold suitable for the current working face is formed.

[0098] The data of each monitoring time point in the advancing stage of the working face are respectively analyzed and calculated in the application, so that the application can dynamically obtain the dynamic change of the overburden fracture in the advancing stage.

[0099] It should be noted that the apparent penetration of the application is the overburden fracture penetration obtained by analyzing the borehole image.

[0100] S330, the analysis mode of the overburden fracture stress penetration degree is: using K-means clustering algorithm to cluster the surface microseismic information, calculating the cluster center coordinates, cluster energy sum and cluster event density of each cluster. The cluster event density is the number of cluster events in the monitoring time range.

[0101] The process of obtaining the cluster center coordinates, cluster energy sum and cluster event density of each cluster is: collecting the surface microseismic original data in the monitoring time range through the microseismic sensor arranged on the ground, including the occurrence time, surface microseismic coordinates and microseismic energy value of each microseismic event.

[0102] The K value is set in combination with the working face collection area range (the data collection boundary of the ground covering the projection outer edge of the working face with a preset length) and the microseismic event distribution characteristics. If the microseismic events are dispersedly distributed in the collection area, the K value is taken as 3-5; if the microseismic events are centrally distributed, the K value is taken as 2-3, so as to avoid that the K value is too large to cause excessive dispersion of clustering (unable to identify the dense area) or too small to cause excessive aggregation of clustering (masking the local dense characteristics).

[0103] The Euclidean distance between each microseismic event and each initial cluster center is calculated, and the microseismic event is assigned to the nearest cluster, forming K initial cluster clusters. For each initial cluster cluster, the average value of the surface microseismic coordinates of all microseismic events in the cluster is calculated, and the average value is taken as the new cluster center coordinates to replace the original initial center.

[0104] The above steps are repeated until the cluster center coordinate variation of adjacent two iterations is less than a preset threshold, or the assignment result of the microseismic events in the cluster cluster no longer changes, the iteration is stopped, and the final K cluster clusters are determined.

[0105] The cluster center coordinates are calculated: taking the final new cluster center coordinates of each cluster cluster after iteration convergence as the cluster center coordinates of the cluster cluster, which represents the centralized distribution position of the microseismic events of the cluster.

[0106] The cluster energy sum is calculated: for each cluster cluster, the microseismic energy values of all microseismic events in the cluster are accumulated to obtain the cluster energy sum, which reflects the total strength of the overburden rock fracture in the region corresponding to the cluster. The higher the energy sum is, the more intense the fracture is.

[0107] The cluster event density is calculated: according to the definition that the cluster event density is the number of cluster events in the monitoring time range, the total number of microseismic events in each cluster cluster is counted, which is directly taken as the cluster event density of the cluster. It reflects the frequency of overburden rock fracture in the region. The higher the cluster event density is, the more frequent the fracture is.

[0108] If the cluster event density of a cluster is greater than or equal to the set event density threshold, and the cluster energy sum is greater than or equal to the first set energy sum threshold, the area corresponding to the cluster is determined to be a dense overburden fracture area, and the coordinates of the area are used as the ground microseismic coordinates.

[0109] During the initial advancement period, the monitoring period is short, the total number of microseismic events is small, and the threshold can be set to 3-5. During the stable advancement period, the monitoring period is long, the total number of microseismic events is large, and the threshold can be set to 5-8. Hard overburden fracture requires higher energy, and the microseismic energy value is generally large, so the threshold can be set to 6×10 4 Quality 8×10 4 J; The energy required for the fracture of soft overburden is low, and the microseismic energy value is small. The threshold can be set as 3×10 4 to 5×10 4 J, to ensure that the energy requirement of the rock fracture is matched. In the specific embodiment of the present invention, for example, the event density threshold is set to 5, and the first energy sum threshold is set to 5×10 4 J.

[0110] If the stress change detected by the stress sensor exceeds a set stress change threshold, and the duration of the stress change exceeds a stress duration threshold, the area is identified as a stress relief zone, and the coordinates of the area are used as the downhole stress relief coordinates. For example, the stress change threshold is set at 1.1 times the initial stress, and the duration threshold is set at 18 hours.

[0111] If the displacement rate of the displacement sensor in the stress relief area exceeds the displacement rate increase threshold, and the sum of the cluster energy at the corresponding position in the area is greater than or equal to the second set energy sum threshold, then the stress penetration in the area is verified; the displacement rate represents the displacement per unit time. For example, the displacement rate increase threshold is 300%; the second set energy sum threshold is 3×10 4 J.

[0112] The ratio of the overlapping area of ​​the vertical projections of the surface microseismic coordinates and the downhole unloading coordinates to the total area of ​​the fracture-intensive zone is taken as the stress connectivity, and the stress connectivity level is determined based on this ratio. If the stress connectivity is not lower than the first stress connectivity threshold, it is determined to be high stress connectivity.

[0113] If the stress connectivity is lower than the first stress connectivity threshold and not lower than the second stress connectivity threshold, it is determined to be moderate stress connectivity.

[0114] If the stress connectivity is lower than the second stress connectivity threshold, it is determined to be low stress connectivity.

[0115] Exemplarily, the first stress connectivity threshold and the second stress connectivity threshold are 0.6 and 0.4, respectively.

[0116] The vertical projection overlapping area of the ground microseismic coordinates and the underground pressure relief coordinates refers to projecting the overburden rock fracture dense area corresponding to the ground microseismic and the underground stress relief area to the same horizontal reference plane respectively, and the area of the overlapping part of the two projected areas, and the unit is usually square meters, wherein the same horizontal reference plane is usually taken as the horizontal plane where the open-off cut of the working face is located. The essence is to quantify the overlapping degree of the ground macroscopic fracture and the underground microscopic stress response in space, and to reflect the mechanical connectivity of the overburden rock fracture in the vertical direction.

[0117] The specific acquisition process of the vertical projection overlapping area of the ground microseismic coordinates and the underground pressure relief coordinates is that the ground microseismic coordinates and the underground pressure relief coordinates need to be converted to the same coordinate system to eliminate the projection deviation caused by the difference between the ground and underground coordinate reference.

[0118] The region boundary corresponding to the ground microseismic is determined by using the minimum circumscribed polygon method, and the minimum polygon containing all microseismic event coordinates is taken as the fracture dense area boundary.

[0119] The underground pressure relief area boundary is determined by connecting the positions of all stress sensors whose stress change value exceeds the set threshold and whose duration meets the standard according to the stress sensor monitoring data to form a closed area, which is the underground pressure relief area boundary.

[0120] The vertical projection operation of the ground microseismic coordinates and the underground pressure relief coordinates is performed, the Z-axis (vertical direction) difference between the ground microseismic coordinates and the underground pressure relief coordinates is ignored, only the X / Y-axis (horizontal direction) coordinates are retained, and the two areas are projected vertically downward to the same horizontal reference plane to obtain two two-dimensional plane areas.

[0121] The overlapping area calculation is performed by using the graphic intersection algorithm to calculate the intersection area of the two two-dimensional projected areas, and the area is the vertical projection overlapping area.

[0122] The total area of the fracture dense area refers to the projection area of the overburden rock fracture dense area determined by the K-means clustering algorithm in the ground microseismic monitoring on the horizontal reference plane, and the unit is square meters. The total area of the fracture dense area represents the overall spatial range of the overburden rock fracture in the ground monitoring. The specific acquisition process of the total area of the fracture dense area is that if the microseismic events in the clustering cluster are scattered, the minimum circumscribed circle is used to calculate the area, wherein the radius of the minimum circumscribed circle is the horizontal distance from the clustering center to the farthest microseismic event.

[0123] If the microseismic events are continuously distributed in a strip or block, the polygon fitting method is used to connect the microseismic event coordinates in sequence to form a closed polygon, and the polygon area is calculated by the coordinate analytical method, which is the total area of the fracture dense area.

[0124] The prior art has the defect that single monitoring cannot correlate surface and downhole data, surface microseismic can only locate the fracture zone, and downhole stress can only monitor the pressure relief zone, but cannot determine whether the two are caused by the same overburden crack connection. The stress penetration degree is calculated by the vertical projection overlap area / fissure density area, which upgrades the correlation of surface and downhole space from qualitative judgment to quantitative judgment, and provides an objective basis for stress connectivity level determination.

[0125] The first stress connectivity threshold value is used as the determination boundary of high stress connectivity, and is used for identifying a high-risk area where the overburden crack has formed a stable mechanical channel. When the stress penetration degree is large, it indicates that the spatial overlap degree of the surface fracture dense area and the downhole pressure relief area is high, and the overburden crack has formed an effective connection in the vertical and horizontal directions. Such an area is easy to become the main path of air leakage and harmful gas migration in the goaf, and high-intensity prevention and control measures such as grouting or nitrogen injection need to be taken preferentially to avoid the risk of missing the high-risk area due to ambiguous judgment.

[0126] The second stress connectivity threshold value is used as the division boundary of medium stress connectivity and low stress connectivity. When the stress penetration degree is small, it is determined as medium stress connectivity, indicating that the spatial correlation of the surface and the downhole is moderate. Although the crack has not formed a completely stable channel, there is a local connection risk, and the monitoring frequency needs to be increased. When the stress penetration degree is smallest, it is determined as low stress connectivity, indicating that the surface fracture and the downhole pressure relief have no obvious correlation, and the crack connectivity is poor, and only routine monitoring is needed to avoid cost waste caused by excessive prevention and control.

[0127] The acquisition methods of the first stress connectivity threshold value and the second stress connectivity threshold value are the same as those of the first apparent penetration threshold value, the second apparent penetration threshold value, the first bifurcation coefficient threshold value and the second bifurcation coefficient threshold value, which can be easily obtained by those skilled in the art, and will not be described in detail here.

[0128] S340, the analysis method of the overburden crack gas penetration degree is: extracting the oxygen concentration change monitored by the gas sensor in the goaf buried pipe, if the oxygen concentration change exceeds the set concentration change threshold value, and the position of the gas sensor in the footage-time coordinate system deviates from the space-time projection of the area where the stress penetration degree has been determined by less than the preset deviation threshold value, it is determined that the position has gas penetration.

[0129] In the specific implementation process of the present application, the goaf buried pipe and the gas sensor are dynamically arranged according to the working face footage stage, the sensor migrates synchronously with the working face advancement, and the oxygen concentration data in the goaf is collected in real time, and the specific time of each concentration monitoring and the downhole physical position of the corresponding sensor are recorded.

[0130] The drilling footage-time coordinate system is built and the data is mapped. The drilling footage-time coordinate system is built with the drilling footage distance of the working face as the X-axis and the time as the Y-axis. The following data is mapped to the coordinate system: gas sensor data, the underground physical position of the sensor is converted into the X-axis coordinate (corresponding to the drilling footage distance), and the concentration monitoring time is converted into the Y-axis coordinate, forming a three-dimensional data point of drilling footage distance-monitoring time-oxygen concentration.

[0131] The stress breakthrough region data is converted into a space-time rectangular range in the coordinate system. The X-axis is the drilling footage distance interval corresponding to the region The Y-axis is the time window during which the stress breakthrough state of the region is stable , The stress stable duration.

[0132] The space-time coordinate deviation of the gas sensor and the stress breakthrough region is determined. The spatial deviation (X-axis direction) is calculated by the deviation of the drilling footage distance corresponding to the gas sensor from the drilling footage interval of the stress breakthrough region If is within , where D is a preset spatial deviation threshold, the spatial deviation is qualified.

[0133] The time deviation (Y-axis direction) is calculated by the deviation of the sensor monitoring time from the time window of the stress breakthrough region If is within , where T is a preset time deviation threshold, the time deviation is qualified.

[0134] For example, the stress breakthrough region drilling footage interval is [100m, 120m], the time window is [8:00 on the 5th day, 20:00 on the 5th day], the preset spatial deviation D=5m, and the time deviation T=6h; a gas sensor corresponds to =103m (within 95m-125m), =10:00 on the 5th day (within 2:00 on the 5th day-2:00 on the 6th day), and the space-time deviation is qualified.

[0135] If the sensor meets both the spatial deviation qualification and the time deviation qualification, it means that the oxygen concentration change is highly related to the stress breakthrough region; if either deviation is not qualified, it is determined that the concentration change is not related to the stress breakthrough fracture, and the gas breakthrough is excluded.

[0136] The oxygen concentration change is extracted and compared with the set threshold. Specifically, the oxygen concentration change of a single sensor is calculated, the oxygen concentration data of the same gas sensor in adjacent two monitoring periods is selected, and the absolute value of the difference between the oxygen concentration changes in adjacent two monitoring periods is taken as the concentration change.

[0137] The preset oxygen concentration change threshold is called, and if the concentration change amount is greater than the set concentration change threshold, it indicates that the oxygen concentration in the sensor monitoring area changes significantly, and the next step of space verification is entered, if the concentration change amount is less than or equal to the set concentration change threshold, it is determined that there is no obvious gas concentration fluctuation in the area, and it is temporarily determined as a gas penetration.

[0138] Comprehensive determination of the above two steps, if the oxygen concentration change amount exceeds the set concentration change threshold, and the position of the gas sensor in the footage-time coordinate system and the space-time projection deviation of the area where the stress penetration degree has been determined are less than the preset deviation threshold, it is finally determined that the position corresponding to the gas sensor has gas penetration, that is, the overburden rock crack has formed an effective channel that allows oxygen to flow, if any condition is not met, it is determined that there is no gas penetration at the position, and only subsequent concentration changes need to be continuously monitored.

[0139] S400, based on the analysis results of the apparent penetration degree, stress penetration degree and gas penetration degree, the penetration degree grade of the overburden rock crack is determined, and the corresponding fire prevention and extinguishing measures are matched through the penetration degree grade.

[0140] The apparent penetration degree is whether the apparent penetration degree and the bifurcation system quantified crack form a structural apparent penetration network, which solves the problem that only the shape cannot confirm whether there is an actual channel.

[0141] The stress penetration degree verifies whether the crack forms a mechanical transmission channel through the spatial correlation of the ground microseismic and the downhole pressure relief area, which solves the problem of whether the structural apparent penetration network has a stable structure.

[0142] The gas penetration degree verifies whether the crack has a gas flow function through the space-time matching of the oxygen concentration change and the stress penetration area, which solves the problem of whether the stable structure becomes a safe hidden danger channel.

[0143] The present application can correlate and analyze the overburden rock crack from three aspects of apparent penetration degree, stress penetration degree and gas penetration degree, form a whole chain verification of phenomenon→essence→function, and solve the problem that the prior art cannot distinguish between invalid crack network and effective hidden danger channel. Further accurately determine whether the overburden rock crack is penetrated, increase the comprehensiveness and accuracy of the overburden rock crack analysis, and it is more convenient to perform corresponding processing according to the penetration condition.

[0144] S410, the determination method of the overburden rock crack penetration degree grade is: if the overburden rock crack simultaneously satisfies the apparent high penetration degree, the stress high connectivity, and the oxygen concentration change amount exceeds the gas concentration change threshold, it is determined as completely penetrated.

[0145] If the overburden rock fissure meets the low connectivity of the appearance and the low connectivity of the stress at the same time, and the oxygen concentration variation is not more than the gas concentration reference threshold, it is determined that it is not penetrated. The exemplary gas concentration reference threshold is 0.5%.

[0146] In addition to complete penetration and non-penetration, other cases are determined to be partially penetrated.

[0147] The completely penetrated area needs to use the preset grouting and nitrogen injection pipeline to inject slurry and nitrogen to prevent further oxidation reaction of the residual coal in the area. The grouting uses yellow mud slurry or fly ash slurry.

[0148] The partially penetrated area needs to increase the grouting amount, and can also use the way of injecting fire prevention and extinguishing materials to wrap the residual coal.

[0149] The non-penetrated area only needs to be treated with daily grouting operation.

[0150] The present application also provides a coal seam working face overburden fissure condition monitoring and analysis system, comprising: a region division module, a monitoring arrangement module, an overburden fissure data monitoring module, an overburden fissure analysis module and a measure matching module, wherein the region division module is connected with the monitoring arrangement module, the monitoring arrangement module is connected with the overburden fissure data monitoring module, the overburden fissure data monitoring module is connected with the overburden fissure analysis module and the measure matching module respectively, and the overburden fissure analysis module and the measure matching module are connected.

[0151] The region division module is used to determine the data acquisition boundary of the ground and underground according to the basic parameters of the coal seam working face, and form an acquisition region.

[0152] The monitoring arrangement module dynamically arranges the ground and underground monitoring units in the acquisition region according to the footage stage of the working face.

[0153] The overburden fissure data monitoring module obtains the monitoring data at each monitoring time point after the working face advances a preset distance, the monitoring data includes surface subsidence data and underground monitoring data, the monitoring data is cleaned, and the surface subsidence data and the underground monitoring data related to the working face overburden are determined.

[0154] The overburden fissure analysis module spatially verifies and time-aligns the surface subsidence data and the underground monitoring data, analyzes the appearance penetration, stress penetration and gas penetration of the working face overburden fissure, determines the penetration grade of the overburden fissure through the three groups of penetration, and the penetration grade is divided into complete penetration, partial penetration and non-penetration.

[0155] The measure matching module matches the corresponding fire prevention and extinguishing measures through the penetration grade.

[0156] Although the embodiments of the present application have been shown and described above, it is to be understood that the above-described embodiments are merely exemplary, and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made thereto without departing from the scope of the present application.

Claims

1. A method for monitoring and analyzing the overburden crack condition of a mid-coal seam working face, characterized in that: include: Obtain basic parameters of the coal seam working face, determine the data collection boundary between the ground and underground based on the basic parameters, and delineate the monitoring and collection area; According to the advancement stage of the working face, the mining process of the working face is divided into three stages: the initial advancement stage, the stable advancement stage, and the final advancement stage. According to the advancement stage, the surface monitoring units and the underground monitoring units are dynamically deployed in the collection area. After the working face advances to a preset distance, the monitoring data at each monitoring time point is collected. Screen out monitoring data related to the overburden at the working face; perform spatial verification and temporal alignment on the screened monitoring data to analyze the apparent penetration, stress penetration, and gas penetration of the overburden cracks at the working face; Based on the analysis results of the apparent penetration, stress penetration and gas penetration, the penetration level of the overburden fracture is determined, and corresponding fire prevention and extinguishing measures are matched according to the penetration level.

2. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 1, characterized in that: The step of obtaining basic parameters of the coal seam working face, determining the data collection boundary between the ground and the underground based on the basic parameters, and defining the monitoring and collection area specifically includes: The basic parameters of the working face include the strike length, inclined length, mining height and expected footage speed of the working face; The data acquisition boundary of the ground covers a preset length of the outer edge of the projected working surface; The data collection boundary of the underground well is a closed area formed by the upper and lower lanes of the working face, the open cutting hole and the stop-mining line.

3. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 1, characterized in that: The monitoring data is obtained by: The monitoring data includes surface settlement data and downhole monitoring data; wherein the surface settlement data includes surface microseismic events, surface microseismic coordinates, and microseismic energy collected by microseismic sensors; The acquisition and processing methods of the downhole monitoring data include: Obtain original images of cracks through a borehole peep instrument; A feature extraction method based on image edge detection and morphological analysis is used to extract the length, direction and bifurcation characteristics of the cracks. The stress and displacement data of overburden rocks are collected by stress-displacement sensors; The gas concentration data of the goaf is collected through gas sensors.

4. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 3, characterized in that: The division criteria of the working face footage stages are: The stage from the start of the cut to the first preset footage distance is defined as the initial advancement period; The stage from when the working face advances to the second preset advance distance from the stop mining line is defined as the tail-end advancement period; The advancement period between the initial advancement period and the final advancement period is defined as the stable advancement period.

5. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 3, characterized in that: The specific method of the spatial calibration is: using the fracture position obtained by drilling downhole as a reference, calibrating the vertical coordinates of the surface microseismic events; The specific method of time alignment is: using the working face footage distance as the time correlation benchmark, constructing a footage-time coordinate system, where the working face footage distance is the X-axis and time is the Y-axis, and uniformly mapping the surface microseismic data, overburden stress value data and gas concentration data to this coordinate system to achieve alignment of the time dimension.

6. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 5, characterized in that: The analysis method of the apparent penetration of the overburden fracture is as follows: The number of fracture intersections within the observation section of a single borehole was counted and recorded as the number of nodes; Count the number of interconnected fracture sections within a single borehole observation section; Calculate the standard deviation of the angles between the strikes of all fractures and the strike of the working face within a single observation section, and record it as the fracture strike consistency; The ratio of the number of interconnected fractures to the total number of fractures in a single observation section multiplied by the correction coefficient of fracture trend consistency is taken as the apparent penetration degree. Calculate the ratio of the number of bifurcations of a single crack to the crack length, which is recorded as the bifurcation coefficient; The apparent penetration level is determined based on the combination of apparent penetration and bifurcation coefficient: If the appearance penetration is not lower than the first appearance penetration threshold, and the bifurcation coefficient is not lower than the first bifurcation coefficient threshold, it is determined to be a high appearance penetration; If the appearance penetration is lower than the first appearance penetration threshold and not lower than the second appearance penetration threshold, and the bifurcation coefficient is lower than the first bifurcation coefficient threshold and not lower than the second bifurcation coefficient threshold, it is determined to be appearance medium penetration; If the appearance penetration is lower than the second appearance penetration threshold, and the bifurcation coefficient is lower than the second bifurcation coefficient threshold, it is determined to be appearance low penetration.

7. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 6, characterized in that: The analysis method of the stress penetration of the overburden fracture is as follows: The K-means clustering algorithm is used to cluster the surface microseismic information and calculate the cluster center coordinates, cluster energy sum and cluster event density of each cluster. If the cluster event density of a cluster is greater than or equal to the set event density threshold, and the cluster energy sum is greater than or equal to the first set energy sum threshold, the area corresponding to the cluster is determined to be a dense overburden fracture area, and the coordinates of the area are used as the ground microseismic coordinates; If the stress change value monitored by the stress sensor exceeds the set stress change threshold, and the stress change state duration exceeds the stress duration threshold, the area is determined to be a stress relief area, and the coordinates of the area are used as the downhole relief coordinates; If the displacement rate of the displacement sensor in the stress relief area exceeds the displacement rate increase threshold, and the sum of the cluster energies at the corresponding positions in the area is greater than or equal to the second set energy sum threshold, then it is verified that stress penetration exists in the area; The ratio of the overlapping area of ​​the vertical projections of the surface microseismic coordinates and the downhole pressure relief coordinates to the total area of ​​the fracture-intensive zone is taken as the stress connectivity, and the stress connectivity level is determined based on this ratio, where: If the stress connectivity is not lower than the first stress connectivity threshold, it is determined to be high stress connectivity; If the stress connectivity is lower than the first stress connectivity threshold and not lower than the second stress connectivity threshold, it is determined to be stress medium connectivity; If the stress connectivity is lower than the second stress connectivity threshold, it is determined to be low stress connectivity.

8. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 7, characterized in that: The analysis method of the gas permeability of the overburden fracture is as follows: The change in oxygen concentration monitored by the gas sensor in the buried pipe in the goaf is extracted. If the change in oxygen concentration exceeds the set concentration change threshold, and the space-time projection deviation between the position of the gas sensor in the footage-time coordinate system and the area where stress penetration has been determined is less than the preset deviation threshold, it is determined that gas penetration exists at that position.

9. The method for monitoring and analyzing overburden crack conditions at a mid-coal seam working face according to claim 8, characterized in that: The determination method of the overburden fracture penetration level is as follows: If the overburden fractures meet both the apparent high permeability and stress high connectivity, and the oxygen concentration change exceeds the gas concentration change threshold, they are judged to be completely permeable; If the overburden fractures meet both the apparent low connectivity and stress low connectivity criteria, and the change in oxygen concentration does not exceed the gas concentration benchmark threshold, they are judged as not connected; All other situations except complete penetration and non-penetration are judged as partial penetration.

10. A monitoring and analysis system for overburden crack conditions at a mid-coal seam working face, characterized in that: include: The regional division module is used to determine the data collection boundaries of the ground and underground according to the basic parameters of the coal seam working face to form the collection area; Monitoring deployment module, dynamically deploying surface and underground monitoring units within the acquisition area according to the working face's advancement stage; The overburden fracture data monitoring module obtains monitoring data at each monitoring time point after the working face advances a preset distance. The monitoring data includes surface settlement data and downhole monitoring data. The monitoring data is cleaned to determine the surface settlement data and downhole monitoring data associated with the overburden at the working face. The overburden fracture analysis module spatially verifies and temporally aligns surface subsidence data with downhole monitoring data to analyze the apparent penetration, stress penetration, and gas penetration of overburden fractures at the working face. The three sets of penetrations are used to determine the penetration level of overburden fractures, which are categorized as fully penetrated, partially penetrated, and not penetrated. The measures matching module matches the corresponding fire prevention and extinguishing measures according to the penetration level.

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