Method for judging collapse degree of overlying strata based on micro-seismic data

Abstract

The invention discloses an overlying strata caving degree discrimination method based on micro-seismic data. The method is specifically implemented according to the following steps: step 1, obtaining geomechanical parameters corresponding to a histogram in a range of a vertical distance of 100m above a coal seam roof of a certain working face; 2, obtaining the height of a fissure zone and the position of a rock stratum key layer through geomechanical parameters and a fissure zone empirical regression formula; step 3, judging a layer position which can be fractured to generate energy; step 4, collecting and screening out micro-seismic signals of an overlying strata caving form; 5, projection is conducted on the inclined section of the designated working face according to the micro-seismic signals, and the caving height and the caving angle range of the overlying strata in the working face stoping period are calculated. According to the method for judging the collapse degree of the overlying strata based on the micro-seismic data, the problems that in the prior art, due to the fact that exploration drilling holes are drilled from a roadway to a top plate, horizon judgment errors are caused, and the timeliness of a test result is poor are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine roof disaster monitoring methods, and specifically relates to a method for discriminating the caving degree of overlying strata based on microseismic data. Background Technique

[0002] In recent years, with the increase in the mining intensity of underground coal mines in China, the proportion of roof disaster accidents in the total number of coal mine accidents has been increasing year by year. Especially for working faces with thick and hard roofs, the energy generated by the fracture of the hard roof will be transmitted to the working face in the form of dynamic and static loads, which will further lead to disasters such as support crushing, water and sand inrush in the working face, sharp reduction of roadway section, and roof fall, posing a serious threat to the life safety of coal miners. Therefore, obtaining the caving degree of overlying strata in the coal mining face in real time is of great significance for working face roof management, mine pressure analysis, and roof disaster accident prediction.

[0003] The caving degree of overlying strata in the coal mining face is a crucial parameter for the real-time prediction of cantilever length, periodic weighting interval, and mine pressure manifestation, and then for targeted roof management. However, in the actual coal mine underground site, the method of drilling exploration holes from the roadway to the roof is still mainly adopted, such as methods like drilling leakage volume test and drilling CT test for detection. Such methods have good accuracy, but the drilling method is a single-point discrete detection, and the control range of a single hole is only a few meters around the hole, making it difficult to cover the overlying strata space above the entire working face and unable to capture the cross-regional rock fracture linkage effect, resulting in insufficient correlation analysis between local data and the overall caving law; moreover, the caving of overlying strata is a dynamic evolution process with the advancement of coal mining, while the drilling construction period is long, the single-hole construction takes 4 - 8 hours, and the data processing for drilling CT imaging takes 2 - 3 hours, and frequent coal mining stops are required for cooperation, resulting in the monitoring results lagging far behind the real-time mining progress and unable to meet the timeliness requirements of dynamic mine pressure analysis; secondly, in thick and hard rock strata, the drilling is prone to deviation, leading to layer discrimination errors and poor timeliness of test results, and unable to fully monitor the on-site roof management situation. Based on the fact that a large number of mines have installed microseismic monitoring and there is sufficient microseismic data during coal mining, a method for discriminating the caving degree of overlying strata based on microseismic data is proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for discriminating the caving degree of overlying strata based on microseismic data, which solves the problems of layer discrimination errors and poor timeliness of test results existing in the prior art when adopting the method of drilling exploration holes from the roadway to the roof.

[0005] The technical solution adopted by the present invention is a method for discriminating the caving degree of overlying strata based on microseismic data, which is specifically implemented according to the following steps: Step 1, obtain the geomechanical parameters corresponding to the histogram within a range of 100 m vertically above the coal seam roof of a certain working face; Step 2: Obtain the height of the fractured zone and the position of the key strata in the rock formation based on the geomechanical parameters obtained in Step 1 and the empirical regression formula for the fractured zone. Step 3: Determine the strata where energy can be generated by fracture according to the height of the fractured zone and the position of the key strata in the rock formation obtained in Step 2. Step 4: Collect and screen the microseismic signals of the overlying strata caving shape based on the geomechanical parameters obtained in Step 1, the height of the fractured zone obtained in Step 2, the position of the key strata in the rock formation, and the strata where energy can be generated by fracture obtained in Step 3. Step 5: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively, and calculate the caving height and the range of caving angle of the overlying strata during the coal face mining.

[0006] The technical solution of the present invention is further characterized in that The geomechanical parameters in Step 1 include rock formation type, layer thickness hi , the vertical distance H to the coal seam i , bulk density γ, and elastic modulus E.

[0007] Specifically, obtaining the height of the fractured zone in Step 2 is as follows: Obtain the height of the fractured zone through the empirical regression formula for the fractured zone: (1) In the formula: H is the height of the fractured zone, m; M is the mining thickness, m.

[0008] Specifically, obtaining the position of the key strata in the rock formation in Step 2 is as follows: (2) In the formula, represents the load formed by the m-th layer of rock formation on the first layer of rock formation; γi represents the bulk density of the i-th rock formation, (i = 1, 2,..., m); Ei represents the elastic modulus of the i-th rock formation, (i = 1, 2,..., m).

[0009] (3) When for the (m + 1)-th layer of rock formation, the bending subsidence amount of the lower rock formation is greater than that of this layer, the rock formations above the (m + 1)-th layer do not require the lower rock formations to bear the load, then: (4) The specific method for determining the position of the key strata in the rock formation is: Assume that the rock formations above the coal seam are the 1st, 2nd, 3rd... m-th... n-th layers in sequence (m < n). Start calculating from the 1st layer of rock formation, and stop calculating when formula (4) holds to obtain the position of the key strata in the rock formation.

[0010] Step 3 specifically includes: Based on the fracture zone height and key strata of the rock formation calculated in Step 2, combined with the energy formula (5) for rock formation fracture, calculate the strata positions that can generate fracture energy and the corresponding magnitudes of the generated energy, and finally obtain the key stratum - fracture energy table, which is specifically expressed as: (5) In the formula, represents the bending moment of the roof strata above the coal wall; represents the rotation angle of the roof strata during bending subsidence; represents the reduced load per unit length of the mass of the roof strata and the additional load of the overlying strata; represents the moment of inertia of the cross - section of the roof strata, , where is the thickness of the overlying strata of the roof strata; represents the overhanging length of the roof strata; After coal seam mining, the i - th strata above the coal seam generally fractures and releases energy from bottom to top in sequence. The released energies are respectively denoted as E K1 , E K2 , E K3 , …, E Ki . The distances from the seismic sources to the mined coal body are r1, r2, r3, …, ri. This energy decays exponentially in the rock mass with a decay exponent of η. When E K’ decays to the energy of the coal body, it is: (6) And convert the energy released by rock formation fracture and the energy decayed to the coal body into the corresponding released energy levels and decay energy levels.

[0011] The microseismic signals in Step 4 include date, time, XYZ coordinates, and energy.

[0012] The specific steps for screening out the microseismic signals of the overlying strata caving shape in Step 4 are as follows: A. Compare the contour map of the coal seam roof and floor with the strata position where the microseismic event occurs. The vertical position is within the range of 100 m from the coal seam roof to the vertical distance of the coal seam; B. For the microseismic data energy generated during the mining period, its strata position and the corresponding energy should correspond to those in the key stratum - fracture energy table, and the difference should not exceed 1000 J.

[0013] Step 5 specifically includes: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively. Through the projection of the microseismic events on the dip section of the specified working face, then conduct sketching, and calculate the caving height and caving angle range of the overlying strata during the mining of the working face.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The method for distinguishing the degree of overburden collapse based on microseismic data provided by the present invention can efficiently screen out effective microseismic signals reflecting the actual overburden collapse morphology by accurately identifying the height of the fracture zone and the position of the key layer of the rock strata, significantly eliminating the interference of mining noise and non-collapse events, and greatly improving the reliability and pertinence of signal discrimination. By spatially projecting and dynamically analyzing the screened microseismic signals on the working face inclination profile, the collapse height and collapse angle range of the overburden strata during mining can be calculated in real time and accurately, providing key basic data for estimating the length of the roof cantilever, predicting the periodic pressure step distance, and analyzing the law of mine pressure manifestation. This method breaks through the technical bottleneck of traditional drilling detection with large engineering volume and poor timeliness, realizes dynamic and continuous monitoring of characteristic parameters of overburden collapse, and can provide accurate guidance for the optimization of working face support parameters, advance warning of roof disasters, and safe and efficient mining. It has significant engineering application value in mine pressure management and disaster prevention and control of thick and hard roof working faces. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the method for determining the extent of overburden collapse based on microseismic data of the present invention; Figure 2 Schematic diagram of the collapse morphology of the overlying rock strata in Example 6 of the present invention. DETAILED DESCRIPTION

[0016] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 The present invention provides a method for determining the extent of overburden collapse based on microseismic data, such as Figure 1 As shown, the specific implementation steps are as follows: Step 1, as shown in Table 1, obtain the geomechanical parameters corresponding to the bar graph within a vertical distance of 100m above the coal seam roof of a certain working face; Table 1 Schematic diagram of drilling geomechanical parameters

[0018] In Table 1, hi is the thickness of the rock layer with the specified serial number, and Hi is the vertical distance from the coal seam roof to the coal seam (i=1, 2,…, m, n, (m<n)).

[0019] Step 2, obtaining the height of the fracture zone and the position of the key layer of the rock formation through the geomechanical parameters obtained in step 1 and the fracture zone empirical regression formula; Step 3, determining the layer that can be fractured to generate energy according to the height of the fracture zone and the position of the key layer of the rock formation obtained in step 2; Step 4: Collect and screen the microseismic signals of the overlying strata caving shape according to the geomechanical parameters obtained in Step 1, the fracture zone height, the position of the key strata in the strata, and the strata where energy can be generated by fracturing obtained in Step 3; Step 5: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively, and calculate the caving height and caving angle range of the overlying strata during the coal mining of the working face.

[0020] Example 2 On the basis of Example 1, Step 2 is specifically as follows: (1) Judge and identify the calculation of the "fracture zone" height Based on the measured data of a specific working face, considering the working face coal thickness factor, substitute the following general empirical formula for the fracture zone: (1) In the formula: H is the fracture zone height, m; M is the coal thickness, m.

[0021] Note: The accuracy of the calculation results of this formula is slightly affected by the particularity of different mining areas and mines. Numerical simulation, overlying strata theoretical analysis, microseismic and other monitoring data analysis can be used, combined with a large number of on-site measured data of the mining area or coal mine for regression calculation, so as to obtain more accurate results.

[0022] (2) Calculate and identify the key strata in the strata according to the above geomechanical parameters According to the lithology and classification of the overlying strata of the working face, substitute the coal and rock mechanical parameters into the key strata discrimination formula (2) for calculation, and thus judge the position of the key strata.

[0023] Judgment of key strata: (2) In the formula: represents the load formed by the m-th layer of strata on the first layer of strata; γi represents the unit weight of the i-th layer of strata, (i = 1, 2,..., m); Ei represents the elastic modulus of the i-th layer of strata, (i = 1, 2,..., m).

[0024] (3) When for the m + 1-th layer of strata, the bending subsidence amount of the lower strata is greater than the bending subsidence amount of this layer, the strata above the m + 1-th layer of strata do not require the lower strata to bear the load, then there must be: (4) The specific method for judging the key strata is: assume that the strata above the coal seam are successively the 1st, 2nd, 3rd... mth... nth layers (m < n), start calculating from the 1st layer of strata, and stop calculating when formula (4) holds. Example 3 Based on Example 2, Step 3 is specifically as follows: According to the determined height of the fissure zone and the position of the key strata, comprehensively determine the layer range and energy range where the layer that can generate energy by fracture fractures. The specific discrimination method is as follows: Based on the key strata of the rock formation and the height of the fissure zone calculated in Step 2, calculate the corresponding possible fracture layers and the magnitudes of the energies generated by them through the rock formation fracture energy formula (5), as shown in Table 2. Finally, obtain the key strata - fracture energy summary table.

[0025] (5) In the formula, represents the bending moment of the roof rock formation above the coal wall; represents the rotation angle of the roof rock formation bending and subsiding; represents the unit - length converted load of the mass of the roof rock formation and the additional load of the overlying rock formation; represents the moment of inertia of the cross - section of the roof rock formation, , where is the thickness of the overlying rock of the roof rock formation; represents the overhanging length of the roof rock formation.

[0026] After coal seam mining, the i - layer rock formation above the coal seam generally fractures and releases energy from bottom to top in sequence. The released energies are respectively denoted as EK1, EK2, EK3, …, EKi, and the distances from the seismic source to the mined coal body are r1, r2, r3, …, ri. This energy decays in an exponential form in the rock mass, and the decay exponent (damping) is η. The energy EK’ decays to the coal body energy as: (6) And convert the energy released by rock formation fracture and the energy decayed to the coal body into the corresponding release energy levels and decay energy levels for subsequent comparative analysis.

[0027] Table 2 Key strata - fracture energy summary table

[0028] Example 4 Based on Example 3, Step 4 is specifically as follows: Collect the micro - seismic data during the coal mining of a certain working face. The micro - seismic data includes date, time, XYZ coordinates, and energy, and the data volume should reach a certain value, as shown in Table 3: Table 3 Micro - seismic event energy summary table

[0029] (2)Screen the micro - seismic data during the coal mining of a certain working face, and screen out the effective data for discriminating the caving degree of the overlying rock. The screening criteria are as follows: A. Compare with the microseismic event generation horizon according to the contour map of the coal seam roof and floor. The vertical position is within the range of 100 m from the coal seam roof to the vertical distance of the coal seam. During the coal mining period, for the energy of the microseismic data generated, the horizon and the corresponding energy should correspond to the energy values of each horizon in Table 2 (Summary Table of Key Strata - Fracture Energy) (attenuated to the energy of the coal body / E K’ ), and the difference should not exceed 1000 J.

[0030] Example 5 Based on Example 4, Step 5 is specifically as follows: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively. Through the projection of the microseismic events on the dip section of the specified working face, then conduct sketching, and calculate the caving height and caving angle range of the overlying strata during the coal mining of the working face.

[0031] Example 6 This example provides a method for discriminating the caving degree of overlying strata based on microseismic data. It is calculated using the formula provided in the above example. The specific steps are as follows: A1. Extract the geomechanical parameters such as the layer thickness, vertical distance from the roof to the coal seam, unit weight, and elastic modulus in the columnar section about 100 m above the coal seam roof in the core hole or columnar section near the fracturing engineering implementation area, and compile the serial numbers according to the following table to form Table 4 Geological Mechanical Parameter Table of Boreholes.

[0032] Table 4 Geological Mechanical Parameter Table of Boreholes

[0033] A2. Substitute the coal mining thickness of 5 m of the working face into the empirical regression formula (1) of the fractured zone to calculate, and the height of the fractured zone is obtained as 43 ± 5.6 m; A3. Substitute the parameters in Table 4 into Formula (1) and Formula (2) for calculation. When the load formed by the m-th layer of rock strata on the first layer of rock strata is greater than the load formed by the (m + 1)-th layer of rock strata on the first layer of rock strata, it indicates that the rock strata above the (m + 1)-th layer of rock strata do not require the lower rock strata to bear the load, that is, the (m + 1)-th layer of rock strata is the first key stratum. By analogy, the key strata within 100 m above the coal seam roof can be calculated. In particular, if both the n-th layer and the (n + 1)-th layer are key strata, then the n-th layer and the (n + 1)-th layer are combined key strata. The calculation results are shown in the remarks of Table 4.

[0034] A4. Substitute the relevant parameters of the coal seam and roof of a certain working face into Formula (5) and Formula (6) for calculation. Among them, the first layer of rock strata above the coal seam roof is relatively thin and belongs to the immediate roof, which caves in with the mining, so the influence of this value on the mine pressure is ignored. Calculate the energy generated by the fracture of the roof rock strata and the energy attenuated to the coal body, and then convert it into energy level. The calculation results are shown in the last two columns of Table 4.

[0035] A5. Compare and screen with the microseismic data collected during the coal face mining, and obtain the effective data for judging the caving degree of overlying strata through the discrimination criteria described above.

[0036] A6. Plot the effective data in A5 on a graph using an equal-proportion coordinate system in Surfer software or other mapping software, obtain the projections of microseismic events on the strike profile and dip profile of the specified working face, then conduct sketching, calculate the caving height and caving angle range of the overlying strata during the coal face mining. In this embodiment, the caving angles of the lower strata in the dip profile are 41° and 51°, and the caving angles of the middle and upper strata are 32° and 38°; the caving height is 20 - 40 m. The caving shapes of the lower strata and the middle and upper strata are as Figure 2 shown by the dotted lines, and judge the caving degree through the caving height and caving angle range of the overlying strata.

Claims

1. A method for judging the caving degree of overlying strata based on microseismic data, characterized in that The implementation is specifically carried out according to the following steps: Step 1: Obtain the geomechanical parameters corresponding to the columnar section within a range of 100 m vertically above the coal seam roof of a certain working face; Step 2: Obtain the fracture zone height and the position of the key strata in the rock formation through the geomechanical parameters obtained in Step 1 and the empirical regression formula for the fracture zone; Step 3: Determine the strata that can generate energy through fracture according to the fracture zone height and the position of the key strata in the rock formation obtained in Step 2; Step 4: Collect and screen the microseismic signals of the overlying strata caving shape according to the geomechanical parameters obtained in Step 1, the fracture zone height obtained in Step 2, the position of the key strata in the rock formation, and the strata that can generate energy through fracture obtained in Step 3; Step 5: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively, and calculate the caving height and the range of caving angle of the overlying strata during the coal mining of the working face.

2. The method for determining the caving degree of overlying strata based on microseismic data according to claim 1, characterized in that, The geomechanical parameters described in Step 1 include rock stratum type, layer thickness hi , vertical distance H to the coal seam i , bulk density γ, elastic modulus E.

3. The method for discriminating the caving degree of overlying strata based on microseismic data according to claim 2, characterized in that, Specifically, the obtaining of the fracture zone height in Step 2 is as follows: Obtain the fracture zone height through the empirical regression formula for the fracture zone: （1） In the formula: H is the height of the fissure zone, m; M is the mining thickness, m.

4. The method for discriminating the caving degree of overlying strata based on microseismic data according to claim 2, wherein Specifically, the obtaining of the position of the key strata in the rock formation in Step 2 is as follows: （2） In the formula, represents the load formed by the m-th layer of rock stratum on the 1st layer of rock stratum; γi represents the unit weight of the i-th rock stratum, i = 1, 2, …, m; Ei represents the elastic modulus of the i-th rock stratum, i = 1, 2, …, m; （3） When for the (m + 1)-th rock stratum, the bending subsidence amount of the lower rock strata is greater than that of this layer, the rock strata above the (m + 1)-th layer do not require the lower rock strata to bear the load, then: （4） The specific method for determining the position of the key strata in the rock formation is: Assume that the rock strata above the coal seam are the 1st, 2nd, 3rd … mth … nth layers in sequence, m < n. Start calculating from the 1st rock stratum and stop calculating when formula (4) holds to obtain the position of the key strata in the rock formation.

5. The method for discriminating the caving degree of overlying strata based on microseismic data according to claim 1, characterized in that, Specifically, Step 3 is as follows: According to the fracture zone height and the key strata calculated in Step 2, combine with the formula (5) for the energy generated by rock stratum fracture to calculate the strata that can generate energy through fracture and the corresponding energy generated, and finally obtain the key stratum - fracture energy table, which is specifically expressed as: （5） In the formula, represents the bending moment of the roof rock stratum above the coal wall; represents the rotation angle of the roof rock stratum due to bending and subsidence; represents the converted load per unit length of the mass of the roof rock stratum and the additional load of the overlying rock stratum; represents the moment of inertia of the cross-section of the roof rock stratum, , where is the thickness of the overlying rock of the roof rock stratum; represents the overhanging length of the roof rock stratum; After coal seam mining, the i-th rock stratum above the coal seam generally fractures and releases energy from bottom to top in sequence. The released energies are respectively denoted as E K1 , E K2 , E K3 , …, E Ki . The distances from the seismic sources to the mined coal body are r1, r2, r3, …, ri. This energy decays exponentially in the rock mass, and the decay exponent is η. When E K’ decays to the coal body energy, it is: （6） And convert the energy released by rock stratum fracture and the energy attenuated to the coal body into the corresponding release energy level and attenuation energy level.

6. The method for discriminating the caving degree of overlying strata based on microseismic data according to claim 1, wherein The microseismic signals in Step 4 include date, time, XYZ coordinates, and energy.

7. The method for judging the caving degree of overlying strata based on microseismic data according to claim 1, characterized in that, Specifically, the steps for screening the microseismic signals of the overlying strata caving shape in Step 4 are as follows: A. Compare according to the contour map of the coal seam roof and floor and the strata where the microseismic events occur, and the vertical position is within the range of 100 m vertically from the coal seam roof to the coal seam; B. For the energy magnitude of the microseismic data generated during coal mining, the strata and the corresponding energy should correspond to those in the key stratum - fracture energy table, and the difference should not exceed 1000 J.

8. The method for discriminating the caving degree of overlying strata based on microseismic data according to claim 1, characterized in that Specifically, Step 5 is as follows: Project the microseismic signals screened in Step 4 onto the dip section of the specified working face respectively. Through the projection of the microseismic events on the dip section of the specified working face, and then make a sketch to calculate the caving height and the range of caving angle of the overlying strata during the coal mining of the working face.

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