Mining overlying strata high-permeability area judgment method

Abstract

The invention discloses a mining overlying strata high-permeability area judgment method, and relates to the technical field of coal mine gas extraction, and the method specifically comprises the following steps: S1, gas migration area judgment: obtaining fracture characteristic parameters through a physical similar simulation experiment, comprehensively determining the area range of the gas migration area in a fracture field from the transverse direction and the longitudinal direction, and determining the area range of the gas migration area; wherein the transverse direction is parallel to the coal seam propelling direction, and the longitudinal direction is vertical to the coal seam propelling direction; s2, judging a high-permeability area: acquiring the gas emission amount of coal mining, calculating a model gas quality source item, and carrying out a numerical simulation experiment to determine the high-permeability area; according to the method, accurate recognition of the pressure relief gas high-permeability area is achieved, the extraction efficiency of pressure relief gas is improved, gas prevention and control are achieved, resource utilization is further optimized by determining the mining overlying strata high-permeability area, waste of extraction resources is avoided, extraction energy consumption is reduced, extraction efficiency is guaranteed, and coal mining safety is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine gas drainage, and specifically relates to a method for determining highly permeable areas in overlying strata affected by mining Background Art

[0002] Coal seam gas is not only a disastrous gas but also a unique resource in coal mines. Realizing gas drainage during the coal seam mining process can not only prevent gas disasters, reduce environmental pollution, but also increase energy utilization efficiency, achieving multiple effects such as safe mine production, environmental protection, and new energy supply

[0003] The existing invention patent with the publication number CN118273763A discloses a method for coordinated and efficient gas drainage in different regions of a fully mechanized caving face in thick coal seams. It constructs a spatial layout of "low + high" multi-layered pressure-relief gas drainage, fully considering the conditions for pressure-relief gas drainage. By reasonably dividing different regions in the drainage area, a method for gas drainage in different regions suitable for fully mechanized caving mining in thick coal seams is formed, effectively improving the gas drainage flow rate, drainage concentration, and on-site gas drainage effect, achieving the standard of the comprehensive evaluation result of the gas drainage system in thick coal seams and ensuring safe and efficient coal mining

[0004] However, this invention patent still has the following problems: Its gas drainage method in different regions is only applicable to thick coal seams and is not suitable for coal seams with other occurrence conditions, such as thin coal seams, inclined thick coal seams, etc. Secondly, the gas drainage area is not accurately divided. Only the drainage area is divided into multiple sub-regions, but the accurate identification of the gas drainage area is not achieved, resulting in resource waste and low drainage efficiency Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining highly permeable areas in overlying strata affected by mining, which solves the problems raised in the above background art

[0006] To solve the above technical problems, the present invention specifically provides the following technical solutions

[0007] A method for determining highly permeable areas in overlying strata affected by mining specifically includes the following steps

[0008] S1, Determination of the gas migration area: Obtain the fracture characteristic parameters through physical similarity simulation experiments, and comprehensively determine the range of the gas migration area in the fracture field from the horizontal and vertical directions. The horizontal direction is parallel to the direction of coal seam advancement, and the vertical direction is perpendicular to the direction of coal seam advancement

[0009] S2, Determination of the highly permeable area: Obtain the gas emission volume during coal mine mining, calculate the gas mass source term of the model, and conduct numerical simulation experiments to determine the highly permeable area

[0010] S3, In-situ inversion of the highly permeable area: Conduct microseismic monitoring and borehole peephole tests on-site, and invert the highly permeable area of the overlying strata affected by mining based on microseismic events and fracture conditions

[0011] As a preferred embodiment of the present invention, in the step S1, the specific method for determining the gas migration area includes:

[0012] S101, collect on-site materials, analyze the coal seam occurrence conditions, hydrogeological conditions, and overlying rock types based on the on-site materials, and conduct two-dimensional physical similarity simulation experiments based on the on-site materials to obtain overlying rock fracture characteristic parameters, where the overlying rock fracture characteristic parameters include separation amount, fracture density, penetration degree, and surface fracture rate;

[0013] S102, construct a discrimination criterion for the gas migration area based on the overlying rock fracture characteristic parameters;

[0014] S103, divide the specific range of the gas migration area according to the gas migration area determination criterion for the physical similarity simulation experiment results.

[0015] As a preferred embodiment of the present invention, in the step S101, the two-dimensional physical similarity simulation experiment is carried out using a physical similarity model. The physical similarity model uses dry river sand as the aggregate for simulating the rock formation, and gypsum and putty powder as the binder. After mixing the aggregate and the binder evenly, the model is built. The specific ingredient formula is as follows:

[0016] G = (lmhγ m ×10 3 ) / g

[0017] where G is the total mass of the materials required for the rock formation of each lithology; l is the length of the physical similarity model, in m; m is the thickness of the physical similarity model, in m; h is the height of the bedding division in the physical similarity model, in m; and g is the acceleration due to gravity.

[0018] As a preferred embodiment of the present invention, in the step S102, the discrimination criterion for the gas migration area is specifically as follows:

[0019] Horizontal boundary: Divide the horizontal boundary of the gas migration area in the fracture field according to the surface fracture rate (10 < B < 20, where B is the surface fracture rate) and the separation amount (>1.5);

[0020] Vertical boundary: Divide the vertical boundary of the gas migration area in the fracture field according to the fracture density (>6.5 fractures / m) and the penetration degree (>0.2);

[0021] Area range: Finally, determine the area range of the gas migration area in the fracture field according to the horizontal boundary and the vertical boundary.

[0022] As a preferred embodiment of the present invention, in the step S2, the specific steps for determining the high-permeability area are as follows:

[0023] S201. Identify and depict the fissures in the results of the physical similarity simulation experiment, and then import them into the numerical simulation software for numerical modeling to obtain the model gas mass source term;

[0024] S202. Input the gas emission amount and the model gas mass source term into the model to conduct a numerical simulation experiment, obtain the migration law of the pressure-relieved gas in the gas migration area, and obtain the distribution of the gas pressure;

[0025] S203. Based on the distribution of the gas pressure, divide the gas migration area into a diffusion area and a high-permeability area.

[0026] As a preferred solution of the present invention, in the S202, the gas emission amount is calculated based on the on-site gas emission amount detection data, and the model gas mass source term is further calculated. The gas emission amount detection includes the gas emission amount of the residual coal in the goaf, the gas emission from the adjacent coal seams, and the gas emission amount of the working face. The model gas mass source term is the source term for releasing gas in the numerical simulation, and the gas emission amount and the model gas mass source term are calculated according to the formula.

[0027] As a preferred solution of the present invention, the calculation formulas for the gas emission amount in the goaf and the model gas mass source term are as follows:

[0028] Gas emission amount in the goaf: Q1 = Q d +Q2+Q3

[0029] Gas mass source term:

[0030] Among them, Q1 is the gas emission amount in the goaf, Q d is the gas emission amount of the bottom coal body, with the unit of m 3 / min; Q2 is the relative gas emission amount of the adjacent layer, with the unit of m 3 / t; Q3 is the gas extraction amount in the goaf, with the unit of m 3 / min;

[0031] Q s is the model gas mass source term, with the unit of kg / (m 3 / s); Q g is the gas emission amount, with the unit of m 3 / s, obtained through on-site testing; ρ g is the gas density, ρ g = 0.7167 kg / m 3 ; V is the total volume occupied by the gas mass source term, with the unit of m 3 .

[0032] As a preferred solution of the present invention, in the S3, the specific steps for in-situ inversion of the high-permeability area are as follows:

[0033] S301. Circumscribe the high-permeability area through on-site microseismic tests, and determine the high-permeability area based on the density of microseismic events in the microseismic tests.

[0034] S302. Further determine the gas enrichment area in the coal seam through borehole peephole, and at the same time observe the fracture conditions and fragmentation degrees of the rock strata in the borehole, and analyze to obtain the three-dimensional distribution law of the high-permeability area.

[0035] S303. Understand the development of the high-permeability area through the microseismic data obtained from the microseismic tests and borehole peephole, guide the layout of gas drainage boreholes, and obtain the judgment criteria for the high-permeability area of the overlying strata affected by mining according to the above test results.

[0036] The present invention has the following beneficial effects compared with the prior art:

[0037] Through the accurate identification of the high-permeability area of the depressurized gas, the present invention can not only carry out gas drainage for coal seams with different occurrence conditions, but also improve the drainage efficiency of the depressurized gas, realize gas prevention and control. By determining the high-permeability area of the overlying strata affected by mining, the resource utilization is further optimized, the waste of drainage resources is avoided, the drainage energy consumption is reduced, the drainage efficiency is guaranteed, the safety of coal mine mining is improved, and the occurrence probability of accidents such as gas outbursts is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, other implementation drawings can be obtained by extending according to the provided drawings without creative efforts.

[0039] Figure 1 It is a schematic flow chart of a method for determining the high-permeability area of the overlying strata affected by mining provided by an embodiment of the present invention;

[0040] Figure 2 It is a schematic flow chart of the judgment criteria for the gas migration area provided by an embodiment of the present invention;

[0041] Figure 3 It is a schematic diagram of the gas migration area provided by an embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of the distribution of the high-permeability area provided by an embodiment of the present invention;

[0043] Figure 5 It is a schematic diagram of the microseismic event provided by an embodiment of the present invention;

[0044] Figure 6 It is a schematic diagram of the borehole layout area provided by an embodiment of the present invention;

[0045] Figure 7 Schematic diagram of the flow of the first method for determining the highly permeable area of overlying strata affected by mining according to an embodiment of the present invention;

[0046] Figure 8 Effect diagram of single-hole gas drainage provided by an embodiment of the present invention;

[0047] Figure 9 Effect diagram of gas control provided by an embodiment of the present invention;

[0048] Figure 10 Borehole perspective view provided by an embodiment of the present invention. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] As Figures 1 to 7 shown, the present invention provides a method for determining the highly permeable area of overlying strata affected by mining, specifically including the following steps

[0051] S1. Determination of the gas migration area: Obtain the fracture characteristic parameters through physical similarity simulation experiments, and comprehensively determine the range of the gas migration area in the fracture field from the horizontal and vertical directions, where the horizontal direction is parallel to the coal seam advancement direction, and the vertical direction is perpendicular to the coal seam advancement direction;

[0052] S2. Determination of the highly permeable area: Obtain the gas emission amount during coal mining, calculate the gas mass source term of the model, and conduct numerical simulation experiments to determine the highly permeable area;

[0053] S3. In-situ inversion of the highly permeable area: Conduct microseismic monitoring and borehole peep test on site, and invert the highly permeable area of overlying strata affected by mining according to microseismic events and fracture conditions.

[0054] In the step S1, the specific method for determining the gas migration area includes:

[0055] S101. Collect on-site materials, analyze the coal seam occurrence conditions, hydrogeological conditions, and overlying strata types based on the on-site materials, and conduct two-dimensional physical similarity simulation experiments based on the on-site materials to obtain the overlying strata fracture characteristic parameters, where the overlying strata fracture characteristic parameters include separation amount, broken fracture density, penetration degree, and surface fracture rate;

[0056] S102. Construct a discrimination criterion for the gas migration area based on the overlying strata fracture characteristic parameters;

[0057] S103. Determine the specific range of the gas migration area based on the gas migration area determination criterion for the results of the physical similarity simulation experiment.

[0058] In the step S101, a two-dimensional physical similarity simulation test is carried out using a physical similarity model. The physical similarity model uses dry river sand as the aggregate for the simulated rock stratum, and gypsum and putty powder as the cementing agents. After mixing the aggregate and the cementing agents evenly, the model is built. The specific ingredient formula is as follows:

[0059] G = (lmhγ m × 10 3 ) / g

[0060] Wherein, G is the total mass of the materials required for the rock stratum of each lithology; l is the length of the physical similarity model, in m; m is the thickness of the physical similarity model, in m; h is the height of the bedding division in the physical similarity model, in m; g is the acceleration due to gravity.

[0061] In the step S102, the gas migration area discrimination criterion is specifically as follows:

[0062] Lateral boundary: Divide the lateral area boundary of the gas migration area in the fracture field according to the surface fracture rate (10 < B < 20, B is the surface fracture rate) and the separation amount (> 1.5);

[0063] Longitudinal boundary: Divide the longitudinal boundary of the gas migration area in the fracture field according to the fracture density of broken fractures (> 6.5 fractures / m) and the penetration degree (> 0.2);

[0064] Area range: Finally, determine the area range of the gas migration area in the fracture field according to the lateral boundary and the longitudinal boundary.

[0065] After constructing the physical similarity model, the whole model needs to be air-dried for a period of time before mining. To simulate the mining effect on site, the model mining is carried out by advancing alternately at 2 cm and 3 cm. The overlying rock state after each mining is recorded by a high-definition camera to facilitate subsequent data processing; subsequently, rely on a fracture recognition software (such as PCAS software) to analyze the fracture characteristic parameters of the overlying rock.

[0066] As Figure 2 shown, in the gas migration area discrimination criterion, the overlying rock stratum is divided into a gas migration area and a compacted area according to the characteristic parameters of the overlying rock in the goaf (that is Figure 2In the overlying rock compaction zone), in the discrimination of the gas migration zone, it is divided into horizontal boundary determination and vertical boundary determination. Finally, the gas migration zone area is comprehensively determined based on the horizontal and vertical boundaries. First, it is determined according to the surface fissure rate and the amount of separation. When the values of both meet the range requirements, the horizontal boundary of the gas migration zone is determined. When one or both of the surface fissure rate and the amount of separation do not meet the range requirements, it is determined as the overlying rock compaction zone or the original rock. Subsequently, it is determined according to the range requirements of the fracture fissure density and the penetration degree. When the values of both meet the range requirements, the vertical boundary of the gas migration zone is determined. When one or both of the fracture fissure density and the penetration degree do not meet the range requirements, it is determined as the overlying rock compaction zone or the original rock.

[0067] Among them, Figure 2 B in it represents the surface fissure rate, and D i represents the penetration degree.

[0068] In this embodiment, the specific method of the physical similarity simulation experiment refers to a physical similarity simulation experiment device and experimental research method disclosed in the invention patent with the patent announcement number CN115267060B.

[0069] In the S2, the specific steps for determining the high-permeability zone area are as follows:

[0070] S201, Identify and depict the fissures in the results of the physical similarity simulation experiment, and then import them into the numerical simulation software for numerical modeling to obtain the model gas mass source term;

[0071] S202, Input the gas emission volume and the model gas mass source term into the model to conduct a numerical simulation experiment, obtain the migration law of the depressurized gas in the gas migration zone, and obtain the distribution of the gas pressure;

[0072] S203, Based on the distribution of the gas pressure, divide the gas migration zone into a diffusion zone and a high-permeability zone.

[0073] In the S202, the gas emission volume is calculated based on the on-site gas emission volume detection data, and the model gas mass source term is further calculated. The gas emission volume detection includes the gas emission volume from the residual coal in the goaf, the gas emission from adjacent coal seams, and the gas emission volume at the working face. The model gas mass source term is the source term for releasing gas in the numerical simulation, and the gas emission volume and the model gas mass source term are calculated according to the formula.

[0074] The calculation formulas for the gas emission volume from the goaf and the model gas mass source term are as follows:

[0075] Gas emission volume from the goaf: Q1 = Q d +Q2+Q3

[0076] Gas mass source term:

[0077] Among them, Q1 is the gas emission quantity, and Q d is the gas emission quantity of the bottom coal body, with the unit of m 3 / min; Q2 is the relative gas emission quantity of adjacent seams, with the unit of m 3 / t; Q3 is the gas extraction quantity from the goaf, with the unit of m 3 / min;

[0078] Q S is the gas mass source term of the model, with the unit of kg / (m 3 / s); Q g is the gas emission quantity, with the unit of m 3 / s, obtained through on-site testing; ρ g is the gas density, and ρ g = 0.7167 kg / m 3 ; V is the total volume occupied by the gas mass source term, with the unit of m 3 .

[0079] During the numerical simulation process, parameters such as the upper stress condition, surrounding rock stress, and model influence range need to be fully considered to finally obtain the distribution of gas pressure. In this embodiment, the numerical simulation software is prior art. For example, COMSOL Multiphysics can be used, etc.

[0080] Based on the results of the numerical simulation test, the distribution characteristics of gas pressure in the overlying strata are obtained. The overlying strata are divided according to the gas pressure distribution. The area where the gas pressure is less than 1×10 5 Pa is the compaction zone, and the area where the gas pressure is greater than 1×10 5 Pa and less than 3.5×10 5 Pa is the high-permeability zone. The area where the gas pressure is greater than 3.5×10 5 Pa is the diffusion zone. The diffusion zone is mainly located in the caving zone, and the high-permeability zone is mainly located in the fissure zone. The caving zone and the fissure zone are area divisions made by scholars according to the characteristics of rock strata caving during coal mining; the caving zone is the area where the rock strata above the goaf lose support and then break and collapse; the fissure zone is located above the caving zone, where a large number of fissures are generated in the rock strata but they do not completely collapse, and it is also called the fracture zone. In the diffusion zone, the fissure aperture is large, the fissure distribution is disorderly, and the gas mainly migrates horizontally in a diffusion manner. In the high-permeability zone, the fissure distribution is mainly fracture fissures, and the gas mainly floats upward and moves longitudinally with seepage as the main action. The gas flow in the high-permeability zone is fast, the concentration is high, and the rock strata are more stable than the diffusion zone located in the caving zone. Therefore, the high-permeability zone is set as the gas extraction area.

[0081] In the step S3, the specific steps for on-site inversion of the high-permeability zone are as follows:

[0082] S301. Encircle the high-permeability area through on-site microseismic tests. The microseismic tests determine the high-permeability area based on the density of microseismic events.

[0083] S302. Further determine the gas enrichment area in the coal seam through borehole peeping. At the same time, observe the fracture conditions and fragmentation degrees of the rock strata in the borehole, and analyze to obtain the three-dimensional distribution law of the high-permeability area.

[0084] S303. Understand the development of the high-permeability area through the microseismic data obtained from the microseismic tests and borehole peeping, guide the layout of gas drainage boreholes, and obtain the determination criteria for the high-permeability area of overlying strata affected by mining according to the above test results.

[0085] Since the fractures inside the high-permeability area are highly developed and microseismic events are likely to occur, the density of microseismic events in the high-permeability area is much higher than that in the compacted area, as Figure 5 shown; therefore, further determine the gas enrichment area in the coal seam through borehole peeping.

[0086] The development of the high-permeability area refers to that during the coal seam mining process, due to the mining of the coal seam, the rock strata above the coal seam continuously collapse. During the process of advancing mining forward, the spatial position of the high-permeability area will also change, and the development width and height of the high-permeability area will also change. After obtaining the microseismic data and borehole peeping results, and understanding the development of the high-permeability area, adjust parameters such as the spacing, height, and angle of the boreholes, and thus can guide the position of the gas drainage boreholes, as Figure 6 shown.

[0087] In step S302, the fragmentation degree determines the stability of the borehole, and the fracture condition determines the gas flowability.

[0088] According to the above method of the present application, the high-permeability area of depressurized gas can be accurately identified, which can be applied to coal seams with different occurrence conditions, broadens the applicable range, improves the extraction efficiency of depressurized gas, realizes gas prevention and control, can further optimize resource utilization, avoids waste of extraction resources, reduces extraction energy consumption, and ensures the extraction efficiency.

[0089] In this embodiment:

[0090] 1. For the determination method of the gas migration area described in the present invention, it can be replaced according to other laboratory methods, and the fracture characteristic parameters in the mentioned area criteria can be replaced by other fracture characteristic parameters.

[0091] 2. For the determination method of the high-permeability area described in the present invention, it can be replaced according to other numerical simulation means, and the mentioned area division criteria can be replaced by other characteristic parameters.

[0092] 3. The gas extraction method based on the high-permeability area in the present invention can be replaced according to the actual specific mining conditions of the coal mine.

[0093] Test Example

[0094] As Figures 8 to 10 shown, the test mine takes the (9-15)08 working face of Liuhuanggou Coal Mine in Changji, Xinjiang as the engineering background. In the (9-15)08 working face, high-level boreholes are constructed in the high-level drill field to control the goaf gas. At the same time, due to the large thickness of the main mined coal seam, the position of the overlying rock gas high-permeability area formed is relatively high. After determination, the directional drilling technology is used to construct directional long-distance high-level boreholes in the direction of the cutting eye. Because the gas high-permeability area will change continuously, the boreholes are arranged within 20-45 m from the coal seam floor in the working face. The specific layout parameters are shown in the following table:

[0095] Table 1 Borehole Layout Parameters

[0096]

[0097] The boreholes were arranged according to the distribution of the high-permeability area. The gas extraction effect of one of the boreholes is as Figure 8 shown, and the overall gas extraction effect is as Figure 9 shown. According to Figure 8 shown, the drainage gas extraction concentration gradually decreases as the working face advance distance deepens, while the pure extraction volume first rises and then falls within a certain range as the working face advance distance deepens. This shows that the high-permeability area has changed with the coal seam mining. In Figure 9 , for the layout of the extraction boreholes, as the cumulative advance distance of the working face increases, the absolute gas emission first rises and then falls, and finally remains stable. The air-exhausted gas volume decreases and remains stable, and the total gas drainage volume first rises and then slightly falls and remains stable, indicating that the boreholes have a high gas extraction concentration and maintain a stable continuous extraction state. In summary, the present application can accurately identify the high-permeability area of the drained gas, improve the extraction efficiency of the drained gas, achieve gas prevention and control, reduce the extraction energy consumption, and ensure the extraction efficiency.

[0098] The above embodiments are only exemplary embodiments of the present application and are not used to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the essence and protection scope of the present application, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present application.

Claims

1. A method for determining the high-permeability area of overlying strata affected by mining, characterized in that Specifically, it includes the following steps: S1. Determination of the gas migration area: Obtain the fracture characteristic parameters through physical similarity simulation experiments, and comprehensively determine the range of the gas migration area in the fracture field from the horizontal and vertical directions. The horizontal direction is parallel to the direction of coal seam advancement, and the vertical direction is perpendicular to the direction of coal seam advancement. S2. Determination of the high-permeability area: Obtain the gas emission amount during coal mining, calculate the gas mass source term of the model, conduct numerical simulation experiments, and determine the high-permeability area. S3. In-situ inversion of the high-permeability area: Conduct microseismic monitoring and borehole peephole tests on-site, and invert the high-permeability area of the overlying strata affected by mining according to microseismic events and fracture conditions.

2. The method for determining the highly permeable area of overlying strata affected by mining according to claim 1, wherein In the above S1, the specific method for determining the gas migration area includes: S101. Collect on-site materials, analyze the coal seam occurrence conditions, hydrogeological conditions, and overlying rock types based on the on-site materials, and conduct two-dimensional physical similarity simulation tests based on the on-site materials to obtain the overlying rock fracture characteristic parameters. The overlying rock fracture characteristic parameters include separation amount, fracture density of broken fractures, penetration degree, and surface fracture rate. S102. Construct a discrimination criterion for the gas migration area based on the overlying rock fracture characteristic parameters. S103. Divide the specific range of the gas migration area according to the gas migration area determination criterion for the results of the physical similarity simulation experiment.

3. A method for determining a highly permeable area in overlying strata affected by mining according to claim 2, characterized in that In the above S101, a two-dimensional physical similarity simulation test is carried out using a physical similarity model. The physical similarity model uses dry river sand as the aggregate for simulating the rock layer, and gypsum and putty powder as the binder. After mixing the aggregate and the binder evenly, the model is built. The specific ingredient formula is as follows: G = (lmhγ m × 10 3 ) / g; Where, G is the total mass of materials required for the rock layer of each lithology; l is the length of the physical similarity model, in m; m is the thickness of the physical similarity model, in m; h is the height of bedding division in the physical similarity model, in m; g is the acceleration of gravity.

4. The method for determining a highly permeable area in overlying strata affected by mining according to claim 2, wherein In the above step S102, the discrimination criterion for the gas migration area is specifically: Horizontal boundary: Divide the horizontal boundary of the gas migration area in the fracture field according to the surface fracture rate (10 < B < 20, B is the surface fracture rate) and the separation amount (> 1.5). Vertical boundary: Divide the vertical boundary of the gas migration area in the fracture field according to the fracture density of broken fractures (> 6.5 fractures / m) and the penetration degree (> 0.2). Area range: Finally, determine the area range of the gas migration area in the fracture field according to the horizontal boundary and the vertical boundary.

5. A method for determining a highly permeable area in overlying strata affected by mining, according to claim 1, characterized in that, In the above S2, the specific steps for determining the high-permeability area are as follows: S201. Identify and depict the fractures in the results of the physical similarity simulation experiment, and then import them into numerical simulation software for numerical modeling to obtain the gas mass source term of the model. S202. Input the gas emission amount and the gas mass source term of the model into the model to conduct numerical simulation experiments, obtain the migration law of the pressure-relieved gas in the gas migration area, and obtain the distribution of the gas pressure. S203. Based on the distribution of the gas pressure, divide the gas migration area into a diffusion area and a high-permeability area.

6. The method for determining the highly permeable area of overlying strata affected by mining according to claim 5, wherein In S202, the gas emission amount is calculated based on on-site gas emission detection data, and the model gas mass source term is further calculated. The gas emission detection includes the gas emission amount from residual coal in the goaf, the gas emission from adjacent coal seams, and the gas emission amount at the working face. The model gas mass source term is the source term for releasing gas in numerical simulation. The gas emission amount and the model gas mass source term are calculated according to the formula.

7. The method for determining the highly permeable area of overlying strata affected by mining according to claim 6, characterized in that, The calculation formulas for the gas emission amount from the goaf and the model gas mass source term are as follows: Gas emission volume in goaf: Q1 = Q d + Q2 + Q3 Gas mass source term: Among them, Q1 is the gas emission volume from the goaf, and Q d is the gas emission volume from the bottom coal body, with the unit of m 3 / min; Q2 is the relative gas emission volume of adjacent seams, with the unit of m 3 / t; Q3 is the gas extraction volume from the goaf, with the unit of m 3 / min; Q s is the mass source term of model gas, with the unit of kg / (m 3 / s); Q g is the gas emission rate, with the unit of m 3 / s, obtained through on-site tests; ρ g is the gas density, ρ g = 0.7167 kg / m 3 ; V is the total volume occupied by the mass source term of gas, with the unit of m 3 .

8. The determination method of the high-permeability area in overlying strata affected by mining according to claim 1, wherein In S3, the specific steps for on-site inversion of the high-permeability area are as follows: S301, delineate the high-permeability area through on-site microseismic tests. The microseismic tests determine the high-permeability area based on the density of microseismic events; S302, further determine the gas enrichment area in the coal seam through borehole peeping. At the same time, observe the fracture conditions and fragmentation degree of the rock strata in the borehole, and analyze the three-dimensional distribution law of the high-permeability area; S303, understand the development of the high-permeability area through the microseismic data obtained from microseismic tests and borehole peeping, guide the layout of gas drainage boreholes, and obtain the judgment criteria for the high-permeability area of overlying strata affected by mining according to the above test results.

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