A method for estimating coal loss caused by underground coal fires

Abstract

The present invention discloses a method for estimating the amount of regional coal loss caused by underground coal fires, which belongs to the field of coal loss assessment. First, by collecting data, studying regional coal industry composition analysis and mechanical experiments, the density of coal in the underground coal fire area, the ash thickness of the coal seam and the ash compression rate are obtained; then, by using the synergistic relationship between underground coal fire and surface subsidence and the obtained regional surface subsidence value caused by underground coal fire, the size of the underground coal fire burnout zone is inverted, and finally, the amount of coal loss caused by the underground coal fire is calculated based on the density of coal in the underground coal fire area, the thickness of the coal seam, the ash thickness, the ash compression rate and the size of the underground coal fire burnout zone. The calculation steps of this method are simple, in line with the actual coal loss caused by underground coal fires, and a variety of calculation and assessment methods are provided according to different types of combustion control zones to meet different needs, and provide strong technical support for the assessment of coal loss caused by large-scale underground coal fires and the decision-making on underground coal fire management and utilization.

Description

Technical Field

[0001] The present invention relates to a method for estimating coal loss caused by underground coal fire, and is particularly suitable for determining the location of underground coal fire burnout zones and evaluating the amount of coal loss caused by coal fire, belonging to the field of coal loss evaluation. Technical Background

[0002] Underground coal fires are coalfield and mine fires that occur naturally or due to human intervention. When the temperature reaches a critical level (80-130°C), the coal begins to smolder and burn. Underground coal fires occur in many countries around the world, including China, the United States, India, Australia, and South Africa. Because underground coal fires pose a significant threat to precious energy, the environment, and human health and safety, affected countries are actively conducting research on fire suppression and utilization.

[0003] Estimating the amount of coal lost due to coal fires is fundamental to making decisions about underground coal fire extinguishing and utilization. Accurately assessing the amount of coal lost due to underground coal fires is also a crucial basis for government efforts to manage coal fires. However, no relevant methods are currently available. However, many researchers have conducted research on underground coal fire detection and monitoring methods. These methods are primarily categorized as underground detection technologies, ground-based detection technologies, aerial remote sensing, and satellite-based remote sensing. Underground detection technologies include drilling and underground gas measurement. However, these methods are time-consuming, expensive, and pose health risks, making them rarely used. Ground-based detection technologies include surface temperature measurement, ground mapping of surface features, self-potential methods, two-dimensional electrical methods, transient electromagnetic methods, and magnetic techniques. These ground-based detection technologies generally suffer from time-consuming and limited detection scales. Furthermore, due to the concealed and difficult-to-detect characteristics of underground coal fires, ground-based monitoring often poses significant risks to personnel and equipment. Airborne and satellite-based detection technologies are the development trend in underground coal fire detection and monitoring, offering advantages such as accurate, time-saving, and efficient large-scale detection of coal fires. These two methods primarily monitor ground temperature and determine the location of underground coal fires using temperature function inversion methods. Because these two methods rely on temperature inversion equations based on the time and location of detection, their application is limited, particularly for coal fires buried deeper than 40 meters. Furthermore, these methods cannot accurately determine the location, size, and shape of the underground burnout zone, resulting in a lack of scientific basis for coal loss assessment and underground coal fire extinguishing and utilization. Summary of the Invention

[0004] In response to the above-mentioned technical deficiencies, the method for estimating the amount of coal loss caused by underground coal fires of the present invention can quickly and effectively calculate the amount of coal loss caused by underground coal fires based on the study of the relationship between the amount of coal loss and the underground coal fire burnout zone, as well as the synergistic relationship between the underground coal fire burnout zone and surface subsidence. The method has simple steps and good use effect, and can provide technical support for underground coal fire management and utilization decision-making.

[0005] To achieve the above technical objectives, the present invention provides a method for estimating the amount of coal loss caused by underground coal fires. The method first obtains the density of coal in the underground coal fire area to be estimated, the ash thickness of the coal seam, and the ash compressibility through data collection, industrial composition analysis, and mechanical experiments. Then, the method utilizes the synergistic relationship between underground coal fires and surface subsidence and obtains the regional surface subsidence caused by underground coal fires to obtain the size of the underground coal fire burnout zone. Finally, the method calculates the amount of coal loss caused by underground coal fires based on the density of the coal in the underground coal fire area, the coal seam thickness, the ash thickness, the ash compressibility, and the size of the underground coal fire burnout zone.

[0006] The specific steps are as follows:

[0007] First, the density and stratigraphic conditions of the coal in the underground coal fire area are determined using mining data, and the thickness of the coal seam is obtained. At the same time, the physical and mechanical properties of the coal seam at that location are confirmed, and the composition of the coal seam is analyzed.

[0008] Then, the thickness of the ash remaining after spontaneous combustion of the coal seam is determined based on the physical and mechanical properties of the coal seam and the results of component analysis. The ash compression rate of the coal seam in the underground coal fire area is obtained by testing the compression performance of the coal seam ash.

[0009] Using D-InSAR technology, satellites are used to observe the surface of the underground coal fire area twice or more times, and interferometry is performed on the SAR images of the underground coal fire area to obtain regional surface subsidence information caused by the underground coal fire.

[0010] Then, the volume of underground coal fire void area is calculated based on random medium theory, surface subsidence law and geometric method according to the different shapes of underground coal fire void area, which are divided into regular and irregular cases.

[0011] Finally, the amount of coal loss caused by underground coal fires was calculated based on the density of coal in the underground coal fire area, coal seam thickness, ash thickness remaining after spontaneous combustion of the coal seam, ash compression rate and the size of the underground coal fire void area.

[0012] Furthermore, the stratum conditions include the geological mining conditions of the underground coal fire area and the physical, chemical and mechanical properties of the coal samples in the area, the thickness of the coal seam m, and the thickness of the ash remaining after spontaneous combustion in the coal fire area m determined based on the physical, mechanical properties and composition information of the coal seam. a The specific steps for testing the compression performance of coal seam ash in underground coal fire areas are as follows: using a borehole to obtain coal samples from the coal seams in the underground coal fire area, then burning the collected coal samples and collecting the ash after combustion, and then performing a pressure test on the ash to obtain the relationship between pressure x and ash compression rate ε: Then the ash compression rate of the coal fire area is calculated. a, b, and c are constant coefficients, which are determined according to the test results of different places or coal samples.

[0013] Furthermore, the steps for obtaining surface subsidence in the underground coal fire area are as follows: assuming that the surface height of the target point P in the coal fire area changes during the two satellite imaging processes, and the surface subsidence occurs and moves from point P to P', then the deformation variable Δr = R1-R2, R1 and R2 represent the distance between the satellite and the target point during the two imaging processes of the target point. The deformation variable is obtained to monitor each target point within the coal fire area to obtain the regional surface subsidence information caused by the underground coal fire.

[0014] Furthermore, the specific steps for calculating the volume of underground coal fire void areas are as follows: confirming the shape of the underground coal fire void area based on the shape produced by surface subsidence, identifying the underground coal fire void area as a regular void area or an irregular void area based on its shape, estimating the amount of coal loss in the underground coal fire void area based on random medium theory, surface subsidence law, or geometric method for regular coal fire void areas; estimating the amount of coal loss in the underground coal fire void area based on random medium theory or geometric method for irregular coal fire void areas; among them, the coal loss assessment method based on random medium theory and geometric method is applicable to coal seams with different inclination angles, the random medium theory method is relatively complex but has high accuracy, the set method is simple to operate but has low accuracy, and is only applicable to nearly horizontal coal seams, and the coal loss assessment method based on surface subsidence law is only applicable to nearly horizontal and regular underground void areas; the corresponding calculation method is selected according to actual needs.

[0015] Furthermore, the volume calculation steps of the regular underground coal fire void zone based on random medium theory are as follows: Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the plane area S1 and thickness H1 of the regular underground coal fire void zone are obtained by inversion using uniform design or orthogonal experiment, and then the volume of the regular underground coal fire void zone is calculated;

[0016]

[0017] Where: W cm The maximum surface subsidence under full mining conditions is expressed by the formula: W cm =mq·cosα, where m is the mining thickness of the coal seam, q is the subsidence coefficient, α is the inclination of the coal seam, L and l are the mining width calculated along the dip direction and the mining length along the strike direction after the mining inflection point is translated, r is the main influencing radius, and x and y are the coordinates of the unknown point.

[0018] Furthermore, the calculation steps for the volume of the regular combustion void area of underground coal fire based on the surface subsidence law are as follows:

[0019] Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the value of the maximum subsidence point W is determined. max and location;

[0020] The surface subsidence curve of the main section is extracted along the direction of underground coal fire through the maximum subsidence point;

[0021] Extract the surface subsidence curve of the main section along the vertical direction of the underground coal fire combustion, and then determine the inflection point based on the surface subsidence curve of the main section and the maximum subsidence value. The position of the underground coal fire can be obtained by calculating the plane area S2 of the underground coal fire empty zone;

[0022] Referring to the relationship between the thickness of the coal seam and the maximum value of the surface subsidence during coal mining, it is found that there is a relationship between the thickness H of the combustion zone of underground coal fire and the maximum value of the surface subsidence W0: W0 = Hqcosα; q is the subsidence coefficient, α is the inclination of the coal seam, and the volume of the regular combustion zone of the underground coal fire is calculated based on the thickness H of the combustion zone of the underground coal fire.

[0023] Furthermore, the steps for calculating the volume of the regular combustion void zone of underground coal fire based on the geometric method are as follows:

[0024] The boundary of the subsidence basin with a surface subsidence of 10 mm is delineated by the boundary angle δ, and the plane area of the regular combustion zone of the underground coal fire is inferred to be S3;

[0025] Referring to the relationship between the thickness of coal seams and the maximum value of surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fires and the maximum value of surface subsidence are related: W0 = Hqcosα;

[0026] According to this formula, the thickness H of the combustion void zone of underground coal fire is calculated, and then the volume of the regular combustion void zone of underground coal fire is calculated.

[0027] Furthermore, the calculation steps for the volume of the irregular combustion void zone of underground coal fire based on random medium theory are as follows:

[0028] The irregular underground coal fire void area is divided into multiple independent triangular units using the Delaunay triangulation algorithm and the point-by-point insertion algorithm. The bending settlement at the center of a single triangular unit is taken as the bending settlement corresponding to each triangular unit.

[0029] The surface subsidence caused by the bending settlement of each triangular unit is superimposed to obtain the surface subsidence caused by the underground coal fire;

[0030] Based on the surface subsidence data caused by underground coal fires acquired by D-InSAR, the planar area S4 and thickness H4 of the irregular underground coal fire void zone can be obtained by using optimization algorithms such as uniform design or orthogonal experiments and the Delaunay triangulation method. The volume of the irregular underground coal fire void zone can then be calculated using the following formula:

[0031]

[0032] Furthermore, the steps for calculating the volume of the irregular combustion void area of underground coal fire based on the geometric method are as follows:

[0033] Based on the surface subsidence basin data caused by underground coal fires obtained by D-InSAR, the plane area S5 of the irregular underground coal fire burnout zone was obtained by delineating the 10 mm boundary line and the boundary angle δ of the subsidence basin.

[0034] Referring to the relationship between coal seam thickness and maximum surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fire and the maximum surface subsidence are related: W0 = Hqcosα; the thickness H of the combustion zone of underground coal fire is calculated according to this formula, and then the volume of the irregular combustion zone of underground coal fire is calculated.

[0035] Furthermore, the size of the empty zone Δ is calculated based on the plane area S and the thickness H of the empty zone of the underground coal fire. The density ρ of the coal in the underground coal fire area, the thickness m of the coal seam, and the ash thickness m of the coal are calculated. a And ash compressibility ε, using the formula The coal loss M in the underground coal fire area is calculated.

[0036] Beneficial effects: The present invention combines the regular and irregular shapes of underground coal fire combustion zones and adopts high-precision and easy-to-operate schemes including random medium theory, surface subsidence laws and geometric methods to determine the location and size of underground coal fire combustion zones. It combines high-precision SAR images and D-InSAR technology to monitor the subsidence and deformation of coal fire areas, effectively assess the amount of coal loss caused by coal fires, and provide technical support for actively making decisions on underground coal fire extinguishing and utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of overburden movement and surface subsidence caused by underground coal fire in the present invention.

[0038] Figure 2 This is a schematic diagram of the height of the combustion void zone formed naturally after different types of coal in the present invention.

[0039] Figure 3 This is a schematic diagram of determining the plane area of the regular combustion void zone of an underground coal fire based on the law of surface subsidence in the present invention.

[0040] Figure 4 This is a schematic diagram of determining the plane area of the regular combustion void zone of an underground coal fire based on the geometric method in the present invention.

[0041] Figure 5 This is a schematic diagram of obtaining the plane area of the irregular underground coal fire combustion zone based on the geometric method in the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the figures and specific implementation process:

[0043] like Figure 1 and Figure 2 As shown, the present invention provides a method for estimating the amount of coal loss caused by underground coal fires. First, the density of the coal in the underground coal fire area to be estimated, the ash thickness of the coal seam, and the ash compressibility are obtained through data collection, industrial composition analysis, and mechanical experiments. Then, the size of the underground coal fire burnout zone is obtained by utilizing the synergistic relationship between underground coal fires and surface subsidence and obtaining the regional surface subsidence caused by underground coal fires. Finally, the amount of coal loss caused by the underground coal fire is calculated based on the density of the coal in the underground coal fire area, the coal seam thickness, the ash thickness, the ash compressibility, and the size of the underground coal fire burnout zone.

[0044] The specific steps are as follows:

[0045] First, the density and stratigraphic conditions of the coal in the underground coal fire area are determined using mining data to obtain coal seam thickness information. At the same time, the physical and mechanical properties of the coal seam are confirmed and the composition of the coal seam is analyzed. The stratigraphic conditions include the geological mining conditions of the underground coal fire area and the physical, chemical and mechanical properties of the coal samples in the area. The coal seam thickness (m) is determined based on the physical and mechanical properties and composition information of the coal seam to determine the remaining ash thickness (m) after spontaneous combustion in the coal fire area. a The specific steps for testing the compression performance of coal seam ash in underground coal fire areas are as follows: using a borehole to obtain coal samples from the coal seams in the underground coal fire area, then burning the collected coal samples and collecting the ash after combustion, and then performing a pressure test on the ash to obtain the relationship between pressure x and ash compression rate ε: Then the ash compression rate of the coal fire area is calculated. a, b, and c are constant coefficients, which are determined according to the test results of different places or coal samples.

[0046] Then, the thickness of the ash remaining after spontaneous combustion of the coal seam is determined based on the physical and mechanical properties of the coal seam and the results of component analysis. The ash compression rate of the coal seam in the underground coal fire area is obtained by testing the compression performance of the coal seam ash.

[0047] like Figure 3 As shown, the D-InSAR technology is used to observe the surface of the underground coal fire area twice or multiple times by using a satellite, and interferometric measurement is performed on the SAR images of the underground coal fire area to obtain the regional surface subsidence information caused by the underground coal fire. The steps for obtaining the surface subsidence of the underground coal fire area are as follows: assuming that the surface height of the target point P in the coal fire area changes during the two satellite imaging processes, and the surface subsidence moves from point P to P' after the surface subsidence occurs, then the deformation variable Δr=R1-R2, R1 and R2 represent the distance between the satellite and the target point during the two imaging processes of the target point. The deformation variable is obtained to monitor each target point within the coal fire area to obtain the regional surface subsidence information caused by the underground coal fire.

[0048] like Figure 4 and Figure 5 As shown, the underground coal fire void area is divided into regular and irregular shapes according to different shapes, and the volume of the underground coal fire void area is calculated based on random medium theory, surface subsidence law and geometric method; the specific steps for calculating the volume of the underground coal fire void area are: confirm the shape of the underground coal fire void area according to the shape produced by surface subsidence, identify it as a regular void area or an irregular void area according to the shape of the underground coal fire void area, and estimate the coal loss of the underground coal fire void area based on random medium theory, surface subsidence law or geometric method for regular coal fire void area; estimate the coal loss of the underground coal fire void area based on random medium theory or geometric method for irregular coal fire void area; among them, the coal loss assessment method based on random medium theory and geometric method is applicable to coal seams with different inclination angles, the random medium theory method is relatively complex but has high accuracy, the set method is simple to operate but has low accuracy and is only applicable to nearly horizontal coal seams, and the coal loss assessment method based on surface subsidence law is only applicable to nearly horizontal and regular underground void areas; the corresponding calculation method should be selected according to actual needs.

[0049] The calculation steps for the volume of the regular underground coal fire void zone based on random medium theory are as follows: Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the uniform design or orthogonal test is used to obtain the plane area S1 and thickness H1 of the regular underground coal fire void zone through inversion, and then the volume of the regular underground coal fire void zone is calculated;

[0050]

[0051] Where: W cm The maximum surface subsidence under full mining conditions is expressed by the formula: W cm =mq·cosα, where m is the mining thickness of the coal seam, q is the subsidence coefficient, α is the inclination of the coal seam, L and l are the mining width calculated along the dip direction and the mining length along the strike direction after the mining inflection point is translated, r is the main influencing radius, and x and y are the coordinates of the unknown point.

[0052] The calculation steps for the volume of the regular combustion void area of underground coal fire based on the surface subsidence law are as follows:

[0053] Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the value of the maximum subsidence point W is determined. max and location;

[0054] The surface subsidence curve of the main section is extracted along the direction of underground coal fire through the maximum subsidence point;

[0055] Extract the surface subsidence curve of the main section along the vertical direction of the underground coal fire combustion, and then determine the inflection point based on the surface subsidence curve of the main section and the maximum subsidence value. The position of the underground coal fire can be obtained by calculating the plane area S2 of the underground coal fire empty zone;

[0056] Referring to the relationship between the thickness of the coal seam and the maximum value of the surface subsidence during coal mining, it is found that there is a relationship between the thickness H of the combustion zone of underground coal fire and the maximum value of the surface subsidence W0: W0 = Hqcosα; q is the subsidence coefficient, α is the inclination of the coal seam, and the volume of the regular combustion zone of the underground coal fire is calculated based on the thickness H of the combustion zone of the underground coal fire.

[0057] The steps for calculating the volume of the regular combustion void zone of underground coal fire based on the geometric method are as follows:

[0058] The boundary of the subsidence basin with a surface subsidence of 10 mm is delineated by the boundary angle δ, and the plane area of the regular combustion zone of the underground coal fire is inferred to be S3;

[0059] Referring to the relationship between the thickness of coal seams and the maximum value of surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fires and the maximum value of surface subsidence are related: W0 = Hqcosα;

[0060] According to this formula, the thickness H of the combustion void zone of underground coal fire is calculated, and then the volume of the regular combustion void zone of underground coal fire is calculated.

[0061] The steps for calculating the volume of the irregular combustion void zone of underground coal fire based on random medium theory are as follows:

[0062] The irregular underground coal fire void area is divided into multiple independent triangular units using the Delaunay triangulation algorithm and the point-by-point insertion algorithm. The bending settlement at the center of a single triangular unit is taken as the bending settlement corresponding to each triangular unit.

[0063] The surface subsidence caused by the bending settlement of each triangular unit is superimposed to obtain the surface subsidence caused by the underground coal fire;

[0064] Based on the surface subsidence data caused by underground coal fires acquired by D-InSAR, the planar area S4 and thickness H4 of the irregular underground coal fire void zone can be obtained by using optimization algorithms such as uniform design or orthogonal experiments and the Delaunay triangulation method. The volume of the irregular underground coal fire void zone can then be calculated using the following formula:

[0065]

[0066] Furthermore, the steps for calculating the volume of the irregular combustion void area of underground coal fire based on the geometric method are as follows:

[0067] Based on the surface subsidence basin data caused by underground coal fires obtained by D-InSAR, the plane area S5 of the irregular underground coal fire burnout zone was obtained by delineating the 10 mm boundary line and the boundary angle δ of the subsidence basin.

[0068] Referring to the relationship between coal seam thickness and maximum surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fire and the maximum surface subsidence are related: W0 = Hqcosα; the thickness H of the combustion zone of underground coal fire is calculated according to this formula, and then the volume of the irregular combustion zone of underground coal fire is calculated.

[0069] Finally, the amount of coal loss caused by underground coal fires was calculated based on the density of coal in the underground coal fire area, coal seam thickness, ash thickness remaining after spontaneous combustion of the coal seam, ash compression rate and the size of the underground coal fire void area.

[0070] The size of the empty space Δ is calculated based on the plane area S and the thickness H of the empty space in the underground coal fire area. The density ρ of the coal in the underground coal fire area, the thickness m of the coal seam, and the ash thickness m of the coal are used to calculate the size of the empty space Δ. a And ash compressibility ε, using the formula The coal loss M in the underground coal fire area is calculated.

[0071] Example 1:

[0072] Step 1: For a specific underground coal fire area, collect relevant data on the geological mining conditions in the study area and the physical, chemical, and mechanical properties of the coal, and determine the density of the coal to be 1.4g / cm 3 , the coal seam thickness is 3m, the subsidence coefficient is 0.9, the coal seam inclination is 2°, and the ash thickness remaining after spontaneous combustion of the coal seam is 0.9m;

[0073] Step 2: Drilling is used to obtain coal samples from the underground coal fire area. The coal samples are burned in the laboratory and then the ash content after combustion is tested using a pressure testing machine. The test shows that the ash compression rate is 20% when the pressure is 6 MPa.

[0074] Step 3: Determine that the underground coal fire area is an irregular combustion void area, and calculate the volume of the irregular combustion void area using a geometric method. The 10mm boundary line of the combustion void area subsidence basin is obtained through D-InSAR data, and its boundary angle is 10°. The calculated plane area of the boundary line is 550㎡. Figure 3 、 Figure 4 and Figure 5 As shown;

[0075] Step 4: The maximum subsidence value of the burnout zone is 1100 mm, which is obtained from D-InSAR data. The thickness of the burnout zone of the underground coal fire is calculated to be 1.22 m using the formula W0 = Hqcosα.

[0076] Step 5: By formula The calculated coal loss in the underground coal fire area is 1.46776×10 6 kilogram.

[0077] This paper takes into account that spontaneous combustion of underground coal seams buried deeper than 40 meters will form underground burnout zones, which can cause stress re-analysis and displacement of the overlying rock strata, which in turn is transmitted to the surface, causing surface subsidence. This indicates that there is a quantitative relationship between the size of the burnout zone formed by underground coal fires and surface subsidence. Therefore, based on this synergistic relationship, the location, size, and shape of the burnout zone formed by underground coal fires can be determined using the surface subsidence obtained. Furthermore, the combustion characteristics of the coal seam can be used to assess the loss of underground coal fire resources.

Claims

1. A method for estimating coal loss caused by underground coal fires, characterized by: First, the density of the coal in the underground coal fire area to be estimated, the ash thickness of the coal seam, and the ash compressibility were obtained through data collection, industrial composition analysis, and mechanical experiments. Then, the size of the underground coal fire burnout zone was determined by using the synergistic relationship between underground coal fire and surface subsidence and the regional surface subsidence caused by underground coal fire. Finally, the amount of coal loss caused by underground coal fire was calculated based on the density of the coal in the underground coal fire area, coal seam thickness, ash thickness, ash compressibility, and the size of the underground coal fire burnout zone. The specific steps are as follows: First, the density and stratigraphic conditions of the coal in the underground coal fire area were determined using mining data, and the coal seam thickness information was obtained. The physical and mechanical properties of the coal seam at that location were also confirmed, and the composition of the coal seam was analyzed. Then, the thickness of the ash remaining after spontaneous combustion of the coal seam is determined based on the physical and mechanical properties of the coal seam and the results of component analysis. The ash compression rate of the coal seam in the underground coal fire area is obtained by testing the compression performance of the coal seam ash in the underground coal fire area. The formation conditions include the geological mining conditions of the underground coal fire area and the physical, chemical and mechanical properties of the coal samples in the area. The thickness of the coal seam m is determined based on the physical and mechanical properties and component information of the coal seam. a The specific steps for testing the compression performance of coal seam ash in underground coal fire areas are as follows: using a borehole to obtain coal samples from the coal seams in the underground coal fire area, then burning the collected coal samples and collecting the ash after combustion, and then performing a pressure test on the ash to obtain the relationship between pressure x and ash compression rate ε: Then the ash compressibility of the coal fire area is calculated, where a, b, and c are constant coefficients, which are determined based on the test results of different places or coal samples; Using D-InSAR technology, satellites are used to observe the surface of the underground coal fire area twice or more times, and interferometry is performed on the SAR images of the underground coal fire area to obtain regional surface subsidence information caused by the underground coal fire. Then, based on the different shapes of underground coal fire voids, which are divided into regular and irregular ones, the volume of the underground coal fire voids is calculated based on random medium theory, surface subsidence laws, and geometric methods. The specific steps for calculating the volume of the underground coal fire voids are: confirming the shape of the underground coal fire voids based on the shape caused by surface subsidence, identifying the underground coal fire voids as regular or irregular based on the shape of the underground coal fire voids, and estimating the amount of coal loss in the underground coal fire voids based on random medium theory, surface subsidence laws, or geometric methods for regular coal fire voids. For irregular coal fire void areas, the coal loss in underground coal fire void areas is estimated based on random medium theory or geometric methods. The coal loss assessment methods based on random medium theory and geometric methods are applicable to coal seams with different inclination angles. The random medium theory method is relatively complex but has high accuracy. The ensemble method is simple to operate but has low accuracy and is only applicable to nearly horizontal coal seams. The coal loss assessment method based on surface subsidence laws is only applicable to nearly horizontal and regular underground void areas. The corresponding calculation method should be selected according to actual needs. Finally, the amount of coal loss caused by underground coal fires was calculated based on the density of coal in the underground coal fire area, coal seam thickness, ash thickness remaining after spontaneous combustion of the coal seam, ash compression rate and the size of the underground coal fire void area.

2. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The steps for obtaining surface subsidence in the underground coal fire area are as follows: suppose the surface height of the target point P in the coal fire area changes during two satellite imaging processes, and the surface subsidence occurs and moves from point P to P′. Then the deformation variable Δr = R1-R2, where R1 and R2 represent the distance between the satellite and the target point during the two imaging processes. The deformation variable is used to monitor each target point within the coal fire area to obtain regional surface subsidence information caused by the underground coal fire.

3. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The calculation steps for the volume of the regular underground coal fire void zone based on random medium theory are as follows: Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the uniform design or orthogonal test is used to obtain the plane area S1 and thickness H1 of the regular underground coal fire void zone through inversion, and then the volume of the regular underground coal fire void zone is calculated; W(x,y)=W cm C' x C' y Where: W cm The maximum surface subsidence under full mining conditions is expressed by the formula: W cm =mq·cosα, where m is the mining thickness of the coal seam, q is the subsidence coefficient, α is the inclination of the coal seam, L and l are the mining width calculated along the dip direction and the mining length along the strike direction after the mining inflection point is translated, r is the main influencing radius, and x and y are the coordinates of the unknown point.

4. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The calculation steps for the volume of the regular combustion void area of underground coal fire based on the surface subsidence law are as follows: Based on the surface subsidence data caused by underground coal fires obtained by D-InSAR, the value of the maximum subsidence point W is determined. max and location; The surface subsidence curve of the main section is extracted along the direction of underground coal fire through the maximum subsidence point; Extract the surface subsidence curve of the main section along the vertical direction of the underground coal fire combustion, and then determine the inflection point based on the surface subsidence curve of the main section and the maximum subsidence value. The position of the underground coal fire can be obtained by calculating the plane area S2 of the underground coal fire empty zone; Referring to the relationship between the thickness of the coal seam and the maximum value of the surface subsidence during coal mining, it is found that there is a relationship between the thickness H of the combustion zone of underground coal fire and the maximum value of the surface subsidence W0: W0 = Hqcosα; q is the subsidence coefficient, α is the inclination of the coal seam, and the volume of the regular combustion zone of the underground coal fire is calculated based on the thickness H of the combustion zone of the underground coal fire.

5. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The steps for calculating the volume of the regular combustion void zone of underground coal fire based on the geometric method are as follows: The boundary of the subsidence basin with a surface subsidence of 10 mm is delineated by the boundary angle δ, and the plane area of the regular combustion zone of the underground coal fire is inferred to be S3; Referring to the relationship between the thickness of coal seams and the maximum value of surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fires and the maximum value of surface subsidence are related: W0 = Hqcosα; According to this formula, the thickness H of the combustion void zone of underground coal fire is calculated, and then the volume of the regular combustion void zone of underground coal fire is calculated.

6. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The steps for calculating the volume of the irregular combustion void zone of underground coal fire based on random medium theory are as follows: The irregular underground coal fire void area is divided into multiple independent triangular units using the Delaunay triangulation algorithm and the point-by-point insertion algorithm. The bending settlement at the center of a single triangular unit is taken as the bending settlement corresponding to each triangular unit. The surface subsidence caused by the bending settlement of each triangular unit is superimposed to obtain the surface subsidence caused by the underground coal fire; Based on the surface subsidence data caused by underground coal fires acquired by D-InSAR, the uniform design or orthogonal experimental optimization algorithm and the Delaunay triangulation method can be used to obtain the plane area S4 and thickness H4 of the irregular underground coal fire void zone, and then calculate the volume of the irregular underground coal fire void zone. The calculation formula is as follows:

7. The method for estimating coal loss caused by underground coal fire according to claim 1, characterized in that: The steps for calculating the volume of the irregular combustion void area of underground coal fire based on the geometric method are as follows: Based on the surface subsidence basin data caused by underground coal fires obtained by D-InSAR, the plane area S5 of the irregular underground coal fire burnout zone was obtained by delineating the 10 mm boundary line and the boundary angle δ of the subsidence basin. Referring to the relationship between coal seam thickness and maximum surface subsidence during coal mining, it is found that the thickness of the combustion zone of underground coal fire and the maximum surface subsidence are related: W0 = Hqcosα; the thickness H of the combustion zone of underground coal fire is calculated according to this formula, and then the volume of the irregular combustion zone of underground coal fire is calculated.

8. The method for estimating coal loss caused by underground coal fire according to any one of claims 1 to 7, characterized in that: The size of the empty zone Δ is calculated based on the plane area S and the thickness H of the empty zone in the underground coal fire area. The density ρ of the coal in the underground coal fire area, the thickness m of the coal seam, and the ash thickness m of the coal are used to calculate the size of the empty zone Δ. a And ash compressibility ε, using the formula The amount of coal loss M in the underground coal fire area is calculated by ρ.

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