A surface geochemical detection method for free coalbed methane enrichment area in coal mine goaf

Abstract

The present invention discloses a surface geochemical detection method for free coal-bed methane enriched areas in coal mine goafs, which specifically includes the following steps: designing a preliminary exploration sampling grid survey line on the surface of a work area, determining preliminary exploration sampling points, obtaining methane and carbon dioxide concentrations at the preliminary exploration sampling points according to the soil free gas collection steps, identifying concentration abnormal points, and dividing preliminary exploration abnormal areas; using the sampling points in the preliminary exploration abnormal area, according to the soil free gas collection steps, testing the methane and carbon dioxide concentrations at different depths, and determining the optimal monitoring depth L0; in the preliminary exploration abnormal area, designing and deploying a re-exploration sampling grid survey line in the work area, determining re-exploration sampling points, obtaining methane, carbon dioxide, ethane, and hydrogen sulfide concentrations according to the soil free gas collection steps according to the optimal monitoring depth L0, demarcating geochemical abnormal areas, and delineating free coal-bed methane enriched areas in goafs. The present invention can achieve lower costs under the premise of being easy to operate, and is particularly suitable for detecting free coal-bed methane enriched areas in goafs.

Description

Technical Field

[0001] The invention relates to a coalbed methane surface detection method, in particular to a surface geochemical detection method for free coalbed methane enriched areas in coal mine goafs, belonging to the technical field of coalbed methane exploration in coal mine goafs. Background Art

[0002] Coalbed methane, commonly known as "gas", is a gas mineral resource associated with coal. Coalbed methane is a hydrocarbon gas mainly adsorbed on the surface of coal matrix particles, partially free in coal pores or dissolved in coal seam water, with methane as the main component. It is an unconventional natural gas. my country is rich in coalbed methane resources, ranking third in the world. Coalbed methane has been included as an important carrier to promote the revolution in energy production and consumption.

[0003] With the exploitation of coal resources, more and more production mines are abandoned due to the depletion of coal resources, and some outdated mines are facing closure or abandonment. Coalbed methane is a strong greenhouse gas, and its greenhouse effect after escape is 21 times that of carbon dioxide. The development and utilization of coalbed methane in coal goafs can not only eliminate the safety hazards caused by the accumulation of gas in abandoned mine goafs, but also increase energy supply and reduce greenhouse gas emissions.

[0004] At present, the main method of developing and utilizing coalbed methane resources in goafs is surface drilling. In addition to the adsorbed gas in the mined coal bodies, coal pillars and residual coal seams, adjacent unmined coal seams and surrounding rocks, the coalbed methane in the goafs of abandoned mines also includes some free gas. That is, under the influence of mining pressure relief, the coalbed methane in some pressure relief areas will be desorbed into free gas and enriched in the mining fracture area of ​​the goaf, forming a free coalbed methane enriched area in the goaf. The free coalbed methane enriched area in the goaf has a good communication path with the adsorbed gas of the residual coal in the goaf. Therefore, clarifying the free coalbed methane enriched area in the goaf is a prerequisite for the deployment of ground wells, and it is also the key to the efficient development of coalbed methane in the goaf by ground wells. However, the existing free coalbed methane enriched areas in goafs mainly rely on drilling, geophysical exploration and other methods, which have high accuracy, but the workload is large and the cost is too high. When the number of goafs is large, this shortcoming is particularly prominent. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a surface geochemical detection method for free coalbed methane-rich areas in coal mine goafs, which can achieve low costs while being easy to operate, and is particularly suitable for detecting free coalbed methane-rich areas in goafs.

[0006] To achieve the above purpose, the surface geochemical detection method of free coalbed methane enriched area in the coal mine goaf specifically includes the following steps:

[0007] S1: Design the preliminary sampling grid survey line of the work area, determine the preliminary sampling points, obtain the methane and carbon dioxide concentrations at the preliminary sampling points according to the soil free gas collection steps, identify the concentration abnormal points, and divide the preliminary abnormal areas;

[0008] S2: Using the sampling points in the initial exploration abnormal area, according to the soil free gas collection steps, test the methane and carbon dioxide concentrations at different depths and determine the optimal monitoring depth L0;

[0009] S3: In the initial exploration abnormal area, design and deploy the re-exploration sampling grid survey line of the work area, determine the re-exploration sampling points, obtain the concentrations of methane, carbon dioxide, ethane, and hydrogen sulfide at the optimal monitoring depth L0 according to the soil free gas collection steps, delineate the geochemical anomaly area, and circle the free coalbed methane enrichment area in the goaf.

[0010] Furthermore, the soil free gas collection steps are as follows:

[0011] a. After determining the sampling depth L of free gas in the surface soil, use a backpack drill to vertically drill a borehole with a depth of l1 on the surface, and satisfy l1<L. Then insert a hollow steel probe from the borehole, and make the bottom end of the steel probe be inserted into the soil at the bottom of the borehole to a depth of l2, and satisfy l1+l2=L. Finally, seal the hole to complete the positioning and installation of the steel probe;

[0012] b. Arrange a negative pressure pump, a water container and a gas collection bottle on the surface. The gas collection bottle has an opening at the bottom and a rubber stopper at the top. Fill the gas collection bottle with water and then empty it. Then inject water into the water container and place the gas collection bottle in the water container so that the water in the gas collection bottle and the water in the water container are connected by atmospheric pressure. The suction and discharge port on the top of the steel probe is sealedly connected to the input end of the negative pressure pump through a pipeline. The output end of the negative pressure pump is connected to a hose. The output end of the hose is submerged below the liquid level of the water container and then placed in the gas collection bottle through the opening at the bottom of the gas collection bottle to complete the installation of the surface collection equipment.

[0013] c. Start the negative pressure pump, and after the free gas is discharged into the gas collection bottle, use the negative pressure extractor to pierce the rubber stopper to collect the free gas in the gas collection bottle. After collection, measure the concentration of the gas in the negative pressure extractor through the gas detector.

[0014] Furthermore, in step a, the sampling depth L of the surface soil free gas is based on the previous test background value of the area in the work area. If there is no previous test background value, the initial sampling depth is 1.00 to 1.5 m.

[0015] Furthermore, when designing the sampling grid survey line for the preliminary exploration of the work area on the surface in S1, for the investigation area where the location of the goaf is unclear, the sampling grid size can be 50m×50m; for the investigation area where the location of the goaf is clear, the sampling grid size can be designed to be 30m×50m on the surface, 20m outside the goaf boundary and 100m inside the goaf boundary, with a spacing of 30m between measuring points for the dip width of the goaf and 50m between measuring points for the strike length of the goaf.

[0016] Furthermore, in S1, the background values ​​of soil methane and carbon dioxide concentrations are used to identify concentration anomaly points and divide the initial exploration anomaly areas. The background values ​​of soil methane and carbon dioxide concentrations adopt the background values ​​of previous tests in the area. If there are no previous test background values, the background values ​​are first determined using the methane and carbon dioxide concentrations of the measuring points in the non-mined-out areas, and then the soil methane and carbon dioxide concentration anomaly measuring points are determined based on the background values, contour lines and cross-sectional diagrams are drawn, and the initial exploration anomaly areas are delineated.

[0017] Furthermore, when testing the methane and carbon dioxide concentrations at different depths and determining the optimal monitoring depth in S2, first select two adjacent preliminary sampling points where the methane and carbon dioxide concentrations are obviously abnormal; according to the soil free gas collection test steps, obtain the methane and carbon dioxide concentrations at a depth of 0 to 3.0 m at a depth interval of 0.3 m; analyze the change pattern of gas concentration with depth, and use the depth with the maximum methane concentration, or the depth where the carbon dioxide concentration no longer decreases significantly, as the optimal monitoring depth L0 for soil free gas monitoring.

[0018] Furthermore, the working area is clearly defined according to the location of the goaf. In S3, the method of intensive and extended point distribution is adopted around the initial exploration abnormal area at 20m outside the goaf boundary and 100m inside the goaf boundary on the surface. The re-exploration sampling points are set according to the grid line size of 10×50m, with the interval of 10m between the measuring points of the goaf dip width and 50m between the measuring points of the goaf strike length. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-section diagrams of the four monitored gases are drawn to divide the gas concentration abnormal area and delineate the free coalbed methane enrichment area in the goaf.

[0019] For the work area where the location of the goaf is unclear, in S3, the method of encrypted and extended point distribution is adopted around the initial exploration abnormal area, and re-exploration sampling points are set according to the grid survey line size of 50×50m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the re-exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the second exploration abnormal area is divided; in the second exploration abnormal area, the method of encrypted and extended point distribution is adopted, and the third exploration sampling points are set according to 10×25m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the third exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the gas concentration abnormal area is divided, and the free coalbed methane enrichment area in the goaf is delineated.

[0020] Compared with the existing technology, the surface geochemical detection method of free coalbed methane enriched area in coal mine goaf utilizes the surface micro-seepage phenomenon of coalbed methane in underground coal mine goaf, and is based on the near-vertical characteristics of light hydrocarbon or methane micro-seepage mechanism and the microbial transformation of coalbed methane micro-seepage process, which causes the formation of abnormal concentrations of methane, carbon dioxide, ethane, hydrogen sulfide, etc. in the overlying surface soil. First, the surface preliminary sampling grid survey line of the work area is designed, the preliminary sampling points are determined, and the methane and carbon dioxide concentrations are obtained, the concentration abnormal points are identified, and the concentration abnormal points are marked. The initial exploration anomaly area is divided into two parts. Secondly, the sampling points in the initial exploration anomaly area are used to test the methane and carbon dioxide concentrations at different depths and determine the optimal monitoring depth L0. Finally, the re-exploration sampling grid survey lines are designed and deployed in the initial exploration anomaly area, and the re-exploration sampling points are determined. The methane, carbon dioxide, ethane and hydrogen sulfide concentrations are obtained according to the optimal monitoring depth L0, and the geochemical anomaly area and the free coalbed methane enrichment area in the goaf are delineated. This can achieve low cost under the premise of easy operation and is particularly suitable for detecting free coalbed methane enrichment areas in goaf areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the geochemical anomaly response of free gas in the surface soil of the free coalbed methane enrichment area in the coal mine goaf. Figure 1 a is a cross-sectional diagram of the coal mine goaf, Figure 1 b is a schematic diagram of the horizontal projection of the coal mine goaf;

[0022] Figure 2 is a flow chart of the present invention;

[0023] Figure 3 It is a structural schematic diagram of drilling a borehole in the soil free gas collection step of the present invention;

[0024] Figure 4 It is a schematic structural diagram of the soil free gas collection of the present invention.

[0025] In the figure: 1. Backpack drill; 2. Drill hole; 3. Steel probe; 4. Soil; 5. Hose; 6. Negative pressure pump; 7. Water container; 8. Hole sealer; 9. Gas collection bottle; 10. Rubber stopper; 11. Negative pressure extractor; 13. Sieve hole structure; 14. Free gas. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] like Figure 1 As shown in Figure 2, coalbed methane in underground coal mine goaf has surface micro-leakage phenomenon, such as Figure 1 As shown in Fig. 2, under the combined effects of mining disturbance and surface settlement, the goaf and overlying strata will form a compacted area and an O-shaped mining fracture ring, and the free coalbed methane desorbed by mining pressure relief will be enriched in the O-shaped mining fracture ring to form a coalbed methane enrichment area. Based on the near-vertical characteristics of the light hydrocarbon or methane micro-leakage mechanism, as shown in Fig. Figure 1 As shown in a, free coalbed methane micro-seepage in the goaf and the microbial transformation during the coalbed methane micro-seepage process will form abnormal concentrations of methane, carbon dioxide, ethane, hydrogen sulfide, etc. in the overlying surface soil of the O-shaped mining fracture ring structure in the goaf. The present invention utilizes the chemical anomaly zone of the overlying surface soil caused by coalbed methane micro-seepage to delineate the free coalbed methane enrichment area in the coal mine goaf.

[0028] like Figure 2 As shown, the surface geochemical detection method for free coalbed methane enrichment area in the coal mine goaf includes the following steps:

[0029] S1: Design the preliminary sampling grid survey line of the work area, determine the preliminary sampling points, obtain the methane and carbon dioxide concentrations at the preliminary sampling points according to the soil free gas collection steps, identify the concentration abnormal points, and divide the preliminary abnormal areas;

[0030] S2: Using the sampling points in the initial exploration abnormal area, according to the soil free gas collection steps, test the methane and carbon dioxide concentrations at different depths and determine the optimal monitoring depth L0;

[0031] S3: In the initial exploration abnormal area, design and deploy the re-exploration sampling grid survey line of the work area, determine the re-exploration sampling points, obtain the concentrations of methane, carbon dioxide, ethane, and hydrogen sulfide at the optimal monitoring depth L0 according to the soil free gas collection steps, delineate the geochemical anomaly area, and circle the free coalbed methane enrichment area in the goaf.

[0032] The specific steps for collecting soil free gas are as follows:

[0033] a. After determining the sampling depth L of the surface soil free gas (unit: m, generally using the previous test background value of the area in the work area. If there is no previous test background value, the initial sampling depth can be 1.00-1.5m). Figure 3As shown, a backpack drill 1 is used to vertically drill a borehole 2 with a depth of l1 on the ground surface, and l1<L is satisfied, and then Figure 4 As shown, a hollow steel probe 3 is inserted into the borehole 2, and the sieve structure 13 at the bottom of the steel probe 3 is inserted into the soil 4 at the bottom of the borehole 2 to a depth of l2, and l1+l2=L is satisfied, and finally the hole is sealed by a sealer 8 to complete the positioning and installation of the steel probe 3;

[0034] b. Set up a negative pressure pump 6, a water container 7 and a gas collection bottle 9 on the surface, such as Figure 4 As shown, the bottom of the gas collection bottle 9 has an opening and the top is provided with a rubber plug 10. After the gas collection bottle 9 is filled with water and emptied, water is injected into the water container 7 and the gas collection bottle 9 is placed in the water container 7, so that the water in the gas collection bottle 9 and the water in the water container 7 are connected by atmospheric pressure, and the suction and discharge port on the top of the steel probe 3 is sealedly connected to the input end of the negative pressure pump 6 through a pipeline, and the output end of the negative pressure pump 6 is connected to the hose 5, and the output end of the hose 5 is immersed below the liquid level of the water container 7 and then placed in the gas collection bottle 9 through the bottom opening of the gas collection bottle 9, and the installation of the surface collection equipment is completed;

[0035] c. Start the negative pressure pump 6, and after the free gas 14 is discharged into the gas collection bottle 9, use the negative pressure extractor 11 to pierce the rubber stopper 10 to collect the free gas 14 in the gas collection bottle 9. After collection, measure the concentration of the gas in the negative pressure extractor 11 through a gas detector.

[0036] When designing the sampling grid survey line for the preliminary exploration of the work area on the surface in S1, the sampling grid size can be 50m×50m for the investigation area where the location of the goaf is unclear; for the investigation area where the location of the goaf is clear, the sampling grid size can be designed to be 30m×50m on the surface 20m outside the goaf boundary and 100m inside the goaf boundary, with a spacing of 30m between measuring points for the dip width of the goaf and 50m between measuring points for the strike length of the goaf.

[0037] In S1, the background values ​​of soil methane and carbon dioxide concentrations are used to identify concentration anomaly points and divide the initial exploration anomaly areas. The background values ​​of soil methane and carbon dioxide concentrations are generally based on the previous test background values ​​of the area. If there are no previous test background values, mathematical statistics are used for analysis. First, the background values ​​are determined using the methane and carbon dioxide concentrations of the non-mined-out area measurement points, and then the soil methane and carbon dioxide concentration anomaly measurement points are determined based on the background values. Contour lines and cross-section diagrams are drawn to delineate the initial exploration anomaly areas.

[0038] When testing the methane and carbon dioxide concentrations at different depths and determining the optimal monitoring depth in S2, first select two adjacent preliminary sampling points where the methane and carbon dioxide concentrations are obviously abnormal; according to the soil free gas collection test steps, obtain the methane and carbon dioxide concentrations at a depth of 0 to 3.0 m at a depth interval of 0.3 m; analyze the change pattern of gas concentration with depth, and use the depth with the maximum methane concentration, or the depth where the carbon dioxide concentration no longer decreases significantly, as the optimal monitoring depth L0 for soil free gas monitoring.

[0039] According to the location of the goaf, the work area is clearly defined. In S3, on the surface, 20m outside the goaf boundary and 100m inside the goaf boundary, an encrypted and extended point distribution method is adopted around the initial exploration abnormal area. The spacing between measuring points is 10m for the goaf dip width and 50m for the goaf strike length. The re-exploration sampling points are set according to the grid survey line size of 10×50m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, the contour lines and cross-sectional diagrams of the four monitored gases are drawn, the gas concentration abnormality area is divided, and the free coalbed methane enrichment area in the goaf is delineated.

[0040] For the work area where the location of the goaf is unclear, in S3, the method of encrypted and extended point distribution is adopted around the initial exploration abnormal area, and re-exploration sampling points are set according to the grid survey line size of 50×50m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the re-exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the second exploration abnormal area is divided; in the second exploration abnormal area, the method of encrypted and extended point distribution is adopted, and the third exploration sampling points are set according to 10×25m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the third exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the gas concentration abnormal area is divided, and the free coalbed methane enrichment area in the goaf is delineated.

Claims

1. A method for surface geochemical detection of free coalbed methane enriched areas in coal mine goafs, characterized in that: The specific steps include: S1: Design the preliminary sampling grid survey line of the work area, determine the preliminary sampling points, obtain the methane and carbon dioxide concentrations at the preliminary sampling points according to the soil free gas collection steps, identify the concentration abnormal points, and divide the preliminary abnormal areas; S2: Using the sampling points in the initial exploration abnormal area, according to the soil free gas collection steps, test the methane and carbon dioxide concentrations at different depths and determine the optimal monitoring depth L0; When determining the optimal monitoring depth L0, first select two adjacent preliminary sampling points where the methane and carbon dioxide concentrations are obviously abnormal; according to the soil free gas collection test steps, obtain the methane and carbon dioxide concentrations at a depth of 0 to 3.0 m at a depth interval of 0.3 m; analyze the law of gas concentration change with depth, and take the depth with the maximum methane concentration, or the depth where the carbon dioxide concentration no longer decreases significantly, as the optimal monitoring depth L0 for soil free gas monitoring; S3: In the initial exploration abnormal area, design and deploy the re-exploration sampling grid survey line of the work area, determine the re-exploration sampling points, obtain the concentrations of methane, carbon dioxide, ethane, and hydrogen sulfide at the optimal monitoring depth L0 according to the soil free gas collection steps, delineate the geochemical anomaly area, and circle the free coalbed methane enrichment area in the goaf.

2. The method for surface geochemical detection of free coalbed methane enriched areas in coal mine goafs according to claim 1, characterized in that: The specific steps for collecting soil free gas are as follows: a. After determining the sampling depth L of the free gas in the surface soil, a borehole (2) with a depth of l1 is drilled vertically on the surface using a backpack drill (1), and l1 < L is satisfied. Then, a hollow steel probe (3) is inserted from the borehole (2), and the bottom end of the steel probe (3) is inserted into the soil at the bottom of the borehole (2) to a depth of l2, and l1 + l2 = L is satisfied. Finally, the hole is sealed to complete the positioning and installation of the steel probe (3); b. Arrange a negative pressure pump (6), a water container (7) and a gas collection bottle (9) on the ground surface. The bottom of the gas collection bottle (9) has an opening and the top is provided with a rubber stopper (10). After the gas collection bottle (9) is filled with water and emptied, water is injected into the water container (7) and the gas collection bottle (9) is placed in the water container (7) so that the water in the gas collection bottle (9) and the water in the water container (7) are connected by atmospheric pressure. The suction and discharge port on the top of the steel probe (3) is sealedly connected to the input end of the negative pressure pump (6) through a pipeline. The output end of the negative pressure pump (6) is connected to a hose (5), and the output end of the hose (5) is immersed below the liquid level of the water container (7) and then placed in the gas collection bottle (9) through the bottom opening of the gas collection bottle (9), thereby completing the installation of the surface collection equipment; c. Start the negative pressure pump (6), and after the free gas (14) is discharged into the gas collection bottle (9), use the negative pressure extractor (11) to pierce the rubber stopper (10) to collect the free gas (14) in the gas collection bottle (9). After collection, the concentration of the gas in the negative pressure extractor (11) is measured by a gas detector.

3. The surface geochemical detection method for free coalbed methane enrichment area in coal mine goaf according to claim 2 is characterized in that: In step a, the sampling depth L of the surface soil free gas uses the previous test background value of the work area. If there is no previous test background value, the initial sampling depth is 1.00 to 1.5 m.

4. The method for surface geochemical detection of free coalbed methane enriched areas in coal mine goafs according to claim 1, 2 or 3, characterized in that: When designing the sampling grid survey line for the preliminary exploration of the work area on the surface in S1, the sampling grid size can be 50m×50m for the investigation area where the location of the goaf is unclear; for the investigation area where the location of the goaf is clear, the sampling grid size can be designed to be 30m×50m on the surface 20m outside the goaf boundary and 100m inside the goaf boundary, with a spacing of 30m between measuring points for the dip width of the goaf and 50m between measuring points for the strike length of the goaf.

5. The method for surface geochemical detection of free coalbed methane enriched areas in coal mine goafs according to claim 1, 2 or 3, characterized in that: In S1, the background values ​​of soil methane and carbon dioxide concentrations are used to identify concentration anomaly points and divide the initial exploration anomaly areas. The background values ​​of soil methane and carbon dioxide concentrations adopt the background values ​​of previous tests in the area. If there are no previous test background values, the background values ​​are first determined using the methane and carbon dioxide concentrations of the measuring points in the non-mined-out areas, and then the abnormal measuring points of soil methane and carbon dioxide concentrations are determined based on the background values, contour lines and cross-sectional diagrams are drawn, and the initial exploration anomaly areas are delineated.

6. The method for surface geochemical detection of free coalbed methane enriched areas in coal mine goafs according to claim 1, 2 or 3, characterized in that: According to the location of the goaf, the work area is clearly defined. In S3, on the surface, 20m outside the goaf boundary and 100m inside the goaf boundary, around the initial exploration abnormal area, the method of intensified and extended point distribution is adopted. The interval between measuring points is 10m for the goaf dip width and 50m for the goaf strike length, and the re-exploration sampling points are set according to the grid line size of 10×50m. After obtaining the concentrations of methane, carbon dioxide, ethane, and hydrogen sulfide at the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane, and hydrogen sulfide are determined respectively, and the contour lines and cross-section diagrams of the four monitored gases are drawn to divide the gas concentration abnormal area and delineate the free coalbed methane enrichment area in the goaf. For the work area where the location of the goaf is unclear, in S3, the method of encrypted and extended point distribution is adopted around the initial exploration abnormal area, and re-exploration sampling points are set according to the grid survey line size of 50×50m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the re-exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the second exploration abnormal area is divided; in the second exploration abnormal area, the method of encrypted and extended point distribution is adopted, and the third exploration sampling points are set according to 10×25m. After obtaining the concentrations of methane, carbon dioxide, ethane and hydrogen sulfide at the third exploration sampling points according to the optimal monitoring depth L0, the background values ​​and concentration abnormal points of methane, carbon dioxide, ethane and hydrogen sulfide are determined respectively, and the contour lines and cross-sectional diagrams of the four monitoring gases are drawn, and the gas concentration abnormal area is divided, and the free coalbed methane enrichment area in the goaf is delineated.

Images