A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas

Abstract

The present invention discloses a soil free gas emission flux monitoring system for coalbed methane micro-leakage in goaf areas, wherein a goaf area overlying stratum simulation system in the system is used for the goaf area overlying stratum simulation system; a goaf area coalbed methane O-shaped gas source simulation and control system in the system is used for simulating goaf area free coalbed methane and providing a gas source and controlling the gas source pressure, component concentration, and storage position; a soil layer micro-leakage gas emission flux test sampling and testing device in the system is used for collecting gas samples of micro-leakage to the surface soil, so as to facilitate testing of soil free gas component concentration and emission flux; the system can simulate the micro-leakage of coalbed methane in underground coal goaf areas under different gas pressures, methane concentrations, storage space positions, etc. indoors, and sample and test the surface soil free gas methane, carbon dioxide concentrations and emission flux.

Description

Technical Field

[0001] The invention relates to the field of soil free gas emission flux monitoring of coal bed methane micro-leakage in goaf areas, and in particular to a soil free gas emission flux monitoring system of coal bed methane micro-leakage in goaf areas. Background Art

[0002] There are micro-seepage phenomena of methane or light hydrocarbons on the solid earth surface. For example, most of the known oil and gas reservoirs at home and abroad have micro-seepage of light hydrocarbons near the surface. Geochemical exploration of oil and gas is to use the micro-seepage of light hydrocarbons in underground oil and gas reservoirs to form geochemical anomalies near the surface, and to delineate and identify underground oil and gas reservoirs. Micro-seepage of coalbed methane in underground coal mine goafs has been found on the surface of coal mining areas in Poland, the Czech Republic and other places. This kind of micro-seepage of coalbed methane can also form geochemical anomalies in the surface soil, including abnormal concentrations and emission fluxes of free methane and carbon dioxide in the soil. However, the micro-seepage of coalbed methane in underground goafs formed in domestic underground coal mines has not yet received attention from academia and industry, and relevant reports on micro-seepage of coalbed methane in underground goafs have not been seen in public reports.

[0003] After the formation of the goaf, a caving zone, (fracture) fissure zone, and curved subsidence zone will be formed vertically in the overlying strata, and a mining fissure O-ring will be formed on the plane. The free coalbed methane desorbed by mining unloading is enriched in the mining fissure O-ring on the plane. Some component molecules of the coalbed methane enriched in the underground mining fissure O-ring migrate to the surface relatively quickly through the overlying rock strata in the form of colloidal-sized microbubbles. Such microbubbles pass through the overlying coal and rock strata and aquifers in the goaf in a nearly vertical manner, i.e., microseepage. The microseepage gas will form geochemical anomalies such as free gas components and free gas emission flux in the surface soil. The location and abnormal indicators of geochemical anomalies in the surface soil are closely related to the occurrence characteristics of coalbed methane in the goaf. However, there is currently no relevant indoor experimental equipment that can simulate the occurrence form of coalbed methane in the goaf (such as gas pressure, methane concentration, and occurrence space location) and analyze the response relationship between the occurrence characteristics of coalbed methane in the goaf and geochemical anomalies such as free gas components and displacement flux in the surface soil under the condition of micro-leakage of coalbed methane in the goaf. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a soil free gas emission flux monitoring system for coalbed methane micro-leakage in goaf areas, which can simulate the micro-leakage of coalbed methane in underground coal goaf areas under different gas pressures, methane concentrations, storage space positions and other conditions indoors, and sample and test the surface soil free gas methane, carbon dioxide concentrations and emission fluxes.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas, which is used for simulating the micro-leakage process of coal bed methane in underground goaf areas passing through overlying strata to near-surface soil layers and sampling and analyzing micro-leakage gas in surface soil layers, including a goaf overlying strata simulation system, a goaf coal bed methane O-shaped gas source simulation and control system, and a soil layer micro-leakage gas emission flux test sampling device;

[0007] The goaf overlying stratum simulation system is used to simulate the overlying stratum of the goaf, and comprises a stratum simulation chamber and a simulated stratum, wherein the simulated stratum is filled in the stratum simulation chamber;

[0008] The goaf coalbed methane O-shaped gas source simulation and control system is used to simulate free coalbed methane in the goaf, provide gas source and control gas source pressure, component concentration and storage location, and includes an O-shaped simulated fracture ring and a gas source control device. The O-shaped simulated fracture ring is placed at the bottom of the simulated formation, and the gas source control device is located outside the formation simulation chamber and is connected to the O-shaped simulated fracture ring through a pipeline.

[0009] The soil layer micro-leakage gas emission flux test sampling device is placed on the top of the simulated stratum to collect gas samples that micro-leak to the surface soil, so as to facilitate testing of soil free gas component concentration and emission flux.

[0010] Preferably, the simulated strata are filled in sequence from bottom to top in a columnar shape with reference to the overlying strata of the goaf, and are filled with simulated rock strata, simulated coal seams and soil layers in sequence from bottom to top.

[0011] Preferably, the soil layer micro-leakage gas emission flux test sampling device includes a plurality of test cavities, the bottom of the test cavity is opened and placed in a simulated stratum, the top of the test cavity is provided with an air outlet and a detachable sealing rubber plug, and the air outlet is used for a gas collector to collect gas.

[0012] Preferably, the formation simulation chamber is a cubic structure, the bottom surface and four side surfaces and the connected side surfaces are all sealed, the top of the formation simulation chamber is open, and in order to prevent gas from escaping from the gap between the simulated formation and the formation simulation chamber, a colloid sealing layer is coated around the simulated formation and the formation simulation chamber, and the soil layer on the top of the simulated formation is open.

[0013] Preferably, the simulated rock strata and simulated coal seams in the simulated strata are based on similarity principles, refer to the physical properties of the overlying rock strata and coal seams in the goaf and are made of similar materials. The materials for making the skeleton in the simulated rock strata include quartz sand, barite, and pumice powder, and the binders are hydrated gypsum and sodium silicate; the materials for making the skeleton in the simulated coal seams include coal powder and sand, and the binder is gypsum.

[0014] Preferably, the gas source control device includes a gas cylinder, and the outlet of the gas cylinder is connected to the switch valve, the pressure constant valve, the first pressure gauge, the gas storage valve, the gas storage bin, the gas sample collection controller, the second pressure gauge, the air intake valve, and the O-shaped simulated crack ring in sequence through a pipeline.

[0015] Preferably, the O-shaped simulated crack ring includes a cross rod and a hollow annular pipeline, the four ends of the cross rod are respectively fixed to the four sides of the annular pipeline to form a field shape, and the annular pipeline is provided with a plurality of air outlet sieve holes connected to its inner cavity, and the inner cavity of the annular pipeline is connected to the gas cylinder in the gas source control device through a pipeline.

[0016] The present invention also provides a monitoring method of the soil free gas emission flux monitoring system for the coal bed methane micro-leakage in the goaf area, comprising the following steps:

[0017] S1. Prepare the gas source of coal-bed methane in the goaf of coal mines according to its gas composition and concentration, and pour it into the gas cylinder;

[0018] S2. Use gas cylinders to complete the gas filling of the gas storage bin, and the injection pressure is the actual coal mine goaf coalbed methane gas pressure;

[0019] S3. After the gas storage bin is filled with gas, the gas storage valve is closed, the air inlet valve is opened, and the gas flows into the O-shaped simulated crack ring;

[0020] S4. When the pressure of the second pressure gauge drops by 0.1 MPa, multiple test cavities are arranged on the soil layer, and the sampling points cover the soil layer;

[0021] S5. Place the test cavity with the sealing rubber plug removed 10-30 mm below the surface of the soil layer to allow gas to flow into the test cavity;

[0022] S6. After 3-5 minutes, the test cavity is sealed with a sealing rubber plug, and a gas collector is passed through the sealing rubber plug and extended into the test cavity to collect gas samples;

[0023] S7. At predetermined time intervals, use a gas collector to extract gas samples from the test chamber into a gas sample bottle, use a gas chromatograph to determine the gas composition and concentration in the sample, obtain a curve of gas concentration changing with sampling time, and calculate the gas composition and emission flux.

[0024] Preferably, the time interval in step S7 is set to 0 min, 2 min, 4 min, 8 min, 10 min and so on.

[0025] The beneficial effects of the present invention are:

[0026] (1) The overlying strata simulation system of the goaf in the present invention provides geological conditions for coalbed methane micro-leakage in the goaf by setting up simulated strata in the strata simulation chamber, thereby realizing the construction of the overlying geological model of the goaf;

[0027] (2) The O-shaped gas source simulation and control system of the goaf coalbed methane in the present invention simulates the key goaf coalbed methane storage conditions such as gas pressure, component concentration, storage location, etc., and provides controllable and monitorable experimental conditions;

[0028] (3) The soil layer micro-leakage gas emission flux test sampling device of the present invention can obtain soil layer gas samples at different plane positions and at different times from the micro-leakage of coalbed methane to the surface in the goaf, so as to test and analyze the emission flux and free gas component concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A schematic diagram of the structure of a soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the structure of an O-shaped simulated crack ring provided by an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of the installation of a test chamber provided in an embodiment of the present invention.

[0033] Description of reference numerals:

[0034] 1. Gas cylinder; 2. Switch valve; 3. Pressure constant valve; 4. First pressure gauge; 5. Pipeline; 6. Gas storage valve; 7. Gas storage chamber; 8. Gas sample collection controller; 9. Second pressure gauge; 10. Inlet valve; 11. O-shaped simulated fracture ring; 12. Formation simulation chamber; 13. Simulated rock formation; 14. Simulated coal seam; 15. Soil layer; 16. Test cavity; 17. Sealing rubber plug; 18. Gas collector; 19. Gas outlet sieve hole; 20. Cross rod. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] like Figures 1 to 3 As shown, a soil free gas emission flux monitoring system for coalbed methane micro-leakage in goaf areas is used to simulate the micro-leakage process of coalbed methane in underground goaf areas passing through the overlying strata to the near-surface soil layer and sample and analyze the micro-leakage gas in the surface soil layer.

[0037] Before assembling the system, we first obtain experimental background information, such as the columnar structure of the overlying strata in a coal mine goaf, the physical properties of the main rock strata (such as lithology, rock mechanical properties, pore parameters, etc.), the coalbed methane gas pressure in the goaf, the gas component concentration, etc., and collect soil samples near the surface of the overlying goaf;

[0038] The system includes a simulation system for overlying strata in goaf areas, a simulation and control system for coalbed methane O-shaped gas sources in goaf areas, and a sampling device for testing the emission flux of micro-leakage gas in the soil layer.

[0039] The goaf overlying stratum simulation system is used to simulate the overlying stratum of the goaf, and comprises a stratum simulation chamber 12 and a simulated stratum, wherein the simulated stratum is filled in the stratum simulation chamber;

[0040] The simulated strata are filled in sequence from bottom to top in a columnar shape with reference to the overlying strata of the goaf, and are filled with simulated rock strata 13, simulated coal seams 14, and soil layers 15 in sequence from bottom to top.

[0041] The total thickness of the simulated stratum is 1.4 m, and the thickness of the soil layer 15 is 0.4 m; the soil layer 15 in the simulated stratum is filled with the near-surface soil collected from the coal mine goaf.

[0042] The simulated rock layer 13 and the simulated coal seam 14 in the simulated stratum are made based on the principle of similarity, with reference to the physical properties of the overlying rock layer and coal seam in the goaf and using similar materials. The materials for making the skeleton in the simulated rock layer 13 include quartz sand, barite, and pumice powder, and the binder is hydrated gypsum and sodium silicate; the materials for making the skeleton in the simulated coal seam 14 include coal powder and sand, and the binder is gypsum.

[0043] The formation simulation chamber is a cubic structure, and its bottom surface and four side surfaces and the connected side surfaces are all sealed. The top of the formation simulation chamber 12 is open. In order to prevent gas from escaping from the gap between the simulated formation and the formation simulation chamber 12, a colloid sealing layer is coated around the simulated formation and between the formation simulation chamber 12. The soil layer 15 on the top of the simulated formation is open.

[0044] The goaf coalbed methane O-shaped gas source simulation and control system is used to simulate free coalbed methane in the goaf, provide gas source and control gas source pressure, component concentration and storage location, and includes an O-shaped simulated fracture ring 11 and a gas source control device. The O-shaped simulated fracture ring 11 is placed at the bottom of the simulated formation, and the gas source control device is located outside the formation simulation chamber 12 and is connected to the O-shaped simulated fracture ring 11 through a pipeline.

[0045] The soil layer micro-leakage gas emission flux test sampling device is placed on the top of the simulated stratum to collect gas samples that micro-leak to the surface soil, so as to facilitate testing of soil free gas component concentration and emission flux.

[0046] The soil layer micro-leakage gas emission flux test sampling device includes a plurality of test cavities 16, each of which has a diameter of 50 mm. The bottom of the test cavity 16 is open and placed in a simulated stratum. The top of the test cavity 16 is provided with an air outlet and a detachable sealing plug 17. The air outlet is used for a gas collector 18 to collect gas.

[0047] The gas source control device includes a gas cylinder 1, and the outlet of the gas cylinder 1 is connected to the switch valve 2, the pressure constant valve 3, the first pressure gauge 4, the gas storage valve 6, the gas storage bin 7, the gas sample collection controller 8, the second pressure gauge 9, the air intake valve 10, and the O-shaped simulated crack ring 11 in sequence through the pipeline 5.

[0048] The gas storage bin 7 is a high-pressure resistant sealed gas bin, which is used to provide a stable gas source of fixed volume under different pressures, and is combined with the second pressure gauge 9 to monitor the gas pressure change caused by the escape of coalbed methane in the goaf;

[0049] The O-shaped simulated crack ring 11 includes a cross rod 20 and a hollow annular pipeline. The four ends of the cross rod 20 are respectively fixed to the four sides of the annular pipeline to form a field shape. The annular pipeline is provided with a plurality of air outlet sieve holes 19 connected to its inner cavity. The inner cavity of the annular pipeline is connected to the gas cylinder 1 in the gas source control device through the pipeline 5.

[0050] The O-shaped simulated fracture ring 11 in this embodiment has a size of 50×50 cm, and the annular pipeline of the O-shaped simulated fracture ring 11 is arranged with 12 gas outlet sieve holes, and the diameter of each gas outlet sieve hole is 2.0 cm. The O-shaped simulated fracture ring 11 is placed in the lower part of the simulated formation, 10 cm away from the bottom of the formation simulation chamber 12. The O-shaped simulated fracture ring 11 is used to simulate the mining fracture O-ring, and after ventilation, a free coalbed methane enrichment area in the simulated goaf is formed.

[0051] The present invention also provides a monitoring method of the soil free gas emission flux monitoring system for the coal bed methane micro-leakage in the goaf area, comprising the following steps:

[0052] S1. Prepare the coal-bed methane source in the goaf area of ​​the coal mine with reference to its gas composition and concentration, and inject it into gas cylinder 1;

[0053] S2, using gas cylinder 1 to complete the gas filling of gas storage bin 7, the injection pressure is the actual coal mine goaf coal bed methane gas pressure;

[0054] S3, after the gas storage bin 7 is filled with gas, the gas storage valve 6 is closed, the air inlet valve 10 is opened, and the gas flows into the O-shaped simulated crack ring 11;

[0055] S4. When the pressure of the second pressure gauge 9 drops by 0.1 MPa, a plurality of test cavities 16 are arranged on the soil layer 15, and the sampling points cover the soil layer 15;

[0056] S5, placing the test cavity 16 with the sealing rubber plug 17 removed 10-30 mm below the surface of the soil layer 15, so that gas can flow into the test cavity 16;

[0057] S6. After 3-5 minutes, the test cavity 16 is sealed with a sealing rubber plug 17, and a gas collector 18 is passed through the sealing rubber plug 17 and extends into the test cavity 16 to collect gas samples;

[0058] S7. At predetermined time intervals, use the gas collector 18 to extract gas samples from the test chamber 16 into a gas sample bottle, use a gas chromatograph to measure the gas components and concentrations in the sample, such as CH4 and CO2, obtain a curve of gas concentration changing with sampling time, and calculate the emission flux of gas components such as CH4 and CO2.

[0059] In step S7, the time intervals are set to 0 min, 2 min, 4 min, 8 min, 10 min and so on.

[0060] The present invention realizes a true simulation of the geological body overlying the goaf of a coal mine. The goaf coalbed methane O-shaped gas source simulation and control system simulates the key goaf coalbed methane occurrence states such as gas pressure, component concentration, and occurrence position, and provides controllable and monitorable experimental conditions; the soil layer micro-leakage gas emission flux test sampling device can collect the soil layer gas at different plane positions and different times from the goaf coalbed methane micro-leakage to the surface, so as to test and analyze the gas emission flux and free gas component concentration. The present invention can analyze the occurrence characteristics of goaf coalbed methane (such as gas pressure, methane concentration, occurrence space position) and the response relationship between the surface soil geochemical anomalies under the condition of goaf coalbed methane micro-leakage.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A soil free gas emission flux monitoring system for coalbed methane micro-leakage in goaf areas, used for simulating the micro-leakage process of coalbed methane in underground goaf areas passing through the overlying strata to the near-surface soil layer and sampling and analyzing the micro-leakage gas in the surface soil layer, Features: It includes the overlying strata simulation system of the goaf, the O-shaped gas source simulation and control system of the goaf coalbed methane, and the soil layer micro-leakage gas emission flux test sampling device; The goaf overlying stratum simulation system is used to simulate the stratum overlying the goaf, and comprises a stratum simulation chamber (12) and a simulated stratum, wherein the simulated stratum is filled in the stratum simulation chamber; The goaf coalbed methane O-shaped gas source simulation and control system is used to simulate free coalbed methane in the goaf, provide a gas source, and control the gas source pressure, component concentration, and storage location. It includes an O-shaped simulated fracture ring (11) and a gas source control device. The O-shaped simulated fracture ring (11) is placed at the bottom of the simulated formation. The gas source control device is located outside the formation simulation chamber (12) and is connected to the O-shaped simulated fracture ring (11) through a pipeline. The soil layer micro-leakage gas emission flux test sampling device is placed on the top of the simulated stratum to collect gas samples that micro-leak to the surface soil, so as to facilitate testing of soil free gas component concentration and emission flux.

2. A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas as claimed in claim 1, Features: The simulated strata are filled in sequence from bottom to top in a columnar shape with reference to the overlying strata of the goaf, and are filled in sequence from bottom to top with simulated rock strata (13), simulated coal seams (14), and soil layers (15).

3. A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas as claimed in claim 2, Features: The soil layer micro-leakage gas emission flux test sampling device comprises a plurality of test cavities (16), wherein the bottom of the test cavity (16) is open and is placed in a simulated stratum, and the top of the test cavity (16) is provided with an air outlet and a detachable sealing rubber plug (17), wherein the air outlet is used for a gas collector (18) to collect gas.

4. A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas as claimed in claim 1, Features: The formation simulation chamber is a cubic structure, and its bottom surface and four side surfaces and the connected side surfaces are sealed. The top of the formation simulation chamber (12) is open. In order to prevent gas from escaping from the gap between the simulated formation and the formation simulation chamber (12), a colloid sealing layer is coated around the simulated formation and between the formation simulation chamber (12). The soil layer (15) on the top of the simulated formation is open.

5. The soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf area as claimed in claim 1, Features: The simulated rock layer (13) and the simulated coal seam (14) in the simulated stratum are made based on the principle of similarity, with reference to the physical properties of the rock layer and coal seam overlying the goaf and using similar materials. The materials for making the skeleton in the simulated rock layer (13) include quartz sand, barite, and pumice powder, and the binder is hydrated gypsum and sodium silicate; the materials for making the skeleton in the simulated coal seam (14) include coal powder and sand, and the binder is gypsum.

6. A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas as claimed in claim 3, Features: The gas source control device comprises a gas cylinder (1), wherein the outlet of the gas cylinder (1) is connected in sequence to a switch valve (2), a pressure constant valve (3), a first pressure gauge (4), a gas storage valve (6), a gas storage bin (7), a gas sample collection controller (8), a second pressure gauge (9), an air inlet valve (10), and an O-shaped simulated crack ring (11) via a pipeline (5).

7. A soil free gas emission flux monitoring system for coal bed methane micro-leakage in goaf areas as claimed in claim 1, Features: The O-shaped simulated crack ring (11) comprises a cross rod (20) and a hollow annular pipeline, wherein the four ends of the cross rod (20) are respectively fixed to the four sides of the annular pipeline to form a field shape, and the annular pipeline is provided with a plurality of air outlet sieve holes (19) connected to its inner cavity, and the inner cavity of the annular pipeline is connected to the gas cylinder (1) in the gas source control device through a pipeline (5).

8. A method for monitoring the soil free gas emission flux monitoring system of coal bed methane micro-leakage in goaf areas as claimed in claim 6, It is characterized in that The following steps are involved: S1. Prepare the coal-bed methane source in the goaf of the coal mine with reference to its gas composition and concentration, and inject it into the gas cylinder (1); S2. Using the gas cylinder (1), the gas storage bin (7) is filled with gas, and the injection pressure is the actual coal bed methane gas pressure in the coal mine goaf; S3, after the gas storage bin (7) is filled with gas, the gas storage valve (6) is closed, the gas inlet valve (10) is opened, and the gas flows into the O-shaped simulated crack ring (11); S4. When the pressure of the second pressure gauge (9) decreases by 0.1 MPa, a plurality of test cavities (16) are arranged on the soil layer (15), and the sampling points cover the soil layer (15); S5, placing the test cavity (16) with the sealing rubber plug (17) removed 10-30 mm below the surface of the soil layer (15) to allow gas to flow into the test cavity (16); S6. After 3-5 minutes, the test cavity (16) is sealed with a sealing rubber plug (17), and a gas collector (18) is passed through the sealing rubber plug (17) and extended into the interior of the test cavity (16) to collect gas samples; S7. At predetermined time intervals, a gas sample is extracted from the test chamber (16) into a gas sample bottle using a gas collector (18), and the gas composition and concentration in the sample are determined using a gas chromatograph to obtain a curve of the change of gas concentration with sampling time, and the gas composition and emission flux are calculated.

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