Simulation experiment system and method for gas desorption dynamic behavior of closed water-flooded coal seam of coal mine

Abstract

The invention belongs to the technical field of closed coal mine water-flooded coal seam simulation experiments, and provides a closed coal mine water-flooded coal seam gas desorption dynamic behavior simulation experiment system and method.The experiment system comprises an experiment cavity, a stress loading device, a methane supply module, a water injection module, a gas desorption testing device, a monitoring unit and a control system; the concentration and flow of desorbed gas are monitored by the gas desorption testing device, the monitoring unit comprises a pressure sensor, a water level sensor and a humidity sensor array, and the humidity sensor array is used for monitoring the humidity degree of the surface of the coal sample. According to the experimental system capable of simulating the gas desorption in the water logging process of the gas-containing coal seam under the background that the coal mine is closed, the condition of the gas desorption under the water logging condition of the coal seam can be more truly restored, the gas desorption rule in the water logging process is accurately simulated in an experiment, effective data support is provided, and the experiment efficiency is improved. Therefore, a scientific basis is provided for gas emission management and safety monitoring after the coal mine is closed.

Description

Technical Field

[0001] The invention belongs to the technical field of simulation experiments on water-flooded coal seams in closed coal mines, and in particular relates to a simulation experiment system and method for dynamic behavior of gas desorption in water-flooded coal seams in closed coal mines. Background Art

[0002] A closed coal mine refers to a coal mine that has been closed and abandoned due to depletion of coal resources, non-compliance with safe mining conditions or policies, etc. After the closure of a coal mine, under the influence of groundwater levels, surface rainfall, etc., the mine water gradually floods the coal seam. The closure of a coal mine causes the underground coal seam to be flooded with accumulated water, forming a complex water pressure environment. During this process, the gas desorption behavior inside the coal body is of great significance to the safety of the closed coal mine. In the prior art, although there have been certain studies on the gas desorption problem of flooded coal seams, there is a lack of experimental equipment that can truly simulate the gas desorption process of flooded coal seams.

[0003] After searching, no similar technical solution to the present invention has been disclosed. Summary of the invention

[0004] The present invention aims to solve the technical problems existing in the prior art. The first purpose of the present invention is to provide an experimental system for simulating the dynamic behavior of gas desorption in flooded coal seams in a closed coal mine. The second purpose of the present invention is to provide an experimental method based on the aforementioned experimental system.

[0005] To achieve the above-mentioned first purpose, the present invention adopts the following technical scheme: a closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system, including an experimental chamber, a methane gas supply module, a water injection module, a gas desorption test device, a monitoring unit and a control system; a clamp for fixing the coal sample is installed in the experimental chamber, and the clamp is connected to a stress loading device for applying ground stress to the coal sample; the methane gas supply module is connected to the gas injection port of the experimental chamber, and is used to inject methane gas into the experimental chamber so that the coal sample can adsorb methane gas; the water injection module is connected to the water injection port of the experimental chamber, and is used to inject water into the experimental chamber to submerge the coal sample, and the enabling end of the water injection module is connected to the control system; the gas desorption test device is connected to the sampling port of the experimental chamber, and the separation unit is connected to the sampling port of the experimental chamber. The methane gas after water vapor enters the gas desorption test device, and the gas desorption test device monitors the concentration and flow of the desorbed gas. The signal output end of the gas desorption test device is connected to the control system; the monitoring unit includes a pressure sensor arranged in the experimental cavity, a water level sensor arranged in the experimental cavity for monitoring water level changes, and a plurality of humidity sensors arranged on the outer wall of the coal sample and distributed along its height and circumference. The signal output end of the pressure sensor is connected to the pressure input end of the control system, the signal output end of the water level sensor is connected to the control system, and a plurality of humidity sensors form a humidity sensor array. The humidity sensor array is used to monitor the wetness of the coal sample surface, and the signal output end of the humidity sensor array is connected to the humidity input end of the control system.

[0006] The above technical scheme applies axial stress to the coal sample through the stress loading device to truly simulate the ground stress of the coal seam in the closed coal mine; injects methane gas into the experimental cavity by setting up a methane gas supply module so that the coal sample adsorbs methane gas; injects water into the experimental cavity through the water injection module to simulate the flooded coal seam in the closed coal mine; sets up a gas desorption test device to monitor the changes in gas concentration and flow rate during the desorption process and transmits them to the control system; monitors the water level of the experimental cavity, the water pressure in the experimental cavity and the wetness of the coal sample surface through the sensors of the monitoring unit, and transmits them to the control system. Using the data analysis algorithm, a dynamic correlation model of water level-water pressure-gas desorption amount-humidity is established, and a curve is generated in real time.

[0007] The present invention provides an experimental system which can simulate the gas desorption during the flooding of gas-containing coal seams under the background of coal mine closure. The experimental system can more realistically restore the gas desorption situation under the condition of coal seam flooding, accurately simulate the gas desorption law during the flooding process in the experiment, and provide effective data support, thereby providing a scientific basis for gas emission management and safety monitoring after the closure of the coal mine.

[0008] In a preferred embodiment of the present invention, the water injection port includes a bottom water injection port arranged at the bottom of the experimental cavity, the position of the bottom water injection port is lower than the bottom of the coal sample, and the water injection module has a water injection valve for controlling the opening and closing of each water injection port.

[0009] The above technical solution simulates the flooded coal seam by setting a bottom water injection port and adopting a bottom single-point water injection method.

[0010] In a preferred embodiment of the present invention, the bottom of the experimental chamber has a water injection buffer zone located below the coal sample, a water injection buffer baffle is provided in the water injection buffer zone, a plurality of water holes are provided on the water injection buffer baffle, and the water discharged from the bottom water injection port passes through the water injection buffer baffle and enters the experimental chamber above it.

[0011] In the above technical solution, during the process of water injection from the bottom water injection port, the water injection buffer baffle will directly migrate the methane gas caused by water injection upward, thereby minimizing the impact of high methane concentration at the top, making the experimental results more accurate.

[0012] In a preferred embodiment of the present invention, the water injection port further comprises a plurality of side water injection ports spaced apart along the height direction of the experimental chamber, and the water injection module comprises a water injection valve for controlling the opening and closing of each water injection port.

[0013] The above technical scheme, by adding multiple side water injection ports, can not only use bottom single-point water injection, but also carry out layer-by-layer water injection, simulating the infiltration of fissure water in closed mines and the inflow of mine water near the goaf; comparing the gas desorption behavior of layer-by-layer water injection and bottom single-point water injection, analyzing the impact of layer-by-layer water injection on the wettability of the coal body and the gas desorption behavior, and evaluating the effect of layer-by-layer water injection on the coal seam gas emission efficiency.

[0014] In a preferred embodiment of the present invention, a plurality of water level sensors corresponding to a plurality of water injection ports are provided at intervals along the height direction in the experimental chamber, the water level sensors are positioned higher than the corresponding water injection ports, the uppermost water level sensor is positioned higher than the top of the coal sample, and the control system controls the closing of the water injection valve of the corresponding water injection port according to the signal of the water level sensor.

[0015] In the above technical scheme, the water level sensor is linked with the water injection valve of the water injection port. When studying the influence of layer-by-layer water injection on gas adsorption and desorption, when the water level reaches the water level sensor, the water injection valve will be linked to close the corresponding water injection port. After keeping stable for a period of time, the water injection valve of the next water injection port will be linked to open to inject water into the experimental chamber, thereby realizing automatic step-by-step water injection.

[0016] To achieve the above second purpose, the present invention adopts the following technical solution: an experimental method for closing a coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system, comprising the following steps:

[0017] S1. Coal sample preparation: select a standard coal column as a coal sample, put it into a drying box to dry it, ensure that the coal sample is completely dry, install the coal sample into the holder of the experimental cavity, apply axial stress to the coal sample through a stress loading device, and attach the humidity sensor array to the surface of the coal sample;

[0018] S2, gas adsorption of coal samples: methane gas is injected into the experimental chamber through the methane gas supply module, and a static pressure of a set value is applied for a period of time to make the coal sample reach a saturated state of gas adsorption, and the gas supply of the methane gas supply module is closed to complete the gas adsorption of the coal sample;

[0019] S3. Inject water into the experimental cavity: open the water injection port, slowly inject water into the experimental cavity until the water level rises to the first layer monitoring point, keep stable for a period of time, continue to inject water to the second layer monitoring point, repeat the stabilization process, continue to inject water layer by layer, until the water completely submerges the coal sample, and keep stable for a period of time;

[0020] S4, gas desorption: After the gas adsorption of the coal sample is completed, the valve of the sampling port is opened to introduce the methane gas desorbed from the coal sample into the gas desorption test device;

[0021] S5. Data collection: Use a water level sensor to collect water level changes in the experimental chamber and generate water level rise rate data; use a humidity sensor array to collect real-time changes in the wetness of the coal sample surface and record the coal body infiltration and expansion rate; use a gas desorption test device to monitor the concentration and flow of desorbed gas, and generate a gas desorption rate curve based on time; use a pressure sensor to monitor the internal pressure of the experimental chamber in real time, and during the gas desorption process, record the impact of pressure changes on desorption behavior;

[0022] S6. Data analysis and processing: including water flooding dynamic simulation analysis, wet diffusion dynamic analysis and gas desorption behavior modeling;

[0023] Dynamic simulation analysis of flooding: Calculate the rising rate curve of water level in the experimental chamber over time based on the water level sensor data; Establish a water pressure-water level dynamic model in the experimental chamber to evaluate the response characteristics of gas desorption under different water pressure conditions;

[0024] Dynamic analysis of wetting diffusion: Map the distribution data of the humidity sensor array to the surface of the coal sample to generate a three-dimensional wetting expansion map; calculate the relationship between the water absorption rate and the wetting depth of the coal sample through curve fitting; analyze the hysteresis effect of the wetting process inside the coal body on the gas desorption rate;

[0025] Gas desorption behavior modeling: Combine gas concentration and flow data to generate a desorption volume-time curve, which is a gas desorption rate curve; divide the desorption stages according to the water level changes in the experimental chamber during the experiment; fit the relationship between the desorption rate and the water pressure and the wetness of the coal sample surface to establish a desorption kinetic model;

[0026] S7. Result output: Output the experimental report based on data analysis and processing.

[0027] In another preferred embodiment of the present invention, n pressure sensors are arranged at intervals along the height direction of the test cavity, and all pressure sensors can be submerged in water. The water pressure P in the test cavity is obtained by the following method. avg :

[0028]

[0029] Where n is the number of pressure sensors and Pi is the detection value of the i-th sensor.

[0030] In the above technical solution, multiple pressure sensors are arranged in the height direction to monitor the water pressure, and the average value of the detection values ​​of the multiple pressure sensors is calculated to obtain the water pressure in the experimental cavity, so that the result is more accurate.

[0031] In another preferred embodiment of the present invention, in step S3, the water injection method includes two types: bottom single-point water injection and layer-by-layer water injection; wherein, bottom single-point water injection is to inject water into the experimental chamber only through the bottom water injection port; layer-by-layer water injection is to first inject water into the experimental chamber through the bottom water injection port until the water level rises to the first-layer monitoring point, keep stable for a period of time, and then continue to inject water to the second-layer monitoring point through the side water injection port corresponding to the height position of the first-layer monitoring point, repeat the stabilization process, and then continue to inject water to the third-layer monitoring point through the side water injection port corresponding to the height position of the second-layer monitoring point, repeat the stabilization process, continue to inject water layer by layer, until the water completely submerges the coal sample, and keep stable for a period of time; compare the gas desorption behavior of layer-by-layer water injection and bottom single-point water injection, analyze the influence of layer-by-layer water injection on the wetness of the coal body and the gas desorption behavior, and evaluate the effect of layer-by-layer water injection on the coal seam gas emission efficiency.

[0032] In another preferred embodiment of the present invention, during the data analysis and processing, multivariate regression analysis is used to couple the gas desorption amount with the water level rise rate, the wetting expansion rate, and the water pressure, and to establish a dynamic correlation model of "water level-water pressure-wetting-desorption"; the influence of different water injection rates on the gas desorption amount is analyzed to form a comparison chart.

[0033] In another preferred embodiment of the present invention, the wetting extension rate is obtained in the following manner:

[0034] W(t)=W0·(1-e -αt )

[0035] Among them, W (t) is the moisture content at time t, W0 is the final saturated moisture content, α is the fitting constant, and t is the time.

[0036] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0038] Figure 1 It is a structural schematic diagram of a closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system of the first embodiment.

[0039] Figure 2 It is a top view schematic diagram of arranging sensors in the experimental chamber.

[0040] Figure 3 It is a top view schematic diagram of the water injection buffer partition in the first embodiment.

[0041] The figure marks in the drawings of the specification include: experimental chamber 10, water injection port 10a, upper cover 11, water injection buffer zone 12, water injection buffer baffle 13, water hole 131, methane gas supply module 20, high-pressure gas cylinder 21, pressure reducing valve 22, gas injection pipe 23, gas injection valve 24, water injection module 30, water injection control system 31, water injection pipe 32, water injection valve 33, pressure gauge 34, gas desorption test device 40, sampling tube 41, water vapor separator 42, sampling valve 43, control system 50, stress loading device 60, pressure sensor 71, water level sensor 72, humidity sensor 73, coal sample A. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0043] In the description of the present invention, it is to be understood that the terms “longitudinal”, “lateral”, “vertical”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside” and “outside” etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0044] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0045] Embodiment 1

[0046] This embodiment provides a closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system, such as Figure 1As shown, in a preferred embodiment, the experimental system includes an experimental chamber 10, a methane gas supply module 20, a water injection module 30, a gas desorption test device 40, a monitoring unit and a control system 50. Among them, the experimental chamber 10 is a high-strength stainless steel cylinder with a diameter of 15 cm and a height of 30 cm, which is specifically corrosion-resistant and has a pressure resistance of up to 20 MPa. The top of the experimental chamber 10 is detachably connected with a cover for closing its top opening. A clamp for fixing the coal sample A is installed in the experimental chamber 10, and the clamp is connected with a stress loading device 60 for applying ground stress to the coal sample A. The clamp fixes and clamps the coal sample A up and down, and the top pressure is evenly transmitted to the coal sample A through the stress loading device 60 to simulate ground stress.

[0047] The methane gas supply module 20 is connected to the gas injection port at the top of the experimental chamber 10, and is used to inject methane gas into the experimental chamber 10 so that the coal sample A can adsorb the methane gas. Specifically, the methane gas supply module 20 includes a high-pressure gas cylinder 21 filled with methane gas, and the gas outlet of the high-pressure gas cylinder 21 is connected to the gas injection port through a gas injection pipe 23. The gas injection port is provided on the cover, and a pressurizing valve and a gas injection valve 24 are provided on the gas injection pipe 23. The gas injection valve 24 is arranged close to the gas injection port.

[0048] The water injection module 30 is connected to the water injection port 10a of the experimental chamber 10, and is used to inject water into the experimental chamber 10 to submerge the coal sample A. The enabling end of the water injection module 30 is connected to the control system 50. Specifically, the water injection module 30 includes a water injection control system 31, and the water outlet of the water injection control system 31 is connected to the water injection port 10a through a water injection pipe 32. The water injection port 10a is arranged at the bottom and / or the side wall of the experimental chamber 10. The water injection pipe 32 is provided with a pressure gauge 34 and a water injection valve 33. The water injection valve 33 is an electric regulating valve, which is used to adjust the water injection rate and the water injection pressure.

[0049] The gas desorption test device 40 is connected to the sampling port of the experimental chamber 10. The methane gas after water vapor separation enters the gas desorption test device 40 through the sampling port. The gas desorption test device 40 monitors the concentration and flow of the desorbed gas. The signal output end of the gas desorption test device 40 is connected to the control system 50. Among them, the sampling port is arranged on the cover, and the sampling port is connected to the gas desorption test device 40 through the sampling tube 41. The sampling tube 41 is provided with a valve close to the sampling port, and the valve is a one-way flow sampling valve 43. The sampling tube 41 is also provided with a water vapor separator 42. The methane gas after water vapor separation by the water vapor separator 42 enters the gas desorption test device 40. The gas desorption test device 40 is equipped with a gas concentration sensor and a flow meter to record the concentration and flow changes of the desorbed gas in real time.

[0050] The monitoring unit includes a pressure sensor 71 disposed in the experimental cavity 10, a water level sensor 72 disposed in the experimental cavity 10 for monitoring water level changes, and a plurality of humidity sensors 73 disposed on the outer wall of the coal sample A and distributed along its height and circumference. A plurality of pressure sensors 71 are disposed along the height direction of the experimental cavity 10, and the plurality of pressure sensors 71 can be submerged in water. For example, a pressure sensor 71 is disposed near the bottom, middle and top of the coal sample A, respectively. The plurality of pressure sensors 71 can also be disposed at intervals along the circumference of the coal sample, and the signal output end of the pressure sensor 71 is connected to the pressure input end of the control system 50; a plurality of water level sensors 72 are disposed along the height direction of the experimental cavity 10, and the plurality of water level sensors 72 can also be disposed at intervals along the circumference of the coal sample, and the signal output end of the water level sensor 72 is connected to the control system 50; a plurality of humidity sensors 73 form a humidity sensor 73 array (combined with Figure 2 As shown, a plurality of circles of humidity sensors 73 may be arranged along the height direction of the coal sample A, and each circle has a plurality of humidity sensors 73 arranged at circumferential intervals. The humidity sensor 73 array is used to monitor the wetness of the surface of the coal sample A, and the signal output end of the humidity sensor 73 array is connected to the humidity input end of the control system 50.

[0051] like Figure 1 As shown, in one embodiment of the present invention, the water injection port 10a includes a bottom water injection port 10a provided at the bottom of the experimental chamber 10, the bottom water injection port 10a is located lower than the bottom of the coal sample A, and the water injection module 30 has a water injection valve 33 for controlling the opening and closing of each water injection port 10a, thereby enabling single-point water injection at the bottom through the bottom water injection port 10a. Preferably, the bottom of the experimental chamber 10 has a water injection buffer zone 12 located below the coal sample A, and a water injection buffer partition 13 is provided in the water injection buffer zone 12, such as Figure 3 As shown, the water injection buffer baffle 13 is provided with a plurality of water holes 131 , and the water discharged from the bottom water injection port 10 a passes through the water injection buffer baffle 13 and enters the experimental cavity 10 above it.

[0052] In another preferred embodiment, the water injection port 10a also includes a plurality of side water injection ports 10a spaced apart in the height direction of the experimental cavity 10, and a water injection valve 33 for controlling the opening and closing of each water injection port 10a is provided on the water injection pipe 32 of the water injection module 30, and the water injection rate and the water injection pressure are regulated by the water injection valve 33. The bottom water injection port 10a and the side water injection port 10a are arranged in parallel and opened in a selective manner, for example, two side water injection ports 10a are arranged, a total of three water injection ports 10a, from bottom to top, the first water injection port 10a, the second water injection port 10a and the third water injection port 10a, the three water injection ports 10a are arranged equidistantly in the height direction, and water injection can be realized layer by layer to simulate the infiltration of fissure water in a closed mine and the inflow of mine water adjacent to the goaf.

[0053] Further preferably, a plurality of water level sensors 72 corresponding to the plurality of water injection ports 10a are arranged at intervals along the height direction in the experimental cavity 10, the position of the water level sensor 72 is higher than the corresponding water injection port 10a, the position of the top water level sensor 72 is higher than the top of the coal sample A, and the control system 50 controls the closing of the water injection valve 33 of the corresponding water injection port 10a according to the signal of the water level sensor 72. Three water level sensors 72 are arranged corresponding to the three water injection ports 10a, the first water injection port 10a from bottom to top corresponds to the first water level sensor 72 from bottom to top, and so on. When water is injected layer by layer, when the water injected from the first water injection port 10a reaches the first water level sensor 72, if the influence of water injection layer by layer on gas adsorption and desorption is to be studied, then when the water level reaches the first water level sensor 72, the water injection valve 33 will be linked to close the first water injection port 10a, and after being kept stable for 30 minutes, the water injection valve 33 of the second water injection port 10a will be linked to open, and water will be injected into the experimental cavity 10, and so on.

[0054] Embodiment 2

[0055] This embodiment provides an experimental method for simulating the dynamic behavior of gas desorption in a closed coal mine flooded coal seam based on the first embodiment, including the following steps:

[0056] S1. Preparation of coal sample A: Select a standard coal column with a diameter of 5 cm and a height of 10 cm as coal sample A, put it into a drying oven and dry it for 24 hours to ensure that coal sample A is completely dry; install coal sample A into the clamp of the experimental cavity 10, and apply axial stress to coal sample A through the stress loading device 60 to truly simulate the ground stress conditions of the coal seam in the closed coal mine; calibrate the humidity sensor 73, and attach the humidity sensor 73 array to the surface of coal sample A to ensure stable signal output.

[0057] S2. Gas adsorption of coal sample A: methane gas is injected into the experimental chamber 10 through the methane gas supply module 20, and a static pressure of a set value (for example, 2 MPa, detected by the pressure sensor 71 in the experimental chamber 10, and specifically, the average value of the detection values ​​of multiple pressure sensors 71 can be used) is applied for a period of time, such as 12 hours, so that the coal sample A reaches a saturated state of gas adsorption, and then the methane gas supply module 20 is turned off to complete the gas adsorption of coal sample A.

[0058] S3. Inject water into the experimental cavity 10: open the water injection port 10a, slowly inject water into the experimental cavity 10 until the water level rises to the first-layer monitoring point (monitored by the water level sensor 72), and remain stable for a period of time, such as 30 minutes; then continue to inject water to the second-layer monitoring point, repeat the stabilization process (stable for 30 minutes), and continue to inject water layer by layer until the water completely submerges the coal sample A, and remain stable for a period of time (stable for 30 minutes).

[0059] S4. Gas desorption: After the gas adsorption of coal sample A is completed, the sampling valve 43 of the sampling port is opened. The methane gas desorbed from coal sample A is separated from water vapor by the water vapor separator 42 and then introduced into the gas desorption test device 40 through the sampling tube 41. The gas desorption test device 40 monitors the changes in gas concentration and flow rate.

[0060] S5. Data collection: Use the water level sensor 72 to collect the water level changes in the experimental cavity 10, generate water level rise rate data, and generate a real-time change curve; use the humidity sensor 73 array to collect the real-time changes in the wetness of the coal sample A surface, record the coal body infiltration and expansion rate, and generate a real-time change curve; use the gas desorption test device 40 to monitor the concentration and flow rate of the desorbed gas, and generate a gas desorption rate curve based on time; use the pressure sensor 71 to monitor the internal pressure of the experimental cavity 10 in real time, and during the gas desorption process, record the impact of pressure changes on the desorption behavior.

[0061] The data of all sensors are transmitted to the central data processing unit of the control system 50 through the wireless communication module, and the dynamic changes are recorded using a high-frequency sampling rate (such as once per second). The noise signal is removed by using a filtering algorithm (such as Kalman filtering); the outputs (units and ranges) of different sensors are standardized to ensure data consistency; and the multi-parameter data are aligned by time stamps to form a time series.

[0062] S6. Data analysis and processing: including water flooding dynamic simulation analysis, wet diffusion dynamic analysis and gas desorption behavior modeling, as follows:

[0063] Dynamic simulation analysis of flooding: According to the data of the water level sensor 72, the rising rate curve of the water level in the experimental chamber 10 over time is calculated; the water pressure in the experimental chamber 10 (measured by the pressure sensor 71 in the experimental chamber 10) - water level dynamic model is established to evaluate the response characteristics of gas desorption under different water pressure conditions. Specifically, the water pressure P in the experimental chamber can be obtained by the following method avg :

[0064]

[0065] Where n is the number of pressure sensors and Pi is the detection value of the i-th sensor.

[0066] Dynamic analysis of wetting diffusion: Map the array distribution data of humidity sensor 73 to the surface of coal sample A to generate a three-dimensional wetting expansion map; calculate the relationship between the water absorption rate and the wetting depth of coal sample A through curve fitting; analyze the hysteresis effect of the wetting process inside the coal body on the gas desorption rate.

[0067] Modeling of gas desorption behavior: The gas concentration and flow data are combined to generate a desorption amount-time curve, which is a gas desorption rate curve; the desorption stages are divided according to the water level changes in the experimental chamber 10 during the experiment; the Langmuir equation is used to expand the model, fit the relationship between the desorption rate and the water pressure and the surface wetness of the coal sample A, and establish a desorption kinetic model.

[0068] S7. Result output: Output the experimental report based on data analysis and processing.

[0069] In step S3 of the present invention, the water injection method includes two types: bottom single-point water injection and layer-by-layer water injection. Among them, the bottom single-point water injection is to slowly inject water into the experimental cavity 10 only through the bottom water injection port 10a; the layer-by-layer water injection is to first inject water into the experimental cavity 10 through the first water injection port 10a at the bottom until the water level rises to the first layer monitoring point of the first water level sensor 72, and keep stable for 30 minutes, and then continue to inject water through the second water injection port 10a to the second layer monitoring point of the second water level sensor 72, repeat the stabilization process, and then continue to inject water through the third water injection port 10a to the third layer monitoring point of the second water level sensor 72, repeat the stabilization process, and continue to inject water layer by layer until the water completely submerges the coal sample A and keeps stable for a period of time.

[0070] Comparative analysis of layer-by-layer water injection and bottom single-point water injection: Compare the gas desorption behavior of layer-by-layer water injection and bottom single-point water injection, analyze the impact of layer-by-layer water injection on the wettability of the coal body and the gas desorption behavior, and evaluate the effect of layer-by-layer water injection on the gas emission efficiency of coal seams; use statistical significance analysis (such as analysis of variance ANOVA) to verify the differences in desorption rates of different water injection methods.

[0071] In step S6 of the present invention, during the data analysis and processing, multivariate regression analysis is used to couple the gas desorption amount with the water level rise rate, the wetting expansion rate, and the water pressure, to establish a dynamic correlation model of "water level-water pressure-wetting-desorption", and generate a curve in real time; the influence of different water injection rates on the gas desorption amount is analyzed to form a comparison chart.

[0072] In reality, the flooding process of coal seams is usually a dynamic, nonlinear wetting and expansion process. In the experiment, the humidity sensor 73 monitors the wetness of the surface of the coal sample A in real time and provides continuous humidity data. According to the wetness (usually relative humidity or water content) recorded by the humidity sensor 73, the wetting and expansion rate is reflected by fitting the water absorption rate. For example, the wetting and expansion rate is usually fitted using an exponential or linear equation, and the fitting formula is as follows:

[0073] W(t)=W0·(1-e -αt )

[0074] Among them, W (t)is the moisture content at time t, W0 is the final saturated moisture content, α is the fitting constant, and t is the time.

[0075] In the description of this specification, the description with reference to the terms "preferred embodiment", "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0076] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system, characterized in that: It includes an experimental chamber, a methane gas supply module, a water injection module, a gas desorption test device, a monitoring unit and a control system; A holder for fixing the coal sample is installed in the experimental cavity, and the holder is connected to a stress loading device for applying geostress to the coal sample; The methane gas supply module is connected to the gas injection port of the experimental cavity and is used to inject methane gas into the experimental cavity so that the coal sample can absorb the methane gas. The water injection module is connected to the water injection port of the experimental cavity and is used to inject water into the experimental cavity to submerge the coal sample. The enabling end of the water injection module is connected to the control system. The gas desorption test device is connected to the sampling port of the experimental chamber, and the methane gas after the water vapor is separated enters the gas desorption test device. The gas desorption test device monitors the concentration and flow of the desorbed gas, and the signal output end of the gas desorption test device is connected to the control system; The monitoring unit includes a pressure sensor arranged in the experimental cavity, a water level sensor arranged in the experimental cavity for monitoring water level changes, and a plurality of humidity sensors arranged on the outer wall of the coal sample and distributed along its height and circumference. The signal output end of the pressure sensor is connected to the pressure input end of the control system, the signal output end of the water level sensor is connected to the control system, and the plurality of humidity sensors form a humidity sensor array. The humidity sensor array is used to monitor the wetness of the coal sample surface, and the signal output end of the humidity sensor array is connected to the humidity input end of the control system.

2. The closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system according to claim 1 is characterized in that: The water injection port comprises a bottom water injection port arranged at the bottom of the experimental cavity, the position of the bottom water injection port is lower than the bottom of the coal sample, and the water injection module has a water injection valve for controlling the opening and closing of each water injection port.

3. The closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system according to claim 2 is characterized in that: The bottom of the experimental cavity has a water injection buffer zone located below the coal sample, in which a water injection buffer baffle is provided, and the water injection buffer baffle is provided with a plurality of water holes. The water discharged from the bottom water injection port enters the experimental cavity above the water injection buffer baffle after passing through the water injection buffer baffle.

4. The closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system according to claim 2 is characterized in that: The water injection port also includes a plurality of side water injection ports spaced apart along the height direction of the experimental cavity, and the water injection module has a water injection valve for controlling the opening and closing of each water injection port.

5. The closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system according to claim 4 is characterized in that: A plurality of water level sensors corresponding to a plurality of water injection ports are arranged at intervals along the height direction in the experimental cavity. The positions of the water level sensors are higher than the corresponding water injection ports. The position of the top water level sensor is higher than the top of the coal sample. The control system controls the closing of the water injection valve of the corresponding water injection port according to the signal of the water level sensor.

6. An experimental method based on the closed coal mine flooded coal seam gas desorption dynamic behavior simulation experimental system according to any one of claims 1 to 5, characterized in that: The steps include: S1. Coal sample preparation: select a standard coal column as a coal sample, put it into a drying box to dry it, ensure that the coal sample is completely dry, install the coal sample into the holder of the experimental cavity, apply axial stress to the coal sample through a stress loading device, and attach the humidity sensor array to the surface of the coal sample; S2, gas adsorption of coal samples: methane gas is injected into the experimental chamber through the methane gas supply module, and a static pressure of a set value is applied for a period of time to make the coal sample reach a saturated state of gas adsorption, and the gas supply of the methane gas supply module is closed to complete the gas adsorption of the coal sample; S3. Inject water into the experimental cavity: open the water injection port, slowly inject water into the experimental cavity until the water level rises to the first layer monitoring point, keep stable for a period of time, continue to inject water to the second layer monitoring point, repeat the stabilization process, continue to inject water layer by layer, until the water completely submerges the coal sample, and keep stable for a period of time; S4, gas desorption: After the gas adsorption of the coal sample is completed, the valve of the sampling port is opened to introduce the methane gas desorbed from the coal sample into the gas desorption test device; S5. Data collection: Use a water level sensor to collect water level changes in the experimental chamber and generate water level rise rate data; use a humidity sensor array to collect real-time changes in the wetness of the coal sample surface and record the coal body infiltration and expansion rate; use a gas desorption test device to monitor the concentration and flow of desorbed gas, and generate a gas desorption rate curve based on time; use a pressure sensor to monitor the internal pressure of the experimental chamber in real time, and during the gas desorption process, record the impact of pressure changes on desorption behavior; S6. Data analysis and processing: including water flooding dynamic simulation analysis, wet diffusion dynamic analysis and gas desorption behavior modeling; Dynamic simulation analysis of flooding: Calculate the rising rate curve of water level in the experimental chamber over time based on the water level sensor data; Establish a water pressure-water level dynamic model in the experimental chamber to evaluate the response characteristics of gas desorption under different water pressure conditions; Dynamic analysis of wetting diffusion: Map the distribution data of the humidity sensor array to the surface of the coal sample to generate a three-dimensional wetting expansion map; calculate the relationship between the water absorption rate and the wetting depth of the coal sample through curve fitting; analyze the hysteresis effect of the wetting process inside the coal body on the gas desorption rate; Gas desorption behavior modeling: Combining gas concentration and flow data to generate a desorption volume-time curve, which is a gas desorption rate curve; According to the change of water level in the experimental chamber during the experiment, the desorption stages are divided; the relationship between the desorption rate, water pressure and the wetness of the coal sample surface is fitted to establish a desorption kinetic model; S7. Result output: Output the experimental report based on data analysis and processing.

7. The experimental method according to claim 6, characterized in that: n pressure sensors are arranged at intervals along the height direction of the test cavity, and all pressure sensors can be submerged in water. The water pressure P in the test cavity is obtained by the following method: avg : Where n is the number of pressure sensors, and Pi is the detection value of the i-th sensor.

8. The experimental method according to claim 6, characterized in that: In step S3, the water injection method includes two types: bottom single point water injection and layer-by-layer water injection; Among them, the bottom single-point water injection is to inject water into the experimental chamber only through the bottom water injection port; The layer-by-layer water injection is to first inject water into the experimental cavity through the bottom water injection port until the water level rises to the first layer monitoring point, keep it stable for a period of time, then continue to inject water to the second layer monitoring point through the side water injection port corresponding to the height position of the first layer monitoring point, repeat the stabilization process, then continue to inject water to the third layer monitoring point through the side water injection port corresponding to the height position of the second layer monitoring point, repeat the stabilization process, and continue to inject water layer by layer until the water completely submerges the coal sample and keeps it stable for a period of time; The gas desorption behavior of layer-by-layer water injection and bottom single-point water injection is compared, the influence of layer-by-layer water injection on the wettability of coal body and gas desorption behavior is analyzed, and the effect of layer-by-layer water injection on coal seam gas emission efficiency is evaluated.

9. The experimental method according to any one of claims 6 to 8, characterized in that: During the data analysis and processing, multivariate regression analysis was used to couple the gas desorption amount with the water level rise rate, wetting expansion rate, and water pressure, and to establish a dynamic correlation model of "water level-water pressure-wetting-desorption". The influence of different water injection rates on the gas desorption amount was analyzed to form a comparison chart.

10. The experimental method according to claim 9, characterized in that: The wetting extension rate is obtained in the following manner: W(t)=W0·(1-e -αt ) Among them, W (t) is the moisture content at time t, W0 is the final saturated moisture content, α is the fitting constant, and t is the time.

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