Method, device and system for directly measuring coal seam gas content underground

Abstract

The invention provides a method and a device for directly measuring the coal seam gas content underground. The method comprises the following steps: recording the total sampling time and the coal sample mass from the beginning of coal sample collection to the loading of a coal sample into a sealed measuring container; a coal sample gas natural analysis rapid decline stage in the sampling process is determined, a curve of the rapid decline stage is obtained, a plurality of gas analysis models are adopted for fitting verification, and the mean square error of each model is analyzed and calculated; a model with the minimum mean square error is selected, and the gas loss amount in the sampling process is calculated in combination with the total sampling time; crushing the coal sample to a specified specification, and recording a crushing analysis amount in a preset time period; and finally calculating the coal seam gas content. According to the method, the efficiency and the precision of underground direct measurement of the coal seam gas content are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine roadway engineering, and particularly to a method and device for directly measuring the gas content in coal seams underground. Background Art

[0002] The gas content in coal seams is a basic parameter for projects such as the prevention and control of coal and gas outbursts, the design of gas drainage, and the prediction of gas emission volume. It restricts the reliability of the prediction of gas hazard in mines and affects the effectiveness and economy of gas drainage measures formulated based on the gas content. At present, a large number of studies on the measurement of gas content in coal seams have been carried out at home and abroad, but it is impossible to obtain the gas content in coal seams in real time and dynamically during the mining process. The main problems are as follows: (1) Time-consuming: It is necessary to measure in stages underground and on the ground, and the measurement period for a set of parameters is more than 3 days; (2) Large error: The estimation of the lost gas volume relies on semi-empirical formulas, and the measurement error can reach more than 30%; (3) Complicated operation: During the underground measurement process, it is necessary to manually read and record the gas desorption data. At present, a new type of method for directly measuring the gas content in coal seams underground has emerged, which can greatly make up for the above deficiencies. For example, the Chinese invention patent "A Method for Directly Measuring the Gas Content in Coal Seams Underground" with the publication number CN113049440A discloses a method for directly measuring the gas content in coal seams underground. The gas (coalbed methane) content is divided into four parts: drilling loss, sampling loss, underground desorption amount, and pulverization desorption amount. Among them, the drilling loss is calculated using the relationship between the gas emission flow rate during the drilling stage and the drilling time, and the sampling loss is calculated using the fractional-order anomalous diffusion model based on the relationship between the underground desorption amount and the underground desorption time. Finally, the gas volume in each stage is corrected to the standard state, and the gas (coalbed methane) content in the coal seam can be obtained. Compared with the traditional gas content measurement method, this invention adds the calculation of the dynamic gas loss during the drilling process, making up for the deficiency that the gas (coalbed methane) content value measured by the traditional method is too small. However, when calculating the gas loss amount in the above invention, the influence of the adsorption equilibrium pressure on the gas desorption in the coal sample is not considered. After the coal sample is broken and peeled off, the gas molecules adsorbed on the surface of the coal sample start to desorb a large amount of desorbed gas into free gas. The free gas in the macropores and pores with good connectivity can flow out quickly, and the free gas in the micropores and pores with good connectivity is difficult to diffuse and then re-converts into adsorbed gas. In the early stage of gas desorption of the coal sample, the natural desorption rate of gas is high and shows a rapid downward trend. In the later stage of coal sample desorption, a large amount of free gas is lost. After the desorption of adsorbed gas is no longer affected by micropores, the adsorbed gas in the coal sample desorbs slowly, and the natural desorption rate shows a slow downward trend. In the early stage of coal sample gas desorption, the diffusion law of free gas dominates, and in the later stage of coal sample gas desorption, the desorption law of adsorbed gas dominates.

[0003] Therefore, in the gas loss, the rate of natural desorption shows a rapid downward trend. Taking the relationship between the total natural desorption amount before coal sample crushing and time as the basis for back-calculating the gas loss amount during the sampling period will inevitably bring huge errors. At the same time, the waiting time for its natural desorption is also relatively long, resulting in low efficiency in measuring gas content. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the efficiency and accuracy of direct underground measurement of coal seam gas content.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] The present invention provides a method for direct underground measurement of coal seam gas content, including:

[0007] S1. Record the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M;

[0008] S2. Based on the changing trend of the natural gas desorption rate, determine its rapid decline stage and obtain the scatter plot curve of natural gas desorption based on time and the total natural desorption amount in this stage;

[0009] S3. Based on the scatter plot curve obtained in step S2, use several gas desorption models to fit and verify respectively, and analyze and calculate the mean square error MSE of each model;

[0010] S4. Select the model with the smallest mean square error MSE, and calculate the gas loss amount X during the sampling process in combination with the total sampling time T0 l ;

[0011] S5. Crush the coal sample to the specified specification and record the crushing desorption amount X within the preset time period f ;

[0012] S6. Calculate the coal seam gas content W based on the above steps.

[0013] Further, the S2 includes the following steps:

[0014] S21. Define the natural desorption amount of coal sample gas per unit time as X n ;

[0015] S22. Continuously calculate the changing trend A of X n in sequence until A n is less than the set threshold, stop the natural desorption measurement, and record the curve of X n based on the unit time; n S23. Calculate the total natural desorption amount X

[0016] S23. Calculate the total natural desorption amount X s;

[0017] Furthermore, the unit time described in S2 is 10 seconds.

[0018] Furthermore, the threshold value described in S2 is 0.

[0019] Furthermore, the calculation X described in S2 n The changing trend of A n The following steps are involved:

[0020] (1) Calculate the difference a between two consecutive natural analytical quantities in unit time n , the formula is as follows:

[0021] a n =X n -X n+1

[0022] Where n=1,2...n, represents the nth unit time;

[0023] (2) Calculate X n The changing trend of A n , the formula is as follows:

[0024] A n =a n+1 -a n =(X n+1 -X n+2 )-(X n -X n+1 )

[0025] Wherein, n=1,2...n represents the nth unit time.

[0026] Furthermore, the total amount of natural analysis X described in S2 s Specifically:

[0027]

[0028] Among them, k represents when A n The kth unit time when the value is less than the threshold.

[0029] Furthermore, the specific calculation formula for the coal seam gas content W described in S6 is as follows:

[0030]

[0031] Among them, X e It is the unresolvable amount of coal sample gas.

[0032] The present invention also provides a device for directly measuring coal seam gas content underground, comprising an explosion-proof mobile phone with a built-in software system, which executes the above method when the system is running.

[0033] The device for directly measuring the underground coal seam gas content further includes a flow meter and a pneumatic pulverizing tank; the flow meter is connected to an explosion-proof mobile phone through a signal line; the pneumatic pulverizing tank is connected to the flow meter through a ventilation hose.

[0034] The present invention also provides a system for directly measuring the underground coal seam gas content, characterized in that when the system operates, it executes the above method, including the following modules:

[0035] A sampling record module, used to record the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M;

[0036] A rapid decline stage determination module, used to determine its rapid decline stage based on the change trend of the natural gas desorption rate, and obtain the natural gas desorption scatter plot curve based on time and the total natural desorption amount in this stage;

[0037] A data fitting module, used to respectively fit and verify using several gas desorption models based on the scatter plot curve obtained by the rapid decline stage determination module, and analyze and calculate the mean square error MSE of each model;

[0038] A gas loss amount calculation module, used to select the model with the smallest mean square error MSE, and combine the total sampling time T0 to calculate the gas loss amount X during the sampling process l ;

[0039] A pulverizing desorption amount calculation module, used to pulverize the coal sample to a specified specification and record the pulverizing desorption amount X within a preset time period f ;

[0040] A gas content output module, used to calculate the coal seam gas content W based on the above modules.

[0041] The advantages of the present invention are as follows:

[0042] (1) The present invention determines the rapid decline stage in the natural gas desorption curve of the coal sample, fits with this curve, analyzes and calculates the desorption model with the smallest mean square error, and uses this model to calculate the gas loss amount during the coal sample sampling process. By only using the curve in the above rapid decline stage, the time for natural gas desorption of the coal sample is reduced, and the time for inversely calculating the gas loss amount is greatly saved. At the same time, the curve in the rapid decline stage is closer to the actual value of the gas loss amount of the coal sample during the sampling process, greatly reducing the calculation error of the gas loss amount. At the same time, the gas loss amount during the sampling process, as an important part of the coal sample gas content, also further improves the calculation accuracy of the coal sample gas content.

[0043] (2) The present invention adopts a variety of calculation models for fitting and verification, and selects the model with the smallest fitting error as the estimated gas loss model for the current coal seam, improving the versatility and measurement accuracy for the characteristics of different coal seams. Description of the Drawings

[0044] Figure 1 It is a schematic flow chart of the method for directly measuring the in-situ gas content of the coal seam in the embodiment of the present invention;

[0045] Figure 2 It is a schematic structural diagram of the device for directly measuring the in-situ gas content of the coal seam in the embodiment of the present invention. Detailed Embodiments

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] Embodiment 1

[0048] The embodiment of the present invention provides a method for directly measuring the in-situ gas content of a coal seam. This method is based on the device for directly measuring the in-situ gas content of a coal seam, such as Figure 2 shown, including an explosion-proof mobile phone; the explosion-proof mobile phone is built with a software system, and when the system runs, it executes the method described in this embodiment.

[0049] As Figure 2 shown, the device for directly measuring the in-situ gas content of a coal seam further includes a flow meter and a pneumatic crushing tank; the flow meter is connected to the explosion-proof mobile phone through a signal line; the pneumatic crushing tank is connected to the flow meter through a ventilation hose.

[0050] The method process is as Figure 1 shown, including:

[0051] S1. Record the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M; during the actual measurement process, first use a drill to take samples from the coal seam. Usually, a coal core tube is used to collect coal cores or fixed-point sampling is used to collect coal cuttings. The sampling depth should exceed the influence range of the roadway at the drilling construction site. The sampling depth is generally determined according to the exposure time of the mining and excavation face and shall not be less than 12 meters. Record the total sampling time from the start of sampling to when the coal sample is loaded into the pneumatic crushing tank, and at the same time weigh the mass of the sampled coal sample.

[0052] S2. Based on the changing trend of the natural gas desorption rate, determine its rapid decline stage and obtain the scatter plot curve of the natural gas desorption based on time and the total amount of natural gas desorption in this stage. The specific implementation steps are as follows:

[0053] S21. Define the natural gas desorption amount of the coal sample per unit time as X n ; According to experience, set the unit time to 10 seconds.

[0054] S22. Continuously calculate the changing trend A n of X n until A n is less than the set threshold, stop the natural gas desorption measurement, and record the curve of X n based on the unit time; In specific implementation, the threshold is set to 0.

[0055] S23. Calculate the total amount of natural gas desorption X s ; The natural gas desorption amount of the coal sample is measured by a flow meter and the data is transmitted to the software system of the explosion-proof mobile phone for calculation.

[0056] The calculation of the changing trend A n of X n includes the following steps:

[0057] (1) Calculate the difference a n between the natural gas desorption amounts in two consecutive unit times, and the formula is as follows:

[0058] a n =X n -X n+1

[0059] where n = 1, 2... n, representing the nth unit time;

[0060] (2) Calculate the changing trend A n of X n [[ID=5l]]and the formula is as follows:

[0061] A n =a n+1 -a n =(X n+1 -X n+2 )-(X n -X n+1 )

[0062] where n = 1, 2... n, representing the nth unit time.

[0063] It can be seen from the above formula that the changing trend A n of X nCharacterizes the decreasing trend of gas desorption rate. From the start of sampling the coal sample, the desorbed amount per unit time decreases over time. However, the decrease in the desorbed amount per unit time gradually becomes stable from the initial rapid decrease. Therefore, it is necessary to find the turning point in the stage of rapid decrease in the desorbed amount, use this as the end point of the stage of rapid decrease in gas desorption, and use the curve of natural gas desorption over time in this stage of rapid decrease as the accurate fitting data for the gas loss amount during the coal sample sampling stage. When calculating to the k-th unit time, satisfying A n Less than 0, it is considered that at this time, the stage of rapid decrease ends. In engineering applications, the threshold can also be adjusted accordingly up and down near the 0 value according to experience. By determining the stage of rapid decrease in gas, not only can the speed of directly measuring gas content underground be greatly accelerated, but also the error in estimating the gas loss amount during the sampling process can be reduced.

[0064] Sum up the desorbed amounts within all unit times before this moment to calculate the total natural desorption amount X s Specifically:

[0065]

[0066] Among them, k represents when A n Is less than the threshold value at the k-th unit time.

[0067] S3. Based on the curve obtained in step S2, use several gas desorption models to fit and verify respectively, and analyze and calculate the mean square error MSE of each model. The specific implementation method is: the software system of the explosion-proof mobile phone has built-in common gas desorption models in coal mining enterprises, such as the square root method, power function method, fractal dynamics model, positive pressure countercurrent sampling compensation model, polynomial fitting model, exponential decay model, etc., and use them to fit and verify respectively, and analyze and calculate the mean square error MSE of each model. The above fitting and verification methods are all existing technologies, and the methods are not limited, so they will not be elaborated in this embodiment.

[0068] S4. Select the model with the smallest mean square error MSE, and combine the total sampling time T0 to calculate the gas loss amount X during the sampling process l ;

[0069] S5. Crush the coal sample to the specified specification, and record the crushed desorption amount X within the preset time period f ;

[0070] S6. Based on the above steps, calculate the coal seam gas content W. The specific calculation formula is as follows:

[0071]

[0072] Among them, X e$V_{unres}$ is the unresolvable amount of gas in the coal sample, referring to the amount of gas that cannot be resolved from the coal body under normal pressure. This part of the gas usually exists in the micropores of the coal in an adsorbed state. The estimation formula for the unresolvable amount is as follows:

[0073] V d $_{unres}$ = K × V × (1 - A d ) / 100 × T c / 100 × A / (1 + A)

[0074] where K is the empirical coefficient, V is the fixed carbon content, A d is the ash content, T c is the total carbon content, and A is the ash of the coal. The calculation method of the unresolvable amount belongs to the prior art and does not affect the direct underground measurement method of the coal seam gas content in this embodiment, so it will not be elaborated here.

[0075] Example 2

[0076] The embodiment of the present invention also provides a system for directly measuring the underground coal seam gas content, which is characterized in that when the system runs, it executes the method described in Example 1 and includes the following modules:

[0077] Sampling and recording module, used to record the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M;

[0078] Fast decline stage determination module, used to determine its fast decline stage based on the change trend of the natural gas resolution speed, and obtain the natural gas resolution scatter plot curve based on time and the total natural resolution amount in this stage;

[0079] Data fitting module, used to respectively fit and verify using several gas resolution models based on the scatter plot curve obtained by the fast decline stage determination module, and analyze and calculate the mean square error MSE of each model;

[0080] Gas loss amount calculation module, used to select the model with the smallest mean square error MSE, and calculate the gas loss amount X during the sampling process in combination with the total sampling time T0 l [[ID=3 June]];

[0081] Crushing and resolution amount calculation module, used to crush the coal sample to the specified specification and record the crushing and resolution amount X f ;

[0082] Gas content output module, used to calculate the coal seam gas content W based on the above modules.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for directly measuring the underground coal seam gas content, characterized in that Including: S1. Record the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M; S2. Based on the changing trend of the natural gas desorption rate, determine its rapid decline stage and obtain the scatter plot curve of the natural gas desorption based on time and the total natural desorption amount during this stage; S3. Based on the scatter plot curve obtained in step S2, use several gas desorption models to fit and verify respectively, and analyze and calculate the mean square error MSE of each model; S4. Select the model with the smallest mean square error (MSE), and calculate the gas loss X during the sampling process in combination with the total sampling time T0. l ; S5. Crush the coal sample to the specified specification and record the crushing analysis amount X within the preset time period f ; S6. Based on the above steps, calculate the coal seam gas content W.

2. The method for directly measuring the underground coal seam gas content according to claim 1, characterized in that, The S2 includes the following steps: S21. Define the natural desorption amount of coal sample gas per unit time as X n ; S22. Continuously calculate the change trend A of X in sequence n until A n is less than the set threshold, stop the natural parsing measurement, and record the curve of X n at this time based on the unit time; n ​ S23. Calculate the total natural parsing quantity X s .

3. The method for directly measuring the underground coal seam gas content according to claim 2, characterized in that, In S21, the unit time is 10 seconds.

4. The method for directly measuring the underground coal seam gas content according to claim 2, characterized in that In S22, the threshold is 0.

5. The method for directly measuring the underground coal seam gas content according to claim 2, characterized in that, The calculation of X described in S2 n The change trend A n comprises the following steps: (1) Calculate the difference a between the natural parsing amounts in two consecutive unit times n , and the formula is as follows: a n = X n - X n+1 Where n = 1, 2... n, representing the nth unit time; (2) Calculate X n The change trend A of n is as follows: A n = a n+1 -a n = (X n+1 - X n+2 ) - (X n - X n+1 ) Where n = 1, 2... n, representing the nth unit time.

6. The method for directly measuring the underground coal seam gas content according to claim 2, characterized in that, The total natural analysis quantity X described in S2 s Specifically: where k represents the k-th unit time when A n is less than the threshold value.

7. The method for directly measuring the underground coal seam gas content according to claim 6, characterized in that The specific calculation formula for the coal seam gas content W in S6 is as follows: Among them, X e is the non-analyzable amount of gas in the coal sample.

8. An apparatus for directly measuring in - mine coal - seam gas content, including an explosion - proof mobile phone, is characterized in that, The explosion-proof mobile phone is built with a software system, and when the software system runs, it executes the method described in any one of claims 1 - 7.

9. The device for directly measuring the underground coal seam gas content according to claim 8, characterized in that, It further includes a flow meter and a pneumatic crushing tank; the flow meter is connected to the explosion-proof mobile phone through a signal line; the pneumatic crushing tank is connected to the flow meter through a ventilation hose.

10. A system for directly measuring the gas content in coal seams underground, characterized in that, When the system runs, it executes the method described in any one of claims 1 - 7, including the following modules: A sampling record module for recording the total sampling time T0 from the start of coal sample collection to when the coal sample is loaded into the sealed measurement container and the coal sample mass M; A rapid decline stage determination module for determining its rapid decline stage based on the changing trend of the natural gas desorption rate and obtaining the scatter plot curve of the natural gas desorption based on time and the total natural desorption amount during this stage; A data fitting module for using several gas desorption models to fit and verify respectively based on the scatter plot curve obtained by the rapid decline stage determination module, and analyzing and calculating the mean square error MSE of each model; The gas loss calculation module is used to select the model with the smallest mean squared error (MSE), and combined with the total sampling time T0, calculate the gas loss X during the sampling process l ; The pulverization analysis quantity calculation module is used to pulverize the coal sample to a specified specification and record the pulverization analysis quantity X within a preset time period f ; A gas content output module for calculating the coal seam gas content W based on the above modules.

Images