A method for determining coal seam original gas pressure and permeability by multi-parameter inversion

Abstract

The present invention discloses a method for determining the original gas pressure and permeability of a coal seam by multi-parameter inversion. First, a mathematical model of gas flow around a borehole is determined based on the geological characteristics of the target coal seam and the on-site working conditions. The relevant parameters and assumed pressure and permeability values determined in advance through laboratory and field tests are input into a PLC controller, and a geological geometric model and its boundary conditions are constructed. Subsequently, a borehole is drilled in the underground coal seam, and a manual pump is used to inject water into the capsule to expand it to achieve rapid sealing and prevent air from flowing into the borehole. The flow meter is connected to the extraction pipe through a quick connector, and the flow value is recorded once at a certain interval. The data acquisition instrument transmits the data to the PLC controller. After the on-site gas flow measurement is completed, an objective function is established in the PLC controller based on the actual flow value and the simulated value calculated by the simulation module. After the objective function is optimized using an optimization algorithm, the original gas pressure and permeability values of the coal seam obtained by inversion are output.

Description

Technical Field

[0001] The invention relates to a method for measuring original gas pressure and permeability of a coal seam by multi-parameter inversion, and belongs to the technical field of safe extraction and utilization of coal mine gas. Background Art

[0002] Coal seams contain large amounts of gas. During coal mining, gas accidents such as coal and gas outbursts and gas explosions pose a serious threat to coal mine safety. Furthermore, as a highly efficient and clean energy source, gas is in high demand. Therefore, the safe extraction and utilization of coal mine gas has become a key research topic in the coal mining industry. Determining coal seam gas pressure and permeability is essential for achieving this goal.

[0003] The accurate measurement of coal seam gas pressure and permeability has always been a difficult problem that has plagued scholars at home and abroad. Currently, the main method used is the radial flow method, which has achieved certain results in measuring coal seam permeability. However, the radial flow method performs a series of transformations and simplifications on the gas flow equation, and cannot fully reflect the essence of gas flow around the borehole. As a result, there is a certain error between the results calculated by this method and the true value, and there are situations such as requiring multiple trial calculations and sometimes no solution. At the same time, the radial flow method also requires obtaining the original gas pressure of the coal seam in advance. The current gas pressure measurement method still has many problems, such as long testing cycles and gas leakage during the measurement process causing the measured value to be less than the actual value.

[0004] In summary, there is an urgent need for a new method that can quickly and accurately obtain the original gas pressure and permeability of coal seams in the mine, so as to obtain the actual parameters of the coal seams. This is the research direction required by the present invention. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides a method for determining the original gas pressure and permeability of coal seams by multi-parameter inversion, which can quickly and accurately obtain the original gas pressure and permeability of coal seams synchronously underground, thereby obtaining the actual parameters of the coal seams.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for determining the original gas pressure and permeability of coal seams by multi-parameter inversion, the specific steps of which are:

[0007] A. Determine the mathematical model: Based on the geological characteristics of the target coal seam and the on-site working conditions, a mathematical model of gas flow around the borehole that conforms to the actual on-site conditions is built into the PLC controller. The mathematical models are all existing models and can be directly selected based on the on-site working conditions.

[0008] B. Establish a geological geometric model: Construct a geological geometric model and its boundary conditions based on the borehole radius and the geological characteristics of the target coal seam, and grid the established geological geometric model to complete the construction of the geological geometric model for simulating the shape of the coal seam. The above-mentioned gas flow model is a numerical model, that is, a model composed of formulas. However, the numerical model alone cannot be directly simulated, and a geometric model is also required. The geometric model simulates the size of the actual coal seam and can be simplified into a two-dimensional plane geometric model without affecting the calculation results. Therefore, it is necessary to combine the geometric model with the numerical model, so that after the inversion is completed, the dynamic evolution cloud map of permeability, gas content, gas pressure, etc. can be seen through the geometric model. Monitoring lines and monitoring points can also be arranged on the geometric model to analyze the dynamic changes of the parameters on the points and lines. The gas flow numerical model is equivalent to a framework, and the geometric model is the carrier for realizing the subsequent visualization and analyzability of the framework.

[0009] C. Obtaining model input parameters and calculating simulated gas flow: First, set the original coal seam gas pressure and permeability values. Then, obtain the coal seam porosity, coal elastic modulus, and borehole extraction pressure through laboratory and field tests. These data are then used as input parameters in the mathematical model of gas flow around the borehole (step A). These data are then combined with the geological geometry model (step B) to calculate the simulated gas flow.

[0010] D. Determine on-site gas flow: Select a location in the tunnel and drill a hole into the target coal seam until the hole penetrates the coal seam. After drilling is completed, extend one end of the extraction pipe to the bottom of the borehole. Use a manual pump to inject water into the sealing capsule installed on the extraction pipe to expand it, which quickly seals the pore between the extraction pipe and the borehole and prevents air from flowing into the borehole. Connect a flow meter to the other end of the extraction pipe via a quick connector. The flow meter records the instantaneous flow value at regular intervals and transmits the data to the PLC controller via a data acquisition device.

[0011] E. Inversion of the original gas pressure and permeability values of the coal seam: After step D is completed, the instantaneous flow value obtained in step D and the simulated flow value calculated in step B are used to establish an objective function in the PLC controller. Optimization parameter constraints and optimization stop conditions are set, and the African Vulture Optimization Algorithm (AVOA) is used to optimize the objective function. When the optimization stop conditions are met, the original gas pressure and permeability values of the coal seam obtained by inversion are output;

[0012] F. Determine the actual parameters of the coal seam at that location: Replace the original gas pressure and permeability values of the coal seam set in step B with the original gas pressure and permeability values obtained by inversion in step E, input them into the mathematical model of step A, and combine them with the geological geometry model of step B. After recalculation, obtain the residual gas content, residual gas pressure, and effective extraction radius of the drill hole in the corresponding area of the coal seam;

[0013] G. Determine the actual parameters of different areas of the coal seam: Select multiple different locations in the tunnel and repeat steps D to F respectively, so as to measure the actual parameters of different areas of the entire coal seam.

[0014] Furthermore, the original gas pressure and permeability values of the coal seam set in step B are arbitrary values.

[0015] Furthermore, the drill holes constructed are as perpendicular to the coal seam dip as possible, and the deviation does not exceed 10°.

[0016] Furthermore, in step D, the time when the flow meter reading starts to change is recorded as the initial time.

[0017] Furthermore, the objective function in step E is the sum of squares of the differences between the simulated flow value and the instantaneous flow value, specifically:

[0018]

[0019] Where: i represents the i-th moment; N represents the total number of measured gas flow values; Represents the simulated flow value at the i-th moment, m 3 / s; Indicates the instantaneous flow value at the i-th moment, m 3 / s.

[0020] Furthermore, the time point of selecting the simulated flow value in the objective function is consistent with the time point of the instantaneous flow value.

[0021] Furthermore, the optimization stopping condition is set to one of the maximum number of function calculations, the maximum number of iterations, the maximum calculation time and the minimum objective function value, and the appropriate stopping condition is selected according to the site requirements.

[0022] Compared to existing technologies, the present invention first builds a mathematical model of gas flow around the borehole into a PLC controller based on the geological characteristics of the target coal seam and on-site operating conditions, tailored to the actual site conditions. Assuming the original gas pressure and permeability values for a coal seam, the relevant parameters previously determined through laboratory and field tests, along with the assumed pressure and permeability values, are input into the PLC controller. A geological geometric model and its boundary conditions are then constructed based on the borehole radius and the geological characteristics of the coal seam. Subsequently, a borehole is drilled into the underground coal seam. A manual pump is used to inject water into the capsule, causing it to expand and quickly seal the hole, preventing air from flowing into the borehole. A flowmeter is connected to the extraction pipe via a quick connector, recording flow rates at regular intervals. A data acquisition device then transmits the data to the PLC controller. Once the on-site gas flow measurement is complete, an objective function is established in the PLC controller based on the measured flow rate and the simulated values calculated by the simulation module. This objective function is then optimized using a specific optimization algorithm until the optimization stop condition is reached, outputting the original gas pressure and permeability values of the coal seam obtained by inversion. This output then provides data on the residual gas content, residual gas pressure, and effective extraction radius of the borehole in the corresponding area of the coal seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the layout for testing gas pressure and permeability in the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below.

[0025] like Figure 1 As shown, the specific steps of the present invention are:

[0026] A. Determine the mathematical model: Based on the geological characteristics of the target coal seam and the on-site working conditions, a mathematical model of gas flow around the borehole that conforms to the actual on-site conditions is built into the PLC controller. The mathematical models are all existing models and can be directly selected based on the on-site working conditions.

[0027] B. Establish a geological geometric model: Construct a geological geometric model and its boundary conditions based on the borehole radius and the geological characteristics of the target coal seam, and grid the established geological geometric model to complete the construction of the geological geometric model for simulating the shape of the coal seam. The above-mentioned gas flow model is a numerical model, that is, a model composed of formulas. However, the numerical model alone cannot be directly simulated, and a geometric model is also required. The geometric model simulates the size of the actual coal seam and can be simplified into a two-dimensional plane geometric model without affecting the calculation results. Therefore, it is necessary to combine the geometric model with the numerical model, so that after the inversion is completed, the dynamic evolution cloud map of permeability, gas content, gas pressure, etc. can be seen through the geometric model. Monitoring lines and monitoring points can also be arranged on the geometric model to analyze the dynamic changes of the parameters on the points and lines. The gas flow numerical model is equivalent to a framework, and the geometric model is the carrier for realizing the subsequent visualization and analyzability of the framework.

[0028] C. Obtaining model input parameters and calculating simulated gas flow: First, set the original coal seam gas pressure and permeability values. Then, obtain the coal seam porosity, coal elastic modulus, and borehole extraction pressure through laboratory and field tests. These data are then used as input parameters in the mathematical model of gas flow around the borehole (step A). These data are then combined with the geological geometry model (step B) to calculate the simulated gas flow.

[0029] D. Determine on-site gas flow: Select a location in the tunnel and drill a hole into the target coal seam until the hole penetrates the coal seam. The drill hole should be as perpendicular to the coal seam as possible, with a deviation of no more than 10°. After the drilling is completed, extend one end of the extraction pipe to the bottom of the borehole. Use a manual pump to inject water into the sealing capsule installed on the extraction pipe to expand it and quickly seal the pore between the extraction pipe and the borehole to prevent air from flowing into the borehole. Connect a flow meter to the other end of the extraction pipe via a quick connector. The initial moment is recorded when the flow meter reading begins to change. The flow meter records the instantaneous flow value at regular intervals and transmits this data to the PLC controller via a data acquisition device.

[0030] E. Inversion of coal seam original gas pressure and permeability values: After step D is completed, the instantaneous flow value obtained in step D and the simulated flow value calculated in step B are used to establish an objective function in the PLC controller. The objective function is the sum of squares of the difference between the simulated flow value and the instantaneous flow value, specifically:

[0031]

[0032] Where: i represents the i-th moment; N represents the total number of measured gas flow values; Represents the simulated flow value at the i-th moment, m 3 / s; Indicates the instantaneous flow value at the i-th moment, m 3 / s; the time point of the simulated flow value selected in the objective function is consistent with the time point of the instantaneous flow value.

[0033] Setting optimization parameter constraints and optimization stop conditions, wherein the optimization stop condition is set to one of the maximum number of function calculations, the maximum number of iterations, the maximum calculation time, and the minimum objective function value, and the appropriate stop condition is selected based on site requirements; and optimizing the objective function using the African Vulture Optimization Algorithm (AVOA) until the optimization stop condition is met, i.e., the original gas pressure and permeability values of the coal seam obtained by inversion are output;

[0034] F. Determine the actual parameters of the coal seam at that location: Replace the original gas pressure and permeability values of the coal seam set in step B with the original gas pressure and permeability values obtained by inversion in step E, input them into the mathematical model of step A, and combine them with the geological geometry model of step B. After recalculation, obtain the residual gas content, residual gas pressure, and effective extraction radius of the drill hole in the corresponding area of the coal seam;

[0035] G. Determine the actual parameters of different areas of the coal seam: Select multiple different locations in the tunnel and repeat steps D to F respectively, so as to measure the actual parameters of different areas of the entire coal seam.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining the original gas pressure and permeability of a coal seam by multi-parameter inversion, characterized in that: The specific steps are: A. Determine the mathematical model: Based on the geological characteristics of the target coal seam and the on-site working conditions, a mathematical model of gas flow around the borehole that conforms to the actual on-site conditions is built into the PLC controller; B. Establishing a geological geometric model: Constructing a geological geometric model and its boundary conditions based on the borehole radius and the geological characteristics of the target coal seam. Gridding the established geological geometric model completes the construction of the geological geometric model to simulate the shape of the coal seam. C. Obtaining model input parameters and calculating simulated gas flow: First, set the original coal seam gas pressure and permeability values. Then, obtain the coal seam porosity, coal elastic modulus, and borehole extraction pressure through laboratory and field tests. These data are then used as input parameters in the mathematical model of gas flow around the borehole (step A). These data are then combined with the geological geometry model (step B) to calculate the simulated gas flow. D. Determine on-site gas flow: Select a location in the tunnel and drill a hole into the target coal seam until the hole penetrates the coal seam. After drilling is completed, extend one end of the extraction pipe to the bottom of the borehole. Use a manual pump to inject water into the sealing capsule installed on the extraction pipe to expand it, which quickly seals the pore between the extraction pipe and the borehole and prevents air from flowing into the borehole. Connect a flow meter to the other end of the extraction pipe via a quick connector. The flow meter records the instantaneous flow value at regular intervals and transmits the data to the PLC controller via a data acquisition device. E. Inversion of the original gas pressure and permeability of the coal seam: After step D is completed, the instantaneous flow value obtained in step D and the simulated flow value calculated in step B are used to establish an objective function in the PLC controller. The objective function is the sum of squares of the difference between the simulated flow value and the instantaneous flow value, specifically: ； Where: i represents the i-th moment; N represents the total number of measured gas flow values; Indicates the simulated flow value at the i-th moment, in m 3 / s; Indicates the instantaneous flow value at the i-th moment, in m 3 / s; Set optimization parameter constraints and optimization stop conditions, and use the African vulture optimization algorithm to optimize the objective function until the optimization stop conditions are met, that is, the original gas pressure and permeability values of the coal seam obtained by inversion are output; F. Determine the actual parameters of the coal seam at that location: Replace the original gas pressure and permeability values of the coal seam set in step B with the original gas pressure and permeability values obtained by inversion in step E, input them into the mathematical model of step A, and combine them with the geological geometry model of step B. After recalculation, obtain the residual gas content, residual gas pressure, and effective extraction radius of the drill hole in the corresponding area of the coal seam; G. Determine the actual parameters of different areas of the coal seam: Select multiple different locations in the tunnel and repeat steps D to F respectively, so as to measure the actual parameters of different areas of the entire coal seam.

2. The method for determining coal seam original gas pressure and permeability by multi-parameter inversion according to claim 1, characterized in that: The original gas pressure and permeability values of the coal seam set in step B are arbitrary values.

3. The method for determining coal seam original gas pressure and permeability by multi-parameter inversion according to claim 1, characterized in that: The drill holes constructed are as perpendicular to the coal seam dip as possible, with a deviation of no more than 10°.

4. The method for determining coal seam original gas pressure and permeability by multi-parameter inversion according to claim 1, characterized in that: In step D, the time when the flow meter reading starts to change is recorded as the initial time.

5. The method for determining original gas pressure and permeability of coal seams by multi-parameter inversion according to claim 1 is characterized in that: The time point of selecting the simulated flow value in the objective function is consistent with the time point of the instantaneous flow value.

6. The method for determining original gas pressure and permeability of coal seams by multi-parameter inversion according to claim 1 is characterized in that: The optimization stopping condition is set to one of the maximum number of function calculations, the maximum number of iterations, the maximum calculation time and the minimum objective function value, and the appropriate stopping condition is selected according to the site requirements.

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