A monitoring system and prediction method for creep-seepage response of coal mass

Abstract

The present invention provides a coal body creep-seepage response monitoring system and prediction method, belonging to the technical field of coal body creep-seepage response monitoring and prediction; it overcomes the technical problem that the current experiments on the creep deformation and seepage law of coal bodies cannot reproduce the in-situ high-stress environment deep in the mine, resulting in poor accuracy of the obtained data; the adopted technical solution is: the in-situ creep-seepage test chamber includes a chamber body with openings at both the upper and lower ends. A coal body specimen is filled inside the chamber body. The top of the chamber body is installed with an upper end cover through fixing bolts. A pressurizing end for transmitting the in-situ axial pressure to the coal body specimen is arranged at the central position of the upper end cover. The bottom of the chamber body is installed with a lower base through fixing bolts. A convex platform for fixing the coal body specimen is arranged at the central position of the lower base; the present invention is applied to the monitoring of the coal body creep-seepage response.

Description

Technical Field

[0001] The present invention provides a coal body creep-seepage response monitoring system and a prediction method, belonging to the technical field of coal body creep-seepage response monitoring and prediction. Background Technique

[0002] In the field of coal mining, gas control work has always been the key to ensuring the safe production and efficient operation of coal mines. Due to the low permeability of coal bodies deep in the mine, the migration resistance of gas in the coal pore-fracture network is large, resulting in a long time for gas extraction. As coal mining extends deeper, the in-situ stress state faced by coal seams increases significantly. Due to the long-term high-temperature and high-pressure environment of deep coal bodies, creep phenomena are significant. This creep process will promote the appearance of pore-fracture structures inside the remolded coal body, greatly changing the gas occurrence and migration channels, making the permeability of the coal body in dynamic change and more likely to cause dangerous hidden dangers such as gas outbursts. To analyze the complex characteristics of the environment and evolution characteristics faced by deep coal bodies and accurately simulate the in-situ stress environment deep in the ground and analyze the creep deformation and seepage laws of coal bodies in this environment have become the key points of gas control.

[0003] At present, for the research on the creep deformation and seepage laws of coal bodies, corresponding experimental devices are mainly used to comprehensively and deeply analyze the mechanical and seepage characteristics of coal bodies. However, most traditional experimental devices are designed based on the simulation of conventional stress environments and are difficult to accurately reproduce the in-situ high-stress environment deep in the mine, resulting in a large deviation between the data of the mechanical and seepage characteristics of coal bodies obtained in the laboratory and the actual situation deep in the mine, and unable to provide a reliable basis for the formulation of extraction plans during the gas control process of deep coal seams. Therefore, to achieve the safe and efficient mining of deep high-gas coal mines, it is necessary to provide an accurate and reliable coal body creep-seepage response monitoring plan under the in-situ stress state of coal bodies near the coal mining face. Summary of the Invention

[0004] In order to overcome the technical problem that the current experiments on the creep deformation and seepage laws of coal bodies cannot reproduce the in-situ high-stress environment deep in the mine, resulting in poor accuracy of the obtained data, the present invention provides a coal body creep-seepage response monitoring system and a prediction method.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A coal body creep-seepage response monitoring system, including an in-situ creep-seepage test chamber, an oil-gas two-phase pressure monitoring and response box, and a data acquisition and control box. The in-situ creep-seepage test chamber is installed in the underground coal wall for experiments and records data in real time. The in-situ creep-seepage test chamber includes a chamber body with upper and lower openings. Inside the chamber body, a coal body sample is filled. The top of the chamber body is installed with an upper end cover through fixing bolts. At the central position of the upper end cover, a pressurizing end is provided for transmitting in-situ axial pressure to the coal body sample. The bottom of the chamber body is installed with a lower base through fixing bolts. At the central position of the lower base, a convex platform is provided for fixing the coal body sample. The gas transmission pipe led out from the bottom of the convex platform is connected to the air inlet of the oil-gas two-phase pressure monitoring and response box. The gas transmission pipe led out from the top of the pressurizing end is connected to the air outlet of the oil-gas two-phase pressure monitoring and response box;

[0006] An oil injection port and an oil discharge port are also opened on the side wall of the chamber body. The inner side of the oil injection port is arranged opposite to the upper end face of the coal body sample. The inner side of the oil discharge port is arranged opposite to the lower end face of the coal body sample. The outer side of the oil injection port is connected to the oil outlet of the oil-gas two-phase pressure monitoring and response box through an oil transmission pipe. The outer side of the oil discharge port is connected to the oil inlet of the oil-gas two-phase pressure monitoring and response box through an oil transmission pipe;

[0007] Strain gauges for monitoring the deformation of the coal body are also pasted on the surface of the coal body sample. The strain gauges send the coal body deformation data to the data acquisition and control box through data lines;

[0008] A hydraulic tray capable of adjusting the height is installed at the bottom of the in-situ creep-seepage test chamber. A limit bolt for fixing the axial displacement of the tray is also provided on the side of the hydraulic tray. The oil transmission pipe led out from the bottom of the hydraulic tray is connected to the oil outlet of the oil-gas two-phase pressure monitoring and response box;

[0009] Pressure sensors are also provided inside the underground coal seam at the monitoring location and above the in-situ creep-seepage test chamber. The signal output end of the pressure sensor is connected to the data acquisition and control box through a data line;

[0010] Hydraulic oil gauges are also provided at the oil inlet and oil outlet of the oil-gas two-phase pressure monitoring and response box. The hydraulic oil gauges send the oil pressure data generated by the hydraulic oil in the in-situ creep-seepage test chamber to the data acquisition and control box through data lines;

[0011] Barometers are also provided at the air inlet and air outlet of the oil-gas two-phase pressure monitoring and response box. The barometers send the air pressure data at both ends of the coal body sample to the data acquisition and control box through data lines.

[0012] The oil-gas two-phase pressure monitoring and response box specifically inputs and recovers in-situ gas into and from the in-situ creep-seepage test chamber through a gas pipeline.

[0013] The oil-gas two-phase pressure monitoring and response box specifically inputs and recovers hydraulic oil into and from the in-situ creep-seepage test chamber through an oil pipeline.

[0014] A plurality of display screens for displaying the data collected by the sensors are installed on the side wall of the oil-gas two-phase pressure monitoring and response box.

[0015] The data acquisition and control box receives and processes the acquisition data sent by each sensor to obtain the true in-situ stress data, and controls the oil pump in the oil-gas two-phase pressure monitoring and response box to inject hydraulic oil into the hydraulic tray and the in-situ creep-seepage test chamber according to the true in-situ stress data, so as to provide axial and lateral stresses.

[0016] Sealing plugs are provided at the connection positions of the in-situ creep-seepage test chamber, the hydraulic tray, the oil-gas two-phase pressure monitoring and response box with each oil pipeline, gas pipeline and data line.

[0017] The coal sample filled in the in-situ creep-seepage test chamber is specifically a cylindrical coal body with a diameter of 50 mm and a height of 100 mm.

[0018] The surface of the coal sample is also wrapped with an oil isolation film.

[0019] A method for predicting the creep-seepage response of coal includes the following prediction steps:

[0020] Select a deep coal seam roadway as the in-situ experiment site;

[0021] Use tools to cut a cubic cavity in the coal wall to obtain a cubic coal sample, and then cut out a cylindrical coal sample with a diameter of 50 mm and a height of 100 mm from the mined cubic coal sample;

[0022] Assemble the in-situ creep-seepage test chamber: Fix two horizontal and vertical strain gauges on the coal sample, then wrap the coal sample with an oil isolation film to ensure complete sealing, and then fix the coal sample on the convex platform of the lower base of the in-situ creep-seepage test chamber. Subsequently, install the lower base at the bottom of the chamber body, install the pressurizing end and the upper cover at the top of the chamber body, and install a pressure sensor on the upper part of the pressurizing end;

[0023] Check the airtightness of the devices inside the in-situ creep-seepage test chamber and the air duct, use fixing bolts to fasten the entire in-situ creep-seepage test chamber, and install a hydraulic tray at the bottom of the in-situ creep-seepage test chamber;

[0024] Install pressure sensors in the pre-drilled holes around the coal seam cavity for measuring in-situ axial pressure, lateral pressure, and gas pressure. The signal output ends of all pressure sensors, hydraulic oil gauges, and barometers send the collected data to the data acquisition and control box through data lines respectively;

[0025] Connect the oil-gas two-phase pressure monitoring and response box to the in-situ creep-seepage test chamber and the hydraulic tray respectively using oil pipelines, and connect the oil-gas two-phase pressure monitoring and response box to the in-situ creep-seepage test chamber using a gas pipeline;

[0026] Process the data collected by each pressure sensor in the coal seam through the data acquisition and control box to obtain the actual true value of the in-situ stress, and adjust the oil-gas two-phase pressure monitoring and response box to make the data of the pressure sensor on the top of the in-situ creep-seepage test chamber and the hydraulic oil gauge on the oil-gas two-phase pressure monitoring and response box consistent with the readings on the data acquisition and control box;

[0027] After the monitoring system is installed, start the experiment on the creep-seepage response of coal under in-situ stress conditions:

[0028] First, read and record the readings of the strain gauges on the surface of the coal specimen in real time, as well as the barometer readings in the oil-gas two-phase pressure monitoring and response box. Import the collected data set into the origin fitting software, calculate according to the existing creep model and permeability model, determine the specific parameters in the model, obtain the in-situ coal creep deformation prediction formula and the permeability evolution empirical formula, and through the obtained multiple groups of in-situ experimental data, repeatedly modify the undetermined parameters in the model to narrow the model error range, so as to realize the long-term prediction of coal creep data and permeability under in-situ stress conditions.

[0029] When predicting the creep-seepage response of coal under in-situ stress conditions, the in-situ coal creep deformation prediction formula adopted is specifically based on the Westphalian model framework, introducing the fractional-order operator which is good at describing nonlinear deformation problems, and establishing an improved Westphalian model based on fractional-order derivatives. The improved Westphalian model includes a Hookean body, a viscoelastic body, and a viscoplastic body, and the expression is:

[0030] ;

[0031] ;

[0032] Among them: ε is the axial creep strain, including elastic strain ε 1 , viscoelastic strain ε 2 , viscoplastic strain ε 3 ;

[0033] σ is the axial stress; σ s is the yield stress;

[0034] E 1is the elastic modulus; E 2 is the elastic modulus of the viscoelastic body; λ is the fractional order;

[0035] η 1 and η 2 is the viscosity coefficient; α 0 is the viscosity attenuation parameter;

[0036] t is the time; E λ,1 and E 1,1+λ are both Mittag-Leffler function operators;

[0037] Through the in-situ creep deformation data measured in the early stage, the improved Xiyuan model is fitted and analyzed to determine the physical and mechanical parameters in the creep model, and then the creep deformation calculation formula under the in-situ stress conditions of deep coal seams is obtained.

[0038] When predicting the creep-seepage response of coal under in-situ stress conditions, the empirical formula for permeability evolution is adopted. Specifically, combined with the transient pulse test method, the fractional derivative is introduced, and the transient method permeability calculation formula is redefined. Among them, the change of the gas pressure difference at the upper and lower ends of the coal sample with time is described by the Mittag-Leffler function, and the expression is:

[0039] ;

[0040] ;

[0041] Where: is the Mittag-Leffler function; k g is the gas permeability;

[0042] At the beginning of the experiment, a stable in-situ gas pressure is applied to the coal sample. When the in-situ gas is introduced into the coal sample, an initial pressure difference P 0 is formed instantaneously and gradually returns to the final equilibrium value P (t) with the passage of time. By fitting the gas pressure difference on both sides of the coal sample with the experimental data, the parameter Φ is determined, and the relevant experimental data is substituted to deduce the calculation formula of permeability as:

[0043] ;

[0044] Where: is the inverse function of the Mittag-Leffler function, P (t) and P 0 are the final in-situ gas pressure difference and the initial in-situ gas pressure difference; t is the time; k E is the experimental gas permeability; μ is the gas viscosity coefficient; β is the gas compressibility coefficient;

[0045] L is the length of the specimen; A is the cross-sectional area of the specimen; V is the volume of the cylinder;

[0046] Then, by combining the deep coal mass creep deformation data and permeability evolution data, an empirical formula for permeability evolution considering the influence of creep deformation is established as follows:

[0047] ;

[0048] Where: k M is the model permeability, k 0 is the initial permeability, Δε 1 is the elastic strain increment, Δε 2 is the viscoelastic strain increment, Δε 3 is the viscoplastic strain increment, and a and b are undetermined coefficients, which are specifically determined by the experimental data of permeability evolution over time.

[0049] The beneficial effects of the present invention compared with the prior art are as follows: In order to accurately monitor the influence of in-situ high ground stress in deep coal seams on coal mass creep and measure the evolution of permeability during the creep process, the present invention provides a monitoring system and prediction method for coal mass creep-seepage response under in-situ stress conditions in mines to conduct long-term monitoring and prediction of coal mass creep-seepage response; this solution avoids the pressure measurement error caused by changes in environmental conditions after the sample is taken out of the ground. The in-situ creep-seepage test chamber used can accurately reflect its true situation in a specific environment, improving the accuracy of monitoring; at the same time, the present invention uses a model to predict the system response and performs parameter fitting based on experimental data at a specific location, which can fully consider the influence of local geological conditions, temperature, humidity, stress state, etc. on the creep characteristics of materials. The changes in local factors at a specific location can be well incorporated into the model, and it can be optimized according to the engineering requirements of a specific location, thereby verifying and correcting the existing general creep empirical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The following further describes the present invention with reference to the accompanying drawings:

[0051] Figure 1 is a schematic structural diagram of the coal mass creep-seepage monitoring system of the present invention;

[0052] Figure 2 is a top view of the in-situ creep-seepage test chamber of the present invention;

[0053] Figure 3 is a schematic wiring structure diagram of the data acquisition and control box and sensors of the present invention;

[0054] Figure 4 is a schematic structural diagram of the fractional-order West Yuan model used for predicting coal mass creep-seepage of the present invention;

[0055] Figure 5 This is a comparative analysis diagram of the creep model and experimental data in the embodiments of the present invention;

[0056] Figure 6 This is a comparative analysis diagram of differential pressure decay data in the embodiments of the present invention;

[0057] Figure 7 This is a comparative analysis diagram of the permeability evolution under the influence of creep deformation in the embodiments of the present invention;

[0058] The meanings of the serial numbers in the figure are as follows: 1 is the in-situ creep-seepage test chamber, 2 is the oil-gas two-phase pressure monitoring and response box, 3 is the data acquisition and control box, 4 is the coal sample, 5 is the strain gauge, 6 is the oil separation film, 7 is the pressurizing end, 8 is the fixing bolt, 9 is the hydraulic tray, 10 is the limit bolt, 11 is the pressure sensor, 12 is the hydraulic oil gauge, 13 is the barometer, 14 is the oil pipeline, 15 is the gas pipeline, 16 is the data line, 17 is the upper end cover, 18 is the main body of the chamber, and 19 is the lower base. Specific embodiments

[0059] As Figures 1 to 7 shown, the present invention provides a monitoring system for the creep-seepage response of coal under in-situ stress conditions in mines and a prediction method adopted. Specifically, in a deep coal seam roadway meeting the conditions, a cubic cavity is chiseled out using tools, and an experimental coal sample is prepared using the chiseled cube. According to the requirements for monitoring the creep-seepage response of the coal, the monitoring system is assembled and its airtightness is checked; as Figure 1 and Figure 3 shown, the dot array areas represent the coal seam, and then sensors are installed in the pre-drilled holes around the coal seam to measure various in-situ data and transmit the data to the experimental device. By adjusting each device, the coal sample in the experimental device is in the in-situ state, and an in-situ stress condition coal creep-seepage experiment is carried out, and the data collected by each sensor is recorded; the present invention constructs a creep deformation prediction formula and a permeability evolution prediction formula, combines the recorded on-site experimental data, executes the corresponding fitting program, and finally obtains the prediction model and formula parameters, providing a theoretical method for predicting the creep-seepage response of coal under in-situ stress conditions in the mine.

[0060] The present invention uses a coal creep-seepage response monitoring system to simulate the in-situ pressure in the mine. The in-situ pressure in the mine can directly reflect the actual pressure situation in the mine, avoiding the pressure measurement error caused by the change of environmental conditions after the sample is taken out of the ground, so as to more accurately reflect the mechanical properties and physical states of the coal seam or other geological bodies in the original state.

[0061] The in-situ gas is used in the coal body creep-seepage response monitoring system of the present invention. The in-situ gas has not undergone any migration or treatment, and its physical and chemical properties such as composition and concentration remain in the original state, which can accurately reflect its true situation in a specific environment, avoiding the change of gas properties caused by external factors during the collection and transportation process, thus providing a reliable data basis for relevant research and analysis.

[0062] In the present invention, the pressurizing end 7 and the hydraulic tray 9 in the coal body creep-seepage response monitoring system are used to apply pressure in the axial direction. By adjusting the pressure of the hydraulic tray 9, the vertical stress can be accurately applied to the coal sample according to the requirements of the experimental design. The pressurizing steel core can withstand a large pressure without obvious performance changes due to environmental factors during the long-term in-situ stress experiment.

[0063] The experimental instruments such as the air pump and oil pump used in the coal body creep-seepage response monitoring system of the present invention can be installed in a portable suitcase. At the same time, the experimental tank body and the data acquisition and control box are portable and can be easily placed in the trunk of a car, a backpack, etc., without occupying too much space, which is convenient for people to carry when traveling and can better meet people's needs for using it anytime and anywhere. Since the functional components are integrated in a suitcase, there is no need to separately prepare and connect each individual device in the traditional way, which greatly saves the time for equipment installation, debugging and preparation and improves work efficiency.

[0064] The coal body creep-seepage response monitoring system provided by the present invention mainly includes an in-situ creep-seepage test chamber 1, an oil-gas two-phase pressure monitoring and response box 2, and a data acquisition and control box 3. When in use, the in-situ creep-seepage test chamber 1 is set in the coal wall underground to conduct experiments and record data in real time;

[0065] The set in-situ creep-seepage test chamber 1 is a steel cylindrical container, including: an upper end cover 17, a lower base 19, a chamber body main body 18, a pressurizing end 7, and fixing bolts 8. Each part has air holes, liquid holes, and wire holes;

[0066] The lower base 19 is a disc with holes. The lower base 19 has a boss for fixing the coal body sample 4, and the bottom of the boss is connected to the outside through a gas transmission pipe 15;

[0067] The chamber body main body 18 is a sealed and perforated steel wall. There are data line channels and hydraulic oil input and recovery pipes around the chamber body main body 18, and all are equipped with sealing plugs to ensure the airtightness of the device;

[0068] The chamber body main body 18 is fixed to the upper end cover 17 and the lower base 19 by eight fixing bolts 8.

[0069] The above-mentioned oil-gas two-phase pressure monitoring and response box 2 is a compact and lightweight portable suitcase, with a handle installed thereon, having a certain mechanical strength; two display screens are installed on its surface, and the screens are divided into different blocks, respectively representing the readings of different sensors;

[0070] The oil-gas two-phase pressure monitoring and response box 2 is respectively provided with two gas pipelines 15 and an oil pipeline 14 extending outwards, to respectively input and recover in-situ gas and hydraulic oil into the in-situ creep-seepage test chamber 1.

[0071] The above-mentioned data acquisition and control box 3 is a data acquisition and real-time control integrated device, which is connected to each sensor through a data line 16, receives the data of each sensor, and is finally connected to a display; the data collected from each sensor is analyzed and processed here to obtain real in-situ stress data. At the same time, a hydraulic tray 9 is installed at the bottom of the in-situ creep-seepage test chamber 1, and the oil pump in the oil-gas two-phase pressure monitoring and response box 2 is controlled according to the in-situ stress data to inject hydraulic oil into the hydraulic tray 9 and the in-situ creep-seepage test chamber 1 to provide axial and lateral stresses.

[0072] The extraction of the above-mentioned coal specimen 4 is from the in-situ coal produced by excavating a cavity for installing the in-situ creep-seepage test chamber 1. Specifically, a cylinder with a diameter of 50 mm and a height of 100 mm is cut out from the coal seam. The surface of the coal specimen is as complete and smooth as possible, without obvious cracks.

[0073] When setting the coal specimen 4, a strain gauge 5 is pasted on the surface of the coal specimen 4 to monitor the deformation amount of the coal specimen 4 when it is compressed by external stress, and the coal specimen 4 is wrapped with an oil separation film 6 to prevent the hydraulic oil filled inside the outer in-situ creep-seepage test chamber 1 from invading the coal structure and affecting the coal permeability, and at the same time ensure that the gas will not leak laterally. The oil separation film 6 is a thermoplastic material, having good mechanical properties and chemical stability and low cost.

[0074] The above-mentioned pressurizing end 7 is a dense solid cylinder steel column with an air duct in the center, installed in the in-situ creep-seepage test chamber 1, used to transmit the in-situ axial pressure to the coal specimen 4, and there is also a data transmission channel for transmitting the change data of the strain gauge 5 in the coal sample inside it, which can transmit the deformation data of the strain gauge 5 to the data acquisition and control box 3.

[0075] The above-mentioned fixing bolt 8 is a common connecting piece, used for axial positioning and fixing in the in-situ creep-seepage test chamber 1 to ensure that the in-situ creep-seepage test chamber 1 has sufficient strength.

[0076] The hydraulic tray 9 is installed at the bottom of the in-situ creep-seepage test chamber 1, and the height of the tray can be adjusted according to the in-situ stress of the coal seam provided by the data acquisition and control box 3. After reaching the predetermined stress value, the limit bolt 10 on the side of the hydraulic tray 9 is operated to fix the axial displacement of the hydraulic tray 9, and the axial displacement of the hydraulic tray 9 is kept constant.

[0077] Meanwhile, the monitoring system also installs pressure sensors 11 in the coal seam near the experimental site and above the in-situ creep-seepage test chamber 1, and connects the pressure sensors 11 and the data acquisition and control box 3 through the data line 16;

[0078] The hydraulic oil gauge 12 is also installed at the oil inlet and outlet of the oil-gas two-phase pressure monitoring and response box 2, and the oil pressure data generated by the hydraulic oil in the in-situ creep-seepage test chamber 1 is transmitted to the data acquisition and control box 3 through the data line 16;

[0079] The barometer 13 is also installed at the air inlet and outlet of the oil-gas two-phase pressure monitoring and response box 2 to measure the air pressure at both ends of the coal specimen 4 respectively, and the barometer monitoring data is transmitted to the data acquisition and control box 3 through the data line 16.

[0080] The present invention also proposes a prediction method for the creep-seepage response of coal bodies, which includes: a creep response prediction method and a seepage response prediction method. By fitting with the field data, the parameters in each formula are determined, and the time-series prediction of creep and permeability can be realized.

[0081] In terms of establishing a theoretical model capable of describing the creep of coal bodies, the present invention takes the traditional Westphal model as the framework, introduces the fractional-order operator which is good at describing nonlinear deformation problems, and establishes an improved Westphal model based on fractional-order derivatives. This model includes a Hooke body, a viscoelastic body, and a viscoplastic body, corresponding to three mechanical elements respectively, such as Figure 4 the three mechanical elements in the schematic diagram of the fractional-order Westphal model shown. From left to right, they are the Hooke body, the viscoelastic body, and the viscoplastic body. The specific expressions are:

[0082] ;

[0083] ; (1)

[0084] where: ε refers to the axial creep strain, including: elastic strain ε 1 , viscoelastic strain ε 2 , viscoplastic strain ε 3 ; σ refers to the axial stress, MPa; σ s refers to the yield stress, MPa; E 1 refers to the elastic modulus, GPa; E 2E represents the elastic modulus of the viscoelastic body, in GPa; λ represents the fractional order; η 1 and η 2 represents the viscosity coefficient, in GPa·h λ ; α 0 represents the viscosity attenuation parameter;

[0085] t is time; E λ,1 and E 1,1+λ are both Mittag-Leffler function operators.

[0086] Through the in-situ creep deformation data measured in the early stage, the improved Xiyuan model is fitted and analyzed to determine the physical and mechanical parameters in the creep model, and then the creep deformation calculation formula under the in-situ stress conditions of deep coal seams is obtained, so as to predict the long-term creep deformation value. Combining the specific experimental data in formula (1) with the evolution trend of the creep model as Figure 5 and Figure 6 shown.

[0087] Aiming at the change in the permeability of deep coal seams caused by nonlinear deformation, the present invention has monitored the gas pressure changes at both ends of the coal sample using an in-situ experimental device. In order to accurately calculate the evolution law of permeability, the present invention: combines the transient pulse test method, introduces the fractional derivative, and redefines the transient method permeability calculation formula, where the change in the gas pressure difference between the upper and lower ends of the coal sample with time can be described by the Mittag-Leffler function, that is:

[0088] ; (2)

[0089] ; (3)

[0090] Among them: refers to the Mittag-Leffler function; k g is the gas permeability.

[0091] At the beginning of the test, a stable in-situ gas pressure is applied to the coal sample, and an initial pressure difference P 0 is instantaneously formed when the in-situ gas is introduced into the coal sample, and gradually returns to the final equilibrium value P (t) over time. Through the fitting of the experimental data for the gas pressure difference on both sides of the coal sample, the parameter Φ is determined.

[0092] After the parameter Φ is determined, substituting the relevant experimental data can further deduce the permeability formula as:

[0093] ; (4)

[0094] Among them: refers to the inverse function of the Mittag-Leffler function, P(t) With P 0 refers to the final in-situ gas pressure difference and the initial in-situ gas pressure difference, MPa; t refers to time; k E refers to the experimental gas permeability, m 2 ; μ refers to the gas viscosity coefficient, Pa·s; β refers to the gas compressibility coefficient, Pa -1 ; L refers to the specimen length, m; A refers to the specimen cross-sectional area, m 2 ; V refers to the cylinder volume, m 3 .

[0095] According to the modeling idea of the permeability model, especially the construction framework of the cubic model, the present invention combines the creep deformation data and permeability evolution data of deep coal seams to establish an empirical formula for permeability evolution considering the influence of creep deformation:

[0096] The empirical formula for permeability evolution is as follows:

[0097] ; (5)

[0098] Where: k M is the model permeability, k 0 is the initial permeability, Δε 1 is the elastic strain increment, Δε 2 is the viscoelastic strain increment, Δε 3 is the viscoplastic strain increment, a and b are undetermined coefficients, which are specifically determined by the experimental data of permeability evolution with time.

[0099] It should be noted that the undetermined parameters in the permeability empirical formula are determined by the experimental data of permeability evolution with time. As Figure 7 shown, the calculation formula for the permeability of deep coal seams under the influence of creep is constructed. Combining the specific expressions of formula (1) and formula (5), a theoretical prediction method for creep-seepage response is finally formed.

[0100] Using the above analysis and prediction method, the present invention also provides a prediction method for the creep-seepage response of coal seams under in-situ stress conditions in mines based on the coal seam creep-seepage response monitoring system and the model response prediction system, including the following prediction steps:

[0101] 1. Select a deep coal seam roadway with relatively flat surface, appropriate wind speed, high visibility and relatively good lighting conditions as the in-situ experimental site;

[0102] 2. Use relevant tools to cut a cubic cavity with a side length of 300 mm on the coal wall, and cut out a cylindrical experimental coal sample 4 with a diameter of 50 mm and a height of 100 mm from the mined cubic coal sample;

[0103] 3. Assemble the in-situ creep-seepage test chamber 1: Fix two strain gauges 5, one horizontal and one vertical, on the cylindrical coal specimen 4. Then wrap the coal specimen 4 with a thermoplastic oil separation film 6 to ensure complete sealing. Next, fix the specimen 4 on the boss of the lower base 19 of the in-situ creep-seepage test chamber 1. Subsequently, assemble the lower base 19 and the chamber body 18, and install the pressurizing end 7 and the upper cover 17 of the in-situ creep-seepage test chamber 1. At the same time, install the pressure sensors 11 thereon;

[0104] 4. Check the airtightness of the devices inside the in-situ creep-seepage test chamber 1 and the air ducts, and tighten the entire in-situ creep-seepage test chamber 1 with the fixing bolts 8. Install the hydraulic tray 9 at the bottom of the in-situ creep-seepage test chamber 1, and connect the hydraulic tray 9 to the oil-gas two-phase pressure monitoring and response box 2;

[0105] 5. Install pressure sensors 11 in the pre-drilled holes around the coal seam cavity to measure the in-situ axial pressure, lateral pressure and gas pressure. Connect all the pressure sensors 11, hydraulic oil gauges 12 and barometers 13 to the data acquisition and control box 3 using data lines 16, and transmit various types of data to the data acquisition and control box 3;

[0106] 6. Connect the oil-gas two-phase pressure monitoring and response box 2 to the in-situ creep-seepage test chamber 1 and the hydraulic tray 9 with an oil pipeline 14; connect the oil-gas two-phase pressure monitoring and response box 2 to the in-situ creep-seepage test chamber 1 with a gas pipeline 15;

[0107] 7. Process the readings of each pressure sensor 11 in the coal seam in the data acquisition and control box 3 to obtain the actual true value of the in-situ stress. Adjust the oil-gas two-phase pressure monitoring and response box 2 to make the data of the pressure sensor 11 at the top of the in-situ creep-seepage test chamber 1 and the hydraulic oil gauge 12 inside the in-situ creep-seepage test chamber 1 consistent with the readings of the data acquisition and control box 3;

[0108] 8. After the above devices are installed, start the experiment on the creep-seepage response of the coal body under in-situ stress conditions. Read and record the readings of the strain gauges 5 on the surface of the coal specimen in real time, as well as the barometer readings in the oil-gas two-phase pressure monitoring and response box 2;

[0109] 9. Import the collected data set into relevant fitting software such as origin, calculate according to the existing creep model and permeability model, determine the specific parameters in the model, and obtain the in-situ coal body creep deformation prediction formula and the permeability evolution empirical formula;

[0110] 10. Through the above-obtained multiple groups of in-situ experimental data, repeatedly modify the undetermined parameters in the model to narrow the model error range, so as to achieve the purpose of long-term predicting the creep data and permeability of the coal body under in-situ stress conditions.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; 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 or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coal creep-seepage response monitoring system, comprising an in-situ creep-seepage test chamber (1), an oil-gas two-phase pressure monitoring and response box (2), and a data acquisition and control box (3), characterized in that: The in-situ creep-seepage test chamber (1) is installed in an underground coal wall to conduct experiments and record data in real time. The in-situ creep-seepage test chamber (1) comprises a chamber body (18) with upper and lower openings. The chamber body (18) is filled with a coal sample (4). An upper end cover (17) is installed on the top of the chamber body (18) via fixing bolts (8). A pressurizing end head (7) for transmitting in-situ axial pressure to the coal sample (4) is provided at the center of the upper end cover (17). A lower base (19) is installed on the bottom of the chamber body (18) via fixing bolts (8). A boss for fixing the coal sample (4) is provided at the center of the lower base (19). An air delivery pipe (15) connected to the outside of the bottom of the boss is connected to the air inlet of the oil-gas two-phase pressure monitoring and response box (2). An air delivery pipe (15) connected to the outside of the top of the pressurizing end head (7) is connected to the air outlet of the oil-gas two-phase pressure monitoring and response box (2). An oil filling port and an oil discharge port are also provided on the side wall of the cabin body (18); the inner side of the oil filling port is arranged opposite to the upper end surface of the coal body sample (4); the inner side of the oil discharge port is arranged opposite to the lower end surface of the coal body sample (4); the outer side of the oil filling port is connected to the oil outlet of the oil-gas two-phase pressure monitoring and response box (2) through an oil delivery pipe (14); and the outer side of the oil discharge port is connected to the oil inlet of the oil-gas two-phase pressure monitoring and response box (2) through an oil delivery pipe (14); A strain gauge (5) for monitoring the deformation of the coal body is also attached to the surface of the coal body sample (4), and the strain gauge (5) sends the coal body deformation data to the data acquisition and control box (3) via a data line (16); A hydraulic tray (9) capable of adjusting the height is installed at the bottom of the in-situ creep-seepage test chamber (1), and a side of the hydraulic tray (9) is also provided with a limit bolt (10) for fixing the axial displacement of the tray, and an oil delivery pipe (14) connected to the bottom of the hydraulic tray (9) is connected to the oil outlet of the oil-gas two-phase pressure monitoring and response box (2); A pressure sensor (11) is also provided inside the underground coal seam at the monitoring location and on the top of the in-situ creep-seepage test chamber (1), and a signal output end of the pressure sensor (11) is connected to the data acquisition and control box (3) via a data line (16); A hydraulic oil meter (12) is also provided at the oil inlet and the oil outlet of the oil-gas two-phase pressure monitoring and response box (2), and the hydraulic oil meter (12) sends the oil pressure data generated by the hydraulic oil in the in-situ creep-seepage test chamber (1) to the data acquisition and control box (3) via a data line (16); A barometer (13) is also provided at the air inlet and the air outlet of the oil-gas two-phase pressure monitoring and response box (2). The barometer (13) sends the air pressure data at both ends of the coal sample (4) to the data acquisition and control box (3) via a data line (16).

2. A coal creep-seepage response monitoring system according to claim 1, characterized in that: The oil-gas two-phase pressure monitoring and response box (2) specifically inputs and recovers in-situ gas to the in-situ creep-seepage test chamber (1) through a gas transmission pipe (15); The oil-gas two-phase pressure monitoring and response box (2) specifically inputs and recovers hydraulic oil into the in-situ creep-seepage test chamber (1) through an oil pipeline (14).

3. A coal creep-seepage response monitoring system according to claim 1, characterized in that: A plurality of display screens for displaying data collected by sensors are installed on the side walls of the oil and gas two-phase pressure monitoring and response box (2).

4. A coal creep-seepage response monitoring system according to claim 1, characterized in that: The data acquisition and control box (3) receives and processes the acquired data sent by each sensor to obtain real in-situ stress data, and controls the oil pump in the oil-gas two-phase pressure monitoring and response box (2) to inject hydraulic oil into the hydraulic tray (9) and the in-situ creep-seepage test chamber (1) based on the real in-situ stress data, thereby providing axial and lateral stresses.

5. A coal creep-seepage response monitoring system according to claim 1, characterized in that: Sealing plugs are provided at the locations where the in-situ creep-seepage test chamber (1), the hydraulic tray (9), the oil-gas two-phase pressure monitoring and response box (2) are connected to the oil pipelines (14), the gas pipelines (15), and the data lines (16).

6. A coal creep-seepage response monitoring system according to claim 1, characterized in that: The coal body sample (4) filled in the in-situ creep-seepage test chamber (1) is specifically a cylindrical coal body with a diameter of 50 mm and a height of 100 mm.

7. A coal creep-seepage response monitoring system according to claim 1, characterized in that: The surface of the coal sample (4) is also coated with a layer of oil-isolating film (6).

8. A method for predicting coal creep-seepage response using a coal creep-seepage response monitoring system as claimed in claim 1, characterized in that: The prediction steps include the following: The deep coal seam tunnel was selected as the in-situ experimental site; A cubic cavity is excavated on the coal wall using a tool to obtain a cubic coal sample, and then a cylindrical coal body sample (4) with a diameter of 50 mm and a height of 100 mm is cut out from the mined cubic coal sample; Assembling the in-situ creep-seepage test chamber (1): fixing two horizontal and vertical strain gauges (5) on the coal sample (4), then wrapping the coal sample (4) with an oil-isolating film (6) to ensure complete sealing, and then fixing the coal sample (4) on the boss of the lower base (19) of the in-situ creep-seepage test chamber (1), then installing the lower base (19) on the bottom of the chamber body (18), installing the pressurizing end head (7) and the upper end cover (17) on the top of the chamber body (18), and installing a pressure sensor (11) on the upper part of the pressurizing end head (7); Check the air tightness of the devices inside the in-situ creep-seepage test chamber (1) and inside the air duct, use the fixing bolts (8) to tighten the entire in-situ creep-seepage test chamber (1), and install the hydraulic tray (9) at the bottom of the in-situ creep-seepage test chamber (1); Pressure sensors (11) are installed in prefabricated boreholes around the coal seam cavity to measure the in-situ axial pressure, lateral pressure, and gas pressure. The signal output ends of all pressure sensors (11), hydraulic oil gauges (12), and barometers (13) send the collected data to the data collection and control box (3) via data lines (16); The oil-gas two-phase pressure monitoring and response box (2) is connected to the in-situ creep-seepage test chamber (1) and the hydraulic tray (9) respectively by using an oil pipeline (14), and the oil-gas two-phase pressure monitoring and response box (2) is connected to the in-situ creep-seepage test chamber (1) by using an air pipeline (15); The data collected by each pressure sensor (11) in the coal seam is processed by the data acquisition and control box (3) to obtain the actual true value of the in-situ stress, and the oil-gas two-phase pressure monitoring and response box (2) is adjusted so that the data of the pressure sensor (11) at the top of the in-situ creep-seepage test chamber (1) and the hydraulic oil gauge (12) on the oil-gas two-phase pressure monitoring and response box (2) are consistent with the reading on the data acquisition and control box (3); After the monitoring system was installed, the coal creep-seepage response experiment under in-situ stress conditions began: First, the strain gauge (5) readings on the surface of the coal sample (4) and the barometer readings in the oil and gas two-phase pressure monitoring and response box (2) are read and recorded in real time. The collected data set is imported into the origin fitting software, and calculations are performed based on the existing creep model and permeability model to determine the specific parameters in the model, thereby obtaining the in-situ coal creep deformation prediction formula and the permeability evolution empirical formula. Through the acquisition of multiple sets of in-situ experimental data, the undetermined parameters in the model are repeatedly modified to narrow the model error range, thereby realizing long-term prediction of coal creep data and permeability under in-situ stress conditions.

9. A method for predicting creep-seepage response of coal according to claim 8, characterized in that: The in-situ coal creep deformation prediction formula used in the prediction of coal creep-seepage response under in-situ stress conditions is based on the Western model as a framework, introducing fractional-order operators that are good at describing nonlinear deformation problems, and establishing an improved Western model based on fractional-order derivatives. The improved Western model includes Hookean body, viscoelastic body, and viscoplastic body, and the expression is: ； ； Where: ε is the axial creep strain, including elastic strain ε1, viscoelastic strain ε2, and viscoplastic strain ε3; σ is the axial stress; σ s is the yield stress; E1 is the elastic modulus; E2 is the elastic modulus of the viscoelastic body; λ is the fractional order; η1 and η2 are viscosity coefficients; α0 is the viscosity attenuation parameter; t is time; E λ,1 With E 1,1+λ All are Mittag-Leffler function operators; Through the in-situ creep deformation data measured in the early stage, the improved Xiyuan model was fitted and analyzed, the physical and mechanical parameters in the creep model were determined, and then the creep deformation calculation formula under the in-situ stress conditions of deep coal body was obtained.

10. A method for predicting creep-seepage response of coal according to claim 9, characterized in that: The empirical formula for permeability evolution used in the prediction of creep-seepage response of coal under in-situ stress conditions is specifically combined with the transient pulse test method, and the fractional derivative is introduced to redefine the transient permeability calculation formula. The change of gas pressure difference between the upper and lower ends of the coal sample with time is described by the Mittag-Leffler function, which is expressed as follows: ； ； in: is the Mittag-Leffler function; k g is the gas permeability; At the beginning of the experiment, a stable in-situ gas pressure is applied to the coal sample (4). When the in-situ gas is introduced into the coal sample (4), an initial pressure difference P0 is formed instantly, and gradually recovers to the final equilibrium value P as time goes by. (t) , the gas pressure difference between the upper and lower sides of the coal sample (4) is fitted through the experimental data to determine the parameter Φ, and then the relevant experimental data are introduced to derive the calculation formula of the permeability: ； in: is the inverse function of the Mittag-Leffler function, P (t) and P0 is the final in-situ gas pressure difference and the initial in-situ gas pressure difference; t is time; k E is the experimental gas permeability; μ is the gas viscosity coefficient; β is the gas compressibility coefficient; L is the length of the specimen; A is the cross-sectional area of ​​the specimen; V is the volume of the cylinder; Then, combining the deep coal body creep deformation data and permeability evolution data, an empirical formula for permeability evolution considering the influence of creep deformation is established: ； Where: k M is the model permeability, k0 is the initial permeability, Δε1 is the elastic strain increment, Δε2 is the viscoelastic strain increment, Δε3 is the viscoplastic strain increment, and a and b are unknown coefficients, which are determined by the experimental data of the evolution of permeability over time.

Images