CN115372223B - Coal-gas multi-physical field coupling experimental device and method - Google Patents

Abstract

The invention discloses a novel coal-gas multi-physical field coupling experimental device which comprises a triaxial loading subsystem, a confining pressure control subsystem, an air pressure control subsystem and a temperature control subsystem, wherein the triaxial loading subsystem is respectively communicated with the confining pressure control subsystem and the air pressure control subsystem through a honeycomb duct, and the outer surface of the triaxial loading subsystem is connected with the air pressure control subsystem. The using method comprises seven steps of equipment detection, coal sample prefabrication, confining pressure loading and vacuumizing, continuous gas injection, driving a gas pressure control subsystem to operate, long-time period cyclic measurement, and experiment ending reset, data processing and calculation. Compared with the prior art, the invention has the following beneficial effects: the device and the method effectively solve the problem that the permeability, axial strain, radial strain, integral strain and fracture strain of the coal rock sample cannot be measured periodically for a long time in the existing coal rock permeability measuring device and method; the data processing capability is strong, and the measurement accuracy is high.

Description

Coal-gas multi-physical field coupling experimental device and method

Technical Field

The invention relates to a coal-gas multi-physical field coupling experimental device and a using method thereof, and belongs to the technical field of coal rock seepage-deformation testing.

Background

The permeability is a physical quantity for measuring the difficulty of gas migration in a pore medium, and is an important parameter for determining the exploitation effect of unconventional natural gas such as coalbed methane, tight sandstone gas, shale gas and the like. The control mechanism of permeability of coal and rock under the coupling of multiple physical fields such as different boundaries (such as stress boundary and displacement boundary), different environments (temperature and humidity), different gases (adsorptive and non-adsorptive gases) and the like is clear, and is a key for realizing efficient exploitation of unconventional natural gas, petroleum exploitation, gas control and bottom plate water control. Therefore, a set of coal-rock seepage measurement device and method capable of realizing the multi-physical field coupling is the basis for developing related researches.

Studies have shown that: the permeability and the porosity of the coal rock are positively correlated, and the coal rock has obvious time evolution characteristics. In the resource exploitation and disaster prevention process, the change of the environment of multiple physical fields where the coal and the rock are located causes the change of the volumes of the whole coal and the rock and the internal cracks, thereby controlling the change of the permeability. Many researchers have built a series of multi-category strain (global strain, fracture strain, matrix strain) controlled permeability models for exploring the time evolution law of permeability under the condition of multi-physical field coupling. Therefore, to justify these assumptions and theories, on the one hand, it is necessary to measure the permeability of the coal rock, while further measuring the mechanical parameters of the coal rock (modulus of elasticity, poisson's ratio), multi-scale strain (global strain, fracture strain, matrix strain); on the other hand, the parameters are necessary to be periodically measured for a long time, and the change rule of the parameters and the permeability along with the gas injection/gas production time is explored, so that the method has important significance in researching the control mechanism of the coal rock permeability.

In recent years, as the field of coal-rock seepage is widely focused, a device and a method for measuring coal-rock permeability are developed and perfected by many researchers. In the aspect of improvement of a permeability measuring device, researchers combine equipment such as an electronic Computed Tomography (CT), an acoustic emission device, a strain analyzer, a displacement meter and the like on the basis of a triaxial loading device to realize measurement of parameters such as pore structure, overall deformation and the like of coal and rock. For example: (1) liang Tianbo, zhou Fujian, zhang Mengchuan, yang Kai, qu Hongyan, yao Erdong, li Ben, hu Xiaodong, wang Bo, left clean a relative permeability measurement system and method based on split flow model and CT scan [ P ]. Beijing: CN113295594a,2021-08-24; (2) liang Weiguo, jiang Yulong, li Wenda, wu Peng a true triaxial frac seepage test apparatus and method [ P ]. Shanxi province: CN111272576a,2020-06-12; (3) wang Hanpeng, liu Zhongzhong, yuan Liang, zhang Bing, zhang Jiangyong, wang Wei, hou Weitao, zhang Chong, xue Yang. Rock triaxial mechanical permeability tester and test method [ P ]. Shandong province: CN109253952B,2021-12-28; (4) zhao Yaoyao, liu Jishan, cui Dongxue, wei Mingyao. A device and method for measuring permeability, overall strain and fracture strain of coal rock [ P ]. Beijing: CN112525791B,2022-02-15. The disclosed permeability measuring method can accurately measure the permeability of coal and rock under the conditions of different pressures, different confining pressures, different temperatures, different gases and the like. But long-time periodic measurements of coal rock permeability and other parameters cannot be achieved.

Therefore, the experimental research on the evolution rule of coal rock permeability, fracture strain, overall strain and mechanical parameters along with gas injection time/gas production time still belongs to the blank. There is a strong need for an apparatus and method of use that can periodically measure coal rock permeability and multi-class strain over a long period of time.

Disclosure of Invention

The invention aims to overcome the defects and provide a coal-gas multi-physical field coupling experimental device and a method.

In order to achieve the above purpose, the present invention is realized by the following technical scheme:

the utility model provides a coal-gas multi-physical field coupling experimental apparatus, including triaxial loading subsystem, confining pressure control subsystem, atmospheric pressure control subsystem, data transmission and collection subsystem, temperature control subsystem, wherein triaxial loading subsystem passes through the honeycomb duct and communicates with confining pressure control subsystem, atmospheric pressure control subsystem respectively, triaxial loading subsystem surface atmospheric pressure control subsystem is connected with temperature control subsystem in addition, triaxial loading subsystem, confining pressure control subsystem, atmospheric pressure control subsystem and temperature control subsystem all are with data transmission and collection subsystem between electrical connection, temperature control subsystem includes the water bath case, the heating blanket, temperature sensor, the water bath case, the heating blanket is all at least one, wherein the water bath case is connected with triaxial loading subsystem surface, the water bath case is connected with atmospheric pressure control subsystem, and at least one temperature sensor is all established in each water bath case, the heating blanket.

Further, the pneumatic control subsystem comprises a power gas storage bottle, a gas injection gas storage bottle, a gas pressure regulator, an upper standard bottle, a lower standard bottle, a tail gas collector, a pressure reducing valve, an electromagnetic valve, a vacuum pump, a pressure sensor and a flow sensor, wherein the power gas storage bottle and the gas injection gas storage bottle are at least one, the power gas storage bottle and the gas injection gas storage bottle are mutually connected in parallel and are respectively communicated with the gas pressure regulator through the flow guide pipe, the gas pressure regulator is communicated with the vacuum pump, the upper standard bottle and the gas inlet end of the three-axis loading subsystem through the flow guide pipe, the vacuum pump, the upper standard bottle and the three-axis loading subsystem are mutually connected in parallel, the downstream standard bottle and the tail gas collector are connected in parallel and are communicated with the exhaust end of the three-axis loading subsystem through the flow guide pipe, the upper standard bottle and the lower standard bottle are connected in parallel and are embedded in the water bath box of the temperature control subsystem, the pressure sensor is arranged on the flow guide pipe section between the upper standard bottle and the vacuum pump, the pressure sensor and the tail gas collector are respectively arranged on the flow guide pipe between the lower standard bottle and the tail gas collector, the vacuum pump is communicated with the vacuum pump through the flow guide pipe, the upper standard bottle, the lower standard bottle and the three-axis loading subsystem, the air collector are communicated with the air collector, the air collector and the three-axis standard bottle and the three-axis collector through the electromagnetic valve and the vacuum pump.

Further, the confining pressure control subsystem comprises an axial pressure control pump, a circumferential pressure injection port, a shaft pressure injection port and a control valve, wherein the axial pressure control pump and the circumferential pressure control pump are uniform and are mutually connected in parallel, the axial pressure control pump is communicated with the shaft pressure injection port through a flow guide pipe, the circumferential pressure control pump is communicated with the circumferential pressure injection port through a flow guide pipe, the circumferential pressure injection port and the shaft pressure injection port are embedded on the side surface of the triaxial loading subsystem and are communicated with the triaxial loading subsystem, the flow guide pipe is communicated with the axial pressure control pump, the circumferential pressure injection port and the shaft pressure injection port through the control valve, and the control valve is further electrically connected with the data transmission and acquisition subsystem.

Further, the triaxial loading subsystem comprises an outer end cover, an inner end cover, a guide cylinder body, a detection cylinder body, a rubber isolation sleeve, a drainage tube, an axial piston, an upstream gas injection cushion block, a downstream gas injection cushion block, a transition cushion block, a displacement sensor, a resistance strain gauge and a pressure plate, wherein the guide cylinder body, the detection cylinder body and the rubber isolation sleeve are hollow columnar structures with rectangular axial sections, the rear end surface of the detection cylinder body is connected with the outer end cover, the front end surface is connected with the inner end cover, the inner end cover is connected with the guide cylinder body and is connected with the outer end cover through the guide cylinder body, the outer end cover, the inner end cover, the detection cylinder body are coaxially distributed, through holes coaxially distributed with the detection cylinder body are respectively arranged on the outer end cover and the inner end cover and are communicated through the through holes, the rubber isolation sleeve is embedded in the detection cylinder body and coaxially distributed with the detection cylinder body, the front end surface of the rubber isolation sleeve is propped against the inner end cover through the transition cushion block, the rear end face is propped against the outer end cover through the inner end cover and communicated with the through hole, a ring pressing cavity with the length not more than 80% of the length of the rubber isolation sleeve is arranged between the outer side face of the rubber isolation sleeve and the inner side face of the detection cylinder body, at least two diversion holes uniformly distributed around the axis of the detection cylinder body are arranged on the side wall of the detection cylinder body corresponding to the ring pressing cavity, the diversion holes are vertically distributed and intersected with the axis of the detection cylinder body, the intersection point is positioned at the midpoint position of the detection cylinder body, the diversion holes are communicated with the ring pressing injection hole, two pressure plates are embedded in the rubber isolation sleeve, are coaxially distributed with the rubber isolation sleeve and are in sliding connection with the inner side face of the rubber isolation sleeve, the two pressure plates are symmetrically distributed at the two end faces of the rubber isolation sleeve, a detection cavity is formed between the two pressure plates, one pressure plate is propped against the transition cushion block through an upstream gas injection cushion block, the other pressure plate is propped against the transition cushion block through a downstream gas injection cushion block, the resistance strain gauge is at least two and is positioned in the detection cavity, at least one resistance strain gauge detection axis is distributed in parallel with the detection cavity axis, at least one resistance strain gauge detection axis is distributed vertically with the detection cavity axis, the axial piston is embedded in the guide cylinder body, is coaxially distributed with the guide cylinder body and is in sliding connection with the inner surface of the guide cylinder body, an axial pressure cavity is formed between the axial piston and the front half part of the guide cylinder body, at least two axial pressure injection ports uniformly distributed around the axis of the guide cylinder body are arranged on the side wall of the guide cylinder body corresponding to the axial pressure cavity, at the same time, the front end surface of the axial piston is positioned outside the outer end cover, the rear end surface of the axial piston is positioned in the detection cylinder body through the through hole and is propped against the upstream gas injection cushion block, the axial piston, the upstream gas injection cushion block and the downstream gas injection cushion block are internally provided with gas guide cavities communicated with the detection cavity, the drainage tube is positioned at the rear end surface of the detection cylinder body, the front half part of the drainage tube is embedded in the detection cylinder body and is propped against the downstream gas injection cushion block, the gas guide cavity of the downstream gas cushion block is communicated with the drainage tube, the rear end surface is positioned outside the detection cylinder body, and at least one sensor is connected with the displacement sensor in an axial direction sensor and is connected with the displacement sensor in an electrical sensor system.

Further, the transition cushion block comprises an elastic sealing sleeve and a metal guide sleeve, the elastic sealing sleeve is of a round table structure with an isosceles trapezoid axial section, the metal guide sleeve is of a hollow tubular structure with a rectangular axial section, the metal guide sleeve is embedded in the rear end face of the elastic sealing sleeve and is coaxially distributed with the elastic sealing sleeve, the metal guide sleeve is coated outside the axial piston and is in sliding connection with the axial piston, at least two transition holes uniformly distributed around the axis of the metal guide sleeve are formed in the side wall of the metal guide sleeve, the axis of each transition hole is intersected with the axis of the metal guide sleeve and forms an included angle of 30-60 degrees, and the transition holes are communicated with the air guide cavity of the axial piston.

Further, the data transmission and collection subsystem comprises a data processing computer, a driving circuit based on an industrial computer and a strain analyzer, wherein the driving circuit based on the industrial computer is electrically connected with the data processing computer, the strain analyzer, the triaxial loading subsystem, the confining pressure control subsystem, the air pressure control subsystem and the temperature control subsystem respectively, and the strain analyzer is electrically connected with the triaxial loading subsystem.

The application method of the coal-gas multi-physical field coupling experimental device comprises the following steps:

S1, equipment detection, namely firstly assembling and assembling a triaxial loading subsystem, a confining pressure control subsystem, an air pressure control subsystem, a data transmission and acquisition subsystem and a temperature control subsystem to obtain a multi-physical field coupling experimental device, then driving the confining pressure control subsystem and the air pressure control subsystem to operate and maintaining the pressure of the triaxial loading subsystem to realize the operation function and air tightness detection of the multi-physical field coupling experimental device; simultaneously recording calculation steps and calculation functions in a data transmission and acquisition subsystem;

s2, prefabricating a coal sample, measuring a sample to be measured by using a vernier caliper, putting the sample to be measured into a drying box, and drying for 24 hours under 40-60; selecting 2 resistance strain gauges with the length close to the length of a sample to be tested, checking and ensuring that the resistance is 120 omega, and respectively and tightly adhering the 2 resistance strain gauges to the side surface of the sample to be tested along the axial direction and the circumferential direction of the sample to be tested; loading a sample to be tested, to which the resistance strain gauge is attached, into a triaxial loading subsystem, and checking the resistance strain gauge by using an ohmmeter to ensure that the resistance value is normal; finally, connecting the resistance strain gauge with a strain analyzer of a data transmission and acquisition subsystem through a data transmission line; measuring each resistance strain gauge by a strain analyzer, and verifying the measurement accuracy of the resistance strain gauge;

S3, confining pressure loading and vacuumizing, namely driving a confining pressure control subsystem to operate, and respectively injecting pressure liquid with the pressure of 6MPa into a shaft pressure chamber and a ring pressure chamber of the triaxial loading subsystem by an axial pressure control pump and a ring pressure control pump of the confining pressure control subsystem and maintaining the pressure; and then driving a vacuum pump to operate, vacuumizing the detection cavity of the triaxial loading subsystem, and maintaining the pressure for 24 hours.

S4, continuously injecting gas, driving the gas pressure control subsystem to operate, regulating the pressure of the power gas storage bottle and the gas in the gas injection gas storage bottle by a gas pressure regulator, and simultaneously continuously injecting the gas with the pressure of 3MPa into the triaxial loading subsystem and the upper standard bottle;

s5, circularly measuring for a long time period, and after the step S4 is completed, setting the regulation and control period of the output gas pressure of the gas pressure regulator to be 4h by utilizing a data transmission and acquisition subsystem, wherein the amplitude is 0.2MPa, and the cycle repetition number is 60 times; simultaneously setting the opening and closing action period of each electromagnetic valve; finally, the change of the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline along with time are recorded and counted by using an upstream pressure sensor and a downstream pressure sensor respectively;

s6, resetting after the experiment is ended, periodically measuring for 240h (60 cycles) through the step S5, stopping measuring work, and resetting each equipment part after the measuring work is completed;

And S7, data processing and calculation are carried out on each data measured in the step S5, and the data transmission and acquisition subsystem carries out data calculation by utilizing the calculation step and the calculation function set in the step S1, so that test data can be obtained.

Further, in the step S5, the long-period cyclic measurement operation includes the following steps:

first, measuring the phase of the upper half cycle period: when the gas pressure in the upstream pipeline is equal to that in the downstream pipeline, the electromagnetic valve is closed; the gas pressure regulator injects gas with the pressure of 3.2MPa into the upstream standard bottle; the solenoid valve and the gas pressure regulator are then closed, the time at this moment being defined as the initial time of the last half of the cycle; when the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline are balanced and equal, recording the balanced pressure value;

second, measuring the phase of the next half cycle period: when the cycle time is 2 hours, regulating the gas pressure output by the gas pressure regulator to be 2.8MPa; and after the gas pressure in the upstream pipeline is 2.8MPa, the time at the moment is defined as the initial time of the lower half cycle of the cycle; and the gas pressure in the upstream pipeline and the downstream pipeline reaches a new balance; when the period measurement time reaches 4 hours, ending the single period measurement; the operation is then repeated to perform the measurement operation for the next cycle.

Further, in the step S7, the calculating step and the calculating function are specifically:

since the data processing and calculation methods of each measurement period are the same, only the processing and calculation methods of experimental data measured in the T (T takes any value of 1 to 60) th period will be described in detail below:

the first step, the method for calculating the permeability is based on Darcy's law and conservation of mass law,

fitting according to the relationship between the pressure difference of 0.2MPa and time to obtain the permeability of the sample to be tested:

wherein k is _Tj When the permeability value is the T period, the permeability value of the sample 11 to be measured obtained by fitting is utilized, when j is taken to be 1, the permeability value measured in the upper half period of the T period is represented, and when j is taken to be 2, the permeability value measured in the lower half period of the T period is represented; ΔP ₂ For the difference between the upstream and downstream gas pressures, the embodiment takes 0.2MPa; beta is the compressibility coefficient of the gas, pa ^-1 The method comprises the steps of carrying out a first treatment on the surface of the t is the gas injection time corresponding to the initial time of the half measurement period of (i 1)/lower (i 2) of the current measurement period, and s; v (V) _up Taking 1×10 for the total volume of the upstream pipeline and the upstream standard bottle ^-4 m ³ ；V _dn 1X 10 for the total volume of the downstream piping and downstream standard bottle ^-4 m ³ ；k _T The average permeability value obtained for the T-th cycle;

in the second step, the axial strain, the radial strain and the overall strain are calculated, because the axial strain and the radial strain are continuously monitored by the resistive strain gauge 56, in the T-th measurement period, strain values at a plurality of different times are observed, in order to reduce the number of measurement results and facilitate the calculation of the matrix strain, the average value of all the axial strains in the T-th period is taken as the axial strain value of the T-th period, the average value of all the radial strains in the T-th period is taken as the radial strain value of the T-th period, and the geometric relationship between the overall strain and the radial strain and the axial strain is satisfied:

In the method, in the process of the invention,

for the strain values measured in period T, when i is a +.>

Represents axial strain, when i is r +.>

Representing radial strain; e (E) _out The output voltage of the low-purine differential amplifier is mu V; e (E) _g Supplying voltage, V, to the bridge; e (E) _g The sensitivity coefficient of the resistance strain gauge; k (K) _L Gain for a low purine differential amplifier; epsilon _b For the overall strain of the test specimen ε _bT The overall strain value for the T-th cycle;

and thirdly, calculating the volume of the crack and the strain of the crack. From equations 16 and 17, it can be seen that the fracture volume and fracture strain are satisfied by the T-th cycle measurement

Wherein V is _f0 The fracture volume, m, measured for cycle 1 ³ ；V _fT For the fracture volume, m, measured in the T-th cycle ³ ；

The initial upstream gas pressure for the half cycle on the T-th cycle is 3.2MPa; />

The initial upstream gas pressure for the next half-cycle of the T-th cycle is 2.8MPa; />

The equilibrium gas pressure, pa, is the upper half-cycle of the T-th cycle; />

Balance gas pressure, MPa, for the next half-cycle of the T-th cycle; />

The initial upstream gas pressure for the upper half-cycle of the T-th cycle is 3.0MPa; />

An initial upstream gas pressure, pa, for the next half-cycle of the T-th cycle;

and fourthly, calculating the matrix strain. As can be seen from equation 19, the matrix strain satisfies:

Wherein ε _mT Strain for the T-th cycle substrate; v (V) _b1 For the initial whole volume of the sample to be measured obtained by the 1 st period measurement, m ³ ；V _f1 The fracture volume, m, of the sample to be measured is measured for the 1 st period ³ ；

The data of all periods obtained by measurement are processed according to the method, and the evolution of values of all permeability, axial strain, radial strain, overall strain, fracture strain and matrix strain of 60 measurement periods in 240 hours with time is obtained.

Compared with the prior art, the invention has the following beneficial effects: the invention can realize the long-time periodic measurement of the permeability, axial strain, radial strain, overall strain and fracture strain of the coal rock sample, and also can realize the measurement of mechanical parameters (such as elastic modulus, poisson ratio and compressive strength) of the coal rock sample; meanwhile, the system meets the measurement methods of three permeabilities of a steady state method, a transient state method and a periodic oscillation method, and is suitable for measuring coal samples with permeabilities of different levels; the device and the method effectively solve the problem that the permeability, axial strain, radial strain, overall strain and fracture strain of the coal rock sample cannot be periodically measured for a long time in the existing coal rock permeability measuring device and method; the method can also realize the development of a great deal of related researches on the multi-category strain and permeability evolution relation of the coal and rock mass under the multi-scale multi-physical field, and has good use flexibility and universality; in addition, the invention has the advantages of simple structure, simple operation method, strong data processing capability and high measurement precision, and can be popularized and applied in the field of coal rock seepage and deformation measurement.

Drawings

FIG. 1 is a schematic diagram of the structure of the present invention;

FIG. 2 is a schematic top view of a metal liner;

FIG. 3 is a schematic top view of a partial structure of a plugging plate;

fig. 4 is a flow chart of the method of the present invention.

Detailed Description

As shown in fig. 1-3, a coal-gas multi-physical-field coupling experimental device comprises a triaxial loading subsystem 1, a confining pressure control subsystem 2, an air pressure control subsystem 3, a data transmission and acquisition subsystem 4 and a temperature control subsystem 5, wherein the triaxial loading subsystem 1 is respectively communicated with the confining pressure control subsystem 2 and the air pressure control subsystem 3 through a flow guide pipe, the outer surface of the triaxial loading subsystem 1 is further connected with the air pressure control subsystem 3, the triaxial loading subsystem 1, the confining pressure control subsystem 2, the air pressure control subsystem 3 and the temperature control subsystem 5 are electrically connected with the data transmission subsystem 4 and the acquisition subsystem 5, the temperature control subsystem 5 comprises at least one water bath box 51, a heating blanket 52 and a temperature sensor 53, the water bath box 51 and the heating blanket 52 are respectively connected with the outer surface of the triaxial loading subsystem 1, the water bath box 51 is connected with the air pressure control subsystem 3, and at least one temperature sensor 53 is respectively arranged in each water bath box 51 and heating blanket 52.

Further preferably, the temperature control subsystem 5 is adjusted to be in a range of room temperature to 100 ℃, wherein the volume of the water bath tank 51 is 10L, and the power is 800W.

In this embodiment, the air pressure control subsystem 3 includes a power bomb 31, an air injection bomb 32, a gas pressure regulator 33, an upstream standard bomb 34, a downstream standard bomb 35, a tail gas collector 36, a pressure reducing valve 37, an electromagnetic valve 38, a vacuum pump 39, a pressure sensor 301, and a flow sensor 302, at least one of the power bomb 31 and the air injection bomb 32 is connected in parallel with each other and is respectively connected with the gas pressure regulator 33 through a flow guide pipe, the gas pressure regulator 33 is connected with the vacuum pump 39, the upstream standard bomb 34 and an air inlet end of the three-axis loading subsystem 1 through the flow guide pipe, the vacuum pump 39, the upstream standard bomb 34 and the three-axis loading subsystem 1 are connected in parallel, the downstream standard bomb 35 and the tail gas collector 36 are connected in parallel and are connected with an air outlet end of the three-axis loading subsystem 3 through the flow guide pipe, the upstream standard bomb 34 and the downstream standard bomb 35 are connected in parallel and are embedded in a water bath 51 of the temperature control subsystem 5, the upstream standard bomb 34 and the vacuum pump 39 are connected with each other through the flow guide pipe, the upstream standard bomb 34, the pressure regulator 35, the three-axis pressure sensor 33 is connected with the three-axis collecting subsystem 1, the three-axis measuring bomb 35, the air collector 35, the air pressure sensor 33 is connected with the three-axis collecting subsystem 1, the three-pressure sensor 33, the downstream standard bomb 34 and the tail gas collector 35 and the three-axis measuring bomb 34 and the three-axis collecting subsystem 1 are connected with the air collector 35, the downstream standard bomb 34 and the tail gas collector 35, the tail gas collector and the vacuum sensor is connected with the three-gas collector and the vacuum sensor, the flow sensors 302 are each electrically connected to the data transmission and acquisition subsystem 4.

In this embodiment, the confining pressure control subsystem 2 includes an axial pressure control pump 21, a circumferential pressure control pump 22, a circumferential pressure injection port 23, an axial pressure injection port 24 and a control valve 25, where the axial pressure control pump 21 and the circumferential pressure control pump 22 are uniformly connected in parallel, the axial pressure control pump 21 is communicated with the axial pressure injection port 24 through a flow guiding pipe, the circumferential pressure control pump 22 is communicated with the circumferential pressure injection port 23 through a flow guiding pipe, the circumferential pressure injection port 23 and the axial pressure injection port 24 are embedded in the side surface of the triaxial loading subsystem 1 and are communicated with the triaxial loading subsystem 1, the flow guiding pipe is communicated with the axial pressure control pump 21, the circumferential pressure control pump 22, the circumferential pressure injection port 23 and the axial pressure injection port 24 through the control valve 25, and the control valve 25 is electrically connected with the data transmission and collection subsystem 4.

Wherein: the axial pressure control pump provides axial pressure for the sample to be tested. The axial pressure conduction path is as follows: axial pressure control pump, axial pressure chamber, transition cushion block, upstream gas injection cushion block and front end face of sample to be tested;

the hoop pressure control pump provides hoop pressure to the sample to be tested. The hoop pressure conduction path is as follows: circumferential pressure control pump, circumferential pressure chamber, rubber isolation sleeve and side surface of sample to be tested.

The triaxial loading subsystem 1 comprises an outer end cover 11, an inner end cover 12, a guide cylinder 13, a detection cylinder 14, a rubber isolation sleeve 15, a drainage tube 16, an axial piston 17, an upstream gas injection cushion block 18, a downstream gas injection cushion block 19, a transition cushion block 101, a displacement sensor 102, a resistance strain gauge 103 and a pressure plate 104, wherein the guide cylinder 13, the detection cylinder 14 and the rubber isolation sleeve 15 are hollow columnar structures with rectangular axial sections, the rear end surface of the detection cylinder 14 is connected with the outer end cover 11, the front end surface is connected with the inner end cover 12, the inner end cover 12 is connected with the guide cylinder 13 and is connected with the outer end cover 11 through the guide cylinder 13, the outer end cover 11, the inner end cover 12, the guide cylinder 13 and the detection cylinder 14 are coaxially distributed, through holes 105 coaxially distributed with the detection cylinder 14 are respectively arranged on the outer end cover 11 and the inner end cover 12, the rubber isolation sleeve 15 is embedded in the detection cylinder body 14 and is coaxially distributed with the detection cylinder body 14 through the through holes 105, the front end surface of the rubber isolation sleeve is propped against the inner end cover through the transition cushion block 101, the rear end surface of the rubber isolation sleeve is propped against the outer end cover through the inner end cover 12 and is communicated with the through holes 105, a ring pressure cavity 106 with the length not more than 80% of the length of the rubber isolation sleeve 15 is arranged between the outer side surface of the rubber isolation sleeve 15 and the inner side surface of the detection cylinder body 14, at least two diversion holes 107 uniformly distributed around the axis of the detection cylinder body 14 are arranged on the side wall of the detection cylinder body 14 corresponding to the ring pressure cavity 106, the diversion holes 107 are vertically distributed and intersected with the axis of the detection cylinder body 14, the intersection point is positioned at the midpoint position of the detection cylinder body 14, the diversion holes 107 are additionally communicated with the ring pressure injection port 23, the pressure disk 104 is embedded in the rubber isolation sleeve 15, is coaxially distributed with the rubber isolation sleeve 15 and is slidingly connected with the inner side surface of the rubber isolation sleeve 15, the two pressure plates 104 are symmetrically distributed on the two end surfaces of the rubber isolation sleeve 15, a detection cavity 108 is formed between the two pressure plates 104, meanwhile, one pressure plate 104 is propped against the transition cushion block 101 through the upstream air injection cushion block 18, the other pressure plate 104 is propped against the transition cushion block 101 through the downstream air injection cushion block 19, at least two resistance strain gauges 103 are positioned in the detection cavity 108, at least one resistance strain gauge 103 detection axis is distributed in parallel with the detection cavity 108 axis, at least one resistance strain gauge 103 detection axis is vertically distributed with the detection cavity 108 axis, the axial piston 17 is embedded in the guide cylinder 13, is coaxially distributed with the guide cylinder 13 and is in sliding connection with the inner surface of the guide cylinder 13, an axial pressure cavity 109 is formed between the axial piston 17 and the front half part of the guide cylinder 13, at least two axial pressure injection ports 24 uniformly distributed around the guide cylinder 13 axis are arranged on the side wall of the guide cylinder 13 corresponding to the axial pressure cavity 109, meanwhile, the front end face of the axial piston 17 is located outside the outer end cover 11, the rear end face of the axial piston is located in the detection cylinder 14 through the through hole 105 and is propped against the upstream gas injection cushion block 18, gas guide cavities 100 communicated with the detection cylinder 14 are formed in the axial piston 17, the upstream gas injection cushion block 18 and the downstream gas injection cushion block 19, the gas guide cavities 100 are communicated with the detection cavity 108, the drainage tube 16 is located at the rear end face of the detection cylinder 14, the front half part of the drainage tube 16 is embedded into the detection cylinder 14 through the through hole 105 and is propped against the downstream gas injection cushion block 19, the gas guide cavity 100 of the downstream gas injection cushion block 19 is communicated with the drainage tube 16, the rear end face of the drainage tube 16 is located outside the detection cylinder 14, at least one displacement sensor 102 is connected with the axial piston 17, and the displacement sensor 102 is further electrically connected with the data transmission and acquisition subsystem 4.

Wherein, the resistance strain gauge is rectangular flake. The resistance strain gauge is closely attached to the surface of the sample to be measured, and the direction can be arranged according to the measurement requirement, for example: the resistance strain gauge is arranged along the axial direction of the sample to be measured, and the measured strain result is axial strain; the resistance strain gauge is arranged along the circumferential direction of the sample to be measured, and the measured strain result is radial strain. In addition, the length of the resistance strain gauge can be selected according to the measurement requirement, and the length dimension of the resistance strain gauge is generally 100mm, 80mm, 50mm, 30mm, 20mm, 10mm, 5mm and the like.

Meanwhile, the transition block 101 comprises an elastic sealing sleeve 1011 and a metal guide sleeve 1012, the elastic sealing sleeve 1011 is a round platform structure with an isosceles trapezoid axial section, the metal guide sleeve 1012 is a hollow tubular structure with a rectangular axial section, the metal guide sleeve 1012 is embedded in the rear end face of the elastic sealing sleeve 1012 and is coaxially distributed with the elastic sealing sleeve 1011, the metal guide sleeve 1012 is coated outside the axial piston 17 and is in sliding connection with the axial piston 17, at least two transition holes 1013 uniformly distributed around the axis of the metal guide sleeve 1012 are arranged on the side wall of the metal guide sleeve 1012, the axis of the transition holes 1013 is intersected with the axis of the metal guide sleeve 1012 and forms an included angle of 30-60 degrees, and the transition holes 1013 are communicated with the air guide cavity 100 of the axial piston 17.

In this embodiment, the data transmission and collection subsystem 4 includes a data processing computer 41, an industrial computer-based driving circuit 42, and a strain analyzer 43, where the industrial computer-based driving circuit 42 is electrically connected to the data processing computer 41, the strain analyzer 43, the triaxial loading subsystem 1, the confining pressure control subsystem 2, the air pressure control subsystem 3, and the temperature control subsystem 5, and the strain analyzer 43 is further electrically connected to the triaxial loading subsystem 1.

As shown in fig. 4, a method for using a coal-gas multi-physical field coupling experimental device includes the following steps:

s1, equipment detection, namely firstly assembling and assembling a triaxial loading subsystem, a confining pressure control subsystem, an air pressure control subsystem, a data transmission and acquisition subsystem and a temperature control subsystem to obtain a multi-physical field coupling experimental device, then driving the confining pressure control subsystem and the air pressure control subsystem to operate and maintaining the pressure of the triaxial loading subsystem to realize the operation function and air tightness detection of the multi-physical field coupling experimental device; simultaneously recording calculation steps and calculation functions in a data transmission and acquisition subsystem;

s2, prefabricating a coal sample, measuring a sample to be measured by using a vernier caliper, wherein the sample to be measured is a standard cylinder, the length of the sample to be measured is 50-105mm, and the radius of the sample to be measured is 48-52mm; placing the sample to be tested into a drying box, and drying for 24 hours at 40-60; selecting 2 resistance strain gauges with the length close to the length of a sample to be tested, checking and ensuring that the resistance is 120 omega, and respectively and tightly adhering the 2 resistance strain gauges to the side surface of the sample to be tested along the axial direction and the circumferential direction of the sample to be tested; loading a sample to be tested, to which the resistance strain gauge is attached, into a triaxial loading subsystem, and checking the resistance strain gauge by using an ohmmeter to ensure that the resistance value is normal; finally, connecting the resistance strain gauge with a strain analyzer of a data transmission and acquisition subsystem through a data transmission line; measuring each resistance strain gauge by a strain analyzer, and verifying the measurement accuracy of the resistance strain gauge;

S3, confining pressure loading and vacuumizing, namely driving a confining pressure control subsystem to operate, and respectively injecting pressure liquid with the pressure of 6MPa into a shaft pressure chamber and a ring pressure chamber of the triaxial loading subsystem by an axial pressure control pump and a ring pressure control pump of the confining pressure control subsystem and maintaining the pressure; and then driving a vacuum pump to operate, vacuumizing the detection cavity of the triaxial loading subsystem, and maintaining the pressure for 24 hours.

S4, continuously injecting gas, driving the gas pressure control subsystem to operate, regulating the pressure of the power gas storage bottle and the gas in the gas injection gas storage bottle by a gas pressure regulator, and simultaneously continuously injecting the gas with the pressure of 3MPa into the triaxial loading subsystem and the upper standard bottle;

s5, circularly measuring for a long time period, and after the step S4 is completed, setting the regulation and control period of the output gas pressure of the gas pressure regulator to be 4h by utilizing a data transmission and acquisition subsystem, wherein the amplitude is 0.2MPa, and the cycle repetition number is 60 times; simultaneously setting the opening and closing action period of each electromagnetic valve; finally, the change of the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline along with time are recorded and counted by using an upstream pressure sensor and a downstream pressure sensor respectively;

s6, resetting after the experiment is ended, periodically measuring for 240h (60 cycles) through the step S5, stopping measuring work, and resetting each equipment part after the measuring work is completed;

And S7, data processing and calculation are carried out on each data measured in the step S5, and the data transmission and acquisition subsystem carries out data calculation by utilizing the calculation step and the calculation function set in the step S1, so that test data can be obtained.

In the step S5, the long-period cyclic measurement operation includes the following steps:

first, measuring the phase of the upper half cycle period: when the gas pressure in the upstream pipeline is equal to that in the downstream pipeline, the electromagnetic valve is closed; the gas pressure regulator injects gas with the pressure of 3.2MPa into the upstream standard bottle; the solenoid valve and the gas pressure regulator are then closed, the time at this moment being defined as the initial time of the last half of the cycle; when the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline are balanced and equal, recording the balanced pressure value;

second, measuring the phase of the next half cycle period: when the cycle time is 2 hours, regulating the gas pressure output by the gas pressure regulator to be 2.8MPa; and after the gas pressure in the upstream pipeline is 2.8MPa, the time at the moment is defined as the initial time of the lower half cycle of the cycle; and the gas pressure in the upstream pipeline and the downstream pipeline reaches a new balance; when the period measurement time reaches 4 hours, ending the single period measurement; the operation is then repeated to perform the measurement operation for the next cycle.

The key points are that in the step S7, the calculating step and the calculating function are specifically as follows:

since the data processing and calculation methods of each measurement period are the same, only the processing and calculation methods of experimental data measured in the T (T takes any value of 1 to 60) th period will be described in detail below:

the first step, the method for calculating the permeability is based on Darcy's law and conservation of mass law,

fitting according to the relationship between the pressure difference of 0.2MPa and time to obtain the permeability of the sample to be tested:

wherein k is _Tj When the permeability value is the T period, the permeability value of the sample 11 to be measured obtained by fitting is utilized, when j is taken to be 1, the permeability value measured in the upper half period of the T period is represented, and when j is taken to be 2, the permeability value measured in the lower half period of the T period is represented; ΔP ₂ For the difference between the upstream and downstream gas pressures, the embodiment takes 0.2MPa; beta is the compressibility coefficient of the gas, pa ^-1 The method comprises the steps of carrying out a first treatment on the surface of the t is the gas injection time corresponding to the initial time of the half measurement period of (i 1)/lower (i 2) of the current measurement period, and s; v (V) _up Taking 1×10 for the total volume of the upstream pipeline and the upstream standard bottle ^-4 m ³ ；V _dn 1X 10 for the total volume of the downstream piping and downstream standard bottle ^-4 m ³ ；k _T The average permeability value obtained for the T-th cycle;

in the second step, the axial strain, the radial strain and the overall strain are calculated, because the axial strain and the radial strain are continuously monitored by the resistive strain gauge 56, in the T-th measurement period, strain values at a plurality of different times are observed, in order to reduce the number of measurement results and facilitate the calculation of the matrix strain, the average value of all the axial strains in the T-th period is taken as the axial strain value of the T-th period, the average value of all the radial strains in the T-th period is taken as the radial strain value of the T-th period, and the geometric relationship between the overall strain and the radial strain and the axial strain is satisfied:

In the method, in the process of the invention,

for the strain values measured in period T, when i is a +.>

Represents axial strain, when i is r +.>

Representing radial strain; e (E) _out The output voltage of the low-purine differential amplifier is mu V; e (E) _g Supplying voltage, V, to the bridge; e (E) _g The sensitivity coefficient of the resistance strain gauge; k (K) _L Gain for a low purine differential amplifier; epsilon _b For the overall strain of the test specimen ε _bT The overall strain value for the T-th cycle;

and thirdly, calculating the volume of the crack and the strain of the crack. From equations 16 and 17, it can be seen that the fracture volume and fracture strain are satisfied by the T-th cycle measurement

Wherein V is _f0 The fracture volume, m, measured for cycle 1 ³ ；V _fT For the fracture volume, m, measured in the T-th cycle ³ ；

The initial upstream gas pressure for the half cycle on the T-th cycle is 3.2MPa; />

The initial upstream gas pressure for the next half-cycle of the T-th cycle is 2.8MPa; />

For week TBalance gas pressure, pa, of the upper half period of the period; />

Balance gas pressure, MPa, for the next half-cycle of the T-th cycle; />

The initial upstream gas pressure for the upper half-cycle of the T-th cycle is 3.0MPa; />

An initial upstream gas pressure, pa, for the next half-cycle of the T-th cycle;

and fourthly, calculating the matrix strain. As can be seen from equation 19, the matrix strain satisfies:

Wherein ε _mT Strain for the T-th cycle substrate; v (V) _b1 For the initial whole volume of the sample to be measured obtained by the 1 st period measurement, m ³ ；V _f1 The fracture volume, m, of the sample to be measured is measured for the 1 st period ³ ；

The data of all periods obtained by measurement are processed according to the method, and the evolution of values of all permeability, axial strain, radial strain, overall strain, fracture strain and matrix strain of 60 measurement periods in 240 hours with time is obtained.

Compared with the prior art, the invention has the following beneficial effects: the invention can realize the long-time periodic measurement of the permeability, axial strain, radial strain, overall strain and fracture strain of the coal rock sample, and also can realize the measurement of mechanical parameters (such as elastic modulus, poisson ratio and compressive strength) of the coal rock sample; meanwhile, the system meets the measurement methods of three permeabilities of a steady state method, a transient state method and a periodic oscillation method, and is suitable for measuring coal samples with permeabilities of different levels; the device and the method effectively solve the problem that the permeability, axial strain, radial strain, overall strain and fracture strain of the coal rock sample cannot be periodically measured for a long time in the existing coal rock permeability measuring device and method; the method can also realize the development of a great deal of related researches on the multi-category strain and permeability evolution relation of the coal and rock mass under the multi-scale multi-physical field, and has good use flexibility and universality; in addition, the invention has the advantages of simple structure, simple operation method, strong data processing capability and high measurement precision, and can be popularized and applied in the field of coal rock seepage and deformation measurement.

Compared with the prior art, the invention has the following beneficial effects: the coal-gas multi-physical field coupling experimental device and the use method thereof provided by the invention can realize long-time periodic measurement of the permeability, axial strain, radial strain, overall strain and fracture strain of a coal rock sample. The invention can also realize the measurement of mechanical parameters (such as elastic modulus, poisson's ratio and compressive strength) of the coal rock sample. In addition, the system meets the measurement methods of three permeabilities of a steady state method, a transient state method and a periodic oscillation method, and is suitable for measuring coal samples with permeabilities of different levels. The device and the method solve the problem that the permeability, axial strain, radial strain, overall strain and fracture strain of the coal rock sample cannot be periodically measured for a long time in the conventional coal rock permeability measuring device and method. Researchers can develop a great deal of related researches on the multi-category strain and permeability evolution relation of coal and rock mass under the multi-scale and multi-physical field on the basis of the invention. The long-time periodic measurement work realized by the invention is mainly automatically regulated, measured, analyzed and stored by a computer, the fluid pipeline and the data transmission line of the device are simple, the operation method is simple, and the device is worthy of popularization and application in the field of coal rock seepage and deformation measurement.

The foregoing has shown and described the basic principles and main features of the present invention and the advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (6)

1. A coal-gas multi-physical field coupling experimental device is characterized in that: the coal-gas multi-physical-field coupling experimental device comprises a triaxial loading subsystem, a confining pressure control subsystem, an air pressure control subsystem, a data transmission and acquisition subsystem and a temperature control subsystem, wherein the triaxial loading subsystem is respectively communicated with the confining pressure control subsystem and the air pressure control subsystem through a flow guide pipe, the outer surface of the triaxial loading subsystem is additionally connected with the temperature control subsystem, the triaxial loading subsystem, the confining pressure control subsystem, the air pressure control subsystem and the temperature control subsystem are all electrically connected with the data transmission and acquisition subsystem, the temperature control subsystem comprises a water bath box, a heating blanket and a temperature sensor, at least one of the water bath box and the heating blanket is connected with the outer surface of the triaxial loading subsystem, the water bath box is connected with the air pressure control subsystem, and at least one temperature sensor is arranged in each water bath box and each heating blanket; the system comprises a pressure control subsystem, a pressure control subsystem and a data transmission subsystem, wherein the pressure control subsystem comprises a power gas storage bottle, a gas injection gas storage bottle, a gas pressure regulator, an upper standard bottle, a lower standard bottle, a tail gas collector, a pressure reducing valve, an electromagnetic valve, a vacuum pump, a pressure sensor and a flow sensor; the confining pressure control subsystem comprises an axial pressure control pump, a circumferential pressure injection port, a shaft pressure injection port and a control valve, wherein the axial pressure control pump and the circumferential pressure control pump are uniform and are mutually connected in parallel, the axial pressure control pump is communicated with the shaft pressure injection port through a flow guide pipe, the circumferential pressure control pump is communicated with the circumferential pressure injection port through a flow guide pipe, the circumferential pressure injection port and the shaft pressure injection port are embedded on the side surface of the triaxial loading subsystem and are communicated with the triaxial loading subsystem, the flow guide pipe is communicated with the axial pressure control pump, the circumferential pressure injection port and the shaft pressure injection port through the control valve, and the control valve is further electrically connected with the data transmission and acquisition subsystem; the triaxial loading subsystem comprises an outer end cover, an inner end cover, a guide cylinder body, a detection cylinder body, a rubber isolation sleeve, a drainage tube, an axial piston, an upstream gas injection cushion block, a downstream gas injection cushion block, a transition cushion block, a displacement sensor, a resistance strain gauge and a pressure plate, wherein the guide cylinder body, the detection cylinder body and the rubber isolation sleeve are hollow columnar structures with rectangular axial sections, the rear end surface of the detection cylinder body is connected with the outer end cover, the front end surface is connected with the inner end cover, the inner end cover is connected with the guide cylinder body and is connected with the outer end cover through the guide cylinder body, the outer end cover, the inner end cover, the guide cylinder body and the detection cylinder body are coaxially distributed, through holes coaxially distributed with the detection cylinder body are formed in the outer end cover and the inner end cover and are communicated through the through holes, the rubber isolation sleeve is embedded in the detection cylinder body and coaxially distributed with the detection cylinder body, the front end surface of the rubber isolation sleeve is propped against the inner end cover through the transition cushion block, the rear end face is propped against the outer end cover through the inner end cover and communicated with the through hole, a ring pressing cavity with the length not more than 80% of the length of the rubber isolation sleeve is arranged between the outer side face of the rubber isolation sleeve and the inner side face of the detection cylinder body, at least two diversion holes uniformly distributed around the axis of the detection cylinder body are arranged on the side wall of the detection cylinder body corresponding to the ring pressing cavity, the diversion holes are vertically distributed and intersected with the axis of the detection cylinder body, the intersection point is positioned at the midpoint position of the detection cylinder body, the diversion holes are communicated with the ring pressing injection hole, two pressure plates are embedded in the rubber isolation sleeve, are coaxially distributed with the rubber isolation sleeve and are in sliding connection with the inner side face of the rubber isolation sleeve, the two pressure plates are symmetrically distributed at the two end faces of the rubber isolation sleeve, a detection cavity is formed between the two pressure plates, one pressure plate is propped against the transition cushion block through an upstream gas injection cushion block, the other pressure plate is propped against the transition cushion block through a downstream gas injection cushion block, the resistance strain gauge is at least two and is positioned in the detection cavity, at least one resistance strain gauge detection axis is distributed in parallel with the detection cavity axis, at least one resistance strain gauge detection axis is distributed vertically with the detection cavity axis, the axial piston is embedded in the guide cylinder body, is coaxially distributed with the guide cylinder body and is in sliding connection with the inner surface of the guide cylinder body, an axial pressure cavity is formed between the axial piston and the front half part of the guide cylinder body, at least two axial pressure injection ports uniformly distributed around the axis of the guide cylinder body are arranged on the side wall of the guide cylinder body corresponding to the axial pressure cavity, at the same time, the front end surface of the axial piston is positioned outside the outer end cover, the rear end surface of the axial piston is positioned in the detection cylinder body through the through hole and is propped against the upstream gas injection cushion block, the axial piston, the upstream gas injection cushion block and the downstream gas injection cushion block are internally provided with gas guide cavities communicated with the detection cavity, the drainage tube is positioned at the rear end surface of the detection cylinder body, the front half part of the drainage tube is embedded in the detection cylinder body and is propped against the downstream gas injection cushion block, the gas guide cavity of the downstream gas cushion block is communicated with the drainage tube, the rear end surface is positioned outside the detection cylinder body, and at least one sensor is connected with the displacement sensor in an axial direction sensor and is connected with the displacement sensor in an electrical sensor system.

2. The coal-gas multi-physical field coupling experimental device according to claim 1, wherein: the transition cushion block comprises an elastic sealing sleeve and a metal guide sleeve, wherein the elastic sealing sleeve is of a round table structure with an isosceles trapezoid axial section, the metal guide sleeve is of a hollow tubular structure with a rectangular axial section, the metal guide sleeve is embedded in the rear end face of the elastic sealing sleeve and is coaxially distributed with the elastic sealing sleeve, the metal guide sleeve is coated outside the axial piston and is in sliding connection with the axial piston, at least two transition holes uniformly distributed around the axis of the metal guide sleeve are formed in the side wall of the metal guide sleeve, the axis of each transition hole is intersected with the axis of the metal guide sleeve and forms an included angle of 30-60 degrees, and the transition holes are communicated with an air guide cavity of the axial piston.

3. The coal-gas multi-physical field coupling experimental device according to claim 1, wherein: the data transmission and acquisition subsystem comprises a data processing computer, a driving circuit based on an industrial computer and a strain analyzer, wherein the driving circuit based on the industrial computer is electrically connected with the data processing computer, the strain analyzer, the triaxial loading subsystem, the confining pressure control subsystem, the air pressure control subsystem and the temperature control subsystem respectively, and the strain analyzer is electrically connected with the triaxial loading subsystem.

4. The method for using the coal-gas multi-physical field coupling experimental device according to claim 1, wherein the method comprises the following steps: the application method of the coal-gas multi-physical field coupling experimental device comprises the following steps:

s1, equipment detection, namely firstly assembling and assembling a triaxial loading subsystem, a confining pressure control subsystem, an air pressure control subsystem, a data transmission and acquisition subsystem and a temperature control subsystem to obtain a multi-physical field coupling experimental device, then driving the confining pressure control subsystem and the air pressure control subsystem to operate and maintaining the pressure of the triaxial loading subsystem to realize the operation function and air tightness detection of the multi-physical field coupling experimental device; simultaneously recording calculation steps and calculation functions in a data transmission and acquisition subsystem;

s2, prefabricating a coal sample, measuring a sample to be measured by using a vernier caliper, putting the sample to be measured into a drying box, and drying for 24 hours under 40-60; selecting 2 resistance strain gauges with the length close to the length of a sample to be tested, checking and ensuring that the resistance is 120 omega, and respectively and tightly adhering the 2 resistance strain gauges to the side surface of the sample to be tested along the axial direction and the circumferential direction of the sample to be tested; loading a sample to be tested, to which the resistance strain gauge is attached, into a triaxial loading subsystem, and checking the resistance strain gauge by using an ohmmeter to ensure that the resistance value is normal; finally, connecting the resistance strain gauge with a strain analyzer of a data transmission and acquisition subsystem through a data transmission line; measuring each resistance strain gauge by a strain analyzer, and verifying the measurement accuracy of the resistance strain gauge;

S3, confining pressure loading and vacuumizing, namely driving a confining pressure control subsystem to operate, and respectively injecting pressure liquid with the pressure of 6MPa into a shaft pressure chamber and a ring pressure chamber of the triaxial loading subsystem by an axial pressure control pump and a ring pressure control pump of the confining pressure control subsystem and maintaining the pressure; then driving a vacuum pump to operate, vacuumizing a detection cavity of the triaxial loading subsystem, and maintaining the pressure for 24 hours;

s4, continuously injecting gas, driving the gas pressure control subsystem to operate, regulating the pressure of the power gas storage bottle and the gas in the gas injection gas storage bottle by a gas pressure regulator, and simultaneously continuously injecting the gas with the pressure of 3MPa into the triaxial loading subsystem and the upper standard bottle;

s5, circularly measuring for a long time period, and after the step S4 is completed, setting the regulation and control period of the output gas pressure of the gas pressure regulator to be 4h by utilizing a data transmission and acquisition subsystem, wherein the amplitude is 0.2MPa, and the cycle repetition number is 60 times; simultaneously setting the opening and closing action period of each electromagnetic valve; finally, the change of the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline along with time are recorded and counted by using an upstream pressure sensor and a downstream pressure sensor respectively;

s6, resetting after the experiment is ended, periodically measuring for 60 periods through the step S5, stopping measuring work, and resetting parts of each device after the measuring work is completed;

And S7, data processing and calculation are carried out on each data measured in the step S5, and the data transmission and acquisition subsystem carries out data calculation by utilizing the calculation step and the calculation function set in the step S1, so that test data can be obtained.

5. The method for using the coal-gas multi-physical field coupling experimental device according to claim 4, wherein the method comprises the following steps: in the step S5, the long-time period cyclic measurement operation includes the following steps:

first, measuring the phase of the upper half cycle period: when the gas pressure in the upstream pipeline is equal to that in the downstream pipeline, the electromagnetic valve is closed; the gas pressure regulator injects gas with the pressure of 3.2MPa into the upstream standard bottle; the solenoid valve and the gas pressure regulator are then closed, the time at this moment being defined as the initial time of the last half of the cycle; when the gas pressure in the upstream pipeline and the gas pressure in the downstream pipeline are balanced and equal, recording the balanced pressure value;

second, measuring the phase of the next half cycle period: when the cycle time is 2 hours, regulating the gas pressure output by the gas pressure regulator to be 2.8MPa; and after the gas pressure in the upstream pipeline is 2.8MPa, the time at the moment is defined as the initial time of the lower half cycle of the cycle; and the gas pressure in the upstream pipeline and the downstream pipeline reaches a new balance; when the period measurement time reaches 4 hours, ending the single period measurement; the operation is then repeated to perform the measurement operation for the next cycle.

6. The method for using the coal-gas multi-physical field coupling experimental device according to claim 4, wherein the method comprises the following steps: the step S7 is specifically that the calculation step and the calculation function are as follows:

since the data processing and calculating methods of each measurement period are the same, the processing and calculating method of experimental data measured in the T-th period, wherein T takes any value of 1-60:

the first step, the method for calculating the permeability is based on Darcy's law and conservation of mass law,

fitting according to the relationship between the pressure difference of 0.2MPa and time to obtain the permeability of the sample to be tested:

wherein k is _Tj When the permeability value is the T period, the permeability value of the sample to be measured obtained by fitting is utilized, when j is taken to be 1, the permeability value measured in the upper half period of the T period is represented, and when j is taken to be 2, the permeability value measured in the lower half period of the T period is represented; ΔP ₂ Taking 0.2MPa for the pressure difference between the upstream gas and the downstream gas; beta is the compressibility coefficient of the gas, pa ^-1 The method comprises the steps of carrying out a first treatment on the surface of the t is the gas injection time corresponding to the initial time of the upper (j 1)/lower (j 2) half of the current measurement period, and s; v (V) _up Taking 1×10 for the total volume of the upstream pipeline and the upstream standard bottle ^-4 m ³ ；V _dn 1X 10 for the total volume of the downstream piping and downstream standard bottle ^-4 m ³ ；k _T The average permeability value obtained for the T-th cycle;

In the second step, the axial strain, the radial strain and the overall strain are continuously monitored by the resistive strain gauge, so that in the T-th measurement period, a plurality of strain values at different times are observed, in order to reduce the number of measurement results and facilitate the calculation of matrix strain, the average value of all the axial strains in the T-th period is taken as the axial strain value of the T-th period, the average value of all the radial strains in the T-th period is taken as the radial strain value of the T-th period, and the geometric relationship between the overall strain and the radial strain and the axial strain is satisfied:

in the method, in the process of the invention,

for the strain values measured in period T, when i is a +.>

Represents axial strain, when i is r +.>

Representing radial strain; v (V) _out The output voltage of the differential amplifier, μV; e (E) _g Supplying voltage, V, to the bridge; e (E) _g The sensitivity coefficient of the resistance strain gauge; k (K) _L Is the gain of the differential amplifier; epsilon _b For the overall strain of the test specimen ε _bT The overall strain value for the T-th cycle;

third, calculating the fracture volume and fracture strain, and measuring the fracture volume and fracture strain in the T-th period to meet the requirements of

Wherein V is _f0 The fracture volume, m, measured for cycle 1 ³ ；V _fT For the fracture volume, m, measured in the T-th cycle ³ ；

The initial upstream gas pressure for the half cycle on the T-th cycle is 3.2MPa; />

The initial upstream gas pressure for the next half-cycle of the T-th cycle is 2.8MPa; />

The equilibrium gas pressure, pa, is the upper half-cycle of the T-th cycle; />

Balance gas pressure, MPa, for the next half-cycle of the T-th cycle; />

The initial upstream gas pressure for the upper half-cycle of the T-th cycle is 3.0MPa; />

An initial upstream gas pressure, pa, for the next half-cycle of the T-th cycle;

fourth, calculating the matrix strain, wherein the matrix strain meets the following conditions:

wherein ε _mT Strain for the T-th cycle substrate; v (V) _b1 For the initial whole volume of the sample to be measured obtained by the 1 st period measurement, m ³ ；V _f1 The fracture volume, m, of the sample to be measured is measured for the 1 st period ³ ；

The data of all periods obtained by measurement are processed according to the method, and the evolution of values of all permeability, axial strain, radial strain, overall strain, fracture strain and matrix strain of 60 measurement periods in 240 hours with time is obtained.

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