CN112067480A - Deep gas-containing coal rock pulsating fracturing experimental device and experimental method - Google Patents
Deep gas-containing coal rock pulsating fracturing experimental device and experimental method Download PDFInfo
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Abstract
The invention discloses a deep gas-containing coal rock pulsating fracturing experimental system which comprises a three-shaft holder, wherein the three-shaft holder is connected with six loading devices for applying pressure to a coal sample, and the six loading devices are connected with a pulsating pump for providing loading pressure and a first electric control device for controlling the loading devices; the gas inlet of the pulse pump is connected with a carbon dioxide gas cylinder, and the pulse pump is connected with a second electric control device for controlling the pulse pump; the air inlet interface of the three-axis clamp holder is connected with an air main pipe, and the air main pipe is connected with a gas injection device for enabling a coal sample to adsorb gas, a helium gas injection device for carrying out gas tightness inspection and a vacuumizing device for vacuumizing. The invention also discloses a corresponding experimental method. The method can more accurately simulate the stress, seepage and temperature conditions of the coal bed under the deep mining condition, provides guidance for deep coal body fracturing permeability increase and regional coal and gas outburst prevention, and has practical and valuable practical significance.
Description
Technical Field
The invention relates to the technical field of coal mines, in particular to a deep gas-containing coal rock pulsating fracturing experimental device.
Background
China 'three-high one-low' (high stress, high gas pressure, high gas content and low permeability) deep coal seam gas occurrence is mainly characterized, low gas permeability of the coal seam is a bottleneck of coal mine gas extraction, and for a protruding coal seam with low gas permeability and difficult extraction, in order to improve the pre-extraction coal seam gas effect, the coal seam is subjected to pressure relief and permeability increase through various means.
The traditional measures such as hydraulic fracturing are not ideal in pressure relief and permeability increase effect, and especially when the coal seam enters deep low permeability coal seam mining, the traditional measures for pressure relief and permeability increase are not satisfactory. Meanwhile, the gas-containing coal body is generally in a three-direction pressure condition, and the three-direction pressure is different under the influences of geological structural conditions such as a coal seam inclination angle, thickness and occurrence condition, and mechanical disturbance such as structural movement, and the stress environment is usually in a three-direction unequal pressure state, namely a true triaxial stress state.
Aiming at the problems, a deep gas-containing coal rock pulsating fracturing experiment system is developed, research on factors influencing the fracturing and expanding of the deep gas-containing coal pulsating fracturing fracture under a true triaxial condition is carried out, the theory of the influence of the underground coal mine pulsating fracturing fracture and expanding mechanism and the pulsating fracturing on the gas migration of a coal seam is disclosed, and guidance is provided for preventing and controlling coal and gas outburst in a deep coal rock mass fracturing permeability-increasing area.
Disclosure of Invention
The invention aims to provide a deep gas-containing coal rock pulsating fracturing experiment system, which can more accurately simulate the stress, seepage and temperature conditions of a deep coal bed, obtain more accurate fracturing experiment data and provide guidance for deep coal body fracturing permeability increase and regional coal and gas outburst prevention.
In order to achieve the purpose, the deep gas-containing coal rock pulsating fracturing experiment system comprises a triaxial clamp holder for clamping and loading a coal sample, wherein the triaxial clamp holder is provided with an air inlet interface and an air outlet interface for exhausting air after the experiment is finished;
the three-shaft clamp holder is connected with six sets of loading devices for applying pressure to the coal sample, the six sets of loading devices are respectively positioned in front of, behind, on the left of, on the right of, above and below the coal sample, and the six sets of loading devices are all connected with a pulse pump for providing loading pressure and a first electric control device for controlling the loading devices;
the gas inlet of the pulse pump is connected with a carbon dioxide gas cylinder, and a third pressure reducing valve, a third valve and a third pressure gauge are arranged on an outlet pipeline of the carbon dioxide gas cylinder; the pulsation pump is connected with a second electric control device for controlling the pulsation pump;
the gas inlet interface of the three-axis clamp holder is connected with a gas main pipe, and the gas main pipe is connected with a gas injection device for enabling a coal sample to adsorb gas, a helium gas injection device for performing gas tightness inspection and a vacuumizing device for vacuumizing; the gas main pipe at the air inlet interface of the three-shaft holder is provided with a fourth pressure gauge, an electric heater is arranged in the three-shaft holder and surrounds the coal sample, the electric heater is connected with a temperature controller used for controlling the electric heater through a line, and the temperature controller is positioned outside the three-shaft holder.
The air outlet interface of the three-axis clamp holder is connected with a discharge device;
the discharging device comprises a gas outlet main pipe connected with a gas outlet interface of the three-axis clamp holder, the gas outlet main pipe is connected with a gas-liquid separator, a fourth valve and a back pressure valve are arranged on the gas outlet main pipe, a gas outlet of the gas-liquid separator is connected with a gas exhaust pipe, a dryer is arranged on the gas exhaust pipe, and the tail end of the gas exhaust pipe is connected with a gas flowmeter which is communicated with the atmosphere; the liquid outlet of the gas-liquid separator is connected with a liquid flowmeter which is communicated with the environment.
The gas main pipe is also connected with a supercharging device for improving the gas pressure absorbed by the coal sample; the supercharging device comprises a reference tank filled with gas, the reference tank is connected with a supercharging pump through a pipeline, and an exhaust port of the supercharging pump is communicated with a gas main pipe; and a fifth valve and a precise flowmeter are arranged on a pipeline between the reference tank and the booster pump.
A refrigerating unit for cooling the carbon dioxide gas is connected in series between the pulse pump and the carbon dioxide gas bottle.
The gas injection device comprises a gas cylinder, the gas cylinder is connected with a gas outlet pipe, and the gas outlet pipe is connected with a gas main pipe; a first pressure reducing valve, a first valve and a first pressure gauge are arranged on the gas outlet pipe;
the helium gas injection device comprises a helium tank, the helium tank is connected with a helium gas outlet pipe, and the helium gas outlet pipe is connected with a gas main pipe; a second pressure reducing valve, a second valve and a second pressure gauge are arranged on the helium gas outlet pipe;
the vacuumizing device comprises a vacuum pump, the vacuum pump is connected with a vacuumizing pipeline, the vacuumizing pipeline is connected with a gas main pipe, and a vacuum valve used for controlling the on-off of the vacuumizing pipeline is arranged on the vacuumizing pipeline.
The invention also discloses an experimental method carried out by adopting the deep gas-containing coal rock pulsating fracturing experimental system, which comprises the following steps:
the first step is the connection;
the second step is the air tightness check;
the third step is vacuum pumping;
the fourth step is gas adsorption and pulse loading;
the fifth step is fracture loading;
the sixth step is to exhaust, and the experiment is ended.
The first step is specifically:
connecting all the devices together through pipelines, and closing all the valves; clamping a coal sample in a three-axis clamp holder;
the second step is specifically: opening a second valve and a pneumatic valve, adjusting a second pressure reducing valve, injecting high-pressure helium into the gas main pipe and the three-axis clamp until the pressure reaches a preset value, if the reading of a fourth pressure gauge is reduced after the pressure is maintained for 2 hours, carrying out gas tightness inspection and plugging a leakage point, and carrying out the second step again; if the reading of the fourth pressure gauge is not reduced after the pressure is maintained for 2 hours, closing the second valve and the pneumatic valve, and performing a third step;
the third step is to open a vacuum valve, a pneumatic control valve and a vacuum pump, vacuumize the gas main pipe and the three-axis clamp holder, and discharge the gas in the system into the environment; after vacuumizing for 5-10 minutes, closing the vacuum valve, the air control valve and the vacuum pump, and entering a fourth step;
the fourth step is specifically that the first valve, the pneumatic control valve, the refrigerating unit and the third valve are opened, the first pressure reducing valve and the third pressure reducing valve are adjusted, the pulse pump is opened through the second electric control device, the six sets of loading devices are opened through the first electric control device, and the electric heater is opened through the temperature controller, so that the temperature condition in the deep part of the stratum is simulated; the six sets of loading devices enable the coal sample to be subjected to pulse loading of preset pressure so as to simulate the stress condition of coal in a specific stratum; injecting gas into the coal sample in the three-shaft clamp holder through the gas main pipe, so that the coal sample absorbs the gas under the condition of pulsating loading pressure;
after keeping the adsorption state for 24 hours, closing the first valve and the pneumatic control valve, and performing a fifth step;
the fifth step is that the pulsating pressure applied to the coal sample by the six sets of loading devices is slowly increased through the first electric control device until the coal sample is fractured; recording pressure data of pulse pressurization of six sets of loading devices when a coal sample is fractured, and providing guidance for deep coal fracturing permeability increase and regional coal and gas outburst prevention; closing the refrigerating unit and the third valve, closing the pulse pump through the second electric control device, and closing the six sets of loading devices through the first electric control device to perform a sixth step;
and the sixth step is specifically to open the fourth valve and the back pressure valve, so that the gas in the three-shaft holder enters a gas-liquid separator, the separated water is discharged into the environment through a liquid flowmeter, and the separated gas is discharged into the atmosphere through a gas flowmeter.
In the fourth step, the fifth valve and the booster pump are opened while the first valve is opened, and gas in the reference tank is injected into the gas main pipe by the booster pump, so that the gas pressure in the gas main pipe and the gas pressure in the three-shaft clamp holder are increased, and the gas adsorption speed is increased.
In the fourth step, when six sets of loading devices enable the coal sample to be subjected to pulse loading of preset pressure, a preset pressure-time curve is a sine line or a residual string line.
The invention has the following advantages:
the method can simulate the stress, seepage and temperature conditions under the same conditions aiming at the deep mining conditions, and more accurately simulate the actual stress conditions of the coal in the stratum through sine lines or residual strings, thereby obtaining more accurate fracturing experimental data, providing guidance for deep coal fracturing permeability increase and regional coal and gas outburst prevention, and having practical and valuable practical significance.
Supercharging device can accelerate gas adsorption speed through increase gas pressure, more can ensure fully to adsorb in the same adsorption time, promotes the experimental efficiency and makes the experimental result more accurate.
The refrigerating unit can reduce the temperature of carbon dioxide gas, and carbon dioxide gas can rise when passing through the pulsation pump, consequently sets up the temperature that refrigerating unit can neutralize and rise because of the pulsation pump pressure boost, provides the basis for better control loading temperature.
The coal sample is subjected to pulsating loading pressure, and compared with constant loading pressure, the stress condition of the coal in the stratum can be better simulated.
The pressure-time line is preferably a sine line or a cosine line, which can more accurately simulate the actual stress condition of the coal in the stratum.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Detailed Description
As shown in fig. 1, the deep gas-containing coal rock pulsating fracturing experimental system of the invention comprises a triaxial clamp 1 for clamping and loading a coal sample, wherein the triaxial clamp 1 is provided with an air inlet interface and an air outlet interface for exhausting air after the experiment is finished;
the three-shaft clamp holder 1 is connected with six sets of loading devices 2 for applying pressure (namely stress) to the coal sample; the six sets of loading devices 2 are respectively positioned in front of, behind, on the left, on the right, above and below the coal sample, and the six sets of loading devices 2 are all connected with a pulse pump 3 for providing loading pressure and a first electric control device 4 for controlling the loading devices 2;
the gas inlet of the pulse pump 3 is connected with a carbon dioxide gas cylinder 5, and an outlet pipeline 6 of the carbon dioxide gas cylinder 5 is provided with a third pressure reducing valve 7, a third valve 8 and a third pressure gauge 9; the pulsation pump 3 is connected with a second electric control device 10 for controlling the pulsation pump 3;
the gas inlet interface of the three-axis clamp holder 1 is connected with a gas main pipe 11, and the gas main pipe 11 is connected with a gas injection device for enabling a coal sample to adsorb gas, a helium gas injection device for performing gas tightness inspection and a vacuumizing device for vacuumizing; a fourth pressure gauge 12 is arranged on a gas main pipe 11 at an air inlet interface of the three-axis clamp holder 1, an electric heater is arranged in the three-axis clamp holder 1 and surrounds a coal sample, the electric heater is connected with a temperature controller 13 used for controlling the electric heater through a line, and the temperature controller 13 is positioned outside the three-axis clamp holder 1.
The six sets of loading devices 2 are all constant-speed constant-pressure pumps of TC-100D type produced by Jiangsu Tuotu scientific research Limited. The first electric control device 4 and the second electric control device 10 both adopt a single chip microcomputer or an integrated circuit or an industrial control computer, and memories are arranged in the first electric control device 4 and the second electric control device 10. The electric heater is conventional in the art and is not shown.
The air outlet interface of the three-axis clamp holder 1 is connected with a discharging device; the discharging device comprises a gas outlet main pipe 14 connected with a gas outlet interface of the three-axis clamp 1, the gas outlet main pipe 14 is connected with a gas-liquid separator 15, the gas outlet main pipe 14 is provided with a fourth valve 16 and a back pressure valve 17, a gas outlet of the gas-liquid separator 15 is connected with a gas exhaust pipe 18, the gas exhaust pipe 18 is provided with a dryer 19, the tail end of the gas exhaust pipe 18 is connected with a gas flowmeter 20, and the gas flowmeter 20 is communicated with the atmosphere; the liquid outlet of the gas-liquid separator 15 is connected with a liquid flow meter 21, and the liquid flow meter 21 is communicated with the environment.
The gas main pipe 11 is also connected with a supercharging device for improving the gas pressure absorbed by the coal sample; the supercharging device comprises a reference tank 22 filled with gas, the reference tank 22 is connected with a supercharging pump 23 through a pipeline, and an exhaust port of the supercharging pump 23 is communicated with the gas main pipe 11; a fifth valve 24 and a precision flow meter 25 are arranged on a pipeline between the reference tank 22 and the booster pump 23. The reference tank 22 has a vent 26.
A refrigerating unit 27 for cooling the carbon dioxide gas is connected in series between the pulsation pump 3 and the carbon dioxide gas cylinder 5.
The refrigerating unit 27 can reduce the temperature of the carbon dioxide gas, and the temperature of the carbon dioxide gas can be increased when the carbon dioxide gas passes through the pulse pump 3, so that the refrigerating unit 27 can neutralize the temperature increased by the pressurization of the pulse pump 3, and a basis is provided for better controlling the loading temperature.
The gas injection device comprises a gas cylinder 28, the gas cylinder 28 is connected with a gas outlet pipe 29, and the gas outlet pipe 29 is connected with the gas main pipe 11; a first pressure reducing valve 30, a first valve 31 and a first pressure gauge 32 are arranged on the gas outlet pipe 29;
the helium gas injection device comprises a helium tank 33, the helium tank 33 is connected with a helium gas outlet pipe 34, and the helium gas outlet pipe 34 is connected with the gas main pipe 11; a second pressure reducing valve 35, a second valve 36 and a second pressure gauge 37 are arranged on the helium outlet pipe 34;
the vacuumizing device comprises a vacuum pump, the vacuum pump 38 is connected with a vacuumizing pipeline 39, the vacuumizing pipeline 39 is connected with the gas main pipe 11, and a vacuum valve 40 used for controlling the on-off of the vacuumizing pipeline 39 is arranged on the vacuumizing pipeline 39.
The invention also discloses an experimental method carried out by using the deep gas-containing coal rock pulsating fracturing experimental system, which comprises the following steps:
the first step is the connection;
the second step is the air tightness check;
the third step is vacuum pumping;
the fourth step is gas adsorption and pulse loading;
the fifth step is fracture loading;
the sixth step is to exhaust, and the experiment is ended.
The first step is specifically:
connecting all the devices together through pipelines, and closing all the valves; clamping a coal sample in a three-shaft clamp holder 1;
the second step is specifically: opening a second valve 36 and a pneumatic valve, adjusting a second pressure reducing valve 35, injecting high-pressure helium gas into the gas main pipe 11 and the three-axis clamp 1 to a preset pressure, if the indication number of a fourth pressure gauge 12 is reduced after the pressure is maintained for 2 hours, carrying out gas tightness inspection and plugging a leakage point, and carrying out the second step again; if the reading of the fourth pressure gauge 12 is not reduced after the pressure is maintained for 2 hours, closing the second valve 36 and the pneumatic valve, and performing a third step;
the third step is specifically to open the vacuum valve 40, the pneumatic control valve and the vacuum pump 38, vacuumize the gas main pipe 11 and the three-axis clamp 1, and discharge the gas in the system into the environment; after vacuumizing for 5-10 minutes (including two end values), closing the vacuum valve 40, the pneumatic control valve and the vacuum pump 38, and entering the fourth step;
the fourth step is specifically to open the first valve 31, the pneumatic control valve, the refrigerating unit 27 and the third valve 8, adjust the first pressure reducing valve 30 and the third pressure reducing valve 7, open the pulse pump 3 through the second electric control device 10, open the six sets of loading devices 2 through the first electric control device 4, and open the electric heater through the temperature controller 13 so as to simulate the temperature condition in the deep part of the stratum; the six sets of loading devices 2 enable the coal sample to be subjected to pulse loading of preset pressure so as to simulate the stress condition of coal in a specific stratum; injecting gas into the coal sample in the three-shaft clamp holder 1 through the gas main pipe 11, so that the coal sample absorbs the gas under the condition of pulsating loading pressure;
after keeping the adsorption state for 24 hours, closing the first valve 31 and the pneumatic control valve, and performing the fifth step;
the fifth step is that the pulsating pressure applied to the coal sample by the six sets of loading devices 2 is slowly increased through the first electric control device 4 until the coal sample is fractured; recording pressure data of pulse pressurization of the six sets of loading devices 2 when the coal sample is fractured, and providing guidance for deep coal fracturing permeability increase and regional coal and gas outburst prevention; closing the refrigerating unit 27 and the third valve 8, closing the pulse pump 3 through the second electric control device 10, and closing the six sets of loading devices 2 through the first electric control device 4 to perform a sixth step;
the sixth step is specifically to open the fourth valve 16 and the back pressure valve 17, so that the gas in the triaxial gripper 1 enters the gas-liquid separator 15, the separated (small amount of) water is discharged to the environment through the liquid flow meter 21, and the separated gas is discharged to the atmosphere through the gas flow meter 20.
The coal sample is subjected to pulsating loading pressure, and compared with constant loading pressure, the stress condition of the coal in the stratum can be better simulated.
In the fourth step, the fifth valve 24 and the booster pump 23 are opened while the first valve 31 is opened, and the booster pump 23 injects the gas in the reference tank 22 into the gas manifold 11, so as to increase the gas pressure in the gas manifold 11 and the gas pressure in the three-axis clamp 1, and increase the gas adsorption speed.
In the fourth step, when the six sets of loading devices 2 enable the coal sample to be subjected to pulsating loading with preset pressure, a preset pressure-time curve is a sine line or a residual string line.
The pressure-time line is preferably a sine line or a cosine line, which can more accurately simulate the actual stress condition of the coal in the stratum.
Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.
Claims (9)
1. Deep contains gas coal rock pulsating fracturing experimental system, including being used for the loaded triaxial holder of coal sample centre gripping, its characterized in that: the three-axis clamp holder is provided with an air inlet interface and an air outlet interface for exhausting air after the experiment is finished;
the three-shaft clamp holder is connected with six sets of loading devices for applying pressure to the coal sample, the six sets of loading devices are respectively positioned in front of, behind, on the left of, on the right of, above and below the coal sample, and the six sets of loading devices are all connected with a pulse pump for providing loading pressure and a first electric control device for controlling the loading devices;
the gas inlet of the pulse pump is connected with a carbon dioxide gas cylinder, and a third pressure reducing valve, a third valve and a third pressure gauge are arranged on an outlet pipeline of the carbon dioxide gas cylinder; the pulsation pump is connected with a second electric control device for controlling the pulsation pump;
the gas inlet interface of the three-axis clamp holder is connected with a gas main pipe, and the gas main pipe is connected with a gas injection device for enabling a coal sample to adsorb gas, a helium gas injection device for performing gas tightness inspection and a vacuumizing device for vacuumizing; the gas main pipe at the air inlet interface of the three-shaft holder is provided with a fourth pressure gauge, an electric heater is arranged in the three-shaft holder and surrounds the coal sample, the electric heater is connected with a temperature controller used for controlling the electric heater through a line, and the temperature controller is positioned outside the three-shaft holder.
2. The deep gas-containing coal rock pulsating fracturing experimental system of claim 1, wherein: the air outlet interface of the three-axis clamp holder is connected with a discharge device;
the discharging device comprises a gas outlet main pipe connected with a gas outlet interface of the three-axis clamp holder, the gas outlet main pipe is connected with a gas-liquid separator, a fourth valve and a back pressure valve are arranged on the gas outlet main pipe, a gas outlet of the gas-liquid separator is connected with a gas exhaust pipe, a dryer is arranged on the gas exhaust pipe, and the tail end of the gas exhaust pipe is connected with a gas flowmeter which is communicated with the atmosphere; the liquid outlet of the gas-liquid separator is connected with a liquid flowmeter which is communicated with the environment.
3. The deep gas-containing coal rock pulsating fracturing experimental system of claim 2, wherein: the gas main pipe is also connected with a supercharging device for improving the gas pressure absorbed by the coal sample; the supercharging device comprises a reference tank filled with gas, the reference tank is connected with a supercharging pump through a pipeline, and an exhaust port of the supercharging pump is communicated with a gas main pipe; and a fifth valve and a precise flowmeter are arranged on a pipeline between the reference tank and the booster pump.
4. The deep gas-containing coal rock impulse fracturing experimental system of any one of claims 1 to 3, wherein: a refrigerating unit for cooling the carbon dioxide gas is connected in series between the pulse pump and the carbon dioxide gas bottle.
5. The deep gas-containing coal rock pulsating fracturing experimental system of claim 4, wherein: the gas injection device comprises a gas cylinder, the gas cylinder is connected with a gas outlet pipe, and the gas outlet pipe is connected with a gas main pipe; a first pressure reducing valve, a first valve and a first pressure gauge are arranged on the gas outlet pipe;
the helium gas injection device comprises a helium tank, the helium tank is connected with a helium gas outlet pipe, and the helium gas outlet pipe is connected with a gas main pipe; a second pressure reducing valve, a second valve and a second pressure gauge are arranged on the helium gas outlet pipe;
the vacuumizing device comprises a vacuum pump, the vacuum pump is connected with a vacuumizing pipeline, the vacuumizing pipeline is connected with a gas main pipe, and a vacuum valve used for controlling the on-off of the vacuumizing pipeline is arranged on the vacuumizing pipeline.
6. The experimental method carried out by adopting the deep gas-containing coal rock pulsating fracturing experimental system in claim 5 is characterized by comprising the following steps of:
the first step is the connection;
the second step is the air tightness check;
the third step is vacuum pumping;
the fourth step is gas adsorption and pulse loading;
the fifth step is fracture loading;
the sixth step is to exhaust, and the experiment is ended.
7. The experimental method according to claim 6, characterized in that:
the first step is specifically:
connecting all the devices together through pipelines, and closing all the valves; clamping a coal sample in a three-axis clamp holder;
the second step is specifically: opening a second valve and a pneumatic valve, adjusting a second pressure reducing valve, injecting high-pressure helium into the gas main pipe and the three-axis clamp until the pressure reaches a preset value, if the reading of a fourth pressure gauge is reduced after the pressure is maintained for 2 hours, carrying out gas tightness inspection and plugging a leakage point, and carrying out the second step again; if the reading of the fourth pressure gauge is not reduced after the pressure is maintained for 2 hours, closing the second valve and the pneumatic valve, and performing a third step;
the third step is to open a vacuum valve, a pneumatic control valve and a vacuum pump, vacuumize the gas main pipe and the three-axis clamp holder, and discharge the gas in the system into the environment; after vacuumizing for 5-10 minutes, closing the vacuum valve, the air control valve and the vacuum pump, and entering a fourth step;
the fourth step is specifically that the first valve, the pneumatic control valve, the refrigerating unit and the third valve are opened, the first pressure reducing valve and the third pressure reducing valve are adjusted, the pulse pump is opened through the second electric control device, the six sets of loading devices are opened through the first electric control device, and the electric heater is opened through the temperature controller, so that the temperature condition in the deep part of the stratum is simulated; the six sets of loading devices enable the coal sample to be subjected to pulse loading of preset pressure so as to simulate the stress condition of coal in a specific stratum; injecting gas into the coal sample in the three-shaft clamp holder through the gas main pipe, so that the coal sample absorbs the gas under the condition of pulsating loading pressure;
after keeping the adsorption state for 24 hours, closing the first valve and the pneumatic control valve, and performing a fifth step;
the fifth step is that the pulsating pressure applied to the coal sample by the six sets of loading devices is slowly increased through the first electric control device until the coal sample is fractured; recording pressure data of pulse pressurization of six sets of loading devices when a coal sample is fractured, and providing guidance for deep coal fracturing permeability increase and regional coal and gas outburst prevention; closing the refrigerating unit and the third valve, closing the pulse pump through the second electric control device, and closing the six sets of loading devices through the first electric control device to perform a sixth step;
and the sixth step is specifically to open the fourth valve and the back pressure valve, so that the gas in the three-shaft holder enters a gas-liquid separator, the separated water is discharged into the environment through a liquid flowmeter, and the separated gas is discharged into the atmosphere through a gas flowmeter.
8. The experimental method according to claim 7, characterized in that: in the fourth step, the fifth valve and the booster pump are opened while the first valve is opened, and gas in the reference tank is injected into the gas main pipe by the booster pump, so that the gas pressure in the gas main pipe and the gas pressure in the three-shaft clamp holder are increased, and the gas adsorption speed is increased.
9. The experimental method according to claim 7, characterized in that: in the fourth step, when six sets of loading devices enable the coal sample to be subjected to pulse loading of preset pressure, a preset pressure-time curve is a sine line or a residual string line.
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