CN109342298B - Experimental method for high-power pulse wave induced cracking of gas-containing coal body - Google Patents
Experimental method for high-power pulse wave induced cracking of gas-containing coal body Download PDFInfo
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Abstract
The invention relates to the technical field of coal bed gas (mine gas) mining, in particular to an experimental method for fracturing a gas-containing coal body by high-power pulse waves, which comprises the steps of preparing a coal sample; installing a high-power pulse generating mechanism; installing an acoustic emission detection mechanism; the method comprises the steps of enabling the high-power pulse generating mechanism to emit high-power pulses to the coal sample to crack the coal sample, enabling the acoustic emission detecting mechanism to detect and analyze acoustic emissions in the coal sample, and further comprising the step of installing a shock wave detecting mechanism, enabling the shock wave detecting mechanism to detect and analyze shock wave characteristics in the coal sample. The beneficial effects of the invention are as follows: the method can determine the pulse energy required when the coal body cracking effect is good, analyze the acoustic emission time-space evolution rule in the cracking process of the gas-containing coal under high confining pressure and high gas pressure, discuss the influence of the gas pressure on the acoustic emission characteristic, carry out experimental research on the shock wave characteristic and the shock wave cracking coal sample rule, and carry out numerical calculation analysis on the shock wave cracking rule with different waveform energy.
Description
Technical Field
The invention relates to the technical field of coal bed gas (mine gas) exploitation, in particular to an experimental method for fracturing a gas-containing coal body by high-power pulse waves.
Background
In recent years, with the development of science and technology, China makes breakthrough progress on the development of coal beds. With the annual increase of the coal demand in China, the exploitation of coal seams in China gradually shifts to deep parts. The gas pressure of the deep coal seam is large, the gas content is high, and coal and gas outburst dynamic disasters are easily caused in the production process of a mine. In order to prevent coal and gas outburst disasters and ensure safe production, before mining the coal bed, gas in the coal bed needs to be extracted. However, the permeability of deep coal seams is generally low, so that the difficulty of gas extraction is high, and measures need to be taken to increase the permeability of the coal seams before gas extraction in order to reduce the difficulty of gas extraction.
The coal seam cracking and permeability increasing technology is an important method for solving the problems of microporosity, low permeability and high adsorption of deep low-permeability coal seams, and scholars at home and abroad explore the coal seam cracking and permeability increasing technology in a large quantity and make a certain progress. The currently common coal seam permeability increasing technology mainly comprises the following steps: mining protective layers, intensive drilling, hydraulic fracturing, high-pressure water jet slotting, deep hole loosening blasting and the like. The technologies generally have the defects of complex process, large construction amount, high cost, limited application range and the like.
In recent years, a high-power pulse technology is proposed to be applied to the field of coal bed permeability increasing, and a good effect is achieved in field application. In the process of increasing the permeability of the coal bed by adopting a high-power pulse technology, researchers find that the permeability increasing effect of the high-power pulse technology acting on the coal bed is influenced by pulse energy and the physical and chemical characteristics of the coal body, namely when the high-power pulse is adopted to crack the coal body, high-power pulses with different pulse energies are selected to crack the coal body with the same physical and chemical characteristics, and the permeability of the cracked coal body is different; high-power pulses with the same pulse energy are selected to crack coal bodies with different physical and chemical characteristics, and the permeability of the cracked coal bodies is different.
In the process of coal seam mining, the coal seams in different areas have different physical and chemical characteristics. When high-power pulse fracturing coal bodies are adopted, in order to ensure that the fractured coal bodies have better permeability, the pulse energy required when the fracturing effect on the coal bodies is better needs to be determined in advance.
Disclosure of Invention
The invention aims to: aiming at the problem of how to determine the pulse energy required by a good coal body fracturing effect when a high-power pulse fracturing coal body is adopted, an experimental method for fracturing a gas-containing coal body by using a high-power pulse wave is provided.
In order to achieve the purpose, the invention adopts the technical scheme that:
an experimental method for cracking coal containing gas by high-power pulse waves comprises
Step a: making a coal sample;
step b: installing a high-power pulse generating mechanism, and connecting the high-power pulse generating mechanism with the coal sample through a lead;
step c: installing an acoustic emission detection mechanism, and enabling the acoustic emission detection mechanism to be matched with the coal sample;
step d: and enabling the high-power pulse generating mechanism to emit high-power pulses to the coal sample, cracking the coal sample, and enabling the acoustic emission detection mechanism to detect and analyze acoustic emission characteristics in the coal sample.
The high power pulse of the present application means a pulse having a pulse power of 10KW or more. In order to ensure the discharging effect in the scheme, after one end of the lead connected with the coal sample is connected with the discharging electrode, the discharging electrode is connected with the coal sample, so that when the coal sample is discharged, the high-power pulse mechanism emits high-power pulse to the coal sample through the discharging electrode. The acoustic emission detection mechanism in the scheme can adopt a commercially common acoustic emission detector. The experimental method for cracking the gas-containing coal body by the high-power pulse waves in the scheme comprises a high-power pulse generation mechanism and an acoustic emission detection mechanism. Multiple identical coal samples were made according to the experimental requirements before the start of the experiment. During the experiment, the sensor of the acoustic emission detection mechanism is attached to the surface of the coal sample, then the high-power pulse generation mechanism cracks the coal samples of different groups by high-power pulses with different pulse energies, and the pulse energies corresponding to the coal samples of each group are recorded one by one. The high-power pulse generating mechanism emits high-power pulses to crack the coal sample, different areas in the coal sample are gradually cracked, acoustic emission signals are generated, the acoustic emission detection mechanism detects the acoustic emission signals generated when the different areas are cracked, and the sequence of the detected acoustic emission signals is recorded. After the coal sample is cracked, the acoustic emission detection mechanism analyzes the acquired acoustic emission signals, and a computer is adopted for modeling, so that the dynamic process of the coal sample in which different areas are damaged can be clearly reflected on the computer, and the size of the damaged area in the coal sample can be accurately obtained. By comparing the sizes of the damaged areas in different groups of coal samples, a group of coal samples with the largest internal damaged area can be determined. The pulse energy required when the coal sample is enabled to have a good fracturing effect can be determined by inquiring the pulse energy corresponding to the group of coal samples, so that the problem of how to determine the pulse energy required when the coal body is enabled to have a good fracturing effect when a high-power pulse is adopted to fracture the coal sample is solved.
In the process of fracturing the coal body by adopting the high-power pulse, researchers find that in the process of fracturing the same coal body by adopting the high-power pulse with the same pulse energy, when the fracturing frequencies of the same coal body are different, namely the fracturing times of the same coal body are different in a certain time, the fracturing effects of the coal body are different. In order to ensure that the cracked coal body has better permeability, the selection frequency of cracking the coal body needs to be determined in advance.
When the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave is used for carrying out experiments, different pulse energies are selected for carrying out the experiments under the condition that the fracturing frequency of the coal body is kept to be the same, and the pulse energy required when the fracturing effect is good is determined; and then, under the condition of keeping the pulse energy of the high-power pulse unchanged, different frequencies are adopted to crack different groups of coal samples. After fracturing is completed, the insides of different groups of coal samples are detected, and a group of coal samples with the largest porosity is determined, namely the fracturing effect of the coal samples can be determined when the coal samples are fractured at a certain frequency.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step e: installing a three-axis pressurization system and a gas injection system;
step f: and applying three-axis pressure to the coal sample by the three-axis pressurization system, so that the gas injection system injects gas into the coal sample.
Coal resources are one of main energy sources in China, and with the development of economy, the exploitation of the coal resources gradually changes to deep parts. The characteristics of high ground stress, high gas, low permeability and the like of a deep coal seam seriously affect the safe mining of coal. Therefore, the research on the acoustic emission characteristics of the gas-containing coal rock under complex stress, particularly under higher confining pressure and high gas pressure is carried out, and the method has important significance for revealing the space-time distribution characteristics of the deep high gas coal rock micro-fracture test piece under different stress environments and ensuring the safe exploitation of the deep high gas coal seam.
The experimental method for the high-power pulse wave fracturing of the gas-containing coal body in the preferred scheme further comprises a triaxial pressurizing system and a gas injection system, wherein during experiment, the triaxial pressurizing system applies triaxial pressure to the coal sample to simulate high ground stress on a deep coal bed, and the gas injection system injects gas into the coal sample to simulate high gas pressure existing in coal rocks. In the experiment process, the acoustic emission detection mechanism collects and analyzes acoustic emission signals inside the coal body, and an acoustic emission spatial distribution rule can be obtained, so that researchers can analyze acoustic emission temporal and spatial evolution rules in the gas-containing coal fracture process under high confining pressure and high gas pressure, and study the influence of the gas pressure on acoustic emission characteristics.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step g: and installing a shock wave detection mechanism, and enabling the shock wave detection mechanism to detect and analyze the shock wave characteristics in the coal sample.
The shock wave detection mechanism in the preferred scheme can select a common shock wave detector on the market. Multiple groups of the same coal samples are prepared according to the experiment requirement before the experiment begins. During the experiment, a plurality of sensors of the shock wave detection mechanism are buried at different positions in the coal sample, then the high-power pulse generation mechanism punctures the liquid filled in the drill holes of the coal samples of different groups by the high-power pulses with different pulse energies, so that the liquid generates shock waves to crack the coal samples, and the pulse energies corresponding to the coal samples of the groups are recorded one by one. The failure modes of coal samples can be divided into tensile failure and compressive failure, and the failure in the vicinity of a borehole is usually compressive failure. The tensile strength of the coal sample is smaller than the compressive strength of the coal sample, the destructive capacity of the shock wave is gradually reduced along with the propagation of the shock wave in the coal sample, and when the shock wave cannot cause the compressive destruction of the coal sample, the destruction form of the coal sample is converted into the tensile destruction. The shock wave detection mechanism analyzes the collected shock wave signals, can know the damage form of different areas in the coal sample, and simultaneously analyzes the position of the collected shock wave signals, so that the size of the damaged area in the coal sample can be obtained. By comparing the sizes of the damaged areas in different groups of coal samples, a group of coal samples with the largest internal damaged area can be determined. The pulse energy required for the coal sample with a good cracking effect can be determined by inquiring the pulse energy corresponding to the group of coal samples. The system has the advantages that the shock wave detection mechanism is adopted to detect and analyze shock wave signals in the coal sample, so that researchers can analyze the generation and propagation mechanism of high-power pulse shock waves and the cracking mechanism of the coal sample, can also perform experimental research on shock wave characteristics and the shock wave cracking rule of the coal sample, and perform numerical calculation analysis on the shock wave cracking rule with different waveform energy. Meanwhile, the internal fracture range of the coal sample can be accurately obtained by analyzing the acoustic emission and the shock wave together.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step h: and installing a gas pressure detection mechanism to enable the gas pressure detection mechanism to detect the gas pressure in the coal sample.
The permeability increasing effect of the high-power pulse technology on the coal bed is influenced by the pressure of the coal bed gas in the coal bed, namely when the pressure of the coal bed gas in the coal bed is different, the fracturing effect of fracturing the coal body by adopting high-power pulses with the same pulse energy is different. In the above preferred scheme, through setting up gas pressure detection mechanism, realized the detection to the inside gas pressure of coal sample to can definitely obtain under what gas pressure of coal sample, the fracturing effect that receives the high power pulse is the best.
Preferably, the lead comprises a first lead segment, a second lead segment and a third lead segment, and the step b of installing the high power pulse generating mechanism comprises
Step b 1: installing a high-power pulse power supply, a high-power pulse switch and a high-power pulse capacitor;
step b 2: connecting the high-power pulse power source and the high-power pulse capacitor through a first wire segment;
step b 3: connecting the positive electrode of the high-power pulse capacitor with one end of the coal sample through a second lead section;
step b 4: connecting the negative electrode of the high-power pulse capacitor with the other end of the coal sample through a third lead section;
step b 5: and the high-power pulse switch is arranged on the second lead section or the third lead section and is used for controlling the on-off state of a circuit between the high-power pulse capacitor and the coal sample.
In the above preferred embodiment, the high power pulse generating mechanism includes a high power pulse power source, a high power pulse switch and a high power pulse capacitor, the high power pulse power source is connected to the high power pulse capacitor through a first lead segment, the positive electrode of the high power pulse capacitor is connected to one end of the coal sample through a second lead segment, the negative electrode of the high power pulse capacitor is connected to the other end of the coal sample through a third lead segment, and the high power pulse switch is disposed on the second lead segment or the third lead segment. When the device is used, the high-power pulse switch is firstly switched off, the high-power pulse power supply is used for charging the high-power pulse capacitor, and the pulse energy stored in the high-power pulse capacitor can be calculated by measuring the voltage between the anode and the cathode of the high-power pulse capacitor. When the electric quantity charged into the high-power pulse capacitor meets the experimental requirements, the high-power pulse power supply stops charging the high-power pulse capacitor, then the high-power pulse switch is closed, and at the moment, the high-power pulse capacitor releases high-voltage pulses with specific pulse energy to crack the coal sample. Meanwhile, the coal sample can be cracked at a specific frequency by controlling the times of charging the high-power pulse capacitor by the high-power pulse power supply within a certain time and the times of closing the high-power pulse switch.
When the experiment method for fracturing the gas-containing coal body by using the high-power pulse wave in the preferred scheme is used for carrying out experiments, the coal sample can be conveniently fractured by using the high-power pulse with specific pulse energy, and the coal sample can be conveniently fractured at a specific frequency.
Preferably, in the step e, installing a triaxial pressurizing system comprises
Step e 1: installing a closable pressure chamber for containing the coal sample;
step e 2: through holes are respectively formed in the side walls of the pressure chamber in the x direction, the y direction and the z direction;
step e 3: the sliding block is arranged on the through hole in a sliding mode, one end, corresponding to the inner side of the pressure chamber, of the sliding block is a pressing end, and the end portion of the pressing end is in pressing fit with the coal sample.
In the above preferred embodiment, the triaxial pressurizing system includes a closable pressure chamber. During the experiment, place the coal sample in the pressure chamber to seal the pressure chamber, oppress the end portion through the oppression that promotes the sliding block messenger sliding block to the coal sample, can realize applying triaxial pressure to the coal sample, it is very convenient to operate.
Preferably, in the step e, installing the triaxial pressurizing system further comprises
Step e 4: and installing a hydraulic oil cylinder to enable the hydraulic oil cylinder to correspond to the sliding block, and enabling the hydraulic oil cylinder and the sliding block to be in linkage fit.
Among the above-mentioned preferred scheme, through setting up hydraulic cylinder to make hydraulic cylinder and sliding block corresponding, under linkage cooperation between hydraulic cylinder and sliding block, when making hydraulic cylinder flexible, hydraulic cylinder promotes or stimulates the sliding block and slides, makes the sliding block oppress the coal sample or separate with the coal sample, thereby when exerting triaxial pressure to the coal sample, it is more convenient.
Preferably, the sliding block is made of an insulating material.
Preferably, one of the sliding blocks is a communicating sliding block, one end of the coal sample departing from the communicating sliding block is a first corresponding end, and the step e of installing the three-axis pressurization system further includes
Step e 5: installing a connecting block on the first corresponding end, and penetrating one end of the connecting block through the pressure chamber to extend to the outside of the pressure chamber;
step e 6: a first channel which can be closed is arranged on the connecting block;
step e 7: and a second channel which can be closed is arranged on the communicating sliding block, and the gas injection system is communicated with the first channel.
In the above preferred embodiment, the gas injection system is communicated with the first passage by providing a closable second passage on the communicating sliding block, so that the injected gas flows into the pressure chamber through the first passage and flows out of the pressure chamber through the second passage.
Preferably, one end of the coal sample corresponding to the communication sliding block is a second corresponding end, and in the step b3, the connection between the positive electrode of the high-power pulse capacitor and the coal sample includes
Step b 31: connecting the second wire segment with the first corresponding end after passing through the first channel;
in the step b4, the connection between the negative electrode of the high-power pulse capacitor and the other end of the coal sample comprises
Step b 41: and connecting the third lead segment with the second corresponding end after passing through the second channel.
Among the above-mentioned preferred scheme, through set up the first passageway that can seal on the connecting block, set up the second passageway that can seal on the intercommunication sliding block to the second wire segment can pass first passageway and get into the pressure chamber in be connected with the one end of coal sample, and the third wire segment can pass the second passageway and get into the pressure chamber in and be connected with the other end of coal sample, and is very convenient. After the first lead section and the second lead section are respectively connected with two ends of a coal sample, the first channel and the second channel are plugged, so that gas in the pressure chamber can be prevented from flowing out of the pressure chamber along the first channel or the second channel during an experiment.
Preferably, in the step e, installing the gas injection system comprises
Step e 8: the installation has the pressure bottle of storage gas, adopts first pipeline will the pressure bottle with communicate between the first passageway.
Preferably, in the step e8, the first pipe is detachably connected to the first channel.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step i: a second pipeline is arranged on the second channel;
step j: and a flowmeter is arranged on the second pipeline, and the flowmeter is matched with the second pipeline to meter the gas flowing through the second channel.
In the process of the experiment, the experimenter finds that after the coal body is fractured by adopting the high-power pulse, the gas can penetrate through the coal body and flow to the outside of the communicating sliding block along the second channel. When the cracking effect of the coal sample is better, the flowing flow rate of the gas is higher. In the above preferred scheme, the second pipeline is arranged on the second channel, and the flowmeter is arranged on the second pipeline, so that the gas flowing through the second channel is measured, and after the coal sample is cracked, the flow displayed by the flowmeters corresponding to the coal samples of different groups is compared, so that the cracking effect of the coal sample of which group is the best can be determined. The whole process of determining the internal permeability of the coal sample does not need the cooperation of other instruments, so that the experiment cost is saved, and the method is very convenient.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step k: installing a Rogowski coil on the lead;
step l: and installing an oscilloscope, and connecting the Rogowski coil with the oscilloscope through a data line.
In the process of repeated experiments, researchers find that when the liquid is punctured by pulse currents in different discharge forms, the intensity of shock waves generated after the liquid is punctured is different, and therefore the cracking effect on a coal sample is different. In order to ensure the best effect on cracking of the coal body, it is therefore determined in advance in what form the electric discharge is in, which form the shock wave generated after the liquid breakdown is the greatest in intensity. Under different discharge forms, the current waveforms corresponding to the generated pulse current are different.
In the preferred scheme, the rogowski coil and the oscilloscope are installed, the current waveforms corresponding to different pulse currents can be measured under the cooperation of the rogowski coil and the oscilloscope, and the cracking effect on the coal body can be best when the liquid is punctured by the pulse current with which waveform is determined by comparing the cracking effect of the coal sample under different waveforms. The discharge form of the high-power pulse mechanism is adjusted to enable the waveform corresponding to the pulse current generated by the high-power pulse mechanism to be a specific waveform, and the high-power pulse mechanism can be realized by adopting the conventional mode. Therefore, after the current waveform of the pulse current with the best coal sample cracking effect is obtained, the coal body cracking effect can be best by adjusting the discharge form of the high-power pulse.
Compared with the prior art, the invention has the beneficial effects that: when the high-power pulse is adopted to crack the coal body, the pulse energy required when the cracking effect on the coal body is good can be accurately determined, meanwhile, the acoustic emission spatiotemporal evolution rule in the process of breaking the coal containing gas under high confining pressure and high gas pressure can be analyzed, and the influence of the gas pressure on the acoustic emission characteristic is discussed.
Drawings
FIG. 1 is a schematic view of the present invention;
FIG. 2 is a cross-sectional view of a coal sample according to the present invention placed within a pressure chamber;
FIG. 3 is a cross-sectional view of a pressure chamber according to the present invention;
figure 4 is a cross-sectional view of the pressure chamber according to the invention in another direction,
the labels in the figure are: 1-acoustic emission detection mechanism, 2-coal sample, 3-shock wave detection mechanism, 4-gas pressure detection mechanism, 5-high-power pulse power supply, 6-high-power pulse switch, 7-high-power pulse capacitor, 8-first lead segment, 9-second lead segment, 10-third lead segment, 11-pressure chamber, 12-sliding block, 13-hydraulic oil cylinder, 14-connecting block, 15-pressure bottle, 16-first pipeline, 17-second pipeline, 18-flowmeter, 19-Rogowski coil, 20-oscilloscope, 111-through hole, 121-second channel and 141-first channel.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
An experimental method for cracking coal containing gas by high-power pulse waves comprises
Step a: making a coal sample 2;
step b: installing a high-power pulse generating mechanism, and connecting the high-power pulse generating mechanism with the coal sample 2 through a lead;
step c: installing an acoustic emission detection mechanism 1, and enabling the acoustic emission detection mechanism 1 to be matched with the coal sample 2;
step d: and enabling the high-power pulse generating mechanism to transmit high-power pulses to the coal sample 2, fracturing the coal sample 2, and enabling the acoustic emission detection mechanism 1 to detect and analyze acoustic emission characteristics in the coal sample 2.
The high power pulse of the present application means a pulse having a pulse power of 10KW or more. In order to ensure the discharging effect in the above scheme, after the end of the lead wire connected with the coal sample 2 is connected with the discharging electrode, the discharging electrode is connected with the coal sample 2, so that when the coal sample 2 is discharged, the high-power pulse mechanism emits high-power pulse to the coal sample 2 through the discharging electrode. The acoustic emission detection mechanism 1 in the above scheme can select a commercially common acoustic emission detector. The experimental method for cracking the gas-containing coal body by the high-power pulse waves in the scheme comprises a high-power pulse generation mechanism and an acoustic emission detection mechanism 1. Multiple identical coal samples 2 were made according to the experimental requirements before the start of the experiment. During the experiment, the sensor of the acoustic emission detection mechanism 1 is attached to the surface of the coal sample 2, then the high-power pulse generation mechanism cracks the coal samples 2 of different groups by high-power pulses with different pulse energies, and the pulse energies corresponding to the coal samples 2 of each group are recorded one by one. The high-power pulse generating mechanism emits high-power pulses to crack the coal sample 2, different areas in the coal sample 2 are gradually cracked, acoustic emission signals are generated, the acoustic emission detection mechanism 1 detects the acoustic emission signals generated when the different areas are cracked, and the sequence of the detected acoustic emission signals is recorded. After the coal sample 2 is cracked, the acoustic emission detection mechanism 1 analyzes the acquired acoustic emission signals, and a computer is adopted for modeling, so that the dynamic process of the coal sample 2 in which different areas are damaged can be clearly reflected on the computer, and the size of the damaged area in the coal sample 2 can be accurately obtained. By comparing the sizes of the damaged areas in the different groups of coal samples 2, the group of coal samples 2 with the largest internal damaged area can be determined. The pulse energy required when the coal sample 2 is cracked with good effect can be determined by inquiring the pulse energy corresponding to the group of coal samples 2, so that the problem of how to determine the pulse energy required when the coal body is cracked with good effect when the high-power pulse is adopted to crack the coal sample 2 is solved.
In the process of fracturing the coal body by adopting the high-power pulse, researchers find that in the process of fracturing the same coal body by adopting the high-power pulse with the same pulse energy, when the fracturing frequencies of the same coal body are different, namely the fracturing times of the same coal body are different in a certain time, the fracturing effects of the coal body are different. In order to ensure that the cracked coal body has better permeability, the selection frequency of cracking the coal body needs to be determined in advance.
When the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave is used for carrying out experiments, different pulse energies are selected for carrying out the experiments under the condition that the fracturing frequency of the coal body is kept to be the same, and the pulse energy required when the fracturing effect is good is determined; and then, under the condition of keeping the pulse energy of the high-power pulse unchanged, different frequencies are adopted to crack different groups of coal samples 2. After fracturing is completed, the insides of different groups of coal samples 2 are detected, and a group of coal samples 2 with the largest porosity is determined, namely the fracturing effect of the coal samples 2 is good when the coal samples 2 are fractured at a certain frequency.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step e: installing a three-axis pressurization system and a gas injection system;
step f: and applying three-axis pressure to the coal sample 2 by the three-axis pressurization system, and injecting gas into the coal sample 2 by the gas injection system.
Coal resources are one of main energy sources in China, and with the development of economy, the exploitation of the coal resources gradually changes to deep parts. The characteristics of high ground stress, high gas, low permeability and the like of a deep coal seam seriously affect the safe mining of coal. Therefore, the research on the acoustic emission characteristics of the gas-containing coal rock under complex stress, particularly under higher confining pressure and high gas pressure is carried out, and the method has important significance for revealing the space-time distribution characteristics of the deep high gas coal rock micro-fracture test piece under different stress environments and ensuring the safe exploitation of the deep high gas coal seam.
The experimental method for the high-power pulse wave fracturing of the gas-containing coal body in the preferred scheme further comprises a triaxial pressurizing system and a gas injection system, wherein during experiment, the triaxial pressurizing system applies triaxial pressure to the coal sample 2 to simulate high ground stress on a deep coal bed, and the gas injection system injects gas into the coal sample 2 to simulate high gas pressure existing in coal rocks. In the experiment process, the acoustic emission detection mechanism 1 collects and analyzes acoustic emission signals inside a coal body, and an acoustic emission spatial distribution rule can be obtained, so that researchers can analyze acoustic emission temporal and spatial evolution rules in the process of breaking gas-containing coal under high confining pressure and high gas pressure, and discuss the influence of the gas pressure on acoustic emission characteristics.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step g: and installing a shock wave detection mechanism 3, and enabling the shock wave detection mechanism 3 to detect and analyze the shock wave characteristics in the coal sample 2.
The shock wave detection mechanism 3 in the above preferred embodiment can be a commercially available shock wave detector. Multiple identical coal samples 2 were made according to the experimental requirements before the start of the experiment. During the experiment, a plurality of sensors of the shock wave detection mechanism 3 are buried at different positions in the coal sample 2, then the high-power pulse generation mechanism punctures the liquid filled in the drill holes of the coal samples 2 of different groups by the high-power pulses with different pulse energies, the liquid generates shock waves to fracture the coal samples 2, and the pulse energies corresponding to the coal samples 2 of each group are recorded one by one. The failure modes of the coal sample 2 can be divided into tensile failure and compressive failure, and the failure in the vicinity of the borehole is generally compressive failure. The tensile strength of the coal sample 2 is smaller than the compressive strength thereof, the destructive capacity of the shock wave is gradually reduced along with the propagation of the shock wave in the coal sample 2, and when the shock wave cannot cause the compressive destruction of the coal sample 2, the destruction form of the coal sample 2 is converted into the tensile destruction. The shock wave detection mechanism 3 analyzes the collected shock wave signals, the damage form of different areas in the coal sample 2 can be known, and meanwhile, the shock wave detection mechanism 3 analyzes the positions of the collected shock wave signals, so that the size of the damaged area in the coal sample 2 can be obtained. By comparing the sizes of the damaged areas in the different groups of coal samples 2, the group of coal samples 2 with the largest internal damaged area can be determined. The pulse energy required for the coal sample 2 to have a good fracturing effect can be determined by querying the pulse energy corresponding to the group of coal samples 2. The shock wave detection mechanism 3 is adopted to detect and analyze shock wave signals in the coal sample 2, so that researchers can analyze the generation and propagation mechanism of high-power pulse shock waves and the fracture mechanism of the coal sample 2, can also perform experimental research on shock wave characteristics and the law of cracking the coal sample 2 by the shock waves, and perform numerical calculation analysis on the shock wave cracking laws with different waveform energy. Meanwhile, the internal fracture range of the coal sample 2 can be obtained more accurately by analyzing the acoustic emission and the shock wave together.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step h: a gas pressure detection means 4 is installed so that the gas pressure detection means 4 detects the gas pressure in the coal sample 2.
The permeability increasing effect of the high-power pulse technology on the coal bed is influenced by the pressure of the coal bed gas in the coal bed, namely when the pressure of the coal bed gas in the coal bed is different, the fracturing effect of fracturing the coal body by adopting high-power pulses with the same pulse energy is different. In the above preferred scheme, the gas pressure detection mechanism 4 is arranged, so that the gas pressure inside the coal sample 2 is detected, and the cracking effect of the coal sample 2 under which gas pressure is subjected to high-power pulse can be clearly obtained.
Preferably, the lead comprises a first lead segment 8, a second lead segment 9 and a third lead segment 10, and the step b of installing the high power pulse generating mechanism comprises
Step b 1: installing a high-power pulse power supply 5, a high-power pulse switch 6 and a high-power pulse capacitor 7;
step b 2: connecting the high-power pulse power source 5 and the high-power pulse capacitor 7 by a first wire segment 8;
step b 3: connecting the positive electrode of the high-power pulse capacitor 7 with one end of the coal sample 2 through a second lead segment 9;
step b 4: connecting the negative electrode of the high-power pulse capacitor 7 with the other end of the coal sample 2 through a third lead segment 10;
step b 5: the high-power pulse switch 6 is arranged on the second lead section 9 or the third lead section 10 and is used for controlling the on-off state of the circuit between the high-power pulse capacitor 7 and the coal sample 2.
In the above preferred embodiment, the high-power pulse generating mechanism includes a high-power pulse power source 5, a high-power pulse switch 6 and a high-power pulse capacitor 7, the high-power pulse power source 5 and the high-power pulse capacitor 7 are connected by a first wire segment 8, the positive electrode of the high-power pulse capacitor 7 is connected with one end of the coal sample 2 by a second wire segment 9, the negative electrode of the high-power pulse capacitor 7 is connected with the other end of the coal sample 2 by a third wire segment 10, and the high-power pulse switch 6 is disposed on the second wire segment 9 or the third wire segment 10. When the pulse energy calculating device is used, firstly, the high-power pulse switch 6 is switched off, the high-power pulse power supply 5 is enabled to charge the high-power pulse capacitor 7, and the pulse energy stored in the high-power pulse capacitor 7 can be calculated by measuring the voltage between the positive electrode and the negative electrode of the high-power pulse capacitor 7. When the electric quantity charged into the high-power pulse capacitor 7 meets the experimental requirements, the high-power pulse power supply 5 stops charging the high-power pulse capacitor 7, then the high-power pulse switch 6 is closed, and at the moment, the high-power pulse capacitor 7 releases high-voltage pulses with specific pulse energy to crack the coal sample 2. Meanwhile, the coal sample 2 can be cracked at a specific frequency by controlling the times of charging the high-power pulse capacitor 7 by the high-power pulse power supply 5 within a certain time and the times of closing the high-power pulse switch 6.
When the experiment method for the high-power pulse wave fracturing of the gas-containing coal body in the preferred scheme is used for carrying out experiments, not only can the coal sample 2 be conveniently fractured by the high-power pulse with specific pulse energy, but also the coal sample 2 can be conveniently fractured by specific frequency.
Preferably, in the step e, installing a triaxial pressurizing system comprises
Step e 1: a closable pressure chamber 11 mounted for containing the coal sample 2;
step e 2: through holes 111 are respectively arranged on the side walls of the pressure chamber 11 in the x direction, the y direction and the z direction;
step e 3: sliding block 12 is slidably disposed on through hole 111, and one end of sliding block 12 corresponding to the inner side of pressure chamber 11 is a pressing end, so that the end of the pressing end is in press fit with coal sample 2.
In the preferred embodiment described above, the triaxial pressurizing system comprises a closable pressure chamber 11. During the experiment, place coal sample 2 in pressure chamber 11 to seal pressure chamber 11, oppress end tip through promoting sliding block 12 messenger sliding block 12 to coal sample 2, can realize exerting triaxial pressure to coal sample 2, it is very convenient to operate.
Preferably, in the step e, installing the triaxial pressurizing system further comprises
Step e 4: hydraulic cylinder 13 is installed to correspond hydraulic cylinder 13 to sliding block 12, so that hydraulic cylinder 13 and sliding block 12 are in linkage fit.
In the above preferred scheme, by arranging hydraulic oil cylinder 13 and making hydraulic oil cylinder 13 correspond to sliding block 12, under linkage fit between hydraulic oil cylinder 13 and sliding block 12, when hydraulic oil cylinder 13 stretches out and draws back, hydraulic oil cylinder 13 pushes or pulls sliding block 12 to slide, making sliding block 12 press coal sample 2 or separate from coal sample 2, thereby when applying triaxial pressure to coal sample 2, it is more convenient.
Preferably, slider 12 is made of an insulating material.
Preferably, one of the sliding blocks 12 is a communicating sliding block, an end of the coal sample 2 away from the communicating sliding block is a first corresponding end, and the step e of installing the three-axis pressurization system further includes
Step e 5: mounting a connecting block 14 on the first corresponding end, and extending one end of the connecting block 14 through the pressure chamber 11 to the outside of the pressure chamber 11;
step e 6: a first closable channel 141 is provided on the connecting piece 14;
step e 7: a second channel 121 which can be closed is arranged on the communicating sliding block, and the gas injection system is communicated with the first channel 141.
In the above preferred embodiment, the communication slide block is provided with a closable second passage 121, so that the gas injection system is communicated with the first passage 141, and the injected gas flows into the pressure chamber 11 through the first passage 141 and flows out of the pressure chamber 11 through the second passage 121.
Preferably, one end of the coal sample 2 corresponding to the communication sliding block is a second corresponding end, and in the step b3, the connection between the positive electrode of the high-power pulse capacitor 7 and the coal sample 2 includes
Step b 31: connecting the second wire segment 9 to the first corresponding end after passing through the first channel 141;
in the step b4, the connection between the negative electrode of the high-power pulse capacitor 7 and the other end of the coal sample 2 comprises
Step b 41: the third wire segment 10 is connected to the second corresponding end after passing through the second channel 121.
In the above preferred embodiment, the first channel 141 that can be closed is provided on the connecting block 14, and the second channel 121 that can be closed is provided on the communicating sliding block, so that the second lead segment 9 can enter the pressure chamber 11 through the first channel 141 to be connected with one end of the coal sample 2, and the third lead segment 10 can enter the pressure chamber 11 through the second channel 121 to be connected with the other end of the coal sample 2, which is very convenient. After the first lead segment 8 and the second lead segment 9 are respectively connected with two ends of the coal sample 2, the first channel 141 and the second channel 121 are blocked, so that gas in the pressure chamber 11 can be prevented from flowing out of the pressure chamber 11 along the first channel 141 or the second channel 121 during an experiment.
Preferably, in the step e, installing the gas injection system comprises
Step e 8: a pressure bottle 15 storing gas is installed, and the pressure bottle 15 is communicated with the first passage 141 by a first pipe 16.
Preferably, in the step e8, the first pipe 16 is detachably connected to the first channel 141.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step i: a second pipeline 17 is arranged on the second channel 121;
step j: a flow meter 18 is disposed on the second pipe 17, and the flow meter 18 is matched with the second pipe 17 to meter the gas flowing through the second passage 121.
In the course of the experiment, the experimenter found that after fracturing the coal body with the high power pulse, the gas would pass through the coal body and flow along the second channel 121 to the outside of the communicating sliding block. When the cracking effect of the coal sample 2 is better, the flow rate of the flowing gas is larger. In the above preferred embodiment, the second pipeline 17 is arranged on the second channel 121, and the flow meter 18 is arranged on the second pipeline 17, so that the gas flowing through the second channel 121 is measured, and after the fracturing of the coal samples 2 is completed, the flow rate displayed by the flow meter 18 corresponding to the coal samples 2 of different groups is compared, so that the best fracturing effect of the group of coal samples 2 can be determined. The whole process of determining the internal permeability of the coal sample 2 does not need the cooperation of other instruments, so that the experiment cost is saved, and the method is very convenient.
Preferably, the experimental method for fracturing the gas-containing coal body by using the high-power pulse wave further comprises
Step k: a rogowski coil 19 is mounted on the lead;
step l: an oscilloscope 20 is installed, and the rogowski coil 19 and the oscilloscope 20 are connected through a data line.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (7)
1. An experimental method for fracturing a gas-containing coal body by high-power pulse waves is characterized by comprising the following steps: comprises that
Step a: making a coal sample (2);
step b: installing a high-power pulse generating mechanism, and connecting the high-power pulse generating mechanism with the coal sample (2) through a lead; the conducting wire is provided with a Rogowski coil (19), and the oscilloscope (20) is connected with the Rogowski coil (19) through a data wire to obtain the current waveform of the pulse current;
step c: installing an acoustic emission detection mechanism (1) to enable the acoustic emission detection mechanism (1) to be matched with the coal sample (2);
step d: enabling the high-power pulse generating mechanism to emit high-power pulses to the coal sample (2), fracturing the coal sample (2), and enabling the acoustic emission detection mechanism (1) to detect and analyze acoustic emission characteristics in the coal sample (2);
manufacturing a plurality of groups of same coal samples (2), attaching a sensor of an acoustic emission detection mechanism to the surface of the coal samples (2), enabling a high-power pulse generation mechanism to crack the coal samples (2) of different groups by high-power pulses with different pulse energies, recording pulse energy corresponding to each group of coal samples (2) one by one, and then cracking the coal samples (2) of different groups by adopting different frequencies under the condition of keeping the pulse energy of the high-power pulses unchanged; detecting acoustic emission signals generated when different areas break by using an acoustic emission detection mechanism, and recording the sequence of the detected acoustic emission signals; modeling by adopting a computer, and analyzing the acoustic emission signals collected by the acoustic emission detection mechanism;
step e: installing a three-axis pressurization system and a gas injection system, the installing of the three-axis pressurization system comprises
Step e 1: -installing a closable pressure chamber (11) for containing the coal sample (2);
step e 2: through holes (111) are respectively arranged on the side walls of the pressure chamber (11) in the x direction, the y direction and the z direction;
step e 3: a sliding block (12) is arranged on the through hole (111) in a sliding mode, one end, corresponding to the inner side of the pressure chamber (11), of the sliding block (12) is a pressing end, and the end portion of the pressing end is in pressing fit with the coal sample (2); one of the sliding blocks (12) is a communicating sliding block, and a closable second channel (121) is arranged on the communicating sliding block;
further comprising the steps of: and installing a gas pressure detection mechanism (4) to enable the gas pressure detection mechanism (4) to detect the gas pressure in the coal sample (2).
2. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 1, characterized in that:
also comprises
Step f: and applying three-axis pressure to the coal sample (2) by the three-axis pressurization system, and injecting gas into the coal sample (2) by the gas injection system.
3. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 1 or 2, characterized in that:
also comprises
Step g: and installing a shock wave detection mechanism (3), and enabling the shock wave detection mechanism (3) to detect and analyze the shock wave characteristics in the coal sample (2).
4. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 1, characterized in that:
in step e, installing the three-axis pressurization system further comprises
Step e 4: and installing a hydraulic oil cylinder (13), enabling the hydraulic oil cylinder (13) to correspond to the sliding block (12), and enabling the hydraulic oil cylinder (13) and the sliding block (12) to be in linkage fit.
5. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 1, characterized in that:
one end of the coal sample (2) departing from the communication sliding block is a first corresponding end, and in the step e, the installation of the three-axis pressurization system further comprises
Step e 5: mounting a connecting block (14) on the first corresponding end, and penetrating one end of the connecting block (14) through the pressure chamber (11) to extend to the outside of the pressure chamber (11);
step e 6: a first closable channel (141) is provided on the connecting piece (14);
step e 7: communicating the gas injection system with the first passageway (141).
6. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 5, wherein:
in the step e, installing the gas injection system comprises
Step e 8: and installing a pressure bottle (15) storing gas, and communicating the pressure bottle (15) with the first channel (141) by adopting a first pipeline (16).
7. The experimental method for high-power pulse wave induced cracking of gas-containing coal bodies according to claim 6, wherein:
also comprises
Step i: a second duct (17) is arranged on the second channel (121);
step j: and a flow meter (18) is arranged on the second pipeline (17), and the flow meter (18) is matched with the second pipeline (17) to meter the gas flowing through the second channel (121).
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