High-energy acoustoelectric physical field fracturing and permeability increasing experiment system and method

Abstract

The invention provides a high-energy acoustoelectric physical field fracturing and permeability increasing experiment system and method. The experiment system comprises an anti-explosion and anti-explosion cavity, and a test loading system, an acoustoelectric fracturing system, a gas injection system, an extraction system and a parameter monitoring system which are mounted in the anti-explosion and anti-explosion cavity. Strong electric stress and shock waves generated by high-voltage discharge and vibration and cavitation effects caused by a high-strength sound field jointly act on a coal sample. Under the action of an electro-acoustic coupling field, microscopic cracks are generated in the coal sample and are expanded into a net, so that the permeability is improved; and meanwhile, physical field energy promotes desorption of gas molecules and accelerates the diffusion process, and finally efficient extraction of unconventional natural gas is achieved. According to the invention, breakthroughs are made in the aspects of fracturing energy, fracturing action range, in-situ observation capability and the like, a simulation experiment of fracturing and permeation enhancement of the deep ultra-low permeability reservoir under the action of a high-energy acoustoelectric physical field is realized, and an experiment platform is provided for research on a permeation enhancement transformation mechanism of the deep ultra-low permeability reservoir.

Description

Technical Field

[0001] This invention belongs to the field of coal and rock fracturing and permeability enhancement, specifically relating to a high-energy acoustic-electrophysical field fracturing and permeability enhancement experimental system. Background Technology

[0002] With the rapid growth of my country's natural gas consumption demand, its dependence on foreign natural gas has exceeded 40%. To ensure energy security, the exploration and development of unconventional natural gas resources such as coalbed methane and shale gas has been listed as a national strategic priority. Exploration data shows that my country has abundant reserves of deep coalbed methane and shale gas, with deep shale gas resources accounting for more than 60% and recoverable deep coalbed methane reserves reaching 4 trillion cubic meters, making it a major replacement area for future reserve and production increases.

[0003] Currently, the core technical challenge facing deep unconventional natural gas development lies in the fact that reservoirs generally exhibit tightness characteristics, with permeability mostly ranging from Nadarcy to microdarcy (10⁻¹⁰). -9 ~10 -6 μm 2 This ultra-low permeability characteristic results in extremely poor reservoir fluid seepage capacity. Conventional fracturing technology struggles to create efficient seepage channels, leading to low gas desorption-diffusion-migration efficiency. This results in rapid decline in single-well production and a resource utilization rate of less than 30%, severely hindering the commercial development process.

[0004] Traditional hydraulic fracturing techniques (such as those disclosed in CN201780043735.4 and CN201711045891.2) have limited fracture propagation range in ultra-low permeability reservoirs. The fracturing fluid is prone to causing reservoir damage and secondary blockage, and it is difficult to effectively connect micro- and nano-sized pores. Existing acoustic-electric fracturing systems (such as those disclosed in CN202311546127.9) suffer from insufficient fracturing energy, limited permeability enhancement effect, and small impact range. In addition, the theory of acoustic-electric fracturing in deep reservoirs is still incomplete, making these technologies currently unsuitable for the stimulation, permeability enhancement, and pressure relief control needs of deep reservoirs. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the first aspect of the present invention is to provide a high-energy acoustic-electrophysical field-induced fracturing and permeation-enhancing experimental system. The second aspect, based on the same inventive concept, also provides a method based on the aforementioned high-energy acoustic-electrophysical field-induced fracturing and permeation-enhancing experimental system.

[0006] In this embodiment of the invention, the high-energy acoustic-electrophysical field-induced fracturing and permeability enhancement experimental system includes an explosion-proof and explosion-resistant cavity, and a test loading system, an acoustic-electrophysical fracturing system, a gas injection system, an extraction system, and a parameter monitoring system installed in the explosion-proof and explosion-resistant cavity. The test loading system includes a sample chamber with a sealed top for placing coal samples, a stress loading device for applying confining pressure and axial pressure to the coal samples in the sample chamber, and a temperature control device for heating the coal samples in the sample chamber. The temperature output terminal of the control system is connected to the temperature control terminal of the temperature control device. The top of the coal sample is provided with a detonation hole. The gas injection system is used to inject target gas into the sample chamber to simulate the flow field in the coal sample. The extraction system is used to extract the target gas from the coal sample. The acoustic-electrophysical fracturing system includes a discharge electrode that can be placed in the detonation hole of the coal sample for high-voltage discharge, and a discharge electrode embedded in the discharge electrode. The system includes a piezoelectric acoustic-electric transducer on the electrode surface, an acoustic field emission control device located outside the sample chamber connected to the acoustic-electric transducer, and a high-voltage power supply device connected to the discharge electrode via a high-voltage transmission cable to provide it with high-voltage electricity. The parameter monitoring system includes a first flow monitoring device for monitoring the flow rate of the target gas injected into the gas injection system, a second flow monitoring device for monitoring the flow rate of the target gas extracted by the extraction system, a vibration sensor for monitoring the fracture development status of the coal sample in the sample chamber, an acoustic emission sensor for monitoring the acoustic emission signal in the sample chamber, and a strain sensor for monitoring the dynamic strain of the coal sample during the fracturing process in the sample chamber. The signal output terminals of the first flow monitoring device, the second flow monitoring device, the vibration sensor, the acoustic-electric sensor, and the strain sensor are connected to the corresponding input terminals of the control system.

[0007] The experimental method of this invention embodiment is based on the above-mentioned high-energy acoustic-electrophysical field-induced fracturing and permeability enhancement experimental system, and includes the following steps: S1, acquiring deep-seated coal and rock samples, tightly fixing them in a sample chamber, and sealing the sample chamber; S2, adjusting the confining pressure, axial pressure, and ground temperature through the experimental loading system according to the actual environment of the coal and rock samples before collection to achieve environmental reproduction of the collection depth; S3, injecting target gas into the coal and rock samples in the sample chamber through the gas injection system to simulate the flow field within the coal and rock samples. After the target gas reaches a preset concentration, the extraction system is opened for extraction; simultaneously, the confining pressure, axial pressure, and ground temperature are adjusted in real time through the experimental loading system to meet the experimental conditions; S4, waiting for the confining pressure, axial pressure, ground temperature, and the flow field within the coal and rock samples to reach a preset concentration. After the experimental parameters such as gas concentration stabilize, water is injected into the sealed area where the discharge electrode is located. The discharge electrode is then subjected to high-voltage discharge using a high-voltage power supply device. Simultaneously, the acoustic-electric transducer and acoustic field emission control device begin to emit acoustic signals to induce fracturing of the coal and rock sample through a high-energy acoustic-electric physical field. During the experiment, the concentration and desorption flow rate of the extracted target gas are continuously monitored using a second flow monitoring device. The distribution and evolution of pores and fractures inside the coal and rock sample are monitored using a vibration sensor. Acoustic emission signals are detected using an acoustic emission sensor. The dynamic strain of the coal and rock sample during the fracturing process is detected in real time using a strain sensor. The dynamic strain and the detected acoustic emission signals are processed by the control system to determine the effectiveness of the acoustic-electric physical field fracturing and permeability enhancement.

[0008] Compared with the prior art, the advantages of the superior technical solution of the present invention include:

[0009] 1. This invention provides a high-energy acoustic-electrophysical field-induced fracturing and permeability enhancement experimental system. This system can simulate multi-field coupling conditions such as temperature, pressure, and stress in deep reservoirs within a laboratory environment. It is used to study the spatiotemporal evolution of desorption, diffusion, and seepage behaviors of deep unconventional natural gas (CH4, etc.) under the combined effects of stress loading, strong electric fields, and high-energy acoustic fields, either individually or in combination. This experimental system achieves uniform volumetric fracturing through high-energy tunable multi-stage discharge and a high-power broadband acoustic field. Combined with multi-modal sensing technology (stress, temperature, vibration, acoustic emission, strain, and gas flow rate, etc.), it monitors the fracturing and permeability enhancement process in situ, thereby revealing the physical mechanisms of full-pore permeability enhancement and enhanced desorption in reservoirs.

[0010] 2. The core operating mechanism of this invention lies in utilizing the strong electrical stress and shock waves generated by high-voltage discharge, as well as the vibration and cavitation effects induced by the high-intensity sound field, to act together on the coal sample. Under the action of the electro-acoustic coupling field, microscopic cracks are generated in the coal sample and expand into a network, increasing permeability; at the same time, the physical field energy promotes the desorption of gas molecules and accelerates the diffusion process, ultimately achieving efficient extraction of unconventional natural gas.

[0011] 3. This invention achieves breakthroughs in fracturing energy, fracturing range, and in-situ observation capabilities, enabling simulation experiments of fracturing and permeability enhancement in deep ultra-low permeability reservoirs under the action of high-energy acoustic-electrophysical fields, and providing an experimental platform for the study of permeability enhancement and transformation mechanisms in deep ultra-low permeability reservoirs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the high-energy acoustic-electrophysical field-induced cracking and permeation experimental system in Example 1.

[0013] Figure 2 yes Figure 1 A schematic diagram of the internal structure after the explosion-proof and explosion-resistant cavity is concealed.

[0014] The reference numerals in the accompanying drawings include: explosion-proof and explosion-resistant cavity 10, sample chamber 21, cover 22, sealing joint 221, stress loading device 23, side wall rubber sleeve 231, bottom rubber sleeve 232, hydraulic device 232, temperature control device 24, heater 241, temperature sensor 242, discharge electrode 31, acoustic-electric transducer 32, sound field emission control device 33, high-voltage transmission cable 34, high-voltage power supply device 35, high-voltage charging power supply 351, high-voltage energy storage box 352, output control cabinet 353, discharge control switch 354, sleeve 36, water injection system 37, water injection pipe 371, water injection equipment 372, first flow monitoring device 41, second flow monitoring device 42, vibration sensor 43, acoustic emission sensor 44, strain sensor 45, gas injection system 50, gas injection pipe 51, gas source 52, extraction system 60, extraction pipe 61, extraction equipment 62. Detailed Implementation

[0015] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0016] Example 1

[0017] This embodiment provides a high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system, such as... Figure 1 and Figure 2 As shown, in a preferred embodiment, the experimental system includes an explosion-proof and explosion-resistant cavity 10, and a test loading system, an acoustic-electric fracturing system, a gas injection system 50, an extraction system 60, and a parameter monitoring system installed in the explosion-proof and explosion-resistant cavity 10.

[0018] The explosion-proof and blast-resistant chamber 10 has a diameter of 2000mm and a length of 4000mm, is blast-resistant to 4MPa, and is equipped with an observation window and a video monitoring device. The video monitoring device is an explosion-proof multi-functional camera with 4 megapixels, a maximum resolution of 2688×1520, and a maximum supplementary lighting distance of 30m. At the start of the experiment, the door of the explosion-proof and blast-resistant chamber 10 was closed, and the video monitoring device started running continuously, monitoring the operation of the equipment inside the explosion-proof and blast-resistant chamber 10 through the observation window.

[0019] The test loading system includes a top (for placing coal samples, i.e., coal rock samples). Figure 1 The sample chamber 21 with a cover 22 is located on the left side. A stress loading device 23 applies confining pressure and axial pressure to the coal sample in the sample chamber 21. A temperature control device 24 heats the coal sample in the sample chamber 21 to simulate the ground temperature. The temperature output terminal of the control system is connected to the temperature control terminal of the temperature control device 24. An explosion hole is provided on the top of the coal sample.

[0020] The sample chamber 21 has sidewalls and bottoms lined with pads made of flexible, wear-resistant material. The coal sample is located within the space enclosed by the sidewall and bottom pads to prevent wear during pressurization. The stress loading device 23 includes independently operable sidewall rubber sleeves 231 and 232, respectively located outside the sidewall and bottom pads. Both sidewall and bottom rubber sleeves 231 and 232 are connected to a hydraulic device 232. Hydraulic oil (such as methyl silicone oil) is injected into the sidewall rubber sleeves 231 via the hydraulic device 232 to generate hydraulic pressure. This hydraulic pressure acts on the sidewall pads through the sidewall rubber sleeves 231 and is ultimately evenly applied to the coal sample, applying confining pressure to the coal sample in the sample chamber 21. Hydraulic oil (such as methyl silicone oil) is injected into the bottom rubber sleeves 232 via the hydraulic device 232 to generate hydraulic pressure. This hydraulic pressure acts on the bottom pads through the bottom rubber sleeves 232 and is ultimately evenly applied to the coal sample, applying axial pressure to the coal sample in the sample chamber 21. The applied confining pressure and axial pressure simulate the ground stress, and the applied confining pressure and axial pressure can be adjusted independently to meet the actual situation.

[0021] It should be noted that a force-applying plate can also be slidably connected to the bottom of the sample chamber 21. The force-applying plate is connected to the end of the hydraulic cylinder. After the cover 22 of the sample chamber 21 is fixed, the hydraulic cylinder applies axial force to the force-applying plate to apply axial pressure to the coal sample in the sample chamber 21.

[0022] The temperature control device 24 includes a heater 241 for heating the hydraulic oil in the sidewall rubber sleeve 231, and a temperature sensor 242 for monitoring the heating temperature. The signal output terminal of the temperature sensor 242 is connected to the temperature input terminal of the control system, and the temperature output terminal of the control system is connected to the temperature control terminal of the heater 241. For example, the heater 241 is a heating wire installed in the sidewall rubber sleeve 231, with a temperature adjustment range of room temperature to 65°C. The temperature sensor 242 is a thermocouple, with the working end located inside the sample chamber 21 and the free end located outside the sample chamber 21. The temperature control principle of the heater 241 is to control the oil bath heating of the sidewall rubber sleeve 231 by detecting the temperature of the temperature sensor 242, and to adjust the heating power of the heater 241 to adjust the heating temperature. The heating signal of the heater 241 is transmitted to the control system through a high-precision communication instrument to achieve digital control. All of these are existing technologies and will not be described in detail here.

[0023] The gas injection system 50 is used to inject a target gas (such as methane) into the sample chamber 21 to simulate the gas flow field in the coal sample. Specifically, the gas injection system 50 includes a gas injection pipe 51 that passes through the cap 22 and enters the inner wall of the sample chamber 21. For example, the outer end of the cap 22 is provided with a sealing joint 221. The gas injection pipe 51 passes through the sealing joint 221 and extends into the inner wall of the sample chamber 21 to achieve a sealed connection between the gas injection pipe 51 and the cap 22. The gas inlet end of the gas injection pipe 51 is connected to a gas source 52 (such as a methane cylinder).

[0024] The extraction system 60 is used to extract target gas from a coal sample to simulate gas extraction from the coal sample. Specifically, the extraction system 60 includes an extraction pipe 61 that passes through a sealing joint 221 on the cover 22 and enters into an explosion hole, with the outlet end of the extraction pipe 61 connected to the extraction device 62.

[0025] The acoustic-electric fracturing system includes a discharge electrode 31 that can be placed in the detonation hole of the coal sample to perform high-voltage discharge, a piezoelectric acoustic-electric transducer 32 embedded in the surface of the discharge electrode 31, a sound field emission control device 33 (a broadband generator) connected to the acoustic-electric transducer 32 and located outside the sample chamber 21, and a high-voltage power supply device 35 connected to the discharge electrode 31 via a high-voltage transmission cable 34 to provide it with high-voltage electricity. The high-voltage power supply device 35 charges the discharge electrode 31, which performs high-voltage discharge to fracture the coal sample. At the same time, the acoustic-electric transducer 32 embedded in the surface of the discharge electrode 31 uses the piezoelectric effect to convert electrical energy into sound energy and emits a sound field to fracture the coal sample.

[0026] The high-voltage power supply device 35 includes a high-voltage charging power supply 351, a high-voltage energy storage box 352 connected to the high-voltage charging power supply 351 via a high-voltage transmission cable 34, and an output control cabinet 353 connected to the high-voltage energy storage box 352 via a high-voltage transmission cable 34. The output control cabinet 353 is connected to the discharge electrode 31 via a high-voltage transmission cable 34 equipped with a discharge control switch 354. The high-voltage charging power supply 351 charges the high-voltage energy storage box 352 via the high-voltage transmission cable 34. When the charging voltage reaches the working threshold, it reaches the output control cabinet 353 via the high-voltage transmission cable 34, which transmits the stored electrical energy to both ends of the discharge electrode 31 via the high-voltage transmission cable 34, and the discharge electrode 31 undergoes high-voltage discharge to cause cracking.

[0027] Among them, the high-voltage charging power supply 351 adopts 380V; the high-voltage energy storage box 352 has a 120μF*20 energy storage capacitor bank with a voltage of 30kV and a storage energy of up to 1000kJ. The discharge energy is adjustable from 0-1000kJ through the output control cabinet 353; the high-voltage transmission cable 34 has a withstand voltage of 30kV; the discharge electrode 31 is an impact-resistant and high-voltage-resistant electrode, capable of 500 discharges at 15kV. It achieves high energy, multi-level adjustable, and cyclic fracturing, which is in contrast to existing electric pulse equipment (100kJ, not pure electric, limited number of fracturing cycles).

[0028] In this invention, the discharge electrode 31 is a cylindrical electrode composed of an inner conductor and an outer conductor, both of equal length and insulated from each other. The resistance of the inner and outer conductors at 20°C is no greater than 0.272 Ω / km. A high-voltage charging power supply 351 is connected to the inner conductor. The outer conductor is also cylindrical and surrounds the inner conductor, with its tip not connected to the inner conductor. A cylindrical cavity with a pointed tip is formed between the inner and outer conductors, and the radial distance between them is the electrode gap. Depending on the experimental conditions, various sizes of discharge electrodes 31 can be configured, such as Φ30mm, Φ50mm, and Φ90mm. This size refers to the outer diameter of the discharge electrode 31, which can be achieved by replacing the inner and outer conductors with different sizes. The electrode gap can also be adjusted, for example, using 3mm, 4mm, and 5mm, which can be adjusted by changing (replacing) the sizes of the inner and outer conductors.

[0029] The acoustic-electric transducer 32 and the sound field emission control device 33 constitute an ultrasonic device, which is a high-power ultrasonic device with a continuously adjustable voltage of 50-300V, a continuously adjustable frequency of 15-30kHz, a peak power of 0-60kW, and a continuously adjustable duty cycle of 10-20%. The ultrasonic-specific cable has a transmission efficiency of >75% per kilometer. The equipped acoustic-electric transducer 32 is a deep-well high-temperature and high-pressure resistant ultrasonic transducer with a rated power of 60-100kW and an electromechanical matching efficiency of >80%. It realizes wideband, high-power, and high-transmission ultrasonic excitation, which contrasts with the existing point-frequency, low-power (3-5kW), and inefficient (5%) ultrasonic devices.

[0030] During the experiment, the discharge electrode 31 is charged, and the discharge electrode 31 and the acoustic-electric transducer 32 located in the sleeve 36 are simultaneously turned on, which can realize high-energy adjustable multi-stage discharge fracturing of the acoustic-electric physical field and high-power broadband acoustic field fracturing. Among them, multi-stage discharge is achieved by gradually increasing the energy or intensity of the discharge of the discharge electrode 31, specifically by changing the voltage, the action time and the frequency.

[0031] The parameter monitoring system includes a first flow monitoring device 41 for monitoring the flow rate of the target gas injected by the gas injection system 50, a second flow monitoring device 42 for monitoring the flow rate of the target gas extracted by the extraction system 60, a vibration sensor 43 for monitoring the fracture development of the coal sample in the sample chamber 21, an acoustic emission sensor 44 for monitoring the acoustic emission signal in the sample chamber 21, and a strain sensor 45 (using an optical fiber deformation sensor) for monitoring the dynamic strain of the coal sample in the sample chamber 21 during the fracturing process. The signal output terminals of the first flow monitoring device 41, the second flow monitoring device 42, the vibration sensor 43, the acoustic-electric sensor, and the strain sensor 45 are connected to the corresponding input terminals of the control system. The vibration sensor 43, the acoustic-electric sensor, and the strain sensor 45 are all installed on the padding layer of the inner wall of the sample chamber 21.

[0032] Preferably, a vibration sensor array consisting of several vibration sensors 43 and an acoustic emission sensor array consisting of several acoustic emission sensors 44 are installed on the inner wall of the sample chamber 21. The vibration sensor array and the acoustic emission sensor array form a micro-vibration / acoustic emission testing system, which visualizes the distribution and evolution of pores and fractures inside the reservoir in space. The system has three basic models of chassis with 16 channels, 32 channels, and 64 channels; a single channel sampling rate of 10M points / second; full waveform storage; voltage input range of ±10V, adjustable to ±5V, ±2V, ±1V, ±0.1V; 16-bit A / D conversion; signal threshold triggering and external triggering; and an operating temperature of -10℃ to +45℃.

[0033] By adopting the above technical solution, in the actual experiment, the development of cracks in the coal sample in the sample chamber 21 can be detected by the acoustic emission sensor 44 and vibration sensor 43 on the inner wall of the sample chamber 21, achieving the effect of approximate simulation of the scene and accurate experimental results, and enabling precise quantitative analysis of the coal and rock mass within the effective radius.

[0034] In another preferred embodiment of the invention, the acoustic-electric fracturing system further includes a sleeve 36 connected to the cap 22 and located within the sample chamber 21, and a water injection system 37 connected to the cap 22. The discharge electrode 31 is located in the sleeve 36, preferably with the sleeve 36 and the sample chamber 21 on the same axis. When the sample chamber 21 is sealed by the cap 22, the sleeve 36 extends into the detonation hole at the top of the coal sample. The water injection system 37 is used to inject water into the sleeve 36 to immerse the discharge electrode 31, allowing the discharge electrode 31 to operate in a water environment. The interior of the sleeve 36 is a sealed area (the sleeve 36 and the cap 22 are sealed by an existing sealing structure), preventing water from entering the cracks in the coal sample. For example, the water injection system 37 includes a water injection pipe 371 extending into the sleeve 36 through a sealing joint 221 on the cap 22, with the inlet end of the water injection pipe 371 connected to a water injection device 372. Both the water injection pipe 371 and the extraction pipe 61 are located near the center of the axial direction of the sample chamber 21 and are independent of each other. The water injection pipe 371 is located inside the casing 36, and the extraction pipe 61 is located in the blast hole outside the casing 36, using extraction.

[0035] Water is injected into the sleeve 36 through the water injection pipe 371, so that the discharge electrode 31 is immersed in water. The output control cabinet 353 transmits the electrical energy stored in the high-voltage energy storage box 352 to both ends of the discharge electrode 31 through the high-voltage transmission cable 34. When the field strength between the two poles of the discharge electrode 31 reaches the breakdown field strength of the water medium, a discharge channel is formed between the two poles of the discharge electrode 31 to generate a water shock wave effect, thereby improving the fracturing effect.

[0036] In this invention, the cap 22 is threadedly connected to the sample chamber 21. The cap 22 is a threaded coupling disc, and its outer end has two operating handles. By rotating the two operating handles, the rotational torque is converted into a force that moves the cap 22 left and right, thereby enabling the cap 22 to be installed or removed. The area enclosed by the sleeve 36 forms an inner seal, and the cap 22 seals the port of the sample chamber 21 as an outer seal to isolate the inside of the sample chamber 21 from the outside, preventing air leakage that could lead to inaccurate experimental results.

[0037] Example 2

[0038] This embodiment provides a high-energy acoustic-electrophysical field-induced fracturing and permeation enhancement experimental method, which is implemented based on the high-energy acoustic-electrophysical field-induced fracturing and permeation enhancement experimental system of Embodiment 1, and includes the following steps:

[0039] S1. Obtain a coal and rock sample collected from deep within the sample chamber, φ600mm*1200mm, and secure it tightly inside the sample chamber 21. Seal and fix the sample chamber 21 with the cap 22.

[0040] S2, based on the actual environment before coal and rock sample collection (or the experimental environment simulated as needed), the confining pressure, axial pressure, and ground temperature are adjusted through the test loading system to reproduce the environment at the collection depth. Specifically, the confining pressure (e.g., 20 MPa) is adjusted using hydraulic device 232, sidewall rubber sleeve 231, and hydraulic oil (methyl silicone oil medium); the axial pressure (e.g., 25 MPa) is adjusted using hydraulic device 232, bottom rubber sleeve 232, and hydraulic oil; and the ground temperature is adjusted using temperature control device 24. The specific methods of applying confining pressure, axial pressure, and adjusting temperature are all existing technologies and will not be detailed here.

[0041] S3, the target gas is injected into the coal and rock sample in the sample chamber 21 through the gas injection pipe 51 of the gas injection system 50 to simulate the flow field in the coal and rock sample. The control methods include flow control, step pressure control and constant pressure control (all of which are conventional adjustment methods in this field). After the target gas reaches the preset concentration, the extraction pipe 61 of the extraction system 60 is opened for extraction. During extraction, the concentration and desorption flow rate of the extracted target gas are continuously monitored by the second flow monitoring device 42.

[0042] S4. After the experimental parameters stabilize, clean water is injected into the sealed area where the discharge electrode 31 is located through the water injection pipe 371. Then, the high-voltage power supply device 35 is used to make the discharge electrode 31 perform high-voltage discharge. At the same time, the acoustic-electric transducer 32 and the sound field emission control device 33 start working to emit sound field to induce fracturing of the coal and rock sample through the high-energy acoustic-electric physical field. The water injection near the discharge electrode 31 can simulate the actual fracturing environment at the water injection borehole during the real fracturing process, and at the same time, the discharge electrode 31 acts on the acoustic-electric transducer 32 on its surface to induce fracturing.

[0043] S5. During the experiment, the concentration and desorption flow rate of the target gas are continuously monitored using the second flow monitoring device 42. At the same time, the distribution and evolution of pores and fractures inside the coal and rock sample are monitored by the vibration sensor 43, the acoustic emission signal is detected by the acoustic emission sensor 44, and the dynamic strain of the coal and rock sample during the fracturing process is detected in real time by the strain sensor 45 (fiber optic deformation sensor). The dynamic strain and the detected acoustic emission signal are comprehensively processed by the control system (integrated in the computer) to determine the effectiveness of the acoustic-electrophysical field fracturing and permeability enhancement. The experiment ends here. For example, the effectiveness of fracturing and permeability enhancement can be judged by analyzing the changing trends of parameters such as the frequency distribution, amplitude, and nonlinear characteristics of the acoustic emission signal.

[0044] In step S4, the experimental parameters are obtained using the following formula:

[0045]

[0046] Where D is the statistical parameter of pore fracture after coal sample experiment; K is the correction parameter; n is the number of times electro-detonation fracture is induced; C is the discharge capacitance, μF; U is the discharge voltage, kV; T is the power ultrasonic treatment time, h; W is the ultrasonic power, watts; f is the ultrasonic frequency, Hz; F is the experimental temperature of coal sample, ℃; σ1 is the axial pressure applied to coal sample, Pa; σ2 is the confining pressure applied to coal sample, Pa. The gas concentration in the coal sample is mg / m³. 3 λ represents the porosity of the coal sample, %; V represents the bulk density of the coal sample, kg / m³. 3 ;σ b σ represents the tensile strength of the coal sample, in Pa; c σ represents the compressive strength of the coal sample, in Pa; s K represents the shear strength of the coal sample, in Pa; α is the energy superposition coefficient related to the number of electric blast shocks and the duration of power ultrasonic treatment; β is the jump index related to the experimental environment; and θ is the adjustment index related to the mechanical properties of the coal sample. K, α, β, and θ are all constants that can be obtained experimentally.

[0047] The electric detonation and ultrasonic testing methods used in this application are experimental methods. The experimental parameters on the right side of the aforementioned formula are preset according to the formation environment. The ultimate goal is to obtain the statistical parameter D of the pore fracture after the coal sample experiment. If the statistical parameter of the pore fracture of the coal sample is known, an empirical formula can be obtained by fitting multiple sets of experimental results. Alternatively, the experimental conditions and parameters can be deduced.

[0048] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system, characterized in that, It includes an explosion-proof and explosion-resistant cavity, as well as a test loading system, an acoustic-electric fracturing system, a gas injection system, an extraction system, and a parameter monitoring system installed in the explosion-proof and explosion-resistant cavity; The test loading system includes a sample chamber with a sealed top for placing coal samples, a stress loading device for applying confining pressure and axial pressure to the coal samples in the sample chamber, and a temperature control device for heating the coal samples in the sample chamber. The temperature output terminal of the control system is connected to the temperature control terminal of the temperature control device. The top of the coal sample is provided with a detonation hole. The gas injection system is used to inject target gas into the sample chamber to simulate the flow field in the coal sample; The extraction system is used to extract the target gas from the coal sample; The acoustic-electric fracturing system includes a discharge electrode that can be placed in the detonation hole of the coal sample to perform high-voltage discharge, a piezoelectric acoustic-electric transducer embedded in the surface of the discharge electrode, a sound field emission control device located outside the sample chamber connected to the acoustic-electric transducer, and a high-voltage power supply device that provides high-voltage electricity to the discharge electrode via a high-voltage transmission cable. The parameter monitoring system includes a first flow monitoring device for monitoring the flow rate of the target gas injected into the gas injection system, a second flow monitoring device for monitoring the flow rate of the target gas extracted by the extraction system, a vibration sensor for monitoring the fracture development of the coal sample in the sample chamber, an acoustic emission sensor for monitoring the acoustic emission signal in the sample chamber, and a strain sensor for monitoring the dynamic strain of the coal sample in the sample chamber during the fracture process. The signal output terminals of the first flow monitoring device, the second flow monitoring device, the vibration sensor, the acoustic emission sensor, and the strain sensor are connected to the corresponding input terminals of the control system.

2. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 1, characterized in that, The explosion-proof and explosion-resistant cavity is equipped with an observation window and a video monitoring device. The video monitoring device can monitor the operation of the equipment inside the explosion-proof and explosion-resistant cavity through the observation window. And / or the cap is threadedly connected to the sample compartment, and the outer end of the cap is provided with two operating handles.

3. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 1, characterized in that, The sample chamber has a cushion layer made of flexible material on its side walls and bottom. The coal sample is located in the space enclosed by the side wall cushion layer and the bottom cushion layer. The stress loading device includes an independently working side wall rubber sleeve and a bottom rubber sleeve respectively located outside the side wall cushion layer and the bottom cushion layer. Both the side wall rubber sleeve and the bottom rubber sleeve are connected to a hydraulic device. The hydraulic device injects hydraulic oil into the side wall rubber sleeve and applies pressure to apply confining pressure to the coal sample in the sample chamber. The hydraulic device injects hydraulic oil into the bottom rubber sleeve and applies pressure to apply axial pressure to the coal sample in the sample chamber.

4. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 3, characterized in that, The temperature control device includes a heater for heating the hydraulic oil in the sidewall rubber sleeve and a temperature sensor for monitoring the heating temperature. The signal output terminal of the temperature sensor is connected to the temperature input terminal of the control system, and the temperature output terminal of the control system is connected to the temperature control terminal of the heater.

5. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 1, characterized in that, The gas injection system includes a gas injection pipe that passes through the cap and enters the inner wall of the sample chamber, and the gas inlet end of the gas injection pipe is connected to a gas source. And / or the extraction system includes an extraction pipe that passes through a cap and enters a detonation hole, with the outlet end of the extraction pipe connected to the extraction equipment.

6. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 1, characterized in that, The high-voltage power supply device includes a high-voltage charging power supply, a high-voltage energy storage box connected to the high-voltage charging power supply via a high-voltage transmission cable, and an output control cabinet connected to the high-voltage energy storage box via a high-voltage transmission cable. The output control cabinet is connected to the discharge electrode via a high-voltage transmission cable equipped with a discharge control switch.

7. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to any one of claims 1-6, characterized in that, The acoustic-electric fracturing system also includes a sleeve located inside the sample chamber connected to the cap, and a water injection system connected to the cap. The discharge electrode is located in the sleeve, which can extend into the detonation hole at the top of the coal sample. The water injection system is used to inject water into the sleeve to soak the discharge electrode. The inside of the sleeve is a sealed area.

8. The high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to claim 7, characterized in that, The water injection system includes a water injection pipe that passes through the cap and extends into the sleeve, with the inlet end of the water injection pipe connected to the water injection equipment.

9. The experimental method based on the high-energy acoustic-electrophysical field-induced cracking and permeation-enhancing experimental system according to any one of claims 1-8, characterized in that, Includes the following steps: S1, Obtain coal and rock samples collected from deep within the sample chamber, and seal the sample chamber for fixation; S2, based on the actual environment of the coal and rock samples before collection, the confining pressure, axial pressure and ground temperature are adjusted through the test loading system to achieve environmental reproduction of the collection depth; S3, the target gas is injected into the coal and rock sample in the sample chamber through the gas injection system to simulate the flow field inside the coal and rock sample. After the target gas reaches the preset concentration, the extraction system is turned on for extraction. At the same time, the confining pressure, axial pressure and ground temperature are adjusted in real time through the test loading system to meet the experimental conditions. S4. After the experimental parameters such as confining pressure, axial pressure, ground temperature and gas concentration in the coal and rock sample stabilize, water is injected into the sealed area where the discharge electrode is located. The high-voltage power supply device is used to make the discharge electrode discharge at high voltage. At the same time, the acoustic-electric transducer and the acoustic field emission control device start working to emit acoustic field to crack the coal and rock sample through the high-energy acoustic-electric physical field. S5. During the experiment, the concentration and desorption flow rate of the target gas were continuously monitored using a second flow monitoring device. The distribution and evolution of pores and fractures inside the coal and rock samples were monitored by a vibration sensor. Acoustic emission signals were detected by an acoustic emission sensor. The dynamic strain of the coal and rock samples during the fracturing process was detected in real time by a strain sensor. The dynamic strain and the detected acoustic emission signals were processed by the control system to determine the effectiveness of the acoustic-electrophysical field fracturing and permeability enhancement.

10. The experimental method according to claim 9, characterized in that, In step S4, the experimental parameters are obtained using the following formula: In the formula, D is the statistical parameter of pore fracture after coal sample experiment; K is the correction parameter; n is the number of times electric detonation induced fracture; C is the discharge capacitance; U is the discharge voltage; T is the power ultrasonic treatment time; W is the ultrasonic power; f is the ultrasonic frequency; F is the experimental temperature of coal sample; σ1 is the axial pressure applied to coal sample; σ2 is the confining pressure applied to coal sample. σ represents the gas concentration within the coal sample; λ represents the porosity of the coal sample; V represents the bulk density of the coal sample; σ b σ represents the tensile strength of the coal sample. c σ represents the compressive strength of the coal sample. s α represents the shear strength of the coal sample; α is the energy superposition coefficient related to the number of electric shocks and the duration of power ultrasonic treatment; β is the jump index related to the experimental environment; and θ is the adjustment index related to the mechanical properties of the coal sample.

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