A methane in-situ explosion fracturing and evaluation simulation integrated test device and method

Abstract

The present invention discloses an integrated test device and method for in-situ methane explosion fracturing and evaluation simulation. Through the cooperation of a gas distribution system and a remote control system, remote and precise gas distribution of dangerous explosion gases is realized; through the combination of a high-energy electric ignition system, a high-frequency signal acquisition system and a remote control system, microsecond-level synchronous triggering of electric ignition detonation and high-frequency data acquisition is realized; by arranging a plurality of through-holes in the explosion cavity to simulate perforations, accurate monitoring of the explosion load in the wellbore perforations is realized; through a three-axis core holder and a permeability measurement system, in-situ testing of the permeability of rock samples after the explosion load is applied is realized without decompression; finally, load curves, force curves, temperature curves and fracturing morphological parameters of rock sample fracturing under conditions of different wellbore temperatures and pressures, different ground stress states, different methane concentrations and different ignition processes are obtained, thereby providing a large amount of measured data and analysis samples for the subsequent application of methane in-situ explosion fracturing technology.

Description

Technical Field

[0001] The invention relates to a methane in-situ explosion fracturing and evaluation simulation integrated test device and method, belonging to the technical field of unconventional natural gas exploitation and fracturing production increase. Background Art

[0002] Unconventional natural gas represented by shale gas and tight sandstone gas usually exists in tight gas-producing rocks in adsorbed and free states. Compared with conventional natural gas reservoirs, unconventional natural gas reservoirs generally have the characteristics of low porosity and low permeability. To achieve commercial exploitation of unconventional natural gas, it is necessary to artificially fracture the reservoir to form a connected fracture network, provide a channel for efficient migration of natural gas, and thus greatly increase the gas well production. Hydraulic fracturing is one of the main technologies for large-scale exploitation of unconventional natural gas at present. It can significantly improve the macroscopic permeability of the reservoir and has a wide range of applicability. However, hydraulic fracturing technology often faces problems such as expansion of reservoir clay minerals and increased water saturation of the formation due to retention of fracturing fluid. At the same time, hydraulic fracturing often consumes a lot of water resources and is prone to water pollution problems. It is necessary to treat the fracturing backflow fluid, which increases the construction cost of hydraulic fracturing.

[0003] In this context, some scholars have proposed the process technology of methane in-situ explosion fracturing. Methane, as the main component of unconventional natural gas, is a flammable and explosive gas that can produce a strong dynamic impact effect after explosion. By artificially injecting a gas combustion aid such as pure oxygen and mixing it with the methane desorbed in situ from the reservoir, igniting and exploding, a shock wave and a high-pressure gas wedge are formed to fracture the unconventional natural gas reservoir and construct a complex fracture network, thereby realizing the efficient development of unconventional natural gas. Under the guidance of this technical idea, the invention patent with publication number CN112878973A discloses a shale reservoir methane in-situ multi-stage pulse concentrated explosion fracturing method, which uses a perforating gun to form concentrated perforations in a horizontal well, and generates an explosive load and high-temperature and high-pressure gas through the coordinated explosion of the combustion aid and methane gas, and fracturing the shale reservoir along the concentrated perforations to construct a fracture network in a direction. This method forms a methane explosion load in the perforation, achieving increased permeability and production of shale gas reservoirs, while protecting the horizontal wells from damage by explosion shock waves, providing a useful reference for in-situ methane explosion fracturing.

[0004] Before the above-mentioned energy-gathering explosion process can be applied in practice, a large number of physical simulations are required to determine the key technical parameters before subsequent applications can be carried out. However, the current physical simulation research on methane in-situ explosion fracturing technology has the following defects: 1. Equivalent pulse wave fracturing samples are generated by means of separate Hopkinson pressure bars, high-pressure air blasting, water-based pulses, etc. These load forms are essentially different from the methane explosion fracturing load; 2. It is impossible to simulate the high temperature and high pressure state in the wellbore space of deep unconventional natural gas reservoirs; 3. It is impossible to simultaneously realize the explosion impact load and axial pressure and confining pressure loading on rock samples, resulting in a large difference between the physical simulation and the actual reservoir ground stress state; 4. There is no accurate test of the load curve formed by methane explosion in the perforations around the wellbore; 5. It is impossible to synchronously obtain the methane explosion load curve in the perforation and the fracturing characteristic parameters of the perforated rock sample.

[0005] In summary, there is an urgent need to provide a new test device and method that can perform standardized test measurements on the technical parameters required for in-situ methane explosion fracturing, thereby overcoming the above-mentioned defects and providing key technical indicators for subsequent practical applications. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides an integrated test device and method for methane in-situ explosion fracturing and evaluation simulation, which can perform standardized test measurements on the technical parameters required for methane in-situ explosion fracturing, thereby overcoming the above-mentioned defects and providing key technical indicators for subsequent practical applications.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a methane in-situ explosion fracturing and evaluation simulation integrated test device, including a high-temperature and high-pressure explosion reactor, a three-axis core holder, a gas distribution system, a high-energy electric ignition system, a high-frequency data acquisition system, a permeability measurement system and a remote control system;

[0008] The high-temperature and high-pressure explosion reactor comprises an explosion chamber, a pre-tightening protective jacket, a heating tile, an insulation sleeve, an end cover assembly and a pressure cover; the explosion chamber and the pre-tightening protective jacket are assembled by a hard pressing process, and a plurality of through holes penetrating the side wall of the explosion chamber are provided on one side of the explosion chamber, and each through hole is respectively connected to one end of a high-pressure seamless steel pipe of different pipe diameters and lengths to simulate the perforation around the wellbore; three channels penetrating the side wall of the explosion chamber are arranged on the other side of the explosion chamber, one of which is connected to a high-pressure pneumatic solenoid valve and a vent valve in sequence through a pipeline to discharge the gas in the explosion chamber; the other The channels are connected to high-pressure pneumatic solenoid valve 2, low-frequency pressure sensor 1 and low-frequency thermocouple in sequence through pipelines to monitor the pressure and temperature of the gas in the explosion cavity; the last borehole is connected to the air compressor through a pipeline via a high-pressure resistant ball valve to increase the pressure in the explosion cavity; the end cover assembly is installed at one end of the explosion cavity and is tightened and fixed by a pressure cover, and boreholes 1, 2, 3 and 4 are provided on the end cover assembly; the heating tile is installed on the outer surface of the explosion cavity to heat the explosion cavity; the insulation sleeve wraps the heating tile and the explosion cavity to maintain the temperature of the explosion cavity;

[0009] The triaxial core holder is installed at the other end of the explosion cavity and is used to place the rock sample and apply prestress to the rock sample;

[0010] The gas distribution system includes a high-pressure methane gas cylinder, a high-pressure oxygen gas cylinder, a high-pressure air gas cylinder, a methane gas flow controller, an oxygen gas flow controller, an air gas flow controller, a four-way valve, a vacuum pump and three high-pressure pneumatic solenoid valves; the high-pressure methane gas cylinder, the high-pressure oxygen gas cylinder and the high-pressure air gas cylinder are respectively connected to the three ports of the four-way valve through pipelines, and the remaining one port of the four-way valve is connected to the borehole one through the main pipeline. The methane gas flow controller, the oxygen gas flow controller and the air gas flow controller are respectively installed on the three pipelines, and are respectively used to control the flow rate of the high-pressure methane gas cylinder, the high-pressure oxygen gas cylinder and the high-pressure air gas cylinder to transport the gas into the explosion cavity; the three high-pressure pneumatic solenoid valves are installed on the main pipeline to control the on-off of the main pipeline; the vacuum pump is connected to the main pipeline to vacuum the explosion cavity;

[0011] The high-energy electric ignition system includes a high-energy electric ignition controller, a high-voltage cable and an ignition rod; the high-energy electric ignition controller is connected to the ignition rod through the high-voltage cable; the ignition rod extends into the explosion cavity through the second drilling hole; the high-energy electric ignition controller is connected to the remote control system through the line, and is used to control the electric spark generated by the ignition rod;

[0012] The high-frequency signal acquisition system includes an ultra-high-speed signal acquisition instrument, a high-frequency pressure sensor, a high-frequency piezoelectric force sensor and a fast-response thermocouple; the high-speed signal acquisition instrument is remotely connected to the high-frequency pressure sensor, the high-frequency piezoelectric force sensor and the fast-response thermocouple through a transmission line; the high-frequency pressure sensor is respectively installed at the other end of the high-pressure seamless steel pipe connecting each through hole, and is used to test the transient load curve in the perforations at different positions of the wellbore; the high-frequency piezoelectric force sensor is fixed at the end of the rock sample away from the perforation, and is used to obtain the transient load data of the rock sample; the fast-response thermocouple is installed at three locations of the borehole, and is used to obtain the transient temperature data of the detonation wave; the transient impact load in the perforation during the combustion and explosion of methane, the transient temperature of the detonation wave, the process of deflagration to detonation, the propagation velocity of the detonation wave and the transient load characteristics of the rock sample are collected and processed by the high-frequency signal acquisition system;

[0013] The permeability measurement system comprises a gas source, a gas booster pump, a low-frequency pressure sensor 2 and a flow meter; the gas source is connected to the inlet of the gas booster pump through a connecting pipe, the outlet of the gas booster pump is connected to the borehole 4 through a pipeline, the low-frequency pressure sensor 2 is installed at the outlet end of the triaxial core holder, and the outlet end of the triaxial core holder is connected to the flow meter through a pipeline;

[0014] The remote control system includes a cabinet, an industrial computer and a low-frequency signal acquisition system; the low-frequency signal acquisition system is used to monitor the state parameters of the explosion cavity, the core clamp and the gas distribution system; the low-frequency pressure sensor 1 and the low-frequency thermocouple in the high-temperature and high-pressure explosion reactor, the methane gas flow controller, the oxygen gas flow controller, the air gas flow controller in the gas distribution system, the horizontal flow pump flow meter of the core clamp, the low-frequency pressure sensor 2 and the flow meter are all connected to the low-frequency signal acquisition system, and the low-frequency signal acquisition system collects data on the temperature and pressure in the high-temperature and high-pressure explosion reactor, the horizontal flow pump flow, pressure and gas distribution gas flow in the core clamp, and transmits them to the cabinet for analysis and processing, and controls the high-pressure pneumatic solenoid valve 1, the high-pressure pneumatic solenoid valve 2, the high-pressure pneumatic solenoid valve 3, the methane gas flow controller, the oxygen gas flow controller and the air gas flow controller.

[0015] Furthermore, the triaxial core holder comprises a holder body, a horizontal flow pump, a rock sample, a connecting flange and a screw; a triaxial loading mechanism is arranged in the holder body, the rock sample is placed in the triaxial loading mechanism, and a prefabricated perforation is drilled at one end of the rock sample; the horizontal flow pump is connected to the triaxial loading mechanism through two branch pipelines, and is used to control the triaxial loading mechanism to apply triaxial confining pressure to the rock sample, so as to simulate the actual stress state of unconventional natural gas wells; ports are provided at both ends of the holder body, namely an inlet end and an outlet end, wherein the inlet end is sealedly connected to the detonation port, and a plug is provided on the outlet end, which is used to block or open the outlet end; the rock sample is tightly wrapped by a heat shrink sleeve, and one end of the prefabricated perforation is aligned with the detonation port; the connecting flange fixes the triaxial core holder to the explosion cavity through a screw, and the detonation port is connected to the inside of the explosion cavity.

[0016] Furthermore, the borehole one, borehole two, borehole three and borehole four have different apertures; the end cover assembly and one end of the explosion cavity are sealed by a graphite sealing ring.

[0017] Furthermore, the pipelines where the high-pressure methane cylinders, oxygen cylinders and air cylinders are located are each equipped with a pressure reducing valve, a one-way valve and a high-pressure resistant ball valve. The pressure reducing valve is used to buffer the gas passing through the pipeline, the one-way valve is used to control the one-way flow of the gas to prevent gas backflow, and the high-pressure resistant ball valve is used to control the on-off of the pipeline.

[0018] Furthermore, flame arresters are installed on the pipelines between the high-pressure pneumatic solenoid valve 1, the high-pressure pneumatic solenoid valve 2 and the high-pressure pneumatic solenoid valve 3 and the explosion cavity to prevent the flames generated by the explosion from affecting each pneumatic solenoid valve.

[0019] Furthermore, it also includes a flip bracket, on which the explosion cavity is mounted, for adjusting the position of the explosion cavity.

[0020] Furthermore, the core sample is a cylindrical core with a diameter of 50 mm and a height of 100 mm. The prefabricated perforation diameter of the core sample is between 3 mm and 5 mm, the perforation depth is between 40 mm and 60 mm, and the cone angle of the bottom of the perforation is not greater than 120°, which is used to simulate concentrated energy perforation.

[0021] Furthermore, the acquisition frequency of the high-speed signal acquisition instrument is not less than 1MHz, the high-frequency pressure sensor adopts a piezoelectric pressure sensor, the maximum range is not less than 150MPa, and the frequency response is not less than 5MHz; the maximum range of the high-frequency piezoelectric force sensor is not less than 300kN, and the frequency response is not less than 5MHz; the maximum range of the fast response thermocouple is not less than 3000K, and the frequency response is not less than 1MHz.

[0022] Furthermore, the pressure-bearing capacity of each of the high-pressure pneumatic solenoid valve 1, the high-pressure pneumatic solenoid valve 2 and the high-pressure pneumatic solenoid valve 3 is not less than 150 MPa.

[0023] The working method of the above-mentioned methane in-situ explosion fracturing and evaluation simulation integrated test device comprises the following specific steps:

[0024] Step 1: Device assembly and airtightness test

[0025] S11: Keep both ends of the high-temperature and high-pressure explosion reactor open, and use an air compressor to generate 0.8MPa high-pressure air to purge residual moisture, carbon deposits and other impurities in the explosion chamber; after the inner wall of the pipeline is free of foreign matter, assemble the end cover assembly, and seal and connect the high-pressure seamless steel pipe with simulated perforation on one side of the explosion chamber to the high-frequency pressure sensor;

[0026] S12: Use a heat shrink sleeve to tightly wrap the rock sample, then point one end of the prefabricated perforation of the rock sample toward the explosion cavity, and tightly connect the other end to the high-frequency piezoelectric force sensor, and put it into the triaxial core holder; the triaxial core holder is sealed and connected to the other end of the high-temperature and high-pressure explosion reactor through a connecting flange and a screw; control the triaxial loading mechanism through a horizontal flow pump to apply confining pressure and axial pressure to the rock sample to the set value;

[0027] S13: Use an air compressor to inject high-pressure air to 0.8MPa into the explosion chamber through one of the channels on the high-temperature and high-pressure explosion reactor, and check the air tightness of the explosion chamber; open the second high-pressure pneumatic solenoid valve, and monitor the pressure change in the explosion chamber within 300s through the low-frequency pressure sensor one; if the pressure decay is less than 0.005MPa, it is determined that the air tightness of the high-temperature and high-pressure explosion reactor is good; after completing the air tightness check, open the first high-pressure pneumatic solenoid valve to release the high-pressure air inside the explosion chamber;

[0028] Step 2: Prepare the explosion gas

[0029] S21: Close the high-pressure pneumatic solenoid valve 1, and at the same time open the high-pressure pneumatic solenoid valve 3 connecting the high-temperature and high-pressure reactor and the gas distribution system; turn on the vacuum pump to evacuate the explosion chamber and the gas distribution system pipeline until the vacuum degree is higher than 0.95, stop evacuating, and complete the vacuum process;

[0030] S22: setting a preset temperature of the high-temperature and high-pressure reactor through a remote control system, and heating the high-temperature and high-pressure reactor through a heating tile; monitoring the actual temperature in the explosion cavity through a low-frequency thermocouple until the actual temperature reaches the preset temperature;

[0031] S23: Set the rated injection flow rates of methane, oxygen and air respectively through the remote control system; open the pressure reducing valve, high-pressure resistant ball valve and high-pressure pneumatic solenoid valve 2 of the pipeline where the high-pressure methane cylinder is located in turn, and first inject methane into the explosion chamber; during the air intake process, the air intake flow rate is fed back in real time through the methane flow controller, and the pressure of the explosion chamber is monitored through the low-frequency pressure sensor 1; when the injection pressure reaches the set value, the methane flow controller automatically stops the air intake; then, according to needs, if methane and air need to be mixed, open the pressure reducing valve and high-pressure resistant ball valve of the pipeline where the high-pressure air cylinder is located in turn, and pass The air flow controller feeds back the intake flow in real time, and when the injection pressure reaches the set pressure, the air flow controller automatically stops the intake. If methane and oxygen need to be mixed, the pressure reducing valve and the high-pressure ball valve of the pipeline where the high-pressure oxygen cylinder is located are opened in turn, and the intake flow is fed back in real time through the oxygen flow controller, and when the injection pressure reaches the set pressure, the oxygen flow controller automatically stops the intake. The methane concentration in the explosion chamber is accurately calculated by the ratio of the cumulative injection amount of methane and air or oxygen to verify the accuracy of the gas distribution result. After the gas distribution is completed, it is left to stand for 90 minutes to allow the explosion gas to be fully mixed.

[0032] Step 3: Explosive fracturing and data collection

[0033] S31: After the combustible gas configuration is completed, close the second high-pressure pneumatic solenoid valve; then use analog signals to detect the working status of the ultra-high-speed signal acquisition instrument, the high-frequency pressure sensor, the high-frequency piezoelectric force sensor and the fast-response thermocouple, and set the trigger state of the ultra-high-speed signal acquisition instrument to a high-level external trigger;

[0034] S32: Setting the ignition voltage and ignition duration through the high-energy electric ignition controller;

[0035] S33: Manually start the high-energy electric ignition system in the remote control system, and discharge high voltage at the positive and negative poles of the ignition rod through the high-voltage cable to generate high-energy electric sparks to ignite the explosion gas in the explosion chamber; at the same time, the remote control system synchronously triggers the ultra-high-speed signal acquisition instrument to monitor the instantaneous pressure, temperature and sample load parameters in the explosion chamber during the explosion process;

[0036] S34: After the pressure in the explosion chamber is stabilized, the high-pressure pneumatic solenoid valve 1 is opened to release the pressure of the gas in the explosion chamber;

[0037] Step 4: Permeability test and sampling of rock samples after explosive fracturing

[0038] S41: After the pressure relief is completed, close the high-pressure pneumatic solenoid valve 1, start the gas booster pump to control the gas in the gas source to be injected into the prefabricated perforations of the rock sample through the combustion and explosion cavity, and measure its permeability; use low-frequency pressure sensor 1, low-frequency pressure sensor 2 and flowmeter to monitor the inlet pressure, outlet pressure and gas flow of the rock sample respectively, and feed back to the remote control system; the remote control system calculates the collected data to obtain the permeability of the rock sample after the combustion and explosion fracturing. The specific formula is as follows:

[0039]

[0040] Where: k is the permeability of the rock sample, m 2 ; q is the gas flow rate, m 3 / s; μ is the gas dynamic viscosity coefficient, MPa·s; l is the sample length, m; P 0 is the atmospheric pressure; A is the cross-sectional area of ​​the rock sample, m 3 ;P 1 is the intake pressure, MPa; P 2 is the outlet pressure, MPa;

[0041] S42: Control the horizontal flow pump to unload the confining pressure and axial pressure of the rock sample, then remove the screw and connecting flange between the high-temperature and high-pressure explosion reactor and the triaxial core holder, take the rock sample together with the heat shrink sleeve from the triaxial core holder, clean it, and seal it with foam paper and sample bags for subsequent testing and analysis;

[0042] S43: Select another rock sample, reset the initial temperature, gas injection pressure, explosion gas ratio, ignition energy, ignition time, axial pressure value and confining pressure value of the high-temperature and high-pressure explosion reactor, repeat steps one to four, and obtain the explosion load characteristic parameter curve and the explosion fracturing transformation effect of the rock sample under different working conditions; repeat this process many times to obtain the load curve, force curve, temperature curve and fracturing morphology parameters of the rock sample under different wellbore temperatures and pressures, different ground stress states, different methane concentrations and different ignition processes, so as to provide a large amount of measured data and analysis samples for the subsequent application of methane in-situ explosion fracturing technology.

[0043] Compared with the prior art, the present invention adopts a combination of a high-temperature and high-pressure combustion and explosion reactor, a three-axis core holder, a gas distribution system, a high-energy electric ignition system, a high-frequency data acquisition system, a permeability measurement system and a remote control system to achieve synchronous physical simulation of explosion load and rock sample fracturing under different reservoir ambient temperatures, ambient pressures and formation stress conditions; through the coordinated design of the gas distribution system and the remote control system, remote and precise gas distribution of dangerous combustion and explosion gases is achieved; through the integration of the high-energy electric ignition system, the high-frequency signal acquisition system and the remote control system, microsecond-level synchronous triggering of electric ignition detonation and high-frequency data acquisition is achieved; by arranging multiple channels on the side of the high-temperature and high-pressure combustion and explosion reactor The holes are simulated for perforation, and the through holes are connected to high-frequency pressure sensors through high-pressure resistant seamless steel pipes, thereby realizing accurate monitoring of the explosion load in the simulated wellbore perforation; the three-axis core holder and permeability measurement system are used to realize the in-situ test of the permeability of the rock sample after the explosion load is applied, without decompression; in summary, the present invention can simulate the load characteristics and fracturing process of in-situ explosion fracturing of methane in the perforations of unconventional natural gas reservoirs, and obtain experimental data under different process conditions, which is of great significance for the determination of the combustion-supporting gas and proportion of methane in-situ explosion fracturing, the selection of wells and layers, and the evaluation of fracturing effects, and at the same time provides a scientific basis and theoretical foundation for the later in-situ explosion fracturing experiments of methane in unconventional natural gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0045] Figure 2 It is a structural schematic diagram of a high temperature and high pressure explosion reactor in the present invention;

[0046] Figure 3 is a schematic diagram of drilling holes of the end cover assembly in the present invention;

[0047] Figure 4 It is a structural schematic diagram of a triaxial core holder and a permeability measurement system in the present invention;

[0048] Figure 5 It is a schematic diagram of the structure of the remote control system in the present invention;

[0049] Figure 6 It is a structural schematic diagram of the flip bracket in the present invention.

[0050] In the figure: 1. High-temperature and high-pressure explosion reactor; 1-1. Explosion chamber; 1-2. High-pressure pipeline; 1-3. Pre-tightening protection jacket; 1-4. Heating tile; 1-5. Insulation sleeve; 1-6. Graphite sealing ring; 1-7. Gland; 1-8. Through hole; 2. High-pressure connection assembly; 3. Flame arrester; 4. High-pressure pneumatic solenoid valve 1; 5. Vent valve; 6. High-pressure pneumatic solenoid valve 2; 7. Low-frequency pressure sensor 1; 8. Low-frequency thermocouple; 9. High-pressure ball valve; 10. Air compressor; 11. End cover assembly; 11-1. Borehole 1; 11-2. Borehole 2; 11-3. Borehole 3; 11-4. Borehole 4; 12. Three-axis core holder; 12-1. Three-axis loading mechanism; 12-2. Axial force loading mechanism; 12-3. Axial force loading oil circuit; 12-4. Outlet end; 12-5. Connecting flange; 12-6. Screw; 13. Horizontal flow pump; 14. Hydraulic ball valve 1; 15. Hydraulic ball valve 2; 16. Explosion port; 17. Rock sample; 18. Gas distribution system; 19. High-pressure methane cylinder; 20. High-pressure oxygen cylinder; 21. High-pressure air cylinder; 22. Pressure reducing valve; 23. Methane gas flow controller; 24. Oxygen gas flow controller; 25. Air gas flow controller; 26. One-way valve; 27. High-pressure pneumatic solenoid valve three; 28. Vacuum pump; 29. ​​High-energy electric ignition system; 30. Ignition rod; 31. Ultra-high-speed signal acquisition instrument; 32. High-frequency pressure sensor; 33. High-frequency piezoelectric force sensor; 34. Fast Response thermocouple; 35. Gas booster pump; 36. Low-frequency pressure sensor 2; 37. Flow meter; 38. Remote control system; 38-1. Cabinet; 38-2. Industrial computer; 38-3. Low-frequency signal acquisition system; 38-4. Display screen; 39. Confining pressure sensor; 40. Axial pressure sensor; 41. Flip bracket; 41-1 Vertical seat bearing; 41-2. Worm reducer; 41-3. Rotating handle; 41-4. Reducer bracket; 41-5. Bracket frame. DETAILED DESCRIPTION

[0051] The present invention will be further described below.

[0052] As shown in the figure, a methane in-situ explosion fracturing and evaluation simulation integrated test device includes a high-temperature and high-pressure explosion reactor 1, a three-axis core holder 12, a gas distribution system 18, a high-energy electric ignition system 29, a high-frequency data acquisition system, a permeability measurement system and a remote control system 38;

[0053] like Figure 2 and 3As shown, the high-temperature and high-pressure explosion reactor 1 includes an explosion chamber 1-1, a pre-tightening protection jacket 1-3, a heating tile 1-4, an insulation sleeve 1-5, an end cover assembly 11 and a pressure cover 1-7; the explosion chamber 1-1 and the pre-tightening protection jacket 1-3 are assembled by a hard pressing process, and a plurality of through holes 1-8 penetrating the side wall of the explosion chamber are provided on one side of the explosion chamber 1-1, and each through hole 1-8 is respectively connected to one end of a high-pressure seamless steel pipe of different pipe diameters and lengths, so as to simulate the perforation around the wellbore; three channels penetrating the side wall of the explosion chamber are arranged on the other side of the explosion chamber 1-1, one of which is connected to a high-pressure pneumatic solenoid valve 4 and a vent valve 5 in sequence through a pipeline for discharging the gas in the explosion chamber 1-1; the other channel is connected to a high-pressure pneumatic solenoid valve 6, a low-frequency pressure sensor 7 and a low-frequency thermocouple 8 in sequence through a pipeline for monitoring Measure the pressure and temperature of the gas in the explosion cavity 1-1; the last borehole is connected to the air compressor 10 through a pipeline through a high-pressure ball valve 9, which is used to increase the pressure in the explosion cavity 1-1; the end cover assembly 11 is installed at one end of the explosion cavity 1-1 and is tightened and fixed by a pressure cover 1-7, and the end cover assembly 11 is provided with borehole one 11-1, borehole two 11-2, borehole three 11-3 and borehole four 11-4; the heating tile 1-4 is installed on the outer surface of the explosion cavity 1-1, which is used to heat the explosion cavity 1-1; the insulation sleeve 1-5 wraps the heating tile 1-4 and the explosion cavity 1-1, which is used to maintain the temperature of the explosion cavity 1-1; the apertures of the borehole one 11-1, borehole two 11-2, borehole three 11-3 and borehole four 11-4 are different; the end cover assembly 11 and one end of the explosion cavity 1-1 are sealed by a graphite sealing ring 1-6.

[0054] like Figure 4 As shown, the triaxial core holder 12 is installed at the other end of the explosion chamber 1-1, and is used to place a rock sample 17 and apply prestress to the rock sample 17; the triaxial core holder 12 includes a holder body, a horizontal flow pump 13, a rock sample 17, a connecting flange 12-5 and a screw 12-6; a triaxial loading mechanism 12-1 is arranged in the holder body, and the rock sample 17 is placed in the triaxial loading mechanism 12-1, and a prefabricated perforation is drilled at one end of the rock sample 17; the horizontal flow pump 13 is connected to the triaxial loading mechanism 12-1 through two branch pipelines, and is used to control the triaxial loading mechanism 12 -1 applies triaxial confining pressure to the rock sample 17 to simulate the actual stress state of unconventional natural gas wells; ports are opened at both ends of the clamp body, namely the inlet end and the outlet end 12-4, wherein the inlet end is sealed and connected with the detonation port 16, and a plug is arranged on the outlet end 12-4 to seal or open the outlet end 12-4; the rock sample 17 is tightly wrapped by a heat shrink sleeve, and one end of the prefabricated perforation is aligned with the detonation port 16; the connecting flange 12-5 fixes the triaxial core clamp 12 to the explosion cavity 1-1 through the screw 12-6, and the explosion port 16 is connected to the inside of the explosion cavity 1-1.

[0055] like Figure 1 As shown, the gas distribution system 18 includes a high-pressure methane gas cylinder 19, a high-pressure oxygen gas cylinder 20, a high-pressure air gas cylinder 21, a methane gas flow controller 23, an oxygen gas flow controller 24, an air gas flow controller 25, a four-way, a vacuum pump 28 and a high-pressure pneumatic solenoid valve 27; the high-pressure methane gas cylinder 19, the high-pressure oxygen gas cylinder 20, and the high-pressure air gas cylinder 21 are respectively connected to the three ports of the four-way through pipelines, and the remaining port of the four-way is connected to the borehole 11-1 through the main pipeline. The methane gas flow controller 23, the oxygen gas flow controller 24, and the air gas flow controller 25 are respectively installed on the three pipelines, and are respectively used for Monitor and control the flow of gas delivered by high-pressure methane cylinder 19, high-pressure oxygen cylinder 20 and high-pressure air cylinder 21 into the explosion chamber 1-1; high-pressure pneumatic solenoid valve three 27 is installed on the main pipeline to control the on-off of the main pipeline; vacuum pump 28 is connected to the main pipeline to evacuate the explosion chamber 1-1; the pipelines where the high-pressure methane cylinder 19, oxygen cylinder 20 and air cylinder 21 are located are equipped with pressure reducing valve 22, one-way valve 26 and high-pressure resistant ball valve 9, the pressure reducing valve 22 is used to buffer the gas passing through the pipeline, the one-way valve 26 is used to control the one-way flow of gas to prevent gas backflow, and the high-pressure resistant ball valve 9 is used to control the on-off of the pipeline. The high-pressure pneumatic solenoid valve one 4, high-pressure pneumatic solenoid valve two 6 and high-pressure pneumatic solenoid valve three 27 are each equipped with a flame arrester 3 on the pipeline between them and the explosion chamber 1-1 to prevent the flame generated by the explosion from affecting each pneumatic solenoid valve.

[0056] like Figure 1 As shown, the high-energy electric ignition system 29 includes a high-energy electric ignition controller, a high-voltage cable and an ignition rod 30; the high-energy electric ignition controller is connected to the ignition rod 30 through the high-voltage cable; the ignition rod 30 extends into the explosion cavity 1-1 through the drilling hole 11-2; the high-energy electric ignition controller is connected to the remote control system 38 through the line, and is used to control the electric spark generated by the ignition rod 30;

[0057] like Figure 1As shown, the high-frequency signal acquisition system includes an ultra-high-speed signal acquisition instrument 31, a high-frequency pressure sensor 32, a high-frequency piezoelectric force sensor 33 and a fast-response thermocouple 34; the high-speed signal acquisition instrument 31 is remotely connected to the high-frequency pressure sensor 32, the high-frequency piezoelectric force sensor 33 and the fast-response thermocouple 34 through a transmission line; the high-frequency pressure sensor 32 is respectively installed at the other end of the high-pressure seamless steel pipe connecting each through hole 1-8, and is used to test the transient load curve in the perforations at different positions of the wellbore; the high-frequency piezoelectric force sensor 33 is fixed at the end of the rock sample 17 away from the perforation, and is used to obtain the transient load data of the rock sample; the fast-response thermocouple 34 is installed at the borehole 11-3, and is used to obtain the transient temperature data of the detonation wave; the transient impact load in the perforation during the combustion and explosion of methane, the transient temperature of the detonation wave, the process of deflagration to detonation, the propagation velocity of the detonation wave and the transient load characteristics of the rock sample are collected and processed by the high-frequency signal acquisition system;

[0058] like Figure 4 As shown, the permeability measurement system includes a gas source, a gas booster pump 35, a low-frequency pressure sensor 2 36 and a flow meter 37; the gas source is connected to the inlet of the gas booster pump 35 through a connecting pipe, the outlet of the gas booster pump 35 is connected to the borehole 4 11-4 through a pipeline, the low-frequency pressure sensor 2 36 is installed at the outlet end of the triaxial core holder 12, and the outlet end of the triaxial core holder 12 is connected to the flow meter 37 through a pipeline;

[0059] like Figure 5 As shown, the remote control system 38 includes a cabinet 38-1, an industrial computer 38-2 and a low-frequency signal acquisition system 38-3; the low-frequency signal acquisition system 38-3 is used to monitor the state parameters of the explosion chamber, the core holder and the gas distribution system; the low-frequency pressure sensor 7 and the low-frequency thermocouple 8 on the high-temperature and high-pressure explosion reactor 1, the methane gas flow controller 23, the oxygen gas flow controller 24, the air gas flow controller 25 in the gas distribution system 18, the horizontal flow pump flow meter of the core holder, the low-frequency pressure sensor 7 and the low-frequency thermocouple 8 on the high-temperature and high-pressure explosion reactor 1, the methane gas flow controller 23, the oxygen gas flow controller 24, the air gas flow controller 25, the horizontal flow pump flow meter of the core holder, the low-frequency pressure sensor 7 and the low-frequency pressure sensor 8 on the high-temperature and high-pressure explosion reactor 1, the methane gas flow controller 23, the oxygen gas flow controller 24, the air gas flow controller 25 in the gas distribution system 18, the low-frequency pressure sensor 7 and the low-frequency pressure sensor 8 on the high-temperature and high-pressure explosion reactor 1 ... Sensor 2 36 and flow meter 37 are both connected to the low-frequency signal acquisition system. The low-frequency signal acquisition system 38-3 collects data on the temperature and pressure in the high-temperature and high-pressure explosion reactor 1, the flow rate, pressure and distribution gas flow rate of the horizontal flow pump in the core clamp, and transmits them to the cabinet 38-1 for analysis and processing, and controls the high-pressure pneumatic solenoid valve 1 4, the high-pressure pneumatic solenoid valve 2 6, the high-pressure pneumatic solenoid valve 3 27, the methane gas flow controller 23, the oxygen gas flow controller 24 and the air gas flow controller 25.

[0060] As an improvement of the present invention, it further comprises a flip bracket 41, on which the explosion cavity 1-1 is mounted, for adjusting the position of the explosion cavity 1-1.

[0061] As another improvement of the present invention, the core sample 17 is a cylindrical core with a diameter of 50 mm and a height of 100 mm. The prefabricated perforation diameter of the core sample 17 is between 3 mm and 5 mm, the perforation depth is between 40 mm and 60 mm, and the cone angle of the bottom of the perforation is not greater than 120°, which is used to simulate energy-focused perforation. The acquisition frequency of the high-speed signal acquisition instrument 31 is not less than 1 MHz, and the high-frequency pressure sensor 32 adopts a piezoelectric pressure sensor with a maximum range of not less than 150 MPa and a frequency response of not less than 5 MHz; the maximum range of the high-frequency piezoelectric force sensor 33 is not less than 300 kN, and the frequency response is not less than 5 MHz; the maximum range of the fast-response thermocouple 34 is not less than 3000 K, and the frequency response is not less than 1 MHz. The pressure-bearing capacity of the high-pressure pneumatic solenoid valve 1 4, the high-pressure pneumatic solenoid valve 2 6 and the high-pressure pneumatic solenoid valve 3 27 is not less than 150MPa; the detonation port 16 is used in conjunction with the rock sample 17, and the end of the detonation port 16 facing the explosion cavity 1-1 is a trumpet-shaped variable diameter structure, which changes from a diameter of 55mm to a prefabricated perforation diameter of the rock sample, and the length of the variable diameter section is 50mm; after the variable diameter section is a non-changing diameter drill hole with the same perforation diameter, and the length of the drill hole is 100mm.

[0062] The above-mentioned three-axis core holder 12, flip bracket 41, various pipelines, low-frequency pressure sensor, high-frequency pressure sensor 32, gas booster pump 35, ultra-high-speed signal acquisition instrument 31, solenoid valve, vacuum pump 28, flow meter 37 and other hardware components are all existing equipment or devices and can be purchased on the market; Figure 6 As shown, the flip bracket 41 includes a vertical seat bearing 41-1, a worm reducer 41-2, a rotating handle 41-3, a reducer bracket 41-4 and a bracket frame 41-5. The vertical seat bearing 41-1, the worm reducer 41-2 and the reducer bracket 41-4 are all installed on the bracket frame 41-5. The high-temperature and high-pressure explosion reactor 1 is coaxially connected with the rotating shaft of the worm reducer 41-2 and the vertical seat bearing 41-1 through a rotating rod, so that the worm reducer 41-2 can drive the high-temperature and high-pressure explosion reactor 1 to partially rotate around the rotating rod to adjust the posture; the worm reducer 41-2 is provided with a rotation angle scale to ensure the accuracy of the angle adjustment.

[0063] The working method of the above-mentioned methane in-situ explosion fracturing and evaluation simulation integrated test device comprises the following specific steps:

[0064] Step 1: Device assembly and airtightness test

[0065] S11: Keep both ends of the high-temperature and high-pressure explosion reactor 1 open, use the air compressor 10 to generate 0.8MPa high-pressure air to purge the residual moisture, carbon deposits and other impurities in the explosion cavity 1-1; after the inner wall of the pipeline is free of foreign matter, assemble the end cover assembly 11, and seal the high-pressure seamless steel pipe with simulated perforation on one side of the explosion cavity 1-1 with the high-frequency pressure sensor 32;

[0066] S12: Use a heat shrink sleeve to tightly wrap the rock sample 17, then point one end of the prefabricated perforation of the rock sample 17 toward the explosion cavity 1-1, and tightly connect the other end to the high-frequency piezoelectric force sensor 33, and put it into the triaxial core holder 12; the triaxial core holder 12 is sealed and connected to the other end of the high-temperature and high-pressure explosion reactor 1 through the connecting flange 12-5 and the screw 12-6; control the triaxial loading mechanism 12-1 through the horizontal flow pump 13 to apply confining pressure and axial pressure to the rock sample 17 to the set value;

[0067] S13: Use the air compressor 10 to inject high-pressure air to 0.8MPa into the explosion cavity through one of the channels on the high-temperature and high-pressure explosion reactor 1, and perform an airtightness check on the explosion cavity 1-1; open the high-pressure pneumatic solenoid valve 26, and monitor the pressure change in the explosion cavity 1-1 within 300s through the low-frequency pressure sensor 7; if the pressure decay is less than 0.005MPa, it is determined that the airtightness of the high-temperature and high-pressure explosion reactor 1 is good; after completing the airtightness check, open the high-pressure pneumatic solenoid valve 14 to release the high-pressure air inside the explosion cavity 1-1;

[0068] Step 2: Prepare the explosion gas

[0069] S21: close the high-pressure pneumatic solenoid valve 1-4, and open the high-pressure pneumatic solenoid valve 3-27 connecting the high-temperature and high-pressure reactor 1 and the gas distribution system 18; turn on the vacuum pump 28, and evacuate the explosion chamber 1-1 and the gas distribution system 18 pipeline until the vacuum degree is higher than 0.95, stop evacuating, and complete the evacuation process;

[0070] S22: Setting a preset temperature of the high-temperature and high-pressure reactor 1 through the remote control system 38, and heating the high-temperature and high-pressure reactor 1 through the heating tiles 1-4; monitoring the actual temperature in the explosion cavity 1-1 through the low-frequency thermocouple 8 until the actual temperature reaches the preset temperature;

[0071] S23: Set the rated injection flow rates of methane, oxygen and air respectively through the remote control system 38; open the pressure reducing valve 22, high-pressure resistant ball valve 9 and high-pressure pneumatic solenoid valve 6 of the pipeline where the high-pressure methane cylinder 19 is located in turn, and first inject methane into the explosion chamber 1-1; during the air intake process, the air intake flow rate is fed back in real time through the methane flow controller 23, and the pressure of the explosion chamber 1-1 is monitored through the low-frequency pressure sensor 7; when the injection pressure reaches the set value, the air intake is automatically stopped through the methane flow controller 23; then, if methane and air need to be mixed as needed, open the pressure reducing valve 22 and high-pressure resistant ball valve of the pipeline where the high-pressure air cylinder 20 is located in turn. 9, and the air flow rate is fed back in real time through the air flow controller 24, and when the injection pressure reaches the set pressure, the air flow controller 24 automatically stops the air intake; if methane and oxygen need to be mixed, the pressure reducing valve 22 and the high-pressure ball valve 9 of the pipeline where the high-pressure oxygen cylinder 21 is located are opened in turn, and the air flow rate is fed back in real time through the oxygen flow controller 25, and when the injection pressure reaches the set pressure, the oxygen flow controller 25 automatically stops the air intake; the methane concentration in the explosion cavity 1-1 is accurately calculated by the ratio of the cumulative injection amount of methane and air or oxygen, and the accuracy of the gas distribution result is verified. After the gas distribution is completed, it is left to stand for 90 minutes to allow the explosion gas to be fully mixed;

[0072] Step 3: Explosive fracturing and data collection

[0073] S31: After the combustible gas configuration is completed, close the high-pressure pneumatic solenoid valve 26; then use analog signals to detect the working status of the ultra-high-speed signal acquisition instrument 31, the high-frequency pressure sensor 32, the high-frequency piezoelectric force sensor 33 and the fast-response thermocouple, and set the trigger state of the ultra-high-speed signal acquisition instrument 31 to a high-level external trigger;

[0074] S32: Setting the ignition voltage and ignition duration through the high-energy electric ignition controller;

[0075] S33: The high-energy electric ignition system is manually started in the remote control system 38, and high-voltage discharge is performed at the positive and negative electrodes of the ignition rod 30 through the high-voltage cable to generate high-energy electric sparks to ignite the explosion gas in the explosion cavity 1-1; at the same time, the remote control system 38 synchronously triggers the ultra-high-speed signal acquisition instrument 31 to monitor the instantaneous pressure, temperature and sample load parameters in the explosion cavity 1-1 during the explosion process;

[0076] S34: After the pressure in the explosion chamber 1-1 is stabilized, the high-pressure pneumatic solenoid valve 1-4 is opened to release the pressure of the gas in the explosion chamber 1-1;

[0077] Step 4: Permeability test and sampling of rock samples after explosive fracturing

[0078] S41: After the pressure relief is completed, the high-pressure pneumatic solenoid valve 1-4 is closed, and the gas booster pump 35 is started to control the gas in the gas source to be injected into the prefabricated perforations of the rock sample 17 through the explosion cavity 1-1, and the permeability thereof is measured; the low-frequency pressure sensor 1-7, the low-frequency pressure sensor 2-36 and the flow meter 37 are used to monitor the inlet pressure, outlet pressure and gas flow of the rock sample 17 respectively, and the feedback is sent to the remote control system 38; the remote control system 38 calculates the collected data to obtain the permeability of the rock sample 17 after the explosion fracturing, and the specific formula is as follows:

[0079]

[0080] Where: k is the permeability of the rock sample, m 2 ; q is the gas flow rate, m 3 / s; μ is the gas dynamic viscosity coefficient, MPa·s; l is the sample length, m; P 0 is the atmospheric pressure; A is the cross-sectional area of ​​the rock sample, m 3 ;P 1 is the intake pressure, MPa; P 2 is the outlet pressure, MPa;

[0081] S42: Control the horizontal flow pump 13 to unload the confining pressure and axial pressure of the rock sample 17, then remove the screw 12-6 and the connecting flange 12-5 between the high-temperature and high-pressure explosion reactor 1 and the triaxial core holder 12, take the rock sample 17 together with the heat shrink sleeve from the triaxial core holder 12, clean it, and seal it with foam paper and a sample bag for subsequent testing and analysis;

[0082] S43: Select another rock sample 17, reset the initial temperature, gas injection pressure, explosion gas ratio, ignition energy, ignition time, axial pressure value and confining pressure value of the high-temperature and high-pressure explosion reactor 1, repeat steps 1 to 4, obtain the explosion load characteristic parameter curve and the explosion fracturing transformation effect of the rock sample under different working conditions; repeat this process many times to obtain the load curve, force curve, temperature curve and fracturing morphology parameters of the rock sample under different wellbore temperatures and pressures, different ground stress states, different methane concentrations and different ignition processes, so as to provide a large amount of measured data and analysis samples for the subsequent application of methane in-situ explosion fracturing technology.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A methane in-situ explosion fracturing and evaluation simulation integrated test device, characterized in that: It includes high temperature and high pressure explosion reactor, three-axis core holder, gas distribution system, high energy electric ignition system, high frequency signal acquisition system, permeability measurement system and remote control system; The high-temperature and high-pressure explosion reactor comprises an explosion chamber, a pre-tightening protective jacket, a heating tile, an insulation sleeve, an end cover assembly and a pressure cover; the explosion chamber and the pre-tightening protective jacket are assembled by a hard pressing process, and a plurality of through holes penetrating the side wall of the explosion chamber are provided on one side of the explosion chamber, and each through hole is respectively connected to one end of a high-pressure seamless steel pipe of different pipe diameters and lengths to simulate the perforation around the wellbore; three channels penetrating the side wall of the explosion chamber are arranged on the other side of the explosion chamber, one of which is connected to a high-pressure pneumatic solenoid valve and a vent valve in sequence through a pipeline to discharge the gas in the explosion chamber; the other The channels are connected to high-pressure pneumatic solenoid valve 2, low-frequency pressure sensor 1 and low-frequency thermocouple in sequence through pipelines to monitor the pressure and temperature of the gas in the explosion cavity; the last borehole is connected to the air compressor through a pipeline via a high-pressure resistant ball valve to increase the pressure in the explosion cavity; the end cover assembly is installed at one end of the explosion cavity and is tightened and fixed by a pressure cover, and boreholes 1, 2, 3 and 4 are provided on the end cover assembly; the heating tile is installed on the outer surface of the explosion cavity to heat the explosion cavity; the insulation sleeve wraps the heating tile and the explosion cavity to maintain the temperature of the explosion cavity; The triaxial core holder is installed at the other end of the explosion cavity and is used to place the rock sample and apply prestress to the rock sample; The gas distribution system includes a high-pressure methane gas cylinder, a high-pressure oxygen gas cylinder, a high-pressure air gas cylinder, a methane gas flow controller, an oxygen gas flow controller, an air gas flow controller, a four-way valve, a vacuum pump and three high-pressure pneumatic solenoid valves; the high-pressure methane gas cylinder, the high-pressure oxygen gas cylinder and the high-pressure air gas cylinder are respectively connected to the three ports of the four-way valve through pipelines, and the remaining one port of the four-way valve is connected to the borehole one through the main pipeline. The methane gas flow controller, the oxygen gas flow controller and the air gas flow controller are respectively installed on the three pipelines, and are respectively used to monitor and control the flow rates of the high-pressure methane gas cylinder, the high-pressure oxygen gas cylinder and the high-pressure air gas cylinder respectively transporting gases into the explosion cavity; the three high-pressure pneumatic solenoid valves are installed on the main pipeline to control the on-off of the main pipeline; the vacuum pump is connected to the main pipeline to vacuum the explosion cavity; The high-energy electric ignition system includes a high-energy electric ignition controller, a high-voltage cable and an ignition rod; the high-energy electric ignition controller is connected to the ignition rod through the high-voltage cable; the ignition rod extends into the explosion cavity through the second drilling hole; the high-energy electric ignition controller is connected to the remote control system through the line, and is used to control the electric spark generated by the ignition rod; The high-frequency signal acquisition system includes an ultra-high-speed signal acquisition instrument, a high-frequency pressure sensor, a high-frequency piezoelectric force sensor and a fast-response thermocouple; the high-speed signal acquisition instrument is remotely connected to the high-frequency pressure sensor, the high-frequency piezoelectric force sensor and the fast-response thermocouple through a transmission line; the high-frequency pressure sensor is respectively installed at the other end of the high-pressure seamless steel pipe connecting each through hole, and is used to test the transient load curve in the perforations at different positions of the wellbore; the high-frequency piezoelectric force sensor is fixed at the end of the rock sample away from the perforation, and is used to obtain the transient load data of the rock sample; the fast-response thermocouple is installed at three locations of the borehole, and is used to obtain the transient temperature data of the detonation wave; the transient impact load in the perforation during the combustion and explosion of methane, the transient temperature of the detonation wave, the process of deflagration to detonation, the propagation velocity of the detonation wave and the transient load characteristics of the rock sample are collected and processed by the high-frequency signal acquisition system; The permeability measurement system comprises a gas source, a gas booster pump, a low-frequency pressure sensor 2 and a flow meter; the gas source is connected to the inlet of the gas booster pump through a connecting pipe, the outlet of the gas booster pump is connected to the borehole 4 through a pipeline, the low-frequency pressure sensor 2 is installed at the outlet end of the triaxial core holder, and the outlet end of the triaxial core holder is connected to the flow meter through a pipeline; The remote control system includes a cabinet, an industrial computer and a low-frequency signal acquisition system; a low-frequency pressure sensor 1 and a low-frequency thermocouple in a high-temperature and high-pressure explosion reactor, a methane gas flow controller, an oxygen gas flow controller, an air gas flow controller in a gas distribution system, a flow meter for a horizontal flow pump of a core holder, a low-frequency pressure sensor 2 and a flow meter are all connected to the low-frequency signal acquisition system, and the low-frequency signal acquisition system collects data on the temperature and pressure in the high-temperature and high-pressure explosion reactor, the flow rate and pressure of the horizontal flow pump in the core holder, and the flow rate of the gas distribution gas, and transmits the data to the cabinet for analysis and processing, and controls a high-pressure pneumatic solenoid valve 1, a high-pressure pneumatic solenoid valve 2, a high-pressure pneumatic solenoid valve 3, a methane gas flow controller, an oxygen gas flow controller and an air gas flow controller.

2. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1, characterized in that: The triaxial core holder comprises a holder body, a horizontal flow pump, a rock sample, a connecting flange and a screw; a triaxial loading mechanism is arranged in the holder body, the rock sample is placed in the triaxial loading mechanism, and a prefabricated perforation is drilled at one end of the rock sample; the horizontal flow pump is connected to the triaxial loading mechanism through two branch pipelines, and is used to control the triaxial loading mechanism to apply triaxial confining pressure to the rock sample, so as to simulate the actual stress state of unconventional natural gas wells; ports are provided at both ends of the holder body, namely an inlet end and an outlet end, wherein the inlet end is sealedly connected to the detonation port, and a plug is provided on the outlet end, which is used to block or open the outlet end; the rock sample is tightly wrapped by a heat shrink sleeve, and one end of the prefabricated perforation is aligned with the detonation port; the connecting flange fixedly connects the triaxial core holder to the explosion cavity through a screw, and the detonation port is connected to the inside of the explosion cavity.

3. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1 is characterized in that: The boreholes 1, 2, 3 and 4 have different apertures; the end cover assembly is sealed with one end of the explosion cavity by a graphite sealing ring.

4. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1 is characterized in that: The pipelines of the high-pressure methane cylinders, oxygen cylinders and air cylinders are each equipped with a pressure reducing valve, a one-way valve and a high-pressure resistant ball valve. The pressure reducing valve is used to buffer the gas passing through the pipeline, the one-way valve is used to control the one-way flow of the gas to prevent gas backflow, and the high-pressure resistant ball valve is used to control the on-off of the pipeline.

5. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1 is characterized in that: Flame arresters are installed on the pipelines between the high-pressure pneumatic solenoid valve 1, the high-pressure pneumatic solenoid valve 2 and the high-pressure pneumatic solenoid valve 3 and the explosion chamber to prevent the flame generated by the explosion from affecting each pneumatic solenoid valve.

6. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1, characterized in that: It also includes a flip bracket, on which the explosion cavity is mounted, and is used to adjust the position of the explosion cavity.

7. The integrated test device for methane in-situ explosion fracturing and evaluation simulation according to claim 2, characterized in that: The rock sample is a cylindrical core with a diameter of 50 mm and a height of 100 mm. The prefabricated perforation diameter of the rock sample is between 3 mm and 5 mm, the perforation depth is between 40 mm and 60 mm, and the cone angle at the bottom of the perforation is not greater than 120°, which is used to simulate concentrated energy perforation.

8. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1 is characterized in that: The acquisition frequency of the high-speed signal acquisition instrument is not less than 1MHz. The high-frequency pressure sensor adopts a piezoelectric pressure sensor with a maximum range of not less than 150MPa and a frequency response of not less than 5MHz; the maximum range of the high-frequency piezoelectric force sensor is not less than 300kN and the frequency response is not less than 5MHz; the maximum range of the fast-response thermocouple is not less than 3000K and the frequency response is not less than 1MHz.

9. The integrated test device for in-situ methane explosion fracturing and evaluation simulation according to claim 1, characterized in that: The pressure-bearing capacity of each of the high-pressure pneumatic solenoid valve 1, the high-pressure pneumatic solenoid valve 2 and the high-pressure pneumatic solenoid valve 3 is not less than 150 MPa.

10. A working method of the methane in-situ explosion fracturing and evaluation simulation integrated test device according to any one of claims 1 to 9, characterized in that: The specific steps are: Step 1: Device assembly and airtightness test S11: Keep both ends of the high-temperature and high-pressure explosion reactor open, and use an air compressor to generate 0.8MPa high-pressure air to purge residual moisture, carbon deposits and other impurities in the explosion chamber; after the inner wall of the pipeline is free of foreign matter, assemble the end cover assembly, and seal and connect the high-pressure seamless steel pipe with simulated perforation on one side of the explosion chamber to the high-frequency pressure sensor; S12: Use a heat shrink sleeve to tightly wrap the rock sample, then point one end of the prefabricated perforation of the rock sample toward the explosion cavity, and tightly connect the other end to the high-frequency piezoelectric force sensor, and put it into the triaxial core holder; the triaxial core holder is sealed and connected to the other end of the high-temperature and high-pressure explosion reactor through a connecting flange and a screw; control the triaxial loading mechanism through a horizontal flow pump to apply confining pressure and axial pressure to the rock sample to the set value; S13: Use an air compressor to inject high-pressure air to 0.8MPa into the explosion chamber through one of the channels on the high-temperature and high-pressure explosion reactor, and check the air tightness of the explosion chamber; open the second high-pressure pneumatic solenoid valve, and monitor the pressure change in the explosion chamber within 300s through the low-frequency pressure sensor one; if the pressure decay is less than 0.005MPa, it is determined that the air tightness of the high-temperature and high-pressure explosion reactor is good; after completing the air tightness check, open the first high-pressure pneumatic solenoid valve to release the high-pressure air inside the explosion chamber; Step 2: Prepare the explosion gas S21: Close the high-pressure pneumatic solenoid valve 1, and at the same time open the high-pressure pneumatic solenoid valve 3 connecting the high-temperature and high-pressure reactor and the gas distribution system; turn on the vacuum pump to evacuate the explosion chamber and the gas distribution system pipeline until the vacuum degree is higher than 0.95, stop evacuating, and complete the vacuum process; S22: setting a preset temperature of the high-temperature and high-pressure reactor through a remote control system, and heating the high-temperature and high-pressure reactor through a heating tile; monitoring the actual temperature in the explosion cavity through a low-frequency thermocouple until the actual temperature reaches the preset temperature; S23: Set the rated injection flow rates of methane, oxygen and air respectively through the remote control system; open the pressure reducing valve, high-pressure resistant ball valve and high-pressure pneumatic solenoid valve 2 of the pipeline where the high-pressure methane cylinder is located in turn, and first inject methane into the explosion chamber; during the air intake process, the air intake flow rate is fed back in real time through the methane flow controller, and the pressure of the explosion chamber is monitored through the low-frequency pressure sensor 1; when the injection pressure reaches the set value, the methane flow controller automatically stops the air intake; then, according to needs, if methane and air need to be mixed, open the pressure reducing valve and high-pressure resistant ball valve of the pipeline where the high-pressure air cylinder is located in turn, and pass The air flow controller feeds back the intake flow in real time, and when the injection pressure reaches the set pressure, the air flow controller automatically stops the intake. If methane and oxygen need to be mixed, the pressure reducing valve and the high-pressure ball valve of the pipeline where the high-pressure oxygen cylinder is located are opened in turn, and the intake flow is fed back in real time through the oxygen flow controller, and when the injection pressure reaches the set pressure, the oxygen flow controller automatically stops the intake. The methane concentration in the explosion chamber is accurately calculated by the ratio of the cumulative injection amount of methane and air or oxygen to verify the accuracy of the gas distribution result. After the gas distribution is completed, it is left to stand for 90 minutes to allow the explosion gas to be fully mixed. Step 3: Explosive fracturing and data collection S31: After the combustible gas configuration is completed, close the second high-pressure pneumatic solenoid valve; then use analog signals to detect the working status of the ultra-high-speed signal acquisition instrument, the high-frequency pressure sensor, the high-frequency piezoelectric force sensor and the fast-response thermocouple, and set the trigger state of the ultra-high-speed signal acquisition instrument to a high-level external trigger; S32: Setting the ignition voltage and ignition duration through the high-energy electric ignition controller; S33: Manually start the high-energy electric ignition system in the remote control system, and discharge high voltage at the positive and negative poles of the ignition rod through the high-voltage cable to generate high-energy electric sparks to ignite the explosion gas in the explosion chamber; at the same time, the remote control system synchronously triggers the ultra-high-speed signal acquisition instrument to monitor the instantaneous pressure, temperature and sample load parameters in the explosion chamber during the explosion process; S34: After the pressure in the explosion chamber is stabilized, the high-pressure pneumatic solenoid valve 1 is opened to release the pressure of the gas in the explosion chamber; Step 4: Permeability test and sampling of rock samples after explosive fracturing S41: After the pressure relief is completed, close the high-pressure pneumatic solenoid valve 1, start the gas booster pump to control the gas in the gas source to be injected into the prefabricated perforations of the rock sample through the combustion and explosion cavity, and measure its permeability; use low-frequency pressure sensor 1, low-frequency pressure sensor 2 and flowmeter to monitor the inlet pressure, outlet pressure and gas flow of the rock sample respectively, and feed back to the remote control system; the remote control system calculates the collected data to obtain the permeability of the rock sample after the combustion and explosion fracturing. The specific formula is as follows: ； Where: k is the permeability of the rock sample, m 2 ; q is the gas flow rate, m 3 / s; μ is the gas dynamic viscosity coefficient, MPa·s; l is the specimen length, m; P 0 is atmospheric pressure, MPa; A is the cross-sectional area of ​​the rock sample, m 2 ; P 1 is the intake pressure, MPa; P 2 is the outlet pressure, MPa; S42: Control the horizontal flow pump to unload the confining pressure and axial pressure of the rock sample, then remove the screw and connecting flange between the high-temperature and high-pressure explosion reactor and the triaxial core holder, take the rock sample together with the heat shrink sleeve from the triaxial core holder, clean it, and seal it with foam paper and sample bags for subsequent testing and analysis; S43: Select another rock sample, reset the initial temperature, gas injection pressure, explosion gas ratio, ignition energy, ignition time, axial pressure value and confining pressure value of the high-temperature and high-pressure explosion reactor, repeat steps 1 to 4, and obtain the explosion load characteristic parameter curve and the explosion fracturing transformation effect of the rock sample under different working conditions; repeat this process many times to obtain the load curve, force curve, temperature curve and fracturing morphology parameters of the rock sample under different wellbore temperatures and pressures, different ground stress states, different methane concentrations and different ignition process conditions, thereby providing a large amount of measured data and analysis samples for the subsequent application of methane in-situ explosion fracturing technology.

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