CN114646535A - Liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and experiment method - Google Patents

Abstract

The invention belongs to the technical field of liquid nitrogen ultralow temperature phase change fracturing, and particularly relates to a liquid nitrogen ultralow temperature and phase change fracturing effect similar simulation experiment device and an experiment method, wherein the liquid nitrogen ultralow temperature and phase change fracturing effect similar simulation experiment device comprises a two-dimensional similar simulation experiment table, a liquid nitrogen supply system, a similar material mixing system, a stress monitoring system, a microseismic monitoring system, a drilling imaging system and an XTDIC monitoring system; the beneficial effects are that: the liquid nitrogen ultralow temperature and phase change fracturing effect similar simulation experiment device and the experiment method provided by the invention simulate the permeability increase of liquid nitrogen in the coal seam by utilizing physical similar simulation, observe the liquid nitrogen ultralow temperature and phase change fracturing effect and the displacement and deformation of the overlying rock stratum, monitor the stress change condition by the pressure sensor, and observe the fracture development and evolution rule by presetting a drill hole.

Description

Simulation experimental device and experimental method of liquid nitrogen ultra-low temperature and phase transition cracking effect similar

technical field

The invention belongs to the technical field of liquid nitrogen ultra-low temperature phase transition cracking, and particularly relates to a liquid nitrogen ultra-low temperature and phase transition cracking effect similar simulation experiment device and experimental method.

Background technique

First of all, my country is rich in coal resources, and the production and consumption of coal also ranks in the forefront of the world. As my country's basic energy, coal will account for 56.8% of my country's primary energy consumption in 2020. The coal seam gas content is closely related to the mining depth. With the rapid increase of the mining depth, the coal seam gas content and gushing volume gradually increase. According to statistics, nearly half of the key coal mines in the country are high gas mines or gas outburst mines. Second, coal is a natural geological body with defective structures such as micro-cracks, pores and low strength. Gas reservoirs in most mining areas in my country have the occurrence characteristics of "three highs and two lows" (three highs: high gas content in coal seams, high plasticity structure, high gas adsorption capacity, two lows: low coal seam permeability, and conventional coal seam fractures under strengthening measures. According to statistics, my country's high-gas mines account for more than 37% of my country's mines, of which 95% of the coal seams are low-permeability coal seams. Therefore, how to improve the permeability of low-permeability coal seams is a matter of gas extraction and One of the keys to disaster prevention and control, the expansion of coal micro-cracks and the initiation of new cracks will directly affect the permeability of coal. Furthermore, liquid nitrogen has no pollution to the environment, is easy to prepare and has low cost, and has an extremely low temperature (-196°C). New fissures, forming freeze-thaw induced fissures. In the limited space of the coal seam, the volume of liquid nitrogen expands rapidly after gasification, resulting in a huge expansion force to crack the coal seam. At 21 °C, the volume of ^1m3 liquid nitrogen gasification expands about 696 times, forming a gasification high-pressure cracking zone. At the same time, high-pressure nitrogen can Drive out and replace coal seam gas with partial pressure, and promote gas desorption and seepage flow, especially liquid nitrogen cyclic freezing and thawing, and repeated freezing and thawing to crack coal seam, which has a more significant effect on improving coal seam permeability. At the same time, liquid nitrogen volatilization needs to absorb heat, which will play a role in cooling coal seam. certain effect. Then, gas is the main factor leading to coal mine gas accidents, and it is also a strong greenhouse gas. Its damage to the ozone layer and its greenhouse effect are 7 times and 21 times that of CO ₂ , respectively. In contrast to catastrophes, gas is a clean energy available in coal seams and has broad development prospects. The gas resources in shallow depths below 2000m in China are about 36.8 trillion m ³ , and the mining value is significant. Therefore, the safe and efficient co-mining of coal and gas resources can not only effectively prevent gas disasters and reduce air pollution, but also use gas as a clean energy to achieve mine safety production, environmental protection and new energy supply and other purposes.

With the development of science and technology, in order to solve the problem of insufficient technology in the previous coal seam enhancement, the coal seam gas is efficiently pre-drained and utilized to prevent gas accidents and reduce environmental pollution problems, and maximize economic benefits. Ultra-low temperature fluids such as liquid nitrogen are used as The waterless fracturing technology of fracturing fluids has gradually received attention. Chinese invention patent CN201810527377.0 discloses an experimental device for real-time monitoring of the effect of liquid nitrogen-induced cracking of coal samples; Chinese invention patent CN202110344249.4 discloses an experimental device for testing the spatiotemporal evolution and mechanical parameters of cracks in liquid nitrogen immersed coal samples; Chinese invention patent CN202022500372.4 discloses an experimental device for observing the thermal performance and structural damage of a coal body injected with liquid nitrogen. At present, most of the current researches use laboratory experiments to conduct liquid nitrogen freezing and thawing, liquid nitrogen injection and other research on the occurrence of coal samples, which can provide a certain effective basis and theoretical support for the field application of liquid nitrogen to coal seam anti-reflection gas extraction. However, most laboratory experiments can only observe the surface cracks, internal pores, and mechanical properties of coal samples before and after liquid nitrogen freezing and thawing, and liquid nitrogen injection. At present, there are few equipments related to liquid nitrogen ultra-low temperature and phase change fractured coal seams, and there are few related equipment for similar simulation experiments on the effects of liquid nitrogen ultra-low temperature and phase change fractured coal seams and the effect on overlying rocks.

In view of the above technical requirements, it is necessary to propose a similar simulation experimental device and experimental method for liquid nitrogen ultra-low temperature and phase transition cracking effect.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a liquid nitrogen ultra-low temperature and phase transition cracking effect similar simulation experiment device and experimental method in view of the problems raised in the background technology, so as to improve the effect of liquid nitrogen ultra-low temperature and phase transition cracking on coal seams and the impact on overlying rock formations similar simulations.

For achieving the above object, the technical scheme adopted in the present invention is:

A liquid nitrogen ultra-low temperature and phase transition cracking effect similar simulation experimental device and experimental method are characterized in that: including a two-dimensional similar simulation test bench, a liquid nitrogen supply system, a similar material mixing system, a stress monitoring system, a microseismic monitoring system, and a borehole imaging system. system and XTDIC monitoring system.

Preferably, the two-dimensional similar simulation test bench includes a test bench base 42, the test bench base 42 is an I-shaped, and two similar test bench supports 41 are welded on the test bench base 42. The similar test bench supports 41 are respectively located at both ends of the test bench base 42, the two similar test bench supports 41 have a certain width, and the bottom beams 36 are welded to the lower ends of the two similar test bench supports 41. The upper end of the similar test bench support 41 is detachably connected with two baffles 8, and the two baffles 8 are symmetrically installed on the front and rear sides of the similar test bench support 41, so that the two similar test bench supports are 41. The bottom beam 36 and the two baffles 8 form an uncapped cubic space, the bottom of the cubic space is poured into the coal seam 27, and the top of the coal seam 27 is poured into the mixed overlying rock similar material 10; the Several support columns 35 are fixedly connected between the base 42 of the test bench and the bottom beam 36 .

Preferably, the two similar test bench supports 41 are made of channel steel, a plurality of support bolt holes 7 are formed on the two similar test bench supports 41 , and the two ends of the two baffles 8 are respectively provided with stoppers Plate bolt holes 801, two baffle plates 8 are installed between the two similar test bench supports 41 through bolts and nuts 9.

Two baffles 8 are installed between two similar test bench supports 41, the two described baffles 8 are symmetrical front and rear, while the similar test bench supports 41 have width, and the two baffles 8 are similar to the left and right symmetrical similar test bench supports. 41 and the bottom beam 36 form an uncapped cubic space, mix the similar material 10 of the overlying rock and pour it into the upper part of the coal seam 27, pass the bolts through the bracket bolt holes 7 of the similar test bench bracket 41 and the baffle plate of the baffle plate 8 Bolt hole 801, then tighten the nut 9, and proceed simultaneously on the left and right two similar test bench supports 41; the two baffles 8 are installed upward in sequence according to the thickness and final height of the similar material 10 of the overlying rock each time compaction.

Preferably, the liquid nitrogen supply system includes a self-pressurized liquid nitrogen tank 2, a universal wheel 1 is installed at the bottom of the self-pressurized liquid nitrogen tank 2, and an ultra-low temperature is connected to the top of the self-pressurized liquid nitrogen tank 2 Insulation pipe 6, the other end of the ultra-low temperature insulation pipe 6 is connected to the coal seam pre-buried liquid nitrogen pipeline 39 through the ultra-low temperature resistant butt valve 46, and the middle part of the coal seam pre-buried liquid nitrogen pipeline 39 is pre-buried in the coal seam 27, so The end of the coal seam pre-embedded liquid nitrogen pipeline 39 exposed to the coal seam is put into the liquid nitrogen collection tank 25, the coal seam pre-buried liquid nitrogen pipeline 39 is provided with a number of liquid nitrogen outflow outlets 3901, the self-pressurized liquid nitrogen tank A tank valve 3 and a pressure gauge 4 are installed on the top of 2, a liquid outlet valve 5 is installed on the ultra-low temperature thermal insulation pipe 6, and the liquid outlet valve 5 is set close to the self-pressurized liquid nitrogen tank 2. A liquid nitrogen shut-off valve 26 is installed on the nitrogen pipeline 39 , and the liquid nitrogen shut-off valve 26 is close to the liquid nitrogen collection tank 25 .

Preferably, an ultra-low temperature-resistant sealing ring is provided at the connection between the ultra-low temperature insulation pipe 6 and the ultra-low temperature resistant butt valve 46 .

Turn on the switch of the universal wheel 1 to push the self-pressurized liquid nitrogen tank 2 to a suitable position, connect the ultra-low temperature insulation pipe 6 with the ultra-low temperature resistant docking valve 46, and open the ultra-low temperature resistant docking valve 46 to allow the liquid nitrogen to pass through, and open the liquid nitrogen collection The tank 25 puts the end of the coal seam pre-buried liquid nitrogen pipeline 39 exposed to the coal seam into the tank, opens the liquid nitrogen shut-off valve 26, then opens the tank valve 3, and then opens the liquid outlet valve 5, and the liquid nitrogen flows from the self-pressurized liquid nitrogen tank. 2. After the pressure gauge 4, the liquid outlet valve 5, the ultra-low temperature insulation pipe 6, and then the ultra-low temperature resistant docking valve 46 to reach the coal seam pre-buried liquid nitrogen pipeline 39, and then the liquid nitrogen shut-off valve 26 flows into the liquid nitrogen collection tank 25. At this time, the liquid nitrogen is cut off The valve 26 is closed, and the liquid nitrogen flows into the coal seam from the liquid nitrogen outlet 3901. When the pressure gauge 4 continues to increase significantly, close the ultra-low temperature resistant docking valve 46, the tank valve 3 and the liquid outlet valve 5, and remove the liquid nitrogen collection tank 25. To the ultra-low temperature resistant docking valve 46, the ultra-low temperature insulation pipe 6 is disassembled, and the liquid nitrogen in the pipeline flows into the liquid nitrogen collection tank 25.

Liquid nitrogen has a very low temperature. First, it absorbs the heat of the coal seam to generate temperature stress, which causes the coal seam to crack, and the liquid nitrogen obtains heat from liquid to gas to generate a huge expansion force to further crack the coal seam.

Preferably, the similar material mixing system comprises a chassis 18, the bottom of the chassis 18 is mounted with chassis wheels 17, one side of the chassis 18 is connected with a movable armrest 11 through a bearing, and the top of the chassis 18 is connected with a bearing through a bearing. A rotating shaft 19, a similar material mixing chamber 13 is fixedly connected to the top of the rotating shaft 19, a stirrer 12 is installed in the similar material mixing chamber 13, and a motor 14 is installed on the top of the chassis 18, and the motor 14 is used for The rotating shaft 19 is driven, and the motor 14 is electrically connected with the controller 16 through the control wire 15 .

Preferably, the stirrer 12 includes a top plate 1203 , a stirring head 1202 is fixedly connected to the middle of the lower end surface of the top plate 1203 , and scraper blades 1201 are fixedly connected to the edge of the lower end surface of the top plate 1203 .

First, lift the agitator 12 together with the scraping blade 1201 and the stirring head 1202, pour the similar materials mixed in proportion into the similar material mixing chamber 13, put down the agitator 12, the scraping blade 1201, and the stirring head 1202, and operate the controller 16 The motor 14 starts to work through the control line 15, and the motor 14 drives the rotating shaft 19 and the similar material mixing chamber 13 to start to rotate. The stirring head 1202 stirs the similar material. After stirring evenly, an appropriate amount of water is added. When the mixing chamber 13 rotates, the stirring head 1202 keeps stirring while the scraping blade 1201 scrapes off the material attached to the inner wall of the mixing chamber 13 of similar materials. , lift the stirrer 12, scraper 1201, stirring head 1202, put down the similar material mixing chamber 13 through the movable handrail 11, lift the movable handrail 11 and return the similar material mixing chamber 13 after pouring out the material.

Preferably, the stress monitoring system includes a bottom wireless pressure sensor 40 installed between the coal seam 27 and the bottom beam 36 and several wired pressure sensors C embedded in the similar material 10 of the overburden, the bottom wireless pressure sensor 40 and The wired pressure sensor C is connected to a pressure signal receiving processor 44 through a pressure signal transmission line 45 , and the pressure signal receiving processor 44 is electrically connected to a pressure data display 43 .

The pressure acquisition is divided into two modules. One module is the bottom wireless pressure sensor 40 at the bottom of the coal seam 27, which receives and transmits the pressure changes caused by the ultra-low temperature of liquid nitrogen and the coal seam caused by phase transition to the pressure signal receiving processor 44 for preprocessing. And read it on the pressure data display 43; another module is when the overburden is constructed, the wired pressure sensor C is pre-buried in the overburden simulated by similar materials, and the liquid nitrogen ultra-low temperature and the phase change cause the fractured coal seam. As a result, the change of the force in the overlying stratum is received by the wired pressure sensor C, transmitted by the pressure signal transmission line 45 to the pressure signal receiving processor 44 for preprocessing, and displayed on the pressure data display 43, and the liquid nitrogen ultra-low temperature and phase change process can be obtained. Variation and redistribution of pressure in the middle coal seam and overlying strata as a whole and in the overlying strata.

Preferably, the microseismic monitoring system includes a microseismic sensor A embedded in the similar material 10 of the overlying rock, the microseismic sensor A is electrically connected with a microseismic signal processor 28, and the microseismic signal processor 28 passes the first signal A display screen 30 is connected to the transmission line 29 .

The microseismic sensor A receives the signals generated by the ultra-low temperature of liquid nitrogen and the cracking of the overlying rock layers and transmits them to the microseismic signal processor 28 for processing, and the processing results are displayed on the display screen 30 through the first signal transmission line 29; The microseismic sensor A placed in the overlying rock layer captures the vibration signal generated by the micro-fracture of the rock layer due to the pressure change process, analyzes and processes it, and obtains the "time, space, and intensity" information such as the time, location, magnitude, and energy of the rock layer fracture. According to the fusion and clustering of a large number of microseismic event information, the stability of the overlying coal seam fractured by liquid nitrogen is evaluated.

Preferably, the borehole imaging system includes a plurality of prefabricated boreholes B arranged in the similar material 10 of the overburden, and a borehole speculum 20 is installed in the prefabricated boreholes B, and the borehole speculum 20 passes through the first borehole B. The distance sensor 22 is connected to the second signal transmission line 21 , and the distance sensor 22 is connected to the borehole imaging controller 24 through the distance measurement signal line 23 .

Preferably, the distance sensor 22 and the distance measuring signal line 23 are slidably connected, and the distance measuring signal line 23 has a fixed pulley at the left and right lower parts of the distance sensor 22, and a fixed pulley above the middle.

Set by the borehole imaging controller 24, connect the foremost end of the borehole peep instrument 20 to be flush with the top of the prefabricated borehole B, select start acquisition on the borehole imaging controller 24, and slowly and uniformly extend the borehole peep instrument 20 into the prefabricated borehole B. Borehole B, the detected pictures and videos are transmitted to the borehole imaging controller 24 through the second signal transmission line 21 and the distance measuring signal line 23, and the distance sensor 22 judges the borehole peep instrument by sensing the length of the distance measuring signal line 23 through the pulley 20 reaches the distance, and the borehole imaging controller 24 generates continuous pictures through the pictures transmitted by the borehole speculum 20 and the distance fed back by the distance sensor 22 .

Preferably, the XTDIC system includes an XTDIC observation main body 37 and a compensation light source 34, a high-definition camera 38 is installed on the top of the XTDIC observation main body 37, and the high-definition camera 38 is electrically connected to the XTDIC system controller 33, and the XTDIC system controls The device 33 is connected with the XTDIC system analysis processor 31 through the connection line 32 , and the XTDIC system analysis processor 31 is electrically connected with the display screen 30 .

Preferably, the compensation light source 34 includes a tripod 3401, a light source is installed on the top of the tripod 3401, the front end of the light source is the light source search end 3404, the rear end of the light source is the light source control end 3403, the light source controls The end 3403 is connected with a high-definition camera 38 through a power line 3402, and the tripod 3401 is provided with an angle adjustment knob 3405, a height adjustment knob 3406 and a top fixing knob 3407; the height adjustment knob 3406 adjusts the height of the tripod 3401, and the top is fixed The knob 3407 fixes the light source parts such as the light source control end 3403, the light source search end 3404, and the angle control knob 3405 on the tripod 3401. The angle control knob 3405 adjusts the illumination angle of the light source of the light source search end 3404.

Before the observation, the surface of the coal seam 27 and the surface of the similar material 10 of the overlying rock layer is subjected to speckle threshold processing, and each part is connected, and the display screen 30, the XTDIC system analysis processor 31, and the XTDIC system controller 33 are turned on, and the display screen 30 is displayed. The software controls the XTDIC system analysis processor 31, and then the high-definition camera 38 is turned on through the XTDIC system controller 33, the compensation light source 34 is turned on, and the light source control end 3403 is adjusted. After the intensity of the picture observed on the display screen 30 is suitable, the light source stops adjusting, and the original position calibration is carried out before the coal seam caused by phase transition is not started; the high-definition camera 38 observes the signal and transmits it to the XTDIC system controller 33, and then through the The connection line 32 is transmitted to the XTDIC system analysis processor 31, and finally displayed on the display screen 30XTDIC software.

Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects:

(1) Liquid nitrogen ultra-low temperature and phase-change induced fracturing coal seam have not been applied in the field, and it is still the direction of further research to provide effective basis and theory for the field application of liquid nitrogen to the coal seam anti-permeability drainage gas field application. At the same time, the technical means for observing the structural damage changes before and after the action of liquid nitrogen on the coal body and during the action process are gradually improved. Complete.

(2) Due to the complex occurrence of coal seams, the natural coal seams contain moisture and the coal seams have different temperatures due to burial depth and surrounding rock permeability. Liquid nitrogen freezes and thaws the coal body in this case, which makes cracking and permeability increase. The effect of gas displacement is more obvious, which is more conducive to efficient gas drainage. The present invention simulates the occurrence of coal seams in the laboratory, performs liquid nitrogen permeability enhancement on the coal seams, and observes the effects of liquid nitrogen ultra-low temperature and phase change cracked coal seams and the influence on the overlying rock layers, so as to increase liquid nitrogen ultra-low temperature and phase change cracked coal seams. The field application of through-draining gas provides effective basis and theory.

(3) The previous devices used technical means to observe the coal samples frozen and thawed by liquid nitrogen, and then analyze the structural damage of the coal body. The effect of fission, as well as the displacement and deformation of the overlying strata, and the stress changes are monitored through pressure sensors, and the development and evolution laws of cracks are observed through preset boreholes.

Description of drawings

For a clearer understanding of the present invention, the present disclosure will be further introduced by combining the accompanying drawings and schematic embodiments of the description. The accompanying drawings and embodiments are used for explanation and do not constitute a limitation on the disclosure.

Fig. 1 is a similar simulation experiment system diagram of liquid nitrogen ultra-low temperature and phase transition cracking effect of the present invention;

Fig. 2 is the structural representation of agitator in the present invention;

3 is a schematic structural diagram of a wired pressure sensor pre-buried in an overlying rock formation in the present invention;

Fig. 4 is the structural representation of baffle plate in the present invention;

5 is a schematic structural diagram of a microseismic sensor in the present invention;

Fig. 6 is the structural representation of XTDIC observation system in the present invention;

FIG. 7 is a partial enlarged view of the coal seam pre-buried liquid nitrogen pipeline in the present invention.

As shown in the picture: universal wheel 1, self-pressurized liquid nitrogen tank 2, tank valve 3, pressure gauge 4, liquid outlet valve 5, ultra-low temperature insulation pipe 6, bracket bolt hole 7, baffle 8, baffle bolt hole 801, nut 9, overlying rock similar material 10, movable handrail 11, agitator 12, scraper 1201, stirring head 1202, top plate 1203, similar material mixing chamber 13, motor 14, control line 15, controller 16, chassis Wheel 17, chassis 18, rotating shaft 19, borehole peep instrument 20, transmission line 21, distance sensor 22, ranging signal line 23, borehole imaging controller 24, liquid nitrogen collection tank 25, liquid nitrogen shut-off valve 26, coal seam 27 , Microseismic signal processor 28, signal transmission line 29, display screen 30, XTDIC system analysis processor 31, connecting line 32, XTDIC system controller 33, compensation light source 34, tripod 3401, power line 3402, light source control terminal 3403, light source detector Illumination end 3404, angle adjustment knob 3405, height adjustment knob 3406, top fixing knob 3407, support column 35, bottom beam 36, XTDIC observation body 37, high-definition camera 38, coal seam pre-buried liquid nitrogen pipeline 39, liquid nitrogen outlet 3901 , Bottom wireless pressure sensor 40, similar test bench support 41, test bench base 42, pressure data display 43, pressure signal receiving processor 44, pressure signal transmission line 45, and ultra-low temperature resistant docking valve 46.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

A liquid nitrogen ultra-low temperature and phase transition cracking effect similar simulation experimental device and experimental method are characterized in that: a two-dimensional similar simulation test bench, including a liquid nitrogen supply system, a similar material mixing system, a stress monitoring system, a microseismic monitoring system, and a borehole imaging system and XTDIC monitoring system.

The two-dimensional similar simulation test bench includes a test bench base 42, the test bench base 42 is an I-shaped, and two similar test bench supports 41 are welded on the test bench base 42. The test bench supports 41 are respectively located at both ends of the test bench base 42, the two similar test bench supports 41 have a certain width, and the bottom beams 36 are welded to the lower ends of the two similar test bench supports 41. The upper end of the similar test bench support 41 is detachably connected with two baffles 8, and the two baffles 8 are respectively installed symmetrically on the front and rear sides of the similar test bench support 41, so that the two similar test bench supports 41, the bottom The beam 36 and the two baffles 8 form an uncapped cubic space, the bottom of the cubic space is poured into the coal seam 27, and the top of the coal seam 27 is poured into the mixed overlying rock similar material 10; Several support columns 35 are fixedly connected between the seat 42 and the bottom beam 36 . The two similar test bench supports 41 are made of channel steel, a number of support bolt holes 7 are provided on the two similar test bench supports 41, and the two ends of the two baffles 8 are respectively provided with baffle bolt holes. 801 , two baffles 8 are installed between the two similar test bench supports 41 through bolts and nuts 9 .

The liquid nitrogen supply system includes a self-pressurized liquid nitrogen tank 2, a universal wheel 1 is installed at the bottom of the self-pressurized liquid nitrogen tank 2, and an ultra-low temperature insulation pipe 6 is connected to the top of the self-pressurized liquid nitrogen tank 2. , the other end of the ultra-low temperature insulation pipe 6 is connected to the coal seam pre-buried liquid nitrogen pipeline 39 through the ultra-low temperature resistant butt valve 46, and the middle part of the coal seam pre-buried liquid nitrogen pipeline 39 is pre-buried in the coal seam, and the coal seam is pre-buried The end of the liquid nitrogen pipeline 39 exposed to the coal seam is put into the liquid nitrogen collection tank 25 , the coal seam pre-buried liquid nitrogen pipeline 39 is provided with several liquid nitrogen outflow outlets 3901 , and the self-pressurized liquid nitrogen tank 2 is installed on the top There is a tank valve 3 and a pressure gauge 4, a liquid outlet valve 5 is installed on the ultra-low temperature insulation pipe 6, and the liquid outlet valve 5 is set close to the self-pressurized liquid nitrogen tank 2, and the coal seam is pre-buried in the liquid nitrogen pipeline 39 A liquid nitrogen shut-off valve 26 is installed thereon, and the liquid nitrogen shut-off valve 26 is close to the liquid nitrogen collection tank 25 . An ultra-low temperature-resistant sealing ring is provided at the connection between the ultra-low temperature insulation pipe 6 and the ultra-low temperature resistant butt valve 46 .

Liquid nitrogen has a very low temperature. First, it absorbs the heat of the coal seam to generate temperature stress, which causes the coal seam to crack, and the liquid nitrogen obtains heat from liquid to gas to generate a huge expansion force to further crack the coal seam.

The similar material mixing system includes a chassis 18 , a chassis wheel 17 is mounted on the bottom of the chassis 18 , a movable armrest 11 is connected to one side of the chassis 18 through a bearing, and a rotating shaft 19 is connected to the top of the chassis 18 through a bearing. , a similar material mixing chamber 13 is fixedly connected to the top of the rotating shaft 19, a stirrer 12 is installed in the similar material mixing chamber 13, and a motor 14 is installed on the top of the chassis 18, and the motor 14 is used to drive the rotating shaft 19. The motor 14 is electrically connected to the controller 16 through the control wire 15. The agitator 12 includes a top plate 1203 , a stirring head 1202 is fixedly connected to the middle of the lower end surface of the top plate 1203 , and a scraper 1201 is fixedly connected to the edge of the lower end surface of the top plate 1203 .

The stress monitoring system includes a bottom wireless pressure sensor 40 installed between the coal seam 27 and the bottom beam 36 and several wired pressure sensors C embedded in the overburden similar material 10, the bottom wireless pressure sensor 40 and the wired pressure sensor C is connected to the pressure signal receiving processor 44 through the pressure signal transmission line 45 , and the pressure signal receiving processor 44 is electrically connected to the pressure data display 43 .

The pressure acquisition is divided into two modules. One module is the bottom wireless pressure sensor 40 at the bottom of the coal seam 27, which receives and transmits the pressure changes caused by the ultra-low temperature of liquid nitrogen and the coal seam caused by phase transition to the pressure signal receiving processor 44 for preprocessing. And read it on the pressure data display 43; another module is when the overburden is constructed, the wired pressure sensor C is pre-buried in the overburden simulated by similar materials, and the liquid nitrogen ultra-low temperature and the phase change cause the fractured coal seam. As a result, the change of the force in the overlying stratum is received by the wired pressure sensor C, transmitted by the pressure signal transmission line 45 to the pressure signal receiving processor 44 for preprocessing, and displayed on the pressure data display 43, and the liquid nitrogen ultra-low temperature and phase change process can be obtained. Variation and redistribution of pressure in the middle coal seam and overlying strata as a whole and in the overlying strata.

The microseismic monitoring system includes a microseismic sensor A embedded in the similar material 10 of the overlying rock layer, the microseismic sensor A is electrically connected with a microseismic signal processor 28, and the microseismic signal processor 28 is connected through a first signal transmission line 29. There is a display screen 30 .

The microseismic sensor A receives the signals generated by the ultra-low temperature of liquid nitrogen and the cracking of the overlying rock layers and transmits them to the microseismic signal processor 28 for processing, and the processing results are displayed on the display screen 30 through the first signal transmission line 29; The microseismic sensor A placed in the overlying rock layer captures the vibration signal generated by the micro-fracture of the rock layer due to the pressure change process, analyzes and processes it, and obtains the "time, space, and intensity" information such as the time, location, magnitude, and energy of the rock layer fracture. According to the fusion and clustering of a large number of microseismic event information, the stability of the overlying coal seam fractured by liquid nitrogen is evaluated.

The borehole imaging system includes a plurality of prefabricated boreholes B arranged in the similar material 10 of the overburden, in which a borehole speculum 20 is installed, and the borehole speculum 20 passes through a second signal transmission line 21 is connected with a distance sensor 22 , and the distance sensor 22 is connected with a borehole imaging controller 24 through a distance measuring signal line 23 . The distance sensor 22 and the distance measuring signal line 23 are slidably connected, and the distance measuring signal line 23 has a fixed pulley at the left and right lower parts of the distance sensor 22, and a fixed pulley above the middle.

The XTDIC system includes an XTDIC observation main body 37 and a compensation light source 34. A high-definition camera 38 is installed on the top of the XTDIC observation main body 37, and the high-definition camera 38 is electrically connected to the XTDIC system controller 33. The XTDIC system controller 33 passes The connection line 32 is connected with the XTDIC system analysis processor 31 , and the XTDIC system analysis processor 31 is electrically connected with the display screen 30 . The compensation light source 34 includes a tripod 3401, a light source is installed on the top of the tripod 3401, the front end of the light source is the light source search end 3404, and the rear end of the light source is the light source control end 3403, and the light source control end 3403 passes through. The power line 3402 is connected with a high-definition camera 38, and the tripod 3401 is provided with an angle adjustment knob 3405, a height adjustment knob 3406 and a top fixing knob 3407; the height adjustment knob 3406 adjusts the height of the tripod 3401, and the top fixing knob 3407 The light source parts such as the light source control end 3403 , the light source search end 3404 , and the angle control knob 3405 are fixed on the tripod 3401 , and the angle control knob 3405 adjusts the illumination angle of the light source of the light source search end 3404 .

Example 2

The working process of the present invention is:

First, assemble the two-dimensional similar simulation experimental bench, pass the bolts through the bracket bolt holes 7 of the similar experimental bench bracket 41 and the baffle bolt holes 801 of the baffle plate 8, then tighten the nuts 9, and the left and right similar experimental bench brackets 41 At the same time, the baffles 8 are installed on the similar experimental bench supports 41, the two baffles 8 are symmetrical in front and back, and at the same time, the similar experimental bench supports 41 have a width, and the two baffles 8 are symmetrical with the left and right similar experimental bench supports 41 and 41. The bottom beam 36 forms an uncapped cubic space, and the bottom wireless pressure sensors 40 are placed in series on the bottom beam 36 of the lowermost layer, and A4 paper is laid on the bottom wireless pressure sensor 40 to prevent the upper layer material from falling from the gap. A coal seam 27 is laid on top, and a coal seam pre-buried liquid nitrogen pipeline 39 is embedded in the coal seam 27 .

Next, configure similar simulation materials, according to the designed similarity ratio, weigh the sand, gypsum, and white powder of each layer of the overlying rock layer by layer, and lift the mixer 12 with 1201 scraper blade and 1202 mixing head, as shown in Figure 2. Start, pour the similar materials mixed in proportion into 1 similar material mixing chamber 3, put down the stirrer 12, 1201 scraper, 1202 stirring head, operate the controller 16 to start the motor 14 through the control line 15, and the motor 14 drives the rotation The shaft 19 together with the similar material mixing chamber 13 also starts to rotate, the stirring head 1202 stirs the similar material, and after stirring evenly, an appropriate amount of water is added. The scraping blade 1201 scrapes off the material adhering to the inner wall of the mixing chamber 13 of similar materials. After the stirring is appropriate, the controller 16 controls the motor 14 to stop stirring, and lifts the stirrer 12, scraping blade 1201, and stirring head 1202 through the movable handrail. 11 Put the similar material mixing chamber 13 down, pour the material in the similar material mixing chamber 13 into the coal seam 27 The two baffles 8 and the left and right symmetrical similar test bench supports 41 and the bottom beam 36 form an uncapped cubic space Inside, use tools to smooth and compact, after compaction, make joints in the direction of vertical baffle 8, the depth is about the lower layer, then sprinkle mica chips and then compact, continue to lay a layer of material, and place the A and C sensors as shown in Figure 1. In the position shown, the overlying stratum is buried during the laying process, and the C sensor is buried as shown in Figure 3. The B is pre-buried in the construction process and the round pipe is pre-buried. After the construction is completed, the round pipe is pulled out and the preset drilling is formed. Let it dry for the next experiment.

Next, observe the prefabricated borehole B that is not affected by the liquid nitrogen cracking, connect the borehole peep instrument 20, the transmission line 21, the distance sensor 22, the ranging signal line 23, and the borehole imaging controller 24 in sequence, and turn on the borehole. The switch of the borehole imaging controller 24 makes the borehole imaging system start to work, and the connection front end of the borehole peep instrument 20 is flush with the top of the prefabricated borehole B. The peeping instrument 20 is slowly and uniformly inserted into the prefabricated borehole B, and the detected pictures and videos are transmitted to the borehole imaging controller 24 through the transmission line 21 and the ranging signal line 23. The distance sensor 22 senses the length of the ranging signal line 23 through the pulley to judge the drill The penetration distance of the borehole peep instrument 20, the borehole imaging controller 24 generates continuous pictures through the pictures transmitted by the borehole peep instrument 20 and the distance fed back by the distance sensor 22, and the system is temporarily shut down after the acquisition is completed.

Then, set up the XTDIC system before observation, perform speckle threshold processing on the surface of the coal seam and the overlying rock layer, connect all parts, as shown in Figure 6, turn on the display screen 30, the XTDIC system analysis processor 31, and the XTDIC system controller. 33, and control the XTDIC system analysis processor 31 through the software on the display screen 30, and then turn on the high-definition camera 38 through the XTDIC system controller 33, turn on the compensation light source 34, and adjust the light source search end 3404 through the light source control end 3403 to hit the similar rock formation , the light intensity on the coal seam, after observing the light intensity of the picture on the display screen 30 is suitable, stop the light source adjustment, perform the original position calibration before the coal seam is fractured by phase transformation, and then keep the XTDIC monitoring system stable to ensure that the position cannot be moved.

Furthermore, to operate the stress monitoring system, as shown in FIG. 1, the pressure signal transmission line 45 is connected to the pressure signal receiving processor 44; the bottom wireless pressure sensor 40 transmits the signal to the pressure signal receiving processor 44 through wireless transmission; The data display 43 is connected and turned on with the pressure signal receiving processor 44, and the data should be stable when the fracturing is not started.

Finally, make the microseismic monitoring system operate, as shown in Figure 1, install and connect all parts; as shown in Figure 5, the signal line of the microseismic sensor A is connected to the microseismic signal processor 28, and the microseismic signal processor 28 is turned on to display On the screen 30, when the cracking has not started, the received data is empty.

After each observation system is turned on, as shown in Figures 1 and 7, turn on the switch of the universal wheel 1 to push the self-pressurized liquid nitrogen tank 2 to a suitable position, connect the ultra-low temperature insulation pipe 6 with the ultra-low temperature resistant docking valve 46, and open it. The ultra-low temperature-resistant docking valve 46 allows the liquid nitrogen to pass through, and the liquid nitrogen collection tank 25 is opened. Then open the liquid outlet valve 5, the liquid nitrogen from the self-pressurized liquid nitrogen tank 2, through the pressure gauge 4, through the liquid outlet valve 5, through the ultra-low temperature insulation pipe 6, and then through the ultra-low temperature resistant docking valve 46 to reach the coal seam pre-buried liquid nitrogen pipeline 39, by The liquid nitrogen shut-off valve 26 flows into the liquid nitrogen collection tank 25. At this time, the liquid nitrogen shut-off valve 26 is closed, and the liquid nitrogen flows into the coal seam from the liquid nitrogen outlet 3901; when the pressure gauge 4 continues to increase significantly, close the ultra-low temperature resistant docking valve 46 With the tank valve 3 and the liquid outlet valve 5, move the liquid nitrogen collection tank 25 to the ultra-low temperature resistant docking valve 46, disassemble the ultra-low temperature insulation pipe 6, and flow the liquid nitrogen in the pipeline into the liquid nitrogen collection tank 25.

Carry out continuous observation. After the data of the XTDIC monitoring system and the stress monitoring system are stable, stop the acquisition of the stress monitoring system, the microseismic monitoring system, and the XTDIC monitoring system, repeat the borehole imaging to observe the prefabricated borehole B, and turn on the borehole imaging control. Switch on and off the device 24 to make the borehole imaging system start working, connect the front end of the borehole peep instrument 20 to be flush with the top of the prefabricated borehole B, select to start acquisition on the borehole imaging controller 24, and slowly connect the borehole peep instrument 20 to the top of the prefabricated borehole B. Stretching into the prefabricated borehole B at a constant speed, the detected pictures and videos are transmitted to the borehole imaging controller 24 through the transmission line 21 and the ranging signal line 23, and the distance sensor 22 senses the length of the ranging signal line 23 through the pulley to judge the borehole peep instrument 20. The penetration distance, the borehole imaging controller 24 generates continuous pictures through the pictures transmitted by the borehole peep instrument 20 and the distance fed back by the distance sensor 22. Compared with the borehole shape before cracking, see the ultra-low temperature of liquid nitrogen and the cracking caused by phase transition. Effect and regularity of coal seam on the internal fractures of overlying rock.

The experimental device of the present invention can realize the two-dimensional similarity simulation of liquid nitrogen ultra-low temperature and phase-transition-induced fractured coal seams through the above process. Deformation and the development of internal fractures are tested to test the effect of liquid nitrogen ultra-low temperature resulting in thermal stress-induced coal seam fracturing and liquid nitrogen phase change resulting in huge expansion force fracturing coal seam effect.

Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the The technical solutions described in the foregoing embodiments may be modified, or some technical features thereof may be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. Liquid nitrogen ultralow temperature and phase change fracturing effect similar simulation experiment device and experiment method are characterized in that: the device comprises a two-dimensional analog simulation experiment table, a liquid nitrogen supply system, an analog material mixing system, a stress monitoring system, a microseismic monitoring system, a borehole imaging system and an XTDIC monitoring system.

2. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 1 are characterized in that: the two-dimensional similar simulation experiment table comprises an experiment table base (42), wherein the experiment table base (42) is I-shaped, two similar experiment table supports (41) are welded on the experiment table base (42), the two similar experiment table supports (41) are respectively positioned at two ends of the experiment table base (42), the two similar experiment table supports (41) have a certain width, a bottom cross beam (36) is welded at the lower end of the two similar experiment table supports (41), two baffles (8) are detachably connected at the upper end of the two similar experiment table supports (41), the two baffles (8) are respectively symmetrically arranged at the front side and the rear side of the similar experiment table supports (41), so that the two similar experiment table supports (41), the bottom cross beam (36) and the two baffles (8) form an unsealed cubic space, and a coal seam (27) is poured into the bottom of the cubic space, pouring mixed overburden-like material (10) into the top of the coal seam (27); a plurality of supporting columns (35) are fixedly connected between the experiment table base (42) and the bottom cross beam (36).

3. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 2 are characterized in that: the liquid nitrogen supply system comprises a self-pressurization liquid nitrogen tank (2), universal wheels (1) are installed at the bottom of the self-pressurization liquid nitrogen tank (2), the top of the self-pressurization liquid nitrogen tank (2) is connected with an ultra-low temperature heat preservation pipe (6), the other end of the ultra-low temperature heat preservation pipe (6) is connected with a coal seam pre-embedded liquid nitrogen pipeline (39) through an ultra-low temperature resistant butt joint valve (46), the middle part of the coal seam pre-embedded liquid nitrogen pipeline (39) is pre-embedded in a coal seam (27), the end of the coal seam pre-embedded liquid nitrogen pipeline (39) exposed out of the coal seam is placed into a liquid nitrogen collection tank (25), a plurality of liquid nitrogen outflow ports (3901) are arranged on the coal seam pre-embedded liquid nitrogen pipeline (39), a tank body valve (3) and a pressure gauge (4) are installed at the top of the self-pressurization liquid nitrogen tank (2), a liquid outlet valve (5) is installed on the ultra-low temperature heat preservation pipe (6) and is close to the self-pressurization liquid nitrogen tank (2), and a liquid nitrogen stop valve (26) is installed on the coal seam pre-buried liquid nitrogen pipeline (39), and the liquid nitrogen stop valve (26) is close to the liquid nitrogen collecting tank (25).

4. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 1 are characterized in that: the similar material mixing system comprises a chassis (18), a chassis wheel (17) is installed at the bottom of the chassis (18), a movable handrail (11) is connected to one side of the chassis (18) through a bearing, a rotating shaft (19) is connected to the top of the chassis (18) through a bearing, a similar material mixing cavity (13) is fixedly connected to the top of the rotating shaft (19), a stirrer (12) is installed in the similar material mixing cavity (13), a motor (14) is installed at the top of the chassis (18), the motor (14) is used for driving the rotating shaft (19), and the motor (14) is electrically connected with a controller (16) through a control line (15).

5. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 2 are characterized in that: the stress monitoring system comprises a bottom wireless pressure sensor (40) installed between a coal seam (27) and a bottom cross beam (36) and a plurality of wired pressure sensors (C) buried in overburden similar materials (10), wherein the bottom wireless pressure sensor (40) and the wired pressure sensors (C) are connected with a pressure signal receiving processor (44) through pressure signal transmission lines (45), and the pressure signal receiving processor (44) is electrically connected with a pressure data display (43).

6. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 2 are characterized in that: the microseismic monitoring system comprises a microseismic sensor (A) embedded in an overburden similar material (10), the microseismic sensor (A) is electrically connected with a microseismic signal processor (28), and the microseismic signal processor (28) is connected with a display screen (30) through a first signal transmission line (29).

7. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 1 are characterized in that: the drilling imaging system comprises a plurality of prefabricated drill holes (B) arranged in overburden similar materials (10), drilling peeping instruments (20) are installed in the prefabricated drill holes (B), the drilling peeping instruments (20) are connected with distance receptors (22) through second signal transmission lines (21), and the distance receptors (22) are connected with a drilling imaging controller (24) through ranging signal lines (23).

8. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 7 are characterized in that: the distance sensor (22) is connected with the distance measuring signal line (23) in a sliding mode, the distance measuring signal line (23) penetrates through the distance sensor (22), fixed pulleys are arranged on the left lower portion, the right lower portion and the middle upper portion of the distance sensor (22).

9. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 1 are characterized in that: the XTDIC system includes XTDIC observation main part (37) and compensation light source (34), high definition digtal camera (38) are installed at XTDIC observation main part (37) top, high definition digtal camera (38) electric connection has XTDIC system control ware (33), XTDIC system control ware (33) are connected with XTDIC system analysis treater (31) through connecting wire (32), XTDIC system analysis treater (31) electric connection has display screen (30).

10. The liquid nitrogen ultralow temperature and phase change cracking effect similar simulation experiment device and the experiment method according to claim 9 are characterized in that: the compensation light source (34) comprises a tripod (3401), a light source is installed at the top of the tripod (3401), the front end of the light source is a light source searchlighting end (3404), the rear end of the light source is a light source control end (3403), the light source control end (3403) is connected with a high-definition camera (38) through a power transmission line (3402), and an angle regulation knob (3405), a height adjustment knob (3406) and a top end fixing knob (3407) are arranged on the tripod (3401).

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