CN115013733A - Liquid nitrogen high-pressure multi-stage pulse fracturing overall-process true triaxial test system - Google Patents

Liquid nitrogen high-pressure multi-stage pulse fracturing overall-process true triaxial test system Download PDF

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CN115013733A
CN115013733A CN202210627225.4A CN202210627225A CN115013733A CN 115013733 A CN115013733 A CN 115013733A CN 202210627225 A CN202210627225 A CN 202210627225A CN 115013733 A CN115013733 A CN 115013733A
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liquid nitrogen
reaction kettle
pressure
cavity
coal sample
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林海飞
李博涛
李树刚
王裴
罗荣卫
魏宗勇
赵鹏翔
丁洋
秦雷
严敏
李莉
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Xian University of Science and Technology
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Xian University of Science and Technology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D1/00—Pipe-line systems
    • F17D1/08—Pipe-line systems for liquids or viscous products
    • F17D1/082—Pipe-line systems for liquids or viscous products for cold fluids, e.g. liquefied gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/18—Stationary reactors having moving elements inside
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L59/00—Thermal insulation in general
    • F16L59/02—Shape or form of insulating materials, with or without coverings integral with the insulating materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L59/00—Thermal insulation in general
    • F16L59/04—Arrangements using dry fillers, e.g. using slag wool which is added to the object to be insulated by pouring, spreading, spraying or the like
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D1/00—Pipe-line systems
    • F17D1/08—Pipe-line systems for liquids or viscous products
    • F17D1/14—Conveying liquids or viscous products by pumping
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D3/00—Arrangements for supervising or controlling working operations
    • F17D3/01—Arrangements for supervising or controlling working operations for controlling, signalling, or supervising the conveyance of a product
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D5/00—Protection or supervision of installations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
    • G01N3/12—Pressure testing

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  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
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Abstract

The invention discloses a liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system, which relates to the technical field of liquid nitrogen true triaxial fracturing coal body test systems. The experiment system can be used for researching the influence of different injection pressures and flow rates and the research of liquid nitrogen fracturing under different injection times, and is powerful in function and strong in practicability.

Description

Liquid nitrogen high-pressure multi-stage pulse fracturing overall-process true triaxial test system
Technical Field
The invention relates to the technical field of liquid nitrogen true triaxial fracturing coal body test systems, in particular to a liquid nitrogen high-pressure multistage pulse fracturing overall process true triaxial test system.
Background
Coal is the main energy and bottom energy of China, and is still a stabilizer and ballast stone which are safe for the energy of China for a long time. With the increasing mining intensity and the increasing mining depth of coal, shallow resources are increasingly exhausted, and many mines enter a deep mining stage. Most deep coal seams in China have the characteristics of high gas, high stress, low permeability and the like, particularly low permeability coal seams are generally developed in micropore structures, the gas adsorption capacity is strong, the desorption seepage resistance is large, and the coal seam gas pre-pumping effect is severely limited. Aiming at the current on-site underground coal seam fracturing process, a liquid nitrogen pulse fracturing mode is proposed by a scholarer, and under the combined action of water-ice phase change frost heaving force, liquid nitrogen gasification swelling force and damage of low-temperature liquid nitrogen to a coal body, macroscopic cracks and microscopic cracks are promoted to be expanded and communicated to form a crack network so as to increase the air permeability of the coal seam.
The liquid nitrogen has the characteristics of low temperature (-195.8 ℃), no pollution, simple preparation, wide raw material source and the like, and has a good application prospect in the aspect of improving the permeability of the coal bed. In order to research the change rule of the pore structure and the mechanical property of the coal body under the action of liquid nitrogen, students at home and abroad perform some laboratory fracturing tests of injecting liquid nitrogen into the coal body, but the injection pressure and the flow rate of the liquid nitrogen in the current test are lower, the cold insulation measures are not easy to control, the large temperature difference isolation is not easy to realize with cold insulation, the liquid nitrogen with low flow rate is rapidly heated and gasified after contacting with the wall surface of a conveying pipeline to form large pressure, and the test risk exists. In part high pressure liquid nitrogen injection pump, because the low boiling point (-147 ℃), high volatility and high phase transition expansibility (696 times) of liquid nitrogen, liquid nitrogen promotes the container through high pressure after entering injection pump injection container, impels the liquid nitrogen into the coal sample test piece, because the difference in temperature is great in middle container, is difficult for forming fine cold insulation measure and effect, can lead to container pressure shock rise, causes the damage to liquid nitrogen injection pump. In the process of injecting the coal sample liquid nitrogen, the liquid nitrogen is difficult to inject into the coal sample test piece in a liquid fluid state due to the low-temperature characteristic and the abnormally low boiling point of the liquid nitrogen. In the conventional test sensor, the conventional test sensor can generate low-temperature shrinkage deformation under the action of liquid nitrogen at ultralow temperature, the sensitivity is reduced, so that the conventional test sensor cannot be directly and normally measured, in the conventional liquid nitrogen fracturing coal sample test, only the damage deformation of the coal sample before and after liquid nitrogen fracturing is generally researched, the influence on the damage evolution rule caused by the action time and the injection speed of the liquid nitrogen is not clear, and the research on the influence mechanism of factors such as the reservoir temperature, the stress state and the like is still not deep enough. Therefore, it is necessary to provide a whole-process liquid nitrogen high-pressure multi-stage pulse test system which considers factors such as reservoir stress, temperature and the like and monitors factors such as temperature, pressure displacement and the like in a coal sample in real time so as to meet the technical requirements.
Disclosure of Invention
In order to solve the technical problems, the invention provides a true triaxial test system for the whole process of liquid nitrogen high-pressure multistage pulse fracturing, which considers factors such as reservoir stress, temperature and the like and can monitor factors such as temperature, pressure displacement and the like in a coal sample in real time.
In order to achieve the purpose, the invention provides the following scheme:
the invention provides a true triaxial test system for the whole process of liquid nitrogen high-pressure multistage pulse fracturing, which comprises a triaxial reaction kettle, wherein the triaxial reaction kettle comprises a reaction kettle cavity, a reaction kettle sealing cover and a triaxial loading rod; the top of the reaction kettle cavity is open, a reaction kettle inner cavity for containing a test piece is arranged inside the reaction kettle cavity, the reaction kettle sealing cover is arranged at the top of the reaction kettle cavity, and the periphery of the reaction kettle cavity is respectively provided with the three-axis loading rod;
the test piece comprises a square rubber cylinder, the top of the square rubber cylinder is open, the square rubber cylinder is used for containing a test coal sample, a coal sample loading plate is arranged around the outside of the square rubber cylinder, and the loading end of the triaxial loading rod is in contact with the coal sample loading plate; a square pressing plate is arranged at the top of the square rubber cylinder, and a heat-preservation cold cavity is arranged above the square pressing plate; the lower ends of a coaxially arranged liquid nitrogen injection rod and a nitrogen reverse discharge pipeline penetrate through the heat-preservation cold cavity and the square pressing plate and then extend into the test coal sample; the upper part of the liquid nitrogen injection rod is communicated with a liquid nitrogen tank; the heat-insulating material is arranged in the heat-insulating cold cavity;
the intelligent control system also comprises a control box, a data acquisition unit, a data analysis module, an intelligent control terminal and an explosion-proof control box; the data acquisition unit, the data analysis module and the intelligent control terminal are all arranged in the control box, and the data acquisition unit, the data analysis module and the intelligent control terminal are electrically connected with the explosion-proof control box through connecting wires.
Optionally, a pipeline pressing flange is arranged at the top of the heat-preservation cold cavity, the pipeline pressing flange is detachably connected with the top of the heat-preservation cold cavity, and a heat-insulation baffle is arranged between the pipeline pressing flange and the heat-preservation material; the heat insulation material is heat insulation cotton yarn.
Optionally, a sealing assembly is arranged between the heat-preservation cold cavity and the nitrogen reverse-discharging pipeline.
Optionally, packing locking threads are arranged on the outer wall of the lower portion of the nitrogen reverse-discharging pipeline, and the nitrogen reverse-discharging pipeline is connected with the square pressing plate through the packing locking threads.
Optionally, a coal sample temperature and pressure measuring assembly and a heating temperature control assembly are arranged at the bottom of the cavity of the reaction kettle, and the coal sample temperature and pressure measuring assembly and the heating temperature control assembly are electrically connected with the data collector.
Optionally, the liquid nitrogen tank is communicated with an inlet of a plunger liquid nitrogen pump through a liquid nitrogen pump liquid inlet pipeline, and an outlet of the plunger liquid nitrogen pump is communicated with the liquid nitrogen injection rod; the plunger liquid nitrogen pump is in transmission connection with an explosion-proof motor, and the explosion-proof motor is electrically connected with the explosion-proof control box.
Optionally, a control pipeline of the plunger liquid nitrogen pump is sequentially provided with a second check valve, a damper, a vaporizer, a pressure gauge and a first check valve; the first check valve is electrically connected with the explosion-proof control box.
Optionally, a displacement sensor and an acoustic emission sensor are arranged on a loading rod of the three-axis testing machine; the loading rod of the three-axis testing machine is used for providing load for the three-axis loading rod; the displacement sensor and the acoustic emission sensor are electrically connected with the data acquisition unit.
Optionally, the system further comprises a system base, and the triaxial reaction kettle is arranged on the system base.
Optionally, a low-temperature-resistant sealant is arranged between the bottom of the square pressing plate and the top of the test coal sample.
Compared with the prior art, the invention has the following technical effects:
1. the liquid nitrogen injection rod is a vacuum heat insulation pipe, the interlayer design is adopted, the liquid nitrogen injection pipeline is arranged in the middle of the liquid nitrogen injection rod, the interlayer is a nitrogen reverse discharge pipeline, a through pipeline is formed, the liquid nitrogen is ensured to be injected into the coal sample in a fluid state, high-pressure nitrogen vaporized by the liquid nitrogen can be discharged, and the problem that the liquid nitrogen is difficult to be injected into the coal sample test piece in a liquid fluid state can be effectively solved.
2. The cold cavity that keeps warm carries out cold insulation cotton yarn packing parcel liquid nitrogen injection pole, treats that thermal-insulated cotton yarn fills up to install retaining ring and O type circle after being full of and seals, carries out the compaction to cold insulation cotton yarn with thermal-insulated baffle, and it is fixed to install pipeline hold-down flange and adjusting nut in proper order on the thermal-insulated baffle and carry out secondary locking to the injection pole, and it is fixed to carry out circumference locking to the cold cavity that keeps warm through top locking double-screw bolt. In addition, a polyurethane heat insulation layer is arranged on the outer side of the triaxial reaction kettle, so that temperature transfer exchange is reduced by minimum heat exchange in the liquid nitrogen injection process, and liquid nitrogen consumption is reduced.
3. Triaxial loading and temperature heating can be carried out, and a whole-process liquid nitrogen high-pressure multistage pulse fracturing experiment which considers factors such as reservoir stress and temperature and monitors factors such as temperature and pressure displacement in a coal sample in real time can be carried out.
4. The problem that the acoustic emission sensor cannot directly contact with the coal sample is solved by using the acoustic emission guide rod, and the acoustic emission guide rod is embedded in the triaxial loading rod and symmetrically arranged. The liquid nitrogen injection fracturing coal sample internal crack propagation and temperature and pressure real-time monitoring of the whole process can be realized through the coal sample temperature and pressure measuring component.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a true triaxial test system in the whole process of liquid nitrogen high-pressure multi-stage pulse fracturing;
FIG. 2 is a schematic structural diagram of a triaxial reaction vessel in a true triaxial test system in the whole process of liquid nitrogen high-pressure multistage pulse fracturing;
FIG. 3 is a schematic structural diagram of a cold insulation injection assembly in the true triaxial test system in the whole process of liquid nitrogen high-pressure multi-stage pulse fracturing;
FIG. 4 is a schematic view of a top view structure of the true triaxial test system in the whole process of liquid nitrogen high-pressure multi-stage pulse fracturing.
Description of reference numerals: 1. a control box; 2. a data acquisition unit; 3. a data analysis module; 4. an intelligent control terminal; 5. a displacement sensor; 6. an acoustic emission sensor; 7. a three-axis testing machine; 8. a first check valve; 9. a pressure gauge; 10. a triaxial reaction kettle; 11. a nitrogen reverse discharge pipeline; 12. a liquid nitrogen injection rod; 13. a cabin penetration assembly; 14. testing a coal sample; 15. a flow meter; 16. a vaporizer; 17. a damper; 18. a second check valve; 19. a liquid inlet pipeline of a liquid nitrogen pump; 20. a liquid nitrogen tank; 21. a plunger liquid nitrogen pump; 22. an explosion-proof motor; 23. an explosion-proof control box; 24. connecting an electric wire; 25. a coal sample temperature and pressure measuring component; 26. heating the temperature control assembly; 27. a system base; 28. a three-axis loading rod; 29. a reaction kettle cavity; 30. sealing the reaction kettle; 31. adjusting the nut; 32 cold-insulation and heat-insulation cotton yarns; 33. m36 hex screw; 34. a square rubber cylinder; 35. a coal sample loading plate; 36. the inner cavity of the reaction kettle; 37. a rubber cylinder bottom plate supporting column; 38. a rubber cylinder bottom plate; 39. a set screw; 40. a gas-permeable joint; 41. a square pressing plate; 42. packing locking threads; 43. a seal assembly; 44. a heat preservation cold cavity; 45. a retainer ring; 46. an O-shaped ring; 47. a top locking stud; 48. a heat insulation baffle; 49. the pipeline compresses the flange; (ii) a 50. M12 inner angle screws; 51. a lateral loading oil cylinder; 52. an axial loading oil cylinder; 53. an O-shaped ring of the reaction kettle.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 4, the present embodiment provides a true triaxial test system in the whole process of liquid nitrogen high-pressure multistage pulse fracturing, which includes a triaxial reaction vessel 10, where the triaxial reaction vessel 10 includes a reaction vessel cavity 29, a reaction vessel sealing cover 30 and a triaxial loading rod 28; the top of the reaction kettle cavity 29 is open, a reaction kettle inner cavity 36 for containing a test piece is arranged in the reaction kettle cavity 29, a reaction kettle sealing cover 30 is arranged at the top of the reaction kettle cavity 29, and three-axis loading rods 28 are respectively arranged on the periphery of the reaction kettle cavity 29; the test piece comprises a square rubber cylinder 34, the top of the square rubber cylinder 34 is open, the square rubber cylinder 34 is used for containing the test coal sample 14, a coal sample loading plate 35 is arranged on the periphery of the outside of the square rubber cylinder 34, and the loading end of the triaxial loading rod 28 is in contact with the coal sample loading plate 35; a square pressing plate 41 is arranged at the top of the square rubber cylinder 34, and a heat-preservation cold cavity 44 is arranged above the square pressing plate 41; the lower ends of a liquid nitrogen injection rod 12 and a nitrogen reverse discharge pipeline 11 which are coaxially arranged penetrate through a heat preservation cold cavity 44 and a square pressing plate 41 and then extend into a test coal sample 14; the upper part of the liquid nitrogen injection rod 12 is communicated with a liquid nitrogen tank 20; the heat-insulating material is arranged in the heat-insulating cold cavity 44; the intelligent control system also comprises a control box 1, a data acquisition unit 2, a data analysis module 3, an intelligent control terminal 4 and an explosion-proof control box 23; data collection station 2, data analysis module 3 and intelligent control terminal 4 all set up in control box 1, and data collection station 2, data analysis module 3 and intelligent control terminal 4 are connected with explosion-proof control box 23 electricity through connecting wire 24.
In a more specific embodiment, a reaction vessel O-ring 53 is disposed between the reaction vessel cavity 29 and the reaction vessel sealing cover 30, and is connected thereto by M36 hex screws 33.
The bottom of the square pressure plate 41 is provided with a plurality of gas permeable joints 40 to remove excess or overpressure gas during the installation, sealing and testing of the sample coal.
The bottom of the square rubber cylinder 34 is provided with a rubber cylinder bottom plate 38, the rubber cylinder bottom plate 38 is arranged between the bottom of the coal sample loading plate 35 and the top of the rubber cylinder bottom plate 38, and the rubber cylinder bottom plate 38 is used for fixing the position of the test coal sample 14. And a rubber cylinder bottom plate supporting column 37 is arranged around the rubber cylinder bottom plate 38, and the bottom of the rubber cylinder bottom plate supporting column 37 is connected with the bottom in the reaction kettle cavity 29 so as to support the square rubber cylinder 34.
A pipeline pressing flange 49 is arranged at the top of the heat preservation cold cavity 44, the pipeline pressing flange 49 is connected with the top of the heat preservation cold cavity 44 through M12 inner angle screws 50, and a heat insulation baffle 48 is arranged between the pipeline pressing flange 49 and a heat preservation material; the heat-insulating material is heat-insulating cotton yarn. More specifically, the top of the outer side of the pipeline pressing flange 49 is a flange plate, the lower part of the flange plate is provided with a cover-shaped structure, the flange plate is connected with the top of the heat preservation cold cavity 44 through an M12 inner angle screw 50, a sealing ring is arranged between the outer wall of the cover-shaped structure and the inner wall of the heat preservation cold cavity 44, and the heat insulation baffle plate 48 is arranged in the cover-shaped structure. Furthermore, an adjusting nut 50 is arranged between the top of the heat insulation baffle plate 48 and the inner top of the cover type structure, and the adjusting nut 50 is in threaded connection with the nitrogen back-exhaust pipeline 11.
The upper part of the outer wall of the heat-preservation cold cavity 44 is provided with a retainer ring 45 and an O-shaped ring 46 for sealing with the triaxial reaction kettle 10.
And a sealing assembly 43 is arranged between the heat-preservation cold cavity 44 and the nitrogen back-discharge pipeline 11.
Packing locking threads 42 are arranged on the outer wall of the lower portion of the nitrogen reverse exhaust pipeline 11, and the nitrogen reverse exhaust pipeline 11 is connected with the square pressing plate 41 through the packing locking threads 42.
The bottom of the reaction kettle cavity 29 is provided with a coal sample temperature and pressure measuring component 25 and a heating temperature control component 26, and both the coal sample temperature and pressure measuring component 25 and the heating temperature control component 26 are electrically connected with the data acquisition unit 2. More specifically, the coal sample temperature and pressure measuring assembly 25 penetrates through the bottom of the rubber cylinder bottom plate 38 and the bottom of the square rubber cylinder 34, the heating temperature control assembly 26 penetrates through the reaction kettle cavity 29, and the heating temperature control assembly 26 is located around the rubber cylinder bottom plate 38.
The liquid nitrogen tank 20 is communicated with the inlet of the plunger liquid nitrogen pump 21 through a liquid nitrogen pump liquid inlet pipeline 19, and the outlet of the plunger liquid nitrogen pump 21 is communicated with the liquid nitrogen injection rod 12; the plunger liquid nitrogen pump 21 is in transmission connection with the explosion-proof motor 22, and the explosion-proof motor 22 is electrically connected with the explosion-proof control box 23.
A control pipeline of the plunger liquid nitrogen pump 21 is sequentially provided with a second check valve 18, a damper 17, a vaporizer 16, a pressure gauge 9 and a first check valve 8; the first check valve 8 is electrically connected to the explosion-proof control box 23.
A loading rod of the triaxial testing machine 7 is provided with a displacement sensor 5 and an acoustic emission sensor 6; the loading rod of the triaxial tester 7 is used for providing load to the triaxial loading rod 28; the displacement sensor 5 and the acoustic emission sensor 6 are both electrically connected with the data acquisition unit 2. Furthermore, a lateral loading cylinder 51 of the triaxial testing machine 7 is simultaneously provided with the displacement sensor 5 and the acoustic emission sensor 6, another lateral loading cylinder 51 of the triaxial testing machine 7 is provided with the acoustic emission sensor 6, and an axial loading cylinder 52 of the triaxial testing machine 7 is provided with the displacement sensor 5.
The liquid nitrogen high-pressure multi-stage pulse fracturing whole-process true triaxial test system in the embodiment further comprises a system base 27, and the triaxial reaction kettle 10 is arranged on the system base 27.
And the low-temperature-resistant sealant is arranged between the bottom of the square pressing plate 41 and the top of the test coal sample 14.
The outlet end of the nitrogen back-discharge pipeline 11 is sequentially provided with a pressure gauge 9 and a first check valve 8.
The anti-explosion control box 23 is provided with a pressure gauge 9 and a flow meter 15 for monitoring the pressure and flow of nitrogen in the test process.
In a further specific embodiment, the liquid nitrogen injection rod 12 is a vacuum heat insulation pipe, and adopts an interlayer design, the middle is a liquid nitrogen injection pipeline, and the interlayer is a nitrogen reverse discharge pipeline 11 to form a through pipeline, so that the liquid nitrogen is ensured to be injected into the coal sample in a fluid state, high-pressure nitrogen vaporized by the liquid nitrogen can also be discharged, and the problem that the liquid nitrogen is difficult to be injected into the coal sample test piece in a liquid fluid state can be effectively solved.
The reaction kettle cavity 29 is provided with a plurality of cabin penetrating components 13 in a penetrating mode, the cabin penetrating components 13 are used for introducing connecting wires into the reaction kettle inner cavity 36 from the outside, interfaces and air inlet interfaces can be reserved, external air inlet pipelines can be matched with the air-permeable connector 40, and a coal sample permeability test experiment and experiments with other functions can be carried out subsequently.
The coal sample temperature and pressure measuring assembly 25 is arranged in 9 temperature and pressure measuring holes, 3 pressure and temperature probes are arranged in each drilling hole in the vertical direction, 3 points 9 are 27 measuring points in total, and the all-dimensional three-dimensional real-time monitoring of the internal pressure and temperature of the coal sample in the whole process of liquid nitrogen fracturing can be realized.
Cold-insulated cotton yarn 32 of cold insulation of keeping warm 44 fills, and it is sealed to wait to install retaining ring 45 and O type circle 46 after thermal-insulated cotton yarn fills up, compacts cold-insulated cotton yarn 32 with thermal-insulated baffle 48, installs pipeline hold-down flange 49 and adjusting nut 50 in proper order on the thermal-insulated baffle 48 and carries out secondary locking fixedly to the injection pole, carries out circumference locking fixedly to cold-insulated chamber 44 through top locking double-screw bolt, and M12 interior angle screw 50 carries out axial locking fixedly. The reaction kettle sealing cover 30 and the reaction kettle cavity 29 are sealed through the reaction kettle O-shaped ring 53, and the M36 hexagon screw 33 is used for locking the two. In addition, a heat insulating layer is arranged on the outer side of the triaxial reactor 10 to ensure that the temperature transfer exchange is reduced with minimum heat exchange and the liquid nitrogen consumption is reduced in the liquid nitrogen injection process.
The coal sample size was 150mm by 150 mm; the O-shaped ring is 46-shaped, the barrel is made of low-temperature-resistant polytetrafluoroethylene, the axial experimental force is 1500kN, the three-axis maximum loading pressure is 25MPa, the simulation temperature of the test piece is-196-200 ℃, and the whole-process liquid nitrogen high-pressure multi-stage pulse fracturing experiment which considers factors such as reservoir stress, temperature and the like and monitors factors such as temperature, pressure displacement and the like in a coal sample in real time can be carried out.
The liquid nitrogen injection pump adopts an explosion-proof motor 22 control system to control the motor rotating speed, the explosion-proof motor 22 adopts a servo motor, and then the injection speed of the liquid nitrogen can be accurately adjusted and the injection amount of the liquid nitrogen can be accurately measured. The plunger liquid nitrogen pump 21 is a horizontal piston type vacuum pump, and has a flow rate: 0-70L/h (gasification amount), inlet pressure: 0.02-1.2 MPa, outlet pressure: 0-45 MPa, design temperature: 196 ℃ below zero.
The system adopts a low-temperature self-pressurization liquid nitrogen tank 20 to store industrial liquid nitrogen, the capacity of the liquid nitrogen tank 20 is 1000L, the self-pressurization liquid nitrogen tank 20 is made of high-quality stainless steel, and the container is provided with a pressure boosting system and can generate pressure to continuously discharge liquid. The control system mainly comprises a liquid inlet/outlet valve, a pressure increasing valve, an emptying valve, a double safety valve, a liquid level meter, a pressure gauge 9 and 4 trundles which are independently braked.
The device is provided with a displacement sensor 5 and an acoustic emission sensor 6, wherein the acoustic emission sensor 6 and the displacement sensor 5 are embedded in a triaxial loading rod 28, the acoustic emission sensors 6 are symmetrically arranged, and the displacement sensors 5 are adjacently arranged.
Before the experiment, the core of the experimental coal sample is firstly made, the experimental coal sample is a cubic coal sample of 150 × 150mm, then the test piece is drilled with holes through a drill, and the depth of the holes with the diameter of 15mm is 70 mm. 9 temperature measurement pressure taps are opened to drilling below, pressure tap 3 x 3 arranges, after the coal sample preparation was accomplished, put the coal sample inside the packing element, the injection pipe passes through square clamp plate 41 embedding experiment coal sample, behind injection pipe and the roof combination subassembly, tightly laminate the coal sample test piece, packing locking screw 42 fixes tight injection pipe, then seal the gap between square clamp plate 41 and the packing element through sealed glue of nai low temperature, later place the subassembly and dry in shady and cool ventilation department, the laying time is about 36 hours, after sealed glue dries, place square packing element 34 on packing element bottom plate 38 in triaxial reation kettle 10, packing element bottom plate 38 carries out the packing element position through packing element bottom plate support column 37 and packing element bottom plate 38 of below and fixes. And in the installation process, the air-permeable joint 40 is opened, and the air-permeable joint 40 is closed after the position of the rubber cylinder is fixed. And then placing the coal sample temperature and pressure measuring component 25 in 9 temperature and pressure measuring holes, wherein 3 pressure and temperature probes are respectively arranged in each drilling hole in the vertical direction, 3 points 9 are 27 measuring points in total, and the all-dimensional three-dimensional real-time monitoring of the internal pressure and temperature of the coal sample in the whole process of liquid nitrogen fracturing can be realized. After the packing element rigidity is accomplished, seal assembly 43, cold cavity 44 that keeps warm passes the injection pipeline in proper order and installs, cold cavity 44 that keeps warm carries out cold insulation cotton yarn 32 and fills, it seals to wait to insulate against heat after cotton yarn fills up to install retaining ring 45 and O type circle 46, it compacts cold insulation cotton yarn 32 to keep warm with thermal-insulated baffle 48, it is fixed to install pipeline hold-down flange 49 and adjusting nut 50 in proper order on the thermal-insulated baffle 48 and carry out secondary locking to the injection pole, it is fixed to carry out circumference locking to cold cavity 44 that keeps warm through top locking double-screw bolt, M12 interior angle screw 50 carries out axial locking fixed. The reaction kettle sealing cover 30 and the reaction kettle cavity 29 are sealed through the reaction kettle O-shaped ring 53, and the M36 hexagon screw 33 is used for locking the two. In addition, a thermal insulation layer is disposed on the outside of the tri-axial reactor 10 to ensure that temperature transfer exchange is reduced with minimal heat exchange during liquid nitrogen injection. After the coal sample is installed, water is injected into the inner cavity 36 of the reaction kettle for pressure measurement through the cabin penetrating assembly, the three-axis testing machine 7 is opened after the pressure measurement is finished, the lateral loading oil cylinder 51 and the axial loading oil cylinder 52 jointly load a loading plate on the outer side of a rubber cylinder of the test piece through the three-axis loading rod 28, the maximum main stress and the middle main stress are provided, the inner cavity 36 of the reaction kettle is loaded with purified water pressure, a pressure enclosing and sealing environment is provided for the rubber cylinder outside the test piece, and the heating temperature control assembly 26 is opened to simulate the temperature of the reservoir.
And after the ground stress loading system and the coal sample are installed, debugging and running of the liquid nitrogen injection system are carried out, firstly, a liquid nitrogen tank 20 is opened to feed liquid, a liquid nitrogen pump fills liquid into the container, an emptying valve is opened firstly, a metal hose for transfusion is connected to a liquid inlet valve, the liquid inlet valve is opened, the liquid nitrogen can be added from the liquid inlet valve, a pressure gauge 9 is observed, and after the liquid filling is finished, the liquid inlet valve is closed. The anti-explosion control box 23 and the anti-explosion motor 22 are started, the rotating speed of the motor is adjusted, the rotating speed is increased to be more than 600rpm, then the damper 17, the vaporizer 16 and the check valve are sequentially opened to pre-cool the liquid nitrogen pump, meanwhile, the data acquisition device 2, the data analysis module 3, the intelligent control terminal 4, the pressure gauge 9, the flow meter 15, the displacement sensor 5 and the acoustic emission sensor 6 of the control box 1 are started to perform data acquisition and analysis, and when an external pipeline of the liquid nitrogen pump frosts for 3 minutes, the liquid nitrogen pump is indicated to be completely cooled. And subsequently, a liquid inlet valve is opened to perform a liquid nitrogen high-pressure multi-stage pulse fracturing whole-process experiment under true triaxial loading, a pressure gauge 9 and a check valve on a reverse discharge pipeline are opened in the experiment process to form a through pipeline, so that liquid nitrogen is ensured to be injected into a coal sample in a fluid state, and high-pressure nitrogen vaporized by the liquid nitrogen can also be discharged.
According to the liquid nitrogen high-pressure multistage pulse fracturing whole-process true triaxial test system, a sample coal rock is prefabricated and drilled, high-pressure liquid nitrogen is injected into the prefabricated drilled hole, the sample is fractured through the high-pressure liquid nitrogen, the fracture strike and expansion can be related to the depth and position of a fracture induction hole and the injection of the high-pressure liquid nitrogen, the fracture strike and fracture strike of a fracture can be detected in real time through a pre-embedded sound wave probe, the displacement and strain of the coal rock are detected through a displacement-strain monitoring technology system, the temperature and pressure of a coal sample in the fracturing whole process are detected through a coal sample temperature and pressure measuring assembly 25, and experimental data are recorded and analyzed through a data collector 2, a data analysis module 3 and an intelligent control terminal 4 of a control box 1. The experiment system can be used for researching the influence of different injection pressures and flow rates and the research of liquid nitrogen fracturing under different injection times, and is powerful in function and strong in practicability.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference signs in the claims are not intended to be construed as limiting the claim concerned.
The principle and the implementation mode of the present invention are explained by applying specific examples in the present specification, and the above descriptions of the examples are only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system is characterized by comprising a triaxial reaction kettle, wherein the triaxial reaction kettle comprises a reaction kettle cavity, a reaction kettle sealing cover and a triaxial loading rod; the top of the reaction kettle cavity is open, a reaction kettle inner cavity for containing a test piece is arranged inside the reaction kettle cavity, the reaction kettle sealing cover is arranged at the top of the reaction kettle cavity, and the periphery of the reaction kettle cavity is respectively provided with the three-axis loading rod;
the test piece comprises a square rubber cylinder, the top of the square rubber cylinder is open, the square rubber cylinder is used for containing a test coal sample, a coal sample loading plate is arranged around the outside of the square rubber cylinder, and the loading end of the triaxial loading rod is in contact with the coal sample loading plate; a square pressing plate is arranged at the top of the square rubber cylinder, and a heat-preservation cold cavity is arranged above the square pressing plate; the lower ends of a coaxially arranged liquid nitrogen injection rod and a nitrogen reverse discharge pipeline penetrate through the heat-preservation cold cavity and the square pressing plate and then extend into the test coal sample; the upper part of the liquid nitrogen injection rod is communicated with a liquid nitrogen tank; the heat-insulating material is arranged in the heat-insulating cold cavity;
the intelligent control system also comprises a control box, a data acquisition unit, a data analysis module, an intelligent control terminal and an explosion-proof control box; the data acquisition unit, the data analysis module and the intelligent control terminal are all arranged in the control box, and the data acquisition unit, the data analysis module and the intelligent control terminal are electrically connected with the explosion-proof control box through connecting wires.
2. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein a pipeline pressing flange is arranged at the top of the heat-preservation cold cavity, the pipeline pressing flange is detachably connected with the top of the heat-preservation cold cavity, and a heat insulation baffle is arranged between the pipeline pressing flange and the heat-preservation material; the heat insulation material is heat insulation cotton yarn.
3. The full-process true triaxial test system for liquid nitrogen high-pressure multistage pulse fracturing according to claim 2, wherein a sealing assembly is arranged between the heat-preservation cold cavity and the nitrogen inverted-discharge pipeline.
4. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein packing locking threads are arranged on the outer wall of the lower portion of the nitrogen inverted pipeline, and the nitrogen inverted pipeline is connected with the square pressing plate through the packing locking threads.
5. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein a coal sample temperature and pressure measuring assembly and a heating temperature control assembly are arranged at the bottom of the reaction kettle cavity, and both the coal sample temperature and pressure measuring assembly and the heating temperature control assembly are electrically connected with the data acquisition unit.
6. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein the liquid nitrogen tank is communicated with an inlet of a plunger liquid nitrogen pump through a liquid nitrogen pump liquid inlet pipeline, and an outlet of the plunger liquid nitrogen pump is communicated with the liquid nitrogen injection rod; the plunger liquid nitrogen pump is in transmission connection with an explosion-proof motor, and the explosion-proof motor is electrically connected with the explosion-proof control box.
7. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 6, wherein a control pipeline of the plunger liquid nitrogen pump is sequentially provided with a second check valve, a damper, a vaporizer, a pressure gauge and a first check valve; the first check valve is electrically connected with the explosion-proof control box.
8. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein a displacement sensor and an acoustic emission sensor are arranged on a loading rod of a triaxial test machine; the loading rod of the three-axis testing machine is used for providing load for the three-axis loading rod; the displacement sensor and the acoustic emission sensor are electrically connected with the data acquisition unit.
9. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, further comprising a system base, wherein the triaxial reaction vessel is arranged on the system base.
10. The liquid nitrogen high-pressure multistage pulse fracturing overall-process true triaxial test system according to claim 1, wherein a low-temperature-resistant sealant is arranged between the bottom of the square pressure plate and the top of the test coal sample.
CN202210627225.4A 2022-06-06 2022-06-06 Liquid nitrogen high-pressure multi-stage pulse fracturing overall-process true triaxial test system Pending CN115013733A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115078121A (en) * 2022-08-23 2022-09-20 太原理工大学 Indirect visual rock multi-cluster fracturing indoor test device and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115078121A (en) * 2022-08-23 2022-09-20 太原理工大学 Indirect visual rock multi-cluster fracturing indoor test device and method
CN115078121B (en) * 2022-08-23 2022-12-09 太原理工大学 Indirect visual rock multi-cluster fracturing indoor test device and method

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