Test apparatus for determining type I fracture parameters of coal and rock mass under supercritical carbon dioxide.

Abstract

The invention belongs to the technical field of geological storage of carbon dioxide and efficient exploitation of unconventional natural gas, and is a test device for determining type I fracture parameters of coal rock mass under the action of supercritical carbon dioxide; the device comprises a loading system, a carbon dioxide fluid injection and recovery system, a pressure and temperature control system, a specimen positioning system, a specimen crack displacement monitoring system and a data acquisition system; the device can simulate the effect of supercritical carbon dioxide on type I fracture behavior of coal rock mass under a high ground stress environment, and conduct experimental research on type I fracture characteristics of coal rock mass under conditions of supercritical carbon dioxide at different temperatures and pressures and different infiltration times; a three-point bending loading test of the specimen is realized through a three-point bending loading frame; and the problem that the existing equipment cannot accurately determine the opening degree of the preset crack tip of the coal rock specimen.

Description

Technical Field

[0001] The invention belongs to the technical field of geological storage of carbon dioxide and efficient exploitation of unconventional natural gas, and relates to a test device for determining type I fracture parameters of coal rock mass under the action of supercritical carbon dioxide. Background Art

[0002] Supercritical carbon dioxide is considered to be the most ideal fracturing medium for the exploitation of unconventional natural gas, including shale gas and coalbed methane. It can achieve geological storage of carbon dioxide while fracturing the underground target reservoir. The most critical thing is to explore the fracture behavior characteristics of coal rock in this process, especially the study of the tension type, i.e., type I fracture characteristics of coal rock under the action of supercritical carbon dioxide. Due to the special physical and chemical properties of supercritical carbon dioxide, it has a deteriorating effect on the mechanical properties of coal rock. Coal rock undergoes ductile fracture behavior under this condition. The traditional linear elastic fracture theory is no longer applicable to the characterization of the fracture behavior of coal rock under the action of supercritical carbon dioxide. Therefore, in-depth research on the type I fracture characteristics of coal rock under the action of supercritical carbon dioxide under different conditions plays a vital role in clarifying the crack propagation mechanism of coal rock induced by supercritical carbon dioxide and thus guiding engineering practice.

[0003] At present, domestic and foreign experts have not conducted much research on the fracture characteristics of coal rock under the action of supercritical carbon dioxide. The most difficult problem to solve is how to implement stable fracture tests while supercritical carbon dioxide is acting. Therefore, establishing a method for coal rock specimens with good sealing properties and capable of achieving type I fracture tests under different supercritical carbon dioxide conditions is the basis for exploring the mechanism of supercritical carbon dioxide-induced cracking of coal rock.

[0004] At present, the Chinese invention patents related to the testing devices and methods for the parameters related to the type I fracture of coal and rock masses mainly include: "An NSCB specimen preparation device for testing the type I fracture toughness of compacted clay and its use method (CN109459290A)" by Chongqing Jiaotong University; "A method for determining the crack propagation velocity and fractal dimension of the type I fracture of rock (CN109738311A)" by Henan University of Technology; "An experimental device for testing the fracture toughness of rock (CN103604702A)" by the Wuhan Institute of Rock and Soil Mechanics, Chinese Academy of Sciences; "An experimental system and method for testing the type I fracture toughness of deep rock mass (CN109001046A)" by North China University of Water Resources and Hydropower. However, these existing coal rock type I fracture parameter testing equipment have the following problems: 1. Since the shape of the specimens for measuring rock fracture parameters is generally special, most test methods cannot simulate high ground stress. Even if there is a method to apply high hydrostatic pressure to the coal rock specimens, the test stability cannot be guaranteed; 2. The existing test methods cannot guarantee the sealing of supercritical carbon dioxide and the stability of coal rock specimens infiltrated with supercritical carbon dioxide for a long time; 3. The existing test methods cannot accurately measure the opening degree of the preset crack tip of the coal rock specimen; 4. The existing test methods cannot conduct research on coal rock specimens of different scales. Summary of the invention

[0005] The invention overcomes the shortcomings of the prior art and provides a test device for measuring type I fracture parameters of coal and rock mass under the action of supercritical carbon dioxide.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions.

[0007] The invention discloses a test device for determining type I fracture parameters of coal rock mass under the action of supercritical carbon dioxide, comprising a triaxial pressure autoclave and an axial loading device; a positioning base is arranged at the bottom of the triaxial pressure autoclave; the axial loading device is arranged at the top of the triaxial pressure autoclave for loading axial force on the specimen; support columns are symmetrically arranged on the surface of the positioning base along the central axis; the specimen is arranged on two support columns; the axial loading device, the support columns and the specimen are in point contact or line contact; the axis of the specimen, the loading center line of the axial loading device and the central axis of the positioning base are located in the same vertical plane; the loading point where the axial loading device contacts the specimen and the two support columns form a three-point bending loading frame.

[0008] The cavity of the triaxial pressure autoclave is connected to the carbon dioxide liquefaction device through an input pipeline; the input pipeline is provided with an axial flow pump, a first heating device and a pressure sensor; the triaxial pressure autoclave is connected to a second heating device, and the second heating device is connected to a temperature sensor.

[0009] The test piece is provided with a crack, and a crack displacement monitoring device is provided in the crack for measuring the opening displacement of the tip of the preset crack of the test piece.

[0010] The pressure sensor, temperature sensor and crack displacement monitoring device are connected to a data acquisition system.

[0011] Preferably, the support columns are connected with a distance adjustment device for adjusting the distance between the two support columns.

[0012] Preferably, the axial loading device comprises a servo loading system and an axial loading rod, a loading column is provided at the bottom of the axial loading rod, and both the loading column and the supporting column are cylindrical structures.

[0013] Furthermore, the axial loading rod is connected to a displacement extensometer for measuring the axial deformation of the specimen.

[0014] Furthermore, the triaxial pressure autoclave comprises an upper cover and a base, wherein the upper cover and the base are sealed and detachably connected; and the axial loading rod is slidingly and sealingly connected to the upper cover.

[0015] Preferably, the cavity of the triaxial pressure autoclave is connected to a carbon dioxide recovery device via an output pipeline; the output pipeline is connected to a pressure sensor.

[0016] Preferably, the crack displacement monitoring device comprises a connected fiber optic Bragg grating and a clamp-on extensometer.

[0017] Preferably, the inner wall of the triaxial pressure autoclave is connected with a specimen positioning device for fixing the specimen above the supporting column.

[0018] Furthermore, a specimen positioning device is symmetrically arranged on the inner wall of the triaxial pressure autoclave, and the specimen positioning device includes a positioning rod, a positioning nut and a positioning roller. The positioning rod is connected to the inner wall of the triaxial pressure autoclave, and the positioning nut is arranged on the positioning rod for adjusting the length of the positioning rod. The positioning roller is arranged at the end of the positioning rod, and the specimen is positioned by two opposite positioning rollers.

[0019] Preferably, the specimen is a type I semicircular block coal rock specimen.

[0020] The beneficial effects of the present invention compared with the prior art are as follows:

[0021] The present invention can simulate the effect of supercritical carbon dioxide on type I fracture behavior of coal rock mass under high ground stress environment, can realize experimental research on type I fracture characteristics of coal rock mass under supercritical carbon dioxide of different temperature and pressure and different infiltration time conditions, and can solve the problem that existing equipment cannot realize accurate measurement of the opening degree of preset crack tip of coal rock specimen; in addition, the device is also equipped with an adjustable three-point bending loading frame, which can realize three-point bending loading test on type I semi-disc specimen of coal rock mass with a diameter of 50mm~100mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of a test device for measuring type I fracture parameters of coal and rock mass under the action of supercritical carbon dioxide according to the present invention.

[0023] Figure 2 It is a front view of the three-point bending loading frame in the present invention.

[0024] Figure 3 It is the left view of the three-point bending loading frame in the present invention.

[0025] Numbers in the figure:

[0026] 1-External microcomputer-controlled electro-hydraulic servo loading system; 2-High-precision displacement extensometer; 3-Three-axis pressure steel kettle upper cover; 4-Temperature sensor; 5-Axial loading rod; 6-Flange; 7-Axial corrosion-resistant sealing rubber ring; 8-High-temperature heating resistance wire; 9-Insulating heat preservation sleeve; 10-Upper loading cylinder; 11-I-type semi-disc coal and rock specimen; 12-Fixed steel sleeve; 13-Encircling corrosion-resistant sealing rubber sleeve; 14-Fluid input pipeline; 15-Fluid output pipeline; 16-Inlet three-way valve; 17-Input end pressure sensor; 18-Outlet three-way valve; 19-Output end pressure sensor; 20-Carbon dioxide recovery device; 21-High-purity carbon dioxide cylinder; 22- Gas valve; 23-CO2 liquefier; 24-fluid pipeline; 25-high-pressure axial flow pump; 26-pipeline heater; 27-computer; 28-fiber Bragg grating; 29-pre-set cracks in coal and rock specimens; 30-lower left supporting cylinder; 31-lower right supporting cylinder; 32-lower left positioning slider; 33-lower right positioning slider; 34-clamp-type extensometer; 35-lower left data cable connector; 36-lower right data cable connector; 37-rigid base of three-point bending loading frame; 38-base of three-axis pressure steel kettle; 39-rear positioning rod; 40-rear positioning nut; 41-rear positioning roller; 42-front positioning rod; 43-front positioning nut; 44-front positioning roller; 45-positioning slideway. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings, but the scope of protection is not limited thereto.

[0028] like Figure 1-3As shown, this embodiment proposes a test device for determining type I fracture parameters of coal rock mass under the action of supercritical carbon dioxide, which is used for experimental research on type I fracture characteristics of coal rock mass under the action of supercritical carbon dioxide at different temperatures and pressures and under different infiltration time conditions. The test device consists of a loading system, a carbon dioxide fluid injection and recovery system, a pressure control system, a temperature control system, a sealing system, a specimen positioning system, a specimen crack displacement monitoring system, and a data acquisition system.

[0029] The loading system consists of an external microcomputer-controlled electro-hydraulic servo loading system 1, a triaxial pressure steel kettle upper cover 3, an axial loading rod 5, a fixed steel sleeve 12, and a triaxial pressure steel kettle base 38, wherein the symmetry center of the axial loading rod 5 is at the same position as the symmetry center of the triaxial pressure steel kettle upper cover 3, wherein the axial loading rod 5 is connected to a high-precision displacement extensometer 2, and is used to measure the axial deformation of the I-type semi-circular disc coal and rock specimen 11 during the test; the triaxial pressure steel kettle upper cover 3 and the triaxial pressure steel kettle base 38 are closed by the fixed steel sleeve 12 to form a complete and closed triaxial pressure kettle body; in addition, in order to complete the three-point bending test of the coal and rock semi-circular disc specimen, a three-point bending loading frame is simultaneously installed in the triaxial pressure steel kettle cavity, and the three-point bending loading frame consists of an upper loading cylinder 10, a lower left support The three-point bending loading frame is composed of a supporting cylinder 30, a lower right supporting cylinder 31, a lower left positioning slider 32, a lower right positioning slider 33, and a rigid base 37 of a three-point bending loading frame; the three-point bending loading frame is placed in the cavity of a triaxial pressure steel kettle, and the symmetry center of the three-point bending loading frame coincides with the symmetry center of the axial loading rod 5, wherein the upper loading cylinder 10 is connected to the lower end surface of the axial loading rod 5 through a positioning hole, the lower left supporting cylinder 30 is connected to the lower left positioning slider 32 through a positioning hole, the lower right supporting cylinder 31 is connected to the lower right positioning slider 33 through a positioning hole, the lower left positioning slider 32 and the lower right positioning slider 33 are connected to the rigid base of the three-point bending loading frame through a positioning slide 45, and at the same time, the span between the lower left supporting cylinder 30 and the lower right supporting cylinder 31 can be adjusted.

[0030] The carbon dioxide fluid injection and recovery system consists of a high-purity carbon dioxide gas cylinder 21, a gas valve 22, a carbon dioxide liquefier 23, a fluid pipeline 24, a high-pressure axial flow pump 25, a fluid input pipeline 14, a fluid output pipeline 15, an inlet three-way valve 16, an outlet three-way valve 18, and a carbon dioxide recoverer 20. The high-purity carbon dioxide gas flows from the high-purity carbon dioxide gas cylinder 21 through the gas valve 22 into the carbon dioxide liquefier 23, and the high-purity carbon dioxide gas is liquefied by the carbon dioxide liquefier 23. The liquefied carbon dioxide is sucked into the high-pressure axial flow pump 25 through the fluid pipeline 24. The high-pressure axial flow pump 25 can increase the fluid pressure to a maximum of 70 MPa, the liquid carbon dioxide pressure is increased to the set value by the high-pressure axial flow pump 25 and then discharged, and the pressurized carbon dioxide fluid enters the interior of the triaxial pressure steel kettle through the inlet three-way valve 16 and the fluid input pipeline 14. After the test is completed, the carbon dioxide fluid in the triaxial pressure steel kettle cavity enters the carbon dioxide recovery device 20 through the fluid output pipeline 15 and the outlet three-way valve 18, and the carbon dioxide fluid is recycled through the carbon dioxide recovery device 20.

[0031] The pressure control system is composed of an input pressure sensor 17, an inlet three-way valve 16, an output pressure sensor 19, and an outlet three-way valve 18. The carbon dioxide outputs a high-pressure carbon dioxide fluid through a high-pressure axial flow pump 25. The upper end of the inlet three-way valve 16 is connected to the input pressure sensor 17. The high-pressure carbon dioxide fluid flows through the inlet three-way valve 16. The pressure of the carbon dioxide fluid in the input three-axis pressure steel kettle is measured by the input pressure sensor 17. At the same time, when the pressure of the carbon dioxide fluid exceeds a certain threshold, the carbon dioxide fluid can enter the fluid input pipeline 14 through the inlet three-way valve 16. The upper end of the outlet three-way valve 18 is connected to the output pressure sensor 19. The carbon dioxide fluid in the cavity of the three-axis pressure steel kettle flows through the fluid output pipeline 15 and is output to the outlet three-way valve 18. The pressure of the carbon dioxide fluid is measured by the output pressure sensor 19. At the same time, when the pressure of the output carbon dioxide fluid exceeds a certain threshold, the carbon dioxide fluid can enter the carbon dioxide recovery device 20 through the outlet three-way valve 18.

[0032] The temperature control system consists of a pipeline heater 26, a temperature sensor 4, a high-temperature heating resistor 8, and an insulating sleeve 9. The pipeline heater 26 is used to heat the carbon dioxide fluid discharged from the high-pressure axial flow pump 25, and the high-temperature heating resistor 8 is used to heat the entire triaxial pressure steel kettle. At the same time, the insulating sleeve 9 is used to insulate the triaxial pressure steel kettle. The temperature of the triaxial pressure steel kettle can be increased to 200°C at most. The temperature is monitored in real time by the temperature sensor 4, so that the overall temperature of the triaxial pressure steel kettle can be maintained at a certain value.

[0033] The sealing system consists of a flange 6, an axial corrosion-resistant sealing rubber ring 7, and a circumferential corrosion-resistant sealing rubber sleeve 13, wherein the axial loading rod 5 is positioned by the flange 6, the corrosion-resistant sealing rubber ring 7 is used to ensure the axial sealing of the carbon dioxide fluid in the triaxial pressure steel kettle, and the circumferential corrosion-resistant sealing rubber sleeve 13 is used to ensure the sealing of the connection between the triaxial pressure steel kettle upper cover 3 and the triaxial pressure steel kettle base 38.

[0034] The specimen positioning system consists of a rear positioning rod 39, a rear positioning nut 40, a rear positioning roller 41, a front positioning rod 42, a front positioning nut 43, a front positioning roller 44, and a positioning slide 45, wherein the positioning slide 45 is used to position the lower left positioning slider 32 and the lower right positioning slider 33, and finally fix the span of the lower left supporting cylinder 30 and the lower right supporting cylinder 31 in the lower three-point bending loading frame of the I-type semi-disc coal and rock specimen 11, and the extension and retraction of the rear positioning rod 39 and the front positioning rod 42 are achieved by adjusting the rear positioning nut 40 and the front positioning nut 43 respectively, so that the rear positioning roller 41 and the front positioning roller 44 connected to the ends of the rear positioning rod 39 and the front positioning rod 42 are in direct contact with the I-type semi-disc coal and rock specimen 11, and the symmetry center of the I-type semi-disc coal and rock specimen 11 and the loading center line of the upper loading cylinder 10 are kept in the same vertical plane.

[0035] The specimen crack displacement monitoring system is composed of a fiber Bragg grating 28, a clip-on extensometer 34, a lower left data line connector 35, and a lower right data line connector 36. The fiber Bragg grating 28 is used to measure the opening displacement of the tip of the preset crack 29 of the coal and rock specimen in real time, and the clip-on extensometer 34 is used to measure the opening displacement of the bottom opening of the preset crack 29 of the coal and rock specimen in real time. The data acquisition system is composed of a computer 27 and corresponding data transmission lines, and is used to collect data such as axial deformation, pressure changes of carbon dioxide fluid entering and exiting the triaxial pressure steel autoclave, opening displacement changes of the preset crack tip, opening displacement changes of the preset crack opening, and temperature changes of the triaxial pressure autoclave during the test.

[0036] The device can realize the research of coal rock type I fracture test under different temperature and pressure supercritical carbon dioxide and different infiltration time conditions. Its sealing system can realize long-term sealing of supercritical carbon dioxide fluid under different temperature and pressure conditions in the triaxial pressure steel reactor cavity. The axial corrosion-resistant sealing rubber ring 7 and the circumferential corrosion-resistant sealing rubber sleeve 13 constituting the sealing system are made of perfluororubber, which can withstand the corrosion of supercritical carbon dioxide and high temperature.

[0037] By adjusting the lower left positioning slider 32 and the lower right positioning slider 33 on the positioning slide 45, the device can realize the three-point bending test research on the I-type semi-circular disc coal rock specimen with a diameter of 50mm~100mm under different supercritical carbon dioxide action conditions. It can realize real-time monitoring of the opening displacement of the preset crack tip of the I-type coal rock semi-circular disc specimen of the coal rock mass during the three-point bending test under supercritical carbon dioxide infiltration conditions under different temperature and pressure conditions. At the same time, it can realize the recycling of carbon dioxide fluid.

[0038] The device is used to carry out a test method for determining the type I fracture parameters of coal and rock mass. In this embodiment, a type I semi-circular coal mass specimen with a diameter of 80 mm is taken as an example, and the device is used to achieve the determination of the type I fracture parameters of coal mass under supercritical carbon dioxide conditions at different pressures. The specific implementation steps are as follows:

[0039] Step 1, prepare the test specimen: use a wire-cut CNC machine tool to make a semi-disc specimen with a diameter of 80 mm from the original coal sample, cut the coal semi-disc specimen to a thickness of 30 mm, and preset an artificial crack with a diameter of 16 mm along the symmetry axis starting from the midpoint of the bottom edge of the coal semi-disc specimen to prepare a coal I-type semi-disc three-point bending specimen.

[0040] Step 2, three-point bending loading frame installation: starting from the center position along the positioning slide 45, adjust the lower left positioning slider 32 to move 30 mm to the left and the lower right positioning slider 33 to move 30 mm to the right and fix them so that the span of the lower left supporting cylinder 30 and the lower right supporting cylinder 31 reaches 60 mm.

[0041] Step three, placing the coal body type I semi-disc specimen 11: place the coal body type I semi-disc specimen on the lower left supporting cylinder 30 and the lower right supporting cylinder 31, align the symmetry center of the specimen with the center position of the slideway, and realize the extension and retraction of the rear positioning rod 39 and the front positioning rod 42 by adjusting the rear positioning nut 40 and the front positioning nut 43 respectively, so that the rear positioning roller 41 and the front positioning roller 44 connected to the ends of the rear positioning rod 39 and the front positioning rod 42 are in direct contact with the specimen to realize positioning, and the fiber grating 28 is fixed to the tip of the preset crack of the coal semi-disc specimen by using high temperature and corrosion resistant resin epoxy glue, and the fiber grating 28 is connected to the lower right data line connector 36 through the data line, and the two measuring pieces in the clamp-type extensometer 34 are connected to the two ends of the preset crack opening of the coal semi-disc specimen by using high temperature and corrosion resistant resin epoxy glue, and the clamp-type extensometer 34 is connected to the lower left data line connector 35 through the data line.

[0042] Step 4, installing the triaxial pressure steel kettle: connect the upper loading cylinder 10 with the axial loading rod 5 through the positioning hole, and then fix the triaxial pressure steel kettle upper cover 3 with the triaxial pressure steel kettle base 38 through the fixed steel sleeve 12.

[0043] Step 5, injecting carbon dioxide fluid: open the high-purity carbon dioxide gas cylinder 21 and the gas valve 22, liquefy the high-purity carbon dioxide gas through the carbon dioxide liquefier 23, and the liquid carbon dioxide is sucked into the high-pressure axial flow pump 25 through the fluid pipeline 24. The high-pressure axial flow pump 25 increases the pressure of the liquid carbon dioxide to a set value and then discharges it. The pressurized liquid carbon dioxide fluid passes through the inlet three-way valve 16, and the pressure of the carbon dioxide fluid at the inlet end of the triaxial pressure autoclave is recorded by the input end pressure sensor 17. This process will continue to slowly inject carbon dioxide fluid into the triaxial pressure autoclave, and the carbon dioxide pressure in the triaxial pressure autoclave is controlled by the output end pressure sensor 19 and the outlet three-way valve (18), and the outlet end fluid pressure is recorded.

[0044] Step six, simulating supercritical carbon dioxide environments at different pressures: setting the discharge fluid pressure of the high-pressure axial flow pump 25 to 8 MPa (exceeding the critical pressure of carbon dioxide 7.38 MPa), turning on the pipeline heater 26 to heat the carbon dioxide fluid in the pipeline, and turning on the high-temperature heating resistor 8 at the same time, setting the temperature of the heated triaxial pressure autoclave to 40°C (higher than the critical temperature of carbon dioxide 31.1°C) through the temperature sensor 4, so that the carbon dioxide fluid forms its supercritical state in the triaxial pressure autoclave body, setting different discharge pressures through the high-pressure axial flow pump 25 to simulate the infiltration environment of the coal body I-type semi-disc specimen with supercritical carbon dioxide at different pressures, and maintaining the infiltration for more than 4 hours under each condition before conducting the subsequent three-point bending loading experiment.

[0045] Step seven, three-point bending loading test: turn on the external microcomputer-controlled electro-hydraulic servo loading system 1, apply axial load to the axial loading rod 5, and during the test, the opening displacement at the preset crack tip and the displacement change at the opening of the specimen are recorded in real time by the fiber grating 28 and the clamp-on extensometer 34, and the vertical displacement change is recorded in real time by the high-precision displacement extensometer 2.

[0046] Step 8, recovering carbon dioxide: after the test is completed, the outlet three-way valve 18 is opened to discharge the carbon dioxide fluid in the cavity of the triaxial pressure reactor into the carbon dioxide recovery device 20 for reuse in the next test.

[0047] Step nine, remove the test piece and organize the test equipment.

[0048] Step 10, analyzing various data during the entire test process, and plotting the specimen load-vertical displacement curve, load-crack tip opening displacement change curve, and load-crack opening opening displacement deformation curve under different supercritical carbon dioxide pressure conditions.

[0049] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. A test device for determining type I fracture parameters of coal and rock mass under supercritical carbon dioxide, characterized in that: It includes a triaxial pressure autoclave and an axial loading device; a positioning base is arranged at the bottom of the triaxial pressure autoclave; the axial loading device is arranged at the top of the triaxial pressure autoclave for loading axial force on the specimen; support columns are symmetrically arranged on the surface of the positioning base along the central axis; the specimen is arranged on two support columns; the support columns are connected with a distance adjustment device for adjusting the distance between the two support columns; the axial loading device, the support columns and the specimen are in point contact or line contact; the axis of the specimen, the loading center line of the axial loading device and the central axis of the positioning base are located in the same vertical plane; the loading point where the axial loading device contacts the specimen, and the two support columns form a three-point bending loading frame; the axial loading device includes a servo loading system and an axial loading rod, a loading column is arranged at the bottom of the axial loading rod, and both the loading column and the support column are cylindrical structures; the axial loading rod is connected with a displacement extensometer for measuring the axial deformation of the specimen; The cavity of the triaxial pressure autoclave is connected to the carbon dioxide liquefaction device through an input pipeline; the input pipeline is provided with an axial flow pump, a first heating device and a pressure sensor; the triaxial pressure autoclave is connected to a second heating device, and the second heating device is connected to a temperature sensor; The test piece is provided with a crack, and a crack displacement monitoring device is provided in the crack for measuring the opening displacement of the tip of the preset crack of the test piece; The pressure sensor, temperature sensor and crack displacement monitoring device are connected to a data acquisition system.

2. The test device for measuring type I fracture parameters of coal and rock mass under supercritical carbon dioxide according to claim 1, characterized in that: The triaxial pressure autoclave comprises an upper cover and a base, wherein the upper cover and the base are sealed and detachably connected; and the axial loading rod is slidably and sealably connected to the upper cover.

3. The test device for measuring type I fracture parameters of coal and rock mass under supercritical carbon dioxide according to claim 1, characterized in that: The cavity of the triaxial pressure autoclave is connected to the carbon dioxide recovery device through an output pipeline; the output pipeline is connected to a pressure sensor.

4. The test device for measuring type I fracture parameters of coal and rock mass under supercritical carbon dioxide according to claim 1, characterized in that: The crack displacement monitoring device comprises a connected optical fiber grating and a clamp-on extensometer.

5. The test device for measuring type I fracture parameters of coal and rock mass under the action of supercritical carbon dioxide according to claim 1, characterized in that: The inner wall of the triaxial pressure autoclave is connected with a specimen positioning device for fixing the specimen above the supporting column.

6. The test device for measuring type I fracture parameters of coal and rock mass under the action of supercritical carbon dioxide according to claim 5, characterized in that: The inner wall of the triaxial pressure autoclave is symmetrically provided with a specimen positioning device, which includes a positioning rod, a positioning nut and a positioning roller. The positioning rod is connected to the inner wall of the triaxial pressure autoclave, and the positioning nut is arranged on the positioning rod for adjusting the length of the positioning rod. The positioning roller is arranged at the end of the positioning rod, and the specimen is positioned by two opposite positioning rollers.

7. The test device for measuring type I fracture parameters of coal and rock mass under supercritical carbon dioxide according to claim 1, characterized in that: The test piece is an I-type semicircular block coal rock test piece.

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