Convection heat transfer test device and method of supercritical CO2 in rock crack

Abstract

The invention discloses a convective heat transfer test device and method for supercritical CO2 in rock cracks, and relates to the technical field of deep geothermal resource development, the convective heat transfer test device comprises a confining pressure loading system, a seepage system, a heating system and a temperature and pressure data acquisition system, the confining pressure loading system comprises a confining pressure chamber and a sample with cracks placed in the confining pressure chamber, and the temperature and pressure data acquisition system is connected with the confining pressure chamber. Confining pressure is applied to the sample; the seepage system is used for injecting supercritical CO2 into the sample; the heating system is used for heating the confining pressure chamber so as to simulate a high-temperature environment of a reservoir; the temperature and pressure data acquisition system is used for measuring the temperature and pressure of fluid at an inlet and an outlet of the sample and the temperature of the inner wall surface of the crack so as to calculate the convective heat transfer coefficient of supercritical CO2 in the sample under the corresponding temperature and pressure conditions; the convective heat exchange test device with critical CO2 as heat exchange fluid is built, and the limitation that an existing test device can only carry out a water heat exchange test is solved.

Description

Technical Field

[0001] The present application relates to the technical field of deep geothermal resource development, and in particular to a device and method for testing convective heat transfer of supercritical CO2 in rock fractures. Background Art

[0002] As a promising clean and renewable energy, geothermal resources have the characteristics of sustainability, wide spatial distribution, large reserves, and high economic benefits, and have broad application prospects. Traditional geothermal systems (H2O-EGS) with water as the circulating fluid have problems such as water waste and scale formation in ground transmission pipelines. Supercritical CO2 has the characteristics of low viscosity and good fluidity. The use of supercritical CO2 instead of water as the circulating fluid in geothermal exploitation has been widely recognized, and it can also achieve partial storage of CO2.

[0003] The exploitation of geothermal resources is essentially a heat transfer process of heat exchange fluids in high-temperature fractured rock masses. The heat exchange characteristics between high-temperature fractured rock masses and low-temperature flowing fluids are important scientific issues in geothermal development and are of great significance for the correct understanding and evaluation of geothermal exploitation efficiency. In previous studies, most of them used water as the heat transfer fluid, but the physical properties of CO2 are very sensitive to changes in temperature and pressure. Simply using previous equipment will lead to inaccurate calculation results.

[0004] Therefore, it is urgent to develop a supercritical CO2 convective heat transfer test device in rock fractures, so as to accurately evaluate the heat transfer characteristics between supercritical CO2 and high-temperature fractured rock through real-time monitoring of fluid temperature and pressure. Summary of the invention

[0005] In order to solve the above problems, the present application provides a supercritical CO2 convective heat exchange test device and method in rock fractures. The present application builds a supercritical CO2 convective heat exchange test device as a heat exchange fluid, which solves the limitation that the existing test device can only carry out water heat exchange tests. The technical solution is as follows:

[0006] The first aspect of the present application provides a supercritical CO2 convective heat transfer test device in rock fractures, comprising a confining pressure loading system, a seepage system, a heating system and a temperature and pressure data acquisition system, wherein the confining pressure loading system comprises a confining pressure chamber and a sample with fractures placed in the confining pressure chamber to apply confining pressure to the sample; the seepage system is used to inject supercritical CO2 into the sample; the heating system is used to heat the confining pressure chamber to simulate the high temperature environment of the reservoir; the temperature and pressure data acquisition system is used to measure the fluid temperature and pressure at the inlet and outlet of the sample and the wall temperature of the fracture to calculate the convective heat transfer coefficient of supercritical CO2 in the sample under corresponding temperature and pressure conditions.

[0007] For example, in the supercritical CO2 convective heat exchange test device in rock fractures provided in one embodiment, the confining pressure loading system also includes a low-pressure hydraulic station and a confining pressure servo pump connected to the confining pressure chamber through a hydraulic pipeline, and high-temperature resistant hydraulic silicone oil is injected into the confining pressure chamber through the low-pressure hydraulic station, and the confining pressure is loaded to the required working condition through the confining pressure servo pump.

[0008] For example, in the supercritical CO2 convective heat exchange test device in rock fractures provided in one embodiment, the confining pressure chamber, the low-pressure hydraulic station and the confining pressure servo pump form a closed-loop hydraulic circuit, an injection valve is provided on the hydraulic silicone oil injection pipeline, and a discharge valve is provided on the hydraulic silicone oil return pipeline.

[0009] For example, in the convective heat exchange test device of supercritical CO2 in rock fractures provided in one embodiment, the seepage system includes a CO2 gas storage tank, a supercritical CO2 pump, a preheater, a back pressure valve and an exhaust gas collection device connected by a seepage pipeline, the CO2 stored in the CO2 gas storage tank is transported to the preheater via the supercritical CO2 pump to pressurize and heat the CO2 to a supercritical state, the outlet end of the preheater is connected to the inlet end of the sample to inject supercritical CO2 into the sample, the back pressure valve is connected to the outlet end of the sample, and the supercritical CO2 after flowing through the sample enters the exhaust gas collection device through the back pressure valve to collect the exhaust gas generated during the test.

[0010] For example, in the supercritical CO2 convective heat exchange test device in rock fractures provided in one embodiment, the seepage system also includes an electric heating belt wrapped around the pipeline at the outlet end of the back pressure valve, and the exhaust gas collection device is connected to the end of the electric heating belt; a safety valve and a pressure gauge are provided on the seepage pipeline connecting the CO2 storage tank and the supercritical CO2 pump.

[0011] For example, in the supercritical CO2 convective heat exchange test device in rock fractures provided in one embodiment, the heating system includes an electric heating sleeve and a temperature controller electrically connected to the electric heating sleeve, and the target temperature is set by the temperature controller. The electric heating sleeve is arranged on the periphery of the confining pressure chamber to heat the hydraulic oil in the confining pressure chamber and heat the sample to simulate the high temperature environment of the reservoir.

[0012] For example, in the convective heat transfer test device of supercritical CO2 in rock fractures provided in one embodiment, the temperature and pressure data acquisition system includes several temperature sensors inserted in the sample and pressure transmitters arranged on the upstream and downstream seepage pipelines of the sample. The temperature sensors are respectively arranged at the sample inlet, the sample outlet and the middle of the sample to measure the fluid temperature at the inlet and outlet of the sample and the temperature of the inner wall of the fracture. The fluid pressure at the inlet and outlet of the sample is measured by the pressure transmitter to calculate the convective heat transfer coefficient of supercritical CO2 in the sample under corresponding temperature and pressure conditions.

[0013] For example, in the supercritical CO2 convective heat exchange test device in rock fractures provided in one embodiment, the temperature and pressure data acquisition system also includes a temperature data acquisition instrument electrically connected to the temperature sensor and a computer electrically connected to the pressure transmitter, the temperature sensor transmits the collected data to the temperature data recorder, the pressure transmitter transmits the collected data to the computer, and the confining pressure servo pump is electrically connected to the computer.

[0014] The second aspect of the present application provides a method for testing the convective heat transfer of supercritical CO2 in rock fractures, comprising the following steps:

[0015] S1 Sample processing: Perform wire cutting or splitting tests on standard cylindrical samples to produce cracked samples with different roughness; drill several temperature measuring holes on the side of the sample, insert the temperature sensor into the temperature measuring hole, and seal the end of the temperature measuring hole with high temperature and high pressure sealant; evenly apply high temperature and high pressure sealant to the edge of the crack on the side of the sample to seal; put the sample into a high temperature and high pressure heat shrink sleeve, and use a hot air gun to heat it so that the heat shrink sleeve shrinks evenly until it fits tightly with the sample;

[0016] S2 Heating the confining pressure chamber and applying confining pressure: Place the sample in the confining pressure chamber, open the injection valve, close the discharge valve, and fill the confining pressure chamber with high temperature and high pressure resistant hydraulic silicone oil through the low pressure hydraulic station; turn on the temperature controller, set the target temperature, heat the hydraulic oil in the confining pressure chamber through the electric heating sleeve, and keep the injection valve in the open state; after reaching the target temperature, close the injection valve, control the confining pressure servo pump through the computer, and apply confining pressure to the sample;

[0017] S3 starts the seepage system to inject supercritical CO2 into the sample: set the back pressure valve to the target value, turn on the preheater and set the target temperature, turn on the electric heating belt, open the safety valve, start the supercritical CO2 pump and set the target flow rate, monitor the temperature data acquisition instrument, and complete the test when the temperature of the temperature sensor no longer decreases significantly and tends to be stable. At the same time, the computer records the data collected by the pressure sensor and calculates the convective heat transfer coefficient;

[0018] S4: Close the safety valve and the supercritical CO2 pump. When the temperature of the temperature sensor returns to the initial value, change the flow rate or confining pressure and other conditions, repeat the above operations, and start the test under the next set of operating conditions.

[0019] For example, in the convective heat transfer test method of supercritical CO2 in rock fractures provided in one embodiment, in S3, the calculation method of the convective heat transfer coefficient is: since the heat Q absorbed by CO2 in the entire fracture channel of the sample is equal to the convective heat transfer between CO2 and the inner surface of the fracture, that is:

[0020] Q=H out MH in M

[0021] The calculation method of supercritical CO2 convection heat transfer coefficient satisfies the following formula:

[0022]

[0023] Where M is the mass flow rate; H in and H out are the enthalpy values ​​of the fluid at the fracture inlet and outlet, T in and T out are the fluid temperatures at the inlet and outlet of the sample, T i1 and T i2 are the crack wall temperature, C out and C in are the heat capacity of the fluid under the corresponding temperature and pressure conditions of the sample inlet and outlet, A s is the crack surface area.

[0024] The beneficial effects brought about by a supercritical CO2 convective heat transfer test device and method in rock fractures provided in some embodiments of the present application are as follows: the present application solves the problem that existing equipment can only carry out water heat exchange experiments, but cannot carry out supercritical CO2 convective heat transfer experiments in rock fractures. By measuring the supercritical CO2 temperature and pressure at the inlet and outlet of the sample, as well as the temperature of the inner wall of the fracture, the fluid heat capacity under the corresponding temperature and pressure conditions can be obtained, and then the convective heat transfer coefficient can be calculated; the test operation of the present application is simple and effective, and the sample can be restored to the actual reservoir temperature and pressure conditions, making the test results more accurate, which is of great significance to actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is a schematic diagram of the overall structure of the supercritical CO2 convection heat transfer test device in rock fractures of the present application. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0029] The first aspect of the present application provides a supercritical CO2 convection heat transfer test device in rock fractures, such as Figure 1 As shown, including:

[0030] A confining pressure loading system, comprising a confining pressure chamber 7 and a cracked specimen 8 placed in the confining pressure chamber 7, so as to apply confining pressure to the specimen 8;

[0031] A seepage system for injecting supercritical CO2 into the sample 8;

[0032] A heating system, used for heating the confining pressure chamber 7 to simulate a high temperature environment of the reservoir;

[0033] The temperature and pressure data acquisition system is used to measure the inlet and outlet fluid temperature and pressure of sample 8 and the inner wall temperature of the crack to calculate the convection heat transfer coefficient of supercritical CO2 in sample 8 under corresponding temperature and pressure conditions.

[0034] Among them, the confining pressure loading system also includes a low-pressure hydraulic station 14 and a confining pressure servo pump 15 connected to the confining pressure chamber 7 through a hydraulic pipeline. High-temperature resistant hydraulic silicone oil is injected into the confining pressure chamber 7 through the low-pressure hydraulic station 14, and the confining pressure is loaded to the required working condition through the confining pressure servo pump 15. The confining pressure chamber 7 and the low-pressure hydraulic station 14 and the confining pressure servo pump 15 form a closed-loop hydraulic circuit. An injection valve 16-1 is provided on the hydraulic silicone oil injection pipeline, and a discharge valve 16-2 is provided on the hydraulic silicone oil return pipeline.

[0035] like Figure 1 As shown, the seepage system includes a CO2 gas storage tank 1, a supercritical CO2 pump 4, a preheater 5, a back pressure valve 17 and a tail gas collection device 19 connected by a seepage pipeline. The CO2 stored in the CO2 gas storage tank 1 is transported to the preheater 5 via the supercritical CO2 pump 4 to pressurize and heat the CO2 to a supercritical state. The outlet end of the preheater 5 is connected to the inlet end of the sample 8 to inject supercritical CO2 into the sample 8. The back pressure valve 17 is connected to the outlet end of the sample 8 to ensure that the supercritical pressure state is maintained in the seepage channel. The supercritical CO2 after flowing through the sample 8 enters the tail gas collection device 19 through the back pressure valve 17 to collect the tail gas generated during the test.

[0036] For example, in the supercritical CO2 convection heat transfer test device in rock fractures provided in one embodiment, Figure 1 As shown, the seepage system also includes an electric heating belt 18 wound around the pipeline at the outlet end of the back pressure valve 17 to prevent freezing caused by the rapid expansion and heat absorption of high-pressure CO2. The exhaust gas collection device 19 is connected to the end of the electric heating belt 18. A safety valve 2 and a pressure gauge 3 are provided on the seepage pipeline connecting the CO2 storage tank 1 and the supercritical CO2 pump 4.

[0037] like Figure 1 As shown, the heating system includes an electric heating sleeve 12 and a temperature controller 13 electrically connected to the electric heating sleeve 12. The target temperature is set by the temperature controller 13. The electric heating sleeve 12 is mounted on the periphery of the confining pressure chamber 7 to heat the hydraulic oil in the confining pressure chamber 7 and heat the sample 8 to simulate the high temperature environment of the reservoir.

[0038] like Figure 1 As shown, the temperature and pressure data acquisition system includes several temperature sensors inserted in the sample 8 and pressure transmitters arranged on the upstream and downstream seepage pipelines of the sample 8. The temperature sensors are respectively arranged at the inlet of the sample 8, the outlet of the sample 8 and the middle of the sample 8 to measure the inlet and outlet fluid temperatures of the sample 8 and the inner wall temperature of the crack. The inlet and outlet fluid pressures of the sample 8 are measured by the pressure transmitter 6 to calculate the convective heat transfer coefficient of supercritical CO2 in the sample under the corresponding temperature and pressure conditions.

[0039] The temperature and pressure data acquisition system also includes a temperature data acquisition instrument 10 electrically connected to the temperature sensor and a computer 11 electrically connected to the pressure transmitter 6. The temperature sensor 9 transmits the collected data to the temperature data recorder 10, the pressure transmitter 6 transmits the collected data to the computer 11, and the confining pressure servo pump 15 is electrically connected to the computer 11.

[0040] Specifically, Figure 1 As shown, an inlet temperature sensor 9-1 is inserted at the inlet end of the side of the sample 8 near the bottom, an outlet temperature sensor 9-4 is inserted at the outlet end of the side of the sample 8 near the top, and a first crack inner wall temperature sensor 9-2 and a second crack inner wall temperature sensor 9-3 are inserted at the side of the sample 8, wherein the inlet temperature sensor 9-1 monitors the fluid temperature at the inlet of the sample 8, the outlet temperature sensor 9-4 monitors the fluid temperature at the outlet of the sample 8, the first crack inner wall temperature sensor 9-2 and the second crack inner wall temperature sensor 9-3 are used to monitor the crack inner wall temperature of the sample 8; an upstream pressure transmitter 6-1 is set on the upstream seepage pipeline of the sample 8, and a downstream pressure transmitter 6-2 is set on the downstream seepage pipeline of the sample 8.

[0041] The second aspect of the present application provides a method for testing the convective heat transfer of supercritical CO2 in rock fractures, using the above-mentioned supercritical CO2 convective heat transfer test device in rock fractures to conduct the test, comprising the following steps:

[0042] S1 Sample processing: Perform wire cutting or splitting tests on a standard cylindrical (50 mm in diameter, 100 mm in height) sample 8 to manufacture cracked samples with different roughness; drill several temperature measuring holes on the side of the sample 8, insert the temperature sensor into the temperature measuring hole, and seal the end of the temperature measuring hole with a high temperature and high pressure sealant to prevent the hydraulic oil from entering the temperature measuring hole; before placing the cracked sample 8 into the confining pressure chamber 7, evenly apply a high temperature and high pressure sealant to the edge of the crack on the side of the sample 8 to prevent the hydraulic oil from generating stress concentration at the crack; place the sample 8 into a high temperature and high pressure heat shrink sleeve, and heat it with a hot air gun to shrink the heat shrink sleeve evenly until it fits tightly with the sample 8 to prevent the hydraulic oil from entering the sample 8;

[0043] Specifically, a temperature measuring hole with a diameter of 2 mm and a depth of 25 mm was drilled at 5 mm from the top of the sample 8 using a diamond drill bit, and the outlet temperature sensor 9-4 was placed; a temperature measuring hole with a diameter of 2 mm and a depth of 25 mm was drilled at 5 mm from the bottom of the sample 8 using a diamond drill bit, and the inlet temperature sensor 9-1 was placed; in the middle of the sample 8, 25 mm above and below the center point, temperature measuring holes with a diameter of 2 mm and a depth of 23 mm were drilled, and the first crack inner wall temperature sensor 9-2 and the second crack inner wall temperature sensor 9-3 were placed respectively;

[0044] S2 Heating the confining pressure chamber and applying confining pressure: Place the sample 8 in the confining pressure chamber 7, open the injection valve 16-1, close the discharge valve 16-2, and fill the confining pressure chamber 7 with high-temperature and high-pressure hydraulic silicone oil through the low-pressure hydraulic station 14; turn on the temperature controller 13, set the target temperature, and heat the hydraulic oil in the confining pressure chamber 7 through the electric heating sleeve 12. During this process, the injection valve 16-1 must be kept in an open state to prevent the pressure in the confining pressure chamber 7 from increasing due to thermal stress; after reaching the target temperature, close the injection valve 16-1, control the confining pressure servo pump 15 through the computer 11, apply confining pressure to the sample 8 and maintain stability;

[0045] S3 starts the seepage system to inject supercritical CO2 into the sample: set the back pressure valve 17 to the target value, open the preheater 5 and set the target temperature, open the electric heating belt 18, open the safety valve 2, start the supercritical CO2 pump 4 and set the target flow rate, obtain the inlet and outlet pressures of the sample 8 through the upstream pressure transmitter 6-1 and the downstream pressure transmitter 6-2, and send the data to the computer 11, obtain the inlet and outlet fluid temperatures of the sample 8 and the inner wall temperature of the crack through each temperature sensor, and send the temperature to the temperature data acquisition instrument 10, monitor the temperature data acquisition instrument 10, when the temperature of the temperature sensor is no longer significantly reduced and tends to be stable, it can be considered that the thermal equilibrium state is reached and the test is completed, and at the same time the computer 11 records the data collected by the pressure sensor 6, and calculates the convective heat transfer coefficient according to the data collected by the temperature data acquisition instrument 10, and can also calculate the permeability, opening and other parameters;

[0046] Among them, the calculation method of the convective heat transfer coefficient is: considering that the heat Q absorbed by CO2 in the entire crack channel of the specimen is equal to the convective heat transfer between CO2 and the inner surface of the crack, that is:

[0047] Q=H out MH in M

[0048] The formula is derived based on the existing convection heat transfer coefficient:

[0049]

[0050] Further deduction shows that the calculation method of supercritical CO2 convective heat transfer coefficient satisfies the following formula:

[0051]

[0052] Where M is the mass flow rate; H in and H out are the enthalpy values ​​of the fluid at the fracture inlet and outlet, T in and T out are the fluid temperatures at the inlet and outlet of the sample, T i1 and T i2 are the crack wall temperature, C out and C in are the heat capacity of the fluid under the corresponding temperature and pressure conditions of the sample inlet and outlet, A s is the crack surface area, and the real surface area of ​​the crack surface can be obtained by three-dimensional scanning technology; C out and C in The standard data in NIST Chemistry WebBook are obtained by querying the measured temperature and pressure parameters.

[0053] S4 closes the safety valve 2, turns off the supercritical CO2 pump 4, and when the temperature of the temperature sensor returns to the initial value, changes the flow rate or confining pressure and other conditions, repeats the above operations, and starts the test under the next set of operating conditions.

[0054] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the specification and implementation modes, and it can be fully applicable to various fields suitable for the present application. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A supercritical CO2 convection heat transfer test device in rock fractures, characterized in that: include: A confining pressure loading system, comprising a confining pressure chamber and a cracked specimen placed in the confining pressure chamber, so as to apply confining pressure to the specimen; A seepage system, used to inject supercritical CO2 into the sample; A heating system, used for heating the confining pressure chamber to simulate a high temperature environment of the reservoir; The temperature and pressure data acquisition system is used to measure the temperature and pressure of the fluid at the inlet and outlet of the sample and the temperature of the inner wall of the crack to calculate the convection heat transfer coefficient of supercritical CO2 in the sample under corresponding temperature and pressure conditions.

2. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 1, characterized in that: The confining pressure loading system also includes a low-pressure hydraulic station and a confining pressure servo pump connected to the confining pressure chamber through a hydraulic pipeline. High-temperature resistant hydraulic silicone oil is injected into the confining pressure chamber through the low-pressure hydraulic station, and the confining pressure is loaded to the required working condition through the confining pressure servo pump.

3. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 2, characterized in that: The confining pressure chamber, the low-pressure hydraulic station and the confining pressure servo pump form a closed-loop hydraulic circuit. An injection valve is provided on the hydraulic silicone oil injection pipeline, and a discharge valve is provided on the hydraulic silicone oil return pipeline.

4. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 3 is characterized in that: The seepage system includes a CO2 gas storage tank, a supercritical CO2 pump, a preheater, a back pressure valve and an exhaust gas collection device connected by a seepage pipeline. The CO2 stored in the CO2 gas storage tank is transported to the preheater via the supercritical CO2 pump to pressurize and heat the CO2 to a supercritical state. The outlet end of the preheater is connected to the inlet end of the sample to inject supercritical CO2 into the sample. The back pressure valve is connected to the outlet end of the sample. The supercritical CO2 after flowing through the sample enters the exhaust gas collection device through the back pressure valve to collect the exhaust gas generated during the test.

5. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 4 is characterized in that: The seepage system also includes an electric heating belt wound around the pipeline at the outlet end of the back pressure valve, and the tail gas collection device is connected to the end of the electric heating belt; a safety valve and a pressure gauge are provided on the seepage pipeline connecting the CO2 gas storage tank and the supercritical CO2 pump.

6. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 5, characterized in that: The heating system includes an electric heating sleeve and a temperature controller electrically connected to the electric heating sleeve. The target temperature is set by the temperature controller. The electric heating sleeve is arranged on the periphery of the confining pressure chamber to heat the hydraulic oil in the confining pressure chamber and heat the sample to simulate the high temperature environment of the reservoir.

7. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 6 is characterized in that: The temperature and pressure data acquisition system includes several temperature sensors inserted in the sample and pressure transmitters arranged on the seepage pipelines upstream and downstream of the sample. The temperature sensors are respectively arranged at the sample inlet, the sample outlet and the middle of the sample to measure the fluid temperature at the sample inlet and outlet and the temperature of the inner wall of the crack. The fluid pressure at the sample inlet and outlet is measured by the pressure transmitter to calculate the convective heat transfer coefficient of supercritical CO2 in the sample under corresponding temperature and pressure conditions.

8. The supercritical CO2 convection heat transfer test device in rock fractures according to claim 7, characterized in that: The temperature and pressure data acquisition system also includes a temperature data acquisition instrument electrically connected to the temperature sensor and a computer electrically connected to the pressure transmitter. The temperature sensor transmits the collected data to the temperature data recorder, the pressure transmitter transmits the collected data to the computer, and the confining pressure servo pump is electrically connected to the computer.

9. The test method of the supercritical CO2 convection heat transfer test device in rock fractures according to claim 8, characterized in that: The following steps are involved: S1 Sample processing: Perform wire cutting or splitting tests on standard cylindrical samples to produce cracked samples with different roughness; drill several temperature measuring holes on the side of the sample, insert the temperature sensor into the temperature measuring hole, and seal the end of the temperature measuring hole with high temperature and high pressure sealant; evenly apply high temperature and high pressure sealant to the edge of the crack on the side of the sample to seal; put the sample into a high temperature and high pressure heat shrink sleeve, and use a hot air gun to heat it so that the heat shrink sleeve shrinks evenly until it fits tightly with the sample; S2 Heating the confining pressure chamber and applying confining pressure: Place the sample in the confining pressure chamber, open the injection valve, close the discharge valve, and fill the confining pressure chamber with high temperature and high pressure resistant hydraulic silicone oil through the low pressure hydraulic station; turn on the temperature controller, set the target temperature, heat the hydraulic oil in the confining pressure chamber through the electric heating sleeve, and keep the injection valve in the open state; after reaching the target temperature, close the injection valve, control the confining pressure servo pump through the computer, and apply confining pressure to the sample; S3 starts the seepage system to inject supercritical CO2 into the sample: set the back pressure valve to the target value, turn on the preheater and set the target temperature, turn on the electric heating belt, open the safety valve, start the supercritical CO2 pump and set the target flow rate, monitor the temperature data acquisition instrument, and complete the test when the temperature of the temperature sensor no longer decreases significantly and tends to be stable. At the same time, the computer records the data collected by the pressure sensor and calculates the convective heat transfer coefficient; S4: Close the safety valve and the supercritical CO2 pump. When the temperature of the temperature sensor returns to the initial value, change the flow rate or confining pressure and other conditions, repeat the above operations, and start the test under the next set of operating conditions.

10. The method for testing convective heat transfer of supercritical CO2 in rock fractures according to claim 9, characterized in that: In S3, the calculation method of the convective heat transfer coefficient is: since the heat Q absorbed by CO2 in the entire crack channel of the sample is equal to the convective heat transfer between CO2 and the inner surface of the crack, that is: Q=H out M-H in M The calculation method of supercritical CO2 convection heat transfer coefficient satisfies the following formula: Where M is the mass flow rate; H in and H out are the enthalpy values ​​of the fluid at the fracture inlet and outlet, T in and T out are the fluid temperatures at the inlet and outlet of the sample, T i1 and T i2 are the crack wall temperature, C out and C in are the heat capacity of the fluid under the corresponding temperature and pressure conditions of the sample inlet and outlet, A s is the crack surface area.

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