Device and method for monitoring migration of CO2 in sediment based on time domain reflection method

Abstract

The invention belongs to the field of ocean geophysical exploration, and particularly provides a device and a method for monitoring migration of CO2 in sediment based on a time domain reflectometry, the monitoring device comprises a reaction kettle, a vacuumizing and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, a dielectric constant test control system and a data acquisition and processing system; the dielectric constant test control system comprises a time domain reflection tester and a time domain reflection sensor assembly, wherein the time domain reflection sensor assembly comprises a plurality of axial time domain reflection sensors inserted from the bottom of the reaction kettle and a plurality of radial time domain reflection sensors inserted from the side surface of the reaction kettle. According to the device and the method, anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in the ocean sediment can be realized, and combined characterization of CO2 saturation and CO2 plume front migration dynamics in the sediment sample in the CO2 migration process can be realized, so that accurate evaluation of the storage efficiency and leakage risk of CO2 in the ocean sediment is realized, the monitoring effect is good, and the operation is simple.

Description

Technical Field

[0001] This invention belongs to the field of marine geophysical exploration, and specifically relates to a device and method for monitoring CO2 migration in sediments based on time-domain reflectometry. Background Technology

[0002] Global warming significantly impacts Earth's climate change, posing a serious threat to ecosystem stability, biodiversity, and human life and production. Carbon dioxide (CO2), as a greenhouse gas, has been proven to be one of the most significant contributors to global warming. CO2 geological sequestration is considered a feasible and sustainable method to effectively reduce atmospheric CO2 concentrations, thus playing a crucial role in mitigating global warming. In marine sediments, hydrate-based CO2 sequestration technology has attracted widespread attention worldwide due to its high sequestration density and wide sequestration range. CO2 sequestration efficiency and stability (i.e., both CO2 hydrate formation and decomposition leakage can cause CO2 migration), which are closely related to CO2 migration, are key indicators for evaluating the success of CO2 geological sequestration. Therefore, accurately monitoring the CO2 migration process in marine sediments is essential for assessing CO2 storage efficiency and safety.

[0003] Conventional geophysical methods (such as seismic detection based on sound velocity or attenuation, and resistivity-based electrical resistivity methods) have become important techniques for monitoring gas migration in marine sediments. However, both seismic and electrical resistivity methods have their limitations. Specifically, seismic detection is not sensitive enough to the type and content of fluids in sediment pores; in contrast, although resistivity-based electrical resistivity methods are more sensitive to the type and content of fluids in pores, resistivity is easily affected by pore water salinity and reservoir temperature. Therefore, seismic and electrical resistivity methods have varying degrees of shortcomings in accurately monitoring gas migration in marine sediments. Compared with the above two detection methods, dielectric property-based detection techniques can not only effectively identify the type of fluid in pores and directly calculate its content, but are also minimally affected by pore water salinity and temperature, thus providing a new approach for the accurate monitoring of CO2 migration in marine sediments.

[0004] In recent years, time-domain reflectometry (TDRS) based on the detection of dielectric constant has been widely used for monitoring and evaluating conventional soil moisture content, frozen soil thickness and freeze-thaw processes, and water content in methane hydrate sediments. Significant progress has also been made in the development of corresponding monitoring devices based on TDRS. However, to date, no research has been reported on the continuous dynamic monitoring of supercritical CO2 migration processes in marine sediments using TDRS. Furthermore, currently available devices and methods for monitoring water content based on TDRS lack anisotropic monitoring capabilities and cannot achieve joint characterization of CO2 saturation and its plume front in experimental samples. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as the inability to continuously and dynamically monitor the supercritical CO2 migration process in marine sediments using time-domain reflectometry (TDRS), the lack of anisotropic monitoring capabilities, and the inability to jointly characterize CO2 saturation and its plume front in experimental samples, this invention proposes a CO2 migration monitoring device and method in sediments based on TDRS. This device and method possess anisotropic monitoring capabilities and can jointly characterize CO2 saturation and its migration front in experimental samples using TDRS as a single technology.

[0006] The proposed solution is as follows: A CO2 migration monitoring device in sediments based on time-domain reflectometry includes a reaction vessel, a vacuum and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, and a data acquisition and processing system. It also includes a dielectric constant testing and control system. The reaction vessel is connected to the vacuum and saturation system, the supercritical carbon dioxide preparation and injection system, the temperature control system, and the dielectric constant testing and control system, respectively. The dielectric constant testing and control system is connected to the data acquisition and processing system. The dielectric constant test and control system includes a time-domain reflectometry instrument and a time-domain reflectometry sensor assembly connected to the time-domain reflectometry instrument. The time-domain reflectometry sensor assembly includes multiple axial time-domain reflectometry sensors inserted into the reactor from the bottom and multiple radial time-domain reflectometry sensors inserted into the reactor from the side.

[0007] Furthermore, the plurality of axial time-domain reflectometry sensors are arranged in a square at the bottom of the reactor, and the square is located at the midpoint of the radius of the circular cross-section at the bottom of the reactor.

[0008] Furthermore, the plurality of radial time-domain reflectometry sensors are distributed at equal intervals from top to bottom within the reactor.

[0009] Furthermore, the supercritical carbon dioxide preparation and injection system includes a connected CO2 cylinder, a CO2 pressurizing device, a cooling water bath device, a supercritical CO2 injection pump, and a preheating device. The CO2 pressurizing device and the cooling water bath device pressurize and cool the CO2 gas released from the CO2 cylinder to form liquefied CO2. The supercritical CO2 injection pump discharges the liquefied CO2 and, after passing through the preheating device, forms supercritical CO2, which is then injected into the marine sediments in the reactor.

[0010] Furthermore, the temperature control system includes a connected temperature regulating device and a temperature sensor. The temperature sensor is inserted into the reactor to detect the temperature of the sediment inside the reactor in real time. The temperature regulating device is used to adjust the temperature of the sediment inside the reactor so that the supercritical CO2 entering the marine sediment is maintained in a supercritical state.

[0011] Furthermore, the vacuuming and saturation system includes a pore water injection pump and a vacuum pump, which operate sequentially. Fluid channels are provided at both the top and bottom of the reactor, and the fluid channel at the top of the reactor is connected in sequence to the pore water injection pump and the vacuum pump.

[0012] Furthermore, the top and bottom of the reactor are each provided with annular mesh grooves connected to corresponding fluid channels; the fluid channel at the bottom of the reactor is equipped with a back pressure valve to allow supercritical carbon dioxide and water to automatically flow out of the reactor after exceeding a certain pore pressure; a pore water metering device is provided below the back pressure valve to measure the volume of displaced pore water.

[0013] A method for monitoring CO2 migration in sediments based on time-domain reflectometry, applied to the aforementioned monitoring device, includes the following steps: S1. Sample preparation and obtaining sample porosity, water saturation of the sample and ensuring that the internal temperature of the reactor reaches above the supercritical CO2 critical temperature; S2. Inject supercritical CO2 into the reactor to displace the pore water in the sediment. The volume of displaced pore water is the volume of CO2 in the sediment sample. The ratio of the CO2 volume to the pore volume of the sample is used to calculate the real-time changing overall CO2 saturation of the sample. S3. The dielectric constant of the deposits in the reactor at different CO2 saturations is continuously measured using radial time-domain reflectometry and axial time-domain reflectometry, respectively, in directions perpendicular to and parallel to the CO2 migration direction. S4. Combining the real-time changing overall CO2 saturation of the sample obtained in step S2 and the average value of the dielectric constant measured by the axial time-domain reflectometry sensor under different CO2 saturations in step S3, plot the graph of the dielectric constant changing with CO2 saturation with CO2 saturation as the X-axis and the dielectric constant as the Y-axis, respectively, and further fit to establish the relationship between CO2 saturation and dielectric constant. S5. Using the dielectric constant measured by the radial time-domain reflectometry sensor, and combining the relationship between CO2 saturation and dielectric constant in step S4, calculate the local CO2 saturation gradient changes of multiple radial time-domain reflectometry sensors from top to bottom in the corresponding sediment regions. S6. Compare the gradient change of local CO2 saturation in the corresponding sediment region obtained by measuring the dielectric constant based on the radial time-domain reflectometry sensor in step S5 to characterize the migration dynamics of CO2 in the sample, and then locate the position of the CO2 plume front. S7. When all the fluid flowing out of the fluid channel at the bottom of the reactor is CO2, stop working; Steps S2 and S3 are performed simultaneously.

[0014] Furthermore, step S1 includes: S11. After washing and drying the marine sediment simulation medium, it is loaded into the reaction vessel. Based on the volume of the sample in the reaction vessel and the mass and density of the marine sediment simulation medium, the porosity of the sample in the reaction vessel is calculated. S12. Use a vacuum pump to evacuate the sample, then use a pore water injection pump to inject brine into the sediment until the supercritical CO2 critical pressure is reached, and record the initial pore water volume injected. S13. Adjust the temperature of the sediment in the reactor, ensure that the internal temperature of the reactor reaches above the supercritical CO2 critical temperature through a temperature sensor, and monitor the temperature of different layers of sediment in the reactor through a temperature sensor.

[0015] Compared with the prior art, the advantages of the present invention are as follows: This invention can simultaneously monitor the anisotropic response characteristics of the dielectric properties of marine sediments parallel and perpendicular to the CO2 migration direction, enabling anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in marine sediments. It can also jointly characterize the CO2 saturation in sediment samples and the dynamic migration of the CO2 plume front during CO2 migration, thereby achieving accurate assessment of CO2 sequestration efficiency and leakage risk in marine sediments. The invention features high monitoring accuracy, minimal influence from pore water salinity and temperature, and simple operation, making it significant for accurately monitoring the CO2 migration process in marine sediments using dielectric properties. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the anisotropy monitoring device for CO2 migration process in marine sediments based on time-domain reflectometry as described in this invention. Figure 2 This is a schematic diagram of the longitudinal section structure inside the reactor of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure inside the reactor of the present invention; Figure 4 This is a schematic diagram of the annular mesh groove structure at the top or bottom of the reactor of the present invention.

[0017] In the above figures: A. Reactor; B. Temperature control system; C. Dielectric constant testing and control system; D. Supercritical carbon dioxide preparation and injection system; E. Vacuuming and saturation system; F. Data acquisition and processing system; 1. Fluid channel; 2. Permeable stone; 3. Insulating cylinder; 4. Sediment sample; 5. Temperature sensor; 6. Time domain reflectance sensor assembly; 7. Reactor shell; 8. Pore water injection pump; 9. Vacuum pump; 10. Valve; 11. Preheating device; 12. Supercritical CO2 injection pump; 13. Refrigeration water bath device; 14. CO2 pressurization device; 15. CO2 cylinder; 16. Time domain reflectance tester; 17. Back pressure valve; 18. Pore water metering device; 19. Temperature regulating device; 20. Annular grid groove. Detailed Implementation

[0018] To facilitate understanding of the present invention by those skilled in the art, specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0019] Working principle: Accurately estimating CO2 saturation in marine sediments and precisely detecting the CO2 plume front during CO2 injection are crucial indicators for effectively characterizing, monitoring, quantifying, and locating CO2 migration dynamics. This provides a scientific basis for successfully evaluating CO2 sequestration efficiency (sequestration and injection volume) and stability (leakage risk). When CO2 migrates in sediments along a certain direction, it forces pore water in the sediments to move in that direction (CO2 displaces pore water), resulting in significant anisotropy in the sediments during CO2 migration—that is, a significant difference in dielectric properties parallel to and perpendicular to the CO2 migration direction.

[0020] However, current devices and methods for monitoring water content based on time-domain reflectometry lack anisotropic monitoring capabilities, failing to achieve joint characterization of CO2 saturation and its plume front in experimental samples. This invention proposes a time-domain reflectometry-based device and method for monitoring CO2 migration in sediments. This method enables anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in marine sediments, and also allows for joint characterization of CO2 saturation and its dynamic migration of the CO2 plume front in sediment sample 4 during CO2 migration. This facilitates accurate assessment of CO2 sequestration efficiency and leakage risk in marine sediments.

[0021] Example 1 like Figures 1-4As shown, this invention proposes a CO2 migration monitoring device in sediments based on time-domain reflectometry, comprising a reaction vessel A, a vacuum and saturation system E, a supercritical carbon dioxide preparation and injection system D, a temperature control system B, a dielectric constant testing and control system C, and a data acquisition and processing system. The reaction vessel A is connected to the vacuum and saturation system E, the supercritical carbon dioxide preparation and injection system D, the temperature control system B, and the dielectric constant testing and control system C, respectively. The dielectric constant testing and control system C is connected to the data acquisition and processing system F.

[0022] For handling complex reactions such as marine sediment treatment, the reactor A of this invention is, by default, a high-pressure reactor. In this embodiment, reactor A is a cylindrical reactor.

[0023] Specifically, the reactor A includes a reactor shell 7 and an insulating cylinder 3. The insulating cylinder 3 is tightly embedded in the reactor shell 7. The insulating cylinder 3 contains a marine sediment sample 4, in which experiments on the transport of supercritical carbon dioxide in sediments can be carried out, and various parameters during the experiment can be measured.

[0024] Two layers of permeable and breathable stone were added to the marine sediment sample 4. The two layers of permeable and breathable stone were located at the top and bottom of the reactor A, respectively, in order to ensure that supercritical carbon dioxide and water flowed in and out evenly at the top and bottom of the reactor A.

[0025] To facilitate the inflow and outflow of supercritical carbon dioxide and water, fluid channels 1 are provided at the center of both the top and bottom of reactor A. Fluid channels 1 are connected to the vacuum and saturation system E, and valves 10 are installed between them.

[0026] In order to enable supercritical carbon dioxide and water to automatically flow out of reactor A after exceeding a certain pressure, a back pressure valve 17 is also provided in the fluid channel 1 at the bottom of reactor A.

[0027] Furthermore, a pore water metering device 18 is provided below the back pressure valve 17 of the fluid channel 1 at the bottom of reactor A to measure the volume of displaced pore water, which is the volume of CO2 in the sample.

[0028] like Figure 4 As shown, in order to promote the uniform inflow and outflow of fluid at the top and bottom of the test sample, the top and bottom of the reactor A are both equipped with annular mesh grooves 20 connected to the fluid channel 1.

[0029] The dielectric constant testing and control system C includes a connected time-domain reflectometry sensor assembly 6 and a time-domain reflectometry tester 16. The time-domain reflectometry sensor assembly 6 includes multiple axial time-domain reflectometry sensors inserted into reactor A from the bottom and multiple radial time-domain reflectometry sensors inserted into reactor A from the side. The axial time-domain reflectometry sensors are used to measure the dielectric constant of the sediment sample 4 at different locations parallel to the CO2 migration direction, while the radial time-domain reflectometry sensors are used to measure the dielectric constant of the sediment sample 4 at different locations perpendicular to the CO2 migration direction.

[0030] Specifically, multiple axial time-domain reflectometry sensors simultaneously measure the dielectric constant of the sediment at different orientations, and multiple radial time-domain reflectometry sensors simultaneously measure the dielectric constant of the sediment at different depths.

[0031] The time-domain reflectometry instrument 16 is connected to the control computer of the data acquisition and processing system F. The control software of the control computer can control the operation of different time-domain reflectometry sensors separately. The control method used by this software is existing technology.

[0032] In this embodiment, the time-domain reflectometry sensor assembly 6 consists of two groups of eight components: four radial time-domain reflectometry sensors and four axial time-domain reflectometry sensors. These sensors can simultaneously measure the dielectric constant of the sediment in directions perpendicular to and parallel to the carbon dioxide migration direction.

[0033] The vacuum and saturation system E is connected to the top of the reactor A and is used to vacuum and saturate the pore water in the marine sediment.

[0034] Specifically, the vacuum and saturation system E includes a pore water injection pump and a vacuum pump 9. The vacuum pump 9 and the pore water injection pump 8 operate sequentially. The fluid channel 1 at the top of the reactor A is connected in sequence to the pore water injection pump 8 and the vacuum pump 9.

[0035] The supercritical carbon dioxide preparation and injection system D is also connected to the top of the reactor A to inject supercritical carbon dioxide into the marine sediments.

[0036] Specifically, the supercritical carbon dioxide preparation and injection system D includes a CO2 cylinder 15, a CO2 pressurization device 14, a cooling water bath device 13, a supercritical CO2 injection pump 12, and a preheating device 11. The CO2 gas released from the CO2 cylinder 15 is pressurized and cooled by the CO2 pressurization device 14 and the cooling water bath device 13, causing it to liquefy. The supercritical CO2 injection pump 12 then discharges the liquefied CO2, which passes through the preheating device 11, thus forming supercritical CO2 which is then injected into marine sediments.

[0037] Temperature control system B houses reactor A and provides the required temperature conditions for supercritical carbon dioxide, ensuring that the supercritical CO2 entering the marine sediments remains in a supercritical state. Temperature control system B includes a connected temperature regulating device 19 and a temperature sensor 5. The temperature sensor 5 extends from the side of reactor A through the outer shell 7 into the insulating cylinder 3 to detect the temperature of the marine sediments. Temperature regulating device 19 is used to adjust the temperature of the sediments inside reactor A.

[0038] In this embodiment, such as Figure 2 As shown, four temperature sensors 5 are set up and are evenly distributed from top to bottom on the side of the reactor A and perpendicular to the direction in which the radial time domain reflection sensor enters the reactor A. In this way, the temperature at different locations of the sediment is monitored by the four temperature sensors 5 to ensure that CO2 is in a supercritical state.

[0039] In this embodiment, the temperature control device 19 includes a refrigerator and a circulating liquid conduit. The reactor A has a built-in circulating liquid inlet and a circulating liquid outlet. The circulating liquid inlet and the circulating liquid outlet are respectively connected to the constant temperature chamber in the refrigerator through the circulating liquid conduit.

[0040] The data acquisition and processing system F collects data from the time-domain reflectometry sensor component 6 and the temperature sensor 5, and displays the data on the control computer after data processing. Example 2

[0041] This invention also proposes a method for monitoring CO2 migration in sediments based on time-domain reflectometry, comprising the following steps: The specific implementation steps of this device are as follows: Step S1: Sample preparation and obtaining sample porosity, saturating the sample with water and ensuring that the internal temperature of reactor A reaches above the supercritical CO2 critical temperature.

[0042] Specifically, the marine sediment simulation medium, such as quartz sand, is washed, dried, and then loaded into reactor A. The porosity of the sample in reactor A is calculated based on the volume of the sample in reactor A and the mass and density of the quartz sand loaded into it. The sample was evacuated for 12 hours using vacuum pump 9. Then, brine was injected into the sediment using pore water injection pump 8 until the supercritical CO2 critical pressure was reached. The initial volume of injected pore water was recorded. The operating temperature control system B regulates the temperature of the sediment in reactor A, and ensures that the internal temperature of reactor A reaches above the supercritical CO2 critical temperature through temperature sensor 5, and monitors the temperature of different layers of sediment in reactor A through temperature sensor 5.

[0043] Step S2: Run the supercritical carbon dioxide preparation and injection system D, inject supercritical CO2 into the sediment in reactor A at a pressure higher than that of the pore water in the sediment, thereby displacing the pore brine in the sediment. The pore brine flows out from the low-end channel of reactor A, and the volume of pore brine displaced by CO2 injection is measured by the pore water metering device 18. The ratio of the volume of CO2 to the initial volume of pore brine in the injected sample can be used to calculate the real-time changing overall CO2 saturation of the sample.

[0044] Step S3: Run the dielectric constant test control unit and use the radial time domain reflection sensor and the axial time domain reflection sensor to continuously measure the dielectric constant of the deposits in reactor A at different CO2 saturations in directions perpendicular to and parallel to the CO2 migration direction.

[0045] This allows for the measurement of the anisotropic dielectric constant of sediment sample 4 during supercritical CO2 migration. Specifically, the dielectric constant of the marine sediment as a whole is measured using an axial time-domain reflectometry sensor parallel to the CO2 migration direction, while the dielectric constant of sediment sample 4 at different locations perpendicular to the CO2 migration direction is measured using a radial time-domain reflectometry sensor.

[0046] Steps S2 and S3 are performed simultaneously.

[0047] Step S4: Combining the real-time changing overall CO2 saturation of the sample obtained in Step S2 and the average value of the dielectric constant measured by the axial time-domain reflectometry sensor under different CO2 saturations in Step S3, the data is assigned to the Origin plotting software. The graphs of the dielectric constant changing with CO2 saturation are plotted with CO2 saturation and dielectric constant as the X-axis and Y-axis, respectively. Furthermore, a formula with CO2 saturation as the independent variable and dielectric constant as the dependent variable is fitted and established. Step S5: Using the dielectric constant measured by the radial time-domain reflectometry sensor, and combining it with the relationship formula between CO2 saturation and dielectric constant in step S4, calculate the local CO2 saturation gradient changes in the corresponding sediment regions from top to bottom using multiple radial time-domain reflectometry sensors.

[0048] Step S6: Compare the gradient change of local CO2 saturation in the corresponding sediment region obtained by measuring the dielectric constant based on the radial time-domain reflectometry sensor in step S5 to characterize the migration dynamics of CO2 in the sample, and then locate the position of the CO2 plume front.

[0049] The specific dynamics of CO2 migration in the sample are as follows: CO2 is injected from the top of sediment sample 4, and the CO2 displaces the pore water in sediment sample 4 from top to bottom, causing the CO2 plume front to migrate from top to bottom. During the migration of the CO2 plume front from top to bottom, the CO2 saturation in sediment sample 4 also changes from top to bottom (i.e., the CO2 saturation gradually increases from top to bottom). This change in saturation can be detected by four radial time-domain reflectometry sensors distributed from top to bottom.

[0050] Ultimately, a joint characterization of CO2 saturation in sediment sample 4 and the dynamic migration of the CO2 plume front was achieved during CO2 migration.

[0051] Step S7: When all the fluid flowing out of the fluid channel 1 at the bottom of reactor A is CO2, all systems stop working.

[0052] This invention, through the aforementioned monitoring method, enables the joint characterization of CO2 saturation and the dynamic migration of the CO2 plume front in sediment sample 4 during CO2 migration, thereby achieving accurate assessment of CO2 sequestration efficiency and leakage risk in marine sediments. The monitoring method is highly accurate, less affected by pore water salinity and temperature, and simple to operate, which is of great significance for accurately monitoring the CO2 migration process in marine sediments using dielectric properties.

[0053] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A device for monitoring CO2 migration in sediments based on time-domain reflectometry, comprising a reaction vessel, a vacuum and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, and a data acquisition and processing system, characterized in that, It also includes a dielectric constant testing and control system. The reactor is connected to a vacuum and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, and a dielectric constant testing and control system. The dielectric constant testing and control system is connected to a data acquisition and processing system. The dielectric constant test and control system includes a time-domain reflectometry instrument and a time-domain reflectometry sensor assembly connected to the time-domain reflectometry instrument. The time-domain reflectometry sensor assembly includes multiple axial time-domain reflectometry sensors inserted into the reactor from the bottom and multiple radial time-domain reflectometry sensors inserted into the reactor from the side.

2. The monitoring device according to claim 1, characterized in that, The plurality of axial time-domain reflectometry sensors are arranged in a square at the bottom of the reactor, and the square is located at the midpoint of the radius of the circular cross-section at the bottom of the reactor.

3. The monitoring device according to claim 1, characterized in that, The plurality of radial time-domain reflectometers are distributed at equal intervals from top to bottom inside the reactor.

4. The monitoring device according to claim 1, characterized in that, The supercritical carbon dioxide preparation and injection system includes a connected CO2 cylinder, a CO2 pressurizing device, a cooling water bath device, a supercritical CO2 injection pump, and a preheating device. The CO2 pressurizing device and the cooling water bath device pressurize and cool the CO2 gas released from the CO2 cylinder to form liquefied CO2. The supercritical CO2 injection pump discharges the liquefied CO2 and, after passing through the preheating device, forms supercritical CO2, which is then injected into the marine sediments in the reactor.

5. The monitoring device according to claim 1, characterized in that, The temperature control system includes a connected temperature regulating device and a temperature sensor. The temperature sensor is inserted into the reactor to detect the temperature of the sediment in the reactor in real time. The temperature regulating device is used to adjust the temperature of the sediment in the reactor so that the supercritical state of CO2 entering the marine sediment is maintained in a supercritical state.

6. The monitoring device according to claim 1, characterized in that, The vacuuming and saturation system includes a pore water injection pump and a vacuum pump, which operate sequentially. Fluid channels are provided at both the top and bottom of the reactor, and the fluid channel at the top of the reactor is connected to the pore water injection pump and the vacuum pump in sequence.

7. The monitoring device according to claim 6, characterized in that, The reactor has annular mesh grooves at both the top and bottom ends that are connected to corresponding fluid channels; the fluid channel at the bottom end of the reactor is equipped with a back pressure valve to allow supercritical carbon dioxide and water to automatically flow out of the reactor after exceeding a certain pore pressure; a pore water metering device is provided below the back pressure valve to measure the volume of pore water displaced.

8. A method for monitoring CO2 migration in sediments based on time-domain reflectometry, applied to the monitoring device described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Sample preparation and obtaining sample porosity, water saturation of the sample and ensuring that the internal temperature of the reactor reaches above the supercritical CO2 critical temperature; S2. Inject supercritical CO2 into the reactor to displace the pore water in the sediment. The volume of displaced pore water is the volume of CO2 in the sediment sample. The ratio of the CO2 volume to the pore volume of the sample is used to calculate the real-time changing overall CO2 saturation of the sample. S3. The dielectric constant of the deposits in the reactor at different CO2 saturations is continuously measured using radial time-domain reflectometry and axial time-domain reflectometry, respectively, in directions perpendicular to and parallel to the CO2 migration direction. S4. Combining the real-time changing overall CO2 saturation of the sample obtained in step S2 and the average value of the dielectric constant measured by the axial time-domain reflectometry sensor under different CO2 saturations in step S3, plot the graph of the dielectric constant changing with CO2 saturation with CO2 saturation as the X-axis and the dielectric constant as the Y-axis, respectively, and further fit to establish the relationship between CO2 saturation and dielectric constant. S5. Using the dielectric constant measured by the radial time-domain reflectometry sensor, and combining the relationship between CO2 saturation and dielectric constant in step S4, calculate the local CO2 saturation gradient changes of multiple radial time-domain reflectometry sensors from top to bottom in the corresponding sediment regions. S6. Compare the gradient change of local CO2 saturation in the corresponding sediment region obtained by measuring the dielectric constant based on the radial time-domain reflectometry sensor in step S5 to characterize the migration dynamics of CO2 in the sample, and then locate the position of the CO2 plume front. S7. When all the fluid flowing out of the fluid channel at the bottom of the reactor is CO2, stop working; Steps S2 and S3 are performed simultaneously.

9. The monitoring method according to claim 8, characterized in that, Step S1 includes: S11. After washing and drying the marine sediment simulation medium, it is loaded into the reaction vessel. Based on the volume of the sample in the reaction vessel and the mass and density of the marine sediment simulation medium, the porosity of the sample in the reaction vessel is calculated. S12. Use a vacuum pump to evacuate the sample, then use a pore water injection pump to inject brine into the sediment until the supercritical CO2 critical pressure is reached, and record the initial pore water volume injected. S13. Adjust the temperature of the sediment in the reactor, ensure that the internal temperature of the reactor reaches above the supercritical CO2 critical temperature through a temperature sensor, and monitor the temperature of different layers of sediment in the reactor through a temperature sensor.

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