A device and method for monitoring the migration of CO2 in a deposit based on time domain reflectometry

Abstract

The application belongs to the field of marine geophysical exploration, and specifically provides a device and method for monitoring CO2 migration in sediments based on time domain reflectometry, which comprises a reaction kettle, a vacuum extraction and saturation system, a supercritical CO2 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 reflectometry tester and a time domain reflectometry sensor assembly, and the time domain reflectometry sensor assembly comprises multiple axial time domain reflectometry sensors inserted from the bottom of the reaction kettle and multiple radial time domain reflectometry sensors inserted from the side of the reaction kettle. The application can realize anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in marine sediments, and can also realize joint characterization of the CO2 saturation in the sediment sample and the migration dynamics of the CO2 plume front during the CO2 migration process, so as to realize accurate evaluation of the CO2 storage efficiency and leakage risk in marine sediments, and the monitoring effect is good and the operation is simple.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of marine geophysical exploration, and particularly relates to a device and method for monitoring CO2 migration in sediments based on time domain reflectometry. BACKGROUND

[0002] Global warming can significantly affect the Earth's climate change, and in turn pose a serious threat to the stability of the ecological system, biodiversity and human production and life. Carbon dioxide (CO2) as a greenhouse gas has been proven to be one of the most important factors leading to global warming. CO2 geological storage technology is considered a feasible and sustainable method that can effectively reduce the concentration of CO2 in the atmosphere, and thus has important significance for mitigating global warming. In marine sediments, CO2 storage technology based on hydrate method has attracted widespread attention from countries around the world due to its high storage density and wide storage range. CO2 storage efficiency and stability (i.e., CO2 migration can be caused by both CO2 hydrate generation and decomposition leakage) closely related to CO2 migration are key indicators for evaluating the success of CO2 geological storage. Therefore, accurately monitoring the migration process of CO2 in marine sediments is crucial for assessing the efficiency and safety of CO2 storage.

[0003] Conventional geophysical methods (such as seismic exploration techniques based on sound velocity or attenuation, and electrical exploration techniques based on resistivity) have become important technical means for monitoring gas migration in marine sediments. However, both seismic and electrical exploration techniques have their own limitations, specifically: seismic exploration has insufficient sensitivity to the type and content of fluids in the sediment pores; in contrast, although electrical exploration based on resistivity has higher sensitivity to the type and content of fluids in the pores, resistivity is significantly affected by the salinity of pore water and reservoir temperature. Therefore, seismic and electrical exploration techniques have different degrees of defects in accurately monitoring gas migration in marine sediments. Compared with the above two detection methods, detection techniques based on dielectric properties not only can effectively identify the type of fluid in the pores and directly calculate its content, but also are minimally affected by the salinity of pore water and temperature, thus providing a new way for accurate monitoring of CO2 migration in marine sediments.

[0004] In recent years, time domain reflectometry based on the detection of dielectric constant has been widely used for monitoring and evaluation of conventional soil moisture content, frozen soil thickness and freeze-thaw processes, and water content in methane hydrate sediments. The corresponding monitoring devices developed based on time domain reflectometry have also made breakthrough progress. However, as of now, there have been no reports on the continuous dynamic monitoring of supercritical CO2 migration in marine sediments using time domain reflectometry. Moreover, the currently developed devices and methods for monitoring water content based on time domain reflectometry do not have anisotropic monitoring function, and cannot achieve joint characterization of CO2 saturation and plume front in experimental samples. SUMMARY

[0005] In order to solve the defects that the prior art cannot use time domain reflection technology to continuously and dynamically monitor the supercritical CO2 migration process in marine sediments, does not have anisotropic monitoring function, and cannot realize the joint representation of CO2 saturation and plume front in the experimental sample, the present application provides a CO2 migration monitoring device and method in sediments based on time domain reflection method, which has anisotropic monitoring function and can represent CO2 saturation and migration front in the experimental sample through time domain reflection technology.

[0006] The scheme is as follows:

[0007] A CO2 migration monitoring device in sediments based on time domain reflection method, comprising a reaction kettle, a vacuum extraction and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, a data acquisition and processing system, and a dielectric constant test control system, wherein the reaction kettle is connected with the vacuum extraction and saturation system, the supercritical carbon dioxide preparation and injection system, the temperature control system, and the dielectric constant test control system respectively, and the dielectric constant test control system is connected with the data acquisition and processing system.

[0008] The dielectric constant test control system comprises a time domain reflection tester and a time domain reflection sensor assembly connected with the time domain reflection tester, wherein the time domain reflection sensor assembly comprises a plurality of axial time domain reflection sensors inserted into the reaction kettle from the bottom of the reaction kettle and a plurality of radial time domain reflection sensors inserted into the reaction kettle from the side of the reaction kettle.

[0009] Further, the plurality of axial time domain reflection sensors are distributed in a square shape at the bottom end of the reaction kettle, and the square is located at the middle point of the radius of the circular cross section at the bottom end of the reaction kettle.

[0010] Further, the plurality of radial time domain reflection sensors are equally spaced from top to bottom in the reaction kettle.

[0011] Further, the supercritical carbon dioxide preparation and injection system comprises a CO2 gas cylinder, a CO2 pressurizing device, a refrigerated water bath device, a supercritical CO2 injection pump, and a preheating device connected in sequence, wherein the CO2 pressurizing device and the refrigerated water bath device pressurize and cool the CO2 gas released from the CO2 gas cylinder to form liquefied CO2, and the supercritical CO2 injection pump discharges the liquefied CO2 and forms supercritical CO2 through the preheating device and injects it into the marine sediments in the reaction kettle.

[0012] Further, the temperature control system comprises a temperature adjusting device and a temperature sensor connected thereto, the temperature sensor is inserted into the reactor for real-time detection of the temperature of the sediments in the reactor, and the temperature adjusting device is used to adjust the temperature of the sediments in the reactor, so that the supercritical CO2 entering the marine sediments is maintained in a supercritical state.

[0013] Further, the vacuumizing and saturating system comprises a pore water injection pump and a vacuum pump, the vacuum pump and the pore water injection pump are operated in sequence, and the top end and the bottom end of the reactor are respectively provided with fluid channels, and the fluid channel at the top end of the reactor is sequentially connected with the pore water injection pump and the vacuum pump.

[0014] Further, the top end and the bottom end of the reactor are respectively provided with annular grid grooves connected with the fluid channels corresponding thereto, and the fluid channel at the bottom end of the reactor is provided with a back pressure valve to automatically flow out the supercritical CO2 and water from the reactor when the pore pressure exceeds a certain value, and the back pressure valve is provided below with a pore water metering device to meter the volume of the displaced pore water.

[0015] A method for monitoring the migration of CO2 in sediments based on time domain reflectometry, applied to the monitoring device, comprising the following steps:

[0016] S1, sample preparation and obtaining sample porosity, saturating the sample with water and ensuring that the temperature inside the reactor reaches above the critical temperature of supercritical CO2;

[0017] S2, injecting supercritical CO2 into the reactor to displace the pore water in the sediments, and the volume of the displaced pore water is the volume of CO2 in the sample, and the ratio of the volume of CO2 to the pore volume of the sample is used to calculate the real-time change of the overall CO2 saturation of the sample;

[0018] S3, using radial time domain reflectometry sensors and axial time domain reflectometry sensors to continuously measure the dielectric constant of the sediments in the reactor at different CO2 saturations in the perpendicular and parallel directions to the migration direction of CO2;

[0019] S4, combining the real-time change of the 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 at different CO2 saturations in step S3, taking CO2 saturation and dielectric constant as X-axis and Y-axis respectively, drawing a graph of the change of dielectric constant with CO2 saturation, and further fitting to establish the relationship between CO2 saturation and dielectric constant;

[0020] S5, using the dielectric constant measured by the radial time domain reflectometry sensor, combining the relationship between CO2 saturation and dielectric constant in step S4, and calculating the local CO2 saturation gradient change in the corresponding sediment region of each radial time domain reflectometry sensor from top to bottom.

[0021] S6, contrast the gradient change of the local CO2 saturation degree in the corresponding sediment area obtained based on the dielectric constant measured by the radial time domain reflection sensor in step S5, to represent the migration mode of CO2 in the sample, and further locate the position of the CO2 plume front;

[0022] S7, stop working when the fluid channel at the bottom end of the reaction kettle flows out only CO2;

[0023] Wherein, steps S2 and S3 are performed simultaneously.

[0024] Further, step S1 comprises:

[0025] S11, after the marine sediment simulation medium is washed and dried, it is loaded into the reaction kettle, and the porosity of the sample in the reaction kettle is calculated according to the volume of the sample in the reaction kettle and the mass and density of the loaded marine sediment simulation medium;

[0026] S12, vacuumizing the sample by using a vacuum pump, then injecting brine into the sediment by using a pore water injection pump, and reaching the critical pressure of supercritical CO2, and recording the initial pore water volume injected;

[0027] S13, temperature adjustment is performed on the sediment in the reaction kettle, the temperature inside the reaction kettle is ensured to reach above the critical temperature of supercritical CO2 by a temperature sensor, and the temperature of different layers of the sediment in the reaction kettle is monitored by the temperature sensor.

[0028] Compared with the prior art, the advantages of the present application are as follows:

[0029] The present application can simultaneously monitor the anisotropic response characteristics of the dielectric properties of marine sediments parallel and perpendicular to the CO2 migration direction, can realize the anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in marine sediments, can realize the joint representation of the CO2 saturation degree in the sediment sample and the migration mode of the CO2 plume front during the CO2 migration process, and can realize the accurate evaluation of the CO2 storage efficiency and leakage risk in marine sediments, with high monitoring precision, small influence of pore water salinity and temperature, and simple operation, which has important significance for accurately monitoring the migration process of CO2 in marine sediments by using dielectric properties. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a structure schematic view of the marine sediment CO2 migration process anisotropy monitoring device based on time domain reflection method according to the present application;

[0031] Figure 2 It is a longitudinal section structure schematic view of the reaction kettle according to the present application;

[0032] Figure 3The schematic diagram of the transverse section structure in the reaction kettle of the present application is shown in the figure.

[0033] Figure 4 The schematic diagram of the annular grid groove structure at the top or bottom end of the reaction kettle of the present application is shown in the figure.

[0034] In the above figures: A, reaction kettle; B, temperature control system; C, dielectric constant test control system; D, supercritical carbon dioxide preparation and injection system; E, vacuum extraction and saturation system; F, data acquisition and processing system; 1, fluid channel; 2, air and water permeable stone; 3, insulating cylinder; 4, sediment sample; 5, temperature sensor; 6, time domain reflection sensor assembly; 7, kettle body shell; 8, pore water injection pump; 9, vacuum pump; 10, valve; 11, preheating device; 12, supercritical CO2 injection pump; 13, refrigerated water bath device; 14, CO2 pressurizing device; 15, CO2 gas cylinder; 16, time domain reflection tester; 17, back pressure valve; 18, pore water metering device; 19, temperature adjusting device; 20, annular grid groove. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to understand the present application, the specific embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0036] Working principle:

[0037] In the process of injecting CO2 into marine sediments, accurate estimation of the CO2 saturation in marine sediments and accurate detection of the plume front of CO2 in the sediments are important indicators for effectively characterizing, monitoring, quantifying and positioning the CO2 migration dynamics, thereby providing a scientific basis for successfully evaluating the CO2 storage efficiency (storage amount and injection amount) and stability (leakage risk). When CO2 migrates in a certain direction in the sediments, it will force the pore water in the sediments to migrate in the same direction (CO2 displaces pore water), thereby making the sediments in the CO2 migration process exhibit significant anisotropic characteristics, i.e., there is a significant difference in dielectric properties parallel to the CO2 migration direction and perpendicular to the direction.

[0038] However, the devices and methods for monitoring water content based on time domain reflection technology developed at present do not have anisotropic monitoring function and cannot realize the joint characterization of CO2 saturation and its plume front in the experimental sample. The CO2 migration monitoring device and method in sediments based on time domain reflection method proposed in the present application can realize the anisotropic dynamic monitoring of the continuous migration process of supercritical CO2 in marine sediments, and can also realize the joint characterization of the CO2 saturation in the sediment sample 4 and the migration dynamics of the CO2 plume front in the CO2 migration process, thereby realizing the accurate evaluation of the CO2 storage efficiency and leakage risk in marine sediments.

[0039] Example one

[0040] As Figures 1-4 shown, the application proposes a CO2 migration monitoring device in sediment based on time domain reflectometry, comprising a reactor A, a vacuum extraction and saturation system E, a supercritical carbon dioxide preparation and injection system D, a temperature control system B, a dielectric constant test control system C, a data acquisition and processing system, the reactor A is connected with the vacuum extraction and saturation system E, the supercritical carbon dioxide preparation and injection system D, the temperature control system B and the dielectric constant test control system C, and the dielectric constant test control system C is connected with the data acquisition and processing system F.

[0041] For dealing with complex reactions such as marine processing sediment, the reactor A of the application defaults to a high-pressure reactor. In this embodiment, the reactor A is a cylindrical reactor.

[0042] Specifically, the reactor A comprises a reactor body shell 7 and an insulation cylinder 3, the insulation cylinder 3 is tightly embedded in the reactor body shell 7, and the marine sediment sample 4 is contained in the insulation cylinder 3, so that the supercritical carbon dioxide migration experiment in the sediment can be carried out therein, and various parameters in the experiment process can be measured.

[0043] Two layers of air and water permeable stones 2 are added in the marine sediment sample 4, and the two layers of air and water permeable stones 2 are respectively located at the top end and the bottom end of the reactor A, so that the supercritical carbon dioxide and water can uniformly flow into and out of the top end and the bottom end of the reactor A.

[0044] In order to meet the inflow and outflow of supercritical carbon dioxide and water, the fluid channel 1 is arranged at the center position of the top end and the bottom end of the reactor A. The fluid channel 1 is connected with the vacuum extraction and saturation system E, and a valve 10 is arranged therebetween.

[0045] In order to make the supercritical carbon dioxide and water automatically flow out of the reactor A after exceeding a certain pressure, the fluid channel 1 at the bottom end of the reactor A is further provided with a back pressure valve 17.

[0046] Further, the back pressure valve 17 of the fluid channel 1 at the bottom end of the reactor A is provided below with a pore water metering device 18 to meter the pore water volume displaced, that is, the volume of CO2 in the sample.

[0047] As Figure 4 shown, in order to promote the uniform inflow and outflow of fluid at the top end and the bottom end of the test sample, the top end and the bottom end of the reactor A are both provided with an annular grid groove 20 connected with the fluid channel 1.

[0048] The dielectric constant test control system C comprises the time domain reflection sensor assembly 6 and the time domain reflection tester 16 connected with each other. The time domain reflection sensor assembly 6 comprises a plurality of axial time domain reflection sensors inserted into the reactor A from the bottom of the reactor A and a plurality of radial time domain reflection sensors inserted into the reactor A from the side of the reactor A. The axial time domain reflection sensors are used to measure the dielectric constant of the sediment sample 4 at different positions in parallel to the migration direction of CO2, and the radial time domain reflection sensors are used to measure the dielectric constant of the sediment sample 4 at different positions in vertical to the migration direction of CO2.

[0049] Specifically, the plurality of axial time domain reflection sensors measure the dielectric constant of the sediment at different positions respectively and simultaneously, and the plurality of radial time domain reflection sensors measure the dielectric constant of the sediment at different depths respectively and simultaneously.

[0050] The time domain reflection tester 16 is connected with 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 reflection sensors respectively. The control method adopted by the control software is the prior art.

[0051] In this embodiment, the time domain reflection sensor assembly 6 is two groups of eight, and the radial time domain reflection sensors and the axial time domain reflection sensors are four respectively, which can measure the dielectric constant of the sediment in vertical and parallel to the migration direction of CO2 respectively and simultaneously.

[0052] The vacuumizing and saturating system E is connected with the top end of the reactor A, and is used to vacuumize the marine sediment and saturate the pore water.

[0053] Specifically, the vacuumizing and saturating system E comprises the pore water injection pump 8 and the vacuum pump 9, and the vacuum pump 9 and the pore water injection pump 8 are operated in sequence, and the fluid channel 1 at the top end of the reactor A is connected with the pore water injection pump 8 and the vacuum pump 9 in sequence.

[0054] The supercritical CO2 preparation and injection system D is also connected with the top end of the reactor A, and is used to inject the supercritical CO2 into the marine sediment.

[0055] Specifically, the supercritical CO2 preparation and injection system D comprises the CO2 gas cylinder 15, the CO2 pressurizing device 14, the refrigerated water bath device 13, the supercritical CO2 injection pump 12 and the preheating device 11. The CO2 gas released from the CO2 gas cylinder 15 is pressurized and cooled by the CO2 pressurizing device 14 and the refrigerated water bath device 13, so as to be liquefied, and then is discharged by the supercritical CO2 injection pump 12 and passes through the preheating device 11, so as to form the supercritical CO2 and be injected into the marine sediment.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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

[0060] This invention also proposes a method for monitoring CO2 migration in sediments based on time-domain reflectometry, comprising the following steps:

[0061] The specific implementation steps of this device are as follows:

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Step S2: Run the supercritical carbon dioxide preparation and injection system D to inject supercritical CO2 into the sediment in the reactor A at a pressure higher than the pore water in the sediment, thereby displacing the pore brine in the sediment, making the pore brine flow out of the lower end of the reactor A, and using the pore water metering device 18 to meter the volume of the pore brine displaced by the CO2 injection, and the ratio of the volume of CO2 to the initial volume of the pore brine in the sample can be calculated to obtain the real-time changing overall CO2 saturation of the sample.

[0067] Step S3: Run the dielectric constant test control unit to continuously measure the dielectric constant of the sediment in the reactor A at different CO2 saturations in the perpendicular and parallel directions to the CO2 migration direction using the radial time domain reflectometry sensor and the axial time domain reflectometry sensor, respectively.

[0068] In this way, the anisotropic dielectric constant of the sediment sample 4 during the supercritical CO2 migration process can be measured, that is, the dielectric constant of the overall marine sediment in the parallel direction to the CO2 migration direction is measured by the axial time domain reflectometry sensor, and the dielectric constant of the sediment sample 4 at different positions in the perpendicular direction to the CO2 migration direction is measured by the radial time domain reflectometry sensor.

[0069] Wherein, steps S2 and S3 are performed simultaneously.

[0070] Step S4: Combine 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 at different CO2 saturations in step S3, assign the data to the Origin drawing software, and draw the image of the change of the dielectric constant with the CO2 saturation as the X-axis and the Y-axis, respectively, and further fit to establish the formula with the CO2 saturation as the independent variable and the dielectric constant as the dependent variable.

[0071] Step S5: Using the dielectric constant measured by the radial time domain reflectometry sensor, and combining the relationship between the CO2 saturation and the dielectric constant in step S4, the local CO2 saturation gradient changes in the corresponding sediment regions of the multiple radial time domain reflectometry sensors from top to bottom are calculated, respectively.

[0072] Step S6: Compare the local CO2 saturation gradient changes in the corresponding sediment regions obtained based on the dielectric constant measured by the radial time domain reflectometry sensor in step S5 to characterize the migration state of CO2 in the sample, and further locate the position of the CO2 plume front.

[0073] The migration state of CO2 in the sample is characterized as follows: CO2 is injected from the top of the sediment sample 4, and the CO2 will displace the pore water in the sediment sample 4 from top to bottom, so that the CO2 plume front in the sample migrates from top to bottom; during the migration of the CO2 plume front from top to bottom, the CO2 saturation in the sediment sample 4 also changes from top to bottom (i.e., the CO2 saturation gradually increases from top to bottom), and this change in saturation can be detected by the four radial time-domain reflection sensors distributed from top to bottom.

[0074] Finally, the CO2 saturation in the sediment sample 4 during the migration of CO2 and the migration state of the CO2 plume front thereof are jointly characterized.

[0075] Step S7: When the fluid flowing out of the fluid channel 1 at the bottom end of the reaction kettle A is all CO2, all the systems stop working.

[0076] The above monitoring method can realize the joint characterization of the CO2 saturation in the sediment sample 4 during the migration of CO2 and the migration state of the CO2 plume front thereof, thereby realizing the accurate evaluation of the CO2 storage efficiency and leakage risk in marine sediments, and has high monitoring precision, small influence of pore water salinity and temperature, and simple operation, and is of great significance for accurately monitoring the migration process of CO2 in marine sediments by using dielectric properties.

[0077] The above-mentioned embodiments of the present application do not constitute a limitation on the protection scope of the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A device for monitoring the migration of CO2 in a deposit based on time domain reflectometry, comprising a reaction kettle, a vacuum extraction and saturation system, a supercritical carbon dioxide preparation and injection system, a temperature control system, a data acquisition and processing system, characterized in that, The dielectric constant test control system is connected with the data acquisition and processing system. The dielectric constant test control system comprises a time domain reflection tester and a time domain reflection sensor assembly connected with the time domain reflection tester.

2. The monitoring device of claim 1, wherein, The plurality of axial time domain reflection sensors are distributed in a square shape at the bottom end of the reactor, and the square is located at the middle point of the radius of the circular cross section at the bottom end of the reactor.

3. The monitoring device of claim 1, wherein, The plurality of radial time domain reflection sensors are distributed in the reactor in an equal interval from top to bottom.

4. The monitoring device of claim 1, wherein, The supercritical CO2 preparation and injection system comprises a CO2 cylinder, a CO2 pressurizing device, a refrigerated water bath device, a supercritical CO2 injection pump and a preheating device connected in sequence.

5. The monitoring device of claim 1, wherein, The temperature control system comprises a temperature regulating device and a temperature sensor connected in sequence.

6. The monitoring device of claim 1, wherein, The vacuum and saturation system comprises a pore water injection pump and a vacuum pump.

7. The monitoring device of claim 6, wherein, The top end and the bottom end of the reactor are provided with fluid channels, and the fluid channel at the top end of the reactor is connected with the pore water injection pump and the vacuum pump in sequence.

8. A method for monitoring the migration of CO2 in a deposit based on time domain reflectometry, applied to the monitoring device according to any one of claims 1 to 7, characterized in that, The top end and the bottom end of the reactor are provided with annular grid grooves connected with the fluid channels corresponding thereto. The bottom end of the reactor is provided with a back pressure valve to automatically flow out the supercritical CO2 and water from the reactor when the pore pressure exceeds a certain value. The following steps are included: S1, sample preparation and obtaining sample porosity, saturating the sample with water and ensuring that the internal temperature of the reactor reaches above the critical temperature of supercritical CO2; S2, injecting supercritical CO2 into the reactor to displace the pore water in the sediment, and measuring the volume of the displaced pore water, which is the volume of CO2 in the sediment sample, and calculating the real-time change of the overall CO2 saturation of the sample by the ratio of the volume of CO2 to the pore volume of the sample; S3, using radial time domain reflection sensors and axial time domain reflection sensors to continuously measure the dielectric constant of the sediment in the reactor at different CO2 saturations in the perpendicular and parallel directions of CO2 migration respectively. S4, combining the real-time changing sample overall CO2 saturation obtained in step S2 and the average value of dielectric constant measured by the axial time domain reflect sensor at different CO2 saturations in step S3, taking CO2 saturation and dielectric constant as X axis and Y axis respectively, drawing the image of dielectric constant changing with CO2 saturation, and further fitting to establish the relationship formula taking CO2 saturation as independent variable and dielectric constant as dependent variable; S5, using the dielectric constant measured by the radial time domain reflect sensor, combining the relationship formula of CO2 saturation and dielectric constant in step S4, calculating the local CO2 saturation gradient change in the corresponding sediment area of each radial time domain reflect sensor from top to bottom; S6, comparing the local CO2 saturation gradient change in the corresponding sediment area obtained based on the dielectric constant measured by the radial time domain reflect sensor in step S5, representing the migration mode of CO2 in the sample, and further positioning the position of CO2 plume front; S7, when the fluid flowing out of the fluid channel at the bottom end of the reactor is all CO2, stop working; Wherein, steps S2 and S3 are carried out at the same time.

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 reactor, and according to the volume of the sample in the reactor and the mass and density of the loaded marine sediment simulation medium, the porosity of the sample in the reactor is calculated; S12, using a vacuum pump to vacuum the sample, then using a pore water injection pump to inject brine into the sediment, and reaching the critical pressure of supercritical CO2, recording the initial pore water volume injected; S13, adjusting the temperature of the sediment in the reactor, ensuring that the temperature inside the reactor reaches above the critical temperature of supercritical CO2 through a temperature sensor, and monitoring the temperature of different layers of the sediment in the reactor through the temperature sensor.

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