A rapid indoor simulation and non-destructive evaluation method for hydrate-bearing sediments

Abstract

This invention relates to the field of marine clean energy simulation technology, and discloses a rapid indoor simulation non-destructive evaluation method for hydrate-containing sediments, comprising the following steps: S1, preparing an indoor simulation system for simulation: the indoor simulation system includes a sample saturation component, a sample component, an acoustic testing component, a temperature control component, and a data acquisition component; S2, preparing and saturating the sample. This invention can rapidly generate hydrates and directly prepare saturated sediment samples under indoor conditions, significantly shortening the sample preparation cycle; it avoids hydrate decomposition or structural disturbance during saturation, improving sample structural stability and experimental repeatability; the sample remains within the ring cutter throughout the preparation and testing process, eliminating the need for demolding and significantly simplifying the experimental procedure; it achieves non-destructive evaluation of hydrate saturation through acoustic testing, and can combine temperature monitoring to reflect the internal phase transition process and latent heat effect of the sample in real time.

Description

Technical Field

[0001] This invention relates to the field of marine clean energy simulation technology, and in particular to a rapid indoor simulation and non-destructive evaluation method for hydrate-containing sediments. Background Technology

[0002] Natural gas hydrates, as a potential clean energy source, have attracted widespread attention due to their significant applications in energy and geological disaster prevention. However, due to the technical difficulties and high costs of on-site temperature and pressure sampling, the formation, decomposition, and related characteristics of natural gas hydrates are typically studied in a controlled laboratory environment. Therefore, it is necessary to simulate the preparation of hydrate-bearing sediment samples similar to marine reservoirs. Currently, commonly used materials for hydrate formation in laboratories include methane, carbon dioxide, and tetrahydrofuran (THF). Natural gas hydrate-bearing sediments (HBS) refer to sediments containing solid, ice-like hydrates formed under low temperature and high pressure. Their preparation conditions are demanding and challenging. For example, methane poses high safety risks during laboratory operations, and its hydrate formation requires high pressure and low temperature conditions, placing high demands on experimental equipment. While carbon dioxide is relatively safer than methane, it has limitations in simulating naturally occurring natural gas hydrates. In contrast, tetrahydrofuran (THF), as an organic compound, has significant advantages in preparing hydrate sediments. The formation of THF hydrates does not require experimental pressure; they can form spontaneously at atmospheric pressure and temperatures below 4.4°C, which greatly reduces the reliance on high-pressure equipment and improves the safety and operability of the experiment.

[0003] Natural hydrates are primarily found in saturated sediment environments such as the ocean, while existing laboratory studies mostly utilize unsaturated sediments as the medium, indicating a significant difference in their occurrence conditions. Current laboratory methods typically involve first synthesizing gaseous hydrates in unsaturated samples and then achieving saturation through water injection. However, this process has a long saturation cycle, and the hydrates are prone to decomposition or structural disturbance during water injection, making it difficult to efficiently and stably prepare saturated hydrate sediment samples. Therefore, it is necessary to develop a rapid indoor preparation method based on THF aqueous solutions that can directly saturate sediments while controlling the theoretical saturation of hydrates through solution ratios, thereby improving sample preparation efficiency and saturation control precision.

[0004] The formation and decomposition of THF hydrates involves a phase transition process from liquid to solid and vice versa. To detect this process, microscopic techniques such as acoustic detection are commonly used. Acoustic detection technology can clearly detect the formation and decomposition of hydrates, and significant changes in acoustic signals occur during this process. By characterizing the acoustic propagation characteristics of hydrate-bearing sediments using wave velocity during the formation and decomposition of THF hydrates, it is possible to effectively evaluate the internal phase changes of sediments and the real-time hydrate saturation under continuous phase transition conditions.

[0005] This invention proposes a rapid method for preparing hydrate-saturated sediments in the laboratory, and uses acoustic detection technology to test the rapidly prepared samples, performing non-destructive evaluation of the internal phase changes and hydrate saturation of the sediments, thus verifying the reliability of the rapid preparation method. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a rapid indoor simulation non-destructive evaluation method for hydrate-containing sediments.

[0007] This invention employs the following technical solution: a rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments, comprising the following steps:

[0008] S1. Prepare the indoor simulation system for the simulation:

[0009] The indoor simulation system includes a sample saturation component, a sample component, an acoustic testing component, a temperature control component, and a data acquisition component.

[0010] S2. Prepare the sample and saturate the sample:

[0011] Sediments were selected as the storage medium for phase change materials. Based on the porosity conditions of the reservoir, cylindrical samples were prepared. Filter paper and permeable stones were placed on the top and bottom of the samples. The samples were saturated by vacuum negative pressure aspiration. The saturation solution was a mixture of tetrahydrofuran (THF) and water.

[0012] S3. Install the saturated sample into the indoor simulation system in preparation for simulation testing:

[0013] The saturated sample is installed in the sample assembly, and the acoustic testing assembly, temperature control assembly and data acquisition assembly are installed and connected, and the sample simulation test is awaited.

[0014] S4. Conduct acoustic testing and temperature monitoring on the samples using an indoor simulation system:

[0015] A freezing test with progressively decreasing temperature was conducted on the sample. Temperature and acoustic data were collected during the sample testing process. The internal temperature change of the sample was monitored in real time. The shear wave velocity was determined by a combination of cross-correlation method and initial arrival wave method, and temperature-time data were recorded simultaneously.

[0016] S5. Evaluation of internal phase changes in the sediment of the sample:

[0017] By combining acoustic and thermodynamic characteristics, the specific temperature ranges for the formation of THF hydrates and ice, as well as the phase changes within the sediments, can be determined.

[0018] S6. Perform non-destructive evaluation of hydrate saturation on the sample:

[0019] The shear wave velocity of the sample was normalized by using the shear wave velocity of the hydrate-saturated sediment under the same test conditions as the baseline.

[0020] The acoustic equivalent saturation of hydrates is calculated based on the normalized shear wave velocity. Combined with the THF mass conservation relationship and a pre-established calibration table or database, the acoustic equivalent saturation is corrected to obtain the true hydrate saturation of the sample, thus realizing non-destructive evaluation of THF-containing hydrate-saturated sediments under continuous phase change conditions.

[0021] As a further improvement to the above scheme, in step S1, the sample saturation assembly includes a sealed box, a vacuum pump, a vacuum barrel, a pressure gauge, a pad, a THF aqueous solution storage tank, and a saturator.

[0022] The sample assembly includes a ring cutter for storing the sample, a ring cutter top cover set on the top of the ring cutter, and a ring cutter bottom cover set on the bottom of the ring cutter. Both the ring cutter top cover and the ring cutter bottom cover are provided with sealing rings for sealing. A fixing screw is provided between the ring cutter top cover and the ring cutter bottom cover for fastening connection. The fixing screw is used to achieve a sealed connection between the ring cutter top cover and the ring cutter bottom cover, thereby ensuring the sealing of the sample during the test process.

[0023] The acoustic testing assembly includes acoustic probes positioned at the top and bottom ends of the sample, and the acoustic probes are connected to the data acquisition assembly via radio frequency lines;

[0024] The temperature control components include a constant temperature water bath device and a temperature sensor. The constant temperature water bath device is used to implement gradient cooling and heating control of the sample. The temperature sensor is located at the center of the ring cutter cover, and its probe is inserted into the sample to monitor the temperature change inside the sample in real time.

[0025] The data acquisition components include a temperature acquisition unit, an oscilloscope, a signal generator, and a filter. The signal generator is used to generate acoustic signals, the filter is used to filter the received signals, the oscilloscope is used to display and record the acoustic signals, and the temperature acquisition unit is used to synchronously record temperature data.

[0026] As a further improvement to the above scheme, in step S2, the prepared sample is placed in the sample saturation assembly and fixed. First, the sample is evacuated. After the evacuation is completed, the prepared THF aqueous solution is adsorbed under negative pressure until the sample is saturated.

[0027] As a further improvement to the above scheme, in step S3, the saturated sample is taken out, the sample is installed on the sample assembly, and the acoustic testing assembly, temperature control assembly and data acquisition assembly are arranged and connected.

[0028] As a further improvement to the above scheme, in step S6, the normalization of the sample shear wave velocity is performed using the following formula: , where V s V represents the steady-state wave velocity of the THF hydrate sample at temperature T. s,0 V is the wave velocity of a pure water-saturated sample at the same temperature. s,n Dimensionless.

[0029] As a further improvement to the above scheme, in step S6, based on the monotonically increasing trend of wave velocity with theoretical saturation, and based on the normalized shear wave velocity, the least squares method passing through the origin is used to calibrate the k value, and a linear relationship is used to represent the acoustic equivalent saturation of the hydrate:

[0030] ,

[0031] ,

[0032] Where k is the proportionality coefficient determined through calibration experiments. x represents the acoustic equivalent saturation, which is dimensionless. i =V s,n -1, y i = / 100; When the calculation result exceeds the physically reasonable range, upper and lower limits are imposed on the acoustic equivalent saturation, i.e., 0 < <1.

[0033] As a further improvement to the above scheme, in step S6, THF satisfies the mass conservation relationship between the hydrate solid phase and the pore liquid phase. Combined with a pre-established "initial THF mass fraction - actual achievable hydrate saturation" correction table or database, the acoustic equivalent hydrate saturation is corrected to obtain the true hydrate saturation of the sample. The formula is as follows:

[0034] ,

[0035] in, According to the independent variable and dependent variable Performing ordinary least squares regression yields the following: By calculating the normalized wave velocity, the dependent variable... Obtained by looking up the table; β represents the overall level of acoustic equivalent saturation, and β represents the sensitivity of the acoustic response in the low saturation region to hydrates.

[0036] As a further improvement to the above scheme, in step S6, the parameters obtained by fitting are used. The calculation formula is as follows:

[0037] ,

[0038] in, To determine the actual achievable hydrate saturation under the tested temperature conditions. The overall equivalent hydrate saturation is based on acoustic testing.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. This invention uses THF aqueous solution as the hydrate formation medium, which can rapidly generate hydrates and directly prepare saturated sediment samples under indoor conditions, significantly shortening the sample preparation cycle;

[0041] 2. Compared with the traditional method of first synthesizing hydrates and then saturating them with water, this invention avoids the decomposition or structural disturbance of hydrates during the saturation process, thereby improving the structural stability of the sample and the repeatability of the experiment.

[0042] 3. The sample remains inside the ring cutter throughout the entire preparation and testing process, eliminating the need for demolding and significantly simplifying the experimental procedure;

[0043] 4. Acoustic testing enables non-destructive evaluation of hydrate saturation, and temperature monitoring can be combined to reflect the internal phase transition process and latent heat effect of the sample in real time. Attached Figure Description

[0044] Figure 1 A flowchart of a rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments provided by the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the sample assembly provided by the present invention;

[0046] Figure 3 This is a schematic diagram of the assembly structure of the indoor simulation system provided by the present invention;

[0047] Figure 4 This is a schematic diagram of the saturated sample structure provided by the present invention;

[0048] Figure 5 The temperature-time curve of the test process in Example 3 of this invention;

[0049] Figure 6 A comparison diagram of acoustic signals before and after hydrate formation in Example 3 of this invention;

[0050] Figure 7 The graph shows the change of wave velocity with temperature in stage I of embodiment 3 of the present invention.

[0051] Explanation of key symbols:

[0052] 1. RF cable; 2. Temperature sensor; 3. S-wave probe; 4. Ring cutter top cover; 5. Fixing screw; 7. Ring cutter; 8. Sealing ring; 9. Ring cutter bottom cover; 10. P-wave probe; 11. Water bath; 12. Water bath box; 13. Temperature acquisition device; 14. Oscilloscope; 15. Signal generator; 16. Filter; 21. Vacuum pump; 22. Vacuum tank; 23. Pressure gauge; 24. Pad; 25. THF aqueous solution storage tank; 26. Saturator; 27. Sealing box. Detailed Implementation

[0053] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0054] Example 1:

[0055] Please combine Figure 1 This embodiment of a rapid indoor simulation non-destructive evaluation method for hydrate-containing sediments includes the following steps:

[0056] S1. Prepare the indoor simulation system for the simulation:

[0057] The indoor simulation system includes a sample saturation component, a sample component, an acoustic testing component, a temperature control component, and a data acquisition component.

[0058] S2. Prepare the sample and saturate the sample:

[0059] Sediments were selected as the storage medium for phase change materials. Based on the porosity conditions of the reservoir, cylindrical samples were prepared. Filter paper and permeable stones were placed on the top and bottom of the samples. The samples were saturated by vacuum negative pressure aspiration. The saturation solution was a mixture of tetrahydrofuran (THF) and water.

[0060] The prepared sample is placed in the sample saturation assembly and fixed. First, the sample is evacuated. After evacuation, the prepared THF aqueous solution is adsorbed into the sample under negative pressure until it is saturated.

[0061] S3. Install the saturated sample into the indoor simulation system in preparation for simulation testing:

[0062] The saturated sample is installed in the sample assembly, and the acoustic testing assembly, temperature control assembly and data acquisition assembly are installed and connected, and the sample simulation test is awaited.

[0063] Remove the saturated sample, install the sample on the sample assembly, and complete the arrangement and connection of the acoustic testing assembly, temperature control assembly, and data acquisition assembly.

[0064] S4. Conduct acoustic testing and temperature monitoring on the samples using an indoor simulation system:

[0065] A freezing test with progressively decreasing temperature was conducted on the sample. Temperature and acoustic data were collected during the sample testing process. The internal temperature change of the sample was monitored in real time. The shear wave velocity was determined by a combination of cross-correlation method and initial arrival wave method, and temperature-time data were recorded simultaneously.

[0066] S5. Evaluation of internal phase changes in the sediment of the sample:

[0067] By combining acoustic and thermodynamic characteristics, the specific temperature ranges for the formation of THF hydrates and ice, as well as the phase changes within the sediments, can be determined.

[0068] S6. Perform non-destructive evaluation of hydrate saturation on the sample:

[0069] The shear wave velocity of the sample was normalized by using the shear wave velocity of the hydrate-saturated sediment under the same test conditions as the baseline.

[0070] The normalization of the shear wave velocity of the sample was performed using the following formula: , where V s V represents the steady-state wave velocity of the THF hydrate sample at temperature T. s,0 V is the wave velocity of a pure water-saturated sample at the same temperature. s,n Dimensionless;

[0071] The acoustic equivalent saturation of hydrates is calculated based on the normalized shear wave velocity. Combined with the THF mass conservation relationship and a pre-established calibration table or database, the acoustic equivalent saturation is corrected to obtain the true hydrate saturation of the sample, thus realizing the non-destructive evaluation of THF-containing hydrate-saturated sediments under continuous phase change conditions.

[0072] Based on the monotonically increasing trend of wave velocity with theoretical saturation, and using the normalized shear wave velocity, the k-value is calibrated using the least squares method passing through the origin, and a linear relationship is used to represent the acoustic equivalent saturation of the hydrate:

[0073] ,

[0074] ,

[0075] Where k is the proportionality coefficient determined through calibration experiments. x represents the acoustic equivalent saturation, which is dimensionless. i =V s,n -1, y i = / 100; When the calculation result exceeds the physically reasonable range, upper and lower limits are imposed on the acoustic equivalent saturation, i.e., 0 < <1;

[0076] THF satisfies a mass conservation relationship between the hydrate solid phase and the pore liquid phase. Using a pre-established correction table or database of "initial THF mass fraction – actual achievable hydrate saturation," the acoustic equivalent hydrate saturation is corrected to obtain the true hydrate saturation of the sample. The formula is as follows:

[0077] ,

[0078] in, According to the independent variable and dependent variable Performing ordinary least squares regression yields the following: By calculating the normalized wave velocity, the dependent variable... Obtained by looking up the table; β represents the overall level of acoustic equivalent saturation, and β represents the sensitivity of the acoustic response in the low saturation region to hydrates.

[0079] Using the parameters obtained from the fitting The calculation formula is as follows:

[0080] ,

[0081] in, To determine the actual achievable hydrate saturation under the tested temperature conditions. The overall equivalent hydrate saturation is based on acoustic testing.

[0082] Example 2:

[0083] Combination Figure 2-4Based on Example 1, this embodiment is further improved in that: the sample saturation assembly includes a sealed box 27, a vacuum pump 21, a vacuum barrel 22, a pressure gauge 23, a pad 24, a THF aqueous solution storage tank 25, and a saturator 26. The vacuum pump 21 is connected to the vacuum barrel 22 through a pipe 1, and the vacuum barrel 22 is connected to the THF aqueous solution storage tank 25 through a pipe 2. The saturator 26 includes a base plate and a top plate set on top of the base plate. A fastening screw for fixing is installed between the top plate and the base plate. Valves are installed on both pipe 1 and pipe 2.

[0084] During the sample saturation process, soil is selected as the storage medium for phase change material. A cylindrical sample with a certain degree of compaction and initial water content (compaction degree 0-95%, and water content range 0-20%) is prepared in the ring cutter 7. The sample diameter is variable (0-50 mm) and the height is variable (0-100 mm). Filter paper and permeable stone are placed on the top and bottom of the sample, and then it is fixed with the saturator 26. The fixed sample is placed in the sealed box 27. At this time, the lid of the sealed box 27 is open and not sealed. Then, the sealed box 27 containing the sample is placed in the vacuum barrel 22. At the same time, a pad 24 is placed at the bottom of the vacuum barrel 22. The function of the pad 24 is to reduce the drop of the solution during the aspiration process and minimize the impact of the strong volatility of THF. The sealed box 27 is placed in the pad 24, the vacuum barrel 22 is closed, and the vacuum pump 21 is used to evacuate the vacuum barrel 22 for no less than 2.5 hours.

[0085] After vacuuming is completed, the THF aqueous solution with the target saturation is placed in the THF aqueous solution storage tank 25 and sucked into the sealed box 27 in the vacuum tank 21 by negative pressure. After the solution fills the entire sealed box 27, the pressure is released and the sealed box 27 is taken out. A layer of plastic wrap is sealed on the top of the sealed box 27, and then the sealed lid of the sealed box 27 is put on and placed in a dark place at room temperature for one day to saturate.

[0086] The sample assembly includes a ring cutter 7 for storing the sample, a ring cutter upper cover 4 set on the top of the ring cutter 7, and a ring cutter lower cover 9 set at the bottom of the ring cutter 7. Both the ring cutter upper cover 4 and the ring cutter lower cover 9 are provided with sealing rings 8 for sealing. A fixing screw 5 is provided between the ring cutter upper cover 4 and the ring cutter lower cover 9 for fastening connection. The fixing screw 5 is used to achieve a sealed connection between the ring cutter upper cover 4 and the ring cutter lower cover 9, thereby ensuring the sealing of the sample during the test process.

[0087] After saturation, wipe off the excess water on the saturator 26, remove the saturator 26, place the sample and the ring cutter 7 between the ring cutter upper cover 4 and the ring cutter lower cover 9, and seal them with the sealing ring 8. Place the acoustic probe and temperature sensor 3 on the corresponding ring cutter upper cover 4 or ring cutter lower cover 9, and finally fix them with the fixing screw 5.

[0088] The acoustic testing assembly includes acoustic probes disposed at the upper and lower ends of the sample. The acoustic probes are connected to the data acquisition assembly via radio frequency line 1. The acoustic probes include an S-wave probe 3 and a P-wave probe 10. The S-wave probe 3 and the P-wave probe 10 are connected to the data acquisition assembly via radio frequency line 1.

[0089] The temperature control component includes a constant temperature water bath device and a temperature sensor 2. The constant temperature water bath device is used to implement gradient cooling and heating control of the sample. The temperature sensor 2 is located at the center of the ring cutter cover 4, and its probe is inserted into the sample to monitor the temperature change inside the sample in real time. The constant temperature water bath device includes a water bath box 12 for adjusting the sample temperature and a water bath tank 11 set in the water bath box 12 for placing the sample.

[0090] The data acquisition component includes a temperature acquisition unit 13, an oscilloscope 14, a signal generator 15, and a filter 16. The signal generator 15 is used to excite acoustic signals, the filter 16 is used to filter the received signals, the oscilloscope 14 is used to display and record acoustic signals, the temperature acquisition unit 13 is used to synchronously record temperature data, the temperature acquisition unit 13 is connected to the temperature sensor 2, the signal generator 15 and the filter 16 are both connected to the S-wave probe 3 and the P-wave probe 10, and the oscilloscope 14 is connected to both the signal generator 15 and the filter 16.

[0091] Example 3:

[0092] This embodiment uses the same steps as in Embodiment 1 to conduct the experiment:

[0093] Without prior knowledge of the actual hydrate saturation of the sample, the prepared THF-containing hydrate-saturated sediment sample was installed in an indoor simulation system and subjected to stepwise cooling and heating in a constant temperature water bath 12. During the heating process, when the sample temperature stabilized at the preset evaluation temperature point, the shear wave acoustic signal of the sample was collected and the corresponding shear wave velocity was calculated.

[0094] Using the shear wave velocity of the 0% hydrate control sample obtained in Example 1 at the same evaluation temperature as a benchmark, the measured shear wave velocity was normalized, and the acoustic equivalent hydrate saturation of the sample was calculated based on the calculation method established in Example 1.

[0095] Based on the correction relationship between acoustic equivalent hydrate saturation and actual hydrate saturation established in Example 1, the acoustic equivalent hydrate saturation is corrected, thereby achieving a non-destructive quantitative evaluation of the hydrate saturation of THF-containing hydrate-saturated sediments without damaging the sample structure, taking pore fluid, or performing mass measurement.

[0096] in, Figure 5The measured temperature change over time during the experiment (15.2 wt%) shows that the freeze-thaw process can be divided into the following stages. Stage I is the hydrate formation stage (4.0℃→0.0℃), with a system composition of H(s)+Water(l)+THF(l); Stage II is the ice-hydrate formation stage (-1.5℃→-10.0℃), with a system composition of H(s)+Ice(s)+THF(l); Stage III is the ice melting stage (-10.0℃→0.0℃), with a system composition of H(s)+Water(l)+THF(l); Stage IV is the secondary hydrate formation stage (0.0℃→1.0℃), with a system composition of H(s)+Water(l); Stage V is the hydrate decomposition stage (4.0℃→8.0℃). The figure clearly shows the process of latent heat release during phase transition within the sediment. Stage I has two exothermic peaks. The first peak is small, rising only 0.1℃ before dropping to 0.0℃. After about 4 hours, the second exothermic peak begins, rising 1.4℃. The entire process lasts 12 hours. h, this stage is the formation of hydrates; continue cooling to -2.5℃, a second heat release is observed in stage II, which causes the temperature to rise by 0.9℃, this stage is the formation of ice.

[0097] in, Figure 6 , 7 These are the acoustic test signals before and after the material's phase change. The acoustic test signals can be used to analyze the acoustic properties of the material after the phase change.

[0098] Figure 6 The acoustic response inside the sediment was shown when the temperature dropped from 8.0℃ to the hydrate phase transition temperature (0.0-1.0℃ range). The waveforms before and after hydrate formation in the three sets of samples were clearly compared. It can be seen that the formation of hydrate significantly changed the composition state inside the sediment, resulting in obvious changes in the waveform and a significantly faster arrival time of the received signal.

[0099] Figure 7 The changes in wave velocity of samples after saturation with aqueous solutions of different THF mass fractions from 8.0 to 0.0℃ are shown, which are consistent with the temperature curve (a phase transition occurs near 0.0-1.0℃). The wave velocity also increases significantly in this temperature range, which is caused by the formation of hydrates.

[0100] This invention uses THF aqueous solution as the hydrate generation medium, which can rapidly generate hydrates and directly prepare saturated sediment samples under indoor conditions, significantly shortening the sample preparation cycle. Compared with the traditional method of first synthesizing hydrates and then injecting water for saturation, this method avoids hydrate decomposition or structural disturbance during saturation, improving the structural stability and experimental repeatability of the samples. The samples are kept inside the ring cutter throughout the entire preparation and testing process, eliminating the need for demolding and significantly simplifying the experimental procedure. The acoustic testing enables non-destructive evaluation of hydrate saturation, and temperature monitoring can be combined to reflect the internal phase transition process and latent heat effect of the samples in real time.

[0101] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A rapid indoor simulation and non-destructive evaluation method for hydrate-bearing sediments, characterized in that, Includes the following steps: S1. Prepare the indoor simulation system for the simulation: The indoor simulation system includes a sample saturation component, a sample component, an acoustic testing component, a temperature control component, and a data acquisition component. S2. Prepare the sample and saturate the sample: Sediments were selected as the storage medium for phase change materials. Based on the porosity conditions of the reservoir, cylindrical samples were prepared. Filter paper and permeable stones were placed on the top and bottom of the samples. The samples were saturated by vacuum negative pressure aspiration. The saturation solution was a mixture of tetrahydrofuran (THF) and water. S3. Install the saturated sample into the indoor simulation system in preparation for simulation testing: The saturated sample is installed in the sample assembly, and the acoustic testing assembly, temperature control assembly and data acquisition assembly are installed and connected, and the sample simulation test is awaited. S4. Conduct acoustic testing and temperature monitoring on the samples using an indoor simulation system: A freezing test with progressively decreasing temperature was conducted on the sample. Temperature and acoustic data were collected during the sample testing process. The internal temperature change of the sample was monitored in real time. The shear wave velocity was determined by a combination of cross-correlation method and initial arrival wave method, and temperature-time data were recorded simultaneously. S5. Evaluation of internal phase changes in the sediment of the sample: By combining acoustic and thermodynamic characteristics, the specific temperature ranges for the formation of THF hydrates and ice, as well as the phase changes within the sediments, can be determined. S6. Perform non-destructive evaluation of hydrate saturation on the sample: The shear wave velocity of the sample was normalized by using the shear wave velocity of the hydrate-saturated sediment under the same test conditions as the baseline. The acoustic equivalent saturation of hydrates is calculated based on the normalized shear wave velocity. Combined with the THF mass conservation relationship and a pre-established calibration table or database, the acoustic equivalent saturation is corrected to obtain the true hydrate saturation of the sample, thus realizing non-destructive evaluation of THF-containing hydrate-saturated sediments under continuous phase change conditions.

2. The rapid indoor simulation and non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S1, the sample saturation assembly includes a sealed box, a vacuum pump, a vacuum barrel, a pressure gauge, a pad, a THF aqueous solution storage tank, and a saturator. The sample assembly includes a ring cutter for storing the sample, a ring cutter top cover set on the top of the ring cutter, and a ring cutter bottom cover set on the bottom of the ring cutter. Both the ring cutter top cover and the ring cutter bottom cover are provided with sealing rings for sealing. A fixing screw is provided between the ring cutter top cover and the ring cutter bottom cover for fastening connection. The fixing screw is used to achieve a sealed connection between the ring cutter top cover and the ring cutter bottom cover, thereby ensuring the sealing of the sample during the test process. The acoustic testing assembly includes acoustic probes positioned at the top and bottom ends of the sample, and the acoustic probes are connected to the data acquisition assembly via radio frequency lines; The temperature control components include a constant temperature water bath device and a temperature sensor. The constant temperature water bath device is used to implement gradient cooling and heating control of the sample. The temperature sensor is located at the center of the ring cutter cover, and its probe is inserted into the sample to monitor the temperature change inside the sample in real time. The data acquisition components include a temperature acquisition unit, an oscilloscope, a signal generator, and a filter. The signal generator is used to generate acoustic signals, the filter is used to filter the received signals, the oscilloscope is used to display and record the acoustic signals, and the temperature acquisition unit is used to synchronously record temperature data.

3. The rapid indoor simulation and non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S2, the prepared sample is placed in the sample saturation assembly for fixation. First, the sample is evacuated. After evacuation, the prepared THF aqueous solution is adsorbed under negative pressure until the sample is saturated.

4. The rapid indoor simulation and non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S3, the saturated sample is taken out, the sample is installed on the sample assembly, and the acoustic testing assembly, temperature control assembly and data acquisition assembly are arranged and connected.

5. The rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S6, the normalization of the sample shear wave velocity is performed using the following formula: , where V s V represents the steady-state wave velocity of the THF hydrate sample at temperature T. s,0 V is the wave velocity of a pure water-saturated sample at the same temperature. s,n Dimensionless.

6. The rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S6, based on the monotonically increasing trend of wave velocity with theoretical saturation, and based on the normalized shear wave velocity, the least squares method passing through the origin is used to calibrate the k value, and a linear relationship is used to represent the acoustic equivalent saturation of the hydrate: ， ， Where k is the proportionality coefficient determined through calibration experiments. x represents the acoustic equivalent saturation, which is dimensionless. i =V s,n -1, y i = / 100; When the calculation result exceeds the physically reasonable range, upper and lower limits are imposed on the acoustic equivalent saturation, i.e., 0 < <1.

7. The rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S6, THF satisfies the mass conservation relationship between the hydrate solid phase and the pore liquid phase. Using a pre-established "initial THF mass fraction – actual achievable hydrate saturation" correction table or database, the acoustic equivalent hydrate saturation is corrected to obtain the true hydrate saturation of the sample. The formula is as follows: ， in, According to the independent variable and dependent variable Performing ordinary least squares regression yields the following: By calculating the normalized wave velocity, the dependent variable... Obtained by looking up the table; β represents the overall level of acoustic equivalent saturation, and β represents the sensitivity of the acoustic response in the low saturation region to hydrates.

8. The rapid indoor simulation non-destructive evaluation method for hydrate-bearing sediments as described in claim 1, characterized in that, In step S6, the parameters obtained by fitting are used. The calculation formula is as follows: ， in, To determine the actual achievable hydrate saturation under the tested temperature conditions. The overall equivalent hydrate saturation is based on acoustic testing.

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