A pore pressure response model test system and operation method for gas-containing silt sediment

Abstract

The present invention discloses a pore pressure response model test system for gas-containing silt sediment and an operation method, which is composed of a gas release unit, a saturation unit and a control module unit. The gas release unit includes a top plate and a bottom plate, a cylindrical protective shell is fixedly connected between the outer sides of the top plate and the bottom plate, two baffles are fixedly connected inside the protective shell, and seabed sediments are arranged between the two baffles. A fixed cylinder is fixedly connected to the central side wall of each baffle, and each fixed cylinder passes through the side walls of the top plate and the bottom plate respectively. The present invention is established through a gas release unit, a saturation unit and a control module unit, and then the influence of seawater depth on slope stability in slope damage caused by gas diffusion of gas-containing silt is studied respectively under the assumption that the gas diffusion amount of gas-containing silt is the same, so as to provide a certain basis for the study of seabed gas-containing sediments, and the practicability is high.

Description

Technical Field

[0001] The invention relates to the technical field of seabed gas-containing sediments, and in particular to a pore pressure response model test system for gas-containing silt sediments and an operation method thereof. Background Art

[0002] Shallow gas in seafloor gas-bearing sediments often exists in the form of high-pressure gas pockets, and its pressure is generally higher than atmospheric pressure. When the accumulated high-pressure shallow gas escapes, the pressure of the gas-bearing formation drops sharply, and the gas scours the formation, disturbing the gas-bearing soil layer and the overlying or underlying formations.

[0003] While seafloor gas-bearing sediments bring new energy prospects to mankind, they also pose severe challenges to the human living environment. Once methane gas escapes from gas-bearing sediments, it will change the physical properties of gas-bearing sediments and have a serious impact on the stability of the seabed. Therefore, understanding the microscopic characteristics of gas-bearing sediments, mastering their engineering mechanical properties, and analyzing the impact of gas escape on the stability of seafloor formations are of great significance to oil exploration, development and transportation near gas-bearing sediments, as well as the construction of seafloor engineering facilities. Therefore, a model test system and operation method suitable for the pore pressure response of gas-bearing silt sediments triggered by gas escape are needed. Summary of the invention

[0004] The present invention provides a gas-containing silt sediment pore pressure response model test system and an operation method to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A pore pressure response model test system for gas-containing silt sediments, composed of a gas release unit, a saturation unit and a control module unit, wherein the gas release unit comprises a top plate and a bottom plate, a cylindrical protective shell is fixedly connected between the outer sides of the top plate and the bottom plate, two baffles are fixedly connected inside the protective shell, and seabed sediments are arranged between the two baffles, a fixed cylinder is fixedly connected to the central side wall of each baffle, each of the fixed cylinders penetrates the side walls of the top plate and the bottom plate respectively, a fixed plug is fixedly connected to one end of each fixed cylinder, a piston is slidably connected to the inside of each fixed cylinder, a sliding rod is fixedly connected to the side wall of each piston, each sliding rod penetrates the side wall of the fixed plug, a load sensor is fixedly connected to the upper end of the sliding rod located above, a gas collecting device is arranged on the side wall of each baffle, a measuring tube is fixedly connected to the side wall of the baffle located above, the measuring tube penetrates the side wall of the top plate and is fixedly connected to the pore pressure sensor, and a supporting device is arranged on the side wall of the bottom plate;

[0007] The saturation unit includes two water tank tubes and an air pump, the upper and lower ends of each water tank tube are respectively fixedly connected with an upper cover plate and a lower cover plate, the output end of the air pump is fixedly connected with a fifth connecting pipe, the interior of the air pump stores methane, and each water tank tube is filled with seawater. A fourth connecting pipe is fixedly connected to the side wall of each upper cover plate, and the upper end of each fourth connecting pipe is fixedly connected to the side wall of the fifth connecting pipe. A pressure relief device is provided on the side wall of each upper cover plate, and a first connecting pipe and a second connecting pipe are respectively fixedly connected to the side walls of the two lower cover plates, one end of the first connecting pipe passes through the side wall of the top plate and is fixedly connected to the side wall of the upper baffle plate, one end of the second connecting pipe passes through the side wall of the bottom plate and is fixedly connected to the side wall of the lower baffle plate, a first pressure gauge is provided on the first connecting pipe, and a second pressure gauge is provided on the second connecting pipe;

[0008] The control module unit comprises a computer control end, and the load sensor, the first pressure gauge, the second pressure gauge, and the pore pressure sensor are all electrically connected to the computer control end.

[0009] As a further improvement of the present technical solution: each of the gas collecting devices includes an annular gas collecting bag, and each of the gas collecting bags has two gas outlet pipes fixedly connected to the side wall, one end of the two gas outlet pipes is fixedly connected to the side wall of the baffle, and each of the gas collecting bags is provided with a bender element inside, and each of the bender elements is electrically connected to the computer control end.

[0010] As a further improvement of the technical solution: the support device includes three support legs, and the three support legs are fixedly connected to the outer side wall of the base plate in a circular array.

[0011] As a further improvement of the technical solution: each of the pressure relief devices includes a third connecting pipe, each of the third connecting pipes is fixedly connected to the side wall of the upper cover plate, each of the third connecting pipes is provided with a safety valve, and each of the upper cover plates is provided with a pressure gauge.

[0012] As a further improvement of the technical solution: porous stone layers are provided on both the upper and lower sides of the seabed sediment.

[0013] As a further improvement of the technical solution: the protective shell and the water tank tube are both made of PMMA XT type organic glass.

[0014] As a further improvement of the technical solution: the thickness of the protective shell is 15 mm.

[0015] The present invention also provides an operating method of a gas-containing silt sediment pore pressure response model test system, comprising the following steps:

[0016] S1, inputting methane into the two water tanks through the fifth connecting pipe and the fourth connecting pipe by an air pump, so that the seawater in the two water tanks is saturated with methane gas at a pressure of kPa for at least 48 hours;

[0017] S2, the reshaped seafloor sediment is placed between two baffles, and then a pressure difference is applied in the two water tanks to generate a hydraulic gradient, causing saturated seawater to flow through the seafloor sediment;

[0018] S3, grab the sliding rod and manually move the piston until it contacts the seabed sediment, so that the upper piston starts to move at a loading speed of 0.12 mm / h and the lower piston starts to move at an unloading speed of 0.5 mm / h. The maximum total load is configured according to the target value of the pore pressure. When the piston moves, the gas escaping from the seabed sediment enters the gas collection bag. The bending machine element can detect the changes in the gas collection bag to measure the P wave velocity and the changes in the gas reservoir pressure in the escaping gas collection bag during the shallow gas release process.

[0019] S4, during the degassing process, the piston is manually lifted to allow the gas to expand or dissolve and the sediment to swell, and the two safety valves are opened for full or partial decompression. The two valves are opened simultaneously so that the decompression acts on both sides of the seabed sediments, and the P-wave velocities before and after decompression are compared to detect the presence of free gas;

[0020] S5, after degassing, the contact between the piston and the seabed sediment is manually carried out, and the change in sample height during the expansion of the seabed sediment is calculated to further deduce the gas saturation of the gas-bearing sediment. According to the consolidation degree of the gaseous sediment before and after the gas escapes, the P-wave velocity and permeability are measured to determine the influence of shear strength, creep characteristics, and seepage characteristics on the parameters.

[0021] As a further improvement of the present technical solution: in S4, in order to ensure complete degassing, this stage is maintained for about 15 hours.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention establishes a gas release unit, a saturation unit and a control module unit, and then studies the influence of seawater depth on slope stability in slope destruction caused by gas diffusion of gas-containing silt under the assumption that the gas diffusion amount of gas-containing silt is the same, thereby providing a certain basis for the study of seabed gas-containing sediments and having high practicality.

[0024] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. The specific implementation of the present invention is given in detail by the following embodiments and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of the structure of a pore pressure response model test system for gas-containing silt sediments proposed by the present invention;

[0027] Figure 2 A data transmission structure schematic diagram of a gas-containing silt sediment pore pressure response model test system proposed by the present invention;

[0028] Figure 3 Schematic diagram of excess pore pressure values ​​at different seawater depths;

[0029] Figure 4 Schematic diagram of safety factor and excess pore pressure ratio at different seawater depths.

[0030] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0031] 1. Pore pressure sensor; 2. Top plate; 3. Measuring tube; 4. Porous stone layer; 5. Baffle; 6. Gas collecting bag; 7. Protective shell; 8. Load sensor; 9. Fixed plug; 10. Sliding rod; 11. First connecting pipe; 12. Fixed cylinder; 13. Piston; 14. Seabed sediment; 15. Air outlet pipe; 16. First pressure gauge; 17. Bottom plate; 18. Air pump; 19. Support leg; 20. Second pressure gauge; 21. Second connecting pipe; 22. Lower cover plate; 23. Water tank cylinder; 24. Third connecting pipe; 25. Safety valve; 26. Upper cover plate; 27. Fourth connecting pipe; 28. Fifth connecting pipe. DETAILED DESCRIPTION

[0032] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. The present invention is described in more detail by way of example with reference to the accompanying drawings in the following paragraphs. The advantages and features of the present invention will become clearer according to the following description and claims. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0033] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a component centered. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a component centered. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a component centered. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0035] See also Figures 1 to 3 In an embodiment of the present invention, a pore pressure response model test system for gas-containing silt sediment is characterized in that it is composed of a gas release unit, a saturation unit and a control module unit. The gas release unit includes a top plate 2 and a bottom plate 17. A cylindrical protective shell 7 is fixedly connected between the outer sides of the top plate 2 and the bottom plate 17. Two baffles 5 are fixedly connected inside the protective shell 7. Seabed sediment 14 is arranged between the two baffles 5. A fixed cylinder 12 is fixedly connected to the central side wall of each baffle 5. Each fixed cylinder 12 passes through the side walls of the top plate 2 and the bottom plate 17 respectively. A fixed plug 9 is fixedly connected to one end of each fixed cylinder 12. A piston 13 is slidably connected inside each fixed cylinder 12, a sliding rod 10 is fixedly connected to the side wall of each piston 13, each sliding rod 10 penetrates the side wall of the fixed plug 9, a load sensor 8 is fixedly connected to the upper end of the sliding rod 10 located above, a gas collecting device is provided on the side wall of each baffle 5, a measuring tube 3 is fixedly connected to the side wall of the upper baffle 5, the measuring tube 3 penetrates the side wall of the top plate 2 and is fixedly connected to the pore pressure sensor 1, a supporting device is provided on the side wall of the bottom plate 17, the supporting device includes three supporting legs 19, and the three supporting legs 19 are fixedly connected to the outer side wall of the bottom plate 17 in a ring array;

[0036] The saturation unit includes two water tank barrels 23 and an air pump 18. The upper and lower ends of each water tank barrel 23 are respectively fixedly connected with an upper cover plate 26 and a lower cover plate 22. The output end of the air pump 18 is fixedly connected with a fifth connecting pipe 28. The air pump 18 stores methane inside. Each water tank barrel 23 is filled with seawater. A fourth connecting pipe 27 is fixedly connected to the side wall of each upper cover plate 26. The upper end of each fourth connecting pipe 27 is fixedly connected to the side wall of the fifth connecting pipe 28. A pressure relief device is provided on the side wall of each upper cover plate 26. The side walls of the two lower cover plates 22 are respectively fixedly connected with the first connecting pipe 11. and a second connecting pipe 21, one end of the first connecting pipe 11 passes through the side wall of the top plate 2 and is fixedly connected to the side wall of the upper baffle 5, one end of the second connecting pipe 21 passes through the side wall of the bottom plate 17 and is fixedly connected to the side wall of the lower baffle 5, the first connecting pipe 11 is provided with a first pressure gauge 16, the second connecting pipe 21 is provided with a second pressure gauge 20, each water tank tube 23 is connected to the top or bottom of the gas release unit, the pressure difference between the top and bottom of the seabed sediment 14 is applied in the two water tank tubes 23, and the seawater and methane can be circulated in the sample according to the test requirements, quantitatively and at a fixed gas reservoir pressure;

[0037] The control module unit includes a computer control end, and the load sensor 8, the first pressure gauge 16, the second pressure gauge 20, and the pore pressure sensor 1 are all electrically connected to the computer control end. The computer control end adopts a real-time monitoring method to record and control different test parameters. Considering the change laws of the consolidation degree, shear strength, creep characteristics, seepage characteristics, etc. of the gas-containing silt before and after gas escape under extreme gas reservoir pressure, the relationship between the pore water pressure and various parameters during the gas escape process is obtained.

[0038] Specifically, each gas collecting device includes an annular gas collecting bag 6, and two gas outlet pipes 15 are fixedly connected to the side wall of each gas collecting bag 6. One end of the two gas outlet pipes 15 is fixedly connected to the side wall of the baffle 5. A bender element is provided inside each gas collecting bag 6, and each bender element is electrically connected to the computer control end.

[0039] Specifically, each pressure relief device includes a third connecting pipe 24, each third connecting pipe 24 is fixedly connected to the side wall of the upper cover plate 26, each third connecting pipe 24 is provided with a safety valve 25, and each upper cover plate 26 is provided with a pressure gauge. If the water tank tube 23 reaches the pressure threshold, the safety valve 25 can be controlled to discharge methane gas.

[0040] Specifically, porous stone layers 4 are provided on both the upper and lower sides of the seabed sediment 14. The function of the porous stone is to ensure that the disturbance of the sediment is reduced during the loading process.

[0041] Specifically, the protective shell 7 and the water tank tube 23 are both made of PMMA XT type organic glass. The thickness of the protective shell 7 is 15 mm, the elastic modulus thereof is 3.3 GPa, and the yield stress is 70-80 MPa.

[0042] The present invention also provides an operating method of a gas-containing silt sediment pore pressure response model test system, comprising the following steps:

[0043] S1, methane is introduced into the two water tanks 23 through the fifth connecting pipe 28 and the fourth connecting pipe 27 by the air pump 18, so that the seawater in the two water tanks 23 is saturated with methane gas at a pressure of 300 to 800 kPa for at least 48 hours;

[0044] S2, placing the reshaped seabed sediment 14 between the two baffles 5, and then applying a pressure difference in the two water tanks 23 to generate a hydraulic gradient, so that the saturated seawater flows through the seabed sediment 14;

[0045] S3, grasp the sliding rod 10, and manually move the piston 13 until it contacts the seabed sediment 14, so that the upper piston starts to move at a loading speed of 0.12 mm / h and the lower piston starts to move at an unloading speed of 0.5 mm / h, and the maximum total load is configured according to the target value of the pore pressure. When the piston 13 moves, the gas escaping from the seabed sediment 14 enters the gas collection bag 6, and the bending machine element can detect the changes in the gas collection bag 6 to measure the P wave velocity and the changes in the gas reservoir pressure in the escaping gas collection bag 6 during the shallow gas release process;

[0046] S4, during the degassing process, the piston 13 is manually lifted to allow the gas to expand or dissolve and the sediment to expand, and the two safety valves 25 are opened for full or partial decompression. The two valves are opened simultaneously so that the decompression acts on both sides of the seabed sediment 14. The longitudinal wave velocities before and after decompression are compared to detect the presence of free gas. In order to ensure complete degassing, this stage is maintained for about 15 hours;

[0047] S5, after degassing, the piston 13 and the seabed sediment 14 are manually contacted, and the change in sample height during the expansion of the seabed sediment 14 is calculated to further deduce the gas saturation of the gas-bearing sediment. According to the consolidation degree of the gaseous sediment before and after the gas escapes, the P-wave velocity and permeability are measured to determine the influence of the shear strength, creep characteristics, and seepage characteristics on the parameters.

[0048] Finally, the study shows that the accumulation trend of excess pore pressure is basically the same under different water depths. As the amount of gas dissipated from aerated soil increases, the excess pore pressure gradually increases, but the accumulation rate gradually slows down. This is because the gas dissipation from aerated soil causes the pressure to increase, and the pressure increase will inhibit the dissipation of subsequent steps. As the pressure continues to increase, the inhibition becomes more obvious, so the value of excess pore pressure in the later stage of dissipation remains basically unchanged. Compared with the cumulative positive value of excess pore pressure, the seawater depth has a greater impact on its accumulation rate. It can be seen that when the water depth is 300m, the accumulation rate is significantly faster than other water depths. This is because when the seawater depth is shallow, the stable zone of aerated soil can release a larger volume of gas under the action of a smaller seawater static pressure. According to the compression-rebound characteristics of the soil, the greater the deformation of the soil, the greater the change in the effective stress of the formation. Therefore, it can be seen that the excess pore pressure accumulates faster when the water depth is 300m:

[0049] from Figure 3 and Figure 4 It can also be seen that when the water depth is 300m, the seabed safety factor first reaches 1, and damage may occur when the gas-bearing soil spill is 2.5%, which also reflects that the accumulation rate of excess pore pressure in the formation is high. The development trend of the excess pore pressure ratio is consistent with the excess pore pressure. This is because the change in water depth has no effect on the initial soil weight of the formation, so the two trends are consistent. In addition, it is found that when the critical damage state is in place, the values ​​of the excess pore pressure ratio in the three formations with different water depths are all 0.5, which also shows that the value of the critical excess pore pressure ratio has nothing to do with the seawater depth. In summary, in the seabed destruction induced by gas spillage of gas-bearing soil, the seawater depth has an impact on the stability of the seabed. The deeper seawater depth has an inhibitory effect on the gas spillage of gas-bearing soil and can enhance the stability of the slope.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A pore pressure response model test system for gas-containing silt sediments, characterized in that: The invention is composed of a gas release unit, a saturation unit and a control module unit. The gas release unit comprises a top plate (2) and a bottom plate (17). A cylindrical protective shell (7) is fixedly connected between the outer sides of the top plate (2) and the bottom plate (17). Two baffles (5) are fixedly connected inside the protective shell (7). Seabed sediment (14) is provided between the two baffles (5). A fixed cylinder (12) is fixedly connected to the central side wall of each baffle (5). Each fixed cylinder (12) passes through the side walls of the top plate (2) and the bottom plate (17) respectively. One end of each fixed cylinder (12) is fixedly connected to a fixed plug (9). ), each of the fixed cylinders (12) is slidably connected to a piston (13) inside, each of the pistons (13) is fixedly connected to a sliding rod (10) on the side wall, each of the sliding rods (10) passes through the side wall of the fixed plug (9), and a load sensor (8) is fixedly connected to the upper end of the sliding rod (10) located above, a gas collecting device is provided on the side wall of each of the baffles (5), a measuring tube (3) is fixedly connected to the side wall of the baffle (5) located above, the measuring tube (3) passes through the side wall of the top plate (2) and is fixedly connected to a pore pressure sensor (1), and a supporting device is provided on the side wall of the bottom plate (17); The saturation unit comprises two water tank barrels (23) and an air pump (18), the upper and lower ends of each water tank barrel (23) are respectively fixedly connected to an upper cover plate (26) and a lower cover plate (22), the output end of the air pump (18) is fixedly connected to a fifth connecting pipe (28), the interior of the air pump (18) stores methane, each water tank barrel (23) is filled with seawater, the side wall of each upper cover plate (26) is fixedly connected to a fourth connecting pipe (27), the upper end of each fourth connecting pipe (27) is fixedly connected to the side wall of the fifth connecting pipe (28), and each A pressure relief device is provided on the side wall of the upper cover plate (26); a first connecting pipe (11) and a second connecting pipe (21) are fixedly connected to the side walls of the two lower cover plates (22), respectively; one end of the first connecting pipe (11) passes through the side wall of the top plate (2) and is fixedly connected to the side wall of the upper baffle plate (5); one end of the second connecting pipe (21) passes through the side wall of the bottom plate (17) and is fixedly connected to the side wall of the lower baffle plate (5); a first pressure gauge (16) is provided on the first connecting pipe (11), and a second pressure gauge (20) is provided on the second connecting pipe (21); The control module unit comprises a computer control end, and the load sensor (8), the first pressure gauge (16), the second pressure gauge (20), and the pore pressure sensor (1) are all electrically connected to the computer control end.

2. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: Each of the gas collection devices comprises an annular gas collection bag (6), two gas outlet pipes (15) are fixedly connected to the side wall of each of the gas collection bags (6), one end of the two gas outlet pipes (15) is fixedly connected to the side wall of the baffle (5), and a bender element is provided inside each of the gas collection bags (6), and each of the bender elements is electrically connected to a computer control terminal.

3. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: The supporting device comprises three supporting legs (19), and the three supporting legs (19) are fixedly connected to the outer side wall of the bottom plate (17) in a circular array.

4. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: Each of the pressure relief devices comprises a third connecting pipe (24), each of the third connecting pipes (24) is fixedly connected to the side wall of the upper cover plate (26), each of the third connecting pipes (24) is provided with a safety valve (25), and each of the upper cover plate (26) is provided with a pressure gauge.

5. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: The seabed sediment (14) is provided with porous stone layers (4) on both the upper and lower sides.

6. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: The protective shell (7) and the water tank tube (23) are both made of PMMA XT type organic glass.

7. The pore pressure response model test system of gas-containing silt sediment according to claim 1 is characterized in that: The thickness of the protective shell (7) is 15 mm.

8. The method for operating the pore pressure response model test system of gas-containing silt sediment according to claims 1-7 is characterized in that: The following steps are involved: S1, using an air pump (18) to input methane into the two water tank barrels (23) through the fifth connecting pipe (28) and the fourth connecting pipe (27), so that the seawater in the two water tank barrels (23) is saturated with methane gas at a pressure of 300 to 800 kPa for at least 48 hours; S2, placing the reshaped seafloor sediment (14) between two baffles (5), and then applying a pressure difference in two water tanks (23) to generate a hydraulic gradient, so that saturated seawater flows through the seafloor sediment (14); S3, grasp the sliding rod (10) and manually move the piston (13) until it contacts the seabed sediment (14), so that the upper piston starts to move at a loading speed of 0.12 mm / h and the lower piston starts to move at an unloading speed of 0.5 mm / h, and the maximum total load is configured according to the target value of the pore pressure. When the piston (13) moves, the gas escaping from the seabed sediment (14) enters the gas collection bag (6), and the bender element can detect the changes in the gas collection bag (6) to measure the P wave velocity and the changes in the gas reservoir pressure in the escaping gas collection bag (6) during the shallow gas release process; S4, when the degassing process is carried out, the piston (13) is manually lifted to allow the gas to expand or dissolve and the sediment to expand, and the two safety valves (25) are opened to fully or partially decompress the pressure, and the two valves are opened simultaneously so that the decompression acts on both sides of the seabed sediment (14), and the longitudinal wave velocities before and after decompression are compared to detect the presence of free gas; S5, after degassing, the piston (13) and the seafloor sediment (14) are manually contacted, and the change in sample height during the expansion of the seafloor sediment (14) is calculated to further deduce the gas saturation of the gas-bearing sediment. According to the consolidation degree of the gaseous sediment before and after the gas escapes, the P-wave velocity and permeability are measured to determine the influence of the shear strength, creep characteristics, and seepage characteristics on the parameters.

9. The operating method of the gas-containing silt sediment pore pressure response model test system according to claim 8 is characterized in that: In the S4, in order to ensure complete degassing, this stage is maintained for about 15 hours.

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