A gradient-based simulation system and method for methane leakage from natural gas hydrate decomposition

Abstract

This invention discloses a gradient-based simulation system and method for methane leakage from natural gas hydrate decomposition, relating to the technical field of marine engineering. The system includes: a hydrate reservoir simulation subsystem to simulate the formation and decomposition of natural gas hydrates in the marine environment; an overlying sedimentary layer simulation subsystem to simulate the migration and transformation of leaked methane within the sedimentary layer; an overlying seawater layer simulation subsystem to simulate the migration and transformation of leaked methane in seawater layers at different depths; a pressure control subsystem to simulate the pressure of the vertical migration process of leaked methane; and a temperature control subsystem to simulate the temperature of the vertical migration process of leaked methane. This invention achieves vertical gradient simulation of temperature and pressure between the various simulation subsystems, ensuring that the simulation processes of each subsystem do not interfere with each other. This solves the problem that existing indoor methane leakage process simulation technologies cannot accurately reproduce the distortion of research results caused by vertical pressure and temperature changes in the in-situ marine environment.

Description

Technical Field

[0001] This invention relates to the technical field of marine engineering, and more specifically, to a gradient-based methane leakage simulation system and method for natural gas hydrate decomposition. Background Technology

[0002] Natural gas hydrates are a promising alternative resource, widely distributed in permafrost regions, continental margins, and deep-water environments, with marine environments accounting for 97% of global hydrate resources. Under standard conditions, the decomposition of 1 volume of natural gas hydrate yields approximately 164 volumes of methane gas. Natural gas hydrates are characterized by high energy density, wide distribution, and virtually pollution-free combustion. Over the past few decades, the development of natural gas hydrates has received widespread global attention; however, current research mainly focuses on hydrate extraction technologies and their derivatives, with limited experimental simulation studies on methane leakage during hydrate production and seabed methane seepage closely related to natural gas hydrate decomposition. Research on the migration and transformation characteristics of leaked methane in the overlying sedimentary and aquatic layers is crucial for ensuring the safe development of natural gas hydrates and the marine methane cycle.

[0003] A key factor limiting the development of this research is that most reported simulation devices can only construct closed hydrate reservoirs, primarily focusing on the dissociation phase transition, heat transfer, mass transfer, and reservoir deformation of natural gas hydrates. However, in actual marine environments, significant pressure and temperature gradients exist between the overlying seawater layer and the overlying sedimentary layer and hydrate reservoir. As the depth from the ocean surface to the hydrate reservoir increases, pressure can gradually increase from atmospheric pressure to tens of megapascals (MPa) or even hundreds of MPa, while temperature can gradually decrease from atmospheric temperature (approximately 25°C) to near 0°C at the seabed and then gradually rise to around 10°C or even higher in the hydrate reservoir. Due to these large temperature and pressure ranges, the migration and transformation characteristics of methane vary significantly at different ocean depths. However, for laboratory simulations, limitations in equipment size, particularly height, make it difficult to simulate the pressure and temperature gradients of the marine environment within the same chamber where pressure and heat transfer occur. The existing simulation devices all operate within the same pressure and temperature environment, encompassing the hydrate reservoir, overlying sedimentary layer, and overlying seawater layer. This makes it impossible to replicate the pressure and temperature gradient changes in the in-situ marine environment, hindering the accurate understanding of the migration and transformation characteristics of leaked methane during vertical transport in the ocean. Therefore, there is an urgent need for a simulation device capable of constructing an environment with varying vertical pressure and temperature gradients in the ocean. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies that simulate methane leaks by deviating from the actual vertical pressure and temperature gradients in the ocean, leading to distorted research results, this invention provides a gradient-based methane leak simulation system and method based on natural gas hydrate decomposition. This system accurately simulates the vertical pressure and temperature gradients of the marine environment in the laboratory, which is beneficial for studying the migration and transformation characteristics of leaked methane in the entire marine stratum during the decomposition of natural gas hydrates or hydrate development, resulting in more accurate research results.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] This invention provides a gradient-based methane leakage simulation system for natural gas hydrate decomposition. The system includes a hydrate reservoir simulation subsystem, an overlying sedimentary layer simulation subsystem, an overlying seawater layer simulation subsystem, a pressure control subsystem, and a temperature control subsystem, wherein:

[0007] The hydrate reservoir simulation subsystem is used to simulate the formation and decomposition process of natural gas hydrates in marine environments;

[0008] The overlying sedimentary layer simulation subsystem is used to simulate the migration and transformation process of methane leaking through the hydrate reservoir simulation subsystem in the sedimentary layer.

[0009] The overlying seawater layer simulation subsystem is used to simulate the migration and transformation process of methane leaking through the overlying sedimentary layer simulation subsystem in seawater layers at different depths.

[0010] The pressure control subsystem includes several pressure control modules. Each pressure control module is used to vertically connect adjacent simulation subsystems and independently adjust the pressure of each simulation subsystem to realize the pressure simulation of the vertical migration process of methane leakage.

[0011] The temperature control subsystem includes several temperature control modules, each of which is used to independently adjust the temperature of each simulation subsystem to simulate the temperature of the vertical migration process of methane leakage.

[0012] Preferably, the hydrate reservoir simulation subsystem includes a hydrate simulation layer, a gas injection valve, and a water injection valve; the pressure control subsystem includes a first pressure control module; and the temperature control subsystem includes a first temperature control module.

[0013] The bottom of the hydrate simulation layer is provided with an air injection port and a water injection port, and the top of the hydrate simulation layer is provided with a first air outlet.

[0014] The air injection valve is connected to the air injection port, and the water injection valve is connected to the water injection port;

[0015] One end of the first pressure control module is connected to the first air outlet, and the other end of the first pressure control module is connected to the overlying sediment layer simulation subsystem.

[0016] The first temperature control module is used to adjust the temperature of the hydrate simulation layer.

[0017] The first pressure control module and the first temperature control module independently control the pressure and temperature of the hydrate simulation layer, simulating the pressure and temperature of an in-situ reservoir in the ocean. Methane gas and pure water are injected through gas injection valves and water injection valves. Under stable temperature and pressure conditions for hydrates, methane gas and pure water form natural gas hydrates in the hydrate simulation layer. Outside of these stable temperature and pressure conditions, the natural gas hydrates decompose to generate water and methane fluid. The pressure of the hydrate simulation layer is controlled by the first pressure control module at the top. When the pressure exceeds the pressure threshold of the first pressure control module, the module opens, and the methane fluid migrates upwards to the overlying sedimentary layer simulation subsystem due to the pressure difference until the pressure falls below the pressure threshold. The hydrate reservoir simulation subsystem simulates the process of hydrate formation and destabilization decomposition in an in-situ natural gas hydrate reservoir.

[0018] Preferably, the overlying sedimentary layer simulation subsystem includes a sediment simulation layer, the pressure control subsystem further includes a second pressure control module, and the temperature control subsystem further includes a second temperature control module;

[0019] The bottom of the sediment simulation layer is provided with a second air inlet, and the top of the sediment simulation layer is provided with a second air outlet;

[0020] The second air inlet is connected to the other end of the first pressure control module, the second air outlet is connected to one end of the second pressure control module, and the other end of the second pressure control module is connected to the overlying seawater layer simulation subsystem.

[0021] The second temperature control module is used to adjust the temperature of the sediment simulation layer.

[0022] The second pressure control module and the second temperature control module independently control the pressure and temperature of the sediment simulation layer, simulating the pressure and temperature of in-situ sedimentary layers in the ocean. Methane fluid migrates from the hydrate simulation layer to the sediment simulation layer under pressure. When the pressure of the sediment simulation layer exceeds the pressure threshold of the second pressure control module, the second pressure control module activates, and the methane fluid migrates upwards to the overlying seawater simulation subsystem due to the pressure difference, until the pressure falls below the pressure threshold. The sediment simulation subsystem simulates the process of in-situ methane fluid migrating from an in-situ natural gas hydrate reservoir to the sediment layer and undergoing migration and transformation within the sediment layer.

[0023] Preferably, the overlying seawater layer simulation subsystem includes a first seawater simulation chamber, a second seawater simulation chamber, and a third seawater simulation chamber; the pressure control subsystem further includes a third pressure control module, a fourth pressure control module, and a fifth pressure control module; the temperature control subsystem further includes a third temperature control module, a fourth temperature control module, and a fifth temperature control module.

[0024] The third seawater simulation chamber has a third air inlet at the bottom and a third air outlet at the top; the second seawater simulation chamber has a fourth air inlet at the bottom and a fourth air outlet at the top; the first seawater simulation chamber has a fifth air inlet at the bottom and a fifth air outlet at the top.

[0025] The third air inlet is connected to the other end of the second pressure control module, and the third air outlet is connected to one end of the third pressure control module; the other end of the third pressure control module is connected to the fourth air inlet, and the fourth air outlet is connected to one end of the fourth pressure control module; the other end of the fourth pressure control module is connected to the fifth air inlet, and the fifth air outlet is connected to one end of the fifth pressure control module, with the other end of the fifth pressure control module suspended.

[0026] The third temperature control module is used to adjust the temperature of the third seawater simulation chamber, the fourth temperature control module is used to adjust the temperature of the second seawater simulation chamber, and the fifth temperature control module is used to adjust the temperature of the first seawater simulation chamber.

[0027] The first, second, and third seawater simulation chambers are used to simulate seawater layers at different depths, corresponding to the surface low-pressure seawater layer, the middle medium-pressure seawater layer, and the bottom high-pressure seawater layer, respectively. The third pressure control module and the third temperature control module independently control the pressure and temperature of the third seawater simulation chamber; the fourth pressure control module and the fourth temperature control module independently control the pressure and temperature of the second seawater simulation chamber; and the fifth pressure control module and the fifth temperature control module independently control the pressure and temperature of the first seawater simulation chamber, simulating the pressure and temperature of in-situ surface seawater, middle seawater, and bottom seawater in the ocean, respectively. Methane fluid, driven by pressure, flows from the sediment... The methane fluid migrates from the in-situ sedimentary cloud to the third seawater simulation chamber. When the pressure in the third seawater simulation chamber exceeds the pressure threshold of the third pressure control module, the third pressure control module opens, and the methane fluid migrates to the second seawater simulation chamber due to the pressure difference until the pressure falls below the pressure threshold. When the pressure in the second seawater simulation chamber exceeds the pressure threshold of the fourth pressure control module, the fourth pressure control module opens, and the methane fluid migrates to the first seawater simulation chamber due to the pressure difference until the pressure falls below the pressure threshold. When the pressure in the first seawater simulation chamber exceeds the pressure threshold of the fifth pressure control module, the fifth pressure control module opens, and the methane fluid migrates upward and exits the overlying seawater layer simulation subsystem. The overlying seawater layer simulation subsystem simulates the process of in-situ methane fluid migrating from the in-situ sedimentary cloud to the bottom high-pressure seawater layer, then to the middle medium-pressure seawater layer, and finally to the surface low-pressure seawater layer.

[0028] Preferably, the first pressure control module, the second pressure control module, the third pressure control module, the fourth pressure control module and the fifth pressure control module have the same structure, and each includes a programmable controller, a solenoid valve, a throttle valve and a pneumatic valve;

[0029] The programmable controller is connected to the control terminal of the solenoid valve, and the actuating terminal of the solenoid valve is connected to the valve core of the pneumatic valve; one end of the pneumatic valve is connected to the corresponding air outlet, the other end of the pneumatic valve is connected to one end of the throttle valve, and the other end of the throttle valve is connected to the corresponding air inlet.

[0030] Solenoid valves are used to convert electrical control signals into pneumatic control signals. A programmable logic controller (PLC) supplies power to the solenoid valve's coil, causing the valve core inside the solenoid valve to move, controlling the opening and closing of the circuit, thus controlling the flow direction of the compression control. Pneumatic valves control the valve opening by receiving pneumatic signals to change the position of the valve core. When the pressure is below a threshold, the valve closes to prevent pressure leakage. For example, when natural gas hydrates in a hydrate simulation layer decompose to produce a large amount of methane gas, the pressure in the hydrate simulation layer rises. When this pressure exceeds the set pressure threshold, the pneumatic valve opens, and methane fluid flows through the pneumatic valve to a throttle valve. The throttle valve controls the fluid flow rate, and the methane fluid after passing through the throttle valve flows towards the sediment simulation layer. At this time, the pressure in the hydrate simulation layer decreases as the fluid flows out. When the pressure drops below the set pressure threshold, the pneumatic valve closes, achieving pressure control and regulation of the hydrate simulation layer. By controlling the pressure threshold of the corresponding simulation chamber or simulation layer through the pressure control module, each simulation subsystem can be interconnected and can also simulate the pressure profile of the in-situ vertical gradient, realizing the process of vertical migration of methane leakage under in-situ marine pressure in the laboratory.

[0031] Preferably, the first temperature control module, the second temperature control module, the third temperature control module, the fourth temperature control module and the fifth temperature control module have the same structure, and each includes a water bath and a temperature controller;

[0032] The water bath tank is used to house the corresponding simulation layer or simulation chamber;

[0033] The thermostat is electrically connected to the water bath and is used to regulate the temperature of the water bath.

[0034] By adjusting the temperature of the water bath using a thermostat, the temperature of the corresponding simulation layer or simulation chamber is controlled, simulating the temperature profile of the in-situ vertical gradient and realizing the process of vertical migration of methane leakage under in-situ ocean temperature in the laboratory.

[0035] Preferably, the system further includes a data monitoring and acquisition subsystem;

[0036] The data monitoring and acquisition subsystem includes several pressure sensors, several temperature sensors, and several sampling valves;

[0037] One pressure sensor is connected to one pressure control module.

[0038] Each pair of temperature sensors is connected to a seawater simulation chamber, specifically to the top and bottom of the chamber.

[0039] Each pair of sampling valves is connected to a seawater simulation chamber or sediment simulation layer, respectively connected to the top and bottom of the seawater simulation chamber or sediment simulation layer.

[0040] The data monitoring and acquisition subsystem includes a first pressure sensor, a second pressure sensor, a third pressure sensor, a fourth pressure sensor, and a fifth pressure sensor, which are respectively connected to the first pressure control module, the second pressure control module, the third pressure control module, the fourth pressure control module, and the fifth pressure control module.

[0041] The data monitoring and acquisition subsystem includes a first temperature sensor, a second temperature sensor, a third temperature sensor, a fourth temperature sensor, a fifth temperature sensor, and a sixth temperature sensor. The first and second temperature sensors are respectively connected to the bottom and top of the third seawater simulation chamber, the third and fourth temperature sensors are respectively connected to the bottom and top of the second seawater simulation chamber, and the fifth and sixth temperature sensors are respectively connected to the bottom and top of the first seawater simulation chamber.

[0042] The data monitoring and acquisition subsystem includes a first sampling valve, a second sampling valve, a third sampling valve, a fourth sampling valve, a fifth sampling valve, a sixth sampling valve, a seventh sampling valve, and an eighth sampling valve. The first and second sampling valves are connected to the bottom and top of the sediment simulation layer, respectively. The third and fourth sampling valves are connected to the bottom and top of the third seawater simulation chamber, respectively. The fifth and sixth sampling valves are connected to the bottom and top of the second seawater simulation chamber, respectively. The seventh and eighth sampling valves are connected to the bottom and top of the first seawater simulation chamber, respectively.

[0043] Preferably, the system further includes a processing terminal;

[0044] The processing terminal includes a processor, a memory, and a display;

[0045] The processor's input terminal is electrically connected to the output terminals of several pressure sensors, several temperature sensors, and several sampling valves, respectively, for receiving and processing monitoring data to obtain data processing results.

[0046] The processor is electrically connected to the memory, which is used to store monitoring data and data processing results.

[0047] The processor's output is connected to the display's input, and the display is used to show monitoring data and data processing results.

[0048] This invention also provides a gradient-based method for simulating methane leakage from natural gas hydrate decomposition, implemented based on the aforementioned simulation system, comprising:

[0049] S1: Construct the environments for the hydrate simulation layer, sediment simulation layer, third seawater simulation chamber, second seawater simulation chamber, and first seawater simulation chamber;

[0050] S2: Inject a preset amount of methane gas into the hydrate simulation layer through the gas injection valve, inject a preset amount of pure water or salt water into the hydrate simulation layer through the water injection valve, inject different pressures into the corresponding simulation layer or simulation chamber through each pressure control module, and adjust the temperature of the corresponding simulation layer or simulation chamber through each temperature control module.

[0051] S3: The hydrate simulation layer forms and decomposes natural gas hydrates in a high-pressure, low-temperature environment required for the formation of natural gas hydrates; the decomposition of natural gas hydrates increases the pressure of the hydrate simulation layer. When the pressure exceeds the pressure threshold of the first pressure control module, the first pressure control module opens, and the methane fluid moves upward to the sediment simulation layer.

[0052] S4: The pressure of the sediment simulation layer increases. When the pressure exceeds the pressure threshold of the second pressure control module, the second pressure control module opens, and the methane fluid moves upward to the third seawater simulation chamber.

[0053] S5: The pressure in the third seawater simulation chamber increases. When the pressure exceeds the pressure threshold of the third pressure control module, the third pressure control module opens, and the methane fluid moves upward to the second seawater simulation chamber.

[0054] S6: The pressure in the second seawater simulation chamber increases. When the pressure exceeds the pressure threshold of the fourth pressure control module, the fourth pressure control module opens, and the methane fluid moves upward to the first seawater simulation chamber.

[0055] S7: The pressure in the first seawater simulation chamber increases. When the pressure exceeds the pressure threshold of the fifth pressure control module, the fifth pressure control module opens, and the methane fluid is discharged.

[0056] S8: The pressure and temperature sensors are used to monitor the temperature and pressure distribution and changes in each simulation layer and simulation chamber in real time, and the sampling valve is used to sample the methane fluid in each simulation layer and simulation chamber.

[0057] S9: By processing, storing, and displaying monitoring data and data processing results through the processing terminal, the simulation of the natural gas hydrate decomposition and methane leakage process is completed until all natural gas hydrates in the hydrate simulation layer are completely decomposed.

[0058] Preferably, step S1 includes:

[0059] The hydrate simulation layer is filled with silty sediments to act as a porous medium, and the sediment simulation layer is filled with a clay layer.

[0060] A preset amount of seawater is filled into the hydrate simulation layer, sediment simulation layer, third seawater simulation chamber, second seawater simulation chamber, and first seawater simulation chamber.

[0061] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0062] This invention establishes a hydrate reservoir simulation subsystem to simulate the formation and decomposition of natural gas hydrates in in-situ marine reservoirs; an overlying sedimentary layer simulation subsystem to simulate the migration and transformation of leaked methane in in-situ sedimentary layers; and an overlying seawater layer simulation subsystem to simulate the migration and transformation of leaked methane in seawater layers at the same depth. Pressure control modules are installed between adjacent simulation subsystems for vertical connectivity and independent pressure adjustment of each subsystem, simulating the pressure profile of the in-situ vertical gradient and realizing the vertical migration of leaked methane under simulated marine in-situ pressure in a laboratory setting. A temperature control module is also included for each subsystem to independently adjust its temperature, simulating the temperature profile of the in-situ vertical gradient and realizing the vertical migration of leaked methane under simulated marine in-situ temperature in a laboratory setting. This invention achieves full-profile simulation of methane leakage from hydrate reservoirs to overlying sedimentary layers and then to overlying seawater layers, while simultaneously studying the methane migration and transformation characteristics of each layer during the leakage process. Under the premise of ensuring the connectivity of each simulation subsystem and realizing fluid transport between them, it also simulates the vertical temperature and pressure gradients between the subsystems. The simulation processes of each subsystem do not interfere with each other, solving the problem of distortion in research results caused by the inability of existing indoor methane leakage process simulation technologies to accurately reproduce the vertical pressure and temperature changes in the in-situ environment. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the structure of a gradient-type natural gas hydrate decomposition methane leakage simulation system described in Example 1;

[0064] Figure 2 This is a schematic diagram of the structure of a gradient-type natural gas hydrate decomposition methane leakage simulation system described in Example 2;

[0065] Figure 3 This is a schematic diagram of the pressure control module described in Example 2;

[0066] Figure 4 This is a flowchart of a gradient-based method for simulating methane leakage from natural gas hydrate decomposition, as described in Example 3.

[0067] In the diagram, 1-hydrate reservoir simulation subsystem, 2-overlying sedimentary layer simulation subsystem, 3-overlying seawater layer simulation subsystem, 4-pressure control subsystem, 5-temperature control subsystem, 6-data monitoring and acquisition subsystem, 7-processing terminal, 11-hydrate simulation layer, 12-air injection valve, 13-water injection valve, 21-sediment simulation layer, 31-first seawater simulation chamber, 32-second seawater simulation chamber, 33-third seawater simulation chamber, 41-first pressure control module, 42-second pressure control module, 43-third pressure control module, 44-fourth pressure control module, 45-fifth pressure control module, 51-first temperature control module, 52-second temperature control module, 53-third temperature control module, 54-fourth temperature control module, 55-fifth temperature control module. 71-Processor, 72-Memory, 73-Display, 401-Programmable Controller, 402-Solenoid Valve, 403-Throttle Valve, 404-Pneumatic Valve, 611-First Pressure Sensor, 612-Second Pressure Sensor, 613-Third Pressure Sensor, 614-Fourth Pressure Sensor, 615-Fifth Pressure Sensor, 621-First Temperature Sensor, 622-Second Temperature Sensor, 623-Third Temperature Sensor, 624-Fourth Temperature Sensor, 625-Fifth Temperature Sensor, 626-Sixth Temperature Sensor, 631-First Sampling Valve, 632-Second Sampling Valve, 633-Third Sampling Valve, 634-Fourth Sampling Valve, 635-Fifth Sampling Valve, 636-Sixth Sampling Valve, 637-Seventh Sampling Valve, 638-Eighth Sampling Valve. Detailed Implementation

[0068] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0069] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;

[0070] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0071] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0072] Example 1

[0073] This embodiment provides a gradient-based methane leakage simulation system based on the decomposition of natural gas hydrates, such as... Figure 1 As shown, the system includes a hydrate reservoir simulation subsystem 1, an overlying sedimentary layer simulation subsystem 2, an overlying seawater layer simulation subsystem 3, a pressure control subsystem 4, and a temperature control subsystem 5, wherein:

[0074] The hydrate reservoir simulation subsystem 1 is used to simulate the formation and decomposition process of natural gas hydrates in the marine environment;

[0075] The overlying sedimentary layer simulation subsystem 2 is used to simulate the migration and transformation process of methane leaking through the hydrate reservoir simulation subsystem 1 in the sedimentary layer.

[0076] The overlying seawater layer simulation subsystem 3 is used to simulate the migration and transformation process of methane leaking through the overlying sedimentary layer simulation subsystem 2 in seawater layers at different depths.

[0077] The pressure control subsystem 4 includes several pressure control modules. Each pressure control module is used to vertically connect adjacent simulation subsystems and independently adjust the pressure of each simulation subsystem to realize the pressure simulation of the vertical migration process of methane leakage.

[0078] The temperature control subsystem 5 includes several temperature control modules, each of which is used to independently adjust the temperature of each simulation subsystem to simulate the temperature of the vertical migration process of methane leakage.

[0079] In the specific implementation process, this embodiment sets up a hydrate reservoir simulation subsystem to simulate the formation and decomposition process of natural gas hydrates in in-situ reservoirs in the ocean, an overlying sedimentary layer simulation subsystem to simulate the migration and transformation process of leaked methane in the in-situ sedimentary layer, and an overlying seawater layer simulation subsystem to simulate the migration and transformation process of leaked methane in the seawater layer at the same depth. Pressure control modules are set up between adjacent simulation subsystems for vertical connection and independent adjustment of the pressure of each simulation subsystem, simulating the pressure profile of the in-situ vertical gradient, realizing the process of vertical migration of leaked methane under simulated in-situ ocean pressure in the laboratory. Temperature control modules are set up for each simulation subsystem to independently adjust the temperature of each simulation subsystem, simulating the temperature profile of the in-situ vertical gradient, realizing the process of vertical migration of leaked methane under simulated in-situ ocean temperature in the laboratory. The simulation system provided in this embodiment realizes the simulation of the full-profile methane leakage process from the hydrate reservoir to the overlying sedimentary layer and then to the overlying seawater layer. At the same time, it studies the methane migration and transformation characteristics of each layer during the methane leakage process. Under the premise of ensuring the connectivity of each simulation subsystem and realizing the fluid transport between each simulation subsystem, it also realizes the simulation of the vertical temperature and pressure gradient between each simulation subsystem. The simulation processes of each simulation subsystem do not interfere with each other, which solves the problem that existing indoor methane leakage process simulation technology cannot accurately reproduce the in-situ environment vertical pressure and temperature changes, resulting in the distortion of research results.

[0080] Example 2

[0081] This embodiment provides a gradient-based methane leakage simulation system based on the decomposition of natural gas hydrates, such as... Figure 1As shown, the system includes a hydrate reservoir simulation subsystem 1, an overlying sedimentary layer simulation subsystem 2, an overlying seawater layer simulation subsystem 3, a pressure control subsystem 4, a temperature control subsystem 5, a data monitoring and acquisition subsystem 6, and a processing terminal 7, wherein:

[0082] The pressure control subsystem 4 includes a first pressure control module 41, a second pressure control module 42, a third pressure control module 43, a fourth pressure control module 44, and a fifth pressure control module 45.

[0083] The first temperature control module 51, the second temperature control module 52, the third temperature control module 53, the fourth temperature control module 54, and the fifth temperature control module 55;

[0084] The hydrate reservoir simulation subsystem 1 is used to simulate the formation and decomposition process of natural gas hydrates in the marine environment, including a hydrate simulation layer 11, a gas injection valve 12, and a water injection valve 13;

[0085] The bottom of the hydrate simulation layer 11 is provided with an air inlet and a water inlet, and the top of the hydrate simulation layer 11 is provided with a first air outlet.

[0086] The air injection valve 12 is connected to the air injection port, and the water injection valve 13 is connected to the water injection port;

[0087] One end of the first pressure control module 41 is connected to the first air outlet, and the other end of the first pressure control module 41 is connected to the overlying sedimentary layer simulation subsystem 2.

[0088] The first temperature control module 51 is used to adjust the temperature of the hydrate simulation layer 11;

[0089] The overlying sedimentary layer simulation subsystem 2 is used to simulate the migration and transformation process of methane leaking through the hydrate reservoir simulation subsystem 1 in the sedimentary layer, including the sedimentary simulation layer 21;

[0090] The bottom of the sediment simulation layer 21 is provided with a second air inlet, and the top of the sediment simulation layer 21 is provided with a second air outlet.

[0091] The second air inlet is connected to the other end of the first pressure control module 41, the second air outlet is connected to one end of the second pressure control module 42, and the other end of the second pressure control module 42 is connected to the overlying seawater layer simulation subsystem 3.

[0092] The second temperature control module 52 is used to adjust the temperature of the sediment simulation layer 21;

[0093] The overlying seawater layer simulation subsystem 3 is used to simulate the migration and transformation process of methane leaking through the overlying sedimentary layer simulation subsystem 2 in seawater layers at different depths, and includes a first seawater simulation chamber 31, a second seawater simulation chamber 32 and a third seawater simulation chamber 33.

[0094] The third seawater simulation chamber 33 has a third air inlet at the bottom and a third air outlet at the top; the second seawater simulation chamber 32 has a fourth air inlet at the bottom and a fourth air outlet at the top; the first seawater simulation chamber 31 has a fifth air inlet at the bottom and a fifth air outlet at the top.

[0095] The third air inlet is connected to the other end of the second pressure control module 42, and the third air outlet is connected to one end of the third pressure control module 43; the other end of the third pressure control module 43 is connected to the fourth air inlet, and the fourth air outlet is connected to one end of the fourth pressure control module 44; the other end of the fourth pressure control module 44 is connected to the fifth air inlet, and the fifth air outlet is connected to one end of the fifth pressure control module 45, with the other end of the fifth pressure control module 45 suspended.

[0096] The third temperature control module 53 is used to adjust the temperature of the third seawater simulation chamber 33, the fourth temperature control module 54 is used to adjust the temperature of the second seawater simulation chamber 32, and the fifth temperature control module 55 is used to adjust the temperature of the first seawater simulation chamber 31.

[0097] The data monitoring and acquisition subsystem 6 includes several pressure sensors, several temperature sensors, and several sampling valves;

[0098] One pressure sensor is connected to one pressure control module.

[0099] Each pair of temperature sensors is connected to a seawater simulation chamber, specifically to the top and bottom of the chamber.

[0100] Each pair of sampling valves is connected to a seawater simulation chamber or sediment simulation layer 21, respectively connected to the top and bottom of the seawater simulation chamber or sediment simulation layer 21.

[0101] In this embodiment, the data monitoring and acquisition subsystem 6 includes a first pressure sensor 611, a second pressure sensor 612, a third pressure sensor 613, a fourth pressure sensor 614, and a fifth pressure sensor 615, which are respectively connected to the first pressure control module 41, the second pressure control module 42, the third pressure control module 43, the fourth pressure control module 44, and the fifth pressure control module 45.

[0102] The data monitoring and acquisition subsystem 6 includes a first temperature sensor 621, a second temperature sensor 622, a third temperature sensor 623, a fourth temperature sensor 624, a fifth temperature sensor 625, and a sixth temperature sensor 626. The first temperature sensor 621 and the second temperature sensor 622 are respectively connected to the bottom and top of the third seawater simulation chamber 33, the third temperature sensor 623 and the fourth temperature sensor 624 are respectively connected to the bottom and top of the second seawater simulation chamber 32, and the fifth temperature sensor 625 and the sixth temperature sensor 626 are respectively connected to the bottom and top of the first seawater simulation chamber 31.

[0103] The data monitoring and acquisition subsystem 6 includes a first sampling valve 631, a second sampling valve 632, a third sampling valve 633, a fourth sampling valve 634, a fifth sampling valve 635, a sixth sampling valve 636, a seventh sampling valve 637, and an eighth sampling valve 638. The first sampling valve 631 and the second sampling valve 632 are respectively connected to the bottom and top of the sediment simulation layer 21. The third sampling valve 633 and the fourth sampling valve 634 are respectively connected to the bottom and top of the third seawater simulation chamber 33. The fifth sampling valve 635 and the sixth sampling valve 636 are respectively connected to the bottom and top of the second seawater simulation chamber 32. The seventh sampling valve 637 and the eighth sampling valve 638 are respectively connected to the bottom and top of the first seawater simulation chamber 31.

[0104] The processing terminal 7 includes a processor 71, a memory 72, and a display 73;

[0105] The input terminal of the processor 71 is electrically connected to the output terminals of several pressure sensors, several temperature sensors and several sampling valves, respectively, for receiving monitoring data and processing it to obtain data processing results;

[0106] The processor 71 is electrically connected to the memory 72, and the memory 72 is used to store monitoring data and data processing results.

[0107] The output terminal of the processor 71 is connected to the input terminal of the display 73, which is used to display monitoring data and data processing results.

[0108] like Figure 3 As shown, the first pressure control module 41, the second pressure control module 42, the third pressure control module 43, the fourth pressure control module 44 and the fifth pressure control module 45 have the same structure, and each includes a programmable controller 401, a solenoid valve 402, a throttle valve 403 and a pneumatic valve 404.

[0109] The programmable controller 401 is connected to the control terminal of the solenoid valve 402, and the actuating terminal of the solenoid valve 402 is connected to the valve core of the pneumatic valve 404. One end of the pneumatic valve 404 is connected to the corresponding air outlet, and the other end of the pneumatic valve 404 is connected to one end of the throttle valve 403. The other end of the throttle valve 403 is connected to the corresponding air inlet.

[0110] Solenoid valve 402 is used to convert electrical control signals into pneumatic control. Programmable controller 401 supplies power to the coil of solenoid valve 402. Under the action of the coil, the valve core inside solenoid valve 402 actuates, controlling the opening and closing of the circuit, thus completing the flow direction control for compression. Pneumatic valve 404 receives pneumatic signals to change the position of the valve core, thereby controlling the valve opening. When the pressure is below a threshold, the valve closes to prevent pressure leakage. For example, when the natural gas hydrate in hydrate simulation layer 11 decomposes to produce a large amount of methane gas, the pressure in hydrate simulation layer 11 rises. When the pressure exceeds the set pressure threshold, pneumatic valve 404 opens, and methane fluid flows through pneumatic valve 404 to throttle valve 403. Throttling valve 403 controls the fluid flow rate, and the methane fluid after passing through throttle valve 403 flows to sediment simulation layer 21. At this time, the pressure of the hydrate simulation layer decreases as the fluid flows out. When it drops below the set pressure threshold, pneumatic valve 404 closes, realizing pressure control and regulation of hydrate simulation layer 11. By controlling the pressure threshold of the corresponding simulation chamber or simulation layer through the pressure control module, each simulation subsystem can be interconnected and can also simulate the pressure profile of the in-situ vertical gradient, realizing the process of vertical migration of methane leakage under in-situ marine pressure in the laboratory.

[0111] The first temperature control module 51, the second temperature control module 52, the third temperature control module 53, the fourth temperature control module 54 and the fifth temperature control module 55 have the same structure, and each includes a water bath and a temperature controller.

[0112] The water bath tank is used to house the corresponding simulation layer or simulation chamber;

[0113] The thermostat is electrically connected to the water bath and is used to regulate the temperature of the water bath.

[0114] By adjusting the temperature of the water bath using a thermostat, the temperature of the corresponding simulation layer or simulation chamber is controlled, simulating the temperature profile of the in-situ vertical gradient and realizing the process of vertical migration of methane leakage under in-situ ocean temperature in the laboratory.

[0115] In the specific implementation process, the first pressure control module 41 and the first temperature control module 51 independently control the pressure and temperature of the hydrate simulation layer 11, simulating the pressure and temperature of an in-situ reservoir in the ocean. Methane gas and pure water are injected through the gas injection valve 12 and the water injection valve 13. Under stable temperature and pressure conditions for hydrates, the methane gas and pure water form natural gas hydrates in the hydrate simulation layer 11. Outside of stable temperature and pressure conditions, the natural gas hydrates decompose to generate water and methane fluid. The pressure of the hydrate simulation layer 11 is controlled by the first pressure control module 41 at the top of the hydrate simulation layer 11. When the pressure exceeds the pressure threshold of the first pressure control module 41, the first pressure control module 41 opens, and the methane fluid migrates upwards to the overlying sedimentary layer simulation subsystem 2 due to the pressure difference until the pressure falls below the pressure threshold. The hydrate reservoir simulation subsystem 1 simulates the process of hydrate formation and decomposition in an in-situ natural gas hydrate reservoir.

[0116] The second pressure control module 42 and the second temperature control module 52 independently control the pressure and temperature of the sediment simulation layer 21, simulating the pressure and temperature of in-situ sedimentary layers in the ocean. Methane fluid migrates from the hydrate simulation layer 11 to the sediment simulation layer 21 under pressure. When the pressure of the sediment simulation layer 21 exceeds the pressure threshold of the second pressure control module 42, the second pressure control module 42 is activated, and the methane fluid migrates upwards to the overlying seawater layer simulation subsystem 3 due to the pressure difference, until the pressure falls below the pressure threshold. The sedimentary layer simulation subsystem simulates the process of in-situ methane fluid migrating from an in-situ natural gas hydrate reservoir to the sedimentary layer and undergoing migration and transformation within the sedimentary layer.

[0117] The first seawater simulation chamber 31, the second seawater simulation chamber 32, and the third seawater simulation chamber 33 are used to simulate seawater layers at different depths, corresponding to the surface low-pressure seawater layer, the middle medium-pressure seawater layer, and the bottom high-pressure seawater layer, respectively. The third pressure control module 43 and the third temperature control module 53 independently control the pressure and temperature of the third seawater simulation chamber 33, the fourth pressure control module 44 and the fourth temperature control module 54 independently control the pressure and temperature of the second seawater simulation chamber 32, and the fifth pressure control module 45 and the fifth temperature control module 55 independently control the pressure and temperature of the first seawater simulation chamber 31, respectively simulating the pressure and temperature of in-situ surface seawater, middle seawater, and bottom seawater in the ocean. Methane fluid, driven by pressure, flows from the sediment... The simulated layer 21 is moved to the third seawater simulation chamber 33. When the pressure in the third seawater simulation chamber 33 is greater than the pressure threshold of the third pressure control module 43, the third pressure control module 43 is opened, and the methane fluid moves to the second seawater simulation chamber 32 due to the pressure difference until the pressure is lower than the pressure threshold. When the pressure in the second seawater simulation chamber 32 is greater than the pressure threshold of the fourth pressure control module 44, the fourth pressure control module 44 is opened, and the methane fluid moves to the first seawater simulation chamber 31 due to the pressure difference until the pressure is lower than the pressure threshold. When the pressure in the first seawater simulation chamber 31 is greater than the pressure threshold of the fifth pressure control module 45, the fifth pressure control module 45 is opened, and the methane fluid moves upward and is discharged from the overlying seawater layer simulation subsystem 3. The overlying seawater layer simulation subsystem 3 simulates the process of in-situ methane fluid migrating from the in-situ sedimentary cloud to the bottom high-pressure seawater layer, then to the middle medium-pressure seawater layer, and finally to the surface low-pressure seawater layer.

[0118] The pressure sensor 61 and temperature sensor 62 are used to monitor the temperature and pressure distribution and changes of each simulation layer and simulation chamber in real time, and the sampling valve 63 is used to sample the methane fluid of each simulation layer and simulation chamber.

[0119] Example 3

[0120] This embodiment provides a gradient-based method for simulating methane leakage from natural gas hydrate decomposition, implemented based on the simulation system described in Embodiment 1 or 2, such as... Figure 4 As shown, it includes:

[0121] S1: Constructing the environment for the hydrate simulation layer 11, sediment simulation layer 21, third seawater simulation chamber 33, second seawater simulation chamber 32, and first seawater simulation chamber 31; including:

[0122] The hydrate simulation layer 11 is filled with silty sediments to serve as a porous medium, and the sediment simulation layer 21 is filled with a clay layer.

[0123] A preset amount of seawater is filled into the hydrate simulation layer 11, sediment simulation layer 21, third seawater simulation chamber 33, second seawater simulation chamber 32 and first seawater simulation chamber 31;

[0124] S2: Inject a preset amount of methane gas into the hydrate simulation layer 11 through the gas injection valve 12, inject a preset amount of pure water or salt water into the hydrate simulation layer 11 through the water injection valve 13, inject different pressures into the corresponding simulation layer or simulation chamber through each pressure control module, and adjust the temperature of the corresponding simulation layer or simulation chamber through each temperature control module.

[0125] S3: The hydrate simulation layer 11 forms and decomposes natural gas hydrates in a high-pressure, low-temperature environment required for the formation of natural gas hydrates; the decomposition of natural gas hydrates causes the pressure of the hydrate simulation layer 11 to increase. When the pressure is greater than the pressure threshold of the first pressure control module 41, the first pressure control module 41 is opened, and the methane fluid moves upward to the sediment simulation layer 21.

[0126] S4: The pressure of the sediment simulation layer 21 increases. When the pressure is greater than the pressure threshold of the second pressure control module 42, the second pressure control module 42 opens, and the methane fluid moves upward to the third seawater simulation chamber 33.

[0127] S5: The pressure in the third seawater simulation chamber 33 increases. When the pressure exceeds the pressure threshold of the third pressure control module 43, the third pressure control module 43 opens, and the methane fluid moves upward to the second seawater simulation chamber 32.

[0128] S6: The pressure in the second seawater simulation chamber 32 increases. When the pressure exceeds the pressure threshold of the fourth pressure control module 44, the fourth pressure control module 44 opens, and the methane fluid moves upward to the first seawater simulation chamber 31.

[0129] S7: The pressure in the first seawater simulation chamber 31 increases. When the pressure exceeds the pressure threshold of the fifth pressure control module 45, the fifth pressure control module 45 opens, and the methane fluid is discharged.

[0130] S8: The pressure and temperature sensors are used to monitor the temperature and pressure distribution and changes of each simulation layer and simulation chamber in real time, and the sampling valve is used to sample the methane fluid in each simulation layer and simulation chamber.

[0131] S9: The monitoring data and data processing results are processed, stored and displayed by the processing terminal 7 until all the natural gas hydrate in the hydrate simulation layer 11 is completely decomposed, thus completing the simulation of the methane leakage process of natural gas hydrate decomposition.

[0132] The same or similar labels correspond to the same or similar parts;

[0133] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0134] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A gradient-based methane leakage simulation system for natural gas hydrate decomposition, characterized in that, The system includes a hydrate reservoir simulation subsystem (1), an overlying sedimentary layer simulation subsystem (2), an overlying seawater layer simulation subsystem (3), a pressure control subsystem (4), and a temperature control subsystem (5), wherein: The hydrate reservoir simulation subsystem (1) is used to simulate the formation and decomposition process of natural gas hydrates in the marine environment; The hydrate reservoir simulation subsystem (1) includes a hydrate simulation layer (11), an injection valve (12), and a water injection valve (13); the bottom of the hydrate simulation layer (11) is provided with an injection port and a water injection port, and the top of the hydrate simulation layer (11) is provided with a first air outlet; the injection valve (12) is connected to the injection port, and the water injection valve (13) is connected to the water injection port; The overlying sedimentary layer simulation subsystem (2) is used to simulate the migration and transformation process of methane leaking through the hydrate reservoir simulation subsystem (1) in the sedimentary layer; The overlying sedimentary layer simulation subsystem (2) includes a sediment simulation layer (21); the bottom of the sediment simulation layer (21) is provided with a second air inlet, and the top of the sediment simulation layer (21) is provided with a second air outlet; The overlying seawater layer simulation subsystem (3) is used to simulate the migration and transformation process of methane leaking through the overlying sediment layer simulation subsystem (2) in seawater layers at different depths; The overlying seawater layer simulation subsystem (3) includes a first seawater simulation chamber (31), a second seawater simulation chamber (32), and a third seawater simulation chamber (33); the third seawater simulation chamber (33) has a third air inlet at its bottom and a third air outlet at its top; the second seawater simulation chamber (32) has a fourth air inlet at its bottom and a fourth air outlet at its top; the first seawater simulation chamber (31) has a fifth air inlet at its bottom and the second seawater simulation chamber (32) has a fifth air outlet at its top; The pressure control subsystem (4) includes several pressure control modules. Each pressure control module is used to vertically connect adjacent simulation subsystems and independently adjust the pressure of each simulation subsystem to realize the pressure simulation of the vertical migration process of methane leakage. The temperature control subsystem (5) includes several temperature control modules, each of which is used to independently adjust the temperature of each simulation subsystem to simulate the temperature of the vertical migration process of methane leakage.

2. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 1, characterized in that, The pressure control subsystem (4) includes a first pressure control module (41), and the temperature control subsystem (5) includes a first temperature control module (51). One end of the first pressure control module (41) is connected to the first air outlet, and the other end of the first pressure control module (41) is connected to the overlying sedimentary layer simulation subsystem (2). The first temperature control module (51) is used to adjust the temperature of the hydrate simulation layer (11).

3. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 2, characterized in that, The pressure control subsystem (4) further includes a second pressure control module (42), and the temperature control subsystem (5) further includes a second temperature control module (52); The second air inlet is connected to the other end of the first pressure control module (41), the second air outlet is connected to one end of the second pressure control module (42), and the other end of the second pressure control module (42) is connected to the overlying seawater layer simulation subsystem (3). The second temperature control module (52) is used to adjust the temperature of the sediment simulation layer (21).

4. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 3, characterized in that, The pressure control subsystem (4) further includes a third pressure control module (43), a fourth pressure control module (44), and a fifth pressure control module (45); the temperature control subsystem (5) further includes a third temperature control module (53), a fourth temperature control module (54), and a fifth temperature control module (55); The third air inlet is connected to the other end of the second pressure control module (42), and the third air outlet is connected to one end of the third pressure control module (43); the other end of the third pressure control module (43) is connected to the fourth air inlet, and the fourth air outlet is connected to one end of the fourth pressure control module (44); the other end of the fourth pressure control module (44) is connected to the fifth air inlet, and the fifth air outlet is connected to one end of the fifth pressure control module (45), with the other end of the fifth pressure control module (45) suspended. The third temperature control module (53) is used to adjust the temperature of the third seawater simulation chamber (33), the fourth temperature control module (54) is used to adjust the temperature of the second seawater simulation chamber (32), and the fifth temperature control module (55) is used to adjust the temperature of the first seawater simulation chamber (31).

5. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 4, characterized in that, The first pressure control module (41), the second pressure control module (42), the third pressure control module (43), the fourth pressure control module (44) and the fifth pressure control module (45) have the same structure, and each includes a programmable controller (401), a solenoid valve (402), a throttle valve (403) and a pneumatic valve (404). The programmable controller (401) is connected to the control terminal of the solenoid valve (402), and the actuating terminal of the solenoid valve (402) is connected to the valve core of the pneumatic valve (404). One end of the pneumatic valve (404) is connected to the corresponding air outlet, and the other end of the pneumatic valve (404) is connected to one end of the throttle valve (403), and the other end of the throttle valve (403) is connected to the corresponding air inlet.

6. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 4, characterized in that, The first temperature control module (51), the second temperature control module (52), the third temperature control module (53), the fourth temperature control module (54) and the fifth temperature control module (55) have the same structure, and each includes a water bath and a temperature controller. The water bath is used to house the corresponding simulation layer or simulation chamber; The thermostat is electrically connected to the water bath and is used to regulate the temperature of the water bath.

7. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 4, characterized in that, The system also includes a data monitoring and acquisition subsystem (6); The data monitoring and acquisition subsystem (6) includes several pressure sensors, several temperature sensors and several sampling valves; One pressure sensor is connected to one pressure control module. Each pair of temperature sensors is connected to a seawater simulation chamber, specifically to the top and bottom of the chamber. Each pair of sampling valves is connected to a seawater simulation chamber or sediment simulation layer (21), respectively connected to the top and bottom of the seawater simulation chamber or sediment simulation layer (21).

8. The gradient-type natural gas hydrate decomposition methane leakage simulation system according to claim 7, characterized in that, The system also includes a processing terminal (7); The processing terminal (7) includes a processor (71), a memory (72), and a display (73); The input terminal of the processor (71) is electrically connected to the output terminals of several pressure sensors, several temperature sensors and several sampling valves, respectively, for receiving monitoring data and processing it to obtain data processing results; The processor (71) is electrically connected to the memory (72), which is used to store monitoring data and data processing results; The output of the processor (71) is connected to the input of the display (73), which is used to display monitoring data and data processing results.

9. A gradient-based method for simulating methane leakage from natural gas hydrate decomposition, implemented based on the simulation system described in claim 8, characterized in that, include: S1: Construct the environment for the hydrate simulation layer (11), sediment simulation layer (21), third seawater simulation chamber (33), second seawater simulation chamber (32) and first seawater simulation chamber (31); S2: Inject a preset amount of methane gas into the hydrate simulation layer (11) through the gas injection valve (12), inject a preset amount of pure water or salt water into the hydrate simulation layer (11) through the water injection valve (13), inject different pressures into the corresponding simulation layer or simulation chamber through each pressure control module, and adjust the temperature of the corresponding simulation layer or simulation chamber through each temperature control module. S3: The hydrate simulation layer (11) forms and decomposes natural gas hydrate in a high-pressure and low-temperature environment required for the formation of natural gas hydrate; the decomposition of natural gas hydrate causes the pressure of the hydrate simulation layer (11) to increase. When the pressure is greater than the pressure threshold of the first pressure control module (41), the first pressure control module (41) is opened, and the methane fluid moves upward to the sediment simulation layer (21). S4: The pressure of the sediment simulation layer (21) increases. When the pressure is greater than the pressure threshold of the second pressure control module (42), the second pressure control module (42) opens, and the methane fluid moves upward to the third seawater simulation chamber (33). S5: The pressure in the third seawater simulation chamber (33) increases. When the pressure is greater than the pressure threshold of the third pressure control module (43), the third pressure control module (43) opens, and the methane fluid moves upward to the second seawater simulation chamber (32). S6: The pressure in the second seawater simulation chamber (32) increases. When the pressure is greater than the pressure threshold of the fourth pressure control module (44), the fourth pressure control module (44) opens, and the methane fluid moves upward to the first seawater simulation chamber (31). S7: The pressure in the first seawater simulation chamber (31) increases. When the pressure exceeds the pressure threshold of the fifth pressure control module (45), the fifth pressure control module (45) opens and the methane fluid is discharged. S8: The pressure and temperature sensors are used to monitor the temperature and pressure distribution and changes of each simulation layer and simulation chamber in real time, and the sampling valve is used to sample the methane fluid in each simulation layer and simulation chamber. S9: The monitoring data and data processing results are processed, stored and displayed by the processing terminal (7) until all natural gas hydrates in the hydrate simulation layer (11) are completely decomposed, thus completing the simulation of the natural gas hydrate decomposition and methane leakage process.

10. The gradient-based method for simulating methane leakage from natural gas hydrate decomposition according to claim 9, characterized in that, Step S1 includes: The hydrate simulation layer (11) is filled with silty sediments to serve as a porous medium, and the sediment simulation layer (21) is filled with a clay layer. A preset amount of seawater is filled into the hydrate simulation layer (11), sediment simulation layer (21), third seawater simulation chamber (33), second seawater simulation chamber (32) and first seawater simulation chamber (31).

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