Simulation device and method for measuring content of methane in overlying sediments decomposed by layered hydrate

Abstract

The invention relates to the technical field of natural gas hydrate monitoring, in particular to a layered hydrate decomposition overlying sediment methane content measurement simulation device and method. Comprising a high-pressure reaction kettle, a screen is fixed in the high-pressure reaction kettle, a cavity of the high-pressure reaction kettle is divided into an upper cavity containing an overlying sediment layer and a lower cavity containing a hydrate layer by the screen, and an electric heating coil is arranged at the bottom of the cavity of the high-pressure reaction kettle; and the resistivity signal testing unit comprises a plurality of resistivity measuring probes which are arranged in the overlying sediment layer at intervals. The method is low in cost, can accurately measure the change of the methane content in the overlying sediment of the hydrate, and provides theoretical guidance for the measurement of the methane content of the overlying sediment of a natural gas hydrate reservoir in a sea area.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas hydrate monitoring, in particular to a device and method for simulating the measurement of methane content in overlying sediments during decomposition of layered hydrate. Background Art

[0002] Natural gas hydrates are widely distributed in the seafloor sediments at the edge of the continental shelf and in abundant reserves. Natural gas hydrates are ice-like crystalline substances formed by methane and water under high pressure and low temperature conditions. They can only exist relatively stably under specific temperature and pressure conditions. Seafloor tectonic activities (seafloor earthquakes, volcanic eruptions), geochemical activities, and hydrate mining activities will all cause changes in the temperature and pressure of the hydrate reservoir, leading to unstable decomposition of hydrates. The decomposition of layered hydrates will not only cause landslides in the seafloor strata, but the large amount of gas produced will also pose a danger to the seafloor ecological environment and mining projects.

[0003] At present, the research on the decomposition of natural gas hydrate mainly uses methods such as seabed seismic and water quality analysis, which have problems such as low measurement accuracy, high cost, and delayed results. In order to obtain the in-situ physical property data of hydrates to understand their decomposition, it is necessary to drill holes in the hydrate layer, which is not only costly but also easy to cause the instability of the hydrate reservoir.

[0004] The gas produced by hydrate decomposition will migrate to the sediments overlying the hydrate due to the difference in density. By measuring the changes in the methane content in the sediments overlying the hydrate area, the decomposition of the hydrate can be understood, and various risks caused by the decomposition of the hydrate can be warned in advance. At present, there is no relevant method to understand the decomposition of hydrates by measuring the changes in the methane content in the overlying sediments. It is necessary to develop a simulation device for measuring the changes in the methane content in the sediments overlying hydrates, simulate the process of the gas produced by hydrate decomposition moving upward into the overlying sediments, and establish a method for measuring the methane content in the sediments overlying hydrates to understand the decomposition of hydrates. At the same time, it provides theoretical guidance for the measurement of the methane content in the sediments overlying natural gas hydrate reservoirs in the sea area. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and propose a simulation device and method for measuring the methane content in the overlying sediments of layered hydrate decomposition. The device and method have low cost and can accurately measure the changes in the methane content in the overlying sediments of hydrates, thus providing theoretical guidance for the measurement of the methane content in the overlying sediments of marine natural gas hydrate reservoirs.

[0006] The technical solution of the present invention is: a device for measuring the methane content of overlying sediments during the decomposition of layered hydrates, comprising a high-pressure reactor, wherein a screen is fixed inside the high-pressure reactor, the screen divides the cavity of the high-pressure reactor into an upper cavity containing an overlying sediment layer and a lower cavity containing a hydrate layer, and an electric heating coil is provided at the bottom of the cavity of the high-pressure reactor; Also included is a resistivity signal testing unit, which includes a plurality of resistivity measuring probes spaced apart and arranged in the overlying sediment layer.

[0007] In the present invention, the mesh number of the screen is smaller than the mesh number corresponding to the particle size of the overlying sediment layer above it, and the screen is fixed to the inner wall of the high-pressure reactor by a screen holder; The bottom of the high-pressure reactor is provided with an air inlet connected to the gas circuit, the top of the high-pressure reactor is provided with a reactor cover, the reactor cover is sealed and connected to the high-pressure reactor, and the reactor cover is provided with an air outlet; The electric heating coil is connected to the heating power supply controller.

[0008] The resistivity signal testing unit also includes a resistivity collector, and the resistivity measuring probes are connected to the resistivity collector through data communication line connection connectors. Interfaces connected to the data communication line connection connectors are provided in the reactor cover.

[0009] The resistivity measurement probe includes: Insulating fiber rods; Four annular electrodes are arranged at equal intervals along the axial direction of the insulating fiber rod, which are, from top to bottom, a first power supply electrode, a first measuring electrode, a second measuring electrode, and a second power supply electrode. The four annular electrodes are connected to corresponding data communication line connection connectors through wires, and each data communication line connection connector is connected to a resistivity collector through a data communication line.

[0010] Also included is a pressure control unit comprising: A methane gas cylinder connected to the gas inlet of the gas booster pump; The gas booster pump has its outlet connected to the air inlet at the bottom of the high-pressure reactor, and a pressure reducing valve and a back-pressure valve are arranged on its connecting pipeline. The back-pressure valve is connected to the air inlet of the high-pressure reactor, and the gas booster pump is connected to the air booster.

[0011] Also included is a temperature control unit comprising: The reactor temperature control jacket, the high pressure reactor is arranged in the reactor temperature control jacket; The low-temperature water bath controller circulates low-temperature water between the low-temperature water bath controller and the temperature control jacket of the reactor through the water bath circulation conduit, thereby achieving cooling of the high-pressure reactor.

[0012] Also included is a temperature and pressure data test unit, which includes: a first temperature sensor connected to a first temperature probe, the first temperature probe being inserted into a lower portion of the overlying sediment layer; a first pressure sensor for measuring the pressure of an overlying sediment layer; a second temperature sensor connected to a second temperature probe, wherein the second temperature probe is inserted into the middle of the hydrate layer; A second pressure sensor is located on a connecting pipeline between the back pressure valve and the air inlet of the high pressure reactor; The temperature and pressure collector is connected to the first temperature sensor, the first pressure sensor, the second temperature sensor and the second pressure sensor respectively.

[0013] The present invention also includes a method for measuring the methane content of overlying sediments by using the above-mentioned layered hydrate decomposition simulation device, which includes the following steps: S1. Ice powder for generating layered hydrates is placed in the lower chamber of the autoclave, a screen is fixed on the top of the ice powder, muddy sediment is placed on the screen, several resistivity measuring probes are fully inserted into the muddy sediment, the autoclave cover is sealed and installed, and after the autoclave is sealed, the temperature, pressure, and resistivity acquisition test values ​​are recorded; S2, cooling the autoclave. When the temperature and pressure in the autoclave meet the conditions for hydrate formation, the ice powder gradually transforms into hydrate, and the pressure in the autoclave gradually decreases. When the pressure no longer changes, hydrate formation ends. S3. As the temperature of the electric heating coil increases, the hydrate gradually decomposes, and the pressure in the high-pressure reactor changes until the pressure value stops changing; S4. Calculate the amount of methane gas based on the resistivity value collected by the resistivity measurement probe.

[0014] In step S1, the resistivity signal collector is turned on to collect the resistivity value detected by the resistivity measurement probe; the temperature and pressure collector is turned on to collect the temperature and pressure values ​​of the high-pressure reactor; In step S2, the low-temperature water bath controller is turned on, and the high-pressure reactor is refrigerated by circulating low-temperature water between the low-temperature water bath controller and the temperature control jacket of the reactor, thereby cooling the high-pressure reactor; In step S3, the heating power controller is turned on to increase the temperature of the electric heating coil.

[0015] In step S4, , Among them, S g is the methane gas saturation, %; α is the lithology coefficient; m is the cementation index; n is the saturation index; R tis the resistivity of the methane gas deposit, Ω·m, i.e., the resistivity measured by the resistivity measurement probe; R w is the pore water resistivity, Ω·m; φ is the sediment porosity; Furthermore, the amount of hydrate decomposition is calculated based on the amount of methane gas: , the volume of methane gas: , Where V is the pore volume of the sediment, cm 3 ; The mass of methane gas is: , Among them, ρ g is the density of methane gas, g / cm 3 ; The molecular formula of methane hydrate generated in the laboratory is , therefore, the volume of the decomposed hydrate is: , Among them, m h is the mass of the hydrate, g; ρ h is the density of the hydrate, 0.9 g / cm 3 ;M h is the molar mass of methane hydrate, 124 g / mol; M g is the molar mass of methane gas, 16 g / mol; Right now .

[0016] The beneficial effects of the present invention are: (1) This application proposes a simulation device and method for measuring the methane content in the overlying sediments during the hydrate decomposition process, realizing a simulation experimental study on the measurement of the methane content in the overlying sediments during the layered hydrate decomposition process; (2) By placing an electric heating coil at the bottom of the hydrate layer, the temperature of the hydrate layer is increased by the electric heating coil without changing the temperature of the muddy / sandy sediment layer, thereby promoting the decomposition of hydrates. This can more accurately measure the changes in the methane content in the sediments overlying the hydrates, thereby indicating the decomposition of hydrates in the hydrate layer; (3) By adopting a combination of multiple resistivity probes, the changes in methane content in the sediments overlying hydrates can be measured more accurately, providing theoretical guidance for measuring the methane content in the sediments overlying marine natural gas hydrate reservoirs and monitoring the decomposition of hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the connection structure of the simulation device of the present invention; Figure 2 It is a schematic diagram of the structure of the measuring probe.

[0018] In the figure: 1 high pressure reactor; 2 screen holder; 3 screen; 4 reactor temperature control jacket; 5 resistivity measurement probe; 6 wire; 7 exhaust port; 8 data communication line connection joint; 9 resistivity collector; 10 reactor cover; 12 sealing ring; 13 overlying sediment layer; 14 first pressure sensor; 15 first temperature sensor; 16 first temperature probe; 17 hydrate layer; 18 second temperature sensor; 19 second temperature probe; 20 temperature and pressure collector; 21 heating power supply controller; 22 air inlet; 23 second pressure sensor; 24 back pressure valve; 25 pressure reducing valve; 26 air compressor; 27 gas booster pump; 28 methane gas cylinder; 29 low temperature water bath controller; 30 electric heating coil; 31 first power supply electrode; 32 first measuring electrode; 33 second measuring electrode; 34 second power supply electrode; 35 data communication line. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] In the following description, specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] The methane content measurement simulation device for overlying sediments during layered hydrate decomposition of the present invention comprises a hydrate generation and decomposition simulation unit, a pressure control unit, a temperature control unit, a resistivity signal testing unit, and a temperature and pressure data testing unit. The hydrate generation and decomposition simulation unit is respectively connected to the pressure control unit, the temperature control unit, the resistivity signal testing unit, and the temperature and pressure data testing unit.

[0022] The hydrate formation and decomposition simulation unit includes a high-pressure reactor 1 and an electric heating module. Figure 1 As shown, the top of the high-pressure reactor 1 is connected to the reactor cover 10, and a sealing ring 12 is provided at the connection between the high-pressure reactor 1 and the reactor cover 10, and the high-pressure reactor 1 is sealed by the sealing ring 12. An air inlet 22 is provided at the bottom of the high-pressure reactor 1, and the air inlet 22 is connected to the gas path. An exhaust port 7 is provided at the reactor cover 10.

[0023] In this embodiment, the autoclave 1 is cylindrical, so a cylindrical cavity is provided in the autoclave, and a screen 3 is provided in the middle of the cavity. The screen 3 is made of insulating material, and the screen 3 is fixed to the inner wall of the autoclave 1 through a screen holder 2. The cavity in the autoclave 1 is divided into an upper cavity and a lower cavity by the screen 3, wherein the upper cavity contains an overlying sediment layer 13, and the lower cavity contains a hydrate layer 17, and the mesh number of the screen 3 is smaller than the mesh number corresponding to the particle size of the overlying sediment layer 13, and the screen 3 effectively separates the upper floating sediment layer 13 and the lower hydrate layer 17.

[0024] The electric heating module includes an electric heating coil 30 and a heating power controller 21. The electric heating coil 30 is arranged at the bottom of the high-pressure reactor 1, that is, the electric heating coil 30 is located at the bottom of the hydrate layer 17. The heating temperature of the electric heating coil 30 is controlled by the heating power controller 21. The temperature of the hydrate layer 1 is increased by the electric heating coil 30 to promote the decomposition of the hydrate. The electric heating coil 30 in this embodiment adopts an electromagnetic heating heating method, which does not change the temperature of the overlying muddy sediment layer or sandy sediment layer, avoids the change of the gas's own properties and distribution due to the influence of temperature, and ensures the accuracy of resistivity measurement.

[0025] The pressure control unit includes a methane gas cylinder 28 and a gas booster pump 27, wherein the methane gas cylinder 28 is connected to the air inlet of the gas booster pump 27 through a connecting pipeline, and the air outlet of the gas booster pump 27 is connected to the air inlet 7 at the bottom of the high-pressure reactor 1 through a connecting pipeline. A pressure reducing valve 25 and a back pressure valve 24 are sequentially arranged on the connecting pipeline between the air outlet and the air inlet 7 of the gas booster pump 27, wherein the back pressure valve 24 is connected to the air inlet 7 at the bottom of the high-pressure reactor 1. The gas booster pump 27 is connected to an air compressor 26.

[0026] The methane gas in the methane cylinder 28 is pressurized by the gas booster pump 27 , passes through the pressure reducing valve 25 and the back pressure valve 24 in sequence, and after being adjusted to a specified pressure value, enters the high-pressure reactor 1 through the air inlet 7 .

[0027] The temperature control unit includes a reactor temperature control jacket 4 and a low-temperature water bath controller 29, wherein the reactor temperature control jacket 4 is located outside the annular portion of the high-pressure reactor 1, and the reactor temperature control jacket 4 is filled with low-temperature water. The low-temperature water is circulated between the reactor temperature control jacket 4 and the low-temperature water bath controller 29 through a water bath circulation conduit. During the circulation of the low-temperature water between the reactor temperature control jacket 4 and the low-temperature water bath controller 29, the temperature of the low-temperature water is controlled by the low-temperature water bath controller 29, and the high-pressure reactor 1 is cooled after the low-temperature water flows into the reactor temperature control jacket 4.

[0028] The temperature and pressure data test unit includes two temperature sensors, two pressure sensors, and a temperature and pressure collector 20, wherein the two temperature sensors include a first temperature sensor 15 and a second temperature sensor 18, and the pressure sensor includes a first pressure sensor 14 and a second pressure sensor 23. The two temperature sensors and the two pressure sensors are respectively connected to the temperature and pressure collector 20, and the temperature and pressure collector 20 collects the values ​​detected by the two temperature sensors and the two pressure sensors.

[0029] The first temperature sensor 15 and the first pressure sensor 14 are connected to the upper cavity of the autoclave 1, one end of the first temperature probe 16 extends into the bottom of the overlying sediment layer 13 of the upper cavity, and the other end of the first temperature probe 16 is connected to the first temperature sensor 15. The temperature of the overlying sediment layer is detected in real time by the first temperature sensor 15, and the pressure of the overlying sediment layer is detected in real time by the first pressure sensor 14.

[0030] The second temperature sensor 18 is connected to the lower cavity of the high-pressure reactor 1, one end of the second temperature probe 19 extends into the middle position of the hydrate layer 17 of the lower cavity, and the other end of the second temperature probe 19 is connected to the second temperature sensor 18, and the temperature of the hydrate layer is detected in real time through the second temperature sensor 18.

[0031] The second pressure sensor 23 is disposed between the back pressure valve 24 and the air inlet 22 . The pressure of the methane gas entering the high-pressure reactor is detected in real time through the second pressure sensor 23 .

[0032] The resistivity signal test unit includes a plurality of resistivity measuring probes 5 and a resistivity collector 9. The plurality of resistivity measuring probes 5 are arranged at intervals in the overlying sediment layer 13. Each resistivity measuring probe 5 is connected to the resistivity collector 9 through a data communication line connection connector 8. The resistivity collector 9 is located outside the high-pressure reactor 1. A connector interface is reserved in the reactor cover 10. The data communication line connection connector 8 is connected to these connector interfaces respectively. The resistivity measuring probe 5 is connected to the corresponding data communication line connection connector 8 through a wire 6. Each data communication line connection connector 8 is connected to the resistivity collector 9 through a data communication line 35.

[0033] like Figure 2As shown, the resistivity measuring probe 5 includes four equally spaced annular electrodes and an insulating fiber rod connecting the electrodes. In this embodiment, the maximum pressure bearing of the resistivity measuring probe is 20 MPa. The four annular electrodes are respectively connected to the data communication line connection connector 8 through the wire 6, and the wires do not contact each other. The insulating fiber rod serves as a supporting skeleton, and the four annular electrodes are equally spaced along the axial direction of the insulating fiber rod. The internal pores of the insulating fiber rod are perfused with crystal glue, thereby ensuring that the positions of the four annular electrodes and the wires are relatively fixed, preventing the annular electrodes from being deformed or even broken under high pressure.

[0034] In order to effectively reduce the electrode polarization effect of the two-electrode method, the resistivity measurement in this application adopts the quadrupole method. The four annular electrodes in the resistivity measurement probe in this application include a first power supply electrode 31 located at the top and a second power supply electrode 34 located at the bottom. The first power supply electrode 31 and the second power supply electrode 34 are annular main electrodes and are opposite power supply electrodes. A first measuring electrode 32 and a second measuring electrode 33 are provided between the first power supply electrode 31 and the second power supply electrode 34. The first power supply electrode 31, the first measuring electrode 32, the second measuring electrode 33, and the second power supply electrode 34 are arranged in equal intervals along the axial direction of the probe.

[0035] Assuming that the midpoint between the first power supply electrode 31 and the second power supply electrode 34 is O, when the first power supply electrode 31 and the second power supply electrode 34 are powered, the current density at point O is: , Wherein, L is the distance between point O and the first power supply electrode 31 .

[0036] Assume that point P is located on the perpendicular midline of the first power supply electrode 31 and the second power supply electrode 34, and the distance between point P and point O is h. At this time, the current density at point P is the vector sum of the current densities of the first power supply electrode 31 and the second power supply electrode 34 at point P: , Only when the current density at point P is large enough can the medium anomaly at point P be detected. That is:

[0037] j h AB j O AB = cos 3 θ = 1 [ (1+ h L ) 2 ] 3 2 , It can be seen that the current density ratio at point P and point O increases with The increase of decreases rapidly, therefore, The ratio cannot be too large. That is, when the diameter of the reactor is fixed, When fixed, the distance between the first power supply electrode and the second power supply electrode should be as large as possible. When the diameter of the reactor is the distance between the power supply electrodes AB, that is, h=L, the resistivity method can affect the lateral range of the entire reactor. When the diameter of the reactor is greater than (or much greater than) the distance between the first power supply electrode and the second power supply electrode, the multi-probe joint arrangement is used for measurement to ensure that the joint measurement range is the lateral range of the reactor.

[0038] The present application also includes a method for measuring and calculating the amount of methane gas using the above method, which includes the following specific steps.

[0039] In the first step, ice powder is loaded into the lower part of the autoclave 1 and compacted appropriately to generate layered hydrates. The screen 3 is installed above the ice powder and fixed inside the autoclave 1 by the screen holder 2. Considering that the experimental period is short and hydrates are not easily generated in muddy sediments, muddy sediments are loaded into the upper cavity of the autoclave above the screen to simulate the overlying sediments of the layered hydrates and compacted appropriately.

[0040] In the second step, the resistivity measuring probe 5 is inserted into the muddy sediment according to the prescribed layout scheme, ensuring that the annular electrode on the probe is completely in the muddy sediment. The resistivity probe is connected to the connector interface inside the reactor cover to seal the reactor cover 10 and the high-pressure reactor 1.

[0041] The third step is to open the valve connected to the gas line at the air inlet 22 at the bottom of the high-pressure reactor, add methane gas into the high-pressure reactor 1 through the air inlet 22 until the pressure in the reactor reaches the pressure required for the experiment, and perform a sealing test on the reactor.

[0042] The fourth step is to confirm that the sealing of the high-pressure reactor is good, turn on the resistivity signal collector 9 and the temperature and pressure collector 20, perform temperature, pressure and resistivity acquisition tests, and start recording the above parameter values.

[0043] The fifth step is to turn on the low-temperature water bath controller 29 and set the temperature of the low-temperature water to the temperature required for hydrate formation. During the circulation of the low-temperature water between the low-temperature water bath controller 29 and the reactor temperature control jacket 4, the high-pressure reactor in the reactor temperature control jacket 4 is refrigerated in a circulating manner to cool the high-pressure reactor.

[0044] When the temperature and pressure in the autoclave meet the conditions for hydrate formation, the ice powder in the lower chamber gradually transforms into hydrate, and the pressure in the autoclave gradually decreases. When the pressure no longer changes, hydrate formation ends.

[0045] Step 6: Turn on the heating power controller 21. As the temperature of the electric heating coil 30 increases, the hydrate in the high-pressure reactor 1 begins to decompose.

[0046] Step 7: During the hydrate decomposition process, the resistivity, temperature and pressure data are collected in real time until the pressure in the high-pressure reactor stops changing, and the experiment ends; In the eighth step, the resistivity measured by the resistivity measuring probe 5 is used to calculate the amount of methane gas, thereby obtaining the volume of the decomposed hydrate.

[0047] , Among them, S g is the methane gas saturation, %; α is the lithology coefficient; m is the cementation index; n is the saturation index; R t is the resistivity of the methane gas deposit, Ω·m, i.e., the resistivity measured by the resistivity measurement probe; R w is the pore water resistivity, Ω·m; φ is the sediment porosity.

[0048] Furthermore, the amount of hydrate decomposition is calculated based on the amount of methane gas. , the volume of methane gas:

[0049] , Where V is the pore volume of the sediment, cm 3 .

[0050] The mass of methane gas is: , Among them, ρ g is the density of methane gas, g / cm 3 .

[0051] The molecular formula of methane hydrate generated in the laboratory is , therefore, the volume of the decomposed hydrate can be calculated: , Among them, m h is the mass of the hydrate, g; ρ h is the density of the hydrate, 0.9 g / cm 3 ;M h Methane hydrate (molecular formula ) has a molar mass of 124 g / mol; M g is the molar mass of methane gas, 16 g / mol.

[0052] Right now .

[0053] The above is a detailed introduction to the device and method for measuring the methane content of overlying sediments for decomposition of layered hydrates provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be obvious to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A simulation device for measuring the methane content of overlying sediments during the decomposition of layered hydrates, comprising a high-pressure reactor, characterized in that: A screen is fixed inside the autoclave, and the screen divides the cavity of the autoclave into an upper cavity containing an overlying sediment layer and a lower cavity containing a hydrate layer. An electric heating coil is provided at the bottom of the cavity of the autoclave; Also included is a resistivity signal testing unit, which includes a plurality of resistivity measuring probes spaced apart in the overlying sediment layer.

2. The device for measuring the methane content of overlying sediments during the decomposition of layered hydrates according to claim 1, characterized in that: The mesh number of the screen is smaller than the mesh number corresponding to the particle size of the overlying sediment layer above it, and the screen is fixed to the inner wall of the high-pressure reactor by a screen holder; The bottom of the high-pressure reactor is provided with an air inlet connected to the gas circuit, the top of the high-pressure reactor is provided with a reactor cover, the reactor cover is sealed and connected to the high-pressure reactor, and the reactor cover is provided with an air outlet; The electric heating coil is connected to the heating power supply controller.

3. The device for measuring the methane content of overlying sediments during layered hydrate decomposition according to claim 2, characterized in that: The resistivity signal testing unit also includes a resistivity collector, and the resistivity measuring probes are connected to the resistivity collector through data communication line connection connectors. Interfaces connected to the data communication line connection connectors are provided in the reactor cover.

4. The device for measuring the methane content of overlying sediments during layered hydrate decomposition according to claim 3 is characterized in that: The resistivity measurement probe includes: Insulation fiber rods, Four annular electrodes are arranged at equal intervals along the axial direction of the insulating fiber rod, which are, from top to bottom, a first power supply electrode, a first measuring electrode, a second measuring electrode, and a second power supply electrode. The four annular electrodes are connected to corresponding data communication line connection connectors through wires, and each data communication line connection connector is connected to a resistivity collector through a data communication line.

5. The device for measuring the methane content of overlying sediments during layered hydrate decomposition according to claim 1, characterized in that: Also included is a pressure control unit comprising: A methane gas cylinder connected to the gas inlet of the gas booster pump; The gas booster pump has its outlet connected to the air inlet at the bottom of the high-pressure reactor, and a pressure reducing valve and a back-pressure valve are arranged on its connecting pipeline. The back-pressure valve is connected to the air inlet of the high-pressure reactor, and the gas booster pump is connected to the air booster.

6. The device for measuring the methane content of overlying sediments during layered hydrate decomposition according to claim 1, characterized in that: Also included is a temperature control unit comprising: The reactor temperature control jacket, the high pressure reactor is arranged in the reactor temperature control jacket; The low-temperature water bath controller circulates low-temperature water between the low-temperature water bath controller and the temperature control jacket of the reactor through the water bath circulation conduit, thereby achieving cooling of the high-pressure reactor.

7. The device for measuring the methane content of overlying sediments during layered hydrate decomposition according to claim 5, characterized in that: Also included is a temperature and pressure data test unit, which includes: a first temperature sensor connected to a first temperature probe, the first temperature probe being inserted into a lower portion of the overlying sediment layer; a first pressure sensor for measuring the pressure of an overlying sediment layer; a second temperature sensor connected to a second temperature probe, wherein the second temperature probe is inserted into the middle of the hydrate layer; A second pressure sensor is located on a connecting pipeline between the back pressure valve and the air inlet of the high pressure reactor; The temperature and pressure collector is connected to the first temperature sensor, the first pressure sensor, the second temperature sensor and the second pressure sensor respectively.

8. A method for measuring the methane content of overlying sediments by using the device for measuring the methane content of layered hydrate decomposition as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Ice powder for generating layered hydrates is placed in the lower chamber of the autoclave, a screen is fixed on the top of the ice powder, muddy sediment is placed on the screen, several resistivity measuring probes are fully inserted into the muddy sediment, the autoclave cover is sealed and installed, and after the autoclave is sealed, the temperature, pressure, and resistivity acquisition test values ​​are recorded; S2, cooling the autoclave. When the temperature and pressure in the autoclave meet the conditions for hydrate formation, the ice powder gradually transforms into hydrate, and the pressure in the autoclave gradually decreases. When the pressure no longer changes, hydrate formation ends. S3. As the temperature of the electric heating coil increases, the hydrate gradually decomposes, and the pressure in the high-pressure reactor changes until the pressure value stops changing; S4. Calculate the amount of methane gas based on the resistivity value collected by the resistivity measurement probe.

9. The method according to claim 8, characterized in that In step S1, the resistivity signal collector is turned on to collect the resistivity value detected by the resistivity measurement probe; the temperature and pressure collector is turned on to collect the temperature and pressure values ​​of the high-pressure reactor; In step S2, the low-temperature water bath controller is turned on, and the high-pressure reactor is refrigerated by circulating low-temperature water between the low-temperature water bath controller and the reactor temperature control jacket, thereby cooling the high-pressure reactor; In step S3, the heating power controller is turned on to increase the temperature of the electric heating coil.

10. The method according to claim 8, characterized in that In step S4, ， Among them, S g is the methane gas saturation, %; α is the lithology coefficient; m is the cementation index; n is the saturation index; R t is the resistivity of the methane gas deposit, Ω·m, i.e., the resistivity measured by the resistivity measurement probe; R w is the pore water resistivity, Ω·m; φ is the sediment porosity; Furthermore, the amount of hydrate decomposition is calculated based on the amount of methane gas: , the volume of methane gas: ， Where V is the pore volume of the sediment, cm 3 ; The mass of methane gas is: , Among them, ρ g is the density of methane gas, g / cm 3 ; The molecular formula of methane hydrate generated in the laboratory is , therefore, the volume of the decomposed hydrate is: ， Among them, m h is the mass of the hydrate, g; ρ h is the density of the hydrate, 0.9 g / cm 3 ;M h is the molar mass of methane hydrate, 124 g / mol; M g is the molar mass of methane gas, 16 g / mol; Right now 。

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