Simulation device and method for measuring methane content in sediments overlying layered hydrate decomposition

Abstract

The present invention relates to the field of natural gas hydrate monitoring technology, and in particular to a device and method for simulating the measurement of methane content in sediments overlying the decomposition of layered hydrates. The device comprises a high-pressure reactor with a screen fixed within it. The screen divides the chamber of the high-pressure reactor into an upper chamber containing an overlying sediment layer and a lower chamber containing a hydrate layer. An electric heating coil is provided at the bottom of the chamber of the high-pressure reactor. The device also comprises a resistivity signal testing unit comprising a plurality of resistivity measurement probes spaced apart within the overlying sediment layer. The device is low-cost and can accurately measure changes in methane content in sediments overlying hydrates, providing theoretical guidance for measuring methane content in sediments overlying marine natural gas hydrate reservoirs.

Description

Technical Field

[0001] The present 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 hydrates. Background Art

[0002] Natural gas hydrates are abundant and widely distributed in seafloor sediments along terrestrial permafrost and continental shelf margins. Natural gas hydrates are ice-like crystalline substances formed by methane and water under high pressure and low temperature conditions. They are relatively stable only under specific temperature and pressure conditions. Seafloor tectonic activity (undersea earthquakes, volcanic eruptions), geochemical activity, and hydrate extraction can all cause changes in the temperature and pressure of hydrate reservoirs, leading to hydrate destabilization and decomposition. The decomposition of layered hydrates not only causes submarine landslides but also produces large amounts of gas, posing a threat to the seafloor ecosystem and extraction projects.

[0003] Current research on natural gas hydrate decomposition primarily relies on methods such as seafloor seismic analysis and water quality analysis, which suffer from low measurement accuracy, high costs, and delayed results. Obtaining in-situ physical property data to understand hydrate decomposition requires drilling into the hydrate layer, which is not only costly but also prone to destabilizing the hydrate reservoir.

[0004] Due to density differences, the gas produced by hydrate decomposition migrates into the sediments overlying the hydrate. By measuring changes in the methane content in the sediments overlying the hydrate zone, we can understand the hydrate decomposition process and provide early warning of various risks caused by hydrate decomposition. Currently, there is no method to understand hydrate decomposition by measuring changes in the methane content in the overlying sediments. Developing a simulation device to measure changes in the methane content in the sediments overlying hydrates, simulating the upward migration of gas produced by hydrate decomposition into the overlying sediments, and establishing a method for measuring methane content in the sediments overlying hydrates are essential for understanding hydrate decomposition. This method also provides theoretical guidance for measuring methane content in sediments overlying marine natural gas hydrate reservoirs. 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 sediments overlying the decomposition of layered hydrates. The device and method are low-cost and can accurately measure the changes in the methane content in the sediments overlying the hydrates, providing theoretical guidance for the measurement of the methane content in the sediments overlying the 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 dividing 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;

[0007] The device also includes a resistivity signal testing unit, which includes a plurality of resistivity measuring probes spaced apart and arranged in the overlying sediment layer.

[0008] 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;

[0009] 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 to the high-pressure reactor, and the reactor cover is provided with an air outlet;

[0010] The electric heating coil is connected to the heating power controller.

[0011] The resistivity signal testing unit also includes a resistivity collector. The resistivity measuring probes are connected to the resistivity collector via data communication line connectors. Interfaces connected to the data communication line connectors are provided in the reactor cover.

[0012] Resistivity measurement probe includes:

[0013] Insulating fiber rods;

[0014] Four annular electrodes are arranged at equal intervals along the axial direction of the insulating fiber rod, which are, from top to bottom, the first power supply electrode, the first measuring electrode, the second measuring electrode, and the second power supply electrode. The four annular electrodes are connected to the corresponding data communication line connection connectors through wires, and each data communication line connection connector is connected to the resistivity collector through a data communication line.

[0015] Also included is a pressure control unit comprising:

[0016] A methane gas cylinder connected to the gas inlet of the gas booster pump;

[0017] 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 provided 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.

[0018] Also included is a temperature control unit comprising:

[0019] The reactor temperature control jacket, the high-pressure reactor is arranged in the reactor temperature control jacket;

[0020] 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.

[0021] Also included is a temperature and pressure data test unit, which includes:

[0022] 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;

[0023] a first pressure sensor for measuring the pressure of an overlying sediment layer;

[0024] a second temperature sensor connected to a second temperature probe, wherein the second temperature probe is inserted into the middle of the hydrate layer;

[0025] The second pressure sensor is located on the connecting pipeline between the back pressure valve and the air inlet of the high-pressure reactor;

[0026] The temperature and pressure collectors are connected to the first temperature sensor, the first pressure sensor, the second temperature sensor, and the second pressure sensor respectively.

[0027] 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:

[0028] S1. The lower chamber of the autoclave is filled with ice powder for forming layered hydrates. A screen is fixed above the ice powder and muddy sediment is placed on the screen. Several resistivity measurement probes are fully inserted into the muddy sediment. The autoclave cover is sealed and installed. After performing a seal test on the autoclave, the temperature, pressure, and resistivity test values are recorded.

[0029] S2. Cooling the autoclave. When the temperature and pressure inside the autoclave meet the hydrate formation conditions, the ice powder gradually transforms into hydrates, and the pressure inside the autoclave gradually decreases. When the pressure stops changing, hydrate formation ends.

[0030] 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;

[0031] S4. Calculate the amount of methane gas based on the resistivity value collected by the resistivity measurement probe.

[0032] 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;

[0033] 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;

[0034] In step S3, the heating power controller is turned on to increase the temperature of the electric heating coil.

[0035] In step S4,

[0036] ,

[0037] 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, which is the resistivity measured by the resistivity measurement probe; R w is the pore water resistivity, Ω·m; φ is the sediment porosity;

[0038] Furthermore, the amount of hydrate decomposition is calculated based on the amount of methane gas: the saturation of methane gas is known. , the volume of methane gas:

[0039] ,

[0040] Where V is the pore volume of the sediment, cm 3 ;

[0041] The mass of methane gas is: ,

[0042] Among them, ρ g is the density of methane gas, g / cm 3 ;

[0043] The molecular formula of laboratory-generated methane hydrate is , therefore, the volume of the decomposed hydrate is:

[0044] ,

[0045] 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;

[0046] Right now

[0047] .

[0048] The beneficial effects of the present invention are:

[0049] (1) This application proposes a simulation device and method for measuring the methane content in overlying sediments during the decomposition of hydrates, which realizes the simulation experimental research on the measurement of methane content in overlying sediments during the decomposition of layered hydrates;

[0050] (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 the hydrate. This allows for more accurate measurement of the change in the methane content in the sediments overlying the hydrate, thereby indicating the decomposition of the hydrate in the hydrate layer.

[0051] (3) By using a combination of multiple resistivity probes, the changes in the methane content in the sediments overlying the hydrate can be measured more accurately, providing theoretical guidance for measuring the methane content in the sediments overlying the marine natural gas hydrate reservoir and monitoring the decomposition of the hydrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a schematic diagram of the connection structure of the simulation device of the present invention;

[0053] Figure 2 It is a structural diagram of the measuring probe.

[0054] 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 connector; 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 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

[0055] 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.

[0056] The following description sets forth specific details to facilitate a thorough 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 will be able to make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0057] The methane content measurement simulation device for overlying sediments of layered hydrate decomposition described in the present invention includes 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.

[0058] 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 autoclave 1 is connected to the reactor cover 10, and a sealing ring 12 is provided at the connection between the autoclave 1 and the reactor cover 10 to seal the autoclave 1. The bottom of the autoclave 1 is provided with an air inlet 22, which is connected to the air circuit. The reactor cover 10 is provided with an exhaust port 7.

[0059] In this embodiment, the autoclave 1 is cylindrical, and therefore a cylindrical cavity is provided within the autoclave. A screen 3 is provided in the middle of the cavity. The screen 3 is made of an insulating material and is secured to the inner wall of the autoclave 1 via a screen holder 2. The screen 3 divides the cavity within the autoclave 1 into upper and lower cavities. The upper cavity contains an overlying sediment layer 13, while the lower cavity contains a hydrate layer 17. The mesh size of the screen 3 is smaller than the mesh size corresponding to the particle size of the overlying sediment layer 13. The screen 3 effectively separates the upper floating sediment layer 13 from the lower hydrate layer 17.

[0060] The electric heating module includes an electric heating coil 30 and a heating power controller 21. The electric heating coil 30 is disposed at the bottom of the autoclave 1, that is, at the bottom of the hydrate layer 17. The heating power controller 21 controls the heating temperature of the electric heating coil 30. The electric heating coil 30 raises the temperature of the hydrate layer 1, promoting hydrate decomposition. The electric heating coil 30 in this embodiment uses electromagnetic heating, which does not change the temperature of the overlying muddy or sandy sediment layer. This prevents temperature-dependent changes in the gas's properties and distribution, ensuring accurate resistivity measurements.

[0061] The pressure control unit includes a methane cylinder 28 and a gas booster pump 27. The methane cylinder 28 is connected to the gas inlet of the gas booster pump 27 via a connecting pipeline. The gas outlet of the gas booster pump 27 is also connected to the gas inlet 7 at the bottom of the autoclave 1 via a connecting pipeline. A pressure reducing valve 25 and a back-pressure valve 24 are sequentially installed on the connecting pipeline between the gas outlet and the gas inlet 7 of the gas booster pump 27. The back-pressure valve 24 is connected to the gas inlet 7 at the bottom of the autoclave 1. The gas booster pump 27 is connected to an air compressor 26.

[0062] 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 .

[0063] The temperature control unit includes a reactor temperature-control jacket 4 and a low-temperature water bath controller 29. The reactor temperature-control jacket 4 is located outside the annular structure of the autoclave 1 and is filled with low-temperature water. A water bath circulation conduit circulates the low-temperature water between the reactor temperature-control jacket 4 and the low-temperature water bath controller 29. As the low-temperature water circulates between the reactor temperature-control jacket 4 and the low-temperature water bath controller 29, the low-temperature water is temperature-controlled by the low-temperature water bath controller 29. Once the low-temperature water flows into the reactor temperature-control jacket 4, it cools the autoclave 1.

[0064] The temperature and pressure data testing unit includes two temperature sensors, two pressure sensors, and a temperature and pressure collector 20. The two temperature sensors include a first temperature sensor 15 and a second temperature sensor 18, and the pressure sensors include 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, which collects the values detected by the two temperature sensors and the two pressure sensors.

[0065] A first temperature sensor 15 and a first pressure sensor 14 are connected to the upper chamber of the autoclave 1. One end of a first temperature probe 16 extends into the bottom of the overlying sediment layer 13 of the upper chamber, 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.

[0066] 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 in the lower cavity, and the other end of the second temperature probe 19 is connected to the second temperature sensor 18. The temperature of the hydrate layer is detected in real time through the second temperature sensor 18.

[0067] The second pressure sensor 23 is provided 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 .

[0068] The resistivity signal testing unit includes several resistivity measurement probes 5 and a resistivity collector 9. The resistivity measurement probes 5 are spaced apart within the overlying sediment layer 13, and each resistivity measurement probe 5 is connected to the resistivity collector 9 via a data communication line connector 8. The resistivity collector 9 is located outside the autoclave 1. The autoclave cover 10 includes connector interfaces, to which the data communication line connectors 8 are connected. The resistivity measurement probes 5 are connected to their corresponding data communication line connectors 8 via wires 6, and each data communication line connector 8 is connected to the resistivity collector 9 via a data communication line 35.

[0069] like Figure 2 As shown, the resistivity measurement probe 5 includes four equally spaced ring electrodes and an insulating fiber rod connecting the electrodes. In this embodiment, the resistivity measurement probe has a maximum pressure resistance of 20 MPa. The four ring electrodes are connected to the data communication line connector 8 via conductors 6, and the conductors do not touch each other. The insulating fiber rod serves as a supporting framework, and the four ring electrodes are equally spaced along the axial direction of the insulating fiber rod. The internal pores of the insulating fiber rod are infused with crystal glue, ensuring the relative position of the four ring electrodes and the conductors, preventing the ring electrodes from deforming or even breaking under high pressure.

[0070] 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-polarity 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 at equal intervals along the axial direction of the probe.

[0071] 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:

[0072] ,

[0073] Wherein, L is the distance between point O and the first power supply electrode 31 .

[0074] Assume that point P is located on the perpendicular bisector 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:

[0075] ,

[0076] Only when the current density at point P is large enough can the dielectric anomaly at point P be detected. That is:

[0077] j h AB j O AB = cos 3 θ = 1 [ (1+ h L ) 2 ] 3 2 ,

[0078] It can be seen that the current density ratio at point P and point O increases with The increase of decreases rapidly, so The ratio cannot be too large. That is to say, when the diameter of the reactor is fixed, that is, When fixed, the distance between the first and second power supply electrodes should be as large as possible. When the reactor diameter is equal to the distance between the power supply electrodes AB (i.e., h = L), the resistivity method can measure the entire lateral range of the reactor. When the reactor diameter is larger (or much larger) than the distance between the first and second power supply electrodes, a multi-probe joint arrangement should be used for measurement to ensure that the combined measurement range covers the entire lateral range of the reactor.

[0079] 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.

[0080] In the first step, ice powder was placed in the lower portion of the autoclave 1 and compacted appropriately to generate layered hydrates. A screen 3 was installed above the ice powder and secured to the interior of the autoclave 1 using a screen holder 2. Given the short experimental period and the difficulty of hydrate formation in muddy sediments, muddy sediment was placed in the upper chamber of the autoclave above the screen to simulate the overlying sediments of layered hydrates and compacted appropriately.

[0081] The second step is to insert the resistivity probe 5 into the muddy sediment according to the specified layout, ensuring that the ring electrode on the probe is completely submerged in the muddy sediment. The resistivity probe is connected to the connector interface inside the reactor cover, sealing the reactor cover 10 to the high-pressure reactor 1.

[0082] The third step is to open the valve connecting the air inlet 22 at the bottom of the high-pressure reactor to the gas line, and 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 then perform a sealing test on the reactor.

[0083] 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.

[0084] 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 circulated and refrigerated to cool the high-pressure reactor.

[0085] When the temperature and pressure inside the autoclave meet the conditions for hydrate formation, the ice powder in the lower chamber gradually transforms into hydrates, and the pressure inside the autoclave gradually decreases. When the pressure stops changing, hydrate formation ends.

[0086] 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.

[0087] Step 7: During the hydrate decomposition process, resistivity, temperature, and pressure data were collected in real time until the pressure in the autoclave stopped changing, and the experiment ended.

[0088] 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.

[0089] ,

[0090] 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, which is the resistivity measured by the resistivity measurement probe; R w is the pore water resistivity, Ω·m; φ is the sediment porosity.

[0091] Furthermore, the amount of hydrate decomposition is calculated based on the amount of methane gas. , the volume of methane gas:

[0092] ,

[0093] Where V is the pore volume of the sediment, cm 3 .

[0094] The mass of methane gas is: ,

[0095] Among them, ρ g is the density of methane gas, g / cm 3 .

[0096] The molecular formula of laboratory-generated methane hydrate is , therefore, the volume of the decomposed hydrate can be calculated:

[0097] ,

[0098] 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.

[0099] Right now

[0100] .

[0101] The above is a detailed introduction to the device and method for simulating the measurement of methane content in sediments overlying the 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 intended to help understand the methods and core ideas of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications may 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 those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may 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 scope consistent with the principles and novel features disclosed herein.

Claims

1. A simulation method for measuring the methane content in overlying sediments during layered hydrate decomposition, characterized in that: The measurement is performed using a device for measuring the methane content of overlying sediments during the decomposition of layered hydrates. The device includes a high-pressure reactor with a screen fixed inside. 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. An electric heating coil is installed 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 an overlying sediment layer; The method for measuring by the device comprises the following steps: S1. The lower chamber of the autoclave is filled with ice powder for forming layered hydrates. A screen is fixed above the ice powder and muddy sediment is placed on the screen. Several resistivity measurement probes are fully inserted into the muddy sediment. The autoclave cover is sealed and installed. After performing a seal test on the autoclave, the temperature, pressure, and resistivity test values are recorded. S2. Cooling the autoclave. When the temperature and pressure inside the autoclave meet the hydrate formation conditions, the ice powder gradually transforms into hydrates, and the pressure inside the autoclave gradually decreases. When the pressure stops changing, 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; Among them, 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, which is 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 methane gas saturation S is known. g , 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 laboratory-generated methane hydrate 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 。 2. The method for simulating the measurement of methane content in overlying sediments during layered hydrate decomposition according to claim 1, characterized in that: The mesh number of the sieve is smaller than the mesh number corresponding to the particle size of the overlying sediment layer above it, and the sieve is fixed to the inner wall of the high-pressure reactor by a sieve 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 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 controller.

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

4. The method for simulating the measurement of methane content in overlying sediments during layered hydrate decomposition according to claim 3, characterized in that: 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, the first power supply electrode, the first measuring electrode, the second measuring electrode, and the second power supply electrode. The four annular electrodes are connected to the corresponding data communication line connection connectors through wires, and each data communication line connection connector is connected to the resistivity collector through a data communication line.

5. The method for simulating the measurement of methane content in 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 provided 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 method for simulating the measurement of methane content in 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 method 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; The second pressure sensor is located on the connecting pipeline between the back pressure valve and the air inlet of the high-pressure reactor; The temperature and pressure collectors are connected to the first temperature sensor, the first pressure sensor, the second temperature sensor, and the second pressure sensor respectively.

8. The method for simulating the measurement of methane content in overlying sediments during layered hydrate decomposition according to claim 1, 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 temperature of the reaction vessel is circulated between the low-temperature water bath controller and the temperature control jacket of the reactor. The flowing low-temperature water circulates and refrigerates the high-pressure reactor to achieve cooling of the high-pressure reactor; In step S3, the heating power controller is turned on to increase the temperature of the electric heating coil.

Images