Natural gas hydrate combined mining system and method utilizing geothermal energy

Abstract

The invention relates to the technical field of natural gas hydrate exploitation, in particular to a natural gas hydrate combined exploitation system and method utilizing geothermal energy. An offshore operation platform is used for receiving natural gas hydrate produced by a depressurization exploitation module; the depressurization mining module obtains natural gas hydrates through a depressurization method; the geothermal energy circulation heating module is located in a vertical shaft of the space below the offshore operation platform and provided with multiple layers of heat collection pipes and heat dissipation pipes, the heat dissipation pipes are arranged in the natural gas hydrate reservoir in the depth direction of the heat reservoir, and the heat collection pipes and the heat dissipation pipes are filled with working liquid. The working liquid absorbs geothermal energy in the heat reservoir through the heat collecting pipe, and the geothermal energy is released into the natural gas hydrate reservoir through the heat dissipating pipe. Geothermal energy is used for heating the natural gas hydrate reservoir, depressurization method-thermal excitation method combined mining is formed, and the mining efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrate exploitation, and particularly to a combined exploitation system and method of natural gas hydrate using geothermal energy. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Natural gas hydrates are formed under high-pressure and low-temperature conditions and are widely distributed in terrestrial permafrost environments and deep-water formations. Because of their similar appearance to ice, they are also known as "flammable ice". Since the combustion produces carbon dioxide and water, and the pollution degree is much lower than that of fuels such as petroleum and coal, the development potential is huge.

[0004] For the exploitation of natural gas hydrates, at present, most methods achieve the decomposition of solid hydrates by destroying the equilibrium state of natural gas hydrates to collect gaseous methane. There are methods such as the pressure reduction method, the thermal stimulation method, the replacement method, the chemical inhibitor method, and the solid method, and the above methods can also be used in combination. At present, such exploitation methods are still in the trial production stage and it is difficult to meet the standards of commercial exploitation.

[0005] The pressure reduction method is to reduce the pressure at the exploitation wellhead, so that the local pore pressure of the hydrate drops to a state lower than the phase equilibrium pressure, and the equilibrium state of the hydrate is destroyed to achieve the decomposition purpose. The construction process of the pressure reduction method is relatively simple and has continuous excitability, so it is suitable for large-scale exploitation. However, the hydrate decomposition process is an endothermic process, and during the collection, due to the temperature decrease, the hydrate will be synthesized again, thus having a negative impact on the exploitation efficiency and making it difficult to meet the requirements of commercial exploitation.

[0006] The thermal stimulation method is to inject hot water, steam or use a heating device to heat the hydrate reservoir to raise its temperature above the phase equilibrium temperature to achieve the effect of decomposing the hydrate. The hydrate reservoir is located below the ground or the sea surface, and the depth can reach more than one thousand meters. Injecting hot water and steam will consume a large amount of heat during pipeline transportation, and a large amount of heat reaching the gas storage layer will also be lost to other formations. Although using an electric heating device to heat the hydrate reservoir can avoid this heat loss, its process is complex, the cost is high, and the energy consumption is high.

[0007] The replacement method utilizes the characteristic that carbon dioxide hydrate is more stable than methane hydrate, injects carbon dioxide gas into the hydrate reservoir to displace methane, and achieves the purpose of exploiting the hydrate. However, its reaction rate is slow, and the technical difficulty is high and the equipment cost investment is large.

[0008] The chemical inhibitor method is to inject chemical reagents into the hydrate reservoir to destroy the equilibrium state of the hydrate to achieve the decomposition purpose. However, the input cost of chemical reagents is high, the reaction rate is low, and it is easy to cause serious pollution to the ecological environment.

[0009] The solid method uses a device to break the hydrate solid into small pieces and then transports them to shallow layers for decomposition. This method requires precise mechanical equipment, which is prone to failure in the complex underground deep environment, and the hydrate structure will also be damaged when physically breaking the hydrate solid.

[0010] In summary, the current extraction methods for natural gas hydrates are still in the trial production stage and it is difficult to meet the standards for commercial extraction. Summary of the Invention

[0011] To solve the technical problems existing in the above-mentioned background technology, the present invention provides a combined extraction system and method for natural gas hydrates using geothermal energy. By integrating existing extraction methods and utilizing the characteristics of hydrate decomposition in a low-pressure and high-temperature environment, a combined extraction method of pressure reduction method and thermal stimulation method is proposed.

[0012] To achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a combined extraction system for natural gas hydrates using geothermal energy, including: An offshore operation platform, having a liquid storage tank and a gas-liquid separator, for receiving natural gas hydrates produced by the pressure reduction extraction module; A pressure reduction extraction module, having at least one set of collection pipelines and a pressure pump, changing the pressure of the natural gas hydrate reservoir in the collection pipelines through the pressure pump to obtain natural gas hydrates; A geothermal energy circulating heating module, located in a shaft in the space below the offshore operation platform, having a heat extraction pipe and a heat dissipation pipe. The heat dissipation pipe is arranged in the natural gas hydrate reservoir, and the heat extraction pipe is arranged in multiple layers along the depth direction of the heat reservoir. There is a working liquid in the heat extraction pipe and the heat dissipation pipe. The working liquid absorbs geothermal energy in the heat reservoir through the heat extraction pipe and releases the geothermal energy into the natural gas hydrate reservoir through the heat dissipation pipe.

[0013] Further, an air-liquid separator connected to each set of collection pipelines and a circulating pump a for providing power to the working liquid are provided on the offshore operation platform. The air-liquid separator is connected to a gas storage tank through a gas pipeline. The inlet of the circulating pump a is connected to the liquid storage tank through a pipeline, and the liquid storage tank and all air-liquid separators are connected through a waste liquid return pipe.

[0014] Further, a vertical pipe passing through the overlying mud layer on the seabed and reaching the natural gas hydrate reservoir is provided inside the collection pipeline. The bottom end of the vertical pipe is connected to the outlet of the pressure pump, and the inlet of the pressure pump is connected to a horizontal pipe; water or gas in the natural gas hydrate reservoir is sucked through the pressure pump to change the pressure of the natural gas hydrate reservoir. The produced mixture reaches the air-liquid separator on the offshore operation platform through the horizontal pipe and the vertical pipe, and is sent to the gas storage tank for storage after gas-liquid separation.

[0015] Furthermore, the geothermal energy circulation heating module has a heat collection input pipe located in the vertical shaft and a control valve group connected to the heat collection input pipe, and the control valve group is respectively connected to the heat collection pipe and the heat dissipation pipe to form a heating circulation loop and a heat dissipation circulation loop.

[0016] Furthermore, the control valve group includes a heat collection main control valve arranged on the heat collection input pipe, and the outlet of the heat collection main control valve is respectively connected to the inlet of the circulation pump b, the liquid separator and the second heat dissipation control valve through pipelines. The outlet of the circulation pump b is connected to the first temperature sensor through a pipeline, and then connected to the first heat dissipation control valve and the liquid collector respectively. The liquid separator is connected to the first heat collection control valve through a pipeline, and the liquid collector is connected to the second heat collection control valve through a pipeline.

[0017] Furthermore, the heat collection pipe includes multiple groups of heat collection branch pipes arranged on the same plane, one end of all the heat collection branch pipes is closed, and the other end is fixed on the connecting piece, each group of heat collection branch pipes has a U-shaped heat pipe, and the heat pipes in all the heat collection branch pipes are connected end to end, the head end of the heat pipe in the first group of heat collection branch pipes forms a heat collection liquid inlet, and the tail end of the heat pipe in the last group of heat collection branch pipes forms a heat collection liquid outlet, and a second temperature sensor is provided on the heat collection liquid outlet.

[0018] Furthermore, the heat dissipation pipe includes multiple groups of heat dissipation branch pipes arranged on the same plane, one end of all the heat dissipation branch pipes is closed, and the other end is fixed on the connecting piece, each group of heat dissipation branch pipes has a U-shaped heat pipe, and the heat pipes in all the heat dissipation branch pipes are connected end to end, the head end of the heat pipe in the first group of heat dissipation branch pipes forms a heat dissipation liquid inlet, and the tail end of the heat pipe in the last group of heat dissipation branch pipes forms a heat dissipation liquid outlet.

[0019] Furthermore, the heating circulation loop includes: the circulation pump b drives the working fluid to enter each group of heat collection tubes through the liquid distributor, the working fluid flowing out of the heat collection tubes is collected in the liquid collector, and returns to the circulation pump b through the opened heat dissipation circulation control valve.

[0020] Furthermore, the heat dissipation circulation loop includes: the working liquid flowing out of the liquid collector enters the heat dissipation pipe through the opened first heat dissipation control valve, the working liquid flowing out of the heat dissipation pipe returns to the liquid distributor through the opened second heat dissipation control valve, and the working liquid between the liquid distributor and the liquid collector passes through the heat collection pipe.

[0021] A second aspect of the present invention provides a method for combined exploitation of natural gas hydrates using geothermal energy, comprising the following steps: The circulating pump B drives the working fluid to enter each group of heat collection pipes through the liquid distributor, absorbs the geothermal energy in the heat storage layer, and returns to the circulating pump B after passing through the liquid collector; When the temperature obtained by the second temperature sensor exceeds the set value, the first heat dissipation control valve and the second heat dissipation control valve are opened, and the heat dissipation circulation circuit of the working liquid is connected to the temperature-raising circulation circuit. The working liquid after absorbing heat is pumped into the heat dissipation pipe to heat the natural gas hydrate reservoir, and the pressure pump in the pressure reduction mining module works to mine natural gas hydrate by the pressure reduction method; When the temperature obtained by the first temperature sensor is lower than the set value, the first heat dissipation control valve and the second heat dissipation control valve are closed, and the heat dissipation circulation circuit of the working liquid is no longer connected to the temperature-raising circulation circuit; The mined natural gas hydrate enters the gas-liquid separator through the collection pipe and the filter to obtain the required gas and liquid.

[0022] Compared with the prior art, the above one or more technical solutions have the following beneficial effects: 1. Using geothermal energy to heat the temperature of the natural gas hydrate reservoir avoids the heat loss during the liquid transportation process when using the thermal stimulation method, forms a combined mining method of pressure reduction method - thermal stimulation method, and avoids the phenomenon of secondary synthesis of hydrate due to temperature reduction during pressure reduction mining. Compared with single-mode mining, the mining efficiency is improved.

[0023] 2. Both the heat extraction pipe and the heat dissipation pipe are designed to extend horizontally on the side of the vertical pipe, which is convenient for construction; the formed radial layout type can radiate to the largest possible area and improve the heat extraction and heat dissipation efficiency.

[0024] 3. The heat extraction pipe has multiple layers, and each layer of the heat extraction pipe is connected to the liquid distributor and the liquid collector through the corresponding control valve. It can access different numbers of heat extraction pipes according to the heat demand of pressure reduction mining, and the adjustment is more flexible. At the same time, both the pressure reduction mining module and the heat dissipation pipe are located in the natural gas hydrate reservoir. Since the position and quantity of the pressure reduction mining module are not restricted, the multi-layer heat extraction pipe method makes the position selection of the heat dissipation pipe relatively free during design.

[0025] 4. The working liquid can be water and the liquid in the formation during mining, and can be recycled, saving resources and transportation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0027] Figure 1 is a schematic structural diagram of the mining system provided by one or more embodiments of the present invention; Figure 2 is a schematic structural diagram of the control valve group in the mining system provided by one or more embodiments of the present invention; Figure 3It is a schematic structural diagram of a heat extraction pipe in the extraction system provided by one or more embodiments of the present invention; Figure 4 It is a schematic structural diagram of a heat dissipation pipe in the extraction system provided by one or more embodiments of the present invention.

[0028] Figure 1 In the figure: 1 - Offshore operation platform, 2 - Collection pipeline, 3 - Heat extraction input pipe, 4 - Heat dissipation pipe, 5 - Heat extraction pipe a, 6 - Heat extraction pipe b, 7 - Heat extraction pipe c, 10 - Monitoring unit, 11 - Gas storage tank, 12 - Gas-liquid separator, 13 - Waste liquid return pipe, 14 - Circulation pump a, 15 - Liquid storage tank, 20 - Manifold, 31 - Main heat extraction control valve, 32 - Circulation pump b, 33 - Heat dissipation circulation control valve, 34 - First temperature sensor, 35 - First heat dissipation control valve, 36 - Second heat dissipation control valve; Figure 2 In the figure: 21 - Divider, 22 - Collector, 23 - First heat extraction control valve, 24 - Second heat extraction control valve, 25 - Exhaust valve; Figure 3 In the figure: 51 - Heat extraction liquid inlet, 52 - Heat extraction liquid outlet, 53 - Second temperature sensor, 54 - Heat extraction branch pipe; Figure 4 In the figure: 41 - Heat dissipation liquid inlet, 42 - Heat dissipation liquid outlet, 43 - Heat dissipation branch pipe. Specific embodiments

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0031] The following embodiments provide a combined natural gas hydrate extraction system and method using geothermal energy. Combining existing extraction methods and utilizing the characteristics of hydrate decomposition in a low-pressure and high-temperature environment, a combined extraction method of pressure reduction method and thermal stimulation method is proposed. Among them, the thermal stimulation method uses the geothermal energy in the lower part of the natural gas hydrate reservoir to provide energy. Currently, technologies using geothermal energy include ground source heat pumps, energy piles, etc., and most of them are applied to shallow strata, without considering the problems of heat transfer loss in deep strata and the difficulty of arranging heat extraction devices in deep strata. By collecting the geothermal energy in the lower part of the natural gas hydrate reservoir and circulatingly heating the natural gas hydrate reservoir. This method avoids the heat loss of the thermal stimulation method, combines with the pressure reduction method for combined extraction to improve the extraction rate, and the construction is relatively simple, which is conducive to the commercial extraction of natural gas hydrates.

[0032] Embodiment 1: The natural gas hydrate combined exploitation system proposed in this embodiment utilizes heat extraction pipes to absorb geothermal energy to heat the liquid in the heat extraction pipes. The liquid is powered by a circulation pump, and through a water distributor, the liquid is respectively transported to each layer of heat extraction pipes and then concentrated at the water collector after heating. After the temperature reaches the usage requirement, the liquid is transported to the heat dissipation pipes in the natural gas hydrate reservoir. A pressure reduction exploitation device is placed in the natural gas hydrate reservoir for exploitation. At the same time, the heat dissipation pipes transfer heat to the external low-temperature environment to prevent the secondary synthesis of hydrates and raise the temperature above the equilibrium temperature to accelerate the decomposition of hydrates. When the liquid temperature does not meet the usage standard, the liquid in the heat dissipation pipes is sent back to the middle and deep heat storage layer, and is shunted to each layer of heat extraction pipes through the water distributor for reheating. The liquid heated in the middle and deep heat storage layer returns to the heat dissipation pipes in the natural gas hydrate reservoir again, and this cycle repeats until the exploitation ends.

[0033] A natural gas hydrate combined exploitation system utilizing geothermal energy, comprising: An offshore operation platform, having a liquid storage tank and a gas-liquid separator, for receiving the natural gas hydrates produced by the pressure reduction exploitation module; A pressure reduction exploitation module, having a collection pipeline and a pressure pump, which changes the pressure of the natural gas hydrate reservoir in the collection pipeline through the pressure pump to obtain natural gas hydrates; A geothermal energy circulating heating module, located in a shaft in the space below the offshore operation platform, having heat extraction pipes and heat dissipation pipes. The heat dissipation pipes are arranged in the natural gas hydrate reservoir, and the heat extraction pipes are arranged in multiple layers along the depth direction of the heat storage layer. There is a working liquid in the heat extraction pipes and the heat dissipation pipes. The working liquid absorbs the geothermal energy in the heat storage layer through the heat extraction pipes, and the geothermal energy is released into the natural gas hydrate reservoir through the heat dissipation pipes.

[0034] As Figure 1 shown, in this embodiment, taking the exploitation of natural gas hydrates in the ocean area as an example, a shaft is set in the exploitation area of natural gas hydrates. The shaft is located below the offshore operation platform 1, successively passing through the seabed, the overlying mud layer and the natural gas hydrate reservoir, and reaching the set position of the middle and deep heat storage layer. The pressure reduction exploitation module is located in the natural gas hydrate reservoir. The heat extraction pipes a5, heat extraction pipes b6 and heat extraction pipes c7 in the geothermal energy circulating heating module are all located in the middle and deep heat storage layer and are arranged in multiple layers along the depth direction. The heat dissipation pipes 4 are arranged in the natural gas hydrate reservoir and are located in the space below the horizontal pipes in the pressure reduction exploitation module. The space in the shaft accommodates the heat extraction input pipe 3, the circulation pump b32 and the control valve group of the geothermal energy circulating heating module. The offshore operation platform 1 is then arranged with the gas-liquid separator 12 and the liquid storage tank 15 required for the pressure reduction exploitation module and the geothermal energy circulating heating module to support the normal operation of the pressure reduction exploitation module and the geothermal energy circulating heating module.

[0035] As a further embodiment, a gas-liquid separator 12 connected to each group of collection pipes 2 and a circulation pump a14 for providing power to the working liquid are provided on the offshore operation platform 1.

[0036] As a further embodiment, the gas-liquid separator 12 is connected to the gas storage tank 11 through a gas pipeline, and the inlet of the circulation pump a14 is connected to the liquid storage tank 15 through a pipeline.

[0037] As a further embodiment, the liquid storage tank 15 and all the gas-liquid separators 12 are connected through a waste liquid return pipe 13.

[0038] The pressure reduction and production module includes a collection pipe 2 and a pressure pump located inside the collection pipe 2. The collection pipe 2 has a vertical pipe passing through the overlying mud layer on the seabed and reaching the natural gas hydrate reservoir. The bottom end of the vertical pipe is connected to the outlet of the pressure pump, and the inlet of the pressure pump is connected to a horizontal pipe. Water or gas in the natural gas hydrate reservoir is sucked through the pressure pump to change the pressure of the natural gas hydrate reservoir. The produced methane gas reaches the gas-liquid separator 12 on the offshore operation platform 1 through the horizontal pipe and the vertical pipe, and is sent to the gas storage tank 11 for storage after gas-liquid separation.

[0039] As a further embodiment, a filter is provided at the inlet of the gas-liquid separator 12.

[0040] As a further embodiment, a sealing device is provided between the inner wall surface of the collection pipe 2 and the outer wall surface of the vertical pipe to block some substances in the natural gas hydrate reservoir from reaching the offshore operation platform 1.

[0041] The sealing device is a mature existing technology, and the specific structure is not described in detail in this embodiment. For example, a grouting sealing device disclosed in CN222008893U can be used, or a packer for oil production well pipes proposed in CN119266762A can be used, or a packer proposed in CN114837596A can be used. The specific structure is not limited.

[0042] As a further embodiment, the heat input pipe 3 and the control valve group are both located in the shaft below the offshore operation platform 1, and the outlet of the circulation pump a14 is connected to the heat input pipe 3.

[0043] As Figure 1 - Figure 2 shown, the control valve group includes a main heat control valve 31 provided on the heat input pipe 3. The outlet of the main heat control valve 31 is respectively connected to the inlet of the circulation pump b32 and the manifold 20 through pipelines. The manifold 20 includes a diverter 21 and a collector 22.

[0044] As Figure 1 - Figure 2As shown in the figure, the control valve group includes a main heat extraction valve 31 provided on the heat extraction input pipe 3. The outlet of the main heat extraction valve 31 is connected to the inlet of the circulation pump b32, the liquid distributor 21, and the second heat dissipation control valve 36 through pipelines respectively. After the outlet of the circulation pump b32 is connected to the first temperature sensor 34 through a pipeline, it is respectively connected to the first heat dissipation control valve 35 and the liquid collector 22. The liquid distributor 21 is connected to the first heat extraction control valve 23 through a pipeline, and the liquid collector 22 is connected to the second heat extraction control valve 24 through a pipeline.

[0045] As a further implementation manner, the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are respectively connected to the inlet and outlet of the heat dissipation pipe 4.

[0046] As a further implementation manner, the first heat extraction control valve 23 and the second heat extraction control valve 24 are respectively connected to the inlet and outlet of the corresponding heat extraction pipe.

[0047] As a further implementation manner, an exhaust valve 25 is provided on the liquid collector 22.

[0048] As a further implementation manner, a filter is provided on the inlet pipeline of the liquid distributor 21.

[0049] In this embodiment, three layers of heat extraction pipes are taken as an example, namely heat extraction pipe a5, heat extraction pipe b6, and heat extraction pipe c7. In practical applications, the specific number of layers of heat extraction pipes is not limited.

[0050] In this embodiment, the structures of the three layers of heat extraction pipes are the same. Taking Figure 3 the structure of the heat extraction pipe a5 shown in the figure as an example to illustrate this solution. The heat extraction pipe a5 includes multiple groups of heat extraction branch pipes 54 arranged on the same plane. One end of all the heat extraction branch pipes 54 is closed, and the other end is fixed on the connector. Each group of heat extraction branch pipes 54 has a U-shaped heat pipe inside. The heat pipes in adjacent heat extraction branch pipes 54 are connected end to end. The head end of the heat pipe in the first group of heat extraction branch pipes 54 forms a heat extraction liquid inlet 51, and the tail end of the heat pipe in the last group of heat extraction branch pipes 54 forms a heat extraction liquid outlet 52. A second temperature sensor 53 is provided on the heat extraction liquid outlet 52.

[0051] As a further implementation manner, the number of the heat extraction branch pipes 54 is not limited. In this embodiment, there are six heat extraction branch pipes 54, which are evenly distributed along the circumferential direction around the connector, forming a radial arrangement with the connector.

[0052] In this embodiment, considering that the hydrate is stored in the seabed formation and the reservoir range is wide, the radial arrangement can increase the heat exchange area and improve the exploitation efficiency.

[0053] Meanwhile, the radial structure can increase the stability of the overall system structure. The radial structure is arranged in a centrally symmetric manner with the shaft axis as the center, forming a supporting effect on the formation at the depth where the heat dissipation pipes are located. When the hydrate decomposes, the formation where the decomposed part is located will subside. The radial structure can ensure that the hydrate in the formation decomposes as evenly as possible, ensuring that the subsidence of the formation is also uniform. This structure is conducive to ensuring the stability of pipelines, valves, and the entire offshore platform.

[0054] As Figure 4 shown, the heat dissipation pipe 4 includes multiple groups of heat dissipation branch pipes 43 arranged on the same plane. One end of all the heat dissipation branch pipes 43 is closed, and the other end is fixed to the connecting piece. Each group of heat dissipation branch pipes 43 has a U-shaped heat pipe inside. The heat pipes in adjacent heat dissipation branch pipes 43 are connected end to end. The head end of the heat pipe in the first group of heat dissipation branch pipes 43 forms a heat dissipation liquid inlet 41, and the tail end of the heat pipe in the last group of heat dissipation branch pipes 43 forms a heat dissipation liquid outlet 42.

[0055] As a further implementation method, the number of heat dissipation branch pipes 43 is not limited. In this embodiment, there are six heat dissipation branch pipes 43, which are evenly distributed along the circumferential direction around the connecting piece, forming a radial arrangement pattern.

[0056] The working principle of the natural gas hydrate combined exploitation system is as follows: When the system is first operated, the heat extraction main control valve 31 is opened, the circulation pump a14 is opened, and the first heat extraction control valve 23 and the second heat extraction control valve 24 corresponding to each group of heat extraction pipes are opened. The working liquid in the liquid storage tank 15 is transported through the heat extraction input pipe 3 to the heat extraction pipes a5, heat extraction pipes b6, and heat extraction pipes c7 located in the middle and deep heat storage layers; the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are opened to fill the heat dissipation circulation loop with the working liquid, and the gas in the working liquid is discharged through the exhaust valve 25 on the liquid collector 22. When the system is filled with the working liquid, the heat extraction main control valve 31 and the circulation pump a14 are closed.

[0057] During operation, the system has a heating-up circulation loop and a heat dissipation circulation loop.

[0058] The circulation pump b32 is opened, the heat dissipation circulation control valve 33 is opened, and the first heat extraction control valve 23 and the second heat extraction control valve 24 corresponding to each group of heat extraction pipes are opened. The working liquid enters the heat extraction liquid inlet 51 of each group of heat extraction pipes through the liquid distributor 21 and flows out from the heat extraction liquid outlet 52 and is collected in the liquid collector 22 to form a heating-up circulation loop; during the heating-up circulation, the working liquid absorbs the geothermal heat in the middle and deep heat storage layer and heats up.

[0059] When the second temperature sensor 53 corresponding to each group of heat collection pipes reaches the set value, it is considered that the working fluid has absorbed enough geothermal heat at this time and can be pumped into the heat dissipation pipe 4. Then the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are opened to connect the heat dissipation circulation circuit of the working fluid with the temperature rise circulation circuit, and the heated working fluid is pumped into the heat dissipation pipe 4 by the circulation pump b32.

[0060] The working fluid heats the natural gas hydrate reservoir area where the heat dissipation pipe 4 is located, and the pressure pump in the pressure reduction mining module works to mine natural gas hydrates by the pressure reduction method; specifically: the heated working fluid enters the heat pipe from the heat dissipation liquid inlet 41, sequentially passes through each group of heat dissipation branch pipes 43, and flows out from the heat dissipation liquid outlet 42. During this period, the carried geothermal heat is released into the natural gas hydrate reservoir to raise the temperature of the area where the horizontal pipe in the pressure reduction mining module is located, thereby accelerating the gas methane obtained by the pressure reduction mining module, avoiding the secondary synthesis of hydrates during the pressure reduction mining, and improving the mining efficiency.

[0061] When the temperature obtained by the first temperature sensor 34 is lower than the set value, it is considered that the temperature at this time is not sufficient to support the mining of natural gas hydrates by the pressure reduction method, then the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are closed, and the heat dissipation circulation circuit of the working fluid is no longer connected to the temperature rise circulation circuit.

[0062] The decomposed hydrates enter the gas-liquid separator 12 through the collection pipeline and the filter. The separated gas enters the gas storage tank for storage, and the separated liquid flows into the liquid storage tank 15 through the waste liquid return pipe 13 for recycling.

[0063] As a further implementation method, a monitoring unit 10 is provided in the offshore operation platform 1 to monitor the working states of each circulation pump and control valve in the system. The monitoring unit 10 is a mature existing technology, and the specific structural form is not limited. For example, it can be a data collector.

[0064] This solution uses geothermal energy to heat the temperature of the natural gas hydrate reservoir, avoiding the loss of heat during the liquid transportation process when using the thermal stimulation method, forming a combined mining method of pressure reduction method - thermal stimulation method, avoiding the phenomenon of secondary synthesis of hydrates due to temperature reduction during pressure reduction mining, and improving the mining efficiency compared with single - mode mining.

[0065] Both the heat collection pipe and the heat dissipation pipe are designed to extend horizontally on the side of the vertical pipe, which is convenient for construction; the formed radial layout can radiate to the largest possible area, improving the heat collection and heat dissipation efficiency.

[0066] The heat extraction pipe has multiple layers. Each layer of the heat extraction pipe is connected to the liquid distributor and the liquid collector through corresponding control valves. It can access different numbers of heat extraction pipes according to the heat demand of pressure reduction mining, and the adjustment is more flexible. At the same time, both the pressure reduction mining module and the heat dissipation pipe are located in the natural gas hydrate reservoir. Since the position and number of the pressure reduction mining modules are not restricted, the multi-layer heat extraction pipe method makes the position selection of the heat dissipation pipe relatively free during design.

[0067] The working liquid can be water or the liquid in the formation during mining, and it can be recycled, saving resources and transportation costs.

[0068] Embodiment 2: A method for jointly mining natural gas hydrates using geothermal energy, comprising the following steps: The circulation pump b drives the working liquid to enter each group of heat extraction pipes through the liquid distributor, absorbs the geothermal energy in the heat storage layer, and returns to the circulation pump b after passing through the liquid collector; When the temperature obtained by the second temperature sensor exceeds the set value, the first heat dissipation control valve and the second heat dissipation control valve are opened, and the heat dissipation circulation loop of the working liquid is connected to the temperature increase circulation loop. The heat-absorbed working liquid is pumped into the heat dissipation pipe to heat the natural gas hydrate reservoir, and the pressure pump in the pressure reduction mining module works to mine natural gas hydrates by the pressure reduction method; When the temperature obtained by the first temperature sensor is lower than the set value, the first heat dissipation control valve and the second heat dissipation control valve are closed, and the heat dissipation circulation loop of the working liquid is no longer connected to the temperature increase circulation loop; The mined natural gas hydrates enter the gas-liquid separator through the collection pipeline and the filter to obtain the required gas and liquid.

[0069] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A natural gas hydrate joint mining system using geothermal energy, characterized in that: include: An offshore operating platform, having a liquid storage tank and a gas-water separator, for receiving the natural gas hydrate produced from the depressurization production module; A pressure reduction production module, comprising at least one set of collecting pipes and a pressure pump, which changes the pressure of the natural gas hydrate reservoir in the collecting pipes through the pressure pump to obtain natural gas hydrates; The geothermal energy circulation heating module is located in the vertical shaft below the offshore operating platform and has heat collection pipes and heat dissipation pipes. The heat dissipation pipes are arranged in the natural gas hydrate reservoir. The heat collection pipes are arranged in multiple layers along the depth direction of the heat reservoir. The heat collection pipes and the heat dissipation pipes contain working liquid. The working liquid absorbs geothermal energy in the heat reservoir through the heat collection pipes and releases the geothermal energy into the natural gas hydrate reservoir through the heat dissipation pipes.

2. A natural gas hydrate joint mining system utilizing geothermal energy as claimed in claim 1, characterized in that: The offshore operating platform is provided with a circulation pump a for providing power for the working fluid, and a gas-liquid separator respectively connected to each group of collecting pipes, the gas-liquid separator is connected to the gas storage tank through a gas pipeline, the inlet of the circulation pump a is connected to the liquid storage tank through a pipeline, and the liquid storage tank and all the gas-liquid separators are connected through a waste liquid return pipe.

3. A natural gas hydrate joint mining system utilizing geothermal energy as claimed in claim 1, characterized in that: The collecting pipeline has a vertical pipe inside that passes through the mud layer overlying the seabed and reaches the natural gas hydrate reservoir. The bottom end of the vertical pipe is connected to the outlet of the pressure pump, and the inlet of the pressure pump is connected to the horizontal pipe. The water or gas in the natural gas hydrate reservoir is sucked by the pressure pump to change the pressure of the natural gas hydrate reservoir. The produced mixture passes through the horizontal pipe and the vertical pipe to reach the gas-liquid separator on the offshore operating platform, and is sent to the gas storage tank for storage after gas-liquid separation.

4. A natural gas hydrate joint mining system using geothermal energy as claimed in claim 1, characterized in that: The geothermal energy circulation heating module comprises a heat collection input pipe located in the vertical shaft and a control valve group connected to the heat collection input pipe. The control valve group is respectively connected to the heat collection pipe and the heat dissipation pipe to form a heating circulation loop and a heat dissipation circulation loop.

5. A natural gas hydrate joint mining system using geothermal energy as claimed in claim 4, characterized in that: The control valve group includes a heat collection main control valve arranged on the heat collection input pipe. The outlet of the heat collection main control valve is connected to the inlet of the circulation pump b, the liquid separator and the second heat dissipation control valve through pipelines. The outlet of the circulation pump b is connected to the first temperature sensor through a pipeline, and then connected to the first heat dissipation control valve and the liquid collector respectively. The liquid separator is connected to the first heat collection control valve through a pipeline, and the liquid collector is connected to the second heat collection control valve through a pipeline.

6. A natural gas hydrate joint mining system using geothermal energy as claimed in claim 4, characterized in that: The heat collection pipe includes multiple groups of heat collection branch pipes arranged on the same plane. One end of all the heat collection branch pipes is closed and the other end is fixed on the connecting piece. Each group of heat collection branch pipes has a U-shaped heat pipe. The heat pipes in adjacent heat collection branch pipes are connected end to end. The head end of the heat pipe in the first group of heat collection branch pipes forms a heat collection liquid inlet, and the tail end of the heat pipe in the last group of heat collection branch pipes forms a heat collection liquid outlet. A second temperature sensor is provided on the heat collection liquid outlet.

7. A combined natural gas hydrate production system utilizing geothermal energy as claimed in claim 4, characterized in that: The heat dissipation pipe comprises a plurality of groups of heat dissipation branch pipes arranged on the same plane, one end of all the heat dissipation branch pipes is closed and the other end is fixed on a connecting piece, each group of heat dissipation branch pipes has a U-shaped heat pipe, the heat pipes in adjacent heat dissipation branch pipes are connected end to end, the head end of the heat pipe in the first group of heat dissipation branch pipes forms a heat dissipation liquid inlet, and the tail end of the heat pipe in the last group of heat dissipation branch pipes forms a heat dissipation liquid outlet.

8. A natural gas hydrate joint mining system utilizing geothermal energy as claimed in claim 4, characterized in that: The temperature rise circulation loop includes: the circulation pump b drives the working liquid to enter each group of heat collection tubes through the liquid distributor, the working liquid flowing out of the heat collection tubes is collected in the liquid collector, and returns to the circulation pump b through the opened heat dissipation circulation control valve.

9. A natural gas hydrate joint mining system using geothermal energy as claimed in claim 4, characterized in that: The heat dissipation circulation loop includes: the working liquid flowing out of the liquid collector enters the heat dissipation pipe through the opened first heat dissipation control valve, the working liquid flowing out of the heat dissipation pipe returns to the liquid distributor through the opened second heat dissipation control valve, and the working liquid between the liquid distributor and the liquid collector passes through the heat collection pipe.

10. A method for joint exploitation of natural gas hydrates using geothermal energy, implemented based on the joint exploitation system for natural gas hydrates according to any one of claims 1 to 9, characterized in that: The following steps are involved: The circulating pump B drives the working fluid to enter each group of heat collection pipes through the liquid distributor, absorbs the geothermal energy in the heat storage layer, and returns to the circulating pump B after passing through the liquid collector; When the temperature obtained by the second temperature sensor exceeds the set value, the first heat dissipation control valve and the second heat dissipation control valve are opened, the heat dissipation circulation loop of the working liquid is connected to the heating circulation loop, the working liquid after absorbing heat is pumped into the heat dissipation pipe to heat the natural gas hydrate reservoir, the pressure pump in the pressure reduction mining module works, and the natural gas hydrate is mined by the pressure reduction method; When the temperature acquired by the first temperature sensor is lower than the set value, the first heat dissipation control valve and the second heat dissipation control valve are closed, and the heat dissipation circulation loop of the working fluid is no longer connected to the temperature increase circulation loop; The mined natural gas hydrate enters the gas-liquid separator through a collection pipeline and a filter to obtain the required gas and liquid.

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