A natural gas hydrate combined exploitation system and method using geothermal energy

Abstract

The present application relates to natural gas hydrate exploitation technical field, specifically for a kind of natural gas hydrate combined exploitation system and method using geothermal energy, the offshore operation platform for receiving natural gas hydrate from the output of pressure reduction exploitation module;Pressure reduction exploitation module obtains natural gas hydrate using pressure reduction method;Geothermal energy circulation heating module is located in the shaft in the space below offshore operation platform, with heat pipe and heat dissipation pipe, heat dissipation pipe is arranged in natural gas hydrate reservoir, heat pipe is arranged multilayer along the depth direction of thermal reservoir, heat pipe and heat dissipation pipe have working liquid, working liquid is absorbed heat reservoir in geothermal energy by heat pipe, and geothermal energy is released into natural gas hydrate reservoir by heat dissipation pipe.The temperature of natural gas hydrate reservoir is heated using geothermal energy, pressure reduction method-thermal stimulation method combined exploitation is formed, and exploitation efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas hydrate exploitation, in particular to a natural gas hydrate combined exploitation system and method using geothermal energy. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] Natural gas hydrate is formed under high pressure and low temperature conditions, and is widely distributed in land permafrost environments and deep water strata. It is also known as "combustible ice" due to its ice-like appearance. Due to the production of carbon dioxide and water during combustion, the pollution level is much lower than that of oil, coal and other fuels, so the development potential is huge.

[0004] For the exploitation of natural gas hydrate, the current method is to destroy the balance state of natural gas and water to decompose solid hydrate to collect gas methane. There are methods such as depressurization, thermal stimulation, replacement, chemical inhibitor and solid method, and the above methods can also be used in combination. At present, such exploitation methods are still in the stage of trial production, and it is difficult to meet the standards of commercial exploitation.

[0005] The depressurization method is to lower the pressure at the wellhead to make the local pore pressure of the hydrate drop below the phase equilibrium pressure, thereby destroying the balance state of the hydrate to achieve the purpose of decomposition. The construction process of the depressurization method is relatively simple and has continuous stimulation, so it is suitable for large-scale exploitation. However, the hydrate decomposition process is an endothermic process, and when collecting, the temperature will decrease, causing the hydrate to be synthesized again, thereby negatively affecting the efficiency of the exploitation, making it difficult to meet the needs of commercial exploitation.

[0006] The thermal stimulation method is to inject hot water, steam into the hydrate reservoir or use heating devices to heat the hydrate, so that its temperature rises above the phase equilibrium temperature, thereby achieving the effect of decomposing the hydrate. The hydrate reservoir is located below the ground or sea surface, and the depth can reach more than one thousand meters. The injection of hot water and steam will consume a large amount of heat during pipeline transportation, and the heat reaching the gas reservoir will also be lost to other strata. While using electric heating equipment to heat the hydrate reservoir can avoid such heat loss, the process is complex, the cost is high, and the energy consumption is high.

[0007] The replacement method is to use the characteristic that carbon dioxide hydrate is more stable than methane hydrate to inject carbon dioxide gas into the hydrate reservoir to displace methane, thereby achieving the purpose of exploiting hydrates. However, the reaction rate is slow, and the technology is difficult and the equipment cost is high.

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

[0009] Solid method is to use device to break hydrate solid into small pieces, and then transport to shallow layer for decomposition. The method needs precise mechanical equipment, and the mechanical equipment is prone to failure in the complex environment of deep underground, and the structure of hydrate is also damaged when physically breaking the hydrate solid.

[0010] In summary, the current exploitation method of natural gas hydrate is still in the trial production stage, and it is difficult to meet the standard of commercial exploitation. SUMMARY

[0011] In order to solve the technical problems existing in the above background art, the present application provides a natural gas hydrate combined exploitation system and method using geothermal energy, which combines the existing exploitation methods, uses the characteristics of hydrate decomposition in low pressure and high temperature environment, and proposes a combined exploitation method of pressure reduction method and thermal stimulation method.

[0012] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0013] The first aspect of the present application provides a natural gas hydrate combined exploitation system using geothermal energy, comprising:

[0014] The offshore operation platform has a liquid storage tank and a gas-water separator for receiving natural gas hydrate produced from the pressure reduction exploitation module;

[0015] The pressure reduction exploitation module has at least one set of collection pipelines and a pressure pump, which changes the pressure of the natural gas hydrate reservoir in the collection pipeline by the pressure pump to obtain natural gas hydrate;

[0016] The geothermal energy circulation heating module is located in the vertical shaft of the space below the offshore operation platform, has a heat collecting pipe and a heat dissipating pipe, the heat dissipating pipe is arranged in the natural gas hydrate reservoir, the heat collecting pipe is arranged in multiple layers along the depth direction of the heat reservoir, and the heat collecting pipe and the heat dissipating pipe have working liquid therein, the working liquid absorbs the 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.

[0017] Further, the offshore operation platform is provided with a gas-liquid separator connected with each set of collection pipelines, and a circulating pump a for providing power for the working liquid, the gas-liquid separator is connected with a gas storage tank through a gas pipeline, the inlet of the circulating pump a is connected with 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.

[0018] Further, the collecting pipeline has a vertical pipe inside, which penetrates the overlying sediment and reaches the natural gas hydrate reservoir, the bottom end of the vertical pipe is connected with the outlet of the pressure pump, and the inlet of the pressure pump is connected with the horizontal pipeline; 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, and the output mixture reaches a gas-liquid separator on the offshore operation platform through the horizontal pipeline and the vertical pipe, and is sent into a gas storage tank after gas-liquid separation.

[0019] Further, the geothermal energy circulation heating module has a heat extraction input pipe in the vertical shaft and a control valve group connected with the heat extraction input pipe, the control valve group is connected with the heat extraction pipe and the heat dissipation pipe respectively to form a temperature rising circulation loop and a heat dissipation circulation loop.

[0020] Further, the control valve group includes a heat extraction main control valve arranged on the heat extraction input pipe, the outlet of the heat extraction main control valve is connected with the inlet of the circulation pump b, the distributor and the second heat dissipation control valve through pipelines respectively, the outlet of the circulation pump b is connected with the first heat dissipation control valve and the liquid collector after passing through the first temperature sensor, the distributor is connected with the first heat extraction control valve through a pipeline, and the liquid collector is connected with the second heat extraction control valve through a pipeline.

[0021] Further, the heat extraction pipe includes a plurality of groups of heat extraction branch pipes arranged on the same plane, one end of all the heat extraction branch pipes is closed, and the other end is fixed on a connecting piece, each group of heat extraction branch pipes has a heat pipe in a U shape, the heat pipes in all the heat extraction branch pipes are connected end to end, the first end of the heat pipe in the first group of heat extraction branch pipes forms a heat extraction liquid inlet, and the tail end of the heat pipe in the last group of heat extraction branch pipes forms a heat extraction liquid outlet, and a second temperature sensor is arranged on the heat extraction liquid outlet.

[0022] Further, the heat dissipation pipe includes 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 heat pipe in a U shape, the heat pipes in all the heat dissipation branch pipes are connected end to end, the first 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.

[0023] Further, the temperature rising circulation loop includes that the working liquid is driven by the circulation pump b to enter each group of heat extraction pipes through the distributor, the working liquid flowing out of the heat extraction pipes is collected in the liquid collector, and the working liquid returns to the circulation pump b through the opened heat dissipation circulation control valve.

[0024] Further, the heat dissipation circulation loop includes that 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 distributor through the opened second heat dissipation control valve, and the working liquid between the distributor and the liquid collector passes through the heat extraction pipe.

[0025] The second aspect of the present application provides a natural gas hydrate combined exploitation method using geothermal energy, comprising the following steps:

[0026] The circulating pump b drives the working liquid to pass through the distributor into each group of heat extraction pipes, absorbs the geothermal energy in the heat storage layer, and returns to the circulating pump b through the liquid collector;

[0027] When the temperature obtained by the second temperature sensor exceeds the set value, the first and second heat dissipation control valves are opened, the heat dissipation circulation loop of the working liquid is communicated with the temperature rise circulation loop, the heat-absorbed working liquid is pumped into the heat dissipation pipe to heat the natural gas hydrate reservoir, the pressure pump in the pressure reduction exploitation module works, and the natural gas hydrate is exploited by using the pressure reduction method;

[0028] When the temperature obtained by the first temperature sensor is lower than the set value, the first and second heat dissipation control valves are closed, and the heat dissipation circulation loop of the working liquid is no longer communicated with the temperature rise circulation loop;

[0029] The exploited natural gas hydrate enters the gas-liquid separator through the collecting pipeline and the filter, and the required gas and liquid are obtained.

[0030] Compared with the prior art, the above one or more technical solutions have the following beneficial effects:

[0031] 1. The geothermal energy is used to heat the natural gas hydrate reservoir temperature, which avoids the heat loss in the liquid transportation process when using the thermal stimulation method, forms a pressure reduction method-thermal stimulation method combined exploitation, avoids the secondary synthesis of hydrates due to temperature reduction during pressure reduction exploitation, and improves the exploitation efficiency compared with single mode exploitation.

[0032] 2. The heat extraction pipe and the heat dissipation pipe are designed to extend horizontally on the side of the vertical pipeline, which is convenient for construction; the formed radial arrangement type can radiate to the largest possible area, and the heat extraction and heat dissipation efficiency is improved.

[0033] 3. The heat extraction pipe has multiple layers, each layer of heat extraction pipe is connected with the distributor and the liquid collector through the corresponding control valve, different numbers of heat extraction pipes can be connected according to the demand for heat during pressure reduction exploitation, and the adjustment is more flexible. At the same time, the pressure reduction exploitation module and the heat dissipation pipe are both in the natural gas hydrate reservoir, and the position and number of the pressure reduction exploitation module are not limited, and the multi-layer heat extraction pipe mode makes the position selection of the heat dissipation pipe relatively free during design.

[0034] 4. The working liquid can be water and liquid in the stratum during exploitation, and can be recycled, which saves resources and transportation cost. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated herein by reference. The illustrations are shown schematically and are not intended to limit the application.

[0036] Figure 1 is a structural schematic diagram of the exploitation system provided by one or more embodiments of the present application;

[0037] Figure 2 is a structural schematic diagram of the control valve group in the exploitation system provided by one or more embodiments of the present application;

[0038] Figure 3 is a structural schematic diagram of the heat extraction pipe in the exploitation system provided by one or more embodiments of the present application;

[0039] Figure 4 is a structural schematic diagram of the heat dissipation pipe in the exploitation system provided by one or more embodiments of the present application.

[0040] Figure 1 in which: 1 - offshore 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 - circulating pump a, 15 - liquid storage tank, 20 - collection and distribution device, 31 - heat extraction main control valve, 32 - circulating pump b, 33 - heat dissipation circulation control valve, 34 - first temperature sensor, 35 - first heat dissipation control valve, 36 - second heat dissipation control valve;

[0041] Figure 2 in which: 21 - distribution device, 22 - collection device, 23 - first heat extraction control valve, 24 - second heat extraction control valve, 25 - exhaust valve;

[0042] Figure 3 in which: 51 - heat extraction liquid inlet, 52 - heat extraction liquid outlet, 53 - second temperature sensor, 54 - heat extraction branch pipe;

[0043] Figure 4 in which: 41 - heat dissipation liquid inlet, 42 - heat dissipation liquid outlet, 43 - heat dissipation branch pipe. DETAILED DESCRIPTION

[0044] The present application will be further described with reference to the drawings and examples.

[0045] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0046] The following embodiments give a natural gas hydrate combined exploitation system and method using geothermal energy, which combines the existing exploitation methods, uses the characteristics of hydrate decomposition in low pressure and high temperature environment, and proposes a combined exploitation method of pressure reduction method and thermal stimulation method. The thermal stimulation method uses the geothermal energy of the lower part of the natural gas hydrate reservoir to provide energy, and the current geothermal energy utilization technologies include ground source heat pump, energy pile, etc., most of which are applied to shallow strata without considering the heat transport loss problem of deep strata and the difficult arrangement problem of deep strata heat extraction devices. The geothermal energy of the lower part of the natural gas hydrate reservoir is collected to circulate and heat the natural gas hydrate reservoir. The method avoids the heat loss of the thermal stimulation method, combines the pressure reduction method to improve the exploitation rate, and is relatively simple in construction, which is beneficial to the commercial exploitation of natural gas hydrate.

[0047] Embodiment one:

[0048] The natural gas hydrate combined exploitation system proposed in this embodiment uses the heat extraction pipe to absorb geothermal energy to heat the liquid in the heat extraction pipe. The liquid is powered by the circulating pump, and is transported to each layer of the heat extraction pipe through the water distributor. After heating, the liquid is concentrated at the water collector. After the temperature reaches the use requirement, the liquid is transported to the heat dissipation pipe in the natural gas hydrate reservoir. The natural gas hydrate reservoir is placed in the pressure reduction exploitation device for exploitation, and the heat dissipation pipe transfers heat to the external low temperature environment to prevent the secondary synthesis of hydrate, and the temperature is increased to above the equilibrium temperature to accelerate the decomposition of hydrate. When the temperature of the liquid does not reach the use standard, the liquid in the heat dissipation pipe is sent back to the middle-deep heat storage layer, and is divided into each layer of the heat extraction pipe through the water distributor for heating again. The liquid heated in the middle-deep heat storage layer is returned to the heat dissipation pipe in the natural gas hydrate reservoir for repeated circulation until the exploitation is completed.

[0049] A natural gas hydrate combined exploitation system using geothermal energy, comprising:

[0050] An offshore operation platform having a liquid storage tank and a gas-water separator for receiving natural gas hydrate produced from a pressure reduction exploitation module;

[0051] 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 by the pressure pump to obtain natural gas hydrate;

[0052] A geothermal energy circulation heating module located in a vertical shaft in the space below the offshore operation platform, having a heat extraction pipe and a heat dissipation pipe, the heat dissipation pipe being arranged in the natural gas hydrate reservoir, the heat extraction pipe being arranged in multiple layers along the depth direction of the heat reservoir, and the heat extraction pipe and the heat dissipation pipe having working liquid therein, the working liquid absorbing geothermal energy in the heat reservoir through the heat extraction pipe, and releasing the geothermal energy to the natural gas hydrate reservoir through the heat dissipation pipe.

[0053] As Figure 1As shown, in this embodiment, taking the exploitation of marine areas of natural gas hydrates as an example, a vertical shaft is arranged in the exploitation area of natural gas hydrates, the vertical shaft is located below the offshore operation platform 1, sequentially passes through the seabed, the overlying mud layer and the natural gas hydrate reservoir, and reaches the set position of the middle-deep heat storage layer. The depressurization exploitation module is located in the natural gas hydrate reservoir, the heat extraction pipes a5, b6 and c7 in the geothermal energy circulation heating module are all located in the middle-deep heat storage layer and arranged in multiple layers along the depth direction, and the heat dissipation pipe 4 is arranged in the natural gas hydrate reservoir and located below the space of the horizontal pipe in the depressurization exploitation module. The space in the vertical shaft accommodates the heat extraction input pipe 3, the circulation pump b32 and the control valve group of the geothermal energy circulation heating module. The offshore operation platform 1 arranges the gas-liquid separator 12 and the liquid storage tank 15 required by the depressurization exploitation module and the geothermal energy circulation heating module, for supporting the normal operation of the depressurization exploitation module and the geothermal energy circulation heating module.

[0054] As a further embodiment, the offshore operation platform 1 is provided with a gas-liquid separator 12 connected with each group of collection pipes 2, and a circulation pump a14 for providing power for the working liquid.

[0055] As a further embodiment, the gas-liquid separator 12 is connected with the gas storage tank 11 through a gas pipe, and the inlet of the circulation pump a14 is connected with the liquid storage tank 15 through a pipe.

[0056] 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.

[0057] The depressurization exploitation module includes the collection pipe 2 and a pressure pump located inside the collection pipe 2, the collection pipe 2 has a vertical pipe passing through the seabed overlying mud layer and reaching the natural gas hydrate reservoir, the bottom end of the vertical pipe is connected with the outlet of the pressure pump, and the inlet of the pressure pump is connected with the horizontal pipe. The water or gas in the natural gas hydrate reservoir is sucked through the pressure pump, the pressure of the natural gas hydrate reservoir is changed, 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 saved in the gas storage tank 11 after gas-liquid separation.

[0058] As a further embodiment, a filter is arranged at the inlet of the gas-liquid separator 12.

[0059] As a further embodiment, a sealing device is arranged between the inner wall surface of the collection pipe 2 and the outer wall surface of the vertical pipe, for blocking part of the substances in the natural gas hydrate reservoir from reaching the offshore operation platform 1.

[0060] The packer is a mature prior art, and the specific structure is not described in the embodiment. For example, the grouting packer disclosed in CN222008893U can be used, the packer for oil well pipe disclosed in CN119266762A can be used, or the packer disclosed in CN114837596A can be used, and the specific structure is not limited.

[0061] As a further embodiment, the heat extraction pipe 3 and the control valve group are located in the vertical shaft below the offshore operation platform 1, and the outlet of the circulating pump a14 is connected to the heat extraction pipe 3.

[0062] As shown in Figures 1-2 , the control valve group includes a heat extraction main control valve 31 arranged on the heat extraction pipe 3, and the outlet of the heat extraction main control valve 31 is connected to the inlet of the circulating pump b32 and the collecting and distributing device 20 through pipes, respectively.

[0063] As shown in Figures 1-2 , the control valve group includes a heat extraction main control valve 31 arranged on the heat extraction pipe 3, and the outlet of the heat extraction main control valve 31 is connected to the inlet of the circulating pump b32, the distributing device 21 and the second heat dissipation control valve 36 through pipes, respectively. The outlet of the circulating pump b32 is connected to the first temperature sensor 34 through a pipe, and then connected to the first heat dissipation control valve 35 and the collecting device 22, respectively. The distributing device 21 is connected to the first heat extraction control valve 23 through a pipe, and the collecting device 22 is connected to the second heat extraction control valve 24 through a pipe.

[0064] As a further embodiment, the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are connected to the inlet and outlet of the heat dissipation pipe 4, respectively.

[0065] As a further embodiment, the first heat extraction control valve 23 and the second heat extraction control valve 24 are connected to the inlet and outlet of the corresponding heat extraction pipe, respectively.

[0066] As a further embodiment, the collecting device 22 is provided with an exhaust valve 25.

[0067] As a further embodiment, a filter is arranged on the inlet pipe of the distributing device 21.

[0068] The embodiment takes three layers of heat extraction pipes as an example, i.e., the heat extraction pipe a5, the heat extraction pipe b6 and the heat extraction pipe c7, and the number of heat extraction pipes is not limited in actual application.

[0069] In the embodiment, the structures of the three layers of heat extraction pipes are the same, and the structures of the heat extraction pipe a5, the heat extraction pipe b6 and the heat extraction pipe c7 are taken as an example. Figure 3The structure of the heat collecting pipe a5 is shown as an example to illustrate the scheme. The heat collecting pipe a5 includes a plurality of groups of heat collecting branch pipes 54 arranged on the same plane. All the heat collecting branch pipes 54 are closed at one end and fixed on the connecting piece at the other end. Each group of heat collecting branch pipes 54 has a U-shaped heat pipe. The heat pipes in adjacent heat collecting branch pipes 54 are connected end to end. The heat pipes in the first group of heat collecting branch pipes 54 form a heat collecting liquid inlet 51 at the first end. The heat pipes in the last group of heat collecting branch pipes 54 form a heat collecting liquid outlet 52 at the tail end. The heat collecting liquid outlet 52 is provided with a second temperature sensor 53.

[0070] As a further embodiment, the number of heat collecting branch pipes 54 is not limited. In the embodiment, the heat collecting branch pipes 54 have six branches and are evenly distributed in the circumferential direction of the connecting piece, forming a radial arrangement with the connecting piece.

[0071] In the embodiment, considering that the hydrate is stored in the formation of the seabed, the range of the reservoir is wide, and the radial arrangement can increase the heat exchange area and improve the exploitation efficiency.

[0072] At the same time, the radial structure can increase the stability of the overall structure of the system. The radial structure is arranged in a central symmetric manner with the shaft axis as the center, forming a support for the formation at the depth position of the heat dissipation pipe. When the hydrate is decomposed, the formation where the decomposed part is located will produce subsidence. The radial structure can ensure that the hydrate in the formation is as uniformly decomposed as possible, and ensure that the subsidence of the formation is also uniform. This structure is beneficial to ensure the stability of the pipeline, valve and the entire offshore platform.

[0073] As shown in Figure 4 The heat dissipation pipe 4 includes a plurality of groups of heat dissipation branch pipes 43 arranged on the same plane. All the heat dissipation branch pipes 43 are closed at one end and fixed on the connecting piece at the other end. Each group of heat dissipation branch pipes 43 has a U-shaped heat pipe. The heat pipes in adjacent heat dissipation branch pipes 43 are connected end to end. The heat pipes in the first group of heat dissipation branch pipes 43 form a heat dissipation liquid inlet 41 at the first end. The heat pipes in the last group of heat dissipation branch pipes 43 form a heat dissipation liquid outlet 42 at the tail end.

[0074] As a further embodiment, the number of heat dissipation branch pipes 43 is not limited. In the embodiment, the heat dissipation branch pipes 43 have six branches and are evenly distributed in the circumferential direction of the connecting piece, forming a radial arrangement.

[0075] The working principle of the natural gas hydrate combined exploitation system is as follows:

[0076] When the system is first run, the heat collection main control valve 31 is opened, the circulating pump a14 is opened, the first heat collection control valve 23 and the second heat collection control valve 24 corresponding to each group of heat collection pipes are opened, the working liquid in the liquid storage tank 15 is transported to the heat collection pipes a5, heat collection pipes b6 and heat collection pipes c7 located in the middle-deep heat storage layer through the heat collection input pipe 3; the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are opened, the working liquid fills the heat dissipation circulation loop, 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 working liquid, the heat collection main control valve 31 and the circulating pump a14 are closed.

[0077] When working, the system has a heating circulation loop and a heat dissipation circulation loop.

[0078] The circulating pump b32 is opened, the heat dissipation circulation control valve 33 is opened, the first heat collection control valve 23 and the second heat collection control valve 24 corresponding to each group of heat collection pipes are opened, the working liquid enters the heat collection liquid inlet 51 of each group of heat collection pipes through the liquid distributor 21, and flows out from the heat collection liquid outlet 52 to gather in the liquid collector 22 to form a heating circulation loop; during the heating circulation, the working liquid absorbs the geothermal heat in the middle-deep heat storage layer to heat it up.

[0079] When the second temperature sensor 53 corresponding to each group of heat collection pipes reaches the set value, it is considered that the working liquid has absorbed enough geothermal heat at this time, which 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, so that the heat dissipation circulation loop of the working liquid is communicated with the heating circulation loop, and the heated working liquid is pumped into the heat dissipation pipe 4 by the circulating pump b32.

[0080] The working liquid heats the natural gas hydrate reservoir area where the heat dissipation pipe 4 is located, the pressure pump in the depressurization module works, and the natural gas hydrate is mined by the depressurization method; specifically: the heated working liquid enters the heat pipe from the heat dissipation liquid inlet 41, and flows out from the heat dissipation liquid outlet 42 in turn through each group of heat dissipation branch pipes 43, during which the carried geothermal heat is released into the natural gas hydrate reservoir, the area where the horizontal pipe in the depressurization module is located is heated up, thereby accelerating the gas methane obtained by the depressurization module, avoiding the secondary synthesis of hydrate during the depressurization mining, and improving the mining efficiency.

[0081] 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 enough to support the depressurization method to mine natural gas hydrate, then the first heat dissipation control valve 35 and the second heat dissipation control valve 36 are closed, and the heat dissipation circulation loop of the working liquid is no longer communicated with the heating circulation loop.

[0082] The decomposed hydrate enters 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.

[0083] As a further embodiment, a monitoring unit 10 is provided in the offshore platform 1 for monitoring the working conditions of the circulating pumps and control valves in the system. The monitoring unit 10 is a mature prior art and is not limited to a specific structure type. For example, it can be a data collector.

[0084] The present scheme uses geothermal energy to heat the temperature of the natural gas hydrate reservoir, avoiding the heat loss in the liquid transportation process when using thermal stimulation method, forming a combined exploitation of depressurization method and thermal stimulation method, and avoiding the secondary synthesis of hydrates due to temperature drop during depressurization exploitation. Compared with single mode exploitation, the exploitation efficiency is improved.

[0085] Both the heat extraction pipes and the heat dissipation pipes are designed to extend horizontally on the side of the vertical pipes, facilitating construction; the formed radial arrangement type can radiate to the largest possible area, improving the heat extraction and heat dissipation efficiency.

[0086] The heat extraction pipes have multiple layers, and each layer of heat extraction pipes is connected to the liquid distributor and the liquid collector through the corresponding control valve, enabling different numbers of heat extraction pipes to be connected according to the heat demand of depressurization exploitation, and the adjustment is more flexible. At the same time, the depressurization exploitation module and the heat dissipation pipes are both in the natural gas hydrate reservoir, and due to the position and number of the depressurization method exploitation module being unrestricted, the multi-layer heat extraction pipe method makes the position selection of the heat dissipation pipes relatively free during design.

[0087] The working liquid can be water or the liquid in the formation during exploitation, which can be recycled, saving resources and transportation costs.

[0088] Embodiment two:

[0089] A natural gas hydrate combined exploitation method using geothermal energy, comprising the following steps:

[0090] The circulating 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 circulating pump b through the liquid collector;

[0091] 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 communicated with the temperature rising circulation loop, the working liquid after heat absorption is pumped into the heat dissipation pipes to heat the natural gas hydrate reservoir, and the pressure pump in the depressurization exploitation module works to exploit the natural gas hydrate by depressurization method;

[0092] 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 communicated with the temperature rising circulation loop;

[0093] The mined natural gas hydrates pass through a collection pipe and filter into a gas-liquid separator, obtaining the desired gas and liquid.

[0094] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall fall into the scope of protection of the present application.

Claims

1. A natural gas hydrate combined exploitation system using geothermal energy, characterized by, The application relates to a marine operation platform, a gas-water separator and a liquid storage tank for receiving natural gas hydrate produced by a depressurization mining module. The depressurization mining module comprises at least one set of collecting pipes and a pressure pump, the pressure of a natural gas hydrate reservoir in the collecting pipes is changed by the pressure pump to obtain natural gas hydrate. The geothermal energy circulation heating module is arranged in a vertical shaft in a space below the marine operation platform, comprises heat collecting pipes and heat radiating pipes, the heat radiating pipes are arranged in the natural gas hydrate reservoir, the heat collecting pipes are arranged in multiple layers along the depth direction of the heat reservoir, working liquid is arranged in the heat collecting pipes and the heat radiating pipes, the working liquid absorbs geothermal energy in the heat reservoir through the heat collecting pipes, and the geothermal energy is released into the natural gas hydrate reservoir through the heat radiating pipes. The geothermal energy circulation heating module comprises heat collecting input pipes arranged in the vertical shaft and a control valve group connected with the heat collecting input pipes, the control valve group is connected with the heat collecting pipes and the heat radiating pipes to form a temperature rising circulation loop and a heat radiating circulation loop. The control valve group comprises a heat collecting main control valve arranged on the heat collecting input pipes, the outlet of the heat collecting main control valve is connected with the inlet of a circulating pump b, a distributor and a second heat radiating control valve through pipes, the outlet of the circulating pump b is connected with a first heat radiating control valve and a liquid collector after passing through a first temperature sensor, the distributor is connected with a first heat collecting control valve through a pipe, and the liquid collector is connected with a second heat collecting control valve through a pipe. The heat collecting pipes comprise multiple sets of heat collecting branch pipes arranged on the same plane, all the heat collecting branch pipes are closed at one end and fixed on connecting pieces at the other end, each set of heat collecting branch pipes is provided with heat pipes in U shape, the heat pipes in adjacent heat collecting branch pipes are connected end to end, the heat pipes in the first set of heat collecting branch pipes form a heat collecting liquid inlet at the first end, and the heat pipes in the last set of heat collecting branch pipes form a heat collecting liquid outlet at the tail end. The marine operation platform is provided with a circulating pump a for providing power for the working liquid and gas-liquid separators connected with each set of collecting pipes, the gas-liquid separators are connected with a gas storage tank through gas pipes, the inlet of the circulating pump a is connected with the liquid storage tank through a pipe, and the liquid storage tank and all the gas-liquid separators are connected through waste liquid return pipes.

2. The natural gas hydrate combined exploitation system using geothermal energy according to claim 1, characterized in that, The collecting pipes are internally provided with vertical pipes penetrating through overlying mud layers on the seabed and reaching the natural gas hydrate reservoir, the bottom end of the vertical pipes is connected with the outlet of the pressure pump, and the inlet of the pressure pump is connected with 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 gas-liquid separators on the marine operation platform through the horizontal pipe and the vertical pipe, and is sent into the gas storage tank after gas-liquid separation.

3. The natural gas hydrate exploitation system in combination with geothermal energy use according to claim 1, characterized in that, The heat radiating pipes comprise multiple sets of heat radiating branch pipes arranged on the same plane, all the heat radiating branch pipes are closed at one end and fixed on connecting pieces at the other end, each set of heat radiating branch pipes is provided with heat pipes in U shape, the heat pipes in adjacent heat radiating branch pipes are connected end to end, the heat pipes in the first set of heat radiating branch pipes form a heat radiating liquid inlet at the first end, and the heat pipes in the last set of heat radiating branch pipes form a heat radiating liquid outlet at the tail end.

4. The natural gas hydrate exploitation system in combination with geothermal energy use according to claim 1, characterized in that, ​ 5. The natural gas hydrate exploitation system in combination with geothermal energy use according to claim 1, characterized in that, The heating cycle circuit comprises that the circulating pump b drives the working liquid to pass through the distributor into each group of heat collecting pipes, the working liquid flowing out of the heat collecting pipes is collected into the liquid collector, and then returns to the circulating pump b through the opened heat dissipation cycle control valve.

6. The natural gas hydrate exploitation system in combination with geothermal energy use according to claim 1, characterized in that, The heat dissipation cycle circuit comprises that 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 distributor through the opened second heat dissipation control valve, and the working liquid between the distributor and the liquid collector passes through the heat collecting pipe.

7. A method for combined exploitation of natural gas hydrates using geothermal energy, implemented on the basis of a system for combined exploitation of natural gas hydrates according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: The circulating pump b drives the working liquid to pass through the distributor into each group of heat collecting pipes, absorbs the geothermal energy in the heat storage layer, and then returns to the circulating pump b 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 cycle circuit of the working liquid is communicated with the heating cycle circuit, the working liquid after heat absorption is pumped into the heat dissipation pipe to heat the natural gas hydrate reservoir, the pressure pump in the pressure reduction exploitation module works, and the natural gas hydrate is exploited by using 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 cycle circuit of the working liquid is no longer communicated with the heating cycle circuit; The exploited natural gas hydrate enters the gas-liquid separator through the collecting pipeline and the filter, and the required gas and liquid are obtained.

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