Device and method for decomposing natural gas hydrate by using circulating water supply of over-deep geothermal layer

Abstract

The invention relates to a device and method for decomposing natural gas hydrate through circulating water supply of an over-deep geothermal stratum.The device comprises an ocean platform, an exploitation well and a water circulation pipeline, the exploitation well comprises a horizontal part, and the horizontal part of the exploitation well is located in a natural gas hydrate reservoir; the water circulation pipeline comprises a water tank, a deep geothermal layer pipeline, a water inlet pipe part and a water return pipe part; the water inlet pipe part and the water return pipe part respectively penetrate through the natural gas hydrate reservoir; when water in the water circulation pipeline passes through the deep geothermal layer pipeline, geothermal energy is absorbed from the deep geothermal layer, and when the water absorbing the geothermal energy passes through the water inlet pipe part and the water return pipe part corresponding to the natural gas hydrate reservoir, the absorbed geothermal energy is transferred to the natural gas hydrate reservoir, so that natural gas in the natural gas hydrate reservoir is released, and the natural gas hydrate reservoir is used for storing natural gas. The natural gas extraction efficiency of the natural gas hydrate reservoir is improved by reusing the geothermal energy of the deep geothermal layer and heating the natural gas hydrate reservoir.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and specifically to an apparatus and method for decomposing natural gas hydrates using circulating water supply from deep geothermal layers. Background Technology

[0002] Natural gas hydrate is a cage-like crystalline compound formed by water and natural gas molecules in a low-temperature, high-pressure environment. 1 m 3 The decomposition of natural gas hydrates can release approximately 160 m³ of gas. 3 Natural gas. Therefore, it has extremely high energy density. Among the many methods for extracting natural gas hydrates, the depressurization method is recognized as the method with the greatest potential for commercial application. However, the slow decomposition and gas production stage of hydrates is the main production stage of hydrate decomposition gas and occupies more than half of the extraction time. The reasons for the slow gas production at this time are: (1) The pore pressure is basically constant and cannot provide an environment with lower pressure and higher decomposition driving force for hydrates. (2) The sensible heat loss of the reservoir is serious, and the weak heat transfer capacity of the surrounding environment alone cannot provide the large-scale heat required for rapid decomposition of hydrates. Among the many heat injection methods, the significant difference between geothermal energy injection and other traditional heat injection methods such as hot water and hot steam injection is that geothermal energy is a naturally occurring renewable energy source that exists in hot gas, hot water or dry hot rock, while other traditional heat injection methods require the construction of large-scale heating equipment and the consumption of a large amount of fossil energy for heating medium or generating electricity, which increases the extraction cost and also pollutes the ecological environment. Depressurization combined with geothermal energy injection is a method that is expected to achieve both enhanced hydrate decomposition and improved extraction cleanliness and economy in the combined extraction of natural gas hydrates. Reported methods for developing geothermal energy to enhance hydrate decomposition include: (1) using natural or artificial pressure differences to induce the upwelling of geothermal-rich fluids (underlying gas or water) below the hydrate reservoir to the hydrate layer. (2) artificially constructing pipelines connecting the hydrate layer and the geothermal layer, allowing media such as seawater or carbon dioxide to be injected into the hydrate layer after absorbing geothermal energy. Artificially constructing circulating water pipelines connecting the mining platform, the hydrate layer, and the geothermal layer can both utilize circulating water to transport geothermal energy to the hydrate layer and avoid the negative impact of hydrothermal upwelling on the production of hydrate decomposition gas.

[0003] However, the current process of extracting natural gas hydrate reservoirs from deep geothermal layers beneath the seabed cannot utilize the geothermal energy from these deep layers to heat the natural gas hydrate reservoirs, thus limiting extraction efficiency. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide an apparatus and method for decomposing natural gas hydrates using circulating water supply from deep geothermal layers. This addresses the issue that current processes for mining natural gas hydrate reservoirs beneath the seabed and in deep geothermal layers cannot utilize the geothermal energy from these layers to heat the natural gas hydrate reservoirs, thus limiting extraction efficiency.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention discloses an apparatus for decomposing natural gas hydrates using a circulating water supply from a deep geothermal layer, for mining natural gas hydrate reservoirs on the seabed above a deep geothermal layer, wherein the seabed comprises, from top to bottom, an overlying layer, a natural gas hydrate reservoir interlayer, and a deep geothermal layer, characterized in that the apparatus comprises: An offshore platform, floating on the sea surface; A production well includes a vertical section and a horizontal section, with the bottom end of the vertical section and the end of the horizontal section connected, wherein the horizontal section of the production well is located within a natural gas hydrate reservoir; The water circulation pipeline includes a water tank, a deep geothermal layer pipeline, an inlet pipe section, and a return pipe section. The water tank is installed on the offshore platform, and the deep geothermal layer pipeline is installed inside the deep geothermal layer. The inlet and return ends of the deep geothermal layer pipeline are connected to the water tank through the inlet pipe section and the return pipe section, respectively. The inlet pipe and the return pipe pass through the natural gas hydrate reservoir, and both the inlet pipe and the return pipe within the natural gas hydrate reservoir include a horizontal section of the natural gas hydrate reservoir water pipe. When water in the water circulation pipeline passes through the deep geothermal layer pipeline, it absorbs geothermal heat from the deep geothermal layer. After absorbing geothermal heat, the water passes through the inlet pipe and the return pipe corresponding to the natural gas hydrate reservoir, and then transfers the absorbed geothermal heat to the natural gas hydrate reservoir so that the natural gas in the natural gas hydrate reservoir can be released. This method of reusing the geothermal heat of the deep geothermal layer to heat the natural gas hydrate reservoir improves the natural gas extraction efficiency of the natural gas hydrate reservoir.

[0006] Preferably, a water pump is installed inside the water tank, the inlet of the water pump is connected to the interior of the water tank, the outlet of the water pump is connected to the inlet of the water inlet pipe, the outlet of the water inlet pipe is connected to the inlet of the return water pipe through the deep geothermal layer pipe, and the outlet of the return water pipe extends upward into the water tank and is connected to the interior of the water tank.

[0007] Preferably, the wellhead of the production well is connected to the offshore platform via a production manifold. The production manifold is equipped with a gas production monitor, which is used to monitor the gas production rate of natural gas extracted from the production well.

[0008] Preferably, a gas-liquid separator is also provided on the production manifold, and the gas-liquid separator is located on the production manifold between the wellhead of the production well and the gas production monitor.

[0009] Preferably, a second temperature sensor is installed on the deep geothermal layer pipeline; A first temperature sensor is installed at the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe section. A third temperature sensor is installed at the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe in the return water pipe section.

[0010] Preferably, a second regulating valve is provided at the end of the return water end of the deep geothermal layer pipeline; A first regulating valve is installed at the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe in the inlet pipe section, and a third regulating valve is installed at the inlet end of the horizontal section of the natural gas hydrate reservoir water pipe in the return pipe section.

[0011] Preferably, a booster pump is provided at the end of the return water end of the deep geothermal layer pipeline.

[0012] Preferably, the marine platform is equipped with a controller, and the first temperature sensor, the second temperature sensor, the third temperature sensor, the first regulating valve, the second regulating valve, the third regulating valve, and the booster pump are respectively connected to the controller.

[0013] Secondly, the present invention discloses a method for decomposing natural gas hydrates using a circulating water supply from a deep geothermal layer, employing the aforementioned apparatus, and the method includes the following steps: Step S1: With the first regulating valve, the second regulating valve, and the third regulating valve fully open and the booster pump closed, start the water pump to input the water in the water tank into the water circulation pipeline until the water flows back to the water tank, and start the water circulation. Step S2: Close the second regulating valve and the water pump, and monitor the water temperature change in the deep geothermal layer pipeline through the second temperature sensor until the temperature displayed by the second temperature sensor reaches the first temperature set value. Step S3: Open the second regulating valve, water pump and booster pump to increase the flow rate of water circulation in the water circulation pipeline until the temperature monitored by the first temperature sensor reaches the second temperature set value, then close the first regulating valve, the third regulating valve and the booster pump to stop water circulation. Step S4: During the process of stopping water circulation, the hot water in the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe and the return pipe exchanges heat with the natural gas hydrate reservoir, and the temperature of the natural gas hydrate reservoir rises until at least one of the first temperature sensor and the third temperature sensor reaches the third temperature set value. Step S5: Open the first regulating valve and the third regulating valve to restart the water circulation in the water circulation pipeline; Step S6: Repeat steps S2 to S5 until the gas production rate detected by the gas production monitor reaches the set value of the gas production rate.

[0014] Preferably, the first temperature setpoint is higher than the temperature of the natural gas hydrate reservoir; The second temperature setting is 20°C; The temperature difference between the third temperature setpoint and the natural gas hydrate reservoir is less than 5°C. The gas production rate is set to 600 m. 3 / h.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (I) This invention discloses an apparatus for decomposing natural gas hydrates using circulating water supply from a deep geothermal layer, comprising an offshore platform, a production well, and a water circulation pipeline. The offshore platform floats on the sea surface; the production well includes a vertical section and a horizontal section, with the horizontal section located within the natural gas hydrate reservoir; the water circulation pipeline includes a water tank, a deep geothermal layer pipeline, an inlet pipe, and a return pipe. The water tank is located on the offshore platform, and the deep geothermal layer pipeline is located within the deep geothermal layer. The inlet and return ends of the deep geothermal layer pipeline are connected to the water tank via the inlet pipe and return pipe, respectively; wherein, the inlet pipe and return pipe... The pipeline passes through the natural gas hydrate reservoir, and both the inlet and return water sections within the natural gas hydrate reservoir include horizontal sections of the natural gas hydrate reservoir water pipe. When water in the water circulation pipeline passes through the deep geothermal layer pipeline, it absorbs heat from the deep geothermal layer. After absorbing heat, the water passes through the corresponding inlet and return water sections of the natural gas hydrate reservoir and then transfers the heat to the natural gas hydrate reservoir, so that the natural gas in the natural gas hydrate reservoir can be released. This method of reusing the heat from the deep geothermal layer to heat the natural gas hydrate reservoir improves the natural gas extraction efficiency of the natural gas hydrate reservoir.

[0016] (II) This invention discloses a method for decomposing natural gas hydrates by using circulating water supply from deep geothermal layers. On the one hand, the geothermal energy from the deep geothermal layer is used to heat the natural gas hydrate reservoir through a water circulation pipeline. On the other hand, the temperature of the natural gas hydrate reservoir and the deep geothermal layer is monitored in real time by a temperature sensor. The water circulation pipeline is then opened according to the actual working conditions. While achieving extraction efficiency, attention is paid to reducing energy consumption so as to better control the circulating water rate to achieve a balance between extraction efficiency and energy consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the device provided in Embodiment 1 of the present invention, which utilizes circulating water supply from deep geothermal layers to decompose natural gas hydrates, applied to a seafloor stratum.

[0018] Explanation of reference numerals in the attached figures: 1-Offshore platform; 2-Production well, 20-Gas production monitor, 21-Gas-liquid separator; 31-Water tank, 32-Deep geothermal layer pipe, 33-Inlet pipe section, 34-Return pipe section; T1 - First temperature sensor, T2 - Second temperature sensor, T3 - Third temperature sensor; D1 - First regulating valve, D2 - Second regulating valve, D3 - Third regulating valve; w-Boost pump. Detailed Implementation

[0019] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0020] Example 1: A device for decomposing natural gas hydrates using circulating water supply from deep geothermal layers. Embodiment 1 of the present invention provides a device for decomposing natural gas hydrates by utilizing the circulating water supply from deep geothermal layers. Its structure is described in detail below.

[0021] refer to Figure 1 This device, which utilizes circulating water from a deep geothermal layer to decompose natural gas hydrates, is used to extract natural gas hydrate reservoirs beneath the seabed and above a deep geothermal layer. The seabed, from top to bottom, comprises an overlying layer, a natural gas hydrate reservoir interlayer, and a deep geothermal layer. The device includes: A marine platform 1, floating on the sea surface; A production well 2 includes a vertical section and a horizontal section, with the bottom end of the vertical section and the end end of the horizontal section connected. The horizontal section of the production well 2 is located within a natural gas hydrate reservoir. A water circulation pipeline includes a water tank 31, a deep geothermal layer pipeline 32, an inlet pipe section 33, and a return pipe section 34. The water tank 31 is installed on the offshore platform, and the deep geothermal layer pipeline 32 is installed inside the deep geothermal layer. The inlet and return ends of the deep geothermal layer pipeline are connected to the water tank 31 through the inlet pipe section 33 and the return pipe section 34, respectively. The inlet pipe section 33 and the return pipe section 34 pass through the natural gas hydrate reservoir, and both the inlet pipe section 33 and the return pipe section 34 within the natural gas hydrate reservoir include a horizontal section of the natural gas hydrate reservoir water pipe.

[0022] When the water in the water circulation pipeline passes through the deep geothermal layer pipeline 32, it absorbs geothermal heat from the deep geothermal layer. After absorbing geothermal heat, the water passes through the inlet pipe section 33 and the return pipe section 34 corresponding to the natural gas hydrate reservoir, and then transfers the absorbed geothermal heat to the natural gas hydrate reservoir so that the natural gas in the natural gas hydrate reservoir can be released. This method of reusing the geothermal heat of the deep geothermal layer to heat the natural gas hydrate reservoir improves the natural gas extraction efficiency of the natural gas hydrate reservoir.

[0023] Specifically, a water pump is installed inside the water tank 31. The inlet of the water pump is connected to the interior of the water tank 31, and the outlet of the water pump is connected to the inlet of the water inlet pipe 33. The outlet of the water inlet pipe 33 is connected to the inlet of the return water pipe 34 through the deep geothermal layer pipe 32. The outlet of the return water pipe 34 extends upward into the water tank 31 and is connected to the interior of the water tank 31.

[0024] In one specific implementation, the wellhead of the production well 2 is connected to the offshore platform via a production manifold, and a gas production monitor 20 is installed on the production manifold to monitor the gas production rate of the natural gas extracted from the production well 2.

[0025] In order to separate the gas-liquid mixture containing natural gas hydrate extracted from the natural gas hydrate reservoir into natural gas gas and liquid, a gas-liquid separator 21 is also installed on the production manifold. The gas-liquid separator 21 is located on the production manifold between the wellhead of the production well 2 and the gas production monitor 20.

[0026] In order to monitor the temperature on the deep geothermal layer pipeline 32, a second temperature sensor T2 is installed on the deep geothermal layer pipeline 32 to monitor the temperature of the water in the deep geothermal layer pipeline 32 after absorbing heat from the deep geothermal layer in real time. In order to monitor the temperature of the water in the inlet pipe section 33 of the natural gas hydrate reservoir, a first temperature sensor T1 is installed on the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe section 33.

[0027] In order to monitor the temperature of the water in the return water pipe section 34 of the natural gas hydrate reservoir, a third temperature sensor T3 is installed at the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the return water pipe section 34.

[0028] The first temperature sensor T1 and the third temperature sensor T3 are used to monitor the temperature of the water in the inlet pipe section 33 and the return pipe section 34 of the natural gas hydrate reservoir, respectively.

[0029] In order to facilitate continuous heating of the water in the deep geothermal layer pipeline 32, a second regulating valve D2 is provided at the end of the return water end of the deep geothermal layer pipeline 32. In order to continuously transfer the heat of the water in the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe section 33 and the return pipe section 34 to the natural gas hydrate reservoir, a first regulating valve D1 is provided at the end of the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe section 33, and a third regulating valve D3 is provided at the end of the inlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the return pipe section 34.

[0030] In order to allow the water flow through the second regulating valve D2 to quickly reach the horizontal section of the natural gas hydrate reservoir water pipe in the return water section 34, a booster pump w is installed at the end of the return water end of the deep geothermal layer pipe 32.

[0031] To facilitate the control of temperature sensors, regulating valves, and booster pumps on the offshore platform 1, a controller is provided on the offshore platform 1. The first temperature sensor T1, the second temperature sensor T2, the third temperature sensor T3, the first regulating valve D1, the second regulating valve D2, the third regulating valve D3, and the booster pump W are respectively connected to the controller.

[0032] Example 2: A method for decomposing natural gas hydrates using circulating water supply from deep geothermal layers. Embodiment 2 of the present invention provides a method for decomposing natural gas hydrates using circulating water supply from deep geothermal layers. The method employs the apparatus of Embodiment 1. Before using the apparatus, the natural gas hydrate reservoir surrounding the production well is first depressurized. Then, the gas production rate of the natural gas extracted from the production well is monitored by a gas production monitor 20. If the gas production rate monitored by the gas production monitor 20 is less than a set gas production rate value, for example, 600 m³ / s, the method is called to determine the appropriate method. 3 / h, then proceed with the following steps: Step S1: Make the first regulating valve D1, the second regulating valve D2 and the third regulating valve D3 fully open and keep the booster pump w in the closed state, start the water pump, input the water in the water tank 31 into the water circulation pipeline until the water flows back to the water tank 31, and start the water circulation. Step S2: Close the second regulating valve D2 and the water pump, and monitor the water temperature change in the deep geothermal layer pipeline 32 through the second temperature sensor T2 until the temperature displayed by the second temperature sensor T2 reaches the first temperature set value, wherein the first temperature set value is higher than the temperature of the natural gas hydrate reservoir. Step S3: Open the second regulating valve D2, the water pump and the booster pump w to increase the flow rate of water circulation in the water circulation pipeline until the temperature monitored by the first temperature sensor T1 reaches the second temperature set value, for example, 20°C. Then close the first regulating valve D1, the third regulating valve D3 and the booster pump w to stop water circulation. Step S4: During the process of stopping water circulation, the hot water in the horizontal section of the water pipe of the natural gas hydrate reservoir in the water inlet pipe 33 and the water return pipe 34 exchanges heat with the natural gas hydrate reservoir, and the temperature of the natural gas hydrate reservoir rises until at least one of the first temperature sensor T1 and the third temperature sensor T3 reaches the third temperature set value. Specifically, the temperature difference between the third temperature set value and the temperature of the natural gas hydrate reservoir is less than 5°C. Step S5: Open the first regulating valve D1 and the third regulating valve D3 to restart the water circulation in the water circulation pipeline; Step S6: Repeat steps S2 to S5 until the gas production rate detected by the gas production monitor 20 reaches the set gas production rate value, for example, 600m³ / h. 3 / h.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An apparatus for decomposing natural gas hydrates using circulating water supply from a deep geothermal layer, used for mining natural gas hydrate reservoirs within the seabed and above a deep geothermal layer, wherein the seabed comprises, from top to bottom, an overlying layer, a natural gas hydrate reservoir interlayer, and a deep geothermal layer, characterized in that, The device includes: The offshore platform (1) floats on the sea surface; A production well (2) includes a vertical section and a horizontal section, with the bottom end of the vertical section and the end of the horizontal section connected together, wherein the horizontal section of the production well (2) is located within a natural gas hydrate reservoir; The water circulation pipeline includes a water tank (31), a deep geothermal layer pipeline (32), an inlet pipe (33), and a return pipe (34). The water tank (31) is installed on the offshore platform, and the deep geothermal layer pipeline (32) is installed in the deep geothermal layer. The inlet and return ends of the deep geothermal layer pipeline are connected to the water tank (31) through the inlet pipe (33) and the return pipe (34), respectively. The water inlet pipe (33) and the water return pipe (34) pass through the natural gas hydrate reservoir, and both the water inlet pipe (33) and the water return pipe (34) in the natural gas hydrate reservoir include a horizontal section of the natural gas hydrate reservoir water pipe. When the water in the water circulation pipeline passes through the deep geothermal layer pipeline (32), it absorbs geothermal heat from the deep geothermal layer. After absorbing geothermal heat, the water passes through the inlet pipe (33) and return pipe (34) corresponding to the natural gas hydrate reservoir, and then transfers the absorbed geothermal heat to the natural gas hydrate reservoir so that the natural gas in the natural gas hydrate reservoir can be released. This method of reusing the geothermal heat of the deep geothermal layer to heat the natural gas hydrate reservoir improves the natural gas extraction efficiency of the natural gas hydrate reservoir.

2. The apparatus according to claim 1, characterized in that, A water pump is installed inside the water tank (31). The inlet of the water pump is connected to the interior of the water tank (31). The outlet of the water pump is connected to the inlet of the water inlet pipe (33). The outlet of the water inlet pipe (33) is connected to the inlet of the return water pipe (34) through the deep geothermal layer pipe (32). The outlet of the return water pipe (34) extends upward into the water tank (31) and is connected to the interior of the water tank (31).

3. The apparatus according to claim 2, characterized in that, The wellhead of the production well (2) is connected to the offshore platform via a production manifold. A gas production monitor (20) is installed on the production manifold, which is used to monitor the gas production rate of natural gas extracted from the production well (2).

4. The apparatus according to claim 3, characterized in that, A gas-liquid separator (21) is also installed on the production manifold, which is located on the production manifold between the wellhead of the production well (2) and the gas production monitor (20).

5. The apparatus according to claim 3, characterized in that, A second temperature sensor (T2) is installed on the deep geothermal layer pipeline (32); A first temperature sensor (T1) is installed on the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe (33). A third temperature sensor (T3) is installed at the outlet end of the horizontal section of the natural gas hydrate reservoir water pipe of the return water pipe section (34).

6. The apparatus according to claim 5, characterized in that, A second regulating valve (D2) is provided at the end of the return water end of the deep geothermal pipeline (32). The end of the outlet of the horizontal section of the natural gas hydrate reservoir water pipe of the inlet pipe section (33) is provided with a first regulating valve (D1), and the end of the inlet of the horizontal section of the natural gas hydrate reservoir water pipe of the return pipe section (34) is provided with a third regulating valve (D3).

7. The apparatus according to claim 6, characterized in that, A booster pump (w) is installed at the end of the return water end of the deep geothermal pipeline (32).

8. The apparatus according to claim 7, characterized in that, The marine platform (1) is equipped with a controller, and the first temperature sensor (T1), the second temperature sensor (T2), the third temperature sensor (T3), the first regulating valve (D1), the second regulating valve (D2), the third regulating valve (D3), and the booster pump (w) are respectively connected to the controller.

9. A method for decomposing natural gas hydrates using a circulating water supply from a deep geothermal layer, employing the apparatus of claim 8, the method comprising the following steps: Step S1: Make the first regulating valve (D1), the second regulating valve (D2) and the third regulating valve (D3) fully open and keep the booster pump (w) closed. Start the water pump to input the water in the water tank (31) into the water circulation pipeline until the water flows back to the water tank (31) and start the water circulation. Step S2: Close the second regulating valve (D2) and the water pump, and monitor the water temperature change in the deep geothermal layer pipeline (32) through the second temperature sensor (T2) until the temperature displayed by the second temperature sensor (T2) reaches the first temperature set value; Step S3: Open the second regulating valve (D2), water pump and booster pump (w) to increase the flow rate of water circulation in the water circulation pipeline until the temperature monitored by the first temperature sensor (T1) reaches the second temperature set value, then close the first regulating valve (D1), the third regulating valve (D3) and the booster pump (w) to stop water circulation; Step S4: During the process of stopping water circulation, the hot water in the horizontal section of the water pipe of the natural gas hydrate reservoir in the water inlet pipe (33) and the water return pipe (34) exchanges heat with the natural gas hydrate reservoir, and the temperature of the natural gas hydrate reservoir rises until at least one of the first temperature sensor (T1) and the third temperature sensor (T3) reaches the third temperature set value. Step S5: Open the first regulating valve (D1) and the third regulating valve (D3) to restart the water circulation in the water circulation pipeline; Step S6: Repeat steps S2 to S5 until the gas production rate detected by the gas production monitor (20) reaches the set value of the gas production rate.

10. The method according to claim 9, characterized in that, The first temperature setpoint is higher than the temperature of the natural gas hydrate reservoir; The second temperature setting is 20°C; The temperature difference between the third temperature setpoint and the natural gas hydrate reservoir is less than 5°C. The gas production rate is set to 600 m. 3 / h.

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