Method and system for exploiting hydrates through super-long gravity assisted heat pipe assisted depressurization

Abstract

The invention belongs to the technical field of natural gas hydrate (combustible ice) exploitation, and particularly relates to a method and system for exploiting hydrates through super-long gravity assisted heat pipes in a depressurization mode. According to the invention, the offshore drilling platform is used for drilling the open hole well, the super-long gravity heat pipe is placed in the open hole well, one section of the super-long gravity heat pipe is arranged in the high-temperature lower coating, and the other section of the super-long gravity heat pipe is arranged in the hydrate reservoir or the ice-containing shallow layer, so that the working medium in the super-long gravity heat pipe is driven to circulate through the high temperature of the lower coating; the heat of the lower covering layer is continuously transmitted to the hydrate reservoir or the ice-containing shallow layer to be dissipated, so that the temperature of the hydrate reservoir or the ice-containing shallow layer is increased, the phase balance of the hydrate is broken, the hydrate is decomposed to produce gas, and the natural gas is transmitted to a natural gas collecting tank on the offshore drilling platform through the vertical well to be stored, so that the effect of exploiting the natural gas hydrate is achieved.

Description

Technical Field

[0001] This invention belongs to the field of natural gas hydrate (combustible ice) extraction technology, specifically relating to a method and system for depressurization extraction of hydrates assisted by an ultra-long gravity heat pipe. Background Technology

[0002] Currently, the mainstream extraction methods include depressurization, thermal activation, and chemical inhibitors. Among them, depressurization may lead to reservoir icing and blockage of flow channels; thermal activation, if it uses direct injection of hot fluid, has low thermal energy utilization efficiency and may damage reservoir stability; chemical inhibitors are costly and may pollute the environment.

[0003] Gravity heat pipes are highly efficient two-phase heat transfer devices that rely on the phase change of the working fluid and gravity-driven circulation to transfer enormous amounts of heat without the need for external pumps. However, conventional heat pipes have limited length, and their application in the exploitation of hydrate reservoirs at depths of hundreds to thousands of meters has not yet been proposed. Therefore, a new, efficient, stable, environmentally friendly, and precisely controllable exploitation technology is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a method and system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization.

[0005] To address the problems existing in the prior art, the present invention adopts the following technical solution: A method for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization includes the following steps: Drilling open-hole wells deep into the underlying overburden on offshore drilling platforms; An ultra-long gravity heat pipe system was fabricated, and a working fluid was injected into the ultra-long gravity heat pipe in the ultra-long gravity heat pipe system; An ultra-long gravity heat pipe filled with working fluid is lowered into an open-hole well, with one section placed in the overburden and the other in the hydrate reservoir or shallow ice-bearing layer. The temperature in the overburden drives the working fluid inside the ultra-long gravity heat pipe to circulate within it, backfilling the open-hole well and forming a backfill section to prevent natural gas leaks from hydrate decomposition along the wellbore. The heat from the overburden is transferred to the hydrate reservoir or shallow ice-bearing layer for dissipation, raising the temperature of the hydrate reservoir or shallow ice-bearing layer, thereby decomposing the hydrates in the hydrate reservoir or shallow ice-bearing layer into natural gas. Vertical and horizontal wells extending to the hydrate reservoir are drilled using an offshore drilling platform to complete cementing and well completion operations. Natural gas generated from hydrate decomposition is collected through an offshore gas production system.

[0006] As an improvement to the technical solution of the method for depressurization-assisted extraction of hydrates using an ultra-long gravity heat pipe according to the present invention, the method further includes the following steps: Repeat the above steps to drill multiple open-hole wells on the offshore drilling platform, with each open-hole well corresponding to the placement of an ultra-long gravity heat pipe; and drill multiple horizontal wells, all connected to the vertical wells, in the hydrate reservoir or ice-bearing shallow layer to collect natural gas decomposed from hydrates in the hydrate reservoir or ice-bearing shallow layer.

[0007] As an improvement to the technical solution of the method for depressurization extraction of hydrates assisted by ultra-long gravity heat pipes of the present invention, in the step of collecting natural gas through an offshore gas production system, the subsea gas production tree of the offshore gas production system is connected to vertical wells and horizontal wells, the subsea gas production tree is connected to a depressurization pump through a gas production pipeline, and the depressurization pump is connected to a natural gas collection tank. The natural gas produced by decomposition is transported to the natural gas collection tank through the subsea gas production tree, the gas production pipeline and the depressurization pump.

[0008] As an improvement to the technical solution of the method for depressurization mining of hydrates assisted by ultra-long gravity heat pipes of the present invention, in the step of preparing an ultra-long gravity heat pipe system, multiple gravity heat pipe segments are spliced ​​together by heat pipe connecting sections to form an ultra-long gravity heat pipe system. The airtightness of the spliced ​​ultra-long gravity heat pipe system is checked, and a working medium is injected into the system through the working medium injection interface to complete the sealing.

[0009] A system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization includes: An offshore gas production system includes an offshore drilling platform, a gas production channel, and a natural gas collection tank. The gas production channel includes interconnected gas production pipelines, vertical wells, and horizontal wells. An ultra-long gravity heat pipe system, comprising at least one ultra-long gravity heat pipe equipped with a working fluid injection port; At least one open-hole well is drilled using the offshore drilling platform for deploying the ultra-long gravity heat pipe. After the ultra-long gravity heat pipe is deployed, part of it is placed in the underlying layer and the other part is placed in the hydrate reservoir or ice-bearing shallow layer. The heat from the underlying layer is transferred to the hydrate reservoir or ice-bearing shallow layer through the ultra-long gravity heat pipe. The heat decomposes the hydrate reservoir or ice-bearing shallow layer into natural gas, which is then transported to the natural gas collection tank through the gas production channel.

[0010] As an improvement to the technical solution of the system for assisted depressurization mining of hydrates using ultra-long gravity heat pipes of the present invention, the offshore gas production system also includes a pressure reducing pump, and the gas production channel also includes an underwater gas production tree for controlling the gas flow in the open hole well. The vertical well extends through the overlying layer into the hydrate layer. The horizontal well is located within the hydrate layer and communicates with the vertical well. The subsea gas production tree is connected to the wellhead of the vertical well. The subsea gas production tree is connected to the pressure reducing pump via a gas production pipeline. The pressure reducing pump is connected to the natural gas collection tank. Both the natural gas collection tank and the pressure reducing pump are fixedly installed on the offshore gas production platform.

[0011] As an improvement to the technical solution of the system for depressurization mining of hydrates assisted by ultra-long gravity heat pipes of the present invention, the system for depressurization mining of hydrates assisted by ultra-long gravity heat pipes also includes a monitoring and control system. The monitoring and control system includes a temperature sensor, a pressure sensor, a pressure reducing pump control system, and a flare system. The temperature sensor and pressure sensor are respectively installed downhole and at the wellhead. The signal output terminals of the temperature sensor and pressure sensor are connected to the signal input terminals of the pressure reducing pump control system to transmit the collected temperature and pressure data to the pressure reducing pump control system. The control output terminal of the pressure reducing pump control system is connected to the control input terminal of the pressure reducing pump to adjust the operating parameters of the pressure reducing pump. The flare system is connected to the natural gas collection tank to process excess natural gas.

[0012] As an improvement to the technical solution of the system for depressurization mining of hydrates assisted by ultra-long gravity heat pipes of the present invention, a backfill section is provided in the annulus area of ​​the open hole well. The backfill section is densely filled between the ultra-long gravity heat pipe system and the well wall of the open hole well to block the gas leakage channel.

[0013] As an improvement to the technical solution of the system for depressurization mining of hydrates assisted by ultra-long gravity heat pipes of the present invention, multiple sets of ultra-long gravity heat pipe systems are set up and respectively lowered into multiple open-hole wells in the target mining area. The multiple sets of ultra-long gravity heat pipe systems are equidistantly distributed in the hydrate layer.

[0014] As an improvement to the technical solution of the system for assisted pressure reduction mining of hydrates using an ultra-long gravity heat pipe of the present invention, the ultra-long gravity heat pipe system includes: a working fluid injection interface, a working fluid, an insulation layer, an outer shell, and a heat pipe body. The working fluid injection interface is fixedly installed at the top of the heat pipe body. The working fluid is filled inside the heat pipe body. The insulation layer is wrapped around the outer surface of the insulation section of the heat pipe body. The outer shell is fitted over the insulation layer. The ultra-long gravity heat pipe is made of high-strength titanium alloy and has spiral fins welded to its outer wall to enhance heat exchange.

[0015] The beneficial effects of this invention are: 1. In this invention, an open-hole well is drilled using an offshore drilling platform, and an ultra-long gravity heat pipe is placed in the open-hole well. One end of the ultra-long gravity heat pipe is placed in a high-temperature overburden layer, and the other end is placed in a hydrate reservoir or ice-containing shallow layer. The high temperature of the overburden layer drives the circulation of the working fluid inside the ultra-long gravity heat pipe, continuously transferring the heat of the overburden layer to the hydrate reservoir or ice-containing shallow layer for dissipation. This causes the hydrate reservoir or ice-containing shallow layer to heat up, breaking the phase equilibrium of the hydrate and causing it to decompose and produce gas. The natural gas is then transported through a vertical well to a natural gas collection tank on the offshore drilling platform for storage, thereby achieving the effect of extracting natural gas hydrates.

[0016] 2. In this invention, the latent heat of phase change of the working fluid and gravity-driven circulation are used to efficiently transport deep heat to the surface. Theoretically, only a small amount of cooling system power is consumed, and the energy utilization efficiency far exceeds that of the traditional hot fluid injection method.

[0017] 3. In this invention, there is no large-scale fluid injection or extraction, which maximizes the maintenance of reservoir geomechanical stability, reduces the risk of sand production and formation collapse, and the closed-loop system operation of this invention greatly reduces the risk of methane leakage and formation contamination.

[0018] 4. The ultra-long gravity heat pipe has no moving parts, has a simple structure, high reliability, and is suitable for long-term, unattended operation in the deep sea or remote areas. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention.

[0020] Explanation of reference numerals in the attached diagram: 1 - Offshore drilling platform; 2 - Natural gas collection tank; 3 - Monitoring and control system; 4 - Pressure reducing pump; 5 - Gas production pipeline; 6 - Subsea gas tree; 7 - Vertical well; 8 - Backfill section; 9 - Horizontal well; 10 - Working fluid injection interface; 11 - Working fluid; 12 - Insulation layer; 13 - Heat pipe connection; 14 - Heat. Detailed Implementation

[0021] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0022] To improve the extraction efficiency of natural gas hydrates, this invention provides a method for depressurization extraction of hydrates assisted by an ultra-long gravity heat pipe, comprising the following steps: Drill an open-hole well into the underlying overburden on offshore drilling platform 1; An ultra-long gravity heat pipe system was prepared, and working fluid 11 was injected into the ultra-long gravity heat pipe in the ultra-long gravity heat pipe system; An ultra-long gravity heat pipe filled with working fluid 11 is lowered into an open-hole well, with one section placed in the overburden and the other in the hydrate reservoir or ice-bearing shallow layer. The temperature in the overburden drives the working fluid 11 inside the ultra-long gravity heat pipe to circulate within the pipe, backfilling the open-hole well and forming a backfill section 8 to prevent natural gas from leaking along the wellbore. The heat 14 from the overburden is transferred to the hydrate reservoir or ice-bearing shallow layer for dissipation, raising the temperature of the hydrate reservoir or ice-bearing shallow layer, thereby decomposing the hydrates in the hydrate reservoir or ice-bearing shallow layer into natural gas. Vertical wells 7 and horizontal wells 9 extending to the hydrate reservoir are drilled using an offshore drilling platform 1 to complete cementing and well completion operations. Natural gas generated from hydrate decomposition is collected through an offshore gas production system.

[0023] In this invention, an open-hole well is drilled using an offshore drilling platform 1, and an ultra-long gravity heat pipe is lowered into the open-hole well. One end of the ultra-long gravity heat pipe is placed in a high-temperature overburden layer, and the other end is placed in a hydrate reservoir or ice-containing shallow layer. The high temperature of the overburden layer drives the circulation of the working fluid 11 inside the ultra-long gravity heat pipe, continuously transferring the heat 14 of the overburden layer to the hydrate reservoir or ice-containing shallow layer for dissipation. This causes the hydrate reservoir or ice-containing shallow layer to heat up, breaking the phase equilibrium of the hydrate and causing it to decompose and produce gas. The natural gas is then transported through a vertical well 7 to a natural gas collection tank 2 on the offshore drilling platform 1 for storage, thereby achieving the effect of extracting natural gas hydrates.

[0024] It should be noted that this invention utilizes ultra-long gravity heat pipes applied at the meter level to the thousands of meters of geothermal extraction, thereby achieving efficient and pump-free heat extraction. In this invention, ultra-long gravity heat pipes are used to penetrate deep into the high-temperature region of the underlying layer to obtain higher and more heat.

[0025] In some embodiments of the present invention, the method for depressurization extraction of hydrates using ultra-long gravity heat pipes further includes the following steps: Repeat the above steps to drill multiple open-hole wells on offshore drilling platform 1, with each open-hole well corresponding to the placement of an ultra-long gravity heat pipe; and drill multiple horizontal wells 9 in the hydrate reservoir or ice-bearing shallow layer, all of which are connected to the vertical well 7, to collect the natural gas decomposed from the hydrate in the hydrate reservoir or ice-bearing shallow layer.

[0026] In detail, as a specific embodiment of the method for depressurization mining of hydrates assisted by ultra-long gravity heat pipes of the present invention, when the present invention is implemented, an open-hole well is first drilled using an offshore drilling platform 1, and sections of manufactured gravity heat pipes are connected into an ultra-long gravity heat pipe through heat pipe connection 13.

[0027] An airtightness test was performed on the ultra-long gravity heat pipe. After the test was passed, working medium 11 was injected into the ultra-long gravity heat pipe through the working medium injection port 10. Then the ultra-long gravity heat pipe was sealed. After sealing, the ultra-long gravity heat pipe was lowered into the open hole well, with one section of the ultra-long gravity heat pipe placed in the high-temperature region of the underlying layer and the other section located in the hydrate reservoir or ice-bearing shallow layer.

[0028] Backfilling the open hole creates a backfill section 8 within it. The backfill section 8 helps maintain the ultra-long gravity heat pipe in a compacted state, preventing leakage after the hydrates decompose into natural gas.

[0029] The working fluid 11 inside an ultra-long gravity heat pipe placed in the high-temperature region of the underlying layer absorbs heat 14 through the high-temperature stratum and is driven to circulate (the circulation process includes evaporation, rising, condensation and reflux). This continuously "extracts" the heat 14 from the underlying layer to the hydrate reservoir or ice-containing shallow layer, thereby raising the temperature of the hydrate reservoir or ice-containing shallow layer, breaking the hydrate phase equilibrium, and causing the hydrate to decompose and produce natural gas.

[0030] Drill another vertical well 7 on the offshore drilling platform 1 into the hydrate reservoir or ice-bearing shallow layer. The vertical well 7 is connected to the natural gas collection tank 2 through the gas production pipeline 5. Finally, after cementing and well completion, natural gas is collected through the gas production channel to achieve the effect of natural gas hydrate extraction.

[0031] To further improve the efficiency of extraction and collection, two or more open-hole wells are drilled on the offshore drilling platform 1. As a specific embodiment of the method for depressurization extraction of hydrates assisted by ultra-long gravity heat pipes of the present invention, according to the actual operation, four open-hole wells are drilled on the offshore drilling platform 1, and the above steps are repeated to install and lower four ultra-long gravity heat pipes. In addition, multiple horizontal wells 9 connected to the vertical well 7 are drilled according to the resource volume. Finally, after cementing and well completion, natural gas is collected into the natural gas collection tank 2 through the gas production channel.

[0032] In some embodiments of the present invention, in the step of collecting natural gas through an offshore gas production system, the subsea gas production tree 6 of the offshore gas production system is connected to the vertical well 7 and the horizontal well 9. The subsea gas production tree 6 is connected to the pressure reducing pump 4 through the gas production pipeline 5. The pressure reducing pump 4 is connected to the natural gas collection tank 2. The natural gas produced by decomposition is transported to the natural gas collection tank 2 through the subsea gas production tree 6, the gas production pipeline 5 and the pressure reducing pump 4.

[0033] The subsea gas production tree 6 is used to control the gas flow in the open hole well. Its structure is similar to conventional technology, mainly including a main valve, a wing valve, a throttle valve, a pressure gauge, and pipelines, which will not be described in detail here. The subsea gas production tree 6 connects the vertical well 7 and the offshore drilling platform 1.

[0034] In some embodiments of the present invention, in the step of preparing an ultra-long gravity heat pipe system, an ultra-long gravity heat pipe system is formed by splicing multiple gravity heat pipes by connecting 13 sections of heat pipes, and an airtightness check is performed on the spliced ​​ultra-long gravity heat pipe system. After the working fluid 11 is injected into the ultra-long gravity heat pipe system through the working fluid injection port 10, the system is sealed.

[0035] Another aspect of the present invention provides a system for depressurization extraction of hydrates using an ultra-long gravity heat pipe, comprising: The offshore gas production system includes an offshore drilling platform 1, a gas production channel and a natural gas collection tank 2. The gas production channel includes interconnected gas production pipelines 5, vertical wells 7 and horizontal wells 9. An ultra-long gravity heat pipe system, comprising at least one ultra-long gravity heat pipe equipped with a working fluid injection interface 10; At least one open-hole well is drilled using an offshore drilling platform 1 for the placement of an ultra-long gravity heat pipe. After the ultra-long gravity heat pipe is placed, part of it is placed in the underlying layer and the other part is placed in the hydrate reservoir or ice-bearing shallow layer. The heat 14 of the underlying layer is transferred to the hydrate reservoir or ice-bearing shallow layer through the ultra-long gravity heat pipe. The heat 14 decomposes into natural gas in the hydrate reservoir or ice-bearing shallow layer and the natural gas is transported to the natural gas collection tank 2 through the gas production channel.

[0036] In some embodiments of the present invention, the offshore gas production system further includes a pressure reducing pump 4, and the gas production channel further includes a subsea gas production tree 6 for controlling the gas flow in the open hole well. Vertical well 7 extends through the overlying layer into the hydrate layer. Horizontal well 9 is located in the hydrate layer and communicates with vertical well 7. Subsea gas production tree 6 is connected to the wellhead of vertical well 7. Subsea gas production tree 6 is connected to pressure reducing pump 4 through gas production pipeline 5. Pressure reducing pump 4 is connected to natural gas collection tank 2. Natural gas collection tank 2 and pressure reducing pump 4 are both fixedly installed on the offshore gas production platform.

[0037] In some embodiments of the present invention, the system for assisted depressurization mining of hydrates using ultra-long gravity heat pipes also includes a monitoring and control system 3; The monitoring and control system 3 includes a temperature sensor, a pressure sensor, a pressure reducing pump 4 control system, and a flare system. The temperature sensor and pressure sensor are respectively installed downhole and at the wellhead. The signal output terminals of the temperature sensor and pressure sensor are connected to the signal input terminals of the pressure reducing pump 4 control system to transmit the collected temperature and pressure data to the pressure reducing pump 4 control system. The control output terminal of the pressure reducing pump 4 control system is connected to the control input terminal of the pressure reducing pump 4 to adjust the operating parameters of the pressure reducing pump 4. The flare system is connected to the natural gas collection tank 2 to process excess natural gas.

[0038] In some embodiments of the present invention, a backfill section 8 is provided in the annular region of the open hole well. The backfill section 8 is densely filled between the ultra-long gravity heat pipe system and the well wall of the open hole well to block the gas leakage channel.

[0039] In some embodiments of the present invention, multiple sets of ultra-long gravity heat pipe systems are provided, and the multiple sets of ultra-long gravity heat pipe systems are respectively deployed into multiple open-hole wells within the target mining area, and the multiple sets of ultra-long gravity heat pipe systems are equidistantly distributed within the hydrate layer.

[0040] In some embodiments of the present invention, the ultra-long gravity heat pipe system includes: a working fluid injection port 10, a working fluid 11, an insulation layer 12, an outer shell, and a heat pipe body. The working fluid injection port 10 is fixedly disposed at the top of the heat pipe body, the working fluid 11 is filled inside the heat pipe body, the insulation layer 12 is wrapped around the outer surface of the heat insulation section of the heat pipe body, and the outer shell is fitted over the insulation layer 12. The ultra-long gravity heat pipe is made of high-strength titanium alloy and has spiral fins welded to its outer wall to enhance heat exchange.

[0041] In detail, the ultra-long gravity heat pipe of the present invention includes a condensation section, an insulation section and an evaporation section connected in sequence. The condensation section is located in a hydrate reservoir or a shallow ice-containing layer. The insulation section is the middle part of the ultra-long gravity heat pipe and its outer wall is provided with a vacuum insulation layer 12. The evaporation section is located deep in the lower cover layer.

[0042] The invention will be better illustrated below with two examples.

[0043] Example 1 In this embodiment, the length of the ultra-long gravity heat pipe is 1000 meters, of which the length of the condensation section located in the hydrate reservoir (temperature is 10°C) is 100 meters; the working fluid 11 is cyclopentane, which has a boiling point of 49.2°C.

[0044] In this embodiment, during implementation, an open-hole well is first drilled using an offshore drilling platform 1, and then a series of manufactured gravity heat pipes are connected into an ultra-long gravity heat pipe through heat pipe connection 13.

[0045] An airtightness test was performed on the ultra-long gravity heat pipe. After the test was passed, cyclopentane (with a boiling point of 49.2°C) was injected into the ultra-long gravity heat pipe through the working fluid injection port 10. Then the ultra-long gravity heat pipe was sealed. After sealing, the ultra-long gravity heat pipe was lowered into the open hole well, with one section placed in the high-temperature region of the deep overburden and the other section located in the hydrate reservoir, with a length of 100 meters in the hydrate reservoir.

[0046] Backfilling the open hole creates a backfill section 8 within it. The backfill section 8 helps maintain the ultra-long gravity heat pipe in a compacted state, preventing leakage after the hydrates decompose into natural gas.

[0047] The working fluid 11 inside an ultra-long gravity heat pipe placed in the high-temperature region of the underlying layer absorbs heat 14 through the high-temperature stratum and is driven to circulate (the circulation process includes evaporation, rising, condensation and reflux). This continuously "extracts" the heat 14 from the underlying layer into the hydrate reservoir and dissipates it, thereby raising the temperature of the hydrate reservoir, breaking the hydrate phase equilibrium, and causing the hydrate to decompose and produce natural gas.

[0048] As the temperature of the hydrate reservoir gradually rises above the hydrate phase equilibrium temperature (17°C for methane hydrate at 15 MPa pressure), the hydrate begins to decompose. The natural gas produced by the decomposition is transported to the natural gas collection tank 2 on the offshore drilling platform 1 via horizontal well 9, vertical well 7, and pressure relief pump 4.

[0049] Drill another vertical well 7 on the offshore drilling platform 1 into the hydrate reservoir. The vertical well 7 is connected to the natural gas collection tank 2 through the gas production pipeline 55. After cementing and well completion, natural gas is collected through the gas production channel to achieve the effect of natural gas hydrate extraction.

[0050] During the natural gas extraction process, the monitoring and control system 3 installed on the offshore drilling platform 1 monitors the temperature and pressure changes of the hydrate reservoir and the natural gas collection tank 2 in real time. The decomposition rate is adjusted by controlling the depressurization rate, i.e. by the depressurization pump 4, to prevent excessively rapid decomposition from causing formation instability.

[0051] Example 2 In this embodiment, the length of the ultra-long gravity heat pipe is 500 meters, of which the length of the condensation section located in the shallow ice layer (temperature is 14°C) is 50 meters; the working fluid 11 is n-pentane, which has a boiling point of 36.1°C.

[0052] In this embodiment, during implementation, an open-hole well is first drilled using an offshore drilling platform 1, and then a series of manufactured gravity heat pipes are connected into an ultra-long gravity heat pipe through heat pipe connection 13.

[0053] An airtightness test was performed on the ultra-long gravity heat pipe. After the test was passed, n-pentane (boiling point 36.1℃) was injected into the ultra-long gravity heat pipe through the working fluid injection port 10. Then the ultra-long gravity heat pipe was sealed. After sealing, the ultra-long gravity heat pipe was lowered into the open hole well, with one section of the ultra-long gravity heat pipe placed in the high-temperature region of the deep overburden and the other section located in the shallow ice-bearing layer, with a length of 50 meters in the shallow ice-bearing layer.

[0054] Backfilling the open hole creates a backfill section 8 within it. The backfill section 8 helps maintain the ultra-long gravity heat pipe in a compacted state, preventing leakage after the hydrates decompose into natural gas.

[0055] The working fluid 11 inside an ultra-long gravity heat pipe placed in the high-temperature region of the underlying layer absorbs heat 14 through the high-temperature stratum and is driven to circulate (the circulation process includes evaporation, rising, condensation and reflux). This continuously "extracts" the heat 14 from the underlying layer to the ice-containing shallow layer, thereby raising the temperature of the ice-containing shallow layer, breaking the hydrate phase equilibrium, and causing the hydrate to decompose and produce natural gas.

[0056] As the temperature in the shallow ice-bearing layer gradually rises above the hydrate phase equilibrium temperature (17°C for methane hydrate at 15 MPa pressure), the hydrate begins to decompose. The natural gas produced by the decomposition is transported to the natural gas collection tank 2 on the offshore drilling platform 1 via horizontal well 9, vertical well 7, and pressure relief pump 4.

[0057] Drill another vertical well 7 on the offshore drilling platform 1 into the ice-bearing shallow layer. The vertical well 7 is connected to the natural gas collection tank 2 through the gas production pipeline 55. After cementing and well completion, natural gas is collected through the gas production channel to achieve the effect of natural gas hydrate extraction.

[0058] During the natural gas extraction process, the monitoring and control system 3 installed on the offshore drilling platform 1 monitors the temperature and pressure changes of the ice-bearing shallow layer and the natural gas collection tank 2 in real time. By controlling the depressurization rate, i.e. through the depressurization pump 4, the decomposition rate is adjusted to prevent excessively rapid decomposition from causing formation instability.

[0059] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for extracting hydrates using ultra-long gravity heat pipe-assisted pressure reduction, characterized in that, Includes the following steps: Drilling open-hole wells deep into the underlying overburden on offshore drilling platforms; An ultra-long gravity heat pipe system was fabricated, and a working fluid was injected into the ultra-long gravity heat pipe in the ultra-long gravity heat pipe system; An ultra-long gravity heat pipe filled with working fluid is lowered into an open-hole well, with one section placed in the overburden and the other in the hydrate reservoir or shallow ice-bearing layer. The temperature in the overburden drives the working fluid inside the ultra-long gravity heat pipe to circulate within it, backfilling the open-hole well and forming a backfill section to prevent natural gas leaks from hydrate decomposition along the wellbore. The heat from the overburden is transferred to the hydrate reservoir or shallow ice-bearing layer for dissipation, raising the temperature of the hydrate reservoir or shallow ice-bearing layer, thereby decomposing the hydrates in the hydrate reservoir or shallow ice-bearing layer into natural gas. Vertical and horizontal wells extending to the hydrate reservoir are drilled using an offshore drilling platform to complete cementing and well completion operations. Natural gas generated from hydrate decomposition is collected through an offshore gas production system.

2. The method for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 1, characterized in that, The method for extracting hydrates using ultra-long gravity heat pipe-assisted pressure reduction also includes the following steps: Repeat the above steps to drill multiple open-hole wells on the offshore drilling platform, with each open-hole well corresponding to the placement of an ultra-long gravity heat pipe; and drill multiple horizontal wells, all connected to the vertical wells, in the hydrate reservoir or ice-bearing shallow layer to collect natural gas decomposed from hydrates in the hydrate reservoir or ice-bearing shallow layer.

3. The method for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 1, characterized in that, In the step of collecting natural gas through an offshore gas production system, the subsea gas production tree of the offshore gas production system is connected to vertical and horizontal wells. The subsea gas production tree is connected to a pressure reducing pump through a gas production pipeline. The pressure reducing pump is connected to a natural gas collection tank. The natural gas produced by decomposition is transported to the natural gas collection tank through the subsea gas production tree, gas production pipeline, and pressure reducing pump.

4. The method for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 1, characterized in that, In the process of preparing an ultra-long gravity heat pipe system, multiple gravity heat pipe segments are spliced ​​together by heat pipe connection sections to form an ultra-long gravity heat pipe system. The airtightness of the spliced ​​ultra-long gravity heat pipe system is checked, and a working fluid is injected into the system through the working fluid injection port to complete the sealing.

5. A system for extracting hydrates using ultra-long gravity heat pipe-assisted pressure reduction, characterized in that, include: An offshore gas production system includes an offshore drilling platform, a gas production channel, and a natural gas collection tank. The gas production channel includes interconnected gas production pipelines, vertical wells, and horizontal wells. An ultra-long gravity heat pipe system, comprising at least one ultra-long gravity heat pipe equipped with a working fluid injection port; At least one open-hole well is drilled using the offshore drilling platform for deploying the ultra-long gravity heat pipe. After the ultra-long gravity heat pipe is deployed, part of it is placed in the underlying layer and the other part is placed in the hydrate reservoir or ice-bearing shallow layer. The heat from the underlying layer is transferred to the hydrate reservoir or ice-bearing shallow layer through the ultra-long gravity heat pipe. The heat decomposes the hydrate reservoir or ice-bearing shallow layer into natural gas, which is then transported to the natural gas collection tank through the gas production channel.

6. The system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 5, characterized in that, The offshore gas production system also includes a pressure relief pump, and the gas production channel also includes a subsea gas tree for controlling the gas flow in the open hole well. The vertical well extends through the overlying layer into the hydrate layer. The horizontal well is located within the hydrate layer and communicates with the vertical well. The subsea gas production tree is connected to the wellhead of the vertical well. The subsea gas production tree is connected to the pressure reducing pump via a gas production pipeline. The pressure reducing pump is connected to the natural gas collection tank. Both the natural gas collection tank and the pressure reducing pump are fixedly installed on the offshore gas production platform.

7. The system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 5 or 6, characterized in that, It also includes a monitoring and control system; The monitoring and control system includes a temperature sensor, a pressure sensor, a pressure reducing pump control system, and a flare system. The temperature sensor and pressure sensor are respectively installed downhole and at the wellhead. The signal output terminals of the temperature sensor and pressure sensor are connected to the signal input terminals of the pressure reducing pump control system to transmit the collected temperature and pressure data to the pressure reducing pump control system. The control output terminal of the pressure reducing pump control system is connected to the control input terminal of the pressure reducing pump to adjust the operating parameters of the pressure reducing pump. The flare system is connected to the natural gas collection tank to process excess natural gas.

8. The system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 5, characterized in that, The annular area of ​​the open hole well is provided with a backfill section, which is densely filled between the ultra-long gravity heat pipe system and the well wall of the open hole well to block the gas leakage channel.

9. The system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 5, characterized in that, Multiple sets of the ultra-long gravity heat pipe system are installed and deployed into multiple open-hole wells within the target mining area. The multiple sets of ultra-long gravity heat pipe systems are equidistantly distributed within the hydrate layer.

10. The system for extracting hydrates using ultra-long gravity heat pipe-assisted depressurization according to claim 5, characterized in that, The ultra-long gravity heat pipe system includes: a working fluid injection port, a working fluid, an insulation layer, an outer shell, and a heat pipe body. The working fluid injection port is fixedly located at the top of the heat pipe body. The working fluid is filled inside the heat pipe body. The insulation layer is wrapped around the outer surface of the heat pipe body's insulation section. The outer shell is fitted over the insulation layer. The ultra-long gravity heat pipe is made of high-strength titanium alloy and has spiral fins welded to its outer wall to enhance heat exchange.

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