Natural gas hydrate reservoir heating and recovery system based on separately controlled electric floor heating

Abstract

The application discloses a natural gas hydrate reservoir heating and recovery system based on a separate control type electric floor heating, relates to the technical field of marine energy development, and realizes multi-energy comprehensive collaborative power generation of a sea surface energy collection power supply platform and energy supply for a recovery system; a separate control type electric floor heating device realizes zoned temperature control and decomposition rate adjustment of a reservoir through a zoned heating mode; a seawater temperature-raising self-circulation pipe network is located in the reservoir, realizes efficient heat exchange between surface warm seawater and a deep hydrate reservoir through pump control push-pull circulation, and provides a cold source for seawater temperature difference energy power generation; reservoir pyrolysis and gas recovery pipe networks realize zoned intelligent recovery through opening and closing of a control switch valve group; a sea surface work ship energy processing module is used for recovering gas and interacts with the recovery system to realize remote monitoring and control. The application constructs an energy self-sufficient, uniform heating, zonally controllable and environment-friendly efficient heating and recovery system, and realizes stable and safe gas recovery under the condition of low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of marine energy development technology, and in particular to a natural gas hydrate reservoir heating and recovery system based on a distributed control electric underfloor heating system. Background Technology

[0002] Natural gas hydrate (also known as "combustible ice") is a crystalline compound formed by methane molecules and water under high pressure and low temperature conditions. With enormous reserves, it is considered an important clean energy source after oil and natural gas. However, due to its unique burial environment (deep-sea high pressure, low temperature, and low-permeability sedimentary layers), the safe, controllable, and economical extraction of hydrates has long been a key issue restricting its commercial utilization.

[0003] The current technology system has the following limitations: (1) Strong dependence on energy supply: Traditional heating systems generally rely on single sea surface power supply or fuel oil power generation, which makes it difficult to continuously supply energy in the open sea, resulting in limited recovery efficiency. (2) Uneven heat distribution and slow reservoir response: Hot water injection and cable heating methods both show the characteristics of "overheating near the well and low temperature in the far area", with a thermal energy utilization rate of only 30% to 40%. Due to the limited heat conduction path, the heat attenuation is serious, which can easily lead to local collapse and gas outburst. (3) Low comprehensive utilization rate of marine energy: Most of the existing marine wind energy, tidal energy and wave energy power generation systems operate independently and have not yet been coupled with hydrate mining. Renewable energy cannot provide continuous energy supply for reservoir heating according to local conditions. (4) Lack of precise zoning for thermal recovery control: Electric heating systems are generally controlled by a single well and lack zoning power regulation and real-time temperature feedback. The reservoir heating process is lagging behind, which can easily cause overheating in some areas and insufficient dissociation in some areas. (5) Environmental disturbance and gas leakage hazards: The deep-sea operating environment is complex. If an effective heat-production synergy channel is not established, the gas released by the decomposition of hydrates may be directly discharged into the sea through pores or cracks, resulting in methane leakage, which poses a high risk to the environment. Summary of the Invention

[0004] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a natural gas hydrate reservoir heating and recovery system based on a split-control electric underfloor heating system.

[0005] The technical solution adopted by this invention to solve its technical problem is: a natural gas hydrate reservoir heating and recovery system based on a split-control electric underfloor heating system, including a marine energy collection and power supply platform, a split-control electric underfloor heating device, a seawater temperature raising self-circulation pipeline network, a reservoir pyrolysis and gas recovery pipeline network, a marine operation vessel energy processing module, and a control and automation module. The marine energy collection and power supply platform realizes the comprehensive and coordinated power generation of wind energy, solar energy, wave energy, tidal energy and thermal energy difference, and supplies energy to the recovery system.

[0006] The separately controlled electric floor heating device is installed near and inside the seawater warming self-circulation pipeline network, and achieves zoned temperature control and decomposition rate regulation of the reservoir through zoned heating.

[0007] The seawater warming self-circulation pipeline network is located inside the reservoir. It achieves efficient heat exchange between the surface warm seawater and the deep hydrate reservoir through pump-controlled push-pull circulation.

[0008] The reservoir pyrolysis and gas recovery pipeline network includes several horizontal pipelines, and a group of control valves is installed on the horizontal pipelines to achieve intelligent regional recovery by controlling the opening and closing of the valve groups.

[0009] The energy processing module of the surface vessel is used to collect gas and interacts with the collection system to achieve remote monitoring and control.

[0010] The control and automation module is used for overall coordination and control of the harvesting system.

[0011] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed electric underfloor heating also includes an adjustable buoyancy and risk avoidance module. This module adjusts the buoyancy of the offshore energy collection and power supply platform according to the size of the wind and waves to ensure the safety and stability of the platform.

[0012] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed-control electric underfloor heating includes a marine energy collection and power supply platform comprising a wind power generation module, a solar cell array, a wave and tidal energy conversion device, a seawater thermal energy conversion module, an energy management and storage module, and a communication module. The seawater thermal energy conversion module generates electricity using the temperature gradient between deep cold water and surface warm water. The energy management and storage module coordinates the power distribution of the wind power generation module, solar cell array, wave and tidal energy conversion device, and seawater thermal energy conversion module in real time, and achieves power balance and short-term energy storage. The communication module extends to the seabed, providing a power and data transmission channel for the system.

[0013] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed electric underfloor heating includes a seawater temperature difference energy power generation module comprising a seawater temperature difference energy cooling module and a seawater temperature difference energy heating module. Cold water from the deep hydrate reservoir flows into the seawater temperature difference energy cooling module through a seawater heating self-circulation pipeline network, where it exchanges heat with the low-temperature working fluid. The cooled low-temperature working fluid is then transported to the seawater temperature difference energy heating module, where it exchanges heat with the surface seawater, is heated and vaporized, and then drives a turbine generator set to generate electricity.

[0014] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed electric underfloor heating includes a seawater warming self-circulation network comprising a surface water intake pump, a downlink main pipe, an uplink main pipe, a subsea horizontal branch pipe, a reservoir heat exchange capillary array, an outlet confluence pipe, and a return pump. The surface water intake pump draws surface seawater and sends it through the downlink main pipe to the subsea horizontal branch pipe and the reservoir heat exchange capillary array. The cooled seawater after heat exchange flows from the reservoir heat exchange capillary array into the outlet confluence pipe and returns to the sea surface through the uplink main pipe via the return pump.

[0015] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed electric underfloor heating includes a power supply control unit and heating units. The power supply control unit receives temperature commands in real time and independently starts, stops, and adjusts the power of each heating zone. The heating units are composite sheathed electric heating cable structures. Temperature sensors and micro-pressure detectors are installed at intervals in each heating unit. The temperature sensors and micro-pressure detectors collect data and transmit it to the control and automation module. The control and automation module analyzes the reservoir temperature distribution, gas generation rate, and pressure changes in real time. Based on the temperature and pressure changes, the control and automation module sends commands to the power supply control module, which adjusts the start / stop and power of each heating zone.

[0016] The aforementioned natural gas hydrate reservoir heating and recovery system based on distributed electric underfloor heating has an inner layer of nickel-chromium alloy heating wire or resistance band, a middle layer of high thermal conductivity silicone rubber or composite thermal pad, and an outer layer of corrosion-resistant alloy or polytetrafluoroethylene composite sheath. The composite sheath electric heating cable structure is wrapped with a thin insulating coating.

[0017] The beneficial effects of this invention are that the multi-source marine energy integrated platform of this invention can simultaneously utilize wind energy, solar energy, wave energy, tidal energy, and seawater temperature difference energy to generate electricity to form a hybrid power system, supplemented by an energy storage unit to achieve continuous power supply, eliminating the dependence on the heating system for external cable power transmission, and significantly improving the system's independence and economy.

[0018] This invention employs a distributed control electric underfloor heating structure, with each heating zone equipped with an independent temperature and power control module. Through real-time feedback adjustment of the electrical power, the temperature distribution within the reservoir becomes more uniform, significantly improving thermal energy utilization. Experimental simulations show that the system's energy utilization efficiency can be improved by approximately 30%–40%.

[0019] This invention combines a seawater heating and self-circulating device, utilizing the natural convection of seawater temperature differences to assist heating, which can reduce the amount of electrical heat input by 20%–30%. This mechanism avoids the heat loss caused by long transmission distances in traditional hot water injection methods, thus improving overall energy conversion efficiency.

[0020] This invention establishes a continuous process of "heating – reservoir pyrolysis – gas collection," avoiding the localized cold zones caused by "distance from the heat source and insufficient heating" in traditional technologies. The zoned control mechanism keeps the hydrate decomposition rate stable, increases gas yield with small fluctuations, and improves average gas production stability by approximately 25% compared to traditional thermal recovery.

[0021] This invention incorporates a closed gas collection hood and a negative pressure exhaust mechanism in the mining area, which can rapidly capture escaping gas and prevent methane from being directly released into seawater. Simultaneously, each section is equipped with temperature and micro-pressure sensors, which are monitored in real time by the control system. This system can automatically limit power and issue alarms in case of abnormal temperature rises or overpressure, reducing the risk of ground subsidence and environmental pollution.

[0022] This invention features a simplified structure and convenient installation and maintenance. The electric underfloor heating module uses a flexible cable and a pressure-resistant sheath, allowing it to be laid on the seabed using horizontal directional drilling, eliminating the need for complex drilling or heat injection pipelines. The module can be installed or replaced in sections using an underwater robot, reducing construction costs and the difficulty of subsequent maintenance.

[0023] The power supply and heating unit of this invention adopts a modular design, allowing for flexible addition or removal of power generation units and heating circuits based on different water depths, temperatures, and reservoir sizes. Without altering the main system architecture, it can adapt to the energy conditions and operational needs of different regions, demonstrating feasibility for engineering implementation.

[0024] The system of this invention requires no external fuel combustion throughout the entire process, producing no waste gas or oil pollution; seawater circulation and heat exchange utilize natural energy gradients, without damaging the marine ecosystem. Simultaneously, the multi-energy platform on the sea surface can serve as a node in a regional microgrid, operating collaboratively with other marine observation and energy devices to achieve comprehensive optimization of the energy system.

[0025] In summary, this invention effectively solves the long-standing problems of traditional natural gas hydrate thermal recovery technology in terms of energy dependence, high energy consumption, uneven heating, and environmental risks through an innovative combination of marine multi-energy self-supply, distributed electric underfloor heating, seawater warming assistance, and intelligent regulation and recovery. It realizes a continuous, stable, and low-energy-consumption hydrate decomposition and recovery process in the deep-sea environment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the system of the present invention;

[0027] Figure 2 This is a schematic cross-sectional view of the submarine pipeline of the present invention;

[0028] Figure 3 This is a schematic diagram of the harvesting pipe control valve of the present invention;

[0029] Among them, 1. Wind turbine, 2. Photovoltaic module, 3. Hydraulic wave energy conversion device and turbine power flow unit, 4. Energy storage component, 5a. Cooling chamber, 5b. Heating chamber, 6. Main controller, 7. Turbine, 8a. Surface water intake pump, 8b. Return pump, 9. Downstream main pipe, 10. Upstream main pipe, 11. LNG liquefaction module, 12. Ballast tank, 13. Subsea horizontal branch pipe, 14. Reservoir heat exchange capillary array, 15. Platform, 16. Hydrate reservoir, 17. Main control center, 18. Production pipe, 19. Inlet pipe, 20. Outlet pipe, 21. Heating cable, 22. Pipeline outer wall, 23. Main power supply cable, 24. Electric sub-control valve, 25. Temperature and pressure sensor. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] This invention relates to the field of deep-sea energy extraction and multi-energy synergistic power supply technology, specifically a natural gas hydrate reservoir heating and harvesting system based on a distributed-control electric underfloor heating system. The system aims to achieve low-energy decomposition and efficient, safe harvesting of seabed natural gas hydrates through the synergistic coupling of a "multi-energy self-powered platform + distributed-control electric underfloor heating module + seawater warming and circulation system + intelligent regulation and harvesting".

[0032] This embodiment combines Figure 1-3 Taking subsea natural gas hydrate reservoirs as the subject, the following detailed description of the system structure, equipment configuration, operation process, and control logic is provided. All dimensions and parameters are typical design values ​​in a conventional deep-sea (1000–1500m) environment, and technicians can make equivalent substitutions and adjustments according to site conditions.

[0033] I. System Overall Structure and Principles

[0034] The system of this invention is generally composed of a floating offshore energy collection and power supply platform, a seabed thermal control and harvesting area, and an energy recovery and control unit, forming an integrated structure of multi-energy complementarity and decentralized operation. The system achieves integrated operation of three major functional subsystems: wind-solar-wave-tidal-temperature difference multi-energy coordinated power supply, and geothermal decentralized heating + seawater push-pull heat exchange + zoned gas harvesting and recovery. (See details...) Figure 1 .

[0035] Its working principle is as follows:

[0036] The surface platform continuously harnesses energy from wind, sunlight, waves, tides, and seawater temperature differences, which is then integrated by the energy management system to output stable direct current (DC). This electricity is transmitted via a deep-sea photovoltaic composite cable to the hydrate reservoir, powering the electric underfloor heating and sensor control nodes. Simultaneously, a seawater warming pipeline network between the platform and the reservoir transports warm surface seawater into the reservoir for combined heating with the electric underfloor heating. Once the reservoir temperature rises above the equilibrium temperature, the hydrate slowly decomposes, releasing methane gas. Driven by osmotic pressure and temperature differences, the gas enters the production pipeline and is gradually discharged by control valves to the surface processing module, achieving the safe recovery and utilization of methane.

[0037] This embodiment of the system includes a marine energy collection and power supply platform, a separately controlled electric underfloor heating device, a seawater warming self-circulation pipeline network, a reservoir pyrolysis and gas recovery pipeline network, a marine vessel energy processing module, and a control and automation module. The marine energy collection and power supply platform enables integrated and coordinated power generation from wind, solar, wave, tidal, and thermal energy differentials, and supplies power to the recovery system. The separately controlled electric underfloor heating device is installed near and within the seawater warming self-circulation pipeline network, achieving zoned temperature control and decomposition rate regulation of the reservoir through zoned heating. The seawater warming self-circulation pipeline network is located inside the reservoir, achieving efficient heat exchange between the surface warm seawater and the deep hydrate reservoir through pump-controlled push-pull circulation. The reservoir pyrolysis and gas recovery pipeline network includes several horizontal pipes, with separately controlled switch valve groups installed on the horizontal pipes, achieving zoned intelligent recovery by controlling the opening and closing of the switch valve groups. The marine vessel energy processing module is used to recover gas and interacts with the recovery system to achieve remote monitoring and control. The control and automation module is used for overall coordinated control of the recovery system.

[0038] I. Offshore Energy Collection and Power Supply Platform

[0039] The offshore energy collection platform is an integrated floating multi-energy power generation device with a three-layer structure. The lower layer houses a seawater thermal energy conversion module, enabling comprehensive and coordinated power generation from wind, solar, wave, tidal, and thermal energy sources. This platform is a floating combined energy unit, typically approximately 35 meters in diameter, with a three-layer ring-shaped deck and a total weight of approximately 30 tons. Its components are as follows:

[0040] (1) Upper-level wind power generation module

[0041] Install 8–12 vertical shaft wind turbine generators (single unit power 2–5kW); equipped with a hydraulic pitch and wind speed feedback control system, capable of stable output within a wind speed range of 2–25m / s; each generator outputs DC power through an independent inverter, connected in parallel with the main DC bus.

[0042] (2) Mid-layer solar cell array

[0043] It adopts flexible CIGS thin-film photovoltaic modules 2 with a power efficiency of about 22%; the array outer diameter is the same as that of the platform and is located in the deck ring area, with a total power generation of about 20kW; it is equipped with aluminum alloy mounting brackets, anti-corrosion primer and anti-slip coating; it is equipped with MPPT control and overvoltage protection circuit, and automatic maximum power point tracking output during the day.

[0044] (3) Lower periphery - Wave and tidal energy conversion device

[0045] The platform is equipped with a buoy-hydraulic wave energy conversion device and a turbine tidal current generator unit at its bottom. Wave actuators drive hydraulic pumps to achieve bidirectional energy recovery; the turbine tidal current generator operates stably in currents of ≥0.5m / s to ensure continuous power supply; the array distribution reduces the impact of waves and currents on the platform's vibration.

[0046] A seawater temperature difference (TTC) power generation module is installed in the lower central area. This module includes a seawater temperature difference cooling module and a seawater temperature difference heating module. Cold water from the deep hydrate reservoir flows into the seawater temperature difference cooling module through a self-circulating seawater heating network, where it exchanges heat with the low-temperature working fluid. The cooled working fluid is then transported to the seawater temperature difference heating module, where it exchanges heat with surface seawater, is heated and vaporized, and drives a turbine generator to generate electricity. Figure 1 As shown, it includes: a cold source section (cooling chamber 5a): low-temperature seawater from the reservoir circulation condenses the working fluid in the enclosure chamber, liquefying it. This stage is not only used for heat exchange of the power generation working fluid, but also helps maintain the temperature of the platform equipment compartment and has a waste heat regulation function. A heat source section (heating chamber 5b): the fluid is guided to the surface warm seawater heating chamber 5b, where it absorbs heat and vaporizes to drive the turbine 7 to generate electricity; the exhaust gas from the turbine 7 flows back to the cooling chamber 5a through the condenser, realizing a closed loop.

[0047] The entire system is connected in parallel to the main DC bus with wave energy, tidal energy and solar power, and the power output ratio can be dynamically adjusted according to sea conditions.

[0048] This seawater thermal energy system generates electricity by utilizing the temperature gradient between deep cold water and surface warm water (the temperature difference between deep and shallow water is about 10°C). It can operate stably under low wind and solar conditions, improve the continuity of power supply day and night, and increase the overall energy utilization rate of the platform by about 15%–25%.

[0049] (4) Energy management and energy storage module

[0050] All submodule outputs are connected in parallel to the 600V bus after being regulated by DC / DC converters; the main controller 6 (EMS) automatically adjusts the power distribution according to load demand and battery state of charge; the energy storage component 4 includes a 500kWh lithium battery and a supercapacitor array with a response time of <100ms.

[0051] (5) Optoelectronic composite cable and communication channel

[0052] It adopts a three-core power line + single-core optical fiber composite armor structure with a resistance of less than 0.08Ω / m per unit length; the main power cable 23 is installed to the seabed by a horizontal directional drilling machine, which not only transmits electrical energy but also undertakes signal communication tasks; the optical fiber part is directly connected to the industrial Ethernet interface of the control center, with a data rate of 100Mbps.

[0053] II. Adjustable buoyancy and safety module

[0054] The platform has a dual-chamber pressure ballast tank 12 at its bottom, with a volume of approximately 120m³ on each side. 3 Buoyancy control is achieved by adjusting the cabin density through inlet and outlet valves and compressed air pipelines: normally, the cabin contains approximately 25% air, and the platform floats on the sea surface; when the weather warning system detects wind speeds >30m / s or wave heights >5m, it automatically floods and submerges 10m to enter the wave-sheltered layer; after a disaster, it uses air pumps to drain the water and resurface to restore its operational position. The entire system supports both remote and automatic modes, and has built-in attitude sensors for attitude trim.

[0055] III. Seawater Warming Self-Circulation Pipeline

[0056] The system is used for seawater-reservoir heat exchange and cold source recovery, providing auxiliary heat energy for low-energy heating. The overall design adopts a dual-pump circulation + gravity flow design. The seawater warming self-circulation pipeline network includes a surface water intake pump 8a, a downlink main pipe 9, an uplink main pipe 10, a seabed horizontal branch pipe 13, a reservoir heat exchange capillary array 14, an outlet confluence pipe, and a return pump 8b. The surface water intake pump 8a draws surface seawater and sends it through the downlink main pipe to the seabed horizontal branch pipe 13 and the reservoir heat exchange capillary array 14. The cooled seawater after heat exchange is collected by the reservoir heat exchange capillary array 14 and flows into the outlet confluence pipe, and then returns to the sea surface through the uplink main pipe via the return pump 8b.

[0057] (1) Pipeline structure

[0058] The downlink main pipe 9 and the uplink main pipe 10 are made of Φ200mm composite heat-insulating metal pipes with a 10mm thick insulation layer; the reservoir heat exchange capillary array 14 is made of Φ20–40mm high thermal conductivity and corrosion-resistant composite capillary pipes with a burial depth of 1–2m; the bottom of the downlink main pipe 9 and the uplink main pipe 10 are provided with annular diversion and collection cavities to ensure uniform flow.

[0059] (2) Work process

[0060] 1. Surface warm water (15–25°C) is pushed into the down main pipe 9 by the surface water intake pump 8a, and the return pump 8b is installed at the end of the up main pipe 10 to form a push-pull structure, which improves circulation efficiency and system stability.

[0061] 2. After flowing to the seabed, it splits into a horizontal branch pipe 13. Warm water enters the hydrate reservoir 16 for heat exchange through the reservoir heat exchange capillary array 14. The reservoir heat exchange capillary array 14 is divided into an inlet pipe 19 and an outlet pipe 20 (e.g., ...) within the seabed pipeline. Figure 2 (As shown), the temperature of the hydrate reservoir is increased through circulation;

[0062] 3. After heat exchange, the seawater temperature drops to about 5–8℃ and is sent to the sea surface thermal energy system as a cold source through the return pipe;

[0063] 4. After releasing the cold energy in the temperature difference system, it is discharged into the open sea to form a closed loop.

[0064] (3) Control and Operation

[0065] The inlet and outlet pump sets operate at power of 3–5 kW, with flow rates controlled at 0.4–0.6 m³ / h. 3 / s; the pipeline network is equipped with temperature, flow rate, and pressure sensors to monitor the circulation status in real time; the control system automatically matches the flow rate according to the reservoir temperature and platform power. This pipeline network provides approximately 20–30% of the heat to the reservoir and a stable cold source for the thermoelectric energy system, realizing the cascade recycling of energy.

[0066] Except for the reservoir heat exchange capillary array 14, all pipes adopt a multi-layer insulation structure and are wrapped with a composite anti-corrosion coating. The reservoir heat exchange capillary array 14 is made of a composite material with high thermal conductivity and high corrosion resistance to adapt to the deep-sea salt corrosion environment. Since its interior is fully filled with seawater and the internal and external pressure difference is small, it does not need to bear the additional high pressure load requirement, and the thermal conductivity and flexibility can be optimized while ensuring corrosion resistance.

[0067] The internal fluid velocity is controlled at 0.5–1.2 m / s to ensure sufficient heat exchange and prevent deposit blockage.

[0068] The seawater warming self-circulation pipeline network achieves closed-loop energy coupling of "heat energy transfer downwards + cold energy return upwards": it assists in reservoir heating by providing approximately 20-30% additional heat input, reducing the power consumption of underfloor heating; it provides cooling for thermoelectric power generation by stably providing low-temperature seawater at 5-10℃, effectively improving the thermal efficiency of the thermoelectric energy cycle; it reduces seawater disturbance and discharge by allowing cold water to directly enter the thermoelectric energy system for circulation, reducing mixing with the surrounding environment and minimizing environmental impact; and it enhances the energy chain closure by forming a closed-loop thermal chain with the underfloor heating module and the thermoelectric energy system, enabling the entire platform to achieve multi-energy complementarity and cascade utilization.

[0069] In summary, the seawater warming self-circulating pipeline system of this embodiment combines pump-controlled drive, temperature difference energy utilization, and reservoir coupled heat exchange into a triple mechanism, realizing bidirectional energy utilization and efficient circulation. It provides a continuous heat source for the separately controlled underfloor heating system and provides cold source support for the platform's temperature difference energy module, greatly improving the overall efficiency and sustainability of the energy system.

[0070] IV. Distributed control electric floor heating device

[0071] This module, deployed along the production and heat exchange pipeline network, is a key energy subsystem of this invention. Installed near and within the hydrate reservoir pipeline network, it achieves directional temperature control and decomposition rate regulation of the reservoir through zoned heating. The system features a simple structure, low material cost, and high durability, making it suitable for long-term subsea operation. The design focuses on low cost, long lifespan, and precise, zoned temperature control.

[0072] (1) Structural composition

[0073] The main power cable 23 is introduced from platform 15 and branched into 10–20 branch cables via a distribution box. Each branch cable corresponds to a reservoir section and is 50–100m long. The distribution box contains a microprocessor, power module, and communication interface, which collects temperature feedback and refreshes control commands. The heating cable 21 has a multi-layer composite structure: the inner layer is a nickel-chromium alloy heating wire or resistance band, which has stable conductivity and low cost; the middle layer is a high thermal conductivity silicone rubber or composite thermal pad layer to ensure uniform heat release; the outer layer is a corrosion-resistant alloy or polytetrafluoroethylene composite sheath, which has resistance to seawater corrosion and good flexibility; the cable is wrapped with a thin insulating coating and can be spirally wound or laid parallel along the pipeline as needed. The average power density is 20W / m, and the total power design is approximately 100kW.

[0074] (2) Layout method

[0075] The heating elements are laid close to the outer wall of the pipeline or around it. In some sections, they are in contact with the pipeline body through fixing clamps, and the heat transfer efficiency is >85%. The density of the heating elements in key heating areas is doubled to make the reservoir temperature rise more uniform.

[0076] (3) Monitoring and control

[0077] 25 PT100 temperature and pressure sensors are embedded every 25m, located at the ends and middle sections, to detect pore gas pressure and temperature. The sensor data is transmitted via cable to the control center for real-time analysis of reservoir temperature distribution, gas generation rate, and pressure changes, supporting intelligent control algorithms. The system employs a PID-based dynamic power regulation algorithm: when a local temperature exceeds the set value by +2℃, the power of that zone is automatically reduced by 10%; when the temperature falls below the set value by -2℃, the rated power is restored; when the decomposition rate is insufficient or gas production decreases, the power can be locally increased by 5% based on the thermal response curve. This achieves uniform reservoir heating and controllable decomposition rate, avoiding structural instability and energy waste caused by overheating or sudden changes.

[0078] (4) Protection and maintenance

[0079] Each circuit is equipped with an independent circuit breaker and leakage current monitoring; the outer sheath resistance is ≥50MΩ to ensure long-term underwater insulation; the heating element has an average lifespan of >50,000 hours. This module is low-cost, easy to maintain, and can operate stably for a long time, providing a precise heat source for reservoir decomposition.

[0080] In summary, this distributed electric floor heating device features a simple structure, flexible zoning, high temperature control accuracy, low cost, corrosion resistance, and long service life. It can effectively achieve step-by-step heating and safe decomposition control of natural gas hydrate reservoirs, providing a stable heat source for efficient recovery.

[0081] V. Reservoir Pyrolysis and Gas Recovery System

[0082] In this embodiment, the distributed electric underfloor heating device and the seawater warming self-circulation pipeline form a synergistic thermal field in the target reservoir, enabling the reservoir to gradually heat up to the decomposition temperature range under controlled temperature conditions, thereby achieving stable gas release and segmented harvesting.

[0083] (1) Decomposition mechanism

[0084] The individually controlled electric underfloor heating system works in conjunction with the seawater warming self-circulation pipeline network to continuously provide heat to the hydrate layer.

[0085] When the temperature of hydrate reservoir 16 is about 10°C higher than the equilibrium temperature, the stable structure of the hydrate breaks down, releasing methane gas and water. Under the influence of temperature difference, pore pressure, and permeability gradient, the generated gas migrates along natural pores and thermal pores, and flows into the gas recovery pipeline network deployed within the reservoir.

[0086] (2) Harvesting pipe structure

[0087] The production system consists of several horizontal pipes, primarily constructed of highly corrosion-resistant composite materials, providing excellent sealing and medium-pressure strength. The inner walls of the pipes are equipped with a microporous pressure-equalizing structure and anti-clogging filters, ensuring uniform gas intake and preventing sediment ingress. The production pipe 18 uses Φ50–80mm composite material tubing; branch pipes are spaced 10–15m apart, penetrating the reservoir and overlying formations; all branch pipes converge into the main gas gathering pipe, which then sends the gas to the sea surface via a vertical trunk.

[0088] (3) Design of separate control switches

[0089] like Figure 3 As shown, each branch of the harvesting pipe 18 is spaced 20m apart and equipped with electrically operated sub-control valves 24, controlled by a distributed control node. When the temperature and pressure sensor 25 detects that a region has reached the decomposition threshold, the electrically operated sub-control valve 24 is automatically opened; valves in other regions remain closed to maintain the local pressure gradient and ensure gas harvesting. The system adjusts the number of electrically operated sub-control valves 24 open in real time according to changes in gas flow and pressure, achieving intelligent zoned gas harvesting. This sub-control strategy ensures stable gas production in each section and prevents early depressurization or reverse seepage.

[0090] The harvesting channel is flexibly connected to the upstream delivery pipe, and the gas is pressurized and delivered to the surface vessel for further processing. Each sub-control valve and main pipeline is equipped with an automatic overpressure unloading and venting protection device, which automatically diverts the flow when the local pressure exceeds the limit to prevent system overpressure damage or gas leakage.

[0091] This reservoir pyrolysis and gas recovery module features controlled recovery: gas is extracted only from the target decomposition zone, precisely controlling the gas production range; pressure equalization: it avoids pressure differential disturbances caused by suction from non-target zones, stabilizing the reservoir structure; corrosion resistance and anti-clogging: the composite material combined with the microporous filter design ensures long-term operation without scaling or clogging; safe and closed: the gas is recovered in a fully enclosed manner, eliminating the risk of leakage and environmental pollution; efficient collaboration: it works in conjunction with the controlled heating and temperature-raising circulation system to form a dynamic control system integrating heating, decomposition, and recovery.

[0092] In summary, this reservoir pyrolysis and gas recovery module, through its "distributed recovery" and "pressure zone management" design, achieves precise decomposition and safe recovery of hydrate reservoirs, ensuring the stability and efficiency of the gas production process.

[0093] VI. Energy Processing Unit for Surface Vessels

[0094] (1) Power storage module

[0095] The offshore platform is equipped with a 500kWh lithium-ion battery pack and a superconducting magnetic energy storage system for peak-valley compensation and emergency power supply; the charge-discharge efficiency is >92%.

[0096] (2) Gas handling system

[0097] The collected methane is sent to the LNG liquefaction module 11 via a compressor unit, with a liquefaction temperature of -162℃; some of the gas enters the methane reforming unit to generate hydrogen and CO2, and after separation, the hydrogen is used for fuel cells or generators.

[0098] (3) Communication and control interface

[0099] The ship is interconnected with the platform and deep-sea nodes through a fiber-optic-acoustic hybrid communication link to achieve data monitoring, fault alarm and remote optimization control.

[0100] VII. Control and Automation Systems

[0101] The system adopts a hierarchical architecture: the main control center 17 is responsible for power generation scheduling, power supply management, and overall safety protection; the sub-control nodes are distributed in the electric underfloor heating zones and harvesting pipe sections, and perform local temperature control and switch control.

[0102] Operating logic: 1. Real-time acquisition of power generation and reservoir parameters; 2. Determination of heating zone status and adjustment of power; 3. Automatic adjustment of harvesting valve opening based on pressure and gas production rate; 4. Automatic alarm and switching to safety mode when temperature, pressure, or current exceeds limits. The main communication channel is a fiber optic ring network structure, with acoustic communication as redundancy to ensure stable deep-sea signals.

[0103] The specific implementation process of the harvesting system in this embodiment is as follows:

[0104] 1. Deployment Phase

[0105] Deep-sea directional drilling was used to control the layout of heat conduction holes and production pipelines, lay cables and sensors, and install platform 15 and cable guide system.

[0106] 2. Start-up Phase

[0107] The seawater warming self-circulation pipeline system continuously raises the hydrate reservoir to a stable temperature of approximately 25°C; the offshore platform starts generating electricity, and the electric underfloor heating zones are sequentially powered on to raise the temperature; once the reservoir temperature reaches the target (approximately 10°C above the equilibrium temperature), it is kept constant.

[0108] 3. Heating and Harvesting Stage

[0109] The reservoir continuously decomposes and releases gas, and the control system opens the sub-control valves according to the gas production area to achieve continuous harvesting and zoned production adjustment.

[0110] 4. Gas processing stage

[0111] Methane is transported to ships via subsea pipelines to complete the compression, liquefaction, and hydrogen production processes.

[0112] 5. Shutdown and Restart Phase

[0113] When the system shuts down, gradually reduce power and temperature, close all sub-control valves, and seal the underwater robot's execution interface.

[0114] Upon restart, the system will automatically restore to a stable operating condition based on the original partition settings.

[0115] The recovery system in this embodiment has stable thermal balance: the reservoir temperature difference is controlled within ±1℃, and the decomposition rate is controllable; energy consumption is reduced: the overall energy utilization efficiency is improved by more than 30%; recovery is safe: the sub-control valves precisely limit pressure to prevent sudden release and collapse; it is clean and environmentally friendly: the closed recovery system prevents methane from escaping; the system lifespan and reliability are high: each module has a lifespan of 5–10 years, and maintenance and replacement are simple; it is economical: modular assembly and multi-energy self-powered systems reduce the unit gas production cost by about 40%.

[0116] This implementation demonstrates a complete and executable process from energy harvesting to gas processing. The system utilizes a synergistic power supply from five energy sources—wind, solar, wave, tide, and temperature difference—combined with individually controlled underfloor heating, zoned gas extraction, and closed-loop processing, to achieve low-energy, safe, and efficient harvesting of natural gas hydrates. It exhibits excellent engineering applicability and potential for widespread adoption.

[0117] Based on this specification, those skilled in the art can directly implement this invention in various deep-sea environments.

[0118] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and spirit, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A system for heating and production of natural gas hydrate reservoirs based on a split-controlled electric floor heating, characterized in that, The sea surface energy collection power supply platform, the separately controlled electric floor heating device, the seawater temperature raising self-circulation pipe network, the reservoir pyrolysis and gas recovery pipe network, the sea surface operation ship energy processing module, and the control and automation module are combined to form the system. The separately controlled electric floor heating device is installed near and in the seawater temperature raising self-circulation pipe network, and realizes the zonal temperature control and decomposition rate adjustment of the reservoir through zonal heating. The seawater temperature raising self-circulation pipe network is located in the reservoir, and realizes the efficient heat exchange between the surface warm seawater and the deep water hydrate reservoir through pump control push-pull circulation. The reservoir pyrolysis and gas recovery pipe network comprises a plurality of horizontal pipelines, and a separately controlled switch valve group is arranged on the horizontal pipelines to realize the zonal intelligent recovery by controlling the opening and closing of the switch valve group. The sea surface operation ship energy processing module is used for recovering gas and interacting with the recovery system to realize remote monitoring and control. The control and automation module is used for overall coordinated control of the recovery system. The sea surface energy collection power supply platform comprises a wind power generation module, a solar cell array, a wave and tidal energy conversion device, a seawater temperature difference energy power generation module, an energy management and energy storage module, and a communication module. The seawater temperature difference energy power generation module utilizes the temperature difference gradient between the deep cold water and the surface warm water to generate power. The energy management and energy storage module realizes the real-time coordination of the power distribution of the wind power generation module, the solar cell array, the wave and tidal energy conversion device, and the seawater temperature difference energy power generation module, and realizes the power balance and short-time energy storage.

2. The hydrate reservoir heating and production system based on the electric floor heating with the local control according to claim 1, characterized in that, The communication module extends to the seabed to provide a power supply and data transmission channel for the system. The seawater temperature difference energy power generation module comprises a seawater temperature difference energy cooling module and a seawater temperature difference energy heating module. The deep hydrate reservoir cold water flows into the seawater temperature difference energy cooling module through the seawater temperature raising self-circulation pipe network, exchanges heat with the low-temperature working medium, and the cooled low-temperature working medium is transported to the seawater temperature difference energy heating module to exchange heat with the surface seawater, and the heated and gasified working medium drives the turbine generator set to generate power. The seawater temperature raising self-circulation pipe network comprises a surface water pump, a descending main pipe, an ascending main pipe, a seabed horizontal branch pipe, a reservoir heat exchange fine pipe array, an outlet converging pipe, and a backflow pump. The adjustable buoyancy and safety avoiding module adjusts the buoyancy of the sea surface energy collection power supply platform according to the size of the wind and wave to ensure the safety and stability of the sea surface energy collection power supply platform.

3. The hydrate reservoir heating and production system based on the electric floor heating with the separated control according to claim 1, characterized in that, The power supply sub-control unit receives temperature instructions in real time, and independently starts, stops and adjusts the power of each heating area; the heating unit is a composite sheath electric heating cable structure, temperature sensors and micro-pressure detectors are arranged at intervals between each heating unit, the temperature sensors and micro-pressure detectors collect data and transmit to the control and automation module, the control and automation module analyzes the reservoir temperature distribution, gas generation rate and pressure change in real time, and sends instructions to the power supply sub-control module according to the temperature and pressure change, and the power supply sub-control module adjusts the start, stop and power of each heating area.

4. The hydrate reservoir heating and production system based on the electric floor heating with the local control according to claim 3, characterized in that, The inner layer of the heating unit is a nickel-chromium alloy heating wire or a resistance band, the middle layer is a high-thermal-conductivity silicone rubber or a composite thermal-conductivity pad layer, and the outer layer is a corrosion-resistant alloy or a polytetrafluoroethylene composite sheath, and the composite sheath electric heating cable structure is wrapped with a thin layer of insulating coating outside.

Images