Natural gas hydrate in-situ drilling and drilling fluid treatment system

Abstract

A natural gas hydrate in-situ drilling and drilling fluid treatment system, comprising an offshore control platform (16), a natural gas hydrate subsea in-situ drilling device, a disassembly and assembly servo system, a drilling fluid feeding system, a wellhead flowback drilling fluid treatment system, a hydrate decomposition gas treatment system, a wellhead flowback drilling fluid tailings treatment system, a buoyancy control system (15), and a main control electric-power communication support system (17) connected to each system and controlling same, wherein the natural gas hydrate subsea in-situ drilling device and the drilling fluid feeding system are separately detachably connected to the wellhead flowback drilling fluid treatment system; and the hydrate decomposition gas treatment system is separately connected to the wellhead flowback drilling fluid treatment system, the natural gas hydrate subsea in-situ drilling device and the drilling fluid feeding system. Using unattended automation technology realizes the operation of the natural gas hydrate in-situ drilling and drilling fluid treatment system, such that the production process is simplified, automation and modularization are achieved, and subsea in-situ drilling can be performed on a large scale, thus greatly reducing the operation costs.

Description

A natural gas hydrate in-situ drilling and drilling fluid treatment system Technical field:

[0001] The present invention relates to the technical field of natural gas hydrate in-situ drilling, and in particular to a natural gas hydrate in-situ drilling and drilling fluid processing system. Background technology:

[0002] Natural gas hydrate is an ice-like solid formed by gas (or volatile liquid) and water under certain temperature and pressure conditions. It is commonly known as combustible ice and is widely distributed in sediments below the surface of permafrost zones and under the seabed of continental margins. Natural gas hydrate has a huge natural gas storage capacity. The world's natural gas hydrate reserves are very large, equivalent to 2×10 5 100 million tons of oil equivalent, which is twice the total carbon content of conventional fuels in the world.

[0003] Natural gas hydrate deposits have been discovered in 79 countries and regions worldwide. However, large-scale commercial production of combustible ice faces numerous challenges. Natural combustible ice is solid and does not spontaneously flow like oil. In 2017 and 2020, my country successfully conducted exploratory and experimental production of natural gas hydrates in the Shenhu area of ​​the South China Sea, respectively. However, high production costs, low yields, and poor gas production sustainability remain the main obstacles hindering the commercialization of natural gas hydrates.

[0004] Currently, pilot production plans for natural gas hydrates, both domestically and internationally, still rely on conventional offshore oil and gas extraction methods, employing conventional offshore platforms and drilling technology. Long drilling cycles and substantial platform operating expenses are the primary factors contributing to the high cost of hydrate extraction. Therefore, there is an urgent need to address the geological conditions and characteristics of marine natural gas hydrates, break through traditional oil and gas extraction approaches, and innovate to develop new extraction technologies and equipment to reduce costs and increase production.

[0005] The low permeability of natural gas hydrate reservoirs necessitates well clusters with spacing significantly smaller than that of conventional oil and gas reservoirs to achieve commercial production. Furthermore, the shallow burial depth and weakly cemented formations of natural gas hydrates result in relatively shallow well depths (approximately 200 meters) and relatively low construction difficulty. Therefore, conventional ultra-deep drilling technology based on offshore drilling platforms is not suitable for natural gas hydrate extraction. In recent years, researchers have proposed the use of rig-free subsea in-situ drilling and completion technologies and equipment for natural gas hydrate extraction. By shifting drilling equipment from surface platforms to the seabed, this technology significantly accelerates well construction and reduces extraction costs. Furthermore, subsea in-situ extraction is less susceptible to marine climate conditions, presenting significant advantages and promising feasibility, leading to the development of related technologies and patents. By developing new, lightweight, and flexible key equipment and technologies for subsea in-situ extraction, a high-density, low-cost, shallow-depth well cluster extraction solution suitable for natural gas hydrate extraction can be established, achieving efficient and low-cost extraction of natural gas hydrates to meet the requirements of commercial development.

[0006] To date, there is no mature technology and equipment for in-situ extraction of subsea natural gas hydrates internationally. A few companies, such as Germany's Bauer, the UK's BGS, and the US's Williamson & Associates, have developed subsea drilling sampling equipment. In my country, only Hunan University of Science and Technology has developed a 60-meter subsea drilling sampling device. However, these subsea drilling sampling devices cannot be directly applied to subsea natural gas hydrate extraction, and foreign technology in this area is blocked and monopolized. The drilling mud circulation system is one of the eight major components of oilfield drilling engineering. In-situ extraction of subsea natural gas hydrates requires overcoming issues such as high subsea pressure, hydrate decomposition, and operational difficulties. Summary of the invention:

[0007] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a natural gas hydrate in-situ drilling and drilling fluid treatment system, which is a supporting treatment system for the in-situ drilling of shallow natural gas hydrates or shallow marine gas under marine conditions.

[0008] The present invention is realized through the following technical solutions: a natural gas hydrate in-situ drilling and drilling fluid treatment system, comprising an offshore control platform, a natural gas hydrate seabed in-situ drilling device, a disassembly and assembly private service system, a drilling fluid feeding system, a wellhead flowback drilling fluid treatment system, a hydrate decomposition gas treatment system, a wellhead flowback drilling fluid tailings treatment system, a buoyancy control system, and a main control power communication support system connected to and controlled by each system; the natural gas hydrate seabed in-situ drilling device and the drilling fluid feeding system are respectively detachably connected to the wellhead flowback drilling fluid treatment system; the disassembly and assembly private service system is installed on the wellhead flowback drilling fluid treatment system for monitoring natural gas hydrate. the hydrate decomposition gas treatment system is installed in the wellhead flowback drilling fluid treatment system, and the hydrate decomposition gas treatment system is respectively connected to the wellhead flowback drilling fluid treatment system, the natural gas hydrate seabed in-situ drilling device, and the drilling fluid feeding system; the wellhead flowback drilling fluid tailings treatment system is connected to the wellhead flowback drilling fluid treatment system; the buoyancy control system is installed on the drilling fluid feeding system, and the buoyancy control system controls the lifting and lowering of the drilling fluid feeding system and the wellhead flowback drilling fluid treatment system; the offshore control platform is respectively connected to the natural gas hydrate seabed in-situ drilling device and the wellhead flowback drilling fluid treatment system.

[0009] The offshore control platform is used for the assembly, launching and recovery operations of the natural gas hydrate in-situ drilling and drilling fluid treatment system, the lowering, installation, control and recovery of the natural gas hydrate seabed in-situ drilling equipment, the connection, disassembly, installation and control of the natural gas hydrate seabed in-situ drilling equipment and the wellhead return drilling fluid treatment system, and supports the main control power and communication support system.

[0010] The wellhead flowback drilling fluid treatment system includes a drilling fluid treatment system shell, in which a mud pump, a vibrating screen, a screw conveyor, a desander, a desilter, a plate and frame filter press, a centrifuge, a plunger sea discharge pump, a drilling fluid stirring tank, etc. and corresponding connectors, pipelines, one-way valves and seals are arranged; the hydrate decomposition gas treatment system includes a gas-liquid-solid separator and a gas collection tank, and the hydrate decomposition gas treatment system is installed in the drilling fluid treatment system shell; the gas-liquid-solid separator is respectively connected to the mud pump, the vibrating screen and the gas collection tank; the vibrating screen, the screw conveyor, the plate and frame filter press and the plunger sea discharge pump are connected in sequence; the vibrating screen, the desander, the desilter and the centrifuge are connected in sequence, and the screw conveyor is respectively connected to the desander, the desilter and the centrifuge; the centrifuge is connected to the drilling fluid stirring tank; the drilling fluid stirring tank is respectively connected to the drilling fluid feeding system and the natural gas hydrate seabed in-situ drilling device. The wellhead flowback drilling fluid treatment system works in conjunction with the hydrate decomposition gas treatment system to ensure that solids such as waste slurry and cuttings brought up from the bottom of the well undergo screening, sand removal, and other solids control treatments before entering the circulation system. The gas-liquid-solid separator separates the drilling fluid and gas, with the separated gas discharged through an exhaust pipe at the top of the separator to the sea or into a gas collection tank. The degassed drilling fluid exits the separator through a drain pipe and enters the drilling circulation system, returning to the wellbore for the next cycle.

[0011] The natural gas hydrate seabed in-situ drilling device includes a deep-sea in-situ drilling system shell and a wellbore connected thereto, wherein a drilling rig main body mechanism, a casing, a casing installation mechanism, a guide mechanism and an in-situ drilling control mechanism are arranged in the deep-sea in-situ drilling system shell; the drilling rig main body mechanism includes a drill bit, a wellhead device and a drilling-while-driving motor, the wellhead device is installed at the wellhead of the wellbore, the drill bit is located in the wellbore, and the other end of the drill bit passes through the wellhead device and is connected to the drilling-while-driving motor; the drill bit and the drilling-while-driving motor are installed on the guide mechanism and are raised and lowered according to the control thereof; the connecting pipe of the mud pump is connected to the deep-sea in-situ drilling system shell through a first flange and communicates with the wellbore, the connecting pipe of the drilling fluid stirring tank is connected to the deep-sea in-situ drilling system shell through a second flange and communicates with the wellbore, and the lower end of the connecting pipe is located in the drill bit; the casing is installed on the casing installation structure; the drilling-while-driving motor is connected to the in-situ drilling control mechanism. The natural gas hydrate seabed in-situ drilling rig is responsible for drilling, installing casing, cementing, installing wellhead equipment and completing wells, ultimately completing the wellbore construction.

[0012] The private server disassembly and assembly system includes a private server base and a disassembly and assembly monitoring system. The private server base is provided with a shock-absorbing structure and a displacement adjustment mechanism for adjusting displacement. The drilling fluid treatment system housing is mounted on the displacement adjustment mechanism, and the shock-absorbing structure is provided on the underside of the drilling fluid treatment system housing. The disassembly and assembly monitoring system is mounted on the drilling fluid treatment system housing and aligned with the first and second flanges. The displacement adjustment mechanism can adjust the displacement of the drilling fluid treatment system housing in the front, back, left, right, and up and down directions. The disassembly and assembly monitoring system can monitor the installation and removal of the first and second flanges and is aligned with the installation position of the deep-sea in-situ drilling system housing to fix the position after installation.

[0013] The drilling fluid feeding system includes a solid-phase drilling fluid storage tank, a liquid-phase drilling fluid storage tank, a solid-phase feeding controller, and a feeding control system. The solid-phase drilling fluid storage tank and the liquid-phase drilling fluid storage tank are respectively connected to the drilling fluid mixing tank, and the solid-phase feeding controller is installed on the connecting pipe between the solid-phase drilling fluid storage tank and the drilling fluid mixing tank. The feeding control system is respectively connected to the liquid-phase drilling fluid storage tank and the solid-phase feeding controller. The structural configuration of the drilling fluid feeding system can achieve solid phase control and specific gravity control of the drilling fluid, reduce filtration loss, and facilitate drilling progress of the drill bit.

[0014] The wellhead flowback drilling fluid tailings treatment system includes a drilling fluid tailings treatment monitoring system and a subsea automated bulldozer. The drilling fluid tailings treatment monitoring system is mounted outside the drilling fluid treatment system housing and aligned with the subsea automated bulldozer, which is located on the seabed outside the discharge pipe of the plunger seawater pump. The wellhead flowback drilling fluid tailings treatment system ensures tailings removal without affecting the subsequent smooth discharge of drilling fluid tailings.

[0015] The buoyancy control system includes a pressure water tank, which houses a buoyancy system housing, a piston mounted and slidable within the housing, and a servo motor for driving the piston. The housing is connected to the exterior of the pressure water tank via a pipeline, and the servo motor drives the piston to load seawater into the housing, or to pump seawater out of the housing. The buoyancy system housing is fixedly connected to the drilling fluid treatment system housing. The buoyancy control system coordinates the system's deadweight and buoyancy through the coordination of the piston and servo motor, controlling the amount of seawater loaded, thereby reducing operational complexity.

[0016] The master control power and communication support system includes a master control system, a power and communication support system, and a power battery pack. The master control system and the power and communication support system are connected and both are located in the wellhead flowback drilling fluid processing system. The master control system connects to each system and controls its operation and start / stop. The power and communication support system provides energy and communication for the entire system.

[0017] The drilling fluid treatment system housing is a pressure-resistant cavity structure with a manhole. The pressure-resistant cavity structure can be designed according to the depth of the target water area, and the manhole is provided for easy maintenance and debugging.

[0018] Compared with the existing technology, the advantages of the present invention are: this system does not require a complex offshore drilling platform, uses unmanned automation technology to realize the operation of the drilling fluid system, simplifies the production process, realizes automation and modularization, can carry out large-scale in-situ seabed drilling, greatly reduces operating costs, and thus achieves the purpose of commercial exploitation of natural gas hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic structural diagram of an embodiment of the present invention.

[0020] The meanings of the reference numerals in the figure are as follows: 1. Mud pump; 2. First flange; 3. Wellbore; 4. Drill bit; 5. Wellhead assembly; 6. Casing; 7. Drilling motor; 8. Casing installation mechanism; 9. Deep-sea in-situ drilling system housing; 10. Second flange; 11. Disassembly and assembly monitoring system; 12. Solid-phase feeding controller; 13. Solid-phase drilling fluid storage tank; 14. Liquid-phase drilling fluid storage tank; 15. Buoyancy control system; 16. Offshore control platform; 17. Power communication support system; 18. Personnel Hole; 19. Drilling fluid tailings treatment monitoring system; 20. Private server system base; 21. Main control system; 22. Vibrating screen; 23. Screw conveyor; 24. Plate and frame filter press; 25. Plunger sea discharge pump; 26. Gas-liquid-solid separator; 27. Desander; 28. Desilter; 29. ​​Centrifuge; 30. Drilling fluid mixing tank; 31. Gas collection tank; 32. Subsea automatic bulldozer; 33. Upper sediment layer; 34. Hydrate layer; 35. Lower sediment layer; 36. Seawater. Specific implementation method:

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example

[0023] Natural gas hydrates are envelope-like crystals formed by the reaction of gas or volatile liquids with water. They exist only under high pressure and low temperature. Natural gas hydrate reservoirs are characterized by shallow burial depths, weak cementation, and low permeability. However, conventional offshore platforms and drilling techniques make extraction of natural gas hydrates prohibitively expensive, with long drilling cycles and substantial platform operating costs being the most significant factors.

[0024] Referring to FIG1 , a natural gas hydrate in-situ drilling and drilling fluid treatment system is shown, which includes an offshore control platform 16, a natural gas hydrate seabed in-situ drilling device, a disassembly and assembly private service system, a drilling fluid feeding system, a wellhead flowback drilling fluid treatment system, a hydrate decomposition gas treatment system, a wellhead flowback drilling fluid tailings treatment system, a buoyancy control system 15, and a main control power communication support system 17 connected to and controlled by each system; the natural gas hydrate seabed in-situ drilling device and the drilling fluid feeding system are detachably connected to the wellhead flowback drilling fluid treatment system; the disassembly and assembly private service system is installed on the wellhead flowback drilling fluid treatment system to monitor the natural gas hydrate in-situ drilling device and the drilling fluid feeding system. A natural gas hydrate seabed in-situ drilling device; a hydrate decomposition gas treatment system is installed in the wellhead flowback drilling fluid treatment system, and the hydrate decomposition gas treatment system is respectively connected to the wellhead flowback drilling fluid treatment system, the natural gas hydrate seabed in-situ drilling device, and the drilling fluid feeding system; the wellhead flowback drilling fluid tailings treatment system is connected to the wellhead flowback drilling fluid treatment system; a buoyancy control system 15 is installed on the drilling fluid feeding system, and the buoyancy control system 15 controls the raising and lowering of the drilling fluid feeding system and the wellhead flowback drilling fluid treatment system; an offshore control platform 16 is respectively connected to the natural gas hydrate seabed in-situ drilling device and the wellhead flowback drilling fluid treatment system.

[0025] The offshore control platform 16 is used for the assembly, launching and recovery operations of the natural gas hydrate in-situ drilling and drilling fluid treatment system, the lowering, installation, control and recovery of the natural gas hydrate seabed in-situ drilling equipment, the connection, disassembly, installation and control of the natural gas hydrate seabed in-situ drilling equipment and the wellhead return drilling fluid treatment system, and supports the main control power and communication support system 17.

[0026] The wellhead flowback drilling fluid treatment system includes a drilling fluid treatment system housing, in which are arranged a mud pump 1, a vibrating screen 22, a screw conveyor 23, a desander 27, a desilter 28, a plate and frame filter press 24, a centrifuge 29, a plunger sea pump 25, a drilling fluid mixing tank 30, etc., as well as corresponding connectors, pipes, one-way valves and seals; the hydrate decomposition gas treatment system includes a gas-liquid-solid separator 26 and a gas collection tank 31, and the hydrate decomposition gas treatment system is installed in the drilling fluid treatment system housing; the gas-liquid-solid Separator 26 is connected to mud pump 1, vibrating screen 22, and gas collection tank 31, respectively. Vibrating screen 22, screw conveyor 23, plate and frame filter press 24, and plunger sea pump 25 are connected in sequence. Vibrating screen 22, desander 27, desilter 28, and centrifuge 29 are connected in sequence, and screw conveyor 23 is connected to desander 27, desilter 28, and centrifuge 29, respectively. Centrifuge 29 is connected to drilling fluid mixing tank 30, which is connected to the drilling fluid feeding system and the natural gas hydrate subsea in-situ drilling device, respectively. The wellhead flowback drilling fluid treatment system works in conjunction with the hydrate decomposition gas treatment system to ensure that solid matter such as waste slurry and cuttings brought up from the bottom of the well undergoes solid control treatment such as screening and sand removal before entering the circulation system. The gas-liquid-solid separator 26 separates the drilling fluid and gas. The separated gas is discharged to the sea or into the gas collection tank 31 through the exhaust pipe at the top of the gas-liquid-solid separator 26; the degassed drilling fluid is discharged from the gas-liquid-solid separator 26 through the drain pipe and enters the drilling circulation system, returning to the wellbore 3 for the next round of circulation.

[0027] The natural gas hydrate submarine in-situ drilling device includes a deep-sea in-situ drilling system shell 9 and a wellbore 3 connected thereto. The deep-sea in-situ drilling system shell 9 is provided with a drilling rig main body mechanism, a casing 6, a casing installation mechanism 8, a guide mechanism and an in-situ drilling control mechanism; the drilling rig main body mechanism includes a drill bit 4, a wellhead device 5 and a drilling-while-driving motor 7. The wellhead device 5 is installed at the wellhead of the wellbore 3. The drill bit 4 is located in the wellbore 3, and its other end passes through the wellhead device 5 and is connected to the drilling-while-driving motor 7; the drill bit 4 and the drilling-while-driving motor 7 are installed on the guide mechanism and are raised and lowered according to the control thereof; the connecting pipe of the mud pump 1 is connected to the deep-sea in-situ drilling system shell 9 through a first flange 2 and communicates with the wellbore 3, and the connecting pipe of the drilling fluid mixing tank 30 is connected to the deep-sea in-situ drilling system shell 9 through a second flange 10 and communicates with the wellbore 3, and the lower end of the connecting pipe is located in the drill bit 4; the casing 6 is installed on the casing 6 installation structure; the drilling-while-driving motor 7 is connected to the in-situ drilling control mechanism. The natural gas hydrate seabed in-situ drilling device is responsible for drilling, installing casing 6, cementing, installing wellhead equipment 5 and completing the well, and finally completing the construction of the well body 3.

[0028] The detachable private service system includes a private service system base 20 and a detachable monitoring system 11; the private service system base 20 is provided with a shock-absorbing structure and a displacement adjustment mechanism for adjusting displacement; the drilling fluid treatment system housing is mounted on the displacement adjustment mechanism, and the shock-absorbing structure is disposed on the underside of the drilling fluid treatment system housing; the detachable monitoring system 11 is mounted on the drilling fluid treatment system housing and aligned with the first flange 2 and the second flange 10. The displacement adjustment mechanism can adjust the displacement of the drilling fluid treatment system housing in the front-to-back, left-to-right, and up-to-down directions. The detachable monitoring system 11 can monitor the installation and removal of the first flange 2 and the second flange 10, and is aligned with the installation position of the deep-sea in-situ drilling system housing 9 to fix the position after installation. The displacement adjustment mechanism can adjust the drilling fluid treatment system housing in the front-to-back, left-to-right, and up-to-down directions. The displacement adjustment mechanism is an existing device and can be selected by combining a screw and a slider to form movement in three axial directions, without the need for detailed structural analysis. The shock-absorbing structure is an existing device and does not require detailed structural analysis. In this embodiment, the "disassembly and assembly" in the "disassembly and assembly of the private server system" includes two functions: "installation and removal".

[0029] The drilling fluid feeding system includes a solid-phase drilling fluid storage tank 13, a liquid-phase drilling fluid storage tank 14, a solid-phase feeding controller 12, and a feeding control system. The solid-phase drilling fluid storage tank 13 and the liquid-phase drilling fluid storage tank 14 are each connected to a drilling fluid mixing tank 30, and the solid-phase feeding controller 12 is mounted on a connecting pipe between the solid-phase drilling fluid storage tank 13 and the drilling fluid mixing tank 30. The feeding control system is connected to the liquid-phase drilling fluid storage tank 14 and the solid-phase feeding controller 12, respectively. This structural arrangement of the drilling fluid feeding system enables solid phase and specific gravity control of the drilling fluid, reduces filtration loss, and facilitates drilling progress of the drill bit 4.

[0030] The wellhead flowback drilling fluid tailings treatment system includes a drilling fluid tailings treatment monitoring system 19 and a subsea automatic bulldozer 32. The drilling fluid tailings treatment monitoring system 19 is mounted outside the drilling fluid treatment system housing and aligned with the subsea automatic bulldozer 32, which is located on the seabed outside the discharge pipe of the plunger sea pump 25. The wellhead flowback drilling fluid tailings treatment system ensures tailings removal without affecting the subsequent smooth discharge of drilling fluid tailings.

[0031] The buoyancy control system 15 includes a ballast tank housing a buoyancy system, a piston mounted and slidable within the housing, and a servo motor for driving the piston. The housing is connected to the exterior of the ballast tank via a pipe. The servo motor drives the piston to load seawater 36 into the housing, or pump seawater 36 out of the housing. The housing is fixedly connected to the drilling fluid treatment system housing. The buoyancy control system 15 coordinates the system's deadweight and buoyancy by controlling the amount of seawater 36 loaded, reducing operational complexity.

[0032] The main control power and communication support system 17 includes a main control system 21, power and communication support system 17, and a power battery pack. The main control system 21 and power and communication support system 17 are connected and both are located in the wellhead flowback drilling fluid processing system. The main control system 21 connects to each system and controls their operation and start / stop. The power and communication support system 17 provides energy and communication for the entire system.

[0033] The drilling fluid treatment system housing is a pressure-resistant cavity structure with a manhole 18. The pressure-resistant cavity structure can be designed according to the depth of the target water area and the deadweight of the entire system. The setting of the manhole 18 can facilitate maintenance and debugging.

[0034] In this embodiment, the entire system is installed on the seabed and is surrounded by seawater 36. The offshore control platform 16 floats on the seawater 36. The seabed is composed of an upper sediment layer 33, a hydrate layer 34, and a lower sediment layer 35 from top to bottom. The wellbore 3 passes through the upper sediment layer 33 from top to bottom, and the bottom of the wellbore 3 is located in the hydrate layer 34.

[0035] In this embodiment, many structural systems are involved, all of which are generalized structures with certain performance. The systems involved are existing technologies and there is no need to carry out specific structural analysis. The system can use a processor, which can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The processor is the control center of this device, and various interfaces and lines are used to connect various parts.

[0036] The working process of this embodiment is as follows:

[0037] (1) System ground installation, transportation, and diving

[0038] After the system is manufactured, it is assembled and tested on the surface before being carried or towed from a platform to a designated sea area. After charging, the natural gas hydrate subsea in-situ drilling rig is lowered to the designated location. The system then dives and connects to the subsea in-situ drilling rig via quick-connect flanges and an underwater robot.

[0039] (2) Drilling

[0040] After the connection is complete, an automatic airtightness test is performed. If qualified, the system will operate simultaneously with the natural gas hydrate subsea in-situ drilling rig. Communication with the subsea in-situ drilling rig can be achieved via wireless transmission. Drilling fluid is pumped from the drilling fluid mixing tank 30. By maintaining a certain pressure, the drilling fluid can enter the wellbore from the bottom of the well. At the same time, waste slurry, rock cuttings, and other materials in the drilling fluid are discharged from the bottom of the well to ensure the stability of the wellbore wall. The returned drilling fluid passes through solids control equipment such as the gas-liquid-solid separator 26, vibrating screen, desander 27, desilter 28, and centrifuge 29 to purify the drilling fluid. The separated drilling fluid enters the drilling fluid mixing tank 30, where the dosage is controlled using a weighing sensor and flow sensor. The drilling fluid properties are adjusted using the solid-phase drilling fluid storage tank 13 and the liquid-phase drilling fluid storage tank 14. The adjusted drilling fluid is then recycled. The separated rock debris, sand, and some mud are separated by the desander 27, desilter 28, and centrifuge 29 and then enter the plate and frame filter press 24. Finally, they are discharged from the system by the plunger sea pump 25. The removed rock debris is pushed to a slightly farther distance by the seabed automatic bulldozer 32 to ensure smooth drilling.

[0041] (3) Recycling

[0042] When the drilling is completed, a seabed robot is used to separate the system from the natural gas hydrate seabed in-situ drilling device, and the system is floated up and merged with the offshore control platform 16 .

[0043] The above detailed description is a specific description of a feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the patent scope of this case.

Claims

1. A natural gas hydrate in-situ drilling and drilling fluid treatment system, characterized in that: It includes an offshore control platform, a natural gas hydrate seabed in-situ drilling device, a disassembly and assembly private service system, a drilling fluid feeding system, a wellhead return drilling fluid treatment system, a hydrate decomposition gas treatment system, a wellhead return drilling fluid tailings treatment system, a buoyancy control system, and a main control power communication support system connected and controlled with each system; the natural gas hydrate seabed in-situ drilling device and the drilling fluid feeding system are respectively detachably connected with the wellhead return drilling fluid treatment system; the disassembly and assembly private service system is installed on the wellhead return drilling fluid treatment system, and is used to monitor the natural gas hydrate seabed in-situ drilling device; The hydrate decomposition gas processing system is installed in the wellhead return drilling fluid processing system, and the hydrate decomposition gas processing system is respectively connected to the wellhead return drilling fluid processing system, the natural gas hydrate seabed in-situ drilling device, and the drilling fluid feeding system; the wellhead return drilling fluid tailings processing system is connected to the wellhead return drilling fluid processing system; the buoyancy control system is installed on the drilling fluid feeding system, and the buoyancy control system controls the lifting and lowering of the drilling fluid feeding system and the wellhead return drilling fluid processing system; the offshore control platform is respectively connected to the natural gas hydrate seabed in-situ drilling device and the wellhead return drilling fluid processing system.

2. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 1, characterized in that: The wellhead flowback drilling fluid treatment system comprises a drilling fluid treatment system shell, in which a mud pump, a vibrating screen, a screw conveyor, a desander, a desilter, a plate and frame filter press, a centrifuge, a plunger sea discharge pump, a drilling fluid stirring tank, etc. and corresponding connectors, pipelines, one-way valves and seals are arranged; the hydrate decomposition gas treatment system comprises a gas-liquid-solid separator and a gas collecting tank, and the hydrate decomposition gas treatment system is installed in the drilling fluid treatment system shell; the gas-liquid-solid separator is connected to the mud pump, the vibrating screen and the gas collecting tank respectively; the vibrating screen, the screw conveyor, the plate and frame filter press and the plunger sea discharge pump are connected in sequence; the vibrating screen, the desander, the desilter and the centrifuge are connected in sequence, and the screw conveyor is connected to the desander, the desilter and the centrifuge respectively; the centrifuge is connected to the drilling fluid stirring tank; the drilling fluid stirring tank is connected to the drilling fluid feeding system and the natural gas hydrate seabed in-situ drilling device respectively.

3. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 1, characterized in that: The natural gas hydrate seabed in-situ drilling device comprises a deep-sea in-situ drilling system shell and a wellbore connected thereto, wherein the deep-sea in-situ drilling system shell is provided with a drilling rig main body mechanism, a casing, a casing installation mechanism, a guide mechanism and an in-situ drilling control mechanism; the drilling rig main body mechanism comprises a drill bit, a wellhead device and a drilling-while-driving motor, wherein the wellhead device is installed at the wellhead of the wellbore, the drill bit is located in the wellbore, and the other end of the drill bit passes through the wellhead device and is connected to the drilling-while-driving motor; the drill bit and the drilling-while-driving motor are installed on the guide mechanism and are lifted and lowered by the control thereof; the connecting pipe of the mud pump is connected to the deep-sea in-situ drilling system shell through a first flange and communicated with the wellbore, the connecting pipe of the drilling fluid stirring tank is connected to the deep-sea in-situ drilling system shell through a second flange and communicated with the wellbore, and the lower end of the connecting pipe is located in the drill bit; the casing is installed on the casing installation structure; the drilling-while-driving motor is connected to the in-situ drilling control mechanism.

4. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 3, characterized in that: The private server disassembly and assembly system includes a private server system base and a disassembly and assembly monitoring system; the private server system base is provided with a shock absorbing structure and a displacement adjustment mechanism for adjusting displacement; the drilling fluid treatment system shell is installed on the displacement adjustment mechanism, and the shock absorbing structure is arranged on the lower side of the drilling fluid treatment system shell; the disassembly and assembly monitoring system is installed on the drilling fluid treatment system shell and aligned with the first flange and the second flange.

5. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 2, characterized in that: The drilling fluid feeding system includes a solid-phase drilling fluid storage tank, a liquid-phase drilling fluid storage tank, a solid-phase feeding controller and a feeding control system; the solid-phase drilling fluid storage tank and the liquid-phase drilling fluid storage tank are respectively connected to the drilling fluid stirring tank, and the solid-phase feeding controller is installed on the connecting pipe between the solid-phase drilling fluid storage tank and the drilling fluid stirring tank; the feeding control system is respectively connected to the liquid-phase drilling fluid storage tank and the solid-phase feeding controller.

6. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 2, characterized in that: The wellhead return drilling fluid tailings treatment system includes a drilling fluid tailings treatment monitoring system and a submarine automatic bulldozer; the drilling fluid tailings treatment monitoring system is installed outside the drilling fluid treatment system shell and is aimed at the submarine automatic bulldozer, and the submarine automatic bulldozer is located on the seabed outside the discharge pipe outlet of the plunger sea discharge pump.

7. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 2, characterized in that: The buoyancy control system includes a pressure water tank, in which a buoyancy system shell, a piston installed in the buoyancy system shell and capable of sliding along the shell, and a servo motor for driving the piston to move are arranged; the shell is connected to the outside of the pressure water tank through a pipeline, the piston is driven by the servo motor to load seawater into the buoyancy system shell, or the piston is driven by the servo motor to pump seawater out of the buoyancy system shell; the buoyancy system shell is fixedly connected to the drilling fluid treatment system shell.

8. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 2, characterized in that: The main control power communication support system includes a main control system, a power communication support system and a power battery pack for powering the system; the main control system and the power communication support system are connected and are both arranged in the wellhead return drilling fluid treatment system; the main control system is connected to each system and controls its operation and start and stop.

9. The natural gas hydrate in-situ drilling and drilling fluid treatment system according to claim 2, characterized in that: The drilling fluid treatment system shell is a pressure-resistant cavity structure, and a manhole is provided in the drilling fluid treatment system shell.

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