Full-directional drilling rig, natural gas hydrate mining equipment and mining method

Abstract

The present invention relates to an all-round drilling rig, a natural gas hydrate mining device and a mining method. The all-round drilling rig includes a mining device and two drill heads installed at both the head and the tail ends of the mining device. The mining device includes a fixing part and at least three retractable mining modules arranged circumferentially along the fixing part and extending radially. The drill head includes a bracket, a drill housing and a drilling drive mechanism. The bracket is fixedly connected to the fixing part. The drill housing is rotatably supported on the fixing part or the bracket. A spiral conveyor blade is loaded on the outer peripheral wall of the drill housing. The drilling drive mechanism is arranged between the bracket and the drill housing and is used to drive the drill housing to rotate. The present invention can mine natural gas hydrates by drilling in multiple directions and has high flexibility.

Description

Technical Field

[0001] The present invention relates to the field of natural gas hydrate exploitation, and particularly to an all-round drilling rig, a natural gas hydrate exploitation equipment and an exploitation method. Background Art

[0002] As a future energy source with great potential, the worldwide research on the exploitation of natural gas hydrates has now entered the stage of actual trial exploitation. During the on-site trial exploitation process, there is a problem that the natural gas production gradually decreases and commercial exploitation cannot be continuously carried out. Existing solutions all adopt fixed production wells, such as horizontal wells, vertical wells or branched wells, etc., and their technical solutions have poor reusability of the production wells, small amount of exploitable hydrates, and can only be exploited locally. In recent years, the solid fluidization scheme can only exploit shallow surface hydrates, and it is harmful to the geological environment and destroys the seabed surface ecological environment.

[0003] Current natural gas hydrate exploitation equipment can only achieve local fluid injection and exploitation. Since most natural gas hydrates are stored in muddy silt reservoirs, relying only on fixed wells to exploit hydrates will cause the permeability of the reservoir to decrease, trigger blockage, and make the gas production during the exploitation process gradually decrease over time. The solid fluidization exploitation can only exploit the hydrates in the shallow seabed surface layer, and its exploitation efficiency is low. In summary, the current existing hydrate exploitation equipment has poor flexibility, small amount of exploitable hydrates, and low exploitation efficiency, and cannot meet the requirements of commercial exploitation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an all-round drilling rig that can drill in multiple directions to exploit natural gas hydrates with high flexibility.

[0005] To solve the above technical problem, the technical solution of the present invention is: an all-round drilling rig, comprising:

[0006] An exploitation device, the exploitation device includes a fixed part and at least three retractable exploitation modules that are circumferentially arranged along the fixed part and radially extend;

[0007] Two drilling rig heads installed at both ends of the exploitation device, each drilling rig head includes a bracket, a drilling rig housing and a drilling drive mechanism. The bracket is fixedly connected to the fixed part. The drilling rig housing is rotatably supported on the fixed part or the bracket. A spiral conveyor blade is loaded on the outer peripheral wall of the drilling rig housing. The drilling drive mechanism is arranged between the bracket and the drilling rig housing and is used to drive the drilling rig housing to rotate.

[0008] A specific structure of a drilling drive mechanism is further provided. The drilling drive mechanism includes an internal gear ring, a gear, and a motor. The body of the motor is fixed on the bracket. The internal gear ring is arranged on the inner peripheral wall of the drill casing. The gear meshes with the internal gear ring and is connected to the output shaft of the motor to drive its rotation through the motor.

[0009] A specific structure of a telescopic mining module is further provided. The telescopic mining module includes a hydraulic telescopic rod, a mining shaft, and a hydraulic control box. The hydraulic control box is connected to the hydraulic telescopic rod to control the telescoping of the hydraulic telescopic rod. The hydraulic telescopic rod is connected to the mining shaft to drive the telescoping of the mining shaft through its telescoping.

[0010] The present invention also provides a natural gas hydrate mining equipment, including:

[0011] An all-round drilling rig;

[0012] An offshore platform located above the sea level. The offshore platform includes a purification and collection system, an offshore central control console, and an injection liquid management system. The purification and collection system and the injection liquid management system are respectively connected to the offshore central control console to work under the control of the offshore central control console;

[0013] A subsea workstation fixed on the seabed surface. The subsea workstation includes a data acquisition and control circuit cabin, an injection liquid buffer tank, and a production separation tank. The data acquisition and control circuit cabin is respectively connected to the offshore central control console and the all-round drilling rig through pipelines. The injection liquid buffer tank is respectively connected to the injection liquid management system and the all-round drilling rig through pipelines. The production separation tank is respectively connected to the purification and collection system and the all-round drilling rig through pipelines.

[0014] Further, in order to facilitate the retraction and deployment of the pipeline connected between the subsea workstation and the all-round drilling rig, the subsea workstation further includes a pipeline retraction and deployment device. The pipelines connected between the subsea workstation and the all-round drilling rig are integrated into a bundle of reservoir integrated pipelines, and the reservoir integrated pipelines are coiled on the pipeline retraction and deployment device.

[0015] Further, in order to prevent the pipeline connected between the subsea workstation and the all-round drilling rig from rotating with the drill casing, a bearing is installed at the end of the drill casing at the tail of the all-round drilling rig, and the reservoir integrated pipeline passes through the bearing and is connected to the pipeline inside the all-round drilling rig.

[0016] Further, in order to facilitate the lifting and movement of the subsea workstation, a plurality of hooks are fixed on the subsea workstation.

[0017] The present invention also provides a method for exploiting natural gas hydrates, based on the natural gas hydrate exploitation equipment. The method includes:

[0018] Sending a drill rig status instruction from an offshore central console to a data acquisition and control circuit cabin; after receiving the drill rig status instruction, the data acquisition and control circuit cabin sends a status check instruction to an all-round drilling rig. The all-round drilling rig confirms its status through self-inspection and sends the status to the data acquisition and control circuit cabin. After signal relay processing by the data acquisition and control circuit cabin, the status is sent back to the offshore central console. The self-inspection and confirmation of the status include the status of two drilling drive mechanisms and the data collected by the sensor groups at the sensor collection ports of each telescopic exploitation module. The sensor groups at least include a positioning sensor, a temperature sensor, and a pressure sensor;

[0019] Based on the result sent back by the data acquisition and control circuit cabin, when the offshore central console performs a drilling control action, it controls the output purification and collection system to close and the injection liquid management system to open; when the subsea workstation receives a drilling instruction, it executes the closing of the output separation tank and the opening of the injection liquid buffer tank; after receiving the drilling instruction transmitted from the subsea workstation, the all-round drilling rig retracts the telescopic exploitation module in the corresponding direction into the drill rig according to the drilling direction; the two drill rig drive mechanisms control the forward or reverse rotation of the two drill rig casings according to the drilling direction; each sensor group transmits the real-time status of the drill rig back to the data acquisition and control circuit cabin through the reservoir integrated pipeline, and the data acquisition and control circuit cabin then transmits it back to the offshore central console;

[0020] When the offshore central console detects that it has advanced to the hydrate reservoir area, it issues an instruction to exploit the hydrates. At this time, the drill rig drive mechanisms stop operating, and it controls the telescopic exploitation module to extend and enter the state of waiting for exploitation; after the drill rig enters the state of waiting for exploitation, the offshore central console controls the output purification and collection system to open and the output separation tank to open; due to the pressure difference, the pressure in the exploitation wellbore area of the telescopic exploitation module decreases, the hydrates decompose, and the produced gas, water, and sand are sent to the output separation tank and finally transported to the output purification and collection system through pipelines, completing the pressure reduction exploitation of the hydrates. In the case where it is necessary to inject gas and liquid to promote the decomposition of the hydrates, the offshore central console controls the injection liquid management system, and the gas and liquid in the injection liquid buffer tank are injected into the reservoir through the injection pipeline in the reservoir integrated pipeline and the exploitation wellbore, thereby realizing synchronous injection and production;

[0021] When the production of hydrates in a reservoir area fails to meet the commercial exploitation requirements, the subsea workstation and the all-round drilling rig are transferred, and the all-round drilling rig drills back to recover the pipeline between the subsea workstation and the all-round drilling rig.

[0022] Further, during the drilling process of the omnidirectional drilling rig, all retractable production well modules are in the retracted state. When the omnidirectional drilling rig changes the drilling direction, the retractable production module in the corresponding direction extends. After the direction is adjusted to the specified direction, the retractable production module is then controlled to retract.

[0023] After adopting the above technical solution, the present invention has the following beneficial effects:

[0024] 1. The production device of the present invention has at least three retractable production modules evenly distributed circumferentially. The retractable production modules enable the present invention to locally extract natural gas hydrates in situ; the extension and retraction of the retractable production modules in different directions can change the drilling direction of the omnidirectional drilling rig, enabling the omnidirectional drilling rig to drill omnidirectionally. The retractable production modules can be retracted into the drilling rig, allowing the drilling rig to continue drilling, thereby making the hydrate production wellbore flexible and variable, and greatly increasing the amount of hydrates that can be extracted; both the front and rear drilling rig casings are equipped with spiral conveyor blades. During the drilling process of the drilling rig, the spiral conveyor blades can continuously transport the reservoir mud in the advancing direction of the drilling rig to the rear of the drilling rig, thereby keeping the reservoir relatively stable and safe during the extraction process.

[0025] 2. The natural gas hydrate production equipment of the present invention includes an offshore platform, a subsea workstation, and an omnidirectional drilling rig. The offshore platform serves as the personnel operation area. Its main functions are to remotely control the operation of the subsea workstation and the omnidirectional drilling rig, control the injection fluid, purify and collect the produced gas, receive, analyze, and display the collected data, and control actions such as the movement of the subsea workstation, the omnidirectional drilling of the drilling rig, and the telescoping of the production wellbore; the subsea workstation serves as a processing and temporary storage area, connecting to the offshore platform above and the omnidirectional drilling rig below, and can move and be fixed on the seabed surface; the omnidirectional drilling rig is in the drilling and production area, ensuring the safety of personnel and equipment. The omnidirectional drilling rig can drill omnidirectionally in the reservoir and extend the production wellbore directionally, and can perform operations such as injecting fluid, injecting heat, and replacement to promote the extraction of natural gas hydrates and the collection of reservoir environmental parameters. In addition, the omnidirectional drilling rig of the present invention is driven by two motors, front and rear, has multiple production wellbores, and also has multiple sensor groups. Different operations and collections enable the drilling rig to drill, extract, and monitor omnidirectionally. Description of the Drawings

[0026] Figure 1 It is a drilling schematic diagram of the omnidirectional drilling rig of the present invention;

[0027] Figure 2 It is a drilling direction schematic diagram of the omnidirectional drilling rig of the present invention;

[0028] Figure 3 It is a left view of the omnidirectional drilling rig of the present invention;

[0029] Figure 4 Front view of the omnidirectional drilling rig of the present invention;

[0030] Figure 5 Top view of the omnidirectional drilling rig of the present invention;

[0031] Figure 6 Disassembly schematic diagram of the omnidirectional drilling rig of the present invention;

[0032] Figure 7 Structural schematic diagram of the natural gas hydrate mining equipment of the present invention;

[0033] In the figure:

[0034] 1. Telescopic mining module; 11. Hydraulic telescopic rod; 12. Mining shaft; 13. Hydraulic control box; 14. Sensor acquisition port;

[0035] 21. Bracket; 22. Drill rig housing; 23. Drilling drive mechanism; 231. Internal gear ring; 232. Gear; 233. Motor;

[0036] 3. Sea level;

[0037] 41. Purification and collection system; 42. Offshore central console; 43. Injection liquid management system;

[0038] 5. Seabed surface;

[0039] 61. Data acquisition and control circuit cabin; 62. Injection liquid buffer tank; 63. Output separation tank;

[0040] 7. Bearing;

[0041] 8. Hook;

[0042] 9. Ocean integrated pipeline. Specific embodiments

[0043] In order to make the content of the present invention easier to be clearly understood, the present invention will be further described in detail below according to specific embodiments in conjunction with the accompanying drawings.

[0044] Embodiment 1

[0045] As shown in Figure 1 , 2 , 3, 4, 5, 6, 7, an omnidirectional drilling rig includes:

[0046] A mining device, the mining device includes a fixed part and at least three circumferentially arranged and radially extending telescopic mining modules 1 along the fixed part;

[0047] Two drill heads installed at both the head and tail ends of the mining device. The drill head includes a bracket 21, a drill housing 22, and a drilling drive mechanism 23. The bracket 21 is fixedly connected to the fixed part. The drill housing 22 is rotatably supported on the fixed part or the bracket 21. A spiral conveyor blade 24 is loaded on the outer peripheral wall of the drill housing 22. The drilling drive mechanism 23 is arranged between the bracket 21 and the drill housing 22 and is used to drive the drill housing 22 to rotate. The spiral drill housing 22 is driven to rotate by the drilling drive mechanism 23, enabling the drill to drill in the hydrate reservoir.

[0048] In this embodiment, the conical head of the drill housing 22 at the head end faces forward, and the conical head of the drill housing 22 at the tail end faces backward. During drilling, the two drill housings 22 at the head and tail rotate driven by two rotary drive mechanisms, and all the telescopic mining modules 1 retract into the drill.

[0049] In this embodiment, the drill housing 22 is installed on the fixed part or the bracket 21 through a rotary bearing, so that the front and rear spiral drill housings 22 can rotate and drill without rotating the telescopic mining modules 1.

[0050] Specifically, the mining device of this embodiment has at least three telescopic mining modules 1 evenly distributed circumferentially. The telescopic mining modules 1 enable local in-situ mining of natural gas hydrates in this embodiment. The extension and retraction of the telescopic mining modules 1 in different directions can change the drilling direction of the omnidirectional drilling rig, enabling the omnidirectional drilling rig to drill omnidirectionally. The telescopic mining modules 1 can retract into the drill, allowing the drill to continue drilling, thus making the hydrate production wellbore 12 flexible and variable, and greatly increasing the amount of hydrates that can be mined. The drill housings 22 at the head and tail are both equipped with spiral conveyor blades 24. During the drilling of the drill, the spiral conveyor blades 24 can continuously transport the reservoir mud in the forward direction of the drill to the tail of the drill, so that the reservoir remains relatively stable and safe during the mining process.

[0051] As Figure 1 、 2 As shown in Figures 3, 4, 5, 6, 7, the drilling drive mechanism 23 includes an internal gear ring 231, a gear 232, and a motor 233. The body of the motor 233 is fixed on the bracket 21. The internal gear ring 231 is arranged on the inner peripheral wall of the drill housing 22. The gear 232 meshes with the internal gear ring 231 and is connected to the output shaft of the motor 233 to drive its rotation through the motor 233.

[0052] As Figure 1 、 2As shown in FIGS. 3, 4, 5, 6, and 7, the telescopic mining module 1 includes a hydraulic telescopic rod 11, a mining shaft 12, and a hydraulic control box 13. The hydraulic control box 13 is connected to the hydraulic telescopic rod 11 to control the telescopic movement of the hydraulic telescopic rod 11. The hydraulic telescopic rod 11 is connected to the mining shaft 12 to drive the telescopic movement of the mining shaft 12 through its telescopic movement.

[0053] In this embodiment, there are 4 telescopic mining modules 1. The hydraulic control boxes 13 of the four telescopic mining modules 1 facing the front of the drill are independently controlled respectively. Figure 2 If the indicated drilling direction is upward, the upper mining shaft 12 and the hydraulic telescopic rod 11 extend out of the hydraulic control box 13. In this way, when the drill is drilling, the front drill housing 22 will tilt upward, thus changing the drilling direction. When the direction is adjusted to the specified direction, then control the upper telescopic mining well module 1 to retract, so that the mining shaft 12 and the hydraulic telescopic rod 11 retract into the hydraulic control box 13, and the drilling direction will no longer change; the control of the drilling direction downward, left, and right is the same reason.

[0054] Embodiment Two

[0055] As Figure 1 、 2 As shown in FIGS. 3, 4, 5, 6, and 7, a natural gas hydrate mining equipment includes:

[0056] The all-round drilling rig described in Embodiment One;

[0057] An offshore platform, which is located above the sea level 3. The offshore platform includes a purification and collection system 41, an offshore central control console 42, and an injection liquid management system 43. The purification and collection system 41 and the injection liquid management system 43 are respectively connected to the offshore central control console 42 to work under the control of the offshore central control console 42;

[0058] An undersea workstation, which is fixed on the seabed surface 5. The undersea workstation includes a data acquisition and control circuit cabin 61, an injection liquid buffer tank 62, and a production separation tank 63. The data acquisition and control circuit cabin 61 is respectively connected to the offshore central control console 42 and the all-round drilling rig through pipelines. The injection liquid buffer tank 62 is respectively connected to the injection liquid management system 43 and the all-round drilling rig through pipelines. The production separation tank 63 is respectively connected to the purification and collection system 41 and the all-round drilling rig through pipelines.

[0059] In this embodiment, in order to prevent the pipelines connected between the offshore platform and the undersea workstation from being messy, the pipelines connected between the offshore platform and the undersea workstation are integrated into a bundle of marine integrated pipelines 9.

[0060] In this embodiment, the data acquisition and control circuit cabin 61 is respectively connected to the offshore central console 42 and the omnidirectional drilling rig through circuit pipelines. The liquid injection buffer tank 62 is respectively connected to the injection liquid management system 43 and the omnidirectional drilling rig through injection pipelines. The production separation tank 63 is respectively connected to the purification and collection system 41 and the omnidirectional drilling rig through production pipelines. The injection pipelines include hydraulic injection pipelines and production injection pipelines. Due to the presence of injection pipelines, natural gas hydrates can be exploited by multiple principles, such as thermal injection, chemical reagent injection, and replacement method for hydrate exploitation.

[0061] Specifically, the natural gas hydrate exploitation equipment in this embodiment includes an offshore platform, a subsea workstation, and an omnidirectional drilling rig. The offshore platform serves as the personnel operation area, and its main functions are to remotely control the operation of the subsea workstation and the omnidirectional drilling rig, control the injection liquid, purify and collect the produced gas, receive and analyze and display the collected data, and control actions such as the movement of the subsea workstation, the omnidirectional drilling of the rig, and the telescoping of the production wellbore 12. The subsea workstation serves as a processing and temporary storage area, connecting to the offshore platform above and the omnidirectional drilling rig below, and can move and be fixed on the seabed surface 5. The omnidirectional drilling rig is in the rig exploitation area, ensuring the safety of personnel and equipment. The omnidirectional drilling rig can drill omnidirectionally in the reservoir and extend the production wellbore 12 directionally, and can perform operations such as liquid injection, heat injection, replacement, etc. to promote the exploitation of natural gas hydrates and collect reservoir environment parameters. In addition, the omnidirectional drilling rig of the present invention is driven by two motors 233 at the front and rear, has multiple production wellbores 12, and also has multiple sensor groups. Different operations and collections enable the rig to drill, exploit, and monitor omnidirectionally.

[0062] As Figure 7 shown, the subsea workstation further includes a pipeline retracting and deploying device 64. The pipelines connecting the subsea workstation and the omnidirectional drilling rig are integrated into a bundle of reservoir integrated pipelines 65, and the reservoir integrated pipelines 65 are coiled on the pipeline retracting and deploying device 64.

[0063] In this embodiment, the pipeline retracting and deploying device 64 includes a control wheel support, a control wheel rotatably supported on the control wheel support, and a fixed pulley. The control wheel can be driven to rotate. The reservoir integrated pipelines 65 are coiled on the control wheel and bypass the fixed pulley. During the process of the rig drilling back, the control wheel rotates to retract the reservoir integrated pipelines, so that the omnidirectional drilling rig retracts and is fixed to the subsea workstation.

[0064] As Figure 1 、 2As shown in Figures 3, 4, 5, 6, and 7, a bearing 7 is installed at the tail end of the drill housing 22 at the tail of the all-round drilling rig. The reservoir integrated pipeline 65 passes through the bearing 7 and is connected to the pipelines inside the all-round drilling rig. The bearing 7 enables the drill housing 22 at the tail of the rig not to rotate along with the reservoir integrated pipeline 65 during drilling.

[0065] In this embodiment, the hydraulic valves at the roots of the respective production wellbores 12 can be remotely controlled, so that the production wellbores 12 are switched to communicate with the production injection pipeline or the production pipeline of the rig; the hydraulic control pipeline, the production injection pipeline, the production pipeline, and the circuit pipeline of the rig are assembled into the internal integrated pipeline of the rig and then connected to the reservoir integrated pipeline 65.

[0066] As Figure 7 shown, a plurality of hooks 8 are fixed on the subsea workstation. The hooks are released from the offshore platform and connected to the hooks 8 on the subsea workstation, and then moved to other areas, so that the subsea workstation and the all-round drilling rig can repeat the exploitation in other places.

[0067] Embodiment 3

[0068] A method for exploiting natural gas hydrates, based on the natural gas hydrate exploitation equipment described in Embodiment 2, the method includes:

[0069] Sending a rig status instruction from the offshore control console 42 to the data acquisition and control circuit module 61; after receiving the rig status instruction, the data acquisition and control circuit module 61 sends a status check instruction to the all-round drilling rig. The all-round drilling rig confirms its status through self-check and sends the status to the data acquisition and control circuit module 61. After signal transfer and processing by the data acquisition and control circuit module 61, it is then transmitted back to the offshore control console 42. The self-check confirmation status includes the status of the two drilling drive mechanisms 23 and the data collected by the sensor groups at the sensor collection ports 14 of each retractable production module 1. The sensor groups at least include a positioning sensor, a temperature sensor, and a pressure sensor;

[0070] Based on the results transmitted back by the data acquisition and control circuit module 61, when the offshore control console 42 performs a drilling control action, it controls the production purification and collection system 41 to close and the injection liquid management system 43 to open; when the subsea workstation receives a drilling instruction, it executes the closing of the production separation tank 63 and the opening of the injection liquid buffer tank 62; after receiving the drilling instruction transmitted from the subsea workstation, the all-round drilling rig retracts the corresponding retractable production module 1 in the specified direction into the rig according to the drilling direction; the two rig drive mechanisms control the two drill housings 22 to rotate forward or backward according to the drilling direction; each sensor group transmits the real-time status of the rig back to the data acquisition and control circuit module 61 through the reservoir integrated pipeline 65, and the data acquisition and control circuit module 61 then transmits it back to the offshore control console 42;

[0071] When the offshore central control console 42 detects that it has advanced into the hydrate reservoir area, it issues an instruction to extract hydrates. At this time, the drilling rig drive mechanism stops operating, and the retractable extraction module 1 is controlled to extend and enter the state of waiting for extraction. After the drilling rig enters the state of waiting for extraction, the offshore central control console 42 controls the output purification and collection system 41 to open, and the output separation tank 63 is opened. Due to the pressure difference, the pressure in the extraction wellbore 12 area of the retractable extraction module 1 decreases, the hydrates decompose, and the produced gas, water and sand are sent to the output separation tank 63, and finally transported to the output purification and collection system 41 through pipelines, completing the pressure reduction extraction of hydrates. In the case where it is necessary to inject gas and liquid to promote the decomposition of hydrates, the offshore central control console 42 controls the injection liquid management system 43, and the gas and liquid in the injection liquid buffer tank 62 are injected into the reservoir through the injection pipeline in the reservoir integrated pipeline 65 and the extraction wellbore 12, so as to realize synchronous injection and production;

[0072] When the output of hydrate extraction in a reservoir area fails to meet the requirements of commercial extraction, the subsea workstation and the omnidirectional drilling rig are transferred, and the omnidirectional drilling rig drills back to recover the pipeline between the subsea workstation and the omnidirectional drilling rig.

[0073] In this embodiment, during the drilling process of the omnidirectional drilling rig, all retractable extraction well modules are in the retracted state. When the omnidirectional drilling rig changes the drilling direction, the retractable extraction module 1 in the corresponding direction extends, and the retractable extraction module 1 is controlled to retract after the direction is adjusted to the specified direction.

[0074] Inspired by the above ideal embodiment according to the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for exploiting natural gas hydrate, characterized in that: It is carried out based on natural gas hydrate exploitation equipment, and the natural gas hydrate exploitation equipment includes: An all-round drilling rig, including an exploitation device and two drill heads installed at both ends of the exploitation device. The exploitation device includes a fixed part and at least three retractable exploitation modules (1) arranged circumferentially along the fixed part and extending radially; the drill head includes a bracket (21), a drill housing (22) and a drilling drive mechanism (23). The bracket (21) is fixedly connected to the fixed part. The drill housing (22) is rotatably supported on the fixed part or the bracket (21). A spiral conveyor blade (24) is loaded on the outer peripheral wall of the drill housing (22). The drilling drive mechanism (23) is arranged between the bracket (21) and the drill housing (22) and is used to drive the drill housing (22) to rotate; An offshore platform, which is located above the sea level (3). The offshore platform includes a purification and collection system (41), an offshore central control console (42) and an injection liquid management system (43). The purification and collection system (41) and the injection liquid management system (43) are respectively connected to the offshore central control console (42) to work under the control of the offshore central control console (42); An undersea workstation, which is fixed on the seabed surface (5). The undersea workstation includes a data acquisition and control circuit cabin (61), an injection liquid buffer tank (62) and a production separation tank (63). The data acquisition and control circuit cabin (61) is respectively connected to the offshore central control console (42) and the all-round drilling rig through pipelines. The injection liquid buffer tank (62) is respectively connected to the injection liquid management system (43) and the all-round drilling rig through pipelines. The production separation tank (63) is respectively connected to the purification and collection system (41) and the all-round drilling rig through pipelines; The method includes: Sending a drill state instruction to the data acquisition and control circuit cabin (61) through the offshore central control console (42); after receiving the drill state instruction, the data acquisition and control circuit cabin (61) sends a state check instruction to the all-round drilling rig. The all-round drilling rig confirms its state through self-check and sends the state to the data acquisition and control circuit cabin (61). After signal transfer and processing, the data acquisition and control circuit cabin (61) sends it back to the offshore central control console (42). The self-check and confirmed state includes the states of the two drilling drive mechanisms (23) and the data collected by the sensor groups of the sensor acquisition ports (14) of each retractable exploitation module (1). The sensor groups at least include a positioning sensor, a temperature sensor and a pressure sensor; Based on the results transmitted back by the subsea control console (42) from the data acquisition and control circuit module (61), when performing drilling control actions, the subsea control console (42) controls the production purification and collection system (41) to close and the injection fluid management system (43) to open; when the subsea workstation receives a drilling instruction, it executes the closing of the production separation tank (63) and the opening of the injection fluid buffer tank (62); after the omnidirectional drilling rig receives the drilling instruction transmitted from the subsea workstation, it retracts the retractable mining module (1) in the corresponding direction into the interior of the rig according to the drilling direction; the two drilling drive mechanisms control the forward or reverse rotation of the two drill casings (22) according to the drilling direction; each sensor group transmits the real-time state of the rig back to the data acquisition and control circuit module (61) via the reservoir integrated pipeline (65), and the data acquisition and control circuit module (61) then transmits it back to the subsea control console (42). When the subsea control console (42) detects that it has advanced into the hydrate reservoir area, it issues a hydrate mining instruction. At this time, the drilling drive mechanism stops operating, and it controls the retractable mining module (1) to extend and enter the state of waiting for mining; after the rig enters the state of waiting for mining, the subsea control console (42) controls the production purification and collection system (41) to open and the production separation tank (63) to open; due to the pressure difference, the pressure in the mining wellbore (12) area of the retractable mining module (1) decreases, the hydrate decomposes, and the produced gas, water, and sand are sent to the production separation tank (63), and finally transported to the production purification and collection system (41) through pipelines, completing the pressure reduction mining of hydrates. In the case where it is necessary to inject gas and liquid to promote the decomposition of hydrates, the subsea control console (42) controls the injection fluid management system (43), and the gas and liquid in the injection fluid buffer tank (62) are injected into the reservoir through the injection pipeline in the reservoir integrated pipeline (65) and the mining wellbore (12), thereby realizing synchronous injection and production. When the production of hydrates in a reservoir area fails to meet the requirements of commercial mining, the subsea workstation and the omnidirectional drilling rig are relocated. The omnidirectional drilling rig drills back and retrieves the pipeline between the subsea workstation and the omnidirectional drilling rig.

2. The method for mining natural gas hydrates according to claim 1, wherein the drilling drive mechanism (23) includes an internal gear ring (231), a gear (232), and a motor (233). The body of the motor (233) is fixed on the bracket (21). The internal gear ring (231) is arranged on the inner peripheral wall of the drill casing (22). The gear (232) meshes with the internal gear ring (231) and is connected to the output shaft of the motor (233) to drive its rotation through the motor (233).

3. The method for mining natural gas hydrates according to claim 1, wherein the retractable mining module (1) includes a hydraulic telescopic rod (11), a mining wellbore (12), and a hydraulic control box (13). The hydraulic control box (13) is connected to the hydraulic telescopic rod (11) to control the telescoping of the hydraulic telescopic rod (11). The hydraulic telescopic rod (11) is connected to the mining wellbore (12) to drive the telescoping of the mining wellbore (12) through its telescoping.

4. The natural gas hydrate exploitation method according to claim 1, characterized in that the subsea workstation further includes a pipeline retracting and deploying device (64), and pipelines connected between the subsea workstation and the omnidirectional drilling rig are integrated into a bundle of reservoir integrated pipelines (65), and the reservoir integrated pipelines (65) are coiled on the pipeline retracting and deploying device (64).

5. The natural gas hydrate exploitation method according to claim 4, characterized in that a bearing (7) is installed at the tail end of the drill housing (22) at the tail of the omnidirectional drilling rig, and the reservoir integrated pipeline (65) passes through the bearing (7) and is connected to the pipeline inside the omnidirectional drilling rig.

6. The natural gas hydrate exploitation method according to claim 1, characterized in that a plurality of hooks (8) are fixed on the subsea workstation.

7. The natural gas hydrate exploitation method according to claim 1, characterized in that during the drilling process of the omnidirectional drilling rig, all retractable exploitation modules are in the retracted state. When the omnidirectional drilling rig changes the drilling direction, the retractable exploitation module (1) in the corresponding direction extends, and then the retractable exploitation module (1) is controlled to retract after the direction is adjusted to the specified direction.

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