A method and apparatus for combined annular drilling and production of natural gas hydrates.

Abstract

This invention discloses a method and apparatus for the combined annular drilling and production of natural gas hydrates. A large-diameter wellbore structure is established as the production well, with an internal wellbore structure for drilling and production enhancement wells. Vertically, a flared gas-gathering structure is drilled into the hydrate reservoir area of ​​the production well, and a large amount of consolidable coating sand is injected to establish a high-permeability flow zone. The internal production enhancement well continuously drills and modifies the hydrate reservoir from multiple directions, establishing multiple decomposition-promoting branch wells, and injecting supporting ceramic aggregates to support the connecting channels. This allows for continuous production from the external production well while the internal production enhancement well continuously modifies the reservoir. The drilled connecting channels, combined with the high-permeability flow zone, provide sufficient methane gas from hydrate decomposition to the production well. This apparatus enables large-scale development, reduces the cost of hydrate extraction, significantly increases production capacity, improves economic efficiency, and thus promotes the industrialization of natural gas hydrate development.

Description

Technical Field

[0001] This invention relates to the field of natural gas hydrate extraction equipment technology, and in particular to a method and apparatus for natural gas hydrate extraction that combines annular drilling and extraction. Background Technology

[0002] Currently, my country faces multiple development obstacles, including energy shortages, carbon emission reduction, and a complex international environment. Accelerating the exploitation and utilization of clean energy is crucial to ensuring the stability of its self-sufficiency. At present, my country's dependence on imported natural gas has reached 45%, and this trend is continuing to increase. The industrial-scale development of natural gas hydrates will help increase my country's natural gas production, alleviate the tight supply of domestic natural gas resources, reduce the demand for natural gas imports, reduce the use of heavily polluting coal, and promote the optimization of the energy structure.

[0003] As one of the countries vigorously conducting research on natural gas hydrate resource extraction technology, my country has successfully implemented two rounds of pilot production projects for natural gas hydrates, verifying the technical feasibility of natural gas hydrate reservoir extraction. The next step in research aims to advance the industrialization of natural gas hydrate extraction and realize its energy application as soon as possible. The research goals for the industrialization of natural gas hydrate development technology should be to achieve economies of scale, reduce the cost of industrial extraction, and improve economic efficiency. The high cost and low efficiency of natural gas hydrate reservoir extraction are mainly due to the high costs of drilling platform operation, long horizontal well construction, reservoir modification, and other procedures, as well as the low hydrate recovery rate, which makes continuous and stable gas production impossible, rendering current hydrate extraction uneconomical. Therefore, how to improve natural gas hydrate extraction technology, simplify extraction procedures, and significantly increase production capacity is a key issue that urgently needs to be addressed for the industrialization of natural gas hydrate extraction. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for the combined drilling and extraction of natural gas hydrates in the annulus.

[0005] This invention is achieved through the following technical solution: a method for the combined drilling and production of natural gas hydrates in the annulus, comprising the following steps:

[0006] Step 1: Select a suitable natural gas hydrate reservoir as the target for exploitation. Construct an exploitation platform in the offshore area, placing drilling equipment and casing required for well construction, as well as depressurization and separation / collection equipment necessary for exploiting the hydrate reservoir. Construct multiple gas production pipelines between the production well casing structure and the exploitation platform in the seawater area. Run the production well casing structure into the seabed formation area. Run an enlarged gas gathering structure into the hydrate reservoir area to establish a high-permeability guiding zone composed of consolidable coated sand. The production well consists of multiple gas production pipelines, sealing cap structures, production well casing structures, and gas gathering structures. In addition, an internal production enhancement well casing structure constitutes a production enhancement well. The production enhancement well runs from top to bottom through the four areas: the offshore area, the seawater area, the seabed formation area, and the hydrate reservoir area. Inside the production enhancement well casing structure, drill pipes are run from the exploitation platform to the hydrate reservoir area for multi-directional hydrate reservoir connectivity and modification.

[0007] Step 2: Conduct the well construction process for the production well. Use jet drilling to drill the wellbore structure of the production well casing. The wellbore depth should reach two-thirds of the depth of the hydrate reservoir. Then, run in the flared gas gathering structure and the production well casing structure.

[0008] Step 3: Install the sand control structure into the production well casing structure, down to the top of the hydrate reservoir area;

[0009] Step 4: Carry out the well construction process for the production enhancement well. In the middle position inside the production well casing structure, pass through the hollow channel of the sand control structure, lower the production enhancement well casing structure and secure it.

[0010] Step 5: Construct the high-permeability diversion zone in the hydrate reservoir area. Run a coiled tubing with a nozzle from inside the production well to the bottom, inject consolidable coating sand into the high-permeability diversion zone of the hydrate reservoir area, and fill the entire hydrate reservoir area inside the production well. After the consolidable coating sand is injected, remove the coiled tubing from inside the production well.

[0011] Step Six: Install a sealing cover structure on top of the production well casing structure, sealing it to the top of the production well casing structure, located at the mud surface in the seabed strata area; connect multiple gas production pipelines in a ring shape on top of the sealing cover structure as needed, enabling simultaneous gas production through multiple channels during hydrate extraction;

[0012] Step 7: Simultaneously carry out the construction of multiple decomposition-promoting branch wells and the production well extraction process of the production enhancement well; drill pipe is run into the casing structure of the production enhancement well, with a drill bit connected to the bottom of the drill pipe. According to the actual reservoir and engineering implementation design, multi-directional connectivity and modification are carried out in the bottom area of ​​the hydrate reservoir, drilling multiple decomposition-promoting branch wells. Supporting ceramic particles are injected into the decomposition-promoting branch wells to establish flow channels and increase the decomposition range of the hydrate reservoir. At the same time, the gas production pipeline of the production well is opened to continuously pump natural gas formed by the decomposition of hydrates in the annulus area of ​​the production well casing structure. The natural gas is then extracted through the platform's separation and storage equipment to realize the extraction of hydrates.

[0013] A combined annular drilling and production natural gas hydrate extraction device includes a construction and extraction platform, a separation and storage device, gas production pipelines, a sealing cover structure, a production well casing structure, a production enhancement well casing structure, a sand control structure, and a gas gathering structure. The construction and extraction platform is built in an offshore area where a natural gas hydrate reservoir has been discovered. In the seawater area, several gas production pipelines are constructed between the construction and extraction platform and the production well casing structure. The lower ends of the gas production pipelines communicate with the interior of the production well casing structure. The separation and storage device is installed on the construction and extraction platform and connected to the gas production pipelines. The production well casing structure is located within a seabed formation area, and the gas gathering structure is located within a hydrate reservoir area. The lower part of the production well casing structure is connected to the top of the gas gathering structure, and the sand control structure is located at the bottom inner side of the production well casing structure. The gas gathering structure is filled with a consolidable coated sand group. The production well casing structure is equipped with a sealing cover structure at its top, which is located at the mud surface of the seabed strata. The production well casing structure runs through four areas from top to bottom: the offshore area, the seawater area, the seabed strata area, and the hydrate reservoir area. The production well casing structure is fixed to the construction and mining platform. The device is equipped with a drill pipe, a drill bit installed at the end of the drill pipe, and a continuous tubing with a nozzle. During the application process, the continuous tubing, drill pipe, and drill bit are lowered from the production well casing structure into the hydrate reservoir area. The continuous tubing with a nozzle injects consolidable coating sand into the hydrate reservoir area to form a high-permeability flow zone. The drill pipe and drill bit perform multi-directional interconnection and transformation in the hydrate reservoir area to form several decomposition-promoting branch wells. Supporting ceramic particles for establishing flow communication channels are injected into the decomposition-promoting branch wells.

[0014] The wellbore depth of the production well reaches two-thirds of the depth of the hydrate reservoir area, and the wellbore is enlarged using rotary jet drilling; the sand control structure is lowered to the top of the hydrate reservoir area.

[0015] The gas collecting structure is an inverted funnel structure with a downward flaring opening, and it is inserted from the top of the hydrate reservoir region to one-third of the depth of the hydrate reservoir region.

[0016] The production well casing structure forms a production annulus region inside, and the sand control structure separates the production annulus region from the high-permeability diversion region; the sand control structure is a ring structure and is fitted around the outer periphery of the production enhancement well casing structure; the contact area between the sand control structure and the production well casing structure is provided with an expansion sealing material layer.

[0017] The production enhancement well casing structure is lowered to half the depth of the hydrate reservoir area, and its bottom position is deeper than the bottom depth of the gas gathering structure and located inside the high-permeability guiding area; the decomposition-promoting branch well has a structural overlap area with the high-permeability guiding area.

[0018] The high-permeability diversion zone extends from the top of the hydrate reservoir region to two-thirds of the depth of the hydrate reservoir region.

[0019] The solidifiable coated sand is a coated sand that can bond and solidify at low temperatures to form an organic whole that has both flow channels and interconnections.

[0020] The sealing cover structure is an annular structure with a hollow channel, and the production enhancement well casing structure passes through the hollow channel of the sealing cover structure; the contact area between the hollow channel of the sealing cover structure and the production enhancement well casing structure is provided with an expansion sealing material layer; the sealing cover structure is provided with several through holes for connecting the gas production pipeline to the construction and mining platform.

[0021] Compared with existing technologies, the advantages of this invention are as follows: The annular drilling and production combined natural gas hydrate extraction method of this application innovatively proposes an annular well structure to achieve a combined drilling and production extraction mode. It directly uses decomposition-promoting branch wells as reservoir modification measures for hydrate reservoirs. On the one hand, this simplifies the extraction process and improves gas production efficiency. The external production well separates the gas-producing annular region and the high-permeability guiding region. Decomposed hydrates enter the gas-producing annular region after passing through the high-permeability guiding region and sand control structure. The large-size vertical well structure design facilitates the upward migration of natural gas from hydrate decomposition, making extraction through the gas production channel easier. On the other hand, it solves the problems of low stability and small impact range of hydrate reservoir modification. A large-size, stable flow channel is established by supporting the ceramic aggregate combination through the high-permeability guiding region and decomposition-promoting branch wells. The decomposition-promoting branch wells extend in multiple directions, connecting distant hydrate reservoirs and expanding the extraction range. Through reasonable extraction scheme design, economies of scale can be achieved, reducing the cost of hydrate extraction, significantly increasing production capacity, improving economic efficiency, and thus promoting the industrialization of natural gas hydrate development. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the structure of an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of a structure with multiple decomposition-promoting branch wells in an embodiment of the present invention.

[0024] The meanings of the labels in the attached diagram are as follows: 1. Separation and storage equipment; 2. Construction and production platform; 3. Gas production pipeline; 4. Sealing cover structure; 5. Production well casing structure; 6. Production enhancement well casing structure; 7. Sand control structure; 8. Gas gathering structure; 9. High permeability guiding zone; 10. Consolidable coated sand; 11. Drill pipe; 12. Drill bit; 13. Supporting ceramsite; 14. First decomposition branch well; 15. Second decomposition branch well; 16. Third decomposition branch well; A. Seawater area; B. Submarine strata area; C. Hydrate reservoir area; D. Offshore area. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Example

[0027] See Figures 1 to 2 This relates to a method and apparatus for the combined drilling and extraction of natural gas hydrates in the annulus, the method comprising the following steps:

[0028] Step 1: Select a suitable natural gas hydrate reservoir as the extraction target. Construct an extraction platform 2 in offshore area D. Place drilling equipment and casing required for well construction on the extraction platform 2, as well as depressurization equipment and separation and storage equipment 1 required for extracting the hydrate reservoir. Construct multiple gas production pipelines 3 between the production well casing structure 5 and the extraction platform 2 in seawater area A. Run the production well casing structure 5 into the seabed strata area B. Run a flared gas gathering structure 8 into the hydrate reservoir area C, and establish a consolidable coated sand 1. The high-permeability guiding zone 9 consists of 0; the production well is composed of multiple gas production pipelines 3, sealing cover structure 4, production well casing structure 5, and gas gathering structure 8; in addition, the internal production enhancement well casing structure 6 constitutes the production enhancement well, which runs from top to bottom through four areas: offshore area D, seawater area A, seabed strata area B, and hydrate reservoir area C. Inside the production enhancement well casing structure 6, drill pipe 11 is lowered from the construction and production platform 2 to the hydrate reservoir area C to carry out multi-directional hydrate reservoir connectivity and transformation; the production enhancement well is composed of the production enhancement well casing structure 6.

[0029] Step 2: Conduct the well construction process for the production well. Use jet drilling to drill the wellbore structure of the production well. The wellbore depth reaches two-thirds of the depth of the hydrate reservoir. Then, run in the flared gas gathering structure 8 and the production well casing structure 5.

[0030] Step 3: Install the sand control structure 7 into the production well casing structure 5, down to the top of the hydrate reservoir area;

[0031] Step 4: Carry out the well construction process of the production enhancement well. In the middle position inside the production well casing structure 5, pass through the hollow channel of the sand control structure 7, and lower the production enhancement well casing structure 6 and fix it.

[0032] Step 5: Construct the high-permeability guiding zone 9 of the hydrate reservoir area C. Run a continuous tubing with a nozzle from inside the production well to the bottom, inject consolidable coated sand 10 into the high-permeability guiding zone 9 of the hydrate reservoir area, and fill the entire hydrate reservoir area inside the production well. After the consolidable coated sand 10 is injected, remove the continuous tubing from inside the production well.

[0033] Step 6: Insert the sealing cover structure 4 into the top of the production well casing structure 5 and seal it to the top of the production well casing structure 5. It is located at the mud surface of seabed strata area B. Multiple gas production pipelines 3 are connected to the top of the sealing cover structure 4 as needed to achieve simultaneous gas production through multiple channels during hydrate extraction.

[0034] Step 7: Simultaneously carry out the construction of multiple decomposition-promoting branch wells of the production enhancement well and the extraction process of the production well; drill pipe 11 is inserted into the casing structure 6 of the production enhancement well, and drill bit 12 is connected to the bottom of drill pipe 11. According to the actual reservoir and engineering implementation design, multi-directional connection and modification are carried out to the bottom area of ​​the hydrate reservoir, and multiple decomposition-promoting branch wells are drilled. Supporting ceramic particles 13 are injected into the decomposition-promoting branch wells to establish a flow channel and increase the decomposition range of the hydrate reservoir. At the same time, the gas production pipeline 3 of the production well is opened to continuously pump the natural gas formed by the decomposition of hydrate in the annulus area of ​​the casing structure 5 of the production well. The natural gas is then extracted through the separation and storage equipment 1 of the platform to realize the extraction of hydrate.

[0035] A combined annular drilling and production natural gas hydrate extraction device includes a construction and extraction platform 2, a separation and storage device 1, gas production pipelines 3, a sealing cover structure 4, a production well casing structure 5, a production enhancement well casing structure 6, a sand control structure 7, and a gas gathering structure 8. The construction and extraction platform 2 is built in an offshore area D where a natural gas hydrate reservoir has been discovered. In seawater area A, several gas production pipelines 3 are constructed between the construction and extraction platform 2 and the production well casing structure 5. The lower ends of the gas production pipelines 3 communicate with the interior of the production well casing structure 5. The separation and storage device 1 is installed on the construction and extraction platform 2 and connected to the gas production pipelines 3. The production well casing structure 5 is located in the seabed strata area B, and the gas gathering structure 8 is located in the hydrate reservoir area C. The lower part of the production well casing structure 5 is connected to the top of the gas gathering structure 8, and the sand control structure 7 is located at the bottom inner side of the production well casing structure 5. The interior of the gas gathering structure 8 is filled with a high-permeability conductive zone composed of consolidable coated sand 10. 9; The top of the production well casing structure 5 is equipped with a sealing cover structure 4 that is sealed to it. The sealing cover structure 4 is located at the mud surface of the seabed stratum area B; The production enhancement well casing structure 6 runs through four areas from top to bottom: the offshore area D, the seawater area A, the seabed stratum area B, and the hydrate reservoir area C. The construction and mining platform 2 is connected to the production enhancement well casing structure 6; The device is equipped with a drill pipe 11, a drill bit 12 installed at the end of the drill pipe 11, and a continuous tubing with a nozzle. The continuous tubing, drill pipe 11, and drill bit 12 are lowered into the hydrate reservoir area from the production enhancement well casing structure 6 during the application process. The continuous tubing with a nozzle injects consolidable coating sand into the hydrate reservoir area to form a high-permeability guiding area 9. The drill pipe 11 and drill bit 12 perform multi-directional interconnection and transformation in the hydrate reservoir area C to form several decomposition-promoting branch wells. Supporting ceramic particles 13 for establishing guiding and communication channels are injected into the decomposition-promoting branch wells.

[0036] The wellbore depth of the production well reaches two-thirds of the depth of the hydrate reservoir area C, and the wellbore is enlarged using rotary jet drilling; the sand control structure 7 is lowered to the top of the hydrate reservoir area C.

[0037] The gas gathering structure 8 is an inverted, downward-expanding funnel structure, inserted from the top of the hydrate reservoir region C to one-third of the depth of the hydrate reservoir region C. The downward-expanding funnel structure serves two purposes: firstly, it strengthens the wellbore stability formed after the production well is constructed, reducing the risk of sediment settling into the production well; secondly, it expands the high-permeability flow zone 9 of the hydrate, increasing the flow guidance area after hydrate decomposition.

[0038] The production well casing structure 5 forms a production annulus. The sand-control structure 7 separates the production annulus from the high-permeability guiding zone 9, ensuring that covering sand and formation sand do not enter the production annulus during subsequent hydrate extraction. The sand-control structure 7 is a ring-shaped structure, fitted around the outer periphery of the production enhancement well casing structure 6 (i.e., the hollow channel formed by the ring-shaped sand-control structure 7 allows the production enhancement well casing structure to pass through). An expansion sealing material layer is provided at the contact area between the sand-control structure 7 and the production well casing structure 5. The expansion sealing material layer ensures the airtightness after separation.

[0039] The production-enhancing well casing structure 6 is lowered to half the depth of the hydrate reservoir region C, with its bottom extending beyond the bottom depth of the gas-gathering structure 8 and located within the high-permeability flow-conducting region 9. The decomposition-promoting branch wells and the high-permeability flow-conducting region 9 have structural overlap. The bottom of the production-enhancing well casing structure 6 is located within the high-permeability flow-conducting region 9, meaning there is a certain distance between the production-enhancing well casing structure and the bottom of the high-permeability flow-conducting region 9. This ensures that multiple decomposition-promoting branch wells have structural overlap with the high-permeability flow-conducting region 9, establishing a unified flow-conducting communication channel. (See also...) Figure 2 In this embodiment, three decomposition-promoting branch wells are set up, namely the first decomposition-promoting branch well 14, the second decomposition-promoting branch well 15 and the third decomposition-promoting branch well 16.

[0040] The high-permeability flow zone 9 extends from the top of hydrate reservoir region C to two-thirds of the depth of hydrate reservoir region C. The function of the high-permeability flow zone 9 is to establish a hydrate flow area with high permeability and high conductivity. A large amount of consolidable coated sand 10 is injected from the top of hydrate reservoir region C to two-thirds of the depth of hydrate reservoir region C to establish a stable, large-area communication channel, connecting multiple decomposition-promoting branch wells in the lower hydrate reservoir. This constructs a high-conductivity flow path after hydrate decomposition, enabling the hydrates from long-distance decomposition to enter the annular production well area via this flow path, achieving large-area hydrate exploitation.

[0041] The consolidable coated sand 10 is a type of coated sand that can bond and solidify at low temperatures to form an organic whole that has both flow channels and interconnections. The consolidable coated sand 10 has stable performance in reservoir environments, maintains gas production channels, increases flow capacity, and the coated sand particles have good toughness, which strengthens the support capacity for the formation.

[0042] The sealing cover structure 4 is an annular structure with a hollow channel, and the production well casing structure 6 is installed inside the hollow channel of the sealing cover structure 4. The contact area between the hollow channel of the sealing cover structure 4 and the production well casing structure 6 is provided with an expansion sealing material layer to ensure the sealing performance after separation. The sealing cover structure 4 is provided with several through holes for connecting the gas production pipeline 3 to the construction and production platform 2.

[0043] In this embodiment, the specific number, path direction, extension length, and other parameters of the decomposition-promoting branch wells in the hydrate reservoir are comprehensively considered based on the actual resource distribution of the hydrate reservoir, the specific engineering implementation design, the existing construction technology capabilities, development effects, and benefits, to obtain the mining scheme that best meets the reservoir mining conditions and production benefits.

[0044] In step seven of the mining method in this embodiment, the casing structure 6 of the production enhancement well can be used not only to run coiled tubing for the construction of a high-permeability diversion zone, but also to run drill pipe 11 and drill bit 12 for the construction of a decomposition-promoting branch well. In addition, it can also be used to run coiled tubing equipped with corresponding functional tools for mining auxiliary measures such as formation energy replenishment, promoting hydrate decomposition, and downhole pressure regulation.

[0045] This embodiment designs a method for the combined drilling and production of natural gas hydrates in the annulus. Based on the vertical strata and environment, the extraction method is divided into four regions: offshore region D, seawater region A, strata region, and hydrate reservoir region C.

[0046] This embodiment employs a combined annular drilling and production method. A large-diameter production well structure (production well casing structure 5) is established, with an internal production enhancement well (production well casing structure 6) serving as the well structure for running coiled tubing or drill pipe 11. Vertically, a flared gas-gathering structure 8 is run into the hydrate reservoir region C, and a large amount of consolidable coated sand 10 is injected to establish a high-permeability flow zone 9. The internal production enhancement well continuously runs drill pipe 11 in multiple directions to connect and modify the hydrate reservoir, establishing multiple decomposition-promoting branch wells, and injecting supporting ceramic aggregate to support the connecting channels. This allows for continuous production from the external production well while the internal production enhancement well continuously modifies the reservoir. The drilled connecting channels, in conjunction with the high-permeability flow zone 9, provide sufficient methane gas from hydrate decomposition to the production well. In this embodiment, the "annular space" refers to the two-layered annular structure jointly established by the production well and the production enhancement well.

[0047] The above detailed description is a specific description of feasible embodiments of the present invention. These embodiments are not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included in the patent scope of this case.

Claims

1. A method for the combined drilling and production of natural gas hydrates in the annulus, characterized in that, Includes the following steps: Step 1: Select a suitable natural gas hydrate reservoir as the target for exploitation. Construct an exploitation platform in the offshore area, placing drilling equipment and casing required for well construction, as well as depressurization and separation / collection equipment necessary for exploiting the hydrate reservoir. Construct multiple gas production pipelines between the production well casing structure and the exploitation platform in the seawater area. Run the production well casing structure into the seabed formation area. Run an enlarged gas gathering structure into the hydrate reservoir area to establish a high-permeability guiding zone composed of consolidable coated sand. The production well consists of multiple gas production pipelines, sealing cap structures, production well casing structures, and gas gathering structures. In addition, an internal production enhancement well casing structure constitutes a production enhancement well. The production enhancement well runs from top to bottom through the four areas: the offshore area, the seawater area, the seabed formation area, and the hydrate reservoir area. Inside the production enhancement well casing structure, drill pipes are run from the exploitation platform to the hydrate reservoir area for multi-directional hydrate reservoir connectivity and modification. Step 2: Conduct the well construction process for the production well. Use jet drilling to drill the wellbore structure of the production well. The wellbore depth should reach two-thirds of the depth of the hydrate reservoir. Then, run in the flared gas gathering structure and the production well casing structure. Step 3: Install the sand control structure into the production well casing structure, down to the top of the hydrate reservoir area; Step 4: Carry out the well construction process for the production enhancement well. In the middle position inside the production well casing structure, pass through the hollow channel of the sand control structure, lower the production enhancement well casing structure and secure it. Step 5: Construct the high-permeability diversion zone in the hydrate reservoir area. Run a coiled tubing with a nozzle from inside the production well to the bottom, inject consolidable coating sand into the high-permeability diversion zone of the hydrate reservoir area, and fill the entire hydrate reservoir area inside the production well. After the consolidable coating sand is injected, remove the coiled tubing from inside the production well. Step Six: Install a sealing cover structure on top of the production well casing structure, sealing it to the top of the production well casing structure, located at the mud surface in the seabed strata area; connect multiple gas production pipelines in a ring shape on top of the sealing cover structure as needed, enabling simultaneous gas production through multiple channels during hydrate extraction; Step 7: Simultaneously carry out the construction of multiple decomposition-promoting branch wells of the production enhancement well and the production well's extraction process; drill pipes are inserted into the casing structure of the production enhancement well, with drill bits connected to the bottom of the drill pipes. Based on the actual reservoir conditions and engineering implementation design, multi-directional connectivity and modification are carried out in the bottom area of ​​the hydrate reservoir, drilling multiple decomposition-promoting branch wells. Supporting ceramic particles are injected into the decomposition-promoting branch wells to establish flow channels and increase the decomposition range of the hydrate reservoir. At the same time, the gas production pipeline of the production well is opened to continuously pump natural gas formed by hydrate decomposition in the annulus area of ​​the production well casing structure. The natural gas is then extracted through the platform's separation and storage equipment to realize the extraction of hydrates; the consolidable coated sand is a type of coated sand that can bond and solidify at low temperatures to form an organic whole that has both flow channels and interconnections; The apparatus also includes a method for developing natural gas hydrates through combined annular drilling and production. The apparatus comprises a development platform, separation and storage equipment, gas production pipelines, a sealing cover structure, a production well casing structure, a production enhancement well casing structure, a sand control structure, and a gas gathering structure. The development platform is erected in an offshore area where natural gas hydrate reservoirs have been discovered. In the seawater area, several gas production pipelines are constructed between the development platform and the production well casing structure. The lower ends of the gas production pipelines communicate with the interior of the production well casing structure. The separation and storage equipment is installed on the development platform and connected to the gas production pipelines. The production well casing structure is located within a seabed stratum region, and the gas gathering structure is located within a hydrate reservoir region. The lower part of the production well casing structure is connected to the top of the gas gathering structure, and the sand control structure is located at the bottom inner side of the production well casing structure. The interior of the gas gathering structure is filled with a solidifiable material. The device comprises a high-permeability flow zone composed of coated sand; the production well casing structure is topped with a sealing cover structure that is sealed to it, and the sealing cover structure is located at the mud surface of the seabed strata; the production enhancement well casing structure runs through four areas from top to bottom: the offshore area, the seawater area, the seabed strata area, and the hydrate reservoir area, and the production enhancement well casing structure is connected and fixed to the construction and mining platform; the device is equipped with a drill pipe, a drill bit installed at the end of the drill pipe, and a continuous tubing with a nozzle. During the application process, the continuous tubing, drill pipe, and drill bit are lowered from the production enhancement well casing structure into the hydrate reservoir area. The continuous tubing with a nozzle injects consolidable coated sand into the hydrate reservoir area to form a high-permeability flow zone. The drill pipe and drill bit perform multi-directional interconnection and modification in the hydrate reservoir area to form several decomposition-promoting branch wells. Supporting ceramic particles for establishing flow communication channels are injected into the decomposition-promoting branch wells. The gas collecting structure is an inverted funnel structure with a downward flaring opening, and the gas collecting structure is inserted from the top of the hydrate reservoir region to one-third of the depth of the hydrate reservoir region. The production enhancement well casing structure is lowered to half the depth of the hydrate reservoir area, and its bottom position is deeper than the bottom depth of the gas gathering structure and located inside the high-permeability guiding area. The decomposition-promoting branch well and the high-permeability diversion zone have structurally overlapping areas; The solidifiable coated sand is a coated sand that can bond and solidify at low temperatures to form an organic whole that has both flow channels and interconnections.

2. The method for combined annular drilling and production of natural gas hydrates according to claim 1, characterized in that: The wellbore depth of the production well reaches two-thirds of the depth of the hydrate reservoir area, and the wellbore is enlarged using rotary jet drilling; the sand control structure is lowered to the top of the hydrate reservoir area.

3. The method for combined annular drilling and production of natural gas hydrates according to claim 1, characterized in that: The production well casing structure forms a production annulus region inside, and the sand control structure separates the production annulus region from the high-permeability diversion region; the sand control structure is a ring structure and is fitted around the outer periphery of the production enhancement well casing structure; the contact area between the sand control structure and the production well casing structure is provided with an expansion sealing material layer.

4. The method for combined annular drilling and production of natural gas hydrates according to claim 1, characterized in that: The high-permeability diversion zone extends from the top of the hydrate reservoir region to two-thirds of the depth of the hydrate reservoir region.

5. The method for combined annular drilling and production of natural gas hydrates according to claim 1, characterized in that: The sealing cover structure is an annular structure with a hollow channel, and the production enhancement well casing structure passes through the hollow channel of the sealing cover structure; the contact area between the hollow channel of the sealing cover structure and the production enhancement well casing structure is provided with an expansion sealing material layer; the sealing cover structure is provided with several through holes for connecting the gas production pipeline to the construction and mining platform.

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