Natural gas hydrate seabed in-situ mining method

Abstract

Disclosed is a natural gas hydrate seabed in-situ mining method, comprising: on the basis of a natural gas hydrate simulation mining model, obtaining a well pattern arrangement diagram of a natural gas hydrate mining block; according to the well pattern arrangement diagram, using a vessel having deepwater equipment deployment capacity to carry a seabed in-situ mining system and go to a target sea area, and carrying out wellhead position selection; after the wellhead position selection is completed, lowering a drilling device from the water surface, and performing drilling by using a casing drilling technique; lowering a well completion device from the water surface, placing a well completion string into the well, and at the wellhead, connecting the well completion device to a seabed wellhead, and performing well completion operation; lowering a wellhead device from the water surface, connecting the wellhead device to the well completion string, performing a depressurization mining process, reducing the pressure at the underground reservoir, and gas water flowing into a production pipeline to complete mining. In the present invention, the mining devices, especially the drilling device, are transferred from the sea surface platform to the seabed, such that the mining efficiency is improved, the mining cost is reduced, and the potential risks in sea surface mining are reduced.

Description

A method for in-situ mining of natural gas hydrates on the seabed Technical field:

[0001] The present invention relates to a natural gas hydrate mining technology, and in particular to a natural gas hydrate seabed in-situ mining method. Background technology:

[0002] 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.

[0003] The low permeability of natural gas hydrate reservoirs requires 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 shallow well depths (approximately 200 meters) and relatively low well construction difficulty. Consequently, conventional ultra-deep drilling technology based on offshore drilling platforms is not suitable for natural gas hydrate extraction.

[0004] At present, the pilot production plans for natural gas hydrates at home and abroad still follow the conventional marine oil and gas production methods, using conventional offshore platforms and drilling technologies for pilot production; the long drilling cycle and huge platform operating costs are the most important factors leading to the excessively high cost of natural gas hydrate production.

[0005] Both the production rate and the cost of natural gas hydrate production trials at home and abroad are far from meeting the requirements of commercial production. The main reason is that the decomposition rate of natural gas hydrates is limited by heat transfer and seepage. Before the hydrates decompose, the permeability of natural gas hydrate deposits in the South my country Sea is very low, resulting in slow heat transfer. Therefore, the effective radius of single well production is much smaller than that of traditional oil and gas reservoirs. However, the cost of drilling high-density well patterns using traditional offshore drilling platforms is too high.

[0006] Summary of the invention:

[0007] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a method for in-situ mining of natural gas hydrates on the seabed to increase mining efficiency and reduce mining costs.

[0008] To achieve the above object, the technical solution of the present invention is:

[0009] A method for in-situ mining of natural gas hydrates on the seabed, comprising:

[0010] Based on the natural gas hydrate simulation mining model, a well pattern layout diagram of the natural gas hydrate mining block is obtained;

[0011] According to the well pattern layout, a vessel with deepwater equipment deployment capability carries a subsea in-situ mining system to the target sea area to select a wellhead location; the subsea in-situ mining system includes a drilling device, a completion device, and a wellhead device;

[0012] Lower the drilling rig from the water surface and use casing drilling technology to drill the well;

[0013] Lower the completion device from the water surface, run the completion string into the well, connect the completion device to the seabed wellhead at the wellhead, and perform the completion operation;

[0014] The wellhead device is lowered from the water surface, connected to the completion string, connected to the production pipeline, and the wellhead device valve is opened to start the pressure reduction mining process, thereby reducing the pressure in the downhole reservoir and causing the natural gas hydrates in the reservoir to decompose into gas and water. The gas and water flow into the production pipeline to complete the mining.

[0015] The method of obtaining a well pattern layout diagram of a natural gas hydrate production block based on a natural gas hydrate production model includes:

[0016] Obtain the address data and geophysical and chemical parameters of the target natural gas hydrate block, establish a natural gas hydrate extraction model that simulates real conditions at the laboratory scale, and conduct extraction simulations under different well network layout schemes. At the same time, combine numerical simulation methods to repeatedly deduce production data under different well network layout schemes, select the optimal well network layout scheme, and design the well network layout diagram of the target natural gas hydrate extraction block.

[0017] Furthermore, the well pattern layout diagram marks the location, depth and inclination of a single well, and the direction and spacing between multiple wells.

[0018] Furthermore, the step of lowering the drilling device from the water surface and drilling the well using the casing drilling technique includes:

[0019] First, the subsea drilling rig is lowered to the target location, and the subsea wellhead is deployed and the drilling rig is placed steadily on the seabed through the control of the mechanical mechanism;

[0020] After confirming that the submarine wellhead is correctly positioned and the drilling rig is placed stably, drilling begins using casing drilling technology. The drilling process is repeated according to the steps of pipe string access and connection - rotary drilling - pipe string access and connection - rotary drilling. During this period, the drilling mud is circulated and discharged. The entire process is completed by remote operation and control from the water surface.

[0021] Furthermore, the well completion device is lowered from the water surface, the completion string is lowered into the well, and the well completion device is connected to the seabed wellhead at the wellhead to perform the well completion operation, including:

[0022] The completion device is lowered from the water surface and connected to the submarine wellhead at the wellhead. Cement slurry is injected between the casing and the wellbore wall. After the cement slurry solidifies and the cementing operation is completed, and the reservoir and wellbore are connected, the completion string carried by the completion device is lowered into the well. Then, the wellhead device is lowered from the water surface and connected to the completion string. The entire process is completed by remote operation and control from the water surface.

[0023] Furthermore, during the entire process of drilling, completion and mining, the supporting vessel provides energy and electricity, the underwater hydraulic system provides power for various mechanical structures, the seabed monitoring system provides operational data and monitoring images, and the electrical and automation control system provides power transmission, voltage changes, signal communication transmission, operation and control, and provides emergency response signals in the event of an emergency.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In view of the characteristics of natural gas hydrates, such as deep water, shallow burial and weak cementation, the present invention transfers mining equipment, especially drilling equipment, from the sea surface platform to the seabed, thereby accelerating mining efficiency, significantly reducing mining costs, and minimizing potential risks of sea surface mining. At the same time, by increasing the density of the well network layout, it can effectively increase mining output and mining economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a flow chart of a method for in-situ seabed mining of natural gas hydrates according to an embodiment of the present invention;

[0027] FIG2 is a schematic diagram of the equipment components involved in the in-situ extraction of natural gas hydrates on the seabed;

[0028] Figure 3 is a schematic structural diagram of a drilling device;

[0029] Figure: 1. Drilling rig; 2. Wellhead assembly; 3. Production pipeline; 4. Subsea monitoring system; 11. Frame; 12. Portal guide rail; 13. Manipulator; 14. Lower hydraulic clamp; 15. Upper hydraulic clamp; 16. Top drive; 17. Pipe rack. 100. Pipe string. Specific implementation method:

[0030] Example:

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0032] 1 , the method for in-situ extraction of natural gas hydrates from the seabed provided in this embodiment mainly includes the following steps:

[0033] Step 1: Obtain a well pattern layout diagram of the natural gas hydrate mining block based on the natural gas hydrate simulation mining model.

[0034] In this step, by analyzing the address information of the target natural gas hydrate block and the basic data of the geophysical and chemical parameters, a natural gas hydrate extraction model simulating real conditions is established to obtain the optimal well network layout plan. The well network layout diagram of the target natural gas hydrate extraction block is designed to improve the efficiency of natural gas hydrate extraction and reduce extraction costs.

[0035] Step 2: Based on the well pattern, a vessel equipped with deepwater equipment deployment capabilities, carrying the subsea in-situ mining system, travels to the target sea area and selects a wellhead location. Specifically, the subsea in-situ mining system consists of a drilling rig 1 (with a guide tube underneath for wellhead positioning), a completion rig (including a completion string), and a wellhead rig 2.

[0036] In this step, compared with the traditional conventional marine oil and gas ultra-deep drilling technology based on offshore drilling platforms, this method uses drilling platform-free seabed in-situ drilling and completion technology and equipment to exploit natural gas hydrates, transferring drilling equipment from the sea surface platform to the seabed, which can greatly speed up well construction and reduce mining costs. At the same time, the impact of marine climate conditions on seabed in-situ mining will also be reduced, which has obvious advantages and good feasibility.

[0037] Step 3: Lower the drilling device 1 from the water surface and drill the well using the casing drilling technology.

[0038] In this step, casing is used to replace traditional drill pipe to complete the drilling.

[0039] Step 4: Lower the completion device from the water surface, lower the completion string into the well, connect the completion device to the seabed wellhead at the wellhead, and perform the completion operation;

[0040] Step 5: Lower the wellhead device 2 from the water surface, connect the wellhead device 2 to the completion string, connect the wellhead device to the production pipeline 3, open the valve of the wellhead device 2, start the pressure reduction mining process, reduce the pressure in the downhole reservoir, and decompose the natural gas hydrate in the reservoir to form gas and water. The gas and water flow into the production pipeline to complete the mining.

[0041] It can be seen that this method takes advantage of the characteristics of natural gas hydrates, such as deep water, shallow burial, and weak cementation, to transfer mining equipment, especially drilling equipment, from the sea surface platform to the seabed, thereby accelerating mining efficiency, significantly reducing mining costs, and reducing potential risks of sea surface mining. At the same time, by increasing the density of the well network layout, it can effectively increase mining output and mining economy.

[0042] In a specific embodiment, the above step 1 specifically includes:

[0043] Supported by the address data of a target natural gas hydrate block in the South my country Sea and basic data on geophysical and chemical parameters, a laboratory-scale natural gas hydrate extraction model simulating real-world conditions was established. Extraction simulations were conducted under different well pattern layouts. Simultaneously, numerical simulation methods were used to repeatedly deduce production data under different well pattern layouts. The optimal well pattern was selected, and a well pattern diagram for the target natural gas hydrate extraction block was designed. This approach improves the efficiency of natural gas hydrate extraction and reduces extraction costs. Specifically, the well pattern diagram indicates the location, depth, and inclination of individual wells, as well as the orientation and spacing between multiple wells, to facilitate the arrangement of wellheads on the seabed.

[0044] In a specific embodiment, the above step 3 specifically includes:

[0045] Based on the well pattern layout that indicates the location, depth, inclination of individual wells, and the direction and spacing between multiple wells, a vessel with deepwater equipment deployment capabilities will carry the subsea in-situ mining system to the target sea area and complete the device's location selection and deployment.

[0046] First, the subsea drilling rig is lowered to the target location, and the subsea wellhead is deployed and the drilling rig is placed steadily on the seabed through the control of the mechanical mechanism;

[0047] After confirming that the submarine wellhead is correctly positioned and the drilling rig is placed stably, drilling begins using casing drilling technology. The drilling process is repeated according to the steps of pipe string access and connection - rotary drilling - pipe string access and connection - rotary drilling. During this period, the drilling mud is circulated and discharged. The entire process is completed by remote operation and control from the water surface.

[0048] In this way, through casing drilling technology, the well construction steps are reduced, the seabed drilling efficiency is accelerated, and the well wall risk during the well construction process is reduced.

[0049] In a specific embodiment, the above step 4 specifically includes:

[0050] The completion device is lowered from the water surface and connected to the submarine wellhead at the wellhead. Cement slurry is injected between the casing and the wellbore wall. After the cement slurry solidifies and the cementing operation is completed, and the reservoir and wellbore are connected, the completion string carried by the completion device is lowered into the well. Then, the wellhead device is lowered from the water surface and connected to the completion string. The entire process is completed by remote operation and control from the water surface.

[0051] In addition, during the entire process of drilling, completion and mining, the support vessel provides energy and electricity, the underwater hydraulic system provides power for various mechanical structures, the seabed monitoring system 4 provides operation data and monitoring images, the electrical and automation control system provides power transmission, voltage change, signal communication transmission, operation and control, and provides emergency response signals in emergency situations.

[0052] Specifically, as shown in Figure 3, the drilling device 1 includes an underwater drilling rig, which includes a frame 11, in which a portal guide rail 12 and a manipulator 13 are installed, a lower hydraulic clamp 14 is installed at the bottom of the frame 11, and an upper hydraulic clamp 15 is arranged coaxially above the lower hydraulic clamp 14. The coaxial section between the upper hydraulic clamp 15 and the lower hydraulic clamp 14 is the drill string placement position, that is, the center position of the wellhead; the upper hydraulic clamp 15 is connected to the center pipe of the top drive 16 and rotates with the center pipe. The top drive 16 is assembled in the portal guide 12 to move up and down in the height direction of the portal guide rail 12; a pipe rack 17 is provided within the rotation range of the manipulator, and the pipe rack 17 is used to store and place the pipe string 100, and the manipulator 3 is used to grab the pipe string 100 between the upper hydraulic clamp 5 and the upper hydraulic clamp 4. In this way, by using a top drive, upper hydraulic clamps, and lower hydraulic clamps to connect and disconnect drill strings, and a manipulator to transfer individual drill strings between the wellhead center and the pipe rack, the manipulator is positioned between the wellhead center and the pipe rack. This reduces the amount of equipment deployed at the wellhead and occupies minimal space, making the entire subsea in-situ drilling and completion system compact. As shown in Figure 4-7, the subsea drilling rig completes the drilling process by repeating the steps of pipe string access and connection - rotary drilling - pipe string access and connection - rotary drilling.

[0053] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the essence of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for in-situ mining of natural gas hydrate on the seabed, characterized in that: include: Based on the natural gas hydrate simulation mining model, a well pattern layout diagram of the natural gas hydrate mining block is obtained; According to the well pattern layout, a vessel with deepwater equipment deployment capability carries a seabed in-situ mining system to the target sea area to select a wellhead location; the seabed in-situ mining system includes a drilling device, a completion device, and a wellhead device; Lower the drilling device from the water surface and use the casing drilling technology to drill the well; Lower the completion device from the water surface, lower the completion string into the well, connect the completion device with the seabed wellhead at the wellhead, and perform the completion operation; The wellhead device is lowered from the water surface, connected to the completion string, connected to the production pipeline, and the wellhead device valve is opened to start the depressurization process, thereby reducing the pressure in the downhole reservoir and causing the natural gas hydrate in the reservoir to decompose into gas and water. The gas and water flow into the production pipeline to complete the extraction.

2. The method for in-situ exploitation of natural gas hydrate on the seabed according to claim 1, characterized in that: The method of obtaining a well pattern layout diagram of a natural gas hydrate production block based on a natural gas hydrate production model includes: The address data and geophysical and chemical parameters of the target gas hydrate block are obtained, a gas hydrate production model simulating real conditions is established at the laboratory scale, and production simulations under different well network layouts are carried out. At the same time, the production data under different well network layouts are repeatedly deduced using numerical simulation methods, the most optimized well network layout is selected, and the well network layout diagram of the target gas hydrate production block is designed.

3. The method for in-situ mining of natural gas hydrate on the seabed according to claim 1 or 2, characterized in that: The well pattern layout diagram marks the location, depth and inclination of a single well, and the direction and spacing between multiple wells.

4. The method for in-situ exploitation of natural gas hydrate on the seabed according to claim 1, characterized in that: The method of lowering the drilling device from the water surface and drilling with casing drilling technology includes: First, the subsea drilling rig is lowered to the target location, and the subsea wellhead is deployed and the drilling rig is stably placed on the seabed through the control of the mechanical mechanism; After confirming that the position of the seabed wellhead is correct and the drilling rig is placed stably, drilling begins using casing drilling technology. The drilling process is repeated according to the steps of tubing access and connection - rotary drilling - tubing access and connection - rotary drilling. During this period, the drilling mud is circulated and discharged. The entire process is completed by remote operation and control from the water surface.

5. The method for in-situ mining of natural gas hydrate on the seabed according to claim 1, characterized in that: The method of lowering the completion device from the water surface, lowering the completion string into the well, connecting the completion device with the seabed wellhead at the wellhead, and performing the completion operation includes: lowering the completion device from the water surface, connecting the completion device with the seabed wellhead at the wellhead, injecting cement slurry between the casing and the wellbore wall, and completing the cementing operation after the cement slurry solidifies and the step of connecting the reservoir and the wellbore is completed, then lowering the completion string carried by the completion device into the well, and then lowering the wellhead device from the water surface, and connecting the wellhead device with the completion string. The whole process is completed by remote operation and control from the water surface.

6. The method for in-situ mining of natural gas hydrate on the seabed according to claim 1, characterized in that: During the entire process of drilling, completion and mining, the supporting vessel provides energy and electricity, the underwater hydraulic system provides power for various mechanical structures, the seabed monitoring system provides operating data and monitoring images, the electrical and automation control system provides power transmission, voltage change, signal communication transmission, operation and control, and provides emergency response signals in emergency situations.

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