METHOD FOR UNDERSEA IN-SITU EXPLOITATION OF NATURAL GAS HYDRATES

Abstract

A method for undersea in-situ exploitation of natural gas hydrates is provided. The method includes: obtaining a well pattern layout diagram of a natural gas hydrate exploitation block based on a natural gas hydrate simulation exploitation model; carrying an undersea in-situ exploitation system to a target sea area using a ship configured to deploy deep-water equipment, selecting the well location according to the well pattern layout diagram; lowering a drilling device using a casing drilling technique; lowering a completion device, lowering a completion pipe string into the well, and connecting the completion device to an undersea wellhead to perform completion operation; and lowering the wellhead device, connecting the wellhead device to the completion pipe string, connecting the wellhead device to a production pipeline, and starting a depressurization exploitation process to reduce the pressure at a reservoir to make gas and water flow into the production pipeline to be extracted.

Claims

1. A method for undersea in-situ exploitation of natural gas hydrates, comprising: obtaining a well pattern layout diagram of a natural gas hydrate exploitation block based on a natural gas hydrate simulation exploitation model; carrying an undersea in-situ exploitation system to a target sea area using a vessel configured to deploy a deep-water equipment, and selecting a well location according to the well pattern layout diagram, wherein the undersea in-situ exploitation system comprises a drilling device, a completion device, and a wellhead device; lowering the drilling device from a sea surface, and drilling a well using a casing drilling technique; lowering the completion device from the sea surface, lowering a completion pipe string into the well, and connecting the completion device to an undersea wellhead at the undersea wellhead to perform a completion operation; and lowering the wellhead device from the sea surface, connecting the wellhead device to the completion pipe string, connecting the wellhead device to a production pipeline, and opening a valve of the wellhead device to start a depressurization exploitation process to reduce a pressure at a reservoir depth to decompose the natural gas hydrates in a reservoir into a gas and water, wherein the gas and the water flow into the production pipeline to be extracted.

2. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 1, wherein the step of obtaining the well pattern layout diagram of the natural gas hydrate exploitation block based on the natural gas hydrate exploitation model comprises: obtaining geological data and geophysical and geochemical parameters of a target natural gas hydrate block to establish the natural gas hydrate exploitation model; and conducting exploitation simulation experiments under a plurality of well pattern layout schemes, and meanwhile, repeatedly deducing production data under the plurality of well pattern layout schemes using a numerical simulation method to select an optimal well pattern layout scheme to design a well pattern layout diagram of a target natural gas hydrate exploitation block; wherein the natural gas hydrate exploitation model simulates real conditions on a laboratory scale.

3. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 1, wherein the well pattern layout diagram indicates a location, a depth, and a dip angle of individual well, as well as a direction and a distance between different wells.

4. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 1, wherein the step of lowering the drilling device from the sea surface to drill the well using the casing drilling technique comprises: completing a lowering of an undersea drilling rig at a target location firstly, and completing a deployment of the undersea wellhead and a stable placement of the undersea drilling rig under a control of a mechanical mechanism; and after confirming that a location of the undersea wellhead is correct and the undersea drilling rig is placed stably, starting to drill the well using the casing drilling technique, completing a drilling process by repeating the drilling process following steps of pipe string accessing and connecting, rotating and drilling, pipe string accessing and connecting, rotating and drilling, and meanwhile, completing a circulation and discharge of drilling mud, wherein a whole process is completed by a remote operation and control on the sea surface.

5. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 1, wherein the step of lowering the completion device from the sea surface, lowering the completion pipe string into the well, and connecting the completion device to the undersea wellhead at the undersea wellhead to conduct the completion operation comprises: lowering the completion device from the sea surface; connecting the completion device to the undersea wellhead at the undersea wellhead, injecting cement slurry between a casing and a borehole of the well; after the cement slurry solidifies to complete a well cementing operation and a connection between the reservoir and a wellbore space is completed, lowering the completion pipe string carried by the completion device into the well; and then lowering the wellhead device from the sea surface, and connecting the wellhead device to the completion pipe string, wherein a whole process is completed by a remote operation and control on the sea surface.

6. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 1, wherein in a whole process of drilling, completion, and exploitation, a support vessel provides energy and electricity, an underwater hydraulic system provides hydraulic power for each mechanical structure, an undersea monitoring system provides operating data and monitoring images, and an electrical and automatic control system provides electricity transmission, voltage change, signal communication transmission, operation, and control, and provides emergency disposal signals in an emergency.

7. The method for the undersea in-situ exploitation of the natural gas hydrates according to claim 2, wherein the well pattern layout diagram indicates a location, a depth, and a dip angle of individual well, as well as a direction and a distance between different wells.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a flow diagram of a method for undersea in-situ exploitation of natural gas hydrates according to an embodiment of the present invention;

[0026] FIG. 2 is a schematic diagram of equipment composition involved in undersea in-situ exploitation of natural gas hydrates; and

[0027] FIGS. 3A-3B show structural schematic diagrams of a drilling device.

REFERENCE NUMERALS

[0028] 1. drilling device; 2. wellhead device; 3. production pipeline; 4. undersea monitoring system; 11. frame; 12. gantry guide rail; 13. manipulator; 14. lower hydraulic tong; 15. upper hydraulic tong; 16. top drive; 17. pipe rack; 18. leveling leg; 100. completion pipe string.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments

[0029] Technical solutions of the present invention are further described hereinafter with reference to the accompanying drawings and embodiments.

[0030] Referring to FIG. 1, the method for undersea in-situ exploitation of the natural gas hydrates according to the embodiment includes the following steps:

[0031] S1: obtaining a well network layout diagram of a natural gas hydrate exploitation block based on a natural gas hydrate simulation exploitation model.

[0032] In this step, a natural gas hydrate exploitation model that simulates real conditions is established by analyzing basic data of address data and geophysical and geochemical parameters of a target natural gas hydrate block to obtain an optimal well pattern layout scheme to design a well pattern layout of the natural gas hydrate target block to improve the efficiency of natural gas hydrate exploitation and reduce the exploitation cost.

[0033] S2: carrying an undersea in-situ exploitation system to a target sea area using a vessel with the ability to deploy deep-water equipment, and selecting the well location according to the well pattern layout diagram, wherein the undersea in-situ exploitation system includes a drilling device 1 (with a conduit below, which is responsible for wellhead positioning), a completion device (including a completion pipe string 100), and a wellhead device 2.

[0034] In this step, compared with a conventional offshore oil and gas ultra-deep drilling technique based on an offshore drilling platform, the method adopts undersea in-situ drilling and completion techniques and equipment without a drilling platform to extract the natural gas hydrates, and transfers the drilling equipment from a platform on the sea to the undersea, which can greatly increase the well construction speed and reduce the exploitation cost. Meanwhile, undersea in-situ exploitation is affected less by oceanic climatic conditions, thereby having obvious advantages and good feasibility.

[0035] S3: lowering the drilling device 1 from the sea surface to drill a well using a casing drilling technique;

[0036] In this step, casing is used instead of a traditional drill pipe to complete drilling.

[0037] S4: lowering the completion device from the sea surface, lowering a completion pipe string 100 into the well, and connecting the completion device to an undersea wellhead at the wellhead to perform completion operation; and

[0038] S5: lowering the wellhead device 2 from the sea surface, connecting the wellhead device 2 to the completion pipe string 100, connecting the wellhead device 2 to a production pipeline 3, and opening a valve of the wellhead device 2 to start a depressurization exploitation process to reduce the pressure at the reservoir depth to decompose natural gas hydrates in the reservoir into gas and water which flow into the production pipeline 3 to be extracted.

[0039] It can be seen that the method transfers exploitation equipment, especially drilling equipment, from a platform on the sea to the undersea based on the characteristics of deep water, shallow burial and weak cementation of the natural gas hydrate reservoirs, which improving the exploitation efficiency, greatly reducing the exploitation cost, and reducing potential risks of exploitation on the sea. At the same time, the exploitation output and exploitation economical efficiency can be effectively improved through a denser well pattern layout.

[0040] In a specific embodiment, S1 specifically includes: [0041] with the support of basic data of address data and geophysical and geochemical parameters of a target natural gas hydrate block in the South China Sea, establishing a natural gas hydrate exploitation model which simulates real conditions on a laboratory scale; and conducting exploitation simulation experiments under different well pattern layout schemes, and at the same time, repeatedly deducing production data under the different well pattern layout schemes using numerical simulation method to select the optimal well pattern layout scheme to design the well pattern layout diagram of the target natural gas hydrate exploitation block, so as to improve the efficiency of natural gas hydrate exploitation and reduce the exploitation cost. Specifically, the well pattern layout diagram indicates the location, depth and dip angle of individual well, as well as direction and distance between different wells.

[0042] In a special embodiment, S3 specifically includes: [0043] carrying the undersea in-situ exploitation system to the target sea area using the vessel with the ability to deploy the deep-water equipment, and selecting the well location according to the well pattern layout diagram that indicates the location, depth and dip angle of individual well, as well as direction and distance between different wells; [0044] completing the lowering of an undersea drilling rig at a target location firstly, and completing the deployment of the undersea wellhead and the stable placement of the undersea drilling rig under the control of a mechanical mechanism; and [0045] after confirming that the location of the undersea wellhead is correct and the drilling rig is placed stably, starting to drill the well using the casing drilling technique, completing the drilling process by repeating a drilling process following the steps of pipe string 100 accessing and connecting, rotating and drilling pipe string 100 accessing and connecting, rotating and drilling, and at the same time completing the circulation and discharge of drilling mud, wherein the whole process is completed by remote operation and control on the sea surface.

[0046] Thus, owing to the casing drilling technique, steps of well construction steps are reduced, the efficiency of undersea drilling is increased, and well wall risks in a well construction process are lowered.

[0047] In a special embodiment, S4 specifically includes: [0048] lowering the completion device from the sea surface; connecting the completion device to the at the head of undersea borehole, injecting cement slurry between a casing and the borehole of the well; after the cement slurry solidifies to complete well cementing operation and connection between the reservoir and the wellbore space is completed, lowering the completion pipe string 100 carried by the completion device into the well; and then lowering the wellhead device 2 from the sea surface, and connecting the wellhead device 2 to the completion pipe string 100. The whole process is completed by remote operation and control on the sea surface.

[0049] Further, in the whole process of drilling, completion and exploitation, a support vessel provides energy and electricity, an underwater hydraulic system provides hydraulic power for each mechanical structure, an undersea monitoring system 4 provides operating data and monitoring images, and an electrical and automatic control system provides electricity transmission, voltage change, signal communication transmission, operation and control, and provides emergency disposal signals and the like in an emergency.

[0050] Specifically, as shown in FIGS. 3A-3B, the drilling device 1 includes an undersea drilling rig; the undersea drilling rig includes a frame 11; a gantry guide rail 12 and a manipulator 13 are installed in the frame 11; a lower hydraulic tong 14 is installed at the bottom of the frame 11; an upper hydraulic tong 15 is arranged coaxially above the lower hydraulic tong 14; and a coaxial section between the upper hydraulic tong 15 and the lower hydraulic tong 14 is a drill string setting position, that is, the central position of a wellhead. The upper hydraulic tong 15 is connected with a central pipe of a top drive 16 and rotates with the central pipe; and the top drive 16 is assembled in the gantry guide rail 12 to move up and down in the height direction of the gantry guide rail 12. A pipe rack 17 is arranged within the rotation range of the manipulator 13; the pipe rack 17 is used for storing and holding the pipe string 100; and the manipulator 13 is used for grabbing the pipe string 100 and placing the pipe string 100 between the upper hydraulic tong 15 and the lower hydraulic tong 14. In this way, the drill string is assembled and disassembled through the top drive 16, the upper hydraulic tong 15 and the lower hydraulic tong 14, the manipulator 13 is used to pass the single drill string between the center of the wellhead and the pipe rack 17, the manipulator 13 is arranged between the center of the wellhead and the pipe rack 17, little equipment is arranged at the wellhead, and the space occupied is small, so that the space of the whole undersea in-situ drilling and completion device is compact. The undersea drilling rig repeats the drilling process according to the steps of string access connection, rotary drilling, string access connection and rotary drilling.

[0051] The above embodiments are only intended to illustrate the technical idea and characteristics of the present invention, aim to enable persons of ordinary skill in the art to understand the content of the present invention and implement it accordingly, and are not intended to limit the protection scope of the present invention. All equivalent changes or modifications made in accordance with the substance of the content of the present invention are within the protection scope of the present invention.