Self-entry Gravity Anchor for Marine Gas Hydrate Exploitation
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Solution Overview
Problem
Current methods for exploiting marine natural gas hydrates, such as drilling depressurization and superficial exploitation, face challenges like wellbore instability, high costs, and limited efficiency due to the decomposition of hydrates and the need for deep-sea drilling ships, which hinder long-term stable and commercial exploitation.
Innovation Solution
A self-entry exploitation device comprising a gravity anchor with a sand control device and a gas-liquid lifting system, including an electric pump, gas-liquid separator, and jet injection system, which allows for depressurization and hydraulic fracturing to extract hydrates without the need for deep-sea drilling, reducing costs and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If drilling depressurization method is used to exploit natural gas hydrates, then exploitation depth can reach 10m-500m below seabed, but wellbore instability occurs due to reservoir strength reduction and silt surging
Solution Approach 1:
The patent introduces a protective hood as an intermediary structure between the exploitation device and the hydrate reservoir. This hood prevents direct contact between the depressurization zone and the wellbore, thereby avoiding silt surging and wellbore collapse while maintaining effective exploitation depth of 10m-500m below seabed
Solution Approach 2:
The invention extracts the protective function from the wellbore structure itself and separates it into a dedicated protective hood component. This allows the wellbore to focus on exploitation while the hood handles the stabilizing function, resolving the contradiction between depth and stability
2Length of stationary object
If deep-sea drilling ship is used for drilling exploitation, then exploitation depth can reach 10m-500m below seabed, but exploitation cost increases to about 200,000,000 RMB per drilling cycle
Solution Approach 1:
The patent replaces the complex mechanical drilling system (requiring deep-sea drilling ships costing 200,000,000 RMB per cycle) with a simplified gravity-based self-entry system. The exploitation device uses gravitational potential energy for entry and achieves depressurization through a much less expensive platform, reducing cost while maintaining 10m-500m exploitation depth
Solution Approach 2:
The invention employs a disposable or reusable exploitation device that can be deployed and retrieved multiple times without the need for expensive drilling ship operations. Each device costs fraction of the drilling ship rental (7,000,000 RMB/day), making commercial exploitation viable at 10m-500m depths
3Ease of operation
If superficial exploitation method is used to collect natural gas hydrates, then exploitation equipment can be directly lowered to seabed surface, but exploitation range is limited to several meters below seabed surface
Solution Approach 1:
The patent designs a universal exploitation device that combines the simplicity of superficial exploitation (direct lowering to seabed) with the capability to reach 10m-500m depths. The device performs multiple functions: self-entry via gravity, protected depressurization, and gas collection, thereby achieving both ease of operation and deep exploitation range
4Reliability
If protective hood is used in capping depressurization method, then wellbore stability can be improved, but gas production efficiency decreases due to limited depressurization range
Solution Approach 1:
The patent makes the protective hood a dynamic structure that can expand and contract. During exploitation, the hood expands to increase the depressurization range and gas production efficiency. When not in use, it contracts to minimize interference with gas flow, thereby resolving the contradiction between stability and productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The self-entry device enables efficient and cost-effective exploitation of marine natural gas hydrates by reducing formation pressure, stabilizing the wellbore, and expanding the exploitation range, overcoming the limitations of traditional methods and facilitating commercial production.
Implementation Method 1
the gas-liquid lifting system is used to lift liquid in the cavity, so as to reduce the formation pressure
Implementation Method 2
the formation pressure around the self-entry structural body is reduced to enable natural gas hydrates around the self-entry structural body to be decomposed into natural gas and water
Implementation Method 3
high-pressure water containing solid particles is injected into the stratum around through the jet injection system; under the effect of the high-pressure water, the natural gas hydrate reservoir fractures
Implementation Method 4
The self-entry structural body is a gravity anchor... the self-entry structural body enters, together with the gas-liquid lifting system and the sand control device, the natural gas hydrate reservoir
Data Source
AI summary
A self-entry exploitation device and method for marine natural gas hydrates is provided. The exploitation device includes a self-entry structural body (1), a sand control device (2) and a gas-liquid lifting system. The self-entry structural body (1) is a gravity anchor. The sand control device (2) and the gas-liquid lifting system are mounted on the self-entry structural body (1). At least one cavity (21) is formed between the self-entry structural body (1) and the sand control device (2), and the cavity (21) is communicated with at least one channel. The sand control device (2) allows liquid and gas to pass through to enter the cavity (21) and is able to filter out silt. The gas-liquid lifting system includes at least one lifting power device (31) and has an end connected to the cavity (21) and an end extending out through a pipeline. By adoption of the exploitation device, drilling is not needed, the self-entry structural body (1) can enter a natural gas hydrate reservoir or a free gas layer below the natural gas hydrate reservoir, so that depressurizing exploitation can be realized, an exploitation system can be withdrawn, and the exploitation cost of natural gas hydrates can be greatly reduced.