Hydrate reformation characteristics in natural gas hydrate dissociation process: A review
- Hydrate reformation during exploitation is caused mainly by insufficient heat supply.
Hydrate reformation is likely to occur in the depressurization process.
The depressurization process should be combined with thermal stimulation.
A new system is designed to investigate hydrate reformation under various conditions
Natural gas hydrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane clathrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. (Source: Wikipedia)
Natural gas hydrates are considered as some of the most promising energy sources. However, economical, safe, and commercial exploitation of marine hydrates has not yet been achieved. One of the main obstacles is hydrate reformation in the process of hydrate exploitation, which needs to be properly addressed. The processes of hydrate dissociation and reformation under depressurization and thermal stimulation are discussed in this review. It is necessary to understand the manner in which various factors affect hydrate reformation during dissociation. Therefore, the effects of critical factors on hydrate reformation during thermal stimulation and depressurization dissociation are analysed to provide a comprehensive explanation of the hydrate reformation mechanism. In addition, several measures used to prevent hydrate reformation during the exploitation process are discussed. Finally, an experimental system was designed to investigate the exploitation methods and optimization of various hydrate-bearing sediments. Future efforts should focus on finding effective methods and evaluating the combined sequences, which can prevent hydrate reformation with acceptable exploitation efficiency.
Gas hydrate exploitation
Fig. 1. Schematic diagram of methane hydrate phase equilibrium
Fig. 2. Schematic diagram of hydrate dissociation process under thermal stimulation (modified from Jamaluddin et al. ).
Fig. 3. Schematic diagram of the hydrate dissociation process under depressurization (modified from Hong ).