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Transformations in methane hydrates.
I M Chou1, A Sharma, R C Burruss
1954 National Center and 956 National Center, United States Geological Survey, Reston, VA 20192, USA. imchou@usgs.gov
Summary
High pressure reveals two new methane hydrate structures: structure II and structure H. Structure II may dominate in deep ocean sediments, impacting gas hydrate stability.
Area of Science:
- Geochemistry
- Materials Science
- Crystallography
Background:
- Methane hydrate, a crystalline solid, forms under high pressure and low temperature conditions.
- Existing knowledge primarily describes structure I methane hydrate.
- Understanding methane hydrate structures is crucial for energy resource exploration and climate change studies.
Purpose of the Study:
- To investigate the high-pressure structural behavior of pure methane hydrate.
- To identify and characterize novel methane hydrate structures.
- To assess the potential prevalence of different methane hydrate structures in geological settings.
Main Methods:
- In situ optical microscopy
- Raman spectroscopy
- X-ray microprobe analysis
- Diamond anvil cell for high-pressure generation
Main Results:
- Discovery of two new methane hydrate structures: structure II and structure H.
- Characterization of structure II (cubic, a = 17.158(2) Å, V = 5051.3(13) ų) at 250 MPa.
- Characterization of structure H (hexagonal, a = 11.980(2) Å, c = 9.992(3) Å, V = 1241.9(5) ų) at 600 MPa.
- Compositions of the new structures remain undetermined.
Conclusions:
- High pressure induces the formation of previously unknown methane hydrate structures.
- Structure II methane hydrate is predicted to be more stable than structure I in deep marine sediments.
- These findings have implications for understanding gas hydrate stability and distribution in the Earth's subsurface.