Raman spectroscopy of ocean
and laboratory hydrates
Keith Hester and E. Dendy Sloan
Colorado School of Mines
Thursday, June 5, 2003
12:00 p.m. – Pacific Forum
Raman spectroscopy can determine hydrate structure
and single-guest hydrate cage occupancies. Methane hydrate non-stoichiometry
causes cage occupancies to change, depending on whether hydrate formed in
a laboratory, gas-rich environment or an ocean floor, gas-lean
environment. Hydrates formed in nature could, therefore, have different
properties than laboratory hydrates.
A conceptual understanding has been developed for sII
structural transitions with mixtures of simple sI binary guests such as CH4
+ C2H6. An sII transition should occur when one
simple sI-forming guest is near the lower size limit of sI formation, and
the other simple sI-forming guest is near the upper size limit.
As recently as ODP Leg 204, ethane was measured from
cores in sufficient quantity to induce sII formation. From all
diffraction/spectroscopy measurements on Leg 204 recovered samples, only
sI has been found. The structure, along with the hydrate cage occupation,
aid understanding of mechanisms for in-situ hydrates.
Understanding in-situ hydrate properties via
Raman spectroscopy is crucial for energy recovery, CO2
sequestration, and seafloor stability.
Next: Physiology of deep-sea
animals: Implications for CO2 sequestration