1 / 24

Gas Hydrate Stability: Dissolution vs. Dissociation

Gas Hydrate Stability: Dissolution vs. Dissociation. Rachel Marie Wilson , Laura L. Lapham, Jeff Chanton,. Dissociation: occurs when the hydrate is exposed to P/T regimes not in the stability zone. Dissolution:

vanna-stanley
Télécharger la présentation

Gas Hydrate Stability: Dissolution vs. Dissociation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gas Hydrate Stability: Dissolution vs. Dissociation Rachel Marie Wilson ,Laura L. Lapham, Jeff Chanton,

  2. Dissociation: occurs when the hydrate is exposed to P/T regimes not in the stability zone Dissolution: the hydrate is stable at the P/T regime, but surrounding gas concentration is under-saturated 4 Primary Factors Controlling Hydrate Stability Pressure Temperature Salinity Guest concentration in the surrounding environment

  3. Pressure Temperature Guest Concentration Lapham , et al. (2010) Earth and Planetary Science Letters

  4. Hydrate Dissolution Rates Synthetic Hydrate taken down into the water column within the hydrate stability zone: • Hester et al. (2009) 110 cm/yr • Rehder et al. (2004) 167 cm/yr Pressure and Temperature  OK Methane concentration  below stability

  5. Hydrate stability: seafloor observations 2006 2004 Barkley Canyon, Cascadia Margin Photos Ross Chapman

  6. Bush Hill, Gulf of Mexico MacDonald et al. (2005)

  7. 17 cm 10 cm 24 cm 2004 Based on CH4 concentrations measured at these sites: Diffusion controlled dissolution = 30 cm/yr 2002 2003 Observed rate = 3.5 cm/yr Lapham et al. (2010) Earth and Planetary Science Letters

  8. Lapham, et al. (2010) Earth and Planetary Science Letters

  9. Recap • Exposed hydrate mounds present on the seafloor in under-saturated conditions should be rapidly dissolving • Evidence does not support dissolution at the rate we would expect • Observed rates of exposed hydrate dissolution appear to be an order of magnitude lower than we would expect • Something is acting to slow the hydrate dissolution • Hydrate may be re-supplied from below

  10. Bigalke et al. (2009) have demonstrated that hydrate dissolution rates are diffusion controlled (i.e. kd = D/z) • We want to ask: What are the influences on z (boundary layer) that could be enhancing hydrate stability in the natural environment? • Hydrate Composition • Oil/biofilms • Sediment Figure from Bigalke, N Rehder, G and Gust, G (2009) Marine Chemistry 115: 226–234

  11. Could the presence of other guest molecules (ethane, propane) be acting to slow the dissolution rate?

  12. Gas inlet Gas and water inlet Experimental Setup (How) Original drawing in Google SketchUp by LLL

  13. Gas inlet Gas and water inlet * * *Hydrate forming Procedure • ~300mL SDS solution introduced to chamber • “source” gas (methane) introduced to Pressurize (700-800psi) • Stir slowly to stimulate hydrate formation • Hydrate evolution monitored by P/T • Once P/T stabilizes, hydrate formation is considered complete • Headspace is flushed w/ N2 to replace CH4 at pressure Original drawing in Google SketchUp by LLL

  14. Could methane be dissolving into the oil layer?

  15. Summary and Future Work • Results indicate that mixed gas hydrates have similar dissolution rates to pure methane hydrate formations • The addition of mineral oil significantly increased dissolution rates, contrary to expectations. • Oil was methane-free, in nature oil would be saturated with methane • Incorporating oil into hydrate structure? • Incorporating methane into oil? • More complex oil mixtures? • Hydrate dissolution rates may be slowed by biofilm armoring or coatings • Salinity is potentially an important factor to consider

  16. Biofilms • sediment studies

  17. Proposed Work gas headspace Hydrate Filter on port tip Saturated water layer Dissolution of hydrate lens in sands We expect hydrate dissolution to be diffusion controlled thus the two experiments should yield similar rates. However if surface interaction effects do influence hydrate dissolution, the dispersed hydrate will be more affected (greater interaction area) “filling-type” hydrate Water-wet sand layer Dissolution of “filling-type” hydrate in sands

  18. methane N2 O2 Ar

  19. Bubbly Gulch, gas-active, buried hydrates

  20. *Note Scale Differences Biogenic methane

  21. Acknowledgments • Collaborators • Brian Anderson, West Virginia University • NagasreeGarapati, WVU • Funding Agencies • NETL Hydrate Research via the Department of Energy • Gulf of Mexico Hydrate Research Consortium • Mississippi Mineral Resources Institute

More Related