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Gas Hydrates – Geological Perspective and Global Change

Gas Hydrates – Geological Perspective and Global Change. Keith A. Kvenvolden 大氣所碩一 闕珮羽 R98229016. Introduction. Deep ocean and permafrost The total amount of methane hydrate likely exceeds 10 9 g of methane carbon Greenhouse gas Potential energy resource Geological hazard

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Gas Hydrates – Geological Perspective and Global Change

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  1. Gas Hydrates – Geological Perspective and Global Change Keith A. Kvenvolden 大氣所碩一 闕珮羽 R98229016

  2. Introduction • Deep ocean and permafrost • The total amount of methane hydrate likely exceeds 109g of methane carbon • Greenhouse gas • Potential energy resource • Geological hazard • Global climate change

  3. Definition • Solid comprised of water molecules forming a rigid lattice of cages, each containing a molecule of natural gas, mainly methane.

  4. Controls • Temperature • Pressure • Composition • Enormous methane Assume pure water and pure methane system

  5. http://cgsweb.moeacgs.gov.tw/Result/publish/19730001/020001/90%E5%B9%B4_%E5%9C%B0%E8%B3%AA077-102.pdfhttp://cgsweb.moeacgs.gov.tw/Result/publish/19730001/020001/90%E5%B9%B4_%E5%9C%B0%E8%B3%AA077-102.pdf

  6. Locations

  7. Geophysics • Bottom Simulating Reflection • High sonic velocity

  8. Geophysics • Wire line logs

  9. Geochemistry

  10. Aspects of Gas Hydrates • Potential Energy Resource • Geologic Hazard • Global Climate Change

  11. 1. Potential Energy Resource Attractive: • (1) enormous amount of methane • (2) wide geographical distribution of the gas hydrate Production methods: • Thermal stimulation :ΔH dissociation 54.2kJ/mol • Inhibitor injection :methanol, low efficiency • Depressurization :suitable

  12. 2. Geologic Hazard • Natural • Anthropogenic

  13. 3. Global Climate Change • During global warming, deep-sea gas hydrates become more stable, but gas hydrates of polar continents and continental shelves are destabilized, leading to methane release over long time scales.

  14. Past climate change • Uncontrolled release of methane? • The release methane enhances global warming and triggers deglaciation. • Limiting the extent of glaciation during a glacial cycle. Nisbet et al. Paull et al.

  15. Present climate change • Kvenvolden have suggested that gas hydrate deposits of the polar continental shelves are presently most vulnerable to climate change. • The polar shelves has experience a +10°C or more change in temperature over at least the past 10,000 year. • Sea level rise about 100m • The amount of methane released by this process has been estimated to be about 3*1012g/yr of methane carbon.

  16. A test of this idea was conducted on the continental shelf north from Oliktok Point, Alaska [Kvenvolden et al. ,1992]. • We discovered that methane concentrations in the water under the ice are 6 to 28 times greater than the atmospheric equilibrium concentration. • Questions: destabilized gas or methane contributes to the seasonal cycle of atmospheric methane?

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