Transcript 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 109g of methane carbon
• Greenhouse gas
• Potential energy resource
• Geological hazard
• Global climate change
Definition
• Solid comprised of water molecules
forming a rigid lattice of cages, each
containing a molecule of natural gas,
mainly methane.
Controls
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Temperature
Pressure
Composition
Enormous methane
Assume pure water and
pure methane system
http://cgsweb.moeacgs.gov.tw/Result/publish/19730001/020001/90%E5%B9%B4_%E5%9C%B0%E8%B3%AA077-102.pdf
Locations
Geophysics
• Bottom Simulating Reflection
• High sonic velocity
Geophysics
• Wire line logs
Geochemistry
Aspects of Gas Hydrates
1. Potential Energy Resource
2. Geologic Hazard
3. Global Climate Change
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
2. Geologic Hazard
• Natural
• Anthropogenic
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.
Past climate change
Nisbet et al.
Paull et al.
• Uncontrolled release of
methane?
• The release methane
enhances global
warming and triggers
deglaciation.
• Limiting the extent of
glaciation during a
glacial cycle.
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.
• 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?