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Gas HydratesJeff Chanton, Department of Earth, Ocean &
Atmospheric Sciences, Florida State University
Photo by Ian MacDonald
“Flammable Ice”• Gas hydrate, methane hydrate and clathrate
• Naturally occurring cage-like structures
–
Host molecule = H2
0•
Forms expanded framework with void spaces
–
Guest molecule = CH4•
Fills void spaces
Photo by Rick Coffin
Figure from Suess et al., 1999
Gas hydrate•
A relatively new discovery, first found in nature in 1980
•
Ratio of 1/6 CH4
/H2
O•
CH4
/H2
O volumetric ratio of 164 when dissociated at standard T and P
•
Addition of ethane, propane and butane yield additional hydrate stability ~10%
•
Can be formed from either biogenic microbial methane or thermogenic “petro-genic”
methane.
•
Often found at “seep sites”----
Hydrocarbon seeps are natural springs where liquid and gaseous hydrocarbons leak out of the subsurface
Gas Hydrate
Found in places of
1.low temperature 2.high pressures 3.high CH4
Why do we study hydrates?
• Methane hydrates represent a future energy resource (if it can be extracted).
• Methane is a strong greenhouse gas
• Hydrates have been suggested to have a role in the control of past climates and may affect future climate.
• “Geo-hazard” hydrates can destabilize continental slopes and cause submarine slumping
Slide from Ray Boswell
From Suess et al., 1999
Biogenic Methane
Thermogenic Methane
Gas hydrate resource pyramid of Boswell and Collett (2006)
The Iġnik
Sikumi
#1 well is a field trial of a potential gas hydrate production technology that utilizes the injection of CO2 into gas hydrate-bearing sandstone reservoirs, resulting in a chemical exchange reaction that releases methane gas (CH4) while simultaneously sequestering CO2 in a solid hydrate structure as CO2-hydrate.
•
Started the flow test and confirmed gas production: March 12, 2013
•
Ended the flow test: March 18, 2013 •
Gas flowed 5 days, pipe clogged with sand.
•
Methane hydrate in place, the amount equivalent to approximately 40tcf or approximately 1.1trillion m3 of methane in the eastern Nankai
trough.
•
Equivalent to eleven years of the amount of LNG imported into Japan.
Nankai
Trough
Hydrates in Flow Assurance
•
Hydrate formation in oil/gas flow lines
•
#1 problem in flow assurance
•
Costly to prevent
•
Costly to remove
•
Safety concern
Hydrate plug removed from oil pipeline
Hydrates Cause Major Economic & Safety Risks During Energy Production & Transportation
24
How do we detect gas hydrates?
Check for the occurrence of a Bottom Simulating Reflector BSR
BSR marks bottom of hydrate occurrence
www.netl.doe.gov
Acoustic blank or wipe out zones
Inline 27
30 cm
SLIDE SHOW 1
Photo Ian MacDonald
Chemosynthetic bacteria store elemental SLike “fat” for when H2 S supply cut off
Photo Ian MacDonald
2004 2006
Barkley Canyon, Cascadia Margin
Observed little morphological change in hydrate outcrops over 1 year(MacDonald et al., 2005)
Hydrate stability: seafloor observations
Photos borrowed from www.hydrate.org
Photo by Jonathan BlairPhoto by Charles Fisher
Photo by Ian MacDonald
Photo Ian MacDonald
Photo Ian MacDonald
Photo Ian MacDonald
Are hydrates more stable than predicted by diffusion alone?Kinetic-controlled, surface armoring, ….
From Fisher et al., 2000
Hydrate stability: seafloor observations
Ice worms, a unique life form live in burrows in the hydrate icePhoto Ian MacDonald
Gas Hydrate Stability?
Effect on Climate
•
Ice core records show that atmospheric methane concentrations are tightly correlated with temperature over the past 800,000 years. When methane is elevated in the atmosphere, climate is warmer.
•
Massive gas hydrate dissociation may have been an positive feedback factor during hyperthermals
such as the Paleocene –
Eocene
Thermal Maximum (PETM).
how do we get a longer record?
Reading the ice archive
Reading the ice archive: the gas archive
Human activities havechanged the composition
of the atmospheresince the
pre- industrial era
40% anthropogenic increase.
240% anthropogenic increase
15%
Glacial Period
• Maximum extent of ice 20,000 years ago (last glacial maximum)
• Today major continental ice is present on:– Antarctica– Greenland
http://www.jamestown-ri.info/northern_appalachians.htm
Cody scarp
Deep Horizon Oil Spill
1500 m
1505 m
Daily dose:~60,000 bbl oil, ~30,000 BOE gas
Questions?
