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
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
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
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
Are hydrates more stable than predicted by diffusion alone?Kinetic-controlled, surface armoring, ….
From Fisher et al., 2000
Hydrate stability: seafloor observations
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).
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
1500 m
1505 m
Daily dose:~60,000 bbl oil, ~30,000 BOE gas