1. Methane Hydrates Jake Ross and Yuliana Proenza
The Three Questions
What is a Gas Hydrate?
What is their potential as an energy resource?
What role do they play in global climate change?

2. What is a Gas Hydrate?
A gas hydrate is a crystalline solid; its building blocks consist of a gas molecule surrounded by a cage of water molecules.
It is similar to ice, except that the crystalline structure is stabilized by the guest gas molecule within the cage of water molecules.
Suitable gases are: carbon dioxide, hydrogen sulfide, and several low-carbon-number hydrocarbons. Most gas hydrates , however are Methane Hydrates.

3. Hydrate Samples
Gas hydrates in sea-floor mounds Here methane gas is actively dissociating from a hydrate mound.
Gas hydrate can occur as nodules, laminae, or veins within sediment.

4. CH4 Hydrate Stability

5. Where are Methane Hydrates located?
Found in 4 major location types
Subduction zones (e.g., Nankai Trough Japan, Cascadia Basin)
Passive Margins (e.g., Blake Ridge on the southeast cost of the US)
Off-shore hydrocarbon (e.g., Gulf of Mexico, North Slope Alaska)
On-shore Arctic Permafrost (e.g., Mackenzie Delta, Arctic Russia, Arctic Alaska)

6. Where are Methane Hydrates located?
Methane hydrate occurs in a zone referred to as the hydrate stability zone.
The zone lies roughly parallel to the land or seafloor surface.
Permafrost regions,
depths about m below the surface.
In oceanic sediment
ocean is at least 300 m deep,
depths of 0 - 1,100 m below the seafloor.

7. Where are Methane Hydrates located?
Hydrate concentration occurs at depocenters
Where there is a rapid accumulation of organic detritus (from which bacteria generate methane). Carbon isotope analyses indicate most of the methane in hydrates is microbial, however thermogenic sources have been identified in the Gulf of Mexico
Where there is a rapid accumulation of sediments (which protect detritus from oxidation).

9. What is the potential of CH4 Hydrates as an energy resource

10. The estimated conventional gas resources and reserves in the United States alone are 1,400 trillion cubic feet.
If it could be safely and economically recovered, one 50 by 150 kilometer area off the coast of North and South Carolina is estimated to hold enough methane to supply the needs of the United States for over 70 years

11. Conceptual Drawing of Blake Ridge

12. Why are CH4 Hydrates a good energy resource
The gas is held in a crystal structure, therefore gas molecules are more densely packed than in conventional or other unconventional gas traps.
Hydrate forms as cement in the pore spaces of sediment and has the capacity to fill sediment pore space and reduce permeability. CH4 - hydrate-cemented strata thereby act as seals for trapped free gas
Production of gas from hydrate-sealed traps may be an easy way to extract hydrate gas because the reduction of pressure caused by production can initiate a breakdown of hydrates and a recharging of the trap with gas

13. A Proposed Method
For the gas production from hydrates and the seabed stability after the production, we proposed a new concept. The figure illustrates the molecular mining method by means of CO2 injection in order to extract CH4 from gas hydrate reservoirs. The concept is composed of three steps as follows; 1) injection of hot sea water into the hydrate layer to dissociate the hydrates, 2) produce gas from the hydrate, 3) inject CO2 to form carbon dioxide hydrate with residual water to hold the sea bed stable

14. CH4 Hydrates and Climate Change
Methane is a very effective greenhouse gas. It is ten times more potent than carbon dioxide.
There is increasing evidence that points to the periodic massive release of methane into the atmosphere over geological timescales. Are these enormous releases of methane a cause or an effect of global climate change?

15. Global warming may cause hydrate destabilization through a rise in ocean bottom water temperatures. The increased methane content in the atmosphere in turn would be expected to accelerate warming, causing further dissociation, potentially resulting in run away global warming.
Sea level rise, however, during warm periods may act to stabilize hydrates by increasing hydrostatic pressure, thereby acting as a check on warming.
Hydrate dissociation may act as a check on glaciations, whereby reduced sea levels may cause seafloor hydrate dissociation, releasing methane and warming the climate.

16. This diagram illustrates the affect sea level change has on the stability of hydrates.

17. The Past
A prominent negative shift in δ 13C has been recorded in Late Paleocene sediments worldwide.
The late Paleocene-early Eocene interval (55.5 mya) was a thermal maximum
Ocean bottom waters warmed rapidly by as much 4 degrees C, along with a concurrent rapid shift in δ 13C values of all the carbon reservoirs in the global carbon cycle
Data from sediments cores suggest that the isotopic shift occurring within no more than a few thousand years
Only a catastrophic infusion of δ 12C-enriched carbon from methane hydrates could cause such a rapid shift.

18. CH4 Hydrates and the Atmosphere
An important aspect of methane hydrates and their affect on climate change is their potential to enter the atmosphere
Methane concentration in seawater is observed to decrease by 98% between a depth of 300m and the sea surface as a result of microbial oxidation.
The flux of methane into the atmosphere is thus lowered 50-fold (Mienert et al., 1998)
However during catastrophic events such as large–scale sediment slumping much higher proportions of methane would be released.

20. The Future of Methane Hydrates
Worldwide gas production in the next years
Areas with unique economic and/or political motivations could see substantial production within 5-10 years
We need to better understand the mechanisms of hydrate disassociation and its role in global warming, either as an accelerator or and inhibitor