Methane HydratesMethane HydratesJake Ross and Yuliana ProenzaJake Ross and Yuliana Proenza

The Three QuestionsThe Three Questions What is a Gas Hydrate?What is a Gas Hydrate? What is their potential as an energy resource?What is their potential as an energy resource? What role do they play in global climate What role do they play in global climate

change?change?

What is a Gas Hydrate?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.

Hydrate SamplesHydrate 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.

CHCH44 Hydrate Stability Hydrate Stability

Where are Methane Hydrates Where are Methane Hydrates located?located?

Found in 4 major location typesFound in 4 major location types

Subduction zones (e.g., Nankai Trough Japan, Cascadia Basin)Subduction zones (e.g., Nankai Trough Japan, Cascadia Basin) Passive Margins (e.g., Blake Ridge on the southeast cost of the US)Passive Margins (e.g., Blake Ridge on the southeast cost of the US) Off-shore hydrocarbon (e.g., Gulf of Mexico, North Slope Alaska)Off-shore hydrocarbon (e.g., Gulf of Mexico, North Slope Alaska) On-shore Arctic Permafrost (e.g., Mackenzie Delta, Arctic Russia, On-shore Arctic Permafrost (e.g., Mackenzie Delta, Arctic Russia,

Arctic Alaska) Arctic Alaska)

Where are Methane Hydrates Where are Methane Hydrates located?located?

Methane hydrate occurs in a zone referred to as the Methane hydrate occurs in a zone referred to as the

hydrate stability zone.hydrate stability zone. The zone lies roughly parallel to the land or seafloor The zone lies roughly parallel to the land or seafloor

surface.surface. Permafrost regions, Permafrost regions,

depths about 150 - 2000 m below the surface.depths about 150 - 2000 m below the surface. In oceanic sediment In oceanic sediment

ocean is at least 300 m deep, ocean is at least 300 m deep, depths of 0 - 1,100 m below the seafloor.depths of 0 - 1,100 m below the seafloor.

Where are Methane Hydrates Where are Methane Hydrates located?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).

What is the potential of What is the potential of CHCH4 4 Hydrates as an energy resourceHydrates as an energy resource

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

Conceptual Drawing of Blake RidgeConceptual Drawing of Blake Ridge

Why are CHWhy are CH4 4 Hydrates a good energy Hydrates a good energy

resourceresource The gas is held in a crystal structure, therefore gas molecules are The gas is held in a crystal structure, therefore gas molecules are

more densely packed than in conventional or other unconventional more densely packed than in conventional or other unconventional gas traps. gas traps.

Hydrate forms as cement in the pore spaces of sediment and has the Hydrate forms as cement in the pore spaces of sediment and has the capacity to fill sediment pore space and reduce permeability. capacity to fill sediment pore space and reduce permeability. CHCH44 - - hydrate-cemented strata thereby act as seals for trapped free gashydrate-cemented strata thereby act as seals for trapped free gas

Production of gas from hydrate-sealed traps may be an easy way to Production of gas from hydrate-sealed traps may be an easy way to extract hydrate gas because the reduction of pressure caused by extract hydrate gas because the reduction of pressure caused by production can initiate a breakdown of hydrates and a recharging of production can initiate a breakdown of hydrates and a recharging of the trap with gasthe trap with gas

A Proposed MethodA Proposed Method For the gas production from For the gas production from

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

CHCH4 4 Hydrates and Climate ChangeHydrates and Climate Change

Methane is a very effective greenhouse gas. It is ten times more Methane is a very effective greenhouse gas. It is ten times more potent than carbon dioxide.potent than carbon dioxide.

There is increasing evidence that points to the periodic massive There is increasing evidence that points to the periodic massive

release of methane into the atmosphere over geological timescales. release of methane into the atmosphere over geological timescales. Are these enormous releases of methane a cause or an effect of global Are these enormous releases of methane a cause or an effect of global climate change?climate change?

• Global warming may cause hydrate destabilization through a rise in ocean Global warming may cause hydrate destabilization through a rise in ocean bottom water temperatures. The increased methane content in the bottom water temperatures. The increased methane content in the atmosphere in turn would be expected to accelerate warming, causing atmosphere in turn would be expected to accelerate warming, causing further dissociation, potentially resulting in run away global warming. further dissociation, potentially resulting in run away global warming.

• Sea level rise, however, during warm periods may act to stabilize hydrates Sea level rise, however, during warm periods may act to stabilize hydrates by increasing hydrostatic pressure, thereby acting as a check on warming. by increasing hydrostatic pressure, thereby acting as a check on warming.

• Hydrate dissociation may act as a check on glaciations, whereby reduced Hydrate dissociation may act as a check on glaciations, whereby reduced sea levels may cause seafloor hydrate dissociation, releasing methane and sea levels may cause seafloor hydrate dissociation, releasing methane and warming the climatewarming the climate..

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

The PastThe Past A prominent negative shift in A prominent negative shift in δδ 1313C has been recorded in Late C has been recorded in Late

Paleocene sediments worldwide. Paleocene sediments worldwide. The late Paleocene-early Eocene interval (55.5 mya) was a thermal The late Paleocene-early Eocene interval (55.5 mya) was a thermal

maximummaximum Ocean bottom waters warmed rapidly by as much 4 degrees C, along Ocean bottom waters warmed rapidly by as much 4 degrees C, along

with a concurrent rapid shift in with a concurrent rapid shift in δδ 1313C values of all the carbon reservoirs C values of all the carbon reservoirs in the global carbon cyclein the global carbon cycle

Data from sediments cores suggest that the isotopic shift occurring Data from sediments cores suggest that the isotopic shift occurring within no more than a few thousand yearswithin no more than a few thousand years

Only a catastrophic infusion of Only a catastrophic infusion of δδ 1212C-enriched carbon from methane C-enriched carbon from methane hydrates could cause such a rapid shifthydrates could cause such a rapid shift..

CHCH44 Hydrates and the Atmosphere Hydrates and the Atmosphere

An important aspect of methane hydrates and their affect on climate An important aspect of methane hydrates and their affect on climate change is their potential to enter the atmospherechange is their potential to enter the atmosphere

Methane concentration in seawater is observed to decrease by 98% Methane concentration in seawater is observed to decrease by 98% between a depth of 300m and the sea surface as a result of microbial between a depth of 300m and the sea surface as a result of microbial oxidation.oxidation.

The flux of methane into the atmosphere is thus lowered 50-fold The flux of methane into the atmosphere is thus lowered 50-fold (Mienert et al., 1998)(Mienert et al., 1998)

However during catastrophic events such as large–scale sediment However during catastrophic events such as large–scale sediment slumping much higher proportions of methane would be released. slumping much higher proportions of methane would be released.

The Future of Methane HydratesThe Future of Methane Hydrates

Worldwide gas production in the next 30-50 yearsWorldwide gas production in the next 30-50 years Areas with unique economic and/or political motivations could see Areas with unique economic and/or political motivations could see

substantial production within 5-10 yearssubstantial production within 5-10 years We need to better understand the mechanisms of hydrate We need to better understand the mechanisms of hydrate

disassociation and its role in global warming, either as an accelerator disassociation and its role in global warming, either as an accelerator or and inhibitoror and inhibitor