A Proposal Into the Origin and Future of Clatharates.

By Damion Knudsen

 

Gas clathrates also known as gas hydrates have brought about a new dawn in scientific investigation. Since 1970 Clathrates have been found in many area’s along the ocean floor and as of very recently in the fresh water rift lake, Lake Baikal in Russia. The unusualness about this formation is that it is very near the surface at around 150m. There are two way that the methane in clathrates is formed and one is called biogenic which is what most of Lake Baikal is formed from and thermogenic which is formed by non-biologic means such as the reduction of CO2 ascending from magmatic depths or gas seeps from existing oil and gas reserves. If the formation in Lake Baikal could possibly represent ancient clathrate formation during ice ages indeed there could have been a massive dissociation of this material during an initial warming. One area that is largely debated right now is whether the methane spikes in the paleo record happened before or after the temperature rise coming out of glacial periods. Thus was it the dissociation of gas and methane clathrates that caused the warming trends or warming trends that caused clathrate dissociation. The main hypothesis for quite awhile has been that it was swamp and slew gas that caused the massive spikes in the record. Another area not agreed upon is actually how much methane clathrate is present on the Earth. Most of the scientists investigating this have come to the conclusion that there is simply a lot of this material on the earth whether sub-marine or sub-terrestrial in permafrost. Average consensus is around 12 teratons of methane are locked into clathrates which is an amount about twice the weight of all the oil reserves.

 

 


 Figure 1.) Photograph of an active gas hydrate mound ~1.5m across at a depth of 543m

 in the Gulf of Mexico. From Sassen et al. (1999).

 

I.)                 What are Gas Clathrates?

a.)    Chemical Structure

1.)    Three types of crystal structure.

2.)    sI, sII and sH. Other various possible structures emerging.

 

b.)    Chemical processes leading to formation.chemical properties.

1.)    Gas is dissolved in water under pressure.

2.)    This forces water to form cages around gas using hydrogen bonding. Surface tensions similar to that encountered on water surface around gas molecule.

3.)    Cages align in orderly fashion which is generally a cubic crystal system. sH is a hexagonal form of clathrate. sH clathrates have recently been found in the Gulf of Mexico.

 

c.)    Chemical and Physical Properties.

1.)    1 cm^3 of gas clathrate or 0.8cm^3 fresh water can hold 164cm^3 of gas (CH4, CO2, etc…)

2.)    Much stronger compressional strength in relation to normal ice. Probably due to the “diamond” lattice structure of sI CH4 Clathrate or the garnet lattice structure of sII CH4, ethane (CH3CH3), Propane(CH3CH2CH3) Clathrates. SII needs a larger molecule similar to propane in dimension.

3.)    CH4 clathrate is actually less dense than water and will float while CO2 clathrate is denser and sinks.

4.)    Abrasive in nature where as water ice is slippery.

5.)    Properties not usual for water ice. Gas clathrates left in open will take quite along time to melt but if put into water warmer than its temps for dissociation will dissociate very rapidly.

6.)    Temps for dissociation of gas clathrates range from around 3 deg. C for ethane clathrates to around 11 deg. C for some halocarbon clathrates. In other words the clathrate can reach upto 11 deg. C before it “melts.” Depends on the B.P of gas component.

 

d.)    P/T diagrams for its formation and relation to hydrate stability zone (HSZ).

 

II.)              History of Gas Clathrates.

a.)    Chronological history.

1.)    1810 first gas clathrate found was Cl2 hydrate by Sir Humphrey Davy

2.)    1934 as a problem plugging gas pipelines.

3.)    1970 First occurrence of natural gas clathrates recovered from Blake Ridge off east coast of U.S.

4.)    1999 First occurrence of freshwater clathrates at Lake Baikal, Russia. at depths greater than 150m. This is quite shallow and consequently highly susceptible to dissociation from the influx of warm water.

 

III.)           Economic Importance.

a.)    Amount stored in ocean and permafrost

1.)    More than 50% of the 18.8 teratons of carbon on Earth is stored as gas hydrates.  

2.)    30% of Russian well production is from the disassociation of clathrates. Well location in arctic tundra.

 

b.)    Methods of retrieval

1.)    Depressurizing the free gas zone.

·        Very long horizontal wells.

·        Multilateral well bores.

·        Circulating heated water from the surface or a deeper formation.

·        Circulating oil from deeper formations.

·        Carbon dioxide replacement

2.)    Submarine robotic arm recovery.

 

c.)    Years that it would be available.

1.)    Estimates are around 1000~4000 years for the U.S. if indeed they can be produced from wells. Reference Russian well.

 

d.)    Locations world wide and in other parts of solar system.

1.)    Oceans

·        At times clathrates are associated with salt diapirs. HSZ often takes on diapir appearance. NaCl is formed when seawater clathrates formed. Associated with mud volcanoes on sea floor.

 

2.)    Permafrost

3.)    Fresh water lakes. Lake Baikal, Siberia source of quite shallow gas hydrates. Very new data. Hydrates as shallow as 150m from surface.

4.)    Formations in other parts of the Solar system like on Mars. Southern pole of Mars contains CO2 clathrates. Not much glacial movement there. May be explained by the unflowing and abrasive nature of the clathrates as also their structural stability. Saturn’s rings are possibly composed of clathrates also.

5.)    There is evidence that comets are composed of clathrates also.

6.)    Outer planetary sources may offer energy source in space travel.

 

e.)    Possible conversion of CO2 into CH4 (sink/reduction farm). Conversion of CO2   into CH4 for energy use.

1.)    What is the capacity of methanogenic bacteria to reduce CO2?

 

IV.)           Main debates and questions. Opposing Viewpoints.

a.)    Amount of gas clathrates on Earth. Varies greatly among scientists.

1.)    Methods of determining how much hydrate is available,

·        Well logs

·        Sonar

·        Other various methods.

 

b.)    The origin of the gas that forms in the clathrate lattice.

1.)    Methods of determining their origin

·        Carbon isotope fractionation as also Hydrogen isotope fractionation by means of stable isotopes.

·        Terms for gas origin are biogenic and thermogenic.

·        Biogenic origins come from biologic source mainly bacteria converting CO2 to CH4.

·        Thermogenic means the source is gas seeps from natural gas outlets or CO2 reduction by non-biologic means.

 

c.)    How much of an impact clathrate dissociation has on global climate and its change.

1.)    Some believe it as a major contributer to global warming others that CH4is simply a marker of global warming in the past record.

·        HSZ or Hydrate Stability Zones for methane and CO2 clathrates. CO2 HSZ is higher than methane hydrate.

·        What is the rate of dissociated CH4  oxidation to CO2 in the ocean?

·        Gas Clathrates are highly unstable in presence of warmer water in relation to dissociation temperature. Almost explosive in nature.

·        They have been found at depths as shallow as 150m. This is quite shallow and consequently highly susceptible to dissociation from the influx of warm water of only a few degrees warmer than the clathrates.

·        Theories on sources of methane associated in past climate record.

i.)                  Swamp gas.

ii.)                 Dissociated Methane clathrates.

 

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