Saturday, May 3, 2008

Gas Hydrates

Gas hydrates are an ice-like structure that can contain particles in them -- namely methane.  They exist wherever temperature and pressure conditions are right, which on land is permafrost regions, and off-shore at certain water depths.  The amount of methane contained in gas hydrates is massive.  For example, there is a gas hydrate deposit offshore South Carolina that contains 30 times the annual US natural gas consumption.  And that's just one deposit.  The US coasts are lined with gas hydrate deposits, so there is tons of energy potential.  The problem is, though, hydrates are solids, AKA impossible to produce.  So there are different methods being investigated on how to produce these methane hydrates.  One way injects steam to raise the temperature of the deposit and cause the gas to dissociate and therefore become producible.  Another way is injecting an inhibitor that shifts the thermodynamic properties of the hydrate.  Similarly, this causes the methane to dissociate.  A third way lowers pressure to encourage methane dissociation.  Personally, I think this method has the most potential and the best economics.  A well is drilled past the hydrate, and produces free gas below the hydrate deposit.  As the free gas is produced, the pressure in the rock decreases, and the methane dissociate, effectively feeding the free gas zone.  I like this method because nothing has to be injected (steam or inhibitor).  This has to help the economics and energy ratio of the project.  Inhibitors such as methanol are expensive, and injecting steam requires energy to create the steam.

Hydrates are known in other contexts such as petroleum drilling and production operations as a nuisance.  Especially in deepwater conditions, they can plug pipelines and threaten drilling well control.  Also, hydrates could have some global warming implications.  As sea levels rise, hydrates in permafrost regions are released to the atmosphere.  Methane, as a green house gas, then could encourage further global warming create a positive feedback.  

I think as energy demands increase, production from hydrates is a very real possibility.  There are currently no economic hydrate projects, but the government is actively funding research.

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