Gas Hydrates In The Ocean
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A Representative diagram for in-situ gas hydrates is shown above for deep ocean regions. The hydrate stability zone (HSZ) is an area determined from the phase diagram, where the temperature and pressure conditions are ideal for formation. The lower edge of the HSZ occurs, in general ,some distance below the ocean floor since the temperature increases due to the geothermal gradient. This point is believed to coincide with the 3-phase point (gas, hydrate, water) with hydrate above and dissociated gas and water below. The upper end of the HSZ occurs higher in elevation because the pressure is decreasing. In the case of permafrost regions the hydrates can be stable at this low pressure since the temperatures can be quite cold. In most cases the top of the hydrate layer doesn't coincide with the sea floor but exists some distance below the sediment.
In recent years experts have come to
believe that there are massive quantities of methane gas stored in the
form of hydrates at the bottom of the ocean. This information has
mainly been inferred from bottom simulating reflectors (BSR) that were
dragged along the ocean floor and verified by core samples. Since an
estimated 1 m3 sample of pure hydrate would yield approximately 180 m^3
of methane gas, many people have come to believe that there is more
energy stored in all the hydrates (an estimated 10^19 g of carbon) than
all the fossil fuel reserves on earth. With all this methane many
people have proposed ways of mining it for use as the next energy
source when fossil fuels become too expensive. Some people on the other
hand are afraid of global warmer if the gas were to ever reach the
surface since methane gas is 23 times more effective than carbon
dioxide as a green house gas on a per-mole basis.
The methane hydrates contained at the bottom of the ocean have the
potential to dissolve into the water if the dissolved gas concentration
is low enough or pass through the 3-phase equilibrium point if the
temperature, pressure and salt concentrations are right. The gas that
has left its cage will percolate through the sediment, generally along
fractures, and rise to the ocean surface. Since the ocean is
essentially a giant capacitor for dissolved methane gas the bubbles
will only reach the atmosphere if the time scale for dissolution is
much longer than the gas residence time in the water. The dissolved gas
may also enter the atmosphere on a much longer time scale only if the
rate of transport is faster than the rate of bacterial oxidation.
The specific goals of the project are:
