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Click on a graphic for an
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| To use methane hydrate as an energy resource, production
methods need to be established to extract methane-rich hydrocarbons
from methane hydrate. How can we recover hydrocarbons from methane
hydrate efficiently? |
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Conventional production method
for oil and natural gas |
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In their natural storage environment
underground (reservoir), oil and natural gas are subject to pressure
applied by the layers of earth above. This pressure increases with
greater depths. When we drill a hole down into these strata, the oil,
gas, and other fluids existing under this incredible pressure seek
to release this pressure by rising up through the well until they
reach the drilling rig. This process is referred to as "flowing."
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| However, because methane hydrate is
a solid, it is unlikely to flow out in the same way as oil and natural
gas. But if we could devise some method to make methane hydrate dissociate
underground and generate methane gas, it would be possible to apply
the same techniques used in the production of oil and natural gas. |
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Consequently, finding an efficient,
safe method of triggering the dissociation of methane hydrate is an
important factor in production. Below are three methods used for oil
and natural gas production and currently being explored for application
in production. |
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Thermal
recovery method |
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In this method, a well is drilled to the methane hydrate-bearing layer,
and methane hydrate is dissociated by heating using a fluid (hot water or
steam) heated at the surface in a boiler or similar device and circulated
down through the well. This causes methane hydrate to decompose and generates
methane gas. The methane gas mixes with the hot water and returns to the
surface, where the gas and hot water are separated.
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The main problem with this method
is working out how to apply the heat to the methane hydrate-bearing
layer. Simply circulating hot water through the well is an inefficient
way to transfer heat throughout a methane hydrate-bearing layer. The
method requires further research.
This method also presents the possibility
that hot water pumped down the well from the offshore rig will cool
before it reaches the methane hydrate bearing-layers. Because methane
hydrate bearing-layers are found in deep seas, the surrounding sea
water will reduce the temperature of the heating fluid, even though
it passes through a conduit known as a riser pipe.
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Generating the hot water to be pumped down to the methane hydrate-bearing
layers requires tremendous amounts of energy, increasing production costs.
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Depressurization
method |
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As with geological formation, methane hydrate bearing
layers are subject to be pressurized by the combined overburden
weight of seawater and the formation pressure. In drilling for formations
subjected to such pressures, it is customary to use a drilling mud
with a specific gravity higher than this pressure.
Conversely, the depressurization method lowering
the pressure inside the well and encouraging the methane hydrate
to dissociate. (Methane hydrate dissociates into methane gas and
water when depressurized.)
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However, depressurizing inside the well will not necessarily lead to depressurization
of the entire methane hydrate-bearing layer. Research continues in an effort
to find an efficient method of evenly reducing the pressure of methane hydrate-bearing
layers. |
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Inhibitor
injection method |
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In this method, inhibitor such as methanol is injected
from surface down to methane hydrate-bearing layers. This method
enables methane hydrate dissociation without changing the pressure
or temperature of the methane hydrate-bearing layer.
However, research is still being carried
out to devise a means of injecting the inhibitor evenly throughout
the entire methane hydrate-bearing layer.
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In March 2002, the first-ever production test was carried out on a methane
hydrate-bearing layer under land in Canada's Mackenzie Delta region. On
this occasion, both the hot water circulation method and depressurization
method were applied to induce methane hydrate decomposition. A certain amount
of methane gas was produced as a result of the test. Research is continuing,
with the goal of improving production techniques and devising even more
efficient production methods. |
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Simulation
study of production performance |
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The ideal way to verify these methane hydrate production methods
would be to actually drill wells and try out each of the different
methods. But drilling wells and carrying out production tests is
extremely costly.
For this reason, computers are used to simulate the amount of methane
gas generated by each of the various methods. A number of production
simulation software packages have been developed for use in the
oil and natural gas industry, and these are in the process of being
modified for use in the simulation of production of methane hydrate..
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Accurate simulation study requires accurate data for methane hydrate's
physical properties. Working with other groups and organizations
dedicated to studying methane hydrate's properties, we are currently
undertaking research with the goal of improving the accuracy of
these simulations.
By applying the results of production tests in the future on methane
hydrate-bearing layers, we hope to further tune-up the simulation
software, eventually creating effective tools for commercial production
of methane hydrate.
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