Methane from Gas Hydrates
337
the equipment. At fixed temperature, operate at pressure below hydrate
formation pressure.
4. Reduce water concentration to avoid hydrate formation. Change feed
composition.
5. Add compounds such as methanol, salts, or other kinetic inhibitors to prevent hydrate formation. Also prevent hydrate clustering by using hydrate
growth modifiers or covering working surfaces with hydrophobic substances [86–93,104,105].
With conventional oil and gas exploration methods extending into progressively
deeper waters, the potential hazards gas hydrates can pose to operation are becoming
increasingly more important. Two possible events—the release of overpressurized
gas (or fluids) trapped below the zone of hydrate stability and destabilization of
in situ hydrates—can be hazardous. Care must be taken to avoid these incidences
[96–102,113–116].
12.3.3 nATurAl gAS hydrATeS verSuS liqueFied
nATurAl gAS in TrAnSPorTATion
Since methane clathrates are stable at a higher temperature than liquefied natural
gas (LNG) (−20°C vs. −162°C) [108], there is some interest in converting natural
gas into clathrates rather than liquefying it when transporting it by seagoing vessels.
A significant advantage would be that the production of NGH from natural gas at
the terminal would require a smaller refrigeration plant and less energy than LNG
would. Offsetting this, for 100 tons of methane transported, 750 tons of methane
hydrate would have to be transported. Since this would require a ship of 7.5 times
greater displacement, or require more ships, an application of this approach has not
been economically attractive.
12.4 enVirOnmental imPaCts OF Gas hydrates
Gas hydrates alter the physical properties of the sediment. In the absence of hydrates,
fluids and gas migrate freely at seafloor. The solid hydrates reduce permeability and
restrict sediment consolidation, fluid expulsion, and cementation. The hydrate dissociation leads to increased pore fluid pressure and underconsolidated sediments,
with a reduced cohesive strength compared to overlying hydrate-bearing sediments,
forming a zone of weakness. This zone of weakness could act as a site of failure in
the event of increased gravitational loading or seismic activity. The link between seafloor failure and gas hydrate destabilization is a well-established phenomenon [1−15].
The exploration of hydrates from ocean floor by drilling through hydrate zones can
create the problem of destabilizing support foundations for platforms and production
wells. The disruption of ocean floor can also result in surface slumping or faulting,
which can endanger work crews and the environment [1−15].
Since hydrates prevent sediment compaction, their in situ dissociation can also cause
climate change and falling of sea level. If the hydrate breaks down, it will weaken the
337
the equipment. At fixed temperature, operate at pressure below hydrate
formation pressure.
4. Reduce water concentration to avoid hydrate formation. Change feed
composition.
5. Add compounds such as methanol, salts, or other kinetic inhibitors to prevent hydrate formation. Also prevent hydrate clustering by using hydrate
growth modifiers or covering working surfaces with hydrophobic substances [86–93,104,105].
With conventional oil and gas exploration methods extending into progressively
deeper waters, the potential hazards gas hydrates can pose to operation are becoming
increasingly more important. Two possible events—the release of overpressurized
gas (or fluids) trapped below the zone of hydrate stability and destabilization of
in situ hydrates—can be hazardous. Care must be taken to avoid these incidences
[96–102,113–116].
12.3.3 nATurAl gAS hydrATeS verSuS liqueFied
nATurAl gAS in TrAnSPorTATion
Since methane clathrates are stable at a higher temperature than liquefied natural
gas (LNG) (−20°C vs. −162°C) [108], there is some interest in converting natural
gas into clathrates rather than liquefying it when transporting it by seagoing vessels.
A significant advantage would be that the production of NGH from natural gas at
the terminal would require a smaller refrigeration plant and less energy than LNG
would. Offsetting this, for 100 tons of methane transported, 750 tons of methane
hydrate would have to be transported. Since this would require a ship of 7.5 times
greater displacement, or require more ships, an application of this approach has not
been economically attractive.
12.4 enVirOnmental imPaCts OF Gas hydrates
Gas hydrates alter the physical properties of the sediment. In the absence of hydrates,
fluids and gas migrate freely at seafloor. The solid hydrates reduce permeability and
restrict sediment consolidation, fluid expulsion, and cementation. The hydrate dissociation leads to increased pore fluid pressure and underconsolidated sediments,
with a reduced cohesive strength compared to overlying hydrate-bearing sediments,
forming a zone of weakness. This zone of weakness could act as a site of failure in
the event of increased gravitational loading or seismic activity. The link between seafloor failure and gas hydrate destabilization is a well-established phenomenon [1−15].
The exploration of hydrates from ocean floor by drilling through hydrate zones can
create the problem of destabilizing support foundations for platforms and production
wells. The disruption of ocean floor can also result in surface slumping or faulting,
which can endanger work crews and the environment [1−15].
Since hydrates prevent sediment compaction, their in situ dissociation can also cause
climate change and falling of sea level. If the hydrate breaks down, it will weaken the