EXPLOITATION OF GAS HYDRATES AS AN ENERGY RESOURCE

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EXPLOITATION OF GAS HYDRATES AS AN ENERGY RESOURCE
K. Muralidhar Department of Mechanical
Engineering Indian Institute of Technology
Kanpur Kanpur 208016 India
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Organization of the talk

• Energy scenario
• What are gas hydrates
• Resource availability
• Exploitation of gas hydrates
• Environmental aspect

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Assessing energy sources

1. Demand
2. Availability
3. Technology
4. Efficiency
5. Environmental impact
6. Cost

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The 21st century imbalance

• Annual population increases at 2.
• Energy use per capita increases at 2 per year.
• As a result, energy consumption increases at 4
  per year.
• Doubles every 36 years!

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World fossil consumption (1950-2003)
Coal
Oil
Natural Gas
Source World Watch Institute, 2003
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Projected world energy supply
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Efficiencies of power technologies
80
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CO2 emissions includes Construction/Operation/Fue
l Preparation
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Cost of electricity (global average, 1998)
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Equipment cost in IRs/kWh for electricity
generation
Solar Thermal 6 - 8 Nuclear 5 - 9 Natural
Gas 5 - 9 Hydro 5 - 18.5 Wind 4.5 -
7 Coal 3.5 - 7 Geothermal 4.25 -
7 Biomass 4.15 - 8
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Operations and maintenance costs IRs/kWh
Wind 1.3 Coal 2 Nuclear 2.2 Geotherma
l 2.7 Gas 3.1 Wood 3.1 Oil 4.1 Wa
ste 4.5
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Hydrogen substitution
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Summary

• Using every yardstick availability, efficiency,
  environment, and cost, the 21st century will see
  an irrevocable shift towards gas-based energy
  generation

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Large scale power production from gas

• Energy production from gas relies on the
  following technologies
• Gas turbines
• Fuel cells (futuristic)
• Gas hydrates are a source of methane and can be
  integrated with these technologies.

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Indian scenario

• With no major findings of gas reserves it is
  essential to look for other alternative resources
  such as gas hydrates.
• Vast continental margins with substantial
  sediment thickness and organic content, provide
  favorable conditions for occurrence of gas
  hydrates in the deep waters adjoining the Indian
  continent.

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Indian scenario (continued)

• Caution Gas hydrates hold the danger of natural
  hazards associated with sea floor stability,
  release of methane to ocean and atmosphere, and
  gas hydrates disturbed during drilling pose a
  safety problem.
• Research Development of a field model is quite
  necessary before the installation of a full scale
  setup in the sea bed.

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What are gas hydrates

• A gas hydrate consists of a water lattice in
  which light hydrocarbon molecules are embedded
  resembling dirty ice.

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What are gas hydrates (continued)

• Naturally occurring gas hydrates are a form of
  water ice which contains a large amount of
  methane within its crystal structure.
• They are restricted to the shallow lithosphere
  (2000-4000 m depth)
• With pressurization, they remain stable at
  temperatures up to 18C.

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What are gas hydrates (continued)

• The average hydrate composition is 1 mole of
  methane for every 5.75 moles of water.
• The observed density is around 0.9 g/cm3.
• One liter of methane clathrate solid would
  contain 168 liters of methane gas (at STP).

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Where are gas hydrates located?
It is present in oceanic sediments along
continental margins and in polar continental
settings.
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The ocean scenario
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Various issues related to extraction of gas
hydrates
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Recovery of Methane Gas from Gas Hydrates

• Modifying the equilibrium conditions by
• Depressurization
• Inhibitor injection
• Thermal stimulation

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Phase equilibrium diagram
stable
unstable
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Decomposition of hydrates by depressurization,
thermal, and chemical techniques
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Exploitation schemes

1. DEPRESSURISATION At fixed temperature, operating
   at pressures below hydrate formation pressure.
2. INHIBITION Inhibition of the hydrate formation
   conditions by using chemicals such as methanol
   and salts.
3. HEAT SUPPLY At fixed pressure, operating at
   temperatures above the hydrate formation
   temperature. This can be achieved by insulation
   or heating of the equipment.

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Schematic representation of production from a
hydrate reservoir with underlying free gas
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Research aspects

• Hydrate dissociation and formation
• Molecular structure
• Phase equilibrium diagram
• Flow, transport, and chemical reactions in a
  complex pore network

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Schematic drawing of gas exchanges
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Mass transfer at constant pressure and temperature
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Mathematical Model
Fluid flow
? is the porosity and K, the permeability.
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Mathematical Model
Heat transfer
Fluid
Solid
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Mathematical Model
Species transport equation
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List of undetermined parameters

• Dispersion coefficient
• Permeability tensor
• Inter-phase transport coefficient

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Unanswered questions

• Stability boundary
• Destabilization dynamics
• Flow and transport in a hierarchical pore network
• System development
• Disaster management
• Cost considerations

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Environmental impact

• Carbon sequestration
• Carbon capture and storage
• Carbon trap technologies

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Conclusions

• Irreversible shift towards gaseous fuels.
• Gas hydrates are secondary gas sources
  (internationally) but are primary, in the
  national context.
• Safe exploitation of methane from hydrate
  reservoirs calls for a massive research program.

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• Thank you!