EXPLOITATION OF GAS HYDRATES AS AN ENERGY RESOURCE K. Muralidhar Department of Mechanical Engineering Indian Institute of Technology Kanpur Kanpur 208016 India
Organization of the talk • Energy scenario • What are gas hydrates • Resource availability • Exploitation of gas hydrates • Environmental aspect
Assessing energy sources • Demand • Availability • Technology • Efficiency • Environmental impact • Cost
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!
World fossil consumption (1950-2003) Coal Oil Natural Gas Source: World Watch Institute, 2003
CO2 emissions [includes Construction/Operation/Fuel Preparation]
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
Operations and maintenance costs IRs/kWh Wind 1.3 Coal 2 Nuclear 2.2 Geothermal 2.7 Gas 3.1 Wood 3.1 Oil 4.1 Waste 4.5
Summary • Using every yardstick: availability, efficiency, environment, and cost, the 21st century will see an irrevocable shift towards gas-based energy generation
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.
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.
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.
What are gas hydrates • A gas hydrate consists of a water lattice in which light hydrocarbonmolecules are embedded resembling dirty ice.
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 18°C.
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).
Where are gas hydrates located? It is present in oceanic sediments along continental margins and in polar continental settings.
Recovery of Methane Gas from Gas Hydrates • Modifying the equilibrium conditions by • Depressurization • Inhibitor injection • Thermal stimulation
Phase equilibrium diagram stable unstable
Decomposition of hydrates by depressurization, thermal, and chemical techniques
Exploitation schemes • DEPRESSURISATION: At fixed temperature, operating at pressures below hydrate formation pressure. • INHIBITION: Inhibition of the hydrate formation conditions by using chemicals such as methanol and salts. • HEAT SUPPLY: At fixed pressure, operating at temperatures above the hydrate formation temperature. This can be achieved by insulation or heating of the equipment.
Schematic representation of production from a hydrate reservoir with underlying free gas
Research aspects • Hydrate dissociation and formation • Molecular structure • Phase equilibrium diagram • Flow, transport, and chemical reactions in a complex pore network
Mathematical Model Fluid flow is the porosity and K, the permeability.
Mathematical Model Heat transfer Fluid Solid
Mathematical Model Species transport equation
List of undetermined parameters • Dispersion coefficient • Permeability tensor • Inter-phase transport coefficient
Unanswered questions • Stability boundary • Destabilization dynamics • Flow and transport in a hierarchical pore network • System development • Disaster management • Cost considerations
Environmental impact • Carbon sequestration • Carbon capture and storage • Carbon trap technologies
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.