EXPLOITATION OF GAS HYDRATES AS AN ENERGY

RESOURCE

Organization of the talk

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

Assessing energy sources

1. Demand

2. Availability

3. Technology

4. Efficiency

5. Environmental impact

6. 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!

0

500

1000

1500

2000

2500

3000

3500

4000

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52

World fossil consumption (1950-2003)

Source: World Watch Institute, 2003

Coal

Oil

Natural Gas

Projected world energy supply

Hyd

ro

Gas

-Com

bin

ed c

ycle

Coa

l

Gas

Tu

rbin

e cy

cle

Nu

clea

r

Win

d

Sol

ar T

her

mal

Sol

ar-P

V

Geo

ther

mal

Bio

mas

s

0

10

20

30

40

50

60

70

80

Ele

ctri

cal

Eff

icie

ncy

(%

)

.

1 8 10 15

25

33 38

43

58

80 80

Efficiencies of power technologies

Win

d

Nuc

lear

Sola

r-PV

Biom

ass/

Ste

am

Nat

ural

Gas

Coa

l

Geo

ther

mal

Hyd

ro

0

0.2

0.4

0.6

0.8

1

1.2

1.4

CO

2 E

mis

sion

s (k

g C

O2/k

Wh)

0.025

0.47

0.004 0.060.025

0.38

1.18

0.020.1

0.790.58

1.04

CO2 emissions [includes Construction/Operation/Fuel Construction/Operation/Fuel

PreparationPreparation]

50-75

12

532 2

56

2

19

14

4 4

108 7

17

So

lar-

PV

Nu

clea

r

Gas

Co

al

Hyd

ro

Win

d

Bio

mas

s

Geo

ther

mal

So

lar

Th

erm

al0

5

10

15

20

25

30

35

Cos

t of E

lect

ricity

(cen

ts/k

Wh)

Cost of electricity (global average, 1998)

Equipment cost in IRs/kWh for electricity generation

Solar ThermalSolar Thermal 6 - 86 - 8NuclearNuclear 5 - 95 - 9Natural GasNatural Gas 5 - 95 - 9Hydro Hydro 5 - 18.55 - 18.5WindWind 4.5 - 74.5 - 7CoalCoal 3.5 - 73.5 - 7Geothermal Geothermal 4.25 - 74.25 - 7BiomassBiomass 4.15 - 84.15 - 8

Solar ThermalSolar Thermal 6 - 86 - 8NuclearNuclear 5 - 95 - 9Natural GasNatural Gas 5 - 95 - 9Hydro Hydro 5 - 18.55 - 18.5WindWind 4.5 - 74.5 - 7CoalCoal 3.5 - 73.5 - 7Geothermal Geothermal 4.25 - 74.25 - 7BiomassBiomass 4.15 - 84.15 - 8

Operations and maintenance costs IRs/kWh

WindWind 1.31.3CoalCoal 22NuclearNuclear 2.22.2GeothermalGeothermal 2.72.7GasGas 3.13.1WoodWood 3.13.1OilOil 4.14.1WasteWaste 4.54.5

WindWind 1.31.3CoalCoal 22NuclearNuclear 2.22.2GeothermalGeothermal 2.72.7GasGas 3.13.1WoodWood 3.13.1OilOil 4.14.1WasteWaste 4.54.5

Hydrogen substitution

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 hydrocarbon molecules 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).

It is present in oceanic sediments along continental margins and in polar It is present in oceanic sediments along continental margins and in polar continental settings. continental settings.

Where are gas hydrates located?

The ocean scenario

Various issues related to extraction of gas hydrates

Recovery of Methane Gas from Gas HydratesRecovery of Methane Gas from Gas Hydrates

Modifying the equilibrium conditions by

1. Depressurization2. Inhibitor injection 3. Thermal stimulation

Phase equilibrium diagram

stable

unstable

Decomposition of hydrates by depressurization, thermal, and chemical techniques

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.

Schematic representation of production from a

hydrate reservoir with underlying free gas

Hydrate dissociation and formation Molecular structurePhase equilibrium diagramFlow, transport, and chemical reactions in a complex pore network

Research aspects

Schematic drawing of gas exchanges

Mass transfer at constant pressure and temperature

Mathematical Model

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K

f

Kp

dt

d

2

uuuu

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d

Fluid flow

is the porosity and K, the permeability.

Mathematical Model

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TC

,..

u

sfseffsp QTkt

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,.1

Heat transfer

Solid

Fluid

Species transport equation

Mathematical Model

gji

n

j

gijii

i Mt

g

1

.. Ju

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

1. Irreversible shift towards gaseous fuels.

2. Gas hydrates are secondary gas sources (internationally) but are primary, in the national context.

3. Safe exploitation of methane from hydrate reservoirs calls for a massive research program.