2. INTRODUCTION
Gas hydrates are cage-like structures of water
molecules, surrounding molecules of gas, primarily
methane.
Methane is the principal component of natural gas.
They form when water and natural gas combine at
sufficiently low temperatures and high pressures.
They seen in the regions of permafrost and in
subseafloor sediments.
Theoretically estimated that maximum of 270 million
trillion cubic feet of natural gas exist in hydrate deposits.
3. HISTORY
Russian scientists in the late 1960s were the first to
propose that gas hydrate might occur naturally in marine
and onshore locations (Makogon and Medovskiy,1969)
In the early 1970s, scientists found that gas hydrate
existed below the permafrost and in marine sediments
(Stollet al., 1971; Bily and Dick, 1974).
Deep sea drilling expeditions confirmed that gas hydrate
occurred naturally in deepwater sediments along outer
continental margins (Paull et al., 1996; Tréhu et al.,
2003;Riedel et al., Proceedings of the ODP, 2006).
4. OCCURANCE
Natural gas hydrates are solid, crystalline, ice-like
substances composed of water, methane, and usually a
small amount of other gases,
With the gases being trapped in the interstices of a
water-ice lattice.
They form under moderately high pressure and at
temperatures near the freezing point of water.
In the United States, very large methane hydrate
deposits are located both on- and offshore northern
Alaska.
5. OCCURANCE
Fig:3 Location of known and inferred gas hydrate
occurrences
Kvenvolden and Rogers, 2005)
Reproduced with permission from Keith Kvenvolden and Bruce Rogers.
6. HYDRATE STABILITY
stability of the gas hydrate mostly depends on pressure
and temperature.
the mechanical properties of gas hydrate are similar to
those of ice because gas hydrate contains about 85 %
water by mass.
It may look like ice, it does not behave like ice — for
example, it burns when lit with a match.
colder temperatures and/or higher pressures — the gas
hydrate is stable.
8. NATURAL GAS HYDRATES
Gas hydrates form when water and natural gas combine
at low temperatures and high pressures.
Gas hydrates are cage-like structures of water
molecules.
surrounding molecules of gas, primarily methane.
Methane is the principal component of natural gas.
They are members of a highly varied class of substances
called clathrates.
9. NATURAL GAS HYDRATES cont..
Natural gas hydrate is a potentially vast source of
hydrocarbon energy that is currently unexploited.
They are seen in the regions of permafrost and in marine
subseafloor sediments.
They substances composed of water, methane, and
usually a small amount of other gases.
It has been estimated that a maximum of 270 million
trillion cubic feet of natural gas could theoretically exist in
hydrate deposits
10. NATURAL GAS HYDRATES cont..
It is highly inflammable and are called "Fiery ice"
or ―Ice that burns‖
12. PRODUCTION METHODS
There are three mainly used production methods are
1. DEPRUSSURIZATION.
2. THERMAL STIMULATION
3. CHEMICAL INHIBITION
13. PRODUCTION METHODS Cotd..
1. DEPRUSSURIZATION.
Its objective is to lower the pressure in the free-gas
zone immediately beneath the hydrate stability zone,
causing the hydrate at the base of the hydrate stability
zone to decompose and the freed gas to move toward
a wellbore.
.
14. PRODUCTION METHODS Cotd..
2. THERMAL STIMULATION.
which a source of heat provided directly in the form of
injected steam or hot water or another heated liquid, or
indirectly via electric or sonic means.
It is applied to the hydrate stability zone to raise its
temperature, causing the hydrate to decompose.
The direct approach could be accomplished in either of
two modes: a frontal sweep similar to the steam floods
that are routinely used to produce heavy oil, or by
pumping hot liquid through a vertical fracture between
an injection well and a production well.
15. PRODUCTION METHODS Cotd..
3. CHEMICAL INHIBITION.
It is similar in concept to the chemical means presently
used to inhibit the formation of water ice.
This method seeks to displace the natural gas hydrate
equilibrium condition beyond the hydrate stability
zone’s thermodynamic conditions through injection of a
liquid inhibitor chemical adjacent to the hydrate.
16. PRODUCTION METHODS Cotd..
Fig:3 Schematic of proposed gas hydrate production
methods: (a) thermal injection (b) depressurization, and (c)
inhibitor or other additive.
17. TRANSPORTATION
There are at least three ways to transport the gas
ashore;
by conventional pipeline;
by converting the gas hydrates to liquid middle distillates
via the newly-improved Fischer-Tropsch process and
loading it onto a conventional tanker or barge; or
by reconverting the gas into solid hydrate and shipping it
ashore in a close-to-conventional ship or barge
18. SAFETY &ENVIRONMENTAL
CONCERNS
Normal drilling can generate enough downhole heat to
decompose surrounding hydrates, possibly resulting in
loss of the well.
While large volumes of oceanic natural gas hydrate
deposits are known to have decomposed in the past
absent human influence.
It is clear that the release of large quantities of methane
into the atmosphere, can cause increase its greenhouse
capability since methane is 21 times more potent a
greenhouse gas than is CO2.
20. CHALLENGES
During drilling wells as part of the development of gas
hydrate will produce significant amount of cuttings
containing methane gas.
CO2 produced when methane is burned as a fuel.
methane itself is a greenhouse gas with 21 times than of
carbon dioxide.
High cost for long pipe lines across unstable continental
slops.
21. COMPARISONS
The natural gas is found is gaseous state, while gas
hydrate is a solid .
When natural gas is burned, it emits CO2, leads to
global warming. But the amount released is less than
that of coal or oil is burned.
Oil and coal, emit air pollutants like SO2 & nitrogen
oxides. But in natural gas no such emissions.
Methane gas is the cleanest fuel, because it emits
minimum residue in the environment.
22. CONCLUSION
exploration and quantification of gas- hydrates are very
much required for evaluating the resource potential and
hazard assessment.
Proper exploitation of methane at one hand can meet
the ever-increasing demand of energy and on the other
hand will reduce the environmental and submarine geo-
hazard.
There are several technical problems in extracting and
producing gas from gas-hydrates at this moment.
The recoverability of gas from gas hydrate may be
evaluated if the hydrate occurs in unfrozen sandy
sediments
23. REFERENCES
Sain, K., ZeIt, C.A., and Reddy,P.R., 2002.Imaging of subvolcanic
Mesozoics using traveltime inversion of wide-angle seismic data in the
Saurastra peninsula of India, Geophysical Journal International, 150,
Global Resource Potential of Gas Hydrate – ANew Calculation By Arthur H.
Johnson (Hydrate Energy International) ,vol 11,issue 2,methane hydrate
news letter .
The 2nd South Asain Geoscience Conference and
Exhibition,GEOIndia2011, 12-14th Jan,2011,Gearter Noida,New Delhi,India
,Asit Kumar Samadder, Petrophysist, ONGC , Mumbai,India Exploration of
Gas Hydrate and the present global scenario.
Gas Hydrates Resource Potential of South Asia, Published by SAARC
Energy Centre Plot No. 18, Street No. 6, Sector - H9/1 Islamabad,
Pakistan ,Mr .m .jamaluddin, Mr .malcolm v. lall.
Alternative energy sources: Methane hydrates – in from the cold By Michael
Richardson For the Straits Times, 12 April 2010.
