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COAL BED METHANE
By: Dr. Rohit Verma
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Coalbed Methane (CBM) - Methane contained in coal
seams. Often referred to as virgin coalbed methane, or coal
seam gas.
Coalmine Methane (CMM) - CBM that is released from the
coal seams during coal mining.
Abandoned Mine Methane (AMM) - Methane that
continues to be released from closed and sealed mines. May
also be referred to as coal mine methane because the
liberated methane is associated with past coal mining
activity.
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COAL BED METHANE
CBM IS NATURAL GAS GENERATED DURING
COALIFICATION PROCESS AND STORED IN COAL
SEAMS IN THE ADSORBED STATE ON THE
INTERNAL SURFACES OF COAL MATRIX.
THE ABILITY OF COAL TO STORE GAS IS AFUNCTION OF RANK AND DEPTH OF BURIAL.
COAL SERVES AS BOTH THE SOURCE AS
WELL AS THE RESERVOIR ROCK FOR CBM AND
CAN HOLD FIVE TO SIX TIMES THE AMOUNT OF
GAS STORED IN A CONVENTIONAL SANDRESERVOIR OF COMPARABLE SIZE.
THE PRODUCTION OF CBM IS RELATED TO
PERMEABILITY &TAKES PLACE ON
DEPRESSURISATION OF COAL BEDS THROUGH
DEWATERING.
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Coalbed methane is generated during coalification process
which gets adsorbed on coal at higher pressure.
It is a mining hazard. Presence of CBM in underground mine
not only makes mining works difficult and risky, but also
makes it costly.
Even, its ventilation to atmosphere adds green house gascausing global warming.
CBM is a remarkably clean fuel if utilized efficiently. CBM is a
clean gas having heating value of approximately 8500 KCal/kg
compared to 9000 KCal/kg of natural gas.
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Porosity: The porosity of coal bed reservoirs is usually very
small, ranging from 0.1 to 10%.
Adsorption capacity : Volume of gas adsorbed per unit mass
of coal. The range is usually between 100 to 800 SCF/ton.
Fracture permeability: Acts as the major channel for the gas
to flow. Higher the permeability, higher is the gas production.
Thickness of formation and initial reservoir pressure
Intrinsic Properties of Coal Affecting Gas Production
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Extraction of CBM
To extract the gas, a steel-encased hole is drilled into
the coal seam (1001500 meters below ground).
As the pressure within the coal seam declines due to
natural production or the pumping of water from the
coal bed, both gas and 'produced water' come to thesurface through tubing.
Then the gas is sent to a compressor station and intonatural gas pipelines.
The water typically contains dissolved solids such as
sodium bicarbonate and chloride.
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Vertical Drilling Well
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IN-SEAM HORIZONTAL CBM WELL DRILLING IN
SOHAGPUR BLOCKS
Drilling in seam - directional well from a distance of 1000 m.
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CBM In-seam drilling
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CBM Gas Burning Along Fractured Zone,
Nonia Nalla, Asansol, Raniganj Coalfield
Nalla,
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Commercial exploitation of CBM began in 1995 when
one block was awarded to a foreign operator.
By 2001, the country started auctioning CBM assets,
armed with an elaborate policy.
Compared to the oil and gas sector, the CBM policy is
relatively more investor-friendly, both in fiscal terms
as well as contractual obligations.
Investors interest was most pronounced in the third
round of bidding (2006), when 54 bids were received
for 10 blocks.
CBM POLICY & BLOCKS IN INDIA
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CBM POLICY & BLOCKS IN INDIACBM Policy formulated in 1997
Attractive Fiscal & Contractual Terms
First offer of Blocks under Round-I in 2001
So far, 4 rounds of bidding completed and 33
CBM blocks covering 17,000 km awarded but only
four blocks have come to production so far. The
DGH offered 8 blocks in the first round, 9 in thesecond round, 10 in the third round and 10 in the
fourth round.
The Directorate General of Hydrocarbons will soon offer
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GAS RESOURCE BASEPrognosticated Gas Resources : 400 TCF (In 15 Basin)
CBM Gas Resources Resources : 60 TCF (For 33
Blocks)
Total Gas Resources : 450 TCF (Approx)
pp
Gas Reserves Established (As on 01.08.2010)
- From Hydrocarbon Gas Resources : 104 TCF-
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l b l h l b l
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Global Reserves: The largest CBM resource bases lie in
the former Soviet Union, Canada, China, Australia and the
United States, however, much of the potential remains
untapped.In 2006 it was estimated that of global resources totaling
143 trillion cubic meters, only 1 trillion cubic metres was
actually recovered from reserves.
This is due to a lack of incentive in some countries
particularly in parts of the former Soviet Union where
conventional natural gas is abundant.
In the USA today coalbed methane (CBM) representsbetween two and three per cent of all gas production.
Exploitation in Canada has been somewhat slower than in
the US, but is expected to increase with the development
of new ex loration and extraction technolo ies.
l b l
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Global CBM Activities
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Major coal fields and CBM blocks in India
I di R
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Indian ReservesThe Directorate General of Hydrocarbons of India estimates
that deposits in major coal fields (in twelve states of India
covering an area of 35,400 km2) contain approximately 4.6TCM of CBM.
Coal in these basins ranges from high volatile to low-volatile
bituminous with high ash content (10 to 40 percent), and its
gas content is between 3-16 m3/ton depending on the rank ofthe coal, depth of burial, and geotectonic settings of the
basins as estimated by the CMPDI.
In the Jharia Coalfield which is considered to be the most
prospective area, the gas content is estimated to be between
7.3 and 23.8 m3 per ton of coal within the depth range of
150m to 1200 m. Analysis indicates every 100-m increase in
depth is associated with a 1.3 m
3
increase of methanecontent.
S A WIS IS I U IO O C LOCKS
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STATEWISE DISTRIBUTION OF CBM BLOCKS
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i h fi l i bl k i h
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With five exploration blocks, Essar is the
biggest firm exploring CBM in India having
prospective resources of 7.6 trillion cubic feet ofCBM gas.
RIL holds 3.6 trillion cubic feet of gas in itsCBM blocks.
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E i t l I t
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Environmental Impacts
CBM production entails both environmental benefits
and concerns. Air quality benefits arise from
(1) Substituting clean-burning methane for dirtier
fuels
(2) the burning, rather than venting into the
atmosphere, of coal bed methane released as a resultof coal mining activities (methane is 21 times more
potent a greenhouse gas than is CO2).
However, disposal of the large volumes of water
that are produced from CBM wells, in a way that
is environmentally acceptable and yet
economicall feasible is a concern.
While the regulator announces a huge prognostic reserve of 4 6
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,While the regulator announces a huge prognostic reserve of 4.6trillion cubic m of methane gas in the countrys vast coal fields,
insiders in the CBM exploration sector allege a serious mismatchbetween such estimates and the reality.
OVERESTIMATIONWhile the DGH Web site suggests that only three blocks have beenrelinquished till May 2010, unofficial estimates point out thatoperators of at least one-third of the CBM blocks (out of 33) have
either relinquished their interests, or have approached theregulator to relinquish interests, till date.Insiders say operators in seven out of eight blocks awarded in thesecond round of bidding and four out of 10 blocks in the much-hyped third round (2006) have reportedly failed to establishviable reserves and preferred to forgo assets, after completion ofphase-1 of the work programme.The general observation is that Indias CBM potential is largelyrestricted to eight blocks, three of which were awarded on
nomination basis, and the rest in the first round of bidding.
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