COAL BED GAS GENERATION

1. COAL BED GAS GENERATION
NARMEEN HAROON
ROLL NO: 12
4TH SEMESTER
CENTRE FOR COAL TECHNOLOGY
UNIVERSITY OF THE PUNJAB
LAHORE.

2. What is Coal Bed Gas ?
 Coal bed gas also known as Coal bed methane (
CBM ) is a form of natural gas extracted from coal
beds.
 The term refers to methane adsorbed into the solid
matrix of the coal.
 Methane is stored within the coal by a process
called adsorption.
 It is called 'sweet gas' because of its lack
of hydrogen sulfide.
 Coal bed methane contains very little heavier
hydrocarbons.
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3.  The methane is in a near-
liquid state lining the insides
of the pores within the coal
(called the matrix).
 The open fractures in the
coal (called the cleats) can
also contain free gas or can
be saturated with water.
 During the extraction, as the
pores shrink, the overall
matrix shrinks as well, which
may eventually increase the
space the gas can travel
through (the cleats),
increasing gas flow.
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4. Composition Of CBM
The composition of methane gas from coal
mines is variable but it is essentially a high
concentrated methane gas as shown below:
CH4 = 93 – 99 %
C2 H6 = 0 – 3 %
CO2 = 0 – 4 %
N2 = 2 – 6 %
Hydrogen and Rare gases are present in traces.

5. How CBM is formed
 CBM is generated either through
chemical reactions or bacterial action.
 Thermogenic Production.
 Biogenic Method.
 High Rank Coal.
 Low Rank Coal.
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6. Where does CBM exists?
According to the CBM Association of Alabama, 13% of the
land in the lower 48 United States has some coal under it,
and some of this coal contains methane - either in the form
we know as traditional natural gas or as CBM. According to
the United States Geological Survey, the Rocky Mountain
Region has extensive coal deposits bearing an estimated 30-
58 trillion cubic feet (TCF) of recoverable CBM. While
impressive, this represents only one third of the total 184 TCF
of natural gas in the Rocky Mountain region (Decker, 2001).
Within the Rocky Mountain Region, untapped sources of
CBM exist in the Powder River Basin of Wyoming and
Montana, the Greater Green River Basin of Wyoming,
Colorado, and Utah, the Uinta-Piceance Basin of Colorado
and Utah, and the Raton and San Juan Basins of Colorado
and New Mexico. An estimated 24 TCF of recoverable CBM
resources may lie below the Powder River basin of Montana
and Wyoming (Decker, 2001).
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8. How the estimation is done?
There are two popular methods of estimating
recoverable methane gas from a coal seam:-
 One method requires estimating methane reserves
by boring to the top of the coal seam, then extracting a
core from the coal.
The amount of methane recovered from the coal core
is used to estimate gas content per unit volume of
coal. If a number of cores are drilled and methane gas
release is observed, one can estimate the amount of
gas available in a region.
The limitations to this method are:
1) there is much disturbance to the coal seam core
before gas release is measured.
2) it is expensive.
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9.  Another method is through a series of calculations
based on information known about the coal in the
region and the feasibility of CBM development.
 For instance, the Montana Bureau of Mines and
Geology estimated the amount of recoverable CBM in
the Powder River Basin using the following information:
 A coal seam has favorable reserves if it produces 50-
70 ft3 CBM per ton of coal.
 CBM extraction is economical at 50 ft3 per ton of coal
when a coal seam is 20 feet thick or more.
 Coal bed methane exists only in areas where the
dominant chemistry of the water in the coal seam is
sodium bicarbonate and where the coal seam is
buried deeply enough to maintain sufficient water
pressure to hold the gas in place.
 The Environmental Impact Statement for CBM
development in the Powder River Basin estimated the
amount of coal in the region based on the total reported
tonnage of coal in the region multiplied by 50 ft3 of
methane per ton of coal, regardless of seam thickness,
depth or proximity to outcrop. 9COAL BED GAS GENERATION

10. CBM is removed by removing water
pressure which holds CBM in place.
Methane that was held in place by
water pressure tends to follow the water
as it is pumped to the surface, where it
is captured and transported through
pipelines. Fracturing fluids are often
first injected into the coal bed to break
up the coal, making it easier for the
water and gas to flow to the surface.
How is coal bed methane removed?
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11. Gas
Water
(production
fluid)
Coal Bed
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12. Since CBM travels with ground water in coal seams, extraction of CBM
involves pumping available water from the seam in order to reduce the
water pressure that holds gas in the seam. CBM has very low solubility
in water and readily separates as pressure decreases, allowing it to be
piped out of the well separately from the water. Water moving from the
coal seam to the well bore encourages gas migration toward the well.
CBM producers try not to dewater the coal seam, but rather seek to
decrease the water pressure (or head of water) in the coal seam to just
above the top of the seam. However, sometimes the water level drops into
the coal seam.
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13.  Methane will stay in a coalbed as long as the
water table remains above the gas saturated
coal.
 Gas is released from the coalbed when cleat
pressure is reduced by dewatering.
 Some wells may never become economic if
coals can’t be dewatered
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14. Extraction
 A steel-encased hole is drilled into the
coal seam (100 – 1500 meters below
ground).
 Gas and produced water.
 Then the gas is sent to a compressor
station and into natural gas pipelines.
 Coal bed methane wells often produce at
lower gas rates than conventional
reservoirs, typically peaking at near
300,000 cubic feet (8,500 m3) per day
(about 0.100 m³/s).
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15. Intrinsic Properties Affecting Gas
Production
 Gas contained in coal bed methane is
mainly methane and trace quantities
of ethane, nitrogen, carbon
dioxide and few other gases.
 Porosity.
 Adsorption Capacity.
 Fracture Permeability.
 Thickness of formation and initial
reservoir pressure.
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16. CBM wells are required to be spaced at least 1000 feet apart.
The 1000 feet distance is based on what is called the “cone of
depression.”
Pumping from wells lowers the water table.
This area is known as the cone of depression.
Groundwater flow is diverted towards the well
as it flows into the cone of depression.
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17. Fate of CBM product water-
(a) Quantity of CBM product
water
Extraction of CBM involves pumping large
volumes of water from the saturated coal seam in
order to release the water pressure holding the
gas in the coal seam.
 CBM product water is a source of much debate.
Each well produces 5 to 20 gallons of water per
minute.
 At 12 gallons per minute, one well produces a
total of 17,280 gallons of water per day.
 It is common to have one well every 80 acres,
and in the Powder River Basin, there are up to
three methane-bearing coal seams. Therefore,
there may be up to three wells per 80 acres.
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18. (b) The quality of CBM product water
and its effects on soil:
 CBM product water has a moderately high salinity
hazard and often a very high sodium hazard based on
standards used for irrigation suitability.
 Irrigation with water of CBM product water quality on
range or crop lands should be done with great care and
managed closely.
 With time, salts from the product water can accumulate
in the root zone to concentrations which will affect plant
growth.
 Saline conditions stunt plant growth because plants
must work harder to extract water from the soil.
 the production fluid is subjected to pH adjustments and
aeration if necessary and settling. Once the water has
been treated, it can then be discharged.
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19. Effect on soil:-
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20. The quality of CBM product water and
its effect on plants:
 Disposal of the quantities of CBM
product water into stream channels and
on the landscape poses riparian and
wetland
 High salinity and sodium levels in
product water may alter plant
communities by causing replacement of
salt intolerant species with more salt
tolerant species.
 It is well recognized that encroachment
of such noxious species as salt cedar,
Russian olive, and leafy spurge is
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21. Left: An example of soils of eastern Montana
that are high in swelling (montmorillonitic)
clay.
Right: Complete dispersion of the same
soil following a season of exposure to
high saline/sodic water.
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22. The current management practices
for disposal of CBM product water
 Discharged into a stream channel - Although direct stream
discharge is no longer permitted on new wells, existing
operations were "grandfathered" and are still discharging directly
into streams. Also, proposals are being advanced to allow regulated
discharges during certain flow conditions.
 Impounded - This method involves constructing a pond in which
CBM product water is stored or allowed to infiltrate to the
subsurface. There are several terms for these impoundments:
"holding ponds", "zero discharge ponds" or "infiltration ponds".
Although they do not directly discharge water on the land surface,
most impoundments are not lined and do discharge to the
subsurface. Some percentage of seepage flow from impoundments
is likely to reach stream channels via subsurface flow.
 Land applied to crop or rangeland - through some form of
irrigation equipment.
 Other uses - CBM product water is also used for dust control and, in
some cases, is being used by coal mines.
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23. Areas of Coal Bed Methane
Australia
• Bowen Basin, (Fairview, Scotia, Spring Gully), Queensland, Australia
• Surat Basin, Berwyndale, Windibri, Kogan, Daandine, Tipton West, Queensland, Australia
Canada
• Telkwa coalfield, British Columbia
• Western Canadian Sedimentary Basin, Alberta
South
Africa
• Molteno Coal Field, Eastern Cape
United
Kingdom
• Cheshire, Lancashire, Staffordshire
United
States
• Appalachian Basin, Alabama, Pennsylvania, Ohio, Wyoming , Colorado and New Mexico
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24. Reserves
 A U.S. Geological Survey predicts more than 700
trillion cubic feet (20 Tm³) of methane within the US.
 At a natural gas price of US$6.05 per million Btu
(US$5.73/GJ), that volume is worth US$4.37 trillion.
 At least 100 trillion cubic feet (2.8 Tm³) of it is
economically viable to produce.
 In Canada, British Columbia is estimated to have
approximately 90 trillion cubic feet (2,500 km3) of
coal bed gas
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26. CBM as an Energy Resource
 Coal bed Methane Moves from Unconventional to
Mainstream Energy Resource.
 Coal bed methane is now a significant part of Nation's
natural gas supply and less methane is released to the
atmosphere.
 Currently considered a non-renewable resource
 There is evidence by the Alberta Research
Council, Alberta Geological Survey and others showing
coal bed methane is a renewable resource.
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27. Environmental Impacts
 CBM wells are connected by a network of roads,
pipelines, and compressor stations.
 Water withdrawal may depress aquifers over a large
area and affect groundwater flows
 The release of CBM into the atmosphere adversely
affects the global climate.
 Operators are required to obtain building permits for
roads, pipelines and structures, obtain wastewater
(produced water) discharge permits, and prepare
Environmental Impact Statements.
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28. Facts
 Coal is the world′s most abundant energy source
 Coal is a major source of hydrocarbons such as
methane gas
 When plant material is converted into coal it generates
large quantities of methane-rich gas
 Methane gas is then stored within the coal beds making
coal a reservoir as well as a gas source
 Coal bed methane is currently a huge undeveloped
energy resource
 Coal bed methane can be used as an clean energy
source
 It is a safe, efficient and an environmentally more
acceptable energy source
 Over the last two decades, the development of domestic
natural gas supplies declined while consumption
increased. There is now greater world market demand for
cleaner fuels like Coal Bed Methane Gas and Natural 28COAL BED GAS GENERATION

29. Recommend: Most Sustainable
Practice
 Reinjection into aquifers depleted by
CBM production.
 Injection or percolation into depleted
aquifers with water treatment as required
protecting and/or enhancing water quality.
 Replace other uses where quality allows.
 Surface discharges with water treatment
as required resulting in improved stream
flows.
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30. References:
 www.wikipedia.org
 http://www.ml.com/media/43347.pdf
 www.eurenergyresources.com
 http://www.eia.doe.gov/
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31. CBM- GAS OF THE PAST, PRESENT
AND THE FUTURE
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