Enhanced Coal Bed Methane (ECBM) - Australian Institute of Energy

Enhanced Coal Bed Methane (ECBM) and CO 2
storage in Australian coals
Dr Abouna Saghafi
Coal Seam Methane and Greenhouse Gas Research
CSIRO Energy Technology, P.O. Box 330, Newcastle, NSW, Australia
abouna.saghafi@csiro.au
www.csiro.au

Gas in coal
Coal is a sedimentary reservoir
rock but it differs markedly from
other conventional reservoirs in
its capacity to retain significant
volumes of gas in its pore
system.
Though coal pore volume is
small (

Outline
Aspects of coal seam gas (CSG) in Australia
Mine safety
Greenhouse gas emissions
Coal seam methane (CSM)
Petroleum and coal seam gas production
Enhanced methane recovery (ECBM) and CO 2
sequestration
CO 2 occurrence in Australian coal seams
CO 2 and methane storage and diffusion properties of
coal (Sydney Basin)
Estimates of CO 2 storage potential in Australian coal
seams

Aspects of coal seam gas, mine safety
In the past the occurrence
of seam gas has been the
cause of myriad of
explosions, fire and
fatalities in Australian coal
mines
Some coal mines closed
because of severity and
frequency of gas emissions,
Nymboida colliery
(1975); Clarence-
Moreton Basin
Leichhardt (1983);
Bowen Basin
Outburst (Photo Photo Courtesy Tahmoor Mine)
Moura (1994) gas and
spon-com; Bowen
Basin Tahmoor Colliery Gas outburst (Year 1985) – Relatively
small gas-rock event: 330 tonnes of rock/coal and
3000 m 3 of gas filled the roadway in few seconds.
High gas emissions and gas outbursts occur frequently
in underground coal mines around the world.

By early 1990’s,
some 30,000 gas
outbursts had
been occurred
worldwide.
The gas outburst
can be very large
e.g. in in Gagarin
Colliery (Donetsk
coalfield, Russia)
some outbursts
caused the
ejection of
14,500 tonnes of
coal and release
of 60,000 m 3 of
methane in few
seconds
(Lama and
Saghafi, 2002).
History of gas outburst in underground
coal mines
China
14,000
6,814
France
4,689
Ukraine
Number of gas outbursts
(recorded before 1990)
1,792
Poland
920 669 600 521 487 482 411 359 250 200 60 58 45 20 5
Japan
Australia
Hungary
Russia
Belgium
Czech Rep.
Canada
… and some
700 outbursts
in Sydney Basin
Germany
Bulgaria
UK
Taiwan
Turkey
Kazakstan
Romania
S. Africa
14000
12000
10000
8000
6000
4000
2000
0

Annual methane emissions (Mm 3 )
Annual Methane Emission (Mm 3 )
90
80
70
60
50
40
30
20
10
Aspects of coal seam gas, greenhouse emissions
0
140
120
100
80
60
40
20
0
Methane emissions from Australian u/g mines
Ventilation
Drainage
Specific emission
Q = 4.13 P.C i
Wyee
Teralba
Munmorah
Nth Goonyella
Wallsend
Newstan
Gordonstone
Oaky Creek
Metropolitan
South Bulli
South Bulga
Tahmoor
Cordeaux
Westcliff
Central Colliery
Tower
Appin
Haenke
Dartbrook
Oakdale
0 5 10 15 20 25 30 35
Methane volume in mined coal
Emission
from
underground
Total
emission
Fitted
emission
90
80
70
60
50
40
30
20
10
0
Specific emission (m 3 /t)
More than a
billion m 3 of
methane is
vented to the
atmosphere
each year
from
Australian
underground
coal mines

Coal Mine Methane (CMM), from a
safety hazard to a source of Energy
Since 1980’s gas from
active mines were
used for local use
initially).
The first significant
coal gas project in
Australia was the
Appin-Tower project
with a nominal
electricity production
of 94 MW.
The operation is still
running (since 1996)
though at lower
capacity of

Mine Gas Utilisation (Appin-Tower
Project)
The 54 engines at Appin colliery uses the
drained gas but also uses the mine ventilation
air as combustion air, thereby destroying all
methane from the coal mine.
The project reduces GHGE by ~2.5 Mt/y CO 2 -e.
Appin-Tower is the largest mine gas GHGE
reduction in the world.

Aspects of coal seam gas, a new ‘green
energy’ for Australia
Many Australian coal
seams contain high
volumes of methane gas
(up to 25 m 3 /t).
With continuos reduction in the
cost of seam gas production
and depletion of conventional
energy resources, combined
with the greenhouse gas
benefits, the CSM is rapidly
developing in Australia
CH 4

Australian commercial
CBM production started
in 1996 in the state of
Queensland
Coal seam gas compensates the
shortfall in natural gas!
Queensland
NSW
Bowen and Sydney coal basins

Qld has a
CSM
resources
of 150 to
500 kPJ
(250 TCF)
and
reserves of
up to 6 kPJ
(6 TCF)
Evolution of CSM production
(QLD)
1800
1600
1400
1200
1000
800
600
400
200
0
Methane
production
(million m 3 )
CSM productioin in Queensland
1994 1996 1998 2000 2002 2004 2006
Year
90
80
70
60
50
40
30
20
10
0
Methane
production
x 10 15 joules
Mm3
PJ

Coal Seam Methane, Queensland
1996 – Production from Dawson Valley gas field and Moura Mine
started; gas supplied to Wallumbilla-Gladstone pipeline
1998 – Production from Fairview field started; gas supplied to
Wallumbilla-Gladstone pipeline.
2001 – Peat gas field came into production.
2002 – Scotia gas field came into production.
2002 – Queensland government released the new energy policy
mandating 13% electricity generation from natural gas (by 2005).
2004 – Mungi field near Moura came into production.
2005 – Moranbah project, producing gas for electricity generation
in Townsville, as part of the project a pipeline between Moranbah
and Townsville was constructed. Also innovative horizontal 1 km
in-seam drilling was used.
Currently 40% of Qld gas consumption is sourced from coal
seam gas.

Coal seam methane (CSM), New South
Wales
NSW Government has no set target for natural gas
use. But a greenhouse gas mitigation scheme
penalises energy producers for over reliance on
coal
NSW government had sponsored a project managed
by Sydney Gas Company to optimise the
production of CBM from Sydney Basin
Tens of exploration and production gas wells to
depths of >900 m were drilled in the Southern
and Hunter Valley coalfields in Sydney Basin

Coal seam methane (CSM) production in
Australia, well flowrates of 20-25 x10 3 m 3 /day
Australian 20 CSM production (PJ/y)
18
16
14
12
10
8
6
4
2
0
Origin Energy
Santos/ Tipperary
BHP
CH4
Anglo Coal
Sydney Gas
Arrow
CS Energy
Current (year 2005) active CSM
fields are: Southern Sydney
Basin, Moranbah, Fairview
(Comet Ridge), Durhm Ranch
(Spring Gully), Dawson Valley,
Moura, Peat, Walloons, and
Scotia.
In Queensland ~55 PJ/y of coal
seam methane is now (2005)
produced from Bowen and
Surat Basins, this constitutes
40% of the total gas
consumption in Queensland
(~120 PJ/y)

Coal Seam Gas and Petroleum Gas
Resources and production
Coal Seam Methane
Qld CSM resources: ~150,000 - 500,000 PJ
Qld CSM reserves:
3P (proved, probable and possible) : ~6000 PJ
Qld gas consumption: 110-130 PJ per year
Petroleum Gas
Australia total petroleum gas reserves: ~140,000 PJ
Petroleum gas is mainly destined for exportation;
Australia is 5 th world largest exporter of LNG
415 PJ/y to Japan, USA, S Korea,..
160 PJ/y to China alone for 25 years (from 2006)

ustralian
Natural Gas
reserves
and
distribution
(2001) :
52.7
%
16.2%
19.5%
Reserves ~140,000 PJ,
Production :1,200 PJ/y
Cooper Basin
200 PJ/y
production.
Reservoir
is depleting at a
rate of 10% per
year!
4.2%
Cooper
Basin
Proposed PNG
gas pipeline,
starts 2009/10
7.5%

Greenhouse gas emissions and Australian
dependence on fossil fuel
NSW and Queensland secures 90-95% of their electricity
from coal-fired and to a lesser extent from gas-fired
power plants.
There are no realistic prospects in the foreseeable future
that this heavy dependence on fossil fuel (coal and gas)
will decrease.
Demand for electricity meanwhile continues to rise
steadily, to 50% by year 2020, meaning that the overall
emissions of CO 2 are set to rise, probably substantially.
Increasingly, carbon capture and sequestration (CCS) is
seen as a means whereby we can continue our
dependence upon coal and gas to generate electricity
without consequential increases in atmospheric carbon
dioxide levels.

Per capita Australia is the most intensive GHG
Emitter
In absolute
terms
Australia
contributes
to 1.3% of
total world
GHGE
and 3.4% of
the Annex 1
emissions.
Spain
France
Italy
Japan
Germany
UK
Russia
Ireland
Canada
US
Australia
0.4
0.1
0.6
0.5
1.0
0.7
0.7
0.5
1.4
2.0
7.0
9.3
9.5
9.5
10.9
12.1
12.6
13.7
x 10 9 tonnes per year
GhGE, CO2-e
Annex 1 countries (UNFCCC, 2001)
United Nations Framework Convention on Climate Change
tonnes per year (per capita)
17.5
23.0
23.8
25.5
0 5 10 15 20 25 30

Enhanced Coal Bed Methane (ECBM)
Injection
well
Diluting
gas
mixture
(flue gas)
CH 4
Production
well
ECBM is the
process of
injecting a pure or
a mixture of gases
(flue gas into a
coal seam to
enhance the
recovery of
coalbed methane
(CBM).

Enhanced gas recovery from coal seams,
N2-ECBM CO2-ECBM Injection
well
N 2 or CO 2
CH 4
Production
well
N 2 or CO 2 can be injected
into coal seams to
enhance methane release.
N 2 is a diluent reducing
partial pressure of
methane and hence
stimulates its release; CO 2
adsorbs stronger to the
coal, would replace
methane and enhance its
release
Simultaneous CO 2 storage
and CH 4 capture is an
appealing option because
of combined GhGE
mitigation and energy
recovery benefits

Field experiences of ECBM
So far there has been no ECBM trial in Australia; worldwide
limited pilot operation have been conducted in USA (St Juan
Basin), Canada (Manville) and China (Qinshui Basin)
The first small scale N 2 -ECBM trial was undertaken in
December 1993 in the St Juan Basin from Fruitland
formation in Colorado (BP-Amoco).
Alberta Research Council (ARI) and partners performed a
CO 2 -ECBM into the Manville Formation coal seams at the
Fen Big Valley in Alberta.
A Canadian consortium (CIDA) and China United CBM
corporation are currently (year 2005) undertaking a micro
pilot operation in Shanxi province injecting CO 2 into semianthracite
coal seams of Qinshui Basin.

ECBM research issues
Coal capacity for storing seam gases
Adsorbed gas; preferential CO 2/CH /CH4 sorption into coal and controls of
gas saturation levels
Free gas storage
Diffusive gas flow in coal
Preferential CO 2/CH /CH4 diffusive flow
Coal water/gas permeability and variations with
adsorption/desorption
Relative permeability
Effect of swelling/shrinkage
• Origin of gas in coal seam and variations in gas types
• Biogenic/thermogenic origin
• CO2, CH4 and C2+

ECBM/CBM issues, water
Formation water in Australian coal measures of Sydney and
Bowen Basins do not occur in large volumes and so far
water production from CBM in Australia has been relatively
small (less than 500 barrels of water per day and per well).
Such volumes of water could be dealt with by evaporation in
water ponds.
However with increase in Australian CBM production and
move to younger basins where CBM production is
accompanied with high volumes of water (such as Surat
Basin in Queensland) other solutions including reinjecting
of water in depleted wells are envisaged. Reinjecting could
take place after a reverse osmosis treatment to remove
salts.
Also for CBM wells close to potential consumption points
the use of water for irrigation, coal washeries and coal fired
plants ( cooling water) is being studied.

Coal seam reservoir, storage size
How much gas is (could be) stored in coal?
Total gas volume in-situ = adsorbed phase + free phase
per tonne of coal
m 3 /t
= f ( p,
T , coal rank & type)
+
pM
RT
ε
ρ
c

CO 2 /CH 4 storage in rock/coal, free phase
Compared to other
seam gases much
less void space is
required to store
CO 2 (free phase
gas)
m 3 of
void
space
required
to store
one
tonne of
gas
CH4
N2
CO2
1000
100
10
1
Measurement at 55°C
0 2 4 6 8 10 12 14 16
Gas pressure, MPa

CO 2 /CH 4 storage in coal, adsorbed phase
Compared to other
seam gases
much less mass
of coal is
required to store
CO 2
(adsorbed phase)
Tonne of
coal
required
to store
one tonne
of gas
N2
CH4
CO2
1000
100
10
1
Gas adsorbed at 55°C
0 2 4 6 8 10 12 14 16
Absolute pressure (MPa)

c
Gas is retained in coal by adsorption forces
Adsorption isotherm
p
Gas is adsorbed
in coal following
a micro-pore
filling
mechanism,
Once micro-pores
are filled no
further
adsorption
occurs.
c
=
p
V
L
+
Majority of
pores in
coal are of
order of
nano-meter
size
p
P
L
~nm
Free phase
gas
pressure:
p
Coal gas content: c
Adsorbed gas
Coal

Gas storage capacity of Bowen Basin coals
At a mining depth
of 300 m some
Bowen Basin
coal can retain
up to 20 m 3 /t of
CH 4 and 40 m 3 /t
of CO 2 .
50
40
30
20
The storage
capacity
10
increases with
depth 0
Coal as received, Gas adsorption at 27°C
Gas content (m
60
3 /t)
100 m 200 m 300 m 400 m
Depth
CH 4
CO 2
Absolute pressure (kPa)
0 1000 2000 3000 4000 5000 6000

Measurement of gas flow/storage
properties of coal
⎛ K P M ⎞ ⎛ M −αt
−∇•
⎜
⎜(
ρa
+ Dsε
) ∇P
=
e c
Pa
z R T ⎟
⎜
⎜−ε
+ ( 1−
) ρ ρ
⎝ η ⋅ ⋅ ⎠ ⎝ zR⋅T
1 – Laminar flow of free gas
by permeation ( Darcy’s
law)
2 –Desorption and flow of
desorbed gas by
diffusion (slipping flow,
Knudsen flow, Fick’s law)
a
V P
L
L
( P+
P )
L
2
⎞∂P
⎟
⎠ ∂t
Gas flow
k ∂p
ψ 1 = −
η ∂x
ψ
2
∂c
= −D
∂x
1
2
2
2

Measurement of rate of diffusion of coal seam gases,
Bowen Basin coal
Access of gas to the
micropores where
most of gas is stored
occurs only by
diffusion.
Therefore the injection
and storage of gas in
coal is ultimately
controlled by the rate
of diffusive flow of gas
in coal.
The diffusivity values
obtained are:
CO 2 :6.37 x 10 -10 m 2 /s
CH 4 : 3.41 x 10 -10 m 2 /s
Gas volume diffused per
unit surface area of coal
(Litre/m 2 )
80
70
60
50
40
30
20
10
0
CO 2
0 20 40 60 80 100 120
Time elapsed (hour)
CH 4
12.1
mL/min/m 2
6.7
mL/min/m 2

Fate of coalification generated CO 2
Transformation of peat to lignite to bituminous
coal (coalification) has been an ongoing
process over many millions of years.
Coalification process produces high volumes
of CO 2 ,CH 4 and water.
This occurs through various chemical
reactions such as: decarboxylation,
dehydration and, de-alkalisation.
Though much more CO 2 than CH 4 had
been generated during coallification, and
that coal can retain much more CO 2 than
CH 4 most world coal seams contain mainly
methane.
Gas generation (m 3 /t)
250
200
150
100
50
0
Gas generation from laboratory coalification
Australian coal
CO2
CH4
Vitrinite reflectance (%)
0 0.5 1 1.5 2 2.5 3 3.5
Lignite
High/low voltaile
bituminous
Maturation
Anthracite
The reason for the absence of primary CO 2 is
that most had been dissolved in water produced
during coalification. The dissolved CO 2 had
then either migrated away or have formed
carbonate in the coal fractures and
neighbouring formations.

Sources of secondary CO 2 generation
in coal
Though methane is dominant seam gas, Australian
coal basins including Sydney Basin contain various
amount of CO 2
The secondary sources of CO 2 in coal seams could
be,
Thermal destruction of carbonate and
carbonate dissolution
Bacterial activities (hydrocarbon oxidation,
degradation of organic matters)
Igneous activities and magma migration

Sources of CO 2 in Sydney Basin coal
It is believed that most of CO 2 in Sydney
Basin is of igneous origin (Smith et al, 1985),
because:
High CO 2 content areas have generally
isotopic compositions corresponding to
CO 2 magmatic sources (d 13 C=-7 ‰)
The highest concentrations of CO 2 are
localised laterally along major faults.

Sydney Basin CO 2 adsorption study
Some 27 coals
from 17 seams in
13 locations in
Sydney Basin were
measured. The
coal seams depths
varied from less
than 57 to more
than 723 m.
Coal rank varied
from low volatile
bituminous to high
volatile bituminous
(Rv= 0.66 to 1.45%)
0
100
200
300
400
500
600
700
0 10 20 30 40 50
800
Seam depth (m)
Metamorphosed
coals
Volatile matter (%)

CO 2 adsorption capacity of Sydney Basin coal
Gas adsorption
behaviour was
presented by
Langmuir type
isotherm:
c
=
p
V
L
+
Difference in
adsorption
capacity (V L )
across Sydney
Basin was
twofold
p
P
L
Gas adsorbed, daf (m 3 /t)
80
70
60
50
40
30
20
10
0
Coal13
Coal14
0 2000 4000 6000 8000
Absolute gas pressure (kPa)

Preferential storage of gas in coal
CO 2 , CH 4 and N 2
adsorb to coal in
decreasing
strength of
adsorption,
For this coal, 2-
2.5 molecules of
CO 2 would
replace
1 molecule of CH 4
depending on gas
pressure
Total gas adsorbed (m 3 /t)
40
35
30
25
20
15
10
5
0
Carbon dioxide
Methane
Nitrogen
0 1000 2000 3000 4000 5000 6000
Absolute pressure (kPa)

Storage capacity Sydney Basin coals; Effect of
coal maturation
Capacity increases
with rank; and two
trends can be
observed for
higher and lower
rank coals of the
Sydney Basin in
the North and
South Coalfields
This could have
important
implications for a
pilot CO 2
sequestration
project in Australia
Langmuir volume (m 3 /t)
100
90
80
70
60
50
40
30
20
Northern
Sydney
Basin
coalfields
0.50 0.70 0.90 1.10 1.30 1.50
Vitrinite reflectance (%)
Southern
Sydney Basin
coalfields
Coal maturation

CO 2 storage at different depths, Sydney Basin
coals
CO 2 adsorption
capacity of the
Sydney Basin
coals increases
with seam depth
following a
power function.
This could have
important
implications for
a pilot CO 2
sequestration
project in
Australia.
0
100
200
300
400
500
600
700
800
900
1000
CO2 storage capacity (m 3 /t)
0 20 40 60 80
Seam depth (m)
C = C 0 (h/h 0) a

Estimate of CO 2 sequestration potential of
NSW coals (1)
NSW coal
•Demonstrated: 34 billion tonnes
•Inferred resources: 57 billion tonnes
Assume all demonstrated
resources are mined and all
inferred resources are used
for CO 2 storage (57 Bt)
An average in-situ CO 2
adsorption capacity of
~40 m 3 /t
can be used based on the
developed equation
100
200
300
400
500
600
700
800
900
1000
CO2 storage capacity (m 3 /t)
0 20 40 60 80
0
Seam depth (m)
C = C 0 (h/h 0) a
Depth >600 m
Storage = or
> 40 m 3 /t

Estimate of CO 2 storage potential of NSW coals
(2)
If only the inferred coal resources (57 Bt) are
used for the sequestration projects then total
CO 2 storage capacity of NSW is
CO 2 storage =
2.28 trillion m 3
4.1 billion tonnes
45 years NSW electricity emissions

Estimate of CO 2 sequestration potential of
Queensland coals
• Assuming that
the unmineable
reserves of coal
in Queensland
is as much as
the
underground
mineable
reserves
• Seam depths
of >700 m
Estimate of Qld CO 2 storage potential
Qld coal reserves
Open cut
Underground
CO 2 storage
capacity of Qld
coal based on
CSIRO studies
CO 2 potential
38.94
15.91
23.03
40.00
921.20
32.53
1.7
Bt
Bt
Bt
m 3 /t
billion m 3
tcf
billion
tonnes (gt)

Summary (1)
Australia’s CBM Industry is growing as a results of
depletion in conventional petroleum gas reservoir,
advance in drilling and completion technology, and
better understating of the behaviour of coal gas
interaction.
Measurement of storage and flow properties of numerous
Australian coals shows that,
CO 2 storage capacity of Sydney Basin coal varies from 40 to 80 m 3
per tonne of coal.
CH 4 adheres weaker to coal than CO 2, coal capacity for CH 4 is half of
its capacity for CO 2.
CO 2 diffuses much faster than CH 4 in coal and gas injection rate is
diffusion rate dependent.

Summary (2)
NSW has large resources of coal and if only
the deferred coal resources are used for CO 2
sequestration, then up to 4.1 billion tonnes of
CO 2 can be sequestered in NSW.
If there were as much unmineable coal at
depth of 700 m and over in Qld than at current
underground depths then there would be a
capacity of 1.7 billion tonnes CO 2 storage in
unmineable coal seams of Qld.