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2t
Acknowledgements• This project was made possible by funds from the CATO
project, Shell International and TNO.• The technical staff members of the Laboratory for High
Pressure and Temperature Research of Utrecht University, especially Peter van Krieken and Gert Kastelein, are thanked for their valuable support and suggestions in the experiments and interpretation.
• Harry Veld and Kathrin Reimer of TNO are acknowledged for their support and suggestions in the coal characterization and gas analyses.
• The Central Mining Institute and the Brzeszcze mine in Poland and Delft University of Technology are acknowledged for providing the coal samples
3t
Introduction
• CO2 sequestration in coal while producing (enhanced) coal bed methane (ECBM-CO2) considered to be a niche option for CO2 sequestration for those areas with large industrial sources and few sequestration alternatives
• Critical factors• Permeability (swelling)• Exchange ratio at reservoir conditions
• Field experiment ongoing to test the feasibility
• Laboratory experiments required to understand the fundamental processes
• This project aims at the integration of field and laboratory results!
4t
Injection and production in in-situ coal
Injection Production
Cleat system:determines permeability
Matrix blocks:determines Diffusion
Micro pore system:Adsorption/desorption processes from coal surface
5t
Coal-gas interaction
• CO2 interacts with the in-situ coal, causing
e.g. swelling
• Classical idea: Physical process
• Recent idea: Physical process + chemical process
Low P High P
Adsorbed phase
Low P High P
Adsorbed phase
6t
Characteristics pure processes
• Physisorption• Effects are largely reversible, partly irreversible
• Coal structure can change mechanically• Effects are strongly P dependent
• Absolute effects are P dependent (i.e. higher P, more swelling), e.g. by a Langmuir relation
• (Negative) relation between P and reaction time
• Chemisorption• Effects are largely irreversible, partly reversible
• Coal structure changes chemically• Effects are concentration dependent, for a gas thus P dependent
• Strong (negative) relation between concentration (P) and reaction time • Absolute effects are P independent
• once the sample looses its reactivity, it becomes inert
7t
vitrinite
liptinite
inertinite
pyrite
364-4; 300x300 (µm)
8
13
18
23
28
40080012001600200024002800320036004000
Wavenumber (cm-1)
(KM
)-A
bs
orp
tio
n
H-b
onde
d O
H a
nd H
2O
arom
atic
CH
alip
hatic
CH
free
C=
Ois
olat
ed C
=C
arom
atic
rin
g,
poss
ibly
enh
ance
d by
con
juga
ted
OH
-bo
nded
C=
O-g
roup
s
arom
atic
rin
g
alip
hatic
CH
2 an
d C
H3
CH
3 ,
cycl
ic C
H2
C-O
- an
d -C
-O-C
- ,
Si-O
- (a
sh)
poly
cycl
ic a
rom
atic
ske
leto
n
Organic material - aliphatic groups - aromatic groups - etc.
– C – C – – C = C –
– C – H
– C – O – C – • Chemisorption will take place at the molecular level
• Chemisorption is assumed to affect mostly non-carbon-carbon bonds (oxygen functional groups, Goodman 2005)
- relation with C content (rank)
8t
• Focused on
• Registration of exerted stress after
introduction of CO2
• Determination of volumetric expansion of coal
under the influence of CO2
• Reversibility / irreversibility of expansion, possible indication of chemical processes
Laboratory ExperimentsApproach
10t
Laboratory Experiments Approach
• Sample• Activated Carbon (reference material)• Low volatile bituminous coal (Germany)• High volatile bituminous coal (Poland)
• Sample treatment• Dried and physically ‘homogenised’
• 63-212 (µm), approx. 10 (gram)• Pre-compaction under vacuum at 65 (MPa)
• He porosity circa 15-20%
• Gas• CO2
• Helium (Reference gas)• Nitrogen (data still under evaluation)
11t
• Step 0: compaction in vacuum at constant load of 65 MPa
• HVB coal & LVB coal become pellets, AC remains powder
sample
piston
Porous plate
Sealing o-ring
Approach
Piston in contact with porous plate, experiences stress of 65
MPa
12t
sample
piston
Porous plate
Sealing o-ring
Approach• Step 1: constant volume of sample
(piston fixed)
Piston just in contact with porous plate, experiences
stress of circa 0 MPa
13t
• Step 2: constant volume of sample (piston fixed)
Introduction of gas
• In case of swelling, excess stress is measuredexcess stress = observed stress – gas stress
Approach
sample
piston
Porous plate
Sealing o-ringPiston just in contact with porous plate, experiences
stress executed by
gas
16t
Results - interpretation
• Exerted force by the sample after
introduction of CO2 is significant
• P relationship indicates possibility of chemical reactions
• However, similar behavior could be expected from physisorption
17t
• Step 3: piston removed from sample
Approach
sample
piston
Porous plate
Sealing o-ringPiston not in contact with porous plate, experiences
stress executed by
gas
18t
• Step 3: piston removed from samplevolume changes of sample allowed
Approach
sample
piston
Porous plate
Sealing o-ringPiston not in contact with porous plate, experiences
stress executed by
gas
19t
• Step 3: piston put back on sample, determination of new sample volume
• Strain =
Approach
sample
piston
Porous plate
Sealing o-ringPiston just in contact with porous plate, experiences
stress executed by
gas
(measured sample volume – initial sample volume)
initial sample volume
20t
• Activated carbon• Strain data unreliable
because of powder form
• HVB coal (1)• Apparent irreversible strain
(swelling) of circa 0.045 • Apparent reversible strain
(swelling) of circa 0.01
Results
21t
• HVB coal (2), first introduction of CO2 • Apparent irreversible strain (swelling) of circa 0.042• Apparent reversible strain (swelling) of circa 0.005
• HVB coal (2), repeat introduction of CO2 • Apparent reversible strain (swelling) of circa 0.01 – 0.015
Results
22t
• LVB coal, first introduction of CO2 • Apparent irreversible strain (swelling) of circa 0.04• Apparent reversible strain (swelling) of circa 0.01
• LVB coal, repeat introduction of CO2 • Apparent reversible strain (swelling) of circa 0.01 – 0.015
Results
23t
Results - interpretation
• Volumetric expansion is significant
• Strong indications for irreversible chemical reactions, in addition to expansion due to physical sorption
24t
• Step 4: constant volume of sample (piston fixed)
release of gasanalysis of released gas by GC-MS
Approach
sample
piston
Porous plate
Sealing o-ringPiston just in contact with porous plate
GC-MS
Gas
25t
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
3 4 5 6 7 8 9 10 11 12 13
Retention time [min]
Ab
un
da
nc
e
2005091320 2005091321 2005091322
High Volatile Bituminous Coal
Helium
N.B.: corrected for sulphur coompounds, that could be attibuted to rubber
26tN.B.: corrected for sulphur coompounds, that could be attibuted to rubber
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
3 5 7 9 11 13 15 17 19
Retention time [min]
Ab
un
da
nc
e
2005090820 2005090821 2005090822
Activated Carbon
27tN.B.: corrected for sulphur coompounds, that could be attibuted to rubber
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
3 5 7 9 11 13 15 17 19
Retention time [min]
Ab
un
da
nc
e
2005090817 2005090818 2005090819
C3
p-C4
C4
p-C5
C? ->
C5
High Volatile Bituminous Coal
28tN.B.: corrected for sulphur coompounds, that could be attibuted to rubber
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
3 5 7 9 11 13 15 17 19
Retention time [min]
Ab
un
da
nc
e
2005090992 2005090993 2005090994
C3 p-C4 C4
p-C5
C5
C? ->
AnthraciteLVB coal
29t
Results - interpretation
• Chemical reactions proven by release of higher alkanes (at least up to pentane)
30t
HVB coal
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10
Gas Pressure (MPa)
Tim
e [h
]
t(0.5ESmax)
unaffectedcoal
unaffectedcoal
Results – interpreation• Evaluation of “reaction time”, i.e. time at which
half of the extrapolated maximum excess stress is exerted
• Expectation: shorter reaction time at higher P
• Indications that the coal becomes more chemically inert (“loss of reactivity”) after first
introduction of CO2
HVB coal
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10
Gas Pressure (MPa)
Tim
e [h
]
t(0.5ESmax)
t(0.5ESmax)
affectedcoal
unaffectedcoal
affectedcoal
31t
• After CO2-introduction in coal, chemical reactions are
likely to occur next to physisorption• Results in permanent coal expansion• Force executed by coal expansion is significant
• Observed effects probably dependent on coal characteristics• Rank, composition, etc.
• Numerical models usually relate adsorption and swelling to P alone, while coal characteristics seem to play an important role • Coal becomes chemically “inert” after being in contact with CO2
• 2-step modelling? First stage “chemical” modelling and second stage “physical modelling?
• Observed (chemical) expansion highly relevant to field applications• RECOPOL results showed a decrease in injectivity,
attributed to swelling, which was irreversible• Returning to a similar injection P after build-up and fall-off did not result
in similar injectivity
Conclusion and implications
32t
Swelling or shrinkage ?
• Preliminary experiments under constant load show shrinkage and swelling, depending on stress
CO2
33t
Swelling or shrinkage ?
• Preliminary experiments under constant load show shrinkage and swelling, depending on stress
CO2
34t
Workshop observations (Frank & Saikat)
• Other possibilities besides bi-modal pore structure to explain two different diffusion times (Andreas & Nikolai).
• Dirk was able to explain the sorption CH4 by
the a bi-modal pore distribution but had
difficulties with CO2.
• Several groups did observe differences in
response to multiple cycles of CO2 exposure
• More effort should go behind looking into the right way of doing diffusion experiments (e.g polycyclic stress conditions)
35t
Workshop observations (Frank & Saikat)
• More dynamic void volume corrections to sorption data (using swelling coeff.)• Nikolai: First pressure steps fast (order of hrs.) and subsequent
steps slow (order of >3 days)
• Swelling cannot be explained simply by the volume of the adsorbed phase (Nikolai)