1

t

CO2 / coal interaction

Frank van Bergen, Sander Hol, Chris Spiers, Colin Peach

Coal-seq 2005

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

9t

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

14t

Low excess stress with HVB & He

Decrease in excess stress with carbon content

Results

LVB

15t

Applying higher P does not result in much additional excess stress

Results

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)