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University of AlbertaPresenter: Hossein Akbarzadeh
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• Introduction to Underground Coal Gasification (UCG)
• UCG Process Simulation
• Numerical Study of UCG at the University of Alberta
• The early idea of UCG: Sir William Siemens, a
German scientist, in 1868 Dmitri Mendeleyev, a
Russian scientist, suggested UCG including the idea of drilling injection and production wells
Coupled Thermal-Hydro-Chemical-Mechanical
• Gas loss if cavity pressure >
hydrostatic pressure
• Contaminant transport
• Impact of coal and rock
spalling on gasification
reactions
• Gas loss through fractures
caused by spalling
• Wellbore damage
• Sansgiry, P.S. (1990) University of Wyoming 2-D cavity growth model
• Combustion simulations CFD based software Reservoir Software (STARS)
• Seifi, M., et al.(2011) University of Calgary Software: STARS
• Daggupati, S. et al. (2010) IIT Bombay, Mumbai, India & UCG Group, Gujarat, India • 29 tests on lignite coal samples
• Akbarzadeh, H. & Chalaturnyk, R.J. (2012), 2nd UCG Workshop, Banff, AB, Canada
• Cavity : 6 x 6 x 6 m • Geomechanics: FLAC3D • Depth: 1400 m • Coupling:
Thermal-Mechanical Thermal-Fluid Mechanical-Fluid
Fully coupled Convergence issue
Sequential coupling STARS 2012 (CMG) FLAC3D 4.00 (ITASCA) Programming
T P
Cavity Geometry
GEOMECHANICAL MODULE
Deformation and/or stress
Level 2 Coupling: Perm = f(stress/deformation) Poro = f(stress/deformation)
GASIFICATION MODULE
Level 1 Coupling: Perm = f(poro)
(Kariznovi , M. et al. 2013)
Reaction Reaction Name Reaction Frequency Factor
Pyro
lysi
s
Pyrolysis 0 188.28
Char
Rea
ctio
ns
Coal combustion -393 100
Boudouard +172 249
Steam gasification +131 156
Hydrogen gasification
-75 200
Carbon monoxide oxidation
-283 247
Forward water shift
-41 12.6
Reverse water shift +41 12.6
Forward methane steam reforming
+206 30
Reverse methane steam reforming
-206 30
(Nourozieh, H. et al. 2010; Seifi, M. et al. 2011; Kariznovi, M. et al. 2013; Swan Hills Synfuels 2012)
Fixed carbon Volatile Matter Ash Moisture
55.6 30.4 9.2 4.8
Parameter Unit Value
Reservoir Initial Properties
Void porosity (coal and initial fluid) fraction 0.95 Fluid porosity fraction 0.0866 Absolute permeability mD 1 Pressure MPa 11.5 Temperature C 60 Water saturation Fraction 0.7 Gas saturation Fraction 0.3 Initial fluid in the reservoir - CH4 Coal density Kg/m3 1200 Char density Kg/m3 1740
Solids and Fluids Thermal Properties
Rock volumetric heat capacity J/(m3*C) 3.0E+06 Rock thermal conductivity J/(m*day*C) 2.0E+05 Char heat capacity J/(gmole oC) 17 Coal heat capacity J/(gmole oC) 17 Solid thermal conductivity J/(m*day*C) 4.5E+05 Gas thermal conductivity J/(m*day*C) 4000 Water thermal conductivity J/(m*day*C) 48384 Water/steam densities, viscosities and enthalpies - STARS defaults
K = 0.0063e16.728(∅−∅0 ) R² = 0.9079
0.001
0.01
0.1
1
10
100
-0.1 0 0.1 0.2 0.3 0.4 0.5
K, D
arcy
∆∅
0
3
6
9
12
15
0
50
100
150
200
0 2 4 6 8 10
Pore
Pre
ssur
e (M
Pa)
Tem
pera
ture
(°C
)
Time (day)
temp
pp
-0.01
0
0.01
0.02
0.03
0.04
0
50
100
150
200
250
300
0 2 4 6 8 10
Vol.
Stra
in (f
ract
ion)
Mea
n E
ff. S
tres
s (M
Pa)
Time (day)
mean_eff_stress
vol_strain
0
3
6
9
12
15
0
50
100
150
200
0 2 4 6 8 10
Pore
Pre
ssur
e (M
Pa)
Tem
pera
ture
(°C
)
Time (day)
temp pp
-0.01
0
0.01
0.02
0.03
0.04
0
50
100
150
200
250
300
0 2 4 6 8 10
Vol.
Stra
in (f
ract
ion)
Mea
n E
ff. S
tres
s (M
Pa)
Time (day)
mean_eff_stress
vol_strain
0
3
6
9
12
15
0
50
100
150
200
0 2 4 6 8 10
Pore
Pre
ssur
e (M
Pa)
Tem
pera
ture
(°C
)
Time (day)
temp pp
-0.01
0
0.01
0.02
0.03
0.04
0
50
100
150
200
250
300
0 2 4 6 8 10
Vol.
Stra
in (f
ract
ion)
Mea
n E
ff. S
tres
s (M
Pa)
Time (day)
mean_eff_stress
vol_strain
0
20
40
60
80
100
0 25 50 75 100 125
Mea
n E
ffec
tive
Stre
ss (M
Pa)
Reservoir Length (m)
Initial 4 Days 6 Days 10 Days
0.00
0.01
0.02
0.03
0.04
0.05
0 25 50 75 100 125
Vert
ical
Dis
plac
emen
t (m
)
Reservoir Length (m)
4 Days 6 Days 10 Days
• A numerical methodology was developed for sequential coupling of reservoir-
geomechanical simulation of UCG
• An existing correlation for coal permeability-porosity during drying and
pyrolysis was modified
• The coupling package allows tracking of cavity growth and the impact on
geomechanical response of coal seam and surrounding rocks
• Large deformation happened around the cavity
• Additional stress and mechanical failure occurred in coal and rocks
• Area of enhanced permeability is expected in coal and rock around the
gasification chamber
• Hot water and superheated steam was observed beyond the cavity………risk
of contaminant transfer