Coupled Reservoir and Geomechanical Simulation of Underground Coal Gasification

Hossein Akbarzadeh Chair: Dr. Rick Chalaturnyk

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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

(Couch, G.R. 2009)

(Swan Hills Synfuel, 2012)

(Couch, G.R. 2009)

• 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)

• Coal Gasification Simulation

• Geomechanical Simulation The entire geometry

(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

Hossein Akbarzadeh

[email protected]