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1
GeoGAS
Moranbah North Coal Seam Gas Development – Technical and
Statutory
Anglo Coal Australia Pty. Ltd./GeoGAS Pty. Ltd.ACARP Gas and Outburst Workshop
Mackay 29th June 2007
Hugh Luckhurst-Smith, Anglo Coal Australia Pty. Ltd.Ray Williams, GeoGAS Pty. Ltd.
GeoGAS
To Cover
Statutory and Legal (Hugh Luckhurst-Smith)Technical (Ray Williams)
2
GeoGAS
Queensland recent Statutory history.Coal Mine Health & Safety Act & Regulations 2000Petroleum & Gas Act & Regulations 2004“Surface activities related to [petroleum &] gas activities’
Regulations
GeoGAS
ACA History
Moura-> Dawson opencut mine: PL94/ATPs acquisition 2006Grasstree U/G mine: 32MW Power station 2006Moranbah North U/G mine:Gas sales 2006/Power station 2008
U/G mines; gas drainage for ‘mineability & greenhouse
3
GeoGAS
Petroleum & Gas Act target compliance
Moranbah North 1st quarter 2007Dawsonlate 2007Grasstree mid 2008
GeoGAS
Legal Aspects.
Operational: Separate SSMs-Underground; Surface Coal; Surface Gas; Power StationDrilling: Each rig has own SSM. Clear signage & separation eg valve or flange.Where jurisdictions overlapCMHSA always takes precedence!
4
GeoGAS
Compliance issues.AS4801: Corporate overview complianceACA solution: Parallel HSEMSs
Recommendations1.Adopt as many as possible of existing mine procedures2. Conduct joint Risk Assessments3. Audits, inspections to be based on SafeOP-a good tool!
GeoGAS
Introduction
Statutory and Legal (Hugh Luckhurst-Smith)Technical (Ray Williams)
Objectives to Produce gas at the required rateAs uniformly and as long as possibleAt minimum cost (maximum spacing/drainage times)Meeting requirements for mine gas management as the priority
For this presentation:To demonstrate the forecasting processTo highlight issues related to meeting the twin needs of mine gas emission control and gas utilisation.To comment on risk and uncertainty
5
GeoGAS
Outline of Forecasting Process
Mine Plan Mine Schedule
Assign Gas Drainage Boreholes
Geology and Gas Reservoir Properties
Predrainage Models
Empirical Data, History
Define Reservoir Regions
Model Flow Curves forEach Region
Predrainage Borehole Spacing
Test Time Available Remaining Gas Content Uniformity of gas production
Longwall Ventilation Capacity
Longwall emission
modelling
Sum Gas Production from Various Sources
Longwall Model
Calibration
Assess Uncertainty
Well Schedule/Sequencing
GeoGAS
Gas Reservoir
6
GeoGAS
Gas Content
0 100 200 300 400 500
Depth (m)
Mea
sure
d G
as C
onte
nt @
15%
Ash
(m3/
t)
GM SeamGL SeamP Seam & splitsQA/QB SeamsLinear (GM Seam)
MNCGasContentMasterAug2006.xls{Main(2)}
GeoGAS
Gas Sorption Isotherms
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Pressure (kPa, abs)
Gas
Ads
orbe
d (m
3 /t, r
es te
mp)
MN0035 33°C MN0037 33°C WB1-04 40.9°CNM1-11 43.5°C NM1-10 43.5°C NM1-10 43.5°C
IsothermsMNCDec06.xls{GM}
Ash 17.5%, Reservoir
Temperature 33.0°C
7
GeoGAS
Permeability
0 50 100 150 200 250 300 350 400 450 500
Depth of Cover (m)
Perm
eabi
lity
(mD)
{log
sca
le}
GM Low Perm Domain
GM Seam High Perm DomainGL Seam
P Seam - High Perm DomainGU, Q, P Seam Low Perm Domain
Perm domain boundaryGL seam assumed Permeability
MNC_Permeability.xls {AllPermSorted}
Low Perm Domain
High Perm Domain
GeoGAS
Effect of Stress
12 fold reduction in permeability for every Mpaincrease in stress
0.1
1
10
100
10000 500 1000 1500 2000 2500 3000
Effective Stress (kPa)
Perm
eabi
lity
(mD
)
8
GeoGAS
Gas Saturation
As important as permeability to gas deliverability
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0 250 500 750 1000 1250 1500 1750 2000 2250 2500
Absolute Pressure (kPa)
Gas
Abs
orbe
d (m
3 /t)
saturation.xls{Sheet1}
Gas desorption pressure
Original reservoir pressure
A
B
Gas saturation = A / B %
GeoGAS
Comparing Different Gas Saturations
0
2
4
6
8
10
12
14
16
18
0 1000 2000 3000 4000 5000Absolute Pressure (kPa)
Gas
Ads
orbe
d (m
3/t)
ExampleIsotherm.xls
Critical gas desorption pressure = 1999 kPaa
Gas saturation= 81%
Gas saturation= 75%
Gas saturation= 70%
Even though gas content and permeability might be the same, changes in gas saturationhave an enormous effect on gas production, gas content reduction and how the well will operate.
Getting gas out is all about reducing pressurethroughout the reservoir.Gas sat of 70% may notseem too different from80%, but the additionalimpost on pressurereduction is enormous.
Then there is also the effect on permeability of increasing effective stress
9
GeoGAS
Predrainage Gas
GeoGAS
Underground In-Seam (UIS) Flow Curves
Basic curve defined empirically.
Application to each riser is based:• Material balance• Adjustment flow to account for actual metres drilled• A flow factor producing 70~80% recovery with 1~2 m3/t remaining gas content.
0 50 100 150 200 250 300 350 400 450 500
Time on Line (days)
Gas
Flo
w (l
/m/m
in)
Gas
Rec
over
y
107-36a107-31a/b107-16107-23MG108-3Average
Moranbah THE CHART 20-9-06RW.xls{107-
10
GeoGAS
UIS Gas Total
Gas flows summed according to drilling schedule
Nov-06 Nov-07 Nov-08 Nov-09 Nov-10 Nov-11 Nov-12 Nov-13 Nov-14 Nov-15
Gas
Pro
duct
ion
(TJ/
day)
UIS risers
RegionProduction.xls{WellConstants}
GeoGAS
Surface to In-Seam (SIS) Drilling
Modelling uses SIMED II Models calibrated on SIS wells INGM001~3 to fix the not so easily measured parameters (compressibility, porosity, relperm, n factor, skin).Model includes reduction in perm with increasing effective stress (n factor) and matrix shrinkage. Utilises experience from MGP.
11
GeoGAS
Reservoir Regions
Concept of “reservoir regions” is applied to model the continuum of changing reservoir parameters with depth of cover.Parameters within each region are assumed constant – only for the purpose of managing the modelling.Applied to GM and P seams
GeoGAS
GM Seam Reservoir Regions
Before Mining
Mining Affected
Reg
ion
Are
a (k
m2)
Dep
th (m
)
Mea
sure
d G
as C
onte
nt a
t Se
am A
sh, 2
0°C
Qm
(m3/
t)
Perm
eabi
lity
(mD
)
Seam
Ash
%
Seam
RD
g/c
c
Thic
knes
s (m
)
Pore
Pre
ssur
e (k
Paa)
Gas
Sat
urat
ion
%
LV @
Sea
m A
sh c
alc
20°C
&
Res
Tem
p (m
3/t)
Res
ervo
ir Te
mpe
ratu
re °C
Pore
Pre
ssur
e (k
Paa)
Gas
Sat
urat
ion
%
1 1.17 260 4.5 160 20 1.46 5.5 2161 47.5 21.44 37.8 739 93.22 0.79 250 6 160 17 1.43 5.6 2063 61.1 22.53 37.3 984 95.33 0.98 230 4.5 160 19 1.45 5.9 1867 49.2 22.46 36.2 690 94.24 2.64 245 6 160 19 1.45 6.1 2014 62.7 22.17 37.0 1131 88.15 2.41 300 7.5 80 18 1.44 5.5 2554 71.5 21.28 40.0 1475 95.56 1.56 290 9 80 17 1.43 5.6 2456 84.7 21.77 39.5 1867 97.17 1.78 290 7.5 80 18 1.44 6.1 2456 72.3 21.47 39.5 1475 94.88 4.47 305 8 80 18 1.44 5.9 2603 75.7 21.19 40.3 2112 83.69 1.32 345 9.5 25 20 1.46 5.7 2995 88.9 19.83 42.4 2995 88.9
10 2.76 340 11 25 18 1.44 5.8 2946 99.5 20.52 42.2 3241 95.711 3.19 335 10 25 18 1.44 6 2897 91.3 20.62 41.9 2897 91.312 1.47 335 11 25 19 1.45 5.9 2897 101.2 20.32 41.9 2995 99.713 1.16 320 9 25 17 1.43 5.9 2750 82.4 21.20 41.1 2750 82.414 2.96 375 11.25 7.5 19 1.45 5.75 3290 101.6 19.56 44.1 3437 99.915 3.25 360 11 6 18 1.44 6 3142 98.6 20.14 43.2 3142 98.616 0.80 350 10 6 19 1.45 6.2 3044 91.2 20.18 42.7 3044 91.217 2.14 395 10.75 3.5 20 1.46 5.55 3486 98.4 18.88 45.1 3486 98.418 1.52 350 10.5 0.5 19 1.45 6.35 3044 95.4 20.18 42.7 3044 95.4
Cla
ssifi
ed
Before Mining
Mining Affected
Reg
ion
Are
a (k
m2)
Dep
th (m
)
Mea
sure
d G
as C
onte
nt a
t Se
am A
sh, 2
0°C
Qm
(m3/
t)
Perm
eabi
lity
(mD
)
Seam
Ash
%
Seam
RD
g/c
c
Thic
knes
s (m
)
Pore
Pre
ssur
e (k
Paa)
Gas
Sat
urat
ion
%
LV @
Sea
m A
sh c
alc
20°C
&
Res
Tem
p (m
3/t)
Res
ervo
ir Te
mpe
ratu
re °C
Pore
Pre
ssur
e (k
Paa)
Gas
Sat
urat
ion
%
1 1.17 260 4.5 160 20 1.46 5.5 2161 47.5 21.44 37.8 739 93.22 0.79 250 6 160 17 1.43 5.6 2063 61.1 22.53 37.3 984 95.33 0.98 230 4.5 160 19 1.45 5.9 1867 49.2 22.46 36.2 690 94.24 2.64 245 6 160 19 1.45 6.1 2014 62.7 22.17 37.0 1131 88.15 2.41 300 7.5 80 18 1.44 5.5 2554 71.5 21.28 40.0 1475 95.56 1.56 290 9 80 17 1.43 5.6 2456 84.7 21.77 39.5 1867 97.17 1.78 290 7.5 80 18 1.44 6.1 2456 72.3 21.47 39.5 1475 94.88 4.47 305 8 80 18 1.44 5.9 2603 75.7 21.19 40.3 2112 83.69 1.32 345 9.5 25 20 1.46 5.7 2995 88.9 19.83 42.4 2995 88.9
10 2.76 340 11 25 18 1.44 5.8 2946 99.5 20.52 42.2 3241 95.711 3.19 335 10 25 18 1.44 6 2897 91.3 20.62 41.9 2897 91.312 1.47 335 11 25 19 1.45 5.9 2897 101.2 20.32 41.9 2995 99.713 1.16 320 9 25 17 1.43 5.9 2750 82.4 21.20 41.1 2750 82.414 2.96 375 11.25 7.5 19 1.45 5.75 3290 101.6 19.56 44.1 3437 99.915 3.25 360 11 6 18 1.44 6 3142 98.6 20.14 43.2 3142 98.616 0.80 350 10 6 19 1.45 6.2 3044 91.2 20.18 42.7 3044 91.217 2.14 395 10.75 3.5 20 1.46 5.55 3486 98.4 18.88 45.1 3486 98.418 1.52 350 10.5 0.5 19 1.45 6.35 3044 95.4 20.18 42.7 3044 95.4
Cla
ssifi
ed
12
GeoGAS
P Seam Reservoir Regions
Reg
ion
Are
a (k
m2)
Dep
th (m
)
Mea
sure
d G
as C
onte
nt a
t Se
am A
sh, 2
0°C
Qm
(m3/
t)
Perm
eabi
lity
(mD
)
Seam
Ash
%
Seam
RD
g/c
c
Thic
knes
s (m
)
Pore
Pre
ssur
e (k
Paa)
LV @
Sea
m A
sh c
alc
20°C
&
Res
Tem
p (m
3/t)
Res
ervo
ir Te
mpe
ratu
re °C
Gas
Sat
urat
ion
%
1 2.15 263 4.8 46.7 28 1.53 4.5 2186 18.99 38.0 56.12 2.03 288 5.9 27.1 28 1.53 4.5 2431 18.51 39.3 66.53 2.84 313 7.0 15.7 28 1.53 4.5 2676 18.04 40.7 76.74 1.41 332 7.9 10.3 28 1.53 4.5 2868 17.67 41.7 84.7
Classified
Reg
ion
Are
a (k
m2)
Dep
th (m
)
Mea
sure
d G
as C
onte
nt a
t Se
am A
sh, 2
0°C
Qm
(m3/
t)
Perm
eabi
lity
(mD
)
Seam
Ash
%
Seam
RD
g/c
c
Thic
knes
s (m
)
Pore
Pre
ssur
e (k
Paa)
LV @
Sea
m A
sh c
alc
20°C
&
Res
Tem
p (m
3/t)
Res
ervo
ir Te
mpe
ratu
re °C
Gas
Sat
urat
ion
%
1 2.15 263 4.8 46.7 28 1.53 4.5 2186 18.99 38.0 56.12 2.03 288 5.9 27.1 28 1.53 4.5 2431 18.51 39.3 66.53 2.84 313 7.0 15.7 28 1.53 4.5 2676 18.04 40.7 76.74 1.41 332 7.9 10.3 28 1.53 4.5 2868 17.67 41.7 84.7
Classified
GeoGAS
GM & P Seam Production Profiles
Based on well spacing 390 mLateral length in coal 900 mLaterals run down dip to vertical wellWhere structure permits, dual laterals are usedWells are oriented to avoid intersection by gateroads
13
GeoGAS
GM Production Profiles
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Times (years)
Gas
Pro
duct
ion
(MC
FD)
Region 8 Region 9Region 10 Region 11Region 12 Region 13Region 14 Region 15Region 16 Region 17Region 18
RegionProduction.xls{RegionProduction}
Goonyella Middle Seam
GeoGAS
Example of Bottom Hole Pressures Applied
0
500
1000
1500
2000
2500
3000
3500
0 50 100 150 200 250 300 350 400 450 500
Time (Days)
Botto
m H
ole
Pres
sure
(kPa
a) Production constrained to 1200 MCFD
Unconstrained gas production
Region12bSpac390mProd.xls{BHPCompare}
14
GeoGAS
Gas Recovered Per Well and Remaining Gas Content
(1) Target is < 4 m3/t these wells
Remaining Gas Content Qm GM Seam
Region SIMED Data
File Days to Target Qm
Years to < 3 m3/t
PJ/Well to 50
MCFD
8 Reg8a 400 1.1 0.71 9 Reg9a 900 2.5 0.81 10 Reg10a 900 2.5 0.96 11 Reg11a 1000 2.7 0.93 12 Reg12a 900 2.5 1.00 13 Reg13a 1100 3.0 0.79 14 Reg14a 3000 8.2 0.93 15 Reg15a 2500 6.8(1) 0.96 16 Reg16a 2500 6.8(1) 0.90 17 Reg17a 3000 8.2(1) 0.78 18 Reg18a 9 m3/t after 15 yrs N/A N/A 8 Reg8b 600 1.6 1.44 12 Reg12b 1200 3.3 2.09 9 Reg9_192 350 1.0 0.52 9 Reg9_268 800 2.2 0.93
Cla
ssifi
ed
Remaining Gas Content Qm GM Seam
Region SIMED Data
File Days to Target Qm
Years to < 3 m3/t
PJ/Well to 50
MCFD
8 Reg8a 400 1.1 0.71 9 Reg9a 900 2.5 0.81 10 Reg10a 900 2.5 0.96 11 Reg11a 1000 2.7 0.93 12 Reg12a 900 2.5 1.00 13 Reg13a 1100 3.0 0.79 14 Reg14a 3000 8.2 0.93 15 Reg15a 2500 6.8(1) 0.96 16 Reg16a 2500 6.8(1) 0.90 17 Reg17a 3000 8.2(1) 0.78 18 Reg18a 9 m3/t after 15 yrs N/A N/A 8 Reg8b 600 1.6 1.44 12 Reg12b 1200 3.3 2.09 9 Reg9_192 350 1.0 0.52 9 Reg9_268 800 2.2 0.93
Cla
ssifi
ed
GeoGAS
P Seam Production Profiles
Wells peak lower and later than GM
0 1 2 3 4 5 6 7 8
Times (years)
Gas
Pro
duct
ion
(MCF
D)
Region 1
Region 2
Region 3
Region 4
RegionProduction.xls{RegionProduction}
P Seam
For single 900 m lateral
Remaining Gas Content
PJ/Well to 50 MCFD P Seam
Region Data File
*.dat Days to Target
Qm Years to <
3 m3/t Single Lateral
Dual Lateral
1 RegP1a 700 1.9 0.25 0.54 2 RegP2a 1300 3.6 0.33 0.69 3 RegP3a 2500 6.8 0.40 0.91 4 RegP4a 2500 6.8 0.46 1.06
Classified
Remaining Gas Content
PJ/Well to 50 MCFD P Seam
Region Data File
*.dat Days to Target
Qm Years to <
3 m3/t Single Lateral
Dual Lateral
1 RegP1a 700 1.9 0.25 0.54 2 RegP2a 1300 3.6 0.33 0.69 3 RegP3a 2500 6.8 0.40 0.91 4 RegP4a 2500 6.8 0.46 1.06
Classified
15
GeoGAS
Well Sequencing
58 wells in allFirst 28 shown here
Seam Data File
*.dat Well No Well Sequence
Single or Dual
LateralDate on Gas Mined
ThroughDays on
LineDays
NeededGas Drained
< Target
GM Reg9_192 INGM006 1 Single 15/05/07 1/10/13 2331 350 OK
GM Reg9_192 INGM007 2 Single 15/05/07 1/10/13 2331 350 OK
GM Reg9_268 INGM008 3 Single 15/05/07 1/05/16 3274 800 OK
GM Reg8a R8-01 4 Single 15/09/07 1/06/12 1720 400 OK
GM Reg8b R8-02 5 Dual 13/10/07 1/01/13 1906 600 OK
GM Reg8a R8-03 6 Single 28/10/07 1/07/13 2073 400 OK
GM Reg8a R8-04 7 Single 12/11/07 1/06/14 2393 400 OK
GM Reg8a R8-06 8 Single 26/11/07 1/01/17 3323 400 OK
GM Reg10a R10-01 9 Single 11/12/07 1/09/14 2456 900 OK
GM Reg10a R10-02 10 Single 25/12/07 1/02/15 2594 900 OK
GM Reg10a R10-03 11 Single 9/01/08 1/07/15 2730 900 OK
GM Reg9a R9-01 12 Single 19/03/08 1/02/14 2145 900 OK
P RegP1a R1-01(P) 13 Dual 28/05/08 1/09/12 1557 700 OK
P RegP1a R1-02(P) 14 Single 6/08/08 1/11/18 3739 700 OK
GM Reg8a R8-07 15 Single 15/10/08 1/01/14 1904 400 OK
GM Reg8a R8-08 16 Single 4/03/09 1/06/16 2646 400 OK
GM Reg8b R8-05 17 Dual 22/07/09 1/02/15 2020 600 OK
GM Reg14a R14-01 18 Single 6/08/09 1/02/20 3831 3000 OK
GM Reg14a R14-02 19 Single 20/08/09 1/06/20 3937 3000 OK
GM Reg10a R10-06 20 Single 7/01/10 1/02/19 3311 900 OK
GM Reg11a R11-01 21 Single 18/03/10 1/01/17 2480 1000 OK
GM Reg15a R15-02 22 Single 2/04/10 1/05/19 3316 2500 OK
GM Reg15a R15-01 23 Single 16/04/10 1/05/19 3301 2500 OK
GM Reg14a R14-04 24 Single 25/06/10 1/11/21 4146 3000 OK
P RegP2a R2-01(P) 25 Dual 24/07/10 1/07/15 1803 1300 OK
GM Reg14a R14-03 26 Single 11/12/10 1/02/21 3705 3000 OK
GM Reg17a R17-03 27 Single 25/12/10 1/06/22 4175 3000 OK
GM Reg13a R13-01 28 Single 9/01/11 1/09/16 2062 1100 OK
Cla
ssifi
ed
Seam Data File *.dat Well No Well
Sequence
Single or Dual
LateralDate on Gas Mined
ThroughDays on
LineDays
NeededGas Drained
< Target
GM Reg9_192 INGM006 1 Single 15/05/07 1/10/13 2331 350 OK
GM Reg9_192 INGM007 2 Single 15/05/07 1/10/13 2331 350 OK
GM Reg9_268 INGM008 3 Single 15/05/07 1/05/16 3274 800 OK
GM Reg8a R8-01 4 Single 15/09/07 1/06/12 1720 400 OK
GM Reg8b R8-02 5 Dual 13/10/07 1/01/13 1906 600 OK
GM Reg8a R8-03 6 Single 28/10/07 1/07/13 2073 400 OK
GM Reg8a R8-04 7 Single 12/11/07 1/06/14 2393 400 OK
GM Reg8a R8-06 8 Single 26/11/07 1/01/17 3323 400 OK
GM Reg10a R10-01 9 Single 11/12/07 1/09/14 2456 900 OK
GM Reg10a R10-02 10 Single 25/12/07 1/02/15 2594 900 OK
GM Reg10a R10-03 11 Single 9/01/08 1/07/15 2730 900 OK
GM Reg9a R9-01 12 Single 19/03/08 1/02/14 2145 900 OK
P RegP1a R1-01(P) 13 Dual 28/05/08 1/09/12 1557 700 OK
P RegP1a R1-02(P) 14 Single 6/08/08 1/11/18 3739 700 OK
GM Reg8a R8-07 15 Single 15/10/08 1/01/14 1904 400 OK
GM Reg8a R8-08 16 Single 4/03/09 1/06/16 2646 400 OK
GM Reg8b R8-05 17 Dual 22/07/09 1/02/15 2020 600 OK
GM Reg14a R14-01 18 Single 6/08/09 1/02/20 3831 3000 OK
GM Reg14a R14-02 19 Single 20/08/09 1/06/20 3937 3000 OK
GM Reg10a R10-06 20 Single 7/01/10 1/02/19 3311 900 OK
GM Reg11a R11-01 21 Single 18/03/10 1/01/17 2480 1000 OK
GM Reg15a R15-02 22 Single 2/04/10 1/05/19 3316 2500 OK
GM Reg15a R15-01 23 Single 16/04/10 1/05/19 3301 2500 OK
GM Reg14a R14-04 24 Single 25/06/10 1/11/21 4146 3000 OK
P RegP2a R2-01(P) 25 Dual 24/07/10 1/07/15 1803 1300 OK
GM Reg14a R14-03 26 Single 11/12/10 1/02/21 3705 3000 OK
GM Reg17a R17-03 27 Single 25/12/10 1/06/22 4175 3000 OK
GM Reg13a R13-01 28 Single 9/01/11 1/09/16 2062 1100 OK
Cla
ssifi
ed
GeoGAS
GM & P Seam Pre Drainage Gas Production
Time (years)
Gas
Pro
duct
ion
(TJ/
day)
P SIS WellsLW Goaf GasUIS risersGM SIS Wells
RegionProduction xls{WellConstants}
16
GeoGAS
Uncertainty
GeoGAS
Predrainage Gas Production
UISDelays in mining will impact on gas production Air dilution under negative pressure □
SISNot tied to mining Pipeline quality gas Design and operational risks Changes to mine plan and schedule
17
GeoGAS
Modelling Uncertainty
Uses the three main variable parametersGas contentSorption capacityPermeability
Aiming for combined output of 1 standard deviation for these parameters
1 param 2 params 3 paramsP90 0.1257 0.01253 0.001253P68.3 0.4088 0.1265 0.04005P50 0.6745 0.3186 0.1573P31.7 1 0.6221 0.41P10 1.645 1.311 1.101
# of Standard DeviationsP Case
GeoGAS
Gas Production Distribution
0 100 200 300 400 500 600 700 800 900 1000
Days on Line
Gas
Pro
duct
ion
(MCF
D)
Mean
1x Std Dev
2x Std Dev
Probability.xls{Outputs}
Region 12
18
Probability Distribution SIS Well Production
Days Required to Reach Target Gas Content
Time (years)G
as P
rodu
ctio
n (T
J/da
y)
Probability.xls{ProbSummaryOutput}
Mean +/- 1 Standard Deviation
1 to 2 Standard Deviations
Num
ber o
f SIS
Wel
ls
Probability xls{Wells}
Region X Region Y+2*1 Std Dev 650 2000+1 Std Dev 750 2250Mean 900 2750-1 Std Dev 1200 4000-2 Std Dev 1750 5500
GeoGAS
Conclusions
A drilling and drainage schedule was defined that utilised the available drainage time at the widest spacing to produce the required level of gas but with priority on satisfying mine gas management requirements. The power station off-take is a managed, but independent and subsidiary outcome to mine gas management. Gas production begins to tail down with the completion of SIS well drilling from 2016~2020. Maintenance of gas production beyond this time is expected with higher rates of gas capture of longwall gas and with capture of gas from the destressed reservoir above the GM seam.The SIS methodology has been deliberately “simple” and timely.
19
GeoGAS
Conclusions (cont)
An assessment of SIS well modelling output has shown a wide range of production variability on a well-by-well basis. This uncertainty can be managed by bringing forward production wells and operating at higher well head pressures if production exceeds demand and is consistent with mining requirements.As indicated in probability modelling, variations in remaining gas content from SIS drilling can be high.Realisation of the project gas production rates will require operating the field at as low a well head pressure as possible. Modelling assumed a wellhead pressure of 150 kPag. Intended field pressure beyond 2010 is 100 kPag.