Numerical Modelling and Prediction of Abandoned Mine Methane Recovery: Field Application at the Saar Coalfield,
Germany
.
© Imperial College London
Sevket DURUCANJi-Quan Shi, Anna KORRE
Minerals, Energy and Environmental Engineering Research GroupDepartment of Earth Science and Engineering
Royal School of Mines Imperial College London
Outline
Background on Imperial CBM simulator METSIM2
Abandoned mines methane extraction in the Saar Coalfield
Abandoned mine model development
History matching of field production data (Hangard shaft)
Production forecasts for two new boreholes
Summary and conclusions
© Imperial College LondonPage 2
Saarland
Krakow 28 February 2018
Coal as a Reservoir Rock
Page 3
Uniform and orthogonal fracture (CLEAT) structure
free gas
adsorbed gas
Coal Matrixcontaining
pores
face cleat
butt cleat
CH4
Macropores > 50 nm
Mesopores 2 – 50 nm
Micropores < 2 nm
Cleat system (2mm - 25 mm)
Pore surface area 20 – 200 m2/gm
Pressure (MPa)0 1.4 2.8 4.2 5.6 7
CH4
Gas
con
tent
(m3 /t
)
10
5
0 pPpVV +=
LL
Langmuir isotherm, T = C
© Imperial College London Krakow 28 February 2018
Imperial College In-House Coalbed Methane Simulator METSIM 2
Page 4
Permeability of coal is both Stress and Pore Pressure dependent
)(30
0f σ−σ−= cekkFlow
Bundled matchstick model
ba
σ – σ0 - changes in effective horizontal stress
)1(3)()(
10
00 ν−−α
+−ν−
ν−=σ−σ
VVEpp S
E – Young’s modulusν – Poisson’s ratio
αS – shrinkage coefficient
V – adsorbed gas volumeshrinkage termcompaction term
(after Seidle et al., 1992)
cf – cleat volume compressibility
abk
3
121=
© Imperial College London Krakow 28 February 2018
Shi and Durucan Permeability Model
Mining History in the Saar Basin
Page 5
Frankenholz Colliery is known as one of the most gassy mines in Europe
Upper Carboniferous age (formed 350-285 Million years ago)
1816 Mining activities began 1879/82 Construction of shafts Frankenholz 1 and 2 and later
Frankenholz 3, 4 and 5 (5=Hangard) 1903 Start of production 1908 Known CH4 gas explosions in Saarland workings 1930 2.822 workers produced 484.228 tons coal 1941 Greatest explosion and subsequent mine closure 1946 Reopening of Frankenholz colliery 1954 Opening of St. Barbara colliery 1960 Connection of St. Barbara and Frankenholz mines and upcast
ventilation from the Hangard shaft 1984 Filling of Hangard shaft (= Frankenholz 5) 1992 Filling of Anna shafts 1 and 2, later known as Kohlwald
© Imperial College London Krakow 28 February 2018
Saar Coalfield: Operating mine methane drainage and AMM
Page 6
Until 2002 DSK produced mine gas from 13 shafts, with methane concentrations in the produced gas varying from 30 to 90%.
In 2003 the gas production activities have been transferred to a regional energy producer, STEAG Saar Energie AG (now STEAG New Energies GmbH).
Mine Volume flow rate per day Methane Concentration
Hangard 40,000 m3 73,0 %Kohlwald 75,000 m3 52,8 %Sinnerthal 24,000 m3 35,4 %Reden 50,000 m3 34,5 %Itzenplitz 102,000 m3 42,0 %Erkershöne 71,000 m3 30,8 %Camphausen 125,000 m3 37,3 %Göttelborn 75,000 m3 29,1 %Alsbach 127,000 m3 34,6 %Delbrück 174,000 m3 50,0 %Velsen 130,000 m3 43,6 %Warndt 195,000 m3 49,2 %Nordschacht 18,000 m3 32,9 %
© Imperial College London Krakow 28 February 2018
Frankenholz – St. Barbara Mining Complex
Page 7
Up to 32 seams of varying thickness between 0.3 – 3 m in the Frankenholz - St. Barbara mining complex, dipping in Northwest direction. Between levels 1 and 11 (- 470 m), where the water level was before filling of the Hangard shaft in 1984, the total thickness of coal is calculated as 40 metres in 430 metres of coal measures strata.
Allenfeld Shaft
© Imperial College London
The water level in the mining complex rose from level 11 (– 470 m) to between levels 9 and 10 (– 244 m) by 1984 and has remained at the same level sinceFrom 1833 to 1959, Frankenholz and St. Barbara Collieries jointly mined a total coal surface area of 4.5 km2
Krakow 28 February 2018
Historical Gas Production from the Hangard Shaft
Page 8
Gas extraction from the Hangard shaft reached over 26 million m3 per annum with a methane concentration of over 57% in the first few years of production.
The back-filling of Hangard Shaft in 1984 resulted in an immediate recovery in both the gas rates and methane concentration, reaching approximately 20 million m3 per annum and 55% respectively.
The produced gas quality was further boosted to a high of 90% methane following the filling of the Kohlwald Shaft in 1992.
0
5000
10000
15000
20000
25000
30000
1960 1965 1970 1975 1980 1985 1990 1995 2000Year
Ann
ual p
rodu
ctio
n (1
03m
3 )
0
0.2
0.4
0.6
0.8
1
Met
hane
con
cent
ratio
ntotal gas
methaneKohlwaldShaft backfiledHangard Shaft
backfilled 0
5000
10000
15000
20000
25000
30000
1960 1965 1970 1975 1980 1985 1990 1995 2000Year
Ann
ual p
rodu
ctio
n (1
03m
3 )
0
0.2
0.4
0.6
0.8
1
Met
hane
con
cent
ratio
ntotal gas
methaneKohlwaldShaft backfiledHangard Shaft
backfilled
0
5
10
15
20
25
1960 1970 1980 1990 2000Year
Ann
ual m
etha
ne r
ates
(m
illio
n m3 ) drainage + ventilation
drainage only
Hangard has vented an average of 6 million m3 of methane per annum between 1981 and 1984.
After the filling of Hangard shaft in 1984 the free methane gas in the mine air was also recovered.
Assuming that an average volume of 6 million m3 methane was lost through ventilation in the period from 1960 to 1984, the total methane flow rates at the Hangard shaft were plotted.
© Imperial College London Krakow 28 February 2018
Abandoned Mine Reservoir Model Development
Page 9
An areal model with a uniform thickness of 40 m (the net thickness of all the seams down to - 470 m) was built.
A uniform grid of 710 active gridblocks (100m x 100m) used.
5.0 million m2 in the Northeast region (I) and 2.1 million m2 in the Southwest region (II) yielding a net coal volume of 7.1 m2 x 40 m = 284 million m3.
I
II
Hangard shaft
Allenfeld Shaft
© Imperial College London Krakow 28 February 2018
In situ Gas Content and Initial Gas-in-place
Page 10
Düpre and Barth [1980] 2,700 million m3 of methane in situ in virgin conditions and 15m3/tonne for the Frankenholz – St Barbara mining area
Kneuper and Muller [1971] 10.77 m3/tonne for the coal seams in the Saar coalfield.
Hebel [1999] approximately 4,000 million m3 gas in situ between levels 1 and 11 in the area defined as regions I and II in the areal model 10.8 m3/t
0
5
10
15
20
0 10 20 30 40 50 60 70 80Sorption pressure (bar)
Met
hane
con
tent
(m3 /
t)(40, 11.5)
(30, 9.7)
In situ gas content estimates at Frankenholz – St. Barbara Mining Complex
Initial gas content: Zone I = 11.5 m3/tZone II = 9.7 m3/t
Total initial methane in-place = 4,000 million m3
Residual methane after abandonment = 1.800 million m3
© Imperial College London Krakow 28 February 2018
History Matching of Field Data at Hangard Shaft
Page 11
05
101520
2530
1960 1970 1980 1990 2000
Year
Ann
ual m
etha
ne r
ates
(m
illio
n m3 )
50 md
40 md
30 mdfield
050
100150200250300
1960 1970 1980 1990 2000Year
Suct
ion
pres
sure
(mba
r)
field
model
Enhancedpermeability
Base Permeability1 md
I
II
Hangard shaft
© Imperial College London Krakow 28 February 2018
Hypothetical shaft
1960
Methane Production Predictions
Page 12
Methane pressure distribution with production from Hangard shaft only20002000
HangardShaft
AllenfeldShaft
Frankenholz – St. Barbara Complex
6.5
7
7.5
8
8.5
9
2001 2003 2005 2007 2009 2011 2013 2015
Year
Annu
al m
etha
ne p
rodu
ctio
n
(milli
on m
3)
Hangard shaft only
© Imperial College London
6.5
7
7.5
8
8.5
9
2001 2003 2005 2007 2009 2011 2013 2015Year
Annu
al m
etha
ne p
rodu
ctio
n (m
illion
m3 )
Hangard shaft only
Krakow 28 February 2018
Methane Production Predictions
Page 13
Frankenholz – St. Barbara Complex
Residual methane contents with production from Hangard shaft only
20002000
HangardShaft
AllenfeldShaft
7.5-87-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaftFrankenholzshafts 1 & 2
Allenfeldshaft
Residual Gas Content
(m3/t)
7.5-87-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaftFrankenholzshafts 1 & 2
Allenfeldshaft
Residual Gas Content
(m3/t)
2000
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Residual Gas Content
(m3/t)
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Residual Gas Content
(m3/t)
2015
© Imperial College London
Methane Production Predictions
Page 14
Allenfeld shaft was seen to be emitting 5m3/min (2.6 million m3 per annum) CH4
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Allenfeldshaft
Residual Gas Content
(m3/t)
6.5-76-6.55.5-6
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Allenfeldshaft
Residual Gas Content
(m3/t)
2015
Residual methane contents with production from both Hangard and Allenfeld shafts
1.5
2
2.5
3
3.5
4
2001 2003 2005 2007 2009 2011 2013 2015Year
Ann
ual m
etha
ne p
rodc
utio
n (m
illio
n m
3 )
Allenfeld
Methane Production Forecast from the Allenfeld Shaft
© Imperial College London Krakow 28 February 2018
Methane Production Predictions
Page 15
Methane Production Forecast from the Frankenholz Shaft
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft Frankenholz shaft 1 & 2
Allenfeld shaft
Residual Gas Content (m3/t)
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.5
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft Frankenholz shaft 1 & 2
Allenfeld shaft
Residual Gas Content (m3/t)
2015
Residual methane contents with production from Hangard, Allenfeld and Frankenholz shafts
Predicted annual methane production at Frankenholz
6
7
8
9
10
11
12
13
2006 2008 2010 2012 2014Year
Ann
ual m
etha
ne p
rodc
utio
n (m
illio
n m
3 )
Frankenholz
© Imperial College London Krakow 28 February 2018
Krakow 28 February 2018
579
1113151719212325
2001 2003 2005 2007 2009 2011 2013 2015
Year
Ann
ual m
etha
ne p
rodu
ctio
n (m
illio
n m
3 )
Hangard
Hangard + Allenfeld + Frankenholtz
Hangard + Allenfeld
Predicted annual methane production for the 3 shafts
Methane Production Predictions
Page 16
Methane Production Forecast from the Frankenholz – St. Barbara Complex3 Shafts Producing Simultaneously
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Allenfeldshaft
Residual Gas Content
(m3/t)
6.5-76-6.55.5-6
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Allenfeldshaft
Residual Gas Content
(m3/t)
2015
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Residual Gas Content
(m3/t)
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
7-7.56.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft
Residual Gas Content
(m3/t)
2015
© Imperial College London
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft Frankenholz shaft 1 & 2
Allenfeld shaft
Residual Gas Content (m3/t)
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.5
6.5-76-6.55.5-65-5.54.5-54-4.53.5-43-3.52.5-32-2.51.5-21-1.5
Hangard shaft Frankenholz shaft 1 & 2
Allenfeld shaft
Residual Gas Content (m3/t)
2015
Conclusions
Page 17 © Imperial College London
A general gas-water two-phase CBM simulator METSIM2 has been modified to simulate methane extraction from abandoned coal mines
Reservoir characterisation was carried out and abandoned mine models were developed for an abandoned coal mine complex in the Saar coalfield of Germany
A methodology for reservoir characterisation of abandoned mines has beenformulated
An areal model to represent the lumped effect of all coal seams thatcontribute to methane production was developed and used in the predictions
Predictions carried out at Imperial College involved the assessment ofpotential gas production from additional boreholes at the Allenfeld andFrankenholz sectors for the future.
Krakow 28 February 2018
Acknowledgements
Page 18 © Imperial College London
The authors wish to thank Mr Hans-Jurgen Kaltwang, MrGerhard Hebel and Mr Jörg Lehmann of former Saarberg (laterDSK-Saar) who have contributed to the work carried out at ImperialCollege at the time of the project described here.
STEAG New Energies GmbH’s permission to reproduce some of thefigures and data included in this presentation is also acknowledged.
The funding provided by DG-TREN of the European Commissionfor the project METSIM at the time is also gratefully acknowledged
Sevket Durucan [email protected] 28 February 2018