© Imperial College LondonPage 1
Numerical Modelling and Prediction of Abandoned Mine Methane Recovery: Field Application from the
Saar Coalfield, Germany
Sevket Durucan, Ji-Quan Shi and Anna Korre
Minerals, Energy and Environmental Engineering Research GroupDepartment of Earth Science and Engineering
Royal School of MinesImperial College London
© Imperial College LondonPage 2
Outline
� Background
� Abandoned mine 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 3
Background
� The coal bearing strata surrounding an abandoned coal mine constitutes a naturally
fractured, naturally stimulated reservoir with up to 80% of the original gas resource
being available for subsequent extraction and utilisation.
� This very favourable characteristic presents abandoned coal mine reservoirs as a very
attractive prospect for unconventional natural gas production.
� Saar Coalfield represents one of the best examples of abandoned mines methane
utilisation in Europe
© Imperial College LondonPage 4
Location: Saar Coalfield and Study Area in Germany
Saarland
© Imperial College LondonPage 5
Geology and Mining History in the Saar Basin
Saarbrucken
Stefan B+CStefan AWestfal DWestfal C
(vermutet)Abschabunbg (vermutet)“Melaphyr” – LagerangHolzer KonglomeratAbbaugrenzeShnittlinieSchachtBohrungStaatsgrenzeBasislinie
Settelachse(vermutet)Muldenachse (vermutet)Umbiegungsachse(vermutet)Auf- bzw. Uberschiabung
Saarbrucken
Stefan B+CStefan AWestfal DWestfal C
(vermutet)Abschabunbg (vermutet)“Melaphyr” – LagerangHolzer KonglomeratAbbaugrenzeShnittlinieSchachtBohrungStaatsgrenzeBasislinie
Settelachse(vermutet)Muldenachse (vermutet)Umbiegungsachse(vermutet)Auf- bzw. Uberschiabung
Upper Carboniferous age
(formed 350-285 Million years ago)
Section 1 - 1
Section 2 - 2
Study Area
© Imperial College LondonPage 6
Mining History
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 Large gas explosion with 41 fatalities and subsequent mine closure
1946 Reopening of Frankenholz colliery
1954 Opening of St. Barbara colliery connection to Frankenholz
1959 Both mines closed
1960 Connection of Allenfeld and Hangard shafts and upcast ventilation from Hangard
1983 Filling of Hangard shaft (= Frankenholz 5)
1992 Filling of Anna shafts 1 and 2, later known as Kohlwald
Frankenholz Colliery is known as the most gassy mine in Europe
Scale 1: 50,000
Saar Coalfield: Coal Mines, Power Stations and Gas Network
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, and
later in 2011 STEAG Power Saar GmbH.
MineVolume flow rate
per dayMethane Concentration
Hangard 40,000 m3
73,0 %Kohlwald 75,000 m
352,8 %
Sinnerthal 24,000 m3
35,4 %Reden 50,000 m
334,5 %
Itzenplitz 102,000 m3
42,0 %Erkershöne 71,000 m
330,8 %
Camphausen 125,000 m3
37,3 %Göttelborn 75,000 m
329,1 %
Alsbach 127,000 m3
34,6 %Delbrück 174,000 m
350,0 %
Velsen 130,000 m3
43,6 %Warndt 195,000 m
349,2 %
Nordschacht 18,000 m3
32,9 %
Seam Depth and Thicknesses: Frankenholz and St Barbara Mines
Scale 1: 50,000
Mittelfeld Ostfeld 1 Ostfeld 2
Seam depth (m) thickness (m) depth (m) thickness (m) depth (m) thickness (m)
Tonstein 1 56 0.40 8 0.54 - -Fl Kallnbrg 81 1.24 36 0.50 - -Floz Serlo 100 2.00 63 0.94 - -Floz Kliver 103 1.00 81 0.45 - -Floz A 159 0.85 136 0.85 - -Floz HGd 2 189 0.6 170 0.45 - -Floz HGd 1 199 0.95 176 0.95 159 0.59Floz B 205 0.98 182 0.75 164 0.30floz 1 211 0.88 186 0.50 170 1.50floz nn 216 0.30 193 0.30 180 0.20floz nn 244 0.45 203 0.30 200 0.90floz 2 267 1.33 237 0.75 212 1.25floz nn 272 0.38 252 0.38 227 0.25floz nn 280 0.35 260 0.20 - -floz 3 311 1.05 276 0.80 241 1.55floz 4 330 0.40 284 0.40 246 0.95floz 5 338 0.60 312 0.60 265 1.60floz nn 375 0.30 320 0.35 275 0.25floz 6 385 0.66 337 0.97 291 0.80floz 7 407 2.12 352 1.65 303 1.20floz 8 422 1.70 362 0.80 310 2.70floz 9/10 439 2.20 383 1.60 336 1.45floz 11/12 446 1.30 395 1.50 347 1.50floz 13 457 0.51 408 0.50 364 0.65floz 14 461 0.37 414 0.70 373 1.10floz 15 475 0.55 427 0.70 389 1.95floz 16 484 1.80 431 1.70 393 1.35floz 17 502 0.50 449 0.65 399 1.20floz18 505 0.74 457 0.70 404 2.45floz 19 511 1.10 460 0.71 408 0.40floz 20 535 0.20 469 1.10 414 0.40floz 21 541 0.80 475 0.30 425 0.55floz 22 554 0.40 486 0.40 432 0.15floz 23 560 1.00 492 0.45 437 0.24floz 24 576 1.60 455 1.35 445 1.30floz 25 581 1.86 462 1.30 465 1.70
Up to 32 seams of varying thickness between 0.3 – 3 m in the Frankenholz - St. Barbara mining complex, dipping in Northwest direction.
Frankenholz – St. Barbara Mining Complex
Mining sequence, mined out areas and
seam footprint, methane extraction shafts
Between levels 1 and 11 (-470 m), the total thickness of coal is 40 metres in 430 metres of coal measures strata.
From 1833 to 1959, Frankenholz and St. Barbara Collieries jointly mined a total coal surface area of 4.5 km2
Mined out
Area
St Barbara Shaft
Hangard Shaft
Frankenholz I and II Shafts
Mined out
Area
St Barbara Shaft
Hangard Shaft
Frankenholz I and II Shafts
Allenfeld Shaft
Historical gas production from the Hangard shaft
0
5
10
15
20
25
1960 1970 1980 1990 2000Year
Annual m
eth
ane r
ate
s
(mill
ion m
3) drainage + ventilation
drainage only
0
5000
10000
15000
20000
25000
30000
1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
An
nu
al
prod
uct
ion
(10
3m
3)
0
0.2
0.4
0.6
0.8
1
Met
han
e con
cen
trati
on
total gas
methane
Kohlwald
Shaft
backfiledHangard Shaft
backfilled 0
5000
10000
15000
20000
25000
30000
1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
An
nu
al
prod
uct
ion
(10
3m
3)
0
0.2
0.4
0.6
0.8
1
Met
han
e con
cen
trati
on
total gas
methane
Kohlwald
Shaft
backfiledHangard Shaft
backfilled
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.
It was measured that 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 LondonPage 11
Abandoned Mine Reservoir Model
� Only gas phase (above mine water level) is accounted for
� While the free gas phase in old mine workings and other voids is a mixture of methane,
nitrogen, carbon dioxide and other minor gas components, the adsorbed phase consists
of mainly methane, which is at equilibrium with the methane partial pressure in the mine.
� By working with methane (partial) pressure and an immobile water phase, our in-house
CBM simulator (METSIM) was used to describe methane flow in an abandoned mine
reservoir.
© Imperial College LondonPage 12
Abandoned Mine Reservoir Model
An areal model with a uniform thickness of 40 m in 430 metres of coal measures strata (the net thickness of all the seams down to -470 m) was built.
A uniform grid of 710 active grid blocks (100m x 100m) used.
A total coal area of 5.1 million m2 in the mined out Northeast region (I) and 2 million m2 in the unminedSouthwest region (II) yielding a net coal volume of 7.1 million m2 x 40 m = 284 million m3.
Initial gas content: Zone I = 11.5 m3/tZone II = 9.7 m3/t
I
II
Hangard
shaft
Total initial methane in-place @ average gas content of 11 m3/t = 4,060 million m3
Total gas emission until abandonment in 1960 = 2,200 million m3
Residual methane after abandonment = 1.800 million m3
0
5
10
15
20
0 10 20 30 40 50 60 70 80
Sorption pressure (bar)
Meth
ane c
onte
nt
(m3/t
)(40, 11.5)
(30, 9.7)
© Imperial College LondonPage 13
Abandoned Mine Reservoir Simulation
� The model domain covers the entire mined surface areas and natural geological
features such as faults are used to form the boundaries of model domain.
� An enhanced permeability zone is introduced in order to represent the impact of early
mining activity on the permeability of the strata surrounding the mine workings.
� The magnitude of the enhanced permeability to be determined through history matching
the field gas production data.
� The initial gas content represents the average in situ gas content of both the coal seams
and other methane-bearing strata in the region.
� In order to account for historic methane emissions, a pre-extraction production period is
introduced. This approach has the advantage that a spatial gradient in the residual gas
content is established in the domain to reflect the fact that the remaining seams have
been subjected to different degrees of degassing prior to abandonment in 1961.
© Imperial College LondonPage 14
Historical Gas Emission and Residual Gas Content Distribution
I
II
Hangard shaft
By 1960, when the mines were abandoned, approximately 2,200 million m3 methane had been emitted since the start of mining back in 1880’s.
In order to account for this gas depletion in the model, a pre-extraction production period is included in the simulations.
Using a base permeability of 1 md, methane is drained from an imaginary shaft situated at the centre of the mined out region and, when the pre-defined amount of methane has been drained, the production switches to Hangard shaft.
Hypothetical shaft
1960
Enhanced
permeability
Base permeability Base
Permeability
1 md
© Imperial College LondonPage 15
Field Permeability Characterisation
0
5
10
15
20
25
30
1960 1970 1980 1990 2000
Year
Annual m
eth
ane r
ate
s
(mill
ion m
3)
50 md
40 md
30 mdfield
0
50
100
150
200
250
300
1960 1970 1980 1990 2000
Year
Suction p
ressure
(m
bar) field
model
Enhancedpermeability
Base
Permeability
1 md
History matching of field production data at Hangard Shaft using
Imperial College in-house Coalbed Methane simulator METSIM
Permeability of mining affected zone (I) = 40md
Permeability of unaffected zone (II) = 1 md
© Imperial College LondonPage 16
Production Forecast for the Frankenholz – St. Barbara Complex
Hypothetical
shaft
1960Methane pressure distribution with
production from Hangard shaft only
20002000
HangardShaft
AllenfeldShaft
6.5
7
7.5
8
8.5
9
2001 2003 2005 2007 2009 2011 2013 2015
Year
An
nu
al m
eth
an
e p
rodu
ctio
n
(mill
ion
m3)
with Allenfled & Frankenholz
Hangard shaft only
with Allenfeld
© Imperial College LondonPage 17
Production Forecast for the Frankenholz – St. Barbara Complex
Residual methane contents with
production from Hangard shaft only20002000
Hangard
Shaft
AllenfeldShaft
7.5-8
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Frankenholz
shafts 1 & 2
Allenfeld
shaft
Residual Gas Content
(m3/t)
7.5-8
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Frankenholz
shafts 1 & 2
Allenfeld
shaft
Residual Gas Content
(m3/t)
2000
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Residual Gas Content
(m3/t)
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Residual Gas Content
(m3/t)
2015
© Imperial College LondonPage 18
Methane Production Forecast from the Allenfeld Shaft
Allenfeld shaft was seen to be emitting 5m3/min (2.6 million m3 per annum) CH4
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Allenfeld
shaft
Residual Gas Content
(m3/t)
6.5-7
6-6.5
5.5-6
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Allenfeld
shaft
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 2015
Year
Annual m
eth
ane p
rodcution
(mill
ion m
3)
Allenfeld
Predicted annual methane production at Allenfeld
© Imperial College LondonPage 19
Methane Production Forecast from the Frankenholz Shaft
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft Frankenholz
shaft 1 & 2
Allenfeld
shaft
Residual Gas Content (m3/t)
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
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 2014
Year
Annual m
eth
ane p
rodcution
(mill
ion m
3)
Frankenholz
© Imperial College LondonPage 20
Methane Production Forecast from the Allenfeld Shaft
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft Frankenholz
shaft 1 & 2
Allenfeld
shaft
Residual Gas Content (m3/t)
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft Frankenholz
shaft 1 & 2
Allenfeld
shaft
Residual Gas Content (m3/t)
2015
5
7
9
11
13
15
17
19
21
23
25
2001 2003 2005 2007 2009 2011 2013 2015
Year
An
nu
al m
eth
an
e p
rod
ucti
on
(millio
n m
3)
Hangard
Hangard + Allenfeld +
Frankenholtz
Hangard + Allenfeld
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Allenfeld
shaft
Residual Gas Content
(m3/t)
6.5-7
6-6.5
5.5-6
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Allenfeld
shaft
Residual Gas Content
(m3/t)
7.5-8
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Frankenholz
shafts 1 & 2
Allenfeld
shaft
Residual Gas
Content (m3/t)
7.5-8
7-7.5
6.5-7
6-6.5
5.5-6
5-5.5
4.5-5
4-4.5
3.5-4
3-3.5
2.5-3
2-2.5
1.5-2
1-1.5
Hangard shaft
Frankenholz
shafts 1 & 2
Allenfeld
shaft
Residual Gas
Content (m3/t)
2000
2015
Predicted annual methane production
for all three shafts draining
© Imperial College LondonPage 21
Summary and Conclusions
� A general gas-water two-phase CBM simulator METSIM 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 been
formulated
� An areal model to represent the lumped effect of all coal seams that contribute to
methane emission
� Predictions carried out at Imperial College led to two new boreholes,
Allenfeld and Frankenholz to be planned and implemented in 2001 and 2006
