Numerical Modelling and Prediction of Abandoned Mine

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=


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


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 %


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


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


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.


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


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


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


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


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



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


(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


(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


(m3/t)

2015



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


(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


(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



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


Allenfeld shaft


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



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


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


(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


(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


(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


(m3/t)

2015


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


Allenfeld shaft


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


Allenfeld shaft


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.


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

Documents

Numerical Modelling and Prediction of Abandoned Mine