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Method of methane drainage

with using the cased long boreholes

Economic Commission for EuropeCommittee on Sustainable EnergyGroup of Experts on Coal Mine MethaneEleventh session Geneva, 24–25 October 2016

with using the cased long boreholes

Dariusz OBRACAJ, Justyna SWOLKIEŃ

Faculty of Mining & Geo-engineeringDepartment of Underground MiningMickiewicz Av. 3030-059 CracowPOLAND

Balance of methane and its utilizationin Polish coal mining industry

for the past 10 years

Year 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Overall methane emission, in millions of cubic metres per

year851.1 870.3 878.9 880.9 855.7 834.9 828.8 828.2 847.8 891.1 933.0

Ventilation air methane, in millions of cubic metres per

year595.8 580.8 610.1 606.7 595.9 579.0 578.6 561.5 581.7 570.1 594.0

Amount of methane captured Amount of methane captured through drainage, in millions

of cubic metres per year255.3 289.5 268.8 274.2 259.8 255.9 250.2 266.7 276.6 321.0 339.0

Amount of utilised methane, in millions of cubic metres per

year144.8 158.3 165.7 156.5 159.5 161.1 166.3 178.6 187.7 211.4 197.1

Methane emitted into the atmosphere, in millions of cubic

metres per year595.8 580.8 610.1 606.7 595.9 579.0 578.6 649.6 660.1 679.7 735.9

Number of hard coal mines 33 33 31 31 31 32 31 31 30 30 30

Annual hard coal output, in millions of tonnes

97.1 94.3 87.4 83.6 77.3 76.1 75.5 79.2 76.5 72.5 72.1

Emission of methane from coal seams

Geological conditions of coal seams (porosity, permeability,reservoir pressure, diffusivity), seam methane content and lowdesorption of Polish coal seams result in low gas emission notdisturbing the structure of rock-mass.

Emission of methane from coal seams

Geological conditions of coal seams (porosity, permeability,reservoir pressure, diffusivity), seam methane content and lowdesorption of Polish coal seams result in low gas emission notdisturbing the structure of rock-mass.

Methods for methane drainage in Polish coal mines:

• methane drainage in development headings,

• pre-mining drainage,

• mining methane drainage,

• post-mining methane drainage.

very low effectivenessv

low effectiveness

satisfied effectiveness

good effectiveness

Emission of methane from coal seams

Geological conditions of coal seams (porosity, permeability,reservoir pressure, diffusivity), seam methane content and lowdesorption of Polish coal seams result in low gas emission notdisturbing the structure of rock-mass.

Sources of methane emission into face of longwalls in Polish coal mines

Worked out coal seam

Roadway

Coal seam

Workingcoal seam

Methane emissionfrom overburden

50-60%CH4

6

Workingcoal seam

Roadway

Roadway

CH4

Methane emissionfrom underburden

10-20%

20-40%

Methane emissionfrom mining seam

The most frequently ventilation systemsof longwall panels used in Polish coal mines

76% of longwall panels in coal mines with methane emission

22% of longwall panelsin coal mines with methane emission

U-tube ventilation system Y - return side ventilation system

Tailgate road

GO

AF

GO

AF

Tailgate road

Headgate road

- intake air - return air

Headgate road

Parallel return gateroad

Headgate road

Tailgate road

GO

AF

U-tube ventilation system with parallel return roadway

2% of longwall panels in coal mines with methane emission

Methane drainage of longwall panelby an overlying drainage heading

U-tubeventilation

system

The most popular methane drainage systems in Polish coal mines

Tailgate Road

desorption zone of upper layers(gas emission zone)

AA

Overlying methane drainage heading

Cross-measureboreholes

KEY:intake airreturn airmethane drainage pipeline

cross-measure boreholeregulatormine seal

Headgate Road

Tailgate Road

s=(0.15 - 0.50) L

hmin> 5hs but min. 12m

The most popular methane drainage systems in Polish coal mines

Methane drainage of longwalls from return roadway

c) ventilation system with parallel return roadway

a) U-tube ventilation system b) Y return-side ventilation system

Longwallventilation

specification

Overall methane emission, m3/minAverage

efficiency of methane drainage, %

80

Panles with U-tubeventilation system

38.5 39.0 40.6 38.3 48.8 64.0 x x x 41.2

Effectiveness of methane drainage of longwalls for different ventilation and methane drainage

systems

ventilation system

Panels with Y ventilation system

33.8 43.7 52.4 56.1 49.9 46.2 57.9 x x 48.7

Ventilation system with parallel return

roadwayx x 58.0 60.1 62.2 64.2 64.5 68.3 71.5 63.9

Panles with U-tubeventilation system

with a drainage heading

49.0 58.6 60.2 62.6 68.4 64.7 68.6 68.8 76.0 63.4

Proposal of methane drainage method with using cased long boreholes

Conventional cross-measure boreholes

Casedlong boreholes

boreholesboreholes

½ L

Bo

Tailgate RoadB

Bi

AA

hmin = 5 x hs

AA

Proposal of methane drainage method with using cased long boreholes

Stand pipe

Perforated pipe

2/5

L

½ L

Headgate Road

B

hs

hmin = 5 x hs

hs

BB

Coal seam

Coal seam

Gas emission

zone

Worked out seam

Proposal of methane drainage method with using cased long boreholes

Coal seam

Roadway

Mining seam

Roadway

Coal seam

Coal seam

Coal seam

Coal seam

zone

hs

25 m

A

100

m

175 m102 mTailgate Road

80 m

200

m

A

Proposal of methane drainage method with using cased long boreholes

The exampleLongwall panel B-12

Headgate Road

2 cased long boreholes

192 m, 200m

3 conventionalfan boreholes

60-100 m hmin ~ 13 m

+35o÷+65o

ho ~ 30 m+30o,+25o

AA

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