Page 270 - Advanced Mine Ventilation

P. 270

Premining Degasiﬁcation of Coal 15

Seams

Chapter Outline

15.1 Coal Seam Reservoir Parameters 248
15.1.1 Degree of Gassiness 248
15.1.2 Speciﬁc Gas Production 249
15.1.3 Speciﬁc Gob Gas Production 249
15.2 Premining Degasiﬁcation 249
15.2.1 In-Mine Horizontal Drilling 249
15.2.1.1 The Drill Rig 250
15.2.1.2 The Auxiliary Unit 251
15.2.1.3 The Guidance Systems 252
15.2.1.4 The Downhole Drill Monitor 254
15.2.2 Gas Production From Horizontal and Vertical Wells 256
15.2.2.1 Production From Horizontal Boreholes 256
15.2.2.2 Gas Production From Vertical Wells 257
15.3 Application of In-Mine Horizontal Drilling 258
15.4 Application of Vertical Wells With Hydraulic Fracturing 259
15.5 Application of Horizontal Boreholes Drilled From Surface 261
15.6 Optimum Widths of Longwall Panels 262
15.6.1 Estimation of Total Methane Emissions at the Longwall Tailgate by Direct
Measurements 263
15.6.2 Mathematical Derivation of Limiting Methane Concentration at the Tailgate 264
15.7 Field Observations of Optimum Longwall Panel Width 265
Problems 265
References 266

Majority of global coal production comes from underground mining which is done
by two methods: (1) room and pillar and (2) longwall mining. As shallow coal seams
are mined out and mining reaches greater depths, longwall mining becomes the
preferred method of mining. In United States, more than 50% of all underground
mined coal is mined by the longwall method. The trend for panel sizes and mining
equipment in the coal industry is to continue to go upward pushing production capac-
ities and productivity to higher levels. Another reason for increasing the longwall
panel size is that development sections cannot keep up with the rate of longwall
advance. Increasing the width of the longwall panel slows down the rate of advance.
Today it is quite realistic to plan longwall panels in mildly gassy coal seams that are

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