Reasonable Scope of Kilometer Drilling in Lower Layer of Extrathick Coal Seam: A Case Study of Tingnan Coal Mine, China

Table 1

Basic parameter test result of coal seam gas in 205 working face.

Coal seam		4#
Gas content (m^3·t^−1)		6.74∼6.86
Gas adsorption constant	a (m^3·t^−1·r^−1)	21.578∼22.321
	b (MPa^−1)	0.879∼0.926
Industrial analysis	Moisture (%)	4.78∼5.46
	Ash (%)	7.43∼7.88
	Volatile (%)	29.45∼32.65
Gas pressure (MPa)	0.54∼0.624
Coal porosity (m^3·m^−3) (%)	8.48∼8.86
Initial velocity of gas emission (∆p)	0.775
Coal seam permeability coefficient (m^2·MPa^−2·d^−1)	0.0424
Natural gas flow attenuation coefficient of borehole (d^−1)	0.0243
Coal dust explosive	Risk of explosion
Coal seam spontaneous combustion tendency	Type II spontaneous combustion