Numerical Optimization of Drilling Parameters for Gas Predrainage and Excavating-Drainage Collaboration on Roadway Head

Table 1

Numerical simulation parameters.

Parameter	Value	Parameter	Value
Initial CH4 pressure (, MPa)	0.80	Gas sorption time CH4 (, )	4.34
Young’s modulus of coal seam (, MPa)	3500	Coal density (, kg·m^-3)	1380
Young’s modulus of skeleton (, MPa)	8469	Klinkenberg factor (, MPa)	0.62
Poisson’s ratio of coal ()	0.30	Original temperature (, )	289.15
Langmuir volume constant of CH4 (, m^3·kg^-1)	0.0323	Matrix initial porosity ()	0.04
Langmuir pressure constant of CH4 (, MPa)	2.0833	Initial porosity of fracture ()	0.018
Initial permeability (, m^2)		Residual gas saturation ()	0.15
Dynamic viscosity of water (, Pa·s)		Initial water saturation ()	0.6
Dynamic viscosity of CH4 (, Pa·s)		Irreducible water saturation ()	0.42