Investigation of the Ultrasonic Stimulation Performance on Permeability Enhancement in Coal Seam: Field Tests and In Situ Permeability Evaluation

Table 1

Data analysis of gas concentration in borehole.

Zone	Borehole	Distance from the antireflection borehole	Average concentration	Increment
Zone 0	Average	/	6.52%	/
Zone 1	#1	8 m	11.62%	82.8%
	#2	4 m	12.83%	101.4%
	#3	2 m	21.34%	227.3%
Zone 2	#1	8 m	11.83%	81.4%
	#2	4 m	14.98%	129.8%
	#3	2 m	17.44%	167.5%