Power ultrasound assisted coalbed methane enhancement recovery: Field application and performance evaluation in underground coal mine

•Field test of power ultrasound assisted CBM enhancement recovery is implemented in underground coal mine.•Methane production significantly increases after ultrasound stimulation in coalseam.•Ultrasonic anti-reflection influence radius exceeds 8 m in the target coalseam with water injection.•Methane production increment in single borehole decreases with the distance increase from ultrasound source. Power ultrasonic assisted reservoir modification is a promising technique for enhanced coalbed methane recovery. The current studies confirm the coal structural alteration and the improvement of gas deliverability in coal pores with ultrasound stimulation. However, the in-site performance of ultrasound-assisted CBM production has not yet been revealed. In the current study, the in-situ antireflection test was conducted with high power ultrasound ∼18 kW in underground coal seam, and the antireflection performance was evaluated by measuring the borehole drainage gas data in the field test zone. The result shows, within 40 days’ drainage after ultrasonic antireflection in coal seam, the average gas concentration of single borehole in the experimental group increased by 81.4% ∼ 227.3% than that in control group, the average borehole gas flowrate has a 20% ∼106% improvement over the control group, and the pure methane production in single borehole increased by about 3.83 times. The ultrasonic anti-reflection influence radius exceeds 8 m in the coalseam with water injection in this study, and the increment of methane production in single borehole decreases with the distance increase from the ultrasound source, which is due to the energy attenuation of ultrasound propagation in the porous coalseam. This study preliminarily demonstrates the on-site implementability and effectiveness of power ultrasound in enhancing coalbed methane recovery.