Coalbed methane stimulation by hydraulic punching with air cannon

ABSTRACT

The permeability of coal seam is one of the main factors restricting the safe and efficient production of Coal Bed Methane (CBM). In order to improve the extraction efficiency of CBM and reduce the probability of coal and gas outburst, it is of great significance to adopt artificial measures to enhance the fracture network of coal seam. In this paper, a field test of air cannons after hydraulic punching was carried out. The results showed that the gas concentration and gas flow rate were greatly improved, which indicates that the pores and fractures of the coal reservoir are effectively connected. The pure gas extraction volume increased by about 0.7–2.2 times than of non-blasting. According to the experimental results, the paper studies the action mechanism of air cannons, mainly including three aspects of action. The first is the continuous impact of air cannons, which gradually breaks the coal body around the hole, and forms a fracture network of different sizes in the coal body. Air cannon blasting performs secondary treatment on the punched holes, accelerates and promotes the creep of the coal body around the borehole to the free surface, makes the cracks develop deeper, and expands the pressure relief range. Third, it has the function of pulse gas injection to displace the CH₄, which broke the original adsorption balance, promoted the conversion of the adsorbed gas to the free state. The role of three aspects ultimately achieves efficient gas drainage.

KEYWORDS:

• Hydraulic punching
• Air cannon
• Coal bed methane
• Permeability
• Pulse gas injection

Acknowledgments

The authors are grateful for the financial support from the Natural Science Foundation of China (No. 51874122 and No. 51704100), Key Scientific Research Projects Plan of Henan Higher Education Institutions (19A440008), Key Laboratory of Gas and Fire Control for Coal Mines (China University of Mining and Technology), Program for Innovative Research Team of Henan Polytechnic University.

Additional information

Funding

This work was supported by the Key Scientific Research Projects Plan of Henan Higher Education Institutions [19A440008]; the Natural Science Foundation of China [No. 51874122 and No. 51704100].