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.

摘要

煤层渗透率是制约煤层气安全高效生产的主要因素之一。为了提高煤层气的开采效率，降低煤与瓦斯突出的概率，采取人工措施加强煤层裂缝网络具有重要意义。本文对空气炮液压冲压后进行了现场试验。结果表明，瓦斯浓度和瓦斯流速均有较大提高，表明煤储层孔缝有效连通。纯气提取量比非爆破增加约0.7-2.2倍。根据实验结果，本文对空气炮的作用机理进行了研究，主要包括三个方面的作用。首先是空气炮的连续冲击，逐渐将孔周围的煤体破碎，在煤体内形成大小不一的裂缝网络。空气炮爆破对冲孔进行二次处理，加速和促进钻孔周围煤体向自由面蠕变，使裂缝发展得更深，扩大泄压范围。三、具有脉冲注气置换CH的功能₄、打破了原有的吸附平衡，促进了吸附气体向游离态的转化。三方面的作用最终实现瓦斯高效抽采。