With the increasing energy and environmental protection demands, coalbed methane (CBM) have attracted worldwide attentions. A cost-effective way of using nitrogen-gas as the fluid media of abrasive jet for radial jet drilling (RJD) in CBM exploitation was proposed in this paper. Laboratory experiments were carried out to investigate the influence of parameters including jetting pressure, nozzle diameter, dimensionless standoff distance, bedding direction, abrasive diameter, duration time and coal strength on coal-breakage efficiency. Besides, sensitivity analysis was conducted to evaluate the effect of jetting parameters on erosion performance. Moreover, the surface morphologies of jet-drilled holes were measured by a 3D profilometer. Finally, the coal-breakage mechanisms of abrasive nitrogen-gas jet were illustrated. The results indicated that the key factors for improving coal-breakage efficiency by abrasive nitrogen-gas jet were dimensionless standoff distance and nozzle diameter. Four major factors that contribute to the coal-breakage mechanisms can be summarized as: fractures generation, edge chipping, repeated erosion and gas entrainment effect. Moreover, jetting direction plays an important role in generating fractures. Fractures tend to be generated along the parallel bedding direction on the coal since tensile failures are easier to be occurred. Furthermore, a regular and smooth hole generated by the abrasive nitrogen-gas jet made it suitable for RJD drilling in CBM wells. The experimental results are expected to provide a viable alternative for efficient, economical and safe exploitations in CBM reservoirs.

随着能源和环境保护需求的增长，煤层气（CBM）引起了全世界的关注。提出了一种在煤层气开采中利用氮气作为磨料射流的流体介质进行径向射流钻井（RJD）的经济有效的方法。进行了实验室实验，研究了喷射压力，喷嘴直径，无量纲间隔距离，层理方向，磨料直径，持续时间和煤强度等参数对煤破碎效率的影响。此外，进行敏感性分析以评估喷射参数对侵蚀性能的影响。此外，喷射钻孔的表面形貌通过3D测量轮廓仪。最后，阐述了磨料氮气射流的破煤机理。结果表明，通过磨料氮气流提高煤破碎效率的关键因素是无量纲的距离和喷嘴直径。造成断煤机理的四个主要因素可以概括为：裂缝的产生，边缘碎裂，反复的侵蚀和夹带气体的作用。而且，喷射方向在产生裂缝中起重要作用。由于容易发生拉伸破坏，所以在煤上沿着平行的顺层方向容易产生裂缝。此外，由研磨性氮气流产生的规则且光滑的孔使其适合于在煤层气井中进行RJD钻井。实验结果有望为有效，煤层气储层。