The Bottom Hole Assembly (BHA) is a drill string component that is used to drill wells. Above drill bit and below drill pipe, a BHA can be found in the drill string. The drill collar is the most important part of BHA. The primary goal of designing a bottom hole assembly with special requirements is to generate a desired reactive side force on bit from the formation. This paper is particularly focused on Bottom Hole Assembly (BHA), its parts and on the complications faced by BHA during the process of drilling unconventional coal bed methane (CBM) wells. The CBM industry continues to be plagued by bottom hole assembly component failures, resulting in annual direct and indirect costs in the millions of pounds. Present trends in industries for deep drilling, deviation in wellbores have exacerbated this widespread issue. The investigations not only revealed some design flaws, but the most common causes of failure are mechanical fatigue, corrosion fatigue and simple overloading. [ABSTRACT FROM AUTHOR]