Exploiting coalbed methane (CBM) not only provides clean energy but also reduces the risk of gas explosions in coal mining. CBM reservoirs have low mechanical strength due to poor continuity, strong heterogeneity, and rich natural fractures, which bring about wellbore collapse and leakage during the drilling operations of CBM wells. As for fragmented coalbed methane reservoirs, plugging the leakage channel and increasing the density of drilling fluid would result in new collapse problems and leakage. To achieve this, we developed a cohesive fuzzy ball drilling fluid (FBDF) to adhere fragmented coal particles from the discontinuous phase to the continuous phase and strengthen their mechanical properties to prevent collapse and leakage. The microcosmic interaction of coal seams with different fluid systems and adhesive properties have been comprehensively evaluated. The mechanical parameters of coal plugs treated with common potassium chloride drilling fluid (PCDF), polymer drilling fluid (PDF), and FBDF were carefully compared through uniaxial and triaxial experiments. Additionally, the adhesive mechanism of FBDF to coal fines was comprehensively discussed. The results showed that the FBDF would form an elastic mesh structure through hydrophobic association, and bond the small particles of coal debris together to form a stable structure similar to “steel bar-concrete” “macromolecule-particle”. The viscous force on the surface of coal rocks treated by FBDF was higher than that of coal plungers treated by PCDF or PDF. The uniaxial compressive strength of core samples treated by FBDF was increased by 47.1%, while the modulus of elasticity, Poisson's ratio, and brittleness coefficient were decreased by 19.94%, 11.95%, and 4%, respectively, compared to dry coal plug. FBDF also showed preferential plugging and permeability recovery abilities. The FBDF fluids have been successfully applied in two CBM wells characterized by “top leakage and bottom collapse”, neither collapse nor leakage occurred during the drilling process. It provided a new internal blocking and bonding technology for fragmented reservoirs.