Abstract: When drilling into the black carbonaceous mudstone section of the upper part of Badaowan Formation (J₁b³) in the No.1 coalbed methane FK70 well in Baiyang mining area of Fukang, three times of well wall instability and drilling tool jamming occurred. Through analyzing the mechanism of strata instability, it is found that the influencing factors include high clay mineral content, large dip angle strata, micro crack development, and undercompaction, etc. During the third time of side drilling construction, the chemical film-forming sealing and anti-collapse technology, mainly based on the film-forming sealing agent, polyvinyl high polymer emulsion FDM-1, is adopted for the first time, the sealing and anti-collapse performance of the well drilling fluid system is optimized by combining the nanoscale and sub-micron level sealing agents, and the collapsed section is successfully drilled through.