Selection and application of drill bit for directional section of ?311.2 mm well in Jiaoshiba Block

In line with long directional interval in horizontal ?311.2 mm wellbore of shale gas, encountering complex formations and strong heterogeneity in Jiaoshiba Block, which may easily lead to rapid bit failure and low ROP, etc. A method of drill bit selection was built on formation drillability and evaluation of actual drilling effectiveness. The logging data is used to obtain formation rock mechanical parameters, build the profile of rock drillability and determine the proper bit type. The bit performance assessment index was built based on virtual intensity index principle by comprehensively considering the formation rock breaking efficiency and footage, and quantitative evaluation was made to the effectiveness of bits used in drilling and completion. Using this method, the drill bit selection scheme was recommended by formations for directional interval of ?311.2 mm hole in Jiaoshiba Block, and was used in five wells such as Jiaoye-49-1HF well. The average ROP was increased by 207%, and average footage of individual bit was increased by 139.2 m. The application effect shows that the method of drill bit selection based on formation drillability and actual drilling effectiveness can qualitatively select the bit type and quantitatively evaluate the bit performance, hence effectively improving the matching between the bit and the formation.