Keywords: 
• Gravel layer /
• increasing the drilling speed /
• inserted roller bit /
• North Yaken

Abstract: The extraordinary thick gravel layer in Quatemary system and upper formation of Kuche member in the North Yaken cause stick-slip and low efficiency during drilling. Based on study and analysis of feature of gravel layer and difficulty of drilling, the thesis optimizes and designs insert roller bit with large size and matched drilling technology in aspects of drilling bit parameter, drilling rig structure and drilling parameter. The drilling practice indicates that the drilling process in gravel layer of the North Yaken is successful. The service life of roller bit with large size in gravel layer is up to 404 hours and rate of penetration is increased by 84.62%. Meanwhile, the number of bits needed is greatly reduced, the time of tripping is decreased, and the efficiency of the drilling is also improved. The study provides guidance and reference for making the scheme to improve the drilling speed in Northern Yaken .