ABSTRACT
The drilling process in Wujiaping Formation of Shuangyushi structure in Northwest Sichuan province always meets difficulties such as low average ROP, short bit life, and unsatisfactory drilling effect with PDC bit, cone bit, and hybrid drill bit. This article makes experimental research on the drillability, abrasiveness, and drilling resistance mechanism of cropping flint and siliceous limestone core in Wujiaping Formation. Results show that the drilling resistance of Wujiaping Formation is extremely strong with 9.65 average drillability level in which high content of silicon is the key factor, meanwhile, the obvious difference lies in the drilling resistance mechanism between Wujiaping Formation and sandstone formation due to the high content of the calcareous layer. Through the combination of rock mechanics and bit cutting surface microscopic observation, evidence shows that the reasons for bit slipping are difficult penetration of bit cutter and smooth cutting surface due to high strength and hardness of siliceous limestone, besides, the main reason for extremely strong drilling resistance of rock is difficult cutting due to tight cementation and high hardness of flint which leads to breaking rocks by impact grinding. Therefore, the optimization of bit acceleration in Wujiaping Formation in the middle part of Shuangyushi structure should focus on enhancing bit tooth penetration and overall impact resistance, to improve the efficiency of rock breaking and service life of the bit.
