Technology for Drilling Speed Increase Using Stable WOB/Torque for Hard Formations

When a PDC bit is used to drill hard rock, the large torque is required, and the fluctuating torque would cause severe vibration and short service life of drill bit, hence resulting in low ROP and long drilling period. By establishing a calculation model for the required threshold torque of rock breaking, a stable WOB/torque technology for increasing drilling speed in hard formation has been developed based on quantitative calculation of threshold torque, adhering to smooth transmitting of drill string strain energy. By means of optimizing the wellbore size, selecting the appropriate bit and impact-assisted rock breaking tools, the threshold torque and WOB of rock breaking can be reduced. By selecting the appropriate PDM drilling tools, the sufficient rock breaking energy for the bit can be provided. Through optimization of appropriate shock-absorbing tools and drilling parameters, the new technologies can reduce vibration and ensure smooth operation of drill bit. During the field test in Paleozoic hard formation of Well Xiahe-1, the ROP in Permian strata was increased by 485.6% and the whole well ROP increased by 70.4%, achieving remarkable effects for increasing drilling rate. The research results showed that stable WOB/torque drilling technology could effectively improve the ROP in hard formation, and provide reference for increasing drilling rate in complex formations.