Combined Percussive-Rotary Drilling to Increase Rate of Penetration and Life of Drill Bit in Drilling Hard Rock Formation

It is generally recognized that stick-slip motion of polycrystalline diamond compact (PDC) bits is responsible for the low rate of penetration (ROP) and premature wearing of drill bits while drilling hard rock formations. An innovative tool designated combined percussion jet (CPJ) was developed in this work to solve the problem. Because the tool generates both axial and torsional percussion, drilling with CPJ is referred as combined percussion-rotary drilling approach (CPRDA). The results of dynamics modeling and stress computation showed that the CPRDA induces more shear stresses in rock formations compared to axial percussion drilling and axial percussion-rotary drilling. The CPRDA was tested on two wells drilled in hard rock formation. The results demonstrated that the CPRDA increased ROP by 56.1-60.4% and extended drill bit life. However, for solving the high stress problem, the tool needs to be optimized further.