Optimal design of a global force-balanced polycrystalline diamond compact bit considering wear condition

Abstract

Polycrystalline diamond compact bits are one of the most widely used oil and gas drilling tools in the world. With wear, a large unbalanced lateral force and bending moment exist. These force and moment contribute not only to bit lateral vibration and whirl but also to wellbore tilt and enlargement, which will then cause early bit failure and low drilling efficiency. In this article, considering wear condition, a single cutter force model is proposed. Lateral force and bending moment models are constructed based on space-force theory. An optimal cutter layout model considering cutter wear is established. The matching approach for the optimal model is discussed based on Kriging surrogate model and genetic algorithm. Then, an optimization case is presented. The results show that the bit force models are in line with the actual drilling condition. The optimal approach is efficient. After optimization, the lateral force to weight on bit ratio is reduced by 10.99%, and the bending moment to torque on bit ratio is reduced by 30.43%. This result is a significant improvement in the force condition and stability of the polycrystalline diamond compact bit; ultimately, the whirl and tilt motion can be reduced, and the drilling efficiency can be improved.