Factors Affecting PDC Bit Directional Behaviors: Numerical Simulation and Applications

This paper describes how a new bit–rock interaction model shows the combined effects of cutting structure design, gauge pad configuration, and depth of cut controllers (DOCC) on bit directional behaviors for polycrystalline diamond compact (PDC) bits. Many elements of a typical PDC bit are used for directional drilling: cutters, DOCCs, and gauge pads. Bit directional behaviors include bit drilling efficiency, build rate, walk rate, and torque fluctuation. By simulating the bit–rock interaction, the forces acting on each element on the bit, such as steer force and walk force, can be calculated; therefore, each element’s contribution to bit directional behaviors is calculated. New force models of different types of elements have been derived from thousands of single element tests in the laboratory. Rock chips generated by each element can be modeled and removed by updating the bottomhole during bit–rock interaction. The removal of rock chips significantly changes the engagement of elements with rock. In this study, the following factors affecting PDC bit directional behaviors were simulated: (1) bit profile, (2) gauge pad configuration, (3) cutter layout, and (4) tip-ground level. This study shows that proper design of face aggressiveness, including bit profile, layout of cutters, and DOCCs, is crucial for determining a bit’s drilling efficiency. Gauge pad aggressiveness, particularly its length, is a key factor in determining bit directional behavior. The bit–rock interaction model has been validated by bit testing in a laboratory under controlled conditions. This paper presents several case studies to verify the model’s ability to determine steerability based on the design of PDC bits when used in rotary steerable systems (RSSs).