Toolface Control is widely regarded as one of the greatest challenges when drilling directionally with a FC (Fixed Cutter) drill bit on a Positive Displacement Motor (PDM).

Toolface offset is proportional to the torque generated by the bit. FC bits, by nature, generate high levels of torque. If an external force acting on the bit causes a FC bit to over-engage, a large change in downhole torque is typically produced, which causes rotation of the drill string, and loss of toolface orientation. It is therefore desirable for a FC bit to produce a torque response that does not vary greatly with changes in the external forces applied.

This paper examines the effect of varied components of a FC drill bit to determine the key design requirements to deliver a smooth torque response and improved directional performance. This includes evaluation of the results from a comprehensive series of laboratory tests to determine the effectiveness of a number of varied, removable Torque Controlling Components (TCC). The goal was to establish a configuration that would provide predictable torque response to applied weight on bit, allowing cutting structures to be independently optimized for overall higher penetration rates.

A novel gauge geometry was engineered to reduce drag and deliver a smoother borehole. This would provide less torque when sliding and beneficial gauge pad interaction with the borehole when in rotating mode.

Field performance studies clearly demonstrate that matching TCC, an optimized cutting structure, and gauge geometry to a steerable assembly delivers smooth torque response and improved directional control. Benefits within rotary vertical applications are also demonstrated. Successful application has resulted in significant time and cost savings.

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