Using downhole dynamics to better understand the drilling process with positive displacement motors and PDC bits

Abstract

Abstract Downhole dynamics is now better understood through the application of downhole instrumentation. Vibration measurements at the bit have given us a precise understanding of PDC bit behavior from stick-slip to backwards whirl with pendulum and packed hole rotary assemblies. Many PDC bits are however run on downhole motors for directional and performance reasons prompting testing to be done with an instrumented bit below such motors. This paper will present how PDC bits behaved below low speed and high speed motors. Measurements were taken while drilling both in rotary and sliding modes and also with straight and bent housing motors to obtain results over a wide spectrum of motor applications. Besides the effects on bit performance this paper will present, for the first time, the actual characteristics of a positive displacement motor operating in a downhole environment. The subsequent integration of bit and motor design will lead to the development of a more efficient and reliable drilling system. The PDC bits tested incorporated a new three dimensional design so as to minimize downhole vibrations.