Bottom-hole assemblies control the vibration response of drill strings because they are much heavier and stiffer than drill pipe. The length of bottom-hole assemblies is also a factor and the present practice of determining drill collar length often leads to natural tuning with drill bit displacement frequencies. As a result, bottom-hole assemblies are unintentionally designed to vibrate. This paper explains the causes of severe drill string vibrations and gives guidelines for controlling them.

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