Patent ID: 8640791

Claim:
A method of monitoring the operation of a drill string having a drill bit drilling into an earthen formation, comprising the steps of: rotating said drill bit at a rotational speed so that said drill bit forms a bore hole in said earthen formation during a drilling operation; measuring lateral vibration of the drill string vibrating in a lateral vibration mode during the drilling operation so as to obtain measured lateral vibration data; generating a signal representative of said lateral vibration data of said drill string in said lateral vibration mode as said drill bit rotates so as to drill into said earthen formation during the drilling operation; determining the backward whirl frequency of said drill string in said lateral vibration mode based on the signal that is representative of the measured lateral vibration data and a predicted lateral vibration data, the predicted lateral vibration data being representative of a prediction of the lateral vibration mode for the drilling operation; and determining the diameter of said bore hole being drilled by said drill bit based on measured rotational speed of the drill bit and said backward whirl frequency.