Process for controlling a drilling operation

Claim 1

Process for detecting and signalling the presence of periodic instabilities in the rotation of a drill string in order to control a drilling operation, during which a tool is set in rotation in a well by means of a drill rod, the process comprising the following steps: continuously measuring the rotational speed of the upper end of the rod; continuously measuring the torque exerted on the upper end of the rod; ascertaining the variation in the torque; determining the period of variation of the torque, if the amplitude of this variation exceeds a predetermined threshold; checking the stability of this period; if this period is stable, comparing said period with at least one predetermined theoretical period; and signalling the results obtained to a user in order to make it possible to control the drilling operation such that (a) if the amplitude of the torque variation does not exceed the predetermined threshold, transmitting a signal to the user that the current drilling operation can be maintained; (b) if the period is not stable or if the period is stable but does not correspond to a predetermined theoretical period, transmitting a signal to the user to modify the current drilling operation; and (c) if the period is stable and corresponds to a predetermined theoretical period, transmitting a signal to the user that a potential instability in the drilling operation may exist.