ABSTRACT
By analysing simultaneous downhole and surface dynamic drilling measurements, it has been possible to characterize the drill string behaviour and, more precisely, the stick-slip motion.
Based on three thousand five hundred hours of real time field measurements, this paper presents the study of bit and drill string behaviour when the stick-slip phenomenon occurs.
Using correlations between downhole and surface recordings, it shows how, applied solely to surface drilling data such as torque and rotational speed, a simple mathematical calculation enables the detection of the stick-slip motion, estimation of its period, its sticking time and the maximum bit rotational speed.
It also demonstrates that it is possible to reduce and eliminate stick-slip by modifying certain drilling parameters such as weight on bit, rotational speed or mud characteristics. In addition, power swivel control can suppress the first mode but may also emphasize a higher mode of the stick-slip phenomenon.
Looking at the numerous hours of recordings which have been analysed, during 50 % of the time this phenomenon is seen to be permanently present while rotating.
As drill pipe fatigue and bit wear can be linked to the stick-slip motion, the possibility of controlling and limiting it by simple surface monitoring is a very attractive concept.
