Optimizing drilling efficiency: Comparative study of stick-slip vibration of steel and aluminum drill strings

This study investigates the torsional stick-slip behavior of steel and aluminum drill strings under varying levels of aggressiveness, which refers to the intensity with which the drill bit interacts with the rock formation. Aggressiveness is primarily influenced by critical factors such as torque on bit (TOB), weight on bit (WOB), and rotational speed (RPM). It is quantitatively expressed as the ratio of TOB to WOB, a key determinant in the drilling process that influences how effectively the bit penetrates the formation. A small-scale drill string model was developed and tested under varying aggressiveness and RPMs using a numerical simulator. The objective was to assess how the different materials respond to torsional stick-slip vibrations across a range of operational parameters. The simulations were conducted over 30 s intervals with both stable and varying RPMs, allowing for a detailed comparison of the material's dynamic behaviors. The RPM limits, which indicate the maximum RPM beyond which severe stick-slip occurs, were calculated for both materials. Results revealed that steel drill strings exhibited superior stability, with fewer torsional oscillations and shorter sticking periods, particularly at higher aggressiveness ratios. While aluminum drill strings, being lightweight, showed greater susceptibility to torsional oscillations, especially at lower rotational speeds, leading to longer periods of stick-slips. Also, as the aggressiveness reduces, the RPM limits for both materials increases. This emphasizes the importance of identifying optimal RPM limits and material selection to minimize vibrations and improve drilling efficiency.