While drilling horizontal sections, an operator experienced tool-joint wear, which in extreme cases was one-sided, necessitating the replacement of many drill-pipes to minimize the risk of drill-string failure. Since there were no observable signs of the wearing process, the strategy has been to trip midway through the section to inspect the pipes. With the goal to drill the section in one run, an investigation of the root causes of the abnormal wear has been started.

To check whether some hidden signal patterns could help detecting under which circumstances the tool-joints were worn out, a play back of some of those drilling operations has been undertaken with specific attention to whether transient hydraulic and mechanical models could help differentiate abnormal measurement signatures. In parallel, it has been investigated with computational fluid dynamic (CFD) software whether synchronous whirl of tool-joints would generate a specific pressure signature that could easily be recognized. As the asymmetrical wear of the tool-joints indicated the presence of synchronous whirl, it has also been analyzed how side forces were distributed along the drill-string.

Neither the playback nor the CFD analyses pointed to conditions leading to tool-joint wear. On the other hand, the side force analysis showed that because of extensive directional work linked to geosteering, reaction forces on the tool-joints were very unevenly distributed on the first 500m of drill-string behind the BHA. However, the distribution of the positions of the high and low side forces changed radically for different bit positions. Numerous hard-stringers were encountered while drilling which suggests that the irregular distributions of side-forces on the string have been maintained for longer periods of time. As a result, these conditions have allowed drill-string whirl to be kept sufficiently steady with the consequence of severely damaging the tool-joints.

Mathematical modelling of the drill-string behavior can help determining the critical rotational speed as a function of the weight on bit by which whirl can take place. With this information at hand, it is then possible to give concrete advice to the drilling team on which drilling parameters to use to minimize the risk of tool-joint wear.

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