Loads on Drillpipe During Jarring Operations

Jarring implies heavy loads on the drillstring. The highest load on the drillpipe before jarring is at the rig floor. This paper discusses loads on drillpipe before, under, and after jarring. We show that for most situations, the shock wave from the jar impact does not imply additional load on the drillpipe compared with static load. The theoretical results are confirmed by measurements of a jarring operation with stuck point at ≈ 1200 m measured depth. Loads on the drillpipe can be a limiting factor in jarring operations because fear of possible additional loads from jarring dynamics may restrict the trip force (overpull) on the jar. Our main conclusion is that dynamic jar forces do not give additional loads on drillpipe. This information can be used to set an optimal trip force on the jar.