Neutral Point

Drillstring Design

The neutral point in a drill string is the point in the string that is neither in compression or tension.

Since the drill string is held at surface, normally by a top drive, the weight of the string puts most of the pipe in tension. In order to apply weight to the bit for drilling, some of this weight at surface is let off which applies weight at the bit. Since some weight is being applied, the bottom of the string will be in compression and will naturally change to tension at some point in the string. For BHA design, it is important to make sure this neutral point remains in the Drill Collars or BHA as these are more rigid and will restrict buckling that would happen in the drillstring.