Drilling Tendency Behavior For Bottom Hole Assembly
The purpose of the drilling bottom hole assembly BHA is to drill a useful vertical hole with full gauge, smooth bore and free of doglegs and ledges.From the below drawing which shows the simplest bottom hole assembly (slick assembly) which consists of a bit and drill collars and no stabilizers, you will notice the following:

- In the vicinity of the bit, the string does not contact the wall of the hole. 
- At some distance above the bit, the string contacts the wall. 
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