Historical problems with slim hole drilling
In the past small holes could not be drilled safely and effectively. The article describes the main historical problems encountered when trying to introduce slim wells:
The tri-cone rock bit, rotated from surface by a rotary table, has a low aggressiveness which requires bit weight to make it drill. In small vertical holes this resulted in large numbers of collars (20 to 30) being run.
"Bit bounce", which increases the weight on bit momentarily, which in turn increases the torque on bit, generated torsional vibrations in the collars . . .