keyseats

There are three types of pipe sticking:-

  1. Differential pipe sticking
  2. Mechanical pipe sticking
  3. Keyseats
In this post we will be focusing on Keyseat.

Keyseat is the small diameter extra hole dig to the side of the main hole .Keyseat is generally formed in a dog leg hole containing weak formation.While drilling a dog leg hole drillpipe tries to straighten itself due to tension, which creates a lateral force.This lateral force combined with rotary motion of drillpipe digs an extra hole into the weak formation around the dogleg.This extra hole is termed as keyseat.

Drilling hole problemDrilling hole problem

Conditions for keyseat:-

  • high dogleg
  • weak formation at dogleg
  • high lateral force due to the string weight below dogleg

Keyseat identification:-

  • downward motion but no upward motion of the drillstring
  • increased torque and drag
  • full circulation
Keyseat are generally drilled by small diameter drillpipe hence keyseat's have smaller diameter and while pulling out drill collar with larger diameter tends to stuck at these keyseat. That's why downward motion happens while upward motion of the string is restricted.

Preventing keyseat:-

  • try drilling straight hole
  • keep the dogleg value low to avoid sharp turn
Keyseat can be removed by regularly reaming the hole and if the string is stuck try using upward jarring action.

3 comments: