Mud Related Drilling Problems Differential Sticking –Reduce Hydrostatic-Key Seating

Reduce Hydrostatic

•Reducing the hydrostatic pressure and therefore the differential pressure with the use of nitrogen has been tried as another alternative.
–Considerations regarding wellbore stability and potential well control problems must be evaluated prior to implementing this method.
–The well is displaced partially or completely with nitrogen
–The method will normally have some hole sloughing issues related with it

Key Seating

•Keyseating is a situation frequently encountered in deviated or crooked holes when the drillpipe wears into the wall. The normal drilling rotation of the drillstring cuts into the formation wall in deviated areas where the drillpipe tension creates pressure against the sides of the hole.
•Keyseating is diagnosed when the drillpipe can be reciprocated within the range of tool joint distances or until collar reaches the keyseat, while pipe rotation and circulation remain normal
–May not be able to rotate when the tool joint is jammed into the keyseat
he friction generated by drillpipe rotation against the bore wall cuts a narrow channel, or keyseat, into the formation.
•A preventive measure is to carefully control upper hole deviation and dogleg severity throughout the well path.
–This action will eliminate the force that leads to keyseat creation.
–Once a keyseat is formed, the best solution is to ream out the small-diameter portions of the hole with reaming tools.
–This action will solve the immediate stuck-pipe problem, but the keyseat can be formed again unless preventive steps are taken.

Attach a reamer to the drill assembly to widen the keyseat.