Mill 2,200 ft of cement in poorly bonded liner
A long portion of liner was incorrectly cemented during completion due
to surface equipment failure. As a result, 2,200 ft [671m] of cement needed to
be milled inside the 4 1/2-in [114-mm] completion liner. The operator
determined that the job would require a 3 1/8-in- [79.4-mm] OD motor with
torque greater than 1,000 ft.lbf [1,356 N] to efficiently remove the cement
from the well. The operator predicted that the torque and flow rate that the
existing motor could sustain would induce several stalls, increasing the time
to complete the job.
Schlumberger proposed using a 3 1/8-in-diameter, 3.3-stage DynaForce TT
motor with 7/8 lobes to complete the job. The DynaForce TT motor can provide
more than 1,500 ft.lbf [2,034 N] of torque and sustain constant flow rates up
to 210 galUS/min [48 m3/h].
Additionally, Schlumberger suggested using the Dyna-Drill NBR-HR
elastomer, which delivers up to 30% more power compared with competitors’
elastomers while minimizing the risk of premature chunking. Combined with the
NBR-HR elastomer, a specially formulated adhesive enables the motor to
withstand high temperatures in water-base fluid environments to eliminate the
possibility of debonding.
Completed the operation in one run and 12 hours ahead of schedule
The operator scheduled 72 hours to complete the milling operation. After
only 60 hours, the 2,200-ft section of cement was successfully milled, and the
well was fully circulated in a single run. The cement was milled at a constant
ROP of 1 ft/min with a flow rate that fluctuated between 190 and 210 galUS/min.
Using the DynaForce TT motor, the operator was able to avoid all stalls and
save 12 hours of rig time. Postjob surface evaluation of the motor did not show
any damage to the components aside from expected wear.
