Mill 34 fracturing plugs in a horizontal section at a depth of 12,700 ft and a bottomhole temperature (BHT) of 350 degF in a single run.

Mill fracturing plugs in HT environment

Milling in extreme downhole temperatures is challenging due to the speed at which the stator’s elastomer degrades and leads to premature chunking, rendering the power section ineffective and forcing a change of motor to continue with the job.

A CT tools company was awarded a milling job in the Haynesville-Bossier shale play in East Texas where BHTs reach 350 degF. The company had two prior jobs of a similar nature in which two to three motors were required per well. This method not only added costs but induced more cycling on the 2 3/8 in string due to unplanned changes on BHA.

Deploy thru-tubing motor with proprietary elastomer

SLB use coiled tubing (CT) and DynaForce TT™ high-performance thru-tubing motor’s power section with NBR-HR proprietary elastomer to complete the job without the risk of premature chunking. We milled 34 fracturing plugs in 40 h, from start to finish, in a single run with the motor functional post job.

SLB engineers recommended the use of the 2 7/8 in 7-stage DynaForce TT thru-tubing motor in a 5/6-lobe configuration with proprietary NBR-HR elastomer with a 3-loose fit, achieved by installing a double-undersized rotor (2US) and an oversized stator (1OS). The NBR-HR elastomer has a controlled expansion ratio and holds hardness at high temperatures to deliver optimal power while minimizing the risk of premature chunking. The possibility of a debonded stator at such high BHTs is largely eliminated by the implementation of specially formulated adhesives.

Successfully mill a 7,400-ft section in a single run

The job required only one thru-tubing motor dressed with a Dyna-Drill power section to complete the work in a single run. In total, 34 fracturing plugs were milled on 4½-in casing in a 7,400-ft horizontal section with total well depth of just above 12,700 ft. The plugs milled were rated to 12,000 psi and the run averaged 9 min/plug. Circulating pressure averaged 7,600 psi throughout the job with pumping rates of 2.0 to 3.2 bbl/min.