This is a case study for a well intervention job that was conducted in the Prudhoe Bay Unit field, Alaska. It describes the successful use of an electric line milling system to remove a protective frac sleeve that was stuck in a subsurface safety valve (SSSV) landing nipple.
Past attempts to remove the sleeve with conventional methods were unsuccessful. Those attempts included slickline, coiled tubing (CT), and pulling 110,000 lbf with a workover rig using a through-tubing work string. At the time, the sleeve did not interfere with production, so it was left in the well. However, an unrelated tubing leak developed below the stuck frac sleeve. The well had to be shut in until the frac sleeve could be pulled to allow installation of a tubing patch.
Milling the frac sleeve with coiled tubing or replacing the entire tubing string with a workover rig was considered. However, cost and time could be reduced if the frac sleeve could be milled with an electric-line (e-line) conveyed bottomhole assembly (BHA).
The e-line tool string included a wireline release device, an electric-over-hydraulic tractor with stroking tool, electric milling motor, and burning shoe with integral centralizer and no-go. The burning shoe was designed to reduce the outside diameter (OD) of the frac sleeve but preserve the packing bore inside diameter (ID) of the SSSV landing nipple. The tractorstroker- miller tool string was run in the well and tagged the sleeve at 2,119 ft measured depth (MD) where milling continued for approximately 4 ½ hours. After E-line milling was completed, slickline was rigged up for fishing operations and successfully pulled the frac sleeve. The tubing repair was completed and the well was returned to production.
This intervention technology can be used in other wellbores requiring precision milling. The solution proved successful and is a cost-effective alternative to conventional methods for milling obstructions.