A new application of running wireline stroker technology in combination with wireline milling technology has been proven successful in the Norwegian Sector of the North Sea. In August 2008, on an offshore platform, a wireline stroker and wireline milling rotational unit were used to mill out and remove a permanent type bridge plug at 1,264m (approximately 4,147 ft) MD (50° deviation).
The 3.25" high expansion bridge plug was inadvertently set in the tubing in March 2008 at 1,264 m. It was decided to attempt to mill out the plug on electric wireline to regain production from the well. A study was initiated to evaluate if it would be feasible to develop a wireline conveyed stroker and milling system capable of removing the plug. During a two months design period, several different bits and milling tools where designed and tested. It was confirmed that by combining a wireline miller with a modified wireline stroker to act as feed control, it should be possible to mill out the retaining rings and collapsing the plug. The milling system included a control unit allowing the WOB (weight on bit) to be optimized for each application. In addition it also controls the reactive torque and force generated when the milling bit engages the plug.
The offshore operation was successfully completed in three days.
The milling tool has proven to be an effective solution to down hole problems that require milling of metal or hardened materials. The technical solution was developed within the design parameters and in accordance with the timeline set out for the project. This new method for milling well completion hardware and other well bore obstructions offers a cost-efficient alternative technology to existing methods using coil tubing or snubbing. The success of the milling operation is a significant milestone and has pushed the limits for what is possible to achieve on electric wireline.
By applying new technology, the well was quickly put back in production. The operation was conducted as a live well intervention without the need for using the drilling derrick.
This paper will examine the challenges and solution chosen in an operation of milling a bridge plug on electric wireline.