Milling of Permanent Bridge Plug Performed Successfully on Wireline

Abstract

Summary A technological breakthrough within the application of wireline technology has been achieved. In August 2008 on an offshore platform on the Norwegian continental shelf, a wireline tractor and a new wireline milling system were used to mill and remove a permanent bridge plug at 4,147 ft measured depth (MD). The operator decided to mill out the plug on electric wireline and worked closely with the service company to develop this novel solution. Having developed and tested several bits and milling tools, results showed that by combining the wireline miller with hydraulically provided weight on bit (WOB), it would be possible to mill out the retaining rings of the plug, which would cause the plug to collapse. The milling-control unit allows the WOB to be adjusted for each application and also controls the reactive torque—the force generated when the milling bit engages the plug. The service company was able to develop the solution within the client's parameters and in accordance with the timeline set out for this project. The offshore operation was completed in 3 days, to the operator's satisfaction. In another platform well, a permanent bridge plug had been set in 2003 in the sealbore between two screen sections [3-ft seal- bore, 67° well angle, 4.75-in. inner diameter (ID)]. The plug was set in order to isolate the somewhat higher water cut in the lower reservoir zone to prolong oil production from the well. In 2006, the well drowned after a 2-week-maintenance period. Two years later, a coiled-tubing (CT) gas lift operation was carried out with good results. It was then decided to remove the permanent bridge plug to reopen for production before another CT gas lift operation was carried out. A method for milling the permanent bridge plug was developed on the basis of lessons learned from the other plugmilling operation and by extensive testing at the service company's facilities. The operation was completed successfully in 13 days. This new application for milling completion hardware and other wellbore obstructions offers a cost-efficient alternative to existing methods. The success of the milling operation is a significant achievement and has pushed the limits for what is possible on electric wireline. This paper will examine two cases of milling bridge plugs on electric wireline and the technical challenges that had to be overcome in offshore operations.The first case used the well stroker as WOB, and the second cased used the well tractor as WOB.