After a 13 3/8-in. expandable liner collapsed in a Gulf of Mexico ultradeepwater well, an operator considered a whipstock sidetrack, exiting as deep as possible to finish drilling and completion operations. Exiting the 16-in. casing, industry standards would have called for redrilling and casing an entire hole section. Exiting the expandable liner was an alternative option, but would require a unique solution to operate in the larger internal diameter (ID) and maintain the existing hole size. The service provider created a fit-for-purpose solution to install a casing window in the 13.77-in. ID expandable liner. The standard casing exit system accommodates 13 3/8-in. casing through 14-in. casing and requires minimal modifications to anchor the actual concave assembly to support a 12.25-in. pilot window. Additional mill runs would then open the 12.25-in. pilot window to a full bore 13 1/2-in. outside diameter (OD) window. Despite never having performed an installation in this size of expandable liner, the provider had a run history for exits with similar modifications and extra trips to enlarge and elongate windows. Job challenges included thin-wall, channeled cement; limited flow rates because of liner pressure limits; equipment availability; and a short lead time. The 11 1/2-in. OD assembly was quickly modified to enable the anchor engagement in the 13.77-in. ID liner. Within days the mills were dressed to the custom ODs required to enlarge the 12.25-in. pilot window to 13.50-in. On the first run, the whipstock was hydraulically set in the liner. Kickoff was achieved at 19,609-ft to cut a 27.5-ft window and ream a 45-ft rathole in 22 hours. The second bottom hole assembly (BHA) consisted of three mills with 12 1/2-in., 12 3/4-in., and 13-in. ODs. Milling and reaming took 6 hours. The third and final BHA to open the window to a 13 1/2-in. OD consisted of a 13 1/4-in. OD mill and two full-drift mills above. Milling and reaming with this BHA took 29 hours before coming back in with a motor assembly to drill ahead. This installation is the first sidetrack conducted with a whipstock in a 13 3/8-in. expandable. This paper will show that it is possible to safely and reliably install a casing exit system in difficult applications, such as deep expandable liners, that might previously have been considered unfeasible. This approach provides an opportunity for the industry to significantly reduce non-productive time in such scenarios.
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