In October 2010 the deepest set sealed multilateral junction in the industry was installed at 6900 m MD in Oseberg South well 30/9-F-9 AY1/Y2.
The differential pressure across the junction in the well is expected to be in the range of 250 bars. To meet this pressure requirement, a multilateral (ML) junction rated to 370 bars was identified. The high pressure junction components and entire multilateral system has undergone an extensive testing and qualification program, including several component tests and a full scale system interface and integration test.
A 10 ¾″ pre-cut window with an outer aluminium tube was installed as an integral part of the 10 ¾″ liner. The plan was to perform the milling operation through this window. A stuck string incident during the 10 ¾″ liner installations accidentally caused the liner to drop in hole. The liner ended up at the wrong orientation, and the window could consequently not be used.
The mainbore was drilled to TD at 8583 m MD and the 7″ liner was run and cemented. After the liner perforation the MLT operations started with the installation of a multilateral anchor packer to allow for installation of a latch interface assembly (LIA) and milling system. The LIA was installed and locked into the multilateral packer on a separate run.
The milling operation was done in a two step operation with milling of a 1st pass window using a 10 ¾″ milling machine prior to installation of whipstock and performing the 2nd pass milling operation.
The lateral branch was drilled to TD at 8258 m MD and a 5 ½″ screen completion was run and dropped off into the 8 ½″ open hole. The drilling whipstock was retrieved from the well and a completion deflector was installed. The junction was finally stung into the deflector, simultaneously as an open hole seal stinger entered top of the screen liner in open hole, tying the branches together.
A 6900 m long upper completion string with inflow control valves was finally installed to allow for surface control of the two branches.