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.
In October 2010, the deepest-set sealed multilateral (ML) junction in the industry was installed at 6900-m measured depth (MD) in Oseberg South Well 30/9-F-9 AY1/Y2. The differential pressure across the junction in the well was expected to be in the range of 250 bar. To meet this pressure requirement, a junction system rated to 370 bar was identified. The high-pressure junction components and entire multilateral system have undergone an extensive testing and qualification program, including several component tests and a full-scale system interface and integration test.A 10 3 =4-in. precut window was installed as an integral part of the 10 3 =4-in. liner. The plan was to perform the milling operation through this window. A stuck-string incident during the 10 3 =4-in. liner installation accidentally caused the liner to drop in the hole. The liner ended up at the wrong orientation, and the window could consequently not be used.The main bore was drilled to total depth (TD) at 8583-m MD, and the 7-in. liner was run and cemented. After the liner perforation, the BL operations started with the installation of an anchor packer and a latch interface assembly (LIA). The milling operation was performed in a two-step operation with milling of a first-pass window by use of a downhole milling machine before installing a whipstock and performing the second-pass milling operation.The lateral branch was drilled to TD at 8258-m MD, and a 5 1 =2in. screen completion was run and dropped off into the 8 1 =2-in. open hole. The junction was finally stung into a completion deflector, simultaneously with an openhole seal stinger entering the top of the screen liner in the open hole, tying the branches together. A 6900-m upper completion string with inflow control valves was finally installed to allow for surface control of the two branches.Despite severe drilling problems in the transport sections of the well, the ML operations were deemed successful. Major risk and challenges with this well design involved orientation of the 10 3 =4-in. liner (to position the premilled window) at this depth, debris management after milling operations, and general depth control during junction construction. Debris management in particular became essential as the backup ML solution meant milling steel rather than aluminum.Although the two different reservoirs could be drained by two conventional extended-reach-drilling (ERD) wells, this would be a less cost-efficient solution. Furthermore, the construction of an ML well means that the aforementioned challenges drilling the transport sections had to be handled only once. The successful installation at this depth has proved that ML technology is feasible for use in ERD wells, either to improve the total reservoir exposure or to reach multiple targets from one well.
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