Magnus: Utilization of Conductor Sharing Wellhead Technology To Access Additional Hydrocarbons With a Slot-Constrained Platform


The Magnus platform, UK northern North Sea, has been producing since 1983 with all 20 original slots now occupied. Additional infill and extend-reach-drilling (ERD) production targets were identified and a means of access was required while maintaining base field production. Platform modification was selected because of significant commercial advantage over alternative developments. The Magnus jacket was modified to permit running of four additional large conductors into which two smaller casings could be installed respectively.

A tapered jacket profile necessitated preinstalled conductor guide frames to build to 4° inclination at seabed, requiring initial use of the large conductor as a conduit for drilling assemblies. Custom-manufactured and specialist equipment was designed and procured to enable successful underreaming to 54 in. and installation of 46-in. conductor. Drilling-assembly design and initial pilot-hole profile were deemed critical to subsequent success in running rigid open-ended 46-in. conductor. Well-critical structural cement was pumped to seabed by use of a 16-in. inflatable packer and inner string. Unguided installation of two 18 5/8-in. casing strings inside 46-in. conductor was then achieved. The 18 5/8-in. casing strings were cemented in place using light cement to preserve (shallow) casing-shoe integrity. High-resolution multishot gyro surveys and a newly developed “gamma-wipe” survey technique were used to obtain critical 18 5/8-in. relative-shoe-orientation information before subsequent kickoff.

Two wells were batch set successfully to the 13 3/8-in. casing shoe by means of one conductor. Modification of existing wellhead technology for close proximity has proved successful. Access to additional Magnus resources by means of an otherwise full template has been delivered by this conductor-sharing-wellhead (CSW) technology.