A North Sea operator's well design required 9⅝-in casing to surface with metal-to-metal connections throughout. Wellbore instability was a common occurrence in the field, and the 3,604-m [11,824-ft] interval included 728 m [2,388 ft] of open hole that was likely to hinder access. Long, heavy casing strings require extremely high torque to rotate, making it difficult to ream with casing and increasing the likelihood of multiple attempts—interspersed with wiper trips—to run the casing string to depth.
To minimize rig time and optimize costs, the alternative was to install a shorter, lighter liner across the unstable openhole section and tie it back to the wellhead with a separate tieback string. However, conventional liner equipment does not provide the metal-to-metal, gas-tight connection required.
SLB proposed a liner system with a setting adapter and a metal-to-metal, gas-tight liner tieback system. This full-axial-load-bearing, V0 ISO 14310–certified system connects a liner to a tieback string of casing with a permanent, durable seal.
The proprietary technology enabled the operator to run the lower part of the casing as a liner on drillpipe, with all the advantages of push, pull, rotation, and circulation to address borehole restrictions and reach TD in one run. Subsequently, the tieback string was run in hole with the liner tieback system stinger on the bottom. The stinger was expanded into the tieback system receptacle at the top of the liner, achieving the required V0-rated, metal-to-metal downhole casing connection integrity.
Compared with running a long casing string to depth and assuming at least one wiper trip to recondition the hole during the process, the innovative SLB system saved an estimated 5 days of rig time. The operator plans to use this system on other wells in the field.
