Hydraulic pressure assisted casing tensioning system

摘要

A tensioning system for a tieback string of casing between a subsea wellhead and a surface wellhead employs hydraulic pressure. A mandrel is connected into the tieback string. A casing hanger mounts to the mandrel and an internal gripping member between the casing hanger and the mandrel allows upward movement of the mandrel relative to the casing hanger but prevents downward movement. The operator lowers the string into the well with the casing hanger in an extended upward position and secures the tieback. The operator then closes the blowout preventer and applies hydraulic pressure in the annulus below the blowout preventer. Seals seal the casing hanger to the surface wellhead and also seal the inner diameter of the casing hanger to the running conduit. The hydraulic pressure forces the casing hanger down onto an internal landing shoulder in the surface wellhead.