Tie-back connection apparatus and method

Abstract

A tie-back connection apparatus effects a metal-to-metal type seal between a riser run from an overhead vessel and a subsea well casing suspended from a casing hanger in a subsea wellhead member. The apparatus includes a tubular mandrel connected to and run by the riser into the wellhead. A metal-to-metal type annular seal ring, mounted at the lower end of the mandrel, is landed upon the casing hanger, with the end of the mandrel in coaxial alignment with the casing hanger. The seal ring effects a seal between the riser and the casing when compressive force is applied to the seal ring. A seal activating mechanism, operated by a tool run from the vessel, engages the casing hanger and applies the compressive force to effect the seal. The seal activating mechanism includes three locking collets, a reaction sleeve, and a drive sleeve. One collet engages the casing hanger. The tool first rotates the drive sleeve to move the reaction sleeve upwardly to maintain the first collet in engagement with the casing hanger and to engage the second locking collet. Thereafter, hydraulic force is applied to the reaction sleeve via the second collet to urge the mandrel downwardly against the casing hanger via the third collet to apply the compressive force to the seal. Thereafter, the drive sleeve is rotated against the mandrel to maintain the compressive force and allow the hydraulic force to be released and the operating tool removed. A method is also provided for effecting a metal-to-metal type seal between the riser and the casing.