AOG

Clamping Unseated Wellheads for Life Extension – Nicholas Pacewicz, General Manager, Aberdeen

11th March 2020 – 11:15 am  ⋅  Perth, Australia

Operators worldwide are looking to extend life of increasing numbers of older wells. Some wells use non-rigid lockdown wellheads, where the wellhead housings are held in place using a lock ring, with some relative movement between the housings under load. These wellheads can be prone to integrity issues as they age. If the lock ring fails, the HP housing may become unseated from thermal well loads or bending imparted by a connected riser. This reduces the wellhead’s strength and residual fatigue resistance.

Chevron have observed multiple instances of the HP housing unseating in their Captain B development, in the Outer Moray Firth, UKCS, likely caused by casing thermal growth during hot injection operations. In some instances, only the retainer ring is holding the HP housing in place, causing significant fatigue accumulation at the HP housing weld. In others, the retainer ring has failed entirely and the HP housing has moved upwards.

This paper presents the process by which a custom clamp has been designed by Chevron in coordination with 2H Offshore, to reposition the HP housing relative to the LP housing; the device is designed to exert a specified downwards force to overcome the combined thermal and bending loads it will experience. The design is segmental to allow installation by divers whilst the subsea tree remains in place. This solution is applicable to other older wellheads with lockdown integrity issues to allow safe future workover and decommissioning.

More information: AOG 2020

Clamping Unseated Wellheads for Life Extension – Nicholas Pacewicz, General Manager, Aberdeen

11th March 2020 – 11:15 am  ⋅  Perth, Australia

Operators worldwide are looking to extend life of increasing numbers of older wells. Some wells use non-rigid lockdown wellheads, where the wellhead housings are held in place using a lock ring, with some relative movement between the housings under load. These wellheads can be prone to integrity issues as they age. If the lock ring fails, the HP housing may become unseated from thermal well loads or bending imparted by a connected riser. This reduces the wellhead’s strength and residual fatigue resistance.

Chevron have observed multiple instances of the HP housing unseating in their Captain B development, in the Outer Moray Firth, UKCS, likely caused by casing thermal growth during hot injection operations. In some instances, only the retainer ring is holding the HP housing in place, causing significant fatigue accumulation at the HP housing weld. In others, the retainer ring has failed entirely and the HP housing has moved upwards.

This paper presents the process by which a custom clamp has been designed by Chevron in coordination with 2H Offshore, to reposition the HP housing relative to the LP housing; the device is designed to exert a specified downwards force to overcome the combined thermal and bending loads it will experience. The design is segmental to allow installation by divers whilst the subsea tree remains in place. This solution is applicable to other older wellheads with lockdown integrity issues to allow safe future workover and decommissioning.

More information: AOG 2020