Metal-to-metal annulus packoff

An all-metal, well annulus packoff assembly 10 for establishing a metal-to-metal seal between a wellhead housing 12 and a casing hanger 14, includes an annular metallic seal element 16 having a generally upstanding U-shaped cross section. An inner tubular portion 34 of the seal element 16 includes sealing ridges 42 for co-operation with a tapered surface 44 of the hanger 14 and an outer lip portion 36 of the seal element 16 includes sealing ridges 46 for co-operation with the wellhead housing 12. The seal element is energized by a mandrel 18 which carries an axially slidable locking mandrel 28. An outwardly biassed locking ring 24 is forced into a groove 84 on the hanger 14 by the locking mandrel 28 to secure the seal element 16 to the hanger 14. A further locking ring 26 may be forced into a groove 76 in the housing 12 by the locking mandrel 28 to secure the hanger 14 and packoff assembly 10 against upward movement.