High-pressure wellhead seal

Abstract

A tubing head, tubing head adapter and tubing hanger are sealed against annulus fluid or downhole pressure by an upper and a lower, pressure-energizing sealing assembly. The sealing assemblies are bi-directional, pressure-energizing and operate under working pressures of up to 30,000 psi. Each assembly consists of a metal seal ring made of highly elastic and ductile 316 stainless steel with a yield strength of approximately 30,000 psi, having a frustoconical shape, with the upper and lower tips of the cone enclosing an angle of approximately 28.degree. in the prestressed state. In the axial direction, the seal ring engages a support ring on one end and a tubing hanger shoulder at the other end, both of which form inclines of 30.degree. with the vertical (radial) plane. The support ring and the tubing hanger shoulders are made of materials having yield strengths of 50,000 psi and 75,000 psi, respectively. The preload applied to the seal assemblies is such that the seal ring plastically conforms to the harder surrounding surfaces and assumes a cone taper angle of 30.degree., in conformity with the mating support ring and tubing hanger shoulder. Thereafter, working pressure applied from either axial direction will be resolved along the incline of interacting surfaces into radial components which further enhance the sealing pressure along the inner and outer sealing surfaces. Because of this bidirectional pressure-enhancement, both seal assemblies may be tested through the application of test pressure from one common test port located between the two assemblies.