A cup tool for use with a mandrel of a wellhead isolation tool has a substantially
right-angled stepped shoulder over which an elastomeric sealing element is forced
by elevated fluid pressures. A top end of the elastomeric sealing element is inhibited
from extrusion past the stepped shoulder during the insertion of the mandrel, thereby
reducing the risk of damaging the sealing element before the mandrel is fully inserted
through the wellhead. Once the sealing element is exposed to elevated fluid pressures,
the top end of the elastomeric sealing element is forced upwardly over the stepped
shoulder, and extruded into an annulus between the mandrel and a well casing or
production tubing to provide a high-pressure fluid seal.
