Nested stack-down casing hanger system for subsea wellheads for annulus pressure monitoring

A wellhead system (52) for petroleum producing wells comprises a "stack-down" casing hanger configuration. In this stack-down system, the hanger for each successively smaller diameter casing string is landed or "nested" within the hanger for the next larger casing string. This approach allows the pack-off for each casing hanger to be retrieved independently, thus allowing fluid communication to be established with any of the casing annuli after all of the casing strings and hangers have been installed. Thus the pressure in each annulus may be monitored while the well is in production mode.