Subsea wellhead system and method for drilling shallow water flow formations

摘要

A shallow water flow subsea drilling system is disclosed. A wellhead system is provided with a 36'' conductor pipe in which a 26'' casing and 26'' wellhead housing are landed. The 26'' casing extends to a depth above a shallow water flow zone. A borehole through the shallow water flow zone is sized to accept a 20'' casing to the top of which is secured an 18¾'' wellhead housing. An annulus between the 26'' and 18¾'' housings communicates with cement returns from the 20'' casing. Flow-by holes in the 26'' wellhead housing are sealed with a retrievable seal assembly and actuating mechanism run on the same running tool with the 20'' casing and 18¾'' wellhead housing. A hydraulic feedback mechanism is provided to sense at the service vessel whether or not the seal assembly has been correctly positioned in the annulus. The seal assembly is pressure tested in the same trip while in its pack-off condition and can be retrieved with a second running tool trip.