Subsea wellhead apparatus

摘要

There are disclosed two embodiments of subsea wellhead apparatus each of which includes a subsea wellhead housing installed at the ocean floor, a casing hanger connectable to the to the upper end of a casing string and supported in the bore of the housing to suspend the casing string in the well bore, and a tubing hanger connectable to the upper end of a tubing string and also supported within the housing bore above the casing hanger for suspending the tubing string within the casing string. A primary valve and a secondary backup valve are installed in series for controlling a passageway in the tubing hanger, and during the completion process, with an additional passageway in a Christmas tree which is installed on the head above the tubing hanger.