SUBSEA MASTER VALVE FOR USE IN WELL TESTING

摘要

In accordance with illustrative embodiments of the present invention, a new and improved subsea test tree includes a hydraulically operable control unit and shut-in valve unit that are releasably latched together. The control unit includes an integral retainer valve system at the upper end thereof. The main shut-in valve, which is a ball valve, is a fail-close device under the influence of a spring and nitrogen pressure. Additional assistance in closing the valve may be provided if needed by hydraulic pressure applied to a surface control line. Internal pressure may be vented prior to unlatching the control unit in case of an emergency.