An apparatus for retaining fluid in a pipe includes an elongated body adapted to be positioned within a sub sea wellhead assembly. The elongated body has an end adapted for connection to the pipe, a flow passage for fluid communication with the pipe, and an outer surface for engagement with a sealing member in the sub sea wellhead assembly. A first chamber is defined within the elongated body and connected to receive pressure from above the sub sea wellhead assembly. A second chamber is defined within the elongated body and connected to receive pressure from below the sub sea wellhead assembly. A valve is supported in the elongated body for movement in response to pressure differential between the first and the second chambers. The valve is movable between an open position to permit fluid flow through the flow passage and a closed position to prevent fluid flow through the flow passage.Typically, the safety shut-in system includes a subsea test tree which is landed inside the blowout preventer stack on a pipe string. The subsea test tree generally includes a valve portion which has one or more normally closed valves that can automatically shut-in the well. The subsea test tree also includes a latch portion which enables the portion of the pipe string above the subsea test tree to be disconnected from the subsea test tree. The subsea test tree may be used in conjunction with a retainer valve and a bleed-off valve. The retainer valve is commonly arranged in the pipe string to prevent fluid from being dumped from the pipe string into the riser when the pipe string is disconnected from the valve portion. The bleed-off valve allows controlled venting of pressure that may be trapped between the closed retainer valve and the closed valve portion of the subsea test tree. Generally, the subsea test tree, the retainer valve, and the bleed-off valve are controlled by fluid pressure in control lines which extend from a pressure source on the vessel to the subsea test tree, the retainer valve, and the bleed-off valve.
The retainer valve may be a normally-open or fail-safe-open retainer valve or may be a normally-closed or fail-safe-close retainer valve. When pressure is lost in the control line connected to the retainer valve, a fail-safe-open retainer valve defaults to the open position while a fail-safe-close retainer valve defaults to the closed position. For a fail-safe-close retainer, if the retainer- valve control line is inoperable, e.G., if the retainer- valve control line is inadvertently severed, the fail-safe-close retainer valve remains closed. However, it may be necessary to re-open the retainer valve to permit other operations to be carried out on the well, e.G., kill the well or retrieve a portion of a tubing or wire line which was severed when the retainer valve was closed. Thus, it would be desirable to provide a secondary means through which the retainer valve can be opened if the retainer- valve control line is inoperable.
