Abstract: A pressure compensated plug for use with subsea trees is described in which a reservoir of compressible fluid is located from a cavity within a horizontal tree (10) whereby allowing temperature induced volume changes to be absorbed by the compressible fluid without resulting in significant increase in pressure. This is achieved by providing a pressure compensation apparatus (80) in the cavity, the apparatus comprising a housing (82) with a floating piston (86) in a chamber (84). The lower face (96) of the chamber is exposed to compressible fluid in the form of an inert gas, such as nitrogen, which is pre-charged at the surface to the appropriate hydrostatic pressure of the seabed. The volume of gas trapped between the lower piston face and the lower face of the cylinder forms the gas reservoir (94). A compensation cylinder can be attached to the upper section of the lower plug (70) and run and retrieved at the same time as the plug, thereby reducing the number of intervention runs.

Abstract: A dual bore completion sub-sea test tree (10) is described which has main bore (18) and an auxiliary or annulus bore (20). Two identical ball valves (22, 24) are located in series within the main bore (18) and two smaller identical ball valves (26, 28) are located in series in the annulus bore (20). The ball valves (22, 24, 26, 28) are operated by respective independent control lines acting on the operating mechanisms of the respective valves within the test tree (10) to move the valves between open and closed positions to allow or deny communication through the respective bores (18, 20). The completion sub-sea test tree (10) provides isolation of the main bore (18) and/or the annulus bore (20) when required by application of hydraulic pressure to assist closure to spring forces sufficient to cut coil tubing in the event of an emergency situation requiring rapid disconnect.

Abstract: Apparatus and method of isolating a well to allow intervention equipment to be installed in the upper section of tubing and surface equipment to be tested prior to running in the well is described which enables a surface test tree to be leak-off tested on a regular basis and enables the SSTT valves to be pressure tested before opening and after relatch. This is achieved by providing a completion lubricator valve comprising a fail open valve (18) located above a conventional downhole safety valve (20), the fail open valve (18) being closable by the application of hydraulic closure pressure (42) to allow a pressure differential to be supported from above. The valves (18, 20) are flapper valves and are spring-biased to open or closed positions as necessary. This allows the intervention equipment to be installed in the upper section of the tubing and the surface equipment to be tested prior to running in the well and enables the injection head to be installed immediately upon the production tree.

Abstract: After the drilling of an oil well bore there is normally carried out testing using a test tool string. Following completion of the test, the test tools must be shut down, and the test string removed. It is an advantage if the string incorporate some means of isolating the upper portion of the its tubing, and of subsequently providing a communication route between this tubing and the annulus, so that tubing-contained well liquid above the test string can be circulated out of the tubing before it is raised to the surface. Previous apparatus suggested for this purpose performs quite satisfactorily, but commonly is a "one-off" system; once activated, the several operations resulting therefrom are irreversible, and the tool cannot easily be put back into the initial state.

Abstract: A well testing system is described which comprises a ball valve (10) having a plurality of fluid lines coupled thereto (20a, 20b, 20c). The ball valve (10) is located between a process fluid flow line (16) and a vent line (18) with each fluid line (20a, 20b, 20c) being coupled to a respective piece of well-test equipment rated at a certain pressure value. Pressure relief means (22a, 22b, 22c) are located in each fluid line (20a, 20b, 20c) between the piece of equipment and said ball valve (10) and each pressure relief means (22a, 22b, 22c) is operable when the in-line fluid pressure exceeds a predetermined value to pass said fluid to said ball valve (10).

Abstract: A pressure relief valve includes an apertured ball valve element which is spring loaded and is rotatably and axially mounted in the valve bore so that when an over pressure situation arises fluid forces the ball axially off the valve seat against the force of a spring and causes the ball valve to rotate such that the aperture in the ball valve connects the inlet bore and outlet bore of the valve housing so that fluid can flow through the pressure relief valve. When pressure at the inlet falls beneath a predetermined value, the spring forces the ball to rotate and move back against the valve seat, thus closing the valve. With this arrangement there is minimal pressure exerted on the valve housing and the valve will operate with a back pressure up to 50% of the inlet pressure. This means that much smaller bore outlet piping can be used with a savings in weight and, consequently, cost.