Valve for well testing and sampling string - has closure bias increased by annulus pressure and is operable by increasing annulus press

摘要

A valve for use in a well testing tool is arranged to be exposed to the pressures interiorly and exteriorly of the tool and while these pressures are equal assumes an open position in which it allows the exterior pressure to act to increase the bias applied to an actuator, e.g. a test valve actuator, in the tool. Upon setting a packer below the tool and increasing the pressure exteriorly thereof, the valve assumes a closed position in which further increases in exterior pressure are not effective to increase the bias applied to the actuator but are effective to displace the actuator against the existing bias, e.g. to open the test valve.