Patent ID: 7293614

Claim:
A hydraulic jarring tool for suspending in a well from a wireline or tubular string or drill string to release a tool stuck in the well, or for positioning along a drill string to release the drill string stuck in the well, the jarring tool comprising: an upper jarring section including an upper housing supported on one of the wireline, the tubular string or the drill string; an upper piston axially movable within the upper housing when tension is applied to the wireline, the tubular string or the drill string; an upper biasing member for biasing the upper piston in a selected axial direction; an upper fluid metering device for metering fluid within the upper housing axially past the upper piston; an upper release mechanism for holding an upper hammer in an initial position and releasing the upper hammer to strike an upper anvil in response to movement of the upper piston to produce an axial jarring force; a lower jarring section including a lower housing supported on the one of the wireline, the tubular string or the drill string below the upper jarring section; a lower piston axially movable within the lower housing when tension is applied to the wireline, the tubular string or the drill string; a lower biasing member for biasing the lower piston in a selected axial direction; a lower fluid metering device for metering fluid within the lower housing axially past the lower piston; a lower release mechanism for holding a lower hammer in an initial position and releasing the lower hammer to strike a lower anvil in response to movement of the lower piston to produce an axial jarring force in the same direction as the force produced by the upper release mechanism; a timing mechanism for releasing one of the upper and lower hammers subsequent to releasing the other of the upper and lower hammers, thereby resulting in a timed delay between the impact of one hammer striking the respective anvil and an impact of the other hammer striking the respective anvil; and a selector switch for selecting a number of times fluid is metered past one of the upper and lower pistons prior to increasing flow past the respective metering device and thereby reducing metering time.