Patent ID: 6182775
Filing Date: 2001-02-06
Classification: E21B

Abstract:
A downhole jar apparatus for use in oil and gas wells, comprising:a) an elongated tool body having an upper end portion and a lower end portion, and a longitudinal flow bore that enables fluid to flow through the tool body from the upper end to the lower end;b) an upper piston mounted at the upper end portion of the tool body, movable between upper and lower positions and having a valve seat;c) a lower piston mounted below the upper piston, movable between upper and lower positions and having a valve seat;d) a first valving member for sealing the valve seat of the upper piston so that hydrostatic pressure can build up above the upper piston;e) a second valving member disposed in between the upper and lower piston and having a lower valving end portion that forms a seal with the lower piston valve seat, the second valving member being movable downwardly in the tool body bore responsive to a pressure increase above the upper piston;f) a trip mechanism for separating the second valving member from the lower piston valve seat when a predetermined pressure value is overcome;g) a return mechanism for returning the lower piston to its upper position when the trip mechanism separates the second valving member from the lower piston valve seat; andh) wherein the tool body has an anvil portion positioned above the lower piston for receiving force from the lower piston when it is returned to its upper position by the return mechanism.