Firing head for a tubing-conveyed perforating gun and method of perforating

摘要

A firing head for actuating a tubing conveyed perforating gun, comprising a housing (20); an actuation mechanism (22) within said housing, said actuation mechanism comprising an actuation piston (30), a first firing piston (48), a second firing piston (62) and retaining means (36), said actuation piston being moveable from a first position in response to force applied generally along the longitudinal axis of said firing head, said first firing piston being in coaxial relation to said actuation piston and being moveable from a first position to a second position, said first firing piston being retained in said first position when said actuation piston is in its respective said first position, said second firing piston being in coaxial relation to said first firing piston and being moveable from a first position to a second position, and said means for releasably retaining said second piston in said first position being releasable in response to hydraulic pressure; said firing head also including an initiator (82) responsive to movement of said first or second firing piston to cause detonation of said perforating gun.