Abstract: The method and apparatus for actuating a perforating gun by pressure includes a pressure actuated gun firing head disposed on the perforating gun for detonating the shaped charges of the gun. The gun is attached to a pipe string and located downhole adjacent the formation to be perforated. The pressure actuated firing head includes a housing with a plug and piston. The piston has a firing pin adapted for engagement with the initiator of a perforating gun upon reciprocation within the housing. Initially, the piston is pressure balanced until the time of actuation. The plug is responsive to fluid pressure of a predetermined magnitude at the time of the actuation of the gun firing head. Upon effecting pressure on the plug, the plug unbalances the piston causing the piston to reciprocate. Upon reciprocation of the piston, the firing pin engages the initiator to detonate the shaped charges of the perforating gun. Pressure may be effected on the firing head through the pipe string, or the annulus, or both.

Abstract: An apparatus for actuating a tool downhole in a borehole. The apparatus includes a body; a port to admit fluid pressure into the body; and apparatus within the body in fluid pressure communication with the port for actuating the tool in response to (1) a fluid pressure level communicated through the port in excess of a first fluid pressure level greater than the hydrostatic pressure level, followed by (2) a decrease in the fluid pressure level communicated through the port from the first fluid pressure level to a second fluid pressure level less than the first fluid pressure level.