Perforating gun automatic release mechanism

Apparatus for disconnecting a perforating gun from a string of drill tubing, comprising:

• a housing member attached to said drilling string, said housing member having a bore with an internal annular groove, and a port in a sidewall of said housing member;
• a coupling member having a first end for attachment to said perforating gun and a second end for insertion into the bore of said housing member for connection thereto, said coupling member having a plurality of finger heads attached thereto and engageable with said annular groove for releasably attaching said coupling member to said housing member;
• an arming assembly held within said coupling member and actuable for causing a detonation;
• a first cylindrical piston sealed to and moveable between said arming assembly and said coupling member, said first piston being operative to move from a first position covering said port and maintaining said finger heads engaged with said annular groove, to a second position uncovering said port and allowing said finger heads to become released from said groove;
• a second cylindrical piston sealed to and moveable between said arming assembly and said coupling member, said second piston being responsive to said detonation for engaging said first piston and moving said first piston from said first position to said second position to thereby effect withdrawal of said coupling member from said housing member for disconnection therefrom.