Hydraulically activated firing head for well perforating guns

Abstract

A separable fluid pressure activated firing mehanism for a perforating gun comprises a pressure-operated tubing valve, a packer, and a tubular housing assembly defining a plurality of fluid pressure chambers therein. The first chamber contains a light density, clean, compressible fluid which is subject to well annulus pressure above the packer to provide a reference pressure. A second chamber sealably mounts a piston-type firing pin, which is normally secured by a locked latch in an elevated position above a detonatable primer and the lower portion of said firing pin is exposed to the reference pressure. The latch is unlocked through the application of a predetermined annulus pressure above the packer to a locking piston which moves to unlock the latch and trap the reference pressure in the first chamber. A further increase in said annulus pressure opens the tubing valve. A still further increase in said annulus pressure releases the firing pin from the latch and drives the firing pin downwardly to detonate the primer. Additional features of the disclosure are the provision of a cross-over tool between the packer and the tubular housing assembly to permit underbalance perforating, the provision of a detachable connection between the cross-over tool and the packer, and the provision of a shiftable sleeve valve effecting the closing of a connection from the packer bore to the annulus upon disconnection of the packer from the cross-over tool.