Firing head with metered delay

Apparatus operatively positionable within a subterranean well, the apparatus comprising:

• a piston assembly axially reciprocably disposed within a housing assembly having at least first and second inner diameters, the piston assembly sealingly engaging the first diameter when disposed therein, and the piston assembly being sealingly disengaged from the second diameter when disposed therein;
• a weight attached to the piston assembly and forcing the piston assembly from within the first diameter, to within the second diameter of the housing assembly;
• and
• the piston assembly including a metering device regulating displacement of the piston assembly relative to the housing assembly when the piston assembly is within the first diameter.

A firing head for use in conjunction with an explosive device operatively positioned within a subterranean wellbore, the explosive device including a detonation receiver, the firing head comprising:

• a weight;
• a housing assembly having a detonator disposed therein, the housing assembly being configured for cooperative engagement with the explosive device within the wellbore, and the detonator being capable of detonating and thereby causing detonation of the detonation receiver;
• and
• a delay mechanism responsive to the weight to thereby regulate displacement of the weight relative to the housing assembly, the delay mechanism including a piston attached to the weight, a fluid chamber and a fluid metering device, the metering device restricting flow of fluid from the chamber.

A method of detonating an explosive device within a subterranean well, the method comprising the steps of:

• positioning the explosive device within the well;
• providing a firing head including a weight and a delay mechanism responsive to the weight, the delay mechanism including a piston attached to the weight, the piston being sealingly received within a fluid chamber, and a metering device for regulating fluid flow from the chamber;
• and
• then engaging the firing head with the explosive device within the well.