Abstract: In the representative embodiments of the several methods and apparatus of the invention, a barrier formed of a low-temperature fusible metal alloy having a selected melting point is arranged between a receptor explosive and a typical electrically-initiated detonator enclosed in an explosion-proof housing for blocking the transmission of detonation forces from the detonator to the receptor explosive until the detonator has been subjected to well bore temperatures which are greater than the melting point of the fusible alloy. By selecting a fusible metal alloy which has a melting point less than the known temperatures of the well bore fluids, when the tool is exposed to those elevated temperatures, the barrier will be predictably transformed to its liquid state thereby allowing the liquid alloy to flow to a non-blocking position away from the detonation path of the donor explosive.

Abstract: In the representative embodiments of the several methods and apparatus of the invention, a barrier formed of a low-temperature fusible metal alloy having a selected melting point greater than the anticipated well bore temperatures is arranged between a receptor explosive and a typical electrically-initiated detonator enclosed in a housing for blocking the transmission of detonation forces from the detonator to the receptor explosive until the barrier has been heated by an electrical heater adjacent to the barrier. By selecting a fusible metal alloy which has a melting point higher than the known temperatures of the well bore fluids, when the tool is exposed to those elevated temperatures, the barrier will be predictably maintained in its solid state to continue blocking the detonation path of the donor explosive if the heater fails thereby allowing the well tool carrying the explosives to be safely recovered from the well bore.

Abstract: In the representative embodiments of the several methods and apparatus of the invention disclosed herein, a movable detonating member is arranged to be selectively impelled against an impact-responsive detonator on a well bore perforator having one or more explosive devices. The movable detonating member is initially restrained from moving in relation of the tool body by a heat-responsive material which, in one embodiment, is operative to release the detonating member when an electrical heater on the tool is initiated from the surface for melting the bonding material or, in another embodiment, releases the detonating member when the material melted by elevated well bore temperatures.