Methods and apparatus for disarming and arming explosive detonators

A well tool to be suspended in a well bore containing fluids at an elevated temperature and comprising:

• a body;
• an explosive device on said body;
• means for setting off said explosive device including an explosive detonator mounted on said body and having a hollow detonator shell and donor and receptor explosives arranged in opposite end portions of said hollow detonator shell;
• at least one barrier member comprised of a normally-solid fusible metal alloy arranged in the intermediate portion of said detonator shell for obstructing the detonation path of said donor explosive through said detonator shell to prevent detonation of said receptor explosive by said donor explosive so long as said fusible metal alloy has not been transformed to its liquified state by the heating from well bore fluids exterior of said detonator shell having elevated temperatures greater than the melting point of said fusible metal alloy;
• passage means in said detonator shell operable only upon the transformation of said fusible metal alloy to its said liquified state for removing the liquified fusible metal alloy from said intermediate portion of said detonator shell and thereby opening said detonation path through said detonator shell so that the detonation of said donor explosive will detonate said receptor explosive for setting off said explosive device;
• and
• means for detonating said explosive detonator to set off said explosive device after said fusible metal alloy in said barrier member has been transformed to its said liquified state and removed from said intermediate portion of said detonator shell.

An explosive detonator comprising:

• a hollow shell;
• a donor explosive in said hollow shell;
• and
• detonation barrier means in said hollow shell and including at least one barrier member comprised of a normally-solid fusible metal alloy and operative for attenuating the detonation forces produced by said donor explosive until said barrier member has been melted by an elevated temperature outside of said hollow shell greater than the predetermined melting point of said fusible metal alloy to allow the liquified fusible metal alloy to move away from the detonation path of said donor explosive.

An explosive detonator comprising:

• a hollow shell;
• a donor explosive in said hollow shell;
• a receptor explosive positioned in the detonation path of said donor explosive through said hollow shell and spatially disposed from said donor explosive for defining an enclosed space in said hollow shell between said donor and receptor explosives;
• an opening in said hollow shell communicating the exterior of said hollow shell with said enclosed space;
• detonation barrier means in said enclosed space including at least one barrier member comprised of a normally-solid fusible metal alloy and operative for attenuating the detonation forces produced by said donor explosive until said barrier member has been melted by an elevated temperature outside of said hollow shell greater than the melting point of said fusible metal alloy to allow the liquified fusible metal alloy to move out of said enclosed space through said opening;
• a reservoir on said hollow shell in communication with said opening for receiving said liquified fusible metal alloy moved out of said enclosed space;
• and
• means operatively arranged on said hollow shell for returning said liquified fusible metal alloy in said reservoir back into said enclosed space for disabling said detonator if it is still unfired before being returned to normal ambient temperatures.

A method for performing a well service operation with a well tool having an explosive device and an explosive detonator for selectively detonating said explosive device and having a donor explosive and a receptor explosive spatially disposed from one another and comprising the steps of:

• mounting a barrier comprised of a normally-solid fusible metal alloy between said donor and receptor explosives for deactivating said detonator until said fusible metal alloy is heated to its melting point;
• lowering said tool into a well bore containing well fluids at temperatures greater than said melting point for conducting a well service operation at a selected depth interval therein;
• postponing the detonation of said detonator for a sufficient length of time for said fusible metal alloy to melt;
• and
• selectively detonating said detonator for carrying out said well service operation at said selected depth interval after said barrier has been melted by the well fluids around said well tool.

A method for perforating a well bore with a perforating gun having an enclosed fluid-tight carrier carrying an explosive perforating device and a detonator having a donor explosive and a receptor explosive cooperatively arranged in the direction path of the donor explosive for setting off the explosive perforating device and comprising the steps of:

• measuring the temperature of the well bore fluids in at least one selected interval of said well bore;
• arranging a detonation barrier from a selected normally-solid fusible metal alloy having a predetermined melting point less than the temperature of the well bore fluids in said selected well bore interval;
• mounting said detonation barrier in said detonator for temporarily obstructing said detonation path between said donor and receptor explosives to reliably render said detonator ineffective for setting off said explosive perforating device so long as said selected fusible metal alloy remains in its normal solid state;
• and
• positioning said perforating gun in said selected well bore interval for heating said barrier to the predetermined melting point of said selected fusible metal alloy and liquefying said detonation barrier so that the liquified fusible metal alloy will be removed from said detonation path to prepare said detonator for setting off said explosive perforating device.