Downhole severing tool

Abstract

The pipe cutting capacity of a explosive pipe cutter may be improved by mixing the explosive material with powdered metal to increase the explosive gas density or directing colliding shock fronts from opposite axial directions against a disc of metal having a shock impedance substantially corresponding to the shock impedance capacity of the explosive material

1 . An explosive cutting system comprising:
 A substantially cylindrical column of explosive/metal mixture including high explosive material mixed with one or more powdered metals, the explosive/metal mixture having a density greater than the high explosive material alone;   an explosive detonator at opposite ends of said column; and   means to initiate said detonators substantially simultaneously.   
     
     
         2 . An explosive cutting system as described by  claim 1  wherein said cylindrical column comprises a plurality of contiguously aligned pellets of explosive/metal mixture 
     
     
         3 . An explosive cutting system as described by  claim 1  wherein said high explosive material is selected from the group comprising HMX, RDX, HNS, PYX, TATB and PETN. 
     
     
         4 . An explosive cutting system as described by  claim 1  wherein said metal is selected from the group comprising aluminum, copper, lead, tin, bismuth, tungsten, iron, lithium, sulfur, tantalum, zirconium, boron, niobium, titanium, cesium, zinc, magnesium, selenium, tellurium, manganese, nickel, molybdenum, and palladium. 
     
     
         5 . An explosive cutting system comprising:
 A substantially cylindrical column comprising a coaxial alignment of at least one metallic disc contiguously between adjacent cylinders of high explosive material, the shock impedance of said disc or discs being substantially the same as the shock impedance of said explosive;   an explosive detonator at opposite ends of said column; and   means to initiate said detonators substantially simultaneously.   
     
     
         6 . An explosive cutting system as described by  claim 5  wherein said column comprises a plurality of contiguously aligned pellets of high explosive material. 
     
     
         7 . An explosive cutting system as described by  claim 5  wherein said high explosive material is selected from the group comprising HMX, RDX, HNS, PYX, TATB and PETN. 
     
     
         8 . An explosive cutting system as described by  claim 5  wherein said metallic disc or discs comprises an integral compression of powdered material selected from the group comprising aluminum, copper, lead, tin, bismuth, tungsten, iron, lithium, sulfur, tantalum, zirconium, boron, niobium, titanium, cesium, zinc, magnesium, selenium, tellurium, manganese, nickel, molybdenum, and palladium. 
     
     
         9 . A method of cutting pipe structures comprising the steps of substantially simultaneously detonating a column of explosive material to generate a pair of explosions for propagating a pair of colliding shock fronts transmitted along a substantially common axis to cause a radial expansion of explosion gas within a plane substantially normal to said axis wherein said explosion gas is a mixture of high explosive gas and fluidized metal, with said explosion gas having an explosive density greater than the explosive density of said high explosive gas independent of said metal. 
     
     
         10 . A method of cutting pipe structures as describe by  claim 9  wherein said explosive material is pressed into discs that are aligned face-to-face along said axis in a column that is detonated substantially simultaneously at opposite ends thereof to generate said pair of colliding shock fronts. 
     
     
         11 . A method of cutting pipe structures as described by  claim 9  wherein high explosive and powdered metal are mixed to form said explosive material with an explosive density greater than the explosive density of said high explosive gas independent of said metal. 
     
     
         12 . A method of cutting pipe structures as described by  claim 9  wherein said column of explosive material is positioned contiguously adjacent opposite faces of said metallic disc or discs, said explosive material and said disc having substantially the same shock impedance. 
     
     
         13 . A method of cutting pipe structures as described by  claim 9  wherein said metal comprises an element selected from the group comprising aluminum, copper, lead, tin, bismuth, tungsten, iron, lithium, sulfur, tantalum, zirconium, boron, niobium, titanium, cesium, zinc, magnesium, selenium, tellurium, manganese, nickel, molybdenum, and palladium. 
     
     
         14 . A method of cutting pipe structures as described by  claim 9  wherein said explosive material comprises material selected from the group comprising HMX, RDX, HNS, PYX, TATB and PETN. 
     
     
         15 . A method of cutting pipe structures as described by  claim 9  wherein said column of explosive material is substantially simultaneously detonated by detonating cords of prescribed length. 
     
     
         16 . A method of cutting pipe structures as described by  claim 9  wherein opposite ends of said column of explosive material are substantially simultaneously detonated by one or more detonators selected from the group comprising EBWs, EFIs, SCBs and hot-wire initiators.