GB837900A - Well perforator - Google Patents

Abstract

837,900. Blasting cartridges. DRESSER INDUSTRIES Inc. Feb. 1, 1957 [Feb. 1, 1956], No. 3630/57. Class 9(1) Apparatus housing hollow charges for perforating well casings and earth formations surrounding well bores is provided with means for preventing the escape of the slug formed by collapse of the metal liner of each charge after firing of the charge. The apparatus comprises a thickwalled steel tube 10 closed at the base by a tapered plug 11 and at the top by a cable head 12 and sleeve 13. A cable 16, through which extends an insulated electrical conductor 17, is anchored in the head 12 and serves to lower the apparatus into the well. The conductor 17 is connected by a conductor 18 to an electric detonator 20 housed in a sleeve 21, which is crimped over one end of a detonator fuze cord 24 and is supported by a diaphragm 23. The hollow charge units 30 are aligned with ports 25 in the tube 10, the ports being staggered around the tube e.g. the ports may lie along a helix. Each unit 30 has a cylindrical boss 33 which enters a recess 32 in the tube 10 and is held in alignment with the port 25 by a retainer 35, which engages a port seal 28. The retainer 35 is frusto-conical and has thickened ends 36, 37, the intermediate portion 39 being of flexible resilient material such as rubber or neoprene. Fuze cord 24 is threaded through a bore 63 in the boss 33 and is preferably a P.E.T.N. reinforced Primacord, while the hollow charge 45 is preferably high explosive in cast, pressed or pellet form, e.g. R.D.X. The liner 57 may be aluminium or steel but copper is preferred, while the charge housing 46 may be of metal or synthetic plastic material. The metal port seal 28 has an axial passage 65 closed at the outer end until the charge is fired. The closure 66 is then pierced by the gas jet, but the passage is too narrow to allow the subsequent escape of the slug and debris from the housing 46. In Fig. 3 escape of the slug is prevented by a member 69 which is hemispherical and has a gas-escape passage 65a coaxial with the liner 57. The member 69 is preferably made of steel. In a further modification the tube 10 has, instead of the ports 25, apertures to allow the passage of the perforating jets but of too small diameter to let the slugs pass. The apertures are counter-bored at the outer surface of the tube 10 to form seats for fluid seals. A further modification, Fig. 5, may be used in the housing 10 or as a self-contained unit. The charge 45 is housed in a fluid-tight metal shell 75 having a hemispherical shield 76 at the forward end. Coaxial with the charge is a passage 65c extending nearly to the outer surface of the member 76, the passage being opened by the jet when the charge is fired and being too narrow to allow escape of solid fragments.