Patent GB-828306-A (GB)
Title: Improvements in or relating to perforating apparatus utilising explosives as perforating medium
IPC: E21B43/118
Filed: 1956-05-17
Abstract: 828,306. Explosive devices for perforating well casings. SCHLUMBERGER WELL SURVEYING CORPORATION. May 17, 1956 [May 23, 1955], No. 15478/56. Class 9(1) A device for perforating well casings comprises laterally spaced supports 10, 11 between which are mounted shaped charge units 14, 15, 16 so arranged that, on firing, the jet from the lowermost unit 14 initiates the unit 15, which in turn initiates the unit 16. The supports 10, 11 may be of frangible, electrically-conducting material e.g. an aluminium alloy. The unit 14 comprises a housing 18, e.g. of moulded plastic, for a shaped charge 17 fitted with a liner 20 of thin steel, copper or zinc and having a cylindrical end 21 abutting an electric blasting cap 22. One lead 24 from the cap is connected to the support 11 and the other lead 25 is taken to the suspension head of the device, so that the cap 22 may be fired by an electric energy source (not shown) connected to the support 11 and lead 25. The units 15, 16 are similar to unit 14 but the charges are larger and the cap 22 is omitted. On discharging the cap 22, the charge 17 is fired and the jet produced fires the primer 30 of unit 15 to ignite charge 29. Charge 29 in turn fires the unit 16 in addition to perforating casing 13. Any number of perforating units may be mounted on the supports 10, 11. It is stated that the metal slug, formed by the collapse of a charge liner, is either disintegrated by the explosion of the primer section of the charge immediately above or deflected by such explosion, so that plugging of the perforation formed, by the first mentioned charge, in the well liner is prevented. In a modification. Fig. 2A, a cylinder 50 houses units 51, 52, 53 inclined to the longitudinal axis 57 as before, the lowermost unit 51 being connected to a booster 62 which abuts a blasting cap 63. On firing, the cap 63 ignites booster 62, which in turn initiates the primer 61 to fire the hollow charge 59. The jet of gases from charge 59 initiates a booster 65 connected to the adjacent unit 52. At the top of housing 50 is an annular charge fired by a booster initiated by the topmost shaped charge, to sever the housing from its head and allow withdrawal of the head. In Fig. 4 the units are mounted in a system of levers forming a lazy tongs with a weight 94 at the bottom. The uppermost levers 82 have latch arms 78 engaging a spring-pressed armature 77 of a solenoid 76 within a housing 75. The armature holds the lazy tongs in the collapsed position, so that the device may be lowered through a tube 72 by means of cable 71, the charges being aligned along the axis of the device. On reaching the required depth in the well, the solenoid 76 is energized so that armature 77 releases the latches 78, whereupon spring 79 cause the levers to move to the position shown. In place of the lazy tongs, the units may be jointed together and connected by springs which bias the units to the firing position, the units being held in the 'collapsed position by a wire extending from the bottom of the device to an electrical release in the head.