Patent GB-686530-A (GB)
Title: Improvements in apparatus for perforating well casing
IPC: E21B43/117
Filed: 1949-01-18
Abstract: 686,530. Apparatus for perforating well casings by means of explosives. GULF RESEARCH & DEVELOPMENT CO. Jan. 18, 1949. No. 1406/49. Class 9(i) [Also in Group XXII] A well-boring apparatus comprises a hollow sealed housing with means for positioning the housing in the well, at least one cavity charge being mounted within the housing so that the housing forms an expansion chamber partly or wholly surrounding the charge or charges, means being provided for detonating the charge. Fig. 15 shows a steel cylinder 101 with openings 102 leading to cavity high explosive charges 115, each cavity having a liner 111 attached to a container 110 for the charge. In each opening is welded a ring 103 grooved to receive a split lock-ring 105 holding a metal cap 107 in place to prevent well fluids entering the apparatus. The inner end of the container 110 is closed by a screw-threaded cap 112 through which passes a fuze-cord 114 joined to a main fuze-cord 117 extending upwards through a member 119 biased upwards by a spring 120 bearing against a supporting member 122. The spring tends to force the conical end 123 of the member 119 into the socket of a fuze-chamber 125 and the fuze 117 is held by a pin 127. In the fuze-chamber is an electrically actuated detonator 30 having one lead grounded to the wall of the chamber while the other is connected to a clock mechanism 132 and a switch 133. The terminals of a battery 134 are connected to the clock mechanism and the fuze-chamber respectively. The fuze-chamber 125 is screw-threaded into an end piece 136 sealing the uper end of the cylinder 101. In the end piece 136 is a pressure-sensitive switch 138 connected to a metallic ring 139 insulated from the end piece and in electrical contact with the switch 133. The lower end of the cylinder-is sealed by an end piece 14 and the apparatus is lowered into a well-bore by a line 142. The charges 115 may be 50-50 pentolite cast or pressed into the containers 110, a length of primacord 114 being embedded in the charge during the filling process. To prevent loss of explosive by melting, packing material 116 such as putty may be placed within the cap 112 closing the container 110. Premature detonation is prevented since the contact 146 and hence the detonator is grounded while the fuze-chamber is not attached to the end piece 136. When the fuze-chamber is threaded into the end-piece another grounding circuit is completed through the bush 141, the ring 139 and the switch 138. The grounding circuit remains closed until the apparatus is lowered to a pre-determined depth when the hydrostatic pressure opens the switch 138. The clock mechanism connects the battery 134 to the detonator for a short interval and if the detonator fails to fire, the clock breaks the connection so that the apparatus can be safely withdrawn, the switch 138 again closing as the pressure falls. In a modification, Fig. 16, the cylinder is of expendable material such as wood, or cement, provided with pockets for the shaped charges. A cylindrical block 201 has an axially arranged cavity 203 at one end forming the fuze chamber from which extends an axial bore 205 accommodating a fuze cord, e.g. primacord. Cavities are drilled diametrically through the block to house the charges, which may be arranged helically around the axis or with several cavities in any given horizontal plane and any desired vertical separation between the planes. Each cavity has a part cylindrical section 225 and a part conical section 207 expanding from the first section. Into the section 207 extends a liner 212 over which is a sealing disc 214, a second sealing disc 216 being placed at the entrance to the section 225. A weight 219 is attached to the block to sink the apparatus. Specification 645,059 is referred to.