SAFETY SWITCH FOR EXPLOSIVE WELL TOOLS

Abstract: In accordance with illustrative embodiments of the present invention as disclosed herein, a safety switch (13) for preventing accidental firing of an explosive well tool includes a tubular metal body (22) connected between the cable head (14) and the well tool, a conductor wire (48) extending through such body for carrying current from the cable to the well tool, and a contact plug (36) mounted in a side opening (33) in the body and arranged to be selectively advanced into shorting contact with the conductor wire.

Description: APPLICATION FOR ENT 1 TITLE: SAFETY SWITCH FOR EXPLOSIVE WELL TOOLS FIELD OF THE INVENTION This invention relates generally to explosive well tool safety devices, and particularly to a new and improved grounding switch that can be activated to greatly reduce the possibility of accidental firing of an explosive well tool until it has been lowered below the rig floor or other area where personnel mav be present. BACKGROUND OF THE INVENTION Serious accidents resulting in personal injurv, maiming, and loss of life have occurred due to premature detonation of various explosive wireline tools such as perforating guns, casing or tubin cutters, string shot rods, et cutters and the like. All such devices include powerful explosives that are extremely dangerous and which must be handled with great care. Even though great care is exercised, there still have been instances where premature firinσ has occurred after assembly of the tool onto the end of the cable, and before it has been inserted in the well. It is believed that such accidental firing can have many causes. For example, stray currents due to power leakage from defective wiring, generators, motors, electric welders and the like can be the cause. Other causes mav be static charges produced by dust and electrical storms in the area, and bv certain other atmospheric conditions. Ground currents produced by lightning, power lines, and galvanic action due to different soil strata can cause detonation. Some accidents have been thought to be due to operation mobile, two-wav communication equipment in the area. There has been a continued and long-felt need for a safety device that will greatlv reduce the posεibilitv of accidental firing of the explosive due to causes such as those enumerated above. Injury to personnel most often occurs when the explosive goes off at the surface, either while rigging the tool up, or while the tool is being placed in the casing or tubing. -> The general object of the present invention is to provide a new and improved safety switch that will prevent premature firing of an explosive well tool. Another object of the present invention is to provide a new and improved safety switch that functions to prevent flow in of electric current to the explosive wireline tool while the tool is being handled at the surface, and until it has been positioned well below the rig floor where service personnel might be present. 1^ SUMMARY OF THE INVENTION These and other objects are attained in accordance with the concepts of the present invention through the provision of a grounding switch apparatus which preferably is installed between the electric wireline cable head and the upper end of 20 the bod-"- of the explosive tool. The switch apparatus includes a tubular metal bodv having a hollow interior and a side opening through the wall thereof. One end of the bodv has means for connecting it to a cable head to which the electric wireline is attached, and the other end of the body is provided 25 with means for connecting to the bodv of the explosive tool. An insulated conductor which couples electrical signals from the cable to the tool extends through said interior past said opening. The conductor has at least a portion of its insulation removed at a location opposite said opening to 30 provide a bare surface area. An electrical contact in the form of a metal contact plug is mounted in said opening for movement between a first position out of contact with said bare surface area, and a second position in contact therewith. When in the first or 35 "closed" position, the contact plug shorts the conductor to the body, and thus to the armor wires of the cable. Since the detonator normallv included in the explosive tool has a finite electrical resistance, current flowing toward the tool from the cable will be shorted to ground via the contact plug. When the switch is placed in the. second or "open" position, the 5 explosive tool can be operated in the usual manner. The grounding switch of the present invention is placed in the "closed" position and attached to either the tool body or the cable head before the complete rig up is made, and is left in the "closed" position until the tool has been lowered into 10 the upper section of the well conduit, which may be casing, tubing or drill pipe. At this point the explosive portion of the tool will be well below the rig floor where personnel mav be standing. When the switch bodv is -iust above the upper end of the conduit, the operator, using an appropriate instrument l*. such as an alien wrench or screwdriver, can position the switch in its "open" position by rotating and retracting the contact plug so that it no longer engages the bare portion of the conductor within the body passage. Until this has been done, it is not possible in most cases for the explosive tool to be *> -) fired, whether intentionally, or accidentallv as discussed above. Thus the safety of using explosive well tools is greatlv enhanced, and the risk of injury reduced to nil. The physical construction of the switch assemblv and its various component parts can take various forms, and several 25 embodiments are disclosed in detail herein. The invention has other objects, features and advantages which will become more fullv apparent in connection with the following detailed description, taken in conjunction with the appended drawings. 30 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a somewhat schematic view of the top of a well with an explosive tool being lowered therein? Figure ? is a longitudinal, sectional exploded view of one embodiment of the present invention with the contact plug and 5 adapter bushing removed and shown in side elevation; Figure 3 is a sectional view similar to Figure 2 showing another embodiment of the present invention; Figure 4 is a view from a different direction of the contact plug of Figure 3 to illustrate further detail thereof; =; and Figure 5 is a longitudinal sectional view of a third embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 10 Referring initiall y to Figure 1, a wireline tool 10 that includes an explosive device 11 on its lower end is shown being lowered into a well conduit 12, which mav be casing, tubing or drill pipe. A safety switch assembly 13 in accordance with the present invention is attached between the uppermost end of the 15 bodv of the tool 11 and a cable head 14 to which the electric wireline 15 is attached. The wireline 15 extends upward and over a sheave 16, and then outward to the winch of a service truck (not shown) . Tvpiσally, the wireline 15 that is used for running explosive tools is a monocable that has a single T) insulated conductor wire in the center of a core, and around which metal armor wires are laid to provide tensile strenαth. The conductor is coupled through a collector ring and brush arrangement on the winch spool to a power circuit in the truck, such circuit being provided with a normally open firing switch 25 that is turned on when it is desired to fire the explosive charge carried in the tool 10. As shown in dotted lines in Figure 1, the conductor wire 17 extends from the cable 15 down through the tool 10 to a detonator 18 for the explosive charge 11. The tool body and the armor wires of the cable provide a 30 ground return for current in conductor wire 17. The wireline tool 10 is shown as having been lowered into the top of the well conduit until the safety switch 13 is located just above the rig floor 20. The tool 10 is then stopped where the switch 13 is still accessible to operating personnel. At such 35 location, the explosive charge 11 is well below the rig floor 20 , so that even if the charge were to be accidentall y fired at this time, most personnel on the floor would be out of harm's way. A first embodiment of the present invention is shown in Figure 2. The switch assembly 13 includes a tubular, metallic body 22 having a male end portion 23 and a female end portion 24. The male portion 23 has a reduced outer diameter provided with external threads 25 and seal rings 26 which are used to provide a leak-proof connection of the body 22 with the lower end of the cable head 14. The female end portion 24 has internal threads 30 and a seal bore surface 31 by which the body 22 is connected in a leakproof manner to the upper end of the body of the well tool 10. Of course the cable head 14 has a female arrangement of threads and seal surface that preferably is identical to that of the lower end portion 23 of the switch body 22. The body 22 has a internal passage 32 that is intersected by a radial opening 33 through the wall of the bodv. The central region 34 of the passage 32 can be laterally offset toward the side of the body 22 to provide a region 35 of increased wall thickness which surrounds the side openin 33. A metal contact plug 36 has an inner section 37 that is arranσed to be received in a reduced diameter inner portion 38 of the opening 33. An external groove in the outer wall of the inner section 37 carries an O-ring seal 40 which sealingly engages the wall of the opening 38 to prevent fluid leakage. The enlarged diameter outer portion 42 of the opening 33 is threaded, as shown, to receive an annular adapter 43 having a central bore (shown in dash lines) which is threaded to receive the companion threads 44 on the outer section 45 of the contact plug 36. The outer end surface of the plug 36 is provided with a suitable recess such as a diametrical slot, or a depression having polygonal walls, so that a suitable instrument such as a screwdriver or an alien wrench can be employed to turn the plug and advance it radially inward or outward with respect to the longitudinal axis of the body 22. A section of conductor wire 48 extends in a slack manner throuσh the passage 32. The opposite ends of the wire 48 are electricallv connected to suitable connectors, such as banana pins 49 and 50, which can be mounted on nonconductive discs 51, ^ 52 fixed at the respective opposite ends of the passage 32. When assembled together with the cable head 14 and the bodv of the tool 10 , the conductor wire 48 forms a section of the wire 17 shown in dash lines in Figure 1. At a location on the wire 48 directly opposite the opening 22, a portion of the in insulation is removed from that side of the wire which faces the end surface 53 of the contact plug 36. Thus when the plug 36 is advanced inward bv turning the same as described above, the end surface 53 will engage the bare surface 55 of the conductor wire 48 and short it with respect to the bodv 22. 1.5 The plug 36 can be advanced inward until the outer insulated side of the wire 48 is pushed against the wall surface 54 of the passage 22 to ensure a firm electrical contact between the plug and the bare surface 49 of the wire 48. To open the switch, the contact plug 36 is turned in the opposite-hand * >π direction to advance it outward to a position where the lower surface 53 no longer engages the bare surface 55 of the wire 48. Current can then flow for the full length thereof and into the wire 1 ~~ that leads to the detonator 18. Another embodiment of the present invention is shown in 25 Figure 3. Elements that are identical to those previouslv described have been given the same reference numbers. In this embodiment the passage 59 is concentric with the axis of the body 22', and has a reduced diameter mid-portion 60 that is intersected by the side opening 33. The inner portion 61 of 30 the opening 33 is enlarged somewhat in diameter, and the contact plug 62 has an integral threaded flange 63 at its outer end which is arranged to be received in a threaded counterbore 64 of the body 22'. For .convenience of illustration, the contact plug 62 is shown at 90° with respect to its actual 35 orientation when installed in the body opening 33. The mid-section of the plug 62 has an external recess which receives an O-ring seal 65 that sealingly engages the wall of the inner portion 61 of the opening 33. The inner section of the plug 62 is provided with spaced-apart legs 66, 67 which define an opening 80 5 therebetween. As illustrated in Figure 4, which is enlarged somewhat and shows the plug 62 rotated 90° from its position shown in Figure 3, the leg 67 has a flat front wall surface 81 . that lies in a horizontal plane through the longitudinal axis of the plug 62, and a rear surface 82 that curves outward to n the outer diameter of the mid-section 83. The opposite leg 66 is similarly shaped, except that its rear surface 84 lies in such horizontal plane, and the front surface 85 curves outward to the diameter of the mid-section 83. As shown in Figure 3, the conductor wire section 68 has 5 the insulation removed completely around it for a length 69 approximately equal to the diameter of the inner opening 61, so that the legs 66, 67 straddle such bare portion 69 when the contact plug is positioned in the opening 33. In the "open" position of the switch embodiment 0 illustrated in Figure 3, the contact plug 62 is rotationallv oriented such that the bare wire portion 69 does not touch either of the legs 66, 67 but extends with equidistant spacing therebetween. To close the switch, the plug 62 is rotated bv a hand-held instrument through a small angle, as previously 5 described, until the edges of the surfaces 82, 85 on the respective legs 66, 67 touch opposite sides of the bare wire portion 69 to short the wire to the body 22 τ of the switch. Suitable indicia (not shown) can be provided including alignment marks on the exterior surface of the body 22' and the 0 flange 63 of the plug 62 to show at what angular position the switch is "open" or "closed". Suitable stops (not shown) also can be provided in the open and closed positions to ensure that the bare section 69 is not yielded as the switch is operated. Still another embodiment of the present invention is shown 5 in Figure 5. In this example, the conductor wire section 70 is formed as a relatively rigid rod having an enlarged diameter center portion 71. Connectors 49 and 50 are secured to the respective opposite ends of the rod 70, and non-conducting plastic sheaths, 72, 73 are provided on the respecting outer sections 74 and 75 thereof. The sheath 74 fits snugly inside the upper section 76 of the passage 32, and has an outer diameter substantially equal to the outer diameter of the center portion 71. The sheath 75 is similarlv shaped, but has an outwardly directed threaded flange 77 at its outer end which is secured in a threaded counterbore 78 in the bodv 22' '. The contact plug 62 having depending legs 66, 67 is identical in construction to that arrangement shown in Figures 3 and , and thus need not be further described. In the "open" position of the switch shown in Figure 5, there is clearance between all walls defining the inner peripheries of the legs 66, 67 and the external cylindrical surface 79 of the conductor section 71. To close the switch, the plug 62 is rotated through a small angle to bring edges of the legs 66, 67 into contact with adjacent outer surfaces of the section 71, thereby providing a short between the conductor rod 70 and the body 22' '. To assemble each of the embodiments shown in Figures 3 and 5, the contact plug 62 is first engaged in the side opening 33 and rotationallv oriented such that the opening 80 between the legs 66, 67 is aligned with the longitudinal axis of the body 22' ' . Then the conductor assembly 70, 72, 73 is inserted through the body passage and secured by the flange 77 as shown. OPERATION In operation, a switch 13 in accordance with anv disclosed embodiment of the present invention is connected to the upper end of the bodv of the explosive well tool 10 bv engaging the threads 30 therewith. Before the cable head 14 is connected to the opposite end of the switch body 22, the contact plug 36 or 62 is rotated to the "closed" position to short the conductor wire to the body 22. Then, and only then, is the cable head 14 connected to the male end section 23 of the body 22. The wireline tool 10 is then raised to the vertical by the cable 15, and then lowered into the top of the well conduit 12 until the switch 13 is located just above the rig floor 20, where lowering is halted. During all such assembly and handling, an electrical current from any source, or any static charge induced in the cable for any reason, will be shorted to ground 5 through the contact plug 36, and can not reach the detonator 18. Thus the risk of premature or accidental firing of the explosive charge 11 in the tool 10 during rigging-up and placement of the tool in the well is greatly reduced, if not eliminated altogether. in With the tool 10 stopped in the position shown in Figure 1, an operator places the switch 13 to the "open" position by rotating the plug 36 or 62 as described. At this point in time, the explosive charge 11 is well below the rig floor 20, and even if the explosive charge 11 should go off prematurely, 5 there would be little likelihood of an injury to personnel. VTith the switch 13 in the "open" position, the wireline tool is lowered into the well to the selected depth where the explosive 11 is to be fired, and the explosive detonated by the main switch in the service truck. 0 It now will be apparent that a new and improved safety switch has been disclosed for the purpose of preventing premature or accidental firing of an explosive well tool. Since various changes or modifications can be made in the disclosed embodiments without departing from the inventive 5 concepts involved, it is the aim of the appended claims to cover all such changes and modifications falling within the true spirit and scope of the present invention. 0 5

Claims: WHAT IS CT,AIMF.r. ; 1. A safety switch apparatus for use in preventing accidental or premature detonation of an explosive well tool, comprising: a hollow tubular bodv having a radial opening 5 through the wall thereof; an insulated conductor extending through the interior of said body for providing an electrical connection between an armored electric cable and an explosive well tool, said conductor having a bare surface; contact means mounted on said body for movement between a first position in engaging said bare surface to short said conductor to said body, and a second position disengaged from said bare surface to enable electric current to flow the full length of said conductor. 15 2. The apparatus of claim 1 wherein said contact means includes an elongated plug mounted in said opening; and further including axial cam means on said plug and said body for moving said plug between said first and second positions in response to rotation of said plug. 20 3. The apparatus of claim 2 further including coengaσeable means on said plug and said body for preventing fluid leakage past said plug. 25 4. The apparatus of claim 2 wherein said plug has recess means on its outer end for enabling rotation of said plug by a hand tool. 5. The apparatus of claim 4 further including indicia 30 means on said outer end of said plug and the exterior of said body for providing an observable indication of the rotational position of said plug. 6. The apparatus of claim 2 wherein said plug has an end 35 surface enqageable with said bare surface of said conductor in said first position, there being lateral clearance between said end surface and said conductor in said second position. 7. The apparatus of claim 2 wherein said plug has a pair 5 of spaced-apart legs on its inner end portion, said legs each having an edge surface engageable with said bare surface of said conductor in said first position, there being clearance between said legs and said conductor in said second position. i 8. The apparatus of claim 2 wherein the hollow interior of said body has a central region that is radiallv offset with respect to the longitudinal axis of said bodv to provide a thickened wall section of said bodv through while said opening extends . 5 9. The apparatus of claim 8 wherein said bare surface is provided only on the side of said conductor which faces said plug, said conductor having insulation on the side thereof opposite said bare surface. 0 10. The apparatus of claim 9 wherein said body has an external counterbore at the outer end of said opening; said axial cam means on said body being formed on a ring which is secured in said counterbore. 5 11. The apparatus of claim 2 wherein the hollow interior of said body has a reduced diameter portion that is intersected bv said opening, said conductor extending axially through said reduced diameter portion. 0 12. The apparatus of claim 11 wherein said bodv has an external counterbore at the outer end of said opening, said axial cam means on said body being formed on wall surfaces of said counterbore. 5 13. The apparatus of claim 2 wherein said conductor has an enlarged diameter cylindrical section between its ends which is positioned adjacent said opening, said cylindrical section be free of insulation to provide said bare surface. 5 14. The apparatus of claim 13 further including first insulator means on said conductor extending from said cylindrical section to one end of said body; and second insulator means extending from said cylindrical section to the in other end of said body: said second insulator means being fixed to said body to hold said conductor in place within the interior of said body. 15. The apparatus of claim 14 further including pin 15 connection means fixed to the opposite ends of said conductor for making electrical connections with adjacent conductor wires. 16. The apparatus of claim 2 further including plate 20 means mounted within the opposite end sections of said body; and pin connector means mounted on each of said plate means, said conductor means extending between and electricallv connected to said pin connector means. 25 17. A method of preventing accidental or premature firing of an explosive well tool that is adapted to be lowered into a well conduit on an armored electric cable, said cable being terminated adjacent said well tool bv a cable head, comprising the steps of: attaching a conductive tubular body having a 30 hollow interior between said cable head and the upper end of said explosive well tool, said body having an insulated conductor extending therethrough for providing current flow from said cable to said well tool; shorting said conductor to said bodv prior to attaching said cable head thereto; 35 positioning said explosive well tool in the upper portion of said well conduit and lowerin said well tool until onl" said tubular body is located above the said upper end of said well conduit; and then disabling said short between said conductor and said tubular body to permit said explosive well tool to be fired. 18. The method of claim 17 wherein said shorting step is carried out by advancing a metallic contact on said bodv inwardly thereof until said contact engages a bare surface of said conductor. 19. The method of claim 18 wherein said disabling step is carried out bv advancing said contact outwardly of said body to cause said contact to disengage from said bare surface of said conductor.

Inventors: LANGSTON THOMAS J, LANGSTON, THOMAS, J.
Applicants: LANGSTON THOMAS J, LANGSTON, THOMAS, J.
Application year: 1989
Main classification: E21B43
IPC codes: E21B43, F42D1