US3517757A - Switching apparatus for selectively actuating explosive well-completion devices - Google Patents

Description

June 30, 1970 H. J. HART 3,517,757

SWITCHING APPARATUS FOR SELECTIVELY ACTUATING EXPLOSIVE WELL-COMPLETION DEVICES Filed sept. 25. 1968 019 v 3/ as 70\ .22 J3 fle/u er 2 flaw z .INVENTOR.

ATTORNEY United States Patent SWITCHING APPARATUS FOR SELECTIVELY ACTUATING EXPLOSIVE WELL-COMPLE- TION DEVICES Herbert J. Hart, Houston, Tex., assignor to Schlumberger Technology Corporation, New York, N.Y., a corporation of Texas Filed Sept. 23, 1968, Ser. No. 761,410 Int. Cl. E21b 43/117 US. Cl. 1754.55 11 Claims ABSTRACT OF THE DISCLOSURE This disclosure is directed to shock-resistant switching apparatus for controlling well-completion tools having a plurality of explosive devices such as shaped charge perforators that are to be successively operated. The shock-resistant switching apparatus is normally retained in one position by an electrical resistor that is of substantial mechanical strength but is selectively adapted to fail upon passage therethrough of a predetermined electrical current. Upon passage of sufficient current through the resistor to cause its failure, the switch moves to another position to connect one or more associated explosive devices into a firing circuit for subsequent detonation.

Present day well-completion techniques often require that a plurality of electrically-actuated devices such as shaped charge perforators be selectively actuated so that only a single trip into a w ll is required to perforate the well at a number of different depths. Those skilled in the art will, of course, appreciate that whatever arrangement is used to selectively detonate these explosive devices must be highly reliable to, for example, avoid perforating a well casing at an incorrect depth. Accordingly, heretofore, typical control systems have employed either successively-indexed multi-contact switches or various types of normally-open switches that are closed only as a result of the detonation of a previous shaped charge. Although control switches of this nature have generally been successful, many of these switches are either fairly expensive or are unduly susceptible to damage from the extreme impact shocks typically experienced by a well perforator. Thus, there is still a need for selectively-operable control switches that are sufiiciently reliable and shock-resistant for use with typical well-perforating apparatus but without being unduly elaborate or expensive.

Accordingly, it is an object of the present invention to provide new and improved impact-resistant and relatively fool-proof switching apparatus for selectively controlling the plurality of explosive perforating devices.

This and other objects of the present invention are attained by an electrical switch having a movable member that is releasably secured in a first position by an electrical resistor from moving to a second position operatively connecting a power source to one or more electrically-responsive explosive perforating devices that are to be operated together. To actuate the switch, suflicient current must first be passed through the resistor to cause its mechanical failure and allow the movable member to move to its second position for connecting the explosive devices into a firing circuit for subsequent operation.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts a switch arranged in accordance with the principles of the present invention; and

3,517,757 Patented June 30, 1970 'ice FIG. 2 schematically illustrates perforating apparatus adapted for control by a number of the new and improved switches shown in FIG. 1.

Turning now to FIG. 1, a preferred embodiment is shown of a control switch 10 arranged in accordance with the present invention. Although the switch 10 could, of course, be simply disposed within one of the housing sections of a typical well-completion tool, it is preferred to arrange the switch to be secured in an access port in the tool housing for purposes of convenience. In this preferred embodiment, the control switch 10 has a tubular case 11 with a suitably arranged closure member 12 on its outer end just ahead of a circumferential sealing ring groove 13 and external threads 14. By making at least a substantial portion of the tubular case 11. of an electricallyconductive material, once the switch 10 is inserted into an access port in a tool body and the threads 14 are matingly engaged with complementary threads in this port, the tubular case 11 will be electrically connected to the tool body. A plurality of fixed electrical contacts 15- 18 are spatially disposed along the internal bore 19 of the case 11 and electrically insulated from one another and the case by suitable non-conductive materials which may be conveniently formed as a stack of insulating spools or sleeves 20-24. In the preferred manner of arranging these fixed contacts 15-18, small garter springs of electrically-conductive materials are employed.

A shaft 25 of an electrically-nonconductive material and carrying a conductive contact member, such as a tube 26, on its intermediate portion is suitably positioned in the case 11 for axial movement from the position shown to a more-forward position. To urge the shaft 25 forwardly with a predetermined force, means are provided such as a compression spring 27 around the forward end of the shaft that is yieldably constrained between a transverse pin 28 thereon and an inwardly-directed shoulder 29 on the insulating sleeve 24. The shaft 25 is, however, releasably retained in the illustrated position by an electricallydestructible resistance element such as a composition or a common carbon resistor 30 of a selected power rating that is secured in tension between the trailing end of the shaft and the case 11. The body of the resistor 30, of course, has a normal mechanical strength greater than the spring force of the spring 27.

It will be further appreciated, from FIG. 1 that the conductive sleeve 26 is cooperatively arranged to interconnect the contact springs 16 and 17 so long as the shaft 25 is held in its normal position. In this shaft position, the conductive sleeve 26 has radially expanded the contact springs 16 and 17 somewhat in relation to a more relaxed contracted position (such as the illustrated position of the non-contacted spring 18) to insure satisfactory electrical contact. Forward movement of the axial shaft 25 will, however, drive the sleeve 26 into the center of the forward contact spring 18 and expand that spring as the rearward contact spring 16 relaxes onto the insulated shaft to the rear of the conductive sleeve. Conductors 31-33 are respectively connected to the contact springs 16-18 and routed out the rear of the case 11 by way of circumferentially-spaced longitudinal slots or grooves, as at 34, formed in the walls of the insulating sleeves 20-23. To retain the contact springs 15-18 in their respective spaced positions, the insulating sleeves 20-23 are preferably formed with inwardly-projecting shoulders as at 35.

Since the axial shaft 25 is of a nonconductive material, a coupling 36 of an electrically-conductive material is secured (as by the illustrated threads) to the rearward or trailing end of the shaft. The forward terminal lead 37 of the resistor 30 is preferably passed through a suitable opening in the coupling 36 and clamped thereto as by a set screw 38. The contact spring is suitably positioned to at least be initially in electrical contact with the coupling 36 and has a conductor 39 connected thereto that is routed out the rear of the case 11 by Way of a longitudinal groove 40 in the insulating sleeve 20. The rearward terminal lead 41 of the resistor 30 is passed through a suitable opening and soldered, as at 42, to an electrically-conductive cross-shaped, transverse member 43. To facilitate the replacement of the resistor 30, the transverse member 43 is preferably secured against a rearwardly-directed case shoulder 44 by a suitable threaded lock ring 45. It will also be noted that in addi tion to assuring satisfactory electrical contact between the case 11 and transverse member 43, the insulating sleeves -24 are appropriately arranged to have a stacked height just sufficient to be snugly clamped into their respective positions by the transverse member.

Accordingly, it will be appreciated that so long as the resistor 30 remains intact, it will secure the axial shaft to the case 11 and retain the shaft in its rearward position against the predetermined biasing force of the spring 27. By selecting the resistor to have a minimum wattage rating as well as a particularly-low electrical resistance, it will be quite easy to pass sufficient electrical current through the resistor to quickly disrupt or destroy the mechanical strength of the resistor body so that the spring 27 will be capable of repositioning the shaft 25 once the body of the resistor parts. For example, if the resistor 30 is a typical carbon resistor with a relativelylow resistance and a selected power rating of, for example, A-watt, application of only a very low voltage will be sufficient to cause a relatively-high current fiow through the resistor 30. The excessive power dissipation caused by such high current flow through the resistor 30 will, of course, quickly destroy the physical strength of the resistor. As a particular matter, therefore, it has been found that the body of such a low-resistance, low-wattage resistor will often be either completely parted or sufficiently weakened mechanically very quickly by such currents. Thus, although the resistor 30 is initially sufficiently stout to Withstand severe impact shocks and the extreme environmental conditions of a well bore, the resistor body can always be reliably parted with a minimum of current flow.

Turning now to FIG. 2, a schematic representation is shown of electrical circuitry employing control switches arranged in accordance with the present invention for selectively controlling perforating apparatus 51 such as, for example, that disclosed in Pat No. 3,329,218. It will be realized, of course, that the control circuitry 50 can be either distributed throughout the apparatus 51 in any convenient arrangement or else the circuitry can be concentrated into a single section thereof. However, to arrange the various elements of the circuitry 50 into fullyinterchange'able integrated units as well as to allow any number of these integrated units to be assembled without special consideration, the perforating apparatus 51 includes a plurality of tandemly-connected, fluid- tight housing sections 52, 53 and 54 that are adapted for suspension as a single body in a wel bore (not shown) from a cable 55 that is spooled in the usual manner on a Winch (not shown) at the surface. As is typical, the suspension cable 55 has a single central conductor 56 that is enclosed Within an electrically-conductive armored sheath 57 which serves as another electrical conductor. Both of these conductors 56 and 57 are appropriately connected to the surface by a conventional reversing switch 58 to a selectively-operable power source 59 such as provided by a battery 60 having a potentiometer 61 across it and in series with an ammeter 62 and a control switch 63. In this manner, an operator may conveniently select both the polarity and the voltage potential that is to be applied to the conductors 56 and 57 as well as to regulate the magnitude of the current flowing through the cable conductors.

Perforating means are provided such as typical shaped charges 64 that are respectively fluidly sealed within each of the housing sections '52 and oriented along a laterallydirected perforating axis intersecting a replaceable closure 65 in the side of each section. The perforating means further include electrically-responsive detonating means, such as typical initiators 66, that are arranged Within detonating proximity of the rear of each of the shaped charges 64. Inasmuch as the armored sheath 57 is electrically connected to all of the housing sections 5254, each of the initiators 66 is arranged so that one side of its filament is in electrical contact with the assembled housing sections (as schematically shown in FIG. 2) and the other side of the filament is connected to a conductor 67 that is passed through a fluid-tight seal or connector plug (as at 68) into the adjacent housing section 53. In this manner, well-bore fluids entering the housing sections 52 upon detonation of the shaped charges 64 will be excluded from the housing sections 53 and come into contact with the various components of the circuitry 50.

The particular manner of connecting the circuitry 50 to the surface equipment is, of course, dependent upon the number of electrical conductors in the suspension cable employed. Where, for example, a multi-conductor cable is used, one cable conductor may be connected to the housing sections and two other cable conductors are simply connected to separate conductors, as at 69 and 70, that begin in the upper housing section 54 and are respectively carried through appropriate fluid-tight seals or mating connector plugs, as at 71, into the alternatelydisposed housing sections 52 and 53 depending therebelow. On the other hand, since it is usually preferred to use less-bulky monoconductor suspension cables, as at 55, for perforators, one or more oppositely-poled diodes as at 72 and 73 in the upper housing section 54 are both connected to the central cable conductor 56 and respectively connected to the conductors 69 and 70. Thus, when the reversing switch 58 is thrown so as to connect the positive pole of the battery 60 to the central cable conductor 56, current will readily flow through the diodes 72 and the conductor 69, and the diodes 73 will block current flow through the conductor 70. On the other hand, when the reversing switch 58 is in its other operating position, current will flow only through the diodes 73 and the conductor 70, and no current will flow through the conductor 69.

The circuitry 10 also includes a number of switches 74 arranged in accordance with the present invention as single-pole double-throw switches that are respectively mounted in each of the housing sections 53 and are selectively operable from the surface for the successive detonation of the shaped charges 64. It will be recognized, of course, that by mounting the switches 74 in the separate housing sections 53, the switches will be shielded from the shaped charges 64.

In the preferred manner of connecting these switches 74, their moving contact 75 is initially engaged with the first fixed contact 76 and is movable to the second fixed contact 77 only upon the physical failure of the resistor 78 upon passage of excessive current therethrough. An electrical insulator 79 isolates the resistor 78 from the switch contacts 75-77. The conductors 67 from the explosive initiators 66 are respectively connected to the second fixed contact 77 of their associated control switch 74, and preferably have a current-limiting resistor 80 serially connected between this contact and the initiator. Conductors 81 are also connected between each of the second fixed contacts 77 of one switch 74 and the resistor 78 in the next successive switch.

As is schematically depicted in FIG. 2, the conductors 69 and 70 extend the full length of the apparatus '51 and are alternately divided and successively connected in a staggered sequence to the moving and fixed contacts 75 and 76 of the several switches 74. Thus, as illustrated, the

conductor 69, for example, is divided and connected only to the odd-numbered switches (as at 74a and 740) and the conductor 70 is divided and connected only to the even-numbered switches (as at 7412). It will be realized, of course, that to facilitate their connection and disconnection as well as to make the units fully interchangeable, the conductors 69, 70 and 81 are all connected to fluidtight electrical plugs, as at 82, that are readily mated as the housing sections 52, 53 and 54 are assembled. Thus, since only three duplicate units are shown in FIG. 2, the conductor 81d has no mating contact in the uppermost housing section 54 and the conductor 81a must be connected, as by a jumper 83 to the lowermost end of the conductor 70 to complete the circuitry 50. It will also be appreciated, of course, that those portions of the conductors 69, 70 and 81 passing through the housing sections 52 should be protected in some manner from the explosive forces of the shaped charges 64.

Accordingly, once the perforating apparatus 51 is assembled and the circuitry 50 is connected as shown in FIG. 2, the apparatus is lowered on the suspension cable 55 to the first position in a well bore (not shown) where a perforation is to be made. It will be appreciated that so long as the switches 74 of the invention are in their depicted positions, not only will the initiators 66 be disconnected from the firing circuit (as represented by the conductors 69 and 70) but the initiators will also be safely shunted by their respective resistors 78 and 80. Thus, stray electrical currents cannot inadvertently detonate the disabled shaped charges 64 and the perforating apparatus 51 cannot be armed until the power source 59 is connected in a selected manner to the cable conductors 56 and 57 and a current of a predetermined magnitude is obtained.

Once the perforating apparatus 51 is positioned in the well bore so as to bring the lowermost shaped charge 64a to a selected depth, the reversing switch 58 is thrown to the left (as viewed in FIG. 2) to connect the negative pole of the battery 60 to the central cable conductor 56. Then, after the switch 63 is closed, the potentiometer 61 is advanced (as shown by the arrow 84) to increase the current flowing through the firing circuit conductor 70. It will be appreciated that at this point all current flowing through the conductor 70 must pass (by way of the jumper 83) through the resistor 78a. Thus, by continuing to advance the potentiometer 61,the magnitude of current flowing through the resistor 7 8a will ultimately exceed the predetermined current level required to destroy the resistor 78a and release the movable switch contact 75a for movement to the fixed contact 77a. It will be appreciated that the insulator 79a electrically isolates the switch 74a itself from the resistor 78a.

Once passage of current through the conductor 70 fails, the resistor 78a and the movable switch contact 75a has moved into engagement with the fixed contact 77a, the other conductor 69 of the firing circuit is then connected through the fixed contact 77a to the initiator 66a as well as to the resistor 78b. At this time, however, the diodes 72 prevent any current from flowing in the firing circuit conductor 69. Thus, the shaped charge 64a cannot be detonated until the reversing switch 58 is thrown (to the right as viewed in FIG. 2) to its other operating position.

It should be noted also that failure of the resistor 78a will open the circuit path so that upon seeing the amsistance in relation to the resistance of the resistors 78, most of the current initially flowing in the firing circuit conductor 69 will pass through the resistor 78b until the body of the resistor fails. Once the resistor 78b has failed, however, all of the current flowing in the conductor 69 will be diverted to the initiator 66a. Then, if necessary, the potentiometer 61 is advanced until the shaped charge 64a is detonated. Here again, once the shaped charge 64a is detonated, the circuit will be broken and the cessation of current flow as indicated by the ammeter 62 will provide a reliable indication at the surface that the shaped charge 64a has been detonated.

Detonation of the next shaped charge 64b requires that the reversing switch 58 again be reversed. Upon reversal of the switch 58, the initiator 66b and the resistor 78c are initially paralleled. In the same manner as already described, the resistor 780 is first failed to actuate the switch 740. Then, once sufficient current fiows through the initiator 66b, the shaped charge 64b will be detonated and the ammeter 62 will again provide a positive indication at the surface. It will be appreciated that if additional shaped charges 64 and switches 74 were positioned between the housing sections 52c and 53b, the successive actuation of these other switches 74 and detonation of these additional shaped charges 64 would, of course, be accomplished in the same fashion by alternately applying current to the first one and then the other of the firing circuit conductors 69 and 70 in successive turns.

The last control switch 74 in the perforating apparatus 51 is preferably actuated prior to the detonation of the next-to-last shaped charge 64. Thus, referring again to FIG. 2, it will be recognized that when the reversing switch 58 is operated to direct the current flow to the fixed switch contact 77b, the resistor 780 will initially be failed to actuate the uppermost switch 74c before the shaped charge 64b is detonated. Once the next-to-last shaped charge 64b is detonated, only the last initiator 66c is now connected to the firing circuit. Thus, upon the subsequent reversal of the switch 58, all current flowing in the conductor 69 will pass through the initiator 660.

Accordingly, although there are a variety of prior-art fuse-actuated switches that presumably are functionally equivalent to those of the present invention, those skilled in the well tool art will appreciate that few-if anyof these prior-art switches woud be capable of reliably functioning in typical perforating apparatus such as at 51. For example, in addition to the extreme pressures and temperatures typically encountered in well bores, any successful control switch of this nature must be of exceptionally rugged construction to withstand the severe physical shocks or impacts successively imposed on the switches during the course of even a routine perforating operation. It will also be appreciated that for purposes of economy, the control switches of the present invention are particularly attractive.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. In a well tool adapted for suspension in a well bore and including explosive means adapted for detonation in response to passage of electrical current therethrough, circuit means adapted for selectively operating said explosive means comprising: switching means on said well tool and having at least one fixed electrical contact and one movable electrical contact movable from a first position to a second position for making an electrical connection with said fixed contact; an electrical resistor of a selected power rating electrically isolated from and secured between said movable contact and said well tool, said resistor having a body with sufficient physical strength for restraining said movable contact from moving from its said first position until passage of electrical current through said resistor exceeds said selected power rating sufficiently to mechanically weaken said resistor body; spring means having a predetermined spring force normally urging said movable contact toward its said second position and adapted to move said movable contact there to only upon weakening of said resistor body; first con ductor means adapted for connecting said resistor to a source of electrical power; and second conductor means connected to said electrical contacts and adapted for connecting said explosive means to a source of electrical power only when said movable contact is in its said second position.

2. The well too] of claim 1 wherein said explosive means include perforating means adapted to perforate a wall surface in a well bore; and further including means on said well tool for shielding said switching means from the detonation of said perforating means.

3. The well tool of claim 1 wherein said movable contact is adapted for movement along a selected axis from said first position to said second position axially spaced therefrom; and said resistor is generally in coincidental alignment with said selected axis so as to be tensioned by said predetermined spring force, one lead of said resistor being mechanically connected to and electrically insu lated from said movable contact and the other lead of said resistor being mechanically connected to said well tool and electrically insulated from said one resistor lead and said electrical contacts.

4. The well tool of claim 3 further including an elongated body movable along said selected axis and carrying said movable contact; and a second fixed contact axially spaced from said first-mentioned fixed contact and adapted for engagement by said movable contact upon movement to its said second position to electrically interconnect said fixed contacts.

5. The well tool of claim 4 further including a tubular case around said electrical contacts and elongated body; and electrical insulating means isolating said fixed contacts from one another and from said tubular case.

6. The well tool of claim 5 wherein said tubular case is mounted to said well tool; and further including a third fixed contact secured to said tubular case to which said other resistor lead is secured.

7. A selectively-operable switch for use in a well-completion tool and comprising: a tubular case having a longitudinal bore; an elongated body movably supported in said case and adapted for axial movement therein between first and second longitudinally-spaced positions along said bore; first electrical contact means on said movable body; second electrical contact means on said case and adapted to be engaged with said first contact means in one of said positions of said movable body and to be disengaged therefrom in the other of said positions of said movable body; electrical-insulating means for isolating said electrical contact means from said case and from one another whenever said movable body is in its said other position; biasing means operatively arranged between said case and said movable body for urging said movable body toward its said second position with a predetermined force; an electrical resistor of a selected power rating connected between said case and said movable body for releasably securing said movable body in its said first position, said resistor having a body with a normal mechanical strength greater than said predetermined biasing force for retaining said movable body in its said first position until suificient electrical current has passed through said resistor to exceed said selected power rating and reduce said mechanical strength of said resistor body below said biasing force; and conductor means connected to said resistor and adapted for connection to a source of electrical power.

'8. The switch of claim 7 wherein said resistor is in generally-coincidental alignment with said movable body and adjacent to the rearward end thereof so as to be in tension for retaining said movable body against forward movement to its said second position.

9. The switch of claim 8 wherein said conductor means further include a first electrical contact on said rearward end of said movable body; means on said first electrical contact for securing the forward lead of said resistor thereto; a second electrical contact in said case and engaged with said first electrical contact at least when said movable body is in its said first position; a third electrical contact secured in said case; means on said third electrical contact for securing the rearward lead of said resistor thereto; and further including second electricalinsulator means for electrically isolating said first and second electrical contacts from one another as well as from said third electrical contact.

10. The switch of claim 9 wherein said movable body is constructed of electrically-nonconductive material; and said first electrical contact means and said first electrical contact are constructed of electrically-conductive material secured on said movable body.

11. A selectively-operable switch for use in a wellcompletion tool and comprising: a tubular case having a longitudinal bore; an elongated body coaxially supported in said case and adapted for axial movement in one direction therein between first and second axially-spaced positions; first and second electrical contacts spaced apart on said movable body; first, second and third fixed contacts on an electrically-conductive material mounted in said case at axially-spaced intervals therein, said first and second fixed contacts being adapted for engagement by said first electrical contact on said movable body whenever said movable body is in its said first position, said second and third fixed contacts being adapted for engagement by said first electrical contact whenever said movable body is in its said second position; first electricalinsulating means for electrically isolating said fixed contacts from one another; second electrical-insulating means on said movable body for electrically isolating said first and second electrical contacts from one another; spring means operatively arranged between said case and said movable body for urging said movable body toward its said second position with a predetermined force; an electrical resistor of a selected power rating adjacent to the trailing end of said movable body and coincidentally aligned therewith and having its forward end connected to said second electrical contact and its rearward end secured to said case so as to be in tension for releasably securing said movable body in its said first position, said resistor having a body with a normal tensile strength greater than said predetermined biasing force for retaining said movable body in its said first position until sufficient electrical current has passed through said resistor to exceed said selected power rating and reduce said mechanical strength of said resistor body below said biasing force; and conductor means connected to said resistor leads and adapted for connection to a source of electrical power,

References Cited UNITED STATES PATENTS 2,762,884 9/1956 Van Eyk 337- 2,832,265 4/1958 Reid et al. 337-145 3,010,396 11/1961 Coleman -455 3,246,707 4/ 1966 Bell 175-455 X 3,327,791 6/1967 Harrigan 175-455 3,441,093 4/1969 Boop 175-455 DAVID H. BROWN, Primary Examiner US. Cl. X.R. 337-145

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