US2871784A - Firing system for electrically detonated borehole equipment - Google Patents

Description

Feb. 3, 1959 w. BLAIR 2,371,784

FIRING SYSTEM FOR ELECTRICALLY DETONATED BOREHOLE EQUIPMENT Filed July 5. 1951 /7 I Z/ Y QT'TO ENEYS.

u i l wa a e 2,871,784 FiRING SYSTEM non ELECTRICAL LY Daro- NATED BOREHOLE EQUIPMENT V Wint'on Blair,- Houston, Tex'., assignor, by mesrie assignments, 'to Schluinberg'e'r Well Surveying Corporation, Houston, Tex., a corporation of Texas 'Ah iiiirih sa s, 1551, ssanna 235,172 7 Claims. 01. 102-216 paratus including a plurality of electrically detonated,

explosively-propelled projectiles disposed in a pressure r sistant housing and adapted'to be lowered into a borehole by means of an electric cable. The number of projectiles that may be conveniently accommodated in a single housing is limited, however, by the length of the housing, which must be short enough to enable it to be convenientl transported from one location'to another. When a contemplated sample taking or perforating opr'ation calls'for more projectiles than can be placed in a single housing, it is common practice to couple a plurality of such h usings'together electrically an'd'to lower them into the borehole as a string. 'In such case it is custo'm'a'ry to include in the assembly lowered into the well a commutating switch or the likelfor supplying electric current from a source at the surface selectively and successively to the firing circuits in the respective housings to enable the projectiles in each housing to be'di'scharged selectlvely or simultaneously, '"as desired.

Apparatus of the above charac er has 'n Jt beenfound entirely satisfactory because it is complex in constructidn, and thus subject -t'o frequent misoper'ations and breakdawns, causing mush adde jexpense a'iid los cram Further, the number of housings that may be assembled in a string as described above is limited by the'number of contacts on the switchingunit. Moreover, s'irjlcefeach housing requires at least one sepa'r'ateelectrical con c'tion tothe switching unit, the physical design is very complicated,par'tidularly"at the con Tctiiins between housings.

It "has also been proposed reconnect the electrical deto'riatirig circuits in a plurality of housings in series, so that the projectiles in 'all the housings are discharged simultaneously. Such an arrangement is not particularly desirable since it does notperrnit the projectiles in a given housing to be discharged selectively 0r simulta neously at a desired level. Also, the simultaneous discharge of a large number of projectiles frorna gun perforator often causes ,the well casing to split, and in the case of asampletaker it woul d b e likelyto cause the housings to become stuck intheborefliole. Further, a' single -misfire will usually result finjtheifailure to discharge of all the remaining, unfired projectiles'in all the housings since they'iare inseries. V

QO thcr systems hat/ hee "devised for selectively-controllingthe firing offa group otcharg'es within onen ssing, such systems utilizing switches for coupling succes s o' b i' 9 l i ffal, '2 ,syid i provision is not inane for removing igniters "from the 2,871,784 Patented Feb. 3, 1959 ice 2 circuit in the event of misfiring, and firing of subsequent igniters may be prevented altogether or seriously impaired. It is an object of the invention, therefore, to provide new and improved firing systems for electrically fired explosive charges which are free of the deficiencies of the prior art as noted above.

It is another objectof the present invention, to provide an improved firing system utilizing components which are reliable in their operation.

Another object of the present invention is to provide simple and effective switching apparatus which may be used to supply current selectively to any number of gun perforator or side wall sample taker housings in succession.

A further object of the invention is to provide appara'tu's for switching electric current'to a plurality of housings successively but which requires only one conductor between housings regardless of the number of said housings.

These and other objects of the invention are attained by providing, in each housing for a group of explosively propelled projectiles, firing circuit means for the group of projectiles, by-pass conductor means extending along 'the housing to the next adjacent housing and switching means for selectively controlling the connection of an energi'zing conductor to saidfiring circuit means and to said conductor means. Preferably, the switching means is made responsive tothe current supplied by the energizing conductor.

in a preferred embodiment, the switching means in the topmost housing in the string has a contact arm which normally connects an energizing conductor from the surface of the earth to the firing circuit means for the projectiles in the housing. However, when the current from the energizing conductor is increased to a high enough value (greater than the maximum current value required for firing all of the projectiles in the housing selectively and successively,or simultaneously) the switching means conta'ct arm is automatically disconnected from the firing circuit means and engages a contact connected to the by-pass conductor means, thus'supply'ing current from the energizing conductor through the by-pass conductor to the contact arm of the switching means in the housing immediately below.

With this construction, the projectiles in the topmost housing maybe fired either successively or simultaneously as des'ired,'whereupon the current may be increased to the value re'qui'red ior'operation of the switching means in the housing. This disconnects the energizing conductor from the firing'ci'rcuit means in the topmost housing and connects it to the bypass conductor means which then serves as the 'energ'izingconductor for the housing immediately below.

The invention may be better understood from the following 'detaile'd description of a typical embodiment thereof, taken in"conjunctionwith the accompanying drawing in which the only figure represents a schematic diagram of an electrical circuit constructed in accordance with the invention. Although the preferred embodiment of the invention 'issho'wn 'as controlling the firing of a plurality of explosive charges separated into groups of chargescontained in a 'string'of borehole tools, and operated from'the surface of thee'arth, it will be understood that the inventionis of general utility for firing groups of explosive charges from aremote point. 4

:In the drawing, a borehole 10 which may be cased, or iincas ed asshown isfilled with conductive fiuid 11, though itmay bedry or filled with non-conductive fluid in certain instances. Into the borehole is lowered a'plurality or string ofhous ings 12, 13 and 14,- whichinay be, for-ex ample'gun perfo'rator units of the type d'isclo'sedin' the 3 copending application Serial No. 128,386, filed November 19, 1949, now U. S. Patent No. 2,736,260, by Marcel Schlumberger for Electrical Firing System for Explosively Operated Borehole Tools. The igniter portions of each of the housings or gun units are substantially identical and may comprise a plurality of igniters which are grounded at one terminal. The other terminals of the igniters are connected to a common electrical conductor 16. Between each successive pair of igniters, the conductor 16 affords a fixed resistance or impedance value, represented in the drawing by the resistors 17. The igniter network of each gun unit is terminated in its characteristic impedance 18.

The igniter networks of each of the gun units 12, 13 and 14 are connected through switch means, described more fully below, to an insulated conductor 19, which may be incorporated in the supporting cable for the string of gun units. The upper end of the conductor 19 is connected to one terminal of a source of electrical energy, such as a battery 20, for example, the other terminal of which is grounded. Preferably a variable, series resistor or rheostat 21 is connected in the circuit, the resistance of the rheostat having a maximum value which is high relatively to that of each individual igniting network. An ammeter 22, or other current indicating device, may be inserted in series in the conductor 19 for the use of the operator of the system.

The energizing system as described will set off the explosive charges in any given gun unit all at once. If it is desired, as it is in many cases, to set off the charges in a given gun unit one at a time, a conventional concussion responsive switch 23 may be disposed in the head 30 of the string of gun units 12, 13 and 14 and connected in series with the conductor 19. Such switch operates simply to interrupt the circuit during a concussion period, closing it immediately thereafter. For cooperation with the concussion switch 23, there is provided a hold-in switch 24 having a hold-in coil 24 which holds the switch 24 closed as long as current flows. Once opened, the circuit cannot be closed except by manual actuation of the switch 24.

Disposed at the input ends of the igniting networks of the several gun units 12 and 13 are current actuated switches 25 and 26, respectively. These may be conventional fuse switches, for example, or alternatively, any type of current overload switch, magnetic, thermal or otherwise may be used. The conductor 19 from the surface of the earth is connected to the pole 25a of the first switch 25, which pole is normally connected to or held by a fuse wire 25b, the other end of which is connected to the conductor 16 of the first gun unit. The switch 25 is furnished with a normally open contact 250 which is connected by means of a conductor 27 to the pole 26a of the similar current actuated switch 26 at the input end of the next succeeding unit 13. The pole 25a is spring biased by means of a spring 25d in the direction of the contact 250. The second switch 26 is connected to the gun unit 13 in the same manner with its normally open contact 260 being connected by a conductor 28 to the next gun unit 14. Since the gun unit 14 is the last of the illustrated string, it need have no current actuated switch.

When current of sufficient amplitude is applied to the first igniter 15 in the first gun unit 12 by means of the battery and the rheostat 21 via the conductor 19, said igniter will discharge the explosively propelled projectile controlled thereby. This detonation momentarily opens the concussion-responsive switch 23, which will open the hold-in switch 24 at the surface before current can be applied to the next igniter. The operator at the surface may then close hold-in switch 24 when the borehole apparatus is in position for the next detonation, and the entire operation is repeated. The electrical operation of this circuit is more fully explained in the afore-mentioned application Serial No. 128,386.

After the last igniter in housing 12 has been discharged and if it is desired to begin propelling projectiles from the next housing 13, the hold-in switch 24 is again closed and will remain closed since current will flow through the characteristic impedance 18 in housing 12. This current is also flowing through the fuse portion 25b of the switch 25, which is retaining the pole 25a in its normal position. The current through the fuse 25b is then increased by manipulating rheostat 21 until the fuse 25b melts, thus allowing the spring biased pole 25a to connect the conductor 19 directly to shunting conductor 27 to the next gun unit 13. Of course, the minimum amplitude current to melt fuse 25b should be considerably higher than the maximum required to discharge igniters 15.

When the fuse-switch 25 is being switched from one terminal to another, it momentarily opens the circuit through the conductor 19, thus opening the hold-in switch 24. Since the shunting conductor 27 is connected directly to the electrical igniter circuit in housing 13, the operator at the surface may now begin discharging'the projectiles in housing 13 by succesisvely closing the hold-in switch 24, after having reduced the current in conductor 19 to the maximum required for igniters 15. After the projectiles have all been discharged from housing 13, the current supplied thereto may be increased so as to operate the fuse-switch 26. This in turn connects housing 14 to the electrical circuit. This sequence of operations may be repeated until the projectiles in all the housings have been discharged.

Thus, it can be seen that means are supplied for sequen tially connecting as many housings as desired to a source of electrical energy. If an igniter or series of igniters in one housing misfires, the equipment need not be withdrawn to the surface, since the next housing may be readily connected to the source of electrical energy. Moreover, the switches which may be employed are rugged, practically fool-proof, and relatively inexpensive.

It is, of course, understood that, if bore-hole 10 is dry or filled with a non-conductive fluid, or if it is otherwise desirable, the ground connections may comprise another conductor in the cable (not shown). It will be further understood that other types of detonating circuits may be employed in place of the one shown in the drawing. Any

well known electrically controlled means may be em-- ployed for simultaneously discharging the projectiles in a particular housing. For example, the igniters may all be arranged in series in each housing for simultaneous firing provided means are available to maintain an electrical circuit through the switch to ground after detonation. Also, any well known electrically controlled means may be employed for selectively discharging the projectiles within each housing, and either alternating or direct current may be used to actuate the system. Accordingly, the invention should not be limited in scope save as defined in the following claims.

What is claimed is:

1. In a system for controlling the firing of a plurality of explosive charges, said charges being disposed in two or more groups, each having a plurality of charges therein, electrical igniters associated with said charges, a transmission channel and a controlled source of electrical energy for energizing the channel, an electrical switch individual to the first group of charges and having a normally opened contact and anormally closed contact, means connecting the igniters of the second group of charges to said normally opened contact, said normally closed contact electrically connecting the igniters corresponding to the first group of charges to said channel, said igniters being connected in shunt in the channel in a network including a terminating impedance shunting the channel, and current responsive means connected in series with said network for actuating the switch to connect the igniters of the second group of charges to the said source and to disconnect the said network therefrom, said current responsive means being responsive only to a current greater than that required to fire any or all of said first group of charges.

2. In a system for controlling the firing of a plurality of explosive charges, the combination of a controlled source of electrical energy, an electrical transmission channel including a plurality of electrical igniters of substantially equal impedance connected in shunt in the channel, a plurality of equal impedances connected in series in the channel between adjacent igniters, an impedance connected to said channel at one end thereof and being substantially equal to the characteristic impedance of the channel, said igniters and impedances forming a first network, at least one additional network substantially duplicating the first, an electrical switch individual to the first network having a normally closed contact electrically connected to the first network and electrically connected through the switch to the source of electrical energy, said switch having a normally opened contact electrically connected to one of said additional networks, and current responsive means connected in series with the first network for actuating the said switch to connect the source of electrical energy to said second network and to disconnect the first network therefrom, said current responsive means being responsive only to a current greater than that required to energize any or all of said electrical igniters in said first network for firing explosive charges associated therewith.

3. In a system for controlling the firing of a plurality of groups of spaced-apart explosive charges in bore hole tools which are adapted to be lowered into a bore hole in the earth, said tools being adapted to 'be connected together as a string of spaced-apart units, each bore hole tool having a plurality of charges and corresponding elec trical igniters, an electrical conductor associated with each tool, the opposite ends of each igniter to be connected respectively to ground and to a point on said conductor so that the conductor introduces equal amounts of impedance between adjacent igniters, a controlled source of electrical energy at the surface of the earth having one terminal connected to ground, an electrical switch individual to one bore hole tool of the string and disposed in the bore hole therewith, an electrical conductor connecting the other terminal of the said source of electrical energy to the said switch, means connecting the electrical conductor of said one tool to the switch, an electrical conductor connecting the switch to the electrical conductor of another tool in the string, and current responsive means associated with said switch for connecting said conductor of said another tool to the source of electrical energy and for disconnecting said conductor of said one tool from the source, said current responsive means being responsive only to a current greater than that required to fire any or all of said plurality of charges of said one bore hole tool.

4. In a system as set forth in claim 3 including concussion responsive switching means operatively associated with the bore hole tools for breaking the connections between the source of electrical energy and said bore hole tools after each explosion.

5. In a system as set forth in claim 4, including a 'holdin switch connected in series with the concussion responsive switch, thereby to hold the circuit closed until such times as the concussion responsive switch is actuated.

6. In a system as set forth in claim 3, said electrical switch comprising a single-pole, double-throw switch, the movable contact arm of which is connected to said source of electrical energy, one contact of the switch being connected to the electrical conductor of said one tool and another contact being connected to the electrical conductor of said another tool, said movable contact arm being normally biased in the direction of said other contact, said current responsive means comprising fuse means holding the movable contact arm in engagement with the one con tact and being connected in series with the said electrical conductor of said one tool, whereby control of said source of electrical energy at the surface of the earth melts the fuse to actuate the switch.

7. In a system for controlling the firing of a plurality I of groups of spaced-apart explosive charges in bore hole tools which are adapted to be lowered into a bore hole in the earth, said tools being adapted to be connected together as a string of spaced-apart units, an adjustable source of electrical energy, each bore hole tool having a plurality of charges, corresponding electrical igniters and an electrical network terminated in its characteristic impedance and having said igniters in shunt relation therein, means connecting said source in series with a first network associated with a first bore hole tool including a first current responsive switch individual to said first bore hole tool and responsive only to a current greater than that required to fire any or all of said plurality of charges of said first bore hole tool, said first switch having a normally closed contact connecting said source to said first network and a normally open contact adapted to be closed when said normally closed contact is opened, and means connecting said normally open contact of said first switch means to a second network associated with a second bore hole tool including a second current responsive switch means individual to said second bore hole tool, said second switch means having a normally closed contact in series with the normally open contact of said first switch means and said second network so as to place said second network in series with said source when the normally opened contact of said first switch means is closed.

References Cited in the file of this patent UNITED STATES PATENTS 2,055,506 Schlumberger Sept. 29, 1936 2,062,974 Lane Dec. 1, 1936 2,264,450 Mounce Dec. 2, 1941 2,276,544 Miller Mar. 17, 1942 2,307,729 Foster Jan. 5, 1943 2,331,058 Stick Oct. 5, 1943 2,363,234 Doll Nov. 21, 1944 2,369,238 Kaveler et al. Feb. 13, 1945 2,736,260 Schlumberger Feb. 28, 1956 FOREIGN PATENTS 757,734 France Oct. 16, 1933 985,093 France Mar. 7, 1951

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