US 2724333 A
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Description (OCR text may contain errors)
Nov. 22, 1955 F. R. SEAVEY,
PROTECTIVE APPARATUS FOR PERFORATING WELL CASINGS AND THE LIKE Filed Nov. 6, 1950 FIG. 3.
INVENTOR. FREDERICK R. SEAVEY ATTORNEYS United States Patent PiioTECTWE APPA AT S-non PERFORATING- WELL CASINGS AND THE LIKE Fraaenck R. Seav'ey, Alton, 111., assigl'ior to Olin Mathisson heniical fibrpo'rati'on, a corporation ofVirginia This invention relates generally to the detonation of explosives, and particularly to the perforation of well casings, cement linings, and the walls of thebore holes in oil. wells. The invention has particular reference to the protection. of the usual perforating gun in the. event that the gun should become laden with well liquids. I
United States Patent No. 2,494,256 to Muskat et ah discloses several species of an apparatus for perforating Well casings and well walls utilizing. shaped. charges of explosive. In one form of apparatus. there disclosed, a plurality of. shaped charges of explosive. is supported interiorlyof a cylindrical barrel, the space between the charges being occupied by air,- and. the. barrel is hermetically sealed to prevent the ingress of oil or water when the barrel. is lowered into. the. well. The several shaped charges are detonated by an electric. blasting. cap acting through a detonatingfuse, which is attached to each of the shaped charges. With. an apparatus. of the character mentioned, it is important that the space within the. barrel and between the several shaped charges, of explosive be maintained free of liquid, i. e., occupied by gas, which is a compressible fluid and therefore absorbs the reaction resulting from the explosions. On. the contrary, if the space within the barrel be permitted to become occupied by liquid, the reaction from the explosion will be transrni't'ted to the walls of the barrel and. resultlin destruction of the barrel itself, as 'well, not infrequently, asth'e wedging of the barrel within the casing so that it cannot be removed without great difliculty. V I I While, in such devices as that above referred. to, it is the primary intention of the operators to maintain the interior of the barrel free of liquids, and careful-..piecautions are taken to seal the several parts against the ingress of well liquids, leakage nonetheless does some times occur. I I I The object of the present invention, generally stated, is to provide a protective device to prevent the explosion of charges in the perforating barrel when the latter leaks. A further object of the invention is to provide anelectric blasting cap, which is automatically rendered inoperative when ambient pressures in excess of normal values are encountered.
These and other objects of the invention, which will become apparent to those skilled: in the art when the following description is read in connection with the accompanying drawings, are accomplished by providing, within the sealed interior of the barrel of a perforating gun, a pressure-sensitive electric switch, the terminals of which are so connected in the firing circuit for the. electric V 2,724,333 Patented Nov. 22, 1955 Ant important aspect. of the present invention is the provision of such a pressure-sensitive electric switch as an element of the blasting cap itself, which contributes greatlyto the. convenience of installation and. eliminates the necessity of makingseparate electrical. connectionsto a separate PI'CSSUI'flrSBllSltiVfi? switch.
In theaccompanying drawings, Figure 1, is; a vertical sectional view of a typical perforating gun of the character above referred to, provided with the protective dcvice-,of. the present invention; I
Figure]. is a viewin: side elevation of one embodiment of anelectric blasting cap embodying the protective device of the present invention, part being shown in section to reveal the relationship of the parts;
I Figure 3 is a view correspondingto'Figure 2, butshowing; asection in ninety-degree displacement from that shown in Figure--94; 1
Figure 4 is a view correspondingto Figure 2, but showing anot-her embodiment of the invention;
Figure 5 is a viewcorresponding to Figure 3., but showing the embodiment of Figure 4;
I Figure 6 is a sectional view taken along line 6-6 of Figure 3; and
Figure 7 is a sectional view taken along line 7--7 of Figure 5.
Referring now to Figure l of the drawings for an, illustrative. embodiment. of, the invention, the perforating gun consists of a cylindrical barrel 1, the. respective endsof which are. closed by capsv 2 and 3 so as. to hermetically seal the interior of the barrel 1. I I I A Disposed within the barrel 1 is. a. plurality of shaped charges. of explosive of a type well understood by those skilled. in the. art and suitably disposed adjacent sealed portsin the. barrel 1. Each of the charges 4 is connected to a cord. 5 of detonating explosive, detonation of which is initiated by an electric. blasting cap 6. The electric blasting cap is provided. with lead wires 7 and 8, which extend to a battery 2, or other source of electric energy, disposed either. within the barrel 1 or above the surface of the. ground. The firing. circuit may extend to the surface of the ground in association with a supporting cable 10 or ma be self-contained within the barrel i and arranged to be. energized by a suitable clock device The several parts just described are conventional with, perforatin'g' uns of the character referred. to, and. individually constitute no part of the present invention.
I In accordance with the present invention, the firing circuit of the electric blasting cap is provided with a pressure-sensitive switch so c nnected as to short-circuit the ignition element of the blasting cap when the. pres sure within the barrel '1 becomes abnormal. In the embodiment shown in Figure 1, a pressure-sensitive switch 11"0f the type which is normally in its open circuit position, but adapted to close when the ambient pressure increases, is provided. The -pressure-sensitive switch 11 is connected in the firing circuit for the cap 6 so as to short-circuit the latter when the contacts thereof close, i. e., the switch 11 is connected in parallel circuit relation with the bridge wire or other initiator element within the blasting cap '6. The pressure-sensitive switch 11 may be of any type well known. in the. electrical control arts wherein the contacts are normally open but become closed when the switch is subjected to predetermined. pressure. I I I I the o' eratioh of the embodiment shown in Figure 1, the switch 11. is normally open and consequently does not affect the firing circuit except upon abnormal'condi tions. The particular abnormal condition against which the switch 11 protects-the apparatus is that of leakage of well liquids into the barrel 1 which, as aforesaid, is normally filled with air. When the barrel 1 leaks, either at the bottom or at the top or at an intermediate zone,
so as to permit ingress of liquids, the pressure within barrel 1 increases, as at this time the barrel will be submerged within the well liquids and at a substantial depth below the surface. Upon such increase in pressure within the barrel 1, the contacts of the'pressuresensitive switch 11 close and thus the blasting cap 6 does not function when the firing circuit thereto is energized. Accordingly, in the event of such abnormality, the several charges 4 remain u ndetonatetl and'the device may be lifted out of the well for such repair and replace- 'ment as is necessary without any. damage having been done to the gun or to the well. 6
It will be understood, of course, that the pressuresensitive switch 11 is disposed in such positionwithin the barrel 1 that it is subjected to the pressure existing within the-barrel and about the explosive charges 4. Where the electric blasting cap and battery are, as in some-cases, enclosed within a special sealed compartment within the barrel 1, the pressure-sensitive switch is so disposed-as to be subjected to the pressure prevailing in the space about the explosivecharges 4.
Referring to Figures 2, 3, and 6 for an embodiment of-the invention wherein the pressure-sensitive switch constitutes a part of the electric blasting cap, it will be understood that the explosive components of the blasting cap are of the type usually employed for such purposes and are encased within a cup 20 provided with an igniter element 21, shown in the form of abridg'e wire extending between two lead wires 22and '23. The lead wires 22 and 23 pass through the usual supporting and sealing plugs (hereinafter termed the igniter plugs), and above the latter a pressure-sensitive 'switch'is provided for electrically interconnecting the lead wires 22 and 23 when the device is subjected to abnormal pressures. In' the embodiment shown in Figures 2, 3, and 6, the pressure-sensitive switch is formed by baring and flattening short sections of the respective lead wires 22 and 23, so as to form diaphragms 24 and 25. j Between the diaphragms 24 and 25, an insulating washer 26 is provided. The washer 26 is annular and disposed tomaintain the diaphragms 24 and 25 peripherally out of engagement. The diaphragms 24 and 25 are preferably fiattened to a thickness on the order of two thousandths of an inch so as to be quite readily flexible. The insulating washer 26 is appropriately sealed to the diaphragms 24'and25 so as to provide an hermetically sealed interior space between the diaphragms and within the open ing of the washer.
The pressure-sensitive switch just described is supported centrally within the case of the blasting cap,
and the lead wires 22 and 23 extend through a sealing plug 27 at the upper end of the case 20. The lead wires are secured within the plug 27 so as to centralize the diaphragms 24 and within the case 20 and prevent their making electrical contact with the case 20. Alternatively, the case 20 or the exterior periphery of the diaphragms 24 and 25 may be covered with a layer of insulating material to prevent short-circuiting of the respective diaphragms 24 and 25 through the case 20.
The portion of the case 20 which surrounds the diaphragms 24 and 25 is provided with a plurality of perforations 28 to assure that the ambient pressures to which the exterior of the blasting cap is subject will be communicated to the diaphragm parts 24 and 25. When such pressures reach a value sufiicient to flex the diaphragm parts 24 and 25 toward each other to the extent that they make electrical contact, it will be understood that the bridge wire 21 is thereby short-circuited and cannot function to initiate detonation of the cap upon normal energization of the circuit through leads 22 and 23.
In the embodiment shown in Figures 4, 5, and 7, the blasting cap comprises a case 30 charged with the usual explosives and having a bridge wire '31 connected be tween the terminals of lead wires 32 and 33. The lead wires extend through the usual supporting and sealing plugs to a section above the latter where the lead wires are bared of insulation and passed horizontally in spaced relation, as shown at 34 and 35 in Figure 7. Therebeyond, the lead wires pass through a flexible diaphragm 36, which closes the mouth of case 30. The diaphragm 36 may be formed of rubber or rubber-like material and appropriately sealed to case 30 and about the insulation upon lead wires 32 and 33. Between the positions whereat the lead wires 32 and 33 penetrate the diaphragm 36, a suflicient distance should be left that a substantial flexing area of the diaphragm is provided. Secured centrally of the diaphragm 36, between the lead wires 32 and 33, is a stem 37 which depends from the diaphragm and supports at its lower end a contact bridge 38 normally disposed in spaced relation above the bared portions 34 and 35 of the lead wires 32 and 33. When the pressure about the cap shown reaches an abnormally high value, the diaphragm 36 will flex inwardly to such an extent that contact bridge 38 engages both the bared portion 34 and the bared portion 35 of the lead wires, thus short-circuiting the bridge wire 31 and preventing its functioning to initiate detonation of the charges within the case 30.
In the use of the embodiments shown in Figures 2, 3, and 6, as well as the embodiment shown in Figures 4, 5, and 7, it will be understood that no separate pressuresensitive switch is required to be connected into the firing circuit; To connect the blasting cap into the firing circuit, all that is necessary is to make the connection between the lead wires 22 and 23, or 32 and 33, and the adjacent parts of the firing circuit. In order to prevent initiation of detonation upon leakage into the barrel of a perforating gun, it will be understood, of course, that the electric blasting caps embodying the built-in pressure-sensitive switches, as shown and described, require to be disposed within the barrel in a position where they are subjected to the same pressure which exists about the several shaped charges of explosive. I
From the foregoing description those skilled in the art should readily understand the construction and operation of the invention and realize that, when a pressure-sensitive switch, as shown in Figure l, or when the electric blasting caps containing the built-in pressure-sensitive switches, as shown in the other figures, are utilized with a perforating gun of the character described, the gun is rendered inoperative upon the ingress of well liquids into the barrel. Accordingly, the barrel may be lowered into position for firing at the selected stratum and the firing circuit may be energized without fear of the consequences of barrel-leakage because, if the latter has occurred, energization of the firing circuit will not detonate the explosive.
While three embodiments of the invention have been disclosed in detail, itis not to be understood that the invention is limited to those embodiments. On the contrary, the several embodiments have been disclosed merely to illustrate the construction and application of the invention. It is realized that many modifications of the disclosed embodiments will present themselves to those skilled in the art without departing from the spirit of the invention, and it is therefore to be distinctly understood that such modifications are contemplated by and gized when the pressure within the barrel exceeds a predetermined value.
2. In an electric blasting cap having a cup-shaped case, an explosive charge within the cup-shaped case at one end thereof, an electrical igniter in said explosive charge, a sealing closure within said cup-shaped case and confining said explosive charge, said case extending for a substantial distance outwardly of said sealing closure, a pair of lead wires extending into said case from the exterior thereof and through said sealing closure and connected with said igniter, a sealed chamber within said cup-shaped case outwardly of said sealing closure, said chamber having a wall movable relative to said case between a normal position whereat the pressure on the exterior of said case is substantially the same as the pressure on the interior of said chamber and an abnormal position whereat the pressure on the exterior of said case substantially exceeds the pressure on the interior of said chamber, said wall having an electric circuit controlling part movable therewith for maintaining said igniter deenergized When said Wall is in said abnormal position.
3. The combination of claim 2 wherein each of the lead wires includes a web portion, said web portions are peripherally sealed together by insulating material to form said sealed chamber, the central portion of said webs being arranged to flex under pressure sufliciently to make electrical contact with each other, and means for maintaining said web portions free of engagement with said case, said case being vented adjacent said web portions.
4. The combination of claim 2 wherein the said movable wall constitutes the end closure for said case, a contact bridge arranged to move with said movable wall, and contact parts on said lead wires outwardly of said sealing closure and disposed to 0e engaged by said contact bridge when in said abnormal position.
References Cited in the file of this patent UNITED STATES PATENTS 1,022,865 Nicolai Apr. 9, 1912 1,091,021 Schafiier' Mar. 24, 1914 1,244,528 May Oct. 30, 1917 1,962,168 Andrus June 12, 1934 2,141,827 Schlumberger Dec. 27, 1938 2,247,384 Hayett July 1, 1941 2,494,256 Muskat Jan. 10, 1950 2,566,682 Sweetman Sept. 4, 1951