US2739535A - Electric explosion initiators - Google Patents

Description

March 27, 1956 e. F. ROLLAND ETAL 2,739,535

ELECTRIC EXPLOSION INITIATORS Filed July 14. 1950 6. v, QW

VENT Rs 1 FlGll ELECTRIC ExPLosroN INITIATORS Guy F. Rolland, McKeansburg, Le Roy A. Shoeucr, East Brunswick Township, Schuylkill County, and Aubrey A. Young, Tamaqua, Pa., assignors to Atlas Powder Company, Wilmington, Del., a corporation of Delaware Application July 14, 1959, Serial No. 173,862

5 Claims. (Cl. 102-28) This application relates to electric explosion initiators.

An object of the invention is the provision of an electric explosion initiator which is rendered inoperative by the action of water or other liquids.

Another object of the invention is the provision of an electric explosion initiator which is rendered inoperative by the action of fluid mud or other similarly viscous materials.

Other objects of the invention will be apparent from the following description.

in the process of obtaining oil through an oil well it sometimes becomes desirable to perforate the sides of the well. Recently it has become customary to employ for this purpose a perforating gun lowered into the Well. A perforating gun commonly used in the art includes a bomb-like shell provided with a series of spaced shaped charges arranged to discharge through the walls of the well. The perforating guns employed are reusable and are fitted out with a new series of shaped charges after one set has been used. The shaped charges in the guns are ordinarily initiated by detonating fuse which in turn is initiated by an electric blasting cap contained in the gun. In one type of gun the electric blasting cap is located in the bottom of the gun with its business end (i. e. the end containing explosive charge) pointed up.

Often oil wells contain considerable heads of liquid such as oil, water, or fluid mud, and occasionally perforating guns of the sort described will leak before they are fired. When a leak occurs, it is sometimes found that when the charges are fired the casing of the perforating gun becomes damaged and permanently wedged in the oil well casing, thereby impairing the usefulness of the well. It is preferred that the perforating gun not function at all when leakage has occurred. In a bomb of the sort just described the electric blasting cap, being in the bottom of the bomb, is the first part to be immersed by entering liquid, and, of course, if the initiator does not function neither will any part of the bomb.

According to the present invention an electric explosion initiator is provided which will fail to function if it is immersed in liquid. In general, electric explosion initiators of the invention may be made in the conventional form of an electric blasting cap except each is provided with at least two ports spaced longitudinally along the shell. These ports are arranged so that, when an initiator is held business end upwards and liquid rises around it, the liquid will first enter a port most removed from the business end of the initiator, and a second port will permit the escape of air from the initiator. The entering liquid immerses the ignition element of the initiator and provides a cushion between the ignition element and the explosive so as to prevent detonation of the initiator when the ignition element is fired.

Since the arrangement just described will not always cause the initator to fail if a viscous liquid such as a mud is seeping into the bomb, the initiator of the invention in a preferred embodiment also includes a shield sealed to the initiator shell between the ports just described and nited 'ffi ate'nt extending in the direction of the business end of the cap. The shield is provided with an exit to the air at a point beyond the port in the cap nearest the business end of the initiator. Without the shield construction just described a viscous mud will sometimes seal the air vent in the initiator shell and prevent egress of air before the mud has been able to fill the initiator sufliciently to prevent its functioning. With the exit portion of the shield sufficiently removed from the second port, the shield construction prevents the mud from impeding egress of air until the mud level has reached a height such that sufficient air must have escaped that the interior of the cap is well filled with mud. Conveniently the shield is so constructed that it also serves as a means of connecting detonating fuse to the initiator.

The invention will be further and more specifically described in connection with the accompanying drawings in which:

Figure 1 is a sectional view of the lower portion of a bomb of a type in which the initiator of the present invention is advantageously used.

Figure 2 is a longitudinal elevation of an initiator of the invention and its associated shield parts in unassembled condition; and

Figure 3 is a sectional view, taken on line 33 of Figure 2, of the initiator and shield construction in assembled condition.

Referring to Figure 1, 11 represents the shell of a bomb represented generally as 12. Shell 11 is closed by bottom end member 13 which is screwed into shell 11 and against gasket 15. 17, 19, 21, and 23 are indents providing grips for tools so that shell 11 and end piece 13 may be brought up tightly against gasket 15. 25 generally represents a shaped charge assembly. Shaped charge assembly 25 is made up of a sheath 27 preferably of lead into which is pressed explosive charge 29 preferably composed of cyclonite. Pressed onto charge 29 is metal cone 31. Shaped charge assembly 25 rests in indentation 33 in shell 11 and is held in place by plug 35 which is driven through a port in wall 11. Plug 35 is preferably made of lead and is expendable. When shaped charge assembly 25 is detonated the force of the explosion blows through plug 35 and through the walls of the oil well in which the bomb is placed.

Shaped charge assembly 25 at its opposite end from cone 31 is provided with a tunnel through which detonating fuse 37 is threaded. Detonating fuse 37 initiates charge 29 in shaped charge assembly 25. Detonating fuse 37 is detonated by means of an electric blasting initiator represented generally at 39. Electric blasting initiator 39 is in its turn initiated by an electric current which is passed through leg wires 41 and 4-3.

Figure 1 shows only the bottom portion of bomb 12. Bomb 12 contains several more shaped charge assemblies like assembly 25 threaded on detonating fuse 37 in an upwardly ascending spiral. Bomb 12 is sealed tightly at its top and leg wires 41 and 43 (or wires connected to them) are sealed in the top of the bomb and passed up the oil well bore to a source of current.

The present invention does not relate to the construction of the bomb or to the charges employed in it, but rather to the electric blasting initiator 39 This initiator .will be described in connection with Figures 2 and 3 which illustrate an instantaneous type initiator. It comprises a conventional shell 45 containing two explosive charges 47 and 49 pressed into the closed end of the shell. These charges may be cyclonite and lead azide, respectively. While other explosive or explosives may be used, these are particularly desirable because of their resistance to the conditions of high temperature which often obtain in oil well bore holes. Spaced from charge 49 is electric match assembly 51. Electric match assembly 51 is also conventional although it is usually desirable that match head 53 include a heat resistant ignition compound. Lead mononitroresorcinate is a desirable ignition compound for the present purpose. Soldered to electric match assembly 51 are leg Wires 41 and 43 which pass through conventional rubber plug 54 which closes the mouth of shell 45. Surrounding electric match assembly 51 and protecting it from shell 45 is insulating tube 55 held in place in shell 45 by means of stake marks 57, 59, 61, and 63. Below match assembly 51, shell 45 is provided with a normally open port 65, and between match head 53 and charge 49 is located a normally open port 67. Preferably port 67 is placed adjacent explosive charge 49, and preferably port 65 is placed adjacent plug 54.

Thus, it is seen that when initiator 39 is positioned with its business end upwards water seeping into the bomb will enter port 65 pushing air out of port 67, and eventually filling the space between match head 53 and port 67. Match head 53 is located far enough from charge 49 that even if it fires, the flame produced will be drowned and will not initiate the explosive 49.

However, if the material entering the bomb is a viscous mud and the explosition initiator, as described so far, is used alone, port 67 may be covered with mud before the mud has seeped up to cover match head 53 sufliciently. It is found that when port 67 is covered with mud further egress of air is effectively blocked and further entrance of mud through port 65 and into the initiator is prevented.

To overcome the difficulty just described shield 69 is provided. Shield 69 is sealed to shell 45 by means of gasket 71 which is conveniently made of rubber tubing and is cemented on shell 45 so that a substantially water tight seal between shell 45 and shield 69 is provided between ports 65 and 67. Shield 69 is provided with a normally open port 73. In order to aid in aflixing detonating fuse to the blasting cap, shield 69 is provided with a necked down portion which snugly receives detonating fuse and holds it against the business end of the initiator proper.

Sinc'e shield 69 is spaced from shell 45 a continuous passage is provided for the egress of air from port 67 in shell 45 through port 73 in shield 69. Thus, mud seeping into the bomb will enter port 65 in shell 45 and will rise inside shell 45 as air passes out port 67 in shell '45 and port 73 in shield '69. Moreover shield 69 protects port 67 from blockage by mud until mud -reaches port 73. By this time the mud will have had sufiicient opportunity to climb inside shell 45 and cover r'natc h head 53 suificiently to protect explosive charges 47 and 49 against ignition.

It will be noted that, as shown in the drawing, ports 67 and 73 are smaller than port 65. In a specific embodiment in which the shell 45 is 2 /8 inches long and 0.275

inch in outside diameter, port 65 is /s inch in diameter whereas ports 67 and 73 are but 7 inch in diameter. Since port 65 is designed to permit the ingress of viscous material such as mud and ports 67 and '73 only have to pass air, it is not necessary that the latter ports be as large as port 65.

It is to be noted that the match head is spaced from the explosive charge in the cap shown in the drawings. Usually it is desirable that this space he at least inch to prevent detonation of explosive charges 47 and 49 through the liquid which may enter the cap.

initiators of the dimensions and type just described without the shield were tested by immersing them in oil and in water with their business ends up. It was found in each case that the initiators would fail to detonate within 15 seconds after immersion. However, when fiuid mud from an oil well was substituted for oil or water, failure of the caps often could not be secured. The mud test was then repeated with caps onwhich'the shields had been placed, and it was foun'din each, case that the caps would fail to detonate within 15 seconds of immer- SlOIl.

Where, in the present specification and in the subjoined claims, we recite that the ports 65, 67 and 73 are normally open ports, we refer to the fact that these ports are open at the time when the explosion initiator of our present invention is placed in operative position within the bomb-like shell of a well-perforating gun and is ready to be fired therein, or is placed in some other position or location where it is ready to be fired to serve its intended function as an explosion initiator.

What is claimed is:

1. An instantaneous electric explosion initiator capable, when in a vertical position in the presence of rising liquid, such as in a well perforating gun, of being rendered inoperative relatively rapidly comprising a shell, an explosive fixed in said shell, an electric initiating element including an ignition compound spaced therefrom in said shell and normally operative to ignite said explosive, open space being provided between said initiating element and said explosive, said shell being so constructed as to provide a normally open port adjacent the surface of said explosive and between said explosive and said initiating element and communicating with said open space and a normally open port on the other side of said initiating element from said explosive also communicating with said open space.

2. An instantaneous electric explosion initiator capable, when in a vertical position in the presence of rising liquid, such as in a Well perforating gun, of being rendered inoperative relatively rapidly comprising a shell, an explosive pressed in said shell, an electric initiating element including an ignition compound spaced therefrom in said shell and normally operative to ignite said explosive, open space being provided between said initiating element and said explosive, two normally open ports spaced longitudinally along said shell, one of said normally open ports being positioned between said initiating element and said explosive and communicating with said open space, and the other of said normally open ports being positioned on the other side of said initiating element from said explosive and in communication with said first normally open port through the interior of said initiator.

3. An instantaneous electric explosion initiator capable, when in a vertical position in the presence of rising liquid, such as in a well perforating gun, of being rendered inoperative relatively rapidly comprising a shell, an explosive pressed in said shell, an electric match spaced therefrom in said shell and normally operative to ignite said explosive, open space being provided between the headof said match and said explosive, two normally open ports spaced longitudinally along said shell, one of said normally open ports being positioned between the head of said match and said explosive and communicating with said open space, and the other of said normally open ports being positioned on the other side of the head of said match from said explosive and in communication with said first normally open port through the interior of said initiator.

4. An electric explosion initiator comprising a shell, an

explosive pressed in said shell, an electric initiating element spaced therefrom in said shell, open space being provided between said initiating element and said explosive, two open ports 'spaced'longitudinally along said shell, one of saidopen ports being positioned between said initiating elemerit and said explosive and communicating with said open s ace, and the other of said-open ports being spaced more remotely from said explosive and in communication with said 'first port through the interior of said initiator, and a shield fitting over the explosive end of said initiator "tind'sealed ina substantially Water-tight manner to said initiatorbetween said ports, said shield being open at a'point'beyond'sai'd first p'ort and defining a passageway from saidffirst port 'tosaid 'point beyond said first port. '5. An electric explosion initiator comprising a shell,

an explosive pressed in said shell, an electric match spaced therefrom in said shell, open space being provided between the head of said match and said explosive, two

beyond said first port and defining a passageway from said first port to said point beyond said first port.

References Cited in the file of this patent UNITED STATES PATENTS 1,901,469 Piccard Mar. 14, 1933 1,964,788 Cooper July 3, 1934 FOREIGN PATENTS 416,349 Great Britain Sept. 7, 1934 577,873 Great Britain June 4, 1936 481,071 Germany Aug. 13, 1929

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