United States Patent: 3554299

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( 20347 of 20347 )

United States Patent	3,554,299
Sullivan	January 12, 1971

WELL-PERFORATING TOOL

Abstract

A perforating tool which is intended for use in a well bore. The tool includes a longitudinally extending body. A spring means is selectively movable longitudinally of the body along a predetermined path. A peripheral path surface on the body extending along the predetermined path faces toward the spring means. The spring means includes a free end resiliently biased in a transverse direction into contact with the path surface. A plurality of explosive perforating units are spaced along the body. Each perforating unit includes detonating means projecting into the predetermined path extending outwardly of the path surface. A plurality of projecting means connected with the body, spaced along the predetermined path alternately between the detonating means, cause the free end of the spring means to be successively deflected away from the path surface. Each projecting means terminates adjacent the next detonating means in the direction of motion so that the free end of the spring means springs back toward the path surface to exert a hammering action upon the adjacent detonating means.

Inventors:	Sullivan; James P. (Cheyenne, WY)
Assignee:	Aquatech Corporation (Houston, TX)
Appl. No.:	04/760,750
Filed:	September 19, 1968

Current U.S. Class: 175/4.55 ; 175/4.56; 175/4.57

Current International Class: E21B 43/116 (20060101); E21B 43/11 (20060101); E21b 043/116 ()

Field of Search: 175/4.55,4.56,4.59,4.57 166/55.1

References Cited [Referenced By]

U.S. Patent Documents


1835722	December 1931	Rembert
2142572	January 1939	Metzner
2203265	June 1940	Kniss
2317238	April 1943	Mennecier
2356430	August 1944	Raymond
2540184	February 1951	Broyles

Primary Examiner: Brown; David H.

Claims

I claim:

1. A perforating tool for use in a well bore, the tool comprising:

a longitudinally extending body adapted to be disposed generally vertically when in a well bore;

a plurality of vertically spaced explosive perforating units mounted in said body;

firing means movably connected with said body, said firing means including cam operable actuating means for causing firing of each of said perforating units upon movement into registry therewith;

pulling means connected with said firing means adapted for the application of upward pulling force to said pulling means to cause selective motion of said firing means, including said cam operable actuating means, along said body into successive registry with each of said perforating units; and

a plurality of independent camming means connected with said body and independent of said pulling means for activating said cam operable actuating means by successive engagement therewith prior to movement thereof into registry with each of said perforating units.

2. A perforating tool as defined in claim 1 wherein said cam operable actuating means comprises spring means deflected by said camming means prior to movement of said cam operable actuating means into registry with each of said perforating units.

3. A well-perforating tool for use in a well bore, the tool comprising:

a longitudinally extending body adapted to be disposed generally vertically when in a well bore;

a plurality of vertically spaced explosive perforating units mounted in said body;

firing means movably connected with said body;

pulling means connected with said firing means adapted for the application of upward pulling force to said pulling means to cause selective motion of said firing means along said body into successive registry with each of said perforating units, said firing means causing firing of each of said perforating units upon motion into registry therewith;

impedance means connected with said body for causing an increase in the pulling force required to be applied to said pulling means whenever said firing means in intermediate two adjacent ones of said perforating units and for causing a diminution in the pulling force required to be exerted whenever said detonating means is in registry with one of said perforating units;

whereby the relative magnitude of the pulling force to be exerted provides an indication of the location of said firing means in registry with one of said perforating units.

4. A perforating tool for use in a well bore, the tool comprising:

a longitudinally extending body adapted to be disposed vertically when in the well bore;

spring means selectively movable longitudinally of said body along a predetermined path;

said body having a peripheral path surface extending along said predetermined path, said path surface facing toward said spring means;

said spring means further including a free end resiliently biased in a transverse direction into contact with said path surface;

a plurality of explosive, perforating units connected with said body spaced vertically therealong, each said perforating unit including:

detonating means projecting into said predetermined path extending transversely outwardly of said path surface, said detonating means upon application of a transverse impact thereto causing detonation of the associated perforating unit; and

a plurality of projecting means connected with said body spaced along said predetermined path alternately between said detonating means, each said projecting means extending transversely outwardly from said path surface to cause said free end of said spring means upon contact with said projecting means to be moved away from said path surface, each said projecting means terminating adjacent the next one of said detonating means to enable said free end of said spring means to spring back towards said path surface and impinge upon the adjacent said detonating means to apply sufficient impact thereto to detonate the associated said perforating unit.

5. A perforating tool as defined in claim 4 further including:

supporting means connected with said body for supporting said body at a predetermined location within the well bore;

actuating means connected with said spring means adjusted to extend to the surface of said well bore for causing selective longitudinal motion of said means relative to said body; and

guiding means connected with said body contacting said spring means for guiding said spring means along said predetermined path.

6. A perforating tool as defined in claim 5 wherein said spring means further includes:

a body member of sufficient length to extend bridgingly across at least two adjacent ones of said projecting means to be supported thereby in transversely spaced relation from said path surface; and

a leaf spring having one longitudinal end fixedly secured to said member with an opposite longitudinal end of said leaf spring defining said free end.

7. A perforating tool as defined in claim 6 wherein:

said leaf spring intermediate said longitudinal ends thereof is bowed transversely away from said path surface; and

wherein said guiding means includes a channel member connected with said body extending along said predetermined path, said channel member including:

an internal longitudinal surface extending in transversely spaced, opposed relation to said path surface, said internal surface slidably contacting said bowed portion of said leaf spring to press said spring and said member toward said path surface.

8. A perforating tool as defined in claim 6 wherein:

each said projecting means further includes a generally polygonal transversely projecting body having:

longitudinally spaced forward and rearward edge surfaces disposed in generally perpendicular relation to said path surface;

a flat longitudinally extending outer surface extending between said edge surfaces parallel to and spaced transversely outwardly of path surface; and

wherein said spring is bowed transversely outwardly intermediate said longitudinal ends to cause the internal bowed surface of said leaf spring to have a camming action upon contact with said forward edge surface of each said projecting body to deflect said free end of said leaf spring transversely outwardly.

9. A perforating tool as defined in claim 4 wherein:

each said perforating unit further includes:

a transverse bore having an open end facing outwardly of said body on an opposite side thereof from said path surface;

an explosive cartridge mounted in said body in alignment with said transverse bore, said cartridge upon explosion thereof directing an explosive blast outwardly of said bore;

wherein each said detonating means further includes, a transversely extending detonating pin having one end positioned adjacent said cartridge for detonation thereof and an opposite end projecting into said predetermined path to be acted upon by said free end of said spring means; and

a plurality of nails, each of said nails being separately insertable into the open end of an associated one of said transverse bores, each said nail subsequently being propelled out of the associated bore upon detonation of the associated said explosive cartridge.

10. A perforating tool as defined in claim 9 wherein each said nail further includes a sealing plug connected with and surrounding said nail, said sealing plug sealingly contacting the walls of the associated said transverse bore upon insertion of said nail into said bore to exclude water from entry into said bore.

11. A perforating tool as defined in claim 9 wherein each said nail includes:

a pressure surface extending completely across the associated said transverse bore to be acted upon by high pressure gases generated upon explosion of said cartridge; and

a pointed head facing toward said opening of said bore.

12. A perforating tool as defined in claim 9 wherein:

said body includes longitudinally extending, first and second bodies releasably connected together, said transverse bores being provided in said first body, said perforating unit further including:

a plurality of cartridge receiving bores, each of the cartridge receiving bores being associated with a corresponding one of said transverse bores in communication therewith at an opposite end of said transverse bore to said open end thereof, each said cartridge receiving bore slidably receiving one of said explosive cartridges when said second body is removed from said first body; and

said second body upon connection to said first body blocking release of said cartridges from said cartridge receiving bores.

13. A perforating tool as defined in claim 12 wherein:

said transversely extending detonating pin is mounted for transverse sliding motion within and relative to said second body, said detonating pin in an initial position thereof having said opposite end projecting into said predetermined path; and

resilient biasing means connected with said detonating pin and said second body for urging said detonating pin to the initial position thereof.

Description

BACKGROUND OF INVENTION

This invention relates to an explosive perforating tool for use in a well bore.

In performing operations on a cased well bore it is sometimes necessary to perforate the well casing adjacent certain earth strata so that liquid may enter the well bore through the perforations and pass outwardly through the casing. Such operations are, for example, necessary in cased water wells to allow water to pass from aquiferous strata into the casing so that the water may be delivered to the surface. Similar operations may need to be conducted in well bores intended for extraction of oil and other liquids.

To provide such perforations it is common to use so-called perforating tools which are often of the explosive type. These tools usually include a tubular body adapted to be lowered in the well bore to a position adjacent the desired strata, with a plurality of vertically spaced perforating units mounted in the tool body. Each perforating unit usually includes a projectile which may be propelled transversely from the perforating tool by detonation of an explosive charge through the casing to provide a perforation therein. Various systems for detonating the explosive charges are known including both electrical and mechanical systems. Although the electrical systems are widely used, they are frequently complex, costly and unreliable and attempts have therefore been made to devise a satisfactory mechanical system for detonating perforating tools.

One such mechanical system (see, for example, Rembert U.S. Pat. No. 1,835,722) includes a plurality of vertically spaced perforating units, each of which includes a stressed spring held out of contact with an adjacent detonator by an actuating rod contacting all the springs of the separate perforating units. Vertical motion of the actuating rod frees all the springs simultaneously to impinge upon their associated detonating units to fire all the perforating units simultaneously.

Although such a system may be sometimes satisfactory, a device of this type may not be suitable under certain circumstances. For example, it may be desirable to conduct perforating operations at several vertically spaced locations within a well bore utilizing only one run of the tool. However, this would not be possible utilizing a tool where all the perforating units are detonated simultaneously without any provision being made for selective control of individual perforating units. Another disadvantage may arise if there should be a misfire of one of the perforating units, as there would be no way of detecting this misfire at the surface during the simultaneous explosion of the other, operative perforating units. If this should happen, not only would there be inadequate perforation at the desired zone but, in addition, serious hazards might arise at the surface once the tool bearing a live but defective perforating unit unknown to personnel at the surface was brought to the top.

Another prior mechanical detonation system provides for sequential firing of the perforating units, but required all the perforating units in the sequence to be fired on each operation of the tool. Thus again, this prior system would not be suitable for perforating at different tool locations within the well bore on a single run of the tool. In addition, in this prior system, the only surface indication that a perforating unit has fired is the sound of the explosion so that in the event of a misfire, no indication of the location of the misfiring unit in the tool would be available, thus causing similar problems to these just discussed for the first prior tool.

OBJECTS AND SUMMARY OF INVENTION

It is, therefore, a general object of the invention to provide a perforating tool for use in a well bore, which is intended to obviate or minimize problems of the type generally noted.

It is the particular object of the invention to provide a perforating tool having a plurality of spaced perforating units fired by a detonating device moved successively past the perforating units, wherein the arrival of the detonating device at each of the perforating units is indicated positively to an operator, whether or not the perforating unit fires.

It is another object of the invention to provide a perforating tool for use in well bores in which firing of the perforating units may be selectively and successively controlled, utilizing a particularly simple structure which may be provided at low cost.

An apparatus constructed in accordance with a preferred embodiment of the invention intended to accomplish at least some of the foregoing objects is intended for successively and selectively detonating a plurality of explosive perforating units mounted in and spaced along a perforating tool disposed in a well bore. The apparatus includes detonating means adapted to be movably mounted on the perforating tool for motion therealong successively past the perforating units. The detonating means upon movement into registry with each of the perforating units causes detonation thereof. Pulling means is connected with the detonating means adapted to be manipulated at a well head to apply a pulling force to the detonating means. The pulling force causes relative motion of the detonating means along the perforating tool to successively and selectively position the detonating means in registry with each of the perforating units for detonation thereof. A plurality of impedance means is adapted for connection with the perforating tool. The impedance means successively contact the detonating means to cause an increase in the pulling force required to be applied to the pulling means whenever the detonating means is positioned intermediate the various perforating units and to cause a sudden decrease in the pulling force required to be exerted as the detonating means reaches the particular perforating unit to be detonated.

It will be realized that by this construction, an operator at the surface is informed when the detonating device has reached each perforating unit by a sudden decrease in the pulling force he is required to exert. Thus, for example, in a tool having a number of perforating units, the operator may count the number of increases and decreases in pulling force experienced by him to ascertain which particular one of the perforating units is currently in registry with detonating device. This indication is entirely separate from any audible indication the operator may have of direct explosion of the perforating unit. Thus, for example, if one of the perforating units misfires the operator is immediately informed because the decrease in pulling force experienced by him will not be accompanied by the usual audible sound of explosion from down the well bore. The indication of misfire thus provided is extremely valuable for informing the operator of the precise location of the live but defective perforating unit in the tool when the latter is brought to the surface. Also, the operator is informed that a particular location in the well has not been perforated as desired.

In more structural detail, a perforating tool for use in a well bore, according to one preferred embodiment of the invention, includes a longitudinally extending body adapted to be disposed vertically when in the well bore. Spring means movably connected with the body is selectively movable longitudinally thereof along a predetermined path. The body includes a peripheral, path surface extending along the predetermined path facing towards the spring means. The spring means includes a free end resiliently biased in a transverse direction into contact with the path surface. A plurality of explosive perforating units connected with the body is spaced vertically therealong. Each perforating unit includes detonating means projecting into the predetermined path extending transversely outwardly of the path surface. Application of a transverse impact to the detonating means causes detonation of the associated perforating unit. A plurality of projecting means is connected with the body spaced along the predetermined path alternately between the detonating means. Each projecting means projects transversely outwardly from the path surface to cause the free end of the spring means upon contact with the projecting means, to be deflected resiliently away from the path surface. Each projecting means terminates adjacent the next detonating means in the direction of motion of the spring means, to enable the free end to spring back towards the path surface and impinge upon the adjacent detonating means with sufficient impact to fire the associated perforating unit.

THE DRAWINGS

A perforating tool constructed in accordance with a preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a simplified, cross-sectional, view of a perforating tool according to one preferred embodiment of the invention with the tool disposed in a cased well bore;

FIG. 2 is a cross-sectional view generally corresponding to that of FIG. 1 but with the tool shown moved to a different location in the well bore to perforate the casing adjacent a different strata;

FIG. 3 is a perspective view of a detonating device forming a part of the present invention;

FIG. 4 is a perspective view of a perforating nail utilized in the present invention;

FIG. 5 is a side view, partially in cross section, of the perforating tool shown in FIG. 1;

FIG. 6 is a cross-sectional side view on an enlarged scale of a portion of the perforating tool shown in FIG. 5 in the area 6-6 of FIG. 5;

FIG. 7 is a cross-sectional top view of a portion of the tool shown in FIG. 5 as indicated therein by the lines 7-7 on an enlarged scale; and

FIG. 8 is a perspective view of the perforating tool shown in FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1 of the drawings, a perforating tool 2 according to a preferred embodiment of the invention, is shown positioned within a generally vertical well bore 4 which, for exemplary purposes, is shown to extend vertically through three different earth strata, A, B and C. The well bore 4 is also provided with a well casing 6. It will be assumed for the purposes of discussion that it is desired to perforate the casing opposite the strata A and C but not opposite the intermediate strata B. The tool 2 (FIG. 5) includes a longitudinally extending first, solid metal, barlike body 8 of rectangular cross section, which is disposed generally vertically when in the well bore. The first body 8 includes vertically extending, generally flat, parallel front and rear faces 9 and 10, respectively, spaced transversely apart. At its upper end, the first body 8 is provided with a connecting eye 11 which receives a cable 12. The cable 12 extends to the surface of the well bore and supports the tool 2 at a predetermined desired location within the well bore adjacent the strata to be perforated.

Spaced vertically along the first body 8 are a plurality of identical explosive perforating units 13, one of which is shown in more detail in FIG. 6. Each perforating unit 13 is mounted within a horizontal, opening 14 extending transversely entirely through the forward member from the vertical forward face 9 thereof to the vertical rear face 10, generally laterally centrally of the body. The opening 14 receives a concentric sleeve 20 fixedly secured to the first body by an interference fit. However, the sleeve 20 may be secured by other methods, such as, for example, by threaded connection, welding or the like. The sleeve 20 at its forward end is flush with the forward surface 9 of the first body, with an opposite rear end of the sleeve 20 being spaced inwardly from the rear surface 10 of the first body to constitute a shoulder 21 projecting radially into the opening 14.

A transverse inner bore 22 extending concentrically through the sleeve 20 has an open forward end 22a. A transversely extending, cartridge receiving recess 26 concentric with the inner transverse bore 22 is provided in the inner sleeve 20 adjacent the rear end thereof. The cartridge receiving recess 26, in the preferred embodiment, is shaped to receive a 0.38 caliber blank cartridge 28 of conventional construction, with the outer surface of the head of the cartridge being flush with the shoulder 21.

The function of the cartridge 28 is to propel a perforating nail 29 (to be described in more detail hereinafter) inserted into the transverse bore 22, outwardly therefrom in a forward direction to be forced through the casing 6 of the well bore to perforate it.

To retain the cartridge 28 within the cartridge receiving recess 26, once it has been loaded therein, each perforating unit 13 includes a generally cylindrical, sleevelike, retaining member 30 having its forward end slidably and snugly received within the rearward portion of the opening 14. The retaining member 30 on its forward face abuts the shoulder 21 of the inner sleeve 20 and the rear end of the cartridge 28 to retain the cartridge within the cartridge receiving recess 26. The retaining member 30 projects rearwardly beyond the rear surface 10 of the first body 8 and extends through an outer transverse bore 34 in a second, solid metal, barlike body 36. Motion of the retaining member 30 relative to the second body 36 may be prevented by interference fit between the retaining member 30 and second body and/or by interengaging shoulders 36a and 36b on the second body 36 and retaining member 30, respectively. Alternatively, a threaded connection, welding or other form of fixed connection may be provided.

The second body 36 is longitudinally and laterally coextensive with the first body 8 and is of generally rectangular cross section. A forward face 37 of the second body is parallel to and spaced rearwardly from the rear face 10 of the first body with a rear face 40 of the second body parallel to and spaced rearwardly of the front face 37.

The second body 36 is connected with the first body 8 by a plurality of vertically spaced threaded connectors 44 (FIGS. 5 and 6). The threaded connectors 44 may be tightened up to cause the retaining members 30 to be pressed firmly against the bases of their associated cartridges 28. Each connector 44 includes a conventional head portion 45 having a flat surface 46 generally parallel to the rear surface 40 spaced transversely rearwardly therefrom. A plurality of edge surfaces 48 disposed in a generally hexagonal pattern extend perpendicularly from the surface 46 to the rear surface 40 of the second body. The elongate connectors 44 are spaced at uniform intervals in alternate relation between the firing units 13, with the surfaces 46 of the headed portions of the connectors 44 disposed in a common plane parallel to and spaced rearwardly from the rear surface 40 of the second body.

To detonate the cartridge 28, each perforating unit 13 is provided with a detonating pin 49. The detonating pin 49 includes a horizontal, transversely extending, slender, generally cylindrical pin body 50. This pin 50 has a forward end 51 which, in an initial position of the pin body, lightly contacts the conventional detonating cap of the explosive cartridge 28. Rearwardly, the pin body 50 includes a rear end 52 projecting outwardly beyond the rear surface 40 of the second body 56. A violent impact imparted to the rear end 52 of the detonating pin causes the forward end 51 to strike the cartridge detonating cap with sufficient force to explode the cartridge 28 to drive the nail 29 out through the casing.

The detonating pin 49 is guided for transverse motion by an enlarged concentric, cylindrical portion 53 of the pin. This portion 53 is slidably and snugly received within an internal transverse bore 54 in the retaining member 30. The firing pin 49 is located in its initial position by abutting contact between a rear radial surface of the enlarged portion 53 and a forward surface of an annular constricted portion 55 which is integral with the retaining member 30 and slidably receives the pin body 50. The detonating pin is resiliently biased to its initial position by a compression, coil spring 58 which encircles the pin body 50. One end of the spring 58 contacts a forward radial shoulder of the enlarged portion 53. The opposite end of the spring contacts an annular insert 60 which is press fitted within the forward end of the bore 54.

Of particular interest, in the context of the present invention, is firing structure utilized to effect selective and sequential firing of the various perforating units 13 in the tool body. For this purpose, a firing device 70 (FIGS. 3 and 5) is provided. The firing device 70 includes a longitudinally extending, rigid, movable member 72 of striplike configuration. The length of the movable member 72 is sufficient to allow it to extend in bridging relation over the heads 45 of at least two at a time of the previously mentioned elongate connectors 44 utilized to secure the second body 36 to the first body 8.

The movable member may be selectively pulled upwardly along the tool tube by a flexible line or cable 76 connected to the upper end of the movable member with the line 76 extending upwardly of the well bore to the surface to be grasped and pulled manually by an operator or raised by a hoisting device. The forward end of movable strip 72 is bent transversely away from the heads of the connectors 44 at the point of connection to the line 76 to assist the strip 72 in passing smoothly over the connectors and to avoid interference between the line 76 and the connectors.

The movable member 72 is guided along a predetermined path, during its upward motion, by a channel member 78 (FIGS. 7 and 8), secured to the rear surface of the second body 36 and extending vertically along the length thereof. This channel member 78 guidingly contacts an arcuate, resilient, leaf spring 80 secured to the movable member 72. A rear wall 82 of the channel member 78 is supported in rearwardly spaced, opposed relation to the rear surface 40 of the second body by two forwardly and oppositely diverging sidewalls 84. The sidewalls 84 terminate in side flanges 86 abutting the rear surface 40 of the second body and connected thereto by a plurality of vertically spaced elongate threaded connectors 88.

The previously mentioned leaf spring 80 (FIG. 3) has one end fixedly secured to the movable member 72 and extends longitudinally therefrom to a free end 90. The area of the free end 90 of the leaf spring is increased (for a purpose to be described), by securing thereto a generally rectangular striker plate 91. Intermediate its opposite longitudinal ends, the leaf spring 80 is bowed transversely outwardly away from the second body, with the bowed portion operable to be disposed in sliding contact with the inner surface of the rear wall 82 of the channel guide member (FIGS. 5 and 7). The free end 90 is operable to contact the rear surface 40 of the second body 36 and is resiliently biased into contact therewith by virtue of the engagement between the bowed portion of the leaf spring and the rear wall 82 of the channel member.

As the firing device 70 is moved upwardly along the tool in the predetermined path, it may be considered that the rear surface 40 of the second body 36, intermediate the headed connectors 44, constitutes a path surface against which the free end of the leaf spring is resiliently biased.

An operator applies a pull to the line 76 to move the firing device 70 from an initial position at the bottom of the tool in which the free end of the spring is against the path surface 40. The firing device 70 is moved upwardly, under a light pulling resistance afforded by frictional contact between (1) the ends of the spring 90 with the rear surface 40 of the second body, and (2) between the bowed portion of the leaf spring and the rear wall 82 of the channel member. As the operator pulls upward on the line 76, the weight of the body of the tool, including the solid bar members 8 and 36, prevents corresponding upward movement of the firing devices 70 and the operating detents or abutments 48. In certain instances, it may be appropriate to provide drag springs on the exterior of the tool body to facilitate the stabilizing of the tool body as the firing device 70 is pulled upwardly.

Upon continued motion, the internal of the bowed portion 80 of the leaf spring moves into contact with the lower edge surface 48 of the head of the lowermost one of the elongate connectors 44. As this occurs, the corner of the head 45 exerts a camming action upon the internal bowed surface of the leaf spring tending to deflect it transversely outwardly so that the leaf spring 80 starts to ride over the connector head 45.

At this time, the operator experiences or observes a considerable increase in the pulling force that is required to be exerted to continue upward motion of the movable member. This increase in required force is a consequence of the spring 80 being in a compressed condition and providing greater frictional resistance or impedance to motion along the channel member 78 and the path surface 40 and also a consequence of the impediment to movement afforded by head 45. Continued upward motion moves the free end 90 of the leaf spring and its associated strike plate 91 across the top surface 48 of the head 45, with the spring 80 remaining in a compressed condition, so that it is necessary to continue to exert the relatively increased level of pulling force.

When the free end 90 of the spring 80 and the striker plate 91 passes the opposite, upper edge surface 48 of the headed connector 44, the leaf spring springs back violently against the rear surface 40 of the second body. The positioning of the detonating pin 49 of the lowermost perforating unit 13 is such that upon this springing back, the striker plate 91, at the free end 90 of the spring, impinges violently upon the projecting rear end 52 of the detonating pin 49. The detonating pin 49 is thus struck with sufficient impact to cause detonation of the cartridge 28 so that the perforating unit 13 is fired.

The striker plate 91 extends over a sufficient area to embrace the relatively small head of the detonating pin 49 so as to ensure that the impact provided by the free end of the spring 90 is transmitted to the detonating pin.

The relative arrangement of the next succeeding headed connectors 44 and perforating units 13 is similar to that described for the lowermost connector and perforating unit. Thus, the sequence outlined may be selectively and successively performed for each of the perforating units 13 in the tool. Accordingly, a renewed upward pull on the line 76 causes the firing device to move on up to the next perforating unit to fire that unit, and so on.

It will be appreciated that the firing arrangement thus provided offers significant advantages. For example, on a single run of the tool into and from the well it becomes possible to select individual perforating units for firing with the tool in one location (such as zone A in FIG. 1) and then to move the tool to a different location within the well, (such as zone C in FIG. 2) for selective firing of different perforating units in the tool.

Particularly significant is the manner in which the frictional impedance to the pulling force exerted on line 76 is relatively smaller or larger dependent upon whether the firing device is in registry with one of the perforating units or not. Thus, for example, after starting with the firing device in the bottom position, the operator knows that the three successive increases and decreases in pulling force must locate the firing device in registry with the fourth perforating unit from the bottom, to fire that unit. If no audible sound of explosion is heard at that time, the operator is informed that a misfire has occurred and that a live but defective round is to be expected in the position of the fourth perforating unit when the tool is eventually brought to the surface.

Additionally, in the event of such a misfire, he may take remedial action to move the tool in the well bore so that he may provide for a subsequent detonation of another perforating unit at the previous location that the misfiring unit has failed to perforate.

The operator may continue to selectively advance the firing device 70 upwardly relative to the tool to fire the remaining perforating units as and when required. When, by counting the number of increases and decreases in pulling force applied, he is aware that the last perforating unit has been fired, the tool may be returned to the surface for reloading and other operations.

The previously mentioned nails 29 (FIG. 4) are explosively set nails of a commercially available type. Each nail includes a cylindrical rear portion 100 fitting slidably and snugly (FIG. 6) within the associated bore and having a rear radial surface which is acted upon by the exploding cartridge gases to propel the nail outwardly of the bore. A concentric, generally cylindrical shank 102 (FIG. 4) extending forwardly from the rear portion 100, integral therewith but of smaller diameter, has a pointed forward end 104. Sleeved about the pointed end portion 104 of the shank is a plastic, elastomeric end cap 106 shaped conformingly to the portion 104 and retained thereon by frictional engagement, engagement. A rim 108 integral with the rear end of the plastic cap extends outwardly into sealing contact with the walls of the bore 22 (FIG. 6). The plastic cap 106 excludes well water from entering the bore 22 behind the cap 106 so that the energy of the explosive blast is not dissipated by having to force the nail through water in that passage.

In addition, the cap 106 frictionally retains the nail in the bore 22 upon manual insertion of the nail into the bore, and assists in supporting the shank 102 in generally concentric relation to the bore 22.

In loading the perforator, the tool may be lowered into the well with the nails being successively inserted into the openings 22 one by one just prior to the movement of each bore 22 below the surface of the ground. Thus, the live perforating units 13 may be immediately moved below the ground on which the operator is positioned, thereby offering significant safety advantages.

SUMMARY OF ADVANTAGES

It will be appreciated that in constructing a well tool according to the present invention, certain significant advantages are provided.

Particularly significant is the use of a firing device controlled by a pulling force which varies in the magnitude required to be exerted in accordance with the location of the firing device relative to the perforating units. This arrangement facilitates precise control of the perforating operations.

For example, by counting the successive increases and decreases in pull required, an operator is informed of whichever perforating unit should be firing at a particular stage in the operation of the tool. In the event of a misfire, the operator is immediately informed both that a misfire has occurred and of the location of the live but defective perforator unit in the tool. This is important not only for safety of personnel at the well head but, also for enabling the location of the tool to be adjusted so as to permit subsequent perforation by another perforating unit at the location of the misfire.

Very importantly, the tool permits selective operation of some of the perforating units with the tool in one location in the well bore followed by movement of the tool to another location and selective operation of other of the perforating units at the second location. This process which may be repeated at other locations enables a number of different perforating operations to be conducted in a single run of the tool, thereby affecting significant operating economies.

Also very valuable is the simple low-cost construction of the perforating unit which renders it suitable for use by well operators not having access to the significant capital required for certain more complex electrical perforating tools commercially available.

* * * * *

Current U.S. Class:	175/4.55 ; 175/4.56; 175/4.57
Current International Class:	E21B 43/116 (20060101); E21B 43/11 (20060101); E21b 043/116 ()
Field of Search:	175/4.55,4.56,4.59,4.57 166/55.1