US2968243A - Tubing gun - Google Patents

Description

Jan. 17, 1961 G. F. TURECHEK 2,963,243

TUBING GUN Filed July 9, 1956 2 Shets-Sheet 2 n I I I r*. 57 SS-f {I :5 F7 [I], III, 2'! 24 I I T t I l i Lani 650265 F. ruesmez 2] INVENTOR.

United States Patent 2,968,243 TUBING GUN George F. Turechek, Los Angeles, Calif assignor, by mesne assignments, to Borg-Warner Corporation, Vernon, Califl, a corporation of Illinois Filed July 9, 1956, Ser. No. 596,722 8 Claims. (Cl. 102-20) This invention relates to tubing guns employing shaped charge explosive units to perforate the side walls of oil wells and the like, and more particularly to an improved single-use, self-destructible gun of unusually compact design especially suited for use in small bore wells without sacrificing the size of. the explosive charges used or the size of perforating cavities made by these charges.

For some years it has'been common practice to utilize shaped charge units to form cavities extending radially into the side walls of boreholes to facilitate the recovery of petroleum and other fluids from earth formations. The two types of guns heretofore employed for this purpose may be classified as the non-destructible tubing gun and the destructible tubing gun. In the former, unsealed shaped charge units are housed within a ported thickwalled tube capable of withstanding both the high hydraulic pressures encountered in deep boreholes as well as the explosive forces of the charges themselves. In the latter type, the individual charges are sealed within separate frangible casings not crushed by the hydraulic pressures but which shatter upon the detonation of the contained explosive charge.

The non-destructible thiclewalled gun, although possessing certain important advantages, is restricted to use in boreholes above a certain minimum diameter owing to the very thick wall required to counteract the powerful forces to which it is subjected. The second type of conventional gun utilizing separate sealed shaped charge units submerged directly in the well fluids has undesirably low efliciency in deep wells due to several factors including inadequate expansion space for the charge radially of the perforating jet. Contrary to theoretical considerations, confining the expansion of the gases during detonation of the charge to the space within the shaped charge case does not increase the effectiveness of the penetrating jet stream but, on the contrary, appears to have a decided detrimental effect increasing with the depth at which the gun is used. Furthermore, both of the commonly employed types of guns are costly to manufacture andto service.

In view of the foregoing factors and conditions characteristic of tubing guns used in perforating the side walls of boreholes, it is a primary object of this invention to provide an improved gun especially suited for use in small diameter boreholes and featuring unsealed shaped charge units supported in a unique manner in a chamber having provision for the lateral expansion of the charge on detonation.

Another object of the invention is the provision of a new gun design which remains hydraulically sealed until the explosive charges enclosed therein are detonated and which, upon being fired, is shattered into small size debris along with the shaped charge casings.

Still another object of the invention is the provision of a small diameter tubing gun having an imperforate thinwalled exterior shell supported interiorly by shatterable material, the latter being designed to support a plurality of shaped charge units spaced axially of the gun.

A further object of the invention is the provision of a shaped charge perforator assembly formed from a series of frangible tubular spacer members arranged in alignment and shaped to support a shaped charge explosive unit between their adjacent ends, together with ten- Patented Jan. 17, 1 961 sion members extending lengthwise along the opposite sides of the assembly.

Yet another object is the provision of a tubing gun which is readily variable in length by the simple expedient of adding a greater or lesser number of explosive units and spacer elements and by cutting the encasing tube to appropriate length for use therewith.

More specifically, it is an object of the invention to provide a tubing gun assembled from similar frangible spacer.

elements formed to hold explosive units captive in predetermined oriented position with the detonating end thereof exposed to a detonating cord grooveway extending lengthwise of the assembly.

Another object of the invention is to provide a tubing gun having a thin-walled outer tube supported against inward collapse by a frangible tubular assembly supporting a plurality of explosive units in spaced relation.

A further object of the invention is to provide self-destructible tubing gun formed by a plurality of ceramic spacers disposed in alignment between a series of shaped charge units and held in assembled relation by igniter wire means and a detonating cord. extending lengthwise of the gun and arranged to detonate each of the units in rapid succession.

These and other more specific objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawings to which they relate.

Referring now to the drawings in which preferred embodiments of the invention are illustrated:

Figures la, 1b, taken together, comprise a longitudinal sectional view through a tubing gun according to one preferred embodiment of the invention;

Figure 2 is an end view of a frangible spacer element and of a shaped charge unit seated therein, the view being taken generally along the line 2-2 on Figure lb;

Figure 3 is a longitudinal sectional view taken through a pair of spacer elements along the plane indicated by line 33 on Figure 2;

Figure 4 is a side elevational view of the bull plug employed at the lower end of the gun;

Figure 5 is a fragmentary longitudinal sectional view through the midsection of an alternate embodiment of the invention; and

Figure 6 is a perspective viewof a frangible supple mental spacer used to obtain greater axial spacing of the shaped charge units.

Referring to the drawings and more particularly to Figures 1a and 1b, a tubing gun incorporating the present invention will be seen to include a cable head assembly 10 securely fixed to a flexible high-strength cable 11 having an electrical conductor extending into the cable head and secured to an insulating bushing assembly 12. The lower end of bushing assembly 12 extends into a chamber 14 formed in the upper end of coupling member 15, to which the head is threaded, there being a suitable fluid-tight seal provided between the coupled parts by an O-ring l6.

The body of the tubing gun comprises a thin-walled tube 17 having a snug telescopic fit with the lower end of coupling member 15 and held assembled thereto, as by screws 18. Forming a fluid-tight seal between the coupling 15 and the tube 17 is a resilient flexible seal such as that provided by O-ring 19seated in an annular groove 20 of the coupling. Tube 17 may be formed of aluminum, plastic or the like material adapted for manufacture in accurately-sized seamless tubing, the accurate and uniform sizing of the tubing being of greater importance than its strength for reasons which will become apparent presently.

Housed within the imperforate tube '17 and forming an important sub-assembly of the present gun is a series of similar readily-frangible spacer elements 21 preferably formed from inexpensive readily-moldable material such as plastic or ceramic materials having high compressive but low tensile strengths. As is best shown in Figures 2 and 3, elements 21 have mating cavities 22, 23 in their opposite ends suitably shaped to seat firmly a conventional shaped charge unit 24. Although the present drawings show a pair. of elements 21 arranged end to end to support a pair of shaped charge units at the desired spacing axially of tube 17, it will be recognized that a single spaced element may be used. in either case, the axes of cavities 22, 23 at the opposite ends of the spacer elements are preferably oriented 90 degrees from one another.

As herein shown, the shaped charge units 24 comprise a readily frangible exterior casing 25 having a generally conical portion 26 at the rear closed end thereof adapted to seat in recesses 22 of a pair of abutting spacer elements 21. The opposite or discharge end of casing 25 seats in recess 23 of the spacer elements and includes a comically-shaped liner element 27 holding the usual charge of explosive material captive within the casing. Embedded withinthe base of the explosive charge is a detonator 28 having one end opening into the base of a U-shaped groove 29 extending transversely across the end of casing 25 and adapted to form a snug frictional seat for an explosive firing cord 30 of the type commercially known as Primacord. The firing cord fits in a helical groove 31 formed along the exterior surface of spacer elements 21 and opening into the opposite ends of grooves across the closed ends of the shaped charge units. As is best shown in Figure 3, the opposite or discharge ends of the explosive units are in axial alignment with the conical recess 32 formed by-the abutting ends of the spacer elements, the purpose of this depression being to provide an area of minimum wall thickness opposite the point to be pierced by the jet of the associated shaped charge unit 24 when the latter is detonated. A secondary and equally important purpose is to provide a greater stand-off between the side wall of the gun and the apex of liner 27, thereby assuring adequate space for the formation of the piercing jet before the latter encounters substantial resistance and begins its actual piercing operation. It will, of course, be appreciated that the depth of recess 32 should not be such as to defeat the primary and vital function of spacer elements 21 in providing interior support for casing 17 of the gun, as otherwise the high well fluid pressures might cause the latter to collapse.

As best shown in Figure 1b, a second shallow groove 33 extends helically along spacer elements 21. Preferably, this groove is spaced 180 circumferentially from the Primacord groove 31 and spirals in the same direction in order that the igniter wire 34 extending therealong may cooperate with the Primacord in holding the spacer elements and the shaped charge units in position prior to the time outer casing 17 is assembled thereover.

Although not essential, it is preferable to avoid sharp turns in both Primacord 30'and.ignite r wire 34. To this end the opposite ends of the interior core assembly of frangible elements include a pair of similar frangible end rings 38 having inclined passages 39, 40 extending along the wall thereof for igniter wire 34 and Primacord 30 respectively. Suitable resilient washers 41 are preferably used between the exterior ends of rings 38 and the closure plugs at the opposite ends of the gun, these gaskets serving to prevent end play of the spacer elements and making limited allowance for variations in manufacturing tolerances.

Closing the lower end of tube 17 is a suitable bull plug 44 preferably formed from high density frangible material This plug has a close fit with the lower end of tube 17 and is provided with an annular groove seating an O-ring 45 to form a fluid-tight seal. As is best shown in Figure 4, bull plug 44 is provided with several groups of threaded bores 46, each group lying in a different transverse plane along the plug and providing seats for assembly screws 47. By locating the bores 46 in this manner, screws 47 may be assembled to the group of bores best suited to prevent lost motion and end play between the spacer elements 21 and to assure continuous interior support for the thin-walled outer casing.

A well 48 centrally of bull plug 44 provides a chamber for the electrical blasting cap 49 secured to the lower end of Primacord 30, it being understood that the end of the igniter wire 34 extends into the blasting cap and is effective to detonate the latter when the firing circuit is closed. Owing to the location of the blasting cap and its igniter wire at the lower end of the gun, the final assembly of these components may be and preferably is completed in the field immediately prior to the use of the gun.

The manner of assembly of the gun parts will be quite evident from the foregoing detailed description of the components. According to a preferred mode, spacer elements 21 and end rings 38 are placed in a V-shaped trough and oriented to the proper position to receive the shaped charge units 24, following which the shaped charges are inserted in recesses 22, 23 between the ends of the spacer elements. One end of the Primacord 30 is then inserted through passage 40 in the upper end ring 38 and its end taped as indicated at 50' to anchor the end of the cord in place. The remainder of the cord is then fed into groove '31 and into recess 29 at the detonating end of each of the explosive units 24, the lower end of the Primacord being fed through the passage 40 in the lower end ring 38 and anchored in place by wrapping friction tape 50 about the cord interiorly of ring 38. The end of the Primacord may then be clipped to a suitable length for the attachment of blasting cap 49 or, in the alternative, this latter step may be left for completion in the field.

The insulated igniter wire 34 is then assembled through passage 39 of the upper end ring '38 and along helical groove 33 of the spacer elements. Although not shown, it will be understood that split ring type deformable gripping washers or the like cord anchoring devices customarily used in the electrical wiring art may be clenched about the igniter wire opposite the inner end of passages 39 to hold this wire in place in its groove and to maintain the same under slight tension. Likewise, such devices may be employed in lieu of the friction tape anchors 50 for holding the Primacord in place under slight tension. When assembled in this manner it will be evident that the igniter wire and the Primacord cooperate with the spiral grooveways in which they are located to hold the spacer elements accurately aligned with one another and fully seated in their respective grooves. When so held, it is a simple operation to telescope the outer casing 17 over the core assembly without danger of the elements becoming misaligned either ra dially or circumferentially.

The final factory assembly operation comprises slipping casing 17 over the core assembly and thereafter attaching the cable head 10. Once the latter is secured in place by screws 18, bull head 44 and gasket 41 are assembled to the lower end of the casing, care being taken to press the bull head into the casing as far as it will go and aligning the openings for screws 47 with the appropriate group of threaded bores 46. This latter operation is carried out by pressing the bull head into tube 17 and rotating it until the screw holes match a group of the threaded bores 46.

Before the gun is lowered into a borehole and discharged, it is necessary to remove the bull plug and connect the igniter wire 34 with blasting cap 49. In some instances the blasting cap is not assembled to the detonating cord 31 at the factory. In this event it is necessary to attach the cap to the end of cord 31 as well as to crimp the igniter wire to the cap. Thereafter the bull plug is reassembled, care being taken to replace assembly screws 47 in the lowest possible group of threaded bores 46.

The assembled gun is now ready for lowering into a borehole by the aid of cable 11. After a given length of cable has been released from the control drum it is known that the gun is at a given level in the borehole.

During the lowering operation the fluid filling the borehole will place casing 17 under high hydraulic pressure but this will not collapse the casing owing to the continuous interior support provided by the frangible spacer elements 21 and the end rings 38. Since sealing rings 16, 19 and 45 prevent the well fluids from entering the gun, the hollow core of the gun remains under atmospheric pressure and provides a low pressure chamber of limited size into which the shaped charges expand upon being detonated.

Firing of the gun is accomplished by closing an electrical circuit to the igniter wire 34 to fire blasting cap 49 and ignite Primacord 30. The burning of the Primacord proceeds so rapidly as to fire the shaped charge of detonators 28 substantially instantaneously. The detonation of each shaped charge unit 24 creates an extremely high velocity jet stream axially of the liner cones 27. This jet cuts through the spacer elements as well as casing 17 and pierces a finger-like cavity of several inches length into the rock formation of the borehole. In addition, these tremendously powerful explosions shatter the shaped charge casings along with ceramic spacer elements 21 and the enclosing casing 17 forming smallparticle debris which settles through the borehole fluid. It will be understood, therefore, that the entire gun assembly, except cable head 10, is destroyed as an incident to the firing of the gun. Bull head 44 is the only likely survivorof the firing of the gun but, being frangible, it is easily disintegrated by a drill tool should it ever become desirable to extend the borehole.

It is emphasized that the hollow core provided interiorly of spacer elements 21, though small in volume, provides adequate and essential expansion space for the shaped charge units 24. The mechanics of the reaction are not fully understood, but it has been definitely deter mined that deeper and larger cavities are produced in rock formations from shaped charge units detonated in a, low pressure gas-filled chamber rather than in a rigid confining chamber closely embracing the shaped charge unit.

An alternate mode of assembling the gun in accordance with the principles of the present invention is illustrated in Figures and 6 wherein the same or similar elements as in the first-described embodiment are designated by the same reference characters distinguished by the use of a prime. This embodiment differs merely in the use of additional frangible spacer elements designated 55 interposed between the abutting ends of spacer members 21' for the purpose of spacing units 24 a greater distance apart. As is made clear by Figure 5, the inserts 55 are provided with axially extending grooveways 56 and 57 on diametrally opposed sides thereof for receiving Primacord 30 and igniter wire 34' respectively.

It is to be understood that the components of the alternate embodiment are assembled similarly to those of the first embodiment and that the gun is used in the same manner, the principal difference being the provision for spacing units 24' a greater distance from one another.

While the particular tubing guns herein shown and described in detail are fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that the two described embodiments are merely illustrative of the presently preferred mode of practicing the invention, and that no limitations are intended to' the details of construction or design herein shown other than as defined in the appended claims.

I claim:

1. In combination, a self-destructible tubing gun comprising, a plurality of elongated, frangible outwardly cylindrical, tubular spacer elements arranged in end to end abutting relation, said spacer elements having equal di ameters and having mating recesses at selected abutting ends thereof formed to embrace a shaped charge explosive unit, a shaped charge explosive unit having a detonator held captive in each of said recesses, said elements providing a pair of opposed, substantially helical grooves encircling said elements and opening into the outward cylindrical surfaces thereof, an explosive detonator cord extending along one of said grooves and closely associated with the detonator of each of said explosive units, electric igniter means extending along the other of said grooves and connected at one end with means for initiating detonation of said cord, said cord and igniter means cooperating to hold said frangible elements in assembled, end-to-end position.

2. A tubing gun for use in perforating the wall of an earth borehole comprising: a thin-walled imperforate outer tubular casing incapable per se of withstanding hydraulic pressures encountered in a deep borehole; fluidtight means for closing the upper end of said casing and suspending the same in a borehole; a plurality of rightcylindrical tubular elements arranged in end to end abutting relation within said casing and extending substantially the entire length thereof, said plurality of tubular elements having a close sliding fit with the interior surface of said casing and further providing a coaxial internal chamber extending therethrough, selected abutting pairs of said elements each pair providing two diametrically-opposed recesses in the inner wall of said chamber, said recesses being intersected by the plane of the abutting surfaces of each said pair of elements; explosive shaped charge units mounted in said chamber, each with its opposite ends seated in an opposed pair of recesses; said tubular elements having portions interposed between the ends of said shaped charge units and the inner wall of said tubular casing, said portions abutting the inner wall of said casing and being adapted to provide interior support for said casing adjacent to the ends of said units against the force of pressure external to said casing, and the walls of each said diametrically-opposed recesses restraining the charge unit seated therein from movement in any direction; means for detonating said explosive units; and fluid-tight means sealing the lower end of said casing; said elements being frangible and having low tensile and high compressive strength and being adapted to reinforce said casing against collapse from external hydraulic pressure, said explosive units being effective on detonation substantially to disintegrate said elements and said casing and to perforate the wall of the borehole thereopposite.

3. A tubing gun for use in perforating the wall of an earth borehole comprising: a thin-walled imperforate outer tubular casing incapable per se of withstanding hydraulic pressures encountered in a deep borehole; fluidtight means for closing the upper end of said casing and suspending the same in a borehole; a plurality of rightcylindrical tubular elements arranged in end to end abutting relation within said casing and extending substantially the entire length thereof, said plurality of tubular elements having a close sliding fit with the interior surface of said casing and further providing a coaxial internal chamber extending therethrough, selected abutting pairs of said elements each pair providing two diametrically-opposed recesses in the inner wall of said chamber, said recesses being intersected by the plane of the abutting surfaces of each said pair of elements; explosive shaped charge units mounted in said chamber, each with its opposite ends seated in an opposed pair of recesses; said tubular elements providing a groove extending along the exterior of said elements from the uppermost to the lowermost element; a detonator cord anchored to said uppermost and lowermost elements and lying in said groove in detonating relation to said explosive units, said detonator cord being under tension and cooperating with the walls of said groove to hold said elements in place; means for detonating said explosive cord; and fluid-tight means sealing the lower end of said casing; said elements being frangible and having low tensile and high compressive strength and being adapted to reinforce said casing against collapse from external hydraulic pressure, said explosive units being effective on detonation substantially to disintegrate said elements and said casing and to perforate the wall of the borehole thereopposite.

4. A tubing gun for use in perforating the wall of an earth borehole comprising: a thin-walled imperforate outer tubular casing incapable per se of withstanding hydraulic pressures encountered in a deep borehole; fluidtight means for closing the upper end of said casing and suspending the same in a bore hole; a plurality of rightcylindrical tubular elements arranged in end to end abutting relation within said casing and extending substantially the entire length thereof, said plurality of tubular elements having a close sliding fit with the interior surface of said casing and further providing a coaxial internal chamber extending therethrough, selected abutting pairs of said elements each pair providing two diametrically-opposed recesses in the inner wall of said chamber,

' said recesses being intersected by the plane of the abutting surfaces of each said pair of elements; explosive shaped charge units mounted in said chamber, each with its opposite ends seated in an opposed pair of recesses; means for detonating said explosive units including means providing a first groove extending along the exterior of said elements from the uppermost to the lowermost element, a detonator cord anchored to said uppermost and lowermost elements and lying under tension in said first groove in detonating relation to said explosive units, means providing a second groove extending along the exterior of said elements from the uppermost to the lowermost element, and electric igniter means stretched along said second groove from said uppermost to said lowermost element and connected to. the lower end of said detonator cord for igniting the same, said detonator cord and said electric igniter means cooperating with the walls of the respective grooves to hold said elements in place; means for actuating said electric igniter means; and fluid-tight means sealing the lower end of said casing; said elements being frangible and having low tensile and high compressive strength and being adapted to reinforce said casing against collapse from external hydraulic pressure, said explosive units being effective on detonation substantially to disintegrate said elements and said casing and to perforate the wall of the borehole thereopposite.

5. A tubing gun for use in perforating the wall of an earth borehole comprising, a thin-walled imperforate outer tubular casing incapable of withstanding hydraulic pressures encountered in lowering the gun into a deep borehole, fluid-tight means for closing one end of said casing and suspending the same in a borehole, a plurality of selfsupporting frangible tubular elements arranged end to end, said elements having mating recesses at selected abutting ends thereof formed to embrace a shaped charge explosive unit and having a close sliding fit with the interior surface of said casing, said frangible elements being adapted to reinforce said tubular casing against collapse from external hydraulic pressure while the gun is lowered into a fluid-filled borehole, a shaped charge explosive unit held captive in each of said recesses, said frangible tubular elements being constructed to space said explosive units substantially from each other and to provide expansion spaces in the interior of said tubular elements between adjacent shaped charge units, means sealing the lower end of said gun, said frangible elements providing a groove along the exterior of said frangible elements, a detonator cord extending along said groove and across one end of said explosive units in detonating relation thereto,

said tubular casing overlying and closing said groove to hold said cord in place therein, said detonator cord coopcrating with said groove to hold said frangible elements in place, and means for detonating said detonator cord.

6. That improvement in tubing guns which comprises a plurality of generally tubular, frangible spacer elements disposed in end to end abutting arrangement with each other and having mating recesses at selected abutting ends thereof formed to embrace a shaped charge explosive unit, a plurality of shaped charge explosive units supported by said spacer elements in the mating recesses thereof, a detonating cord groove means extending spirally about the exterior of said plurality of elements, said shaped charge explosive units each having a U-shaped detonator recess opening into said groove means, a detonating cord stretched along said groove and through said U-shaped detonator recesses of said explosive units for holding said spacer elements in axial alignment, and means for detonat ing said detonating cord.

7. That improvement in tubing guns which comprises a plurality of generally tubular, frangible spacer elements disposed in end to end abutting arrangement with each other and having mating recesses at selected abutting ends thereof formed to embrace a shaped charge explosive unit, a plurality of shaped charge explosive units supported by said spacer elements in the mating recesses thereof, a detonating cord groove means extending spirally about the exterior of said plurality of elements, said shaped charge explosive units each having a U-shaped detonator recess opening into said groove means, a detonating cord stretched along said groove and through said U-shaped detonator recesses of said explosive units, sec ond groove means extending spirally about the exterior of said frangible elements, and an electric igniter means stretched along said last-mentioned groove means and connected to said detonating cord for igniting the same,

said igniter means cooperating with said cord to hold said frangible elements in alignment from the opposite longitudinal sides thereof.

8. That improvement in tubing guns which comprises a plurality of generally tubular, frangible spacer elements disposed in end to end abutting arrangement with each other and having mating recesses at selected abutting ends thereof formed to embrace a shaped charge explosive unit, a plurality of shaped charge explosive units supported by said spacer elements in the mating recesses thereof, a detonating cord groove means extending spirally along the exterior surface of said plurality of elements, said shaped charge explosive units each having a U-shaped detonator recess extending diametrically across the end thereof and opening into said groove means, a detonating cord stretched along said groove and through said U-shaped detonator recesses of said explosive units for holding said spacer elements in axial alignment, means for detonating said detonating cord, and a thin-walled imperforate outer tube closely surrounding the exterior surface of said spacer elements and holding said detonating cord in place in said groove and in said U-shaped recesses.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,153 Elliott June 18, 1946 2,433,231 Martin Dec. 23, 1947 2,649,046 Davis Aug. 18, 1953 2,669,928 Sweetman Feb. 23, 1954 2,749,840 Babcock June 12, 1956 2,756,677 McCullough July 31, 1956 2,779,278 Klotz Jan. 29, 1957 ,811,921 Hodgson Nov. 5, 1957 2,833,213 Udry May 6, 1958 ,833,214 Spencer May 6, 1958 FOREIGN PATENTS 660,285 Great Britain NOV. 7, 1951 3,832 France Jan. 7, 1953 7 1, 74 Great Britain Dec. 16, 1953 Disclaimer and Dedication 2,968,243.-Ge09e F. TLW6C/L676, Los Angeles, Calif. TUBING GUN. Patent dated J an. 17, 1961. Disclaimer and dedication filed Nov. 14, 1967, by

the assignee, Borg- Warner Gorpomtion. Hereby disclaims and dedicates to the Public the terminal portion of the term of the patent subsequent to Dec. 31, 1966.

[Oficz'al Gazette Mamh 12, 1,968.]

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