Well Perforating Apparatus

Abstract

As an illustrative embodiment of the present invention, an elongated thick-wall tubular perforating carrier is provided with one or more pairs of aligned openings formed at spaced intervals along the opposed walls of the carrier. Typical shaped explosive charges are respectively enclosed within fluid-tight thick-wall containers which are complementally shaped for reception in the openings and adapted to be supported therein by the opposed carrier walls. A container is secured in each pair of the openings and a detonating cord is passed through the interior of the carrier and successively looped outwardly around the rear of each container within detonating proximity of each shaped charge. In this manner, the new and improved apparatus can be employed for perforating operations without leaving debris in the well bore or damaging the casing.

Description

In completing oil wells, the casing and cement sheath surrounding the casing must, of course, be perforated to provide fluid communication between the producible earth formations and the interior of the casing. Typically, these perforations are produced by perforating apparatus including a so-called "carrier" which is suspended from an appropriate electrical cable and carries one or more shaped explosive charges that are respectively arranged to produce a laterally-directed perforation through the casing and surrounding cement. In general, the perforating carriers which have been typically employed heretofore are either a so-called "expendable carrier" (such as those shown in U.S. Pat. No. 3,048,101, U.S. Pat. No. 3,100,443 or U.S. Pat. No. 3,282,213) or a so-called "enclosed carrier" (such as those shown in U.S. Pat. No. 3,246,707 or U.S. Pat. No. 3,329,218).

Those skilled in the art will, of course, appreciate that each of these two basic types of carriers -- i.e., the expendable carrier and the enclosed carrier -- have certain advantages as well as disadvantages in relation to one another. For example, with an expendable carrier, the shaped charges are respectively encased in fluid-tight capsules constructed of a frangible material such as aluminum, glass or ceramic. Thus, by virtue of the relatively-small size of these expendable carriers, the capsules mounted thereon can be fairly large in relation to the internal diameter of the casing in which they are to be used so that greater explosive forces can accordingly be provided for producing perforations.

Such expendable carriers and encapsulated shaped charges are, however, disadvantageous from several points. First of all, although these capsules are frangible and readily break into small particles, the debris from the capsules and, in some instances, portions of the supporting carriers will be left in the well bore to possibly damage production equipment should this debris be subsequently brought to the surface by the connate fluids being produced from the well. Moreover, inasmuch as the capsules are completely fragmented upon detonation, severe laterally-directed explosive forces are imposed on the well casing which, in some instances, have been found to swell the casing as well as crack the cement sheath therebehind. Furthermore, since the capsules are exposed to the well bore fluids as the perforating apparatus is being positioned, these high-pressure fluids may leak into the capsules and render them at least partially defective. It is also not at all uncommon for the exposed detonating cord typically used for detonating the encapsulated shaped charges to be damaged as the perforating apparatus is being lowered into the well bore.

Accordingly, it has recently become more common for enclosed carriers to be used instead of the aforementioned expendable carriers. Primarily, enclosed carriers are used to avoid damage to the casing as well as to prevent the deposit of debris and the like in the well bore. The major disadvantage of typical enclosed carriers is that since the shaped charges are wholly contained within the tubular carrier, there is a significant reduction in the physical size and, therefore, the operational performance of the shaped charges which may be employed within a given well bore. Moreover, such enclosed carriers are somewhat expensive particularly when it is considered that they are often irreparably damaged after only a few operations by the successive explosive forces which are imposed internally thereof each time the carrier is used.

Accordingly, it is an object of the present invention to provide new and improved perforating apparatus which will provide most, if not all, of the advantages of both expendable and non-expendable carriers while eliminating their respective disadvantages.

This and other objects of the present invention are attained by mounting a shaped explosive charge in a uniquely-arranged container having an explosion-resistant hollow body and an expendable pressure-resistant cover of reduced thickness which is secured over the forward end of the hollow body for fluidly sealing the shaped charge therein. One or more of such fluidly-sealed shaped charge containers are respectively disposed in complementally-shaped transverse openings formed at selected intervals through the walls of a reusable tubular carrier. To selectively detonate the shaped charges, a detonating cord is extended through the longitudinal bore of the tubular carrier and successively directed around the rear of each of the hollow bodies for reliably detonating the shaped charges enclosed therein.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts a preferred embodiment of the perforating apparatus of the present invention as it will appear when disposed in a well bore;

FIG. 2 is a cross-sectional view taken along the lines 2--2 in FIG. 1; and

FIG. 3 is a cross-sectional view in elevation taken along the lines 3--3 of FIG. 2.

Turning now to FIG. 1, perforating apparatus 10 arranged in accordance with the present invention is depicted as being suspended from an electrical cable 11 and disposed within a casing 12 secured within a borehole 13 by a column of cement 14. As will subsequently be explained by reference to the succeeding figures, the perforating apparatus 10 of the present invention includes a plurality of shaped charges 15 which are respectively enclosed within separate fluid-tight containers 16 that are uniquely mounted in opposed pairs of axially-aligned lateral openings 17 and 18 which are formed at longitudinally-spaced intervals in the walls of a tubular carrier 19. To selectively actuate the shaped charges 15, the perforating apparatus 10 further includes detonating means such as an electrically-initiated detonator 20 that is operatively coupled to a detonating cord 21 which is, in turn, disposed within detonating proximity of each shaped charge. The perforating apparatus 10 also includes a conventional cable-connector head 22 and, if desired, suitable depth-indicating means such as a casing-collar locator 23.

Turning now to FIG. 2, to illustrate the principles of the present invention, an enlarged cross-sectional view is shown of the carrier 19 and one of the enclosed shaped charges 15. As is typical, the shaped charge 15 is comprised of a frusto-conical liner 24 of a suitable material such as copper or the like which is symmetrically arranged around a selected perforating axis 25 and complementally fitted within the open end of a hollowed, frusto-conical pellet 26 of a suitable high-order explosive such as RDX. Of particular significance to the present invention, it will be noted that instead of being a frangible capsule, the new and improved container 16 is especially arranged and designed to withstand all explosive forces produced by the detonation of the shaped charge 15 except, of course, the forwardly-directed forces of the perforating jet (not shown) which will be developed along the axis 25. Thus, in the preferred embodiment of the invention, the container 16 is symmetrically arranged about the axis 25 and is comprised of a hollow cylindrical body 27 of a strong material, such as steel, and an expendable cap 28 covering the open forward end 29 of the body. By shaping the interior of the body 27 to defined a forwardly-diverging, frusto-conical cavity 30 which is symmetrically arranged about the axis 25, it will be recognized that the rear wall 31 and the side walls 32 of the body will be of substantial thickness for withstanding the rearwardly and laterally-directed explosive forces of the shaped charge 15. It will, of course, be appreciated by those skilled in the art that the configuration of the body 27 will allow the shaped charge 15 to be formed either directly in the cavity 30 or else in a suitable die (not shown) for subsequent placement in the cavity.

Once the shaped charge 15 is disposed within the cavity 30, the open forward end 29 of the body 27 is closed by the cover or cap 28 which, in the preferred embodiment, has a generally-hemispherical exterior face, as illustrated, and is secured as by threads 33 over the open forward end of the body. A fluid seal, such as an O-ring 34, is appropriately arranged for sealing the cap 28 to the body 27. It should be particularly noted that the forward wall of the expendable cap 28 is reduced in thickness, as at 35, to define a weakened, but pressure-resistant, web portion around the intersection of the axis 25 with the cap.

The rearward wall 31 of the body 28 is preferably formed in a generally-hemispherical exterior configuration as illustrated and is provided with a rearwardly-facing groove 36 which extends substantially across the exterior surface of the rear wall. Thus, by shaping the groove 36 for snugly receiving the detonating cord 21, once the container 16 is disposed within the opposed openings 17 and 18 in the thick-wall carrier 19, the detonating cord will be securely retained immediately adjacent a typical high-order initiating explosive 37 which is preferably disposed within a shallow recess or counterbore 38 formed in the base of the cavity 30 so as to be in detonating proximity of the explosive pellet 26. It will be appreciated, of course, that the thickness of the metal web as at 39 separating the internal recess 38 and the exterior groove 36 will be sufficient to withstand anticipated well bore pressures but without significantly diminishing the explosive forces realized upon detonation of the detonating cord 21 for initiating the detonation of the explosive primer 37 and the explosive pellet 26.

In one manner of securing the container 16 in the transverse openings 17 and 18, a circumferential groove 40 is formed at a convenient location around the body 27 for receiving the forward end of a screw, as at 41, which is threadedly engaged within one wall of the carrier 19. It will, of course, be appreciated that by making the container 16 cylindrical, it may be readily positioned in the carrier 19 and turned within the openings 17 and 18 as required to orient the groove 36 in an upright position for receiving the detonating cord 21. Then, once the detonating cord 21 is in position, the screw 41 can be tightened for securing the container 16 within the carrier 19. It will also be noted that by forming the circumferential groove 41 around the middle of the container 16 as illustrated, the container can be mounted in the carrier 19 so as to be facing in either of two directions along the axis 25.

As best seen in FIG. 3, the detonating cord 21 is arranged to pass through the interior bore 42 of the carrier 19; and, as depicted, by partially extending a loop of the detonating cord outwardly through the rear opening 17, the container 16 can be moved through the forward opening 18 so as to readily dispose the detonating cord within the receptive groove 36 as the rear wall 31 enters the rear opening. It will, of course, be recognized that the containers 16 can be faced in either or both of the two alternate lateral directions without interferring with the arrangement of the detonating cord 21. Moreover, by appropriately forming the rear face of the container wall 31 to conform to the shape of the carrier 19, the looped portion of the detonating cord 21 will be fully guarded against contact with the well casing 12 as the perforating apparatus 10 is moved therethrough.

It will be appreciated by comparison of the physical size of the shaped charge 15 in relation to the internal diameter of the carrier 19 shown by the dashed line 43) that the shaped charge is substantially larger than could otherwise be contained within a conventional carrier having the same internal and external diameters. Moreover, by virtue of the greater permissible size of the shaped charge 15, a significant increase can be provided in the so-called "stand off distance" between the forward end of the liner 24 and the rearward face of the web 35 portion in the cover 28. Those skilled in the art will, of course, appreciate that by increasing the stand off distance in this manner, a far-superior jet formation will be realized before the perforating jet (not shown) has reached the web 35 so as to significantly minimize any interference with the formation of the jet which could otherwise be realized with conventional enclosed-carrier shaped charge devices.

By virtue of the unique arrangement of the containers 16, detonation of their respective shaped charges 15 will not subject the internal walls of the carrier 19 to the severe laterally-directed explosive forces to which a conventional enclosed carrier is exposed. Thus, instead of having to replace the carrier 19 after only a minimum number of perforating operations, the carrier should last indefinitely. Moreover, it will be recognized that since the bodies 27 are designed to withstand the several explosive forces imposed thereon each time the shaped charges 15 are detonated it is possible to even re-use the hollow bodies. This is, of course, a further advantage over and above the benefits gained by not leaving any debris from the containers 16 as the perforating apparatus 10 is being used.

Accordingly, it will be appreciated that the present invention has provided new and improved perforating apparatus which is capable of repetitive service without contributing to debris in the well bore of subjecting the casing to possible damage. By arranging the perforating apparatus in the manner described herein, a more-efficient and reliable perforating operation can be obtained without risking the possibility of leaving debris and the like in the well bore.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

Claims

What is claimed is:

1. Perforating apparatus comprising: a tubular carrier having openings in opposite sides thereof and coincidentally aligned with one another along a selected axis; a hollow body mounted in said openings and extended across said carrier along said axis, said body having a forwardly-diverging chamber formed symmetrically about said axis and selectively arranged within said body to define a wall around and to the rear of said chamber having sufficient thickness to withstand rearwardly and outwardly directed explosive forces imposed within said chamber, said wall having a selected portion proximate to the intersection of said axis with said wall and of a reduced thickness for transmitting inwardly-directed explosive forces into said chamber; shaped explosive charge means mounted in said chamber and operatively arranged, upon detonation, for developing a perforating jet along said axis; a cover fluidly sealed and secured across the forward end of said body for enclosing said shaped charge means in said chamber; and detonating means including an explosive detonating cord disposed within said carrier and operatively arranged adjacent to said selected wall portion for detonating said shaped charge means.

2. The perforating apparatus of claim 1 wherein said body is complementally fitted within said openings.

3. The perforating apparatus of claim 2 wherein said body is generally cylindrical and its rearward face is shaped to conform with the exterior shape of the rear side of said carrier adjacent to said rearward face of said body.

4. The perforating apparatus of claim 3 wherein the forward face of said cover is shaped to conform with the exterior shape of the front side of said carrier adjacent to said forward face of said cover.

5. The perforating apparatus of claim 3 wherein said selected wall portion includes an exterior groove formed in said rearward face of said body and arranged for at least partially receiving said detonating cord.

6. The perforating apparatus of claim 2 further including means operatively securing said body to said carrier.

7. Perforating apparatus comprising: a cylindrical tubular carrier having diametrically-opposed circular openings in opposite sides thereof and coaxially arranged about a selected lateral axis; a cylindrical body mounted in said openings and extended across said carrier along said axis, said body having a forwardly-diverging, generally-conical chamber formed symmetrically about said axis and selectively arranged within said body to define a circumferential wall around said chamber and a rear wall behind said chamber respectively having sufficient thickness to withstand outwardly-directed and rearwardly-directed explosive forces imposed within said chamber, said rear wall having a rearwardly-opening diametrical groove formed in its exterior surface and defining a portion of reduced thickness proximate to the intersection of said axis with said rear wall for transmitting inwardly-directed explosive forces into said chamber; shaped explosive charge means mounted in said chamber and operatively arranged, upon detonation, for developing a forwardly-directed perforating jet along said axis; a cover fluidly sealed across the forward end of said body for enclosing said shaped charge means in said chamber and adapted for perforation by said perforating jet; and detonating means including an explosive detonating cord disposed within said carrier and passed outwardly through the rearward one of said openings along said exterior groove and across said reduced-thickness portion of said rear wall.

8. The perforating apparatus of claim 7 wherein said detonating cord is returned inwardly through said rearward opening and back into said carrier.

9. The perforating apparatus of claim 8 further including means securing said body to said carrier and maintaining said exterior groove in a selected position in relation to said carrier.

10. The perforating apparatus of claim 7 wherein said exterior surface of said rear wall is curved to be flush with the exterior of said carrier.

11. The perforating apparatus of claim 10 wherein the forward face of said cover is curved to be flush with the exterior of said carrier and the rearward face of said cover is shaped to define a portion of reduced thickness on said axis for facilitating the penetration of said cover by said perforating jet.

12. The perforating apparatus of claim 7 wherein the forward face of said cover is curved to be flush with the exterior of said carrier.

13. The perforating apparatus of claim 12 wherein said exterior surface of said rear wall is curved to be flush with the exterior of said carrier.