US3429384A - Perforating apparatus - Google Patents

Description

Feb; 25, 1969 J. B. SHORE 3,429,384

PERFORATING APPARATUS Filed oCt- 9, 1967 Ja'me: .5. J/zore INVENTOR.

United States Patent 3,429,384 PERFORATING APPARATUS James B. Shore, Friendswood, Tex., assignor to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed Oct. 9, 1967, Ser. N0. 673,665 US. Cl. 175--4.6 Int. Cl. E21b 43/116; E21c 19/00 8 Claims ABSTRACT OF THE DISCLOSURE Accordingly, as will subsequently become apparent, the present invention pertains to perforating apparatus. More particularly, the present invention relates to new and improved shaped charge perforating apparatus and to methods for producing such apparatus, which apparatus includes an expendable-type, enclosed retrievable carrier that is particularly adapted for service in wells having one or more strings of small-diameter tubing through which the perforating apparatus must pass.

To complete many wells today, the borehole is typically cased and a small-diameter tubing string extended through a conventional packer set just above the uppermost producing zone therein. Where two or more productive intervals are to be completed in a particular well, packers are set above each of the producing zones, with a separate small-diameter tubing string being extended to each of these packed-off intervals for communication therewith. Thus, to perforate a well bore having one or more productive intervals completed in this manner, the perforating apparatus must be passed through a smalldiameter tubing string and then lowered below the lower open end of that tubing string. After emerging from the tubing string, the perforating apparatus is brought into position and actuated to perforate the casing and cement and establish communication with that particular formation interval adjacent thereto.

Where the perforating apparatus is of the so-called enclosed carrier type, it is, of course, essential that the carrier be appropriately arranged for reliable recovery through the open lower end of a tubing string. In accordance with this requirement, shape charge perforating apparatus as shown in Patent No. 3,048,102 has been recognized for many years as being a highly successful perforator that can be reliably retrieved from wells as just described. As fully explained in this patent, a small recess or concavity is formed in the outer wall of an enclosed tubular carrier immediately in front of each shaped charge therein where, upon their detonation, the resulting perforating jet from each shaped charge will pass through the carrier wall at one of these indentations. In this manner, at least a substantial portion of the irregular outward protrusion or so-called burr that is typically formed around the place where each perforating jet exits from the carrier will lie within the circumferential bounds defined by the external diameter of the carrier. Thus, when the expended carrier is recovered, it will easily pass through even a close clearance without being stuck 3,429,384 Patented Feb. 25, 1969 as might otherwise occur should the burrs protrude too far beyond the outer wall of the carrier.

It is, of course, recognized that the distance that a perforating jet can travel as it is being formed before meeting an obstruction will significantly affect the performance of a shaped charge. In general, therefore, for a given shaped charge, its penetrating capability will increase in direct relation to the length of this free travel or so-called stand-off distance until an optimum penetration depth is reached at a particular stand-off distance. Those skilled in the art will appreciate, however, that where the largest possible shaped charge is confined with in a given size of a tubular carrier such as that shown in Patent No. 3,048,102, the resulting stand-off distance is well below the optimum stand-off distance for that shaped charge.

Accordingly, it is an object of the present invention to provide new and improved shaped charge perforating apparatus including an enclosed expendable carrier which provides an increased stand-off distance for the shaped charges therein while still preventing the expended carrier from becoming stuck by outwardly projecting burrs and the like formed upon detonation of the shaped charges.

It is a further object of the present invention to provide methods for fabricating a new and improved expendable shaped charge carrier.

These and other objects of the present invention are obtained by forming a recess or concavity in the outer wall surface of a tubular carrier immediately in front of the intended location of each shaped charge therein with a small outwardly-projecting dimple extending from within the concavity to about the circumferential bounds defined by the outside wall diameter of the carrier. In this manner, a significant increase in available stand-01f distance is provided while still minimizing undesirable projectons of burrs formed upon detonation of the shaped charges in the carrier.

The novel features of the present invention are set forth with particularity in the appended claims. The operation, together with further objects and advantages thereof, may best be understod by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 shows perforating apparatus arranged in accordance with the principles of the present invention as it is being positioned in a typical well bore;

FIGURE 2 is a transverse cross-sectional view of the perforator shown in FIGURE 1;

FIGURE 3 is a partial elevational cross-sectional view of the perforator depicted in FIGURE 2 as it might appear after detonation 0f the shaped charges contained therein; and

FIGURES 4 and 5 are partial elevational views illustrating one manner of forming the perforator illustrated in FIGURES 1-3.

Turning now to FIGURE 1, perforating apparatus 10 is shown as it is being positioned in a typical cased well bore 11 adjacent to a producible earth formation 12. As is customary, a small-diameter string of tubing 13 is suspended in the well bore 11 and extended through a typical packer 14 set therein above the earth formation 12. If, perchance, the well bore 11 traverses another producible formation (not shown) below the formation 12, a second tubing string 15 is also extended through the packer 14 to the lower zone and packed-off there by a similar packer (not shown) so as to isolate the two producing zones from one another and from that portion of the well bore above the upper packer.

The perforating apparatus 10 issuspended in the usual manner from a suitable cable 16 that is spooled from a winch (not shown) at the surface and connected to a cable head 17 on the upper end of the perforating apparatus. A typical casing collar locator 18 is employed for providing indications at the surface representative of the depth of the perforating apparatus 10. To insure that the perforating apparatus is correctly positioned, a positioning device 19 such as that shown in Patent No. 3,338,- 317 is connected between the collar locator 18 and a perforator 20 arranged in accordance with the present invention. It will be appreciated, of course, that other positioning devices such as that shown in Patent No. 3,110,257 could just as well be employed if such positioning devices are ever needed.

Turning now to FIGURE 2, an enlarged transverse cross-sectional view is shown of the perforator 20 to illustrate the present invention. The perforator 20 includes a fiuid-tight, elongated tubular carrier 21 having upper and lower closure members and in which perforating means including a plurality of laterally directed shaped charges 22 (only one shown) are supported by an elongated plate 23 extending parallel to the longitudinal axis of the carrier and having longitudinally spaced apertures 24 therein for receiving the shaped charges. As is customary, the perforating means include a detonating cord 25 that is extended through the carrier 21 and maintained in operative relation to the shaped charge 22 as by an external groove 26 formed in the rear of each shaped charge. The detonating cord 25 is, of course, coupled to a conventional detonator (not shown) in the carrier 21 that is electrically connected by way of the suspension cable 16 to a suitable power source (not shown) at the surface.

As fully described in Patent No. 3,048,102, the materials employed as well as the particular dimensional relationships of the carrier 21 will, of course, be determined by the well bore pressures to be expected as well as by the quantity of explosives contained in the shaped charges 22. In general, therefore, the same parameters defined in Patent No. 3048,102 will be applicable to carriers, as at 21, embodying the present invention.

In accordance with the present invention, that portion of the wall of the carrier 21 immediately in front of each shaped charge 22 is appropriately machined in a concavoconvex fashion to provide an outwardly-directed protrusion or dimple 27 having a wall thickness less than that of the other portions of the carrier, with this dimple being completely confined within an inwardly-directed concavity 28 formed in the external wall of the carrier. As shown in FIGURE 2, by forming the dimple 27 within the concavity 28, the forward surface of the dimple does not extend beyond the bounds defined by the outer circumference of the carrier 21. Thus, the dimples 27 will in no way hamper the passage of the carrier 21 through a tubing string as at 13.

Of even greater significance, it will be appreciated from FIGURE 2 that by forming each of the dimples 27 uniformly about the perforating axis 29 of their respectively associated shaped charge 22, the outwardly-directed concavity or recess 30 inside of each dimple will result in a substantial increase in the stand-oft" distance between the shaped charge and the interior Wall of the carrier 21. Although the actual distance gained may be only a fraction of an inch, those skilled in the art will appreciate that even such a slight dimensional increase will provide a significant increase in the depth to which the resulting perforating jet will penetrate a given target. For example, comparative tests conducted in accordance with standard A.P.I. RP-43 procedures have shown that, with all else being equal, the perforator 19 as shown in FIG- URE 2 produced perforations that were in the order of to deeper than the perforations obtained withperforators arranged as shown in Patent No. 3,048,102. It will be appreciated, therefore, that such increased penetration depths are of significance to the industry.

Turning now to FIGURE 3, an elevational view in cross section is shown of a portion of the carrier 21 after the shaped charges 22 have been detonated. It will be noted that although an outwardly projecting burr 31 is formed in the central portion of the dimple 27, little or none of this burr will extend beyond the bounds defined by the outer circumference of the carrier 21. Moreover, by virtue of the external concavity 28 and the reduced thickness of the dimple 27, even if some portion of the burr 31 were to protrude beyond the diameter of the carrier 21, these protruding portions would be so weak that they would not hamper the return of the carrier through a tubing string such as at 13. It will also be noted in FIG- URE 3 that some swelling, as at 32, will be experienced in the Walls of the carrier 21 in the vicinity of each shaped charge 22. Hereagain, however, as discussed in Patent No. 3,048,102, the degree of this swelling can be regulated as deemed necessary.

It will be recognized, of course, that the dimples 27 and recesses 28 can be formed in several different manners. It has been found particularly economical, however, to form the dimples 27 and recesses 28 as shown in FIGURES 4 and 5. Accordingly, as seen in FIGURE 4, the carrier 21 is initially formed in accordance with the teachings of Patent No. 3,048,102, with a scalloped-out concavity 28 being machined in the external surface immediately in front of where each of the shaped charges 22 are to be located. In the preferred embodiment of the present invention, the surface of each concavity 28 can be defined as being the intersection of an imaginary cylinder at right angles to the carrier 21, with this imaginary cylinder being of about the same or a slightly smaller diameter as the carrier and having a longitudinal axis that perpendicularly intersects the perforating axis 29 at a point sufficiently in front of the carrier as to leave a minimum wall thickness at least adequate to withstand anticipated well bore pressures.

Once the concavities 2 8 are formed, a hydraulicallyactuated forming tool 33 is inserted into the interior of the carrier 21. As shown in FIGURE 4, this forming tool 33 preferably includes a piston 34 having a hemisphericallyshaped forward head portion of forming mandrel 35, with the piston being slidably received in a lateral bore 36 in a cylindrical body 37. O-rings 38 or the like fluidly seal the piston 34 in the bore 36 and provide an enclosed chamber 39 in the body 37 at the rear of the piston which is in communication with a pressure source (not shown) by way of a suitable conduit such as a pipe 40. A stop shoulder 41 is arranged on the piston 34 to engage an opposed shoulder 42 on the tool body 37 and limit the forward travel of the piston.

Accordingly, by positioning the forming tool 33 within the carrier 21 so that the longitudinal axis of the piston 34 is coincidentally aligned with the perforating axis 29 intersecting the concavity 28 and then applying a substantial hydraulic pressure to the chamber 39, the hemispherical head 35 will produce the complementarilyshaped dimple 27 as shown in FIGURE 5 which circumscribes the perforating axis, with a substantial portion of the dimple having a uniform radius of curvature. It will be appreciated, moreover, that either the forming tool 33 can be successively positioned adjacent to each recess 28 in turn or a forming tool (not shown) having a plurality of forming mandrels similar to that at 35 can be employed.

It will be recognized, therefore, that the present invention has provided a new and improved perforator which, in service, will produce substantially deeper perforations than can be obtained with comparable perforations known heretofore. Moreover, by forming the perforator in accordance with the methods set out above, protruding burrs that might otherwise cause the perforator to become stuck whenever it is to be retrieved are eliminated or at least minimized.

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.

What is claimed is:

=1. Perforating apparatus comprising: a tubular carrier adapted for passage through a Well bore and having in an outer wall surface thereof a recess defining an integral wall portion of reduced thickness in relation to adjacent 'Wall portions therearound, said reduced-thickness Wall portion including a smaller central portion thereof projecting outwardly from within said recess to about the bounds defined by said outer wall surface of said adjacent wall portions and defining an outwardly-directed concavity in the inner wall surface of said central portion; and perforating means in said carrier including a shaped charge mounted therein and facing said concavity with the perforating axis of said shaped charge intersecting said concavity.

2. Th perforating apparatus of claim 1 wherein: said carrier is cylindrical and said recess defines an integral wall portion of varying thickness uniformly decreasing from a maximum thickness above and below said rec ss to a minimum reduced thickness in the center of said smaller central portion; and said perforating axis intersects said concavity substantially at said center of said smaller central portion.

3. The perforating apparatus of claim 1 wherein: a major portion of said inner wall surface of said concavity has a substantially uniform radius of curvature.

4. The perforating apparatus of claim 3 wherein: said carrier is cylindrical and said recess defines an integral wall portion of varying thickness uniformly decreasing from a maximum thickness above and below said recess to a minimum reduced thickness in the center of said smaller central portion; and said perforation axis intersects said concavity substantially at said center of said smaller central portion.

5. A perforating carrier comprising: an elongated tubular cylindrical body of substantially uniform wall thickness and having a plurality of inwardly-directed concavities at longitudinally-spaced intervals along the outer wall surface thereof, each of said inwardly-directed concavities defining an integral wall portion of reduced thickness and encompassing an outwardly-directed dimple projecting therefrom to about the circumferential bounds defined by said outer wall surface, and each of said dimples having an inner wall surface defining an outwardlyextending concavity.

6 -6. Perforating apparatus comprising: an elongated tubular cylindrical body of substantially uniform wall thickness and having a plurality of inwardly-directed concavities at longitudinally-spaced intervals along the outer of said dimples having an inner wall surface defining an outwardly-extending concavity; perforating means in said carrier including a plurality of shaped charges mounted at longitudinally-spaced intervals therein and respectively facing said outwardly-extending concavities with their respective perforating axes intersecting said dimples; and

means adapted for fluidly sealing said perforating means Within said carrier.

7. A perforating carrier comprising: a tubular cylindrical member adapted for passage through a well bore and having internal and external wall surfaces defining an integral wall of a uniform thickness, said member having at least one concavo-convex wall portion of a reduced thickness defining an outwardly-directed protrusion forming an outwardly-directed recess in said internal wall surface and extending outwardly from within an inwardlydirected recess in said external wall surface to a termination within the circumfer ntial bounds of said external wall surface so that a shaped charge disposed within said member and facing said outwardly-directed recess will, upon detonation, perforate said reduced-thickness wall portion at said termination of said protrusion, said inwardly-directed recess serving to effectively contain any significant burr resulting from such perforation within said circumferential bounds defined by said external wall surface.

8. The perforating carrier further comprising: perforating means including a shaped charge mounted within said member adjacent to said reduced-thickness wall portion and facing said outwardly-directed recess therein.

References Cited UNITED STATES PATENTS 2,734,456 2/1956 Swe'etman 4.6 3,128,702 4/1964 Christopher 1754.6 3,190,219 6/1965 Venghiattis 1022.0

DAVID H. BROWN, Primary Examiner.

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