WELL PERFORATING GUN WITH STRESS RELIEVED SCALLOPS

TECHNICAL FIELD

The present disclosure relates generally to equipment utilized and operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a well perforating gun with stress relieved scallops.

BACKGROUND

With the ever-increasing explosive loads in perforating guns, the material used to manufacture the gun bodies is being stressed to the point of failure. When the gun body material does fail, this may lead to expensive fishing operations, obstruction in a wellbore, possible failure of surrounding casing, etc. To solve this problem, perforating gun manufacturers must continue to provide more creative designs to prevent failure of gun bodies when perforating guns are detonated.

A perforating gun body may include a scallop (i.e., a recess) formed into an outer surface of the gun body. Current scallop designs on typical perforating guns (see

FIG. 1) incorporate a radius 10 at the bottom of the scallops 12, but at the top of the scallops where they meet the gun body 14 outer diameter, there is a sharp corner 16. This sharp corner 16 is an area of high stress, and is where many cracks originate when a gun is subjected to the internal pressure of a detonation.

Depending on the scallop 12 pattern, the cracks normally will propagate from one scallop to the next adjacent scallop. The highest stress area on the sharp edge 16 is typically along a vertical centerline of the scallop 12, parallel with a longitudinal axis of the gun body 14.

Therefore, it may be seen that improvements are needed in the art of perforating gun design and manufacture.

SUMMARY

In carrying out the principles of the present disclosure, a perforating gun scallop design is provided which solves at least one problem in the art. One example is described below in which a juncture between the scallop and an outer surface of a gun body is radiused or chamfered. Another example is described below in which the radius or chamfer extends partially or completely about a perimeter of the scallop where it intersects the outer surface of the gun body. In one aspect of this disclosure, a well perforating gun is provided which includes a gun body having at least one scallop formed in a sidewall of the gun body. At least one stress relief element, such as a radius or chamfer, is formed between the scallop and an outer surface of the gun body. The radius or chamfer may extend in a plane which extends longitudinally or laterally relative to the gun

body, and may intersect a centerline of the scallop. The radius or chamfer reduces stress in the gun body due to a pressure increase in the interior of the gun body.

In a preferred embodiment, stresses are spread out by removing sharp corners in areas of highest stress at scallops in perforating gun bodies. Preferably the sharp corners are removed by radiusing or chamfering them. Such a radius or chamfer stress relief element does not necessary extend completely around a perimeter of a scallop where it meets an outer diameter of a gun body. Instead, the radius or chamfer may only be proximate a plane passing through a centerline of the scallop and parallel to a longitudinal axis of the gun body.

The radius or chamfer stress relief element should be sufficiently large to significantly reduce stress concentration at the perimeter of the scallop. A dimension of at least 2mm (.08 inch) is preferred, and a dimension of at least 4mm (.16 inch) is most preferred for the radius or chamfer. These and other features, advantages, benefits and objects will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the disclosure hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers .

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (Prior Art) is a cross-sectional view of a typical well perforating gun body having a scallop formed in a sidewall thereof;

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FIG. 2 is a schematic cross-sectional view of a well perforating gun body having a stress-relieved scallop formed in a sidewall thereof, the perforating gun embodying principles of the present disclosure; FIG. 3 is a schematic cross-sectional view of the perforating gun body of FIG. 2, taken along line 3-3 of FIG. 2 ; and

FIG. 4 is a schematic cross-sectional view of an alternate configuration of the gun body of FIG. 3.

DETAILED DESCRIPTION

It is to be understood that the various embodiments of the present disclosure described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments.

Representatively illustrated in FIG. 2 is a portion of a perforating gun 20 which embodies principles of the present disclosure. The perforating gun 20 includes a generally tubular gun body 22 having a sidewall 24 between inner and outer surfaces 26, 28 thereof. In this example, the inner and outer surfaces 26, 28 are cylindrical in shape, but other shapes (such as polygonal, etc.) may be used if desired.

A recess or scallop 30 is formed into the outer surface 28. Only one scallop 30 is depicted in FIG. 2, but any number, pattern and/or positioning of scallops may be used

in keeping with the principles of this disclosure. In addition, the scallop 30 of FIG. 2 is cylindrical in shape and has a centerline 32, but other shapes may be used if desired. The scallop 30 has a generally planar bottom surface 34 and a cylindrical shaped side surface 36. A juncture between the side surface 36 of the scallop 30 and the outer surface 28 of the gun body 22 is provided with a radius 38 stress relief element on each side of the centerline 32. The radius 38 could extend completely about the perimeter of the scallop 30 where it intersects the outer surface 28 of the gun body 22, or the radius could extend only partially about the perimeter. As depicted in FIG. 2, the radius 38 is formed at least in a plane which extends parallel to a longitudinal axis 40 of the gun body 22, and which intersects the centerline 32 of the scallop 30.

Referring additionally now to FIG. 3, a cross-sectional view of the perforating gun 20 is representatively illustrated, taken along line 3-3 of FIG. 2. In this view, it may be seen that the radius 38 may also, or alternatively, be formed in a plane which is orthogonal to the longitudinal axis 40 of the gun body 22, and which intersects the centerline 32 of the scallop 30.

The radius 38 prevents failure of the gun body 22 by reducing stresses in the sidewall 24 which result from increased pressure in the interior of the gun body. Such increased pressure may be caused by detonation of perforating charges in the gun body 22. The stresses are preferably reduced by more evenly distributing the stresses in the gun body 22 due to the radiused juncture between the scallop 30 and the outer surface 28.

Referring additionally now to FIG. 4, a cross-sectional view of an alternate configuration of the perforating gun 20 is representatively illustrated. In this view, it may be seen that a chamfer 42 stress relief element may be used in place of the radius 38 stress relief element.

The chamfer 42 may be formed in a plane which extends parallel to the longitudinal axis 40 of the gun body 22, and which intersects the centerline 32 of the scallop 30. The chamfer 42 may also, or alternatively, be formed in a plane which is orthogonal to the longitudinal axis 40 of the gun body 22, and which intersects the centerline 32 of the scallop 30. The chamfer 42 may extend completely around the perimeter of the scallop 30.

The chamfer 42 prevents failure of the gun body 22 by reducing stresses in the sidewall 24 which result from increased pressure in the interior of the gun body. Such increased pressure may be caused by detonation of perforating charges in the gun body 22. The stresses are preferably reduced by more evenly distributing the stresses in the gun body 22 due to the chamfered juncture between the scallop 30 and the outer surface 28.

It may now be fully appreciated that the present disclosure provides significant improvements in the art of perforating gun design and manufacture. In particular, this disclosure provides a well perforating gun 20 including a gun body 22 having at least one scallop 30 formed in a sidewall 24 of the gun body. At least one stress relief element, such as a radius 38 or scallop 42, is formed between the scallop 30 and an outer surface 28 of the gun body 22.

The gun body outer surface 28 may be an outer diameter of the gun body 22. The radius 38 or chamfer 42 may be

formed in a plane which extends parallel to a longitudinal axis 40 of the gun body 22. The plane may intersect a centerline 32 of the scallop 30.

Alternatively, or in addition, the radius 38 or chamfer 42 may be formed in a plane which extends orthogonal to the longitudinal axis 40 of the gun body 22. In this case also, the plane may intersect the centerline 32 of the scallop 30.

The radius 38 or chamfer 42 may reduce stress in the gun body 22 caused by a pressure increase within an interior of the gun body.

The radius 38 or chamfer 42 may extend completely about a juncture between the scallop 30 and the outer surface 28 of the gun body 22. The radius 38 or chamfer 42 may extend only partially about a juncture between the scallop 30 and the outer surface 28 of the gun body 22.

The radius 38 or chamfer 42 may be formed between the outer surface 28 of the gun body 22 and a surface 36 of the scallop 30 which extends in a direction parallel to the centerline 32 of the scallop. The radius 38 or chamfer 42 should be sufficiently large to significantly reduce stress concentration at the perimeter of the scallop. A dimension of at least 2mm (.08 inch) is preferred, and a dimension of at least 4mm (.16 inch) is most preferred for the radius 38 or chamfer 42. Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of the present disclosure. Accordingly,

the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.