Drillable Slip

Abstract

A drillable slip having a generally wedge-shaped cross-section with a plurality of longitudinally extending perforations or holes confined at least partially within the cross-section to provide weakened sections to facilitate breakage of the slip into a plurality of segments.

Description

This invention relates generally to well tools that are anchored in a well conduit or casing, and more particularly to a new and improved slip structure for use in anchoring a well packer in permanent yet drillable condition in a well casing.

A so-called "permanent" bridge plug, used to pack-off or plug a well casing, is usually designed to be readily drillable in the event that removal of the plug is desirable. The bridge plug normally has elastomeric packing disposed between upper slips and lower slips that are shifted outwardly by expander cones into gripping contact with the casing in order to prevent movement in either longitudinal direction. The drillability of the slips is dependent upon a number of factors including the number of slip segments, the size of the segments and of course the material from which the slip is made. As a general rule, it has been found that the number of segments should be maximized, and the amount of metal should be minimized in order to provide optimum drilling time.

On the other hand, it should be kept in mind that the effectiveness of the slip in anchoring against movement is related to the distribution of the slip teeth on the casing. Here it is desirable to maximize the area of slip teeth in contact with the casing in order to provide a uniform gripping action of the slip segments against the casing.

The principle object of the present invention is to provide a new and improved slip having a construction satisfying the foregoing conditions so as to be readily drillable while providing an effective and uniform gripping action with the casing.

Another object of the present invention is to provide a new and improved drillable slip that is simple to manufacture at low cost.

These and other objects are attained in accordance with the concepts of the present invention by a slip structure comprising a solid annular ring having an inner inclined surface and serrations or teeth on its outer periphery. The ring is provided with a plurality of axially extending perforations or holes preferably with a circular cross-section, extending through the ring. Thus when sufficient outward pressure is applied by the expander to the inner inclined surfaces of the slip, the ring will break into a plurality of segments that can be expanded outwardly until the teeth bite into the casing. As continued pressure is exerted by the expander, the ring will finally break up into a number of segments equal to the number of perforations in the slip. The circular formation of the perforations leaves each individual slip segment with maximum inner surface area to prevent crushing of the segment as well as a maximum of outer surface area so as to provide uniform distribution of teeth against the casing. Through use of circular perforations as opposed to rectangular channels as in the prior art, the slip is actually constructed of a lesser amount of materials, thereby reducing the time required to drill the slip away with a drill bit.

These and other objects and advantages of this invention will become more clearly apparent in connection with the following detailed description of a preferred embodiment, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view with portions in side elevation of a well tool having slips constructed in accordance with the principles of the present invention;

FIG. 2 is an isometric, partially sectioned view of the slips; and

FIG. 3 is a cross-sectional view showing the slip broken into segments and set against the casing by the expander cone.

Referring initially to FIG. 1, a bridge plug 10 is somewhat schematically illustrated, although the present invention is equally usable with other well tools such as cement retainers. The bridge plug 10 includes a mandrel or body member 11 having a lower guide and abutment 12 and carrying one or more elastomeric packing rings 13 disposed between an upper expander cone 14 and a lower expander cone 15. The upper cone 14 has an upwardly and inwardly inclined outer surface 16, whereas the lower expander cone 15 has a reverse tapered surface 17. A split expansible and contractible lock ring 18 is located within an annular recess 19 in the upper cone 14 and has internal teeth 20 that coact with external teeth 21 on the mandrel 11, and external cam teeth 22 that coact with companion teeth 23 on the cone in such a manner that the mandrel 11 can be moved upwardly within the cone, however the cone can not be moved upwardly along the mandrel. The particular lock ring is conventional and is further described in U. S. Pat. No. 2,647,584, issued Aug. 4, 1953. Shear pins 24 and 25 can be used to control the relative movement sequence of various parts of the packer during setting in a typical manner. Other conventional elements, such as detent rings, anti-extrusion rings and the like, normally found in typical well packers can be provided but are not shown in order to simplify this description.

An upper slip 30, constructed in accordance with the principles of the present invention have external wickers or teeth 31 and an inner inclined surface 32. In similar fashion, a lower slip 33 has external teeth 34 and an inner inclined surface 35. Both of the slips 31 and 33 are formed by an initially solid or continuous annulus ring of metal such as gray iron that is readily drillable. The upper slip 30 can be provided with an annular band 36 that is force-fitted within a groove surrounding the slip in order to maintain segments of the slip in the same horizontal plane during expansion. The particular construction of the band and groove is more fully described in U. S. Pat. No. 3,530,934, issued Sept. 29, 1970.

The slips 30 and 33 can be broken into segments by lateral pressure applied thereto by the respective expander cones 14 and 15 during setting. In order to facilitate breakage in a controlled manner, as shown in FIG. 2 each slip is provided with a plurality of axially disposed perforations or holes 40 extending through the slip 30. Each perforation 40 is preferably circular in cross-section with its center-line located intermediate the inner and outer surfaces 41 and 42 of the thickened end of the slip. Thus, that portion of the slip located immediately inwardly of holes 40 remains circumferentially continuous. As outward pressure is applied by the expander, the ring will initially break at several points located along radial lines intersecting the axis of the perforations 40, and the segments created by breaking are then shifted outwardly against the casing.

Due to the fact that each slip 30 or 33, initially having a small diameter than that of the casing, has a greater curvature than the inner wall surface of the casing, the expander cones 14 and 15 will cause the respective slips to break into a number of segments equal to the number of perforations 40. The completely set upper slip 30 is shown in FIG. 3. Due to the formation of the perforations 40 in the interior of the slip body each segment after breaking will still retain the maximum internal surface area in engagement with the expander cone 14 to prevent crushing. Moreover, the outer peripheral area of each segment having teeth in contact with the casing 43 is at a maximum to optimize teeth distribution and insure uniform gripping action with the casing. Further, the perforations 40 reduce the amount of metal actually present in the slip 30, so that the slip can be drilled up in a minimum amount of time.

In operation, the parts can be assembled as shown in the drawings and lowered and set in the casing 43 in a conventional and well known manner. The packing rings 13 are foreshortened longitudinally and expanded against the casing to provide a pack off or seal. The slips 30 and 33 are broken into segments as previously described and shifted outwardly by the respective expanders 14 and 15 into set positions of anchoring engagement with the casing 43. The lock ring 18 ratchets downwardly over the mandrel teeth 21 and traps the compression loading in the packing rings 13. The slips 30 and 33 will anchor the tool against movement in either longitudinal direction in the well bore.

The slips 30 and 33 can be formed as castings in order to reduce the cost of manufacture. If desired, the perforations 40 can have alternately larger and smaller diameters or other appropriate configurations in order to control the breaking sequence thereof.

It will now be apparent that a new and improved slip construction has been disclosed that is readily drillable in minimum time while providing maximum and uniform gripping action with the casing. Since certain changes or modifications will occur to those skilled in the art without departing from the concept involved, it is the aim of the appended claims to cover all such changes or modifications falling within the true spirit and scope of the present invention.

Claims

I claim:

1. A slip for use in anchoring a well tool in a well bore comprising an annular member having an inner inclined surface and a toothed outer periphery, said member having a plurality of weakened sections to facilitate breakage of said member into segments, said weakened sections being provided by circular openings extending longitudinally and completely within the body of said member so that the outer peripheral surfaces and a major portion of the inner peripheral surfaces of said member are circumferentially continuous.

2. A slip for use in anchoring a well tool in a well bore, comprising an arcuate body having inner inclined surfaces and toothed outer surfaces, said body being weakened at arcuately spaced points by circular openings extending longitudinally and completely within said body, said openings disposed within a major portion of said body in such a manner that inner and outer peripheral surfaces of said major portion are circumferentially continuous.

3. A slip for use in anchoring a well tool having an expander in a well bore, comprising an annular body having a generally wedge-shaped cross-section with an inner inclined surface slidably engaging said expander and a toothed outer periphery adapted to grippingly engage a well conduit wall, said body having a plurality of circumferentially spaced weakened sections provided by longitudinally extending circular holes disposed between the inner and outer wall surfaces of the thickest portion of said body, said body being adapted to be broken at said weakened sections into a plurality of separate segments by outward pressure exerted by said expander, said outward pressure being applied in part over internal surfaces disposed immediately inwardly of said holes.

4. A slip for use in anchoring a well tool in a well bore, comprising: an annular member having an outer toothed surface, an end surface and an inner wall surface, said inner wall surface having a vertically extending portion and an inclined portion, said member having a plurality of elongated circular bores formed therein with each bore extending generally parallel to said outer toothed surface and to said vertically extending portion of said inner wall surface, each bore opening at one end through said end surface and at the other end through said inclined portion of said inner wall surface, the longitudinal axis of each circular bore being spaced radially with respect to said vertically extending portion of said inner wall surface by a distance greater than the radius dimension of said bore, the plurality of said bores providing weakened sections to facilitate breakage of said member into a plurality of arcuate segments.