Caged slip system and release methods

Details Caged slip system and release methods Caged slip system and release methods

1999-10-13

2001-06-05

Neuder, William (Department: 3672)

Wells

Packers or plugs

With expanding anchor

C166S137000, C166S217000

Reexamination Certificate

active

06241017

ABSTRACT:

FIELD OF THE INVENTION
The field of this invention relates to retention devices for downhole tools, particularly slip systems located in cages and release methods for such systems.
BACKGROUND OF THE INVENTION
Slips are used in downhole tools such as packers to retain the position of the tool. Slips can be provided in a cage where a sleeve has openings through which the slips extend, separated by structural components of the cage to give it the integrity needed to withstand forces applied during the operation of the tool. These conventional caged slip systems offer protection to the slips while running in the hole. Apart from protecting the slips during run-in, the cage itself typically serves as a pickup device when retrieving slips. One of the design drawbacks of existing caged slip systems is a limitation on the extendable diametrical range of the slips. The longitudinal elements which define the openings through which the slips extend also serve as travel stops. Since these longitudinal components require a predetermined structural strength, they cannot be thinned to allow additional slip extension. This concept is illustrated in
FIG. 1
which shows the prior art. In
FIG. 1
a prospective view of a slip
10
is shown. The cross-section of the slip
10
is U shaped and the longitudinal strip
12
extends within the U and acts as an outward travel stop for the caged slip
10
. The openings or windows
14
are defined between the longitudinal strips
12
. Accordingly, in the prior art, the requisite thickness of the longitudinal strips
12
limited the amount of outward travel of the slips
10
. Additionally, in the prior art designs, the cones which would force the slips outwardly were located inside the cage as represented graphically by arrow
16
. One such product is the Model SC-2P retrievable packer made by Baker Oil Tools. The placement of the cones within the cage defined by longitudinal members
12
reduced the available bearing area of the cones on the slips and therefore limited the capacity of the slips to resist differential forces which are present in the wellbore. Thus, these two significant limitations of prior caged slip designs amounted to lower performance ratings of the overall tool, as well as the need to have more tools available for varying sizes of casing. The reason for this was that depending on the casing weight per foot, its inside dimension would vary. Thus, different tools might be needed in the prior art to extend sufficiently far if lighter wall casing was in use.
Thus, some of the objectives of the present invention are to allow greater extension of the slips while retaining or expanding the ability of the slip system to withstand differential loads. Additionally, another objective is to allow within a given tool body size sufficient rangeability and slip extension so as to avoid stocking a large inventory of tools to handle a variety of situations. Another objective is to uniquely position the cone within the openings of the cage so that the cones extend outwardly as far as the outer extremity of the cage. All this is accomplished while at the same time retaining the beneficial qualities of a caged slip during run-in. Another objective, which is accomplished by putting the cones in the windows of the cage, allows the cage thickness to be increased to improve its tensile strength without reduction of the amount of slip extension. Finally, another objective is to be able to retain the slips to a predetermined extension diametrically outwardly. Thus, the slips are limited in radial extension to prevent them from escaping the cage if they are extended in an unsupported condition. Yet another objective of the present invention is to facilitate release of the slips by mechanically driving the lower cone out from the lowermost slips, as opposed to trying to pull and disengage slips off of a stationary cone. The objective of the release system is to be able to unsupport the slips, regardless of whether the mandrel of the packer is in tension or compression so that the slip is not pulled away from a cone when the cone forces the wickers of the slip against a casing or tubular. Those and other features of the present invention will become more apparent to those skilled in the art from a review of the preferred embodiment described below.
SUMMARY OF THE INVENTION
An improved caged slip system is disclosed. The cage is constructed so that the cones which actuate the slips extend into the cage openings. The radial extension of the slips is limited so as to retain them if they are extended in an unsupported situation. The cones have a maximum outside dimension equal to the outside dimension of the cage so as to increase the rating of the slips by increasing the bearing area of the cones on the slips. The beneficial features of the cage design are retained while a greater degree of radial expansion of the slips is possible allowing minimization of tool inventory for situations where a lighter wall casing requires further slip extension. The release system allows the lower cones to be driven out from under the lower slips, thus facilitating release of the grip of the lower slips from the casing for extraction of the packer. The mechanical release is functional through the mandrel, whether tension or compression is placed on the mandrel. Alternative designs are presented for the capture of the lower cone by the cage.


REFERENCES:
patent: 3291220 (1966-12-01), Mott
patent: 4664188 (1987-05-01), Zunkel et al.
patent: 4750559 (1988-06-01), Greenlee et al.
patent: 4984636 (1991-01-01), Bailey et al.
patent: 6119774 (2000-09-01), Doane et al.

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