Wells – Packers or plugs – With expanding anchor
Reexamination Certificate
1998-12-07
2001-04-10
Bagnell, David (Department: 3671)
Wells
Packers or plugs
With expanding anchor
C166S138000, C166S140000, C166S217000
Reexamination Certificate
active
06213204
ABSTRACT:
FIELD OF THE INVENTION
The field of this invention relates to slip systems for downhole packers, particularly those that require a high load from uphole or downhole directions.
BACKGROUND OF THE INVENTION
Slip systems are typically used to anchor packers to the casing. A typical slip system comprises a cone, slips and a body. The cone is typically a cylindrical component which has a shallow angle cut on the outside diameter of one end. The slips are segments cut from a cylinder and have the same angle as the cone on the inside diameter, as well as sharp teeth on the outside face. The cone and slips slide over the body, which is also cylindrical. When the packer is set, the cone pushes against the slips through the shallow angle, causing them to move radially until the sharp teeth contact the casing. Load applied to the packer is transmitted to the cone, which causes the slips to bite deeper into the casing to prevent the packer from moving. Therefore, in most slip systems, a radial load is applied to the cone when the packer is loaded due to the angles cut on the cone and slips. If the load applied to the packer is great enough, the cone will collapse until the inside diameter of the cone contacts the outside diameter of the body. At times, the applied load can cause the body to collapse. The limitation of the amount of load a packer can hold is often determined by when the cone collapses onto the body, causing it to collapse. Thinner slip systems, because of their reduced cross-section, are less resistant to collapse from the applied radial load and hold less force than thicker systems. However, thick slip systems have a disadvantage of requiring additional space, which decreases the available bore size in the packer for a given casing size.
Another design which has been used in the past on packers is illustrated in
FIGS. 1-3
, as well as in U.S. Pat. No. 4,711,326.
FIG. 1
is a perspective of a slip without the wickers, illustrating opposed beveled surfaces
10
and
12
. Each of those surfaces has an elongated tab
14
and
16
, respectively. Referring to
FIGS. 2 and 3
, the elongated tabs
14
and
16
ride in grooves
18
and
20
. Grooves
18
and
20
are wider than the width of the tabs
14
and
16
to allow easy movement for guiding the slip
22
along the cone
24
. As seen in
FIG. 3
, the cone
24
has opposed surfaces
26
and
28
which are disposed to engage the beveled surfaces
10
and
12
on slip
22
shown in FIG.
1
. Thus, the extension of the tabs
14
and
16
into grooves
18
and
20
serves to guide the slip
22
with respect to cone
24
, while at the same time the engagement of the beveled surfaces
10
and
12
on slip
22
to surfaces
26
and
28
of cone
24
acts to transfer the radial load from the casing through the slip
22
into the cone
24
. Because of the beveled cut on surfaces
10
and
12
, a near-circumferential component of the radial force applied to the slips
22
is communicated into the cone
24
. This design has been used traditionally to hold forces from only one direction and in permanent installations. The present invention is more suitable for retrievable packers and systems which need to hold forces from both directions (bidirectional). The present invention retrieves because there is only one angle between the slip and cone instead of the combined angles in the prior art shown in
FIGS. 1-3
. This combined angle causes a wedging effect between the slips and cone which increases the retrieval force. Tests have shown that in some cases, the retrieval force is so high that the tails
15
are pulled off the ends of the slips due to a tensile failure at narrow region
17
(see FIG.
1
). When this happens, the slips cannot be retrieved.
In the preferred embodiment, the present invention uses bidirectional slips which have a ramp angle on each end. The prior art slips of
FIGS. 1-3
only have a ramp angle on one end. The prior art system of
FIGS. 1-3
is not readily convertible to a bidirectional design, and even if it could be, it would still be very costly, highly complex, and not as reliable as the present invention.
These and other advantages of the present invention will be more readily understood by those skilled in the art from a review of the preferred embodiment described below.
SUMMARY OF THE INVENTION
A high-load slip system allows better transmission of loads from the slips to the body. The cone comprises longitudinal slots and the body comprises tabs which are disposed in those slots. The load is transferred from the slips to the cone and into the tabs which reside in the slots. The arrangement can be configured to share the load between the tabs extending from the body and the actual body itself after a small amount of collapse on the cone, leaving the body to support the cone, both through the tabs and on the outside diameter.
REFERENCES:
patent: Re. 30988 (1982-07-01), Crickmer
patent: 2735497 (1956-02-01), Brumleu et al.
patent: 3910348 (1975-10-01), Pitts
patent: 4359090 (1982-11-01), Luke
patent: 4523641 (1985-06-01), Manderscheid
patent: 4576230 (1986-03-01), Tapp et al.
patent: 4595052 (1986-06-01), Kristiansen
patent: 4711326 (1987-12-01), Baugh et al.
patent: 4750563 (1988-06-01), Baugh
patent: 4762177 (1988-08-01), Smith, Jr.
patent: 5086845 (1992-02-01), Baugh
patent: 5449040 (1995-09-01), Milner et al.
patent: 5487427 (1996-01-01), Curington
patent: 5647437 (1997-07-01), Braddick et al.
patent: 5720343 (1998-02-01), Kilgore et al.
patent: 2323869 (1998-10-01), None
Bagnell David
Baker Hughes Incorporated
Duane Morris & Heckscher LLP
Petravick Meredith C.
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