U.S. patent number RE30,988 [Application Number 06/192,096] was granted by the patent office on 1982-07-06 for well tool.
This patent grant is currently assigned to Otis Engineering Corporation. Invention is credited to Charles D. Crickmer.
United States Patent |
RE30,988 |
Crickmer |
July 6, 1982 |
Well tool
Abstract
A well tool and more particularly a hanger assembly having an
improved design for more effectively, reliably and economically
hanging a liner or other well equipment in a well casing or the
like.
Inventors: |
Crickmer; Charles D. (Houston,
TX) |
Assignee: |
Otis Engineering Corporation
(Dallas, TX)
|
Family
ID: |
26887718 |
Appl.
No.: |
06/192,096 |
Filed: |
September 29, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
671209 |
Mar 29, 1976 |
04047565 |
Sep 13, 1977 |
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Current U.S.
Class: |
166/217;
166/66.5 |
Current CPC
Class: |
E21B
17/003 (20130101); E21B 43/10 (20130101); E21B
23/01 (20130101) |
Current International
Class: |
E21B
17/00 (20060101); E21B 23/01 (20060101); E21B
23/00 (20060101); E21B 43/10 (20060101); E21B
43/02 (20060101); E21B 033/129 () |
Field of
Search: |
;166/217,206,208,65,120,134,118,65M |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Attorney, Agent or Firm: Vinson & Elkins
Claims
What is claimed is:
1. A well tool for suspending well equipment in a well, the well
tool comprising:
an elongated hanger mandrel;
a plurality of cones axially spaced on said mandrel;
a plurality of sets of slips axially spaced around said mandrel,
each set of slips including a plurality of slips circumferentially
spaced around said mandrel and positioned with respect to a
different one of said cones to engage said one cone upon relative
axial movement between the set of slips and the cone;
a plurality of elongated slip reins circumferentially spaced around
said mandrel for controlling alignment of said slips during
relative axial movement between the .[.set.]. .Iadd.sets
.Iaddend.of slips and the cones, each slip rein being secured to
.[.a of slip from a.]. .Iadd.one slip of each set of said
.Iaddend.plurality of .[.said.]. sets of slips and each slip rein
controlling the alignment of each slip to which it is secured.
2. A well tool as specified in claim 1 wherein relative axial
movement between said slips and an associated cone produces radial
outward movement of said slips.
3. A well tool as specified in claim 1 wherein said reins move
radially with respect to said mandrel during relative movement
between said slips and said cones and extend substantially parallel
to the axis of said mandrel during the entire extent of relative
movement between said slips and said cones.
4. A well tool as specified in claim 1 additionally comprising
actuator means connected to said reins for producing relative axial
movement between said slips and said cones.
5. A well tool as specified in claim 1 wherein said cones are fixed
relative to said mandrel and said sets of slips are movable with
respect to said mandrel.
6. A well tool as specified in claim 1 wherein each slip set
includes a plurality of slips circumferentially and equally spaced
around said mandrel, and a slip from one slip set being aligned
with a respective slip from each of the other slip sets along a
slip axis parallel to the longitudinal axis of said mandrel.
7. A well tool as specified in claim 6 wherein said reins have
longitudinal axes coinciding with respective ones of said slip
axes.
8. A well tool for suspending well equipment in a well, the well
tool comprising:
an elongated hanger mandrel;
a plurality of cones axially spaced on said mandrel;
a plurality of sets of slips axially spaced around said mandrel,
each set of slips including a plurality of slips circumferentially
spaced around said mandrel and each set of slips being positioned
with respect to a different one of said cones and adapted to engage
said one cone upon relative movement between the set of slips and
the cone;
a plurality of elongated slip reins circumferentially spaced around
said mandrel, each slip rein being secured to .[.a.]. .Iadd.one
.Iaddend.slip .[.from a plurality.]. .Iadd.of at least two sets
.Iaddend.of said sets of slips;
annular rein housing means on said mandrel in communication with
said reins; and
spring means associated with said annular rein housing means for
urging said reins radially inwardly with respect to said
mandrel.
9. A well tool as specified in claim 8 wherein said rein housing
means is slidable with respect to said mandrel and movable in an
axial direction with said reins.
10. A well tool as specified in claim 8 wherein said rein housing
means is fixed to said mandrel and a portion of each of said reins
moves axially within said housing means.
11. A well tool for supporting well equipment in a well, the well
tool comprising:
an elongated hanger mandrel;
at least one tapered cone on said mandrel;
at least one set of slips spaced around said mandrel, including a
plurality of slips circumferentially spaced around said mandrel and
positioned to engage said cone upon relative axial movement between
the set of slips and the cone;
elongated rein means for supporting each slip around said mandrel,
said rein means extending substantially parallel to the
longitudinal axis of said mandrel during the entire extent of
relative axial movement between the set of slips and the cone and
extending beyond both axial limits of said set of slips;
annular rein housing means on said mandrel and in communication
with one axial end portion of said rein means;
spring means in said housing means for urging said rein means
radially inwardly with respect to said mandrel.
12. A well tool as specified in claim 11 additionally comprising
actuator means on said mandrel connected to the other axial end
portion of said rein means for axially moving said rein means and
the slips connected thereto with respect to said cone.
13. A well tool for suspending well equipment in a well, the well
tool comprising:
an elongated hanger mandrel;
at least one tapered cone on said mandrel;
at least one set of slips including a plurality of slips
circumferentially spaced around said mandrel and positioned to
engage said cone upon relative axial movement between said set of
slips and said cone;
elongated rein means for supporting each slip around said mandrel,
said rein means movable radially outwardly with respect to said
mandrel and extending substantially parallel to the longitudinal
axis of said mandrel during the entire extent of relative axial
movement between the set of slips and the cone.
14. A well tool as specified in claim 13 additionally
comprising:
at least one other tapered cone on said mandrel and axially spaced
from said first mentioned cone;
at least one other set of slips on said mandrel and axially spaced
from said first mentioned set of slips including a plurality of
slips circumferentially spaced around said mandrel and positioned
relative to said other cone for engagement therewith upon relative
axial movement between said other set of slips and said other
cone;
said rein means supporting said other set of slips and including a
plurality of elongated reins, each elongated rein being secured to
.[.a.]. .Iadd.one .Iaddend.slip .[.from.]. .Iadd.of .Iaddend.each
of said sets of slips.
15. The well tool of claim 13 wherein:
said cone includes axial slot means therein; and
said rein means extend through said slot means, extend beyond the
axial limits of said cone, are constrained to move in a direction
substantially parallel to the axis of said mandrel by said slot
means, and are allowed to move radially with respect to said
mandrel by said slot means.
Description
The invention relates to a well tool known in the art as a hanger
for hanging liners and other such well equipment within well casing
and the like. For convenience, the invention will be described with
reference to a liner hanger.
Liner hangers are usually employed to attach an inner string of
well casing to the lower end or at some other point of a larger
diameter well casing. Liner hangers ordinarily comprise an
apparatus attachable to the liner and including a set of casing
gripping slips which are arranged to be moved into gripping
engagement with the interior of the larger diameter casing to
thereby secure the smaller diameter casing or liner thereto.
Thereafter, the liner will frequently be cemented, which requires
the circulation of fluids through the interior of the liner and
upwardly about the exterior thereof between the liner and the outer
casing or well bore.
Usually, the liners comprise long and heavy strings of casing
extending below the hanger and therefore require large slip contact
areas in order to assure effective attachment of the liner within
the larger casing. However, because of the close clearances which
must frequently exist between the liner and the surrounding well
casing providing sufficient slip area to support a long and heavy
liner string will frequently tend to greatly decrease the annular
space between the liner and the surrounding well wall, thus
severely restricting the flow of fluid necessary in cementing of
the liner and increasing the probability of the hanger sticking in
the well bore when it is being lowered or "run-in" into the
well.
It has been recognized in the art as is exemplified by U.S. Pat.
No. 3,195,646, issued July 20, 1975 by C. Brown, that by placing a
plurality of axially spaced slip sets on the hanger mandrel it is
possible to provide sufficient slip contact area in order to assure
effective attachment of the liner within the well casing and also
to provide sufficient annular space between the liner and the
surrounding well casing for sufficient fluid flow. It is common in
the prior art to provide a circumferential collar which is axially
slidable with respect to the hanger mandrel and to which are
connected a plurality of spring arms for the purpose of mounting
the slips (as can be seen in FIGS. 1 and 2 of the Brown patent).
Upon relative movement between the collar and the hanger mandrel
the tapered slips engage oppositely tapered cones, thereby wedging
the slips outwardly into gripping engagement with the inside wall
of the well casing. Since the spring arm is secured from radial
movement at the connection with the collar, the slip will have the
undesirable tendency to pivot or cock with respect to the cone
thereby producing only a partial engagement between the serrated
surface of the slip and the inner surface of the well casing. Also,
where slips are supported by spring arms as shown by Brown it is
necessary that for each set of slips there be a corresponding
collar to which the spring arms are attached, and in order to
reduce the chance of cocking of the slip, it is necessary to
provide relatively long spring arms. Therefore, this configuration
dictates that the hanger have a substantial overall length
increasing the possibility of the hanger sticking in the well
casing during run-in thereof.
It is an object of the present invention to provide a novel well
tool which overcomes the above-cited disadvantages by utilizing a
unique slip-cone arrangement having a plurality of axially spaced
slip sets wherein a single collar or rein housing may be used to
mount a plurality of slip sets, and wherein nonbending slip reins
which move parallel to the liner hanger mandrel are substituted for
spring arms alleviating the possibility of the slips cocking on the
cone, thereby producing a hanger which is more effective and
substantially shorter than those of the prior art.
It is a further object to provide an inexpensive slip-cone
arrangement wherein the slip reins move radially outwardly from the
hanger mandrel in a manner parallel to the axis of the mandrel to
alleviate the possibility of the slips cocking on the cones.
Other objects and advantages will become apparent to one of
ordinary skill in the art from the following detailed description
of preferred embodiments of the invention when read in conjunction
with the accompanying drawings wherein:
FIG. 1 is a longitudinal quarter-sectional view of a liner hanger
including one embodiment of the novel slip-cone arrangement of the
present invention;
FIG. 1A is an enlarged cross-sectional view of a portion of FIG.
1;
FIG. 2 is an enlarged partial cross-sectional view of the liner
hanger taken along line II--II of FIG. 1;
FIG. 3 is an enlarged partial cross-sectional view of the liner
hanger taken along line III--III of FIG. 1;
FIG. 4 is a perspective view of an alternate embodiment of the
invention showing the nonactuated or run-in position and wherein
one rein and the associated slips thereof have been removed for
purposes of clarity; and
FIG. 5 is a perspective view of the embodiment of FIG. 4, slightly
modified, showing the liner hanger in the actuated or set
position.
Referring to the drawings, and FIG. 1 in particular, a liner hanger
and setting tool assembly 10 is depicted in the run-in or
nonactuated position. The assembly 10 includes a generally tubular
liner hanger 12 and a generally cylindrical setting tool 14
coaxially inserted within the hanger 12. The setting tool 14 is
releasably secured to the liner hanger 12 in any well known manner
(not shown) such as that described in U.S. Pat. No. 3,291,220 so
that the entire assembly 10 may be lowered into a well casing C
(FIG. 4) as a unit by a run-in string (not shown) until such time
as the liner hanger is positioned at the desired location and set.
The setting tool 14 can then be detached and removed therefrom (see
FIG. 5).
The setting tool 14 is lowered into a well and supported from the
surface by a run-in string (not shown) connected to a setting tool
connecting assembly (not shown) which in turn is connected to
member 16 and coupling 18. Connected below the coupling 18 is a
setting tool tubular mandrel 20 fabricated of a nonmagnetic
material such as stainless steel. (It is noted that for purposes of
this specification the term "nonmagnetic" material refers to any
material which will not conduct a substantial amount of magnetic
flux and thus will allow the lines of flux to pass directly
therethrough substantially unabated, and the term "magnetic"
material refers to any material which may be magnetically coupled
to a magnet by means of a magnetic force field.) An annular magnet
22 is slidably positioned coaxially around the setting tool mandrel
20 and is preferably fabricated of vertically stacked annular
permanent magnets. Directly above and below the magnet structure 22
are situated annular magnetic pole pieces 22a and 22b fabricated of
soft iron or the like and which may be tapered radially outward as
indicated by the broken lines for a purpose to be explained
hereinafter.
An annular nonmagnetic piston 24 slidably surrounds mandrel 20 and
is positioned below lower pole piece 22b within an annular
nonmagnetic cylinder 26. The cylinder 26 along with piston 24
define an annular, sealed variable volume hydraulic fluid chamber
28 having circumferentially spaced inlet ports 30 extending through
the wall of mandrel 20 to allow hydraulic fluid to pass from the
interior of mandrel 20 to the chamber 28 for reasons to be fully
explained hereinafter. Above upper pole piece 22a is situated an
annular magnetic insulator 32 of nonmagnetic material. A helical
compression spring 34 surrounds mandrel 20 and extends between a
radially outwardly extending face 18a of coupling 18 and a radially
outwardly extending face 32a of insulator 32. The spring 34 serves
to positively bias the setting tool magnet 22 in a nonactuated
position until such time as it is desired that it be actuated by
pressurizing hydraulic fluid in chamber 28 as will be explained
hereinafter.
The liner hanger 12, is, as explained hereinbefore, initially
releasably connected to setting tool 14 and extends
circumferentially therearound in a coaxial relationship therewith
(FIGS. 1 and 4). The liner hanger includes a tubular mandrel 39
comprised of a nonmagnetic portion 40 and preferably a lower
mandrel portion 46 of any suitable rigid material attached
therebelow in a manner to form smooth interior and exterior
surfaces at the junction thereof.
The nonmagnetic portion 40 completely surrounds magnet 22 and pole
pieces 22a, 22b of setting tool 14 and extends vertically a
distance at least as great as the extent of possible vertical
movement of upper pole piece 22a. The upper end of nonmagnetic
mandrel portion 40 may be secured to any of a number of well tools
such as a well known packer assembly 42 (only a portion of which is
shown) by a threaded coupling 44. A conventional coupling 48 is
shown on the lower end of mandrel 39 for the connection of a
conventional liner (not shown).
Slidably supported on mandrel portion 40 is an annular
magnet-follower member 50 of a magnetic material. Member 50 has a
tubular main body portion 50a which is coaxial with mandrel portion
40 and which is spaced slightly outwardly therefrom by upper and
lower radially inwardly extending annular flanges 50b and 50c which
may be tapered radially inwardly as shown by the broken lines for
reasons to be explained hereinafter. As shown, the flanges 50b and
50c are situated to correspond to the vertical positions of
respective pole pieces 22a and 22b. Respectively above and below
member 50 are vertically movable annular nonmagnetic members 51 and
53. Placed between the upper member 51 and coupling 44 is a helical
compression spring 55 having a low spring force relative to the
helical spring 34 on the setting tool 14.
Surrounding mandrel 39 are annular tapered members 52 and 54 known
in the art as "cones." The cones 52 and 54 may be affixed by any
suitable means to mandrel portion 46 and preferably are formed
unitarily therewith. As shown, the walls of the cones gradually
increase in thickness from the axial lower end to the upper end
thereof. Adapted to slidably engage the cones are, preferably, two
axially spaced sets of serrated gripping members 56 and 58 known as
"slips" in the art. Each set of slips comprises a plurality of
individual slips, preferably four, which are equally spaced around
the respective cones associated therewith. With particular
reference to FIG. 1 it can be seen that each individual slip of
slip set 56 (for example slip 56a) is situated directly above and
is connected to an individual slip (in the EXAMPLE, slip 58a) of
slip set 58 by a straight rod or rein 60 of which there are four
equally spaced around mandrel 39 and which extend in an axial
direction with respect thereto. As can be seen in FIG. 2, the reins
60 may pass through cones 52 and 54 without obstruction by means of
slots 62 which are formed axially through the cones 52 and 54. The
slots 62 also act to constrain the reins 60 to move in a direction
substantially parallel to the axis of the mandrel 39 while allowing
the reins 60 to move radially with respect to the mandrel 39 to a
limited extent. It is noted that between the slots 62, the cones
may be either solid as shown on the left side of FIG. 2 or they may
be fluted as shown on the right side of FIG. 2, for the purpose of
creating a greater fluid flow area between the hanger 12 and the
casing C (FIGS. 4 and 5) for reasons well known in the art. With
particular reference to FIGS. 1 and 3, it can be seen that the
slips of slip sets 56 and 58 are securely attached to the reins 60
by any suitable means such as by screws 64 which pass through the
slips into axial slots 66 in the slips to provide a space for the
reins to contact the slips without precluding contact of the inner
surface of the slips with the mandrel 46. Further, the screw heads
are countersunk in the slips as at 68 to allow unobstructed contact
between the outer serrated surface 69 of the slips with a well
casing when the slips are actuated as will be more fully explained
hereinafter.
The upper ends of the reins 60 pass through the annular vertically
movable magnetic insulator member 53 having slots therethrough for
this purpose and also through slots in the lower annular flange 50c
of member 50. A plurality of pins 72a and 72b (see FIG. 1A) couple
the reins to the member 50 for captive vertical movement therewith
in a manner allowing limited radial movement of the reins as will
be further explained. The lower ends of the reins 60 are mounted in
an annular vertically movable rein housing 74 having an axially
extending flange 74a. Connected between the lower end of the reins
and the flange 74a by means of pins 75 is a compression spring
means 76, which may be of any suitable construction, biasing the
reins radially inwardly yet allowing radially outward movement of
the reins upon a sufficient force being exerted to overcome the
spring force. It is noted that if desired a compression spring
means 77 could also be placed in magnetic insulator member 53 to
provide a more positive radial inward bias on the reins.
When it is desired to set the liner hanger in a well casing, the
setting tool 14 is mechanically coupled to the liner hanger 12 in a
releasable manner by any well known means (not shown) so that the
tool 14 and hanger 12 are situated with respect to each other as
shown in FIG. 1, i.e., the pole pieces 22a, 22b of magnet 22 are
directly opposite the respective flanges 50b, 50c of member 50 and
are separated by a gap only slightly greater than the thickness of
mandrel 39.
The magnet 22 will produce a magnetic field having lines of flux
which travel axially through the magnet 22 and which are directed
radially outwardly by pole piece 22a through nonmagnetic mandrel
portion 40. The lines of flux then pass into flange 50b and axially
downward through member 50, body portion 50a being of magnetic
material, and thence radially inwardly through flange 50c passing
through mandrel portion 40 back to lower pole piece 22b. The
members 32, 51, 53 and 24, all being of nonmagnetic material, help
to concentrate the lines of flux into the above-enumerated desired
path. In order to further concentrate the lines of flux within the
gap between the magnet pole pieces 22a, 22b and the respective
flanges 50b, 50c it may be desired to taper the pole pieces
radially outwardly and the flanges radially inwardly as shown by
the broken lines in FIG. 1. In this manner the member 50 will be
magnetically coupled to the magnet 22 for axial movement therewith
relative to the mandrels 39 and 20.
In operation, the liner hanger and setting tool assembly is lowered
in a "run-in" position (FIG. 1) from the surface into a well casing
by means of a "run-in" string (not shown). As the assembly is being
lowered, relatively strong spring 34 prevents the magnet 22 from
moving upward with respect to the mandrels 20 and 39. Due to the
above-described magnetic coupling, member 50 is also held
stationary with respect to the mandrels which in turn prevents the
reins 60 and the slips sets 56, 58 from moving upwardly and
prematurally setting in the well casing. Also, the spring 55 aids
in preventing premature movement of the member 50; however, it is
important to note that spring 55 on liner hanger 12 is not
essential for this purpose, but is primarily included in the
assembly to return the slips to the run-in position after being set
to allow the hanger to be removed or relocated in the well. It can
thus be seen that spring 55 may be very thin so as not to add any
thickness to the hanger 12. Also, the slips are prevented from
moving radially outwardly by spring means 76 in rein housing 74
during the run-in of the assembly.
When the assembly 10 has reached the desired location within the
well casing, it may be actuated by pumping hydraulic fluid, for
example water, down into connector 16 or pressurizing fluid already
present in the run-in string. The pressurized hydraulic fluid
passes through ports 30 in mandrel 20 creating a pressure
differential on annular piston 24. When the pressure differential
on the piston 24 is sufficient to overcome the forces of spring 34
and that of gravity, the piston 24 will be forced upwardly into the
position shown in FIG. 4 pushing the magnet 22 upwardly therewith.
The magnetic coupling of member 50 described above is of sufficient
force to overcome the force of gravity and spring 55 thus moving
member 50 upwardly with respect to hanger mandrel 39.
As the member 50 is moved upwardly with respect to mandrel 39 the
slip reins 60 are pulled upwardly therewith forcing the slips sets
56 and 58 to slide upwardly upon the respective cones 52 and 54
which are stationary with respect to mandrel 39. As the slips slide
upon the cones, it is evident that the slips must move radially
outwardly due to the increasing outside diameter of the cones and
the matching angle of the inner surface of the slips. The radial
force created by the cones is sufficient to overcome the force of
the spring means 76 in the rein housing 74; therefore, the reins
may follow the respective slips connected thereto in a radial
outward direction within the respective cone slots 62. Since the
relative movement of the slips of upper slip set 56 is identical to
the relative movement of the slips of the lower slip set 58 the
reins 60 will always be in substantially parallel relation to the
axis of mandrel 39. This design ensures that substantially the
entire serrated surfaces 69 of the slips will engage the interior
wall of the well casing (see FIG. 5) to produce a strong engagement
therewith.
After the slips have been moved upwardly and outwardly into
engagement with the casing, the run-string is lowered slightly to
lower the cones with respect to the slips and thereby place the
weight of the liner on the slips further driving them radially
outward into firm engagement with the inner wall of well casing C.
The slips are then able to hold the weight of the entire assembly
within the well casing.
After the slips are set in the manner described above, the setting
tool 14 is released from engagement with the hanger 12 by well
known means, and it may be raised to the surface by the run-in
string. If it is desired to relocate the hanger 12 within the well,
it is only required that the tool 14 be mechanically reconnected to
hanger 12 by means of a well known connecting assembly whereby the
hanger may be lifted slightly and by means of gravity and the force
of spring 55 the slips will fall back into the original position
thereof as depicted in FIG. 1. The hanger may then be relocated to
the desired position whereafter the above setting operation is
again performed.
FIG. 4 shows a modified form of the present invention including
three axially spaced sets of slips 110, 120, 130 and is shown in
the run-in position within a well casing C. FIG. 5 depicts a
slightly modified form of the hanger of FIG. 4 and illustrates the
set position wherein the serrated surfaces of the slips are in
engagement with the inner wall of the well casing C. While each of
the embodiments of FIGS. 4 and 5 are adapted to include four
circumferentially spaced reins 160, the forwardmost rein and the
associated slips thereof have been removed for the sake of clarity.
The embodiment of FIG. 4 shows the construction of the cones 112,
122, 132 on mandrel 139 and the rein housing 140 being of a fluted
design while the embodiment of FIG. 5 depicts alternative nonfluted
cones 114, 124, 134 and a nonfluted rein housing 142. It can be
seen that the embodiment of FIG. 4 will allow a greater flow of
fluid between the hanger mandrel and the well casing due to the
increased flow cross section created by the flutes 116, 126, 136 in
the cones and the flutes 146 in the rein housing 140. FIGS. 4 and 5
clearly show that any number of axially spaced cones and associated
slip sets may be provided on the hanger mandrel of the present
invention. Also it is clear that the reins may be moved axially by
any means; the actuator need not be the magnetic device as
described hereinabove with respect to the preferred embodiment of
FIG. 1. FIGS. 4 and 5 also show a modified form of the rein housing
shown in FIG. 1. The rein housings of FIGS. 4 and 5 are stationary
with respect to the hanger mandrel and thus do not move along with
the rein as the reins are actuated into the set position.
Compression spring means (not shown) within the rein housing urge
the reins radially inwardly with respect to the hanger mandrel;
however, the spring means and rein housing are not connected to the
reins as described in the embodiment of FIG. 1. Instead, the bottom
end of the rein freely moves axially within the rein housing in
slidable engagement with the spring means, and the rein housing has
an axial length sufficient to captively surround the ends of the
reins throughout the extent of the axial movement thereof.
It is to be particularly noted that while a few preferred
embodiments of the invention have been described and shown, it is
clear that numerous modifications may be made thereto without
departing from the spirit and scope of the invention. For example,
the slip reins may be pulled or pushed upwardly by any means
including manually; the slip reins may be held axially stationary
with respect to the hanger mandrel as axially movable cones are
moved into engagement with the slips to thereby force the slips
radially outwardly; it is not necessary that each rein carry a slip
from each slip set, for example, a hanger having four axially
spaced slip sets, each set containing only two slips, may provide
four slip reins, each rein secured to only two slips; each slip
rein may carry only a single slip. It is therefore requested that
the scope of the invention be limited only by the following
claims.
* * * * *