[0001] This invention relates generally to downhole tools for use in wellbores and, more
particularly, to such tools having a packer element, and to improvements in preventing
undesired extrusion of packer seal elements between segmented non-metallic packer
element shoes.
[0002] In the drilling or reworking of oil wells, a great variety of downhole tools are
used. For example, but not by way of limitation, it is often desirable to seal tubing
or other pipe in the casing of the well, such as when it is desired to pump cement
or other slurry down the tubing and force the cement or slurry around the annulus
of the tubing or out into a formation. It then becomes necessary to seal the tubing
with respect to the well casing and to prevent the fluid pressure of the slurry from
lifting the tubing out of the well or for otherwise isolating specific zones in which
a wellbore has been placed. Downhole tools referred to as packers and bridge plugs
are designed for these general purposes and are well-known in the art of producing
oil and gas.
[0003] When it is desired to remove many of these downhole tools from a wellbore, it is
frequently simpler and less expensive to mill or drill them out rather than to implement
a complex retrieving operation. In milling a milling cutter is used to grind the packer
or lug, for example, or at least the outer components thereof, out of the wellbore.
Milling is a relatively slow process, but when milling with conventional tubular strings,
it can be used on packers or bridge plugs having relative hard components such as
erosion-resistant hard steel. One such packer is disclosed in U.S. Patent No. 4,151,875
to Sullaway, assigned to the assignee of the present invention and sold under the
trademark EZ Disposal® packer.
[0004] In drilling, a drill bit is used to cut and grind up the components of the downhole
tool to remove it from the wellbore. This is a much faster operation than milling,
but requires the tool to be made out of materials which can be accommodated by the
drill bit. Typically, soft and medium hardness cast iron are used on the pressure
bearing components, along with some brass and aluminum items. Packers of this type
include the Halliburton EZ Drill® and EZ Drill® Super Surge SV squeeze packers.
[0005] The EZ Drill® Super Surge SV squeeze packer, for example, includes a lock ring housing,
upper slip wedge, lower slip wedge, and lower slip support made of soft cast iron.
These components are mounted on a mandrel made of medium hardness cast iron. The EZ
Drill® Super Surge bridge plug is also similar, except that it does not provide for
fluid flow therethrough.
[0006] All of the above-mentioned packers are disclosed in Halliburton Services - Sales
and Service Catalog No. 43, pages 2561-2562, and the bridge plug is disclosed in the
same catalog on pages 2556-2557.
[0007] The EZ Drill® packer and bridge plug and the EZ Drill® SV packer are designed for
fast removal from the wellbore by either rotary or cable tool drilling methods. Many
of the components in these drillable packing devices are locked together to prevent
their spinning while being drilled, and the harder slips are grooved so that they
will be broken up in small pieces. Typically, standard "tri-cone" rotary drill bits
are used which are rotated at speeds of about 75 to about 120 rpm. A load of about
5,000 to about 7,000 pounds of weight is applied to the bit for initial drilling and
increased as necessary to drill out the remainder of the packer or bridge plug, depending
upon its size. Drill collars may be used as required for weight and bit stabilization.
[0008] Such drillable devices have worked well and provide improved operating performance
at relatively high temperatures and pressures. The packers and bridge plugs mentioned
above are designed to withstand pressures of about 10,000 psi (700 Kg/cm z) and temperatures
of about 425° F (220° C) after being set in the wellbore. Such pressures and temperatures
require using the cast iron components previously discussed.
[0009] However, drilling out iron components requires certain techniques. Ideally, the operator
employs variations in rotary speed and bit weight to help break up the metal parts
and reestablish bit penetration should bit penetration cease while drilling. A phenomenon
known as "bit tracking" can occur, wherein the drill bit stays on one path and no
longer cuts into the downhole tool. When this happens, it is necessary to pick up
the bit above the drilling surface and rapidly recontact the bit with the packer or
plug and apply weight while continuing rotation. This aids in breaking up the established
bit pattern and helps to reestablish bit penetration. If this procedure is used, there
are rarely problems. However, operators may not apply these techniques or even recognize
when bit tracking has occurred. The result is that drilling times are greatly increased
because the bit merely wears against the surface of the downhole tool rather than
cutting into it to break it up.
[0010] In order to overcome the above long standing problems, the assignee of the present
invention introduced to the industry a line of drillable packers and bridge plugs
currently marketed by the assignee under the trademark FAS DRILL®. The FAS DRILL®
line of tools consist of a majority of the components being made of non-metallic engineering
grade plastics to greatly improve the drillability of such downhole tools. The FAS
DRILL® line of tools have been very successful and a number of U.S. patents have been
issued to the assignee of the present invention, including U.S. Patent No. 5,271,468
to Streich et al., U.S. Patent No. 5,224,540 to Streich et al., and U.S. Patent No.
5,390,737 to Jacobi et al. The preceding patents are specifically incorporated herein
by reference.
[0011] Notwithstanding the success of the FAS DRILL® line of drillable downhole packers
and bridge plugs, the assignee of the present invention discovered that certain metallic
components still used within the FAS DRILL® line of packers and bridge plugs at the
time of issuance of the above patents were preventing even quicker drill out times
under certain conditions or when using certain equipment. Exemplary situations include
milling with conventional jointed tubulars and in conditions in which normal bit weight
or bit speed could not be obtained. Other exemplary situations include drilling or
milling with nonconventional drilling techniques such as milling or drilling with
relatively flexible coiled tubing.
[0012] When milling or drilling with coiled tubing, which does not provide a significant
amount of weight on the tool being used, even components made of relatively soft steel,
or other metals considered to be low strength, create problems and increase the amount
of time required to mill out or drill out a downhole tool, including such tools as
the assignee's FAS DRILL® line of drillable non-metallic downhole tools.
[0013] Furthermore, packer shoes and optional back up rings made of a metallic material
are employed not so much as a first choice but due to the metallic shoes and back
up rings being able to withstand the temperatures and pressures typically encountered
by a downhole tool deployed in a borehole.
[0014] Another shortcoming with using metallic packer shoes and optional backup rings is
that upon deployment of the tool, the typically brass packer shoe may not flare outwardly
as the packer portion is being compressed and therefore not expand outwardly as desired.
If the brass shoe does not properly flare, it can lead to unwanted severe distortion
of the shoes and subsequent cutting of the packer element which reduces its ability
to hold to its rated differential pressure or lead to a complete failure of the tool.
[0015] To address the preceding shortcomings, the assignee hereof filed a U.S. patent application
on May 5, 1995, Serial No. 08/442,448, which issued on May 30, 1996, as U.S. Patent
No. 5,540,279 (the '279 patent), describing and claiming an improved downhole tool
apparatus preferably utilizing essentially all non-metallic materials such as engineering
grade plastics, resins, or composites. The '279 patent describes a wellbore packing
type apparatus making use of essentially only non-metallic components in the downhole
tool apparatus for increasing the efficiency of alternative drilling and milling techniques
in addition to conventional drilling and milling techniques and further provided for
a segmented non-metallic back-up ring in lieu of a conventional metallic packer shoe
having a metallic supporting ring. The tool discussed in the '279 patent preferably
employed the general geometric configuration of previously known drillable non-metallic
packers and bridge plugs such as those disclosed in U.S. Patent No. 5,271,468 to Streich
et al., U.S. Patent No. 5,224,540 to Streich et al., and U.S. Patent No. 5,390,737
to Jacobi et al. while replacing essentially all of the few remaining metal components
of the tools disclosed in the preceding patents with non-metallic materials which
can still withstand the pressures and temperatures found in many wellbore applications.
In the '279 patent, the apparatus also includes specific design changes to accommodate
the advantages of using essentially only plastic and composite materials and to allow
for the reduced strengths thereof compared to metal components. Additionally, the
'279 embodiment comprised a center mandrel and slip means disposed on the mandrel
for grippingly engaging the wellbore when in a set position, a packing means disposed
on the mandrel for sealingly engaging the wellbore when in a set position, a slip
means comprising a slip wedge positioned around the center mandrel, a plurality of
slip segments disposed in an initial position around the mandrel and adjacent to the
slip wedge, and retaining means for holding the slip segments in an initial position.
The slip segments would then expand radially outward upon being set so as to grippingly
engage the wellbore. Hardened inserts can be molded, or otherwise installed into the
slips, and can be metallic such as hardened steel, or non-metallic such as a ceramic
material.
[0016] In the preferred embodiment of the '279 patent, the slip means included a slip wedge
installed on the mandrel and the slip segments, whether retained by a retaining band
or whether retained by an integral ring portion, have co-acting planar, or flat portions,
which provided a superior sliding bearing surface especially when the slip means were
made of a non-metallic material such as engineering grade plastics, resins, phenolics,
or composites.
[0017] Furthermore, in the '279 patent prior art packer element shoes and back up rings,
such as those referred to as elements 37 and 38, 44 and 45 in the present assignee's
U.S. Patent No. 5,271,468, were replaced by a non-metallic packer shoe having a multitude
of co-acting non-metallic segments and at least one retaining band, and preferably
two non-metallic bands, for holding the shoe segments in place after initial assembly
and during the running of the tool into the wellbore and prior to the setting of the
associated packer element within the wellbore.
[0018] Notwithstanding the success of the invention described in the '279 patent in that
tools made in accordance thereto are able to withstand the stresses induced by relatively
high differential pressures and high temperatures found within wellbore environments,
the assignee of the present invention discovered that when using larger packer type
tools, or when using packer type tools in higher temperature and/or higher differential
pressure environments, such as those having nominal diameters exceeding six (6) inches,
temperatures exceeding 250° F, or differential pressures exceeding 10,000 psi, there
was a possibility for the non-metallic segmented packer element back-up shoes, also
referred to as back-up rings, to allow the packer element to extrude through gaps
that are designed to form between the back-up ring segments upon the segments being
forced radially outward toward the wellbore surface when the packer element was activated.
Upon certain conditions, the larger O.D. packer elements, and smaller O.D. packer
elements upon being subjected to elevated pressures and temperatures, were subject
to being extruded through these gaps thereby possibly damaging the packer element
and jeopardizing the integrity of the seal between the wellbore and the packer elements.
[0019] To address the issue of unwanted extrusion, the assignee of the present invention
filed a patent application on March 29, 1996, which issued as U.S. Patent No. 5,701,959
(the '959 patent) on December 30, 1997, the details of which are incorporated by reference.
The '959 invention, like the '279 invention, included a non-metallic shoe having a
multitude of co-acting non-metallic segments and at least one retaining band, and
preferably two retaining bands for holding the shoe segments in place after initial
assembly and during the running of the tool into the wellbore and prior to the sealing
of the associated packer element within the wellbore. The invention described in the
'959 patent provided a disk, to act as a gap spanning, structural member. The shoe
segments described in the '959 patent include disk pockets on an inner surface thereof.
Each disk pocket is centered over the gap that it is to bridge, so that a pocket for
a single disk comprises two half pockets located on adjacent shoe segments. The disk
in the '959 patent was designed to span the gap between adjacent segments that increases
in size when the packer element is set in the wellbore.
[0020] Although the inventions described in the '959 and '279 patents work well for their
intended purpose, there is a further need for an easily drillable downhole packer-type
tool apparatus preferably being made at least partly, if not essentially entirely,
of non-metallic, such as, but not limited to, composite components, and which include
expandable packer elements to be partially retained by non-metallic segmented packer
element shoes, or retaining rings that prohibit, or at least significantly reduce,
unwanted extrusion of packer elements between gaps of such segmented shoes or segmented
rings. While the invention described in the '279 patent works well in many cases,
there is still a need for a retaining shoe that will prohibit, or at least limit unwanted
extrusion of the packer element in high pressure, high temperature wells of up to,
and exceeding 350° F and 15,000 psi.
[0021] In one aspect, the present invention provides a downhole apparatus for use in a wellbore
having a casing therein, the apparatus comprising: a packer mandrel; a packer element
assembly disposed about said packer mandrel, said packer element assembly having an
upper end and a lower end, and being movable from an unset to a set position wherein
said packer element assembly engages said casing in said set position; and at least
one retaining shoe for axially retaining said packer element assembly, said retaining
shoe comprising: a first shoe, said first shoe comprising a plurality of first shoe
segments disposed about said packer mandrel, said plurality of first shoe segments
engaging one of said upper and lower ends of said sealing element assembly, adjacent
ones of said first shoe segments having gaps therebetween; and a second shoe, said
second shoe comprising a plurality of second shoe segments disposed about and engaging
said first plurality of shoe segments, adjacent ones of said plurality of said second
shoe segments having gaps therebetween, said retaining shoe having an initial position
and a radially expanded second position, wherein said retaining shoe moves from said
initial position to said second position when said packer element assembly moves from
said unset to said set position, and wherein a width of said gaps between said first
shoe segments and a width of said gaps between said second shoe segments increases
when said retaining shoe moves from said initial to said second position, said first
shoe segments covering said gaps between said second shoe segments, and said second
shoe segments covering said gaps between said first shoe segments in said initial
and said second position of said retaining shoe.
[0022] In another aspect, the invention provides a retaining shoe for limiting the extrusion
of a packer element assembly disposed about a packer mandrel, said packer element
assembly being movable from an unset to a set position in a wellbore, wherein in said
set position said packer element assembly seals against a casing in said wellbore,
the retaining shoe comprising: a plurality of first shoe segments encircling said
packer mandrel, said first shoe segments defining a sloped, arcuate inner surface
for engaging an end of said packer element assembly, adjacent ones of said first shoe
segments having gaps therebetween; and a plurality of second shoe segments disposed
about said first shoe segments said second shoe segments defining a sloped, arcuate
inner surface for engaging a sloped arcuate outer surface of said first shoe segments,
said second shoe segments having gaps therebetween; wherein a width of said gaps between
said first shoe segments and a width of said gaps between said second shoe segments
increases when said packer element assembly moves from said unset to said set position,
and wherein said first shoe segments cover said gaps between said second shoe segments
and said second shoe segments cover said gaps in said first shoe segments.
[0023] In a further aspect, the invention provides a downhole apparatus for use in a wellbore
having casing therein, the apparatus comprising: a mandrel having an axial centerline;
a packer element assembly disposed about said mandrel, said packer element assembly
having an upper end and a lower end and being movable from an unset position wherein
said packer assembly and said casing define an annular gap therebetween, to a set
position wherein said packer element assembly sealingly engages said casing; an upper
retaining shoe for axially retaining said packer element, the upper retaining shoe
comprising an inner retainer and outer retainer, the inner retainer comprising: a
generally cylindrical shoe body disposed about said mandrel; and a fin connected to
and extending radially outwardly from said body, wherein said fin engages said upper
end of said packer element assembly, the outer retainer being disposed about said
inner retainer, said inner and outer retainers comprising expandable retainers movable
from an initial position corresponding to said unset position of said packer element
assembly wherein an annular gap exists between said upper retaining shoe and said
casing, to an expanded position, corresponding to said set position of said packer
element assembly wherein said upper retaining shoe engages said casing; and a lower
retaining shoe, the lower retaining shoe comprising an inner retainer and an outer
retainer, the inner retainer comprising: a generally cylindrical shoe body disposed
about said mandrel; and a fin connected to and extending radially outwardly from said
body, wherein said fin engages said upper end of said packer element assembly, the
outer retainer being disposed about said inner retainer, said inner and outer retainers
comprising expandable retainers movable from an initial position corresponding to
the onset position of the packer element assembly wherein an annular gap exists between
said lower retaining shoe and said casing, to an expanded position corresponding to
the set position of the packer element assembly, wherein said lower retaining shoe
engages said casing.
[0024] The present invention provides for a downhole apparatus for preventing the extrusion
of a packer element assembly installed about a mandrel. The invention includes a mandrel
having a longitudinal central axis, a slip means disposed on the mandrel for grippingly
engaging the wellbore when set into position, and a packer element assembly which
includes at least one packer element to be axially retained about the mandrel. The
invention also includes at least one packer element assembly retaining shoe disposed
about the mandrel for axially retaining the packer element assembly and for preventing
extrusion of the packer element assembly when the tool is set into position. The retaining
shoe includes a first or inner shoe and a second or outer shoe. The inner shoe is
comprised of a plurality of inner shoe segments. Adjacent ones of the inner shoe segments
have gaps therebetween which may be zero when initially installed but which will expand
from the initial installed position, wherein the gaps may be zero or slightly greater
than zero, to a greater width when the tool is set into position. The inner shoe may
comprise a generally cylindrical body which will engage the mandrel and a fin sloping
radially outwardly therefrom which will engage the end of the packer element assembly.
Each inner shoe segment thus comprises a body portion having a fin portion extending
radially outwardly therefrom.
[0025] The second or outer shoe of the retaining shoe likewise is comprised of a plurality
of outer shoe segments. Adjacent ones of the outer shoe segments will spread apart
so that the width of a gap therebetween will expand as the retaining shoe moves from
its initial position to an expanded position wherein the retaining shoe engages the
casing. The expanded position of the retaining shoe corresponds to the set position
of the tool in the wellbore in which the packer element assembly engages the wellbore
or casing disposed in the wellbore. In the expanded position of the retaining shoe,
the retaining shoe engages the casing and prevents, or at least limits extrusion of
the packer element assembly.
[0026] In order that the invention may be more fully understood, the following detailed
description of a preferred embodiment is given in conjunction with the accompanying
drawings which illustrate a preferred embodiment of the present invention. In the
drawings:
FIG. 1 is a cross-sectional side view of a packer apparatus having upper and lower
retaining shoes embodying the present invention.
FIG. 2 is a cross-sectional side view of a packer element assembly and the retaining
shoes of the present invention.
FIG. 3 is a cross-sectional side view of a packer apparatus of the present invention
in a set position.
FIG. 4 is a top view of an inner shoe of a retaining shoe of the present invention.
FIG. 5 is a perspective view of a single inner shoe segment.
FIG. 6 is a top view of the outer shoe of a retaining shoe of the present invention.
FIG. 7 is a perspective view of a single outer shoe segment of the present invention.
FIG. 8 is a perspective view of a retaining shoe of the present invention.
FIG. 9 is a cross-sectional side view of a prior art packer element and a retainer
shoe.
FIG. 10 shows a cross-section of another embodiment of a retaining shoe of the present
invention.
[0027] Referring now to FIGS. 1 and 2, downhole tool, or downhole apparatus 10 is shown
in an unset position 11 in a well 15 having a wellbore 20 with a casing 22 cemented
therein. Apparatus 10 is shown in set position 13 in FIG. 3. Casing 22 has an inner
surface 24. An annulus 26 is defined by casing 22 and downhole tool 10. Downhole tool
10 has a mandrel 28, and may be referred to as a bridge plug due to the tool having
a plug 30 being pinned within mandrel 28 by radially oriented pins 32. Plug 30 has
a seal means 34 located between plug 30 and the internal diameter of mandrel 28 to
prevent fluid flow therebetween. The overall tool structure, however, is adaptable
to tools referred to as packers, which typically have at least one means for allowing
fluid communication through the tool. Packers may therefore allow for the controlling
of fluid passage through the tool by way of a one or more valve mechanisms which may
be integral to the packer body or which may be externally attached to the packer body.
Such valve mechanisms are not shown in the drawings of the present document. Packer
tools may be deployed in wellbores having casings or other such annular structure
or geometry in which the tool may be set.
[0028] Mandrel 28 has an outer surface 36 an inner surface 38, and a longitudinal central
axis, or axial centerline 40. An inner tube 42 is disposed in, and is pinned to mandrel
28 to help support plug 30.
[0029] Tool 10, which may also be referred to as packer apparatus 10, includes the usage
of a spacer ring 44 which is preferably secured to mandrel 28 by pins 46. Spacer ring
44 provides an abutment which serves to axially retain slip segments 48 which are
positioned circumferentially about mandrel 28. Slip retaining bands 50 serve to radially
retain slips 48 in an initial circumferential position about mandrel 28 as well as
slip wedge 52. Bands 50 are made of a steel wire, a plastic material, or a composite
material having the requisite characteristics of having sufficient strength to hold
the slips in place prior to actually setting the tool and to be easily drillable when
the tool is to be removed from the wellbore. Preferably bands 50 are inexpensive and
easily installed about slip segments 48. Slip wedge 52 is initially positioned in
a slidable relationship to, and partially underneath slip segments 48 as shown in
FIG. 1. Slip wedge 52 is shown pinned into place by pins 54. The preferred designs
of slip segments 48 and co-acting slip wedges 52 are described in U.S. Patent No.
5,540,279, the details of which are incorporated herein by reference.
[0030] Located below slip wedge 52 is a packer element assembly 56, which includes at least
one packer element, and as shown in FIG. 1 includes three expandable elements 58 positioned
about mandrel 28. Packer element assembly 56 has unset and set positions 57 and 59
corresponding to the unset and set positions 11 and 13 of tool 10. Assembly 56 has
upper end 60 and lower end 62.
[0031] FIG. 9 shows a prior art arrangement wherein a single metallic shoe, such as shoe
64 is disposed about the upper and lower ends 60 and 62, respectively, of the packer
element assembly 56. Referring to FIG. 1, the present invention has retaining rings
66 disposed at the upper and lower ends of packer element assembly 56. Retaining rings
or retaining shoes 66 may be referred to as an upper retaining shoe or upper retainer
68 and a lower retaining shoe or lower retainer 70. A slip wedge 72 is disposed on
mandrel 28 below lower retaining shoe 70 and is pinned with a pin 74. Located below
lower slip wedge 72 are lower slip segments 76. Lower slip wedge 72 and lower slip
segments 76 are like upper slip wedge 52 and upper slip segments 48. At the lowermost
portion of tool 10 is an angled portion referred to as mule shoe 78, secured to mandrel
28 by pin 79. Lowermost portion 78 need not be a mule shoe but can be any type of
section which will serve to terminate the structure of the tool or serves to be a
connector for connecting the tool with other tools, a valve or tubing, etc. It will
be appreciated by those in the art that pins 32, 46, 54, 74 and 79 if used at all
are preselected to have shear strengths that allow for the tool to be set and deployed
and to withstand the forces expected to be encountered in a wellbore during the operation
of the tool.
[0032] Referring now to FIGS. 2 and 4-8, the retaining shoes of the present invention will
be described. Upper and lower retaining shoes 68 and 70 are essentially identical.
Therefore, the same designating numerals will be used to further identify features
on each of retaining shoes 68 and 70, which are referred to collectively herein as
retaining shoes 66. Retaining shoes 66 comprise an inner shoe or inner retainer 80
and an outer shoe or outer retainer 82. Inner and outer shoes 80 and 82 may also be
referred to as first and second shoes or retainers 80 and 82. Outer shoe 82 is preferably
made of a phenolic material available from General Plastics & Rubber Company, Inc.,
5727 Ledbetter, Houston, Texas 77087-4095, which includes a direction-specific laminate
material referred to as GP-B35F6E21K. Alternatively, structural phenolics available
from commercial suppliers may be used. Inner shoes 80 are preferably made of a composite
material available from General Plastics & Rubber Company, Inc., 5727 Ledbetter, Houston,
Texas 77087-4095. A particular suitable material for at a portion of the inner shoe
80 includes a direction specific composite material referred to as GP-L45425E7K available
from General Plastics & Rubber Company, Inc. Alternatively, structural phenolics available
from commercial suppliers may be used.
[0033] Referring now to FIGS. 2, 4, 5 and 8, inner shoe 80 has a body 88 and a fin or wing
90 extending radially outwardly therefrom. Inner shoe 80 has an inner surface 92 and
an outer surface 94. As shown in FIG. 2, upper and lower ends 60 and 62 of packer
element assembly 56 reside directly against upper and lower retainers 68 and 70 and
preferably directly against wing 90 of inner shoe 80 at both the upper and lower ends
60 and 62 thereof. Inner shoe 80 is preferably comprised of a plurality of first or
inner shoe segments 96 to form an inner shoe 80 that encircles mandrel 28. Inner surface
92 of inner shoe 80 is shaped to accommodate the ends 60 and 62 of the packer element
assembly and thus is preferably sloped as well as arcuate to provide a generally truncated
conical surface which transitions from having a greater radius proximate to an outer
end, or outer face 98 of fin 90 to a smaller radius at an internal diameter 100 which
is defined by body 88. Inner shoe 80 also has an inner end, or inner face 99. Inner
surface 92 also defines a cylindrical surface on body 88 that engages mandrel 28 in
an initial or running position of the tool. Each inner shoe segment 96 has ends 102
and 104 which are flat and convergent with respect to a center reference point which,
if the shoe segments are installed about a mandrel will correspond to longitudinal
central axis 40 of the mandrel as depicted in FIG. 1. End surfaces 102 and 104 need
not be flat and can be of other topology.
[0034] Each segment 96 has a fin portion 93 and a body portion 95. Fin portions 93 and body
portions 95 comprise body 88 and fin 90, respectively of inner shoe 80. FIG. 4 illustrates
inner shoe 80 being made of a total eight inner shoe segments 96 to provide a 360°
annulus encircling structure to provide a maximum amount of end support for packer
elements to be retained in the axial direction. A lesser amount, or greater amount,
of shoe segments can be used depending on the nominal diameters of the mandrel, the
packer elements, and the wellbore or casing in which the tool is to be deployed. Inner
diameter 100 generally approaches the inner diameter of the packer element assembly.
As is apparent from the drawings, outer surface 94 faces outwardly away from the tool.
The slope of surface 92 on fin 90 is preferably approximately 45° as shown in FIG.
2. However, the exact slope will be determined by the exterior configuration of the
packer element ends that are to be positioned and eventually placed to the contact
with retaining shoe 66 and inner surface 92 on fin 90. Inner face 99 of inner shoe
80 is slightly sloped, approximately 5° if desired, but it is also best determined
by the surface of the tool which it eventually abuts against when apparatus 10 is
centered in the wellbore.
[0035] A gap 106 is defined by adjacent ends 104 and 102 of segments 96 before or after
downhole tool 10 is set in the well. Gap 106 has a width 109 which can be essentially
zero when the segments are initially installed about mandrel 28, and before the tool
is moved from the set to the unset position. However, a small gap, for example a gap
of .06" may be provided for on initial installation. The width 109 of gap 106, as
will be described in more detail herein below, will increase from that which exists
on initial installation as the tool 10 is set.
[0036] Referring now to FIG. 6, outer shoe 82 has an inner surface 105 and an outer surface
107. Outer shoe 82 preferably has a plurality of individual shoe segments 108 to form
outer shoe 82 which encircles inner shoe 80 and thus encircles mandrel 28. Shoe segments
108 have an inner surface 110, and an outer surface 116. Inner surface 105 of outer
shoe 82 defines an inner diameter 112 and thus defines a generally cylindrical surface
114 adapted to engage outer surface of body 88 on inner shoe 80. Inner surface 105
likewise defines a truncated conical surface 115 to accommodate the outer surface
of fin 90 and thus transitions from a greater radius proximate external, or outer
surface 107 to the inner diameter 112. Ends 118 and 120 of segments 108 are flat and
convergent with respect to a center reference point, which if the shoe segments are
installed about a mandrel, corresponds to the longitudinal axial centerline such as
longitudinal central axis 40 of mandrel 28. End surfaces 118 and 120 need not be flat
and can be of other topology.
[0037] FIG. 6 illustrates outer shoe 82 being made of a total of eight shoe segments to
provide a 360° annulus, or encircling structure to provide the maximum amount of end
support. A lesser or greater amount of shoe segments can be used depending upon the
nominal diameters of the mandrel, the packer elements in the wellbore or casing in
which the tool is to be deployed. A base 121 of outer shoe 82 is slightly sloped,
approximately 5°, if desired but is also best determined by the surface of the tool
which the shoe will eventually abut against, as for example in this case, the slip
wedges 52 and 72. An O-ring 122 is received in a groove 124 in outer shoe 82. Retaining
bands 126 are received in grooves 127 to initially hold the segments in place prior
to actually setting the tool 10. Gap 128 is a space between adjacent ends 118 and
120 of segments 108 before or after the tool 10 is set. Gap 128 has a width 129 that
can be essentially zero when the segments are initially installed about tool 10, but
a small gap, such as .06" may exist after initial installation. The gap will increase
in width when the apparatus 10 is set. Retaining bands 126 are preferably made of
a non-metallic material, such as composite materials available from General Plastics
& Rubber Company, Inc., 5727 Ledbetter, Houston, Texas 77087-4095. However, shoe retaining
bands 126 may be alternatively made of a metallic material such as ANSI 1018 steel
or any other material having sufficient strength to support and retain the shoes in
position prior to actually setting a tool employing such bands. Furthermore, retaining
bands 126 may have either elastic or non-elastic qualities depending on how much radial,
and to some extent axial, movement of the shoe segments can be tolerated prior to
enduring the deployment of the associated tool into a wellbore. Referring now to FIGS.
1 and 2, apparatus 10 is shown in its unset position 11 and thus the packer element
assembly 56 is in its unset position 57. FIG. 3 shows the set position 13 of the tool
10 and the corresponding set position 59 of the packer element assembly 56.
[0038] In unset position 57, retaining bands 126 serve to hold segments 108 in place, and
thus also hold segments 96 in place. Prior to the tool being set, inner shoe 80 engages
mandrel 28 about the upper and lower ends of the packer element assembly 56. Inner
shoe 80 of the lower retaining shoe engages lower end 62 of packer element assembly
56 and inner shoe 80 of the upper retaining shoe 68 engages the upper end 60 of packer
element assembly 56 in the unset position of tool and the packer element assembly.
When the tool has reached the desired location in the wellbore, setting tools as commonly
known in the art will move the tool 10 and thus the packer element assembly 56 to
their set positions as shown in FIG. 3.
[0039] As shown in the perspective view of FIG. 8, inner shoe segments 96 are positioned
so that gaps 106 which, as described before, may be zero when initially installed
but may also be slightly greater than zero, will be located between the ends 118 and
120 of outer shoe segments 108. Likewise, gaps 128 between ends 118 and 120 of the
outer shoe segments 108 will be positioned between the ends 102 and 104 of inner shoe
segments 96. Gaps 106 are thus offset angularly from gaps 128. Gaps 128 are thus covered
by segments 96, and gaps 106 are covered by segments 108. When the tool is moved to
its set position retaining bands 126 will break and retaining shoes 66, namely both
of retaining shoes 68 and 70, will move radially outwardly to engage inner surface
24 of casing 22. The radial movement will cause width 109 and width 129 of gaps 106
and 128, respectively, to increase. However, gaps 106 and 128 will still be angularly
offset, and thus gaps 128 will remain covered by inner shoe segments 96 of inner shoe
80 while gaps 106 will remain covered by outer shoe segments 108 of outer shoe 82.
O-ring 122 will exert a force radially inwardly on outer shoe 82, and will transfer
the force to inner shoe 80 as the tool is being moved to its set position 13. The
inward force applied by the O-ring 122, along with the friction between inner shoe
80 and outer shoe 82, provides for a generally equal separation between segments 96
and between segments 108, as retaining shoe 66 expands radially outwardly. In other
words, the width 109 of each of gaps 106 and the width 129 of gaps 128, will be essentially
uniform, or will vary only slightly as the retaining shoe 66 moves radially outwardly
to its expanded position.
[0040] When the tool is moved to its set position, external, or outer surface 107 of shoe
82 will engage inner surface 24 of casing 22 as will outer end 98 of inner shoe 80.
The extrusion of packer elements 58 is essentially eliminated, since any material
extruded through gaps 106 will engage segments 108 of outer shoe 82 which will prevent
further extrusion. Extrusion is likewise limited by upper and lower slip wedges 52
and 72, respectively. Retaining shoes 66 are thus expandable retaining shoes and will
prevent or at least limit the extrusion of the packer elements. Inner and outer retainers
80 and 82 may also be referred to as expandable retainers. The arrangement is particularly
useful in high pressure, high temperature wells, since there is no extrusion path
available. It should be understood however, that the disclosed retaining shoes may
be used in connection with packer-type tools of lesser or greater diameters, differential
pressure ratings, and operating temperature ratings than those set forth herein.
[0041] Although the inner shoe in the embodiment described herein has a fin and a body,
the body portion may be eliminated so that the inner face of the outer shoe will extend
so that it engages the outer surface of the mandrel in the unset position. In other
words, the inner shoe may comprise only the wing portion so that it will engage the
upper and lower ends of the packer element assembly. Such an arrangement is shown
in FIG. 10 in cross-section. As shown in FIG. 10, a retaining shoe 150 may be disposed
about mandrel 28 and may include a first or inner shoe 152 and a second or outer shoe
154. Inner shoe 152 is generally identical in all aspects to inner shoe 80, except
that it does not include a body 88. Outer shoe 154 likewise is similar to outer shoe
82. However, as is apparent from the drawing, outer shoe 154 will engage mandrel 28
in the unset position of the tool. Inner shoe 152 and outer shoe 154, like inner and
outer shoes 80 and 82, are comprised of a plurality of segments that will have gaps
therebetween when retaining shoe 150 expands radially outwardly to engage a casing
in the well. The segments are positioned so that the gaps between segments in inner
shoe 152 are covered by the segments that make up outer shoe 154. Likewise, the gaps
between segments in outer shoe 154 will be covered by the segments that comprise inner
shoe 152. Thus, retaining shoe 150 will prevent, or at least limit, the extrusion
of the packer element assembly when it is in the set position.
1. A downhole apparatus for use in a wellbore having a casing therein, the apparatus
comprising: a packer mandrel; a packer element assembly disposed about said packer
mandrel, said packer element assembly having an upper end and a lower end, and being
movable from an unset to a set position wherein said packer element assembly engages
said casing in said set position; and at least one retaining shoe for axially retaining
said packer element assembly, said retaining shoe comprising: a first shoe, said first
shoe comprising a plurality of first shoe segments disposed about said packer mandrel,
said plurality of first shoe segments engaging one of said upper and lower ends of
said sealing element assembly, adjacent ones of said first shoe segments having gaps
therebetween; and a second shoe, said second shoe comprising a plurality of second
shoe segments disposed about and engaging said first plurality of shoe segments, adjacent
ones of said plurality of said second shoe segments having gaps therebetween, said
retaining shoe having an initial position and a radially expanded second position,
wherein said retaining shoe moves from said initial position to said second position
when said packer element assembly moves from said unset to said set position, and
wherein a width of said gaps between said first shoe segments and a width of said
gaps between said second shoe segments increases when said retaining shoe moves from
said initial to said second position, said first shoe segments covering said gaps
between said second shoe segments, and said second shoe segments covering said gaps
between said first shoe segments in said initial and said second position of said
retaining shoe.
2. The apparatus of claim 1, wherein said first shoe segments engage said mandrel in
said initial position and engage said casing in said second position, and wherein
said second shoe segments and said casing define a space therebetween in the initial
position of said retaining shoe, and wherein said second segments engage said casing
in said second position of said retaining shoe.
3. The apparatus of claim 1, wherein an inner surface of said second shoe segments engages
an outer surface of said first shoe segments, and wherein said second shoe segments
engage said casing in said second position of said retaining shoe and do not engage
said mandrel in said initial or said second position of said retaining shoe.
4. The apparatus of claim 1, said first shoe segments having an arcuate inner surface
adapted to engage one of said upper and lower ends of said packer element assembly.
5. The apparatus of claim 1, wherein each said first shoe segment comprises: a body portion,
wherein said body portion engages said mandrel when said retaining shoe is in said
initial position; and a fin portion extending radially outwardly from said body portion
for engaging one of said upper or lower ends of said packer element assembly, wherein
said body portions of said first shoe segments define a body of said first shoe, and
wherein said fin portions of said first shoe segments define a fin of said first shoe.
6. The apparatus of claim 5 comprising an upper retaining shoe and a lower retaining
shoe, said upper retaining shoe being disposed at said upper end of said packer element
assembly and said lower retaining shoe being disposed at said lower end of said packer
element assembly, wherein said fin on said upper retaining shoe engages said upper
end of said packer element assembly, and wherein said fin on said lower retaining
shoe engages said lower end of said packer element assembly.
7. The apparatus of claim 6, wherein said body generally defines a cylindrical shape
when disposed about said mandrel, and wherein said fin extends radially outwardly
from said body.
8. The apparatus of claim 5, wherein an inner surface of said second shoe defines a generally
truncated cone shape for engaging said fin of said first shoe.
9. A retaining shoe for limiting the extrusion of a packer element assembly disposed
about a packer mandrel, said packer element assembly being movable from an unset to
a set position in a wellbore, wherein in said set position said packer element assembly
seals against a casing in said wellbore, the retaining shoe comprising: a plurality
of first shoe segments encircling said packer mandrel, said first shoe segments defining
a sloped, arcuate inner surface for engaging an end of said packer element assembly,
adjacent ones of said first shoe segments having gaps therebetween; and a plurality
of second shoe segments disposed about said first shoe segments said second shoe segments
defining a sloped, arcuate inner surface for engaging a sloped arcuate outer surface
of said first shoe segments, said second shoe segments having gaps therebetween; wherein
a width of said gaps between said first shoe segments and a width of said gaps between
said second shoe segments increases when said packer element assembly moves from said
unset to said set position, and wherein said first shoe segments cover said gaps between
said second shoe segments and said second shoe segments cover said gaps in said first
shoe segments.
10. The retaining shoe of claim 9 said retaining shoe being movable from an initial position
corresponding to the unset position of said packer element, to an expanded position
corresponding to the set position of the packer element assembly, wherein said retaining
shoe and said casing define a gap therebetween when said retaining shoe is in said
initial position, and wherein said retaining shoe engages said casing in said expanded
position.
11. The retaining shoe of claim 10, wherein said first shoe segments engage said mandrel
in said initial position and engage said casing in said expanded position, and wherein
said second shoe segments engage said casing in said second position.
12. The retaining shoe of claim 9, wherein each said first shoe segment comprises: a body
portion; and a fin portion connected to said body portion, said fin portion sloping
outwardly from said body portion.
13. The retaining shoe of claim 12, wherein said fin portion engages said casing in said
expanded position of said retaining shoe.
14. The retaining shoe of claim 13, wherein each said second shoe segment has an inner
surface and an outer surface, said inner surface being configured to engage an outer
surface of said fin portion and said body portion of said first segments, wherein
said outer surface of each said second shoe segment engages said casing in said expanded
position of said retaining shoe.
15. The retaining shoe of claim 12, wherein said first shoe segments define a first shoe
and said second segments define a second shoe, body portions of said first shoe segments
defining a body of said first shoe, and said fin portions of said first shoe segments
defining a fin of said first shoe, said body having a generally cylindrical shape,
and said fin extending radially outwardly from said shoe body for engaging an end
of said packer element assembly.
16. A downhole apparatus for use in a wellbore having casing therein, the apparatus comprising:
a mandrel having an axial centerline; a packer element assembly disposed about said
mandrel, said packer element assembly having an upper end and a lower end and being
movable from an unset position wherein said packer assembly and said casing define
an annular gap therebetween, to a set position wherein said packer element assembly
sealingly engages said casing; an upper retaining shoe for axially retaining said
packer element, the upper retaining shoe comprising an inner retainer and outer retainer,
the inner retainer comprising: a generally cylindrical shoe body disposed about said
mandrel; and a fin connected to and extending radially outwardly from said body, wherein
said fin engages said upper end of said packer element assembly, the outer retainer
being disposed about said inner retainer, said inner and outer retainers comprising
expandable retainers movable from an initial position corresponding to said unset
position of said packer element assembly wherein an annular gap exists between said
upper retaining shoe and said casing, to an expanded position, corresponding to said
set position of said packer element assembly wherein said upper retaining shoe engages
said casing; and a lower retaining shoe, the lower retaining shoe comprising an inner
retainer and an outer retainer, the inner retainer comprising: a generally cylindrical
shoe body disposed about said mandrel; and a fin connected to and extending radially
outwardly from said body, wherein said fin engages said upper end of said packer element
assembly, the outer retainer being disposed about said inner retainer, said inner
and outer retainers comprising expandable retainers movable from an initial position
corresponding to the onset position of the packer element assembly wherein an annular
gap exists between said lower retaining shoe and said casing, to an expanded position
corresponding to the set position of the packer element assembly, wherein said lower
retaining shoe engages said casing.
17. The apparatus of claim 16, wherein said inner retainer of said upper retaining shoe
comprises a plurality of upper inner shoe segments, adjacent ones of said upper inner
shoe segments having gaps therebetween, wherein a width of said gap increases when
said upper retaining shoe moves from said initial to said expanded position, and wherein
said upper outer retainer comprises a plurality of upper outer shoe segments, adjacent
ones of said upper outer shoe segments having a gap therebetween, wherein a width
of said gap increases when said upper retaining shoe moves from said initial to said
expanded position, wherein said upper outer shoe segments cover the gaps between said
upper inner shoe segments and said upper inner shoe segments cover the gaps between
said upper outer shoe segments.
18. The apparatus of claim 17, wherein said lower inner retainer of said lower retaining
shoe comprises a plurality of lower inner shoe segments, adjacent ones of said lower
inner shoe segments having gaps therebetween, wherein a width of said gap increases
when said lower retaining shoe moves from said initial to said expanded position,
and wherein said lower outer retainer comprises a plurality of lower outer shoe segments,
adjacent ones of said lower outer shoe segments having a gap therebetween, wherein
a width of said gap increases when said lower retaining shoe moves from said initial
to said expanded position, wherein said lower outer segments cover the gaps between
said lower inner segments and said lower inner shoe segments cover the gaps between
said lower outer shoe segments.
19. The apparatus of claim 18, wherein each said upper inner segment comprises a generally
vertical body portion having arcuate inner and outer surfaces, and a fin portion sloping
outwardly from said body portion, said fin portion having arcuate inner and outer
surfaces, and wherein said lower inner segments comprise a generally vertical body
portion having arcuate inner and outer surfaces, and a fin portion sloping outwardly
from said body portion, said fin portion having arcuate inner and outer surfaces.
20. The apparatus of claim 19, wherein said upper outer shoe segments are configured to
engage said body portion and said fin portion of said upper inner shoe segments, and
will engage said casing in the expanded position, and wherein said lower outer shoe
segments are configured to engage said body portion and said fin portion of said lower
inner shoe segments, and will engage said casing in the expanded position.