Note: Descriptions are shown in the official language in which they were submitted.
CA 02568945 2006-11-27
LOW PRESSURE-SET PACKER
FIELD OF THE INVENTION
The field of this invention relates to packers set in wellbores of hydrocarbon-
producing
formations by applied pressure, and methods for using same.
BACKGROUND OF THE INVENTION
For wells in low-pressure formations that do not require the use of steel
tubing,
corrosion issues that may arise can be avoided by instead employing plastic
tubing. In
running in tubing using applied pressure, the bottomhole pressure (typically
about 800
psi in such low-pressure wells) must still be overcome in order to set
packers, and
conventional tools can generate just enough force with the application of the
equivalent
of the bottomhole pressure to set the packers. As packers are typically set
inside
casings, the force of setting such a tool may be transferred through the tool
into the
casing. However, the pressure required to generate the setting force is
transferred to
the well formation through perforations in the casing wall whenever the pump-
out plug
below the packer is shifted and opens communication between the tubing string
and
well below the packer, which can result in damage. Also, the pressure can act
to cause
failures in the connections of the tubing string. Although such failures may
in some
cases be avoided by strengthening the connections, this may further complicate
the
normal handling of the plastic tubing. So, since even as little as 800 psi can
damage
well formations and plastic tubing, there is a need for an improved packer
tool that
requires the application of less pressure and thus is less likely to cause
damage.
SUMMARY
In one aspect of the invention, there is provided a packer tool for use in a
wellbore
having a bottomhole pressure p, the tool comprising: mandrel assembly; a
stabilizer on
the mandrel assembly, for releasably engaging the wellbore; a packing element
in an
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annular recess having a floor and two facing walls, the annular recess being
transversely compressible into a compressed position and disposed about the
mandrel
assembly; and a piston assembly for driving compression of the packing element
annular recess, the piston assembly having a plurality of pistons connected to
act in
tandem, the pistons having a total piston face surface area a such that an
application of
pressure of p'to the piston assembly generates a force f greater than p.
In another aspect of the invention, the packer tool may further include a
quantity of
sealing element disposed in the annular recess and being resiliently
deformable into
sealing engagement with the wellbore.
In yet another aspect of the invention, the packer tool may be set in response
to the
application of pressure less than 800 psi.
In accordance with another aspect of the present invention, there is provided
downhole
assembly comprising: a plastic tubing string including an inner diameter; and
a packer
connected to the plastic tubing string and in fluid communication with the
inner diameter
of the plastic tubing string, the packer including: a mandrel assembly; a
stabilizer on the
mandrel assembly, for releasably engaging the wellbore; a packing element in
an
annular recess having a floor and two facing walls, the annular recess being
transversely compressible into a compressed position and disposed about the
mandrel
assembly; and a piston assembly for driving compression of the packing element
annular recess, the piston assembly having a plurality of pistons connected to
act in
tandem, the pistons capable of driving compression of the packing element
annular
recess at applied pressures of less than 800 psi.
In accordance with another broad aspect, there is provided a method for
setting a
production string in a wellbore, the method comprising: running into a
wellbore a plastic
tubing string with an expandable packer installed thereon, the expandable
packer
including a mandrel assembly; a stabilizer on the mandrel assembly, for
releasably
engaging the wellbore; a packing element in an annular recess having a floor
and two
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facing walls, the annular recess being compressible into a compressed position
and
disposed about the mandrel assembly; and a piston assembly for driving
compression
of the packing element annular recess, the piston assembly having a plurality
of pistons
connected to act in tandem, the expandable packer being in fluid communication
with
surface through an inner diameter of the plastic tubing string; setting the
stabilizer to
engage the wellbore, and applying pressure of less than 800 psi to drive the
piston
assembly to drive compression of the packing element annular recess to pack
off about
the packer.
It is to be understood that other aspects of the present invention will become
readily
apparent to those skilled in the art from the following detailed description,
wherein
various embodiments of the invention are shown and described by way of
illustration.
As will be realized, the invention is useful for other and different
embodiments and its
several details are capable of modification in various other respects, all
without
departing from the spirit and scope of the present invention. Accordingly the
drawings
and detailed description are to be regarded as illustrative in nature and not
as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings wherein like reference numerals indicate similar
parts
throughout the several views, several aspects of the present invention are
illustrated by
way of example, and not by way of limitation, in detail in the figures,
wherein:
Figure 1A to Figure 1F are longitudinal sections of a packer tool in
accordance with an
embodiment of the invention.
Figure 2 is a sectional detail of an annular recess of a packer tool in
accordance with an
embodiment of the invention.
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Figure 3 is a sectional detail of a ratchet locking system of a packer tool in
according
with an embodiment of the invention.
Figure 4 is a schematic elevation of a packer tool and tubing system according
to the
present invention.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
The detailed description set forth below in connection with the appended
drawings is
intended as a description of various embodiments of the present invention and
is not
intended to represent the only embodiments contemplated by the inventor. The
detailed
description includes specific details for the purpose of providing a
comprehensive
understanding of the present invention. However, it will be apparent to those
skilled in
the art that the present invention may be practiced without these specific
details.
In the following description of the invention, it is to be understood that
although the
reference is made to a borehole wall, it is to be understood that the borehole
could be
open hole or lined. For example, without limitation, the invention may be used
in an
open hole or in wellbore liners such as casing.
Tools of the invention may generate sufficient force to overcome bottomhole
hydrostatic
pressure and set packer elements by decreasing the quantum of applied pressure
while
increasing the piston surface area by which such pressure is applied. Given
bottomhole
conditions, pistons in tools of the invention may be placed above or below the
packer
element, and piston and piston abutment surface area may be increased either
by
simply increasing the size of these components, or, where the diameter of the
borehole
is a limiting factor, by increasing the number of pistons to thereby increase
the piston
face area.
As shown in Figures 1, in an embodiment of the invention, the packer tool 100
may
include an inner mandrel 1 including an upper end la and a lower end lb.
Although not
shown, upper and lower ends la, lb of the inner mandrel are formed for
connection to a
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tubing string. A bore 1c of the inner mandrel is in fluid communication with
the inner
bore of tubing string thereabove. Bore 1c either includes a plug to seal
against fluid
flow out through lower end or a plug is positioned in a tubing string
connected below the
packer, as in the illustrated embodiment, such that fluid pressure can be
applied to
actuate the packer.
Positioned about inner mandrel 1, in slidable engagement therewith, is an
outer mandrel
3. Positioned about outer mandrel 3 is a piston housing 6 in slidable
engagement with
the lateral surface of outer mandrel 3.
The tool may include a stabilizer for stabilizing the tool against the
borehole wall A, such
as, without limitation, an anchor assembly or a slip and cone assembly. In the
embodiment shown in Figure 1, the stabilizer includes upper cone element 7,
lower
cone element 11, slips 10, and slip retaining elements 9. In such embodiments,
one or
both of the upper and lower cone elements may slidably approach one another to
push
the slips out into anchoring engagement with the borehole, and in some of
these
embodiments, may slide away from each other in order to allow the slips to
fall back in
and disengage from the borehole. In the illustrated embodiment, upper cone
element 7
may include an end 7a forming a piston face such that the cone can be driven
by fluid
pressure toward lower cone element 11 to set the stabilizer. Upper cone
element 7
may be positioned coaxially in slidable relation between outer mandrel 3 and
piston
housing 6.
Since the wellbore has a bottomhole pressure p inhibiting the insertion and
setting of
the packer, in order to set the packer an opposing force f is applied to the
tool to
overcome the bottomhole pressure; typically, opposing force f of about 5000
lbs is
required to do so. In the piston assembly of the present invention, the force
applied to
the tool is transmitted by the one or more pistons to compress the packer
seal, the
operative piston face surface area being selected to exceed f/p. Given that
the
dimensions of the wellbore may present some limitations on the diameter of the
tool and
therefore the operative surface area of the piston, a plurality of pistons may
be
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connected to act in tandem in order to provide a total operative surface area
a that
exceeds f/p. Thus, where conventional tools may generate just enough force at
800 psi
to set in low pressure wells, in the present invention the required pressure
can be
reduced by increasing the operative piston surface area; for example, if the
surface area
is increased by three times (as compared to conventional packers requiring 800
psi to
set), then sufficient force would be generated at somewhat less than 300 psi
(that is,
upon the application of a pressure p' that exceeds f/a). In one embodiment of
a tool
according to the present invention, the tool has a 3.8 inch diameter and the
total
operative piston area may be greater than 6.25 square inches and in one
embodiment
greater than about 15 square inches divided over a plurality of, for example,
four pistons
acting in tandem.
In the particular embodiment illustrated in Figure 1, piston assembly 6
includes pistons
19, each with a piston face 17, all connected to piston assembly. Outer
mandrel 3 may
be formed or assembled to provide piston abutments 21 to cooperate with
pistons 19 to
form piston chambers 23. While in some embodiments the pistons and/or the
piston
abutments may be annular, it is not necessary that these elements take such a
configuration and in other embodiments non-annular pistons and/or abutments
may be
provided. Further, the embodiment in this figure includes a plurality of
pistons and
cooperating abutments, but it is to be understood that a single
piston/abutment pair may
be provided in accordance with the invention.
Tool 100 of the embodiment in Figure 1 further includes annular recess 22 that
may be
narrowed for the purpose of compressing a quantity of sealing element 5 so
that it forms
a pack-off seal between the tool 100 and the borehole wall. In some
embodiments, the
annular recess may be widened from the narrowed (that is, compressed) position
in
order to allow the sealing element to relax and thereby disengage from the
borehole
wall. In embodiments compression of the annular recess is facilitated by at
least one of
two side walls of the annular recess being slidable toward each other. In the
embodiment shown in Figure 1, the outer mandrel 3 forms a first annular recess
wall
20a while the piston housing 6 forms the other annular recess wall 20b.
Annular recess
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wall 20b is moveable toward and away from wall 20a by action of the piston
housing.
While Figure 1 illustrates an embodiment in which the packer sealing element 5
is
disposed above the piston assembly, it is to be understood that in some
embodiments
the piston assembly may be disposed above the annular recess. In embodiments
having the piston assembly disposed between the annular recess and the
stabilizer
assembly and seals (such as o-rings) for the engagement of the various sliding
parts,
the placement the piston assembly below the packer sealing element 5 prevents
leakage past the tool if at some point after the tool is set any of the seals
fail, since all
such leakage would be located below the primary seal of the annular sealing
element to
the wellbore wall.
The characteristics of the elastomer comprising the sealing element and its
geometry
are relevant to the operation of tool; the composition of elastomer should be
selected to
withstand the temperature, depth, and other conditions of the wellbore
location at which
the tool is to be set. As well, on one hand, the quantity (that is, volume) of
sealing
element must be enough to permit it to withstand a selected differential
pressure across
the sealing element; a differential pressure of 5,000 psi is often the upper
limit of what
tools in most wells encounter, even though some tools are expected to only
accommodate lower differential pressures, such as around 800 psi. On the other
hand,
in accordance with this invention the sealing element may be completely packed
off with
as low a force as possible to avoid damaging the tubing or the well. Too great
a
quantity of sealing element 5 will require a greater pack-off force, while not
enough will
reduce the sealing element's ability to withstand differential pressure and
thus affect the
tool's integrity. Elastomer selection and geometry for given well and
component
conditions would be understood by those skilled in the art.
The geometry of the annular recess on both sides of the sealing element may
also be
selected to assist in sealing the sealing element against the mandrel
assembly; for
example, in the embodiment shown in Figure 2, gauge rings 215 may be provided
on
either side of annular recess 222 and configured to trap sealing element 205
and
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generate a force against it that helps provide a seal between sealing element
205 and
mandrel 203.
Shear elements (such as pins, screws, etc.) may also be provided in some
embodiments of the present invention, to ensure that movement of particular
components is inhibited until desired, for example to act against accidental
setting
and/or to control the sequential movement of parts. For example, in the
embodiment of
Figure 1, tool 100 is provided with packer-setting shear elements 4 and slip-
setting
shear elements 8 and 13 each having specific shear values. Slip-setting shear
elements 8, 13 prevent movement of lower cone element 7 and slip retainers 9,
respectively, and therefore engagement of slips 10 with the borehole, and
packer-
setting shear elements 4 prevent movement of piston housing 6, and therefore
compression of sealing element 5, at least until the shearing force exceeds
the specific
shear values of these shear elements. The specific shear value of shear
elements will
bear upon the pressure under which you wish a particular part to move. For
example, if
it is desired to set the sealing element at 200 psi, elastomers that can be
set at that
pressure are selected and shear elements having a shear value less than 200
psi (for
example, 150 psi) to prevent premature shearing are selected. (However,
although
shear elements having shear values as low as about 50 psi are available, such
shear
elements would not be necessary if the selected elastomers settable at such
low
pressures cannot withstand the differential pressure conditions of the well.)
Where a
higher setting pressure is desired, shear elements that can withstand higher
shear
values may be selected, and/or more shear elements can be provided.
Referring to Figures 1A and 1B, in operation the packer tool 100, including
the tubing
string with packer, is first run to setting depth. Once at setting depth,
pressure applied
to tool 100 (such as by a pump at surface) communicates through setting port
12
(located on inner mandrel 1), passes along a microannulus between inner
mandrel 1
and outer mandrel 3 and through ports 27 to be conveyed to pistons 7a and 19
to drive
operation of the tool. Various seals such as seals 18, 18a, 18b, contain and
direct the
fluid pressure through the packer. As fluid pressure builds in chambers 23,
shear
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elements 8 holding upper cone element 7 are selected to fail first. The shear
value of
shear elements 8 is pre-selected to be greater than that pressure required to
locate the
tubing string 100 at the desired position in the borehole. For those
circumstances in
which sudden stops in running the tubing string into the well (which may
result in the
linear momentum of the cone elements causing them to "sling shot" into the
slips) or
vibration are a risk, it may be desirable to select a minimum shear value that
is higher
than the force that would be applied on the shear elements by such vibration
or sudden
stops in order to avoid premature setting. Once the cone shear elements 8
shear, the
tubing pressure then drives the upper cone 7 longitudinally towards lower cone
11 of
cone assembly 15, thereby pushing slips 10 to ride up cone assemblies 7 and 11
and
radially outwards toward the casing wall. Such motion causes slips 10 to exert
pressure
on slip cages 9 to move out of the slip path, causing the shearing of slip-
setting shear
elements 13 and the longitudinal movement of slip cages 9 away from slips 10.
Once
slips 10 are no longer restrained by slip cages 9, continued longitudinal
compression of
cone assembly 15 causes slips 10 to continue to ride up the upper and lower
cones 7
and 11 until slips 10 engage the casing wall A and thus stabilize the position
of the
packer and the tubing string within the borehole. While in the embodiment
shown in
Figure 1 the cone shear elements 8 are disposed in the upper cone assembly 7,
it is to
be understood that they may be disposed in any component of the device that
may be
used to prevent the slips from being prematurely displaced. In other
embodiments, a
mechanical anchor or other stabilizing element may be used instead of a slip
and cone
assembly.
Referring to Figure 1C, once slips 10 set, tubing pressure can be further
increased to
shear the packer-setting shear elements 4. In embodiments having slip-setting
and
packer-setting shear elements, the shear value of the packer-setting shear
elements
may be higher than that of the slip-setting shear elements so that the
stabilizer is
operated to hold the packer in position in the wellbore before the packer is
set. Once
shear elements 4 shear, fluid pressure against piston faces 17 and reacted
against
abutments 21 cause piston housing 6 to slide along the outer mandrel thereby
generating the setting force. The piston housing 6 travels up and wall 20b
compresses
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sealing element 5 to pack it off. In some embodiments, a locking system may be
provided to ensure force is always trapped in the tool to prevent the piston
housing 6
from sliding back to unset the packer. Referring to Figure 3, for example, a
ratchet
system may be used, including ratchet fingers 324 extending from piston
assembly 306
that operatively engage ratchet thread 325 along the outer surface of upper
cone
assembly 307. While such a locking system may not necessarily stop further
setting
motion (and indeed in some circumstances it may be desirable to allow the tool
to pack
off more whenever it is exposed to a pressure differential greater than the
setting
pressure), it can be used to ensure that force is always in the tool to
inhibit release of
the tool.
In the embodiment, illustrated in Figure 1, the tool can be unset, if desired,
for retrieval
to surface. Referring to Figure 1D, to remove the tool 100 from the borehole,
with the
packer set in the borehole, a pulling force is applied upwardly to the inner
mandrel 1. At
a predetermined shear value brass shear screws 2 between the inner mandrel and
outer mandrel 3 will be sheared, allowing inner mandrel assembly 1 to move
upward
within outer mandrel 3 until shoulder 14 of inner mandrel assembly 1 contacts
and stops
against complementary shoulder 16 of outer mandrel assembly 3. After tool 100
has
been released by pulling inner mandrel 1 into tension, the setting ports 12 on
the inner
mandrel assembly 1 shift past the 0-ring 18 and are thus exposed to the
annulus above
the packing element 5. Differential pressure in the well from above and below
can then
equalize across the tool 100 through the setting ports 12.
Referring to Figures lE and 1F, with the engagement of shoulders 14 and 16,
the inner
mandrel assembly 1 picks up the outer mandrel assembly 3 and moves it upward.
The
upward movement of the outer mandrel assembly 3 pulls wall 20a away from wall
20b,
allowing sealing element 5 to relax and unset.
Movement of inner mandrel 1 relative to outer mandrel also positions a small
diameter
section on the inner mandrel assembly 1 below collet fingers 26 on the outer
mandrel
assembly 3, thus allowing the collet fingers to collapse and be pulled axially
to engage
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in a groove on the inner side of the lower cone 11, and as the outer mandrel
assembly 3
continues to move back up, it picks up the piston assembly 6 and upper cone
assembly
7 to pull it from under slips 10. Then the upper cone assembly 7 picks up the
slip cage 9
to release the lower side of the slips 10, such that the tool 100 is fully
released and can
be pulled out from the well. In this fashion, the tubing can then be serviced
and the
packer can be repaired for and refit with shear elements for reuse.
With reference to Figure 4, a packer 400 including multiple pistons connected
to act in
tandem to drive a piston housing against an expandable packer element 405 such
as
for example with reference to those of Figures 1 to 3, may provide a packer
capable of
packing off at pressures lower than 800 psi, for example, between about 150
and 800
psi and possibly about 300 psi. Such a packer may be useful in assemblies
including a
plastic tubing string 450 from surface, such as in some production strings.
Such
assemblies may include connections 452 that are susceptible to failure or
damage at
pressures normally used for setting hydraulically set packers. While
previously it may
be believed that such connections 452 would have to be strengthened in order
to
employed a hydraulically set packer therewith, use of a packer according to
the present
invention may avoid such detrimental effect to connections without the need to
strengthen them. One such connection 452 may include for example a tension
release
mechanism, including shear screws 454 and seals 456, of a grapple sub.
An assembly using plastic tubing string 450 and packer 400 may include a
plastic tubing
string segment 458 connected below the packer and which may include a plug 460
for
holding pressure in the packer bore 401c for actuation thereof. Plug 460 may
include a
blow out mechanism for removal of the plug, if desired.
While a particular embodiment of the present invention has been described in
the
foregoing, it is to be understood that other embodiments are possible within
the scope
of the invention and are intended to be included herein. It will be clear to
any person
skilled in the art that modifications of and adjustments to this invention,
not shown, are
possible without departing from the spirit of the invention as demonstrated
through the
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exemplary embodiment. The invention is therefore to be considered limited
solely by
the scope of the appended claims, wherein reference to an element in the
singular,
such as by use of the article "a" or "an" is not intended to mean "one and
only one"
unless specifically so stated, but rather "one or more". All structural and
functional
equivalents to the elements of the various embodiments described throughout
the
disclosure that are know or later come to be known to those of ordinary skill
in the art
are intended to be encompassed by the elements of the claims.
=
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