Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2011/121277 PCT/GB2011/000427
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CONVERTIBLE DOWNHOLE ISOLATION PLUG
[0001] This disclosure relates to downhole tools for use in oil and gas
wellbores and to
methods for treating wellbores. This disclosure particularly relates to
downhole packers that
are convertible from a bridge plug to a frac plug without removing the packer
from the
wellbore.
[0002] In the drilling or reworking of oil wells, numerous varieties of
downhole tools are.
used. For example, but not by way of limitation, it is often desirable to seal
tubing or other
pipe in a well casing when it is desired to pump cement or other slurry down
the tubing and
force the slurry out into a formation. Thus, it 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. Downhole tools, referred to as packers and bridge
plugs, are designed
to provide for the ability to seal tubing or other pipe in the well casing,
and are well known in
the art of producing oil and gas.
[0003] Packers and bridge plugs typically make use of metallic or non-metallic
slip
elements, or slips. The slips are initially retained in close proximity to the
mandrel, but are
subsequently forced outwardly away from the mandrel to engage a casing that
was previously
installed within the wellbore. Thus, when the tool is positioned at the
desired depth, the slips
are forced outward against the wellbore to secure the packer, or bridge plug,
so the tool will
not move relative to the casing during operations. Some non-limiting example
operations
include testing, stimulating production of the well, or plugging all or a
portion of the well.
[0004] One problem encountered by well operators using packers and bridge
plugs is that
the packer and/or plug must be removed prior to the installation of other
types of plugs. A
frac plug is a good example. A frac plug is essentially a downhole packer with
a ball seat for
receiving a sealing ball. When the packer is set and the sealing ball engages
the ball seat, the
casing, or other pipe in which the frac plug is set, is sealed. Once the
sealing ball is set, the
operator is able to pump fluid into the well, and pumped fluid may be forced
into a formation
above the frac plug. Often, it is necessary to completely block flow from a
lower zone to
facilitate treatment of an upper zone, or conduct some other process in the
upper zone. After
the initial treatment or other process is complete, it may be desirable to
allow flow from the
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lower zone, and to be able to restrict that flow. There is a need for tools
that can be set in the
well to act as a bridge plug, and can be converted to a frac plug while in the
well.
SUMMARY
[0005] One disclosed embodiment is a downhole tool for use in a well. The
downhole
tool comprises a mandrel defining a central flow passage therethrough and a
ball seat
thereon. A sealing element is disposed about the mandrel. The downhole tool is
movable
from an unset to a set position in the well in which the sealing element
engages the well. A
solid plug for blocking flow through the downhole tool is removably connected
in the
mandrel. A sealing ball is positioned in the well and is longitudinally spaced
from the ball
seat. The application of a predetermined pressure in the well will
simultaneously remove the
solid plug and move the sealing ball into engagement with the ball seat.
[0006] Another embodiment provides a downhole tool for use in a well. The
downhole
tool comprises a mandrel having an upper and a lower end. The mandrel defines
a
longitudinal central flow passage therethrough. The mandrel also defines a
ball seat on the
upper end thereof. A sealing element is disposed about the mandrel for
sealingly engaging
the well. A plug is detachably retained within the mandrel and a rod is
disposed within the
longitudinal central flow passage. The rod has a first end contacting the
plug, and a second
end contacting a sealing ball to space the sealing ball from the ball seat.
[0007] Another embodiment provides a method for converting a downhole tool
positioned in a well from a bridge plug to a frac plug. The method comprises
lowering the
downhole tool into the well. The downhole tool defines a longitudinal central
flow passage
therethrough. The method further includes the step of setting the downhole
tool in the well,
where the downhole tool engages the well. Flow through the tool is blocked in
both an
upward and a downward direction through the longitudinal central flow passage
with a solid
plug detachably connected to the tool. A sealing ball is positioned in the
well above the
longitudinal central flow passage. Pressure is increased in the well, thereby
causing the solid
plug to detach from the downhole tool and move the sealing ball into
engagement with a ball
seat that is positioned on the downhole tool. When the sealing ball is in
engagement with the
ball seat, downward flow through the downhole tool is prevented but upward
flow
therethrough is permitted.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 schematically shows two downhole tools positioned in a well.
[0009] FIG. 2 is a cross-sectional view of the downhole tool in an unset
position.
[00010] FIG. 3 is a cross-sectional view of the downhole tool in a set
position.
[00011] FIG. 4 is a cross-sectional view of the downhole tool with the plug
detached.
DETAILED DESCRIPTION
[00012] In the description that follows, similar parts are marked throughout
the
specification and drawings with the same reference numerals, respectively. The
drawings are
not necessarily to scale, and the proportions of certain parts have been
exaggerated to better
illustrate details and features of the invention. In the following
description, the terms
"upper," "upward," "lower," "below," "downhole" and the like as used herein
shall mean in
relation to the bottom or furthest extent of the surrounding wellbore. This
applies even
though the well or portions of it may be deviated or horizontal. The terms
"inwardly" and
"outwardly" are directions toward and away from, respectively, the geometric
center of a
referenced object. Where components of relatively well-known designs are
employed, their
structure and operation will not be described in detail.
[00013] Referring to the drawings, and in particular FIG. 1, the downhole tool
of the
present invention is shown and designated by the numeral 10. Downhole tool 10
has an
upper end 11 and a lower end 13. In FIG. 1, two downhole tools 10 are shown,
and may be
referred to herein as lower downhole tool 10a and second or upper downhole
tool 10b.
Downhole tools 10a and 10b may be identical, and the subscripts a and b are
used to
designate simply that the tools are at different positions in the well.
[00014] FIG. 1 schematically depicts downhole tools 10 in set positions in
well 14, which
is comprised of wellbore 12 with a casing 16 cemented therein. Well 14 may
intersect one or
more formations or zones, such as first zone 18 and second zone 20. Downhole
tools 10 are
shown after being lowered into well 14 with a setting tool 22. Setting tool 22
may be any
type known in the art. One example of setting tool 22 is depicted in FIG. 2.
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[00015] Referring to FIG. 2, a cross-section of downhole tool 10 is shown with
setting tool
22 attached thereto for running downhole tool 10 into well 14. Downhole tool
10 is in an
unset position in FIG. 2. Downhole tool 10 is commonly referred to as a
packer, and herein
is referred to as packer 24. Packer 24 comprises mandrel 26 with first, or
upper end 28, and
second, or lower end 30. Mandrel 26 defines longitudinal central flow passage
32 to allow
fluid communication therethrough. Mandrel 26 defines ball seat 34 on the upper
end 28
thereof. Ball seat 34 has a lower end 33 positioned where ball seat 34 flows
into longitudinal
central flow passage 32. Sealing ball 35 is positioned between setting tool 22
and ball seat 34
and is spaced from ball seat 34. Sealing ball 35 maybe referred to as frac
ball 35.
[00016] Packer 24 is designed to be set in well 14. Thus, mandrel 26 has
sealing element
36 disposed thereabout. A spacer ring 38 is secured to mandrel 26 with pins
40. Spacer ring
38 provides an abutment which serves to axially retain slip segments 42, which
are
positioned circumferentially about mandrel 26. Slip segments 42 may utilize
ceramic buttons
44 as described in detail in U.S. Pat. No. 5,984,007, which is incorporated by
reference
herein. Slip retaining bands 46 serve to radially retain slip segments 42 in
an initial
circumferential position about mandrel 26. Slip retaining bands 46 may be made
of a steel
wire, a plastic material, or a composite material having the requisite
characteristics of
sufficient strength to hold the slip segments 42 in place prior to setting
downhole tool 10, and
are drillable. Preferably, slip retaining bands 46 are inexpensive and easily
installed about
slip segments 42. Slip wedge 48 is initially positioned in a slidable
relationship to, and
partially underneath, slip segment 42. Slip wedge 48 is shown pinned into
place by pins 50.
Located below the upper slip wedge 48 is at least one sealing element 36. The
embodiment
of FIG. 2 has a packer element assembly 52 consisting of three expandable
sealing, or packer
elements 36 disposed about mandrel 26. Packer shoes 56 are disposed at the
upper and lower
ends of packer element assembly 52 and provide axial support thereto. The
particular packer
seal or element arrangement shown in FIG. 2 is merely representative, as there
are several
packer element arrangements known and used within the art.
[00017] Located below a lower slip wedge 48 are a plurality of slip segments
42. A mule
shoe 58 is secured to mandrel 26 by radially oriented pins and/or epoxy glue
60. Mule shoe
58 extends below the lower end 30 of mandrel 26 and has a lower end 62, which
comprises
lower end 13 of downhole tool 10. The lowermost portion of downhole tool 10
need not be a
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mule shoe 58, but could be any type of section, which serves to terminate the
structure of
downhole tool 10, or serves as a connector for connecting downhole tool 10
with other tools,
a valve, tubing or other downhole equipment.
[00018] Referring back to FIG. 2, mandrel 26 has a recess 66 positioned at or
near lower
end 30 thereof. Longitudinal central flow passage 32 has first inner diameter
68 and second
inner diameter 70 which defines recess 66. Second inner diameter 70 is thus
greater than first
inner diameter 68. Recess 66 also defines a shoulder 72. A solid plug 74 is
removably
disposed in mandrel 26, preferably in recess 66. Plug 74 is detachably
connected to mandrel
26 with a shear pin 76 or other retention method. Plug 74 has a receptacle 78
in an upper end
80 thereof. Plug 74 has O-ring 82 to sealingly engage recess 66.
[000191 A rod 84 having upper end 86 and lower end 88 is disposed in
longitudinal central
flow passage 32. Lower end 88 engages solid plug 74, and is received in
receptacle 78,
making contact therewith. Upper end 86 extends beyond lower end 33 of ball
seat 34 to
space ball seat 34 from sealing ball 35 and to prevent sealing ball 35 from
prematurely
seating in ball seat 34. In an alternative embodiment, receptacle 78 is not
utilized, and rod 84
simply contacts upper end 80 of plug 74.
[000201 The operation of downhole tool 10 is as follows. Downhole tool 10 is
lowered
into wellbore 12 with setting tool 22, which is a setting tool of a type known
in the art. As
downhole tool 10 is lowered into wellbore 12, flow through longitudinal
central flow
passageway 32 will be prevented due to solid plug 74. Sealing ball 35 is
positioned and
spaced from ball seat 34 by rod 84. Once downhole tool 10 has been lowered to
a desired
position in well 14, setting tool 22 is utilized to move downhole tool 10 from
its unset
position to the set position, as depicted in FIGS. 2 and 3, respectively. A
setting sleeve (not
shown) will engage spacer ring 38, so that as setting tool 22 moves upwardly,
spacer ring 38
is held in place. Once set, all upward and downward fluid communication from
above and
below plug 74 is prevented. Tool 10 thus acts as a bridge plug to prevent flow
in the well.
Tool 10 may be set in the well above a previously perforated and fractured
zone, for example,
second zone 20 in FIG. 1. A zone thereabove, for example, first zone 18, may
be fractured,
and tool 1 Oa, acting as a bridge plug, prevents fluid from zone 20 from
passing upwardly, and
likewise prevents fluid pressure from above tool 1 Oa from acting on zone 20.
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[000211 To convert downhole tool 10, plug 74 is removed from mandrel 26.
Removing
plug 74 requires the exertion of a predetermined pressure to create a
sufficient force upon
plug 74 to detach or remove plug 74. In one embodiment, plug 74 is retained
with shear pin
76 and the predetermined pressure force will shear pin 76. The fluid pressure
required to
remove plug 74 will be less than the pressure used to fracture a zone
thereabove, so that tool
automatically converts to a frac plug upon the fracturing of a zone
thereabove. The
shearing of shear pin 76 allows plug 74 and rod 84 to fall through well 14.
Upon the
detaching of plug 74, tool 10 performs as a standard frac plug where sealing
ball 35 seats and
unseats from ball seat 34 according to the pressure of communicated fluid from
above.
Removing solid plug 74 and contacting sealing ball 35 with ball seat 34 is
simultaneous in
the described embodiment.
[00022] Using FIG. 1 for exemplary purposes, first tool 10a may be lowered
into well 14
and set above formation 20, which will have been perforated and fractured
prior to setting
tool 10a in well 14. Pressure may be increased to fracture zone 18 thereabove.
When
initially set in well 14 tool 10 will act as a bridge plug to prevent flow
upwardly through the
tool from formation 20. The fracture pressure will be greater than that
required to move or
disconnect plug 74 from mandrel 26 in tool 10a so that the application of the
fracturing
pressure will automatically convert tool 10a into a frac plug. Conversion
simply results from
the increased pressure which will act upon plug 74 to remove it therefrom and
simultaneously
move sealing ball 35 into engagement with seat 34. Fracturing thus continues
in the normal
manner. Once zone 18 has been fractured, pressure may be relieved and fluid
from zones 20
and 18 may pass upwardly to the surface. Thus, tool 10a acts simply as a frac
plug. If
desired, the process may be repeated such that a second tool referred to in
FIG. 1 as tool l Ob
may be set in the well above zone 18 and the process described herein
repeated. The process
can be repeated as many times as desired in a well. Thus, as described herein,
the tool 10
may be converted from a bridge plug to a frac plug while in the well to
effectively prevent
communication from a lower zone into an upper zone and vice versa until
fracturing is
complete. The automatic conversion to the frac plug will allow all zones to
communicate to
the surface once all fracturing has been completed.
[00023] Thus, it is seen that the apparatus and methods of the present
invention readily
achieve the ends and advantages mentioned as well as those inherent therein.
While certain
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preferred embodiments of the invention have been illustrated and described for
purposes of
the present disclosure, numerous changes in the arrangement and construction
of parts and
steps may be made by those skilled in the art, which changes are encompassed
within the
scope and spirit of the present invention as defined by the appended claims.
