Note: Descriptions are shown in the official language in which they were submitted.
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TOP SET PLUG AND METHOD
BACKGROUND
TECHNICAL FIELD
[0001] Embodiments of the subject matter disclosed herein generally relate
to
downhole tools used for perforating and/or fracturing operations, and more
specifically, to a downhole plug that is configured to be set from its top.
DISCUSSION OF THE BACKGROUND
[0002] In the oil and gas field, once a well 100 is drilled to a desired
depth H
relative to the surface 110, as illustrated in Figure 1, and the casing 102
protecting
the wellbore 104 has been installed and cemented in place, it is time to
connect the
wellbore 104 to the subterranean formation(s) 106 to extract the oil and/or
gas. This
process of connecting the wellbore to the subterranean formation may include a
step
of isolating a stage of the casing 102 with a plug 112, a step of perforating
the casing
102 with a perforating gun assembly 114 such that various channels 116 are
formed
to connect the subterranean formations to the inside of the casing 102, a step
of
removing the perforating gun assembly, and a step of fracturing the various
channels
116.
[0003] Some of these steps require to lower into the well 100 a wireline
118 or
equivalent tool, which is electrically and mechanically connected to the
perforating
gun assembly 114, and to activate the gun assembly and/or a setting tool 120
attached to the perforating gun assembly. Setting tool 120 is configured to
hold the
plug 112 prior to isolating a stage and also to set the plug. Figure 1 shows
the
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setting tool 120 disconnected from the plug 112, indicating that the plug has
been set
inside the casing.
[0004] Figure 1 shows the wireline 118, which includes at least one
electrical
connector, being connected to a control interface 122, located on the ground
110,
above the well 100. An operator of the control interface may send electrical
signals
to the perforating gun assembly and/or setting tool for (1) setting the plug
112 and
(2) disconnecting the setting tool from the plug. A fluid 124, (e.g., water,
water and
sand, fracturing fluid, etc.) may be pumped by a pumping system 126, down the
well,
for moving the perforating gun assembly and the setting tool to a desired
location,
e.g., where the plug 112 needs to be deployed, and also for fracturing
purposes.
[0005] The above operations may be repeated multiple times for perforating
and/or fracturing the casing at multiple locations, corresponding to different
stages of
the well. Note that in this case, multiple plugs 112 and 112' may be used for
isolating
the respective stages from each other during the perforating phase and/or
fracturing
phase.
[0006] These completion operations may require several plugs run in series
or
several different plug types run in series. For example, within a given
completion
and/or production activity, the well may require several hundred plugs
depending on
the productivity, depths, and geophysics of each well. Subsequently,
production of
hydrocarbons from these zones requires that the sequentially set plugs be
removed
from the well. In order to reestablish flow past the existing plugs, an
operator must
remove and/or destroy the plugs by milling or drilling the plugs.
[0007] A typical frac plug for such operations is illustrated in Figure 2
and
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includes plural elements. For example, the frac plug 200 has a central,
interior,
mandrel 202 on which all the other elements are placed. The mandrel acts as
the
backbone of the entire frac plug. The following elements are typically added
over the
mandrel 202: a top push ring 203, upper slip ring 204, upper wedge 206,
elastic
sealing element 208, lower wedge 210, lower slip ring 212, a bottom push ring
216,
and a mule shoe 218.
[0008] When a setting tool 300 is used to set the frac plug 200, as
illustrated
in Figure 3, the setting tool 300 applies a force F on the push ring 203 on
one side
and applies an opposite force on the bottom push ring 216, from the other
side. As a
consequence of these two opposite forces, the intermediate components of the
plug
200 press against each other causing the sealing element 208 to elastically
expand
radially and seal against the casing 102. Upper and lower wedges 206 and 210
press not only on the seal 208, but also on their corresponding slip rings 204
and
212, separating them into plural parts and at the same time forcing the
separated
parts of the slip rings to press radially against the casing. In this way, the
slip rings
maintain the sealing element into a tension state to seal against the casing
of the
well and prevent the elastic sealing element from returning to its initial
position.
When the upper and lower wedges 206 and 210 swage the elastic sealing element
to seal against the casing, the elastic sealing element elastically deforms
and
presses against the entire circumference of the casing.
[0009] Traditionally, the setting tool 300 has a main body 301 to which is
attached a setting sleeve 304, which contacts the upstream end of the frac
plug 200.
A mandrel 306 of the setting tool 300 extends from the main body 301 all the
way
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through a bore 201 of the plug 200, until a distal end 306A of the mandrel
exits the
mule shoe 218. A disk or nut 308 is attached to the distal end 306A of the
mandrel
306. If a disk is used, then a nut 310 may be attached to the mandrel 306 to
maintain
in place the disk 308. An external diameter D of the disk 308 is designed to
fit inside
the bore 201 of the mule shoe 218, but also to be larger than an internal
diameter d
of the shear ring 216 or another element (e.g., a collet) that may be used for
engaging the mandrel.
[0010] Because the mandrel 306 extends through the entire frac plug 200
and
the disk 308 applies a force on the bottom part (the part closest to the toe
of the well)
of the frac plug, this type of plug is called a bottom set plug. A
disadvantage of such
a plug is the fact that a typical bottom set plug does not allow for an
operation that is
known in the art as a "ball in place" mode, which means that a ball that is
used to
close the bore 201 of the frac plug 200 is run into the wellbore along with
the plug.
This mode is in contrast to a traditional mode in which the frac plug 200 is
first set
up, the setting tool 300 is removed from the well, and then the ball is pumped
down
the wellbore, from the surface, to seal the bore 201 of the frac plug 200.
Such an
operation increases water usage, costs, and operational inefficiency. Further,
the
frac plug shown in Figure 2 has many parts that need to fit together, which
increases
its cost. Furthermore, when the frac operation is completed, the frac plug
needs to
be removed, which is currently achieved by milling it. This process further
adds to
the complexity of the well exploration and also adds to the oil extraction
cost, as the
milling operation is expensive and time consuming.
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[0011] Thus, there is a need for a simplified plug design that has fewer
components, can be manufactured to be easily removable, and also can perform
the
ball in place operation.
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BRIEF SUMMARY OF THE INVENTION
[0012] According to an embodiment, there is a top set plug for sealing
against
a casing of a well. The plug includes a mandrel having a throughout bore that
extends from a top end to a bottom end, a connecting mechanism located at the
top
end of the mandrel, wherein the connecting mechanism is configured to connect
to a
setting tool and the connecting mechanism is attached with a shear member to
the
mandrel, a sealing element located around the mandrel and configured to be
pushed
toward an internal wall of the casing, an upper wedge configured to push the
sealing
element against the casing, and a slip ring configured to push the sealing
element
over the upper wedge and also to engage the inner wall of the casing with
buttons
for preventing the plug to slide along the casing. The shear member is
manufactured
to break before any other part of the mandrel to release the connecting
mechanism,
and there is no lower wedge to push against the sealing element.
[0013] According to another embodiment, there is a top set plug for sealing
against a casing of a well. The plug includes a mandrel having a throughout
bore
that extends from a top end to a bottom end, a connecting mechanism that is
configured to connect to a setting tool, wherein the connecting mechanism is
attached through a shear member to the mandrel, a sealing element partially
located
around the mandrel and having a top end and a bottom end, wherein the top end
is
configured to be pushed toward an internal wall of the casing and acts as a
seal
while the bottom end is configured as a ramp, and a slip ring configured to
engage
the inner wall of the casing with buttons for preventing the plug to slide
along the
casing. The bottom end of the sealing element enters into a bore of the slip
ring and
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pushes the slip ring radially outward toward the inner wall of the casing. The
shear
member is manufactured to break before any other part of the mandrel to
release the
connecting mechanism.
[0014] According to yet another embodiment, there is a method for plugging
a
casing in a well. The method includes a step of attaching a setting tool to a
frac plug,
wherein a ball is placed inside the setting tool; a step of lowering the
setting tool, the
ball and the frac plug to a desired depth into the casing of the well; a step
of
activating the setting tool to set up the frac plug, wherein a connection
between the
setting tool and the frac plug is located at a top end of the frac plug; a
step of
removing the setting tool after the connection between the setting tool and
the frac
plug is broken; and a step of pressuring the ball to seat onto a seat formed
into a
mandrel of the frac plug.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Fora more complete understanding of the present invention,
reference
is now made to the following descriptions taken in conjunction with the
accompanying drawings, in which:
[0016] Figure 1 is a schematic diagram of a well in which a setting tool
and a
plug have been deployed;
[0017] Figure 2 is a schematic diagram of a frac plug;
[0018] Figure 3 illustrates a setting tool that sets up a frac plug at the
bottom
of the plug;
[0019] Figure 4 illustrates a top set frac plug;
[0020] Figure 5 illustrates the top set frac plug having a ball seated
deep
inside an internal mandrel for providing structural reinforcement;
[0021] Figure 6 illustrates an activation of the setting tool for setting
the top set
plug;
[0022] Figure 7 illustrates a ball from another top set plug interacting
with a
current top set plug;
[0023] Figure 8 illustrates a pattern of a slip ring of the top set plug;
[0024] Figure 9 illustrates a cross-section of the slip ring of the top
set plug;
[0025] Figure 10 illustrates another top set plug that has a sealing
element as
the top most element;
[0026] Figure 11 illustrates the another top set plug after the setting
tool has
been removed and a ball is seated inside the plug; and
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[0027] Figure 12 is flowchart of a method for setting up the top set plug
in a
casing of a well.
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DETAILED DESCRIPTION OF THE INVENTION
[0028] The following description of the embodiments refers to the
accompanying
drawings. The same reference numbers in different drawings identify the same
or
similar elements. The following detailed description does not limit the
invention.
Instead, the scope of the invention is defined by the appended claims. The
following
embodiments are discussed, for simplicity, with regard to a frac plug.
However, the
embodiments to be discussed next are not limited to a frac plug, but they may
be
applied to other types of plugs or other devices that need to be set up in a
narrow
conduit.
[0029] Reference throughout the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure or characteristic
described in
connection with an embodiment is included in at least one embodiment of the
subject
matter disclosed. Thus, the appearance of the phrases "in one embodiment" or
"in
an embodiment" in various places throughout the specification is not
necessarily
referring to the same embodiment. Further, the particular features, structures
or
characteristics may be combined in any suitable manner in one or more
embodiments.
[0030] According to an embodiment, a novel frac plug is configured to have
less parts and to be set up at the top part and not at the bottom part as the
traditional
plugs. In one embodiment, one or more parts, even all the parts, of the frac
plug are
made of a dissolvable material so that there is no need for milling the plug
after the
frac operation of a given stage is over. In one embodiment, the novel frac
plug can
be used in a ball in place mode, due to the top set up operation. In yet
another
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embodiment, the slip part of the frac plug is configured in a zig-zag pattern
to
maximize a gripping with the casing. The zig-zag pattern also prevents the
fingers of
the slip part to break apart when in the well. The above noted features may be
combined in any desired way for a given frac plug, depending on its
application.
[0031] According to an embodiment illustrated in Figure 4, a top set plug
410
is configured to be set up at a top part. The terms "top" and "bottom" are
defined in
this application with regard to a placement of the plug in a vertical or
horizontal well,
where the top points toward the head of the well and the bottom points toward
the
toe of the well. Thus, a top part of the frac plug is well defined as being
the part that
contacts the setting tool, while the bottom part of plug is the part that is
facing toward
the toe of the well and opposite from the setting tool.
[0032] The top set plug 410 is shown in Figure 4 as being part of a system
400 that also includes a setting tool 470 that is connected to the top set
plug 410.
The top set plug 410 is placed inside a casing 102 and has a mandrel 412 that
is
configured with a connecting mechanism 414, at its top end 412A, so that the
connecting mechanism 414 is configured to contact and connect to an inner
sleeve
472 of the setting tool 470. In one embodiment, the connecting mechanism 414
is a
thread and the inner sleeve 472 has a mating thread 474. However, in another
embodiment, the connecting mechanism is a breakable pin. Other implementations
of the connecting mechanism may be used by those skilled in the art.
Irrespective of
the implementation of the connecting mechanism, it ensures that the plug 410
is
fixedly attached to the setting tool while the plug is lowered to the desired
location
inside the casing.
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[0033] The
connecting mechanism 414 is attached to the mandrel 412 through
a shear member 416. The shear member 416 is attached to a flared-up portion
417
of the mandrel 412. Figure 4 shows the flared-up portion 417 of the mandrel
having a
larger internal diameter D1 than a diameter D2 of the remaining portion of the
mandrel. The flared-up portion 417 is configured in this way to press against
an
upper wedge 422, and to push the upper wedge 422 toward the inner wall of the
casing 102, as discussed later. The shear member 416 may be made from the same
material as the mandrel 412 and the connecting mechanism 414. However, in one
application, these elements may be made of different materials and as
separated
parts. In this embodiment, these three elements are made integrally as part of
the
mandrel. When the time comes to separate the setting tool 470 from the plug
410,
the inner sleeve 472 is pulled apart from the plug 410 until the shear member
416
breaks and releases the setting tool. Note that the only part that keeps the
plug 410
attached to the setting tool 470 is the connecting mechanism 414. Once the
shear
member 416 breaks, the plug is freed from the setting tool. For this reason,
the shear
member 416 is made to break when a desired force is applied to it. While the
shear
member 416 is shown in Figure 4 as being implemented as a thin part of the
mandrel
412, those skilled in the art would understand that the shear member may be
implemented in different configurations, e.g., made of a material that is
weaker than
the material of the mandrel and the connecting member 414. The shear member
416
is shaped and/or made of a material so that is breaks before any other part of
the
mandrel.
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[0034] The bottom end 412B of the mandrel 412 is configured to engage with
a guide member 418, for example, through threads 420. Other mechanisms may be
used for attaching the guide member 418 to the mandrel 412. The guide member
418 may have an external diameter D that is slightly (e.g., about 10 to 30 %)
smaller
than an interior diameter of the casing 102, so that the guide member guides
the
plug inside the casing while being lowered to its desired location.
[0035] Between the guide member 418 and the connecting mechanism 414,
the following elements are distributed along the mandrel 412. Starting from
the
connecting mechanism 414, the upper wedge 422 (or tapered cone or ramp or
wedge-shaped body) is distributed around the mandrel and is configured to push
radially out on a sealing ring element 424. The ramp part 422A of the upper
wedge
422 contacts directly the underside of the sealing ring element 424 and pushes
the
sealing ring element toward the casing 102 when the upper wedge 422 is pushed
by
the external sleeve 480 of the setting tool 470. The upper wedge 422 may
include
one or more seals 423, that are placed between the upper wedge body and the
mandrel 412, to prevent a well fluid to move past the upper wedge. The sealing
ring
element 424 also can include one or more seals 425A and 425B, located between
the sealing element and the casing and/or the upper wedge 422 to further
prevent
the escape of the well fluid past the plug 410. Note that all these elements
of the
plug 410 are shown in Figure 4 as being separated from each other by a
considerable distance when in fact, this distance is infinitesimal or non-
existent, i.e.,
these elements are tightly packed together. The large distance between these
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elements is used in this figure to more clearly illustrate each element and
the
relationships between these elements.
[0036] The plug 410 also includes a slip ring 426 disposed around the
mandrel 412. In one embodiment, the plug includes only one slip ring. The slip
ring
426 includes one or more buttons 428, which are made from a hard material, and
are
configured to directly engage with the casing 102 when the frac plug is set.
The
direct contact between the buttons 428 and the casing 102 ensures that the
plug
does not move along a longitudinal axis X of the well when the plug is exposed
to an
upstream pressure.
[0037] A bore 413 of the mandrel 412 is configured to have one or two
seats.
A seat is defined herein as being a portion of the mandrel, in the bore, that
is shaped
to receive and mate a ball 440. For example, the mandrel 412 may be shaped to
have a large seat 430 or a smaller seat 432. In one embodiment, the mandrel
412
may be shaped to have both seats. The large seat 430 is a side seat, i.e., it
is
formed at the side of the mandrel 412. However, the smaller seat 432 is an
internal
seat, i.e., it is formed in a region of the bore that is not at the side of
the frac. An
advantage of having an internal seat is that when the ball 440 is seated
against such
deep seat 432, as shown in Figure 5, the ball 440 exerts a force 510 (only one
force
is shown although the ball exerts the same force all around the mandrel 412)
on the
mandrel 412, which structurally supports the entire plug 410 from being
compressed
along the radial direction by the pressure exerted by the pumped fluid in the
well. In
other words, because the ball 440 is seated deep into the plug 410, as shown
in
Figure 5, the deep-set ball imparts additional structural integrity to the
plug in that it
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resists an inward radial movement of the slips and wedge, which would
otherwise
loosen the plug's grip on the casing. It is noted that if one or more elements
of the
plug move radially inward toward the central point of the bore 413, a seal
between
the sealing ring element 424 and the casing 102 may be weakened, which may
result in the collapse of the plug and the well fluid rushing past the plug.
[0038] The inventors have found that by having the plug 410 configured to
allow the ball 440 to enter deep inside the mandrel 412, i.e., at least past
the ends of
the mandrel, for example, close to a middle point of the mandrel, as shown in
Figure
5, it achieves this structural advantage. In one embodiment, the ball 440 is
considered to enter deep inside the mandrel 412 when the ball is at the same
position, along the longitudinal axis X, as the sealing ring element 424, or
as the slip
ring 426. Note that Figure 5 shows the frac plug 410 being set, i.e., the
shear
element 416 has been broken, so that the setting tool 470 has been freed and
removed (although spaces between the elements of the plug and also spaces
between the plug and the casing are still shown).
[0039] Returning to Figure 4, the setting tool 470 is configured to carry
the ball
440 while also being attached to the plug 410, i.e., to be able to perform the
ball in
place mode. For this mode, the ball 440 is placed inside the inner sleeve 472
of the
setting tool. To prevent the ball 440 from moving unintentionally while the
setting tool
is moved in the well to the desired position where the plug needs to be set
up, the
outer mandrel 480 includes a retention element 482, for example a pin, that
prevents
the ball from moving upstream. To prevent the ball to move in a downstream
direction, the inner sleeve 472 includes a retaining mechanism 476, for
example, a
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spring. The ball 440 is placed between the retention element 482 and the
retaining
mechanism 476 while the setting tool is lowered into the casing. As the
setting tool
and the ball move downstream in the casing, the fluid well needs a passage to
bypass this tandem. For this reason, one or more slots 484 may be made into
the
external sleeve 480. In this way, the fluid well 490 is able to pass through
the setting
tool 470 and through the bore 413 of the plug 410, as indicated by path 492.
[0040] The retention element 482, which is fixedly attached to the external
sleeve 480, is allowed to move relative to the inner mandrel 472, to push the
ball 440
past the retaining mechanism 476, due to a slot 473 formed into the wall of
the inner
mandrel 472. In this way, when the plug 410 needs to be set, and the setting
tool
470 is activated so that the internal sleeve 472 moves upstream while the
outer
sleeve 480 remains stationary (or the other way around), the retention element
482
effectively moves downstream relative to the inner sleeve 472, and pushes the
ball
440 over the retaining mechanism 476. Once the ball 440 has moved past the
retention mechanism 476, due to the well pressure exerted by the pumps at the
well
head, the ball 440 moves until is seated in the large seat 430, or the deep
seat 432,
depending on its size. Note that if the ball 440 is sized to seat the large
seat 430, it
cannot move past this seat to reach the deep seat 432.
[0041] Figure 6 illustrates the situation in which the setting tool 470 has
been
activated, the external sleeve 480 is preventing the upper wedge 422 from
moving
along the axial direction X, the inner sleeve 472 has moved in an upward
direction
relative to the external sleeve 480, opposite to the longitudinal direction X,
thus
pulling the mandrel 412 along the same direction. As a consequence of the
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movement of the mandrel 412 while the upper wedge 422 is stationary, the
guiding
element 418 has moved toward the upper wedge 422, pressing the slip ring 426
and
the sealing ring element 424 up the ramp of the wedge element 422, so that the
sealing ring element 424 is pressing against the casing 102, effectively
sealing the
casing's bore.
[0042] In addition, the retaining mechanism 476 has also moved toward the
retention element 482, thus forcing the ball 440 to move past the retaining
mechanism 476, as shown in the figure. The ball 440 is now freed and when the
fluid
490 is pressurized from the surface and moves along direction 492, it moves
the ball
440 into the large seat 430 or the deep seat 432, depending on the size of the
ball.
Note that Figure 6 shows the setting tool 470 being activated but not yet
freed from
the mandrel 412.
[0043] Figure 7 shows the ball 440 being seated in the deep seat 432 and
the
setting tool 470 freed from the plug 410 as the inner mandrel has exerted the
force
on the plug 410 and the shear member 416 broke. Also note that the mandrel 412
has been moved together with the guiding element 418 relative to the other
members of the plug 410, so that the upper wedge 422 is now removed from the
large seat 430. The upper wedges 422 was either in direct contact with the
large
seat 430 in Figure 4, or very close to it.
[0044] Figure 7 shows that one or more slots 434 may be formed in the
bottom end 412B of the mandrel 412 so that when a ball 440' from a previous
frac
plug is contacting the bottom end 412B, the fluid inside the well still can
pass from
the toe of the well toward the head (e.g., during a backflow operation) of the
well,
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past this ball and the frac plug. Figure 7 further shows how the ball 440
seated in the
deep seat 432 provides structural support to the upper wedge 422 and the slip
ring
426, to prevent these elements from moving radially inward, toward the bore
413 of
the mandrel 412. In one embodiment, the deep seat 432 is formed in the mandrel
so
that the deep seat is directly opposite to the slip ring 426 relative to the
mandrel. In
another embodiment, the deep seat is manufactured to be located directly
across the
upper wedge 422. In still another embodiment, the deep seat is manufactured to
be
located across the sealing element 424. One skilled in the art would
understand from
this disclosure that the deep seat 432 can be formed anywhere internal to the
mandrel to be across any of the elements to support them. When a large
pressure is
applied to the well fluid, the mandrel 412 can slide relative to the sealing
element
424 and the upper wedge 422, as illustrated in Figure 5, due to the force
imparted by
the ball 440. Due to the flared-up part 417 of the mandrel, it can add
additional
support to the upper wedge 422.
[0045] In one embodiment, to enhance the adherence of the slip ring 426 to
the casing 102, the slip ring 426 is configured to have a ring 810 and
alternating slots
812, which partially extend radially around the ring 810 to form a zig-zag
pattern, as
illustrated in Figure 8. Note that the buttons 428 may be configured to have a
surface
inclination relative to the casing, such that a better grip between the
buttons and the
casing is obtained. This zig-zag patterned slip(s) then maximizes the surface
area
gripping the casing wall, thereby increasing the axial hold force. In other
embodiments, the slips may be made of several fingers formed from slots all
extending from one end of the ring. An advantage of the alternating slots 812,
or zig-
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zag patterned slips, is that upon setting, the slip ring 426 will have a
tendency to
remain intact as compared to the individual fingers. If a finger or section of
the slip
ring separates, it may dislodge from the others, thereby weakening the plug's
adherence to the casing. The buttons 428 of the slip ring 426 "bite" into the
casing
102 and increase the axial holding force of the plug. In this context, the
"axial hold
force" refers to the resistance to axial movement along the longitudinal axis
X of the
wellbore casing 102. Typically, the force is expressed in terms of the
wellbore
pressure (in pounds per square inch (psi)) times the sealed inner area of the
casing
required to overcome the plugs adherence to the casing inner wall and move the
plug axially.
[0046] A sectional view of the slip ring 426 is shown in Figure 9, together
with
two cross-sections AA and BB from Figure 8. Figure 9 shows the ring 810 and
the
fingers 814 that are connected to the ring 810. The slots 812 between the
fingers
814 are shown being positioned in a first configuration, toward the bottom end
412B,
then those at the top end 412A. Figure 9 shows that the slots at the two ends
are
offset with a given angular displacement, for example, 90 degrees.
[0047] In one embodiment, the plug 410 components may be manufactured
as machined or molded composites, or as dissolvable materials or a combination
of
the two. In one application, all the parts of the plug 410 are made of
dissolvable
materials. This means that after the frac operation for a given stage is
completed,
instead of using a drill to mill the plug, the well fluid or a special fluid
is pumped into
the well, which after interacting for a given amount of time with the plug,
dissolves
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the components of the plug. This is very advantageous because lowering in the
well
the drilling equipment is time consuming and thus, expensive.
[0048] When the traditional plug of Figure 2 is compared to the novel plug
410
of Figure 4, one can observe that the plug 410 has less components. For
example,
the plug 410 does not have the upper slip ring 204 and the upper wedge 206. In
one
embodiment, the plug 410 also does not have the bottom push ring 216. Because
of
these features, a volume of the plug 410 may be reduced to less than 80 in3,
from a
volume of 250 in3, which customary for an existing frac plug. Further, the
reduced
volume of the plug 410 ensures, in one application, that the well fluid that
passes
through it is increased, which prevents large pressure differentials across
the plug.
[0049] In another embodiment, as illustrated in Figure 10, a frac plug has
even
less components than the plug 410 discussed above. A frac plug relies on the
structural integrity of its components to withstand the stresses applied
during its use
in the well. The available plugs do not use the ball or a restrictive plugging
element
to aid in the support of the plug during the frac operation. As such, the
available
plugs use force supportive members (ramps or wedges) that may or may not be
backed up by inner mandrels to preserve the overall structural integrity.
However,
such mandrels have an overall inner diameter just less than about 2.0". This
design
often results in plugs longer than 18" with a total volume exceeding 250 in3
(in a
typical 5.5" casing application).
[0050] This configuration restricts the amount of well fluid that can be
transmitted through the plug when advancing through the well. Thus, this
existing
configuration may create large pressure differentials across the plug.
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[0051] Furthermore, the available plugs use opposing taper angles or ramps
of wedges 206 and 210, as illustrated in Figure 2, to draw either a sealing
area 208
or a gripping area 212 of the plug into its final set position, against the
wall of the
casing. The opposing ramps design also requires excess plug length as the full
travel of the ramps needs to be included in both the swaging element and the
element to be expanded (the seal).
[0052] The novel plug 1010 shown in Figure 10 overcomes these problems by
placing the sealing element 1024 at the top end of the plug. This means that
there is
no wedge or ring or other element upstream of the sealing element 1024 for
pushing
onto the sealing element, as is the case for the existing frac plugs. In
addition, this
plug is configured, similar to the plug 410, to be a top set plug. The sealing
element
1024 is configured to have two functions: the top end part 1024A acts as the
sealing
member while the bottom end part 1024B is shaped and acts as a ramp for
driving
the slip ring 1026 toward the casing 102. In other words, the bottom end part
1024B
of the sealing element 1024 acts as the upper wedge 422. The slip ring 1026
may
have buttons 1028, similar to the slip ring element 426.
[0053] An inner mandrel 1012 allows for load transfer between the setting
tool
1070, which is attached at the top end 1012A of the mandrel, and the guiding
element 1018, which is located at the bottom end 1012B of the mandrel. In this
embodiment, the guiding element 1018 is attached to the mandrel 1012 by a
shoulder 1019, which is configured to fit in a corresponding groove 1015
formed in
the outer wall of the mandrel 1012. In another embodiment, the guiding element
1018 may be attached with threads, as the guiding element 418 in Figure 4.
Those
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skilled in the art, having the benefit of this disclosure, might chose various
other
implementations for this element. The setting tool 1070 is configured, similar
to that
of Figure 4, to connect to the upper part of the mandrel 1012, for example,
through a
connecting mechanism 1014 that connects to the inner sleeve 1072. In this
figure,
the connecting mechanism 1014 is implemented as threads. However, the
connecting mechanism may be implemented as a breakable pin, etc. A shear
member 1016 is present on the mandrel 1012 to allow the top part to break away
after the setting tool has set up the plug. Figure 10 further shows the outer
sleeve
1080 of the setting tool being in direct contact with the sealing member 1024.
[0054] The frac plug 1010 further includes a single piece slip 1026, which
includes a base ring 1027 with slips 1029 machined such that they are attached
solely at the base of each geometric slip section. Included on the outward
surface of
the slip 1026 is a hardened insert or button 1028. This hardened material may
be
comprised of ceramic, carbide, cast iron, etc. A transitionary seal 1023 may
be
located between the mandrel 1012 and the sealing element 1024. The
transitionary
seal allows the plug to actuate through its full range of motion while
maintaining the
pressure differential integrity. This feature is not required in that when the
tool is in its
fully set state and has been stroked down due to wellbore isolation pressures,
a
metal to metal seal may be achieved between the mandrel 1012 and the main
swage
body.
[0055] One or more grooves 1025 may be formed in the sealing element
1024, facing the casing 102, and they are aiding in obtaining a positive metal
to
metal seal between the frac plug outer diameter and the inner diameter of the
cased
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wellbore. These grooves can be either ran as shown or with the addition of an
elastomeric sealing element nested inside each groove.
[0056] The frac plug 1010 and the setting tool 1070, configured as
discussed
in this embodiment, can carry a ball 1040 while being deployed from the
surface,
thus being capable of achieving a ball in place mode. After the setting tool
1070 is
activated and removed from the plug, the ball 1040 enters inside the plug
1010, and
seats on the deep seat 1032, as shown in Figure 11, thus sealing or blocking a
bore
1013 of the mandrel 1012. The deep seat 1032 is located under the sealing
element
1024, so that the force F that is applied by the well fluid 1090 onto the ball
1040 is
partially spread radially outward on the inner wall of the sealing element
1024, to
enhance the integrity of the seal and to further press the sealing element
against the
inner wall of the casing 102. In one embodiment, the deep seat is configured
to be
across the slip ring 1026. While Figure 11 shows that the ball 1040
interacting only
with the deep seat 1032, formed in the mandrel 1012, in one embodiment it is
possible to configure the plug 1010 so that the ball 1040 also directly
contacts the
sealing element 1024.
[0057] A method for plugging a casing in a well for a frac operation is now
discussed with regard to Figure 12. The method includes a step 1200 of
attaching a
setting tool to a frac plug, wherein a ball is placed inside the setting tool,
a step 1202
of lowering the setting tool, the ball and the frac plug to a desired depth
into the
casing of the well, a step 1204 of activating the setting tool to set up the
frac plug,
wherein a connection between the setting tool and the frac plug is located at
a top
side of the frac plug, a step 1206 of removing the setting tool after the top
connection
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between the setting tool and the frac plug is broken, and a step 1208 of
pressuring
the ball to seat into a deep seat inside a mandrel of the frac plug, away from
a top
end and a bottom end of the mandrel, to provide structural support to the frac
plug.
In one application, the frac plug has a single wedge, for example, the upper
wedge
and not a lower wedge. In another application, the frac plug 410 has only the
elements shown in Figure 4 and the frac plug 1010 has only the elements shown
in
Figure 10, i.e., much less elements than the existing plug 200.
[0058] The disclosed embodiments provide a top set plug for use in a well
for
isolating one stage from another. The top set plug is configured to have less
parts
than an available plug. It should be understood that this description is not
intended to
limit the invention. On the contrary, the embodiments are intended to cover
alternatives, modifications and equivalents, which are included in the spirit
and
scope of the invention as defined by the appended claims. Further, in the
detailed
description of the embodiments, numerous specific details are set forth in
order to
provide a comprehensive understanding of the claimed invention. However, one
skilled in the art would understand that various embodiments may be practiced
without such specific details.
[0059] Although the features and elements of the present embodiments are
described in the embodiments in particular combinations, each feature or
element can
be used alone without the other features and elements of the embodiments or in
various combinations with or without other features and elements disclosed
herein.
[0060] This written description uses examples of the subject matter
disclosed to
enable any person skilled in the art to practice the same, including making
and using
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any devices or systems and performing any incorporated methods. The patentable
scope of the subject matter is defined by the claims, and may include other
examples
that occur to those skilled in the art. Such other examples are intended to be
within the
scope of the claims.
