Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
Improved Frac Plug
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of United States Provisional Patent
Application Serial Number 62/537,448 entitled "Frac Plug" filed on July 26,
2017; and United
States Provisional Patent Serial Number 62/670,234 entitled "Frac Plug" filed
on May 11, 2018,
both of which are incorporated by reference herein.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
[0001] Not applicable.
BACKGROUND
Field
[0002] Embodiments according to the present disclosure relate to flow control
devices
for use in oil and gas wells, and particularly to flow control devices used
for isolating the portion
of the well above the device from portions below the device. Such flow control
devices may
be used to isolate one region of the wellbore, and/or tubing installed in the
wellbore, from other
portions thereof and are commonly used in the completion of multiple
formations accessed by
a single well, multiple stage completions of a single formation, or other
activities in which it is
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desirable to prevent fluid communication across a desired location within the
well.
Description of Related Art
[0003] Bridge plugs and frac plugs, including plugs made from composite or
degradable
materials are known in the art. Such plugs are generally set in casing to
isolate a previously
treated section of a hydrocarbon producing formation from the next section to
be treated. By
setting such plugs upwell of each treated section, the wellbore can be
treated, such as by
fracturing or other treatment, in numerous sections. Once all desired sections
of the well are
treated, the plugs are typically drilled up and the resulting debris flows to
the surface with
wellbore fluids. The time required to drill or mill out such plugs adds cost
to the well's
completion and reducing the drill out/ mill out time is desirable to minimize
such costs.
[0004] Despite the desire for faster drill out, frac plugs must be amenable to
installation
in the well, at a desired location, and be able to isolate fluid pressure
above the frac plug from
the fluid environment below the plug. It is desirable that such frac plugs
have sufficient
integrity to maintain at least 5,000 psi differential across the plug when
fluid is pumped from
the surface, more preferably be able to maintain at least 7,500 psi
differential across the plug
and even more preferably be able to maintain at least 10,000 psi differential
across the plug.
[0005] Reducing drill out time typically involves selection of materials that
are more
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machinable (e.g. more easily drilled or milled) and by reducing the total
volume of material that
must be removed. However, materials that are more machinable can have less
material strength,
either generally, in one or more key stress planes, and/or in one or more
directions. Thus,
thicker and/or longer components may be needed when more machinable material
(such as
commonly used composites) are employed so that the plug may withstand the same
forces as a
plug or baffle of a less machinable material (e.g. ductile iron or steel).
Therefore, it is desirable
to optimize frac plug design such that the plugs may be manufactured from
composite, or other
high machinability, materials while minimizing the volume of material in the
plug.
[0006] One component of frac plugs that receives relatively high loads are the
slip
bodies, though forming slip bodies of composite or other easily machinable
materials remains
desirable. Some composite slip bodies may need a mandrel or other structure
around and over
which they are assembled and which help to maintain their generally tubular
configuration as
the slip bodies move to their expanded, set state. This requirement for a
mandrel inside the slip
bodies increases the total material volume, and total length, of the frac plug
in its set position,
both of which increase the drill out or mill out time of the tool. Such
mandrels also increase
the amount of material released to move within the well following mill out of
the lowest slips.
Certain embodiments of the present disclosure reduce and/or eliminate the need
for a mandrel
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to extend through the slips in the unset state, helping to minimize the volume
of material in and
the length of the frac plug, thereby minimizing drill out/mill out time.
[0007] Additionally, current frac plugs designed to be milled or drilled out
typically
contain a clutch system of some type to facilitate complete drill out/mill out
of the plug. The
clutch is necessary because a portion of each frac plug is typically released
to freely spin and
move down the well once the lowest slip bodies are milled or drilled away. A
clutch element
at the bottom of the lower end mates with a corresponding clutch at the upper
end of the next
downwell plug. Engagement of these two clutch elements allows the mill or bit
to work through
the remaining portion of the upper plug before beginning on the next one. In
some
circumstances, an upper clutch element may not be available because the next
lower plug is
degradable or there is no next lower plug. An improved plug requiring little
or no mill out/drill
out of components below the lowest slips or slip bodies is therefore
desirable.
Brief Description
[0008] Embodiments according to the present disclosure strike a balance of the
various
requirements and forces needed for operation of the frac plug. Embodiments
herein provide for
a short tool with relatively thin walls so that the volume of material to
drill out is reduced.
Further, embodiments herein avoid or limit tensile forces and in favor of
compressive forces
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and friction.
[0009] Embodiment plugs may include a floating key system to positionally
maintain
the slip bodies in a desired configuration while the tool is the run-in state
without requiring a
mandrel around and over which the slip bodies may slide. Such floating key
system may engage
the bottom section of an embodiment plug to prevent axial skewing while
permitting the slip to
expand radially outward when moving to the set position.
[0010] Embodiment plugs may have an angular surface for expansion of the
element
ring and the slips. Such angular surface may be shallow, such as between about
four degrees
and about fifteen degrees. Such shallow angle reduces the tendency of the
angular surface to
be pushed out of the slip bodies and reduces the shear forces applied to the
material at the
angular surface.
[0011] Further embodiments of the present disclosure may contain an element
system
in which movement of the slip bodies applies longitudinal force into the
element, increasing the
pack off force of the rubber, elastomer, or other element. Elements may have a
profile that fits
into a recess, in the outer surface of the plug's mandrel, permitting the
element to include a
greater volume of rubber and providing resistance to movement of the element
while the plug
is run into the well. Such element systems may provide a fluid seal against
both the plug and
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the casing in a single piece of rubber, elastomer, or other appropriate
material and permit a
uniform sealing force between the plug and casing. Use of an element whose
body is made of
an extrudable material such as rubber may also facilitate a stronger seal
between the element
and each of the casing and plug mandrel respectively as well as facilitate the
use of a single size
plug in casing sizes having varying inner diameters.
[0012] Still further embodiments of the present disclosure may be installed in
casing or
other host tubing such that the annulus between the upper end of the plug and
the host tubing
act as a thimble for an element ring of the plug. The characteristics of the
element ring in such
embodiments may be configured to cooperate with the annulus size in order to
limit extrusion
or other movement of the element between the plug and host tubing.
[0013] Further embodiments of the present disclosure may include plugs whose
components below the slip bodies are comprised of degradable materials¨that is
materials that
retain structural integrity as needed for a given component's function, but
dissolve, disintegrate
or otherwise are substantially reduced in size over a relatively short time
without intervention
such as fishing, mill out or drill out. The reduced length of the mandrel in
such embodiments,
e.g. the mandrel does not run through the slip bodies in the unset position,
may facilitate the
creation of such a hybrid tool. Hybrid plug embodiments may permit drill out
of the plug
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through the slip bodies with sufficiently small debris and without needing to
drill out
components below the slip bodies. Such embodiments obviate the need for an
adjacent lower
plug with a corresponding clutch.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] Fig. 1 is a sectional elevation of an embodiment plug according to the
disclosure
herein.
[0015] Fig. 2 is a sectional elevation of another embodiment plug and
connected WLAK
according to the disclosure herein.
[0016] Fig. 3A is an external elevation of one embodiment retainer ring which
may be
used in certain embodiment plugs according to the disclosure herein.
[0017] Fig. 3B is a sectional elevation of one embodiment retainer ring which
may be
used in certain embodiment plugs according to the disclosure herein.
[0018] Fig. 4A is a top view of one embodiment slip body which may be used in
certain
embodiment plugs to the disclosure herein.
[0019] Fig. 4B is an orthogonal view of one embodiment slip body which be used
with
certain embodiment plugs according to the disclosure herein.
[0020] Fig. 5 is cross sectional view through the bottom portion of one
embodiment
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plug in the unset or run-in state.
[0021] Fig. 6 is a cross sectional view through the bottom portion of one
embodiment
plug in the set state.
[0022] Fig. 7 is a sectional view of another embodiment plug according to the
present
disclosure.
[0023] Fig. 8 is an orthogonal view of one embodiment mandrel according to the
present
disclosure.
[0024] Fig. 9 is a sectional view of an embodiment plug connected to one
embodiment
wireline adaptor kit.
[0025] Fig. 10 is a sectional view of an embodiment plug set inside a tubular.
[0026] Fig. 11 is an embodiment retainer ring according to the present
disclosure.
[0027] Fig. 12 is a plurality of slip bodies arranged in an embodiment
retainer ring.
[0028] Fig. 13 is a series of plugs arranged along a host tubular.
[0029] Fig. 14 is a sectional view of an embodiment plug according to the
present
disclosure.
[0030] Fig. 15 is an orthogonal view of one embodiment retainer ring according
to the
present disclosure.
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[0031] Fig. 16 is an orthogonal view of one embodiment shear ring according to
the
present disclosure.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0032] When used with reference to the figures, unless otherwise specified,
the terms
c`upwell," "above," "top," "upper," "downwell," "below," "bottom," "lower,"
and like terms
are used relative to the direction of normal production and/or flow of fluids
and or gas through
the tool and wellbore. Thus, normal production results in migration through
the wellbore and
production string from the downwell to upwell direction without regard to
whether the tubing
string is disposed in a vertical wellbore, a horizontal wellbore, or some
combination of both.
Similarly, during the fracing process, fracing fluids and/or gasses move from
the surface in the
downwell direction to the portion of the tubing string within the formation.
[0033] Figure 1 shows an embodiment frac plug 100 according to the present
disclosure.
The embodiment of Figure 1 comprises a mandrel 110, backup ring 120, element
130,
expansion ring 140, slip bodies 150, bottom section 160 and retainer ring 170
(see Figures 3A
and 3B). In Figure 1, one finger 172 of retainer ring 170 is visible. Back up
ring 120 and
expansion ring 140 may be made of suitable materials known in the art such as
commercially
available nylons while the element may be made of rubber or other suitable
materials. The
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other components may be preferably made of millable materials such as wound
composites or
other non-metallic materials, though frac plugs of any suitable material are
within the scope of
the present disclosure. Mandrel 110 comprises a conical or angular outer
surface 111 and
crenels 112 which may serve as the upper clutch for assisting in drill
out/mill out of the lower
sections of an upwell plug. Lower section 160 may also contain crenels as the
corresponding
clutch element for adjacent plugs. Mandrel 110 also has an inner surface which
may have a
seat 118¨such as a shoulder, a generally conical surface, or other feature¨for
receiving a
flapper, ball, dart or other element to seal the interior of the mandrel 110
against flow
therethrough. The embodiment of Figure 1 is illustrated with a flapper 180 and
associated seat
118 but embodiments of the present disclosure are not limited to flappers and
flapper seats for
sealing the passage through the mandrel 110.
[0034] Outer surface 111 of mandrel 110 may have a recessed section 115 for
receiving
a portion of the element 130, the backup ring 120, or both. Such recessed
section allows for the
volume of the element 130 and/or backup ring 120 to be increased without
lengthening the
element 130 and/or back up ring 120 and without increasing their outer
diameter. Further,
engagement of element 130 and/or back up ring 120 in the recessed section may
assist to prevent
the element and back up ring from swabbing over the mandrel 110 when the plug
100 is being
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pumped or otherwise run into a well.
[0035] A plurality of slip bodies 150 are arranged with slip body ends
adjacent to the
expansion ring 140 and surrounding a portion of the mandrel 110. In the
embodiment of Figure
1, an assembly ring 152 connects mandrel 110 with the upper end of slip bodies
150. Other
components for connecting slip bodies 150 to the lower end of mandrel 110,
including but not
limited to brass or nylon screws, dowels or other connectors, may be used for
such engagement.
Buttons 156 are installed in the slip bodies 150 for penetrating into the
casing or tubing into
which the frac plug is being installed. Such buttons may be of carbide,
aluminum oxide, or
other materials know in the art.
[0036] It will be appreciated that other forms of slip bodies may be used with
embodiment frac plugs. Such slip bodies may include sections or complete slips
that break
apart as the frac plug transitions from the run in state to the set state.
Gripping elements other
than buttons, such as teeth, wickers, abrasives and others may be used and are
within the scope
of the present disclosure.
[0037] The slip bodies 150 may further comprise a ring 154 which may be made
of
elastomeric or other suitable materials. Such ring may assist in retaining the
plurality of slip
bodies 150 in the retracted position until the desired location in the well is
reached.
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[0038] Bottom section 160 and retainer ring 170 are connected via shear pins
162.
Retainer ring 170 may also have a circular base 174 which fits into a recess
of bottom section
160. Slip bodies 150 may have an extension or key 158 extending into and
engaging the bottom
section 160 and/or the retainer ring 170.
[0039] In operation, embodiments of the present disclosure may be run into a
well on
wireline using a setting tool such as a conventional Baker 10, Baker 20, or Go-
Shorty hydraulic
setting tool or other setting tool. Such setting tools are known in the art
and may include a
suitable or custom wireline adaptor kit (WLAK) for the specific embodiment
frac plug, may be
connected to the device via setting shear pins 162 connecting a setting
mandrel to the bottom
of the baffle. Setting tools for plugs conveyed downwell and set using tubing
instead of wireline
are also know in the art. Assemblies for wireline conveyed plug installation
and tubing
conveyed plug installation may be referred to collectively as setting
assemblies.
[0040] Figure 2 illustrates an embodiment frac plug assembled on a
corresponding
WLAK. Setting mandrel 260 is connected to the setting tool (not shown) via one
or more
crossovers 210, and to frac plug 100 at lower section 160 and retainer ring
170 through setting
shear pins 162. Shear retainer 270 may be connected to end of shear mandrel
260 to secure
shear mandrel to the plurality of shear pins 162 and be configured to capture
the ends of shear
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pins following the setting operation. Setting piston 240 may be connected to
the setting tool
via crossover 230 and to the frac plug 100 via the upper end of mandrel 110.
Mandrel 110 may
have a shoulder machined into its upper end for receiving a lip of setting
piston 240. Further,
setting piston 240 may have an inner surface 250 configured to receive crenels
(112 inf Fig. 1)
or the upper end of crenels. During such run in, the upper section of mandrel
110 and the
bottom section 160 may serve as gauge rings, each having a larger outer
diameter than that of
the slip bodies 150, element 130, back up ring 120 and expansion ring 140.
[0041] When the setting tool is actuated, force is applied to the setting
piston 240
forcing the setting piston 240 and shear pins 162 toward one another. The
force of the setting
piston 240 is transferred to the mandrel 110 such that the crenels 112 are
forced towards the
bottom section 160 and retainer ring 170. Movement of the bottom section 160
and retainer ring
170 towards the mandrel pushes the slip bodies 150, and thereby the expansion
ring 140,
element 130 and retainer ring 120 along the angular outer surface 111 of
mandrel 110, causing
each to radially expand.
[0042] As the slip bodies 150 and element 130 expand, they come into contact
with the
casing or other tubing in which the frac plug is being installed. As mandrel
110 continues to
move into element 130 and slip bodies 150, thereby forcing element 130 and
slip bodies 150
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into such casing or tubing, buttons 156 of slip bodies 150 penetrate the
casing to mechanically
anchor the frac plug. Expansion of the element 130 causes it to seal against
both the outer
surface of mandrel 110, both on and above the angular outer surface 111, and
the tubing or
casing, substantially preventing fluid communication around the frac plug 100.
[0043] It will be appreciated that element systems of certain embodiments
herein
provide greater pack off force than other element systems using separate
pieces to seal against
the mandrel and against the casing respectively. As the element 130 back up
ring 120, and
expansion ring 140 move over the mandrel, the frictional and compressive
mechanical forces
increase and resist movement of the back up ring 120 and element 130 over the
mandrel's
conical outer surface 111.. More energy is required to continue movement of
the back up ring
120 and element 130 over the mandrel as the outer diameter 111 of the mandrel
110 increases.
Elements made of rubber or other sufficiently elastic materials will absorb
that energy and may
begin to extrude, including extrusion radially outward, increasing the outer
diameter of the
element. Such extrusion is in addition to an increase, if any, in the
element's outer diameter
from movement along the mandrel's angular outer surface 111. When the element
extrudes
sufficiently to contact the host casing, friction between the element and host
casing further
resists movement of the element over the mandrel surface. The back up ring 120
and the
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decreasing annular space between the mandrel outer surface 111 and the host
casing limit the
ability of the element 130 to extrude longitudinally.
Thus, the element 130 becomes
constrained in all directions by the back up ring 120, the mandrel outer
surface 111, the
expansion ring 140 and the host casing. Because of these constraints, the
element may store
setting energy applied from the slip segment via the expansion ring,
increasing the pack off of
element 130 against both the mandrel 110 and the host casing. This increase in
energy stored
by an elastomeric element allows the element to more readily resist the
pressure differential the
plug experiences during treatment operations.
[0044] When the strength of shear pins 162 is exceeded by the force required
to further
move the mandrel 110 into back up ring 120, element 130, expansion ring 140
and slip bodies
150, the shear pins 162 can break and release the WLAK from the frac plug 100,
leaving frac
plug 100 installed in the tubing or casing.
[0045] For the embodiment of Figure 1, removal of the WLAK, and specifically
of
setting mandrel 260, permits flapper 180 to close against its seat 118 via a
spring connected to
the hinge of the flapper 180. Fluid pressure, such as may be applied from
pumps at the surface,
against flapper 180 may complete or reinforce the seal of flapper 180 against
seat 118 and
operations for treating sections of the well above the frac plug may begin
immediately.
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[0046] For embodiment frac plugs configured to receive balls, darts or other
elements
introduced into the well from surface, a seat configured to receive such
element may be included
in the plug. The mandrel of such plug may have an entry section at an angle of
about 5 to 10
degrees, and preferably about 6 degrees, leading to a seat 118 having an angle
between 25 and
40 degrees, preferably about 30 degrees. In some embodiments, such seat
section 118 may be
longitudinally below the element 130 when the frac plug 100 is in the set
state. In some
embodiments, the diameter of a ball used to seal the interior of the frac plug
100 may be between
.035 and .250 inches larger than the largest diameter of the seat section,
preferably between .08
and .20 inches larger. In one embodiment, made entirely of wound composite
materials with
aluminum oxide buttons, a 3.25 inch diameter ball seated in a frac plug having
a largest seat
section diameter of 3.09 inches held 10,000 psi in a pressure test without any
movement of the
plug within the test casing.
[0047] Tools according to the present disclosure may incorporate a floating
key
assembly comprising keys and non-restrictive keyways to permit the tool to
operate without the
mandrel 110 extending through the slip bodies 150 in the run-in position. Such
floating key
assembly may assist in maintaining the location and orientation of the slip
bodies during
assembly and run-in while permitting the slip bodies freedom of movement
during the setting
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process.
[0048] Figures 3A and 3B show external views of retainer ring 170. As
discussed with
respect to Figure 1, retainer ring 170 may be connected to bottom section 160
through shear
pins 162and engagement of circular base 174 of the retainer ring 170 with a
groove in bottom
section 160. Retainer ring 170 has a plurality of fingers 172 defining key
ways between each
finger pair. Key ways may include slots 178, which may be adjacent to the base
ring 174 of
retainer ring 170. The fingers 172 may be configured such that the gap between
fingers at the
interior diameter of the fingers is smaller than the gap at the outer
diameter.
[0049] Figures 4A and 4B show external views of certain embodiment slip bodies
150
according to the present disclosure. Slip body 150 has a generally rectangular
profile with an
inner surface and an outer surface. Holes 157 for buttons and one or more taps
159 for shear
pins may be machined into the outer surface of or through slip bodies 150,
respectively. The
outer surface may also have a channel 155 for receiving ring 154 (described
with respect to
Figure 1, above). Slip bodies 150 according to the present disclosure may also
have key section
158 extending from the generally rectangular profile.
Such key section 158 may be
manufactured as a single piece with the rectangular body or may be a separate
piece connected
to the rectangular body via threaded connections, adhesives, or other
fastening during assembly.
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[0050] Key section 158 may be complimentary to the key ways between fingers
172 of
retainer ring 170. For example, the enlarged end of key section 158 may be
wider than the gap
between the fingers but fit into slots 178. Further, the sides of key section
158 may be tapered
such that the inner surface of key section 158 is narrower than the outer
surface of key section
158, permitting an elongated or shaft portion of key section 158 to fit
between fingers 172 while
reducing the contact between key section 158 and fingers 172.
[0051] During assembly of the frac plug 100, key section 158 of each of the
plurality of
slip bodies 150 may placed into the key way between two fingers 172 of
retainer ring 170. The
engagement of the key sections 158 with the key ways of retainer ring 170 may
postion the
plurality of slip bodies 150 in a generally tubular arrangement. The retainer
ring 170 with
associated slip bodies 150 may then be placed inside the bottom section 160.
Bottom section
160 may then be connected to fingers 172 via shear pins 162.
[0052] Figure 5 shows a cross section of the assembled retainer ring 170,
bottom
section 160, and plurality of slip bodies 150 at a location just below the
shear pins. In this
arrangement, movement of slip bodies 150 is constrained circumferentially by
the placement of
of key sections 158 in keyways between fingers 172. The slip bodies 150 are
constrained
longitudinally by the insertion of the enlarged end of key section 158 into
slots 178 as well as
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engagement of rectangular section of the slip bodies 150 against the opposing
end of both
fingers 172 and, in some embodiments, bottom section 160. Ring 154 may be
placed into
groove (155 in Fig. 4A and 4B), generally prior to connecting the slip
bodies150 with the
mandrel 110.
[0053] The upper portion of the frac plug may be assembled by sliding the back
up ring
120, element 130 and expansion ring 140 onto the lower end of mandrel 110 and
seating the
element 130 and/or back up ring 120 into the recessed area 115 in the angular
outer surface 111.
If present, assembly ring 152 may be installed after the expansion ring 140.
The upper end of
slip bodies 150 may then be installed over the lower end of mandrel 110 and
the slip bodies
connected to the mandrel by assembly ring 152 or by other connecters. The WLAK
may then
be installed through the mandrel 110, slip bodies 150, and bottom section 160
and connected to
the shear pins 162 via the shear retainer 270.
[0054] Figure 6 shows the same cross section as Figure 5, but with respect to
a frac plug
in the set position. Key sections 158 have expanded outward between fingers
172, but the key
ways are configured such that the sides 159 of key sections 158 no longer
engage fingers 172.
It will be appreciated that some limited contact between key sections 158 and
fingers 172 may
occur, but the wider keyway between fingers 178 limits such contact and allows
the slip bodies
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150 to expand and set against the host casing without substantial interference
from the key
sections 158.
[0055] Figure 7 shows an embodiment frac plug 300 according to the present
disclosure.
The embodiment of Figure 7 comprises a mandrel 310, element 330, expansion
ring 340, slip
bodies 350, bottom section 360 and retainer ring 370 (see Figure 11) as
reflected by the location
of finger 372. Mandrel 310 comprises a conical outer surface 311, and crenels
312 which may
serve as the upper clutch for assisting in drill out/mill of the lower
sections of an upwell plug.
Lower section 360 may also contain crenels as the corresponding clutch element
for adjacent
plugs. Mandrel 310 also has an inner surface which may have a seat 318¨such as
a shoulder,
a generally conical surface, or other feature¨for receiving a flapper, ball,
dart or other element
to seal the interior of the mandrel 310 against flow therethrough. In some
embodiments, the
seat 318 may be on the inner diameter generally adjacent to the apex 317 on
the outer diameter.
[0056] As can be seen more clearly in Fig. 8, the conical outer surface 311 of
mandrel
310 may have a generally continuous angular profile with a recessed section
315 which may
engage a portion of the element 330. The engagement of element 330 in recess
315 is illustrated
in Fig. 7. Such recessed section allows for the volume of the element 330 to
be increased by
increasing its radial cross-section without increasing the element's 330
length or outer diameter.
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Further, engagement of element 330 in the recessed section may assist to
prevent the element
330 swabbing over the mandrel 310 when the plug 300 is being pumped or
otherwise run into
a well. Shear pin taps 353 may be included for pinning slip bodies 350 to
mandrel 310.
[0057] Some embodiment elements, such as element 330 may be run without a back
up
ring, e.g. back up ring 120 in Fig.1, or the element may be extended such that
the back up ring
function is at least partially incorporated into the element itself It will be
appreciated that
element 330 is elongated on the side closer to the seat 318 compared with
element 130 in Fig.
1. It is preferred, though not required, that the leading edge of the
elongated portion be at least
thick enough, from inner diameter to outer diameter, to fill the annular space
between the casing
and the upper portion 319, between apex 317 and crenels 312, and conical outer
surface 311.
In some embodiments, the leading edge may be configured to fill the annular
space based on
the published nominal inner diameter for the host casing. Thus, for a frac
plug whose upper
end has an outer diameter of 4.375 inches and is settable in casing having a
5.5 inch outer
diameter and a weight to length ratio of 20 pounds per foot, the leading edge
of the element
may be about 0.21 to 0.22 inches thick. However, elements with a leading edge
both smaller
and larger than the annular space at the apex 317 of the conical outer surface
311 of the mandrel
310 are within the scope of the present disclosure, including the use of an
element with a 0.21
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to 0.22 inch thick leading edge in an annular space that is, based on nominal
casing inner
diameter, about 0.15 inches.
[0058] The recess has an entry section leading to the recess's reduced
diameter. The
leading section may have an angle of about 13 degrees. The entry section
reduces the outer
diameter of the mandrel in order to accommodate the extra thickness of the
element. The recess
may also have an exit section, at an angle of about 20 degrees leading out of
the recess's reduced
diameter and adjacent to the expansion ring. The exit section may help define
the reduced
diameter and aid in firmly positioning the element along the outer conical
surface. Further, the
exit section may assist in preventing the element from swabbing over the
mandrel, and off of
the tool, during run in.
[0059] Referring to Fig. 7, a plurality of slip bodies 350 are each positioned
about the
end of mandrel 310 adjacent to the expansion ring 340. Screws, such as brass
shear pins, may
connect each slip body 350 to the mandrel 310. Such screws or other connector
may serve as
an anti-preset device in addition to fixing the upper end of slip bodies 350
in place with respect
to mandrel 310. Other components for connecting slip bodies 350 to the lower
end of mandrel
310, including but not limited to nylon screws, dowels, elastic rings or other
connectors, may
be used for such engagement. Buttons 356 may be installed in the slip bodies
350 for
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penetrating into the casing or tubing into which the frac plug is being set.
Such buttons may be
of carbide, aluminum oxide, or other materials known or which become known in
the art and
other gripping elements such as teeth, wickers or others may be used in lieu
of such buttons.
[0060] The slip bodies may be engaged by a ring 354 which may be made of
elastomeric
or other suitable materials. Such ring 354 may assist in retaining the
plurality of slip bodies
350 in the retracted position until the desired location with the well is
reached.
[0061] Bottom section 360 and retainer ring 370 may be threadedly connected by
complimentary threads on the interior surface of the bottom section 360 and
the outer surface
of fingers 372. Shear ring 374 may be positioned between bottom section 360
and retainer ring
370. Slip bodies 350 may have an extension or key 358 extending into and
engaging the retainer
ring 370 within the interior of bottom section 360.
[0062] In operation, embodiments of the present disclosure may be run in on
wireline
using a setting tool such as a conventional Baker 10, Baker 20, or Go-Shorty
hydraulic setting
tool or other setting tool. Such setting tools are known in the art. Such
setting tool, which
may also include a suitable or custom wireline adaptor kit (WLAK) for the
specific embodiment
frac plug, may be connected to the device via setting shear pins connecting a
setting mandrel to
the bottom of the baffle.
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[0063] Figure 9 illustrates an embodiment frac plug assembled on a
corresponding
WLAK. Setting mandrel 460 is connected to the setting tool (not shown) via one
or more
crossovers 410, and to frac plug 300 at shear ring 374 positioned between
lower section 360
and retainer ring 370. Shear ring 374 may be preferred over shear pins in
embodiments made
of certain materials, such as wound composites, due to the avoidance of point
loads where the
shear pin is pulled or pushed against another component as the frac plug is
being set. ... Shear
retainer 470 may be connected to end of shear mandrel 460 to secure shear
mandrel 460 to the
shear ring 374 and be configured to capture the section of shear ring 374
broken away during
the setting procedure. Setting piston 430 may be connected to the setting tool
via setting nut
405 and to the frac plug 300 via the upper end of mandrel 310. Mandrel 310 may
have a shoulder
machined into its upper end for receiving a lip of setting piston 430.
Further, setting piston 430
may have an inner surface configured to receive crenels 362, or the upper end
of crenels 362.
[0064] When the setting tool is actuated, force is applied to the setting
piston 430 to
force the setting piston 430 towards the shear mandrel 460 and shear ring 374.
The force of
the setting piston 430 is transferred to the mandrel 310 such that the crenels
362 are forced
towards the bottom section 360 and retainer ring 370. Force from the shear
mandrel 460 is
transferred to the retainer ring 370 via the shear ring 374. Movement of
retainer ring 370
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towards the mandrel 310 (or the mandrel towards the retainer ring) causes the
plurality of slip
bodies 350, and thereby the expansion ring 340 and element 330 to be moved
relative to the
angular outer surface 311 of mandrel 310, each of which then radially expands.
[0065] As the slip bodies 350 and element 330 expand, they come into contact
with the
casing or other tubing in which the frac plug is being installed. As mandrel
310 continues to
move into element 330 and slip bodies 350, thereby forcing element 330 and
slip bodies 350
into such casing or tubing, buttons 356 of slip bodies 350 penetrate the
casing to mechanically
anchor the frac plug 300. Expansion of the element 330 causes it to seal
against both the outer
surface of mandrel 310 (including conical outer surface 311) and the tubing or
casing,
substantially preventing fluid communication around the frac plug 300.
[0066] It will be appreciated that element systems of certain embodiments
provide
greater pack off force than element systems having separate components which
seal against the
mandrel and against the casing respectively. The increased pack off force
results from the force
of slip bodies 350, applied through the expansion ring 340, which
longitudinally compresses
element 330. More particularly, the transition of frac plug 300 from the unset
to the set position
moves element 330 over the mandrel 310 across the increasing diameter of outer
conical surface
311. Such movement progressively increases frictional forces resisting
movement. Further,
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the elasticity of rubber or other elastomer from which the element 330 may be
made may cause
such element to resist movement along the conical outer surface's
progressively larger outer
diameter. Elements of sufficiently elastic materials will absorb that energy
and may begin to
extrude, including extrusion radially outward, increasing the outer diameter
of the element.
When the element extrudes sufficiently to contact the host casing, friction
between the element
and host casing further resist movement of the element over the mandrel
surface. Further, as
the element reaches and or passes apex 317 at the upper end of outer conical
surface 311, the
element 330 becomes constrained, or substantially constrained, in all
directions¨by the annular
space between the plug and the casing, the mandrel outer surface 311, the
expansion ring 340,
and the host casing¨and the element 330 may receive and store the setting
energy applied from
the slip bodies 350 via the expansion ring 340. Such stored energy increases
the pack off of
element 330 against both the mandrel 310 and the host casing.
[0067] When the strength of shear ring 374 is exceeded by the force required
to further
move the mandrel 310 into element 330, expansion ring 340 and slip bodies 350,
the shear ring
374 can break and release the WLAK from the frac plug 300, leaving frac plug
300 installed in
the host tubing or casing.
[0068] Figure 10 illustrates an embodiment frac plug set inside a host tubing
or casing
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500. Mandrel 310, element 330, expansion ring 340 slip bodies 350, bottom
section 360 and
retainer ring 370 are as generally described with respect to Figure 7.
However, each slip body
is engaged with a side or section of mandrel 310 along at least most of the
slip body and the
element 330 and expansion ring 340 have moved along the mandrel 310 so they
are positioned
adjacent to the apex of the conical outer diameter 311 and become expanded to
contact and grip
the casing. Element 330 may be partially extruded in the annulus between the
upper end of frac
plug 310 and the casing 500. The length of the upper end of frac plug 300,
between apex 317
and the crenels 362, may be selected to prevent such element 330 from
extruding onto and or
between the crenels 362. In one embodiment, such arrangement positions the
element 330,
around the exterior of the mandrel 310, adjacent to the seat 318 on the
interior of the of mandrel
310 and may prevent the formation of a pressure differential across the
mandrel wall when a
ball or other plug are engaged on the seat. 318
[0069] Referring to Figure 11, embodiment retainer rings may be constructed in
various
configurations. While the retainer 170 of Figures 1, 3A and 3B extend from a
circular base, the
retainer 370 of Figures 7 and 11 has fingers 372 inscribed into a tubular
structure. As shown in
Fig. 12, keys 358 of slip bodies 350 are positioned between the fingers 372
and ring 354 may
be installed around the slip bodies 350 to maintain the slip bodies' 350
arrangement in the
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retainer ring 370. Further, shear spins may be connected to slip bodies 350
and mandrel 310
through shear pins in shear pin taps 355 and 353 in the slip bodies 350 and
mandrel 310
respectively. It will be appreciated in such embodiment, keys 358 may rest on
the outer surface
of the tubular structure between fingers 372, rather than resting against both
walls of adjacent
fingers 172, as shown in Fig. 5.
[0070] Another advantage of the embodiments herein is that different sections
of the
tool experience significantly different forces and may be readily constructed
from different
materials. For example, the key section (158, 358) of slip bodies (150, 350)
retainer ring
(170,370) bottom section 160 and shear element (shear pins 162, shear ring 374
or other shear
element) primarily functionally serve during run in and setting of the frac
plug. Thus, it is
possible to make a hybrid tool in which the mandrel (110, 310) and the general
portions of the
slip bodies (150, 350) which engage and support the engagement with the casing
when in the
set position may be manufactured with wound composites, or other highly
machinable
materials, while portions of the slip bodies and components below the slip
bodies¨the key
sections (158, 358) bottom section (160, 360) and retainer ring (170, 370)¨may
be made from
materials such as magnesium and/or aluminum alloys or other materials¨that
efficiently
degrade in the wellbore without further intervention. After installation, the
mandrel 110, back
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up ring 120, element 130 expansion ring 150 and slip bodies 150 remain
functional even after
the lower elements (e.g. key section 158, 358 bottom section 160, 360 and
retainer ring 170,
370) degrade away. Key section, bottom section and retainer ring may be
referred to as a lower
setting ring assembly as these components are assembled together below the
slip bodies 150,
350 and are used to transfer setting force from the setting tool to the slip
bodies and element.
A hybrid plug, such as the described plug with components of the lower setting
assembly
manufactured from degradable materials, could be placed at the bottom of the
well or as the
bottom most plug above fully degradable plugs, sliding sleeves, large bore
plugs or other toe
section completion. Positioned thus, the hybrid plug could provide the clutch
needed to drill
out/mill out the bottom portions of the plug(s) upwell after which the mandrel
110, slip bodies
150 and other upper elements of the hybrid plug may be milled out and the
bottom portions
degrade away.
[0071] Referring to Figure 13, such a hybrid plug 700 may be used as a
transition
between plugs 600, such as fully composite plugs, intended for drill out and
fully degradable
plugs 800. In some embodiments, at least one plug 600 intended to be fully
drilled out, such as
a fully composite frac plug, is installed in host casing upwell of hybrid plug
700. The bottom
section, retaining ring and keys of certain embodiment plugs, such as can be
seen in Figure 10,
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do not expand during setting and therefore are not held against the walls of
the casing, but are
held in place via the keys' connection to their respective slip bodies. During
drillout, these
components become free or loose in the well after the slip bodies have been
drilled away. The
drill bit or mill may push these components of plug 600 downwell until they
engage the hybrid
plug 700. The crenels of bottom section in the fully drillable plug 600 (e.g.
Fig. 7, crenels 364)
can then engage upper crenels (Fig. 7, upper crenels 312) to facilitate
drillout of these remaining
portions of plug 600.
[0072] With respect to the drillout of hybrid plug 700, the mandrel, element,
expansion
ring and slip bodies may be comprised primarily of wound composite or other
readily millable
materials while the keys, retaining ring and bottom section are comprised of
degradable material
such as magnesium, magnesium and/or aluminum alloys or other degradable
materials. The
readily millable components may be drilled out, which releases the keys,
retainer ring, shear
ring and bottom section from the host casing. Because these components are
comprised of
degradable materials, they may have already degraded away or may be left in
the well to degrade
following drillout of the components above them. Because the entirety of lower
plug 800 is
made of degradable components, there is no need to drill out any portion of
it. Therefore, the
drillout assembly may be removed from the well once the upper portions of
hybrid plug 700 are
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milled out.
[0073] While it may be desirable that the upper section of hybrid plug 700
mate with
the bottom section of plug 600, the other components of hybrid plug 700 are
not required to
match with plug 600, provided that the components below the slip bodies or
slip bodies of
hybrid plug 700 are made of degradable material. Further, fully degradable
plug 800 may be
of any configuration that meets the performance requirements¨such as pressure
rating and
degradation time¨of the treatment application for which it is installed. One
example of a fully
degradable plug which my be used below a hybrid plug is the Kronos Plug sold
by Applicant.
[0074] Other features may be incorporated into the slip bodies themselves to
facilitate
the formation of such a hybrid frac plug. For example, it may be desirable to
utilize hybrid slip
bodies, e.g. slip bodies in which the slip bodies are manufactured from
drillable materials to a
point past the lowest button or other gripping element which is then joined
with a degradable
material. Alternatively, the gripping elements may be positioned in the slip
bodies such that
debris from drillout of the slip body is small enough for efficient removal
from the well.
[0075] Degradable materials are known in the art. Some degradable materials
include
alloys of magnesium and/or aluminum, but other degradable materials for use in
hybrid plugs
are within the scope of the present disclosure provided such materials retain
structural integrity
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until the hybrid plug is set. In some embodiments, the degradable material
will permit loss of
mass, over 30 days, for the particular component(s) such that the largest
remaining piece will
be less than about 20% of the mass of the original component.. Degradable
materials that allow
for the largest remaining pieces to be less than about 10% of the mass of the
original component
after 30 days are preferred and materials allowing degradation such that the
largest remaining
piece is less than about 5% of the components mass after 30 days are more
preferred. However,
materials with faster and slower degradation times, provided they may be
efficiently removed
from the well without intervention, are within the scope the present
disclosure.
[0076] Fig 14 is another embodiment plug according to the present disclosure.
Mandrel
910 with angular surface 911, element 950 in recess, expansion ring 940, slip
bodies 950 with
shear pins 952, ring 954 and buttons 956, lower section 960, retainer ring 970
and shear ring
974 are generally arranged as described with respect to Fig. 7.
[0077] Slip bodies 950 may have scores or grooves 955 on their outer surface
(e.g. the
surface that contacts the host casing when installed). Such grooves may assist
the outer surface
of slip bodies 950 to conform to the inner surface of the casing in which the
frac plug is installed
and thereby improve the slip body's engagement with and holding power against
the casing. In
some installations, the drill bit or mill may not effectively remove the
outermost layer one or
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more of the slip bodies or portions thereof because the bit or mill is smaller
than the inner
diameter of the host casing. The grooves 956, when present, may be machined to
ensure that
the bit or mill can be selected to remove the slip bodies 950 to at least the
depth of such grooves
956, Thus, any fragments of the slip bodies that remain by mill out may be
limited to the spaces
between grooves 956 that our outside the diameter of the mill that is used.
Further, in certain
embodiment hybrid tools, the grooves may reduce the size of debris from drill
out of the portion
of the slips below the buttons or other gripping elements, which may be
particularly useful in
hybrid plugs.
[0078] As shown in Fig. 15, retainer ring 970 may have a setting shoulder 973
positioned between the setting ring 974 and fingers 972 as shown in Figure 15.
Such setting
shoulder 973 facilitates more even loading around the circumference of the
shear ring's 974
face during setting of the plug.
[0079] Figure 16 illustrates one embodiment shear ring 974 according to the
present
disclosure. Such shear ring 974 may be made from magnesium, an alloy or
magnesium or
other degradable materials with suitable shear properties. Shear ring 974 may
have a tab or
shoulder, such as tab 975 for engaging a slot, recess or shoulder to prevent
shear ring 974 from
spinning, and acting as a thrust washer, during mill out or drill out. Shear
ring 974 may also
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have a shear plane 976, which may be configured empirically for a given batch
of raw material,
so that it shears at a desired force, such as at or about 25,000 pounds of
force.
[0080] The advantages of the present embodiments become readily apparent,
allowing
for a tool that minimizes the amount of required material and permitting
highly machinable
materials, such as wound composite material or degradable material to be used.
Some
embodiment plugs may be formed using Lamitex G-13 wound composite material,
obtained
from Franklin Fibre-Lamitex Corp in Wilmington Delaware. In some embodiments,
slip bodies
may be formed from Lamitex G-13 with a varying wind angle that is shallower
nearer the innder
diameter (e.g. the fibers generally run more circumferentially under the
buttons) and the angle
of the wind becomes steeper moving towards the outer diameter. This
arrangement assists in
preventing the buttons from pushing through the slip bodies as the casing is
engaged while
helping prevent shear of the slip bodies due to longitudinal force against the
shaft of the buttons.
Further, the use of wound composites may also increase the friction forces
between the conical
outer surface and each of the element and the slip bodies, helping to hold the
frac plug in the
set state.
[0081] Embodiment plugs have may an outer conical surface with a shallow
angle, such
as about five degrees. Such shallow angle provides for a longer outer conical
surface and
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therefore longer slip bodies. Such additional length may increase the
frictional forces between
the slip bodies and the outer conical surface. Further, the length between the
seat, such as seat
318, and the lower end of the mandrel may be increased, providing additional
strength against
the shear forces applied to the seat by the ball, dart, flapper or other
sealing device for which
the seat is configured.
[0082] In one embodiment the recessed section in such outer surface may have a
minimum outer diameter that is decreased relative to the angular outer surface
of mandrel by
about 0.1 inches. The element may have an inner diameter that is complimentary
to the recess
and .0625 to .125 inches diametrically smaller than the outer surface of the
recess to reduce
swabbing of the element off of the plug during run in. While the embodiment
recesses (e.g. 11
specifically disclosed with respect to the drawings herein have particular
configurations, any
recess including grooves, scallops, reduced o.d. and shoulder, indentations or
other structure
are within the scope of the present disclosure provided that such recess
enables, in comparison
with a continuation of the angular outer surface, a greater volume of element
material without
requiring increased element length or outer diameter.
[0083] In some embodiments shown to operate successfully downhole and to
maintain
pressure differentials of at least 10,000 psi in shop tests, the element was
comprised of rubber
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having a durometer of at least 80 and more preferably of at least 84, and
elements made of
rubber or other elastomers or extrudable materials and having durometers lower
than 80 and
higher than 84 are within the scope of the present disclosure. s Use of higher
durometer
materials may reduce extrusion of element in the annular space between the
upper section of
the mandrel and the host casing, thereby assisting the thimble effect of such
annulus while use
of lower durometer elements may increase extrusion and permit use of a single
size plug across
a wider range of host casing internal diameters.
[0084] Further embodiment plugs may have a shear ring whose shear surface is
configured smaller than the inner diameter of the mandrel. For example, one
embodiment plug
may have a mandrel with a minimum internal diameter 2.78 inches. In order for
the sheared
off portion of shear ring, such as shear ring 974, to fit through the mandrel
without pulling the
mandrel out of the slip bodies, the shear section 976 of shear ring 974 may
have a maximum
outer diameter of 2.5 inches, providing sufficient clearance for removal of
the sheared portion
of shear ring without interfering with mandrel positioning and therefore tool
operation.
[0085] In some embodiments, the expansion ring may be configured with a longer
surface extending over the upper end of slips. Such longer surface may limit
the ability of slip
bodies to pivot such that the upper end of slip body (e.g. adjacent to shear
taps 355 in Fig. 7)
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rises away from the mandrel. Such pivoting may prevent the slips from properly
engaging the
inner surface of the casing and prevent the frac plug from holding its
designed pressure and
possibly cause plug failure.
[0086] Devices according to the present disclosure are described with
reference to
specific embodiments. Alternatives to the described arrangements will be
apparent from a
review of the embodiments of the disclosure and such alternatives are within
the scope of the
invention as claimed. Further, while the embodiments may be described as being
made of
particular materials or particular types of materials, the invention as
claimed is not limited to
embodiments so constructed.
37
