U.S. patent application number 14/730672 was filed with the patent office on 2015-12-10 for decomposable extended-reach frac plug, decomposable slip, and methods of using same.
The applicant listed for this patent is McClinton Energy Group, LLC. Invention is credited to Stanley Keeling, Buster Carl McClinton, Tony D. McClinton.
Application Number | 20150354313 14/730672 |
Document ID | / |
Family ID | 54767582 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150354313 |
Kind Code |
A1 |
McClinton; Tony D. ; et
al. |
December 10, 2015 |
DECOMPOSABLE EXTENDED-REACH FRAC PLUG, DECOMPOSABLE SLIP, AND
METHODS OF USING SAME
Abstract
A plug for hydraulic fractionation can have a first driver; a
first pressure arm rotatably connected to the first driver; a
second driver; a second pressure arm rotatably connected to the
second driver; and a first slip rotatably connected to the first
pressure arm and rotatably connected to the second pressure arm.
The frac plug can also have a third driver; a third pressure arm
rotatably connected to the third driver; a fourth driver; a fourth
pressure arm rotatably connected to the fourth driver; and a second
slip rotatably connected to the third pressure arm and rotatably
connected to the fourth pressure arm. Preferably at least a portion
of the frac plug is a material formulated to decompose in one to
twenty-four hours under typical wellbore conditions. Moreover, a
decomposable slip is provided for use with any frac plug known to
one of ordinary skill.
Inventors: |
McClinton; Tony D.; (Odessa,
TX) ; Keeling; Stanley; (Odessa, TX) ;
McClinton; Buster Carl; (Odessa, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McClinton Energy Group, LLC |
Odessa |
TX |
US |
|
|
Family ID: |
54767582 |
Appl. No.: |
14/730672 |
Filed: |
June 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62007698 |
Jun 4, 2014 |
|
|
|
Current U.S.
Class: |
166/135 |
Current CPC
Class: |
E21B 23/06 20130101;
E21B 33/128 20130101; E21B 33/1293 20130101 |
International
Class: |
E21B 33/128 20060101
E21B033/128; E21B 23/06 20060101 E21B023/06; E21B 33/129 20060101
E21B033/129 |
Claims
1. A fractionation plug comprising: a first driver; a first
pressure arm rotatably connected to the first driver; a second
driver; a second pressure arm rotatably connected to the second
driver; and a first slip rotatably connected to the first pressure
arm and rotatably connected to the second pressure arm.
2. The fractionation plug of claim 1 further comprising: a third
driver; a third pressure arm rotatably connected to the third
driver; a fourth driver; a fourth pressure arm rotatably connected
to the fourth driver; and a second slip rotatably connected to the
third pressure arm and rotatably connected to the fourth pressure
arm.
3. The fractionation plug of claim 2 further comprising: at least
one seal; a first seal back-up fixedly connected to and/or integral
with the second driver and comprising a bevel complementary to a
first portion of the at least one seal; and a second seal back-up
fixedly connected to and/or integral with the third driver and
comprising a bevel complementary to a second portion of the at
least one seal that is at an opposite end of the at least one seal
from the first portion.
4. The fractionation plug of claim 1 wherein the first driver
comprises an axial slot into which a portion of the first pressure
arm inserts.
5. The fractionation plug of claim 4 wherein the first driver
comprises a socket in which a pin is positioned to extend through
the portion of the first pressure arm inserted into the axial
slot.
6. The fractionation plug of claim 1 wherein the first pressure
arm, the first slip, and the second pressure arm each comprise an
aperture through which a pin is inserted to connect the first
pressure arm, the first slip, and the second pressure arm to each
other.
7. A fractionation plug comprising a material formulated to
decompose in one to twenty-four hours under typical wellbore
conditions.
8. The fractionation plug of claim 7, having an outside diameter
configured such that the fractionation plug can be installed in
casing or tubing with an inside diameter from 2 inches to 4
inches.
9. The fractionation plug of claim 8, configured to be expanded to
set in casing or tubing with an inside diameter from 2 inches to
5.5 inches.
10. The fractionation plug of claim 7, designed to be installed and
maintain isolation of hydrocarbon bearing zones for a predetermined
period of time.
11. The fractionation plug of claim 7 wherein the fractionation
plug is configured to begin to decompose and release from a
wellbore in which the fractionation plug is positioned, when
subjected to a chemical selected from the group consisting of
water, acid, alkaline and non-alkaline.
12. The fractionation plug of claim 7 wherein the fractionation
plug is configured to undergo decomposition catalyzed by a
temperature of a wellbore and/or a fluid in a wellbore.
13. The fractionation plug of claim 7 wherein the fractionation
plug is configured to be installed on at least one of e-line,
wireline or coil tubing.
14. The fractionation plug of claim 7 wherein the fractionation
plug is configured to be drilled out with conventional tubing or
coiled tubing.
15. A slip configured to be mounted on a mandrel of a fractionation
plug, the slip comprising: a body comprising a decomposable
material; and a coating at least partially covering the body, the
coating comprising a metal material.
16. The slip of claim 15, wherein the metal material is formulated
to at least partially decompose within one to twenty-four hours
after being exposed to a temperature between 150 and 380.degree.
F., and the slip is configured such that the at least partial
decomposition of the metal material exposes at least a portion of
the body that was previously covered by the coating.
17. The slip of claim 15, comprising teeth comprising exterior
surfaces comprising at least a portion of the coating.
18. The slip of claim 17, wherein the teeth form an outer side of
the slip, and the coating completely covers the body on at least
the outer side of the slip.
19. The slip of claim 15, wherein the decomposable material of the
body comprises a decomposable resin.
20. The slip of claim 15, wherein the decomposable material of the
body comprises a resin-fiber mixture comprising metallic or
non-metallic particulates.
Description
PRIORITY CLAIM
[0001] The present application claims priority to U.S. provisional
application Ser. No. 62/007,698, filed on Jun. 4, 2014, the entire
contents of which are incorporated herein by reference.
BACKGROUND
[0002] The present disclosure relates generally to devices for
hydraulic fracturing ("fracking"). More specifically, the present
disclosure is directed to frac plugs and slips that can be at least
partially decomposable and/or can use pressure arms to radially
extend the slip from the plug.
[0003] The fracking process begins by drilling a wellbore into the
earth to reach hydrocarbons trapped in shale formations. A
perforating gun or other device is then used to create small holes
in the wall of the wellbore. Fluid is pumped into the wellbore to
form a pressure greater than the fracture gradient of the
surrounding formation. This pressure creates large fractures in the
shale formation, thus providing access to the oil or natural gas
trapped within the formation.
[0004] To fracture a wellbore, the wellbore is divided into
separate zones so that the necessary pressure can be established in
the zones. The bottom-most zone is typically fractured first, using
the above-described process. The driller next inserts a frac plug
at the top/uphole side of the fracked zone. A frac plug can stop
fluid flow in one or both directions. The frac plug isolates the
previously-fracked lower zone from the next zone uphole in the
wellbore, thus ensuring that the hydraulic pressure is applied to
the unfracked zone and not the previously-fracked lower zone. This
process of plugging and fracking continues until the entire
production area of the wellbore has been fracked and plugged. The
process can involve a dozen or more frac plugs per wellbore.
[0005] To position the frac plug within the wellbore, components of
a frac plug (known as the "slips" and the "seal") expand to engage
wellbore sidewalls and create a barrier separating upper and lower
regions of the wellbore. The process of expanding the plug is
called "setting," and involves pulling upward on the body of the
plug with a setting tool while pushing downward on the slips and
the seal with a setting sleeve. This axial compression causes the
slips to move outward along a conical element, thus radially
expanding the slips into engagement with the wellbore sidewalls to
maintain the position of the plug in the wellbore. The setting
pressure also causes the malleable seal, usually made from rubber,
to expand outward against the well casing to prevent liquid or gas
from passing around the plug.
[0006] There are several problems with known frac plugs. First, the
design of the frac plug generally limits its use to wellbores of a
diameter that corresponds to the diameter of the expanded slip. For
example, if a frac plug is used in a wellbore that is so wide that
the expanded slip does not reach the wall of the wellbore, such a
frac plug cannot be used in the wellbore; the desired position of
the frac plug cannot be maintained in such a wellbore.
[0007] A second problem arises from the need to remove the frac
plugs to allow oil and gas to move toward the surface. Typically a
tool is used to drill or mill through the plug. After the tool cuts
through the slips, the remaining head member is free to move
through the well casing and is difficult, if not impossible, to
drill by itself. As a result, the tool pushes the head down the
well casing until stopped by the next plug. The lower plug holds
the upper head member in place so that the drilling process can
continue. The time, equipment, labor and energy expended in this
process of removing the plugs are costly and thus delay hydrocarbon
extraction and decrease profitability.
SUMMARY
[0008] In a general embodiment, the present disclosure provides a
frac plug comprising a first driver; a first pressure arm rotatably
connected to the first driver; a second driver; a second pressure
arm rotatably connected to the second driver; and a first slip
rotatably connected to the first pressure arm and rotatably
connected to the second pressure arm.
[0009] In an embodiment, the frac plug further comprises a third
driver; a third pressure arm rotatably connected to the third
driver; a fourth driver; a fourth pressure arm rotatably connected
to the fourth driver; and a second slip rotatably connected to the
third pressure arm and rotatably connected to the fourth pressure
arm.
[0010] In an embodiment, the frac plug comprises at least one seal,
the second driver is fixedly connected to and/or integral with a
first seal back-up that has a bevel complementary to a first
portion of the at least one seal, and the third driver is fixedly
connected to and/or integral with a second seal back-up that has a
bevel complementary to a second portion of the at least one seal
that is at an opposite end of the at least one seal from the first
portion.
[0011] In an embodiment, the first driver comprises an axial slot
into which a portion of the first pressure arm inserts.
[0012] In an embodiment, the first driver comprises a socket in
which a pin is positioned to extend through the portion of the
first pressure arm inserted into the axial slot.
[0013] In an embodiment, the first pressure arm, the first slip,
and the second pressure arm each comprise an aperture through which
a pin is inserted to connect the first pressure arm, the first
slip, and the second pressure arm to each other.
[0014] In another general embodiment, the present disclosure
provides a fractionation plug comprising a material formulated to
decompose in one to twenty-four hours under typical wellbore
conditions.
[0015] In an embodiment, the fractionation plug has an outside
diameter configured such that the frac plug can be installed in
casing or tubing with an inside diameter from 2 inches to 4 inches,
such as an inside diameter of 2.259 inches as a non-limiting
example.
[0016] In an embodiment, the fractionation plug is configured to be
expanded to set in casing or tubing with an inside diameter from 2
inches to 5.5 inches, such as an inside diameter of 5.5 inches as a
non-limiting example.
[0017] In an embodiment, the fractionation plug is designed to be
installed and maintain isolation of hydrocarbon bearing zones for a
predetermined period of time.
[0018] In an embodiment, the fractionation plug is configured to
begin to decompose and release from a wellbore in which the
fractionation plug is positioned, when subjected to a chemical
selected from the group consisting of water, acid, alkaline and
non-alkaline, such as brine water as a non-limiting example.
[0019] In an embodiment, the fractionation plug is the
fractionation plug is configured to undergo decomposition catalyzed
by a temperature of a wellbore and/or a fluid in a wellbore.
[0020] In an embodiment, the fractionation plug is configured to be
installed on at least one of e-line, wireline or coil tubing.
[0021] In an embodiment, the fractionation plug is configured to be
drilled out with conventional tubing or coiled tubing.
[0022] In another general embodiment, the present disclosure
provides a slip configured to be mounted on a mandrel of a
fractionation plug. The slip comprises: a body comprising a
decomposable material; and a coating at least partially covering
the body, the coating comprising a metal material.
[0023] In an embodiment, the metal material is formulated to at
least partially decompose within one to twenty-four hours after
being exposed to a temperature between 150 and 380.degree. F., and
the slip is configured such that the at least partial decomposition
of the metal material exposes at least a portion of the body that
was previously covered by the coating.
[0024] In an embodiment, the slip comprises teeth comprising
exterior surfaces comprising at least a portion of the coating.
[0025] In an embodiment, the teeth form an outer side of the slip,
and the coating completely covers the body on at least the outer
side of the slip.
[0026] In an embodiment, the decomposable material of the body
comprises a decomposable resin.
[0027] In an embodiment, the decomposable material of the body
comprises a resin-fiber mixture comprising metallic or non-metallic
particulates, such as magnesium particulates as a non-limiting
example.
[0028] An advantage of the present disclosure is to provide an
improved frac plug.
[0029] Another advantage of the present disclosure is to provide an
improved frac plug slip.
[0030] Still another advantage of the present disclosure is to
provide a frac plug and/or a slip that can decompose within one to
twenty-four hours under typical wellbore conditions.
[0031] Yet another advantage of the present disclosure is to
provide a decomposable frac plug designed to isolate zones in a
wellbore until a chemical, such as an acid or brine water mixture,
is applied to initiate decomposition and release of the plug from
the walls of the wellbore.
[0032] Another advantage of the present disclosure is to provide a
decomposable frac plug that uses the temperature of the wellbore as
a catalyst to begin decomposition.
[0033] Still another advantage of the present disclosure is to
provide an extended reach frac plug with an outside diameter small
enough to install in casing or tubing with a small inside diameter,
for example an inside diameter of about 2.259''.
[0034] Yet another advantage of the present disclosure is to
provide an extended reach frac plug that can be installed through
tubing, for example 27/8'' or 31/2'' tubing, and upon reaching
setting depth being capable of expanding to set in a casing with a
wider diameter, for example 51/2'' casing.
[0035] Another advantage of the present disclosure is to provide an
extended reach frac plug capable of being installed and maintaining
isolation of zones for a predetermined period of time.
[0036] Still another advantage of the present disclosure is to
provide an extended reach decomposable frac plug capable of being
installed on e-line, wireline, or coil tubing.
[0037] Yet another advantage of the present disclosure is to
provide an extended reach decomposable frac plug capable of being
drilled out with conventional tubing or coiled tubing.
[0038] Another advantage of the present disclosure is to provide an
extended reach frac plug capable of being installed in wellbores
with significantly different diameters.
[0039] Additional features and advantages are described herein and
will be apparent from the following Detailed Description and the
Figures.
BRIEF DESCRIPTION OF THE FIGURES
[0040] FIG. 1 shows a side plan view of an embodiment of a frac
plug provided by the present disclosure, in the pre-setting
configuration.
[0041] FIG. 2 shows a side plan view of an embodiment of a frac
plug provided by the present disclosure, in a set
configuration.
[0042] FIG. 3A shows a side plan view of a slip in an embodiment of
a frac plug provided by the present disclosure.
[0043] FIG. 3B shows an above plan view of a slip in an embodiment
of a frac plug provided by the present disclosure.
[0044] FIG. 4A shows a side plan view of a pressure arm in an
embodiment of a frac plug provided by the present disclosure.
[0045] FIG. 4B shows an above plan view of a pressure arm in an
embodiment of a frac plug provided by the present disclosure.
[0046] FIG. 5A shows a cross-section view of a driver in an
embodiment of a frac plug provided by the present disclosure.
[0047] FIG. 5B shows a side plan view of a driver in an embodiment
of a frac plug provided by the present disclosure.
[0048] FIG. 6A shows a side plan view of a pin in an embodiment of
a frac plug provided by the present disclosure.
[0049] FIG. 6B shows an above plan view of a pin in an embodiment
of a frac plug provided by the present disclosure.
[0050] FIG. 7A shows a side cross-section view of a first seal
back-up integral with the second driver in an embodiment of a frac
plug provided by the present disclosure.
[0051] FIG. 7B shows a side cross-section view of a second seal
back-up integral with the third driver in an embodiment of a frac
plug provided by the present disclosure.
[0052] FIG. 8A shows an above plan view of an embodiment of a
decomposable slip provided by the present disclosure, in a
non-expanded configuration.
[0053] FIG. 8B shows a side cross-section view of a segment of an
embodiment of a decomposable slip provided by the present
disclosure.
[0054] FIG. 8C shows a side perspective view of a body of an
embodiment of a decomposable slip provided by the present
disclosure.
[0055] FIG. 8D shows a side perspective view of a coating of an
embodiment of a decomposable slip provided by the present
disclosure.
[0056] FIG. 8E shows a side plan view of a coating of an embodiment
of a decomposable slip provided by the present disclosure.
[0057] FIG. 8F shows an above plan view of the embodiment of a
decomposable slip shown in FIG. 8A, in an expanded
configuration.
[0058] FIG. 9A shows a side perspective view of a frac plug in
which an embodiment of a decomposable slip provided by the present
disclosure can be used.
[0059] FIG. 9B shows a side cross-section view of the frac plug of
FIG. 9A along line X-X.
[0060] FIG. 10A shows a side cross-section view of an embodiment of
a decomposable slip provided by the present disclosure.
[0061] FIG. 10B shows an above plan view of the embodiment of a
decomposable slip shown in FIG. 10A.
[0062] FIG. 10C shows an above plan view of a segment of the
embodiment of a decomposable slip shown in FIGS. 10A and 10B.
[0063] FIG. 10D shows a side perspective view of the embodiment of
a decomposable slip shown in FIGS. 10A-10C.
[0064] FIG. 11A shows a side cross-section view of an embodiment of
a decomposable slip provided by the present disclosure.
[0065] FIG. 11B shows an above plan view of the embodiment of a
decomposable slip shown in FIG. 11A.
[0066] FIG. 11C shows an above plan view of a segment of the
embodiment of a decomposable slip shown in FIGS. 11A and 11B.
[0067] FIG. 11D shows a side perspective view of the embodiment of
a decomposable slip shown in FIGS. 11A-11C.
[0068] FIG. 12A shows a side cross-section view of an embodiment of
a decomposable slip provided by the present disclosure.
[0069] FIG. 12B shows an above plan view of the embodiment of a
decomposable slip shown in FIG. 12A.
[0070] FIG. 12C shows an above plan view of a segment of the
embodiment of a decomposable slip shown in FIGS. 11A and 11B.
[0071] FIG. 12D shows a side perspective view of the embodiment of
a decomposable slip shown in FIGS. 11A-11C.
[0072] FIG. 13A shows a side cross-section view of an embodiment of
a decomposable slip provided by the present disclosure.
[0073] FIG. 13B shows an above plan view of the embodiment of a
decomposable slip shown in FIG. 13A.
[0074] FIG. 13C shows an above plan view of a segment of the
embodiment of a decomposable slip shown in FIGS. 13A and 13B.
[0075] FIG. 13D shows a side perspective view of the embodiment of
a decomposable slip shown in FIGS. 13A-13C.
[0076] FIG. 14A is a side cross-section of an embodiment of a
mandrel provided by the present disclosure.
[0077] FIG. 14B is a side cross-section of the embodiment of a
mandrel shown in FIG. 14A.
[0078] FIG. 15A is a side cross-section of an embodiment of a load
ring provided by the present disclosure.
[0079] FIG. 15B is a side cross-section of the embodiment of a load
ring shown in FIG. 15A.
[0080] FIG. 16A is a side cross-section of an embodiment of a
combination of a mandrel, a load ring and a decomposable slip
provided by the present disclosure.
[0081] FIG. 16B is a side cross-section of the embodiment of a
combination of a mandrel, a load ring and a decomposable slip shown
in FIG. 16A.
DETAILED DESCRIPTION
[0082] As used in this disclosure and the appended claims, the
singular forms "a," "an" and "the" include plural referents unless
the context clearly dictates otherwise. The words "comprise,"
"comprises" and "comprising" are to be interpreted inclusively
rather than exclusively. Likewise, the terms "include," "including"
and "or" should all be construed to be inclusive, unless such a
construction is clearly prohibited from the context. However, the
devices disclosed herein may lack any element that is not
specifically disclosed. Thus, a disclosure of an embodiment using
the term "comprising" includes a disclosure of embodiments
"consisting essentially of" and "consisting of" the components
identified.
[0083] An embodiment of a frac plug 10 provided by the present
disclosure is shown in FIGS. 1 and 2. FIG. 1 shows the frac plug 10
before the frac plug 10 is set in a wellbore. FIG. 2 shows the frac
plug 10 after the frac plug 10 is set in a wellbore.
[0084] The frac plug 10 can comprise a mandrel 20 to which a nose
cone 21 can be fixedly connected at one end and a crown 24 can be
fixedly connected at the opposite end. For example, the nose cone
21 can be connected to or formed on a lower end of the mandrel 20,
and the crown 24 can be formed on or connected to an upper end of
the mandrel 20. In an embodiment, the nose cone 21 is connected to
the mandrel 20 by a brass pin.
[0085] The nose cone 21 can comprise a slot 22 that can extend
through the nose cone 21 in a direction parallel to the mandrel 20.
In an embodiment, an end of the nose cone 21 can be tapered, for
example at about thirty-five degrees relative to the axis of the
frac plug 10. The crown 24 can comprise one or more grooves 25 with
a shape that is complementary to the nose cone 21. The tapered end
of the nose cone 21 of the frac plug 10 can insert into the one or
more grooves 25 of a lower frac plug (not shown) during drill-out
operations. Accordingly, the nose cone 21 of the frac plug 10 can
engage the crown 24 of a lower frac plug to prevent rotation of the
frac plug 10 during drill-out.
[0086] The frac plug 10 can comprise a first driver 41 which may be
adjacent to the nose cone 21. The frac plug 10 can further comprise
a second driver 42 on an opposite side of the first driver 41
relative to the nose cone 21. The frac plug 10 can comprise a third
driver 43 and can further comprise a fourth driver 44 that is
adjacent to the crown 24. The third driver 43 can be positioned on
an opposite side of the fourth driver 44 relative to the crown 24.
The first, second, third and fourth drivers 41-44 can be
cylindrical rings that can slide on the mandrel 20 and can rotate
on the mandrel 20.
[0087] Each of the first, second, third and fourth drivers 41-44
preferably has an inner diameter that is substantially the same as
the outer diameter of the mandrel 20. In an embodiment, this
diameter can be about 1.25 inches. The first, second, third and
fourth drivers 41-44 preferably have an outer diameter that is
substantially the same relative to each other. In an embodiment,
this diameter can be about 2.625 inches. In an embodiment, the
non-tapered portion of the nose cone 21 has an outer diameter that
is substantially the same as that of the first, second, third and
fourth drivers 41-44. These dimensions are non-limiting and
illustrative only, and one of ordinary skill will recognize that
the specific dimensions implemented in the frac plug 10 can be
adjusted based on the parameters of the operation, such as wellbore
size, and proportionality to other components of the frac plug
10.
[0088] The frac plug 10 can comprise one or more slips disposed
about the mandrel 20 between the crown 21 and the nose cone 22. For
example, the frac plug 10 can comprise first slips 31 and a second
slips 32. Each of the first and second slips 31,32 can be moveably
mounted on the frac plug 10. The first slips 31 and/or the second
slips 32 can be used to set the frac plug 10 within a wellbore.
Preferably, the frac plug 10 comprises four of the first slips 31,
each positioned at ninety degrees relative to each other at the
same axial distance along the frac plug 10, and the frac plug 10
comprises four of the second slips 32, each positioned at ninety
degrees relative to each other at the same axial distance along the
frac plug 10. However, the frac plug 10 can comprise any number of
first slips 31 and any number of second slips 32, and the first and
second slips 31,32 can be at any position relative to each
other.
[0089] In an embodiment, one or more of the first and second slips
31,32 comprise a metal, such as brass, through which a tool is
drilled during a drill-out operation to remove the first and second
slips 31,32 from the wellbore. In an embodiment, one or more of the
first and second slips 31,32 comprise a decomposable material so
that a drill-out operation is not necessary and/or is minimized, as
discussed in further detail later in this application.
[0090] FIGS. 3A and 3B generally illustrate a slip 100 that can be
used as one or more of the first and second slips 31,32. In a
preferred embodiment, each of the first and second slips 31,32 are
one of the slip 100. The slip 100 can comprise one or more sets of
ridges or teeth 102.
[0091] To set the frac plug 10 in the wellbore, the first and
second slips 31,32 can be moved outward relative to the mandrel 20
to engage the one or more sets of ridges or teeth 102 with an inner
surface of a casing or production tubing. Preferably the one or
more sets of ridges or teeth 102 of the first slips 31 are sloped
toward the nose cone 21 such that they face the nose cone 21 and
the one or more sets of ridges or teeth 102 of the second slips 32
are sloped toward the crown 24 such that they face the crown
24.
[0092] The slip 100 can comprise a first leg 106 and a second leg
108 that extend from the one or more sets of ridges or teeth 102.
The slip 100 can comprise a channel 104 that extends through the
first leg 106 and/or the second leg 108. The channel 104 can be
used to connect the slip 100 to the first and second drivers 41,42
or to the third and fourth drivers 43,44, as discussed in more
detail hereafter.
[0093] Referring again to FIGS. 1 and 2, the first slip 31 can be
rotatably connected to a first pressure arm 35 and a second
pressure arm 36. The first pressure arm 35 can be rotatably
connected to the first driver 41, and the second pressure arm 36
can be rotatably connected to the second driver 42. Preferably one
end of the first pressure arm 35 is rotatably connected to the
corresponding first slip 31 by a pin, and an opposite end of the
first pressure arm 35 is rotatably connected to the first driver 41
by another pin. Preferably one end of the second pressure arm 36 is
rotatably connected to the corresponding first slip 31 by still
another pin, and an opposite end of the second pressure arm 36 is
connected to the second driver 42 by yet another pin.
[0094] Each of the second slips 32 can be rotatably connected to a
third pressure arm 37 and a fourth pressure arm 38. The third
pressure arm 37 can be rotatably connected to the third driver 43,
and the fourth pressure arm 38 can be rotatably connected to the
fourth driver 44. Preferably one end of the third pressure arm 37
is rotatably connected to the corresponding second slip 32 by a
pin, and an opposite end of the third pressure arm 37 is rotatably
connected to the third driver 43 by another pin. Preferably one end
of the fourth pressure arm 38 is rotatably connected to the
corresponding second slip 32 by still another pin, and an opposite
end of the fourth pressure arm 38 is connected to the fourth driver
44 by yet another pin.
[0095] FIGS. 4A and 4B generally illustrate a pressure arm 110 that
can be used as one or more of the first, second, third and fourth
pressure arms 35-38. In a preferred embodiment, each of the first,
second, third and fourth pressure arms 35-38 are one of the
pressure arm 110. The pressure arm 110 can comprise a first
aperture 111 by which the pressure arm 110 can be connected to the
slip 100. The portion of the pressure arm 110 comprising the first
aperture 111 can insert between the first leg 106 and the second
leg 108 of the slip 100 to align the first aperture 111 with the
channel 104 through the slip 100. A pin can insert through the
first aperture 111 of the pressure arm 110 and through the channel
104 of the slip 100 to rotatably connect the slip 100 to the
pressure arm 110.
[0096] The pin through the channel 104 of the slip 100 can connect
the slip 100 to two pressure arms 110. For example, the first slip
31 may have the form of the slip 100, and the pin therein can
extend through the channel 104 of the first slip 31, the first
aperture 112 of the first pressure arm 35, and the first aperture
111 of the second pressure arm 36. Similarly, the second slip 32
may have the form of the slip 100, and the pin therein can extend
through the channel 104 of the second slip 32, the first aperture
111 of the third pressure arm 37, and the first aperture 111 of the
fourth pressure arm 38.
[0097] The pressure arm 110 can comprise a second aperture 112 by
which the pressure arm 110 can be connected to one of the first,
second, third and fourth drivers 41-44. For example, as shown in
FIG. 5A which depicts a cross-section of a driver 150 (one of the
first, second, third and fourth drivers 41-44), a pin 120 can
insert through the second aperture 112 of the pressure arm 110 into
a socket in the corresponding driver 150. As a result, the pressure
arm 110 can be rotatably connected to the corresponding driver 150.
As shown in FIG. 5B which depicts a side plan view of the driver
150, the pin 120 can insert into the driver 150 through a first
hole 151 and/or a second hole 152 in the driver 150 in order to
insert through the second aperture 112 of the pressure arm 110.
[0098] As shown in FIG. 5B, the pressure arm 110 can insert into
the corresponding driver 150 using an axial slot 153 in the driver.
The axial slot 153 can extend into the driver 150 so that the
second aperture 112 of the pressure arm 110 can align with the
first and second holes 151,152 of the corresponding driver 150.
[0099] As shown in FIGS. 6A and 6B, the pin 120 can be a
cylindrical pin, but the pressure arm 110 can be rotatably
connected to the corresponding driver 150 using any means known to
one of ordinary skill. The pin that connects the pressure arm 110
to the slip 100 can be the same as or similar to the pin 120 that
connects the pressure arm 110 to the corresponding driver 150, but
the pressure arm 110 can be rotatably connected to the slip 100
using any means known to one of ordinary skill.
[0100] FIG. 5A also shows that the driver 150 comprises an axial
passage 155 through which the mandrel 20 extends when the driver
150 is seated thereon. In a preferred embodiment, the mandrel 20
extends through the axial passage 155 of the first, second, third
and fourth drivers 41-44. The inner diameter of the axial passage
155 can be substantially the same as the outer diameter of the
mandrel 20.
[0101] As shown in FIG. 2, movement of one or both of the first and
second drivers 41,42 toward each other can angle the first and
second pressure arms 35,36 outward to thereby move the first slips
31 outward relative to the mandrel 20. Movement of one or both of
the third and fourth drivers 43,44 toward each other can angle the
third and fourth pressure arms 37,38 outward to thereby move the
second slips 32 outward relative to the mandrel 20. Consequently,
as noted above, the first and second slips 31,32 can be moved
outward relative to the mandrel 20 to engage the one or more sets
of ridges or teeth 102 of the first and second slips 31,32 with an
inner surface of a casing or production tubing.
[0102] Referring again to FIGS. 1 and 2, the frac plug 10 can
comprise a seal 50 positioned between the first slip 31 and the
second slip 32. The seal 50 can have a hole aligned with and
continuous with the axial passage 151 of the first, second, third
and fourth drivers 41-44. Preferably the hole of the seal 50 has an
inner diameter that is substantially the same as the outer diameter
of the mandrel 20. The mandrel 20 can extend through the hole of
the seal 50 so that the seal 50 sits on the mandrel 20, can slide
on the mandrel 20, and can rotate on the mandrel 20. The seal 50
can be an elastomeric seal and can be configured to withstand the
environment of the wellbore. For example, the seal 50 can be
configured to withstand contact with sour gas and high
temperatures. The seal 50 can be a single segment seal or
preferably can comprise a plurality of segments. For example, the
seal 50 can comprise a central seal 51 positioned between two
smaller seals, such as a first seal 52 and a second seal 53.
[0103] In an embodiment, the first seal 53 can have a bevel, for
example a forty degree bevel, which rests on a complementary bevel
of a first seal back-up 54. As shown in FIG. 7A, the first seal
back-up 54 can be integral with and/or fixedly connected to the
second driver 42. The second seal 52 can have a bevel, for example
a forty degree bevel, which rests on a complementary bevel of a
second seal back-up 55. As shown in FIG. 7B, the second seal
back-up 52 can be integral with and/or fixedly connected to the
third driver 43. The central seal 51 can have bevels, for example
seventy degree bevels, that rest on complementary bevels of the
first and second seals 52,53. These bevel angles are non-limiting
and illustrative only, and one of ordinary skill will recognize
that the specific angles implemented in the frac plug 10 can be
adjusted based on the parameters of the operation, such as wellbore
size, and proportionality to other components of the frac plug
10.
[0104] The first and second seal back-ups 54,55 can sit on the
mandrel 20, can slide on the mandrel 20, and can rotate on the
mandrel 20. The first and second seal back-ups 54,55 preferably
have an inner diameter that is substantially the same as the outer
diameter of the mandrel 20. The first and second seal back-ups
54,55 preferably have an outer diameter that is substantially the
same relative to each other and the first, second, third and fourth
drivers 41-44.
[0105] Preferably one or more of the mandrel 20, the first driver
41, the first pressure arms 35, the first slips 31, the second
pressure arms 36, the second driver 42, the first seal back-up 54,
the second seal back-up 55, the third driver 43, the third pressure
arms 37, the second slips 32, the fourth pressure arms 38, the
fourth driver 44 and the crown 24 (collectively hereafter "the
components") comprise a decomposable non-metallic material, such as
a composite material. "Decomposable" means that the material is
stable at the time of use and then is separated into smaller pieces
by chemical and/or thermal conditions. Preferably the pieces formed
by decomposition can be washed to surface by directing fluid
through the wellbore.
[0106] For example, one or more of the components can comprise a
decomposable resin, such as a fiber e.g. a glass fiber. As another
example, one or more of the components can comprise a resin-fiber
mixture comprising metallic or non-metallic particulates (e.g.
magnesium particulates) which can react with chemicals directed
into the wellbore to initiate and/or accelerate decomposition. As
yet another example, one or more of the components can comprise a
material that is water soluble and/or dissolves in saline water,
brine water, or chemicals such as hydrogen chloride or another
acid, and such liquids can be directed down the wellbore to the
frac plug 10. In this regard, chemicals such as hydrogen chloride
can initiate and/or accelerate the decomposition. Additionally or
alternatively, decomposition can be initiated and/or accelerated by
the temperature in the wellbore, for example a temperature between
150 and 380.degree. F.
[0107] In a preferred embodiment, the first and second slips 31,32
comprise a decomposable material that is coated with a thin metal
coating that breaks down within one to twenty-four hours after
being exposed to the temperature of the wellbore. After the thin
metal coating breaks down, at least a portion of the decomposable
material previously covered by the coating is exposed, and
decomposition of the slip can be initiated and/or accelerated as
discussed above.
[0108] The frac plug 10 can be positioned and set in the wellbore,
for example as discussed hereafter. Coil tubing, wire lines and/or
other devices can be used to position the frac plug 10 in the
wellbore. For example, a hydraulic setting tool can be used to set
the frac plug 10. The hydraulic setting tool can comprise a rod
that connects to the mandrel 20, e.g. by inserting into a ring
connected to the mandrel 20. In a preferred embodiment, the rod
connects to the mandrel 20 by complementary threads. The hydraulic
setting tool can comprise a sleeve that can abut the fourth driver
44.
[0109] The setting tool can receive a signal from the surface, such
as an electric charge, and can respond by pulling the rod upward
relative to the sleeve. The pulling of the rod upward also pulls
the crown 24 and the mandrel 20 upward into the sleeve. As a result
of the sleeve abutting the fourth driver 44, the fourth driver 44
is pushed downward on the mandrel 44. The nose cone 21 is pulled
upward with the mandrel 20 and thus pushes the first driver 41
upward.
[0110] As shown in FIG. 2, these axial forces move the first and
second drivers 41,42 closer to each other such that the first and
second pressure arms 35,36 rotate outward relative to the mandrel
20 and extend the first slips 31 outward. The second and third
drivers 42,43 are moved closer to each other such that the first
and second seal backups 54,55 move closer to each other and force
the seal 50 to expand outward. The third and fourth drivers 43,44
are moved closer to each other such that the third and fourth
pressure arms 37,38 rotate outward relative to the mandrel 20 and
extend the second slips 32 outward.
[0111] As a result, the first and second slips 31,32 can be moved
outward relative to the mandrel 20 to engage the one or more sets
of ridges or teeth 102 with an inner surface of a casing or
production tubing. That first and second seal back-ups 54,55 can be
moved toward each other to expand the seal 50 into engagement with
an inner surface of a casing or production tubing. The
complementary threads by which the rod of the setting tool is
connected to the mandrel 20 can be configured to shear after the
rod has pulled the mandrel 20 upward to the extent necessary to set
the frac plug 10. The shearing of the complementary threads can
disconnect the rod from the mandrel 20 and allow the setting tool
to be pulled upward away from the frac plug 10 and removed from the
wellbore.
[0112] Then an upper frac plug 10 can be positioned and set in the
wellbore in a substantially similar way so that the seals 50 of the
two frac plugs 10 isolate a hydrocarbon-bearing zone. The first and
second slips 31,32 of the two frac plugs 10 can maintain the
positions of the two frac plugs 10 within the wellbore. The
isolated hydrocarbon-bearing zone can then be fractured. At least a
portion of each of the frac plugs 10 can decompose as discussed
above. Any remainder of the frac plugs 10 can be removed from the
wellbore by drilling or milling out.
[0113] Accordingly, another aspect of the present disclosure is a
method for using a frac plug in a wellbore. The method can comprise
one or more of: (i) positioning the frac plug in the wellbore at a
desired depth, (ii) setting the frac plug, the setting of the frac
plug comprising decreasing the axial distance between one of the
drivers and an adjacent driver to rotate pressure arms outward to
engage the wellbore or a casing in the wellbore with a slip
rotatably attached to the pressure arms, (iii) engaging a seal with
the wellbore or the casing in the wellbore, and (iv) after at least
a portion of the frac plug decomposes, drilling through any
remainder of the frac plug.
[0114] Step (ii) can comprise using a setting tool to pull a
mandrel and/or a nose cone attached thereto upward while
maintaining the position of the uppermost driver or while pushing
the uppermost driver downward. Step (ii) can comprise decreasing
the axial distance between another one of the drivers and an
adjacent driver to rotate additional pressure arms outward to
engage the wellbore or the casing in the wellbore with an
additional slip rotatably attached to the additional pressure arms.
Step (iii) can occur at least partially contemporaneously with Step
(ii) and can comprise decreasing the axial distance between a seal
back-up and an adjacent seal back-up to force the seal to expand.
In an embodiment, the seal back-up can be pushed toward the
adjacent seal-back-up as a result of the pulling of the mandrel
and/or the nose cone attached thereto. For example, the seal
back-up can be fixedly attached to and/or integral with one of the
drivers, and the adjacent seal back-up can be fixedly attached to
and/or integral with another one of the drivers. The decomposition
in Step (iv) preferably begins within one to twenty-four hours
after the frac plug is introduced into the wellbore and more
preferably is completed within one to twenty-four hours after the
frac plug is introduced into the wellbore
[0115] In yet another aspect of the present disclosure, a
decomposable slip 200 is provided as generally illustrated in FIGS.
8A-8F. The decomposable slip 200 can comprise a body 201 comprising
a decomposable material, and the decomposable slip 200 can further
comprise a coating 202. The decomposable slip 200 can comprise an
aperture 203 through which the mandrel of a frac plug can extend,
and the coating 202 can cover at least the outer side of the body
201 opposite from the aperture 203. The inner diameter of the body
201 can form the aperture 203.
[0116] Preferably at least a portion of the aperture 203 of the
decomposable slip 200 has an inner diameter that is substantially
the same as the outer diameter of the mandrel on which the
decomposable slip 200 is intended for use. In an embodiment, the
decomposable slip 200 sits on the mandrel, can slide on the
mandrel, and can rotate on the mandrel. Preferably the body 201 has
a thickness greater than that of the coating 202. For example, the
body 201 can have an outer diameter of about 4.25 inches and can
have at least a portion having an inner diameter of about 3.1
inches, and the coating 202 can have a thickness of about 0.05
inches. These dimensions are non-limiting and illustrative only,
and one of ordinary skill will recognize that the specific
dimensions implemented in the decomposable slip 200 can be adjusted
based on the parameters of the operation, such as wellbore size,
and proportionality to other components of the frac plug 10.
[0117] The coating 202 can comprise a metal material that breaks
down within one to twenty-four hours after being exposed to the
temperature of the wellbore. After the coating 202 breaks down, the
body 201 of decomposable material is exposed. For example, the body
201 can comprise a decomposable resin, such as a fiber e.g. a glass
fiber. As another example, the body 201 can comprise a resin-fiber
mixture comprising magnesium particulates which can react with
chemicals directed into the wellbore to initiate and/or accelerate
decomposition. As yet another example, the body 201 can comprise a
material that is water soluble and/or dissolves in saline water,
brine water, or chemicals such as hydrogen chloride or another
acid, and such liquids can be directed down the wellbore to a frac
plug comprising the slip 200. In this regard, chemicals such as
hydrogen chloride can initiate and/or accelerate the decomposition.
Additionally or alternatively, decomposition can be initiated
and/or accelerated by the temperature in the wellbore, for example
a temperature between 150 and 380.degree. F.
[0118] The decomposable slip 200 can have an outer diameter having
one or more sets of ridges or teeth 210. The one or more sets of
ridges or teeth 210 can be configured to engage an inner diameter
of a casing or production tubing when the frac plug is set.
Preferably the coating 202 of the decomposable slip 200 comprises
the exterior surfaces of the one or more sets of ridges or teeth
210. For example, as shown in FIGS. 8A and 8F, the body 201 of the
decomposable slip 200 can be positioned inward relative to the
coating 202 in a radial direction. The one or more sets of ridges
or teeth 210 can form the outer side of the slip 200 in the radial
direction, and the coating 202 can cover some or all of the outer
side of the slip 200.
[0119] In an embodiment, the decomposable slip 200 can be used on a
frac plug comprising a mandrel having a crown on one end and a nose
at the other end. Any number of the decomposable slips 200 can be
disposed about the mandrel between the crown and the nose. The frac
plug can comprise one or more seals disposed between the
decomposable slips 200. Each of the one or more seals can be an
elastomeric seal.
[0120] In an embodiment, a first slip back-up can be positioned on
the mandrel, adjacent to the decomposable slip 200 that is adjacent
the crown. In addition, a second slip back-up can be positioned on
the mandrel, adjacent to the decomposable slip 200 that is adjacent
to the nose.
[0121] FIGS. 10A-10D show an embodiment of the decomposable slip
200 in which the one or more sets of ridges or teeth 210 comprise
buttress-style teeth. Each of the buttress-style teeth can present
a flat outer surface generally parallel to the axis of the frac
plug on which the decomposable slip 200 is positioned. For each of
the buttress-style teeth, one of the sides extending inward from
the outer surface can have an angle and/or a length that is
different than that of the other side extending inward from the
outer surface.
[0122] FIGS. 11A-11D show an embodiment of the decomposable slip
200 in which the one or more sets of ridges or teeth 210 comprise
acme-style teeth. Each of the acme-style teeth can present a flat
outer surface generally parallel to the axis of the frac plug on
which the decomposable slip 200 is positioned. For each of the
acme-style teeth, the sides extending inward from the outer surface
can be generally symmetrical. As shown in these figures, flat base
surfaces from which the acme-style teeth extend outward can
separate each of the acme-style teeth from the adjacent teeth.
[0123] FIGS. 12A-12D show an embodiment of the decomposable slip
200 in which the one or more sets of ridges or teeth 210 comprise
parallelogram-style teeth. Each of the parallelogram-style teeth
can present a flat outer surface generally parallel to the axis of
the frac plug on which the decomposable slip 200 is positioned. For
each of the parallelogram-style teeth, the sides extending inward
from the outer surface can be generally parallel to each other. As
shown in these figures, flat base surfaces from which the
parallelogram-style teeth extend outward can separate each of the
parallelogram teeth from the adjacent teeth.
[0124] FIGS. 13A-13D show an embodiment of the decomposable slip
200 in which the one or more sets of ridges or teeth 210 comprise
buttress-style teeth, and the number of the buttress-style teeth is
less than that of the embodiment shown in FIGS. 10A-10D.
[0125] As generally illustrated in FIGS. 8F, 10B, 10C, 11B, 11C,
12B, 12C, 12B, 12C, 13B and 13C, the decomposable slip 200 can be
formed by segments to facilitate the expansion of the decomposable
slip. Each segment can be connected to adjacent segments to form a
continuous ring before expansion, and then expansion (e.g., under
axial pressure) can separate at least a portion of the segment from
the adjacent segments. The connections between segments can be any
suitable mechanical connection known to the skilled artisan, such
as a male-female connection, a non-limiting example of which is the
dovetail-type connection shown in the figures. However, the segment
connections are not limited to a specific embodiment. Moreover,
although each embodiment of the decomposable slip 200 is shown with
four segments, the segments are not limited to a specific number
thereof.
[0126] FIGS. 9A and 9B show an embodiment of a frac plug 300 in
which the decomposable slip 200 can be used. The frac plug 300 can
comprise a mandrel 305, a crown 307, a load ring 380, a first slip
310, a second slip 312, a first slip back-up 320, a second slip
back-up 322, a first anti-extrusion ring 330, a second
anti-extrusion ring 332, a seal 340, a nose 350, and a pump-down
ring 360. Each of the first slip 310 and the second slip 312 can be
the decomposable slip 200.
[0127] The first slip back-up 320 can be adjacent to the first slip
310. At least a portion of the first slip back-up 320 can be
tapered to at least partially rest within the first slip 310 so
that axial force pushing the first slip back-up 320 toward the
first slip 310 (such as the axial exerted during setting of the
frac plug 300) can expand the first slip 310 into the inner
diameter of the casing of the wellbore (as generally shown in FIG.
8F). The second slip back-up 322 can be adjacent the second slip
312. Similarly, at least a portion of the second slip back-up 322
can be tapered to at least partially rest within the second slip
312 so that axial force pushing the second slip back-up 322 toward
the second slip 312 (such as the axial force exerted during setting
of the frac plug 300) can expand the second slip 312 into the inner
diameter of the casing of the wellbore (as generally shown in FIG.
8F).
[0128] For example, as shown in FIG. 8B, the decomposable slip 200
(one or both of first and second slips 310,312 in FIG. 9B) can have
a bevel 220 on the inner diameter, opposite from the one or more
sets of ridges or teeth 210. As shown in FIG. 9B, the bevel of the
first slip 310 can be complementary to a bevel of the first slip
back-up 320. The bevel of the second slip 312 can be complementary
to a bevel of the second slip back-up 322.
[0129] Setting the frac plug 300 can move the first slip back-up
320 toward the first slip 310 in an axial direction such that the
first slip back-up 320 forces the first slip 310 to expand outward.
Similarly, setting the frac plug 300 can move the second slip
back-up 322 toward the second slip 312 in an axial direction such
that the second slip back-up 322 forces the second slip 312 to
expand outward.
[0130] The decomposable slip 200 shown in FIGS. 8A-8F that can be
one or both of first and second slips 310,312 in FIG. 9B can have
reliefs cut therein so that the decomposable slip 200 has a
plurality of segments, for example four or five segments. The axial
movement of the adjacent slip back-up into and under the
decomposable slip 200 can expand each of the segments outward to
engage the wellbore or a casing in the wellbore. In an embodiment,
the decomposable slip 200 can comprise male connectors, e.g.
tongues, and each of the male connectors can extend from a side of
a corresponding segment into a female connector, e.g. a hole, in
the side of the adjacent segment. The male-female connections can
maintain alignment of the segments of the decomposable slip 200
prior to expansion.
[0131] The mandrel 305 can have the crown 307 on an upper or first
end, and the nose 350 can be disposed about or connected to the
mandrel 305 at a lower or second end. The mandrel 305 can be
similar to the mandrel 20 discussed previously herein or another
mandrel used in downhole operations.
[0132] The first anti-extrusion ring 330 can be disposed about the
mandrel 305 adjacent the first slip back-up 320. The first
anti-extrusion ring 330 can be disposed between the first slip
back-up 320 and the seal 340. The second anti-extrusion ring 332
can be disposed about the mandrel 305 adjacent the second slip back
up 322. The lower anti-extrusion ring 332 can be disposed between
the seal 340 and the second slip back up 322. The seal 340 can be
disposed between the anti-extrusion rings 330 and 332. The seal 340
is depicted having three segments, but the seal 340 can include one
or more segments.
[0133] The load ring 380 can be disposed about the mandrel 305
adjacent or proximate to the crown 307. The load ring 380 can
reinforce a portion of the mandrel 305 to enable the mandrel 305 to
withstand high pressures.
[0134] The pump down ring 360 can be disposed about the nose 350.
For example, the pump down ring 360 can be placed within a groove
formed into the nose 350. The nose 350 can thread or otherwise
connect to the lower or second end of the mandrel 305.
[0135] FIGS. 14A, 14B, 15A, 15B, 16A and 16B show the mandrel 305,
the load ring 380, and their interaction with the decomposable slip
200 in the frac plug 300 in greater detail. The mandrel 305 is
generally illustrated in FIGS. 14A and 14B, the load ring 380 is
generally illustrated in FIGS. 15A and 15B, and the interaction of
the mandrel 305 and the load ring 380 with the decomposable slip
200 in the frac plug 300 is generally illustrated in FIGS. 16A and
16B.
[0136] FIGS. 9A, 9B, 16A and 16B and the corresponding disclosure
above are merely directed to non-limiting examples of a frac plug
300 in which the decomposable slip 200 can be used. These examples
are non-limiting and illustrative only; the decomposable slip 200
can be used on any frac plug known to one of ordinary skill. For
example, the decomposable slip 200 can be used on the frac plug 10
such that the frac plug 10 comprises the first slips 31 and, uphole
from the first slips 31, the decomposable slip 200. As another
example, the decomposable slip 200 can be used on the frac plug 10
such that the frac plug 10 comprises the second slips 32 and,
downhole from the second slips 32, the decomposable slip 200. As
yet another example, the slip 100 and the pressure arms 110 can be
used on the frac plug 300 such that one of the first and second
slips 310,312 comprises the slip 100 and the pressure arms 110 and
the other one of the first and second slips 310,312 comprises the
decomposable slip 200. In this regard, one of ordinary skill will
understand that features of the frac plug 10 and the frac plug 300
can be interchanged.
[0137] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *