U.S. patent application number 15/814234 was filed with the patent office on 2018-05-24 for wiper plug seal integrity system and method.
This patent application is currently assigned to GEODynamics, Inc.. The applicant listed for this patent is GEODynamics, Inc.. Invention is credited to Kevin R. George, Raymond C. Shaffer.
Application Number | 20180142528 15/814234 |
Document ID | / |
Family ID | 62144317 |
Filed Date | 2018-05-24 |
United States Patent
Application |
20180142528 |
Kind Code |
A1 |
George; Kevin R. ; et
al. |
May 24, 2018 |
WIPER PLUG SEAL INTEGRITY SYSTEM AND METHOD
Abstract
An efficient wiper plug seal integrity system and method for
deviated/horizontal wellbore is disclosed. The system/method
includes a wellbore casing installed into a wellbore along with
restriction elements, a secondary engagement sub, a float collar
and a shoe. A wiper plug is deployed into the wellbore casing after
cement slurry is pumped into the wellbore casing. The secondary
engagement sub provides a tapered entry guide directly above the
float collar. The entry guide has a reduced inside diameter that
serves to enhance the sealing integrity of the wiper plug and also
aligns the wiper plug to properly latch into a locked position. In
another system, a stepped diameter wiper plug with a reduced nose
is disclosed. The reduced nose provides for an improved seal
integrity that fits and latches into a smaller internal diameter
secondary engagement sub.
Inventors: |
George; Kevin R.; (Cleburne,
TX) ; Shaffer; Raymond C.; (Burleson, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GEODynamics, Inc. |
Millsap |
TX |
US |
|
|
Assignee: |
GEODynamics, Inc.
Millsap
TX
|
Family ID: |
62144317 |
Appl. No.: |
15/814234 |
Filed: |
November 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62425509 |
Nov 22, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 33/05 20130101;
E21B 33/16 20130101; E21B 21/10 20130101 |
International
Class: |
E21B 33/05 20060101
E21B033/05; E21B 33/16 20060101 E21B033/16 |
Claims
1. An apparatus for sealing a casing with a wiper plug; said
apparatus comprising (a) a hollow tubular shaped secondary
engagement sub having a toe sub end and a heel sub end; and (b) an
inner diameter surface having an entry guide portion near the heel
sub end; wherein said wiper plug enters said heel sub end and
engages he inner diameter surface; wherein said wiper plug produces
a fluid seal with the secondary engagement sub.
2. The apparatus of claim 1 wherein the inner diameter surface of
said secondary engagement sub is configured to enable substantially
unobstructed entry of said wiper plug into said secondary
engagement sub.
3. The apparatus of claim 1 further comprises: (c) a float collar
coupled to the toe sub end; and (d) a wellbore casing coupled to
the heel sub end of the secondary engagement sub.
4. The apparatus of claim 3 wherein said wellbore casing has an
inner diameter and a ratio of said inner diameter of said secondary
engagement sub to the inner diameter of said wellbore casing is
less than 0.9.
5. The apparatus of claim 1 wherein an inner diameter of said toe
sub end and an inner diameter of said heel sub end are equal.
6. The apparatus of claim 1 wherein an inner diameter of said toe
sub end is smaller than an inner diameter of said heel sub end.
7. A wiper plug seal integrity method, said method operating in
conjunction with a wiper plug seal integrity system in a wellbore
casing comprising a secondary engagement sub; said secondary
engagement sub is a hollow tubular member that is positioned
upstream of a float collar; said float collar is integrated at a
toe end of said wellbore casing; an inner diameter of said
secondary engagement sub is configured to enable substantially
unobstructed entry of said wiper plug; and said secondary
engagement sub is configured to latch said wiper plug thereon into
a locked position when said wiper plug enters said secondary
engagement sub; wherein said method comprises the steps of: (1)
pumping cement into said wellbore casing; (2) pumping said wiper
plug at a pumping rate into said wellbore casing; (3) pumping a
fluid behind said wiper plug; (4) slowing said pumping rate when
said wiper plug approaches close to said secondary engagement sub;
(5) providing an entry guide portion for said wiper plug into said
secondary engagement sub; (6) centralizing and aligning said wiper
plug in said secondary engagement sub; and (7) locking and latching
said wiper plug into said float collar.
8. The method of claim 7 wherein said inner diameter of said
secondary engagement sub is configured to enable substantially
unobstructed entry of said wiper plug into said secondary
engagement sub.
9. The method of claim 7 wherein ratio of said inner diameter of
said secondary engagement sub to an inner diameter of said wellbore
casing is less than 0.9.
10. The method of claim 7 wherein said secondary engagement sub
further comprises a toe sub end and a heel sub end; said toe sub
end coupled to an end of said float collar; and said heel sub end
coupled to said wellbore casing.
11. The method of claim 7 wherein an inner diameter of said toe sub
end and an inner diameter of said heel sub end are equal.
12. The method of claim 7 wherein an inner diameter of said toe sub
end is substantially smaller than an inner diameter of said heel
sub end.
13. A stepped wiper plug for use in a wellbore casing; said stepped
wiper plug comprising (a) a hollow cylindrical shaped first section
and (b) a hollow cylindrical shaped second section attached to and
extending from said first section; wherein said first section has a
diameter larger than a diameter of said second section; said first
section configured to wipe an inner portion of said casing; said
second section configured to wipe inner portions of downhole tools
in said casing.
14. The stepped wiper plug of claim 13 wherein a ratio of said
diameter of said first section to said diameter of said second
section ranges from 0.4 to 0.9
15. The stepped wiper plug of claim 13 wherein said diameter of
said second section is equal to a diameter of a secondary
engagement sub.
16. The stepped wiper plug of claim 13 wherein said first section
and said second section further comprises fins extending from an
outer surface of said first section and said second section
respectively.
17. The stepped wiper plug of claim 13 further comprises (c) a
third section that is attached and extending from an end of said
second section.
18. The stepped wiper plug of claim 17 wherein a diameter said
third section is less than an inner diameter of said downhole
tools.
19. The stepped wiper plug of claim 17 wherein a ratio of said
diameter of said second section to said diameter of said third
section ranges from 0.2 to 0.9
20. The stepped wiper plug of claim 13 wherein said downhole tools
are selected from a group comprising: sliding sleeve valves,
restrictions, or toe valves.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to wiper plugs that
are used in the oil and gas industry to wipe a well casing, and
more particularly to an improved apparatus for sealing a well
casing.
PRIOR ART AND BACKGROUND OF THE INVENTION
[0002] In the oil and gas producing industry, the process of
cementing casing into the wellbore of an oil or gas well generally
comprises several steps. For example, a conductor pipe is
positioned in the hole or wellbore and may be supported by the
formation and/or cemented. Next, a section of a wellbore is drilled
with a drill bit which is slightly larger than the outside diameter
of the casing which will be run into the well.
[0003] Thereafter, a string of casing is run into the wellbore to
the required depth where the casing lands in and is supported by a
well head in the conductor. Next, cement slurry is pumped into the
casing to fill the annulus between the casing and the wellbore. The
cement serves to secure the casing in position and prevent
migration of fluids between formations through which the casing has
passed.
[0004] The primary cementing can form a protective sheath around
the casing, segregating producing formations to prevent migration
of undesirable fluids. Secondary cementing takes place after the
primary cementing and can be used to squeeze cement into the
perforations in the casing or to seal off, isolate or repair parts
of the well. Plug back cementing is used to place cement at desired
points in the well or to shut off the bottom water or reduce the
depth of the well.
[0005] Two of the apparatuses or pipe attachments routinely used in
the cementing operations are the collar and the shoe. These are
typically cement restrictions or shoulders which are attached to a
pipe string as a part of the pipe string. The collar, for example,
a float collar, is inserted between the top and bottom of a casing
string usually one or two joints above a float shoe which is
attached to the bottom of a pipe string. Shoes and collars, among a
number of things, help prevent the back flow of cement during the
cementing operation. The collars and the shoes are usually equipped
with a check valve (often a ball valve means) to aid in the
prevention of back flow of cement. The shoes and collars are
typically an outer cylindrical housing or pipe and an inner cement
tube communicating with and fixed to the inner surface of the
cylindrical housing, with a fluid passage running the length of the
cement tube. When there is a check valve, it is usually part of an
inner housing in concentric spaced relationship with the outer
housing so that the cement tube fills the space between the two
housings and the inner housing forms part of the fluid passage.
[0006] In addition to the collars and shoes, typical cementing
operations employ one or more pump down plugs. Pump down wipe plugs
can serve three purposes: (1) to separate or serve as the interface
between the wet cement from the fluid it is displacing or the fluid
which is being used to pump the wet cement to the desired level;
(2) to wipe off the inner surface of the pipe string as it passes;
and (3) to help prevent back flow while the cement is setting
up.
[0007] The wiper plug designs used in today's horizontal wellbores
were initially developed for use in vertical wellbores. The
horizontal wellbores present a more challenging trajectory for the
equipment due to the extended casing length and concentrated
friction on only one side of the wiper plug. As a consequence, the
elastomeric fins can become worn on one side and rendered incapable
of sealing properly in the dimensions of the conventional shoe
joint. This causes a phenomena called "wet shoe." FIG. 1
illustrates a wiper plug (0101) that is worn out on one side
(0102a) and transformed into a reduced diameter wiper plug (0102).
The downfalls of having a wet shoe in a cemented wellbore casing
include possible leak paths, lack of isolation, and no pressure
integrity of the casing (10). Therefore, when a pressure casing
integrity test fails, the cause of the failure is either a wet shoe
or leak in the casing.
[0008] As generally seen in the flow chart of FIG. 2 (0200), a
preferred exemplary wiper plug seal integrity method with an
exemplary secondary sub integrated to a well casing may be
generally described in terms of the following steps: [0009] (1)
drilling a wellbore in a hydrocarbon formation (0201); [0010] (2)
installing a wellbore casing in the wellbore along with a float
collar and a shoe (0202); [0011] (3) pumping cement into the
wellbore casing (0203); [0012] (4) pumping the wiper plug at a
pumping rate into the wellbore casing (0204); [0013] (5) pumping
water with inhibiting agents behind the wiper plug (0205); [0014]
(6) slowing the pumping rate when the wiper plug approaches the
float collar (0206); and [0015] (7) bumping the wiper plug against
the float collar (0207). [0016] The wiper plug worn on one side
bumps against a float collar and causes water to flow past the
plug. This may create a wet shoe condition.
[0017] The prior art as detailed above suffers from a number of
deficiencies. First, prior art systems do not provide for
effectively avoiding wet shoe in a horizontal wellbore casing. Once
the wiper plug is damaged, cement will flow past it. Also, prior
art systems do not provide for efficient wiper plug seal integrity
in a horizontal wellbore casing. A need exists for a system of
ensuring that even a damaged wiper plug creates an effective seal.
Prior art systems do not provide for efficiently locking wiper plug
fins that are undersized to the actual casing. Finally, prior art
systems and methods do not provide for inexpensive solutions to
prevent wet shoe conditions.
BRIEF SUMMARY OF THE INVENTION
System Overview
[0018] The present invention in various embodiments addresses one
or more of the above objectives in the following manner. The
present invention provides a system which includes a wellbore
casing installed into a wellbore along with restriction elements, a
secondary engagement sub, a float collar and a shoe. A wiper plug
is deployed into the wellbore casing after cement slurry is pumped
into the wellbore casing. The secondary engagement sub provides a
tapered entry guide directly above the float collar. The entry
guide has a reduced inside diameter that serves to enhance the
sealing integrity of the wiper plug and also aligns the wiper plug
to properly latch into a locked position. In another system, a 3
stepped diameter wiper plug with a reduced nose is disclosed. The
reduced nose provides for an improved seal integrity that fits and
latches into a smaller internal diameter secondary engagement
sub.
[0019] The present invention system may be utilized in the context
of an overall wiper plug seal integrity method, wherein the wiper
plug seal integrity apparatus as described previously is controlled
by a method having the following steps: [0020] (1) drilling a
wellbore in a hydrocarbon formation; [0021] (2) installing a
wellbore casing in the wellbore along with the secondary engagement
sub, a float collar and a shoe; [0022] (3) pumping cement into the
wellbore casing; [0023] (4) pumping the wiper plug at a pumping
rate into the wellbore casing; [0024] (5) pumping water with
inhibiting agents behind the wiper plug; [0025] (6) slowing the
pumping rate when the wiper plug approaches close to the secondary
engagement sub; [0026] (7) providing an entry guide for the wiper
plug into the secondary engagement sub; [0027] (8) centralizing and
aligning the wiper plug in the secondary engagement sub; and [0028]
(9) locking and latching the wiper plug into the float collar.
[0029] Integration of this and other preferred exemplary embodiment
methods in conjunction with a variety of preferred exemplary
embodiment systems are described herein in anticipation by the
overall scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] For a fuller understanding of the advantages provided by the
invention, reference should be made to the following detailed
description together with the accompanying drawings wherein:
[0031] FIG. 1 illustrates a prior art wiper plug and a worn wiper
plug.
[0032] FIG. 2 shows a prior art method for sealing wiper plugs in a
cemented wellbore casing.
[0033] FIG. 3 illustrates an exemplary system cross section of the
secondary engagement sub deployed along with a wellbore casing
according to a preferred embodiment of the present invention.
[0034] FIG. 4A illustrates an exemplary cross section of secondary
engagement sub according to a preferred embodiment of the present
invention.
[0035] FIG. 4B illustrates an exemplary perspective section of
secondary engagement sub according to a preferred embodiment of the
present invention.
[0036] FIG. 5 illustrates an exemplary flowchart method for wiper
plug seal integrity with a secondary engagement sub according to a
preferred embodiment of the present invention.
[0037] FIG. 6A illustrates an exemplary system cross section of a
three stepped diameter wiper plug according to a preferred
embodiment of the present invention.
[0038] FIG. 6B illustrates an exemplary perspective view of a three
stepped diameter wiper plug according to a preferred embodiment of
the present invention.
DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS
[0039] While this invention is susceptible of embodiment in many
different forms, there is shown in the drawings and will herein be
described in detailed preferred embodiment of the invention with
the understanding that the present disclosure is to be considered
as an exemplification of the principles of the invention and is not
intended to limit the broad aspect of the invention to the
embodiment illustrated.
[0040] The numerous innovative teachings of the present application
will be described with particular reference to the presently
preferred embodiment, wherein these innovative teachings are
advantageously applied to the particular problems of a wiper plug
seal integrity system and method. However, it should be understood
that this embodiment is only one example of the many advantageous
uses of the innovative teachings herein. In general, statements
made in the specification of the present application do not
necessarily limit any of the various claimed inventions. Moreover,
some statements may apply to some inventive features but not to
others.
[0041] Accordingly, the present invention will address the
deficiencies in the prior art and achieve a number of objectives.
For example, the present system will prevent wet shoe in a
horizontal wellbore casing. Specifically, it will provide for
efficient plug seal integrity in a horizontal wellbore casing. The
present invention provides a reduced internal seal bore into which
the fins of the wiper plug can fully and properly seat. It also
provides for efficiently locking wiper plug fins that are
undersized to the actual casing. Finally, it is an inexpensive
solution to prevent wet shoe conditions.
[0042] While these objectives should not be understood to limit the
teachings of the present invention, in general these objectives are
achieved in part or in whole by the disclosed invention that is
discussed in the following sections. One skilled in the art will no
doubt be able to select aspects of the present invention as
disclosed to affect any combination of the objectives described
above.
[0043] The present invention may be seen in more detail as
generally illustrated in FIG. 3 (0300), wherein a secondary
engagement sub (0303) is deployed along with a wellbore casing
(0301) in a formation 20. The sub (0303) may be installed above or
upstream of a float collar (0304). A shoe (0305) at the toe may be
set by cement pumped into the casing. The casing may further be
integrated with downhole tools (0302) such as restrictions, sliding
sleeve valves, toe valves and the like. When a wiper plug is
deployed into a well casing in front of pumped cement, the wiper
plug wipes cement stringers off the casing at the same time the
lateral length of the horizontal casing may erode or abrade the
wiper plug on one side causing a reduction in the overall diameter
of the plug. The reduced diameter on one side may enable fluids
pumped behind the plug to bypass the plug and create a wet
shoe.
[0044] According to a preferred embodiment, an apparatus for
sealing a horizontal wellbore casing (0301) with a wiper plug
comprises a hollow tubular shaped secondary engagement sub (0303)
positioned upstream of a float collar (0304) in the wellbore
casing; wherein when the wiper plug enters the secondary engagement
sub, the secondary engagement sub centralizes the wiper plug such
that said wiper plug aligns into the float collar and substantially
obstructs fluid flow past the wiper plug. Cement sets in the toe
(0305) when fluids are not bypassed. The exemplary secondary sub
(0303) obstructs the fluids from bypassing and therefore cement may
be set without causing a potential wet shoe. According to a
preferred exemplary embodiment, an inner diameter of the secondary
engagement sub is configured to enable substantially unobstructed
entry of the wiper plug into the secondary engagement sub. For
example, a casing with a 4.67 inch inner diameter may be integrated
with a sub with a 4.25 inner diameter so that a wiper plug with a
diameter of 4.67 inch may be guided and aligned into the sub even
with a lower diameter after eroding inside the casing. The lower
diameter of the sub may enable an eroded wiper plug to be
centralized and latched or engaged in a float collar.
[0045] In one embodiment, the secondary engagement sub (0400) has
an inner diameter surface 410, a ratio of the inner diameter of the
secondary engagement sub to an inner diameter of the wellbore
casing is less than 0.9. According to another embodiment the
secondary engagement sub further comprises a toe sub end (0402) and
a heel sub end (0401). The toe sub end may be mechanically coupled
to an end of the float collar. The heel sub end may be mechanically
coupled to the wellbore casing. The heel sub end (0401) may be
configured to be threaded or attached by other means to the well
casing. Similarly, the toe sub end (0402) may be configured to be
threaded or attached by other means to the float collar. According
to another embodiment the inner diameter of the toe sub end and
inner diameter of the heel sub end are equal. In another embodiment
the inner diameter surface (0410) tube in the sub is tapered. The
inner diameter of the toe sub end is substantially smaller than the
inner diameter of the heel sub end. For example, the diameter of
the toe sub end may be 4.25 inches and the diameter of the heel sub
end may be 4.67 inches. The sub may be tapered gently to allow for
the wiper plug to gradually enter the sub without bumping into the
sub or the float collar as the pumping rate is slowed down. The
angle of the taper may range from 5.sup.0 to 45.sup.0. A ratio of
the inner diameter of the heel sub end (0401) to an inner diameter
of the toe sub end (0402) may range from 0.2 to 0.5. As illustrated
in both FIG. 4A and FIG. 4B, a guide portion (0420) has a larger
inner diameter so that a wiper plug may be guided and aligned into
the toe sub end (0402).
[0046] As generally seen in the flow chart of FIG. 5 (0500), a
wiper plug seal integrity method with an exemplary secondary sub
integrated to a well casing may be generally described in terms of
the following steps: [0047] (1) drilling a wellbore in a
hydrocarbon formation (0501); [0048] (2) installing a wellbore
casing in the wellbore along with the secondary engagement sub, a
float collar and a shoe (0502); [0049] (3) pumping cement into the
wellbore casing (0503); [0050] (4) pumping the wiper plug at a
pumping rate into the wellbore casing (0504); [0051] The pumping
rate typically ranges from 3 barrels per minute to 15 barrels per
minute; [0052] (5) pumping water with inhibiting agents behind the
wiper plug (0505); [0053] inhibiting agents may be pumped with
water to inhibit premature setting of the cement; [0054] (6)
slowing the pumping rate when the wiper plug approaches close to
the secondary engagement sub (0506); [0055] The pumping rate may be
slowed down such that the worn wiper plug does bump into the sub or
the float collar. The pumping rate may slow down to a range from 3
barrels per minute to 4 barrels per minute; [0056] (7) providing an
entry guide for the wiper plug into the secondary engagement sub
(0507); [0057] The sub may be tapered gently to allow for the wiper
plug to gradually enter the sub without bumping into the sub or the
float collar as the pumping rate is slowed down. The smaller
diameter of the sub. The sub provides a tapered entry guide and
seal sub directly above the float collar [0058] (8) centralizing
and aligning the wiper plug in the secondary engagement sub (0508);
and [0059] The entry guide has a reduced inside diameter that
serves to enhance the sealing integrity of the wiper plug and also
aligns the wiper plug to ensure it is properly latched into the
locked position. [0060] (9) locking and latching the wiper plug
into the float collar (0509). [0061] The latching or sealing the
worn wiper plug into a float collar or the secondary sub obstructs
water from bypassing the plug and prevents a wet shoe. The
secondary sub enables the cement to set without creating a wet shoe
and furthermore enable a pressure integrity test to be performed
without a leak in the toe of the casing.
[0062] The horizontal wellbores present a more challenging
trajectory for the equipment due to the extended casing length and
concentrated friction on only one side of the wiper plug. As a
consequence, the elastomeric fins can become worn on one side and
rendered incapable of sealing properly in the dimensions of the
conventional shoe joint. According to a preferred exemplary
embodiment, a secondary sub provides an improved seal configuration
that will provide a reduced internal seal bore into which the fins
of the wiper plug can fully and properly seat. The secondary sub
may reduce the number of wet shoes by properly aligning the wiper
plug into the float collar and by the improved seal integrity.
[0063] The secondary sub may be adapted to many styles of wiper
plugs to achieve a seal integrity with a variety of wiper plugs
including but not limited to chevron stacks or a certain number of
wiper fins that are undersized to the actual casing while being
optimized to seal within the specific seal sub.
[0064] According to another preferred exemplary embodiment, a
stepped wiper plug (0600) for use in a horizontal wellbore casing
may comprise a hollow cylindrical shaped first plug section (first
section) (0601) and a hollow cylindrical shaped second plug section
(second section) (0602) as illustrated in FIG. 6A (0600) and FIG.
6B (0620). The second section (0602) may be attached or connected
to the first section (0601) at an end (0604) of the first plug
(0601) and said second section (0602) may extend outwards from the
connected end (0604) of the first section (0601). The first section
(0601) may have a diameter (0611) larger than a diameter (0612) of
the second section (0602). As cement is pumped down in front of the
stepped wiper plug, stringers or cement debris may be stuck to the
inside of the casing and the inside of the downhole tools. The
diameter (0611) of the first section (0601) is chosen such that the
first section may wipe an inner or inside portion of the casing.
For example, if the inner diameter of the casing is 4.67 inches,
the diameter of the first section of the wiper plug may be chosen
to be about 4.67 inches. According to a preferred exemplary
embodiment the diameter the first section (0611) is substantially
equal to an inner diameter of the casing. The diameter of the first
section may range from 3 inches to 8 inches. The diameter (0612) of
the second section (0602) may be designed to wipe inner portions of
downhole tools in the casing. For example, if the smallest inside
diameter of the downhole tools such as a sliding sleeve valve is
3.25 inches, the diameter of the second section may be chosen to be
about 3.25 inches. According to another preferred exemplary
embodiment, the diameter of the second section is substantially
equal to the smallest inner diameter of all the downhole tools. The
diameter (0612) of the second section may range from 1 inch to 6
inches. According to a preferred exemplary embodiment, when the
stepped wiper plug (0600) enters a secondary sub in a toe end of
the casing, the second section aligns into the sub and
substantially obstructs fluid flow past the stepped wiper plug.
According to another preferred exemplary embodiment the secondary
sub is positioned upstream of a float collar in the casing. The
secondary sub may be similar to the sub (0303) as illustrated in
FIG. 3. According to a further preferred exemplary embodiment a
ratio of the diameter (0611) of the first section (0601) to the
diameter (0612) of the second section (0602) ranges from 0.4 to
0.9. According to yet another preferred exemplary embodiment the
diameter of the second section is equal to an inside diameter of
the secondary sub. An outer section of the second section is
substantially not eroded when the second section wipes the downhole
tools. The first section (0601) may wipe longer lateral distances
in the casing that may range from 5,000 to 25,000 feet. The second
section (0602) may wipe shorter distances inside of downhole tools
and the distances may range from 500 to 2,000 feet. The first
section and the second section may further comprise fins extending
from an outer surface of the first section and the second section
respectively. The fins may be elastomeric or rigid.
[0065] According to a preferred exemplary embodiment, the stepped
wiper plug may further comprise a third plug section (third
section) (0603) that is attached and extending from an end (0605)
of the second section (0602). The end (0605) is away from the end
(0604) attached to the first section (0601). The third section may
be a chevron stack or the like. According to another preferred
exemplary embodiment the diameter (0613) the third section (0603)
is substantially less than the smallest inner diameter of all the
downhole tools. For example, if the smallest inside diameter of the
downhole tools such as a sliding sleeve valve is 3.25 inches, the
diameter of the third section may be chosen to be less than 3.25
inches. The diameter of the third section may range from 1 to 3
inches. The third section may be a hollow cylindrical element or a
solid piece extending from the end (0605) of the second section.
According to a preferred exemplary embodiment a ratio of the
diameter (0612) of the second section (0602) to the diameter (0613)
of the third section (0603) ranges from 0.2 to 0.9. According to
another preferred exemplary embodiment the diameter of the third
section is configured to fit into the secondary sub. The diameter
of the third section and the diameter of the sub are chosen such
that the third section latches into place while obstructing fluid
flow past the plug. The latching of the third section into the sub
creates a seal and may further avoid creation of wet shoe in the
toe of the casing. The smaller diameter of third section enables an
outer section of the third section to substantially be not touched
or eroded when the stepped wiper plug wipes the downhole tools and
the casing. The third section (0603) may further comprise fins
extending from an outer surface of the third section. According to
another preferred exemplary embodiment wherein the downhole tools
are selected from a group comprising: sliding sleeve valves,
restrictions, or toe valves.
[0066] An alternate preferred embodiment is a spiral wiper plug
configured with a spiral tail attached to an upstream end such that
the tail rotates in the casing while wiping the cement. The
rotation of the wiper plug with the spiral tail enables the wiper
plug to be worn equally on all sides. An equally worn wiper plug
may fit into a conventional float collar with a reduced diameter
and provide a tight seal and obstruct fluid bypass into the shoe of
the casing. The spiral tail may further comprise a rudder to steer
and rotate the wiper plug. The spiral tail may comprise fins that
rotate about a longitudinal axis along the casing.
[0067] This general method summary may be augmented by the various
elements described herein to produce a wide variety of invention
embodiments consistent with this overall design description. The
present invention anticipates a wide variety of variations in the
basic theme of oil and gas extraction. The examples presented
previously do not represent the entire scope of possible usages.
This basic system and method may be augmented with a variety of
ancillary embodiments. For example, in one alternative, an inner
diameter of the secondary engagement sub is configured to enable
substantially unobstructed entry of the wiper plug into the
secondary engagement sub. In another embodiment, the ratio of inner
diameter of the secondary engagement sub to inner diameter of the
wellbore casing is less than 0.9. In another embodiment, the
secondary engagement sub further comprises a toe sub end and a heel
sub end; the toe sub end mechanically coupled to an end of the
float collar; and the heel sub end mechanically coupled to the
wellbore casing.
[0068] Further, in another embodiment, the inner diameter of the
toe sub end and inner diameter of the heel sub end are equal. In
another embodiment, the hollow tube is tapered; inner diameter of
the toe sub end is smaller than the inner diameter of the heel sub
end. An embodiment wherein the secondary sub is positioned upstream
of a float collar in the casing. An embodiment wherein the diameter
of the first section is substantially equal to an inner diameter of
the casing. An embodiment wherein the diameter of the second
section is substantially equal to the smallest inner diameter of
all the downhole tools. An embodiment wherein a ratio of the
diameter of the first section to the diameter of the second section
ranges from 0.4 to 0.9. An embodiment wherein the diameter of the
second section is equal to a diameter of the secondary sub. An
embodiment wherein an outer section of the second section is
substantially not eroded when the second section wipes the downhole
tools. An embodiment wherein the first section and the second
section further comprises fins extending from an outer surface of
the first section and the second section respectively.
[0069] An alternative embodiment further comprises a third plug
section that is attached and extending from an end of the second
section; the end away from the end attached to the first section.
In this embodiment, the diameter of the third section is
substantially less than the smallest inner diameter of all the
downhole tools. A ratio of the diameter of the second section to
the diameter of the third section ranges from 0.2 to 0.9. In this
embodiment the diameter of the third section is configured to fit
into the secondary sub. Further, an outer section of the third
section is substantially not touched when the stepped wiper plug
wipes the downhole tools and the casing.
* * * * *