U.S. patent application number 13/875007 was filed with the patent office on 2013-11-07 for method and apparatus for launching objects in dual gradient systems.
The applicant listed for this patent is BLACKHAWK SPECIALTY TOOLS, LLC. Invention is credited to Joseph Boudreaux, Brad Groesbeck, John E. Hebert, J. Christopher Jordan, James G. Martens, Juan Carlos Mondelli.
Application Number | 20130292135 13/875007 |
Document ID | / |
Family ID | 49511676 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130292135 |
Kind Code |
A1 |
Jordan; J. Christopher ; et
al. |
November 7, 2013 |
Method and Apparatus for Launching Objects in Dual Gradient
Systems
Abstract
An apparatus for launching objects, such as during casing
cementing operations, in wells having dual gradient fluid systems
or certain downhole internal diameter restrictions. A launching
assembly is located below a dual gradient valve or other
restriction. In one embodiment, control lines extend from the
earth's surface to the launching assembly and control actuation of
the launching assembly. In an alternative embodiment, a receptacle
assembly is positioned above a dual gradient valve or other
restriction, with control lines extending from the receptacle
assembly to the launching assembly. A dart or other triggering
object is launched from the earth's surface to the receptacle
assembly in order to control actuation of the launching
assembly.
Inventors: |
Jordan; J. Christopher;
(Houston, TX) ; Martens; James G.; (Houston,
TX) ; Mondelli; Juan Carlos; (Houston, TX) ;
Groesbeck; Brad; (Houston, TX) ; Hebert; John E.;
(Houma, LA) ; Boudreaux; Joseph; (Houma,
LA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BLACKHAWK SPECIALTY TOOLS, LLC |
Houston |
TX |
US |
|
|
Family ID: |
49511676 |
Appl. No.: |
13/875007 |
Filed: |
May 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61640802 |
May 1, 2012 |
|
|
|
Current U.S.
Class: |
166/381 ;
166/53 |
Current CPC
Class: |
E21B 33/076 20130101;
E21B 23/00 20130101 |
Class at
Publication: |
166/381 ;
166/53 |
International
Class: |
E21B 23/00 20060101
E21B023/00 |
Claims
1. An apparatus for launching an object within a wellbore having a
dual gradient fluid system and equipped with a dual gradient valve
comprising: a) an automated launching assembly disposed below said
dual gradient valve; and b) at least one control line extending
from said launching assembly to a triggering assembly situated
above said dual gradient valve.
2. The apparatus of claim 1, wherein said triggering assembly is
situated on a drilling rig.
3. The apparatus of claim 2, wherein said triggering assembly
further comprises: a) a hydraulic power source; and b) a hydraulic
swivel assembly having an input and an output, wherein said input
is in fluid communication with said power source and said output is
in fluid communication with said at least one control line.
4. The apparatus of claim 1, wherein said triggering assembly
comprises a receptacle assembly disposed within said wellbore above
said dual gradient valve, having a central through bore and at
least one sliding sleeve adapted to receive a triggering
object.
5. The apparatus of claim 4, wherein said sliding sleeve defines a
first position and a second position, said central through bore is
isolated from fluid communication with said at least one control
line in said first position, and said central through bore and said
at least one control line are in fluid communication in said second
position.
6. The apparatus of claim 1, wherein said automated launching
assembly further comprises: a) at least one cage assembly for
receiving a launch-able object; b) a hinged door disposed under
said launch-able object; and c) at least one actuator for
selectively opening said hinged door.
7. The apparatus of claim 6, wherein said at least one actuator
comprises a motorized pin puller.
8. A method for launching an object within a wellbore having a dual
gradient fluid system and equipped with a dual gradient valve
comprising: a) loading at least one launch-able object within a
launching assembly; b) installing said launching assembly below
said dual gradient valve; and c) triggering launch of said
launch-able object from above said dual gradient valve.
9. The method of claim 8, wherein said launching assembly further
comprises: a) at least one cage assembly for receiving a
launch-able object; b) a hinged door disposed under said
launch-able object; and c) at least one actuator for selectively
opening said hinged door.
10. The method of claim 9, wherein said at least one actuator
comprises a motorized pin puller.
11. The method of claim 8, further comprising the step of
installing at least one control line from said launching assembly
to a drilling rig.
12. The method of claim 11, further comprising the step of
supplying hydraulic pressure through said at least one control line
to actuate said launching assembly.
13. The method of claim 12, wherein said hydraulic pressure is
supplied from a hydraulic power unit situated at said drilling
rig.
14. The method of claim 8, further comprising installing at least
one control line from said launching assembly to a receptacle
assembly disposed within said wellbore above said dual gradient
valve.
15. The method of claim 14, wherein said receptacle assembly
comprises a central through bore and at least one sliding
sleeve.
16. The method of claim 15, wherein said sliding sleeve defines a
first position and a second position, said central through bore is
isolated from fluid communication with said at least one control
line in said first position, and said central through bore and said
at least one control line are in fluid communication in said second
position.
17. The method of claim 16, wherein said step of triggering launch
of said launch-able object from above said dual gradient valve
further comprises shifting said sliding sleeve from said first
position to said second position.
18. The method of claim 17, wherein said step of shifting said
sliding sleeve from said first position to said second position
further comprises: a) launching a trigger object from a drilling
rig; b) seating said trigger object in said receptacle assembly;
and c) applying fluid pressure to said central through-bore of said
receptacle assembly.
Description
CROSS REFERENCES TO RELATED APPLICATION
[0001] PRIORITY OF U.S. PROVISIONAL PATENT APPLICATION Ser. No.
61/640,802, FILED MAY 1, 2012, INCORPORATED HEREIN BY REFERENCE, IS
HEREBY CLAIMED.
STATEMENTS AS TO THE RIGHTS TO THE INVENTION MADE UNDER FEDERALLY
SPONSORED RESEARCH AND DEVELOPMENT
[0002] NONE
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention pertains to a method and apparatus for
selective launching of darts, balls or other objects in well bores.
More particularly, the present invention pertains to a method and
apparatus for selective launching of such darts, balls or other
objects in wells equipped with dual gradient fluid systems or
having other downhole internal diameter restrictions.
[0005] 2. Brief Description of the Prior Art
[0006] Many offshore wells, and particularly those in deep water
environments, are drilled using moveable drilling rigs such as
drill ships, semi-submersible rigs and jack-up rigs before a
permanent platform or other production facility is ever installed.
Drilling operations conducted from such moveable drilling rigs
differ from operations conducted from platform-supported drilling
rigs in many respects. One such important difference is the
location of the blowout preventor and wellhead assemblies.
[0007] When drilling from floating drilling rigs, blowout preventor
and wellhead assemblies are not located on such rigs, but rather at
or near the sea floor. A large diameter, relatively flexible pipe
known as a riser serves as a conduit to connect the offshore rig to
subsea blowout preventor and wellhead assemblies and, ultimately,
the well below. During drilling operations, drill pipe and other
downhole equipment is lowered from the rig through the riser, the
subsea blowout preventor and wellhead assemblies, and into the well
bore which extends into the earth's crust below.
[0008] Once a well has been drilled to a desired depth, large
diameter pipe called casing is frequently installed in the well and
cemented in place. Such casing is typically installed to provide
structural integrity to the well-bore and keep geologic formations
isolated from one another. The lower portion of each casing string
is typically cemented in place, while the top end of each casing
string is seated and secured within a subsea wellhead assembly.
[0009] When running casing, individual sections of pipe are
inserted into a well-bore and joined together at the drilling rig
using threaded connections until the casing reaches a desired
length. After the final section of casing has been added, the
entire length of casing, commonly referred to as a "casing string,"
must typically be conveyed into a desired position within the
well-bore, such that the upper portion of the casing string is
seated within the subsea wellhead assembly.
[0010] After the casing has been landed in a desired position
within a well, cement is pumped down the internal diameter of the
casing, out the bottom or distal end of the casing and into the
annular space formed between the outer surface of the casing and
the inner wall of the well bore. During such cementing operations,
it is frequently beneficial to launch certain pump-able
objects--such as darts, plugs, balls or other objects--into the
cement being pumped into the well. These pump-able objects are
typically constructed of rubber or other material having similar
properties and characteristics, and are used to wipe the internal
diameter of the casing string while maintaining separation of the
cement and the mud during cementing operations.
[0011] In many instances, such darts, balls, plugs and/or other
objects (sometimes collectively referred to herein as "pump-able
objects") are suspended within a cementing head until the objects
are released or "launched" at desired points during the cement
pumping process. Such darts, balls, plugs and/or other objects
should be beneficially held in place within the slurry flow passing
through the cement head prior to being launched or released without
being damaged or washed away by such slurry flow. Once released,
such pump-able objects join the cement slurry flow and can be
pumped down hole directly into a well.
[0012] During conventional cementing operations (such as, for
example, wells equipped with conventional single-gradient fluid
systems), such pump-able objects are typically held in a cement
head or other similar apparatus at or near a drilling rig. After
being launched, said pump-able objects can progress substantially
the entire length of the casing and/or any landing string though
the unrestricted internal bores of such tubular goods.
[0013] However, in certain circumstances (such as, for example, on
subsea wells utilizing a dual gradient fluid system where the
drilling riser is displaced with seawater or other relatively
light-weight fluid), a special valve known as a drill string valve
or dual gradient valve ("DGV") is installed above the casing or
liner to be cemented. Such DGV's permit one-directional flow
through said DGV's (typically in a downward direction) while
creating a significant restriction into the internal diameter of
such casing or liner to be cemented.
[0014] As a result of the restriction caused by the DGV, darts,
balls, plugs and/or other objects cannot pass through such DGV's.
As a result, conventional plug dropping cement heads positioned at
or above a rig floor cannot be used in connection with dual
gradient fluid systems and/or wells equipped with DGV's.
[0015] Thus, there is a need for an apparatus that can be used in a
well having a dual gradient fluid system, or a restriction in the
flow bore of a well (including, without limitation, a DGV), to
release at least one plug, dart, ball or other object into said
well. Said apparatus should also be beneficially capable of
operating other tool or assemblies situated below said DGV or other
restriction.
SUMMARY OF THE INVENTION
[0016] The present invention comprises an apparatus for staging and
launching darts, balls, plugs and/or other objects including,
without limitation, pump-able objects used during casing cementing
operations. The apparatus of the present invention can function in
subsea drilling applications including, without limitation, in
wells having dual gradient fluid systems and/or equipped with a
DGV.
[0017] In a preferred embodiment, the present invention utilizes a
receptacle device positioned above the DGV to receive a ball, dart
or other object, and to transmit a hydraulic or other signal to a
releasing device situated below said DGV. A ball, dart or other
triggering object is dropped from a drilling rig, and seats within
said receptacle device. Application of fluid pressure from above
causes a sliding sleeve mechanism within said receptacle device to
shift, thereby exposing at least one control line to fluid
pressure. In this manner, such fluid pressure is transmitted
through said control line to a launching device disposed below said
DGV in order to actuate said launching device.
[0018] It is to be observed that said signal can also be conveyed
via means other than hydraulic fluid pressure. For example, said
signal can be transmitted mechanically, electrically or in another
manner, or some combination thereof, without departing from the
scope of the present invention.
[0019] In an alternative embodiment, the present invention also
provides a means for controlling the launching of balls, plugs,
darts or other objects from a downhole launching device using at
least one control line extending from a rig. Such control line(s)
can be connected to a swivel mechanism (such as, for example, the
swivel disclosed in pending U.S. non-provisional patent application
bearing Ser. No. 12/657,558, which is incorporated by reference
herein for all purposes) at the surface that permits a pipe string
to be rotated during cementing operations, but which still permits
the launching device to function downhole with hydraulic pressure
pumped from the drilling rig via such control line(s).
BRIEF DESCRIPTION OF DRAWINGS/FIGURES
[0020] The foregoing summary, as well as any detailed description
of the preferred embodiments, is better understood when read in
conjunction with the drawings and figures contained herein. For the
purpose of illustrating the invention, the drawings and figures
show certain preferred embodiments. It is understood, however, that
the invention is not limited to the specific methods and devices
disclosed in such drawings or figures.
[0021] FIG. 1 depicts a side view of a floating drilling rig
vessel, such as a vessel that could be used to drill a well using a
dual gradient fluid system.
[0022] FIG. 2 depicts a side partial sectional view of a remotely
actuated launching assembly of the present invention disposed
within certain subsea components of a well.
[0023] FIG. 3 depicts a side, partial sectional view of a first
embodiment launching assembly of the present invention.
[0024] FIG. 4 depicts a side, partial sectional view of said first
embodiment launching assembly of the present invention after a
first dart has been launched.
[0025] FIG. 5 depicts a side, partial sectional view of said first
embodiment launching assembly of the present invention after a
second dart has been launched.
[0026] FIG. 6 depicts a side, partial sectional view of an
alternative launching assembly of the present invention.
[0027] FIG. 7 depicts a side, partial sectional view of certain
downhole components of said alternative launching assembly of the
present invention.
[0028] FIG. 8 depicts a side, partial sectional view of certain
downhole components of said alternative launching assembly of the
present invention after a first dart has been launched.
[0029] FIG. 9 depicts a side, partial sectional view of certain
downhole components of said alternative launching assembly of the
present invention.
[0030] FIG. 10 depicts a side, partial sectional view of certain
downhole components of said alternative launching assembly of the
present invention after a second dart has been launched.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0031] FIG. 1 depicts a side view of a floating drilling rig vessel
100 which floats on or near water surface 200. Said floating
drilling vessel 100 generally comprises underwater substructure 101
and upper work support section 105 which extends above water
surface 200. Derrick 102 extends upward from said upper work
support section 105 and is generally disposed over rig floor 103.
Riser assembly 104 comprises a tubular conduit that extends from
floating drilling rig vessel 100 to subsea assemblies situated at
or on the sea floor (not depicted in FIG. 1).
[0032] FIG. 2 depicts a side partial sectional view of a remotely
actuated launching assembly 10 of the present invention disposed
within certain subsea components of a well. Specifically, subsea
wellhead assembly 108 and subsea BOP assembly 109 are disposed on
sea floor 300, and provide access into a length of wellbore 111
previously drilled into the earth's crust. Riser 104 extends from
said BOP assembly to floating drilling rig 100 (not shown in FIG.
2) situated on the water surface.
[0033] Still referring to FIG. 2, remotely actuated launching
assembly 10 can be conveyed into riser 104 on landing string 110.
Landing string 110, in turn, is used to land casing string 106
within a subterranean portion of said wellbore 111 in a manner well
known to those having skill in the art. Float collar assembly 107
is disposed within said casing string 106 at or near the distal end
of the casing string 106.
[0034] FIG. 3 depicts a side, partial sectional view of launching
assembly 10 of the present invention. Subsea wellhead assembly 108
and subsea BOP assembly 109 are disposed on sea floor 300, and
provide access into the upper opening of wellbore 111 previously
drilled into the earth's crust. Riser 104 extends from said BOP
assembly to floating drilling rig 100 (not shown in FIG. 3)
situated on the water surface.
[0035] Remotely actuated launching assembly 10 is conveyed into
riser 104 via landing string 110. Casing 106 is connected to casing
hanger 112 which is depicted as landed within wellhead assembly
108. A plug staging assembly having wiper plugs 113 and 114 is
disposed below said casing hanger 112.
[0036] Still referring to FIG. 3, remotely actuated launching
assembly 10 of present invention is situated below dual gradient
valve ("DGV") 150. Said DGV 150 and launching assembly 10 permit
cement and/or other fluid to flow through such components and into
a wellbore below. Remotely actuated launching assembly 10 of the
present invention also permits the use of darts, setting plugs,
balls, wipers and/or other objects which can be held in place
within said remotely actuating assembly 10 without being damaged or
washed away by cement slurry flow, but which can be selectively
launched or released into said slurry flow at desired points during
the cementing process.
[0037] Remotely actuated launching assembly 10 generally comprises
a central body member having a longitudinal bore extending though
said central body member. At least one cage assembly is disposed
within said longitudinal bore, and at least one dart or other
launch-able object is mounted within said cage assembly; as
depicted in FIG. 3, darts 120 and 121 are depicted as being loaded
within axially stacked cage assemblies. Cement slurry can be pumped
into said remotely actuated launching assembly 10 via an inlet
port, into said central bore, past said cage assemblies, and,
ultimately, into casing string 106 situated there-below. Objects
held within said at least one cage assembly, such as a darts 120
and 121 or other launch-able object(s), can be selectively released
into such cement slurry and the well below.
[0038] At least one pin puller assembly is provided for each cage
assembly. As depicted in FIG. 3, remotely actuated launching
assembly 10 is equipped with pin puller assemblies 11 and 12. Each
of said pin puller assemblies 11 and 12 comprise a side-entry
motorized assembly that is used to suspend darts (such as darts 120
and 121, respectively) on a hinged door until such time as release
of said darts is desired. Said pin puller assemblies 11 and 12 are
motorized assemblies equipped with fluid actuated motors well known
to those having skill in the art. When launching of a dart is
desired, motors of pin puller assemblies 11 and/or 12 are
selectively actuated using fluid pressure to selectively open said
hinged door(s) and allow passage of suspended objects.
[0039] Still referring to FIG. 3, hydraulic control lines 13 and 14
(such as, for example, 1/4'' stainless steel tubing) extend from a
surface facility (such as floating drilling vessel 100, not
pictured in FIG. 3) through riser 104 to motorized pin puller
assemblies 11 and 12, respectively. Hydraulic power control unit 16
is connected to said control lines 13 and 14, and provides power
for actuating motorized pin puller assemblies 11 and 12. Control
lines 13 and 14 can be connected to a swivel mechanism (such as,
for example, the swivel disclosed in pending U.S. non-provisional
patent application bearing Ser. No. 12/657,558, which is
incorporated by reference herein for all purposes) that permits
landing string 110 to be rotated during cementing operations, while
still permitting remotely actuated launching assembly 10 to
function downhole via hydraulic pressure conveyed through control
lines 13 and 14.
[0040] FIG. 4 depicts a side, partial sectional view of launching
assembly 10 of the present invention after a first dart 121 has
been launched. Hydraulic fluid pressure supplied by hydraulic power
control unit 16 is transmitted through control line 14 from a
surface facility (such as floating drilling vessel 100, not
pictured in FIG. 4) past DGV 150 to lower motorized pin puller
assembly 12. Such fluid pressure transmitted via control line 14
permits actuation of lower motorized pin puller assembly 12,
resulting in launching of dart 121 from launching assembly 10.
[0041] Although different well configurations are possible without
departing from the scope of the present invention, as depicted in
FIG. 4, first dart 121 is received within wiper plug member 114.
Said first dart 121 can be coupled with said wiper plug member 114,
which can be pumped downhole through the inner through bore of
casing string 106.
[0042] FIG. 5 depicts a side, partial sectional view of launching
assembly 10 of the present invention after a second dart 120 has
been launched. Hydraulic fluid pressure supplied by hydraulic power
control unit 16 is transmitted through control line 13 from a
surface facility (such as floating drilling vessel 100, not
pictured in FIG. 5) past DGV 150 to upper motorized pin puller
assembly 11. Such fluid pressure transmitted via control line 13
permits actuation of upper motorized pin puller assembly 11,
resulting in launching of dart 120 from launching assembly 10.
[0043] Although different well configurations are possible without
departing from the scope of the invention, as depicted in FIG. 5,
second dart 120 can be received within wiper plug member 113; wiper
plug member 114 having already been launched as set forth above.
Said second dart 120 can be coupled with said wiper plug member 113
and pumped downhole through the inner through bore of casing string
106.
[0044] FIG. 6 depicts a side, partial sectional view of an
alternative launching assembly 10 of the present invention. As
discussed above, remotely actuated launching assembly 10 is
conveyed into riser 104 on landing string 110. Casing 106 is
connected to casing hanger 112 which is depicted as landed within
wellhead assembly 108. Plug staging assembly having wiper plugs 113
and 114 is disposed below said casing hanger 112.
[0045] Still referring to FIG. 6, remotely actuated launching
assembly 10 of present invention is situated below DGV 150. As
noted herein, said DGV 150 and launching assembly 10 permit cement
and/or other fluid to flow through such components and into a
wellbore below. Remotely actuated launching assembly 10 of the
present invention also permits the use of darts, setting plugs,
balls, wipers and/or other objects which can be held in place
within the launching assembly 10 without being damaged or washed
away by cement slurry flow, but which can be selectively launched
or released into said slurry flow at desired points during the
cementing process.
[0046] Still referring to FIG. 6, in a preferred embodiment, the
present invention utilizes a receiving or receptacle assembly 20
positioned above DGV 150 to receive a ball, dart or other
triggering object, and to transmit a hydraulic signal to remote
launching assembly 10 situated below the DGV. A plug dropping
cement head assembly 30 is positioned at or near the rig floor of a
drilling rig vessel. When desired, a ball, dart or other triggering
object is selectively launched from said plug dropping cement head
assembly 30 at said drilling rig, and seats within said receptacle
assembly 20.
[0047] Said receptacle assembly has a central through-bore and a
sliding sleeve assembly defining first and second positions. In
said first position, said central through bore is isolated from
fluid communication with said at least one control line. In said
second position (that is, after said sliding sleeve has been
shifted), said through bore and said at least one control line are
in fluid communication with one another.
[0048] Following the seating of such ball, dart or other triggering
object within said receptacle assembly 20, application of fluid
pressure from above causes at least one sliding sleeve mechanism
within said receptacle assembly 20 to shift, thereby exposing at
least one control line (extending from said receptacle assembly 20
to said remotely actuated launching assembly 10) to such fluid
pressure. In this manner, such fluid pressure is transmitted
through said control line to said remotely actuated launching
assembly 10 disposed below DGV 150 in order to actuate said
launching assembly.
[0049] It is to be observed that said signal can also be conveyed
via means other than hydraulic fluid pressure. For example, said
signal can be transmitted mechanically, electrically or in another
manner, or some combination thereof, without departing from the
scope of the present invention.
[0050] Referring to FIG. 7, hydraulic control lines 23 and 24 (such
as, for example, 1/4'' stainless steel tubing) extend from
receptacle assembly 20 to motorized pin puller assemblies 12 and
11, respectively. First dart 121 and second dart 120 are loaded
within said launching assembly 10.
[0051] When desired, a first triggering object 31 is launched from
said plug dropping cement head assembly 30 positioned at or near a
rig floor (such as, for example, rig floor 103 depicted in FIG. 1),
and seats within a first sliding sleeve assembly within said
receptacle assembly 20. Following the seating of such triggering
object 31 within said receptacle assembly 20, application of fluid
pressure from above causes said first sliding sleeve assembly
within said receptacle device 20 to shift, thereby exposing control
line 23 extending from such receptacle assembly 20 to said remotely
actuated launching assembly 10 to such fluid pressure.
[0052] FIG. 8 depicts a side, partial sectional view of said
alternative launching assembly 10 of the present invention. Fluid
pressure is transmitted through control line 23 past DGV 150 to
lower motorized pin puller assembly 12 of launching assembly 10.
Such fluid pressure transmitted via control line 23 permits
actuation of lower motorized pin puller assembly 12, resulting in
launching of first dart 121 from launching assembly 10.
[0053] Although different well configurations are possible without
departing from the scope of the invention, as depicted in FIG. 8,
first dart 121 is received within wiper plug member 114. Said first
dart 121 can be coupled with said wiper plug member 114 and pumped
downhole through the inner through bore of casing string 106.
[0054] Referring to FIG. 9, when desired, a second triggering
object 32 can be launched from said surface plug dropping cement
head assembly 30, and seats within a second sliding sleeve assembly
within said receptacle assembly 20. Following the seating of such
second triggering object 32 within said receptacle assembly 20,
application of fluid pressure from above causes a second sliding
sleeve assembly within said receptacle assembly 20 to shift,
thereby exposing control line 24 to such fluid pressure. Such
hydraulic fluid pressure is transmitted through control line 24
past DGV 150 to upper motorized pin puller assembly 11.
[0055] FIG. 10 depicts a side, partial sectional view of said
alternative launching assembly 10 of the present invention. Such
fluid pressure transmitted via control line 24 permits actuation of
upper motorized pin puller assembly 11, resulting in launching of
second dart 120 from launching assembly 10. Although different well
configurations are possible without departing from the scope of the
invention, second dart 120 can be received within wiper plug member
113 (wiper plug member 114 having already been launched as set
forth above). Said second dart 120 can be coupled with said wiper
plug member 113 and pumped downhole through the inner through bore
of casing string 106.
[0056] The above-described invention has a number of particular
features that should preferably be employed in combination,
although each is useful separately without departure from the scope
of the invention. While the preferred embodiment of the present
invention is shown and described herein, it will be understood that
the invention may be embodied otherwise than herein specifically
illustrated or described, and that certain changes in form and
arrangement of parts and the specific manner of practicing the
invention may be made within the underlying idea or principles of
the invention.
* * * * *