Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02514676 1998-09-14
1
A Plug For Use In Wellbore Operations, An Apparatus For
Receiving Said Plug, A Plug Landing System And A Method For
Cementing Tubulars In A Wellbore
This is a divisional application of Canadian Patent
Application Serial No. 2,303,091 filed on September 14,
1998.
This invention relates to a plug for use in wellbore
operations, to an apparatus for receiving said plug and to
a plug landing system, particularly but not exclusively for
use in cementing operations. The invention also relates to
a method for cementing tubulars in a wellbore. It should
be understood that the expression "the invention" and the
like encompasses the subject matter of both the parent and
the divisional application.
In the construction of an oil or gas well, a wellbore
is bored into the ground. A string of tubulars is then
lowered into the wellbore and hung, either from surface or
from the end of a previously hung string of tubulars. These
strings of tubulars are known as casing strings and liners
respectively.
The casing strings or liners are generally cemented in
place. This is generally carried out by launching a first
plug from the top of the casing string or liner; following
the first plug down with cement and launching a second plug
after the cement.
The first plug lands on float shoe or collar fixed
near to or at the bottom of the casing string or liner, at
which point pressure builds up behind the first plug and
bursts a bursting disk in the first plug allowing cement to
flow therethrough, through the float shoe and if provided,
through the float collar, out of the bottom of the casing
CA 02514676 1998-09-14
la
string or liner and up into the annulus between the casing
string or liner and the wellbore. The second plug
eventually lands on top of the first plug.
Other plugs can be launched prior to or subsequent to
this operation in order to complete other operations such
as cleaning the casing string or liner.
It is important for the first plug to allow the cement
to flow therethrough upon landing on the float
CA 02514676 1998-09-14
2
shoe or collar to enable cement to flow into the annulus. It is also important
to move
the cement from the surface to the annulus between the casing string or liner
and the
wellbore as quickly as possible in order to reduce rig time and to prevent the
cement
from setting inside the casing string liner.
US Patent No. 2,075,882 discloses a plug with flexible members wllich are
deformable to allow fluid to pass between the plug and tubular.
According to the present invention, there is provided a plug for use in
wellbore
operations which plug is deformable such that, in use, upon fluid pressure
reaching a
predetermined level, said plug deforms allowing fluid to pass between said
plug and a
tubular in which said plug is located, the plug comprising a body having a
thin wall
which deforms inwardly in use to allow fluid to pass between the plug and the
tubular.
In one embodiment, the plug further comprises at least one fin. The plug may
further comprise a collapsible core.
The plug may further comprise a nose portion provided with a flow channel. In
one embodiment, the flow channel may be provided with at least one side port
to allow
fluid to flow from the area between said plug and said tubular to a central
bore.
The plug may further comprise a central passage through said plug for
optionally
allowing fluid flow therethrough. In one embodiment, the central passage may
be
provided with a landing seat for a dart or ball. In one embodiment, the
central passage
may be provided with at least one bursting disk such that, in use, at a
predetermined fluid
pressure above said plug said bursting disk fails, allowing fluid flow through
said central
passage.
In another embodiment, the nose may comprise a rotation locking member.
There is also provided an apparatus for receiving a plug comprising a baffle
which baffle comprises a hollow cylinder with at least one port thereih for
allowing fluid
to flow from said annulus through said apparatus, wherein said baffle further
comprises
at least one port therein to allow fluid to flow from a central bore in said
plug to said
apparatus.
In one embodiment, the baffle may be bell shaped. The bell shaped baffle and
said at least one port may be arranged such that said plug remains
rotationally fixed with
respect to said apparatus upon receipt of said plug thereon.
CA 02514676 1998-09-14
2a
In another embodiment, the apparatus may comprise a hollow cylinder for
receiving said plug, said hollow cylinder comprising at least two spaced apart
projections
for contacting fins of said plug, said projections defining a flow path. The
apparatus may
also comprise at least two spaced apart sharp edged projections for cutting a
flow path in
said fins of said plug.
There is also provided a plug landing system comprising a landing collar with
a
cylindrical body, a ring disposed therein, said ring having a tapered surface,
corresponding to a tapered surface of a wellbore plug for sealing contact
therebetween
and for locking therebetween.
In one embodiment, the ring may be made of drillable material.
In another embodiment, the system may include a wellbore plug. The wellbore
plug may be made of drillable material. The wellbore plug may have a nose at a
bottom
end thereof for contacting the ring, the nose and the ring made from a
material from the
group consisting of aluminum, aluminum alloy, zinc, zinc alloy, brass, low
grade steel,
and cast iron.
There is also provided a method of cementing tubulars in a wellbore comprising
the steps of launching a first plug in said tubular, pumping cement thereafter
and
launching a second plug thereafter, said first plug landing on a float collar
or a float
shoe and pumping cement across or through said first plug characterised in
that said
second plug lands on a landing collar above said first plug.
CA 02514676 2006-04-11
2b
In another aspect, the invention provides a weilbore
plug landing system, comprising a landing collar with a
hollow cylindrical body with a bore therethrough from a top
end thereof to a bottom end thereof, and a ring disposed in
the hollow cylindrical body and having a ring opening
therethrough for fluid flow therethrough, the ring having a
top and a bottom, the ring having a tapered surface
surrounding the ring opening, the tapered surface tapering
inwardly from the top of the ring, and the ring's tapered
surface being tapered to correspond to a tapered surface of
a wellbore plug for sealing contact of the wellbore plug
with the ring and for wedge locking of the wellbore plug
with the ring.
In another aspect, the invention provides a wellbore
plug, comprising a body with a top and a bottom, a nose on
the bottom, and a tapered surface on the nose and extending
therearound and tapering inwardly toward the bottom of the
plug.
In another aspect, the invention provides a wellbore
plug, comprising a body with a bore therethrough defined by
an inner wall of the body, and at least one fin projecting
out from and extending around an exterior wall of the body,
the body having a thickness between the inner wall and the
exterior wall of less than one-half inch, and the body made
of plastic material.
In another aspect, the invention provides a float
collar for wellbore operations, the float collar comprising
a hollow cylindrical body having a body bore therethrough,
a float valve mounted in the bore for controlling fluid
flow through the float collar, and a baffle having a fluid
CA 02514676 2006-04-11
2c
flow bore therethrough in fluid communication with the body
bore and mounted above the float valve for preventing a
foreign object from clogging the float valve, the baffle
further comprising a body ring with a ring fluid flow bore
therethrough, and a plurality of spaced apart projections
extending downwardly from the body ring with fluid flow
spaces between adjacent projections, and a plurality of top
ribs projecting upwardly from the body ring and the top
ribs disposed and sized for receipt within openings of a
plug landing on the ribs so that the plug will not rotate
with respect to the baffle.
In another aspect, the invention provides a float
collar for wellbore operations, the float collar comprising
a hollow cylindrical body having a body bore therethrough,
a float valve mounted in the bore for controlling fluid
flow through the float collar, a baffle having a fluid flow
bore therethrough in fluid communication with the body bore
and mounted above the float valve for preventing a foreign
object from clogging the float valve, and a hollow cylinder
within the hollow cylindrical body for receiving a plug
pumped down to the float collar, the cylinder having a
cylinder bore therethrough and at least two spaced-apart
projections extending into the cylinder bore for contacting
fins of a plug, the projections defining a fluid flow path
therebetween.
In another aspect, the invention provides a float
collar for wellbore operations, the float collar comprising
a hollow cylindrical body having a body bore therethrough,
a float valve mounted in the bore for controlling fluid
flow through the float collar, and a baffle having a fluid
flow bore therethrough in fluid communication with the body
CA 02514676 2006-11-15
2d
bore and mounted above the float valve for preventing a
foreign object from clogging the float valve, the baffle
further comprising a body ring with a ring fluid flow bore
therethrough, the body ring providing a roof over the body
bore of the hollow cylindrical body, and a plurality of
spaced apart projections extending vertically and
downwardly from the body ring with fluid flow spaces
between adjacent projections.
In another aspect, the invention provides a wellbore
plug, comprising:
a body with a top and a bottom;
a nose on the bottom; and
a tapered surface on the nose and extending therearound
and tapering inwardly toward the bottom of the plug;
wherein the tapered surfaces are such that the wellbore
plug is wedge lockable with the landing ring.
CA 02514676 1998-09-14
- 3 -
For a better understanding of the invention, refer-
ence will now be made, by way of example, to the accom-
panying drawings, in which:
Figure la is a cross-sectional side view of an
apparatus for launching plugs including a plug in accor-
dance with the present invention;
Figure lb is a bottom plan view of the apparatus of
Figure la;
Figure lc is a cross-sectional side view of the
apparatus of Figure la in a first stage of operation;
Figure id is a cross-sectional side view of part of
the apparatus of Figure la in a second stage of opera-
tion;
Figure 2a is a cross-sectional side view of an
apparatus for receiving a plug in accordance with the
present invention;
Figure 2b is a top plan view of the apparatus of
Figure 2a;
Figure 2c is a cross-sectional side view of part of
the apparatus of Figure 2a taken along the line 2c-2c of
Figure 2a; '
Figure 2d is a top plan view of part of the appara-
tus of Figure 2a;
Figure 3 is a cross-sectional side view of parts of
the apparatus of Figures la-d and of Figures 2a-d in
use;
Figure 4 is a cross-sectional side view of part of
Figure la-d in use;
Figure 5a is a cross-sectional side view of a
second embodiment of the present invention;
Figure 5b is a cross-sectional view taken along the
line 5b-5b of Figure 5a;
Figure 6a is a cross-sectional side view of a third
embodiment of the present invention;
Figure 6b is a cross-sectional view taken along the
CA 02514676 1998-09-14
- 4 -
line 6b-6b of Figure 6a;
Figure 7 is a part cross-sectional side view of the
apparatus of Figure la-d, Figure 2a-d and Figure 4 in
use;
Figure 8 is a part cross-sectional side view of the
apparatus of Figures la-ld, Figures 2a-2d and Figure 4
in use with a combined float collar and float shoe.
Referring to Figures la-d there is shown a plug set
100 according to the present invention having a top
crossover sub 1 made of metal, e.g. steel. The sub 1
has a body 2 with a central flow bore 3 extending there-
through. A snap ring 4 in a recess 5 holds a seal ring
6 in place against part (an upper shear ring)=of a top
dart receiver 20.
The seal ring 6 has an 0-ring 7 in a recess 8 to
seal the interface between the seal ring 6 and the body
2; and an 0-ring 9 in a recess 10 seals the interface
between the seal ring 2 and the top dart receiver 20. A
recess 11 accommodates an upper shear ring 25 of the top
dart receiver 20. A plurality of collets 12 extend from
a main collet ring 15 out from the lower end 16 of the
sub 1 each terminating in a bottom collet member 14.
(The shear ring 25, and any shear ring herein, may be a
complete circular ring or it may include only portions
thereof; e.g. three fifty degree portions spaced apart
by seventy degree voids. Any shear ring may be grooved
or indented to facilitate rupture or shearing.)
Initially the bottom collet members 14 are disposed
in a collet groove 33 of a top plug cylinder 30 and are
held therein by the exterior surface of the top dart
receiver 20. The top dart receiver 20 has a body 21
with a fluid flow bore 22 extending therethrough from
one end to the other. The upper end of the top dart
receiver 20 has the upper shear ring 25 projecting
therefrom into the recess 11 of the seal ring 6. The
CA 02514676 1998-09-14
- 5 -
upper shear ring 25 initially rests on the top of the
main collet ring 15 thereby holding the top dart receiv-
er 20 within the sub 1 with its lower end 27 thereof
projecting into a top plug cylinder 30. The top dart
receiver 20 has a lower lip 23 which, after dart receipt
within the top dart receiver 20, rests on an inner
shoulder of the top plug cylinder 30. The top dart
receiver 20 has an upper seat surface 24 against which
rests and seals part of a top dart.
The top plug cylinder 30 has a body 31 with a flow
bore 32 extending therethrough. A retainer ring 34
rests in a recess 35. The retainer ring 34 is released
when the top dart receiver 20 moves downwardly in the
top plug cylinder 30 past the retainer ring 34. Then
the retainer ring 34 contracts radially to prevent the
top dart receiver 20 from moving back up within the top
plug oylinder 30. An 0-ring 36 in a recess 37 seals the
interface between the top dart receiver 20 and the top
plug cylinder 30.
The top plug cylinder 30 is held within a central
bore 83 of a top plug 80, e.g. by any suitable fastener
or adhesive, e.g. epoxy adhesive. The top plug cylinder
30 may be made of any suitable metal, ceramic, cement,
composite, plastic or fiberglass material, as may each
component of.the plug set 100.
In the embodiment shown the top plug cylinder 30 is
made of composite plastic or of aluminium, the core 84
of the top plug 80 is made of filled urethane or pheno-
lic plastic material, and epoxy adhesive holds the two
together. In one aspect, a top plug cylinder (e.g.,
made of plastic, fiberglass, or metal; made of, e.g.,
PDC-drillable material) is molded into a plug core
(e.g., a core of filled urethane, urethane or phenolic
material) during the plug molding manufacturing process.
An 0-ring 49 in a recess 48 seals the interface
CA 02514676 1998-09-14
WO 99/ t 4461 PCTiC 89S/02722
- 6 -
between the top plug cylinder 30 and the top part of a
bottom dart receiver 50. A recess 39 is formed in the
lower end 42 of the body 31.
The bottom dart receiver 50 has a body 51 with a
fluid flow bore 52 extending therethrough. An upper
shear ring 53 secured to or formed integrally of the
body 51 projects out from the body 51 and initially
rests on the shoulder 38 of the top plug cylinder 30.
This can be a segmented shear ring of less than three
hundred sixty degrees in extend and/or it can be
grooved, cut, or indented to facilitate breaking.
Initially a secondary burst sleeve 55 blocks fluid
flow through a port 54. As a fail safe measure, more
than one port can be provided, with the weakest being
the one to open. The secondary burst sleeve 55 is held
in place by a friction fit, by an adhesive, by thermal
locking, or fusion, or some combination thereof. In one
aspect, the secondary burst sleeve 55 is made of alumi-
num, e.g. 0.44mm (0.0175 inches) thick to burst at a
fluid pressure of 70.75 bar (1026 p.s.i.). In one
aspect such a sleeve is made by using two hollow cylin-
drical aluminum members, heating one, cooling the other,
then inserting the cooled member into the heated member.
As the two members reach ambient temperature they are
firmly joined as the heated member cools to shrink onto
the cooled member and the cooled member expands against
the cooled heated member. In one aspect the port is
covered by a portion of the sleeve at which the two
pieces of aluminum overlap. In another aspect a single
molded piece is used.
The bottom dart receiver 50 has an inner seating
surface 56 against which rests and seats a sealing face
of a bottom dart. The lower shoulder 58 of the body 51
rests on a bottom plug cylinder 60. Fluid pressure
equalization ports 57 extend through the body 51 and
CA 02514676 1998-09-14
- 7 -
permit fluid flow from within the bottom dart receiver
to an interior space 88 within the nose 81 and from
there to space between the top plug 80 and bottom plug
90 so that the two plugs in place in a wellbore (in
place beneath the surface from which a wellbore extends
down) do not lock together due to the hydrostatic pres-
sure of fluids on the two plugs pushing them together.
The bottom dart receiver 50 has a lower end 59 that
projects down into the bottom plug cylinder 60 that
extends from a top of the bottom plug 90 to a point near
the plug's bottom above a nose 92. The bottom plug 90
has a body 91 with a deformable core 94 and a central
fluid flow bore 93. In the bottom plug 90 of the system
100 it is preferred that the wall thickness of the body
91 "t" be reduced as compared to the wall thickness of
typical bottom plugs (and, e.g. as compared to the wall
thickness of a top plug having a thickness "T" as in the
top plug 80). In certain aspects of a bottom plug with
a body made of urethane, filled urethane, or polyure-
thane or a similar material, the wall thickness "t" is
about 1.27cm (h inch) or about lcm (3/8 of an inch).
Such a wall thickness facilitates bending downwardly of
fins 97 of the bottom plug 90, thereby providing an
additional bypass flow path between the fins (and the
plug) and an interior casing wall. Such a flow path
increases flow area when the burst tube functions as
desired; and for example provides an alternative flow
path around the plugs in the event that the hole 65 is
not opened so that a cementing operation is still pos-
sible.
The top plug 80 has a nose ring 81 made of e.g.
aluminum (or of a similar material, metal, or alloy)
with a lower projecting portion 82 which facilitates
installation of the plugs into a casing by preventing
the top fin 85 from interfering with the nose ring 81.
CA 02514676 1998-09-14
WO 99/14461 PCT/G B98/02722
- 8 -
The bottom plug cylinder 60 has a body 61 with a hole 65
therethrough (more than one hole may be used) and a
lower end 64.
A primary burst tube 70 with a body 71 encircles
part of the bottom plug cylinder 60 and, initially,
blocks fluid flow through the hole 65. An enlarged
lower end 72 rests on an inner shoulder 99 of the bottom
plug 90. This enlarged end facilitates correct emplace-
ment of the primary bursting tube 70 on the bottom plug
cylinder 60 and hinders the extrusion of the burst out
from within the bottom plug 90 between the exterior of
the bottom plug cylinder 60 and the inner surface of the
central fluid flow bore 93.
In one typical operation of the plug set 100 a ball
or a bottom dart BD free falls or is pumped down and is
received within the bottom dart receiver 50, seating
against the inner seating surface 56. As pressure
builds up, the upper shear ring 53 shears (e.g. at about
110 bar (1600 p.s.i.)), releasing the bottom dart re-
ceiver 50 and bottom plug 90. This combination moves
down in the cased wellbore, e.g. to contact a float shoe
already positioned in the wellbore at a desired loca-
tion. The dart seated on the inner seating surface 56
and the intact primary burst tube 70 prevent fluid from
flowing through the central fluid flow bore 93 of the
bottom plug 90.
Figure 1c shows the bottom plug 90 after launching.
Once the bottom plug 90 is positioned and seated as
desired, fluid pressure (e.g. cement) is increased and
fluid flows down in an interior space 95 and, when a
desired pressure is reached, e.g. about 48 bar to 55 bar
(700 to about 800 p.s.i.), the primary burst tube 70
bursts at the hole 65 permitting fluid to flow through
the bottom plug 90 to the float shoe. If, for any
reason, the primary burst tube 70 fails to burst, or if
CA 02514676 1998-09-14
- 9 _
the bottom plug does not have bursting disks or tubes,
or simply to increase bypass area, an increase in fluid
pressure above the bottom plug 90 may initiate a flexing
in the thin walled body 91 of the bottom plug 90 which
allows the wiper fins 87 and the fins 97 to flex down-
wardly, allowing fluid from above the bottom plug 90 to
pass in an annulus between the body 91 of the bottom
plug 90 and the tubular in the wellbore, past the wiper
fins 87 and fins=97.
The bottom plug 90 is provided with a nose 92
provided with a bottom exit flow port 96 and side flow
ports 98.
When it is desired to launch the top plug 80, If
for example, to follow down a predetermined quantity of
cement, or to separate two types of fluid) a top dart TD
is introduced into the string above the top cross-over
sub 1 and is pumped down so that the dart seats on the
upper seat surface 24 of the top dart receiver 20. When
fluid pressure then reaches a sufficient level, e.g.
about 83 bar (1200 p.s.i.), the upper shear ring 25
shears releasing the top dart receiver 20 from the sub 1
and pushing the top dart receiver 20 down in the top lug
cylinder 30.
This frees the bottom collet members 14, releasing
the top plug cylinder 30 and the top plug 80. The top
dart prevents fluid flow through the central bore 83 of
the top plug 80 and fluid pressure moves the top plug 80
down to contact the bottom plug 90. The central bore 83
of the top plug 80 is sized and configured to receive
the bottom dart receiver 50. The nose projecting por-
tion 82 of the top plug 80 contacts and seals against
the bottom plug 90.
If for some reason the top plug 80 launches with
the bottom plug 90, bursting of the secondary burst
sleeve 55 provides a fluid flow path through the top
CA 02514676 1998-09-14
WO 99/14461 PCT/G898/02722
- 10 -
plug 80 which would not normally be possible with the
top plug 80 seated on the bottom plug 90. For example,
if the bottom dart is inadvertently pumped down too fast
with too much momentum when it hits the bottom plug 90
the impact may be sufficient to break the collet members
14, launching the two plugs 80, 90 together. In such a
situation the secondary bursting tube acts as a pressure
spike or pulse relief system and, although the two plugs
launch together, it may still be possible to complete a
cementing operation. More particular, when pumping a
bottom dart down at a high rate, e.g. rates exceeding
3181/min (2 barrels per minute) (84 US gallons per
minute) or dart velocity exceeding 2m/s (7 feet per
second), a pressure pulse or spike is created, e.g. as
high as 159 bar (2,300 p.s.i.). Such a pulse may last
one second, a half second. a fifth of a second, or three
hundredths of a second or less. In one situation such a
high pressure was recorded over a lapse time of 2/100 of
a second on large plugs for pipe 31cm (12.25") in dia-
meter. The reason for these pressure pulses or spikes
is because the bottom dart is moving at a high velocity
and the bottom plug is stationary. The bottom dart
receiver 50 in the bottom plug 90 catches the dart,
stopping its movement, and the pump pressure and fluid
momentum behind the dart cause. the pressure spike or
pulse which bursts the secondary bursting sleeve 55.
Once the pulse is relieved through the blown secondary
bursting sleeve 55 the pump pressure is then applied to
the entire top of the bottom plug 90. This pressure
causes the bottom plug 90 to start moving and separate
from the top plug 80 by shearing the bottom dart receiv-
er 50 away from the top plug 80. However, the required
shear pressure, typically less than 13.8 bar (200
p.s.i.), applied to the entire top of the bottom plug 90
is much less than the pressure required to burst the
CA 02514676 1998-09-14
- 11 -
primary burst tube 70, typically 48 to 55 bar (700 to
800 p.s.i.). Each plug 80, 90 has two wipers 87 and two
fins 97 respectively.
In one aspect the bottom plug cylinder 60 is fiber-
glass and the bottom dart receiver 50 is plastic, fiber-
glass, or aluminum; and the two are secured together
with a suitable adhesive, e.g. epoxy. In one aspect,
the secondary burst sleeve 55 has a body made of plas-
tic, fiberglass or composite with a portion made of
aluminum. This portion is sized to overlap the port(s)
54 in the bottom dart receiver 50. In one aspect the
top dart receiver 20 is made from aluminum and, in one
aspect, the bottom dart receiver 50 is made from alumi-
num.
Fig. ic shows a bottom plug 90 properly separated
from the top plug 80 with a bottom dart BD in the bottom
dart receiver 50. Fig. ld shows the top plug 80 separa-
ted from the top crossover sub 1 with a top dart 79 in
the top plug cylinder 30.
Fig. 2a shows a float collar 200 according to the
present invention with an outer hollow cylindrical body
101 having threaded ends 102 (top, interior threads) and
103 (bottom, exterior threads) with an amount of hard-
ened material 104 (e.g. adhesive or cement) holding a
valve 120 (e.g. either a known typical prior art float
valve or a valve as disclosed in issued U.S. Patent
5,511,618. Positioned above the valve 120 is a flow
baffle 105 (see also Fig. 33c) with a body 106, descend-
ing arms 107, and flow openings or spaces 108 between
the arms. A base 109 secured to or formed integrally of
the body 106 is held in the hardened material 104.
Fluid is flowable through a top flow bore 110 in the
body 106.
Fig. 3 shows a bottom plug 90 that has moved to
seat on the baffle 105 of the float collar 200. Arrows
CA 02514676 1998-09-14
- 12 -
indicate two fluid flow paths from above the plug 90 to
the valve 120. A first path 121 includes flow: between
the plug 90 (and bent down fins 97, i.e_ bent down due
to fluid force more than is shown in Fig_ 3) and an
interior 123 of the casing to and through the spaces 96,
through the top flow bore 110 of the baffle 105 and
thence to the valve 120. A second path 122 includes
flow: between the plug 90 (and bent down fins 97, i.e.,
bent down more than is shown in Fig. 3 so flow is per-
mitted) and the interior 123 of the casing, to and
through the spaces 108 of the baffle 105, and thence to
the valve 120. Either the first path 121, the second
path 122, or both paths ma_v include flow in through the
hole65 and through the bore 93 when the hole 65 is not
blocked to flow.
Fig. 4 shows a landing collar 150 useful with plug
release systems and plug landing devices for receiving a
plug and seating it against a landing ring. Plug 80
is shown within the landing collar 150. A plug
landing ring 152'is held within a hollow collar body 151
with a retaining ring 153. Alternatively the landing
ring may be formed integrallv of the collar body_ A
tapered surface 155 on the landing ring 152 and, when
driven together by fluid pressure, the two surfaces
"wedge-lock" together. The body 15.1 is threaded at both
ends. In one particular embodiment the landi-ng ring
and/or retaining ring are made of drillable material,
including, but not limited to: aluminum, aluminum alloy,
zinc, zinc allov, plastic, fiberglass, composite, carbon
fiber material, wood, low grade steel, brass, cast iron,
or a combination thereof_ in one aspect the nose of
plug 80 is made of aluminum or some other drillable
material.
In certain plug systems, a bottom cementing plug of
a plug set functions to wipe the casing or pipe ahead of
CA 02514676 1998-09-14
- 13 -
the cement and to separate the cement slurry or spacer
which is behind the plug from drilling fluid or a spacer
in front of the plug. When the bottom plug lands on the
float collar it bursts or ruptures a disk or diaphragm
to allow cement to pass through the plug unobstructed.
In prior art stage cementing equipment the top cementing
plug goes behind the cement and wipes the pipe and
separates the cement slurry from well fluids pumped
behind the top cementing plug. The top cementing plug
lands on top of the bottom cementing plug effecting a
shut off of the fluid being pumped into the well. In
some cases, the top cementing plug is used to pressure
test the casing or pipe immediately after the plug is
landed. In prior art stage cementing equipment, a first
stage top cementing plug lands on a baffle above a
bottom cementing plug. Often the bottom cementing plug
and top cementing plug perform their respective jobs as
required. However, a bottom cementing plug may fail to
allow cement through the bottom plug. When this occurs,
the entire mix of cement in the pipe cannot exit, and
thus sets in the pipe.
Bottom plug cores taken when the bottom plug has
shut off the flow of fluid in the well and the cement
set up inside the casing have been studied and have
contained rust, scale, and other debris stuck to the
casing or pipe interior on top of the bottom plug. The
bottom plug "pop's off" the debris-from the interior of
the pipe or casing while the bottom plug is being pumped
down the casing allowing it to settle on top of the
bottom plug. In other cases debris (such as large
pieces of wood and slicker suits) pumped down by the
bottom plug effects the shut off. In a few instances
nothing but set cement has been found, indicating the
cement directly on top of the plug set prior to the
cement exiting the casing.
CA 02514676 1998-09-14
WO 99/14461 PCT/G898/02722
- 14 -
Another problem with bottom plugs, particularly in
high angle holes, is that the bottom plug pushes debris
ahead to the flow collar and compacts the material prior
to rupturing or bursting the diaphragm. The compacted
debris settles to the "bottom side" and fluid flows
around the material into the float collar. However,
when the top plug lands on top of the bottom plug it
cannot effect or seal a good seal .(cementing plugs in
general depend on a face seal to stop the flow of fluid)
because the bottom plug is not sealed against the col-
lar. Thus wipers on the top and bottom plug turn and
the cement can be over displaced, i.e. pushed too far up
in the annulus creating an undesirable situation re-
ferred to as a "wet shoe".
A float collar like the float collar 200 has a
landing baffle 105 that provides a "roof" over the inlet
to the float collar. The baffle forces fluid to go
around the edges and then back into the float valve.
interior. The baffle prevents debris (such as wood or a
slicker suit) from shutting off the flow of the fluid
into the float valve and to protect the float valve from
debris pumped down the casing such as rocks, gloves,
eyeglasses, etc. and possibly knocking the plunger out
of the float valve. The bottom plug allows fluid to
flow through the center of the plug (e.g. as in the
conventional bottom SSR plugs), but it also allows fluid
by-pass around the outer fins if the center of the plug
is blocked to flow with debris such as rust, wire, or
set cement. The baffle and plug are designed to lock
together during drill out. The ribs 111 of the baffle
105 are received and held in the spaces 196 between the
member 95 of the plug 90. Such locking may not occur
when the plug initially lands on the baffle, but will be
effected when drilling of the plug commences.
In one aspect the top plug is a 9e" top plug landed
CA 02514676 1998-09-14
- 15 --
on the landing collar 150 located some distance above
the float collar. The landing ring has an inner dia-
meter of 7.75" (197mm) and thus allows a standard bottom
plug to pass at between 250 and 400 p.s.i. pumped fluid
pressure. Certain embodiments of a bottom plug 90 will
pass at an even.lower pressure, e.g. at about 120 p.s.i.
or less. In this particular embodiment, the maximum
outer diameter of the plug nose is 8.23" (209mm) for use
in standard API casiing- ID's (inner diameters) for 9e"
including 9e" 53.5n with a nominal ID of 8.535"
(216.8mm) and a drift ID of 8.379" (212.8mm). Applying
pressure to the nose and landing ring causes the two
pieces to lock together as two wedges, one driven
against the other. Such "wedge locking" is known in the
prior art for locking two rings together. Thus, in
certain aspects, meeting the requirements for non-rota-
ting for drill out. The maximum pump pressure of cer-
tain embodiments of such a system is 7,500 p.s_i.(52 MPa)
("Bump pressure" is pressure applied to a casing inner
diameter after a top plug has landed.)
Fig. 5a and 5b show a system 300 like the system of
Fig. 3 (like numerals indicate the same components), but
with an inner cylinder 201 having flat-ended projections
202 for compressing fins 97 of the plug 90. Disposed
between projections 202 are flow areas 203 which provide
flow path area or additional flow path area for fluid
flowing from above the plug 90 to the valve 120.
Fig. 6a and 6b show a system 250 like the systems
of Fig. 3 and Fig. 5a (like numerals i.ndicate the same
comoonents), but with an inner cylinder 2.51 having sharp
edged projections 252 fcr cutting fins 97 of the plug
90. Disposed between projections 252 are flow areas 253
which provide flow path area or additional flow path
area for fluid flowing from above the plug 90 to the
valve 120.
CA 02514676 1998-09-14
- 16 -
Referring now to Figs. 7 and 8, there is shown two
example arrangements in which the above described appar-
atus could be used. Figs. 7 and 8 show the plugs in
their final resting positions after the cementing opera-
tion is complete. The bottom plug 90 is shown received
on a float collar 200. The nose 92 of the bottom plug
90 is rotationally locked with respect to the float
collar 200 to facilitate drilling out at a later stage.
The top plug 80 'is received by the landing collar 150.
The nose 81 of the upper plug 80 is sized such that
tapered surface face 155 thereof mates with tapered
surface 154 of the landing ring 152. The float shoe is
spaced from the float collar in Fig. 7 in two.separate
units. The float shoe and float,collar are combined
into one unit 230 in Fig. B.
The landing collar 150 as shown in Fig. 4 may be
provided with castilations and/or rounded castilations.
The nose 81 of the top plug 80 may be provided with
corresponding castilations such that in use, when the
plug 80 is received by the landing collar 150, the
castilations engage, rotationally locking therebetween.
This will facilitate fast drill through thereof.
