Note: Descriptions are shown in the official language in which they were submitted.
1(~6~148
--1--
SUBSEA WELL INSTALLATION
- This invention relates to subsea well installations, espe-
cially oil or gas wells.
This is a divisional applica~ional of Serial No. 276,937.
Heretofore, casing strings have been cemented in well
5 bores in multiple stages. In multiple stage cementing, a
first stage or first increment of cement slurry is pumped down
the well casing string, out through first stage cementing ports
adjacent the bottom of the string, and into the well bore.
- The slurry rises in the annular space between the casing and
lD'3the well bore to a predetermined level, and is there maintained
in a quiescent condition until it sets. A second stage or
second increment of cement slurry is pumped down the casing,
out through second stage cementing ports, and into the well
bore at a level at or above the top of the column of first
15 stage cement. The second stage of slurry rises in the annulus
between the casing and the well bore to a second predetermined
level, and is maintained quiescent while setting. Sometimes,
a third or even a fourth stage of cement slurry is introduced
into the annulus above a preceding stage. The cement bonds
J 20 the casing to the walls of the well and prevents migration of
fluids through the annulus.
Multiple stage cementing has many advantages over single
stage cementing, in which but a single charge of cement slurry
is deposited around the entire length of casing.
A multiple stage cementing operation reduces the likeli-
,. . - :: i :.
.
14~3
hood of breaking down a weak earth formation with the hi~h
fluid pressures required to lift a long signle column of
cement slurry, thus minimizing the loss of slurry to thieving
formations. Such a cementing procedure reduces the required
5 pump pressures to magnitudes lower than those needed for a
corresponding single stage job.
~ qultiple stage operations also reduce the length of travel
of the slurry in contact with the earth formations surrounding
the casing, to thereby reduce contamination of the slurry and
10 insure the strength of the cement when it has cured.
Such multiple stage procedures reduce the quantity of
; cement required to cement widely separated intervals, as in
dual zone wells.
~ultiple stage cementing reduces channeling of the cement
15 slurry into drilling mud in the annulus, thereby providing
a stronger bond of the cement with the case and the earth
formations.
One previously known system for multiple stage cementing
is described in Composite Catalog of Oil Field Equipment and
20 Services, 31st Revision (1974-75), published by World Oil, a
Gulf Publishing Company Publication, Houston, Texas, U.S.~.,
1974, pages 334 to 341. Another such system is described in
the foregoing Composite Catalog on pages 2434 to 2440. These
known systems employ a casing string having a first-stage
25 cementing port device disposed near the bottom of the $tring,
and a stage collar disposed at an intermediate location in the
string. First stage cementing plug structures are used in con-
nection with the first stage cementing port device. Other plugs
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are used to open and close the ports of the stage cementing
collar.
These known systems are practicable for use in cementing
casing in the bores of land based wells, where the top of
5 the casing is adjacent to the earth's surface, and the plugs
can be launched directly into the top of the casing string.
However, these systems are not easily adapted for use in cement-
ing casing in marine based or subsea wells,where the top of
the casing terminates at the ocean floor, which may be many
10 hundreds of feet below the surface of the water at which the
drilling vessel or platform is located. In those instances,
the casing string has to be extended from the ocean floor up
to the floating drilling vessel or platform though a riser pipe,
so that the plugs can be launched into the casing. The modi-
15 fications required for adapting these known systems to marineoperations are time-consuming and costly.
A subsea well stage cementing system is disclosed in
applicant's prior U.S. Patent No. 3,730,267 issued May 1, 1973.
In the system of that prior patent, the top of the casing string
'~ 20 terminates at the ocean floor, and fluid connection to the
floating or stationary platform at the surface o~ the water is
established through a string of drill pipe. A stage cementing
collar is located in the casing string at an intermediate
point. A hollow top plug for the first stage of cement slurry
25 is releasably positioned in the casing string belo~ the stage
cementing collar. The normally closed stage ce~enting collar
is opened for the second stage cementing operation by dropping
an opening~ball into the string of drill pipe and allowing it
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--4--to drop to the stage collar, and thereafter applying fluid
pressure in the casing string above the stage collar. A dart-
actuated, hollow top plug for the second stage of cement slurry
is releasably secured to a hollow mandrel adjacent to the top
5 of the casing string. This dart-actuated top plug also serves
to close the ports of the stage cementing collar after the
second stage of cement slurry has heen expelled into the an-
nulus in the well bore.
A principal shortcoming of the system of the foregoing
10 prior patent is that, prior to conducting the second stage of
cementing, there is no provision for wiping the interior walls
of the casing string above the stage collar to remove adherent
cement slurry left thereon by the first stage of cement slurry.
The time that elapses between the first and second stages of
15 cementing may be such that the adherent cement slurry sets up
on the interior walls of the casing, thereby to interfere with
subsequent operations. Moreover, the first- and second-stage
cementing plugs are mounted in the casing string at widely
separated locations, which entails two plug-mounting steps.
20 ~lso, due to the narrowness of the bore of the string of drill
pipe, it is not practicable to drop a trip-plug therethrou~h to
open the stage collar.
The invention resides in a subsea well installation in-
cluding a composite well casing string suspended within a sub-
25 sea well bore from a casing hanger supported by a subsea wellhead, said composite well casing string being adapted to be
connected through running tool ~eans and a string o~ drill pipe
to hoisting and cementing equipment dispQsed adjacent to the
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surface of the sea above the well head; said composite well
casing string having first-stage cementing port means for
communicating the interior of said composite string with the
: exterior and adapted to be closed by a first-stage cementing
5 plug; and initially closed, but openable and closeable second-
stage cementing port means for communicating the interior
of said casing string with the exterior, said second-stage
cementing port means being disposed above said first-stage
cementing port means and below the top of said casing string
10 and adapted to be opened by a trip-plug and cloased by a shut-
off plug; a mandrel extending longitudinally into the well
casing string and providing a longitudinal passage in fluid
communication with the string of drill pipe- a shut-off plug
: in the well casing string and adapted to close said second-
15 stage cementing port means; first releasable means connecting
~: said shut-off plug to said mandrel; a trip-plug in the well
casing string and adapted to open said second stage cementing
~: port means; second releasable means connecting said trip-plug
directly to said shut-off plug; a first-stage cementing plug
20 in the well casing string and adapted to close said first-stage
cementing port means; third releasable means connecting said
first-stage cementing plug directly to said trip-plug, means
defining a passage through each plug for the flow of cementing
fluids from the longitudinal passage of the mandrel into the
25 well casing string; said first-stage cementing plug having
means copperative with a first closure member in said cementing
fluid to close the passage in said first-stage cementing plug
and effect release of said third releasable means responsive
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to cementing fluid pressure to launch said first~stage cement-
ing port means; said trip-plug having means cooperative with
a second closure member in said cementing fluid to close the
passage in said trip-plug to effect release of said second
5 releasable means res2onsive to cementing fluid pressure to
launch said trip-plug for travel down said casing string to
open said second-stage cementing port means; and said shut-off
plug having means cooperative with a third closure member in
said cementing fluid to close the passage in said shut-off
10 plug and effect release of said first releasable means re-
sponsive to cementing fluid pressure to launch said shut-off
plug for travel down said casing string to close said second-
stage cementing port means.
Other aims, features and advantages of the invention are
15 set forth in or will be apparent from the following detailed
description of preferred embodiments taken in connection with
the accompanying drawings.
In the drawings:
-; Fig. 1 is a vertical sectional view, partly in elevation,
20 of the uppermost part of a marine well, and showing a drilling
vessel afloat in the water above the well, important components
of the well installation, and exemplary components of cementing
equipment in accordance with the invention;
Fig. 2 is a vertical sectional View on a larger scale o~
25 a part of the well shown in Fig.l;
Figs. 3A, 3B and 3C are, respectively, views of an upPer
part, an intermediate part, and a lower part of the well of Fi~.
1, with certain components of the equip~ent of the in~ention
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installed therein preparatory to the introduction of cement
slurry;
Figs. 4A, 4B and 4C are, respectively, views similar to the
views of Figs. 3A, 3B and 3C, but subsequent to the placement
5 of the first stage of cement slurry,
Figs. 5A, 5B and 5C are, respectively, views similar to
those seen in Figs. 4A, 4B and 4C, but with the stage collar
conditioned Eor the placement of the second stage of cement
slurry;
Figs. 6A, 6B and 6C are, resepctively, views similar to
those of Figs. 5A, 5B and 5C, but subsequent to the placement
of the second stage of cement slurry;
Fig. 7 is an enlarged, quarter-sectional view of a plug
stack assembly in accordance with the invention;
Fig. 8 is an elevational view of actuators for the plugs
of the plug stack assembly of Fig. 7;
Fig. 9 is an axial sectional view, partly in elevation,
of a trip plug in accordance with the invention;
Fig. 10 is a longitudinal sectional view taken along the
20 line 10-10 of Fig. 11 of a crated plug stack assembly of the
invention, the plug stack being shown in elevation;
Fig. 11 is a sectional view taken along the line 11-11
of Fig. 10 and looking in the direction of the arrows, and
Fig. 12 is an axial sectional view of a swivel component
25 of the cementing equipment.
Referring to the drawings, particularly to Fig. 1, there
is shown a well 21 which has been drilled into the earth 22
beneath the sea 23 or other body of water. A subsea wellhead
- :
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4~
structure 23 is emplaced on the floor 25 of the sea at the
top of the well. Suspended in the well from the well head is
a string of well casing 2~ having inserted therein a plug
stack assembly 27, to be described in detail hereinafter. A
5 riser pipe 28 is connected to the wellhead by a quickly re-
leasable connector 29 and communicates with the casing string
through passages in the well head. The riser pipe extends up
through the water to a drilling ship or vessel 31 floating on
the surface 32 of the sea directly over the wellhead. The
10 riser pipe extends up through an opening or moonhole (not
shown) in the ship, and the top (not shown) of the riser pipe
is exposed above the waterline and within the vessel. A string
of drill pipe 33 extends within the riser pipe 28 upwardly
from the connector 29 and terminates at the top in an actuator
15 launching head 34 accessible from the deck 35 of the drilling
vessel. A bumper sub 36 is included in the string of drill
pipe to compensate for the heaving of the vessel due to wave
action. The drilling vessel is equipped with a derrick struc-
ture 37. Guide lines 38 extend between the vessel 31 and the
. .
20 wellhead structure 24. The riser pipe 28 may have a blowout
preventer stack (not shown) located above and closely adjacent
- t~ the quickly releasable connector 29.
Turning now to Fig. 2, it is seen that the wellhead
structure 24 generally includes an annular support member 39
25 wh~ch is affixed to the upper end of an outer casing 41 and
has vertically extending guide posts 42 slidably receiving
guide tubes 43 which are guided on the lines 38,pxeviously
described. The riser pipe 28 is secured to a wellhead body
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44 by the previously mentioned connector 29. This connector
is well-known and includes releasable latch dogs 45 shiftable
to inner positions to secure the connector 29 on the well-
head body 44 in response to movement of an annular latch pis-
5 ton 46 downwardly, the latch dogs 45 being releasable upon up-
ward movement of the latch piston 46. Piston chambers 47 and
48 are provided and are adapted to be pressurized through
respective conduits 49 and 51 to shift the piston upwardly and
downwardly, as desired. The riser pipe 28 is connected to the
10 quickly releasable connector 29 by fasteners 52.
A universal running tool 53 is threadedly connected to
the lower end of the drill string 33, and a casing hanger body
54 is threaded to the running tool. The well casing string
26 is threadedly fastened to the bottom of the casing hanger
15 body 54. The casing string 26 is run into the well on the
drill pipe string 33 until the casing hanger body 54 lands
upon a casing hanger 55 supported by the wellhead body 44.
Grooves 56 are provided in the casing hanger 55 to allow cir-
culation of fluids from the annulus 57 below the casing hanger
20 body 54 into the riser pipe 28 thereabove.
~ The wellhead structure described hereinbe~ore 1s~cQnyen~
-~ tlonal and needs no further deta~led description herein.
As best seen if Fig. 2, a plug launching mandrel 58 de-
pends from the universal running tool 53. This ~andrel has an
25 upper mandrel section 59 connected to the running tool by
threads 61. At its lower end, the mandrel section 59 connects
with a swivel, designated b~ the general reference numeral 62,
to be described in detail hereinafter with reference to Fig. 12.
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A lower mandrel section 63 extends downwardly from the swivel
62 and is connected at its bottom end to a shut-off plug 64.
A surge chamber 65, also to be described hereinafter, surrounds
the lower mandrel section 63 between the shut-off plug 64 and
the swivel 62. At the bottom of the shut-off plug there is
5 connected a trip plug 66, which, in turn, carries a first-
stage cementing plug 67. These three pluas will be described
more fully hereinafter, but it is here remarked that these
plugs are received within the top portion of the well casing
string 26.
~eferring to Fig. 12, the s~ivel 62 connects the upper
mandrel section 59 to the lower mandrel section 63 to permit
relative rotation o.f the two sections about their common longi-
tudinal axis, so that the universal running tool 53 can be
screwed into the casing hanger body 54 without rotating the
15 plugs 64,66 and 67 in the casing string 26. For this purpose,
the uppoer mandrel section 59 has a lower cylindrical end 68
rotatably received within an upwardly extended end 69 of the
lower mandrel section 63. Suitable seal means 71 may be pro-
vided between the mandrel section ends 68 and 69. The swivel
.. ~ 20 means further includes outturned flanges 72 and 73 on the re-
spective mandrel sections 59 and 63, these flanges being held
together for relative rotation by a split, channeled ring 7~,
which is retained in place by a collar 75 held in place by a ~ : -
. snap ring 76.
The surge chamber 65 ~s shown In CrOsS se.ction in ~ig. 3A,
to which reference is now made. The surge chambe.r ha~s. an upper
head 77 that is threaded to the lower mandrel section 63 by
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--11--
thread means 78. An O-ring seal 79 provides a static seal
between the upper head 77 and the lower mandrel section 63.
A cylindrical body portion 81 is welded at ~2 to the upper
head 77. A lower head 83 is welded at 84 to the bottom of
5 the body portion 81 and is sealed to the lower mandrel section
63 by another O-ring seal 85. The upper and lower heads and
the cylindrical body portion cooperate with the lower mandrel
section to provide an annular space 86. This annular space
is in fluid ocmmunication through ports 87 with the bore 88
10 of the lower mandrel section. The ports slope downwardly and
inwardly and are located at the bottom of the annular space
86 to permit liquid to drain from the annular space into the
bore of the lower mandrel section.
~he bottom of the lower mandrel section 63 has exterior
15 threads 89 to which a bushing 91 is secured by mating interior
threads. An O-ring seal 92 seals the bushing to the lower
mandrel section.
As best seen in Figs. 3A and 7,'the shut-off plug 64,
previously referred to, has an inner body 93 with an upstanding
20 bell 94 of enlarged diameter that surrounds the bushing 91 and
has a sliding fit therewith. The bell is releasably secured
to the bushing by circumferentially arranged shear pins 95 and
is sealed to the bushing by an Q-ring 96. A seri,es, of l~ngi-
tudinally spaced, rubber cups 97 is ~ounted on the central part
25 98 of the inner body 93. The cups have upwardly and out~ardly
sloped flanges 99 that yieldingly engage the inner wall of
the well casing 26. Retainer rings 101 hold the cups and space
them along the central part of the body. The uppermost cup 97
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10~4~3
-12-
is retained in an annular T-slot provided between the bell 94
and the upper ring 101; the middle cup is held in an annular
T-slot provided between the upper and lower retainer rings;
and the bottommost cup is held in an annular T-slot provided
5 between the lower retainer ring and a nose piece 102. The
nose piece is fastened by threads 103 to the bottom of the
inner body 93 of the shut-off plug 64, an O-ring 104 being
provided to seal the nose piece to the inner body. The nose
piece is fitted with a downwardly tapering, rubber sealing
10 rings 105, the purpose of which will be set forth hereinafter.
It will be seen that the inner body 93 provides an axial passage
106 that communicates with the bore 88 of the lower mandrel
section.
The trip-plug 66, previously referred to and shown to
15 advantage in Figs. 3A and 7, has a body portion 107 with
an upstanding bell 108 of larger diameter and a depending nose
portion 109 of smaller diameter. The bell 108 slidably engages
a reduced diameter portion 111 of the nose piece 102 of the
superjacent shut-off plug 64, and is releasably attached thereto
20 by circumferentially arranged shear pins 112. The bell 108 is
sealed to the reduced diameter portion by an O-ring 113. A
downwardly tapered sealing ring 114 is mounted on the bell 108
of the trip-plug. The body portion 107 has relatively thick
walls that are spaced radially inwardly from the bore of the
25 casing 26 and that provide a central liquid flo~ passage 115
communicating with the passa~e la6 in the shut-Qff plug immedi-
ately thereabove.
The first-stage ce~enting plug 67, previously mentioned
. .
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106i~14~
-13-
and now described with reference to Figs. 3A and 7, is re-
leasably suspended from the trip-plug 66. The first-stage
cementing plug has an inner body 116 with an upstanding bell
117 of enlarged diameter. The bell 117 is slidably fitted on
5 the nose portion lO9 of the superjacent trip-plug 66 and is
releasably secured thereto by a circular row of shear pins llO.
An O-ring 100 seals the bell 117 to the nose portion 109.
Threaded at 118 to the bottom of the inner body 116 is a nose
piece ll9 having an axial opening 121 therethrough. The axial
10 opening 121 communicates fluidically w;th a bore 122 in the
inner body 116, which, in turn, is in fluid communication with
the passage 115 in the trip-plug. A plurality, specifically
three, elastomeric cups 123a, 123b and 123c are mounted on the
inner body 116 of the first-stage cementing plug. The cups
15 have upwardly and outwardly sloped ~langes 124 that are in
` flex'ble engagement with the inner wall of the casing 26. Cup
123a is mounted in an annular T-slot provided between retainer
rings 125a and 125b. Cup 123b is similarly mounted between
retainer rings 125b and 125c. In like fashion, cup 123c is
20 mounted between retainer rings 125c and 125d. A rubber flange
number 126 is mounted between the retainer ring 125d and the
~ nose piece 119, which is threaded to the inner body 116 and
- which secures the retainer rings and the elastomeric cups upon
the inner body.
As best seen in Fig. 3B, a stage cementing collar, desig-
nated by the general reference numeral 127, is located in the
casing string 26 below the plug stac~ assembly 27 and at a
depth where it is desired to introduce the second stage of
- - - - . , . ~.
.
48
-14-
cement slurry into the annulus 57 between the casing and
the wall of the well 21. The stage cementing collar has a
tubular body 128, the upper, internal end o:f which has tapered
threads 129 engaged with mating threads 131 on the exterior
5 of the casing 26. The bottom of the boay 127 has tapered,
external threads 132 that are threaded into the mating threads
133 of a casing collar 134. The casing collar is threadedly
coupled at 135 to a lower extension of the casing string 26.
Thus, the body 128 of the casing collar provides, in effect,
10 a continuous joint of the casing string. An outer sleeve
136 is secured to the body 128 by threads 137~ and is sealed
to the body by an O-ring 138. Stage cementing ports 139 are
provided in the body 128, and ports 141 are provided in the
outer sleeve 136 and arranged in alignment with ports 139.
The body 128 has a central portion 142 of reduced outer
: diameter that provides with the outer sleeve 136 an annular
cylindrical chamber 143. It is seen that the O-ring 138,
previously mentioned, is above the chamber 143 and thus seals
the top of the chamber against leakage between the threads
20 137. Openings 144 extend fromthe top of the cha~ber 143 in-
wardly through the central portion 142 of the body 128. The
lower part of the annular chamber 143 is enlarged to form an
annular chamber portion 145. A port 146 in the outer sleeye
136 communicates the annular chamber portion 145 with the well-
25 casing annulus 57.
Slidably disposed within the annular cylindrical chamber
143 and above the ports 139, 141, is a shut-ofg sleeve 147.
Shear pins 148, circumferentially disposed, releasably secure
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-15-
the shut-off sleeve to the central portion 142 oE the body 128.
An O-ring 149 is floatingly disposed in the annular cylindrical
chamber 143 and on top of the shut-off sleeve 147 to provide a
seal between the shut-off sleeve and the walls of the annular
5 chamber. Ratch notches 151 are circumscribed on the outer
periphery of the central portion 142 of the body. A split
detent ring 152, received in a circumferential groove 153 on
the inner periphery of the shut-off sleeve 147, is adapted
to spring into engagement with one of the ratch notches 151
10 when the shut-off sleeve is in a lower position, thereby to
hold the shut-off sleeve in said lower position.
Just below the ports 139, an O-ring 154 is positioned
in a circumferential groove in the outer surface of the
central portion 142 of the body. This O-ring is retained in
15 its groove by a surrounding O-ring retainer sleeve 155 re-
leasably fastened to the central portion 142 by shear pins 156.
The shut~off sleeve has an annular tapered counterbore 157
provided in its bottom portion, for a purpose which will be
explained hereinafter.
20 Slidably mounted within the central portion 142 of the body
128 is lower or port opening sleeve 158. This sleeve is re-
leasably held by shear pins 159 in a position to close the ports
139. This lower sleeve has circumferential O-rings 161 and 162
~ positioned, respectively, above and below the ports 139 to seal
- 25 the sleeve to the central portion 142 above and below the ports.
A tapered stop member 163 is provided adjacent to the bottom of
the lower sleeve 158. This stop member is adapted to abut the
upper/ stepped surface 164 of a split stop ring 165 when the
. .
. .
. -: ,
10~
-16-
lower sleeve 158 moves downwardly, thereby to limit such down-
ward movement. The stop ring 165 is received in a groove 166
in the bore of the body 128. The bore 167 of the lower sleeve
is circumscribed at the top by a chamfer 168 which forms a
5 seat for an actuator or trip-plug, which will be described
hereinafter.
Immediately superjacent to the lower sleeve 158 an upper
or port-closing sleeve 169 is slidably mounted in the body 128.
This sleeve carries an O-ring 171 in a groove around its outer
10 surface for sealing the sleeve to the bore of the body. The
upper sleeve is releasably pinned to the bore of the body
128 by shear pins 172, and, when the shear pins are broken,
is adapted to slide downwardly in the bore of the body. A cham-
fer 173 circumscribes the top of the vertical passage 174
15 through the upper sleeve, this chamfer forming a seat for an
actuator or shut-off plug, to be described hereinafter.
It will be seen from Fig. 3B that the diameter of the
seat or chamfer 168 on the lower sleeve 158 is greater than
the diameter of the bore 167 of the lower sleeve, yet less than
2a the diameter of the vertical passage 174 through the upper
i sleeve 169, which, in turn, has a diameter less than the seat
or chamfer 173 of the upper sleeve. The reasons for these
diametral relationships will be set forth hereinafter.
As will be seen from Figs. 3B and 3C, the casing 26 ex-
25 tends downwardly in the well 21 to a cement float collar 175.This float collar is conventional. It has a tubular body 176
- threaded at 177 to the casing 26, and at 178 to a casing
coupling 179.
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A block of concrete 181 is cast within the body 176 and about
a cage 182 to support the cage centrally of the body. The
cage has an upper fluid passageway 183 having a valve seat
184 at its lower end. The passageway 183 communicates fluidi-
5 cally with the casing 26 thereabove through a duct 185 pro-
vided in the cement block. The cage has a fluid passage 186 at
the bottom. A plurality of upstanding arcuately spaced ribs
187 is provided at the bottom of the cage, and a ball valve
188 is seen, in Fig. 3, resting on the ribs. Fluid may flow
10 downwardly throught the float collar 175, passing through the
passages 185, 183 and 186, and flowing past the ball valve
188 throught the spaces between the ribs 187. Upward flow of
fluid throught the float collar will be stopped by the seating
of the valve ball 188 on the valve seat 184 (see Fig. 4C).
Referring further to Fig. 3C, a length of casing 26 is
threaded at 189 into the casing collar 179, previously referred
to, and extends to a depth near the bottom 191 of the well 21.
~` A cement float show 192 is secured to the bottom of the casing
26 by a threaded connection 193. This float shoe is similar in
20 construction and operation to the float collar 175 described
in the immediately preceding paragraph. From a consideration of
Fig. 3C taken with the foregoing description,it will be ap~
arent that fluid can flow down through the float show 192 and
out into the well bore, but that return flow from the well bore
25 up through the float shoe into the casing will be prevented
by the seating of the ball valve 194 on the valve seat 195.
Turnin~ now to Fig. 7, the plug stack assembly 27 is seen
in quarter section. In this view, the rubber flanges 99 and
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106~:14~3
-18-
124 of the shut-off plug 64 and the first-stage cementing plug
67, respectively, are shown in their unflexed condition. It
will also be seen that the trip-plug 66 is provided with cir-
cumferentially spaced, longitudinal grooves 196 on the outer
5 surface of the body portion 107 which facilitate the fall of
this plug through a column of liquid in the well casing 26.
As seen in Fig. 7, the plug stack assembly 27 is fitted
with a discoid assembly plate 197 overlying the bushing 91 and
the bell 94 of the shut-off plug 64. The assembly plate has
10 a central hold 198 through which a tie rod 199 extends. The
end 201 of the tie rod is threaded and fitted with a comple-
mentary threaded nut 202. Another discoid assembly plate 203
is disposed at the other ena of the plug stack assembly in a-
butting relation to the free end o the nose piece 119. The
15 assembly plate 203 has a central hole 204 through which the
other end 205 of the tie rod 199 projects, such other end being
threaded and fitted with a nut 206.
The plug stack assembly may be put together in the fol-
lowing manner. The plugs 64, 66 and 67 and the bushing 91
20 initially do not have holes for the shear pins 95, 112 and 110.
The bushing 91 with its O-ring 96 is fitted into the bell
portion 94 of the shut-off plug 64. The reduced diameter por-
t~on 111 of the shut-off plug 64 with its O-ring 113 is inserted
into the bell 108 o~ the trip-plug 66, with the annular surface
25 207 on the shut-off plu~ in abutment with the cooperating an-
nular sur~ace 208 on the trip-plug. Then, the nose portion
109 of the trip-plug 66, ~ith its O-rin~ 100 is inserted into
the bell 117 of the first-st~ge ce~enting plug 67. The coop-
~.. . .. ...
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:, , .,, ,:,: . : ., ,,:, .: , .. :: ' . : ' : :,.:, :., .. . : .
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--19--
erating annular surfaces 209 on the trip-plug and 211 on
the first-stage cementing plug 67 are placed in abutting
relation. Thereafter, the tie rod 199 is disposed through the
assembly of plugs, the assembly plates 197 and 203 are placed
5 on the tie rod, and the nuts 202 and 206 are threaded on
the ends of the tie rod and tightened to hold the assembly to-
gether. Thereafter, the holes for the shear pins 95, 112
and 110 are drilled, and the shear pins inserted in the re-
spective holes.
As shown in Figs. 10 and 11, the completed plug stack
assembly 27, for purposes of storage or shipment, is packed
in a crate designated by the general reference numeral 212.
The crate has a lower half 213 and an upper half 214. Only
the lower half need be described, as the upper half is iden-
15 tical to it. The lower half has an elongated rectangularbottom panel 215 and two opposed upstanding side panels 216
and 217, integral with suitably joined to the bottom panel.
End panels 218 and 219 are provided for the lower half of the
crate. A spacer 221 is located in the left end of the lower
20 half of the crate, as seen in Fig. 10. This spacer abuts
the assembly plate 197 of the plug stack assembly, and prevents
the latter from moving to the left. A notch 222 i5 cut in the
spacer to accommodate the end of the tie rod 199 and the nut
202. A similar spacer or end support member 223 is provided
25 at the right-hand end of the lower half of the crate to contact
the assembly plate 203 and prevent the stack assembly from
moving to the right. A notch 224 is provided in the space~
to receive the end of the tie rod and the nut 206,
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-20-
A central bulkhead 225 is mounted between the bottom
panel 215 and the side panels 216 and 127. This bulkhead
has a semicircular notch 226 contoured to the trip-plug 66
to cradle the latter. A similar bulkhead 227 supports the
5 bell 94 of the shut-off plug 64. In like fashion, another
bulkhead 228 is arranged to support the first-stage cementing
plug 67.
The upper half 214 of the crate is placed on the lower
half 213, as seen in Fig. 11, and a number of steel bands
10 229a, 229b,229c and 229d are passed about the crate, tight-
ened, and fastened by buckles 231a, 231b, 231c and 231d.
It will be understood that the tie rod means holds the
plus stack in compression and keeps the shear pins substant-
ially free from stresses. The crate 212, with its bulkheads
15 and spacers, supports the plug stack assembly in a manner to
~ prevent bending and longitudinal shifting of the plug stack
- assembly, thereby further protecting the shear pins from
damage. It will also be understood that the tie rod means is
removed from the plug stack assembly before the assembly is
20 fitted to the lower section 63 of the plug launching mandrel
in preparation for a stage cementing operation.
Actuators or plug closure devices for the se~eral plugs
of the plug stack assembly 27 are illustrated ;n Fig. 8 ! to
which reference is now made. The actuator for the first-
25 stage cementing plug 67 is deslgnated by the general refer~ence numeral 232, that for the trip-plug 66 by the general
reference numeral 233 and that for the shut-off plu~ 64 by the
general reference numeral 234.
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-21-
The actuator 232 is shown in side elevation in Fig. 8
and takes the form of a dart. In Fig. 4C, the dart is shown
in longitudinal section and seated in the bore of the first-
stage cementing lug 67. The dart has a metal body 235,
5 preferably formed of an easily drillable metal such as alumi-
num or magnesium alloy. The body has a shank 236. a flange
237 adapted to enter the bore 122 of the plug 67 and to be-
come seated upon a seat 238 provided in the bore 122, and a
nose portion 239 adapted to be received with a close sliding
10 fit in a reduced diameter section 241 of the bore to main-
tain the dart aligned with the plug 67 when the dart seated.
A unitary, elastomeric outer portion 242 is bonded to the
shank 236 . The outer portion has a forward wiper cup 243
adjacent to the flange 237 and a rear wiper cup 244 at the
15 back. Intermediate the wiper cups 243 and 244 is a seal
cup 245 having a substantially smaller diameter than the
wiper cups. The wiper cups and the seal cup extend outwardly
and rearwardly from a longitudinal portion 246 of the elasto-
- meric outer portion 242.
- 20 The wiper cups have equal diameters so~ewhat larger
than the inside diameter of the drill pipe string 33 and are
adapted to form a good running seal w~i,th the inner w~ll$ of
the drill pipe string and to wipe these inner w,all,s when
pumped down the drill pipe string as de$cribed hereinafter.
25 These wiper cups will also enable the dart to be p~m,ped
through the bores of the uni~ersal running tool 53, the mandrel
~, sections 59 and 63, and the plugs 64 and 66 and to wipe these
bores. When the dart is seated in the first-stage cementing
~:
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plug 67, the bore 122 of which has a smaller diameter than
the bore of the drill pipe string 33, the wiper cups are folded
back to such an extent that they become fluted like a folded
umbrella and do not provide a very e~fective seal with the
5 bore 122 of the first-stage cementing plug. The seal cup 245
has a diameter somewhat greater than the diameter of the bore
122, and is adapted to be slightly compressed in the bore
without being distorted sufficiently to become fluted; in
this way the seal cup 245 forms an effective seal with the
10 bore 122. As seen in Fig. 4C, the seal cup 245 is spaced
rearwardly from the root of the forward wiper cups 243 far
enough to allow the forward wiper cup to collapse into the
- longitudinal rubber portion 246 without substantially over-
lapping the seal cup 245 and without breaking the seal be-
15 tween the latter and the bore 122. As exemplary of the di-
mensions involved: where the inside diameter of the drill
pipe 33 is 3-5/8 inches and the inside diameter of the bore
122 of the first-stage cementing plug is 2 inches, the outside
diameter of the wiper cups 243 and 244 may be 4-3/4 inches and
20 the outside diameter of the seal cup 245 may be 2-1/4 inches.
The actuator 233 for the trip-plug 66 and its manner of
cooperation with the trip plug will be described with reference
to Figs. 8, 9 and 4A. Referring particularly to Fig. 9, the
trip-plug 66 is shown prior to the drilling therein of holes
- 25 for the shear pins 110 and 112, previously mentioned. The
body portion 107 is tubular and is adapted to receive the
actuator 233 within its bore, as shown in Fig. 4A. The act-
uator has a head 247, a shank 248, a downwardly tapering portion
:
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- - :
1~)6i~14~
-23-
249, and a truncated conical nose 251. The shank 248 is pro-
vided with an annular sealing ring groove 252 of L-shaped
cross section. The upright portion 253 of the groove tapers
downwardly to meet the deeper cut horizontal portion 254 of
5 the groove. A rubber or elastomeric sealing ring 255, of
conforming L-shaped cross section is disposed within the
groove 252. The bottom 256 of the sealing ring has the same
outside diameter as the shank 248, and it flares upwardly and
outwardly to form a shoulder 257 that extends outwardly from
10 the shank. At the bottom of the head 247, there is provided
a shoulder 258 that tapers inwardly to intersect the shank 248.
The bore of the trip-plug 66 has a reduced diameter sec-
tion 259a, 259b adapted to slidingly receive the shank 248
of the actuator 233 and to align the actuator with the bore
15 of the trip plug. Within the reduced diameter section is
provided a downwardly tapering groove 261 having a downwardly
facing shoulder 262 at the top. A counterbore 253 is pro-
vided above the reduced diameter section 259a and an upwardly
facing, tapered shoulder 264 is formed between the counter-
20 bore and the reduced diameter section 259a. The bore of thetrip plug has an enlarged cylindrical section 265 extending
; from the reduced diameter section 259b to the bottom of the
plug. When the actuator 233 is inserted into the bore of the
trip-plug 66 from the top, as seen in Fig. 4A, the head 247
25 is received in the counterbore 263 with the shoulder 258 a-
butting the shoulder 264 to stop downward movement of the ac-
tuator. The rubber sealin~ ring 255 is received In the tapered
- groove 261 to seal thereagainst while the shoulder 257 at the
.
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top of the sealing ring underlies the shoulder 262 at the top
of the groove to retain the actuator in the bore of the plug
so that it cannot be removed upwardly. The tapered portions
249 and 251 of the actuator project into the cylindrical
5 section 265 of the bore.
The trip-plug 66 and the actuator 233 may be made of cast
iton, which has a relatively high specific gravity,yet is read-
ily drillable. The high specific gravity of the actuator
233 enables it to fall reasonably rapidly through liquid in
10 the drill pipe string, and the high speciflc gravity of the
combined trip-plu~ and actuator provide a rapid rate of fall
through liquid in the casing, as will be described hereinafter.
The easy drillability of the trip-plug and its actuator make
; it easy to remove these elements by drilling them from the
15 casing following the cementing operation.
The actuator or closure member 234 for the shut-off plug
64 is shown in side elevation in Fig. 8 and in longitudinal
cross section in Fig. 6B. The actuator has a body 266 of
an easily drillable metal, such as magnesium alloy. The body
20 has a shank 267 and a nose portion 268, slidably received in
the axial passage 106 of the shut off plug 64. A flange 269 on
the body has a downwardly facing shoulder 271 that abuts a
a shoulder 272 in the axial pas$age 106 to limit downward move~
ment of the actuator. A rubber or elastomeric cup assembly
25 273 is molded about and bonded to the shank 267 and the upper
surface of the flange 269. Upwardly and outwardly flaring cups -
274a, 274b and 274c are provided, these being of a diameter
adequate to wipe the interior of the drill pipe string 33 as it
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-25-
is pumped downward therein, and adequate to seal the axial
passage 106 of the shut-off plug 64 when it has come to rest
therein, as seen in Fig. 6B.
Referring to Fig. 2, the actuator launching head 34 has an
5 elongated cylindrical chamber 275 that communicates downwardly
with the bore of the drill pipe string 33. An easily re-
movable cap 276 is threaded on the top of the head. A pipe
fitting 277 is provided in the side of the launching head
and is connectible to a pumping system (not shown) for pump-
10 ing various fluids into the head and down the drill pipestring. An actuator, such as the actuator 232 is introduced
into the top of the chamber 275 with the cap 276 removed, the
cap then being replaced. The actuator is releasably retained
in place by a pin detent 278 slidable in a cylinder 279 and
15 retractable by a handle 281 to release the actuator to permit
it to drop into the liquid in the chamber 275. Any suitable
launching head may be used, such as the one that accommodates
three-plug actuators at one time.
The o~eration of the stage cement~ng equi,pment o~ the in-
20 vention will now be described. The equipment is assembledand positioned in the well as shown in Figs. 1, 2, 3A, 3B and
-~ and 3C.
The li~uid pumping system is connected to the pipe fitting
277, and the well may be conditioned for cementing as by pump-
25 ing a clear conditioning fluid down the drill pipe string andplug stack assembly, down the casing string, out through the
float shoe and up the annulus and riser pipe to flush drilling
mud from the well.
.
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-26-
Next, a first stage of cement slurry, the volume of which
has been calculated to fill the well annulus from the bot-
tom of the hole to a level just below the stage cementer ports
139, 141 is pumped down the drill pipe casing followed by
5 displacing fluid which may be water. As the tail end of
the first stage of cement slurry passes through the actuator
launching head 34, the latch 278 is retracted to release the
actuator dart 232 which, being driven by the displacing fluid
behind it, follows the first stage of cement slurry down the
10 string of drill pipe 33, and, as it travels, wiping the inner
walls of the drill pipe free from cement slurry. The actuator
or dart 232 is of such a size that it passes through the
opening in the universal running tool, through the mandrel
58, through the axial passage 106 in the shut-off plug 64,
15 through the passage 115 of the trip-plug, and seats on the
seat 238 in the bore 122 of the first-stage cementing plug
to close the bore therethrough, as previously descrîbed. The
pressure pulse induced in the displacing fluid behind the
actuator 232 when it suddenly seats is cushioned by the compre-
20 ssion of air in the surge chamber 65, so that the first-stage
cementing plug is not jarred loose from the trip-plug 66. The
pump pressure on the displacing liquid is increased to a value
at which the shear pins 110 are sheared to release the first-
stage cementing plug from the trip-plug. The trip-plug with
25 its actuator are displaced down the casing string by the fur-
ther pumping of displacing fluid until the first-stage cement-
ing plug comes to rest on the float collar 175, as seen in
Fig. 4C. In this portion, the flange member 126 of the first-
. .
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, . . ..
6~l4~
stage cementing plug seals against the top surface 282 of thefloat collar. This causes an increase in pump pressure,
which indicates that the first stage of cement slurry 283 has
been displaced into the well annulus, as seen in Figs. 4C and
5 4B. The rubber flanges 124 of the first-stage cementing
plug in moving down the casing string will have wiped the
bore of the casing string clear of cement slurry. The pumps
may now be stopped, whereupon the ball valves 188 and 194
will be moved into contact with their respective seats 184
10 and 195 to prevent any appreciable reverse flow of cement
slurry from the well annulus back into the casing string,
and to maintain the first-stage of cement slurry in position
in the annulus until it sets.
- A second stage of cement slurry may then be emplaced in
15 the well annulus above the first-stage of cement. It is
- first necessary to open the stage cementing ports 139, 141
from the closed condition, as shown in Figs. 3B and 4B, and
to plug the bore of the casing below these ports. To ac-
complish this, the trip-plug actuator or trip-plug bar 233 is
20 dropped through the actuator launching head 34 into the column
of displacing fluid in the drill pipe string and the casing.
The bar gravitates through the static column of displacing
'! fluid in the drill pipe string, down through the axial passage
106 of the shut-off plug 64, and into the passage 115 of the
25 trip-plug 66. Pump pressure is then applied to the displacing
liquid to seat the trip-plug bar in the trip-plug with the
shoulder 258 of the head 247 abutting the shoulder 264 in the
trip-plug and the sealing ring 255 i`~n ~ealing relat~n to the
'
,. . . . . .
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-28-
downwardly tapering groobe 261, as previously described, to
thereby close the passage 115. Pump pressure is increased
sufficiently to break the shear pins 112 and release the
trip-plug 66 with its actuator 233 from the shut-off plug 64,
5 as shown in Fig. 4A.
; When the trip-plug and its actuator have been launched,
as aEoresaid, the pumps are stopped, and the trip-plug and
its actuator are permitted to fall as a unit through the dis-
placing fluid in the casing string into the lower sleeve 158
10 of the stage cementing collar 127; see Fig. 5B. The trip-
plug is stopped inthe lower sleeve when the tapered sealing
ring 114 of the trip-plug is received on the chamfered surface
168 or seat at the top of the lower sleeve, thereby closing the
bore 167 through the lower sleeve. Pump pressure is applied
15 to the displacing fluid to breakdthe shear pins 159 and allow
~- the lower sleeve to move down to the position shown in Fig. 5s
to open the stage cementing ports 139 and 141. ~1hen the ports
have been opened, the pumps are stopped.
; The required volume of a second stage of cement slurry is
20 now pumped into the actuator launching head 34 through the
- fitting 277, followed by a second stage of displacing fluid,
~ which may be water. The actuator 234 for the shut-off plug 64,
- the actuator previously having been loaded into the actuator
launching head, is released into the interface between the
25 second stage of cement slurry and the second stage of displa-
cing fluid which follows it. Pumping is continued to drive the
actuator 234 down the drill pipe string 33, through the passage
284 in the universal launching tool 53, down through the mandrel
, .
: ~. . . . , ~ ................. . . . . .
. . .
; . .. . . . .:
06;~48
-29-
58 and into the axial passage 106 of the shut-off plug 64.
The actuator 234 lands on the shoulder 272 in the passage 1~6
of the shut-off plug, thereby closing the passage. The shock
pulse setup in the second stage of displacing fluid when the
5 actuator seats on the shoulder 272 is cushioned in the surge
chamber 65. Pump pressure is increased to break the shear
pins 95 and separate the shut-off plug 64 from the bushing
91, which remains attached to the lower mandrel section 63,
as seen in Fig. 6A.
The shut-off plug actuator 234,as it is pumped down the
drill pn~pe string 33, separates the second displacement fluid
from the second stage of cement slurry. This actuator also
wipes the interior walls of the drill pipe string to remove
cement slurry therefrom.
After the shut-off plug 64 with its actuator have been
launched from the mandrel 58, pumping is continued to drive
the second stage of cement slurry 285 down the casing and out
through the ports 139 , 141 in the stage cementing collar
and into the well-casing annulus 57 above the first stage
20 cement 283. The shut-off plug acts as a piston which is
moved by the second displacement fluid and which drives the
- second stage of cement slurry ahead of it. In moving down
the casingl the rubber cups 97 of the shut-off plug wipe the
interior walls of the casing. Fluid is returned to the sur-
25 face from the annulus 21 through the grooves 56 in the universal
running tool 53 and through the riser pipe 28.
When the shut off plug reaches the stage cementing collar
127, the second stage of cement slurry will have been emplaced
- - . . - .. .. ~ . ~ ... . - - - .
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- . - . .. .: , . : ,
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.. .... :. .. : . . . . . . . .
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-30-
in the annulus 57. The shut-off plug then functions the
upper sleeve to close the cementing ports 139,141.
These ports are shown in the open position in Fig. 5B and in
the closed position in Fig. 6s. The shut-off plug lands in
5 the upper sleeve 169 of the stage cementing collar, the sealing
ring 105 of the shut-off plug sealing against the chamfer
173 of the sleeve. Pump pressure is increased to shear the
shear pins 172 and move the upper sleeve downward to abut the
lower sleeve 158 and close the ports 139,141,as seen in Fig. 6B.
A further increase in pump pressure moves the shut-off
sleeve 147 from the position shown in Fig. 5B down to the
position shown in Fig. 6s to permanently close the ports 139,
141 so that they will remain closed after the bore of the
stage cementing collar has been drilled out. This is effected
15 by increasing the pump pressure so that the hydraulic pressure
in the annular cylindrical chamber 143 produces a downward
force on the shut-off sleeve sufficient to break the shear
pins 148 and alllow the shut-off sleeve to be moved to its
lower position as seen in Fig. 6B. In moving downwardly, the
20 shut-off sleeve contacts the retainer sleeve 155, breaking the
shear pins 156, and moving the retainer sleeve from its Fig. 5B
position to its Fig. 6B position. The O-ring 154 is thereby
uncovered and immediately thereafter is covered by the shut-off
sleeve to seal the latter to the central portion 142 of the
25 stage cementing collar 127. The counterbore 157 in the bottom
of the shut-off sleeve enables the shut-off sleeve to easily
ride over and seal against the O-ring 154. The shut-off
sleeve is held in its port-closing position by engagement of
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14~
-31-
the split detent ring 152 in one of the ratch notches 151.
When the ports 139,141 have been closed, the second
stage of cement is allowed to set in the annulus 57. The
universal running tool 53 and drill pipe string 33 are un-
5 screwed from the casing hanger body 54 and retrieved throughthe riser pipe 28. Thereafter, the stage cementing collar
127, the cement float collar 175, and the cement float shoe
192 may be drilled through, and futher operations conducted
in the well.
It will be understood that the shear pins 110 releasably
retaining the first-stage cementing plug 67 on the trip-plug
are designed to part and release the first-stage cementing
plug in response to a force substantially less than the force
needed to part the shear pins 112 and effect launching of the
15 trip-plug 66. In turn, the force required to break the shear
pins 112 is substantially less than that which is effective
to part the shear pins 95 that releasably retain the shut-off
plug 64 on bhe bushi~g 91. Accordingly, the first-stage ce-
; menting plug 67 can be launched without breaking the shear
20 pins 112 and 95. Then, the trip-plug 66 can be launched
without breaking the shear pins 95. Thereafter, the shut-off
plug can be launched.
Releasable devices other than shear pins may be employed
for releasably mounting one or more of the plugs in the plug
25 stack assembly 27. For example, and without limitation
thereto, a double collet release mechanism, such as that
disclosed in U.S. Patent 3,915,226, issued October 28, 1975,
could be used in lieu of shear pins.
.
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-32-
Moreover, actuators or closure members, other than those
shown in Fig. 8, may be substituted for the actuators speci-
fically disclosed. Actuators, such as solid or elastomeric
balls, may be employed to advantage.
It is generally advantageous to use a drop bar or gravity
type actuator, such as the drop bar 233, to launch the trip-
plug, because the drop bar can be used long after the first
stage of cement has been emplaced in the annulus. However,
a dart or other pum~-down closure member may be used instead
10 of the drop bar to launch the trip-plug, provided it is
timed to land in and launch the trip-plug just before the
first-stage cementing plug closes the opening 185 in the
float collar 175.
~ Although the present invention is partiaularly adapted
- 15 for stage cementing marine wells, it may also be used for
stage cementing land based wells.
.
.
:'
.
