Note: Descriptions are shown in the official language in which they were submitted.
CA 02223517 2003-06-12
MILL GUIDE AND ANCHOR ASSEMBLY FOR
SU~i~'ERRANEAN WELL CASINGS
BACKGROUND OF THE INVENTION
The present inventYion generally relates to the art of
completing subterranean wells and, in a preferred embodiment
thereof, more :particul,rrly relates to apparatus and methods for
milling a side wall ~,vz.ndow in a parent wellbore casing in
preparation fair subseq~.iently extending a lateral wellbore from
the parent wel7_bore _
It is well known in the art of dril.Ling subterranean wells
to form a parent bore into the earth and then to form one or
more bores extending laterally therefrom. Generally, the
parent bore is first cased and cemented, and then a tool known
as a whipstock. is positioned in the parent bore casing atop an
anchor structure locked into place in the parent wellbore
casing. The whipstock is specially configured to deflect a
drill bit in a desired direction for forming a lateral bore.
The drill bit is then :L.owered into the parent bore suspended
from drill pip<~ and i:- radially outwardly deflected by the
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whipstock to drill a window in the parent bore casing and
cement. Directional drilling techniques may then be employed
to direct further drilling of the lateral bore as desired.
The lateral bore is then cased by inserting a tubular
liner from the parent bore, through the window previously cut
in the parent bore casing and cement, and then into the lateral
bore. In a typical lateral bore casing operation, the liner
extends somewhat upwardly into the parent bore casing and
through the window when the casing operation is finished. In
this way, an overlap is achieved wherein the lateral bore liner
is received in the parent bore casing above the window.
Several whipstock/anchor structures have been previously
proposed for use in cutting the side wall window in the parent
wellbore casing to facilitate the subsequent addition of a
lateral wellbore thereto. Each of these structures, however,
has one or more disadvantages which make its use inconvenient
or uneconomical. Some of these disadvantages include
inaccurate positioning and orienting of the window opening to
be cut, complexity in setting and releasing portions of the
window forming apparatus, undesirable torque-created rotational
shifting of the apparatus, and danger of leaving portions of
the apparatus in the well necessitating a subsequent fishing
operation.
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From the foregoing it can be seen that it would be quite
desirable to provide improved apparatus and methods for forming
a side wall window opening in a parent wellbore casing which
are convenient and economical to use, which provide accurate
positioning and orienting of the opening to be cut, which have
setting and release reliability, are not complex from setting
and release standpoints, and which reduce the danger of leaving
portions of the apparatus in the well. It is accordingly an
object of the present invention to provide such improved
apparatus and associated methods for forming a casing side wall
window opening.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in
accordance with a preferred embodiment thereof, a specially
designed tubular anchor assembly with an elongated mill guide
projecting upwardly from its top end is used in conjunction
with a pipe-supported mill bit to mill out a casing side wall
window in a generally vertical parent wellbore to permit the
subsequent connection of a lateral wellbore thereto. To
facilitate the efficiency of the milling operation and the
retrieval from the casing of the anchor assembly, a specially
designed tubular retrieval structure is also provided.
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According to one milling method of the invention a tubular
anchor structure is provided and has a top end from which the
elongated mill guide longitudinally projects. Along its length
the upwardly projecting mill guide has a mill bit deflection
surface positioned thereon and angled relative to the
longitudinal axis of the tubular anchor structure. The tubular
anchor structure is coaxially and releasably locked within the
casing somewhat below the casing side wall portion to be milled
out to form the desired window.
A length of milling pipe is provided and has a bottom end
to which a mill bit is secured, a radially outwardly extending
outer side projection disposed above the mill bit, and a
tubular retrieval structure coaxially and releasably secured to
the milling pipe above its outer side projection.
At least a portion of the casing side wall window is
milled out by lowering the mill bit end of the milling pipe
through a tubular fishing neck secured to a tubular upper end
portion of the mill guide, rotating the milling pipe, and
laterally deflecting the rotating mill bit into cutting
engagement with the casing side wall by bringing the rotating
mill bit into contact with the mill guide deflection surface.
Next, the milling pipe is pushed further downwardly to
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responsively cause the retrieval structure to enter and become
latched within the fishing neck.
Next, the tubular anchor structure is retrieved on the
milling pipe by upwardly pulling the milling pipe out of the
casing and sequentially (1) causing the milling pipe to break
free from the retrieval structure and move upwardly through the
retrieval structure, and (2) causing the milling pipe outer
side projection to upwardly abut an interior portion of the
retrieval structure and responsively create in the tubular
anchor structure an upward force that unlocks the anchor
structure from the casing and permits it to be pulled out of
the casing with the retrieval structure, the fishing neck and
the mill guide.
The tubular anchor structure and associated mill guide and
retrieval structure may be used to progressively mill out the
casing side wall window using, for example, first and second
differently configured mill bits used in first and second
milling pipe run-ins. On the first of these run-ins the
milling pipe is releasably secured coaxially within the tubular
upper end portion of the milling guide, with the interior of
the milling pipe being communicated with the interior of a
setting piston pressure chamber within the anchor structure via
a passage structure extending from the milling pipe through the
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mill guide. When the anchor assembly is appropriately
positioned within the casing pressurized fluid is forced
through the milling pipe and into the anchor assembly pressure
chamber to cause movement of the setting piston and
responsively cause slip portions of the anchor assembly to grip
the casing and releasably lock the anchor assembly therein. On
the last milling pipe run-in (illustratively the second run-in)
the retrieval structure is used to release and remove the
anchor structure and its upwardly projecting mill guide.
The tubular anchor assembly is uniquely configured to
provide it with a desirable thin sidewall configuration and
substantially enhanced retrievability. In a preferred
embodiment thereof the anchor assembly comprises a tubular
inner mandrel, upper and lower tubular slip carriers coaxially
circumscribing the tubular inner mandrel in radially outwardly
spaced relationships therewith, and circumferentially spaced
series of upper and lower toothed slips respectively positioned
between the upper and lower slip carriers and the inner
mandrel. The slips are radially movable through slip windows
in their associated carriers between inwardly retracted release
positions and outwardly extended setting or casing gripping
positions.
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According to one feature of the invention, the slips are
resiliently biased toward their radially retracted release
positions by a compact biasing structure including
circumferentially spaced series of arcuate, elongated spring
members disposed in the annular spaces between the slip
carriers and the inner mandrel and interdigitated with the
circumferentially spaced series of slips. The spring members
have longitudinally central portions secured to their
associated slip carrier, and outer end portions of the springs
enter outer side recesses in the slips and slidingly engage the
slips.
According to another feature of the invention which
advantageously reduces the overall sidewall thickness of the
tubular anchor assembly, radially inner side portions of the
slips are slidably carried in axially spaced apart upper and
lower circumferentially spaced series of axially extending
pockets formed in the outer side surface of the inner mandrel.
The upper and lower slips are preferably in an opposing
relationship, with a tubular wedge member coaxially and
slidably circumscribing the inner mandrel between the facing
toothed and ramped ends of the upper and lower slips. A ramped
upper end portion of the wedge member has a continuous, solid
annular configuration, while a circumferentially spaced series
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of axial sidewall slots extend upwardly through the lower wedge
member end. The slots form a circumferentially spaced series
of collet finger portions on the wedge member, with lower ends
of the collet fingers having ramped configurations.
The inner mandrel, the upper and lower slips, and the
colleted wedge member are relatively movable in axial
directions between (1) a set position in which the outer ends
of the collet finger portions outwardly overlie and are
radially supported by nonpocketed areas of the inner mandrel,
with the opposite ends of the wedge member rampingly engaging
the tapered ends of the upper and lower slips, and (2) a
release position in which the outer ends of the collet finger
portions overlie the second series of inner mandrel pockets and
may be radially deflected thereinto in response to an axially
directed engagement force between the outer ends of the collet
finger portions and the tapered ends of the second slips. In
this manner, the release of the tubular anchor assembly from
the casing is substantially facilitated.
In a preferred embodiment thereof the retrieval structure
comprises a tubular body having upper and lower ends, and a
circumferentially spaced series of axially extending side wall
slots formed in the body and having upper and lower ends
respectively spaced axially inwardly of the upper and lower
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ends of the body. The slots form therebetween a
circumferentially spaced series of axially extending collet
fingers resiliently deflectable radially inwardly and outwardly
relative to the balance of the body. Each of the collet
fingers has a radially outwardly extending outer side
projection and a radially inwardly extending inner side
projection.
The inner side collet finger projections have bottom faces
which are upwardly and radially outwardly sloped at a first
angle relative to a reference plane transverse to the
longitudinal axis of the retrieval structure body; the outer
side collet finger projections have top faces which are
downwardly and radially outwardly sloped at a second angle
relative to a reference plane transverse to the longitudinal
axis of the retrieval structure body; and the outer side collet
finger projections have bottom faces which are upwardly and
radially outwardly sloped at a third angle relative to a
reference plane transverse to the longitudinal axis of the
retrieval structure body.
The first angle is less than the second angle which, in
turn, is less than the third angle. Preferably, the first
angle is approximately 10 degrees; the second angle is
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approximately 20 degrees; and the third angle is approximately
45 degrees.
Near the upper end of the fishing neck at the top of the
mill guide is an annular side surface recess having an annular
upper end ledge having a slope parallel to the slopes of the
upper ends of the outer retrieval structure collet finger
projections, and an annular lower end ledge having a slope
parallel to the slopes of the lower ends of the outer retrieval
structure collet finger projections. Because of these slope
angles, the retrieval structure outer collet finger projections
may be snapped into the fishing neck recess as the retrieval
structure is inserted into the fishing neck, but are locked in
the recess against upward removal therefrom. Accordingly, the
retrieval collet structure is a "one way" structure that
facilitates the releasing and removal of the anchor assembly
from the casing.
The milling pipe preferably has an outwardly projecting
annular flange thereon with an upper face that has a slope
angle essentially to the slope angles on the bottom ends of the
inner collet finger projections on the tubular retrieval
structure. This milling pipe flange functions as a pickup
abutment that upwardly engages the inner collet finger
projections, during upward movement of the milling pipe after
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it has been disconnected from the tubular retrieval structure,
to transmit a releasing force to the anchor assembly, via the
retrieval structure, the fishing neck and the mill guide, and
then upwardly carry the retrieval structure and attached
fishing neck, mill guide and anchor assembly out of the casing
with the balance of the milling pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are highly schematic partly elevational
cross-sectional views through a portion of a subterranean well
and illustrate specially designed mill guide and anchor
apparatus, embodying principles of the present invention, being
used to form a side wall window in the well casing;
FIG. 2 is a highly schematic cross-sectional view through
the subterranean well portion and illustrating an upper portion
of a lateral bore liner operatively installed therein
subsequent to the formation of the casing window;
FIGS. 3A-3E are cross-sectional views through downwardly
successive longitudinal portions of the milling guide and
anchor assembly of the present invention, with the components
of the milling guide and anchor assembly being in their initial
run-in orientations;
FIGS. 4A and 4B, 5A and 5B, and 6A and 6B are reduced
scale partial quarter sectional views of downwardly successive
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longitudinal portions of the anchor portion of the assembly and
sequentially illustrate the setting of the anchor portion in
the well casing;
FIG. 7 is a quarter sectional view of a tubular upper end
portion of the milling guide illustrating its receipt of a
specially designed double-ended retrieval collet structure
embodying principles of the present invention;
FIG. 8 is an enlarged scale cross-sectional view through a
portion of one of the collet structure finger portions taken
along line 8-8 of FIG. 7;
FIG. 9 is a partial quarter sectional view through an
upper end portion of the mill guide and illustrated a locking
engagement between the collet structure and the milling pipe
during a mill guide and anchor assembly retrieval operation;
and
FIG. 10 is an enlarged scale cross-sectional view through
the anchor portion of the assembly taken along line 10-10 of
FIG. 3D.
DETAILED DESCRIPTION
Schematically illustrated in FIGS. 1A-2 is a first-
drilled, or "parent", wellbore 10 which is generally vertically
formed in the earth. The parent wellbore 10 is lined with a
generally tubular and vertically oriented metal casing 12.
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Cement 14 fills an annular area radially between the casing 12
and the earth.
As a result of a milling operation subsequently described
herein and embodying principles of the present invention, the
parent wellbore 10 has a side wall window 16 formed through the
casing 12 (see FIGS. 1B and 2). A lateral wellbore 18 extends
outwardly from the window 16 and includes a tubular liner
structure 20 with cement 14 filling the annular space radially
between the liner 20 and the earth. Liner 20 has an upper
longitudinal portion 20a coaxially extending upwardly through
the parent bore wellbore casing 12 and has an open upper end
20b upwardly spaced apart from the casing window 16. The upper
longitudinal liner portion 20a defined with the interior side
surface of the casing 12 an annular space which is also filled
with cement 14.
The present invention is directed to forming the side wall
window opening 16 in the casing 12 as shown in FIG. 2. As will
be subsequently described in greater detain herein, window 16
is formed utilizing a specially designed retrievable anchor
assembly 22 (see FIGS. 1A and 1B) embodying principles of the
present invention. Anchor assembly 22 has a hollow tubular
configuration and has an elongated mill guide member 24
extending upwardly from the top end of the anchor assembly 22
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in a laterally offset relationship with its longitudinal axis.
Mill guide member 24 has a thickened lower end portion 26
having, as representatively illustrated in FIGS. 1A and 1B, a
downwardly and leftwardly sloping guide surface 28 thereon.
FIGS. 1A and 1B, in highly schematic form, sequentially
illustrate the use of the milling guide member 24, and its
associated tubular anchor assembly 22, to form the casing
window 16 shown in FIG. 2. Referring initially to FIG. 1A, the
lower end of a tubular fishing neck 74 is coaxially secured to
a tubular upper end portion 24a of the mill guide member 24.
In a manner subsequently described, the upper mill guide member
end portion 24a coaxially receives and is secured to a lower
end portion of a tubular milling pipe 30 having a generally
disc-shaped first rotary mill bit 32 affixed to its lower end.
When the mill guide member end portion 24a is initially
installed on the mill pipe 30, the bottom end of the milling
bit 32 is downwardly adjacent the open lower end of the mill
guide member end portion 24a as schematically indicated in FIG.
1A.
With the tubular fishing neck 74, mill guide 24 and anchor
assembly 22 secured to the lower end of the milling pipe 30 as
shown in FIG. 1A, the milling pipe 30 is lowered into the
casing 12 until, as indicated in FIG. 1A, the mill guide member
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24 is in a predetermined vertical position and rotational
orientation within the casing 12 relative to the desired
location of the casing window 16 (see FIG. 2) to be
subsequently formed. During its run-in, the overall milling
and anchor structure may be rotationally oriented within the
casing 12 utilizing, for example, a conventional gyroscope.
After the anchor assembly 22 and its associated mill guide
member 24 are vertically and rotationally oriented within the
casing 12, the anchor assembly 22 is hydraulically set, in a
manner subsequently described herein, using pressurized fluid
within the milling pipe 30. The setting portion of the anchor
assembly 22 includes an annular elastomeric trash barrier seal
member 36 coaxially carried by the anchor assembly 22
downwardly adjacent its upper end 38; a circumferentially
spaced series of upper slips 40 below the seal member 36; and a
circumferentially spaced series of lower slips 42 below the
upper slips 40. The setting process moves the seal member 36,
and the slips 40 and 42, radially outwardly into gripping
engagement with the facing inner side surface of the casing 12,
thereby rotationally and translationally locking the anchor
assembly 22 (and thus the mill guide member 24 and the tubular
fishing neck 74 as well) within the casing 12.
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With the anchor assembly 22 set in the casing 22, the
milling pipe 30 is forcibly moved in a vertical direction to
break it free from the tubular upper end portion 24a of the
mill guide member 24. The milling pipe 30 is then rotationally
driven (representatively in a clockwise direction as viewed
from above) and further lowered through the fishing neck 74 and
upper mill guide member end portion 24 into casing 12, as
indicated by the arrow 44 in FIG. 1A, parallel to the vertical
casing axis 46. When the rotating mill bit 32 engages the
sloping mill guide member surface 28 the bit is laterally
deflected to the left, as indicated by the arrow 48 in FIG. 1A,
into engagement with the casing 12 to thereby form an initial
window opening 16a therein. After the formation of this
initial casing window opening 16a, the rotation of the milling
pipe 30 is stopped, and the milling pipe 30 and mill mit 32 are
pulled upwardly through the upper mill guide member end portion
24a and attached fishing neck 74 and out of the casing 12,
leaving the anchor assembly 22, the mill guide member 24, and
the tubular fishing neck 74 in place within the casing 12.
The first mill bit 32 is then replaced with a second mill
bit 52 (see FIG. 1B) on the lower end of the withdrawn milling
pipe 30, the second bit 52 having a generally conical leading
end portion 52a. Additionally, a specially designed tubular
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retrieval collet structure 54 is coaxially secured to the
withdrawn milling pipe 30 somewhat above the second mill bit
52. As schematically shown in FIG. 1B, the withdrawn milling
pipe 30 is then lowered into the casing 12, and through the
tubular fishing neck 74, until the mill bit 52 downwardly exits
the upper mill guide member end portion 24a. The milling pipe
30 is then rotated and further lowered, as indicated by the
arrow 56 in FIG. 1B. As the rotating mill bit 52 contacts the
sloping mill guide surface 28 the bit 52 is leftwardly
deflected, as indicated by the arrow 58, into engagement with
the casing 12 and downwardly enlarges the previously milled
casing side wall opening 16a (see FIG. 1A) to form the desired
casing window opening 16 shown in both FIG. 1B and FIG. 2.
After this second liner casing step is completed, the
rotation of the milling pipe 30 is stopped, and the milling
pipe 30 then forced further downwardly to push the retrieval
collet structure 54 into the open top end 74a of the tubular
fishing neck 74. In a manner later described herein, this
causes the collet structure 54 to latch itself within the
interior of the fishing neck 74. The milling pipe 30 is then
pulled upwardly. In a manner also later described herein, this
separates the milling pipe 30 from the latched collet structure
54 and permits the milling pipe 30 to be drawn upwardly through
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the interiors of the fishing neck 74 and the collet structure
54. A shoulder portion (not shown in FIG. 1B) on the upwardly
traveling milling pipe 30 then latches onto the collet
structure 54 and transfers the upwardly directed milling pipe
retrieval force to an interior portion of the anchor assembly
22, via the collet structure 54 and the mill guide member 24,
in a manner releasing the anchor assembly 22 from the casing 12
by retracting the anchor assembly seal and slip portions 36,40
and 42.
The released anchor assembly 22, together with the fishing
neck 74 and the mill guide member 24, are then pulled out of
the casing 12 on the mill pipe 30 with the latched collet
structure 54 and the mill bit 52. It should be noted that, due
to the use of the specially designed retrieval collet structure
54, the anchor assembly 22, together with the mill guide member
24 and the fishing neck 74 secured thereto, are retrieved in
conjunction with the second milling step (or the first milling
step is only one mill bit is used to form the desired casing
window 16), and does not require a subsequent separate
anchor/mill guide structure retrieval step. After retrieval of
the anchor assembly, the mill guide member 24 and the fishing
neck 74 as just described, the lateral bore liner 20 may be
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installed in the casin~:~ ~.2, i.n a suitable conventional. manner,
as shown in FIG. 2.
Structure of Anchor 22" Mill Guide 24, and Fishing Neck 74
In FIGS. 3A-3E downwardly successive longitudinal portions
of the overall anchor, mill guide and fishing neck assembly
22,24,74 of the pr~~~~ent invention are cross-sectionally
illustrated in greater detail, and. at a larger scale, with the
milling pipe 30 extending coaxially through the interior of the
fishing neck 74 and r:~eing shown in elevation. The tubular
anchor assembly 22 is shown in FIGS. 3C-3F within the casing
12, with the various relatively shiftable components of the
anchor assembly 22 (as later described herein) being in their
initial run-in positions. Anchor assembly 22 is substantially
similar in constructioio to the anchox- assembly 22 illustrated
and described in i.J,S. Patent rda. 5,832,997, issued
November 10, 1'398 to Wluite et al . , but for convenience will be
for the most part described in detail herein as well.
The tubular fishing neck 74 (see FIG. 3A) has, adjacent
its upper end 74a, an annular interior side surface recess 76
having a downwardly and :radially outwardly sloped upper annular
end ledge surface 78, and a downwardly and radially inwardly
sloped lower annular erd ledge surface 80. Near its lower end
the fishing neck 74 has an annular interior stop flange portion
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81. The lower end of the fishing neck 74 is threaded, as at
82, exteriorly onto the tubular upper end portion 24a of the
mill guide member 24. A tubular lower end portion 24b of the
mill guide member 24, in turn, is threaded as at 86 exteriorly
onto main inner mandrel 88 (see FIG. 3C). To prevent relative
rotation between the threadingly connected lower mill guide end
portion 24b and the upper end of the main inner mandrel 88, an
anti-rotation lug 89 (see FIG. 3C) is operatively placed in
axially facing slots 89a,89b formed in the mill guide end
portion 24b and upper end portion of the main mandrel 88.
Immediately below the bottom end potion 24a of the mill
guide member 24 is an annular outwardly projecting exterior
shoulder portion 90 of the main mandrel 88. The previously
mentioned annular elastomeric seal member 36 circumscribes the
main mandrel 88 and upwardly abuts the downwardly facing
annular side surface of the annular mandrel shoulder 90. With
the components of the anchor assembly 22 in their run-in
orientations shown in FIGS. 3C-3E the bottom end of the seal
member 36 (see FIG. 3C) is upwardly spaced apart from the top
end 96 of a tubular upper slip carrier 98 (see also FIG. 3D)
that outwardly and slidably circumscribes the main mandrel 88.
Turning now to FIG. 3D, a lower end portion of the upper
slip carrier 98 has a circumferentially spaced series of upper
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and lower slip window openings 100,102 that outwardly overlie a
series of axially extending pocket areas 104 (see also FIG. 10)
formed in and circumferentially spaced around the outer side
surface of the main inner mandrel 88. The upper slips 40 are
circumferentially spaced around the main mandrel 88, are
slidably received in the pocket areas 104, and have upper and
lower portions 40a,40b which are respectively received in the
slip windows 100,102. Each of the upper slips 40 has a
recessed area 40c disposed between its upper and lower portions
40a and 40b. Lower slip portions 40b have exterior side
surface gripping teeth 106 formed thereon. Teeth 106 spiral
downwardly in a clockwise direction as viewed from above (i.e.,
in the same rotational direction as the rotation of the milling
pipe 30 during the milling operations).
With reference now to FIG. 10, the upper slips 40 are
resiliently biased in a radially outward direction, in a manner
biasing their upper and lower portions 40a,40b outwardly
through their respective slip windows 100 and 102, by means of
a unique and highly compact spring system comprising a
circumferentially spaced series of elongated arcuate metal
spring plate members 108 disposed in the annular space between
the main mandrel 88 and the upper slip carrier 98 as
illustrated in FIG. 10. Springs 108 are arranged to have their
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convexly curved sides facing in a radially outward direction,
and have longitudinally central portions thereof positioned
between circumferentially adjacent pairs of upper slips 40 and
anchored to the inner side surface of the upper slip carrier 98
by screws 110.
As illustrated, at each upper slip 40 facing end portions
of circumferentially adjacent pairs of springs 108 extend into
the recessed slip area 40c and slidingly bear on the radially
thinned slip portion disposed between the slip portions 40a and
40b. When the anchor assembly 22 is set in the casing 12 as
subsequently described herein the slips 40 are forced radially
outwardly into biting engagement with the casing 12. This
radially outward setting movement of the upper slips 40 is
resiliently resisted by the springs 108 as their outer ends
slide along their associated slip members and are temporarily
moved toward straightened orientations by the outwardly moving
slips 40. When the radially outwardly directed setting force
is removed from the slips 40, the spring end portions return to
their FIG. 10 curved orientations, thereby radially retracting
the slips 40 toward their FIG. 10 orientations.
Slidingly circumscribing the main mandrel 88 below the
upper slips 40 is an annular wedge member 112 (see FIG. 3D) .
Wedge member 112 has a circumferentially continuous upper end
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portion 114 that underlies the bottom end of the upper slip
carrier 98 and is releasably anchored thereto by two
circumferentially spaced shear pins 116. A circumferentially
spaced series of sloping, generally planar exterior side
surface "flat" areas 118 are formed on the upper wedge end 114
face corresponding sloping interior side surface "flat" areas
120 on the bottom ends of the upper slips 40. When the facing
flat areas 118,120 engage upon setting of the slips 40 they
serve to prevent undesirable relative rotation between the
wedge 112 and the slips 40.
A circumferentially spaced series of axial slits extend
upwardly through the wedge 112 to its upper end portion 114,
thereby forming on the wedge 112 a circumferentially spaced
series of downwardly extending collet finger portions 124.
Collet fingers 124, as illustrated in FIG. 3D, are radially
thinned relative to the upper wedge end portion 114, and have
radially thickened lower end portions 126. With the components
of the anchor assembly 22 in their run-in orientations shown in
FIGS. 3A-3D, these lower collet finger end portions 126, as
shown in FIG. 3B, outwardly overlie a circumferentially spaced
series of axially extending pocket areas 128 formed in the
exterior side surface of the main mandrel 88.
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The lower collet finger end portions 126 have sloping flat
exterior side surface areas 130 and underlie an upper end
portion of a tubular lower slip carrier 132 that slidably
circumscribes the main mandrel 88. Five circumferentially
spaced shear pins 134 releasably anchor the upper end of the
lower slip carrier 132 to underlying ones of the collet finger
lower end portions 126. The circumferentially spaced lower
slips 42 are in opposing relationships with the upper slips 40,
are slidably carried in the mandrel pockets 128, and have upper
and lower portions 42a,42b which are respectively received in
upper and lower slip windows 136,138 formed in the lower slip
carrier 132 and outwardly overlying the mandrel pockets 128.
Each of the lower slips 42 has a recessed area 42c disposed
between its upper and lower portions 42a and 42b. At the upper
end of each of the lower slips 42 is a sloping interior side
surface flat area 139 which faces a corresponding flat area 130
on one of the wedge member collet fingers 124.
Upper slip portions 42a have exterior side surface
gripping teeth 140 formed thereon. Teeth 140 spiral downwardly
in a counterclockwise direction as viewed from above, thereby
having an opposite "hand" than that of the upper slip gripping
teeth 106. The lower slips 42 are resiliently biased in a
radially outward direction, by springs 108, in a manner
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identical to that described for the upper slips 40 in
conjunction with FIG. 10. Accordingly, when the upper and
lower slips 40,42 are set into gripping engagement with the
casing 12 as later described herein, they very strongly resist
rotation of the anchor assembly 22 relative to the casing 12 in
either direction about its vertical axis 46.
Still referring to FIG. 3D, the main inner mandrel 88 is
rotationally locked to the upper and lower slip carriers 98 and
132, in a manner permitting relative axial shifting between the
mandrel 88 and the slip carriers 98 and 132 as later described
herein, by three downwardly successive sets of torque pins
142,144 and 146. Torque pins 142 extend inwardly through the
upper slip carrier 98 and are slidably received in axially
elongated slots 148 in the inner mandrel. Torque pins 144
extend inwardly through the upper slip carrier 98 and are
slidably received in axially elongated slots 150 formed in the
upper slip carrier 98 and in substantially longer axially
elongated slots 152 formed in the inner mandrel 88. Torque
pins 146 extend inwardly through the lower slip carrier 132 and
are slidingly received in the mandrel slots 152 and in shorter
axially elongated slots 154 formed in the lower slip carrier
132.
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With continued reference to FIG. 3D, an annular,
downwardly facing exterior ledge 156 is formed on a bottom end
portion of the lower slip carrier 132 beneath its lower slip
windows 138. This bottom end portion of the lower slip carrier
132 is outwardly overlapped by an upper end portion of a
tubular piston retainer member 158 that circumscribes the main
mandrel 88 in a radially outwardly spaced relationship
therewith. At its upper end, the retainer member 158 is
threaded, as at 159, onto the lower slip carrier 132 just above
the ledge 156. A tubular piston member 160 (see FIGS. 3D and
3E) is coaxially and slidably carried in the annular space
between the mandrel 88 and the piston retainer 158, and is
slidingly sealed to the facing side surfaces of the mandrel 88
and piston retainer 158 by the indicated O-ring seals 162 and
164.
Tubular piston 160 has an upper end 166 (see FIG. 3D)
downwardly spaced apart from the annular lower slip carrier
ledge 156, and a bottom end 168 (see FIG. 3E). As indicated in
FIG. 3D, an upper end portion of the piston retainer 158 is
releasably anchored to the underlying upper end portion of the
piston 160 by shear pins 170. Referring now to FIG. 3E, spaced
downwardly apart from the bottom piston end 168 is a tubular
slip mandrel 172 which is slidably received in the annular
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space between the main mandrel 88 and the piston retainer
member 158 and slidingly sealed to their facing side surfaces
by the indicated O-ring seals 174,176.
The upper end 178 of the slip mandrel 172 is spaced
downwardly apart from the bottom end 168 of the tubular piston
160 and forms therewith an annular pressure chamber 180 between
the main mandrel 88 and the piston retainer member 158. A
lower end portion of the slip mandrel 172 extends downwardly
beyond the lower end 182 of the retainer member 158 and is
releasably anchored to the main mandrel 88 by a
circumferentially spaced series of shear pins 184. A
longitudinally extending series of ratchet teeth 186 are formed
on the outer side surface of the slip mandrel 172 and are
operatively engaged by corresponding teeth on an annular
ratchet slip member 188 captively retained in an annular
interior side surface pocket 190 formed in a lower end portion
of the piston retainer member 158. In a conventional manner
the ratchet slip member 188 permits the piston retainer member
158 to move upwardly along the slip mandrel 172 but not
downwardly therealong. The ratchet slip member 188 is upwardly
biased in the pocket 190 by wave spring members 192 therein.
With reference now to FIGS. 3B-3E, with the overall
anchor, mill guide and fishing neck assembly 22,24,74 in their
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previously described run-in orientations, a lower end portion
of the milling pipe 30 (see FIG. 3B) is releasably secured
within the tubular upper mill guide portion 24a by shearable
setting pin members 60, with the illustrated setting pin 60a
being hollow and communicating the interior of the milling pipe
30 with the upper end of an elongated fluid supply tube 62
which is recessed in a vertically extending groove 64 formed in
the exterior side surface of the milling guide member 24
opposite its sloping side surface 28. As illustrated in FIG.
3C, the bottom end of the tube 62 is communicated with
interconnected internal passages 66,68 formed in the lower end
of the mill guide member 24. Passage 68, in turn, is connected
by a threaded fitting 69 to the upper end of a second fluid
supply tube 70 that centrally extends downwardly through the
anchor assembly 22. As illustrated in FIG. 3E, the lower end
of the tube 70 is secured to the inner mandrel 88 by a threaded
fitting 72 and communicates with the pressure chamber 180.
For purposes subsequently described herein, as illustrated
in FIG. 3A the milling pipe 30 has formed thereon a
diametrically enlarged annular exterior flange 198 positioned
immediately below an annular exterior side surface groove 200
formed in the milling pipe 30. A downwardly facing annular,
upwardly and radially outwardly sloped ledge 202 is formed at
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the upper side of the annular groove 200; an upwardly facing
annular, downwardly and radially outwardly sloped ledge 204 is
formed at the upper side of the flange 198; and a downwardly
facing annular, upwardly and radially outwardly sloped ledge
206 is formed at the bottom side of the flange 198.
Structure of the Retrieval Collet 54
Turning now to FIGS. 7 and 8, the retrieval collet 54 has
a tubular body 222 with open upper and lower ends 224,226. A
circumferentially spaced series of axially extending slots 228
are formed in the body 222, with the top ends of the slots 228
being downwardly spaced apart from the upper end 224 of the
collet body 222, and the bottom ends of the slots 228 being
upwardly spaced apart from the lower end 226 of the collet body
222. Slots 228 form therebetween a circumferentially spaced
series of axially extending double ended collet finger portions
230 which are resiliently deflectable in radially inward and
outward directions relative to the balance of the retrieval
collet body 222.
As best illustrated in FIG. 8, longitudinally intermediate
sections 230a of the fingers 230 are radially thickened to form
on each finger 230 a radially outwardly extending projection
232 and a radially inwardly extending projection 234.
Projection 232 has an upper end surface 236 which is sloped
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downwardly and radially outwardly at an angle A relative to a
reference plane extending transversely to the longitudinal axis
of collet body 222, and a lower end surface 238 which is sloped
upwardly and radially outwardly at an angle B relative to a
reference plane extending transversely to the longitudinal axis
of collet body 222. Projection 234 has a lower end surface 240
which is sloped upwardly and radially outwardly at an angle C
relative to a reference plane extending transversely to the
longitudinal axis of collet body 222, and an upper end surface
242 which is sloped downwardly and radially outwardly at an
angle D relative to a reference plane extending transversely to
the longitudinal axis of collet body 222.
Relative to a reference plane transverse to the
longitudinal axis of the collet body 222, the slope of the end
surface 240 is less than the slope of the end surface 236
which, in turn, is less than the slope of the end surface 238.
Representatively, the end surface 242 is generally parallel to
the end surface 238. Preferably, angle C is approximately 10
degrees, angle A is approximately 20 degrees, and angle B is
approximately 45 degrees.
Operation of the Anchor Assembly 22 and Collet Structure 54
When the interconnected milling pipe 30, fishing neck 74,
mill guide 24 and anchor assembly 22 are initially run
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downwardly into the casing 12 to their predetermined FIG. 1A
vertical and rotational orientations, the anchor assembly 22 is
hydraulically set within the casing 12 by forcing pressurized
fluid downwardly through the interior of the milling pipe 30
and, via the tube 62, the passages 66 and 68, and the tube 70
(see FIGS. 3B-3E) into the annular pressure chamber 180 (see
FIG. 3E) .
Referring now to FIGS. 4A-6B, which sequentially
illustrate the operation of the tubular anchor assembly 22,
when the hydraulic setting pressure within the chamber 180
reaches a first predetermined magnitude, the resulting upward
pressure force on the bottom piston end 168 causes the pins 170
(see FIG. 4B) to shear. This, in turn, causes the pressure in
chamber 180 to drive the piston 160 upwardly from its run-in
position along the main mandrel 88. The upper end 166 of the
piston 160 then strikes the annular ledge 156 on the lower slip
carrier 132 (see FIG. 4A) and forces the interconnected lower
slip carrier 132, slips 40 and 42, wedge member 112, upper slip
carrier 98 and piston retainer 158 upwardly to their positions
shown in FIGS. 4A and 4B in which the upper end 96 of the upper
slip carrier 98 upwardly engages the annular elastomeric seal
member 36, axially compresses it, and radially outwardly
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deforms it into sealing engagement with the inner side surface
of the casing 12.
Next, as illustrated in FIGS. 5A and 5B, a further
pressure increase in the chamber 180 drives the piston 160
further upwardly along the main mandrel 88 until the pins 116
shear and permit the upwardly moving piston to drive the upper
end 114 of the wedge member 112 into forcible camming
engagement (via the facing wedge and slip surfaces 118,120)
with the upper slips 40, thereby radially driving the upper
slips 40, against the resilient biasing forces of their
associated springs 108, outwardly into setting engagement with
the casing 12 as shown in FIG. 5A. At this point, the bottom
ends 126 of the wedge member collet fingers 124 are moved
upwardly past the mandrel pockets 128 and are radially
supported by an underlying, nonpocketed outer side surface
portion of the main mandrel 88.
Finally, as illustrated in FIGS. 6A and 6B, a further
increase in pressure within the chamber 180 shears the pins 134
and causes the piston 160 to move further upwardly along the
main mandrel 88 in a manner bringing the facing wedge and lower
slip member surfaces 130,139 into forcible camming engagement,
thereby radially driving the lower slips 42, against the
resilient biasing forces of their associated springs 108,
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outwardly into setting engagement with the casing 12 as shown
in FIG. 6A.
With the anchor assembly 22 set in the casing 12 in this
manner, the milling pipe 30 is freed from the tubular upper
mill guide end portion 24a (see FIG. 3B) by forcibly moving the
milling pipe 30 up and down to shear its setting pins 60,60a.
The freed milling pipe 30 is then lowered and rotated to
perform the first milling step previously described herein in
conjunction with FIG. 1A.
The milling pipe 30 is then upwardly removed from the
casing 12, leaving the anchor assembly 22, the mill guide 24
and the fishing neck 74 secured therein, and readied for the
second milling step previously described herein in conjunction
with FIG. 1B. Specifically (as shown in FIG. 7) the retrieval
collet structure 54 is coaxially secured to the milling pipe 30
with shearable mounting screws 244, and the first mill bit 32
(see FIG. 1A) is replaced with the second mill bit 52 (see FIG.
1B). Milling pipe 30 is then again lowered into the casing 12,
and the second milling step previously described herein in
conjunction with FIG. 1B is performed.
Referring now to FIG. 7, after this second milling step is
performed, the milling pipe 30 is pushed downwardly to cause
the retrieval collet structure 54 to enter the top end 224 of
CA 02223517 1997-12-04
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the fishing neck 74. As the collet structure 54 enters the
fishing neck 74, the outer collet finger projections 232 are
radially inwardly deflected by an upper interior end surface
portion of the fishing neck 74 and then resiliently snap
radially outwardly into the interior fishing neck recess 76.
The downward insertion movement of the collet structure 54
through the fishing neck 74 is automatically limited by the
interior fishing neck flange 89 which functions as an abutment
for the lower end 226 of the collet structure 54.
While the relatively shallow lower shoulder surface angle
B of the outer collet projections 232 permits the projections
232 to be readily deflected inwardly to then permit them to
outwardly snap into the fishing neck recess 76, the much more
steeply sloped upper shoulder surface angle A essentially
prevents the outer collet finger projections 232 from exiting
the recess 76 when the collet structure 54 is pulled upwardly
relative to the anchor assembly 22. As indicated in FIG. 7,
the upper fishing neck annular interior ledge 78 is essentially
parallel to the outer collet finger projection upper end
surfaces 236, and the lower fishing neck annular interior ledge
80 is essentially parallel to the outer collet finger
projection lower end surfaces 238.
CA 02223517 1997-12-04
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With the one-way collet structure 54 locked into place in
this manner within an upper end portion of the fishing neck 74,
the milling pipe 30 is pushed,further down the casing 12 to
shear the collet mounting pins 244 to thereby free the milling
pipe 30 from the collet structure 54. The now freed milling
pipe 30 is then pulled upwardly relative to the collet
structure 54, thereby raising the second mill bit 52 (see FIG.
1B) back into a lower end portion of the anchor structure 22,
while at the same time also upwardly moving the annular milling
pipe outer side surface groove 200 (see FIG. 3A) toward the
inner collet finger projections 234 (see FIGS. 7-9).
As the milling pipe annular ledge 204 upwardly engages the
downwardly facing annular surfaces 240 of the inner collet
finger projections 234, further upward movement of the milling
pipe relative to the collet structure 54 is stopped, and the
upward retrieval force being exerted on the milling pipe 30 is
transferred to the inner mandrel 88 via the collet structure
54, the fishing neck 76 and the mill guide member 24. This
upward retrieval force now being transferred to the main
mandrel 88 shears the pins 184 (see the bottom of FIG. 6B),
thereby permitting the fishing neck 76, the mill guide member
24 and the main mandrel 88 to be pulled upwardly relative to
the balance of the anchor assembly 22, thereby returning the
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main mandrel 88 to its initial run-in position shown in FIGS.
3C-3E.
In turn, this permits the upper and lower slips 40,42 to
retract, and the annular seal member 36 to return to its
axially uncompressed run-in configuration, thereby releasing
the anchor structure 22 and permitting it to be pulled out of
the casing 12 along with the milling pipe 30, the collet
structure 54, the fishing neck 74 and the mill guide member 24.
Quite advantageously, this allows removal of the anchor
structure 22 in conjunction with the second milling step
instead of requiring a subsequent separate run down the casing
to secure and retrieve the anchor apparatus.
After the shearing of the pins 184, the upward movement of
the main mandrel 88 creates in the anchor assembly 22 the
following release sequence via interactions between the torque
pins 142,144,146 and their associated slots 148,150,152 and 154
shown in FIG. 3D. First, the upwardly moving inner mandrel 88
picks up the torque pins 142, thereby upwardly moving the upper
slip carrier 98 and moving the upper slips 40 off the upper end
114 of the wedge 112 to thereby permit the upper slips to
retract. Next, the torque pins 144 are picked up and upwardly
moved by the mandrel 88 to thereby move the wedge 112 upwardly
off the lower slips 42 to permit them to retract. Finally, the
CA 02223517 1997-12-04
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torque pins 146 are picked up to thereby pick up the lower slip
carrier 132 and eliminate any further relative movement among
the slip and wedge parts of the assembly 22.
The uniquely configured anchor assembly 22 with its
upwardly projecting mill guide portion 24, and the retrieval
collet structure 54, provide a variety of desirable advantages
over conventional downhole milling apparatus and associated
methods. For example, as can readily be seen in FIGS. 3C-3E,
compared to conventionally configured tubular anchoring devices
(such as packers) the anchor assembly 22 has quite a thin
overall sidewall thickness, with a maximum of three metal
member thicknesses along its entire length. Because it is
substantially thinner than conventionally constructed downhole
anchoring devices the anchor assembly 22, for a given outer
diameter, provides an appreciably larger interior diameter to
correspondingly provide easier passage therethrough of various
tools and other structures.
In the present invention this reduced wall thickness
attribute is provided in part by the provision of the
previously described main mandrel pockets 104,128 (see FIG. 3D)
in which radially inner side portions of the upper and lower
slips 40,42 are recessed and slidably carried to thereby
position the outer sides of the slips further inwardly in their
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run-in positions. These pockets 104 and 128, in conjunction
with the specially designed colleted wedge member 112, also
facilitate the release of the opposing upper and lower slips
40,42 in response to the pulling up of the main mandrel 88
relative to the balance of the anchor assembly 22 as previously
described herein.
Specifically, as the main mandrel 88 is pulled upwardly
relative to the balance of the previously set anchor assembly
22, the upper slips 40 (via the contacting ramped wedge and
slip surfaces 118,120) exert a downward force on the upper end
of the wedge member 112. Because of the colleted configuration
of the lower portion of the wedge member 112, downward
releasing motion of the wedge member 112 is permitted due to a
simultaneous radially inward flexing of the collet fingers 124
into the underlying mandrel pockets 128 as the wedge member 112
is forcibly moved downwardly along the main mandrel 88.
Also contributing to the desirable reduction in total wall
thickness in the anchor assembly 22 are the specially
configured and positioned slip biasing spring members 108 shown
in FIG. 10. The shape of these springs, and the way then
operatively engage their associated slips, permits them to
perform their intended biasing function in the narrow annular
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space between the main mandrel 88 and their associated slip
carrier (carrier 98 or 132 as the case may be).
In addition to these and other desirable configurational
attributes, the anchor assembly 22 also has substantially
improved stability and retrievability characteristics. For
example, because the gripping teeth on the upper and lower
slips 40,42 spiral in opposite directions relative to the
vertical casing axis 46, the in place anchor assembly 22 is
able to strongly resist torsionally created rotational
displacement in either direction relative to the casing 12.
Additionally, as previously described herein, by using the
specially designed one way tubular collet structure 54, the
anchor assembly 22 can be released and retrieved in conjunction
with a milling operation as opposed to having to retrieve the
anchor assembly in a subsequent separate retrieval operation
requiring an additional downhole trip.
Additionally, if the intended anchor assembly retrieval
technique is unsuccessful the structure of the anchor assembly
22 permits it to be partially milled out, to permit a secondary
retrieval process to be carried out, without the anchor
assembly falling further down the casing 12 and necessitating a
fishing-out process. Specifically, if the anchor assembly 22
becomes stuck in the casing 12 such that it cannot be pulled up
CA 02223517 1997-12-04
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on the milling pipe 30, the upward force on the milling pipe 30
can simply be increased to the point where an annular radially
thinned safety shear portion 24c interiorly formed in the lower
mill guide end portion 24a (see FIG. 3C) pulls apart, in which
case the fishing neck 74 and the portion of the mill guide 24
above the threaded connection will be pulled up on the milling
pipe 30, leaving the still set anchor assembly 22 in the casing
12. Appropriate milling apparatus can then be lowered into the
casing 12 and used to downwardly mill away a top part of the
remaining anchor assembly 22 to just below the upper slips 40.
As can be seen in FIG. 3D, the gripping teeth 140 on the
lower slips 42 are, in cross-section, angled downwardly so that
from a vertical standpoint the lower slips 42 serve primarily
to prevent downward movement of the set anchor assembly 22
through the casing 12. Accordingly, after the milling away of
the upper slips 42, and the removal of the milling apparatus
from the casing 12, the remaining lower slips 42 hold the
balance of the anchor assembly 22 in place and prevent it from
simply falling further down the casing 12. The balance of the
anchor assembly 22 can then be removed from the casing 12
using, for example, conventional spearing apparatus.
The foregoing detailed description is to be clearly
understood as being given by way of illustration and example
CA 02223517 1997-12-04
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only, the spirit and scope of the present invention being
limited solely by the appended claims.
WHAT IS CLAIMED IS:
