Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02617072 2007-12-21
SUBTERRANEAN WELLBORE APPARATUS
BACKGROUND OF THE INVENTION
[0002] This invention generally relates to a method of hydrocarbon well
completion and the associated apparatus for practicing the method. More
particularly, the invention provides a subterranean wellbore apparatus.
Description Of the Prior Art
[0003] To extract hydrocarbons such as natural gas and crude oil from the
earth's subsurface formations, boreholes are drilled into hydrocarbon bearing
production zones. To maintain the productivity of a borehole and control the
flow
of hydrocarbon fluids from the borehole, numerous prior art devices and
systems
have been employed to prevent the natural forces from collapsing the borehole
and obstrticting or terminating fluid flow therefrom. One such prior art
system
provides a full depth casement of the wellbore whereby the wellbore wall is
lined
with a steel casing pipe that is secured to the bore wall by an annulus of
concrete
between the outside surface of the casing pipe and the wellbore wall. The
steel
casing pipe and surrounding concrete annulus is thereafter perforated by
ballistic
or pyrotechnic devices along the production zone to allow the desired
hydrocarbon fluids to flow from the producing formation into the casing pipe
interior. Usually, the casing interior is sealed above and below the producing
zone whereby a smaller diameter production pipe penetrates the upper seal to
provide the hydrocarbon fluids a smooth and clean flowing conduit to the
surface.
[0004] Another prior art well completion system protects the well borewall
production integrity by a tightly packed deposit of aggregate comprising sand,
gravel or both between the raw borewall and the production pipe thereby
avoiding
the time and expense of setting a steel casing from the surface to the
production
zone which may be many thousands of feet below the surface. The gravel
packing is inherently permeable to the desired hydrocarbon fluid and provides
structural reinforcement to the bore wall against an interior collapse or flow
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degradation. Such well completion systems are called "open hole" completions.
The apparatus and process by which a packed deposit of gravel is placed
between the borehole wall and the production pipe is encompassed within the
definition of an "open hole gravel pack system". Unfortunately, prior art open
hole
gravel pack systems for placing and packing gravel along a hydrocarbon
production zone have been attended by a considerable risk of precipating a
borehole wall collapse due to fluctuations in the borehole pressure along the
production zone. These pressure fluctuations are generated by surface
manipulations of the downhole tools that are in direct fluid circulation
within the
well and completion string.
[0005] Open hole well completions usually include one or more screens
between the packed gravel annulus and a hydrocarbon production pipe. The term
"screen" as used herein may also include slotted or perforated pipe. If the
production zone is not at the bottom terminus of the well, the wellbore is
closed by
a packer at the distal or bottom end of the production zone to provide bottom
end
support for the gravel pack volume. The upper end of the production zone
volume
is delineated by a packer around the annulus between the wellbore and the pipe
column, called a "completion string", that carries the hydrocarbon production
to
the surface. This upper end packer may also be positioned between the
completion string and the inside surface of the well casing at a point
substantially
above the screens and production zone.
[0006] Placement of these packers and other "downhole" well conditioning
equipment employs a surface controlled column of pipe that is often
characterized
as a "tool string". With respect to placement of a gravel pack, a surface
controlled
mechanism is incorporated within the tool string that selectively directs a
fluidized
slurry flow of sand and/or gravel from within the internal pipe bore of the
tool string
into the lower annulus between the raw wall of the wellbore and the outer
perimeter of the completion string. This mechanism is positioned along the
well
depth proximate of the upper packer. As the mechanism directs descending
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within the formation. Such a pressure imbalance, even briefly, may collapse
the borehole
or otherwise damage the productivity of the production zone borehole wall or
damage the
filter cake. Highly deviated or horizontal production zone boreholes are
particularly
susceptible to damage due to such a pressure imbalance. Consequently, it is an
object
of the present invention to provide a flow cross-over mechanism that will
provide a
positive (overburden) pressure against a borehole wall throughout all phases
of the gravel
packing process.
[0008] It is also an object of an aspect of the invention to provide a
procedure and
mechanism for maintaining fluid pressure on the production zone wellbore wall
below the
upper packer that is at least equal or greater than the natural hydrostatic
pressure after
the packer is set and while a greater fluid pressure is imposed on the
wellbore annulus
above the upper packer for testing the seal integrity of the packer.
[0009] Another object of an aspect of the present invention to provide an
apparatus design that facilitates a substantially uniform overburden pressure
within a
borehole production zone throughout the cross-flow changes occurring during a
gravel
packing procedure.
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SUMMARY OF THE INVENTION
[0010] A preferred embodiment of the present invention includes a gravel pack
extension tube that is permanently secured within a wellbore casing;
preferably in or
near the well production zone thereof. Near the upper end of the gravel pack
extension tube is a packing seal that'obstructs fluid flow through an annular
section of
the casing between the internal casing wall and the external perimeter of the
gravel
pack extension tube. The lower end of the gravel pack extension tube includes
an
open bore pipe that may be extended below the casing bottom and along the open
borehole into the production zone. The distal end of the lower end pipe is
preferably
closed with a bull plug. Along the lower end of the pipe extension, within the
hydrocarbon production zone and above the bull plug, are one or more gravel
screens
that are sized to pass the formation fluids while excluding the formation
debris.
[0011] Internally, the upper end of the gravel pack extension tube provides
two,
axially separated, circular seal surfaces having an annular space
therebetween.
Further along the gravel pack extension tube length, several, three for
example, axially
separated, axial indexing lugs are provided to project into the extension tube
bore
space as operator indicators.
[0012] The dynamic or operative element of the present packing apparatus is a
crossover flow tool that is attached to the lower end of a tool string.
Concentric axial
flow channels around the inner bore channel are formed in the upper end of the
upper
end of the crossover flow tool. An axial indexing collet is secured to the
crossover tool
assembly in the axial proximity of the indexing lugs respective to the
extension tube. A
ball check valve rectifies the direction of fluid flow along the inner bore of
the crossover
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flow tool. A plurality of transverse fluid flow ports penetrate through the
outer tube wall into the
concentric flow channels. Axial positionment of the crossover flow tool
relative to the inner
seals on the gravel pack extension seals controls the direction of fluid flow
within the
concentrically outer flow channels. At all times and states of flow direction
within the gravel
packing procedure and interval, the production zone bore wall is subjected to
at least the
fluid pressure head standing in the wellbore above the production zone by
means of the
transverse flow channels and the concentric outer flow channels.
[0012a] Accordingly, in one aspect of the present invention there is provided
an
apparatus operatively positionable within a subterranean wellbore opposite a
formation
intersected by the wellbore, the apparatus comprising:
an assembly having first and second opposite ends and including a
packer, a screen and a flow directing mechanism, the flow directing mechanism
configured to permit fluid communication longitudinally through an interior of
the assembly
between the first and second opposite ends when the assembly is conveyed into
the
wellbore and to longitudinally move to selectively permit and prevent fluid
communication
between an interior of the screen and a first annulus formed between the
assembly and
the wellbore and extending to the earth's surface when the packer is set in
the wellbore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a thorough understanding of the present invention, reference is
made
to the following detailed description of the preferred embodiment, taken in
conjunction with the
accompanying drawings, in which like elements have been given like reference
characters throughout the several figures of the drawings:
FIG. I is a sectional elevation of a completed oil well borehole having the
present
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invention gravel pack extension secured therein;
FIG. 2 is a sectional elevation of the present invention crossover tool;
FIG. 3 is a partially sectioned elevation of an anti-swabbing tool having
combination utility
with the present invention;
FIGS 4A-4E schematically illustrate the operational sequence of the indexing
collet; FIG. 5 is a
sectional elevation of the gravel pack extension and the crossover tool in
coaxial assembly
for downhole positionment;
FIG. 6 is an enlargement of that portion of FIG. 5 within the detail boundary
A;
FIG. 7 is a sectional elevation of the gravel pack extension and the crossover
tool in
coaxial assembly suitable for setting the upper packer;
FIG. 8 is an enlargement of that portion of FIG. 7 within the detail boundary
B;
FIG. 9 is a sectional elevation of the gravel pack extension and the crossover
tool in
coaxial suitable for testing the hydrostatic seal pressure of the upper
package;
FIG. 10 is an enlargement of that portion of FIG. 9 within the boundary C;
FIG. 11 is a sectional elevation of the gravel pack extension and the
crossover tool in
coaxial assembly suitable for circulating a gravel packing slurry into the
desired
production zone;
FIG. 12 is an enlargement of that portion of FIG. 11 within the detail
boundary D;
FIG. 13 is a sectional elevation of the gravel pack extension and the
crossover tool in
coaxial assembly suitable for a flush circulation of the setting tool pipe
string;
FIG. 14 is an enlargement of that portion of FIG. 13 within the detail
boundary E.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The sectional elevation of FIG. 1 illustrates a hydrocarbon producing
well
having an upper casing 12. The well casing 12 is preferably secured to the
wall 10 of the
wellbore by an annular concrete jacket 14. Near the lower end of the casing
12, within
the internal bore of the casing, a gravel pack body 20 is secured by slips and
a pressure
seal packer 22. Generally, the gravel pack body is an open flowpipe 21 having
one or
more cylindrical screen elements 16 near the lower end thereof. The flowpipe
lower end
projects into the hydrocarbon bearing production zone 18. In the annular space
between
the wellbore wall 10 and the screen elements 16 is a tightly consolidated
deposit 24 of
aggregate such as sand and gravel, for example. This deposit of aggregate is
generally
characterized in the art as a "gravel pack". Although tightly consolidated,
the gravel pack
is highly permeable to the hydrocarbon fluids desired from the formation
production zone.
Preferably, the gravel pack 24 surrounds all of the screen 16 flow transfer
surface and
extends along the borehole length substantially coextensively with the
hydrocarbon fluid
production zone. The flowpipe lower end is terminated by a bull plug 25, for
example.
COMPONENT DESCRIPTION
[0015] The upper end of the gravel pack body 20 comprises a pair of internal
pipe
sealing surfaces 26 and 28 which are short lengths of substantially smooth
bore, internal
pipe wall having a reduced diameter. These internal sealing surfaces 26 and 28
are
separated axially by a discreet distance to be subsequently described with
respect to the
crossover tool 50.
[0016] The upper end of the gravel pack body 20 also integrates a tool joint
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thread 30, a tool shoulder 32 and a limit ledge 34. Below the pipe sealing
surfaces 26
and 28 along the length of the gravel pack extension tube 23 are three collet
shifting
profiles 36, 37 and 38. The axial separation dimensions between the pipe
sealing
surfaces 26 and 28 are also critically related to the axial separation
distances between
collet shifting ledges 36, 37 and 38 as will be developed more thoroughly with
regard
to the crossover tool 50.
[0017] Hydrocarbon production fluid flow, therefore, originates from the
production zone 18, passes through the gravel pack 24 and screens 16 into the
internal void volume of the flowpipe 21. From the screens 16, the fluid enters
and
passes through the terminal sub 44 and into the production pipe 42. The
production
pipe 42 carries the fluid to the surface where it is appropriately channeled
into a field
gathering system.
[0018] The aggregate constituency of the gravel pack 24 is deposited in the
wellbore annulus as a fluidized slurry. Procedurally, the slurry is pumped
down the
internal pipe bore of a completion string that is mechanically manipulated
from the
surface. Generally, completion string control movement includes only rotation,
pulling
and, by gravity, pushing. Consequently, with these control motions the slurry
flow
must be transferred from within the completion string bore into the annulus
between
the wellbore wall and the gravel pack extension flow pipe 21 above the screens
16.
The screens 16 separate the fluid carrier medium (water, for example) from the
slurry
aggregate as the carrier medium enters the internal bore of the flow pipe 21.
The flow
pipe channels the carrier medium return flow up to a crossover point within
the
completion string where the return flow is channeled into the annulus between
the
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internal casing walls 12 and the outer wall surfaces of the completion string.
From the
crossover point, the carrier medium flow is channeled along the casing annulus
to the
surface.
[0019] When the desired quantity of gravel pack is in place, the internal bore
of
the completion string must be flushed with a reverse flow circulation of
carrier medium
to remove aggregate remaining in the completion string above the crossover
point.
Such reverse flow is a carrier medium flow that descends along the carrier
annulus to
the cross-over point and up the completion string bore to the surface.
Throughout
each of the flow circulation reversals, it is necessary that a net positive
pressure be
maintained against the producing zone of the wellbore to prevent any borewall
collapse. To this objective, a crossover tool 50 as illustrated by FIG. 2 is
constructed to
operatively combine with the gravel pack body 20.
[0020] Generally, the crossover tool 50 assembles coaxially with the gravel
pack
body 20 and includes a setting tool 52 that is attached to the lower end of
the
completion string 46. The setting tool 52 comprises a collar 54 having a lower
rim face
58 that mates with the tool shoulder 32 of the gravel pack body 20 when the
crossover
tool 50 is structurally unitized by a mutual thread engagement 55 with the
gravel pack
body 20. Transverse apertures 56 perforate the collar 54 perimeter.
[0021] Internally of the collar 54 rim, an inner tube 60 is structurally
secured
therewith. As best seen from the detail of FIGs. 5 and 6, a thread collar 62
surrounds
the upper end of the inner tube 60 to provide an upper void chamber 64 between
the
thread collar 62 and the tube 60. The thread collar 62 is perforated for fluid
pressure
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transmission between the collar apertures 66 and the void chamber 64. Fluid
pressure
transmission channels are also provided between the void chamber 64 and an
upper
by-pass chamber 66. The upper by-pass chamber 66 is an annular void space
between the inner tube 60 and an outer lip tube 68. Axially, the upper by-pass
chamber 66 is terminated by a ring-wall 70. An upper by-pass flow channel 72
opens
the chamber 66 to the outer volume surrounding the outer lip tube 68. An upper
o-ring
74 seals the annular space between the outer lip tube 68 and the inner sealing
surface
26 of the packer 22. The outer perimeter of the ring-wall 70 carries o-ring 76
for the
same purpose when the crossover tool 50 is axially aligned with the sealing
surface
26.
[0022] A lower sleeve 80 coaxially surrounds the inner tube 60 below the ring-
wall 70 to create a lower by-pass chamber 82. A lower by-pass flow channel 84
opens
the chamber 82 to the outer volume surrounding the lower sleeve 80. O-ring 86
cooperates with the packer sealing surface 26 and the o-ring 76 to selectively
seal the
lower by-pass flow channel 84.
[0023] At the lower end of the inner tube 60, a check valve ball seat 90 is
provided on an axially translating sleeve 91. The seat 90 is oriented to
selectively
obstruct downward fluid flow within the inner tube 60. Upward flow within the
tube is
relatively unobstructed since a cooperative check valve ball 92 is uncaged.
Upward
fluid flow carries the check valve ball away from the seat 90 and upward along
the tool
string 46 bore. Above the check valve seat 90 is a crossover port 94 between
the bore
of the inner tube 60 and the outer volume surrounding the lower sleeve 80. O-
rings 96
and 98 cooperate with the lower seal bore 102 of the lower seal ring 100 to
isolate the
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crossover port 94 when the crossover tool is correspondingly aligned. Below
the
check valve seat 90 are by-pass flow channels 99 in the sleeve 91 and flow
channels
88 in the inner tube 60. When aligned by axial translation of the sleeve 91,
the flow
channels 88 and 99 open a fluid pressure communication channel between the
lower
by-pass chamber 82 and the internal bore of the lower sleeve 80 below the
valve seat
90. Alignment translation of the sleeve 91 occurs as a consequence of the
hydraulic
pressure head on the sleeve 91 when the ball 92 is seated. By-pass flow
channels 29
are also provided through the wall of gravel pack extension tube 23 between
the inside
sealing surfaces 26 and 28 of the packer body 20.
[0024] Below the lower sleeve 80 but structurally continuous with the
crossover
tool assembly are an anti-swabbing tool 110 and an axial indexing collet 150.
The
purpose of the anti-swabbing tool is to control well fluid loss into the
formation after the
gravel packing procedure has been initiated but not yet complete. The axial
indexing
collet 140 is a mechanism that is manipulated from the surface by selective up
or down
force on the completion string that positive locate the several relative axial
positions of
the crossover tool 50 to the gravel pack body 20.
[0025] In reference to FIG. 3, the anti-swabbing tool 110 comprises a mandrel
112 having internal box threads 113 for upper assembly with the lower sleeve
80. The
mandrel 112 is structurally continuous to the lower assembly thread 114. At
the lower
end of the mandrel 112, it is assembled with a bottom sub 115 having external
pin
threads 116. Within the mandrel 112 wall is a retaining recess for a pivoting
check
valve flapper 117. The flapper 117 is biased by a spring 118 to the
down/closed
position upon an internal valve seat 120. However, the flapper is normally
held in the
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open position by a retainer button 119. The retainer button is confined behind
a
selectively sliding key slot 126 that is secured to a sliding housing sleeve
124. The
housing sleeve 124 normally held at the open position by shear screws 128. At
the
upper end of the housing sleeve 124 is an operating collet 121 having profile
engagement shoulders 122 and an abutment base 123. A selected up-stroke of the
completion string causes the collet shoulders 122 to engage an internal
profile of the
completion string. Continued up-stroke 'force presses the collet abutment base
123
against an abutment shoulder on the housing sleeve. This force on the housing
sleeve
shears the screws 128 thereby permitting the housing sleeve 124 and key slot
126 to
slide downward and release the flapper 117. The downward displacement of the
housing sleeve also permits the collet 121 and collet shoulders 122 to be
displaced
along the mandrel 112 until the profile of the collet shoulders 122 fall into
the mandrel
recess 126. When retracted into the recess 126, the shoulder 122 perimeter is
sufficiently reduced to pass the internal activation profile thereby allowing
the device to
be withdrawn from the well after the flapper has been released..
[0026] Coaxial alignment of the crossover tool 50 with the gravel pack body 20
is largely facilitated by the axial indexing collet 140 shown by FIG. 4A-4E.
The collet
140 is normally secured to the lower end of the crossover tool 60 and below
the anti-
swabbing tool 110. With respect to FIG. 4, a structurally continuous mandrel
142
includes exterior surface profiles 146 and 148. The profile 146 is a cylinder
cam
follower pin. The profile 148 is a collet finger blocking shoulder. Both
profiles 146 and
148 are radial projections from the cylindrical outer surface of the mandrel
142.
Confined between two collars 152 and 154 is a sleeve collet 144 and a coiled
compression spring 150. The bias of spring 150 is to urge the collet sleeve
downward
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against the collar 154.
[0027] Characteristic of the collet 144 is a plurality of collet fingers 147
around
the collet perimeter. The fingers 147 are integral with the collet sleeve
annulus at
opposite finger ends but are laterally separated by axially extending slots
between the
finger ends. Consequently, each finger 147 has a small degree of radial
flexure
between the finger ends. About midway between the finger ends, each finger is
radially profiled, internally and externally, to provide an internal bore
enlargement 149
and an external shoulder 148. The outside diameter of the collet shoulder
section 148
is dimensionally coordinated to the inside diameter of the indexing profiles
36, 37 and
38 to permit axial passage of the collet shoulder 148 past an indexing profile
only if the
fingers are permitted to flex radially inward. The internal bore enlargement
149 is
dimensionally coordinated to the mandrel profile projection 148 to permit the
radial
inward flexure necessary for axial passage. The outside diameter of the
mandrel
projection 148 is also coordinated to the inside diameter of the collet
fingers 147 so as
to support the fingers 147 against radial flexure when the mandrel projections
148 are
axially displaced from radial alignment with the finger enlargements 149.
Hence, if the
mandrel projection section 148 is not in radial alignment with the collet
finger
enlargement section 149, the collet sleeve will not pass any of the axial
indexing
profiles 36, 37 and 38 of the gravel pack body extension tube 23.
[0028] The internal bore of the collet sleeve 144 is formed with a female
cylinder
cam profile to receive the cam follower pin 146 whereby relative axial
stroking between
the collet sleeve 144 and the mandrel 142 rotates the sleeve about the
longitudinal
axis of the sleeve by a predetermined number of angular degrees. The cam
profile
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provides two axial set positions for the collet sleeve relative to the mandrel
142. At a
first set position, the mandrel blocking profile 148 aligns with the internal
bore
enlargement area 149 of the fingers. At the second set position, the mandrel
blocking
profile 148 aligns with the smaller inside diameter of the collet fingers 144.
The
mechanism is essentially the same as that utilized for retracting point
writing
instruments: a first stroke against a spring bias extends the writing point
and a second,
successive, stroke against the spring retracts the writing point.
OPERATING SEQUENCE
[0029] Referring to FIGs. 5 and 6, in preparation for downhole positionment
within a desired production zone, the gravel pack body 20 is attached to the
crossover
tool 50 by a threaded connection 55 for a gravel pack assembly 15. A threaded
connection 48 also secures the gravel pack assembly 15 to the downhole end of
the
completion string 46. At this point, the packer seal 22 is radially collapsed
thereby
permitting the assembly 15 to pass axially along the bore of casing 12. The
indexing
collet 140 is set in the expanded alignment of FIG. 4A to align the mandrel
profile 148
with the finger bore enlargement area 149. Consequently, the collet finger
support
shoulders 145 will constrict to pass through the tube 23 restriction profiles
36, 37 and
38.
[0030] Normally, the casing bore 12 and open borehole 10 below the casing 12
will be filled with drilling fluid, for example, which maintains a hydrostatic
pressure
head on the walls of the production zone. The hydrostatic pressure head is
proportional to the zone depth and density of the drilling fluid. The drilling
fluid is
formulated to provide a hydrostatic pressure head in the open borehole that is
greater
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than the natural, in situ, hydrostatic pressure of the formation. Since the
packer seal is
collapsed, this well fluid will flow past the packer 22 as the completion
string is lowered
into the well thereby maintaining the hydrostatic pressure head on the
borehole wall.
Consequently, placement of the assembly will have no pressure effect on the
production zone. If desired, well fluid may be pumped down through the
internal bore
of the completion string 46 and back up the annulus around the assembly 15 and
completion string in the traditional circulation pattern.
[0031] When the completion string screens 16 are suitably positioned at the
first
index position along the borehole length, the check valve ball 92 is placed in
the
surface pump discharge conduit for pumped delivery along the completion string
bore
onto the check valve seat 90 as illustrated by FIGs. 7 and 8. Closure of the
valve seat
90 permits pressure to be raised within the internal bore 46 of the completion
string to
secure the completion string location by setting the packer slips and seals
22. When
the packer seals 22 are expanded against the internal bore of casing 12, fluid
flow and
pressure continuity along the casing annulus is interrupted. It is to be noted
that the
by-pass port 94 of the crossover tool is located opposite from the lower seal
bore 102
between the o-ring seals 96 and 98, thereby effectively closing the by-pass
port 94.
However, the restricted by-pass flow routes provided by the collar apertures
56, the
void chamber 64, the upper by-pass chamber 66, and the upper by-pass flow
channels
72 and 29 prevent pressure isolation of the production zone bore wall 10.
[0032] Next, the crossover tool 50, which is directly attached to the
completion
string 46, may be axially released from the gravel pack body 20 and positioned
independently by manipulations of the completion string 46. The completion
string 46
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is first rotated to disengage the crossover tool threads 55 from the threads
30 of the
gravel pack body 20. With the assembly threads 30 and 55 disengaged, the
crossover
tool 50 is lifted to a second index position relative to the gravel pack body
20. With
respect to FIG. 4B, the completion string is lifted to draw the collet fingers
147 through
a tube restriction profile. The draw load is indicated to the driller as well
as the load
reduction when the collet fingers clear the restriction. Additionally, the
draw load on
the collet sleeve strokes and rotates the sleeve to reset the follower pin in
the sleeve
cam profile. Accordingly, when the driller reverses and lowers the completion
string,
mandrel blocking profile 148 aligns with the smaller inside diameter of the
collet fingers
147. The external finger shoulders 145 engage the tube profile to prevent
further
downhole movement of the completion string and positively locate the crossover
tool
50 relative to the gravel pack body 20 at a second axial index position as
shown by
FIG 4C.
[0033] With respect to the upper end of the crossover tool assembly 50 as
illustrated by FIGs. 9 and 10, the ring-wall o-ring seal 74 engages the
sealing surface
26 of the packer 22 to seal the annulus 104 between the gravel pack extension
tube
23 and the crossover tool sleeve 80 from by-pass discharges past the packer
22.
Simultaneously, the crossover flow port 94 from the internal bore of the inner
tube 60
is opened into the annular volume 104 and ultimately, into the casing annulus
below
the packer 22. Here, the seal integrity of packer 22 may be verified by
elevating fluid
pressure within the borehole annulus above the packer 22 to a suitable
pressure
magnitude that is greater than the natural, hydrostatic formation pressure and
also
greater than the pressure below the packer 22. Simultaneously, wellbore
annulus
pressure below the packer 22 is also maintained above the natural hydrostatic
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formation pressure via fluid delivered from surface pumps, for example, along
the
internal bore of the completion string 46, into the internal bore of the inner
tube 60 to
exit through the port 94 into annulus 104 between the crossover tool sleeve 80
and the
gravel pack extension tube 23. From the annulus 104, pressurized working fluid
exits
through the by-pass channels 29 into the casing annulus below the packer 22.
[0034] With a confirmation of the seal and fixture of packer 22, the crossover
tool 50 is axially indexed a third time to the relationship of FIGs. 11 and 12
whereat the
ring wall 70 and the lower by-pass flow channel 84 from the lower by-pass
chamber 82
are positioned above the sealing surface 26. However, the o-ring seal 86
continues to
seal the space between the sealing surface 26 and the lower sleeve 80. At this
setting, a fluidized gravel slurry comprising aggregate and a fluid carrier
medium may
be pumped down the completion string 46 bore into crossover flow ports 94
above the
check valve 90. From the crossover flow ports 94, the gravel slurry enters the
annular
chamber 104 and further, passes through the by-pass channels 29 into the
casing
annulus below the packer 22.
[0035] From the by-pass channels 29, the slurry flow continues along the
casing
annulus into the open borehole annulus within the production zone 18. Fluid
carrier
medium passes through the mesh of screen elements 16 which block passage of
the
slurry aggregate constituency. Accordingly, the aggregate accumulates around
the
screen elements 16 and, ultimately, the entire volume between the raw wall of
the
open bore 10 and the screens 16.
10036] Upon passing the screens 16, carrier medium enters the gravel pack
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extension flow pipe 21 and the internal bore of lower sleeve 80. Below the
check valve
90, the carrier medium enters the lower by-pass chamber 82 through the check
valve
by-pass flow channels 88. At the upper end of the by-pass chamber 82, the
carrier
medium flow is channeled through the lower. by-pass 84 into the casing annulus
above
the packer 22. The upper casing annulus conducts the carrier medium flow back
to
the surface to be recycled with another slurry load of aggregate.
[0037] Unless it is possible predetermine the exact volume of aggregate
necessary to fill the open hole annulus within the production zone 18, excess
aggregate will frequently remain in the completion string bore when the gravel
pack 24
is complete. Usually, it is desirable to flush any excess aggregate in the
completion
string bore from the completion string before withdrawing the completion
string and
attached crossover tool. With reference to FIGs. 13 and 14, the crossover tool
50 is
withdrawn from the gravel pack extension 20 to a fourth index position at
which the
crossover port 94 is open directly to the casing annulus above the upper
packer 22.
Unslurried well fluid is pumped into the casing annulus in a reverse
circulation mode.
The reverse circulating fluid enters the inner tube 60 bore above the check
valve 90 to
fluidize and sweep any aggregate therein to the surface. However, to maintain
the
desired hydrostatic pressure head on the open hole production zone, reverse
circulating well fluid also enters the lower by-pass chamber 82 through the
lower by-
pass flow channel 84. Fluid is discharged from the chamber 82 through the
check
valve by-pass flow channels 88 into the volume below the packer 22 thereby
reducing
any pressure differential across the packer.
[0038] With the gravel pack 24 in place, the crossover tool 50 may be
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CA 02617072 2010-12-10
completely extracted from the gravel pack body 20 with the completion string
and
replaced by a terminal sub 44 and production pipe 42, for example.
[0039] Utility of the anti-swabbing tool with the crossover assembly 50 arises
with the circumstance of unexpected loss of well fluid into the formation
after the gravel
packing procedure has begun. Typically, a portion of filter cake has stuffed
from the
borehole wall and must be replaced by an independent mud circulation
procedure. As
a first repair step, fluid loss from within the completion string bore must be
stopped.
This action is served by releasing the flapper 117 to plug the bore
notwithstanding the
presence of the ball plug 92 on the valve seat 90.
[0040] The foregoing detailed description of our invention is directed to the
preferred embodiments of the invention. Various modifications may appear to
those of
ordinary skill in the art. It is accordingly intended that all variations
within the scope
and spirit of the appended claims be embraced by the foregoing disclosure.
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