U.S. patent application number 11/662373 was filed with the patent office on 2008-08-14 for method for drilling oil and gas wells.
This patent application is currently assigned to BP Exploration Operating Company Limited. Invention is credited to Philip Head, Paul George Lurie.
Application Number | 20080190624 11/662373 |
Document ID | / |
Family ID | 33186716 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080190624 |
Kind Code |
A1 |
Head; Philip ; et
al. |
August 14, 2008 |
Method for Drilling Oil and Gas Wells
Abstract
When drilling or completing an oil or gas well, it is often
desirable to drill a borehole at an angle to the initial borehole.
A process for deflecting a well tool towards the wall of a well
bore comprises positioning within the well bore a radially
expandable pipe designed to curve longitudinally when its diameter
is expanded, expanding the diameter of the radially expandable pipe
thereby causing the pipe to curve and passing the well tool through
the curved pipe: The process is particularly suitable for
through-tubing operations in which a lateral bore is initiated from
a production well having within the well a smaller diameter
production tubing (14) comprising (i) passing through the
production tube (14) a radially expandable pipe (1) designed to
curve longitudinally as its diameter is expanded, into a section of
well bore (12) having a diameter greater than the diameter of the
production tubing (14) (ii) expanding the diameter of the radially
expandable pipe (1) thereby causing the pipe to curve, (iii)
passing through the curved pipe a milling device or drill bit and
(iv) milling the casing or drilling into the well bore wall.
Inventors: |
Head; Philip; (Surrey,
GB) ; Lurie; Paul George; (Surrey, GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
BP Exploration Operating Company
Limited
Middlesex
GB
XL Technology Limited
Middlesex
GB
|
Family ID: |
33186716 |
Appl. No.: |
11/662373 |
Filed: |
August 5, 2005 |
PCT Filed: |
August 5, 2005 |
PCT NO: |
PCT/GB2005/003102 |
371 Date: |
February 13, 2008 |
Current U.S.
Class: |
166/384 ;
166/207 |
Current CPC
Class: |
E21B 17/1021 20130101;
E21B 7/06 20130101; E21B 43/103 20130101 |
Class at
Publication: |
166/384 ;
166/207 |
International
Class: |
E21B 43/10 20060101
E21B043/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 9, 2004 |
GB |
0420002.8 |
Claims
1-13. (canceled)
14. A process for deflecting a well tool towards the wall of a well
bore comprising positioning within the well bore a radially
expandable pipe designed to curve longitudinally when its diameter
is expanded, expanding the diameter of the radially expandable pipe
thereby causing the pipe to curve and passing the well tool through
the curved pipe.
15. A process as claimed in claim 14 in which a lateral well bore
is initiated from a production well having within the well bore a
smaller diameter production tubing comprising (i) passing through
the production tube a radially expandable pipe designed to curve
longitudinally as its diameter is expanded, into a section of well
bore having a diameter greater than the diameter of the production
tubing, (ii) expanding the diameter of the radially expandable pipe
thereby causing the pipe to curve, (iii) passing through the curved
pipe a milling device or a drill bit and (iv) milling the casing or
drilling into the well bore wall.
16. A process as claimed in claim 15 in which a lateral well bore
is initiated from a cased production well having within the well
bore a smaller diameter production tubing comprising (i) milling a
window in the casing of the well bore, (ii) passing through the
production tube a radially expandable pipe designed to curve
longitudinally as its diameter is expanded, into a section of well
bore having a diameter greater than the diameter of the production
tubing, (iii) orienting the radially expandable pipe within the
well bore, (iv) expanding the diameter of the radially expandable
pipe thereby causing the pipe to curve into the milled window, (v)
passing through the curved pipe a drill bit and (vi) drilling into
the well bore wall.
17. A process as claimed in claim 14 or claim 15 in which the
radially expandable pipe is oriented within the well bore prior to
expansion.
18. A process as claimed in claim 14 or claim 15 in which at least
one spacer is used to support the curved tube within the well
bore.
19. A process as claimed in claim 15 in which the angle of
deviation of the lateral bore is from about 0.4 to about 1.0
degree.
20. A radially expandable pipe for use in the process as claimed in
claim 14 or claim 15 which has over at least part of its length in
asymmetrical wall thickness.
21. A radially expandable pipe as claimed in claim 20 in which the
asymmetrical wall thickness is provided by securely fixing a length
of steel longitudinally on the outer surface of a cylindrical
pipe.
22. A radially expandable pipe as claimed in claim 20 in which the
length of steel comprises a cylindrical section having an internal
surface which is an arc of a circle having a central angle of from
2 to 20 degrees and a radius which is the same as or slightly
larger than the external radius of the pipe.
23. A radially expandable pipe having at least one spacer fixed to
the outer surface, the spacer comprising an elongate element having
a first and second end each of which is securely fixed to the pipe
such that the change in length as the pipe is expanded deforms the
elongate element, increasing its maximum radial distance from the
centre of the pipe.
24. A radially expandable pipe as claimed in claim 23 in which the
spacer is substantially cylindrical and expands substantially
symmetrically.
25. A radially expandable pipe as claimed in claim 23 in which the
spacer is substantially cylindrical and has elements that are
designed to expand asymmetrically about the center of the pipe.
26. A radially expandable pipe as claimed in claim 23 having a
plurality of spacers positioned along the length and/or around the
circumference of the radially expandable pipe such that when the
pipe is expanded they expand to different radial lengths to hold
the curved pipe in place within the well bore.
Description
[0001] The present invention relates to a method and apparatus for
drilling oil and gas wells. In particular, the invention relates to
a method and apparatus for opening a window in a well bore to
initiate a lateral well bore and for drilling a well bore through
such a window.
[0002] When drilling or completing an oil or gas well, it is often
desirable to drill a borehole at an angle to the initial,
substantially vertical, borehole. For example, it may be necessary
to establish a new drilling course for directional or horizontal
drilling, or it may be necessary to sidetrack the original borehole
to avoid a section of damaged bore, junk in the hole, or other
negative well conditions.
[0003] In order to initiate or "kick-off" a deviated well, it is
necessary to deflect the drilling tool through the wall of the
initial well bore. A deflecting tool known as a "whipstock" has
been known and used for many years to achieve the deflection of the
drilling tool. Whipstocks can be used in both cased and open hole.
Where the initial well bore is cased, a window is first milled in
the casing and then the drilling tool is deflected through the
window to drill the lateral well. Although other methods, such as
the use of bent subs and mud motors have been developed, whipstocks
are still widely used to deflect the milling and drilling tools to
kick-off lateral wells. Some whipstock designs are intended to be
left downhole, whereas others are designed to be retrieved.
[0004] The standard whipstock is generally an elongate tool,
typically about 3 m to 6 m long, which has the general
cross-sectional shape of a right triangle. The short base of the
right triangle is the bottom of the whipstock in the well bore. An
upstanding back surface intersects the base at essentially a right
angle. The hypotenuse is the gently sloping guide surface of the
whipstock which is designed to direct the well tools into a
direction which is at an angle to the longitudinal axis of the
initial well bore.
[0005] To be effective, the whipstock must be positioned and
secured in the well bore at the required location and orientation.
A whipstock can be set on the bottom of the initial well bore, or
on top of a suitable anchor or cement plug. Some designs of
whipstock may be used in the open hole. The upstanding back surface
of the whipstock may rest on the wall of the well bore or the
casing lining the well bore. When secured in this manner the
whipstock provides a stable platform for guiding the mill or
drilling tool.
[0006] A common problem with known whipstocks is that the starter
mill or drill can damage the whipstock, adversely affecting the
drilling of the lateral. In some cases the attempt to drill the
lateral may have to be abandoned and begun again at a different,
usually higher, location in the initial well bore. This will entail
significant cost and loss of time.
[0007] Sometimes the interior of the initial well bore has one or
more restrictions along its length that reduce the cross-sectional
area of the wellbore. For example, the well bore may have a string
of production tubing that is carried concentrically within the main
wellbore and that is of a smaller internal diameter than the
wellbore or any casing lining the wellbore. Typically, the wellbore
has an internal diameter of about 5 inches (12.7 cm) to about 10
inches (25.4 cm), for example 7 inches (17.8 cm) and the production
tubing has an internal diameter of about 2.5 inches (6.4 cm) to
about 6 inches (15.2 cm), for example 4.5 inches (11.4 cm). This
means that any tool that is passed down the interior of that well
bore, including a whipstock, has to be small enough in
cross-section to pass through the restriction in order to reach
lower levels in the wellbore. This is called through-tubing
operations in that any well operations that are to be carried out
in the well bore below the end of the production tubing require the
equipment to be passed through the interior of the production
tubing before it can reach the area where the well operation is to
be carried out. The alternative would be to remove the production
tubing in its entirety from the well bore, which is an expensive
and time consuming process. Thus, it is very desirable to be able
to pass well tools that are to be used in well operations through
the interior of the smaller diameter production tubing down below
the end of that tubing into the larger diameter wellbore and then
carrying out well operations with those tools in that larger area
of the wellbore.
[0008] Unfortunately, some tools that are made small enough to pass
through restrictions such as production tubing do not operate as
well in the larger diameter well bore area below the end of the
production tubing and this includes whipstocks. This is because the
small tools do not adequately take up the space afforded by the
larger well bore area. In particular, the upstanding back surface
of the whipstock may not be adequately supported. Some
through-tubing whipstocks are set diagonally across the larger
diameter bore hole and so only the top section rather than
substantially the full length of the back surface is in contact
with the wall or casing opposite the wall in which the window is to
be milled and the bottom of the guide surface of the whipstock is
positioned against the wall into which the window is to be milled.
In this position, the whipstock may flex or bend when contacted by
the milling or drilling tools, which can result in the mill or
drill jumping off the guide surface of a whipstock. Some designs of
whipstock have hinged sections that can be opened after the
whipstock has been passed through the restriction to provide
improved support for the whipstock. However, these more complex
devices may still provide insufficient guidance to the milling and
drilling tools. Sometimes the through-tubing whipstock can slip
within the hole and as a result may provide inadequate guidance to
the milling and drilling tools.
[0009] The present invention relates to an alternative method of
initiating or drilling a lateral well and more specifically to a
method that can be used in the larger diameter area of a well bore
below the end of a restriction through which the tools must
pass.
[0010] The term "side track well" is sometimes used to describe a
branch from an existing wellbore where the existing wellbore no
longer produces hydrocarbon fluid and the term "lateral well" is
sometimes used to describe a branch from an existing wellbore where
the existing wellbore continues to produce hydrocarbon fluid. The
present invention can be used in any wellbore from which a second,
branched, wellbore is to be drilled. References herein to lateral
wells or bores should be understood to include any such wells,
whether or not the existing well continues to produce. Indeed,
should the need arise; the invention could be used to drill a
lateral well in an injection well.
[0011] Thus, according to the present invention, a process for
deflecting a well tool towards the wall of a well bore comprises
positioning within the well bore a radially expandable pipe
designed to curve longitudinally when its diameter is expanded,
expanding the diameter of the radially expandable pipe thereby
causing the pipe to curve and passing the well tool through the
curved pipe.
[0012] The present invention is particularly suitable for
through-tubing operations and includes a process for initiating a
lateral bore from a production well having within the well a
smaller diameter production tubing comprising (i) passing through
the production tube a radially expandable pipe designed to curve
longitudinally as its diameter is expanded, into a section of well
bore having a diameter greater than the diameter of the production
tubing (ii) expanding the diameter of the radially expandable pipe
thereby causing the pipe to curve, (iii) passing through the curved
pipe a milling device or drill bit and (iv) milling the casing or
drilling into the well bore wall.
[0013] The milling device or drill bit may be attached to the lower
end of a drill string or may be used at the end of a wireline. The
present invention can be used with remotely controlled drilling
devices. Such devices are known. For example, U.S. Pat. No.
6,305,469 and PCT Patent Application WO 2004/011766 disclose
methods for drilling a wellbore using a remotely controlled
drilling device. By controlling stabilisers for the remotely
controlled drilling device, the drill bit can be tilted in the
wellbore to start drilling a curved wellbore section. The drilling
device may be provided with a remotely operable steering means, for
example, a steerable joint, which can be used to adjust the
trajectory of the new wellbore section as it is drilled.
[0014] The present invention includes a radially expandable pipe
for use in the process, which has over at least part of its length
an asymmetrical wall thickness.
[0015] The asymmetrical wall thickness can be provided by any known
method. For example, the pipe may be manufactured by rolling or
extrusion such that the wall thickness is not symmetrical over at
least a portion of the pipe. The asymmetry may be provided by
machining the internal or external surfaces of a pipe that
initially has a substantially uniform wall thickness. Suitable
material may also be fixed to the external surface of the pipe to
provide a thicker wall.
[0016] The radially expandable pipe is generally made of steel and
any material fixed to the outer surface is also preferably steel.
Suitably, the pipe comprises a steel pipe of substantially uniform
wall thickness and at least one length of steel is securely
attached to the outer surface of the steel pipe. Conveniently, the
length of steel may be attached to the pipe by welding around all
or part of its periphery. The length of steel may be of any shape
but preferably comprises a cylindrical section having an internal
surface which is an arc of a circle having a central angle of from
about 2 to about 160 degrees, typically from about 2 to about 20
degrees or 5 to about 20 degrees, and a radius which is
substantially the same as, or slightly larger than, the external
radius of the pipe. The length of steel attached to the pipe may be
of substantially uniform thickness. In this case, there will be a
step change in the wall thickness. It is preferable that the wall
thickness gradually increases and decreases around the pipe. The
length of steel welded to the pipe may therefore preferably be
crescent shaped in cross-section.
[0017] The asymmetric wall thickness may extend along the whole
length of the pipe or only a part of the length.
[0018] The relative thicknesses of the wall of the pipe and the
length of the asymmetry are selected to achieve the desired
curvature in the pipe as it is expanded. Since the pipe is to be
curved down the well bore, it must be designed such that expanding
the pipe to the desired internal diameter results in the desired
curvature without exerting unacceptable stresses on the well bore.
For example, in an uncased wellbore, it may be undesirable if the
expansion would result in a greater curvature of the pipe, but for
the limitations of space in the well bore, resulting in the walls
of the well bore being put under compressive stress, as this could
result in damage to the formation.
[0019] The person skilled in the art could readily determine the
design of the pipe that will provide the appropriate curvature on
expansion of the pipe. This may require some trials with pipe of
the size and material to be used. When drilling a deviated well,
the amount of deviation from the vertical may typically be of the
order of 1 or 2 inches (2.54 to 5.08 cm) per 10 feet (3 m) of
depth, i.e. the angle of deviation of the lateral bore may be of
the order of about 0.4 to about 1.0 degree although greater or
smaller deviations may be used in some applications.
[0020] Expandable pipe for use in oil and gas wells is known. For
example, it is known to position pipe downhole and then expand it.
This technology is used, for example, in producing monobore casing
or production tubing where a tubing string of smaller diameter is
lowered through wider diameter tubing and then expanded to
substantially the same diameter as the wider diameter tubing.
[0021] Any of the known methods for expanding pipe may be used in
the present invention such as by urging a mandrel or conical
expander through the pipe or using a system of rolling the pipe
using balls or rollers, which are urged outwardly against and
rotated around the inner surface of the pipe. An example of the
latter type of expanding apparatus is disclosed in US Patent
Application Publication US 2001/0045284. When a pipe is expanded
using a mandrel forced through the pipe, the diameter of the pipe
may be typically increased by about 10 to 20% and the overall
length reduces by about 5%. Whereas, when the expansion is achieved
using rotating balls or rollers, an expansion of about 10 to 20% in
diameter is accompanied by an increase in the overall length of the
pipe of about 5%.
[0022] Due to the asymmetric wall thickness of the expandable pipe
the pipe expands preferentially where it is less thick. This causes
the pipe to become curved.
[0023] The expandable pipe may be oriented before or after
expansion, but is preferably oriented before expansion. Known
techniques can be used to orient the pipe within the well bore so
that after expansion the curved pipe will direct the well tools in
the desired direction.
[0024] Preferably spacers are used to support the curved pipe in
the well bore. Spacers are therefore preferably positioned around
the circumference and along the length of the curved pipe. Suitable
spacers are known and include, for example, bow spring
centralizers.
[0025] The upper end of the curved pipe is preferably centralised
and held securely within the well bore. Suitable spacers to achieve
this would be substantially cylindrical and expand substantially
symmetrically around the circumference of the pipe. However, in
order to support the curved pipe in the substantially straight
hole, the supports along the length of the curved pipe will have to
bridge a wider gap at one side of the curved pipe than at the
other. Thus, the radially expandable pipe preferably has spacers
that are designed to expand asymmetrically about the centre of the
pipe. This could be for example, a substantially cylindrical spacer
having elements that are designed to expand asymmetrically about
the centre of the pipe. The invention includes a radially
expandable pipe having a plurality of spacers positioned along the
length and around the circumference of the radially expandable pipe
such that when the pipe is expanded the spacers expand to different
radial lengths to hold the curved pipe in place within the well
bore.
[0026] The invention includes a radially expandable pipe having at
least one spacer positioned along its length the spacer comprising
a deformable elongate member having a first end and a second end,
each of said ends being attached to the radially expandable pipe
such that as the pipe is expanded the change in the length of the
pipe deforms the elongate member so that it projects radially from
the centre of the pipe. The amount of radial expansion required for
the spacer will depend on the location in which it is to be used.
An expansion of up to and in some cases exceeding 80% of the
initial radial length may be desired for the spacer. For example,
in order to be capable of passing through a 4.5 inch (11.4 cm)
internal diameter production tubing, the radial length of the
radially expandable pipe and spacer would be about 2 inches (5 cm)
and in order to support the pipe in a 7 inch (17.8 cm) internal
diameter casing, the expanded radial length would be about 3.5
inches (8.9 cm); an expansion of about 75% of the original radial
length.
[0027] The outer surface of the spacer may be provided with means
to improve the grip with the casing or wellbore wall after
expansion. For example, the outer surface may be shaped, coated or
treated to provide a rough surface. A suitable surface can be
provided by thermally spraying the surface with a metal
carbide.
[0028] The deformable elongate member can be a bow spring attached
at each end such that a reduction in the length of the pipe, such
as occurs when the pipe is expanded using a mandrel, forces the
ends towards each other and the bow spring bows outwardly. The bow
spring can initially lie substantially flat against the surface of
the pipe. This facilitates movement of the expandable pipe down the
well and into position. Expansion of the pipe causes the bow spring
to expand and engage the wall of the well bore or the casing of the
well.
[0029] Preferably, the spacer comprises a plurality of bow springs
arranged around the circumference of the radially expandable pipe.
The bow springs can be attached together at the ends to form a
substantially cylindrical cage structure. By selecting different
shapes, lengths, thicknesses and/or materials, the bow springs can
be made to bow more or less for the same reduction in length of the
expandable pipe. The bow spring must be made of material and
designed to provide sufficient stiffness to provide support for the
expanded pipe.
[0030] In another embodiment, the deformable elongate member can be
an articulated element, each end of which is attached to the
expandable pipe such that an increase in the length of the pipe,
such as occurs when the pipe is expanded using a rolling ball or
roller expander, causes the ends of the deformable elongate member
to move away from each other and the articulated member moves from
a first position close to the surface of the expandable pipe to a
second position which is radially extended from the centre of the
pipe. For example, the articulated element may be a folded element
that is a single piece of material folded to form the folded
element. Another embodiment of the articulated element comprises
two or more pieces of material fixed together to form the
articulated element. The articulated element may have a joint
towards one or both ends and/or along its length. An example of a
suitable articulated element comprises a length of material folded
into two unequal legs and attached by the end of each leg to the
expandable pipe such that in cross-section, the external wall of
the pipe and the two legs of the deformable elongate member have
the form of an obtuse triangle. The obtuse angle is preferably
greater than 120 degrees in order that in the first position, the
articulated element lies close to the wall of the pipe. A similar
articulated element comprises two lengths of material fixed
together at one end and the other ends are attached to the
pipe.
[0031] A person skilled in the art will readily be able to select
or design one or more spacers that will support the curved pipe in
the well bore.
[0032] The process according to the present invention is
particularly suitable where it is necessary to pass the well tools
required to initiate and drill a lateral well through the interior
of a smaller diameter production tubing down below the end of that
tubing into the larger diameter well bore and then carrying out the
initiation or drilling of the lateral well with those tools in that
larger area of the well bore. The radially expandable pipe is
lowered down the well bore, through the smaller diameter production
tubing and down into a cased or open hole of greater diameter. The
radially expandable pipe can be centralised within the larger
diameter well bore, using suitable centralising equipment. Means
for expanding the radially expandable pipe are introduced into the
interior of the pipe and the pipe expanded. The pipe can
conveniently be expanded to substantially the same as the internal
diameter of the last section of the production tubing. As it
expands, the asymmetric wall thickness causes the pipe to curve.
Spacers can be provided to support the pipe within the well bore.
These can be of the type described above that are fixed to the pipe
and are deployed as the pipe is expanded. Optionally, the spacers
initially support the pipe centrally, but are distorted as the pipe
expands and curves.
[0033] In an embodiment of the invention, a window is first milled
in the casing and then the radially expandable pipe is lowered into
position adjacent the window and then expanded and curved such that
the window provides more space to accommodate the curved pipe. A
suitable method for forming a window in the production tube or
casing is disclosed in PCT Patent Application WO 2004/046499. The
disclosed method of cutting a window in a tubular, in particular a
casing, comprises using a remotely controlled electrically powered
cutting tool that has a pivotally mounted cutting head that can be
pivoted towards the wall of the tubular.
[0034] The invention will now be described with reference to the
accompanying drawings in which:
[0035] FIG. 1 is an isometric drawing of part of a radially
expandable pipe suitable for use in the present invention.
[0036] FIG. 2 is a cross-sectional drawing of the expandable pipe
of FIG. 1 taken through A-A.
[0037] FIG. 3 is a cross-sectional drawing of another embodiment of
a radially expandable pipe suitable for use in the present
invention.
[0038] FIG. 4 is a schematic sectional drawing of the radially
expandable pipe being expanded and curved by an expanding
device.
[0039] FIG. 5 is a schematic sectional drawing of a bow spring
spacer before expansion of the radially expandable pipe.
[0040] FIG. 6 is a schematic sectional drawing of the bow spring
spacer of FIG. 5 after expansion of the radially expandable
pipe.
[0041] FIG. 7 is a schematic sectional drawing of a folded spacer
before expansion of the radially expandable pipe.
[0042] FIG. 8 is a schematic sectional drawing of the folded spacer
of FIG. 7 after expansion of the radially expandable pipe.
[0043] FIG. 9 is a schematic sectional drawing of an alternative
articulated spacer before expansion of the radially expandable
pipe.
[0044] FIG. 10 is a schematic sectional drawing of the alternative
articulated spacer of FIG. 9 after expansion of the radially
expandable pipe. FIG. 10a illustrates an expanded cross-section of
the spacer showing a profile of the legs 9 and 10.
[0045] FIG. 11 is an illustration of an expanded pipe in place in
the well bore.
[0046] FIGS. 1 and 2 illustrate part of a radially expandable pipe
1 which has, over at least part of its length, an asymmetrical wall
thickness. The asymmetrical wall thickness is provided by securely
fixing to the outside surface 4 of the pipe a length of steel 2.
The length of steel 2 comprises a cylindrical section having an
internal surface that is an arc of a circle having a central angle
.theta. of about 90.degree. and a radius which is substantially the
same as the external radius of the pipe. The length of steel 2 is
fixed to the pipe by welding along the outer edges 3, that are
transverse to the longitudinal axis of the expandable pipe 4. Thus
the length of steel 2 is not welded along the longitudinal edges
5.
[0047] FIG. 3 is a cross section of an alternative radially
expandable pipe in which the asymmetrical wall thickness is
provided by the inner surface 6 and outer surface 4 being
eccentric.
[0048] FIG. 4 is a schematic drawing of an expandable pipe 1 in
which, as for FIG. 1, the asymmetrical wall thickness is provided
by a length of steel 2 securely fixed to the outer surface 4 of the
pipe by welding along the outer edges 3. The pipe has been expanded
and curved by the action of an expanding device 16. The expanding
device can be any suitable expanding device such as a mandrel
expander or a ball or roller type expander as shown, for example,
in US Patent Application Publication US 2001/0045284.
[0049] FIGS. 5 to 10 are schematic sectional drawings illustrating
spacers that could be used in the present invention.
[0050] FIGS. 5 and 6 show a spacer 7 comprising a length of
material fixed at each end to the radially expandable pipe 4. The
spacer is designed to act like a bow spring. In the first position
shown in FIG. 5, the spacer lies alongside the outer surface 4 of
the expandable pipe. As the radially expandable pipe 4 is expanded,
for example by pulling a mandrel through the pipe, the axial length
of the pipe decreases; the fixed ends of the bow spring 7 move
towards each other causing the spring to bow and extend radially
from the pipe surface as shown in FIG. 6.
[0051] FIGS. 7 and 8 show a folded spacer 8 fixed to the outer
surface 4 of a radially expandable pipe. The folded spacer is
folded at each end and, as shown in FIG. 7, initially lies in a
first position alongside the outer surface 4 of the expandable
pipe. Expansion of the radially expandable pipe 4, for example by
using a rolling ball or roller expander, causes the fixed ends of
the folded spacer 8 to move away from each other and the spacer is
unfolded such that it extends radially from the surface of the
expandable pipe, as shown in FIG. 8.
[0052] FIGS. 9 and 10 show another embodiment of an articulated
spacer, which comprises two legs 9 and 10. The two legs are of
unequal length and could have been formed by folding a single piece
of material, but as shown more clearly in FIG. 10 the spacer
comprises two, initially separate, pieces of material joined, e.g.
by welding at one end 11. The other ends of the legs are fixed to
the surface of the radially expandable pipe 4. As shown in FIG. 9,
the spacer comprising the two legs 9 and 10 initially lies in a
first position alongside the outer surface 4 of the expandable
pipe. Expansion of the radially expandable pipe 4 causes the fixed
ends of the spacer to move away from each other and the spacer
unfolds such that it extends radially from the surface of the
expandable pipe, as shown in FIG. 10. FIG. 10a shows the profile of
the legs 9 and 10 taken along B-B of FIG. 10. Such a profile can
provide additional stiffness to the spacers as compared with flat
substantially rectangular sections. When the spacer is lying
adjacent the surface of the radially expandable pipe 4 as shown in
FIG. 9, the two legs 9 and 10 and the surface of the pipe form an
obtuse triangle with the obtuse angle being about 170 degrees. When
the spacer is extended, the triangle is still obtuse, but the
obtuse angle is shown as about 100 degrees.
[0053] It will be appreciated that if identical spacers are placed
around the circumference of the pipe at about the same axial
position and are subjected to the same change in the length of the
expandable pipe 4, then the spacers will be displaced from the
surface 4 of the expandable pipe by substantially the same amount
and the arrangement will tend to centralise the expandable pipe. By
using different spacers, e.g. spacers of different lengths then
they will be deflected from the surface 4 of the expandable pipe by
different amounts and the spacers will provide asymmetric
support.
[0054] FIG. 11 illustrates a curved expanded pipe 1 in the cased
well bore 12. As the curved expanded pipe 1 is wider than the cased
well bore 12, it is apparent that the window 13 was milled through
the casing 12 and into the formation before the radially expandable
pipe 1 was expanded and curved. This could be achieved, for
example, by using the apparatus and method disclosed in PCT Patent
Application WO 2004/046499. After milling the window 13, the
radially expandable pipe 1 was passed down the well bore and
through the production tube 14. It was centralised in the well bore
using centraliser 15. The radially expandable pipe was then
expanded to substantially the same internal diameter of the
production tube 14. Due to the asymmetric wall thickness of the
radially expandable pipe in the region 17, expansion of the pipe
caused it to bend at 18. The lower end of the pipe passed through
the window 13. As the pipe expanded, the spacers 19 fixed to the
surface of the pipe extended to support the curved pipe in the well
bore.
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