Note: Descriptions are shown in the official language in which they were submitted.
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ME T HOD OF RADIALLY EXPANDING A TUBULAR ELEMENT
The present invention relates to a method of radially
expanding a tubular element in a wellbore.
The technology of radially expanding tubular elements
in wellbores is increasingly applied in the industry of
oil and gas production from subterranean formations.
Wellbores are generally provided with one or more casings
or liners to provide stability to the wellbore wall,
and/or to provide zonal isolation between different earth
formation layers. The terms "casing" and "liner" refer to
tubular elements for supporting and stabilising the
wellbore wall, whereby it is generally understood that a
casing extends from surface into the wellbore and that a
liner extends from a downhole location further into the
wellbore. However, in the present context, the terms
"casing" and "liner" are used interchangeably and without
such intended distinction.
In conventional wellbore construction, several
casings are set at different depth intervals, and in a
nested arrangement, whereby each subsequent casing is
lowered through the previous casing and therefore has a
smaller diameter than the previous casing. As a result,
the cross-sectional wellbore size that is available for
oil and gas production, decreases with depth. To
alleviate this drawback, it has become general practice
to radially expand one or more tubular elements at the
desired depth in the wellbore, for example to form an
expanded casing, expanded liner, or a clad against an
existing casing or liner. Also, it has been proposed to
radially expand each subsequent casing to substantially
the same diameter as the previous casing to form a
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monobore wellbore. It is thus achieved that the available
diameter of the wellbore remains substantially constant
along (a portion of) its depth as opposed to the
conventional nested arrangement.
EP 1438483 B1 discloses a method of radially
expanding a tubular element in a wellbore whereby the
tubular element, in unexpanded state, is initially
attached to a drill string during drilling of a new
wellbore section. Thereafter the tubular element is
radially expanded and released from the drill string.
To expand such wellbore tubular element, generally a
conical expander is used with a largest outer diameter
substantially equal to the required tubular diameter
after expansion. The expander is pumped, pushed or pulled
through the tubular element. Such method can lead to high
friction forces that need to be overcome, between the
expander and the inner surface of the tubular element.
Also, there is a risk that the expander becomes stuck in
the tubular element.
EP 0044706 A2 discloses a method of radially
expanding a flexible tube of woven material or cloth by
eversion thereof in a wellbore, to separate drilling
fluid pumped into the wellbore from slurry cuttings
flowing towards the surface.
Although in some applications the known expansion
techniques have indicated promising results, there is a
need for an improved method of radially expanding a
tubular element.
In accordance with the invention there is provided a
method of radially expanding a tubular element extending
into a wellbore formed in an earth formation, the method
comprising
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- inducing a wall of the tubular element to bend
radially outward and in axially reverse direction so as
to form an expanded tubular section extending around a
remaining tubular section of the tubular element, wherein
said bending occurs in a bending zone of the tubular
element;
increasing the length of the expanded tubular section
by inducing the bending zone to move in axial direction
relative to the remaining tubular section;
wherein one of the tubular element and the wellbore wall
is provided with at least one seal member arranged to
induce sealing of the expanded tubular section relative
to the wellbore wall.
Thus, the tubular element is effectively turned
inside out during the bending process. The bending zone
of a respective layer defines the location where the
bending process takes place. By inducing the bending zone
to move in axial direction along the tubular element it
is achieved that the tubular element is progressively
expanded without the need for an expander that is pushed,
pulled or pumped through the tubular element.
Furthermore, by virtue of the expanded tubular
section being sealed relative to the wellbore wall,
undesired outflow of wellbore fluid from the wellbore, or
undesired inflow of formation fluid into the wellbore
past the expanded tubular section, is prevented.
Suitably, each seal member is provided at the tubular
element, wherein the seal member is positioned at one of
the outer surface and the inner surface of the expanded
tubular section.
The seal member can be fixedly connected to the
expanded tubular section by suitable connecting means, or
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it can be integrally formed with the expanded tubular
section.
It is preferred that the wall of the tubular element
includes a material that is plastically deformed in the
bending zone, so that the expanded tubular section
retains an expanded shape as a result of said plastic
deformation. In this manner it is achieved that the
expanded tubular section remains in expanded form due to
plastic deformation, i.e. permanent deformation, of the
wall. Thus, there is no need for an external force or
pressure to maintain the expanded form. If, for example,
the expanded tubular section has been expanded against
the wellbore wall as a result of said bending of the
wall, no external radial force or pressure needs to be
exerted to the expanded tubular section to keep it
against the wellbore wall. Suitably the wall of the
tubular element is made of a metal such as steel or any
other ductile metal capable of being plastically deformed
by eversion of the tubular element. The expanded tubular
section then has adequate collapse resistance, for
example in the order of 100-150 bars.
If the tubular element extends vertically in the
wellbore, the weight of the remaining tubular section can
be utilised to contribute to the force needed to induce
downward movement of the bending zone.
Suitably the bending zone is induced to move in axial
direction relative to the remaining tubular section by
inducing the remaining tubular section to move in axial
direction relative to the expanded tubular section. For
example, the expanded tubular section is held stationary
while the remaining tubular section is moved in axial
direction through the expanded tubular section to induce
said bending of the wall.
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In order to induce said movement of the remaining
tubular section, preferably the remaining tubular section
is subjected to an axially compressive force acting to
induce said movement. The axially compressive force
preferably at least partly results from the weight of the
remaining tubular section. If necessary the weight can be
supplemented by an external, downward, force applied to
the remaining tubular section to induce said movement. As
the length, and hence the weight, of the remaining
tubular section increases, an upward force may need to be
applied to the remaining tubular section to prevent
uncontrolled bending or buckling in the bending zone.
If the bending zone is located at a lower end of the
tubular element, whereby the remaining tubular section is
axially shortened at a lower end thereof due to said
movement of the bending zone, it is preferred that the
remaining tubular section is axially extended at an upper
end thereof in correspondence with said axial shortening
at the lower end thereof. The remaining tubular section
gradually shortens at its lower end due to continued
reverse bending of the wall. Therefore, by extending the
remaining tubular section at its upper end to compensate
for shortening at its lower end, the process of reverse
bending the wall can be continued until a desired length
of the expanded tubular section is reached. The remaining
tubular section can be extended at its upper end, for
example, by connecting a tubular portion to the upper end
in any suitable manner such as by welding. Alternatively,
the remaining tubular section can be provided as a coiled
tubing which is unreeled from a reel and subsequently
inserted into the wellbore.
As a result of forming the expanded tubular section
around the remaining tubular section, an annular space is
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formed between the unexpanded and expanded tubular
sections. To increase the collapse resistance of the
expanded tubular section, a pressurized fluid can be
inserted into the annular space. The fluid pressure can
result solely from the weight of the fluid column in the
annular space, or in addition also from an external
pressure applied to the fluid column.
The expansion process is suitably initiated by
bending the wall of the tubular element at a lower end
portion thereof by any suitable means.
Advantageously the wellbore is being drilled with a
drill string extending through the unexpanded tubular
section. In such application the unexpanded tubular
section and the drill string preferably are lowered
simultaneously through the wellbore during drilling with
the drill string.
Optionally the bending zone can be heated to promote
bending of the tubular wall.
To reduce any buckling tendency of the unexpanded
tubular section during the expansion process, the
remaining tubular section advantageously is kept
centralised within the expanded section.
The invention will be described hereinafter in more
detail and by way of example, with reference to the
accompanying drawings in which:
Fig. 1 schematically shows a first embodiment of a
wellbore system during an initial stage of eversion of a
liner;
Fig. 2 schematically shows the first embodiment
during a subsequent stage of eversion of the liner;
Fig. 3 schematically shows detail A of Fig. 2;
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Fig. 4 schematically shows a second embodiment of a
wellbore system during an initial stage of eversion of a
liner;
Fig. 5 schematically shows the second embodiment
during a subsequent stage of eversion of the liner;
Fig. 6 schematically shows a third embodiment of a
wellbore system during an initial stage of eversion of a
liner;
Fig. 7 schematically shows the third embodiment
during a subsequent stage of eversion of the liner;
Fig. 8 schematically shows detail B of Fig. 7; and
Fig. 9 schematically shows the first embodiment,
modified in that a drill string extending through the
wellbore liner.
In the Figures and the description like reference
numerals relate to like components.
Referring to Figs. 1-3 there is shown, in
longitudinal section, the first embodiment comprising a
wellbore 1 extending into an earth formation 2, and a
tubular element in the form of liner 4 extending
downwardly into the wellbore 1. The liner 4 has been
partially radially expanded by eversion of the wall of
the liner whereby a radially expanded tubular section 10
of the liner 4 has been formed, which has an outer
diameter substantially equal to the wellbore diameter. A
remaining tubular section 8 of the liner 4 extends
concentrically within the expanded tubular section 10.
The wall of the liner 4 is, due to eversion at its
lower end, bent radially outward and in axially reverse
(i.e. upward) direction so as to form a U-shaped lower
section 16 of the liner interconnecting the remaining
liner section 8 and the expanded liner section 10. The U-
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shaped lower section 16 of the liner 4 defines a bending
zone 18 of the liner.
The expanded liner section 10 is axially fixed to the
wellbore wall 19 by virtue of frictional forces between
the expanded liner section 10 and the wellbore wall 19
resulting from the expansion process. Alternatively, or
additionally, the expanded liner section 10 can be
anchored to the wellbore wall by any suitable anchoring
means (not shown).
The liner 4 is provided with a plurality of annular
seal members 20 axially spaced along the liner 4. For
ease of reference, only one seal member 20 is shown. At
the remaining liner section 8, each seal member 20 is
positioned at the inner surface of the remaining liner
section 8 (Fig. 1). After eversion of the liner, the seal
members 20 become positioned at the outer surface of the
expanded liner section 10 (Fig. 2). Further, each seal
member 20 is pressed against the wellbore wall 19 so as
to form a seal between the expanded liner section 10 and
the wellbore wall 19.
The seal members 20 can be made of any suitable
material adapted to withstand compression against the
wellbore wall 19, such as, for example, steel, rubber,
composite material etc.
Furthermore, the seal members 20 can be fixedly
connected to the liner 4 by suitable connecting means, or
the seal members 20 can be integrally formed with the
liner 4.
Referring further to Figs. 4 and 5 there is shown, in
longitudinal section, the second embodiment, which is
substantially similar to the first embodiment. However,
instead of annular seal members being connected to the
liner, in the second embodiment annular seal members 25
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are connected to the wellbore wall 19. The seal
members 25 can be fixedly connected to the wellbore
wall 19 by suitable means, or the seal members 25 can be
integrally formed with the wellbore wall. In the latter
case, the seal members 25 can be formed, for example, as
annular ridges extending radially inward from the
wellbore wall 19.
Referring to Figs. 6-8 there is shown, in
longitudinal section, the third embodiment, which is
substantially similar to the first embodiment. However in
the third embodiment, annular seal members 30 are
provided at the outer surface of the remaining liner
section 8, rather than at the inner surface thereof. Like
in the first embodiment, the seal members 30 can be
connected to the liner 4 by any suitable connecting
means, or the seal members 30 can be integrally formed
with the liner 4. As shown in Fig. 7, the seal members 30
become located at the inner surface of the expanded liner
section 10 after the eversion process whereby, at the
position of each seal member 30, the wall of the expanded
liner section 8 extends further radially outward than at
adjacent locations where no seal member is positioned
(Fig. 8).
Referring further to Fig. 9, there is shown, in
longitudinal section, the first embodiment, modified in
that a drill string 40 extends from surface through the
unexpanded liner section 8 to the bottom of the
wellbore 1. The drill string 40 has a bottom hole
assembly including a downhole motor 42 and a drill bit 44
driven by the downhole motor 42. The drill bit 44
comprises a pilot bit 46 with gauge diameter slightly
smaller than the internal diameter of the remaining liner
section 8, and a reamer section 48 with gauge diameter
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adapted to drill the wellbore 1 to its nominal diameter.
The reamer section 48 is radially retractable to an outer
diameter allowing it to pass through unexpanded liner
section 8, so that the drill string 40 can be retrieved
through the unexpanded liner section 8 to surface.
During normal operation of the first embodiment
(Figs. 1-3), a lower end portion of the liner 4 is
initially everted, that is, the lower portion is bent
radially outward and in axially reverse direction. The U-
shaped lower section 16 and the expanded liner section 10
are thereby initiated. Subsequently, the short length of
expanded liner section 10 that has been formed is
anchored to the wellbore wall by any suitable anchoring
means. Depending on the geometry and/or material
properties of the liner 4, the expanded liner section 10
alternatively can become anchored to the wellbore wall
automatically due to friction between the expanded liner
section 10 and the wellbore wall 19.
A downward force F of sufficient magnitude is then
applied to the unexpanded liner section 8 in order to
move the unexpanded liner section 8 gradually downward.
As a result, the unexpanded liner section 8 is
progressively everted thereby progressively transforming
the unexpanded liner section 8 into the expanded liner
section 10. During the eversion process, the bending zone
18 moves in downward direction at approximately half the
speed of movement of the unexpanded liner section 8.
During the eversion process, the seal members 20 move
from the inside of the remaining liner section 8 to the
outside of the expanded liner section 10. Since the outer
surface of the expanded liner section 10 is of a diameter
substantially equal to the wellbore diameter, and because
the seal members 20 extend radially outward from said
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outer surface, the seal members become compressed between
the expanded liner section 10 and the wellbore wall 19.
The seal members are thereby subjected to a radially
inward reaction force from the wellbore wall 19, which
induces a slight elastic deformation of the wall of the
expanded liner section 10. Due to this elastic
deformation, the seal members 20 remain pressed against
the wellbore wall 19 so that the expanded liner section
is permanently sealed against the wellbore wall 19.
10 In this manner it is achieved that fluid from the
wellbore, or fluid from the surrounding earth formation,
cannot leak between the expanded liner section 10 and the
wellbore wall 19.
If desired, the diameter and/or wall thickness of the
liner 4 can be selected such that portions of the
expanded liner section 10 inbetween adjacent seal members
become pressed against the wellbore wall 19 as a
result of the expansion process so as to seal against the
wellbore wall and/or to stabilize the wellbore wall. In
20 such case, the seal members 20 provide additional sealing
capacity.
Since the length, and hence the weight, of the
unexpanded section 8 gradually increases, the magnitude
of downward force F can be decreased gradually in
correspondence with the increased weight of section 8.
Normal operation of the second embodiment is
substantially similar to normal operation of the first
embodiment, however differing in that the seal members 25
are connected to, or integrally formed with, the wellbore
wall 19 prior to eversion of liner 4. As the bending
zone 18 steadily moves downward during eversion of the
liner 4, the seal members 25 successively become
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compressed between the expanded liner section 10 and the
wellbore wall 19 (Fig. 5).
Normal operation of the third embodiment (Figs. 6-8)
is substantially similar to normal of the first
embodiment. As mentioned hereinbefore, the seal members
30 become located at the inner surface of the expanded
liner section 10 after the eversion process. The bending
resistance of the wall of the liner 4 is higher at
locations where the seal members 30 are connected to the
liner, than at adjacent locations where no seal members
are located. Therefore, at the location of each seal
member 30, the wall of the liner 4 bends at a larger
bending radius during the eversion process than at
adjacent locations where no seal member is positioned.
In view thereof, at the location of each seal
member 30, a portion 32 of the wall of the expanded liner
section 8 extends further radially outward than at the
adjacent locations (Fig. 8).
Each wall portion 32 thereby become pressed against
the wellbore wall 19 and is subjected to a radially
inward reaction force from the wellbore wall 19, which
induces a slight elastic deformation of the wall
portion 32. This elastic deformation causes the wall
portions 32 to remain pressed against the wellbore
wall 19 so that the expanded liner section 10 is
permanently sealed against the wellbore wall 19.
In this manner it is achieved that fluid from the
wellbore, or fluid from the surrounding earth formation,
cannot leak between the expanded liner section 10 and the
wellbore wall 19.
If desired, the diameter and/or wall thickness of the
liner 4 can be selected such that portions of the
expanded liner section 10 inbetween the wall portions 32
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also become pressed against the wellbore wall 19 as a
result of the expansion process. In such case, the wall
portions 32 provide additional sealing capacity.
Normal operation of the modified first embodiment
shown in Fig. 9 is substantially similar to normal
operation of the first embodiment regarding eversion of
the liner 4. In addition, the following features apply to
normal operation of the modified first embodiment. The
downhole motor 42 is operated to rotate the drill bit 44
so as to deepen the wellbore 1 by further drilling.
Thereby, the drill string 40 gradually moves downward
into the wellbore 1. The remaining liner section 8 is
simultaneously moved downward in a controlled manner, and
at substantially the same speed as the drill string 40,
whereby it is ensured that the bending zone 18 remains at
a short distance above the drill bit 44. Such controlled
lowering of the remaining liner section 8 can be achieved
by controlling the downward force F referred to
hereinbefore.
Initially the downward force F needs to be applied to
the unexpanded liner section 8 to induce lowering thereof
simultaneously with lowering of the drill string 40. As
the length, and hence the weight, of the unexpanded liner
section 8 increases, the magnitude of downward force F
can be gradually decreased, and eventually may be
replaced by an upward force to prevent buckling of the
unexpanded liner section 8. Such upward force can be
applied to the remaining liner section 8 at surface, or
it can be applied to the drill string 40 and transmitted
to the remaining liner section 8 by suitable force
transmission means (not shown). The weight of the
unexpanded liner section 8, in combination with the force
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F (if any), also can be used to provide a thrust force to
the drill bit 44 during drilling of the wellbore 1.
Simultaneous lowering of the remaining liner section
8 and the drill string 40 also can be achieved by axially
restraining the remaining liner section 8 to the drill
string 40. For example, the drill string 40 can be
provided with a bearing device (not shown) that supports
the U-shaped lower section 16 of the liner 4.
As drilling proceeds, pipe sections are added at the
top of unexpanded liner section 8 in correspondence with
its lowering into the wellbore, as is normal practice for
installing casings or liners into wellbores.
When it is required to retrieve the drill string 40
to surface, for example when the drill bit 44 is to be
replaced or when drilling of the wellbore 1 is complete,
the reamer section 42 brought to its radially retracted
mode. Subsequently the drill string 24 is retrieved
through the unexpanded liner section 8 to surface.
In practicing the method of the invention, any
combination of the first, second and third embodiments
may be applied. Thus, seal members may be provided at the
inner surface of the remaining liner section, at the
outer surface of the remaining liner section, and at the
wellbore wall in a single application.
Furthermore, the annular seal members preferably are
made of, or include, a swellable elastomer susceptible of
swelling upon contact with wellbore fluid and/or
formation fluid. It is thereby achieved that sealing of
the seal members against the wellbore wall, after
swelling of the swellable elastomer, is enhanced. To
prevent premature swelling of the swellable elastomer
during installation into the wellbore, suitably each
annular seal member is provided with a protective coating
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that ruptures upon radial expansion of the seal member as
it passes through the bending zone, or upon compression
of the seal member between the expanded liner section and
the wellbore wall. After rupturing of the protective
coating, the swellable elastomer becomes exposed to the
wellbore fluid or formation fluid and thereby starts
swelling. If there is little or no space for the seal
member to swell, the seal member becomes more firmly
compressed between the wellbore wall and the expanded
liner section thereby enhancing its sealing
functionality.
With the method described above, it is achieved that
the wellbore is progressively lined with the everted
liner directly above the drill bit, during the drilling
process. As a result, there is only a relatively short
open-hole section of the wellbore during the drilling
process at all times. The advantages of such short open-
hole section will be most pronounced during drilling into
a hydrocarbon fluid containing layer of the earth
formation. In view thereof, for many applications it will
be sufficient if the process of liner eversion during
drilling is applied only during drilling into the
hydrocarbon fluid reservoir, while other sections of the
wellbore are lined or cased in conventional manner.
Alternatively, the process of liner eversion during
drilling may be commenced at surface or at a selected
downhole location, depending on circumstances.
In view of the short open-hole section during
drilling, there is a significantly reduced risk that the
wellbore fluid pressure gradient exceeds the fracture
gradient of the rock formation, or that the wellbore
fluid pressure gradient drops below the pore pressure
gradient of the rock formation. Therefore, considerably
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longer intervals can be drilled at a single nominal
diameter than in a conventional drilling practice whereby
casings of stepwise decreasing diameter must be set at
selected intervals.
Also, if the wellbore is drilled through a shale
layer, such short open-hole section eliminates possible
problems due to heaving of the shale.
After the wellbore 1 has been drilled to the desired
depth and the drill string 40 has been removed from the
wellbore 1, the length of unexpanded liner section 8 that
is still present in the wellbore 1, can be left in the
wellbore or it can be cut-off from the expanded liner
section 10 and retrieved to surface.
In case the length of unexpanded liner section 8 is
left in the wellbore 1, there are several options for
completing the wellbore. These are, for example, as
follows.
A) A fluid, for example brine, is pumped into the
annular space between the unexpanded and expanded liner
sections 8, 10 so as to pressurise the annular space and
increase the collapse resistance of the expanded liner
section 10. Optionally one or more holes are provided in
the U-shaped lower section 16 to allow the pumped fluid
to be circulated.
B) A heavy fluid is pumped into the annular space so as
to support the expanded liner section 10 and increase its
collapse resistance.
C) cement is pumped into the annular space in order to
create, after hardening of the cement, a solid body
between the unexpanded liner section 8 and the expanded
liner section 10, whereby the cement may expand upon
hardening.
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D) the unexpanded liner section 8 is radially expanded
(i.e. clad) against the expanded liner section 10, for
example by pumping, pushing or pulling an expander
through the unexpanded liner section 8.
In the above examples, expansion of the liner is
started at surface or at a downhole location. In case of
an offshore wellbore whereby an offshore platform is
positioned above the wellbore, at the water surface, it
can be advantageous to start the expansion process at the
offshore platform. In such process, the bending zone
moves from the offshore platform to the seabed and from
there further into the wellbore. Thus, the resulting
expanded tubular element not only forms a liner in the
wellbore, but also a riser extending from the offshore
platform to the seabed. The need for a separate riser
from is thereby obviated.
Furthermore, conduits such as electric wires or
optical fibres for communication with downhole equipment
can be extended in the annular space between the expanded
and unexpanded sections. Such conduits can be attached to
the outer surface of the tubular element before expansion
thereof. Also, the expanded and unexpanded liner sections
can be used as electricity conductors to transfer data
and/or power downhole.
Since any length of unexpanded liner section that is
still present in the wellbore after the eversion process
is finalised, is subjected to less stringent loading
conditions than the expanded liner section, such length
of unexpanded liner section may have a smaller wall
thickness, or may be of lower quality or steel grade,
than the expanded liner section. For example, it may be
made of pipe having a relatively low yield strength or
relatively low collapse rating.
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Instead of leaving a length of unexpanded liner
section in the wellbore after the expansion process, the
entire liner can be expanded with the method of the
invention so that no unexpanded liner section remains in
the wellbore. In such case, an elongate member, for
example a pipe string, can be used to exert the necessary
downward force F to the unexpanded liner section during
the last phase of the expansion process.
In order to reduce friction forces between the
unexpanded and expanded tubular sections during the
expansion process described in any of the aforementioned
examples, suitably a friction reducing layer, such as a
TM
Teflon layer, is applied between the unexpanded and
expanded tubular sections. For example, a friction
reducing coating can be applied to the outer surface of
the tubular element before expansion. Such layer of
friction reducing material furthermore reduces the
annular clearance between the unexpanded and expanded
sections, thus resulting in a reduced buckling tendency
of the unexpanded section. Instead of, or in addition to,
such friction reducing layer, centralizing pads and/or
rollers can be applied between the unexpanded and
expanded sections to reduce the friction forces and the
annular clearance there-between.
Instead of expanding the expanded liner section
against the wellbore wall (as described above), the
expanded liner section can be expanded against the inner
surface of another tubular element already present in the
wellbore.
