Note: Descriptions are shown in the official language in which they were submitted.
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RADIALLY EXPANDING A TUBULAR ELEMENT
The present invention relates to a method of radially
expanding a tubular element.
Expansion of tubular elements finds application in
various fields of technology such as, for example, the
production of hydrocarbon fluid from a wellbore formed in
an earth formation. 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" normally refer to wellbore tubulars
for supporting and stabilising the wellbore wall, whereby
it is generally understood that a casing extends from a
downhole location to surface, whereas a liner does not
fully extend to surface. However, in this specification
the terms "casing" and "liner" are used interchangeably
and without intended distinction.
In conventional wellbore construction, several
casings are set at different depth intervals in a nested
arrangement whereby each subsequent casing is lowered
through the previous casing and therefore must have a
smaller diameter than the previous casing. As a result,
the cross-sectional wellbore size available for oil and
gas production decreases with depth. To alleviate this
drawback, it has been practiced to radially expand
tubular elements in the wellbore after lowering thereof
to the required depth. Such expanded tubular element
forms, for example, an expanded casing section or an
expanded clad against a previously installed existing
casing. Also, it has been proposed to radially expand
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subsequent casing sections to about the same diameter so
that the available diameter in the wellbore remains
substantially constant along (a portion of) its depth, as
opposed to the conventional nested arrangement whereby
the available diameter decreases with depth.
EP-044706-A2 discloses a method of radially expanding a
tubular element by eversion of an inner tube to form an
outer tube around a portion of the inner tube, the tubes
being interconnected at their respective forward ends to
present a rollover area capable of being moved forwardly.
The rollover area is induced to move forward by
pumping driving fluid into the annular space between the
inner and outer tubes.
It is a drawback of the known system and method that
there is a risk that damage occurs to the tubular element
as a result of the eversion process in the rollover area
where the inner tube deforms into the outer tube,
particularly for applications wherein the inner and outer
tubes have a relatively large wall thickness.
Thus there is a need for an improved method of
radially expanding a tubular element, which overcomes the
drawbacks of the prior art.
In accordance with the invention there is provided a
method of radially expanding a tubular element, the
method comprising inducing the wall of the tubular
element to bend radially outward and in axially reverse
direction so as to form an expanded tubular section
extending around an unexpanded section of the tubular
element, said wall having a bending stiffness and a
resistance to stretching in circumferential direction,
wherein said wall is provided with at least one of
primary means for increasing the bending stiffness of the
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wall, and secondary means for reducing the resistance to
stretching in circumferential direction of the wall.
It is to be understood that the expression "bending
the wall radially outward and in axially reverse
direction" refers to eversion of the tubular element
whereby a U-shaped wall portion is formed of which one
leg forms the unexpanded section and the other leg forms
the expanded section.
The resulting bending radius of the wall, and thus
the degree of radially outward movement of the wall,
depends on the bending stiffness of the wall and the
resistance to stretching in circumferential direction of
the wall. More specifically, the bending radius tends to
increase with increasing bending stiffness and to
decrease with increased resistance to stretching in
circumferential direction. Therefore the actual bending
radius follows from a balance between the effect of the
bending stiffness tending to increase the bending radius,
and the effect of the resistance to stretching in
circumferential direction tending to decrease the bending
radius. By providing the wall with means for increasing
the bending stiffness and / or means for reducing the
resistance to stretching in circumferential direction, it
is achieved that the balance is shifted in favour of a
larger bending radius. By virtue of such larger bending
radius, the (equivalent) strains in the wall become less
severe and consequently the risk of damage to the wall is
reduced.
Suitably said primary means comprises at least one
stiffening member connected to said wall, each stiffening
member extending in longitudinal direction of the tubular
element. The stiffening member can be connected, for
example, to the outer surface and / or the inner surface
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of the wall by suitable connecting means, or it can be
integrally formed with the wall. Furthermore, the
stiffening member can be arranged parallel to the central
longitudinal axis of the tubular element, or at an angle
relative to the central longitudinal axis. In the latter
case, the stiffening member suitably extends in a spiral-
shape along the tubular element.
In a preferred embodiment, the primary means
comprises a plurality of said stiffening members
regularly spaced along the circumference of the tubular
element.
Said secondary means suitable comprises at least one
groove formed in said wall, each groove extending in
longitudinal direction of the tubular element. The groove
can be formed, for example, in at least one of the outer
surface and the inner surface of said wall.
Preferably the secondary means comprises a plurality
of said grooves regularly spaced along the circumference
of the tubular element.
To progressively form the expanded tubular section,
said bending of the wall occurs in a bending zone of the
tubular element, and the method further comprises
progressively increasing the length of said expanded
tubular section by inducing the bending zone to move in
axial direction along the tubular element.
The bending zone defines the location where the
instantaneous 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 has to be pushed, pulled or pumped through
the tubular element. Moreover, if the tubular element
extends in vertical direction, for example into a
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wellbore, the weight of the unexpanded tubular section
can be utilised to contribute to the force needed to
induce downward movement of the bending zone.
Suitably said wall is induced to bend by moving the
5 unexpanded tubular section in axial direction relative to
the expanded tubular section. For example, the expanded
tubular section can be held stationary while the
unexpanded tubular section is moved in axial direction
through the expanded section.
In a preferred embodiment the tubular element extends
into a wellbore formed in an earth formation whereby, for
example, the expanded tubular section extends between the
wellbore wall and the unexpanded section of the tubular
element. The expansion process is carried out in an
effective manner if the expanded tubular section is kept
substantially stationary in the wellbore and the
unexpanded tubular section is moved in downward direction
of the wellbore to induce said bending of the wall.
Further, the expansion process suitably can be
initiated by bending the wall of the tubular element at a
lower end portion thereof.
If the weight of the unexpanded tubular section is
insufficient to induce movement of the bending zone,
suitably a downward force is exerted to the unexpanded
tubular section to move the unexpanded tubular section in
downward direction of the wellbore.
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.
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Optionally the bending zone can be heated to promote
bending of the tubular wall.
To reduce any buckling tendency of the unexpanded
section during the expansion process, the unexpanded
section advantageously is centralised in the expanded
section using any suitable centralising means.
Bending of the tubular wall can be promoted by
providing longitudinal grooves at the outer surface of
the tubular element before expansion.
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 an example of a tubular
element during expansion thereof, not in accordance with
the invention;
Fig. 2 schematically shows an embodiment of a tubular
element during expansion in accordance with the
invention;
Fig. 3 schematically shows cross-section 3-3 of
Fig. 2;
Fig. 4 schematically shows a cross-section of an
alternative embodiment of a tubular element during
expansion in accordance with the invention;
Figs. 5a-5f schematically show various examples of
stiffening members for use in the embodiments of
Figs. 2-4;
Fig. 6 schematically shows the tubular element of
Fig. 2 during expansion in a wellbore; and
Fig. 7 schematically shows the tubular element of
Fig. 2 during expansion in a wellbore while the wellbore
is being drilled.
In the Figures and the description like reference
numerals relate to like components.
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Referring to Fig. 1 there is shown a radially
expandable tubular element 1 comprising an unexpanded
section 2 and a radially expanded section 4 extending
around the unexpanded section 2. The unexpanded and
expanded sections 2, 4 are interconnected at their
respective lower ends by a U-shaped wall portion 6 having
a bending radius R1. The expanded section 4 is formed by
bending the lower end of the wall of the tubular element
1 radially outward and in axially reverse direction.
Subsequently the unexpanded section 2 is moved downward
relative to the expanded section 4 so that, as a result,
the unexpanded section 2 gradually becomes everted to
form the expanded section 4. The resulting bending radius
R1 at the U-shaped wall portion 6 results from an
equilibrium between the tendency of the wall to assume a
relatively large bending radius due to the inherent
bending stiffness of the wall, and the tendency of the
wall to assume a relatively small bending radius due to
the inherent resistance to stretching of the wall.
Referring to Fig. 2 there is shown a radially
expandable tubular element 10 comprising an unexpanded
section 12 and a radially expanded section 14 extending
around the unexpanded section 12, the unexpanded and
expanded tubular sections 12, 14 being interconnected at
their lower ends by a U-shaped wall portion 16 having a
bending radius R2. The tubular element 10 is
substantially similar to the tubular element 1 of Fig. 1
with regard to material properties, wall thickness and
unexpanded diameter. However the tubular element 10 is
additionally provided with a plurality of longitudinal
stiffening members 20 extending along the outer surface
of the unexpanded section 12 and the inner surface of the
expanded section 14. The expanded section 14 is formed by
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bending the wall of the tubular element 10, at the lower
end thereof, radially outward and in axially reverse
direction, and subsequently moving the unexpanded section
12 downward relative to the expanded section 14 so that,
as a result, the unexpanded section 12 is gradually
everted to form the expanded section 14. The resulting
bending radius R2 at the U-shaped wall portion 16 results
from an equilibrium between the tendency of the wall to
assume a relatively large bending radius due to the
inherent bending stiffness of the wall, and the tendency
of the wall to assume a relatively small bending radius
due to the inherent resistance to stretching of the wall.
By virtue of the stiffening members 20, the bending
stiffness of the tubular element 10 is larger than the
bending stiffness of the tubular element 1 of Fig. 1 so
that, as a result, the equilibrium between said tendency
of the wall to assume a relatively large bending radius
and said tendency of the wall to assume a relatively
small bending radius shifts towards a larger bending
radius for the tubular element 10. In other words: R2 >
R1.
In Fig. 3 is shown a cross-sectional view of the
unexpanded section 12 of tubular element 10 whereby a
layer 22 of metal, or other suitable material, is
arranged around the outer surface of the tubular
element 10. The layer 22 is provided with a plurality of
longitudinal grooves 24 regularly spaced in
circumferential direction of the tubular element 10. Each
stiffening member 20 is defined in-between a respective
pair of adjacent grooves 24. The layer 22 can be
connected to the outer surface of the tubular element 10
in any suitable manner, or it can be integrally formed
with the tubular element 10. In the latter case, the
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tubular element 10 and the layer 22 can be machined from
one piece.
In Fig. 4 is shown a cross-sectional view of an
alternative embodiment of a tubular element 26 to be
expanded with the method of the invention. The tubular
element 26 is at its inner surface provided with a layer
28 provided with a plurality of longitudinal grooves 30
regularly spaced in circumferential direction of the
tubular element 10. The grooves 30 define a plurality of
longitudinal stiffening members 32, whereby each
stiffening member 32 is defined in between a respective
pair of adjacent grooves 30. The metal layer 28 can be
connected to the inner surface of the tubular element 26
in any suitable manner, or it can be integrally formed
with the tubular element 26.
Figs. 5a-5f show various embodiments, in cross-
sectional view, of stiffening members for a tubular
element to be expanded with the method of the invention.
In each of Figs. 5a-5f, reference sign 34 indicates
the wall of the tubular element, and the respective
stiffening members are indicated by reference signs 35,
36, 37, 38, 39, 40.
Similarly to the embodiments shown in Figs. 3 and 4,
the stiffening members 35, 36, 37, 38, 39, 40 can be
arranged at the outer surface or the inner surface of the
unexpanded tubular element.
In Fig. 6 is shown the tubular element 10 of Fig. 2
in a wellbore 42 formed in an earth formation 44.
During normal operation the lower end portion of the
wall of the (yet unexpanded) tubular element 10 is bent
radially outward and in axially reverse direction by any
suitable means so as to initially form the U-shaped lower
section 16. Subsequently, a downward force is applied to
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the unexpanded section 12 to move the unexpanded section
12 gradually downward. The unexpanded section 12 thereby
becomes progressively everted to form into the expanded
section 14. During the eversion process, the U-shaped
5 lower section 16 moves downward at approximately half the
speed of the unexpanded section 12. By virtue of the
enhanced bending stiffness of the wall of the tubular
element 10 due to the stiffening members 20, the bending
radius R2 of the U-shaped lower section is relatively
10 large so that the tubular element 10 is expanded to a
relatively large diameter. If desired, the tubular
element 10 and / or the stiffening members 20 can be
selected such that the expanded tubular section 14
becomes firmly expanded against the wellbore wall so that
a seal is formed between the expanded tubular section 14
and the wellbore wall.
Referring to Fig. 7 there is shown the tubular
element 10 of Fig. 2 in combination with a drill string
48 extending from surface through the unexpanded section
12, and further to the bottom of the wellbore 42. The
drill string 48 is provided with a tubular guide member
52 for guiding and supporting the U-shaped lower section
16 of the tubular element 10, the guide member 52 being
supported by a support ring 54 connected to the drill
string 48. The support ring 54 is made radially
retractable so as to allow it to pass in retracted mode
through the guide member 52 and the unexpanded section
12.
Furthermore, the drill string 48 is provided with a
drill bit 56 that is driven in rotation either by a
downhole motor (not shown) or by rotation of the drill
string 48 itself. The drill bit 56 comprises a pilot bit
58 and a collapsible reamer 60 for drilling the wellbore
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48 to its nominal diameter. The pilot bit 58 and the
reamer 60, when in collapsed mode, have a maximum
diameter slightly smaller than the internal diameter of
the guide member 52 so as to allow the pilot bit 58 and
the reamer 60 to be retrieved to surface through the
guide member 52 and through the unexpanded tubular
section 12.
During normal operation the drill bit 56 is driven in
rotation to deepen the wellbore 42 whereby the drill
string 48 and the unexpanded tubular section 12 move
simultaneously deeper into the wellbore 42. The
unexpanded tubular section 12 can be assembled from
individual pipe sections at surface, as is normal
practice for tubular strings such as drill strings,
casings or liners. Alternatively the unexpanded tubular
section can be supplied as a continuous tubular element,
such as a coiled tubing.
The U-shaped lower portion 16 of the tubular element
10 is supported and guided by the guide member 52.
Initially a downward force needs to be applied to the
unexpanded section 12 to induce lowering thereof
simultaneously with the drill string 48. As the length of
the unexpanded section 12 in the wellbore 42 increases,
the weight of the unexpanded section 12 gradually
replaces the applied downward force. Eventually, after
the weight of the unexpanded section has fully replaced
the applied downward force, an upward force may need to
be applied to the unexpanded section 12 to prevent
overloading of the U-shaped lower portion 16.
The weight of the unexpanded tubular section 12 also
can be used to thrust the drill bit 56 forward during
drilling of the wellbore 42. In the embodiment of Fig. 7
such thrust force is transmitted to the drill bit 56 via
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the guide member 52 and the support ring 54. In an
alternative embodiment, the guide member is dispensed
with and the thrust force is directly transmitted from
the unexpanded tubular section to the drill string, for
example via a suitable thrust bearing (not shown) between
the unexpanded section and the drill string.
Thus, by gradually lowering the unexpanded tubular
section 12 into the wellbore 42, the U-shaped lower wall
portion 16 progressively bends in radially outward and
axially reverse direction, thereby progressively forming
the expanded tubular section 14. During the expansion
process, the U-shaped lower portion 16 is supported and
guided by the guide member 52 so as to promote bending of
the wall of the unexpanded section 12.
When it is required to retrieve the drill string 48
to surface, for example when the drill bit is to be
replaced or after drilling has completed, the support
ring 54 is radially retracted and the reamer bit 60
collapsed. Thereafter the drill string 48 is retrieved
through the unexpanded tubular section 12 to surface. The
guide member 52 can remain downhole. Alternatively the
guide member can be made collapsible so as to allow it to
be retrieved to surface in collapsed mode through the
unexpanded tubular section.
With the method described above it is achieved that
there is only a very short open-hole section in the
wellbore 42 during drilling since the expanded tubular
section 14 extends to near the lower end of the drill
string 48 at any time. The method therefore finds many
advantageous applications. For example, if the expanded
tubular section is a casing, longer intervals can be
drilled without the need to interrupt drilling to set new
casing sections, thereby leading to fewer casing sections
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of stepwise decreasing diameter. Also, if the wellbore is
drilled through a shale layer the substantial absence of
an open-hole section eliminates problems due to shale
heaving.
After drilling of the wellbore 42 has been finalised
and the drill string 48 has been removed from the
wellbore, the length of unexpanded tubular section 12
still present in the wellbore 42 can be cut-off from the
expanded section 14 and subsequently retrieved to
surface, or it can be left in the wellbore. In the latter
case there are several options for completion of the
wellbore, including for example:
i) A fluid, for example brine, is pumped into the
annular space between the unexpanded and expanded
sections 12, 14 so as to increase the collapse resistance
of the expanded section 14. Optionally, an opening can be
made in the wall of the tubular element 10, near its
lower end, to allow the pumped fluid to be circulated
therethrough;
ii) A heavy fluid is pumped into the annular space
between the unexpanded and expanded sections 12, 14 to
support the expanded tubular section 14 and increase its
collapse resistance;
iii) Cement is pumped into the annular space between the
unexpanded and expanded sections 12, 14 to create a solid
body in the annular space after hardening of the cement.
Suitably, the cement expands upon hardening;
iv) The unexpanded section 12 is radially expanded
against the expanded section 14, for example by pumping,
pushing or pulling an expander (not shown) through the
unexpanded section 12.
Optionally a weighted fluid can be pumped into the
annular space between the unexpanded and expanded
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sections, or the annular space can pressurized, during or
after the expansion process, to reduce the collapse
loading on the expanded section 14 and/or to reduce the
burst loading on the unexpanded liner section 12.
Furthermore, electric wires or optical fibres can be
arranged in the annular space between the unexpanded and
expanded sections for downhole data communication or for
downhole electric power transmission. Such wires or
fibres can be attached to the outer surface of the
tubular element 10 before expansion thereof. Also, the
unexpanded and expanded sections 12, 14 can be used as
electric conductors for transferring data and/or power
downhole.
Since the length of unexpanded tubular section that
is left in the wellbore does not need to be expanded,
less stringent requirements regarding material properties
etc. may apply to it. For example, said length may have a
lower or higher yield strength, or a smaller or larger
wall thickness than the expanded tubular section.
Instead of leaving a length of unexpanded tubular
section in the wellbore after the expansion process, the
entire tubular element can be expanded with the method of
the invention so that no unexpanded tubular 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 to the unexpanded tubular
section during the last phase of the expansion process.
Suitably a friction-reducing layer, such as a Teflon
layer, is applied between the unexpanded and expanded
tubular sections during the expansion process to reduce
friction forces. For example, a friction reducing coating
can be applied to the outer surface of the tubular
element before expansion. Such layer of friction reducing
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material has the additional advantage of reducing 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,
5 a friction-reducing layer, centralizing pads and/or
rollers can be applied between the unexpanded and
expanded sections to reduce friction forces.
With the method of the invention, the expanded
tubular section can extend from surface into the
10 wellbore, or it can extend from a downhole location
deeper into the wellbore.
Instead of expanding the tubular element against the
wellbore wall (as described above), the tubular element
can be expanded against the inner surface of a tubular
15 element previously installed in the wellbore.
Furthermore, instead of expanding the tubular element in
downward direction in the wellbore, the tubular element
can be expanded in upward direction whereby the U-shaped
section is located at the upper end of the tubular
element.
Although the examples described above refer to
applications of the invention in a wellbore, it is to be
understood that the method of the invention also can be
applied at the earth surface. For example, the expanded
tubular section can be expanded against the inner surface
of a pipe, for example an existing flowline for the
transportation of oil or gas located at the earth surface
or at some depth below the surface. Thereby the flowline
is provided with a new lining, thus obviating the need to
replace the entire flowline in case of damage or
corrosion of the flowline.
