Note: Descriptions are shown in the official language in which they were submitted.
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TELESCOPING CENTRALIZERS FOR EXPANDABLE TUBULARS
FIELD OF THE INVENTION
100021 The field of this invention relates to completion techniques for
tubulars
that are centralized prior to cementing and subsequently expanded, and more
particularly to telescoping centralizers in this application.
BACKGROUND OF THE INVENTION
100031 When cementing a tubular, centralizers have been used to allow the
cement to work its way fully around the tubular. Without centralizers,
particularly if
there is a deviation in the wellbore, there was a risk that the tubular would
lay up
against the borehole wall on the low side undermining the benefit of the
cement in
trying to seal around the tubular.
(0004) Centralizers of various types have been used in the past. The most
common centralizers comprise a plurality of spaced flexible strips that extend
longitudinally between a pair of end rings. The centralizers are slipped over
the end of
the tubular on makeup or get clamped to the tubular due to a hinge connection
in each
of the two end rings. These centralizers are typically made of steel. The
problem with
these centralizers arises if there is to be any pipe expansion. Expanding
tubulars has
become a more widely used procedure and such centralizers have been known to
cause high stress areas on the underlying tubular during expansion to the
point where
the tubular can split or crack. Attempts to improve on the metal centralizers
described
above by making them from a polymeric material have had mixed results. The
problem there has been that they are not strong enough to hold their shape to
the
extent that their main purpose of centralizing is defeated. Also, their
geometric
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dimensions do not lend themselves to be run through the previous casing string
and
yet still have enough standoff for suitable centralization.
[0005] Centralizing devices have also been used that are bulky and that have
many moving parts. These designs are expensive, require inordinate
maintenance, and
are simply too large to be of use in many applications. Some examples are U.S.
Patent
2,874,783 and PCT Application WO 94/13928.
[0006] Another centralizing technique for cementing tubulars has been to use
telescoping cylinders that can be pushed out when the tubular is in position.
These
cylinders had removable barriers to let flow go through them after extension.
One of
their uses was to centralize a tubular prior to cementing. Some illustrations
of this
type of centralizing system can be found in U.S. Patents 5,228,518; 5,346,016;
5,379,838; 5,224,556; and 5,165,478. None of these centralizers were used in
combination with tubulars that were to be expanded. Yet, despite the use of
extendable cylinders to centralize prior to cementing, in applications where
the
tubular was to be expanded after cementing there was either no attempt to
cement in
an inclined wellbore or centralizers that wrapped around the tubular and
caused stress
failures when expanded were used. As a result, poor cement distribution
occurred that
was compounded by the subsequent expansion of the tubular. What is needed and
addressed by the present invention is an effective way to centralize a tubular
before it
is cemented and subsequently expanded even if it is disposed in a deviated
bore. The
method of the present invention is to centralize using telescoping cylinders
and then
with the cylinders extended to expand the tubular internally to compact the
setting
cement and provide a reliable seal of the tubular despite the angle of
inclination of the
associated wellbore. These and other aspects of the present invention will be
more
apparent to those skilled in the art from a review of the description of the
preferred
embodiment and the claims, which appear below.
SUMMARY OF THE INVENTION
[0007] A method of centralizing tubulars prior to cementing and subsequent
expansion involves using a plurality of telescoping cylinders whose leading or
trailing
end is closed and which are extended by applied internal pressure in the
tubular or
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some mechanical means. The tubular is expanded from its interior with the
cylindrical
telescoping members still extended. The cement is pushed all around the
tubular due to
the centralizers. After the cement is delivered the expansion of the tubular
pushes the
telescoping members into the borehole wall.
[0007a] Accordingly, in one aspect of the present invention there is provided
a
method of positioning a tubular in a borehole, comprising:
delivering the tubular into a borehole;
positioning the tubular in the borehole in a manner that leaves an annular
space
around it; and
expanding the tubular.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007b] Embodiments of the present invention will now be described more
fi.illy
with reference to the accompanying drawings in which:
[0008] Figure 1 is a section view of a telescoping member having a closed
leading end and in the run in position showing the total extension as less
than the
connection or upset dimension;
[0009] Figure 2 is a section view of a telescoping member of Figure 1, shown
in
the extended position;
[0010] Figure 3 is an end view in the borehole with the pistons expanded just
prior to cementing;
[0011] Figure 4 is the view of Figure 3 after cementing and expansion of the
tubular into the cement.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] Referring to Figure 1 the wall of tubular 10 is shown with an opening
12.
The opening 12 is one of a plurality of similar openings distributed around
the tubular 10.
In each opening 12 is a sleeve 14 that is firmly secured in opening 12. It has
a leading
end 16 that is either flush or slightly extending beyond the outer wall
surface 18 of
tubular 10. Leading end 16 should not extend beyond the dimension of the
connection or
upset 17.
[0013] Alternatively, the leading end 16 can be slightly recessed into the
opening
12. An outer piston 20 is slidably mounted to sleeve 14 to extend a
predetermined
amount before travel stop is engaged. An inner piston 22 telescopes with
respect to
the outer piston 20 and has its leading end 24 closed off. The leading end 24
is
advanced by internal fluid pressure or mechanical force into contact with the
borehole
wall 26 in a plurality of directions to centralize the tubular 10 prior to the
pumping of
cement 28. Locking ratchet mechanisms, shown schematically as 30 keep the
outer
piston 20 and the inner piston 22 in the position they achieve after
application of
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pressure to the inside of the tubular 10. In that manner the pumped cement or
other
sealing material 28 cannot push the pistons 20 and 22 back in after they are
extended.
The applied pressure to extend pistons 20 and 22 can come from the actual
delivery of
the cement 28 or a material that precedes it, as the pressure inside tubular
10 will be
greater than the annulus 32 to provide the differential pressure to extend the
pistons
20 and 22. Alternatively, they can be mechanically extended. However, it is
preferred
to first fully extend the pistons 20 and 22 with fluid pressure before pumping
cement
28. In that way, the tubular 10 is securely centralized before cement 28 is
delivered to
annulus 32. Figure 2 shows the set position where the leading end 24 is closed
off and
in contact with the wellbore 26. It should be noted that depending on the
shape of the
wellbore 26 and the total extension of the outer piston 20 and inner piston
22, some of
the leading ends 24 might not be in contact with the wellbore 26 while others
may be
pressed against it or may have penetrated into wellbore 26. In an alternative
=embodiment, the piston 22 can be mounted in the reverse position than shown
in the
Figures, leaving an exposed edge as its leading edge. When so oriented in this
manner, edge 36 can better dig into the wellbore 26, when extended outwardly
by
pressure or mechanical means to improve the fixation of the tubular 10 prior
to
cement delivery as well as after expansion.
100141 As shown in Figure 1, the tubular is expanded using any one of a
variety of techniques. The expansion occurs before the cement 28 sets up. The
expansion tool is shown schematically as 38 and can be a swage or a device
employing applied pressure to the inside of the tubular 10. Since the pistons
20 and 22
are prevented from retracting into the tubular 10 they can dig into the
borehole wall
26 as the tubular 10 is expanded. This occurs more easily with the piston 22
reversed
from the orientation shown in the Figures due to exposure of edge 36. Figure 3
shows
the pistons 22 extended prior to cementing and Figure 4 shows the tubular 10
expanded with the pistons 22 digging into the borehole wall 26. The pistons 20
and 22
fully compensate for some out of roundness of the borehole wall 26. Upon
expansion,
the tubular can conform to the shape of the borehole wall 26 or in some cases
reshape
the borehole wall 26 to a more round configuration. . An alternative
embodiment
could be where the tubular 10 is standing off of the borehole on the high side
and
subsequent expansion moves the pipe away from the low side towards the high
side.
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However, even in this case, cement will be radially displaced around the pipe
before
expansion.
[0015] Those skilled in the art will appreciate that pistons 20 and 22 can be
fully retracted for insertion of the tubular 10 into the borehole 26. The
telescoping
pistons 20 and 22 allow for the use of an effective system of centralization
that will
not hinder the ability to subsequently expand the tubular 10. Where in the
past there
have been either no centralizers used, in which cast the benefit of the
cementing job
may have been lost or where flexible wraparound centralizers were used which
either
impeded expansion or caused regions of high stress leading to tubular failure
or just
simply failed to function when made from non-metallic materials, the method of
the
present invention provides an effective way to centralize and accommodate the
subsequent need to expand the tubular 10 into the cement 28 before it sets up.
In this
manner the cement 28 surrounds the tubular 10 and is further pushed into the
wellbore
as it sets up to enhance the sealing around the tubular 10 and decrease that
possibility
of longitudinal fluid channeling.
100161 The foregoing disclosure and description of the invention are
illustrative and explanatory thereof, and various changes in the size, shape
and
materials, as well as in the details of the illustrated construction, may be
made without
departing from the spirit of the invention.
