Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PREPARING WELLBORE CASING FOR INSTALLATION
Field of the Invention
The present invention relates to method for enhancing the installability of
wellbore
casing and in particular, a method for preparing wellbore casing for
installation.
Background of the Invention
Within the context of petroleum drilling and well completions, wells are
typically
constructed by drilling the well bore using one tubular string, largely
comprised of
drill pipe, then removing the drill pipe string and completing by installing a
second
tubular string, referred to as casing, which is subsequently permanently
cemented in
place. The installation of casing, in this typical construction requires that
the casing
be run into long boreholes, some having horizontal stretches. In these
horizontal
stretches, the casing must be installed by pushing it along the borehole. In
so doing
the casing is pushed in engagement with the borehole wall.
Recent advances in drilling technology have enabled wells to be drilled and
completed with a single casing string, eliminating the need to 'trip' the
drill pipe in
and out of the hole to service the bit and make room for the casing upon
completion
of drilling. This change is motivated by potential cost savings arising from
reduced
drilling time and the expense of providing and maintaining the drill string,
plus
various technical advantages, such as reduced risk of well caving before
installation
of the casing.
However, casing installation through deviated wellbores or by drilling with
casing
challenge the performance requirements of the casing. Installation can place
severe
structural demands on casing since they must survive extended periods of time
in
contact with the borehole wall. Devices, such as centralizers can be mounted
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the casing to act as bearing surfaces that preferentially accommodate contact
with
and space the casing from the borehole wall. However, such devices must be
cost
effective, since they remain downhole and are not recovered. In addition,
these
devices must be connected to the casing in such a way that they do not
compromise
the casing integrity either by their means of attachment or the wear they
induce.
Summary of the Invention
A method has been invented for enhancing the installability of wellbore casing
such
as for example, in preparation, for use to line a borehole through a formation
or to
act as a drill string and to remain in hole, after drilling, to line the
borehole created by
its use. In the method, a device supporting the installation of wellbore
casing into a
wellbore is crimped onto the outer surface of the casing. The device
supporting
casing installation can be to facilitate run in through the borehole, to
maintain
positioning relative to the borehole or to accommodate wear against the wall
of the
borehole into which the casing is run. The devices supporting the installation
of
wellbore casing are attached to the casing to create a connection having
structurally
significant axial and torque load transfer capacity. When using methods
according to
the present invention, the load transfer capacity of the connection between
the
device and the casing can be arranged to substantially prevent significant
relative
movement of the device on the casing under loads that may be encountered when
installing one or more of the casing joints as a liner into a wellbore which
has been
drilled using a conventional drilling operation or when using one or more of
the
casing joints as components of a tubular string used for drilling and lining a
well
bores.
Thus, in accordance with one aspect of the present invention, there is
provided a
method for increasing the installability of wellbore casing, selecting a joint
of casing
having an outer diameter and an outer surface and capable of receiving a
device
thereon by crimping and selecting a device supporting the installation of
wellbore
casing, the device having an outer facing surface, an inner bore sufficiently
large to
allow insertion therethrough of the joint of casing, and at least one tubular
section on
the body, the portion of the inner bore extending through the tubular section
having
an internal diameter capable of loosely fitting about the outer diameter of
the joint of
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casing; positioning the device on the joint of casing such that the joint of
casing
extends through the inner bore; and crimping the device onto the joint of
casing by
applying an inward, substantially radially-directed force to a plurality of
points about
an outer circumference of the tubular section causing it to plastically deform
inwardly
and come into contact with the outer surface of the joint of casing, applying
such
additional inward, substantially radially directed force as required to force
both the
tubular section of the device and the outer surface of the casing to displace
inwardly
an amount at least great enough so that when the force is released, an
interference
fit is created between the device and the casing.
The step of applying substantially radially-directed force to a plurality of
points about
an outer circumference of the tubular section is termed herein as "crimping".
Preferably, by selection of casing, device supporting casing installation
and/or force
applied, the inward displacement of the casing outer surface is not so great
that the
drift diameter of the casing is excessively reduced. In one embodiment, the
casing is
not displaced inwardly beyond the drift diameter. However, in another
embodiment,
the inward displacement of the casing outer surface causes the inner diameter
of the
casing to be reduced beyond the drift diameter of the casing.
In one embodiment the method can be used to produce casing for wellbore
completion and in another embodiment the method can be used to produce casing
for use in a drill string. The device supporting the mstananon can De se~ec~ea
rrorr~
those useful for facilitating run in of the casing, those for controlling the
positioning of
the casing within the borehole, those for accommodating wear against the wall
of the
borehole into which the casing is run or those providing combinations of the
foregoing.
Frictional forces enabled by the interference fit at the inwardly displaced
section
provide the mechanism by which structurally significant axial and torsional
load may
be transferred between the device and the casing substantially without
slippage
therebetween.
The casing on for use in the present invention must be capable of accepting
the
hoop stresses of crimping without becoming unstable, for example, without
buckling
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or crumpling. This generally requires that the casing be thick-walled, for
example,
having an external diameter to thickness ratio ("D/t") less than 100 and
preferably
less than 50.
To be most generally useful for this method, the devices supporting
installation
should be amenable to rapid field installation on joints of casing having at
least one
non-upset end.
The tubular section of the device under application of load at a plurality of
points
about its circumference has an elastic resiliency less than the elastic
resiliency of the
casing onto which it is crimped. The tubular section can rJe cynnancai or
~argery
cylindrical with some radial or axial variations to the internal diameter or
outer
surface. The tubular section should be substantially circumferentially
continuous
such that a hoop stress can be set up during the radially inward displacement
at a
plurality of points about the circumference of the outer surface of the
section. The
tubular section should be capable of accepting the hoop stresses of crimping
without
becoming unstable, for example, without buckling or crumpling. This generally
requires that the section be thick-walled, for example, having an external
diameter to
thickness ratio ("D/t") less than 100 and preferably less than 50.
The loose fit of the section about the casing must be sufficient to
accommodate the
variations of the outer diameter of the casing intended to be used.
A device selected to facilitating run in of the casing can include a tamped
leading
edge to facilitate riding over surface contours on the borehole wall or to
facilitate
raising the casing such that protrusions, such as casing connections, on the
casing
outer surface can pass along the borehole without digging into the formation
or
getting hung up on shoulders in the borehole wall.
A device selected to accommodate wear against the wall of the borehole into
which
the casing is run can include bearing surfaces capable of withstanding
extended
abrasion against borehole surfaces and sufficient to withstand the rigors
encountered during installation into or the drilling of at least one well. The
bearing
surfaces should withstand abrasion better than the material of the casing and
can
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be, for example, hard facing, which is the treatment of steel to increase its
hardness,
ribs, lines of weldments, hardened inserts, etc.
A device selected from those useful for controlling the positioning of the
casing within
the borehole can provide for spacing the casing from the borehole wall in
which it is
to be used and, in particular, centralizing or stabilizing the casing within
the hole.
Thus, in one embodiment, the thickness of the device is selected such that
once the
bearing member is crimped onto the casing, the device extends radially out
beyond
the outer surface of the casing. In addition, the thickness of the bearing
member at
the bearing surfaces can be selected such that the bearing member acts as a
centralizer or a stabilizer, with consideration as to the inner diameter of
the borehole
in which the casing is to be used.
In some aspects of the present invention, differential temperature may be used
to
control interference between the casing and the device according to the well
known
methods of shrink fitting, whereby the differential temperature is obtained by
heating
the device, cooling the casing, or both, prior to crimping.
However, it is preferable to avoid the requirement to either heat the device
or cool
the casing to obtain an interference fit. In particular, preferably sufficient
interference
in the crimped connection is obtained substantially only by mechanical means,
without requiring a significant temperature differential between the device
and the
casing at the time of crimping. This purpose is realized by selecting the
elastic limit
of the device material, in the section to be crimped, to be less than that of
the casing
on which the centralizer is to be installed. In this context, the elastic
limit generally
refers to the strain at which the materials of the parts yield. Having the
material
properties thus selected, it will be apparent to one skilled in the art, that
when the
radial displacement applied during crimping is sufficient to force the hoop
strain of
the metal casing to be at least equal to its elastic limit, upon release of
the load
causing the radial displacement, the metal casing will tend to radially
'spring back' an
amount greater than the centralizer, were both parts separated. Since the
parts are
not separated, the difference in this amount of spring back or resiliency is
manifest
as interference and fulfills the desired purpose of creating interference
substantially
only by mechanical means.
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While a purely mechanical method of obtaining interference through crimping is
desirable for most applications, the present invention can use both thermal
and
mechanical methods for attachment of the device to the casing.
To facilitate the frictional engagement of the crimped bearing member to the
thick-
wall casing, the inside surface of the device, at least over the section to be
crimped
(i.e. at least a portion of the inner surface defining the inner bore through
the tubular
section), can be provided with a roughened surface finish. In another
embodiment, a
friction enhancing material such as, for example, a grit-epoxy mixture is
disposed in
the interfacial region of the crimped section. Similarly, various bonding
materials may
be disposed in the interfacial region prior to crimping to act as glues
augmenting the
frictional aspects of the connection 'once their shear strength is developed
after
setting.
Brief Description of the Drawings
A further, detailed, description of the invention, briefly described above,
will follow by
reference to the following drawings of specific embodiments of the invention.
These
drawings depict only typical embodiments of the invention and are therefore
not to
be considered limiting of its scope. In the drawings:
Figure 1 is a perspective view of a device in the form of a casing centralizer
useful in
the present invention;
Figure 2 is a perspective view of the device shown in Figure 1 placed on a
joint of
casing as it might appear before crimping;
Figure 3 is a partial sectional schematic view through the wall of a device
positioned
coaxially on a casing joint and inside a collet crimping tool prior to
application of
radial crimping displacement;
Figure 4 is the partial sectional schematic view of the assembly shown in
Figure 3 as
it would appear after application of radial crimping displacement;
Figure 5 is a perspective view of a device supporting installation, the device
being in
the form of a casing wear band tool; and
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Figure 6 is an axial sectional view through another device supporting
installation of
casing shown crimped on a joint of casing.
Description of the Preferred Embodiment
The installability of wellbore casing can be enhanced by attachment thereto of
devices supporting the installation of the casing. Attachment by crimping
provides a
rugged interference fit between the casing and the device that is capable of
withstanding the axial and radial load of casing installation and
substantially does not
compromise casing integrity.
A device useful in the present invention is shown in Figure 1. The device is a
centralizer useful for supporting casing installation by at least maintaining
the
position of the casing relative to the borehole and accommodating wear against
the
wall of the borehole into which the casing is run. The centralizer includes
metal body
1 containing an internal bore 2, a cylindrical end 3 forming a section
suitable for
crimping, and a centralizing section 4 on which ribs 5 are placed.
The cylindrical end and the centralizing section are formed integral on the
body and
the internal bore passes through both of them. While the crimpable section in
the
illustrated embodiment is cylindrical end 3, it is to be noted that the
crimpable section
can be formed intermediate a pair of centralizing sections, if desired, rather
than on
an end. Also, it is to be noted that more than one crimpable section and more
than
one centralizing section can be provided on the centralizer, as desired.
Ribs 5 are evenly spaced around the centralizing section. There are at least
three
ribs spaced about the circumference of the centralizing section. Preferably,
each rib
is helically shaped and the number, length and pitch of the rib helixes are
arranged
to ensure that the starting circumferential position of each rib overlaps the
ending
circumferential position of at least one adjacent rib. The ribs may be placed
on the
centralizer body by a variety of methods including milling, casting, welding
or
hydroforming.
The internal bore 2 of the centralizer body is selected to loosely fit over at
least one
end of a thick-wall metal casing 6, shown as a threaded casing joint in Figure
2 onto
which a coupling has been threaded. As shown, the internal diameter of bore 2
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allows the centralizer to be readily inserted over an end of the casing 6 and
placed
somewhere along the length of the casing joint prior to crimping. Thus placed,
crimping provides a means to obtain a significant interference fit even where
the
centralizer and casing material are at similar temperatures prior to crimping.
In
applications where significant heating of the casing and centralizer, after
centralizer
installation, is anticipated, the centralizer is preferably selected to have a
thermal
expansion coefficient that is equal to or less than that of the casing.
Similarly in
applications where cooling subsequent to crimping is anticipated, the opposite
relationship between thermal expansion coefficients is preferred.
Radial displacement required to crimp the centralizer cylindrical end 3 to the
casing
joint 6, on which it is placed, may be accomplished by various methods such as
by
hydroforming, as described in Canadian application 2,328,190, filed December
14,
2000. However, a fixture employing a tapered 'collet in housing' architecture
has
been found to work well in practice. This well known method of applying
uniform
radial displacement, and consequently radial force when in contact with the
exterior
of a cylindrical work piece, employs a device as shown schematically in Figure
3.
The device retains the externally tapered fingers or jaws 7 of a collet
(segments of
an externally conical sleeve) inside a matching internally tapered solid
housing 8.
Application of axial setting force to the housing 8, as shown by vector F,
which is
reacted at the face 7a of the collet jaws 7, as shown by vector R, tends to
induce the
collet jaws 7 to penetrate into the collet housing 8 along the angle of its
conical bore.
This causes the jaws 7 to move radially inwardly and engage the work piece to
be
gripped, in the present case, shown as the cylindrical end 3 of a centralizer.
(Alternately, the action of the collet may be described in terms of setting
displacement, understood as axial displacement of the collet housing 8 with
respect
to the collet jaws 7. In this case the setting force is understood to arise
correlative
with the setting displacement.) The axial force F and reaction R are readily
applied
by, for example, a hollow bore hydraulic actuator (not shown), arranged with
an
internal bore greater than the casing 6 outside diameter.
With this arrangement, upon application of sufficient force (F), the jaws may
be
forced inward to first cause sufficient radial displacement to plastically
deform the
centralizer cylindrical end 3 and bring it into contact with the casing 6.
This amount of
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radial displacement removes the annular clearance of the loose fit initially
required
for placing and positioning the centralizer on the casing 6. Application of
additional
setting force then forces both the centralizer cylindrical end 3, and the
underlying
wall of the casing 6, inward. In the preferred embodiment, the setting
displacement is
preferably applied until the hoop strain in the casing wall at the crimp
location equals
or slightly exceeds its elastic limit. It will be apparent to one skilled in
the art that
radial displacement beyond this point will cause little increase in residual
interference
but will have the effect of reducing the drift diameter of the casing joint 6.
Figure 4
schematically shows the collet, centralizer and casing as they might appear in
the
fully crimped position. After the desired radial displacement is achieved, the
setting
displacement of the collet is reversed which releases it from the centralizer
allowing
the collet to be removed, leaving the centralizer crimped to the casing.
To ensure that this method of cold crimping (i.e., mechanical crimping
unassisted by
thermal effects) results in sufficient residual interference between the
centralizer
cylindrical end 3 and the casing 6, the centralizer material at the
cylindrical end 3 has
an elastic limit less than that of the casing 6. As is typically the case, the
centralizer
and casing material are both made from carbon steel having nearly the same
elastic
modulii. Therefore, the elastic limit may be expressed in terms of yield
strength,
since elastic limit is generally given by yield stress divided by elastic
modulus.
For example, in one trial conducted to assess the torque capacity to be
obtained by
crimping a centralizer to 7inch diameter API grade L80 26ppf casing material
(minimum specified yield strength of 80,OOOpsi), steel centralizer material
having a
measured yield strength of 47,OOOpsi was selected. The centralizer elastic
limit was
thus less than 50% that of the casing. Using this material, a centralizer
having an
outside diameter of 7.625inches, an inside diameter of 7.125inches and a
machined
inside bore, was constructed for one trial. After crimping this centralizer to
the casing
over a 3.5inch section using the method of the present invention described
above,
the axial force required to displace the centralizer was measured to be
approximately
20,000 Ibf. Had this sliding force been applied through torsion, the required
torque to
induce sliding rotation of the centralizer relative to the casing would be
5833 ftlb.
This may be compared to the maximum expected total drilling torque for this
size of
casing, which is in the order of 20,OOOftlb. Given this crimped centralizer
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configuration, the torque transferred between just one such centralizer and
casing,
would need to exceed 25% of the total worst case drilling torque, to induce
slippage
of the centralizer on the casing.
However, in certain applications it may be desirable to further enhance the
load
transfer capacity of a centralizer attached to casing, without increasing the
crimped
length, by improving the frictional engagement achieved for a given level of
interference. While this may be accomplished by various means, roughening one
or
both of the cylindrical end inner wall or the casing outer surface on which
the
centralizer was to be crimped, was found to be particularly effective. In one
trial
using a centralizer configured similar to that described in the preceding
example, but
where the wall surface 9 defining the internal bore 2 of the centralizer was
roughened by grit blasting prior to crimping, the equivalent torque capacity
was
increased approximately 70%.
The length of the section crimped will in general linearly affect the load
transfer
capacity of the crimped connection. For centralizers attached to full length
casing
joints, the length of section suitable for crimping, provided by the
cylindrical end 3
may be extended almost without limit. Similarly the length of the collet jaws
7, do not
limit length that may be crimped. The collet tool may be used to apply the
required
radial displacement at multiple axial locations to incrementally crimp an
extended
length cylindrical end 3. Increased load transfer capacity may thus be readily
achieved by increasing the crimped section length.
Referring to Figure 5, another device supporting the installation of wellbore
casing is
shown that is useful in the present invention. While centralizers as shown in
Figure
1 could be attached to the casing at frequent enough intervals to prevent
wear, other
less elaborate devices, such as the wear band tool of Figure 5 can be used to
facilitate run in and/or to accommodate wear.
The wear band tool includes a metal body 101 containing an internal bore 102,
a
cylindrical mid-section 103 forming a section suitable for crimping, and two
end
intervals 104 on which hard-faced wear bands 105 are placed. As shown, a
concentric wear band 105 is placed at each end of the wear band tool forming
slightly raised diameter intervals. These wear bands are formed by attaching
hard-
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facing material as commonly known to the industry to metal body 101. The wear
band tool is attached to casing by crimping over a portion of cylindrical mid-
section
103 using the methods described above for the centralizer tool.
Another wear band tool is shown in Figure 6 in crimped form on a joint of
casing 6.
The wear band includes a metal body 101 containing an internal bore 102, a
cylindrical end section 106 forming a section suitable for crimping, and an
interval
104 on which a hard-faced wear band 105 is securely mounted. An end 108 of the
wear band tool is ramped to facilitate passage thereover of discontinuities in
the
borehole. End 108 has a leading edge ramp angle a of preferably of less than
60°
and preferably less than 45°.
The wear band tool can, therefore, be used alone to space the casing from the
borehole wall and to accommodate wear, since the hard-faced wear band 105 can
withstand wear better than the casing or standard couplings on the casing. The
wear band tool can also be used downhole of a shoulder on the casing, such as
a
coupling, wherein the ramped leading edge 108 can facilitate passage of the
casing
through the borehole by preventing the casing shoulder from digging into the
formation.
It will be apparent that these and many other changes may be made to the
illustrative embodiments, while falling within the scope of the invention, and
it is
intended that all such changes be covered by the claims appended hereto.
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