Field of the invention
[0001] The present invention relates to the field of downhole devices, and more specifically
but not exclusively to the field of such devices usable in oil and/or gas extraction.
Some arrangements disclosed herein relate to centralizer devices. Some arrangements
disclosed herein relate to devices that are connectable to centralizer devices.
Background to the Invention
[0002] As known to those skilled in the art, centralizers are used in the oil, gas or water
well drilling industries to centre a tubular member (hereinafter referred to as "tubular")
within a borehole or previously installed larger tubular.
[0003] Such tubulars are generally constructed in handleable lengths, e.g. 12m (40 ft),
each length typically being externally male threaded at both ends. The lengths are
assembled together using short female threaded couplings. The assembly of the tubulars
to a predetermined total length is referred to as a 'string'.
[0004] When the string is disposed in a borehole or existing tubular, it is desirable to
position the string substantially centrally within the borehole or existing tubular
thereby forming a substantially annular passageway around the tubular of concern.
This enables passage of material such as fluids, cement slurries in the space around
the tubular.
[0005] To try to achieve this condition, centralizers are disposed at selected intervals
along the length of the string. Retention of the centralizers in a desired position
may be achieved in restricting axial movement by the use of a so-called "stop collar"
being a ring grippingly secured to the tubular. The stop collar design must cope with
free fitment onto tubulars having poorly toleranced outer diameters. Any design applied
must take up this tolerance as pre-requisite to applying sufficient load to give the
desired axial load restraint. To resist axial loading, the stop collar may have, for
example, toughened steel screws radially dispersed around the circumference of the
stop collar that protrude substantially above the outer surface of the stop collar
body.
[0006] Known spring centralizers have a flexible external diameter aimed at making contact
with the bore wall at all times while being capable of flexing to react (restoring
force), the lateral forces created by the tubular conforming to the wellbore profile
and accommodate obstructions or internal dimensional changes. Such centralizers are
comprised of circular end bands between which are affixed a number of leaf springs
commonly referred to as 'bows'.
[0007] It is desired within the industry that the centrality of the tubular as it is being
moved down the borehole to its required final depth position is sufficient to keep
the tubular from contacting the borehole or tubular bore such that undue mechanical
interference and damage is avoided, be it from the centralizer, stop collar protrusions
or couplings.
[0008] Contact forces, e.g. stop collar screws, can cause considerable damage to the previously
installed steel tubular and generated swarf may cause damage elsewhere in the overall
well construction. Too much deflection of centralizer bows will permit contact of,
e.g. stop collar screws, which are affixed to the rotating tubular, cutting into the
wellbore or larger tubular to which the centralizer is being inserted.
[0009] Commonly, especially in well remedial work, the previously installed tubular may
have what is referred to as a 'Window' cut through the side of the tubular to permit
the centralized tubular being run to deflect through the window. It follows that,
for example, hardened stop collar protrusions and couplings could hold fast against
a window edge if lateral forces of deflected centralizer bows are equal to or below
the annular height of the protrusions. Hence, in such arrangement it can be quite
problematic to move centralizer through the bore hole and into position.
[0010] It is furthermore imperative to facilitate the common practice of rotating the tubular
as it passes through to its final depth thereby easing passage through high Dog Leg
Severity (DLS) undulations. Centralizer rotation is stopped against the bore through
which it is being run permitting rotation of the tubular inside the affixed centralizers.
[0011] Evolution of wellbore profile complexity has exacerbated occurrence of such mechanical
interference. Undulations of the profile defined as a rate of 3 dimensional change
referred to as DLS (Dog Leg Severity) per unit length of bore, commonly 30m (100ft)
frequently result in high lateral forces, perpendicular to the tubular axis. These
lateral forces can be such that centralizer spring bows may become flattened or near
flattened at various points of high DLS during passage of the centralizer down a wellbore.
This can result in, for example, couplings and stop collar protrusions, such as hardened
set screws running against the previously installed tubular bore or wellbore. In other
words mechanical interference between these parts of the tubular and the previously
installed tubular bore or wellbore can occur, leading to surface damage to the previously
installed tubular bore or wellbore.
[0012] It is additionally noted that said flattening of bows may result in permanent deformation
of the bows, especially at the point of spring rotation at the meeting point of leaf,
or bow, spring to end band. This can result in the original centralization potential
of the centralizer becoming adversely affected when a desired depth is reached. It
is preferred within the industry that centrality between tubulars or tubular and the
wellbore, when centralized tubular is at its required depth, is maximised or to a
minimum acceptable level. In other words, the tubular is located centrally within
the previously installed tubular or wellbore, or the distance between the tubular
and previously installed tubular or wellbore is maintained above a minimum distance.
[0013] Figure 1 illustrates a known tubular arrangement that has been inserted within a
borehole 50. A centralizer 38 is located on the tubular by way of stop collars 37
located either side of the centralizer 38. Stop collars 37 are used to mount around
the tubular to engage and grip the exterior of the tubular. The stop collars 37 provide
a stop shoulder on the tubular to restrict axial travel along the tubular member of
any further associated product such as a centralizer 38. Each centralizer 38 is therefore
joined to the tubular and arranged to support the tubular within the borehole 50 such
that the tubular is substantially centrally arranged within the borehole 50.
[0014] The one-piece centralizer 38 has first and second opposing end collars 41, 42 that
are axially separated by plural spring bows. Only spring bows 43, 44, 45, and 46 of
the plural spring bows are shown.
[0015] Each spring bow forms a generally convex curve. This is clearly observed for spring
bows 45 and 46. However, the effect of high lateral forces from the tubular has caused
deflection of the centralizer spring bows. This has caused the flattening of spring
bow 43. The lateral forces have caused sufficient deflection for some of the set screws
47 of the stop collar 37 to be pushed hard against the borehole 50.
[0016] This situation can be problematic. This is because the tubular is now contacting
the borehole 50, which can lead to mechanical interference and damage. Furthermore,
contact forces from, for example, the contact screws 47, can cause damage to the borehole
50. Too much deflection of the centralizer spring bows will enable, for example, stop
collar screws 47 to cut into the well bore 50. Considerable damage to the borehole
50 can occur. This damage can also generate swarf that can cause damage elsewhere.
Due to flattening of the spring bow 43, parts of the tubular, for example the stop
collar screws 47 of stop collar 37 that is grippingly attached to the tubular, can
hold fast to the borehole 50 because the stop collar 37 is pushed against the borehole
50. This can constrain the tubular from rotating. This situation also applies for
a tubular inserted within a previously installed tubular rather than within a borehole
50.
[0017] Additionally, spring bow 43 has been flattened to an extent that can cause permanent
or irreversible deformation. Spring bow 43, and any other spring bow that has similarly
been flattened, will not now spring back to its original shape or not spring back
sufficiently to provide the required centring or restraining effect. This means that
centralizer 38 cannot now centralize the tubular optimally. This can occur, for example,
when the tubular is further passing through the borehole 50 or tubular bore 40. When
there are high lateral forces, because the spring bow 43 is now flattened, the centralizer
38 will be offset, or can be more easily offset, and it becomes more likely that mechanical
interference between the tubular and the bore hole 50 or tubular bore 40 will result.
This is because, since spring bow 43 has become flattened, the centralizer 38 cannot
perform its function correctly and centre the tubular within the borehole 50 or tubular
bore 40. Therefore, even lateral forces less than that that were required to flatten
spring bow 43 can now push the tubular hard against the borehole 50 or tubular bore
because spring bow 43 is flattened and cannot resist lateral forces. This pushing
of the tubular against the borehole 50 or tubular bore 40 can cause damage as already
discussed. Also, when the tubular reaches its final depth, centralizer 38 can be located
at a position where the borehole 50 has a wider diameter than that typical for other
parts of the borehole 50. Such a scenario is with so-called "under reamed" bores,
occurring where wellbores are 'opened out' in a region lower than a previously installed
tubular. In such a circumstance, because spring bow 43, and indeed other spring bows,
of the centralizer 38 has or have been flattened, leading to permanent deformation
or otherwise to the spring bows not functioning optimally, the centralizer 38 cannot
mechanically secure the tubular in position at that location. This is because the
flattened spring bow 43, and indeed other flattened spring bows, will not spring back
to their original shape, or will not spring back sufficiently to make the required
contact with the wall of the borehole 50 or tubular bore 40. Therefore, the centralizer
will not make the required robust mechanical connection with the borehole 50 at that
location, and the tubular will neither be centrally located, nor mechanical constrained
to the required degree, within the borehole 50 or tubular bore 40.
[0018] A problem with existing centralizers that are installed on a tubular inserted within
a borehole or previously installed tubular, is that damage can occur to the wall of
the borehole or previously installed tubular. This damage is due to mechanical interference
occurring between, for example the screws on stop collars, and the wall of the borehole
or previously installed tubular, which is further exacerbated by the flattening of
the spring bows.
Summary
[0019] Disclosed herein is a spring centralizer arranged to control and limit the degree
of spring deflection.
[0020] A controlled deflection of a spring centralizer device to a predetermined (e.g.,
minimum) annular width between the tubular upon which the centralizer is mounted and
the borehole or bore of a previously installed tubular member is disclosed.
[0021] There is provided an improvement to a spring centralizer device in supporting a tubular
member to a predefined distance (e.g., minimum) from the wall of a bore.
[0022] The spring centralizer is a device for supporting a tubular member spaced from the
wall of a bore. The spring centralizer device may have a longitudinal axis, and the
spring centralizer device may comprise first and second mutually spaced collar portions
and may have a plurality of bow leaf spring portions disposed between. Each collar
portion may be substantially cylindrical. The centralizer device may extend substantially
around or all around said longitudinal axis. Method of construction may consist of,
but not be limited to, mechanically interlocking parts, welded assembly of parts or
construction from a single piece material.
[0023] Each collar portion may have radially disposed parallel to axis protrusions projecting
above the external diameter of the collar portion. Protrusions may be formed from
the collar portion material or as securely attached added parts.
[0024] Protrusions may be angled and/or shaped to direct fluids into turbulent flow within
the annulus to aid suspension and removal of detritus. The angled and/or shaped protrusion
interrupts laminar flow passing the centralizer, thereby creating a turbulent flow
which aids cleaning of the wellbore of detritus and/or removal of such fluids when
displacing with cement into the annulus between the tubular and the borehole or existing
tubular.
[0025] Protrusions may be applied to a single collar portion only.
[0026] Protrusions may be applied or may be formed on a band that is separate to the collar
portions of a centralizer. The band may be arranged to butt up against, or be secured
or otherwise coupled to the centralizer. The band is not grippingly attached to the
tubular such that the band can freely rotate about the tubular. In other words, the
band may be freely rotatable about the tubular. The band can rotate about the tubular
in the same manner that the centralizer does. The protrusions may be formed on a collar
that sits between the centralizer and a stop collar that is used to support a centralizer.
The collar may then be "free floating" between an end of the centralizer and a contacting
edge of the stop collar. The protrusions may be formed on a band that is located around
a tubular, such that it prevents a stop collar or other such device from mechanically
interfering with the wall of a borehole or previously installed tubular, without the
requirement that the band operate in co-operation with a centralizer.
[0027] The device may consist of protrusions of various designs formed radially outward
on centralizer end collars such that it is not possible to completely flatten the
spring bows. The protrusions may be formed from or may be attached to the end collars
such that they have an axis normal to the surface of the end collars that is angled
to a radius of the centralizer. Spring bow performance integrity may be improved with
removal of permanent deformation from extreme flattening at point of rotation of spring
bow to end collar. The device may consist of protrusions of various designs such that
spring bow performance integrity may be improved with removal of permanent deformation
from extreme flattening at point of rotation of spring bow to end collar.
[0028] Protrusions may be made to ensure contact with associated mechanisms, affixed to
the tubular on one or either side of the centralizer, will not come in contact with
the borehole or previously installed tubular bore. Drag resistance running to depth
may be reduced by removing mechanical interference of associated mechanisms with the
borehole or previously installed tubular bore resulting in passage resistance forces
attributable to the lateral force of the tubular being run conforming to the wellbore
profile multiplied by the customer dictated Coefficient of friction (CoF). The CoF
multiplied by the lateral force is referred to as 'Drag'. If the total Drag of all
parts of the tubular is too large, the tubular will be prevented from being pushed
further into the borehole or existing tubular. Consequently, the tubular will not
be able to reach the final desired depth.
[0029] Contact of, for example stop collar screws, may be reduced through provision of the
protrusions, ensuring rotation of the centralized tubular may only be inside the centralizer
end bands. Height and form of protrusions may permit ease of guidance through apertures
in a previously installed tubular. Protrusions may further be tailored to stop deflection
of spring bows such that a height (standoff), within the annulus between tubular and
borehole may be achieved as a minimum. For example, the standoff may be in accordance
with the dictates of API 10D at 67% standoff or whatever standoff % the end user application
may tolerate or demand.
[0030] According to an aspect, there is provided a centralizer having a longitudinal axis,
the centralizer comprising: first and second opposing end collars positioned around
the axis of the centralizer; and a plurality of spring bows extending from the first
end collar via a generally convex curved portion to the second end collar. A radial
distance from an outwardly facing portion of the first end collar to the axis is greater
than a radial distance from a first outwardly facing portion of a spring bow of the
plurality of spring bows, at a longitudinal axial position where the spring bow extends
from the first end collar, to the axis. A radial distance from an outwardly facing
portion of the first end collar to the axis is less than a radial distance from a
second outwardly facing portion of the spring bow, at a longitudinal axial position
between the first end collar and the second end collar that is farthest from the axis,
to the axis.
[0031] The radial distance from the outwardly facing portion of the first end collar to
the axis may be greater than the radial distance from a third outwardly facing portion
of the spring bow, at a longitudinal axial position where the spring bow extends from
the second end collar, to the axis.
[0032] The outwardly facing portion of the first end collar may comprise at least a portion
of a protrusion. The protrusion may be formed from the first end collar. The protrusion
may be attached to the first end collar. The protrusion may be in the form of a bow.
The bow may comprise a generally convex curved portion. The protrusion or protrusions
may be substantially semi-spherical or hemispherical. The protrusion may be formed
through a process or processes involving a pressing process. The protrusion may be
formed through a process or processes involving a bending process. The protrusion
may be further formed through a process or processes involving a cutting process.
The protrusion may have a length and a width less than the length, and the length
may be angled to the longitudinal axis of the centralizer. The protrusion may be a
first protrusion of a plurality of protrusions. The plurality of protrusions may be
uniformly distributed about a perimeter of the first end collar.
[0033] The outwardly facing portion of the first end collar may have a shape configured
to direct fluid flow into a turbulent flow.
[0034] The centralizer may be made from a single piece material. The centralizer may be
made from mechanically interlocking parts. The centralizer may be made from parts
welded together.
[0035] The centralizer may be configured to support a tubular member to a predefined distance
from a wall of a bore. For example, the centralizer may be configured to accord with
the dictate of API 10D at 67% standoff.
[0036] According to another aspect, there is provided a device having a longitudinal axis,
the device configured to cooperate with a centralizer. The centralizer has a longitudinal
axis and comprises first and second opposing end collars positioned around the axis
of the centralizer, and a plurality of spring bows extending from the first end collar
via a generally convex curved portion to the second end collar. The device comprises
an outwardly facing portion. When the axis of the device and the axis of the centralizer
are substantially aligned co-axially a radial distance from the outwardly facing portion
of the device to the axis is greater than a radial distance from a first outwardly
facing portion of a spring bow of the plurality of spring bows, at a longitudinal
axial position where the spring bow extends from the first end collar, to the axis.
When the axis of the device and the axis of the centralizer are substantially aligned
co-axially a radial distance from the outwardly facing portion of the device to the
axis is less than a radial distance from a second outwardly facing portion of the
spring bow, at a longitudinal axial position between the first end collar and the
second end collar, to the axis.
[0037] The radial distance from the outwardly facing portion of the device to the axis may
be greater than the radial distance from a third outwardly facing portion of the spring
bow, at a longitudinal axial position where the spring bow extends from the second
end collar, to the axis.
[0038] The outwardly facing surface of the device may comprise at least a portion of a protrusion.
The protrusion may be formed from the device. The protrusion may be attached to the
device. The protrusion may be in the form of a bow. The bow may comprise a generally
convex curved portion. The protrusion or protrusions may be substantially semi-spherical
or hemispherical. The protrusion may have a length and a width less than the length,
wherein the length may be angled to the longitudinal axis of the device. The protrusion
may have a shape configured to direct fluid flow into a turbulent flow. The protrusion
may be a first protrusion of a plurality of protrusions. The plurality of protrusions
may be uniformly distributed about a perimeter of the device.
[0039] The outwardly facing surface of the device may have a shape configured to direct
fluid flow into a turbulent flow.
[0040] The device may be made from a single piece material. The device may be made from
mechanically interlocking parts. The device may be made from parts welded together.
The device may have one or more connecting portions for connecting to a centralizer.
[0041] The device may be configured to freely rotate about a tubular.
[0042] The device, in cooperation with the centralizer, may be configured to support a tubular
member to a predefined distance from a wall of a bore. The device, in cooperation
with the centralizer, may be configured to accord with the dictate of API 10D at 67%
standoff.
[0043] The device may have T-shaped projections arranged to extend into corresponding female
T-shaped apertures of the centralizer, for connecting the device to the centralizer.
The centralizer may have T-shaped projections arranged to extend into corresponding
female T-shaped apertures of the device, for connecting the device to the centralizer.
The device may have bayonet fastenings arranged to engage with an end collar of the
centralizer, for connecting the device to the centralizer. The end collar of the centralizer
may have bayonet fastenings arranged to engage with the device, for connecting the
device to the centralizer.
[0044] The device may be a band. The device may be a collar.
[0045] In another aspect, there is provided a system comprising a device, the device being
as described above or anywhere herein. The system may also comprise a centralizer.
The centralizer may have a longitudinal axis. The centralizer may comprise first and
second opposing end collars positioned around the axis of the centralizer, and a plurality
of spring bows extending from the first end collar via a generally convex curved portion
to the second end collar.
[0046] The micro-alloy steel that may be used for the centralizer, protrusion, protrusions
and/or band may be Boron steel. This is one example of the material that can be used
for the centralizer, or protrusions and other suitable materials can be used. The
material that may be used for the centralizer, protrusion, protrusions and/or band
may be heat treatable to improve, for example, shear and tensile section strength
properties. Such heat-treated strength may be of the order 90 tons per square inch.
Brief description of the Drawings
[0047] Specific arrangements of the disclosure shall now be described below by way of example
only and with reference to the accompanying drawings in which:
Figure 1 shows a known arrangement of a tubular received within a borehole, and shows
the effect of high lateral forces from the tubular, within the borehole, thereby causing
deflection of the centralizer spring bows;
Figure 2 shows a centralizer within an existing tubular bore;
Figure 3 shows a centralizer within a borehole;
Figure 4 shows an exemplary blank used in forming the centralizer of figures 2 and
3;
Figure 5 shows a standoff within the annulus between a tubular and a borehole as a
function of load, as required by specification API 10D based upon common size 9-5/8"
casing inside 12-1/4" borehole;
Figure 6 shows a standoff within the annulus between a tubular and a borehole as a
function of load for the centralizer as shown in figures 2 and 3;
Figure 7 shows a standoff within the annulus between a tubular and a borehole as a
function of load, for a centralizer having protrusions with a height greater than
the height of the protrusions for the centralizer of Figures 2 and 3; and
Figure 8 shows a perspective view of an end collar.
Specific Description
[0048] Figure 2 provides an example centralizer arrangement in which a plurality of protrusions
60, 70 are provided on end collars 51, 52 of the centralizer 58 in order to prevent
flattening of the centralizer's spring bows 53, 54, 55, 56 and prevent the screws
47 of the stop collar 37 causing damage to the bore 40. The arrangement of figure
2 shall now be discussed in detail.
[0049] Referring to figure 2, a tubular similar to that shown in figure 1 has been inserted
within an existing tubular bore 40. A centralizer 58 is located on the tubular. In
figure 2, a situation similar to that presented in fig.1 is shown. However, figure
2 shows the effect of radially disposed protrusions beyond the external diameter of
the centralizer collar portions limiting deflection of the spring bows thereby keeping,
for example, typical stop collar set screws clear of the previously installed tubular
internal diameter.
[0050] The one-piece centralizer 38 has first and second opposing end collars 51, 52 that
are axially separated by 6 spring bows, of which only 4 are shown 53, 54, 55, 56.
Each spring bow forming a generally convex curve. The plurality of spring bows extend
from the first end collar 51 to the second end collar 52.
[0051] The first end collar 51 has six protrusions 60 around the circumference of the collar,
of which only the four protrusions 60a, 60b, 60c, and 60d are shown. The second end
collar has six protrusions 70 around the circumference of the collar, of which only
the four protrusions 70a, 70b, 70c, and 70d are shown.
[0052] The protrusions 60, 70 protrude from the first and second end collars 51, 52 and
come into contact with the wall of the existing tubular 40 due to high lateral forces
offsetting the tubular within the existing tubular 40. The protrusions 60, 70 protrude
to a height above the surface of the first and second end collars 51, 52, such that
the stop collars 37 are kept clear from the wall of the existing tubular 40. This
means that stop collar screws 47 are kept away from the wall of the existing tubular
40. Other mechanisms that can be affixed either side of the centralizer are also kept
from contacting the wall of the tubular 40.
[0053] Additionally, the protrusions 60, 70 protrude to a height from the surface of the
first and second end collars 51, 52, such that the plurality of spring bows do not
become completely flattened as the centralizer is pushed up against the wall of the
existing tubular 40. The spring bows may not become completely flattened, however
the protrusions still stop the spring bows from becoming deformed to an extent that
leads to permanent deformation or deformed to an extent that leads to the spring bows
not being able to perform optimally. As seen in figure 2, spring bow 53 has deformed
but has not become completely flattened. The height of the protrusions above the surface
of the first and second end collars 51, 52 is provided such that the spring bows can
deform, but can then spring back as required. For example, as the centralizer moves
to a more central position within the tubular or indeed as the centralizer moves toward
the opposite side of the tubular, bow spring 53 can take the form of bow spring 56,
as shown in figure 2, and bow spring 56 can take the form of bow spring 53. This means
that the spring bows have not suffered permanent deformation, or have not suffered
plastic deformation. In other words the spring bows can continue to operate as intended.
[0054] In figure 3, a similar situation to that shown in, and described with reference to
figure 2, is shown. However, in figure 3 the centralizer 58 is inserted within a borehole
50.
[0055] Contact between the tubular and the wall of the borehole 50 or existing tubular is
via the spring bows of the centralizer and via the spring bows and protrusions at
particular sections of the borehole 50 or existing tubular. The protrusions are appropriately
shaped and formed to have a reduced mechanical interference with the wall of the borehole
50 or existing tubular. This means that the protrusions, when contacting the wall
of the borehole or existing tubular, do not damage the wall of the borehole or tubular.
Therefore, the protrusions stop the tubular parts such as stop collars other than
the centralizer from contacting the wall of the borehole 50 or existing tubular which
leads to a reduced mechanical interference with the wall of the borehole 50 or existing
tubular. Damage to the borehole 50 or existing tubular 40 is reduced. Drag resistance
running to depth is reduced by removing mechanical interference of associated mechanisms
with the borehole 50 or previously installed tubular bore 40. This results in passage
resistance forces only attributable to the lateral force of the tubular being run
conforming to the wellbore profile x the customer dictated CoF (Coefficient of friction).
[0056] The manufacture of the centralizer 58 shown in figures 2 and 3 shall now be described
with reference to figure 4. The centralizer of the described arrangement has spring
bows of equal length, and this means it can be made from a single blank, an example
of which is shown in Figure 4. Referring to figure 4, a blank 300, is formed from
a single sheet of boron steel. The blank has two transverse web portions 302, 303
spaced apart by six spaced longitudinal web portions 304 which extend substantially
parallel to one another and perpendicular to the webs 302, 303. The first and second
transverse web portions 302, 303 are generally rectangular in shape, and are mutually
parallel. The six longitudinal web portions 304 extend between the transverse web
portions 302,303 to define therebetween five apertures 309 of equal size. The outer
longitudinal web portions 304 are inset from the ends of the transverse web portions
by around half the width of the apertures 309 to leave free end portions 310,311 of
the transverse web portions.
[0057] The free end portions are overlappingly secured together so that each first end portion
310 overlaps its corresponding second end portion 311 whereby the centralizer forms
a generally cylindrical device. In other arrangements, the length of the free end
portions is greater, and in these arrangements the free end portions are subsequently
formed into connecting devices.
[0058] The web portions 302, 303 form the collars 51, 52 of figures 4 and 5. The longitudinal
web portions 304 form the spring bows of figures 4 and 5, of which four are shown
as spring bows 53, 54, 55, and 56. Bending operations are performed on the spring
bows to achieve the configuration of Figures 4 and 5.
[0059] The web portions 302 and 303 have a series of parallel cuts 305 that cut all the
way through the blank. Web portions 302 and 303 each have six sets of two parallel
cuts 305 that are centrally aligned with the longitudinal web portions 304 and are
parallel to the web portions 304. The series of parallel cuts 305 in the web portion
302 enable the blank material between the cuts 305 to be formed into protrusions 60,
70 in the first and second end collars 51, 52. The material between the series of
cuts 305 is bent to form protrusions 60 and 70, in the form of convex bows that sit
proud of the surface of the blank. The protrusions 60, 70, in the form of bows are
aligned in the same direction as the spring bows. The protrusions 60, 70 have a longitudinal
axis that is parallel to the longitudinal axis of the centralizer. The protrusions
60, 70 are uniformly distributed about the perimeter of the first and second end collars
51, 52. In other arrangements, protrusions 60, 70 take a form different to that of
convex bows.
[0060] It will, of course, be understood that this is an example blank and is used here
illustratively. Boron steel is only one example of the materials that may be used,
which include mild steel and many other different materials. One class of steel- which
includes boron steel -is the class of micro-alloy steels. This class has been shown
to be generally useful.
[0061] The blank is formed by cutting or punching from the sheet. A preferred technique
is a high accuracy computer-controllable cutting method such as laser-cutting or water
jet- cutting. Such a technique can allow great flexibility, for instance enabling
'specials' to be produced without a need for expensive dedicated tooling. The blank
is then cold-formed into a generally cylindrical shape. This may be accomplished by
rolling or by other techniques known in the art.
[0062] The relatively ductile nature of the boron steel material forming the blank allows
for the blank to remain in its cylindrical state after the forming has taken place.
The boron steel, or other material used for the blank, is heat treatable to improve,
for example, shear and tensile section strength properties. Such heat-treated strength
may be of the order 90 tons per square inch.
[0063] In other arrangements, the protrusions are formed in, or attached to, the end collars
of an existing centralizer rather than being formed in a blank that is then formed
into a centralizer. In one arrangement a series of parallel cuts, similar to those
shown as 305 in figure 4, are cut into the end collars of the existing centralizer,
and the material between the cuts is bent or pressed into the required protrusion
shape, such as a convex bow. In another arrangement, protrusions are securely attached
to the end collars of the existing centralizer. The protrusions could be welded, or
through being mechanically attached to the end collars.
[0064] Figure 5 shows the standoff within the annulus between a tubular and a borehole as
a function of load, as required by specification API 10D based upon a common sized
9-5/8" (24.45cm) casing inside a 12-1/4" (31.12cm) borehole. It can be seen that the
curve extends to near flat, with a resultant increase of load.
[0065] In one embodiment, a centralizer must achieve minimum 1600 lbf (7120N) restoring
force when deflected to 67% 'standoff' of the theoretical 100% annular width. In this
instance this corresponds to a height of 0.879" above zero on the 'Y' axis. This actual
example exceeds the requirement, having a restoring force of 3250 lbf (14460N).
[0066] Figure 6 shows a standoff within the annulus between a tubular and a borehole as
a function of load, for the centralizer as shown in figures 2 and 3. In Fig.6 the
deflection/load curve exhibits an intersection or kink in the curve. This is due to
the radially disposed protrusions around the first and second end collars 51, 52.
In this example the protrusions correspond to the basic protrusion minimum height
ref. "January 2014 the Railroad Commission of Texas USA formulated amendments to their
Rule 13 governing minimum precautions". As may be seen from the point of intersect
the curve extends parallel to the 'X' axis (load), i.e. the spring has bottomed onto
the protrusions. The spring bows of the centralizer are stopped from completely flattening
or suffering deformation that stops them from springing back into shape or otherwise
functioning as intended. Additionally, by bottoming out on the protrusions, the tubular
is maintained above a minimum distance from the wall of the borehole. This means that
that interference between, for example, stop collars and the wall of the borehole
is prevented.
[0067] Figure 7 shows a standoff within the annulus between a tubular and a borehole as
a function of load, for a centralizer having protrusions with a height greater than
the height of the protrusions for the centralizer used to provide data as shown in
figure 6. For the centralizer used to provide data as shown in figure 8, a tailored
height of the protrusion has been determined by an end user. The height of the protrusion
in this example is over and above the basic protrusion height (ref. Fig. 6). In this
instance the height of the protrusions corresponds to ca 70% Standoff (0.919" (2.33cm)).
In this example the end user benefits from flexibility of a spring design until stopping
hard against the 70% required as a minimum Standoff.
[0068] Therefore, the design of the protrusions can be tailored for the specific requirements
of the centralizer.
[0069] In an alternative arrangement, shown in figure 8, the protrusions are not radially
disposed about the first and second end collars 51, 52 of a centralizer. Rather, the
protrusions are radially disposed about one or more bands 90 that are coupled to either
the first or both the first and second end collars 51, 52 of the centralizer. The
one or more bands 90 are freely rotatable about the tubular, meaning that they are
not grippingly attached to the tubular and the tubular can freely rotate within the
bands 90. The band 90 is made in a similar manner to the centralizer as discussed
with reference to figure 4. Band 90 is made from a blank, with cuts formed in the
blank that are bent or pressed into protrusions 95.
[0070] Using bands with protrusions means that an existing centralizer can be retrofitted
by attachment of bands with protrusions to the first and second end collars of a centralizer.
The existing centralizer may need to be modified to enable the bands with protrusions
to be connected to it, but the work required can be less than that associated with
making new centralizers with protrusions on the end collars.
[0071] In some arrangements, the bands may be connected to the centralizer. For example,
in certain arrangements the bands may be connected to the centralizer through T shaped
projections and apertures in the bands and apertures respectively. In other arrangements
the bands are connected to the centralizer through a bayonet fastener.
[0072] In other arrangements, the bands are located on a tubular and do not mechanically
interlock to a centralizer, but are arranged to butt up against a centralizer as the
tubular is inserted down a borehole. In this arrangement, the bands are arranged to
be free floating between an end of the centralizer and a contacting edge of a stop
collar. In other arrangements, the bands are located on a tubular, and are arranged
to ensure that stop collars do not mechanically interfere with the wall of the borehole
without being required to cooperate with a centralizer.
[0073] Alternative arrangements to those described with reference to the figures are now
briefly discussed.
[0074] In other arrangements the centralizer has more than or less than six spring bows.
[0075] In other arrangements the centralizer has more than or less than six protrusions
around the circumference of the first and second end collars. In some arrangements,
the number of protrusions on the first end collar is different to the number of protrusions
on the second end collar. In some arrangements, there are only protrusions on the
first end collar. In some arrangements the protrusions are not uniformly distributed
about the perimeter of the first and/or second end collars.
[0076] In some arrangements there is only one protrusion. For example, in one arrangement
a protrusion may completely encircle an end collar. In another arrangement the single
protrusion doesn't fully encircle the end collar, but has a gap such that the protrusion
forms a horseshoe shape. In yet another arrangement the single protrusion is arranged
helically around the end collar. In arrangements such as the horseshoe and helical
arrangements, the protrusion has a shape arranged to allow for fluid flow within the
annulus between the tubular and the borehole or existing tubular. Furthermore, in
other arrangements there may not be a protrusion, as such. Instead, the end collar
may be raised relative to the bows, or the bows may join the end collar at a point
that is not the maximum radial distance of the end collar from the axis of the centralizer.
In other words the whole of end collar is a protrusion. In such an arrangement, the
end collar prevents flattening of the spring bows without the need for a specific
protrusion.
[0077] In some arrangements, the protrusions are not aligned with the spring bows of the
centralizer.
[0078] In some arrangements, cuts 305 are not parallel. In some arrangements, cuts 305 are
not centrally aligned with web portions 304. In some arrangements, cuts 305 are not
parallel to web portions 304. In some arrangements, the protrusions are formed from
the blank, without the need for cuts 305 in the blank, for example through appropriate
pressing or bending of the blank.
[0079] In other arrangements, the protrusions are attached to the first and/or second end
collars rather than being pressed or punched or bent from the blank.
[0080] In some arrangements, the protrusions have a longitudinal axis that is angled to
the longitudinal axis of the centralizer. This has the benefit that this creates a
shear angle to further aid passage of the centralizer through bore local deformities
or obstructions. In one arrangement, substantially all of the protrusions are angled
similarly.
[0081] In some arrangements, a protrusion has a longitudinal axis that is angled to the
longitudinal axis of the centralizer and is angled to the longitudinal axis of another
protrusion.
[0082] In some arrangements, the protrusions are shaped or angled or angled and shaped in
order to direct fluids into a turbulent flow within the annulus between tubular and
the borehole or existing tubular. This angling and/or shaping of the protrusions is
now further explained. Ideal fluid flow through the annulus between the tubular and
borehole or existing tubular is laminar, i.e. uniform, parallel to the axis. The protrusions
may be angled and/or shaped to deflect the laminar flow, creating turbulent flow beyond
the protrusion in the direction of fluid flow. This has a particular advantage in
terms of unwanted contaminants such detritus, which is particulate matter/debris.
Wells contain various fluids, e.g. 'Drilling Mud', to balance pressure differentials.
Cement flowing into the annulus, from the bottom back towards the surface, is required
to displace these fluids. However, where the tubular is offset in the annulus there
will be fluid/cement contaminated pockets, for example at the position where the tubular
is close to the wall of the borehole and the annulus has a minimum size. Furthermore,
there will be preferential flow at the opposite side of the tubular, where the annulus
has a maximum size. Where the annulus is a minimum, detritus, debris or fluids can
accumulate or build up. The angled and/or shaped protrusions direct the flow into
a turbulent flow and this assists in the removal of unwanted debris or fluids.
[0083] Angling and/or shaping of the protrusions can have the benefit that it enables the
passage of material such as fluids, cement slurries in the annular space around the
tubular between the tubular and the borehole or existing tubular. The presence of
the protrusions, which have an effect of halting or stopping flattening of spring
bows, means that there remains a minimum annular gap between the tubular and bore
hole or existing tubular. There then remains a minimum cement sheath thickness, allowing
for the required flow of cement in the annulus between the tubular and bore hole or
existing tubular.
[0084] In some arrangements, angling and/or shaping of the protrusions aids the suspension
and removal of detritus within the annulus. The skilled person will appreciate how
protrusions can be shaped or angled or shaped and angled in order to change the flow
as described above.
[0085] In some arrangements, the protrusions are symmetrical. For example, they are substantially
semi-spherical or hemispherical in shape and are either attached or pressed from the
blank. In some arrangements, the protrusions are symmetrical, but shaped other than
semi-spheres or hemispheres.
[0086] In another arrangement, the centralizer is not made from a single blank. In some
arrangements, protrusions are attached to the band.
[0087] In some arrangements, the first end collar is symmetrical about its axis, for example
the first end collar may have a cylindrical shape. In some arrangements, the second
end collar is symmetrical about its axis, for example has a cylindrical shape. In
some arrangements, the band is symmetrical about its axis, for example has a cylindrical
shape.
[0088] In some arrangements, the first end collar is asymmetrical about its axis, for example
has a non-cylindrical shape. In some arrangements, the second end collar is asymmetrical
about its axis, for example has a non-cylindrical shape. In some arrangements, the
band is asymmetrical about its axis, for example has a non-cylindrical shape. In some
arrangements the first end collar, second end collar, and or band has a cross section
other than circular. For example, the surfaces of the first end collar, second end
collar and/or band arranged to face the tubular have a polygonal cross section that
is either regular or irregular. It will be appreciated that the irregular shape of
the end collar and/or band may in itself perform the functionality of the protrusions
if the irregular shape provides a portion that protrudes such that flattening of the
spring bows is prevented. It will also be appreciated that while reference has been
made to a 'band', since the shape may be irregular it may not have a band-like shape.
As such, the band can more generally be referred to as a device. Furthermore, in some
arrangements the band or device may be the end stop.
[0089] As described above, centralizers are provided or centralizers can be modified or
bands are provided that can be connected to centralizers, or bands are provided that
operate without be required to cooperate with centralizers. These arrangements negate,
when under extreme lateral forces encountered running the centralizer string into
the well, the flattening of the centralizer with potential permanent set of bow spring
height and damage to the well bores. These arrangements provide for ease of insertion
of the centralizer string into the well. These arrangements provide for ease of insertion
of the tubular into the well. These arrangements provide for modification of the flow
of fluid past the centralizer, and/or band, and may direct that flow into a turbulent
flow. These arrangements provide for modification of the flow that aids the suspension
and removal of detritus.
[0090] Features of the arrangements described and shown in the Figures can be combined in
any combination, as would be understood by the skilled reader as being practicable.
The scope of the present disclosure is not intended to be limited to any particular
described arrangement but instead is defined by the attached claims.
1. A centralizer having a longitudinal axis, the centralizer comprising:
first and second opposing end collars positioned around the axis of the centralizer;
and
a plurality of spring bows extending from the first end collar via a generally convex
curved portion to the second end collar;
wherein a radial distance from an outwardly facing portion of the first end collar
to the axis is:
greater than a radial distance from a first outwardly facing portion of a spring bow
of the plurality of spring bows, at a longitudinal axial position where the spring
bow extends from the first end collar, to the axis, and
less than a radial distance from a second outwardly facing portion of the spring bow,
at a longitudinal axial position between the first end collar and the second end collar
that is farthest from the axis, to the axis.
2. A centralizer according to claim 1, wherein the radial distance from the outwardly
facing portion of the first end collar to the axis is greater than the radial distance
from a third outwardly facing portion of the spring bow, at a longitudinal axial position
where the spring bow extends from the second end collar, to the axis.
3. A centralizer according to claim 1 or 2, wherein the outwardly facing portion of the
first end collar comprises at least a portion of a protrusion.
4. A centralizer according to claim 3, wherein the protrusion is formed from the first
end collar.
5. A centralizer according to claim 3 or 4, wherein the protrusion is in the form of
a bow.
6. A centralizer according to any one of claims 3 to 5, wherein the protrusion is formed
through a process or processes involving one or more of a pressing process, a bending
process, and a cutting process.
7. A centralizer according to any one of claims 3 to 6, wherein the protrusion has a
length and a width less than the length, wherein the length is angled to the longitudinal
axis of the centralizer.
8. A centralizer according to any of claims 3 to 7, wherein the protrusion is a first
protrusion of a plurality of protrusions.
9. A centralizer according to claim 8, wherein the plurality of protrusions are uniformly
distributed about a perimeter of the first end collar.
10. A centralizer according to any preceding claim, wherein the outwardly facing portion
of the first end collar has a shape configured to direct fluid flow into a turbulent
flow.
11. A centralizer according to any preceding claim, wherein the centralizer is made from
a single piece material.
12. A device having a longitudinal axis, the device configured to cooperate with a centralizer
having a longitudinal axis, the centralizer comprising first and second opposing end
collars positioned around the axis of the centralizer, and a plurality of spring bows
extending from the first end collar via a generally convex curved portion to the second
end collar, the device comprising:
an outwardly facing portion, wherein when the axis of the device and the axis of the
centralizer are substantially aligned co-axially a radial distance from the outwardly
facing portion of the device to the axis is:
greater than a radial distance from a first outwardly facing portion of a spring bow
of the plurality of spring bows, at a longitudinal axial position where the spring
bow extends from the first end collar, to the axis, and
less than a radial distance from a second outwardly facing portion of the spring bow,
at a longitudinal axial position between the first end collar and the second end collar,
to the axis.
13. A device according to claim 12, wherein the radial distance from the outwardly facing
portion of the device to the axis is greater than the radial distance from a third
outwardly facing portion of the spring bow, at a longitudinal axial position where
the spring bow extends from the second end collar, to the axis.
14. A device according to claim 12 or 13, wherein the outwardly facing surface of the
device comprises at least a portion of a protrusion.
15. A system comprising a device according to any one of claims 12 to 14, and a centralizer
having a longitudinal axis, the centralizer comprising first and second opposing end
collars positioned around the axis of the centralizer, and a plurality of spring bows
extending from the first end collar via a generally convex curved portion to the second
end collar.