WO2009152223A1

WO2009152223A1 - Modular low-clearance centralizer and method of making modular low-clearance centralizer

Info

Publication number: WO2009152223A1
Application number: PCT/US2009/046868
Authority: WO
Inventors: Jean Buytaert
Original assignee: Frank's International, Inc.
Priority date: 2008-06-11
Filing date: 2009-06-10
Publication date: 2009-12-17
Also published as: EP2294277A1; BRPI0915163A2; CA2727785A1; US20090308615A1

Abstract

A low-clearance bow spring centralizer (10) can be made by providing a plurality of bow spring modules (54), each having an elongate rib (52) with a first integrally- formed collar segment (54) at a first end and a second integrally-formed collar segment (56) at a second end wherein the first collar segment (54) and the second collar segment (56) are joined to adjacent first and second collar segments, respectively. The bow spring modules may be interlinked by welding a seam (55) formed between abutting sides of adjacent pairs of first collar segments and/or second collar segments. The sides (54a) of the first collar segment and the sides (56a) of the second collar segment may each be perpendicular to the axis of the centralizer bore, and seams (55) therebetween may be welded to form a first centralizer collar and a second centralizer collar, coupled one to the other by the ribs (52).

Description

MODULAR LOW-CLEARANCE CENTRALIZER AND METHOD OF MAKING MODULAR LOW-CLEARANCE CENTRALIZER

BACKGROUND OF THE INVENTION Field of the Invention

[0001] This invention is directed to a low-clearance centralizer to center a tubular within a borehole, and to a low-cost method of making a modular low-clearance centralizer that can radially collapse to pass through a restriction, and that can deploy to generally center a tubular within a drilled borehole.

Description of the Related Art

[0002] Centralizers can be secured at spaced intervals along a tubular string to provide radial stand-off between the tubular and the wall of a drilled borehole in which the tubular is installed. Bow spring centralizers generally comprise a pair of aligned collars defining a bore therethrough to receive the tubular, and a plurality of angularly-spaced bow springs biased to provide stand-off. Bow spring centralizers may collapse to pass, e.g., along with the tubular, through restrictions, and to deploy to provide a generally uniform annulus between the exterior of the tubular and the wall of the borehole. A centered tubular string promotes uniform and continuous distribution of cement slurry around the tubular string for cementing the tubular within a targeted interval of the borehole. The resulting cement liner can reinforce the tubular string, isolates the tubular from corrosive formation fluids and prevents fluid flow between penetrated geologic formations. [0003] Bow spring centralizers typically include a pair of axially-spaced and aligned collars coupled one to the other by a plurality of angularly distributed bow springs. Some bow springs centralizers are longitudinally secured along the axis of the tubular using stop collars to block the centralizers from sliding. Stop collars can add substantially to the positive outer diameter (O. D.) of the tubular and can limit passage through a given restriction.

[0004] The collar's radial thickness added to the exterior of a tubular is also an important consideration. Low-clearance centralizers have radially thin collars and bow springs that may collapse and lie flat along the length of a tubular between the collars. Fasteners (e.g., rivet, bolt, etc.) to couple the bow spring to the collars can also add substantially to the positive O. D.. A low-clearance centralizer may be cut from a unitary piece of tubular pipe to minimize the contribution to the positive O. D. This method avoids the need for fasteners to couple the bow springs to the collars and may minimize the positive O. D. of the centralizer. One method of forming low-clearance centralizers from a unitary piece of tubular pipe comprises the steps of cutting elongate coupons from the interior of a tubular to form a cylindrical cage, and bending the ribs of the cage radially outward to form a plurality of angularly-spaced bow springs, for example, but not limited to, a centralizer as described in U.S. Patent Application Serial Number 11/749,544 filed on May 16, 2007 and assigned to the owner of the present application. For example, the elongate coupons may be cut from the pipe using a water-jet or laser. The method may comprise an additional step of heating and quenching the bow spring centralizer to impart resiliency to the bow springs to enable the bow springs to collapse and re-deploy to provide stand-off. [0005] The cost of manufacturing a centralizer is another important consideration. Dozens or even hundreds of centralizers may be installed in a single borehole. Low- clearance bow spring centralizers cut from a unitary piece of tubular may be expensive to make. Special tools may be needed to cut the coupons from the tubular, the tubular to form a cylindrical cage, and special tools may be needed to simultaneously bend the ribs to form bow springs. These special tools can add substantially to the manufacturing cost of the centralizer.

[0006] An alternative method of forming a low-clearance centralizer comprises the steps of forming two cylindrical sleeves and cutting a plurality of notches in each sleeve, each notch to receive the end of a pre-formed bow spring. The end of a bow spring may then be welded to the sleeve along the three-sided perimeter of each notch. A grinder may be used to dress the resulting weld path defining each bow spring/collar connection to reduce the diameter, and the resulting centralizer may be heated and quenched to impart resiliency to the welded connections. The alternative method described is time consuming and may require post-fabrication heat treating and/or quenching to alleviate the heat-affected zones.

[0007] The intended application of the centralizer is an important factor to be considered in designing the centralizer. Depending on the application, an operator may need a bow spring with either few or many bow springs. For example, a thick-walled and/or large diameter tubular to be disposed in a substantially horizontal portion of a borehole may need a greater angular concentration of bow springs to provide the support for adequate stand-off. Conversely, a relatively low-weight tubular to be installed in a substantially vertical section of a borehole may require fewer bow springs to adequately center the tubular.

[0008] What is needed is a method of making a low-clearance bow spring centralizer that reduces the cost of manufacture while retaining the benefits of a close-tolerance bow springs centralizer. What is needed is a method to make a low-clearance bow spring centralizer that does not require special manufacturing tools that may be expensive to purchase and/or operate. What is needed is a bow spring centralizer that is easily customizable for the intended application. What is needed is a low-clearance bow spring centralizer that performs as well as a centralizer cut from a unitary piece of tubular, but is less expensive and easier to make. What is need is a method of making a low-clearance centralizer that maximizes production capacity for a given heating and/or quenching facility.

SUMMARY OF THE PRESENT INVENTION

[0009] An embodiment of the present invention satisfies one or more of the above- stated needs. An embodiment of the invention provides an efficient and inexpensive method to make a low-clearance modular bow spring centralizer to center a tubular within a drilled borehole. A centralizer may be made at a lower cost according to an embodiment of the present invention, and may perform as well as a more expensive centralizer that is made from a unitary piece of tubular material. An embodiment of the invention provides a bow spring module that may be used to make a low-clearance centralizer. [0010] In one embodiment, the method may include the steps of providing a plurality of bow spring modules and interlinking the plurality of bow spring modules together to form a bow spring centralizer with low-clearance centralizer collars. Each of the bow spring modules may comprise an elongate rib having an integrally-formed first collar segment at a first end and an integrally-formed second collar segment at a second end. Each bow spring module may be made by cutting and forming the bow spring module from a plate of suitable material such as, for example, low-carbon steel. More specifically, each bow spring module may be cut and formed using a displaceable male die and a corresponding stationary female die cavity into which the male die may be forcibly inserted using, for example, a hydraulic press. A plate of material, such as, for example, low-carbon steel, may be disposed intermediate the male die and the female die cavity prior to displacement of the male die into the female die cavity to cut and form a bow spring module. The process may be repeated using additional plates. [0011] It should be appreciated by those skilled in the art that the process of forming bow spring modules in this manner may be automated. It should be understood by those skilled in the art that the bow spring module produced in this manner may be shaped according to the corresponding shape of the male die and the female die cavity, and that a large number of generally identical bow spring modules may be inexpensively and/or rapidly produced.

[0012] It should be further understood that bow spring modules produced in this manner may be efficiently stacked and/or handled, and that the residual material stresses resulting from the cold working of a metal, e.g., low-carbon steel, plate material may be removed by heating the bow spring module for a period of time, and then by quenching the bow spring module, e.g., by immersion in water, to impart desired metallurgical resiliency to the metal, e.g., low-carbon steel material.

[0013] In one embodiment, the method of making a low-clearance centralizer may comprise the steps of providing a plurality of bow spring modules, each of the bow springs modules having an elongate rib integrally formed with an arcuate first collar segment at a first end of the rib and an arcuate second collar segment at a second end of the rib, interlinking the plurality of first collar segments to form a first centralizer collar, and interlinking the plurality of second collar segments to form a second centralizer collar. The resulting bow spring centralizer may comprise the first centralizer collar spaced apart from and coupled to the second centralizer collar by and through the generally angularly distributed plurality of ribs.

[0014] In an alternate embodiment, the method comprises the steps of providing a plurality of bow spring modules, each bow spring module having an elongate rib with an integrally formed first collar segment at a first end of the rib and an integrally formed second collar segment at a second end of the rib, imparting a desired arcuate shape to the first collar segment using, for example, a forming block, imparting the desired arcuate shape to the second collar segment, interlinking the plurality of first collar segments to form a first centralizer collar having a bore of a diameter corresponding to the arcuate shape imparted to the collar segments, and interlinking the plurality of second collar segments to form a second centralizer collar of the same bore. It should be understood that this method may be used to modify bow spring modules that have a first collar segment and a second collar segment, each having an original radius of curvature, so that the first and second collar segments will have a larger or a smaller radius of curvature, and interlinking the modified bow spring modules may result in a low-clearance bow spring centralizer for being received on a larger or smaller diameter tubular. It should be understood that the use of, for example, a forming block to modify the curvature of the first collar segment and second collar segment of a set of bow spring modules may change the number of bow spring modules that are interlinked to form a bow spring centralizer in accordance with the disclosed method. For example, but not by way of limitation, a bow spring module may, in one embodiment, comprise a first collar segment and a second collar segment coupled one to the other by an elongate rib, and the first and second collar segments may each comprise a radius of curvature of 9 inches, and each may comprise an angular span of 60 degrees so that a set of six of these bow spring modules may be interlinked in accordance with the disclosed method to form a bow spring centralizer with a first collar having a diameter of 18 inches and a second collar having a corresponding diameter, the second collar coupled to the first collar through the six elongate ribs. If a bow spring centralizer having a diameter of 24 inches is needed, the bow spring modules may be modified using, for example, a forming block to change the shape and the radius of curvature of the first collar segment and the second collar segment of each bow spring module prior to interlinking the bow spring modules to form the bow spring centralizer. For example, but not by way of limitation, if a bow spring module with a first collar segment and a second collar segment, each having a radius of curvature of 9 inches and an angular span of 60 degrees, is modified using a forming block so that the radius of curvature of the first and second collar segments is expanded to 11-5/8 inches, the angular span of the modified first collar segment and second collar segment might be decreased to only about 36 degrees, and the number of the modified bow spring modules that will be interlinked to form a bow spring centralizer would be increased to 10. It should be understood that, where the "take-out" or the arc-length of the first and the second collar segments of a set of bow spring modules that have been modified using, for example, a forming block, does not provide the a desired diameter when interlinked with an integral number of similar or identical modified bow spring modules, one or more spacers may be coupled between two or more adjacent bow spring modules to provide

[0015] In an alternate embodiment, an apparatus may comprises a bow spring module comprising an elongate rib, a first collar segment at a first end of the rib and a second collar segment at a second end of the rib, each of the first and second collar segments having sides disposed generally laterally to the center of the collar segment aligned with the rib. In one embodiment, the apparatus may comprise beveled edges along the sides of the first collar segment and the second collar segment. The beveled edges may facilitate welding of a plurality of the first collar segments together to form a first centralizer collar and welding a plurality of second collar segments to form a second centralizer collar, each having a generally circular cross-section. In one embodiment, the beveled edges on the sides of the first and second collar segments may be formed during the steps of forming the first and second collar segments.

[0016] In one embodiment, a male die and the female die cavity may be machined and formed to simultaneously cut a bow spring module comprising an elongate rib, an integrally-formed first collar segment at a first end of the rib and an integrally-formed second collar segment at a second end of the rib, from the metal plate, and also to impart a desired curvature and/or contour to each of the first integrally- formed collar segment, the second integrally- formed collar segment and the rib of the bow spring module, all as the male die enters and then seats within the female die cavity. Forming of these components of the bow spring module may include imparting a desired curve or contour to the rib between the first collar segment and the second collar segment, and/or imparting a curvature of a uniform radius, in a direction generally transverse to the plane of the arc of the rib, to both the first collar segment and the second collar segment. A generally corresponding curvature may be imparted to each of the first collar segment and the second collar segment, and the imparted curvature may correspond to a desired diameter for the first and second centralizer collars to be formed by coupling the bow spring modules. For example, but not by way of limitation, the male die and the corresponding female die cavity may be formed so that the bow spring modules are formed, upon being cut from a metal plate, to comprise an elongate rib with a first end and a second end, a first integrally- formed collar segment with a radius of curvature of 9 inches at the first end, and a second integrally-formed collar segment with the same radius of curvature at the second end. The first collar segment and the second collar segment may each comprise an arc having an angular span of 60 degrees so that, when six substantially identical bow spring modules are joined together by coupling the sides of the first collar segments to form a first centralizer collar, and by coupling the sides of the second collar segments to form a second centralizer collar, the first and the second centralizer collars will each have a diameter of 18 inches, and the first and the second centralizer collars will be coupled one to the other by the six ribs (for bow spring modules having a single rib). It should be noted that a bow spring centralizer formed using one embodiment of this method may further comprise six generally longitudinal straight welds in the first centralizer collar, and an additional six generally longitudinal straight welds in the second centralizer collar, and the welds will be strategically disposed within portions of the first and second centralizer collars that will bear relatively little stress during installation of the tubular within a well. More specifically, the welds will not be at or adjacent to the critical connections between the first or second ends of the ribs and the first or second collar segments, respectively, which are integrally-formed and remain unaffected by welding. It should also be noted that the rib portion of the bow spring module may comprise a simple curve that may have a generally constant or a variable radius of curvature along the span of the rib. Alternately, the rib portion of the bow spring module may comprise a more complex contour that may have two or more sub-portions, and each sub-portion may comprise a curve that may have a generally constant or a variable radius of curvature along the span of the rib. A bow spring module rib having either of these rib structures, or yet another rib structure, may be included within a bow spring module.

[0017] As a further example, the die and the die cavity may be machined to impart a desired contour to the rib of the bow spring module. It should be noted that a rib of a bow spring may comprise a shape other than an arc, and may comprise a contour that includes a complex shape or a combination of arcs. For example, but not by way of limitation, the rib of each bow spring module made using the die and the die cavity may be generally curved along a center portion that is intermediate the first and second ends of the rib, generally straight along at least a portion of the rib intermediate the first end and the center portion, generally straight along at least a portion of the rib intermediate the second end and the center portion, and again curved, in a direction opposite the direction of curvature of the center portion, at a portion of the rib adjacent to the first end, and also curved, again in a direction opposite the direction of curvature of the center portion, at a portion of the rib adjacent to the second end. This contour may be used to provide smooth transitions along each rib of a bow spring centralizer in order to eliminate stress concentrations and to prevent excessive pressure from being applied to the tubular on which the centralizer is received. It should be understood that the curved portions of the rib may not conform to a constant radius of curvature but may instead comprise transition portions intermediate the center portion and the adjacent portions that are curved in the opposite direction. Specifically, each rib may terminate at the first end and also at the second end in a generally flattened end portion that is adjacent to the connection between the rib / collar segment. This contour prevents undue fatigue and stress concentration at the rib / collar segment connections, and generally distributes the flexure of the rib over the three curved portions of the rib. It should be understood that the contour of the rib of a centralizer may be made according to certain performance parameters such as, but not limited to, the desired stand-off and restoring force. It should be understood that the male die cavity and the female die may be machined to impart other features to each bow spring module. For example, but not by way of limitation, the bow spring module may, in addition to the curvature and the contour described above, be formed with a crease, e.g., a longitudinal crease, in at least a portion of the rib to impart additional structural rigidity and/or to increase the restoring force of the bow spring rib. [0018] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. However, that the appended drawings illustrate some embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Fig. IA is a perspective view of a female die cavity that may be used to produce a bow spring module according to one embodiment of the method.

[0020] Fig. IB is a perspective view of a male die that may be used, along with the female die cavity of Fig. IA, to produce a bow spring module according to one embodiment of the method.

[0021] Fig. 2 is a perspective view of the male die of Fig. IB arranged for the protruding portions to be disposed against and through a metal plate and into the female die cavity of Fig. IA to produce an embodiment of a bow spring module.

[0022] Fig. 3 is an elevation view of one embodiment of a bow spring module that may be produced using the die, die cavity and metal plate of Fig. 2.

[0023] Fig. 4 is a perspective view of the bow spring module of Fig. 3 showing the curved elongate rib, a curved first collar segment at a first end of the rib, and a curved second collar segment at a second end of the rib.

[0024] Fig. 5 is an elevation view of one embodiment of a clamp/mandrel supporting two bow spring modules, each like the one shown in Figs. 3 and 4, one adjacent to the other, and in position to be joined along two seams: a first seam between the two adjacent first collar segments, and a second, aligned seam between two adjacent second collar segments. [0025] Fig. 6 is one embodiment of a modular bow spring centralizer that may be formed by coupling three additional bow spring modules to the two bow spring modules shown in Fig. 5. Specifically, the embodiment of the modular bow spring centralizer of Fig. 6 may be formed by coupling the first collar segments of a plurality of bow springs modules to form a first centralizer collar, and by coupling the second collar segments of the plurality of bow spring modules to form a second centralizer collar. [0026] Fig. 7 is a schematic showing the complex weld pathway that may be used to couple the end of a conventional rib to a conventionally notched low-clearance centralizer collar.

[0027] Fig. 8 is a schematic showing the simple weld pathway that may be used to couple two first collar segments of a pair of adjacent bow spring modules according to one embodiment of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0028] Fig. IA is a perspective view of a female die cavity 22 that may be used to produce one embodiment of a bow spring module according to one embodiment of the invention. The die cavity of Fig. IA comprises a first collar segment recess 22a, a second collar segment recess 22b, and a rib recess 22c connecting the first collar segment recess 22a to the second collar segment recess 22b. It should be understood that the first collar segment recess 22a and the second collar segment recess 22b may be generally identical, and each may comprise a uniformly curved bottom having a generally uniform radius of curvature, and the bottom may be recessed and/or surrounded by a generally vertical wall.

[0029] Fig. IB is a perspective view of a male die 24 that may be used with the female die cavity of Fig. IA to produce an embodiment of a bow spring module according to one embodiment of the invention. The male die 24 comprises a first collar segment protrusion 24a, a second collar segment protrusion 24b and a rib protrusion 24c connecting the first collar segment protrusion 24a and the second collar segment protrusion 24b. The first protrusion 24a, second protrusion 24b and the rib protrusion 24c of the male die 24 may each generally correspond in shape, size and contour to the first collar segment recess 22a, the second collar segment recess 22b and rib recess 22c, respectively. It should be understood that the male die 24 may be receivable into and removable from the mating female die cavity using a press (not shown), e.g., a hydraulic press. It should be further understood that the first collar segment recess 22a, the second collar segment recess 22b and rib recess 22c may be surrounded by a generally vertical base portion that generally matches and is receivable within the vertical wall recess portion of the female die cavity of Fig. IA. For example, but not by way of limitation, the width 23 of the first and second collar segment recesses 22a and 22b of Fig. IA may be only slightly greater than the width 25 of the corresponding first collar segment protrusion 24a and second collar segment protrusion 24b. It should be understood by those skilled in the art that these components cooperate to shear a bow spring module blank from the metal plate 50 shown in Fig. 2 during the process of disposing the male die 24 into and against the female die cavity 22 upon or prior to final seating of the male die with the female die cavity. [0030] The protrusions 24a, 24b and 24c of the male die cavity may each comprise a curved shape and/or contoured shape that generally matches the corresponding recesses 22a, 22b and 22c of the female die cavity, respectively. The contoured shape may, in one embodiment, impart a generally desired bow or curve to the rib of a bow spring module produced by disposing the metal plate 50 intermediate the male die and the female die cavity. Similarly, the curved and/or contoured shapes may impart a generally desired radius to the first collar segment and the second collar segment.

[0031] It should be understood that, in an alternate embodiment, a bow spring module may be produced using an equivalent two-step or a three-step method. For example, in an alternate embodiment of the method, the male die may be flat along its protruding faces, and the female die cavity may also be flat along the corresponding receiving faces to cut a flat bow spring module blank from a metal plate disposed intermediate the male die and the female die cavity. A bow spring module blank produced in this manner may be flat like the metal plate from which it is cut. The resulting flat bow spring module blank may then be formed into a bow spring module using, for example, forming blocks and a press, rollers or other devices used to impart a desired contour or curve to the rib of the bow spring module, and a desired radius of curvature to the first and second collar segments at the first end and the second end of the rib.

[0032] Fig. 2 is a perspective view of the male die 24 (of Fig. IB) positioned to be disposed, in the direction of arrow 21 through a generally flat metal plate and at least partially into the female die cavity 22 (of Fig. IA) to produce an embodiment of a bow spring module. The first collar segment protrusion 24a is aligned with the corresponding first collar segment recess 22a, the second collar segment protrusion 24b is aligned with the corresponding second collar segment recess 22b, and the rib protrusion 24c is aligned with the corresponding rib recess 22c. The metal plate 50 disposed intermediate the male die 24 and the female die cavity 22 may, for example, a flat plate of ASTM D 4310 metal, and may be, for example, 0.125 - 0.20 inches thick. It should, however, be understood that materials other than ASTM D 4310 and thicknesses outside the range of 0.125 - 0.20 inches may be used to achieve the benefits provided by the invention. [0033] Fig. 3 is an elevation view of an embodiment of a bow spring module 51 that may be produced using the die 22, die cavity 24 and the metal plate 50 of Fig. 2. The bow spring module 51 of Fig. 3 comprises a rib 52, a first collar segment 54 coupled to the first end 52a of the rib 52, and a second collar segment 56 coupled to the second end 52b of the rib 52. The contour or curve of the rib 52, and curvature of the first collar segment 54 and the second collar segment 56, are visible in the perspective view of Fig. 4.

[0034] Fig. 4 is a perspective view of the bow spring module 51 of Fig. 3 comprising the contoured or curved rib 52, the curved first collar segment 54 at the first end of the rib 52, and the curved second collar segment 56 at the second end of the rib 52. It should be understood that the bow spring module shown in Figs. 3 and 4 may be produced using either of the embodiments of the method described above, e.g., using a single-step or a dual-step method, or in other embodiments known to those skilled in the art without departure from the spirit and scope of the invention.

[0035] The bow spring module of Fig. 4 comprises a first collar segment 54 disposed at the first end of the rib 52 and a second collar segment 56 at the second end of the rib 52. It should be understood that the first collar segment 54 and the second collar segment 56 are depicted with a generally uniform and common radius of curvature as shown by arrows 59. The first collar segment 54 and the second collar segment 56 shown in Figs. 3 and 4 each comprise sides 54a and 56a, respectively, that are generally lateral to the rib and collar segment connection. The sides 54a and 56a may be, in one embodiment, generally parallel and perpendicular to the plane of the ends 54c and 56c lie. Each of the first collar segment 54 and the second collar segment 56 may be generally formed as a curved plate, and as an angular portion of a cylindrical sleeve. When the correct plurality of the bow spring modules are coupled, such as by welding, along the sides 54a of a first collar segment 54 of a first bow spring module 51 to abutting sides 54a of first collar segments 54 of two adjacent bow spring modules 51, the coupled first collar segments 54 together will form a first centralizer collar having a bore therethrough to encircle a tubular received therethrough, as is shown in Fig. 6. It should be understood that the sides 56a of the second collar segment 56 may be, in one embodiment, generally aligned with the sides 54a of the first collar segment 54, and that positioning two adjacent bow spring modules 51, one adjacent the other, to abut a side 54a of one with a side 54a of the other to form a longer, but circumferentially continuous arc, would also therefore position a side 56a of the second collar segment 56a of the one bow spring module 51 to simultaneously abut with a side 56a of the other bow spring module 51. It should be further understood that joining the abutting sides, such as by welding, would fix the two adjacent bow spring modules 51 in position one relative to the other, and additional bow spring modules 51 may then be joined in a similar fashion until a complete bow spring centralizer, for example, is made. [0036] Fig. 5 is an elevation view of an embodiment of a clamp/mandrel 60 that may be used to secure adjacent bow spring modules 51, one adjacent to the other, and positioned to be interlinked along the two aligned and separated seams, the first seam intermediate adjacent first collar segments 54 and the other seam intermediate adjacent second collar segments 56. The clamp/mandrel 60 of Fig. 5 comprises a generally upright base 6OB having an interior bore to receive therein a generally concentric portion 68 of a cap 6OA. The base 6OB may further comprise a plurality of radially protruding circumferential ridges 65 separated by a plurality of gaps 66 intermediate the ridges 65. The clamp/mandrel 60 may further comprise a plurality of upper clamp brackets 61a, each supporting a clamp 63, and the clamp/mandrel 60 may further comprise a plurality of lower clamp brackets 61b, each supporting a clamp 63.

[0037] In the embodiment of the clamp / mandrel 60 shown in Fig. 5, a bow spring module 51 may be positioned against the clamp / mandrel 60 so that it is supported by one of the ridges 65, and so that each upper clamp bracket 61a and related clamp 63 may be used to secure a first collar segment 54 of a bow spring module 51 to the clamp/mandrel 60, and each clamp bracket 61b and related clamp 63 may be used to secure a second collar segment 56 of a bow spring module 51 to the clamp/mandrel 60 to secure two adjacent bow spring modules 51 in position for the seam 47a formed by sides 54a of abutting first collar segments 54 and the seam 47b formed by sides 56a of abutting first collar segments 56 may be welded or otherwise joined to connect the bow spring modules 51.

[0038] It should be understood that other devices may be used to secure one or more bow spring modules 51 in position to be joined along the sides 54a of the first collar segments 54 and along the sides 56a of the second collar segments 56, and that the clamp/mandrel 60 of Fig. 5 should not be considered to be limiting of the scope of the claims below. Each claimed method may be used, and each claimed apparatus may be made, without the specific embodiment of the clamp/module 60 of Fig. 5. [0039] In one embodiment, the sides 54a and 56a of the first collar segments 54 and the second collar segments 56, respectively, are beveled so that the first seam 47a and/or the second seam 47b each comprise a channel that may be welded by filling the channel with material to fuse the work pieces and to form a welded seam, as shown as element 55 in Fig. 6.

[0040] Fig. 6 is one embodiment of a bow spring centralizer 10 that may be formed by interlinking three additional bow spring modules to the two joined bow spring modules shown in Fig. 5. Specifically, the embodiment of the modular bow spring centralizer of Fig. 6 may be formed by coupling the first collar segments 54 of a plurality of bow springs modules to form a first centralizer collar 20, and by coupling the second collar segments of the plurality of bow spring modules to form a second centralizer collar 30, so that the first collar and the second collar our coupled one to the other through a plurality of bow springs 52. The bow spring centralizer 10 formed according to this method may be formed by positioning two bow spring modules 51, one adjacent the other, as shown in Fig. 5, and by then making two generally straight-line welds 55, one at the first collar segment 54 and another at the second collar segment 56, to couple each bow spring module 51 to an adjacent bow spring module 51. The last joined bow spring module 51 in the illustrated embodiment will require a total of four straight-line welds, two aligned welds to the penultimate bow spring module 51 and two aligned welds to one of the original pair of bow spring modules 51 joined one to the other as shown in Fig. 5. It should be understood that a clamp / mandrel 60 like the one shown in Fig. 5 could be used to secure and position all of the bow spring modules 51 utilized to form a bow spring centralizer 10, and then to weld all of the bow spring modules together to form the centralizer, and that it is not necessary to begin with only a pair of bow spring modules. [0041] Fig. 7 is a schematic showing the complex weld path to couple the generally box end 58 of a conventionally-formed bow spring within a corresponding notch within a conventionally-formed low-clearance collar. The complex weld pathway shown in Fig. 7 comprises a first leg 53a, a second leg 53b, and a third leg 53c, and the three of these legs 53a, 53b and 53c are not aligned one with the others, and each is at an angle with at least one of the other two. It should be understood that the rib / collar connection 53 formed in this manner will comprise a substantial heat-affected zone and require a greater amount of time and skill to weld as compared to the welded seam 55 shown in Figs. 6 and 8. It should be further understood that stresses imparted to the rib / collar connection 53 shown in Fig. 7 as the centralizer is collapsed to pass through restrictions as the tubular on which the centralizer is received is installed in a well are more likely to compromise the connection 53 as a result of the complex geometry and the arrangement of the first leg 53a, the second leg 53b, and the third leg 53c, one relative to the others. [0042] Fig. 8 is a schematic showing the linear weld path 55 used to couple two first collar segments 54 of a pair of adjacent bow spring modules 51 according to one embodiment of the method. Each rib 52 shown in Fig. 8 is connected to the integral first collar segment 54 at an integral connection 52a, and the resulting connection 52a is superior in strength and resilience, and is unaffected by the heat-affected zone, as compared to the complex connection shown in Fig. 7. It should be understood that the first centralizer collar 20 formed in this manner and shown in Figs. 6 and 8 can be generally identical to the corresponding connection at the second centralizer collar (not shown in Fig. 8 - see Fig. 6), and that the position of the weld seam 55 is in a relatively low-stress portion of the collars 20 and 30. The weld seam 55 can be in a low-stress portion of the collars 20 and 30 because the great majority of the forces imparted to the collars 20 and 30 result from friction and interference between the bow spring centralizer 10, which is generally coupled to the pipe string to move down the bore hole with the pipe string, and the wall of the borehole as the pipe string and centralizer are installed into the borehole. These forces imparted to the bow spring centralizer 10 are generally isolated to the bow spring ribs 52 that provide stand-off between the pipe string and the wall of the borehole. The ribs 52 may flex and collapse according to the forces imparted by wall of the borehole, and these forces are transferred, to some extent, to the rib / collar connections. The weld seams 55, however, are subjected to relatively little stress because, under normal circumstances during pipe running operations, there is no expansion of the pipe string within the collars, and the portions of the collars 20 and 30 subjected to forces transferred from the ribs 52 are remote from the weld seams 55. [0043] It should be understood that a bow spring centralizer made according to the method may comprise a plurality of ribs equal in number to the plurality of bow spring modules joined to make the centralizer. It should be understood that one embodiment of a bow spring centralizer may comprise a plurality of ribs on a bow spring module. It should be further understood that, while the appended drawings illustrate a bow spring centralizer comprising bow spring modules with a bow spring / collar connection generally aligned with the center of each first collar segment and also generally aligned with the center of each second collar segment thereon, a bow spring module could comprise a first collar segment and a second collar segment, each having a bow spring / collar segment connection that is not centered in this manner. It should be understood that the first collar segment and/or the second collar segment could be offset or eccentrically connected to the first end or the second end of the rib, respectively. [0044] It should be understood that a spacer, such as, but not limited to, an extender, link, tab or tongue, may be coupled to a first collar segment or to a second collar segment, or both, of a bow spring module to modify or alter the size, reach, span or breadth of the bow spring module without deviating from the general purpose of the bow spring module or from the scope of this invention. Various modifications to the bow spring module to accommodate or to facilitate the coupling of bow spring modules or spacing of bow spring modules within the bow spring centralizer may be employed. [0045] The term "interlinking," as used in the claims and the specification herein, does not mean that each bow spring module is linked or coupled directly to each of the other bow spring modules used in a plurality to make a bow spring centralizer, but instead means that each bow spring module is linked, directly or indirectly through other bow spring modules, to the plurality of the bow spring modules used in a plurality to make a bow spring centralizer.

[0046] The terms "comprising," "including," and "having," as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The term "one" or "single" may be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as "two," may be used when a specific number of things is intended. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0047] While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

CLAIMS[0048] We claim:

1. A method of making a bow spring centralizer to center a tubular string within a borehole comprising the steps of: providing a plurality of bow spring modules having an integrally-formed and curved first collar segment at a first end of an elongate rib, and an integrally-formed and curved second collar segment at the second, opposite end of the rib; and coupling the plurality of first collar segments together to form a first centralizer collar; and coupling the plurality of second collar segments together to form a second centralizer collar.

2. The method of claim 1 further comprising the steps of: bending the first collar segment of a bow spring module to conform to a curvature of a primary forming block; and bending the second collar segment of a bow spring module to conform to the curvature of the primary forming block.

3. The method of claim 2 further comprising the steps of: bending the first collar segment of a bow spring module to conform to a curvature of a secondary forming block; and bending the second collar segment of a bow spring module to conform to the curvature of the secondary forming block.

4. The method of claim 1 further comprising the steps of: coupling a spacer to an uncoupled first collar segment of a module; and coupling a spacer to an uncoupled second collar segment of a module.

5. The method of claim 1 further comprising the step of: heat treating the weld seams of the first centralizer collar or the second centralizer collar.

6. A method of making a bow spring centralizer comprising the steps of: displacing a male die through a metal plate and into a female die cavity to form a bow spring module having an elongate rib, an integrally-formed and curved first collar segment at a first end of the rib and an integrally-formed and curved second collar segment at a second end of the rib; repeating the first step to produce a plurality of bow spring modules; welding the first collar segment to a collar segment of an adjacent bow spring module to form a first centralizer collar; and welding the second collar segment to a collar segment of the adjacent bow spring module to form a second centralizer collar that is spaced-apart from the first centralizer collar by the plurality of ribs.

7. A bow spring module to use in making a bow spring centralizer comprising: an elongate rib having an integrally-formed first collar segment at a first end and an integrally-formed second collar segment at a second end; and wherein the first collar segment comprises two spaced-apart sides and the second collar segment comprises two spaced-apart sides.

8. The bow spring module of claim 7 wherein at least one of the two-spaced apart sides of the first collar segment or at least one of the two-spaced apart sides of the second collar segment are generally parallel to the axis of a bow spring centralizer that may be made by interlinking the bow spring modules.

9. The bow spring module of claim 8 wherein one of the two-spaced apart sides of the first collar segment or one of the two-spaced apart sides of the second collar segment are beveled.

10. A method of making a bow spring centralizer comprising the steps of: providing a plurality of bow spring modules comprising an elongate rib with an integrally-formed first collar segment at a first end and an integrally-formed second collar segment at a second end, the first and second integrally-formed collar segments comprising two spaced-apart sides; and interlinking the plurality of bow spring modules.

11. The method of claim 10 wherein interlinking each first collar segment along each of the sides to an adjacent first collar segment to form a first centralizer collar includes the step of welding, and wherein joining each second collar segment along each of the sides to an adjacent second collar segment to form a second centralizer collar includes the step of welding.

12. The method of claim 11 further comprising the step of dressing the welded joints.

13. The method of claim 10 wherein the sides are generally linear.

14. The method of claim 13 wherein the sides of the first and the second collar segments are beveled so as to form a channel when placed in an abutting position along the side of an adjacent first or second collar segment.

15. A method of making a bow spring centralizer comprising the steps of: providing a plurality of bow spring modules, joining each first collar segment along each of the sides to an adjacent first collar segment to form a first centralizer collar; and joining each second collar segment along each of the sides to an adjacent second collar segment to form a second centralizer collar.

16. The method of claim 1 further comprising the step of coupling a spacer to one of the first collar segment or the second collar segment to alter the size thereof.