Patent Publication Number: US-11384605-B2

Title: Ground-down tubular for centralizer assembly and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application having Ser. No. 62/945,787, which was filed on Dec. 9, 2019, and is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Oilfield tubulars, such as pipes, drill strings, casing, tubing, etc., may be used to transport fluids or to produce water, oil, and/or gas from geologic formations through wellbores. In various stages of wellbore drilling and completion, such tubulars may be positioned within (i.e., “run-in”) the wellbore. During run-in, the oilfield tubulars may be maintained in a generally concentric position within the wellbore, such that an annulus is formed between the oilfield tubular and the wellbore (and/or another, surrounding tubular positioned in the wellbore). 
     Tools known as “centralizers” are employed to maintain this concentricity of the tubular in the wellbore. A variety of centralizers are used, including rigid centralizers, semi-rigid centralizers, and flexible, bow-spring centralizers. Bow-spring centralizers, in particular, are generally formed from two end collars and flexible ribs that extend between the collars. The ribs are expanded outward, and may be resilient, such that the bow-springs centralizers are capable of centralizing the tubular in the wellbore across a range of wellbore sizes. 
     Restrictions may exist in the wellbore in which the oilfield tubular is run. These restrictions may be areas where the inner diameter of the wellbore is reduced, which, in turn, reduce the clearance between the oilfield tubular and the wellbore. Examples of restrictions include lining hangers, the inner diameter of another, previously-run casing, and the wellhead inner diameter. When restrictions are present, bow-spring centralizers may be employed, and may be configured to collapse radially toward the oilfield tubular, allowing the centralizer to pass through the restrictions, while continuing to provide an annular standoff. 
     However, bow-spring centralizers generally have an operating envelope for clearance. When the clearance is too small, the bow-spring centralizers may be damaged when passing through the restriction, which may reduce the ability of the centralizers to provide a standoff below the restriction. Furthermore, oilfield tubulars generally include an amount of tolerance for the outer diameter (e.g., 1%), which can make determining the precise clearance size challenging. 
     SUMMARY 
     Embodiments of the disclosure provide a centralizer assembly including a tubular having a ground-down region and a raised region. A wall thickness of the tubular in the ground-down region is less than a wall thickness of the tubular in the raised region, and the wall thickness of the tubular in the ground-down region is substantially constant as proceeding around the tubular in the ground-down region. The centralizer assembly also includes a centralizer disposed at least partially in the ground-down region. 
     Embodiments of the disclosure also provide a method for positioning a centralizer to a tubular. The method includes forming a ground-down region in an outer surface of the tubular. The tubular defines a wall thickness in the ground-down region, and the wall thickness is substantially constant as proceeding around the tubular in the ground-down region. The method also includes positioning a centralizer at least partially in the ground-down region. 
     Embodiments of the disclosure further provide a centralizer assembly including a tubular having a ground-down region and a raised region. A wall thickness of the tubular in the ground-down region is less than a wall thickness of the tubular in the raised region. The wall thickness of the tubular in the ground-down region is substantially constant as proceeding around the tubular in the ground-down region. The tubular has a non-zero degree of ovality in the ground-down region, and an outer radius of the tubular varies as proceeding around the tubular. The assembly also includes centralizer disposed at least partially in the ground-down region and retained axially therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may best be understood by referring to the following description and accompanying drawings that are used to illustrate some embodiments. In the drawings: 
         FIG. 1  illustrates a side perspective view of a centralizer assembly, according to an embodiment. 
         FIG. 2  illustrates a side, cross-sectional view of a portion of a centralizer assembly, according to an embodiment. 
         FIG. 3  illustrates a side, cross-sectional view of a portion of another centralizer assembly, according to an embodiment. 
         FIG. 4A  illustrates a tubular before and after a lathing operation, according to an embodiment. 
         FIG. 4B  illustrates a tubular before and after a grinding operation, according to an embodiment. 
         FIG. 5  illustrates a flowchart of a method for grinding down a tubular and attaching a centralizer thereto, according to an embodiment. 
         FIG. 6  illustrates a schematic view of a wellsite, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure describes several embodiments for implementing different features, structures, or functions of the invention. Embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference characters (e.g., numerals) and/or letters in the various embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed in the Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the embodiments presented below may be combined in any combination of ways, e.g., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
     Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. In addition, unless otherwise provided herein, “or” statements are intended to be non-exclusive; for example, the statement “A or B” should be considered to mean “A, B, or both A and B.” 
       FIG. 1  illustrates a side perspective view of a centralizer assembly  100 , according to an embodiment. The centralizer assembly  100  may be employed, for example, to maintain an annular clearance between a casing string (or any other type of oilfield tubular) and a surrounding tubular (e.g., another casing or liner, or the wellbore wall in open-hole situations). The centralizer assembly  100  may be affixed to a tubular  102 , which may be casing, drill pipe, or any other tubular that may be run into a well. 
     In some embodiments, the tubular  102  may be formed from the same casing (or tubular) as a remainder of a string to which the centralizer assembly  100  may be attached. Further, the tubular  102  may have a length comparable (e.g., the same, within tolerance, as) the adjacent casing. In a specific embodiment, the length of the tubular  102  (and the other casing) may be about 30 feet (about 9 meters). Moreover, the tubular  102  may be made from the same or a similar material as the remaining casing. In other embodiments, the tubular  102  may be formed from a separate type, material, etc. of pipe, tubing, or the like, and may be longer or shorter than the adjacent casing joints. 
     Further, the tubular  102  may include a first end  104 , a second end  106 , and a ground-down region  108  disposed between the first and second ends  104 ,  106 . In an embodiment, the ground-down region  108  may be spaced axially apart (e.g., along a longitudinal axis  107  of the centralizer assembly  100 ) from the ends  104 ,  106 . In another embodiment, the ground-down region  108  may extend to one of the ends  104 ,  106 . The ends  104 ,  106  may be configured to be attached to axially-adjacent tubulars. Accordingly, in an embodiment, the first end  104  includes a threaded, pin-end connection, and the second end  106  may include a threaded, box-end connection (not visible in  FIG. 1 ). 
     The tubular  102  may define a radius R and a wall thickness T. The ground-down region  108  may define an area of the tubular  102  where the radius R and the wall thickness T are reduced. However, the wall thickness T in the ground-down region  108  may remain substantially consistent (e.g., within about 1% to about 5% of consistent). In at least one embodiment, the ground-down region  108  may be created using a grinder such as the hardband removal device disclosed in U.S. Pat. No. 10,058,976 and U.S. Patent Publication No. 2018/311787, which are incorporated herein by reference in their entirety to the extent not inconsistent with the present disclosure. 
     Further, the ground-down region  108  may be formed as a recess in the tubular  102 , and thus may be spaced apart from the ends  104 ,  106 , such that the tubular  102  may define two raised regions  110 ,  112  having larger radii R and wall thickness T than the ground-down region  108 . Shoulders  114 ,  116  may be defined where the raised regions  110 ,  112  meet or “transition” to the ground-down region  108 . The two raised regions  110 ,  112  may have the same or different outer diameters, which may both be larger than the outer diameter of the ground-down region  108  and/or may be larger than the oilfield tubulars to which the tubular  102  is connected. In some embodiments, however, one or more of the raised regions  110 ,  112  may be omitted. For example, in some embodiments, the ground-down region  108  may extend to either one of the ends  104 ,  106 , such that the tubular  102  is “skimmed.” 
     The centralizer assembly  100  may also include a centralizer  118 , which may be disposed at least partially in the ground-down region  108 . The centralizer  118  may include at least one end collar. In the illustrated embodiment, the centralizer  118  includes two, axially-offset end collars  120 ,  122 . The surfaces of the end collars  120 ,  122  that face away from one another (i.e., the outboard surfaces) may define the axial “extents” of the centralizer  118 . In an embodiment, the end collars  120 ,  122  may be disposed on opposite ends of the ground-down region  108 , e.g., generally adjacent to the shoulders  114 ,  116 , respectively. 
     The centralizer  118  may also include a plurality of ribs  124  which may extend axially between and be connected with (e.g., integrally or via welding, fasteners, tabs, etc.) the end collars  120 ,  122 . In some embodiments, the ribs  124  may be flexible, and may be curved radially outwards from the end collars  120 ,  122 . Such curved, flexible ribs  124  may be referred to as “bow-springs.” In other embodiments, however, the ribs  124  may take on other forms, in shape and/or in elastic properties. In some embodiments, a coating may be applied to the ribs  124 , the end collars  120 ,  122 , and/or the tubular  102 . The coating may be configured to reduce abrasion to the ribs  124 , end collars  120 ,  122 , the tubular  102 , the casing (or another surrounding tubular in which the centralizer  118  may be deployed), or a combination thereof. The coating may, for example, also serve to reduce friction, and thus torque and drag forces, in the wellbore. 
     The centralizer  118  may be formed in any suitable way, from any suitable material. In a specific embodiment, the centralizer  118  may be formed by rolling a flat plate, and then seam welding the flat plate to form a cylindrical blank. The cylindrical blank may then be cut, so as to define the ribs  124  and end collars  120 ,  122 . One such fabrication process may be as described in U.S. Patent Publication No. 2014/0251595, which is incorporated by reference herein in its entirety. 
     In an embodiment in which the tubular  102  is skimmed (ground down to one of the ends  104 ,  106 ), the centralizer  118  may be slid onto the tubular  102  fully assembled. Otherwise, the centralizer  118  may be received laterally onto the tubular  102  at the ground-down region  108  and clamped into place, or temporarily expanded so that it can slide over the non-ground-down region and into the ground-down region  108 . 
     The centralizer assembly  100  may also include a plurality of stop features (e.g., segments)  200 A,  200 B. The stop segments  200 A,  200 B may be disposed generally proximal to the shoulders  114 ,  116 , respectively, and may be spaced axially apart from the shoulders  114 ,  116  so as to define circumferentially-extending channels  202 ,  204  between the stop segments  200 A,  200 B and the shoulders  114 ,  116 , respectively. Further, the stop segments  200 A may be axially-aligned and separated circumferentially apart so as to define axial channels  206  therebetween. Similarly, the stop segments  200 B may be axially-aligned and separated circumferentially apart so as to define axial channels  208  therebetween. 
     The stop segments  200 A,  200 B may be positioned between the axial extents of the centralizer  118 . In other words, the centralizer  118  may be positioned on both axial sides (i.e., opposing first and second axial sides) of the stop segments  200 A,  200 B. For example, as shown, the stop segments  200 A,  200 B may be received at least partially through windows  210 A,  210 B formed in the end collars  120 ,  122 , respectively. 
     The end collars  120 ,  122  may be similar in structure. Referring to the end collar  120  as an example, the end collar  120  may include two offset bands  212 ,  214 , with bridges  216  extending between the bands  212 ,  214 . Adjacent pairs of bridges  216 , in addition to the bands  212 ,  214 , may define the windows  210 A. The bridges  216  may be configured to slide between, in an axial direction, and bear on, in a circumferential direction, the stop segments  200 A. The stop segments  200 A and the windows  210 A may thus cooperate to permit, as well as limit, an axial and/or circumferential range of motion for the centralizer  118  with respect to the tubular  102 . In particular, the bands  212 ,  214  may be configured to engage the stop segments  200 A so as to limit an axial range of motion of the centralizer  118  with respect to the tubular  102 . 
     In some embodiments, the windows  210 A may be larger, axially and/or circumferentially (e.g., have a larger axial dimension and/or larger circumferential dimension), than the stop segments  200 A received therein. This relative sizing may provide a range of rotational and/or axial movement for the centralizer  118 ; however, in other embodiments, the windows  210 A may be sized to more snugly receive the stop segments  200 A, thereby constraining or eliminating movement of the centralizer  118  with respect to the tubular  102 . 
     Moreover, the bands  212 ,  214  of the end collar  120  may be received into the circumferential channels  202 . In some embodiments, engagement between the shoulders  114 ,  116  and the band  214  may limit an axial range of motion of the centralizer  118  with respect to the tubular  102 . For example, an axial range of motion needed to provide for axial expansion of the centralizer  118  during radial collapse of the ribs  124  may be determined, and the spacing of the channels  202 , taking into consideration the thickness of the band  214 , may be calculated. Further, in some situations, the thickness of the bands  214  may be adjusted. 
       FIG. 2  illustrates an enlarged, partial cross sectional view of the centralizer assembly  100 , according to an embodiment. As shown, the centralizer assembly  100  includes the tubular  102  defining the raised regions  110 ,  112  and the ground-down region  108 . The shoulders  114 ,  116 , defined where the ground-down region  108  transitions to the raised regions  110 ,  112 , respectively, may be inclined (e.g., beveled), as shown, so as to form an angle with respect to the longitudinal axis  107 . For example, as proceeding away from the stop segments  200 A,  200 B and/or away from the ground-down region  108 , the outer diameter of tubular  102  at the shoulders  114 ,  116  may increase. The shoulders  114 ,  116  may be inclined so as to reduce stresses in the transition in diameters. In an embodiment, the shoulders  114 ,  116  may be disposed at an any angle between about 1° and about 90°, for example, at an angle in the range of from about 1°, about 5°, or about 10° to about 20°, about 25°, about 30°. In a specific example, the shoulders  114 ,  116  may be inclined at an angle of about 15°. 
     Further, the shoulders  114 ,  116  may extend at least as far radially as the end collars  120 ,  122  and/or the stop segments  200 A,  200 B. That is, the first diameter of the tubular  102  at the raised regions  110 ,  112  may be at least as large as the second diameter of the tubular  102  in the ground-down region  108  plus twice the thickness of the end collars  120 ,  122  (or the stop segments  200 A,  200 B). Accordingly, the raised regions  110 ,  112  may protect the edges and end faces of the bands  212 ,  214  and stop segments  200 A,  200 B from contact with foreign objects in the wellbore. Since the centralizer  118  may be formed from a relatively thin material (e.g., relative to the tubular  102 ), the protection by the shoulders  114 ,  116  may assist in preventing damage to the centralizer  118 . 
     The stop segments  200 A,  200 B may be formed from a material that is different from the material making up the tubular  102  and may be coupled to the tubular  102  in the turned down region  108  using any suitable process. For example, the stop segments  200 A,  200 B may be formed from one or more layers of a thermal spray, such as WEARSOX®, which is commercially available from Innovex Downhole Solutions, Inc. In an embodiment, the thermal spray forming the stop segments  200  may be as described in U.S. Pat. Nos. 7,487,840 or 9,920,412, both of which are incorporated herein by reference in the entirety, to the extent not inconsistent with the present disclosure. 
     In another embodiment, the stop segments  200 A,  200 B may be formed from an epoxy injected into a composite shell, such as, for example, described in U.S. Pat. No. 9,376,871, which is incorporated herein by reference in its entirety, to the extent not inconsistent with the present disclosure. For example, in some embodiments, the stop segments  200 A,  200 B may be formed from an epoxy, a composite, or another molded material connected to the tubular  102 . 
     In still another embodiment, the stop segments  200 A,  200 B may be made from the same material as the tubular  102  and, e.g., may be integrally-formed therewith. For example, the ground-down region  108  may be formed by grinding around the areas designated for the stop segments  200 A, e.g., leaving the channels  202 ,  206  and forming the shoulder  114 . The stop segments  200 B and the channels  204 ,  208  may be similarly formed. 
       FIG. 3  illustrates a side, cross-sectional view of another embodiment of the centralizer assembly  100 . In this embodiment, the ground-down region  108  is bifurcated into two ground-down regions  302 ,  304 , which are separated apart axially along the tubular  102  by a medial stop feature (e.g., stop member)  306 . The end collars  120 ,  122  are positioned in the respective ground-down regions  302 ,  304 , as shown, with the ribs  124  extending over the medial stop member  306  and connecting the end collars  120 ,  122  together. The centralizer  118  may be free to move along a range of motion that is limited by the distance between the shoulder  114  and an end face  308  of the medial stop member  306 , and between the shoulder  116  and an end face  310  of the medial stop member  306 . This distance may be selected such that the ribs  124  may flex inward to avoid damage in tight restrictions, while flexing outward to engage larger surrounding tubular surfaces. The distances between the end face  308  and the shoulder  114  may be the same or different as the distance between the end face  310  and the shoulder  116 , or may be different. Further, the distances may be selected such that the end collar  120  is prevented from engaging the shoulder  114  by the end collar  122  engaging the end face  310 , and likewise, the end collar  122  is prevented from engaging the shoulder  116  by the end collar  120  engaging the end face  308 . Thus, in at least one embodiment, the provision of the medial stop member  306 , in contrast to the stop segments  200 A,  200 B may result in the centralizer  118  being at least partially pulled through a restriction, rather than being pushed through. 
     Additionally, in some embodiments, the end faces  308 ,  310  may be square, so as to provide a generally axially-oriented force couple with the respective end collars  120 ,  122  upon engagement therewith. This may avoid wedging the end collars  120 ,  122  radially outwards, as might occur with beveled or angled end faces  308 ,  310 . 
     The medial stop member  306  may be formed as an integral part of the tubular  102 , i.e., a portion that is not ground down or is ground down less than the ground-down regions  302 ,  304 . In another embodiment, the medial stop member  306  may be formed after grinding down the entire length between the shoulders  114 ,  116 , and then depositing a material, such as a thermal spray metal, epoxy-and-shell combination, a separate metal or composite collar, etc., onto the desired location in the ground-down region  108 . Further, in some embodiments, the stop member  306  may be partially created by grinding down the adjacent ground-down regions  302 ,  304 . The grinding operation may, however, be constrained to a depth that is insufficient to provide a suitable stop surface; as such, another material may be applied to increase the size of the stop surface. for example, a thermal spray material (e.g., WEARSOX®) may be applied to increase the height of the stop member  306 . 
     Before proceeding further with the description, it may be instructive to discuss the difference in grinding the tubular  102  to produce the ground-down region  108 , as opposed to using a lathe or another turning/cutting operation to form a reduced-diameter section in a tubular. Reference is made to  FIGS. 4A and 4B  to aid in an understanding of this difference.  FIG. 4A  represents an example of a typical lathing operation to reduce an outer diameter of the tubular  102 . In such an operation, the tubular  102  is fitted into a chuck, and rotated about its center  400 . A cutter (not shown) is held at a static distance r 2  from the center  400 , such that when the cutting is done, a consistent outer radius r 2  for the outside surface results. 
     However, in many cases, the starting tubular  102  is not precisely round, but has a degree of ovality. Ovality (O) is defined as: 
             O   =       2   ⁢     (     a   -   b     )         a   +   b             
where a is the length of the length of the major axis, and b is the length of the minor axis. For most tubulars, the ovality is non-zero.
 
     Thus, as shown in  FIG. 4A  on the left, an outer radius r 1A  is larger than an outer radius r 1B , although both may be larger than radius r 2 , such that cutting occurs all the way around the tubular  102 . The inner radial surface  402  may be likewise ovular, defining radius r 1C  and radius r 1D . Before cutting the tubular  102 , the tubular  102  may define a wall thickness t i  that is generally uniform all the way around the tubular  102  (i.e., r 1A −r 1D =r 1B −r 1C =t i ). 
     After cutting the tubular  102  down to the outer radius r 2 , however, as shown on the right, the wall thickness may no longer be constant, and may vary between t 1  and t 2 . For example, as shown, t 1 =r 2 −r 1D &lt;t 2 =r 2 −r 1C . This may be a consequence of the lathing operation cutting a varying amount of the tubular  102  away as proceeding around the tubular  102 , as the ovality is greatly reduced. Creating unintended thin areas in the tubular wall, however, may present a risk to burst failure. 
     By contrast, a grinding operation may follow the ovality of the tubular  102  and take a consistent amount of material off the tubular  102 , all the way around the tubular  102 . The result may still reduce the ovality, but to a lesser amount than the lathing, and, more importantly, may result in not changing the consistency of the wall thickness as proceeding around the tubular  102 . Referring to  FIG. 4B , on the left, the tubular  102  prior to grinding is again shown. After grinding, the outer surface  404  of the tubular  102  defines a varying radius, between a minimum at r 2B  and a maximum at r 2A . The thickness tg, however, may remain generally constant (or at least as constant as it was in the tubular  102  prior to grinding), as r 2A −r 2D =r 2B −r 2C =t g . Thus, the thickness is reduced from t i  to t g , and no points are thinned to the extent of t 1 . 
     It should be appreciated that a lathing operation could, potentially, be used to form the ground-down operation, if the ovality of the tubular  102  could be followed by the lathing operation. However, maintaining a uniform thickness is not inherent to lathing operations, as special care would need to be taken to avoid the uneven thickness discussed above. Likewise, other machining processes, sanding, etc. could be used. 
       FIG. 5  illustrates a flowchart of a method  500  for assembling a centralizer onto a tubular, according to an embodiment. The method  500  is described herein with reference to  FIGS. 1-4B , but it will be appreciated that embodiments of the method  500  may employ other structures. Further, the steps disclosed herein for the method  500  may be performed in a different order than presented herein, or may be divided into two or more separate steps, or two or more steps of the method  500  may be combined into a single step. 
     The method  500  may include determining a maximum outer diameter for a tubular  102  to support a centralizer  118 , as at  502 . The tubular  102  may be casing, and in particular casing may be configured through smaller and smaller casing diameters as it is deployed farther into a well. The outer diameter of an actual tubular  102  may be “nominal”, however, because the tubular  102  is subject to manufacturing tolerances, e.g., about 1%, and may be somewhat ovular (having a varying radius). As such, the tubular  102  may not have a precise, a priori known, geometry and size, but may still be considered to have a nominal size. 
     The method  500  may also include determining that the maximum outer diameter is too large to accommodate a centralizer  118 , as at  504 . If the maximum outer diameter of the tubular  102  is too close to the inner diameter of the surrounding tubular (e.g., a casing through which the tubular  102  is deployed) to allow for a centralizer  118 , then a ground-down region  108  may be provided to accommodate at least a portion of the thickness of the centralizer  118 . 
     In such circumstances, the method  500  may include selecting a position for the ground-down region  108  of the tubular  102 , as at  506 . The position may be spaced apart from one or both axial ends of the tubular  102 . Moreover, as mentioned above, the ground-down region  108  may actually include two or more regions (e.g., regions  302 ,  304  as shown in  FIG. 3 ). 
     The method  500  may then include grinding down the tubular  102  at the ground-down region  108  by a constant amount as proceeding circumferentially around the tubular  102 , as at  508 . For example, a generally consistent ⅛″, 1/16″, or any other desired depth may be taken from around the outside of the tubular  102 . By contrast, a lathing operation might remove more material in one angular interval than another to bring the tubular  102  closer to a perfect circle. 
     The method  500  may also include measuring the remaining wall thickness of the tubular  102  in the ground-down region  108 , as at  510 . This may be achieved using an ultrasonic measuring device, for example, although any suitable measuring device may be employed. 
     In some embodiments, the method  500  may optionally include securing a stop feature to the tubular  102  in the ground-down region  108 , as at  512 . In some embodiments, this may be accomplished using a thermal spray material, epoxy-and-shell configuration, or by fastening a metal or composite collar to the tubular  102 . In other embodiments, the stop feature may be provided during grinding at  508 , e.g., by not grinding or not grinding down as much a particular area of the tubular  102  (e.g., to provide the medial stop member  306 ). The ground-down region  108  may extend to an end of the tubular  102 , (“skimmed”) or may be recessed therein. 
     The method  500  may also include positioning a centralizer  118  at least partially in the ground-down region  108 , as at  514 . In a skimmed embodiment of the tubular  102 , such positioning of the centralizer  118  may be accomplished by sliding the fully-assembled centralizer  118  onto the tubular  102  and into position. In an embodiment in which the ground-down region  108  is recessed into the tubular, the centralizer  118  may be received laterally onto the tubular  102  in the ground-down region  108  and/or otherwise expanded and moved into position in the ground-down region  108 . Positioning at  514  may occur before, during, or after securing the stop feature in the ground-down region  108 . The end collars  120 ,  122  of the centralizer  118  may be allowed to slide in the ground-down region  108  over a limited range of motion, sufficient to allow the ribs  124  of the centralizer to flex. The use of a bow-spring centralizer is merely an example, however, as in some embodiments, a rigid centralizer may be used and positioned in the ground-down region  108 . Such a rigid centralizer would not include flexible bow springs. 
       FIG. 6  illustrates a side, conceptual view of a wellsite  600 , according to an embodiment. The wellsite  600  may include a drilling rig  602 , which may have suitable drilling, tubular handling, pumping, etc. equipment to form a well  604 . Further, a string  606  of tubulars  608  may be run into the well  604  using the drilling rig  602 . The tubulars  608  making up the string  606  may be sections or “joints” of tubulars  608  that are connected together, end-to-end. In some embodiments, the tubulars  608  may be casing, which may be cemented into the well  604 . The joints of tubulars  608  may be generally about the same length as one another, e.g., about 10 m in length. 
     The centralizer assembly  100  may be incorporated in the string  606  of tubulars  608 . For example, the tubular  102  of the centralizer assembly  100  may be connected to the tubulars  608 , e.g., uphole and downhole of the tubular  102 . The tubular  102  may have the same or similar construction as the other tubulars  608  of the string  606 . The tubular  102  and the tubulars  608 , for example, may each be about 10 m long, be made from a same material (e.g., a steel alloy), have the same nominal diameter, and/or have the same type of end connections. The tubular  102  may differ from the other tubulars  608  of the string  606  in that it includes the ground-down region  108  and/or the other features discussed above and may include the centralizer  118  extending therefrom. Other downhole tools, including other centralizers, may be positioned elsewhere along the string  606 . 
     The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.