Patent Publication Number: US-9885213-B2

Title: Cutting structures, tools for use in subterranean boreholes including cutting structures and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/826,832, filed Mar. 14, 2013, now U.S. Pat. No. 9,493,991, issued Nov. 15, 2016, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/618,950, filed Apr. 2, 2012, the disclosure of each of which is incorporated herein in its entirety by this reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate generally to cutting structures for use in a subterranean borehole and, more particularly, to cutting structures for use with downhole tools for at least one of enlarging and drilling a subterranean borehole during a drilling operation (e.g., reamers or drill bits having a portion for enlarging a portion of the borehole) and to related methods. 
     BACKGROUND 
     Reamers are typically employed for enlarging subterranean boreholes. Conventionally, in drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the well bore walls from caving into the subterranean borehole while providing requisite shoring for subsequent drilling operation to achieve greater depths. Casing is also conventionally installed to isolate different formations, to prevent cross-flow of formation fluids, and to enable control of formation fluids and pressure as the borehole is drilled. To increase the depth of a previously drilled borehole, new casing is laid within and extended below the previous casing. While adding additional casing allows a borehole to reach greater depths, it has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the existing casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter for installing additional casing beyond previously installed casing as well as to enable better production flow rates of hydrocarbons through the borehole. 
     A variety of approaches have been employed for enlarging a borehole diameter. One conventional approach used to enlarge a subterranean borehole includes using eccentric and bi-center bits. For example, an eccentric bit with a laterally extended or enlarged cutting portion is rotated about its axis to produce an enlarged borehole diameter. An example of an eccentric bit is disclosed in U.S. Pat. No. 4,635,738, which is assigned to the assignee of the present disclosure. A bi-center bit assembly employs two longitudinally superimposed bit sections with laterally offset axes, which, when rotated, produce an enlarged borehole diameter. An example of a bi-center bit is disclosed in U.S. Pat. No. 5,957,223, which is also assigned to the assignee of the present disclosure. 
     Another conventional approach used to enlarge a subterranean borehole includes employing an extended bottom-hole assembly with a pilot drill bit at the distal end thereof and a reamer assembly some distance above the pilot drill bit. This arrangement permits the use of any conventional rotary drill bit type (e.g., a rock bit or a drag bit), as the pilot bit and the extended nature of the assembly permit greater flexibility when passing through tight spots in the borehole as well as the opportunity to effectively stabilize the pilot drill bit so that the pilot drill bit and the following reamer will traverse the path intended for the borehole. This aspect of an extended bottom-hole assembly is particularly significant in directional drilling. The assignee of the present disclosure has, to this end, designed as reaming structures so called “reamer wings,” which generally comprise a tubular body having a fishing neck with a threaded connection at the top thereof and a tong die surface at the bottom thereof, also with a threaded connection. U.S. Pat. Nos. RE36,817 and 5,495,899, both of which are assigned to the assignee of the present disclosure, disclose reaming structures including reamer wings. The upper midportion of the reamer wing tool includes one or more longitudinally extending blades projecting generally radially outwardly from the tubular body and PDC cutting elements are provided on the blades. 
     Expandable reamers may also be used to enlarge a subterranean borehole and may include blades that are pivotably or hingedly affixed to a tubular body and actuated by way of a piston disposed therein as disclosed by, for example, U.S. Pat. No. 5,402,856 to Warren. In addition, U.S. Pat. No. 6,360,831 to Akesson et al., discloses a conventional borehole opener comprising a body equipped with at least two hole opening arms having cutting means that may be moved from a position of rest in the body to an active position by exposure to pressure of the drilling fluid flowing through the body. The blades in these reamers are initially retracted to permit the tool to be run through the borehole on a drill string, and, once the tool has passed beyond the end of the casing, the blades are extended so the bore diameter may be increased below the casing. 
     BRIEF SUMMARY 
     In some embodiments, the present disclosure includes a cutting structure for use with a downhole tool in a subterranean borehole. The cutting structure includes a blade, a plurality of primary cutting elements coupled to the blade, and at least one secondary element rotationally leading the plurality of primary cutting elements in a direction of intended rotation of the cutting structure. The at least one secondary element comprises at least one of a rubbing surface and a cutting surface and is coupled to the blade proximate a rotationally leading surface of the blade. An exposure of at least one primary cutting element of the plurality of primary cutting elements is greater than an exposure of the at least one secondary element. 
     In additional embodiments, the present disclosure includes a reamer for use in a subterranean borehole including a body and a plurality of blades coupled to the body. Each blade includes a plurality of primary cutting elements coupled to the blade and extending along the blade in a direction substantially parallel to a centerline of the blade and at least one secondary element comprising at least one of a rubbing surface and a cutting surface coupled to the blade proximate a rotationally leading surface of the blade and rotationally leading the plurality of primary cutting elements. An exposure of at least one primary cutting element of the plurality of primary cutting elements is greater than an exposure of the at least one secondary element. 
     In yet additional embodiments, the present disclosure includes methods for enlarging a subterranean borehole. The methods include engaging a subterranean borehole with at least one reamer blade coupled to a reamer, reaming a portion of the subterranean borehole with a plurality of primary cutting structures on the at least one blade, pivoting the reamer about the a plurality of primary cutting structures on the at least one blade and engaging the subterranean borehole with at least one secondary element on the at least one blade. 
     In yet additional embodiments, the present disclosure includes methods of forming downhole tools including cutting structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the disclosure, various features and advantages of embodiments of the disclosure may be more readily ascertained from the following description of some embodiments of the disclosure, when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side view of an embodiment of a reamer including a plurality of cutting structures in accordance with an embodiment of the present disclosure; 
         FIG. 2  shows a transverse cross-sectional view of the reamer including the plurality of cutting structures as indicated by section line  2 - 2  in  FIG. 1 ; 
         FIG. 3  shows a longitudinal cross-sectional view of the reamer including the plurality of cutting structures as indicated by section line  3 - 3  in  FIG. 2 ; 
         FIG. 4  shows an enlarged cross-sectional view of a downhole portion reamer including the plurality of cutting structures shown in  FIG. 3 ; 
         FIG. 5  shows an enlarged cross-sectional view of an uphole portion of reamer including the plurality of cutting structures shown in  FIG. 3 ; 
         FIG. 6  shows a partial, longitudinal cross-sectional illustration of a reamer including the plurality of cutting structures in an expanded position; 
         FIG. 7  shows a partial, front view of a cutting structure in accordance with another embodiment of the present disclosure; 
         FIG. 8  shows a top view of the cutting structure of  FIG. 7  coupled to a downhole tool such as a reamer in accordance with another embodiment of the present disclosure; 
         FIG. 9  shows a partial, side view of a cutting structure in accordance with yet another embodiment of the present disclosure; 
         FIG. 10  shows a top view of a cutting structure coupled to a downhole tool such as a reamer in accordance with yet another embodiment of the present disclosure; and 
         FIG. 11  shows a partial, front view of a cutting structure in accordance with yet another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The illustrations presented herein are, in some instances, not actual views of any particular tool, apparatus, structure, element, or other feature of a downhole or earth-boring tool, but are merely idealized representations that are employed to describe embodiments of the present disclosure. Additionally, elements common between figures may retain the same numerical designation. 
     As disclosed herein, embodiments of cutting structures for use with downhole tools (e.g., a reaming tool) may include cutting elements (e.g., primary cutting elements) positioned on a portion of the downhole tool (e.g., an exterior surface or structure of the downhole tool that protrudes from a body of the downhole tool such as, for example, one or more blades). For example, the primary cutting elements may be positioned on surfaces of a downhole tool that at least partially extend only the length of the tool or along the length of the borehole in which the tool is to be utilized. The primary cutting elements may be positioned on the blades at a location trailing the rotationally leading surface (e.g., a leading edge) of the blade. For example, the primary cutting elements may be formed as a row extending along the length of the blade and may be positioned proximate a centerline of the blade (e.g., at the centerline or positioned between the centerline and a trailing surface such as, for example, a trailing edge of the blade). In some embodiments, one or more additional elements comprising a rubbing surface, a cutting surface, or combinations thereof may be coupled to the blade proximate the rotationally leading surface of the blade (e.g., elements to reduce wear of the blade proximate the leading surface). For example, at least one wear element (e.g., hardfacing, inserts, etc.), a second plurality of cutting elements (e.g., secondary cutting elements) or combinations thereof may be positioned proximate the rotationally leading surface of the blade. In other words, the second, additional elements may be positioned to rotationally lead the primary cutting elements. The primary cutting elements may also be positioned on the blade to have an exposure greater than an exposure of the additional elements. 
     Although embodiments of the present disclosure are depicted as being used and employed in a reamer such as an expandable reamer, persons of ordinary skill in the art will understand that the embodiments of the present disclosure may be employed in any downhole tool where use of cutting structures as disclosed herein, is desirable. For example, one or more cutting structures may be utilized with any type of tool or drill bit used at least partially for the enlargement of a wellbore in a subterranean formation (e.g., a reaming tool, a reamer, or a drill bit having a portion thereof for enlarging a borehole). Such reamers may include, for example, fixed reamers, expandable reamers, bicenter bits, and eccentric bits. In other embodiments, one or more cutting structures may be used with any type of tool or drill bit (i.e., downhole tools) for use in boreholes or wells in earth formations. For example, a downhole tool may employ one or more cutting structures used for drilling during the formation or enlargement of a wellbore in a subterranean formation and include, for example, earth-boring rotary drill bits, roller cone bits, core bits, mills, hybrid bits employing both fixed and rotatable cutting structures, and other drilling bits and tools as known in the art. 
     In some embodiments, the expandable reamer described herein may be similar to the expandable apparatus described in, for example, U.S. Patent Application Publication No. US 2008/0102175 A1, entitled “Expandable Reamers for Earth-Boring Applications,” filed Dec. 3, 2007, now U.S. Pat. No. 7,900,717; U.S. patent application Ser. No. 12/570,464, entitled “Earth-Boring Tools having Expandable Members and Methods of Making and Using Such Earth-Boring Tools,” filed Sep. 30, 2009, now U.S. Pat. No. 8,230,951; U.S. patent application Ser. No. 12/894,937, entitled “Earth-Boring Tools having Expandable Members and Related Methods,” and filed Sep. 30, 2010; and United States Patent Application Publication No. US 2012/0111579 A1, entitled “Earth-Boring Tools having Expandable Members and Related Methods,” and filed Nov. 8, 2011, the disclosure of each of which is incorporated herein in its entirety by this reference. 
     An embodiment of an expandable reamer apparatus  100  is shown in  FIG. 1 . The expandable reamer apparatus  100  may include a generally cylindrical tubular body  108  having a longitudinal axis L 108 . The tubular body  108  of the expandable reamer apparatus  100  may have a distal end  190 , a proximal end  191 , and an outer surface  111 . The distal end  190  of the tubular body  108  of the expandable reamer apparatus  100  may include a set of threads (e.g., a threaded male pin member) for connecting the distal end  190  to another section of a drill string (not shown) or another component of a bottom-hole assembly (BHA), such as, for example, a drill collar or collars carrying a pilot drill bit for drilling a well bore. In some embodiments, the expandable reamer apparatus  100  may include a lower sub  109  that connects to the lower box connection of the reamer body  108 . Similarly, the proximal end  191  of the tubular body  108  of the expandable reamer apparatus  100  may include a set of threads (e.g., a threaded female box member) for connecting the proximal end  191  to another section of a drill string or another component of a bottom-hole assembly (BHA). 
     The expandable reamer apparatus  100  may include one or more cutting structures  101  including a blade  106  ( FIG. 2 ) and cutting elements as discussed below. For example, three sliding blades  106  are retained in circumferentially spaced relationship in the tubular body  108  as further described below and may be provided at a position along the expandable reamer apparatus  100  intermediate the first distal end  190  and the second proximal end  191 . The blades  106  may be comprised of steel, tungsten carbide, a particle-matrix composite material (e.g., hard particles dispersed throughout a metal matrix material), or other suitable materials as known in the art. The cutting structures  101  are retained in an initial, retracted position within the tubular body  108  of the expandable reamer apparatus  100 , as illustrated in  FIG. 3 , but may be moved responsive to application of hydraulic pressure into the extended position, as illustrated in  FIG. 6 , and returned to the retracted position when desired. The expandable reamer apparatus  100  may be configured such that the cutting structures  101  engage the walls of a subterranean formation surrounding a well bore in which the expandable reamer apparatus  100  is disposed to remove formation material when the cutting structures  101  are in the extended position, but are not operable to engage the walls of a subterranean formation within a well bore when the cutting structures  101  are in the retracted position. While the expandable reamer apparatus  100  includes three cutting structures  101 , it is contemplated that one, two or more than three cutting structures may be utilized to advantage. Moreover, while the cutting structures  101  of expandable reamer apparatus  100  are symmetrically circumferentially positioned about the longitudinal axis L 108  along the tubular body  108 , the cutting structures  101  may also be positioned circumferentially asymmetrically as well as asymmetrically about the longitudinal axis L 108 . The expandable reamer apparatus  100  may also include a plurality of stabilizer pads to stabilize the tubular body  108  of expandable reamer apparatus  100  during drilling or reaming processes. For example, the expandable reamer apparatus  100  may include upper hard face pads, mid hard face pads, and lower hard face pads. 
       FIG. 2  is a cross-sectional view of the expandable reamer apparatus  100  shown in  FIG. 1 , taken along section line  2 - 2  shown therein. As shown in  FIG. 2 , the elongated cylindrical wall of the tubular body  108  encloses a fluid passageway  192  that extends longitudinally through the tubular body  108 . Fluid may travel through the fluid passageway  192  in a longitudinal bore  151  of the tubular body  108  (and a longitudinal bore of a sleeve member). 
     To better describe aspects of embodiments of the disclosure, in  FIG. 2 , one of cutting structures  101  is shown in the outward or extended position while the other cutting structures  101  are shown in the initial or retracted positions. In the retracted or recessed position, the cutting structures  101  of the expandable reamer apparatus  100  may be substantially disposed within the tubular body  108  of the expandable reamer apparatus  100 . The cutting structures  101  may extend beyond the outer diameter of the tubular body  108  when in the extended position, for example, to engage the walls of a borehole in a reaming operation. 
     The three sliding blades  106  of the cutting structures  101  may be retained in three blade tracks  148  formed in the tubular body  108 . 
     The cutting structures  101  each carry one or more rows of elements configured to engage with the wall of a subterranean borehole during downhole operations. For example, the cutting structures  101  may include a row of cutting elements (e.g., primary cutting elements  120 ) positioned on each blade  106  of the cutting structures  101 . The primary cutting elements  120  are configured to engage material of a subterranean formation defining the wall of an open borehole when the cutting structures  101  are in an extended position. As above, the primary cutting elements  120  may be positioned on the blades  106  at a location trailing a rotationally leading surface  110  of the blade  106 . For example, the primary cutting elements  120  may be formed as a row extending along the length of the blade  106  and may be positioned proximate a centerline (see, e.g.,  FIG. 7 ) of the blade  106  (e.g., at the centerline or positioned between the centerline and a trailing surface  112  of the blade  106 ). 
     One or more additional, secondary elements  118  forming a cutting surface, a rubbing surface, or combinations thereof may be positioned proximate the rotationally leading surface  110  of the blade  106 . In other words, the secondary elements  118  may be positioned to rotationally lead the primary cutting elements  120 . The secondary elements  118  may comprise at least one wear element (e.g., hardfacing, inserts, rubbing or bearing elements, etc.), a second plurality of cutting elements (e.g., secondary cutting elements) or combinations thereof. 
     The primary cutting elements  120  may be configured to be relatively more aggressive than the secondary elements  118 . For example, the primary cutting elements  120  may have an exposure greater than an exposure of the secondary elements  118 . In additional embodiments, the primary cutting elements  120  may have a back rake angle less than a back rake angle of the secondary elements  118 . In such an embodiments, the relatively greater back rake angle of the secondary elements  118  may act to reduce the likelihood that the secondary element  118  will engage (e.g., cut) the formation, thereby, enabling the secondary elements  118  to move along (e.g., slide along) the formation, for example, while stabilizing the cutting structure  101 , as the primary cutting elements  120  remove material (e.g., ream) the formation. In other embodiments, the primary cutting elements  120  may have an exposure greater than an exposure of the secondary elements  118  and may have a back rake angle greater than a back rake angle of the secondary elements  118 . In yet other embodiments, the secondary elements  118  may have a larger chamfer or comprise cutting elements having relatively less aggressive or efficient cutting edge geometries as compared to the primary cutting elements  120 . 
     In some embodiments, the secondary elements  118  and primary cutting elements  120  may be polycrystalline diamond compact (PDC) cutters or other cutting elements known in the art. In embodiments where the secondary elements  118  are configured to remove material from a subterranean borehole (e.g., where the secondary elements  118  comprise a cutting surface), the secondary elements  118  (e.g., secondary cutting elements) may remove material from the formation and act to protect a rotationally leading portion of the blades  106  from substantial wear as the blades  106  contact the subterranean formation. 
     In some embodiments, the secondary elements  118  may be shaped inserts (e.g., circular shaped inserts such as, for example, ovoids) formed from superabrasive materials (e.g., diamond-enhanced materials such as, for example, thermally stable product (TSP) inserts) and/or tungsten carbide materials, other shaped tungsten carbide and diamond-enhanced inserts (e.g., bricks or discs), or combinations thereof. In embodiments where the secondary elements  118  are not configured to primarily remove material from a subterranean borehole (e.g., where the secondary elements  118  are configured as a bearing or rubbing surface), the secondary elements  118  may act to protect a rotationally leading portion of the blades  106  from substantial wear as the blades  106  contact the subterranean formation. 
     In some embodiments, the secondary elements  118  may be configured as substantially chisel-shaped elements, chisel-shaped elements having one or more blunt surfaces, elements configured to have a plowing, gouging, and/or crushing cutting action, or combinations thereof. 
     In some embodiments, the cutting structures  101  may include additional wear features such as, for example, hardfacing on portions of the blades  106  (e.g., at the rotationally leading surface  110  as shown in  FIG. 10 ). 
       FIG. 3  shows a longitudinal cross-sectional view of the expandable reamer apparatus  100  as indicated by section line  3 - 3  in  FIG. 2 . The expandable reamer apparatus  100  may include an actuating feature, such as a push sleeve  115  coupled to extendable and retractable cutting structures  101 . The actuating feature of the reamer apparatus  100  may also include a latch sleeve  117  coupled to the push sleeve  115 . In some embodiments, the latch sleeve  117  may be formed as a portion of the push sleeve  115 . The push sleeve  115  may be directly or indirectly coupled (e.g., by a linkage) to the one or more cutting structures  101  of the expandable reamer apparatus  100 . As discussed below in further detail, the push sleeve  115  may move in an uphole direction  159  in order to transition the cutting structures  101  between the extended and retracted position. The cutting structures  101  of the expandable reamer apparatus  100  may be retained in a retracted position by a retaining feature such as a sleeve member (e.g., a traveling sleeve  102 ). As depicted in  FIGS. 4 through 6 , the length of the traveling sleeve  102  may be varied in different embodiments depending on the application. 
     As shown in  FIG. 4 , the expandable reamer apparatus  100  may include a traveling sleeve  102 , which is movable from a first, initial position, which is shown in  FIG. 4 , in a downhole direction  157  to a second position (e.g., a triggered position) shown in  FIG. 6 . The traveling sleeve  102  may be at least partially received within a portion of the actuating feature of the reamer apparatus  100  (e.g., one or more of a portion of the push sleeve  115  and a portion of the latch sleeve  117 ). For example, the push sleeve  115  and the latch sleeve  117  may be cylindrically retained between the traveling sleeve  102  and the inner surface of the tubular body  108  of the expandable reamer apparatus  100 . 
     The push sleeve  115  may be retained in the initial position by the traveling sleeve  102 . For example, a portion of the traveling sleeve  102  may act to secure a portion of the push sleeve  115  (or another component attached thereto such as, for example, the latch sleeve  117 ) to a portion of an inner wall  107  of the tubular body  108  of the expandable reamer apparatus  100 . 
     Referring still to  FIG. 4 , when the traveling sleeve  102  is in the initial position, the hydraulic pressure may act on the push sleeve  115 , which is coupled the latch sleeve  117 , between an outer surface of the traveling sleeve  102  and an inner surface of the tubular body  108 . With or without hydraulic pressure, when the expandable reamer apparatus  100  is in the initial position, the push sleeve  115  is prevented from moving (e.g., in the uphole direction  159 ) by the latch sleeve  117 . 
     After the traveling sleeve  102  travels sufficiently far enough from the initial position in the downhole direction  157  (e.g., to a triggered position) to enable the latch sleeve  117  to be disengaged from the tubular body  108 , the latch sleeve  117 , which is coupled to the push sleeve  115 , may both move in the uphole direction  159 . In order for the push sleeve  115  to move in the uphole direction  159 , the differential pressure between the longitudinal bore  151  and the outer surface  111  of the tubular body  108  caused by the hydraulic fluid flow must be sufficient to overcome the restoring force or bias of a spring  116 . 
       FIG. 5  shows an enlarged cross-sectional view of an uphole portion of an embodiment of an expandable reamer apparatus  100 . As shown in  FIG. 5 , the push sleeve  115  includes, at its proximal end, a yoke  114  coupled to the push sleeve  115 . The yoke  114  includes three arms  177 , each arm  177  being coupled to one of the cutting structures  101  by a pinned linkage  178 . The pinned linkage  178  enables the cutting structures  101  to rotationally transition about the arms  177  of the yoke  114  as the actuating means (e.g., the push sleeve  115 , the yoke  114 , and the linkage  178 ) transitions the cutting structures  101  between the extended and retracted positions. 
     Referring now to  FIGS. 4 and 6 , the expandable reaming apparatus  100  is now described in terms of its operational aspects. Before “triggering” the expandable reamer apparatus  100  to the expanded position, the expandable reamer apparatus  100  is maintained in an initial, retracted position as shown in  FIG. 4 . While the traveling sleeve  102  is in the initial position, the cutting structure actuating feature (e.g., the push sleeve  115 ) is prevented from actuating the cutting structures  101 . When it is desired to trigger the expandable reamer apparatus  100 , the traveling sleeve  102  is moved in the downhole direction  157  to release the latch sleeve  117 . For example, the rate of flow of drilling fluid through the reamer apparatus  100  is increased to increase the hydraulic pressure at a constricted portion  104  of the traveling sleeve  102  and to exert a force (e.g., a force due to a pressure differential) against the traveling sleeve  102  and translate the traveling sleeve  102  in the downhole direction  157 . In additional embodiments, other methods may be used to constrict fluid flow through the traveling sleeve  102  in order to move the traveling sleeve  102  in the downhole direction  157 . For example, an obstruction may be selectively disposed within the traveling sleeve  102  to at least partially occlude fluid from flowing therethrough in order to apply a force in the downhole direction  157  to the traveling sleeve  102 . 
     As shown in  FIG. 6 , the traveling sleeve  102  may travel sufficiently far enough from the initial position in the downhole direction  157  to enable the latch sleeve  117  to be disengaged from the groove  124  of the tubular body  108 . The latch sleeve  117 , coupled to the pressure-activated push sleeve  115 , may move in the uphole direction  159  under fluid pressure influence (e.g., from fluid supplied through orifices in one or more of the latch sleeve  117 , the traveling sleeve  102 , and a ring  113 ). As the fluid pressure is increased by the increased fluid flow, the biasing force of the spring  116  is overcome enabling the push sleeve  115  to move in the uphole direction  159 . Movement of the push sleeve  115  in the uphole direction  159  may move the yoke  114  and the cutting structures  101  in the uphole direction  159 . In moving in the uphole direction  159 , the cutting structures  101  each follow a ramp or track  148  to which they are mounted (e.g., via a type of modified square dovetail groove  179  ( FIG. 2 )). 
     Whenever the flow rate of the drilling fluid passing through the traveling sleeve  102  is decreased below a selected flow rate value, the traveling sleeve  102  may be returned to the initial position shown in  FIG. 4  under the biasing force of spring  116 . As the traveling sleeve  102  returns to the initial position, the latch sleeve  117  may return to the initial position and the traveling sleeve  102  may again secure the latch sleeve  117  to the tubular body  108 . The push sleeve  115 , the yoke  114 , the cutting structures  101 , and the latch sleeve  117  may also be returned to their initial or retracted positions under the force of the spring  116 . 
     Whenever the flow rate of the drilling fluid passing through traveling sleeve  102  is elevated to or beyond a selected flow rate value, the traveling sleeve  102  may again move in the downhole direction  157  releasing the latch sleeve  117  as shown in  FIG. 6 . The push sleeve  115  with the yoke  114  and cutting structures  101  may then move upward with the cutting structures  101  following the tracks  148  to again ream the prescribed larger diameter in a borehole. In this manner, the expandable reamer apparatus  100  may move the cutting structures  101  between the retracted position and the expanded position in a repetitive manner (e.g., an unlimited amount of times). 
       FIG. 7  shows a partial, front view of a cutting structure  201  including multiple rows (e.g., two) of elements (e.g., cutting elements). In some embodiments, cutting structure  201  may be somewhat similar to the cutting structures  101  discussed above. As shown in  FIG. 7 , the cutting structure  201  including a plurality of secondary elements (e.g., secondary cutting elements  218 ) and a plurality of cutting elements (e.g., primary cutting elements  220 ) may be formed on a portion of a downhole tool. For example, the primary cutting elements  220  and secondary elements  218  may be formed on a portion of the downhole tool that protrudes (e.g., permanently or selectively) from another portion of the downhole tool (e.g., a blade  206  of a reamer such as, for example, and the expandable reamer  100  discussed above). As noted above, in some embodiments, the secondary elements  218  may be formed as bearing or rubbing elements (i.e., configured to move along a surface of the subterranean formation without substantially removing material therefrom) instead of cutting elements. 
     Cutting elements  220  extend along the blade  206  in a position rotationally trailing cutting elements  218 . In other words, cutting elements  220  may trail cutting elements  218  in a direction of indented rotation of the cutting structure  201  during a downhole operation. For example, cutting elements  218  may positioned proximate (e.g., at) the rotationally leading surface of the blade  206 . The cutting elements  220  may be positioned proximate to (e.g., at or rotationally trailing) a centerline C L  of the blade  206 . For example, the cutting elements  220  may be positioned on the blade  206  between the centerline C L  of the blade  206  and a trailing surface  212  of the blade  206 . The cutting elements  220  may extend along the length of the blade  206  (e.g., in direction substantially parallel to the centerline C L ). 
     In some embodiments, the cutting structure  201  may include one or more inserts  208  positioned proximate the cutting elements  218 ,  220  (e.g., on an uphole portion of the blade  206 ) that are configured to provide a rubbing surface that may contact the formation during downhole operation. 
       FIG. 8  shows a top view of the cutting structure of  FIG. 7  coupled to a downhole tool such as a reamer  200 . As shown in  FIG. 8 , cutting elements  220  have an exposure greater than an exposure of the cutting elements  218 . In other words, cutting elements  220  extend relatively further from the surface of the blade  206  on which they are mounted than cutting elements  218 . The relatively greater exposures of the cutting elements  220  will act to engage the cutting elements  220  with a subterranean formation  10  before the cutting elements  218  engage with the formation  10 . In other words, cutting elements  220  will operate as relatively more aggressive, primary cutters and cutting elements  218  will operate as secondary cutters. 
       FIG. 9  shows a partial, side view of a cutting structure  301  that may be somewhat similar to the cutting structures  101 ,  201  discussed above. As shown in  FIG. 9 , primary cutting elements  320  have an exposure D 2  that is greater than an exposure D 1  of the secondary elements  318 . As discussed above, the secondary elements  318  may comprise cutting elements, shaped inserts (e.g., ovoids) formed from superabrasive materials and/or tungsten carbide materials, or combinations thereof. 
     In some embodiments, the primary cutting elements  320  (also, primary cutting elements  120 ,  220  (see  FIGS. 2, 7, and 8 )) may be offset (e.g., laterally offset in a direction substantially transverse to a rotational path of the secondary elements  318 ) from one or more secondary elements  318  (also, secondary elements  118 ,  218  (see  FIGS. 2, 7, and 8 )). For example, one or more of the primary cutting elements  320  may be positioned at a location laterally between two secondary elements  318 . In other embodiments, the primary cutting elements  320  may each be positioned substantially within a rotational path of a corresponding secondary element  318  (e.g., directly trailing). For example, the primary cutting elements  320  may each be positioned in a kerf of a corresponding secondary element  318 . 
       FIG. 10  shows a top view of the cutting structure  401  coupled to a downhole tool such as a reamer  400  that may be somewhat similar to the cutting structures  101 ,  201 ,  301  discussed above. As shown in  FIG. 10 , secondary element  418  may rotationally lead cutting elements  420  and may be formed as a wear-resistance surface (e.g., hardfacing) at rotationally leading portions of the blade  406  (e.g., at leading surface  410 , radially outward surface  411 , or combinations thereof. In such an embodiment, the secondary element  418  may be formed as only a wear-resistance surface or may include additional secondary elements such as, for example, elements  118 ,  218 ,  318  discussed above. 
       FIG. 11  shows a partial, front view of a cutting structure  501  that may be somewhat similar to the cutting structures  101 ,  201 ,  301 ,  401  discussed above. The cutting structure  501  includes secondary elements comprising shaped inserts  502 . As mentioned above, the shaped inserts may comprise one or more of circular shaped inserts  503  (e.g., ovoids), bricks  504 , and discs  505 . Such shaped inserts  502  may be formed from one or more of superabrasive materials (e.g., diamond-enhanced materials such as, for example, thermally stable product (TSP) inserts) and tungsten carbide materials. As above, the shaped inserts  502  may rotationally lead cutting elements  520  and may be positioned at rotationally leading portions of blade  506  (e.g., at leading surface  510 ). 
     Embodiments of the present disclosure may be particularly useful in providing a cutting structure that is relatively more robust in handling drilling and/or reaming dysfunctions during downhole operations (e.g., vibrations caused by operations including a reamer following a pilot bit). For example, referring back to  FIGS. 7 and 8 , positioning the primary cutting elements  220  proximate the centerline C L  of the blade  206  may alter the pivot point of the blade  206 . As discussed above, additional elements (e.g., one or more rubbing, bearing, or cutting elements such as cutting elements  218 ) at the rotationally leading surface  210  of the blade  206  may be formed to act as a dampening or rocking feature to be the second point of contact rather the subsequent blade (see, e.g.,  FIG. 2 ). 
     Cutting structures having primary cutting elements positioned at the rotationally leading surface thereof may, during a dysfunction, cause the primary cutting elements at the leading surface to become lodged in the formation material of the borehole wall, causing the downhole tool (e.g., reamer) to experience forward whirl. In other words, the drill string to which the reamer is attached continues to rotate while one or more cutting structures of the reamer are lodged in the formation (i.e., the reamer is not rotating or rotating at a slower rotational speed than the drill string) causing a rotational force (e.g., a reactive moment in a direction opposite to the direction of rotation of the drill string) to build in the drill string. Such a force will generally cause the reamer to pivot on the primary cutting element engaged with the formation causing one or more adjacent cutting structures of the reamer to be forced into the formation, potentially damaging the blade and the cutting elements thereon. 
     Embodiments of the present disclosure including primary cutting elements positioned away from the rotationally leading edge of the blade may form a pivot point proximate the centerline of the blade (i.e., a pivot point rotationally spaced from the leading edge of the blades). During a dysfunction, the reamer may pivot under a rotation force. However, the primary cutting elements positioned proximate the centerline or trailing surface of the blade may act to pivot the reamer such that the rotationally leading portion of the blade, including additional elements thereon to protect the blade and reamer, may be forced into the formation. Such positioning of a pivot point on the blade and additional, secondary elements at the rotationally leading surface of the blade may reduce the potential damage caused to adjacent cutting structures as compared to cutting structures with primary cutting elements at the leading portion thereof. 
     While particular embodiments of the disclosure have been shown and described, numerous variations and other embodiments will occur to those skilled in the art. Accordingly, it is intended that the disclosure only be limited in terms of the appended claims and their legal equivalents.