Patent Publication Number: US-7900703-B2

Title: Method of drilling out a reaming tool

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/747,651, filed May 11, 2007, now U.S. Pat. No. 7,621,351, issued Nov. 24, 2009, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/800,621 filed May 15, 2006, and the disclosure of each of such applications is incorporated herein in its entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the invention relate to a reaming tool suitable for running on casing or liner, and a method of reaming a bore hole. 
     BACKGROUND 
     When running casing or liner into a predrilled bore hole, it is desirable that the bore hole will have been drilled with intended cylindricity, to its designed diameter, and without marked deviations, such as doglegs, along its path. Unfortunately, due to transitions between formations, irregularities such as stringers within a formation, the use of out-of-tolerance drill bits, damage to drill bits after running into the bore hole, bottom hole assembly (BHA) configurations employed by the driller, and various other factors, the ideal bore hole is rarely achieved. 
     Therefore, it is desirable to provide the casing or liner being run into the existing bore hole with a cutting structure at the leading end thereof to enable enlargement, as necessary, of portions of the bore hole so that the casing or liner may be run into the bore hole to the full extent intended. Various approaches have been attempted in the past to provide a casing or liner string with a reaming capability, with inconsistent results. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the reaming tool of the invention comprise a substantially tubular body having a concave nose portion extending to a side wall through a substantially arcuate shoulder transition region. The reaming tool further comprises cutting structure for enlarging, also termed “reaming,” of a bore hole through contact with the side wall thereof. The term “tool” is used herein in a non-limiting sense, and the apparatus of embodiments of the present invention may also be characterized as a reaming bit or reaming shoe. 
     In some embodiments, the concave nose portion of the reaming tool may have at least one port therethrough extending to an interior of the body. In some embodiments, a plurality of circumferentially spaced, spirally configured blades may extend on an exterior of the body from proximate the shoulder transition region and define junk slots therebetween. An axially leading end of each blade may commence with substantially no standoff from the body and taper radially outwardly to a portion having a substantially constant standoff and having a radially inwardly extending, beveled, axially trailing end. A plurality of cutting elements may be disposed along a rotationally leading edge of each blade of the plurality proximate an axially leading end thereof. 
     Another embodiment of the invention comprises a method of drilling out a reaming tool configured as a shoe having a nose at an axially leading end thereof and a side wall extending axially to the rear thereof. The method comprises initially engaging the nose proximate a central portion thereof with a drill bit, rotating the drill bit inside the reaming tool, and drilling out the nose from the central portion thereof radially outwardly toward a periphery thereof and the side wall of the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a reaming tool according to the present invention; 
         FIG. 2  is a perspective view of another embodiment of a reaming tool according to the present invention; 
         FIG. 3  is a frontal elevation, looking toward the nose of the reaming tool of  FIGS. 1 and 2 ; 
         FIG. 4  is an enlarged, side sectional elevation depicting an ovoid-ended insert disposed in a blade of the reaming tool of  FIGS. 1 and 2  and protruding beyond the major diameter of the tool; and 
         FIGS. 5A through 5C  are schematic depictions of a quarter-section of the reaming tool of the present invention, as depicted in  FIGS. 1 and 2  as a conventional PDC rotary drag bit approaches and drills through the nose, depicting how drillout is effected from the centerline of the nose of the reaming tool toward the side wall of the body. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention comprises a reaming tool, configured as a reaming bit or shoe, suitable for running on a casing or liner string (hereinafter referred to for the sake of convenience as a “casing string” to encompass such general type of tubular string). The reaming tool includes a tubular body having structure at a trailing end thereof for connecting the body to the leading end of a casing string and extending toward a nose at the leading end thereof. 
     The nose is configured with a shallow cone profile surrounding the center thereof, and a plurality of blades extend in a steeply pitched spiral configuration from a periphery of the nose, commencing at their leading ends with substantially no standoff from the body, toward the trailing end of the body. The blades taper axially and radially outwardly from the periphery of the nose to a greater, substantially constant standoff from the body to a location proximate their axially trailing ends and defining junk slots therebetween. The center of the nose includes a port therein through which drilling fluid (and, later, cement) may be circulated downwardly through the casing string, out onto the face of the nose and into the junk slot, which circulation may be enhanced through the use of additional side ports through the periphery of the nose from the interior of the body. 
     The rotationally leading edges (taken in the direction of intended rotation, conventionally clockwise, of the casing string when rotational reaming is contemplated) of each blade between the leading end thereof and a point at which the blade reaches full diameter are provided with a plurality of superabrasive cutting elements, which may comprise polycrystalline diamond compact (PDC) cutting elements facing in the direction of intended rotation. The PDC cutting elements are set outside the pass through diameter of a drill bit intended to be later run into the reaming tool for drillout, to facilitate the drillout process. Cutting elements of other materials, such as, for example, tungsten carbide (WC) may also be employed if suitable for the formation or formations to be encountered, these cutting elements again being set outside the pass through diameter. Radially outer faces of the blades along the tapered portion thereof are provided with a relatively thick layer of crushed tungsten carbide, placed rotationally behind the PDC cutting elements. Bearing elements in the form of, for example, tungsten carbide or PDC ovoids are disposed in recesses in the exterior surfaces of the blades, in the tapered portions thereof, the ovoids being overexposed (extending farther from the radially outer surface of the blades) than the PDC cutting elements and in locations rotationally behind the PDC cutting elements. The bearing elements and their relative exposure prevent potentially damaging contact between the PDC cutting elements and the interior of a larger tubular conduit through which the casing string is run before encountering the open, predrilled bore hole. The radially outer surfaces of the blades axially trailing the tapered portions bearing the PDC cutting elements are provided with a layer of tungsten carbide, at least along the rotationally leading and trailing edges of the blades. The longitudinally trailing ends of the blades may be tapered axially and radially inwardly toward the body, and provided with a relatively thick layer of crushed tungsten carbide. 
     The interior profile of the body is configured to optimize drillout by conventional rotary bits without leaving large segments of material of the remaining tool nose in the bore hole. 
     Referring now to  FIGS. 1 through 4  of the drawings, reaming tool  10  (in two slightly different embodiments, as respectively depicted in  FIGS. 1 and 2 ) comprises tubular body  12 , which may be formed of a single material, such as steel, aluminum, bronze or other suitably hard metal or alloy which is, nonetheless, easily drillable by conventional PDC or roller cone drill bits. The body  12  includes a nose  14 , which may be configured with a shallow, concave profile recessed toward the centerline of the reaming tool  10 . The concave profile may be a shallow cone, or other suitable concave profile. The nose  14  transitions into a side wall  16 , which tapers axially and radially outwardly toward a trailing end of body  10 , which is provided with structure, such as internal threads (not shown) for connecting reaming tool  10  to the leading end of a casing string. The transition between the nose  14  and side wall  16  comprises a transition shoulder wall  18  of substantially arcuate cross-section and which may or may not exhibit a constant radius of curvature. A central port P, opens from the interior of body  12  to the exterior on the nose  14 , and additional side ports P extend from the exterior to the interior of body  12  through transition shoulder wall  18 . 
     A plurality of blades  20  is disposed on the exterior of tubular body  12 , extending from a location proximate the trailing edge of the transition shoulder wall  18  with no standoff therefrom, and increasing in standoff as they taper radially outwardly as they extend toward their respective axially trailing ends to provide a radially outer surface of increasing diameter. The axially trailing ends of the blades  20  comprise beveled or chamfered surfaces  22  of decreasing diameter, extending to the exterior of the body  12 . The blades  20  are configured in a steeply pitched, spiral configuration on the exterior of the body  12 , the circumferential extent of each blade  20  being great enough to ensure complete, 360° coverage of the exterior of body  12  by the plurality of blades  20 . Junk slots  24  are defined on the exterior of side wall  16 , from a position proximate transition shoulder wall  18 , each junk slot  24  being circumferentially aligned with a side port P. Junk slots  24  initially increase in depth from their respective leading ends, following the increase in standoff of blades  20  and being defined between the side edges of the latter. 
     Superabrasive cutting elements in the form of PDC cutting elements  30  are disposed along the rotationally leading edges of each blade  20 . The PDC cutting elements  30  may comprise any suitable PDC cutting element configuration. One nonlimiting example of a suitable PDC cutting element is disclosed in U.S. Pat. No. 5,435,403, assigned to the Assignee of the present invention. As noted above, the PDC cutting elements  30  are set outside the pass through diameter of a drill bit intended to be later run into the reaming tool  10  for drillout, to facilitate the drillout process. It is also contemplated that superabrasive cutting elements other than PDC cutting elements, as well as cutting elements of other materials, may be employed in implementing the present invention. For example, thermally stable product (TSP) diamond cutting elements, diamond impregnated cutting segments, cubic boron nitride (CBN) cutting elements and tungsten carbide (WC) cutting elements may be utilized, in consideration of the characteristics of the formation or formations being reamed and the ability to employ relatively less expensive cutting elements when formation characteristics permit. 
     Radially outer surfaces  32  of the blades  20  along the tapered portion thereof are provided with a relatively thick layer of crushed tungsten carbide  34 , placed rotationally behind the PDC cutting elements  30 . In the embodiment of  FIG. 1 , the layer of crushed tungsten carbide  34  is relatively circumferentially wide, axially short and commences axially above about the mid-point of the row of PDC cutting elements  30 , while in the embodiment of  FIG. 2  it is placed in an elongated groove extending axially at least along the entire axial extent of PDC cutting elements  30 . Bearing elements  36  in the form of, for example, tungsten carbide ovoids are disposed in recesses in the exterior surfaces of the blades  20 , in the tapered portions thereof, circumferentially between the PDC cutting elements  30  and the relatively thick layer of crushed tungsten carbide  34 . It is also contemplated that other types and configurations of bearing elements may be employed, such as, for example, hemispherically headed PDC bearing elements, or bearing elements formed of other suitable materials. The radially outer surfaces  32  of blades  20  axially trailing the PDC cutting elements  30  are provided with one or more layers of tungsten carbide  38 . In the embodiment of  FIG. 1 , a layer of tungsten carbide  38  extends substantially over the entire radially outer surface  32  of each blade  20 , while in the embodiment of  FIG. 2  the tungsten carbide  38  is substantially disposed in two elongated layers in grooves extending along rotationally leading and trailing edges of blades  20 , the rotationally trailing layer of tungsten carbide  38  extending axially toward nose  14  so as to extend rotationally behind the relatively thick layer of tungsten carbide  34  with bearing elements  36  lying circumferentially therebetween. The axially trailing, beveled surfaces  22  at the ends of the blades  20  are provided with a relatively thick layer of crushed tungsten carbide  40 . 
     The nose  14  of the reaming tool  10  is configured with an analytically derived shell (wall) thickness, selected for ease of drillout. A minimum thickness is designed by finite element analysis (FEA) for the intended weight and torque to be applied to the reaming tool  10  during use. The thickness is optimized so that the design affords a safety factor of 2 to 3 over the desired loading parameters under which reaming tool  10  is to be run. 
     The concavity of the nose  14  may be varied in degree, providing the reaming tool  10  the ability to guide itself through a formation while allowing the nose portion to be drilled out without leaving large segments of material in the bore hole. It is also notable that the absence of blades  20  in the nose area projecting above the face of the nose  14  allows for an uninterrupted cut of material of the body shell in the nose, making the reaming tool  10  PDC bit-drillable. 
     As noted previously, the bearing elements  36 , comprising tungsten carbide ovoid-ended inserts or formed of other suitable materials, are overexposed with respect to the PDC cutting elements  30  as well as to the tungsten carbide layer  38 , to prevent damaging contact between the superabrasive cutting elements carried on blades  20  and the interior of casing or liner through which reaming tool  10  may be run. 
     The provision of both PDC cutting elements  30  as well as tungsten carbide layers  34 ,  38  and  40  enables rotational or reciprocating reaming. Full circumferential coverage of the carbide layers  34 ,  38  and  40  enables reciprocating reaming. The PDC cutting elements  30  enable aggressive, rotational reaming in a conventional (clockwise) direction. The carbide layers  34  and,  38 , which extend to the top of the gage on both the rotationally leading and trailing edges of the blades  20 , allow the reaming tool  10  to ream in a counterclockwise rotational direction as well. Blades  20  also incorporate tapered, rotationally leading edges to reduce reactive torque and reduce sidecutting aggressiveness. The thick layer of crushed tungsten carbide  40  on the axially trailing ends of the blades  20  provides an updrill reaming capability. 
     Referring now to  FIGS. 5A through 5C ,  FIG. 5A  depicts an outer, face cutter profile of a conventional PDC rotary drag bit D disposed within body  12  of reaming tool  10  before rotary drag bit D engages the inner surface IS of nose  14 . The PDC cutting elements carried on the face of rotary drag bit D and which together exhibit a cutter profile CP substantially the same as face profile while being exposed thereabove, have been omitted for clarity. In  FIG. 5B , rotary drag bit D has engaged the inner surface IS of nose  14 , and has partially drilled therethrough. As can be seen, the inner surface IS of central, concave portion of nose  14  exhibits a similar cone angle to that of cutter profile CP, while the outer surface OS thereof exhibits a steeper cone angle, resulting in a thinner shell proximate the centerline L of reaming tool  10 , and ensuring that the portion of nose  14  will be drilled out from centerline L toward transition shoulder wall  18 , which will be drilled out last, ensuring the absence of any large material segments from nose  14 . As noted previously, the PDC cutting elements  30  (not shown in  FIGS. 5A through 5C ) are completely removed from and radially outward of the drillout diameter of rotary drag bit D.  FIG. 5C  depicts completion of drillout of the concave portion of nose  14  and partial drillout of transition shoulder wall  18 , the radially inward-to-outward drillout pattern ensuring that no uncut segments of nose  14  remain after drillout. 
     While the present invention has been described in the context of an illustrated, example embodiment, those of ordinary skill in the art will recognize and appreciate that the invention is not so limited. Additions and modifications to, and deletions from, the described embodiments within the scope of the invention will be readily apparent to those of ordinary skill in the art.