Abstract:
Casing bits include an expander for enlarging an inner diameter of expandable casing at least partially disposed within a body of the casing bits. Drilling assemblies include a casing bit attached to an end of expandable casing, and an expander disposed in proximity to the casing bit and a distal end of the expandable casing. Methods of forming casing bits include positioning an expander in proximity to a body of a casing bit. Methods of forming drilling assemblies include positioning an expander in proximity to a body of a casing bit and a distal end of expandable casing, and attaching the casing bit to the end of the expandable casing. Methods of casing a wellbore include one or both of drilling and reaming a wellbore using a casing bit attached to a distal end of expandable casing, and forcing an expander through the expandable casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/174,825, filed May 1, 2009 and entitled “Casing Bits, Drilling Assemblies, and Methods for Use In Forming Wellbores With Expandable Casing,” the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present invention relate to casing bits, drilling assemblies, and methods that may be used to form wellbores using expandable casing. 
       BACKGROUND 
       [0003]    Wellbores are formed in subterranean formations for various purposes including, for example, extraction of oil and gas from the subterranean formation and extraction of geothermal heat from the subterranean formation. A wellbore may be formed in a subterranean formation using a drill bit such as, for example, an earth-boring rotary drill bit. Different types of earth-boring rotary drill bits are known in the art including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), rolling-cutter bits (which are often referred to in the art as “rock” bits), diamond-impregnated bits, and hybrid bits (which may include, for example, both fixed cutters and rolling cutters). The drill bit is rotated and advanced into the subterranean formation. As the drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore. A diameter of the wellbore drilled by the drill bit may be defined by the cutting structures disposed at the largest outer diameter of the drill bit. 
         [0004]    The drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a “drill string,” which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of the formation. Various tools and components, including the drill bit, may be coupled together at the distal end of the drill string at the bottom of the wellbore being drilled. This assembly of tools and components is referred to in the art as a “bottom hole assembly” (BHA). 
         [0005]    The drill bit may be rotated within the wellbore by rotating the drill string from the surface of the formation, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is also coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is mounted, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore. 
         [0006]    It is known in the art to use what are referred to in the art as a “reamer” devices (also referred to in the art as “hole opening devices” or “hole openers”) in conjunction with a drill bit as part of a bottom hole assembly when drilling a wellbore in a subterranean formation. In such a configuration, the drill bit operates as a “pilot” bit to form a pilot bore in the subterranean formation. As the drill bit and bottom hole assembly advances into the formation, the reamer device follows the drill bit through the pilot bore and enlarges the diameter of, or “reams,” the pilot bore. 
         [0007]    After drilling a wellbore in a subterranean earth-formation, it may be desirable to line the wellbore with sections of casing or liner. Casing is relatively large diameter pipe (relative to the diameter of the drill pipe of the drill string used to drill a particular wellbore) that is assembled by coupling casing sections in an end-to-end configuration. Casing is inserted into a previously drilled wellbore, and is used to seal the walls of the subterranean formations within the wellbore. The casing then may be perforated at one or more selected locations within the wellbore to provide fluid communication between the subterranean formation and the interior of the wellbore. Casing may be cemented in place within the wellbore. The term “liner” refers to casing that does not extend to the top of a wellbore, but instead is anchored or suspended from inside the bottom of another casing string or section previously placed within the wellbore. As used herein, the terms “casing” and “casing string” each include both casing and liner, and strings respectively comprising sections of casing and liner. 
         [0008]    As casing is advanced into a wellbore, it is known in the art to secure a cap structure to the distal end of the distal casing section in the casing string (the leading end of the casing string as it is advanced into the wellbore). As used herein, the term “distal” means distal to the earth surface into which the wellbore extends (i.e., the end of the wellbore at the surface), while the term “proximal” means proximal to the earth surface into which the wellbore extends. The casing string, with the casing bit attached thereto, optionally may be rotated as the casing is advanced into the wellbore. In some instances, the cap structure may be configured as what is referred to in the art as a casing “shoe”, which is primarily configured to guide the casing into the wellbore and ensure that no obstructions or debris are in the path of the casing, and to ensure that no debris is allowed to enter the interior of the casing as the casing is advanced into the wellbore. The “shoe” may conventionally contain a check valve, termed a “float valve,” to prevent fluid in the wellbore from entering the casing from the bottom, yet permit cement to be subsequently pumped down into the casing, out the bottom through the shoe, and into the wellbore annulus to cement the casing in the wellbore. 
         [0009]    In other instances, the casing cap structure may be configured as a reaming bit or “shoe,” which serves the same purposes of a casing shoe, but is further configured for reaming (i.e., enlarging) the diameter of an existing wellbore as the casing is advanced into the wellbore. It is also known to employ drill bits configured to be secured to the distal end of a casing string for drilling a wellbore. Drilling a wellbore with such a drill bit attached to casing is referred to in the art as “drilling with casing.” Such reaming bits or shoes, as well as such drill bits, may be configured and employ materials in their structures to enable subsequent drilling therethrough from within using a drill bit run down the casing or liner string. As used herein, the term “casing bit” means and includes such casing bits as well as such reaming bits and shoes configured for attachment to a distal end of casing as the casing is advanced into a wellbore. 
       BRIEF SUMMARY 
       [0010]    In some embodiments, the present invention includes casing bits having a body and at least one cutting structure on an outer surface of the body. The casing bits further include an expander at least partially disposed within the body. The expander is sized and configured to expand expandable casing to which the casing bit is secured as the expander is forced longitudinally through the expandable casing. 
         [0011]    In additional embodiments, the present invention includes drilling assemblies having a casing bit attached to an end of at least one section of expandable casing. The casing bit has a body and at least one cutting structure on an outer surface of the body. An expander is disposed within at least one of the casing bit and the end of the section of expandable casing. The expander is sized and configured to expand expandable casing as the expander is forced longitudinally through the expandable casing. 
         [0012]    In additional embodiments, the present invention includes methods of forming casing bits. To form a casing bit, an expander may be configured to enlarge at least an inner diameter of expandable casing as the expander is forced through the expandable casing, and the expander may be positioned at least partially within a body of the casing bit. 
         [0013]    In additional embodiments, the present invention includes methods of forming drilling assemblies. In accordance with such methods, an expander may be positioned within at least one of a body of a casing bit and an adjacent end of a section of expandable casing, and the body of the casing bit may be attached to the end of the section of expandable casing. The expander may be configured to enlarge at least an inner diameter of expandable casing as the expander is forced through the expandable casing. 
         [0014]    Yet further embodiments of the present invention include methods of casing a wellbore. A wellbore may be drilled and/or reamed using a casing bit attached to a distal end of at least one section of expandable casing. An expander disposed within at least one of the casing bit and the distal end of the section of expandable casing may be forced longitudinally through the section of expandable casing in a proximal direction. As the expander is forced through the expandable casing, at least an inner diameter of the expandable casing may be enlarged. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIGS. 1A through 1F  are simplified, schematic cross-sectional views of a wellbore and equipment therein illustrating a method that may be used to drill a wellbore using a casing bit on expandable casing, and subsequently expanding the expandable casing within the wellbore; 
           [0016]      FIG. 2  is a simplified cross-sectional view of an embodiment of a casing bit of the present invention; 
           [0017]      FIG. 3  is a simplified cross-sectional view of another embodiment of a casing bit of the present invention; 
           [0018]      FIG. 4  is a side view of an embodiment of an outer body of a casing bit of the present invention; and 
           [0019]      FIG. 5  is a side view of another embodiment of an outer body of a casing bit of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The illustrations presented herein are not actual views of any particular drilling system, drilling tool assembly, or component of such an assembly, but are merely idealized representations which are employed to describe the present invention. 
         [0021]    Embodiments of the present invention may be used to drill or ream a wellbore with expandable casing using a casing bit attached to the expandable casing, and to subsequently expand (i.e., enlarge at least an inner diameter of) the expandable casing without tripping the casing bit out from the wellbore. 
         [0022]    An embodiment of a method of the present invention that may be used to form or enlarge at least a section of a wellbore and position casing within the section of the wellbore is described below with reference to  FIGS. 1A through 1F . 
         [0023]    Referring to  FIG. 1A , a drilling assembly may be provided that includes a casing bit  10  attached to a distal end  12  of expandable casing  14 . The expandable casing  14  with the casing bit  10  thereon may be advanced into a previously drilled wellbore  16 . As discussed in further detail below with reference to  FIG. 4 , the casing bit  10  may comprise one or more cutting structures configured for at least one of reaming and drilling a wellbore  16 . The cutting structure or structures may comprise any conventional abrasive or superabrasive material suitable for removing material from the particular formation being reamed or drilled. In some embodiments, at least a portion of the wellbore  16  may have been lined with additional casing  18  prior to advancing the expandable casing  14  into the wellbore  16 . The expandable casing  14  may be advanced into the wellbore  16  until the casing bit  10  is positioned at the bottom of the previously drilled section of the wellbore  16 . The expandable casing  14  and the casing bit  10  attached to the distal end  12  of the expandable casing  14  then may be rotated within the wellbore  16  as axial force, termed “weight on bit” (WOB), is applied to the expandable casing  14  and the casing bit  10  to cause the casing bit  10  to drill an additional section  20  of the wellbore  16  into the subterranean formation  22 . 
         [0024]    The drilling assembly may be rotated within the wellbore  16  by rotating the expandable casing  14  from the surface of the formation, or the drilling assembly may be rotated by coupling the expandable casing  14  to a downhole motor. The motor also may be coupled to a drill string and disposed within the wellbore  16 . The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the expandable casing  14  is attached. The drive shaft and the expandable casing  14  may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, through the expandable casing  14 , through the casing bit  10 , out through fluid passageways extending through the casing bit, and back up to the surface of the formation through the annular space between the outer surface of the expandable casing  14  and the exposed surface of the formation within the wellbore  16 . 
         [0025]    With continued reference to  FIG. 1A , the drilling assembly further includes an expander  24  that may be disposed within and attached to at least one of the casing bit  10  and the expandable casing  14  at a location proximate the distal end  12  of the expandable casing  14 . The expander  24  is sized and configured to expand the diameter of the expandable casing  14  as the expander  24  is forced longitudinally through the interior of the expandable casing  14 . By way of example and not limitation, the expander  24  may be a generally cylindrical, tubular member. A fluid passageway may extend longitudinally through the length of the expander  24 . A tapered, frustoconical surface may be provided on a proximal end of the expander  24  to facilitate the smooth, gradual expansion of the expandable casing  14  as the expander  24  is forced through the casing  14 . The expander  24  may comprise, for example, a metal alloy exhibiting a yield strength sufficiently high that the expander  24  will not undergo any significant plastic deformation, and sufficiently low elastic deformation to allow complete expansion of the expandable casing  14 , as the expander  24  is forced longitudinally through the expandable casing  14 . 
         [0026]    In some embodiments, the expander  24  initially may be partially disposed within an interior region of the casing bit  10 , and partially within an interior region of the distal end  12  of the expandable casing  14 . In additional embodiments, the expander  24  initially may be entirely disposed within an interior region of the casing bit  10 , or entirely within an interior region of the distal end  12  of the expandable casing  14 . 
         [0027]    The expandable casing  14  may comprise a metal alloy having a material composition selected to allow the expandable casing  14  to expand plastically as the expander  24  is forced therethrough. The ultimate strength of the material of the expandable casing  14  should be sufficiently high to prevent the expandable casing  14  from rupturing as the expander  24  is forced through the expandable casing  14 . 
         [0028]    After drilling an additional section  20  of the wellbore  16  using the casing bit  10 , a liquid cement or other hardenable material may be pumped through the expandable casing  14 , and out from the casing bit  10  through fluid passageways  30  extending therethrough, into the annulus between the formation and the casing. The cement or other hardenable material may have a composition selected to harden only after expansion of the expandable casing  14 , as described below. The volume of cement pumped into the annulus may be selected to fill the ultimate volume of the annulus that will be present after expansion of the expandable casing  14 . Initially, when such a volume of cement is pumped into the annulus, it may not surround the casing  14  along the entire length thereof. Upon expansion of the expandable casing  14 , however, the expanding casing  14  may squeegee the cement along the length of the casing  14  to surround the expanded casing  14  along substantially the entire length thereof. The cement may be allowed to solidify within the annular space after expansion of the casing  14 , thereby affixing the expandable casing  14  in place within the wellbore  16 . 
         [0029]    Referring to  FIG. 1B , a pipeline  26  (e.g., a drill string, coiled tubing, a parasitic string, etc.) may be advanced through the interior of the expandable casing  14  and attached to the expander  24 . One or more centralizer devices  65  such as, for example, centralizer springs, may be used to position (e.g., center) the pipeline  26  within the expandable casing  14 . By way of example and not limitation, a threaded pin  28  may be provided on a proximal end of the expander  24 . The threaded pin  28  may be configured to matingly engage a threaded box on a distal end of the pipeline  26 . Thus, the pipeline  26  may be rotated to thread the distal end of the pipeline  26  onto the threaded pin  28  on the expander  24 . Of course, a threaded box may be used on a proximal end of the expander  24 , and a threaded pin on the distal end of the pipeline  26 . In additional embodiments, mechanical attachment between the pipeline  26  and the expander  24  may be obtained using other connection configurations known in the art that require little or no relative rotation between the pipeline and the expander  24 . Many such connections are known in the art and may be employed in embodiments of the present invention. Some such connections are referred to in the art as mechanical “stingers,” and include complementary male and female connection portions (one being provided on the pipeline  26  and the other on the expander  24 ) that mechanically interlock with one another upon insertion of the male connector into the female connector. 
         [0030]    In additional embodiments of the invention, the pipeline  26  (or another type of string) may be attached to the expander  24  prior to drilling the additional section  20  of the wellbore  16  with the casing bit  10  and expandable casing  14 . 
         [0031]    Referring to  FIG. 1C , fluid passageways  30  extending through the casing bit  10  may be plugged. By way of example and not limitation, a plug  32  (e.g., an elongated body, a generally spherical ball, or a dart) may be pumped down through the pipeline  26 , through the expander  24 , and into a receptacle  34  in the casing bit  10  configured to receive the plug  32 , in the manner of a float plug engaging a float shoe. The receptacle  34  may be configured to lockingly engage, and retain therein, the plug  32  to prevent backflow into expandable casing  14  from the wellbore. The casing bit  10  may be configured such that fluid flow through the fluid passageways  30  in the casing bit  10  is interrupted when the plug  32  is disposed and seated within the receptacle  34 . 
         [0032]    Referring to  FIG. 1D , the expander  24  may be forced longitudinally through the expandable casing  14  from the distal end  12  thereof toward a proximal end  36  thereof. The expander  24  may be forced through the expandable casing  14  by pulling the expander  24  through the expandable casing  14  using the pipeline  26  (i.e., by mechanical force), by pumping hydraulic fluid down through the pipeline  26  and into a space  37  distal to the expander  24  at relatively high pressure such that the hydraulic pressure distal to the expander  24  forces the expander  24  through the expandable casing  14  in the proximal direction (i.e., by hydraulic pressure), or by a combination of such methods (i.e., by a combination of mechanical force and hydraulic pressure). 
         [0033]      FIG. 1D  illustrates the expander  24  at a relatively lower intermediate location within the expandable casing  14 . As shown in  FIG. 1D , the section of the expandable casing  14  distal to the expander  24  has a relatively larger expanded inner diameter D E , while the section of the expandable casing  14  proximal to the expander  24  has a relatively smaller unexpanded inner diameter D U . In some embodiments, D E  may be about 105% or more of D U . In additional embodiments, D E  may be about 110% or more of D U , or even about 120% or more of D U . 
         [0034]    As the inner diameter of the expandable casing  14  is expanded from D U  to D E , the overall length of the expandable casing  14  may decrease, the wall thickness of the expandable casing  14  may decrease, or both the overall length and the wall thickness of the expandable casing  14  may decrease. Thus, a desirable final length and a desirable final wall thickness may be considered together with the degree to which the overall length and the wall thickness of the expandable casing  14  decrease upon expansion thereof by the expander  24  when designing an initial, unexpanded section of expandable casing  14  for a particular application. 
         [0035]      FIG. 1E  is similar to  FIG. 1D , but illustrates the expander  24  at a relatively higher intermediate location within the expandable casing  14 . 
         [0036]      FIG. 1F  illustrates the expandable casing  14  after the expander  24  has been passed entirely through the expandable casing  14 , such that the entire length of the casing  14  has been expanded from the relatively smaller unexpanded inner diameter D U  to the relatively larger expanded inner diameter D E , and the expander  24  has been removed from the wellbore  16 . Upon expansion of the proximal end  36  of the expandable casing  14 , the outer surface  38  of the expandable casing  14  at the proximal end  36  thereof may be forced against an inner surface  40  of a previously placed section of additional casing  18 . Optionally, one or more sealing materials may be provided between the outer surface  38  of the expandable casing  14  and the inner surface  40  of the additional casing  18  to ensure that an adequate seal results therebetween upon expansion of the expandable casing  14  by the expander  24 . 
         [0037]    After expanding the expandable casing  14  and removing the expander  24  from the wellbore  16  to provide a structure like that shown in  FIG. 1F , the wellbore  16  may be prepared for production by, for example, perforating the casing  14  and/or the casing  18  at one or more locations along the wellbore  16  within producing regions of the formations. In additional embodiments, an additional section of the wellbore  16  may be drilled distal to the expanded casing  14  using another drill bit to drill through the remaining portions of the casing bit  10  at the distal end of the wellbore  16 . As described in further detail below, the casing bit  10  may be configured to facilitate drilling therethrough by another drill bit. In some embodiments, another casing bit  10  and another section of expandable casing  14  having a relatively smaller outer diameter may be used to drill through the casing bit  10  shown in  FIG. 1F , after which the other section of expandable casing  14  also may be expanded. This process may be repeated as desirable until the wellbore  16  reaches a desirable or limited depth. 
         [0038]      FIG. 2  is an enlarged, simplified, cross-sectional view of an embodiment of a casing bit  10  of the present invention that may be used to position expandable casing  14  within a wellbore  16 , as previously discussed in relation to  FIGS. 1A through 1F . 
         [0039]    As shown in  FIG. 2 , the casing bit  10  has an outer bit body  50 . The outer body  50  may comprise, for example, a metal alloy or a composite material having physical properties that include a strength sufficient to enable the casing bit  10  to be used for drilling, reaming, or both drilling and reaming, but that also allow the outer body  50  to be subsequently drilled through by another drill bit. A plurality of cutting structures for drilling and/or reaming may be provided on an exterior surface of the outer body  50 , as described below, although such cutting structures are not illustrated in the simplified view of  FIG. 2 . By way of example and not limitation, the outer body  50  may comprise an outer body as described in U.S. patent application Ser. No. 11/747,651, which was filed May 11, 2007 and entitled “Reaming Tool Suitable For Running On Casing Or Liner And Method Of Reaming” (U.S. Patent Application Publication No. US 2007/0289782 A1, published Dec. 20, 2007), or as described in U.S. Pat. No. 7,395,882 B2, which issued on Jul. 8, 2008 to Oldham et al., each of which is incorporated herein in its entirety by this reference. 
         [0040]    An expander  24  may be at least partially disposed within the outer body  50 . In the embodiment of  FIG. 2 , the expander  24  is partially disposed within the outer body  50 , but protrudes from a proximal end of the outer body  50 . In other embodiments, the expander  24  may be substantially entirely disposed within the outer body  50 , or the expander  24  may be disposed substantially entirely outside the outer body  50  and attached to a proximal end  52  of the outer body  50 . 
         [0041]    Optionally, the expander  24  may be attached to the outer body  50 . As a non-limiting example, one or more shear pins  54  may be used to attach the expander  24  to the outer body  50 . The shear pins  54  may extend at least partially through the outer body  50  and at least partially through the expander  24 . The shear pins  54  may be sized and configured to shear apart (i.e., fail) when a predetermined force is applied between the expander  24  and the outer body  50  in the longitudinal direction, as occurs when the expander  24  begins to be forced through expandable casing  14  ( FIGS. 1A-1F ) to which the casing bit  10  is attached. To prevent the shear pins  54  from damaging the casing  14  as the expander is forced therethrough, the shear pins  54  may comprise a relatively soft metal alloy or a polymer material, and/or the shear pins  54  may be configured to fail at a location recessed relative to the outer surface of the expander. In yet further embodiments, the shear pins  54  could be disposed at other locations and orientations such that, upon failure of the shear pins  54 , no portion of the shear pin  54  would rub against the casing  14  as the expander  24  is forced through the casing  14 . In other embodiments, a snap ring, or another type of fastener, may be disposed between the inner surface of the outer body  50  and an exterior surface of the expander  24 , and may be configured to be retained within the outer body  50  when sufficient force is applied between the expander  24  and the body  50  to longitudinally separate the same. In a broad sense, structure securing the expander  24  to the outer body  50  may be designed and configured to fail and permit release of expander  24  from the outer body responsive to at least one selected condition applied thereto. Such a condition may include, without limitation, tension, shear, torsion, compression and hydraulic pressure. 
         [0042]    In additional embodiments, the expander  24  may not be fixedly attached to the outer body  50 , and may simply be retained in position relative to the outer body  50  upon attachment of the casing bit  10  to the expandable casing  14  due to mechanical interference between the expander  24  and the outer body  50  and between the expander  24  and the expandable casing  14 . In some embodiments, the expander  24  may be retained snugly so that the expander  24  is substantially restrained from longitudinal movement (e.g., in the distal or proximal directions). In other embodiments, the expander  24  may be retained with some amount of extra longitudinal space allowing the expander  24  to longitudinally separate from the outer body  50  to provide a net force acting on the expander  24  in the proximal longitudinal direction when a fluid is pressurized, as discussed below. 
         [0043]    As previously described, the expander  24  may comprise a tapered, frustoconical surface  56  on a proximal end  58  of the expander  24  to facilitate the smooth, gradual expansion of the expandable casing  14  as the expander  24  is forced through the expandable casing  14  to expand the same. Furthermore, the expander  24  may comprise at least one feature  60  that may be matingly engaged by a string or pipeline (e.g., a drill string, coiled tubing, a parasitic string, a so-called “fishing string,” etc.). By way of example and not limitation, the feature  60  may comprise a threaded pin  28  provided on the proximal end  58  of the expander  24 . As previously discussed, the threaded pin  28  may be configured to matingly engage a threaded box on a distal end of a string such as, for example, a pipeline  26 . Also as previously discussed, it is contemplated that expander  24  may instead comprise a threaded box engageable by a threaded pin at a distal end of pipeline  26  by stabbing the pin into the box and rotating the pipeline. As another alternative, a stinger at the distal end of pipeline  26  may lockingly engage complementary structure of a receptacle at the proximal end of the expander  24 , such complementary structures being known to those of ordinary skill in the art. 
         [0044]    In some embodiments, the expander  24  may comprise a fluid passageway  62  that extends longitudinally through the expander  24 . Furthermore, the expander  24  may have a shape configured to define at least one cavity  64  when the expander  24  is positioned within the casing bit  10 . The cavity  64  may be located and shaped to allow fluid to flow into the cavity  64  from the fluid passageway  62  when fluid is pumped in the distal direction down through the expander  24  through the fluid passageway  62 . The shape of the cavity  64  may be configured to provide a net force acting on the expander  24  in the proximal longitudinal direction when fluid within the fluid passageway  62  and the cavity  64  is pressurized. In some configurations of the casing bit  10 , in the absence of such a cavity  64 , such a net force might not result when the fluid passageway  62  is pressurized until at least some degree of longitudinal separation is attained between the expander  24  and the outer body  50 . The expander  24  may also include one or more fluid ports  34  that extend longitudinally through the expander  24 . These fluid ports  34  are located remote from the fluid passageway  62 , and allow for fluid communication between the spaces within the wellbore above and below the expander  24  to allow fluid above the expander  24  to flow through the expander  24  through the fluid ports  34  to the space below the expander  24  as the expander  24  is forced upward through expandable casing in the wellbore. 
         [0045]    With continued reference to  FIG. 2 , in some embodiments, the casing bit  10  may further comprise an inner body  70 . The inner body  70  may comprise a separate body from the outer body  50 . In such embodiments, the inner body  70  may comprise a material differing from a material of the outer body  50 . For example, the material of the inner body  70  may comprise a metal alloy, a polymer material, or a composite material that is relatively softer and/or of lower strength relative to the outer body  50 . The inner body  70  may not be subjected to the vigorous forces and stresses to which the outer body  50  is subjected during drilling, and, hence, it may be desirable to form the inner body  70  from a material that is relatively easier to subsequently drill through (relative to the outer body  50 ) using another drill bit. 
         [0046]    In additional embodiments, however, the outer body  50  and the inner body  70  may simply be different regions of a common, integral (i.e., monolithic), substantially homogenous body formed of and comprising materials suitable for use as the outer body  50 . 
         [0047]    One or more fluid passageways  30  may extend through the casing bit  10  to allow fluid to be pumped through the expander  24  and out from the casing bit  10  through the fluid passageways  30  during a drilling process. A section of each of the fluid passageways  30  may extend through the inner body  70 , and another section of each of the fluid passageways  30  may extend through the outer body  50 . Each of the fluid passageways  30  may lead to, or pass through, a receptacle  34 , as mentioned above, configured to receive a plug  32  ( FIGS. 1C-1F ) therein for plugging the fluid passageways  30 . The plug  32  also may comprise a material that is relatively easy to subsequently drill through using another drill bit, but that has physical properties sufficient to plug the fluid passageways  30  and withstand the fluid pressure differential across the plug  32  that results upon pressurization of the space  37  ( FIGS. 1D and 1E ) distal to the expander  24  but proximal to the casing bit  10  when the expander  24  is being forced through expandable casing  14 . 
         [0048]    The casing bit  10  may be secured to a distal end  12  of a section of expandable casing  14  by, for example, welding the outer body  50  of the casing bit  10  to the distal end  12  of the expandable casing  14 . In additional embodiments, complementary threads may be formed on the casing bit  10  and the distal end  12  of the expandable casing  14 , and the casing bit  10  may be threaded to the distal end  12  of the expandable casing  14  to secure the casing bit  10  to the expandable casing  14 . In such embodiments, the interface between the casing bit  10  and the expandable casing  14  optionally may be welded to further secure the casing bit  10  to the expandable casing  14  and threading the casing bit  10  to the expandable casing  14 . Other methods such as, for example, brazing, also may be used to secure the casing bit  10  to the expandable casing  14 . 
         [0049]    In yet additional embodiments of the present invention, the expander  24  may be disposed between (e.g., located at least substantially entirely between) the casing bit  10  and the distal end  12  of the expandable casing  14 . For example, a separate, additional sub (e.g., a generally tubular component comprising an inner cavity in which the expander  24  may be disposed) may be provided between the casing bit  10  and the distal end  12  of the expandable casing  14 , and the expander  24  may be positioned within, and optionally secured within, the separate, additional sub. Referring to  FIG. 2 , the portion of the outer body  50  proximal to the dashed lines  67  shown therein may comprise a separate, additional sub in which the expander  24  may be disposed and secured. Such a separate, additional sub may be attached to the casing bit  10  at the location of the dashed lines  67  in manners like those previously described for attaching the distal end  12  of the expandable casing  14  to the casing bit  10  (e.g., one or more of welding, threading, brazing, etc.). The sub could also extend further in the proximal direction such that the expander  24  is at least substantially entirely contained within the sub. 
         [0050]      FIG. 3  is an enlarged, simplified, cross-sectional view of another embodiment of a casing bit  10 ′ of the present invention that may be used to position expandable casing  14  within a wellbore  16 , as previously discussed in relation to  FIGS. 1A through 1F . 
         [0051]    As shown in  FIG. 3 , the casing bit  10 ′ is similar to the casing bit shown in  FIG. 2  and includes an outer bit body  50  and an expander  24 , as discussed hereinabove. However, the casing bit  10 ′ comprises a substantially hollow portion  66  inside of the bit body  50 . The hollow portion  66  is bounded by the bit body  50  at the distal end and around the sides thereof, and by a plate  68  at a proximal end thereof. The plate  68  may comprise a separate body fixedly attached to the outer body  50 . The plate  68  may be positioned so that a distal end of the expander  24  is adjacent a proximal side of the plate  68 . The plate  68  may be fixedly attached to the outer body  50 , for example, by welding the plate  68  to the outer body  50 , using an adhesive, or other known means, as well as combinations thereof. In some embodiments, a shoulder may be formed on the inner surface of the body  50 , such that the plate  68  may rest on the shoulder within the outer body  50 . In such embodiments, the plate  68  also may be welded or otherwise attached to the outer body  50 . The plate  68  may comprise a metal alloy, a polymer material, or a composite material that is relatively softer and/or of lower strength relative to the outer body  50 . The material of the plate  68  may be selected so as to be sufficiently strong and erosion resistant to prevent the plate  68  from damage by hydraulic flow and pressure during drilling operations, but not too strong or wear resistant to prevent subsequent drilling through the plate  68  by another drill bit or tool, as previously discussed. 
         [0052]    In additional embodiments, however, the outer body  50  and the plate  68  may simply be different regions of a common, integral (i.e., monolithic), substantially homogenous body formed of and comprising materials suitable for use as the outer body  50 . 
         [0053]    The plate  68  may have substantially planar sides in some embodiments. In other embodiments, one or both sides of the plate  68  may be non-planar. The plate  68  includes an aperture  72  that extends through a portion thereof. The aperture  72  allows fluid to be pumped through the expander  24  to the fluid passageways  30  during drilling. The aperture  72  may be configured to receive a plug (e.g., ball or dart) trap assembly  74  therein that is configured to receive a plug  32  ( FIGS. 1C-1F ) therein for plugging the hollow portion  66  and inhibiting flow to the hollow portion  66  and the fluid passageways  30 . In some embodiments, the aperture  72  is threaded to receive a plug trap assembly  74  having complementary threads thereon. The plug  32  also may comprise a material that is relatively easy to subsequently drill through using another drill bit, but that has physical properties sufficient to plug the plug trap assembly  74  and withstand the fluid pressure differential across the plug  32  that results upon pressurization of the space  37  ( FIGS. 1D and 1E ) distal to the expander  24  but proximal to the plate  68  when the expander  24  is being forced through expandable casing  14 . 
         [0054]    One or more fluid passageways  30  may extend through the casing bit  10 ′ to allow fluid to be pumped through the expander  24  and the plate  68  and out from the casing bit  10 ′ through the fluid passageways  30  during a drilling process. A section of each of the fluid passageways  30  may extend through the outer body  50  and in communication with the hollow portion  66 . During drilling, a drilling fluid may be pumped through the fluid passageway  62  and the aperture  72  into the hollow portion  66  and out through the fluid passageways  30 . 
         [0055]    As discussed above, the expander  24  may comprise a fluid passageway  62  that extends longitudinally through the expander  24  in some embodiments. Furthermore, the expander  24  may have a shape configured to define at least one cavity  64 ′ when the expander  24  is positioned within the casing bit  10 ′. The cavity  64 ′ may be located and shaped to allow fluid to flow into the cavity  64 ′ from the fluid passageway  62  when fluid is pumped in the distal direction down through the expander  24  through the fluid passageway  62 . The shape of the cavity  64 ′ may be configured to provide a net force acting on the expander  24  in the proximal longitudinal direction when fluid within the fluid passageway  62  and the cavity  64 ′ is pressurized. In some configurations of the casing bit  10 ′, in the absence of such a cavity  64 ′, such a net force might not result when the fluid passageway  62  is pressurized until at least some degree of longitudinal separation is attained between the expander  24  and the plate  68 . 
         [0056]    The casing bit  10 ′ may be secured to a distal end  12  of a section of expandable casing  14  by, for example, welding the outer body  50  of the casing bit  10 ′ to the distal end  12  of the expandable casing  14 . In additional embodiments, complementary threads may be formed on the casing bit  10 ′ and the distal end  12  of the expandable casing  14 , and the casing bit  10 ′ may be threaded to the distal end  12  of the expandable casing  14  to secure the casing bit  10 ′ to the expandable casing  14 . In such embodiments, the interface between the casing bit  10 ′ and the expandable casing  14  optionally may be welded to further secure the casing bit  10 ′ to the expandable casing  14  and threading the casing bit  10 ′ to the expandable casing  14 . Other methods such as, for example, brazing, also may be used to secure the casing bit  10 ′ to the expandable casing  14 . 
         [0057]      FIG. 4  illustrates an embodiment of an outer body  50 ′ of a casing bit  10  ( FIG. 2 ) of the present invention. A casing bit  10 ,  10 ′ comprising an outer body  50 ′ as shown in  FIG. 4  comprises a casing drilling bit, and may be used to drill with expandable casing  14  attached thereto. The outer body  50 ′ may be formed of and comprise, for example, a metal or metal alloy (e.g., steel, aluminum, brass, or bronze), or a composite material including particles of a relatively harder material (e.g., tungsten carbide) embedded within a relatively softer metal or metal alloy (e.g., steel, aluminum, brass, or bronze). The material of the outer body  50 ′ may be selected to exhibit physical properties that allow the outer body  50 ′ to be drilled through by another drill bit after the casing bit  10  has been used to advance a section of expandable casing attached thereto into a subterranean formation. 
         [0058]    Cutting structures may be provided on exterior surfaces of the outer body  50 ′. For example, the outer body  50 ′ may comprise a plurality of blades  80  that define fluid courses  82  therebetween. Fluid passageways  30  may be formed through the outer body  50 ′ or allowing fluid (e.g., drilling fluid and/or cement) to be pumped through the interior of the casing bit  10 ,  10 ′, out through the fluid passageways  30 , and into the annulus between the wall of the formation in which the wellbore  16  is formed and the exterior surfaces of the casing bit  10 ,  10 ′ and the expandable casing  14  to which the casing bit  10 ,  10 ′ may be attached. Optionally, nozzles (not shown) may be secured to the outer body  50 ′ within the fluid passageways  30  to selectively tailor the hydraulic characteristics of the casing bit  10 ,  10 ′. Cutting element pockets may be formed in the blades  80 , and cutting elements  86 , such as, for example, polycrystalline diamond compact (PDC) cutting elements, may be secured within the cutting element pockets. 
         [0059]    Also, each of blades  80  may include a gage region  88  that together define the largest diameter of the outer body  50 ′ and, thus, the diameter of any wellbore  16  formed using the outer body  50 ′ and the casing bit  10 ,  10 ′. The gage regions  88  may be longitudinal extensions of the blades  80 . Wear resistant structures or materials may be provided on the gage regions  88 . For example, tungsten carbide inserts, cutting elements, diamonds (e.g., natural or synthetic diamonds), or hardfacing material may be provided on the gage regions  88  of the outer body  50 ′. 
         [0060]    In some instances, the size and placement of the fluid passageways  30  that are employed for drilling operations may not be particularly desired for cementing operations. Furthermore, the fluid passageways  30  may become plugged or otherwise obstructed during a drilling operation. As shown in  FIG. 4 , the outer body  50 ′ of the casing bit  10 ,  10 ′ may include one or more frangible regions  85  that can be breached (e.g., a metal disc that can be fractured, perforated, ruptured, removed, etc.) to form one or more additional apertures that may be used to provide fluid communication between the interior and the exterior of the outer body  50 ′. Drilling fluid and/or cement optionally may be caused to flow through such frangible regions  85  after breaching the same. 
         [0061]    In additional embodiments, the outer body  50 ′ may not include blades  80  and cutting elements  86 , like those shown in  FIG. 4 . Furthermore, the outer body  50 ′ may comprise other cutting structures such as, for example, deposits of hardfacing material (not shown) on the exterior surfaces of the outer body  50 ′. Such a hardfacing material may comprise, for example, hard and abrasive particles (e.g., diamond, boron nitride, silicon carbide, carbides or borides of titanium, tungsten, or tantalum, etc.) embedded within a metal or metal alloy matrix material (e.g., an iron-based, cobalt-based, or nickel-based metal alloy). 
         [0062]      FIG. 5  illustrates another example embodiment of an outer body  50 ″ of a casing bit  10 ,  10 ′ ( FIGS. 2 and 3 ) of the present invention. A casing bit  10 ,  10 ′ comprising an outer body  50 ″ as shown in  FIG. 5  comprises a casing reaming bit, and may be used to ream a previously drilled wellbore  16  as the casing reaming bit is advanced into the wellbore  16  on a distal end of expandable casing  14 . The outer body  50 ″ may be generally similar to the outer body  50 ′ of  FIG. 4 , and may comprise a plurality of blades  80  that define fluid courses  82  therebetween. Fluid passageways  30  may be formed through the outer body  50 ″ or allowing fluid (e.g., drilling fluid and/or cement) to be pumped through the interior of the casing bit  10 ,  10 ′, out through the fluid passageways  30 , and into the annular space between the walls of the formation in which the wellbore  16  is formed and the exterior surfaces of the casing bit  10 ,  10 ′ and the expandable casing  14  to which the casing bit  10 ,  10 ′ may be attached. Cutting element pockets may be formed in the blades  80 , and cutting elements  86 , such as, for example, polycrystalline diamond compact (PDC) cutting elements, may be secured within the cutting element pockets. In additional embodiments, the outer body  50 ″ may not include blades  80  and cutting elements  86 , like those shown in  FIG. 5 . Furthermore, the outer body  50 ″ may comprise other cutting structures such as, for example, deposits of hardfacing material  87  on the exterior surfaces of the outer body  50 ″. Such a hardfacing material may comprise, for example, hard and abrasive particles (e.g., diamond, boron nitride, silicon carbide, carbides or borides of titanium, tungsten, or tantalum, etc.) embedded within a metal or metal alloy matrix material (e.g., an iron-based, cobalt-based, or nickel-based metal alloy). Wear-resistant bearing elements  84  such as, for example, tungsten carbide ovoids, also may be provided on exterior surfaces of the outer body  50 ″. 
         [0063]    Although the foregoing description contains many specifics, these are not to be construed as limiting the scope of the present invention, but merely as providing certain embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the scope of the present invention. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims, are encompassed by the present invention.