You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
       [0001]    When exploring for or extracting subterranean resources such as oil, gas, or geothermal energy, it is common to form boreholes in the earth. Such boreholes are often formed by suspending a specialized drill bit from a derrick or offshore platform and rotating the drill bit to engage and degrade the earth as it turns. The drill bit may be suspended by coiled tubing or a series of drill pipe sections connected end to end to form a drill string, and rotated at the derrick/platform or by a downhole motor disposed towards an end of the drill string. If a drill bit becomes dull or damaged it may cease to drill efficiently and may need to be replaced before drilling continues. 
         [0002]    In many situations, it may be desirable to gain access to the drill bit as it drills. For example, it may be desirable to discharge drilling fluid flowing through a drill string at a drill bit. This may be done to cool, clean or lubricate the drill bit or carry debris created by the drill bit engaging an earthen formation up a borehole. In another example, it may be desirable to place sensors at a drill bit as it drills. This may be done to gather information about the formation being drilled as far in front of the drill bit as possible or to get the most accurate possible measurements of how the drilling process is progressing. These sensors may measure natural conditions of an earthen formation or responses to energy transmitted into a formation from transmitters also disposed at the drill bit. In yet another example, it may be desirable to control a trajectory of a drill bit as it bores into a formation by manipulating degradation of the formation at the drill bit. This may be accomplished, for example, by placing cutters on an offset mechanical hammer or rotational motor exposed at a drill bit and activating it alternatingly as the drill bit rotates. 
         [0003]    While placing these types of equipment as close to the drill bit as possible may be desirable, placing them on the drill bit may become prohibitively expensive as drill bits may need to be replaced regularly, if not frequently. Accordingly, tools providing access to a drill bit that need not be replaced as often as drill bits may be valuable. 
       BRIEF DESCRIPTION 
       [0004]    A downhole drill bit may comprise a working face, capable of engaging and degrading tough earthen formations, opposite an attachment end, fashioned to attach to a bottom hole assembly. The drill bit may further comprise an opening passing from the attachment end through to the working face. A protrusion on one end of a bottom hole assembly may extend through the opening and be exposed at the working face when the drill bit is attached to the end of the bottom hole assembly. This exposed portion of the protrusion may provide access for equipment housed within the bottom hole assembly to the working face while drilling. For example, in various embodiments, the protrusion may accommodate conduits or nozzles for handling fluids; sensors, transmitters or wires for handling electrical signals; or mechanical hammers, motors or cutters for degrading an earthen formation. In such configurations, the drill bit may be replaced when dull or damaged without requiring replacement of this additional equipment. 
     
    
     
       DRAWINGS 
         [0005]      FIG. 1  is an orthogonal view of an embodiment of a drilling operation comprising a drill bit secured to an end of a drill string suspended from a derrick. 
           [0006]      FIG. 2  is a perspective view of an embodiment of a bottom hole assembly comprising a protrusion on one end thereof and a drill bit capable of attachment to the end of the bottom hole assembly. 
           [0007]      FIG. 3  is a perspective view of the embodiment of the drill bit shown in  FIG. 2  attached to the end of the bottom hole assembly such that the protrusion extends through an opening in the drill bit. 
           [0008]      FIG. 4  is an orthogonal face view of an embodiment of a drill bit with a protrusion extending through an opening therein and an exposed portion of the protrusion comprising a generally circular exposed surface. 
           [0009]      FIGS. 5-1, 5-2, 5-3 and 5-4  are longitude-sectional views of different embodiments of bottom hole assemblies comprising various types of equipment housed therein and exposed at a working face of a drill bit by a protrusion passing through an opening in the drill bit. 
           [0010]      FIG. 6  is a perspective view of an embodiment of a bottom hole assembly comprising a protrusion on one end thereof and a drill bit capable of attachment to the end of the bottom hole assembly. 
           [0011]      FIG. 7  is an orthogonal face view of the embodiment of the drill bit shown in  FIG. 6  with the protrusion extending through an opening therein and an exposed portion of the protrusion comprising a generally non-circular exposed surface. 
           [0012]      FIG. 8-1  is a longitude-sectional view of an embodiment of a bottom hole assembly comprising a protrusion with a periphery surface parallel with a central axis of the bottom hole assembly. The protrusion is aligned with a drill bit capable of attachment to the end of the bottom hole assembly. 
           [0013]      FIG. 8-2  is a longitude-sectional view of the embodiment of the drill bit shown in  FIG. 8-1  attached to the end of the bottom hole assembly with a locking mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  shows an embodiment of a drilling operation comprising a drill string  110  suspended from a derrick  112  into the earth  114 . A bottom hole assembly  100  may be disposed adjacent a distal end of the drill string  110  and comprise any of a number of mechanical, electrical, or fluid systems known in the art to aid in increasing rate of penetration of drilling; steering; gathering, storing, or communicating data; or sensing. A drill bit  118  may be secured to the bottom hole assembly  100  capable of engaging and degrading the earth  114  as it is rotated to form a borehole  116  allowing for the drill string  110  to advance. In many situations, it may be desirable to position the various systems housed within the bottom hole assembly  100  as close to a working face of the drill bit  118  as possible. 
         [0015]      FIG. 2  shows an embodiment of a bottom hole assembly  200  comprising a generally elongate shape. A protrusion  220  may be disposed on one end of the bottom hole assembly  200  and extend out therefrom. The protrusion  220  may be attached to the bottom hole assembly  200  by a spider  228  allowing drilling fluid traveling through the bottom hole assembly  200  to pass the protrusion  220 . In the embodiment shown, the protrusion  220  extends from a threaded pin  227  comprising a generally circular cross section surrounded by threads  221 . The threaded pin  227  may be received by an attachment end  222  of a drill bit  218  comprising a threaded box (hidden). While the present embodiment comprises a threaded pin  227  and box combination, other attachment mechanisms may be similarly suitable. A working face  223  may be disposed on the drill bit  218 , opposite the attachment end  222 , and comprise a plurality of cutters  224 , formed at least partially of superhard material (e.g. polycrystalline diamond), secured thereto. The working face  223  may also comprise a plurality of blades  225  extending therefrom allowing the cutters  224  to dig into a formation to be degraded and debris generated during the degradation to exit through spaces between each of the blades  225 . Additionally, an opening  226  may pass completely through the drill bit  218  from the working face  223  to the attachment end  222 . 
         [0016]      FIG. 3  shows the embodiment of the drill bit  218 , shown in  FIG. 2 , attached to the end of the bottom hole assembly  200 . When attached, the protrusion  220  may extend through the opening  226  passing through the drill bit  218  to be exposed at the working face  223 . In the embodiment shown, an exposed portion  330  of the protrusion  220  comprises a generally circular exposed surface. The exposed portion  330  may also be generally flush with the working face  223 . 
         [0017]      FIG. 4  shows an exposed portion  430  of a protrusion  420  surrounded by a working face  423  of a drill bit  418 . At least one cutter  444 , comprising superhard material (e.g. polycrystalline diamond), may be disposed on the exposed portion  430  of the protrusion  420 . In the embodiment shown, the cutter  444  is positioned within an organized pattern, such as along a blade, with some of the plurality of cutters  424  disposed on the working face  423 . As the drill bit  418  is rotated, those of the plurality of cutters  424  positioned closer to an exterior  441  of the working face  423  may travel at a higher speed relative to a formation being degraded, due to an increased radius, than cutters  424  positioned closer to an axis of rotation  442  of the drill bit  418 . Because of this higher speed, cutters  424  positioned closer to the exterior  441  may be more likely to receive wear or damage than those positioned closer to the axis of rotation  442 . When worn or damaged, the drill bit  418  may be replaced. However, any equipment exposed at the working face  423  through the protrusion  420 , which is also less likely to receive wear due to its position closer to the axis of rotation  442 , may be left in place. 
         [0018]    One example of equipment that may be housed within a bottom hole assembly and exposed at a working face of a drill bit by a protrusion passing through an opening in the drill bit is fluid handling equipment as shown in  FIG. 5-1 . Specifically,  FIG. 5-1  shows drilling fluid  550 - 1  traveling through a hollow center of a bottom hole assembly  500 - 1 . A conduit  551 , passing through a protrusion  520 - 1  extending from the bottom hole assembly  500 - 1 , may channel a portion of the drilling fluid  550 - 1  to a nozzle  552 , secured on an exposed portion  530 - 1  of the protrusion  520 - 1 , where it may be discharged at a working face  523 - 1  of a drill bit  518 - 1 . The drill bit  518 - 1  may be replaced when worn or damaged without affecting the fluid flow path. 
         [0019]    Another example of equipment that may be exposed at a working face by a protrusion is electrical equipment as shown in  FIG. 5-2 . In the example shown, wires  553  may pass through a protrusion  520 - 2  and transmit electrical signals to and from a transmitter  554  and a sensor  555  positioned on an exposed portion  530 - 2  of the protrusion  520 - 2  at a working face  523 - 2  of a drill bit  518 - 2 . The transmitter  554  may send energy in any of a variety of forms, such as for example a magnetic field or gamma rays, into a formation being drilled that may reflect off of the formation, be altered by the formation or cause a reaction in the formation that may be sensed by the sensor  555 . In alternate embodiments, a transmitter may not be necessary and a sensor alone, such as for example an accelerometer or thermometer, may sense naturally occurring phenomena at a working face. 
         [0020]    Yet other examples of equipment that may be exposed at a working face by a protrusion are extra degradation tools such as those shown in  FIGS. 5-3 and 5-4 . For example,  FIG. 5-3  shows at least one cutter  544 - 3  extending from an end of an exposed portion  530 - 3  of a protrusion  520 - 3 . The cutter  544 - 3  may be secured to a hammer mechanism  556  capable of vibrating the cutter  544 - 3  for the purpose of increasing a rate of penetration of a drill bit  518 - 3 , steering the drill bit  518 - 3 , sending an acoustic signal into a formation or for other reasons. In the embodiment shown, a motor  558 - 3  may actuate a valve  559 - 3  to alternating route drilling fluid  550 - 3  traveling through a hollow center of a bottom hole assembly  500 - 3  to the hammer mechanism  556  causing the cutter  544 - 3  to extend and retract. In other embodiments, other types of hammer mechanisms may achieve similar results. 
         [0021]    In another example,  FIG. 5-4  shows at least one cutter  544 - 4  extending from an exposed portion  530 - 4  of a protrusion  520 - 4  and secured to a motor  557  capable of rotating the cutter  544 - 4  about an axis. Similar to the hammer mechanism  556  shown in  FIG. 5-3 , the motor  557  may increase a rate of penetration, steer, send signals into a formation or perform other tasks. In the embodiment shown, the motor  557  comprises a rotor  558 - 4  rotated relative to a stator  559 - 4  by a drilling fluid  550 - 4  traveling through a hollow center of a bottom hole assembly  500 - 4 . Rotation of the rotor  558 - 4  may be passed to the cutter  544 - 4  to increase degradation of a formation. In other embodiments, other types of rotational mechanisms may achieve similar results. 
         [0022]      FIGS. 6 and 7  show an embodiment of a drill bit  618  that may be attached to a bottom hole assembly  600  and allow a protrusion  620  of the bottom hole assembly  600  to pass through. An exposed portion  630  of the protrusion  620  may comprise a non-circular shape. In order to fit the drill bit  618  over the noncircular shape, the protrusion  620  may comprise a periphery surface  661  parallel with a central axis  663  of the bottom hole assembly  600 . The periphery surface  661  may extend from a boundary  662  of the exposed portion  630  at a working face  623  of the drill bit  618  toward the bottom hole assembly  600 . 
         [0023]    The drill bit  618  may comprise a rotatable locking mechanism  667  to secure the drill bit  618  to the bottom hole assembly  600 . While a rotatable locking mechanism  667  is shown in the present embodiment, other styles of locking mechanisms may achieve similar results. As also seen in this embodiment, the working face  623  may comprise at least one cutter  624  disposed encroaching on the boundary  662  of the noncircular exposed surface. It is believed that in some situations this encroachment may aid in maintaining an organized pattern of cutters between the exposed portion  630  of the protrusion  620  and the working face  623 . Some blades  625  extending from the working face  623  may also continue uninterrupted onto the exposed portion  630  in an elevated section  664  of the exposed portion  630 . 
         [0024]      FIGS. 8-1 and 8-2  show an embodiment of a drill bit  718  comprising a rotatable locking mechanism  767  that may secure the drill bit  718  to a bottom hole assembly  700 . The rotatable locking mechanism  767  may rotate freely relative to a remainder of the drill bit  718  thanks to a plurality of ball bearings  770  secured within tracks  771 . This relative rotation may permit the locking mechanism  767  to thread onto a threaded pin  727  of the bottom hole assembly  700  while allowing the remainder of the drill bit  718  to remain rotationally stationary relative to a protrusion  720 . 
         [0025]    In the embodiment shown, the protrusion  720  is held onto the bottom hole assembly  700  by a removable retainer  772 . Using such a removable retainer  772  for attachment may allow for simpler construction and easier maintenance or replacement. For example, in the embodiments shown, at least one snap ring may act as a removable retainer  772  holding the protrusion  720  on the end of the bottom hole assembly  700 . 
         [0026]    Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.

Summary:
A downhole drill bit, of the type used to bore into the earth when searching for or extracting subterranean resources, may comprise a working face opposite an attachment end and an opening passing from the attachment end through to the working face. A protrusion on one end of a bottom hole assembly may extend through the opening and be exposed at the working face when the drill bit is attached to the end of the bottom hole assembly. In various embodiments the exposed portion of the protrusion may house conduits or nozzles for handling fluids; sensors, transmitters or wires for handling electrical signals; or mechanical hammers, motors or cutters for degrading an earthen formation. In this way, the protrusion may bring such elements from the bottom hole assembly to the working face of the drill bit.