Patent Publication Number: US-11643879-B2

Title: Nested drill bit assembly for drilling with casing

Description:
BACKGROUND 
     Wells are constructed in subterranean formations in an effort to extract hydrocarbon fluids such as oil and gas. A wellbore may be drilled with a rotary drill bit mounted at the lower end of a drill string. The wellbore may then be reinforced with a metal casing, which typically involves tripping the drill string out of the wellbore before installing the casing. The wellbore may also be incrementally formed and cased in sections, which increases the number of trips required to complete the wellbore. Each trip into and out of the wellbore is an investment in time and money, which may impact the overall efficiency of constructing the well, and ultimately, the profitability of the well. 
     A more recently developed approach to constructing a wellbore is known alternatively as casing while drilling or drilling with casing (DWC). With DWC, the casing functionally serves as a tubular drill string during drilling, but is then cemented in place downhole as the casing. DWC thereby avoids having to trip out of the wellbore with a drill string and trip in with casing each time a section of casing is to be installed. However, DWC conventionally has its own limitations. For example, after the drill bit has reached its total depth (TD), the drill bit must be drilled out or abandoned. The former approach requires the drill bit to be drillable, which means that the hardness of its cutters is limited, and it may take much time to drill out the drill bit. The latter approach, wherein the drill bit is not drillable, generally means no further drilling can be done. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These drawings illustrate certain aspects of some of the embodiments of the present disclosure and should not be used to limit or define the method. 
         FIG.  1    is an elevation view of a drilling system in which a nested drill bit assembly and other aspects of the present disclosure may be implemented. 
         FIG.  2    is a sectional side view of the nested drill bit assembly according to an example configuration having one child bit nested within the parent bit. 
         FIG.  3    is a sectional side view of the driver drill bit lowered into the casing above the nested drill bit assembly of  FIG.  2   . 
         FIG.  4    is a sectional side view of the drive bit having been received into the cavity of the child bit and connected thereto. 
         FIG.  5    is partially sectioned view of the nested drill bit assembly schematically illustrating an example of a one-way transmission between the parent bit and child bit. 
         FIG.  6    is a side view of a DWC system including a multi-stage cementer according to an example configuration. 
         FIG.  7    is a side view of the DWC system after the drive bit has drilled out leftover cementing materials and connected with the child bit. 
         FIG.  8    is a flowchart outlining a method of drilling and casing a well using a nested drill bit assembly. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is directed, in part, to a nested drill bit assembly that allows for incrementally drilling each of a plurality of wellbore sections with corresponding bits of the nested drill bit assembly. The nested drill bit assembly includes an outermost drill bit that may be referred to in one or more examples as the parent bit, along with one or more child bits nested within the parent bit. The bits in the nested bit assembly may collectively define a primary cutting profile and are initially rotated together. After drilling to a first depth, a driver may be lowered into the wellbore and connected to a child bit, which is then used to drill beyond the parent bit. Various example configurations are also provided of the parent bit, child bit(s), drive bit, and mechanisms for connecting and transferring rotation and torque therebetween. 
     The disclosure is further directed, in part, to a drilling with casing (DWC) system and method that may incorporate the nested drill bit assembly. The parent bit may initially be rotated by a first casing secured to the parent bit, along with the child bit(s) nested therein, which simultaneously drives the casing into the wellbore as it is formed. After drilling to the first depth, the casing may be cemented in place by circulating a cement and cement plugs downhole and up through an annulus between the casing and wellbore. The driver may be configured as a drive bit having a cutting structure to drill through the cement, plugs, and other debris prior to connecting to the child bit. The drive bit may also be driven by an inner tubular, which may be another casing, which may likewise be driven into the wellbore as it is extended and then cemented in place. Any additional child bits may be used to similarly extend the wellbore. 
     As demonstrated below, the use of multiple nested bits allows for incrementally drilling to increased depth, and without having to trip out a first bit before tripping in with a next bit. This saves rig time and cost. Combining the nested drill bit assembly with the disclosed DWC techniques further reduces cost by effectively combining steps such as drilling, casing, and cementing that conventionally might be performed separately and with multiple separate trips. 
       FIG.  1    is an elevation view of a drilling system  10  in which a nested drill bit assembly  40  and other aspects of the present disclosure may be implemented. This system  10  is a non-limiting example configuration for discussion purposes and is not to scale. Although depicted as a land-based drilling operation, those skilled in the art will also appreciate that aspects may be applied to offshore, subsea, or other kinds of drilling operations. 
     The system  10  includes a large support structure, such as a mast or derrick  12 , erected at the wellsite at the location to be drilled. The derrick  12  may be part of a land-based rig as shown, or its equivalent on a jack up rig, floating rig, or offshore fixed structure. The derrick  12  helps support and guide well operations, such as drilling a wellbore  16  into an earthen formation  15 , installing a casing  20 , and cementing the casing  20  in place. The casing  20  is typically a long, metallic tubular structure that can be formed by progressively connecting individual casing segments end to end at the surface  14  of the wellsite to form a tubular casing string. The casing  20  is used to reinforce the wellbore  16  and also functions in DWC as a drill string for driving rotation of one or more drill bits included with the nested drill bit assembly  40 . For example, the casing  20  itself may be suspended from the derrick  12  and rotated, such as by a top drive  22 , which in turn will rotate one or more drill bits of the nested drill bit assembly  40 . As the casing  20  is rotated to drive rotation of the drill bit assembly  40  in order to form one or more segments of the wellbore  16 . As the wellbore  16  is drilled, the casing  20  is thereby advanced into the wellbore  16 , where it will be cemented in place at a desired depth. 
     The nested drill bit assembly  40  according to this disclosure includes an outer (parent) drill bit (i.e., parent bit)  50  and at least one child drill bit (i.e., child bit) nested within the parent drill bit  50 . To illustrate an example of multiple nested drill bits having more than one child bit,  FIG.  1    shows two child bits, namely, a first child bit  60 A nested with the parent bit  50  and a second child bit  60 B nested within the first child bit  60 . There is no express upper limit on the number of nested drill bits that may be included with the nested drill bit assembly  40 , although that number may be practically limited by various parameters such as the overall size and outer diameter (OD) of the drill bit assembly  40 , the desired total depth of the wellbore  16 , the individual depths to which each nested drill bit is expected to drill, and size and design constraints to achieve any performance requirements of each of the nested bits. 
     The system  10  further includes at least one driver  80  to connect to the child bit(s) and drive rotation of the child bit(s) to drill beyond the parent bit  50 . The driver  80  is not initially included when drilling with the nested drill bit assembly  40  and drilling with the parent bit  50 . Rather, the driver  80  is configured (e.g., appropriately sized) so it may be lowered down the casing  20  on a second, inner tubular member (e.g., another casing)  24  to connect to one of the child bits  60 A,  60 B after the parent bit  50  has reached a first depth D1 and the casing  20  has been installed. The driver  80  may be alternately referred to as the drive bit  80  in this example because, as discussed further below, it is additionally configured to drill out material in the casing  20 , such as residual material from a cementing operation, prior to connection with the child bit. 
     The nested drill bit assembly  40 , including the parent bit  50  and the at least one child bit  60 A,  60 B nested therein, are initially all rotated together by the casing  20  to drill the first part of the wellbore  16  extending from the surface  14  of the wellsite to a first depth D1. Thus, the wellbore  16  may be drilled to the first depth D1 by rotating the entire nested drill bit assembly  40  including the parent bit  50  and the child bits  60 A,  60 B nested therein. The casing  20  may then remain in place to reinforce the wellbore from the surface  14  to depth D1. 
     The wellbore  16  may then be extended to a second depth D2 by lowering the drive bit  80  into the casing  20  on the second, inner tubular  24 , connecting the drive bit  80  to the first child bit  60 A, and using the inner tubular  24  to drive rotation of the first child bit  60 A together with the second child bit  60 B. The inner tubular  24  may function as a drill string to drive rotation of the drive bit  80  and the connected child bit, and also as a casing that will be used to reinforce the wellbore  16  from depth D1 to depth D2. The wellbore  16  may then be drilled to a third depth D3 by again lowering the drive bit  80  (which may be the same or a different drive bit) into the wellbore  16  on another tubular (e.g., a third casing), connecting to the second child bit  60 B and using the third tubular to drive rotation of the second child bit  60 B. After drilling to each depth, D1, D2, and D3, the respective casing may be cemented in place. The drive bit  80  may include a cutting structure configured for drilling out any cement or cement plugs that may remain after cementing the most recent casing string in place. 
       FIG.  2    is a sectional side view of the nested drill bit assembly  40  according to a specific example configuration having one child bit  60  nested within the parent bit  50 . The parent bit  50  includes a bit body (i.e., the parent bit body)  52  securable to the casing  20  for driving rotation of the parent bit  50  with the casing  20 . The parent bit  50  also includes a cutting structure (i.e., the parent cutting structure)  54  disposed along an exterior of the parent bit body  52  for engaging the earthen formation  15  while drilling. The parent cutting structure  54  extends along the parent bit body  52  from a leading end or nose  56  to a lateral portion  58 , which may be or include an outer diameter of the parent bit body  52 . The child bit  60  likewise includes a bit body (i.e., the child bit body)  62  and a child cutting structure  64  secured to the child bit body  62 . The child cutting structure  64  extends along the child bit body  62  from a leading end or nose  66  of the child bit body  62  to a lateral portion  68  of the child bit body  62 . The nose  66  of the child bit  60  is contiguous with the parent cutting structure  54  at the nose  56  of the parent bit  50  and is thereby exposed to the formation  15 . The lateral portion  68  of the child cutting structure  64  is internal to the parent bit body  52  and is not exposed to the earthen formation  15  while the child bit  60  is nested within the parent bit  50 . 
     Thus, the parent cutting structure  54  together with a portion (in this case, the nose  66 ) of the child cutting structure  64  form a contiguous primary cutting profile generally indicated at  70 . The contiguous cutting profile  70  may be comparable to the cutting profile of a monolithic drill bit, in that despite being comprised of cutting structures of multiple bits, the cutting profile is configured for drilling a portion of a wellbore as though the profile were defined by a monolithic drill bit. In a related aspect, the contiguous cutting profile  70  is continuous from the outer, parent cutting structure  54  to the portion of the child cutting structure  64  along the nose  66  of the child bit  60  without any appreciable vertical separation as the cutting profile  70  transitions from one to the other. The spacing between cutters along the primary cutting profile  70  may also be substantially uniformly spaced as well, similar to how such cutters might be spaced on a monolithic drill bit. Thus, the cutting structures from both the parent bit  50  and child bit  60  along the primary cutting profile  70  are rotated together and used to drill the wellbore  16  to the first depth D1. In other embodiments having one or more additional child bits (e.g., the second child bit  60 B of  FIG.  1   ), the one or more additional child bits could also include a cutting structure, a portion of which forms a contiguous primary cutting profile with at least a portion of the parent bit and the other child bit(s). 
     Any suitable cutting structures may be used for the parent bit  50  and child bit  60  capable of cutting, shearing, abrading, or otherwise disintegrating the earthen formation  15 . The parent cutting structure  54  and/or the child cutting structure  64  may include a plurality of discrete cutters  53  spaced apart on the respective bit bodies. Examples of discrete cutters include but are not limited to polycrystalline diamond compact (PDC), which may have polycrystalline diamond cutting elements on a tungsten carbide substrate, carbide inserts, abrasive inserts, or other suitable hard and resilient elements for cutting, shearing, abrading, or otherwise disintegrating or destroying the earthen formation as a result of being rotated against the earthen formation  15 . Alternatively, the parent cutting structure  54  and/or the child cutting structure  64  may be a continuous cutting structure, rather than separate and discrete cutters, formed on the respective bit bodies  52 ,  62 . 
     The child bit  60  is releasably coupled to the parent bit  50  so that the child bit  60  remains nested within the parent bit  50  while drilling with the parent bit  50 . One or more features may be provided to axially and/or rotationally constrain the child bit  60  with respect to the parent bit  50 . In the example of  FIG.  2   , a shear member, embodied by way of example as a plurality of shear pins  72 , constrains the child bit  60  at least axially. The shear pins  72  provide interference between the parent and child and require at least a threshold level of axial force on the child bit  60  to shear the shear pins  72 . In the example of  FIG.  2   , the shear pins  72  ride in an annular groove  74 , defined in this example on the child bit  60  allowing relative rotation between the child bit  60  and parent bit  50 . An annular groove may alternately be defined by the parent bit  50  or cooperatively by the parent bit  50  and child bit  60 , with the shear pin(s) or other shear members disposed therein. 
       FIG.  3    is a sectional side view of the driver drill bit (i.e., drive bit)  80  lowered into the casing  20  above the nested drill bit assembly  40  of  FIG.  2   . The child bit  60  includes a cavity  67  for receiving the drive bit  80 . The drive bit  80  is lowered downhole into the casing  20  on the second, inner tubular  24 , which may also function as another casing string. The drive bit  80  is a driver in that after releasing the child bit  60  from the parent bit  50  it may drive rotation of the child bit  60  to extend the wellbore beyond the parent bit  50 . The drive bit  80  in this example is also, more specifically, a drive bit, in that the driver includes its own cutting structure (i.e., drive cutting structure)  84  disposed on a leading (lower) end of a drive bit body  82 . The drive cutting structure  84  is configured to drill out any material, such as cement or cement plugs left over from a cementing operation to cement the casing  20  in place, as further discussed below. 
     Any suitable connection type that allows the drive bit  80  to be connected to the child bit  60  downhole and that allows axial force and torque transfer from the drive bit  80  to the child bit  60 . In the example of  FIG.  3   , the connector includes a connector portion  85  on the drive bit  80  configured for connecting with a connector portion  65  on an interior cavity  67  of the child bit  60 . More particularly, for example, the connector portion  65  of the child bit  60  may comprise a threaded member, and the connector portion  85  on the drive bit  80  may comprise another threaded member configured for threadably engaging the threaded member on the child bit  60 , so that the drive bit  80  may be connected to the child bit  60  by rotation of the drive bit  80  with respect to the child bit  60 . To facilitate making up this threaded connection between the drive bit  80  and child bit  60 , the child bit  60  may be initially held using one or more shear members, e.g., one or more of the pins  72  or other pins, to resist relative rotation between the parent bit  50  and child bit  60  during make-up, and which shear after make-up. Non-limiting examples of other connections between the drive bit  80  and child bit  60  may include a splined connection, a collet connection, and/or an L-shaped slot with a pin that rides in the slot to provide axial and rotational constraints between the child bit  60  and drive bit  80 . Industry standard and/or proprietary threads may also be used for this connection. 
       FIG.  4    is a sectional side view of the drive bit  80  having been received into the cavity  67  of the child bit  60  and connected thereto. The connector portions  65 ,  85  on the child bit  60  and drive bit  80  are threaded members that have been threadably engaged, such as by rotation of the drive bit  80  with respect to the child bit  60 . The thread orientation can be configured so that torque applied to drive the child bit  60  in the intended rotational direction during drilling will tend to maintain and not loosen this threaded connection. Once connected, the drive bit  80  may be used to release the child bit  60  from the parent bit  50 , such as by applying a downward force through the inner tubing string  24  to shear the inner shearing shear pins  72  or other shear member. The connection may then be used to drive rotation and axial force via the inner tubing string  24  through the drive bit  80  to the child bit  60 , for drilling beyond the parent bit  50  using the child bit  60 . 
     The threaded connection also allows for pulling up on the child bit via the inner tubing string  24 . In this embodiment, a shoulder  76  is included on the parent bit body  52  to initially limit upward movement of the child bit  60  with respect to the parent bit  50 , and in particular, to help prevent the child bit  60  from unintentionally coming up out of the parent bit  50 , such as when tripping the nested drill bit assembly  40  downhole or drilling with the parent bit  50  and child bit  60  together. However, the cutting structure of the child bit  60  includes a rear-facing cutting structure portion  69  configured to drill out the shoulder  76  to subsequently allow the child bit body to be retrieved axially up out of the parent bit body  50 . The shoulder  76  and rear-facing cutting portion  69  may be selected to initially provide sufficient retention for the child bit  60  and for the shoulder  76  to be readily drillable by the rear-facing cutting portion  69 . For example, a soft metallic structural material such as aluminum for the shoulder  76  may provide sufficient retention yet be sufficiently drillable. An upward force may be applied to the inner tubing string  24  during rotation of the tubing string to drill out the shoulder  76  using the rear-facing cutting portion  69 . 
     Torque may be transferred from the parent bit  50  to the child bit  60 , so that the child cutting structure  64  moves with the parent cutting structure  54  while drilling with the nested drill bit assembly  40 . This torque transfer may be accomplished in a variety of ways, of which a few non-limiting examples are provided. In one example, a one-way transmission may be provided anywhere along an interface between the parent bit  50  and child bit  60 . The one-way transmission may allow relative rotation between the parent bit  50  and drive bit  60  in one direction so that while drilling with the parent (outer) drill bit  50 , the parent bit  50  transfer torque to the child bit  50 , but while subsequently drilling with the child bit, the child bit  60  is allowed to rotate freely with respect to the parent bit  50 . In another example, the one-way transmission may be omitted, and the shear pins  72  or other shear members could instead be used to both axially and rotationally constrain the child bit  60  within the parent bit  50  by omitting the annular groove  74 . The shear pins  72  may provide sufficient strength to transfer both axial force and torque from the parent bit  50  to child bit  60  while drilling with the parent bit  50 . Once the drive bit  80  is coupled to the child bit  60 , a force may be applied to then shear the shear pins  72  via the inner tubular  24  to free the child bit  60  from the parent bit  50  to allow relative rotation therebetween so that the child bit  60  may be used to drill past the parent bit  50 . 
       FIG.  5    is partially sectioned view of the nested drill bit assembly  40  schematically illustrating an example of a one-way transmission  90  between the parent bit  50  and child bit  60 . The transmission  90  comprises a plurality of pawls  92  circumferentially spaced along the shoulder  76  of the parent bit  50 . The pawls  92  are spring-biased into recesses  94  circumferentially arranged on the child bit  60 . (Another arrangement could alternatively provide pawls on the child bit biased into recesses on the parent bit.) The pawls  92  are angled to engage the child bit  50  during right-hand rotation of the parent bit  50 , but move inwardly to allow relative rotation between the child bit  60  and parent bit  50  in the opposite rotational direction. The one-way transmission  90  thereby allows for transfer of a torque T (in this case, a right-hand torque) about a bit axis  91  from the parent bit  50  to the child bit  60  while the parent bit  50  is driven by the casing  20 , so that the child cutting structure  64  rotates along with the parent cutting structure  54 . The one-way transmission  90  allows relative rotation between the child bit  60  and parent bit  50  when the child bit  60  is later driven by the drive bit. 
     The nested drill bit assembly, such as described by way of example in  FIGS.  1 - 5    above, may therefore be used to incrementally drill a wellbore with a plurality of drill bits that are initially nested. Advantageously, this allows for drilling to a first depth with a first bit (the parent bit) to a total depth of that first bit, and then to drill past the parent bit with one or more child bits. Notably, the nested drill bit assembly avoids the need to trip out of the wellbore with the first bit before drilling further with the next bit. Further, the system may include a drive bit configured for drilling obstructions prior to connecting with a child bit of the nested drill bit assembly. Although not exclusively, this is particularly useful for a multi-stage cementing operation, whereby each bit of the nested drill bit assembly is driven by a tubular that itself will serve as a casing for the section of the wellbore drilled by that bit.  FIGS.  6  and  7    illustrate an example of a drilling with casing (DWC) system and method for use in a multi-stage casing and cementing operation. 
       FIG.  6    is a side view of a DWC system  100  including a tubular cementing sub, referred to in this configuration as a multi-stage cementer  120 . The multi-stage cementer  120  includes a tubular body defined by or otherwise coupled between the nested drill bit assembly  40  and the casing  20 . Three cementing plugs are shown by way of example, including a first (“free fall”) plug  122 , a second (“bottom”) plug  124 , and a third (“top”) plug  126 . During a cementing operation, a cement is flowed downhole down the casing  20  and up through an annulus  25  between the casing  20  and wellbore  16 , thereby forming a column of cement  130  disposed in the annulus  25 . During the cementing operation, the free fall plug  122  may first be disposed downhole into the casing  20  to open up ports  128  on the cementer  120 . The bottom plug  124  may then be dropped, followed by the cement flow down the casing  20 . The cement may flow through the bottom plug  124 , either out the ports  128  in one example or down and out through nozzles on the drill bit assembly  40 , and up the annulus  25 . The cement, while flowable, may be relatively viscous, adding a component of pressure, and the density and flow of the cement may be carefully controlled to balance pressure in the annulus  25  between pore pressure and fracture pressure. The top plug  126  is disposed on the top of the cement column. When the top plug  126  reaches bottom, it will cause a pressure rise at surface as a positive indication that the cement has substantially all been flowed down the column and up the annulus  25 . 
       FIG.  6    thus represents just one of example the kinds of materials that may be present in the casing  20  after a cementing operation, including various plugs and residual cement. The drive bit  80  has subsequently been lowered on the inner casing  24  after the outer casing  20  that has been cemented, and is poised now to drill out the plugs and residual cement. The drive bit  80  may drill out these materials by rotation of the inner casing  24  while moving the drive bit  80  downward with the inner casing  24 . During drilling, a drilling fluid may be flowed downhole through the inner casing  24  and out the drive bit  80  so that the threads or other connector on the drive bit may be relatively clean and free of debris for engagement with the mating threads or other connector on the drive bit  80 . 
       FIG.  7    is a side view of the DWC system  100  after the drive bit  80  has drilled out leftover cementing materials and connected with the child bit  60 . At this point, the inner tubular  24  may be used to separate the child bit  60  from the parent bit  50  such as by pushing down with the inner tubular  24  to shear the shear pins  72 . Then, the inner tubular  24  may drive rotation of the drive bit  80  and connected child bit  60  to drill beyond the parent bit to form the next wellbore segment  116  beyond the wellbore  16  previously formed by the parent bit  50  and child bit  40  of the nested drill bit assembly  40 . 
       FIG.  8    is a flowchart  200  outlining a method of drilling and casing a well using a nested drill bit assembly. The method may involve multi-stage cementing, wherein wellbore segments are consecutively drilled using respective drill bits of a nested drill bit assembly, then cased and cemented. The method may be performed with any of the foregoing systems and apparatus, or another system or apparatus within the scope of this disclosure. A first step  210  involves defining a primary cutting profile with a cutting structure on an outermost bit. In a first iteration, the outermost bit is initially a parent bit with one or more child bits initially nested within the parent bit. In step  220 , the outermost bit is rotated by rotating a casing coupled to the outermost bit. This rotates the outermost bit and child bit together including the cutting profile collectively defined thereby, to drill a wellbore in an earthen formation. Step  230  is to drive the casing into the wellbore as that wellbore segment is drilled to a first depth, and cementing the casing in place as needed. 
     In step  240 , after drilling to a first depth with the casing and parent drill bit, a driver is disposed the casing on an inner tubular (e.g., another casing) and connected to the child bit. The drive bit may be used to drill out any cement plug and other materials above the child drill bit before connecting the drive bit to the child drill bit. In step  250 , the drive bit is used to drive rotation of the child drill bit to further drill the earthen formation with the child drill bit to a further depth. After reaching the further depth, additional cement may be flowed downhole through the inner casing and up into an annulus between the inner casing and the wellbore. 
     In some examples there may be one or more additional child bits to successively drill to further depths. If one or more additional child bits are included as per decisional step  260 , the method returns to step  240 , whereby a drive bit is disposed downhole on another tubular, e.g., another casing or just drill pipe. The casing or other tubular in each iteration may be progressively smaller in order to fit within the most recently drilled section. Again, the drive bit may be coupled to the next child bit, and driven to extent the wellbore as per step  250 . The flowchart contemplates the use of multiple child bits and multiple casing steps. However, the drilling through cement or cement plugs may only occur one time in some drilling while casing scenarios. Also, rather than including additional child bits, in some drilling scenarios, the drilling may instead continue with a conventional bit through the borehole created by the child bit. 
     Accordingly, the present disclosure provides a nested drill bit assembly that allows for incrementally drilling each of a plurality of wellbore sections with corresponding bits of the nested drill bit assembly. The methods, systems, and tools may include any of the various features disclosed herein, including one or more of the following statements. 
     Statement 1. A drilling apparatus for drilling a wellbore, comprising: a parent drill bit including a parent bit body securable to a casing for driving rotation of the parent drill bit with the casing and a parent cutting structure secured to the parent bit body; a child drill bit initially nested within the parent drill bit and including a child bit body releasably coupled to the parent bit body and a child cutting structure secured to the child bit body; and a driver drill bit configured for lowering into the casing and a connector for connecting the driver drill bit to the child drill bit to drive rotation of the child drill bit with respect to the parent drill bit. 
     Statement 2. The drilling apparatus of Statement 1, wherein at least a portion of the parent cutting structure together with at least a first portion of the child cutting structure define a contiguous primary cutting profile configured for drilling an earthen formation while the child bit body is coupled to the parent bit body. 
     Statement 3. The drilling apparatus of Statement 2, wherein a second portion of the child cutting structure is positioned interior to the parent bit body when the child drill bit is nested within the parent drill bit, and wherein the second portion of the child cutting structure is exposed for further drilling the earthen formation when the child drill bit is moved out of the parent drill bit. 
     Statement 4. The drilling apparatus of any of Statements 1 to 3, further comprising: a shoulder interior to the parent bit body that initially blocks movement of the child bit body upward out of the parent bit body; and wherein the child cutting structure comprises a rear-facing cutting structure portion configured to drill out the shoulder to subsequently allow the child bit body to be retrieved axially up out of the parent bit body. 
     Statement 5. The drilling apparatus of any of Statements 1 to 4, further comprising: 
     a one-way transmission operatively coupling the parent and child drill bits allowing the parent drill bit to transfer torque to the child drill bit in one rotational direction and not in an opposing rotational direction. 
     Statement 6. The drilling apparatus of Statement 5, wherein the one-way transmission comprises a ratcheting mechanism disposed between the parent drill bit and the child drill bit. 
     Statement 7. The drilling apparatus of any of Statements 1 to 6, wherein the child bit body is releasably coupled to the parent bit body by a shear member disposed in an annular channel defined by one or both of the parent drill bit and the child drill bit, thereby limiting relative axial movement but allowing relative rotation between the parent bit body and the child bit body. 
     Statement 8. The drilling apparatus of any of Statements 1 to 7, further comprising: a second child drill bit initially nested within the child drill bit and including a second child bit body releasably coupled to the child bit body and a second child cutting structure secured to the second child bit body. 
     Statement 9. The drilling apparatus of any of Statements 1 to 8, wherein the connector for connecting the driver drill bit to the child drill bit comprises a threaded member on the child drill bit and a threaded member on the driver drill bit configured to threadedly connect to the threaded member on the child drill bit. 
     Statement 10. The drilling apparatus of any of Statements 1 to 9, further comprising a cementing sub defining a passageway for allowing cement to flow through during a cementing operation to cement the casing in the wellbore, and wherein the driver bit includes a driver cutting structure configured to drill out a cement plug positioned above the child drill bit as a result of the cementing operation prior to connecting to the child drill bit. 
     Statement 11. A method of drilling and casing a well, comprising: defining a primary cutting profile comprising a parent cutting structure on a parent drill bit and a child cutting structure on a child drill bit initially nested within the parent drill bit; rotating the primary cutting profile, including the parent and child cutting structures together, by rotating a casing coupled to the parent drill bit to drill a wellbore in an earthen formation; driving the casing into the wellbore as the wellbore is drilled; after drilling to a first depth with the casing and parent drill bit, lowering a driver drill bit down the casing and connecting the driver drill bit to the child drill bit; and driving rotation of the child drill bit with the driver drill bit to further drill the earthen formation with the child drill bit to a second depth beyond the first depth. 
     Statement 12. The method of Statement 11, further comprising: after reaching the first depth, flowing a cement downhole through the casing and up into an annulus between the casing and the wellbore; and rotating the driver drill bit to drill out a cement plug above the child drill bit before connecting the driver drill bit to the child drill bit. 
     Statement 13. The method of Statement 12, further comprising: coupling an inner casing to the driver drill bit and rotating the inner casing to perform the step of driving the rotation of the child drill bit with the driver drill bit; and after reaching the second depth, flowing additional cement downhole through the inner casing and up into an annulus between the inner casing and the wellbore. 
     Statement 14. The method of any of Statements 11 to 13, further comprising: initially coupling the child drill bit to the parent drill bit with a shear member prior to drilling to the first depth; and applying force to the drive bit to shear the shear member before drilling with the child drill bit. 
     Statement 15. The method of any of Statements 11 to 14, further comprising: initially blocking movement of the child drill bit axially up out of the parent drill bit with a shoulder interior to the parent bit body; and subsequently using a rear-facing cutting structure on the child drill bit to drill out the shoulder to allow the child bit body to be retrieved axially up out of the parent bit body. 
     Statement 16. A drilling while casing (DWC) system, comprising: a nested drill bit assembly comprising a parent drill bit having a parent cutting structure secured to a parent bit body and a child drill bit nested within the parent bit body and having a child cutting structure secured to a child bit body; a casing securable to the parent bit body and rotatable for driving rotation of the parent bit body for drilling a first wellbore section into an earthen formation and advancing the casing into the wellbore as the wellbore is drilled; and a driver drill bit configured for lowering into the casing and connectable to the child drill bit to drive rotation of the child drill bit with respect to the parent drill bit to drill a second wellbore section beyond the parent drill bit. 
     Statement 17. The DWC system of Statement 16, wherein the parent cutting structure together with the child cutting structure form a contiguous primary cutting profile for drilling an earthen formation. 
     Statement 18. The DWC system of Statement 16 or 17, further comprising: a cementer sub coupled between the nested drill bit assembly and the casing; one or more cement plugs disposable above the nested drill bit assembly to facilitate flow of a cement down the casing an up an annulus between the casing and the wellbore; and wherein the driver drill bit includes a driver cutting structure for drilling out the one or more cement plugs before connecting to the child drill bit. 
     Statement 19. The DWC system of any of Statements 16 to 18, further comprising: an inner casing disposable in the casing for driving rotation of the driver drill bit and advancing the inner casing into the second wellbore section. 
     Statement 20. The DWC system of any of Statements 16 to 19, further comprising: a one-way transmission operatively coupled between the parent drill bit and the child drill bit, the one-way transmission configured for allowing the transfer of torque from the parent bit to the child bit in a drilling rotational direction and for relative rotation between the parent drill bit and the child drill bit in an opposite rotational direction. 
     For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values even if not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited. 
     Therefore, the present embodiments are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Although individual embodiments are discussed, all combinations of each embodiment are contemplated and covered by the disclosure. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure.