Patent Publication Number: US-2005133268-A1

Title: Method and apparatus for casing and directional drilling using bi-centered bit

Description:
BACKGROUND OF INVENTION  
      Wells are generally drilled into the ground to recover natural deposits of hydrocarbons and other desirable materials trapped in geological formations in the Earth&#39;s crust. A well is typically drilled using a drill bit attached to the lower end of a “drill string.” The drill string is a long string of sections of drill pipe that are connected together end-to-end. Drilling fluid, or mud, is typically pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the drill bit, and it carries drill cuttings back to the surface in the annulus between the drill string and the borehole wall.  
      In conventional drilling, a well is drilled to a selected depth, and then the wellbore is typically lined with a larger-diameter pipe, usually called casing. Casing typically consists of casing sections connected end-to-end, similar to the way drill pipe is connected. To accomplish this, the drill string and the drill bit are removed from the borehole in a process called “tripping.” Once the drill string and bit are removed, the casing is lowered into the well and cemented in place. The casing protects the well from collapse and isolates the subterranean formations from each other.  
      Conventional drilling typically has a series of drilling, tripping, casing and cementing, and then drilling again to deepen the borehole. This process is very time consuming and costly. Additionally, other problems are often encountered when tripping the drill string. For example, the drill string may get caught up in the borehole while it is being removed. These problems require additional time and expense to correct.  
       FIG. 1A  shows a prior art drilling operation. A drilling rig  101  and rotary table  104  at the surface are used to rotate a drill string  103  with a drill bit  105  disposed at the lower end of the drill string  103 . The drill bit  105  drills a borehole  107  through subterranean formations that may contain oil and gas deposits. Typically, an MWD (measurement while drilling) or LWD (logging while drilling) collar  109  is positioned just above the drill bit  105  to take measurements relating to the properties of the formation as the borehole  107  is being drilled. In this description, MWD is used to refer either an MWD system or an LWD system. Those having ordinary skill in the art will realize that there are differences between these two types of systems, but the differences are not germane to the embodiments of the invention.  
      The term “casing drilling” refers to using a casing string as a drill string when drilling. A bottom hole assembly (“BHA”), comprising a drill bit, is connected to the lower end of a casing string, and the well is drilled using the casing string to transmit drilling fluid, as well as axial and rotational forces, to the drill bit. Casing drilling enables the well to be simultaneously drilled and cased.  
       FIG. 1B  shows a prior art casing drilling operation. A rotary table  129  at the surface is used to rotate a casing string  123  that is being used as a drill string. The casing  123  extends downwardly into borehole  127 . A drill bit  125  is connected to the lower end of the casing string  123 . When drilling with casing, the drill bit  125  must be able to pass though the casing string  123  so that the drill bit  125  may be retrieved when drilling has been completed or when replacement or maintenance of the drill bit  125  is required. Thus, the drill bit  125  is sized smaller than the inner diameter of the casing string  123 .  
      The drill bit  125  drills a pilot hole  128  that must be enlarged so that the casing string  123  will be able to pass through the borehole  127 . An underreamer  124  is positioned below the casing string  123  and above the drill bit  125  so as to enlarge the pilot hole  128 . A typical underreamer  124  can be positioned in an extended and a retracted position. In the extended position, the underreamer  124  enlarges the pilot hole  128  to the underreamed borehole  127 , and in the retracted position (not shown), the underreamer  124  collapses so that it is able to pass through the inside of the casing string  123 .  
       FIG. 1B  also shows an MWD collar  135  positioned above the drill bit  125  and the underreamer  124 , but below the casing string  123 . The MWD collar  135  takes measurements related to formation properties as drilling is taking place. It should be noted that other positions of these BHA components are possible and are not limited to the figures shown.  
      Casing drilling eliminates the need to trip the drill string before the well is cased. The drill bit may simply be retrieved by pulling it up through the casing. The casing may then be cemented in place, and then drilling may continue. This reduces the time required to retrieve the BHA and eliminates the need to subsequently run casing into the well.  
      Another aspect of drilling is called “directional drilling.” Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction.  
      Directional drilling is advantageous in offshore drilling because it enables many wells to be drilled from a single platform. Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer length of the wellbore to traverse the reservoir, which increases the production rate from the well.  
      A directional drilling system may also be used in vertical drilling operation as well. Often the drill bit will veer off of an planned drilling trajectory because of the unpredictable nature of the formations being penetrated or the varying forces that the drill bit experiences. When such a deviation occurs, a directional drilling system may be used to put the drill bit back on course.  
      One method of directional drilling uses a bottom hole assembly (“BHA”) that includes a bent housing and a mud motor. A bent housing  200  is shown in  FIG. 2A . The bent housing  200  includes an upper section  203  and a lower section  204  that are formed on the same drill collar assembly, but are separated by a bend  201 . The bend  201  is a surface adjustable mechanical joint in the drill collar assembly.  
      With a bent housing  200 , the drill string is not rotated from the surface. Instead, the drill bit  205  is pointed in the desired drilling direction, and the drill bit  205  is rotated by a mud motor (not shown) located in the BHA. A mud motor converts some of the energy of the mud flowing down through the drill pipe into a rotational motion that drives the drill bit  205 . Thus, by maintaining the bent housing  200  at the same azimuthal position with respect to the borehole, the drill bit  205  will drill in the desired direction.  
      When straight drilling is desired, the entire drill string, including the bent housing  200 , is rotated from the surface. The drill bit  205  angulates with the bent housing  200  and drills a slightly overbore, but straight, borehole (not shown).  
      Another method of directional drilling has the use of a rotary steerable system (“RSS”). In an RSS, the drill string is rotated from the surface, and downhole devices cause the drill bit to drill in the desired direction. Rotating the drill string greatly reduces the occurrences of the drill string getting hung up or stuck during drilling.  
      Generally, there are two types of RSS&#39;s—“point-the-bit” systems and “push-the-bit” systems. In a point-the-bit system, the drill bit is pointed in the desired direction of the borehole deviation, similar to a bent housing. In a push-the-bit system, devices on the BHA push the drill bit laterally in the direction of the desired borehole deviation by pressing on the borehole wall.  
      A point-the-bit system works in a similar manner to a bent housing because a point-the-bit system typically includes a mechanism for providing a drill bit alignment that is different from the drill string axis. The primary differences are that a bent housing has a bend at a fixed angle set on the surface and fly coupled and aligned with the drill string rotation, and a point-the-bit RSS has a bend angle that is controlled independently of the drill string rotation.  
       FIG. 2B  shows a point-the-bit RSS  210 . A point-the-bit RSS  210  typically has an drill collar  213  and a drill bit shaft  214 . The drill collar  213  has an internal orientating and control mechanism (not shown) that counter-rotates relative to the drill string. This internal mechanism controls the angular orientation of the drill bit shaft  214  relative to the borehole (not shown).  
      The angle θ between the drill bit shaft  214  and the drill collar  213  may be selectively controlled. The angle θ shown in  FIG. 2B  is exaggerated for purposes of illustration. A typical angle is less than 2 degrees.  
      The “counter rotating” mechanism rotates in the opposite direction of the drill string rotation. Typically, the counter rotation occurs at the same speed as the drill string rotation so that the counter rotating section maintains the same angular position relative to the inside of the borehole. Because the counter rotating section does not rotate with respect to the borehole, it is often called “geo-stationary” by those skilled in the art. In this disclosure, no distinction is made between the terms “counter rotating” and “geo-stationary.” 
      A push-the-bit system typically uses either a rotating or non-rotating stabilizer and/or pad arrangement. The non-rotating stabilizer and/or actuated pad remains at a fixed angle (or geo-stationary) with respect to the borehole wall. When the borehole is to be deviated, an actuator presses a pad against the borehole wall in the opposite direction from the desired deviation. The result is that the drill bit is pushed or actuated in the desired direction.  
       FIG. 2C  shows a typical push-the-bit system  220 . The drill string  223  includes rotating collar  221  that includes one or more extendable and retractable pads  226 . When a pad  226  is extended into contact with the borehole (not shown) during drilling, the drill bit  225  is pushed in the opposite direction, enabling the drilling of a deviated borehole.  
       FIG. 3  shows a prior art drilling system that has both casing drilling and directional drilling. A rotary table  304  is used to rotate a casing string  311  that is being used as a drill string. A drill bit  305  and an underreamer  313  are positioned at the lower end of the casing string  311 . The drill bit  305  drills a pilot hole  308  that is enlarged to an underreamed borehole  307  by the underreamer  313 .  
      The casing drilling system also has an RSS  315  that is positioned blow the casing string  311  and between the drill bit  305  and the underreamer  313 . The RSS  315  is used to change the direction of the drill bit  305 .  
      Nonetheless, a need still exists for an improved drilling system.  
     SUMMARY OF INVENTION  
      An embodiment of the present invention provides an apparatus to drill a borehole with a drillstring. The drillstring has a directional drilling assembly connected to its distal end. The directional drilling assembly has a rotary steerable system, a mud motor, and a bi-centered cutter assembly. The bi-centered cutter assembly has a first cutting surface and a second cutting surface that are spaced apart by an offset. The bi-centered cutter assembly is configured to drill the borehole at a gauge diameter.  
      Another embodiment of the present invention provides an apparatus to drill a borehole with a casing string. The apparatus comprises a directional drilling assembly, a casing latch, and a bi-centered cutter assembly. The directional drilling assembly is connected at a distal end of the casing string. The casing latch is installed at the distal end of the casing string between the casing string and the directional drilling assembly. The casing latch has a pass-through diameter smaller than the inner diameter of the casing string. The bi-centered cutter assembly is configured to be retrieved through the pass-through diameter of the casing latch. The bi-centered cutter assembly has a first cutting surface and a second cutting surface that are offset from one another. The bi-centered cutting assembly is configured to drill the borehole at a gauge diameter that is larger than the pass-through diameter of the casing latch.  
      Another embodiment of the present invention provides a method to drill a borehole with a drillstring. The method comprises attaching a drilling assembly to a distal end of the drillstring. The drilling assembly has a rotary steerable system and a bi-centered cutter assembly. The method further comprises rotating and axially loading the casing string and attached bi-centered cutter assembly to drill a first section of the borehole. The method further comprises orienting the bi-centered cutter assembly with the rotary steerable system. The method further comprises sliding the drillstring deeper into the borehole as it is drilled.  
      Another embodiment of the present invention provides a method to install a casing string into a borehole while drilling. The method comprises attaching a drilling assembly to a distal end of the casing string. The drilling assembly is releasably attached to the casing string by a casing latch having a pass-through diameter smaller than an inner diameter of the casing string. The method further comprising connecting a bi-centered cutter assembly to a distal end of the drilling assembly. The bi-centered cutter assembly is configured to drill the borehole at a gauge diameter that is larger than an outer diameter of the casing string. A first section of the borehole is drilled. The casing string is slid further into the borehole as it is drilled. The drilling assembly is released from the casing latch and the drilling assembly and the bi-centered cutter assembly are retrieved through the casing latch and the casing string. Finally, the casing string is cemented in place.  
      Other aspects and advantages of the invention will be apparent from the following description and the appended claims.  
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1B  shows a prior art drilling operation.  
       FIG. 1B  shows a prior art casing drilling operation.  
       FIG. 2A  shows a prior art bent housing.  
       FIG. 2B  shows a prior art “point-the-bit” system.  
       FIG. 2C  shows a prior art “push-the-bit” system.  
       FIG. 3  shows a prior art directional casing drilling operation.  
       FIG. 4  shows a directional casing drilling system having a bi-centered bit in accordance with one embodiment of the invention.  
       FIG. 5  shows a rotary steerable directional casing drilling system having a bi-centered bit in accordance with another embodiment of the invention.  
       FIG. 6  shows a rotary steerable directional casing drilling system having a bi-centered bit in accordance with another embodiment of the invention.  
       FIG. 7  shows a bi-centered bit in accordance with another embodiment of the invention.  
       FIG. 8  shows a bi-centered bit in accordance with another embodiment of the invention.  
    
    
     DETAILED DESCRIPTION  
      In some embodiments, the invention relates to the use of a bi-centered bit in a directional casing drilling system. In some other embodiments, the invention relates to the use of a bi-centered bit in a rotary steerable casing drilling system. In yet other embodiments, the invention relates to the use of bi-centered bits in a rotary steerable system (RSS).  
      It should be noted that although specific embodiments refer to casing drilling, the teachings of the present invention are equally applicable to drilling while lining. A “liner” is a casing string that does not extend to the top of a well. A liner is typically used when a well is drilled, cased, and then drilled again to deepen the well. The part of the well that is drilled past the initial casing string is cased with “liner.” In practice, the only difference between casing and liner is that the liner has a smaller diameter, and it is suspended from the bottom of the casing string above it. The difference between liner and casing is not germane to the invention; thus, no distinction is made between casing and liner.  
      Referring now to  FIG. 4 , a schematic representation of a directional casing drilling system  450  using a bi-centered cutter assembly  452  is shown. The directional casing drilling assembly  450  has a bottom hole assembly (BHA)  420  that is connected to the casing string  424  through a casing latch  426 . In an embodiment of the present invention, the traditional drill bit and underreamer of the BHA  420  have been replaced by the bi-centered cutter assembly  452 .  
      The illustrated BHA  420  additionally comprises a mud motor and bent sub assembly  432 , a measurement while drilling (MWD) assembly  434 , and an eccentric bushing  436 . However, it should be understood that the component make-up of the BHA  420  is not intended to limit the scope of the present invention.  
      The bi-centered cutter assembly  452  has the benefit of cutting the same diameter bore  454  as would be possible with a traditional bit and underreamer, but without the need for engaging and collapsing the cutting arms of the underreamer. The bi-centered cutting assembly  452  preferably has two cutting surfaces, a first cutting surface  456  and a second cutting surface  458  axially spaced by an offset. The first cutter surface  456  effectively cuts a pilot hole  460  while second cutter surface  458 , eccentrically positioned around the rotation axis of bit  452  and cutting surface  456 , performs the underreaming function and finish cuts the primary bore  454 .  
      One of the benefits of using a bi-centered cutting assembly over a traditional bit and collapsible underreamer is that the task of extending the cutter arms of the underreamer is no longer necessary. Furthermore, there no longer is a risk that the arms of the underreamer will become damaged or broken, thereby necessitating a costly fishing and recovery operation. Additionally, the risk of the underreamer becoming damaged and un-retrievable through the casing latch  426  is avoided as the bi-centered cutting assembly  452  is designed to be retrieved through the same casing latch  426 , but without the need for an intervening configuration step.  
      Referring now to  FIG. 5 , a schematic representation of a directional casing drilling assembly  570  using a bi-centered cutter assembly  552  with a point the bit RSS is shown. The directional casing drilling assembly  570  is similar to that shown in  FIG. 4 , except that a point the bit rotary steerable directional casing drilling system  572  is used in place of the bent housing ( 432  of  FIG. 4 ) to guide the bi-centered cutter assembly  552  to its desired trajectory. Also in the directional casing drilling system  572  is a MWD assembly  574  to communicate to controllers or personnel on the surface how and where to direct drilling operations with the direction casing drilling assembly  572 .  
      Using the point the bit system  572 , the bit axis  576  needed for the desired trajectory of the wellbore  578  is maintained, while the casing string  524  is rotated. This is accomplished through the use of a geostationary angular orientation device that acts in a manner similar to a bent housing. While the casing string  524  (and attached bi-centered cutting assembly  552 ) is rotated, the angular orientation device (not shown) is capable of not rotating with respect to the borehole, thus allowing the angle of the RSS to remain in place while the casing string  524  is rotated from above to drill first a pilot hole  578  and then the completed full gauge borehole  580 .  
      When the borehole  580  is completed, the casing latch  526  can be disengaged and the entire directional casing drilling assembly  570  can be retrieved through the internal bore of the casing string  524 . After the directional casing drilling assembly is removed, a cementing operation can be performed to secure the casing string  524  in place.  
      It should be understood that the point the bit system  575  having the bi-centered bit  552  is fully compatible with traditional drillstring if casing while drilling is not desired.  
      Referring to  FIG. 6 , a schematic representation of a push the bit rotary steerable directional casing drilling assembly  690  using a bi-centered cutter assembly  652  is shown. The drilling assembly  690  has the MWD assembly  574  of  FIG. 5 , but uses a push the bit RSS  692 . The push the bit RSS  692  also has an outer profile that houses at least one kick pad apparatus  694  to steer the drilling of the pilot hole  696  and the completed borehole  698 . Because the kick pad  694  is synchronously and sequentially activated at the same location relative to the borehole  698  while the casing string  624  and RSS  692  is rotated, dynamic pushing and positioning of the bi-centered cutting assembly  652  is possible. The push the bit system  690  is retrievable through the casing latch  626 . Another variant of the push the bit system is one with a stationary, non-rotating, sliding sleeve and kick-pad assembly.  
      As with the point the bit system  570  of  FIG. 5 , the push the bit system  690  is fully compatible with a traditional drillstring if casing while drilling is not desired. If using traditional drillstring, the entire drillstring must first be “tripped out” of the before a casing string can be subsequently installed, if desired.  
      Referring now to  FIG. 7 , a schematic representation of a first bi-centered cutter assembly  700  is shown. The bi-centered cutter assembly  700  is shown attached to a directional drilling assembly  702  to cut a borehole  704 . While no particular directional drilling assembly  702  is shown, it should be understood that directional drilling assembly  702  may have a bent housing, a point the bit RSS, a push the bit RSS, or any other type of directional drilling assembly known to one skilled in the art. The bi-centered cutter assembly has a first cutter  706  and a second cutter assembly  708 . The first and second cutter assemblies  706 ,  708  are not co-axial and are instead axially spaced by an offset (not shown). The first cutter  706  is responsible for cutting a pilot hole  710  and the second cutter assembly is responsible for cutting a region  712  to open up the pilot hole into the full bore  702 . Depending on the type and configuration of the directional drilling assembly  702  used, a kick pad or stabilizer  714  can press against borehole  704  to keep the bi-centered cutting assembly  700  on path.  
      Referring now to  FIG. 8 , a schematic representation of a second bi-centered cutter assembly  820  is shown. The bi-centered cutter assembly  820  has a first cutter m surface in the form of a traditional drill bit  822  along its axis to cut a pilot hole  824 . A second cutter surface  826  is positioned upon a distal end of a directional drilling assembly  828  to open up a pilot hole  824  through a region  830  into a full desired bore  832 . As above, it should be understood that the directional drilling assembly  828  may have a bent housing, a point the bit RSS, a push the bit RSS, or any other type of directional drilling assembly known to one skilled in the art. Also, depending on the type and configuration of the directional drilling assembly  828  used, a kick pad or stabilizer  834  can be employed to press against the borehole  832  to keep the bi-centered cutting assembly  820  on path.  
      While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.