Abstract:
A downhole turbine assembly may comprise a tangential turbine disposed within a section of drill pipe. A portion of a fluid flowing through the drill pipe may be diverted to the tangential turbine generally perpendicular to the turbine&#39;s axis of rotation. After rotating the tangential turbine, the diverted portion may be discharged to an exterior of the drill pipe.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority to U.S. Provisional Pat. App. No. 62/164,933 filed on May 21, 2015 and entitled “Downhole Power Generator”, which is incorporated herein by reference for all that it contains. 
     
    
     BACKGROUND 
       [0002]    In endeavors such as the exploration or extraction of subterranean resources such as oil, gas, and geothermal energy, it is common to form boreholes in the earth. To form such a borehole  111 , a specialized drill bit  112  may be suspended from a derrick  113  by a drill string  114  as shown in  FIG. 1 . This drill string  114  may be formed from a plurality of drill pipe sections  115  fastened together end-to-end. As the drill bit  112  is rotated, either at the derrick  113  or by a downhole motor, it may engage and degrade a subterranean formation  116  to form a borehole  111  therethrough. Drilling fluid may be passed along the drill string  114 , through each of the drill pipe sections  115 , and expelled at the drill bit  112  to cool and lubricate the drill bit  112  as well as carry loose debris to a surface of the borehole  111  through an annulus surrounding the drill string  114 . 
         [0003]    Various electronic devices, such as sensors, receivers, communicators or other tools, may be disposed along the drill string or at the drill bit. To power such devices, it is known to generate electrical power downhole by converting kinetic energy from the flowing drilling fluid by means of a generator. One example of such a downhole generator is described in U.S. Pat. No. 8,957,538 to Inman et al. as comprising a turbine located on the axis of a drill pipe, which has outwardly projecting rotor vanes, mounted on a mud-lubricated bearing system to extract energy from the flow. The turbine transmits its mechanical energy via a central shaft to an on-axis electrical generator which houses magnets and coils. 
         [0004]    One limitation of this on-axis arrangement, as identified by Inman, is the difficultly of passing devices through the drill string past the generator. Passing devices through the drill string may be desirable when performing surveys, maintenance and/or fishing operations. To address this problem, Inman provides a detachable section that can be retrieved from the downhole drilling environment to leave an axially-located through bore without removing the entire drill string. 
         [0005]    The turbine described by Inman is known as an axial turbine because the fluid turning the turbine flows parallel to the turbine&#39;s axis of rotation. An example of an axial turbine  220  is shown in  FIG. 2  connected to a rotor  221  portion of a generator  222 . Both axial turbine  220  and rotor  221  may be disposed within and coaxial with a section of a drill pipe  215 . Drilling fluid  223  flowing through the drill pipe  215  may engage a plurality of vanes  224  disposed about the axial turbine  220  causing both axial turbine  220  and rotor  221  to rotate on a fluid-lubricated bearing system  225 . In the embodiment shown, the rotor  221  comprises a plurality of magnets  226  disposed about the rotor  221 . Movement of the magnets  226  may induce electrical current in coils of wire  227  wound around poles  228  of a stator  229 . 
         [0006]    It may be typical in downhole applications employing an axial turbine to pass around  800  gallons/minute (3.028 m 3 /min) of drilling fluid past such a turbine. As the drilling fluid rotates the axial turbine, it may experience a pressure drop of approximately 5 pounds/square inch (34.47 kPa). Requiring such a large amount of drilling fluid to rotate a downhole turbine may limit a drilling operator&#39;s ability to control other drilling operations that may also require a certain amount of drilling fluid. 
         [0007]    A need therefore exists for a downhole turbine that requires less fluid flow to operate. An additional need exists for a downhole turbine that does not require retrieving a detachable section in order to pass devices through a drill string. 
       BRIEF DESCRIPTION 
       [0008]    A downhole turbine assembly may comprise a tangential turbine disposed within a section of drill pipe. A portion of a fluid flowing through the drill pipe may be diverted to the tangential turbine generally perpendicular to the turbine&#39;s axis of rotation. After rotating the tangential turbine, the diverted portion may be discharged to an exterior of the drill pipe. 
         [0009]    As the pressure difference between fluid inside the drill pipe and fluid outside the drill pipe may be substantial, it may be possible to produce a substantially similar amount of energy from a tangential turbine, as compared to an axial turbine, while utilizing substantially less drilling fluid. For example, while it may be typical in downhole applications to pass around 800 gallons/minute (3.028 m 3 /min) of drilling fluid past an axial turbine of the prior art, as discussed previously, which then may experience a pressure drop of around 5 pounds/square inch (34.47 kPa), diverting around 1-10 gallons/minute (0.003785-0.03785 m 3 /min) of drilling fluid past a tangential turbine and then discharging it to an annulus surrounding a drill pipe may allow that fluid to experience a pressure drop of around 500-1000 pounds/square inch (3,447-6,895 kPa) capable of producing substantially similar energy. 
     
    
     
       DRAWINGS 
         [0010]      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. 
           [0011]      FIG. 2  is a schematic representation of an embodiment of an axial turbine of the prior art disposed within a portion of a drill pipe with fluid flowing therethrough. 
           [0012]      FIG. 3  is a schematic representation of an embodiment of a tangential turbine disposed within a portion of a drill pipe with fluid flowing therethrough. 
           [0013]      FIG. 4  is a perspective view of an embodiment of a downhole turbine device (shown partially transparent for clarity). 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 3  shows one embodiment of a tangential turbine  320  disposed within a section of a drill pipe  315 . A portion of drilling fluid  333  flowing through the drill pipe  315  may be diverted away from a primary drilling fluid  323  flow and discharged to an annulus surrounding the drill pipe  315 . The diverted portion of drilling fluid  333  may be directed toward the tangential turbine  320  within a plane generally perpendicular to an axis of rotation of the tangential turbine  320 . The diverted portion of drilling fluid  333  may cause the tangential turbine  320  and a rotor  321  connected thereto to rotate. The rotor  321  may comprise a plurality of magnets  326  disposed about the rotor  321 . Movement of the magnets  326  may induce electrical current in coils of wire  327  wound around poles  328  of a stator  329  in a generator. Those of skill in the art will recognize that, in various embodiments, a plurality of magnets and coils of wire may be disposed opposite each other on either the rotor or the stator and have the same effect. Further, in various embodiments, a plurality of magnets may be permanent magnets or electromagnets and have the same effect. 
         [0015]    In the embodiment shown, the tangential turbine  320  is disposed within a sidewall of the drill pipe  315 . A rotational axis of the tangential turbine  320  may be parallel to the central axis of the drill pipe while also being offset from the central axis. In this configuration, the primary drilling fluid  323  passing through the drill pipe  315  is not obstructed by the tangential turbine  320 , allowing for objects to be passed through the drill pipe  315  generally unhindered. 
         [0016]    An outlet  332  for discharging the diverted portion of drilling fluid  333  to an exterior of the drill pipe  315  may be disposed on a sidewall of the drill pipe  315 . In the embodiment shown, a check valve  334  is further disposed within the outlet to allow fluid to exit the drill pipe  315  but not enter. 
         [0017]    Polycrystalline diamond (PCD) bearings  331  may support the tangential turbine  320  and rotor  321  allowing them to rotate. It is believed that PCD bearings may require less force to overcome friction than traditional mud-lubricated bearing systems described in the prior art. It is further believed that PDC bearings may be shaped to comprise a gap therebetween sufficient to allow an amount of fluid to pass through while blocking particulate. Allowing fluid to pass while blocking particulate may be desirable to transport heat away from a generator or balance fluid pressures. 
         [0018]      FIG. 4  discloses a possible embodiment of a tangential turbine device (part of which is transparent for clarity). The device comprises a housing  441  with a chamber  442  disposed therein. A tangential turbine  420 , such as an impulse turbine, may be disposed within the chamber  442  and attached to an axle  443  leading to a rotor (not shown). The housing  441  may comprise at least one inlet  444 , wherein drilling fluid may pass through the housing  441  into the chamber  442 . In the embodiment shown, the inlet  444  is disposed on a plane perpendicular to a rotational axis of the tangential turbine  420 . The inlet  444  is also shown offset from the rotational axis of the tangential turbine  420  such that fluid entering the chamber  442  through the inlet  444  may impact a plurality of blades  445  forming part of the tangential turbine  420  to rotate the tangential turbine  420 . Each of the plurality of blades  445  may comprise a concave surface  446  thereon, disposed on a surface generally parallel to the rotational axis of the tangential turbine  420 , to help catch fluid entering the chamber  442  and convert as much energy therefrom into rotational energy of the tangential turbine  420 . In  FIG. 4 , three inlets are shown. However, more or less inlets may be preferable. Additionally, at least one outlet  447  may allow fluid that enters the chamber  442  to escape. 
         [0019]    The tangential turbine  420  may comprise PCD to reduce wear from the fluid entering the chamber  442 . In some embodiments, the tangential turbine  420  may be formed entirely of PCD. 
         [0020]    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.