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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/291,443, filed on Nov. 10, 2008. 
     
    
     BACKGROUND OF DISCLOSURE 
       [0002]    1. Field of the Disclosure 
         [0003]    The embodiments herein relate generally to rotary directional drilling apparatuses for downhole steering of a drill bit and methods for steering a drill string. 
         [0004]    2. Background Art 
         [0005]    During rotary drilling, a drill bit is rotated from the surface of a well by rotating a drill string. It is often desirable to control the direction in which the drilling proceeds through use of a downhole steerable drilling apparatus. Steerable drilling apparatuses include hydraulic devices that apply a lateral bias to a drill string, bent or bendable housing members for drilling at angles, and rotary devices that use a rotatable member, actuators, and/or retractable members to control the direction of the drill string. 
         [0006]    Conventional downhole rotary directional drilling assemblies use gravity and compression to force an under gauge stabilizer to the bottom side of a hole, with a drill collar acting as a lever, and a near bit stabilizer acting as a fulcrum. This lever-like motion pushes the drill bit upward, causing the drill bit to drill on the top of a hole, thereby increasing the angle of the hole. The angle of the drilling can be modified through changes in the length of the drill collar, the diameter of the stabilizers, or modifying one or more drilling parameters. 
         [0007]    Conventional rotary directional drilling assemblies can steer a drill bit only within a single plane, and not along the azimuth. 
         [0008]    A need exists for a rotary directional drilling apparatus that can allow an operator to steer a drill string in any direction, controlling directional changes both in hole angle and along the azimuth. 
         [0009]    A need also exists for a rotary directional drilling apparatus that can utilize fixed steering elements without use of actuators, rather than conventional retractable and movable biasing and thrusting members. 
         [0010]    A further need exists for a rotary directional drilling apparatus able to selectively adjust the orientation of a drill bit through control of the flow of drilling fluid or mud through the mud motor. 
         [0011]    The present embodiments meet these needs. 
       SUMMARY OF DISCLOSURE 
       [0012]    In an embodiment, the present apparatus for steering a drilling string includes a downhole drilling motor having a rotor for imparting rotational movement to the drill bit, and a stator rotatably disposed about the rotor. The stator can be freely rotatable about the rotor, enabling counter rotation of the stator relative to the rotor. One or more bearings, rollers, and/or seals, as known in the art, can be disposed between the rotor and the stator to enable this rotation. 
         [0013]    It should be noted that the drill string is connected to the rotor, rather than to the stator, while conventional rotary directional drilling assemblies typically utilize a connection between the drill string and the stator. Rotation of the drill string, such as when drilling, as known in the art, thereby imparts rotation to the rotor without imparting this rotation to the stator. Various bearings, rollers, and/or seals, as known in the art, can be disposed at each end of the motor to facilitate this rotation and prevent the loss of drilling fluid from the stator. In an embodiment, the drill string can have a concentric stabilizer connected thereon. 
         [0014]    A first passage is disposed through the rotor for flowing drilling fluid through the rotor to the drill bit. One or more fluid passages are disposed through the rotor to flow drilling fluid between the first passage and the stator. The stator can include a fluid passage having vanes, lobes, or similar protrusions, as known in the art, adapted to enable the flow of fluid to impart rotational motion to the stator in a direction counter to the rotation of the rotor imparted by the drill string. The flow rate of drilling fluid or mud to the stator controls the rate of rotation of the stator. In an embodiment, the rotor can include an upper diverter passage disposed through a first end of the rotor and a lower diverter passage disposed through a second end of the rotor. 
         [0015]    In a further embodiment, the first passage can include a flow restrictor for facilitating the flow of drilling fluid to at least one of the fluid passages to cause counter rotation of the stator relative to the rotor. 
         [0016]    One or more seals can be disposed between the rotor and the stator, exterior to each of the fluid passages. 
         [0017]    A valve is disposed in communication with the first passage and one of the fluid passages to the stator for selectively controlling the flow of drilling fluid between the first passage and the stator. The flow rate of drilling fluid conveyed to the stator can be controlled by the valve, thereby controlling the rotational speed of the stator. 
         [0018]    In an embodiment, the valve can be in communication with a measurement while drilling device and can be controlled responsive to data from the measurement while drilling device. In a further embodiment, the valve can include an actuator, a power supply, or combinations thereof. 
         [0019]    One or more blades can be fixedly disposed on the exterior surface of the stator. The one or more blades are usable to orient the drill bit and steer the drill string by providing an asymmetrical moment to the drill string. By selectively controlling the rate of counter rotation of the stator relative to the rotor, the direction of drilling operations can be controlled. The stator can be counter rotated at an equal rate with respect to the rotation of the rotor to maintain the one or more blades in a stationary orientation with respect to a fixed position within a borehole. The one or more blades thereby offset the apparatus&#39; rotational center from the center of the borehole by providing the apparatus with an asymmetrical moment, thereby enabling reorientation of the drill bit in any horizontal or vertical direction through selective positioning of the blades. In an embodiment, the one or more blades can be over-gauge blades. 
         [0020]    The blades are also usable to maintain the orientation of the drill bit and continue drilling in a straight direction by selectively controlling the flow rate of drilling fluid through the stator to maintain constant rotation of the one or more blades with respect to the rotor. 
         [0021]    In an embodiment, the apparatus can include an electronic member in communication with the measurement while drilling device and with the valve for determining the current position of the one or more blades and controlling the valve in response to data obtained from the measurement while drilling device. 
         [0022]    The present embodiments also relate to methods for steering a drill string using similar rotatable asymmetrical moments about a drill string. In an embodiment, a rotary directional drilling assembly, which can include a motor, valve, and blade, as described previously, is provided, coupled with a measurement while drilling device in communication with a drill string. 
         [0023]    Data from the measurement while drilling device is received, and a position of the blade necessary to orient the drill bit in a desired direction is determined. The current location of the blade can be determined using the measurement while drilling device. 
         [0024]    The valve is then controlled to achieve the necessary flow of drilling fluid to the stator, to cause counter rotation of the stator relative to the rotor until the desired position of the blade is reached. The valve can then be adjusted to change the rotational speed of the stator to maintain the blade in the desired position with respect to the borehole. The position of the blade causes reorientation of the drill bit. The valve can then be readjusted to change the rotational speed of the stator to cause drilling to continue in a generally straight direction. 
         [0025]    The valve can be controlled to enable fluid flow to the stator such that the blade remains stationary with respect to a fixed point within the bore hole, thereby causing the drill string to change direction through reorientation of the drill bit. Alternatively, the valve can be controlled to regulate the flow of drilling fluid to the stator such that the stator continuously rotates relative to the rotor, thereby causing the drill string to drill in a constant direction. 
         [0026]    The present embodiments thereby enable steering of a drill string through control of a rotatably moveable asymmetrical moment about a drill string, which can be rotated about the drill string through selective control of the flow of drilling fluid. 
         [0027]    Other aspects and advantages of the disclosure will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]    In the detailed description of the embodiments presented below, reference is made to the accompanying drawings, in which: 
           [0029]      FIG. 1  depicts a cross-sectional view of an embodiment of the present rotary directional drilling apparatus attached to a drill string. 
           [0030]      FIG. 2  depicts a cross sectional view of an embodiment of the motor of the rotary directional drilling apparatus of  FIG. 1 . 
           [0031]      FIG. 3  depicts a cross sectional view of the diverter valve of the rotary directional drilling apparatus of  FIG. 1 . 
           [0032]      FIGS. 4A and 4B  depict an end view of an embodiment of the present rotary directional drilling apparatus showing the rotation of the rotor and the stator. 
           [0033]      FIG. 5  depicts an isometric cross sectional view of the downhole motor of  FIG. 2 . 
       
    
    
       [0034]    The present embodiments are detailed below with reference to the listed Figures. 
       DETAILED DESCRIPTION 
       [0035]    Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular descriptions and that the embodiments can be practiced or carried out in various ways. 
         [0036]    Referring now to  FIG. 1 , a cross-sectional view of an embodiment of the present rotary directional drilling apparatus is depicted, usable to orient a drill bit  36  for steering a drill string  32 . 
         [0037]    The apparatus is shown having a downhole motor  10 , which includes a rotor  12  and a stator  14 . A passage  16  is shown extending through the rotor  12 , which is depicted extending along the central axis of the rotor  12 . 
         [0038]    An upper diverter passage  18  and a lower diverter passage  20  are shown extending through the rotor  12  between the passage  16  and the stator  14 . A blade  22 , which in an embodiment, can include an over-gauge blade, is shown disposed on the exterior surface of the stator  14 . The blade  22  offsets the apparatus&#39; rotational center from the center of a borehole, thereby enabling reorientation of the drill bit  36  through selective placement of the blade  22 . 
         [0039]    The stator  14  is freely rotatable about the rotor  12 , such that the blade  22  can be selectively maintained in a stationary position with respect to a bore hole, to reorient the drill bit  36 , or selectively maintained in constant counter rotational motion with respect to the rotor  12 , to maintain a straight drilling direction. One or more bearings, rollers, or similar devices, as known in the art, can be used to enable the stator  14  to rotate independent of the rotor  12 . Due to the ability of the blade  22  to be positioned on any side of the drill string  32  through rotation of the stator  14 , the blade  22  is usable to orient the drill bit  36  in any horizontal or vertical direction. 
         [0040]    A valve  24  is shown disposed within the upper diverter passage  18  of the rotor  12 , in communication with the passage  16 . A sub  26 , shown connected to the rotor  12 , can contain electronic controls and/or a power supply for the valve  24  and/or a measurement while drilling device, or other similar devices in communication with the drill string  32 . 
         [0041]    The valve  24  is controllable to regulate the flow of drilling fluid from the passage  16 , through the upper diverter passage  18 , to a stator passage ( 25 ,  FIG. 2 ) disposed in the stator  14 . The stator passage can include one or more interior vanes  14 A (e.g., lobes or similar protrusions), as known in the art, such that the flow of drilling fluid through the stator passage imparts rotation to the stator  14  as fluid impacts one or more of the vanes  14 A. The flow rate of drilling fluid to the stator  14  controls the rate of counter rotation of the stator  14  with respect to the rotor  12 . 
         [0042]      FIG. 1  also depicts a measurement while drilling device  30  attached to the sub  26 . The drill string  32  is depicted attached to the measurement while drilling device  30 . A concentric stabilizer  34  is depicted attached to the drill string  32 . Data from the measurement while drilling device  30  is usable to control the valve  24  for positioning of the blade  22  to reorient the drill bit  36 . 
         [0043]    It should be noted that the drill string  32  is attached to the rotor  12 , via the measurement while drilling device  30  and the sub  26 , rather than to the stator  14 , while a conventional rotary directional drilling apparatus utilizes a connection between the drill string and the stator. The rotor  12  is also shown attached to a near-bit stabilizer  35 , which is in turn attached to the drill bit  36 . In an embodiment, the near-bit stabilizer  35  can include a reamer. Bearings and/or rollers, as are known in the art, can be disposed at each end of the rotor  12  to facilitate rotation of the rotor  12 . Bearings and/or seals, as known in the art, can be disposed at each end of the stator  14  to facilitate rotation of the stator  14  and prevent the exodus of drilling fluid from the stator passage into the annulus. 
         [0044]    Referring now to  FIG. 2 , a cross-sectional view of the downhole motor  10  is shown. 
         [0045]    The stator  14 , having the blade  22  disposed thereon, is shown rotatably disposed about the rotor  12 . Bearings and/or rollers, as known in the art, can be disposed between the rotor  12  and the stator  14  to facilitate rotation of the stator  14 . The passage  16  is shown in communication with the upper diverter passage  18  and lower diverter passage  20  for conveying drilling fluid to and from a stator passage  25  within the stator  14 . The stator passage  25  can include various vanes  14 A (and/or other similar protrusions) adapted to enable rotation of the stator  14  as drilling fluid is flowed through the stator passage  25 . The valve  24  is shown disposed within the upper diverter passage  18  in communication with the passage  16 , for controlling the flow of drilling fluid from the passage  16  through the upper diverter passage  18  to the stator  14 , thereby controlling the rotational speed of the stator  14  relative to the rotor  12 . 
         [0046]    An upper seal  38  is shown disposed between the rotor  12  and the stator  14  above the upper diverter passage  18 . A lower seal  40  is shown disposed between the rotor  12  and the stator  14  below the lower diverter passage  20 . 
         [0047]    Referring briefly to  FIG. 5 , a partial isometric cross sectional view of the downhole motor  10  is shown, which further illustrates the components of the motor  10  shown in  FIG. 2 , and as described herein. 
         [0048]    Referring again to  FIG. 2 , there may also be a flow restriction  42  within the passage  16 , which facilitates the flow of drilling fluid to the upper diverter passage  18  via the valve  24 , while allowing excess fluid to flow through the passage  16  to the drill bit. 
         [0049]    Referring now to  FIG. 3 , a cross-sectional view of the valve  24  is depicted.  FIG. 3  depicts an actuator and power supply  44  usable to actuate a movable member  46  until partially or fully aligned with the valve passage  48 . While the actuator and power supply  44  are depicted in close proximity to the valve  24 , in an embodiment, the actuator and power supply could be remote from the motor, such as disposed within an adjacent sub. Through selective actuation of the valve  24 , the flow rate of drilling fluid to the stator can be controlled to achieve a desired rate of counter rotation of the stator relative to the rotor. 
         [0050]    The present rotary directional drilling apparatus is thereby able to use the flow rate of drilling mud to selectively position an exterior blade with respect to a bore hole to orient the direction of a drill bit, without use of thrusting, actuatable, or retractable steering members, by enabling counter rotation of the stator and blade relative to the rotor. 
         [0051]      FIGS. 4A and 4B  depict end views of the rotor  12  having the fluid passage  16  extending therethrough, with the stator  14  rotatably disposed about the rotor  12 .  FIG. 4A  depicts the blade  22  disposed on the exterior surface of the stator  14  in a first position, while  FIG. 4B  depicts the blade  22  in a second position rotationally displaced from the first position. A bearing surface  15 , which can include various bearings and/or rollers as known in the art, can be disposed between the rotor  12  and stator  14  to facilitate the rotation of the stator  14  relative to the rotor  12 . As a drill string connected to the rotor  12  is rotated, such as when drilling, rotation is imparted to the rotor  12  in a first direction  23 . 
         [0052]    Selectively, fluid that flows through the fluid passage  16  to the drill bit can be diverted through diverter passages (shown in  FIGS. 1 and 2 ) to a stator passage  25  disposed within the stator  14 , which can include vanes  14 A (or similar protrusions) adapted to provide counter rotation to the stator  14  in a second direction  27  opposite the first direction  23 . The blade  22  disposed on the exterior of the stator  14  can thereby be rotated to any position about the drill string, as illustrated. 
         [0053]    While the present disclosure 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 may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.

Summary:
An apparatus for steering a drill string that includes at least one blade fixedly disposed on an exterior surface of the drill string, such that the at least one blade is rotatable about the drill string in response to fluid flow through a fluid passage in association with said at least one blade, and the at least one blade rotates independent of the drill string for imparting an asymmetrical moment to the drill string in a selected direction for orienting a drill bit attached to the drill string, thereby steering the drill string.