Abstract:
An apparatus for steering a drill string is disclosed herein, the apparatus comprising a drilling motor comprising a rotor, a stator, and at least one fluid passage for flowing drilling fluid to the stator. A blade is fixedly disposed on the exterior surface of the stator. A diverter valve controls the flow rate of drilling fluid to the stator, to provide counter rotational movement to the stator with respect to the rotor. Placement and movement of the blade is thereby controlled. When the blade is rotated such that it remains stationary with respect to a fixed point in a borehole, the drill bit is turned. When the blade is counter-rotated in a constant motion with respect to the rotor, the drill bit continues to drill in a straight direction.

Description:
FIELD 
     The embodiments herein relate generally to rotary directional drilling apparatuses for downhole steering of a drill bit and methods for steering a drill string. 
     BACKGROUND 
     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. 
     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. 
     Conventional rotary directional drilling assemblies can steer a drill bit only within a single plane, and not along the azimuth. 
     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. 
     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. 
     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. 
     The present embodiments meet these needs. 
     SUMMARY 
     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. 
     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. 
     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. 
     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. 
     One or more seals can be disposed between the rotor and the stator, exterior to each of the fluid passages. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the embodiments presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1  depicts a cross-sectional view of an embodiment of the present rotary directional drilling apparatus attached to a drill string. 
         FIG. 2  depicts a cross sectional view of an embodiment of the motor of the rotary directional drilling apparatus of  FIG. 1 . 
         FIG. 3  depicts a cross sectional view of the diverter valve of the rotary directional drilling apparatus of  FIG. 1 . 
         FIGS. 4A and 4B  depict an end view of an embodiment of the present rotary directional drilling appratus showing the rotation of the rotor and the stator. 
     
    
    
     The present embodiments are detailed below with reference to the listed Figures. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     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. 
     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 ). 
     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 ). 
     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 ). 
     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. 
     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 ). 
     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 , shown in  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 ). 
       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 ). 
     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 hit ( 36 ). In an embodiment, the near-bit stabilizer ( 35 ) can include a reamer. Bearings andior 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. 
     Referring now to  FIG. 2 , a cross-sectional view of the downhole motor ( 10 ) is shown. 
     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 ). 
     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 ). 
       FIG. 2  also depicts 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. 
     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. 
     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. 
       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 ). 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.