Abstract:
An apparatus for rotating an instrument in a wellbore includes a non magnetic housing configured to traverse the interior of the wellbore. The housing has an external diameter smaller than an internal diameter of a casing disposed in the wellbore. A plurality of electromagnets is arranged circumferentially about the interior of the housing and is configured to induce magnetic flux through a wall of the housing when actuated. A controller configured to sequentially rotationally actuate the electromagnets. A method for rotating a wellbore instrument in a wellbore includes causing parts of an instrument housing to be sequentially rotationally magnetically attracted to a casing disposed in the wellbore. The housing has a smaller external diameter than an internal diameter of the casing. The sequential rotational magnetic attraction is continued as needed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to the field of instruments conveyed into subsurface wellbores by armored electrical cable. More specifically, the invention relates to devices for moving such instruments to a selected rotary orientation within a wellbore. 
         [0005]    2. Background Art 
         [0006]    Many types of instruments are used in wellbores drilled through subsurface rock formations. Such instruments can include, among other devices, sensors for measuring properties of the rock formations outside the wellbore, energy sources for various types of surveying or evaluation, mechanical wellbore intervention tools and directional survey instruments, as non limiting examples. Such instruments may be conveyed along the inside of the wellbore by a technique generally known as “wireline” in which an armored cable having one or more insulated electrical conductors therein is extended into and withdrawn from the wellbore using a winch, and in which the instruments are disposed at the end of the cable. 
         [0007]    In some cases, it may be desirable to move the instrument to a selected rotary orientation within the wellbore. Such orientations may include having sensors on the instrument directed toward, for example, the gravitationally upwardmost direction (“high side”) for purposes of surveying the trajectory of the wellbore. Other examples may include having a seismic energy source oriented in the direction of an adjacent wellbore. 
         [0008]    Irrespective of the reason for requiring rotary orientation capability, it has proven impractical to provide such capability when instruments are conveyed into a wellbore by wireline. 
       SUMMARY OF THE INVENTION 
       [0009]    A method for rotating a wellbore instrument in a wellbore according to one aspect of the invention includes causing parts of an instrument housing to be sequentially rotationally magnetically attracted to a casing disposed in the wellbore. The housing has a smaller external diameter than an internal diameter of the casing. The sequential rotational magnetic attraction is continued until the instrument housing is oriented in a selected rotational direction. 
         [0010]    An apparatus for rotating an instrument in a wellbore according to another aspect of the invention includes a non magnetic housing configured to traverse the interior of the wellbore. The housing has an external diameter smaller than an internal diameter of a casing disposed in the wellbore. A plurality of electromagnets is arranged circumferentially about the interior of the housing and is configured to induce magnetic flux through a wall of the housing when actuated. A controller configured to sequentially rotationally actuate the electromagnets. 
         [0011]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows an instrument conveyed into a wellbore as it may be used with an example rotator according to the invention. 
           [0013]      FIG. 2  shows the instrument, the example rotator and associated devices of  FIG. 1  in more detail. 
           [0014]      FIG. 3  shows a cross section of one example of a rotator. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows an instrument  14  conveyed into a wellbore  18  drilled through subsurface rock formations. The wellbore  18  in  FIG. 1  includes a steel pipe or casing  16  installed therein. It is only necessary for purposes of using the invention that the casing  16  is ferromagnetic. Other properties of the casing  16  are not intended to limit the scope of the invention. The instrument  14  in the present example can be conveyed through the interior of the casing using armored cable  22  deployed by a winch  20 . Such conveyance is known as “wireline” as explained in the Background section herein. The cable  22  may include one or more insulated electrical conductors for transmitting power to the instrument  14  and communicating signals from the instrument  14  to a recording and control unit  24  disposed at the surface. For purposes of defining the scope of the invention, other conveyance known in the art called “slickline” in which the cable has a cylindrical, smooth exterior surface and may or may not include electrical conductors therein is intended to be within the definition of “wireline.” An example of slickline having electrical conductors therein is described in U.S. Pat. No. 5,122,209 issued to Moore. 
         [0016]    The instrument  14  is coupled to the cable  22  using a cable head  26 . The cable head  26  may be coupled to a swivel  28  that enables relative rotation between the cable  22  and the instrument  14  while maintaining electrical communication between the instrument  14  and the cable  22 . The swivel  28  may be coupled to one end of a rotator  10 . The other end of the rotator  10  may be coupled to the instrument  14 , in some examples using a flexible coupling  12 . The flexible coupling  12  may be used to enable the instrument  14  to be moved with respect to the rotator  10  by deflection and/or displacement of the axis of the instrument  14  with respect to the axis of the rotator  10 , while maintaining rotational coupling between the instrument  14  and the rotator  10 . See U.S. Pat. No. 5,808,191 issued to Alexy, Jr. et al. for a description of one example of a flexible coupling, although the type of flexible coupling and whether it is used in any example is not intended to limit the scope of the present invention. 
         [0017]    It is also to be understood that the instrument  14  and the rotator  10  may be disposed within the same instrument housing or as part of the same instrument. The description with reference to and the illustration in  FIG. 1  are meant only to provide one non limiting example of how to make and use the present invention. Accordingly, the use of a separate rotator and instrument as shown is not a limit on the scope of the present invention. 
         [0018]    One example of a type of instrument that may be used with a rotator according to the invention is a directional seismic energy source. Such sources may direct a substantial portion of the seismic energy generated in a single lateral direction, or within a limited range of angle with respect to the source longitudinal axis of the source. In the example shown in  FIG. 1 , a seismic receiver  50  may be disposed in another wellbore  18 A, and may be conveyed therein using a second wireline  22 A. One example of such a seismic receiver is described in U.S. Pat. No. 4,715,469 issued to Yasuda et al. In such examples, the seismic energy source if disposed in the wellbore  18  may be rotationally oriented using the rotator  10  so that its signal output is directed toward the other wellbore  18 A. 
         [0019]    The instrument  14 , flexible coupling  12 , rotator  10  swivel  28  and cable head  26  are shown in more detail in  FIG. 2 . In particular, the rotator  10  may include a substantially cylindrical housing  10 B formed from a non-magnetic material, for example, monel, stainless steel, titanium or an alloy sold under the trademark INCONEL, which is a registered trademark of Huntington Alloys Corporation, Huntington, W. Va. The housing  10 B may include through the wall thereof a plurality of longitudinally extending, circumferentially spaced apart magnet pole shoes  10 A. In other examples, depending on the material from which the housing  10 B is made, its thickness and the amount of torque needed to be generated by the rotator  10  to rotate the instrument, the pole shoes  10 A may not protrude through the wall of the housing  10 B. As will be explained with reference to  FIG. 3 , each pole shoe may be associated with one or more electromagnets that may be actuated to cause the rotator  10  to be magnetically attracted to the casing ( 16  in  FIG. 1 ). Sequential actuation of the electromagnets ( FIG. 3 ) will cause rotation of the rotator  10  inside the casing ( 16  in  FIG. 1 ). The rotator housing  10 B may have an external diameter that is smaller than the internal diameter of the casing ( 16  in  FIG. 1 ). Because of the diameter difference between the housing  10 B and the casing, the magnetic rotation of the housing  10 B in the casing will cause the housing  10 B orientation to precess within the casing. That is, the rotational orientation of the housing  10 B will move with respect to the casing as the housing rotates inside the casing in contact therewith. By continuing rotation, the housing  10 B may eventually be oriented in a selected rotational orientation. 
         [0020]    An example structure for causing magnetic rotation of the rotator  10  within the casing ( 16  in  FIG. 1 ) is shown in cross section in  FIG. 3 . The housing  10 B may include a plurality of circumferentially spaced apart pole shoes  10 A as explained above. The pole shoes  10 A may be made from ferromagnetic material such as steel. Each pole shoe  10 A may be associated with one pole of two adjacent ferromagnetic electromagnet cores  30 . The cores  30  may extend longitudinally about the same distance as the pole shoes  10 A and may have end section in approximately the shape of the letter “C” as shown in  FIG. 3 . An electromagnet wire coil  32  may be wound longitudinally around the center of each core  30  as shown in  FIG. 3  such that the magnetic dipole of each coil  32  is substantially perpendicular to the plane of symmetry (not shown) of each core  30 . The configuration shown in  FIG. 3  may have the advantages of generating high magnetic attraction between the pole shoes  10 A associated with the activated electromagnets (each electromagnet consisting of a coil  32  and a core  30 ), while minimizing magnetization of the other pole shoes  10 A, because the C-shape of the core causes magnetic flux to flow in a closed magnetic circuit including the adjacent pole shoes  10 A and the casing ( 16  in  FIG. 1 ) in contact with the pole shoes  10 A. Other configurations may include a separate pole shoe for each open end of each core. In principle, the structure of the cores, coils and pole shoes is intended to induce magnetic flux through the wall of the housing  10 B when each coil is energized. 
         [0021]    The coils  32  are each connected to a electromagnet switching controller  40  which may be any microprocessor based controller associated with suitable power switching circuitry (not shown separately) to apply electrical current to the coils  32  rotationally sequentially, thus causing rotation of the ones of the pole shoes  10 A that are magnetically attracted to the casing ( 16  in  FIG. 1 ). In the example of  FIG. 3 , the controller  40  may be in signal communication with a directional sensor  44  so that the rotational orientation of the rotator  10  (and the instrument connected thereto) with respect to a geodetic reference may be determined. It will be appreciated by those skilled in the art that because the rotator  10  is used in ferromagnetic casing, the directional sensor  44  must be of a type that is not dependent on the Earth&#39;s magnetic field to establish a geodetic reference. One non limiting example of such a directional sensor is described in U.S. Pat. No. 4,611,405 issued to Van Steenwyk, in which geodetic reference is established using an Earth rate gyroscope. In examples using cable having electrical conductors therein, electrical power and signals between the instrument ( 14  in  FIG. 1 ) and the recording unit ( 24  in  FIG. 1 ) may be transferred between the cable ( 22  in  FIG. 1 ), the controller  40  and other devices by a power conditioner/telemetry device  42  of types well known in the art. The example shown in  FIG. 3  in which the controller is disposed inside the rotator is only one example of a device for selectively applying current to the coils to cause the sequential actuation of the electromagnets. In other examples, an individual electrical conductor could be provided in the cable ( 22  in  FIG. 2 ) for each coil  32 . Any other configuration that enables selective actuation of the coils may be used consistent with the scope of this invention. 
         [0022]    In using the rotator made as explained above, the coils  32  are rotationally sequentially energized, causing the pole shoes  10 A to be rotationally sequentially attracted to the casing ( 16  in  FIG. 1 ). Such rotational magnetic attraction causes the rotator  10  to precessionally rotate inside and to contact the interior of the casing. The difference between the internal diameter of the casing and the external diameter of the housing (or the pole shoes  10 A if they are made to extend laterally outwardly from the housing) will determine the amount of precession of the rotational orientation of the rotator  10  with respect to the casing each time the rotator  10  completes a full rotation within the casing. Thus, it may be necessary to rotate the rotator through a number of full rotations inside the casing to provide a selected rotary orientation. In the example shown in  FIG. 1  and  FIG. 2 , the swivel ( 28  in  FIG. 1 ) may be used advantageously to enable the rotator to rotate as much as is required without twisting the cable ( 22  in  FIG. 1 ). In some examples, rotation of the rotator  10  may be made smoother by controlling the current in each of the coils  32  so that magnetization is gradually reduced, while magnetization in the adjacent coil is gradually increased. In such examples, there may be current flowing in two or more adjacent coils at any time to optimize the rotation. 
         [0023]    In other examples, the rotator may be used for substantially continuous rotation for a selected period of time, for example, to operate a drill, mill or grinding device for wellbore repair or intervention operations. It will be appreciated by those skilled in the art that by selection of a suitable rotator outer diameter for a particular casing internal diameter, the rotator may be provided with selected rotation speed and torque for the particular use intended. Larger rotator diameter will result in lower rotation speed and higher torque, and vice versa for smaller diameters. 
         [0024]    A wellbore instrument rotator according to the invention may provide the capability of moving an instrument conveyed along a wellbore by a cable to any selected rotary orientation without the need to rotationally fix any part of the instrument within the wellbore. 
         [0025]    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.