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STATEMENT OF RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/089,461 filed on Aug. 15, 2008. 
     
    
     FIELD OF THE INVENTION  
       [0002]    This application relates to cementing of a casing string in an earthen borehole, and more specifically to methods and devices for improving cement distribution between a casing string and a borehole. 
       BACKGROUND 
       [0003]    It is conventional practice to cement a casing string in a borehole to prevent collapse and stabilize the borehole. A casing string is positioned within the borehole, e.g., using casing centralizers coupled at spaced intervals along the casing string, to form an annulus between the casing string and the borehole. Cement slurry can be displaced through the bore of the casing string using cementing plugs allowing displacement into the annulus. Alternately, an inner cementing string may be run through the bore of the casing string and stung into a float device, e.g., at the end of the casing string. The float device may be a float shoe or a float collar. Cement slurry may be displaced through the inner cementing string, through the float device and into the annulus. 
         [0004]    Borehole curvature and other borehole irregularities may impair an even distribution of cement slurry within the annulus and cause channeling of cement slurry past pockets of drilling fluid or debris. Channeling may compromise the integrity of the cement liner that protects the casing string. 
         [0005]    The quality of a cement liner may benefit from agitation of the cement slurry within the annulus as the cement slurry is displaced along the annulus. Agitation induces turbulent flow, promotes cement bonding to the wall of the borehole and reduces channeling. Reciprocation and/or rotation of the casing string using rig equipment as cement slurry is in the annulus are conventional methods of agitating the cement slurry. 
         [0006]    In substantially vertical boreholes, casing strings hang primarily in tension, and the casing string is more easily moved within the borehole to agitate a cement slurry. In horizontal or highly deviated boreholes, reciprocating or rotating the casing string may be less desirable because the weight of the casing string and contents bears on the floor, or downwardly disposed side, of the borehole, which reacts to support the casing string. Movement of the casing string, whether by rotation or reciprocation, is resisted by friction between the casing string and the borehole causes wear and unwanted stress on the casing string, centralizers and rig equipment. 
         [0007]    What is needed is a system, a method and an apparatus to agitate an annular flow of cement slurry while protecting the casing string, centralizers and rig equipment from wear and/or stress caused by rotation or reciprocating of the casing string within the borehole. 
       SUMMARY 
       [0008]    Embodiments of the invention disclosed herein satisfy one or more of the above-stated needs. One embodiment of a system and apparatus comprises one or more outer sleeve movably received on a casing string and a transfer device(s) to move the outer sleeve relative to the casing string. The transfer device may rotate the outer sleeve or move the outer sleeve longitudinally relative to the casing string, or both, to agitate an annular flow of cement slurry intermediate the outer sleeve and a borehole. In some embodiments, one or more structures may be coupled to or formed on an exterior surface of the outer sleeve to enhance agitation. The structures may comprise, for example, a protuberance, such as a fin, groove, blade, ridge, or bump, or the structures may comprise a cavity, a dimple, trough or other structure that, when the exterior surface is moved against a flow of cement slurry, enhances agitation. “Casing,” “casing string” or “casing segment,” as those terms are used herein, shall refer to any tubular that may be cemented in a borehole, e.g., to stabilize a part or section of the borehole. 
         [0009]    In one embodiment, an outer sleeve and/or the structures thereon are protected from unwanted engagement with the borehole by a centralizer (or centralizers) coupled to the casing string adjacent to the outer sleeve. For example, in one embodiment, an outer sleeve is protected by straddling the outer sleeve with a pair of centralizers to provide stand-off between the casing string and the borehole. It should be understood that the outer sleeve is more exposed to engagement with the borehole in curved or irregular sections of the borehole. 
         [0010]    In one embodiment, the longitudinal movement of the outer sleeve along the casing string may be limited by disposing a stop collar or stop device above or in the uphole direction, relative to the outer sleeve and/or a stop collar or stop device below, or in the downhole direction, relative to the outer sleeve. It should be understood that, in embodiments that provide for reciprocation of the outer sleeve on the casing string, these stop collars or stop devices can be separated a predetermined distance to accommodate reciprocal movement of the outer sleeve. In one embodiment, the centralizers described above may be used for serving this purpose. 
         [0011]    In another embodiment, the frictional resistance to rotation of the outer sleeve may be reduced by treating or conditioning the bore of the outer sleeve and/or the exterior of the portion of the casing string on which the outer sleeve is to be disposed. In one embodiment, one or more bearings, e.g. one or more sleeve bearing, may be disposed intermediate the bore of the outer sleeve and the casing string. 
         [0012]    In embodiments of the system, method and apparatus, a transfer device engages and rotates and/or reciprocates the outer sleeve on a portion of the casing string. In one embodiment, the transfer device comprises a portable power source, such as a battery, coupled to an electric motor that is mechanically coupled to the outer sleeve through one or more gears. In another embodiment, an inner cementing string is run into the bore of the casing string to position and operatively couple a transfer device with the outer sleeve. For example, in one embodiment the transfer device comprises an inner gear positionable within a casing string to mechanically couple the inner cementing string to the outer sleeve. The inner gear on the inner string directly or indirectly engages a sleeve gear through a sealed aperture in the wall of the casing string. In another embodiment, the transfer device comprises one or more magnets on the inner cementing string that are positionable within the outer sleeve to magnetically couple the inner cementing string to the outer sleeve. In these latter two embodiments, the inner cementing string serves the dual purposes of supplying a flow of cement slurry to the annulus and then providing power to move the outer sleeve. For example, an inner cementing string of the kind that can facilitate certain embodiments of method and apparatus disclosed herein is available from Davis-Lynch, Inc. 
         [0013]    An embodiment of a method to cement a casing string in a borehole includes the steps of: movably receiving one or more outer sleeves on a casing string; running the casing string in a borehole to form an annulus between the outer sleeves and the borehole; displacing a cement slurry into the annulus; and moving the outer sleeves relative to the casing string. Another embodiment of the method to cement a casing string in a borehole comprises the steps of: movably receiving one or more outer sleeves on a casing string; coupling a float device having a tag-in receptacle to the casing string; running the casing string in a borehole to form an annulus between the outer sleeves and the borehole; coupling a portion of a torque transfer device to an inner cementing string; running the inner cementing string into the bore of the casing string to sealably engage the tag-in receptacle in the float device and to position the portion of the torque transfer device within the outer sleeves; movably coupling the outer sleeves to the inner cementing string through the torque transfer device; displacing a flow of cement slurry through the inner cementing string and into the annulus; and moving the inner cementing string to move the outer sleeves relative to the casing string. After the cement slurry is displaced to the targeted interval of the annulus or agitation is no longer needed, the transfer device may be disengaged from the outer sleeves and the inner cementing string may be disengaged from the float device and recovered from the bore of the casing string. It should be understood that the inner cementing string, when sealably received within the tag-in receptacle in the float device may function in a manner similar to a swivel used on a rig for delivering a flow of fluid into the bore of a drill string. The tag-in receptacle in the float device facilitates the isolation of the flow of cement slurry delivered through the bore of the inner cementing string from the annulus intermediate the casing string and the inner cementing string so that flow can be provided to the borehole adjacent to the float device. It should be understood that this type of float device may include a rotatable tag-in receptacle to rotate with a “stinger,” or tagged-in portion, of the inner cementing string. Alternately, the inner cementing string may include a stinger that is rotatably and sealably coupled to the end of the inner cementing string so that the stinger may remain stationary and coupled to the receptacle upon rotation of the inner cementing string. In another embodiment, the stinger may be adapted to rotate within the receptacle while maintaining a seal. This latter embodiment may comprise a receptacle and/or stinger of a lubricious material. 
         [0014]    In another embodiment, the transfer device comprises an inner gear on the inner cementing string coupled to mechanically transmit torque to an outer gear on the outer sleeve. 
         [0015]    In one embodiment, the transfer device comprises an inner magnet coupled to the inner cementing string and an outer magnet coupled to the outer sleeve. The inner and outer magnets magnetically interact to enable the transfer of torque (for rotation) and/or a translating force (for reciprocation), or both, from the inner cementing string to the outer sleeve. It should be understood that this embodiment of the transfer device provides magnetic interaction between the inner cementing string and the outer sleeve to provide for the transfer of torque from the inner cementing string to the outer sleeve (to rotate the outer sleeve) without compromising the integrity of the casing string. 
         [0016]    In an alternate embodiment, the transfer device comprises an inner magnet coupled to the inner cementing string and an outer magnetic body coupled to the outer sleeve. Alternately, the transfer device comprises an outer magnet coupled to the outer sleeve and an inner magnetic body coupled to the inner cementing string. In these embodiments, the magnetic attraction between the inner magnet coupled to the inner cementing string and the outer magnetic body coupled to the outer sleeve or, alternately, the magnetic attraction between the outer magnet coupled to the outer sleeve and the inner magnetic body coupled to the inner cementing string, provides a magnetic interaction between the inner cementing string and the outer sleeve to provide for the transfer of torque from the inner cementing string to the outer sleeve. It should be understood that a magnetic body, as that term is used herein, is a body comprising a material that is subjected to a force when the body is placed within a magnetic field, e.g. when positioned proximal a magnet. While these embodiments could be used to provide minimal torque transfer, the size of the magnet and/or magnetic body may present limitations. 
         [0017]    It should be understood that, in some embodiments, the outer sleeve may be adapted to move the flow of cement slurry through the annulus as it agitates the flow. For example, as will be described in greater detail below, the outer sleeve may comprise one or more spiral fins or curved blades that may be rotated to propel the cement slurry in the uphole direction. These embodiments may further improve both the quality of the cement liner and the bond of the cement liner to the borehole by reducing the equivalent circulating density (ECD) of the cement slurry. It should be understood that the flow assistance provided by movement of the outer sleeves reduces the cumulative resistance of the borehole to annular cement flow. The ECD is the effective density exerted by a circulating fluid, such as cement slurry, against geologic formations penetrated by the borehole that takes into account the pressure drop in the annulus uphole relative to the point being considered. 
         [0018]    The foregoing and other features and embodiments of the invention will be best understood with reference to the following detailed description of specific embodiments, when read in conjunction with the accompanying drawings, wherein: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The foregoing and other features and aspects will be best understood with reference to the following detailed description of embodiments of the invention, when read in conjunction with the accompanying drawings, wherein: 
           [0020]      FIG. 1  is an elevation view of an extended reach borehole having a substantial horizontal portion and a casing string disposed therein. A plurality of outer sleeves are movably received on the casing string, each straddled by a pair of centralizers, to agitate a cement slurry displaced between the outer sleeves and the borehole. 
           [0021]      FIG. 2  is an elevation view of an embodiment of an apparatus coupled to a casing string and disposed within a borehole. 
           [0022]      FIG. 3  is an elevation view of an alternate embodiment of an apparatus having an outer sleeve movably coupled to a casing string and driven by a gear on an inner cementing string. 
           [0023]      FIG. 4  is an elevation view of another alternate embodiment of an apparatus having an outer sleeve movably coupled to a casing string and driven by a battery and a motor. 
           [0024]      FIG. 5  is an elevation view of an embodiment of an apparatus having an outer sleeve movably coupled to a casing string and driven by an inner cementing string and a magnetic clutch. The magnetic clutch of  FIG. 5  comprises a plurality of outer magnets on the outer sleeve. 
           [0025]      FIG. 5A  is an elevation view of an embodiment of a transfer device comprising an inner cementing string and a plurality of inner magnets to cooperate with the plurality of outer magnets on the outer sleeve of  FIG. 5 . 
           [0026]      FIG. 6  is an exploded perspective view of the embodiment of the outer sleeve of  FIG. 5  magnetically coupled through the magnetic clutch to the inner cementing string of  FIG. 5A  and enabled by rotation of the inner cementing string. 
           [0027]      FIG. 6A  is a elevation section view of  FIG. 6  along the line  6 A- 6 A, with the top portion of the outer sleeve and the casing string removed for simplicity. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The following detailed description refers to the above-listed drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0029]      FIG. 1  is an elevation view of an extended reach borehole  12  having a substantial horizontal (relative to the surface) portion  70  and a casing string  8  disposed therein. A plurality of outer sleeves  10  are movably received on the casing string  8  in  FIG. 1 , an outer sleeve optionally straddled by a pair of centralizers  20 . Depicted float device  6  is coupled to the end of the casing string  8  to prevent cement slurry displaced from the casing string into the annulus from flowing back into the borehole  12 . 
         [0030]      FIG. 2  is an enlarged elevation view of an embodiment of an outer sleeve  10  movably received on a casing string  8  and disposed within a borehole  12 . The adjacent centralizers  20 A,  20 B straddle the outer sleeve  10  to position the casing string  8  and provide an annulus  4  around the casing string  8 . It should be understood that the borehole in which the casing string  8  and the outer sleeve  10  are disposed may be vertical (as in  FIG. 2 ), horizontal ( FIG. 1 ) or any angle there between, and the drawings merely illustrate some of the orientations in which the invention may be used. The embodiment of the outer sleeve  10  illustrated in  FIG. 2  comprises an exterior surface  14  with a spiral fin  14 ′ disposed thereon. The first centralizer  20 A and a second centralizer  20 B comprise rigid ribs  22 A and  22 B, respectively, extending radially from the casing string  8  to form the annulus  4  between the casing string  8  and the wall  4 A of the borehole  12 . The centralizers  20 A,  20 B may comprise set screws  24 A,  24 B to facilitate coupling the centralizers  20 A,  20 B adjacent to the outer sleeve  10  on the casing string  8 . The centralizers  20 A,  20 B prevent or limit engagement of the exterior surface  14  or the fin  14 ′ with the wall  4 A of the borehole  12 . In other embodiments, the ribs of the centralizers may be pitched at an angle and formed to increase the level of turbulence of the annular flow. 
         [0031]    Rotation of the outer sleeve  10  on the casing string  8  moves spiral fin  14 ′ through the cement slurry  7  within the annulus  4  and the exterior surface  14  of the outer sleeve  10  against the cement slurry in the annulus  4 . Alternately, the outer sleeve  10  may comprise a plurality of generally parallel spiraling fins on the exterior surface  14 . It should be understood that these and other embodiments may be useful, especially in a horizontal portion  70  of a borehole (see  FIG. 1 ) to propel or assist in moving a cement slurry through the annulus  4  and reduce the equivalent circulating density (ECD) of the cement slurry. 
         [0032]      FIG. 2  is also an enlarged elevation view of the float device  6  sealably engaged with a stinger  36 A on the end of an inner cementing string  36 ′ and the portion of the casing string  8  adjacent to the float device  6 . The float device  6  in  FIG. 2  is illustrated with a window revealing the internal features of the float device  6  sealably receiving a stinger  36 A on the end of the inner cementing string  36 . It should be understood that the inner cementing string  36  may be run into the bore of the casing string  8  until the stinger  36 A and stinger guide  36 B seat within the receptacle  57  of the float device  6 .  FIG. 2  illustrates, in dotted outline, a position of the stinger  36 A′ and inner cementing string  36 ′ prior to sealing engagement with the float device  6 . This same position may be assumed upon disengagement of the inner cementing string  6  from the float device  6 . 
         [0033]    The float device  6  illustrated in  FIG. 2  comprises an opening  55  intermediate the engaged stinger  36 A and a ball chamber  56 . The ball  54  is captured within the float device  6  between a ball seat  53  and a ball retainer  52 , e.g., to function like a check valve. In  FIG. 2 , cement slurry  7  has been displaced from the bore  50  of the inner cementing string  36 , through the stinger  36 A, opening  55 , ball chamber  56  and in the direction of arrow  3  through the annulus  4 . 
         [0034]      FIGS. 3 and 4  illustrate embodiments of an outer sleeve  10  rotatable on a casing string  8 .  FIG. 3  is an elevation view of an embodiment of an apparatus comprising an outer sleeve  10  movably coupled to a casing string  8  and a transfer device  30 . A transfer device  30  operatively engages and rotates the outer sleeve  10  (not shown). The transfer device  30  illustrated in  FIG. 3  comprises a drive gear  37  coupled to an inner cementing string  36  rotatably disposed within a bore  27  of the casing string  8 . The drive gear  37  is positioned to engage an intermediate gear  38 A protruding through a sealed aperture  33  in the casing string  8 . The intermediate gear  38 A engages and rotates a first end  39 A of a flexible shaft  39  and an output gear  38 B on the second end  39 B of the flexible shaft  39  engaging the sleeve gear  11  on the outer sleeve  10 . Rotation of the inner cementing string  36  rotates the drive gear  37  that engages and rotates the intermediate gear  38 A, the flexible shaft  39 , the output gear  38 B and the sleeve gear  11  to rotate the outer sleeve  10 . 
         [0035]      FIG. 4  is an elevation view of another alternate embodiment of an apparatus having an outer sleeve  10  movably received on a casing string  8  and driven to rotate using a battery and a motor. The apparatus of  FIG. 4  comprises an outer sleeve  10  rotatably received onto a casing string  8 , the outer sleeve  10  comprising a sleeve gear  11  proximal a transfer device  40 . The transfer device  40  comprises a battery  42  electrically coupled to an electrically-driven motor  41 . The motor  41  is rotates a first end  44 A of a flexible shaft  44  and an output gear  48  at the second end  44 B of the flexible shaft  44 . The output gear  45  drives the outer sleeve gear  11  to rotate the outer sleeve  10 . 
         [0036]      FIG. 5  is an elevation view of an embodiment of an apparatus having an outer sleeve  10  movably received on a non-magnetic casing segment  8 A and rotatable on the casing segment  8 A by a transfer device  34 . The transfer device  34  illustrated in  FIGS. 5  and  5 A comprises an inner cementing string  36  coupled to an inner string  36  through a magnetic clutch. The magnetic clutch magnetically couples the inner cementing string  36  comprising inner magnets  48 A to the outer sleeve  10  comprising outer magnets  48 B. The outer magnets  48 B are arranged on the outer sleeve  10  in a columnar pattern to cooperate with a transfer device  34  shown in  FIG. 5A  and superimposed on  FIG. 5  to illustrate the interior position of the transfer device  34  after it is run and positioned within the bores of the non-magnetic casing segment  8 A and outer sleeve  10 . The outer sleeve  10  comprises an exterior surface  14  comprising a spiral fin  14 ′. It should be understood that a variety of arrangements of the outer magnets  48 B may be used, and the arrangement illustrated in  FIG. 5  is but an example of how the outer magnets  48 B might be arranged on the outer sleeve  10 . 
         [0037]      FIG. 5A  is an elevation view of the embodiment of a transfer device  34  comprising an inner cementing string  36  to which inner magnets  48 A are coupled in an arrangement coinciding with the arrangement of the outer magnets  48 B on the outer sleeve  10  of  FIG. 5 . The inner cementing string  36  comprises a bore (not shown in  FIG. 5A  - see  FIG. 6 ) through which cement slurry may be provided to the float device  6  (not shown in FIG.  5 A—see  FIG. 2 ). The pressure at which the cement slurry is delivered through the inner cementing string must be sufficient to displace cement slurry uphole through a substantial portion of the annulus toward the surface end of the borehole. It should be noted that “uphole” and “downhole” are in relation to the surface end of the borehole and do not necessarily define the inclination of the borehole. 
         [0038]    The transfer device  34  shown in  FIG. 5A  further comprises a first spacer  43 A and a second spacer  43 B straddling the inner magnets  48 A to radially position the inner magnets  48 A within the bore of the non-magnetic casing segment  8 A. It should be understood that the first and/or second spacers  43 A,  43 B may comprise a variety of shapes without loss of function. It should be understood that, when the inner casing string  36  is run into the bore  27  of the casing string  8  to position the transfer device  34  of  FIG. 5A  within the outer sleeve  10  as shown by the dotted lines in  FIG. 5 , spacers  43 A,  43 B on transfer device  34  shown of  FIG. 5A  engage the bore  27  of non-magnetic casing segment  8 A to position the inner magnets  48 A in general alignment with the outer magnets  48 B as shown by the dotted lines in  FIG. 5 . 
         [0039]      FIG. 6  is an exploded perspective view of the embodiment of the outer sleeve  10  of  FIG. 5  magnetically coupled, through the magnetic clutch, to the inner cementing string  36  of  FIG. 5A . Rotation of the outer sleeve  10  within the bore  27  of the casing segment  8 A is obtained by rotating the inner cementing string  36  to magnetically transfer torque using inner magnets  48 A interacting with outer magnets  48 B. In the embodiments shown in  FIGS. 5A and 6 , the inner magnets  48 A are disposed on an enlarged portion  46  of the inner cementing string  36  to more favorably position the inner magnets  48 A to interact with the outer magnets  48 B. It should be noted that, in  FIG. 6 , the outer sleeve  10  is movably received onto casing segment  8 A and straddled by a first and second centralizers  30 A,  30 B having pitched ribs  32 A,  32 B thereon to facilitate agitation of a cement slurry flowing across the outer sleeve  10  as illustrated in detail in connection with the embodiment of  FIG. 2 . 
         [0040]      FIG. 6A  is an elevation section view of  FIG. 6  along the line  6 A- 6 A, with the top portion of the outer sleeve and the casing string removed for simplicity. 
         [0041]    It should be understood that embodiments of the system, apparatus and the method may be used in an open borehole, as illustrated in  FIGS. 1 and 2 , or in a cased hole. The inner magnets and/or outer magnets used in embodiments of the invention may or may not comprise rare earth magnets. It should be understood that the non-magnetic casing segment  8 A is provided to allow unimpaired the magnetic interaction between the inner magnets  48 A and the outer magnets  48 B, and that the non-magnetic casing segment  8 A, which may be, for example, stainless steel, is made up into a casing string and run into a borehole to position the outer sleeve  10  at the targeted interval of the borehole. It should be understood that embodiments of the invention using multiple outer sleeves driven using a magnetic coupling between the inner cementing string and the outer sleeve may continue to effectively function notwithstanding disablement of one or more outer sleeves. For example, should an outer sleeve engage the borehole, for example, at a borehole irregularity or deviation, the inner string is not disabled from continued rotation within the bore of the casing string, and other outer sleeves may continue to rotate in response to rotation of the inner cementing string without damage to or substantial impairment of the intended benefit provided by the invention. 
         [0042]    The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The term “one” or “single” may be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” may be used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. 
         [0043]    From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system for enhancing the quality of cementing operations that is novel has been disclosed. Although specific embodiments of the system are disclosed herein, this is done solely for the purpose of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow. 
         [0044]    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.

Summary:
A method for cementing a casing string in a borehole includes the steps of moveably coupling an outer sleeve on a casing segment; making up the casing segment with the outer sleeve into a casing string; running the casing string in a borehole; displacing a cement slurry into an annulus exterior to the casing string; and moving the outer sleeve relative to the casing string to agitate the cement slurry. A transfer device is used to rotate the outer sleeve against the cement slurry. Multiple outer sleeves may be received on the casing string at spaced intervals. In one embodiment, the transfer device may include a mechanical clutch through which the outer sleeves may be rotated. The mechanical clutch may be driven using an inner cementing string that provides a supply of cement slurry to the annulus.