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This Application is the U.S. National Phase Application of PCT International Application No PCT/GB2005/003137 filed Aug. 11, 2005. The invention relates to a downhole device, and particularly but not exclusively a downhole device adapted for use in wireline or slickline applications. 
     DESCRIPTION OF THE RELATED ART 
     In conventional wireline and slickline operations, a toolstring comprising different tools is lowered into casing, tubing or other tubulars in a borehole from a wire or cable spooled from a drum located at the surface of the wellbore. It is often necessary to perform wireline or slickline operations during for example completion, maintenance and servicing, installation and retrieval of downhole apparatus, intervention and well logging. Toolstrings often comprise one or more devices that collect data from the wellbore such as temperature, salinity etc of recovered fluids. In addition to suspending the string of tools, the wire or cable spooled from a drum may also act as a conduit for power required by the tools to carry out their functions in the wellbore, and may include signal cables for conveying data gathered by downhole sensors back to the surface. 
     Toolstrings operate satisfactorily in vertical and near vertical wells, but problems arise when they are used in deviated wells since contact between the outer diameter of the toolstring and the inner diameter of the wellbore casing or other tubular creates a frictional force which acts against the gravitational forces urging the toolstring downhole, and these frictional forces increase with the deviation of the well. In addition, as deviation increases, the string is more likely to snag on the casing connections or other raised surfaces on the inner wall of the casing or other tubular. 
     Roller bogies incorporated into the toolstring to assist the movement of toolstrings within casing or other tubulars in such deviated wells are available; however, contortions throughout the length of the casing or other tubular, and in the toolstring itself, often results in the rollers of such conventional roller bogies failing to make contact with the inner diameter of the casing or tubular. This reduces or removes the effect of the roller bogie and can result in parts of the toolstring contacting the inner diameter of the casing or other tubular regardless of the provision of the roller bogie. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention there is provided a downhole device for incorporation into a downhole string and movement in a well-bore, the device comprising:
         one body member;   at least one roller arranged on the device to engage the inner surface of the well-bore; and   means to orient the device in the well bore, the means to orient the device is provided on the or each roller.       

     Optionally, the means to orient the device comprises a projecting portion of the or each roller which projects from the body of the device in the direction of the axis of rotation of the or each roller by a distance at least equal to and preferably greater than the diameter of the or each roller. 
     When the dimension along the axis of rotation of the rollers of the device is larger than the diameter of the roller, a degree of eccentricity is provided on the device, in order to allow the device to assume a desirable orientation e.g. with the rollers in contact with the inner surface of the casing or other tubular in which it is run. 
     Optionally, the projecting portion of the or each roller is an eccentrically shaped portion of the or each roller. Typically, the eccentrically shaped portion comprises an oval shape which extends from the outer diameter of the roller to the end of the projecting portion. 
     Alternatively, the means to orient the device is provided by the or each roller being offset from the longitudinal axis of the device such that the or each roller projects from the body of the device in the direction of the axis of rotation of the or each roller by a distance at least equal to and preferably greater than the diameter of the or each roller. 
     Typically, the or each roller comprises a running edge which extends around the outer circumference of the or each roller. Preferably, the running edge is shaped such that it matches the internal surface of the well bore in which the device is to be run. 
     Optionally, the or each roller is secured to the device via a pin which typically also provides an axis of rotation about which the or each roller may rotate. 
     Optionally, the or each roller is provided with rotational friction reducing means adapted to reduce the frictional forces created when the or each roller rotates about the axis of rotation. 
     Typically, the frictional reducing means comprises a bearing arrangement adapted to act between a portion of the or each roller and a portion of the pin. Alternatively, the frictional reducing means comprises a slip surface provided on a portion of the or each roller in abutment with a slip surface provided on a portion of the body member of the device. 
     Optionally, the friction reducing means may also provide an axis of rotation about which the or each roller may rotate. 
     Typically, the slip surfaces comprise a durable low friction material such as ceramic. 
     Optionally, a plurality of rollers are provided on opposing sides of the device. Alternatively, a plurality of rollers are alternately spaced along the device such that a roller is provided on one side of the device at a first location followed by another roller on the other side of the device at a second location followed by a another roller on the same side as the roller at the first location. Typically, this alternation continues along the length of the device for the plurality of rollers. 
     Preferably, the or each rollers are provided in a recess provided in the body of the device. 
     Preferably, the device comprises at least a swivel device. 
     Optionally, a throughbore capable of housing at least an elongate member such as a cable or wire may be provided along the body of the device, typically along the longitudinal axis of the device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1   a  is a planer view of a first embodiment of the device in accordance with the present invention; 
         FIG. 1   b  is a transverse cross-sectional view of the device of  FIG. 1   a  taken through the view  1   b - 1   b;    
         FIG. 1   c  is a cross-sectional view of a roller of the device of  FIG. 1   a  taken through the view  1   c - 1   c;    
         FIG. 2   a  is a planer view of a second embodiment of the device in accordance with the present invention; 
         FIG. 2   b  is a transverse cross-sectional view of the device of  FIG. 2   a  taken through the view  2   b - 2   b;    
         FIG. 2   c  is a cross-sectional view of a roller of the device of  FIG. 2A  taken through the view  2   c - 2   c;    
         FIG. 3  is a cross-sectional view of a roller arrangement of a third embodiment of the device in accordance with the present invention; and 
         FIG. 4  illustrates the cross-sectional view of the device of  FIG. 2   b  inside a casing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1   a ,  1   b  and  1   c  and according to a first embodiment of the present invention, the device comprises a downhole sub  10  having a body  12  provided with suitable connections  14  at either end in order to allow the downhole sub  10  to be attached into a string of wireline tools for e.g. well intervention or MWD operations etc. The connections  14  may be conventional box and pin type connections or any other suitable connections as required to allow connection to rest of the string. Swivels  16  are typically provided at each end of the body  12  in order to allow the downhole sub  10  to rotate independently of the connections  14 , and hence the rest of the toolstring (not shown) in the casing or tubular (not shown) as will be described subsequently. 
     The body  12  of the downhole sub  10  comprises a substantially circular cross-sectioned cylindrical member (best shown in  FIG. 1   c ) having a number of recesses  18  provided at intervals along the length of the body  12 . Each recess  18  comprises an indent on one side of the body  12  and are staggered along the length of the body  12  such that a recess  18 A is positioned on the left hand side of the body  12  and is followed by a recess  18 B on the right hand side of the body  12  which in turn is followed by a recess  18 A on the left hand side of the body  12  and so on along the length of the body. The body  12  connects at either end to a pin  22  which is surrounded by a rotating collar  24  of the swivel  16 . The rotating collar  24  of each swivel  16  is connected to the connections  14  in order to provide a rotational dislocation of the device  10  from the rest of the toolstring (not shown). 
     The staggered arrangement of recesses  18  provides a degree of flexibility in the sub  10  whilst maintaining sufficient structural integrity of the sub  10 . As the sub  10  moves downhole it is able to flex at bridging locations  19  on the body  12  due to the lower bending resistance of the reduced cross-sectional area provided by recessed portions  18 . In this regard it should be noted that although four recesses  18  are shown in the embodiment of  FIGS. 1   a ,  1   b  and  1   c , more or fewer recesses  18  may be provided, and the distance between the recesses  18  can be increased or decreased such that the bending resistance of the body  12  may be altered during manufacture of the sub  10  as required for specific downhole situations. 
     Rollers  20  are housed within each recess  18  and project therefrom. Each roller  20  comprises an oval shaped rotating member having a machined running edge  26  (best shown in  FIG. 1   c ) which circumscribes a portion of the circumference of the roller  20  adjacent its equator. The running edge  26  may be machined during manufacture such that its outer circumference matches the inner circumference of the casing or other tubular in which the sub  10  is to operate. 
     Each roller  20  projects from the body  12  by a small amount, indicated by A in  FIG. 1   c , in the order of 3-25 mm adjacent the machined running edge  26  and by a greater amount, indicated by B in  FIG. 1   c , in the order of 5-30 mm adjacent a securing pin  36 . The projection differential between distances A and B may be provided by an asymmetrically shaped roller  20  which has a greater diameter across one axis than an axis perpendicular to that axis i.e. one half of a three dimensional oval roller  20  or a substantially uniformly dimensioned semi-spherical roller which has been offset from the body  12  longitudinal axis by a sufficient amount to provide the required differential, or may simply be provided by a portion of the apparatus (such as the pin  36 ) extending by the distance B from the body  12 . This gives the sub  10  a degree of asymmetry via the rollers  20 . 
     In the embodiment shown in  FIGS. 1   a ,  1   b  and  1   c  a ball bearing cage  28  is provided in a cavity on the inside of each roller  20  and encloses a number of ball bearings  30  therein. The ball bearing cage  28  has an outer race  32  in communication with the inside of the roller  20  and an inner race  34  in communication with the outside edge of the securing pin  36 . The outer race  32  may be secured to the inside of the roller  20  or may simply form an interference fit therebetween. Likewise the inner race  34  may be secured to the pin  36  or may simply form an interference fit therebetween. The number of ball bearings  30  are housed within the circumference of the ball bearing cage  28 . 
     The securing pin  36  secures each roller  20  to the body  12  by projecting through a throughbore  21  in the roller  20  and into an appropriately dimensioned socket  23  in the body  12  such that the roller  20  is secured to the body  12 . The pin  36  may be held in the socket  23  by a latching pin (not shown) which can be inserted into detent  23   a  provided between the pin  36  and the socket  23  bore. In order to ensure that the rollers  20  are not prevented from rotating by the securing action of the securing pin  36 , a spacer  38  is provided between the ball bearing cage  28  and the recess  18  on the body  12  such that the roller  20  is secured to the body  12  but does not abut thereagainst. 
     Operation of the first embodiment of the downhole sub  10  will now be described. 
     When the toolstring (not shown) is fed downhole from the surface, the sub  10  is incorporated into the toolstring by connecting it thereto at connections  14  such that the downhole sub  10  is integrated into the toolstring. The toolstring including the downhole sub  10  is then progressed into a downhole tubular such as wellbore casing (not shown). When the portion of the toolstring comprising the sub  10  approaches a deviated section of the wellbore, the downhole sub  10  will tend to drift towards one side of the internal diameter of the casing due to the deviation thereof. Depending upon the initial orientation of the downhole sub  10  within the casing as it approaches the internal diameter of the casing, one of the machined running edge  26 , the head of the pin  36  and a portion of the roller  20  therebetween will contact the inner diameter of the casing. Similar contact will occur at each of the rollers  20  along the length of the downhole sub  10 . 
     If the orientation of the downhole sub  10  is such that the machined running edge  26  makes initial contact with the inner diameter of the casing then the downhole sub  10  will tend to run along the edges  26  and thereby ensure minimal frictional resistance between the downhole sub  10  and the inner diameter of the casing. 
     In the event that the initial orientation of the downhole sub  10  is such that the first portion of the downhole sub  10  to contact the inner diameter of the casing is either the outer end of the pin  36  or a curved portion of the roller  20  between the outer end of the pin  36  and the machined running edge  26 , the asymmetry of the rollers  20  projecting from the body  12  will tend to cause the sub  10  to rotate (this is possible due to the provision of swivels  16  at either end of the sub  10 ) until the machined running edge  26  of the roller  20  comes into contact with the bottom of the casing. Therefore regardless of the initial rotational orientation of the sub  10  is as it approaches the inner diameter of a deviated portion of the casing, the asymmetrical nature of the rollers  20  will ensure that the sub  10  and hence the toolstring is able to move through the casing with minimal frictional resistance. 
     A number of subs  10  may be incorporated along the length of the toolstring in order to allow each sub  10  to assume the correct orientation for that particular location in the deviated wellbore. This is possible due to the rotational dislocation between the orientation of the sub  10  and the rest of the toolstring (not shown). 
     It should be noted that in this embodiment the rollers  20  are able to freely rotate independent of one another due to the movement of the toolstring and hence the sub  10  in the casing. The rotation of rollers  20  is assisted by the ball bearing arrangement  28 ,  30 . As each roller  20  attempts to rotate around the pin  36  the internal circumference of outer race  32  rotates ball bearing  30  which acts against the outer circumference of inner race  34 . This action allows the roller  20  to rotate around the pin  36  with minimal frictional resistance. 
     Referring to  FIGS. 2   a ,  2   b  and  2   c  a second embodiment of a downhole sub will now be described. It should be noted that the second embodiment shares many common features with the first embodiment and where applicable these features have been referred to in the following description with similar numerals. A prefix  1  has been given to apparatus where this applies. 
     The downhole sub  110  of  FIG. 2  is provided with indents  118  on either side of the body  112  in order to accommodate rollers  120  on each side of the body  112 . This embodiment provides greater support for the downhole sub  10  on rollers  120  and hence the toolstring to which it is attached (not shown) since fewer portions of the downhole sub  10  are unsupported by rollers  120 . In addition the arrangement of rollers e.g. four on each side of the sub  110  results in the sub  110  having fewer points at which the body  112  of the sub  110  may contact the inner diameter  200  of the casing or other tubular in which the sub  110  is run.  FIG. 4  illustrates the downhole sub inside a casing with the roller  120  contacting the inner diameter  200  of the casing. 
     Referring to  FIG. 2   c , each roller  120  is secured to the body  112  by a pair of interlocking pins  40 ,  42  which project through a throughbore  121  on each roller  120  and the centre of the body  112  in order to engage with one another and thereby secure the rollers  120  to the body  112  and also provide an axis of rotation about which the rollers  120  may rotate. The required asymmetry of the sub  110  may be provided by an asymmetrically shaped roller which has a greater diameter across one axis than an axis perpendicular to that axis i.e. an oval shaped roller or as shown in  FIG. 2   c  a substantially uniformly dimensioned semi-spherical roller which has been offset from the body  12  longitudinal axis by a sufficient amount to provide the required difference in the cross-sectional shape of the body  112 . In this regard it should be noted that the interengagement between pins  40  and  42  is arranged such that the overall dimension of the sub  110  is greater along the axis of rotation of the rollers  120  than the circumference of the rollers  120 . Alternatively the asymmetry may simply be provided by a portion of the apparatus (such as pins  40 ,  42 ) extending from the body  112 . 
     The various other components of the apparatus  110  of the second embodiment are substantially the same as those previously described in relation to the first embodiment and therefore will not be described any further. 
     In operation, the ball bearing arrangement provided by ball bearings  130  and ball bearing cage  128  of the sub  110  allows the rollers  120  to rotate about the interlocking pins  40 ,  42  whilst ensuring minimal frictional forces there between. In this embodiment the rollers  120  may move independently of one another which may be beneficial when e.g. discontinuities in the internal diameter of the casing are encountered i.e. one roller may rotate whilst the other does not. 
     Referring to  FIG. 3  a third embodiment of a downhole sub will now be described. Again, it should be noted that the third embodiment shares many common features with the first embodiment and where applicable these features have been referred to in the following description with similar numerals. A prefix  2  has been given to apparatus where this applies. 
     Referring to  FIG. 3  a further alternative embodiment of the downhole sub  210  is shown whereby the rollers  220  are secured to the body  212  by securing studs  44  on each side of the body  212 . The securing studs  44  secure each roller  220  to the body by way of a threaded socket  46  in the body  212 . In this way the centre of the downhole sub  210  is left free from obstructions and a central throughbore  48  can therefore be provided along the length of the downhole sub  210 . The throughbore  48  may be used to house cables such as power or data cables (not shown) which are often necessary to provide a communication means along the length of the toolstring. 
     The embodiment shown in  FIG. 3  may be used with a ball bearing cage similar to that described in relation to the first and second embodiments; however, due to the limited space available in the body  212  caused by providing throughbore  48  in the body  212  it is preferable to provide alternative means to assist the rotation of the rollers  220  around the pins  44  as shown in  FIG. 3 . Suitable alternative means comprise an inner slip surface  50  provided on a projecting shoulder  54  of the body  212  which abuts against an outer slip surface  52  provided on an inner cavity of each roller  220 . The inner and outer slip surfaces  50 ,  52  are made of a suitable material such that the abutment between each slip surface  50 ,  52  is conducive to rotation of the rollers  220  around the projecting stud  54 , i.e. the material on the surfaces  50 ,  52  is made of a suitable low frictional resistance material such as ceramic in order to cause minimal frictional resistance due to rotation of the rollers  220  relative to the body  212 . 
     The various other components of the apparatus  210  of the third embodiment are substantially the same as those previously described in relation to the first embodiment and therefore will not be described any further. 
     In each embodiment previously described the distance (indicated by A in  FIG. 1   c ) by which the rollers  20 ,  120  and  220  project from the respective body portions  12 ,  112  and  212  is manufactured such that the rollers may wear down during their operational lifetime without being worn down to such an extent that they are flush with the body  12 ,  112 ,  212  since this would cause the body portions to contact the inner diameter of the casing or other tubular. 
     Since the asymmetrical arrangement of the rollers in the embodiments described orientates the downhole sub in order that the running edge of the rollers engage the inner surface of the wellbore casing, this mitigates the possibility that the rollers fail to engage the inner surface of the wellbore casing by for instance the downhole sub resting on a portion not provided with rollers. This allows the sub to operate in highly deviated wells. 
     Modifications and improvements may be incorporated without departing from the scope of the invention, for example; further tools and/or subs such as inclination sensors, vibrators etc. may also be provided on the downhole subs previously described. In addition, drive motors may be provided to rotate the rollers when the deviation in the wellbore is large enough to prevent gravity alone progressing the downhole sub down the casing or other tubular.

Summary:
The invention relates to a downhole device for incorporation into a downhole string and movement in a wellbore. The device comprises a body member, at least one roller arranged on the device to engage the inner surface of the wellbore and means to orient the device in the wellbore. The means to orient the device are provided on the or each roller. Preferably the means to orient the device comprise a projecting portion provided on the or each roller which projects radially outwardly from the body member. The projecting portion can be an eccentrically-shaped portion of the or each roller.