Abstract:
The device contemplated provides a method for positioning the drill bit in a drilling operation to achieve small changes in hole angle or azimuth as drilling proceeds. Two different positions are available to the operator. The first is a straight ahead position where the tool essentially becomes a packed hole stabilizer assembly. The second position tilts the bit across a rotating fulcrum to give a calculated offset at the bit-formation interface. The direction that the bit offset is applied in relation to current hole direction is controlled by positioning the orienting pistons prior to each drilling cycle, through the use of current measurement-while-drilling (MWD) technology. Components of the tool comprise a MWD housing, upper steering and drive mandrel, non-rotating position housing, lower drive mandrel splined with the upper mandrel, rotating fulcrum stabilizer and drill bit.

Description:
RELATED APPLICATIONS 
   This application is a divisional application based on prior application Ser. No. 09/907,480, filed on Jul. 17, 2001 now U.S. Pat. No. 6,595,303, which in turn is based upon prior U.S. provisional application Ser. No. 60/245,188 filed Nov. 3, 2000, which in turn is a U.S. provisional national application of prior Canadian application Serial No. 2,345,560, filed Apr. 27, 2001, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §§119 and 120. 

   FIELD OF THE INVENTION 
   The invention relates to rotary drilling, and more particularly, to steered directional drilling with a rotary drilling tool. 
   BACKGROUND OF THE INVENTION 
   In the earth drilling art, it is well known to use downhole motors to rotate drill bits on the end of a non-rotating drill string. With the increasingly common use of directional drilling, where the well is drilled in an arc to produce a deliberately deviated well, bent subs have been developed for guiding the downhole motors in a desired drilling direction. The bent subs are angled, and thus cannot be used in association with rotating drill strings. 
   This invention is directed towards a tool that permits steered directional drilling with a rotary drilling tool. 
   SUMMARY OF THE INVENTION 
   The device contemplated provides a method for positioning the drill bit in a drilling operation to achieve small changes in hole angle or azimuth as drilling proceeds. Two different positions are available to the operator. The first is a straight ahead position where the tool essentially becomes a packed hole stabilizer assembly. The second position tilts the bit across a rotating fulcrum to give a calculated offset at the bit-formation interface. The direction that the bit offset is applied in relation to current hole direction is controlled by positioning the orienting pistons prior to each drilling cycle, through the use of current measurement-while-drilling (MWD) technology. 
   In one aspect of the invention, components of the tool comprise a MWD housing, upper steering and drive mandrel, non-rotating position housing, lower drive mandrel splined with the upper mandrel, rotating fulcrum stabilizer and drill bit. 
   If, after surveying and orienting during a connection, it is desired to drill with the tool in the oriented position, the rig pumps are activated. The pressure differential created by the bit jets below the tool will cause pistons to open from the ID of the tool into the tool chamber. As the pistons open, they will contact wings that come out into the path of travel of the upper mandrel as it comes down a spline, and bottoms out on the lower drive mandrel. This occurs as the drill string is being lowered to bottom. The extra length provided by the open wings moves a sliding sleeve centered over, but not attached to the upper mandrel, to a new position that in turn forces the orienting pistons to extend out into the borehole annulus. This extrusion pushes the non-rotating sleeve (outer housing) to the opposite side of the hole. When this force is applied across the rotating stabilizer, the stabilizer becomes a fulcrum point, and forces the drill bit against the side of the hole that is lined up with the orienting pistons. The calculated offset at the bit then tends to force the hole in the oriented direction as drilling proceeds. After the drilling cycle is complete, the tool will be picked up off bottom, and as the upper mandrel moves upward on the spline in the lower mandrel, a spring pushes the sliding sleeve back into its normal position, the orienting pistons retract into the outer housing, and the centering pistons come back out into the borehole annulus, thus returning the tool to its normal stabilized position. This cycle may be repeated until the desired result is achieved. 
   Once the desired hole angle and azimuth are achieved, the following procedure may be implemented to drill straight ahead. After making a connection and surveying, slowly lower the drill string to bottom and set a small amount of weight on the bit. Then engage the rig pumps. This time, when the activation pistons from the ID attempt to open the wings, they will be behind the sliding sleeve assembly, and the sliding sleeve will remain in its normal or centered position throughout the following drilling cycle. 
   Skillful alternating of the two above drilling positions will yield a borehole of minimum tortuosity, when compared to conventional steerable methods. 
   These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a side view of a drill string with rotary steerable tool according to the invention; 
       FIGS. 2A-2D  are lengthwise connected sections (with some overlap) through a rotary steerable tool according to the invention showing the tool in pulled back position ready to extend the wings used to move the pistons into the offset drilling position; 
       FIG. 3  is a cross section along section line  3 — 3  in  FIG. 2C ; 
       FIG. 4  is a cross section along section line  4 — 4  in  FIGS. 2C and 8C ; 
       FIG. 5  is a cross section along section line  5 — 5  in  FIGS. 2C and 8C ; 
       FIG. 6  is a cross section along section line  6 — 6  in  FIGS. 2C and 8C ; 
       FIG. 7  is a cross section along section line  7 — 7  in  FIGS. 2B and 8B ; 
       FIGS. 8A-8D  are lengthwise connected sections (with some overlap) through a rotary steerable tool according to the invention showing the tool in straight ahead drilling position; 
       FIG. 9  is a cross section along section line  9 — 9  in  FIG. 8C ; 
       FIG. 10  is a lengthwise section through a rotary steerable tool according to the invention showing the tool in offset drilling position; 
       FIG. 11  is a cross section along section line  11 — 11  in  FIG. 10 ; 
       FIG. 12  is across section along section line  12 — 12  in  FIG. 10 ; 
       FIG. 13  is a cross section along section line  13 — 13  in  FIG. 10 ; 
       FIG. 14  is a cross section along section line  14 — 14  in  FIG. 10 ; 
       FIG. 15  is a perspective view of a rotary steerable tool according to the invention showing wings in the extended position with the housing partly broken away to show the mandrel; 
       FIG. 16  is a perspective view of a rotary steerable tool according to the invention with the housing broken away to show wings in the retracted position; 
       FIG. 17  is a close-up view of mating dog clutch faces for use in orienting the rotary steerable tool according to the invention; 
       FIG. 18  is an end view of a rotary steerable tool according to the invention showing pistons set in the offset drilling position; and 
       FIG. 19  is an end view of a rotary steerable tool according to the invention showing pistons set in the straight ahead drilling position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In this patent document, “comprising” is used in its inclusive sense and does not exclude other elements being present in the device. In addition, a reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present. MWD means measurement-while-drilling. All seals and bearings described herein and shown in the drawings are conventional seals and bearings. 
   Referring to  FIG. 1 , which shows the overall assembly of a drill string according to the invention, a rotary steerable drilling tool  10  is shown located on a conventional drill string  12  between a conventional MWD tool  14  and a conventional drill bit  16 . As shown more particularly in  FIGS. 2A and 2D , rotary steerable drilling tool  10  includes a mandrel  20  having a conventional box connection  22  at an uphole end for connection into drill string  12  and a conventional box connection  24  at a downhole end for connection to a pin connection  26  of a drilling sub  28 . Sub  28  is configured as a rotating stabilizer  17  provided on the drill string between rotary steerable drilling tool  10  and drill bit  16 , and operates as a fulcrum for rotary steerable drilling tool  10  and drill bit  16  to pivot around. Drill bit  16  will conventionally have jets in the bit for egress of fluid from the drill string. At the surface, a conventional rig will include conventional pumps (not shown) for pumping fluid down drill string  12  to drill bit  16  and out the jets in the drill bit. 
   The components of rotary steerable drilling tool  10  are best seen in  FIGS. 2A-2D , which show the tool in the pulled back off-bottom position, ready to set the tool into either a straight ahead drilling position or an offset drilling position.  FIGS. 3-7  are sections corresponding to the section lines on  FIGS. 2A-2D .  FIGS. 15-19  provide perspective views of the tool broken away to show the internal workings.  FIGS. 3-7  are sections corresponding to the section lines on  FIGS. 2A-2D .  FIGS. 8A-8D  show rotary steerable drilling tool  10  in a straight ahead on-bottom drilling position.  FIG. 9  is a section corresponding to the section line  9 - 9  on FIG.  8 C. The other sections shown on  FIGS. 8A-8D  correspond to  FIGS. 4-7  as well, since the sections do not change in those positions.  FIG. 10  shows rotary steerable drilling tool  10  in position for offset drilling, insofar as it is different from the position shown in  FIGS. 8A-8D .  FIGS. 11-14  are sections corresponding to the section lines on FIG.  10 . 
   Referring to  FIGS. 2A-2D ,  3 - 7 ,  8 A- 8 D, and  15 - 19 , and particularly to  FIGS. 2A-2D , a bore  30  is provided within mandrel  20  for communication of fluid from surface to drill bit  16 . A housing  32  is mounted on mandrel  20  for rotation in relation to mandrel  20 . During drilling, housing  32  is held against rotation by frictional engagement with the wellbore and the mandrel rotates, typically at about 120 rpm. Housing  32  is provided with an adjustable offset mechanism that can be adjusted from the surface so that rotary steerable drilling tool  10  can be operated in and changed between a straight ahead drilling position and an offset drilling position. In the straight ahead drilling position, asymmetry of housing  32 , namely thickening  33  of housing  32  on one side, in combination with pistons on the other side of housing  32  yields a tool that is centered in the hole. In an offset drilling position, pistons on the thickened side of housing  32  drive tool  10  to one side of the wellbore, and thus provide a stationary fulcrum in which mandrel  20  rotates to force the drill bit in a chosen direction. Three hole grippers  15  are provided on the exterior surface of housing  32  downhole of thickened section  33 . One of hole grippers  15  is on the opposite side of the thickened section, and the other two are at about 90 degrees to thickened section  33 . Hole grippers  15  are oriented such that when rotary steerable tool  10  is offset in the hole by ½ degree by operation of the adjustable offset mechanism described below, hole grippers  15  will lie parallel to the hole wall, so that hole grippers  15  make maximum contact with the hole wall. Hole grippers  15  grip the wall of the hole and prevent housing  32  from rotating, as well as preventing premature wear of housing  32  against the wellbore. 
   Housing  32  has threaded on its uphole end an end cap  34  holding a piston  36 , and on its downhole end another end cap  40  holding a floating piston seal  42  within chamber  44 . Floating piston  42  accommodates pressure changes caused by movement of the housing on mandrel  20 . Housing  32  rotates on mandrel  20  on seven bearings  46 . Mandrel  20  is formed from an upper mandrel  50  and lower mandrel  52  connected by splines  54 . A sleeve  55 , is held in the bore of lower mandrel  52 , and in the downhole end of upper mandrel  50 , by a pin on sub  28 . Appropriate seals are provided as shown to prevent fluid from the mandrel bore from entering between the upper mandrel  50  and lower mandrel  52  at  57 . Downhole movement of upper mandrel  50  in lower mandrel  52  is limited by respective shoulders  59  and  61 . Housing  32  is supported on lower mandrel  52  by thrust bearings  56  on either side of a shoulder  58  on lower mandrel  52 . 
   The adjustable offset mechanism may for example be formed using plural pistons  60 ,  62  and  64  radially mounted in openings in housing  32 . Pistons  60  and  62  are mounted in openings on thickened side  33  of the sleeve, while pistons  64  are mounted on the opposed side. Thickened side  33  has a larger radius than the opposed side, and pistons  64  are extendable outward to that radius. Pistons  62  are at 120 degrees on either side of piston  60  and extend outward at their maximum extension less than the extension of piston  60  when measured from the center of mandrel  50 . Pistons  60  and  62  extend outward to a radius of a circle that is centered on a point offset from the center of mandrel  50 , as shown in FIG.  18 . As shown in  FIGS. 4-6  and  12 - 14 , hole grippers  65  are also embedded on either side of housing  32  at 90 degrees to piston  60 . Hole grippers  65  are about 5 inches long, and are oriented, as with hole grippers  15 , so that one edge lies furthest outward. Thus, hole grippers  65  assist in preventing housing  32  from rotating by engaging the hole wall with their outermost edge. Hole grippers  15  and  65  should be made of a suitably hard material, and may, for example, be power tong dies since these are readily available and may be easily removed for replacement. Pistons  60 ,  62  and  64  should also be made of a similar hard material. 
   Pistons  60 ,  62  and  64  are radially adjusted by actuation of mandrel  20  as follows. Dog clutch  66  is pinned by pins  68  to mandrel  20  to form a chamber  70  between housing  32  and upper mandrel  50 . Dog clutch  66  has a dog face  67  that bears against dog face  69  on end cap  34  when upper mandrel  50  is raised in the hole. Wings  72  secured on pins  76  in the upper mandrel  50  are operable by fluid pressure in bore  30  of upper mandrel  50  through opening  74 . Fluid pressure in bore  30  urges pistons  71  radially outward and causes wings  72  to swing outward on pins  76  into chamber  70 . Upon reduction of fluid pressure in bore  30 , wave springs  73  surrounding pistons  71  draw pistons  71  back into upper mandrel  50 . A spring (not shown) is also placed around wings  72  seated in groove  77 . Groove  77  is also formed in the outer surface of wings  72  and extends around uppper mandrel  50 . The spring retracts wings  72  when the pressure in bore  30  is reduced and wings  72  are not held by frictional engagement with collar  84 . 
   Chamber  70  is bounded on its housing side by a sleeve  78 , which acts as a retainer for a piston actuation mechanism held between shoulder  80  on end cap  34  and shoulder  82  on housing  32 . The piston actuation mechanism includes thrust bearing  86  held between collars  84  and  88 , cam sleeve  90  and spring  92 , all mounted in that order on mandrel  32 . Cam sleeve  90  is mounted over a brass bearing sleeve  91  that provides a bearing surface for cam sleeve  90 . Spring  92  provides a sufficient force, for example 1200 lbs, to force cam sleeve  90  uphole to its uphole limit determined by the length of sleeve  78 , yet not so great that downhole pressure on upper mandrel  50  cannot overcome spring  92 . Spring  92  may be held in place by screws in holes  93  after spring  92  is compressed into position during manufacture, and then the screws can be removed and holes  93  sealed, after the remaining parts are in place. 
   Cam sleeve  90  is provided with an annular ramped depression in its central portion  94  and thickens uphole to cam surface  96  and downhole to cam surface  98 , with greater thickening uphole. Piston  60  is offset uphole from pistons  64  by an amount L, for example 3½ inches. Cam surface  96  is long enough and spaced from the center of depression  94  sufficiently, that when cam sleeve  90  moves a distance L downward to the position shown in  FIG. 10 , piston  60  rides on cam surface  96 , while pistons  64  ride in the center of depression  94 . Cam surface  98  is long enough and spaced from the center of depression  94  sufficiently, that when cam sleeve  90  is urged uphole by spring  92  to the position shown in  FIG. 2C  or  8 C, pistons  64  ride on cam surface  98 , while piston  60  rides in the center of depression  94 . Thus, when cam sleeve  90  is forced downhole in relation to housing  32 , pistons  60  ride on uphole cam surface  96 , and are pressed outward into the well bore beyond the outer diameter of housing  32 , while pistons  64  may retract into annular depression  94 . When cam sleeve  90  is in the uphole position, pistons  60  are in annular depression  94 , while pistons  64  ride on downhole cam surface  98 . Pistons  62  will also ride on cam sleeve  90 , but are slightly offset downhole from piston  60  and so do not extend as far outward. Since cam surface  98  has a smaller diameter than cam surface  96 , the tool may move more readily in the hole when pistons  64  are extended for the straight ahead drilling position, and piston  64  and housing  32  act as a stabilizer. The stabilizer position or straight ahead drilling position of the pistons is shown in the end view FIG.  19  and the cross sections of  FIGS. 5 and 6 . The offset drilling position of the pistons is shown in the end view of FIG.  18  and the cross sections of  FIGS. 12-14 . 
   An orientation system is also provided on rotary steerable drilling tool  10 . A sensor  102 , for example a magnetic switch, is set in an opening in upper mandrel  50 . A trigger  104 , for example a magnet, is set in end cap  34  at a location where trigger  104  will trip sensor  102  when mandrel  20  rotates in an on-bottom drilling position (either offset or straight). Snap ring  105  should be non-magnetic. A further sensor  106  is set in upper mandrel  50  at a distance below sensor  102  about equal to the amount upper mandrel  50  is pulled back as shown in  FIGS. 2A-2D , which will be slightly greater than the distance L, for example  4  inches when L is 3½ inches. Trigger  104  will therefore trip sensor  106  when mandrel  20  is pulled back and jaw clutch faces  67 ,  69  are engaged. This position allows the tool to be oriented with the MWD tool face. Sensors  104  and  106  communicate through a communication link, e.g. a conductor, in channel  105  with a MWD package in MWD tool  14 . Sensors  102  and  106  are thus sensitive to the rotary orientation of housing  32  in relation to mandrel  20 , and when trigger  104  trips one of sensors  102 ,  106 , sends a signal to the MWD tool  14  that is indicative of the rotary orientation of housing  32  on mandrel  20 . 
   For drilling in the straight ahead position shown in  FIGS. 8A-8D  and  9 , mandrel  50  is set down on lower mandrel  52  so that shoulders  59  and  61  abut. Wings  72  are held in mandrel  50 , and spring  92  urges cam sleeve  90  to the position shown in  FIG. 8B , so that pistons  64  are forced outward by cam surface  98 , and piston  60  lies in annular depression  94 . In this position, pistons  64  and thickened portion of housing  32  form a circular stabilizer and mandrel  20  rotates within housing  32  centrally located in the hole. 
   For drilling in the offset position, rotary steerable drilling tool  10  is altered in position as shown in  FIGS. 10-14 . Upper mandrel  50  is lifted off lower mandrel  52  until dog face  67  engages dog face  69 , and rotated at least 360 degrees to ensure engagement of faces  67  and  69 . The orientation of housing  32  in the hole can then be determined by MWD tool  14  if the engaging position of dog faces  67 ,  69  is programmed in the MWD package. Housing  32  may then be rotated from surface using mandrel  20  into the desired direction of drilling in the offset drilling position. The drilling direction will conveniently coincide with the direction that piston  60  points. With dog faces  67 ,  69  engaged, fluid pressure is applied from surface to bore  30  of mandrel  20  to force wings  72  into a radially extended position. Mandrel  20 , or more specifically upper mandrel  50 , since lower mandrel  52  does not move in this operation, is then moved downward. Upon downward motion of mandrel  20 , wings  72  drive cam sleeve  90  downward and lift piston  60  onto cam surface  96 , thus extending piston  60  outward, while piston  64  moves into annular depression  94 . The action of piston  60  bearing against the wellbore places rotary steerable tool  10  in an offset drilling position using rotary stabilizer  17  as a rotating fulcrum. The ratio of the offset caused by pistons  60 ,  62  to the offset at drill bit  16  is equal to the ratio of the distance of pistons  60 ,  62  from rotary stabilizer  17  to the distance of drill bit  16  from rotary stabilizer  17 . 
   During straight ahead drilling, the location of housing  32  may also be determined by rotating mandrel  20  in housing  32  and taking readings from sensors  106 . The timing of the readings from sensor  106  may be used by the MWD package to indicate the location of housing  32 . 
   Immaterial modifications may be made to the invention described here without departing from the essence of the invention.