Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to direction drilling of bores, particularly (though not exclusively) to produce fluid such as oil or gas from an underground formation.  
           [0002]    When drilling a borehole to extract oil or gas from an underground formation, it is often desirable to drill the borehole so that it includes one or more bends or curves. For example, it may be necessary to avoid an existing well, or to aim for the reservoir to be exploited. Similarly, in drilling a borehole to take piping and/or cables beneath a road or river, it is necessary to guide the course of the borehole.  
           [0003]    Wells are drilled using a drill string which consists of a drill pipe with a bottom hole assembly at its bottom end. Traditionally, the drill string has been rotating. With such a string, directional control is achieved by providing a collar around the bottom hole assembly which can be locked to the sides of the bore. The collar has a hole through which the main rotating body of the bottom hole assembly passes. This hole is offset to skew the body of the bottom hole assembly and so cause the bore to deviate from straightness.  
           [0004]    More recently, drill strings using coiled tubing have become popular. With this, the drill string is non-rotating, and carries a motor at the bottom of the bottom hole assembly. The motor is driven either by the fluid pumped down the drill string or electrically. (Fluid flow through the drill string is required to wash away the debris resulting from the drilling and to lubricate the system.)  
           [0005]    With a coiled tubing drill string, the bottom hole assembly can include a bent sub having nose tubing which carries the motor at its end. The drilling thus automatically tends to deviate from straightness. The bottom hole assembly also includes an orienter which can be operated to turn the bent sub to control the bearing (as seen looking along the bottom hole assembly) of the deviation of the drilling. GB 2 271 791 A (Camco/Pringle) is in essence an example of this.  
           [0006]    The use of a bent sub results in the drilling deviating continuously. Typically, however, it will be desired to drill a borehole which is curved along only a part or parts of its length, with the remainder being straight. There are two techniques of achieving this with the use of a bent sub.  
           [0007]    One is to include the bent sub in the bottom hole assembly only for those portions of the bore where deviation is desired; at the beginning and end of each such portion, the directional drilling assembly is removed from the borehole, the bent sub removed or attached, and the drill string re-introduced to the bore hole. Having to interchange straight and directional drilling assemblies adds to the time and cost of a drilling operation.  
           [0008]    The second technique is to rotate the orienter continuously in order to produce a nearly straight borehole. This is an inefficient and inaccurate way of producing a straight-pathed borehole. Further, rotating the orienter to simulate straight drilling, or to change or control the azimuthal angle of the directional drilling assembly, is made difficult due to friction between the drill string below the angled portion of the bent sub and the walls of the borehole, or the walls may completely block such rotation. It will be seen that this depends on the length of the drill string below the angled portion of the bent sub, the angle of the bent sub, the diameters of the borehole and the drill assembly, and the path of the borehole.  
           [0009]    Another difficulty associated with such a directional drilling assembly is that the rotation of the directional drilling assembly&#39;s drill bit exerts a torsional force upon the bent sub and orienter, acting to change the azimuthal angle of the bent sub. As the drill string beneath the bend in the bent sub is straight, the torque exerted by the drill bit is proportional to, amongst other factors, the angle through which the bent sub is bent, and the distance between the drill bit and the bend of the bent sub. These torsional stresses may be compounded if the drill bit is misaligned relative to the lower portion of the bent sub.  
           [0010]    Further, some orienters cannot rotate whilst there is weight-on-bit, either because of the operation of their actuating mechanism, or because they are simply not powerful enough.  
           [0011]    With bent subs, and with most orienters, there is only one degree of control, the azimuth of the deviation, ie the angle which the bent sub or orienter produces in the 360° range as seen looking longitudinally along the drill string. The magnitude of the deviation is the angle between the axis of the drill string and the bent sub or orienter, is fixed (at a few degrees). However, GB 2 278 137 A (Camco/Pringle &amp; Morris) shows a down hole assembly having a bent sub with a movable joint. The movable body, which is coupled to the main housing by a universal joint, has its upper end enclosed in a bore in the end of the housing, and normally hangs freely in the straight position. A mandrel can withdraw the movable body into the housing; the movable body has an offset head end which forces it to skew relative to the housing. The movable body is keyed to the housing to prevent rotation. Thus this can achieve a certain amount of control over the magnitude of the deviation.  
           [0012]    GB 2 271 795 A, Stirling Design/Head shows an orienter which provides azimuth control. An annular piston can be moved longitudinally, and has helical engagement to convert the movement into rotation. This rotation is splined to a collar with an eccentric bore. The central tube of the assembly passes through this bore (emerging as nose tubing carrying the motor and drill bit at its end), so rotation of the collar bends the tube to the side. In the embodiments of FIGS.  8 - 9  and  14 , magnitude control is also provided. This is achieved by a separate mechanism attached to the nose of the apparatus.  
           [0013]    The main object of the present invention is to provide an improved orienter giving 2 degrees of control.  
         SUMMARY OF THE INVENTION  
         [0014]    According to the invention there is provided an orienter comprising a main body couplable to a drill string, a nose tubing movably mounted in the main body, and a collar with a bore which engages in a cam-like manner with the nose tubing and movable to control the orientation of the nose tubing, wherein the collar is movable longitudinally and circumferentially to control both the magnitude and the azimuth of the nose tubing.  
           [0015]    Preferably the mounting of the nose tubing is a universal joint. Preferably also the collar engages with an extension of the nose tubing on the drill string side of the universal joint. Preferably also the nose tubing is aligned on both sides of the universal joint and the bore of the collar is angled relative to the main axis of the main body.  
           [0016]    The collar is preferably hydraulically or electrically controlled. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0017]    Brief Listing of Drawings  
         [0018]    An orienter embodying the invention will now be described by way of example and with reference to the accompanying drawings, in which:  
         [0019]    [0019]FIG. 1 is a longitudinal view of a prior art directional drill  
         [0020]    [0020]FIG. 2 is a longitudinal view of an embodiment of the directional drilling assembly;  
         [0021]    FIGS.  3  to  5  are longitudinal sections of part of the directional drilling assembly in straight, angled, and differently angled orientations respectively;  
         [0022]    [0022]FIG. 6 is a exploded perspective view of part of another embodiment of the directional drilling assembly;  
         [0023]    [0023]FIG. 7 is a longitudinal section of part of that further directional drilling assembly: and  
         [0024]    [0024]FIG. 8 shows a more detailed embodiment of the present orienter, in  2  sections. 
     
    
     DETAILED DESCRIPTION  
       [0025]    [0025]FIG. 1 shows a known assembly for introducing a curve into a borehole trajectory. The assembly uses an orienting device  12  on the lower end of the drill pipe  10 , and a mud motor  16  and a drill bit  18  on the lower end of the orienting device  12 . (Terms like ‘upper’ and ‘lower’ refer to the borehole path and the drill string in it extending along from the mouth of the borehole, since a directionally drilled borehole may include horizontal regions or even regions where the borehole is steered back towards the surface; the left side of the Figs. corresponds to an upwards direction).  
         [0026]    The orienting device  12  comprises an orienter  13  and a bent sub  14 . The bent sub  14  is set at an angle at the surface corresponding to the degree of curvature desired. The orienter includes a rotatable joint actuated by hydraulic or electrical means so that the bent sub is pointing in the correct direction when considered looking along the drill string immediately above the bent sub (i.e. the correct azimuthal angle). Rather than rotating the entire drill string, which typically occurs in straight drill strings, the drill bit of the directional drilling assembly is driven by a mud motor powered by fluid passed down the drill string, since a rotating drill bit would rotate the azimuthal angle of the bent sub.  
         [0027]    [0027]FIG. 2 shows the present directional drilling assembly, which comprises a pointing orienter  20 , a mud motor  16 , and a drill bit  18 , all suspended from a length of drill string  10 .  
         [0028]    FIGS.  3  to  5  show the present pointing orienter  20  in more detail. The orienter comprises a ball joint  22 , crank arm  24  and bearing  26  secured to a lower housing  30 , and a bearing block  42  mounted in an upper housing  40 . A flowtube  50  runs along the centre axis of the pointing orienter. The upper and lower housings  40 ,  30  are tubes having approximately the same outer diameter of the drill string. The ball joint  22  is spherical and is also approximately the drill string&#39;s diameter. The ball joint  22  is set in the lower housing  30  so that half the sphere  22  extends from the lower housing  30  (half the sphere being contained within the lower housing); the thickness of the tube of the lower housing  30  is bevelled to accommodate the ball joint. The ball joint  22  is securely fixed in some manner to the lower housing  30 , and to mounting blocks  32  set in the inner diameter of the lower housing. The ball joint  22  includes a through bore  23  running along the centre axis of the lower housing, the through bore having a sufficient diameter to accommodate the flowtube  50 .  
         [0029]    A tubular crank arm  24  extends upwards from the ball joint  22 . The crank arm has a smaller diameter than the lower housing  30 , and is coaxial with it. Towards the end opposite the ball joint  22 , there is an annular bearing  26  surrounding the crank arm  24 , the outer surface of the bearing being curved. The shape of the bearing  26  is part of a sphere the central axis of the crank arm intersecting the mid-point of this sphere.  
         [0030]    The bearing block  42  is comprises a cylinder having a chamber formed from both a blind bore  43  excised from it, and a through bore  44  extending beyond the end of the blind bore. The bearing block  42  has an outer diameter somewhat less than the inner diameter of the upper housing  40 , and is slidable moveable therein both axially and rotationally, this movement being effected by electric or hydraulic actuators. The through bore  44  allows the flowtube  50  to pass through the bearing block  42 , the inner surface of the through bore having a sufficient gap to allow the bearing block to move axially and rotationally around the flowtube  50 . The blind bore  43  is cylindrical, has an inner diameter somewhat larger than the outer diameter of the bearing  26 , with the axis of the blind bore  43  being inclined from the axis of the upper housing. The inclination of the -blind bore&#39;s axis from the upper housing&#39;s axis is typically about 4°. The mouth of the blind bore  43  forms a circle whose centre coincides with the central axis of the upper housing (the mouth of the blind bore will actually be somewhat elliptical, and centred slightly off the centre line, but approximates a circle provided the inclination of the blind bore from the upper housing is small).  
         [0031]    The lower end of the upper housing  40  includes a curved bevelled edge which fits against the ball joint  22 , such that the ball joint may typically rotate through approximately 3° relative to the upper housing.  
         [0032]    The upper and lower housings  40 ,  30  are held or joined in a substantially abutting relationship, for example being secured together by a sleeve of material around their abutting ends. The join between the upper and lower ends must be flexible enough to allow the lower housing  40  to pivot about the ball joint  22  to change the lower housing to change its inclination relative to the upper housing, and to change the azimuth of the lower housing, but the join should be strong enough to resist the twisting rotation of the lower housing relative to the upper housing (i.e. the angular displacement of abutting points on the upper and lower housings). An alternative way of forming the pivoting part of the device using a spherical Oldham coupling is described below.  
         [0033]    In FIG. 3, the bearing block  42  is shown positioned at its upper limit, the bearing upon the crank arm  24  just engaging with the bearing block&#39;s mouth. The lower housing and the upper housing are aligned.  
         [0034]    [0034]FIG. 4 shows the bearing block  42  displaced downwards from its position in FIG. 3 (indicated by the arrow ‘a’) by its actuators (the actuators are not shown) to a position about three-quarters of the way between the upper and lower limits of its range and closer to the lower limnit. The upper limit of the bearing block is determined such that the bearing  26  is close to the mouth of the bearing block&#39;s chamber, and the lower limit is such that the end of the crank arm  24  stops short of or abuts the end of the blind bore  40 , or until the crank arm and bearing are constrained from further relative movement between the upper housing and the flowtube.  
         [0035]    Since the blind bore  43  is inclined to the axis of the upper housing  40 , downward axial displacement (indicated by arrow ‘a’) of the bearing block  42  from its lower limit causes the bearing  26  to move radially outwards, pivoting about the ball joint  22 . The lower housing  30 , being secured to the ball joint, pivots to the same degree and direction as the crank arm (indicated by the arrow ‘b’). For small inclinations, the angle of inclination (or “angular magnitude”) of the lower housing&#39;s axis to the upper housing&#39;s axis is directly proportional to the axial displacement of the bearing block. At the position shown in FIG. 4, the inclination (indicated by angle ‘a’) of the lower housing is approximately 2°, a typical maximum angular inclination being 3°.  
         [0036]    Since the mud motor  16  and drill bit  18  are coaxially fixed to the lower housing  30 , the drill bit is inclined to the relative to the drill string immediately above the ball joint Axial displacement of the bearing block  42  therefore causes the drill to bore a curved path according to the inclination from the upper housing.  
         [0037]    The torque caused by the rotation of the drill bit at an inclination to the upper housing  40  is substantially transmitted through the lower housing  30  to the upper housing, and not to the actuators displacing the bearing block  42 . The actuators therefore need only be strong enough to effect the change of orientation.  
         [0038]    Referring to FIG. 5, if the bearing block  42  is rotated (indicated by arrow ‘c’) about the axis of the upper housing  40  (again by actuators which are not shown), the bearing  26  will describe an arc having that degree of rotation of the bearing block, the radius of the arc depending upon the axial displacement of the bearing block (unless the axis of the crank arm is aligned with the upper housing&#39;s axis, in which case rotation of the bearing block will have no effect). The lower housing, and the mud motor and drill bit below, will therefore describe part a cone (indicated by arrow ‘d’). The bearing block is preferably rotatable about a complete 360° turn, ideally it may be rotated with complete freedom.  
         [0039]    By a combination of axial and rotational movement of the bearing block, the drill bit may be oriented to any desired inclination (angular magnitude) within a cone having a slope corresponding to the maximum inclination of the lower housing, and any desired azimuthal angle within that cone.  
         [0040]    The pointing orienter includes sensors which record the axial displacement and angular displacement (i.e. an angle through which rotation has occurred) of the bearing block. Further sensors measure the actual position and orientation of the drill bit. Using these sensors, an operator may set a desired path for the borehole, and monitor the orientation of the pointer orienter and the development of the path, modifying the path as results generated by the sensors appear. Some or all of the control process may of course be automatic, the processing being effected by a processing unit located above ground or installed somewhere in the drill string.  
         [0041]    The flowtube  50  is necessary to allow tools or fluids to pass down the drill string. The flowtube is made from a material sufficiently strong and flexible to bend and remain integral as the pointing orienter pivots about the ball joint.  
         [0042]    [0042]FIGS. 6 and 7 show the ball joint structure in more detail. The upper housing  40  has a protruding spherical end which houses the ball joint  22 . Between the upper housing  40  and the lower housing  30  is a semi-spherical plate  60 . The lower housing  30  has a spherically recessed end. The radii of the ball joint  22 , the spherical end of the upper housing  40 , the plate  60 , and the lower housing  30  are engage firmly as shown in FIG. 7, but allow movement between the respective abutting surfaces. The ball joint  22  is fixed to the lower housing  30  by a stalk  21 , which extends through central circular apertures  61 ,  63  in the upper housing and plate respectively. The radius of the apertures  61 ,  63  is greater than that of the stalk, allowing the ball joint  22  to pivot so as to incline the stalk by approximately 4° away from the axis in any direction.  
         [0043]    The spherical end of the upper housing  40  includes two opposing radial slots  65 ,  66 . The concave surface of the plate  60  includes corresponding splines  67 ,  68  which engage in the slots. The convex surface of the plate  60  includes two opposing radial slots  71 ,  72  similar to those of the upper housing, except that the slots  71 ,  72  are perpendicular to the slots  65 ,  66  and splines  67 ,  68 . The recessed spherical surface of the lower housing  40  includes splines  73 ,  74  which correspond to and engage with the slots  71 ,  72  (the splines  73 ,  74  are, apart from their orientation, similar to the splines  67 ,  68 ).  
         [0044]    It will be seen that the slots  65 ,  66  and splines  67 ,  68  allow the ball joint to pivot in a first plane, whilst the slots  71 ,  72  and splines  73 ,  74  allow the ball joint to pivot in a second plane perpendicular to the first, so giving the ball joint freedom to orient itself within a cone having sides inclined at approximately 4° from the upper housing&#39;s axis; however, no rotation of the lower housing about the upper housing&#39;s axis is permitted. This arrangement thus conveniently couples the upper and lower housings, and transfers torsional forces from the lower housing to the upper housing.  
         [0045]    [0045]FIG. 8 shows the present orienter in more detail. The bearing block or collar  42  is mounted in a journal bearing  80 . A motor  80  is mounted close to the bearing block  42  and coupled to it via a gearbox  82 ; this motor controls the rotation of the bearing block. A second motor  83  is mounted near the up well end of the assembly, and controls the linear movement of the bearing block via a linear actuator  84  which converts the rotation of the motor into longitudinal movement.  
         [0046]    The torsional force upon the pointing orienter depends upon the inclination of the drill string below the pointing orienter, its length, and force generated by the drill bit. At large inclinations, further strengthening of the pointing orienter may be necessary. The lower end of the upper housing may include inwardly directed longitudinal spines on its inner surface, these splines engaging with corresponding grooves on the bearing block when the bearing block is displaced past a predetermined amount and corresponding to a predetermined torque. The splines will then help lock the pointing orienter when large torsional loads are exerted upon it. It will be apparent that the azimuthal angle can only be adjusted when the bearing block is not engaged by the splines, and the angular position of the bearing block beyond the predetermined point of engagement is limited by the number of engaging positions. In order to change the azimuthal angle of the lower housing when highly inclined, the inclination must be reduced until the bearing block disengages, the bearing block re-engaged at a different angular position before the inclination of the lower housing is increased.  
         [0047]    Naturally, the splines may be situated upon the bearing block, engaging with grooves present upon the inner surface of the upper housing or with the splines and grooves distributed between the bearing block and upper housing. Some type of spline mechanism or other torsion limiting mechanism could alternatively or additionally be included elsewhere in the pointing orienter, for example between the bearing and the bearing block, or the ball joint and the housings.  
         [0048]    It will be realized that other types of universal joint may be substituted or combined with the ball joint, such as a Hooke&#39;s joint.  
         [0049]    The dimensions of the pointing orienter are dictated by the drill string it is to be incorporated in, and the environment it is to be used in. The maximum inclination of the lower housing is determined by the inclination of the blind bore. Besides the bearing of the blind bore, the length of the crank arm and the blind bore will determine degree to which the inclination varies as the bearing blocks displacement varies.  
         [0050]    It will be apparent that specific features disclosed herein could be combined with features of known orienter devices. It will be realized that although not deriving the full benefit of the improvements, the present pointing orienter could be combined with a bent sub assembly. Also, alternative driving means may be substituted for the mud motor, for example an electric motor situated between the drill bit and the orienter. An electric power cable, and other cabling, may conveniently be disposed inside the drill string, passing through the orienter; since the housings do not rotate relative to each other, the cabling may be eccentrically disposed and need only be flexible enough to withstand the changes in inclination (magnitude) and azimuth between the upper and lower housings.

Technology Category: e