Abstract:
A technique facilitates control over the orientation of a bottom hole assembly. The bottom hole assembly comprises an orienting tool having a dual-spline drive which, in turn, comprises a first lead screw portion and a second lead screw portion having threads of a first pitch and a second pitch, respectively. A motor is connected to the dual-spline drive to impart rotational motion with respect to the first threads having the first pitch. A difference in pitch between the first pitch and the second pitch enables the rotational motion imparted by the motor to be converted to a slower, higher torque, output via the second lead screw portion. As a result, the orienting tool is able to provide a selective, high torque, low-speed adjustment to the drilling orientation of the bottom hole assembly.

Description:
This is a divisional application of co-pending U.S. patent application Ser. No. 12/974,055, filed on Dec. 21, 2010 which claims priority of U.S. Provisional Patent Application Ser. No. 61/288,487, filed on Dec. 21, 2009, and entitled “Coil Tubing Orienter Tool with Differential Lead Screw Drive,” which is hereby incorporated in their entirety for all intents and purposes by these references. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The subject disclosure relates generally to oilfield drilling, and more particularly to bottom hole assemblies and tools for orienting a bottom hole assembly (BHA). 
     Background of the Related Art 
     In conventional drilling, the BHA is lowered into the wellbore using jointed drill pipes or coiled tubing. Often the BHA includes a mud motor, directional drilling and measuring equipment, measurements-while-drilling tools, logging-while-drilling tools and other specialized devices. A simple BHA having a drill bit, various crossovers, and drill collars is relatively inexpensive, costing a few hundred thousand US dollars, while a complex BHA costs ten times or more than that amount. 
     Many drilling operations require directional control so as to position the well along a particular trajectory into a formation. Directional control, also referred to as “directional drilling,” is accomplished using special BHA configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors, and special BHA components and drill bits. The directional driller can use drilling parameters such as weight-on-bit and rotary speed to deflect the bit away from the axis of the existing wellbore. In some cases, e.g. when drilling into steeply dipping formations or when experiencing an unpredictable deviation in conventional drilling operations, directional-drilling techniques may be employed to ensure that the hole is drilled vertically. 
     Direction control is most commonly accomplished through the use of a bend near the bit in a downhole steerable mud motor. The bend points the bit in a direction different from the axis of the wellbore when the entire drill string is not rotating. By pumping mud through the mud motor the bit rotates (though the drill string itself does not), allowing the bit alone to drill in the direction to which it points. When a particular wellbore direction is achieved, the new direction may be maintained by then rotating the entire drill string, including the bent section, so that the drill bit does not drill in a direction away from the intended wellbore axis, but instead sweeps around, bringing its direction in line with the existing wellbore. As it is well known by those skilled in the art, a drill bit has a tendency to stray from its intended drilling direction, a phenomenon known as “drill bit walk”. A device for addressing drill bit walk is shown in U.S. Pat. No. 7,610,970 to Sihler et al. issued Nov. 3, 2009, which is incorporated herein by reference. 
     The use of coiled tubing with downhole mud motors to turn the drill bit to deepen a wellbore is another form of drilling, one which proceeds quickly compared to using a jointed pipe drilling rig. By using coiled tubing, the connection time required with rotary drilling is eliminated. Coiled tube drilling is economical in several applications, such as drilling narrow wells, working in areas where a small rig footprint is essential, or when reentering wells for work-over operations. 
     In coiled tubing drilling, a BHA with a mud motor is attached to the end of a coiled tubing string. Typically, the mud motor has a fixed or adjustable bend housing to drill deviated holes. Because the coiled tubing is unable to rotate from surface, a so called orienter tool is used as part of the BHA to “orient” the bend of the mud motor into the desired direction. There exists a multitude of different designs for the drive systems of such tools. Some designs support continuous rotation such as electric motor and gearbox drives, while others only permit rotation by a certain limited angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those having ordinary skill in the art to which the disclosed system appertains will more readily understand how to make and use the same, reference may be had to the following drawings. 
         FIG. 1A  is a cross-sectional view of a distal portion of a bottom hole assembly with an orienter tool in accordance with the subject technology. 
         FIG. 1B  is a cross-sectional view of a proximal portion of a bottom hole assembly with the orienter tool in accordance with the subject technology. 
         FIG. 2  is a partial cross-sectional view of another embodiment of an orienter tool in accordance with the subject technology. 
         FIG. 3  is a schematic illustration of a drilling system having a bottom hole assembly utilizing an embodiment of the orienter tool. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present disclosure overcomes many of the prior art problems associated with directing or orienting a bottom hole assembly in coiled tubing applications. The advantages, and other features of the orienting tool disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention and wherein like reference numerals identify similar structural elements. 
     All relative descriptions herein such as left, right, up, and down are with reference to the Figures, and not meant in a limiting sense. Unless otherwise specified, the illustrated embodiments can be understood as providing exemplary features of varying detail of certain embodiments, and therefore, unless otherwise specified, features, components, modules, elements, and/or aspects of the illustrations can be otherwise combined, interconnected, sequenced, separated, interchanged, positioned, and/or rearranged without materially departing from the disclosed systems or methods. Additionally, the shapes and sizes of components are also exemplary and unless otherwise specified, can be altered without materially affecting or limiting the disclosed technology. 
     The subject technology is directed to a mechanical, coiled tubing orienter tool. The orienting rotation is accomplished by using a dual-spline drive, where the driving spline uses a relatively small pitch, and the driven spline uses a relatively large pitch. The difference in pitch provides a means of mechanical power transmission to convert high speed/low torque (e.g. typical for an electric motor) into a low-speed/high torque output. The orienter also can be wired, either by adding a slip-ring type electrical connector box or by stretching a wire from top to bottom inside the flow bore if the rotation is non-continuous. 
     Another embodiment of the present invention includes an orienter tool for a bottom hole assembly (BHA) having an output shaft used in selecting drilling direction. The orienter tool includes an elongated housing defining an interior. A dual-spline drive mounts within the interior. The dual-spline drive includes a first lead screw portion with first threads having a first pitch, a second lead screw portion with second threads having a second pitch, the second pitch being different from the first pitch, a lead screw drive nut held axially fixed about the first lead screw portion and rotationally free within the interior of the housing, and a driving bushing free to move axially along the second lead screw portion which is connected to the output shaft. A motor is connected to the dual-spline drive for rotation thereof. A straight spine mounts about the drive bushing and constrains rotation thereof. When the lead screw nut is rotated, the drive bushing is pushed axially proximally or distally depending upon a direction of rotation and, in turn, the drive bushing imposes a rotation upon the output shaft. 
     In this embodiment, the second pitch is relatively larger than the first pitch. The difference in rotational angle or speed between the lead screw drive nut and the output shaft is equal to a mechanical transmission ratio of the orienter tool. The orienter tool also may include a gear box connected between the motor and the lead screw drive nut, wherein the gear box is substantially not back-drivable, and/or a slip ring connector box for wiring the BHA in an annular fashion in conjunction with a through-bore defined in the interior. 
     In another embodiment, the driving bushing has a portion of free twisting length. In one embodiment, a twisting stiffness of the portion of the free twisting length of the driving bushing approximately matches a twisting stiffness of the output shaft. 
     The present technology also is directed to a method for orienting a bottom hole assembly having an output shaft and an elongated housing defining an interior. The method comprises mounting a dual-spline drive within the interior. The dual-spline drive includes a first lead screw portion with first threads of a first pitch and a second lead screw portion with second threads of a second pitch, the second pitch being different from the first pitch. The method also comprises axially fixing a lead screw drive nut held about the first lead screw for engagement with the first threads, wherein the lead screw drive nut is rotatable within the interior of the housing and driven by motor. The method may further comprise mounting a drive bushing which is free to move axially along the second lead screw for engagement with the second threads, and connecting the second lead screw to the output shaft. The method also may comprise mounting a straight spline about the drive bushing within the interior to constrain rotation thereof, and rotating the dual-spline drive such that as the lead screw drive nut is rotated, the drive bushing is pushed axially proximally/distally depending upon a direction of rotation. In turn, the drive bushing imposes a rotation upon the output shaft. 
     It should be appreciated that the present technology can be implemented and utilized in numerous ways, including without limitation as a process, an apparatus, a system, a device, a method for applications now known and later developed. These and other unique features of the system disclosed herein will become more readily apparent from the following description and the accompanying drawings. 
     In brief overview, the subject technology is directed to a mechanical coiled tubing orienter tool and methods for using the same. The orienting rotation of the BHA is accomplished by using a dual-spline drive in which a first lead screw drive nut is held axially fixed and rotationally free inside the orienter housing. The dual-spline drive is powered by an electric motor and an optional gearbox. When this lead screw drive nut is rotated, the drive bushing is pushed axially down or up, depending on lead screw direction. The drive bushing is constrained against rotation by, for example, a straight spine. When the drive bushing is pushed axially, the drive bushing imposes a rotation of the output shaft by way of a second lead screw drive with a relatively large pitch. The difference in rotational angle or speed between the lead screw drive nut and the output shaft is equal to the inherent mechanical transmission ratio of the design. 
     Referring generally to  FIGS. 1A and 1B , cross-sectional views of a distal portion  102  and a proximal portion  104 , respectively, of a bottom hole assembly (BHA)  100  are illustrated as having an orienter tool  110  in accordance with the subject technology. Matching lines  1 A and  1 B illustrate how to properly connect the distal portion  102  and the proximal portion  104  of  FIGS. 1A and 1B , respectively, to form a continuous cross-sectional view. 
     The BHA  100  comprises coiled tubing or an elongated housing  106  that forms an interior  108  containing the orienter tool  110  and other components. The BHA  100  comprises a fluid swivel device  112  through which the drilling mud and/or water passes centrally. An electric wire  114  passes to an electrical connector box  116  for passing power and for exchanging signals with the BHA  100 . 
     In the example illustrated, the orienter tool  110  comprises a dual-spline drive  118  powered by an electric motor  120  and an optional gearbox  122  mounted about a shaft/tube  124 . The positions of the electric motor  120  and shaft  124  are monitored by sensors, such as a motor encoder  126  and a shaft encoder  128 , respectively. In the embodiment illustrated, the motor  120  is connected to the gearbox  122  to operate a dual-spline  130 . A first lead screw drive portion  132  of the dual-spline  130  has first threads  134  having a first pitch. A second lead screw drive portion  136  has second threads  138  having a second pitch which is different from the first pitch. In the embodiment shown, the second threads  138  have a relatively larger pitch than the first threads  134 , e.g. 2-100 times larger, 100-1000 times larger, or more than 1000 times larger. 
     As illustrated, a lead screw drive nut  140  is mounted axially fixed about an axially movable portion  141  of the first lead screw drive portion  132  to engage the first threads  134  on movable portion  141 . The lead screw drive nut  140  is rotatable within the interior  108  of the housing  106  via motor  120  and gear box  122  to selectively move portion  141  in an axial direction. A driving bushing  142  is engaged by movable portion  141  and is free to move axially along the second lead screw drive portion  136  while engaging the second threads  138 . The driving bushing  142  connects to an output drive shaft  144  of the BHA  100  via the second lead screw drive portion  136 . A straight spline  146  mounts about the drive bushing  142  to constrain rotation thereof. The output drive shaft  144  defines a fluid bore  148  also for carrying drilling mud flow as shown by the arrows “a”. An electrical cable  150  may be positioned in the fluid bore  148  for passing signals, power and the like. 
     In the case of a slip-ring type connector box configuration, an appropriately shielded wire or electrical cable  150  may be stretched through the fluid bore  148  without the use of electrical connector box  116 . As a result, the electrical cable may cope with a smaller twisting angle of the orienter tool  110  e.g. an angle of +/−200 degrees. In some embodiments, a slip-ring type connector box  152  (shown partially in dashed lines) may be used when, for example, the orienter tool is constructed in an annular fashion so that a continuous through-bore may be provided through large portions or through the entire length of the orienter tool  110 . 
     In the embodiment illustrated, the orienting rotation of the BHA  100  is accomplished by using the dual-spline drive  118 . When the lead screw drive nut  140  is rotated via motor  120  working in cooperation with gear box  122  (in this embodiment), the drive bushing  142  is pushed axially down or up (depending on the direction of the lead screw rotation) via axial movement of movable portion  141 . The drive bushing  142  may be constrained against rotation by straight splines  146 . When the drive bushing  142  is pushed axially, the drive bushing  142  imposes a rotation of the output drive shaft  144  by way of the second lead screw portion  136 . A difference in rotational angle or speed between the lead screw drive nut  140  and the output drive shaft  144  occurs because of the difference in pitch of the threads  134 ,  138  on the lead screw drive portions  132 ,  136 , respectively. The difference in rotational angle is equal to the inherent mechanical transmission ratio of the dual-spline design. 
     For example, if the first lead screw drive portion  132  has a pitch of 0.5 mm and the second lead screw drive portion  136  has a pitch of 0.5 m, a mechanical transmission ratio of 1000:1 is accomplished. To further manipulate the mechanical transmission, the gear box  122  between the electric motor  120  and the lead screw drive nut  140  may be employed. As an additional benefit, if the gear box  122  is not back-drivable, the BHA  100  does not require a separate brake. 
     Referring generally to  FIG. 2 , a partial cross sectional view of another embodiment of a BHA  200  in accordance with the subject technology is illustrated. As will be appreciated by those of ordinary skill in the pertinent art, the BHA  200  utilizes similar principles to the BHA  100  described above. Accordingly, like reference numerals preceded by the numeral “2” instead of the numeral “1” are used to indicate like elements. The primary difference of the BHA  200  in comparison to the BHA  100  is use of elastic averaging to even out forces imposed on the BHA  200 . 
     When a large torque is exerted on a tubular structure, the result is elastic deformation in the form of twisting. Such twisting can result in uneven engagement and thus uneven contact forces in areas such as the distal region of the second lead screw drive portion  236 . Furthermore, uneven engagement forces can lead to uneven and increased wear which sometimes results in component failure. 
     To cope with uneven engagement forces, drive bushing  242  utilizes a first portion  243  of free “twisting” length where the drive bushing  242  is not engaged with the straight spline  246 . The drive bushing  242  also utilizes a second portion  245  which is engaged with the straight spline  246 . The twisting stiffness of the free twisting length  243  of the drive bushing  242  may be selected to match the twisting stiffness of the drive shaft  244 . As a result, even engagement of the lead screw drive portion  236  is accomplished by way of such elastic averaging. 
     Referring generally to  FIG. 3 , an example of a well system  250  is illustrated as deployed in a well  252  defined by at least one wellbore  254  having at least one deviated wellbore section  256  being formed. Although the orienter tool  110  of bottom hole assembly  100  may be utilized in a variety of downhole systems to provide improved control over the orienting of a variety of components, a well drilling example is illustrated in  FIG. 3 . In this example, the well system  250  includes a drilling system  258  comprising bottom hole assembly  100  delivered downhole by a suitable conveyance  260 , such as coiled tubing. 
     In the embodiment illustrated, bottom hole assembly  100  includes the orienter tool  110  containing the dual-spline system  130 . The orienter tool  110  and its dual-spline system  130  may be used to ultimately control the drilling orientation of a drill bit  262 . In some drilling operations, the drill bit  262  is powered by a motor  264 , such as a mud motor. Depending on the application, the mud motor  264  may work in cooperation with a bent housing  266  and the orienter tool  110  to control the desired direction of drilling. As known to those of ordinary skill in the art, bottom hole assembly  100  may comprise a variety of other components, including steering components, valve components, sensor components, measurement components, drill collars, crossovers, and/or other components. The actual selection of components depends on, for example, the specifics of the drilling application and/or the characteristics of the environment. 
     As would be appreciated by those of ordinary skill in the pertinent art, the subject technology is applicable to use in a variety of applications with significant advantages for bottom hole assembly applications. The functions of several elements may, in alternative embodiments, be carried out by fewer elements, or a single element. Similarly, in some embodiments, any functional element may perform fewer, or different, operations than those described with respect to the illustrated embodiment. Also, functional elements shown as distinct for purposes of illustration may be incorporated within other functional elements, separated in different hardware or distributed in various ways in a particular implementation. Further, relative size and location are merely somewhat schematic and it is understood that not only the same but many other embodiments could have varying depictions. 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.