Abstract:
A turbine for use in a downhole drill string including an elongated casing defining an interior and a plurality of motor units in the interior. Each motor unit has a rotor and a stator. A torque transmission couplings connects each of the plurality of motor units to the drill string. The torque transmission couplings having flexible linkages. As a result, the power section has tight tolerances for the clearance at the tips of the rotors because the motor units are relatively stiff. The flexing normally obtained by bending the rotor shaft is accomplished and absorbed in the flexible linkages.

Description:
BACKGROUND OF THE DISCLOSURE 
       [0001]    1. Field of the Disclosure 
         [0002]    The subject disclosure relates to drilling turbines, and more particularly to an improved steerable drilling turbine having modular components. 
         [0003]    2. Background of the Related Art 
         [0004]    In oil exploration, drilling is an established method of creating a bore-hole through the earth. Many drilling machines are turbines powered by a turbine blade system. Impulse type drilling turbines are driven by a fluid at atmospheric pressure, while reaction type drilling turbines are driven by fluid pressurised to above atmospheric pressure, possessing energy which is partly kinetic and partly pressure. Drilling turbines are often preferred because of the ability to be successfully deployed in steerable drilling applications. 
         [0005]    In drilling turbine applications, the drilling turbine is used to transfer the hydraulic power of a drilling fluid being pumped through the drilling turbine into rotational power of a rotor element, which is rigidly attached to a drive shaft system. Ultimately, the drive shaft system is connected to a drilling bit for the explicit purpose of boring through the earth&#39;s structure such as rock. The hydraulic fluid is often referred to a drilling mud. The typical drilling turbine is configured as a 20-30 foot long pair of matching helixes with one helix being the stator and one helix being the rotor. 
         [0006]    Despite many advances, there are problems associated with turbine drilling. For example, turbine life can be undesirably short due to the abrasive drilling mud and damage from larger particles in the mud flow. Traditionally, once a portion of the turbine is worn out, the entire turbine assembly is replaced. Such a replacement is a costly approach. 
         [0007]    The conventional drilling turbine also has low efficiency, e.g., 40%, because of the large tip clearances that are required. The tip clearance is needed to allow for shocks and bending of the rotor/stator assembly that are normal during operation. Further, as the drilling turbines are run at high speed, sealed oil bearings are used. Despite being sealed, it is difficult to prevent ingress of mud and other contaminants that reduce bearing speed, effectiveness and life. 
         [0008]    Traditional drilling turbines also use a reduction gearbox that is oil lubricated. The reduction gearbox brings the relatively high working speed of the turbine down to a suitable speed for the cutting tools. This reduction gearbox suffers from similar sealing issues with respect to mud and contaminants as the sealed bearings. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above, there is a need for an improved modular drilling turbine which reduces abrasive wear to increase life, allows for minimal part replacement to conserve cost, establishes tight tolerances to increase efficiency, and/or alleviates strain on seals. 
         [0010]    The subject technology is directed to a turbine for use in a downhole drill string including an elongated casing defining an interior and a plurality of motor units in the interior. Each motor unit has a rotor and a stator. Torque transmission couplings connect each of the plurality of motor units to the drive shaft. The torque transmission couplings having flexible linkages. As a result, the power sections have tight tolerances for the clearance at the tips of the rotors because the motor units are relatively stiff. The flexing normally obtained by bending the rotor shaft is accomplished and absorbed in the flexible linkages. 
         [0011]    Preferably, the casing is generally tubular and defines an axial fixing groove, and the motor units are keyed to the axial fixing groove for limiting rotational movement of the motor units. Each motor unit is self-contained and has a sealed bearing for supporting movement of the rotor. The bearings are sealed by chambers having magneto-rheological fluid. Each motor unit includes a reservoir of pressurized oil for lubricating the bearing. A membrane surrounds the oil reservoir to facilitate pressurizing the oil by using the pressure of the drilling mud acting on the membrane. 
         [0012]    Still another embodiment of the subject technology includes a turbine for use in a downhole drill string including an elongated tubular casing defining an interior and an axial fixing groove. There are at least two motor units in the interior with a rotor and a stator, wherein the motor units are keyed to the axial fixing groove. A bearing in each motor unit supports movement of the rotor. A membrane creates a pressurized oil reservoir around each bearing for lubrication. A torque transmission coupling having flexible linkages extends between the motor units. Preferably, the turbine further includes a shroud formed about the top of the rotor of each motor unit. Each shroud may include a sealing assembly. 
         [0013]    The subject technology is also directed to a method for downhole drilling including the steps of providing two turbine motor units for use in a downhole drill string, each motor unit having a rotor and a stator, surrounding the two turbine motor units with an elongated tubular casing, supporting movement of each rotor with a bearing, surrounding each bearing with a membrane, the membrane having pressurized magneto-rheological fluid therein, and coupling the two motor units together with flexible linkages. 
         [0014]    The method may further include the step of attaching the motor units to the casing by using a method selected from the group consisting of: forming an axial groove in the casing and a mating protrusion on the motor units; engaging an interference fit between the motor units and casing; applying an adhesive between the motor units and casing; passing a setscrew through the casing to engage a motor unit; and combinations thereof. The method may also include the steps of forming a shroud about each motor unit and/or applying a coating on at least one of the rotor and stator. In one embodiment, the method also includes the step of transmitting a rotational energy output of the two turbine motor units to a device for harnessing the output, the harnessing device being selected from the group consisting of a drilling tool, an alternator, a generator, and combinations thereof. 
         [0015]    Still another embodiment of the subject technology is directed to a turbine for use in a downhole drill string including an elongated casing defining an interior, a plurality of motor units in the interior, each motor unit being attached to the elongated casing, and a torque transmission coupling between each of the plurality of motor units. The motor units may be attached to the casing by a coupling selected from the group consisting of an axial groove with mating protrusion, an interference fit, adhesive, a setscrew and combinations thereof. 
         [0016]    It should be appreciated that the present invention can be implemented and utilized in numerous ways, including without limitation as a process, an apparatus, a system, a device, and a method for applications now known and later developed. These and other unique features of the systems and methods disclosed herein will become more readily apparent from the following description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    So that those having ordinary skill in the art to which the disclosed systems and methods appertain will more readily understand how to make and use the same, reference may be had to the drawings wherein: 
           [0018]      FIG. 1  is schematic representation of a turbine module in accordance with the subject technology; and 
           [0019]      FIG. 2  is schematic representation of another turbine module with a shroud in accordance with the subject technology. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    The present disclosure overcomes many of the prior art problems associated with downhole drill strings. The advantages, and other features of the systems and methods 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. 
         [0021]    All relative descriptions herein such as trailing, leading, front, rear, 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. 
         [0022]    Referring now to  FIG. 1 , a schematic representation of a portion of a turbine module  100  in accordance with the subject technology is shown. The turbine module  100  is for use in a downhole drill string  102 . Power is generated by the turbine module  100  by a plurality of motor units  104 . Although a single motor unit  104  is shown in  FIG. 1  for simplicity, a plurality of motor units  104  are used in the drill string  102 . 
         [0023]    Power is transmitted from motor unit  104  to motor unit  104  through the drive shaft  106 . The motor units  104  couple to the drive shaft  106  by a flexible torque transmission joint  108 . Thus, the overall power section is relatively flexible to accomplish the bending that would normally occur in the rotor shaft. By having flexing occur in the torque transmission joints  108  intermediate the motor units  104 , each motor unit  104  may be relatively stiff. This stiffness also allows tight tolerances for the rotor tip clearances which remain relatively unchanged. Thus, the power section has greater efficiency and, in turn, improved power density. 
         [0024]    The plurality of motor units  104  are housed within a respective elongated casing  110 . Each motor unit  104  includes at least one row of stator blades  112  and rotor blades  114 . The stator blades  112  are connected to the casing  110  and turn the fluid flow, denoted by arrow “A”. In contrast, the rotor blades  114  remove the swirl induced by the stator blades  112 . As the rotor blades  114  are connected to the drive shaft  106 , the result is that the rotor blades  114  impart a rotational energy to the drive shaft  106 , which rotates about a central axis identified by dashed line “B”. 
         [0025]    A strut  116  behind the rotor blades  114  supports a rear bearing  118  of the motor unit  104 . Preferably, the strut  116  is a simple aerodynamic fairing that does not turn the fluid flow with the strut  116  arranged so that the associated wake passes into a mid-passage region of the stator blade of the downstream motor unit. At the opposing end of the motor unit  104 , the stator blade  112  supports the front bearing  120  of the motor unit  104 . Each motor unit  104  is separated sufficiently to reduce or minimize any effects of rotor wake and stator blade interaction. 
         [0026]    The stator and rotor blades  112 ,  114  may be fabricated from an elastomer, a composite, an alloy, powdered metal and combinations thereof. The stator and rotor blades  112 ,  114  may also have a coating applied thereto. The material selection and coatings may be designed to improve the efficiency, durability and performance of the motor units  104 . In one embodiment, the coating is an elastomer on alloy blades. The coating can help to provide abrasion resistance and improve the sealing properties. Of course, the rotor blades  114  and stator blades  112  may not be coated at all and a metal on metal seal may perform adequately in terms of erosion and sealing. 
         [0027]    The modular motor units  104  are fixed rotationally within their casing  110  as well. For example, the casing  110  may be generally tubular and define an axial fixing groove (not shown). The motor units  104  are keyed to the axial fixing groove such as by an axial protrusion or the like. The motor units  104  may also be limited rotationally by forming an interference fit between portions of the motor units  104  and casing  110 , applying an adhesive between the motor unit components and casing  110 , passing a setscrew through the casing  110  to engage motor unit components, and like combinations. 
         [0028]    By separating the motor units  104 , each motor unit  104  is self-contained or modular so that if one motor unit wears out or otherwise needs to be replaced, only the defective motor unit  104  needs to be replaced. As a result, when each motor unit  104  has a single row of stator and rotor blades  112 ,  114 , only the worn out row can be replaced rather than the entire power section. Additionally, by having modular motor units  104  that can be added or subtracted, the power section may be increased or decreased in the field to match conditions. Similarly, the drill string may be up-rated as better transmission and motor units become available as replacement parts. Further, by standardizing the motor units of the drill string, many more components may be standaradized such as downhole electricity generators, which may also be reused to lessen inventory requirements. 
         [0029]    The modular motor units  104  include bearings  118 ,  120  for supporting movement of the rotor blades  114 . The bearings  118 ,  120  are sealed to prevent mud ingress. In one embodiment, the bearings  118 ,  120  are sealed by magneto-rheological fluid held in leading and trailing chambers  122   a ,  122   b  that surround the bearings  118 ,  120 . It may be necessary to place baffles (not shown) in front of the magneto-rheological fluid chambers  122   a ,  122   b  to prevent excessive turbulence in the drilling mud from removing the magneto-rheological fluid. By improving the performance of the bearings  118 ,  120  with sealing, the usable speeds and durability of the motor units  104  are enhanced. 
         [0030]    Each motor unit  104  also includes a sealed reservoir of oil for lubricating the bearings  118 ,  120 . Membranes  124  also cover the sealed reservoir of oil, which is pressurized by the drilling fluid acting on the membranes  124 . The membranes  124  may be fabricated from a material selected from the group consisting of an elastomeric material, a machined metal material, and combinations thereof. In operation, as the local fluid pressure increases, the membranes  124  deflect and transmit pressure to the oil to insure a substantially neutral pressure differential across the magnetic fluid chambers  122   a ,  122   b . Although  FIG. 1  shows the membranes  124  schematically, it is envisioned that the membranes  124  are placed so that pressure in the oil transmitted by the membranes  124  is close to the pressure acting on the magneto-rheological fluid chambers  122   a ,  122   b . As shown, the fluid chambers  122   a ,  122   b  are recessed so that the pressure acting on the fluid chambers  122   a ,  122   b  will be close to the static pressure at the respective axial location. 
         [0031]    If there is different static pressure at the leading seal chamber  122   a  compared to the trailing seal chamber  122   b , the turbine module  100  may use two pressure membranes, appropriately located, to match conditions at the faces of the leading and trailing chambers  122   a ,  122   b . As a result, the magneto-rheological fluid will only be exposed to small pressure differentials, such as below 0.5 bar. It is noted that the pressure differential at the rear bearing  118  may be negligible so that compensation may be less important. Preferably, the chambers  122   a ,  122   b  and membranes  124  may be maintained and replaced before and after the turbine module  100  is assembled and will remain sealed until the respective motor unit  104  is replaced. 
         [0032]    The sealing chambers  122   a ,  122   b  and pressurized oil reservoir for the bearings  118 ,  120  may be equally successfully applied to other applications. For example without limitation, typical drill strings have a reduction gearbox to bring down the relatively high working speed of the turbine module, to a speed suitable for cutting tools. Such reduction gearbox can be accomodated with similar or the same sealing chambers and pressurized oil reservoir for the bearings. 
         [0033]    Referring now to  FIG. 2 , a schematic representation of another portion of a turbine module  200  in accordance with the subject technology is shown. As will be appreciated by those of ordinary skill in the pertinent art, the turbine module  200  utilizes similar principles to the turbine module  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 turbine module  200  in comparison to the turbine module  100  is the formation of a shroud  226  on the rotor blades  214  of each motor unit  204 . 
         [0034]    By incorporating a shroud  226 , the turbine module  200  provides an area for tight tip tolerances, performs better under higher pressure differentials, and is more tolerant of debris in the drilling mud. The casing  210  forms an annular recess  228  sized and configured for receiving the shroud  226 . Preventing debris from jamming the turbine module  200  is a particularly desirable feature in many circumstances. The casing  210  and the shroud  226  may overlap to further limit passage of debris such as large particles in the drilling mud. In other words, the shroud  226  may extend into the casing  210  as shown in  FIG. 2 . 
         [0035]    Each shroud  226  also includes a sealing assembly  230  for engaging the casing  210 . Preferably, the sealing assembly  230  is employed on top of the shroud  226 . Conventional seals, such as a labyrinth, brush seal type or other variant, may be used as the sealing assembly  230 , which may be contacting or non-contacting. 
         [0036]    Although the discussion herein has been with respect to using a turbine module to drive a drilling component, it is also envisioned that such turbine modules may be used to provide rotational energy to a variety of components. Examples of components that harness rotational/torque energy, without limitation, include alternators and/or generators that create electrical power. Further, the turbine modules may include means, such as cabling, for transmitting electrical signals, be it power or data signals, across the drill string. The electrical conducting means may couple across each motor unit and pick up additional information from each motor unit for use in a remote location. 
         [0037]    While the invention has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the invention without departing from the spirit or scope of the invention as defined by the appended claims. For example, each claim may depend from any or all claims in a multiple dependent manner even though such has not been originally claimed.