Abstract:
A threaded sleeve stabilizer spans an upper stator connection in a mud driven drilling motor used for borehole drilling. A number of collets are loaded in compression between the stator and the housing of the motor, and are held in compression by a threaded connection.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/319,906 filed on Apr. 1, 2010 which is incorporated by reference herein for all it discloses. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to motors used in downhole drilling applications, and in particular, to downhole drilling motors that may be subjected to unusually high levels of bending stress, such as used in very deep and very extended lateral drilling operations. The downhole motor described herein has internal structures intended to improve its reliability and lengthen its intervals between servicing. 
         [0004]    2. Description of the Related Art 
         [0005]    Downhole drilling motors used in the oil and gas drilling industry typically include a drive shaft assembly connected between a power section and a bearing section. The drive shaft transfers torque from the eccentrically rotating power section to the concentrically rotating bearing assembly to rotate a drill bit as it is pushed against the earthen formation, effecting a drilling action. 
         [0006]    The motor is often configured such that the axis of the power section is angularly offset from the axis of the bearing section and drill bit. The driveshaft assembly may include universal joints, or alternately ‘flex’ joints, on either end to accommodate the mis-alignment of the axes during a drilling operation while allowing transfer of torque from the power section of the motor through the bearing assembly and out to the drill bit. 
         [0007]    During operation, drilling motors are often subjected to extreme, cyclic bending loads, and also rapidly varying compressive loads. In these applications, it may be difficult to maintain the internal components of drilling motors in their proper orientations. Shifting of these components during operation may result in sudden, premature and catastrophic failure of the motor. 
         [0008]    A stabilizer is a drill string component well known in the art that typically has a plurality of blades, or raised portions of material, that extend radially outward from a main tubular body. The blades may extend to a diameter that is slightly less than the diameter of the wellbore. This configuration may permit the stabilizer to travel through the wellbore, while ensuring that the axis of the stabilizer is kept nearly concentric to the axis of the wellbore. The deflection of the drill string at the stabilizer location may, therefore, be limited to that permitted by a gap between the stabilizer blades and the wellbore. Because the outer surfaces of the blades may continually contact the wellbore due to side loading, these surfaces may be coated with abrasion-resistant material to reduce wear. The areas between the blades may form open channels that provide pathways to allow annular flow to pass by the stabilizer. 
         [0009]    One type of stabilizer is a drill string component having top and bottom connections that connect to upper and lower components within the drill string. Another type of stabilizer is in the form of a threaded sleeve that threads to the outer diameter (OD) of one of the drill string components; for example, the lower stabilizer of a mud motor which is typically threaded to the OD a bearing assembly housing. The threaded sleeve option may allow interchangeability between stabilizers of different diameters, depending on the hole size and the amount of clearance desired. 
         [0010]    Despite the advancement in drilling technology, there remains a need for advanced techniques for reinforcing drilling equipment. The present invention is directed at providing such advanced techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic view of a very general and generic arrangement of a typical drilling rig for drilling boreholes into the earth. 
           [0012]      FIG. 2  is a partial cross-section view of a threaded connection portion of a downhole motor of the present invention, illustrating the general arrangements of the individual components making up the connection. 
           [0013]      FIG. 3  is magnified partial section view showing in greater detail the arrangement of selected components of the threaded connection portion of a downhole motor of the present invention as shown in  FIG. 2 , and in particular one arrangement of locking collet members of the present invention. 
           [0014]      FIGS. 4 and 5  are views of the arrangement of the locking collets members used to both preload and stiffen the threaded connection portion of a downhole motor of the present invention as shown in  FIGS. 2 and 3 . 
       
    
    
     BRIEF SUMMARY OF THE INVENTION 
       [0015]    In a typical bottom hole assembly (also known as a BHA) comprising a mud motor, the upper end of the power section stator is connected to a top sub (sometimes referred to as ‘housing’ or ‘motor housing’) which connects to the drill string components above. The connection between the top sub and stator may be susceptible to fatigue damage due to bending loads experienced during drilling operations. This connection can be exposed to excessive cyclic bending loads due to its location and the dynamics of the drill string during operation; however, the connection strength may be limited due to manufacturing and design limitations on the size and thickness of the stator tube. Disclosed herein is a new drilling motor that addresses this issue by providing an external means to strengthen and support the connection during drilling operations. 
         [0016]    Further disclosed is an apparatus that may improve the bending strength of a threaded connection, and in particular the top connection of the stator in a mud powered borehole drilling motor assembly, which may be susceptible to fatigue damage due to bending loads experienced during the drilling operations. 
         [0017]    The invention further encompasses a threaded sleeve stabilizer having a threaded sleeve that connects to the outside diameter (OD) of a “top sub” used with the above described motor. The stabilizer&#39;s threaded sleeve may be located axially over the threaded connection between the top sub and stator. The lower end of the stabilizer&#39;s threaded sleeve may have an internal bore that is located along the stator, outside of the stator tube below the stator box. An annulus may be created between the internal bore of the stabilizer&#39;s threaded sleeve and the OD of the stator which provides a chamber to receive a plurality of wedge like devices, hereinafter called ‘collets’. Either the outer surface of the collets, or an inner surface within the stabilizer bore of the threaded sleeve, or both, may be tapered such that axial force on the bottom of the collets will cause the collets to be wedged between the outside of the stator of the motor and the inside of the stabilizer&#39;s threaded sleeve. 
         [0018]    The collets described herein may have an internal wedge configuration to secure the internal components. The wedge collets may be made of a material having a lower modulus of elasticity than the motor housing. Alternately, the collets may have the same modulus of elasticity, but have a significantly lower hardness than the motor housing. Alternately, the collets may be sized and shaped such that they will operate effectively regardless of their composition or material properties. The wedge shape may be used to help assure that the internal components remain in proper position during operation, and thus help to maintain their relative position within the motor during operation. 
         [0019]    The lower end of the stabilizer&#39;s threaded sleeve may have a threaded box located below the collets into which is threaded a locking sleeve which, when makeup torque has been applied, contacts the collets and provides axial force to wedge them upward between the threaded sleeve and the stator. The wedged collets firmly secure the lower end of the threaded sleeve of the stabilizer to the stator while the upper end of the threaded sleeve of the stabilizer is secured to the top sub through the threaded connection therebetween. This arrangement effectively adds stiffness to the threaded connection between the top sub and stator. In addition, the OD of the threaded sleeve of the stabilizer may be closely sized to the borehole diameter, limiting deflection of the BHA at that location and providing further stability to the stator and top sub connection during drilling operations. 
         [0020]    In one aspect, therefore, a wedge arrangement formed from a plurality of collets may be disposed intermediate the stator and the motor housing. In this configuration the wedge arrangement may include one or more collets. Each collet may be distinct from each other so as to be individually fitted into the motor so as to be independent of each other. They may have generally the same width, or alternately, the collets may be of varying widths to accommodate assembly. 
         [0021]    Further disclosed is a downhole motor adapted for drilling boreholes into the earth having a compression loaded retention device. A number of separate collets may be loaded in compression between the stator and the housing of the motor, and are held in compression by a threaded connection. The collets may be used for the maintaining the compressive loading of the components at a thrust bearing end of a driveshaft assembly for a downhole motor. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  shows a very schematic representation of a drill string  2  suspended by a derrick  4  for drilling a borehole  6  into the earth for minerals exploration and recovery, and in particular petroleum. A bottom-hole assembly (BHA)  8  is located at the bottom of the borehole  6 . Oftentimes, the BHA  8  may have a downhole drilling motor  9  to rotate a drill bit  1 . 
         [0023]    As the drill bit  1  is rotated by the downhole motor  9 , it drills into the earth allowing the drill string  2  to advance, forming the borehole  6 . For the purpose of understanding how these systems may be operated for the type of drilling system as illustrated in  FIG. 1 , the drill bit  1  may be any one of numerous types well known to those skilled in the oil and gas exploration business. This is just one of many types and configurations of bottom hole assemblies  8 , however, and is shown only for illustration. There are numerous arrangements and equipment configurations possible for use for drilling boreholes into the earth, and the present disclosure is not limited to the particular configurations as described herein. 
         [0024]    As shown in  FIG. 2 , the invention disclosed herein may employ a locking (or threaded) sleeve stabilizer  37  that spans an upper stator connection  39  and is secured to a top sub  14  and a stator  10 , for providing additional stiffness to the connection while limiting drill string deflection at this location. 
         [0025]    The downhole drilling motor  9  of  FIG. 1  may comprise the stator  10 , as shown in  FIGS. 2 and 3 . Typically, there is a long tubular body component of the mud motor  9  power section  12 , as shown in  FIG. 2 . During drilling operations, certain conditions can lead to excessive cyclic bending loads at the upper and lower threaded connections, which can ultimately lead to fatigue failure. 
         [0026]    The component of the motor  9  that the top or bottom of the stator  10  is connected to is known as the motor housing  20  (e.g., top sub  14 , lock housing). 
         [0027]    The motor housing  20  is fitted with external threads  22  and an upset  24  for a stabilizer sleeve  30  of the locking sleeve stabilizer  37  to thread onto and shoulder against. 
         [0028]    An additional component of the drilling motor  9  of the present invention is the stabilizer sleeve  30 . The stabilizer sleeve  30  is a threaded sleeve with a plurality of blades  35  that protrude radially outward. Like any drill string stabilizer, as is well known in the art, the blades  35  extend to a diameter that is slightly less than the diameter of the wellbore, which permits the threaded sleeve stabilizer  37  to travel through the wellbore  6  while ensuring that the axis of the threaded sleeve stabilizer  37  is kept nearly concentric to the axis of the wellbore  6 . The blades  35  may be aligned axially with the end connection of the stator  10 , limiting the deflection of the end of the stator  10  to that permitted by a gap between the stabilizer blades  35  and the wellbore  6 . Because the outer surfaces of the blades  35  may continually contact the wellbore  6  due to side loading, these surfaces may be coated with abrasion-resistant material to reduce wear. The areas (not shown) between the blades  35  form open channels that provide pathways for annular flow to pass by the threaded sleeve stabilizer  37 . 
         [0029]    The stabilizer sleeve  30  is threaded at both ends. The first end is rigidly secured to the external threads  22  along the body of the motor housing  20 . The second end is located along the OD of the stator  10 . The internal bore of the stabilizer sleeve  30  provides an annular region along the outside of the stator  10 , into which is inserted a plurality of collets  50 , as shown in more detail in 
         [0030]      FIGS. 4 and 5 . A locking sleeve  40  wedges the collets  50  between the stabilizer sleeve  30  and the stator  10 . In these Figures, the collets  50  are illustrated as fitting together as a smooth cylinder that forms a generally cylindrical ring. However, it is contemplated that these collets  50  may have any one of a variety of shapes, and do not necessary present a smooth outside or inside wall to their mating surfaces. Furthermore, the individual collets do not generally need to have smooth outside surfaces, and may be grooved or roughened on the inside or outside to facilitate fitting. Finally, although the collets  50  as illustrated all have approximately the same width, they may be formed so as also being varied in width. 
         [0031]    Also, it is also possible that one or some of the collets  50  may be formed from a material different from the other collets  50 , and that material may have a hardness or modulus of elasticity differing from the other collets  50 , or from the material of the stator  10  or locking sleeve  40 . 
         [0032]    Preferably, however, the collets  50  as illustrated are made of steel and machined to shape. Alternately, it may be desirable to form the collets  50  in a casting, forging or one of many other well known forming processes. 
         [0033]    Referring to  FIGS. 2 and 3 , the ends of the stabilizer sleeve  30  may be firmly secured along either side of the stator  10  end connection by the collets  50 . The stiffness of the stabilizer sleeve  30  thus may be used to add rigidity to the end connection of the stator  10 , for lowering the cyclic bending stresses induced at this location during drilling operations and providing protection against fatigue failure. 
         [0034]    This new motor design, which incorporates the threaded sleeve stabilizer  37 , may be used to improve the bending strength of the threaded connection. For example, the threaded sleeve stabilizer  37  may be used in the top connection of the stator  10  in the mud motor assembly  9 , which may be susceptible to fatigue damage due to bending loads experienced during drilling operations. 
         [0035]    Furthermore, the threaded sleeve stabilizer  37 , as disclosed herein, may connect to the outside diameter of the top sub  14  in the bottom hole assembly  8 . The threaded sleeve stabilizer  30  may be located axially over the threaded connection between the top sub  14  and stator  10 . The lower end of the stabilizer  30  may have an internal bore that is located along the outside of the stator  10  tube below the stator  10  box as shown in  FIG. 2 . 
         [0036]    An annulus may be created between the internal bore of the stabilizer  30  and the OD of the stator  10  which provides a chamber to receive the plurality of collets  50 . 
         [0037]    As shown in  FIG. 3 , either the outer surface of the collets  50 , or an inner surface within the stabilizer  30  bore, or both, may be tapered such that axial force on the bottom of the collets  50  will cause the collets  50  to be wedged between the outside of the stator  10  and the inside of the stabilizer  30 . The lower end of the stabilizer  30  has a threaded box located below the collets  50  into which is threaded the locking sleeve  40  which, when makeup torque has been applied, contacts the collets  50  and provides axial force to wedge them upward between the stabilizer  30  and the stator  10 . The wedged collets  50  firmly secure the lower end of the stabilizer  30  to the stator  10  while the upper end of the stabilizer  30  is firmly secured to the top sub  14  through the threaded connection therebetween, which effectively adds stiffness to the threaded connection between the top sub  14  (as shown in  FIG. 2 ) and stator  10 . In addition, the OD of the stabilizer  30  is closely sized to the hole diameter of the wellbore, limiting deflection of the BHA at that location and providing further stability to the stator  10  and top sub  14  connection during drilling operations. 
         [0038]    Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention. While the present disclosure describes specific aspects of the invention, numerous modifications and variations will become apparent to those skilled in the art after studying the disclosure, including use of equivalent functional and/or structural substitutes for elements described herein. For example, while certain embodiments have been described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. For example, the collets may be of various shapes and materials to provide the desired results. 
         [0039]    Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. 
         [0040]    Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.