Patent Publication Number: US-10774831-B2

Title: Method for impregnating the stator of a progressive cavity assembly with nanoparticles

Description:
SUMMARY 
     The present invention is directed to a method comprising the steps of providing a stator comprising an inner surface and an inner core formed on the inner surface and defining a groove, and distributing a plurality of nanoparticles within the groove. 
     The present invention is also directed to a method of treating a tubular stator having an internal elastomeric substrate within which at least one helical groove is formed. The method comprises the steps of distributing nanoparticles within the at least one groove, and coating the at least one groove by pressing the distributed nanoparticles into the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a progressive cavity assembly known in the art. A portion of the stator of the assembly has been cut away to better show the rotor. 
         FIG. 2  is a cross-sectional view of the assembly shown in  FIG. 1  taken along line A-A. 
         FIG. 3  is a perspective view of the stator shown in  FIG. 1 . The rotor shown in  FIG. 1  has been removed and replaced with a work rotor. A portion of the stator has been cut away to better show the work rotor. 
         FIG. 4  is a perspective view of the work rotor shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the assembly shown in  FIG. 3  taken along line B-B. A plurality of nanoparticles are shown distributed throughout a groove formed in the inner surface of the stator. 
         FIG. 6  is the same view shown in  FIG. 5 . The plurality of nanoparticles are shown impregnated within the inner core of the stator. 
         FIG. 7  is the same view as  FIG. 2 . The plurality of nanoparticles are shown impregnated within the inner core of the stator. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a progressive cavity assembly  10  or mud motor known in the art is shown. The assembly  10  may be used downhole in underground drilling operations, particularly in oil and gas drilling operations. The assembly  10  is typically used to provide power to a drill bit connected to the assembly (not shown) while drilling. The assembly  10  comprises an elongate outer stator  12  and an elongate inner rotor  14 . A seal or inner core  16  is formed on the inner surface of the stator  12 . The inner core  16  defines a groove  18  within the stator  12 . The rotor  14  is positioned within the groove  18 . 
     With reference to  FIGS. 1-2 , the groove  18  formed by the inner core  16  may be characterized by a plurality of helical lobes  20 . A plurality of helical lobes  22  are also formed on an outer surface of the rotor  14 . As shown in  FIGS. 1-2 , the inner core  16  has five lobes  20 , and the rotor  14  has four lobes  22 . Because the stator  12  has more lobes than the rotor  14 , the rotor will rotate eccentrically within the stator. The eccentric motion of the rotor  14  is transferred as concentric power to the drill bit. 
     The inner core  16  of the stator  12  may have fewer than five lobes or greater than five lobes, if desired. Likewise, the rotor  14  may have fewer than four lobes or greater than four lobes, if desired. The rotor  14  typically has one less lobe than the inner core  16  of the stator  12 . Increasing the number of lobes  20 ,  22  on both the inner core  16  and the rotor  14  typically increases the horsepower created by the assembly  10 . 
     During operation, drilling fluid is used to rotate the rotor  14  within the stator  12 . The inner core  16  may be made of rubber or a polymer material to help maintain drilling fluid within the assembly  10  during operation. The stator  12  and rotor  14  are typically made of metal or steel. The rotor  14  engages with the inner core  16  as it rotates, causing friction during operation. The friction may decrease the power and efficiency of the assembly  10  and cause the assembly  10  overheat. 
     The present invention is directed to a method for reducing friction within the assembly  10 . Friction may be reduced within the assembly  10  by impregnating a plurality of nanoparticles  24 , shown in  FIGS. 5-7 , into a surface layer of the inner core  16  of the stator  12 . The nanoparticles  24  exfoliate the outer surface of the rotor  14  as it rotates. The exfoliation of the rotor  14  reduces friction within the assembly  10  during operation. The exfoliation is done at a microscopic level so as to not affect the integrity of the rotor  14 . 
     The nanoparticles  24  may be formed from different substances capable of reducing friction within the assembly  10 . Preferably, the nanoparticles  24  are made from tungsten disulfide (WS 2 ). The nanoparticles  24  may be of any size or shape desired. Preferably, the nanoparticles  24  are asymmetrical in shape and have a maximum dimension of less than 0.06 nm. 
     With reference to  FIGS. 3-7 , a process for impregnating or coating the inner core  16  of the stator  12  with nanoparticles  24  is described. To start, the original or primary rotor  14  is first removed from the stator  12 . The stator  12  may be heated to a temperature between 120° F. to 150° F. Heating the stator  12  softens the inner core  16  making it more pliable. The plurality of nanoparticles  24  are then distributed uniformly throughout the groove  18  formed by the inner core  16 , as shown in  FIG. 5 . An elongate secondary or work rotor  26  is then installed into the stator  12 , as shown in  FIGS. 3 and 5 . 
     After the work rotor  26  is installed in the stator  12 , it is rotated at a high rate of speed within the stator  12  using a rotatory impact device, such as a power drill. The work rotor  26  operates to press the nanoparticles  24  into a surface layer of the inner core  16  as it rotates, as shown in  FIG. 6 . The rate of rotation of the work rotor  26  may vary as needed throughout the process in order to effectively press the nanoparticles  24  into the inner core  16 . For example, the rate or rotation may vary from 200 rpm to 2000 rpm. It may take several minutes or several hours, depending on the size and shape of the stator  12 , to effectively press all or almost all of the nanoparticles into the surface layer of the inner core  16 . 
     The work rotor  26  is preferably made of metal or steel and has a square cross-sectional shape, as shown in  FIGS. 3 and 5 . The work rotor  26  preferably has radius or rounded corners  28 . Preferably, the corners have a ¼ inch radius. Alternatively, the work rotor  26  may be configured to different shapes and sizes, as desired, such a diamond or star cross-sectional shape. 
     Regardless of how the work rotor  26  is shaped, it preferably has a smaller width than the primary rotor  14 . The work rotor  26  needs to be small enough that it can effectively fit between each lobe  20  of the stator. The work rotor  26  may also be bent along its length, as shown in  FIG. 4 . The bend provides the work rotor  26  with more torque as it rotates within the stator  12 .  FIG. 4  shows a centerline  30  of the work rotor  26  as compared a straight reference line  32 , in order to display the bend. The bend is small enough so that the work rotor  26  still fits within the groove  18  of the stator  12 . For example, the bend may offset the centerline  30  by about 3 degrees. 
     After the inner core  16  is coated with nanoparticles  24 , the work rotor  26  is removed from the stator  12 . The original or primary rotor  14  may then be re-installed into the stator  12 , as shown in  FIG. 7 . The inner core  16  holds the nanoparticles  24  in place so that they are not transferred to or embedded in the primary rotor  14  during operation. 
     Although the preferred embodiment has been described, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention.