Patent Publication Number: US-2012024632-A1

Title: Downhole seal and method of lubricating a downhole tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional application of U.S. Provisional Patent Application No. 61/367,976 filed Jul. 27, 2010 and U.S. Provisional Patent Application 61/371,281 filed Aug. 6, 2010, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Elastomeric parts such as downhole seals, for example, that are used to dynamically seal to other components located within a borehole of an earth formation often have durability issues. These durability issues are often due to wear resulting from frictional engagement between parts. Those who practice in downhole industries would welcome devices and methods to increase the useful life of downhole seals. 
     BRIEF DESCRIPTION 
     Disclosed herein is a downhole seal. The seal includes a body configured to dynamically seal to a portion of a downhole tool and a lubricant microencapsulated in a plurality of shells to form a plurality of micro particles dispersed within the body. 
     Further disclosed herein is a method of lubricating a downhole tool. The method includes, microencapsulating lubricant within a plurality of shells, distributing the plurality of shells micro encapsulating lubricant within at least one of a first component and a second component that dynamically seal to one another, rupturing at least some of the plurality of shells microencapsulating lubricant, and releasing the lubricant 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  depicts a sectioned view of a portion of a downhole mud motor with a downhole seal disclosed herein employed in the mud motor as a stator having two parts; 
         FIG. 2  depicts a sectioned view of a portion of the downhole mud motor of  FIG. 1  showing the downhole seal disclosed herein in relation to a rotor; 
         FIG. 3  depicts a sectioned view of a mud motor having an alternate downhole seal disclosed herein having a single body; and 
         FIG. 4  depicts a sectioned view of an alternate embodiment of a seal disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring to  FIG. 1 , an embodiment of a downhole seal disclosed herein is illustrated generally at  10  as a stator of a motor, such as a mud motor. Alternately, the stator could also be employed in a pump while still remaining within the scope disclosed herein. The stator  10 , in this embodiment includes, a plurality of parts with a first part  14 A being illustrated as a first layer  14 A and a second part  14 B being illustrated as a second layer, although alternate embodiments may have more layers or as few as one layer. The stator  10  is fixedly attached to a housing  16  and allows a rotor  18  engaged therewith to rotate relative thereto in response to fluid flowing between the stator  10  and the rotor  18 . Since a number of lobes  22  (5 in the Figure) of the stator  10  is different than a number of lobes  26  (4 in the Figure) of the rotor  18 , rotation of the rotor  18  results in one of the lobes  22  moving sequentially relative to one of the lobes  26  then to another and to another, and so on. This movement defines relative motion between the stator  10  and the rotor  18 . 
     This relative motion causes some points along the first layer  14 A of the stator  10  to repeatedly make and break contact with the rotor  18  while at other points the first layer  14 A slides tangentially relative to the rotor  18 . Dynamic sealing between the first layer  14 A and the rotor  18  at points of contact and sliding is desirable for improved operation of the motor. The repeated contacting and sliding, however, causes wear of the components. The first layer  14 A, as disclosed herein, is made primarily of an elastomer while the rotor  18  is made of metal. The difference in hardnesses of these materials typically causes the first layer  14 A to wear more quickly than the rotor  18 . Lubrication between a surface  28  of the first layer  14 A and a surface  29  of the rotor  18  can increase the useful life of the first layer  14 A, however, fluid flowing between the first layer  14 A and the rotor  18  tends to purge lubrication from the surfaces  28 , and  29 . 
     Referring to  FIG. 2 , a majority of the first layer  14 A is made of an elastomer  30 . In one embodiment, embedded in the elastomer  30  is at least one lubricant  34 ; small quantities of which are microencapsulated within shells  38 . A multitude of microcapsules  42 , filled with the lubricant  34 , are dispersed throughout a volume of the first layer  14 A. In this embodiment, the dispersion is accomplished by mixing the microcapsules  42  in with the elastomeric compound prior to molding the first layer  14 A. In alternate embodiments the lubricant  34  can be introduced as coated micro or nano particles of carbonaceous nanoparticles, for example, with the coating defining the shell  38 . In such an embodiment the nanoparticles can include, carbon nanotubes (CNT), single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and non-nanotube configurations such as graphenes, fullerenes and diamonds, for example. The lubricant could also be molybdenum disulfide, hexagonal boron nitride, polytetrafluoroethylene (PTFE), or graphite. Regardless of whether the lubricant  34  is solid or fluid, such as a liquid lubricant like oil, the shell  38  is constructed to sufficiently isolate the lubricant  34  from the elastomer  30  during manufacture to minimize degrading the material properties, such as, strength and thermal conductivity, for example, of the first layer  14 A. Yet the shell  38  is fractured when exposed to loads generated as the surfaces  28 ,  29  contact and/or slide relative to one another. Upon fracturing of the shell  38  the lubricant  34  is released from the microcapsules  42  and is able to form a lubricating film  46  on one or both of the surfaces  28  and  29 . As the lubricating film  46  is washed away, the surface  28  wears, and new microcapsules  42  are exposed to loads that fracture the shells  38  thereby releasing additional quantities of the lubricant  34  thereby slowing the wear rate of the first layer  14 A. 
     Referring to  FIG. 3 , an alternate embodiment of a downhole seal disclosed herein is illustrated at  60 . The downhole seal  60  differs from the downhole seal  10  primarily in that the seal  60  is a single body  64 , whereas the seal  10  is made of the first layer  14 A and the second layer  14 B. As such, the seal  60  has the microcapsules  42  of the lubricant  34  dispersed throughout the elastomer  30  of the entire seal  60 . Each of these two embodiments may have advantages over the other. For example, the seal  60  may be less expensive to fabricate since it doesn&#39;t require assembly of two different portions. Alternatively, the seal  10  may have advantages in durability since the second layer  14 B can be made of a material having more robust mechanical properties and fluid chemical resistance while the first layer  14 A is made of material, as described above, that has better friction and wear properties due to the lubricant  34  dispersed therein. 
     Referring to  FIG. 4 , a cross section of an embodiment of a mud motor disclosed herein is illustrated at  110 . The mud motor  110  includes, a stator  114  with a contoured surface  118  configured to functionally engage with a complementary surface  122  of a rotor  126 . In this embodiment the rotor  126  has two parts, an outer layer  126 A and an inner layer  126 B, with at least the outer layer  126 A including a plurality of the microcapsules  42 . Alternate embodiments could have the entirety of the rotor  126 A and  126 B filled with the microcapsules  42  instead of just the outer layer  126 A and the structure could be a single part as opposed to being the two-part configuration illustrated herein. Additionally, the stator  114  can also be a single piece structure or a two-piece structure having the inner layer  114 A and the outer layer  114 B as is illustrated in this embodiment. The material of the stator  114  can vary with one embodiment being steel with an abrasion resistant coating on the surface  118 . In embodiments wherein the stator  114  is metal the part material configuration is essentially reversed to that of the embodiments illustrated in  FIGS. 1 and 3 . 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.