Abstract:
A seal section for use in a downhole submersible pumping system includes a housing and a seal bag located within the housing. The seal bag includes a substrate having a plurality of substrate surfaces and a metal coating layer on at least one of the plurality of substrate surfaces. The substrate can optionally be configured as a cylindrical form that includes an interior surface and an exterior surface. In particularly preferred embodiments, the substrate is seamless and fabricated from an extruded fluoropolymer. The metal coating layer preferably comprises a metal selected from the group consisting of titanium, stainless steel, nickel, chrome, silver and gold. The metalized seal bag exhibits increased durability and decreased permeability to liquids and gases at elevated temperatures.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a seal section separation bag for use within a submersible pumping system. 
       BACKGROUND 
       [0002]    Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids. 
         [0003]    Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provides several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation. Many seal sections employ seal bags to accommodate the volumetric changes and movement of fluid in the seal section. Seal bags can also be configured to provide a positive barrier between clean lubricant and wellbore fluid. 
         [0004]    As the use of downhole pumping systems extends to new applications, traditional bladder systems may fail under inhospitable downhole environments. For example, the use of downhole pumping systems in combination with steam assisted gravity drainage (SAGD) technology exposes bladder components to temperatures in excess of  500 ° F. To increase the resistance of the bladder to degradation under these increasingly hostile environments, manufacturers have employed durable polymers, including various forms of polytetrafluoroethylene (PTFE), as the preferred material of construction. More recently, manufacturers have employed the use of perfluoroalkoxy (PFA) fluoropolymers. The use of PFA as the material of construction in seal bags is disclosed in U.S. Pat. No. 8,246,326 issued Aug. 21, 2012 and assigned to GE Oil &amp; Gas ESP, Inc. 
         [0005]    Although PTFE and PFA provide suitable materials of construction of many pumping applications, at extreme temperatures and elevated pressure differentials, even these materials may exhibit some permeability to liquids and gases. Of particular concern is the potential for liquid water permeation through the seal bags at extreme temperatures. There is, therefore, a need for an improved seal bag, seal sections and submersible pumping systems that overcome the deficiencies of the prior art. It is to this and other needs that the present invention is directed. 
       SUMMARY OF THE INVENTION 
       [0006]    In a preferred embodiment, the present invention provides a seal section for use in a downhole submersible pumping system. The seal section includes a housing and a seal bag located within the housing. The seal bag comprises a substrate having a plurality of substrate surfaces and a metal coating layer on at least one of the plurality of substrate surfaces. The substrate can optionally be configured as a cylindrical form that includes an interior surface and an exterior surface. In particularly preferred embodiments, the substrate is seamless and fabricated from an extruded fluoropolymer. The metal coating layer preferably comprises a metal selected from the group consisting of titanium, stainless steel, nickel, chrome, silver and gold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an elevational view of a submersible pumping system constructed in accordance with a presently preferred embodiment. 
           [0008]      FIG. 2  is a cross-sectional view of a first preferred embodiment of a seal section for use with the submersible pumping system of  FIG. 1 . 
           [0009]      FIG. 3  is a perspective view of a first alternative version of the seal bag of  FIG. 2 . 
           [0010]      FIG. 4  is a perspective view of a second alternative version of the seal bag of  FIG. 2 . 
           [0011]      FIG. 5  is an exaggerated cross-sectional view of an o-ring seal from the seal section of  FIG. 2 . 
           [0012]      FIG. 6  is a cross-sectional view of a mechanical seal that includes a metalized polymer bellows. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    In accordance with a preferred embodiment of the present invention,  FIG. 1  shows an elevational view of a pumping system  100  attached to production tubing  102 . The pumping system  100  and production tubing  102  are disposed in a wellbore  104 , which is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas. The production tubing  102  connects the pumping system  100  to a wellhead  106  located on the surface. Although the pumping system  100  is primarily designed to pump petroleum products, it will be understood that the present invention can also be used to move other fluids. It will also be understood that, although each of the components of the pumping system are primarily disclosed in a submersible application, some or all of these components can also be used in surface pumping operations. 
         [0014]    The pumping system  100  preferably includes some combination of a pump assembly  108 , a motor assembly  110  and a seal section  112 . The motor assembly  110  is preferably an electrical motor that receives power from a surface-mounted motor control unit (not shown). When energized, the motor assembly  110  drives a shaft that causes the pump assembly  108  to operate. The seal section  112  shields the motor assembly  110  from mechanical thrust produced by the pump assembly  108  and provides for the expansion of motor lubricants during operation. The seal section  112  also isolates the motor assembly  110  from the wellbore fluids passing through the pump assembly  108 . Although only one of each component is shown, it will be understood that more can be connected when appropriate. It may be desirable to use tandem-motor combinations, multiple seal sections, multiple pump assemblies or other downhole components not shown in  FIG. 1 . 
         [0015]    Referring now to  FIG. 2 , shown therein is a cross-sectional view of the seal section  112 . The seal section  112  includes a housing  114 , a shaft  116 , a seal bag  118 , a support tube  120  and first and second bag plates  122   a,    122   b.  The seal bag  118  is configured to prevent the contamination of clean motor lubricants with wellbore fluids. The shaft  116  transfers mechanical energy from the motor assembly  110  to the pump assembly  108 . The bag support tube  120  provides support for the seal bag  118  and shields the shaft  116  as its passes through the seal bag  118 . For the purposes of the instant disclosure, the terms “bag seal assembly” will refer to the seal bag  118 , the bag support tube  120  and the first and second bag plates  122   a,    122   b.  In addition to the bag seal assembly, the seal section  112  may also include seal guides  124 , a plurality of ports  126  and one or more o-ring seals  128 . The o-ring seals  128  are located at various positions within the seal section  112  and limit the migration of contaminants and well fluids into the clean lubricant. 
         [0016]    For purposes of illustration, the bag seal assembly is disclosed as contained within the seal section  112 . It will be understood, however, that the bag seal assembly could be installed elsewhere in the pumping system  100 . For example, it may be desirable to integrate the bag seal assembly within the motor assembly  110  or pump assembly  108 . 
         [0017]    Referring now also to  FIGS. 3 and 4 , shown therein is a side perspective view of a preferred embodiment of the seal bag  118 . The seal bag  118  preferably includes a substrate  130 , a first end  132  and a second end  134 . In preferred embodiments, the substrate  130  is substantially configured as an elongated cylinder with an inner surface  136  and an outer surface  138 . 
         [0018]    In preferred embodiments, the substrate  130  is fabricated from an elastomer or other polymer, such as, for example PTFE, PFA, or polyvinyl chloride (PVC). Unlike prior art bladders, the seal bag  118  includes a metal coating layer  140  of chemically stable and inert metal or metal alloy. Presently preferred metals include titanium, stainless steel, nickel, chrome, silver and gold, and alloys for each of these metals. It will be appreciated that the metal coating layer  140  may be produced with combinations of multiple metals and metal alloys. In alternate preferred embodiments, the seal bag  118  is provided with a multilayered coating that includes two or more metal coating layers  140 . For these multilayered embodiments, it will be appreciated that each metal coating layer  140  may be prepared using different metals and metal alloys. 
         [0019]    The metal coating layer  140  is preferably applied to at least one of the exterior surface  138  ( FIG. 3 ) and the interior surface  136  ( FIG. 4 ) with a suitable metal deposition process. Presently preferred metallization processes include vacuum metallization and sputtering. Both deposition processes are well-established in the art. In preferred embodiments, the metal coating layer  140  has a thickness between about 1,000 and about 25,000 angstroms. In a particularly preferred embodiment, the thickness of the metal coating layer  140  is about 10,000 angstroms. The metalized seal bags  118  of the preferred embodiments significantly decrease the liquid and gas permeability through the underlying substrate  130 . 
         [0020]    Alternatively, the metal coating layer  140  is provided as a foil laminate over the substrate  130 . In this alternate embodiment, the foil metal coating layer  140  may be adhered to the substrate with adhesives, mechanical fasteners or chemical bonding. 
         [0021]    In a particularly preferred embodiment, the substrate  130  is manufactured from PFA and includes a titanium or titanium alloy metal coating layer  140  on the exterior surface  138  that is approximately 10,000 angstroms thick. PFA is commercially available from a number of sources, including E.I. du Pont de Nemours and Company and Daikin Industries. Like PTFE, PFA exhibits favorable resistance to corrosive chemicals and elevated temperatures. Unlike PTFE, however, PFA is melt-processable using conventional injection molding and screw extrusion mechanisms. The ability to extrude or mold PFA permits the construction of a seamless, unitary substrate  130 . Furthermore, seal bags  118  manufactured using PFA experience less stretching during the expansion and contraction cycle than comparable PTFE-based bags. These characteristics favor PFA as a substrate for metallization because it is easier to achieve a more uniform coating along the seamless bag, and metal coating layer  140  is less likely to separate, crack, flake or peel from the substrate due to stretching and contraction. 
         [0022]    Turning now to  FIG. 5 , shown therein is a close-up, cross-sectional view of one of the o-ring seals  128 . The o-ring seal  128  includes a ring-shaped body  146  that is preferably manufactured from a durable elastomer, synthetic rubber or fluoropolymer that exhibits favorable wear and permeability characteristics. Suitable elastomers include fluoropolymer elastomers and perfluoropolymer elastomers sold under the Kalrez and Chemraz brands by Greene, Tweed &amp; Co. and the Perlast brand compound sold by Precision Polymer Engineering Ltd. Although the o-ring seal  128  is depicted as having a circular cross-section, it will be appreciated that the o-ring seal  128  may have a different cross-section shape, such as, for example, rectangular, triangular, octagonal or oval. 
         [0023]    The o-ring seal  128  includes an exterior surface  142  and a metal coating layer  144  on the exterior surface  142 . The metal coating layer  144  is preferably prepared under the same techniques, using the same materials described above with reference to the metal coating layer  140  of the seal bag  118 . The metal coating layer  144  increases the durability and lowers the permeability of the o-ring seal  128 . The use of metalized o-ring seals  128  significantly decreases permeation of liquids and gasses across the o-ring seal  128  at elevated temperatures. 
         [0024]    Although the o-ring seals  128  have been described with reference to the seal section  112  and shaft  116 , it will be understood that the o-ring seals  128  will also find utility in other applications. For example, the o-ring seals  128  can be used in other downhole and surface pumping components that include, for example, pothead connectors, motor assemblies, pump assemblies, sensor arrays, and logging tools. 
         [0025]    It will be further understood that the novel use of metalized polymers will find application in other downhole components, including, for example, mechanical seal bellows and pothead connectors. By way of illustration, an alternative embodiment includes the use of a metalized bellows  150  within a mechanical seal  152 . Turning now to  FIG. 5 , shown therein is a cross-sectional view of a mechanical seal  152  constructed in accordance with a preferred embodiment. The mechanical seal  152  includes a rotating assembly  154  secured to a shaft  156  and a stationary face  158  that remains fixed relative to the shaft  156 . The rotating assembly  154  is spring-loaded and configured to axially expand and contract to stay in contact with the stationary face  158  in the event the shaft  156  is axially displaced. 
         [0026]    The bellows  148  is preferably constructed from a polymer substrate  160  and a metalized coating  162 . In preferred embodiments, the polymer substrate  160  is fabricated from a polymer, such as, for example PTFE, PFA, or polyvinyl chloride (PVC). The metalized coating  162  is preferably made by deposition, sputtering, spraying or through use of foil lamination. Preferred metals include titanium, stainless steel, nickel, chrome, silver and gold, and alloys for each of these metals. It will be appreciated that the metalized coating  162  may be produced with combinations of multiple metals and metal alloys. In alternate preferred embodiments, the bellows  148  is provided with a multilayered coating that includes two or more metalized coating  162 . For these multilayered embodiments, it will be appreciated that each metalized coating  162  may be prepared using different metals and metal alloys. With the metalized coating  162 , the bellows  148  is capable of withstanding higher temperatures and is less likely to rupture during explosive decompression. 
         [0027]    It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention.