Abstract:
The present invention provides an electrical submersible pump assembly having a submersible pump, a submersible electrical motor drivingly connected to the pump, and a seal assembly disposed between the submersible pump and the motor. The seal assembly is generally of tubular construction and provides fluid communication between the seal assembly cavity and the motor, such fluid communication being in a circuitous path effecting gravity segregation of contaminants including particulate solids in wellbore fluids. The seal assembly thereby controls and minimizes migration of the contaminants into the body of the seal section and on into the motor.

Description:
RELATED APPLICATIONS 
     This application claims priority to Provisional Application Ser. No. 60/263,920 entitled “U-Tube at Communication Point in Seal Section to Prevent Solids or Heavy Material from Entering” filed Jan. 26, 2001. 
    
    
     FIELD OF INVENTION 
     The present invention relates to the field of electric submersible pump assemblies and associated support equipment, and more particularly but not by way of limitation, to an electric submersible pump assembly having a tube seal section. 
     BACKGROUND OF INVENTION 
     In oil wells and the like from which the production of fluids is desired, a variety of fluid lifting systems have been used to pump the fluids to surface holding and processing facilities. It is common to employ various types of downhole pumping systems to pump the subterranean formation fluids to surface collection equipment for transport to processing locations. 
     One such prior art pumping system is a submersible pumping assembly which is supported immersed in the fluids in the wellbore. The submersible pumping assembly having a pump and a motor to drive the pump to pressurize and pass the fluid through production tubing to a surface location. A typical electric submersible pump assembly (ESP) includes a submersible pump, an electric motor and a seal section interdisposed between the pump and the motor. The purpose of the seal section is to protect the motor from contamination as the wellbore fluid usually contains deleterious substances such as particulate solids and other debris from the formation. Prior art seal sections have not proved effective in preventing environmental contamination of the motor. 
     Thus, there is a need for a seal section capable of effectively preventing deleterious substances, such as particulate solids and other matter contained in formation fluids, from entering the motor where such contaminants can interfere with the efficient operation of the motor and can reduce the operational life of the motor. 
     SUMMARY OF INVENTION 
     The present invention provides an electric submersible pump assembly having a submersible pump, a submersible electric motor drivingly connected to the pump, and a seal assembly disposed between the submersible pump and the motor. The seal assembly is generally of tubular construction and provides fluid communication between the seal assembly cavity and the motor, such fluid communication being in a circuitous path effecting gravity segregation of contaminants, including particulate solids, in wellbore fluids. The seal assembly thereby controls and minimizes migration of particulate solids and the like into the body of the seal section and into the motor. 
    
    
     The objects, advantages and features of the present invention will become clear from the following detailed description and drawings when read in conjunction with the appended claims. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic, semi-detailed view an electric submersible pump assembly constructed in accordance with the present invention and supported in a wellbore shown in cross section. 
     FIG. 2 is an elevational view of the electric submersible pump assembly of FIG.  1 . 
     FIG. 3 is a partial cutaway, elevational view of the seal assembly portion of the electric submersible pump assembly of FIG.  1 . 
     FIG. 4 is a partial cutaway view of a portion of the seal assembly of FIG.  3 . 
     FIGS. 5A and 5B are elevational and plan views, respectively, of the tubular seal member of the seal assembly of FIG.  3 . 
     FIG. 6 is a partial cutaway, alternative seal assembly which is usable in lieu of the seal assembly portion of FIG.  3 . 
    
    
     DESCRIPTION 
     Referring to the drawings in general and particularly to FIG. 1, shown therein is an electric submersible pump assembly  10  constructed in accordance with the present invention and disproportionately drawn to better illustrate various aspects of the present invention. The electric submersible pump assembly  10 , also called herein the ESP assembly  10 , is shown disposed in a wellbore  12  and suspended therein via a tubing  14  extending from the surface  16 . It will be understood that numerous valves, safety devices and other equipment typically used in such installations are omitted herein as such are not necessary for the description of the present invention. 
     The ESP assembly  10  has, from bottom to top, an electric submersible motor  18 , a seal section assembly  20 , and a pump  22  which includes an intake pump section  24  and a pump discharge head  26  that move a production stream  28  through production tubing  14  to the surface  16 . One skilled in the art will understand that it can be advantageous to attach an optional sensor  30  to the motor  18 . It would also be understood that the intake pump section  24  could as well be a gas separator (not shown), as is often used in gaseous wells, or other type of intake section. 
     The motor  18  can be controlled at the surface by a switch board  34  with an optional variable speed device (VSD) via a cable  36 . As one skilled in the art would be aware, a packer  38  can be used to protect casing  40 . The casing  40  will have casing perforations  42  that allow reservoir production  44  to flow into the wellbore  12 . One skilled in the art would understand that the present invention would also work well with other wellbore configurations including those that do not have a standard completion with casing perforations. 
     One skilled in the art will also be aware that various other well accessories, such as an electric submersible motor control can be added to make the ESP assembly  10  perform efficiently such as pressure, temperature, and vibration controls. The ESP assembly  10  can utilize rotary, shaft-driven, gear-driven, progressive cavity pumps (PCP), and preferably multi-stage centrifugal pumps powered by the motor  18 . 
     FIG. 2 shows the ESP assembly  10  in further detail. The seal section assembly  20  can be located above and/or below the motor  18 , to enhance motor performance by preventing wellbore fluids and solids, such as muds, sands, barite and similar particulate and non particulate matter found in a wellbore and hereafter collectively referred to as contaminants, from entering the motor  18 . The various types of damage that can occur due to these materials include both mechanical, such as erosion, and chemical damage, such as corrosion. 
     FIG. 3 shows the seal section assembly  20  which is constructed in a labyrinth style. This seal section is commonly referred to as a labyrinth seal section  20 . The labyrinth seal section  20  has a housing  52  with a base  54 , a seal section housing top  56  and a shaft  58  with an upper coupling  60  and a lower coupling  62 . The housing  52  forms two chambers, an upper labyrinth chamber  64  and a lower labyrinth chamber  66 . The upper labyrinth chamber  64  contains a first labyrinth tube  68  open on both ends to allow fluid movement from an oil expansion hole  70  to the upper labyrinth chamber  64 . The upper labyrinth chamber  64  also contains a second upper labyrinth tube  72  to allow fluid communication from the upper labyrinth chamber  64  to the lower labyrinth chamber  66 . The lower labyrinth chamber  66  is constructed in a manner similar to the upper chamber  64 . 
     A seal section head  74  is attached to the seal section housing  52  at the seal section housing top  56  to connect the labyrinth seal section  20  to the intake pump section  24 . The seal section head  74  has a lubricant overflow cavity  76  containing a mechanical seal  78  that forms a seal between a lower surface  80  of the lubricant overflow cavity  76  and a retaining ring  82 . Above the retaining ring  82  is an upper surface  84  of the seal section head  74  that abuts the intake pump section  24 . 
     In FIG. 4, the seal section head  74  and a portion of the intake pump section  24  are shown in detail, including the retaining ring  82  of the seal section head  74  that abuts the intake pump section  24  and is attached by fasteners  86 . In the present invention, the head  74  has a fill intake port  88  in fluid communication with a separation tube  90 . The separation tube  90  provides fluid communication between the oil expansion hole  70  and a lubricant overflow cavity  76  in communication with fluid from the wellbore  12  through the fill intake port  88 . 
     The separation tube  90  has a first end  92  and a second end  94 . The first end  92  is in fluid communication with the upper labyrinth chamber  64  which is a lubricant holding cavity. The second end  94  is in fluid communication with the lubricant overflow cavity  76 . The separation tube  90  extends circuitously between the first end  92  and the second end  94  thereof so fluid passing through is caused to change flow directions to restrict the flow of contaminants in the fluid from the wellbore  12  as it flows toward the motor  18  via the upper labyrinth chamber  64  and the lower labyrinth chamber  66  in the seal section housing  52 . 
     FIG. 5A shows the separation tube  90  as preferably being a hollow tubular member and having a first portion  96 , a second portion  98 , and a third portion  100 . The first end  92  of the first portion  96  connects to the oil expansion hole  70 , such as with a threaded connection, so there is fluid communication between the upper labyrinth chamber  64  and the lubricant overflow cavity  76 . 
     The second end  94  of the third portion  100  of the separation tube  90  is in fluid communication with the lubricant overflow cavity  76 . The second end  94  contains an opening  102  which can protrude out from the third portion  100  or be flush with the surface of the third portion  100 . The first, second and third portions,  96 ,  98  and  100 , respectively, are angularly disposed to each other in such a way that the fluid passing through is caused to change flow directions to restrict the flow of contaminants in the fluid flow toward the motor  18  via the upper labyrinth chamber  64  and the lower labyrinth chamber  66  in the seal section housing  52 . 
     FIG. 5B shows the separation tube  90  to be positioned in the seal lubricant overflow cavity  76  such that the second portion  98  is near the upper surface  84  of the seal section head  74  where the seal section head  74  abuts the intake pump section  24  and some distance from the lower surface  80  of the lubricant overflow cavity  76 . FIG. 5B shows the separation tube  90  such that the second portion  98  forms an arc that encircles the shaft  58 . The third portion  98  is in fluid communication with the second portion  96  and parallel to the first portion  94 . The construction of the separation tube  90  can be tubular and continuous or jointed, for ease of installation and construction, as one skilled in the art would understand. The separation tube  90  can take a variety of shapes, as will be well understood by one skilled in the art, and can contain a filter  104  at the opening  102  or inside the separation tube  90 . The separation tube  90  can also contain other internal structures, such as baffles  106 , to enhance the gravitational segregation of different density materials. The separation tube  90  of the present invention helps prevent the movement of solids and heavy fluid into the seal section  20  and into the motor  18 , through gravitational segregation. 
     FIG. 6 shows a seal section assembly commonly referred to as a bag-style seal section  110 . The bag-style seal section  110  has a housing  112  with a base  114 , and a top  116 . The bag-style seal section  110  contains a shaft  118  with an upper coupling  120  and a lower coupling  122 . The housing  112  forms two chambers, an upper bag-style chamber  124  and a lower chamber  126 . The upper bag-style chamber  124  has an elastomer bag  128  inside the housing  112  that surrounds the shaft  118 . The lower chamber  126  in this bag-style seal section  110  is similar to the lower labyrinth chamber  66 , in that there is a first tube  130  and a second tube  132  open on both ends to allow fluid movement. 
     A seal section head  134  is attached to the seal section housing  112  at the seal section housing top  116  to connect the bag-style seal section  110  to the intake pump section  24  (see FIG.  2 ). The seal section head  134  has a lubricant overflow cavity  136  containing a mechanical seal  138  that forms a seal between a lower seal surface  140  of the lubricant overflow cavity  136  and a retaining ring  142  similar to that described above in conjunction with the labyrinth seal section  20 . The bag-style seal section  110  has a fill intake port  146  in fluid communication with the upper bag-style chamber  124  via a separation tube  150 . The separation tube  150  provides fluid communication between the upper bag-style chamber  124  and the lubricant overflow cavity  136  in communication with fluid from the wellbore  12  through the fill intake port  146 . 
     The separation tube  150  has a first end  152  and a second end  154 . The first end  152  is in fluid communication with the upper bag-style chamber  124  which is a lubricant holding cavity. The second end  154  is in fluid communication with the lubricant overflow cavity  136 . The separation tube  150  extends circuitously between the first end  152  and the second end  154  thereof so fluid passing through is caused to change flow directions to restrict the flow of contaminants in the fluid from the wellbore  12  as it flows toward the motor  18  via the upper bag-style chamber  124  and the lower chamber  126  in the seal section housing  112 . 
     The separation tube  150  is preferably a tubular member having a first portion  156 , a second portion  158 , and a third portion  160 . The first end  152  of the first portion  156  connects to the upper bag-style chamber  124  so there is fluid communication between the upper bag-style chamber  124  and the lubricant overflow cavity  136  in a manner similar to that described above for separation tube  90 . 
     The second end  154  of the third portion  160  of the separation tube  150  is in fluid communication with the lubricant overflow cavity  136 . The second end  154  contains an opening  162  which can protrude out from the third portion  160  or be flush with the surface of the third portion  160 . The first, second and third portions  156 ,  158  and  160  respectively are angularly disposed to each other in such a way that the fluid passing through is caused to change flow directions to restrict the flow of contaminants in the fluid flow toward the motor  18  via the upper bag-style chamber  124  and the lower chamber  126  in the seal section housing  112 . 
     The separation tube  150  to be positioned in the seal lubricant overflow cavity  136  such that the second portion  158  is near where the seal section head  134  abuts the intake pump section  24  and is some distance from the lower seal surface  140  of the lubricant overflow cavity  136 . As described above, the second portion  158  of the separation tube  150  can form an arc that encircles the shaft  118 . The third portion  158  is in fluid communication with the second portion  156  and can be parallel to the first portion  154 . The construction of the separation tube  150  can be tubular and continuous or jointed, for ease of installation and construction, as one skilled in the art would understand. The separation tube  150  can take a variety of shapes, as will be well understood by one skilled in the art, and can contain a filter (not shown) at the opening or inside the separation tube  150 . The separation tube  150  can also contain other internal structures, such as baffles (not shown), to enhance the gravity segregation of different density materials. The separation tube  150  of the present invention helps prevent the movement of solids and heavy fluid into the seal section  20  and into the motor  18 , through gravity segregation as discussed above. 
     In operation, when the fluid stream enters the wellbore  12  the fluid is drawn by the motor powered pump  22  to the intake pump section  24 , enters the pump  22 , and is pumped to the surface  16 . If there is significant gas present in the fluid stream, it can be advantageous to use a gas separator in place of the standard pump intake or other known methods to handle the gas expansion. 
     When the motor  18  starts operating, the temperature of the motor lubricant rises, causing volume expansion. This additional lubricant volume enters the seal section housing  52 , through tubes as shown in FIG. 3, and the seal section head  74  before finally exiting to the wellbore  12  through the fill intake port  88 . When the motor slows down or stops, the lubricant cools and contracts, causing the lubricant and wellbore fluid to flow into the seal section head  74  from the well bore  12  through the fill intake port  88 . The wellbore fluid can contain solids such as sand and heavy fluid that can damage the motor  18  if allowed to enter the motor  18  through the seal section assembly  20 . The present invention allows the lighter lubricant fluid to rise in the first section  94  and move through the second and third sections  96 ,  98  before entering the seal section  20  via the oil expansion hole  70 . The solids or heavier fluid will not travel up the first section  94  because they are heavier and flow rates are low and thus will remain in the seal section head or lower portion of the first section  94 . 
     There are various types of damage that could occur in the ESP assembly  10  and specifically in the motor  18  due to wear caused by these wellbore materials. Solids will enter the shaft bearings (for instance roller bearings or other types as dictated by the ESP assembly  10 ) and cause wear that consequently results in a side to side movement that results in leakage through the seals. 
     Any abrasives and/or solids in the wellbore fluids can move into the ESP assembly  10  then to the thrust bearings and into the seal section assembly  20 . This abrasive particulate matter could wear the surface of the thrust bearings, once again causing a side to side movement that results in leakage through the seals. All of this particulate matter can filter into the motor  18  and cause additional wear accentuated by any eccentric movement in the motor  18 , downward movement in the motor  18  or at impingement points and in the larger motor cavities where swirl erosion can occur. 
     In the bag-type seal section assembly, contaminants including particulate or solid material can pass by the bag and result in bag collapse. They can also reduce the solid-holding capacity of the seal section assembly by filling up the cavity. 
     The present invention has been described with two specific seal sections, both having a seal section head but one skilled in the art will understand that any oil expansion hole  70  can be altered to include the separation tube of the present invention in fluid communication to prevent the entry of solids and heavy fluid into the seal section head 
     It is clear the present invention is well adapted to carry out the objectives and to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the invention have been described in varying detail for purposes of the disclosure, it will be understood that numerous changes can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed in the above text and in the accompanying drawings.