Abstract:
Disclosed is a bottom-intake pumping system that includes a pump assembly and a motor that drives the pump assembly with a driveshaft assembly. The bottom-intake pumping system includes a first thrust bearing that supports the driveshaft assembly on a first side of the pump assembly and a second thrust bearing that supports the driveshaft assembly on a second side of the pump assembly. The bottom-intake pumping system also includes a shroud assembly and a discharge pipe. The shroud assembly has a lower shroud hanger configured for rigid attachment at a selected location on the pump assembly, a shroud body connectable to the lower shroud hanger and an upper shroud hanger connectable to the shroud body. The upper shroud hanger is configured for sliding engagement with a discharge pipe.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to the field of downhole pumping systems, and more particularly to encapsulated bottom intake pumping systems.  
       BACKGROUND  
       [0002]     Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Submersible pumping systems often include an electric motor coupled to a pump assembly. When driven by a motor, the pump assembly moves fluids from the reservoir to surface facilities through production tubing. In many installations, the discharge from the pump assembly is connected directly to the production tubing. In these installations, the motor is commonly placed below the pump assembly at the terminal end of the equipment string.  
         [0003]     In other applications, however, it is desirable to place the pump assembly below the electric motor. Prior art “bottom intake” pumping systems are often used in combination with a shroud and an intake tailpipe to draw fluids from a lower well zone that has been isolated from the pump assembly by a packer. Although widely used, prior art bottom intake pumping systems are prone to mechanical failure. Furthermore, the shroud assemblies used to encapsulate bottom-intake pumping system must be custom fabricated under strict tolerances for proper fit. There is therefore a need for a more robust and easier to manufacture bottom intake pumping system.  
       SUMMARY OF THE INVENTION  
       [0004]     In a preferred embodiment, the present invention includes a bottom-intake pumping system having a pump assembly, a motor configured to drive the pump assembly and a driveshaft assembly for delivering power from the motor to the pump assembly. A first thrust bearing supports the driveshaft assembly on a first side of the pump assembly and a second thrust bearing supports the driveshaft assembly on a second side of the pump assembly.  
         [0005]     In another aspect, the preferred embodiment includes a shroud assembly and a discharge pipe. The shroud assembly preferably includes a lower shroud hanger configured for rigid attachment at a selected location on the pump assembly, a shroud body connectable to the lower shroud hanger and an upper shroud hanger connectable to the shroud body. The upper shroud hanger is preferably configured for sliding engagement with the discharge pipe. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a front view of a bottom-intake pumping system with a cross-sectional view of the shroud assembly constructed in accordance with a presently preferred embodiment.  
         [0007]      FIG. 2  is a partial cross-section view of the bottom-intake pumping system of  FIG. 1  depicting the internal components of the upper seal section, pump assembly and lower seal section of a preferred embodiment.  
         [0008]      FIG. 3  is a partial cross-sectional view of the pump assembly and lower seal section.  
         [0009]      FIG. 4  is a cross-sectional, exploded view of the shroud assembly of  FIG. 1 .  
         [0010]      FIG. 5  is a cross-sectional view of the shroud assembly of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     In accordance with a preferred embodiment of the present invention,  FIG. 1  shows a front perspective view of a downhole pumping system  100  attached to production tubing  102 . The downhole 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. 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, which may be generically referred to as “wellbore fluids” while in the ground or “produced fluids” on the surface.  
         [0012]     The production tubing  102  connects the pumping system  100  to a wellhead  106  located on the surface. The wellhead  106  is in turn connected to surface facilities for transporting, refining or storing the produced fluids. It will be understood that, although each of the components of the pumping system  100  are primarily disclosed in a submersible application, some or all of the components disclosed herein can also be used in surface pumping operations.  
         [0013]     The pumping system  100  preferably includes some combination of a pump assembly  108 , a motor assembly  110 , an upper seal section  112  and a lower seal section  114 . In a preferred embodiment, the motor assembly  110  is an electrical motor that receives its power from a surface-based source. Generally, the motor assembly  110  converts the electrical energy into mechanical energy, which is transmitted to the pump assembly  108  through a series of connected shafts that are collectively referred to as the driveshaft assembly  116  (not shown in  FIG. 1 ).  
         [0014]     The pump assembly  108  transfers a portion of this mechanical energy to fluids within the wellbore, causing the wellbore fluids to move through the production tubing  102  to the surface. In a particularly preferred embodiment, the pump assembly  108  is a turbomachine that uses one or more impellers and diffusers to convert mechanical energy into pressure head. In an alternative embodiment, the pump assembly  108  is a progressive cavity (PC) pump that moves wellbore fluids with one or more screws or pistons.  
         [0015]     In the preferred embodiment, the pumping system  100  is configured as a shrouded bottom-intake pumping system in which the pump assembly  108  is located below the motor  110 . The pump assembly  108  preferably includes an intake  118  and a discharge  120 . The lower seal section  114  is preferably connected to the intake  118  at the terminal end of the pumping system  100 . The upper seal section is preferably connected between the discharge  120  and the motor  110 . In this way, the upper and lower seal sections  112 ,  114  are connected to a “discharge end” and an “intake end,” respectively, of the pump assembly  108 .  
         [0016]     The pumping system  100  also includes a shroud assembly  122 , a discharge pipe  124  and a cross-over  126 . The discharge pipe  124  is preferably connected to the production tubing  102  and the cross-over  126 . The cross-over  126  is preferably secured to the top of the motor  110 . In this way, the shroud assembly  122  creates a substantially sealed fluid path between the discharge  120  and the cross-over  126  around the external surface of the upper seal section  112  and the motor  110 . Fluids discharged from the pump assembly  108  are retained within the shroud assembly  122  and forced into the discharge pipe  124  through the cross-over  126 . Forcing wellbore fluids through the shroud assembly  122  lowers the temperature of the internal motor lubricant and motor components. Lower operating temperatures result in improved motor life and reduced levels of scaling.  
         [0017]     Turning now to  FIG. 2 , shown therein is a cross-sectional view of the upper seal section  112 . The upper seal section  112  is designed to equalize the pressure inside the motor  110  with the pressure in the wellbore and to compensate for the expansion and contraction of motor lubricants due to changes in the temperature of the motor  110 . In a presently preferred embodiment, the upper seal section  112  is configured as a labyrinth-type seal section that uses a tortuous fluid path and gravity separation to permit the expansion of motor lubricants while preventing contaminated well fluid from reaching the motor  110 . In an alternate embodiment, the upper seal section  112  includes one or more elastomeric bags in addition to, or in place of, the labyrinth-type seal. The elastomeric bags function as a positive barrier between the motor lubricant and corrosive well fluids. The upper seal section  112  preferably also includes an upper thrust bearing  128  that is designed to carry a portion of the axial thrust developed by the pump assembly  108 . In a particularly preferred embodiment, the thrust bearing includes a rotating runner  130  bounded by first and second stationary thrust pads  132 ,  134 .  
         [0018]     Turning to  FIG. 3 , shown therein is a cross-sectional depiction of the lower seal section  114 . In the presently preferred embodiment, the lower seal section  114  is configured as a bag-type seal that includes an elastomeric bag  136 . The elastomeric bag  136  prevents wellbore fluids from the pump assembly  108  from contacting other internal components within the lower seal section  114 . Although a single elastomeric bag  136  is presently preferred, it will be understood that additional elastomeric bags  136  can be used. In an alternate preferred embodiment, the elastomeric bag  136  is replaced by, or used in conjunction with, a labyrinth-type seal mechanism.  
         [0019]     The lower seal section  114  also includes a lower thrust bearing  138  that works in concert with the upper thrust bearing  128  to absorb mechanical shock induced in the driveshaft assembly  116  during operation. Like the upper thrust bearing  128 , the lower thrust bearing  138  preferably includes a rotating runner  140  and first and second thrust pads  142 ,  144 . The axial movement of the driveshaft assembly  116  and runner  140  is limited by the first and second thrust pads  142 ,  144 . In this way, the driveshaft assembly  116  is supported by upper and lower thrust bearings  128 ,  138 , respectively, on opposing ends of the pumping system  100 . Supporting the driveshaft assembly  116  on both ends of the pumping system  100  reduces the likelihood that the driveshaft assembly  116  will become pinned or sheared when subjected to excessive downthrust or torque.  
         [0020]     Turning now to  FIGS. 4 and 5 , shown therein are exploded and assembled elevational views, respectively, of the shroud assembly  122  and the associated other portions of the pumping system  100 . In the presently preferred embodiment, the shroud assembly  122  includes a lower shroud hanger  146 , a shroud body  148  and an upper shroud hanger  150 . The shroud body  148  is preferably configured for mating engagement between the lower shroud hanger  146  and the upper shroud hanger  150 . In a particularly preferred embodiment, the shroud body  148 , upper shroud hanger  150  and lower shroud hanger  148  include threaded portions that permit a secure engagement.  
         [0021]     The lower shroud hanger  146  is preferably secured to the pump assembly  108  below the discharge  120 . In the presently preferred embodiment, the lower shroud hanger  148  is preferably a conventional shroud hanger that rigidly secures the shroud assembly  122  to the pump assembly  108 . The attachment of conventional shroud hangers is well known in the art. The shroud body  148  is preferably configured as an elongated cylinder having a length sufficient to extend above the crossover  126  when secured to the lower shroud hanger  146 .  
         [0022]     The upper shroud hanger  150  preferably includes a central bore  152 , a plurality of central seals  154  and at least one penetrator assembly  156 . The central bore  152  is preferably sized and configured to receive the discharge pipe  124 . The central seals  154  are configured to engage the discharge pipe  124  to form a substantially sealed connection between the discharge pipe  124  and the upper shroud hanger  150 . In a particularly preferred embodiment, the discharge pipe  124  is a polished, non-upset pup-joint connected between the cross-over  126  and the production tubing  102 . In this particularly preferred embodiment, the central seals  154  are configured as “o-rings” with an inner diameter substantially equivalent to the outer diameter of the discharge pipe  124 . The at least one penetrator assembly  156  permits the introduction of power or signal cables into the shroud assembly  122 . During assembly, cables from the motor  110  can be fed through the upper shroud hanger  150  as it is lowered onto the discharge pipe  124 . The upper shroud hanger  150  can then be moved down the discharge pipe  124  a desired extent to connect the components within the shroud assembly  122 .  
         [0023]     Thus, unlike prior art shroud assemblies that are constructed at specific lengths to be secured at specific locations on the pumping system, the shroud assembly  122  of the preferred embodiment can be constructed without requiring specific length and attachment points. With the sliding engagement of the upper shroud hanger  150  on the discharge pipe  124 , a single shroud assembly  122  can be used to encapsulate a variety of pumping systems  100 .  
         [0024]     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.