Abstract:
The present invention provides a electric submersible pump assembly for producing a fluid from a production zone to the surface and operated independently by one or more electric submersible motors using a dual or multiple gearbox, the electric submersible pump assembly including an inlet pump having a section head into which fluid enters from the production zone to the inlet pump, an outlet pump having an intake section communicating with the inlet pump so that fluid received therefrom is discharged through the outlet pump, an electric submersible motor, a first motor interface that connects the electric submersible motor to the inlet pump, and a second motor interface that connects the electric submersible motor to the outlet pump; each motor interface having a gearbox that connects to the electric submersible motor, a pump shaft connector that connects to the pump, and a seal section that joins the pump shaft connector to the gearbox.

Description:
RELATED APPLICATIONS 
     This application claims priority to Provisional Application Ser. No. 60/293,585 entitled “DUAL GEARBOX ELECTRIC SUBMERSIBLE PUMP ASSEMBLY” filed May 25, 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 a dual gearbox electric submersible pump assembly utilized with various pumps including progressive cavity pumps. 
     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 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 includes a submersible pump and an electric motor with a gearbox. The purpose of the gearbox is to allow the motor to operate under different loads by controlling the torque. 
     Prior art gearboxes have not proved effective in handling the requirements of many pumps including the progressive cavity pump (PCP). Thus, there is a need for a gearbox capable of effectively controlling various pumps including progressive cavity pumps in applications that are currently limited by the torque capacity of the reduction gearbox. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electric submersible pump assembly for producing fluid from a production zone to a surface. The electric submersible pump assembly includes an electric submersible motor, a progressive cavity pump and a second pump. The progressive cavity pump is disposed above a lower packer and includes a section head and intake tubing to receive the fluid from the production zone. The second pump is disposed below an upper packer and includes production tubing and an intake section to receive the fluid from the progressive cavity pump. A first motor interface connects the electric submersible motor to the progressive cavity pump and a second motor interface connects the electric submersible motor to the second pump. The first and second motor interfaces include a gearbox, a flex shaft and a seal section. 
     The electric submersible pump assembly includes an inlet pump having a section head such that the fluid enters from the production zone through the inlet pump, an outlet pump having an intake section such that the fluid enters from the inlet pump and is discharged through the outlet pump, an electric submersible motor, a first motor interface that connects the electric submersible motor to the inlet pump, and a second motor interface that connects the electric submersible motor to the outlet pump; each motor interface having a gearbox that connects to the electric submersible motor, a pump shaft connector that connects to the pump, and a seal section that joins the pump shaft connector to the gearbox. 
    
    
     The advantages, features and benefits 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 THE DRAWINGS 
     FIG. 1 is a diagrammatical, elevational semi-detailed view of an electric submersible pump (ESP) assembly constructed in accordance with the present invention and supported in a wellbore. 
     FIG. 2 is a diagrammatical, elevational view of an embodiment of the ESP assembly of FIG.  1 . 
     FIG. 3 is a diagrammatical, elevational view of another embodiment of an ESP assembly, with a shroud, constructed in accordance with the present invention. 
     FIG. 4 is a diagrammatical, elevational view of another embodiment of an ESP assembly with a bypass tubing, constructed in accordance with the present invention. 
     FIG. 5 is a diagrammatical, elevational view of another embodiment of an ESP assembly, with a bypass tubing and an additional motor, constructed in accordance with the present invention. 
    
    
     DESCRIPTION 
     Referring to the drawings in general and particularly to FIG. 1, shown therein is a wellbore  10  containing an electric submersible pump assembly  12 , also called herein the ESP assembly  12 , shown disposed in the wellbore  10 . It will be understood that numerous valves, safety devices and other equipment typically used in such installations are omitted herein as such are unnecessary for the description of the present invention. While the present invention will be described in relation to the ESP assemblies shown in the appended drawings, it will be understood that the present invention can be adapted to other embodiments. 
     The ESP assembly  12  has, from bottom to top, an inlet pump  14 , a section head  16  (similar to those associated with an ESP intake section), a first motor interface  18 , an electric submersible motor  20 , a second motor interface  22 , an intake section  24 , and a outlet pump  26 . The first motor interface  18  includes a first flex-shaft  28  (also referred herein as a pump shaft connector), a first seal section  30 , and a first gearbox  32 . The second motor interface  22  includes a second gearbox  34 , a second seal section  36 , and a second flex-shaft  38 . The ESP assembly  12  is particularly well suited to be used in conjunction with rotary or shaft-driven pumps, preferably a progressive cavity (PC) pump, that can operate independently of other pumps while being powered by the one electric submersible motor  20 . 
     Intake tubing  40  allows a produced fluid stream  42  from a reservoir  44 , also known as a production zone, to enter the inlet pump  14  which is in fluid communication with the outlet pump  26 . After the produced fluid  42  passes through the outlet pump  26 , the produced fluid  42  is pumped through production tubing  46  to a surface  50 . The electric submersible motor  20  can be controlled at the surface by a variable speed device (VSD)  52  via a cable  54  that is run beside the production tubing  46  in an annulus  56 . As one skilled in the art would be aware, a packer can support and centralize casing  58  and be used to protect the casing  58 . 
     FIG. 2 shows an ESP assembly that operates with a progressive cavity pump, herein referred to as an ESP-PCP assembly  60 . The ESP-PCP assembly  60  includes a PC outlet pump  62  with an intake section  64  and a PC inlet pump  66  with a section head  68  that has an opening not shown. A fluid stream, also known as flow stream  42  from the production zone  44  enters the PC inlet pump  66  which is in fluid communication with the PC outlet pump  62 . The first motor interface  18  and the second motor interface  22  transfer rotary motion from the electric submersible motor  20  to both the PC outlet pump  62  and the PC inlet pump  66 . The motor interfaces  18 ,  22  include the flex-shafts  28 ,  38 ; the seal sections  30 ,  36 ; and the gearboxes  32 ,  34 , as discussed above. The flex-shafts  28 ,  38  are capable of transmitting torque from the electric submersible motor  20  to either one or both of the PC pumps  62 ,  66 . A first packer  70  and a second packer  72  are used to create an annular channel  74  that allows the PC inlet pump  66  to be in fluid communication with the PC outlet pump  62 . 
     FIG. 3 shows an ESP-PCP assembly  80  that has a shroud  82 . The shroud  82  provides an alternative fluid channel  84  between a shroud base  86  and a shroud top  88 . As in the ESP-PCP assembly  60 , the ESP-PCP  80  uses the electric submersible motor  20  to power rotary or shaft-driven pumps, preferably progressive cavity pumps. The flow stream  42  from the production zone  44  enters the PC inlet pump  66 , with section head  68  that has an opening not shown, which is in fluid communication with the PC outlet pump  62  through the flow channel  84 . The first motor interface  18  and the second motor interface  22  transfer rotary motion to either one or both of the PC outlet pump  62  and the PC inlet pump  66 . 
     FIG. 4 shows an ESP-PCP assembly  90  that allows fluid communication between the PC inlet pump  66 , with the section head  68 , and the PC outlet pump  62 , with the intake section  64 , through a bypass tube  92 . As in the ESP-PCP assembly  60  described above, the ESP-PCP assembly  90  uses the electric submersible motor  20  to power rotary or shaft-driven pumps, preferably a progressive cavity pumps. The flow stream  42  from the production zone  44  enters the PC inlet pump  66  which is in fluid communication with the PC outlet pump  62  through the bypass tube  92 . The first motor interface  18  and the second motor interface  22  transfer rotary motion to either one or both of the PC inlet pump  66  and the PC outlet pump  62 . 
     FIG. 5 shows an ESP assembly  100  that has a second electric submersible motor  102  and an alternate PC pump  104 . This alternate PC pump  104  has both a discharge section, also known as an alternate section head  106 , and an alternate intake section  108 . The arrangement of components is different from those in the above discussed ESP-PCP assembly  60 . The ESP assembly  100  has, from bottom to top, the second electric submersible motor  102  and an alternate motor interface  110  which includes an alternate seal section  112 , an alternate gearbox  114  and an alternate flex-shaft  116  (as shown in FIG.  5 ), the alternate intake section  108  below the alternate PC pump  104 , and the alternate section head  106 . 
     Above the alternate section head  106  is the electric submersible motor  20 , the second motor interface  22 , the intake section  64 , and an outlet pump  118 . The second motor interface  22  includes the second gearbox  34 , the second seal section  36 , and the second flex-shaft  38 , as discussed above. A single power cable can be used to power both electric submersible motors  20 ,  102  by connecting the electric submersible motor  20  with a first section head  120  (also known as a pothead base) and a second section head  122 , as is shown in FIG. 5, to the second electric submersible motor  102 . This is accomplished by placing the first section head  120  in a conventional location on the upper side of the electric submersible motor  20  in power communication with the electric cable  54 . The second section head  122  is placed upside down on the lower side of the electric submersible motor  20  in power communication with the first section head  120  and the second electric submersible motor  102  which in turn is in mechanical communication with the alternate pump  104 . 
     The ESP assembly  100  uses the bypass tube  92  to allow fluid communication between the alternate PC pump  104  and the outlet pump  118 . Other arrangements, such as the use of two packers or a shroud, could be substituted for the bypass tube  92 . The outlet pump  118  can be any type of pump, such as a centrifugal pump, that will allow maximum efficiency in specific production situations, as will be discussed in more detail below. 
     In operation, the intake tubing string  40 , shown in FIG. 2, can include a tubing packer or a seal section to sting into a packer seal bore (not shown) located above the completion interval. The fluid stream  42  enters the lower or PC inlet pump  66  and is discharged into the annular channel  74 . The flow stream  42  is forced to move up the annular channel  74 . The flow stream  42  is forced into the pump intake section  64  because of the upper or second packer  72 . Finally the fluid stream enters the PC outlet pump  62  and is pumped to the surface  50 . 
     In the ESP-PCP assembly  80  and ESP-PCP assembly  90  shown in FIGS. 3 and 4, the shroud  82 , and the bypass tube  92  eliminates the need for packers  70 ,  72 . In the ESP-PCP assembly  80  (see FIG. 3) and ESP-PCP assembly  90  (see FIG. 4) any free gas can proceed up the annulus  56 . Gas separation can be enhanced by either extending the intake tubing  40  below the production zone  44  or incorporating a reverse shroud on the intake tubing  40 . In the embodiment, shown in FIG. 5, the second electric submersible motor  102  is shown to work in conjunction with the bypass tube  92 . This embodiment would also work well with a shroud or with packers, as discussed above. 
     The present invention has been described with one or two motors but can be utilized with additional motors and additional motor interfaces and pumps. A single power cable can be used for multiple motors by connecting a center tandem motor(s) with a pothead base(s), as is shown in FIG.  5 . For two motors this is accomplished by taking two section heads and placing the first section head  120  in a conventional location on the upper side of the electric submersible motor  20  so that it is in power communication with the power cable  54  and another section head, the second section head  122 , which is placed upside down on the lower side of the motor. The second head  122  is placed to be in power communication with both the first section head  120  and the second electric submersible motor  102  which in turn powers the alternate pump  104 . If there are more motors the same arrangement would be continued for the additional motors as one skilled in the art would understand. 
     If there is significant gas present in the fluid stream, it can be advantageous to use a tapered design and a smaller capacity PC outlet pump  62 , or other known methods to handle the gas expansion. The present invention offers another advantage when there is a significant amount of gas present in the fluid stream. Although the rotary pumps discussed in the above ESP-pump assemblies were described as a PC pump, centrifugal pump or other downhole rotary pumps can also be incorporated. The present invention is very useful in combination with a centrifugal pump when an entire flow stream includes so much free gas that a single centrifugal pump cannot pump the fluid efficiently. The present invention&#39;s lower pump can be a pump that is capable of compressing the free gas, such as a PC pump, and the upper pump can be a pump without a gearbox, such as a centrifugal pump, that doesn&#39;t have a torque limit and is thus able to overcome a higher head (pressure due to a column of fluid) and can consequently lift the fluid stream to the surface. This combination of pumps can efficiently pump the total stream including the free gas. This is especially helpful when the lower pump is a pump capable of compressing gas and the upper pump is not torque limited and thus capable of pumping the fluid to the surface. 
     It is clear that the present invention is well adapted to carry out the objects 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.