Patent Abstract:
An electrical submersible pump (ESP) completion installed in casing perforated for water disposal and production. A packer separates the disposal zone and the production zone. An inverted ESP assembly is located inside of a canister. The ESP and canister are lowered on a tubing string into the casing. The canister has a downwardly extending canister extension flow-directing member that communicates with water in the casing and which passes through the disposal zone. Water is pumped down the canister extension member into the disposal zone and formation. Well fluids are drawn up the extension from the production zone. Various configurations are disclosed to facilitate flowing well fluids, e.g., oil-rich mixture or water, past the motor for cooling the motor of the inverted ESP while maintaining fluid segregation. The completion is particularly suited for production wells wherein the oil and water have a strong tendency to naturally segregate within the wellbore.

Full Description:
FIELD OF THE INVENTION 
   This invention relates generally to an electrical submersible pump (ESP) completion that maintains fluid segregation and ensures motor cooling in a dual stream well, i.e., in a well that exhibits a considerable degree of natural oil/water fluid segregation within the wellbore. More particularly, the invention relates to an inverted ESP deployed within a canister, wherein produced well fluids are directed past the motor for cooling, an oil-rich production mixture is delivered to the surface and produced and water is re-injected in-situ into a separate injection zone. 
   BACKGROUND OF THE INVENTION 
   Fluid in many producing oil and/or gas wells is elevated to the surface of the ground by the action of a pumping unit or a pumping apparatus installed in the lower portion of the well bore, such as an electrical submersible pump (ESP). The electric motor used in such systems typically generates considerable heat. To keep the motor from overheating, the motor is typically cooled by transferring heat to surrounding annular fluids. In many cases, the pumping unit is set in the well casing above perforations located in the well&#39;s producing zone. By placing the pumping unit above the perforations, the unit can make use of the fluid flowing past the motor to cool the motor. Insufficient fluid velocity, however, will cause the motor to overheat and may lead to early motor failure. 
   To increase efficiency, it may be desirable to inject produced water into an injection formation and to deliver partially de-watered or oil-rich fluids to the surface. One ESP configuration that facilitates injecting water into the formation involves inverting the ESP. However, an inverted ESP configuration does not inherently allow for a flow of fluids past the motor when the ESP is located above well perforations. 
   Therefore, it is desirable to facilitate cooling of an ESP motor in an inverted ESP configuration when the ESP is located above well perforations. It is further desirable to produce oil-rich fluids while re-injecting produced water into an injection zone. 
   SUMMARY OF THE INVENTION 
   An electrical submersible pump (ESP) system is disclosed that utilizes a commonly available ESP canister or pod to encase an inverted ESP. A pack-off element is set in the canister to separate a water stream below the pack-off and an oil-rich mixture above the pack-off. The pack-off element is provided to ensure that the water stream will enter an intake of the pump while the oil-rich stream is directed to a tubing string for flow to the surface. 
   In one embodiment, the water is injected into the formation by the inverted pump while the oil-rich stream entering the canister flows past the motor, thereby cooling the motor with flow through an annular space inside the canister. The oil-rich stream then enters the production tubing above the inverted ESP via a perforated tubing joint within the pod, where the oil-rich stream flows to the surface either via natural flow or via artificial lift means. 
   A second embodiment involves the use of an inverted pump and a recirculation pump that are located within a canister or pod. The recirculation pump circulates a portion of the produced water stream over the motor. One or more recirculation tubes may be employed to direct the water to a location proximate the motor of the ESP. A second portion of the water stream is injected back into the disposal zone. This embodiment is advantageous because it eliminates the necessity for a pack-off element within the canister and also because the embodiment utilizes water for cooling the motor flow rather than the oil-rich mixture. Water has better heat transfer characteristics than the oil-rich mixture. In this embodiment, the oil-rich mixture flows to the surface through a perforated joint that is run outside and above the pod/canister. 
   Another embodiment utilizes an inverted shroud within the canister/pod to force the water stream to flow past the motor prior to entering the pump intake. An advantage to this design is that it is simple and has few ancillary equipment requirements. 
   An additional embodiment utilizes a canister within a canister to direct water past the motor for cooling the motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial cut-away view of a first embodiment of an inverted ESP completion of the invention set in a well; 
       FIG. 2  is a partial cut-away view of a second embodiment of an inverted ESP completion of the invention; 
       FIG. 3  is a partial cut-away view of a third embodiment of an inverted ESP completion of the invention; 
       FIG. 4  is a partial cut-away view of a fourth embodiment of an inverted ESP completion of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
   Referring now to  FIGS. 1-4 , shown are various embodiments of the inverted ESP completion of the invention for maintaining fluid segregation and to ensure motor cooling in a dual stream well. Well  10  has a well casing  12  that extends into the earth. Well casing  12  defines disposal perforations  14  ( FIG. 1 ) and production perforations  16  ( FIG. 1 ). Well fluids  18  ( FIG. 1 ) migrate through production perforation  16  and accumulate in well casing  12 . Well fluids  18  comprise an oil-rich mixture  20  and water  22 . An oil/water interface  23  is defined there between. Tubing  24  runs from the surface and extends into well casing  12 . Tubing  24  defines perforated tubing joint  26 . 
   Submersible pumping unit  30  is suspended on tubing  24  below perforated tubing joint  26 . Submersible pumping unit  30  is a submersible pumping unit having a motor  32  above a seal section  34 , which is above a pump  36 . In some embodiments (FIGS.  1  and  3 - 4 ), pump  36  defines pump intake  38  and pump outlet  40 . 
   It should be noted that like elements are assigned the same numerical designation in each figure. Further, it should be understood that although submersible pumping unit  30  is shown along with perforations  14 ,  16  and associated packing only in  FIG. 1 , submersible pumping units  30  in the embodiments of  FIGS. 2-4  are similarly deployed within casing  12 . 
   In another embodiment ( FIG. 2 ) submersible pumping unit  30  is suspended on tubing  24  below perforated tubing joint  26 . Submersible pumping unit  30  includes a submersible pumping unit having a motor  32  above a seal section  34 , which is above a recirculation pump  42 , which is located above a main pump  36 . Recirculation pump  42  defines a recirculation pump intake  44  that feeds recirculation pump  42  and main pump  36 . Main pump  36  defines pump outlet  40 . Recirculation pump  42  preferably produces a greater volume of fluid than main pump  36 . 
   In the embodiment of  FIG. 2 , recirculation tubing  50  is provided in communication with recirculation pump  42  for receiving output from recirculation pump  42  and for delivering a portion of fluid produced by recirculation pump  42  to a location adjacent to or above motor  32 . 
   Variations of the embodiment of  FIG. 2  are also possible. For example, main pump  36  and recirculation pump  42  may each have their own intake ports. Alternatively, recirculation pump  42  may be eliminated entirely and recirculation tubing  50  may tap into main pump  36  to deliver a portion of fluid produced by main pump  36  to a location adjacent to or above motor  32 . The various configurations are generally an inverted adaptation of the embodiments described in U.S. Pat. No. 5,845,709, which is incorporated herein by reference. 
   In another embodiment ( FIG. 3 ), a shroud  60  is provided for surrounding motor  32 , seal section  34  and pump intake  38  of submersible pumping unit  30 . Shroud  60  has an open upper end to allow fluid to enter shroud  60  for directing fluid past motor  32  and into pump intake  38 . 
   In the embodiment of  FIG. 1 , canister  70  surrounds submersible pumping unit  30  and perforated tubing joint  26 . Canister  70  defines canister perforations  72  above pump intake  38 . In the embodiment of  FIG. 4 , a secondary exterior canister  74  surrounds canister  70 . Secondary exterior canister  74  preferably does not enclose perforated tubing joint  26 . 
   In the embodiments of  FIGS. 2 and 3 , canister  70  surrounds the submersible pumping unit but preferably does not enclose perforated tubing joint  26 . 
   In the embodiment of  FIG. 1 , an upper interior packer or pack-off element  80  is provided. Upper interior packer  80  has an inside surface that engages submersible pumping unit  30  between motor  32  and pump  36 . Upper interior packer  80  also has an outside surface that engages canister  70  below canister perforation  72 . 
   Canister  70  further defines a downwardly extending canister extension flow-directing member  82  that extends into fluids  18  ( FIG. 1 ) below the oil/water interface for allowing uptake of water and delivery of water to pump intake  38  ( FIGS. 1 ,  3 ,  4 ) or recirculation pump intake  44  ( FIG. 2 ). 
   A lower packer  90  ( FIG. 1 ) is set in well casing  12  above production perforation  16  of well casing  12 . Lower packer  90  has an outside surface in contact with well casing  12  and has an inside surface in contact with canister extension flow-directing member  82 . Lower packer  90  defines an upper limit of production zone  92  and lower limit of disposal zone  94 . Disposal zone  94  is preferably a separate zone from that of production zone  92 . Although the invention is discussed primarily in the context of an injection zone located below a production zone, it should be understood that the invention may also be deployed in an environment wherein an injection zone is located above a production zone. 
   A central packer  100  is set in well casing  12  above disposal perforations  14  of well casing  12 . Central packer  100  has an outside surface in contact with well casing  12  and has an inside surface in contact with canister extension flow-directing member  82 . Central packer  100  defines an upper limit of disposal zone  94  and a lower limit of pumping zone  102 . In one embodiment, an upper packer  110  is set in well casing  12  above submersible pumping unit  30 . Upper packer  110  has an outside surface in contact with well casing  12  and has an inside surface in contact with tubing  24 . Packer  110  is desirable in instances where gas lift is utilized as a means of artificial lift. If gas lift is not required to lift the oil-rich mixture, then upper packer  110  is not strictly necessary. An oil transfer tube  120  ( FIG. 1 ) passes through central packer  100  and lower packer  90  for allowing oil to flow from production zone  92  to pumping zone  102 . 
   In the embodiments of  FIGS. 1 and 3 , an interior water intake passageway  130  is provided inside of canister extension flow-directing member  82  for communicating production zone  92  with an interior of canister  70  for passing water from production zone  92  to an inside canister  70  for subsequent intake by pump intake  38 . 
   In the embodiment of  FIG. 2 , interior water intake passageway  130  (shown in  FIG. 1 ) is located inside of canister extension flow-directing member  82  for communicating production zone  92  with an interior of canister  70  for passing water from production zone  92  to an inside of canister  70  for subsequent intake by recirculation pump intake  44 . 
   In the embodiment of  FIG. 4 , interior water intake passageway  130  is located inside of canister extension flow-directing member  82  for communicating production zone  92  with an interior of canister  70  for passing water from production zone  92  to an inside of secondary exterior canister  74 . Water inside of secondary exterior canister  74  passes through canister perforations  72  for subsequent flow past motor  32  and into pump intake  38 . 
   Referring now to  FIG. 1 , in one embodiment, a lower interior packer  140  is located in a canister extension flow-directing member  82  and has an outside surface in contact with canister extension flow-directing member  82  and an inside surface in contact with interior water intake passageway  130 . Lower interior packer  140  defines an upper limit of production zone  92  within canister extension flow-directing member  82  and a lower limit of disposal zone  94  in canister extension flow-directing member  82 . Lower interior packer  140  may not be required in all installations. An interior water output annulus  142  communicates pump outlet  40  with disposal zone  94  exterior to canister extension member  82 . Water is introduced into disposal zone  94  through extension outlets  143 . Interior water output annulus  142  is defined by interior water intake passageway  130  and canister extension flow-directing member  82 . 
   Still referring to  FIG. 1 , in one embodiment, a central interior packer  144  is provided inside of canister extension flow-directing member  82 . Central interior packer  144  has an outside surface in contact with canister extension flow-directing member  82  and has an inside surface in contact with interior water output annulus  142 . Central interior packer  144  defines an upper limit of disposal zone  94  within canister extension flow-directing member  82  and defines a lower limit of pumping unit  102  in canister extension flow-directing member  82 . Central interior packer  144  may not be required in all installations. 
   Gas lift valves  150  ( FIG. 1 ) are provided above upper packer  110  for selectively introducing high pressure gas into tubing string  24  to assist in bringing oil-rich mixture  20  to the surface. In wells that do not require additional artificial lift, gas lift valves  150  will not be required. 
   In use, submersible pumping unit  30  and canister  70  is lowered on tubing  24  into well casing  12  to a location above or proximate to disposal perforations  14  and production perforations  16 . Tubing  24  defines perforated tubing joint  26 . Pumping unit  30  is suspended on tubing  24  below perforated tubing joint  26 . Fluids  18  in well casing  12  migrate into well casing  16  through production perforations  16 . Under certain conditions fluids  18  tend to separate into an oil-rich layer  20  and a water layer  22 . The two layers  20 ,  22  define an oil/water interface  23 . 
   In each embodiment, and as shown in  FIG. 1 , lower packer  90  is set in casing  12  above production perforations  16  of well casing  12 . Lower packer  90  has an outside surface in contact with well casing  12  and an inside surface in contact with canister extension flow-directing member  82 . Lower packer  90  defines an upper limit of production zone  92  and a lower limit of disposal zone  90 . 
   Central packer  100  is set in casing  12  above disposal perforations  14  of well casing  12 . Central packer  100  has an outside surface in contact with well casing  12  and an inside surface in contact with canister extension flow-directing member  82 . Central packer  100  defines an upper limit of disposal zone  94  and a lower limit of pumping unit zone  102 . 
   In one embodiment, upper packer  110  is set in casing  12  above said pumping unit  30 . Upper packer  110  has an outside surface in contact with well casing  12  and has an inside surface in contact with tubing  24 . 
   Oil transfer tube  120  passes through central packer  100  and lower packer  90  for allowing oil-rich mixture  20  to flow from production zone  92  to pumping unit zone  102 . Oil-rich mixture  20  may then flow in an annulus defined by an outside of canister  70  ( FIGS. 1-3 ) or an outside of secondary exterior canister  74  ( FIG. 4 ) and an inside of well casing  12 . 
   In the embodiment of  FIG. 1 , oil-rich mixture  20  flows through canister perforations  72 , past motor  32 , and into perforated tubing joint  26 , where oil-rich mixture  20  may then flow through tubing  24  to the surface. Oil-rich mixture  20  cools motor  32  as it flows past motor  32 . In other embodiments ( FIGS. 2 ,  3 ,  4 ), oil-rich mixture  20  flows through oil transfer tube  120  ( FIG. 1 ), into an annulus defined by an outside surface of canister  70  ( FIGS. 2 ,  3 ) or an outside surface of secondary exterior canister  74  ( FIG. 4 ) and an inside surface of well casing  12 . The oil-rich mixture  20  then passes directly into perforated tubing joint  26 , where the oil-rich mixture  20  may then flow through tubing  24  to the surface under either natural flow or via artificial lift means. 
   In each embodiment, canister extension flow-directing member  82  extends downwardly and communicates with water  22 . Water  22  passes into canister extension flow-directing member  82 , inside of water intake passageway  130 , and into canister  70 . 
   In the embodiment of  FIG. 1 , water  22  passes through canister extension flow-directing member  82  and into canister  70  and is prevented from mixing with oil-rich mixture  20  by upper interior packer or pack-off element  80 . Water  22  then flows from lower portion of canister  70  into pump intake  38  of pump  36 . Pump  36  then directs water  22  out of pump outlet  40 , down through canister extension flow-directing member  82  and out extension member outlets  143  into production zone  94 , which is bound by central packer  100 , lower packer  90  and well casing  12 . Water  22  is then forced back into the underground formation through disposal perforations  14 . 
   In the embodiment of  FIG. 2 , water  22  enters canister  70  and passes into pump intake  44  of recirculation pump  42 . A first portion of water  22  is then injected into the disposal perforations  14 , as discussed above with respect to  FIG. 1 . A second portion of water  22  is directed upwards through recirculation tubing  50 , which forces water circulation within canister  70 , thereby providing cooling to motor  32 . 
   In the embodiment of  FIG. 3 , water  22  enters canister  70  and flows around an upper open end of shroud  60  and then downwardly past motor  32  before entering pump intake  38  of pump  36 . The flow of water  22  through the annulus defined by an outside of motor  32  and an inside of shroud  60  results in increased fluid flow velocity and improved cooling of motor  32 . Water  22  is then pumped out of pump outlet  40  and injected into the underground formation through disposal perforations  14 , as discussed above with respect to  FIG. 1 . Oil-rich mixture  20  flows upwardly outside of canister  70  and into tubing  24  through perforated tubing joint  26 , where the oil-rich mixture  20  may then flow to the surface. 
   In the embodiment of  FIG. 4 , water passes into secondary exterior canister  74  before entering canister  70  through canister perforations  72 . Water  22  then flows past motor  32  before entering pump intake  38  of pump  36 . The flow of water  22  through the annulus defined by an outside of motor  32  and an inside of canister  70  results in increased fluid flow velocity and improved cooling of motor  32 . Water  22  then exits pump outlet  40  and is injected into the underground formation through disposal perforations  14 , as discussed above with respect to  FIG. 1 . Oil-rich mixture  20  flows upwardly outside of secondary exterior canister  74  and into tubing  24  through perforated tubing joint  26  where oil-rich mixture  20  may flow to the surface via natural flow or artificial lift. 
   As discussed above, the invention allows an inverted submersible pumping unit  30  to be positioned above production perforations  16  in a manner that facilitates cooling of motor  32  with a flow of fluids directed adjacent motor  32 , e.g., oil-rich mixture  20  inside of canister  70  ( FIG. 1 ), recirculated water flow inside of canister  70  ( FIG. 2 ), water flow inside of shroud  60  inside of canister  70  ( FIG. 3 ), or water flow inside of canister  70  inside of secondary exterior canister  74 . In each of the embodiments, water is injected into the formation through disposal perforations  14  (shown in  FIG. 1 ). 
   In each of the embodiments, oil-rich mixture  20  flows to the surface through tubing  24 . Flow of oil-rich mixture  20  through tubing  24  may be selectively assisted with high pressure gas entering through gas lift valves  150  in a manner known in the art. 
   Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.

Technology Classification (CPC): 4