Patent Publication Number: US-6666269-B1

Title: Method and apparatus for producing fluid from a well and for limiting accumulation of sediments in the well

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a submersible pump for producing fluid from well intersecting a producing formation, preferably a hydrocarbon-producing formation, and more particularly is directed to an apparatus for producing fluid from a well and for limiting the accumulation of sediment in wells in which the formation produces solids along with the production fluids. 
     It is well known that in producing oil and/or gas wells, the fluid in the well may be elevated to the surface by utilizing a pump installed in the well. One type of pump that is often utilized is an electric submersible pump. Electric submersible pumps may be used for a variety of reasons, such as for example in wells where artificial lift is required when formation intersected by the well does not provide the necessary lift to produce the fluid to the surface. 
     Electric submersible pumps, depending upon the application, are often deployed in wells with open rat holes. That is, the pumps are deployed in wells which have casing cemented in a wellbore to a certain depth and wherein the wellbore is drilled to a greater depth so that there is an uncased, or open rat hole below the casing. In some formations intersected by the well, the fluid produced therefrom will contain solids. The solids tend to get deposited in the rat hole, and over time the deposits, also referred to as sediment, can cause production problems such as reduced well productivity, and cause equipment problems, such as motor overheating. If the electric submersible pump system is deployed in the well below the perforations in the casing through which the formation fluid is communicated into the well, there may be insufficient flow of fluid around the motor in the electric submersible pumping system to cool the motor. 
     When an electric submersible pump is placed above the perforations, flowing well fluid will produce some motor cooling. When the system is placed below casing perforations, the motor in the electric submersible pumping system is generally not exposed to flowing well fluid. Thus, there is a need for a method and apparatus for limiting the accumulation of sediments in a rat hole and for providing cooling to a motor used in an electric submersible pumping system when the system is placed below perforations in a well. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for producing fluid from a well, for limiting the accumulation of sediments in the well, and for providing cooling to motors used in electric submersible pump systems when the system is placed below perforations in the well. The apparatus comprises an electric submersible pumping system lowered into a well on a production tubing. The electric submersible pumping system includes a submersible production pump, a seal section connected to a lower end of the pump, and a submersible motor connected to the seal section for driving the production pump. A production pump intake is positioned at or near the lower end of the production pump above the seal section. A submersible auxiliary pump is connected below the motor. The auxiliary pump has an auxiliary pump intake at or near a lower end thereof, and includes an auxiliary pump discharge positioned between the submersible motor and the auxiliary pump. The auxiliary pump discharge is designed such that the motor is effectively sealed from the auxiliary pump discharge to prevent fluid from the auxiliary pump from being pumped or discharged into the submersible motor. The auxiliary pump discharge has at least one and preferably has a plurality of discharge ports. 
     The production tubing preferably has a sufficient length so that the electric submersible pumping system is located in the well below the perforations that communicate the producing formation with the interior of the well. Fluid from the well will be drawn in through the auxiliary pump intake, will be pumped upwardly through the auxiliary pump discharge and then upwardly in the well above the submersible motor, which drives both the production pump and the auxiliary pump. In wells where the producing formation produces sediment along with the fluid, some of the sediment that will naturally flow downward in the well due to gravity will be drawn in through the auxiliary pump intake and will be pumped upwardly in the well along with the fluid pumped by the auxiliary pump. 
     The apparatus preferably includes at least one and preferably a plurality of discharge tubes or discharge tubings connected at a lower end to the auxiliary pump discharge. The discharge tubes extend upwardly in the well past the submersible motor. The tubes may extend upwardly past the production pump intake and may expel the fluid and sediments pumped upwardly therethrough into the interior of the well above the production pump intake. A portion of the fluid expelled from the discharge tubes along with a portion of the sediment will flow downwardly in the well. A portion of the fluid expelled from the discharge tubes along with a portion of the sediment will be taken in through the production pump intake and will, along with other fluid from the well, be produced upwardly by the production pump through the production tubing on which the system is lowered. In a separate embodiment, the upper ends of the discharge tubes may be communicated directly to the production pump intake so that all of the fluid and sediment taken in and pumped upwardly through the discharge tubes by the auxiliary pump will be received in the production pump intake and will be produced upwardly by the production pump through the production tubing. Because the auxiliary pump will pump sediments upwardly so that some sediment can be produced upwardly through the production tubing, the invention limits the accumulation of sediment in the well. 
     In addition to limiting the accumulation of sediment in the well the present invention provides a method and apparatus for cooling the submersible motor in an electric submersible pumping system when the system is placed below perforations in the well. The auxiliary pump of the present invention pumps fluid upwardly in the well which allows for downward flow of fluid in the well past the motor. The auxiliary pump preferably pumps fluid upwardly at a rate sufficient to create a downward flow in the well of preferably at least about 1 ft/second past the motor, so that the downward flow will provide efficient motor cooling. 
     It is therefore an object of this invention to provide a method for producing well fluid from a well in which the producing formation produces sediments along with fluid, and for limiting the accumulation of the sediments in the well. It is a further object of the invention to provide a method for producing fluid from a well in which the pumping system is located below the perforations and for cooling the motor utilized in the pumping system. 
    
    
     The foregoing and other objects, advantages and features of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows the apparatus of the present invention lowered into a well. 
     FIG. 2 shows a second embodiment of the apparatus of the present invention. 
     FIG. 3 shows an embodiment of a discharge head of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and more specifically FIG. 1, an apparatus  10  for producing fluid from a well  15  is shown and described. Apparatus  10  is shown lowered into a well  15  comprising a casing  20  cemented in a wellbore  25 . Casing  20  has a lower end  30 , and thus well  15  has an open or uncased rat hole  32  comprising the lower portion of wellbore  25 . Well  15  has a bottom  33 . Casing  20  defines a casing interior or well interior  34 . Production fluids are communicated into well interior  34  through perforations  36 , which communicate the interior  34  with producing formation  38 . Lower end  30  could be positioned above perforations  32 , or could extend below the cement. In the embodiment shown, lower end  30  is below perforations  36 . Casing  20  and apparatus  10  define an annulus  40  therebetween. 
     Apparatus  10  is shown lowered into well  15  on a production tubing  42 . Apparatus  10  includes an electric submersible pumping system  44  having an auxiliary pump  46  connected to a lower end thereof. 
     Electric submersible pumping system  44  includes an electric submersible pump  48  having upper end  50  connected to production tubing  42  and having a lower end  52 . An intake  54 , having intake ports  55 , is connected to the lower end  52  of electric submersible pump  48 , which may also be referred to as production pump  48 . Intake  54  has upper end  56  and lower end  58 . Production pump intake  54  may be connected to or may be integrally formed with production pump  48 . A motor  60  for driving production pump  48  is connected in electric submersible pumping system  44  below intake  54 . Motor  60  is connected to a power source (not shown) with power cable  61 . The motor  60  has an upper end  62  and a lower end, or motor base  64 . A seal section  66  is connected between motor  60  and intake  54 . Seal section  66  is connected at its upper end  68  to intake  54  and at its lower end  70  to motor  60 . Motor  60  is thus connected to the lower end of pump  48  with seal section  66  and intake  54 . Production pump  48 , intake  54 , motor  60  and seal section  66  are all known in the art. 
     Auxiliary pump  46  is connected at its upper end  71  to the lower end  64  of motor  60  with an auxiliary pump discharge  72 , which may be referred to as a pump discharge head  72 . Auxiliary pump  46  can be a standard electric submersible pump connected to the lower end  64  of motor  60  at auxiliary pump discharge  72 , so that auxiliary pump  46  pumps in the same direction as production pump  48 . The arrangement can be reversed if desired. Auxiliary pump discharge  72  has upper end  74  connected to motor  60  and lower end  76  connected at upper end  71  of auxiliary pump  46 . Auxiliary pump discharge  72  incorporates a high pressure mechanical seal which connects to motor base  64 . Auxiliary pump  46  has an auxiliary pump intake  78  comprising a plurality of intake ports  80  connected to the lower end  81  thereof. Pump intake  78  may be integrally formed with or it may be connected to auxiliary pump  46  in any manner known in the art. 
     Apparatus  10  includes at least one, and in the embodiment shown includes two, discharge tubings  82 . Discharge tubings  82  have a lower end  84  and an upper end  86 . Lower end  84  is connected with auxiliary pump discharge  72  at discharge ports  85 . Discharge tubing  82  extends upwardly therefrom and terminates at upper end  86  above seal  66 . In the embodiment shown in FIG. 1, upper end  86  is positioned above intake ports  55  in intake  54 . FIG. 2 shows an embodiment of the present invention in which upper ends  86  are connected directly to intake  54 . 
     An embodiment of an auxiliary pump discharge  72  is shown in FIG.  3 . Auxiliary pump discharge  72  may comprise an upper portion  90  threadably connected to a lower portion  92 . A shaft portion  94  extends through both upper portions  90  and  92  and as understood in the art will be connected to a shaft that extends upwardly into and through motor  60  to drive electric submersible pump  48  and will also extend downwardly into and will drive auxiliary pump  46 . A spider bearing  96  supports shaft portion  94  and, as known in the art, will allow fluid flow upwardly through discharge head  72 . Shaft portion  94  is sealingly disposed in upper portion  90  with a high pressure seal  98 . As set forth previously, auxiliary pump discharge  72  is connected at its upper end  74 , which is defined on upper portion  90  to motor  60 . Auxiliary pump discharge  72  is connected at its lower end  76  to auxiliary pump  46 . 
     The operation of apparatus  10  is as follows. Apparatus  10  is lowered into the well is on a production tubing  42  until it is positioned below perforations  36 . Fluid from formation  38  is communicated into well interior through perforations  36 . Sediment in fluids from formation  38  may also be communicated into well interior  34  through perforations  36 . Once apparatus  10  is in place, motor  60  is actuated. Motor  60  drives production pump  48  and also drives auxiliary pump  46 . Once motor  60  is actuated to drive pumps  48  and  46 , production pump  48  will draw fluid from interior  34  through intake  54 . Auxiliary pump  46  will draw fluid from interior  34  through ports  80  in intake  78 . Fluid drawn in through intake  78  is discharged through discharge ports  85  in auxiliary pump discharge  72  into discharge tubings  82  through the lower ends  84  thereof. 
     In the embodiment shown in FIG. 1, well fluid from auxiliary pump  46  is discharged out the upper ends  86  of discharge tubings  82 . A portion of the well fluid expelled from discharge tubing  82  will be drawn in through intake  54  and will, along with other well fluid drawn in through intake  54 , be produced up production tubing  42  with production pump  48 . A portion of the fluid expelled from the upper end  86  of tubings  82  will, due to gravity, flow downwardly in the well, some of which will again be taken in through intake  78  along with other fluid in the well. Production pump  48  will produce additional fluid from the well through intake  54  and production tubing  42 , along with the fluid and any sediment pumped upwardly by auxiliary pump  46 . 
     In wells where sediments are produced with fluid from the producing formation, the fluid drawn into auxiliary pump  46  will contain some sediments and will thus keep the sediments from falling to the bottom of the rat hole. Fluid that enters the auxiliary pump, along with the sediments therein, will be pressurized and produced through the discharge tubing  82 . In the embodiment shown in FIG. 1, a portion of that fluid including some of the sediment therein, will be drawn in through intake  54  and produced up the production tubing  42 . In the embodiment shown in FIG. 2, all of the fluid and all of the sediment taken in through intake  78  is communicated through discharge tubings  82  directly into intake  54 , so that all of the fluid and sediment drawn in through intake  78  will be produced upwardly by production pump  48  through tubing  42 . 
     In addition to limiting the amount of sediment that will collect at the bottom of the rat hole, the present design provides for motor cooling in electric submersible pumping systems positioned below perforations. The system may be designed such that pump  46  draws fluid into intake  78  at a rate such that downward flow of the fluid in the well is at a sufficient velocity, preferably at least about 1 ft/second, past the motor. In the embodiment shown in FIG. 2, the auxiliary pump may also act as a charge pump since the fluid therein will have little or no free gas and is communicated directly into intake  54  and thus will reduce the gas fraction feed into the production pump that might otherwise cause gas locking in wells having a high amount of gas. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown in the drawings and have been described in detail by way of example only. It is understood that the invention is not intended to be limited by the particular forms or embodiments disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.