Abstract:
An electrical submersible well pump assembly has upper and lower motors that are filled with oil. During installation in a well, the upper motor lowers into engagement with the lower motor. The drive shafts of the motors have splined ends that engage each other within a central cavity. A vent port leads from the central cavity to the exterior for venting any trapped air located within the central cavity.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to electrical submersible well pumps and in particular to a vent port at the interconnect between upper and lower subs for venting trapped air.  
       BACKGROUND OF THE INVENTION  
       [0002]     Electrical submersible pumps (“ESP”) of the type concerned herein are used for pumping high volumes of well fluid. The pump of this type has at least one electrical motor that normally is a three-phase, AC motor. The motor drives a centrifugal pump containing a large number of stages, each stage comprising an impeller and a diffuser. The motor is filled with a dielectric lubricant or oil. A seal section connects between the pump and the motor for equalizing the pressure of the lubricant contained within the motor with the hydrostatic pressure on the exterior. The seal section is filled with oil that communicates with the oil in the motor. Two or more electrical motors may be connected in tandem to drive large pumps. The connecting adapter between the motors preferably has communication passages so that the oil in each motor communicates with oil in the other motor or motors.  
         [0003]     Techniques are employed to reduce any air pockets that may be trapped within the motor or seal seation, because air within the oil is detrimental. For convenience, the motor and seal section are referred to at times herein as subs of an ESP assembly. Normally the subs are filled with oil at a manufacturer&#39;s facility, then caps are secured to the ends to retain the oil. During filling, the sub is inclined and a vacuum hose connected to a port at the head of the sub. An oil injection hose is connected to a fill port on the base of the sub. After evacuation, the operator pumps oil into the sub, then secures sealing caps to the ends.  
         [0004]     When at the wellsite, normally a workover rig with a derrick will be present for running the ESP on the lower end of a string of production tubing. The operator picks up the motor and suspends it vertically over the wellbore. The operator removes the cap from the seal section and lowers it onto the head of the motor. During this process some oil will usually leak out from the seal section. The drive shaft in the seal section has a lower splined end that is located within a cavity in the base of the seal section. The upper end of the cavity is closed by a shaft bushing which restricts oil from flowing down the central cavity. Once the shipping cap is removed, the lower end is open because it must receive the upper end of the drive shaft of the motor. This downward facing cavity traps air when the motor and seal section are connected together.  
         [0005]     After the connection is made up, the operator tops up the oil in the seal section by pumping oil up through an upper port in the motor. Air, including the trapped air in the cavity, is vented through a port at the top of the lower chamber of the seal section.  
         [0006]     Removing trapped air is more difficult for the interconnection between tandem motors because the components within the upper motor tend to restrict upward air migration during operation. The interconnection between tandem motors is quite similar to the interconnection between the motor and the seal section. Some upper tandem motors may have a check valve to restrict downward flow of oil after the shipping cap is removed and before make-up, however, the trapped air pocket will still exist.  
         [0007]     In some instances, the operator may connect a vacuum pump to an upper port in the upper tandem motor when topping up the oil after make up of the upper tandem motor to the lower tandem motor. While this wellsite vacuum filling procedure may reduce or eliminate trapped air pockets at the interconnection, it takes more time to use the vacuum to top up oil than simply pumping oil in a lower port and venting at an upper port. The additional time is costly because of the cost of the workover rig. Also, vacuum filling of tandem motors at the wellsite is difficult to accomplish in cold climates.  
       SUMMARY OF THE INVENTION  
       [0008]     In this invention, a vent port is provided from the central cavity in the base of the upper sub to the exterior. The operator may use conventional techniques for initially filling the subs with oil. Preferably, the subs are filled by vacuum filling at the manufacturer&#39;s facility, then capped. At the wellsite, the operator suspends the upper sub above the lower sub, opens the vent port and removes the caps. At least some of any oil in the central cavity surrounding the drive shaft of the upper sub will drain out as the upper sub is lowered onto the lower sub, resulting in the entry of air into the central cavity.  
         [0009]     The air within the central cavity is displaced out the vent port once the subs engage each other. The oil in the upper sub flows up into the central cavity, pushing the oil out the vent port. When oil begins the flow out the vent port, the operator closes the vent port. The operator then tops up the oil in the upper sub by pumping oil into an upper port of the lower sub until oil begins to flow out the upper port of the upper sub.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a vertical sectional view illustrating an interconnecting portion in accordance with this invention between two tandem motors of an the electrical submersible pump assembly.  
         [0011]      FIGS. 2A-2C  comprise upper, intermediate and lower sectional views of portions of the tandem motor illustrated in  FIG. 1 .  
         [0012]      FIG. 3  is a transverse sectional view of the interconnecting assembly of  FIG. 1 , taken along the line  3 - 3  of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Referring to  FIGS. 2A and 2B , an upper motor  11  with a head  13  and a base  15  is shown. Head  13  and base  15  are secured to opposite ends of a cylindrical tubular housing  17 . A stator or motor winding  19  is located within the housing  17 . An upper drive shaft  21  extends through stator  19 , drive shaft  21  being driven by a rotor  23  located within stator  19 . In this embodiment, upper motor  11  is a three-phase motor, and three electrical conductors  25  (only one shown) extend from head  13  to stator  19 . Housing  17  is filled with dielectric lubricant or oil and preferably has an upper port  27  located within head  13 . Head  13  secures to a seal section (not shown), which is a sub filled with oil and which has means for equalizing the pressure of the oil in upper motor  11  with the hydrostatic pressure on the exterior.  
         [0014]     Base  15  of upper motor  11  is illustrated in more detail in  FIG. 1 . Base  15  has an upper annular flange  29  that is secured by fasteners  31  to housing  17 . Base  15  has an upper shoulder  33  that extends into housing  17  of stator  19  ( FIG. 1 ). Base  15  has an a lower face  35  and a central cavity  37  that extends upward from lower face  35 . Central cavity  37  is a cylindrical counterbore within base  15  with an open lower end at lower face  35 . A bushing  39  radially supporting upper drive shaft  21  defines the upper end of central cavity  37 . Upper drive shaft  21  has a lower end  41  that contains a plurality of splines. Splined lower end  41  is located within central cavity  37 .  
         [0015]     Referring also to  FIG. 3 , a communication passage  43  extends from upper shoulder  33  to lower face  35  ( FIG. 1 ). Communication passage  43  is a drilled hole in this embodiment that is offset from central cavity  37  and parallel to the axis of upper drive shaft  21 . Base  15  also has three conductor passages  45  ( FIG. 3 ), each containing one of the electrical conductors  25 . The insulation on each conductor  25  forms a seal with conductor passage  45 .  
         [0016]     Referring again to  FIG. 1 , a vent port  47  extends from central cavity  37  to the exterior of base  15 . Vent port  47  is located just below bushing  39 , which defines the upper end of central cavity  37 . A vent port plug  49 , which may be of a variety of types, is used to close and open vent port  47 . Vent port  47  does not intersect communication passage  43 .  
         [0017]     The interior of upper motor  11  is filled with lubricant and a means optionally may be provided to prevent lubricant from flowing out communication passage  43  after the shipping cap (not shown) of upper motor  11  is removed. In this embodiment, this means is provided by a check valve  51 , but it could alternately comprise a rupturable disk. Check valve  51  has a valve element  53  that is movable within communication passage  43 . When seated against a seat  55  at the lower end of communication passage  43 , valve element  53  will block downward flow of oil. Valve element  53  has a valve stem  57  that extends downward. A coil spring  59  urges valve element  53  downward.  
         [0018]     A lower motor  61  has a head  63  on its upper end with a flange  66  that connects to a flange  65  of base  15 . The terms “upper” and “lower” are not used in a limiting manner because lower motor  61  could actually be an intermediate motor, with another motor secured below. Flange  65  is an annular member that extends radially outward from base  15 , and flange  66  is an annular member that protrudes upward from an upper face  73  of head  63 . Flanges  65  and  66  are connected to each other by conventional fasteners. Base  15  has an annular lip portion with seals that extends into the inner diameter of flange  66  in this embodiment.  
         [0019]     A lower drive shaft  67  is rotatably carried within lower motor  61 . Lower drive shaft  67  has an upper splined end that interconnects with splined end  41  by means of a coupling or sleeve  69 . Drive sleeve  69  has internal splines and is preferably carried on lower drive shaft  67  and supported by coil spring  71 . Different types of couplings may be employed, including ones that enable tension to be transferred from upper shaft  21  to lower shaft  67 .  
         [0020]     Upper face  73  of lower head  63  is spaced below lower face  35  of upper base  15  after make-up. Check valve stem  66  contacts upper face  73  when base  15  engages head  63 . A communication passage  75  extends from upper end  73  downward through head  63 . Communication passage  75  is located within a different sectional plane from communication passage  43  in this embodiment. Offsetting communication passages  43  and  75  enables stem  57  to contact a portion of upper face  73  of lower head  63  to open check valve  51 .  
         [0021]     Referring now to  FIG. 2B , lower motor  61  has an upper port  77  that intersects lower communication passage  75  and extends from the exterior. A conventional plug  78  is employed to close port  77 . In this embodiment, a thrust bearing  79  is located within an upper portion of lower motor  61  below head  63 . Lower motor  61  has a base  81 , shown in  FIG. 2C . Lower motor base  81  could be a simple blind plug, but in this embodiment, it is used to connect to a sub (not shown) that contains instrumentation for measuring pressure and temperature. Lower motor base  81  may have a lower port  83 .  
         [0022]     In operation, the operator may initially fill upper motor  11  and lower motor  61  with oil in a conventional manner. Motors  11 ,  61  are preferably filled at the manufacturer&#39;s facility detached from each other, then shipped to the wellsite with caps on the upper and lower ends to retain the oil therein. Normally, the filling is performed on upper motor  11  by inclining it and drawing a vacuum through upper port  27 . Then the operator pumps oil in from a port (not shown) at the lower end. The lower port could be located within the shipping cap (not shown) or it could be a port extending through upper motor base  15  to communication passage  43 . Lower motor  61  is preferably vacuum filled in the same manner by drawing a vacuum through lower motor upper port  78  ( FIG. 2B ) and pumping oil through lower port  83  ( FIG. 2C ).  
         [0023]     At the wellsite, the operator removes the shipping cap from lower motor  61  and suspends it vertically above the well, such as by a workover rig. The oil previously filled in lower motor  61  may extend completely to the upper edge of flange  66  of lower motor head  63 .  
         [0024]     The operator then opens upper port  27 , picks up upper motor  11  with the rig and suspends it vertically above lower motor  61 . Lower flange  65  will initially be spaced a short distance above upper motor head  63 . The operator will open vent port  47  in upper motor  11 . The operator removes the cap secured to upper motor base  15 , which causes any oil in central cavity  37  to leak out. Check valve  51  will remain closed due to the force of spring  59  ( FIG. 1 ), blocking any flow downward through communication passage  43 .  
         [0025]     The operator then lowers upper motor  11  downward until base  15  inserts into lower head  63  as shown in  FIG. 1 . The operator secures the fasteners to flanges  65  and  66 . When base  15  inserts into the counterbore of lower head  63 , check valve  57  opens, communicating the oil in the interior of upper motor  11  with lower motor  61 . Some of the oil will initially flow downward through communication passage  43  and back upward into central cavity  37 . The air trapped in central cavity  37  is displaced by the oil flowing into central cavity  37  and is dispelled out through open vent port  47 . Once oil begins to flow out vent port  47 , the operator replaces plug  49 .  
         [0026]     The operator may then top up the oil within upper motor  11  in a conventional manner. Preferably, this procedure is done by pumping oil into lower head port  78  ( FIG. 2B ) until oil begins to flow out upper motor upper port  27  ( FIG. 2A ). The operator lowers the connected motors  11 ,  61  and places a plug in upper port  27 .  
         [0027]     The operator then will connect the seal section (not shown) to upper motor  11 . This may be done conventionally, or the base (not shown) of the seal section may have a vent port similar to vent port  47  ( FIG. 1 ). If so, the same procedure as described above could be followed. A pump (not shown) will be connected to the seal section in a conventional manner.  
         [0028]     The invention has significant advantages. The inclusion of a vent port for the shaft central cavity in the base allows the trapped air therein to be easily displaced. This procedure may obviate vacuum filling of tandem motors at the wellsite after they are connected together. Avoiding vacuum filling of tandem motors at the wellsite saves rig time and avoids difficulties occurring in cold climates.  
         [0029]     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.