Abstract:
A method and system for downhole treatment and pumping of well fluids enhances the pumping of viscous fluids to the surface. The first step is to separate the oil and water from the well fluid and then channel the oil to a chamber that encloses the motor. The heat from the motor will increase the heat of the crude oil flowing past the motor, thereby lowering the viscosity of the crude oil. The water flows separately past the motor in another passageway, and remixes with the oil. After the oil and water recombine, the treated well fluid has a lower viscosity, and the fluid is then pumped to the surface more efficiently than without treating the oil.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to electrically driven centrifugal submersible well pumps, and in particular to an oil and water separator for separating oil from the well fluid prior to reaching the pump for the purpose of selectively directing oil or water flow into intimate contact with the electric motor.  
           [0003]    2. Description of the Related Art  
           [0004]    The application of ESPs to viscous crude has been increasing in recent years. Today ESPs are applied to heavy crude production where pumping viscosities can exceed 1000 centipoise. At these viscosities, there are considerable losses associated with ingesting viscous crude within the pump and additional losses experienced in discharge head and efficiency of the pump due to the viscosity. These losses limit the flow rate, therefore limiting the amount of crude produced. These losses also cause severe reduction in the head/stage ratio, thereby requiring a significantly larger pump. Furthermore, the losses cause an increase in the horsepower required to produce the crude, resulting in larger equipment and significant increases in power costs.  
           [0005]    A different problem arises in situations where the well fluid entering the well machinery in the well assembly has high temperatures. In this situation, the motor powering the pump experiences temperature problems because the high temperature well fluid passing the motor will not collect the heat from the motor. Therefore, the motor has no way to transfer its heat to the well fluid passing by the motor.  
         SUMMARY OF THE INVENTION  
         [0006]    The system for treating and pumping well fluids of this invention has a downhole motor connected to and below the pump. A shroud encloses a substantial portion of the motor. A separator below the shroud separates the oil and liquid from the well fluid. One of the oil outlets of the separator communicates with the interior of the shroud and the outlet discharges to the exterior of the shroud. The liquid oil and water recombine before entering the pump.  
           [0007]    The shroud prevents the separated oil and water from mixing. In one embodiment, openings in the shroud above the motor allow the water to enter inside the shroud and recombine with the oil before entering the pump. The oil flowing past the motor has a lower thermal conductivity than the water on the exterior of the shroud. The heat generated by the motor lowers the viscosity of the oil.  
           [0008]    The separator may be a hydroclone having a conical separation chamber that uses gravity and centrifugal forces to separate the water and oil from the well fluid. Alternatively, the separator may also be a centrifugal separator, having at least one impeller blade and at least one vane, the blades and vanes shearing through the fluid to create centrifugal forces which separate the water from the oil.  
           [0009]    Another embodiment is used in the situation where the temperature of the well fluid entering the well prevents the transfer of heat from the motor to the well fluid. In this embodiment, the separator directs the oil to the outside of the shroud and the water to the inside of the shroud. The water from the well fluid is more receptive to receiving the heat from the motor than oil because of a higher thermal conductivity. Therefore, the water in intimate contact with the motor cools the motor while the water flows passes by the motor.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIGS. 1A and 1B comprise a cross-sectional view of a fluid treatment system constructed in accordance with this invention and in which the separator is a hydrocyclone separator.  
         [0011]    [0011]FIGS. 2A and 2B comprise a partial cross-sectional view of an alternative embodiment of a fluid treatment system constructed in accordance with the present invention, in which the separator is a centrifugal separator.  
         [0012]    [0012]FIG. 3 is a schematic cross sectional view of the separator of FIG. 2B.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    [0013]FIG. 1A and 1B shows a completed well a downhole fluid treating and pumping system  15  lowered down the casing  17  to above the perforation  19  in the well. The well produces a mixture of viscous oil and water. Generally the viscosity at well formation temperatures will be 500 centipoise or greater. Fluid treating and pumping system  15  has a separator  21  for separating a major portion of the water from the viscous crude. Separator  21  has fluid inlets  23 , water outlets  25 , and oil outlets  27  at its top.  
         [0014]    In the first embodiment, separator  21  is a hydrocyclone separator  21 . In this embodiment, inlets  23  are located tangentially around the circumference of the upper portion of separator  21 . The hydrocyclone separator  21  has a tapered tube  22  below inlets  23 . Liquids enter through tangential inlets  23 . This creates a high velocity swirling action and sets up strong centrifugal forces which cause the denser liquid (water) to form at the outer edge, while the less dense liquids (oil and hydrocarbons) migrate to form a core at the center. These centrifugal forces, combined with differential pressures set up across the hydrocyclone, allow the heavier water to exit at the underflow through water outlets  25 , while the lighter less dense phase falls into reverse flow and exits at the opposite end as the overflow through oil outlets  27 .  
         [0015]    A shroud is sealingly connected to separator  21  above water outlets  25  and below oil outlets  27 . Shroud  31  circumferentially encloses a motor  33 , a seal section  35 , and the inlets  37  to a pump  39 . Motor  33  powers pump  39 , which pumps the well fluids to the surface.  
         [0016]    Oil outlets  27  of separator  21  are located within shroud  31  for discharging separated oil into an annular space surrounding motor  33 . Conduits  42  lead from water outlet  25  to an annular space surrounding shroud  31 . Shroud  31  keeps the water that has been separated from the crude oil in the well fluid from mixing with the oil from the separator while the two fluids travel past motor  33  up the well. Ports  43  are located in the upper end of shroud  31  for causing separated water to enter shroud  31  above motor  33 . A centralizer  41  may be positioned on the lower end of shroud  31 . Centralizer  41  positions fluid treating and pumping system  15  in the center of the well.  
         [0017]    In operation, assembly  15  is lowered down the well on a string of tubing after the well has been completed to a depth just above perforations  19 . Oil, gas, and water flow through perforations  19  into the well casing, and flow into separator inlets  23 . Separator  21  separates the water and oil and delivers the oil into shroud  31 . The oil traverses along the annulus between motor  33  and shroud  31 . The oil is heated due to its intimate contact with the lotor which reduces its viscosity while at the same time cooling motor  33 , keeping it from overheating. The less viscous oil continues to traverse along the annulus inside shroud  31  past seal section  35 . As the oil passes seal section  35 , water that has been traveling in the annular bypass passage along the outside of shroud  31  enters shroud  31  through shroud inlets  43 . The water mixes with the conditioned oil and then the recombined oil and water enter pump  39  through pump inlets  37 , to be pumped up to tree assembly  11  on surface  13 .  
         [0018]    [0018]FIGS. 2A and 2B show another embodiment, in which separator  45  is a centrifugal separator having a series of blades  47  and vanes  49  as illustrated schematically in FIG. 3. Motor  33  is connected to and rotates a separator shaft  21 , to which blades  47 , and vanes  49  are mounted. Separator  45  has well fluid inlets on its lower potion that allow the well fluid to flow into the separator for separation. The rotation of blades  47  applies pressure to the well fluid, causing the well fluid to travel up the separator towards vanes  49 . Vanes  49  impart a swirling motion to the well fluid, causing separation between the heavier and lighter liquids. Water, being the heavier liquid, flows to the outer side of lip  54 . Oil, being the lighter liquid, flows to the inside of lip  54 . The outside of lip  54  leads to water outlets  53 . The inside of lip  54  leads to an optional blending region of separator  45  where blades  57  are mounted on separator shaft  21 . Blades  57  increases the velocity of the separated oil when they are rotated. Blades  57  discharge the separated oil into a passageway that leads to oil outlets  55 , which releases the oil into the annular passage between shroud  31  and motor  33 .  
         [0019]    The well fluid enters separator  45  through inlets  51 , which in this embodiment are located on the lower portion of separator  45 . The blades  47  and vanes  49  of separator  45  shear through the viscous crude, thereby creating centrifugal forces on the well fluid as it passes through centrifugal separator  45 . The geometry of the path the fluid traverses through the blades  47  and vanes  49  also generates centrifugal forces that are exerted on the fluid as it passes through centrifugal separator  45 . The centrifugal forces experienced by the fluids force the heavier water particles to the outer edge of the interior of separator  45  and the lighter crude oil and hydrocarbons to the center of separator  45 . The water that has been forced to the far edge of separator  45  will exit separator  45  via water outlets  53  after traversing through the blades and vanes of separator  45 . Water outlets  53  in this embodiment are located in the upper portion of separator  45 , but below the point in which shroud  31  sealingly connects to separator  45 . The lighter oil and hydrocarbons remaining in the center of separator  45  do not exit through water outlets  53 , but rather are blended by the high speed rotating blades  57 . The high speed rotating blades  57  impart a high rate of fluid shear which can improve the flow properties of fluids like crude oil by increasing the oil&#39;s velocity. Increasing the oil&#39;s velocity helps to reduce the viscosity of the oil. The blended crude then communicates to separator oil outlets  55  above the point where shroud  31  sealingly connects to separator  45 . The blended oil enters the annulus between motor  33  and shroud  31 . Once the blended oil enters the annulus inside shroud  31 , the oil undergoes the same conditioning process as described above in the first embodiment.  
         [0020]    The present invention enhances pumping viscous well fluid by reducing the viscosity of crude oil. The oil heats to a higher temperature when separated than it would if mixed with water. Even when recombined with water, the oil will be less viscous because of its higher temperature. Lowering the viscosity of the fluid being pumped to the surface increases the pump efficiency. A better pump efficiency results in greater flow rates, which leads to increases in oil production. Better efficiency also leads to a reduction in the head to stage ratio, which means for the same amount of fluid delivered to the surface, a smaller pump requiring less horsepower can be used. Lower horsepower requirements means that a smaller motor is needed to drive the pump. All of these results lead to less cost per unit produced.  
         [0021]    The embodiment of FIGS. 2A and 2B may be alternately configured so that the water forced to the outer edge of the interior of separator  45  is routed into the annular passage between motor  33  and shroud  31 , while the oil exits separator  45  below the point at which shroud  31  sealingly connects to separator  45 . The oil traverses along the outside of shroud  31  and then enters shroud  31  through shroud inlets  43 . The water traverses along the annulus between motor  33  and shroud  31 . The heat from motor  33  is transferred to the water passing by motor  33  in intimate contact with motor  33 , therefore cooling motor  33 . The water continues to flow up the annular passage inside shroud  31  past seal section  35  and then mixes with the oil entering shroud  31  through shroud inlets  43 . The mixed oil and water enter pump  39  through pump inlets  37  to be pumped up to tree assembly  11  on surface  13 . Delivering the separated water into shroud  31  could also be done with the embodiment of FIGS. 1A and 1B  
         [0022]    Further, it will also be apparent to those skilled in the art that modifications, changes and substitutions maybe made to the invention in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in he manner consisting with the spirit and scope of the invention herein. For example, the upper end of the shroud could have an opening to discharge oil and be located below the pump inlet. There would be no need for the water to enter the shroud as it would recombine with the oil above the shroud at the pump intake.