Abstract:
A viscosity handling system for facilitating the movement of certain fluids. The system utilizes kinetic energy in the form of a rapidly and repetitively moving component that imparts energy in the form of heat to surrounding fluid. The system is particularly useful in applications, such as downhole pumping systems, used to produce hydrocarbon-based fluids from beneath the surface of the earth. The viscosity handler lowers the viscosity of the fluid produced to permit greater flow rates and more efficient utilization of production pumps.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to movement of fluids, such as wellbore fluids, and particularly to a technique for lowering the viscosity of a fluid to permit more efficient production of the fluid.  
         BACKGROUND OF THE INVENTION  
         [0002]    When pumping viscous fluids, the performance of certain pumps, such as centrifugal pumps, is considerably degraded. For example, the pump head and rate of production are decreased while the horsepower requirement increases drastically. This leads to substantially reduced efficiency of the pump. In certain pumping applications, such as in the production of oil, this low efficiency can add considerably to the cost of oil production or even inhibit the ability to produce from the region.  
           [0003]    Attempts have been made to lower the fluid viscosity prior to pumping. For example, electric heaters have been used in combination with electric submersible pumping systems to heat the oil prior to being drawn into the submersible pump of the overall system. With electric heaters, however, electricity must be supplied downhole by, for example, a power cable. Other attempts to lower viscosity have included the injection of relatively hot vapor or the use of downhole combustion to generate heat. Each of these approaches can add undesirable cost and complexity depending on the particular environment and application.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates generally to a technique for lowering the viscosity of a fluid prior to pumping the fluid. The technique is particularly amenable for use in a downhole environment for the production of oil. The viscous fluid is passed through a viscosity handler prior to being drawn into the production pump which moves a desired fluid from one location to another. The viscosity handler utilizes a movable component that is rapidly and repetitively moved through the fluid. Part of this kinetic energy is translated to the surrounding oil in the form of heat. The heat, in turn, lowers the viscosity of the fluid to permit more efficient production of the fluid by the production pump. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:  
         [0006]    [0006]FIG. 1 is a front elevational view of an exemplary pumping system, according to one embodiment of the present invention;  
         [0007]    [0007]FIG. 2 is a front elevational view of an exemplary pumping system disposed within a wellbore;  
         [0008]    [0008]FIG. 3 is a front elevational view of an exemplary electric submersible pumping system that may be used to pump fluids within a wellbore;  
         [0009]    [0009]FIG. 4 is an enlarged view of the production pump and viscosity handler illustrated in FIG. 3;  
         [0010]    [0010]FIG. 5 is an enlarged cross-sectional view of a radial flow type impeller that may be utilized within the viscosity handler illustrated in FIG. 4;  
         [0011]    [0011]FIG. 6 is an enlarged cross-sectional view of a mixed flow type impeller that may be used with the production pump illustrated in FIG. 4; and  
         [0012]    [0012]FIG. 7 is a front elevational view of an alternate embodiment of the pumping system disposed in a wellbore.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0013]    Referring generally to FIG. 1, a system  10  for facilitating the movement of a viscous fluid is illustrated. Generally, system  10  comprises a production pump  12  that produces a fluid  14  from a reservoir  16  to a desired location, such as holding tank  18 . Production pump  12  draws fluid  14  along an intake pathway  20  and discharges the fluid along an outflow pathway  22  to tank  18 . A viscosity handler  24  is disposed upstream from production pump  12  and is utilized to lower the viscosity of fluid  14  prior to entering the production pump.  
         [0014]    Viscosity handler  24  is designed as an energy translator in which kinetic energy is transferred to fluid  14  in the form of heat. The heat energy lowers the viscosity of fluid  14  to promote better efficiency and greater production from production pump  12 . Viscosity handler  24  comprises a movable component  26  that rapidly and repetitively moves through fluid  14  as it flows through viscosity handler  24  to production pump  12 . For example, movable component  26  may be a rotatable component rotated through fluid  14 . In this example, the rotation of movable component  26  is the action that causes fluid  14  to rise in temperature, consequently lowering its viscosity.  
         [0015]    An exemplary application of system  10  is illustrated in FIG. 2. In this application, an electric submersible pumping system  28  utilizes production pump  12  and viscosity handler  24 . Typically, production pump  12  and viscosity handler  24  are powered by a submersible motor  30 . Also, a variety of other components may be utilized as part of electric submersible pumping system  28  as known to those of ordinary skill in the art.  
         [0016]    System  28  is designed for deployment in a well  32  within a geological formation  34  containing fluid  14 , typically a desirable production fluid such as petroleum. In this application, a wellbore  36  is drilled and lined with a wellbore casing  38 . Fluid passes through wellbore casing  38  into wellbore  36  through a plurality of openings  40 , often referred to as perforations. Then, the fluid is drawn into electric submersible pumping system  28 , the viscosity is lowered by viscosity handler  24 , and the lower viscosity fluid is discharged to a desired location, such as holding tank  18 .  
         [0017]    System  28  is deployed in wellbore  36  by a deployment system  42  that may have a variety of forms and configurations. For example, deployment system  42  may comprise tubing  44  through which fluid  14  is discharged as it flows from electric submersible pumping system  28  through a wellhead  46  to a desired location. Various flow control and pressure control devices  48  may be utilized along the flow path.  
         [0018]    A more detailed illustration of electric submersible pumping system  28  is provided in FIG. 3. In this embodiment, tubing  44  is coupled directly to production pump  12  by a connector  50 . Viscosity handler  24  is coupled to production pump  12  on an end opposite connector  50 . A fluid intake  52  is mounted to viscosity handler  24  at an upstream end to draw fluid  14  into viscosity handler  24  from wellbore  36 . Submersible motor  30  is mounted below fluid intake  52  and typically is coupled to a motor protector  54 . Furthermore, submersible motor  30  receives electrical power via a power cable  56 .  
         [0019]    In the example illustrated, submersible motor  30  is deployed between perforations  40  and fluid intake  52 . Thus, as fluid is drawn into wellbore  36  through perforations  40 , it passes submersible motor  30  to fluid intake  52 . Heat generated by motor  30  is used to begin lowering the viscosity of fluid  14  prior to entering viscosity handler  24 .  
         [0020]    Referring generally to FIG. 4, an exemplary combination of viscosity handler  24  and production pump  12  is illustrated. In this embodiment, production pump  12  is a centrifugal pump having a plurality of stages  58 . Each stage includes an impeller  60  and a diffuser  62 . The impellers  60  drive fluid upwardly through subsequent diffusers and impellers until the fluid is produced or discharged through connector  50  and tubing  44 .  
         [0021]    In this exemplary application, movable component  26  of viscosity handler  24  comprises a plurality of rotatable members  64 , such as impellers. The movable members  64  are separated by a plurality of diffusers  66  to form multiple stages  68 . Movable members  64  cooperate to translate substantial kinetic energy into heat energy within the fluid passing therethrough. The power for imparting kinetic energy to movable members  64  as well as for powering production pump  12  is provided by submersible motor  30  via a shaft or shaft sections  70  and  72  to which movable member  64  and impellers  60 , respectively, are mounted.  
         [0022]    With the particular design illustrated in FIG. 4, movable members  64  and diffusers  66  cooperate to allow fluid movement from intake  52  to production pump  12 . Members  64  may even be configured to facilitate movement of fluid through the viscosity handler. For example, viscosity handler  24  may be designed as a poor efficiency pump able to produce a temperature rise in the fluid and therefore a lower viscosity fluid for production by production pump  12 . In this manner, the use of a low efficiency device promotes higher efficiency of the overall system and allows an application engineer to select a production pump able to produce at a relatively high rate with great efficiency.  
         [0023]    In the embodiment illustrated, the impellers  60  of production pump  12  comprise mixed flow impellers, but may be radial flow impellers in certain lower flow applications. Mixed flow impellers are beneficial in many environments because of their ability to produce a relatively high flow rate with great efficiency. However, the fluid being produced must have sufficiently low viscosity or the performance curve of the production pump is greatly degraded and may render electric submersible pumping system  28  incapable of production. Accordingly, if impellers are utilized as rotating members in viscosity handler  24 , it is desirable to utilize low efficiency impellers, such as radial flow impellers. Exemplary embodiments of a radial flow impeller and a mixed flow impeller are illustrated in FIGS. 5 and 6, respectively.  
         [0024]    In the radial flow design, movable member/impeller  64  is rotationally affixed to shaft section  70  by, for instance, a key (not shown). The impeller comprises an impeller body  74  with a plurality of vanes  76  disposed generally between an upper wall  78  and a lower wall  80 . Walls  78  and  80  as well as vanes  76  define a plurality of flow chambers  82  disposed circumferentially around shaft segment  70 . A recirculation hole  77  extends through upper wall  78  and is helpful in heating the fluid. When impeller body  74  is rotated with shaft segment  70 , fluid is drawn into the flow chamber  82  through an inlet  84  and discharged radially through a radial outlet  86  into adjacent stationary diffuser  66 . The fluid then enters the upper diffuser vanes and is directed through subsequent stages before being drawn into production pump  12 . The inefficient, repetitive motion of members  64  through fluid  14  creates heat and lowers the viscosity of fluid  14 .  
         [0025]    In this example, impellers  60  of production pump  12  are mixed flow type impellers, as illustrated best in FIG. 6. A mixed flow impeller body  88  comprises a plurality of angled vanes  90  that are spaced circumferentially about shaft segment  72 . Each angled vane  90  defines a flow chamber  92 . As impeller body  88  is rotated with shaft segment  72 , each angled vane  90  draws fluid in through an inlet  94 , and the fluid flows through flow chambers  92  until it is discharged through an impeller outlet  96  to diffuser  62 . With mixed flow impellers, the fluid typically is drawn from a lower location through inlet  94  and moved upwardly and outwardly for discharge at a higher location. The fluid is pumped through consecutive impellers and diffusers as it moves through the plurality of stages  58  for discharge through connector  50  and tubing  44 . (See FIG. 4).  
         [0026]    Viscosity handler  24  may be deployed in a variety of environments and in combination with other components that are used in downhole applications or with electric submersible pumping systems. Additionally, component configurations can be designed to supplement the transfer of energy from the viscosity handler  24  to the fluid being produced by production pump  12 . As illustrated in FIG. 7, submersible motor  30  may be located above perforations  40  such that the fluid flows past submersible motor  30  before being drawn into viscosity handler  24 . The heat of the motor assists in lowering the viscosity of the fluid flowing past. Alternatively or in addition to this arrangement of submersible motor  30 , a supplemental heater  98  may be located within the wellbore, as illustrated in FIG. 7. An exemplary supplemental heater  98  is a resistive type heater powered via a power cable, such as power cable  56  or a separate power cable deployed downhole. Such a supplemental heater  98  may be positioned independently within wellbore  36  or it may be combined with electric submersible pumping system  28  to heat fluid as it flows past and external to the heater. Supplemental heater  98  also may be designed for deployment downstream of fluid intake  52 , such that fluid is drawn through the center of the heater prior to or after entering viscosity handler  24 .  
         [0027]    In addition to the components that may be used in combination with the viscosity handler, viscosity handler  24  may use various combinations of stages to facilitate and influence fluid movement through the system. In some environments, a better initiation of fluid movement may be achieved by combining different styles of stages, e.g. at least one mixed flow stage with a plurality of radial flow stages. For example, one combination incorporates mixed flow stages as the lower two stages (as illustrated in FIG. 4) with the remainder being radial flow stages. Using mixed flow stages proximate the viscosity handler intake facilitates initial movement of the fluid particularly when the fluid is fairly viscous. Once movement of fluid is initiated, the subsequent radial stages can continue the fluid flow while imparting heat energy to the fluid. Other variations in the order of the flow stages may be used to obtain differing fluid flow efficiencies.  
         [0028]    It will be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, the viscosity handler may be utilized in conjunction with a variety of pumps for producing fluid from one location to another; the system may be utilized in wellbore or other subterranean applications; and a variety of movable components can be used to impart energy in the form of heat to the fluid flowing through the viscosity hander. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.