Abstract:
A gas separator having an improved flowpath for lighter fluids having a higher concentration of gas decreases total pumping head for an ESP assembly. The ESP assembly includes a rotary primary pump, a motor coupled to the primary pump for driving the pump, a seal assembly between the primary pump and the motor, and a gas separator between the seal assembly and the primary pump. An outlet of the gas separator feeds an intake of the primary pump, and a rotating shaft operationally couples the primary pump to the motor and passes through the seal assembly and the gas separator. The gas separator contains a venting portion, and a diverter positioned within the venting portion having diverter guide vanes formed in a flowpath of the lighter fluid for aiding in a directional change of fluid momentum. A slinger is positioned within the diverter for impelling fluid through the venting port.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates in general to electric submersible pumps (ESPs) and, in particular, to a gas separator with improved flow path efficiency. 
         [0003]    2. Brief Description of Related Art 
         [0004]    Electric submersible pump (ESP) assemblies are disposed within wellbores and operate immersed in wellbore fluids. The ESP assemblies generally include a pump portion and a motor portion. Generally, the motor portion is downhole from the pump portion, and a rotatable shaft connects the motor and the pump. The rotatable shaft may be one or more shafts operationally coupled together. The motor rotates the shaft that, in turn, rotates components within the pump to lift fluid through a production tubing string to the surface. The ESP assembly may also include one or more seal sections coupled to the shaft between the motor and pump. In some embodiments, the seal section connects the motor shaft to the pump intake shaft. The seal section provides an area for the expansion of the ESP motor oil volume, equalizes the internal unit pressure with the wellbore annulus pressures, isolates the clean motor oil from wellbore fluids to prevent contamination, and supports the pump shaft thrust load. 
         [0005]    In some embodiments, the ESP assembly includes a gas separator positioned between the seal section and the pump section. ESPs are designed to handle liquid and will suffer from head degradation and gas locking in the presence of a high percentage of free gas. The gas separator is installed at the intake of the pump section, between the seal section and the pump section. Wellbore fluid enters the gas separator and passes through the gas separator into the pump intake. The wellbore fluid is rotated within the separator, centrifugally separating heavier wellbore fluid from lighter wellbore fluid. Generally, heavier wellbore fluid corresponds with fluid that has a lower gas content, and lighter wellbore fluid corresponds with fluid having a higher gas content. The gas separator then directs the heavier wellbore fluid to the pump section intake and the lighter wellbore fluid back into the annulus of the casing. The flowpath of the lighter fluid generally must make a sharp right-angle turn to exit the gas separator and flow back into the casing annulus. The sharp right angle turn causes an increase in the fluid pressure where the lighter wellbore fluid must make a rapid change in momentum to exit, the separator. This coincides with a change in momentum from a path moving circularly uphole and radially inward to a path moving notal to the previous circular path. This pressure increase causes a notable increase in the amount of pumping head needed within the separator chamber. Thus, there is a need for a gas separator within an improved fluid flowpath to increase the efficiency of the overall ESP assembly. 
       SUMMARY OF THE INVENTION 
       [0006]    These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide an ESP gas flow separator with improved flowpath efficiency. 
         [0007]    In accordance with an embodiment of the present invention, a submersible pump assembly is disclosed. The pump assembly includes a rotary primary pump, a motor operationally coupled to the primary pump for driving the pump, a seal assembly between the primary pump and the motor for sealing the motor from the wellbore, and a gas separator between the seal assembly and the primary pump for separating fluid with high gas content from fluid with low gas content. An outlet of the gas separator feeds an intake of the primary pump. A rotating shaft operationally couples the primary pump to the motor, wherein the rotating shaft passes through the seal assembly and the gas separator. The gas separator contains a venting portion for passing gas from the gas separator into a wellbore. A diverter positioned within the venting portion of the gas separator directs heavier fluid into the intake of the primary pump and lighter fluid toward a venting port of the venting portion. Diverter guide vanes are formed in a flowpath of the lighter fluid for aiding in a directional change of momentum. 
         [0008]    In accordance with another embodiment of the present invention, a submersible pump assembly is disclosed. The pump assembly includes a rotary primary pump, a motor operationally coupled to the primary pump for driving the pump, a seal assembly between the primary pump and the motor for sealing the motor from wellbore fluid, and a gas separator between the seal assembly and the primary pump for separating wellbore fluid having a higher concentration of gas from wellbore fluid having a lower concentration of gas. An outlet of the gas separator feeds an intake of the primary pump. A rotating shaft operationally couples the primary pump to the motor. The rotating shaft passes through the seal assembly and the gas separator. The gas separator contains a venting portion for passing gas from the gas separator into a wellbore. A diverter is positioned within the venting portion of the gas separator for directing heavier fluid into the intake of the primary pump and lighter fluid toward a venting port of the venting portion. Diverter guide vanes are formed in a flowpath of the lighter fluid for aiding in a directional change of momentum. The diverter is a conical member having an upstream end and a downstream end, wherein the downstream end has an inner diameter substantially equivalent to the outer diameter of the rotating shaft, and the upstream end has an inner diameter that is wider than the diameter of the rotating shaft to define a fluid passageway directing fluid toward the downstream end. The conical member defines fluid openings near the downstream end so that fluid entering the fluid passageway at the upstream end may flow into the fluid openings. The diverter guide vanes are formed within the conical member on trailing edges of the fluid openings and extend partially into the fluid passageway so that the diverter guide vanes may direct fluid into the fluid openings. The diverter guide vanes have a thickness that decreases in a direction from the trailing edge of one of the fluid openings toward an adjacent one of the fluid openings, and each guide vane has a curved inner surface. The gas separator includes a gas separator intake for intaking wellbore fluid from an area proximate to an upstream end of the gas separator, an impeller operationally coupled to the gas separator intake downstream of the gas separator intake so that the impeller may impart rotational inertia to the wellbore fluid entering through the separator intake, and a separation chamber operationally coupled to the impeller so that rotating wellbore fluid may pass from the impeller into the separation chamber. The separation chamber is operationally coupled to the venting portion. 
         [0009]    In accordance with yet another embodiment of the present invention, a submersible pump assembly is disclosed. The pump assembly includes a rotary primary pump, a motor operationally coupled to the primary pump for driving the pump, a seal assembly between the primary pump and the motor for sealing the motor from wellbore fluid, and a gas separator between the seal assembly and the primary pump for separating wellbore fluid having a higher gas content from wellbore fluid having a lower gas content. An outlet of the gas separator feeds an intake of the primary pump. A rotating shaft operationally couples the primary pump to the motor, wherein the rotating shaft passes through the seal assembly and the gas separator. The gas separator contains a venting portion for passing gas from the gas separator into a wellbore, a diverter positioned within the venting portion of the gas separator for directing heavier fluid into the intake of the primary pump and lighter fluid toward a venting port of the venting portion, and a slinger positioned within the diverter for impelling fluid through a venting port of the venting portion. Three blades are formed on the slinger, each blade having a blade at least two portions that aid in the movement of wellbore fluid having a higher gas content from the gas separator. The gas separator also includes gas separator intake for intaking wellbore fluid from an area proximate to an upstream end of the gas separator, an impeller operationally coupled to the gas separator intake downstream of the gas separator intake so that the impeller may impart rotational inertia to the wellbore fluid entering through the separator intake, and a separation chamber operationally coupled to the impeller so that rotating wellbore fluid may pass from the impeller into the separation chamber. The separation chamber is operationally coupled to the venting portion. 
         [0010]    An advantage of the disclosed embodiments is that they provide a gas separator with improved flowpath efficiency. As a result, the total pumping head required to lift fluid to the surface is reduced. Additional embodiments include a slinger with modified blades that increase the flow rate of high gas content fluid out of the gas separator and into the wellbore, further increasing efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0012]      FIG. 1  is a schematic representation of an ESP assembly disposed within a cased wellbore. 
           [0013]      FIG. 2  is a schematic representation of a gas separator in accordance with an embodiment of the invention. 
           [0014]      FIG. 3  is a schematic representation of a gas separator wherein a portion of the exterior housing of the gas separator has been removed for an internal view of the gas separator. 
           [0015]      FIG. 4  is a sectional view of a venting portion of the gas separator taken along line  4 A- 4 A of  FIG. 2  and  FIG. 3 . 
           [0016]    FIG.  5 AB is a sectional view of the venting portion of the gas separator taken along line  5 B- 5 B of FIG.  5 AA. 
           [0017]      FIG. 5A  is a sectional view of the venting portion of the gas separator taken along line  5 - 5  of  FIG. 4 . 
           [0018]      FIG. 6  is a sectional view of the venting portion of the gas separator taken along line  5 - 5  of  FIG. 4  illustrating an alternative embodiment of the present invention. 
           [0019]      FIGS. 7 and 8  are front and top views of a slinger of  FIG. 6  in accordance with an embodiment of the present invention. 
           [0020]      FIG. 9  is a sectional view of the slinger of  FIGS. 7 and 8  taken along line  9 - 9  of  FIG. 8 . 
           [0021]      FIG. 10  is a sectional view of the slinger of  FIGS. 7 and 8  taken along line  10 - 10  of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments. 
         [0023]    In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning ESP operation, construction, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
         [0024]    The exemplary embodiments of the downhole assembly of the present invention are used in oil and gas wells for producing large volumes of well fluid. As illustrated in  FIG. 1 , a downhole assembly  11  has an electric submersible pump  13  (“ESP”) with a large number of stages of impellers  25  and diffusers  27 . ESP  13  is driven by a downhole motor  15 , which is a large three-phase AC motor. Motor  15  receives power from a power source (not shown) via power cable  17 . Motor  15  is filled with a dielectric lubricant. A seal section  19  separates motor  15  from ESP  13  for equalizing internal pressure of lubricant within the motor to that of the well bore. A gas separator  21  for at least partially removing gas from the well fluid is installed on a pump intake portion of ESP  13 . Additional components may be included, such as a sand separator, and a pressure and temperature measuring module. Large ESP assemblies may exceed  100  feet in length. An upper end of ESP  13  couples to a production string  23 . 
         [0025]    A rotating shaft  25  may extend from motor  15  up through seal section  19 , gas separator  21 , and ESP  13 . Motor  15  may rotate shaft  25  to, in turn, rotate impellers  27  within ESP  13 . A person skilled in the art will understand that shaft  25  may comprise multiple shafts configured to rotate in response to rotation of the adjacent upstream coupled shaft. Impellers  27  will generally operate to lift fluid within ESP  13  and move the fluid up production string  23 . Impellers  27  perform this function by drawing fluid into a center of each impeller  27  near shaft  25  and accelerating the fluid radially outward. Generally, the fluid accelerated by each impeller  27  will then flow into a diffuser  29  axially above impeller  27 . There, the fluid is directed from a radially outward position to a radially inward position adjacent shaft  25  where the fluid is drawn into a center of the next impeller  27 . 
         [0026]    Referring now to  FIG. 2 , there is shown gas separator  21 . In the illustrated embodiment, gas separator  21  includes an intake portion  31 , a flow inducer portion  33 , a separation chamber  35 , and a venting portion  37 . Intake portion  31  includes an intake  39  that allows flow of wellbore fluid from the area around the gas separator  21  into an interior cavity of gas separator  21 . The intake directs fluid toward flow inducer portion  33 . As shown in  FIG. 3 , flow inducer portion  33  includes an inducer or flow inducer  41 . Flow inducer  41  imparts rotational energy to the wellbore fluid causing the wellbore fluid to rotate around shaft  25  as it flows into separation chamber  35 . In an embodiment, separation chamber  35  includes lower guide vanes  43  at an upstream end of gas separator  21  proximate to flow inducer  41 . Lower guide vanes  43  rotationally direct the wellbore fluid as it passes into separation chamber  35  from Flow inducer portion  33  to increase rotational flow of the fluid. As fluid moves downstream in separation chamber  35 , the rotational momentum imparted to the wellbore fluid by flow inducer  41  and guide vanes  43  centrifugally separates heavier wellbore fluid having a lower gas concentration from lighter wellbore fluid having a higher concentration of gas. The heavier wellbore fluid will then flow downstream along the outer diameter portions of separation chamber  35  and the lighter wellbore fluid will flow downstream along rotating shaft  25 . Heavier wellbore fluid will flow through venting portion  37  and into an intake of ESP  13 , while lighter wellbore fluid will flow into venting portion  37  and be directed back into the area around ESP  13  through venting ports  45 , as described in more detail below. 
         [0027]    Referring to  FIG. 4 , a sectional view of venting portion  37  is shown looking downstream into venting portion  37  from the upstream end of venting portion  37 . As shown, wellbore fluid flows in a counterclockwise manner when looking downstream through venting portion  37 . Venting portion  37  includes a tubular wall  47  defining a central passage  48  and an axis  85 . Rotating shaft  25  is positioned within and concentric with tubular wall  47 . Venting portion  37  includes a crossover or diverter  49 . Diverter  49  is a generally conical member having an inner diameter at the downstream end  51  ( FIG. 5A ) that is approximately equal to the outer diameter of rotating shaft  25 . Diverter  49  has an upstream end  53  ( FIG. 5A ) that is concentric with rotating shaft  25  and has an inner diameter  55  that is wider than the diameter of diverter  49  at downstream end  51 . Upstream end  53  defines an annulus  57  between the inner diameter of tubular wall  47  and the outer diameter of diverter  49 . As shown in  FIG. 4 , annulus  57  may be divided into three portions by lower members  59  of diverter  49 . In the illustrated embodiment, there are three lower members  59  extending between the outer diameter of diverter  49  and the inner diameter of tubular wall  47  a portion of the circumferential distance around the outer diameter of upstream end  53  as shown. In this manner, members  59  create a lower portion of a venting chamber  61  ( FIG. 5A ) having an inlet through diverter  49  and an outlet at venting ports  45 . 
         [0028]    As shown in  FIG. 5A , diverter  49  also includes upper members  63  extending from downstream end  51  to secure to tubular wall  47  at venting port  45  directly over lower members  59 . Venting chamber  61  includes sidewalls  62  ( FIG. 5B ) extending from lower members  59  to upper members  63  so that fluid in annulus  57  may not communicate with fluid in venting chamber  61  or pass from annulus  57  through venting port  45 . In the illustrated embodiment, there are three upper members  63 , one of which is shown in  FIG. 5A , resulting in three venting ports  45 . 
         [0029]    Upstream end  53  also defines a fluid passageway  65  between inner diameter  55  of upstream end  53  and the outer diameter of rotating shaft  25 . Diverter  49  defines an opening  67  ( FIG. 5A ) through a wall of diverter  49  so that fluid may move from fluid passageway  65  into venting chamber  61  as fluid moves downstream within diverter  49 . Opening  67  is proximate to downstream end  51  where the inner diameter of diverter  49  narrows to the outer diameter of rotating shaft  25  and extends upstream to lower member  59 . As shown in  FIG. 4  and  FIG. 5A , diverter guide vanes  69  are formed at each opening  67 . Diverter guide vanes  69  extend partially into fluid passageway  65  and have a leading edge that tapers with the angle of the sidewall of diverter  49  between upstream end  53  and downstream end  51 . Guide vanes  69  have a modified airfoil shape as shown and are located at the trailing edge of each opening  67 . 
         [0030]    As shown in  FIG. 4 ,  FIG. 5A , and  FIG. 58 , centrifugally separated heavier wellbore fluid flowing along tubular wall  47  will flow through annulus  57  around diverter  49 . Lighter wellbore fluid having a higher gas concentration will flow along rotating shaft  25  and into fluid passageway  65 . As fluid passageway  65  narrows ( FIG. 5B ) moving from upstream end  53  toward downstream end  51 , lighter wellbore fluid will be directed into venting chamber  61  by diverter guide vanes  69 . The modified airfoil shape of diverter guide vanes  69  aids in changing the upward and inward momentum of the lighter wellbore fluid. This results in a fluid flowpath that changes direction from along rotating shaft  25  into venting chamber  61  and out venting port  45  with greater velocity and reduced head. 
         [0031]    Referring to  FIG. 6 , in an alternative embodiment, venting portion  37  may also include a slinger  71 . Slinger  71  may be secured to rotating shaft  25  within diverter  49  so that slinger  71  may rotate within diverter  49  in response to rotation of rotating shaft  25 . As shown in  FIGS. 7 and 8 , slinger  71  comprises a cylindrical body  73  having at least one blade  75  formed on an outer diameter portion of cylindrical body  73 . In the illustrated embodiment, the direction of rotation of slinger  71  indicated by the arrow in  FIG. 7 . Each blade  75  has an upstream portion  81  with a first geometric configuration, in this case a substantially square shape, that extends downstream along a portion of cylindrical body  73  to a junction  83 . Upstream portion  81  forms an angle a with axis  85  passing through a center of cylindrical body  73 . As shown in  FIG. 9 , upstream portion  81  has an outer radius R from axis  85  that is constant from an upstream terminal end of upstream portion  81  to junction  83 . 
         [0032]    Each blade  75  has a downstream portion  87  from junction  83  to the downstream end of cylindrical body  73 . As shown in  FIG. 10 , a radius r of downstream portion  87  from axis  85  decreases in width from junction  83  to the downstream end of cylindrical body  73  so that downstream portion  87  tapers to the outer diameter of cylindrical body  73  at the downstream end of cylindrical body  73  from a radius R of upstream portion  81  at junction  83 . Downstream portion  87  of each fin  75  has a leading surface  89  and a trailing surface  91 . As shown in  FIG. 8 , leading surface  89  is concave and trailing surface  91  is convex. Preferably, the curvature of downstream portion  87  from junction  83  to the downstream end of cylindrical body  73  is such that there is a relatively smooth fluid flowpath from upstream portion  81  across junction  83  and downstream portion  87 . In this manner, turbulent flow along blade  75  may be reduced as fluid accelerates out of venting portion  37 . 
         [0033]    In the embodiment of  FIG. 6 , slinger  71  rotates as indicated by the arrow. A tubular wall  93  may be secured to upstream end  53  of diverter  49  extending annulus  57  to the upstream end of tubular wall  93 . Tubular wall  93  will maintain separation of heavier and lighter wellbore fluids as the fluids move past a bearing  95  supporting rotating shaft  25  within separation chamber  35 . In addition, tubular wall  93  will limit inflow of heavier wellbore fluid into diverter  49  during rotation of slinger  71 . Heavier wellbore fluid will flow through annulus  57 , past diverter  49 , and into an intake of ESP  13  ( FIG. 1 ). Lighter wellbore fluid having a higher gas concentration will flow into fluid pathway  65  through a central bore of tubular wall  93 . There, slinger  71  imparts additional rotational energy to the lighter wellbore fluid increasing the flowrate of the lighter wellbore fluid through opening  67 . When used with diverter guide vanes  69  as shown in  FIG. 6 , the increased flowrate and reduction in head loss at opening  67  caused by diverter guide vanes  69  greatly improves the efficiency of gas separator  21 . A person skilled in the art will understand that slinger  71  may be used with a diverter  49  without diverter guide vanes  69 . Similarly, a person skilled in the art will understand that diverter  49  having diverter guide vanes  69  may be used without slinger  69  as shown in  FIG. 4  and  FIG. 5A . 
         [0034]    Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a gas separator having a higher flowrate efficiency. The disclosed embodiments accomplish this by providing guide vanes within the diverter that reduce flow resistance and turbulence by aiding the change in direction of fluid momentum from along the rotating shaft toward an exterior of the gas separator. In addition, the disclosed embodiments provide a slinger that further impels the fluid, increasing the flowrate of separated gas fluid through the venting ports of the gas separator. 
         [0035]    It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.