Abstract:
A gas separator has a separator member that rotates with a shaft for separation of fluid components. A flow divider directs more dense fluid to the pump and less dense fluid into an annulus surrounding the pump. An impeller is located within the flow divider for urging fluid out of a downstream gas exit port. A single large gas exit port is used and may be combined with use of a single large fluid inlet. An auger may be located within the rotary separator member. Holes may be located in the sidewall of the rotary member or chamber. The holes are preferably located in a helical pattern above and adjacent the flights of the auger or are in vertical columns adjacent the baffles. The chamber may have a cylindrical or tapered profile. Alternatively, a series of sub-chambers may be used, each having a smaller radius than the preceding, upstream sub-chambers.

Description:
[0001]    This invention claims the provisional application filing date of May 30, 2001, Serial No. 60/294,548, entitled “Gas Separator Improvements”. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention generally relates to improvements to gas separators and particularly relates to improvements in downhole gas separators used in fluid-producing wells.  
           [0004]    2. Description of the Prior Art  
           [0005]    In fluid wells, naturally-occurring gas bubbles within the fluid may reduce the efficiency of a downhole pump used to pump the fluid to the surface. A gas separator is used to ensure that a high quality, pumpable liquid is fed to the pump. The term “gas separators” is actually a misnomer, in that these are used to divide the fluid into two streams, and both streams may contain liquid. One stream comprises higher quality fluid containing less gas and exits out of the liquid exit port. The second stream, which has a higher gas content, exits out of the separator through gas exit ports.  
           [0006]    [0006]FIGS. 1 and 2 show a prior art separator  11 , which is shown as a component of a downhole, electric, submersible pump (ESP) assembly and located between a pump  15  and a seal section  17 . An annulus  19  is defined by the outer surfaces of ESP  13  and the inner surface of the casing in the well. A central shaft extends upward from a motor (not shown) and through seal section  17  for engaging a central shaft  21  in separator  11  and another (not shown) in pump  15  for rotationally driving separator  11  and pump  15 . Fluid travels up the well and enters separator  11  through openings  23  at its lower end. The fluid is separated by an internal rotating member with blades attached to shaft  21 . The separator may also have an inducer pump or auger at its lower end to aid in lifting the fluid to the rotating separating member. The rotating separator member causes denser fluid to move toward the outer wall of separator  11  due to centrifugal force. The fluid mixture then travels to the upper end of separator  11  and passes through a flow divider  25  or cross-over member, shown in FIG. 2. A radial support bearing is often required to support the span of such a long central shaft, causing pressure head loss in the fluid from flow around this bearing. This loss can limit the flow potential of the separator.  
           [0007]    Divider  25  comprises a circular ring and a conical upper end. Divider  25  is oriented to be parallel to and coaxial with central shaft  21 . One or more gas exit ports  27  communicate an opening in the sidewall of separator  11  and the interior of flow divider  25 . As the fluid nears flow divider  25 , the outer (more dense) fluid remains in the annulus surrounding flow divider  25  and is diverted radially inward and upward to a liquid exit port  29 . The inner (less dense) fluid enters flow divider  25  and is channeled radially outward and upward to gas exit ports  27 . Liquid exit port  29  leads to pump  15 , but gas exit ports  27  open into annulus  19  (FIG. 1).  
           [0008]    A problem with using flow divider  25  in separator  11  is that the flow rate of the fluid through gas exit ports  27  may limit the effectiveness of separator  11 . Liquid loading, or back pressure, may interfere with the exit of gas. A variety of passage shapes have been used for gas exit and liquid exit ports in gas separators. These range from curved diffusion flow paths to straight holes drilled through the side of the separator. The number of holes varies and is dependent on the diameter of the equipment. A separator having a four-inch diameter may have only four holes, whereas a larger unit may have six, eight, or more holes. Each hole has a wetted perimeter that is much smaller than the wetted perimeter of the separator body at the flow divider. The original design criterion was to achieve low resistance and uniform flow around the gas exits. This is not necessary, as there is no advantage to having uniform flow around the gas exit ports. U.S. Pat. No. 6,113,675 discloses an impeller within the flow divider to enhance flow of gas to the exterior. This arrangement is illustrated in FIG. 3, which shows impeller  31  having blades  33  and located within flow divider  25 .  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    In this invention, in one embodiment, a single large gas exit port is used and may be combined with a single large fluid inlet in the separator. The port preferably has a wetted perimeter that is at least 30% of the wetted perimeter of the gas separator housing in the flow divider annulus.  
           [0010]    To provide for a shorter central shaft that does not require a mid-length radial support bearing, another embodiment provides for the separation and lifting functions to be combined in one section of the separator. An inducer or auger is located within a rotary cylinder that leads to a flow divider. The more-dense fluid is accelerated outward and displaces the less-dense fluid, which remains near the central portion of the cylinder. The less-dense fluid moves into the flow divider, which is located along the central axis of the cylinder, and to a gas exit port, whereas the more-dense fluid passes around the flow divider to a liquid exit port.  
           [0011]    To provide for continuous separation of more- and less-dense fluid components, the invention also provides embodiments that have a rotating chamber with at least one hole in the sidewall of the chamber. Each chamber may have an internal auger or may have vertical baffles. In the case of an auger, the holes may be helical slots extending partially around the chamber at the same helix angle as the auger. Alternately, the holes may individual circular holes located above and adjacent the flight of the auger. In the case of vertical baffles, the holes may be in vertical columns adjacent the baffles. The chambers may have tapered profiles. Alternatively, a plurality of sub-chambers may be used, each having a smaller radius than the preceding, upstream sub-chamber. An impeller may optionally be located in the flow divider in all of the embodiments.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The novel features believed to be characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings.  
         [0013]    [0013]FIG. 1 is a cross-sectional view of a well with a prior-art downhole pump assembly installed therein.  
         [0014]    [0014]FIG. 2 is a cross-sectional view of a prior-art flow divider in the gas separator of FIG. 1.  
         [0015]    [0015]FIG. 3 is a cross-sectional view of a prior-art flow divider, showing an impeller located in the flow divider.  
         [0016]    [0016]FIG. 4 is a cross-sectional view of a first embodiment of a gas separator constructed in accordance with the present invention.  
         [0017]    [0017]FIG. 5 is a cross-sectional view of a second embodiment of a gas separator constructed in accordance with the present invention.  
         [0018]    [0018]FIG. 6 is a cross-sectional view of a third embodiment of a gas separator constructed in accordance with the present invention.  
         [0019]    [0019]FIG. 7 is a cross-sectional view of the rotary chamber of the separator in FIG. 6.  
         [0020]    [0020]FIG. 8 is a cross-sectional view of a fourth embodiment of a gas separator constructed in accordance with the present invention.  
         [0021]    [0021]FIG. 9 is a cross-sectional view of a fifth embodiment of a gas separator constructed in accordance with the present invention.  
         [0022]    [0022]FIG. 10 is a cross-sectional view of an sixth embodiment of a gas separator constructed in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Referring to FIG. 4, a lower exit pressure can be achieved through the use of a central flow divider  35  leading to a single, very large gas exit port  36  and by centralizing the ESP within the well to prevent blocking of the exit flow by the well casing. Exit port  36  preferably is circular and has a wetted perimeter equal or greater than 30% of the wetted perimeter of the housing or body  40  of separator  11  measured in the flow divider annulus at the lower end of flow divider  35 . The wetted perimeter refers to the outer perimeter of a passage that is in contact with the fluid flowing through it. In one embodiment, the wetted perimeter of exit port  36  is 45% of the wetted perimeter of body  40  measured in the divider annulus at the lower end of divider  35 . Although shown circular, exit port  36  could be other than circular.  
         [0024]    The single large diameter exit port  36  may be more effective when combined with a large single-hole fluid entrance  37 . For still higher effectiveness, entrance  37  to separator  11  and exit  36  are preferably oriented so that fluid entrance  37  is located on the opposite side of separator  11  as gas exit  36  and near the lower end. Separator  11  may be even more efficient if offset within the well, opening gas port  36  to the largest free-flow area, though tests have shown that the effect of offsetting, and possibly of the opposing orientation of the ports, is reduced in a narrow annulus between the casing and the ESP. Conversely, an increased effect is seen in large-casing installations.  
         [0025]    To overcome the problem of pressure head loss with flow around a radial support bearing, separator  38 , shown in FIG. 5, uses an inducer or auger  39  located within a rotary cylinder  41 . The outer edges of the flights of auger  39  are connected to the inner diameter of cylinder  41 , and auger  39  and cylinder  41  rotate in unison. The inner edges of auger  39  are at shaft  21 . Although not shown, preferably the inner edges of auger  39  are joined to a hub that slides over shaft  21 . This combination is attached to and rotates with a central shaft  43  to provide both lifting and separation functions. The fluid enters separator  38  through openings  45  at the lower end and is drawn into chamber  41  by auger  39 . The pressure of the fluid as it flows up the helical channel defined by auger  39  increases. Also, separation of dense and less dense fluid takes place within the helical channel. Above auger  39  is a standard flow divider  47 , and the fluid is separated as described for FIGS. 2 and 3 before passing to gas exit ports  49  and liquid exit port  51 . This allows shaft  43  to be shorter and obviates the need for an additional radial support bearing. Impeller  46  in flow divider  47  is optional.  
         [0026]    The typical separator produces a fluid flow that travels upward into a separation area, into a flow divider, and then into appropriate exit ports. However, more efficient separation may be obtained if the liquid is continuously removed from the mixture as the separation process occurs. The liquid is allowed to move out of the separation device as the mixture moves upward, and the fluid remaining in the device is directed to the gas exit port. FIGS. 6 through 10 depict several embodiments of continuous liquid-removal devices.  
         [0027]    Referring to FIG. 6, fluid enters a separator  53  through openings  55  at the base and is lifted and partially separated by an auger  57  that rotates with central shaft  59 . In this embodiment, there is no rotating cylinder surrounding auger  57 , as in FIG. 5. The fluid travels upward, and the less dense inner fluid enters a rotary chamber  61 . Chamber  61  is open at both the upper and lower ends and has an outer diameter less than the inner diameter of an inner surface  63 . The more dense outer fluid continues along inner surface  63  of the outer wall of separator  53  and does not enter chamber  61 . Chamber  61  is a vertical cylinder having a plurality of holes  65  in its outer wall  66 , holes  65  being in vertically-aligned columns. A standard flow divider  67  sealingly engages the upper end of chamber  61  and communicates the interior of chamber  61  and gas exit ports  69 . An annulus  71  is defined by wall  66  of chamber  61  and inner surface  63  of separator  53 . The liquid stream flows through annulus  71  and into liquid exit port  73 . Impeller  68  within flow divider  67  is optional.  
         [0028]    As shown in the section view in FIG. 7, four columns of holes  65  are arrayed around chamber  61 . Four vertical baffles  75 , which also may be referred to herein as blades or vanes, connect outer wall  66  of chamber  61  to central shaft  59  and are spaced within chamber  61  and separate chamber  61  into four equal sections. Each baffle  75  extends for approximately the height of chamber  61  and is parallel to and adjacent one of the columns of holes  65 . Chamber  61  is uni-directional, and each baffle  75  is located so that it follows immediately behind the column of holes  65  during rotation. When chamber  61  is rotating, the mixture in each section is forced toward a trailing baffle  75  due to tangential acceleration, and the more dense liquid is forced outward toward holes  65  due to centrifugal acceleration. Referring again to FIG. 6, the liquid flows out of holes  65 , into annulus  71 , and upward to liquid exit port  73 . As the mixture moves upward in chamber  61 , the liquid content is continually reduced. The mixture that remains inside chamber  61  passes through flow divider  67  and directly into gas exit ports  69  and out into the well. Although the vertical columns of holes  65  are shown extending from near the bottom of chamber  61  to near the top, they could begin at a higher point along chamber  61 .  
         [0029]    [0029]FIG. 8 shows an embodiment of a separator  75  having a continuous liquid-removal rotating chamber  77  in which an auger  79  with helical flights is integrally formed, the combination rotating with a central shaft  80 . Rather than being in vertical columns, holes  81  are arrayed around the sidewall of chamber  77  in a helical pattern parallel to and immediately above each helical vane of auger  79 . As chamber  77  rotates, auger  79  draws the fluid from intake openings  83  into chamber  77  and moves the fluid upward while causing the dense fluid to move toward the outside of chamber  77 . The liquid passes out of holes  81  and into an annulus  85  surrounding chamber  77 . To keep the liquid in annulus  85  from traveling back down to openings  83 , the outer surface of the lower portion of chamber  77  seals against an inner surface  87  of the sidewall of separator  75 . The pressure of liquid being forced out of chamber  77  drives the liquid in annulus  85  upward to the liquid exit port  89  at the upper end of separator  75 . As in the embodiment in FIG. 8, a flow divider  91  sealingly engages the top of chamber  77  for directing the mixture remaining in chamber  77  into gas exit ports  93 . Impeller  92  within flow divider  91  is optional. Holes  85  need not begin at the bottom of chamber  77 , rather could begin at higher points along chamber  77 .  
         [0030]    [0030]FIGS. 9 and 10 illustrate additional embodiments of the auger-chamber combination. While the volume of liquid decreases in a rotary chamber as the mixture moves upward in the chamber, the volume of liquid in the annulus outside of the chamber increases. If the diameter of the rotary chamber is constant, then the velocity of the liquid on the outside of the chamber must continuously increase, and the velocity of the mixture on the inside of the chamber must continuously decrease. A tapered (FIG. 9) or stepped (FIG. 10) chamber can provide a more uniform velocity distribution inside and outside of the chamber.  
         [0031]    As shown in FIG. 9, a separator  94  comprises a tapered chamber  95 , the upper end of chamber  95  having a smaller diameter than the lower end. Chamber  95  houses helical vanes  97  for moving and separating the mixture within chamber  95  when chamber  95  and vanes  97  rotate with central shaft  99 . At least one hole  101  and preferably two are located in the sidewall of chamber  95  and immediately above vane  97 . Hole  101  is a helical slot extending partially around the circumference of chamber  95 , such as about 90 degrees. Hole  101  is located near the upper end of chamber  95  and extend at the same helical angle as vanes  97 . Chamber  77  of FIG. 8 could also use one or more helical holes  101  rather than separate circular holes  81 .  
         [0032]    The fluid mixture is separated as in the embodiment in FIG. 8, with liquid flowing out of hole  101  and into annulus  102 . Fluid is held in annulus  102  by a sealing engagement of the lower end of chamber  95  with the inner surface of the sidewall of separator  94 . The upper end of chamber  95  sealingly engages a flow divider  100 . Though shown with a taper in which the diameter of chamber  95  decreases linearly, the taper may also be nonlinear or may be stepped, as discussed below. Impeller  104  within flow divider  100  is optional.  
         [0033]    Chambers  103 ,  105 ,  107 ,  109  of separator  111 , also referred to as sub-chambers and shown in FIG. 10, each contain a set of two half-turn helical vanes  113  having equal diameters. Chambers  103 ,  105 ,  107 ,  109  and vanes  113  rotate with a central shaft  115 . The diameter of vanes  113  in chambers  103 ,  105 ,  107  are larger than vanes  113  in each chamber immediately above, the lowermost chamber  103  having the largest vanes  113 . Each chamber  103 ,  105 ,  107 ,  109  has a generally vertical sidewall  117 , with the lower edge of each sidewall  117  is tapered or curved toward central shaft  115 . The upper edges of chambers  103 ,  105 ,  107  are open to an annulus  119  surrounding the stack of chambers  103 ,  105 ,  107 ,  109 . The upper edge of uppermost chamber  109  sealingly engages a flow divider  121  for directing the flow of the remaining mixture into gas exit ports  123 . The fluid in annulus  119  is prevented from traveling down to intake openings  125  by sealing the lower end of the outer surface of chamber  103  to an inner surface  131  of separator  111 .  
         [0034]    Fluid is drawn into intake openings  125  in the lower portion of separator  111 . As the fluid mixture is moved upward in lowermost chamber  103 , the dense fluid moves toward sidewall  117  of chamber  103 . When the dense fluid (liquid) reaches the upper edge of chamber  103 , it exits chamber  103  into annulus  119  through gap  127  between the upper edge of chamber  103  and the lower edge of chamber  105 , the rounded lower edge providing a larger flow area for the exiting liquid. The inner fluid continues upward into chamber  105 , and the process repeats as for lowermost chamber  103 , the liquid content of the mixture decreasing as the fluid moves out of each chamber  103 ,  105 ,  107  and into the next chamber  105 ,  107 ,  109 . When the fluid reaches the upper end of uppermost chamber  109 , the remaining fluid flows through flow divider  121  to gas exit ports  123 . The liquid in annulus  119  travels upward and out of a liquid exit port  129 . Impeller  122  within flow divider  121  is optional. Rather than helical vanes  113 , vertical baffles or vanes could be located in the various chambers  103 ,  105 ,  107 , and  109 .  
         [0035]    Several embodiments of gas separators have been disclosed, and each is designed to provide more efficient means of separating a mixture into more-dense and less-dense fluid components. An impeller can be added within a gas separator and near a typical flow divider to eliminate liquid loading in gas exit ports. A lower exit pressure can be achieved by having one very large opening for the gas exit. Combining the auger and separating chamber can limit the length of the central shaft and the separator housing and eliminate the need for a radial support bearing to support the shaft. Continuous liquid removal from the mixture is more efficient than the typical flow divider, and reducing the separating chamber diameter as the mixture moves toward the exits increases the efficiency still further.  
         [0036]    While the invention has been shown in only some of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.