Abstract:
An above-motor mixed flow booster pump combined with a fluid crossover that directs up into the inside of an inverted shroud to allow enhanced gas separation. A gas and liquid separator is used to enhance separation. The system is simple and provides increased gas handling capability for high flow or low flow gas well dewatering applications, including vertical wells, horizontal wells, slant wells. The boost pump allows the moving of a mixed flow upwards to the top of an inverted shroud in wells lacking the required pressure.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to shrouds used in the separation of gas from liquid, and in particular to using a boost pump with a crossover in wells lacking the pressure to move a mixed flow upwards to the top of an inverted shroud. 
       BACKGROUND OF THE INVENTION 
       [0002]    In gas well dewatering applications it is desired to draw the well down to the lowest reservoir pressure as possible in order to maximize gas production. To prevent lift pumps from gas locking, inverted shrouds are used as a way to separate gas from liquid. Inverted shrouds are typically long and in effect, raise the intake of the pump to the top of the shroud. Further pressure increase occurs due to the frictional drag in the annulus between the shroud and the casing. 
         [0003]    It is becoming increasingly desirable to dewater a zone by placing the ESP pump in a horizontal well-bore. In horizontal gas wells, however, the gas bubble buoyancy forces are not acting in the optimum direction for moving gas out of the well bore. In these wells much of the gas production goes up the casing/tubing annulus. Because a significant length of well-bore is horizontal, it is very difficult to keep the necessary fluid level over the pump. Thus, static liquid in a horizontal gas well may choke the gas flow. 
         [0004]    A technique is thus needed to boost the gas and liquid to the vertical or high angle to allow the buoyancy forces to separate the gas from liquid. 
       SUMMARY OF THE INVENTION 
       [0005]    In an embodiment of the present invention, a dewatering apparatus with enhanced gas separation is illustrated, with a mixed flow booster pump located above a motor and within a shroud located in a cased well. The shroud may be inverted and can be combined with a fluid crossover assembly that may have mixed flow and liquid chambers that are isolated from each other. The crossover assembly may be connected to the discharge of the booster pump at an upstream end and at a downstream end to an intake of a lift pump. The crossover assembly can receive mixed flow from the well and has an outlet that directs the mixed flow up into the inside of the inverted shroud into an inner annulus formed by the outer diameter of the lift pump and inner diameter of the shroud where separated gas can escape through an open end on the downstream side of the shroud. The booster pump can be used in wells lacking the required pressure to move the mixed flow upwards through the shroud. Thus, the booster pump only needs to provide enough head to move the mixed flow up to the top of the inverted shroud. To further enhance gas separation, the shroud may be perforated near the downstream end and have a vortex inducer near the perforated section that induces fluid rotation such that the high percentage liquid, such as water, is flung outward, through the perforations and into an outer annulus defined by the shroud&#39;s outer diameter and casing inner diameter. High percentage refers to the high percentage of liquid versus gas in the liquid flow. 
         [0006]    Once the high percentage liquid is in the outer annulus, gravity causes the liquid to fall downwards and enters a port in the fluid crossover. The port is in communication with the intake of the lift pump, allowing the lift pump to pump the liquid up through a production tubing string extending through the shroud and leading to a wellhead. A seal or packer may be located in the inner annulus above and below the fluid crossover and another seal could be located in the outer annulus between the upstream end of the shroud and the casing. 
         [0007]    The invention is simple and provides enhanced gas separation and increased gas handling capability for high flow or low flow gas well dewatering applications, including vertical wells, horizontal wells, slant wells. This invention further advantageously allows for pumping mixed flow gas wells such as those that require dewatering. This invention could help gas dewatering operators have much greater production and in effect lower the overall cost of production. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a sectional view of a well installation in accordance with the invention. 
           [0009]      FIG. 2  is an enlarged sectional view of the well installation of  FIG. 1  showing the details of a crossover assembly in accordance with the invention. 
           [0010]      FIG. 3  is cross sectional view of the crossover assembly of  FIG. 1 , taken along the line  3 - 3  of  FIG. 2 , in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Referring to  FIG. 1 , an embodiment of a dewatering apparatus  10  is shown located within the casing  12  of a well having perforations  14  to allow fluid flow from the formation. The dewatering apparatus  10  includes an inverted shroud  16  that may have a separating device or perforated section  18  approximately located at an open top end  20 . A lift pump  22  for pumping fluid to the surface via a production tubing string  24  has an intake  26  that may be connected to a downstream end of a crossover assembly  28 . The lift pump  22  could comprise multiple stages. A discharge end  30  of a booster pump  32  connects to an upstream end of the crossover assembly  28  to pump a mixed fluid flow of liquid and gas up an inner annulus  34  that is defined by the outer diameter of the lift pump  22  and the inner diameter of the shroud  16 . An outer annulus  36  is defined by outer diameter of the shroud  16  and the inner diameter of the casing  12 . The booster pump  32  may have stages for gas handling and impellers suitable for gas handling. 
         [0012]    Both the lift pump  22  and the booster pump  32  are located above a motor  38  in this example, with the motor  38  having a power cable  60  ( FIG. 2 ) that extends to the surface. A shaft  40  is connected to the motor  38  and extends through a seal section  42 , through the booster pump  32 , through the crossover assembly  28  and into the lift pump  22 . This configuration of the shaft  40  allows the motor  40  to drive both the lift pump  22  and the booster pump  32 . Additionally, a sensor  44  may be located on the upstream side of the motor. 
         [0013]    Inner annulus seals may be located upstream and downstream of the crossover assembly  28  to prevent recirculation of fluid. Further, an outer annulus seal  48  can be located at the upstream end of the shroud  16  between the shroud  16  and the casing  12  to create a seal between the mixed flow entering from the formation and the separated liquid in the outer annulus. 
         [0014]    Further, a vortex inducer  50  may be attached to the production tubing  24  at a point below the perforated section  18  of the shroud  16  to further enhance gas separation. The vortex inducer  50  induces the mixed flow in the inner annulus  34  to rotate, thereby causing the heavier liquid to move outward towards the perforations in the perforated section  18  and allowing the lighter gas to flow upwards through the open top end  20  of the shroud  16 . The vortex inducer  50  may comprise helical blades attached to a body that may be clamped onto the production tubing. 
         [0015]    Referring to  FIG. 2 , an enlarged and more detailed view of the crossover assembly  28  and of the booster pump  32  is shown. The booster pump  32  has an intake  62  for receiving the mixed flow from the well. The discharge end  30  of the booster pump  32  is in communication with a mixed flow inlet  64  that opens up into a mixed flow chamber  66  within the crossover assembly  28 . The mixed flow chamber  66  has an outlet  68  in communication with the inner annulus  34 . The crossover assembly  28  further comprises a liquid chamber  70  that may be isolated from the mixed flow chamber  66 . 
         [0016]    An opening  72  in the inverted shroud  16  communicates the outer annulus  36  with the liquid chamber  70  to allow high percentage liquid to flow into the liquid chamber  70  of the crossover assembly  28 . As mentioned above, high percentage liquid refers to the high percentage of liquid versus gas in the liquid flow in the outer annulus  36 . The liquid flow chamber  70  has an outlet  74  in communication with the intake  26  of the lift pump  22 . As illustrated in the cross-sectional view of  FIG. 3 , a central shaft passage  76  is formed in the crossover assembly  28  to allow the shaft  40  to pass through the crossover assembly to drive the lift pump  22 . The passage  76  is isolated from both the mixed flow chamber  66  and the liquid flow chamber  70 . Radial support bearings  78  may be used within the passage  76  to support the shaft  40  and seals  80  between the shaft  40  and the passage  76  prevent recirculation through the shaft passage  40 . 
         [0017]    In operation, referring to  FIGS. 1 and 2 , the mixed flow, identified by arrows and an “M,” containing liquid and gas enters the well casing  12  via the perforations  14  below the dewatering apparatus  10  in this example. The mixed flow circulates upward within the shroud  16  past the motor  38  and seal section  42  and into the booster pump intake  62 . The discharge end  30  of the booster pump  32  discharges into the mixed flow chamber  66  of the crossover assembly  28  via mixed flow inlet  64 . The mixed flow then exits the crossover assembly  28  via mixed flow outlet  68  and into the inner annulus  34 . 
         [0018]    Once in the inner annulus  34 , the head generated by the booster pump  32  is sufficient to lift the mixed flow downstream past the exterior of the lift pump  22 , production tubing  26 , and to the top of the shroud  16 . If the vortex inducer  50  is located within the shroud  16  at approximately the top end of the shroud  16 , the mixed flow will be induced into rotational motion, causing the heavier liquid in the mixed flow to be slung outwards against the inside of the shroud  16  and concentrating the lighter gas towards the center of the shroud  16  where the gas can continue downstream to the surface via the top open end  20 . If the perforated section  18  is included at the top end of the shroud  16 , the heavier liquid slung outwards will move through the perforations in the perforated section  18  and into the outer annulus  36 . The liquid flow in the outer annulus is a high percentage liquid having a high percentage of liquid versus gas. The liquid flow is identified with arrows and an “L” and moves upstream or downward within the outer annulus  36  under gravitational force. In this embodiment, the liquid flow then enters the liquid flow chamber  70  of the crossover assembly  28  via the passage  72  in the shroud  16 . Once in the liquid flow chamber  70 , the liquid flow flows into the lift pump intake  26  via an outlet  74  in communication with the intake  26  of the lift pump  22 . The lift pump  22  then discharges the liquid into the production tubing string  24  where it is pumped up to the surface. 
         [0019]    Although shown as a separate component in the embodiment described above, the crossover assembly  28  may be integral to the shroud  16 , with the chambers  66 ,  70  formed into the shroud  16 . 
         [0020]    While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited and is susceptible to various changes and modifications without departing from the scope of the invention.