Patent Publication Number: US-11041374-B2

Title: Beam pump gas mitigation system

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/648,275 filed Mar. 26, 2018 and entitled “Beam Pump Gas Mitigation System,” the disclosure of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to oilfield equipment, and in particular to surface-mounted reciprocating-beam, rod-lift pumping units, and more particularly, but not by way of limitation, to beam pumping units with systems for mitigating gas slugging. 
     BACKGROUND 
     Hydrocarbons are often produced from wells with reciprocating downhole pumps that are driven from the surface by pumping units. A pumping unit is connected to its downhole pump by a rod string. Although several types of pumping units for reciprocating rod strings are known in the art, walking beam style pumps enjoy predominant use due to their simplicity and low maintenance requirements. 
     In many wells, a high gas-to-liquid ratio (“GLR”) may adversely impact efforts to recover liquid hydrocarbons with a beam pumping system. Gas “slugging” occurs when large pockets of gas are expelled from the producing geologic formation over a short period of time. Free gas entering a downhole rod-lift pump can significantly reduce pumping efficiency and reduce running time. System cycling caused by gas can negatively impact the production as well as the longevity of the system. 
     A number of gas handling technologies have been deployed in the past. These approaches are generally effective in low production wells with moderate gas fractions. However, the existing solutions have proven ineffective at managing elevated gas fractions in higher volume wells. There is, therefore, a need for an improved gas mitigation system for use in connection with a beam pump deployed in a high producing, elevated gas fraction well. 
     SUMMARY OF THE INVENTION 
     In one aspect, embodiments of the present invention include a gas mitigation system for use in connection with a subsurface pump that is configured to lift fluids through a tubing string contained in a well casing. The gas mitigation system includes a shroud hanger that has one or more orifices that permit the passage of fluids through the shroud hanger. A canister connected to the shroud hanger has an open upper end. An intake tube connected to the tubing string extends into the canister. The canister is sized and configured to cause fluids passing around the outside of the canister to accelerate, thereby encouraging the separation of gas and liquid components. The open shroud hanger and canister allow heavier liquid components to fall into the canister as they decelerate, where the liquid-enriched fluid can be drawn into the reciprocating subsurface pump. 
     In another aspect, the present invention provides a gas mitigation system for use in connection with a subsurface pump that is configured to lift fluids through a tubing string contained in a well having a well casing. The gas mitigation system includes a shroud hanger that includes one or more orifices that permit the passage of fluids through the shroud hanger. The gas mitigation system further includes a canister connected to the shroud hanger, where the canister has an open upper end. The gas mitigation system also includes an intake tube that extends into the canister and is in fluid communication with the subsurface pump. The gas mitigation further includes a tail pipe assembly that is connected to the canister. The tail pipe assembly is in fluid communication with the canister. 
     In yet another embodiment, the present invention includes a gas mitigation system for use in connection with a subsurface pump configured to lift fluids through a tubing string contained in a well having a well casing. The gas mitigation system has a shroud hanger that includes one or more orifices that permit the passage of fluids through the shroud hanger, and a canister connected to the shroud hanger, where the canister has an open upper end. The gas mitigation system further includes an intake tube in fluid communication with the subsurface pump. In this embodiment, the gas mitigation system includes a tail pipe assembly that is connected to the canister and a velocity tube connected to the tail pipe assembly. The tail pipe assembly is in fluid communication with the canister. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a beam pumping unit and well. 
         FIG. 2  is a depiction of a first embodiment gas mitigation system deployed in the well of  FIG. 1 . 
         FIG. 3  is a close-up depiction of the can assembly of the gas mitigation system of  FIG. 2 . 
         FIG. 4  is a depiction of a second embodiment of the gas mitigation system deployed in a deviated well. 
         FIG. 5  is a close-up depiction of the solids separator from the second embodiment of the gas mitigation system of  FIG. 4 . 
         FIG. 6  is a depiction of a third embodiment of the gas mitigation system deployed in a deviated well. 
     
    
    
     WRITTEN DESCRIPTION 
       FIG. 1  shows a beam pump  100  constructed in accordance with an exemplary embodiment of the present invention. The beam pump  100  is driven by a prime mover  102 , typically an electric motor or internal combustion engine. The rotational power output from the prime mover  102  is transmitted by a drive belt  104  to a gearbox  106 . The gearbox  106  provides low-speed, high-torque rotation of a crankshaft  108 . Each end of the crankshaft  108  (only one is visible in  FIG. 1 ) carries a crank arm  110  and a counterbalance weight  112 . The reducer gearbox  106  sits atop a sub-base or pedestal  114 , which provides clearance for the crank arms  110  and counterbalance weights  112  to rotate. The gearbox pedestal  114  is mounted atop a base  116 . The base  116  also supports a Samson post  118 . The top of the Samson post  118  acts as a fulcrum that pivotally supports a walking beam  120  via a center bearing assembly  122 . 
     Each crank arm  110  is pivotally connected to a pitman arm  124  by a crank pin bearing assembly  126 . The two pitman arms  124  are connected to an equalizer bar  128 , and the equalizer bar  128  is pivotally connected to the rear end of the walking beam  120  by an equalizer bearing assembly  130 , commonly referred to as a tail bearing assembly. A horse head  132  with an arcuate forward face  134  is mounted to the forward end of the walking beam  120 . The face  134  of the horse head  132  interfaces with a flexible wire rope bridle  136 . At its lower end, the bridle  136  terminates with a carrier bar  138 , upon which a polish rod  140  is suspended. 
     The polish rod  140  extends through a packing gland or stuffing box  142  on a wellhead  144  above a well  200 . A rod string  146  of sucker rods hangs from the polish rod  140  within a tubing string  148  located within the well casing  150 . The rod string  146  is connected to a plunger  147  and traveling valve  149  of a subsurface pump  151  (depicted in  FIG. 3 ). In a reciprocating cycle of the beam pump  100 , well fluids are lifted within the tubing string  148  during the rod string  146  upstroke. In accordance with well-established rod lift pump design, a stationary standing valve  153  and reciprocating traveling valve  149  cooperate to lift fluids to the surface through the tubing string. 
     Turning to  FIG. 2 , shown therein is a depiction of a gas mitigation system  152  deployed within the well casing  150 . The gas mitigation system  152  includes a canister  154 , an intake tube  156  positioned within the canister  154 , and a tail pipe assembly  158  connected to the bottom of the canister  154 . The canister  154  is suspended by a shroud hanger  160  that includes one or more orifices  161  that permit the flow of fluid from the wellbore into the canister  154  through an open upper end  163 . An upper end of the tail pipe assembly  158  is connected to a bottom of the canister  154  and placed in fluid communication with an interior of the canister  154 . A plug  162  secured to the lower end of the tail pipe assembly  158  seals a distal end of the tail pipe assembly  158 . 
     The intake tube  156  is connected directly or indirectly to the tubing string  148  and extends through the shroud hanger  160 . The intake tube  156  optionally includes an intake  164  that is a perforated joint with a sufficient number of perforations to provide unrestricted flow into the intake tube  156 . The intake  164  optionally includes a screen or mesh cover that prevents larger solid particles from entering the intake tube  156 . In some embodiments, the standing valve  153  and other components of the subsurface pump  151  are positioned within the intake tube  156  inside the canister  154  (as depicted in  FIG. 3 ). The placement of the standing valve  153  in the canister  154  may assist with maximizing well drawdown. In other embodiments, the subsurface pump  151  is landed above the canister  154  and the intake tuber  156  extends down into the canister  154  to supply fluid to the subsurface pump  151  (as depicted in  FIG. 4 ). 
     The canister  154  and tail pipe assembly  158  each have an outer diameter that provides a tight clearance with respect to the diameter of the well casing  150 . In some embodiments, the cross-sectional width of the clearance is between about 2.5% to about 12% of the diameter of the well casing  150 . For example, for a 7 inch well casing  150  the canister  154  can be sized to provide a clearance of between about 0.5 inches to about 0.83 inches. For a 5 inch well casing  150 , the canister  154  can be sized such that it provides a clearance of between about 0.153 inches and 0.38 inches. The gas mitigation system  152  provides a larger clearance above the shroud hanger  160 . 
     As noted in  FIG. 3 , the tight clearance between the gas mitigation system  152  and the well casing  150  causes wellbore fluids to accelerate as they pass by the gas mitigation system  152 . A resulting reduction in the pressure of the fluid consistent with Bernoulli&#39;s principle assists with the separation of entrained gases from the liquids. Near the top of the gas mitigation system  152 , the velocity of the liquids and gases rapidly decreases as the cross-sectional annular increases. As the fluids begin to decelerate, the separated heavier liquid components are encouraged to fall into the canister  154  through the shroud hanger  160 , while the lighter gaseous components continue to rise in the annular space around the tubing string  148 . Solid particles entrained in the liquid fall into the canister  154  and into the tail pipe assembly  158 , where the particles are isolated and discouraged from entering the intake tube  156 . This produces a liquid-enriched reservoir inside the canister  154 , which can be drawn into the pump components through the intake tube  156 . Thus, during large gas slugging events, the beam pump unit  100  can continue to operate efficiently using the liquid reserve contained in the gas mitigation system  152 . 
     Turning to  FIG. 4 , shown therein is a depiction of an embodiment of the gas mitigation system  152  deployed in a deviated (horizontal) well  200 . In this embodiment, the gas mitigation system  152  further includes a velocity tube  166  that is connected to the plug  162  of the tail pipe assembly  158 . The velocity tube  166  extends from a vertical portion  202  around a heel portion  204  into the lateral portion  206  of the well  200 . The velocity tube  166  includes an open end  168  that permits the introduction of fluids into the velocity tube  166 . A packer  170  or other wellbore isolation device can be used to prevent or reduce the movement of fluids in the annular space between the velocity tube  166  and the well casing  150 . The velocity tube  166  includes a perforated joint  172  below the tail pipe assembly  158 . 
     Fluids and entrained solids entering the open end  168  pass through the velocity tube  166  to the perforated joint  172 . The fluids and solids are discharged at elevated velocities through the perforated joint  172  into the annular space between the velocity tube  166  and the well casing  150 . As illustrated in  FIG. 5 , the heavier solid particles fall downward while the gas and liquid components rise toward the tail pipe assembly  158 . In this way, the velocity tube  166  and perforated joint  172  of the gas mitigation system  152  cooperate to separate solid particles from the fluid stream before it approaches the canister  154 . 
     In yet another embodiment, the gas mitigation system  152  includes an elongated tail pipe assembly  158 . As depicted in  FIG. 6 , the elongated tail pipe assembly  158  extends into the heel portion  204  leading to the lateral section of the wellbore. The tail pipe assembly  158  may include flexible joints or be manufactured from an impermeable, flexible material that facilitates installation in unconventional wells. The elongated tail pipe assembly  158  has an outer diameter that provides a relatively tight clearance with the well casing  150 . The reduced cross-sectional area of the annular space increases the velocity of fluids passing through the well casing  150  around the tail pipe assembly  158 . The increased gas velocity provides a gas lift function that encourages the removal of liquids to the canister  154 . The enlarged tail pipe assembly  158  and plug  162  also provide a larger container for isolating solid particles separated from fluids in the canister  154 . The pressure in the annulus of the well casing  150  can be adjusted at the wellhead  144  to increase the gas lift function optimized by the elongated tail pipe assembly  158 . In some embodiments, the elongated tail pipe assembly  158  terminates at about 10 to 20 degrees above a lateral axis extending through a lateral portion of the wellbore. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention.