Patent Publication Number: US-6216788-B1

Title: Sand protection system for electrical submersible pump

Description:
TECHNICAL FIELD 
     This invention relates to a method and apparatus for removing sand that collects below an electrical submersible pump in a well. In particular, the invention relates to a method and apparatus for separating sand from well fluids and then pumping the separated sand to the surface. 
     BACKGROUND ART 
     Electrical submersible pumps are widely used in oil wells. It is desirable to remove sand and other solid particles from well fluids before they enter the submersible pump since sand causes wear and plugging of the pump and other components. The subsequent repairs or replacement of a downhole pump can be expensive due to labor, parts costs and loss of production. 
     During oil production from a well, oftentimes sand or other particles that are entrained with well fluids are pumped through the downhole pump. Various sand control systems have been implemented to stop or reduce sand flow into the wellbore. Screens or filter openings have been utilized in the casing or other members to restrict the flow of solid particles. In many wells, the quantity of sand flowing from the formation is relatively small, but is sufficient to wear or plug the downhole pump. One solution is to provide a separator, such as a hydro-cyclone separator to separate sand from well fluids that enter the wellbore. 
     Once the sand is separated from the fluids, the separated sand will settle out within the wellbore. If large quantities of sand are produced, then it may be necessary to remove sand from the wellbore. Since it is expensive to cease production and pull the electrical submersible pump, it is desirable to utilize a method and apparatus for removal of the sand without pulling the electrical submersible pump. 
     DISCLOSURE OF INVENTION 
     An electrical submersible pump (ESP) is suspended on a flow conduit within a well. A separator is provided to separate sand from well fluids before the well fluids enter the pump. A bypass tube is connected from the flow conduit above the pump to a location below the pump where the sand is collected. The electrical submersible pump may be turned off to allow fluid levels within the flow conduit to equalize. The flow conduit is then pressurized at the surface to cause a downward flow of well fluid in the flow conduit below an equilibrium point for the well fluid. After lowering the level of fluid within the flow conduit, the pressure within the flow conduit is then relieved, which causes well fluid to flow back up through the bypass tube to the flow conduit. The upward flow of well fluid results in sand being drawn up the bypass tube into the flow conduit above the pump. The fluid and sand are routed through the bypass tube rather than through the pump since the flow path through the pump is obstructed. A check valve in the bypass tube prevents back-flow of sand and fluid through the bypass tube after the sand and fluid have flowed up through the bypass tube into the flow conduit. Once the fluid and sand have flowed into the flow conduit above the pump, the pump may be restarted and the sand and fluid in the flow conduit may be pumped to the surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic drawing of a sand evacuator system of the invention that utilizes a shroud over the electrical submersible pump assembly. 
     FIG. 2 shows a schematic representation of an alternate embodiment of the sand evacuator system of the invention wherein a separator is mounted within the casing on a packer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, shown is a well  10  having a sand protection system for an electrical submersible pump (ESP)  12 . The ESP  12  has a motor  14 , a seal section  16 , and a pump  18  having an intake  20 . The well  10  has a casing  22  and a flow conduit  24 , such as tubing, that extends through casing  22 . The flow conduit  24  and casing  22  define a casing annulus  26  that surrounds flow conduit  24 . A compressor or pump  28  communicates with an upper end of flow conduit  24  for pressurizing the flow conduit  24  as desired. A valve  30  is located on a lower end of flow conduit  24 . Valve  30  may be a Y-tool  31  (FIG. 1) having a first leg  32  and a bypass leg  33 . A first tube  34  and a bypass tube  35  communicate with Y-tool  31 . First leg  32  communicates with first tube  34  and bypass leg  33  communicates with bypass tube  35 . The electrical submersible pump  12  is located within first tube  34 . Valve  30  may also be a sliding sleeve valve  36  (FIG.  2 ). Sliding sleeve valve  36  has a housing  37  defining a passageway  38  and port  39 . Sleeve  40  is slidingly received within sliding sleeve valve  36  to selectively close off port  39 . Passageway  38  communicates with bypass tube  35  and port  39  communicates with first tube  34 . 
     A hydro-cyclone separator  41  (FIG. 1) is provided below the electrical submersible pump  12 . The separator  41  separates solids, such as sand, from well fluids. The separator  41  has a mixed fluids inlet  42  and a first outlet  44  that transmits fluids upward past the motor  14  and seal section  16  to be drawn in by intake  20  of pump  18  of the electrical submersible pump  12 . The hydro-cyclone separator  41  is affixed to a shroud  46  (FIG. 1) that surrounds the electrical submersible pump  12 . Separated well fluid is delivered out of first outlet  44  into shroud  46  (FIG.  1 ). 
     Referring now to FIG. 2, in an alternate embodiment, the hydro-cyclone separator  48  may be positioned within casing  22  above a packer  50 . Bypass tube  35  communicates with valve  30 , such as sliding sleeve valve  36 , and extends to a location below separator  48  in FIG. 2 to a location proximate the separated solids. Sliding sleeve valve  36  or Y-tool  31  may be used with or without shroud  46 . Y-tool  31  is shown in conjunction with shroud  46  as an example only. 
     Additionally, the invention may include a flow inhibitor  54  positioned in a flow path through pump  18  of ESP  12  to encourage flow through bypass tube  35 . In a preferred embodiment, a check valve  56  is located in bypass tube  35  to prevent backflow through bypass tube  35 . A second check valve  58  may be provided in bypass tube  35  to restrict flow from casing annulus  26  into bypass tube  35 . Second check valve  58  allows backflow from bypass tube  35  to flow into casing annulus  26 . A sand chamber  60  is provided in the lower end of shroud  46  (FIG. 1) to collect separated solids such as sand. In the embodiment without shroud  46  (FIG.  2 ), sand collects above packer  50 . 
     In operation, bypass tube  35  is connected from the flow conduit  24  above the pump  18  of ESP  12  to a location near the separated sand. The separated sand may be in sand chamber  60  (FIG. 1) or may be located above packer  50  within casing  22  (FIG.  2 ). Once it is determined that the separated sand is to be removed, the electrical submersible pump  12  is turned off. Preferably, fluids within the well  10  are allowed to equalize to an equilibrium point. The flow conduit  24  is then pressurized by pump  28  at the surface. The flow conduit  24  is preferably pressurized by pumping a gas into flow conduit  24 . The pressure in flow conduit  24  results in a downward flow of well fluid within the flow conduit  24  to a point below the equilibrium point for the well fluid. The downward flow of well fluids is preferably routed through pump  18 . The bypass tube  35  is kept open and the pressure from the surface on the flow conduit  24  is then relieved. Once the pressure within the flow conduit  24  is relieved, the well fluid will flow back up the flow conduit  24  to its equilibrium point. The upward flow of well fluid will draw sand and fluid up the bypass tube  35  into the flow conduit  24  above the pump  18 . Well fluid flows through bypass tube  35  instead of through first tube  34  since components within ESP  12  provide resistance to flow. To better facilitate flow up bypass tube  35 , a flow inhibitor  54  may be provided to further inhibit flow up through the first tube  34  of the system. 
     A check valve  56  prevents backflow of sand back down the bypass tube  35 . A second check valve  58  may be provided to allow fluids to pour back into the casing annulus  26  in the embodiment of FIG. 1 that utilizes a shroud  46 . After the sand and fluids have flowed up the bypass tube  35 , the pump  18  of the ESP  12  may be started to pump the sand up the flow conduit  24  to the surface. 
     The invention has several advantages. The use of a separator prevents sand from entering into a submersible pump, which increases the life of the pump. The bypass tube allows for the removal of separated sand from the well without pulling the ESP. The result is an increase in efficiency and lower cost to an operator. 
     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.