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[0001]     This application is a continuation of U.S. patent application Ser. No. 10/372,534, entitled “MULTIPLE ENTRANCE SHUNT,” filed on Feb. 21, 2003, which claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application 60/359,568, entitled “MULTIPLE ENTRANCE SHUNT,” filed Feb. 25, 2002. Each of these applications is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]     The invention generally relates to shunt tubes used in subsurface well completions, and particularly to shunt tubes having multiple entrances.  
         [0003]     Conduits providing alternate or secondary pathways for fluid flow are commonly used in well completions. The alternate pathways allow fluid to flow past and emerge beyond a blockage in a primary passageway. In prior art embodiments, the single entrance to an alternate pathway conduit could be covered, blocked, or otherwise become inaccessible to the fluid, thereby preventing the alternate pathway conduit from performing its intended function. Such blockage could occur, for example, when the conduit happened to be positioned on the bottom wall of a horizontal bore. Alternatively, if low viscosity fluids are used in an alpha beta wave pack, or should pumping fail, the conduit may become blocked. Therefore, there is a continuing need for improved entrance mechanisms to provide more reliable access to the alternate pathway conduits.  
       SUMMARY  
       [0004]     In an embodiment of the invention, multiple pathways are provided by which fluid can enter one or more alternate pathway conduits. Entrance tubes can be arranged such that their spacing prevents all of them from being simultaneously obstructed, covered, or otherwise blocked.  
         [0005]     Advantages and other features of the invention will become apparent from the following description, drawings, and claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0006]      FIG. 1  is a schematic diagram of a portion of a completion assembly constructed in accordance with an embodiment of the invention.  
         [0007]      FIG. 2  is a partially cutaway schematic diagram of an alternative embodiment of a completion assembly constructed in accordance with an embodiment of the invention.  
         [0008]      FIG. 3  is a perspective view of the completion assembly of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0009]      FIG. 1  shows a portion of a completion assembly  10  used in a well. A shunt tube  12  having a central passageway  14  is mounted on base pipe  16 . Only one shunt tube  12  is shown, but there may be more than one. Base pipe  16  may be slotted or perforated base pipe or production tubing. Entrance tubes  18  are also mounted on base pipe  16 . Entrance tubes  18  are azimuthally spaced around the circumference of base pipe  16  and connect at their lower ends to shunt tube  12 . Those connections could be made using jumper tubes or other connectors known in the art. Each entrance tube  18  has a passageway  20  in fluid communication with central passageway  14  to accommodate fluid flow through entrance tubes  18  and shunt tube  12 .  
         [0010]     In the embodiment of  FIG. 1 , entrance tubes  18  are joined at a manifold  22 . Entrance tubes  18  may, however, join shunt tube  12  in various places along the length of shunt tube  12 , without relation to the junction of shunt tube  12  and other entrance tubes  18 . Entrance tubes  18  may also join to more than one shunt tube  12 . Entrance tubes  18  may have similar flow capacity to shunt tube  12 , or in an alternative embodiment, entrance tubes  18  may have a smaller flow capacity than shunt tube  12 . The flow capacities and angle of intersection of entrance tubes  18  with shunt tube  12  is chosen so as to prevent blockage from occurring within entrance tubes  18  or shunt tube  12 . That may be a concern, for example, should pumping be halted before a desired operation is completed.  
         [0011]      FIG. 1  shows centralizers  24  radially extending from base pipe  16 . Centralizers  24  are azimuthally spaced around the circumference of base pipe  16  and serve to keep base pipe  16  approximately centered in the wellbore. Shunt tubes  12  and entrance tubes  18  can be run between centralizers  24  and inside or outside a sand screen. (not shown).  
         [0012]     Because shunt tube  12  is an alternate pathway conduit, used to convey fluid past a blockage, it may be desirable to restrict fluid from entering entrance tubes  18  until shunt tube  12  is needed. That could be done by placing restriction members  26  such as valves or rupture discs across the openings of entrance tubes  18 . By using rupture discs, for example, flow into entrance tubes  18 , and therefore shunt tube  12 , would be prevented under normal operating pressures. However, if a blockage (bridging) occurred, pressure in the annular region could be increased until one or more discs burst, allowing fluid to pass.  
         [0013]      FIGS. 2 and 3  shows an alternative embodiment of the invention.  FIG. 2  shows a body  28  having channels  30 . Channels  30  can be milled or formed using other conventional methods. Channels  30  form pathways for fluid flow and essentially serve the functions of entrance tubes  18 . Channels  30  merge to direct their flow into one or more outlets  32 . There may be any number of channels  30 , the openings of which are azimuthally spaced. A cover  34  ( FIG. 3 ) is mounted to body  28  to confine the fluid entering a particular channel  30  to travel through that channel  30  until it reaches an outlet  32 . Outlets  32  join to sand screen assemblies (not shown) using jumper tubes or other known connectors.  
         [0014]     In the embodiment shown in  FIGS. 2 and 3 , there are four channels  30  (though one channel  30  is obscured from view). Because there are two outlets in this instance, those four channels  30  are divided into pairs. The two channels  30  forming one particular pair merge to direct their fluid to one of the outlets  32 . The other pair similarly merges to direct its output to the other outlet  32 . Channels  30  can be merged by groups according to the number of outlets  32  available in any particular embodiment. Restriction members  26  can be placed in channels  30  to control access by the fluid until some operational condition is met. In the embodiment of  FIGS. 2 and 3 , base pipe  16  is preferably not slotted or perforated.  
         [0015]     In operation, a fluid such as a gravel slurry or fracturing fluid is pumped into an annular region between a production zone of the well and base pipe  16 . Often the fluid is initially pumped through a work string down to a crossover mechanism which diverts the flow into the annular region some distance below the well surface. In any case, when the fluid encounters entrance tubes  18 , it flows into entrance tubes  18  and travels through passageway  20 . Because entrance tubes  18  are azimuthally arranged, there is always at least one open fluid path through entrance tubes  18  into central passageway  14  of shunt tube  12 . That insures the fluid can pass into shunt tube  12 .  
         [0016]     The operation of the alternative embodiment is similar. The fluid is pumped into the annulus. When bridging occurs, the fluid backs up and the pressure increases. The fluid finds the openings of channels  30  and, in the absence of restrictor devices, flows into channels  30  and into shunt tubes  12 . In those embodiments employing restrictor members  26 , the fluid may be restricted from passing into the relevant passageway until the restriction member  26  therein is defeated.  
         [0017]     Although only a few example embodiments of the present invention are described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.

Summary:
Multiple pathways are provided by which fluid can enter one or more alternate pathway conduits. Entrance tubes can be arranged such that their spacing prevents all of them from being simultaneously obstructed, covered, or otherwise blocked.