Patent Publication Number: US-9416622-B2

Title: Resilient downhole flow restrictor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national phase under 35 U.S.C. 371 of International Patent Application No. PCT/US2012/054721, titled “Resilient Downhole Flow Restrictor,” filed Sep. 12, 2012, the entirety of which is incorporated herein by reference. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to flow restrictors for controlling fluid flow in a downhole environment of a subterranean formation and, more particularly (although not necessarily exclusively), to flow restrictors for use with alternative path systems and that include resilient flaps that can change position and facilitate downhole operations, such as gravel packing. 
     BACKGROUND 
     Various devices can be installed in a well traversing a hydrocarbon-bearing subterranean formation. Some devices facilitate gravel packing operations, which can involve introducing a slurry mix downhole through a main transport tube for deposition of gravel or sand included in the slurry mix in an annulus in the wellbore. Alternative path systems, such as shunt tubes, can be used as a backup to the main transport tube to allow delivery of the slurry mix in the annulus even if the main transport tube is blocked. Packing tubes may be included with shunt tubes. The packing tubes can include openings through which the slurry can be delivered to the annulus. Slurry can be delivered through the packing tube openings instead of from the shunt tubes because including openings in the shunt tubes may risk high leak off of fluid from the slurry, which may result in gravel or sand blocking flow in the shunt tubes. 
     Simpler alternative path systems, however, are desirable. For example, alternative path systems are desirable that can deliver slurry to an annulus without requiring additional tubes, such as packing tubes, and that avoid issues associated with unintended fluid leak off from the slurry. 
     SUMMARY 
     Certain aspects of the present invention are directed to a flow restrictor that includes resilient flaps that can variably restrict fluid flow based on fluid flow pressure and prevent unintended fluid leak off to avoid the need for additional tubes in a gravel packing system. 
     One aspect relates to a flow restrictor that can be disposed on a component in a wellbore of a subterranean formation. The flow restrictor includes a plurality of resilient flaps that overlap each other. The resilient flaps can flex outwardly into the wellbore to an open position in response to fluid flow pressure in an inner area of the component. The resilient flaps can return to an initial position at which the resilient flaps restrict fluid flow more than in the open position. 
     Another aspect relates to a transport tube that can be an alternative flow path to a main tube in a wellbore. The transport tube includes a flow restrictor on an outer surface of the transport tube. The flow restrictor includes resilient flaps that can at least partially overlap in a closed position. The resilient flaps can flex outwardly to an open position in response to fluid flow pressure in an inner area of the transport tube. The resilient flaps can return to the closed position from the open position. 
     Another aspect relates to a gravel packing assembly that can be disposed in a wellbore. The gravel packing assembly includes: 
     a main tube for providing a main flow path for gravel packing slurry; 
     a transport tube for providing an alternative flow path to the main flow path for the gravel packing slurry; 
     a flow restrictor on a surface of the transport tube, the flow restrictor comprising a plurality of resilient flaps that overlap and that are configured for flexing outwardly to a bend position in response to flow pressure in an inner area of the transport tube and for returning to an initial position, 
     wherein the plurality of resilient flaps are configured for variably restricting flow of the gravel packing slurry between the initial position and the bend position based on the flow pressure in the transport tube. 
     These illustrative aspects and features are mentioned not to limit or define the invention, but to provide examples to aid understanding of the inventive concepts disclosed in this disclosure. Other aspects, advantages, and features of the present invention will become apparent after review of the entire disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a well system having alternative path systems including flow restrictors according to one aspect of the present invention. 
         FIG. 2  is a perspective view of an alternative path system that includes a flow restrictor on a surface thereof according to one aspect of the present invention. 
         FIG. 3A  is a top view of a flow restrictor in a closed position according to one aspect of the present invention. 
         FIG. 3B  is a side view of the flow restrictor of  FIG. 3A  according to one aspect of the present invention. 
         FIG. 4A  is a top view of a flow restrictor in an open position according to one aspect of the present invention. 
         FIG. 4B  is a side view of the flow restrictor of  FIG. 4A  according to one aspect of the present invention. 
         FIG. 5A  is a top view of a flow restrictor returned to the closed position according to one aspect of the present invention. 
         FIG. 5B  is a side view of the flow restrictor of  FIG. 5A  with sand deposed on one side of the flow restrictor according to one aspect of the present invention. 
         FIG. 6  is a top view of a flow restrictor that includes a housing according to one aspect of the present invention. 
         FIG. 7  is a top view of a flap of a flow restrictor according to one aspect of the present invention. 
         FIG. 8  is a side view of a flap of a flow restrictor according to one aspect of the present invention. 
         FIG. 9  is a side view of a flap of a flow restrictor according to another aspect of the present invention. 
         FIG. 10A  is a top view of overlapping flaps of a flow restrictor according to one aspect of the present invention. 
         FIG. 10B  is a bottom view of the overlapping flaps of  FIG. 10A  according to one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and features relate to a flow restrictor including resilient flaps that can flex outward to an open position in response to fluid flow pressure and return to an initial position at which the resilient flaps restrict fluid flow more than in the open position. Examples of flow restrictors include nozzles and valves that can be positioned in a wellbore with a sub-system component. 
     The flow restrictor can be included with a gravel packing sub-system that includes an alternative path system, such as a shunt tube. The flow restrictor may be located on a surface of the alternative path system. The resilient flaps can open in response to fluid flow pressure in the alternative path system exceeding a threshold and allow fluid, which may include a gravel pack slurry, to flow without substantial restriction into an annulus about the alternative path system. Subsequent to an area of the annulus that is proximate to the flow restrictor filling with sand, the flaps can return to the initial position. 
     The resilient flaps may be made from a flexible material and may be normally in a closed position. The resilient flaps can be configured to open in only one direction and return to the initial position after a fluid flow pressure is below a certain threshold. The resilient flaps in the closed position may include a small gap that can reduce pressure differential across the flow restrictor, but reduce leak off of water or other carrier for slurry in the alternative path system. The resilient flaps that can reduce leak off can be used with alternative path systems that do not require use of packing tubes. 
     The flexible material may be any material that is not permanently deformable, does not erode or degrade, and is resilient. Examples of flexible material include stainless steel and elastic material. 
     These illustrative aspects and examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects but, like the illustrative aspects, should not be used to limit the present invention. 
       FIG. 1  depicts a well system  100  with flow restrictors according to certain aspects of the present invention. The well system  100  includes a bore that is a wellbore  102  extending through various earth strata. The wellbore  102  has a substantially vertical section  104  and a substantially horizontal section  106 . The substantially vertical section  104  and the substantially horizontal section  106  may include a casing string  108  cemented at an upper portion of the substantially vertical section  104 . The substantially horizontal section  106  extends through a hydrocarbon bearing subterranean formation  110 . 
     A tubing string  112  extends from the surface within wellbore  102 . The tubing string  112  can provide a conduit for gravel pack slurry to travel from the surface to the substantially horizontal section  106 . A base pipe coupling  114  can couple two sections  116 ,  118  of the tubing string  112 . Included in an annulus about the tubing string sections  116 ,  118  is an alternative path system  120 . The alternative path system  120  includes transport tubes  122 ,  124 , which may be shunt tubes, and a jumper tube  126 . Included on the transport tubes  122 ,  124  are flow restrictors  128 ,  130 . 
     Although  FIG. 1  depicts tubing string sections  116 ,  118  that can include flow restrictors  128 ,  130  positioned in the substantially horizontal section  106 , tubing string sections  116 ,  118  (and flow restrictors  128 ,  130 ) according to various aspects of the present invention can be located, additionally or alternatively, in the substantially vertical section  104 . Furthermore, any number of tubing string sections having flow restrictors, including one, can be used in the well system  100 . In some aspects, tubing string sections having flow restrictors can be disposed in simpler wellbores, such as wellbores having only a substantially vertical section. Flow restrictors can be disposed in open hole environments, such as is depicted in  FIG. 1 , or in cased wells. 
       FIG. 2  depicts part of an alternative path system that is a transport tube  202 . The transport tube  202  includes an inner area (not shown) that can carry fluid, such as slurry. On a surface of the transport tube  202  is an opening in which is located a flow restrictor  204 . The flow restrictor  204  can open in response to fluid flow pressure in the inner area of the transport tube exceeding a threshold. The flow restrictor  204  can subsequently return to an initial position in response to pressure falling below the threshold. 
     The transport tube  202  shown in  FIG. 2  has a rectangular cross-section. Transport tubes according to other aspects may be round or otherwise have cross-sections of a shape other than rectangular. Furthermore, the flow restrictor  204  in  FIG. 2  is circular. Flow restrictors according to other aspects can have shapes other than circular, such as rectangular, square, and five-sided. 
       FIGS. 3A-3B  depict the flow restrictor  204  in an initial or “closed” position. The flow restrictor  204  includes four resilient flaps  206 A-D. Each of the flaps  206 A-D extends from an edge of the flow restrictor  204  toward a gap  208  formed by ends of the flaps  206 A-D. An edge of the flow restrictor  204  may be coupled to the surface of a transport tube or to a housing of the flow restrictor. In the initial or “closed” position, the flaps  206 A-D can substantially restrict fluid from flowing between an inner area of the transport tube to an outer area of the transport tube, but the gap  208  can reduce pressure differential across the flow restrictor  204 . The flaps  206 A-D can overlap each other to increase restriction of flow. 
       FIGS. 4A-4B  depict the flow restrictor  204  in an open position in response to fluid flow pressure from an inner area of the transport tube exceeding a threshold. In the open position, the flaps  206 A-D flex outwardly such that the gap  208  is enlarged to be an opening through which fluid can flow without substantial restriction, as represented by the arrow in  FIG. 4B . For example, at least part of the flaps  206 A-D can bend in response to the fluid flow pressure exceeding a threshold such that the distance between ends of the flaps  206 A-D is enlarged to create the opening. The fluid flow pressure may be a function of slurry fluid pumped into the wellbore. The opening may be any suitable size to allow fluid flow without substantial restriction as compared to the initial or “closed” position. An example of a suitable size is one in the range of one-quarter inch to three-eighths inch. 
     The flaps  206 A-D can transition from the initial position to the open position in response to changes to fluid flow pressure and variably restrict fluid flow based on the fluid flow pressure. For example, after fluid flow pressure exceeds a certain threshold at which the flaps  206 A-D begin to flex, the flaps  206 A-D can flex outwardly at a rate that is based on a rate of increase in the fluid flow pressure. 
       FIGS. 5A-5B  depict the flow restrictor  204  returned to the initial or “closed” position in response to sand  210  or other medium filling the area external to the transport tube and proximate to the flow restrictor  204 . The sand  210  or other medium can cause flow from the area internal to the transport tube to reduce flow rate and pressure exerted on the flaps  206 A-D. The flaps  206 A-D can be resilient by returning the initial or “closed” position after the fluid flow pressure is reduced below a certain threshold. 
       FIG. 6  depicts a flow restrictor  302  according to another aspect. The flow restrictor  302  includes resilient flaps  304 A-D and a housing  306  to which portions of the flaps  304 A-D are coupled. The housing  306  may be made from a rigid metal or other substance and can be coupled to a transport tube or other oilfield sub-assembly. Each of the flaps  304 A-D extends from the housing  306  toward a gap  308  formed by the ends of the flaps  304 A-D. As shown in  FIG. 7 , each flap  304  includes a curved edge  310  and two edges  312 ,  314  that extend from the curved edge  310  to a point that is an end of the flap  304 . 
     Resilient flaps according to various aspects can each have variable thicknesses.  FIG. 8  depicts by side view a resilient flap  402  according to one aspect that has a greater thickness at a first portion  404  than at a second portion  406  with a linear change in thickness between the first portion  404  and the second portion  406 . The first portion  404  may couple the flap  402  to a housing or transport tube. The thickness of the first portion  404  may prevent the first portion  404  from flexing in response to fluid flow pressure above a certain threshold, but below an extraordinary threshold at which pressure may damage the alternative path system in any event. The thickness of the second portion  406 , and at least part of the portion between the first portion  404  and the second portion  406 , may flex outwardly in response to fluid flow pressure above a certain threshold. 
       FIG. 9  depicts a resilient flap  502  according to another aspect that includes two defined portions  504 ,  506  having different thicknesses, the thickness of portion  504  being greater than that of portion  506 . The resilient flap  502  does not include a linear transition from a maximum thickness to a minimum thickness as in the resilient flap  402  of  FIG. 8 . Instead, the thickness between portions  504 ,  506  changes abruptly at transition point  508 . In other aspects, the transition point  508  includes a linear or curved portion that provides a less abrupt transition between the thicknesses than is shown in  FIG. 9 . 
     As described previously, resilient flaps can overlap each other to facilitate fluid flow restriction.  FIGS. 10A-10B  depict two flaps  602 ,  604  that overlap each other to form an overlapping area  606 . An edge of flap  602  is shown as being above flap  604  in  FIG. 10A  and an edge of flap  604  is shown as being below flap  602 . The arrangement is reversed when viewed from the bottom view shown in  FIG. 10B . 
     Resilient flaps according to various aspects can be any shape. In some aspects, flaps of a flow restrictor have different shapes. In some aspects, the flaps can overlap to form a gap or opening that is not centered or otherwise in the middle of an area defined by the flow restrictor. 
     The foregoing description of the aspects, including illustrated aspects, of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of this invention.