Abstract:
In carrying out the principles of the present invention, in accordance with an embodiment thereof, an annular choke apparatus, and methods of use, are provided for use within a subterranean well. In broad terms, a choke tool apparatus is provided which includes an outer housing having an outer housing wall with at least one flow port therethrough, and a variable annular flow-area choke disposed within the outer housing, the variable annular flow-area choke having a first generally tubular member sealingly disposed within the outer housing, the first tubular member having a shoulder with a sealing surface, a second generally tubular member slidingly and sealingly disposed within the outer housing, the second tubular member having a shoulder with a sealing surface, the second member movable between a sealed position wherein the sealing surfaces are in sealing abutment and an open position wherein the sealing surfaces are spaced apart. The sealing surfaces preferably provide a metal-to-metal seal. The variable annular flow-area choke described herein preferably provides for infinite adjustment between open and closed positions for precise flow regulation. The apparatus may include an actuator, locking, adjustment and biasing assemblies.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to apparatus utilized to control fluid flow in a subterranean well and, more particularly provides a choke for selectively regulating fluid flow into or out of a tubing string disposed within a well.  
         BACKGROUND  
         [0002]    Typically, a flow control apparatus is used to throttle or choke fluid flow into a production tubing string of a subterranean hydrocarbon well. Such flow control chokes are particularly useful where multiple zones are produced and it is desired to regulate the rate of fluid flow into the tubing string from each zone. Additionally, regulatory authorities may require that rates of production from each zone be reported, necessitating the use of a choke apparatus or other methods of determining and/or controlling the rate of production from each zone. Safety concerns may also dictate controlling the rate of production from each zone.  
           [0003]    Flow chokes are also useful in single zone completions. For example, in a single wellbore producing from a single zone, an operator may determine that it is desirable to reduce the flow rate from the zone into the wellbore to limit damage to the well, reduce water coning and/or enhance ultimate recovery.  
           [0004]    Downhole valves, such as sliding side doors, are designed for operation in a fully closed or fully open configuration and, thus, are not useful for variably regulating fluid flow therethrough. Downhole chokes typically are provided with a fixed orifice which cannot be variable without intervention. These are placed downhole to limit flow from a certain formation. Unfortunately, conventional downhole valves and chokes are also limited in their usefulness because intervention is required to change the fixed orifice or to open or close the valve. Additionally, it is difficult to open a sliding side door slowly against a large differential pressure (such as, in excess of 2500 psi) without damage to any of the door seals because these seals must pass through the flow.  
           [0005]    What is needed is a flow control apparatus which is rugged, reliable, and long-lived, so that it may be utilized in completions without requiring frequent service, repair or replacement. To compensate for changing conditions, the apparatus should be adjustable. The apparatus should be resistant to erosion, even when it is configured between its fully open and closed positions, and should be capable of accurately regulating fluid flow. Additionally, there is a need for a variable choke which can open against a high differential pressure without excessive damage to the choke seals.  
           [0006]    Such a downhole variable choking device would allow an operator to maximize reservoir production into the wellbore. It would be useful for completions, including any well where it is desired to control fluid flow, such as gas wells, oil wells, and water and chemical injection wells, in sum, in any downhole environment for controlling the flow of fluids.  
           [0007]    This is accordingly an object of the present invention to provide such a flow control apparatus which permits infinitely variable downhole flow choking as well as the ability to shut off fluid flow, and associated methods of controlling fluid flow within a subterranean well.  
         SUMMARY  
         [0008]    In carrying out the principles of the present invention, in accordance with an embodiment thereof, an annular choke apparatus, and methods of use, are provided for use within a subterranean well. In broad terms, a choke tool apparatus is provided which includes an outer housing having an outer housing wall with a least one flow port therethrough, and a variable annular flow-area choke disposed within the outer housing, the variable annular flow-area choke having a first generally tubular member sealingly disposed within the outer housing, the first tubular member having a shoulder with a sealing surface, a second generally tubular member slidingly and sealingly disposed within the outer housing, the second tubular member having a shoulder with a sealing surface, the second member movable between a sealed position wherein the sealing surfaces are in sealing abutment and an open position wherein the sealing surfaces are spaced apart. The sealing surfaces preferably provide a metal-to-metal seal. The variable annular flow-area choke described herein preferably provides for infinite adjustment between open and closed positions for precise flow regulation. The apparatus may include an actuator, locking, adjustment and biasing assemblies. In gas lift and other operations it may be desirable to variably regulate the flow without sealing the valve.  
           [0009]    These and other aspects, features, objects, and advantages of the present invention will be more fully appreciated following careful consideration of the detailed description and accompanying drawings set forth hereinbelow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    FIGS.  1 A-C are sectional views taken along line A-A of FIG. 4, of successive longitudinal portions of a choke embodying principles of the present invention, the choke shown in a configuration for running into a subterranean wellbore;  
         [0011]    [0011]FIG. 2 is a sectional view of the choke shown in a partially open position;  
         [0012]    FIGS.  3 A-C are sectional views taken along line B-B of FIG. 4, of the choke shown in a fully open position;  
         [0013]    [0013]FIG. 4 is an end view of the upper end of the tool assembly;  
         [0014]    FIGS.  5 A-D are detail views of various choke assemblies; and  
         [0015]    [0015]FIG. 6 is a graphical representation of the choke&#39;s open flow-area versus the travel of the choke members. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Illustrated in FIGS.  1 A-C is a tool assembly  10  embodying the principles of the invention. In the following description of the tool assembly  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Although the tool assembly  10  and other apparatus, etc., shown in the accompanying drawings are depicted in successive axial sections, it is to be understood that the sections form a continuous assembly. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention.  
         [0017]    The tool assembly  10 , as shown, includes a choke assembly  12  disposed within a generally tubular outer housing  14 . An actuator assembly  16 , adjustment assembly  18 , locking assembly  20 , and biasing assembly  22  may also be included.  
         [0018]    In a method of using the tool assembly  10 , the variable annular flow-area choke assembly  12  and actuator assembly  16  are positioned within a subterranean well as part of a production tubing string  24  extending to the earth&#39;s surface. As representatively illustrated in FIG. 3A-C, fluid (indicated by arrows  26 ) may flow axially through the tool assembly  10 , and to the earth&#39;s surface via the tubing string  24 . The fluid  26  may, for example, be produced from a zone of the well below the tool assembly  10 . In that case, an additional portion of the tubing string  24  including a packer (not shown) would be attached in a conventional manner to a lower adaptor  40  of the tool assembly  10  and set in the well in order to isolate the zone below the tool from other zones of the well. The tool assembly  10  enables accurate regulation of fluid flow between the external area  28  and an internal axial fluid passage  30  extending through the choke.  
         [0019]    In another method of using the tool assembly  10 , multiple chokes may be installed in the tubing string  24 , with each of the tools corresponding to a respective one of multiple zones intersected by the well, and with the zones being isolated from each other external to the tubing string. Thus, the tool assembly  10  also enables accurate regulation of a rate of fluid flow from each of the multiple zones, with the fluids being commingled in the tubing string  24 .  
         [0020]    It is to be understood that, although the tubing string  24  is representatively illustrated in the accompanying drawings with fluid  26  entering the lower adaptor  40  and flowing upwardly through the fluid passage  30 , the lower connector  40  may actually be closed off or otherwise isolated from such fluid flow in a conventional manner, such as by attaching a bull plug thereto, or the fluid  26  may be flowed downwardly through the fluid passage  30 , for example, in order to inject the fluid into a formation intersected by the well, without departing from the principles of the present invention.  
         [0021]    The outer housing  14  preferably has a lower adapter  40  and upper adapter  42  for attaching the tool assembly  10  as part of a tubing string  24 . The upper adapter  42  is integrally formed with outer housing  14  while the lower adapter  40  is sealingly attached at threads  48  to form part of the housing  14 . It is understood that various portions of the tool assembly may be integrally formed with one another or attached together as is known in the art. As shown, the tool has only a single body joint thread enabling manufacture at a reduced cost compared to other designs. The generally tubular outer housing wall  44  separates an exterior area  28  from an internal fluid passageway  30 . Wall  44  defines an interior surface  46 . The Figures show the generally tubular fluid passage  30  offset from the center of the generally tubular outer housing  14 . Such an arrangement better allows for placement of hydraulic inlets, fluid ports, control lines, and the like. It is understood that any of the generally tubular assemblies and parts described herein may be arranged concentrically or not, as desired, may be circular in cross-section, as shown, or may contain irregularities.  
         [0022]    The variable annular flow-area choke assembly  12  is sealingly attached to the actuator assembly  16 , shown in FIGS.  1 A-C. The actuator assembly  16  is used to operate the variable choke  12 . The actuator assembly shown is only an example of actuators known in the art and hydraulically controlled, but it is understood that the actuator may be hydraulically, electrically, mechanically, magnetically or otherwise controlled as is known in the art.  
         [0023]    The actuator assembly  16  axially displaces mandrel  50  along the interior of outer housing  14 . Preferably, mandrel  50  is connected to choke assembly  12  through locking assembly  20  and adjustment assembly  18 , as shown, however, other arrangements can be employed as desired. Mandrel  50  includes profile sleeve  52  and is attached thereto by latch ring assembly  54 . Mandrel  50  and sleeve  52  may be integrally formed, but for tool assembly purposes are preferably separate. Profile sleeve  52  moves axially along the interior wall surface  46  of the outer housing  14 . Upward movement of sleeve  52  is limited, as seen in FIGS.  3 A-C, by contact between mating shoulder surface  56  on the upper end  60  of mandrel  50  and corresponding shoulder  58  defined by the interior surface  46  of outer housing  14 .  
         [0024]    Mandrel  50  is hydraulically reciprocally actuated. Hydraulic supply lines (not shown) supply hydraulic pressure at upper and lower hydraulic inlets  60  and  62 , as seen in FIG. 4. Pressure is transmitted along upper and lower hydraulic passages  64  and  66  and upper and lower hydraulic ports  68  and  70 , which are preferably defined within housing wall  44  as shown. Hydraulic inlet ports  60  and  62  may be attached to a hydraulic control line fitting  63  as seen in FIG. 3.  
         [0025]    Upper hydraulic port  68  supplies hydraulic pressure to upper hydraulic chamber  72  in the annular space between mandrel  50  and outer housing wall  44 . Upper piston  76  is attached externally about mandrel  50 . Upper piston preferably includes bearing rings  78  and  80  and circumferential seals  82 , preferably a vee-packing seal. Upper piston  76  is engaged with mandrel  50  such that axial movement of the piston  76  by the actuator assembly  16  causes a corresponding axial displacement of the mandrel  50 . Movement of the piston  76  causes movement of the choke assembly  12  from a closed position  150 , as seen in FIGS.  1 A-C, towards an open position  152 , as seen in FIGS.  3 A-C. The variable annular flow-area choke  12  is preferably infinitely variable and is seen in an intermediate or partially open position in FIG. 2.  
         [0026]    The mandrel  50  is sealingly received in the outer housing  14 . Circumferential seal  86  sealingly engages the mandrel  50  externally and permits fluid isolation between the upper hydraulic chamber  72  and lower hydraulic chamber  74 . Seal  86  is preferably a vee-packing seals and may include bearing rings  82  and  84 .  
         [0027]    Lower hydraulic port  62  supplies pressure to lower hydraulic chamber  74  in the annular space between mandrel  50  and wall  44  below seal  86  and is operable to axially move lower piston  90 . Lower piston  90  preferably includes seal  92 , and retaining rings  98  which cooperate with corresponding grooves  96  in mandrel  50 . Axial displacement of lower piston  90  facilitates corresponding axial displacement of mandrel  50  and operates to move the choke assembly  12  from any open position, such as seen in FIGS. 2 and 3, towards a closed position  150 , as in FIG. 1.  
         [0028]    It is understood that selective operation of actuator assembly  16  operates to selectively open and close choke assembly  12 . The choke  12  may be moved to an open position  152 , as in FIG. 3, or a closed position  150 , as in FIG. 1, or any position therebetween, making the choke infinitely variable.  
         [0029]    Axial displacement of the mandrel  50  is accomplished by applying fluid pressure to one of the chambers  72  or  74 , thereby applying an axially directed biasing force to the pistons  76  or  90 , respectively. For example, if it is desired to displace the mandrel  50  axially upward to permit or increase fluid flow through the choke  12  or to decrease resistance to fluid flow therethrough, fluid pressure may be applied to the upper chamber  72 . Conversely, if it is desired to downwardly displace the mandrel  50  to prevent or decrease fluid flow through the choke  12  or to increase resistance to fluid flow therethrough, fluid pressure may be applied to the lower chamber  74 .  
         [0030]    It is understood that the actuator assembly  16  may be of various types, mechanical, hydraulic or others. Alternate actuator assemblies and other tool parts may be found in U.S. Pat. No. 5,979,558 issued to Bouldin, which is hereby incorporated by reference for all purposes.  
         [0031]    Choke assembly  12 , shown in FIGS.  1 A-C, includes upper choke member  110  and lower choke member  112 . Choke members  110  and  112  are generally cylindrical and are circumferentially and sealingly disposed within outer housing  14 .  
         [0032]    Upper choke member  110  is slidably disposed in the outer housing  14  and is operably connected to the actuator assembly  16  for axial movement within the housing. Although it is preferable that the upper choke member be mounted for movement, it is understood that either or both of the choke members may be so mounted. The upper end  114  of the upper choke member  110  is sealingly attached to adjustment assembly  18  by retaining ring  116  and seal  118 , preferably an o-ring seal. The mating end  120  of the upper choke member  110  has a preferably integrally-formed mating shoulder  122  formed thereon for abutment with a similar mating shoulder  124  on the lower choke member  112 . Upper choke member  112  preferably includes annular projection  129  which extends, at least when the upper choke member  110  is in a closed position, as shown in FIGS.  1 A-C, into the interior  158  within the choke end  128  of lower choke member  112 . Projection  129  of upper choke member  110  preferably includes a flow regulating surface  126 .  
         [0033]    The outer surface  126  of projection  128  acts as flow regulator. The shape and features of the projection surface  126  determines the fluid flow rates through the variable annular flow-area port  148  as the choke members are opened or closed along path of travel  154 . The projection surface  126  shape and features can be selected to regulate fluid flow as desired. For example, an arcuate surface, as shown in FIGS.  1 - 3 , produces flow-area characteristics as shown in the graph of FIG. 6 which charts the increase in open flow-area, measured in square inches, versus the axial travel, in inches, of the upper choke number. The arcuate surface provides the desirable ability to open the choke area, and therefore reduce fluid pressure, slowly resulting in less damage to the formation than would occur with sudden pressure loss.  
         [0034]    The flow regulating surface  126  can be of any desired shape and produce any desired flow-area to travel curve. Additionally, other features may be added to the projection surface to regulate fluid flow. Alternate projection shapes and features are shown in FIGS.  5 A-D. FIG. 5A shows a blunt-nosed projection. FIG. 5B shows the addition of a labyrinth seal  131  to the projection surface  126 . Labyrinth seals are known in the art to regulate fluid flow and various types of labyrinth seal can be employed on projection  129 . FIG. 5C shows a stair-stepped projection surface  126  and FIG. 5D shows a conical surface  126 . Other projection shapes and various combinations of the shapes and features may be used. For example, a labyrinth seal  131  can be used in conjunction with the stair-stepped projection surface.  
         [0035]    The lower choke member  112  is preferably slidably and sealingly disposed within outer housing  14 . The mating end  128  of the lower choke member  112  has a preferably integrally-formed mating shoulder  124  formed thereon for abutment with mating shoulder  122  of the upper choke member. Mating shoulder  124  abuts should  125  of the housing wall  46  to prevent upward axial movement of the lower choke member  112  when the choke is open. The lower end  130  of lower choke member  112  abuts a biasing assembly  22 , and specifically bias spring  132 . Recess  134 , integrally formed on lower choke member  112 , forms an annular space for spool assembly  136 . Spool assembly  136  sealingly engages housing  14  at piston seal  140  and rod seal  142 . Alternately, lower choke member  112  may be stationary with respect to upper member  110 , or may be integrally formed with or attached to housing  14 .  
         [0036]    Upper and lower choke members  110  and  112  abut at mating shoulders  122  and  124  forming an infinitely adjustable annular choke at annular seal  144 . The annular seal is preferably of a hard, erosion-resistant material, such as ceramic or metal such as tungsten carbide, stellite or of alloy. Other seals, as are known in the art, may be used. The annular seal  144  may seal against liquid and/or gas pressure, as desired. A hard-surfaced seal, unlike rubber, plastic or other soft seals, is preferred.  
         [0037]    The choke assembly  12 , upper and lower choke members  110  and  112  and annular seal  144  are shown in a closed position  150  in FIGS.  1 A-C. The choke assembly is movable between the closed position  150  and the open position  152 , seen in FIG. 3. The choke assembly is infinitely variable, that is, the choke member may be positioned, as desired, anywhere between the opened and closed positions, as shown for example, in FIG. 2. The exemplary embodiment illustrated can be opened to any position along stroke-path  154  which extends a longitudinal distance  156 . The size of annular flow port  148  is controlled by adjustment of the choke members relative to one another. The stroke-path distance  156  may vary, but preferably allows projection  128  to fully clear the interior space  158  of lower choke member  112 , as seen in FIG. 3.  
         [0038]    Fluid flow from external area  28  into fluid passage  30  of tool assembly  10  is controlled through the infinitely variable annular flow port  148 . The variable choke may be opened slowly against a large differential pressure, up to the working pressure of the choke, without damage to the seals. Typical sliding-door chokes can only be opened against a differential pressure of about 1500 psi without damaging the seals.  
         [0039]    In gas lift and other operations, it may be desirable to maintain the variable annular area valve in a partially open, or cracked-open, position to allow unloading of the well. That is, in such an application, it would be undesirable or unnecessary to seal annular seal  144  or completely close the valve. In such a case the upper member  110  may be maintained in a partially open position, such as seen in FIG. 2, by use of hydraulic pressure or a stop, lock or other movement limiting device employed such that member  110  is prevented from sealing annular seal  144 . The shoulders  122  and  124  would not need to seal off flow through valve  144 . In the partially open position the shoulders  122  and  124  are adjacent one another, thereby restricting, but not eliminating fluid flow. The variable annular flow-area valve can be moved towards and into the fully open position, seen in FIG. 3, to allow greater fluid flow.  
         [0040]    Annular fluid port  148  is preferably adjacent outer housing fluid port  160 , which may consist of multiple openings through housing wall  44 . The housing ports  160  may be placed anywhere along the housing wall  44 ,as long as they are in fluid communication with annular port  148 , and may vary in size, design and placement, as desired.  
         [0041]    The tool preferably includes a biasing assembly  22 , as shown. The bias spring  132  abuts lower choke member  112  at shoulder  164  and abuts the tool housing  14  at shoulder  166 . The bias spring may be of any type known in the art, such as the cylinder spring, shown, or belleville, coil or other springs. The bias spring  132  exerts a seating load on lower choke member  112  such that the annular flow port  148  remains sealed when the actuator assembly exerts little pressure on upper choke member  110 . Further, where the upper choke member  110  is not under any sealing load, such as when in a locked closed run-in position, bias spring  132  acts to seal the annular valve. The bias spring also takes up any tolerances in the choke assembly. The bias spring  132  may have a deflection  168  and bias force as desired, and operates to move lower choke member  112  longitudinally within the outer housing for up to the defection distance.  
         [0042]    The upper choke member  110  may be operably connected to the actuator assembly  16  through an adjustment assembly  18  and a locking assembly  20 . The seat attachment subassembly  170  of the adjustment assembly  18  attaches to upper choke member  110  preferably via a retaining ring assembly  172 , as shown. Other means for attachment may be used as desired. The seat attachment subassembly  170  is a cylindrical mandrel slidably and sealingly engaged within the outer housing  14 . A sealing assembly  174 , which may include spacers  176  and a sealing element  178 , seals the annular space between the exterior of the seat attachment subassembly  170  and the interior wall  46  of the housing  14 . The sealing element  178  is preferably a vee-packing seal, as shown, but may be any suitable.  
         [0043]    The adjustment assembly  18  further includes an adjustment mandrel  180  which is adjustably attached to the seat attachment subassembly  170 , preferably via a threaded assembly  182 , as shown. The overall length of the adjustment assembly  18  may be selected by adjusting the attachment of the adjustment mandrel  180  to the seat attachment subassembly  170 . An adjustment locking mechanism  184  is provided, such as the setscrew shown, to allow the adjustment assembly length to be selectively set. Adjustment mandrel  180  abuts the actuator mandrel  50  at shoulder  186 .  
         [0044]    Locking assembly  20  includes a retainer ring  190  threadingly attached to adjustment mandrel  180 . The retainer ring  190  acts with lock ring assembly  192 , including lock ring  194  and corresponding recess  196 , and expander ring  198  in a manner known in the art. The retainer ring  190  has an inset shoulder  200  that mates with mandrel shoulder  202 .  
         [0045]    In use, the choke tool assembly  10  is run-in to a subterranean well to the desired depth. The tool assembly is preferably part of a tool string which may include numerous choke tool assemblies as well as other downhole tools. The lower and upper adapters  40  and  42  are provided for attachment to a tool string.  
         [0046]    The tool assembly preferably has a locked closed run-in position  151  as shown in FIG. 1. In the locked position  151 , the locking assembly  20  holds the choke assembly  12  in the sealed closed position  150  during run-in operations without hydraulic pressure in the actuator assembly  16 . The locking assembly  20  acts in unison with the biasing assembly to maintain the choke in the closed position. In the locked position, the retainer ring  190  and lock ring assembly  192  maintain the choke assembly  12  in the closed position. Lock ring  194  cooperates with recess  196  in the inner surface  46  of the outer housing wall  44  and the expander ring  198  to prevent mandrel  50  from upward movement.  
         [0047]    The locking assembly  20  may be unlocked, as is known in the art, by hydraulically actuating or mechanically engaging the mandrel  50  or profile sleeve  60  and pulling upwards to unlock the lock ring assembly  192 . Shoulder  202  on mandrel  50  mates with shoulder  200  on the retainer ring  190  such that an upward force on the mandrel  50  will force retainer ring  198  upward as well, thereby forcibly moving the lock ring  194  from the recess  196 . The locking assembly  20  is then in an unlocked position  153 , and the choke may be operated. The locking assembly may be locked closed without requiring hydraulic actuator pressure being maintained.  
         [0048]    The actuator assembly  16  operates to control the choke assembly  12 . To move the upper choke member  110  towards the open position  152 , hydraulic pressure is applied to upper hydraulic chamber  72  of the actuator assembly  16 . Hydraulic pressure is supplied to upper hydraulic inlet  60  via hydraulic lines (not shown) and then along upper hydraulic passage  64 , through upper port  68  and into upper hydraulic chamber  72 . The hydraulic pressure acts upon upper piston  76  thereby moving the mandrel  50  upwards. Mandrel  50 , which is attached to the locking and adjustment assemblies, causes the upper choke member  110  to similarly move in an upward direction, toward the open choke position  152 . Hydraulic pressure can be applied, as desired, to move the upper choke member  110  any desired distance along choke path  154  between the closed and open positions  150  and  152  up to the total stroke distance  156 .  
         [0049]    In the closed position  150 , the upper choke member  110  is sealingly engaged with the lower choke member  112  at mating shoulders  122  and  124  at metal-to-metal seal  144 . As the upper choke member  110  is moved upwardly, the biasing assembly  22  also moves the lower choke member  112  upwardly. The lower choke member  112  will continue to move upwardly for a portion of the deflection distance, as determined by the selection of the deflection device. Once the upper and lower choke members  110  and  112  have moved the deflection distance  168 , continued upward movement by the upper choke member  110  will unseat the mating shoulders  122  and  124  thereby creating an annular flow port  148  defined by the spaced apart mating shoulders.  
         [0050]    The annular flow port  148  allows fluid connection between the external area  28 , via fluid port  160 , and the fluid passage  30 . Fluid flow through the annular port  148  is controlled by selective movement of the upper choke member  110  to regulate the flow area available.  
         [0051]    Preferably, the choke end  120  of the upper choke member  110  includes projection  129  which extends into the interior space  158  of the lower choke member  112 . The outer surface of the projection  129  defines a choke regulating surface  126 . The choke regulating surface  126  may be of any desired shape and may have additional features as desired. The shape of the regulating surface  126 , by defining the shape of the annular port  148 , regulates the flow area into the flow passage  30 . Preferably, the stroke distance  156  of the choke member  110  is greater than the length of projection  129  such that, at the full open position  152 , the projection  129  does not extend into the interior  148  of the lower choke member  112 .  
         [0052]    The upper choke member  110  may be moved downwardly, or towards the closed position  150 , using the actuator assembly  16 . Hydraulic pressure is supplied via hydraulic lines (not shown) to lower hydraulic inlet  62 , through lower hydraulic chamber  74 . An increase in hydraulic pressure within chamber  74  forces lower hydraulic piston  90  downward, thereby moving the mandrel  50  and upper choke member  110  downwardly.  
         [0053]    By regulating the hydraulic pressure supplied to upper and lower chamber  72  and  74 , the upper choke member  110  may be moved, or held stationary, as desired to any location along path  154 , that is, in the open or closed positions,  150  and  152 , or anywhere inbetween. Consequently, the choke is infinitely variable and flow through the annular port  148  can be infinitely regulated. The spacing of the choke member  110  and  112  and the design of projection  128  determine the flow rate through the annular port  148 .  
         [0054]    Described herein, the choke assembly and methods of controlling fluid flow within the well using the choke assembly, which provided reliability, ruggedness, longevity, and do not require complex mechanisms. Of course, modifications, substitutions, additions, deletions, etc., may be made to the exemplary embodiment described herein, which changes would be obvious to one of ordinary skill in the art, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.