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TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates, in general, to completing a well that traverses a hydrocarbon bearing subterranean formation and, in particular, to a system and method for reducing the pressure drop in the fluids produced through a production tubing by expanding the flow area of the production tubing downhole.  
         BACKGROUND OF THE INVENTION  
         [0002]    Without limiting the scope of the present invention, its background will be described with reference to producing fluid from a subterranean formation, as an example.  
           [0003]    After drilling each of the sections of a subterranean wellbore, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation. Conventionally, each section of the casing string is cemented within the wellbore before the next section of the wellbore is drilled. Accordingly, each subsequent section of the wellbore must have a diameter that is less than the previous section.  
           [0004]    For example, a first section of the wellbore may receive a conductor casing string having a 20-inch diameter. The next several sections of the wellbore may receive intermediate casing strings having 16-inch, 13⅜-inch and 9⅝-inch diameters, respectively. The final sections of the wellbore may received production casing strings having 7-inch and 4½-inch diameters, respectively. Each of the casing strings may be hung from a casing head near the surface. Alternatively, some of the casing strings may be in the form of liner strings that extend from near the setting depth of previous section of casing. In this case, the liner string will be suspended from the previous section of casing on a liner hanger.  
           [0005]    Once this well construction process is finished, the completion process may begin. The completion process may include numerous steps such as creating hydraulic openings or perforations through the production casing string, the cement and a short distance into the desired formation or formations so that production fluids may enter the interior of the wellbore, formation stimulation to enhance production, gravel packing to prevent sand production and the like. The completion process also includes installing a production tubing string within the well that extends from the surface to the production interval or intervals. Unlike the casing strings that form a part of the wellbore itself, the production tubing string is used to produce the well by providing the conduit for formation fluids to travel from the formation depth to the surface.  
           [0006]    The diameter of the production tubing that is installed within a well is determined based upon a number of factors. For example, the maximum diameter of the production tubing is limited by the various restrictions within the well including the production casing and any tools within the production casing such as landing nipples. In addition, the production tubing is sized based upon the reservoir pressure, composition of the formation fluids and the expected production rate from the formation. For example, if the production tubing selected for a well is too large, slugging may occur during production in which case a workover may be required to install smaller production tubing or an artificial lift system. On the other hand, if the production tubing selected for a well is too small, the pressure drop in the formation fluids traveling through the production tubing is unnecessarily large and the rate of production from the formation is unnecessarily constrained, in which case, a workover may be required to install larger production tubing.  
           [0007]    A need has therefore arisen for a system and method for completing a well that traverses a subterranean formation that minimize the likelihood of installing a production tubing string that is not properly sized for the production from the traversed formation. A need has also arisen for such a system and method that are capable of reducing the pressure drop in the fluids produced through the production tubing when the formation is capable of producing at a higher rate. Further, a need has arisen for such a system and method that do not require a workover to optimize the size of the production tubing.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention disclosed herein comprises a system and method for completing a well that traverses a subterranean formation that minimize the likelihood of installing a production tubing string that is not properly sized for the production from the traversed formation. The system and method of the present invention are capable of reducing the pressure drop in the fluids produced through the production tubing when the formation is capable of producing at a higher rate. Further, the system and method of the present invention do not require a workover to optimize the size of the production tubing.  
           [0009]    The well completion system of the present invention comprises a production tubing that is positioned within a well casing that lines the wellbore and an expander member positioned within the production tubing that travels longitudinally within the production tubing to expand the production tubing downhole, thereby reducing the pressure drop in fluids produced through the production tubing. The expansion process may proceed from an uphole location to a downhole location or from a downhole location to an uphole location. The force required to expand the production tubing may be generated by pressurizing at least a portion of the production tubing to urge the expander member to travel longitudinally within the production tubing. This fluid pressure may be delivered directly into the production tubing or may be introduced through a coiled tubing that may be coupled to the expander member. Additionally or alternatively, when coiled tubing is used, the coiled tubing may be placed in tension to mechanically urge the expander member to travel longitudinally within the production tubing.  
           [0010]    Broadly stated, one method of the present invention comprises the steps of lining the wellbore with a well casing, disposing the production tubing within the well casing and expanding the production tubing downhole, thereby reducing the pressure drop in fluids produced through the production tubing. The expansion step may be independent of or as a result of first testing the productive capability of the formation traversed by the wellbore to determine whether production from the formation is constrained by the production tubing.  
           [0011]    Another method of the present invention comprises the steps of lining a first section of the wellbore with a first well casing having an inner diameter, lining a second section of the wellbore with a second well casing having an inner diameter that is smaller than the inner diameter of the first well casing, disposing the production tubing within the first and the second well casings and expanding the production tubing downhole that is disposed within the first well casing.  
           [0012]    Yet another method of the present invention comprises the steps of lining at least a main wellbore portion of a multilateral well with a well casing, extending first and second branch wellbores from the main wellbore, the second branch wellbore being farther downhole than the first branch wellbore, disposing a main section of production tubing within the well casing in the main wellbore, a first branch section of production tubing within the first branch wellbore and a second branch section of production tubing within the second branch wellbore and expanding the production tubing downhole that is uphole of the first branch wellbore. In this method, it may be desirable to expand the flow area of the production tubing that is uphole of the first branch wellbore to substantially match the flow area of the first branch section of production tubing and the flow area of the second branch section of production tubing.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0014]    [0014]FIG. 1 is a schematic illustration of an offshore oil and gas platform installing an expandable production tubing string according to the present invention;  
         [0015]    [0015]FIG. 2 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string prior to expansion;  
         [0016]    [0016]FIG. 3 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string after expansion;  
         [0017]    [0017]FIG. 4 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string prior to expansion;  
         [0018]    [0018]FIG. 5 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string after expansion;  
         [0019]    [0019]FIG. 6 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string prior to expansion;  
         [0020]    [0020]FIG. 7 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string after expansion;  
         [0021]    FIGS.  8 A- 8 B are a half sectional views of an expander member for use in expanding the expandable production tubing string according to the present invention in its contacted and expanded positions, respectively;  
         [0022]    [0022]FIG. 9 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string and a liner string prior to expansion; and  
         [0023]    [0023]FIG. 10 is a half sectional view of an expandable production tubing string according to the present invention that is installed within a casing string of a multilateral wellbore prior to expansion.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.  
         [0025]    Referring initially to FIG. 1, an expandable production tubing string of the present invention is being installed from an offshore oil and gas platform that is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including subsea blow-out preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as expandable production tubing string  30 .  
         [0026]    A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . Expandable production tubing string  30  is coupled on its lower end to various tools including sand control screen assemblies  38 ,  40 ,  42  positioned adjacent to formation  14  between packers  44 ,  46  which define production interval  48  including perforations  50 .  
         [0027]    As explained in greater detail below, it may be desirable to expand the flow area within expandable production tubing string  30  to reduce to pressure drop in fluids being produced therethrough. Accordingly, expandable production tubing string  30  of the present invention includes a launcher  52  and a catcher  54  between which an expander member  56  longitudinally travels to plastically deform expandable production tubing string  30 . In the illustrated embodiment, this is achieved by pressurizing expandable production tubing string  30  between a plug  58  and the lower end of expander member  56  by pumping fluid down through a work string such as a jointed tubing string or, as illustrated, a coiled tubing string  60  that is coupled to expander member  56 .  
         [0028]    Referring now to FIGS. 2 and 3, therein are depicted more detailed views of one method for expanding the flow area within expandable production tubing string  30 . As described above, expandable production tubing string  30  is disposed within wellbore  32  having casing  34  cemented therein with cement  36 . Packer  44  provides a fluid seal between expandable production tubing string  30  and casing string  34 . Expandable production tubing string  30  includes launcher  52  and catcher  54 . Initially disposed within launcher  52  is expander member  56 .  
         [0029]    It should be noted, however, by those skilled in the art that instead of installing expandable production tubing string  30  in casing string  34  with expander member  56  already positioned within launcher  52 , an expander member could alternatively be run in after expandable production tubing string  30  has been installed within casing string  34 . In this case, it may be necessary that the expander member have a smaller diameter configuration such that it may be run in expandable production tubing string  30  prior to expansion and a larger diameter configuration suitable for expanding expandable production tubing string  30  as described below. In fact, use of such expander members that have run in and expansion configurations may be preferred in situations wherein the decision to expand the production tubing is dependent upon testing of the productive capability of the formation traversed by the wellbore to determine whether production from the formation will be constrained by the production tubing. When such testing is performed and it is determined that the performance of the well would be enhanced by expanding the flow area of the production tubing, then the expander member may be placed in the production tubing to perform the expansion process.  
         [0030]    In the illustrated embodiment, expander member  56  includes a tapered cone section  62  which includes a receiver portion that is coupled to the lower end of coiled tubing string  60 . Disposed below launcher  52  within expandable production tubing string  30  is plug  58 . The flow area within expandable production tubing string  30  is increased by moving expander member  56  longitudinally through expandable production tubing string  30  from launcher  52  to catcher  54 . In the illustrated embodiment, a fluid is pumped down coiled tubing string  60  into the portion of expandable production tubing string  30  between plug  58  and the lower end of expander member  56 , as indicated by arrows  64 . The fluid pressure urges expander member  56  upwardly such that tapered cone section  62  of expander member  56  contacts the interior wall of expandable production tubing string  30 . As the fluid pressure increases, tapered cone section  62  applies a radially outward force to the wall of expandable production tubing string  30 . When this force is sufficient to plastically deform expandable production tubing string  30 , expander member  56  begins to travel longitudinally within expandable production tubing string  30 .  
         [0031]    As the upward movement of expander member  56  progresses, expandable production tubing string  30  substantially uniformly expands from its original diameter to a diameter slightly larger that the diameter of expander member  56 . It should be noted by those skilled in the art that the force necessary to plastically deform expandable production tubing string  30  is dependant upon a variety of factors including the ramp angle of tapered cone section  62 , the amount of the desired expansion of expandable production tubing string  30 , the material of expandable production tubing string  30  and the like. Also, it should be understood by those skilled in the art that since the increase in the flow area within expandable production tubing string  30  is proportional to the square of the increase in the diameter, large increases in the flow area of expandable production tubing string  30  are possible with rather small increases in diameter.  
         [0032]    For example, if expandable production tubing string  30  has an original diameter of 3½-inches and an expanded diameter of 4½-inches, the diameter is increased by 28.6 percent while the flow area is increased by 65.3 percent. Using conventional carbon steel as the material for expandable production tubing string  30  the increase in the flow area may be between about 20 percent and 50 percent. Increases of more than 50 percent are also achievable depending upon the ductility of the material selected for expandable production tubing string  30 .  
         [0033]    As best seen in FIG. 3, since only a short section of expandable production tubing string  30  is being expanded at any one time, the fluid pumped through coiled tubing string  60  typically provides sufficient upward force to expander member  56  to expand that section of expandable production tubing string  30 . This force may be controlled by adjusting the flow rate and pressure at which the fluid is delivered through coiled tubing string  60 . In addition, the upward force of expander member  56  may be enhanced by pulling on expander member  56  which may be accomplished by placing coiled tubing string  60  in tension. In fact, as best seen in FIGS. 4 and 5, longitudinal movement of expander member  56  may be achieved completely mechanically by pulling expander member  56  through expandable production tubing string  30  by placing coiled tubing string  60  in sufficient tension. In this case, since no fluids are used to upwardly urge expander member  56 , no plug below catcher  52  is necessary.  
         [0034]    It should be apparent to those skilled in the art that the use of direction terms such as above, below, upper, lower, upward, downward and the like are used in relation to the illustrated embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward being toward the bottom of the corresponding figure. Accordingly, it should be noted that the expandable production tubing string of the present invention and the methods for expanding the flow area within the expandable production tubing string of the present invention are not limited to the vertical orientation as they are equally well suited for use in inclined, deviated and horizontal wellbores.  
         [0035]    While FIGS.  1 - 5  have depicted the expansion of expandable production tubing  30  as progressing from a downhole location to an uphole location, the expansion could alternatively progress from an uphole location to a downhole location, as best seen in FIGS. 6 and 7. Specifically, expandable production tubing string  70  is disposed within wellbore  32  having casing string  34  cemented therein with cement  36 . Expandable production tubing string  70  includes a launcher  72  into which an expander member  74  is placed. Expander member  74  includes a tapered cone section  76 , a piston  78  and an anchor section  80 . Anchor section  80  includes a receiver portion that is coupled to the lower end of coiled tubing string  82 .  
         [0036]    In operation, a downward force is applied on expander member  74  by applying the weight of coiled tubing string  82  on expander member  74 . This downward force operates to stroke piston  78  to its compressed position, as best seen in FIG. 7. Once piston  78  completes its downward stroke, fluid is pumped down coiled tubing string  82  which sets anchor section  80  creating a friction grip between anchor section  80  and the interior of expandable production tubing string  70  which prevents upward movement of anchor section  80 . As more fluid is pumped down coiled tubing string  82  into the interior of expander member  74 , as indicated by arrow  84 , the fluid pressure urges tapered cone section  76  downwardly such that tapered cone section  76  places a radially outward force against the wall of expandable production tubing string  70  causing expandable production tubing string  70  to plastically deform. This process continues in a step wise fashion wherein each stroke of expander member  74  expands a section of expandable production tubing string  70 . After the desired length of expandable production tubing string  70  has been expanded, coiled tubing string  82  and expander member  74  may be retrieved to the surface.  
         [0037]    Referring now to FIGS.  8 A- 8 B, therein are depicted more detailed views of expander member  74  in its fully contracted and fully extended positions, respectively. Expander member  74  includes a tapered cone section  76 , a piston  78  and an anchor section  80 . Anchor section  80  includes a receiver portion  81  that may be coupled to the lower end of coiled tubing string  82  (not pictured). Anchor section  80  includes fluid ports  79 , coiled spring  83  and slips  85  that cooperate together such that when a fluid pressure is applied within expander member  74  and into fluid ports  79 , coiled spring  83  is compressed causing slips  85  to outwardly radially expand and grip the interior of expandable production tubing string  70  (not pictured). In addition, the fluid pressure acts on piston  78  on surface  86  and surface  87 , via fluid ports  88 , such that the force of the fluid pressure is multiplied. This force acting on piston  78  causes piston  78 , along with tapered cone section  76 , to be downwardly urged toward the position depicted in FIG. 8B. Once expander member  74  has completed its stroke and expanded a length of expandable production tubing string  70  (not pictured), the fluid pressure in expander member  74  is allowed to bleed off such that expander member  74  may be collapsed back to the configuration depicted in FIG. 8A and another stoke of expander member  74  may begin.  
         [0038]    Referring now to FIG. 9, therein is depicted another embodiment of a method for expanding the flow area within an expandable production tubing string that is designated  90 . Expandable production tubing string  90  is disposed within wellbore  92  having a production casing string liner  94  suspended from an intermediate casing string  96  on a liner hanger  98 . Both production casing string liner  94  and intermediate casing string  96  are cemented within wellbore  92  with cement  100 . Packer  102  provides a fluid seal between expandable production tubing string  90  and production casing string liner  94 . Expandable production tubing string  90  includes launcher  104  and catcher  106 . Initially disposed within launcher  104  is expander member  108 .  
         [0039]    Expander member  108  includes a tapered cone section  110  which includes a receiver portion that is coupled to the lower end of coiled tubing string  112 . Disposed below launcher  104  within expandable production tubing string  90  is plug  114 . In the illustrated embodiment, it is desired to reduce to pressure drop in the fluids being produced through expandable production tubing string  90 , however, the clearance between expandable production tubing string  90  and production casing string liner  94  is not sufficient for the desired expansion of expandable production tubing string  90 . It is nonetheless desirable to expand the flow area within expandable production tubing string  90  above production casing string liner  94  as this expansion will decrease the pressure drop from that point to the surface. Accordingly, by moving expander member  108  longitudinally through expandable production tubing string  90  from launcher  104  to catcher  106 , the pressure drop within expandable production tubing string  90  is reduced.  
         [0040]    While a variety of methods may be used to expand the flow area of expandable production tubing string  90 , in the illustrated embodiment, a fluid is pumped down coiled tubing string  112  into the portion of expandable production tubing string  90  between plug  114  and the lower end of expander member  108  as indicated by arrows  116 . The fluid pressure urges expander member  108  upwardly such that tapered cone section  110  of expander member  108  contacts the interior wall of expandable production tubing string  90  applying a radially outward force thereto which plastically deforms expandable production tubing string  90  as expander member  108  travels longitudinally within expandable production tubing string  90 . The plastic deformation of expandable production tubing string  90  results in substantially uniform expansion of expandable production tubing string  90  from its original diameter to a diameter slightly larger that the diameter of expander member  108 .  
         [0041]    Referring now to FIG. 10, therein is depicted another embodiment of a method for expanding the flow area within an expandable production tubing string that is designated  120 . Expandable production tubing string  120  is disposed within a multilateral wellbore  122 . In the illustrated embodiment, multilateral wellbore  122  has a main wellbore  124  and two branch wellbores  126 ,  128 . A main wellbore casing string  130  is cemented within main wellbore  124  by cement  132 . Likewise, branch wellbore casing strings  134 ,  136  are respectively cemented within branch wellbores  126 ,  128 .  
         [0042]    Expandable production tubing string  120  includes a main wellbore production tubing string  138  and two branch wellbore production tubing strings  140 ,  142 . Packer  144  provides a fluid seal between main wellbore production tubing string  138  and main wellbore casing string  130 . Packer  146  provides a fluid seal between branch wellbore production tubing string  140  and branch wellbore casing string  134 . Packer  148  provides a fluid seal between branch wellbore production tubing string  142  and branch wellbore casing string  136 .  
         [0043]    Expandable production tubing string  120  includes launcher  150  and catcher  152 . Initially disposed within launcher  150  is expander member  154 . Expander member  154  includes a tapered cone section  156  which includes a receiver portion that is coupled to the lower end of coiled tubing string  158 . Disposed below launcher  150  within expandable production tubing string  120  is plug  160 .  
         [0044]    In the illustrated embodiment, when the production stream from branch wellbore production tubing string  140  enters main wellbore production tubing string  138  and is commingled with the production stream originating from branch wellbore production tubing string  142 , the combined flow may be restricted by the size of expandable production tubing string  120 . Accordingly, it may be desirable to increase the flow area of expandable production tubing string  120  from a location proximate, either uphole or downhole, of the depth at which the additional production fluids are introduced into main wellbore production tubing string  138 . In the illustrated embodiment, this is achieved by moving expander member  154  longitudinally through expandable production tubing string  120  from launcher  150  located uphole of branch wellbore production tubing string  140  to catcher  152 .  
         [0045]    While a variety of methods may be used to expand the flow area of expandable production tubing string  120 , in the illustrated embodiment, a fluid is pumped down coiled tubing string  158  into the portion of expandable production tubing string  120  between plug  160  and the lower end of expander member  154  as indicated by arrow  162 . The fluid pressure urges expander member  154  upwardly such that tapered cone section  156  of expander member  154  contacts the interior wall of expandable production tubing string  120  applying a radially outward force thereto which plastically deforms expandable production tubing string  120  as expander member  154  travels longitudinally within expandable production tubing string  120 . The plastic deformation of expandable production tubing string  120  results in substantially uniform expansion of expandable production tubing string  120  from its original diameter to a diameter slightly larger that the diameter of expander member  154 .  
         [0046]    In a multilateral embodiment as depicted in FIG. 9, it may be desirable to match the flow area of expandable production tubing string  120  to the sum of the flow areas of branch wellbore production tubing strings  140 ,  142 . Likewise in multilateral wellbores having more than two branches from which production fluids are commingled, the production tubing expansion techniques as described herein may be used to match the flow area in the main wellbore sections of the production tubing to the sum of the flow areas of the branch wellbore production tubing strings uphole thereof.  
         [0047]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
A well completion system for reducing the pressure drop in fluids produced from a downhole formation ( 14 ) traversed by a wellbore ( 32 ) is disclosed. The well completion system comprises a production tubing ( 30 ) used to bring the formation fluids to the surface that is positioned within a well casing ( 34 ) that lines the wellbore ( 32 ). An expander member ( 56 ) is positioned within the production tubing ( 30 ) and travels longitudinally within the production tubing ( 30 ) to expand the flow area within the production tubing ( 30 ) once the production tubing ( 30 ) has been installed downhole, thereby reducing the pressure drop in fluids produced through the production tubing ( 30 ).