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CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of U.S. application Ser. No 10/654,101 filed Sep. 3, 2003. 
     
    
     BACKGROUND  
       [0002]     The invention generally relates to gravel packing a well.  
         [0003]     When well fluid is produced from a subterranean formation, the fluid typically contains particulates, or “sand.” The production of sand from the well must be controlled in order to extend the life of the well. One technique to accomplish this involves routing the well fluid through a downhole filter formed from gravel that surrounds a sandscreen. More specifically, the sandscreen typically is a cylindrical mesh that is inserted into and is generally concentric with the borehole of the well where well fluid is produced. Gravel is packed between the annular area between the formation and the sandscreen, called the “annulus.” The well fluid being produced passes through the gravel, enters the sandscreen and is communicated uphole via tubing that is connected to the sandscreen.  
         [0004]     The gravel that surrounds the sandscreen typically is introduced into the well via a gravel packing operation. In a conventional gravel packing operation, the gravel is communicated downhole via a slurry, which is a mixture of fluid and gravel. A gravel packing system in the well directs the slurry around the sandscreen so that when the fluid in the slurry disperses, gravel remains around the sandscreen.  
         [0005]     A potential challenge with a conventional gravel packing operation deals with the possibly that fluid may prematurely leave the slurry. When this occurs, a bridge forms in the slurry flow path, and this bridge forms a barrier that prevents slurry that is upstream of the bridge from being communicated downhole. Thus, the bridge disrupts and possibly prevents the application of gravel around some parts of the sandscreen.  
         [0006]     One type of gravel packing operation involves the use of a slurry that contains a high viscosity fluid. Due to the high viscosity of this fluid, the slurry may be communicated downhole at a relatively low velocity without significant fluid loss. However, the high viscosity fluid typically is expensive and may present environmental challenges relating to its use. Another type of gravel packing operation involves the use of a low viscosity fluid, such as a fluid primarily formed from water, in the slurry. The low viscosity fluid typically is less expensive than the high viscosity fluid. This results in a better quality gravel pack (leaves less voids in the gravel pack than high viscosity fluid) and may be less harmful to the environment. However, a potential challenge in using the low viscosity fluid is that the velocity of the slurry must be higher than the velocity of the high viscosity fluid-based slurry in order to prevent fluid from prematurely leaving the slurry.  
         [0007]     Thus, there exists a continuing need for an arrangement and/or technique that addresses one or more of the problems that are set forth above as well as possibly addresses one or more problems that are not set forth above.  
       SUMMARY  
       [0008]     In an embodiment of the invention, a technique that is usable with a subterranean well includes communicating a slurry through a shunt flow path and operating a control device to isolate slurry from being communicated to an ancillary flow path.  
         [0009]     In another embodiment of the invention, a system that is usable with a subterranean well includes a shunt tube and a diverter. The shunt tube is adapted to communicate a slurry flow within the well to form a gravel pack. The diverter is located in a passageway of the shunt tube to divert at least part of the flow.  
         [0010]     In yet another embodiment of the invention, a technique that is usable with a subterranean well includes communicating a slurry through a shunt flow path and operating a control device to isolate the slurry from being communicated to an ancillary flow path.  
         [0011]     Advantages and other features of the invention will become apparent from the following description, drawing and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]      FIG. 1  is a schematic diagram of a gravel packing system according to an embodiment of the invention.  
         [0013]      FIG. 2  is a flow diagram depicting a technique to gravel pack a well in accordance with an embodiment of the invention.  
         [0014]      FIGS. 3 and 4  are schematic diagrams showing operation of a leak control device according to an embodiment of the invention.  
         [0015]      FIGS. 5 and 6  are schematic diagrams depicting operation of another leak control device according to another embodiment of the invention.  
         [0016]      FIG. 7  is a schematic diagram depicting a dampening layer for use with a rupture disk in accordance with an embodiment of the invention.  
         [0017]      FIG. 8  is a top view of a dampener of  FIG. 7  according to an embodiment of the invention.  
         [0018]      FIG. 9  is a schematic diagram of a slurry distribution system according to an embodiment of the invention.  
         [0019]      FIG. 10  is a perspective view of a wedge used in the system of  FIG. 9  according to an embodiment of the invention.  
         [0020]      FIG. 11  is a schematic diagram of a slurry distribution system in accordance with another embodiment of the invention.  
         [0021]      FIG. 12  is a cross-sectional view of a well in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Referring to  FIG. 1 , an embodiment  10  of a gravel packing system in accordance with the invention includes a generally cylindrical sandscreen  16  that is inserted into a wellbore of a subterranean well. The sandscreen  16  is constructed to receive well fluid through its sidewall from one or more subterranean formations of the well. As shown in  FIG. 1 , the sandscreen  16  may be located inside a well casing  12  of the well. An annulus  20  is formed between the interior surface of the well casing  12  and the components of the system  10 . It is noted that in some embodiments of the invention, the well may be uncased well, and thus, in these embodiments of the invention, the annulus  20  may be located between the components of the system  10  and the uncased wall of the wellbore.  
         [0023]     In accordance with some embodiments of the invention, a two-phase gravel packing operation is used to distribute gravel around the sandscreen  16 . The first phase involves gravel packing the well from the bottom up by introducing a gravel slurry flow into the annulus  20 . As the slurry flow travels through the well, the slurry flow loses its fluid through the sandscreen  20  and into the formation. That which enters the sandscreen returns to the surface of the well. During the first phase of the gravel packing operation, one or more bridges may eventually form in the annulus  20  due to the loss of fluid to the formation, thereby precluding further gravel packing via the straight introduction of the slurry flow into the annulus  20 . To circumvent these bridges, the gravel packing enters a second phase in which the slurry flow is routed through alternative slurry flow paths.  
         [0024]     More particularly, in some embodiments of the invention, the alternative flow paths are formed at least in part by shunt flow paths that are established by one or more shunt tubes  22  (one shunt tube depicted in  FIG. 1 ) that extend along the sandscreen  16 . Therefore, as depicted in  FIG. 1 , in some embodiments of the invention, a particular shunt tube  22  may receive a gravel slurry flow  24  for purposes of bypassing one or more bridges that may be formed in the annulus  20 .  
         [0025]     More specifically, as depicted in  FIG. 1 , each shunt tube  22  may be connected to ancillary flow paths that are established by various packing tubes  30  (packing tubes  30   a ,  30   b ,  30   c  and  30   d , depicted as examples) for purposes of distributing slurry through these tubes into the annulus  20 . As shown, in some embodiments of the invention, each packing tube  30  has an upper end that is connected to a radial opening in the shunt tube  22 ; and the packing tube  30  extends along the shunt tube  22  to a lower outlet end at which the packing tube  30  delivers a slurry flow downstream of the radial opening. In some embodiments of the invention, each packing tube  30  may have several outlets that extend along the length of the packing tube  30 .  
         [0026]     As discussed further below, each of the depicted packing tubes  30   a - d  may be associated with a particular section of the well to be packed. For example, as depicted in  FIG. 1 , the packing tubes  30   a - d  may be associated with well sections  44 ,  46 ,  48  and  50 , respectively. Each section may contain more than one packing tube  30  that is connected to the shunt tube  22 ; and each section may contain more than one shunt tube  22 , depending on the particular embodiment of the invention. Furthermore, as depicted in  FIG. 1 , in some embodiments of the invention, the packing tubes  30  of a particular section may be surrounded by an outer shroud  32  that surrounds both the shunt tube(s)  22 , packing tube(s)  30  and sandscreen  16 . Each shroud  32  may include perforations  34  for purposes of receiving the gravel and fluid from the slurry. In this regard, the slurry may flow from the outside of the shroud  32  into the interior of shroud  32 . Ideally, the fluid from the slurry flow  24  enters the screen  16 , returns to the surface, as depicted by the flow  40 , thereby leaving the deposited gravel around the exterior of the sandscreen  16 .  
         [0027]     In some embodiments of the invention, the shunt tube(s)  22  may be located outside of the shrouds  32 ; and in some embodiments of the invention, the shunt tubes  22  may be located both inside and outside of the shrouds  32 . Thus, many variations are possible and are within the scope of the claims.  
         [0028]     As a more specific example of the two phase gravel packing operation,  FIG. 2  depicts a technique  60  that may be used to gravel pack the well using the system  10 . In accordance with the technique  60 , gravel packing initially proceeds from the bottom of the well to the top of the well. Thus, in this initial phase, the gravel slurry is introduced into the annulus  20  of the well. The gravel slurry enters the annulus  20  and proceeds with packing the annulus  20  with gravel from the bottom of the well up. This gravel packing from the bottom up (block  62 ) continues until one or more bridges are formed (diamond  64 ) that significantly impede the flow of slurry through the annulus  20 . As described further below, this bridge increases a pressure in the slurry to activate the second phase of the gravel packing operation in which sections of the well are packed from top to bottom using alternative flow paths.  
         [0029]     More specifically, using  FIG. 1  as an example, at the onset of the second phase of the gravel packing operation, the upper section  44  is packed first, then the section  46 , then the section  48 , which is followed by the section  50 , etc. The packing in a particular section continues until the bridge(s) that form in the annulus  20  and/or packing tubes  30  of that section significantly impede the flow of the slurry. Thus, in accordance with the technique  60 , gravel packing for a particular section continues (block  68  of  FIG. 2 ) until bridge(s) are formed (diamond  70 ) in the section that significantly impede the flow of slurry into that section. For example, for the section  44 , a bridge may form in the packing tube  30   a  and/or other packing tubes  30  (not shown) to impede flow of the slurry enough to trigger a transition to the next section.  
         [0030]     In some embodiments of the invention, the technique  60  includes preventing the communication through the shunt tube(s) between a particular section being packed and the adjacent section until the flow of slurry has been significantly impeded.  
         [0031]     The significance of the blockage of the slurry flow affects the pressure of the slurry flow. Therefore, in some embodiments of the invention, the pressure increase initiates mechanisms (described below) that shut off packing in the current section and route the slurry flow to one or more alternate flow paths in the next section to be gravel packed. More particularly, when the bridge(s) cause the pressure of the slurry to reach a predetermined threshold (in accordance with some embodiments of the invention), communication to the next section to be packed is opened (block  72 ). Thus, slurry flows through the shunt tube(s) to the next section to be packed. Gravel packing thus proceeds to the next adjacent section, as depicted in block  68 .  
         [0032]     In some embodiments of the invention, one or more devices are operated to close off communication through the packing tube or tubes of the section at the conclusion of packing in that section, as described below. By isolating all packing tubes of previously packed sections, fluid loss is prevented from these sections, thereby ensuring that a higher velocity for the slurry may be maintained. This higher velocity, in turn, prevents the formation of bridges, ensures a better distribution of gravel around the sandscreen  16  and permits the use of a low viscosity fluid in the slurry (a fluid having a viscosity less than 30 approximately centipoises, in some embodiments of the invention).  
         [0033]      FIG. 3  depicts a slurry distribution system  100  (in accordance with some embodiments of the invention) that may be used in a particular well section to control slurry flow through alternative flow paths. In accordance with some embodiments of the invention, the system  100  may be located in the vicinity of the union of a shunt tube  22  and a particular packing tube  30 .  
         [0034]     The system  100  includes a plug  112  that is initially partially inserted into a radial opening  125  of the packing tube  30 . In this state, the plug  112  does not impede a slurry flow  102  through the passageway of the packing tube  30 . A spring  116  is located between the plug  112  and a sleeve  120 . The sleeve  120 , in some embodiments of the invention, is coaxial with the shunt tube  22 , is closely circumscribed by the shunt tube  22  and is constructed to slide over a portion of the shunt tube  22  between the position depicted in  FIG. 3  and a lower position that is set by an annular stop  136 . In other embodiments of the invention, the sleeve  120  may be located outside and closely circumscribe the shunt tube  22 . O-rings  130  form a fluid seal between the sleeve  120  and the shunt tube  22 . As an example, for embodiments in which the sleeve  120  is located inside the shunt tube  22 , the O-rings  130  may reside in annular grooves that are formed in the exterior of the sleeve  120 .  
         [0035]     Initially, a shear screw  114  holds the spring  116  in a compressed state and holds the sleeve in the position depicted in  FIG. 3 . The shear screw  114  is attached to the sleeve  120  and extends through the shunt tube  22  and the interior of the spring  116  to the plug  112 . Therefore, in its initial unsheared state, the screw  120  keeps the plug  112  from completely entering the radial opening  125  and obstructing the passageway of the packing tube  30 .  
         [0036]     A lower end  139  of the sleeve  120  contains a rupture disk  134  that controls communication through the end  139 . Initially, the rupture disk  134  blocks the slurry flow  24  from passing through the shunt tube  22 . Thus, the slurry flow  24  exerts a downward force on the sliding sleeve  120  via the contact of the slurry  24  and the rupture disk  134 . When the flow of slurry through the section being gravel packed becomes impeded, the pressure of the slurry  24  acting on the rupture disk  134  increases. The impeded flow may be due to the formation of one or more bridges in the annulus and/or packing tube(s), of the section, such as the exemplary bridge  109  that is shown as being formed in the packing tube  30  of  FIG. 3 . When the slurry flow into the section becomes sufficiently impeded by the bridge(s), the pressure on the rupture disk  134  increases to the point that the sliding sleeve  120 , shears the screw  114 , moves downhole and rests against the stop  134 . A further restriction of slurry flow by the bridging eventually causes the rupture disk  134  to rupture.  
         [0037]     This subsequent state of the system  100  is depicted in  FIG. 4 . As shown, after the shear screw  114  shears, the spring  116  is free to expand and exerts a radial force on the plug  112 , thereby forcing the plug  112  fully into the passageway of the packing tube  30  to seal off the passageway. Thus, entry of the plug  112  into the passageway of the packing tube  30  prevents any further fluid flow through the packing tube  30 . This sealing off of the packing tube  30  serves to further increase the pressure on the rupture disk  134  to facilitate its rupture. As depicted in  FIG. 4 , the rupture of the rupture disk  134  opens communication through the shunt tube  22 .  
         [0038]     An alternative slurry distribution system  160  is depicted in  FIG. 5 . The system  160  includes a sliding sleeve  166  that is concentric with and slides inside the shunt tube  22 , in some embodiments of the invention. Alternatively, the sleeve  166  circumscribes and slides outside of the shunt tube  22 , in other embodiments of the invention. The system  160  includes O-rings  170  that are located between the sleeve  166  and shunt tube  22  to form a fluid seal.  
         [0039]     As depicted in  FIG. 5 , the sleeve  166  includes a radial opening  168  that is initially aligned with the opening between the packing tube  30  and the shunt tube  22 . Furthermore, a lower end  191  of the sliding sleeve  166  includes a rupture disk  190 , thereby initially preventing flow through the shunt tube  22  below the rupture disk  190 . Thus, initially, the slurry flow  24  is routed entirely through the packing tube  30 .  
         [0040]     The sleeve  166  is constructed to move between the position depicted in  FIG. 5  and a position in which the lower end of the sleeve  166  rests on an annular stop  182  that is located below the sleeve  166  inside the shunt tube  22 . However, the sleeve  166  is initially confined to the position depicted in  FIG. 5  by a shear screw  162  that, it its unsheared state, attaches the sleeve  166  to the shunt tube  22 .  
         [0041]     Over time, bridges, such as an exemplary bridge  183  shown in the packing tube  30 , may form to impede the flow of the slurry. The resultant pressure increase in the slurry flow, in turn, creates a downward force on the sleeve  166 . After the flow has been sufficiently impeded, the force on the sleeve  166  shears the shear screw  162  and causes the sleeve  166  to slide to the position in which the bottom end of the sleeve  166  rests against the stop  182 . In this position, the radial opening  168  is misaligned with the opening to the packing tube  30 ; and thus, communication between the shunt tube  22  and packing tube  30  is blocked. This blockage along with any additional bridging increases pressure on the rupture disk  190  so that the rupture disk  190  ruptures.  
         [0042]     This state of the system  160  is in  FIG. 6 . As can be seen, in this state, the slurry flow  24  is isolated from the packing tube  30  and is routed by the system  160  through the shunt  22  to the next section to be packed.  
         [0043]     In some embodiments of the invention, a dampening layer may be included below a particular rupture disk in the shunt tube  22 , such as the rupture disks  134  ( FIGS. 3 and 4 ) and  190  ( FIGS. 5 and 6 ). This dampening layer tends to, as its name implies, dampen a pressure spike that might otherwise propagate through the opening of the rupture disk when the rupture disk ruptures. Such a pressure spike may inadvertently rupture a downstream rupture disk inside the shunt tube  22 .  
         [0044]     An exemplary dampening layer  199 , in accordance with some embodiments of the invention, is depicted in  FIG. 7 . As shown, the dampening layer  199  may be formed from a generally circular disk  204  (see also  FIG. 8 ) that is positioned across the cross-section of the shunt tube  22  and includes several openings  206  for purposes of allowing the slurry to flow therethrough. However, the disk  204  is not entirely open, thereby functioning to dampen a pressure spike, if present, when an upstream rupture disk  203  ruptures. In some embodiments of the invention, a cylindrical spacer  200  may be located between the disk  204  and the rupture disk  203 . Furthermore, in accordance with some embodiments of the invention, the rupture disk  203  may be attached to the end of a sliding sleeve  207  (such as the sleeve  120  ( FIG. 3 ) or  166  ( FIG. 5 ), for example). In some embodiments of the invention, the rupture disks  203  and disk  204  may have shapes other than the circular shapes that are depicted in the figures.  
         [0045]      FIG. 9  depicts another slurry distribution system  300 , in accordance with some embodiments of the invention. The system  300  includes a deflector  304  that may be used to deflect a slurry flow  24  from directly contacting a particular rupture disk  320 . The rupture disk  320  is located inside and initially blocks communication through an outlet of a manifold, or crossover  310 . A shunt tube  321  is connected to this outlet. Therefore, until the rupture disk  320  ruptures, the rupture disk  320  block communication of slurry into the shunt tube  321 . As shown, the crossover  310  includes an inlet that is connected to a shunt tube  22  to receive a slurry flow  24 . The crossover  310  includes two additional outlets that are connected to two packing tubes  30 . Thus, when the rupture disk  320  is intact, the crossover  310  distributes the incoming slurry flow to both packing tubes  30  and does not deliver any slurry to the shunt tube  321 .  
         [0046]     The central passageway of the shunt tube  22  may be generally aligned with the passageway of the lower shunt tube  321 . Therefore, due to inertia, the main flow path along which the slurry flow  24  propagates may generally be directed toward the central passageway of the lower shunt tube  310  and thus, toward the rupture disk  320 . The deflector  304 , however, deflects the slurry flow  24  away from the rupture disk  320  and toward the corresponding packing tubes  30 . As depicted in  FIG. 9 , in some embodiments of the invention, the deflector  304  may include at least two inclined (relative to the direction of the slurry flow  24 ) deflecting surfaces  305  for purposes of dividing the slurry flow  24  into two corresponding flows that enter the packing tubes  30 . More specifically, in some embodiments of the invention, the deflector  304  may generally be a wedge ( FIG. 10 ), with the side surfaces of the wedge forming the deflecting surfaces  305 .  
         [0047]     One function of the deflector  304  is to deflect a potential pressure spike that may be caused by the rupture of an upstream rupture disk. Thus, the deflector  304  may prevent premature rupturing of the rupture disk  320 . Another potential advantage of the use of the deflector  304  is to prevent erosion of the rupture disk  320 . More specifically, in some embodiments of the invention, the rupture disk  320  might erode due to particulates in the slurry  24 . Over time, this erosion may affect the rupture threshold of the rupture disk  320 . Therefore, without such a deflector  304 , the rupture disk  320  may rupture at a lower pressure than desired.  
         [0048]     The third function, which may be the major function of the deflector (in some embodiments of the invention), is to divert the gravel to the packing tube, after the rupture disk burst, in order to seal the packing tubes hydraulically.  
         [0049]     In some embodiments of the invention, the slurry flow  24  gradually erodes the deflector  302  to minimize any local flow restriction. However, this erosion occurs well after the desired rupturing of the rupture disk  320 .  
         [0050]      FIG. 11  depicts another slurry distribution system  350  in accordance with some embodiments of the invention. The system  350  includes two deflectors  354  (wedge-shaped deflectors, for example) that are located inside a crossover  361 . The crossover  361  includes two inlets that each receives a shunt tube  22 . The crossover  361  has two outlets that are connected to two corresponding packing tubes  30 ; and the crossover  361  has a third outlet that is connected to a lower shunt tube  380 . The crossover  361  includes a rupture disk  370  that initially blocks communication of slurry to the lower shunt tube  380 . As shown, the lower shunt tube  380  may be coaxial with the crossover  361 .  
         [0051]     As depicted in  FIG. 11 , the two deflectors  354  divert corresponding slurry flows  24  from the shunt tubes  22  into the corresponding packing tubes  30 . As shown, in some embodiments of the invention, a gap  360  exists between the deflectors  354 . In some embodiments of the invention, each of the deflectors  354  may be a wedge. As a more specific example, each wedge  354  may have an inclined (relative to the deflected flow) deflecting surface  358  for purposes of deflecting the associated slurry flow  24  into the associated packing tube  30 . Furthermore, another surface  356  of each deflector  354  may be generally aligned with the longitudinal axis of the shunt tubes  22  for purposes of permitting flow between the deflectors  354 . However, the flow between the deflectors  354  is not aligned with either slurry flow  24  to prevent the erosion and premature bursting of the rupture disk  370 , as described above in connection the deflector  304  (see  FIG. 9 ).  
         [0052]     Referring to  FIG. 12 , in some embodiments of the invention, alternative flow paths may be provided by structures other than shunt tubes and packing tubes. In this manner, in some embodiments of the invention, an alternative flow path may be provided by an annular space  501  that exists between the outer surface of a sandscreen  502  and the inner surface of an outer circumscribing shroud  504 . Thus, in accordance with some embodiments of the invention, a rupture disk or other flow control device may be located in the annular area  501 . Furthermore, deflectors may be also located in the annulus  501  for purposes of performing the function of the deflectors described above. Additionally, in some embodiments of the invention, the radial paths from the outer shroud  504  may be sealed off for purposes of preventing fluid loss, similar to the arrangements depicted in  FIGS. 3-6  above. Furthermore, structures other than tubes may provide ancillary flow paths. Therefore, the language “flow path” is not restricted to a flow in a particular tube, as the term “flow path” may apply to flow paths outside of tubes, between tubes, other types of flow paths, etc. in some embodiments of the invention.  
         [0053]     Although rupture disks have been described above, it is noted that other flow control devices, such as valves, for example, may be used in place of these rupture disks and are within the scope of the claims.  
         [0054]     Orientational terms, such as “up,” “down,” “radial,” “lateral,” etc. may be used for purposes of convenience to describe the gravel packing systems and techniques as well as the slurry distribution systems and techniques. However, embodiments of the invention are not limited to these particular orientations. For example, the system depicted in  FIG. 1  (and the variations discussed herein) may be used in a lateral wellbore or highly deviated wellbore, for example. Other variations are possible.  
         [0055]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Summary:
A technique that is usable with a subterranean well includes communicating a slurry through a shunt flow path and operating a control device to isolate slurry from being communicated to an ancillary flow path. The system may include a shunt tube and a diverter. The shunt tube is adapted to communicate a slurry flow within the well to form a gravel pack. The diverter is located in a passageway of the shunt tube to divert at least part of the flow. A slurry may be communicated through the shunt flow path, and a control device may be operated to isolate the slurry from being communicated to the ancillary flow path.