Patent Publication Number: US-2011061877-A1

Title: Flow control using a tortuous path

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional of U.S. Ser. No. 11/643,104, filed Dec. 21, 2006, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 60/803,253, filed May 26, 2006, which are both hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to flow control using a tortuous path, in which a cross-sectional flow area of the tortuous path is adjusted to control flow. 
     BACKGROUND 
     A well (e.g., a vertical well, near-vertical well, deviated well, horizontal well, or multi-lateral well) can pass through various hydrocarbon bearing reservoirs or may extend through a single reservoir for a relatively long distance. A technique to increase the production of the well is to perforate the well in a number of different zones, either in the same hydrocarbon bearing reservoir or in different hydrocarbon bearing reservoirs. 
     An issue associated with producing from a well in multiple zones relates to the control of the flow of fluids into the well. In a well producing from a number of separate zones, in which one zone has a higher pressure than another zone, the higher pressure zone may produce into the lower pressure zone rather than to the surface. Similarly, in a horizontal well that extends through a single reservoir, zones near the “heel” of the well (the zones nearer the surface) may begin to produce unwanted water or gas (referred to as water or gas coning) before those zones near the “toe” of the well (the zones further away from the earth surface). Production of unwanted water or gas in any one of these zones may require special interventions to be performed to stop production of the unwanted water or gas. 
     In other scenarios, certain zones of the well may have excessive drawdown pressures, which can lead to early erosion of devices or other problems. 
     To address coning effects or other issues noted above, flow control devices are placed into the well. There are various different types of flow control devices that have conventionally been used to equalize flow rates (or drawdown pressures) in different zones of a well. Some conventional flow control devices employed tortuous paths to provide a flow restriction before fluid is allowed to enter a flow conduit from the surrounding reservoir(s). However, such flow control devices generally suffer from lack of flexibility and/or are relatively complex in design. 
     SUMMARY 
     In general, according to an embodiment, an apparatus for use in a wellbore comprises a flow conduit, and a structure defining a tortuous fluid path proximate the flow conduit. The tortuous fluid path receives a flow of fluid, and is defined by at least first and second members of the structure. The first and second members are movable with respect to each other to adjust a cross-sectional flow area of the tortuous fluid path. 
     Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example arrangement of a completion system that incorporates flow control devices according to some embodiments. 
         FIGS. 2A-2D  illustrate a portion of a flow control device, according to an embodiment having a helical structure for defining a tortuous path having an adjustable cross-sectional flow area, that is usable in the completion system of  FIG. 1 . 
         FIGS. 3A-3D  illustrate various different types of solutions to allow a sealed fit between the helical structure used in the flow control device of  FIGS. 2A-2D  and other portions of the flow control device, according to an embodiment. 
         FIG. 4  illustrates a portion of a flow control device, according to another embodiment, having nested helical structures to provide a tortuous fluid path having an adjustable cross-sectional flow area. 
         FIGS. 5A-5C  illustrate corresponding portions of flow control devices, according to other embodiments, having members that are rotatable with respect to each other to provide tortuous fluid paths having adjustable cross-sectional flow areas. 
         FIGS. 6A-6B  illustrate portions of flow control devices, according to further embodiments, having structures with fingers to provide tortuous fluid paths having adjustable cross-sectional flow areas. 
         FIG. 7  illustrates a portion of a flow control device, according to a further embodiment, having movable disks to provide a tortuous fluid path having an adjustable cross-sectional flow area. 
         FIGS. 8A-8B  are cross-sectional views of two alternative implementations of the flow control device depicted in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
       FIG. 1  illustrates an example completion system installed in a horizontal or substantially horizontal wellbore  102  where the completion system includes multiple flow control devices  104  in accordance with some embodiments. Although the wellbore  102  is depicted as being a horizontal or substantially horizontal wellbore, the flow control devices according to some embodiments can be used in vertical or deviated wellbores in other implementations. The flow control devices  104  are connected to a tubing or pipe  106  (more generally referred to as a “flow conduit”) that can extend to the earth surface or to some other location in the wellbore  102 . Also, sealing elements  108  (e.g., packers) are provided to define different zones  110  in the wellbore  102 . 
     The different zones  110  correspond to different fluid flow zones, where fluid flow in each zone  110  is controlled by a respective flow control device  104 . 
     In a production context, fluid flows from a surrounding reservoir (or reservoirs) into the wellbore  102 , with the flow control devices  104  controlling the flow of such incoming fluids (which can be hydrocarbons) into the pipe  106 . On the other hand, in the injection context, the flow control devices  104  control injection of fluid from inside the pipe  106  out towards the surrounding formation. 
     An issue associated with producing or injecting fluids in a well having multiple zones, such as the wellbore  102  depicted in  FIG. 1 , is the lack of control over the local drawdown pressures in the different zones. The horizontal or substantially horizontal wellbore  102  has a heel  112  (which is a section of the wellbore closer to the earth surface) and a toe  114  (which is a section of the wellbore further away from the earth surface). During production, the local drawdown pressure at the heel  112  tends to be larger than the local drawdown pressure at the toe  114 , which can result in a greater flow rate at the heel  112  than at the toe  114 . The frictional pressure drop caused by flow of fluids (injection fluids or production fluids) in a flow conduit (production or injection conduit) contributes to the variation of local drawdown pressure. As a result of the different local drawdown pressures in the different zones, hydrocarbons in the reservoir portion proximate the heel  112  are prone to depleting at a faster rate than hydrocarbons in the reservoir portion proximate the toe  114 . This can result in an undesirable production profile across the entire well which might lead to the production of unwanted water or gas into the wellbore zone proximate the heel  112  (an effect referred to as water or gas coning). 
     To control the production profile (by controlling the local drawdown pressures and flow rates into the different zones  110  of the wellbore  102 ), the flow control devices  104  are provided. Note that water or gas coning is just one of the adverse effects that can result from uncontrolled drawdown pressures in different zones. Other possible adverse effects include excessive erosion of equipment in zones with larger drawdown pressures, cave-in in a zone having a large drawdown pressure, and others. 
     Although reference is made to production of fluids, it is noted that flow control is also desirable in the injection context. 
     Each flow control device  104  in accordance with some embodiments defines a tortuous path through which fluid flows between the inside and outside of the flow control device  104 . A tortuous path is a path having multiple twists, bends, or turns. The tortuous path is defined proximate a pipe (or other type of flow conduit) of the flow control device. For example, the tortuous path can be provided around the outer surface of the pipe. 
     To provide selective drawdown pressure and flow rate control in the tortuous path of each flow control device  104 , an adjustment mechanism is provided to adjust the cross-sectional flow area of the tortuous path of the corresponding flow control device. The cross-sectional flow area is the flow area available for fluid flow through the tortuous path. A change in flow restriction across the flow control device is related to the change in cross-sectional flow area. Therefore, the ability to adjust the cross-sectional flow area allows a well operator to control the flow restriction across the flow control device (and thus the local drawdown pressure and flow rate of the flow control device). 
     In accordance of some embodiments of the invention, the cross-sectional flow area of the flow control device is adjustable at any one of more of the following locations: at the assembly site, at the well site, or in a downhole location (using either an intervention mechanism or intervention-less mechanism). An intervention mechanism to adjust the cross-sectional flow area of a tortuous path in a flow control device while the flow control device is downhole includes an intervention tool that is run into the wellbore to engage and to actuate the adjustment mechanism of a flow control device that controls the available cross-sectional flow area of the tortuous path. An intervention-less mechanism refers to a mechanism that allows remote actuation of the flow control devices (either by electrical signaling, hydraulic signaling, optical signaling, and so forth) to control the cross-sectional flow areas of the flow control devices. 
     In one embodiment, the tortuous path of a flow control device is defined by a compressible component, such as a helical structure that is generally shaped like a coil spring. The compressible component can be compressed or uncompressed to adjust the cross-sectional flow area of the tortuous path defined by the compressible member. 
     Alternatively, instead of using a compressible element, the flow control device can include other types of members for defining tortuous paths, where at least one or more of the members are movable to adjust the cross-sectional flow area of the tortuous path. Generally, an adjustment mechanism for adjusting a cross-sectional flow area of a tortuous path in a flow control device includes at least two members that are movable with respect to each other to adjust the cross-sectional flow area. In the example where the adjustment mechanism includes a helical structure, the at least two members include different portions of the helical structure. Various different types of adjustment mechanisms for defining tortuous paths in flow control devices are discussed below. 
       FIGS. 2A-2D  illustrate one example adjustment mechanism for defining a tortuous path of a flow control device, where the adjustment mechanism includes a helical structure  202  (e.g., a helical wire, a coil spring, etc.) that is fittable over a section of a base pipe  204  of a flow control device  200 .  FIG. 2A  depicts a partially cut-away view of the flow control device  200  to show an inner bore  206  of the flow control device  200 . The flow control device  200  also includes a sand screen  208  provided around another section of the pipe  204 . The sand screen  208  is used for filtering out sand particles or other particulates such that the sand particles or other particulates do not flow into the inner bore  206  of the pipe  204 . 
     Ports  210  are provided on the pipe  204  to allow flow from an annulus region (defined between the outside of the flow control device  200  and the wall of the wellbore) into the inner bore  206  of the pipe  204 . The pipe  204  also has two sets of threads, including a first set  240  and a second set  242 . The first set  240  of threads is used to threadably connect the flow control device  200  to another downhole component in a tool string. The second set  242  of threads is used to allow threaded rotation of a collar  222  ( FIG. 2C ) for adjusting compression or decompression of the helical structure  202 . 
       FIG. 2B  shows the helical structure  202  mounted onto the pipe  204  such that a spiral path  212  is defined around the outer surface of the pipe  204 . The spiral path  212  is a form of tortuous path. 
     The helical structure  202  has a tight fit with respect to the outer surface of the pipe  204  such that a reduced amount of leakage (or no leakage) occurs between different turns of the spiral path  212 . In other implementations, sealing elements are provided to provide a fluid tight seal between the helical structure  202  and the pipe to prevent fluid leakage. Various forms of these sealing elements are described further below. 
       FIG. 2C  depicts an outer sleeve (or outer cover)  214  to cover the helical structure  202  as well as portions of the pipe  204 . The outer sleeve  214  is provided over and contacted to the outer surface  218  ( FIG. 2B ) of a lower portion of the pipe  204 , the outer surface  216  of the helical structure  202 , and an outer surface  220  of another portion of the pipe  204 . The outer sleeve  214  is sealingly engaged to the outer surfaces  218  and  220  of the different portions of the pipe  204 , such as by use of elastomeric O-ring seals. 
       FIG. 2C  also shows the collar  222  provided on one end of the outer sleeve  214 . As better depicted in  FIG. 2D , the collar  222  is threadably connected to the set  242  of threads of the pipe  204  to allow axial movement of the collar  222  (movement in the direction of the longitudinal axis of the pipe  204 ) when the collar  222  is turned. Axial movement of the collar  222  also causes a corresponding axial movement of the outer sleeve  214 . The collar  222  and outer sleeve  214  are initially at a first position ( FIG. 2C ), in which the helical structure  202  is in a relaxed position (uncompressed position). Note that, in the first position, a gap  226  is provided between the other end  228  of the outer sleeve  218  and a flanged structure  230  provided on the pipe  204 . The gap  226  is provided to enable movement of the outer sleeve  214  toward the flanged structure  230  on the pipe  204 . 
     Thus, as depicted in  FIG. 2D , rotation of the collar  222  has caused axial movement of the outer sleeve  214  such that the outer sleeve  214  has traversed across the gap  226  to abut the flanged structure  230 . In the position of  FIG. 2D  (the final position), the helical structure  202  has been compressed such that the cross-sectional flow area of the spiral path  212  defined by the helical structure  202  is reduced. Note that there are various intermediate positions of the collar  222  and outer sleeve  214  that correspond to respective different compressed states of the helical structure  202 . The continuous movement of the collar  222  allows for continuous adjustment of the compression state of the helical structure  202 , and therefore the continuous adjustment of the cross-sectional flow area of the tortuous path defined by the helical structure  202 . 
     In other implementations, other mechanisms for compressing or uncompressing the helical structure  202  can be used, where such mechanisms generally include a movable component that is translatable with respect to the helical structure  202  to compress or uncompress the helical structure  202 . The movable component can be moved to multiple positions to correspond to multiple compression states of the helical structure  202 . 
     As depicted in  FIG. 2C , the cross-sectional flow area of the spiral path  212  is A 1  when the helical structure  202  is in a relaxed (uncompressed) position. However, as depicted in  FIG. 2D , the cross-sectional area of the spiral path  212  is A 2  after compression of the helical structure  202 , where A 2  is less than A 1 . Due to the reduction in cross-sectional flow area of the spiral path  212  in  FIG. 2D , the flow restriction of the tortuous path is increased. Note that although the cross-sectional flow area of the spiral path  212  has been changed, the overall length of the spiral path  212  remains the same. 
     The collar  222  can be manually rotated by a user, such as at an assembly site or at the wellsite. If adjustment of the collar  222  is desirable while the flow control device  200  is located downhole, then a mechanism can be added to the flow control device  200  to allow for mechanical, electrical, or hydraulic actuation of the collar  222 . The mechanical, electrical, or hydraulic actuation can be performed with or without an intervention tool. 
     In operation, in the production context, fluid flows from the well annulus (outside the flow control device  200 ) through the sand screen  208  into an annular flow path  232  inside the sand screen  208  ( FIG. 2C ). The fluid flows through the annular flow path  232  into a first end  234  of the spiral path  212 . The fluid follows the spiral path  212  until the fluid exits the second end  236  of the spiral path  212 , where the fluid is allowed to flow through the ports  210  on the pipe  204  into the inner bore  206  of the pipe  204 . 
     In the  FIG. 2D  position, where the helical structure  202  has been compressed, the fluid exiting the second end  236  of the spiral path  212  flows into another annular region  231  before the fluid reaches the ports  210  to allow entry into the inner bore  206  of the pipe  204 . 
     The flow path is reversed in the injection context, where fluid is injected from an upstream tubing (such as a tubing that extends to the earth surface) into the inner bore  206  of the flow control device  200 . The injected fluid exits the ports  210  to then follow the spiral path  212  until it reaches the sand screen  208 , at which point the fluid flows from the annular path  232  out of the sand screen  208  into the well annulus. 
     In some implementations, there may be an issue of leakage between the helical structure  202  and the pipe  204  and between the helical structure  202  and outer sleeve  214 . As depicted in  FIG. 3A , this leakage of fluid may occur through an annular clearance  300  between the helical structure  202  and the outer surface of the pipe  204 , and through an annular clearance  302  between the helical structure  202  and the outer sleeve  214 . The leakage occurs between different turns of the spiral path  212  (e.g., turns  212 A,  212 B, and  212 C depicted in  FIG. 3A ). The clearances  300 ,  302  can be caused by a radial deformation of the helical structure  202 , such as due to inexact manufacturing tolerances, worn-out parts, or just by deformation caused by compressing the helical structure  202 . Each clearance  300 ,  302  provides a shortcut for fluid to bypass the spiral path  212 , which can cause the flow restriction across the flow control device to be lower than expected. In a worst-case scenario, the leakage through annular clearances  300 ,  302  can bypass the tortuous path in the flow control device completely. To mitigate this issue, several possible measures can be taken. In one example, instead of using the generally rectangular cross-sectional profile of the helical structure  202  as shown in  FIG. 3A , a different helical structure  202 A can use a curved cross-sectional profile, as depicted in  FIG. 3B . The curved profile depicted in  FIG. 3B  has a generally crescent shape such that elastic deformation of the helical structure  202  is possible to seal the clearances  300 ,  302 . 
     In an alternative embodiment, rather than forming the helical structure  202  of a metal, the helical structure  202  can be formed of an elastomer material (e.g., rubber). The compressible nature of the elastomer material allows the helical structure  202  to maintain a seal against the pipe  204  and the outer sleeve  214  such that the clearances  300 ,  302  do not form. 
     Another possible solution is depicted in  FIG. 3C , where the helical structure  202  (which can be formed of metal, for example) is coated or otherwise covered with elastomer elements  304  and  306 , where the elastomer elements  304  engage the pipe  204 , and the elastomer elements  306  engage the outer sleeve  214 . In this manner, the clearances  300  and  302  can be eliminated. 
     In another arrangement, as depicted in  FIG. 3D , the helical structure  202  can be formed of a metal, except that the helical structure  202  is encased by elastomeric elements  306 ,  308  that sealingly engage both the outer cover  214  and the pipe  204 . The elastomeric elements  306 ,  308  define an inner chamber  310  in which the helical structure  202  is movable during compression of the helical structure  202  or due to other causes. In this manner, the movement of the helical structure  202  does not cause creation of annular clearances  300 ,  302  that can lead to leakage. Note that the elastomeric elements  306 ,  308  and chamber  310  are also generally helically shaped. 
       FIG. 4  shows another type of an adjustment mechanism to provide a tortuous path that has an adjustable cross-sectional flow area. In  FIG. 4 , the assembly includes two nested helical structures  400  and  402  where the helical structure  400  is attached to the outer sleeve  214 , and the helical structure  402  is attached to the pipe  204 . The helical structures  400 ,  402  are movable with respect to each other both in an axial direction (indicated by direction x) and in the radial direction (indicated by directional y) of the pipe  204 . The helical structures  400 ,  402  define a tortuous path  404  whose cross-sectional flow area changes due to relative movement of the helical structures  400 ,  402 . In  FIG. 4 , each of the helical structures  400 ,  402  has a generally triangular cross-sectional profile. In  FIG. 4 , one of the triangles (corresponding to one helical structure) is upside down with respect to the other of the triangles (corresponding to the other helical structure) such that the slanted surface of one of the helical structures is engaged or mated to a corresponding slanted surface of the other helical structure. The engagement or mating of the slanted surfaces of the helical structures  400 ,  402  allows for motion in both the x and y directions, as depicted in  FIG. 4 , to change the cross-sectional flow area of the tortuous path  404 . 
     Note that with the design provided in  FIG. 4 , the issue of annular clearances between the helical structures  400 ,  402  and the outer sleeve  214  and pipe  204  is reduced or eliminated. 
       FIGS. 5A-5C  illustrate adjustment mechanisms according to three alternative configurations where a tortuous path is defined by two members that are rotatable with respect to each other, such as rotation based on threaded engagement of the members.  FIG. 5A  shows an assembly having a first member  500  and a second member  502  that are threaded to each other to allow relative rotation or movement of the members  500  and  502  (in the rotational direction indicated by r). The member  500  has threads  506 , while the member  502  has threads  508 . 
     The two members  500  and  502  define a tortuous path  504 . Relative rotation of the members  500  and  502  causes the cross-sectional flow area of the tortuous flow path  504  to change. In the  FIG. 5A  embodiment, the tooth width of threads of each of the members  500  and  502  varies. The tooth widths of the threads  506  on the member  500  are represented by W 1 , where W 1  for each thread can be different. Similarly, the tooth widths for the threads  508  on the member  502  are represented by W 2 , where W 2  for each thread on the member  502  can be different. In the  FIG. 5A  embodiment, the threads on the members  500  and  502  have constant pitch (the distance between two corresponding points on adjacent screw threads.). 
       FIG. 5B  illustrates an adjustment mechanism according to a different embodiment, where the adjustment mechanism has a first member  510  and a second member  512  that are rotatable with respect to each other by a threaded connection. The first member  510  has threads  516 , and the second member  512  has threads  518 . In the embodiment of  FIG. 5B , the tooth widths of the threads of each of the members  510  and  512  vary, but the pitch of the threads on each of the members  510  and  512  is constant. The members  510 ,  512  define a tortuous path  514 , whose cross-sectional flow area is changed by relative rotation of the first and second members  510 ,  512 . 
       FIG. 5C  shows another adjustment mechanism according to a different embodiment that has members  520  and  522  that are rotatable with respect to each other by a threaded connection. The members  520  and  522  define a tortuous path  524 , whose cross-sectional flow area can change due to relative rotation of the members  520  and  522 . The threads  526 ,  528  of each respective member  520 ,  522  has constant pitch but different diameters D. 
       FIGS. 6A and 6B  illustrate adjustment mechanisms according to other embodiments to define tortuous flow paths whose cross-sectional flow areas can be adjusted. In each of the embodiments of  FIGS. 6A and 6B , the adjustment mechanism includes two cylindrically-shaped structures, where each cylindrically-shaped structure has fingers that interact with each other to form the tortuous flow path. For example, in  FIG. 6A , a first cylindrically-shaped structure  600  has fingers  608 , and a second cylindrically-shaped structure  602  has fingers  610 . The fingers  608  and  610  are intertwined such that each finger  610  is provided between each pair of adjacent fingers  608 . The intertwined fingers  608  and  610  define a tortuous flow path  612 . Note that the cylindrically-shaped structures  600  and  602  are provided around the circumference of the pipe  204 , as depicted in  FIG. 6A . The cylindrically-shaped structures  600  and  602  are movable with respect to each other in the x direction (axial direction of the pipe  204 ) to adjust the cross-sectional flow area of the tortuous flow path  612 . In one embodiment, the position of the cylindrically-shaped structure  600  is fixed, whereas the cylindrically-shaped structure  602  is movable in the x direction by movement of an actuation lug  608  that is movable along the circumference of the pipe  204  in a groove  610 . The groove  610  is formed in the outer surface of the pipe  204 . The actuation lug  608  and the groove  610  essentially form a cylindrical cam mechanism. An actuation mechanism (not shown) is coupled between the actuation lug  608  and the cylindrically-shaped structure  602  such that the movement of the lug  608  in the groove  610  causes axial movement of the cylindrically-shaped structure  602  (in the x direction). In another embodiment, the actuation lug  608  is rigidly connected to the cylindrically-shaped structure  602 . The relative rotation between pipe  204  and the actuation lug  608  (together with the cylindrically-shaped structure  602  and  600 ) causes axial movement of the cylindrically-shaped structure  602  (in the x direction). There can be other embodiments based on the cylindrical cam mechanism for generating the relative axial movement between the cylindrically-shaped structures  600  and  602 . 
     In operation, fluid flows into the tortuous flow path  612  at  604  and exits the tortuous flow path at  606 . Relative movement of the cylindrically-shaped structures  600 ,  602  causes the cross-sectional flow area of the tortuous path to change such that the tortuous path&#39;s flow restriction between  604  and  606  changes accordingly. 
     The fingers  608  and  610  of the cylindrically-shaped structures  600  and  602  are generally rectangular in profile. In an alternative implementation, as depicted in  FIG. 6B , cylindrically-shaped structures  620  and  622  (which are movable with respect to each other in the x direction or the axial direction of the pipe) have fingers  628  and  630 , respectively. The fingers  628  and  630 , rather than being rectangular in profile, have tapered shapes. The fingers  628  and  630  define a tortuous flow path  632 . 
       FIG. 7  illustrates yet another alternative embodiment, in which a tortuous flow path is defined by disks  700 ,  702 ,  704  that are movable with respect to each other in an axial direction (x direction) of the pipe  204 . Although just three disks  700 ,  702 ,  704  are depicted, it is noted that additional disks can be employed in other implementations. The disks  700 ,  702 , and  704  are ring-shaped with an inner, central hole such that the pipe  204  can fit through the inner holes of the disks  700 ,  702 , and  704 . Each of the disks  700 ,  702 , and  704  has a respective port  706 ,  708 , and  710  through which fluid can flow. The position of the ports on successive disks are varied such that the fluid flow follows a tortuous path. For example, in  FIG. 7 , the port  710  is located on a bottom side of the disk  704 , the port  708  is located on a top side of the disk  702 , and the port  706  is located on a bottom side of the disk  700 . More generally, the ports in successive disks are offset with respect to each other in the angular direction a of the disks. 
     Each pair of successive disks  700 ,  702 ,  704  define a corresponding chamber  722 A,  722 B through which fluid flows from one port to another port. For example, as depicted in  FIG. 7 , fluid flows from port  710  through chamber  722 B to port  708 . Fluid from port  708  then passes through the chamber  722 A to port  706 . The combination of the ports  706 ,  708 ,  710  and chamber  722 A,  722 B form a tortuous path  712 . 
       FIG. 8A  is cross-sectional view of a portion of the arrangement depicted in  FIG. 7  to illustrate a fluid flow path through chamber  722 B. In  FIG. 8A , the outer sleeve  214  is depicted such that the chamber  722 B is defined between the outer sleeve  214  and the pipe  204 . Fluid enters into the chamber  722 B through entry port  710 , with the fluid following two symmetric paths  714  and  716  in the chamber  722 B to arrive at the exit port  708  to flow to the next portion of the tortuous path  712 . 
     In an alternative embodiment, as depicted in  FIG. 8B , a barrier  718  can be provided in the chamber  722 B (and in other chambers) such that fluid flow has to follow a single path  720  in the chamber  722 B. The barrier  718  extends radially between the outer sleeve  214  and the pipe  204 . 
     While the invention has been disclosed 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 such modifications and variations as fall within the true spirit and scope of the invention.