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CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application is a continuation application of Ser. No. 10/160,216 filed May 31, 2002 and a continuation-in-part application of Ser. No. 10/796,467 filed Mar. 9, 2004 which is a continuation application of Ser. No. 09/927,217 filed Aug. 10, 2001, now U.S. Pat. No. 6,702,018, which is a continuation-in-part application of Ser. No. 09/800,199 filed Mar. 6, 2001, now U.S. Pat. No. 6,557,634, each of which is incorporated by reference for all purposes. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     This invention relates in general to preventing the production of particulate materials through a wellbore traversing an unconsolidated or loosely consolidated subterranean formation and, in particular to, an apparatus and method for obtaining a substantially complete gravel pack within an interval of the wellbore.  
       BACKGROUND OF THE INVENTION  
       [0003]     Without limiting the scope of the present invention, its background is described with reference to the production of hydrocarbons through a wellbore traversing an unconsolidated or loosely consolidated formation, as an example.  
         [0004]     It is well known in the subterranean well drilling and completion art that particulate materials such as sand may be produced during the production of hydrocarbons from a well traversing an unconsolidated or loosely consolidated subterranean formation. Numerous problems may occur as a result of the production of such particulate. For example, the particulate causes abrasive wear to components within the well, such as tubing, pumps and valves. In addition, the particulate may partially or fully clog the well creating the need for an expensive workover. Also, if the particulate matter is produced to the surface, it must be removed from the hydrocarbon fluids by processing equipment at the surface.  
         [0005]     One method for preventing the production of such particulate material to the surface is gravel packing the well adjacent the unconsolidated or loosely consolidated production interval. In a typical gravel pack completion, a sand control screen is lowered into the wellbore on a work string to a position proximate the desired production interval. A fluid slurry including a liquid carrier and a particulate material known as gravel is then pumped down the work string and into the well annulus formed between the sand control screen and the perforated well casing or open hole production zone.  
         [0006]     The liquid carrier either flows into the formation or returns to the surface by flowing through the sand control screen or both. In either case, the gravel is deposited around the sand control screen to form a gravel pack, which is highly permeable to the flow of hydrocarbon fluids but blocks the flow of the particulate carried in the hydrocarbon fluids. As such, gravel packs can successfully prevent the problems associated with the production of particulate materials from the formation.  
         [0007]     It has been found, however, that a complete gravel pack of the desired production interval is difficult to achieve particularly in long or inclined/horizontal production intervals. These incomplete packs are commonly a result of the liquid carrier entering a permeable portion of the production interval causing the gravel to form a sand bridge in the annulus. Thereafter, the sand bridge prevents the slurry from flowing to the remainder of the annulus which, in turn, prevents the placement of sufficient gravel in the remainder of the annulus.  
         [0008]     Prior art devices and methods have been developed which attempt to overcome this sand bridge problem. For example, attempts have been made to use devices having perforated shunt tubes or bypass conduits that extend along the length of the sand control screen to provide an alternate path for the fluid slurry around the sand bridge. It has been found, however, that shunt tubes installed on the exterior of sand control screens are susceptible to damage during installation and may fail during a gravel pack operation. In addition, it has been found that it is difficult and time consuming to make all of the necessary fluid connections between the numerous joints of shunt tubes required for typical production intervals.  
         [0009]     Therefore a need has arisen for an apparatus and method for gravel packing a production interval traversed by a wellbore that overcomes the problems created by sand bridges. A need has also arisen for such an apparatus that is not susceptible to damage during installation or failure during use. Further, a need has arisen for such an apparatus that is not difficult or time consuming to assemble.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention disclosed herein comprises an apparatus and method for gravel packing a production interval of a wellbore that traverses an unconsolidated or loosely consolidated formation that overcomes the problems created by the development of a sand bridge between a sand control screen and the wellbore. Importantly, the apparatus of the present invention is not susceptible to damage during installation or failure during use and is not difficult or time consuming to assemble.  
         [0011]     The apparatus for gravel packing an interval of a wellbore of the present invention comprises an outer tubular forming a first annulus with the wellbore and a sand control screen disposed within the outer tubular forming a second annulus therebetween. Together, the sand control screen and the outer tubular of the present invention are assembled at the surface and run downhole to a location proximate the production interval. The outer tubular includes a plurality of openings that allow for the production of fluids therethrough and plurality of outlets that allow the distribution of a fluid slurry containing gravel therethrough.  
         [0012]     In the volume within the second annulus between the sand control screen and the outer tubular there are one or more channels that define axially extending slurry passageways with sheet members positioned between the channels and the sand control screen. The sheet members create a barrier to the flow of fluids between the channels and the sand control screen. The volume within the second annulus between adjacent channels forms axially extending production pathways. The channels prevent fluid communication between the production pathways and the slurry passageways. In addition, isolation members at either end of a section of the apparatus of the present invention define the axial boundaries of the production pathways.  
         [0013]     As such, when a fluid slurry containing gravel is injected through the slurry passageways, the fluid slurry exits the slurry passageways through outlets in the channels and the outer tubular leaving a first portion of the gravel in the first annulus. Thereafter, the fluid slurry enters the openings in the outer tubular leaving a second portion of the gravel in the production pathways. Thus, when formation fluids are produced, the formation fluids travel radially through the production pathways by entering the openings in the outer tubular and exiting the production pathways through the sand control screen. The formation fluids pass through the first portion of the gravel in the first annulus prior to entry into the production pathways, which contains the second portion of the gravel, both of which filter out the particulate materials in the formation fluids. Formation fluids are prevented, however, from traveling radially through the slurry passageways as the sheet members prevent such flow.  
         [0014]     In a typical gravel packing operation using the apparatus for gravel packing an interval of a wellbore of the present invention, the first annulus between the outer tubular and the wellbore may serve as a primary path for delivery of a fluid slurry. This region serves as the primary path as it provides the path of least resistance to the flow of the fluid slurry. When the primary path becomes blocked by sand bridge formation, the production pathways of the present invention serves as independent secondary paths for delivery of the fluid slurry. The production pathways serve as the secondary paths as they provide the paths of second least resistance to the flow of the fluid slurry. When the primary path and secondary paths become blocked by sand bridge formation, the slurry passageways serve as independent tertiary paths for delivery of the fluid slurry. The slurry passageways serve as the tertiary paths as they provide the paths of greatest resistance to the flow of the fluid slurry but are least likely to have sand bridge formation therein due to the high velocity of the fluid slurry flowing therethrough and their substantial isolation from the formation.  
         [0015]     Commonly, more than one section of the apparatus for gravel packing an interval of a wellbore must be coupled together to achieve a length sufficient to gravel pack an entire production interval. In such cases, multiple sections of the apparatus of the present invention are coupled together, for example, via a threaded connection. Also, in such cases, the slurry passageways of the various sections are in fluid communication with one another allowing an injected fluid slurry to flow from one such apparatus to the next, while the production pathways of the various sections are in fluid isolation from one another.  
         [0016]     In a method for gravel packing an interval of a wellbore of the present invention, the method comprises providing a wellbore that traverses a formation, either open hole or cased, perforating the casing, in the cased hole embodiment, proximate the formation to form a plurality of perforations, locating a gravel packing apparatus including a sand control screen within the wellbore proximate the formation to form a first annulus between the gravel packing apparatus and the wellbore and a second annulus between the sand control screen and the outer tubular, injecting a fluid slurry containing gravel through slurry passageways formed between sheet members and channels with the second annulus such that the fluid slurry exits through the outlets of the channels and the outer tubular into the first annulus, depositing a first portion of the gravel in the first annulus, depositing a second portion of the gravel in the production pathways by returning a portion of the fluid slurry through openings in the outer tubular and terminating the injection when the first annulus and the production pathways are substantially completely packed with gravel.  
         [0017]     In addition to injecting the fluid slurry containing gravel through the slurry passageways, in some embodiments, the fluid slurry may also be injected down the first annulus. In this case, the method also involves injecting a fluid slurry containing gravel into a primary path defined by the first annulus, diverting the fluid slurry containing gravel into a secondary path defined by the production pathways if the primary path becomes blocked, diverting the fluid slurry containing gravel into a tertiary path defined by the slurry passageways if the primary and secondary paths become blocked and terminating the injecting when the interval is substantially completely packed with the gravel.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     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:  
         [0019]      FIG. 1  is a schematic illustration of an offshore oil and gas platform operating an apparatus for gravel packing an interval of a wellbore of the present invention;  
         [0020]      FIG. 2  is partial cut away view of an apparatus for gravel packing an interval of a wellbore of the present invention in position around a sand control screen;  
         [0021]      FIG. 3  is partial cut away view of an apparatus for gravel packing an interval of a wellbore of the present invention in position around a sand control screen;  
         [0022]      FIG. 4  is a side view of portions of two sections of an apparatus for gravel packing an interval of a wellbore of the present invention that are coupled together;  
         [0023]      FIG. 5  is a side view of portions of two sections of a sand control screen for an apparatus for gravel packing an interval of a wellbore of the present invention that are coupled together;  
         [0024]      FIG. 6  is a cross sectional view of an apparatus for gravel packing an interval of a wellbore of the present invention taken along line  6 - 6  of  FIGS. 4 and 5 ;  
         [0025]      FIG. 7  is a cross sectional view of an apparatus for gravel packing an interval of a wellbore of the present invention taken along line  7 - 7  of  FIGS. 4 and 5 ;  
         [0026]      FIG. 8  is a cross sectional view of an apparatus for gravel packing an interval of a wellbore of the present invention taken along line  8 - 8  of  FIGS. 4 and 5 ;  
         [0027]      FIG. 9  is a cross sectional view of an apparatus for gravel packing an interval of a wellbore of the present invention taken along line  9 - 9  of  FIGS. 4 and 5 ;  
         [0028]      FIG. 10  is a side view of two channels connected together in an area between adjacent screen sections of an apparatus for gravel packing an interval of a wellbore of the present invention;  
         [0029]      FIG. 11  is a cross sectional view of a spacer member for positioning between adjacent screen sections of an apparatus for gravel packing an interval of a wellbore of the present invention;  
         [0030]      FIG. 12  is a cross sectional view of a spacer member for positioning between adjacent screen sections of an apparatus for gravel packing an interval of a wellbore of the present invention;  
         [0031]      FIG. 13  is a cross sectional view of a spacer member for positioning between adjacent screen sections of an apparatus for gravel packing an interval of a wellbore of the present invention;  
         [0032]      FIG. 14  is a half sectional view depicting the operation of an apparatus for gravel packing an interval of a wellbore of the present invention; and  
         [0033]      FIG. 15  is a half sectional view depicting the operation of another embodiment of an apparatus for gravel packing an interval of a wellbore of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]     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.  
         [0035]     Referring initially to  FIG. 1 , several apparatuses for gravel packing an interval of a wellbore operating from an offshore oil and gas platform are 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 blowout preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work string  30 .  
         [0036]     A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . Work string  30  includes various tools including apparatuses  38 ,  40 ,  42  for gravel packing an interval of wellbore  32  adjacent to formation  14  between packers  44 ,  46  and into annular region  48 . When it is desired to gravel pack annular region  48 , work string  30  is lowered through casing  34  until apparatuses  38 ,  40 ,  42  are positioned adjacent to formation  14  including perforations  50 . Thereafter, a fluid slurry including a liquid carrier and a particulate material such as sand, gravel or proppants is pumped down work string  30 .  
         [0037]     As explained in more detail below, the fluid slurry may be injected entirely into apparatus  38  and sequentially flow through apparatuses  40 ,  42 . During this process, portions of the fluid slurry exit each apparatus  38 ,  40 ,  42  such that the fluid slurry enters annular region  48 . Once in annular region  48 , a portion of the gravel in the fluid slurry is deposited therein. Some of the liquid carrier may enter formation  14  through perforation  50  while the remainder of the fluid carrier, along with some of the gravel, reenters certain sections of apparatuses  38 ,  40 ,  42  depositing gravel in those sections. As a sand control screen (not pictured) is positioned within apparatuses  38 ,  40 ,  42 , the gravel remaining in the fluid slurry is disallowed from further migration. The liquid carrier, however, can travel through the sand control screen, into work string  30  and up to the surface in a known manner, such as through a wash pipe and into the annulus  52  above packer  44 . The fluid slurry is pumped down work string  30  through apparatuses  38 ,  40 ,  42  until annular section  48  surrounding apparatuses  38 ,  40 ,  42  and portions of apparatuses  38 ,  40 ,  42  are filled with gravel.  
         [0038]     Alternatively, instead of injecting the entire stream of fluid slurry into apparatuses  38 ,  40 ,  42 , all or a portion of the fluid slurry could be injected directly into annular region  48  in a known manner such as through a crossover tool (not pictured) which allows the slurry to travel from the interior of work string  30  to the exterior of work string  30 . Again, once this portion of the fluid slurry is in annular region  48 , a portion of the gravel in the fluid slurry is deposited in annular region  48 . Some of the liquid carrier may enter formation  14  through perforation  50  while the remainder of the fluid carrier along with some of the gravel enters certain sections of apparatuses  38 ,  40 ,  42  filling those sections with gravel. The sand control screen (not pictured) within apparatuses  38 ,  40 ,  42  disallows further migration of the gravel but allows the liquid carrier to travel therethrough into work string  30  and up to the surface. If the fluid slurry is injected directly into annular region  48  and a sand bridge forms, the fluid slurry is diverted into apparatuses  38 ,  40 ,  42  to bypass this sand bridge such that a complete pack can nonetheless be achieved. The fluid slurry entering apparatuses  38 ,  40 ,  42  may enter apparatuses  38 ,  40 ,  42  proximate work string  30  or may enter apparatuses  38 ,  40 ,  42  from annular region  48  via one or more inlets on the exterior of one or more of the apparatuses  38 ,  40 ,  42 . These inlets may include pressure actuated devices, such as valves, rupture disks and the like disposed therein to regulate the flow of the fluid slurry therethrough.  
         [0039]     Even though  FIG. 1  depicts a vertical well, it should be noted by one skilled in the art that the apparatus for gravel packing an interval of a wellbore of the present invention is equally well-suited for use in deviated wells, inclined wells or horizontal wells. Also, even though  FIG. 1  depicts an offshore operation, it should be noted by one skilled in the art that the apparatus for gravel packing an interval of a wellbore of the present invention is equally well-suited for use in onshore operations.  
         [0040]     Referring now to  FIG. 2 , therein is depicted a partial cut away view of an apparatus for gravel packing an interval of a wellbore of the present invention that is generally designated  60 . Apparatus  60  has an outer tubular  62  that includes a plurality of openings  64  that are substantially evenly distributed around and along the length of outer tubular  62 . In addition, outer tubular  62  includes a plurality outlets  66 . For reasons that will become apparent to those skilled in the art, the density of opening  64  of outer tubular  62  is much greater than the density of outlets  66  of outer tubular  62 . Also, it should be noted by those skilled in the art that even though  FIG. 2  has depicted openings  64  and outlets  66  as being circular, other shaped openings may alternatively be used without departing from the principles of the present invention. Likewise, even though  FIG. 2  has depicted openings  64  as being smaller than outlets  66 , openings  64  could alternatively be larger than or the same size as outlets  66  without departing from the principles of the present invention. In addition, the exact number, size and shape of openings  64  are not critical to the present invention, so long as sufficient area is provided for fluid production therethrough and the integrity of outer tubular  62  is maintained.  
         [0041]     Disposed within outer tubular  62  is a sand control screen  70 . Sand control screen  70  includes a base pipe  72  that has a plurality of openings  74  which allow the flow of production fluids into the production tubing. The exact number, size and shape of openings  74  are not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of base pipe  72  is maintained.  
         [0042]     Spaced around base pipe  72  is a plurality of ribs  76 . Ribs  76  are generally symmetrically distributed about the axis of base pipe  72 . Ribs  76  are depicted as having a cylindrical cross section, however, it should be understood by one skilled in the art that ribs  76  may alternatively have a rectangular or triangular cross section or other suitable geometry. Additionally, it should be understood by one skilled in the art that the exact number of ribs  76  will be dependent upon the diameter of base pipe  72  as well as other design characteristics that are well known in the art.  
         [0043]     Wrapped around ribs  76  is a screen wire  78 . Screen wire  78  forms a plurality of turns, such as turn  80 , turn  82  and turn  84 . Between each of the turns is a gap through which formation fluids flow. The number of turns and the gap between the turns are determined based upon the characteristics of the formation from which fluid is being produced and the size of the gravel to be used during the gravel packing operation. Together, ribs  76  and screen wire  78  may form a sand control screen jacket which is attached to base pipe  72  by welding or other suitable techniques.  
         [0044]     Disposed within an annulus  86  on opposite sides of one another and between outer tubular  62  and sand control screen  70  is a pair of channels  88 , only one being visible. Channels  88  include a web  90  and a pair of oppositely disposed sides  92  each having an end  94 . Ends  94  are attached to a sheet member  96  and, in turn, to sand control screen  70  by, for example, welding or other suitable techniques. Channels  88  includes a plurality of outlets  98  that are substantially aligned with outlets  66  of outer tubular  62 . Together, channels  88  and sheet members  96  define slurry passageways  100 . Between channels  88  are production pathways  102  which are defined by the radial boundaries of outer tubular  62  and sand control screen  70  and the circumferential boundaries of sides  92  of channels  88 . Slurry passageways  100  and production pathways  102  are in fluid isolation from one another.  
         [0045]     It should be understood by those skilled in the art that while  FIG. 2  has depicted a wire wrapped sand control screen, other types of filter media could alternatively be used in conjunction with the apparatus of the present invention, including, but not limited to, a fluid-porous, particulate restricting, sintered metal material such as a plurality of layers of a wire mesh that are sintered together to form a porous sintered wire mesh screen designed to allow fluid flow therethrough but prevent the flow of particulate materials of a predetermined size from passing therethrough.  
         [0046]     More specifically and referring now to  FIG. 3 , therein is depicted a partial cut away view of an apparatus for gravel packing an interval of a wellbore of the present invention that is generally designated  110 . Apparatus  110  has an outer tubular  112  that includes a plurality of openings  114  that are substantially evenly distributed around and along the length of outer tubular  112 , which allow the flow of production fluids therethrough. In addition, outer tubular  112  includes a plurality of outlets  116 .  
         [0047]     Disposed within outer tubular  112  is a sand control screen assembly  118 . Sand control screen assembly  118  includes a base pipe  120  that has a plurality of openings  122  which allow the flow of production fluids into the production tubing. The exact number, size and shape of openings  122  are not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of base pipe  120  is maintained.  
         [0048]     Positioned around base pipe  120  is a fluid-porous, particulate restricting, sintered metal material such as plurality of layers of a wire mesh that are sintered together to form a porous sintered wire mesh screen  124 . Screen  124  is designed to allow fluid flow therethrough but prevent the flow of particulate materials of a predetermined size from passing therethrough. The layers of wire mesh may include drain layers that have a mesh size that is larger than the mesh size of the filter layers. For example, a drain layer may preferably be positioned as the outermost layer and the innermost layer of wire mesh screen  124  with the filter layer or layers positioned therebetween. Positioned around screen  124  is a screen wrapper  126  that has a plurality of openings  128  which allow the flow of production fluids therethrough. The exact number, size and shape of openings  128  is not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of screen wrapper  126  is maintained. Typically, various sections of screen  124  and screen wrapper  126  are manufactured together as a unit by, for example, sintering a number layers of wire mesh that form screen  124  together with screen wrapper  126 , then rolling the unit into a tubular configuration. The two ends of the tubular unit are then seam welded together. Several tubular units of the screen and screen wrapper combination are placed over each joint of base pipe  120  and secured thereto by welding or other suitable technique, as will be explained in greater detail below.  
         [0049]     Disposed in annulus  130  between outer tubular  112  and sand control screen  118  and on opposite sides of each other is a pair of channels  132 , only one channel  132  being visible. Channels  132  include a web  134  and a pair of oppositely disposed sides  136  each having an end  138 . Ends  138  are attached to a sheet member  140  and, in turn, to screen wrapper  126  by welding or other suitable technique. Channels  132  include a plurality of outlets  142  that are substantially aligned with outlets  116  of outer tubular  112  and are preferably formed at the same time by drilling or other suitable technique once gravel packing apparatus  110  is assembled. Together, channels  132  and sheet members  140  form slurry passageways  144 . Also, channels  132  define the circumferential boundary between a slurry passageway  144  and production pathways  146 .  
         [0050]     Referring now to  FIGS. 4 and 5 , therein are depicted portions of two joints of outer tubulars designated  150  and  152  and corresponding portions of two joints of sand control screens designated  154  and  156 , respectively. Outer tubular  150  has a plurality of openings  158  and several outlets  160 . Likewise, outer tubular  152  has a plurality of openings  162  and several outlets  164 , which are not visible in  FIG. 4 .  
         [0051]     As should become apparent to those skilled in the art, even though  FIG. 4  depicts outer tubular  150  and outer tubular  152  at a ninety-degree circumferential phase shift relative to one another, any degree of circumferential phase shift is acceptable using the present invention as the relative circumferential positions of adjoining joints of the apparatus for gravel packing an interval of a wellbore of the present invention does not affect the operation of the present invention. As such, the mating of adjoining joints of the apparatus for gravel packing an interval of a wellbore of the present invention is substantially similar to mating typical joints of pipe to form a pipe string requiring no special coupling tools or techniques.  
         [0052]     Sand control screen  154  includes outer wrapper  166  that has a plurality of openings  168 . Likewise, sand control screen  156  includes outer wrapper  170  that has a plurality of openings  172 . Sand control screen  154  has a pair of channels  174  and a pair of sheet members  176  attached thereto, only one of each being visible in  FIG. 5 . Channels  174  include outlets  178 . Likewise, sand control screen  156  has a pair of channels  180  and a pair of sheet members  182  attached thereto. Channels  180  includes a plurality of outlets  184  which are not visible in  FIG. 5 . In the illustrated embodiment, sand control screens  154 ,  156  would be positioned within outer tubulars  150 ,  152  such that outlets  178  are axially and circumferentially aligned with outlets  160  of outer tubular  150 , as best seen in  FIG. 6  and such that outlets  184  are axially and circumferentially aligned with outlets  164  of outer tubular  152 , as best seen in  FIG. 7 .  
         [0053]     Each joint of the apparatus of the present invention includes a pair of axially spaced apart substantially circumferential isolation members. For example, isolation members  186  are shown on sand control screen  154  in FIGS.  5  and  8 . Likewise, isolation members  188  are shown on sand control screen  156  in  FIGS. 5 and 9 .  
         [0054]     Channels  174  define the circumferential boundaries of production pathways  188  and, together with sheet members  176 , channels  174  define slurry passageways  190 . Isolation members  186  help provide fluid isolation between production pathways  188  and slurry passageways  190 . Channels  180  define the circumferential boundaries of production pathways  192  and, together with sheet members  182 , channels  180  define slurry passageways  194 . Isolation members  188  help provide fluid isolation between production pathways  192  and slurry passageways  194 .  
         [0055]     Importantly, however, slurry passageways  190  and slurry passageways  194  are all in fluid communication with one another such that a fluid slurry may travel in and between these passageways from one joint of the apparatus for gravel packing an interval of a wellbore of the present invention to the next. Specifically, as best seen in  FIGS. 4 and 5 , an annular region  196  exists between outer tubulars  150 ,  152  and sand control screens  154 ,  156  that allows the fluid slurry to travel downwardly from slurry passageways  190  through annular region  196  into slurry passageways  194 . As such, regardless of the circumferential orientation of sand control screen  154  relative to sand control screen  156 , the fluid slurry will travel down through each joint of the apparatus for gravel packing an interval of a wellbore of the present invention.  
         [0056]     It should be apparent to those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. It should be noted, however, that the apparatus for gravel packing an interval of a wellbore is not limited to such orientation as it is equally-well suited for use in inclined and horizontal orientations.  
         [0057]     As should be apparent to those skilled in the art, the apparatus for gravel packing an interval of a wellbore of the present invention may have a variety of configurations including configurations having other numbers of slurry passageways such as one, three, four or more slurry passageways, such configurations being considered within the scope of the present invention.  
         [0058]     Referring next to  FIGS. 10 and 11 , therein are depicted a portion of a joint of the gravel packing apparatus of the present invention with the outer tubular removed wherein two screen sections are attached to the single joint of base pipe. Screen sections  200  and  202  are each attached to a single joint of base pipe  204 . In the illustrated embodiment, screen section  200  includes a screen wrapper  206  and a filter medium  208 . Likewise, screen section  202  includes a screen wrapper  212  and a filter medium  214 .  
         [0059]     As screen sections  200 ,  202  are commonly shorter than base pipe  204 , two or more screen sections are preferably attached to each base pipe joint. This may be achieved by sliding screen sections  200 ,  202  onto base pipe  204  with a spacer member  218  positioned therebetween. In the illustrated embodiment, spacer member  218  is an annular ring having a two tier radial surface configuration that provides support to the respective ends of screen members  200 ,  202  which are secured to spacer member  218  by welding or other suitable technique. The other ends of screen sections  200 ,  202  are attached to base pipe  204  in a similar manner if additional screen sections are adjacent to the other ends of screen sections  200 ,  202 . Alternatively, if screen sections  200 ,  202  are the last screen sections at the ends of base pipe  204 , a simple ring or an isolation member, such as isolation member  188  of  FIG. 9 , may be used to attach the other ends of screen sections  200 ,  202  to base pipe  204 .  
         [0060]     Either before or after screen sections  200 ,  202  have been attached to base pipe  204 , respective sheet members  220 ,  222  and channels sections  224 ,  226  are attached to screen sections  200 ,  202  by welding or other suitable technique. As a gap exists between channels sections  224 ,  226  in this configuration, a channel segment  228  is attached to the adjacent exposed ends of channels sections  224 ,  226  such that a continuous slurry passageway  230  is formed that extends substantially the entire length of the joint of the gravel packing apparatus of the present invention.  
         [0061]     Instead of using an annular ring having a two tier radial surface configuration as the spacer member, a spacer member  240  that comprises an annular ring having a single radial surface configuration could alternatively be used, as best seen in  FIG. 12 . In this embodiment, a pad  242  having approximately the same circumferential width as the channel may be used. Pad  242  is attached to spacer member  240  by welding or other suitable technique. The remaining assembly of the joint of the gravel packing apparatus of the present invention is substantially the same as that described with reference to  FIGS. 10 and 11 .  
         [0062]     Referring next to  FIG. 13 , therein is depicted another embodiment of spacer member that is designated  250 . In this embodiment, spacer member  250  is an annular ring having a single radial surface configuration. The remaining assembly of the joint of the gravel packing apparatus of the present invention is substantially the same as that described with reference to  FIGS. 10 and 11  except that a channel segment  252  is attached to spacer member  250  without the aid of a raised center section or a pad by welding or other suitable technique to complete slurry passageway  230 .  
         [0063]     Referring now to  FIG. 14 , a typical completion process using an apparatus  300  for gravel packing an interval of a wellbore of the present invention will be described. First, interval  48  adjacent to formation  14  is isolated. Packer  44  seals the upper end of annular interval  48  and packer  46  seals the lower end of annular interval  48 . Cross-over assembly  302  is located adjacent to screen assembly  304 , traversing packer  44  with portions of cross-over assembly  302  on either side of packer  44 . When the gravel packing operation commences, the objective is to uniformly and completely fill interval  48  with gravel. To help achieve this result, wash pipe  306  is disposed within screen assembly  304 . Wash pipe  306  extends into cross-over assembly  302  such that return fluid passing through screen assembly  304 , indicated by arrows  308 , may travel through wash pipe  306 , as indicated by arrow  310 , and into annulus  52 , as indicted by arrow  312 , for return to the surface.  
         [0064]     The fluid slurry containing gravel is pumped down work string  30  into cross-over assembly  302  along the path indicated by arrows  314 . The fluid slurry containing gravel exits cross-over assembly  302  through cross-over ports  316  and is discharged into apparatus  300  as indicated by arrows  318 . In the illustrated embodiment, the fluid slurry containing gravel then travels between channels  320  and sheet member  322  as indicated by arrows  324 . At this point, portions of the fluid slurry containing gravel exit apparatus  300  through outlets  326  of channels  320  and outlets  328  of outer tubular  330 , as indicated by arrows  332 . As the fluid slurry containing gravel enters annular interval  48 , the gravel drops out of the slurry and builds up from formation  14 , filling perforations  50  and annular interval  48  around apparatus  300  forming the gravel pack. Some of the carrier fluid in the slurry may leak off through perforations  50  into formation  14  while the remainder of the carrier fluid passes through screen assembly  304 , as indicated by arrows  308 , that is sized to prevent gravel from flowing therethrough. The fluid flowing back through screen assembly  304 , as explained above, follows the paths indicated by arrows  310 ,  312  back to the surface.  
         [0065]     In operation, the apparatus for gravel packing an interval of a wellbore of the present invention is used to distribute the fluid slurry to various locations within the interval to be gravel packed by injecting the fluid slurry into the slurry passageways created by the channels and the sheet members of one or more joints of the apparatus. The fluid slurry exits through the various outlets along the slurry passageway and enters the annulus between the apparatus and the wellbore which may be cased or uncased. Once in this annulus, a portion of the gravel in the fluid slurry is deposited around the apparatus in the annulus such that the gravel migrates both circumferentially and axially from the outlets. This process progresses along the entire length of the apparatus such that the annular area becomes completely packed with the gravel. In addition, a portion of the fluid slurry enters the opening of the outer tubular which provides for the deposit of a portion of the gravel from the fluid slurry in the production pathways between the outer tubulars and the sand control screens. Again, this process progresses along the entire length of the apparatus such that each production pathway becomes completely packed with the gravel. Once both the annulus and the production pathways are completely packed with gravel, the gravel pack operation may cease.  
         [0066]     In some embodiments of the present invention, the fluid slurry may not initially be injected into the slurry passageways. Instead, the fluid slurry is injected directly into the annulus between the apparatus  340  and the wellbore, as best seen in  FIG. 15 . In the illustrated embodiment, the primary path for the fluid slurry containing gravel as it is discharged from exit ports  316 , is directly into annular interval  48  as indicated by arrows  334 . This is the primary path as the fluid slurry seeks the path of least resistance. Under ideal conditions, the fluid slurry travels throughout the entire interval  48  until interval  48  is completely packed with gravel. In addition, the fluid slurry enters the production pathways of apparatus  340  such that this area is also completely packed with gravel.  
         [0067]     It has been found, however, that sand bridges commonly form during the gravel packing of an interval when the fluid slurry is pumped directly into annular interval  48 . These sand bridges are bypassed using the apparatus for gravel packing an interval of a wellbore of the present invention by first allowing the fluid slurry to pass through the outer tubular into the production pathways of apparatus  340 , bypassing the sand bridge and then returning to annular interval  48  through the outer tubular to complete the gravel packing process. These pathways are considered the secondary path for the fluid slurry. If a sand bridge forms in the secondary paths prior to completing the gravel packing operation, then the fluid slurry enters channels  320  as indicated by arrows  318  and as described above with reference to  FIG. 14 . In this embodiment, channels  320  are considered the tertiary path for the fluid slurry.  
         [0068]     In either embodiment, once the gravel pack is completed and the well is brought on line, formation fluids that are produced into the gravel packed interval must travel through the gravel pack in the annulus, then enter the production pathways through the openings in the outer tubular where the formation fluids pass through the gravel pack between the outer tubular and the screen assembly. As such, the apparatus for gravel packing an interval of a wellbore of the present invention allows for a complete gravel pack of an interval so that particulate materials in the formation fluid are filtered out.  
         [0069]     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:
An apparatus ( 110 ) and method for treating an interval of a wellbore comprises an outer tubular ( 112 ) disposed within the wellbore. A sand control screen ( 118 ) is disposed within the outer tubular ( 112 ). A treatment fluid passageway ( 144 ) is formed between the sand control screen ( 118 ) and outer tubular ( 112 ). In addition, a production pathway ( 130 ) is formed between the sand control screen ( 118 ) and outer tubular ( 112 ). When the apparatus ( 110 ) is in an operable position, the region between the outer tubular ( 112 ) and the wellbore serves as a primary path for delivery of a treatment fluid, the production pathway ( 130 ) serves as a secondary path for delivery of the treatment fluid if the primary path becomes blocked and the treatment fluid passageway ( 144 ) serves as a tertiary path for delivery of the treatment fluid if the primary and secondary paths become blocked.