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CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This application is a continuation application of Ser. No. 09/927,217 filed Aug. 10, 2001 entitled Apparatus and Method for Gravel Packing an Interval of a Wellbore, 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 entitled Apparatus and Method for Gravel Packing an Interval of a Wellbore, now U.S. Pat. No. 6,557,634. 

   TECHNICAL FIELD OF THE INVENTION 
   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 
   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. 
   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. 
   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. 
   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. 
   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. 
   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. 
   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 
   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. 
   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 an inner tubular disposed within the outer tubular forming a second annulus therebetween. Typically, the inner tubular is positioned around a sand control screen. Together, the sand control screen and the apparatus of the present invention are assembled at the surface and run downhole to a location proximate the production interval. A portion of the side wall of the outer tubular is an axially extending production section that includes a plurality of openings. Another portion of the side wall of the outer tubular is an axially extending nonproduction section that includes one or more outlets. Similarly, a portion of the side wall of the inner tubular is an axially extending production section that is substantially circumferentially aligned with the production section of the outer tubular. Another portion of the side wall of the inner tubular is an axially extending nonproduction section that is substantially radially aligned with the nonproduction section of the outer tubular. The production section of the inner tubular has a plurality of openings therethrough, but the nonproduction section of the inner tubular has no openings therethrough. 
   In the volume within the second annulus between the nonproduction sections of the outer and inner tubulars there is a channel that defines an axially extending slurry passageway with the nonproduction section of the inner tubular. The volume within the second annulus between the production sections of the outer and inner tubulars is an axially extending production pathway. The channel prevents fluid communication between the production pathway and the slurry passageway. In addition, isolation members at either end of a section of the apparatus of the present invention define the axial boundaries of the production pathway. 
   As such, when a fluid slurry containing gravel is injected through the slurry passageway, the fluid slurry exits the slurry passageway through outlets in the channel 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 pathway. Thus, when formation fluids are produced, the formation fluids travel radially through the production pathway by entering the production pathway through the openings in the outer tubular and exiting the production pathway through the openings in the inner tubular. The formation fluids pass through the first portion of the gravel in the first annulus prior to entry into the production pathway, 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 passageway as there are no openings in the nonproduction section of the inner tubular. 
   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 pathway of the present invention serves as a secondary path for delivery of the fluid slurry. The production pathway serves as the secondary path as it provides the path of second least resistance to the flow of the fluid slurry. When the primary and secondary paths become blocked by sand bridge formation, the slurry passageway serves as a tertiary path for delivery of the fluid slurry. The slurry passageway serves as the tertiary path as it provides the path of greatest resistance to the flow of the fluid slurry but is least likely to have sand bridge formation therein due to the high velocity of the fluid slurry flowing therethrough. 
   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. 
   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 sand control screen within the wellbore proximate the formation, positioning the gravel packing apparatus around the sand control screen to form a first annulus between the gravel packing apparatus and the wellbore, injecting a fluid slurry containing gravel through the slurry passageway 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 pathway 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 pathway are substantially completely packed with gravel. 
   In addition to injecting the fluid slurry containing gravel through the slurry passageway, 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 pathway if the primary path becomes blocked, diverting the fluid slurry containing gravel into a tertiary path defined by the slurry passageway 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 
     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: 
       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; 
       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; 
       FIG. 3  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; 
       FIG. 4  is a side view of portions of two inner tubulars of an apparatus for gravel packing an interval of a wellbore of the present invention that are coupled together; 
       FIG. 5  is a cross sectional view of an apparatus for gravel packing an interval of a wellbore of the present invention taken along line  5 — 5  of  FIGS. 3 and 4 ; 
       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. 3 and 4 ; 
       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. 3 and 4 ; 
       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. 3 and 4 ; 
       FIG. 9  is a cross sectional view of an alternate embodiment of an apparatus for gravel packing an interval of a wellbore of the present invention depicting one slurry passageway and one production pathway; 
       FIG. 10  is a cross sectional view of an alternate embodiment of an apparatus for gravel packing an interval of a wellbore of the present invention depicting one slurry passageway and an isolation member; 
       FIG. 11  is a cross sectional view of an alternate embodiment of an apparatus for gravel packing an interval of a wellbore of the present invention depicting four slurry passageways and four production pathways; 
       FIG. 12  is a cross sectional view of an alternate embodiment of an apparatus for gravel packing an interval of a wellbore of the present invention depicting four slurry passageways and an isolation member; 
       FIG. 13  is a half sectional view depicting the operation of an apparatus for gravel packing an interval of a wellbore of the present invention; and 
       FIG. 14  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 
   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. 
   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 . 
   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 gravel is pumped down work string  30 . 
   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 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. 
   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 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. 
   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. 
   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 . A portion of the side wall of outer tubular  62  is an axially extending production section  64  that includes a plurality of openings  66 . Another portion of the side wall of outer tubular  62  is an axially extending nonproduction section  68  that includes one or more outlets  70 . For reasons that will become apparent to those skilled in the art, the density of opening  66  within production section  64  of outer tubular  62  is much greater than the density of outlets  70  in nonproduction section  68  of outer tubular  62 . Also, it should be noted by those skilled in the art that even though  FIG. 2  has depicted openings  66  and outlets  70  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  66  as being the same size as outlets  70 , openings  66  could alternatively be larger or smaller than outlets  70  without departing from the principles of the present invention. In addition, the exact number, size and shape of openings  66  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. 
   Disposed within outer tubular  62  is an inner tubular  72 . A portion of the side wall of inner tubular  72  is an axially extending production section  74  that is substantially circumferentially aligned with production section  64  of outer tubular  62 . Production section  74  of inner tubular  72  has a plurality of opening  76  therethrough. Again, the exact number, size and shape of openings  76  are not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of inner tubular  72  is maintained. Another portion of the side wall of inner tubular  72  is an axially extending nonproduction section  78  that is substantially circumferentially aligned with nonproduction section  68  of outer tubular  62 . Nonproduction section  78  of inner tubular  72  has no openings therethrough. 
   Disposed within an annulus  80  between outer tubular  62  and inner tubular  72  is a channel  82 . Channel  82  includes a web  84  and a pair of oppositely disposed sides  86  having ends that are attached to inner tubular  72  by, for example, welding or other suitable techniques. Channel  82  includes one or more outlets (not pictured) that are substantially aligned with outlets  70  of outer housing  64 . Together, channel  82  and nonproduction section  78  of inner tubular  72  define a slurry passageway  88 . A production pathway  90  is also defined having radial boundaries of production section  64  of outer tubular  62  and production section  74  of inner tubular  72 . Slurry passageway  88  and production pathway  90  are in fluid isolation from one another. 
   Disposed within inner tubular  72  is a sand control screen  92 . Sand control screen  92  includes a base pipe  94  that has a plurality of openings  96  which allow the flow of production fluids into the production tubing. The exact number, size and shape of openings  96  are not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of base pipe  94  is maintained. 
   Spaced around base pipe  94  is a plurality of ribs  98 . Ribs  98  are generally symmetrically distributed about the axis of base pipe  94 . Ribs  98  are depicted as having a cylindrical cross section, however, it should be understood by one skilled in the art that ribs  98  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  98  will be dependant upon the diameter of base pipe  94  as well as other design characteristics that are well known in the art. 
   Wrapped around ribs  98  is a screen wire  100 . Screen wire  100  forms a plurality of turns, such as turn  102 , turn  104  and turn  106 . 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  98  and screen wire  100  may form a sand control screen jacket which is attached to base pipe  94  by welding or other suitable techniques. 
   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. 
   Referring now to  FIGS. 3 and 4 , therein are depicted portions of two sections of outer tubulars designated  110  and  112  and corresponding portions of two sections of inner tubulars designated  114  and  116 , respectively. Outer tubular  110  has two axially extending production sections  118 ,  120  each including a plurality of openings  122 . Outer tubular  110  also has two axially extending nonproduction sections  124 ,  126 , only one of which is visible in FIG.  3 . Each nonproduction section  124 ,  126  includes several outlets  128 . Likewise, outer tubular  112  has two axially extending production sections  130 ,  132 , only one of which is visible in FIG.  3 . Each production section  130 ,  132  includes a plurality of openings  134 . Outer tubular  112  also has two axially extending nonproduction sections  136 ,  138 , each of which includes several outlets  140 . 
   As should become apparent to those skilled in the art, even though  FIG. 3  depicts outer tubular  110  and outer tubular  112  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 sections 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 sections 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. 
   Inner tubular  114  has two axially extending production sections  142 ,  144  each including a plurality of openings  146 . Inner tubular  114  also has two axially extending nonproduction sections  148 ,  150 , only one of which is visible in FIG.  4 . There are no openings in nonproduction sections  148 ,  150 . Likewise, inner tubular  116  has two axially extending production sections  152 ,  154 , only one of which is visible in FIG.  4 . Each production section  152 ,  154  includes a plurality of openings  156 . Inner tubular  116  also has two axially extending nonproduction sections  158 ,  160 , neither of which include any openings. 
   In the illustrated embodiment, inner tubulars  114 ,  116  would be positioned within outer tubulars  110 ,  112  such that production sections  118 ,  120  of outer tubular  110  are circumferentially aligned with production sections  142 ,  144  of inner tubular  114 , as best seen in  FIG. 5 ; such that nonproduction sections  124 ,  126  of outer tubular  110  are circumferentially aligned with nonproduction sections  148 ,  150  of inner tubular  114 , also as best seen in  FIG. 5 ; such that production sections  130 ,  132  of outer tubular  112  are circumferentially aligned with production sections  152 ,  154  of inner tubular  116 , as best seen in  FIG. 6 ; and such that nonproduction sections  136 ,  138  of outer tubular  112  are circumferentially aligned with nonproduction sections  158 ,  160  of inner tubular  116 , also as best seen in FIG.  6 . 
   Referring to  FIGS. 4 ,  5  and  6 , inner tubular  114  has a pair of channels  170 ,  172  attached thereto, only one of which is visible in FIG.  4 . Likewise, inner tubular  116  has a pair of channels  174 ,  176  attached thereto. Channels  170 ,  172  includes a plurality of outlets  178  that substantially align with outlets  128  of outer tubular  110 . Channels  170 ,  172  also include insert members  180  that provide a seal between outlets  128  and outlets  178 . Likewise, channels  174 ,  176  have plurality of outlets  182  that are substantially aligned with outlets  140  of outer housing  112 . Positioned between channels  174 ,  176  and outer housing  112  is a plurality of insert members  184  that provide a seal between outlets  182  and outlets  140 . 
   Each section 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 inner tubular  114  in  FIGS. 4 and 7 . Likewise, isolation members  188  are shown on inner tubular  116  in  FIGS. 4 and 8 . 
   Channels  170 ,  172  define the circumferential boundaries of production pathways  190 ,  192  and, together with nonproduction sections  148 ,  150 , channels  170 ,  172  define slurry passageways  194 ,  196 . Isolation members  186  help provide fluid isolation between production pathways  190 ,  192  and slurry passageways  194 ,  196 . Further, isolation members  186  provide complete fluid isolation for production pathways  190 ,  192 . 
   Channels  174 ,  176  define the circumferential boundaries of production pathways  198 ,  200  and, together with nonproduction sections  158 ,  160 , channels  174 ,  176  define slurry passageways  202 ,  204 . Isolation members  188  help provide fluid isolation between production pathways  198 ,  200  and slurry passageways  202 ,  204 . Further, isolation members  188  provide complete fluid isolation for production pathways  198 ,  200 . 
   Importantly, however, slurry passageways  194 ,  196  and slurry passageways  202 ,  204  are all in fluid communication with one another such that a fluid slurry may travel in and between these passageways from one section of the apparatus for gravel packing an interval of a wellbore of the present invention to the next. Specifically, as best seen in  FIGS. 3 ,  4 ,  7  and  8  collectively, an annular region  206  exists between outer tubulars  110 ,  112  and inner tubulars  114 ,  116  that allows the fluid slurry to travel downwardly from slurry passageways  194 ,  196  through annular regions  206  into slurry passageways  202 ,  204 . As such, regardless of the circumferential orientation of inner tubular  114  relative to inner tubular  116 , the fluid slurry will travel down through each section of the apparatus for gravel packing an interval of a wellbore of the present invention. 
   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. 
   Referring now to  FIGS. 9 and 10 , therein are depicted cross sectional views of an alternate embodiment of an apparatus for gravel packing an interval of a wellbore that is generally designated  230 . Apparatus  230  is similar to that shown in  FIGS. 5 and 7  except apparatus  230  has a single slurry passageway  232  and a single production pathway  234 . Specifically, apparatus  230  has an outer tubular  236  including a plurality of openings  238  in its production section  240  and a plurality of outlets  242  in its nonproduction section  244 . Apparatus  230  also has an inner tubular  246  including a plurality of openings  248  in its production section  250  and no openings in its nonproduction section  252 . A channel  254  is disposed between outer tubular  236  and inner tubular  246 . Channel  254  is substantially aligned with nonproduction section  252  of inner tubular  246  and is preferably attached to inner tubular  246  by welding. Channel  254  has a plurality of outlets  256  that are substantially aligned with outlets  242  of outer tubular  236 . An insert member  257  is disposed between outlets  256  and outlets  242  to provide a seal therebetween. An isolation member  258  provides fluid isolation between production pathway  234  and slurry passageway  232  and complete fluid isolation for production pathway  234 . 
   Referring now to  FIGS. 11 and 12 , therein are depicted cross sectional views of another embodiment of an apparatus for gravel packing an interval of a wellbore that is generally designated  260 . Apparatus  260  is similar to that shown in  FIGS. 5 and 7  except apparatus  260  has four slurry passageways  262 ,  264 ,  266 ,  268  and four production pathways  270 ,  272 ,  274 ,  276 . Specifically, apparatus  260  has an outer tubular  278  including a plurality of openings  280  in its four production sections  282 ,  284 ,  286 ,  288  and a plurality of outlets  290  in its nonproduction sections  292 ,  294 ,  296 ,  298 . Apparatus  260  also has an inner tubular  300  including a plurality of openings  302  in its production sections  304 ,  306 ,  308 ,  310  and no openings in its nonproduction sections  312 ,  314 ,  316 ,  318 . Four channels  320 ,  322 ,  324 ,  326  are disposed between outer tubular  278  and inner tubular  300  which are substantially aligned with nonproduction sections  312 ,  314 ,  316 ,  318  of inner tubular  300  and are preferably welded thereto. Each channel  320 ,  322 ,  324 ,  326  has a plurality of outlets  328  that substantially align with outlets  290  of outer tubular  300 . An insert member  330  is positioned between outlets  328  and outlets  290  to provide sealing. Isolation members  332  provide fluid isolation between production pathways  270 ,  272 ,  274 ,  276  and slurry passageways  262 ,  264 ,  266 ,  268  and complete fluid isolation for each of the production pathways  270 ,  272 ,  274   276 . 
   As should be apparent from  FIGS. 3-12 , the apparatus for gravel packing an interval of a wellbore of the present invention may have a variety of configurations including configurations having one, two and four slurry passageways. Other configuration having other numbers of slurry passageways are also possible and are considered within the scope of the present invention. 
   In addition, it should be understood by those skilled in the art that use of various configurations of the apparatus for gravel packing an interval of a wellbore of the present invention in the same interval is likely and may be preferred. Specifically, it may be desirable to have a volumetric capacity within the slurry passageways that is greater toward the near end, top, in a vertical well, or heel, in an inclined or horizontal well, of a string of consecutive apparatuses of the present invention than toward the far end, the bottom or toe of the interval. This may be achieved by using apparatuses of the present invention having more slurry passageways proximate the near end of the interval and less slurry passageways proximate the far end of the interval. This may also be achieved by using apparatuses of the present invention having wider slurry passageways proximate the near end of the interval and narrower slurry passageways proximate the far end of the interval. 
   Referring now to  FIG. 13 , a typical completion process using an apparatus  348  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  350  is located adjacent to screen assembly  352 , traversing packer  44  with portions of cross-over assembly  350  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  354  is disposed within screen assembly  352 . Wash pipe  354  extends into cross-over assembly  350  such that return fluid passing through screen assembly  352 , indicated by arrows  356 , may travel through wash pipe  354 , as indicated by arrow  358 , and into annulus  52 , as indicted by arrow  360 , for return to the surface. 
   The fluid slurry containing gravel is pumped down work string  30  into cross-over assembly  350  along the path indicated by arrows  362 . The fluid slurry containing gravel exits cross-over assembly  350  through cross-over ports  364  and is discharged into apparatus  348  as indicated by arrows  366 . In the illustrated embodiment, the fluid slurry containing gravel then travels between channels  368  and the nonproduction sections of the inner tubular  370  as indicated by arrows  371 . At this point, portions of the fluid slurry containing gravel exit apparatus  348  through outlets  372  of channels  368 , outlets  374  of inserts  376  and outlets  378  of outer tubular  380 , as indicated by arrows  382 . 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 screen assembly  352  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  352 , as indicated by arrows  356 , that is sized to prevent gravel from flowing therethrough. The fluid flowing back through screen assembly  352 , as explained above, follows the paths indicated by arrows  358 ,  360  back to the surface. 
   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 inner tubular of one or more sections 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 in the production sections 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 tubular and the inner tubular. 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. 
   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 and the wellbore, as best seen in FIG.  14 . In the illustrated embodiment, the primary path for the fluid slurry containing gravel as it is discharged from exit ports  364 , is directly into annular interval  48  as indicated by arrows  384 . 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  348  such that this area is also completely packed with gravel. 
   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  348 , 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  368  as indicated by arrows  366  and as described above with reference to FIG.  13 . In this embodiment, channels  368  are considered the tertiary path for the fluid slurry. 
   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. 
   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 ( 60 ) and method for treating an interval of a wellbore comprises an outer tubular ( 62 ) disposed within the wellbore. A sand control screen ( 92 ) is disposed within the outer tubular ( 62 ). A slurry passageway ( 88 ) is formed between the sand control screen ( 92 ) and outer tubular ( 62 ). In addition, a production pathway ( 90 ) is formed between the sand control screen ( 92 ) and outer tubular ( 62 ). When the apparatus ( 60 ) is in an operable position, the region between the outer tubular ( 62 ) and the wellbore serves as a primary path for delivery of a fluid slurry, the production pathway ( 90 ) serves as a secondary path for delivery of the fluid slurry if the primary path becomes blocked and the slurry passageway ( 88 ) serves as a tertiary path for delivery of the fluid slurry if the primary and secondary paths become blocked.