Abstract:
An apparatus and method for gravel packing an interval of a wellbore is disclosed. The apparatus comprises an outer tubular ( 110 ) forming a first annulus with the wellbore and an inner tubular ( 114 ) disposed within the outer tubular ( 110 ) forming a second annulus therebetween. The second annulus includes an axially extending slurry passageway ( 194 ) and an axially extending production pathway ( 190 ). The portion of the outer tubular ( 110 ) adjacent the slurry passageway ( 194 ) has an outlet ( 128 ). The portion of both the outer and inner tubulars ( 110, 114 ) adjacent the production pathway ( 190 ) has a plurality of openings ( 122, 146 ). The slurry passageway ( 194 ) is in fluid isolation from the production pathway ( 190 ) such that when a fluid slurry containing gravel is injected through the slurry passageway ( 194 ), the fluid slurry exits through the outlet ( 128 ) leaving gravel in the first annulus, thereby gravel packing the interval.

Description:
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 particulates. For example, the particulates cause abrasive wear to components within the well, such as tubing, pumps and valves. In addition, the particulates 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 workstring 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 workstring 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 particulates 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. 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. 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 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. 
     The volume within the second annulus between the nonproduction sections of the outer and inner tubulars is an axially extending slurry passageway. The volume within the second-annulus between the production sections of the outer and inner tubulars is an axially extending production pathway. An isolation member, which is disposed within the second annulus, defines the circumferential boundaries of the production pathway and the slurry passageway and prevents fluid communication between the production pathway and the slurry passageway. The isolation member also defines 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 the outlet 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 and the second portion of the gravel in the production pathway which filters out any 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. 
     More specifically, the isolation member disposed within the second annulus may have a pair of substantially parallel, circumferentially spaced apart, axially extending members that radially extend between the outer and inner tubulars and a pair of substantially parallel, axially spaced apart, circumferentially extending members that radially extend between the outer and inner tubulars that define the production pathway and the slurry passageway and prevent fluid communication therebetween. 
     In one embodiment of the present invention, an actuatable device may be disposed within each of the outlets to selectively allow and prevent the fluid slurry from flowing therethrough. The actuatable devices may, for example, be pressure actuated devices, electrically actuated devices, acoustically actuated devices or the like. Suitable actuatable devices may include rupture disks or valves, such as one way valves. 
     Alternatively, the outlets may each have an exit tube disposed therein. The exit tubes may, for example, be positioned partially within the second annulus, partially within the first annulus or both. As yet another alternative, an insert member may be disposed at least partially within each of the outlets to prevent erosion of the outlets. 
     In embodiments of the present invention that have more than one outlet, the outlets may have various sizes and shapes. In addition, certain embodiments of the present invention may include multiple production pathways and multiple slurry passageways. In such embodiments, the outlets of the various slurry passageways may be at different axial positions along the outer tubular. 
     Commonly, more than one such 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 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 injecting 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. 
    
    
     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 a circumferential section of 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 a circumferential section of four isolation members; 
     FIG. 13 is a side view of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore of the present invention that has actuatable devices in the outlets of the slurry passageway; 
     FIGS. 14A-14B are side and cross sectional views, respectively, of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore of the present invention including exit tubes in the outlets of the slurry passageway; 
     FIGS. 15A-15B are side and cross sectional views, respectively, of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore of the present invention including insert members in the outlets of the slurry passageway; 
     FIG. 16 is a side view of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore of the present invention having outlets of different sizes; and 
     FIG. 17 is a side view of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore of the present invention that has outlets at different axial positions along the outer tubular for different slurry passageways. 
    
    
     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 sting  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  include 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 workstring  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 workstring  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 workstring  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 , 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 workstring  30  to the exterior of workstring  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  48  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 workstring  30  and up to the surface. If the fluid slurry is partially injected directly into annular region  48  and a sand bridge forms, the portion of the fluid slurry that is injected into apparatuses  38 ,  40 ,  42  will bypass this sand bridge such that a complete pack can nonetheless be achieved. The portion of the fluid slurry entering apparatuses  38 ,  40 ,  42  may enter apparatuses  38 ,  40 ,  42  directly from workstring  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 outlet  70  as being circular, other shaped openings may alternatively be used without departing form the principles of the present invention. Likewise, even though FIG. 2 has depicted openings  66  as being the same size as outlet  70 , openings  66  could alternatively be larger or smaller than outlet  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  74  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 an isolation member  82 . As further explained below, isolation member  82  includes a pair of substantially parallel, circumferentially spaced apart, axially extending members  84 ,  86  that radially extend between outer tubular  62  and inner tubular  72 . In fact, members  84 ,  86  provide circumferential fluid isolation between production section  64  and nonproduction section  68  of outer tubular  62 . In addition, members  84 ,  86  provide circumferential fluid isolation between production section  74  and nonproduction section  78  of inner tubular  72 . As such, members  84 ,  86  define the circumferential boundary between a slurry passageway  88 , having radial boundaries defined by nonproduction section  68  of outer tubular  62  and nonproduction section  78  of inner tubular  72 , and a production pathway  90 , having radial boundaries defined by production section  64  of outer tubular  62  and production section  74  of inner tubular  72 . 
     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 dependent 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 technique. It should be understood by those skilled in the art that while ribs  98  and the sand control screen jacket are depicted in FIG. 2, a wire mesh may alternatively be used in place of either or both to form the barrier to sand production or screen wire  100  may be wrapped directly around base pipe  94 . 
     Referring now to FIGS. 3 and 4, therein is 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 apparatuses 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 apparatuses 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 again to FIG. 4, inner tubular  114  has a pair of isolation members  170 ,  172  attached thereto and inner tubular  116  has a pair of isolation members  174 ,  176  attached thereto, only one of which is visible in FIG.  4 . Isolation member  170  has a pair of circumferentially spaced apart substantially axial members  178 ,  180 , as best seen in FIG. 5 and a pair of axially spaced apart substantially circumferential members, only member  182  being shown in FIGS. 4 and 7. Isolation member  172  has a pair of circumferentially spaced apart substantially axial members  184 ,  166 , as best seen in FIG. 5 and a pair of axially spaced apart substantially circumferential members, only member  188  being shown in FIGS. 4 and 7. Together, members  170 ,  172  define the circumferential boundaries of production pathways  190 ,  192  and slurry passageways  194 ,  196  between outer tubular  110  and inner tubular  114 . Also, members  170 ,  172  provide fluid isolation between production pathways  190 ,  192  and slurry passageways  194 ,  196 . Further, members  170  and  172  provide complete fluid isolation for production pathways  190 ,  192 . 
     Isolation member  174  has a pair of circumferentially spaced apart substantially axial members  200 ,  202 , as best seen in FIG. 6 and a pair of axially spaced apart substantially circumferential members, only member  204  being shown in FIGS. 4 and 8. Isolation member  176  has a pair of circumferentially spaced apart substantially axial members  206 ,  208 , as best seen in FIG. 6 and a pair of axially spaced apart substantially circumferential members, only member  210  being shown in FIG.  8 . Together, members  174 ,  176  define the circumferential boundaries of production pathways  212 ,  214  and slurry passageways  216 ,  218  between outer tubular  112  and inner tubular  116 . Also, members  174 ,  176  provide fluid isolation between production pathways  212 ,  214  and slurry passageways  216 ,  218 . Further, members  174 ,  176  provide complete fluid isolation for production pathways  216 ,  218 . Importantly, however, slurry passageways  194 ,  196  and slurry passageways  212 ,  214  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 apparatuses 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  220  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  220  into slurry passageways  216 ,  218 . 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 apparatuses 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 is 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 an outlet  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 . An isolation member  254  is disposed between outer tubular  236  and inner tubular  246 . Isolation member  254  has a pair of circumferentially spaced apart substantially axial members  256 ,  258  and a pair of axially spaced apart substantially circumferential members, only member  260  being shown in FIG.  10 . Isolation member  254  defines the circumferential boundaries of production pathway  234  and slurry passageway  232  between outer tubular  236  and inner tubular  246 . Also, isolation member  254  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 is 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 pathway  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 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 isolation members  320 ,  322 ,  324 ,  326  are disposed between outer tubular  278  and inner tubular  300 . 
     Isolation member  320  has a pair of circumferentially spaced apart substantially axial members  328 ,  330  and a pair of axially spaced apart substantially circumferential members, only member  332  being shown in FIG.  12 . Isolation member  322  has a pair of circumferentially spaced apart substantially axial members  334 ,  336  and a pair of axially spaced apart substantially circumferential members, only member  338  being shown in FIG.  12 . Isolation member  324  has a pair of circumferentially spaced apart substantially axial members  340 ,  342  and a pair of axially spaced apart substantially circumferential members, only member  344  being shown in FIG.  12 . Isolation member  326  has a pair of circumferentially spaced apart substantially axial members  346 ,  348  and a pair of axially spaced apart substantially circumferential members, only member  350  being shown in FIG.  12 . Isolation members  320 ,  322 ,  324 ,  326  define the circumferential boundaries of production pathways  270 ,  272 ,  274 ,  276  and slurry passageways  262 ,  264 ,  266 ,  268  between outer tubular  278  and inner tubular  300 . Also, isolation members  320 ,  322 ,  324 ,  326  provides 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 configuration 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 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 bottom or toe of the interval. This may be achieved by using apparatuses of the present invention having more slurry passageways near the top or heel of the interval and less slurry passageways near the bottom or toe of the interval. This may also be achieved by using apparatuses of the present invention having wider slurry passageways near the top or heel of the interval and narrower slurry passageways near the bottom or toe of the interval. 
     Also, while the illustrated embodiments have depicted the isolation members of the apparatus of the present invention as having a pair of circumferentially spaced apart substantially parallel axial members, it should be understood by those skilled in the art that other configurations of the isolation members are possible and are considered within the scope of the present invention. For example, the isolation members may have a pair of circumferentially spaced apart substantially axial members that are not parallel to one another wherein the substantially axial members are circumferentially closer together at one end of the inner tubular than at the other end. Likewise, the isolation member may have a pair of circumferentially spaced apart members that are not substantially axial members but instead extend across the length of the inner tubular in an inclined or helical configuration. 
     Referring now to FIG. 13 therein is depicted a side view of a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore that is generally designated  360 . Outer tubular  360  includes a plurality of openings  362  in its production section  364  and outlets  366  in its nonproduction section  368 . Disposed within each outlet  368  is an actuatable device  370 . Actuatable devices  370  are used to selectively allow and prevent the flow of the fluid slurry through a particular outlet  366  such that the gravel packing process may be precisely controlled. For example, actuatable devices  370  could be opened and closed in a particular sequence to further improve the gravel packing process, such as from top to bottom or bottom to top in a substantially vertical wellbore or from heel to toe or toe to heel in a substantially horizontal wellbore. In fact, actuatable devices  370  could be sequenced from heel to toe then from toe to heel in a substantially horizontal wellbore to even further enhance the gravel packing process. Actuatable devices  370  may be operated by a variety of known techniques including pressure actuation, electrical actuation, acoustic actuation or the like. Examples of suitable actuatable devices  370  include rupture disks, valves, such as one way valves and the like. 
     Referring now to FIGS. 14A and 14B therein are depicted a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore that is generally designated  380 . Outer tubular  380  includes a plurality of openings  382  in its production section  384  and outlets  386  in its nonproduction section  388 . Disposed within each outlet  386  is an exit tube  390 . Exit tubes  390  are used to increase the pressure drop of the fluid slurry as the fluid slurry exits a slurry passageway which improves the gravel packing process. In the illustrated embodiment, a portion of each exit tube  390  is disposed within outer tubular  380  and another portion of each exit tube  390  is disposed exteriorly of outer tubular  380 . It should be understood by those skilled in that art, however, the other configurations of exit tubes  390  are possible and are considered within the scope of the present invention. 
     Referring now to FIGS. 15A and 15B therein are depicted a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore that is generally designated  400 . Outer tubular  400  includes a plurality of openings  402  in its production section  404  and outlets  406  in its nonproduction section  408 . Partially disposed within each outlet  406  is an insert member  410  which is also partially disposed in a plate member  412 . Insert members  410  are used to prevent the erosion of outlets  406  which may occur due to the pressure and velocity at which the fluid slurry travels therethrough. Insert members  410  may be made from any suitably nonerosive material such as tungsten carbide. Even though the illustrated embodiment depicts insert members  410  as having a circular cross section, it should be understood by those skilled in that art that insert members having alternate shaped cross sections, such as square or triangular, are also suitable. 
     Referring now to FIG. 16 therein is depicted a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore that is generally designated  420 . Outer tubular  420  includes a plurality of openings  422  in its production section  424  and outlets  426 ,  428 ,  430  in its nonproduction section  432 . As illustrated, outlet  426  is smaller than outlet  428 . In addition, outlet  426  and outlet  428  are smaller than outlet  430 . Having various sized outlets along the length of one or more sections of an apparatus for gravel packing an interval of a wellbore of the present invention can improve the gravel packing process due to the expected pressure drop in the fluid slurry as the fluid slurry travels down through the various slurry passageways of the various sections. 
     Referring now to FIG. 17 therein is depicted a portion of an outer tubular of an apparatus for gravel packing an interval of a wellbore that is generally designated  440 . Outer tubular  440  includes a plurality of openings  442  in the illustrated production section  444  and a pair of outlets  446 ,  448  in the oppositely positioned nonproduction sections  450 ,  452 . As illustrated, outlet  446  is at a different axial position along outer tubular  440  than outlet  448 . Having the position of outlets  446 ,  448  at different axial locations along the length outer tubular  440  can improve the gravel packing process by injecting the fluid slurry in different direction at different axial position. 
     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 of one or more sections of the apparatuses. A portion of 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 outlet. 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 each production pathway of the various sections of the apparatus. 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 only be injected into the slurry passageways, but also injected directly into the annulus to increase the speed at which an interval of the wellbore may be gravel packed. In either embodiment, once the gravel pack is finish 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 in the production pathway prior to exiting the production pathway through the openings in the inner tubular. Notably, the formation fluids are prevented from traveling radially through the slurry passageway as there are no openings in the nonproduction sections of the inner tubular. 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.