Abstract:
The apparatus includes a gravel pack assembly comprising a gravel pack body and a crossover tool. The gravel pack body comprises a pressure set packer, one or more production screens and a plurality of axial position indexing lugs. The crossover tool comprises auxiliary flow chambers, packer by-pass channels, a crossover tool check valve and an axial position indexing collet. The gravel pack body and crossover tool are assembled coaxially as a cooperative unit by a threaded joint and the unit is threadably attached to the bottom end of a tool string for selective placement within the wellbore. Set of the packer secures the gravel pack body to the well casing and seals the casing annulus around the gravel pack assembly. A positive fluid pressure is maintained on the wellbore wall in the production zone throughout the gravel packing procedure and in particular, during the packer seal test interval when fluid pressure that is egual to or greater than the normal hydrostatic pressure is maintained on the production zone wall under the gravel pack body packer while greater test pressure above the hydrostatic is imposed in the wellbore annulus above the packer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the priority benefits of the following: U.S. Pat. No.  6 , 230 , 801  filed Jul. 22, 1999 and issued May 15, 2001; copending U.S. Utility patent application Ser. No. 09/550,439 filed Apr. 17, 2000; and U.S. Provisional Application Serial No. 60/093,714 filed Jul. 22, 1998. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention generally relates to a method of hydrocarbon well completion and the associated apparatus for practicing the method. More particularly, the invention provides an open hole gravel packing system wherein a positive hydrostatic pressure differential within the well borehole is maintained against the production formation walls throughout all phases of the gravel packing procedure.  
           [0003]    2. Description of the Prior Art  
           [0004]    To extract hydrocarbons such as natural gas and crude oil from the earth&#39;s subsurface formations, boreholes are drilled into hydrocarbon bearing production zones. To maintain the productivity of a borehole and control the flow of hydrocarbon fluids from the borehole, numerous prior art devices and systems have been employed to prevent the natural forces from collapsing the borehole and obstructing or terminating fluid flow therefrom. One such prior art system provides a full depth casement of the wellbore whereby the wellbore wall is lined with a steel casing pipe that is secured to the bore wall by an annulus of concrete between the outside surface of the casing pipe and the wellbore wall. The steel casing pipe and surrounding concrete annulus is thereafter perforated by ballistic or pyrotechnic devices along the production zone to allow the desired hydrocarbon fluids to flow from the producing formation into the casing pipe interior. Usually, the casing interior is sealed above and below the producing zone whereby a smaller diameter production pipe penetrates the upper seal to provide the hydrocarbon fluids a smooth and clean flowing conduit to the surface.  
           [0005]    Another prior art well completion system protects the well borewall production integrity by a tightly packed deposit of aggregate comprising sand, gravel or both between the raw borewall and the production pipe thereby avoiding the time and expense of setting a steel casing from the surface to the production zone which may be many thousands of feet below the surface. The gravel packing is inherently permeable to the desired hydrocarbon fluid and provides structural reinforcement to the bore wall against an interior collapse or flow degradation. Such well completion systems are called “open hole” completions. The apparatus and process by which a packed deposit of gravel is placed between the borehole wall and the production pipe is encompassed within the definition of an “open hole gravel pack system.” Unfortunately, prior art open hole gravel pack systems for placing and packing gravel along a hydrocarbon production zone have been attended by a considerable risk of precipating a borehole wall collapse due to fluctuations in the borehole pressure along the production zone. These pressure fluctuations are generated by surface manipulations of the downhole tools that are in direct fluid circulation within the well and completion string.  
           [0006]    Open hole well completions usually include one or more screens between the packed gravel annulus and a hydrocarbon production pipe. The term “screen” as used herein may also include slotted or perforated pipe. If the production zone is not at the bottom terminus of the well, the wellbore is closed by a packer at the distal or bottom end of the production zone to provide bottom end support for the gravel pack volume. The upper end of the production zone volume is delineated by a packer around the annulus between the wellbore and the pipe column, called a “completion string”, that carries the hydrocarbon production to the surface. This upper end packer may also be positioned between the completion string and the inside surface of the well casing at a point substantially above the screens and production zone.  
           [0007]    Placement of these packers and other “downhole” well conditioning equipment employs a surface controlled column of pipe that is often characterized as a “tool string”. With respect to placement of a gravel pack, a surface controlled mechanism is incorporated within the tool string that selectively directs a fluidized slurry flow of sand and/or gravel from within the internal pipe bore of the tool string into the lower annulus between the raw wall of the wellbore and the outer perimeter of the completion string. This mechanism is positioned along the well depth proximate of the upper packer. As the mechanism directs descending slurry flow from the tool string bore into the wellbore annulus, it simultaneously directs the rising flow of slurry filtrate that has passed through screens in a production pipe extended below the upper packer. This rising flow of slurry filtrate is directed from the production pipe bore into the wellbore annulus above the upper packer.  
           [0008]    It is during the interval of manually manipulated change in the slurry flow direction that potential exists for creating a hydrostatic pressure environment within the wellbore annulus below the upper packer that is less than the natural hydrostatic pressure of fluid within the formation. Such a pressure imbalance, even briefly, may collapse the borehole or otherwise damage the productivity of the production zone borehole wall or damage the filter cake. Highly deviated or horizontal production zone boreholes are particularly susceptible to damage due to such a pressure imbalance. Consequently, it is an object of the present invention to provide a flow cross-over mechanism that will provide a positive (overburden) pressure against a borehole wall throughout all phases of the gravel packing process.  
           [0009]    It is also an object of the invention to provide a procedure and mechanism for maintaining fluid pressure on the production zone wellbore wall below the upper packer that is at least equal or greater than the natural hydrostatic pressure after the packer is set and while a greater fluid pressure is imposed on the wellbore annulus above the upper packer for testing the seal integrity of the packer.  
           [0010]    Another object of the present invention to provide an apparatus design that facilitates a substantially uniform overburden pressure within a borehole production zone throughout the cross-flow changes occurring during a gravel packing procedure.  
         SUMMARY OF THE INVENTION  
         [0011]    A preferred embodiment of the present invention includes a gravel pack extension tube that is permanently secured within a wellbore casing; preferably in or near the well production zone thereof. Near the upper end of the gravel pack extension tube is a packing seal that obstructs fluid flow through an annular section of the casing between the internal casing wall and the external perimeter of the gravel pack extension tube. The lower end of the gravel pack extension tube includes an open bore pipe that may be extended below the casing bottom and along the open borehole into the production zone. The distal end of the lower end pipe is preferably closed with a bull plug. Along the lower end of the pipe extension, within the hydrocarbon production zone and above the bull plug, are one or more gravel screens that are sized to pass the formation fluids while excluding the formation debris.  
           [0012]    Internally, the upper end of the gravel pack extension tube provides two, axially separated, circular seal surfaces having an annular space therebetween. Further along the gravel pack extension tube length, several, three for example, axially separated, axial indexing lugs are provided to project into the extension tube bore space as operator indicators.  
           [0013]    The dynamic or operative element of the present packing apparatus is a crossover flow tool that is attached to the lower end of a tool string. Concentric axial flow channels around the inner bore channel are formed in the upper end of the upper end of the crossover flow tool. An axial indexing collet is secured to the crossover tool assembly in the axial proximity of the indexing lugs respective to the extension tube. A ball check valve rectifies the direction of fluid flow along the inner bore of the crossover flow tool. A plurality of transverse fluid flow ports penetrate through the outer tube wall into the concentric flow channels. Axial positionment of the crossover flow tool relative to the inner seals on the gravel pack extension seals controls the direction of fluid flow within the concentrically outer flow channels. At all times and states of flow direction within the gravel packing procedure and interval, the production zone bore wall is subjected to at least the fluid pressure head standing in the wellbore above the production zone by means of the transverse flow channels and the concentric outer flow channels. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like reference characters throughout the several figures of the drawings:  
         [0015]    [0015]FIG. 1 is a sectional elevation of a completed oil well borehole having the present invention gravel pack extension secured therein;  
         [0016]    [0016]FIG. 2 is a sectional elevation of the present invention crossover tool;  
         [0017]    [0017]FIG. 3 is a partially sectioned elevation of an anti-swabbing tool having combination utility with the present invention;  
         [0018]    FIGS.  4 A- 4 E schematically illustrate the operational sequence of the indexing collet;  
         [0019]    [0019]FIG. 5 is a sectional elevation of the gravel pack extension and the crossover tool in coaxial assembly for downhole positionment;  
         [0020]    [0020]FIG. 6 is an enlargement of that portion of FIG. 5 within the detail boundary A;  
         [0021]    [0021]FIG. 7 is a sectional elevation of the gravel pack extension and the crossover tool in coaxial assembly suitable for setting the upper packer.;  
         [0022]    [0022]FIG. 8 is an enlargement of that portion of FIG. 7 within the detail boundary B;  
         [0023]    [0023]FIG. 9 is a sectional elevation of the gravel pack extension and the crossover tool in coaxial assembly suitable for testing the hydrostatic seal pressure of the upper packer;  
         [0024]    [0024]FIG. 10 is an enlargement of that portion of FIG. 9 within the detail boundary C;  
         [0025]    [0025]FIG. 11 is a sectional elevation of the gravel pack extension and the crossover tool in coaxial assembly suitable for circulating a gravel packing slurry into the desired production zone;  
         [0026]    [0026]FIG. 12 is an enlargement of that portion of FIG. 11 within the detail boundary D;  
         [0027]    [0027]FIG. 13 is a sectional elevation of the gravel pack extension and the crossover tool in coaxial assembly suitable for a flush circulation of the setting tool pipe string;  
         [0028]    [0028]FIG. 14 is an enlargement of that portion of FIG. 13 within the detail boundary E.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The sectional elevation of FIG. 1 illustrates a hydrocarbon producing well having an upper casing  12 . The well casing  12  is preferably secured to the wall  10  of the wellbore by an annular concrete jacket  14 . Near the lower end of the casing  12 , within the internal bore of the casing, a gravel pack body  20  is secured by slips and a pressure seal packer  22 . Generally, the gravel pack body is an open flowpipe  21  having one or more cylindrical screen elements  16  near the lower end thereof. The flowpipe lower end projects into the hydrocarbon bearing production zone  18 . In the annular space between the wellbore wall  10  and the screen elements  16  is a tightly consolidated deposit  24  of aggregate such as sand and gravel, for example. This deposit of aggregate is generally characterized in the art as a “gravel pack”. Although tightly consolidated, the gravel pack is highly permeable to the hydrocarbon fluids desired from the formation production zone. Preferably, the gravel pack  24  surrounds all of the screen  16  flow transfer surface and extends along the borehole length substantially coextensively with the hydrocarbon fluid production zone. The flowpipe lower end is terminated by a bull plug  25 , for example.  
         [0030]    Component Description  
         [0031]    The upper end of the gravel pack body  20  comprises a pair of internal pipe sealing surfaces  26  and  28  which are short lengths of substantially smooth bore, internal pipe wall having a reduced diameter. These internal sealing surfaces  26  and are separated axially by a discreet distance to be subsequently described with respect to the crossover tool  50 .  
         [0032]    The upper end of the gravel pack body  20  also integrates a tool joint thread  30 , a tool shoulder  32  and a limit ledge  34 . Below the pipe sealing surfaces  26  and  28  along the length of the gravel pack extension tube  23  are three collet shifting profiles  36 ,  37  and  38 . The axial separation dimensions between the pipe sealing surfaces  26  and  28  are also critically related to the axial separation distances between collet shifting ledges  36 ,  37  and  38  as will be developed more thoroughly with regard to the crossover tool  50 .  
         [0033]    Hydrocarbon production fluid flow, therefore, originates from the production zone  18 , passes through the gravel pack  24  and screens  16  into the internal void volume of the flowpipe  21 . From the screens  16 , the fluid enters and passes through the terminal sub  44  and into the production pipe  42 . The production pipe  42  carries the fluid to the surface where it is appropriately channeled into a field gathering system.  
         [0034]    The aggregate constituency of the gravel pack  24  is deposited in the wellbore annulus as a fluidized slurry. Procedurally, the slurry is pumped down the internal pipe bore of a completion string that is mechanically manipulated from the surface. Generally, completion string control movement includes only rotation, pulling and, by gravity, pushing. Consequently, with these control motions the slurry flow must be transferred from within the completion string bore into the annulus between the wellbore wall and the gravel pack extension flow pipe  21  above the screens  16 . The screens  16  separate the fluid carrier medium (water, for example) from the slurry aggregate as the carrier medium enters the internal bore of the flow pipe  21 . The flow pipe channels the carrier medium return flow up to a crossover point within the completion string where the return flow is channeled into the annulus between the internal casing walls  12  and the outer wall surfaces of the completion string. From the crossover point, the carrier medium flow is channeled along the casing annulus to the surface.  
         [0035]    When the desired quantity of gravel pack is in place, the internal bore of the completion string must be flushed with a reverse flow circulation of carrier medium to remove aggregate remaining in the completion string above the crossover point. Such reverse flow is a carrier medium flow that descends along the carrier annulus to the cross-over point and up the completion string bore to the surface. Throughout each of the flow circulation reversals, it is necessary that a net positive pressure be maintained against the producing zone of the wellbore to prevent any borewall collapse. To this objective, a crossover tool  50  as illustrated by FIG. 2 is constructed to operatively combine with the gravel pack body  20 .  
         [0036]    Generally, the crossover tool  50  assembles coaxially with the gravel pack body  20  and includes a setting tool  52  that is attached to the lower end of the completion string  46 . The setting tool  52  comprises a collar  54  having a lower rim face that mates with the tool shoulder  32  of the gravel pack body  20  when the crossover tool  50  is structurally unitized by a mutual thread engagement  55  with the gravel pack body  20 . Transverse apertures  56  perforate the collar  54  perimeter.  
         [0037]    Internally of the collar  54  rim, an inner tube  60  is structurally secured therewith. As best seen from the detail of FIGS. 5 and 6, a thread collar  62  surrounds the upper end of the inner tube  60  to provide an upper void chamber  64  between the thread collar  62  and the tube  60 . The thread collar  62  is perforated for fluid pressure transmission between the collar apertures  56  and the void chamber  64 . Fluid pressure transmission channels are also provided between the void chamber  64  and an upper by-pass chamber  66 . The upper by-pass chamber  66  is an annular void space between the inner tube  60  and an outer lip tube  68 . Axially, the upper by-pass chamber  66  is terminated by a ring-wall  70 . An upper by-pass flow channel  72  opens the chamber  66  to the outer volume surrounding the outer lip tube  68 . An upper o-ring  74  seals the annular space between the outer lip tube  68  and the inner sealing surface  26  of the packer  22 . The outer perimeter of the ring-wall  70  carries o-ring  76  for the same purpose when the crossover tool  50  is axially aligned with the sealing surface  26 .  
         [0038]    A lower sleeve  80  coaxially surrounds the inner tube  60  below the ring-wall to create a lower by-pass chamber  82 . A lower by-pass flow channel  84  opens the chamber  82  to the outer volume surrounding the lower sleeve  80 . O-ring  86  cooperates with the packer sealing surface  26  and the o-ring  76  to selectively seal the lower by-pass flow channel  84 .  
         [0039]    At the lower end of the inner tube  60 , a check valve ball seat  90  is provided on an axially translating sleeve  91 . The seat  90  is oriented to selectively obstruct downward fluid flow within the inner tube  60 . Upward flow within the tube is relatively unobstructed since a cooperative check valve ball  92  is uncaged. Upward fluid flow carries the check valve ball away from the seat  90  and upward along the tool string  46  bore. Above the check valve seat  90  is a crossover port  94  between the bore of the inner tube  60  and the outer volume surrounding the lower sleeve  80 . O-rings  96  and  98  cooperate with the lower seal bore  102  of the lower seal ring  100  to isolate the crossover port  94  when the crossover tool is correspondingly aligned. Below the check valve seat  90  are by-pass flow channels  99  in the sleeve  91  and flow channels  88  in the inner tube  60 . When aligned by axial translation of the sleeve  91 , the flow channels  88  and  99  open a fluid pressure communication channel between the lower by-pass chamber  82  and the internal bore of the lower sleeve  80  below the valve seat  90 . Alignment translation of the sleeve  91  occurs as a consequence of the hydraulic pressure head on the sleeve  91  when the ball  92  is seated. By-pass flow channels  29  are also provided through the wall of gravel pack extension tube  23  between the inside sealing surfaces  26  and  28  of the packer body  20 .  
         [0040]    Below the lower sleeve  80  but structurally continuous with the crossover tool assembly are an anti-swabbing tool  110  and an axial indexing collet  150 . The purpose of the anti-swabbing tool is to control well fluid loss into the formation after the gravel packing procedure has been initiated but not yet complete. The axial indexing collet  140  is a mechanism that is manipulated from the surface by selective up or down force on the completion string that positive locate the several relative axial positions of the crossover tool  50  to the gravel pack body  20 .  
         [0041]    In reference to FIG. 3, the anti-swabbing tool  110  comprises a mandrel  112  having internal box threads  113  for upper assembly with the lower sleeve  80 . The mandrel  112  is structurally continuous to the lower assembly thread  114 . At the lower end of the mandrel  112 , it is assembled with a bottom sub  115  having external pin threads  116 . Within the mandrel  112  wall is a retaining recess for a pivoting check valve flapper  117 . The flapper  117  is biased by a spring  118  to the down/closed position upon an internal valve seat  120 . However, the flapper is normally held in the open position by a retainer button  119 . The retainer button is confined behind a selectively sliding key slot  126  that is secured to a sliding housing sleeve  124 . The housing sleeve  124  normally held at the open position by shear screws  128 . At the upper end of the housing sleeve  124  is an operating collet  121  having profile engagement shoulders  122  and an abutment base  123 . A selected up-stroke of the completion string causes the collet shoulders  122  to engage an internal profile of the completion string. Continued up-stroke force presses the collet abutment base  123  against an abutment shoulder on the housing sleeve. This force on the housing sleeve shears the screws  128  thereby permitting the housing sleeve  124  and key slot  126  to slide downward and release the flapper  117 . The downward displacement of the housing sleeve also permits the collet  121  and collet shoulders  122  to be displaced along the mandrel  112  until the profile of the collet shoulders  122  fall into the mandrel recess  126 . When retracted into the recess  126 , the shoulder  122  perimeter is sufficiently reduced to pass the internal activation profile thereby allowing the device to be withdrawn from the well after the flapper has been released.  
         [0042]    Coaxial alignment of the crossover tool  50  with the gravel pack body  20  is largely facilitated by the axial indexing collet  140  shown by FIGS.  4 A- 4 E. The collet  140  is normally secured to the lower end of the crossover tool  50  and below the anti-swabbing tool  110 . With respect to FIG. 4, a structurally continuous mandrel  142  includes exterior surface profiles  146  and  148 . The profile  146  is a cylinder cam follower pin. The profile  148  is a collet finger blocking shoulder. Both profiles  146  and  148  are radial projections from the cylindrical outer surface of the mandrel  142 .  
         [0043]    Confined between two collars  152  and  154  is a sleeve collet  144  and a coiled compression spring  150 . The bias of spring  150  is to urge the collet sleeve downward against the collar  154 .  
         [0044]    Characteristic of the collet  144  is a plurality of collet fingers  147  around the collet perimeter. The fingers  147  are integral with the collet sleeve annulus at opposite finger ends but are laterally separated by axially extending slots between the finger ends. Consequently, each finger  147  has a small degree of radial flexure between the finger ends. About midway between the finger ends, each finger is radially profiled, internally and externally, to provide an internal bore enlargement  149  and an external shoulder  148 . The outside diameter of the collet shoulder section  148  is dimensionally coordinated to the inside diameter of the indexing profiles  36 ,  37  and  38  to permit axial passage of the collet shoulder  148  past an indexing profile only if the fingers are permitted to flex radially inward. The internal bore enlargement  149  is dimensionally coordinated to the mandrel profile projection  148  to permit the radial inward flexure necessary for axial passage. The outside diameter of the mandrel projection  148  is also coordinated to the inside diameter of the collet fingers  147  so as to support the fingers  147  against radial flexure when the mandrel projections  148  are axially displaced from radial alignment with the finger enlargements  149 . Hence, if the mandrel projection section  148  is not in radial alignment with the collet finger enlargement section  149 , the collet sleeve will not pass any of the axial indexing profiles  36 ,  37  and  38  of the gravel pack body extension tube  23 .  
         [0045]    The internal bore of the collet sleeve  144  is formed with a female cylinder cam profile to receive the cam follower pin  146  whereby relative axial stroking between the collet sleeve  144  and the mandrel  142  rotates the sleeve about the longitudinal axis of the sleeve by a predetermined number of angular degrees. The cam profile provides two axial set positions for the collet sleeve relative to the mandrel  142 . At a first set position, the mandrel blocking profile  148  aligns with the internal bore enlargement area  149  of the fingers. At the second set position, the mandrel blocking profile  148  aligns with the smaller inside diameter of the collet fingers  144 . The mechanism is essentially the same as that utilized for retracting point writing instruments: a first stroke against a spring bias extends the writing point and a second, successive, stroke against the spring retracts the writing point.  
         [0046]    Operating Sequence  
         [0047]    Referring to FIGS. 5 and 6, in preparation for downhole positionment within a desired production zone, the gravel pack body  20  is attached to the crossover tool  50  by a threaded connection  55  for a gravel pack assembly  15 . A threaded connection  48  also secures the gravel pack assembly  15  to the downhole end of the completion string  46 . At this point, the packer seal  22  is radially collapsed thereby permitting the assembly  15  to pass axially along the bore of casing  12 . The indexing collet  140  is set in the expanded alignment of FIG. 4A to align the mandrel profile  148  with the finger bore enlargement area  149 . Consequently, the collet finger support shoulders  145  will constrict to pass through the tube  23  restriction profiles  36 ,  37  and  38 .  
         [0048]    Normally, the casing bore  12  and open borehole  10  below the casing  12  will be filled with drilling fluid, for example, which maintains a hydrostatic pressure head on the walls of the production zone. The hydrostatic pressure head is proportional to the zone depth and density of the drilling fluid. The drilling fluid is formulated to provide a hydrostatic pressure head in the open borehole that is greater than the natural, in situ, hydrostatic pressure of the formation. Since the packer seal is collapsed, this well fluid will flow past the packer  22  as the completion string is lowered into the well thereby maintaining the hydrostatic pressure head on the borehole wall. Consequently, placement of the assembly will have no pressure effect on the production zone. If desired, well fluid may be pumped down through the internal bore of the completion string  46  and back up the annulus around the assembly  15  and completion string in the traditional circulation pattern.  
         [0049]    When the completion string screens  16  are suitably positioned at the first index position along the borehole length, the check valve ball  92  is placed in the surface pump discharge conduit for pumped delivery along the completion string bore onto the check valve seat  90  as illustrated by FIGS. 7 and 8. Closure of the valve seat  90  permits pressure to be raised within the internal bore  46  of the completion string to secure the completion string location by setting the packer slips and seals  22 . When the packer seals  22  are expanded against the internal bore of casing  12 , fluid flow and pressure continuity along the casing annulus is interrupted. It is to be noted that the bypass port  94  of the crossover tool is located opposite from the lower seal bore  102  between the o-ring seals  96  and  98 , thereby effectively closing the by-pass port  94 .  
         [0050]    However, the restricted by-pass flow routes provided by the collar apertures  56 , the void chamber  64 , the upper by-pass chamber  66 , and the upper by-pass flow channels  72  and  29  prevent pressure isolation of the production zone bore wall  10 .  
         [0051]    Next, the crossover tool  50 , which is directly attached to the completion string  46 , may be axially released from the gravel pack body  20  and positioned independently by manipulations of the completion string  46 . The completion string  46  is first rotated to disengage the crossover tool threads  55  from the threads  30  of the gravel pack body  20 . With the assembly threads  30  and  55  disengaged, the crossover tool  50  is lifted to a second index position relative to the gravel pack body  20 . With respect to FIG. 4B, the completion string is lifted to draw the collet fingers  147  through a tube restriction profile. The draw load is indicated to the driller as well as the load reduction when the collet fingers clear the restriction. Additionally, the draw load on the collet sleeve strokes and rotates the sleeve to reset the follower pin in the sleeve cam profile. Accordingly, when the driller reverses and lowers the completion string, mandrel blocking profile  148  aligns with the smaller inside diameter of the collet fingers  147 . The external finger shoulders  145  engage the tube profile to prevent further downhole movement of the completion string and positively locate the crossover tool  50  relative to the gravel pack body  20  at a second axial index position as shown by FIG. 4C.  
         [0052]    With respect to the upper end of the crossover tool assembly  50  as illustrated by FIGS. 9 and 10, the ring-wall o-ring seal  74  engages the sealing surface of the packer  22  to seal the annulus  104  between the gravel pack extension tube  23  and the crossover tool sleeve  80  from by-pass discharges past the packer  22 . Simultaneously, the crossover flow port  94  from the internal bore of the inner tube  60  is opened into the annular volume  104  and ultimately, into the casing annulus below the packer  22 . Here, the seal integrity of packer  22  may be verified by elevating fluid pressure within the borehole annulus above the packer  22  to a suitable pressure magnitude that is greater than the natural, hydrostatic formation pressure and also greater than the pressure below the packer  22 . Simultaneously, wellbore annulus pressure below the packer  22  is also maintained above the natural hydrostatic formation pressure via fluid delivered from surface pumps, for example, along the internal bore of the completion string  46 , into the internal bore of the inner tube  60  to exit through the port  94  into annulus  104  between the crossover tool sleeve  80  and the gravel pack extension tube  23 . From the annulus  104 , pressurized working fluid exits through the by-pass channels  29  into the casing annulus below the packer  22 .  
         [0053]    With a confirmation of the seal and fixture of packer  22 , the crossover tool is axially indexed a third time to the relationship of FIGS. 11 and 12 whereat the ring wall  70  and the lower by-pass flow channel  84  from the lower by-pass chamber  82  are positioned above the sealing surface  26 . However, the o-ring seal  86  continues to seal the space between the sealing surface  26  and the lower sleeve  80 . At this setting, a fluidized gravel slurry comprising aggregate and a fluid carrier medium may be pumped down the completion string  46  bore into crossover flow ports  94  above the check valve  90 . From the crossover flow ports  94 , the gravel slurry enters the annular chamber  104  and further, passes through the by-pass channels  29  into the casing annulus below the packer  22 .  
         [0054]    From the by-pass channels  29 , the slurry flow continues along the casing annulus into the open borehole annulus within the production zone  18 . Fluid carrier medium passes through the mesh of screen elements  16  which block passage of the slurry aggregate constituency. Accordingly, the aggregate accumulates around the screen elements  16  and, ultimately, the entire volume between the raw wall of the open bore  10  and the screens  16 .  
         [0055]    Upon passing the screens  16 , carrier medium enters the gravel pack extension flow pipe  21  and the internal bore of lower sleeve  80 . Below the check valve  90 , the carrier medium enters the lower by-pass chamber  82  through the check valve by-pass flow channels  88 . At the upper end of the by-pass chamber  82 , the carrier medium flow is channeled through the lower by-pass  84  into the casing annulus above the packer  22 . The upper casing annulus conducts the carrier medium flow back to the surface to be recycled with another slurry load of aggregate.  
         [0056]    Unless it is possible predetermine the exact volume of aggregate necessary to fill the open hole annulus within the production zone  18 , excess aggregate will frequently remain in the completion string bore when the gravel pack  24  is complete. Usually, it is desirable to flush any excess aggregate in the completion string bore from the completion string before withdrawing the completion string and attached crossover tool. With reference to FIGS. 13 and 14, the crossover tool  50  is withdrawn from the gravel pack extension  20  to a fourth index position at which the crossover port is open directly to the casing annulus above the upper packer  22 . Unslurried well fluid is pumped into the casing annulus in a reverse circulation mode. The reverse circulating fluid enters the inner tube  60  bore above the check valve  90  to fluidize and sweep any aggregate therein to the surface. However, to maintain the desired hydrostatic pressure head on the open hole production zone, reverse circulating well fluid also enters the lower by-pass chamber  82  through the lower by-pass flow channel  84 . Fluid is discharged from the chamber  82  through the check valve by-pass flow channels  88  into the volume below the packer  22  thereby reducing any pressure differential across the packer.  
         [0057]    With the gravel pack  24  in place, the crossover tool  50  may be completely extracted from the gravel pack body  20  with the completion string and replaced by a terminal sub  44  and production pipe  42 , for example.  
         [0058]    Utility of the anti-swabbing tool with the crossover assembly  50  arises with the circumstance of unexpected loss of well fluid into the formation after the gravel packing procedure has begun. Typically, a portion of filter cake has sluffed from the borehole wall and must be replaced by an independent mud circulation procedure. As a first repair step, fluid loss from within the completion string bore must be stopped. This action is served by releasing the flapper  117  to plug the bore notwithstanding the presence of the ball plug  92  on the valve seat  90 .  
         [0059]    The foregoing detailed description of our invention is directed to the preferred embodiments of the invention. Various modifications may appear to those of ordinary skill in the art. It is accordingly intended that all variations within the scope and spirit of the appended claims be embraced by the foregoing disclosure.