Abstract:
An isolation string having: an upper packer; and an isolation pipe in mechanical communication with the upper packer, wherein the isolation pipe comprises a pressure activated valve and an object activated valve. A method having: running-in an isolation string on a service tool, wherein the isolation string comprises a pressure activated valve and a object activated valve; setting the isolation string in the casing adjacent perforations in the casing; releasing an object from the service tool, whereby the object travels to the object activated valve; closing the object activated valve with the released object; and withdrawing the service tool from the well.

Description:
TITLE OF THE INVENTION 
     This application is a Continuation-in-Part of application Ser. No. 10/004,956, filed Dec. 5, 2001, issued as U.S. Pat. No. 6,722,440, which claims the benefit of U.S. Provisional Application Ser. No. 60/251,293, filed Dec. 5, 2000. This application also claims the benefit of U.S. Patent Application Ser. No. 09/378,384, issued as U.S. Pat. No. 6,397,949, and filed on Aug. 20, 1990, which claims the benefit of U.S. Provisional Application Ser. No. 60/097,449, filed Aug. 21. 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     Early prior art isolation systems involved intricate positioning of tools which were installed down-hole after the gravel pack. These systems are exemplified by a commercial system which at one time was available from Baker. This system utilized an anchor assembly which was run into the wellbore after the gravel pack. The anchor assembly was released by a shearing action, and subsequently latched into position. 
     Certain disadvantages have been identified with the systems of the prior art. For example, prior conventional isolation systems have had to be installed after the gravel pack, thus requiring greater time and extra trips to install the isolation assemblies. Also, prior systems have involved the use of fluid loss control pills after gravel pack installation, and have required the use of thru-tubing perforation or mechanical opening of a wireline sliding sleeve to access alternate or primary producing zones. In addition, the installation of prior systems within the wellbore require more time consuming methods with less flexibility and reliability than a system which is installed at the surface. 
     Later prior art isolation systems provided an isolation sleeve which was installed inside the production screen at the surface and thereafter controlled in the wellbore by means of an inner service string. For example, as shown in U.S. Pat. No. 5,865,251, incorporated herein by reference, illustrates an isolation assembly which comprises a production screen, an isolation pipe mounted to the interior of the production screen, the isolation pipe being sealed with the production screen at proximal and distal ends, and a sleeve movably coupled with the isolation pipe. The isolation pipe defines at least one port and the sleeve defines at least one aperture, so that the sleeve has an open position with the aperture of the sleeve in fluid communication with the port in the isolation pipe. When the sleeve is in the open position, it permits fluid passage between the exterior of the screen and the interior of the isolation pipe. The sleeve also has a closed position with the aperture of the sleeve not in fluid communication with the port of the isolation pipe. When the sleeve is in the closed position, it prevents fluid passage between the exterior of the screen and the interior of the isolation pipe. The isolation system also has a complementary service string and shifting tool useful in combination with the isolation string. The service string has a washpipe that extends from the string to a position below the sleeve of the isolation string, wherein the washpipe has a shifting tool at the end. When the completion operations are finalized, the washpipe is pulled up through the sleeve. As the service string is removed from the wellbore, the shifting tool at the end of the washpipe automatically moves the sleeve to the closed position. This isolates the production zone during the time that the service string is tripped out of the well and the production seal assembly is run into the well. 
     Prior art systems that do not isolate the formation between tool trips suffer significant fluid losses Those prior art systems that close an isolation valve with a mechanical shifting tool at the end of a washpipe prevent fluid loss. However, the extension of the washpipe through the isolation valve presents a potential failure point. For example, the washpipe may become lodged in the isolation string below the isolation valve due to debris or settled sand particles. Also, the shifting tool may improperly mate with the isolation valve and become lodged therein. 
     Therefore, a need remains for an isolation system for well control purposes and for wellbore fluid loss control which combines simplicity, reliability, safety and economy, while also affording flexibility in use. A need remains for an isolation system which does not require a washpipe with a shifting tool for isolation valve closure. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the invention includes four separate valves in combination: a Radial Flow Valve (RFV), an Annular Flow Valve (AFV), a Pressure Activated Control Valve (PACV), and an Interventionless Flow Valve (IFV). Generally, the RFV is an annulus to inside diameter pressure actuated valve with a double-pin connection at the bottom, the AFV is an annulus to annulus pressure actuated valve with a double-pin connection at the bottom, the PACV is an outside diameter to inside diameter pressure actuated valve, and the IFV is an outside diameter to inside diameter object actuated valve. A double-pin or double-sub connection is one having concentric inner and outer subs. 
     According to one aspect of the invention, there is provided an isolation string having: an upper packer; and an isolation pipe in mechanical communication with the upper packer, wherein the isolation pipe comprises a pressure activated valve and an object activated valve. 
     Another aspect of the invention provides a method having: running-in an isolation string on a service tool, wherein the isolation string comprises a pressure activated valve and a object activated valve; setting the isolation string in the casing adjacent perforations in the casing; releasing an object from the service tool, whereby the object travels to the object activated valve; closing the object activated valve with the released object; and withdrawing the service tool from the well. 
     According to a further aspect of the invention, there is provided an isolation string having: an upper packer; a pressure activated, double-sub valve having first and second concentric subs, wherein the double-sub valve is in mechanical communication with the upper packer; an isolation pipe in mechanical communication with the first sub of the double-sub valve, wherein the isolation pipe comprises an object activated valve; a production pipe in mechanical communication with the second sub of the double-sub valve. 
     In accordance with still another aspect of the invention, there is provided a method having: running-in an isolation string on a service tool, wherein the isolation string comprises a double-sub valve and a object activated valve; setting the isolation string in the casing adjacent perforations in the casing; releasing an object from the service tool, whereby the object travels to the object activated valve; closing the object activated valve with the released object; and withdrawing the service tool from the isolation string. 
     According to an even further aspect of the invention, there is provided an isolation string for multiple zone isolations, the string having: a lower isolation section and an upper isolation section, the lower isolation section having: a lower section upper packer; and a lower section isolation pipe in mechanical communication with the lower section upper packer, wherein the lower section isolation pipe comprises a pressure activated valve and a lower section object activated valve, the upper isolation section having: an upper section upper packer; a double-sub valve having first and second concentric subs, wherein the double-sub valve is in mechanical communication with the upper section upper packer; an upper section isolation pipe in mechanical communication with the first sub of the double-sub valve, wherein the isolation pipe comprises an upper section object activated valve; and a production pipe in mechanical communication with the second sub of the double-sub valve, wherein the upper section isolation pipe and the production pipe sting into the lower section upper packer. 
     According to a another aspect of the invention, there is provided an isolation string for multiple zone isolations, the string having: a lower isolation section and an upper isolation section, the lower isolation section having: a lower section upper packer; a lower section double-sub valve having first and second concentric subs, wherein the lower section double-sub valve is in mechanical communication with the lower section upper packer; a lower section isolation pipe in mechanical communication with the first sub of the double-sub valve, wherein the lower section isolation pipe comprises an lower section object activated valve; and a lower section production pipe in mechanical communication with the second sub of the double-sub valve, the upper isolation section having: an upper section upper packer; a double-sub valve having first and second concentric subs, wherein the double-sub valve is in mechanical communication with the upper section upper packer; an upper section isolation pipe in mechanical communication with the first sub of the double-sub valve, wherein the isolation pipe comprises an upper section object activated valve; and a production pipe in mechanical communication with the second sub of the double-sub valve, wherein the upper section isolation pipe and the production pipe sting into the lower section upper packer. 
     In accordance with still one more aspect of the invention, there is provided an isolation system having and isolation string and an isolation service tool, wherein the isolation string comprises: an upper packer; and an isolation pipe in mechanical communication with the upper packer, wherein the isolation pipe comprises a pressure activated valve and an object activated valve, wherein the isolation service tool comprises: an annular string; a drop object positioned within the string; a plunger positioned within the string and forcefully biased toward the drop object, at least one lock dog that extends through the string to retain the drop object; and a lock mechanically connected to the at least one lock dog, wherein the drop object of the isolation service tool is operable on the object activated valve to manipulate the object activated valve between open and closed configurations. 
     According to another aspect of the invention, there is provided a valve system having: an object holding service tool, the service tool having: an object, an object release mechanism, and a lock of the object release mechanism; and an object activated valve, the object activated valve having: a tube having at least one opening; a sleeve being movably connected to the tube, wherein the sleeve covers the at least one opening in a closed configuration and the sleeve does not cover the at least one opening in an open configuration; and an object seat in mechanical communication with the sleeve, wherein the seat receives an object for manipulating the valve from the open configuration to the closed configuration. 
     In accordance with the present disclosure, there is a drop ball valve for isolating a production zone without using a washpipe. The valve has at least one recess, a ball, and a plurality of fingers having ends. The finger ends are in the recess when the valve is closed. The ends are out of the recess when the valve is open. The ends form a ball seat when the valve is open. The ball is adjacent to the ball seat when the valve is open. The ball forces the valve to change from open to closed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIGS. 1A–1C  show a cross-sectional side view of an AFV, wherein the valve is in an open configuration. 
         FIGS. 2A–2C  show a cross-sectional side view of a portion of the AFV of  FIGS. 1A–1C , wherein the valve is in a closed configuration. 
         FIGS. 3A–3C  show a cross-sectional side view of a RFV, wherein the valve is in an open configuration. 
         FIGS. 4A–4C  show a cross-sectional side view of the RFV of  FIGS. 3A–3C , wherein the valve is in an unlocked-closed configuration. 
         FIGS. 5A–5C  show a cross-sectional side view of the RFV of  FIGS. 3A–3C , wherein the valve is in a locked-closed configuration. 
         FIGS. 6A–6D  are a side, partial cross-sectional, diagrammatic view of half of a PACV in accordance with the present invention in a locked-closed configuration. It will be understood that the cross-sectional view of the other half of the PACV is a mirror image taken along the longitudinal axis. 
         FIGS. 7A–7D  illustrate the PACV of  FIGS. 6A–6D  in an unlocked-closed configuration. 
         FIGS. 8A–8D  illustrate the PACV of  FIGS. 6A–6D  in an open configuration. 
         FIG. 8E  is a cross-section, diagrammatic view taken along line A—A of the PACV of  FIG. 8C  showing the full assembly. 
         FIGS. 9A–9B  illustrate a cross-sectional side view of a ball holding service tool, wherein the service tool is shown in a run-in position holding a drop ball in a locked configuration. 
         FIG. 9C  shows a laid-out side view of a groove and a pin of the ball holding service tool shown in  FIGS. 9A–9B , wherein the pin is shown in three separate positions withing groove. 
         FIGS. 10A–10B  illustrate a cross-sectional side view of the ball holding service tool of  FIGS. 9A–9B , wherein the service tool is in a manipulation position with the drop ball is retained and the lock sleeve is moving between locked and unlocked configurations. 
         FIGS. 11A–11B  show a cross-sectional side view of the ball holding service tool of  FIGS. 9A–9B , wherein the service tool is shown in an unlocked, release position with the drop ball being ejected from the tool. 
         FIGS. 12A–12E  illustrate cross-sectional side views of a ball holding service tool shown with a cross over tool and packer, wherein the service tool is in a run in configuration. 
         FIGS. 13A–13E  illustrate cross-sectional side views of the ball holding service tool of  FIGS. 12A–12E , wherein the service tool is in a dog retainer ring shear configuration. 
         FIGS. 14A–14E  illustrate cross-sectional side views of the ball holding service tool of  FIGS. 12A–12E , wherein the service tool is in a dog release configuration. 
         FIGS. 15A–15E  illustrate cross-sectional side views of the ball holding service tool of  FIGS. 12A–12E , wherein the service tool is in a ball retainer ring shear configuration. 
         FIGS. 16A–16E  illustrate cross-sectional side views of the ball holding service tool of  FIGS. 12A–12E , wherein the service tool is in a drop ball release configuration. 
         FIGS. 17A–17C  illustrate cross-sectional side views of an IFV, wherein the valve above the midline is shown in an open configuration and the valve below the midline is shown in a closed configuration. 
         FIGS. 18A–18C  illustrate cross-sectional side views of an IFV, wherein the valve is in a closed configuration. 
         FIGS. 19A–19C  illustrate cross-sectional side views of the IFV shown in  FIGS. 18A–18C , wherein the valve is in an open configuration. 
         FIGS. 20A–20C  illustrate cross-sectional side views of an IFV, wherein the valve above the midline is shown in an open configuration and the valve below the midline is shown in a closed configuration 
         FIG. 21  illustrates cross-sectional side views of an isolation string having an IFV and PACV and separate isolation and production pipes, wherein the valves on the left are shown in a run-in configuration and the valves on the right are shown in a production configuration. 
         FIG. 22  illustrates cross-sectional side views of an isolation string having an IFV and a PACV, wherein the valves are wire wrapped with a production screen, and wherein the valves on the left are shown in a run-in configuration and the valves on the right are shown in a production configuration. 
         FIG. 23  illustrates cross-sectional side views of an isolation string having an IFV and a RFV and separate isolation and production pipes connected to the RFV, wherein the valves on the left are shown in a run-in configuration and the valves on the right are shown in a production configuration. 
         FIG. 24  illustrates cross-sectional side views of a dual zone isolation string. The lower section of the string has an IFV and a RFV with separate isolation and production pipes connected to the RFV. The upper section of the string has an IFV and a AFV with separate isolation and production pipes connected to the AFV. The valves on the left are shown in a run-in configuration and the valves on the right are shown in a production configuration. 
         FIG. 25  illustrates cross-sectional side views of a dual zone isolation string. The lower section of the string has an IFV and a PACV, wherein both valves are wire wrapped with a production screen. The upper section of the string has an IFV and a AFV with separate isolation and production pipes connected to the AFV. The valves on the left are shown in a run-in configuration and the valves on the right are shown in a production configuration. 
     
    
    
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are illustrated in the Figures, like numeral being used to refer to like and corresponding parts of the various drawings. 
     The isolation strings of the present invention comprise various valves, which are themselves embodiments of the present invention. A Radial Flow Valve (RFV) is an annulus to inside diameter pressure actuated valve with a double pin connection at the bottom. An Annular Flow Valve (AFV) is an annulus to annulus pressure actuated valve with a double pin connection at the bottom. A Pressure Activated Control Valve (PACV) is an outside diameter to inside diameter pressure actuated valve. An Interventionless Flow Valve (IFV) is an outside diameter to inside diameter object actuated valve. 
     Referring to  FIGS. 1A–1C  and  2 A– 2 C, detailed drawings of an AFV are shown. In  FIGS. 1A–1C , the valve is shown in an open position and in  FIGS. 2A–2C , the valve is shown in a closed position. In the open position, the valve enables fluid communication through the annulus between the interior and exterior tubes of the isolation string. Essentially, these interior and exterior tubes are sections of the base pipe  16  and the isolation pipe  17 , wherein a lower annulus  65  is defined between. The AFV comprises a shoulder  52  that juts into the annulus between a small diameter sealing land  58  and a relatively large diameter sealing land  59 . A moveable joint  54  is internally concentric to the shoulder  52  and the sealing lands  58  and  59 . Seals  56  are positioned between the moveable joint  54  and the sealing lands  58  and  59 . The movable joint  54  has a spanning section  62  and a closure section  64 , wherein the outside diameter of the spanning section  62  is less than the outside diameter of the closure section  64 . 
     The AFV is in a closed position, as shown in  FIGS. 2A–2C , when the valve is inserted in the well. In the closed position, the closure section  64  of the movable joint  54  covers lower ports  67 . The AFV is held in the closed position by a shear pin  55 . The shear pin  55  holds a lock ring  53  in a fixed position relative to the isolation pipe  17 . A certain change in fluid pressure differential between an upper annulus  66  of the AFV and the tubing, usually a pressure increase in the tubing, causes the moveable joint  54  to shift. In particular, excess tubing pressure is communicated through ports  51  to operate against annular wall  57 . Because the small diameter sealing land  58  is relatively smaller than the large diameter sealing land  59 , the relatively higher tubing pressure drives the movable joint  54  in the direction of the lock ring  53 . The movable joint  54  continues to drive against the lock ring  53  until the force is sufficient to shear the shear pin  55 . Upon shear, both the lock ring  53  and the movable joint  54  move in the direction of the isolation pipe  17  until the movable joint  54  is in an open configuration, as shown in  FIGS. 1A–1C . When the movable joint  54  is in the open configuration, the spanning section  62  of the movable joint  54  spans the lower ports  67 . This allows fluid to pass freely through the AFV between the lower annulus  65 , through lower ports  67 , through upper ports  68 , and through the upper annulus  66 . 
     The other double-pin valve is the RFV, as shown in  FIGS. 3A–5C . Similar to the AFV shown in  FIGS. 1A–1C  and  2 A– 2 C, the RFV has inner and outer concentric subs. Also, the RFV is pressure activated. In  FIGS. 3A–3C , the RFV is shown in an open configuration. In  FIGS. 4A–4C , the RFV is shown in a closed, unlocked (sheared) configuration. In  FIGS. 5A–5C , the RFV is shown in a closed, locked configuration. 
     Referring to  FIGS. 3A–5C , the a cross-sectional side view of the RFV  300  is shown. The RFV  300  comprises a double-wall construction made up of an inner tube  301  and an outer tube  302 . At the bottom of the valve there are inner and outer subs  303  and  304 , respectively. A fluid flow path is defined by the inner and outer subs  303  and  304  to communicated fluid between the subs up to ports  305 . The RFV  300  also has a sleeve  306  which is slidable within the inner tube  301  of the valve. The lower portion of the sleeve  306  is formed to slide over the ports  305  to completely restrict the flow of fluid through the ports  305 . A pressure chamber  307  is defined by a portion of the sleeve  305  and a portion of a mounting ring  308 . The inner and outer tubes  301  and  302  are mounted to the top of the mounting ring  308  and the inner and outer subs  303  and  304  are mounted to the bottom of the mounting ring  308 . The ports  305  extend through the mounting ring  308 . The valve also has a spring-biased lock ring  309  which engages teeth on the sleeve  306 . 
     Typically, the RFV  300  is run in the well in a closed-locked configuration, as shown in  FIGS. 5A–5C . In the closed-locked configuration, the sleeve  306  covers the ports  305 . The RFV  300  is held in the closed-locked configuration by lock ring  313 . The lock ring  313  has inner and outer rings which telescope into each other. The lock ring  313  is secured in an extended position by shear screws  314 . In the extended position, the shear screws are screwed through both inner and outer rings of the lock ring  313 . Because the lock ring  313  is fixed in an extended position, the lock ring  313  and sleeve  306  are unable to slide in the direction of the inner sub  303 . The sleeve  306  is also secured to the mounting ring  308  to prevent it from sliding in the opposite direction of the inner sub  303 . The sleeve  306  is secured to the mounting ring  308  by a snap ring  318 , which is spring biased to expand itself radially outward. However, in the closed-locked configuration, the snap ring  318  is held in a groove in the outside, lower end of the sleeve  306  by the lowermost portion of the mounting ring  308 . At the lowermost portion of the mounting ring  308 , there is a shoulder  319  which prevents the snap ring  318 , and hence the sleeve  306 , from sliding in a direction away from the inner sub  303 . 
     The RFV  300  may be reconfigured to a closed-unlocked (sheared) configuration, as shown in  FIGS. 4A–4C . The RFV  300  is unlocked by creating a pressure differential between the inner diameter of the sleeve  306  and the pressure chamber  307 . Fluid from the inner diameter bleeds through ports  315  in the sleeve  306  to work against annular wall  316 . The sleeve  306  has a greater outside diameter above the pressure chamber  307  than it has below the pressure chamber  307 . Thus, a relatively higher fluid pressure in the inner diameter of the sleeve  306  compared to the pressure chamber  307 , drives the sleeve  306  toward the inner sub  303 . As the sleeve  306  slides toward the inner sub  303 , it bears on the lock ring  313 . When the downward force becomes great enough, the lock ring  313  shears the shear screws  314  to release the inner and outer rings of the lock ring  313  so they are able to collapse into each other. Upon release, the lock ring  313  collapses and the sleeve  306  continues to move downwardly until they come to rest in the closed-unlocked (sheared) configuration shown in  FIGS. 4A–4C . As the sleeve  306  moves downward, the snap ring  318  is pushed into a larger bore and expands out of the groove in the sleeve  306  to release the sleeve  306  from the mounting ring  308 . In this position, the snap ring  318  holds the lock ring  313  in its sheared position. This RFV configuration is closed because the sleeve  306  is over the ports  305  to completely restrict the flow of fluid through the ports  305 . Seals  317  are positioned above and below the ports  305  to ensure the integrity of the valve. 
     The RFV  300  also has a spring  320  which works between the lock ring  309  and a seal sleeve  321  to bias the sleeve  306  in the direction away from the inner sub  303 . As noted above, the lock ring  309  is secured to the sleeve  306  by teeth  311  on the mating surfaces. In the closed-unlocked configuration of the RFV  300 , the spring  320  is fully compressed, as shown in  FIG. 4A . 
       FIGS. 3A–3C  illustrate the RFV  300  in an open configuration. The valve is opened by reducing the pressure differential between the inner diameter of the sleeve  306  and the pressure chamber  307 . When this pressure differential is reduced, the spring  320  pushes the sleeve  306  away from the ports  305  in a direction opposite from the inner sub  303  until the ports  305  are uncovered and until the lock ring  309  engages a shoulder  312 . The valve also has a ratchet lock ring  322  between the seal sleeve  321  and the sleeve  306 . As the sleeve  306  is pushed by the spring  320 , the ratchet lock ring  322  jumps over the teeth on the sleeve  306  as it moves into the open position. Because of the configuration of the threads on the ratchet lock ring  322  and sleeve  306 , the sleeve  306  is held in the open position by the ratchet lock ring  322  regardless of subsequent changes in the pressure differential. 
     Alternately, the RFV  300  may be opened by engaging the inner diameter profile  323  in the sleeve  306  with any one of several commonly available wireline or coiled tubing tools (not shown). Applying a downward force to the sleeve  306  shears the shear screws  314  and releases the snap ring  318 . The spring  320  then pushes the sleeve  306  away from the ports  305  into the open position as described above. The wireline or coiled tubing tool is then released from the inner diameter profile  323  and removed from the well. 
     Two additional valves are utilized in different embodiments of the isolation strings of the present invention. The valves are placed in an isolation tube, which may be wire wrapped or placed adjacent a production screen as discussed below. One of the valves is pressure activated while the other is object activated. 
     Referring to  FIGS. 6A–6D , there is shown a Pressure Activated Control Valve (PACV) in a production tubing assembly  110 . The production tubing assembly  110  is mated in a conventional manner and will only be briefly described herein. Assembly  110  includes isolation pipe  140  that extends above the assembly and a production screen assembly  112  with the PACV assembly  108  controlling fluid flow through the screen assembly. In this illustration, the production screen assembly  112  is mounted on the exterior of PACV assembly  108 . PACV assembly  108  is interconnected with isolation pipe  140  at the uphole end by threaded connection  138  and seal  136 . Similarly on the downhole end  169 , PACV assembly  108  is interconnected with isolation tubing extension  113  by threaded connection  122  and seal  124 . In the views shown, the production tubing assembly  110  is disposed in well casing  111  and has inner tubing  114 , with an internal bore  115 , extending through the inner bore  146  of the assembly. 
     A PACV is a type of radial flow valve. The production tubing assembly  110  illustrates a single embodiment of a PACV, however, it is contemplated that the PACV assembly may have uses other than at a production zone and may be mated in combination with a wide variety of elements as understood by a person skilled in the art. Further, while only a single isolation valve assembly is shown, it is contemplated that a plurality of such valves may be placed within the production screen depending on the length of the producing formation and the amount of redundancy desired. Moreover, although an isolation screen is disclosed, it is contemplated that the screen may include any of a variety of external or internal filtering mechanisms including but not limited to screens, sintered filters, and slotted liners. Alternatively, the PACV assembly may be placed without any filtering mechanisms. 
     Referring now more particularly to PACV assembly  108 , there is shown outer sleeve upper portion  118  joined with an outer sleeve lower portion  116  by threaded connection  128 . Outer sleeve upper portion  118  includes a plurality of production openings  160  for the flow of fluid from the formation when the valve is in an open configuration. For the purpose of clarity in the drawings, these openings have been shown at a 45° inclination. Outer sleeve upper portion  118  also includes through bores  148  and  150 . Disposed within bore  150  is shear pin  151 , described further below. The outer sleeve assembly has an outer surface and an internal surface. On the internal surface, the outer sleeve upper portion  118  defines a shoulder  188  (see  FIG. 6C ) and an area of reduced wall thickness extending to threaded connection  128  resulting in an increased internal diameter between shoulder  188  and connection  128 . Outer sleeve lower portion  116  further defines internal shoulder  189  and an area of reduced internal wall thickness extending between shoulder  189  and threaded connection  122 . Adjacent threaded connection  138 , outer sleeve portion  118  defines an annular groove  176  adapted to receive a locking ring  168 . 
     Disposed within the outer sleeves is inner sleeve  120 . Inner sleeve  120  includes production openings  156  which are sized and spaced to correspond to production openings  160 , respectively, in the outer sleeve when the valve is in an open configuration. Inner sleeve  120  further includes relief bores  154  and  142 . On the outer surface of inner sleeve there is defined a projection defining shoulder  186  and a further projection  152 . Further inner sleeve  120  includes a portion  121  having a reduced external wall thickness. Portion  121  extends down hole and slidably engages production pipe extension  113 . Adjacent uphole end  167 , inner sleeve  120  includes an area of reduced external diameter  174  defining a shoulder  172 . 
     In the assembled condition shown in  FIGS. 6A–6D , inner sleeve  120  is disposed within outer sleeves  116  and  118 , and sealed thereto at various locations. Specifically, on either side of production openings  160 , seals  132  and  134  seal the inner and outer sleeves. Similarly, on either side of shear pin  151 , seals  126  and  130  seal the inner sleeve and outer sleeve. The outer sleeves and inner sleeve combine to form a first chamber  155  defined by shoulder  188  of outer sleeve  118  and by shoulder  186  of the inner sleeve. A second chamber  143  is defined by outer sleeve  116  and inner sleeve  120 . A spring member  180  is disposed within second chamber  143  and engages production tubing  113  at end  182  and inner sleeve  120  at end  184 . A lock ring  168  is disposed within recess  176  in outer sleeve  118  and retained in the recess by engagement with the exterior of inner sleeve  120 . Lock ring  168  includes a shoulder  170  that extends into the interior of the assembly and engages a corresponding external shoulder  172  on inner sleeve  120  to prevent inner sleeve  120  from being advanced in the direction of arrow  164  beyond lock ring  168  while it is retained in groove  176 . 
     The PACV assembly has three configurations as shown in  FIGS. 6A–8E . In a first configuration shown in  FIGS. 6A–6D , the production openings  156 , in inner sleeve  120  are axially spaced from production openings  160  along longitudinal axis  190 . Thus, PACV assembly  108  is closed and restricts flow through screen  112  into the interior of the production tubing. The inner sleeve is locked in the closed configuration by a combination of lock ring  168  which prevents movement of inner sleeve  120  up hole in the direction of arrow  164  to the open configuration. Movement down hole is prevented by shear pin  151  extending through bore  150  in the outer sleeve and engaging an annular recess in the inner sleeve. Therefore, in this position the inner sleeve is in a locked closed configuration. 
     In a second configuration shown in  FIGS. 7A–7D , shear pin  151  has been severed and inner sleeve  120  has been axially displaced down hole in relation to the outer sleeve in the direction of arrow  166  until external shoulder  152  on the inner sleeve engages end  153  of outer sleeve  116 . The production openings of the inner and outer sleeves continue to be axial displaced to prevent fluid flow therethrough. With the inner sleeve axial displaced down hole, lock ring  168  is disposed adjacent reduced outer diameter portion  174  of inner sleeve  120  such that the lock ring may contract to a reduced diameter configuration. In the reduced diameter configuration shown in  FIG. 7 , lock ring  168  may pass over recess  176  in the outer sleeve without engagement therewith. Therefore, in this configuration, inner sleeve is in an unlocked position. 
     In a third configuration shown in  FIGS. 8A–8E , inner sleeve  120  is axially displaced along longitudinal axis  190  in the direction of arrow  164  until production openings  156  of the inner sleeve are in substantial alignment with production openings  160  of the outer sleeve. Axial displacement is stopped by the engagement of external shoulder  186  with internal shoulder  188 . In this configuration, PACV assembly  108  is in an open position. 
     In the operation of a preferred embodiment, at least one PACV is mated with production screen  112  and, production tubing  113  and  140 , to form production assembly  110 . The production assembly according to  FIG. 4  with the PACV in the locked-closed configuration, is then inserted into casing  111  until it is positioned adjacent a production zone (not shown). When access to the production zone is desired, a predetermined pressure differential between the casing annulus  144  and internal annulus  146  is established to shift inner sleeve  120  to the unlocked-closed configuration shown in  FIG. 7 . It will be understood that the amount of pressure differential required to shift inner sleeve  120  is a function of the force of spring  180 , the resistance to movement between the inner and outer sleeves, and the shear point of shear pin  151 . Thus, once the spring force and resistance to movement have been overcome, the shear pin determines when the valve will shift. Therefore, the shifting pressure of the valve may be set at the surface by inserting shear pins having different strengths. 
     A pressure differential between the inside and outside of the valve results in a greater amount of pressure being applied on external shoulder  186  of the inner sleeve than is applied on projection  152  by the pressure on the outside of the valve. Thus, the internal pressure acts against shoulder  186  to urge inner sleeve  120  in the direction of arrow  166  to sever shear pin  151  and move projection  152  into contact with end  153  of outer sleeve  116 . It will be understood that relief bore  148  allows fluid to escape the chamber formed between projection  152  and end  153  as it contracts. In a similar fashion, relief bore  142  allows fluid to escape chamber  143  as it contracts during the shifting operation. After inner sleeve  120  has been shifted downhole, lock ring  168  may contract into the reduced external diameter of inner sleeve positioned adjacent the lock ring. Often, the pressure differential will be maintained for a short period of time at a pressure greater than that expected to cause the down hole shift to ensure that the shift has occurred. This is particularly important where more than one valve according to the present invention is used since once one valve has shifted to an open configuration in a subsequent step, a substantial pressure differential is difficult to establish. 
     The pressure differential is removed, thereby decreasing the force acting on shoulder  186  tending to move inner sleeve  120  down hole. Once this force is reduced or eliminated, spring  180  urges inner sleeve  120  into the open configuration shown in  FIG. 6 . Lock ring  168  is in a contracted state and no longer engages recess  176  such the ring now slides along the inner surface of the outer sleeve. In a preferred embodiment spring  180  has approximately 300 pounds of force in the compressed state in  FIG. 7 . However, varying amounts of force may be required for different valve configurations. Moreover, alternative sources other than a spring may be used to supply the force for opening. As inner sleeve  120  moves to the open configuration, relief bore  154  allows fluid to escape chamber  155  as it is contracted, while relief bores  148  and  142  allow fluid to enter the connected chambers as they expand. 
     Shown in  FIG. 8E  is a cross-sectional, diagrammatic view taken along line A—A of  FIG. 8C  showing the full assembly. 
     Although only a single preferred PACV embodiment of the invention has been shown and described in the foregoing description, numerous variations and uses of a PACV according to the present invention are contemplated. As examples of such modification, but without limitation, the valve connections to the production tubing may be reversed such that the inner sleeve moves down hole to the open configuration. In this configuration, use of a spring  180  may not be required as the weight of the inner sleeve may be sufficient to move the valve to the open configuration. Further, the inner sleeve may be connected to the production tubing and the outer sleeve may be slidable disposed about the inner sleeve. A further contemplated modification is the use of an internal mechanism to engage a shifting tool to allow tools to manipulate the valve if necessary. In such a configuration, locking ring  168  may be replaced by a moveable lock that could again lock the valve in the closed configuration. Alternatively, spring  180  may be disengageable to prevent automatic reopening of the valve. 
     Further, use of a PACV is contemplated in many systems. One such system is the ISO system is described in U.S. Pat. No. 5,609,204; the disclosure therein is hereby incorporated by reference. A tool shiftable valve may be utilized within the production screens to accomplish the gravel packing operation. Such a valve could be closed as the crossover tool string is removed to isolate the formation. The remaining production valves adjacent the production screen may be pressure actuated valves such that inserting a tool string to open the valves is unnecessary. 
     In some embodiments of the invention, a ball holding service tool is used to drop a drop ball on an IFV to manipulate the IFV. Two different ball holding service tools are illustrated below. 
     Referring now to  FIGS. 9A–11B , side views of a ball holding service tool  800  are shown. In  FIGS. 9A–9B , the ball holding service tool  800  is shown in a run-in position with a ball  808  retained. In  FIGS. 10A–10B , the ball holding service tool  800  is shown in a manipulation position with the ball  808  retained. In  FIGS. 11A–11B , the ball holding service tool  800  is shown in a release position with the ball  808  being ejected from the tool. 
     The ball holding service tool  800  comprises basic components including a support string  802 , a lock sleeve  804 , a plunger  806 , and a drop ball  808 . The inside section  802  does not move. As shown in  FIGS. 10A–10B , the lock sleeve  804  is held in a fixed, run-in, position relative to the support string  802  by a shear pin  810 . Further, the drop ball  808  is retained in the ball holding service tool  800  by lock dogs  812 . In the run-in position, the lock dogs  812  are held in a radial inward position by the lock sleeve  804 , so that the lock dogs  812  protrude into the interior of the support string  802  to support the drop ball  808 . The drop ball is held firmly against the lock dogs  812  by the plunger  806 , which is biased in the direction of the drop ball by a spring  814 . 
     Mandrel lock dogs  805  are mounted on the lock sleeve. The mandrel lock dogs  805  have a locking pin  807  which projects inward. When the lock sleeve  804  is in a close fitting bore (see  FIG. 10A ), the mandrel lock dogs  805  are pushed inward which pushes the locking pins  807  into one of grooves  809 ,  811 , or  813  on the support string  802 . When the locking pins  807  are in any one of the three grooves  809 ,  811 , or  813  on the support string  802 , no relative movement is possible between the support string  802  and the lock sleeve  804 . 
     As shown in  FIGS. 10A–10B , the ball holding service tool  800  is manipulated by sliding the lock sleeve  804  relative to the support string  802 . Of course, the shear pin  810  must be sheared to release the lock sleeve  804 . In the position shown, the lock sleeve  804  has moved relative to the support string  802 , but it has not moved a sufficient distance to release the lock dogs  812 . The lock sleeve  804  has an annular recess groove  816  with beveled shoulders. 
     The lock sleeve  804  is additionally controlled by pin  815  which extends into groove  821  in support string  802 . A laid-out side view of groove  821  is shown in  FIG. 9C , wherein the pin  815  is shown in three separate positions withing groove  821 . Groove  821  in support string  802  is configured so that the lock sleeve  804  must be reciprocated one or more times before the lock sleeve  804  can move far enough to align recess groove  816  with lock dogs  812 . 
     As shown in  FIGS. 11A–11B , when the recess groove  816  becomes aligned with the lock dogs  812 , the lock dogs  812  are free to move radially outward. With the lock dogs  812  no longer constrained, the spring-loaded plunger  806  pushes the drop ball  808  through the lock dogs  812  so as to eject the drop ball  808  from the ball holding service tool  800 . 
     Referring now to  FIGS. 12A–16E , side views of a second embodiment of a ball holding service tool  800  are shown with a cross over tool and packer. In  FIGS. 12A–12E , the ball holding service tool  800  is shown in a run-in position with a drop ball  808  retained. In  FIGS. 13A–13E , the ball holding service tool  800  is shown in a manipulation position with a dog retainer ring  820  sheared. In  FIGS. 14A–14E , the ball holding service tool  800  is shown in a lock dog  812  release position. In  FIGS. 15A–15E , the ball holding service tool  800  is shown in a ball retainer ring  824  shear position. In  FIGS. 16A–16E , the ball holding service tool  800  is shown in a drop ball  808  release position. 
     In the run in configuration as shown in  FIGS. 12A–12E , the drop ball  808  is secured firmly in the ball holding services tool  800 . The drop ball  808  is a ball with a long tail, wherein the tail is secured by the service tool. The ball holding service tool  800  has a holding barrel  826  into which the tail of the drop ball  808  is inserted. The service tool also has an ejector mandrill  827  which is spring loaded. In particular, the ejector mandrell  827  is biased toward the drop ball  808  by spring  828 . The drop ball  808  is held in its loaded position against the spring force by a plurality of balls  829 . The drop ball  808  has a groove in its tail, wherein the balls  829  extend into the groove to hold the drop ball  808  in the holding barrel  826 . The balls  829  are pushed into the groove of the drop ball  808  by a ball retainer ring  824 . The ball retainer ring  824  is secured to the holding barrel  826  by shear screws  830 . The ball holding service tool  800  also has a collet  831  which is squeezed into the crossover tool and packer. Because the collet  831  is made of flexible members, its outside diameter gets smaller as it is squeezed into the crossover tool and packer. 
     To manipulate the ball holding service tool  800 , the service tool is inserted into the crossover tool and packer until the collet  831  has cleared a shoulder  832  as shown in  FIG. 13D . With the collet  831  below the shoulder  832 , the ball holding service tool  800  is pulled uphole while the collet  831  remains stationery relative to the crossover tool and packer. As the remainder of the ball holding service tool  800  moves uphole relative to the stationery collet  831 , the collet  831  drives a push ring  833  to engage dog retainer ring  820 , as shown in  FIG. 13B . A plurality of lock dogs  812  are positioned in a groove around the periphery of the holding barrel  826 . The lock dogs  812  are held in the groove by the dog retainer ring  820 . As shown in  FIG. 13B , the push ring  833  pushes the dog retainer ring  820  to shear screws  834  which are initially screwed between the dog retainer ring  820  and the holding barrel  826 . As shown in  FIG. 13B , the shear screws  834  are sheared and the dog retainer ring  820  is displaced from its position around the periphery of the lock dogs  812 . 
     From the configuration shown in  FIGS. 13A–13E , the ball holding service tool  800  is pulled further uphole to the position shown in  FIGS. 14A–14E . In particular, the ball holding service tool  800  is brought to a position wherein the collet  831  is just above a shoulder  835  of the crossover tool and packer. As the ball holding service tool  800  is again run into the crossover tool and packer, the collet  831  remains stationery against the shoulder  835  so that the push ring  833  remains stationary relative to the downwardly moving holding barrel  826 . As shown in  FIG. 14C , this relative movement moves the lock dogs  812  out from under the push ring  833 . The lock dogs  812  are biased in an uphole direction by a spring  836  such that upon being released by the push ring  833 , the lock dogs  812  pop out of the groove in the holding mandrell  826 . 
     Once the lock dogs  812  are released, the ball holding service tool  800  is pulled uphole until the lock dogs  812  are above the shoulder  835  of the crossover tool and packer. The ball holding service tool  800  is then run downhole into the crossover tool and packer, to the position shown in  FIGS. 15A–15E . In this position, the lock dogs  812  engage a smaller shoulder  837  of the crossover tool and packer. This smaller shoulder  837  holds the lock dogs  812  stationery while the crossover tool continues downhole. The lock dogs  837  work against the ball retaining ring  824  as shown in  FIG. 15E . Shear screws  838  extend from the ball retaining ring  824  into the holding barrel  826 . As the holding mandrell  826  continues downhole, so that the shear screws  838  are eventually sheared. 
     The mandrell  826  continues to move downhole to a position shown in  FIGS. 16A–16E . In this position, the ball retainer ring  824  is moved relative to the holding barrel  826  such that a portion of the ball retainer ring  824  having a relatively larger inside diameter is positioned over the balls  829 . Further, the lock dogs  812  position themselves radially inward behind a shoulder  839  to retain the ball retaining ring  824  in its new position. In this configuration, the balls  829  are free to move radially outward so that they are no longer in the groove of the tail section of the drop ball  808 . The energy stored in the spring  828  is then released to drive the ejector mandrell  827  into the holding barrel  826  to expel the drop ball  808  from the end of the holding barrel  826  (see  FIG. 16E ). 
     Another valve used in various embodiments of the present invention is the IFV. Three different embodiments of the IFV are illustrated herein. 
     Referring to  FIGS. 17A–17C , side views of a first embodiment of the IFV are shown, wherein the IFV  1000  is shown in two different configurations on each side of the center line. Above the center line, the valve is shown in an open configuration and below the line, the valve is shown in a closed configuration. The IFV  1000  comprises basic components including: a string  1002 , a sliding sleeve  1004 , and a basket  1007 . 
     The string  1002  comprises several pipe sections made-up to form a single pipe string. The string  1002  also has a string port section  1012  which allows fluid to flow between the outside diameter and the inside diameter. The sliding sleeve  1004  is positioned concentrically within the string  1002 . The sliding sleeve  1004  has seal section  1016  and a sleeve port section  1017 . The basket  1007  has holes  1021  in its lower end to allow fluid to flow between the inside diameter of the sliding sleeve  1004  above the basket  1007  and the inside diameter of the sliding sleeve  1004  below the basket  1007 . The basket  1007  also has a seat upon which a drop ball  808  may land. 
     In the open configuration (shown above the centerline), the sleeve port section  1017  is positioned adjacent the string port section  1012 . The sliding sleeve  1004  is held in this position by shear screws  1013  which extend between the sliding sleeve  1004  and the string  1002 . Also, in the open configuration of the IFV, the basket  1007  is held within the sliding sleeve  1004  by lock dogs  1009  which extend from the sliding sleeve  1004  into a retaining groove  1011  in the basket  1007 . The lock dogs  1009  are held radially inward by the inside diameter of the string  1002 . 
     The IFV  1000  is closed by dropping a drop ball  808  into the valve. The drop ball  808  lands on the seat  1022  in the basket  1007 . The drop ball  808  mates with the seat  1022  to restrict fluid flow from the inside diameter above the valve, down through the basket  1007 . As fluid pressure increases in the inside diameter above the drop ball  808 , a downward force is exerted on the basket  1007 . This downward force is transferred from the basket  1007  to the sliding sleeve  1004  through the lock logs  1009 . The downward force on the sliding sleeve  1004  becomes great enough to shear the shear screws  1013  to release the sliding sleeve  1004  from the string  1002 . Upon shear of the sear screws  1013 , the sliding sleeve  1004  and basket  1007  travel together down the string  1002  to close the valve. In particular, the seal section  1016  becomes positioned over the string port section  1012  to completely restrict the flow of fluid through the string port section  1012 . Seals  1023  are located above and below the string port section  1012  to insure the integrity of the valve. 
     The sliding sleeve  1004  continues its downward movement until the lock dogs  1009  engage a release groove  1010  and the sliding sleeve  1004  bottoms out on shoulder  1024 . The sliding sleeve  1004  is held in the closed position by a ring  1025  (see  FIG. 17A ) which is positioned within a groove  1026  in the string  1002 . Because the leading end of the sliding sleeve  1004  is tapered to sting into the ring  1025 . The sliding sleeve  1004  is pushed into the ring  1025  until the ring snaps into a groove  1027  in the sliding sleeve  1004 . The ring  1025  is retained in both grooves  1026  and  1027  to prevent the sliding sleeve  1004  from moving back into the open position. 
     When the lock dogs  1009  engage the release groove  1010  of the string  1002 , the lock dogs  1009  are released to move radially outward. The lock dogs  1009  move radially outward from a position protruding into the basket  1007 , through the sliding sleeve  1004 , and to a position protruding into the release groove  1010 . This radial movement of the lock dogs  1009  releases the basket  1007  from the sliding sleeve  1004  to allow both the basket  1007  and drop ball  808  to fall freely out the bottom of the IFV. 
     Referring to  FIGS. 18A–19C , side views of a second embodiment of an IFV are shown, wherein the valve is in an open configuration in  FIGS. 19A–19C  and a closed configuration in  FIGS. 18A–18C . The IFV  1000  comprises basic components including: a string  1002  and a sliding sleeve  1004 . The string  1002  comprises several pipe sections made-up to form a single pipe string. The string  1002  has a slip bore  1006  immediately adjacent a release groove  1010 , wherein the slip bore  1006  and the release groove  1010  are separated by a shoulder  1008 . Thus, the internal radius of the slip bore  1006  is smaller than the internal radius of the release groove  1010  such that the difference is the height of the shoulder  1008 . The string  1002  also has a string port section  1012  having a plurality of lengthwise ports evenly spaced around the string  1002 . 
     The sliding sleeve  1004  of the IFV  1000  is positioned coaxially within the string  1002 . The sliding sleeve  1004  is basically comprised of a plurality of cantilever fingers  1014 , a middle seal section  1016 , a sleeve port section  1017 , and an end seal section  1018 . The cantilever fingers  1014  extend from one end of the middle seal section  1016  and are evenly spaced from each other. Each cantilever finger  1014  has a spreader tip  1015  at its distal end. In the open configuration, shown in  FIGS. 19A–19C , the spreader tips  1015  rest on the slip bore  1006  of the string  1002 , and in the closed position, the spreader tips  1015  rest in the release groove  1010  of the string  1002 . When the spreader tips  1015  rest on the slip bore  1006 , the spreader tips define a relatively smaller diameter sufficient to form a seat for catching a drop ball  808 . The middle seal section  1016  has a cylindrical outer surface for mating with annular seals  1019  and  1020 , which are fixed to the string  1002  above and below the string port section  1012 , respectively. In the open position, the middle seal section  1016  mates only with the annular seal  1019 , but in the closed position, the middle seal section  1016  mates with both annular seal  1019  and  1020 . Further, in the closed position, the middle seal section  1016  spans the string port section  1012  (see  FIGS. 18A and 18B ). The sleeve port section  1017  has a plurality of lengthwise ports evenly spaced around the sliding sleeve  1004 . When the IFV  1000  is in an open configuration, the sleeve port section  1017  is adjacent the string port section  1012 . The end seal section  1018  has a cylindrical outer surface for mating with annular seal  1020  when the valve is in an open configuration. To hold the IFV  1000  in the open position, shear pins  1013  (see  FIG. 19B ) are fastened between the spreader tips  1015  and the slip bore  1006 . 
     The IFV  1000  is reconfigured from the open configuration to the closed configuration by dropping a drop ball  808  from a ball holding service tool  800  onto the seat defined by the spreader tips  1015  of the IFV  1000 . The outside diameter of the drop ball  808  is larger than the inside diameter of a circle defined by the interior of the spreader tips  1015 , when the spreader tips  1015  are seated in the slip bore  1006 . Thus, when the drop ball  808  falls on the spreader tips  1015 , the ball is supported by the spreader tips  1015  and does not pass therethrough. The weight of the drop ball and fluid pressure behind the drop ball  808  combine to produce sufficient force to the spreader tips  1015  to shear the shear pins  1013 . Fluid pressure behind the drop ball  808  then pushes the sliding sleeve  1004  until the middle seal section  1016  mates with both annular seals,  1019  and  1020 , and spans the string port section  1012 . At this position, the spreader tips  1015  clear the shoulder  1008  and snap into the release groove  1010  (see  FIG. 18B ). Because the internal radius of the slip bore  1006  is smaller than the internal radius of the release groove  1010 , the inside diameter of a circle defined by the interior of the spreader tips  1015  becomes larger as the spreader tips snap into the release groove  1010 . The cantilever fingers  1014  are prestressed to bias the spreader tips  1015  radially outward. The circle defined by the interior of the spreader tips  1015  becomes large enough to release the drop ball  808  so that the drop ball  808  passes through the IFV  1000  and down into the rat hole of the well (see  FIG. 18A ). The IFV  1000  becomes locked in the closed configuration because the shoulder  1008  prevents the spreader tips  1015  from reversing direction once they have snapped into the release groove  1010 . 
     An alternate embodiment of an IFV  1000  is shown in  FIGS. 20A–20C . This embodiment is very similar to that illustrated above. In  FIGS. 20A–20C , the configuration illustrated above the center line is an open configuration and that illustrated below the center line is a closed configuration. As before, this IFV  1000  has a string port section  1012  in a string  1002 . However, in this embodiment, the sliding sleeve  1004  is basically comprised of a plurality of cantilever fingers  1014  and a seal section  1016 . The cantilever fingers  1014  extend from one end of the seal section  1016  and are evenly spaced from each other. Each cantilever finger  1014  has a spreader tip  1015  at its distal end. In the open configuration, shown above the center line, the spreader tips  1015  rest on the slip bore  1006  of a tube held within the string  1002 . To hold the IFV  1000  in the open position, shear screws  1013  (see  FIG. 20B ) are fastened between the spreader tips  1015  and the tube defining the slip bore  1006 . In the open position, the seal section  1016  and annular seals  1019  and  1020  are positioned above the string port section  1012 . 
     In the closed position, the spreader tips  1015  rest in the release groove  1010  of the string  1002 . When the spreader tips  1015  rest on the slip bore  1006 , the spreader tips define a relatively smaller diameter sufficient to form a seat for catching a drop ball  808 . The seal section  1016  has a cylindrical outer surface with annular seals  1019  and  1020  fixed to the sliding sleeve  1004  at each end of the seal section  1016 . In the closed position, the seal section  1016  spans the string port section  1012  and annular seal  1019  and  1020  contact the string  1002  on either side to ensure the integrity of the closed valve. The sleeve port section  1017  has a plurality of lengthwise ports evenly spaced around the sliding sleeve  1004 . 
     To manipulate the IFV from the open configuration to the closed configuration, a drop ball  808  is used as described with reference to the IFV embodiment illustrated in  FIGS. 19A–19C . 
     Referring to  FIG. 21 , a side view is shown of a fixed isolation string with a PACV and an IFV. The isolation string  1100  has a packer  1101  at its top for securing and sealing the top of the isolation string  1100  in a well casing. It also has a packer  1102  at its bottom for sealing the bottom of the isolation string  1100 . The string further comprises cross-over ports  1103  for use during a gravel pack operation. A portion of a production tube is shown stung into the isolation string  1100  for seating in a seal bore  1104 . A double-pin sub  1105  is made-up to the string below the seal bore  1104 . A screen pipe  1106  and an isolation pipe  1107  are made-up to the bottom of the double-pin sub  1105 . The bottom of the screen pipe  1106  is made up to the packer  1102 . Further, the isolation pipe  1107  is stung into and landed in a seal bore of the packer  1102  to seal the bottom of the isolation pipe  1107 . The screen pipe  1106  has a production screen  1108  around a perforated base pipe section  1109 . The isolation pipe  1107  has two valves: a PACV  1110  and an IFV  1111 . 
     The isolation system illustrated in  FIG. 21  may be used to complete a well. The isolation string  1100  is run-in the well on a cross-over service tool and set in the casing with the production screen  1108  adjacent perforations in the casing. When the isolation string  1100  is run-in the well, the PACV  1110  is closed and the IFV  1111  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1103  to deposit the gravel pack in the annulus between the production screen  1108  and the casing, while the filtered suspension fluid is circulated through the open IFV  1111 . When the gravel pack operation is complete a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1111  to close the valve and isolate the gravel packed production zone. The service tool is then released from the isolation string  1100  and withdrawn from the well. A production string is then run-in the well and stung into the isolation string  1100 . Pressure differential between the inner bore and the annulus is then used to open the PACV  1110  to bring the well into production. 
     Referring to  FIG. 22 , a side view is shown of a screen wrapped isolation string with a PACV and an IFV. The isolation string  1200  has a packer  1201  at its top for securing and sealing the top of the isolation string  1200  in a well casing. It also has a packer  1202  at its bottom for sealing the bottom of the isolation string  1200 . The string further comprises cross-over ports  1203  for use during a gravel pack operation. A portion of a production tube is shown stung into the isolation string  1200  for seating in a seal bore  1204 . A safety shear sub  1205  is made-up to the string below the seal bore  1204 . A blank pipe  1206  is made-up to the bottom of the safety shear sub  1205 . The bottom of the blank pipe  1206  is made up to the packer  1202 . The blank pipe  1206  has two valves: a PACV  1210  and an IFV  1211 . A wire wrap production screen  1208  is wrapped around the blank pipe  1206 , the PACV  1210 , and the IFV  1211 . 
     The isolation system illustrated in  FIG. 22  may be used to complete a well. The isolation string  1200  is run-in the well on a cross-over service tool and set in the casing with the production screen  1108  adjacent perforations in the casing. The cross-over service tool is not shown in  FIG. 22 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . When the isolation string  1200  is run-in the well, the PACV  1210  is closed and the IFV  1211  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1203  to deposit the gravel pack in the annulus between the production screen  1208  and the casing, while the filtered suspension fluid is circulated through the open IFV  1211 . When the gravel pack operation is complete a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1211  to close the valve and isolate the gravel packed production zone. The service tool is then released from the isolation string  1200  and withdrawn from the well. A production string is then run-in the well and stung into the isolation string  1200 . Pressure differential between the inner bore and the annulus is then used to open the PACV  1210  to bring the well into production. 
     Referring to  FIG. 23 , a side view is shown of a lower zone isolation string with a RFV and an IFV. The isolation string  1300  has a packer  1301  at its top for securing and sealing the top of the isolation string  1300  in a well casing. It also has a packer  1302  at its bottom for sealing the bottom of the isolation string  1300 . The string further comprises cross-over ports  1303  for use during a gravel pack operation. A portion of a production tube is shown stung into the isolation string  1300  for seating in a seal bore  1304 . A safety shear sub  1305  is made-up to the string below the seal bore  1304 . A RFV  1312  is made up to the bottom of the safety shear sub  1305  and is pressure activated to open and allow fluids to flow radially from an annulus below the RFV  1312 . Both a screen pipe  1306  and an isolation pipe  1307  are made-up to the bottom of the RFV  1312 . The bottom of the screen pipe  1306  is made up to the packer  1302 . Further, the isolation pipe  1307  is stung into and landed in a seal bore of the packer  1302  to seal the bottom of the isolation pipe  1307 . The screen pipe  1306  has a production screen  1308  around a perforated base pipe section  1309 . The isolation pipe  1307  has an IFV  1311 . 
     The isolation system illustrated in  FIG. 23  may be used to complete a well. The isolation string  1300  is run-in the well on a cross-over service tool and set in the casing with the production screen  1308  adjacent perforations in the casing. The cross-over service tool is not shown in  FIG. 23 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . When the isolation string  1300  is run-in the well, the RFV  1312  is closed and the IFV  1311  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1303  to deposit the gravel pack in the annulus between the production screen  1308  and the casing, while the filtered suspension fluid is circulated through the open IFV  1311 . When the gravel pack operation is complete, a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1311  to close the valve and isolate the gravel packed production zone. The service tool is then released from the isolation string  1300  and withdrawn from the well. A production string is then run-in the well and stung into the RFV  1312 . Pressure differential between the inner bore and the annulus is then used to open the RFV  1312  to bring the well into production. 
     Referring to  FIG. 24 , a side view is shown of a dual-zone, selective isolation string with AFV, a RFV, and two IFV. The isolation string  1400  has a top packer  1401  at its top for securing and sealing the top of the isolation string  1400  in a well casing. It also has a bottom packer  1402  at its bottom for sealing the bottom of the isolation string  1400 . Further, the string has a middle packer  1413  for sealing the annulus between upper and lower zones. The string further comprises cross-over ports  1403   a  and  1403   b  for use during gravel pack operations. A safety shear sub  1405   a  is made-up to the string below a seal bore  1404   a . An AFV  1414  is made up to the bottom of the safety shear sub  1405   a  and is pressure activated to open and allow fluids to flow from an annulus below the valve  1414  to an annulus above. A portion of a production tube is shown stung into the AFV  1414 . Both a screen pipe  1406   a  and an isolation pipe  1407   a  are made-up to the bottom of the AFV  1414 . The bottom of the screen pipe  1406   a  is stung into and landed out in a seal bore  1404   b  below the middle packer  1413 . Further, the isolation pipe  1407   a  is stung into and landed in a seal bore of a RFV  1412  to seal the bottom of the isolation pipe  1407   a . The screen pipe  1406   a  has a production screen  1408   a  around a perforated base pipe section  1409   a . The isolation pipe  1407   a  has a IFV  1411   a . A safety shear sub  1405   b  is made-up to the string below the seal bore  1404   b . The RFV  1412  is made up to the bottom of the safety shear sub  1405   b  and is pressure activated to open and allow fluids to flow radially from an annulus below the valve  1412  to the inner bore of the valve. Both a screen pipe  1406   b  and an isolation pipe  1407   b  are made-up to the bottom of the RFV  1412 . The bottom of the screen pipe  1406   b  is stung into and landed out in the lower packer  1402 . Further, the isolation pipe  1407   b  is stung into and landed in a seal bore of the lower packer  1402  to seal the bottom of the isolation pipe  1407   b . The screen pipe  1406   b  has a production screen  1408   b  around a perforated base pipe section  1409   b . The isolation pipe  1407   b  has a IFV  1411   b.    
     The isolation system illustrated in  FIG. 24  may be used to complete two production zones in a well. The isolation string  1400  is run-in the well on a cross-over service tool in two separate trips. The lower section  1400   b  of the isolation string  1400  is run-in the well and set in the casing with the production screen  1408   b  adjacent perforations for the lower zone in the casing. The cross-over service tool is not shown in  FIG. 24 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . When the upper section  1400   a  of the isolation string  1400  is run-in the well, the RFV  1412  is closed and the IFV  1411   b  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1403   b  to deposit the gravel pack in the annulus between the production screen  1408   b  and the casing, while the filtered suspension fluid is circulated through the open IFV  1411   b . When the gravel pack operation is complete, a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1411   b  to close the valve and isolate the gravel packed lower production zone. The service tool is then released from the lower section  1400   b  of the isolation string  1400  and withdrawn from the well. 
     In a second trip into the well, the upper section  1400   a  of the isolation string  1400  is run-in the well and set in the casing with the production screen  1408   a  adjacent perforations for the upper zone in the casing. The distal end of the upper section  1400   a  is stung into the lower section  1400   b . In particular, the screen pipe  1406   a  is stung into the middle packer  1413  and the isolation pipe  1407   a  is stung into the RFV  1412 . The cross-over service tool is not shown in  FIG. 24 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . Of course, before running into the well for this second trip, the ball drop service tool  800  is charged with a second drop ball  808 . When the upper section  1400   a  of the isolation string  1400  is run-in the well, the AFV  1414  is closed and the IFV  1411   a  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1403   a  to deposit the gravel pack in the annulus between the production screen  1408   a  and the casing, while the filtered suspension fluid is circulated through the open IFV  1411   a . When the gravel pack operation is complete, a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1411   a  to close the valve and isolate the gravel packed production zone. The service tool is then released from the upper section  1400   a  of the isolation string  1400  and withdrawn from the well. 
     A production string is then run-in the well and stung into the AFV  1414 . Pressure differential between the inner bore and the annulus is then used to open the AFV  1414  and RFV  1412  to bring the well into production. The upper zone production flows through the annulus on the outside of the production string to the surface. The lower zone production flows through the inner bore of the production string to the surface. 
     Referring to  FIG. 25 , a side view is shown of a dual-zone, selective isolation string with an AFV and an IFV for the upper zone, and an IFV and a PACV for the lower zone. The isolation string  1500  has a top packer  1501  at its top for securing and sealing the top of the isolation string  1500  in a well casing. It also has a bottom packer  1502  at its bottom for sealing the bottom of the isolation string  1500 . Further, the string has a middle packer  1513  for sealing the annulus between upper and lower zones. The string further comprises cross-over ports  1503   a  and  1503   b  for use during gravel pack operations. A safety shear sub  1505   a  is made-up to the string below a seal bore  1504   a . An AFV  1514  is made up to the bottom of the safety shear sub  1505   a  and is pressure activated to open and allow fluids to flow from an annulus below the valve  1514  to an annulus above. A portion of a production tube is shown stung into the AFV  1514 . Both a screen pipe  1506   a  and an isolation pipe  1507  are made-up to the bottom of the AFV  1514 . The bottom of the screen pipe  1507  is stung into and landed out in a seal bore  1504   b  below the middle packer  1513 . Further, the isolation pipe  1507  is stung into and landed in a seal bore of the screen pipe  1506   a  to seal the bottom of the isolation pipe  1507 . The screen pipe  1506   a  has a production screen  1508   a  around a perforated base pipe section  1509 . The isolation pipe  1507  has an IFV  1511   a . A safety shear sub  1505   b  is made-up to the string below the seal bore  1504   b . A blank screen pipe  1506  is made-up to the bottom of the safety shear sub  1505   b . The bottom of the blank screen pipe  1506  is made up to the lower packer  1502 . The blank screen pipe  1506  has two valves: a PACV  1510  and an IFV  1511   b . A wire wrap production screen  1508   b  is wrapped around the blank screen pipe  1506   b , the PACV  1510 , and the IFV  1511   b.    
     The isolation system illustrated in  FIG. 25  may be used to complete a well. The isolation string  1500  is run into the well in two separate trips. The lower section  1500   b  of the isolation string  1500  is run-in the well and set in the casing with the production screen  1508   b  adjacent perforations for the lower zone in the casing. The lower section  1500   b  of the isolation string  1500  is run-in the well on a cross-over service tool and set in the casing with the production screen  1508   b  adjacent the lower zone perforations in the casing. The cross-over service tool is not shown in  FIG. 25 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . When the lower section  1500   b  is run-in the well, the PACV  1510  is closed and the IFV  1511   b  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1503   b  to deposit the gravel pack in the annulus between the production screen  1508   b  and the casing, while the filtered suspension fluid is circulated through the open IFV  1511   b . When the gravel pack operation is complete a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1511   b  to close the valve and isolate the gravel packed lower production zone. The service tool is then released from the lower section  1500   b  of the isolation string  1500  and withdrawn from the well. 
     In a second trip into the well, the upper section  1500   a  of the isolation string  1500  is run-in the well and set in the casing with the production screen  1508   a  adjacent perforations for the upper zone in the casing. The distal end of the upper section  1500   a  is stung into the lower section  1500   b . In particular, the screen pipe  1506   a  is stung into the middle packer  1513  and the isolation pipe  1507  is already stung into the distal end of the isolation pipe  1507 . The cross-over service tool is not shown in  FIG. 25 , but it has a ball drop service tool  800  as shown in  FIGS. 9A–16E . Of course, before running into the well for this second trip, the ball drop service tool  800  is charged with a second drop ball  808 . When the upper section  1500   a  of the isolation string  1500  is run-in the well, the AFV  1514  is closed and the IFV  1511   a  is open. A gravel pack operation is performed by circulating a slurry through cross-over ports  1503   a  to deposit the gravel pack in the annulus between the production screen  1508   a  and the casing, while the filtered suspension fluid is circulated through the open IFV  1511   a . When the gravel pack operation is complete, a drop ball  808  is dropped from the service tool having a ball holding service tool  800  (see  FIGS. 9A–16E ). The drop ball  808  operates on the IFV  1511   a  to close the valve and isolate the gravel packed upper production zone. The service tool is then released from the upper section  1500   a  of the isolation string  1500  and withdrawn from the well. 
     A production string is then run-in the well and stung into the AFV  1514  of the isolation string  1500 . Pressure differential between the inner bore and the annulus is then used to open the AFV  1514  and the PACV  1510  to bring the well into production. Production from the upper zone flows through the annulus around the production pipe and production from the lower zone flows through the inner bore of the production pipe. 
     Many of the components described herein are generally available from industry sources as known to persons of skill in the art. For example, packers, cross-over ports, double-pin subs, screen pipe, isolation pipe, production screens, and other components which are generally known to persons of skill in the art may be used in the various embodiments of the present invention. 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the claims.