Abstract:
Multiple producing zones separated by a non-producing zone are gravel packed together. The non-producing zone has locations to take returns so as to get a consistent pack in the non-producing zone. The production string features external seals and/or an internal plug so that no matter which producing zone is aligned to produce, the screens in the non-producing zone are selectively isolated so that the producing zone that is not intended to be produced has only the path through the gravel pack to get to the actual zone being produced. Since the annulus can be long and full of gravel this path will make flow from the zone that is not of interest minimal into the flow from the zone of interest without using a packer between pairs of spaced apart producing zones.

Description:
FIELD OF THE INVENTION 
     The field of the invention is multi-zone subterranean completions and more particularly those that are performed in a single trip where the gravel itself rather than an external packer provides zonal isolation. 
     BACKGROUND OF THE INVENTION 
     Producing zone completions involve insertion of a screen assembly that can be as long as several pay zones with long non-producing formations in between the producing zones. The surrounding annulus around the screens is filled with gravel using a tool called a crossover tool that takes the gravel slurry coming down the tubing string from the surface and redirects it out to the annular space below an isolation packer and outside the screen. The gravel remains in the annular space outside the screens while the carrier fluid goes through the screen and into a wash pipe connected to the crossover. The crossover allows the returning fluid to get through the isolation packer and back to the surface through the upper annular space above the isolation packer. 
     If the producing zones are far apart, the length of borehole between them is spanned by blank pipe and a packer that allows the screen sections to be properly located at the various producing locations. Typically the delivered gravel goes to the furthest (lowest) screen downhole and fills the annulus around it. When that screen is covered, the crossover tool and wash pipe are shifted to allow the setting of a packer in the annulus (between the two zones) to fully isolate the lower zone before further gravel deposition fills the non-producing zone. After the packer is set, pumping of the slurry is resumed, and gravel is deposited on top of the packer, while the returning fluid finds another path of least resistance and starts going through the next higher production screen as the lowermost screen now fully surrounded by gravel is said to “screen out” or resist flow to an extent that sends the returns to the next higher screen. This technique is illustrated in IACC/SPE 77214 by Corbett and Vickery entitled Multiple Zone Open Hole Gravel Packing Techniques with Zonal Isolation. It is limited to separating two zones with a packer in a single trip but is impractical for more than two zones. 
     US Publication 2008/0164026 shows a method of gravel packing multiple zones together and then setting packers into the gravel pack to isolate the producing zones. 
     What is needed and not available is a way to more economically perform a gravel pack of multiple zones that are spaced apart and get a good pack in an intervening non-producing zone while getting effective zonal isolation in the pack between the producing zones without employing packers. Those skilled in the art will appreciate each of the aspects of the present invention, some of which are individually listed above, from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims. 
     SUMMARY OF THE INVENTION 
     Multiple producing zones separated by a non-producing zone are gravel packed together. The non-producing zone has locations to take returns so as to get a consistent pack in the non-producing zone. The production string features external seals and/or an internal plug so that no matter which producing zone is aligned to produce, the screens in the non-producing zone are selectively isolated so that the producing zone that is not intended to be produced has only the path through the gravel pack to get to the actual zone being produced. Since the annulus can be long and full of gravel this path will make flow from the zone that is not of interest minimal into the flow from the zone of interest without using a packer between pairs of spaced apart producing zones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows two producing zones with a non-producing zone in between where the annulus is fully gravel packed; 
         FIG. 2  is the lower part of the production string that fits into the completion in  FIG. 2  to isolate the screens in the non-producing zone and to make access between zones A and C possible only through the gravel pack in the annulus; 
         FIG. 3  shows the start of the gravel pack in zone C; 
         FIG. 4  is the view of  FIG. 3  with the zone C gravel pack finished; 
         FIG. 5  is the view of  FIG. 4  with the start of gravel packing zone B with returns coming through the screen in location  7 ; 
         FIG. 6  is the view of  FIG. 5  with the gravel pack advanced beyond the screen in zone  7 ; 
         FIG. 7  is the view of  FIG. 6  with the gravel pack advanced beyond the screen in zone  5 ; 
         FIG. 8  is the view of  FIG. 7  with the gravel pack advanced into the producing zone A. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows producing zone A separated from producing zone C by non-producing zone B. The entire illustrated wellbore is divided into regions  1 - 10  to simplify the discussion of how the gravel packing will proceed. It should be noted that while two producing zones A and C are shown separated by a non-producing zone B, the pattern can repeat and the distance between producing zones can vary and can be many meters down to a very small gap. The basic idea is to limit cross flow between zones A and C when only one is desired to be produced without using barriers in the annulus  12  below the production packer  14 . The annulus  12  is filled with gravel  16 . If only one of zones A and C are aligned to produce such as, for example if zone A is aligned to produce as indicated by arrows  18  and  20 , any flow from zone C indicated by arrows  22  and  24  will only be able to reach zone A through the annulus  12 , as indicated by arrows  26 . Zone C will not flow into producing screen  28  because the production string  30  can have a plug  32  at its lower end  34  when the string  30  has its lower end shown in  FIG. 2  inserted into a sealing relationship with the production packer  14  shown in  FIG. 1 . The string  30  has a sliding sleeve  38  to selectively cover port  40 . The sleeve  38  can be initially in the desired position and can be shifted with a known shifting tool either initially to open it as well as subsequently to close it to isolate any desired zone for a variety of reasons, such as when it produces excess water, for example. When the string  30  is inside packer  14 , the ported sub  36  is opposite screen  42  in zone A. If it is known from the beginning that zone A is to be produced first, the port  40  can be run in open and the plug  32  in position at the lower end  34  of the string  30 . While attaining a no flow condition from zone C to zone A when producing only from zone A would be ideal, there may be some minimal amount of infiltration from zone C to zone A through the gravel  16  in annulus  12 . The flow resistance between the producing formations A and C depends on many variables such as the distance between them, the density of the packed gravel, the fluid viscosity and the gravel particle size and void volume, to name a few variables. 
     One of the features of the invention is to get a good gravel pack in the zone B. Normally, there is just blank pipe and a packer between producing screens  28  and  42  in prior systems. This mean that when the gravel gets to the point of causing screen  28  to screen out, the slurry fluid that carries the gravel has to return to the surface from screen  42  as it then becomes the path of least fluid resistance. What this means is that gravel and carrier fluid separate at screen  42  and the gravel has only gravity to carry it down the annulus  12  below the producing screen  42 . As a result the pack density of the gravel  16  between screens  42  and  28  is not optimally high. 
     In the present invention, there are completion screens such as  44 ,  46  and  48  located respectively at regions  7 ,  5  and  3 . The spacing of these screens and their individual length can vary as can the number of such non-producing zone B seal bores  2 , 4 , 6 , and  8 . The screens  44 ,  46  and  48  should be shorter than the production screens  28  and  42  due to their limited service during gravel packing but they can also be the same size or larger. The objective is that after screen  28  is covered by gravel  16  and the gravel packing continues, that there are enough return locations for the fluid carrying the gravel to return to the surface at different locations so as to continue to use the fluid velocity to carry the gravel  16  into the non-producing zone B as it fills the annulus  12  in a direction from screen  28  to screen  42 .This is shown graphically in  FIGS. 3-8 . In  FIG. 3 , the gravel covers about half of screen  28  and fluid represented by arrow  50  that carried the gravel in annulus  12  passes through the screen  28  and returns to the surface through the packer  14  and a crossover (not shown) through the annulus above the packer  14 . In  FIG. 4  the screen  28  has screened out and the returns represented by arrow  52  enter screen  44  as the gravel  16  builds above the level of screen  28  and into the non-producing zone B. In  FIG. 5  the gravel  16  has reached screen  44 . In  FIG. 6 , screen  44  has screened out and returns represented by arrow now pass through screen  46 . In  FIG. 7 , screen  46  has screened out and returns represented by arrow  56  go through screen  48 . In  FIG. 8 , screen  48  has screened out and returns represented by arrow  58  enter through screen  42 . Continuing the gravel packing until screen  42  screens out will produce a fully gravel packed annulus  12  with gravel  16  over the top of screen  42 . 
     With the gravel pack complete as shown in  FIG. 1  the crossover and any wash pipe attached (not shown) are removed and the production string of  FIG. 2  is inserted into the packer  14 . When that happens, seal assemblies  60 ,  62 ,  64  and  66  are placed respectively in regions  2 ,  4 ,  6  and  8  so that every screen  44 ,  46 , and  48  is straddled so that no flow can come through it. It essentially converts the portion of the completion in  FIG. 1  between screens  28  and  42  into blank pipe. It also provides flow access into the string  30  through its lower end  34  if there is no plug  32  there so that flow can occur into screen  28  from zone C. Alternatively, the port  40  can be put into or already be in the open position to allow flow from zone A while shutting the lower end  34  with plug  32  to block flow from zone C into screen  28 . 
     The seal assemblies  60 ,  62 ,  64  and  66  can have one or more external seals to the string  30 . The seal type can vary as long as the objective of isolating the screens  44 ,  46 , and  48  from flow is accomplished after the gravel packing is completed. Screens  44 ,  46 , and  48  can be small openings of any shape size and number so as to prevent gravel from getting through during gravel packing. These screens are spaced apart so that the seal assemblies  60 ,  62 ,  64  and  66  can land on blank pipe to seal in regions  2 ,  4 ,  6  and  8 . The lower end  34  is in region  9  inside the screen  34 . If plug  32  is used it can be subsequently removed in a variety of ways. If desired, the zone A and C can be produced together. Any number of producing zones can be completed in this manner and produced in any desired order by manipulating sliding sleeves such as  38  in ported subs  36  that can be positioned in any of the producing zones. The lowermost zone is preferably produced through an opening at the bottom of the string  30 . 
     When the annulus  12  is tightly packed due to the presence in the non-producing zone of return screens  44 ,  46 , and  48  the migration flow between adjacent producing formations can be as low as a few barrels per day or with optimal low pressure differentials between adjacent formations and long spacing between them it is conceivable to effectively get to a no cross flow situation between adjacent producing zones. Clearly, the longer the spacing and the smaller the open hole annulus and the tighter the gravel pack, the amount of cross flow between producing formations is minimized if not eliminated. 
     While production is mentioned through screens  28  and  42 , the term “production” encompasses flow in the reverse direction is contemplated such as in a fracturing mode or in an injection mode such as with steam, for example. 
     The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.