Abstract:
A method is disclosed that allows for sequential treatment of two zones in a single trip while isolating the zones. A fluid loss valve prevents the column of fluid in the tubing from flowing into the lower formation until activated. Zone isolation is accomplished by manipulation of a port on a wash pipe attached to the crossover assembly.

Description:
FIELD OF THE INVENTION  
         [0001]    The field of this invention relates to techniques and equipment to gravel-pack and treat closely spaced zones and more particularly in applications where some degree of isolation is desired between the zones for accommodating different treatment plans.  
         BACKGROUND OF THE INVENTION  
         [0002]    In producing hydrocarbons or the like from loose or unconsolidated and/or fractured formations, it is not uncommon to produce large volumes of particulate material along with the formation fluids. As is well known in the art, these particulates routinely cause a variety of problems and must be controlled in order for production to be economical. A popular technique used for controlling the production of particulates (e.g., sand) from a well is one which is commonly known as “gravel-packing.” 
           [0003]    In a typical gravel-packed completion, a screen is lowered into the wellbore on a work string and is positioned adjacent to the subterranean formation to be completed, e.g., a production formation. Particulate material, collectively referred to as “gravel,” and a carrier fluid is then pumped as a slurry down the work string where it exits through a “cross-over” into the well annulus formed between the screen and the well casing or open hole, as the case may be. The carrier liquid in the slurry normally flows into the formation through casing perforations, which, in turn, is sized to prevent flow of gravel therethrough. This results in the gravel being deposited or “screened out” in the well annulus where it collects to form a gravel pack around the screen. The gravel, in turn, is sized so that it forms a permeable mass, which allows the flow of the produced fluids therethrough and into the screen while blocking the flow of the particulates produced with the production fluids.  
           [0004]    One major problem that occurs in gravel-packing single zones, particularly where they are long or inclined, arises from the difficulty in distributing the gravel over the entire completion interval, i.e., completely packing the entire length of the well annulus around the screen. This poor distribution of gravel (i.e., incomplete packing of the interval) is often caused by the carrier fluid in the gravel slurry being lost into the more permeable portions of the formation, which, in turn, causes the gravel to form “sand bridges” in the annulus before all the gravel has been placed. Such bridges block further flow of slurry through the annulus, which prevents the placement of sufficient gravel (a) below the bridge in top-to-bottom packing operations or (b) above the bridge in bottom-to-top packing operations.  
           [0005]    To address this specific problem, “alternate path” well strings have been developed which provide for distribution of gravel throughout the entire completion interval, even if sand bridges form before all the gravel has been placed. Some examples of such screens include U.S. Pat. Nos.: 4,945,991; 5,082,052; 5,113,935; 5,417,284; 5,419,394; 5,476,143; 5,341,880; and 5,515,915. In these well screens, the alternate paths (e.g., perforated shunts or bypass conduits) extend along the length of the screen and are in fluid communication with the gravel slurry as the slurry enters the well annulus around the screen. If a sand bridge forms in the annulus, the slurry is still free to flow through the conduits and out into the annulus through the perforations in the conduits to complete the filling of the annulus above and/or below the sand bridge.  
           [0006]    One of the problems with the alternate path design is the relatively small size of the passages through them. These tubes are also subject to being crimped or otherwise damaged during the installation of the screen. Thus, several designs in the past have placed these tubes inside the outer surface of the screen. This type of design substantially increases the cost of the screen over commercially available screens. Yet other designs have recognized that it is more economical to place such tubes on the outsides of the screen and have attempted to put yet another shroud over the alternate paths which are on the outside of the screen to prevent them from being damaged during insertion or removal. Such a design is revealed in U.K application No. GB 2317 630 A.  
           [0007]    While such designs can be of some benefit in a bridging situation, they present difficulties in attempting to treat and gravel-pack zones which are fairly close together. Many times zones are so close together that traditional isolation devices between the zones cannot be practically employed because the spacing is too short. For example, situations occur where an upper and lower zone are spaced only 5-20 feet from each other, thus precluding a complete completion assembly in between screens for each of the zones. When these closely spaced zones are encountered, it is desirable to be able to gravel-pack and treat the formations at the same time so as to save rig time by eliminating numerous trips into the well. This method was explained in U.S. Pat. No. 6,230,803. At times these types of completions will also require some degree of isolation between them, while at the same time producing one or the other of the formations. In U.S. Pat. No. 6,230,803 a method was disclosed to facilitate fluid treatments such as fracture stimulation, as well as gravel packing, simultaneously, in two or more adjacent producing zones, while providing limited hydraulic isolation between two or more adjacent zones. That method minimized rig time for the completion by reducing the number of trips required to install the gravel screen assemblies and to treat the formation. The limitation of that method was that the two zones had to be treated simultaneously. This caused problems if the nature of the adjacent formations necessitated a different treatment program. The isolation of the zones after completion was also less than ideal. Accordingly, the present method seeks to allow the treatment of adjacent zones in a single trip one at a time so that different regimens can be used. It provides, in the preferred embodiment, a check valve for retention of fluids in the string against loss into the formation. It provides an option of isolating a zone while treating the other. The method of the present invention can also be used in a single producing zone to minimize bridging problems during gravel distribution by splitting the zone into segments and gravel packing each segment individually. These objectives and how they are accomplished will become clearer to those skilled in the art from a review of the detailed description of the preferred embodiment and the claims, which appear below.  
         SUMMARY OF THE INVENTION  
         [0008]    A method is disclosed that allows for sequential treatment of two zones in a single trip while isolating the zones. A fluid loss valve prevents the column of fluid in the tubing from flowing into the lower formation until activated. Zone isolation is accomplished by manipulation of a port on a wash pipe attached to the crossover assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a section view of the equipment in place and the upper zone being treated while the lower zone is isolated;  
         [0010]    [0010]FIG. 2 is the view of FIG. 1 with the lower zone being treated;  
         [0011]    [0011]FIG. 3 shows both zones treated;  
         [0012]    [0012]FIG. 4 is an enlargement of the fluid loss prevention valve in the assembly;  
         [0013]    [0013]FIG. 5 is a detailed view of the wash pipe in position to allow treatment of the upper zone; and  
         [0014]    [0014]FIG. 6 is the view of FIG. 5 showing the wash pipe positioned for squeezing the lower zone. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    [0015]FIG. 1 shows a wellbore  10  and zones  12  and  14  to be treated. The preferred embodiment illustrates the method for two zones but those skilled in the art will appreciate that additional zones can be treated in a single trip with duplication of the equipment shown for doing two zones in one trip, as will be explained below. A tubular string  16  is used to run in a known crossover tool  18 , which is movable with respect to packer  20  after it is set. In FIG. 1, the packer  20  is shown in the set position and the crossover is set up to circulate to deposit gravel outside of screen  22  and adjacent the perforations  24  of zone  12 . Arrows  26  show the gravel and fluid mixture coming from the surface through the string  16  and going through the packer  20 . The gravel and fluid stream indicated by arrows  26  goes through crossover  18  and through ports  28  in the crossover tool  18 . Sliding sleeve valve  30  is left in the open position during run in so that the ports  32  are open for the gravel and fluid stream  26  to pass into annulus  34 . The stream passes through the screen  22  leaving the gravel in annulus  34  and the fluid to pass through the screen  22  into annular space  36  around the wash pipe  38 . Wash pipe  38  has several openings  40  which are shown in FIG. 1 as above seal  42 . Seal  42  keeps clean fluid from going down around the outside of the wash pipe  38 . Any fluid  26  that gets into the wash pipe  38  through openings  40  is stopped from exiting the lower end of the wash pipe  38  by a ball  44  pushed by the flow against a seat  46 . Return flow  26  passes through passage  48  lifting ball  50  off seat  52 . The return flow passes through passage  54  in crossover  18  and up to the surface via annulus  56  above the set packer  20 . A flapper  58  is held open by wash pipe  38 . When the wash pipe  38  is removed, the flapper  58  closes to prevent the column of fluid from the surface inside the string  16  from flowing into the formation and potentially causing damage.  
         [0016]    Packer  60  is supported by screen  22  and it in turn supports screen  62  at perforations  64 . Packer  60  is multi-bore. The first bore  66  communicates to inside screen  62 . The second bore  68  communicates with a standpipe  70  that is capped at cap  72  at its upper end. As shown in FIG. 1 gravel is deposited around the outside of standpipe  70  and standpipe  70  extends above perforations  24 . After the zone  12  is fully treated, including gravel packing and other operations that may be needed like acidizing, pressure on cap  72  can be raised to break it to provide access to zone  14  through bore  68 . Cap  72  can be a rupture disc or any other type of barrier that can be removed in any number of ways among them pressure, chemical reaction or some applied force. As shown in FIG. 2, the gravel and fluid stream  74  passes through standpipe  70  and bore  68  in packer  60  to lodge in annulus  76  adjacent perforations  64 . Returns pass through screen  62  and into wash pipe  38  to displace ball  44  off of seat  46 . Ports  40  in wash pipe  38  are now below seal  42 . This position of ports  40  effectively isolates zone  12  from returns. The returns  74  pass through passage  48  and return to the surface through annulus  56  in the manner previously described for zone  12 . Thus, although the gravel packing is done from top to bottom, each zone is independent and bridging in zone  12  has no effect on the deposition of gravel in zone  14 .  
         [0017]    [0017]FIG. 3 shows the crossover  18  and wash pipe  38  removed. The flapper  58  has slammed shut to prevent fluid loss to either zone  12  or  14 . Sliding sleeve  30  has been pushed closed by the removal of the wash pipe  38 .  
         [0018]    [0018]FIG. 5 shows the isolation of the lower zone  14  when treating the upper zone  12  by virtue of having openings  40  above seal  42 . Seal  42  seals around the outside of wash pipe  38  and ball  44  on seat  46  prevents returns from treating the zone  12  from reaching zone  14 . Additionally, bore  68  is closed at this time by cap  72  on standpipe  70 . FIG. 6 shows how zone  12  is isolated when treating zone  14 . Here the returns lift ball  44  off of seat  46 . Ports  40  are now below seal  42  forcing all returns to bypass zone  12  and rise to the crossover  18 . It should be noted that the cross-over  18  can be configured to close access to surface annulus  56 , in which case the gravel packing or acid treating or any other procedure will be without returns or by bull heading into the formation.  
         [0019]    [0019]FIG. 4 simply illustrates the flapper  58  held open by the wash pipe  38 . It slams shut as soon as the wash pipe  38  is removed.  
         [0020]    Those skilled in the art will appreciate that the zones can be closely spaced and can be treated separately in a single trip. Two or more zones can be sequentially treated in a single trip. The treatment can be by circulation with returns to the surface or elsewhere or without returns with the fluids driven into the formation being treated. When treating two zones, one is isolated when the other is treated. Finally, a fluid loss prevention feature, which is a flapper  58  in the preferred embodiment retains the liquid column in the tubular  16  and prevents its passage into the formation. The fluid prevention feature can be a flapper or ball device or any other valve that hold up the liquid column when the wash pipe  38  is pulled out.  
         [0021]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: