Patent Publication Number: US-7584790-B2

Title: Method of isolating and completing multi-zone frac packs

Description:
FIELD OF THE INVENTION 
     The field of this invention is well completions and more particularly completions that allow multi-zone completions that call for fracturing, gravel packing and isolation in a single trip. 
     BACKGROUND OF THE INVENTION 
     In the past in the case of a broad pay zone or multi pay zone to be completed the procedure was to break it into sections. The fracturing and gravel packing equipment is run into cased and perforated hole along with an isolation packer. The packer would be set to isolate the lowermost zone and the isolated zone would then be fractured below that packer. Thereafter, gravel would be delivered outside screens through a crossover to fill the annular space around the screen with gravel. After that the packer would remain in the zone just gravel packed along with the screens with gravel on their exterior as the crossover and associated wash pipe were pulled out through the already set packer. After that zone was isolated, fractured, and gravel packed another trip in the hole with a similar assembly as used for the lowest zone would be run in for doing the same for the next zone up. This process continued until all zones or sections of a continuous zone were completed. 
     This technique required many trips in and out of the wellbore and that translated into very high expenses for rig time. One of the reasons that this staged procedure was used was that to do it another way where an entire interval could be isolated and fractured and gravel packed at once required packers to then be set in the annulus after gravel packing. The packers that had been available were not known for reliable sealing against the inside wall of casing if the annular space was full of gravel. 
     More recently packer designs have evolved and sealing in an annulus that is full of gravel is possible. An example of such a packer is U.S. Pat. No. 6,896,049. Other packer designs are illustrated in U.S. Pat. Nos. 6,782,946; 5,988,276; 6,009,951; 7,100,690; 5,184,677 and 6,513,600. 
     The present method involves the use of packers that can reliably seal against casing in an annulus filled with gravel so that in one trip an entire interval or discrete pay zones can be isolated at once and fractured and then gravel packed and then packers that are already in place to either split up one zone or to isolate spaced zones can be set where gravel is present in the annular space. This allows these three procedures to be done in one trip for multiple zones or discrete segments of a single zone and still allow reliable isolation between zones or segments to occur with packers that can get a seal in a gravel environment. Different packer designs are contemplated for this service. These and other aspects of the present invention will be more readily apparent from a review of the description of the preferred embodiment and the associated drawings while recognizing that the claims determine the full scope of the invention. 
     SUMMARY OF THE INVENTION 
     Multiple formations are isolated in the wellbore and fractured and gravel packed together. The bottom hole assembly can have a series of screens that are separated with packers in between and above and below the screen stack. The assembly is positioned where needed in the borehole and the topmost and lowermost packers (if used) are set. The bottom of the interval can alternatively be the hole bottom. With multiple intervals isolated a fracturing operation can take place for the entire isolated interval that can encompass multiple producing zones. The interval can also be gravel packed in a single operation. After the gravel pack of the interval, packers that are on the bottom hole assembly between screens that are aligned with perforations for different zones can be set into the gravel pack and get an effective seal against the casing to isolate the various producing zones from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a run in view of a multi-zone completion in position with a lower packer set; 
         FIG. 1   a  is the view of  FIG. 1  during fracturing; 
         FIG. 2  is the view of  FIG. 1   a  after two zones have been fractured and gravel packed; and 
         FIG. 3  is the view of  FIG. 2  after the packer between screens is set through the gravel to isolate zones in the interval. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1  two adjacent producing zones  10  and  12  are illustrated as a producing interval  14 . The wellbore is cased with casing  16  that has perforations  18  and  20  respectively in zones  10  and  12 . A bottom hole assembly shown in  FIG. 1  comprises a bottom packer  22  which can optionally be eliminated if there are no producing zones below the shown location for packer  22 . From there and working uphole, there is a lower screen  24  followed by a zone isolation packer  26 . Above that are another screen section  28  and an upper packer  30 . Annulus  32  is defined between the casing  16  and the bottom hole assembly between packers  22  and  30 . As an alternative to packers  22  or  30  the tubular  38  can be expanded against the casing  16  for a metal to metal seal. 
     Known fracturing and gravel packing tools such as crossovers are mounted with packer  30  to allow fracturing fluid or gravel to pass packer  30  and enter annulus  32  as shown schematically by arrow  34  and to selectively make a return path to upper annulus  33  above the packer  30  as shown in  FIG. 1   a . Arrow  34  represents the ability to fracture and deliver gravel to the annulus  32 . For fracturing, if done before gravel packing, as shown in  FIG. 1   a , the return path through packer  30  to upper annulus  33  is closed as schematically illustrated in  FIG. 1   a . For gravel packing that same access to the upper annulus  33  is instead open by crossover manipulation in a manner known in the art.  FIG. 2  shows annulus  32  full of gravel  36  between packers  22  and  30 . It should be noted that zones  10  and  12  have by this time been fractured together and gravel packed together between set packers  22  and  30  with packer  26  as yet unset.  FIG. 3  shows the packer or seal  26  set against the casing  16  after pushing the gravel  36  out of the way and preferably creating a metal to metal seal against the casing  16 . Zones  10  and  12  are now isolated from each other in the annulus  32 . 
     Those skilled in the art will appreciate that any number of screen sections separated by packers such as  26  and having a top packer  30  with or without optional packer  22  can be used to fracture and gravel pack more than the two zones illustrated in the FIGS. The zones need not be adjacent as illustrated in the FIGS. Packers  22  and  30  can be of different styles suitable for the application and the anticipated differential pressures. Packers between screen sections should be able to displace a gravel pack  36  to reach the casing  16  to create a seal that will effectively isolate successive zones whether they are close together or not. 
     As an alternative to using packers such as  26  the tubing  38  can be expanded to seal across the annulus  32  using known expansion methods so that the same result is achieved. 
     The advantages over the prior sequential techniques for fracturing and gravel packing one zone at a time can now be appreciated. With the delivery of a single bottom hole assembly, multiple zones can be fractured and gravel packed together using known techniques. Thereafter, those zones can be isolated from each other with a gravel packed annulus leaving all zones ready to be produced in a small fraction of the time it takes to accomplish the same condition using the prior techniques. 
     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.