Abstract:
A completion assembly useful to fracture pack, gravel pack or otherwise treat production intervals traversed by an uncased wellbore to stimulate production and/or prevent production of solid particles from the production intervals and a single trip method to fracture pack, gravel pack or otherwise treat multiple zones in an open-hole wellbore having no liner or casing string installed through a production open hole portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a completion assembly useful to fracture, gravel pack or otherwise treat a plurality of production intervals traversed by an uncased wellbore to stimulate fluid production, prevent production of solid particles, or both, from the production intervals. The invention relates to a single trip method to fracture, gravel pack or otherwise treat multiple zones in an uncased wellbore having no liner or casing string installed. 
       BACKGROUND OF THE INVENTION 
       [0002]    In many instances the treatment of separate production intervals (zones) in a well has been accomplished by casing the well and thereafter perforating a zone to be treated for fracturing, gravel packing or the like. This requires that the well be cased in the zone to be treated and that perforations be placed in the casing to permit access to the subterranean production formation. This can require multiple trips of tubing into the well for operations, to exchange tooling, or the like. Further this can, in some instances, lead to multiple cemented pipe sizes being required to isolate the wellbore from the uppermost to the deepest production interval. Further when cemented pipe is used, it is not always possible to achieve good initial and long term cement isolation between production intervals. Also the area of perforations contributing production to the wellbore are small relative to the inside diameter of the well and can limit the flow rate from the treated formation. 
         [0003]    The geometry of the fracture that can be placed within a cased hole wellbore can also be limited by the casing ID that can be installed across the production intervals and erosion of small flow areas in fracture placement tools and erosion of the casing. 
         [0004]    Multiple intervals have been treated in a cased hole with fracture treatments without the use of screens. However, these operations require either wellbore cleanout to remove the treating fluid, including gravel or proppant from the wellbore after the treatment or each fracture treatment to be over-displaced to the formation. 
         [0005]    These procedures result in substantial expense and pose certain problems with respect to optimum production of fluids from the formation. 
         [0006]    Currently open-hole gravel packing operations are limited to treating single or multiple production intervals in a single treatment operation. In a very few instances, open hole fracture pack operations have been employed but were limited to treating a single production interval or multiple production intervals in a single treatment. This may not provide the optimum treatment or production for each production zone. 
         [0007]    In some instances it has been possible to treat selected zones in open hole wellbores by the use of packers, or packers and valves, to isolate the zones for fracturing and the like. However, all such systems typically require the use of packers which are set to isolate the system to be treated or the like. Further it is generally necessary to remove the treating fluid, including gravel or proppant from the wellbore after the treatment is complete or to over-displace each fracture treatment to the formation and to close mechanical fracturing valves. 
         [0008]    Since in many instances, a plurality of production intervals may be penetrated by a single open hole wellbore it would be highly desirable to be able to treat and produce these intervals independently in an uncased wellbore penetrating these intervals. Accordingly a considerable effort has been directed to developing such a method. 
       SUMMARY OF THE INVENTION 
       [0009]    It has been found that a plurality of production intervals in an open wellbore are readily treated by positioning an open-hole, single trip, multiple zone fracturing, gravel packing and treatment completion assembly for single trip fracturing and gravel packing intervals in an uncased zone of a wellbore. The open hole portion of the wellbore penetrates a plurality of production intervals. The completion assembly comprises an isolation string having an inside and an outside and an upper end adapted for connection with a lower end of a cemented well casing immediately above the production intervals and a lower end adapted for positioning on an open-hole packer at a selected position in the open hole uncased portion of the wellbore with each section of the isolation string being positioned in one of a plurality of the production intervals and including a first treating valve adapted to open and close a first passageway having an inlet, a second treating pressure monitoring valve adapted to open and close a second passageway having an inlet and a third valve adapted to open and close a third passageway having an inlet, the passageways extending from their inlets through a wall of the isolation string and spaced to provide fluid communication between the inside of the isolation string and the inside of the wellbore in each of a plurality of the production intervals and a screen over openings to the second and third passageways from the wellbore. 
         [0010]    The invention further comprises an open-hole, single trip, multiple zone fracturing, gravel packing and treatment completion assembly for single trip fracturing and packing operations in an uncased, open hole portion of a wellbore, the open hole portion penetrating a plurality of production formation intervals, the completion assembly comprising: an isolation string having an inside and an outside and an upper end extending above the completion assembly and adapted for connection in fluid communication with a treating string extending to surface and a lower end which is positioned to carry the completion assembly into the wellbore and adapted to locate the treating string in a selected position in the open hole wellbore; each portion of the treating string being positioned in one of a plurality of production intervals including a first treating valve adapted to open and close a first passageway having an inlet, a second treating pressure monitoring valve adapted to open and close a second passageway having an inlet, the passageways extending from their inlets through a wall of the isolation string and spaced to provide fluid communication between the inside of the treating string and an inside of the wellbore in each of a plurality of the production intervals and a screen over openings to the second and third production passageways from the wellbore. 
         [0011]    The invention additionally comprises a method for multiple zone fracturing, packing and well treatment by a single trip for at least one of fracturing, gravel packing and treating an uncased portion of a wellbore, the uncased zone containing a plurality of production intervals, the method comprising: positioning an isolation string having an inside and an outside and an upper end extending above the zone and adapted for connection with a lower end of a cemented well casing in the wellbore and a lower end positioned on an open-hole packer positioned to support the isolation string in a selected position in the uncased portion; each portion of the isolation string being positioned in one of a plurality of production intervals and including a first treating valve adapted to open and close a first passageway having an inlet, a second treating pressure monitoring valve adapted to open and close a second passageway having an inlet and a third production valve adapted to open and close a third passageway having an inlet, the passageways extending through a wall of the isolation string and spaced to provide fluid communication between the inside of the isolation string and an inside of the wellbore in each of a plurality of the production intervals and a screen over the openings to the second and third passageways from the wellbore; passing an inner treating string having an inside and an outside and a crossover tool adapted to pass fluid from the treating string into a production interval; opening a treating valve and a treating pressure monitoring valve and injecting fluid from the tubular treating string into the production interval to fracture, gravel pack or treat the production interval; closing the treating valve and treating pressure monitoring valve; opening the treating valve and a treating pressure monitoring valve in the second production interval and passing fluid from the crossover tool into the second production interval; repeating the treatment steps above for a plurality of production intervals to fracture, gravel pack or treat the production interval; and, opening production valves for selected or all intervals to produce fluids from the production intervals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a schematic diagram of a development system including an isolation string positioned in a wellbore for treatment of a lowermost production interval; and, 
           [0013]      FIG. 2  shows a schematic diagram of the system of  FIG. 1  after completion of the treatment of a production interval in a formation positioned for treatment of a second production interval in the formation. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    In the discussion of the Figures, the same numbers will be used throughout to refer to the same or similar components. 
         [0015]    In  FIG. 1  a completion assembly  10  is shown positioned in a wellbore  12  which includes a casing  14  cemented in place with cement  16  to a depth above an uncased portion  30 . The well penetrates an overburden  18  with a lower end of the casing  20  ending in overburden  18 . Formations  22 ,  24 ,  26  and  28  are shown and comprise separate production intervals. While not shown, non-production intervals may be, and usually are, positioned between the separate production intervals. These production intervals are penetrated by uncased portion  30  of wellbore  12  which has an upper end  32  and a lower end  34 . A packer and a hanger  36  are set in lower end  20  of casing  14  and sealingly position an upper end  42  of an isolation string  40  in casing  14 . A base open-hole packer  38  is positioned in a lower portion of the uncased wellbore to support isolation string  40  at its lower end  44 . A seal assembly  46  is positioned on packer  38  to sealingly position isolation string  40  in uncased portion  30 . A lower extension  48  of isolation string  40  is used to position the valves and screens used for the treatment of each production interval at a desired position in the production interval to be treated. A similar pipe  100  is used in the upper portion of isolation string  40  to position it relative to lower end  20  of casing  14 . While not shown, isolation string  40  may include pipe spacer sections between each section of isolation string  40  to position the sections ( 86 ,  88 ,  90  and  92 ) for treating the production intervals in the production intervals ( 22 ,  24 ,  26  and  28 ). As shown, isolation string  40  includes a first section  86 , a second section  88 , a third section  90  and a fourth section  92 . 
         [0016]    In each production interval a similar arrangement is used for the treatment of the production interval. The treatment is shown in some detail in  FIG. 1  for the first lowermost production interval in a production formation  28  with the treated area shown as zone  114 . This interval is positioned in a formation  28  and the numeral  114  and the checked area schematically shows the area which has been treated. The treating is accomplished by the use of a first treating valve  50  which opens and closes a first passageway  52  for the passage of treating fluid from inside a treating string  70  positioned inside isolation string  40  and by use of the treating pressure monitoring valve  64 , which opens and closes a passageway through screens  62  for the monitoring of treating pressures. Production intervals  22 ,  24 ,  26  and  28  are isolated by packers  78 ,  80 ,  82  and  84  to separate production intervals for treatment. While fracturing and gravel packing are readily performed using the isolation string, the isolation string can also be used to treat production formations by acid injection and the like. Any treatment delivered as a fluid can be performed, such as scale treatment and the like. 
         [0017]    As shown in  FIG. 1 , the isolation string is positioned in production interval  28  for treatment of the interval. Treating string  70  is positioned in isolation string  40 . Isolation string  40  includes a first treating valve  50  comprising a first passageway  52  from the inside of isolation string  40  to the annulus outside of isolation string  40  and inside wellbore  12 . Treating valve  50  comprises a plurality of slots, other openings or the like, positioned in a plane  106  which is perpendicular to a longitudinal axis  104  of isolation string  40 . The openings (not shown) are opened by moving a first slideable sleeve  54  upwardly and downwardly over the openings. The inside of the sleeve is equipped to matingly engage an opening tool  74  and a closing tool  72  on the outside of treating string  70  which can be used to open and close treating valve  50  and treating pressure monitoring valve  64 . Production valve  56  similarly includes a second passageway  58  and a second slideable sleeve  59 . The production valve  56  is used to produce the formation fluids following treating operations. A treating pressure monitoring valve  64  also includes a third passageway  63  and a third slideable sleeve  62 . The treating pressure monitoring valve  62  provides the ability to monitor treating pressures throughout the treating operations. Further a first screen  62  is positioned to cover the inlet from the wellbore into passageways  58  and  63  so that particulate matter from the treated zone of production interval  28  is not allowed to enter into the inside of isolation string  40 . 
         [0018]    During the treatment of production interval  28 , the treating string is lowered into the inside of isolation string  40  and includes a crossover tool  94 . The crossover tool is equipped with seals  96  and  98  which are effective to prevent the passage of fluids from treating string  70  upwardly or downwardly between the inside of isolation string  40  and an outside  108  of the treating string. Fluid is then injected into zone  114  via crossover tool  72  and first passageway  52  to treat production interval  28 , as shown by zone  114 . During the treatment, treating pressures can be monitored via communication with non-particulate fluids from zone  114  through passageway  63  when the treating pressure monitoring valve  64  is open. Treating pressures may be communicated inside the isolation string  40  and may be passed upwardly through a port  112  into the annulus between an outside  41  of isolation string  40  and the inside  109  of treating string  70 . This communication path may enable detection of pressure in production interval  28  during the treatment process. 
         [0019]    When the treatment is finished treating string  70  may be raised to treat production interval  26 . This same procedure is used and the same arrangement of valves and screen is used in production interval  26 . Similarly production intervals  24  and  22  may also be treated in the same way. When it is desired to produce fluids from a treated production interval, after all intervals have been treated and subsequent upper completion operations are complete, production valves  56 , can be opened, either mechanically by tools conveyed by standard wellbore intervention methods or initially opened by application of pressure from the surface or by pressure cycles to allow production of formation fluids into the wellbore through the screen sections  62 . 
         [0020]    Isolation string  40  may also include an indicating coupling  76  positioned to indicate to a tool on the outside of the treating string  70  when it is in proper position relative to each of the production intervals. The production intervals are shown as intervals in the isolation string at  86 ,  88 ,  90  and  92 . 
         [0021]    The production intervals may each be treated with a treating string which may be used to inject material into each of the production intervals for treatment. The treating string may be flushed of materials after each treatment, if desired, by lifting it into the cased portion of the well and introducing sufficient fluid through the annulus between the outside of the treating string and inside  110  of the casing to flow materials up and out of the treating string which should be removed. After the flushing operation has been completed, the treating string may be returned to the desired position in the isolation string. 
         [0022]    The isolation string, after the treatments of the well have been finished, may be left in place to maintain the wells in condition to produce from the uncased wellbore interval. 
         [0023]    While the treatment of all the sections has not been shown, as indicated the treatment is substantially the same in each interval. 
         [0024]    In  FIG. 2  the treatment of a second production interval  26  by treatment of a zone  118  is shown. 
         [0025]    This treatment permits the use of a single trip downhole with the treating string to set the isolation string in place and perform the selective treatment of multiple intervals. Thus, each of the formations can be treated without a separate setup, isolation of that interval followed by perforation or the like after casing and no cleanout operations to remove treating fluids and proppant from wellbore  12  is necessary. 
         [0026]    Desirably the isolation string is constructed and arranged to position the treating valve, treating pressure monitoring valve and production valves and screen opposite the formation to be treated for each production interval in the area to be spanned by the isolation string. This may require the use of spacing pipes in the isolation string as required. The isolation string is then lowered into the wellbore with whatever spacings may be desirable in the isolation string between each set of three valves and screen to enable the treatment of production intervals at whatever spacings they may require. Similarly spacing pipes can be used at the lower and upper ends of the isolation string as required to facilitate is positioning the upper end of the isolation string in the lower end of the casing and its lower end on the base open-hole packer. 
         [0027]    The use of tools such as the opening and closing tool on the treating string is well known to those skilled in the art and need not be discussed further. 
         [0028]    By use of the method and the apparatus discussed above, it is clear that effective treatment of subterranean zones comprising a plurality of production intervals in an uncased wellbore portion can readily be performed by a single trip method. The method does not require multiple trips in with perforating guns and subsequent fracture packing or gravel packing assemblies and the like to fracture, pack or otherwise treat subterranean formations. Furthermore, the adaptation of open hole isolation packers to the assembly enables multi-zone single trip treating of production intervals in an open hole wellbore. This is a significant advantage and not only eliminates the expense of multiple trips downhole to achieve the desired treatments but also saves the expense of installing casing and cement and eliminates the risk of poor cement jobs which may result in leakage between formations. 
         [0029]    Selective open hole fracturing and/or gravel packing of multiple production intervals will result in enhanced productivity by eliminating the near wellbore mechanical restriction associated with perforated casing, allowing optimum fracture and/or gravel packing operations for each interval and by facilitating independent production and reservoir management of each productive interval. 
         [0030]    Clearly multiple tubes can be positioned downhole into or through the isolation string to produce separately from each of the formations or from a formation beneath the formations treated as known to those skilled in the art. 
         [0031]    As indicated previously, it is believed that it would normally be most desirable to prepare the isolation string at the surface in lengths to position the required valves and screen at each production interval for treatment of the intervals. This will enable the construction of the isolation string, possibly in sections and at distances remote from the oil field. Thus, a tremendous advantage in fabrication can also be achieved. 
         [0032]    While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.