Abstract:
A method of forming a seal circumferentially about a liner having pre-formed openings that is positioned in a wellbore includes the steps of running a perforating device and a seal applicator into the slotted liner, the seal applicator carrying a sealing fluid and a pumping mechanism, creating an aperture through the slotted liner at the region by activating the perforating device and pumping the sealing fluid from the seal applicator through the aperture and circumferentially about the liner to form a sealing plug in the annulus between the slotted liner and the wellbore.

Description:
FIELD OF THE INVENTION 
   The present invention relates in general to wellbore operations and more particularly to a method of isolating zones in a wellbore having a slotted liner. 
   BACKGROUND 
   In many well completions a casing is run into the well after it is drilled. Cement is then pumped into the annulus between the casing and the wellbore wall. The casing and cement is then perforated at the desired formation. By perforating the cemented and sealed casing, isolation of the desired zone is maintained. 
   A significant number of wells are completed with perforated liners without any cement to bond the liner to the wellbore. The annulus between the liner and the wall of the wellbore may then be left empty or packed with gravel. Although slotted liners serve a purpose, they do not provide zonal isolation and permit fluid to flow in the annulus along the length of the liner. Typically, at some point in the well&#39;s life, it is desired to provide zonal isolation in the well for selective treatment of a zone or to prevent encroachment of an undesired fluid. 
   Therefore, it is a desire to provide a system and method for placing a substantially circumferential seal about a perforated liner. It is a still further desire to provide a method of creating zonal isolation about a perforated liner that is cost effective. 
   SUMMARY OF THE INVENTION 
   Methods of forming a seal circumferentially about a liner having pre-formed openings that is positioned in a wellbore are provided. In one embodiment of the invention the method includes the steps of creating an aperture through the slotted liner at the region and pumping a sealing fluid through the aperture and circumferentially about the liner to form a sealing plug in the annulus between the slotted liner and the wellbore. 
   The aperture may be larger in size than the pre-formed openings. The aperture may be created by expanding one or more of the pre-formed openings or by creating a new aperture. The aperture may be created by a perforating gun or by drilling. The sealing fluid may be thixotropic in nature and/or a swellable material to facilitate placement through aperture while forming a suitable sealing plug where desired. 
   In some embodiments of the invention, the method may include conveying a sealing applicator into the liner. The seal applicator may include one or more reservoirs for carrying fluids such as, but not limited to the sealing fluid, spacing fluids, and triggering agents. The seal applicator may include a mechanism, such as a pressure reservoir or pump for energizing the sealing fluid for injection through the aperture. 
   The foregoing has outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and aspects of the present invention will be best understood with reference to the following detailed description of a specific embodiment of the invention, when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic side view of an embodiment of the sealing method of the present invention; and 
       FIG. 2  is a further view of the sealing method illustrated in  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
   As used herein, the terms “up” and “down”; “upper” and “lower”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point. 
     FIG. 1  is a schematic side view of an embodiment of the sealing method of the present invention, generally denoted by the numeral  10 . A portion of a wellbore  12  is completed with a slotted liner  14 . Slotted liner  14  includes a plurality of openings  16  formed along its length. As used herein, slotted liner  14  includes any liner or screen that has openings  16  formed therethrough prior to hanging the tubular in the wellbore. Examples of slotted liners  14  include slotted, perforated, or predrilled liners, or a screen or a pre-packed screen. The annulus  18  between slotted liner  14  and the wall  20  of wellbore  12  may be substantially empty or packed with sand or gravel. 
   It is desired to seal annulus  18  in a region  22 . In the illustrated embodiment it is desired to seal annulus  18  due to water entry  23 . In the first step of sealing method  10 , a perforating apparatus  24  is positioned within slotted liner  14  proximate region  22  via conveyance  26 . Perforating apparatus  24  may include, but is not limited to, perforating guns, drilling mechanisms or cutting mechanisms. Conveyance  26  may be tubing, a wireline or a slickline. 
   In the second step of method  10 , perforating apparatus  24  is activated to create one or more apertures  28 . Each aperture  28  is larger than the pre-existing openings  16 . Aperture  28  may be a new opening formed through liner  14  or the expansion of an existing opening  16 . The formation of one or more apertures  28  is critical for the placement of a sealing fluid sufficient to obtain a desired sealing plug circumferentially about liner  14 . 
   Referring now to  FIG. 2 , aperture  28  has been created through liner  14  for forming sealing plug  32  circumferentially about liner  14 . To form sealing plug  32 , sealing fluid  34  must be suitable for injecting through aperture  28  and for setting into a sealing plug within region  22 . Thus, it is desired that sealing fluid  34  be thixotropic in nature so that it will set and become substantially “self-supporting” relatively quickly. It may further be desired for sealing fluid  34  to be a swellable material, so as to seal aperture  28  and openings  16  in region  22 . The swellable property further facilitates sealing between wellbore  12  and liner  14 . It may further be desired for sealing fluid  34  to have a sufficiently high gel strength so as to remain where placed, yet allow for a degree of gravity-induced flow to the lower portion of region  22 , for example in horizontal wellbores. It is noted that sealing fluid  34  may include one or more of the desired properties. It is further noted, and will be recognized with the following description of the method, that sealing plug  32  may be formed in stages or by one or more sealing fluids  34 . For example, a first sealing fluid  34  being primarily thixotropic in nature may be injected through aperture  28  into region  22  and then followed with a second swellable sealing fluid  34 . The swellable sealing fluid  34  may be followed by a triggering agent. It may also be desired to inject spacing fluids, such as water or drilling fluid, after one or more sealing fluid injections. 
   Examples of suitable sealing fluids  34  include, without limitation, foamed cements; unfoamed cements containing smectic clays such as bentonite and attapulgite, unfoamed cements containing welan gum, aluminum and/or iron sulphate, and/or calcium sulfate as thixotropy agents, thermosetting polymers such as epoxy, vinylester, phenolic and polyester resins, and cross-linking polymer gels (possibly with an added thixotrope). 
   Swellable sealing fluid  34  swells from an unexpanded state to an expanded state when it comes into contact with or absorbs a triggering fluid. The selection of a triggering fluid depends on the selection of the swellable material, and vice versa, as well as the wellbore environment and operation. The triggering fluid may be present naturally in wellbore  12 , present in the formation surrounding wellbore  12  and produced into the wellbore, or be injected into wellbore  12  and region  22 , such as from the surface through tubulars or a downhole seal applicator  30 . 
   Examples of suitable swellable sealing fluids  34  and their corresponding triggering fluids (listed in parenthetical) include, without limitation: ethylene-propylene-copolymer rubber (hydrocarbon oil); ethylene-propylene-diene terpolymer rubber (hydrocarbon oil); butyl rubber (hydrocarbon oil); haloginated butyl rubber (hydrocarbon oil); brominated butyl rubber (hydrocarbon oil); chlorinated butyl rubber (hydrocarbon oil); chlorinated polyethylene (hydrocarbon oil); starch-polyacrylate acid graft copolymer (water); polyvinyl alcohol cyclic acid anhydride graft copolymer (water); isobutylene maleic anhydride (water); acrylic acid type polymers (water); vinylacetate-acrylate copolymer (water); polyethylene oxide polymers (water); carboxymethyl celluclose type polymers (water); starch-polyacrylonitrile graft copolymers (water); highly swelling clay minerals, i.e. sodium bentonite, (water); styrene butadiene (hydrocarbon); ethylene propylene monomer rubber (hydrocarbon); natural rubber (hydrocarbon); ethylene propylene diene monomer rubber (hydrocarbon); ethylene vinyl acetate rubber (hydrocarbon); hydrogenised acrylonitrile-butadiene rubber (hydrocarbon); acrylonitrile butadiene rubber (hydrocarbon); isoprene rubber (hydrocarbon); chloroprene rubber (hydrocarbon); and polynorbornene (hydrocarbon). 
   In the embodiment illustrated in  FIG. 2 , conveyance  26  carries both seal applicator  30  and perforating apparatus  24  to facilitate a single trip into the well to create sealing plug  32  circumferentially about liner  14 . By providing sealing fluid  34  via seal applicator  30  positioned downhole, the Theological requirements of fluid  34  are reduced and it allows for downhole mixing of two-part fluids or the like, for example, epoxy resins, which can set rapidly in region  22 . 
   Seal applicator  30  may include one or more reservoirs carrying fluids and/or pumping means. For example, applicator  30  may include a reservoir carrying sealing fluid  34  and a reservoir carrying a triggering agent fluid for causing sealing fluid  34  to swell. In various embodiments, each reservoir may include a fluid for staging injections to form sealing plug  32 . Sealing applicator  30  may further include aids, such as a source of heat or radiation, to trigger or aid the setting of sealing plug  32 . 
   After aperture  28  is formed, conveyance  26  is run into liner  14  positioning seal applicator  30  proximate aperture  28  and region  22 . Seal applicator  30  is actuated injecting sealing fluid  34 , as shown by the arrows, through aperture  28  into annulus  18  circumferentially about liner  14  within region  22 . In the described embodiment, sealing fluid  34  sets to become substantially self-supporting sealing plug  32 . Further, sealing fluid  34  contacts a triggering agent, that is present in region  22  or injected via conveyance  26  or seal applicator  30 , causing fluid  34  to swell further sealing aperture  28  and openings  16 . 
   From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system and method for placing a annular seal about a slotted liner in a wellbore that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.