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BACKGROUND 
     The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a method of completing a well utilizing an isolation bypass transition joint. 
     One method of completing a well having an intersection between a parent wellbore and a branch wellbore is to position a liner at the intersection, so that an upper end of the liner is in the parent wellbore and a lower end of the liner is in the branch wellbore. The liner may or may not be cemented in place by flowing cement about the liner at the wellbore intersection. 
     In transitioning laterally from the parent wellbore to the branch wellbore, the liner extends across the parent wellbore. To permit flow through the parent wellbore from below to above the wellbore intersection, a sidewall of the liner is typically perforated using conventional perforating guns equipped with a device which aims the guns to shoot through the sidewall in a desired direction. Another method is to mill through the liner sidewall using a deflection device positioned in the liner. However, the use of explosives is very hazardous and milling operations are quite time-consuming. 
     It would be desirable to provide an improved method which does not require the use of explosives, with their inherent dangers, and which does not require milling through the liner sidewall to provide fluid communication therethrough. 
     SUMMARY 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method is provided which utilizes a specially configured isolation bypass transition joint. The transition joint is used in a liner string assembly at the intersection between a parent and branch wellbore. 
     In one aspect of the invention, the transition joint includes two tubular strings, one inside of the other. An annular space is formed between the tubular strings. When installed at the wellbore intersection, a sidewall portion of the transition joint extends across the parent wellbore. 
     In another aspect of the invention, one or more plug devices are disposed in the transition joint sidewall when it is installed. The plug devices are opened to permit flow through the transition joint sidewall. The plug devices may be opened, for example, by cutting a portion of each of the devices, by dissolving a portion of each of the devices, etc. 
     In yet another aspect of the invention, the plug devices prevent flow through the transition joint sidewall prior to being opened. The plug devices may also isolate the annular space from the interior and exterior of the transition joint. The plug devices may continue to isolate the annular space from the interior and exterior of the transition joint after being opened. 
     In still another aspect of the invention, cement is flowed through the annular space, and the plug devices prevent the cement from flowing laterally out of the transition joint sidewall. After the cement has hardened, the plug devices are opened to permit flow through the transition joint sidewall. The plug devices may include generally tubular hollow portions extending from the inner tubular string to the outer tubular string. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional view of a method embodying principles of the present invention; 
     FIG. 2 is a cross-sectional view of the method of FIG. 1, wherein additional steps of the method have been performed. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a method  10  which embodies principles of the present invention. In the following description of the method  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. 
     As depicted in FIG. 1, some steps in the method  10  have already been performed. A casing string  12  has been installed and cemented in a parent wellbore  14 . A branch wellbore  16  has been drilled extending outward from the parent wellbore  14  by deflecting cutting tools, such as mills, reamers, drills, etc. off of a whipstock  18  positioned in the parent wellbore below the intersection between the parent and branch wellbores. 
     Mills, reamers, etc. may be deflected off of the whipstock  18  to form a window  20  laterally through the casing string  12 . The window  20  could alternatively be preformed in the casing string  12 . For example, the window  20  could have a relatively easily milled or drilled covering (e.g., an outer aluminum sleeve) or filling therein (e.g., a fiberglass insert) which is removed when the branch wellbore  16  is drilled. 
     After drilling the branch wellbore  16 , a liner string assembly  22  is conveyed into the parent wellbore  14 . A lower end of the assembly  22  is deflected off of the whipstock  18  and into the branch wellbore  16 . A packer  24  (preferably, an inflatable packer) is set in the branch wellbore  16 , and a packer/liner hanger  26  is set in the parent wellbore  14 . 
     The packer/liner hanger  26  secures the assembly  22  in position and radially oriented as depicted in FIG.  1 . However, other means may be used to position and/or orient the assembly  22 . For example, an orienting latch coupling of the type well known to those skilled in the art may be installed in the casing string  12 , an abutment or shoulder  23  on the assembly  22  may engage the casing at the window  20 , thereby preventing further displacement of the assembly through the window, etc. As another example, a projection, shoulder, abutment or other engagement device (which may be similar in some respects to the abutment  23 ) may engage the whipstock  18 , instead of, or in addition to, engaging the casing  12  at the window  20 . 
     For this purpose, the whipstock  18  could include an upwardly extending tubular neck through which the assembly  22  is displaced before the whipstock deflects the lower end of the assembly into the branch wellbore  16 . The abutment or shoulder  23  on the liner assembly  22  could engage this whipstock  18  upper neck to position the assembly properly with respect to the window  20  and branch wellbore  16 . This engagement could also radially orient the assembly  22  relative to the whipstock  18  if the neck is provided with an orienting profile, such as an orienting latch. In addition, wireline tools, pipe tallies, pip tags, etc. may be used to determine the location of the liner assembly  22  relative to the window  20 . 
     The abutment  23  preferably circumscribes the liner assembly  22  and extends radially outward therefrom, in the nature of a flange. This flanged abutment  23  may serve to prevent debris from the branch wellbore  16  from entering the parent wellbore  14  and accumulating about the whipstock  18 , as well as serving to aid in the positioning of the liner assembly  22 . 
     The assembly  22  includes a transition joint  28  which is positioned at the intersection between the parent and branch wellbores  14 ,  16 . The transition joint  28  includes an inner tubular string  30  and an outer tubular string  32 , with an annular space  34  formed therebetween. Several plug devices  36 ,  38 ,  40  are disposed in a sidewall of the transition joint  28  where it extends laterally across the parent wellbore  14 . The plug devices  36 ,  38 ,  40  are radially oriented so that they are opposite the whipstock  18 . 
     The plug devices  36 ,  38 ,  40  are used to selectively permit flow through the transition joint  28  sidewall. Although three of the plug devices  36 ,  38 ,  40  are depicted in FIG. 1, it is to be understood that any number of plug devices, including one, could be used. 
     The plug devices  36 ,  38 ,  40  are merely illustrated in FIG. 1 as examples of the wide variety of plug devices which may be used. The plug devices  36 ,  38 ,  40  could also be differently configured or positioned in the liner assembly  22  in keeping with the principles of the invention. For example, the plug devices  36 ,  38 ,  40  are oriented so that fluid flows through them in a radial direction relative to the liner assembly  22  as depicted in FIG. 1, but the plug devices could be oriented so that fluid flows through them in the same direction as fluid flow through the whipstock  18 , i.e., in a vertical direction as viewed in FIG.  1 . 
     The plug device  36  has a generally tubular and hollow body extending between the inner and outer strings  30 ,  32 . A cap  42 , which extends into the interior of the inner string  30 , closes off one end of the plug device  36 . When the cap  42  is cut off, the plug device  36  is opened to flow therethrough. 
     The plug device  38  also has a generally tubular and hollow body extending between the inner and outer strings  30 ,  32 . A dissolvable plug  44 , which extends into the interior of the inner string  30 , closes off one end of the plug device  36 . When the plug  44  is dissolved, the plug device  38  is opened to flow therethrough. 
     The plug device  40  also has a generally tubular body extending between the inner and outer strings  30 ,  32 . However, a dissolvable plug  46  prevents fluid flow through the body of the plug device  40 . When the plug  46  is dissolved, the plug device  40  is opened to flow therethrough. 
     Of course, many other types of plug devices could be used. For example, the entire plug device could be dissolvable, the plug device could be opened in other ways, such as by pushing the plug device through the transition joint  28  sidewall, etc. Thus, the description of the specific plug devices  36 ,  38 ,  40  in the exemplary method  10  is not to be taken as limiting the principles of the invention. 
     After the assembly  22  is positioned as depicted in FIG. 1, cement is flowed through the assembly. As used herein, the term “cement”, “cementing”, and similar terms, are used to designate any manner of securing and/or sealing a tubular string in a wellbore by flowing a hardenable substance thereabout. The substance may be cementitious, may be a hardenable gel, polymer resin, such as epoxy, etc. 
     The cement is flowed downwardly through the inner tubular string  30  as indicated by the arrows  48 , from the parent wellbore  14  to the branch wellbore  16 . The cement then flows outwardly through conventional stage cementing equipment (not shown) and upwardly between the tubular string  30  and the branch wellbore  16  as indicated by arrows  52 . The arrows  52 , and another arrow  50 , also indicate how the cement flows upwardly in the annular space  34  between the tubular strings  30 ,  32  in the transition joint  28 . 
     As the cement flows through the annular space  34 , the plug devices  36 ,  38 ,  40  prevent the cement from flowing outward from the annular space, either to the interior or to the exterior of the transition joint  28 . The plug devices  36 ,  38 ,  40  also prevent the cement being delivered into the branch wellbore  16  (as indicated by arrows  48 ) from flowing into the annular space  34 , or from flowing through the plug devices to the parent wellbore  14  below the wellbore intersection. 
     The cement flows from the annular space  34  outwardly to an annulus between the inner string  30  and the wellbore  14  as indicated by arrows  54 . From this annulus, the cement may flow upwardly through a passage in the packer/liner hanger  26  according to conventional cementing practice. 
     Thus, the assembly  22  is cemented in the parent and branch wellbores  14 ,  16  by delivering the cement through the inner string  30  and returning the cement via the annular space  34 . The plug devices  36 ,  38 ,  40  facilitate this process by isolating the cement delivery and return flows, while preventing the cement from flowing into the parent wellbore  14  below its intersection with the branch wellbore  16 . 
     Swab cups  56 , or another suitable sealing device, prevent the cement returned to the annulus between the inner string  30  and the parent wellbore  14  from flowing downwardly in the parent wellbore to its intersection with the branch wellbore  16 . The packer  24 , or another suitable sealing device, prevents the cement flowed from the inner string  30  to the branch wellbore  16  from flowing upwardly in the branch wellbore to its intersection with the parent wellbore  14 . Among other benefits, this configuration prevents the cement from flowing into or accumulating about the whipstock  18 . 
     For well control purposes, a valve  57  may be used to selectively prevent flow through the whipstock  18 . The valve  57  is preferably pressure actuated using pressure applied to the interior of the whipstock  18  after the plug devices  36 ,  38 ,  40  are opened. Pressure actuated sliding sleeve valves, pressure actuated interval control valves, and other types of conventional valves may be used for the valve  57 . Of course, the valve  57  may be actuated by a means other than pressure without departing from the principles of the invention. 
     Referring additionally now to FIG. 2, the method  10  is representatively illustrated after additional steps of the method have been performed. The cement flowed through the transition joint  28  has been allowed to harden. The plug devices  36 ,  38 ,  40  have been opened to thereby permit flow through the sidewall of the transition joint  28 , and the valve  57  has been opened to permit flow through the whipstock  18 , as indicated by arrows  58 . The plug devices  36 ,  38 ,  40  and valve  57  are opened as described above. 
     Note that the flow  58  also passes through an internal passage  60  of the whipstock  18 . Fluid communication is thus provided between the parent wellbore  14  above the wellbore intersection and the parent wellbore below the wellbore intersection. As described above, the plug devices  36 ,  38 ,  40  may be oriented so that the fluid flow  58  through the plug devices is in the same direction as flow through the passage  60 . 
     Flow from the branch wellbore  16  (indicated by arrow  62 ) may commingle with the flow  58  from the lower parent wellbore  14 , so that the flow into the upper parent wellbore (indicated by arrow  64 ) is from both the branch and lower parent wellbores. Of course, the well may be an injection well instead of a production well, in which case the above described flow directions may be reversed, and flow from or into each of the wellbores may be isolated from other wellbore fluid flows. 
     The plug device  36  is opened by conveying a cutting tool, such as a conventional clean-up tool used after cementing operations, or a drill, reamer, etc., into the transition joint  28  and cutting into the cap  42 . Preferably, the cap  42  is completely removed, thereby completely opening the tubular body of the plug device  36  to flow therethrough. Note that, even though the plug device  36  is opened, it still isolates the annular space  34  from the interior and exterior of the transition joint  28 . 
     The plug device  38  is opened by dissolving the plug  44  on the inner end of the plug device. This dissolving step may be performed, for example, by spotting an acid in the transition joint  28  for a time sufficient to dissolve the plug  44 . A similar method may be used to dissolve the plug  46  in the tubular body of the plug device  40 . Other methods of dissolving the plugs  44 ,  46  may be used, without departing from the principles of the invention. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.

Summary:
A method of completing a subterranean well utilizes an isolation bypass transition joint at a wellbore intersection. In a described embodiment, the isolation bypass transition joint has multiple plug devices in a sidewall thereof. The transition joint extends laterally from one wellbore into another. After a cementing operation, the plug devices are opened to permit flow through the transition joint sidewall.