Abstract:
A method of completing an uncemented wellbore junction provides a well completion in which a tubular assembly is installed through a wellbore junction and then is left uncemented in the junction. Fluid communication is permitted between the interior of the assembly and a formation surrounding the junction after the completion. The method is especially useful in situations in which the formation surrounding the junction is relatively impermeable or is in a production zone, and the method additionally permits convenient access to a lower portion of a main wellbore for stimulation or abandonment purposes after the completion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to subterranean well completions and, in an embodiment described herein, more particularly provides a method of completing an uncemented wellbore junction. 
     When a junction of intersecting wellbores is completed, it is generally considered desirable to isolate the formation surrounding the wellbore junction from one or more tubulars extending through the junction. This is due to the fact that fluids produced or injected through the tubulars should typically not be commingled with fluids from the formation surrounding the junction and/or should not be injected into the formation. 
     In order to isolate the formation surrounding the junction from the tubulars, various methods and apparatus have been developed. While being well suited for their intended purpose, they often require a large number of trips into the well, are time-consuming and, therefore, quite expensive in operation. 
     There exist situations in which it may not be necessary to isolate a tubular extending through a wellbore junction from a formation or zone surrounding the junction. For example, where the formation is relatively impermeable, it may be acceptable to permit fluid communication between the tubular and the formation. As another example, the formation may be a producing zone, in which case it may be desirable to permit fluid communication between the tubular and the formation in order to produce fluid from the formation through the tubular. 
     In those situations in which it is not necessary to isolate a tubular extending through a wellbore junction from a formation or zone surrounding the junction, the completion may be greatly simplified by eliminating procedures for providing such isolation, such as cementing the tubular within the junction. Additionally, such a simplified completion may also permit cost savings to be realized when the time comes to abandon the well. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method is provided for completing an uncemented wellbore junction. 
     In broad terms, the method includes the steps of installing a tubular assembly through a wellbore junction and then sealingly engaging each opposite end of the assembly within a respective one of the intersecting wellbores. The sealing engagement of the assembly within the wellbores is accomplished without cementing the assembly within the junction. In this manner, fluid communication is permitted between the assembly and a formation surrounding the junction. 
     In one aspect of the invention, the tubular assembly is conveyed through a main wellbore and a lower end of the assembly is inserted into a branch wellbore intersecting the main wellbore while the upper end of the assembly remains in the main wellbore. The assembly, thus, extends across the main wellbore. In order to provide fluid communication between the main wellbore above and below the assembly, at least one opening is provided through a sidewall of the assembly. 
     In another aspect of the invention, a whipstock assembly may be utilized in drilling the branch wellbore and/or in deflecting the tubular assembly into the branch wellbore from the main wellbore. A fluid passage may be opened or formed through the whipstock assembly to facilitate fluid communication through the main wellbore. This may be accomplished before or after the tubular assembly is installed in the junction. 
     In yet another aspect of the invention, a fluid passage may be formed through the whipstock assembly at the same time one or more openings are provided through the assembly sidewall. For example, a perforating gun may be conveyed into the assembly and fired, thereby perforating the assembly and an upper closure plate of the whipstock at the same time. Alternatively, the whipstock assembly may be provided with a plug which is retrieved prior to installing the tubular assembly. As further alternatives, the whipstock may be provided with an inner core which is drilled through prior to installing the tubular assembly, which is dispersed prior to installing the tubular assembly, or which is dissolved after installing the tubular assembly. 
     In still another aspect of the invention, the tubular assembly may include a screen or a perforated liner. The screen or perforated liner may be positioned adjacent the wellbore junction when the tubular assembly is installed in the well. In this manner, fluid communication is provided through the assembly sidewall without requiring a separate operation to form openings therethrough. 
     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 partially cross-sectional view of a well wherein initial steps in a first method embodying principles of the present invention have been performed; 
     FIG. 2 is a schematic partially cross-sectional view of the well wherein further steps in the first method have been performed; 
     FIG. 3 is a schematic partially cross-sectional view of a second method embodying principles of the present invention; 
     FIG. 4 is a schematic partially cross-sectional view of a third method embodying principles of the present invention; 
     FIG. 5 is a schematic partially cross-sectional view of the well wherein further steps in the first method have been performed; and 
     FIG. 6 is a schematic partially cross-sectional view of a whipstock which may be used in the methods of FIGS. 1-5, and a method of providing a flow passage therethrough. 
    
    
     DETAILED DESCRIPTION 
     Representatively and schematically illustrated in FIG. 1 is a method  10  of completing a subterranean well 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 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., without departing from the principles of the present invention. 
     As depicted in FIG. 1, initial steps of the method  10  have already been performed. A main or parent wellbore  12  has been drilled and lined with protective casing  14  and cement  16 . Note that the reference number “ 12 ” indicates the inner diameter of the casing  14 , since the wellbore is cased. If the wellbore  12  were uncased, the term “wellbore” would more properly refer to the uncased bore of the well. It is to be clearly understood that it is not necessary in the method  10 , or any of the other methods and alternatives thereof described herein for any of the wellbores to be cased. 
     A branch or lateral wellbore  18  has been drilled extending outwardly from the main wellbore  12 . Such drilling of the lateral wellbore  18  may be accomplished using any conventional practices. In the method  10  as representatively illustrated in FIG. 1, a whipstock assembly  20  has been positioned in the wellbore  12  with an upper inclined surface  22  of a whipstock  24  oriented toward a desired location for forming the branch wellbore  18 . One or more cutting tools, such as mills, drill bits, etc. (not shown) have been deflected off of the surface  22  to form an opening or window  26  through the casing  14 , and to drill the branch wellbore  18 . 
     The whipstock assembly  20  as depicted in FIG. 1 includes the whipstock  24 , a packer  28  and a plug  30 . The packer  28  anchors the assembly  20  in the wellbore  12 , seals against the casing  14  to prevent debris, etc. from accumulating during the milling and drilling operations described above, and provides fluid isolation. Note that other means may be used for anchoring the whipstock  24 , without departing from the principles of the present invention. The plug  30  similarly provides fluid isolation since, in the representatively illustrated embodiment shown in FIG. 1, the whipstock  24  is hollow. 
     The main wellbore  12  below the whipstock assembly  20  may have been completed prior to installing the assembly in the well. The plug  30  and packer  28  prevent fluid communication with any completed zone therebelow for well control purposes, prevention of fluid loss, prevention of damage to any completed zone or zones, etc. However, after the branch wellbore  18  is drilled, the plug  30  may be retrieved from the whipstock assembly  20  to thereby open a flow passage  32  through the assembly. 
     Referring additionally now to FIG. 2, further steps in the method  10  are representatively and schematically illustrated. A liner, casing or other tubular member  34  is installed in the branch wellbore  18  by conveying it through the main wellbore  12  and deflecting it off of the surface  22  and into the branch wellbore. The liner  34  is sealingly engaged with the wellbore  18  using an external casing packer or other sealing device  36 . The liner  34  is then cemented within the wellbore  18 . 
     An upper polished bore receptacle (PBR)  38  is attached to the liner  34  and packer  36  assembly. Another tubular assembly  40  is conveyed through the main wellbore  12  and a lower end  42  thereof inserted into the branch wellbore  18 . The lower end  42  carries seals  44  externally thereon, which are sealingly engaged with the PBR  38 . In this manner, the lower end  42  of the assembly  40  is sealingly engaged within the branch wellbore  18 . An upper end  46  of the assembly  40  remains in the main wellbore  12  and is sealingly engaged therein by setting a packer or hanger  48  of the assembly in the main wellbore. 
     It may now be clearly seen that the tubular assembly  40  extends through a junction  50  of the intersecting wellbores  12 ,  18  and is sealingly engaged within each of the wellbores. Fluid from a formation or zone (not shown) intersected by the branch wellbore  18  may now be produced through the liner  34  and the tubular assembly  40 . However, at this point fluid communication is not permitted between the interior of the tubular assembly  40  and the main wellbore  12  below the whipstock assembly  20 . 
     To provide such fluid communication, one or more openings  52  may be formed through a sidewall of the assembly  40  adjacent the junction  50 . For example, a perforating gun  54  may be conveyed into the assembly  40  and fired to form the openings  52 . However, it is to be clearly understood that any other method for forming an opening through the assembly  40  may be utilized without departing from the principles of the present invention. For example, a chemical cutter, torch, mechanical piercing tool, etc. may be used to form the openings  52 . 
     Note that the whipstock  24  as depicted in FIG. 2 has an alternate form compared to that shown in FIG.  1 . The whipstock  24  shown in FIG. 2 has an upper closure plate  56  which initially prevents fluid communication through the whipstock. However, when the perforating gun  54 , or other device, forms the openings  52  through the assembly  40 , openings  58  are also formed through the closure plate  56 , thereby providing a flow passage through the whipstock  24 . In this manner, a separate trip to retrieve the plug  30  from the whipstock assembly  20  is not required, the plug not being used at all in the whipstock assembly as depicted in FIG.  2 . 
     It will now be readily appreciated by one skilled in the art that fluid communication is now permitted between the main wellbore  12  above the assembly  40  and each of the branch wellbore  18  below the assembly  40  and the main wellbore  12  below the whipstock assembly  20  through the assembly  40 . Fluid communication is also provided between the interior of the assembly  40  and a formation or zone  60  surrounding the junction  50 . The formation  60  may be relatively impermeable, in which case little if any actual fluid flow is experienced between the formation  60  and the wellbores  12 ,  18 , or fluid may be produced from, or injected into, the formation in the method  10  if desired. Note that no cement is deposited between the assembly  40  and the wellbores  12 ,  18  within the junction  50 . 
     Referring additionally now to FIG. 3, another method  70  of completing a subterranean well is representatively and schematically illustrated. The method  70  is similar in many respects to the method  10  described above and the same reference numbers are used to indicated elements similar to those described previously. 
     The method  70  differs in one respect from the method  10  in that the whipstock  24  has an alternate construction. The whipstock  24  as shown in FIG. 3 has a relatively easily drillable or millable inner core  72 . The inner core  72  is relatively easily drillable as compared to the remainder of the whipstock  24  (i.e., the outer case thereof), for example, due to its being made of a softer material. The inner core  72  does, however, prevent fluid communication through a flow passage  74  of the whipstock  24 , until the inner core is drilled through. 
     The inner core  72  is shown in dashed lines to indicate that it has already been drilled through as the method  70  is depicted in FIG.  3 . Thus, the inner core  72  is drilled through prior to installing a tubular assembly  76  in the wellbores  12 ,  18 . Note that, when the tubular assembly  76  is installed, it is conveyed through the main wellbore  12  and deflected into the branch wellbore  18  off of the surface  22 , even though the inner core  72  is drilled through. 
     Alternatively, the inner core  72  could be drilled through after the tubular assembly  76  is installed in the wellbores  12 ,  18  by drilling or milling through a sidewall of the assembly and continuing to cut through the inner core. However, as depicted in FIG. 3, openings  52  have been formed through the assembly  76  as described above for the method  10 , i.e., by use of a perforating gun, torch, chemical cutter, etc. 
     The method  70  differs from the method  10  in another respect in that the assembly  76  may be installed in one trip into the well, instead of two trips to install the liner  34  and assembly  40  as described above. The assembly  76  is sealingly engaged within the wellbore  18  using the external casing packer or other sealing device  36 . The assembly  76  is then cemented within the wellbore  18  below the packer  36 . An upper end  78  of the assembly  76  remains in the main wellbore  12  and is sealingly engaged therein by setting the packer or hanger  48  of the assembly in the main wellbore. It is to be clearly understood, however, that it is not necessary in a method incorporating principles of the present invention for the packer  36  to be included in the assembly  76  or for the assembly to be cemented within the wellbore  18 . 
     It may now be clearly seen that the tubular assembly  76  extends through the junction  50  of the intersecting wellbores  12 ,  18  and is sealingly engaged within each of the wellbores. Fluid from a formation or zone (not shown) intersected by the branch wellbore  18  may now be produced through the tubular assembly  76 . Fluid communication is also permitted between the interior of the tubular assembly  76  and the main wellbore  12  below the whipstock assembly  20 , and between the interior of the tubular assembly  76  and the formation  60  surrounding the junction  50 . 
     Note that the whipstock  24  as depicted in FIG. 3 does not necessarily include the inner core  72 , but could alternatively be configured as shown in FIG. 1 or FIG.  2 . Thus it is not necessary in the method  70  for the whipstock assembly  20  to be configured as shown in FIG.  3 . Other whipstocks, including alternate whipstocks described herein, and other types of deflection devices may be utilized, without departing from the principles of the present invention. 
     It will now be readily appreciated by one skilled in the art that fluid communication is now permitted between the main wellbore  12  above the assembly  76  and each of the branch wellbore  18  below the assembly  76  and the main wellbore  12  below the whipstock assembly  20  through the assembly  76 . Fluid communication is also provided between the interior of the assembly  76  and the formation or zone  60  surrounding the junction  50 . The formation  60  may be relatively impermeable, in which case little if any actual fluid flow is experienced between the formation  60  and the wellbores  12 ,  18 , or fluid may be produced from, or injected into, the formation in the method  70  if desired. Note that no cement is deposited between the assembly  76  and the wellbores  12 ,  18  within the junction  50 . 
     Referring additionally now to FIG. 4, another method  80  of completing a subterranean well is representatively and schematically illustrated. The method  80  is similar in many respects to the methods  10 ,  70  described above and the same reference numbers are used to indicated elements similar to those described previously. 
     The method  80  differs in one respect from the methods  10 ,  70  in that the whipstock  24  has an alternate construction. The whipstock  24  as shown in FIG. 4 has a selectively dissolvable inner core  82 . The inner core  82  is selectively dissolvable in that a particular type of fluid will dissolve the inner core when brought into contact with the inner core. For example, the inner core  82  may be readily dissolvable by acid. The inner core  82  does, however, prevent fluid communication through the flow passage  74  of the whipstock  24 , until the inner core is dissolved. 
     The inner core  82  is shown in dashed lines to indicate that it has already been dissolved as the method  80  is depicted in FIG.  4 . The inner core  82  may be dissolved prior to, during, or after installing a tubular assembly  84  in the wellbores  12 ,  18 . Note that, when the tubular assembly  84  is installed, it is conveyed through the main wellbore  12  and deflected into the branch wellbore  18  off of the surface  22 , even though the inner core  82  may have already been dissolved at the time. 
     The inner core  82  may be dissolved before installing the assembly  84  by, for example, circulating a fluid, such as acid, through a tubing string, such as a coiled tubing string, positioned adjacent the inner core. The inner core  82  may be dissolved during installation of the assembly  84  by, for example circulating the fluid through the assembly  84  as it is positioned adjacent the inner core. The inner core may be dissolved after installation of the assembly  84  by, for example, circulating the fluid through a screen or perforated liner  86  interconnected in the assembly. Note that, when the assembly  84  is properly installed in the wellbores  12 ,  18 , the screen  86  is preferably, but not necessarily, positioned within or adjacent the junction  50  as shown in FIG.  4 . 
     The method  80  differs from the method  10  in another respect in that the assembly  84  may be installed in one trip into the well, instead of two trips to install the liner  34  and assembly  40  as described above. The assembly  84  is sealingly engaged within the wellbore  18  using the external casing packer or other sealing device  36 . The assembly  84  is then cemented within the wellbore  18  below the packer  36 . An upper end  88  of the assembly  84  remains in the main wellbore  12  and is sealingly engaged therein by setting the packer or hanger  48  of the assembly in the main wellbore. It is to be clearly understood, however, that it is not necessary in a method incorporating principles of the present invention for the packer  36  to be included in the assembly  84  or for the assembly to be cemented within the wellbore  18 . 
     It may now be clearly seen that the tubular assembly  84  extends through the junction  50  of the intersecting wellbores  12 ,  18  and is sealingly engaged within each of the wellbores. Fluid from a formation or zone (not shown) intersected by the branch wellbore  18  may now be produced through the tubular assembly  84 . Fluid communication is also permitted between the interior of the tubular assembly  84  and the main wellbore  12  below the whipstock assembly  20 , and between the interior of the tubular assembly  84  and the formation  60  surrounding the junction  50 . 
     Note that the whipstock  24  as depicted in FIG. 4 does not necessarily include the inner core  82 , but could alternatively be configured as shown in FIG. 1, FIG. 2 or FIG.  3 . Thus it is not necessary in the method  80  for the whipstock assembly  20  to be configured as shown in FIG.  4 . Other whipstocks, including alternate whipstocks described herein, and other types of deflection devices may be utilized, without departing from the principles of the present invention. 
     It will be readily appreciated by one skilled in the art that fluid communication is now permitted between the main wellbore  12  above the assembly  84  and each of the branch wellbore  18  below the assembly  84  and the main wellbore  12  below the whipstock assembly  20  through the assembly  84 . Fluid communication is also provided between the interior of the assembly  84  and the formation or zone  60  surrounding the junction  50 . The formation  60  may be relatively impermeable, in which case little if any actual fluid flow is experienced between the formation  60  and the wellbores  12 ,  18 , or fluid may be produced from, or injected into, the formation in the method  80  if desired. Note that no cement is deposited between the assembly  84  and the wellbores  12 ,  18  within the junction  50 . 
     It will also be readily appreciated that the above methods  10 ,  70 ,  80  facilitate convenient abandonment of the well. For example, the tubular assembly  40 ,  76  or  84  is not cemented within the junction  50  and is, therefore, much easier to retrieve from the well than if it were cemented therein. To abandon the well in the method  10 , abandonment operations may be performed in the branch wellbore  18 , then the assembly  40  may be cut below the window  26  using conventional techniques, or the assembly  40  may be disengaged from the PBR  38 . The packer  48  may then be released and the assembly  40  retrieved from the well. 
     The whipstock  24  may be retrieved, if desired for abandonment of the lower main wellbore  12 , using a conventional overshot. The remainder of the whipstock assembly  20  may be retrieved by disengaging the packer  28  from the wellbore  12 . Note that, if the whipstock is hollow, such as the whipstock  24  shown in FIGS. 1,  3  &amp;  4 , and the whipstock  90  shown in FIG. 6, it may not be necessary to retrieve the whipstock. Note, also, that these retrieval operations may be performed if desired prior to stimulating the well below the whipstock assembly  20 . 
     Referring additionally now to FIG. 5, the method  10  is depicted in somewhat alternate form, utilizing the tubular assembly  76  instead of the tubular assembly  40 . To facilitate abandonment of the well or stimulation operations, access to the main wellbore  12  on each side of the junction  50  is desired. To accomplish this result, the tubular assembly  76  is severed within the branch wellbore  18 , the packer  48  is unset and the upper end  78  of the tubular assembly is retrieved from the well. If the well is to be abandoned, preferably suitable abandonment operations are performed in the branch wellbore  18  prior to severing the tubular assembly  76  and retrieving the upper end  78  of the tubular assembly from the well. The tubular assembly  76  may be severed by any known method, such as, by chemical cutter, mechanical cutter, explosive cutter, etc. Additionally, if the tubular assembly  40  is used in the method in place of the tubular assembly  76 , the lower end  42  and seals  44  thereof may be disengaged from the PBR  38 , with no need to cut the tubular assembly  40 . A portion of the tubular assembly  76  is shown in FIG. 5 in dashed lines to indicate that it has been retrieved from the well. 
     If the whipstock  24  is provided with a flow passage therethrough, as described above, it may not be necessary to retrieve the whipstock in order to perform abandonment or stimulation operations in the main wellbore  12  below the whipstock. However, if it is desired to retrieve the whipstock  24 , an overshot may be used as described above, or another type of retrieval tool may be used to disengage the whipstock from the packer  28 . Alternatively, the whipstock  24  and packer  28  could be retrieved together from the well by unsetting the packer. The whipstock  24  is shown in dashed lines in FIG. 5 to indicate that it has been retrieved from the well. 
     It will be readily appreciated that, with the upper portion of the tubular assembly  76  and the whipstock  24  retrieved from the well, access is now provided to the main wellbore  12  below the junction  50  for stimulation or abandonment operations therein. Note that the whipstock  24  and the upper portion of the tubular assembly  76  may be reinstalled in the well if desired. If the tubular assembly  40  is used in the method  10 , then reinstallation of the tubular assembly is made more convenient due to the presence of the PBR  38  in the branch wellbore  18 . 
     Referring additionally now to FIG. 6, an alternate whipstock  90  embodying principles of the present invention is representatively and schematically illustrated. The whipstock  90  may be used in place of the whipstock  24  in any of the methods  10 ,  70 ,  80  described above. 
     The whipstock  90  has a plug  92  positioned in the flow passage  74  blocking fluid flow therethrough. The plug  92  is preferably dispersible upon contact with fluid in the well. For example, the plug  92  may be made of a compressed salt and sand mixture which is capable of resisting a pressure differential applied thereacross, but which is structurally compromised when placed in contact with fluid in the well. An example of such a dispersible plug structure is provided in U.S. Pat. No. 5,479,986, the disclosure of which is incorporated herein by this reference. However, it is to be clearly understood that other dispersible plug structures may be used in the whipstock  90  without departing from the principles of the present invention. 
     Barrier members  94  isolate the plug  92  from fluid in the well. The barrier members  94  may be made of an elastomeric material, ceramic material, or other type of material. To expose the plug  92  to the fluid in the well, at least one of the barrier members  94  may be pierced or broken, for example, by impacting it with a wireline or slickline conveyed piercing tool  96 . However, many other ways of exposing the plug  92  to fluid in the well may be utilized as well. For example, a port or a fluid conduit may be opened to permit fluid communication with the plug, etc. Thus, it will be readily appreciated that any manner of providing contact between the plug  92  and fluid in the well may be used, without departing from the principles of the present invention. 
     Of course, a person skilled in the art would, upon consideration of the foregoing detailed description readily appreciate that many additions, substitutions, deletions and other changes may be made to the specific embodiments described above, and these 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.