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BACKGROUND OF THE INVENTION 
     The present invention relates generally to subterranean well systems having multiple tubular strings installed therein and, in one embodiment described herein, more particularly provides a dual string completion system utilizing an improved wye block. 
     It is well known in the art to interconnect an upper tubular string to multiple lower tubular strings in a subterranean well utilizing a device known as a wye block. The wye block typically has an upper threaded connection for attachment to the upper tubular string, and multiple lower threaded connections for attachment to the multiple lower tubular strings. In this manner, fluid communication is established between the upper tubular string and each of the multiple lower tubular strings so that, for example, fluids from different formations or zones intersected by the well and produced through corresponding ones of the multiple lower tubular strings may be flowed to the earth&#39;s surface via the upper tubular string. 
     The wye block derives its name from the fact that it has a generally Y-shaped body or housing when it is configured to interconnect a single upper tubular string to two lower tubular strings. In a more general sense, and as used herein, however, the term “wye block” includes configurations in which two or more tubular strings are interconnected to another tubular string by the wye block body or housing. Additionally, the term “wye block” is not restricted to configurations in which a single tubular string extends in an upward direction therefrom and multiple tubular strings extend in a downward direction therefrom, although this may be the most commonly used configuration. 
     As stated above, the typical wye block provides fluid communication between the interconnected tubular strings via their attachment to the wye block body or housing. However, providing convenient access between each of the tubular strings is a far more difficult proposition. For example, if it is desired to convey a wireline tool or a coiled tubing string from the earth&#39;s surface into a certain one of the lower tubular strings, a device or mechanism should be provided in the wye block to direct the wireline tool or coiled tubing string from the upper tubular string, into the desired one of the lower tubular strings, and not into any other of the lower tubular strings. In addition, the device or mechanism should be capable of being repositioned when it is desired to permit access to another selected one of the lower tubular strings. Furthermore, the device or mechanism should not impede flow through the wye block during fluid production from the well, and should be reliable in operation, convenient to operate, and not subject to damage and deterioration during wellbore operations. 
     One proposed method of accomplishing these objectives is to construct the wye block with a diverter mechanism therein. The diverter mechanism may be a type of hinged flapper which, when positioned to one side in the wye block, will divert the tool or coiled tubing string toward a selected one of two lower tubular strings and, when positioned to the other side in the wye block, will divert the tool or coiled tubing string to the other lower tubular string. Openings may be provided in the flapper to permit fluid flow therethrough. 
     Unfortunately, such diverter mechanisms have several shortcomings. For example, the hinged flapper is subject to erosion and other deterioration, due to substantially constant fluid flow therethrough. Debris may accumulate about the diverter mechanism, preventing its subsequent operation. The openings formed through the flapper are typically not equivalent to a full bore opening. Only two lower tubular strings may be selected among by the diverter mechanism. In addition, a positive indication at the earth&#39;s surface is usually not available for determining whether the diverter mechanism has actually selected the desired lower tubular string for access thereto. 
     In view of the foregoing, it will be appreciated that a need exists for an improved wye block and improved methods of servicing wells in which multiple tubular strings are interconnected. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, an improved wye block is provided in which a guide structure thereof is automatically aligned with a selected one of multiple tubular string connections. In a described method of servicing a subterranean well, the guide structure is separately conveyed as a part of an access control assembly into a housing assembly of the wye block after the wye block has been installed in the well interconnecting multiple tubular strings. 
     In one aspect of the present invention, the wye block housing assembly is installed in the well interconnecting multiple tubular strings. An access control assembly is then separately conveyed into the housing assembly when it is desired to access one of the tubular strings attached to the wye block housing assembly. The access control assembly includes a guide surface which is automatically aligned with a selected one of the tubular strings when the access control assembly is installed in the housing assembly. 
     In another aspect of the present invention, the access control assembly includes at least first and second portions. By securing the first portion relative to the second portion before the access control assembly is installed in the wye block housing assembly, the selected one of the tubular strings is determined before the access control assembly is conveyed into the well. 
     In still another aspect of the present invention, the access control assembly first portion engages an orienting device of the wye block housing assembly when the access control assembly is installed in the housing assembly. The orienting device may be a generally helically-shaped orienting profile, so that the access control assembly second portion is rotationally aligned with the selected one of the tubular strings when the access control assembly is installed in the housing assembly. 
    
    
     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 representative embodiments of the invention hereinbelow and the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematicized view of a method of servicing a subterranean well embodying principles of the present invention; 
     FIGS. 2A-2C are quarter-sectional views of successive axial sections of an access control assembly embodying principles of the present invention; and 
     FIGS. 3A-3E are cross-sectional views of successive axial sections of an access control apparatus embodying principles of the present invention, a housing assembly thereof having the access control assembly of FIGS. 2A-2C installed therein. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a method  10  of servicing a subterranean well, which method 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. 
     In the method  10 , a wye block or access control apparatus  12  is installed in a well interconnecting an upper production tubing string  14  to two lower production tubing strings  16 , 18 . The lower string  16  extends downwardly into a lower main or parent wellbore  20 , wherein it is sealingly engaged within a tubular member  22  utilizing a packer  24 . The tubular member  22  is attached to a hollow whipstock  26  sealingly engaged in the lower parent wellbore  20  via another packer  28 . 
     The lower string  18  extends downwardly from the wye block  12  and laterally outwardly through a window  30  formed through casing  32  and cement  34  lining the parent wellbore. The lower string  18  extends into a branch or lateral wellbore  36  drilled outwardly from the window  30 . A packer  38  provides sealing engagement between the lower string  18  and a liner  40  cemented within the lateral wellbore  36 . 
     It will be readily appreciated that fluid produced from the lateral wellbore  36  may be flowed via the lower string  18  to the wye block  12 , and that fluid from the lower parent wellbore  20  may be flowed via the lower string  16  to the wye block. From the wye block  12 , the commingled fluids may be flowed through the upper string  14  to the earth&#39;s surface. Of course, these directions of fluid flow may be reversed if the strings  14 ,  16 ,  18  are utilized for injection rather than production of fluids. 
     It is to be clearly understood, however, that the method  10  is merely illustrative of the wide variety of methods of servicing a well and configurations of tubular strings and equipment therein which may embody principles of the present invention. For example, there may be more than two tubular strings attached to one end of the wye block  12 , it is not necessary for one of the strings to extend into a lateral wellbore, it is not necessary for one of the strings to extend through a hollow whipstock, it is not necessary for the wye block to be configured or oriented as shown in FIG. 1, etc. Thus, it will be readily appreciated that other methods may be practiced, and many modifications may be made to the depicted method  10 , without departing from the principles of the present invention. 
     In one unique aspect of the method  10 , an access control assembly is conveyed into the wye block  12  after the wye block has been installed in the well interconnecting the tubular strings  14 ,  16 ,  18  and when it is desired to provide access to a selected one of the lower strings. In this manner, the access control assembly is not present in the wye block  12  when access to a particular one of the lower strings  16 ,  18  is not required. Thus, the access control assembly is not left in the wye block  12  to deteriorate, become fouled with debris, and block or restrict fluid flow through the wye block. 
     In another unique aspect of the method  10 , the access control assembly is automatically aligned so that it permits access to the selected one of the lower strings  16 , 18  when it is installed in the wye block  12 . In this manner, it is not necessary to engage the access control assembly with a wireline shifting tool or other tool downhole in order to align the access control assembly with the selected string. Instead, the access control assembly is appropriately configured at the earth&#39;s surface so that, when it is installed within the wye block  12 , a guide structure of the access control assembly is automatically oriented to permit access to the selected string. 
     Referring additionally now to FIGS. 2A-2C, an access control assembly  50  embodying principles of the present invention is representatively illustrated. An orienting lock or upper portion  52  of the assembly  50  is utilized to releasably secure and rotationally orient the assembly within a wye block housing assembly described in further detail below. A guide or lower portion  54  of the assembly  50  is utilized to permit access to a selected string attached to the wye block housing assembly, and to exclude access to other strings attached to the wye block housing assembly. Of course, it is not necessary for the upper portion  52  to be above the lower portion  54 , or for the access control assembly  50  to be otherwise constructed exactly as depicted in FIGS. 2A-2C, in keeping with the principles of the present invention. 
     The upper portion  52  includes a series of circumferentially spaced apart keys  56  which are biased outwardly by a corresponding set of springs  58 . The keys  56  are shaped so that they will cooperatively engage a latching profile formed internally in the wye block housing assembly described below. An internal sleeve  60  maintains the keys  56  in engagement with the latching profile when the sleeve is in its downwardly disposed position as depicted in FIG.  2 A. Note that the sleeve  60  is threadedly attached to a tubular upper connector  62  having an internal profile  64  formed therein so that, when it is desired to retrieve the assembly  50  from within the wye block housing assembly, the upper connector may be engaged by an appropriately configured retrieval tool (not shown) which displaces the upper connector and sleeve upwardly, thereby permitting the keys  56  to retract out of engagement with the wye block housing assembly and permitting the assembly to be retrieved from the well. 
     An orienting key  66  of the upper portion  52  is, however, not configured for cooperative engagement with the wye block housing assembly latching profile. Instead, the orienting key  66  is configured for engagement with an orienting profile of the wye block housing assembly, described more fully below. In a unique aspect of the present invention, the orienting key  66  is rotationally oriented relative to the lower portion  54  prior to conveying the assembly  50  into the wye block housing assembly. 
     To orient the key  66  relative to the lower portion  54 , a threaded hole  68  formed through an inner tubular mandrel  70  is aligned with one of a series of circumferentially spaced apart openings  72  (only one of which is visible in FIG. 2A) formed through an outer sleeve  74 . The key  66  extends outwardly through the sleeve  74 . Thus, by installing a screw  76  in the opening  72  and threading it into the hole  68 , the sleeve  74  is rotationally secured relative to the mandrel  70 , thereby rotationally securing the key  66  relative to the mandrel. 
     The lower portion  54  is threadedly attached to the mandrel  70  and is rotationally secured relative thereto by means of one or more set screws  78 . Before securement with the set screws  78 , proper alignment of the lower portion  54  with the mandrel  70  is ensured by alignment of indicator marks or holes  80 ,  82  formed on the lower portion and mandrel. 
     It may now be seen that, by selecting an appropriate one of the openings  72  in which to install the screw  76 , the lower portion may be conveniently rotationally oriented with respect to the key  66 . For example, if it is desired to select from among two tubular string connections spaced 180 degrees apart in the wye block housing assembly for access thereto, two openings  72  may be correspondingly provided in the outer sleeve  74  spaced 180 degrees apart, so that the lower portion  54  may be oriented in either of two rotational positions spaced 180 degrees apart with respect to the key  66 . If it is desired to select from among three tubular string connections spaced 120 degrees apart in the wye block housing assembly for access thereto, three openings  72  may be correspondingly provided in the outer sleeve  74  spaced 120 degrees apart, so that the lower portion  54  may be oriented in one of three rotational positions spaced 120 degrees apart with respect to the key  66 . It will be readily appreciated that a wide variety of relative rotational orientations may be achieved by providing various numbers and spacings of the openings  72 . In addition, it is to be clearly understood that methods of orienting the upper portion  52  relative to the lower portion  54  in keeping with the principles of the present invention are not limited to those representatively described herein, since they are given for illustrative purposes only. For example, instead of providing multiple spaced apart openings  72 , multiple spaced apart threaded holes  68  could be provided, the key  66  could be selectively oriented with respect to the lower portion  54  by utilizing differently configured sleeves  74 , mandrels  70 , or combinations thereof, etc. 
     The lower portion  54  includes an inclined guide surface  84  formed in a guide structure  86  which has an upper generally tubular end  88  and a lower generally cylindrical end  90 . The upper tubular end  88  is threadedly attached and rotationally secured to the upper portion  52  as described above. The lower end  90  is configured to be received within the wye block housing assembly as described below, in a manner restricting lateral displacement of the guide structure  86  relative to the wye block housing assembly. For this purpose, the lower end  90  has a generally conical shape, but may be otherwise configured without departing from the principles of the present invention. 
     Referring additionally now to FIGS. 3A-3E, a wye block or access control apparatus  100  embodying principles of the present invention is representatively illustrated. The wye block  100  may be utilized for the wye block  12  in the method  10  described above. Of course, the method  10  may be performed utilizing a wye block or access control apparatus other than the wye block  100 , and the wye block  100  may be used in methods other than the method  10 , without departing from the principles of the present invention. 
     As depicted in FIGS. 3A-3E, the wye block  100  has the access control assembly  50  operatively installed therein. When used in the method  10 , it will be appreciated that the access control assembly  50  is not installed in a housing assembly  102  of the wye block  100  until it is desired to access a selected one of tubular strings attached to the housing assembly. Additionally, once such access is no longer desired, the assembly  50  may be retrieved from within the housing assembly  102 , so that flow therethrough is not impeded, debris does not accumulate about the access control assembly, the access control assembly does not deteriorate, etc. 
     The orienting key  66  of the access control assembly  50  has engaged a generally helically-shaped orienting profile  104  in the housing assembly  102 , thereby rotationally orienting the access control assembly  50  relative to the housing assembly. The orienting profile  104  is formed on a sleeve  106  secured within the housing assembly  102 . When the access control assembly  50  is lowered into the housing assembly  102 , the orienting key  66  engages the orienting profile  104  and rotates the access control assembly  50  relative to the housing assembly  102 . Thus, the orienting key  66  and the orienting profile  104  may be considered portions of an overall orienting device for rotationally positioning the guide structure  86  relative to the housing assembly  102 . 
     At the lower end of the orienting profile  104  a substantially vertical slot  108  receives the orienting key  66  and prevents further rotation of the access control assembly  50  within the housing assembly  102 . At this time, the other keys  56  engage a cooperatively shaped internal latching profile  110  formed in the sleeve  106 . The upper connector  62  and inner sleeve  60  of the access control assembly  50  are then displaced downwardly relative to the remainder of the upper portion  52 , thereby securing the access control assembly within the housing assembly  102 . 
     It may now be fully appreciated that, when the access control assembly  50  is operatively installed within the housing assembly  102 , the guide structure  86  is automatically aligned with a selected one of two lower tubular string connections  112 ,  114  formed on the housing assembly. As shown in FIGS. 3D &amp; 3E, the guide surface  84  is positioned to deflect a tool, equipment, etc. into the connection  114 , while the remaining tubular portion of the guide structure  86  prevents access to the other connection  112 . It will also be appreciated that, if the screw  76  were installed in another opening  72  spaced 180 degrees apart from the opening  72  shown in FIG. 3C, the guide surface  84  would be positioned to deflect a tool, equipment, etc. into the connection  112 , while the remaining tubular portion of the guide structure  86  would prevent access to the other connection  114 . 
     The lower end  90  of the guide structure  86  is received in a cooperatively shaped recess  116 , thereby preventing undesirable lateral deflection of the guide structure  86  within the housing assembly  102 , while permitting rotation of the access control assembly  50  as it is installed in the housing assembly. 
     At the upper end of the housing assembly  102 , an upper tubular string connection  118  is provided. Each of the connections  112 ,  114 ,  118  may be provided with threads, seals, etc. as needed for interconnection of the wye block  100  to tubular strings in a well. For example, the upper connection  118  could be connected to the string  14 , and the lower connections  112 ,  114  could be connected to the strings  16 , 18 , in the method  10  described above. 
     Of course, many modifications, additions, substitutions, deletions and other changes to the specific embodiments of the present invention described above will be readily apparent to one skilled in the art upon consideration of the above description, 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.

Summary:
A subterranean well completion system and associated methods of servicing wells provide convenient access to selected ones of multiple tubing strings installed in wells. In a described embodiment, a completion system includes a wye block device which has an access control assembly separately conveyed into a housing assembly installed in a well. The access control assembly is conveyed into the housing assembly when it is desired to access a selected one of multiple tubing strings attached to the housing assembly.