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CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is continuation of U.S. patent application Ser. No. 13/879,689 filed on Apr. 16, 2013, which is a National Stage entry of and claiming priority to International Application No. PCT/US2012/035754 filed on Apr. 30, 2012. 
    
    
     BACKGROUND 
     The present invention relates generally to providing a casing exit for a lateral borehole, and more particularly to systems and methods for providing a casing exit with little or no milling of the casing. 
     Hydrocarbons can be produced through relatively complex wellbores traversing a subterranean formation. Some wellbores can include multilateral wellbores and/or sidetrack wellbores. Multilateral wellbores include one or more lateral wellbores extending from a parent (or main) wellbore. A sidetrack wellbore is a wellbore that is diverted from a first general direction to a second general direction. A sidetrack wellbore can include a main wellbore in a first general direction and a secondary wellbore diverted from the main wellbore in a second general direction. A multilateral wellbore can include one or more windows or casing exits to allow corresponding lateral wellbores to be formed. A sidetrack wellbore can also include a window or casing exit to allow the wellbore to be diverted to the second general direction. 
     The casing exit for either multilateral or sidetrack wellbores can be formed by positioning a casing joint and a whipstock in a casing string at a desired location in the main wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) machines away and eventually penetrates part of the casing joint to form the casing exit in the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore. 
     Milling the casing exit is a time consuming and potentially harmful process. Milling away the material of the casing creates highly abrasive metallic chips that can cause significant wear on equipment located in the wellbore during the milling process and on equipment that subsequently passes through the area in which the milling takes place. Furthermore, because the mill is only used for milling the casing exit, several trips down the wellbore are required before commencing actual drilling of the associated lateral wellbore. 
     SUMMARY OF THE INVENTION 
     The present invention relates generally to providing a casing exit for a lateral borehole, and more particularly to systems and methods for providing a casing exit with little or no milling of the casing. 
     In some embodiments, a method is disclosed. The method may include introducing into a wellbore a casing section having an outer sleeve and an inner sleeve rotatably received within the outer sleeve, the outer sleeve defining an outer window that opens into the wellbore and the inner sleeve defining an inner window rotationally alignable with the outer window, wherein the inner sleeve defines a first alignment portion engageable to rotate the inner sleeve with respect to the outer sleeve, advancing the casing section to a wellbore location with the casing section in a closed configuration where the inner window is rotationally misaligned with the outer window such that the inner sleeve occludes the outer window, securing the casing section at the wellbore location, extending a deflector tool within the casing section such that a second alignment portion provided on the deflector tool engages the first alignment portion, and rotating the deflector tool such that the inner sleeve rotates with respect to the outer sleeve and moves the casing section into an open configuration where the inner window is rotationally aligned with the outer window. 
     In other embodiments, a system may be disclosed and may include a cylindrical outer sleeve having a proximal end and a distal end and defining an outer window extending between the proximal and distal ends, a cylindrical inner sleeve rotatably received within the outer sleeve and defining an inner window rotationally alignable with the outer window, the inner sleeve defining a slot engageable to rotate the inner sleeve with respect to the outer sleeve between a first position, where the inner window is rotationally misaligned with the outer window, and a second position, where the inner window is rotationally aligned with the outer window, one or more bearing assemblies configured to prevent axial displacement between the inner and outer sleeves, and a deflector tool extendable at least partially within the inner sleeve and defining a radially protruding lug configured to engage the slot such that the deflector tool is able to rotate the inner sleeve from the first position to the second position. 
     The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the preferred embodiments that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are included to illustrate certain aspects of the present invention, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure. 
         FIG. 1  is a schematic illustration of an offshore oil and gas platform using an exemplary rotatable window casing, according to one or more embodiments disclosed. 
         FIG. 2  is a perspective view of the rotatable window casing of  FIG. 1  in a closed configuration. 
         FIG. 3  is a section view taken along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is a section view taken along line  4 - 4  of  FIG. 2 . 
         FIG. 5  is an enlarged perspective view showing an alignment portion of an inner sleeve of the rotatable window casing of  FIG. 2 . 
         FIG. 6  is a perspective view of the rotatable window casing of  FIG. 2  in an open configuration. 
         FIG. 7  is a section view taken along line  7 - 7  of  FIG. 6 . 
         FIG. 8  is an enlarged section view similar to  FIG. 3  with the rotatable window casing in the open configuration and showing the alignment portion of  FIG. 4 . 
         FIG. 9  is a perspective view of a deflector tool configured for use with the offshore oil and gas platform of  FIG. 1  and the rotatable window casing of  FIG. 2 . 
         FIG. 10  is an enlarged perspective view of a portion of the deflector tool of  FIG. 9 . 
         FIG. 11  is a perspective view showing the rotatable window casing of  FIG. 2  in partial section, in the closed configuration, and with the deflector tool of  FIG. 5  inserted therein. 
         FIG. 12  is a perspective view similar to  FIG. 11  where the deflector tool has been rotated and latched into position and the rotatable window casing has been moved from the closed configuration to the open configuration. 
         FIG. 13  is a perspective view showing the rotatable window casing of  FIG. 2  in the open configuration with the deflector tool of  FIG. 9  latched into position. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to providing a casing exit for a lateral borehole, and more particularly to systems and methods for providing a casing exit with little or no milling of the casing. 
     Referring to  FIG. 1 , illustrated is an offshore oil and gas platform  10  that uses an exemplary rotatable window casing section  14 , according to one or more embodiments of the disclosure. Even though  FIG. 1  depicts an offshore oil and gas platform  10 , it will be appreciated by those skilled in the art that the exemplary rotatable window casing section  14 , and its alternative embodiments disclosed herein, are equally well suited for use in or on other types of oil and gas rigs, such as land-based oil and gas rigs or any other location. The platform  10  may be a semi-submersible platform  18  centered over a submerged oil and gas formation  22  located below the sea floor  26 . A subsea conduit  30  extends from the deck  34  of the platform  18  to a wellhead installation  38  including one or more blowout preventers  42 . The platform  18  has a hoisting apparatus  46  and a derrick  50  for raising and lowering pipe strings, such as a drill string  54 . 
     As depicted, a main wellbore  58  has been drilled through the various earth strata, including the formation  22 . The terms “parent” and “main” wellbore are used herein to designate a wellbore from which another wellbore is drilled. It is to be noted, however, that a parent or main wellbore does not necessarily extend directly to the earth&#39;s surface, but could instead be a branch of yet another wellbore. A casing string  52 , including the rotatable window casing section  14 , is at least partially cemented within the main wellbore  58 . The term “casing” is used herein to designate a tubular string used to line a wellbore. Casing may actually be of the type known to those skilled in the art as “liner” and may be made of any material, such as steel or composite material and may be segmented or continuous, such as coiled tubing. The rotatable window casing section  14  forms part of the casing string  52  and is positioned along the casing string  52  at a location where it is desired to create a lateral borehole or wellbore  64  (shown in phantom) that intersects the parent or main wellbore  58 . 
     Referring also to  FIG. 2 , the casing section  14  includes a generally cylindrical outer sleeve  66  including a proximal end  70  that, in the illustrated embodiment, is configured for coupling to uphole portions of the casing string  52 , and a distal end  74 . The distal end  74  may be coupled to additional downhole portions of the casing string  52  or may include a plug or other wellbore termination depending upon whether the main wellbore  58  continues beyond the casing section  14  or terminates substantially at the casing section  14 . The outer sleeve  66  may be formed by a generally cylindrical outer sleeve wall  78 . The outer sleeve wall  78  may be formed of steel, aluminum, composites, combinations thereof, or substantially any other suitable material or combination of materials. Once the casing section  14  is properly located within the main wellbore  58 , the outer sleeve wall  78  remains substantially fixed with respect to the main wellbore  58 . The outer sleeve wall  78  includes a pre-formed opening that defines an outer window  82 . By “pre-formed” it is meant that the opening that defines the outer window  82  is formed in the outer sleeve wall  78  before the casing section  14  is introduced into the wellbore. In the illustrated embodiment, the outer window  82  is substantially rectangular and arcuate and extends generally from the proximal end  70  to the distal end  74  of the casing section  14 . 
     Referring also to  FIG. 3 , the casing section  14  also includes a generally cylindrical inner sleeve  86  that is moveably received within the outer sleeve  66 . In the exemplary embodiment of the drawings, the inner sleeve  86  is rotatable with respect to the outer sleeve  66 . The inner sleeve  86  of the exemplary embodiment is closely received by and is in substantial mating engagement with an inner surface  90  of the outer sleeve wall  78 . The inner sleeve  86  includes a proximal end  94  and a distal end  98  that are each rotatably coupled to the outer sleeve  66  by suitable seal and bearing assemblies  102 . In the illustrated embodiment the bearing assemblies  102  permit rotational movement of the inner sleeve  86  with respect to the outer sleeve  66  while substantially preventing or limiting axial movement of the inner sleeve  86  with respect to the outer sleeve  66 . In other embodiments, the inner sleeve  86  may also or alternatively be axially moveable with respect to the outer sleeve  66 . 
     The inner sleeve  86  includes an inner sleeve wall  106 . The inner sleeve wall  106  includes a pre-formed opening that defines an inner window  110 . In the illustrated embodiment the inner window  110  includes a proximal portion  114  that is substantially rectangular and arcuate, and a tapered distal portion  118  having a substantially triangular or truncated triangular profile. It should be understood that the section view of  FIG. 3  only shows substantially one-half of the inner window  110 .  FIG. 3  illustrates the casing section  14  in a first or closed configuration, where the inner window  110  does not communicate with or is otherwise not exposed to the outer window  82  ( FIG. 2 ). 
     For instance, as further shown in  FIG. 4 , when the casing section  14  is in the closed configuration, the inner sleeve  86  is in a first position in which the inner window  110  is misaligned with the outer window  82  of the outer sleeve  66 . In the illustrated embodiment, when the inner sleeve  86  is in the first position the inner window  110  is substantially diametrically opposed to the outer window  82 . With the casing section  14  in the closed configuration, the inner sleeve  86 , and more specifically the inner sleeve wall  106 , underlies and substantially closes the outer window  82 . Because the outer window  82  is closed by the inner sleeve wall  106 , material and debris located outside of the casing section  14  is generally unable to pass into the interior of the casing section  14 , and vice-versa. 
     During formation of the main wellbore  58  and assembly of the casing string  52 , the casing section  14  may be inserted into the casing string  52  at a desired location and advanced into the wellbore while in the closed configuration. When the casing section  14  is in the closed configuration, it can function in substantially the same manner as an otherwise standard section of casing or tubing within the casing string  52 , thereby allowing the drill string and other equipment to be moved along and through the length of the casing section  14  in a substantially unrestricted manner until such time as it is desired to form the lateral borehole or wellbore  64  ( FIG. 1 ). The casing section  14  is inserted into the casing string  52  and advanced along the wellbore  58  until it is located at a desired intersection of the lateral borehole  64  and the main wellbore  58 , at which point the casing section  14  is cemented or otherwise secured within the wellbore  58 . 
     Referring also to  FIG. 5 , the distal end  98  of the inner sleeve  86  includes an alignment portion  122  formed on an inner surface  126  of the inner sleeve wall  106 . The illustrated alignment portion  122  may include an axially-extending slot  130  formed within a reduced-diameter portion  134  of the inner sleeve wall  106 . Angled cam surfaces  138  may be positioned at a proximal end of the slot  130  and extend in a proximal and radial direction to function as alignment aids, as discussed further below. In other embodiments, the alignment portion  122  may be or include an aperture in the inner sleeve wall  106 , a projection extending inwardly from the inner sleeve wall  106 , a curved slot or curved projection that defines a more elongated cam surface  138 , combinations thereof, and the like. Moreover, in still other embodiments the alignment portion  122  may be located at the proximal end  94  of the inner sleeve  86 , or at substantially any location along the length of the inner sleeve  86 . 
     Referring now to  FIGS. 6 through 8 , the inner sleeve  86  is moveable, for example rotatable, with respect to the outer sleeve  66  from the first position of  FIGS. 2 through 4  in which the inner window  110  is misaligned with the outer window  82  to a second position shown in  FIGS. 5 through 7  in which the inner window  110  is substantially aligned with the outer window  82 . When the inner sleeve  86  is in the second position, the casing section  14  is in a second, open configuration whereby the interior of the casing section  14  is exposed or opened to the exterior of the casing section  14 . In this way, tools and other equipment can be guided or diverted out of the main wellbore and against the now exposed inner surface of the main wellbore  58  (see  FIG. 1 ), for example to cut or otherwise form a lateral or secondary borehole or wellbore  64  that diverges away from the main wellbore  58 . As shown, the size and shape of the inner window  110  is substantially similar to and generally compliments the size and shape of the outer window  82  to provide an elongated window or casing exit that extends along a substantial majority of the casing section  14 . Generally speaking, the sizes of the inner window and the outer window  82  will be determined by the size of the system and the outer diameters of the mills and/or drill bits used to form the lateral wellbore  64 . For example, a chord length Li ( FIGS. 4 and 7 ) of the inner opening should be larger than the outer diameter of the largest mill or drill bit that will be used to form the lateral wellbore, and a chord length Lo ( FIGS. 4 and 7 ) of the outer opening should be slightly larger than the chord length Li. 
     To move the inner sleeve  86  from the first position in which the casing section  14  is in the closed configuration to the second position in which the casing section  14  is in the open configuration, suitably configured equipment may be run down the casing string  52  to the casing section  14 . Such equipment is provided with an alignment feature configured to engage with the alignment portion  122  provided on the inner sleeve  86 . The equipment is then operated to apply a force to the alignment portion  122  that in turn causes movement, for example rotation, of the inner sleeve  86  with respect to the outer sleeve  66  until the inner sleeve  86  has been moved to the second position and the inner window  110  is brought into substantial alignment with the outer window  82 . 
     Referring also to  FIG. 9 , although substantially any type of down hole equipment can be used to adjust the casing section  14  from the closed configuration to the open configuration, in the illustrated embodiment, a deflector tool  142  in the form of a whipstock assembly may be configured to engage the alignment portion  122  of the inner sleeve  86  and thereby move the inner sleeve  86  from the first position to the second position. It should be appreciated that deflector tools  142  other than the illustrated whipstock assembly, such as a completion deflector, or a combination deflector that incorporates both a whipstock face and a completion deflector into one deflector face can also be utilized in combination with the casing section  14  and the general teachings and concepts discussed herein. At least one advantage of using the deflector tool  142  to move the inner sleeve  86  is that once the inner sleeve  86  has been moved and the casing section  14  is in the open configuration, the deflector tool  142  is already in position to deflect additional drilling equipment through the opened outer window  82  to begin drilling the lateral borehole  64 . 
     The deflector tool  142  includes a proximal portion  146  that includes an angled deflector surface  150 , an intermediate portion including a second alignment portion or alignment section  154  configured to engage the alignment portion  122 , and distal latching portion  158  for fixedly engaging the distal end  74  of the outer sleeve  66 . As can be appreciated, the deflector tool  142  is sized and configured to fit within the casing section  14 . 
     Referring also to  FIG. 10 , one exemplary embodiment of the alignment section  154  includes an elongated and radially outwardly extending projection or lug  162  sized and configured to fit within the slot  130  of the alignment portion  122  of the inner sleeve  86  (see  FIG. 5 ). The lug  162  may include angled lead-in surfaces  166  at each end that cooperate with the cam surfaces  138  ( FIG. 5 ) of the alignment portion  122  to aid in rotational alignment of the inner sleeve  86  with the deflector tool  142  as the deflector tool  142  is advanced into the casing section  14 . As best shown in  FIG. 9 , the lug  162  extends radially in a direction that is substantially diametrically opposed to the direction in which the deflector surface  150  faces. In other embodiments, the configuration of components may be reversed such that the alignment portion  122  of the inner sleeve  86  includes the lug  162  and the alignment section  154  of the deflector tool  142  defines the slot  130 . Still other embodiments may include a more extensive arrangement of cam surfaces on one or both of the alignment portion  122  and the alignment section  154  such that axial movement of the deflector tool  142  into the casing section  14  engages the cam surfaces and causes the inner sleeve  86  to rotate from the first position to the second position. In still other embodiments, the lug  162  may be moveable between an extended position similar to the position illustrated in  FIG. 10 , and a retracted position whereby the lug  162  is substantially flush with the surrounding surfaces of the deflector tool  142 . In such embodiments, once the deflector tool  142  is advanced to an appropriate location in the casing section  14 , the lug  162  could be extended for engagement with or fitment within a suitably configured alignment portion  122  provided on the inner sleeve  86 . 
       FIG. 11  shows the deflector tool  142  axially advancing into the casing section  14  with the casing section  14  in the closed configuration. In the position shown, the lug  162  is still slightly uphole of the alignment portion  122  and the slot  130 . The lug  162  is also substantially radially aligned with the location of the outer window  82  and substantially diametrically opposed with respect to the inner window  110 . Although not shown, the deflector surface  150  is facing toward the inner window  110 . 
     Referring now to  FIG. 12 , the deflector tool  142  has been axially advanced to insert the lug  162  into the slot  130  of the alignment portion  122 . The deflector tool  142  has also been rotated about 180 degrees to move the inner sleeve  86  from the first position to the second position, thereby changing the casing section  14  from the closed configuration to the open configuration. As shown, the inner window  110  has been brought into substantial alignment with the outer window  82 , and the deflector surface  150  is facing through the now opened inner and outer windows  110 ,  82 . In alternative embodiments, one or both of the deflector tool  142  and the alignment portion  122  may be configured with an appropriate arrangement of cam surfaces such that as the deflector tool  142  is axially advanced into the alignment portion  122 , the cam surfaces cause the inner sleeve  86  to rotate from the first position to the second position. In such alternative embodiments, the deflector tool  142  can be advanced into the casing section  14  with the deflector surface  150  facing toward the outer window  82 . Still other embodiments may rely on a combination of cam surfaces and rotation of the deflector tool  142  to fully rotate the inner sleeve  86  from the first position to the second position. 
     In addition, latching cleats  170  on the latching portion  158  have been extended radially outwardly for engagement with the distal end  74  of the outer sleeve  66 . In the illustrated embodiments, the latching cleats  170  may be extended after the deflector tool  142  has been rotated to move the inner sleeve  86  from the first position to the second position. In other embodiments the latching portion  158  may be rotatable with respect to the remainder of the deflector tool  142 , in which case the latching cleats  170  may optionally be extended after the deflector tool  142  has been advanced axially into the casing section, but before the deflector tool  142  is rotated to move the inner sleeve  110  to the second position. 
     Referring to  FIG. 13 , when the casing section  14  is in the open configuration, the entire deflector surface  150  is substantially exposed to the exterior of the casing section  14 . More specifically, the axial length of the inner and outer windows  110 ,  82  are greater than the axial length of the deflector surface  150 . In this way, tools guided through the casing section  14  and into engagement with the deflector surface  150  may be diverted through the casing exit defined by the inner and outer windows  110 ,  82  and against the interior surface of the main wellbore to form or enter into an already formed lateral wellbore. 
     Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.

Summary:
Disclosed are systems and methods for providing a casing exit. One method includes introducing into a wellbore a casing section having an outer sleeve and an inner sleeve rotatably received within the outer sleeve, the outer sleeve defining an outer window and the inner sleeve defining an inner window rotationally alignable with the outer window, wherein the inner sleeve defines a first alignment portion engageable to rotate the inner sleeve, advancing the casing section to a wellbore location with the inner window rotationally misaligned with the outer window, extending a deflector tool within the casing section such that a second alignment portion provided on the deflector tool engages the first alignment portion, and rotating the deflector tool such that the inner sleeve rotates with respect to the outer sleeve and moves the casing section into an open configuration where the inner window is rotationally aligned with the outer window.