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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
       [0001]    Shifting tools are ubiquitously used in the downhole drilling and completions industry, particularly to selectively open ports in various downhole operations. For example, in a fracturing operation sleeves may be shifted with a shifting tool on a service string for successively opening and fracturing through ports, then closed to force formation fluids, e.g., hydrocarbons, into the production string through sand screens or the like as opposed to the ports. Some of the ports may be unintentionally reopened by the shifting tool while pulling the service string out of the hole in this type of fracturing and sand control operation, adversely affecting production. The industry accordingly well receives advances to overcome the aforementioned and other disadvantages in current systems. 
       BRIEF DESCRIPTION 
       [0002]    A system for performing a downhole operation, including a tubular string having a locking profile non-movably located therewith; at least one member movably mounted with the string and including an engagement profile; and a tool runnable with the string and having at least one sub with a key, the key selectively engagable and disengagable with the engagement profile for enabling the tool to control movement of the member with respect to the string when engaged therewith, the key engagable with the locking profile for restricting relative movement between the string and the tool when engaged therewith. 
         [0003]    A method of performing a downhole operation including running in a tool with a string, the string having at least one member movably mounted with the string, the member having an engagement profile; engaging a key of the tool with the engagement profile of the member; moving the member with a service string connected to the tool; disengaging the key from the engagement profile; and engaging the key with a locking profile non-movably secured to the string for restricting relative movement of the tool with respect to the string. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
           [0005]      FIG. 1  is a three-quarter sectional view of a system including a shifting tool releasably connected to a service string; 
           [0006]      FIG. 2  is a three-quarter sectional view of the system of  FIG. 1  disposed within a tubular string with a sleeve shifted by the tool to a first position; 
           [0007]      FIG. 3  is a three-quarter sectional view of the system of  FIG. 2  with the sleeve shifted to a second position; 
           [0008]      FIG. 4  is a three-quarter sectional view of the system of  FIG. 1  illustrating the tool engaged with a locking profile of a tubular string and released from the service string; 
           [0009]      FIG. 5  is a three-quarter sectional view of a tool having an isolation assembly engaged with a locking profile of a tubular string; and 
           [0010]      FIG. 6  is an enlarged view of the area encircled in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
         [0012]    Referring now to  FIG. 1 , an assembly  10  is shown. The assembly  10  includes a service string  12  coupled to a shifting tool  14 . The service string  12  is, for example, controlled by operators at the surface of a borehole in which the string  12  is run. Regardless of structure, the string  12  and the tool  14  enable the operators or the like to perform operations downhole, such as selectively opening and closing ports by engaging with and shifting sleeves or actuating other members or tools housed in a tubular string. For simplicity of discussion, the term “sleeve” as used herein is intended to refer generally to any shiftable or actuatable member, tool, component, etc., and the terms “movable”, “shiftable”, “actuatable”, etc. are thus interchangeable with respect thereto. Further, the shifting tool  14  is shown and described for illustrative purposes only and it is to be appreciated that other styles of shifting tools could be used, for example, including collet fingers, extendable members, etc. 
         [0013]    Referring now to the embodiment of  FIGS. 1-3 , the tool  14  includes an upper sub  16  and a lower sub  18  in order to shift sleeves, e.g., a sleeve  20 . The sleeve  20  and other sleeves resembling the sleeve  20  are slidably housed in a tubular string  22 , which is, e.g., a production string. The upper and lower subs  16  and  18  are essentially mirror images of each other and arranged for shifting sleeves in two opposite directions, in order to, for example, selectively open and close ports, e.g., frac ports, in the tubular string  22 , such as a port  24  shown in  FIG. 3 . Accordingly, like-components of each sub  16  and  18  are assigned the same reference numeral and are structurally and functionally arranged as described herein (with the exception, as noted, that the subs  16  and  18  are arranged as mirror images of each other). 
         [0014]    In the embodiment of  FIGS. 1-3 , for example, the upper and lower subs  16  and  18  are each arranged with a key  26  on a dog  28  for engaging with a corresponding engagement profile in the tubular string  22 . As shown, multiple dogs each having their own key may be included circumferentially about each sub  16  and  18 . Specifically in this embodiment, the upper sub  16  is arranged to engage with an engagement profile  30  of the sleeve  20 . After engaging the keys  26  and  30  together, pulling out the service string  12  will cause the tool  14  to shift up the sleeve  20  (i.e., to the left with respect to the orientation of  FIG. 2 ). Of course, the tool  14  and/or the sub  16  could be arranged to shift the sleeve  20  in another direction. 
         [0015]    Similarly, the key  26  on the dog  28  of the lower sub  18  is arranged for engaging with a second engagement profile  32  of the sleeve  20  for shifting the sleeve  20  down (i.e., to the right with respect to the orientation of  FIG. 3 ). The second engagement profile  32  is located at the opposite end of the sleeve  20  from the profile  30 , and the two opposite ends of the sleeve  20  resemble, for example, mirror images of each other, similar to the upper and lower subs  16  and  18 . That is, the engagement profile  30  faces substantially the opposite direction than the profile  32 , which is similarly true of the keys  26  on the upper and lower subs  16  and  18 , respectively. In this way, the key  26  of each of the upper and lower subs  16  and  18  is arranged to engage one of the profiles  30  or  32 . 
         [0016]    As shown in  FIG. 3 , the port  24  or a plurality of ports are locatable in the tubular string  22  proximate either end of the sleeve  20  for enabling movement of the sleeve  20  to selectively open the port or ports  24 . In the embodiment of  FIGS. 2-3 , the port  24  is positioned proximate the end of the sleeve  20  that includes the profile  32 . Thus, movement of the sleeve  20  toward the opposite end, e.g., up toward the profile  30  (e.g. to the left as shown), will cause the sleeve  20  to open the port  24  by sliding past the port  24 . Similarly, moving the tool  14  down (e.g., to the right as shown) will cause the sleeve  20  to close the port  24 . Seals (not shown) or the like can be included between the sleeve  20  and the tubular string  22  for sealing the port when it is closed. Is it to be noted again that the tool  14 , sleeve  20 , etc. could be arranged differently, e.g., oppositely, with the upper sub  16  arranged for shifting sleeves down and the lower sub  18  arranged for shifting sleeves up. Multiple sleeves resembling the sleeve  20  could be included along the length of tubular string  22 , e.g., for enabling a plurality of locations to be fractured in a fracturing operation. The keys  26  and engagement profiles  30  and  32  are arranged substantially perpendicular to the axial movement direction for ensuring relative movement between the sleeve  20  and the tool  14  is fully restricted when complementary pairs of the profiles are engaged, although other arrangements are possible depending upon the direction of movement and the amount of interference desired between the engagement profiles and keys. 
         [0017]    In addition to the key  26 , each of the dogs  28  includes a disengagement element  34  for enabling the tool  14  to disengage from and move past the sleeve  20  in either direction of movement of the tool  14 . Specifically, the element  34  resembles a double-sided ramp in the illustrated embodiment, although other structures are possible. The disengagement element  34  is used in conjunction with an ability of the dogs  28  to move or pivot radially inwardly. For example, in one embodiment the dogs  28  are each fixed at a pin  36  and pivotable radially inwardly against the force of a spring element  38 , which urges the dogs  28  radially outward by default. Sloped surfaces of the element  34  thus act to move the dogs  28  radially inwardly when axially pulled or pressed against either of surfaces  40  and  42  of the sleeve  20  and the tubular string  22 , respectively. When moved radially inwardly, the keys  26  of the dogs  28  are precluded from locking or engaging the tool  14  with either the sleeve  20  or the tubular string  22  and relative movement is accomplishable in either axial direction. For example, as in the embodiment of  FIGS. 2-3 , the element  34  will only disengage its corresponding dog  28  after the sleeve  20  has been shifted to a position at which the either the sleeve  20  or the element  34  is supported against the tubular string  22 , such that a predetermined force can be overcome for pivoting the dog  28  inward and enabling relative movement between the tool  14  and the sleeve  20 . Alternate embodiments are appreciable in view of the foregoing, such as radially inwardly facing keys on dogs that are movable radially outwardly for causing disengagement thereof. 
         [0018]    As shown in  FIG. 4 , a locking profile  44  is also included along the tubular string  22 . Unlike the profiles  30  and  32 , the locking profile  44  is rigidly or non-movably affixed to (e.g., integrally formed with) the tubular string  22 . The profile  44  resembles the profile  30  with the exception that the profile  44  is not formed on a slidable sleeve. Accordingly, as the profile  44  is not disposed on a slidable or moveable component, axial force on the tool  14  after engagement with the locking profile  44  will not cause the tool  14  to move. Without movement of the tool  14 , the disengagement element  34  cannot encounter a corresponding surface to effect disengagement of the key  26 . Alternatively stated, once the profile  30  of the tool  14  is engaged with the profile  44 , the tool  14  is locked to the tubular string  22 . 
         [0019]    In order to pull out the service string  12  from the tubular, a releasable connection  46  is included connecting the tool  14  to the service string  12 . In the illustrated embodiment, the releasable connection  46  is formed by shear screws  48 , although other release members, e.g., shear rings, collet fingers, etc. could be substituted therefor. Advantageously, the tool  14  can be locked in the tubular string  22  and a force exerted thereon for releasing the releasable connection  46 , e.g., shearing the shear screws  48 , and pulling out the service string  12 . 
         [0020]    Again, although one embodiment is discussed and shown in detailed, e.g., the tool  14  of the system  10 , one of ordinary skill will immediately appreciate that there are many other shifting tools known in the art. Further, one of ordinary skill would additionally appreciate that these other tools are adaptable for use with a locking profile, e.g. the profile  44 , and a releasable connection, e.g., the connection  46 , as described herein. 
         [0021]    In one exemplary embodiment, the tool  14  and the tubular string  22  are run in together with all of the ports initially closed by their corresponding sleeves (e.g., the port  24  blocked by the sleeve  20 ). In this example, the tool  14  is initially located between the locking profile  44  and the bottom-most sleeve. By pulling out the service string  12 , the upper sub  16  of the tool  14  will engage the bottom-most sleeve and pull it up, opening its corresponding port or ports. Fracturing fluid and/or proppant media is then pumpable through the port as part of a fracturing operation. The sleeve can then open each successive port by shifting the corresponding sleeves for enabling multiple locations to be sequentially fractured. After fracturing all locations, the tool  14  is run back in for engagement with the locking profile  44 , closing all of the ports along the way and preparing the tubular string for receiving formation fluid through, for example, sand screens as opposed to the frac ports. After engagement with the locking profile  44 , the service string  12  is tensioned, the connection  46  released, and the service string  12  pulled out. Since the tool  14  remains downhole, there is no risk of the tool  14  unintentionally opening any ports while it is pulled out. Of course, this is one example only, and other operations and arrangements are possible utilizing the invention as described herein. 
         [0022]    Advantageously, by positioning the profile  44  downhole of all of the sleeves, ports, etc., that are shiftable or controllable by the tool  14 , premature engagement with the locking profile  44  can be avoided. For example, the tool  14  could be run-in with the string  22  up-hole of the profile  44  and the operators would not further insert the service string  12  until the downhole operation, e.g., fracturing, has occurred and the sleeves are in their desired positions, e.g., closed. Moreover, placing the locking profile  44  downhole of the sleeves will ensure that the tool  14  does not block or other disturb the flow of formation or production fluids up through the string  22 . Of course, other arrangements for the profile  44  are possible, depending upon the desired operation to be performed, particular structure of the tubular string or other components, etc. 
         [0023]    In some embodiments, isolation may be desired in the tubular string  22 . For example, the bottom sub  18  of the tool  14  in the embodiment of  FIGS. 5 and 6  is equipped with an isolation assembly  50  for isolating the tubular string  22  on opposite sides of the isolation assembly  50  after the tool  14  is locked at the profile  44 . The isolation assembly  50  could include a seal stack  52  or any other type of seal element(s) for sealingly engaging with the tubular string  22 , e.g., at a seal bore  54 . In this way, for example, fluid and pressure isolation is accomplishable between different zones along the length of the tubular string  22 . 
         [0024]    While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Summary:
A system for performing a downhole operation including a tubular string having a locking profile non-movably located therewith. At least one member is movably mounted with the string and includes an engagement profile. A tool is runnable with the string and has at least one sub with a key. The key is selectively engagable and disengagable with the engagement profile for enabling the tool to control movement of the member with respect to the string when engaged therewith. The key is engagable with the locking profile for restricting relative movement between the string and the tool when engaged therewith. A method of performing a downhole operation is also included.