A mechanical sliding sleeve ( 101 ) includes a sleeve housing ( 105 ) defining a fluid communication port, a first sub ( 103 ) affixed to the sleeve housing, and a second sub ( 107 ) affixed to the sleeve housing. An isolation sleeve ( 201 ) is disposed in an internal bore defined by the sleeve housing, the first sub, and the second sub, and defines a fluid communication port ( 113 ). The isolation sleeve is slidable along interfaces between the first sub, the second sub, and the sleeve housing between an open position, wherein fluid is allowed through the ports, and a closed position, wherein fluid passage through the ports is inhibited. A sealing element is operably associated with the sleeve housing, the first sub, the second sub, and the isolation sleeve to inhibit fluid flow through the ports unless the isolation sleeve is in the open position, and to seal at least a portion of the interfaces from contact with downhole fluids.

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mechanical sliding sleeve for use in downhole, oilfield operations. 
     2. Description of Related Art 
     In downhole oilfield operations, it is often desirable to selectively allow fluid communication between an interior of a tubing string and an annulus defined by the tubing string and a well casing. A “sliding sleeve,” which typically is made up as an integral part of a tubing string, provides such functionality. The sliding sleeve utilizes a sliding isolation sleeve to isolate fluid communication between the annulus and the interior of the tubing string. When in a “closed” configuration, the isolation sleeve is slidingly positioned to inhibit flow between the interior of the tubing string and the annulus. When in an “open” configuration, the isolation sleeve is slidingly positioned to allow flow between the interior of the tubing string and the annulus. 
     Such isolation sleeves are typically operated either by mechanical means or by hydraulic means. Mechanically-operated isolation sleeves are operated by running a “shifting tool” into a bore of the sliding sleeve and using the tool to physically move the isolation sleeve between the open and closed positions. Moving parts of conventional mechanically-operated isolation sleeves, however, are exposed to downhole fluids that contain debris, which can foul the moving parts. Such debris and other deposits from downhole fluids can readily form obstructions about the moving parts of sliding sleeves, sometimes encasing the sleeve in a shell, thus preventing the shifting tool from shifting the sleeve. In thermal wells, the rate and quantity at which deposits form on the sliding sleeve is greatly accelerated, as compared to non-thermal wells. Normally, extensive cleaning of such shifting sleeves is required before the sleeve can be operated. However, cleaning does not always ensure proper operation of such sleeves. Moreover, the position of a conventional mechanically-operated sliding sleeve in a tubing string is often difficult to locate when the shifting tool is lowered into the tubing string. 
     Hydraulically-operated isolation sleeves utilize hydraulic circuits incorporated into the sliding sleeve that route hydraulic fluid to move the isolation sleeve between the open and closed positions. Such hydraulically-operated isolation sleeves are more complex, are susceptible to hydraulic fluid leaks, and have larger annular profiles than mechanically-operated isolation sleeves. Moreover, hydraulically-operated sliding sleeves are more difficult and time consuming to install. Furthermore, a secondary method of shifting hydraulically-operated sliding sleeves is desirable in case the hydraulic system used to primarily operate the sliding sleeve fails. In some cases, providing fluid communication between the tubing string and the annulus may entail machining an opening through the sliding sleeve by, for example, milling. 
     There are many designs of sliding sleeves well known in the art, however, considerable shortcomings remain. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a mechanical sliding sleeve is provided. The mechanical sliding sleeve includes a sleeve housing defining a fluid communication port, a first end and a second end; a first sub affixed to the first end of the sleeve housing; and a second sub affixed to the second end of the sleeve housing. The sleeve housing, the first sub, and the second sub define an internal bore. The mechanical sliding sleeve further includes an isolation sleeve disposed in the internal bore and defining a fluid communication port. The isolation sleeve is slidable along interfaces between the first sub, the second sub, and the sleeve housing between an open position, wherein the fluid communication port of the isolation sleeve is at least generally aligned with the fluid communication port of the sleeve housing, and a closed position, wherein the fluid communication port of the isolation sleeve is misaligned with the fluid communication port of the sleeve housing. The mechanical sliding sleeve further includes at least one sealing element operably associated with the sleeve housing, the first sub, the second sub, and the isolation sleeve. The at least one sealing element inhibits fluid flow through the fluid communication ports unless the isolation sleeve is in the open position and seals at least a portion of the interfaces from contact with downhole fluids. 
     In another aspect, the present invention provides a tubing string. The tubing string includes a production string having an upper portion and a lower portion. The tubing string further includes a mechanical sliding sleeve affixed between and in fluid communication with the upper portion of the production string and the lower portion of the production string. The mechanical sliding sleeve includes a sleeve housing defining a fluid communication port, a first end and a second end; a first sub affixed to the first end of the sleeve housing and to the upper portion of the production string; and a second sub affixed to the second end of the sleeve housing and to the lower portion of the production string. The sleeve housing, the first sub, and the second sub define an internal bore. The mechanical sliding sleeve further includes an isolation sleeve disposed in the internal bore and defining a fluid communication port. The isolation sleeve is slidable along interfaces between the first sub, the second sub, and the sleeve housing between an open position, wherein the fluid communication port of the isolation sleeve is at least generally aligned with the fluid communication port of the sleeve housing, and a closed position, wherein the fluid communication port of the isolation sleeve is misaligned with the fluid communication port of the sleeve housing. The mechanical sliding sleeve further includes at least one sealing element operably associated with the sleeve housing, the first sub, the second sub, and the isolation sleeve. The at least one sealing element inhibits fluid flow through the fluid communication ports unless the isolation sleeve is in the open position and seals at least a portion of the interfaces from contact with downhole fluids. 
     In yet another aspect, a well completion is provided. The well completion includes a wellhead, a production string having an upper portion affixed to the wellhead and a lower portion, and a mechanical sliding sleeve affixed between and in fluid communication with the upper portion of the production string and the lower portion of the production string. The mechanical sliding sleeve includes a sleeve housing defining a fluid communication port, a first end and a second end; a first sub affixed to the first end of the sleeve housing and to the upper portion of the production string; and a second sub affixed to the second end of the sleeve housing and to the lower portion of the production string. The sleeve housing, the first sub, and the second sub define an internal bore. The mechanical sliding sleeve further includes an isolation sleeve disposed in the internal bore and defining a fluid communication port. The isolation sleeve is slidable along interfaces between the first sub, the second sub, and the sleeve housing between an open position, wherein the fluid communication port of the isolation sleeve is at least generally aligned with the fluid communication port of the sleeve housing, and a closed position, wherein the fluid communication port of the isolation sleeve is misaligned with the fluid communication port of the sleeve housing. The mechanical sliding sleeve further includes at least one sealing element operably associated with the sleeve housing, the first sub, the second sub, and the isolation sleeve. The at least one sealing element inhibits fluid flow through the fluid communication ports unless the isolation sleeve is in the open position and seals at least a portion of the interfaces from contact with downhole fluids. 
     The present invention provides significant advantages, including: (1) providing a mechanical sliding sleeve having moving parts that are protected from downhole fluids and, therefore, debris contained in the downhole fluids; (2) providing a mechanical sliding sleeve having an isolation sleeve that is contained within a pressure integral volume; (3) providing a mechanical sliding sleeve that exhibits a slimmer annular profile than conventional sliding sleeves; (4) providing a mechanical sliding sleeve that incorporates integral lubrication; (5) providing a mechanical sliding sleeve having a sealing element that regenerates its seal; (6) providing a mechanical sliding sleeve that is less likely to inadvertently shift between open and closed positions; and (7) providing a mechanical sliding sleeve that is easier to locate with actuation tools than conventional, mechanical sliding sleeves. 
     Additional features and advantages will be apparent in the written description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features characteristic of the invention are set forth in the appended claims. However, the invention itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote the first figure in which the respective reference numerals appear, wherein: 
         FIG. 1  is a side, elevational view of a first illustrative embodiment of a self-contained, mechanical sliding sleeve, shown in a closed configuration; 
         FIG. 2  is a cross-sectional view of the mechanical sliding sleeve of  FIG. 1 , taken along line  2 - 2  in  FIG. 1 ; 
         FIGS. 3 and 4  are enlarged, cross-sectional views of portions of the mechanical sliding sleeve of  FIG. 1 , as indicated in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view of the mechanical sliding sleeve of  FIG. 1  corresponding to the view of  FIG. 2 , depicting the mechanical sliding sleeve in an open configuration; 
         FIGS. 6 and 7  are enlarged, cross-sectional views of portions of the mechanical sliding sleeve of  FIG. 1 , as indicated in  FIG. 5 , depicting the mechanical sliding sleeve in an open configuration; 
         FIG. 8  is a side, elevational view of a second illustrative embodiment of a self-contained, mechanical sliding sleeve, shown in a closed configuration; 
         FIG. 9  is a cross-sectional view of the mechanical sliding sleeve of  FIG. 8 , taken along line  9 - 9  in  FIG. 8 ; 
         FIGS. 10 and 11  are enlarged, cross-sectional views of portions of the mechanical sliding sleeve of  FIG. 8 , as indicated in  FIG. 9 ; 
         FIG. 12  is a cross-sectional view of the mechanical sliding sleeve of  FIG. 8  corresponding to the view of  FIG. 9 , depicting the mechanical sliding sleeve in an open configuration; 
         FIGS. 13 and 14  are enlarged, cross-sectional views of portions of the mechanical sliding sleeve of  FIG. 8 , as indicated in  FIG. 12 , depicting the mechanical sliding sleeve in an open configuration; and 
         FIG. 15  is a stylized, partial cross-sectional view of an exemplary implementation of a mechanical sliding sleeve, such as the mechanical sliding sleeve embodiments of  FIGS. 1-14 . 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     The present invention represents a self-contained, mechanical sliding sleeve for use in downhole, oilfield operations. A shifting mechanism of the mechanical sliding sleeve is disposed in a sealed volume to inhibit debris in downhole fluid from interfering with the operation of the mechanical sliding sleeve. 
       FIGS. 1-7  depict a first illustrative embodiment of a self-contained, mechanical sliding sleeve  101 . In particular,  FIG. 1  depicts a side, elevational view of mechanical sliding sleeve  101  in a “closed” configuration.  FIG. 2  depicts a cross-sectional view of mechanical sliding sleeve  101 , taken along line  2 - 2  in  FIG. 1 .  FIGS. 3 and 4  depict enlarged, cross-sectional views of mechanical sliding sleeve  101 , as indicated in  FIG. 2 .  FIG. 5  depicts a cross-sectional view of mechanical sliding sleeve  101 , also taken along line  2 - 2  in  FIG. 1 , showing mechanical sliding sleeve  101  in an “open” configuration.  FIGS. 6 and 7  depict enlarged, cross-sectional views of mechanical sliding sleeve  101 , as indicated in  FIG. 5 . 
     Referring to  FIGS. 1-7 , mechanical sliding sleeve  101  comprises a first sub  103 , a sleeve housing  105 , a second sub  107 , an isolation sleeve  201 , and one or more sealing elements, such as injectable packing  203 . Isolation sleeve  201  is disposed within a bore  301  of sleeve housing  105 . Isolation sleeve  201  is slidable with respect to sleeve housing  105  at least between a “closed” position (shown in  FIGS. 1-4 ) and an “open” position (shown in  FIGS. 5-7 ) to selectively allow fluid communication between a production bore  205  of mechanical sliding sleeve  101  and an annulus, such as an annulus  1501  (shown in  FIG. 15 ) defined by mechanical sliding sleeve  101  and a well casing  1503  (shown in  FIG. 15 ). First sub  103  is affixed to a first end  109  of sleeve housing  105  and second sub  107  is affixed to a second end  111  of sleeve housing  105 . In the illustrated embodiment, first sub  103  is threadedly engaged with first end  109  of sleeve housing  105  and second sub  107  is threadedly engaged with second end  111  of sleeve housing  105 . Set screws  207  and  209  are provided in the illustrated embodiment to inhibit first sub  103  and second sub  107 , respectively, from becoming loosened or detached from sleeve housing  105 . 
     First sub  103 , sleeve housing  105 , second sub  107 , isolation sleeve  201 , a first ring  213 , and a second ring  215  define a volume  211  in which injectable packing  203  is disposed. First ring  213  is biased away from a shoulder  303  of first sub  103  by one or more first biasing elements  217  and second ring  215  is biased away from a shoulder  401  of second sub  107  by one or more second biasing elements  219 . Accordingly, the one or more biasing elements  217  and  219  energize injectable packing  203 . In the illustrated embodiment, the one or more biasing elements  217  and  219  include a plurality of spring or “Belleville” washers. Injectable packing  203  inhibits fluid communication between production bore  205  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ), via volume  211  defined by first sub  103 , sleeve housing  105 , second sub  107 , and isolation sleeve  201 . Moreover, injectable packing  203  inhibits downhole fluids from contacting at least a portion of the siding surfaces of mechanical sliding sleeve  101 , i.e., between isolation sleeve  201  and first sub  103 , sleeve housing  105 , and second sub  107 . Thus, injectable packing  203  inhibits debris, such as debris found in downhole fluids, from collecting on at least a portion of the sliding surfaces of mechanical sliding sleeve  101 . 
     Examples of materials for injectable packing  203  include, for example, Steam Shield 2000 available from Sealweld Corporation of Calgary, Alberta, Canada, which is a synthetic blend of fiber-reinforced polymer strands and lubricant. Embodiments that include injectable packing, such as injectable packing  203 , generally exhibit smaller annular profiles than embodiments utilizing other types of sealing elements. Moreover, injectable packing  203  provides lubrication to decrease friction between isolation sleeve  201 , first sub  103 , sleeve housing  105 , and second sub  107  when isolation sleeve  201  is slidingly operated between open and closed positions. Furthermore, because injectable packing  203  is contained within volume  211 , injectable packing  203  is displaced within volume  211  when isolation sleeve  201  is shifted between open and closed positions. This displacement causes injectable packing  203  to flow between ends of isolation sleeve  201 . Often, injectable packing  203  regenerates its seal after every shifting operation because injectable packing  203  is forced to flow in areas wherein the seal has been lost or where a void has formed. Additionally, injectable packing  203  can be formulated to endure more severe, e.g., higher temperature, higher pressure, more corrosive, and/or steam-containing, environments than other types of seals. The force required to shift isolation sleeve  201  through injectable packing  203  can also be taken advantage of to inhibit isolation sleeve  201  from inadvertently sliding to an undesired position. 
     Still referring to  FIGS. 1-7 , sleeve housing  105  defines a fluid communication port  113  and isolation sleeve  201  defines a fluid communication port  221 . When mechanical sliding sleeve  101  is in the closed configuration, shown in  FIGS. 1-4 , isolation sleeve  201  is positioned such that fluid communication port  221  of isolation sleeve  201  is offset from, i.e., misaligned with respect to, fluid communication port  113  of sleeve housing  105 . Thus, when mechanical sliding sleeve  101  is in the closed configuration, fluid communication is inhibited between production bore  205  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ), via fluid communication ports  113  and  221 . When mechanical sliding sleeve  101  is in the open configuration, shown in  FIGS. 5-7 , isolation sleeve  201  is positioned such that fluid communication port  221  of isolation sleeve  201  is at least generally aligned with fluid communication port  113  of sleeve housing  105 . Thus, when mechanical sliding sleeve  101  is in the open configuration, fluid communication is allowed between production bore  205  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ), via fluid communication ports  113  and  221 . 
     Referring in particular to  FIGS. 2-7 , isolation sleeve  201  defines a locator groove  223  and a shifting slot  225 . To slide isolation sleeve  201  between the closed position (shown in  FIGS. 1-4 ) and the open position (shown in  FIGS. 5-7 ), a tool (not shown) is run into production bore  205  of mechanical sliding sleeve  101 . The tool is located with respect to isolation sleeve  201  by mating with locator groove  223 . A feature of the tool engages shifting slot  225  of isolation sleeve  201 . The tool is moved generally in a direction corresponding to an arrow  227  (shown in  FIGS. 2 and 5 ) to slide isolation sleeve  201  from the closed position (shown in  FIGS. 1-4 ) to the open position (shown in  FIGS. 5-7 ). The tool is moved generally in a direction counter to arrow  227  to slide isolation sleeve  201  from the open position to the closed position. 
     The present invention contemplates sliding mechanical seal embodiments that use sealing means other than injectable packing  203 , such as, for example, pressure integral seals. Accordingly,  FIGS. 8-14  depict a second illustrative embodiment of a self-contained, mechanical sliding sleeve  801 . In particular,  FIG. 8  depicts a side, elevational view of mechanical sliding sleeve  801  in a “closed” configuration.  FIG. 9  depicts a cross-sectional view of mechanical sliding sleeve  801 , taken along line  9 - 9  in  FIG. 8 .  FIGS. 10 and 11  depict enlarged, cross-sectional views of mechanical sliding sleeve  801 , as indicated in  FIG. 9 .  FIG. 12  depicts a cross-sectional view of mechanical sliding sleeve  801 , also taken along line  9 - 9  in  FIG. 8 , showing mechanical sliding sleeve  801  in an “open” configuration.  FIGS. 13 and 14  depict enlarged, cross-sectional views of mechanical sliding sleeve  801 , as indicated in  FIG. 12 . 
     Referring to  FIGS. 8-14 , mechanical sliding sleeve  801  comprises a first sub  803 , a sleeve housing  805 , a second sub  807 , an isolation sleeve  901 , and one or more sealing elements, such as pressure integral seals  903 ,  905 ,  907 , and  909 . Isolation sleeve  901  is disposed within a bore  1001  of sleeve housing  805 . Isolation sleeve  901  is slidable with respect to sleeve housing  805  at least between a “closed” position (shown in  FIGS. 8-11 ) and an “open” position (shown in  FIGS. 12-14 ) to selectively allow fluid communication between a production bore  911  of mechanical sliding sleeve  801  and an annulus, such as an annulus  1501  (shown in  FIG. 15 ) defined by mechanical sliding sleeve  801  and a well casing  1503  (shown in  FIG. 15 ). First sub  803  is affixed to a first end  809  of sleeve housing  805  and second sub  807  is affixed to a second end  811  of sleeve housing  805 . In the illustrated embodiment, first sub  803  is threadedly engaged with first end  809  of sleeve housing  805  and second sub  807  is threadedly engaged with second end  811  of sleeve housing  805 . Set screws  813  and  913  are provided in the illustrated embodiment to inhibit first sub  803  from becoming loosened or detached from sleeve housing  805 . Set screws  815  and  915  are provided in the illustrated embodiment to inhibit second sub  807  from becoming loosened or detached from sleeve housing  805 . 
     In the illustrated embodiment, fluid communication between first sub  803  and isolation sleeve  901  is inhibited by pressure integral seal  903 , disposed in a groove  1003  defined by isolation sleeve  901 . Similarly, fluid communication between second sub  807  and isolation sleeve  901  is inhibited by pressure integral seal  905 , disposed in a groove  1105  defined by isolation sleeve  901 . Fluid communication between sleeve housing  805  and isolation sleeve  901  is inhibited by pressure integral seals  907  and  909 , which are disposed in grooves  1007  and  1109 , respectively, each defined by isolation sleeve  901 . In the alternative, however, groove  1003  may be defined by first sub  803 , groove  1105  may be defined by second sub  807 , and grooves  1007  and  1109  may be defined by sleeve housing  805 . Pressure integral seals  903 ,  905 ,  907 , and  909  inhibit fluid communication between production bore  911  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ) via interfaces between isolation sleeve  901  and first sub  803 , sleeve housing  805 , and second sub  807 . Moreover, pressure integral seals  903 ,  905 ,  907 , and  909  inhibit downhole fluids from contacting at least a portion of the siding surfaces of mechanical sliding sleeve  801 , i.e., between isolation sleeve  901  and first sub  803 , sleeve housing  805 , and second sub  807 , by sealing a volume about the sliding surfaces. Thus, pressure integral seals  903 ,  905 ,  907 , and  909  inhibit debris, such as debris found in downhole fluids, from collecting on at least a portion of the sliding surfaces of mechanical sliding sleeve  801 . It should be noted that many varieties of seals may be used as pressure integral seals  903 ,  905 ,  907 , and  909 . For example, pressure integral seals  903 ,  905 ,  907 , and  909  may include chevron seals, o-rings, molded seals, or the like. 
     Still referring to  FIGS. 8-14 , sleeve housing  805  defines fluid communication ports  817  and  921 , while isolation sleeve  901  defines fluid communication ports  923  and  925 . When mechanical sliding sleeve  801  is in the closed configuration, shown in  FIGS. 8-11 , isolation sleeve  901  is positioned such that fluid communication ports  923  and  925  of isolation sleeve  901  are offset from, i.e., misaligned with respect to, fluid communication ports  817  and  921  of sleeve housing  805 . Thus, when mechanical sliding sleeve  801  is in the closed configuration, fluid communication is inhibited between production bore  911  of mechanical sliding sleeve  801  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ), via fluid communication ports  817 ,  921 ,  923 , and  925 . When mechanical sliding sleeve  801  is in the open configuration, shown in  FIGS. 12-14 , isolation sleeve  901  is positioned such that fluid communication ports  923  and  925  of isolation sleeve  901  are at least generally aligned with fluid communication ports  817  and  921  of sleeve housing  805 . Thus, when mechanical sliding sleeve  801  is in the open configuration, fluid communication is allowed between production bore  911  and an annulus, e.g., annulus  1501  (shown in  FIG. 15 ), via fluid communication ports  817 ,  921 ,  923 , and  925 . 
     Referring in particular to  FIGS. 9-14 , isolation sleeve  901  defines a locator groove  927  and a shifting slot  929 . To slide isolation sleeve  901  between the closed position (shown in  FIGS. 8-11 ) and the open position (shown in  FIGS. 12-14 ), a tool (not shown) is run into production bore  911  of mechanical sliding sleeve  801 . The tool is located with respect to isolation sleeve  901  by mating with locator groove  927 . A feature of the tool engages shifting slot  929  of isolation sleeve  901 . The tool is moved generally in a direction corresponding to an arrow  931  (shown in  FIGS. 9 and 12 ) to slide isolation sleeve  901  from the closed position (shown in  FIGS. 8-11 ) to the open position (shown in  FIGS. 12-14 ). The tool is moved generally in a direction counter to arrow  931  to slide isolation sleeve  901  from the open position to the closed position. 
       FIG. 15  is a stylized, partial cross-sectional view of an exemplary well completion  1504  including a mechanical sliding sleeve  1505 , such as mechanical sliding sleeve  101  or  801 . In the illustrated embodiment, mechanical sliding sleeve  1505  is disposed in a well  1507  with a wellhead  1509  positioned at a surface  1511  of well  1507 . Well casing  1503  extends from surface  1511  to a position proximate a lower end of well  1507 . A production string  1513  extends from wellhead  1509  into well  1507  via well casing  1503 . Mechanical sliding sleeve  1505  is disposed between an upper portion  1515  of production string  1513  and a lower portion  1517  of production string  1513 . When in the open configuration, fluid communication is allowed between an interior of production string  1513  and annulus  1501 , while when in the closed configuration, fluid communication is inhibited between an interior of production string  1513  and annulus  1501 . 
     While mechanical sliding sleeve  1505  is depicted in a particular implementation in  FIG. 15 , the scope of the present invention is not so limited. Rather, it will be appreciated that mechanical sliding sleeve  1505  may be incorporated into production strings having configurations other than that shown in  FIG. 15  or may be incorporated into completion or workover strings, with wellhead  1509  being removed and a workover or drilling apparatus being positioned relative to well  1507 . 
     The particular embodiments disclosed above are illustrative only, as the 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 embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications.