Patent Publication Number: US-2002011341-A1

Title: Pack-off system

Description:
RELATED APPLICATION  
     [0001] This is a division of U.S. Ser. No. 09/435,388 filed Nov. 6, 1999. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field Of The Invention  
       [0003] This invention is related to wellbore packers and methods of their use; in certain particular aspects, to an hydraulically set wellbore straddle pack-off system and methods of its use; and in one particular aspect to such a system that is set and released without mechanically pulling or pushing on the system.  
       [0004] 2. Description of Related Art  
       [0005] Often in wellbore operations it is desirable to “straddle” an area of interest in a wellbore, e.g. a formation or part thereof or a zone or location in a wellbore packing off the wellbore above and below the area of interest. Typically a packer is set above and another packer is set below the area of interest.  
       [0006] A variety of prior art straddle pack-off tools are available which include two selectively-settable spaced-apart packing elements. Several such prior art tools use a piston or pistons movable in response to hydraulic pressure to actuate packer element setting apparatus. Debris or other material can block or clog the piston apparatus, inhibiting or preventing setting of the packer elements (and preventing un-setting/release of the packer elements.  
       [0007] Various prior art tools have no emergency pressure release feature, useful, e.g. when a formation goes to vacuum.  
       [0008] Many prior art pack-off systems require the application of tension and/or compression to parts of the system (mechanical pulling and/or pushing), to actuate parts of the system. Such systems cannot be used on coiled tubing.  
       [0009] There has long been a need for an efficient and effective wellbore straddle pack-off system. There has long been a need for such a system without a piston that could be clogged by debris. There has long been a need for such a system which can be selectively released in an emergency situation. There has long been a need for such a system which does not require pulling or pushing for actuation. There has long been a need for such a system useful on coiled tubing.  
       SUMMARY OF THE PRESENT INVENTION  
       [0010] The present invention, in certain aspects, discloses a wellbore pack-off system with selectively-settable spaced-apart packing elements. The packing elements are on a tubular member that is interconnected with one or more additional tubular members so that when fluid (e.g introduced to the pack-off system and/or pumped under pressure, e.g. from an earth surface pumping apparatus or from an apparatus within the wellbore) is applied to the tubular members, they telescope apart. Then a movable tubular setting sleeve is moved to set the packing elements. Such a system may be used in an open hole or in a tubular string (tubing, casing, liner, etc.) in a wellbore. It can be set, e.g. (but not limited to): across a formation or part thereof; across a zone of interest; within a gravel pack screen; across a sliding sleeve; and across two previously-set packers.  
       [0011] In certain embodiments such a system is used with tubulars with alignable orifice(s) and exit port(s) or with an injection sub to treat a formation. The tubulars or injection sub may be any suitable length so that the spaced-apart packers, when set, effectively isolate the area of interest between them. Treating fluid is pumped through one or more orifices and/or exit ports into the area of interest in a formation.  
       [0012] A system according to the present invention may be located, set, and used in a wellbore operation (e.g., but not limited to, formation treatment and setting of an external casing packer) and then released and moved to another location in a wellbore without retrieval to the surface.  
       [0013] In certain aspects, fluid under pressure flowing into the system following setting of the packing elements pushes against parts of the system which “boost” the packing elements, enhancing their sealing effect.  
       [0014] In certain aspects a selectively acutatable flow control apparatus or valve is used in a system according to the present invention to provide for the release of fluid under pressure from within the system to equalize pressures inside and outside the system so the packing elements can be selectively released.  
       [0015] Such systems may be run on any suitable tubular string, e.g., coiled tubing, fiber optic line system, slick line, electrically conductive wireline, electrically non-conductive wireline, casing, or tubing.  
       [0016] What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention&#39;s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide new, useful, unique, efficient, nonobvious wellbore pack-off systems and methods of their use;  
       [0017] Such systems without pistons involved in the setting of packing elements, pistons which could be clogged or blocked by debris;  
       [0018] Such system useful in formation treatment operations;  
       [0019] Such systems with a pressure equalizing valve to permit selective release of the packing elements;  
       [0020] Such systems which are releasable and movable within a bore without the necessity of retrieval to a top of the bore;  
       [0021] Such systems which do not require mechanical pushing or pulling on the system to set and release packer elements; and  
       [0022] Such systems which boost the sealing effect of packing elements.  
       [0023] Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.  
       [0024] The present invention recognizes and addresses the previously-mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one skilled in this art who has the benefits of this invention&#39;s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent&#39;s object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements. 
     
    
    
     DESCRIPTION OF THE DRAWINGS  
     [0025] A more particular description of embodiments of the invention briefly summarized above may be had by references to the embodiments which are shown in the drawings which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to improperly limit the scope of the invention which may have other equally effective or legally equivalent embodiments.  
     [0026]FIG. 1 is a side cross-section view of a generally cylindrical system according to the present invention in a “run-in” configuration.  
     [0027]FIGS. 1A, 1B and  1 C present enlargements of portions of the system of FIG. 1A.  
     [0028]FIG. 2 shows the system of FIG. 1A in a packed-off position with packer elements set in a string of tubing.  
     [0029] FIGS.  3 A- 3 C are side cross-section views of a system according to the present invention. FIGS.  3 D- 3 F show the system of FIGS.  3 A- 3 C in a packed-off position with packer elements set in a string of tubing.  
     [0030]FIG. 4A is a side cross-section view of a step in a method for inflating an external casing packer using a system according to the present invention. FIG. 4B shows the system of FIG. 4A in place with respect to the external casing packer.  
     [0031]FIG. 5A is a side cross-section view of a system according to the present invention. FIG. 5B shows the system of FIG. 5A in place in a tubing string. 
    
    
     DESCRIPTION OF EMBODIMENTS PREFERRED  
     AT THE TIME OF FILING FOR THIS PATENT  
     [0032] Referring now to FIG. 1 and FIGS.  1 A- 1 C, a system  10  according to the present invention has a generally cylindrical top sub  12  with a flow bore  11  therethrough from top to bottom and to which is threadedly connected a top pack-off mandrel  20 . An o-ring  13  seals a sub/mandrel interface and set screws  14  prevent unthreading of the top pack-off mandrel  20  from the top sub  12 .  
     [0033] The top sub  12  is connected to a lower end of any suitable tubular string (tubing, casing, etc.), working string, or coiled tubing S, shown schematically in FIG. 1A, for use in a wellbore or within a bore in a tubular string in a wellbore.  
     [0034] Four spaced-apart crossover pins  15  (any suitable number of pins may be used) secure together a top setting sleeve  30  and a top body  45 . The pins  15  extend through slots  22  in the top pack-off mandrel  20  so that the setting sleeve  30  and top body  45  are movable together with respect to the top pack-off mandrel  20  while the pins move in the slots.  
     [0035] A top spring  7  has a lower end that abuts a shoulder  25  of the top pack-off mandrel  20  and an upper end that abuts a shoulder  48  of the top body  45 . Initially the top spring  7  urges apart the top body and the top pack-off mandrel  20 , thus maintaining a top latch  50  (described below) in a latched position thereby preventing setting of a top packing element  40  (described below).  
     [0036] The top setting sleeve  30  has an end  32  with a lip  33  that abuts a top end of the top packing element  40 . The top packing element  40  is positioned around a lower end of the top pack-off mandrel  20 . The packing elements  40 ,  41  may be made of any suitable resilient material, including but not limited to, any suitable elastomeric or polymeric material, and any suitable known prior art element may be used.  
     [0037] The top latch  50  has a top end secured to a lower end of the top pack-off mandrel  20  by pins  24 . The top latch  50  has a plurality of spaced-apart collet fingers  52  that initially latch onto a shoulder  44  of an upper bottom sub  42 . Set screws  39  secure the bottom sub  42  to a lower end of the top body  45 . The top end of the bottom sub  42  is also threadedly connected to the lower end of the top body  45 . An o-ring  39  seals a top body/bottom sub interface.  
     [0038] An injection sub  46  has a top end threadedly connected to a lower end of the upper bottom sub  42  and a lower end threadedly connected to a top end of a lower bottom sub  43 . An orifice  47  permits fluid flow between the interior of the injection sub  46  and space external to the system  10 . Any number of orifices may be used.  
     [0039] Items  20 ,  30 ,  40   42 ,  45 ,  46  and  50  are generally cylindrical in shape, each with a top-to-bottom bore  101 ,  102 ,  103 ,  104 ,  105 ,  106 , and  107 , respectively, therethrough.  
     [0040] The various parts from the lower bottom sub  43  to a bottom pack off mandrel  21  mirror the upper parts in structure and function; i.e., the following parts correspond to each other:  6 - 7 ;  20 - 21 ;  22 - 23 ;  30 - 31 ;  40 - 41 ;  42 - 43 ;  45 - 49 ;  50 - 51 . A lower end of the bottom pack-off mandrel  21  is threadedly connected to an upper end of a crossover sub  55  and set screws  56  secure the bottom pack-off mandrel  21  to the crossover sub  55 . The crossover sub  55  has a top-to-bottom bore  57  therethrough.  
     [0041] O-rings with the following numerals seal the indicated interfaces:  121 , pack-off mandrel  20 /top body  45 ;  122 , bottom sub  42 /top body  45 ;  123 , bottom sub  43 /bottom body  46 ;  124 , bottom pack-off mandrel  21 /bottom body  46 ;  125 , bottom body  46 /bottom pack-off mandrel  21 ;  126 , crossover sub  55 /bottom pack-off mandrel  21 ; and  127 , crossover sub  55 /valve housing  71 .  
     [0042] A flow activated shut-off valve assembly  70  has a housing  71  with a top-to-bottom bore  77  therethrough. A nozzle  60  is threadedly connected to a lower end of the valve housing  71 . A piston  72  is movably disposed in the bore  77 . The piston  72  has a piston body  73 , a piston member  74  with an upper end within the piston body  73 , and a piston orifice member  75  with a top-to-bottom opening  79  also within the piston body  73 . A locking ring  67  holds the piston orifice member  75  and piston member  74  in place. Port  65  provides for pressure equalization between the exterior and interior of the piston member  74 .  
     [0043] A spring  66  has an upper end that abuts a lower end of the piston body  73  and a lower end that abuts a top end of the nozzle  60 . Initially the spring  66  urges the piston  72  upwardly to maintain the piston  72  in the position shown in FIGS. 1 and 1C.  
     [0044] The nozzle  60  has outlet ports  62 , inner ports  63 , and inner ports  64 . The inner ports  63 ,  64  extend through a wall  61  of the nozzle  60 . In the position of the piston  72  shown in FIGS. 1 and 1C, fluid can flow: from the interior of the system  10 ; down to an orifice  79  through the piston orifice member  75 ; through a bore  78  of the piston member  74 ; into a bore  59  of the nozzle  60 ; out through the inner ports  63  into a space between the exterior of the wall  61  and an interior of the valve housing  71 ; in through the inner ports  64  into a plug chamber  58  of the nozzle  60 ; and then out through the outlet ports  62 .  
     [0045] Initially a diverter plug  69  is secured to the nozzle  60  by shear screws  68  so that it does not affect the fluid flow path described in the preceding paragraph and prevents flow directly through the nozzle  60 .  
     [0046] O-rings with the following numerals seal the indicated interfaces:  128 , piston body/valve housing;  129 , nozzle/valve housing;  130 , nozzle/piston member; and  131 , diverter plug/nozzle.  
     [0047] The cross sub  55 , valve housing  71 , piston body  73 , piston member  74 , and piston orifice member  75  are generally cylindrical.  
     [0048] Instead of the valve assembly  70 , optionally a bull plug may be installed at the end of the system  10 . Also, optionally a ball-drop circulation sub may be installed above the crossover and the valve assembly. So that dropping a ball to the ball-drop circulation sub opens to fluid flow permitting pressure equalization above and below the sub and, in one aspect of such a system, the valve assembly  70  can be deleted.  
     [0049] In one particular method of operation of a system  10  according to the present invention (or a system  200 ), the system is run into a tubular string in a wellbore, e.g. like the tubing string  140 , FIG. 2. Using any suitable known locator tool, device, system or apparatus, the system  10  is positioned at a desired location in the tubing string  140 . In one particular aspect, the tubing  140  (and any additional strings in the wellbore outside the tubing  140 , e.g. additional string(s) of tubing or casing that are also perforated) have been perforated at this location to allow production from an earth formation at this location and the packing elements  40 ,  41  are positioned so that the formation of interest is between them. The distance between the packing elements can be adjusted, e.g., by using an injection sub of a desired length and/or by connecting additional tubulars to one or both ends of the injection sub.  
     [0050] Once the system  10  has been located at the desired location in the wellbore within the tubing string  140 , fluid under pressure is pumped from the surface at a rate to achieve sufficient pressure within the system  10  to force the piston  72  down closing off the fluid flow path out through the nozzle  60 . Pressure then increases to pull the collet fingers  52  over the corresponding shoulders on the upper and lower bottom subs  42 ,  43 , thereby forcing the various parts to telescope apart and freeing the setting sleeves  30 ,  31  for movement with respect to their corresponding pack-off mandrels. The top setting sleeve  30  pushes down to set the top packing element  40  and the bottom latch  51  is pulled down against the bottom packing element  41  pushing it against the bottom setting sleeve  31  to set the bottom packing element as shown in FIG. 2.  
     [0051] For operations with a system as depicted in FIG. 1 and  2  and as described above, in one embodiment the system  10  is connected at the lower end of a string of coiled tubing. Coiled tubing is useful in such operations because, among other things, coiled tubing can be moved relatively quickly within a wellbore, coiled tubing can be moved into a wellbore that is subjected to wellbore pressure within the wellbore without having to kill the well; and systems according to the present invention do not require the application of mechanical tension or compression.  
     [0052] Once the packing elements  40 ,  41 , are set, as in FIG. 2, fluid for treating the formation is pumped down to the injection sub  46 , out through the orifice  47 , through perforations  142  in the tubing  140  (and through similar perforations in any other string within the wellbore exterior to the tubing  140 ) and into the formation. The pumping of this fluid under pressure also boosts the sealing effect of the packing elements  40 ,  41  since a portion of the pumped fluid flows within the tubing string  140 , past the bottom subs  42 ,  43 , and forces the latches  50 ,  51  against the packing elements  40 ,  41 , thereby increasing (“boosting”) the sealing effect of the packing elements.  
     [0053] Following delivery of the desired fluid and the desired amount of fluid to the formation, the system  10  can be moved to another location within the wellbore by stopping the pumping of fluid, which allows the springs  6 ,  7 , to re-latch the latches  50 ,  51  resulting in un-setting and release of the packing elements  40 ,  41 . Then the system  10  can be relocated and the packing elements set again as described above for further operations at the new location.  
     [0054] Any suitable fluid may be injected into a formation with a system according to the present invention, (such as the systems  10  or  200 ) including, but not limited to water, and/or chemicals. In certain aspects, water is first pumped to insure that a formation will take fluid and then a treating fluid is pumped, e.g. an acidizing fluid or a gel and/or polymer treatment fluid.  
     [0055] A system according to the present invention, e.g. such as the system  10  or system  200 , is also useful for inflating an external casing packer on casing in a cased wellbore. The system  10  is run into the casing, knocking off the packer&#39;s knock-off device for selective flow of fluid into the external casing packer. Then the system  10  is activated as described above and fluid under pressure flowing through the orifice(s)  47  inflates the external casing packer.  
     [0056] In one aspect, an unloader is used with any system according to the present invention, including but not limited to a system  10  or a system  200 , e.g., but not limited to, an unloader as disclosed in pending U.S. application Ser. No. 09/411,718 entitled “Packer System” naming Ingram, Hoffman, Haugen and Beeman as co-inventors filed Oct. 2, 1999, co-owned with the present invention and incorporated here fully for all purposes. In a situation in which an unloader becomes clogged and fluid pressure cannot be relieved within the system  10  to release the packing elements, fluid is pumped from the surface into the system  10  at a sufficiently high pressure (e.g. 5000 psi) to shear the shear screws  68 , freeing the diverter plug  69 . The diverter plug  69  is then pumped into the plug chamber  58 , thus opening the nozzle  60  for the exit flow of fluid from within the system  10  and out through the outlet ports  62 . With this release of fluid, the packing elements  40 ,  41  are released and the system  10  can be moved and/or retrieved.  
     [0057] Similarly if fluid at relatively high pressure is being held either below the system  10  in a wellbore or between the packing elements  40 ,  41 , the diverter plug  69  can be pumped into the plug chamber  58  to equalize pressure between the exterior of the system  10  and its interior. In formation treating operations when fluid injection ceases and the formation will take no more fluid, a hydrostatic head of high pressure fluid may be created above the system  10 . Again, by pumping fluid under pressure through the system, the shear screws  68  are sheared and the diverter plug is pumped into the plug chamber  58  allowing fluid flow out the nozzle  60  for pressure equalization and subsequent system retrieval.  
     [0058] A system according to the present invention (including any such system disclosed herein, including, but not limited to a system  10  or a system  200 ) may be set within a gravel pack screen located in an earth wellbore adjacent a formation or part thereof to pack-off an area of interest and then perform the steps of a formation treatment operation, e.g. the injection into the formation (or part thereof) of treatment fluid as described above. Similarly, a system according to the present invention may be set across a sliding sleeve to perform such operation; or used with each packing element of the system set within a packer bore of the one of two spaced-apart packers previously set in a bore.  
     [0059] Referring now to FIGS.  3 A- 3 C, a system  200  according to the present invention has a generally cylindrical top sub  212  with a flow bore  211  therethrough from top to bottom and to which is threadedly connected a top pack-off mandrel  220 . An o-ring  213  seals a sub/mandrel interface and set screws  214  prevent unthreading of the top pack-off mandrel  220  from the top sub  212 .  
     [0060] The top sub  212  is connected to a lower end of any suitable tubular string (tubing, casing, etc.), working string, or coiled tubing (e.g., as shown schematically as string S in FIG. 1A), for use in a wellbore or within a bore in a tubular string in a wellbore.  
     [0061] Four spaced-apart crossover pins  215  secure together a top setting sleeve  230  and a top body  245 . The pins  215  extend through slots  222  in the top pack-off mandrel  220  so that the setting sleeve  230  and top body  245  are movable together with respect to the top pack-off mandrel  220  while the pins move in the slots.  
     [0062] A top spring  207  has a lower end that abuts a shoulder  225  of the top pack-off mandrel  220  and an upper end that abuts a shoulder  248  of the top body  245 . Initially the top spring  207  urges apart the top body and the top pack-off mandrel  220 , thus maintaining a top latch  250  (described below) in a latched position thereby preventing setting of a top packing element  240  (described below).  
     [0063] The top setting sleeve  230  has an end  232  with a lip  233  that abuts a top end of the top packing element  240 . The top packing element  240  is positioned around a lower end of the top pack-off mandrel  220 . The packing element  240  (and element  241 ) may be made of material as described above for the element  40 .  
     [0064] The top latch  250  has a top end threadedly secured to a lower end of the top pack-off mandrel  220 . The top latch  250  has a plurality of spaced-apart collet fingers  252  that initially latch onto a shoulder  244  of an upper bottom sub  242 . Set screws  239  secure the bottom sub  242  to a lower end of the top body  245 . The top end of the bottom sub  242  is also threadedly connected to the lower end of the top body  245 . An o-ring  239  seals a top body/bottom sub interface.  
     [0065] An optional spacer tube  246  has a top end connected to a lower end of the upper bottom sub  242 . The spacer tube  246  has a lower end connected to a top end of a lower bottom sub  243 .  
     [0066] Items  220 ,  230 ,  240   242 ,  245 ,  246  and  250  are generally cylindrical in shape, each with a top-to-bottom bore therethrough.  
     [0067] The various parts from the lower bottom sub  243  to a bottom pack off mandrel  221  mirror the upper parts in structure and function; i.e., the following parts correspond to each other:  215 - 315 ;  220 - 221 ;  222 - 223 ;  230 - 231 ;  240 - 241 ;  242 - 243 ;  245 - 249 ;  250 - 251 ;  252 - 282 . A lower end of the bottom pack-off mandrel  221  is threadedly connected to a nozzle  260 .  
     [0068] O-rings with the numerals  321 - 330  seal various interfaces.  
     [0069] A flow activated shut-off assembly  270  has a shut off sleeve  271  with a top-to-bottom bore  277 ,  278 ,  279  therethrough. The nozzle  260  receives a lower end of the sleeve  271 . The sleeve  271  is movable within a housing  272  whose upper end is connected to the lower bottom sub  243 . The lower end of the sleeve  271  moves within the nozzle  260 . A spring  273  has a lower end that abuts a shoulder  274  of the housing  272  and an upper end that abuts a shoulder  275  of the shut-off sleeve  271 . An orifice  276  extends through the sleeve  271  and a port  266  extends through the housing  272 .  
     [0070] The spring  273  urges the sleeve  271  upwardly to maintain the sleeve  271  initially in the position shown in FIG. 3C.  
     [0071] The nozzle  260  has outlet ports  262  and a seal ring  264  in a recess  261  of the nozzle  260 . In the position of the sleeve  271  shown in FIG. 3C fluid can flow: from the interior of the system  200 ; down to the bores  277 - 279 ; into a bore  265  of the nozzle  260 ; and out through the ports  262  into a space between the exterior of the system  200  and an interior of a bore or wellbore in which the system  200  is located.  
     [0072] The sleeve  271  and housing  272  are generally cylindrical.  
     [0073] In one particular method of operation of a system  200  according to the present invention, the system is run into a tubular string in a wellbore (e.g. like the tubing string  140 , FIG. 2). Using any suitable known locator tool, device, system or apparatus, the system  200  is positioned at a desired location in the string. In one particular aspect, the tubing (and any additional strings in the wellbore therearound) has been perforated at this location to allow production from an earth formation F through which the wellbore W extends at this location and the packing elements  240 ,  241  are positioned so that the formation of interest or part thereof is between them. The distance between the packing elements can be adjusted, e.g., by using a spacer tube of a desired length and/or by connecting additional tubulars to one or both ends of the spacer tube.  
     [0074] Once the system  200  has been located at the desired location in the wellbore within the string fluid under pressure is pumped from the surface at a rate to achieve sufficient pressure within the system  200  to force the sleeve  271  down closing off the fluid flow path out through the nozzle  260  (see FIG. 3F). Pressure then increases to pull the collet fingers  252 ,  282  over the corresponding shoulders on the upper and lower bottom subs  242 ,  243 , thereby forcing the parts above the upper bottom sub and below the housing  272  to telescope apart from the spacer tube and freeing the setting sleeves  230 ,  231  for movement with respect to their corresponding pack-off mandrels. The top setting sleeve  230  pushes down to set the top packing element  240  and the bottom latch  251  is pulled down against the bottom packing element  241  pushing it against the bottom setting sleeve  231  to set the bottom packing element as shown in FIGS. 3D, 3F.  
     [0075] For operations with a system as depicted in FIGS.  3 A- 3 F and as described above, in one embodiment the system  200  is connected at the lower end of a string of coiled tubing.  
     [0076] Once the packing elements  240 ,  241 , are set, fluid for treating the formation is pumped down to the orifice  276  and port  266  (aligned as in FIG. 3E), through perforations  242  in the tubing  240  (and through similar perforations in any other string within the wellbore therearound) and into the formation. The pumping of this fluid under pressure also boosts the sealing effect of the packing elements  240 ,  241  since a portion of the pumped fluid flows to force the latches  250 ,  251  against the packing elements thereby increasing (“boosting”) the sealing effect of the packing elements.  
     [0077] Following delivery of the desired fluid and the desired amount of fluid to the formation, the system  200  can be moved to another location within the wellbore by ceasing pumping of fluid, which allows the springs  206 ,  207 , to re-latch the latches  250 ,  251  resulting in un-setting and release of the packing elements  240 ,  241 . Then the system  200  can be relocated and the packing elements set again as described above for further operations at the new location. Any suitable fluid may be injected into a formation with a system  200  according to the present invention.  
     [0078] In one aspect, an unloader is used with any system  200 , e.g., but not limited to, an unloader as disclosed in pending U.S. application Ser. No. 09/411,718 mentioned above. When it is desired to equalize pressure inside and outside the system  200 , e.g. but not limited to an emergency situation, the level at which fluid is pumped to the sleeve  271  is reduced so that the spring  273  pushes the sleeve  271  up to the position of FIG. 3C. With pressure inside and outside the system equalized, the packing elements are released and the system can then be retrieved to the surface or relocated in the bore for further operations.  
     [0079]FIG. 4A shows a system  200  being moved within a casing string  360  to a location of an external casing packer  362  with a packing element  367 . (Packer  362  represents any known external casing packer.) The nozzle  260  of the system  200  has contacted a knock-off device  364  which initially prevents fluid from flowing from within the casing (and from within a system like the system  200 ) to inflate the packer&#39;s packing element  367 . As shown in FIG. 4B, the system  200  has been located so that the packing elements  240 ,  241  isolate (“pack off”) the external casing packer. The knock-off device  364  has been knocked-off so that fluid pumped to and out from the system  200  will inflate the packing element  367 . It is within the scope of this invention to knock off the device  364  with other apparatus prior to running in the system  200 , or this can be done prior to installing the packer  362  in a wellbore.  
     [0080]FIG. 5A shows an alternative embodiment  400  of the system  200  which incorporates a slip-setting mechanism  410  above the lower packing element  241 . (Optionally, such a slip-setting mechanism may be employed above the upper packing element  240 .) The slip-setting mechanism  410  is interposed between a latch  414  (similar to the latch  251 ) and a lower sleeve end  412  (which is like the lower end of the latch  251 , FIG. 3C). The lower sleeve end  412  is threadedly connected to an outer sleeve  416  which has an upper tapered end  418 . The upper tapered end initially abuts a corresponding lower tapered end  419  of a plurality of spaced-apart slips  420  (two, three, four or more may be used), each, preferably, with a toothed outer surface  422  (although any suitable known slip or gripping element may be used). Each slip  420  has an upper slip portion  423  and a mid-portion  425 .  
     [0081] A housing  430  surrounds the slip-setting mechanism  410  and has windows  431 ,  432  through which the slips  420  may project. Springs  433  between the housing  430  and the slip mid-portions  425  urge the slips toward a pack off mandrel  441 , urging the slips  420  inwardly and initially holding the slips  420  in the position shown in FIG. 5A. A stop ring  438  is secured to the pack off mandrel  441 . A spring  436  that abuts a top  437  of the lower sleeve end  412  and a lower surface of the stop ring  438  urges the lower sleeve end  412  and the outer sleeve  416  downwardly, i.e., to a position as shown in FIG. 5A. As shown in FIG. 5B, the pack off mandrel  441  and slip-setting mechanism  410  have moved downwardly, forcing the slips  420  against the upper tapered end  418  of the outer sleeve  416  and thus outwardly through the housing windows  431 ,  432  and into setting engagement with an interior surface of a tubing  470  (or bore, casing, etc.) in which the system is located. The spring  436  has been compressed. By ceasing the pumping of fluid to the system  400 , and moving the system downwardly the slips  420  are released and the system is re-latched, as described above for the system  200 .  
     [0082] In one method according to the present invention, by sizing the packing elements  240 ,  241  with the upper element larger than the lower element, the system  200  can be disposed in a wellbore so that the upper packing element is in a first tubular string having a first inner diameter and the lower packing element is in a second tubular string connected to and below the first tubular string, the second tubular string having an inner diameter less than that of the first tubular string.  
     [0083] Alternatively, in one aspect, the upper packing element  240  of the system  400  is sized for setting in a first upper tubular string and the lower packing element  241  and the slip setting mechanism  410  are sized for setting in a second lower tubular string connected to and below the first tubular string, the second lower tubular string having an inner diameter less than that of the first upper tubular string.  
     [0084] The present invention, therefore, provides in some, but not necessarily all, embodiments a pack-off system for packing off an area of interest (in a wellbore and/or in a bore of an item in a wellbore) in a wellbore, the pack-off system having a body, two spaced-apart selectively settable packing elements on the body for sealing off the area of interest, selectively actuatable setting apparatus connected to the body for selectively setting the two spaced-apart selectively settable packing elements, the selectively actuatable setting apparatus actuatable by fluid introduced into the pack-off system at a desired rate of introduction. Such a system may have one or some (in any possible combination) of the following: release apparatus selectively actuatable by reducing the rate of introduction of fluid introduced to the pack-off system to selectively release the two spaced-apart selectively settable packing elements; the selectively actuatable setting apparatus further comprising at least two movable member apparatuses subject to force of the fluid introduced into the pack-off system, one each of the movable member apparatuses movable in response to the force of the fluid under pressure to contact one of the two spaced-apart selectively-settable packing elements to boost sealing of said elements for sealing off the area of interest; wherein the area of interest is an area adjacent a bore of a tubular string in the wellbore, the pack-off system is disposed in said bore, and the two spaced-apart selectively-settable packing elements are settable to seal off said bore; wherein the area of interest is within a bore of an item in the wellbore; a string to a lower end of which the pack-off system is connected, the string from the group consisting of coiled tubing, fiber optic line system, slick line, electrically conductive wireline, electrically non-conductive wireline, tubing, and casing; a system for straddling part of a bore in which the pack-off system is located, the pack-off system also having two spaced-apart pack-off mandrels, the two spaced-apart selectively-settable packing elements each on one of the spaced-apart pack-off mandrels, a tubular member with a portion within each pack-off mandrel, the tubular member selectively movable with respect to the pack-off mandrels, two spaced-apart setting sleeves secured to and movable with the tubular member, each setting sleeve movable to set one of the two spaced-apart selectively-settable packing elements, two spaced-apart latch apparatuses each latch apparatus connected to one of the spaced-apart pack-off mandrels for releasably holding the tubular member and two spaced-apart pack-off mandrels in a first position in which the two spaced-apart selectively-settable packing elements are not set, the tubular member having a fluid flow bore therethrough with a selectively closable lower end so that fluid pumped under pressure into the pack-off system and into the fluid flow bore of the tubular member moves the tubular member with respect to and apart from the two spaced-apart pack-off mandrels releasing the latch apparatus so that the setting sleeves move with the tubular member to set the two spaced-apart selectively settable packing elements against an interior of the bore in which the pack-off system is located; the body has at least one body flow port through which fluid is flowable from inside the pack-off system to the outside thereof, the release apparatus comprises a shut off sleeve movably mounted in the body and responsive to force of the fluid introduced under pressure into the wellbore and into the pack-off system, the shut-off sleeve having an orifice therethrough and a top-to-bottom fluid flow bore, flow through the orifice initially blocked by a portion of the body, a nozzle connected to the body, the nozzle having a fluid flow bore therethrough initially in fluid communication with the fluid flow bore of the shut-off sleeve, the nozzle having at least one exit port through which fluid can exit from the nozzle, a spring abutting the body and the shut-off sleeve and urging the shut-off sleeve upwardly so that initially the shut-off sleeve does not close off flow to the at least one exit port of the nozzle, the top-to-bottom fluid flow bore through the shut-off sleeve sized so that fluid under pressure is pumpable to the shut-off sleeve at a level sufficient to move the shut-off sleeve downwardly against force of the spring to align the orifice with the at least one body flow port and to close off flow to the at least one exit port of the nozzle so that fluid pressure builds up in the pack-off system and fluid under pressure exits from within the shut-off sleeve through the orifice and flows to the at least one body flow port and exits from the pack-off system; and/or wherein the two-spaced latch apparatuses are movable in response to the fluid under pressure to boost sealing of the area of interest by the two-spaced-apart selectively settable packing element.  
     [0085] The present invention, therefore, provides in some, but not necessarily all, embodiments a pack-off system for packing off an area of interest in a wellbore, the pack-off system having a body, two spaced-apart selectively settable packing elements on the body for sealing off the area of interest, selectively actuatable setting apparatus connected to the body for selectively setting the two spaced-apart selectively settable packing elements, the selectively actuatable setting apparatus actuatable by fluid under pressure introduced into the pack-off system, release apparatus selectively actuatable by reducing pressure of fluid pumped to the pack-off system to selectively release the two spaced-apart selectively settable packing elements, the selectively actuatable setting apparatus further comprising two movable member apparatuses subject to force of the fluid under pressure introduced into the pack-off system, one of the movable member apparatuses movable in response to the force of the fluid under pressure to contact each of the two spaced-apart selectively-settable packing elements to boost sealing of said elements for sealing off the area of interest, wherein the area of interest is an area adjacent a bore of a string in the wellbore, the pack-off system is disposed in said bore, and the two spaced-apart selectively-settable packing elements are settable to seal off said bore, and a string to a lower end of which the pack-off system is connected; such a system wherein the string from the group consisting of coiled tubing, fiber optic line system, slick line, electrically conductive wireline, electrically non-conductive wireline, tubing, and casing; and/or the body has at least one body flow port through which fluid is flowable from inside the pack-off system to the outside thereof, the release apparatus comprises a shut off sleeve movably mounted in the body and responsive to force of the fluid under pressure introduced into the wellbore and into the pack-off system, the shut-off sleeve having an orifice therethrough and a top-to-bottom fluid flow bore, flow through the orifice initially blocked by a portion of the body, a nozzle connected to the body, the nozzle having a fluid flow bore therethrough initially in fluid communication with the fluid flow bore of the shut-off sleeve, the nozzle having at least one exit port through which fluid can exit from the nozzle, a spring abutting the body and the shut-off sleeve and urging the shut-off sleeve upwardly so that initially the shut-off sleeve does not close off flow to the at least one exit port of the nozzle, the top-to-bottom fluid flow bore through the shut-off sleeve sized so that fluid under pressure is pumpable to the shut-off sleeve at a level sufficient to move the shut-off sleeve downwardly against force of the spring to align the orifice with the at least one body flow port and to close off flow to the at least one exit port of the nozzle so that fluid pressure builds up in the pack-off system and fluid under pressure exits from within the shut-off sleeve through the orifice and flows to the at least one body flow port and exits from the pack-off system.  
     [0086] The present invention, therefore, provides in some, but not necessarily all, embodiments a method for packing off an area of interest (in a wellbore or in an item in a wellbore) in a wellbore, the method including installing a pack-off system according to the present invention in the wellbore to pack-off the area of interest, and actuating the selectively actuatable setting apparatus to set each of the two spaced-apart selectively settable packing elements by introducing fluid to the pack-off system; such a method including actuating release apparatus by reducing rate of introduction of the fluid thereby releasing two spaced-apart selectively-settable packing elements; such a method including moving the pack-off system to another location within the wellbore and again setting two spaced-apart selectively settable packing elements; such a method including retrieving the pack-off system from the wellbore; such a method wherein the pack-off system includes movable member apparatus movable in response to fluid pressure for boosting sealing effects of two spaced-apart selectively settable packing elements, and the method includes boosting sealing effects of the two spaced-apart selectively settable packing elements; such a method wherein the pack-off system is connected to a lower end of a string, the string from the group consisting of coiled tubing, fiber optic line system, slick line, electrically conductive wireline, electrically non-conductive wireline, tubing and casing; such a method wherein the pack-off system has fluid exit apparatus for flowing fluid from within the pack-off system to an outside thereof, the method including flowing fluid from within the pack-off system to the outside thereof; such a method wherein the two spaced-apart selectively settable packing elements are set to pack-off a bore through an earth formation area of interest and wherein the fluid flowing from within the pack-off system to the outside thereof is formation treatment fluid that flows from the pack-off system, through any tubular (if any are present) in which the pack-off system is located, to the earth formation area of interest for treatment thereof; such a method wherein the fluid is pumped to the pack-off system from an earth surface pumping apparatus; and/or wherein the fluid flows to and/or is pumped to the pack-off system from an apparatus within the wellbore.  
     [0087] In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein and those covered by the appended claims are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject matter without departing from the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited in any of the following claims is to be understood as referring to all equivalent elements or steps. The following claims are intended to cover the invention as broadly as legally possible in whatever form it may be utilized. The invention claimed herein is new and novel in accordance with 35 U.S.C. § 102 and satisfies the conditions for patentability in § 102. The invention claimed herein is not obvious in accordance with 35 U.S.C. § 103 and satisfies the conditions for patentability in § 103. This specification and the claims that follow are in accordance with all of the requirements of 35 U.S.C. § 112. The inventors may rely on the Doctrine of Equivalents to determine and assess the scope of their invention and of the claims that follow as they may pertain to apparatus not materially departing from, but outside of, the literal scope of the invention as set forth in the following claims.