Patent Publication Number: US-11035189-B2

Title: Compression-set straddle packer with fluid pressure-boosted packer set

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the first application filed for this invention. 
     FIELD OF THE INVENTION 
     This invention relates in general to precision fracking systems and, in particular, to a novel compression-set straddle packer with fluid pressure-boosted packer set that can be used for cased wellbore stimulation or remediation. 
     BACKGROUND OF THE INVENTION 
     Wellbore pressure isolation tools, commonly referred to as “straddle packers”, are known and used to pressure isolate a downhole area of interest in a cased well bore for the purpose of what is known as focused or precision well stimulation or remediation. Straddle packers designed for this purpose are well known, but their use has been associated with operational issues that frequently render them unreliable. Most, straddle packers are also complex tools that are expensive to build and maintain. 
     There therefore exists a need for a novel compression-set straddle packer with fluid pressure-boosted packer set that will operate reliably in a downhole environment. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a compression-set straddle packer with fluid pressure-boosted packer set. 
     The invention therefore provides a compression-set straddle packer, comprising a two-part multicomponent mandrel, and a two-part transition sleeve between an upper part and a lower part of the two-part multicomponent mandrel, the two part transition sleeve comprising a bias element chamber that houses a bias element supported on a bias element support component of the upper part of the two-part multicomponent mandrel below a bias element push component of the upper part of the two-part multicomponent mandrel, the bias element constantly resisting movement of the upper part of the two-part multicomponent mandrel with respect to the two-part transition sleeve. 
     The invention further provides a compression-set straddle packer with fluid pressure-boosted packer set, comprising: a two-part multicomponent mandrel, and a two-part transition sleeve between an upper part and a lower part of the two-part multicomponent mandrel, the two part transition sleeve comprising a bias element chamber that houses a bias element supported on a bias element support component of the upper part of the two-part multicomponent mandrel below a bias element push component of the upper part of the two-part multicomponent mandrel, the bias element constantly resisting movement of the upper part of the two-part multicomponent mandrel with respect to the two-part transition sleeve; an upper packer element supported by a work string connection component of the upper part of the two-part multicomponent mandrel, and a lower packer element supported by an initial set sub mandrel component of a lower part of the two-part multicomponent mandrel; a mandrel flow sub having, at least one mandrel flow sub nozzle, the mandrel flow sub being a component of the upper part of the two-part multicomponent mandrel between the upper packer element and the lower packer element; a packer element piston mandrel component connected to a downhole end of the initial set sub mandrel component and including packer element piston ports; a two-part lower packer element compression sleeve that reciprocates on the packer element piston mandrel component and has an uphole end that abuts the lower packer element, and defines a packer element piston chamber that is in fluid communication with the packer element piston ports; whereby when high pressure fluid is pumped into the straddle packer, the high-pressure fluid exits the at least one flow sub nozzle and flows through the packer element piston ports into the packer element piston chamber to urge the uphole end of the two-part packer element compression sleeve against the lower packer element to pressure-boost the lower packer element set and the bias element equalizes the pressure-boost between the lower packer element and the upper packer element. 
     The invention yet further provides a compression-set straddle packer with fluid pressure-boosted packer set, comprising: a two-part multicomponent mandrel, an upper part of the two-part multicomponent mandrel having a work string connection end that supports a packer element, the multicomponent mandrel extending from the work string connection end to a connection joint of the straddle packer; an upper mandrel tube threadedly connected to the work string connection component; a mandrel flow sub having at least one mandrel flow sub nozzle connected to a downhole end of the upper mandrel tube; a lower mandrel tube connected to a downhole end of the mandrel flow sub; a bias element push component connected to a downhole end of the lower mandrel tube; a bias element support component connected to a downhole end of the bias element push component and a mandrel termination component connected to a downhole end of the bias element support component; a multicomponent sliding sleeve that surrounds the upper part of the two-part multicomponent mandrel below the work string connection end and reciprocates on the upper part of the two-part multicomponent mandrel within a limited range, the multicomponent sliding sleeve including an upper sliding sleeve connected to a compression bell that slides over a downhole end of a packer element sleeve of the work string connection component, the upper sliding sleeve sliding over the upper mandrel tube; a slotted sliding sleeve connected to a downhole end of the upper sliding sleeve, the slotted sliding sleeve sliding over the mandrel flow sub and having slotted sliding sleeve finger components that define slots that expose the at least one mandrel flow sub nozzle; a lower sliding sleeve connected to a downhole end of the slotted sliding sleeve; a transition sleeve upper end connected to a downhole end of the lower sliding sleeve; a transition sleeve lower end connected to a downhole end of the transition sleeve upper end, the upper and lower sliding sleeves providing a bias element chamber that houses the bias element push component and the bias element support component of the multicomponent mandrel; and the connection joint which is connected to the transition sleeve lower end; a bias element supported on the bias element support component of the multicomponent mandrel between the bias element push component and a lower end of the bias element chamber, the bias element constantly resisting any movement of the multicomponent sliding sleeve with respect to the multicomponent mandrel; the lower part of the two-part multicomponent mandrel comprising: an initial set sub mandrel component connected to the connection joint, the initial sub set mandrel component supporting a lower packer element; a packer element piston mandrel component connected to the initial set sub mandrel component; an unload sub mandrel component connected to the packer element piston mandrel component; and, a collar locator mandrel component connected to the unload sub mandrel component; and a two-part lower packer element sleeve having an uphole end that abuts the lower packer element, the two-part lower packer element sleeve reciprocating on the packer element piston mandrel component; a drag block/slip sub below a downhole end of the two-part lower packer element sleeve, the drag block/slip sub supporting mechanical slips for anchoring the compression-set straddle packer in a cased well bore, drag blocks for inhibiting movement of the compression-set straddle packer within the cased well bore, and an auto-J ratchet lug that engages an auto-J ratchet groove in a downhole end of the packer element piston mandrel component; a lower tandem sub connected to the drag block/slip sub; an unload sub sleeve connected to the tandem sub and reciprocating on the unload sub mandrel component; and a collar locator sleeve that supports collar locator ribs, the collar locator sleeve reciprocating on the collar locator mandrel component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an embodiment of a compression-set straddle packer with fluid pressure-boosted packer set in accordance with the invention; 
         FIG. 2  is a cross-sectional view of one embodiment of the compression-set straddle packer with fluid pressure-boosted packer set shown in  FIG. 1 , in a run-in condition; 
         FIG. 3  is a cross-sectional view of another embodiment of the compression-set straddle packer with fluid pressure-boosted packer set shown in  FIG. 1 , in a run-in condition; 
         FIG. 4  is a cross-sectional view of the compression-set straddle packer with fluid pressure-boosted packer set shown in  FIG. 2 , illustrating the straddle packer as it would appear if the straddle packer were in a fluid pressure-boosted, packer-set condition; 
         FIG. 5 a    is a schematic detailed view in partial cross-section of an auto-j ratchet of the straddle packer shown in  FIG. 1 ; and 
         FIG. 5 b    is a schematic detailed view in partial cross-section of the auto-j ratchet shown in  FIG. 5 a    with an auto-J ratchet lug in a slip engage notch of the auto-J ratchet. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides a compression-set straddle packer with pressure-boosted packer set (hereinafter simply “straddle packer”) to provide a straddle packer that may be used in precision well stimulation or remediation treatments in cased well bores (hereinafter referred to simply as “well bores”). The straddle packer has a two-part multicomponent mandrel and a multicomponent sliding sleeve that surrounds an upper part of the two-part multicomponent mandrel and reciprocates within a limited range over the upper part of the two-part multicomponent mandrel. The upper part of the two-part multicomponent mandrel includes a mandrel flow sub component. The mandrel flow sub has at least one abrasion-resistant fluid nozzle used to inject well stimulation or well remediation fluid (hereinafter referred to collectively as “high pressure fluid”) into a section of a wellbore that is pressure isolated by upper and lower packer elements of the straddle packer when the respective packer elements are in a packer set condition. In this document, “flow sub nozzle” means any orifice, permanent or interchangeable, through which high pressure fluid may be pumped, including but not limited to a bore and a slot. In the packer set condition the respective packer elements are in high-pressure sealing contact with a wellbore. The respective packer elements are compressed to the packer set condition by work string weight applied at surface to a work string connected to the straddle packer. When high pressure fluid is pumped into the straddle packer it urges a hydraulic cylinder component of the lower part of the two-part multi-component mandrel to further compress the upper and lower packer elements to boost a seal strength of the respective, packer elements. The higher the fluid pressure in the straddle packer, the greater the boost to packer compression. A bias element is captured between a bias element push component of the upper part of the two-part multicomponent mandrel and a lower end of a bias element chamber provided between the upper and lower parts of the two-part multicomponent mandrel. The bias element constantly resists relative movement of the upper part of the two-part multicomponent mandrel with, respect to the multicomponent sliding sleeve to distribute compression pressure on the upper and lower packer elements when the straddle packer is in a fluid pressure-boosted set condition. 
     An auto-J latch maintains the straddle packer in a run-in condition to prevent packer set in an event that an obstruction is “tagged” while running the straddle packer into a cased well bore. Work string manipulation, well understood in the art, is used to shift the auto-J latch to a packer set condition. High-pressure fluid may then be pumped through the work string into the pressure isolated section of the well bore. When the high-pressure fluid treatment is completed and string weight is released from the work string, the bias element assists unsetting of the respective packers. In one embodiment the bias element is an elastomeric tube received on the upper part of the two-part multicomponent mandrel. In one embodiment, the multicomponent mandrel includes ports under the bias element and the bias element chamber wall includes ports above the bias element. When the packer elements are set, the bias element seals the respective ports in the multicomponent mandrel and the bias element chamber wall. When string weight is released from the uphole end, the bias element relaxes and opens the respective ports, which permits fluid in the multicomponent mandrel to flow around opposite ends of the bias element and into the well bore, which may facilitate recovery from a “screen-out” should one occur. The straddle packer is also provided with a fluid dump sub downhole of the respective packer elements, which automatically dumps fluid from the straddle packer when the straddle packer is moved from the packer set to the run-in condition. 
     
       
         
           
               
               
             
               
                   
               
               
                 Part No. 
                 Part Description 
               
               
                   
               
             
            
               
                  10 
                 Compression-set straddle packer 
               
               
                  11a 
                 Multicomponent mandrel upper part 
               
               
                  11b 
                 Multicomponent mandrel lower part 
               
               
                  12 
                 Work string connection component 
               
               
                  13 
                 Multicomponent mandrel central passage 
               
               
                  14 
                 Work string connection 
               
               
                  15 
                 Packer element compression shoulder 
               
               
                  16 
                 Packer element sleeve 
               
               
                  17 
                 Multicomponent sliding sleeve 
               
               
                  18 
                 Upper packer element 
               
               
                  19 
                 Upper packer element compression ring 
               
               
                  20 
                 Compression bell 
               
               
                  21 
                 Compression bell pressure equalization ports 
               
               
                  22 
                 Upper crossover tube 
               
               
                  23 
                 Upper mandrel tube 
               
               
                  24 
                 Upper sliding sleeve 
               
               
                  26 
                 Upper sliding sleeve coupling 
               
               
                  27 
                 Slotted sliding sleeve female coupling end 
               
               
                  28 
                 Slotted sliding sleeve 
               
               
                  29 
                 Sliding sleeve finger components 
               
               
                  30 
                 Mandrel flow sub 
               
               
                  31 
                 Mandrel flow sub grooves 
               
               
                  32 
                 Mandrel flow sub nozzles 
               
               
                  34 
                 Lower sliding sleeve coupling 
               
               
                  36 
                 Lower sliding sleeve 
               
               
                  38 
                 Slotted sliding sleeve captured end coupling ring 
               
               
                  40 
                 Cap screws 
               
               
                  42 
                 Lower mandrel tube 
               
               
                  44 
                 Bias element push component 
               
               
                  46 
                 Bias element support component 
               
               
                  48 
                 Upper mandrel part termination component 
               
               
                  50 
                 Transition sleeve upper end 
               
               
                  52 
                 Transition sleeve lower end 
               
               
                  54 
                 Connection joint 
               
               
                  56 
                 Bias element chamber 
               
               
                  58 
                 Bias element elastomeric tube 
               
               
                  60 
                 Upper bias element push ring 
               
               
                  62 
                 Lower bias element push ring 
               
               
                  64 
                 Mandrel ports 
               
               
                  66 
                 Transition sleeve ports 
               
               
                  80 
                 Bias element compression spring 
               
               
                  96 
                 Initial set sub mandrel component 
               
               
                  98 
                 Lower packer element compression ring 
               
               
                 100 
                 Lower packer element 
               
               
                 102 
                 Two-part lower packer element compression sleeve 
               
               
                 104 
                 Lower compression sleeve pressure balance ports 
               
               
                 106 
                 Packer element piston ports 
               
               
                 108 
                 Packer element piston mandrel component 
               
               
                 110 
                 Packer element piston 
               
               
                 112 
                 Packer element piston chamber 
               
               
                 116 
                 Mechanical slips 
               
               
                 118 
                 Mechanical slip springs 
               
               
                 120 
                 Drag blocks 
               
               
                 122 
                 Drag block bow springs 
               
               
                 124 
                 Auto-j ratchet lug 
               
               
                 126 
                 Auto-j ratchet groove 
               
               
                  126a 
                 Auto-j ratchet neutral notch 
               
               
                  126b 
                 Auto-j ratchet slip engage notch 
               
               
                  126c 
                 Auto-j ratchet shift notch 
               
               
                 127 
                 Drag block/slip sub 
               
               
                 128 
                 Drag block/slip retainer ring 
               
               
                 130 
                 Drag block/slip retainer screws 
               
               
                 132 
                 Lower tandem sub 
               
               
                 134 
                 Unload sub sleeve 
               
               
                 135 
                 Unload sub sleeve ports 
               
               
                 136 
                 Unload sub mandrel component 
               
               
                 137 
                 Unload sub mandrel ports 
               
               
                 140 
                 Cap screws 
               
               
                 150 
                 Captive seal 
               
               
                 152 
                 Captive seal ring 
               
               
                 158 
                 Unload sub end cap 
               
               
                 161 
                 Collar locator mandrel component 
               
               
                 162 
                 Collar locator ribs 
               
               
                 163 
                 Collar locator sleeve 
               
               
                 166 
                 Collar locator hooks 
               
               
                 168 
                 Upper collar locator retainer ring 
               
               
                 170 
                 Lower collar locator retainer ring 
               
               
                 172 
                 Collar locator retainer screws 
               
               
                 182 
                 Straddle packer guide cap 
               
               
                   
               
            
           
         
       
     
       FIG. 1  is a perspective view of one embodiment of a compression-set straddle packer with fluid pressure-boosted packer set  10  (hereinafter simply “straddle packer  10 ”) in accordance with the invention. The straddle packer  10  has a two-part multicomponent mandrel  11   a  (upper part) and  11   b  (lower part), the majority of which can only be seen in a cross-sectional view (see  FIGS. 2-4 ). The multicomponent mandrel upper part  11   a  is surrounded by a multicomponent sliding sleeve  17 , which reciprocates within a limited range over the multicomponent mandrel upper part  11   a . The multicomponent mandrel upper part  11   a  includes a work string connection component  12  with a work string connection  14  (see  FIG. 2 ). A configuration of the work string connection  14  is a matter of design choice and dependent on whether the straddle packer  10  is to be operated using a coil tubing string (not shown) or jointed tubing string (not shown), as is well understood in the art. 
     The work string connection component  12  has a packer element compression shoulder  15  and a packer element sleeve  16  (see  FIG. 2 ) that supports an elastomeric upper packer element  18 , the function of which is well understood in the art. On a downhole side of the upper packer element  18  is a packer element compression ring  19  that slides on the packer element sleeve  16 . A compression bell  20 , having compression bell pressure equalization ports  21 , is a component of the multicomponent sliding sleeve  17  and is connected to an upper sliding sleeve  24 . The upper sliding sleeve  24  is connected to an upper sliding sleeve female coupling end  26  of a slotted sliding sleeve  28 , having a female coupling end  27  (see  FIG. 2 ) connected to a lower sliding sleeve  36 . In one embodiment, the slotted sliding sleeve  28  has three slotted sliding sleeve finger components  29  that are respectively received in sliding sleeve slots mandrel flow sub grooves  31  (see  FIG. 2 ) of a mandrel flow sub  30  of the multicomponent mandrel upper part  11   a . The slotted sliding sleeve finger components  29  define three slots that respectively expose at least one mandrel flow sub nozzle  32  of the mandrel flow sub  30 . In this embodiment, the mandrel flow sub  30  has a plurality of mandrel flow sub nozzles  32 . It should be understood the number of mandrel flow sub nozzles  32  is a matter of design choice. A downhole end of the sliding sleeve finger components  29  are threadedly connected to a slotted sliding sleeve captured end coupling ring  38  that surrounds a lower sliding sleeve coupling  34  (see  FIG. 2 ) that is threadedly connected to the lower sliding sleeve  36 . Cap screws  40  secure the captured end coupling ring  38 . A downhole end of the lower sliding sleeve  36  is connected to a transition sleeve upper end  50  that is in turn connected to a transition sleeve lower end  52 . A connection joint  54  is connected to a lower end of the transition sleeve lower end  52 . One or more extension pipes (not shown) may be connected to the connection joint  54  to extend a “reach” of the straddle packer  10  (length of cased wellbore pressure-isolated by the straddle packer  10 ). 
     A downhole end of the connection joint  54  is threadedly connected (directly or via the above-referenced extension pipes) to an uphole end of the multicomponent mandrel lower part  11   b , which includes an initial set sub mandrel component  96  that supports a lower packer element compression ring  98  and a lower packer element  100 . A two-part lower packer element compression sleeve  102  surrounds a packer element piston mandrel component  108  (see  FIG. 2 ) threadedly connected to a downhole end of the initial set sub mandrel component  96 . The lower part of the two-part lower packer element compression sleeve  102  includes lower compression sleeve pressure balance ports  104 . 
     The down hole end of the two-part lower packer element compression sleeve  102  is conical and serves as an upper slip ramp to set mechanical slips  116  which are retained by a drag block/slip sub  127 , as will be explained below with reference to  FIG. 4 . The mechanical slips  116  are normally urged to an unset condition (shown in this view) by mechanical slip springs  118  (see  FIG. 2 ) retained by the drag block/slip retainer ring  128 . As will be explained below with reference to  FIGS. 4 and 5   b , the mechanical slips  116  may be set using work string manipulation to shift an auto-J ratchet of the straddle packer  10 . The drag block/slip sub  127  includes a downhole slip ramp for setting the mechanical slips  116  in cooperation with the two-part lower packer element compression sleeve  102 , as will be explained below with reference to  FIG. 5 b   . The drag block/slip sub  127  also retains drag blocks  120 , which are normally urged into engagement with a well bore casing (not shown) by drag block bow springs  122  (see  FIG. 2 ) to provide frictional resistance as the straddle packer  10  is run into a cased well bore using the work string. The drag block/slip sub  127  also supports an auto-J ratchet lug  124  (see  FIG. 2 ) which cooperates with an auto-J ratchet groove  126  (better seen in  FIGS. 5 a  and 5 b   ) milled into a downhole end of the packer element piston mandrel component  108  (see  FIG. 2 ). The operation of the auto-J ratchet will be explained below with reference to  FIGS. 4, 5   a  and  5   b.    
     Threadedly connected to a downhole end of the drag block/slip sub  127  is a lower tandem sub  132 , which is secured from rotation by drag block/slip retainer screws  130 . Connected to a downhole end of the lower tandem sub  132  is an unload sub sleeve  134  having unload sub sleeve ports  135 , the function of which will be explained below with reference to  FIGS. 2 and 4 . Cap screws  140  secure an unload sub end cap  158  to the unload mi sleeve  134 . A collar locator sleeve  163  floats on a lower end of the multicomponent mandrel lower part  11   b . An upper collar locator ring  168  connected to an uphole end of the collar locator sleeve  163  captures an uphole end of a plurality of collar locator ribs  162 . The upper collar locator ring  168  is secured by a plurality of collar locator retainer screws  172  to the collar locator sleeve  163 . A lower collar locator retainer ring  170  captures the downhole ends of the collar locator ribs  162 , and is likewise secured to the collar locator sleeve by a plurality of collar locator retainer screws  172 . As is well understood by those skilled in the art, the collar locator ribs  162  have respective collar locator hooks  166  which “catch” an end of a casing joint as the straddle packer  10  is pulled uphole and the collar locator hooks  166  pass through a casing collar (not shown), which is detectable on the surface as a spike in string weight on an operator&#39;s string weight gauge that alerts the operator that a collar in the casing string has been located. A straddle packer guide cap  182  is connected to a downhole end of the lower mandrel part  11   b  of the two-part multicomponent mandrel. 
       FIG. 2  is a cross-sectional view of the straddle packer  10  shown in  FIG. 1 . As explained above, the elastomeric upper packer element  18  is supported on the packer element sleeve  16  of the work string connection component  12  of the multicomponent mandrel upper part  11   a . The multicomponent mandrel parts  11   a  and  11   b  have a central passage  13  that provides an uninterrupted fluid path from the work string connection  14  to the straddle packer guide cap  182  of the straddle packer  10 . The multicomponent mandrel upper part  11   a  includes the following interconnected components: the work string connection component  12 , which is threadedly connected to an upper crossover tube  22 ; an upper mandrel tube  23  threadedly connected to a lower end of the upper crossover tube  22 ; the mandrel flow sub  30  connected to a downhole end of upper mandrel tube  23 ; the wear-resistant, replaceable mandrel flow sub nozzle(s)  32 ; a lower mandrel tube  42  connected to a downhole end of the mandrel flow sub  30 ; a bias element push component  44  connected to a downhole end of the lower mandrel tube  42 ; a bias element support component  46  having mandrel ports  64  connected to a downhole end of the bias element push component  44 ; an upper mandrel part termination component  48  connected to a lower end of the bias element support component  46 . 
     The multicomponent mandrel lower part  11   b  includes the packer element piston mandrel component  108  threadedly connected to a downhole end of the initial set sub mandrel component  96 . An unload sub mandrel component  136  is threadedly connected to a downhole end of the packer element piston mandrel component  108 . The unload sub mandrel component  136  includes unload sub mandrel ports  137 , which are in fluid communication with the unload sub sleeve ports  135  when the straddle packer  10  is in the run-in condition. This permits any fluid in the central passage  13  to flow out of the straddle packer  10  and into an annulus of a cased well bore, and permits the straddle packer  10  to rapidly return from a packer element set condition to the run-in condition after string weight is released from the straddle packer  10 . A collar locator mandrel component  161  is threadedly connected to a downbole end of the unload sub mandrel component  136 . The straddle packer guide cap  182  is threadedly connected to a downhole end of the collar locator mandrel component  161 . 
     All of the external components of the straddle packer  10  have been described above with reference to  FIG. 1 . However, there is an important operative component of the straddle packer  10  that has not been described. Namely, a bias element housed in a bias element chamber  56  within the transition sleeve upper end  50  and the transition sleeve lower end  52 . In one embodiment the bias element is a bias element elastomeric tube  58  carried on the bias element support component  46 . In another embodiment, the bias element is a bias element compression spring  80  (see  FIG. 3 ) carried on the bias element support component  46 . In one embodiment the bias element elastomeric tube  58  is cast from a hydrogenated nitrile butadiene rubber (HNBR) having a durometer of at least 90. An upper bias element push ring  60  abuts an upper end of the bias element elastomeric tube  58 . A lower bias element push ring  62  abuts a lower end of the bias element elastomeric tube  58 . Both the upper bias element push ring  60  and the lower bias element push ring  62  float on the bias element support component  46 . The bias element elastomeric tube  58  constantly resists any movement of the upper bias element push ring  60  toward the lower bias element push ring  62 , and vice versa, thus resisting any relative movement of the multicomponent sliding sleeve  17  over the multicomponent mandrel  11 . As will be explained below with reference to  FIG. 4 , the bias element elastomeric tube  58  (or a bias element compression spring  80 , see  FIG. 3 ) respectively serve several important functions in the operation of the straddle packer  10 . 
       FIG. 3  is a cross-sectional view another embodiment  10   a  of the straddle packer  10 . All of the components and features of the straddle packer  10   a  have been described above with reference the straddle packer  10  shown in  FIGS. 1 and 2 , except that the bias element of the straddle packer  10   a  is the bias element compression spring  80 . In one embodiment, the straddle packer  10   a  also includes only the upper bias element push ring  60 , and the bias element support component  46  has no ports. Furthermore, there are no fluid ports in the transition sleeve upper end  50 . In one embodiment of the straddle packer  10   a , the bias element compression spring  80  is preloaded with about 2,000 pounds of compression when the straddle packer  10   a  is assembled, and maintains that tension in a run-in condition of the straddle packer  10   a  to ensure the upper and lower packer elements  18 ,  100  do not begin to set if the straddle packer  10   a  “tags” a minor obstruction while it is being run into a cased well bore. The straddle packer  10   a  is operated in the same manner as the straddle packer  10 , which is described below with reference to  FIGS. 4, 5   a  and  5   b.    
       FIG. 4  is a cross-sectional view of the straddle packer  10  showing the straddle packer  10  as it would appear if it were in a pressure-boosted packer-set condition. As will be explained below with reference to  FIGS. 5 a  and 5 b   , after an area of interest is located in a cased well bore, the straddle packers  10 ,  10   a  may be shifted from the run-in condition, shown respectively in  FIGS. 2 and 3 , to a packer set condition using work string manipulation to shift the auto-J ratchet lug  124  into an auto-J ratchet slip-engage notch  126   b , and applying string weight to the work string in a manner well known in the art. When work string weight is applied to the work string connection component  12  the straddle packer  10 ,  10   a  is urged downhole against a resistance of the drag blocks  120 , which begins to compress upper packer element  18  and forces the multicomponent mandrel upper part  11   a  downhole within the multicomponent sliding sleeve  17 . This urges the bias element push component  44  and the upper bias element push ring  60  to compress the bias element elastomeric tube  58  (or the bias element compression spring  80 ) as the bias element support component  46  is forced downhole. The compressed bias element elastomeric tube  58  urges the respective transition sleeve ends  50 ,  52 , the connection joint  54  and the initial set sub mandrel component  96  downhole, which compresses the lower packer element  100  and urges the two-part lower packer element compression sleeve  102  downhole against the resistance of the drag blocks  120 . This forces the mechanical slips  116  up the respective uphole and downhole slip ramps and into engagement with a casing of a cased well bore, thereby locking the straddle packer  10 ,  10   a  in the cased well bore as the mechanical slips  116  bite the well casing (not shown). As the bias element elastomeric tube  58  further compresses under the work string weight load, it increases in diameter to fill the bias element chamber  56  (see  FIG. 2 ) sealing mandrel ports  64  in the bias element support component  46  and transition sleeve ports  66  in the transition sleeve upper end  50  to prevent any escape through the mandrel ports  64  of high-pressure fluid pumped into the straddle packer  10 . Meanwhile, downhole movement of the multicomponent mandrel lower part  11   b  moves the unload sub mandrel ports  137  past the unload sub sleeve ports  135  and a captive seal  150  retained by a captive seal ring  152  inhibits any high-pressure fluid pumped into the straddle packers  10 ,  10   a  from escaping through the unload sub sleeve ports  135 . However, if a screen-out (well understood in the art) occurs, relieving work string weight at the surface lets the bias element elastomeric tube  58  (or bias element compression spring  80 ) relax as shown in  FIGS. 2 and 3 , to move the unload sub mandrel component  136  uphole and provide fluid communication between the unload sub mandrel component ports  137  and the unload sub sleeve ports  135  to dump fluid from the straddle packer  10 ,  10   a . In the event that this fluid path is obstructed for any reason, the mandrel ports  64  provide a fluid path around opposed ends of the relaxed bias element elastomeric tube  58  and out through the transition sleeve ports  66  to permit high-pressure fluid trapped in the straddle packer  10  to drain into an annulus of the well bore. The bias element elastomeric tube  58  (and the bias element compression spring  80 ) also assists the return of the straddle packer  10  to the run-in condition after string weight is removed from the work string, and prevents premature setting of the packer elements  18 ,  100  in the event an obstruction is tagged in the well bore while the straddle packer  10  is being run into the well bore. 
     Once the mechanical slips  116  have been engaged and the upper packer element  18  and lower packer element  100  are in the initial-set condition, high-pressure fluid can be pumped into the straddle packer  10 ,  10   a . The high-pressure fluid exits the flow sub nozzles  32 , but as the pump rate increases the high-pressure fluid is forced through packer element piston ports  106  of the packer element piston mandrel component  108  and into packer element piston chamber  112 , urging the two-part lower packer element compression sleeve  102  uphole away from the packer element piston  110  to boost the setting pressure on the lower packer element  100 . This in turns causes the pressure-boosted compression of the lower packer element  100  to urge the initial set sub mandrel component  96 , the connection joint  54 , and the respective transition sleeves  50 ,  52  uphole, further compressing the bias element elastomeric tube  58  (or the bias element compression spring  80 ) and urging the multicomponent sliding sleeve  17  against the upper packer element to fluid pressure-boost the set of the upper packer element  18 , balancing pressure-boost compression on the upper packer element  18  and the lower packer element  100 . The higher the fluid-pressure in the straddle packer  10 ,  10   a , the greater the fluid pressure-boosted setting of the respective packer elements  18 ,  100 . 
       FIG. 5 a    is a schematic detailed view in partial cross-section of the auto-j ratchet groove  126  of the straddle packer shown in  FIGS. 1-4 . In this view, the auto-J ratchet lug  124  is in a neutral notch  126   a  of the auto-J ratchet groove  126 . In the neutral notch  126   a , the mechanical slips  116  are urged to a retracted position by the slip springs  118 , which are retained by the drag block/slip retainer ring  128 , and the straddle packer  10 ,  10   a  can be pushed downhole against the resistance of the drag blocks  120 . 
       FIG. 5 b    is a schematic detailed view in partial cross-section of the auto-j ratchet lug  124  of the straddle packer  10 ,  10   a  in the slip engage notch  126   b . When the auto-J ratchet lug  124  enters the slip engage notch  126   b , the upper and lower multicomponent mandrel parts  11   a ,  11   b  can be pushed downhole through the straddle packer  10 ,  10   a  which closes the unload sub mandrel ports  137 , sets the mechanical slips  116  and compresses the upper packer element  18  and the lower packer element  100  to the initial set position, as described above with reference to  FIG. 4 . Shifting from the auto-J ratchet neutral notch  126   a  to the auto-J ratchet slip engage notch  126   b , or vice versa, is accomplished by pulling up on the work string, which moves the auto-J ratchet lug  124  into an auto-J ratchet shift notch  126   c . A subsequent downward push on the work string moves the auto-J ratchet to a subsequent notch of the auto-J ratchet groove  126 . The shift occurs automatically and without any action required on the part of the operator aside from the required pull up on the work string followed by a push down on the work string. 
     The explicit embodiments of the invention described above have been presented by way of example only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.