A hydraulic technique for applications with inflatable packers keeps the inflatable packer in a stretched-out condition despite the forces imposed on the packer by circulating fluids. This prevents the inflatable packer from swabbing due to the force of circulating fluids.

FIELD OF THE INVENTION 
     The field of this invention relates to inflatable packers for downhole use and, more particularly, packers which must remain in service after deflation and devices to keep them from bunching up or swabbing due to exposure to circulating fluids. 
     BACKGROUND OF THE INVENTION 
     Rig time is a significant cost item in a drilling program. Thus, techniques that can be used to reduce trips into and out of the hole, particularly during the drilling process but throughout drilling completion or workover are always desirable. One such trip-saving technique involves the use of a drillpipe mounted packer. This packer can be used when the entire casing string is assembled to test the pressure integrity below the packer. Use of this technique allows isolation of areas of the wellbore containing shallow abnormally pressurized sand. Thus, in situations where testing of each casing shoe to ensure pressure integrity is required, a packer is run as part of the drilling bottomhole assembly. 
     Prior techniques required the removal of the drillbit and the insertion of a blanking device for the mudline well template to be picked up on the drillpipe and run down to the sea floor. A remotely operated vehicle (ROV) equipped with a camera was used to establish the position of the drillpipe relative to the well slot in the template. Once that position was established, a submersible drilling vessel was moved to position the drillpipe above the proper slot in the template and the drillpipe was lowered to engage the blanking device into the well slot. Once in position, the casing string and the shoe could be pressure tested for leak off. Once the shoe was successfully tested, the blanking device and the drillpipe were removed and pulled back to the surface. The drill bit was reinstalled and run back into position just above the well template. Again, the vessel had to be repositioned to allow the bottomhole assembly to be run into the proper well slot. Drilling ahead then proceeded at this point. 
     The addition of a packer on the bottomhole assembly for the drilling streamlines this procedure. However, when using this type of technique at the conclusion of the pressure test for the shoe, drilling needed to continue. This involved circulation through the drillstring, through the bit and back up the annulus. The inflatables previously used in this application on a drillstring bottomhole assembly were of the type having a sliding collar to accommodate the expansion of the inflatable element. Upon deflation, the movable collar on the inflatable was subject to forces induced by circulating fluids during the drilling operation. In addition, cuttings from drilling would also come up the annulus around this deflated packer. The forces generated by the circulating fluid during drilling and potentially further combined with mud or cuttings sticking to the inflatable element on the inflatable put substantial forces uphole on the inflatable element. This tended to push the sliding collar uphole and force the inflatable element outwardly. The forces could be so great as to make the now deflated packer act as a piston to virtually drive the drillpipe out of the wellbore. Thus what was needed was an effective technique to hold the slidable collar against the forces created due to the circulating fluid in the annulus. Due to the sometimes large sizes of such packers, i.e., in the order of 13 inches or greater, coil springs were ineffective to provide a sufficient resisting force to the hydraulically induced forces from circulation. Accordingly, the objective of the present invention is to employ hydraulic principals and pressure differentials so as to provide a hydraulic assist to the sliding collar in the now deflated packer to prevent it from swabbing uphole as fluid is circulated during drilling. 
     SUMMARY OF THE INVENTION 
     A hydraulic technique for applications with inflatable packers keeps the inflatable packer in a stretched-out condition despite the forces imposed on the packer by annular circulating fluids. This prevents the inflatable packer from swabbing due to the force of circulating fluids. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a - 1   e  are part section view of the drillstring-mounted packer of the present invention, showing the hydraulic tensioning device at its lower end. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 a - 1   e,  the packer P has an inflatable element  10  which is inflated at the desired depth in the well by displacement of control sleeve  12  by an assembly/object dropped  13  in through the drillstring  14  to block the passage  16  in the drillstring  14 . Downward displacement of the control sleeve  12  allows port  18  to shift below insert  20  which has on it a seal or seals  22 . Pressure applied through port  18  communicates poppet sub  24 , which is biased by a spring  26 . Upon sufficient downward displacement of poppet sub  24  compressing spring  26 , applied pressure through port  18  can communicate through passage  28  to annular space  30  under the inflatable element  10 . Removing pressure applied to port  18  allows spring  26  to push the poppet sub  24  back upwardly to retain the inflate pressure in the packer. 
     The packer P can be deflated by inserting a tool and engaging shoulder  32  to pull up the control sleeve  12 . This allows groove  34  to align with seal  36  so as to create a bypass. The pressure in annular space  30  is in communication with passage  38  and can, thus, escape around seal  36  when groove  34  is aligned opposite seal  36 . The pressure in annular space  30  can then escape by displacing ball  40 , which is biased by spring  42 , thus allowing pressure to escape through port  44  into the annular space  46  around the drillstring  14 . Thus, once released, the packer P cannot have its element  10  reinflated because the annular space  30  is exposed to the same pressure as the surrounding annular space  46 . 
     A rupture disc  47  can also be used as a backup way to deflate. 
     Referring to FIGS. 1 c  and  1   d , it can also be seen that the drillstring  14  has a port  48  which allows fluid communication into a cavity  50 . Cavity  50  is defined by tension housing sub  52 , which is attached to tension housing  54  at thread  56 . Seals  58  and  60  seal off the lower end of cavity  50 . Seals  62  and  64  seal off the upper end of cavity  50 . Tension housing  54  is secured to the lug retainer adapter  66 . Lug retainer adapter  66  is connected to an assembly of parts which ultimately connects to the bottom adapter  68 . Upon pressurization of annular space  30 , the bottom adapter  68  moves upwardly, taking with it the entire assembly of parts between bottom adapter  68  and lug retainer adapter  66 . A torque lug  70  rides in a groove  72  in mandrel  74 . 
     Prior to inflation an assembly/object is dropped  13  in to seal above port  48  preventing inflation pressure for reaching chamber  50 . Those skilled in the art will appreciate that thereafter upon inflation resulting from pressurizing the annular space  30 , the assembly of parts from bottom adapter  68  through the tension housing sub  52  will all move uphole in tandem, thus, in effect, reducing the volume of cavity  50 . As previously stated, testing can go on with the element  10  of packer P inflated, and at the conclusion of the testing, the element  10  is deflated, as previously described. Thereafter, drilling must continue, and a clear passage is presented comprising of passage  16  through control sleeve  12  down to the drillbit. In view of the pressure losses through the drillbit and through the remainder of the drillstring below the packer P, the pressure at port  48  will exceed the outside pressure in annular space  46 . Accordingly, there's a greater pressure applied to surface  76  than to the outer surface of tension housing sub  52 , which is exposed to the annulus pressure in annular space  46 . As a result, there's a net unbalanced downward force on tension housing sub  52  from normal drilling activities. That net unbalanced force is translated through the connected parts as previously described to bottom adapter  68  to pull it down to keep the element  10  in a taut position against the uphole forces of circulating mud with cuttings that are coming uphole in the annular space  46 . The components can be configured so that a substantial downward force can be exerted on the bottom adapter  68  through the port  48  onto surface  76  so as to keep the element  10  in its taut position. Testing can still occur using the inflated element  10  because there is a no-flow condition during the testing, thus there's no differential or unbalanced forces on tension housing sub  52  when the drillstring, in combination with an inflated packer P, is used to test the casing string, for example. 
     Those skilled in the art will appreciate that although one specific embodiment of use of pressure differentials to maintain the packing element  10  in a taut position has been illustrated, other configurations can be employed without departing from the spirit of the invention. Thus, any mechanical execution of parts which takes advantage of the higher pressure inside the drillstring  14 , as compared to the annular space  46 , and employs such pressure differential to exert a downward force on the element  10  to keep it from swabbing, is within the spirit of the invention. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.