Abstract:
A subterranean well packer is inflated by a pumped transfer of rheotropic fluid through a tortuous flow channel into a packer sealing element expansion chamber. The tortuous flow channel and fluid delivery pressure are coordinated with the fluid properties to impose sufficient fluid shear stress for inducement of a substantial phase change in said rheotropic fluid after entry into expansion chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the priority U.S. Provisional Patent Application Ser. No. 60/427,290, filed Nov. 18, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to methods and apparatus for completing and maintaining subterranean wells for producing oil, gas and other fluids and minerals from the earth. In particular, the invention relates to a method and apparatus for setting a well annulus packer or bridge plug.  
           [0004]    2. Description of Related Art  
           [0005]    Packers and bridge plugs are devices for sealing the annulus of a borehole between a pipe string that is suspended within the borehole and the borehole wall (or casing wall). Hereafter, the term “packer” will be used as a generic reference to packers, bridge plugs or other such flow channel obstructions. The functional purpose of a packer is to obstruct the transfer of fluid and fluid pressure along the length of a flow channel such as a borehole.  
           [0006]    Typically, inflatable packer assemblies utilize either mud, water or cement to inflate an elastomer (rubber) bladder from a tubular mandrel. The mandrel is a pipe joint in an assembly string of tubing suspended within a well bore. Inflation of the bladder seals it against a well bore or casing wall to obstruct the annulus continuity between the well wall and tubing string. Inflatable packers expanded by mud or water typically utilize a valve system to maintain fluid pressure in the packer bladder. Cement systems, on the other hand, generally rely on the compressive strength of the cured or hardened cement. Both systems have inherent deficiencies.  
           [0007]    A packer that is inflated with mud or water is dependent solely on the reliability of the valve that confines the fluid pressure charge. Leakage of the valve results in deflation of the packer and loss of the annulus seal. Characteristically, cement is compounded as a pumpable non-heterogeneous liquid. Over a relatively short working time, free water in the compound is captured (cured) to alter the compound phase from liquid to solid. Accordingly, liquid phase cement is needed to inflate this packer bladder. After a curing time of a few hours, sufficient compressive strength to support significant weight above the packer. Considering the fact that the packer setting event occurs under the control and direction of a rig crew and that rig expenses are in the tens of thousands of dollars per hour, the time devoted to cement curing is enormously expensive.  
           [0008]    For a truly long-term or permanent packer, traditional wisdom will hold for the inflating fluid to be solid within the bladder to prevent leakage over time and to resist thermal effects which are generally more dramatic in fluids than in most solids. Consequently, the bladder of permanent packers is most often inflated by cement. The time lapse after mixing phase change from liquid to solid for cement may be controlled to some degree, by formulation. However, temperature and well fluid contamination may sometimes uncontrollably influence the phase change interval.  
           [0009]    Moreover, a significant caveat to the use of a cement inflated packer is the consequence of an error in positioning the packer. If erroneously set within a well fluid production zone, there is great potential for irreparable well damage. Accidental spillage within the wellbore is also a major concern. Use of cement inflated packers, therefore, carries a high risk element.  
           [0010]    U.S. Pat. No. 5,488,994 describes a fluid phase change system for setting a packer wherein the packer bladder is inflated by a polymer resin. As the resin is pumped into the bladder expansion voids, the resin flow is channeled over and mixed with a catalyst material. An in situ phase change of the resin occurs within the bladder voids as a consequence of the catalyst chemical reaction. Similar to cement set packers, the resin that inflates the packer bladder as a liquid, reacts into a solid to permanently secure the inflated profile.  
           [0011]    An object of the present invention, therefore is provision of a phase changing inflation system for well packers that is neither time nor temperature dependent for changing from a liquid phase to inflate the packer to a solid phase to secure the packer.  
           [0012]    Another object of the invention is an inflation system for well packers in which a liquid that is pumped down a tubing or pipe string flow bore is not stimulated to a phase change until actually entering a packer inflation chamber.  
           [0013]    A further object of the invention is an inflation system for well packers in which only liquid that actually enters a packer inflation chamber is stimulated to a phase change.  
           [0014]    Also an object of the invention is reduction, if not elimination, of uncertainties associated with actual bottom hole temperatures the heat generated within a packer inflation fluid as it is being pumped into a well and the time required to complete the operations.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention offers a system for setting a permanent well packer by inflation that is alternative to the time and temperature dependent prior art described above. Pursuant to the present invention, the packer inflation fluid may be a rheotropic liquid that is formulated to phase change from the liquid to solid state only after receiving a predetermined degree of fluid flow shear stress. Fluids of this character are described expansively by U.S. Pat. No. 4,663,366 and PCT Application WO 94/28085. Teachings respective to both of these references are incorporated herein by this reference.  
           [0016]    An activating shear stress parameter for a rheotropic liquid may be a predetermined number and quantity of fluid flow velocity changes as the inflation fluid enters the packer inflation chamber. Such measured flow velocity changes for the inflation fluid are induced by a tortuous flow path into the packer inflation chamber. The required degree of shear stress is substantially greater than the stress induced by the normal pumping required to deliver the inflation fluid to the packer location.  
           [0017]    The tortuous fluid flow path may be a labyrinthine channel within the packer valve collar formed by an alternating series of spaced baffles or discs that are perforated by misaligned apertures. Pump pressure behind the inflation fluid forces the fluid to negotiate the many flow path reversals as it courses into the packer expansion chamber.  
           [0018]    Only fluid that completes the labyrinth traversal into the expansion chamber may solidify or otherwise create a sufficiently high gel strength to be practical. Consequently, much of the risk associated with using a phase change inflation fluid is removed due to the circumstance that until actually entering the packer expansion chamber, the fluid will continue in the liquid state. The factors of time and temperature are also eliminated or significantly reduced from consideration. 
       
    
    
     BRIEF DESCRIPTION OF DRAWING  
       [0019]    For a through understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawing in which:  
         [0020]    [0020]FIG. 1 schematically represents a partial cross-section of the invention taken along a cutting plane parallel with the axis of a packer flow bore; and,  
         [0021]    [0021]FIG. 2 is an enlarged schematic cross-section of the inflating fluid flow labyrinth. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    Giving initial reference to FIG. 1, the present invention packer  10  comprises a tubular mandrel  12  that encompasses a fluid flow bore  14 . The mandrel  12  is an integral element of a well work string. The flow bore  14  is a fluid flow conduit usually having continuity with the well surface and may carry a pumped delivery of well working fluid.  
         [0023]    The packer bladder  16  may be, for example, a reinforced rubber or polymer tube that extends substantially the full length of the mandrel. At each tubular end, the bladder is secured to the mandrel  12  by collars having a lipped overlay  19 . Between the collars, an uninflated bladder tightly overlies the mandrel  12  for running into and placement within the well. When expanded by fluid pressure, the overlaid bladder tube  16  expands from the mandrel surface to form an inflation chamber  30 . One of the collars, the valve collar  18 , is tooled for an inflation conduit  22 . A fluid flow aperture  20  through the mandrel  12  wall is aligned with the collar inflation conduit  22 .  
         [0024]    Between the flow aperture  20  and the packer inflation chamber  30 , the inflation conduit  22  includes several fluid flow control elements comprising a fluid flow check valve,  24  and a flow labyrinth  26 . In some cases, fluid flow through the inflation conduit  22  may also be restricted by pressure responsive opening and closing valves (not illustrated) whereby the inflation conduit  22  is opened at a predetermined threshold pressure and is closed by a second pressure that is greater than the threshold pressure.  
         [0025]    The check valve  24  maybe of traditional design having, for example, a ball element  40  caged within a flow-through housing  42 . A closure seat  44  on the in-flow end of the housing  42  cooperates with the ball element  40  to rectify fluid flow through the check valve. Flow directed through the seat  44  displaces the ball from the seat to permit flow passage. Attempted flow directed in the opposite direction against the ball element imposes a pressure differential force on the ball element that presses the ball element  40  into a fluid seal engagement with the closure seat  44 . Thus, the fluid flow is rectified in a single direction.  
         [0026]    The flow labyrinth  26  may take many forms to induce a predetermined magnitude of hydrodynamic shear into the flow stream of fluid driven through the labyrinth  26  in the collar manifold  29  and expansion chamber  30 . The fluid, a rheotropic liquid such as disclosed by U.S. Pat. No. 4,663,366 and PCT Application WO 94/28085, has the property of changing phase from liquid to solid or semi-solid by undergoing a predetermined quantity of fluid shear such as imposed by sharp flow reversals.  
         [0027]    The presently preferred example of the labyrinth  26  is illustrated in detail in FIG. 2 to include a series of discs or baffles  34  aligned in a chamber volume  32  between the conduit  22  and an expansion chamber port  28 . The baffles  34  are separated by spacer rings  35  to provide fluid flow spaces  37  between the baffles  34 . The baffles  34  are perforated by apertures  39  to communicate the flow space  37  on opposite faces of a baffle  34 . However, the several apertures  39  are arranged in successive off-set alignment to cause a tortuous flow path through the chamber volume. Upon emerging from each aperture  39 , the fluid flow stream is forced to an abrupt flow directional change into the space  37 . Within the space  37 , the flow stream runs transversely to the aperture  39  flow direction into the next successive aperture  39 . Through each successive stage of flow reversal within the labyrinth  26 , the fluid is dynamically sheared to stimulate a rheotropic phase change. The number of baffles used can be varied depending on the shear requirements of the rheotropic fluid.  
         [0028]    In a traditional operation, the tubing string that includes this packer  10  is provided with a flow bore obstruction mechanism to allow the flow bore to be pressurized by a mud supply pump. When the packer is suitably positioned within the well bore, the rheotropic fluid is pumped into the tubing flow bore behind a bore closing device such as a valve ball. When the bore closure ball engages a ball seat below the packer, the flow bore filled with rheotropic fluid may be pressurized to open the collar conduit  22 . When opened, the fluid transverses the labyrinth  26  into the packer expansion chamber  30 .  
         [0029]    Upon emerging from the labyrinth  26 , the stimulated fluid passes through the chamber port  28  into the collar manifold  29  for the distribution about the packer annulus into the expansion chamber  30 . A continued delivery of the stimulated fluid into the expansion chamber  30  enlarges the bladder  16  to compressive engagement with the well bore or casing wall. However, upon achieving quiescence, the fluid within the chamber  30  congeals to a solid or semi-solid phase.  
         [0030]    It is only the fluid that has passed through the labyrinth  26  that has been sufficiently stimulated to congeal. The rheotropic fluid remaining in the tubing flow bore  14  continues in the liquid state. As a liquid, the rheotropic fluid in the flow bore  14  may be further pressurized to open one or more circulation or production sleeves. Through such circulation or production sleeves, the rheotropic fluid in the flow bore may be displaced by other well working fluids or by formation fluid production.  
         [0031]    Although the invention has been described in terms of particular embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.