Abstract:
A technique involves a packer formed as an expandable packer with an internal expandable bladder. The internal expandable bladder is surrounded with a plurality of packer slats oriented in a manner to enable expansion and contraction of the packer. Additional features are incorporated into the bladder and/or slats to facilitate repeated expansion and contraction of the packer while limiting leaks between wellbore regions and preventing extrusion of the bladder.

Description:
BACKGROUND 
     A variety of packers are used in wellbores to isolate specific wellbore regions. A packer is delivered downhole on a tubing string and a packer sealing element is expanded against the surrounding wellbore wall to isolate a region of the wellbore. Often, two or more packers can be used to isolate several regions in a variety of well related applications, including production applications, service applications and testing applications. 
     In some well applications, slat packers are used to isolate specific regions of wellbores. Slat packers generally are able to support higher differential pressures and higher expansion rates because the slats act as an efficient anti-extrusion barrier for an internal bladder. Slat packers are formed with a tubular rubber bladder covered by metallic slats to support the internal pressure and the mechanical stress to which the packer is submitted. The slats are oriented longitudinally so as to have a high recovery ratio, however the recovery ratio decreases during inflation of the packer. As the packer is inflated, the slats generally slide over each other, but the packer remains totally covered by slats when fully inflated. A rubber sleeve is placed over the layer of slats along their exterior to avoid external leaks between the regions of the well isolated by the packer. 
     The ability to prevent extrusion of the tubular rubber bladder is important in high-temperature packers because constituents of the internal bladder lose their elastic and mechanical quality at high temperatures. With a slat packer, the internal bladder acts against the layer of slats. However, inflation and deflation of slat packers can be difficult at high hydrostatic pressure because the pressure inside the packer is not balanced with the pressure of the fluid in the well. As a result, the slats are pressed between the internal rubber bladder and the external rubber sleeve which limits the ability of the slats to slide with respect to each other. After several cycles of the packer, unwanted gaps can occur between slats and render the packer susceptible to extrusion of the tubular rubber bladder. Additionally, the rubber material of the sealing layer created by the rubber sleeve also limits the expansion of a slat packer. If the packer is substantially expanded, the rubber material can tear and create a leak. The use of more elastic materials, however, can result in loss of the elastic properties that allow the rubber material to retain its shape after expansion. As a result, the slat packer can be difficult to deflate in a satisfactory manner when such materials are utilized. 
     SUMMARY 
     In general, the present invention provides a system and method for use in a wellbore to isolate specific regions in a wellbore. The system and methodology utilize a packer formed as an expandable packer with an internal expandable bladder. The internal expandable bladder is surrounded with a plurality of packer slats oriented in a manner to enable expansion and contraction of the packer. Additional features are incorporated into the bladder and/or slats to facilitate repeated expansion and contraction of the packer while preventing both leaks and extrusion of the bladder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a schematic front elevation view of a well system having a packer deployed in a wellbore, according to an embodiment of the present invention; 
         FIG. 2  is a schematic illustration similar to that of  FIG. 1  but showing the packer in an expanded configuration, according to an embodiment of the present invention; 
         FIG. 3  is a schematic cross-sectional view of a portion of one example of the packer, according to an embodiment of the present invention; 
         FIG. 4  is an illustration of one example of a slat for use with the packer, according to an embodiment of the present invention; 
         FIG. 5  is an illustration of another example of a slat for use with the packer, according to an alternate embodiment of the present invention; 
         FIG. 6  is a schematic cross-sectional view of a portion of the packer expanded against a surrounding wall, according to an embodiment of the present invention; 
         FIG. 7  is a schematic cross-sectional view of a portion of another example of the packer, according to an alternate embodiment of the present invention; 
         FIG. 8  is a schematic illustration similar to that of  FIG. 7  but showing the packer partially expanded toward a surrounding wall, according to an embodiment of the present invention; 
         FIG. 9  is a schematic illustration similar to that of  FIG. 7  but showing the packer expanded against the surrounding wall, according to an embodiment of the present invention; 
         FIG. 10  is a schematic cross-sectional view of a portion of another example of the packer, according to an alternate embodiment of the present invention; and 
         FIG. 11  is a schematic illustration similar to that of  FIG. 10  but showing the packer in an expanded configuration, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to a system and method that facilitate formation of seals within a wellbore. For example, many types of production and treatment applications involve isolating a specific region or regions along a wellbore. The isolated regions can be created by expanding one or more packers within the wellbore to isolate regions along the wellbore with respect to each other. As described below, one or more slat packers can be moved to a desired position within a wellbore and expanded to form a seal against a surrounding wall, such as a wellbore casing. 
     In one embodiment, slat packers are uniquely constructed in a manner that reduces friction between slats by forming the slats with coatings. The slat designed enables a good sealing between the axial ends of the packer without using an external sleeve. As result, well fluid can move between the slats and balance the hydrostatic pressure during inflation of the packer. Each slat is linked to an internal bladder in a manner that facilitates expansion/contraction of the packer while ensuring a satisfactory recovery ratio. 
     In other embodiments, the conventional, external sealing sleeve also can be omitted. For example, the external sleeve can be omitted when the bladder is constructed as a folded bladder to increase the expansion ratio. In this embodiment, the slats are linked to corresponding folds in the bladder so there is no undue extension of the bladder during inflation of the packer. Use of the folded bladder also enables implementation of a variety of materials, such as thermoplastic materials and/or metallic materials that can be in the form of thin metallic sheets. The folded bladder design also allows easy deflation of the packer while applying a lengthwise tension. 
     Referring generally to  FIG. 1 , one example of a well system  20  is illustrated as deployed in a wellbore  22 , according to embodiment of the present invention. The well system  20  comprises a well tool string  24  and at least one packer  26  mounted to the well tool string  24 . In this embodiment, packer  26  comprises a slat packer having a plurality of slats  28  that may be disposed in a generally axially directed orientation. In  FIG. 1 , packer  26  is in a radially contracted configuration to enable movement along wellbore  22  within, for example, a tubular structure  30 . By way of example, tubular structure  30  may comprise a well casing or other well tubing. The packer  26  is deployed and retrieved via a conveyance  32  extending downwardly from, for example, a wellhead  34  located at a surface location  36 . The conveyance  32  may comprise coiled tubing, production tubing, wireline, slickline, or other suitable conveyances. 
     As illustrated in  FIG. 2 , packer  26  can be selectively expanded in a radially outward direction to form a seal with a surrounding wellbore wall/surface  38 , such as an inside surface of tubular structure  30 . Expansion of the packer  26  to the sealing configuration isolates regions  40  along wellbore  22 . Depending on the application, a plurality of packers  26  can be combined with well tool string  24  to create additional isolated regions  40  along wellbore  22 . 
     Referring generally to  FIG. 3 , one embodiment of packer  26  is illustrated in a partial cross-sectional view taken generally transversely with respect to the axis of packer  26 . In this embodiment, packer  26  comprises an internal expandable bladder  42  and a plurality of slats  44  surrounding the expandable bladder  42 . By way of example, internal expandable bladder  42  may be formed from an elastomeric material, such as rubber, that allows the expandable bladder  42  to be repeatedly expanded and contracted in a radial direction. In the example illustrated, each slat  44  comprises a stiff core  46  combined with a seal material  48  able to form a secure seal with surface  38  upon expansion of packer  26 . 
     The packer slats  44  are attached to expandable internal bladder  42  at attachment regions  50 . By way of example, slats  44  can be attached to expandable bladder  42  by gluing, vulcanization, or other suitable attachment mechanisms. Furthermore, packer slats  44  are oriented and attached to internal expandable bladder  42  in a manner such that gaps  52  are formed between adjacent slats  44  while packer  26  is in the contracted configuration and during expansion of packer  26  toward surrounding surface  38 . The gaps  52  allow fluid in the well to penetrate into the mechanical structure of packer  26  between adjacent slats  44 , as represented by arrows  54 . The inflow of well fluid between slats  44  enables equalization of hydrostatic pressure so the slats  44  are not pressed against each other under hydrostatic pressure during expansion of packer  26 . The fluid between slats facilitates relative movement of adjacent packer slats during expansion of expandable bladder  42  and packer  26 . The formation of separated slats  44  comprising seal material  48  eliminates the need for an external sealing sleeve. 
     In  FIG. 4 , one example of a slat  44  is illustrated in which the stiff core  46  is coated with seal material  48 . By way of example, seal material  48  may comprise a rubber material or other suitable seal material. Stiff core  46  may be formed from a metal material, such as steel, a composite material, or other relatively stiff materials. In the embodiment of  FIG. 4 , seal material  48  is coated along an exterior side  56  of core  46 . However, the seal material  48  can be located, e.g. coated, on both the exterior side  56  and an interior side  58  of core  46 , as illustrated in  FIG. 5 . 
     During actuation of packer  26  to the sealing configuration illustrated in  FIG. 2 , the diameter of internal expandable bladder  42  is increased by internal fluid pressure, as represented by arrows  60  in  FIG. 6 . As internal expandable bladder  42  expands radially outward, gaps  52  enable the slats  44  to easily slide over each other until the packer  26  is fully expanded into sealing engagement with the surrounding wellbore wall  38 , as illustrated in  FIG. 6 . When the packer  26  transitions to the fully inflated/expanded configuration, all slats  44  are pressed against the surrounding wellbore wall  38  until the gaps  52  between slats  44  disappear. 
     The plurality of slats  44  forms a secure, rigorous seal with respect to the surrounding wall  38 . Because no external sleeve is necessary, the risk of losing the seal as a result of damage to the external sleeve is eliminated. Additionally, the risk of leaks along the slats is reduced because the seal material  48  on each individual slat  44  creates a secure seal both with the surrounding wall and between adjacent slats when the packer  26  is inflated to compress the slats  44  against each other. Additionally, fluid in the well can penetrate ends of packer  26  without affecting the seal so there is no need to incorporate additional components or to fill empty space in an effort to combat absolute pressure. 
     The design of packer  26  also promotes longevity and simplifies the manufacturing process because the packer only requires two layers in the form of expandable bladder  42  and the surrounding layer of slats  44 . The structure of slats  44  also enables the use of harder seal materials, such as a hard rubber, for example a 90 shore A rubber. Furthermore, the overall structure of packer  26  allows the packer to be easily deflated while applying a lengthwise tension by simply removing fluid from an interior  62  of expandable bladder  42 . 
     Referring generally to  FIGS. 7-9 , another embodiment of packer  26  is illustrated. In this embodiment, slats  44  are mounted to a foldable bladder  64  that may be designed to provide a substantial expansion ratio. As illustrated in  FIG. 7 , slats  44  are mounted on corresponding folds  66  of foldable bladder  64 . Each slat  44  can again be formed by combining the stiff core  46  and the seal material  48 . As described above, seal material  48  may comprise an elastomeric material, such as a rubber material, or other suitable seal materials. Stiff core  46  may be formed from a metal material, e.g. steel, a composite material, or other relatively stiff materials. In some embodiments, seal material  48  is coated along an exterior side of core  46  or along both an exterior and an interior side of core  46 . 
     When the packer  26  is in a contracted configuration or during inflation of packer  26  toward surrounding wall  38 , the slats  44  are open in a manner that leaves gaps  52  between adjacent slats. The gaps  52  allow fluid in the well to penetrate the slats which creates a hydrostatic balance that facilitates relative movement of the slats  44  during expansion of packer  26 . As illustrated in  FIG. 8 , radial expansion of packer  26  occurs upon expansion of foldable bladder  64  via transition of the folds  66 . The expansion moves slats  44  into engagement with the surrounding wall  38 . Continued expansion of packer  26  causes the slats  44  to press against each other and close naturally. The folds  66  of foldable bladder  64  are pressed against the slats  44  to further seal against the slats and create a sealing layer  68 , as illustrated in  FIG. 9 . The sealing layer  68  is able to isolate longitudinally adjacent regions  40  of the wellbore. The packer embodiment described with reference to  FIGS. 7-9  enables substantial expansion and easy deflation because the packer can be returned to its original size simply by pulling on the longitudinal extremities of the packer. 
     The foldable bladder  64  can be formed from an elastomeric material, such as a rubber material, that is formed with folds  66  and coupled to slats  44 . In other embodiments, the foldable bladder  64  can be formed with a thermoplastic material or a soft metal material  70  constructed with folds  66 , as illustrated in  FIG. 10 . The slats  44  are attached to the metallic, foldable bladder by, for example, gluing or other bonding techniques. In some applications, soft metal material can be coated or otherwise covered by a rubber material or other elastomeric material. Regardless, expansion of packer  26  causes the folds  66  to transition together as slats  44  are moved into contact with each other and with the surrounding wall  38 , as illustrated in  FIG. 11 . Use of a metallic, foldable bladder enables a high expansion ratio. The metallic material also can facilitate deflation in some applications because transition of the packer from an expanded configuration to a radially contracted configuration does not depend on the elasticity of a rubber material. This allows the packer to be easily transitioned to its original, contracted shape which can facilitate movement of the packer through restrictions in the wellbore. 
     Use of the foldable bladder  64  requires less deformation of the internal bladder and enables dependable, repeatable inflation and deflation of the slat packer  26 . The foldable bladder  64  simply folds and unfolds during corresponding radial movement of the slat packer  26 . 
     The overall well system  20  can be constructed in a variety of configurations for use in many environments and applications. For example, one or more slat packers  26  can be combined with a variety of well tool strings  24  to facilitate well testing operations, well treatment operations, well production operations, and other well related operations. Additionally, the slat packer  26  can be constructed from several types of materials and components. The foldable bladder can be created from various elastomeric materials, metallic materials, composite materials, and other materials that can be folded in a manner to accommodate expansion and contraction of the packer. The slats  44  also can be formed in a variety of shapes and sizes and with individual or combined materials. Depending on the well application and environment, the slat material can be similar or distinct relative to the material used to construct foldable bladder  64 . Furthermore, the slat packer  26  can be constructed in a variety of configurations with a variety of additional components/structures integrated into the packer design. 
     In any of the embodiments described above, the packer  26  may be symmetric about its lateral axis A (see  FIG. 1 ). This allows the packer to be bi-directional. That is, the packer  26  functions equally well whether it is inserted with its top portion T uphole of its bottom portion B, or its bottom portion B uphole of its top portion T. 
     Also, in any of the embodiments described above where a component is described as being formed of rubber or comprising rubber, the rubber may include an oil resistant rubber, such as NBR (Nitrile Butadiene Rubber), HNBR (Hydrogenated Nitrile Butadiene Rubber) and/or FKM (Fluoroelastomers). In a specific example, the rubber may be a high percentage acrylonytrile HNBR rubber, such as an HNBR rubber having a percentage of acrylonytrile in the range of approximately 21 to approximately 49%. Components suitable for the rubbers described in this paragraph include, but are not limited to, internal expandable bladder  42 , seal material  48 , and foldable bladder  64 . 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.