Patent Publication Number: US-8113293-B2

Title: Single packer structure for use in a wellbore

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 61/116,494, filed on Nov. 20, 2008, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Packers are used in wellbores to isolate specific wellbore regions. A packer is delivered downhole on a conveyance and expanded against the surrounding wellbore wall to isolate a region of the wellbore. Two or more packers can be used to isolate one or more regions in a variety of well related applications, including production applications, service applications and testing applications. 
     In some applications, straddle packers are used to isolate specific regions of the wellbore to allow collection of fluid samples. However, straddle packers employ a dual packer configuration in which fluids are collected between two separate packers. The straddle packer configuration is susceptible to mechanical stresses which limit the expansion ratio and the drawdown pressure differential that can be employed. Other multiple packer techniques can be expensive and present additional difficulties in collecting samples and managing fluid flow in the wellbore environment. 
     SUMMARY 
     In general, the present invention provides a system and method for collecting formation fluids through a single packer having at least one drain located within the single packer. The single packer is designed with an outer flexible skin and one or more drains coupled to the outer flexible skin. A mandrel is positioned within the outer flexible skin, and an expansion mechanism is provided to control expansion of the outer flexible skin. For example, portions of the outer flexible skin can be expanded into sealing engagement with a surrounding wall. 
    
    
     
       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 single packer through which formation fluids can be collected, according to an embodiment of the present invention; 
         FIG. 2  is a front view of one example of the single packer illustrated in  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 3  is a view similar to that of  FIG. 2  but showing internal components of the single packer, according to an embodiment of the present invention; 
         FIG. 4  is a view similar to that of  FIG. 3  showing a flow line coupled to guard drains, according to an embodiment of the present invention; 
         FIG. 5  is a view similar to that of  FIG. 3  showing a flow line coupled to sample drains, according to an embodiment of the present invention; 
         FIG. 6  is a view of one example of the single packer in an expanded configuration, according to an embodiment of the present invention; 
         FIG. 7  is another view of one example of the single packer in an expanded configuration, according to an embodiment of the present invention; 
         FIG. 8  is another view of one example of the single packer in an expanded configuration, according to an embodiment of the present invention; 
         FIG. 9  is a view of an alternate single packer having a mechanical expansion system, according to an alternate embodiment of the present invention; 
         FIG. 10  is a view of another single packer example, according to an alternate embodiment of the present invention; 
         FIG. 11  is a schematic illustration of an extensible member used to couple a drain with a flow line, according to an embodiment of the present invention; 
         FIG. 12  is a schematic illustration of pressure acting on the extensible member, according to an embodiment of the present invention; 
         FIG. 13  is a schematic illustration of an alternate extensible member used to couple a drain with a flow line, according to an alternate embodiment of the present invention; 
         FIG. 14  is a schematic illustration of an alternate extensible member used to couple a drain with a flow line, according to an alternate embodiment of the present invention; and 
         FIG. 15  is a view of another example of the single packer, according to an alternate 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 for collecting formation fluids through one or more drains located in a single packer. Use of the single packer enables larger expansion ratios and higher drawdown pressure differentials. Additionally, the single packer configuration reduces the stresses otherwise incurred by the packer tool mandrel due to the differential pressures. In at least some embodiments, the single packer also is better able to support the formation in a produced zone at which formation fluids are collected. This quality facilitates relatively large amplitude draw-downs even in weak, unconsolidated formations. 
     The single packer expands across an expansion zone, and formation fluids can be collected from the middle of the expansion zone, i.e. between axial ends of the single packer. The formation fluid is collected and directed along flow lines, e.g. along flow tubes, from the one or more drains. For example, separate drains can be disposed along the length of the packer to establish collection intervals or zones that enable focused sampling at a plurality of collecting intervals, e.g. two or three collecting intervals. Separate flowlines can be connected to different drains, e.g. sampling drains and guard drains, to enable the collection of unique formation fluid samples. 
     The single packer provides a simplified packer structure that facilitates, for example, focused sampling. In one embodiment, an outer flexible layer, e.g. an outer rubber layer, contains three groups of drains in which a middle group comprises sampling drains and two axially outer groups comprise guard drains. The drains may be coupled to the flowlines through extensible members, or extensible members can be used in other configurations to facilitate expansion and contraction of the single packer without causing damage. 
     Referring generally to  FIG. 1 , one embodiment of a well system  20  is illustrated as deployed in a wellbore  22 . The well system  20  comprises a conveyance  24  employed to deliver at least one single packer  26  downhole. In many applications, packer  26  is deployed by conveyance  24  in the form of a wireline or other cable type conveyance. However, conveyance  24  may have other forms, including coiled tubing or other tubing, for use in other applications. In the embodiment illustrated, packer  26  is a single packer configuration used to collect formation fluids from a surrounding formation  28 . The packer  26  is selectively expanded in a radially outward direction to seal across an expansion zone  30  with a surrounding wall  32 , such as a surrounding wellbore wall in the form of a casing or open wellbore wall. When packer  26  is expanded to seal against wall  32 , formation fluids can be flowed into packer  26 , as indicated by arrows  34 . The formation fluids are then directed to one or more flow lines, as represented by arrows  36 , and produced to a collection location, such as a location at a well site surface  38 . 
     Referring generally to  FIG. 2 , one embodiment of single packer  26  is illustrated. In this embodiment, packer  26  comprises an outer flexible skin  40  in which a plurality of drains  42  is mounted. The outer flexible skin  40  comprises axially outer regions  44  that may be used to form seals with the surrounding wall  32  when single packer  26  is expanded. The drains  42  are disposed between axially outer regions  44  and may comprise one or more sample drains  46  and one or more guard drains  48 . In the example illustrated, a plurality of sample drains  46  is surrounded by a plurality of guard drains  48  that are disposed on both axial sides of the sample drains  46 . For example, the drains may be organized in three groups in which the two outer groups comprise guard drains  48  that are connected to a flow line, as described in greater detail below, to clean formation fluid during sampling. The inner group comprises sampling drains  46  that are connected to another flow line to collect formation fluid for sampling. 
     Referring generally to  FIG. 3 , a more detailed example of single packer  26  is illustrated. As illustrated, a mandrel  50  is located within outer flexible skin  40 , and an expansion mechanism  52  is positioned between mandrel  50  and outer flexible skin  40  to control radial expansion and contraction of the outer flexible skin. In this embodiment, expansion mechanism  52  comprises a pair of expansion members  54  with an individual expansion member  54  positioned at each axial end of the outer flexible skin  40 . The expansion members  54  may be expanded and contracted to control the radial movement of, for example, axially outer regions  44  out of outer flexible skin  40 . Expansion members  54  may comprise a variety of structures, and one suitable structure is an inflatable bladder  56 . The inflatable bladders  56  are positioned generally between the outer flexible skin  40  and mandrel  50  at each axial end of the outer flexible skin. 
     The outer flexible skin  40  may be formed of a polymeric material, e.g. rubber material, that has sufficient thickness to withstand the forces and environmental effects of the downhole environment. The outer flexible skin  40  also may be reinforced with fibers, metallic cables, or other structures designed to provide strength and/or support. Openings are formed through the outer flexible skin  40  for receipt of the drains  46 ,  48 . By way of example, the drains may be formed from a metallic material and bonded to outer flexible skin  40  within the openings formed to receive the drains. Inflatable bladders  56  also can be formed from such materials that include, for example, a rubber component. 
     Mandrel  50  also may comprise a bypass passage  58  to enable pressure equalization between the wellbore and the interior region within outer flexible skin  40 . The bypass  58  may comprise a passage having external ports  60  exposed to an annulus surrounding the mandrel  50  outside of outer flexible skin  40  and expansion members  54 . Bypass  58  also may comprise an internal port  62  exposed within outer flexible skin  40  between expansion members  54 . The external ports  60  and internal port  62  enable fluid flow and thus pressure equalization through the bypass  58 . 
     As further illustrated in  FIGS. 4 and 5 , extensible members  64  can be used to couple drains  46 ,  48  with flow lines. The extensible members  64  enable radial movement of outer flexible skin  40  and drains  46 ,  48  during, for example, expansion of expansion members  54  and/or outer flexible skin  40 . In the embodiment illustrated in  FIG. 4 , extensible members  64  are used to couple guard drains  48  with one or more guard drain flow lines  66 . Similarly, extensible members  64  also can be used to couple sample drains  46  with one or more sample drain flow lines  68 , as illustrated in  FIG. 5 . In this example, the flow lines  66 ,  68  are routed along mandrel  50 , e.g. inside, within, or along the mandrel exterior. 
     The inflatable bladders  56  may be selectively inflated and deflated. In the example provided in  FIG. 6 , the inflatable bladders  56  have been inflated to expand the axially outer regions  44  of outer flexible skin  40  and/or portions of the inflatable bladders  56  against the surrounding wellbore wall  32 . The outer flexible skin  40  is free and can be independently expanded or contracted, e.g. inflated or deflated, depending on the natural pressure balance between an interior  69  of the outer flexible skin  40  and the well pressure. Expansion of the flexible outer skin  40  can be independently achieved via application of pressure through bypass  58 , as further illustrated by arrows  70  in  FIG. 7 . Furthermore, the outer flexible skin  40  may naturally expand when draw down is applied through drains  46 ,  48  to intake fluid, as represented by arrows  72 . Again, expansion of the flexible outer skin  40  is accommodated by the ability to transfer fluid/pressure via bypass  58 . As illustrated in  FIG. 8 , application of sufficient draw down can expand drains and  46 ,  48  and outer flexible skin  40  against the surrounding wellbore wall  32 . If the outer expansion members  54  are pressure resistant, the single packer  26  can be used to perform minifrac operations. 
     An alternate embodiment of single packer  26  is illustrated in  FIG. 9 . In this embodiment, expansion mechanism  52  is constructed with expansion members  54  comprising mechanical expansion members  74 . One or both of the mechanical expansion members  74  is designed to selectively move outer flexible skin  40  in a radial direction toward and/or away from surrounding wall  32 . By way of example, one or both mechanical expansion members  74  can be actuated to expand radially or to move axially so as to force the outer flexible skin  40  to bulge in a radially outward direction during expansion. The mechanical expansion members are designed to ensure that at least a portion of the outer flexible skin  40  conforms to the wall  32  under sufficient pressure/force to provide sealing efficiency. 
     In another embodiment, the drains  46 ,  48  are similarly mounted, e.g. bonded, within outer flexible skin  40 . However, axial ends  76  of outer flexible skin  40  are secured to mandrel  50 , as illustrated in  FIG. 10 . For example, the axial ends  76  can be bonded to mandrel  50  to form the sealed interior region  69  around drains  46 ,  48  between mandrel  50  and outer flexible skin  40 . Expansion and contraction of outer flexible skin  40  is controlled by inflating and deflating the sealed interior region within the outer flexible skin  40 . For example, pressurized fluid can be moved into or out of the sealed interior region  69  via flow paths along mandrel  50 , such as bypass passage  58 . 
     Referring generally to  FIG. 11 , one embodiment of an extensible member  64  for coupling a drain with a flow line is illustrated. In this example, extensible member  64  comprises telescopic tubes  78 ,  80 . The telescopic tubes  78 ,  80  can be used with both guard drains  48  and sample drains  46  but a sample drain is illustrated simply for purposes of explanation. In this example, telescopic tube  78  is connected to one of the sample drains  46  and comprises an inner passage  82  that allows fluid flow from drain  46 . Tube  78  is sized for sliding, telescopic movement within an interior passage  84  of telescopic tube  80  that enables tube  78  to move radially outward and inward with respect to tube  80 . In the embodiment illustrated, telescopic tube  80  is coupled with mandrel  50  to allow flow into the corresponding flow line, e.g. flow line  68 . Additionally, a seal  86 , such as an O-ring seal may be disposed between telescopic tubes  78  and  80  to ensure maintenance of a pressure seal throughout the telescopic movement of tubes  78 ,  80  during expansion and contraction of outer flexible skin  40 . 
     In some applications, the surface of the drain  46  or  48  is specifically sized relative to the surface area of the moving telescopic tube  78 . By optimizing the relative exposed surface areas, system stability can be enhanced. In one example illustrated in  FIG. 12 , the surface areas are selected so that stability is obtained when the drain  46 / 48  seals against the wellbore wall  32 . The pressure differential, as represented by arrows  88 , across the drain surface helps hold the movable telescopic tube  78  in the deployed configuration. 
     Referring generally to  FIG. 13 , another embodiment of extensible member  64  is illustrated. In this embodiment, the drain  46  or  48  is connected to its corresponding flow line  66  or  68  in mandrel  50  via an articulated tube  90 . Articulated tube  90  comprises a plurality of pivot joints  92  that allow the tube to extend or retract during corresponding radial expansion or contraction of flexible outer skin  40 . The articulated member enables deployment at a constant volume, and the system remains stables provided the drain is wider than the articulated tube  90 . 
     Another embodiment of extensible member  64  is illustrated in  FIG. 14 . In this embodiment, the drain  46  or  48  is connected to its corresponding flow line  66  or  68  in mandrel  50  via a flexible tube  94 . Flexible tube  94  comprises a material  96  that allows the tube to fold, bend or otherwise flex to accommodate radial contraction and to similarly unfold, unbend or otherwise flex to accommodate radial expansion of flexible outer skin  40 . By way of example, material  96  may comprise a polymer material or a composite material with sufficient flexibility. The length of flexible tube  94  may vary according to its flexibility. 
     Another alternate embodiment of the single packer  26  is illustrated in  FIG. 15 . In this embodiment, flow lines  66 ,  68  are embedded in at least a portion of the outer flexible skin  40 . The expansion members  54 , e.g. inflatable bladders  56 , may be located within the flow lines. However, the flow lines  66 ,  68  can be redirected back to mandrel  50  at an axially outlying location with respect to expansion members  54 , as illustrated in  FIG. 15 . In this latter example, extensible members  64 , e.g. telescopic members, articulated members, flexible members, or other suitable members, can be positioned at the axially outlying locations as illustrated to accommodate radial expansion and contraction of the outer flexible skin  40 . 
     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, outer flexible skin  40  and inflatable bladders  56 . 
     As described above, well system  20  may be constructed in a variety of configurations for use in many environments and applications. The single packer  26  may be constructed from different types of materials and components for collection of formation fluids from single or multiple intervals within a single expansion zone. The ability to expand the outer flexible skin across the entire expansion zone enables use of packer  26  in many well environments. The various drain features and flow system arrangements also can be constructed in several configurations to provide a more reliable and efficient single packer design. Furthermore, the outer flexible skin can be formed from a variety of materials, including composite materials, for cooperation with various expansion members. Additionally, the mandrel configuration and flow line arrangements can vary between different applications and different environments. 
     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.