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BACKGROUND 
     In the course of producing oil and gas wells typically a well packer along with completion and production equipment are run into cased wellbore. Upon reaching a predetermined depth the packer is set to the casing. A well packer may accommodate several tubular strings passing through the packer although two production tubular strings passing through a single packer is the most common due to wellbore diameter restrictions. 
     In many instances it may be desirable to be able to produce many different formation zones independently such as in multi-lateral wellbores or when the various formation zones have differing mechanical or chemical properties. In some instances each zone may require a separate production tubular or a separate control line. When multiple control lines or production tubulars are required to pass through a packer an at least dual zone packer may be required. 
     The purpose of a dual zone packer is to seal the wellbore against fluid or gas flow at the location of the packer while allowing the production tubulars or control lines to pass through. The packer is provided with slips having camming surfaces which, when activated, cooperate with complimentary opposed wedging surfaces to radially extend to and grip the wellbore casing. The packer also has an annular resilient seal, usually an elastomer, that is typically radially expanded to seal against the casing. Both the resilient seal and the camming surfaces that extend the slips are usually activated by a longitudinal compression of the packer. The longitudinal compression may be effected by mechanical or hydraulic means. When a dual zone packer is run into the wellbore it is usually retained in the unset position, typically by a shear pin or a c-ring. 
     Conventional dual string packers incorporate at least a pair of tubular mandrels on which a packing seal element and slip assembly are mounted. Typically the dual bore packer is prepared for setting by closing one of the mandrels to fluid flow. The fluid flow may be closed by using a ball, plug, dart, or any other device that may form a seal to block the particular tubular. 
     The resilient packer and the slip assembly are typically radially extended by a hydraulic piston that applies longitudinal compressive force in response to hydraulic pressure in the blocked mandrel. Setting forces are applied to the annular seal elements and the anchor by a setting cylinder mounted to the packer mandrel. 
     In certain instances it may be necessary to release the dual string packer in order to remove it from the wellbore. In order to facilitate easy removal of the packer from the wellbore certain features must be incorporated into the dual string packer as it is constructed. Typically the packer is constructed so that tension may be applied from the surface through one of the tubular mandrels to a shear assembly in the body of the packer. The tubular mandrel used to release the tension in the tool is typically referred to as the long side of the dual string packer. When enough tension is applied to the shear assembly from the surface to overcome the shear assembly&#39;s internal resistance and shears the relevant portions of the assembly the longitudinal compression applied to radially extend the slips and the resilient seal is released. The slips and the resilient seal no longer lock and seal the dual string packer to the casing and the dual string packer may be removed to the surface. 
     It is sometimes necessary to use one particular bore and at other times it is necessary to use the other bore as the source of hydraulic pressure to set the slips and the resilient seal. However, because only the long side of the dual string packer can be used to remove the dual string packer from the well and because each mandrel bore may have different requirements due to equipment and other requirements of the well, the operator is not usually able to easily reverse the orientation of the dual string packer prior to its deployment. It is usually necessary to reconfigure the internal portions of the dual string packer. 
     Typically, one of the tubing mandrels has a port built into it so that a flow path is created by the particular mandrel and the internal shifting chamber, while the other tubing mandrel has the necessary shear pins and other components to release the slips and seals when necessary. Since the through tubing mandrels pass through and are attached to the internal components of the dual string packer, a complete top to bottom rebuild of the dual string packer, usually on the rig floor, is called for in order to reconfigure the internal portions of the dual string packer. Such a rebuild takes valuable rig time and leads to possible contamination and potential failure of the tool when the dual string packer is deployed downhole. 
     SUMMARY 
     In order to overcome the need to completely disassemble a dual or even possibly a multiple string packer on the rig floor and to avoid the delays and potential for failure that such a rebuild entails, a crossover module may be attached to the through tubing mandrels at or near the bottom or lower end of the dual string packer. 
     By attaching the crossover module near the bottom of the dual string packer through tubing, the dual string packer may be plumbed so that any of the through tubing mandrels may supply the pressure to the shifting chamber that is required in order to set the slips or the seal. 
     The crossover module typically has a series of through bores that match the bores of the shifting chamber and any of the through tubing mandrels. Additionally, the crossover module has a port that connects at least one of the through tubing mandrels to the usually centrally located shifting chamber. Depending upon the size and orientation of the various through tubing mandrels, the crossover module may have a mirror image from one side of the cassette to the other and may be rotated about an axis orthogonal to the longitudinal axis to allow various through tubing mandrels to provide pressure to the shifting chamber. In other configurations it may be possible to easily loosen the crossover module and rotate the crossover module about its longitudinal axis to the position desired to allow various through tubing mandrels to provide pressure to the shifting chamber. 
     A typical dual string packer with a crossover module has a housing having at least two longitudinal flow passages, a top end, a bottom end, a seal movably mounted on the housing, a slip assembly supported on the housing, a bore in the housing, and a crossover module allowing fluid communication between the bore in the housing and a longitudinal flow passage. In some instances the crossover module is located towards the bottom end of the housing. The bore in the housing usually defines a pressure chamber and the pressure chamber usually is a setting assembly. The setting assembly or pressure chamber applies force to set the slip assembly that in turn sets the seal, if necessary, and sets the slips. Sometimes the seal may be made of a swellable elastomer. Therefore, no setting force is necessary, but may be applied. The crossover module may rotate about a longitudinal axis or about an axis orthogonal to the longitudinal axis to provide fluid communication between the bore in the housing and a longitudinal flow passage. 
     In an alternative embodiment the dual or multiple string packer may have a tubular body mandrel with at least two longitudinal flow passages, a top end, a bottom end, a seal mounted on the tubular body mandrel, a slip assembly supported on the tubular body mandrel, a setting chamber in the tubular body mandrel, and a movable crossover module allowing fluid communication between at least one of the longitudinal flow passages and a setting chamber. The setting chamber applies force to set the slip assembly and if needed to the seal. In some instances the seal may be a swellable seal. The movable crossover module may rotate about a longitudinal axis or about an axis orthogonal to the longitudinal axis to provide fluid communication between the setting chamber and a longitudinal flow passage. 
     A method of assembling a multiple string packer provides for a housing having a top end, a bottom end, at least two longitudinal flow passages, and a usually centrally located bore. A seal and a slip assembly are also mounted on the housing. At some point, a crossover module, usually located towards the bottom end of the housing, may be oriented so that fluid may flow between the bore in the housing and a longitudinal flow passage. In some instances the bore in the housing may be used as a pressure chamber and incorporate a setting assembly. The pressure chamber applies force to set the slip assembly and the seal. In some instances the seal may be a swellable elastomer and setting force may or may not be used. The crossover module rotates about a longitudinal axis or about an axis orthogonal to the longitudinal axis to provide fluid communication between the bore in the housing and a longitudinal flow passage. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic view of a wellbore with at least two formation zones. 
         FIG. 2  depicts a dual string packer. 
         FIG. 3  depicts an end view of a crossover module. 
         FIG. 4  depicts a side view of the crossover module in  FIG. 3 . 
         FIG. 5  depicts a dual string packer with a crossover module located near its lower end. 
         FIG. 6  depicts a crossover module with varying sizes of tubular bores that rotates about a mirror line. 
         FIG. 7  depicts a crossover module with multiple tubular bores that is indexed about its longitudinal axis. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes exemplary apparatuses, methods, techniques, and instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. 
       FIG. 1  depicts a schematic view of a wellbore  10  with at least two formation zones, formation zone  12  and formation zone  14 . The downhole assembly typically consists of at least two upper tubular strings, tubular string  16  and tubular string  18  each extending from the surface  20  to the at least dual string packer  30  with upper slip  32 , lower slip  34 , and seal  36 . Also shown is a packer  38  isolating formation zone  12  and formation zone  14  from one another. The downhole assembly also has at least two lower tubular strings, tubular string  42  and tubular string  44 , each extending from the at least dual string packer  30  to an isolated portion of the wellbore  10  each corresponding to a particular formation zone such as formation zone  12  and formation zone  14 . 
     Typically tubular string  16  and tubular string  42  are fluidly connected through the at least dual string packer  30 . Also, typically tubular string  18  and tubular string  44  are fluidly connected through the at least dual string packer  30 . By isolating the wellbore  10  into at least two formation zones  12  and formation zone  14  while fluidly connecting each formation zones  12  and formation zone  14  to the surface  20  the operator may complete, produce, or otherwise treat each formation zones  12  and formation zone  14  independently of each other. 
       FIG. 2  depicts a more detailed view of the typical at least dual string packer  30 . For ease of reference the top of the figures are designated as up or towards the surface  20  ( FIG. 1 ). The typical dual string packer  30  depicts a packer housing  31 , having at least two longitudinal flow passages shown as tubular bore  70  and tubular bore  72 . The typical dual string packer  30  also depicts a dual string packer upper end  52 , a dual string packer lower end  54 , a resilient elastomeric seal  36 , an upper slip  32 , a lower slip  34 , an upper end  62  of tubular bore  70 , a lower end  64  of tubular bore  70 , an upper end  66  of tubular bore  72 , a lower end  68  of tubular bore  72 , and a bore or internal setting chamber  80  in the housing. 
     Typically the dual string packer  30  is run into the wellbore  10  until the tubular strings  42  and  44  are properly placed and formation zones  12  and  14  are isolated from one another by setting at least packer  38 . A ball, dart, or other movable plug is deposited in the well to seal against a seat in tubular bore  72  but below the location of a port (not shown) in the dual string packer  30  allowing fluid communication between a tubular and the setting chamber  80 . Pressure is then applied from the surface  20  to pressurize the setting chamber  80  and thus supply the necessary mechanical force to compress and thus radially extend the slips  32  and  34  and the resilient elastomeric seal  36  thereby locking the dual string packer into position in wellbore  10  and sealing the dual string packer  30  to the sides of the wellbore  10  forming zones above and below the dual string packer that are isolated from one another with the exception of any tubulars such as tubular string  42  and  44  that pass through the dual string packer  30 . 
     In a dual string packer  30 , one of the tubular bores such as tubular bore  72  is designated as the long side. By being designated as the long side, the components required to release the slips  32  and  34  and seals  36  are linked to that particular side, while another tubular bore such as tubular bore  70  is fluidly connected to the internal setting chamber  80 . In certain instances it may be necessary to change the internal fluid connection between one tubular and another. In these instances due to the linkages between the long side tubular bore  72  and the components necessary to release the slips  32  and  34  and the seal  36  as well as the internal fluid connection between tubular bore  70  and the internal setting chamber  80  it is necessary to completely disassemble the dual string packer  30  in order to change the internal fluid connection from one tubular and another. Such disassembly usually takes place on the rig floor and may lead to delay as well as an increased possibility of the dual string packer failing when deployed. 
     In order to reduce the rig down time and the chance of failure due to contamination of the dual string packer while disassembled on the rig floor a crossover module may be used. 
       FIG. 3  depicts a crossover module  100  from an end view while  FIG. 4  depicts the same crossover module  100  from a side view. The crossover module typically consists of a mandrel  102  having multiple tubular bores shown here as tubular bore  110 , tubular bore  112 , and bore  114 . Bore  114  may or may not pass completely through the crossover module  100 . In those instances where bore  114  does pass through the crossover module  100  there is typically some type of blocking device to seal the lower end of bore  114 . The crossover module also has a port  116  to fluidly connect a tubular bore, here tubular bore  112 , to the bore  114 . In  FIG. 4  bore  114  is shown as it connects to the internal setting chamber  80 . 
     In  FIG. 4  the internal setting chamber  80  is typically a bore in packer housing  31  that utilizes the pressure provided via port  116  from tubular bore  112  to act as the cylinder forcing a piston to provide the mechanical power to set the slips  32  and  34  and if necessary the seal  36 . 
       FIG. 5  depicts a typical dual string packer  101  with a crossover module  100  attached at the lower end of the dual string packer  101 . For ease of reference the top of  FIG. 5  is designated as up or towards the surface  20  ( FIG. 1 ). The dual string packer  101  has a packer housing  120 , having at least two longitudinal flow passages shown as tubular bore  122  and tubular bore  124  and an internal setting chamber  134 . The dual string packer  101  has an upper end  130 , a lower end  132 , a resilient elastomeric seal  136 , an upper slip  138 , a lower slip  140 , an upper end  142  of tubular bore  122 , a lower end  144  of tubular bore  122 , an upper end  146  of tubular bore  124 , and a lower end  148  of tubular bore  124 . 
     Attached to the lower end  132  of the dual string packer is the crossover module  110 . All references to the crossover module remain as noted in  FIGS. 3 and 4 . The crossover module  100  has a tubular bore that aligns with each tubular bore of the dual string packer  101 . In the particular embodiment shown in  FIG. 5  the crossover module  100  has a tubular bore  112  that corresponds to and aligns with the lower end  148  of tubular bore  124 . Tubular bore  110  corresponds to and aligns with the lower end  148  of tubular bore  122 . Bore  114  corresponds to and aligns with the lower end  148  of internal setting chamber  134 . Bore  114  is in fluid communication with a tubular bore, here it is shown to be in fluid communication with tubular bore  112 . Fluid communication between the tubular bore  112  and the internal setting chamber  134  may be easily changed by axially rotating the crossover module  100  such that the tubular bore  112  then aligns with the lower end of tubular bore  122  and tubular bore  110  aligns with tubular bore  124 , thus providing fluid communication to the surface through tubular bore  122  instead of through tubular bore  124 . 
     By allowing easy removal of the lower end of the dual string packer  101  and access to the crossover module  100  the complete disassembly of the dual string packer on the rig floor and the associated loss of rig time and reliability of the dual string packer is avoided. 
     As depicted in  FIG. 6 , in some instances the dual string packer will have varying numbers of tubular bores and each bore may have a different size. The crossover module  164  may have a corresponding number of tubular bores such as tubular bores  160  and  162  that may vary in size from other tubular bores such as tubular bores  170  and  172 . In this particular case the tubular bores are symmetric about a mirror line  174 . 
     In those instances when the tubular bores are symmetric about a mirror line it may be possible to change the fluid access from a bore on one side of the mandrel to a bore on the other side of the mandrel by flipping the crossover module  164  about its mirror line  174 . For example tubular bores  160  and  162  (as well as tubular bores  170  and  172 ) are symmetric to one another with respect to mirror line  174 . Having the tubular bores symmetric about the mirror line  174  allows the operator to flip the crossover module over (with respect to the mirror line  174 ) and each tubular bore would continue to line up with a bore in the main body of the mandrel. However, because the pressure chamber access is to tubular bore  170  (the upper bore in  FIG. 6 ) in the crossover module, when the crossover module is flipped about the mirror line  174  the pressure chamber access is to the lower bore in  FIG. 6 . 
     Various sizes of tubular bores may be necessary depending upon conditions further down the wellbore. It may be necessary to pass small hydraulic control lines, capillary tubes, electric lines, fiber optic, cables, or other lines and control devices through the dual string packer and the crossover module. Any combination may be possible depending upon available wellbore cross-section and symmetry of any of the tubular bores that are to remain open. 
     As depicted in  FIG. 7 , in some cases the dual string packer will have an odd number of tubular bores requiring the crossover module to have a corresponding odd number of tubular bores. In these cases either flipping the crossover module or rotating the crossover module about its longitudinal axis may be used to change the connection between a particular tubular bore and the pressure chamber. 
     As shown, a crossover module  180  has 3 tubular bores  186 ,  188 , and  184  in addition to the bore  190  to allow access to the internal setting chamber. Port  192  provides for fluid communication between tubular bore  184  and bore  190 . This configuration of the crossover module allows the desired tubular bore in the dual string packer to be used to set the slips and seals in the dual string packer by loosening the crossover module  180  and rotating it about its longitudinal axis to index the tubular bore  184  that is ported via port  192  to the internal setting chamber  190  with the desired tubular bore of the dual string packer. 
     While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. In particular references to a dual string packer include multiple string packers. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.

Summary:
A dual string packer may be provided with a crossover module located such that fluid communication may be provided from any tubular bore to the internal shifting chamber without completely disassembling the dual string packer. The crossover module may be attached to the through tubing mandrels at or near the bottom or lower end of the dual string packer.