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BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to subsurface equipment for fluid production wells and more particularly to managing fluid flow in annular flow channels. 
         [0003]    2. Description of the Related Art 
         [0004]    Wellbores are often provided with separate multiple flow channels for moving fluids into and out of subsurface reservoirs. For example, a single injection well may be required to provide injection fluids to two or more layers in a reservoir in which case two separate flow channels are required. As another example, a single wellbore may be used to provide both a means for producing fluid from a reservoir and also provide a supply and return conduit for supplying a working fluid to a subsurface device. 
         [0005]    One way of separating the flow channels is to use separate tubing strings in parallel and placed into a single wellbore. This method is useful for shallow wells having low flow rates but is impractical for wells having higher flow rates or deep wells where pressure drops caused by the required narrow tubing strings are unacceptable. Instead, concentric tubing strings are used wherein one or more tubing strings are nested one inside another creating multiple annular flow channels defined by the inner wall of a first tubing string and the outer wall of a second tubing string passing through the annulus of the first tubing string. As the annular flow channels are separated by the tubing walls, the annular flow channels are isolated from one another in regard to pressure and the exchange of fluids. In addition, insulated tubing strings may also provide some thermal isolation between the annular flow channels. 
         [0006]    One problem associated with concentric tubing strings is that the assignment of the fluids in each annular fluid channel is typically fixed. That is, once a fluid enters one of the annular flow channels, it must remain in that annular fluid channel and cannot be switched with fluid from another annular fluid channel. This may cause a problem, for example, when a subsurface device, such as turbine driven pump, needs to be placed in the wellbore and fluid needs to routed to the device around another intervening device in the tubing string. 
         [0007]    Therefore, a need exists for a way to switch fluids between annular flow channels within a wellbore. Various aspects of the present invention meet such a need. 
       SUMMARY OF THE INVENTION 
       [0008]    A concentric tubing well completion system and subsurface annular flow crossover are provided. The well completion system creates at least three concentric annular flow channels in a wellbore. One or more subsurface flow crossovers provide for switching fluid flow between the annular flow channels within the completed well. A crossover can be used in conjunction with other subsurface equipment to more efficiently manage fluid flows in the completed well for the purposes of produced fluid extraction and supply of a working fluid to a subsurface device. 
         [0009]    In one aspect of the invention, three or more concentric tubing strings create a concentric tubing string with independent annular flow channels from an underground fluid reservoir to ground level or above ground level. A separate device or flow loop is installed at the lower end of the concentric tubing string to create a pressure isolated, continuous, flow loop from the surface end to the underground end of the concentric tubing string. The system uses a flow crossover that allows the fluid in any annulus to be redirected into any of the other annuli while maintaining the pressure and chemical integrity of the fluid. 
         [0010]    In another aspect of the invention, the flow crossover can be mounted at any point in the tubing string. In addition, multiple flow crossovers can be installed downhole to allow movement of the fluid from one annulus to another as desired. 
         [0011]    In another aspect of the invention, the system uses threaded joints with sliding seals at the lower end of the interior tubing strings to allow installation and extraction of the underground equipment with surface lifting equipment alone. No subsurface grappling or latching equipment is required. 
         [0012]    In another aspect of the invention, the system can be assembled into different sections in which the fluid flowing in one annulus may be switched to flow into a different annulus. This can allow changing the flow path of hot and cold fluid streams. The system can be used to recover heat from a fluid stream, control solids precipitation by maintaining fluid temperature, use a heated circulating fluid to lower the fluid viscosity of a produced fluid. 
         [0013]    This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description in connection with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be more readily understood from a detailed description of the exemplary embodiments taken in conjunction with the following figures: 
           [0015]      FIG. 1  is a schematic diagram of a well completion system for a wellbore in accordance with an exemplary embodiment of the invention. 
           [0016]      FIG. 2   a  is a cross-sectional drawing of an upper annular flow crossover and an upper portion of a subsurface heat exchanger in accordance with an exemplary embodiment of the invention. 
           [0017]      FIG. 2   b  is a cross-sectional drawing of a heat exchanger section in accordance with an exemplary embodiment of the invention. 
           [0018]      FIG. 2   c  is a cross-sectional drawings of two heat exchanger sections joined together in accordance with an exemplary embodiment of the invention. 
           [0019]      FIG. 3  is a cross-sectional drawing of a lower annular flow crossover and a lower portion of a subsurface heat exchanger in accordance with an exemplary embodiment of the invention. 
           [0020]      FIG. 4  is a cross-sectional drawing of a subsurface fluidically driven pump in accordance with an exemplary embodiment of the invention. 
           [0021]      FIGS. 5   a  to  5   i  are schematic drawings of an assembly sequence for a well completion system in accordance with an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  is a schematic diagram of a well completion system in accordance with an exemplary embodiment of the invention. The well completion system  100  includes two subsurface sections, a heat exchanger section  101  and a fluidically powered pumping section  102 , that extend into a well bore  103 . As depicted in the diagram, the wellbore is intended for production of geothermally heated brine from a subsurface production zone  104 ; however, it is to be understood that the well completion system is not limited to only geothermal applications. 
         [0023]    The well completion system  100  uses concentric tubing strings having three concentric pipes or tubing strings to create independent flow paths from the production zone  104  to the surface. A separate device or flow loop can be installed at the lower end of the concentric tubing strings to create a pressure isolated, continuous, flow loop from the surface to the underground end of the concentric tubing strings. The well completion system  100  uses annular flow crossovers that allow a fluid in any annular flow channel of the concentric tubing strings to be redirected into any other annular flow channel while maintaining the pressure and chemical integrity of the fluid. The annular flow crossovers can be mounted at any point in the concentric tubing strings. Multiple annular flow crossovers can be installed downhole to allow movement of the fluid from one annular flow channel to another as desired. 
         [0024]    The well completion system  100  uses threaded joints with sliding seals at the lower end of the interior tubing strings of the concentric tubing strings to allow installation and extraction of the underground equipment with surface lifting equipment alone. No subsurface grappling or latching equipment is required. The well completion system  100  can be assembled into different sections in which the fluid flowing in one annular flow channel may be switched to flow into a different annular flow channel. This can allow changing the flow path of hot and cold fluid streams. The well completion system  100  can be used to recover heat from a fluid stream, control solids precipitation by maintaining fluid temperature, use a heated circulating fluid to lower the fluid viscosity of a produced fluid, etc. 
         [0025]    The entire underground assembly consists of sections of concentric tubing strings. A annular flow crossover is installed at the top and bottom of each intermediate section to redirect the fluid flowing in one annular flow channel into a different annular flow channel, if desired. Each separate section is run by assembling joints of the outside tubing string with threaded connections at each end. The bottom section of the outside tubing string of a concentric tubing string supports any type of downhole device installed at the lower end of the tubing string. The device incorporates polished receptacles at the top of the device. These receptacles are capable of accepting a seal assembly installed at the lower end of each interior tubing string. The interior tubing string strings are installed after the outside tubing string is assembled and suspended in the hole. The concentric tubing string strings are installed sequentially from the outer string toward the center string. The lower end of each interior tubing string with the seal installed at the end are assembled and additional sections added until the seal enters the receptacle at the bottom of the adjacent outer string. 
         [0026]    The tubing string being run is suspended by a hanger assembly mounted on the inside of the outer tubing string. The top of each tubing string has a seal receptacle installed. This allows the installation of the annular flow crossover assembly with its seals to isolate each flow path. Subsequent sections can vary in design. Some possible design configurations include single or multiple heat exchanger sections, intermediate concentric tubing string sections, flow limiting sections, and pumping devices. These sections can be interspersed and placed at any intermediate depth in the well. 
         [0027]    The well completion system  100  includes a heat exchanger section  101  connected to an upper concentric tubing string section  105  that has a plurality of annular flow channels. The upper concentric tubing string section  105  is mechanically connected at a lower end to an upper annular flow crossover  106 . The upper annular flow crossover provides both mechanical and fluidic connectivity between the annular flow channels of the upper concentric tubing string section  105  and a heat exchanger  107 . The heat exchanger is connected at a lower end to a lower annular flow crossover  108 . The lower annular flow crossover  108  mechanically and fluidically connects the heat exchanger  107  to a lower concentric tubing string section  110  that is connected to fluidically powered pumping section  102 . The lower concentric tubing string section  110  provides mechanical and fluidic connectivity between the lower flow crossover  108  and a fluidically driven pump  112 . The fluidically driven pump  112  is optionally mechanically and fluidically connected to a tail pipe  114  that extends into the production zone  104 . 
         [0028]    The well completion system  100  and the concentric tubing strings can accommodate a working fluid that both drives the fluidically driven pump  112  and extracts heat from heated brine produced from the production zone  104 . To do so, downwardly flowing working fluid flows through a respective annular flow channel of the concentric tubing strings  105  and  110 . Returning upwardly flowing working fluid flows to the surface through another respective annular flow channel of the concentric tubing strings  105  and  110 . In addition, heated brine produced from the production zone  104  flows through yet another annular flow channel of the concentric tubing strings  105  and  110 . 
         [0029]    In operation, the downwardly flowing working fluid is pumped into the upper concentric tubing string section  105  down through the upper annular flow crossover  106  which routes the downwardly flowing working fluid into the heat exchanger  107 . The downwardly flowing working fluid then flows out of the heat exchanger  107  and into the lower annular flow crossover  108  which routes the downwardly flowing working fluid to the fluidically driven pump  112 . The fluidically driven pump  112  is driven by the downwardly flowing working fluid which draws heated brine from the production zone  104 . The heated brine is pumped toward the surface along with the returning upwardly flowing working fluid. The heated brine and upwardly flowing working fluid travel up through the lower concentric tubing string section  110  in their separate respective concentric flow channels to the lower annular flow crossover  108 . The lower annular flow crossover routes the heated brine into the heat exchanger and the upwardly flowing working fluid through the heat exchanger  107 . In the heat exchanger, heat is extracted from the heated brine into the working fluid. 
         [0030]    After leaving the heat exchanger, the heated brine and upwardly flowing working fluid are produced from the well at the surface. Once at the surface, the heated working fluid is used to power a turbine that in turn drives an electrical generator. The working fluid is then circulated back into the well completion system  100 . Residual heat in the brine may also be extracted and used to power a turbine before the brine is injected back into the production zone. 
         [0031]    As described herein, the well completion system  100  maintains a separated flow channel from the production zone to the surface for brine produced from the production zone. It is to be understood that the well completion system can be used to move brine between different production and injection zones, from more than one production zone, into more than one injection zone etc. as the well completion system  100  can accommodate additional intermediate openings into the tubing strings or well casing. 
         [0032]    In other embodiments of the well completion system  100 , the tail pipe  114  is dispensed with and an alternative completion method is used at the bottom of the wellbore. The alternative completion method can include an open hole completion, another concentric tubing string, etc. 
         [0033]    Having provided an overview of the well completion system in accordance with an exemplary embodiment of the invention, individual components of the well completion system will now be described in greater detail with reference to  FIGS. 2   a ,  2   b ,  2   c ,  3  and  4  where like numbered elements refer to the same features illustrated in the figures.  FIG. 2   a  is a cross-sectional drawing of an upper annular flow crossover in accordance with an exemplary embodiment of the invention. The upper annular flow crossover  106  mechanically and fluidically connects the upper concentric tubing string section  105  to the subsurface heat exchanger  107 . The concentric tubing string  105  has an outermost tubing string  200  and one or more concentric successive tubing strings, such as tubing strings  202  and  204 . Each successive tubing string defines an annular flow channel between an inner surface of a preceding tubing string and an outer surface of the successive tubing string. For example, tubing strings  200  and  202  define one annular flow channel  206  therebetween and tubing strings  202  and  204  define another annular flow channel  208  therebetween. In addition, an innermost annular flow channel  210  is defined by an interior surface of the innermost tubing string  204 . Therefore, a number of successive annular flow channels are defined that succeed from an outermost tubing string flow channel  206  to an innermost tubing string flow channel  210 . 
         [0034]    The upper annular flow crossover  106  has one or more flow channels, such as flow channels  212  and  214 , fluidically connecting a tubing string flow channel of the upper concentric tubing string section  105  to a non-corresponding flow channel in the heat exchanger  107 . For example, flow channel  212  connects annular flow channel  208  to a relatively outer non-corresponding flow channel  216  of the heat exchanger  107 . In addition, flow channel  214  connects annular flow channel  206  to a relatively inner non-corresponding flow channel  218  of heat exchanger  107 . 
         [0035]    In addition, the annular flow crossover  106  may have one or more flow channels that fluidically couple a corresponding flow channel of the upper tubing string  105  to the heat exchanger  107 . For example, flow channel  210  of the concentric tubing string  105  is connected to central flow channel  222  of the heat exchanger  107  via flow channel  220  of the upper annular flow crossover  106 . 
         [0036]    In one embodiment of an annular flow crossover in accordance with the invention, the annular flow crossover  106  is threadably connected to the outermost tubing string  200  and to an outer tube  223  of the heat exchanger  107 . In addition, the annular flow crossover  106  is slidably and rotably coupled to the successive tubing strings, such as tubing strings  202  and  204 , of the upper concentric tubing string section  105  and an inner tube  224  of the heat exchanger  107 . 
         [0037]    The heat exchanger  107  is constructed of an inner tube  224  within an outer tube  223 . The annular flow channel  232  between the inner tube  224  and the outer tube  223  has one or more heat exchange tubes, such as heat exchange tubes  244 ,  246  and  248 , passing therethrough. The heat exchange tubes define one or more isolated internal flow channels, such as internal flow channels  245 ,  247  and  249 , through the heat exchanger. The heat exchange tubes are installed and sealed at an upper plate  250  and a lower plate (not shown) located at a respective each end of the inner tube  224  and the outer tube  223 , thus creating a shell and tube exchanger. A fluid stream flowing through the heat exchange tubes is isolated from a fluid flowing in the annular flow channel  232 . A shell side of the heat exchanger  107  is thus defined as the flow channel  232  between the inner tube  224  and the outer tube  223  and external to the heat exchange tubes. 
         [0038]    Fluid that flows through the shell side of the heat exchanger  107  flows into one or more ports, such as port  252 , cut in a side of the outer tube  223  and through the annular flow channel  216  between an outside surface of the outer tube  223  and a concentric threaded collar  254  that threadably connects the upper annular flow crossover  106  to the heat exchanger  107  via a sealing collar  255  on an exterior surface of the outer tube  223 . The concentric threaded collar  254  provides both a structural connection and a pressure tight seal between the upper annular flow crossover  106  and the heat exchanger  107 . 
         [0039]    In operation, the upper annular flow crossover  106  receives downwardly flowing working fluid (as indicated by flow arrows  225 ,  226 ,  228  and  230 ) from annular flow channel  208  and routes the downwardly flowing working fluid to flow channel  216  of the heat exchanger  107  via flow channel  214 . The downwardly flowing working fluid then flows into flow chamber  232  of heat exchanger  107 . 
         [0040]    In addition, the upper annular flow crossover  106  receives upwardly flowing heated brine (as indicated by flow arrows  234 ,  236  and  238 ) from the heat exchanger  107  and routes the upwardly flowing heated brine from flow channel  218  of the heat exchanger to flow channel  206  of the upper concentric tubing string section  105 . While in the heat exchanger  107 , heat is transferred from the heated brine to the downwardly flowing working fluid. 
         [0041]    The upper annular flow crossover  106  also receives upwardly flowing heated working fluid (as indicated by flow arrows  240  and  242 ) from the heat exchanger  107 . The upper annular flow crossover  106  routes the upwardly flowing heated working fluid into the innermost flow channel  210  of the concentric tubing string  105  from flow channel  222  of the heat exchanger  107  by flow channel  220  of the upper annular flow crossover  106 . 
         [0042]      FIG. 2   b  is a cross-sectional diagram of a heat exchanger in accordance with an exemplary embodiment of the invention. As previously described, the heat exchanger  107  is constructed of an inner tube  224  within an outer tube  223 . An inner surface of the inner tube  224  defines a central flow channel  222 . An annular flow channel  232  is defined between an outer surface of the inner tube  224  and the inner surface of outer tube  223 . The annular flow channel  232  has one or more heat exchange tubes, such as heat exchange tubes  244 ,  246  and  248 , passing therethrough. The heat exchange tubes define one or more isolated internal flow channels, such as internal flow channels  245 ,  247  and  249 , through the heat exchanger  107 . The heat exchange tubes are installed and sealed at an upper plate  250  and a lower plate  350  located at a respective each end of the inner tube  224  and the outer tube  223 , thus creating a shell and tube exchanger. Fluid that flows through the annular flow channel  232  of the heat exchanger  107  flows through one or more ports, such as ports  252  and  352 , cut in a side of the outer tube  223 . 
         [0043]    The outer tube  223  has a sealing assembly  254  and a receptacle  256  for receiving a sealing assembly located at respective ends of the outer tube  223 . The inner tube  224  is similarly constructed as inner tube  224  also has a sealing assembly  258  and a receptacle  260  for receiving a sealing assembly located at respective ends. 
         [0044]    Respective upper and lower sealing collars  255  and  355  are located on an exterior surface of the outer tube  223 . The sealing collars  255  and  355  are used to threadably connect the heat exchanger  107  to a tubing string or an annular flow crossover using a concentric threaded collar as previously described. The sealing collars may be separate components that are connected to the exterior surface of the outer tube  223  or may be part of a machined assembly that incorporates the other features of an end portion of outer tube  223 , such as sealing assembly  254 , receptacle  256 , port  352 , port  252 , etc. as may be desired. 
         [0045]      FIG. 2   c  is a cross-sectional drawings of two heat exchangers joined together in accordance with an exemplary embodiment of the invention. In one embodiment of a subsurface heat exchanger in accordance with the invention, any number of heat exchangers, such as heat exchangers  270  and  272 , can be assembled sequentially in a wellbore in the same way as normal oil field casing or tubing. The flow paths for the fluid flowing through heat exchanger tubes, such as heat exchanger tube  273 , and a central flow channel  274  are isolated using a stab-in type of seal assembly and receptacle, such as seal assembly  280  and receptacle  278  for the central flow channel, and seal assembly  273  and receptacle  276  for the flow flowing through the heat exchanger tubes. Such a seal mechanism provides a seal to prevent any fluid cross flow between the other flow paths. 
         [0046]    The heat exchanger sections  270  and  272  are joined together by a threaded concentric collar  275  that mates with a first sealing collar  292  and a second sealing collar  294 . The threaded concentric collar forms a flow channel  296  around the mated outer sealing assembly  273  and respective receptacle  276 . The flow channel  296  provides a flow channel for fluid flowing through as shell side of the heat exchanger, as indicated by flow arrows  288  and  290 . 
         [0047]    The heat exchanger sections  270  and  272  can be supplied with or without a concentric coupling collar  275  already assembled to one end of a heat exchanger section. Assembly of the concentric coupling collar  275  and heat exchanger sections  270  and  272  can thus be accomplished at a well site using standard oil field equipment. 
         [0048]    As depicted in  FIGS. 2   a ,  2   b  and  2   c , the sealing assemblies and corresponding receptacles are configured such that entry of each sealing assembly into its corresponding receptacle may be confirmed prior to contact of the coupling. In other embodiments of heat exchanger sections, a sealing assembly and its corresponding receptacle may be connected after the threading of a sealing collar with a threaded concentric collar has begun. 
         [0049]      FIG. 3  is a cross-sectional drawing of a lower annular flow crossover in accordance with an exemplary embodiment of the invention. The lower annular flow crossover  108  mechanically and fluidically connects the lower concentric tubing string section  110  to the subsurface heat exchanger  107 . The lower concentric tubing string section  110  has an outermost tubing string  300  and one or more concentric successive tubing strings, such as tubing strings  302  and  304 . Each successive tubing string defines an annular flow channel between an inner surface of a preceding tubing string and an outer surface of the successive tubing string. For example, tubing strings  300  and  302  define one annular flow channel  306  therebetween and tubing strings  302  and  304  define another annular flow channel  308  therebetween. In addition, an innermost annular flow channel  310  is defined by an interior surface of the innermost tubing string  304 . Therefore, a number of successive annular flow channels are defined that succeed from an outermost tubing string flow channel  306  to an innermost tubing string flow channel  310 . 
         [0050]    The lower annular flow crossover  108  has one or more flow channels, such as flow channels  312  and  314 , fluidically connecting a tubing string flow channel of the lower concentric tubing string section  110  to a non-corresponding flow channel in the heat exchanger  107 . For example, flow channel  312  connects annular flow channel  306  to a relatively inner non-corresponding flow channel  318  of the heat exchanger  107 . In addition, flow channel  314  connects annular flow channel  308  to a relatively outer non-corresponding flow channel  316  of heat exchanger  107 . 
         [0051]    In addition, the lower annular flow crossover  108  may have one or more flow channels that fluidically couple a corresponding flow channel of the lower tubing string  110  to the heat exchanger  107 . For example, flow channel  310  of the lower concentric tubing string section  110  is connected to central flow channel  222  of the heat exchanger  107  via flow channel  320  of the lower annular flow crossover  108 . 
         [0052]    In one embodiment of a lower annular flow crossover in accordance with the invention, the lower annular flow crossover  108  is threadably connected to the outermost tubing string  300  and to an outer tube  223  of the heat exchanger  107 . In addition, the annular flow crossover  108  is slidably and rotably coupled to the successive tubing strings, such as tubing strings  302  and  304 , of the lower concentric tubing string section  110  and an inner tube  224  of the heat exchanger  107 . 
         [0053]    As previously described, the heat exchanger  107  consists of an inner tube  224  within an outer tube  223 . The annular flow channel  232  between the inner tube  224  and the outer tube  223  has one or more heat exchange tubes, such as heat exchange tubes  244 ,  246  and  248 , passing therethrough. The heat exchange tubes are installed and sealed at an upper plate (not shown) and a lower plate  350  located at a respective each end of the inner tube  224  and the outer tube  223 , thus creating a shell and tube exchanger. A fluid stream flowing through the heat exchange tubes is isolated from a fluid flowing in the annular flow channel  232 . A shell side of the heat exchanger  107  is thus defined as the flow channel  232  between the inner tube  224  and the outer tube  223  and external to the heat exchange tubes. 
         [0054]    Fluid that flows through the shell side of the heat exchanger  107  flows through one or more ports, such as port  352 , cut in a side of the outer tube  223  and through the annular flow channel  316  between an outside surface of the outer tube  223  and a concentric threaded collar  354  that threadably connects the lower annular flow crossover  108  to the heat exchanger  107  via a sealing collar  355  on an exterior surface of the outer tube  223 . The concentric threaded collar  354  provides both a structural connection and a pressure tight seal between the lower annular flow crossover  108  and the heat exchanger  107 . 
         [0055]    In operation, the lower annular flow crossover  108  receives upwardly flowing heated brine (as indicated by flow arrows  334 ,  336  and  338 ) from flow channel  306  of the lower concentric tubing string section  110  and routes the heated brine via flow channel  312  into flow channel  318  of the heat exchanger  107 . While in the heat exchanger, heat is transferred from the heated brine to the downwardly flowing working fluid. 
         [0056]    In addition, the lower annular flow crossover  108  receives downwardly flowing working fluid (as indicated by flow arrows  325 ,  326 ,  328  and  330 ) from flow channel  316  of heat exchanger  107  and routes the downwardly flowing working fluid to flow channel  308  of the lower concentric tubing string section  110  via flow channel  314 . 
         [0057]    The lower annular flow crossover  108  also receives upwardly flowing heated working fluid (as indicated by flow arrows  340  and  342 ) from the lower concentric tubing string section  110 . The lower annular flow crossover  108  routes the upwardly flowing heated working fluid from the innermost flow channel  310  of the lower concentric tubing string section  110  to flow channel  222  of the heat exchanger  107  by flow channel  320  of the lower annular flow crossover  106 . 
         [0058]      FIG. 4  is a cross-sectional drawing of a subsurface fluidically driven pump in accordance with an exemplary embodiment of the invention. The fluidically driven pump  112  is mechanically and fluidically connected to the lower concentric tubing string section  110 . As previously described, the lower concentric tubing string section  110  has an outermost tubing string  300  and one or more concentric successive tubing strings, such as tubing strings  302  and  304 . Each successive tubing string defines an annular flow channel between an inner surface of a preceding tubing string and an outer surface of the successive tubing string. For example, tubing strings  300  and  302  define one annular flow channel  306  therebetween and tubing strings  302  and  304  define another annular flow channel  308  therebetween. In addition, an innermost annular flow channel  310  is defined by an interior surface of the innermost tubing string  304 . Therefore, a number of successive annular flow channels are defined that succeed from an outermost tubing string flow channel  306  to an innermost tubing string flow channel  310 . A seal assembly, such as seal assembly  410 , is mounted at the lower end each concentric tubing string. Each seal assembly on each concentric tubing string is slipped into a seal receptacle, such as seal receptacle  412 . 
         [0059]    The fluidically driven pump  112  is further coupled to an tail pipe  114  that has a lower opening (not shown) in communication with a reservoir of hot brine. In operation, downwardly flowing working fluid (as indicated by flow arrow  400 ) flows into the fluidically driven pump  112  from the annular flow channel  308  of the lower concentric tubing string section  110 . The fluidically driven pump  114  is then driven by the working fluid and takes in heated brine (as indicated by flow arrow  401 ) from tail pipe  114  and pumps the heated brine (as indicated by flow arrow  402 ) upwardly through the annular flow channel  306  of the lower concentric tubing string section  110 . After driving the fluidically driven pump  112 , the working fluid flows (as indicated by flow arrow  404 ) upwardly through flow channel  310  of the lower concentric tubing string section  110 . 
         [0060]    In the foregoing description, the outermost annular flow channel in the concentric tubing strings  105  and  110  is depicted as containing heated brine, the next successive annular flow channel is depicting as containing downwardly flowing working fluid and the innermost flow channel is depicted as containing heated working fluid. However, in various other embodiments of the invention, the order and assignment of flow channels can be altered in accordance with the needs of the fluids being conveyed as the order and assignment is arbitrary. Furthermore, the order and assignment of the flow channels may be altered such that the different sections of concentric tubing strings have a different order and assignment. In addition, in the foregoing description only three flow channels are depicted. In other embodiments of the invention, fewer or more flow channels may be provided without deviating from the spirit of the invention. 
         [0061]    Having described the individual components of a well completion system in accordance with an exemplary embodiment of the invention, the assembly procedure for such a well completion system will now be described in reference to  FIGS. 5   a  to  5   i  where like numbered elements refer to the same features illustrated in the figures.  FIGS. 5   a  to  5   i  are schematic drawings of an assembly sequence for a well completion system in accordance with an exemplary embodiment of the invention. A fluidically driven downhole pump  500  is a combination fluidically-driven power turbine and pump. The power turbine rotates the pump at sufficient speed to generate a fluid pumping action. The turbine and pump are adjacent to each other and mounted as a common assembly. The power turbine is powered by a working fluid (not shown) descending from the surface as previously described. 
         [0062]    A concentric tubing string provides a circulation loop for the working fluid to return to the surface as previously described. To build the concentric tubing string, the fluidically driven pump  500  is installed on a lower end of an outer tubing string  506  and lowered into a well  508  as with conventional oil field casing and tubing. The outer tubing string  506  with the fluidically driven pump  500  connected to the lower end of the outer tubing string  506  is suspended at the drilling rig floor using conventional casing slips. After reaching a selected depth, a false rotary is installed at a drilling rig floor. This allows the weight of subsequent smaller, inside tubing strings  512  and  514  to be transferred to the rig floor during running of the inside tubing strings  512  and  514 . The false rotary supports a smaller set of slips and to support the inside tubing strings  512  and  514  as they are run into the larger outside tubing string  506 . 
         [0063]    Modified pipe hangers  522  are installed at the top of the outer tubing string  506  to allow suspension of the inside tubing string  512  in the outer tubing string. This same type of arrangement is used to run and suspend all subsequent tubing strings as the pipe size decreases. For example, tubing string  512  has pipe hangers  523  mounted on inner surface of tubing string  512  from which tubing string  514  is suspended. 
         [0064]    A set of seal receptacles are installed at the top of the fluidically driven pump  500  and the inside tubing strings  512  and  514  each have a seal assembly mounted at the lower end of the concentric tubing string as previously described. Each seal assembly on each tubing string is slipped into a respective seal receptacle at the top of the fluidically driven pump  500 . This provides a pressure tight isolation of each of the inside tubing strings  512  and  514 . The seal assemblies allow movement of each seal within the seal&#39;s respective receptacle to compensate for pipe movement because of wellbore temperature changes. The inside tubing strings  512  to  514  are run in sequence from the largest to the smallest. Each inside tubing string is run, stabbed into the seal receptacle at the bottom of the tubing string and suspended by a hanger, such as hanger  522 , at the top of the next larger tubing string. 
         [0065]    The well completion system allows intermediate equipment to be installed in a tubing string with concentric tubing strings and allows pressure isolation between the concentric tubing strings, if desired. The same system for running, sealing and hanging can be used at multiple depths in the well. 
         [0066]    An optional tail pipe  532  is installed below the fluidically driven pump  500  to allow the installation of many different types of devices. Some of the possible devices are screens for filtration of the borehole fluid, slotted pipe to help guide the assembly into the hole and prevent the intrusion of wellbore debris and seal assemblies to isolate fluid flow from lower in the wellbore, mounting of packer assemblies to allow wellbore zonal isolation, centering devices, vibration damping devices, and the like. 
         [0067]    Having presented an overview of the well completion system installation process, the order of installation of the well completion system components will now be presented in reference to  FIGS. 5   a  to  5   i  in sequence. 
         [0068]    As depicted in  FIG. 5   a , the fluidically driven pump  500  is lowered into well  508 . The fluidically driver pump  500  is connected to a lower end of outer tubing string  506 . In  FIG. 5   b , inner tubing string  512  is inserted into outer tubing string  506 . The lower end of inner tubing string  512  has a sealing assembly that is inserted into a sealing receptacle of fluidically driven pump  500 . In  FIG. 5   c , inner tubing string  514  is inserted into inner tubing string  512  and is sealably connected to fluidically driven pump  500  by a respective sealing assembly and sealing receptacle. 
         [0069]    In  FIG. 5   d , a lower annular flow crossover  534  as described in  FIG. 3  is attached to an upper end of the concentric tubing string created from tubing strings  506 ,  512  and  514 . In  FIG. 5   e , one or more heat exchanger sections  536  (as described in  FIG. 2  and  FIG. 3 ) are installed to the lower annular flow crossover  534 . In  FIG. 5   f , an upper annular flow crossover  538  (as described in  FIG. 2 ) is installed on an upper end of heat exchanger  536 . 
         [0070]    As depicted in  FIG. 5   g , an outer tubing string  540  of an upper concentric tubing string is installed. In  FIG. 5   h , an inner tubing string  542  of the upper concentric tubing string is installed. In  FIG. 5   i , another inner tubing string  542  is installed, thus completing the well completion system. 
         [0071]    While the invention has been particularly shown and described with respect to exemplary embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.

Summary:
A concentric tubing well completion method and a subsurface annular flow crossover system are provided. The well completion method creates at least three separate, pressure isolated annular flow channels in a wellbore. The subsurface crossover provides for switching fluid flow between the annular flow channels within the completed well. The crossover system can be used in conjunction with other subsurface equipment to more efficiently manage fluid flows in the completed well. For example, fluid from any subsurface reservoir or separate reservoirs can be delivered to the surface. In addition, flow paths can be provided for a fluid circulation loop from the surface, a subsurface fluid lifted to the surface or a fluid moved to a different depth in the well for reinjection. The subsurface crossover also provides a method to shift the fluids from one annular fluid channel to another. The subsurface annular flow crossover system also allows the installation of a device at any intermediate depth in the well while allowing fluid flow past the device thus eliminating the disruption or blocking of the flow for the purposes of heat and produced fluid extraction. For example, the crossover can be used to maintain separation between a working fluid and produced fluids in a subsurface heat exchanger used in a geothermal well or a subsurface turbomachinery such as a subsurface pump.