Abstract:
A thermoelectric generator for producing electric power from heat in fluids produced from a subsurface wellbore includes a conduit for moving therethrough fluids produced from the Earth&#39;s subsurface and at least one thermoelectric module affixed to an exterior of the conduit. The at least one thermoelectric module includes a collimating heat transfer device in contact with the conduit on a first side and in contact with a first side of a thermoelectric generator thermocouple on a second side. A second side of the thermocouple is in contact with a contact surface of a heat sink. The heat sink is exposed to ambient atmosphere at the Earth&#39;s surface to conduct heat away from the thermocouple.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to the field of thermo-electric power generators. More specifically, the invention relates to using heat from fluids produced from the Earth&#39;s subsurface to generate electric power or heat from heated water as the water is injected into wellbores drilled into the Earth. 
         [0005]    2. Background Art 
         [0006]    Production monitoring and control devices are associated with wellbores drilled through subsurface Earth formations from which useful materials such as petroleum are withdrawn. Such monitoring and control devices can include flow meters, pressure gauges and data recording devices, among others. The monitoring and control devices may also include a wireless telemetry transceiver to communicate measurements made by various sensors to a remotely located production monitoring and control unit that records data from a plurality of such wellbores. 
         [0007]    Irrespective of the type of monitoring and control devices used, and any associated recording and/or telemetry devices, all such devices use electric power for their operation. Accordingly, it is necessary to supply electric power in some form to operate the foregoing devices. In remote areas where grid-supplied electric power is not available, and where it is impractical to provide fuel powered electric generation, it is known in the art to use batteries, which may in some instances be recharged by photovoltaic cells (solar cells). There are circumstances where the use of photovoltaic cells becomes impractical, for example, in arctic regions where the amount of sunlight is limited. Thus, in such circumstances, battery replacement is required and adds substantially to the operating costs of such wells. Battery operation may also be impeded by low ambient temperatures under the same circumstances. 
         [0008]    There continues to be a need for electrical power sources to operate well control and monitoring devices. 
       SUMMARY OF THE INVENTION 
       [0009]    A thermoelectric generator for producing electric power from heat in fluids produced from a subsurface wellbore according to one aspect of the invention includes a conduit for moving therethrough fluids produced from the Earth&#39;s subsurface and at least one thermoelectric module affixed to an exterior of the conduit. The at least one thermoelectric module includes a collimating heat transfer device in contact with the conduit on a first side and in contact with a first side of a thermoelectric generator thermocouple on a second side. A second side of the thermocouple is in contact with a contact surface of a heat sink. The heat sink is exposed to ambient atmosphere at the Earth&#39;s surface to conduct heat away from the thermocouple. 
         [0010]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a wellbore drilled and completed through a producing Earth formation in the subsurface, including an example generator module. 
           [0012]      FIG. 2  shows an example thermoelectric generator. 
           [0013]      FIG. 3  shows one example of one of the modules in the generator of  FIG. 2 . 
           [0014]      FIG. 4  shows an example configuration for a heat sink that may be used with a thermoelectric generator module. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a wellbore  20  drilled through the Earth&#39;s subsurface. The wellbore  20  may include a casing  22  cemented therein to the bottom of the wellbore  20 . The casing  22  may include perforations  28  where the casing  22  passes through a productive subsurface formation  30  such as may contain oil and/or gas. A tubing string  24  may be inserted inside the casing  22  to increase the velocity of fluids produced from the productive formation  30  as they are moved by gravity to the Earth&#39;s surface. The tubing string  24  may be externally sealed near its lower end inside the casing  22  by an annular seal known as a packer  26 . Control valves at the surface in a wellhead  32  are used to adjust the rate at which fluids are moved from the productive formation  30  to the Earth&#39;s surface. The tubing string  24 , through one or more valves in the wellhead  32 , may be connected to a surface flow line  34 . The surface flow line  34  is connected at its other end to various devices (not shown) for processing the fluids that are removed from the productive formation  30 . 
         [0016]    The flow line  34  may include one or more sensors, such as temperature sensors, pressure sensors, flow meters, and the like, shown generally at  36  and coupled externally onto or coupled into the fluid flow path in the surface flow line  34 . Such sensors  36  can measure selected properties of the fluids moved through the flow line  34 . Output from the sensors  36  may be conducted to a control and communication unit  37 . The control and communication unit  37  may include batteries (not shown separately) for providing electrical power to the sensors  36  and to operate various device (not shown separately) in the control and communication unit  37 , particularly during periods of time when there is little or no fluid movement through the flow line  34 . The control and communication unit  37  may include valve actuators (not shown separately) for operating one or more of the valves in the wellhead  32  or elsewhere in the wellbore system, such as in the flow line  34 . 
         [0017]    In the present example, a thermoelectric generator  10  may be affixed to the flow line  34  proximate the wellhead  32 . The exterior of the flow line  34  is preferably covered with insulating material  14 , for example, foamed polyurethane, to retain heat inside the flow line  34  as it passes through the thermo electric generator  10 . Heat is transported from the subsurface formations because they are typically hotter that the formations proximate the surface. During periods of time when there is fluid movement through the flow line  34 , the relatively high temperature of such fluids produced from the formation  30  will cause the flow line  34  to have a higher temperature than the surrounding ambient temperature at the Earth&#39;s surface. Such temperature differential may be used to generate electrical power in the thermoelectric generator  10 . In some implementations a photovoltaic array  33  may be used to supplement electric power from the thermoelectric generator  10  to keep the batteries in control unit  37  at full charge. 
         [0018]    An oblique view of one example of the thermoelectric generator is shown at  10  in  FIG. 2 . The thermoelectric generator  10  can includes a plurality of thermoelectric generator (“TEG”) modules  21  affixed to the exterior of the flow line  34  as will be explained with reference to  FIG. 3 . Portions of the flow line  34  longitudinally disposed between successive TEG modules  21  may be covered with insulating material  14 , or example, foamed polyurethane. Each TEG module  21  can include a heat sink  12  in contact on one side with one side of the module  21 , and exposed to the ambient atmosphere on the other side, which includes heat dissipating fins or ribs ( FIG. 4 ). The heat sink  12  may be made from aluminum or other high thermal conductivity material. In the example shown in  FIG. 2 , pairs of TEG modules  21  are located at a same longitudinal position along the flow line  34  so that there are active components of a TEG module disposed on opposed sides of the flow line  34 . Such configuration is only meant to serve as an example and is not intended to limit the scope of the invention. Typically, the number of, and electrical connection between the TEG modules  21  will be selected to provide the voltage and current required to operate the various devices such as shown in  FIG. 1 . 
         [0019]    An example of a pair of longitudinally collocated TEG modules  21  coupled to the flow line  34  is shown in  FIG. 3 . Each TEG module  21  includes a collimating heat transfer device  13  such as a copper, silver or other high thermal conductivity element having one face thereof shaped to conform to a selected segment of the exterior circumference of the flow line  34 . The other face of the heat transfer device  13  may be substantially planar to conform to a face of a TEG thermocouple  44 . Such TEG thermocouples have two substantially parallel planar faces for contact with a high temperature surface and a low temperature surface, respectively. The low temperature contact face of the TEG thermocouple  44  is in contact with the base of a corresponding heat sink  12 . A clamp  11  that may be used to affix the TEG modules  21  to the flow line  34  may be assembled from two, substantially symmetric clamp components, shown at  11 A and  11 B in  FIG. 3 . Each of the clamp components may be affixed to the collimating heat transfer device  13  using cap screws  15  as shown in  FIG. 3  or any other device for such coupling. Any space between the interior of the clamp component,  11 A or  11 B, and the collimating heat transfer device  13  may be filled with insulating material  16  to cause more of the heat inside the flow line  34  to be caused to move through the TEG thermocouple  14 . As will be appreciated by those skilled in the art, the amount of power generated by a TEG thermocouple is related to the difference in temperature between the high temperature contact point and the low temperature contact point. It is preferable to operate such TEG thermocouples at relatively high differential temperatures, for example 200 degrees C. or more. However, fluids produced from the Earth&#39;s subsurface, except for very deep, very high flow rate wells, will typically not produce such temperature differentials in the flow line  34  with respect to the ambient atmosphere. It has been determined that by using a collimating heat transfer device  13  such as shown in  FIG. 3 , and by having the heat sink  12  include a relatively large heat dissipation area, it is possible to obtain sufficient electric power to operate devices such as explained with reference to  FIG. 1  while maintaining battery charge. 
         [0020]    The two clamp segments  11 A,  1 B may be coupled to each other using cap screws  17  or the like as shown in  FIG. 3 . 
         [0021]    It has been determined that by increasing the available heat dissipation area of the heat sink while keeping the heat path length to such surface area minimized, it is possible to increase the efficiency of the TEG module  21 . One example of a heat sink configuration that may be used in some examples of a TEG module is shown in  FIG. 4 . The heat sink  12  may be made from aluminum as explained earlier herein and includes a basal contact surface  12 A that is configured to contact substantially all of the cold contact face of the TEG thermocouple ( 44  in  FIG. 3 ). Two laterally protruding rib supports  12 B may extend from the basal surface angularly displaced from each other as shown in  FIG. 4 . Heat dissipating ribs  12 C may be affixed to the rib supports  12 B as shown in  FIG. 4 . Thus configured, it is believed that heat moved through the heat sink may result in convection of the air in contact with the ribs  12 C, thus increasing the efficiency of the TEG module  21 . 
         [0022]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.