Abstract:
An apparatus and method for generating electricity from a liquid flowing in a generally vertical direction down a borehole. There is a turbine disposed at a subsurface position and having an intake and a discharge, the turbine being mechanically coupled via an output shaft to an electric generator such that rotation of the output shaft drives the generator to produce electric power. A control valve assembly is positioned below the turbine, the control valve assembly including a valve adapted to receive water discharged from the turbine and a control system operatively connected to the valve for throttling the valve in response to the rate of flow of liquid to the turbine to maintain the rotation of the turbine in a predetermined RPM range.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. patent application Ser. No. 61/394,544 filed on Oct. 19, 2010, the disclosure of which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to hydroelectric generation of power and, more particularly, to the generation of electric power from injection of water into a well. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is a rapidly growing need for environmentally acceptable systems for generating electric power. Clearly, hydroelectric power is one such system. Further, there are many instances when water from various sources must be disposed of in ways that are not deleterious to the environment. One method of dealing with the disposal of water is to inject it into underground reservoirs or other formations. 
         [0004]    There are many existing injection wells in the municipal, agricultural, industrial, petroleum, mining and energy oil fields. In some of these injection wells, water falls a considerable distance to the static water level. In cases where the injected water is falling to a sufficient depth, at a sufficient volume, a turbine with a connection to a generator may be installed to recover this energy. 
         [0005]    Injection wells are also common in aquifer storage and recovery systems used by many water districts, where the right geologic conditions exist. They are also common in geothermal production where the water/brine is re-circulated to mine more of the heat in the strata. Further, some mines inject dewatering effluent. 
       SUMMARY OF THE INVENTION 
       [0006]    It is one object of the present invention to provide an apparatus and method for generating electric power. 
         [0007]    Another object of the present invention is to generate electric power from the injection of water down a well and into a subsurface formation. 
         [0008]    In still another aspect of the present invention there is provided an apparatus and method for generating electric power using a turbine disposed in a downhole location and mechanically coupled to an electric generator. 
         [0009]    In still another aspect of the present invention there is provided a method for generating electric power by introducing a liquid into a turbine disposed in a downhole location and mechanically coupled to an electric generator. 
         [0010]    In still a further aspect of the present invention there is provided a method for generating electric power by introducing a liquid into a turbine disposed downhole and mechanically connected to an electric generator by controlling the flow of water through the turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an elevational view of one embodiment of the apparatus of the present invention. 
           [0012]      FIG. 2A  is an enlarged, elevational view of the upper portion of the apparatus shown in  FIG. 1 . 
           [0013]      FIG. 2B  is an enlarged, elevational view of the lower portion of the apparatus shown in  FIG. 1 . 
           [0014]      FIG. 3  is an enlarged view of one embodiment of a control valve used in the apparatus and method of the present invention, and 
           [0015]      FIG. 4  is a schematic block diagram of one embodiment of the apparatus and method of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    While the present invention will be described with respect to the use of water as the motive force, it will be understood that in certain instances, other liquids may also be used. 
         [0017]    Referring to  FIG. 1 , the apparatus of the present invention is shown disposed in a casing  10 . It will be understood that casing  10  will be positioned in a borehole; i.e., an injection well or the like. Casing  10  extends from a wellhead assembly  12 , which is comprised of mating flanges bolted together. Positioned in casing  10  is a tubing string  14 , tubing string  14  being connected to a flanged inlet pipe  16  into which water from a source not shown is injected. 
         [0018]    In general, tubing string  14  suspends a tubular shroud  17 , a turbine shown generally as  18 , a labyrinth seal shown generally as  20 , a generator shown generally as  22  and a control valve assembly shown generally as  24 . A centralizer  26  serves to maintain the tubing string  14  concentric with respect to the tubular shroud  17 . 
         [0019]    While in the embodiment shown, the generator  22  is disposed downhole, it will be appreciated by those skilled in the art that the generator could be located at the surface and mechanically coupled to the output shaft of the turbine via a line shaft. 
         [0020]    Referring now to  FIG. 2A , the upper portion of the apparatus shown in  FIG. 1  is shown in an enlarged view. Shroud  17  is suspended from a shroud hanger  27  below a pack-off assembly  28  and serves to ensure that injected water passes through turbine  18  to drive turbine  18  and to act as a coolant. Extending through a fitting  30  in wellhead  12 , is an electric power cable  32 , power cable  32  also extending through a fitting  34  in pack-off assembly  28  and shroud hanger  26 , power cable  32  being connected to generator  22  (see  FIG. 2B ). Turbine  18  is a submersible turbine pump, as for example, of the type marketed by Gould Pumps, operated in reverse. Such pumps are generally multi-staged, centrifugal pumps, or specially constructed vane-type turbines. Pressure from flowing water pushes against the vanes, causing them to rotate which in turn rotates an output shaft forming part of the turbine. 
         [0021]    Referring now to  FIG. 2B , water passing through turbine  18  flows past labyrinth seal  20 , generator  22  and centralizer  26  into control valve assembly  24 , described more fully hereafter. The output shaft of turbine  18  is mechanically connected to generator  22 . Accordingly, as turbine  18  rotates, the output shaft thereof rotates and in turn drives generator  22 , which, when operated at a correct speed and provided with enough input force, produces electric power. 
         [0022]    Connected to the bottom of shroud  17  is a valve assembly  24 , through which water discharged from turbine  18  flows into casing  10  to a suitable downhole formation. 
         [0023]    Referring now to  FIG. 3 , valve assembly  24  is shown in greater detail. As can be seen, a flange  38  is connected to the bottom of shroud  17 . Control valve assembly  24  comprises an outer housing shown generally as  39 , which comprises a tubular portion  41  connected on its upper end to a flange  40 , which is connected via bolts  42  to flange  38 . Connected to the lower end of the tubular portion  41 , is a support collar  42 , support collar  42  being provided with a series of radially inwardly projecting ribs  44 , and a centrally located boss  46  and defining an outlet between ribs  44 . 
         [0024]    Disposed in housing  40  is a control valve  48 , control valve  48  comprising a body comprised of a tubular portion  50 , a bottom wall  52 , and a valve bonnet  54 , tubular portion  50  being threadedly connected to valve bonnet  54 . Bottom wall  52  of valve body is mounted in boss  46  by means of a nut on a threaded stud  45  extending down from wall  52  through a bore in boss  46 . It will be understood that water falling through valve assembly  24  falls past ribs  44  into casing  10  and ultimately into a downhole formation. 
         [0025]    Bottom wall  52  has a threaded port  56 , which is connected to a hydraulic line (not shown). Bonnet  54  also has a threaded port  58 , also connected to a hydraulic line (not shown). A piston  60  is disposed in a valve chamber  62  formed by tubular portion  50 , bottom wall  52  and bonnet  54 . Piston  60  reciprocates in chamber  62  and is sealed with an annular seal  64  against the interior wall of tubular portion  50 . Piston  60  is in turn connected to a valve element  66 , which reciprocates in response to reciprocation of piston  60 . As can be seen, flange  40  forms a valve seat  68  against which valve element  66  can seal when moved sufficiently upward by the force of hydraulic fluid in the lower portion of chamber  62  acting against the bottom of piston  60 . As noted, although not shown it will be appreciated that hydraulic lines connected to ports  56  and  58  extend to the surface to a hydraulic power/control system. 
         [0026]    Referring now to  FIG. 4  there is shown a schematic control system for use in the apparatus and method of the present invention. At the outset, it should be noted that the present invention utilizes an existing high head at a much lower volume or flow rate, as compared with high volumes or flow rates with a relatively low head found in most similar hydroelectric generating systems. In this regard, prior art, gravity flow systems for hydroelectric power generation generally use a flow rate in excess of 10,000 gallons per minute with a head of less than 500 feet. In the method of the present invention, the flow rate can be less than about 5,000 gallons per minute while the head is greater than about 1,000 feet. 
         [0027]    Further, one of the aspects of the present invention is the ability to contain the proper flow rate through the turbine  18  to optimize electric power output from the generator  22 . To do this, the rate of flow through the turbine is controlled such that the turbine  18  rotates in a predetermined RPM range. As will be well understood by those skilled in the art, the predetermined RPM range will be that which is optimal based on the specific turbine pump used and the generator. 
         [0028]    Returning then to  FIG. 4 , there is a central valve system, shown generally as  70 , comprised of control valve assembly  24 , a hydraulic power unit  80  operatively connected to control valve assembly  24 , a computer  90 , a controller  100  and the turbine/generator system  110 . As water is injected into tubing  14  and as noted above, it rotates turbine  18  which, being mechanically connected to generator  22 , drives generator  22  to produce electric power. However, as noted, it is important to control the head pressure on the turbine such that the turbine  18  rotates at the optimal speed. Accordingly, in operation, water flowing down tubing  14  drives turbine  18  which in turn drives generator  22 , the falling water from turbine  18  flowing around seal  20  and generator  22  into valve assembly  24  and ultimately into casing  10  to a subsurface formation. Turbine/generator  110  is in communication with controller  100 , which collects all data from turbine generator  110 , the data being sent to computer  90  for processing, computer  90  sending control signals to hydraulic power unit  80 , which in turn controls the operation of valve  48 . 
         [0029]    In operation, if turbine  18  is rotating too fast, valve  48  will be throttled back slowing the release of water into casing  10  and thereby slowing the speed at which turbine  18  is rotating. It could be apparent that when it is desired to slow the release of water from the system, hydraulic fluid will be introduced into the lower portion of chamber  62  to drive piston  60  and valve element  66  upwardly toward valve seat  68 . Conversely, if it is desired to release more water, hydraulic fluid is introduced into inlet  58  to drive piston  60  downwardly, allowing more flow area between valve element  66  and valve seat  68  and conventionally more flow into casing  10 . 
         [0030]    It will be recognized that while the system of the present invention is dynamic in the sense that the flow of water is constantly being monitored and controlled, it is static in the sense that only head pressure and gravity flow are used as opposed to water being injected under pressure; e.g., pumped down hole. 
         [0031]    Also note, while the apparatus and method of the present invention has been described with reference to both the turbine and generator being disposed downhole and in the casing, it will be appreciated that the generator could be at the surface and connected with a lineshaft to the turbine. 
         [0032]    Further, while valve  48  as shown is generally of the needle valve type, it will be appreciated that other type of valves such as sleeve valves may also be employed. In fact, it is only necessary that the valve be of the type which can be controlled; i.e., throttled, as necessary to optimize turbine speed and hence electric power output from the generator. 
         [0033]    The foregoing description and examples illustrate selected embodiments of the present invention. In light thereof, variations and modifications will be suggested to one skilled in the art, all of which are in the spirit and purview of this invention.