Abstract:
A downhole kinetic energy storage system for wellbore completions is configured for installation downhole for extended periods of time, such as 10 year or more. The kinetic energy storage system receives power from a low power source, which can be due to a “power bottleneck” to the downhole location such as inductive coupling, optical fiber, downhole energy harvesting, and/or subsea wellhead configurations. The system stores the available low-power as rotational energy in a flywheel and then when demanded converts the rotational energy into electrical energy at a temporary power level exceeding the low power source. The temporary high power energy is used for wellbore completion applications such as actuating a flow control or other downhole valve.

Description:
FIELD 
       [0001]    The subject disclosure generally relates to wellbore completions. More particularly, the disclosure relates to downhole kinetic energy storage systems for use with wellbore completions. 
       BACKGROUND 
       [0002]    Modern wellbore completions make use of various power consuming devices that are located downhole. Examples include various types of electrically operated valves as well as other flow control devices such as electrically operated flow control sleeves. There are a number of ‘power bottlenecks’ in the wellbore completions systems, causing a limitation to downhole actuation of electrically operated downhole flow control devices. Examples of such power bottlenecks include subsea trees, inductive couplers, optical connections, and fluid flow energy harvesting systems. A completion system that has strong actuators may be limited by the amount of continuous power available at the downhole location due to these power bottlenecks. 
         [0003]    Current technologies of storing downhole energy have operational limitations in permanent applications (˜10 years) and elevated temperatures (&gt;125° C.). This poses a challenge to the designers of completions systems that rely on power intensive actuation applications such as intelligent completions valves. Normally these systems require occasional actuation and hence minimal ‘average’ power over their lifetime; however, due to the limitation in downhole energy storage their power sources are designed for peak demand. 
       SUMMARY 
       [0004]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
         [0005]    According to some embodiments, a downhole kinetic energy storage system is described that includes: a low power downhole source of energy; a rotating mechanical device (e.g. a flywheel) interconnected and configured to receive and store as rotational energy mechanical energy originating from the lower power downhole source of energy; and an electric machine interconnected and configured to convert mechanical energy from the rotating machine into high power electrical energy for use by a wellbore completion device (e.g. flow control valve, formation isolation valve, or safety valve). Actuation of the wellbore completion device temporarily uses energy at a rate exceeding that produced by the low power downhole source. 
         [0006]    According to some embodiments, the electric machine is further interconnected and configured to convert electrical energy from the low power downhole source into mechanical energy for storage by the rotating mechanical device. According to some embodiments, the system is configured for permanent or semi-permanent deployment in a wellbore for more than 5 years. According to some embodiments, the system is configured for deployment in a wellbore for more than 10 years and/or in a wellbore having temperatures greater than 100 degrees Celsius. According to some embodiments the wellbore completion device is a flow control valve that forms part of an intelligent completion 
         [0007]    According to some embodiments, the low power downhole source of energy is energy transmitted through a subsea wellhead, inductive couplers, or optical connections. According to some other embodiments, the low power downhole source of energy is harvested from fluid flowing downhole, or from vibration, thermal and/or rotational energy. 
         [0008]    According to some embodiments, the flywheel is formed at least in part of a fiber reinforced composite material. According to some embodiments, the flywheel is supported by magnetic bearings. The electric machine, for example can be a DC brush, DC brushless, switched reluctance, inductance, or AC electric machine. According to some embodiments, the high power electrical energy from the electrical machine is used to boost power past an inductive coupler such that it can be used by the wellbore completion device. 
         [0009]    According to some embodiments, a method is described for storing kinetic energy for use downhole. The method includes: receiving a low power energy from a low power energy source; converting the received low power energy into rotational energy using an electric machine; and storing the rotational energy in a flywheel system. When needed, the rotational energy stored in the flywheel system is converted into high power electric energy; and a wellbore completion device is actuated using the high power electric energy. Actuating completion device used the high power electric energy at a rate exceeding that produced by the low power energy source. 
         [0010]    Further features and advantages of the subject disclosure will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    It should be appreciated that these drawings depict only illustrative embodiments, and are therefore not to be considered limiting of the scope of this patent specification or the appended claims. The subject matter hereof will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0012]      FIG. 1  is a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions, according to some embodiments; 
           [0013]      FIG. 2  is a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power from a fluid flow energy harvester, according to some embodiments; 
           [0014]      FIG. 3  s a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power through an inductive coupling, according to some embodiments; and 
           [0015]      FIG. 4  is a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power through an optical fiber connection, according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the examples of the subject disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details in more detail than is necessary, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Furthermore, like reference numbers and designations in the various drawings indicate like elements. 
         [0017]    Current technologies of storing downhole energy have operational limitations in permanent applications (˜10 years) and elevated temperatures (&gt;125° C.). This poses a challenge to the designers of completions systems requiring power intensive actuation applications such as intelligent completions valves. Normally these systems require occasional actuation and hence minimal ‘average’ power over their lifetime; however, due to the limitation in downhole energy storage their power sources are designed for peak demand. 
         [0018]    There are a number of ‘power bottlenecks’ in the completions systems, causing a limitation to actuation of downhole devices. Examples of such power bottlenecks include: subsea trees, inductive couplers, optical connections, and flow energy harvesting systems. With a robust downhole energy storage system, a completion system with strong actuators can be energized using continuous power at a fraction of the peak demand. 
         [0019]      FIG. 1  is a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions, according to some embodiments. Kinetic energy storage system (KESS)  100  includes an electric motor/generator  130  and a rotor  140  in the form of a separate flywheel. The system will normally include control electronics  120  to control motor/generator  130 . According to some embodiments, the motor/generator  130  is DC brush, DC brushless, switched reluctance, or inductance and AC electric machines. The flywheel  140  is can be manufactured from various materials. However, according to some embodiments a high energy density system can be designed using fiber reinforced composite materials. 
         [0020]    Flywheel  140  is shown supported by a shaft  142  and bearings  144  and  146 . According to some embodiments the flywheel  140  uses “magnetic bearings” to support the load of the rotor by causing it to magnetically levitate. Further detail of magnetic bearings and magnetic levitation technology for use in downhole flywheel technology can be found in co-owned U.S. Pat. No. 8,033,328 (hereinafter referred to as the “&#39;328 Patent”), which is incorporated herein by reference. 
         [0021]    According to some embodiments the kinetic energy storage system  100  is used in conjunction with a fluid-flow energy-harvesting device to convert the low power output of the harvester into a high-power intermittent power supply and operate completions equipment such as a flow control valve. According to some embodiments, this is accomplished by supplying the system with kinetic energy using the energy harvester. In some cases, rotational energy from the energy harvester can be used to directly (e.g. through a transmission) drive flywheel  140 . According to some other embodiments, the electrical energy output of the harvester is used by the control electronics  120  via electrical leads  110  to increase the speed of the flywheel  140  and thus storing kinetic energy. When sufficient energy is stored, the electric machine  130  is operated as a generator and the energy is supplied to the flow control valve. 
         [0022]    The availability of downhole power may be limited as a consequence of a bottleneck in the completions power transmission systems. Some examples of power bottlenecks are subsea trees, inductive couplings and optical cables. In these cases the KESS can be used to generate a high-power intermittent power for subterranean components using the available low power source. Each of these example cases is described in greater detail below with respect to  FIGS. 2, 3 and 4 . 
         [0023]      FIG. 2  is a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power from a fluid flow energy harvester, according to some embodiments. Wellbore  202  penetrates the earth to production formation rock  200 . Production tubing (or casing)  210  is positioned within wellbore  202  and includes an electrically powered flow control valve  230  to control fluid flow from formation  200  into production tubing  210 . Packers  212  and  214  are used for isolation. For electrical power, a fluid-flow harvesting device  220  is positioned within the tubing  210 . Fluid flowing upwards through tubing  210  through harvester  220  causes a turbine system to rotate, and a generator within harvester  220  is used to produce electrical power therefrom. Unfortunately, the turbine within harvester  220  generates power at rate that is too low for reliable operation of flow control valve  230 . That is, during an actuation “event”, flow control valve  230  uses energy at a rate that exceeds the average rate that energy can be produced by harvester  220 . According to some embodiments, KESS  100  is used to store energy generated by harvester  220  so that the instantaneous energy demand by flow control valve  230  can be met. 
         [0024]    According to some embodiments, instead of using a separate electrical generator within harvester  220 , the mechanical energy from the turbine within harvester  220  is used to directly accelerate flywheel  140  within KESS  100 . In such embodiments, the turbine&#39;s shaft can be connected to transmission (e.g. a continuously variable transmission) to accelerate flywheel  140 . A continuously variable transmission, for example, can be used to gradually bring flywheel  140  up to speed by adjusting the “gear ratio” between the turbine of harvester  220  and the flywheel  140  of KESS  100 . For further details of aspects of using a transmission to accelerate a flywheel in a downhole setting, refer to the &#39;328 Patent. According to some embodiments, instead of harvesting energy from fluid flow, harvester  220  is configured to harvest energy downhole from vibrations, thermal sources and/or other forms of energy. 
         [0025]      FIG. 3  s a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power through an inductive coupling, according to some embodiments. As in the case of  FIG. 2 , wellbore  202  penetrates the earth to production formation rock  200 . Production tubing (or casing)  210  is positioned within wellbore  202  and includes an electrically powered flow control valve  230  to control fluid flow from formation  200  into production tubing  210 . Packers  212  and  214  are used for isolation. In this case, electrical power from the surface is transmitted through downhole electrical cable  310 . An inductive coupling  320  acts as a power bottleneck such that the power passing through inductive coupling  320  is too low to meet the instantaneous power demand for actuation of flow control valve  230 . According to some embodiments, KESS  100  is used to store energy transmitted through inductive coupling  320  so that the instantaneous energy demand by flow control valve  230  can be met. In particular, the power transmitted through inductive coupling  320  is used to accelerate flywheel  140  within KESS  100  (shown in  FIG. 1 ). When demanded for actuation of the flow control valve  230 , the KESS generates electrical energy from the flywheel and provides it to the actuator system for valve  230 . 
         [0026]      FIG. 4  s a schematic diagram illustrating certain aspects of a downhole kinetic energy storage system for wellbore completions that obtains low-power through an optical fiber connection, according to some embodiments. As in the case of  FIGS. 2 and 3 , wellbore  202  penetrates the earth to production formation rock  200 . Production tubing (or casing)  210  is positioned within wellbore  202  and includes an electrically powered flow control valve  230  to control fluid flow from formation  200  into production tubing  210 . Packer  214  is used for isolation. In this case, a downhole optical cable  420  is provided. An optical-electrical transducer  430  converts optical energy from cable  420  into electrical energy for use downhole. However, the optical fiber power transmission system acts as power bottleneck such that the electrical energy available from transducer  430  is too low to meet the instantaneous power demand for actuation of flow control valve  230 . According to some embodiments, KESS  100  is used to store energy from transducer  430  so that the instantaneous energy demand by flow control valve  230  can be met. In particular, the power from transducer  430  is used to accelerate flywheel  140  within KESS  100  (shown in  FIG. 1 ). When demanded for actuation of the flow control valve  230 , the KESS generates electrical energy from the flywheel and provides it to the actuator system for valve  230 . 
         [0027]    According to some embodiments, instead of flow control valve  230  in  FIGS. 2, 3 and 4 , another type of valve is actuated, such as a formation isolation valve or a safety valve. According to some embodiments, the valve  230  in  FIGS. 2, 3 and 4  form part of an intelligent completion. 
         [0028]    The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.