Downhole energy harvesting

Abstract

Downhole electrical energy harvesting and communication in systems for well installations having metallic structure carrying electric current, for example CP current. In some instances there is a harvesting module ( 4 ) electrically connected to the metallic structure ( 2 ) at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure ( 2 ); and the harvesting module ( 4 ) being arranged to harvest electrical energy from the electric current. In addition or alternatively, there may be communication apparatus ( 4, 5, 6 ) for communication by modulation of the current, for example CP current, in the metallic structure ( 2 ).

1 . A downhole electrical power harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage, wherein the harvesting module is configured to modify an input impedance of the electrical circuit to match a source impedance of the electrical circuit to optimize power conversion efficiency. 
     
     
         2 . The downhole electrical power harvesting module according to  claim 1 , wherein the harvesting module is arranged to harvest electrical energy from dc currents. 
     
     
         3 . (canceled) 
     
     
         4 . The downhole electrical power harvesting module according to  claim 1 , wherein the electrical circuit comprises a dc-dc convertor. 
     
     
         5 . The downhole electrical power harvesting module according to  claim 4 , wherein the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         6 . The downhole electrical power harvesting module according to  claim 4 , wherein the dc-dc converter comprises self-start means to allow initiation of energy harvesting when the input voltage available is below a semiconductor band gap voltage of components in the dc-dc convertor. 
     
     
         7 . The downhole electrical power harvesting module according to  claim 4 , wherein the dc-dc converter comprises self-start means to allow initiation of energy harvesting when the input voltage available is below 0.5 volts. 
     
     
         8 . The downhole electrical power harvesting module according to  claim 4 , wherein the dc to dc converter comprises a step-up transformer. 
     
     
         9 . The downhole electrical power harvesting module according to  claim 8 , wherein the dc-dc converter comprises self-start means to allow initiation of energy harvesting when the input voltage available is below 0.5 volts and the self-start means comprises a Field Effect Transistor arranged together with the step-up transformer to form a resonant step-up oscillator. 
     
     
         10 . The downhole electrical power harvesting module according to  claim 8 , wherein the dc-dc converter comprises self-start means to allow initiation of energy harvesting when the input voltage available is below 0.5 volts and the dc-dc convertor comprises an H bridge of transistors arranged under the control of a part of the harvesting module for providing an input to the step-up transformer and the self-start means comprises an auxiliary source of power for said part of the harvesting module for allowing start up. 
     
     
         11 . The downhole electrical power harvesting module according to  claim 8 , wherein a part of the harvesting module is configured to control a turns ratio of the step-up transformer to modify a load generated by the dc-dc converter. 
     
     
         12 . The downhole electrical power harvesting module according to  claim 11 , wherein a secondary winding of the step-up transformer comprises a plurality of tappings and/or the step-up transformer comprises a plurality of secondary windings and said part of the harvesting module is configured to select windings and/or tappings to provide a desired turns ratio. 
     
     
         13 . The downhole electrical power harvesting module according to claim comprising at least a pair of terminals from which connection to the two spaced locations may be made. 
     
     
         14 . The downhole electrical power harvesting module according to  claim 13 , in which, the harvesting module has more than two terminals, wherein each of the terminals is for allowing connection to a respective location and the harvesting module further comprises switch means for selectively electrically connecting two of the more than two terminals across the electrical circuit so allowing selection of which of the respective locations the electrical circuit is connected between. 
     
     
         15 . The downhole electrical power harvesting module according to  claim 1 , comprising an energy storage device for storing harvested energy. 
     
     
         16 . The downhole electrical power harvesting module according to  claim 15 , in which the energy storage device comprises a charge storage device comprising at least one capacitor and/or re-chargeable battery. 
     
     
         17 . The downhole electrical power harvesting module according to  claim 1 , in which the harvesting module is configured for varying a load seen between said two spaced locations in a well installation when the harvesting module is electrically connected between the two spaced locations. 
     
     
         18 . The downhole electrical power harvesting module according to  claim 17 , in which the varying of the load is microprocessor controlled. 
     
     
         19 . The downhole electrical power harvesting module according to  claim 17 , in which the harvesting module is configured to vary the load so as to optimize energy harvesting. 
     
     
         20 . The downhole electrical power harvesting module according to  claim 17 , in which the harvesting module is configured to modulate the load so as to communicate data away from the harvesting module. 
     
     
         21 . The downhole electrical power harvesting module according to  claim 1 , comprising a primary battery such that in use power may be selectively drawn from the power harvested by the circuit and from the primary battery. 
     
     
         22 . The downhole apparatus comprising the harvesting module as claimed in  claim 1 , and a downhole device to accept power from the harvesting module. 
     
     
         23 . The downhole apparatus according to  claim 22 , comprising charge storage means and being configured to control power to the downhole device when sufficient energy is available to power the downhole device. 
     
     
         24 . The downhole apparatus according to  claim 22 , configured for varying the input impedance of the harvesting module to modulate load so as to transmit data from at least one of the electrical power harvesting module and the downhole device. 
     
     
         25 . The downhole apparatus according to  claim 22 , configured for applying a modulated voltage via the electrical connection of the electrical power harvesting module between the two spaced locations so as to transmit data. 
     
     
         26 . The downhole apparatus according to  claim 22 , comprising a primary battery such that in use power may be selectively drawn from the harvested power and from the primary battery. 
     
     
         27 . The downhole apparatus according to  claim 22 , wherein the downhole device comprises at least one of:
 a downhole sensor;   a downhole actuator;   an annular sealing device;   a valve;   a downhole communication module.   
     
     
         28 . The downhole apparatus according to  claim 27 , wherein the valve comprises at least one of:
 a subsurface safety valve;   a bore flow control valve;   a bore to annulus valve;   an annulus to annulus valve;   a bore to pressure compensation chamber valve;   an annulus to pressure compensation chamber valve;   a through packer or packer bypass valve.   
     
     
         29 . The downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure carrying electric current, the system comprising:
 a harvesting module according to  claim 1  electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure; and   the harvesting module being arranged to harvest electrical energy from the electric current.   
     
     
         30 . A downhole electrical power harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage,
 wherein the electrical circuit comprises a dc-dc convertor, the dc to dc converter comprises a step-up transformer, and the dc-dc converter comprises self-start means to allow initiation of energy harvesting when the input voltage available is below 0.5 volts and the dc-dc convertor comprises an H bridge of transistors arranged under the control of a part of the harvesting module for providing an input to the step-up transformer and the self-start means comprises an auxiliary source of power for said part of the harvesting module for allowing start up.   
     
     
         31 . The downhole electrical power harvesting module according to  claim 30  in which the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         32 . A downhole electrical power harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage,
 wherein the electrical circuit comprises a dc-dc convertor, the dc to dc converter comprises a step-up transformer, and a part of the harvesting module is configured to control a turns ratio of the step-up transformer to modify a load generated by the dc-dc converter.   
     
     
         33 . The downhole electrical power harvesting module according to  claim 32 , wherein the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         34 . The downhole electrical power harvesting module according to  claim 32 , wherein a secondary winding of the step-up transformer comprises a plurality of tappings and/or the step-up transformer comprises a plurality of secondary windings and said part of the harvesting module is configured to select windings and/or tappings to provide a desired turns ratio. 
     
     
         35 . A downhole electrical power harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage, wherein the harvesting module is configured for varying a load seen between said two spaced locations in a well installation when the harvesting module is electrically connected between the two spaced locations. 
     
     
         36 . The downhole electrical power harvesting module according to  claim 35 , wherein the electrical circuit comprises a dc-dc convertor and the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         37 . The downhole electrical power harvesting module according to  claim 35 , wherein the varying of the load is microprocessor controlled. 
     
     
         38 . The downhole electrical power harvesting module according to  claim 35 , wherein the harvesting module is configured to vary the load so as to optimize energy harvesting. 
     
     
         39 . The downhole electrical power harvesting module according to  claim 35 , wherein the harvesting module is configured to modulate the load so as to communicate data away from the harvesting module. 
     
     
         40 . A downhole apparatus comprising a downhole electrical power harvesting module and a downhole device to accept power from the harvesting module, the harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage, wherein the downhole apparatus is configured for varying the input impedance of the harvesting module to modulate load so as to transmit data from at least one of the electrical power harvesting module and the downhole device. 
     
     
         41 . The downhole apparatus according to  claim 40 , wherein the electrical circuit comprises a dc-dc convertor and the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         42 . A downhole apparatus comprising a downhole electrical power harvesting module and a downhole device to accept power from the harvesting module, the harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage, wherein the downhole apparatus is configured for varying the input impedance of the harvesting module to modulate load so as to transmit data from at least one of the electrical power harvesting module and the downhole device. 
     
     
         43 . The downhole apparatus according to  claim 42 , wherein the electrical circuit comprises a dc-dc convertor and the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         44 . A downhole apparatus comprising a downhole electrical power harvesting module and a downhole device to accept power from the harvesting module, the harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations which acts as an input voltage, wherein the downhole apparatus is configured for applying a modulated voltage via the electrical connection of the electrical power harvesting module between the two spaced locations so as to transmit data. 
     
     
         45 . The downhole apparatus according to  claim 44 , wherein the electrical circuit comprises a dc-dc convertor and the dc-dc convertor is arranged to operate with input voltages above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volt. 
     
     
         46 . The downhole electrical power harvesting module according to  claim 5 , in which the minimum threshold is not greater than 0.25 volts 
     
     
         47 . The downhole electrical power harvesting module according to  claim 5 , in which the minimum threshold is not greater than 0.05 volts.