Downhole energy harvesting

A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:

• a harvesting module 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 cathodic protection currents flowing in the structure;
• and
• the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the voltage of the surface of the well is, in use, limited to the range minus 0.7 volts to minus 2 volts with respect to a silver/silver chloride reference cell.

A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:

• a harvesting module 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 cathodic protection currents flowing in the structure;
• and
• the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the resistance of the well structure between the first location and the second location is less than 0.1 ohms.

A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:

• a harvesting module 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 cathodic protection currents flowing in the structure;
• and
• the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the uppermost of the first location and the second location is located adjacent to a location which corresponds to a maxima in magnitude of potential caused by the electric current flowing in the structure.

A downhole electrical energy harvesting system for harvesting electrical energy from dc currents in a well installation having metallic structure, the metallic structure being provided with cathodic protection and comprising at least one run of downhole metallic pipe and, the system comprising:

• a harvesting module electrically connected to the at least one run of downhole metallic pipe of the metallic structure at a first location and electrically connected to the at least one run of downhole metallic pipe of the metallic structure at a second location spaced from the first location, the first and second locations being chosen such that, in use, cathodic protection currents flow in the at least one run of downhole metallic pipe between the first and the second location such that there is a potential difference between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe;
• and
• the harvesting module being arranged to harvest electrical energy from dc currents, being connected between the first and second locations and being arranged to harvest electrical energy due to the potential difference which exists between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe.